Heidelberg Coating

7/31/2019 Heidelberg Coating

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Foreword

dear reader,

This issue o Prof Tip is all about coating, drying and powdering.

Youll learn about the advantages and disadvantages o oil-based

varnishes and dispersion coatings as well as best-suited applications

or two-roller systems and chamber doctor blade systems. Well ex-

plain what kinds o deects can come up with dispersion coatings and

how you can correct these. Further topics include inrared dryers

and coating dryers, gloss measurement and the measurement o pile

temperature. In addition, we will introduce you to the various spray

powders and give you tips on how to choose the right type o powder

and reduce the amount used. Thank you or your interest!

Sincerely yours,

the Team o the Print Media Academy


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4 Oil-based Varnish

5 Dispersion Coating

7 Spot Coatings and Text

8 Determination o Viscosity in Dispersion Coatings

9 Tips on Storing and Processing Dispersion Coatings

10 Coating Units12 Problems with Dispersion Coating

22 Drying Systems

24 Measurement o the Pile Temperature with a Hygrometer Probe

25 Gloss Measurement

26 Spray Powder

Contents

3


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The composition o oil-based varnishes is essentially the same as thato oset inks ( % solid substance content as well as drying through

penetration and oxidation). Since these varnishes are intended to create

a highly transparent flm with little coloring, all materials used have to

be o premium quality. The varnishes can be processed ull-surace with-

out dampening (place a ormat sheet under the blanket) in the case o

spot coating, on the other hand, a conventional oset printing plate with

dampening is needed.

advantages

Simpleprocessingaswithoffsetinks

Goodabsorptionofvarnish

Openareaseasytoachievewithoffsetplates

Goodmoistureprotection

Nosolventemissions

Flexiblevarnishlmlayer(noproblemwithcreasesandfolds)

disadvantages

Lowlayerthickness

Dangerofyellowing

Slowdrying

HighamountsofspraypowderneededLowpileheight

Possibleinuenceonsmellandtastewithfoodpackages

Oil-based Varnish


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There are dispersion coatings without pigments (matt, fnishing varnishes,gloss or high gloss coatings) and with pigments (silver and gold coating or

Iriodin). Various polymer dispersions, or so-called modifed acrylates, make

upthebase.Furthercomponentsarewater-solublerosins,waterasasolvent

anddiverseadditiveswhichsignicantlyinuencevariouscharacteristics

like surace tension, wettability and abrasion resistance. Unlike oil-based

varnish which dries via oxidation, in the case o dispersion coating, the

drying process takes place completely physically: Through penetration andthe evaporation water content, the polymer particles move closer together.

The emulsion/polymer particles melt together and build a flm.

Dispersion Coating

Additive %

Solid components,Rosin and polymer particles 3 %

Water %

Suractant 3 %


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dispersion coatingadvantages

Veryfastlmformation

Utilizationoffullpileheight

Reducedspraypowdering

Goodabrasionresistance

Drycoatinglmodor-free

FastprocessingwithcorrespondingmachinecongurationNoeffectonsmellortasteoffood

Noyellowing

Gooddurabilitywhendeep-frozeni.e.forfrozenpackaging

disadvantages

Drycoatingisdifculttoremove

Withprintingstockunder90gsm,problemswithdimensionalstability

can occur

Forspotcoatings,eitherexpensivecoatingplatesareused,orblankets

have to be cut out manually

Thenecessaryamountofcoatingishardtocontrol


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Spot Coatings and Text

blanketsBlanketsareusedforfull-surfacecoatingandcoatingwithsimpleopen

areas (manually cut).

Theblanketusedshouldbecompressiblebutnottoosoft.

Underlayshavetobematchedtotheprintingstock.Whilesmoothprinting

stock can be processed with harder underlays, rough printing stock needs

soter underlays.

Inordertocreatecoating-freeareas(adhesivestraps),blanketscanbemanually cut and stripped. There are also special coating blankets where

the upper layer is easy to pull o.

coating plates

Dependingonstandardsforquality,coatingplatesareusedeitheras

exibleprintingplatesormetalplates.

Thechoiceofunderlaysforthecoatingplate(hard/soft)isdecisive

or the print quality.

Let: ull-suracecoating

Right: manu-ally cut blanketor simple openareas

Coating plates areused or intensivespot coatingsand text


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Themeasurementofowtimewithaowcupisconsideredtobethestandard test method to determine the viscosity o dispersion coatings

because o its simple execution. The coating should always be mixed well

beore measurement.

UsuallytheDINcupDIN53211-4(3.4ounceswitha0.16inchopening

[100mlwitha4mmopening])isusedformeasurement.Recently,this

standardwasreplacedwiththeinternationalnormDINENISO2431.

Manuacturer inormation on the viscosity o the coating is usually based

onatemperatureof68F(20C).Themeasurementiscompletedwhen

the thread o liquid separates. As a general rule, the higher the viscosity,

the thicker the coating!

make sure to follow the data sheet when testing!

During measurement with the fowcup, makesure to pay attention to the temperature!

Comparison o Viscosities(Flow time in seconds)Water-based coating approx. 35 sec.Metallic coating approx. 4550 sec.UV coating approx. 4555 sec.

Determination o Viscosityin Dispersion Coatings

Temperature (C)

Flowtimeinseconds


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Water-basedcoatingshouldbestoredatroomtemperature.Avoidstoragetemperaturesofmorethan104F(40C)orlessthan59F

(15C),inordertopreventchangesinviscosity.

Alwaysmixthecoatingwellandadjustthetemperatureifnecessaryso

that it reaches its initial viscosity again.

Dispersioncoatingsmayonlybestoredforalimitedamountoftime

approx.6months.Effectandblistercoatingsmayonlybestoredfor

3 months.Inthecaseoffull-surfacecoatingwithablanket,thecoatingapplication

should by no means extend beyond the edges o the printing stock.

Forthisreason,aformatsheetattheedgesatleast0.078inches(2mm)

smaller than the printing stock should be placed under the blanket.

Setcoatingapplicationtominimalcompression.

Themajorityofwater-basedcoatingsarealkalescent.Theprintinginks

to be coated thereore need to be insensitive to alkaline materials.

Tips on Storing and ProcessingDispersion Coatings


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two-roller systemIn the two-roller system (see illustration below), a ountain roller scoops

the coating out o an open coating pan and passes this on to the metering

roller. The amount o coating supply is dependent on the preset revolution

speed o the ountain roller. The level o coating in the open coating pan is

monitored by an ultrasonic sensor. An electromechanical diaphragm pump

ensuresacontinuousowofcoating.Theamountappliedisaround3to

gsm wet. The exact amount applied can only be determined by weighing(scale). The two-roller system is suitable or surace and spot coatings.

Compared to the chamber doctor blade system, the application o coating

is more uneven. The application o coating is dependent on speed and is

controlled by a coating characteristics curve.

make sure to adjust the characteristics curve to the

coating used!

1 | Coating cylinder

2 | Coating plate

3 | Metering roller

4 | Fountain roller

5 | Coating

Coating Units

3


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chamberdoctor blade systemThe chamber doctor blade consists o two doctor blades, which, together

with the rame, build a closed chamber in which the coating is in constant

circulation. A laser-engraved, ceramic-coated screen roller is responsible or

metering. The amount o coating can be altered with exchangeable screen

rollers with diering scoop volumes. The screen rollers ensure a defned and

constant applied quantity as well as an even, smooth-coating application.

The chamber doctor blade system is suitable or matt, gloss, blister, UV,

gold and silver coatings and other eect coatings such as pearly luster

coating (Iriodin) as well as or text and intricate designs.

Forconsistentresultswithadenedamountofcoating,thescreenroller

needs to be cleaned thoroughly with water. In addition, a deep cleaning as

well as an ultrasonic bath should also be carried out regularly.

1 | Coating plate

2 | Screen roller

3 | Chamber doctor blade

4 | Coating supply

3


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problem with wettabilityIn the case o a problem with wettability, the coating rolls o the surace

instead o orming a complete flm. This happens when the surace tension

o the coating is higher than that o the ink. A higher surace tension

causes the coating to contract and orms drops or mounds.

remedy

Addsurfactant(followdosageexactly)Useothercoating

Askcoatingmanufacturer

foaming

Strong pumping along with the air intake produces a oam which can cause

uneven and teardrop-ormed deects in the coating application.

remedy

Setcoatingpumpsothatnoairgetssuckedinandmixedin.Positionthe

coatingsuctiondeepunderthefoam.Setthereturnowequallydeep

so that little or no oam is produced.

Reducerotationspeed

Adddefoamer(followdoseexactly)

Problems with Dispersion Coating


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register problem with spot coatingAregisterproblemoccurswhenthecoatingformcannotbeadjusted

totheprintortheregisteructuates.

remedy

Setmountingheightandpro-

cessing or the right printing

length.Incoatingplatemanufacture,

mount guiding ridges with

overlapping breaks. The bars

should be secured in such a

way that the air between the

printing sheet and coating

plate can escape to the sides

at the gaps (see illustration).

Guidingridgesstartatthe

beginning o the plate as a

support or the coating appli-

cation rollers and end ater

the print.

The air between the bars should be able to escape to theback. The diagonal is thereore essential.

Coating plate edge


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Presetforkissprinttoavoidunnecessarydeformationo printing stock.

Settensioningrailstocorrectbasicsetting.

Checkdryersettings(temperature,airsettings)

Adjustcoatingamount

Coating plates are thicker than normal oset plates. This is why they also

have to be exposed in a special drum-type imagesetter. I theres nodrum-type imagesetter available, the master copy should be optically

altered accordingly.

smaller corrections

Smaller corrections can be made by changing the underlays under the

coating plate: I you decrease the strength o the underlays, the coating

orms printed impression becomes longer. I you increase the strength o

the underlays on the other hand, the coating orms printed impression

is shortened.


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crackingCracking reers to the ormation o cracks in the coating flm. These occur

whenthecoatingdriesfasterthantheink(airshock).Theappearance

is then comparable to an old oil painting. The cracks frst originate in areas

with very high ink concentration. Cracking oten only arises during sheet

removal and isnt visible in the pile.

Forinspection,takevefreshlyprintedsheets,allowtoliefor1to2minutesand then assess.

remedy

Checkviscosityofcoating

Reducedryingtemperature

Increaseprintingspeed

Addretardertothecoating

Useanothercoating


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orange peel effectInthecaseofaninhomogeneouscoatingsurface,coatingawsresembling

the surace o an orange peel can occur.

remedy

Reducespeed

Reduceamountofcoating

AdjustviscositycorrectlyChooseanotherprintingstock

not enough gloss

Using gloss coating in fnishing produces a much more noticeable gloss eect.

remedy

Chooseaprintingstockwithaclosed,smoothsurface(glosscoated)

Userightglosscoatingwithcorrectamountofcoating.

Coatwetondry.Waitatleast48hoursbeforestartingthesecondpass.

Incaseoflossofglossafterdrying,usefast,quicklyabsorbedandmore

intense inks.


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poor dryingCoatingshouldbedrytothetouchafter10to15seconds.

remedy

Improveremovalofprocessair,avoidwashhouseeffect

Stircoatingandtestitsviscosity


Checktemperatureatinfrareddryerandincreaseifnecessary. Observe preheating o dryer

Reducemachinespeed

ink buildup on the coating form

The ink penetrates through the coating onto the coating orm, builds

upandleadstoawedcoatingapplication.

remedy

Reducespeed

Increasecoatingamount

Usesuitablecoatingplateunderlays

Optimizepositioningofcoatingrollerstocoatingform

ReduceprintsupplyUsealternativecoating


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ink buildup on coating and fountain rollersCaution: Screen rollers are unusable ater ink application (deep cleaning

necessary)

remedy

Useappropriatescreenroller(payattentiontointerplayofcoatingquantity,

screen rollers and coating)

Checkcoatingpump,cleanorpossiblyexchangediaphragmCleancoatingroller,fountainrollerandcoatingblanketbeforenewstart

crushed edges

Occurs rom coating or ink accumulation on the borders o the print image.

remedy

Monitorandreduce,ifnecessary,mountingheightbetweenmeteringroller

and coating plate as well as between coating plate and printing stock

Usesoftunderlaysunderthecoatingplate(blanketorcutcoatingunder-

lay blanket)

Checkviscosity



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smearing due to contact

I sheet guidance is lacking, the sheet may come into contact with the

deeper lying suraces o the coating plate and transer ink. The built up

ink then transers itsel uncontrolled onto the ollowing sheets.

remedy

Placeguidingridgesonthecoatingplateinthebleed

Ifpossible,stickassistingridgesonthecoatingplate(payattentionto

suitable material and strength)

Guiding ridges on the coating plate support the coating application rollers and prevent contact betweenthe printing sheet and the coating plate.


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squirting

Drops o coating on the printing sheet can cause them to stick together.

remedy

Checksettingsoncoatingunitandcorrectifnecessary

Alignmeteringrollerandfountainrollercentrallytooneanother

Formatsheethastobesmallerthantheusedprintingstock

ReducespeedCleandirtycoatingunitthoroughly

blockingBlockingiswhenthecoatedsheetsinthepilesticktogether.

remedy


Usesuitablepowderincorrectdosage

Optimizepiletemperatureaccordingtomaterialandspeed

AirpileafterprintingUsefastdryingcoatingnotinclinedtoblockingwhenwet

Usefastpenetrating,intenseprintinginks

Donotplaceprintedpilenearheatingunits

Airprintedpile


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streaks in matte coatingStreaks oten develop early on at the contact point between ountain roller

and metering roller and are transerred onto the print.

remedy

Mixmattecoatingwithsilk-mattecoating

Stircoatingwell

DonotdipsuctiontubetoodeepinthecoatingtankPlacereverseowdeepdowninordertokeepthecoatingonthebottom

in motion

Useananiloxrollerwithachamberdoctorbladesystem

Reduceamountofcoatingappliedifnecessary

Inthecaseoftwo-rollersystems,reduceviscosity

paper distortion

Becauseofthehighpercentageofwaterinthecoating,paperdistortioncan

occur, particularly in printing stock with low grammages and especially during

perfecting.

remedy

ReduceamountofcoatingUsesuitablecoating(B+Wcoating)

Chooseappropriateprintingstockthickness


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infrared dryerThis drying system heats the applied printing ink and printing stock with

the energy rom inrared radiation. The thermal eect accelerates the physical

and chemical processes in drying the ink. The lower viscosity o the printing

ink oils leads to a aster penetration. In addition, the warm pile o paper

promotesoxidation.Lowpercentagesofdampeningsolutionintheapplied

ink layer urther accelerates oxidation. The short-wave radiation o the

inrared dryer penetrates predominantly into the paper, while the mid-waveradiation warms the air above the ink layer.

Properly chosen inrared heaters (original Heidelberg service parts) target the

printing ink with heat and simultaneously protect paper and machine. Wave

length, power and gold coating are optimally coordinated. The minimum lie-

time o the heater is , hours.

When dealing with IR heaters, it is advisable to always wear clean gloves,becausehandoilsandsweatburnintothequartztubesandshortentheir

lifespan.Regularlycleanheatersandreectorscarefullywithavacuum

cleaner. Only the ront side o the heater may be cleaned with a sot, lint-ree

cloth soaked in alcohol. The back o the heater, on the other hand, is metal-

izedwithgoldandmayundernocircumstancesbecleanedwithalcohol!

Drying Systems

Inrared heatermetalized with gold


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3

coating dryerInadditiontotheinfraredheaters,hotairjetsareintegratedintothecoating

dryers. Hot, dry air is supplied and the processed air saturated with water is

carried away. In order to achieve a secure removal o the water vapor, more

air is always extracted than supplied by the dryer.

The polymer particles distributed fnely in the solvent move continuously

closer together because o water removal during drying. They are depositedon top o one another and build a hard polymer flm when thoroughly dried.

Thisistermedcoating.

Schematic Illustration1: Hot air system; 2: Inrared heater; 3: Printing sheet;

4: Air jets or sheet guide without contact; 5: Sheet guide plate

3


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At ideal climate conditions in the pressroom,the ground rule is: In the case o paper, the

temperature o the pile at delivery should

beabout14to18F(8to10C)overthe

temperature o the eeder pile. In the case

ofcardboard,itshouldbeabout18to27F

(10to15C)overit.

I the correct pile temperature is exceeded,

the emitted heat in the pile makes the inks

sot again. When this occurs, there is a

danger o set-o!

In the case o double-sided coating, reduce

the temperature in both passes in order to

prevent paper distortion and the coating layer

on the back rom becoming sot.

The ideal pile temperature can be most easily

determined by tests. The test should be car-

ried out together with an application engineer.The right pile temperature is dependent on

many actors: coating characteristics, printing

ink, absorbency o the printing stock, machine

speed, drying path and delivery type, and

control o discharged air.

Measurement o the PileTemperature with a Hygrometer Probe

The temperature read rom thehygrometer probe can deviate up to50 F (10 C) downward o the pilessurace temperature (IR deliverysensor).


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Theglossisalwaysdependentontheprintingstockandcoating.Ifmeasurementsarecompared,itisnecessarytopayattentiontothe

measurement angle.

Aglossmeasurementwithameasurementangleof60isgenerally

customary.

Valuesrangefrom0to100glosspoints

Ifglossmeasurementdoesntalwaysoccuratthesametimeafterprinting,

later measurements experience gloss point loss.70glosspointsisagoodresultforahigh-glosscoatingwet-on-wet

Underidealconditions,80glosspointscanalsobeachievedwiththeappro-

priatecoating.(WhenusingUVcoatingitiseasytoachieve95glosspoints)

Gloss Measurement

A gloss measurement device enables an objective assessment o the gloss eect possible.


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Thejobofspraypowderistocreateaseparationdistancebetweenthereshly printed sheets. This separation eect prevents set-o in the pile and

improves the drying process with oxygen supply.

Afundamentalsignofqualityinspraypowdersistheirparticlesize.Inorder

to achieve an even spacing with small amounts o powder, primarily identical

particlesizesarenecessary.Whentheparticlesizeinthepowderiseven,

each individual powder particle gets used and unnecessary dust ormationin the delivery is reduced. Due to the eects o drying and condensation,

the powder can collect in various spots o the delivery. This can cause

clumps o powder (agglomerates) which lead to visible spots on the printed

sheet when they all down.

It is thereore advisable to only use powders classifed by the Institution

or Statutory Accident Insurance and Prevention (http://www.bgdp.de/

DownloadLeaetPowder).

Only the use o well-sorted powder provides an even separation between

the printed sheet, minimal powder consumption and low dust ormation.

Spray Powder

Well-sorted powder (ideal case)


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tips for choosing the right powder

Uncoatedpapersaremoreabsorbentthancoated.Thismeansthey

also need less powder. Make sure to use a printing ink suitable to the

printing stock.

Thecoarsertheprintingstockis,thelargerthesizeofthepowder

particles should be.

Themoreinkprintedontopofoneanother,themorepowderisneeded.

Inthecaseofprintingstockswithdifferentsurfacenishes(frontand

backside),theroughsideisdecisive.Thesizeofpowderparticles

should be chosen according to this.

Powdertypeandparticlesmustbechosenaccordingtotheprinted

materials later application (ood packaging, perume packaging, etc.) as

well as the ollowing work steps (coating, laminating, hot oil embossing).Heavypowdertypes(calciumcarbonate)canbeappliedtothesheets

more easily and more targeted than lighter ones (starch).

Poorly sorted powders


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spray powder from natural starches

These powders are made rom potato, corn or rice starch, among others.

They are available in hydrophilic or hydrophobic versions.

advantages

Plant-basedpowderissphericalandsoftinstructure.Becauseofits

advantageousowbehavior,itisverygoodtoworkwith.

Starchpowderscanbeuniversallyused

disadvantages

Electrostaticchargepossible

Source: ksl-staubtechnik


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spray powder from calcium carbonate

This is an inorganic mineral product as present in nature.

advantages

Thehighspecicweightisparticularlylow-dustformingandtherefore

easy and economical to use.

Calciumcarbonateiswater-insolubleandnotsensitivetomoistureor

electrostatic charge.

disadvantages

Calciumcarbonatescrystallinestructurecanleadtoscouringeffects

on the printing sheet.

Calciumcarbonatecanreducetheprintingplateslifetime(withmany

machine passes).



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3

spray powder with sugar base

These kinds o powders are special among spray powders. It is a dry,

water-soluble spray agent with crystalline structure and sot particles.

advantages

Usuallypowdersfromsugarareusedinsuccessiveprintprocesses.

The powder only leaves a very small amount o build-up on the blanket,

issolubilizedandlandsinthedampeningsolutioncirculation.

disadvantages

Becauseofitssensitivitytowater,itcannotbeusedwithanIRdryer.

Highmaintenanceofpowderdevicebecauseofdepositsandclogging

in the device.



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spray powders for printing with dispersion coatingsThe spray powder used or printing with dispersion coatings is surace-

treated (coated) and is thus water-repellant (hydrophobic). Water-repellant

powders are particularly advantageous or inline coating. This powder is

also especially well-suited or sensitive materials, since it has a very low

scouring tendency.

Let: Hydrophilic(not suitable or inlinecoating)

Right: Hydrophobic

(suitable or inlinecoating)

A simple test with powder in a water glass shows its

suitability or printing with dispersion coatings.


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3

disadvantages

Becauseofsurface-treatment,thispowdertendstoproducemoredust

in the delivery area.

Inthecaseoflaternishing(coating,laminating),higherdosagescan

cause repellant reactions and wettability problems.

Highermaintenanceofpowderdevicebecauseofdepositsandclogging

inspraynozzlesTendencytowardselectrostaticcharge


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33

Thistableisarecommendationforchoosingtherightparticlesize.

Legalclaimsmaynotbemadefromit.

Printing Stock 15 m 20 m 3 m 45 m

Calendered, machine coated, speciallycoated and one-sided coated papers andpaperboards (chrome papers)

to120g/m

120to170g/m

170to g/m

Original art print and cast-coated papersand paperboards

to150g/m

150to g/m

to g/m

over g/m

Smooth paperboards, or ex. ivory boardandimitationBristol

150to g/m

to3 g/m

3 to g/m

Rough or embossed paperboards 150to g/m

to g/m

Powder typeMultipleruns

Singlerun

Subse-quent jobssuch ascoating orlaminating

Inlineprocess-ing (UVcoating)

Inlineprocessing(Water-basedcoating)

IR DryerUsage

Calciumcarbonate

x x x x x

Calcium carbonate

treatedx x x x

Starch powder x x x x x

Starch powderwater-repellant

x x x x

Fromsugar x

Recommendations or Use o Right Power Types

Help or Choosing Particle Sizes


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3

tips for reducing powder amounts

Usehigh-qualitypowder(minimalpercentageofparticulatematter,

denedparticlesize)

UsesuitableparticlesizeChooselargestpossibleparticlesizeofpowder

Chooseheaviesttypeofpowderpossible(calciumcarbonate)

Regularmaintenanceandidealsettingofpowderdevice


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3

At www.print-media-academy.com, you can order all issues published up

until now or ree. Please tell us the issue you would like and your address,

and you will receive your personal copy promptly.

DampeningSolutions inOset Printing

Feuchtmittel imOffsetdruck

Rollers inInking andDampeningSystems

Walzen in Farb-und Feuchtwerk

Problem Casesin the Pressroom

Problemflleim Drucksaal

Coating, Dryingand Powdering

Lackieren,Trocknen undPudern

Previously published issues romthe Pro Tip series:

Profi Tip

Dampening Solutions in Offset Printing

Print Media Academy

Profi Tip

Rollers in Inking and Dampening Systems

Print Media Academy

Profi Tip

Problem Cases in the Pressroom

Print Media Academy

Profi Tip

Coating, Drying and Powdering

Print Media Academy


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208/01en

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