K Mean Black

• Name: Printing Technology
• Branch: Printing Technology Diploma 6th Sem
• Published: May 25, 2025

Flexography Defects Part - 1

Unit – 4

Flexography Printing Defects

 

1. Bleeding – smudging:

The terms bleeding or smudging are used in situations when colored 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).

Causes	Remedies
The relative humidity is too high. Condensation of water into the solvent-based ink.	Use fresh ink. Adjust the solvent mixture. Increase the performance of the dryer and check the water content of the solvent.
Too much retarder has been used.	Replace the ink with fresh ink. Use a faster solvent for the purposes of reduction (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. Increase the drying speed of the ink.
Unsuitable colorants have been used in the printing ink.	Create a new recipe to replace the undesirable colorants.
There are too many ink layers on top of one another.	Reduce the layers. Design a new printed motif.

 

 

 

2. Blocking:

The ink adheres to the reverse side of the film and causes damage when the substrate is unrolled.

Causes	Remedies
There is too much retarder in the ink.	Replace the ink.
The film temperature at the winder is too high.	Reduce the temperature of the tunnel dryer and check whether the cooling drum is working.
The pretreatment level of the film is too low.	Check the pretreatment and the age of the film. Use the inline corona treatment.
Ink drying is too slow.	Increase the performance of the dryer. Use a faster drying solvent. Reduce the printing speed.
The ink volume transferred is too high.	Select anilox rollers with a lower transferred volume.
The ink viscosity is too high.	Reduce the ink viscosity by adding solvents.
The cooling is not working.	Please contact the service department.
Excessive winding pressure at the winder	Reduce the winding pressure.
The moisture of the wound web is too high.	Increase the performance of the dryer between the printing mechanisms and reduce the cooling.
Coating or pretreatment on both sides of the film.	Check whether the correct ink system is being used.

 

3. Bridging:

Ink connections between individual screen dots of the printing plate are produced. The intermediate depressions are filled with ink

Causes	Remedies
The relative humidity is too high. Water is condensing into the solventbased	Replace with fresh ink. Adjust the solvent mixture. Increase the performance of the dryer between the printing units.
inks.
The ink recipe is not suitable for the printed 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 rollers with a lower transferred volume.
The anilox roller and width of the printing plate raster do not match.	Use a finer anilox roller.

 

 

4. Color strength too high:

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

 

Causes	Remedies
The transferred volume of the anilox roller is too high.	Use an anilox roller with a smaller transferred volume.
The ink viscosity is too high.	Add solvent and/or blended inks in order to adjust the ink viscosity.
The ink recipe for the color matching is too strong.	Add a blend of inks. Optimize the ink recipe.
The settings of the doctor blade are incorrect.	Adjust the pressure of the doctor blade.

 

 

5. Color strength too low:

The color strength is weaker in comparison to previous prints or samples.

Causes	Remedies
The ink dries on the anilox rollers.	Clean the anilox roller. The printing pressure is too high or too low between the plate cylinder and the substrate or between the anilox roller and printing plate.
The color of the printing ink being used his too weak.	Contact your ink supplier or, if possible, 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 or too low between the  plate cylinder and the substrate or between the anilox roller and the plate cylinder.	Adjust the printing pressure.
The ink has dried because a machine has been at a standstill for too long.	Clean the printing plate and the anilox roller.
An anilox roller has been used whose transferred volume was too small.	Select an anilox roller with a higher transferred volume.

 

6. Deformed screen dot:

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

Causes	Remedies
The pressure setting between the plate cylinder and the substrate is too high.	Reduce the pressure setting.
The web tension is too low.	Regulate the web tension.
Excessive thickness fluctuations of the printing plate or the double-sided adhesive tape.	Change the printing plate or use a different adhesive tape.
The relief depth of the printing plate is too high.	Use a printing plate with a smaller relief depth.
There is a speed difference between the plate and impression cylinder.	Check the thickness of the doublesided adhesive tape and the printing plate.

 

 

7. Dot gain too high:

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

Causes	Remedies
The thickness tolerance of the printing plate or the double-sided adhesive tape is too large.	Change the printing plate or the double-sided adhesive tape.
The printing plate is too soft or the double-sided adhesive tape too hard.	Replace the printing plate or the adhesive tape.
The pressure setting between the plate cylinder and substrate is too high.	Reduce the pressure setting.
The thickness tolerance of the film is too high.	Reduce the pressure of the plate cylinder or replace the roller of substrate.
The dot gain has been incorrectly calculated.	Adapt the curve of the dot gain accordingly.
The temperature of the central cylinder is too high or too low.	Please contact the maintenance service department.