Navigating the Chemical Maze of the Screen Printing Process PRODUCTION Visit SGIA at SGIA.org SGIA Journal ■ Second Quarter 2009 | 7 By Ray Greenwood, Technical Services Associate, SGIA One of the most confusing aspects of the screen printing industry is choosing the correct chemicals for the screen reclaiming process and on-press clean-up. On the surface, it seems simple — get a standardized chemical set from a supply dealer and start printing and reclaiming. Time and experience shows most printers that there are a wide range of functions and factors that need to be addressed and they are not the same at every shop. First, ink systems used with these chemicals must be compatible. A few of the main types of ink systems include: water-based, UV, basic solvent/oil based, epoxy, dye-based, acrylic, adhesive, industrial metallic and conductive. A chemical that works for one particular step in the process may need to be changed when the process sequence changes. Many variables differentiate one shop from another. Do you need on- press quick cleaning between color changes, housekeeping chemicals (de- inking, degreasing and floor cleaning), ink degrading prior to reclaiming, ink degrading prior to library storage of screens? Emulsion removal, ghost haze removal, stain removal, degreasing and adhesive removal are all standard process steps of every screen shop’s chemical system. However, even these standard chemistry steps are highly variable from shop to shop. Where to Begin Throughout the last decade, there have been a significant number of new regulatory requirements concerning chemicals. The perception is that it is increasing because rules and regulations concerning air quality, waste water quality and occupational safety are finally being enforced on a regular basis. Additionally, new terminology is being used: drain-safe, eco, California compliant, green, low VOC (volatile organic compounds), no VOC, etc. Today, government regulations can play a large part in your choice of chemicals, but for the purposes of this article, those issues will be dealt with as background material only. The subject of regulation is too large for the limited space of this article. The primary goal here is to outline the correct methodology for choosing chemicals based on production and efficiency needs only. In the early 90’s, the screen printing chemical industry saw an upsurge in the use of the term “drain-safe.” In those days, drain-safe meant that the product had a pH (acid or base level) and solution strength (level of dilution) that would not harm plumbing and was generally acceptable to most sanitary sewer systems. To keep from getting caught up in marketing hype, you must first determine the city sewer and waste water requirements for your area. That specification originally had little correlation to toxicity to humans, animals or the environment as long as heavy metals (chrome, lead, cadmium, silver, etc.) were low. Many, but not all “drain-safe” chemical products were inherently low in toxicity because of efforts to keep pH to a level that would not harm beneficial algae and bacteria in sewers, rivers and streams. Today, to be considered “drain-safe,” a chemical must be plumbing friendly, low VOC, no VOC (or VOC exempt), have low or no toxic metals and solution strengths that can be moderated within normal rinsing and dilution expectations before being discharged to a city sewer system. For the record, there are no chemical reclamation systems that can be reliably recommended for septic systems of any type without pre-treatment. Even the cleanest chemistry uses pH as a primary tool. Emulsion remover is a good example. A chemical that works for one particular step in the process may need to be changed when the process sequence changes.
Transcript
Navigating the Chemical Maze of the Screen Printing Process
P R O D U C T I O N
V i s i t S G I A a t S G I A . o r g S G I A J o u r n a l ■ S e c o n d Q u a r t e r 2 0 0 9 | 7
By Ray Greenwood, Technical Services Associate, SGIA
One of the most confusing aspects of the screen printing industry is choosing the correct chemicals for the screen reclaiming process and on-press clean-up. On the surface, it seems simple — get a standardized chemical set from a supply dealer and start printing and reclaiming. Time and experience shows most printers that there are a wide range of functions and factors that need to be addressed and they are not the same at every shop. First, ink systems used with these chemicals must be compatible. A few of the main types of ink systems include: water-based, UV, basic solvent/oil based, epoxy, dye-based, acrylic, adhesive, industrial metallic and conductive. A chemical that works for one particular step in the process may need to be changed when the process sequence changes.
Many variables differentiate one shop from another. Do you need on-press quick cleaning between color changes, housekeeping chemicals (de-inking, degreasing and floor cleaning), ink degrading prior to reclaiming, ink degrading prior to library storage of screens? Emulsion removal, ghost haze removal, stain removal, degreasing and adhesive removal are all standard process steps of every screen shop’s chemical
system. However, even these standard chemistry steps are highly variable from shop to shop.
Where to BeginThroughout the last decade, there have been a significant number of new regulatory requirements concerning chemicals. The perception is that it is increasing because rules and regulations concerning air quality, waste water quality and occupational safety are finally being enforced on a regular basis. Additionally, new terminology is being used: drain-safe, eco, California compliant, green, low VOC (volatile organic compounds), no VOC, etc. Today, government regulations can play a large part in your choice of chemicals, but for the purposes of this article, those issues will be dealt with as background material only. The subject of regulation is too large for the limited space of this article. The primary goal here is to outline the correct methodology for choosing chemicals based on production and efficiency needs only.
In the early 90’s, the screen printing chemical industry saw an upsurge in the use of the term “drain-safe.” In those days, drain-safe meant that the product had a pH (acid or base level) and solution strength
(level of dilution) that would not harm plumbing and was generally acceptable to most sanitary sewer systems. To keep from getting caught up in marketing hype, you must first determine the city sewer and waste water requirements for your area. That specification originally had little correlation to toxicity to humans, animals or the environment as long as heavy metals (chrome, lead, cadmium, silver, etc.) were low. Many, but not all “drain-safe” chemical products were inherently low in toxicity because of efforts to keep pH to a level that would not harm beneficial algae and bacteria in sewers, rivers and streams.
Today, to be considered “drain-safe,” a chemical must be plumbing friendly, low VOC, no VOC (or VOC exempt), have low or no toxic metals and solution strengths that can be moderated within normal rinsing and dilution expectations before being discharged to a city sewer system. For the record, there are no chemical reclamation systems that can be reliably recommended for septic systems of any type without pre-treatment. Even the cleanest chemistry uses pH as a primary tool. Emulsion remover is a good example.
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A chemical that works for one particular step in the process may need to be changed when the process sequence changes.
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Periodic acid (the working ingredient in most emulsion removers) is a low solution strength acid with a working pH of about 1.5–2.5 (Figure 1). Initial water rinsing raises its at-the-drain pH level to about 3–4.5 (Figure 2). This pH is still lower than you would want in a septic system. In a city sewer system; however, the pH level quickly rises and is no longer a problem.
Ghost-haze removers (especial ly strong ones) are a little more complicated. These are caustics with a pH ranging of 9.5–12 (Figure 3). More importantly, the ingredients used are usually in very high solution strength and contain sodium (sodium hydroxide is the most common). These are strong oxidizers. Some of them even contain VOCs, which are generally not permitted in most city sewer systems. They require a great deal of rinsing to bring the solution strength down to acceptable levels for a city sewer system. There are cleaner, less caustic ghost-haze products on the market, but the trade-off is increased working time.
A few print shops in areas with stringent requirements have addressed these problems by splitting the emulsion removal and de-hazing stages into separate sinks with a separate reservoir for each effluent. Before being discharged to the sewer, they are settled out in catch tanks, roughly filtered and purposefully mixed. The low pH emulsion remover waste solution will act as the “buffer” for the pH of the haze-remover solution. When employed carefully, this simple process can solve important problems (see Diagram 1).
Some municipal water systems do not allow simple dilution of industrial effluent. Depending on the waste product, it must first be “treated” before being released to the drain. That usually means filtration
and buffering with chemicals. If you can document that this same function may be performed by mixing waste streams, you may save time and money.
The vast majority of chemicals dubbed “clean,” “green” or “eco” are working within or toward California’s stringent compliance standards. In a nutshell, this is a classification system designed to keep VOC content extremely low. The vast majority of VOCs contributes to ground level ozone reactivity, the primary building block of smog. By federal classification, a VOC is any carbon-based evaporative compound. The carbon-based gases and liquids that are non-reactive in this manner are exempt from the regulation. The US federal government maintains an exempt list, as do individual states and air quality districts. The current level of VOC, allowed in a compound considered to be California OTC compliant is 350mg per liter. This number can be forced even lower if the VOC is also listed as a toxin or carcinogen. Examples of these chemicals include methylene chloride or methyl-ethyl-ketone. Quality, modern screen printing chemicals have a balance of high flash point (as high as most can get and still contain chemicals that make them effective), low toxicity and low VOC. There are VOC-exempt chemical systems available that technically contain moderate quantities of what may be considered a VOC by definition (i.e. they are a carbon-based evaporative liquid), but are exempt through a combination of high flash point, low toxicity and non-reactivity with ground level ozone.
The main goal of this article is to stress the importance of using the smallest amount of any chemical as possible. I want to help you choose the most effective chemicals for your ink system, be sure you are purchasing it in the most cost-effective manner and apply and use it in a manner that gives the best results per gram of chemical dollar spent. These steps must precede any decision for further time-saving automation and moving to an even more environmentally-friendly chemical system. Start with your local or regional chemical company representative who services your distributor. Most chemical representatives are very knowledgeable about their product line and capabilities. You should also do your own independent testing.
Testing to Select Your Baseline ChemistryAfter selecting your process model (ink system, emulsion system, adhesive system
Reclaim/de-haze SinkPH 13.0+
Stencil Remover SinkPH 1.5-2.5
Degrease and Rinse SinkPH 5.5-7.0
PH11.0
PH8.0 - 9.0
PH5.5 - 7.0
Sewer6.5-
Diagram 1: Chenical Sinks
Figure 1
Figure 2
Figure 3
and process flow), you must perform some simple, specific testing to find out how compatible a given chemical system is with your inks, frames and squeegees as well as to find out how quickly a given chemical will solve your inks and emulsions.
At the on-site level, this is referred to as a surface tension test. It uses a small, measured amount of chemical (for ink degradent and spray and wipe process positions) on screens that have been used and have what would be considered an average amount of ink residue and staining. The chemical is applied either by spray or squirt bottle. The object is to use no mechanical scrubbing action and to see how fast the ink is dissolved by chemical action alone (See Figures 4 & 5).
It is advisable to test some “worst case” screens. For example, if your shop uses a high volume of screens and there is a waiting period before reclaim, you may end up with certain types of ink dried into the mesh. These dried-in screens provide an excellent testing opportunity (Figure 6).
The next step is an emulsification test primarily for those who use a recirculating ink degradent or squeegee washing system. A teaspoon of raw, wet ink is dropped into a few ounces of ink degradent in a clear, covered jar or container. Measure the ratio of ink degradent volume to ink volume (10:1, 20:1, etc.) by weight. There should be about two inches of air space at the top of the container to allow for agitation. Shake the jar lightly and let it settle. The lump of ink should quickly begin to break into smaller particles. Repeat until the ink dissolves entirely, just coloring the liquid. Add another measured amount of ink and repeat the process. Keep adding ink until the ink no longer dissolves properly. Through this test we learn two pieces of information important for using re-circulated chemicals: (1) the ink degradent actually solves the ink system and (2) the amount of ink residue that can be suspended in the degradent before it must be either replaced or filtered (Figure 7).
Press wash and spray-and-wipe chemicals also should be tested with the emulsion system. This is critical in deciding what emulsion system is necessary, and will partially dictate which emulsion removers and ghost-haze removers are used. An older screen will usually need to be sacrificed for this. Begin by making a normal stencil on a screen. Decide on a time interval that represents your average print run length and double it. In the case of solvent, water-based or UV inks, take a small amount of scrap ink and use it to flood the screen (this does not need
to be done with plastisol ink). Cover both sides of the screen with plastic wrap from the grocery store and let the screen stand for the determined time interval. When the time has elapsed, use the press wash you have selected and wash the screen on both sides repeatedly, at least twice for each hour of print run interval. Let the screen-wash dry between each washing. The screen can then be used to run a surface tension reclamation test with your emulsion remover. Difficulties removing pure-photopolymer emulsions will usually dictate a lower VOC content spray-and-wipe product, or a specialty degradent. In cases where unique ink types (e.g., epoxy and catalyzed coatings) are used that require aggressive solvents, a change of stencil technology may also be indicated. This same process should be performed with your ink-degradent chemical as well.
Once the test screen has been reclaimed, surface tension testing with your selected screen degreaser can be performed. This is almost as important as all of the other tests combined. If your facility has hard water, or water that is mechanically softened, you may find difficulties getting a clean enough rinse to prevent screen spotting and emulsion fisheyes. This may result in the need for a stronger degreaser or a degreaser with a rinse additive. The reclaimed screen from spray and wash and ink degradent testing makes a nice test reference. The ability to break surface tension and degrease a screen segment with a measured amount of scrubbing or contact is critical.
Primary Chemical Consideration ParametersThere is a commonly used range of parameters used to make initial chemical choices. Each item on the following list has a range of performance. It is not necessary (and sometimes not even possible) to have every parameter on this list at maximum positive. These parameters must be considered both individually and as a cohesive unit when selecting chemicals if you are to get the best balance of value, performance, speed and safety.
Chemical Effectiveness and Solution Strength (Speed of Solvency vs. Volume Used)This issue is frequently ignored, especially with regard to on-press washers or spray-and-wipes. Press operators often prefer very low vapor pressure (fast evaporating) solvents that allow them to remove a dried ink spot or change colors very quickly without losing
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Figure 6
Figure 4: Surface tension test before and after
Figure 5: Surface tension test detail
Figure 7: Ink emulsification test
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a lot of print time waiting for the solvent to dry. Printers get into the habit of using fast-evaporating solvents because most of them dissolve ink rapidly. They equate slow evaporation with slow solvency. This is not always the case, however, if the press wash is selected properly for the ink.
Most medium-to-large format graphic shops easily use 400 percent more press-wash solvent than is necessary. Typically about 80 percent of all of this solvent is lost through evaporation to the atmosphere. Solvent-blending services generally supply generic solvent “blends” as they are known at low cost per gallon as compared to dedicated, higher flash-point screen solvents. Most screen printers will not justify paying on average three times the cost for screen solvent tuned to their ink, even though they will use inversely three to four times less in quantity with no real measurable loss in print time.
The part of the equation that is usually not taken into account is the cost of wiping materials. The average disposable, lint-free wiping cloth bought in bulk by a graphic print shop costs between three and six cents each. The average quick clean up to stop a press with a 50”x 60” screen using solvent ink uses about 20 wiper sheets with fast-drying hot solvents because the solvent does not remain wet long enough to completely dissolve the ink in the screen. Ink is typically dissolved with free solvent and absorbed into dry or semi-dry wipers and then quickly discarded. UV inks use about half that because the screen does not have to be totally de-inked. A solvent based ink clean-up using a higher flash point on-press cleaner will typically use about half the amount of wiping material than a low flash point solvent.
Chemical Effectiveness/Mechanical StrengthThis factor is illustrated by surface tension testing on dirty screens, emulsification testing with ink degradent and chemical strength testing with emulsion removers (i.e. the effectiveness of the chemicals without scrubbing or mechanical agitation).
Chemical costChemical cost per ounce/pound/gallon is critical to planning correct screen costs, but is generally not the key component. The mechanical efficiency of a chemical will dictate whether it is a high-use or a low-use chemical. If the efficiency is high enough, the savings will offset the purchase price to the point of making a profit.
ToxicityLook for toxins and carcinogens that may dictate personal protective equipment and/or ventilation you cannot afford. Some of the fastest, cheapest and most effective chemicals in the world also are the most toxic.
Environmental concerns and disposalMany chemicals raise concerns such as pH, metals and VOC content. Some regulations are federal and apply to everyone, while some are strictly local and widely vary. It’s important to know what is in the product you plan to use.
Ink system compatibility Surface tension testing makes sure the speed of solvency is usable for your process and ensures there is no polymerization (chemical hardening or thermal reaction) with the chemicals you plan to use.
Flammability/Corrosiveness In many shops, chemicals are selected based on the speed of solvency of dried ink and little thought is given to flammability. If you are using a difficult ink system (epoxy, polyester or polypropylene) the level of solvent you may be forced to use could have a bearing on the cost and sophistication of the equipment you purchase (you may need extensive ventilation, explosion proof motors or lights). In the case of container printing, you may need corona treating instead of open flame treating.
Secondary Chemical Consideration ParametersEvaporation rate for air quality requirementsIf you are losing chemical volume at a high rate through evaporation, you are losing money and you are polluting the air. Depending on regulations in your area, a VOC–exempt product may make sense.
OdorShopping for chemicals based on smell can create dangerous problems. There are chemicals that smell nice but are actually toxic when exposure is too long. By the same token, there are horrible smelling chemical compounds that are inert. In general, if you have a very clean chemical system (according to the MSDS sheets), but the smell is difficult to work with, this can be a signal of poor ventilation or the handling of the chemical is creating an aerosol mixture (spraying in too fine of a mist, or not pre-rinsing before pressure washing).
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Required extra personal safety equipment When working with some of the more aggressive engineering plastic inks, you can end up with more aggressive, toxic chemicals as well. The use of some of the more aggressive solvents and haze removers may require protective gloves with increased chemical resistance. The same generally is true of respirator cartridges. The annual cost for this safety equipment can be very high, and must be captured in the chemical cost on a per-screen basis, and then passed on to the customer. Therefore, when selecting chemicals, you should not arbitrarily select those that are over-strength or over-formulated for your ink system. What little you gain in speed of solvency or cleaning power may be dwarfed by PPE overhead costs.
Required specialty application and containment equipmentA high-volume shop may need automated or semi-automated equipment. This usually requires a vastly different range of chemical characteristics for both speed and machine maintenance.
VentilationSome chemicals require more ventilation than others to keep potentially toxic additives within acceptable levels. Find out if you have enough ventilation before before switching to a new chemical or selecting a new chemical system.
Fresh Water and Wastewater RequirementsThe ef f iciency of your degreaser, degradents and haze-remover (from the surface tension testing discussed earlier) will tell you whether you have chemicals whose solution strength or composition creates long rinse times. Longer rinse times use more water and require more pressure washing (electrical power, water and worn out pumps). This cost must either be captured and passed on or reduced by alternate chemicals choices.
Basic Reclamation Techniques In general, chemicals are selected by what stage in the process they are used. There is no end to the types and numbers of dedicated and specialty chemicals for screen printers. As screen printers, we use everything from ink catalysts, adhesion modifiers, ink viscosity reducers and admixtures, to anti-static and pre-treat chemistry for plastics and films. We will review six main categories:
For the purposes of this article we will not deal with specialty chemicals, only the primary process chemicals. These have six main categories:
• General cleaning products for machinery
• On-press cleaners and spray-and-wipes
• Ink degradents for reclaiming• Emulsion removers• Ghost-haze and stain removers• DegreasersThe last three categories above are
simply called reclaiming chemicals.
Reclamation chemicals make up the bulk volume of all chemicals ordered by screen plants, although they may not always make up the bulk of the chemical costs. Ink admixtures, adhesives, pre-treating chemicals and catalysts can cost more in some plants. In general, however, the improper selection or use of basic reclaiming process chemicals can cost vast quantities of print and labor time and can lead to the increased use of specialty chemicals like emulsion hardener or excessive losses in screens or mesh. The downstream costs of chemical selection are generally more important than their initial budgetary costs.
Sometimes, techniques can cost more time and money than the chemicals used. There are a few different ways to apply and use chemicals: manually with spray bottles, brushes and wipers; semi-automatically with bulk chemical feeding pumps and sprayers, dip-tank systems, single chemical recirculation units and fully-automated application systems (which may actually transport, scrub, rinse and dry screens as well as apply chemicals). Most screen printers consider the choice of which level of automation to use rather simple. Printers generally buy what works best, is most inexpensive and falls within their level of experience. Sometimes it’s that easy, but usually is more complex.
For example, a high volume textile shop (100–200 frames or more per day) may see reclaiming loss-time as the bottle neck and opt for a fully automated system. In reality, they may see labor time decrease, but see chemical costs increase to a level that is high enough to cancel out labor savings. Another shop may opt for a semi-automatic method, such as a recirculating ink-degradent system and a dip tank for emulsion. This practice may reduce both chemical and labor costs to a large degree, but may not save on production time.
In other production facilities, the
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Different brushes, different purposes
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balance of process automation may be excellent but the selection of chemicals is incorrect for the ink or volume of screens. This can cause problems in the print process due to damaged glue on static frames, improper cleaning causing ink contamination or hazes and stains causing print problems. Managing chemical systems can be a delicate balance.
Necessary Accessories: Sinks, etc.All chemicals and chemical systems need basic application accessories. These tools vary in detail by level of automation. All of these accessories have a common element — quality and lifespan. Cheap hardware store brush applicators or non-industrial pressure washers are examples of accessories that can cause not only the failure of chemistry, but also the disarmament of automated equipment as time/labor saving devices.
Examples of this are overly abrasive scrubbing pads that scratch and damage mesh (usually not found until coating or on press) and pads and brushes that stiffen up after use with de-haze and emulsion-removing chemicals, leaving fragments of themselves in mesh and chemical. Through testing, screen chemical manufacturers have produced brushes and cleaning pads with specifications that work better with our chemicals and screens. The best brushes usually have polypropylene bristle construction injection-molded and thermo-set into the handle with specific hardness for each stage of reclamation and chemical work. They are color coded in order to not contaminate chemicals. Pad-type scrubbers, useful for applying solutions such as liquid haze remover and for very fine mesh with thin threads, are specific to screen printing work. They have a softer and finer fiber that rinses more easily to remove grit and debris that can scratch the mesh. These pads are generally heat-bonded to their polypropylene or UHMW handles. This prevents screen chemistry from dissolving the adhesive and detaching the pad from the handle.
Common chemical spray bottles (the ones that work) are another small piece of industrial magic that is usually overlooked. Many shops simply buy the chemical spray bottles that are convenient and cheap. The fact that they quickly spray poorly, or live a short life, is thought of as just part of the cost of doing business. Most sprayers look similar, so the problem is just ignored, and sprayers are bought by the dozen and thrown away on a regular basis. Besides the constant cost of replacement, most screen personnel simply revert to bucket and rag.
This leads to a huge increase in chemical usage, longer pressure washing to fully remove chemicals and increased water usage. Many of the chemicals we use in screen reclaiming are designed to dissolve polymers. Cheap spray bottles, also made of polymers, do not survive. The best spray bottles use HDPE bottles, polypropylene bodies and suction tubes, integral strainers, molded-in mixing graduations and pump seals that are molded in one piece with the plunger, usually of chemically-resistant polypropylene. These bottles also typically have silicone bottle collar seals.
As screen departments advance and get around simple tools (like cheap, reliable sprayer heads), they usually move up a notch in technology and handling speed to hand pump sprayers from five and 30 gallon carboys. Not only does this result in less mixing and spillage, buying chemicals in larger quantities almost always brings a significant cost savings. Most screen chemical companies will install an air-driven, wall mounted pump box with polypropylene tubing and sprayer application wands for very little or for free when your chemical purchase quantities rise to between 20–30 gallons bulk or larger per order. These sprayer systems become quite reliable as they meter and apply chemicals faster and more evenly. There are large savings to gain between better bulk purchasing, faster and less wasteful application and reduced water usage and screen reclamation time. The next incremental step-up from that is usually to install a slightly better grade of chemicals to see if you receive an even better return on reclaiming speed, chemical usage and screen lifespan. Next time your dealer representative or chemical company’s regional representative tries to sell you sprayer bottles with your chemical purchase, take the time to at least look at what he has. You might be surprised at the quality.
Pressure Washer SelectionThe improper selection of pressure washers is one of the most common mistakes made by print shops. The critical factors are volume of usage and output pressure.
If high pressure washing is used, reclaiming screens can be done with chemicals that are much less concentrated or caustic. The higher the pressure, the better the cleaning. The common belief that high pressures (2,000–3,000 psi) harm mesh is a myth. The average 23” x 31” 40ncm textile screen has 1,714 lbs/ft of force locked up in it at rest. Under deflection force from the squeegee at 1/8”
Pad-type scrubbers
off-contact, it experiences roughly 1.5–2 times that force level (2,571 to 3,428 lbs/ft). Breaking mesh with high pressure water is a training and methodology issue, not a pressure issue. Mesh may break when high pressure is used because of broken threads and pin-holes not visible to the eye. No screen will survive either ultra high pressure washing with broken threads or the squeegee and floodbar during production. Getting far too close to the mesh or working too closely at shallow angles to the glue joint area during pressure washing can also cause the mesh to fail. When working with actual pressures of 2,000 psi or higher with a standard 30 degree fan nozzle, about one foot of distance between the washer and the screen is the limit.
Effective cleaning during reclamation requires a combination of chemical and mechanical effort. Higher pressure almost always means lower chemical usage and faster processing times. In the short term, it also means a more expensive pressure washer with shorter load/cycle times. Simply put, if you reclaim more than 25 screens per day, you must have an industrial pressure washer. Non-industrial pressure washers have fewer gallons per minute of water flow at a lower total pressure, meaning that they must run longer and at higher pressure settings to do the same amount of cleaning. Screen shops that have non-industrial pressure washers generally use more degradents, emulsion remover and haze removers; have longer process times and typically cut corners to offset these issues, which leads to screen and emulsion contamination issues and a very short pump life. A typical hardware store variety pressure washer advertising 1,000 psi puts out approximately 650-750 psi at the nozzle due to frictional losses (about the same range as the average car wash). This pressure is only attainable with the pump’s unloader valve knob tightened to maximum restriction/pressure, which causes overheating and high current draw. This constant overheating causes drops in pressure and shortens pump life. These typical cheap units also flow about 1.0–1.5 gpm of water at low pressure settings (250–300 psi) and about .8–1.0 gpm at highest pressure setting. Applying less water to carry away chemicals and debris at maximum pressure settings means longer process times and shorter pump life, or shorter process times and stronger, more expensive chemistry. See the connection? Typical industrial pumps deliver flow rates and pressures in these ranges:
Small: 1,000–1,500 psi at 2.2–2.0 gpm
(good for about 30–50 screens a day maximum)Medium: 1,500–2,000 psi at 2.0–1.9 gpm (good for about 50–100 screens a day maximum)Large: 2,000–3,000 psi at 2.0 gpm or better (good for an almost unlimited number of screens per day).
The pressure ranges and flow rates listed are generalized but accurate enough. You cannot have too much water flow rate for the best advertized working pressure. Most industrial pump dealers will list the “peak” pressure as well as the best working pressure. The numbers above reflect maximum gpm flow rate at the best working pressure.
Doing it Right for Your BusinessThis article presents a basic overview of how to formulate the choices for screen reclamation chemical usage. Too often, chemicals are improperly blamed for efficiency reductions in reclamation. Changes in operator technique (dwell or working time for screen chemicals like haze and emulsion remover), accessory operations (pumps and nozzles, brushes, dip tanks) or printing inks and print parameters cause variations and difficulties in reclaiming.
Up to this point, this article has been an overview of how to test and characterize the chemicals we use for screen reclaiming and press cleaning in order to make informed choices. This last part is not an ROI (Return on Investment) calculation. It is a checklist to make sure you do not forget important details in your ROI that can be used in almost any corner of the industry. Although not every parameter is correct for every shop, this checklist can be used to help ease your decision making processes.
An important aspect of cost calculation is capturing the hidden fees associated with wiping materials, containers, spraying equipment and evaporation. This is not a plug and play calculator, as it will require some footwork on your part. You have to keep track of the amount and type of screens coming through your screen department. At a minimum, you should track every three months before you can assume you have a grasp of your up-front and hidden costs. Once in place, costs can be modified as data can be collected by using simple logs.
Baseline components:Number of screens used per day (weight averaged)
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Reclamation chemicals make up the bulk volume of all chemicals ordered by screen plants, although they may not always make up the bulk of the chemical costs.
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1. Quarterly screen usage numbers (to account for seasonal variations)
2. Size of screens (if more than one is used, always use the larger dimension unless it is more than 33 percent. In that case, average the size.
Chemical stages:On press wash-up /color change: Customized for the type of print. Different types of print work may require more or less screen bottom wiping, and different levels of cleaning or different chemistry is due to ink systems. When different ink systems require different solvents, there will be more than one calculation. On-press operations/Print types
Line work4CP and half-tone4CP and half-tone Specialty graphic printingSpecialty garment embellishmentClean up for storage (library)Pre-reclaim soak (degradent)Palette cleaning chemical
Ink degradent stageBase chemical costGlovesBrushes/scrubbing padsSprayer bottles/headsRecirculation unit disposal fee:(Solvent disposal)Recirculation unit disposal fee:(Bags, pads or spun filters)Wiping clothsInk scraping squeegees
Emulsion removal stageBase chemical costGlovesBrushes/scrubbing padsSprayer bottles/headsDip-tank chemical disposal feeDip tank sludge removal (labor)Rinse water usgaePressure washer usage (labor time)Rinse water usagePressure washer usage Pressure washer interval (labor time)
De-hazing stageBase chemical costGlovesBrushes/scrubbing padsRinse water usage
Pressure washer interval (labor time)
Degreasing stageBase chemical costGlovesBrushes/scrubbing padsRinse water usagePressure washer interval (labor
Notes:With a solvent-based ink, on-press
screen wipe-up typically requires three standard lint-free wiping cloths (split) per square foot of the screen image area.
UV and plastisol ink, on-press wipe-up typically requires two standard lint free wiping cloths (split) per square foot of the screen image area.
Typical usage of latex disposable gloves is three pairs per frame from on-press wipe-up, to finish the reclaim cycle.
Usage of nitrile gloves in reclaim reduces this to one pair of latex (on-press) and two pairs of nitrile gloves per day for a 40–50 SPD cycle. For higher screen cycle numbers (100 SPD and 150 SPD), multiply the original number by a factor of two and three respectively.
The use of butyl gloves in reclaim typically reduces the replacement of gloves to one pair per month based on 40–50 SPD, one pair every two weeks at 100 SPD and one pair every week at 150-plus SPD.
**Pressure washer amor t i zat ion /replacement charge**Sink back light bulb replacement*Drain clean-out fee*Safety glasses*Respirator filters(**) These items are usually an annual cost item for most shops. The better the quality of items, the less frequent their replacement interval. The higher cost of quality pressure washing equipment is always offset by savings in labor time.(*) These are quarterly cost items in many shops and should be tracked and divided into quarterly screen fees.
From this list, you can see that the costs that are not usually added into your screen expenses are charged to your print customers. Even without using the calculator you can begin to feel the losses. Typically, proper tracking and costing of chemicals, prior to making changes in chemistry selection, add an average of 30–50 cents to each screen cost (textile/
garment), 50 cents to $1.50 per mid-sized graphic screen and $1 to $2.50 per large format graphic screen in consumable items alone. This is significant even in a textile shop with 23”x 31” screens that produces an average 50 screens per day. For example, 50 SPD multiplied by 260 average print days per year equals 13,000 screens x .30 cents of uncaptured consumables. This comes to $3,900. An upgrade of chemistry or accessory equipment can be paid for with those savings, and this equipment can typically garner a labor-savings of 25–30 percent. For more information about how to track the items on this list, contact the technical department at SGIA. Once you have a better idea of where you can improve your chemistry, contact the chemical professionals at your local dealer for options.
Ray Greenwood is SGIA’s Technical Services Associate. He is responsible for helping SGIA member companies in all types of imaging-related technical inquiries. Greenwood, who helps the SGIA Digital Lab and SGIA conduct workshops and research projects, has spent the past 20 years of his printing career working with semi-conductors and circuits, as well as textiles and large-format graphics on a variety of substrates.
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LF_SGIA.indd 1 3/19/09 9:16:38 AM
Too often, chemicals are improperly blamed for efficiency reductions in reclamation.
