K Mean Black

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

Flexography Defects Part - 3

 

16. Minor printing defects:

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'.

 

Causes	Remedies
The feed is dirty.	Clean the feed.
The printing plate is dirty or the surroundings are too dusty.	Clean the printing plate.
There are foreign particles in the doctor blade chamber.	Clean the ink feed system.
The substrate is statically charged.	Use antistatic rollers if possible, or replace the reel of substrate.
The substrate is dirty.	Change the substrate.
The feed rollers are dirty.	Clean the feed rollers.

 

17. Moiré effect:

 

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.

Causes	Remedies
The screen angle on the printing plate is wrong.	Adjust the screen angle in the preliminary stage.
The ratio between the line number of the anilox roller and the screen frequency of the printing plate is too low	The ratio should be greater than 4; use at least a 200 anilox roller, for example, for a 48 plate raster.
The ink dries on the anilox roller.	Clean the anilox roller. Add retarder to the ink.
The anilox roller angle and the screen angle on the printing plates is incorrectly adjusted.	Change the anilox roller or revise the repro with more suitable screen angles.

 

18. Pinholes:

 

Small bright points in the solid print area.

Causes	Remedies
The surface of the film or printing plate is uneven.	Increase the pressure setting or replace the film or the printing plate.
The substrate is unevenly wetted.	Use more appropriate material to be printed on or increase the ink layer thickness through a higher viscosity or 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.
An inappropriate white ink has been selected.	Use an appropriate white ink.

 

19. Register:

In combined printing the individual colors are not congruent with one another.

 

Causes	Remedies
The printing plate has been incorrectly mounted.	Repeat the mounting procedure for the printing plate.
The dryer temperature is too high.	Reduce the temperature of the Intermediate ink dryer.
The tensile stress of the printing substrate web is incorrectly adjusted.	Check the web tension, as well as the feed and the winder.
The thickness fluctuations of the substrate are too high.	Replace the reel of substrate.

 

20. Repeat length:

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

Causes	Remedies
The web tension is too high or too low.	Adjust the web tension in accordance with the properties of the substrate.
The thickness deviation of the substrate is too large.	Change the substrate.
The temperature in the tunnel dryer is too high.	Reduce the temperature in the tunnel dryer.

 

21. Tape resistance:

The ink does not pass the adhesive tape test. There is insufficient adhesion of the ink to the substrate.

Causes	Remedies
An inappropriate ink formulation or incorrect ink system was used.	Please ensure that the correct ink system is used.
The corona pretreatment level of the film is too low.	Check the pretreatment and the age of the film.
The pH value of the water inks is much too low in the case of prolonged printing times.	Please use fresh ink. Ensure that the correct solvents are used.
The adhesion between colors is insufficient.	This can occur if two different ink systems are printed one over the other. Ensure that the ink build-up is appropriate.
The film surface is soiled.	Apply an appropriate primer before you begin printing or change to a more 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 first applied displays good initial adhesion and is not dissolved by the following ink.
The wrong side of the film has been printed.	Check the side of the film.