Latest Review of Coating Methods 2 OCT 2016

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[ IntroductionCoating Process Technology is in widespreaduse. Coating is necessary for modification, orimprovement of the substrate to make it moresuitable.Several Industries are based on coatingprocess technology. Adhesive coating ,Printing, Flexible laminates are the fewexamples.]

[ CoatingMethods]

We

Prom

ise to

atte

nd y

our T

echn

ical

nee

d

03 Sept

2016

[ IntroductionCoating Process Technology is in widespreaduse. Coating is necessary for modification, orimprovement of the substrate to make it moresuitable.Several Industries are based on coatingprocess technology. Adhesive coating ,Printing, Flexible laminates are the fewexamples.]

[ CoatingMethods]

Latest Reviewof Coating Methodsfor Adhesives , Oct 2016

By Shrikant AthavalePrathith ConsultantsPune India.Email : [email protected]

Coating Methods

Coating Process Technology is in widespread use.Coating is necessary for modification, or improvement of thesubstrate to make it more suitable.Several Industries are based on coating process technology.Adhesive coating , Printing, Flexible laminates are the fewexamples.The basic steps in continuous production of coated substrates areas follows.1. Preparing the coating solution2. Unwinding the substrate roll3. transporting / passing it through the coater4. applying the coating from the coating solution5. drying the coating6. winding the final coated roll7. Converting the coated substrate to final size

Coating Methods

Coating Process Technology is in widespread use.Coating is necessary for modification, or improvement of thesubstrate to make it more suitable.Several Industries are based on coating process technology.Adhesive coating , Printing, Flexible laminates are the fewexamples.The basic steps in continuous production of coated substrates areas follows.1. Preparing the coating solution2. Unwinding the substrate roll3. transporting / passing it through the coater4. applying the coating from the coating solution5. drying the coating6. winding the final coated roll7. Converting the coated substrate to final size

Coating Methods

There are few other operations that are often used , such as,a) surface treatment on the substrate to improve adhesion.b) cleaning the substrate prior to coating , to reduce contaminationc) lamination with other substrate

Different types of coatings methods are used depending uponthe substrate as well as the end product requirement.

Coating Methods

There are few other operations that are often used , such as,a) surface treatment on the substrate to improve adhesion.b) cleaning the substrate prior to coating , to reduce contaminationc) lamination with other substrate

Different types of coatings methods are used depending uponthe substrate as well as the end product requirement.

These coating machines are available in various sizes , frompilot coaters using narrow webs , 150-600 mm wide and runningat low speeds , 5-10 mtrs / min , to production scale machinesusing wide web's , over 1500 mm wide and coating at 50-200mtrs / min. A typical coating machine is shown below.

Coating Process

The application of a liquid to the traveling web / substrate isaccomplished by one of the many coating methods. Widely usedcoating methods are Reverse Roll, wire wound or mayer rod/bar,direct and offset gravure , slot die, blade, knife over roll , airknife , comma etc.The choice of the method depends on the nature of the web/substrate , the rheology of the coating fluid , the solvent the wetcoating weight desired, the desired coating width and speed, theno of layers or coating to be applied simultaneously , costconsiderations, environmental considerations .

Coating Process

The application of a liquid to the traveling web / substrate isaccomplished by one of the many coating methods. Widely usedcoating methods are Reverse Roll, wire wound or mayer rod/bar,direct and offset gravure , slot die, blade, knife over roll , airknife , comma etc.The choice of the method depends on the nature of the web/substrate , the rheology of the coating fluid , the solvent the wetcoating weight desired, the desired coating width and speed, theno of layers or coating to be applied simultaneously , costconsiderations, environmental considerations .

Coating Process

The coating method should be chosen based on the specificrequirement. many a times a method is selected based on theavailability of a specific coating applicator.even though it may not be the best choice. much time , moneyand raw materials may be wasted by trying to make the productby a process that is not suitable.The coating method may be too narrow at the conditions selectedor it may be impossible even to obtain a quality coating.A process that works well at low speed in laboratory or pilotcoater may not be appropriate for a manufacturing plant , coatingat high speeds . Similarly a high speed coating plant may not beappropriate for laboratory trials.

Coating Process

The coating method should be chosen based on the specificrequirement. many a times a method is selected based on theavailability of a specific coating applicator.even though it may not be the best choice. much time , moneyand raw materials may be wasted by trying to make the productby a process that is not suitable.The coating method may be too narrow at the conditions selectedor it may be impossible even to obtain a quality coating.A process that works well at low speed in laboratory or pilotcoater may not be appropriate for a manufacturing plant , coatingat high speeds . Similarly a high speed coating plant may not beappropriate for laboratory trials.

Coating is a very Important

process involved in the Manufacture

of Adhesive Coated Products

Coating is a very Important

process involved in the Manufacture

of Adhesive Coated Products

The selection of the best roll coating method for anyparticular type of work depends on a number offactors. The key factors that need to be considered areas follows:

1. Type of adhesive2. Thickness of adhesive coating3. Thickness of substrate4. Width of substrate5. Full coat or partial coat6. Handling after coating7. Cleanup

The selection of the best roll coating method for anyparticular type of work depends on a number offactors. The key factors that need to be considered areas follows:

1. Type of adhesive2. Thickness of adhesive coating3. Thickness of substrate4. Width of substrate5. Full coat or partial coat6. Handling after coating7. Cleanup

Gravure Coating

Metering Rod / Myer Bar Coating

Knife over roll coating

Comma Coating

Reverse Roll Coating


Hot Melt Coating / Extrusion coating

Slot Orifice coating

Calendaring

Immersion / Dip coating

Curtain Coating

There are Various Coating Methods available

Gravure Coating



Comma Coating



Hot Melt Coating / Extrusion coating

Slot Orifice coating

Calendaring


Curtain Coating

The Coating Methods can be classified by the principles used tocontrol the coating weight.

There are three basic types:

• Self-Metered : Here in the coating equipment controls thefinal coverage. Examples are Comma roll, reverse roll, dip

• Doctored : Here in the applied coating is metered lateron orapplicator device removes the excess applied coating fluid tocontrol the final coverage. Examples are air knife, Mayer rod andblade & knife coaters

• Pre-metered : Here in all fluid fed to applicator transfers toweb. The volume of solution supplied to the applicator controlsthe final coverage. Examples are slot die, gravure and curtain.

The Coating Methods can be classified by the principles used tocontrol the coating weight.

There are three basic types:

• Self-Metered : Here in the coating equipment controls thefinal coverage. Examples are Comma roll, reverse roll, dip

• Doctored : Here in the applied coating is metered lateron orapplicator device removes the excess applied coating fluid tocontrol the final coverage. Examples are air knife, Mayer rod andblade & knife coaters

• Pre-metered : Here in all fluid fed to applicator transfers toweb. The volume of solution supplied to the applicator controlsthe final coverage. Examples are slot die, gravure and curtain.

Considerations in selecting a coating method

Selecting an appropriate coating method is a challenge becausethere are currently many applicators in routine use and each ofthese has unique capabilities in terms of the coating solutionvariables that they can apply and the resulting coated substrateproperties. Interestingly all of the methods that have beendeveloped since the first roll coater in 1850 are still in routine useThe attached table summarizes the ~ 40 major coating methodcategories by the principle sued to control the wet coating weight,self metered coating, doctored coating and pre-meteredcoating. Each of these methods has several possibleconfigurations so that there is large number of method to choosefrom.

Considerations in selecting a coating method

Selecting an appropriate coating method is a challenge becausethere are currently many applicators in routine use and each ofthese has unique capabilities in terms of the coating solutionvariables that they can apply and the resulting coated substrateproperties. Interestingly all of the methods that have beendeveloped since the first roll coater in 1850 are still in routine useThe attached table summarizes the ~ 40 major coating methodcategories by the principle sued to control the wet coating weight,self metered coating, doctored coating and pre-meteredcoating. Each of these methods has several possibleconfigurations so that there is large number of method to choosefrom.

Considerations in selecting a coating methodContinued

The typical approach to selecting the coating method for a newproduct or an upgraded old product is to establish the productrequirement, coverage level and uniformity, number of layers,physical quality, volume, substrate, drying conditions, andsolutions properties. The requirements are the compared withmethod capabilities and best method selected.However, there are some additional criteria that are often ignoredand should be considered when selecting a method. The coatability window is an operating diagram which indicated the stableprocess regions in which the product can be coated with nodefects. It combines the effects of line speed, coating weight,applicator variables to determine this region. When determinedthis will indicate if there is a viable operating region. The basicvalues in available tables do not show this.


The typical approach to selecting the coating method for a newproduct or an upgraded old product is to establish the productrequirement, coverage level and uniformity, number of layers,physical quality, volume, substrate, drying conditions, andsolutions properties. The requirements are the compared withmethod capabilities and best method selected.However, there are some additional criteria that are often ignoredand should be considered when selecting a method. The coatability window is an operating diagram which indicated the stableprocess regions in which the product can be coated with nodefects. It combines the effects of line speed, coating weight,applicator variables to determine this region. When determinedthis will indicate if there is a viable operating region. The basicvalues in available tables do not show this.


The cost and technical effort to install and develop the coatingapplicator should be considered. The older established method,gravure reverse roll, Mayer Rod are inexpensive and can easilybe installed with the availability of cartridge. There is also a largetechnical base for these methods and they can be relatively easyto operate. Slot die coater is expensive and is technicallysophisticated. Considerably more technical effort is neededto run this process. Often the simpler method is the best choice.High line appears attractive but they may not be suitable for allmethods. With low volume products the start-up time and initiallosses until quality is established can adversely affect costs.


The cost and technical effort to install and develop the coatingapplicator should be considered. The older established method,gravure reverse roll, Mayer Rod are inexpensive and can easilybe installed with the availability of cartridge. There is also a largetechnical base for these methods and they can be relatively easyto operate. Slot die coater is expensive and is technicallysophisticated. Considerably more technical effort is neededto run this process. Often the simpler method is the best choice.High line appears attractive but they may not be suitable for allmethods. With low volume products the start-up time and initiallosses until quality is established can adversely affect costs.


This loss is minimal for a high volume long coating campaigns.However, it can be significant for a small volume product.Therefore, for low volume product a lower line speed which iseasy to start and maintain may be preferred.

Doctored Mode Self-metered Pre-metered

Air knife metering mode Comma direct/indirect Curtain PrecisionDip & scrape Dip ExtrusionDip & scrape Dip Extrusion

Dip & Squeeze Direct Roll FlexoDoctor Blade Direct roll hot melt Gravure directFloating knife Reverse Roll Gravure offset

Kiss coater gravure reverseKnife over roll Hot Melt

Mayer rod Slot DieMetering Bar

After monitoring the coating methods being industriallyused in order to determine the most widely used webcoating methods.The results of the most recent survey are as follows:

This information is very useful to select a method mostappropriate

After monitoring the coating methods being industriallyused in order to determine the most widely used webcoating methods.The results of the most recent survey are as follows:

This information is very useful to select a method mostappropriate

Covered Rollers

A discussion of rollers for the adhesives and sealants sectorwould not be complete without a mention of coating rolls.Regardless of the adhesive application method, some type ofcoating roll is usually used to spread and evenly distribute theadhesive/sealant.Coating rollers may seem mundane, but their makeup anddesign must be finely tuned. Specified tolerances as tight as“half-a-thou” total indicated run out (TIR) are common. That’sone-half of one thousandth of an inch; perfect concentricity is amust. Attribute this exactitude to the familiar need for a verythin, very even layer of adhesive. If the coating roll is out ofround, adhesive application will be uneven.

Covered Rollers

A discussion of rollers for the adhesives and sealants sectorwould not be complete without a mention of coating rolls.Regardless of the adhesive application method, some type ofcoating roll is usually used to spread and evenly distribute theadhesive/sealant.Coating rollers may seem mundane, but their makeup anddesign must be finely tuned. Specified tolerances as tight as“half-a-thou” total indicated run out (TIR) are common. That’sone-half of one thousandth of an inch; perfect concentricity is amust. Attribute this exactitude to the familiar need for a verythin, very even layer of adhesive. If the coating roll is out ofround, adhesive application will be uneven.

Covered Rollers ( Continued )

Coating rolls are virtually always covered (seldom just baresteel), and the compound choice is fairly important. Manymanufacturers say they have a “rubber-covered roller,” but fewroll covers are actually natural rubber. Nitrile is one of the mostcommon roll cover compounds for coating rolls. Nitrile wearswell and supports the most common durometer range forcoating rolls: 55-90 durometer (Shore A). The higher thedurometer value, the harder the compound.Where allowable, some engineers order an extra-thick nitrilecoat (0.75-1.00 in.) and then occasionally order a regrind of theroll face (using a “kiss grind” to remove the top layer ofgunked-up roll cover, usually just a few hundredths of an inch).


Coating rolls are virtually always covered (seldom just baresteel), and the compound choice is fairly important. Manymanufacturers say they have a “rubber-covered roller,” but fewroll covers are actually natural rubber. Nitrile is one of the mostcommon roll cover compounds for coating rolls. Nitrile wearswell and supports the most common durometer range forcoating rolls: 55-90 durometer (Shore A). The higher thedurometer value, the harder the compound.Where allowable, some engineers order an extra-thick nitrilecoat (0.75-1.00 in.) and then occasionally order a regrind of theroll face (using a “kiss grind” to remove the top layer ofgunked-up roll cover, usually just a few hundredths of an inch).


This saves money vs. completely recovering the roller everytime it becomes worn, and it is possible to achieve 2-4 regrindsout of a thick coat.Nitrile is also available in an FDA-approved version, which isrequired in the food and pharmaceutical industries. For FDA-critical applications, it is also preferable to have the roller corefabricated from stainless steel rather than the standard carbonsteel.Ethylene propylene diene monomer (EPDM) is another popularcoating roll compound. This synthetic rubber features good heatand chemical resistance, with fairly good release. It can also beapplied thick and reground.


This saves money vs. completely recovering the roller everytime it becomes worn, and it is possible to achieve 2-4 regrindsout of a thick coat.Nitrile is also available in an FDA-approved version, which isrequired in the food and pharmaceutical industries. For FDA-critical applications, it is also preferable to have the roller corefabricated from stainless steel rather than the standard carbonsteel.Ethylene propylene diene monomer (EPDM) is another popularcoating roll compound. This synthetic rubber features good heatand chemical resistance, with fairly good release. It can also beapplied thick and reground.


High-release silicone is another popular option for coating rolls,given its high release and heat resistance traits. It lacks thedurability of EPDM or nitrile, but there is no substitute for therelease offered by silicone. It is used extensively in plastic filmand paper applications. However, in addition to its higher up-front cost, silicone does not regrind well, so rolls must becompletely recovered when worn.Coating rollers are usually finished in one of two ways: eithervery flat and smooth (“micro polish” finish) or with very tightlyspaced serrations or spirals (16-32 radial serrations per inch).While every plant employs its own proprietary processes,chemicals and techniques to optimize performance, making itdifficult to develop hard and fast rules about what works best,these are very common options.


High-release silicone is another popular option for coating rolls,given its high release and heat resistance traits. It lacks thedurability of EPDM or nitrile, but there is no substitute for therelease offered by silicone. It is used extensively in plastic filmand paper applications. However, in addition to its higher up-front cost, silicone does not regrind well, so rolls must becompletely recovered when worn.Coating rollers are usually finished in one of two ways: eithervery flat and smooth (“micro polish” finish) or with very tightlyspaced serrations or spirals (16-32 radial serrations per inch).While every plant employs its own proprietary processes,chemicals and techniques to optimize performance, making itdifficult to develop hard and fast rules about what works best,these are very common options.


Additional ConsiderationsHigh-tech elastomers and thermal transfer coefficients haveadded complexity to roller technology, but they should not beintimidating. With the right knowledge, you can make themwork wonders for your plant. For plant managers wishing toincrease overall output, one easy method is to increaseweb/stock width. This means increasing the width of all rollers,which is not as difficult as one might think. Existing rollers canbe reverse-engineered, and new rolls can be fabricated with theold diameter and bearing fittings, but with a wider width. Thisis a great way to expand capacity without purchasing entirelynew machines.


Additional ConsiderationsHigh-tech elastomers and thermal transfer coefficients haveadded complexity to roller technology, but they should not beintimidating. With the right knowledge, you can make themwork wonders for your plant. For plant managers wishing toincrease overall output, one easy method is to increaseweb/stock width. This means increasing the width of all rollers,which is not as difficult as one might think. Existing rollers canbe reverse-engineered, and new rolls can be fabricated with theold diameter and bearing fittings, but with a wider width. Thisis a great way to expand capacity without purchasing entirelynew machines.


The final item all engineers should note is balance. Whetheryou’re using coating rolls, wiper rolls or chill rolls, they need tobe balanced for the specific line speed. Rolls should undergostatic and dynamic balancing procedures. Static balancingeliminates loping (which is what happens when the roller stopsand still wants to roll over due to a heavy spot). Dynamicbalancing eliminates operational vibration. The roller makerwill use special balancing machines to set the roll in fullrotation at the designated speed. Special sensors help detectareas of imbalance, so technicians can then adjust the weightdistribution to achieve perfect rotational harmony. Unbalancedrollers result in damage to bearings, wasted stock and poorprocessing results.


The final item all engineers should note is balance. Whetheryou’re using coating rolls, wiper rolls or chill rolls, they need tobe balanced for the specific line speed. Rolls should undergostatic and dynamic balancing procedures. Static balancingeliminates loping (which is what happens when the roller stopsand still wants to roll over due to a heavy spot). Dynamicbalancing eliminates operational vibration. The roller makerwill use special balancing machines to set the roll in fullrotation at the designated speed. Special sensors help detectareas of imbalance, so technicians can then adjust the weightdistribution to achieve perfect rotational harmony. Unbalancedrollers result in damage to bearings, wasted stock and poorprocessing results.


Don’t underestimate the importance of your plant’s rollers.They are bound to touch your products at multiple points alongthe line—not just at the adhesive application station. Keep yourrollers clean and balanced, and don’t be afraid to renew thecovers. These expenditures will pay you back with reducedwaste, higher line speeds, and better finished products.

About Roll Coaters- How roll coaters work- Coating thickness control- Feedroller configurations- Selecting a roll coaterHow Roll Coaters WorkRoll coating machines are commonly used for the applicationof a liquid to the surface of a part. Rollcoaters can be used toapply liquid adhesives, paints, oils, and coatings such asvarnish or clear finish coats. Rollcoaters can take manyforms, from simple paint rollers to sophisticated coatingmachines with multiple rollers. A roll coating machine worksby transferring a layer of coating from the surface of a roller tothe surface of a part. When this happens, a phenomenon knowas “film splitting” occurs. The layer of coating on the surfaceof the roll splits – part of it stays on the roller, and part sticksto the surface of the part. The percentage of coating that sticksto the part (the substrate) depends on the surface

About Roll Coaters- How roll coaters work- Coating thickness control- Feedroller configurations- Selecting a roll coaterHow Roll Coaters WorkRoll coating machines are commonly used for the applicationof a liquid to the surface of a part. Rollcoaters can be used toapply liquid adhesives, paints, oils, and coatings such asvarnish or clear finish coats. Rollcoaters can take manyforms, from simple paint rollers to sophisticated coatingmachines with multiple rollers. A roll coating machine worksby transferring a layer of coating from the surface of a roller tothe surface of a part. When this happens, a phenomenon knowas “film splitting” occurs. The layer of coating on the surfaceof the roll splits – part of it stays on the roller, and part sticksto the surface of the part. The percentage of coating that sticksto the part (the substrate) depends on the surface

Characteristics Of Both The Roller And The Substrate.Coating Thickness ControlWith most rollcoaters, there is some means of controlling thethickness of the coating on the surface of the roller before itcontacts the substrate. The three most common approaches tocontrolling the coating thickness are metering blade, meteringroller, and transfer from anotherroll.Metering BladeA typical arrangement for a metering blade is shown in Figure#1. Coating is picked up from a reservoir by the applicationroller. As the coating clings to the roller and is carried up bythe rotation of the roller, only a certain amount can passthrough the gap between the metering blade and the rollsurface. The excess flows back to the tank. Metering bladesare usually made with some means of adjustment, so coatingthickness changes are made by moving the blade to open orclose the gap.

Characteristics Of Both The Roller And The Substrate.Coating Thickness ControlWith most rollcoaters, there is some means of controlling thethickness of the coating on the surface of the roller before itcontacts the substrate. The three most common approaches tocontrolling the coating thickness are metering blade, meteringroller, and transfer from anotherroll.Metering BladeA typical arrangement for a metering blade is shown in Figure#1. Coating is picked up from a reservoir by the applicationroller. As the coating clings to the roller and is carried up bythe rotation of the roller, only a certain amount can passthrough the gap between the metering blade and the rollsurface. The excess flows back to the tank. Metering bladesare usually made with some means of adjustment, so coatingthickness changes are made by moving the blade to open orclose the gap.

In some cases the metering blade may be moved forward andback on its mount plate, It can also be rotated to change thegap between the metering blade and the roller. Theadvantages of a metering blade over other means of coatingthickness control are low cost, simplicity of design, and thefact that the metering blade system does not require muchspace. Two disadvantages are the potential for clogging andpotential for roller damage. Clogging can occur if debris orforeign matter in the liquid gets caught in the gap between thecoating roller and the metering blade. This can block aportion of the coating from passing through the gap, whichcan cause streaks or inconsistent coating results. In caseswhere the debris is abrasive, it can cause damage to thesurface of the roller. Some types of coatings also tend tocongeal or clump if subjected to situations where there areshear forces on the liquid. This situation occurs between ametering blade and a coating roller.




Metering RollsTypical metering roll arrangements are shown in figure #2. Ina metering roll system, the thickness of the coating iscontrolled by adjusting the gap between two rollers. In atypical bottom coating application the coating is picked upfrom a reservoir and carried up to a nip point by one roll, thenthe excess is metered off by a second roll which also serves asan application roller. A similar concept is used when coatingmust be applied to the top surface of a part. Coating is held inthe valley formed between the metering roller and coatingroller, and the gap between the rollers is adjusted to change thecoating thickness.

For this reason materials such as latex adhesives do not runwell in machines having metering blades. This type ofadhesive would form clumps which would clog themetering blade to roller interface.

Metering RollsTypical metering roll arrangements are shown in figure #2. Ina metering roll system, the thickness of the coating iscontrolled by adjusting the gap between two rollers. In atypical bottom coating application the coating is picked upfrom a reservoir and carried up to a nip point by one roll, thenthe excess is metered off by a second roll which also serves asan application roller. A similar concept is used when coatingmust be applied to the top surface of a part. Coating is held inthe valley formed between the metering roller and coatingroller, and the gap between the rollers is adjusted to change thecoating thickness.

Metering roller systems are more expensive to build thanmetering blade systems, but have several advantages. Theyare more tolerant of debris or foreign matter in the liquid,since it can often pass through the gap between the rolls andgo back into circulation. If the coating roll and metering rollare run at similar surface speeds, shear sensitive materialssuch as latex can be applied without problems. In somesituations, the coating roll and pickup roll are run at differentsurface speeds. This can be done to minimize the formation offoam in the tank, or to help smooth out the layer of coating onthe coating roller.

Reverse Roll CoatingIn reverse roll coating, the surface of the part is fed across thecoating roller in the opposite direction to the surface travel ofthe coating roller. This causes the coating roll to serve both asan application roller and a wiper roller.

Metering roller systems are more expensive to build thanmetering blade systems, but have several advantages. Theyare more tolerant of debris or foreign matter in the liquid,since it can often pass through the gap between the rolls andgo back into circulation. If the coating roll and metering rollare run at similar surface speeds, shear sensitive materialssuch as latex can be applied without problems. In somesituations, the coating roll and pickup roll are run at differentsurface speeds. This can be done to minimize the formation offoam in the tank, or to help smooth out the layer of coating onthe coating roller.

Reverse Roll CoatingIn reverse roll coating, the surface of the part is fed across thecoating roller in the opposite direction to the surface travel ofthe coating roller. This causes the coating roll to serve both asan application roller and a wiper roller.

A small puddle of coating can form at the interface of rollerand substrate, and this flows onto the part as it passes underthe coating roll. A reverse roll coating arrangement is shownin Fig 3.Reverse roll coating is used to apply heavier coatings thanmight be possible with forward roll coating. It is also possibleto apply a very smooth coating by using the reverse rolltechnique. Since the coating is heavier, it tends to flow outbetter, and the flow from the puddle at the roller to partinterface tends to smooth out the coating. The result of thesetwo effects working together can provide coatings that arevery flat and smooth.The difficulties in reverse roll coating are in driving the partand in dealing with any coating build-up on the leading ortrailing edges of the part. In order to travel in the oppositedirection from the coating roller, the part must be driven in apositive manner so that it does not slip.

A small puddle of coating can form at the interface of rollerand substrate, and this flows onto the part as it passes underthe coating roll. A reverse roll coating arrangement is shownin Fig 3.Reverse roll coating is used to apply heavier coatings thanmight be possible with forward roll coating. It is also possibleto apply a very smooth coating by using the reverse rolltechnique. Since the coating is heavier, it tends to flow outbetter, and the flow from the puddle at the roller to partinterface tends to smooth out the coating. The result of thesetwo effects working together can provide coatings that arevery flat and smooth.The difficulties in reverse roll coating are in driving the partand in dealing with any coating build-up on the leading ortrailing edges of the part. In order to travel in the oppositedirection from the coating roller, the part must be driven in apositive manner so that it does not slip.

This can be done with pressure rolls having high frictioncoverings, with vacuum conveyer systems, or with drive beltshaving cogs or raised bosses to push the parts through.If a very heavy coating is being applied, it can drip over thelead edge or trailing edge of the part. With some types ofparts this does not pose a problem, but with others it can causecoating to transfer to the pressure rolls or feed conveyer andrequire cleanup. This problem can usually be controlled byfinding the optimum settings for coating weight, roller speed,and the speed of part travel.Transfer RollsTransfer roll systems (Fig 4) are actually a variation of themetering roll system, and utilize additional rollers to transferthe coating from the reservoir to the final point ofapplication. Because additional rollers are involved, thesesystems are more expensive than designs using only ametering roller and application roller,

This can be done with pressure rolls having high frictioncoverings, with vacuum conveyer systems, or with drive beltshaving cogs or raised bosses to push the parts through.If a very heavy coating is being applied, it can drip over thelead edge or trailing edge of the part. With some types ofparts this does not pose a problem, but with others it can causecoating to transfer to the pressure rolls or feed conveyer andrequire cleanup. This problem can usually be controlled byfinding the optimum settings for coating weight, roller speed,and the speed of part travel.Transfer RollsTransfer roll systems (Fig 4) are actually a variation of themetering roll system, and utilize additional rollers to transferthe coating from the reservoir to the final point ofapplication. Because additional rollers are involved, thesesystems are more expensive than designs using only ametering roller and application roller,

but there are several reasons why transfer rollers are used insome types of equipment. These reasons are coatingthickness, roller space limitations, and special roller surfacematerial requirements.In general transfer roll systems are capable of depositing athinner coating than two roll systems. This is because a filmsplit occurs at every roller interface, so the film of coating willbe thinner on each consecutive roller in the roller train.Roller space limitations also may dictate the use of transferrolls. In some types of equipment, there is not enough spaceto place large diameter metering rollers close to theapplication point, and transfer rolls can be used to carry thecoating from the initial metering point to the application point.Transfer rolls can also be used in situations where theapplication roller must be made of a material that is not wellsuited to use as a metering roll (such as a soft rubber).

but there are several reasons why transfer rollers are used insome types of equipment. These reasons are coatingthickness, roller space limitations, and special roller surfacematerial requirements.In general transfer roll systems are capable of depositing athinner coating than two roll systems. This is because a filmsplit occurs at every roller interface, so the film of coating willbe thinner on each consecutive roller in the roller train.Roller space limitations also may dictate the use of transferrolls. In some types of equipment, there is not enough spaceto place large diameter metering rollers close to theapplication point, and transfer rolls can be used to carry thecoating from the initial metering point to the application point.Transfer rolls can also be used in situations where theapplication roller must be made of a material that is not wellsuited to use as a metering roll (such as a soft rubber).

In these cases, metering of the coating is done with metal rollsor hard surfaced rolls, and the coating is transferred to theapplication roll. This configuration can also be useful insituations where rolls are used to transfer a pattern, such ascertain types of printing presses. The coating is metered out tothe surface of one roller, and the application roll picks up thecoating on a printing plate wrapped around the applicationroll. The plate transfers the coating to the part.Besides cost, one disadvantage of transfer roll systems is thatthey are more difficult to adjust and calibrate than meteringblade or two roll metering systems. In some situationsadditional rolls or wiper blades must be added to prevent anaccumulation of coating on rolls when parts are not beingcoated.Post Application MeteringIn many applications roll coating machines are used to applyan adhesive or finish coating to a part,

In these cases, metering of the coating is done with metal rollsor hard surfaced rolls, and the coating is transferred to theapplication roll. This configuration can also be useful insituations where rolls are used to transfer a pattern, such ascertain types of printing presses. The coating is metered out tothe surface of one roller, and the application roll picks up thecoating on a printing plate wrapped around the applicationroll. The plate transfers the coating to the part.Besides cost, one disadvantage of transfer roll systems is thatthey are more difficult to adjust and calibrate than meteringblade or two roll metering systems. In some situationsadditional rolls or wiper blades must be added to prevent anaccumulation of coating on rolls when parts are not beingcoated.Post Application MeteringIn many applications roll coating machines are used to applyan adhesive or finish coating to a part,

POST APPLICATION METERINGIn many applications roll coating machines are used to applyan adhesive or finish coating to a part, but the thickness orfinish of the layer being applied does not meet therequirements of the end product. In these cases a secondarymetering method can be used after the coating is applied toeither thin out the coating, smooth it, or texture it to meet thefinal requirements.Almost all post application-metering situations are used whenthe material being coated is in the form of a continuousweb. One method that is very popular is the use of a mayerrod or mayer bar. This is a rod wound with a layer of roundwire. This device can be used to both meter and smooth out alayer of coating. The bar is used as a scraper bar to wipe offexcess coating, and the spaces that exist between the roundwires serve to meter out a uniform layer of coating.

POST APPLICATION METERINGIn many applications roll coating machines are used to applyan adhesive or finish coating to a part, but the thickness orfinish of the layer being applied does not meet therequirements of the end product. In these cases a secondarymetering method can be used after the coating is applied toeither thin out the coating, smooth it, or texture it to meet thefinal requirements.Almost all post application-metering situations are used whenthe material being coated is in the form of a continuousweb. One method that is very popular is the use of a mayerrod or mayer bar. This is a rod wound with a layer of roundwire. This device can be used to both meter and smooth out alayer of coating. The bar is used as a scraper bar to wipe offexcess coating, and the spaces that exist between the roundwires serve to meter out a uniform layer of coating.

In most cases the material being metered off will form aseries of peaks and valleys that will flow out to form a smoothuniform layer. Mayer bars may be used in sequence to dorough metering then fine metering/smoothing, and are used onmany production lines that produce pressure sensitive films,tapes, and other materials that require a thin, smooth finishcoating. A configuration using a mayer rod is shown in FIG 5.In certain cases, application rolls can be built with surfacetextures that provide the type of surface finish desired withoutpost-application metering. The ability to do this will oftendepend on the characteristics of the coating being applied, aswell as the characteristics of the substrate. With the rightcombination of characteristics, a simple machine may be ableto produce results that normally would be produced by a morecomplex machine. Some machines are built with applicationrollers having grooves, knurled surfaces, or engraved surfacesdesigned to carry more coating than can be carried by asmooth roller.

In most cases the material being metered off will form aseries of peaks and valleys that will flow out to form a smoothuniform layer. Mayer bars may be used in sequence to dorough metering then fine metering/smoothing, and are used onmany production lines that produce pressure sensitive films,tapes, and other materials that require a thin, smooth finishcoating. A configuration using a mayer rod is shown in FIG 5.In certain cases, application rolls can be built with surfacetextures that provide the type of surface finish desired withoutpost-application metering. The ability to do this will oftendepend on the characteristics of the coating being applied, aswell as the characteristics of the substrate. With the rightcombination of characteristics, a simple machine may be ableto produce results that normally would be produced by a morecomplex machine. Some machines are built with applicationrollers having grooves, knurled surfaces, or engraved surfacesdesigned to carry more coating than can be carried by asmooth roller.

The surface texture can be used as a method of controlling theamount of coating deposited by a roller.

Web CoatingThe majority of coating applications are ones where acontinuous strip (web) of material is coated, then dried (orchilled), and rewound into a roll. Web coating lends itself tohigh production rates, and can be used with almost all types ofadhesives and coatings. Many web coating applicationsutilize roll coaters to apply the adhesive or coating, and mostutilize some form of post-application metering. In general,web coating is done at much higher speeds than sheet coating,and considerable attention must be given to factors such asproper web tracking, web tension control, web flutter, andstretching. Since the web is a continuous strip, it can passover a number of rollers as it is being coated or treated, andsome web coating configurations can be very complex.

The surface texture can be used as a method of controlling theamount of coating deposited by a roller.

Web CoatingThe majority of coating applications are ones where acontinuous strip (web) of material is coated, then dried (orchilled), and rewound into a roll. Web coating lends itself tohigh production rates, and can be used with almost all types ofadhesives and coatings. Many web coating applicationsutilize roll coaters to apply the adhesive or coating, and mostutilize some form of post-application metering. In general,web coating is done at much higher speeds than sheet coating,and considerable attention must be given to factors such asproper web tracking, web tension control, web flutter, andstretching. Since the web is a continuous strip, it can passover a number of rollers as it is being coated or treated, andsome web coating configurations can be very complex.

An engraved roller (gravure roll) is used in many web-coatingapplications. This is used to transfer a very precise amount ofadhesive to the web. Two typical web coating configurationsare shown in Fig 6, both of them utilizing a gravure roller.Pressure Roll ConfigurationsWith any roll coater, the substrate to be coated must bebrought into contact with the application roller to pick upcoating. In some situations the part can be directly pressedagainst the coating roller by a pressure roll, and in others thesubstrate must be guided over the surface of the coating rollerso that it just kisses the roller with enough contact to pick upthe liquid. Pressure rolls are sometimes called feedrolls,backup rolls, or guide rolls.The configuration of the pressure roll relative to the coatingapplication roll is usually determined by the thickness andflexibility of the substrate to be coated.

An engraved roller (gravure roll) is used in many web-coatingapplications. This is used to transfer a very precise amount ofadhesive to the web. Two typical web coating configurationsare shown in Fig 6, both of them utilizing a gravure roller.Pressure Roll ConfigurationsWith any roll coater, the substrate to be coated must bebrought into contact with the application roller to pick upcoating. In some situations the part can be directly pressedagainst the coating roller by a pressure roll, and in others thesubstrate must be guided over the surface of the coating rollerso that it just kisses the roller with enough contact to pick upthe liquid. Pressure rolls are sometimes called feedrolls,backup rolls, or guide rolls.The configuration of the pressure roll relative to the coatingapplication roll is usually determined by the thickness andflexibility of the substrate to be coated.

If the pressure roll is too close to the coating roller there is apossibility that it can pick up excess coating that flows off ofthe substrate, and then transfer this coating on the oppositeside of the substrate. In some cases a droplet of coating cantravel around on the surface of the pressure roll. This canallow it to pick up a bit of coating on each revolution until theroll becomes almost totally covered, requiring that theequipment be stopped for cleanup.When coating thin substrates the pressure rolls must be asufficient distance from the coating roller to avoidcontamination, but still ensure that the substrate can be driventhrough the machine and pick up a coating. This can beaccomplished by locating the pressure rolls in such a way thatthe substrate is forced to bend over the coating roller, or bypressing the part directly against the coating roller with thepressure roll and removing any excess that transfers to thepressure roll with a wiper or cleaning roll.

If the pressure roll is too close to the coating roller there is apossibility that it can pick up excess coating that flows off ofthe substrate, and then transfer this coating on the oppositeside of the substrate. In some cases a droplet of coating cantravel around on the surface of the pressure roll. This canallow it to pick up a bit of coating on each revolution until theroll becomes almost totally covered, requiring that theequipment be stopped for cleanup.When coating thin substrates the pressure rolls must be asufficient distance from the coating roller to avoidcontamination, but still ensure that the substrate can be driventhrough the machine and pick up a coating. This can beaccomplished by locating the pressure rolls in such a way thatthe substrate is forced to bend over the coating roller, or bypressing the part directly against the coating roller with thepressure roll and removing any excess that transfers to thepressure roll with a wiper or cleaning roll.

A third technique is to coat only a portion of the substrate andleave the edges uncoated to avoid any transfer of coating.If the substrate to be coated is sufficiently thick there is lesschance of coating transfer and the pressure roll can be locatedso that it presses the part directly against the coating roller.Different configurations of pressure rolls relative to coatingrolls have been used for various types of equipment. Sometypical configurations are shown here: In the configurationshown in Fig 8 the substrate must flex as it hits the coatingroll, and the deflection creates a slight pressure of thesubstrate to the roll. Once the substrate is in contact with theroll, the surface tension of the adhesive will tend to cause it tostick to the roll and be pulled through the machine. Thestripper points indicated are small knife like fingers designedto break the leading edge of a flexible substrate free of thecoating roller and allow the part to feed through withoutwrapping around the coating roller.

A third technique is to coat only a portion of the substrate andleave the edges uncoated to avoid any transfer of coating.If the substrate to be coated is sufficiently thick there is lesschance of coating transfer and the pressure roll can be locatedso that it presses the part directly against the coating roller.Different configurations of pressure rolls relative to coatingrolls have been used for various types of equipment. Sometypical configurations are shown here: In the configurationshown in Fig 8 the substrate must flex as it hits the coatingroll, and the deflection creates a slight pressure of thesubstrate to the roll. Once the substrate is in contact with theroll, the surface tension of the adhesive will tend to cause it tostick to the roll and be pulled through the machine. Thestripper points indicated are small knife like fingers designedto break the leading edge of a flexible substrate free of thecoating roller and allow the part to feed through withoutwrapping around the coating roller.

This type of single pressure roll configuration is typically usedwith paper.With the roll configuration shown in Fig 9 the two pressurerolls force the part to cup over the coating roller and pick up afull coating. The part flexes upward as it passes under the firstroller and hits the coating application roll, and is forcedaround the coating roller as it hits the second pressure roll.This roller arrangement can be versatile – it can often be usedwith a range of substrate thicknesses, since moving thepressure rolls relative to the coating roller can allow paper tobe coated when the rolls are close to the coating roll, andthicker parts coated as the pressure rolls are moved away fromthe coating roll. By raising the dual rollers high enough abovethe coating roller, it may be possible to also coat rigid andsemi-rigid substrates with this roll configuration. Stripperfingers are generally used with flexible substrates, but may notbe required with stiffer materials.

This type of single pressure roll configuration is typically usedwith paper.With the roll configuration shown in Fig 9 the two pressurerolls force the part to cup over the coating roller and pick up afull coating. The part flexes upward as it passes under the firstroller and hits the coating application roll, and is forcedaround the coating roller as it hits the second pressure roll.This roller arrangement can be versatile – it can often be usedwith a range of substrate thicknesses, since moving thepressure rolls relative to the coating roller can allow paper tobe coated when the rolls are close to the coating roll, andthicker parts coated as the pressure rolls are moved away fromthe coating roll. By raising the dual rollers high enough abovethe coating roller, it may be possible to also coat rigid andsemi-rigid substrates with this roll configuration. Stripperfingers are generally used with flexible substrates, but may notbe required with stiffer materials.

In Figure 10 the part is pressed directly against the coatingroll by the pressure roll. If the part has sufficient thickness,stripper fingers are not needed since the part will not cling tothe coating roll. Pressure rolls may or may not be driven,depending on the type of material being coated and the type ofadhesive, since some types of adhesive generate sufficientdriving force to pull the part through the machine.The configuration shown in Fig 11 is designed to force atravelling strip of material to come in contact with the coatingroller and pick up coating. Web guide rolls do not need to bedriven, since the web is generally pulled by a rewind or take-up roll, and the tension on the web creates the pressure of thesubstrate against the coating roller.In web coating, it is possible to pull the substrate over thecoating roller at a different speed than the surface of theroller. This technique is often used to deposit a thinner layerof coating than would be deposited by the roller running at thesame speed as the web.

In Figure 10 the part is pressed directly against the coatingroll by the pressure roll. If the part has sufficient thickness,stripper fingers are not needed since the part will not cling tothe coating roll. Pressure rolls may or may not be driven,depending on the type of material being coated and the type ofadhesive, since some types of adhesive generate sufficientdriving force to pull the part through the machine.The configuration shown in Fig 11 is designed to force atravelling strip of material to come in contact with the coatingroller and pick up coating. Web guide rolls do not need to bedriven, since the web is generally pulled by a rewind or take-up roll, and the tension on the web creates the pressure of thesubstrate against the coating roller.In web coating, it is possible to pull the substrate over thecoating roller at a different speed than the surface of theroller. This technique is often used to deposit a thinner layerof coating than would be deposited by the roller running at thesame speed as the web.

The travelling action of the web can also cause the coatingroller to act as a wiper bar, so that the coating is smoothed outas it gets squeezed between the web and the coating roller.Selecting A Roll coaterThe selection of the best roll coating machine for anyparticular type of work depends on a number of factors. Thekey questions that need to be considered are as follows:A. Type of adhesiveB. Thickness of substrateC. Width of substrateD. Full coat or partial coatE. Handling after coatingF. CleanupA. Type of adhesive – (or coating)The type of adhesive or coating will influence the way theliquids are brought to the metering point. Although mostadhesives will work for short periods of time in any type ofroll coater,

The travelling action of the web can also cause the coatingroller to act as a wiper bar, so that the coating is smoothed outas it gets squeezed between the web and the coating roller.Selecting A Roll coaterThe selection of the best roll coating machine for anyparticular type of work depends on a number of factors. Thekey questions that need to be considered are as follows:A. Type of adhesiveB. Thickness of substrateC. Width of substrateD. Full coat or partial coatE. Handling after coatingF. CleanupA. Type of adhesive – (or coating)The type of adhesive or coating will influence the way theliquids are brought to the metering point. Although mostadhesives will work for short periods of time in any type ofroll coater,

problems can occur with certain adhesives that would causethe coating results to become inconsistent as the material runsfor longer periods. Some general guidelines are as follows:1) Evaporation of the solvent or water in an adhesive is amajor consideration in how well it will run in a rollcoater. When running solvent based materials, as little surfacearea as possible should be exposed, and material should be inconstant agitation to prevent dead areas which can form a skinof partially dried adhesive. Machines designed for solventbase adhesives or fast setting water base adhesives would haverollers shielded as much as possible, and would include pumpsor other methods to keep the material in constant circulation.2) Machines for latex-based adhesives would be designedto minimize areas where the adhesive would be subject to ashearing action which could cause clumps to form.3) It should be easy to add fresh adhesive to any machine.

problems can occur with certain adhesives that would causethe coating results to become inconsistent as the material runsfor longer periods. Some general guidelines are as follows:1) Evaporation of the solvent or water in an adhesive is amajor consideration in how well it will run in a rollcoater. When running solvent based materials, as little surfacearea as possible should be exposed, and material should be inconstant agitation to prevent dead areas which can form a skinof partially dried adhesive. Machines designed for solventbase adhesives or fast setting water base adhesives would haverollers shielded as much as possible, and would include pumpsor other methods to keep the material in constant circulation.2) Machines for latex-based adhesives would be designedto minimize areas where the adhesive would be subject to ashearing action which could cause clumps to form.3) It should be easy to add fresh adhesive to any machine.

The design of the tank should be a compromise between thecapacity and the exposed surface area. Too large a tank maycause too much surface area to be exposed to evaporation, buttoo small a tank may require constant refilling. Automaticrefill systems can be fitted to some machines to alleviate theneed to refill constantly.4) Some types of materials do not flow well, and need tobe pumped to the metering point. In some cases thesematerials can be carried up by a pickup roll that rotates slowlyenough to be wetted by then adhesive, but in other casespumping systems are required. This is especially true withcertain high viscosity materials such as epoxies, solventcements and urethane adhesives.5) Certain types of adhesives and coatings have specialcharacteristics that must be taken into account when selectingor designing a roll coater to handle them. An example of thisare Ultraviolet cured coatings (UV cure).

The design of the tank should be a compromise between thecapacity and the exposed surface area. Too large a tank maycause too much surface area to be exposed to evaporation, buttoo small a tank may require constant refilling. Automaticrefill systems can be fitted to some machines to alleviate theneed to refill constantly.4) Some types of materials do not flow well, and need tobe pumped to the metering point. In some cases thesematerials can be carried up by a pickup roll that rotates slowlyenough to be wetted by then adhesive, but in other casespumping systems are required. This is especially true withcertain high viscosity materials such as epoxies, solventcements and urethane adhesives.5) Certain types of adhesives and coatings have specialcharacteristics that must be taken into account when selectingor designing a roll coater to handle them. An example of thisare Ultraviolet cured coatings (UV cure).

Machines that are used to apply these coatings must haveshielding or guarding in place to keep the coating shieldedfrom light as much as possible, since light exposure can causeUV cure coatings to catalyze earlier than desired or candegrade the characteristics of the coating.The type of adhesive will affect the choice of materials for therollers and reservoir, the approach to coating thicknesscontrol, the method of machine cleanup, and the way thatcoating gets delivered to the metering point. Certain types ofadhesives (such as hotmelts, waxes and certain high viscositymaterials) require that the machine or the rollers be heated tomelt the material or lower the viscosity to a point where it canbe applied. Some adhesives or coatings will react with certainmetals or other materials, and this can degrade the adhesive asthe machine runs, or cause damage to the coater. Examples ofthis are the reactions of copper containing alloys with latexcements and U.V. cured adhesives.

Machines that are used to apply these coatings must haveshielding or guarding in place to keep the coating shieldedfrom light as much as possible, since light exposure can causeUV cure coatings to catalyze earlier than desired or candegrade the characteristics of the coating.The type of adhesive will affect the choice of materials for therollers and reservoir, the approach to coating thicknesscontrol, the method of machine cleanup, and the way thatcoating gets delivered to the metering point. Certain types ofadhesives (such as hotmelts, waxes and certain high viscositymaterials) require that the machine or the rollers be heated tomelt the material or lower the viscosity to a point where it canbe applied. Some adhesives or coatings will react with certainmetals or other materials, and this can degrade the adhesive asthe machine runs, or cause damage to the coater. Examples ofthis are the reactions of copper containing alloys with latexcements and U.V. cured adhesives.

Other examples of incompatible materials would be aluminumcomponents used with highly acidic adhesives (such as hotanimal glue). In this case the metal components would beattacked and damaged by the glue.Some adhesives are sensitive to a shearing action whichoccurs with a scraper blade, and can tend to congeal whensubjected to this type of force. These adhesives and coatingsmust be run in machines having metering rollers.For adhesives and coatings that must be heated either therollers must be heated directly or the tank which holds thematerial must be heated, and the heat from the tank andmaterial transferred to the application roller. The need forheating can limit the choice of materials for the roller, sinceany material selected must be capable of maintaining criticaldimensions when heated to the operating temperature.With any type of coating machine the type of adhesive orcoating will affect the cleanup method.

Other examples of incompatible materials would be aluminumcomponents used with highly acidic adhesives (such as hotanimal glue). In this case the metal components would beattacked and damaged by the glue.Some adhesives are sensitive to a shearing action whichoccurs with a scraper blade, and can tend to congeal whensubjected to this type of force. These adhesives and coatingsmust be run in machines having metering rollers.For adhesives and coatings that must be heated either therollers must be heated directly or the tank which holds thematerial must be heated, and the heat from the tank andmaterial transferred to the application roller. The need forheating can limit the choice of materials for the roller, sinceany material selected must be capable of maintaining criticaldimensions when heated to the operating temperature.With any type of coating machine the type of adhesive orcoating will affect the cleanup method.

Some types of materials can be easily cleaned – others requireextensive washing with solvents or water to remove anyresidue. Most machines used for the application of hotmeltsdo not require cleanup. The adhesive is simply allowed tocool and hardens up in the machine. One exception to this arethe “reactive” hotmelts or “moisture cure” hotmelts whichmust be purged from the equipment before it is shut down.B. Thickness of substrateThe thickness of the substrate determines the type of feed rollconfiguration that will give the best results in coating thepart. The part must be able to come into full contact with thecoating roller to pick up a consistent coating, but should notcause the coating to transfer to the feed roller (or feed rolls).Thin flexible substrates (such as paper), are usually bestcoated by using an offset pressure roller or dual feed rollerarrangement, and coating of individual sheets will require theuse of stripper fingers.

Some types of materials can be easily cleaned – others requireextensive washing with solvents or water to remove anyresidue. Most machines used for the application of hotmeltsdo not require cleanup. The adhesive is simply allowed tocool and hardens up in the machine. One exception to this arethe “reactive” hotmelts or “moisture cure” hotmelts whichmust be purged from the equipment before it is shut down.B. Thickness of substrateThe thickness of the substrate determines the type of feed rollconfiguration that will give the best results in coating thepart. The part must be able to come into full contact with thecoating roller to pick up a consistent coating, but should notcause the coating to transfer to the feed roller (or feed rolls).Thin flexible substrates (such as paper), are usually bestcoated by using an offset pressure roller or dual feed rollerarrangement, and coating of individual sheets will require theuse of stripper fingers.

Extremely flexible substrates such as fabrics, thin foam, non-woven fabric, thin rubber etc, can be very difficult to coatsince they will tend to bunch up and fold over themselves asthey exit the coating point. In some cases, these types ofmaterial can only be coated using a backing board of sufficientstiffness, coating them in a web form, or by leaving a portionat the leading edge uncoated, and using this part to pull thesubstrate through the coating point. This can be done byloading the part into the coating machine with the feed rolleropen, then bringing the feed roller into a position where it candrive the part while there is some tension on the part to keep itfrom going slack and bunching up.Thicker or stiffer substrates can be driven with a dual feedrollor single feed roll arrangement. In some cases, stiff substratessuch as plywood or fiber board can present problems, sincethey may have high and low spots that will bridge over thecoating roll and create voids in the coating.

Extremely flexible substrates such as fabrics, thin foam, non-woven fabric, thin rubber etc, can be very difficult to coatsince they will tend to bunch up and fold over themselves asthey exit the coating point. In some cases, these types ofmaterial can only be coated using a backing board of sufficientstiffness, coating them in a web form, or by leaving a portionat the leading edge uncoated, and using this part to pull thesubstrate through the coating point. This can be done byloading the part into the coating machine with the feed rolleropen, then bringing the feed roller into a position where it candrive the part while there is some tension on the part to keep itfrom going slack and bunching up.Thicker or stiffer substrates can be driven with a dual feedrollor single feed roll arrangement. In some cases, stiff substratessuch as plywood or fiber board can present problems, sincethey may have high and low spots that will bridge over thecoating roll and create voids in the coating.

For these types of materials a soft faced coating roller may beneeded to contact the entire surface and apply coating.CWidth of SubstrateIn general, the width of a roll coating machine should be atleast 2 inches wider than the widest part to be coated. Withthis extra width, if the part is loaded into the machine slightlycrooked, the full surface will still get coated.D. Full coat or partial coatRoll coating machines are available that can apply coating toonly a portion of a sheet or the full surface. There are alsopattern coaters available that can apply stripes or other typesof patterns in the same manner as a printing press (see transferroll systems). In selecting a coating machine, it is importantto define the area to be coated. Is it full surface, a pattern, or astripe along one edge?

For these types of materials a soft faced coating roller may beneeded to contact the entire surface and apply coating.CWidth of SubstrateIn general, the width of a roll coating machine should be atleast 2 inches wider than the widest part to be coated. Withthis extra width, if the part is loaded into the machine slightlycrooked, the full surface will still get coated.D. Full coat or partial coatRoll coating machines are available that can apply coating toonly a portion of a sheet or the full surface. There are alsopattern coaters available that can apply stripes or other typesof patterns in the same manner as a printing press (see transferroll systems). In selecting a coating machine, it is importantto define the area to be coated. Is it full surface, a pattern, or astripe along one edge?

E. Handling after coatingOnce a part is coated with adhesive, it can become much moredifficult to handle than a dry part, so it is important to thinkabout how the part will be handled once it is coated.The simplest and least inexpensive roll coaters coat the bottomsurface of the part. This means that the part must be handledimmediately as it exits the machine, and must be handled bythe coated surface. With many types of parts this does notpresent a problem, but potential problems with wet gluegetting on operators fingers need to be addressed. If theoperators are able to handle and locate parts withoutcontaminating the clean surfaces there will be no problem, butin some cases the operators will need to use special tools tohandle the parts, or wipe their fingers clean of glue at somepoint in the gluing and assembly operation.With machines designed to apply adhesive or coatings to thetop surface of the parts the issue of glue contamination isdrastically reduced.

E. Handling after coatingOnce a part is coated with adhesive, it can become much moredifficult to handle than a dry part, so it is important to thinkabout how the part will be handled once it is coated.The simplest and least inexpensive roll coaters coat the bottomsurface of the part. This means that the part must be handledimmediately as it exits the machine, and must be handled bythe coated surface. With many types of parts this does notpresent a problem, but potential problems with wet gluegetting on operators fingers need to be addressed. If theoperators are able to handle and locate parts withoutcontaminating the clean surfaces there will be no problem, butin some cases the operators will need to use special tools tohandle the parts, or wipe their fingers clean of glue at somepoint in the gluing and assembly operation.With machines designed to apply adhesive or coatings to thetop surface of the parts the issue of glue contamination isdrastically reduced.

The top surface of the part is coated, and the bottom sideremains clean for handling. Parts can be fed directly onto aconveyer- (which is not possible with bottom-coatedparts). This can be important with large parts which would beawkward to handle by the coated surface. Top Coating isessential for parts which are being coated with a finish coat,since the finish coat must have time to self-level and flow outinto a smooth coating after being applied.F. CleanupWith any roll coater, any adhesive remaining in the machineafter operation is complete must be cleaned completely or itcan dry on the rollers or other parts of the machine and causeproblems. Liquids which do not dry (such as oils) can be leftin the machine, as can most hotmelt adhesives, but other typesof adhesive and coatings must be cleaned out of the machine.Ease of cleanup must be considered when selecting a rollcoater.

The top surface of the part is coated, and the bottom sideremains clean for handling. Parts can be fed directly onto aconveyer- (which is not possible with bottom-coatedparts). This can be important with large parts which would beawkward to handle by the coated surface. Top Coating isessential for parts which are being coated with a finish coat,since the finish coat must have time to self-level and flow outinto a smooth coating after being applied.F. CleanupWith any roll coater, any adhesive remaining in the machineafter operation is complete must be cleaned completely or itcan dry on the rollers or other parts of the machine and causeproblems. Liquids which do not dry (such as oils) can be leftin the machine, as can most hotmelt adhesives, but other typesof adhesive and coatings must be cleaned out of the machine.Ease of cleanup must be considered when selecting a rollcoater.

Most roll coaters are designed for quick cleanup, and mayincorporate features in their design to facilitate this aspect ofoperation. Some design features that are used to makecleanup easier are:a) Wash down systems for rollers and tanksb) Removable coating unitsc) Easily removable tanksd) Separate wash tankse) Built-in flush systems (often used on printing equipment)f) Removable rollersRoll Coater SelectionOnce the factors described above are taken into consideration,the choice of a roll coater suitable for the work to be done willoften be narrowed down to one or two machines. As eachquestion is answered, only one or two machines from anymanufacturer may fit the requirements, so by the time theentire list of questions is reviewed, the choice of the bestmachine for the job will usually be obvious.

Most roll coaters are designed for quick cleanup, and mayincorporate features in their design to facilitate this aspect ofoperation. Some design features that are used to makecleanup easier are:a) Wash down systems for rollers and tanksb) Removable coating unitsc) Easily removable tanksd) Separate wash tankse) Built-in flush systems (often used on printing equipment)f) Removable rollersRoll Coater SelectionOnce the factors described above are taken into consideration,the choice of a roll coater suitable for the work to be done willoften be narrowed down to one or two machines. As eachquestion is answered, only one or two machines from anymanufacturer may fit the requirements, so by the time theentire list of questions is reviewed, the choice of the bestmachine for the job will usually be obvious.

In some cases questions about the suitability of a roll-coatingmachine for a particular application still remains. In thesecases the best way to answer the questions is to run a testusing the roll coater, the adhesive, and the substrate together todetermine if they produce the desired results.

We shall review a few of them those are frequently use inFlexible Packing, Adhesive Tapes, Adhesive Labels , orother packing applications.

Gravure Coating


Comma Coating


Hot Melt Coating Extrusion coating

Gravure Coating


Comma Coating


Hot Melt Coating Extrusion coating

To understand the process of coating on a substrate for themanufacture of Packaging Material is quite simple .

The Adhesive/ Ink/ or specialty coating to be coated must havegood spread ability.

And let’s not forget one must have a right equipment to spread orcoat.

There are some of the other variable factors also involved , but weshall look into coating methods Exclusively.

To understand the process of coating on a substrate for themanufacture of Packaging Material is quite simple .

The Adhesive/ Ink/ or specialty coating to be coated must havegood spread ability.

And let’s not forget one must have a right equipment to spread orcoat.

There are some of the other variable factors also involved , but weshall look into coating methods Exclusively.

CoatingMethod

Viscosityin CPS

Max Speedper Min

Coating Wt .gm per sq. mtr

Gravure 100-2000700

Mtrs. 3.-20.

The Coating methods

Their Capabilities and Limitations

Gravure 100-2000700

Mtrs. 3.-20.

Comma 1000-6000 300 10-200

Reverse Roll Nip 1000-6000 300 10-200

Reverse Roll Pan 200-6000 100 10-200

Hot Melt 500-20000 300 10-300Myer Bar 10-200 200 3.-25.

Knife over Roll 100-20000 1500 3.-15.

The Coating methods

Their Capabilities and Limitations

Knife over Roll 100-20000 1500 3.-15.

Slot Orifice 500-20000 200 20-100

Immersion / Dip Coating 1000-10000 50 Heavy

Curtain 500-20000 200 20-100

The gravure coating process relies on an engraved roller running ina coating bath, which fills the engraved dots or lines of the rollerwith the coating material.

The excess coating on the roller is wiped off by the Doctor Bladeand the coating is then deposited onto the substrate as it passesbetween the Engraved roller and a Pressure Roller.

There are three different ways of gravure roll manufacturing . Onehas to choose a correct type depending upon the required coatinggram mage and the material to be coated

Gravure Coating

The gravure coating process relies on an engraved roller running ina coating bath, which fills the engraved dots or lines of the rollerwith the coating material.

The excess coating on the roller is wiped off by the Doctor Bladeand the coating is then deposited onto the substrate as it passesbetween the Engraved roller and a Pressure Roller.

There are three different ways of gravure roll manufacturing . Onehas to choose a correct type depending upon the required coatinggram mage and the material to be coated

Gravure Coating Capabilities

Viscosity Range : 10 - 2000 CpsWeb Width Range : 300 – 2500mmCoat Weight Range : 1 – 5gsm (Offset Gravure)

: 3-20gsm (Direct Gravure): 10 – 100gsm(reverse Gravure)

Substrates : Paper, Film And Foil.

Gravure CoatingThe Process :

The Main Components:

Coating Tray / Pan

Gravure Roller (Etched Metal roller)

Doctor Blade

Impression Roll (Rubber roller)

The Process:

Pick up of Coating from the Pan

Fill up the Cells in the gravure roller

Wipe out the excess coating by Doctor Blade

Transfer the Coating to the Web

Empty the Gravure Cells after Transferring to Web

Gravure CoatingThe Process :

The Main Components:

Coating Tray / Pan

Gravure Roller (Etched Metal roller)

Doctor Blade

Impression Roll (Rubber roller)

The Process:

Pick up of Coating from the Pan

Fill up the Cells in the gravure roller

Wipe out the excess coating by Doctor Blade

Transfer the Coating to the Web

Empty the Gravure Cells after Transferring to Web

In Gravure CoatingmethodThe Applicator Pan or theTray Plays a veryImportant Role

The Adhesive level has tobe maintained ConstantlyThe Foam generation hasto be minimizedNo settling of SolidsThis is Possible with someof the tray Designs shownin the figure

GravureRoll

Adhesive IN Adhesive OUT

In Gravure CoatingmethodThe Applicator Pan or theTray Plays a veryImportant Role

The Adhesive level has tobe maintained ConstantlyThe Foam generation hasto be minimizedNo settling of SolidsThis is Possible with someof the tray Designs shownin the figure Gravure

Roll

Adhesive INAdhesive OUT

The Gravure Roller performs important Functions

Apply continuous and homogeneous coating acrossand down the web

The etching pattern determines the coating weight

It is a driven toll to manage web tension

At times it is hollow with water circulation to maintaincoating temp and the viscosity of the coating

The Gravure Roller performs important Functions

Apply continuous and homogeneous coating acrossand down the web

The etching pattern determines the coating weight

It is a driven toll to manage web tension

At times it is hollow with water circulation to maintaincoating temp and the viscosity of the coating

In low weight coating or printing, anilox is a method used toprovide a measured amount of ink to a flexo printing plate.An anilox roll is a hard cylinder, usually constructed of a steelor aluminum core which is coated by an industrialceramic whose surface contains millions of very fine dimples,known as cells. Depending on the design of the printing press,the anilox roll is either semi-submerged in the ink fountain, orcomes into contact with a so-called metering roller, which issemi-submerged in the ink fountain. In either instance, a thicklayer of typically viscous ink is deposited on the roll. A doctorblade is used to scrape excess ink from the surface leaving justthe measured amount of ink in the cells. The roll then rotates tocontact with the flexographic printing plate which receives theink from the cells for transfer to the printed material.

In low weight coating or printing, anilox is a method used toprovide a measured amount of ink to a flexo printing plate.An anilox roll is a hard cylinder, usually constructed of a steelor aluminum core which is coated by an industrialceramic whose surface contains millions of very fine dimples,known as cells. Depending on the design of the printing press,the anilox roll is either semi-submerged in the ink fountain, orcomes into contact with a so-called metering roller, which issemi-submerged in the ink fountain. In either instance, a thicklayer of typically viscous ink is deposited on the roll. A doctorblade is used to scrape excess ink from the surface leaving justthe measured amount of ink in the cells. The roll then rotates tocontact with the flexographic printing plate which receives theink from the cells for transfer to the printed material.

The characteristics of an anilox roll determine the amount ofink that will be transferred to the plate: angle of the cells,cell volume, and line screen. A 60 percent angle ensuresmaximum density in a given space. Lower volume makes forless ink. Low line numbers will allow for a heavy layer of inkto be printed, whereas high line numbers will permit finerdetail in printing. Both cell volume and line screen are closelycorrelated.Anilox rolls are often specified by their line screen, which isthe number of cells per linear inch. These often range fromaround 250 to upwards of 2000, though the precise numbersvary by manufacturer. Most rolls sold are within 800 LPI,although a spike in demand for those with 800-1200 lines hasbeen seen. Anilox rolls are almost always designed to beremoved from the press for cleaning and for swapping out withdifferent line screen rolls.

The characteristics of an anilox roll determine the amount ofink that will be transferred to the plate: angle of the cells,cell volume, and line screen. A 60 percent angle ensuresmaximum density in a given space. Lower volume makes forless ink. Low line numbers will allow for a heavy layer of inkto be printed, whereas high line numbers will permit finerdetail in printing. Both cell volume and line screen are closelycorrelated.Anilox rolls are often specified by their line screen, which isthe number of cells per linear inch. These often range fromaround 250 to upwards of 2000, though the precise numbersvary by manufacturer. Most rolls sold are within 800 LPI,although a spike in demand for those with 800-1200 lines hasbeen seen. Anilox rolls are almost always designed to beremoved from the press for cleaning and for swapping out withdifferent line screen rolls.

Depending on the detail of the images to be printed, the pressoperator will select an anilox roll with a higher or lower linescreen. Low line screen rolls are used where a heavy layer ofink is desired, such as in heavy block lettering. Higher linescreens produce finer details and are used in four-colorprocess work such as reproducing photographs. Often a jobwill require a different line screen for each color to be printed.Experienced press operators are skilled at determining theappropriate anilox rolls for a given print job.Though large wide-web flexo rolls are only maneuverable byoverhead crane, on smaller presses anilox rolls are oftenhandled directly by operators. Extreme caution must be takenwhen handling these pieces of hardware as a single bumpagainst a hard surface or sharp corner can destroy the delicatecell structure on the surface and render a roller completelyuseless,

Depending on the detail of the images to be printed, the pressoperator will select an anilox roll with a higher or lower linescreen. Low line screen rolls are used where a heavy layer ofink is desired, such as in heavy block lettering. Higher linescreens produce finer details and are used in four-colorprocess work such as reproducing photographs. Often a jobwill require a different line screen for each color to be printed.Experienced press operators are skilled at determining theappropriate anilox rolls for a given print job.Though large wide-web flexo rolls are only maneuverable byoverhead crane, on smaller presses anilox rolls are oftenhandled directly by operators. Extreme caution must be takenwhen handling these pieces of hardware as a single bumpagainst a hard surface or sharp corner can destroy the delicatecell structure on the surface and render a roller completelyuseless,

at a cost of around US$5000 for even small narrow-webrollers. Nicks and scratches add up quickly, so fine brushes(never brass brushes) are used for cleaning the anilox roll.Similarly, anilox rollers that are used with water, solvent andoil based inks, which dry when left sitting out and unagitated,must be cleaned immediately after use or a problem known asplugging occurs, where minuscule amounts of ink dry in thecells. This leaves tiny, but unacceptable, pinholes in anythingprinted from the roll in the future.Anilox rolls were originally made using a diamond peckingmachine, but modern rolls are laser engraved.Laser engraving, which is different from laser marking,[1] isthe practice of using lasers to engrave an object. Laser markingon the other hand just discolors the surface, without cuttinginto the surface.

at a cost of around US$5000 for even small narrow-webrollers. Nicks and scratches add up quickly, so fine brushes(never brass brushes) are used for cleaning the anilox roll.Similarly, anilox rollers that are used with water, solvent andoil based inks, which dry when left sitting out and unagitated,must be cleaned immediately after use or a problem known asplugging occurs, where minuscule amounts of ink dry in thecells. This leaves tiny, but unacceptable, pinholes in anythingprinted from the roll in the future.Anilox rolls were originally made using a diamond peckingmachine, but modern rolls are laser engraved.Laser engraving, which is different from laser marking,[1] isthe practice of using lasers to engrave an object. Laser markingon the other hand just discolors the surface, without cuttinginto the surface.

The technique does not involve the use of inks, nor does itinvolve tool bits which contact the engraving surface and wearout. These properties distinguish laser engraving fromalternative engraving or marking technologies where inks orbit heads have to be replaced regularly.The impact of laser marking has been more pronounced forspecially designed "laserable" materials and also for somepaints. These include laser-sensitive polymers and novelmetal alloys.The term laser marking is also used as a generic termcovering a broad spectrum of surfacing techniques includingprinting, hot-branding andlaser bonding. The machines forlaser engraving and laser marking are the same, so that the twoterms are sometimes confused by those without knowledge orexperience in the practice.

The technique does not involve the use of inks, nor does itinvolve tool bits which contact the engraving surface and wearout. These properties distinguish laser engraving fromalternative engraving or marking technologies where inks orbit heads have to be replaced regularly.The impact of laser marking has been more pronounced forspecially designed "laserable" materials and also for somepaints. These include laser-sensitive polymers and novelmetal alloys.The term laser marking is also used as a generic termcovering a broad spectrum of surfacing techniques includingprinting, hot-branding andlaser bonding. The machines forlaser engraving and laser marking are the same, so that the twoterms are sometimes confused by those without knowledge orexperience in the practice.

Laser engraving of anilox rollsPrior to 1980 anilox rolls were produced by a variety ofmechanical processes. These metal anilox rolls weresometimes sprayed with ceramic to prolong their life intheflexographic printing press. During the 1980s laserengraving systems were produced which used a carbon dioxidelaser to engrave the required cell pattern directly into thepolished ceramic surface. Since then Q-switched YAG laserswere used for a period as they provided a more focusable laserbeam as well as increased pulsing frequencies capable ofengraving the finer cell configuration demanded by the everevolving flexographic printing process.

Laser engraving of anilox rollsPrior to 1980 anilox rolls were produced by a variety ofmechanical processes. These metal anilox rolls weresometimes sprayed with ceramic to prolong their life intheflexographic printing press. During the 1980s laserengraving systems were produced which used a carbon dioxidelaser to engrave the required cell pattern directly into thepolished ceramic surface. Since then Q-switched YAG laserswere used for a period as they provided a more focusable laserbeam as well as increased pulsing frequencies capable ofengraving the finer cell configuration demanded by the everevolving flexographic printing process.

Since approximately the year 2000 the direct anilox laserengraving process has been dominated by the use of fibrelasers which provide the high powers of the carbondioxidelasers together with the finely focusable beam of the YAGlasers. Optical systems providing the rapid switching ofmultiple beams have allowed the fibre laser system to bedominant in this market. This technology has become knownas Multi-Beam-Anilox or MBA.

Since approximately the year 2000 the direct anilox laserengraving process has been dominated by the use of fibrelasers which provide the high powers of the carbondioxidelasers together with the finely focusable beam of the YAGlasers. Optical systems providing the rapid switching ofmultiple beams have allowed the fibre laser system to bedominant in this market. This technology has become knownas Multi-Beam-Anilox or MBA.

CHARACTERISTICS OFENGRAVED GRAVURE ROLLERS

Type of Engraving Screen Cell Depthmm

Deposit gm/m2

Lines/in Lines/cm

Pyramidal 20040

7916

0.0030.037

2.427.6

20040

7916

0.0030.037

2.427.6

Quadrangular 20016

796

0.0050.065

3.649.5

Trihelical 12024

479

0.0100.055

11.763.1

Pyramidal cells

The Most Common Gravure Cell Patterns

Quadrangular

Tri helical

QuadragravurePyramid

Quad Roto FloRoto-Flo Pyramid

Tri-Helical Quad Channel

The Gravure Cell or Pattern creation

Cell PropertiesBCM: Volume

( Billion Cubic Micron per Square Inch ) : 2 – 200 BCM

LPI: Cell Density = Lines Per Inch : 10 – 1500 LPI

Release / Transfer Rate : % Coating Volume

Released Onto Substrate

Method of Cell Creation :

Mechanical Engraving

Laser Engraving

Electronic Engraving

The Gravure Cell or Pattern creation

Cell PropertiesBCM: Volume

( Billion Cubic Micron per Square Inch ) : 2 – 200 BCM

LPI: Cell Density = Lines Per Inch : 10 – 1500 LPI

Release / Transfer Rate : % Coating Volume

Released Onto Substrate

Method of Cell Creation :

Mechanical Engraving

Laser Engraving

Electronic Engraving

Depth = X

Breadth = YIm

prove Release Property

The Cell PatternThe Cell Pattern

Depth = X - less

Depth = X - less

Improve R

elease Property

Common Patterns in Laser Engraving

30o Channel

60o Hex

Tri-Helical

30o Hex

Common Patterns in ElectronicEngraving

Include Engraving Chart here

Doctor’s Blade , angle of Contact TrailingBlade

GravureRoll

Doctor’s blade Removes or ExcessCoatingOnly the Coating filled up in the CellsremainsThe Cell Determines the Coat WeightAngle of Contact : Trailing Blade ismeant forLow Speed / Low ViscosityHydraulic Forces Can Lift BladeTraps ContaminatesLoading Pressure0.5 – 4.0 pli

GravureRoll

Doctor’s blade Removes or ExcessCoatingOnly the Coating filled up in the CellsremainsThe Cell Determines the Coat WeightAngle of Contact : Trailing Blade ismeant forLow Speed / Low ViscosityHydraulic Forces Can Lift BladeTraps ContaminatesLoading Pressure0.5 – 4.0 pli

Doctor’s Blade , angle of ContactReverse angle

GravureRoll

Doctor’s blade Removes or ExcessCoatingOnly the Coating filled up in the CellsremainsThe Cell Determines the Coat WeightAngle of Contact : Reverse Angle ismeant forIncreased Speed and ViscosityHydraulic Force Helps Hold BladeRejects ContaminatesLoading Pressure0.5 – 4.0 pli

GravureRoll

Doctor’s blade Removes or ExcessCoatingOnly the Coating filled up in the CellsremainsThe Cell Determines the Coat WeightAngle of Contact : Reverse Angle ismeant forIncreased Speed and ViscosityHydraulic Force Helps Hold BladeRejects ContaminatesLoading Pressure0.5 – 4.0 pli

Coating application methods

There are several coating methods, but three are the most commonly used.The blade coater rolls the liquid coating onto the bottom of the paper, thenuses a flexible blade to scrape away the excess coating. This methodproduces a sheet with high gloss, but the resultant variation in coatingthickness can cause inconsistent ink holdout and produce uneven printedsolids (mottle).The trailing blade coating method scrapes away excessive coating, butleaves a thick-and-thin effect.

The trailing bladecoating method scrapesaway excessive coating,but leaves a thick-and-thin effect.

The Doctor Blade holderassembly looks like the figurebelow

Generally fitted with pneumaticmovementThe blade angle is changeableThe blade Oscillation system ismotor driven

The Backup or the Impression Roller

This is a Rubber rollerWidth of this roller has to be slightly lesser than

the web widthThe Rubber should be of Hardness 60-65 Shore A

Rubber Roller

Gravure Roller

Rubber Roller

WEB

The Hardness of the Roller has a Impact on the quality aswell as the quantity of coating

Higher Rubber thickness with a softer Hardness of around60-70 shore A , generally gives more coating weight

Lower Rubber thickness with a higher Hardness of around80-90 shore A , generally gives lower coating weight

For uniform coating across the web the Rubber roller needsto be ground to precision.Generally higher the rubber hardness more uniform is thecoating

The Hardness of the Roller has a Impact on the quality aswell as the quantity of coating

Higher Rubber thickness with a softer Hardness of around60-70 shore A , generally gives more coating weight

Lower Rubber thickness with a higher Hardness of around80-90 shore A , generally gives lower coating weight

For uniform coating across the web the Rubber roller needsto be ground to precision.Generally higher the rubber hardness more uniform is thecoating

The Gravure Coating can be further improvedwith a system called as enclosed applicator

RubberRoll

WebCoatedWeb

GravureRoll

Adhesive INAdhesiveOut

CoatedWeb

Enclosed Applicator

Reverse Gravure

Reverse ApplicationSpeed Range: 90-120%

BenefitsRemoves Cell PatternFilm Split Avoided

Minimizes RibbingAdjust Coat Weight with RollSpeed

Impression Control is CriticalLight / Controlled ImpressionPrecision Required – Better Rolls

Driven Impression RollSuggested for Tension ControlOvercome Reverse Action

RubberRoll WebCoated

Web

GravureRoll

Reverse ApplicationSpeed Range: 90-120%

BenefitsRemoves Cell PatternFilm Split Avoided

Minimizes RibbingAdjust Coat Weight with RollSpeed

Impression Control is CriticalLight / Controlled ImpressionPrecision Required – Better Rolls

Driven Impression RollSuggested for Tension ControlOvercome Reverse Action

WebCoatedWeb

SteelBackup Roll

offset Gravure

3-Roll SystemGravure is Offset from SubstrateRemoves Substrate from Coating Nip

Protects Sensitive Substrates

Roll RotationAll Roll Same Direction

Synchronous Rotation

Two Film SplitsThinner Coatings

Roll SpeedsAll Rolls at 100% Line SpeedSingle Drive is Possible

Gravure Roll is Typically Driven – Idle Mode

Applicator Roll is Nip Driven

Back-up Roll is Web Driven

GravureRoll

RubberRoll

3-Roll SystemGravure is Offset from SubstrateRemoves Substrate from Coating Nip

Protects Sensitive Substrates

Roll RotationAll Roll Same Direction

Synchronous Rotation

Two Film SplitsThinner Coatings

Roll SpeedsAll Rolls at 100% Line SpeedSingle Drive is Possible

Gravure Roll is Typically Driven – Idle Mode

Applicator Roll is Nip Driven

Back-up Roll is Web Driven

Kiss coatingIn this method, coating is lifted up by the drive rolls soaked inthe paint pan, transferred to the top roll and then applied topaper that is pressed against the top roll by the press roll.

Two side Coating at a Time• Very Cost Effective

– Coat Both Sides at OneCoating Station

– Single Dryer vs. DualDryers

– Reduced Overall LineLength

• Direct Application (KissCoating)

– Forward or Reverse Apply– Coat Weight is Susceptible

to Tension Variations

• Limited Range ofApplications

– Thinner Coatings– Same / Similar Functional

Coatings on Both Sides

• Very Cost Effective– Coat Both Sides at One

Coating Station– Single Dryer vs. Dual

Dryers– Reduced Overall Line

Length

• Direct Application (KissCoating)

– Forward or Reverse Apply– Coat Weight is Susceptible

to Tension Variations

• Limited Range ofApplications

– Thinner Coatings– Same / Similar Functional

Coatings on Both Sides

Two side Offset Gravure coating

Two side OffsetKisscoating

Some Modifications of Gravure Printingor coating

5-roll coating systemExtremely slight and precise coating weights are adjustableCoating weight can be increased or reduced, up to 50%, bychanging one cylinder velocity during machine runAccurate repeatability through high precision mechanical stopswith micro-adjustmentsSpecificationsProduction speed up to 1500m/min (4900ft/min)Coating width >3000mm possibleHigh precision cross profile over the whole web width of 2%which is guaranteed by using a special cylinder technology with apatented deflection compensated impression rollApplicationssolvent less coatings with 100% solids

thermal curingUV curingEB curing

5-roll coating systemExtremely slight and precise coating weights are adjustableCoating weight can be increased or reduced, up to 50%, bychanging one cylinder velocity during machine runAccurate repeatability through high precision mechanical stopswith micro-adjustmentsSpecificationsProduction speed up to 1500m/min (4900ft/min)Coating width >3000mm possibleHigh precision cross profile over the whole web width of 2%which is guaranteed by using a special cylinder technology with apatented deflection compensated impression rollApplicationssolvent less coatings with 100% solids

thermal curingUV curingEB curing

5-roll coating head for solventless, 100% solids coatings.

The coating head is designed for a production speed of up to 1500m/min.,

with a coating width of 1700 mm and is equipped with a patentedroll deflection compensating system.

This coating method is especially suitable for low coating weightswith high quality requirements in regard to the coverage andcoating weight tolerances at high production speed.

The precision presetting mechanism ensures highest accuracy inrepeatability of production parameters.

5-roll coating head for solventless, 100% solids coatings.

The coating head is designed for a production speed of up to 1500m/min.,

with a coating width of 1700 mm and is equipped with a patentedroll deflection compensating system.

This coating method is especially suitable for low coating weightswith high quality requirements in regard to the coverage andcoating weight tolerances at high production speed.

The precision presetting mechanism ensures highest accuracy inrepeatability of production parameters.

5-roll coating system

Extremely low and precise coating weights areadjustable

Coating weight can be increased or decreased, up to50%,by changing one cylinder velocity during machinerun

Accurate repeatability through high precisionmechanical stops with micro-adjustments

5-roll coating system

Extremely low and precise coating weights areadjustable

Coating weight can be increased or decreased, up to50%,by changing one cylinder velocity during machinerun

Accurate repeatability through high precisionmechanical stops with micro-adjustments

• Gravure cum Kisscoating method for verylow viscosity coatings


• Gravure cum Kisscoating method for verylow viscosity coatings

• Gravure cum reverseroll coating type one


• Gravure cum reverseroll coating type one

• Gravure cum reverseroll coating type two


• Gravure cum reverseroll coating type two

The Comma coating system is a spreader for processing of highly viscousaqueous and solvent-containing adhesives.

In this process, the system is placed directly at a slightly lower heights ascompared to the Drying Tunnel .It is done so to avoid running-off of the coating compound , as the coated webenters the drying tunnel , allmost immediately after coating. Production ispossible with working widths between 600 and 1,650 mm and a speed up to 100m/min.This system consists of typically 2 rollers , in rare cases 3 rollers might be used

Features and Performance Characteristics:Ensuring of a stable / uniform roller gap due to hydraulic positioning of thecomma bladeFine-adjustment of the roller gap due to step motorsThe coating / adhesive is poured directly on the web to be coated.

The Comma coating system is a spreader for processing of highly viscousaqueous and solvent-containing adhesives.

In this process, the system is placed directly at a slightly lower heights ascompared to the Drying Tunnel .It is done so to avoid running-off of the coating compound , as the coated webenters the drying tunnel , allmost immediately after coating. Production ispossible with working widths between 600 and 1,650 mm and a speed up to 100m/min.This system consists of typically 2 rollers , in rare cases 3 rollers might be used

Features and Performance Characteristics:Ensuring of a stable / uniform roller gap due to hydraulic positioning of thecomma bladeFine-adjustment of the roller gap due to step motorsThe coating / adhesive is poured directly on the web to be coated.

In this coating process, an excess of the coating is depositedonto the substrate as it passes over the bath roller.

The wire-wound metering rod, known as a Meyer Rod,allows the desired quantity of the coating to remain onthe substrate.

The quantity is determined by the diameter of thewire used on the rod.

This process is remarkably tolerant of non-precisionengineering of the other components of the coating machine.

In this coating process, an excess of the coating is depositedonto the substrate as it passes over the bath roller.

The wire-wound metering rod, known as a Meyer Rod,allows the desired quantity of the coating to remain onthe substrate.

The quantity is determined by the diameter of thewire used on the rod.

This process is remarkably tolerant of non-precisionengineering of the other components of the coating machine.

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The market for wire-wound rods has grown rapidly during the past fewdecades, because they provide predictable, accurate coatings time aftertime, at a minimal cost.

Although the technology goes back almost a century, today's highquality materials, multi-wire designs and special wire surfaces havemade this system more popular thanever before.

Rods give users the ability to fine-tune coating thickness quickly andeasily, without altering the chemistry of their coating material, andwithout time-consuming and expensive changeovers.

The market for wire-wound rods has grown rapidly during the past fewdecades, because they provide predictable, accurate coatings time aftertime, at a minimal cost.

Although the technology goes back almost a century, today's highquality materials, multi-wire designs and special wire surfaces havemade this system more popular thanever before.

Rods give users the ability to fine-tune coating thickness quickly andeasily, without altering the chemistry of their coating material, andwithout time-consuming and expensive changeovers.

Wire-wound rods were first used in coating machines built by CharlesMayer in the 1900's to manufacture waxed paper and carbon paper.They are still called “ Mayer Bars “ by many coaters.

Wet coating thickness can be accurately predicted within one tenth of amil (.0001").

Rod selection tables allow coaters to consider coat weight and percentof solids in choosing the proper rod size for each production run.

Bottom-line profits have encouraged many coaters to modify existingmachines, in order to take advantage of the flexibility, the ease of useand the dollar savings associated with rod coating.

Wire-wound rods were first used in coating machines built by CharlesMayer in the 1900's to manufacture waxed paper and carbon paper.They are still called “ Mayer Bars “ by many coaters.

Wet coating thickness can be accurately predicted within one tenth of amil (.0001").

Rod selection tables allow coaters to consider coat weight and percentof solids in choosing the proper rod size for each production run.

Bottom-line profits have encouraged many coaters to modify existingmachines, in order to take advantage of the flexibility, the ease of useand the dollar savings associated with rod coating.

One of the more common methods of coating is the Mayer rodcoater, sometimes called a metering rod coater. This equipmenthas advantages such as low capital cost, ease of coat weightadjustment, ease of operation, and a broad range of coat weightsare possible.

: Mayer Road Coater

In this coating method, an applicator roll delivers adhesive to thesubstrate being coated. The applicator roll may turn either with oragainst the primary web, delivering an excess of adhesive. Wirewound rods are then used to remove the excess. The rods may alsoturn in either direction.

The amount of adhesive removed depends upon the diameter of thewire which is wound around the steel rod. Coat weight is increasedby simply switching to a rod wrapped with larger diameter wire. Tworods in series often give better coating results than a single rod.The first rod has larger diameter wire and removes most of the excessadhesive. The second rod, with smaller diameter wire, smoothes thecoating and produces the final desired coat weight. Mayer rodcoating can deliver a broad range of coat weights.

: Mayer Road Coater

In this coating method, an applicator roll delivers adhesive to thesubstrate being coated. The applicator roll may turn either with oragainst the primary web, delivering an excess of adhesive. Wirewound rods are then used to remove the excess. The rods may alsoturn in either direction.

The amount of adhesive removed depends upon the diameter of thewire which is wound around the steel rod. Coat weight is increasedby simply switching to a rod wrapped with larger diameter wire. Tworods in series often give better coating results than a single rod.The first rod has larger diameter wire and removes most of the excessadhesive. The second rod, with smaller diameter wire, smoothes thecoating and produces the final desired coat weight. Mayer rodcoating can deliver a broad range of coat weights.

TWO-WIRE DRAWDOWN RODS

Where heavier coatings are required, manufactures provide specialdrawdown rods with two wires. A standard single-wire rod is over woundwith a smaller wire which follows the spiral of the base wire. The result isa modified groove between the wires that will produce wet coatings up to19 mils (.019") thick.

TRI-WIRE DRAWDOWN RODS

Three Rod technology developed by for Coatings up to 56 mils (.056") thick canbe produced, using three standard wires wound in a unique configuration.Two wires are wound side by side on a core rod, then a third wire follows onespiral of the base wires. The resulting groove will maximize the area between thewires, producing a coating more than six times the thickness produced by asingle-wire rod!

Metering Rod Application Chart

Thickness(1) Coverage Wet Film Weight

Rod # Mils Microns Ft2/gal m2/l lbs/1000ft2 g/m2

1 0.15 3.8 10,700 263 0.94 3.8

3 0.3 7.6 5,350 131 1.87 7.6

4 0.4 10.2 4,010 98.4 2.49 10.2

5 0.5 12.7 3,210 78.7 3.12 12.7

6 0.6 15.2 2,670 65.6 3.74 15.26 0.6 15.2 2,670 65.6 3.74 15.2

8 0.8 20.3 2,010 49.2 4.99 20.3

10 1.0 25.4 1,600 39.4 6.23 25.4

12 1.2 30.5 1,340 32.8 7.48 30.5

15 1.5 38.1 1,075 26.3 9.36 38.1

18 1.8 45.7 891 21.9 11.2 45.7

22 2.2 55.9 727 17.9 13.7 55.9

30 3.0 76.2 535 13.1 18.7 76.2

Metering Rod Application Chart

Thickness(1) Coverage Wet Film Weight

Rod # Mils Microns Ft2/gal m2/l lbs/1000ft2 g/m2

42 4.2 107 382 9.2 26.2 10742 4.2 107 382 9.2 26.2 107

50 5.0 127 320 7.9 31.2 127

80 8.0 200 201 4.9 50.0 203

100 10.0 254 160 3.9 62.3 254

cut angle comma coating way comma reverse coating waycut angle comma coating way comma reverse coating way

Applicable conditions:viscosity 1000 ~ 20000CPS

Coating amount of 10 ~ 20000g/m²

Applicable conditions:viscosity 1000 ~ 20000CPS

Coating amount of 10 ~ 20000g/m²

Comma direct coatingThis method is a kind of knife coating, and a cutting bladesimilar to the one used for knife coating is incorporated intoa part of the rod. This method is characterized by very highprocessing accuracy and the capability of processing asolution whose viscosity is as high as several thousand cps.Conversely, a processing solution with very low viscosityrequires a viscosity adjustment to prevent leakage. Thecharacteristics of the finished coating surface are that theirregularities on the base material surface are filled to makethe coated surface smooth. In addition, this method issuitable for processing expensive chemicals because theprocessing solution in the pan can be completely used up.

Comma direct coatingThis method is a kind of knife coating, and a cutting bladesimilar to the one used for knife coating is incorporated intoa part of the rod. This method is characterized by very highprocessing accuracy and the capability of processing asolution whose viscosity is as high as several thousand cps.Conversely, a processing solution with very low viscosityrequires a viscosity adjustment to prevent leakage. Thecharacteristics of the finished coating surface are that theirregularities on the base material surface are filled to makethe coated surface smooth. In addition, this method issuitable for processing expensive chemicals because theprocessing solution in the pan can be completely used up.

Comma reverse coatingIn the comma direct coating method, a processing solution isapplied directly to paper. On the other hand, in the commareverse coating method, a processing solution is once appliedto rolls and then the processing solution that came outbetween the rod knife and roll with adjusted clearance istransferred to a paper or nonwoven fabric. This has theadvantage that it is possible to apply a certain amount ofprocessing solution accurately.

Comma reverse coatingIn the comma direct coating method, a processing solution isapplied directly to paper. On the other hand, in the commareverse coating method, a processing solution is once appliedto rolls and then the processing solution that came outbetween the rod knife and roll with adjusted clearance istransferred to a paper or nonwoven fabric. This has theadvantage that it is possible to apply a certain amount ofprocessing solution accurately.

5 Roll Comma Coating Station

Coating films with thickness of under 1 µm can be achievedwith 5 roller system. This application is used e.g. for theproduction of siliconized papers.

The Reverse coating system is a spreader for processing of highlyviscous aqueous and solvent-containing adhesives.In this process, the system is placed directly at a slightly lowerheights as compared to the Drying Tunnel .It is done so to avoid running-off of the coating compound , asthe coated web enters the drying tunnel , allmost immediately aftercoating. Production is possible with working widths between 600and 1,650 mm and a speed up to 100 m/min. This system consistsof typically 3 rollers .Features and Performance Characteristics:Ensuring of a stable / uniform roller gap due to hydraulicpositioning of the comma blade Fine-adjustment of the roller gapdue to step motors . The coating / adhesive is not poured directlyon the web , and a metered film of wet adhesive comes in contactwith the web to be coated , at the other nip formed between backupand applicator roller.

The Reverse coating system is a spreader for processing of highlyviscous aqueous and solvent-containing adhesives.In this process, the system is placed directly at a slightly lowerheights as compared to the Drying Tunnel .It is done so to avoid running-off of the coating compound , asthe coated web enters the drying tunnel , allmost immediately aftercoating. Production is possible with working widths between 600and 1,650 mm and a speed up to 100 m/min. This system consistsof typically 3 rollers .Features and Performance Characteristics:Ensuring of a stable / uniform roller gap due to hydraulicpositioning of the comma blade Fine-adjustment of the roller gapdue to step motors . The coating / adhesive is not poured directlyon the web , and a metered film of wet adhesive comes in contactwith the web to be coated , at the other nip formed between backupand applicator roller.

In this procedure, the coating material is measured ontothe applicator roller by precision setting of the gap betweenthe upper metering roller and the application roller below it.

The coating is 'wiped' off the application roller bythe substrate as it passes around thesupport roller at the bottom.

The diagram illustrates a 3-roll reverse roll coating process,although 4-roll versions are common.

Reverse Roll CoatingIn this procedure, the coating material is measured ontothe applicator roller by precision setting of the gap betweenthe upper metering roller and the application roller below it.

The coating is 'wiped' off the application roller bythe substrate as it passes around thesupport roller at the bottom.

The diagram illustrates a 3-roll reverse roll coating process,although 4-roll versions are common.

Reverse Roll CoaterThe three roll reverse coater is used for many specialty applications.This method is more expensive and generally slower in line speedthan the Mayer rod coater.

However, the versatility in terms of coat weight range and coatingwidth, and the good coat quality of the three roll reverse has made itpopular with many converters.

In this process, the middle roll is coated with a precise thickness ofadhesive, determined by the size of the gap between the top andmiddle rolls.

The adhesive is then transferred as the rubber backing roll brings theweb into contact. The adhesive coat weight can also be varied byincreasing or decreasing the speed of the applicator roll relative to theweb speed. The metering roll speed can be varied to adjust thesmoothness of the coating.

Reverse Roll CoaterThe three roll reverse coater is used for many specialty applications.This method is more expensive and generally slower in line speedthan the Mayer rod coater.

However, the versatility in terms of coat weight range and coatingwidth, and the good coat quality of the three roll reverse has made itpopular with many converters.

In this process, the middle roll is coated with a precise thickness ofadhesive, determined by the size of the gap between the top andmiddle rolls.

The adhesive is then transferred as the rubber backing roll brings theweb into contact. The adhesive coat weight can also be varied byincreasing or decreasing the speed of the applicator roll relative to theweb speed. The metering roll speed can be varied to adjust thesmoothness of the coating.

Figure 2 : Reverse Roll CoaterThere are several variations of the reverse roll coating method, suchas four-roll,nip fed, and pan fed systems. A nip-fed, three roll reverse coater isshown here.Medium to high coat weights are possible with reverse roll.

Figure 2 : Reverse Roll CoaterThere are several variations of the reverse roll coating method, suchas four-roll,nip fed, and pan fed systems. A nip-fed, three roll reverse coater isshown here.Medium to high coat weights are possible with reverse roll.

Reverse roll coating is a roll-to-roll coating method for wet coatings. It isdistinguished from other roll coating methods by having two reverse-running nips. Themetering roll and the applicator roll contra-rotate, with an accurate gap between them.The surface of the applicator roll is loaded with an excess of coating prior to themetering nip, so its surface emerges from the metering nip with a precise thickness ofcoating equal to the gap. At the application nip, the applicator roll transfers all of thiscoating to the substrate, by running in the opposite direction to the movement of thesubstrate, wiping the coating onto the substrate.Reverse roll coating machines demand high specifications in their construction, e.g. forthe machining and bearings of the rollers and for highly uniform speed control. Thismakes them relatively expensive compared to other coating technologies. Unlike manyother coating methods, they can however handle coatings with a very wide range ofviscosities, from 1 to more than 50000 mPas, and are capable of producing extremelypolished finishes on the coatings they apply. They have been produced in a variety of 3-roll an 4-roll configurations.[1]

Products manufactured on reverse roll coating machines include Magnetic Tapes; Foamfabrics; electrographic reproduction papers and pressure sensitive tapes. The rise ofslot-die coating has tended to eclipse reverse roll coaters as in most if not all cases, thesame products can be made on cheaper machinery.

Reverse roll coating is a roll-to-roll coating method for wet coatings. It isdistinguished from other roll coating methods by having two reverse-running nips. Themetering roll and the applicator roll contra-rotate, with an accurate gap between them.The surface of the applicator roll is loaded with an excess of coating prior to themetering nip, so its surface emerges from the metering nip with a precise thickness ofcoating equal to the gap. At the application nip, the applicator roll transfers all of thiscoating to the substrate, by running in the opposite direction to the movement of thesubstrate, wiping the coating onto the substrate.Reverse roll coating machines demand high specifications in their construction, e.g. forthe machining and bearings of the rollers and for highly uniform speed control. Thismakes them relatively expensive compared to other coating technologies. Unlike manyother coating methods, they can however handle coatings with a very wide range ofviscosities, from 1 to more than 50000 mPas, and are capable of producing extremelypolished finishes on the coatings they apply. They have been produced in a variety of 3-roll an 4-roll configurations.[1]

Products manufactured on reverse roll coating machines include Magnetic Tapes; Foamfabrics; electrographic reproduction papers and pressure sensitive tapes. The rise ofslot-die coating has tended to eclipse reverse roll coaters as in most if not all cases, thesame products can be made on cheaper machinery.

VISCOSITY RANGE150 - 150,000 Cps

WEB WIDTH RANGE300 - 2500mm

COAT WEIGHT RANGE10 - 200gsm wet

TYPICAL SUBSTRATESPaper, film and fabric

VISCOSITY RANGE150 - 150,000 Cps

WEB WIDTH RANGE300 - 2500mm

COAT WEIGHT RANGE10 - 200gsm wet

TYPICAL SUBSTRATESPaper, film and fabric

Hot Melt Coating

Hot MeltAdhesive

Applicationof heat upto160 deg C

The coatedproduct is

cooled downto RT.

Adhesive isback to solid

Applicationof heat upto160 deg C

Adhesivemelts andbecomesLiquid

Liquid iscoated using

specialnozzles /

roller / Die

The coatedproduct is

cooled downto RT.

Adhesive isback to solid

Hot Melt CoatingThe name itself suggests these type of adhesives.

A adhesive which melts on application of heat is called as Hot MeltAdhesive

Hot melt adhesives are thermoplastics, based on polymers thatbecome liquid between temperatures of 80 – 220 °C and solidifyagain by cooling down.

They consist of 100 % dry substance and are applied in liquid statewithout using water or solvents.

With respective pre-melt systems, pumps and application units (slotdie, hot roller and powder scattering) an exact dosage andadjustment is possible.

Due to the process only a short binding and setting time isrequested in comparison with dispersions or solutions.

The name itself suggests these type of adhesives.

A adhesive which melts on application of heat is called as Hot MeltAdhesive

Hot melt adhesives are thermoplastics, based on polymers thatbecome liquid between temperatures of 80 – 220 °C and solidifyagain by cooling down.

They consist of 100 % dry substance and are applied in liquid statewithout using water or solvents.

With respective pre-melt systems, pumps and application units (slotdie, hot roller and powder scattering) an exact dosage andadjustment is possible.

Due to the process only a short binding and setting time isrequested in comparison with dispersions or solutions.

In the Slot Die process, the coating is squeezed out bygravity or under pressure through a slot and onto thesubstrate. If the coating is 100% solids, the processis termed 'Extrusion' and in this case, the line speed isfrequently much faster than the speed of the extrusion.This enables coatings to be considerably thinner thanthe width of the slot.

In the Slot Die process, the coating is squeezed out bygravity or under pressure through a slot and onto thesubstrate. If the coating is 100% solids, the processis termed 'Extrusion' and in this case, the line speed isfrequently much faster than the speed of the extrusion.This enables coatings to be considerably thinner thanthe width of the slot.

Slot Die CoaterThe slot die coater does not use rollers to deliver the adhesive to theweb.Instead, adhesive is pumped into a chamber, where it exits through along, narrow slot directly in contact with a moving web. The web isusually supported immediately behind the slot with a rubber or steelbacking roll.

Figure 4 : Slot Die Head Set-UpThe slot die coating method is inherently low foaming, and is capableof producing good quality material at high line speeds. However, theequipment is relatively expensive and requires a high level ofoperator expertise. Moderate to high coat weights are possible withslot die.

Slot Die CoaterThe slot die coater does not use rollers to deliver the adhesive to theweb.Instead, adhesive is pumped into a chamber, where it exits through along, narrow slot directly in contact with a moving web. The web isusually supported immediately behind the slot with a rubber or steelbacking roll.

Figure 4 : Slot Die Head Set-UpThe slot die coating method is inherently low foaming, and is capableof producing good quality material at high line speeds. However, theequipment is relatively expensive and requires a high level ofoperator expertise. Moderate to high coat weights are possible withslot die.

Extrusion Coating Lamination

- It can be used on varioussubstrates as paper, cottoncloth, woven fabrics, jutefabric, aluminium foil, Boppfilm or even a polyester film.

- Can perform eitherextrusion coating or extrusionlamination.

- Highly efficient and durablelamination.

- It can be used on varioussubstrates as paper, cottoncloth, woven fabrics, jutefabric, aluminium foil, Boppfilm or even a polyester film.

- Can perform eitherextrusion coating or extrusionlamination.

- Highly efficient and durablelamination.

Extrusion lamination is a process that is used to combine two different substratesusing molten polymers.

The process of extrusion lamination metal, paper and mainly plastic films. Itcan provide lamination of different thicknesses with level of quality. includes boththe characteristics of extrusion and lamination.

process to coat an additional layer on existing roll stock of paper, cotton cloth,woven fabrics, jute fabric, aluminum foil, Bopp film or polyester film.

This process can be used to improve the characteristics of paper by coating on itwith polyethylene to make it more resistant to water.

The extruded layer can also be used as an adhesive to bring two other materialstogether.

Extrusion lamination is a process that is used to combine two different substratesusing molten polymers.

The process of extrusion lamination metal, paper and mainly plastic films. Itcan provide lamination of different thicknesses with level of quality. includes boththe characteristics of extrusion and lamination.

process to coat an additional layer on existing roll stock of paper, cotton cloth,woven fabrics, jute fabric, aluminum foil, Bopp film or polyester film.

This process can be used to improve the characteristics of paper by coating on itwith polyethylene to make it more resistant to water.

The extruded layer can also be used as an adhesive to bring two other materialstogether.

Film Extrusion,Extrusion Coating,and LaminationProcesses

Extrusion laminating (also known as sandwich laminating) is a process relatedto extrusion coating, but the extrusion-coated layer is used as an adhesive layerbetween two or more substrates.

A secondary layer is applied to the extrusion coating while it is still hot. TheMP50 monitors the melt curtain before the chill roll before the sandwich isformed.

The sandwich is then pressed together by pressure rolls.

In addition to providing adhesion, the extrusion-coated layer may also serve as amoisture barrier.

Extrusion laminating (also known as sandwich laminating) is a process relatedto extrusion coating, but the extrusion-coated layer is used as an adhesive layerbetween two or more substrates.

A secondary layer is applied to the extrusion coating while it is still hot. TheMP50 monitors the melt curtain before the chill roll before the sandwich isformed.

The sandwich is then pressed together by pressure rolls.

In addition to providing adhesion, the extrusion-coated layer may also serve as amoisture barrier.

Extrusion Coating

SOME APPLICATIONS OF EXTRUSION COATING ANDLAMINATION

Sr No. End ProductsApplications Substrate Laminated Coated

With Type of Lamination

1 HDPE/PP woven sacksand tarpaulins

HDPE/PP wovenfabric

LDPE or PP15-50 micron Single sided

PP/HDPE woven forsack laminated withpaper for packing ofcement, fertilizers,polymers

Kraft paper upto 200gsm & HDPE/PPwoven sack

LDPE/PP Sandwich2

PP/HDPE woven forsack laminated withpaper for packing ofcement, fertilizers,polymers

Kraft paper upto 200gsm & HDPE/PPwoven sack

LDPE/PP Sandwich

3 Soap wrapper Paper LDPE20-40 micron Single sided

4 Medical tablet strips Paper & Aluminiumfoil LDPE 25 micron Sandwich

5'Brick' pack for softdrinks, juices, milk, oiletc.

White paper, Kraftpaper, Aluminium foil LDPE 7 layer sandwich

Slot-Curtain Coatingsection displayingManifold and TransferFlows

Slot Die section viewdisplaying internal manifold

Commercial Advantages

Precision Die Coating allowsparticipation in higher-margin markets exclusiveto superior productfunctionality and more frugal manufacturing(reduced waste, higher productivity)when compared with other coatings methodssuch as roll, blade, gravure, rod, etc.

Commercial Advantages

Precision Die Coating allowsparticipation in higher-margin markets exclusiveto superior productfunctionality and more frugal manufacturing(reduced waste, higher productivity)when compared with other coatings methodssuch as roll, blade, gravure, rod, etc.

Slot-bead Coating withapplied vacuum.

Slot Die section view displayinginternal manifold

Transfer flow of slot-beadcoating

we shall now review a few of the other coating methods , notbeing used so commonly , but for some specific application.


Calendaring


Curtain Coating


Calendaring


Curtain Coating


Immersion (Dip) CoatingIn this simple process, the substrate is dipped into a bathof the coating, which is normally of a low viscosity toenable the coating to run back into the bath as thesubstrate emerges. This process is frequently used onporous substrates.

Dip coating, along with brush coating and wire wound rod coating, is one of the oldestcoating methods. There are two basic dip coating process concepts. In the web coatingprocess, the substrate is partially submerged into a coating pan containing the solution tobe coated and a wet film is withdrawn onto the moving web, Figure 1. In the discretemethod, the irregularly shaped discrete objects to be coated, nails, circuit boards,architectural steel members to optical components are inserted into a tank containing thecoating solution. As it is withdrawn a film is attached to the part, which is then dried, sothat the part is useable.The continuous web coating process is still widely used because of the following reasons:

• It can apply a range of coating thickness with reasonable coating quality.• The coating equipment is inexpensive and relatively simple to operate.• High-speed capability of the process should lead to low costs and high

productivity.• Scale-up from laboratory coaters is much easier than for precision coaters such

as slot-die and curtain coating.• Excess coating material can be removed by doctoring devices such as Mayer

Rod, Air Knife, blades, and squeegee rolls to allow wide range of coating weights.

Dip coating, along with brush coating and wire wound rod coating, is one of the oldestcoating methods. There are two basic dip coating process concepts. In the web coatingprocess, the substrate is partially submerged into a coating pan containing the solution tobe coated and a wet film is withdrawn onto the moving web, Figure 1. In the discretemethod, the irregularly shaped discrete objects to be coated, nails, circuit boards,architectural steel members to optical components are inserted into a tank containing thecoating solution. As it is withdrawn a film is attached to the part, which is then dried, sothat the part is useable.The continuous web coating process is still widely used because of the following reasons:

• It can apply a range of coating thickness with reasonable coating quality.• The coating equipment is inexpensive and relatively simple to operate.• High-speed capability of the process should lead to low costs and high

productivity.• Scale-up from laboratory coaters is much easier than for precision coaters such

as slot-die and curtain coating.• Excess coating material can be removed by doctoring devices such as Mayer

Rod, Air Knife, blades, and squeegee rolls to allow wide range of coating weights.

• Understanding the limits of dip coating is important to understanding thebehavior of many other coating techniquesThe wet thickness for the unassisted dip coater is determined by:

• Fluid properties• Coating speed• Withdrawal angle.

The range of operating parameters for dip coating are as follows:Viscosity 20–2000 cP or mPa-sWet thickness 10–200 μ (0.4-8 mil)Line speed 0.5–7.5 m/s (100–1500 fpm)Coverage uniformity ± 10 %

The wet coating thickness increases with viscosity and coating speed. Therefore, whenthin coatings are required at high speeds and viscosity a doctoring device is needed toobtain the desired coverage.

• Understanding the limits of dip coating is important to understanding thebehavior of many other coating techniquesThe wet thickness for the unassisted dip coater is determined by:

• Fluid properties• Coating speed• Withdrawal angle.


The wet coating thickness increases with viscosity and coating speed. Therefore, whenthin coatings are required at high speeds and viscosity a doctoring device is needed toobtain the desired coverage.

Dip coating, along with brush coating and wire wound rodcoating, is one of the oldest coating methods. There are two basicdip coating process concepts. In the web coating process, thesubstrate is partially submerged into a coating pan containing thesolution to be coated and a wet film is withdrawn onto themoving web, Figure 1. In the discrete method, the irregularlyshaped discrete objects to be coated, nails, circuit boards,architectural steel members to optical components are insertedinto a tank containing the coating solution. As it is withdrawn afilm is attached to the part, which is then dried, so that the part isuseable.The continuous web coating process is still widely used becauseof the following reasons:• It can apply a range of coating thickness with reasonablecoating quality.• The coating equipment is inexpensive and relativelysimple to operate.

Dip coating, along with brush coating and wire wound rodcoating, is one of the oldest coating methods. There are two basicdip coating process concepts. In the web coating process, thesubstrate is partially submerged into a coating pan containing thesolution to be coated and a wet film is withdrawn onto themoving web, Figure 1. In the discrete method, the irregularlyshaped discrete objects to be coated, nails, circuit boards,architectural steel members to optical components are insertedinto a tank containing the coating solution. As it is withdrawn afilm is attached to the part, which is then dried, so that the part isuseable.The continuous web coating process is still widely used becauseof the following reasons:• It can apply a range of coating thickness with reasonablecoating quality.• The coating equipment is inexpensive and relativelysimple to operate.

• High-speed capability of the process should lead to low costsand high productivity.• Scale-up from laboratory coaters is much easier than forprecision coaters such as slot-die and curtain coating.• Excess coating material can be removed by doctoring devicessuch as Mayer Rod, Air Knife, blades, and squeegee rolls toallow wide range of coating weights.• Understanding the limits of dip coating is important tounderstanding the behaviour of many other coating techniquesThe wet thickness for the unassisted dip coater is determined by:• Fluid properties• Coating speed• Withdrawal angle.

• High-speed capability of the process should lead to low costsand high productivity.• Scale-up from laboratory coaters is much easier than forprecision coaters such as slot-die and curtain coating.• Excess coating material can be removed by doctoring devicessuch as Mayer Rod, Air Knife, blades, and squeegee rolls toallow wide range of coating weights.• Understanding the limits of dip coating is important tounderstanding the behaviour of many other coating techniquesThe wet thickness for the unassisted dip coater is determined by:• Fluid properties• Coating speed• Withdrawal angle.


The wet coating thickness increases with viscosity and coatingspeed. Therefore, when thin coatings are required at high speedsand viscosity a doctoring device is needed to obtain the desiredcoverage.


The wet coating thickness increases with viscosity and coatingspeed. Therefore, when thin coatings are required at high speedsand viscosity a doctoring device is needed to obtain the desiredcoverage.

Dip Squeeze Coating

This coating method is for coating aliquid of a predetermined concentration inthe tray, soaking a paper or non-wovenfabric with the liquid coating , andsqueezing excess coating with thesqueezing rollers to coat the required coatweight.

It is characterized by the ability ofprocessing various kinds of materials,such as water-soluble resin, emulsionresin, solvent resin, and compound resinfor filler and pigment easily.

In general, base materials requires the wetstrength of 0.5–0.7 kgf/25 mm or higher.

Dip Squeeze Coating

This coating method is for coating aliquid of a predetermined concentration inthe tray, soaking a paper or non-wovenfabric with the liquid coating , andsqueezing excess coating with thesqueezing rollers to coat the required coatweight.

It is characterized by the ability ofprocessing various kinds of materials,such as water-soluble resin, emulsionresin, solvent resin, and compound resinfor filler and pigment easily.

In general, base materials requires the wetstrength of 0.5–0.7 kgf/25 mm or higher.

Curtain Coater

A curtain coating head functions very similarly to a slot die coater except that theslot is position several centimeters above the moving web, and edge guides are usedto control the width of the falling curtain. With carefully designed emulsionproperties such as rheology and surface tension, acrylic emulsion pressure sensitiveadhesives may be coated via curtain coater at speeds in excess of 1000 meters perminute. Elimination of foam in the adhesive is also critical to achieving maximumline speeds with this method.

Curtain CoatingIn the Curtain Coating process, a bath with a slot in the baseallows a continuous curtain of the coating to fall into the gapbetween two conveyors. The object to be coated, such as a door,is passed along the conveyor at a controlled speed and soreceives the coating on its upper face. Smelly and crude versionsof these machines were once common.


This process relies on a coating being applied to the substrate whichthen passes through a 'gap' between a 'knife' and a support roller.

As the coating and substrate pass through, the excessis scraped off.

This process can be used for high viscosity coatings and very highcoat weights, such as plastisols and rubber coatings.

There are innumerable variants of the relatively simple processwhich is rugged, hard-working and somewhat inaccurate.

This process relies on a coating being applied to the substrate whichthen passes through a 'gap' between a 'knife' and a support roller.

As the coating and substrate pass through, the excessis scraped off.

This process can be used for high viscosity coatings and very highcoat weights, such as plastisols and rubber coatings.

There are innumerable variants of the relatively simple processwhich is rugged, hard-working and somewhat inaccurate.

knife coating process can be used to apply coatings to substrates andmaterials like foams, woven textiles, non-wovens, and paper. In applyingcoatings using the knife coating method, we can work with substrates up to80” wide, with weights between 1 oz. and 60 oz./sq. yd.

Knife coating is a method of coating application where the substratematerial is fed on a web over a roll, with a knife set to a predetermined gapheight. When the coating is applied to the substrate and fed through, theknife removes the excess coating material, resulting in an even applicationat the desired thickness.

Knife coating is useful when applying adhesives and other coatings for thepaper, laminating, automotive and other industries.

knife coating process can be used to apply coatings to substrates andmaterials like foams, woven textiles, non-wovens, and paper. In applyingcoatings using the knife coating method, we can work with substrates up to80” wide, with weights between 1 oz. and 60 oz./sq. yd.

Knife coating is a method of coating application where the substratematerial is fed on a web over a roll, with a knife set to a predetermined gapheight. When the coating is applied to the substrate and fed through, theknife removes the excess coating material, resulting in an even applicationat the desired thickness.

Knife coating is useful when applying adhesives and other coatings for thepaper, laminating, automotive and other industries.

This is the coater of choice when the requirement is for very heavy andlevel coating of medium to high viscosity onto uneven surfaces such astextiles, fibreglass mats and non-wovens. Typical applications include preimpregnated composite fibres, embossed and plain flooring, reinforcedplastics and medical dressings.Key features include:Rugged construction to handle the high hydrodynamic forcesHigh precision backing roll manufactured to 5μ TIR or betterGap setting based on pneumatically loaded wedge system adjusted bybacklash free micrometer ball screws actuated via servo drivesOption available:A heated backing roll, blade and dam system.VISCOSITY RANGE500 – 50,000 cpsWEB WIDTH RANGE300 – 2500mmCOAT WEIGHT RANGE100 – 1000gsm wetTYPICAL SUBSTRATESPaper and fabric

This is the coater of choice when the requirement is for very heavy andlevel coating of medium to high viscosity onto uneven surfaces such astextiles, fibreglass mats and non-wovens. Typical applications include preimpregnated composite fibres, embossed and plain flooring, reinforcedplastics and medical dressings.Key features include:Rugged construction to handle the high hydrodynamic forcesHigh precision backing roll manufactured to 5μ TIR or betterGap setting based on pneumatically loaded wedge system adjusted bybacklash free micrometer ball screws actuated via servo drivesOption available:A heated backing roll, blade and dam system.VISCOSITY RANGE500 – 50,000 cpsWEB WIDTH RANGE300 – 2500mmCOAT WEIGHT RANGE100 – 1000gsm wetTYPICAL SUBSTRATESPaper and fabric

Knife over Roll Coater

Air Knife Coating

Air Knife Coating A simple process where the coating is applied to thesubstrate and the excess is 'blown off' by a powerful jet from the airknife. This procedure is typically used for aqueous coatings and isparticularly noisy.

The Air Knife coater, also called Air Doctor is an example of anold coating method that is still widely used and has a role in the coatingprocess. It was widely used to sequentially coat the multiple layers neededfor photographic films because it could apply thin layers from low viscositysolutions. Slide and curtain coating because of improved quality, higherspeeds and multilayer capability replaced it. It is now widely used to applypigmented coatings in the paper industry and for 100% solids coating suchas molten zinc and aluminum in galvanizing applicationsIn this method a coating roll and pan are used to apply the coating solutionto the web and then an air knife is positioned after the pan to regulate thefinal wet-coating weight by applying a focused jet of air to the web. Theexcess solution is collected in an overflow pan and can be eitherrecirculated and used again or scrapped. Figure (1) is a typical air knifeconfiguration.

The Air Knife coater, also called Air Doctor is an example of anold coating method that is still widely used and has a role in the coatingprocess. It was widely used to sequentially coat the multiple layers neededfor photographic films because it could apply thin layers from low viscositysolutions. Slide and curtain coating because of improved quality, higherspeeds and multilayer capability replaced it. It is now widely used to applypigmented coatings in the paper industry and for 100% solids coating suchas molten zinc and aluminum in galvanizing applicationsIn this method a coating roll and pan are used to apply the coating solutionto the web and then an air knife is positioned after the pan to regulate thefinal wet-coating weight by applying a focused jet of air to the web. Theexcess solution is collected in an overflow pan and can be eitherrecirculated and used again or scrapped. Figure (1) is a typical air knifeconfiguration.

The advantage of the air-knife processes are low initial cost, versatility foraqueous coating of coating a variety of webs and solutions, ease ofchanging and maintaining the coating and the good coating quality. Thedisadvantages are line speed and coating weight limitations, noise , solutionviscosity limitations, and susceptibility to streaks and chatter.The air knife can function either in the precision or in the squeegee mode.These give very different types of coating and performance characteristics,although the same name is used for both processes.In the precision mode, the air knife uses low pressures and doctors off someof the coating to control the coating weight and to level the surface to give auniform coating of reasonable quality. The coating weight is a function ofweb speed, viscosity of solution, surface tension and air-knife pressure andthe Coating profile is the same as that of the substrate.

The advantage of the air-knife processes are low initial cost, versatility foraqueous coating of coating a variety of webs and solutions, ease ofchanging and maintaining the coating and the good coating quality. Thedisadvantages are line speed and coating weight limitations, noise , solutionviscosity limitations, and susceptibility to streaks and chatter.The air knife can function either in the precision or in the squeegee mode.These give very different types of coating and performance characteristics,although the same name is used for both processes.In the precision mode, the air knife uses low pressures and doctors off someof the coating to control the coating weight and to level the surface to give auniform coating of reasonable quality. The coating weight is a function ofweb speed, viscosity of solution, surface tension and air-knife pressure andthe Coating profile is the same as that of the substrate.

The process operating conditions are as follows:• Viscosity 1 - 50 centistokes• Wet thickness 1 - 200 microns• Line speed 14:31:09 40 - 400 fpm• Accuracy +/-10%

In the squeegee mode, the air knife operates at much higher pressures andcoating speeds than in the precision mode and effectively doctors off themajority of the coating. This process is used for porous supports, such aspaper, where the coating is absorbed into the voids. After the air knife,which effectively functions as a leveling device, the coating solids remainin the voids and in a thin surface layer.

The process operating conditions are as follows:• Viscosity 1 - 50 centistokes• Wet thickness 1 - 200 microns• Line speed 14:31:09 40 - 400 fpm• Accuracy +/-10%

In the squeegee mode, the air knife operates at much higher pressures andcoating speeds than in the precision mode and effectively doctors off themajority of the coating. This process is used for porous supports, such aspaper, where the coating is absorbed into the voids. After the air knife,which effectively functions as a leveling device, the coating solids remainin the voids and in a thin surface layer.

An air knife is a tool used to blow off liquid or debris fromproducts as they travel on conveyors. Air knives are normallyused in manufacturing or as the first step in a recursiverecycling process to separate lighter or smaller particles fromother components for use in later or subsequent steps, postmanufacturing parts drying and conveyor cleaning, part ofcomponent cleaning. The knife consists of a high intensity,uniform sheet of laminar airflow sometimes knownas streamline flow.An industrial air knife is a pressurized air plenum containing aseries of holes or continuous slots through which pressurized airexits in a laminar flow pattern. The exit air velocity then createsan impact air velocity onto the surface of whatever object the airis directed. This impact air velocity can range from a gentlebreeze to greater than Mach 0.6 (40,000 ft/min) to alter thesurface of a product without mechanical contact.

An air knife is a tool used to blow off liquid or debris fromproducts as they travel on conveyors. Air knives are normallyused in manufacturing or as the first step in a recursiverecycling process to separate lighter or smaller particles fromother components for use in later or subsequent steps, postmanufacturing parts drying and conveyor cleaning, part ofcomponent cleaning. The knife consists of a high intensity,uniform sheet of laminar airflow sometimes knownas streamline flow.An industrial air knife is a pressurized air plenum containing aseries of holes or continuous slots through which pressurized airexits in a laminar flow pattern. The exit air velocity then createsan impact air velocity onto the surface of whatever object the airis directed. This impact air velocity can range from a gentlebreeze to greater than Mach 0.6 (40,000 ft/min) to alter thesurface of a product without mechanical contact.

Air knives remove liquids, control the thickness of liquids, drythe liquid coatings, remove foreign particles, cool productsurfaces or create a hold down force to assist in the mechanicalbonding of materials to the surface. Electrical currents fromanti-static bars can also be injected into the exit air knife streamto neutralize the static electricity charge on some surfaces.In the majority of manufacturing applications for air knives, theair knives are stationary while the product passes through the airvelocity air stream. In other circumstances, the product isstationary and the air knives move (reciprocate or rotate) overthe surface of the stationary product. Although there are veryfew applications where an air knife can actually cut a product(break mechanical bonds between two points), air knives areoften the most efficient method of removing or controllingunwanted or foreign substances on any surface.

Air knives remove liquids, control the thickness of liquids, drythe liquid coatings, remove foreign particles, cool productsurfaces or create a hold down force to assist in the mechanicalbonding of materials to the surface. Electrical currents fromanti-static bars can also be injected into the exit air knife streamto neutralize the static electricity charge on some surfaces.In the majority of manufacturing applications for air knives, theair knives are stationary while the product passes through the airvelocity air stream. In other circumstances, the product isstationary and the air knives move (reciprocate or rotate) overthe surface of the stationary product. Although there are veryfew applications where an air knife can actually cut a product(break mechanical bonds between two points), air knives areoften the most efficient method of removing or controllingunwanted or foreign substances on any surface.

Description of operationAir knives on a production line commonly range from 0.25 to200 inches (6.4 to 5,080.0 mm) in length with a discharge airslot or holes ranging from 0.001 to 0.25 in (0.025 to 6.350 mm).A stationary air knife configuration can require from one to adozen air knives depending on the application criteria. Air isblasted through the air knife slots via an air generator, either anindustrial blower or air compressor, to deliver the predeterminedexit air volume and velocity needed.There are many application, environmental, efficiency and dutycycle aspects to consider when choosing between compressorsand blowers. Compressed air, which is least efficient when usedfor air knives discharging into free air, allows for use of primaryplant air. The piping sizes supplying the air knives can be aslittle as 1⁄4 in (6.4 mm) diameter so they are ideal for confinedspaces.

Description of operationAir knives on a production line commonly range from 0.25 to200 inches (6.4 to 5,080.0 mm) in length with a discharge airslot or holes ranging from 0.001 to 0.25 in (0.025 to 6.350 mm).A stationary air knife configuration can require from one to adozen air knives depending on the application criteria. Air isblasted through the air knife slots via an air generator, either anindustrial blower or air compressor, to deliver the predeterminedexit air volume and velocity needed.There are many application, environmental, efficiency and dutycycle aspects to consider when choosing between compressorsand blowers. Compressed air, which is least efficient when usedfor air knives discharging into free air, allows for use of primaryplant air. The piping sizes supplying the air knives can be aslittle as 1⁄4 in (6.4 mm) diameter so they are ideal for confinedspaces.

Blower powered air knives must be larger in size along withlarger diameter supply piping, but the efficiency improvementover compressed air is easily justified with the electrical powercost savings.Air knife designs today have evolved to where somemanufacturers produce a very efficient “teardrop” shape with a.95 coefficient of discharge. These blower powered air knifedesigns typically have a profile of approximately 3.5 in (89 mm)wide x 5.5 in (140 mm) tall x any length, but the teardrop profilecan range from 1.5 to 10 in (38 to 254 mm) tall depending onthe criteria of the product for which the impact air velocity mustbe engineered. With construction ranging from 1⁄8 in (3.2 mm)thick aluminum extrusion to 11 gage fabricated stainless steel,air knives can weigh 1 lb/ft to 25 lbs/ft. Depending on the widthand speed of the product, the air knife can provide effectiveblow off performance from 0.5 to 12 in (13 to 305 mm) or moreaway from the surface of the product.

Blower powered air knives must be larger in size along withlarger diameter supply piping, but the efficiency improvementover compressed air is easily justified with the electrical powercost savings.Air knife designs today have evolved to where somemanufacturers produce a very efficient “teardrop” shape with a.95 coefficient of discharge. These blower powered air knifedesigns typically have a profile of approximately 3.5 in (89 mm)wide x 5.5 in (140 mm) tall x any length, but the teardrop profilecan range from 1.5 to 10 in (38 to 254 mm) tall depending onthe criteria of the product for which the impact air velocity mustbe engineered. With construction ranging from 1⁄8 in (3.2 mm)thick aluminum extrusion to 11 gage fabricated stainless steel,air knives can weigh 1 lb/ft to 25 lbs/ft. Depending on the widthand speed of the product, the air knife can provide effectiveblow off performance from 0.5 to 12 in (13 to 305 mm) or moreaway from the surface of the product.

Round air nozzles of 1 to 4 in (25 to 102 mm) diameter can beeffective against surfaces which are up to several feet (1 to 2meters) from the product surface when engineered for suchapplications.Types and applicationsThe most common use of air knives is to contain or removefree-standing materials (liquids or solids) from the surface ofmaterial. The applications include drying bottles and cans afterfilling and rinsing, printed circuit boards following the conveyorzed wash to remove solder paste and flux, metals castings afterautomatic machining and many more. They can also deliverheated or cooled air to a surface, or create an invisible air barrierto separate heated or cooled environments from one another inindustrial applications such as continuous metal heat treatingovens, cold process or storage areas in food processing or dustcontainment for the entrance to clean rooms.

Round air nozzles of 1 to 4 in (25 to 102 mm) diameter can beeffective against surfaces which are up to several feet (1 to 2meters) from the product surface when engineered for suchapplications.Types and applicationsThe most common use of air knives is to contain or removefree-standing materials (liquids or solids) from the surface ofmaterial. The applications include drying bottles and cans afterfilling and rinsing, printed circuit boards following the conveyorzed wash to remove solder paste and flux, metals castings afterautomatic machining and many more. They can also deliverheated or cooled air to a surface, or create an invisible air barrierto separate heated or cooled environments from one another inindustrial applications such as continuous metal heat treatingovens, cold process or storage areas in food processing or dustcontainment for the entrance to clean rooms.

There is a variety of uses for air knives in many differentindustries, applications and environments. The invisible highvelocity air streams can be discharged by air knife designs ofnumerous shapes and sizes. These range from “garage built”devices with a low level of precision to the most exotic metalsof construction used in air knives for class 100 clean rooms.In instances where noise reduction and moisture containmentaround a conveyorized air knife installation becomes importantsome manufacturing facilities have installed air knives within anenclosure. These enclosures keep water contained, reduce theamount of air knife noise and even eliminate any liquid thatcould create safety concerns.

There is a variety of uses for air knives in many differentindustries, applications and environments. The invisible highvelocity air streams can be discharged by air knife designs ofnumerous shapes and sizes. These range from “garage built”devices with a low level of precision to the most exotic metalsof construction used in air knives for class 100 clean rooms.In instances where noise reduction and moisture containmentaround a conveyorized air knife installation becomes importantsome manufacturing facilities have installed air knives within anenclosure. These enclosures keep water contained, reduce theamount of air knife noise and even eliminate any liquid thatcould create safety concerns.

Basic design featuresCompressed air powered air knivesThere has always been a wide assortment of blow offappliances. Air knives and nozzles for compressed air blow offrange from home made round pipes with holes to engineeredhigh pressure air knives. In order to achieve the highestefficiency using compressed air, many manufacturers ofcompressed air knives utilize the Coandă effect to improvecompressed air knife design over other types of knives andnozzles. Although the efficiency of compressed air for lowpressure blow off air is much lower than blowers, the Coandainspired air knives entrain ambient air into the high velocitystream to enhance the blow off effect.

Basic design featuresCompressed air powered air knivesThere has always been a wide assortment of blow offappliances. Air knives and nozzles for compressed air blow offrange from home made round pipes with holes to engineeredhigh pressure air knives. In order to achieve the highestefficiency using compressed air, many manufacturers ofcompressed air knives utilize the Coandă effect to improvecompressed air knife design over other types of knives andnozzles. Although the efficiency of compressed air for lowpressure blow off air is much lower than blowers, the Coandainspired air knives entrain ambient air into the high velocitystream to enhance the blow off effect.

Blower powered air knivesThe tear drop shaped air knife having a bulbous plenum whichtapers down to a precise air discharge slot as the standard of theblower driven air knife industry. Whereas a round pipe withholes drilled has an average coefficient of discharge of 0.6 (60%efficient), the tear drop shape air knife is commonly 0.95 (95%efficient) which provides much higher impact air velocity to thesurface at which the air is directed with the lowest blower motorpower demand. These tear drop designs are available inextruded aluminum shapes as well as fabricated carbon andstainless steels.

Blower powered air knivesThe tear drop shaped air knife having a bulbous plenum whichtapers down to a precise air discharge slot as the standard of theblower driven air knife industry. Whereas a round pipe withholes drilled has an average coefficient of discharge of 0.6 (60%efficient), the tear drop shape air knife is commonly 0.95 (95%efficient) which provides much higher impact air velocity to thesurface at which the air is directed with the lowest blower motorpower demand. These tear drop designs are available inextruded aluminum shapes as well as fabricated carbon andstainless steels.

A second coating method solves this problem of an inconsistent coatingthickness. The air knife coating method uses a strong blast of air toremove excess coating and leaves a layer of uniform thickness, but asheet with poor smoothness and reduced gloss. Of course, the sheet willbecome smoother after being polished during the supercalendering stage,but it will still not attain a high gloss level.

The air knife coating methodreplaces the blade with a strongblast of air. The result is a sheetwith consistent coatingthickness, but low smoothness.

An air knife is a tool used to blow off liquid or debris from products as theytravel on conveyors. Air knives are normally used in manufacturing or as thefirst step in a recursive recycling process to separate lighter or smallerparticles from other components for use in later or subsequent steps, postmanufacturing parts drying and conveyor cleaning, part of componentcleaning. The knife consists of a high intensity, uniform sheet of laminarairflow sometimes known as streamline flow.An industrial air knife is a pressurized air plenum containing a series ofholes or continuous slots through which pressurized air exits in a laminarflow pattern. The exit air velocity then creates an impact air velocity ontothe surface of whatever object the air is directed. This impact air velocitycan range from a gentle breeze to greater than 0.6 (40,000 ft/min) to alterthe surface of a product without mechanical contact.

An air knife is a tool used to blow off liquid or debris from products as theytravel on conveyors. Air knives are normally used in manufacturing or as thefirst step in a recursive recycling process to separate lighter or smallerparticles from other components for use in later or subsequent steps, postmanufacturing parts drying and conveyor cleaning, part of componentcleaning. The knife consists of a high intensity, uniform sheet of laminarairflow sometimes known as streamline flow.An industrial air knife is a pressurized air plenum containing a series ofholes or continuous slots through which pressurized air exits in a laminarflow pattern. The exit air velocity then creates an impact air velocity ontothe surface of whatever object the air is directed. This impact air velocitycan range from a gentle breeze to greater than 0.6 (40,000 ft/min) to alterthe surface of a product without mechanical contact.

Air knives remove liquids, control the thickness of liquids, dry the liquidcoatings, remove foreign particles, cool product surfaces or create a holddown force to assist in the mechanical bonding of materials to the surface.Electrical currents from anti-static bars can also be injected into the exit airknife stream to neutralize the static electricity charge on some surfaces.In the majority of manufacturing applications for air knives, the air knivesare stationary while the product passes through the air velocity air stream. Inother circumstances, the product is stationary and the air knives move(reciprocate or rotate) over the surface of the stationary product. Althoughthere are very few applications where an air knife can actually cut a product(break mechanical bonds between two points), air knives are often the mostefficient method of removing or controlling unwanted or foreign substanceson any surface.

Air knives remove liquids, control the thickness of liquids, dry the liquidcoatings, remove foreign particles, cool product surfaces or create a holddown force to assist in the mechanical bonding of materials to the surface.Electrical currents from anti-static bars can also be injected into the exit airknife stream to neutralize the static electricity charge on some surfaces.In the majority of manufacturing applications for air knives, the air knivesare stationary while the product passes through the air velocity air stream. Inother circumstances, the product is stationary and the air knives move(reciprocate or rotate) over the surface of the stationary product. Althoughthere are very few applications where an air knife can actually cut a product(break mechanical bonds between two points), air knives are often the mostefficient method of removing or controlling unwanted or foreign substanceson any surface.

Date post:	09-Jan-2017
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