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FLEXOGRAPHIC

PRINTING GUIDE

Flexographic Printing Guidefor Flexible Packagings



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Siegwerk is one of the world's leading printing ink manufacturers

and stands for innovative strength, a practical approach and state-

of-the-art technologies. With great passion, the people at Siegwerk

develop individual printing ink solutions together with their custom-

ers. And what is more: they also advise them on the development

of new applications and technologies and provide them with rapid

and pragmatic help when they have problems.

For the employees at Siegwerk it is always the customers who are

the focus of attention. They are on hand when it is important to

avoid errors, optimize processes and support customers with all of

their knowledge for printing and packaging production.

Creating the perfect result together



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FLEXOGRAPHIC PRINTING GUIDE ∙ FLEXIBLE PACKAGINGS

In spite of the extensive improvements in flexographic printing tech-

nology, most printing shops do not make use of the full capabilities

offered by their machines.

Studies have shown that 70% of all errors are directly associated

with the processes. This guide is intended to help you to solve

problems with all aspects of printing:

Fault detection

In order to avoid misunderstandings and misinterpretations, you can

identify by means of the illustrated explanations which problems

you are facing in your printing shop.

Cause identification and remedies

The causes and adjustments for the most important corrections are

listed here in order to help you to identify your problem. For further

details, please contact your Siegwerk representative.

The flexographic printing guide published by Siegwerk offers youthe possibility of quickly identifying and correcting problems so that

you can increase your printing productivity.

Who needs a flexographic printing guide?



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Contents

Tape resistance 6

Bleeding – smudging 8

Blocking 10

Bridging 12Deformed screen dot 14

Dot gain too high 16

Inaccurate printing of the screen dots 18

Ink build-up on motif edges 20

Ghosting effect 22

Halo effect/squeezed edge on the screen dot 24

Minor printing defects 26

Large-area printing defects 28

Longitudinal stripes 30

Ink mottling 32

Mechanical damage of the printed image 34

Moiré effect 36

Pinholes 38

Color strength too low 40

Register 42

Repeat length 44

Color strength too high 46

Transverse stripes 48



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Without error



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The ink does not pass the adhesive tape test. There is insufficient

adhesion of the ink to the substrate.

Tape resistance

CAUSES

REMEDIES

An inappropriate ink formulation orincorrect ink system was used.

Please ensure that the correct inksystem is used.

The corona pretreatment level of thefilm is too low.

Check the pretreatment and the ageof the film.

The pH value of the water inks ismuch too low in the case of pro-longed printing times.

Please use fresh ink. Ensure that thecorrect solvents are used.

The adhesion between colors isinsufficient.

This can occur if two different inksystems are printed one over theother. Ensure that the ink build-up isappropriate.

The film surface is soiled. Apply an appropriate primer beforeyou begin printing or change to amore suitable film batch.

The ink viscosity is too low. Increase the viscosity with fresh ink.

Multiple color build-up Please ensure that the ink that is firstapplied displays good initial adhesionand is not dissolved by the followingink.

The wrong side of the film has beenprinted.

Check the side of the film.



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With error

Without error



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The terms bleeding or smudging are used in situations when col-

ored constituents of the printing ink become visible in parts of the

motif which have not been printed.

(The previous ink must be dry enough to be able to absorb the ink that is to

be applied subsequently).

Bleeding – smudging

CAUSES

REMEDIES

The relative humidity is too high.Condensation of water into thesolvent-based ink.

Use fresh ink. Adjust the solvent mix-ture. Increase the performance of thedryer and check the water content ofthe solvent.

Too much retarder has been used. Replace the ink with fresh ink. Usea faster solvent for the purposes ofreduction (accelerated drying).

The ink viscosity is too high. Add solvent to reduce the viscosity.

The transferred volume is too high. Replace the anilox roller.

The printing speed is too high. Reduce the printing speed. Increasethe drying speed of the ink.

Unsuitable colorants have been usedin the printing ink.

Create a new recipe to replace theundesirable colorants.

There are too many ink layers on topof one another.

Reduce the layers. Design a newprinted motif.



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With error

Without error



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The ink adheres to the reverse side of the film and causes damage

when the substrate is unrolled.

Blocking

CAUSES

REMEDIES

There is too much retarder in the ink. Replace the ink.

The film temperature at the winderis too high.

Reduce the temperature of thetunnel dryer and check whether thecooling drum is working.

The pretreatment level of the film istoo low.

Check the pretreatment and the ageof the film. Use the inline coronatreatment.

Ink drying is too slow. Increase the performance of thedryer. Use a faster drying solvent.Reduce the printing speed.

The ink volume transferred is too high. Select anilox rollers with a lowertransferred volume.

The ink viscosity is too high. Reduce the ink viscosity by addingsolvents.

The cooling is not working. Please contact the service depart-ment.

Excessive winding pressure at thewinder

Reduce the winding pressure.

The moisture of the wound web istoo high.

Increase the performance of the dryerbetween the printing mechanismsand reduce the cooling.

Coating or pretreatment on both

sides of the film.

Check whether the correct ink system

is being used.



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With error

Without error



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Ink connections between individual screen dots of the printing plate

are produced. The intermediate depressions are filled with ink.

Bridging

CAUSES

REMEDIES

The relative humidity is too high.Water is condensing into the solvent-based inks.

Replace with fresh ink. Adjust thesolvent mixture. Increase the per-formance of the dryer between theprinting units

The ink recipe is not suitable for theprinted motif.

Replace the ink.

Incorrect selection of the solvent. The

ink dries too quickly.

Empty the ink tank and adjust the

solvent mixture.

The ink viscosity is too high. Reduce the viscosity.

The transferred volume is too high. For the print job, select anilox rollerswith a lower transferred volume.

The anilox roller and width of theprinting plate raster do not match.

Use a finer anilox roller.



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With error

Without error



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The shape of the screen dot in the print deviates considerably from

the original shape.

Deformed screen dot

CAUSES

REMEDIES

The pressure setting between theplate cylinder and the substrate istoo high.

Reduce the pressure setting.

The web tension is too low. Regulate the web tension.

Excessive thickness fluctuations ofthe printing plate or the double-sidedadhesive tape.

Change the printing plate or use adifferent adhesive tape.

The relief depth of the printing plateis too high.

Use a printing plate with a smallerrelief depth.

There is a speed difference betweenthe plate and impression cylinder.

Check the thickness of the double-sided adhesive tape and the printingplate.



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With error

Without error



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Excessive dot gain on the substrate. This reduces the details and the

contrast.

Dot gain too high

CAUSES

REMEDIES

The thickness tolerance of theprinting plate or the double-sidedadhesive tape is too large.

Change the printing plate or thedouble-sided adhesive tape.

The printing plate is too soft or thedouble-sided adhesive tape too hard.

Replace the printing plate or theadhesive tape.

The pressure setting between theplate cylinder and substrate is too

high.


The thickness tolerance of the film istoo high.

Reduce the pressure of the platecylinder or replace the roller ofsubstrate.

The dot gain has been incorrectlycalculated.

Adapt the curve of the dot gainaccordingly.

The temperature of the central cylin-der is too high or too low.

Please contact the maintance servicedepartment.



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With error

Without error



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Uneven edges around the screen dot.

Inaccurate printing of the screen dots

CAUSES

REMEDIES

The ink dries on the printing plate. Clean the printing plate and adjustthe solvent mixture. Add the retarder.Make sure that the hot air fan is notblowing onto the printing plate.

The pressure setting between theanilox roller and the plate cylinder istoo high.


The ink viscosity is too high. Adapt the ink viscosity by adding

solvents.The lint particles from the cleaningcloth are on the printing plate.

Clean the printing plate. Use alint-free cleaning cloth or a cleaningbrush.

The ink recipe is not suitable for theprinted motif.

Replace the ink.

The pressure setting between theplate cylinder and the substrate is

too high.




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With error

Without error



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Ink build-up on the relief edge of the screen dot.

Ink build-up on motif edges

CAUSES

REMEDIES

The transferred volume of the aniloxroller is too high.

Use an anilox roller with a smallertransferred volume.

The printing speed is too low. Clean the printing plate and increasethe printing speed.

The ink viscosity is too high. Reduce the viscosity.

The wrong solvents were used. Replace the ink.

The pressure setting between the

plate cylinder and substrate is toohigh.


The ink recipe is unsuitable. Replace the ink.

The printing plate is worn, the reliefdepth is too small.

Replace the printing plate.

The relative humidity is too high. Thewater condenses into the solvent-based ink.

Adjust the solvent mixture – useretarder and anhydrous solvent.



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With error

Without error



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The ghosting effect is a weak printed image that is visible in one

part of the motif where it should not be. Usually this effect occurs

in the case of a solid print with negative fonts or with windows.

Ghosting effect

CAUSES

REMEDIES

The amount of ink available is toosmall as the transferred volume of theanilox roller is too low.

Use an anilox roller with a highertransferred volume.

The ink dries in the anilox roller cells Add retarder to the ink.

The anilox roller cells are inadequatelyfilled.

Increase the pressure in the chamberdoctor blade system.

The printing speed is too low. Increase the printing speed or theviscosity of the ink.



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With error

Without error



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The screen dot is surrounded by a line or a ring.

Halo effect/squeezed edge on the screendot

CAUSES

REMEDIES

There is a difference in the speedbetween the plate and impressioncylinder.

Check the thickness of the double-sided adhesive tape and the printingplate.


Select an anilox roller with a lowertransferred volume.

The pressure setting between theplate cylinder and substrate is toohigh.


The pressure of the chamber doctorblade system is too low.

Increase the pressure in the chamberdoctor blade system.

The pressure setting between theanilox roller and the plate cylinder istoo high.




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With error

Without error



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Dust particles on the substrate cause spots and defects. This is the

case with solid printing, where dark spots are surrounded by a

white 'halo'.

Minor printing defects

CAUSES

REMEDIES

The feed is dirty. Clean the feed.

The printing plate is dirty or the sur-roundings are too dusty.

Clean the printing plate.

There are foreign particles in the doc-tor blade chamber.

Clean the ink feed system.

The substrate is statically charged. Use antistatic rollers if possible, orreplace the reel of substrate.

The substrate is dirty. Change the substrate.

The feed rollers are dirty. Clean the feed rollers.



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With error

Without error



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Lack of contact between the substrate and the printing plate or

between the printing plate and anilox roller results in the poor

transfer of ink.

Large-area printing defects

CAUSES

REMEDIES

The thickness fluctuations in theprinting plate or double-sided adhe-sive tape are too large.

Change the printing plate or thedouble-sided adhesive tape.

The printing pressure is too low. Increase the pressure between theplate cylinder and anilox roller orbetween the plate cylinder and the

substrate.

The thickness of the substrate is outof tolerance.

Increase the delivery pressure of theplate cylinder or replace the reel ofsubstrate.

The plate cylinder or the anilox rollerare imbalanced.

Check the running of the printingplate cylinder (concentricity etc.).

The transferred volume of the aniloxroller is too low.

Increase the anilox roller volume.

The filling level of the chamber doc-tor blade is too low.

Increase the ink level in the chamberdoctor blade. Check whether the inkpump is working correctly.



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With error

Without error



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Printing error owing to parallel lines in the direction of printing.

Longitudinal stripes

CAUSES

REMEDIES

The doctor blade is worn. Replace the doctor blade.

There is dried ink on the doctorblade.

Clean the doctor blade.

The anilox roller is damaged. Replace the anilox roller.

The anilox roller is blocked or thedrive of the anilox roller is faulty.

Please contact the maintance servicedepartment.

The anilox roller is dirty or the ink on

the anilox roller has dried.

Clean the anilox roller.

There are particles in the ink. Clean the pump system, printingplates, doctor blade and anilox rollerafter you have filtered the particlesout of the ink.



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With error

Without error



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Dotted or marbling printed image of the solid printing area. Weak

ink strength, grainy large-format printing.

Ink mottling

CAUSES

REMEDIES

The surface of the printing plateis cloudy/uneven. Damage to thesurface of the printing plate can beseen.

Create a new printing plate.

The viscosity of the ink is too low. Add fresh ink and/or a blend of inksand ensure that the resulting viscosityis appropriate.

There are foreign bodies or impuritieson the plate cylinder or the aniloxroller.

Clean the plate cylinder carefully.

The surface of the substrate isuneven.

Use softer printing plates.

The film surface is soiled. Filter the ink or use fresh ink.

The ink viscosity is too high. Add solvent to the ink.

The doctor blade pressure is too highor too low.

Adapt to the doctor blade pressureaccordingly.



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With error

Without error



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Insufficient mechanical resistance of the print. Further information

can be found in our brochure 'Rapid tests and test methods for

production control in packaging printing'.

Mechanical damage of the printed image

CAUSES

REMEDIES

The ink recipe is not suitable or theink is damaged.

Empty the ink tank, clean the inkfeed system and replace the ink.

The transferred volume of the aniloxroller is too low.

Replace the anilox roller.

An unsuitable solvent has beenselected.

Use fresh ink with the appropriatesolvent mixture.

The corona pretreatment of the filmis insufficient.

Use inline corona pretreatment.

The abrasion resistance is poor. Add a wax additive to the ink.



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With error

Without error



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In the overprinting of the process colors (CYMK) the individual grid

structures can interact and create a pattern. The type of interaction

can create an undesirable interference pattern , the so-called moiré

effect.

Moiré effect

CAUSES

REMEDIES

The screen angle on the printingplate is wrong.

Adjust the screen angle in the pre-liminary stage.

The ratio between the line numberof the anilox roller and the screenfrequency of the printing plate istoo low.

The ratio should be greater than 4;use at least a 200 anilox roller, forexample, for a 48 plate raster.

The ink dries on the anilox roller. Clean the anilox roller. Add retarderto the ink.

The anilox roller angle and the screenangle on the printing plates is incor-rectly adjusted.

Change the anilox roller or revisethe repro with more suitable screenangles.



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With error

Without error



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Small bright points in the solid print area.

Pinholes

CAUSES

REMEDIES

The surface of the film or printingplate is uneven.

Increase the pressure setting orreplace the film or the printing plate.

The substrate is unevenly wetted. Use more appropriate material to beprinted on or increase the ink layerthickness through a higher viscosityor by exchanging the anilox roller.

The ink foams. Add defoaming agent.

The pH value of the water inks is

too low.

Carry out pH value correction.

The printing pressure is too low. Increase the printing pressure.

An inappropriate white ink has beenselected.

Use an appropriate white ink.



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With error

Without error



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The color strength is weaker in comparison to previous prints or

samples.

Color strength too low

CAUSES

REMEDIES

The ink dries on the anilox rollers. Clean the anilox roller. The printingpressure is too high or too lowbetween the plate cylinder and thesubstrate or between the anilox rollerand printing plate.

The color of the printing ink beingused his too weak.

Contact your ink supplier or, if pos-sible, add a concentrated ink.

The ink is too thin. Increase the viscosity with fresh ink.

The anilox roller is worn. Replace the anilox roller.

The ink is of incorrect quality. Replace this with fresh ink.

The printing pressure is too high ortoo low between the plate cylinderand the substrate or between theanilox roller and the plate cylinder.

Adjust the printing pressure.

The ink has dried because a machinehas been at a standstill for too long.

Clean the printing plate and theanilox roller.

An anilox roller has been used whosetransferred volume was too small.

Select an anilox roller with a highertransferred volume.



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With error

Without error



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In combined printing the individual colors are not congruent with

one another.

Register

CAUSES

REMEDIES

The printing plate has been incor-rectly mounted.

Repeat the mounting procedure forthe printing plate.

The dryer temperature is too high. Reduce the temperature of theIntermediate ink dryer.

The tensile stress of the printing sub-strate web is incorrectly adjusted.

Check the web tension, as well asthe feed and the winder.

The thickness fluctuations of thesubstrate are too high. Replace the reel of substrate.



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With error

Without error



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The printed motif in the direction of printing is too short or too

long.

Repeat length

CAUSES

REMEDIES

The web tension is too high or toolow.

Adjust the web tension in accordancewith the properties of the substrate.

The thickness deviation of the sub-strate is too large.

Change the substrate.

The temperature in the tunnel dryeris too high.

Reduce the temperature in the tunneldryer.



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With error

Without error



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The color strength is too high in comparison to previous prints or

samples.

Color strength too high

CAUSES

REMEDIES


Use an anilox roller with a smallertransferred volume.

The ink viscosity is too high. Add solvent and/or blended inks inorder to adjust the ink viscosity.

The ink recipe for the color matchingis too strong.

Add a blend of inks. Optimize theink recipe.

The settings of the doctor blade areincorrect. Adjust the pressure of the doctorblade.



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With error

Without error




Incorrect printing owing to lines that are perpendicular to the line

of printing.

Transverse stripes

CAUSES

REMEDIESThe diameters of the printing platecylinder and the gear used do notmatch.

Check the amount of unwoundmaterial.

The pressure setting between theplate cylinder and the substrate istoo high.


The printing speed is too high. Reduce the printing speed.

The printing pressure between theanilox roller and the printing plate isincorrect.

Adjust the printing pressure.

There is a mechanical fault. Check the mechanical parts of theprinting machine.



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Imprint

Printed in March 2013Photos: Siegwerk Druckfarben AG & Co. KGaA

Printing ink: Siegwerk Tempo EliteSiegwerk and the Siegwerk logo are registered trademarks of Siegwerk

Subject to technical and other changes

Siegwerk Druckfarben AG & Co. KGaAAlfred-Keller-Str. 55 · 53721 SiegburgGermany [email protected]

