Aqueous Coating Cracks

[aqazi81]

Hi All,
We are facing issue with coating cracks on heavier coverage areas. Low coverage areas have no issue or very little visible.
Please view the attached images of the issue.

 

[Cornishpastythighs]

Here's a couple of troubleshooting guides the answer may be in there somewhere

https://www.fujifilmusa.com/shared/bin/TroubleshootAC.pdf

https://www.fujifilmusa.com/shared/bin/AqueousCoatingGuide.pdf

https://printplanet.com/forum/press-technology/sheetfed-web-offset-discussion/9530-aqueous-coatings


The best answer seems to come right from this forum mud cracking", the coating is drying too fast on top of a heavy build.

Make sure the coating is at least 20 seconds (Zahn#3)
Turn the IR's down, along with the hot air knives
Speed up the press
Increase amount of coating (if you have an adjustible coating system)

Good luck

 

[aqazi81]

Thank you for your reply. We've already tried above mentioned things.

 

[Alois Senefelder]

Hello aqazi81


The problem you see is - Reticulation, trying to overprint Printing Ink with a Water based fluid is not a good idea.

Yes - I know Aqueous OP are widely used, Think- Surface Tension Problem


Regards, Alois

 

[Asures]

Mud Cracking.

The coating is drying faster than the ink underneath. As the coating is applied to the film of ink(s) underneath, it's crawling giving the 'Alligator Skin' look. Talk to your coating suppliers about a slightly slower drying coating.

 

[CKL]

Have you done a AQ coating weight test?
What BCM roller are you running?
Do all your different coating types have the same issue?

 

[Asures]

CKL - Good points. If he's running a roller coater, than BCM is irrelevant. He can certainly check his coating stripe and measure viscosity using a Zahn #3.

Aqazi - Is this happening with Gloss, Satin, or Matte? Or all coatings?

 

[aqazi81]

Asures, This is Gloss Coating.
Luckily we changed the batch and problem is solved.....

 

[DeltaE]

Asures, This is Gloss Coating.
Luckily we changed the batch and problem is solved.....

Congraz guy! I think the coating suppier should add some wax to make the coating layer more flexible after dried.