Do you think this problem is: set-off or blocking?

[DeltaE]

Hello Experts!

We are making a sample. That is a two-pieces rigid box.
The surface was printed with dark blue spot color and full area matt waterbased coating on the Heidelberg offset sheetfed machine.
After printing, we wait for 24 hours before moving to the postpress process for making the box.
This box needs to be tested according to the customer's requirement. The test is putting box in a testing device for 12 hours and in condition 75 degress celcius, 90% huminity.

After testing time, when I took the box out, wait for one hour. Then two parts of this box sticked together. I tried to open it, then the surface in the contact area of two parts peel off the surface. (please see the attached picture)

From my view, the ink layer seems to be taken out of the paper surface.
I am looking for the remedy for this problem.
Do you think this problem is: set-off or blocking?
Please give me any advice or your idea! I am very appreciated!

Thank you!
Regards,
DeltaE

 

[LSW]

I'd expect that the 75 degrees celcius in the test process would be more than hot enough to re-wet the coating and cause blocking.

 

[DeltaE]

I'd expect that the 75 degrees celcius in the test process would be more than hot enough to re-wet the coating and cause blocking.

LSW Yes, I think so. I still do not understand why the printbuyer requested this test. We have the only choice that to find the solution.
I am trying to adjust: viscosity of the varnish (not too thin or too thick); the temperature of drying is just warm enough, using minimum IR; or try using a UV coating layer.

Thank you for your comment!
Regards,
DeltaE

 

[turbotom1052]

converting 78c to Fahrenheit scale has it at over 172f. This temp certainly is high enough as pointed out by LSW to re wet the coating and cause blocking. Under them extremes of temp I would suspect that a specialty ink and or coating would be required. Have you ruled out a weak substrate surface by testing with a different stock?

 

[DeltaE]

turbotom1052 You are right. The testing condition seems to be too hard for a packaging.
I am using coated 157 gsm for printing, and laminated the printed paper on a rigid cardboard in finishing process.
In my opinion, the surface of coated 157 gsm paper is strong enough for this job. But the ink and coating varnish should be considered.
I am still looking for a waterbased coating varnish which has moisture-and-heat-resistance or anti-rewetting properties.
Do you know any brand of coating like that?

Thank you! Merry Xmas and Happy New Year!
Regards,
DeltaE

 

[Alois Senefelder]

Hello DeltaE,

The answer you need to know IS why the box and contents need to be subjected to these extremes ?

because in my opinion this option (Box) is not fit for purpose .


Regards, Alois

 

[turbotom1052]

turbotom1052 You are right. The testing condition seems to be too hard for a packaging.
I am using coated 157 gsm for printing, and laminated the printed paper on a rigid cardboard in finishing process.
In my opinion, the surface of coated 157 gsm paper is strong enough for this job. But the ink and coating varnish should be considered.
I am still looking for a waterbased coating varnish which has moisture-and-heat-resistance or anti-rewetting properties.
Do you know any brand of coating like that?

Thank you! Merry Xmas and Happy New Year!
Regards,
DeltaE

Delta,
I know of no product that fits your needs as Ive never had to find one ,to work under such unrealistic conditions. My suggestion would be to contact a few consumable suppliers to see if such products exist. If you find some that do exist, then I would methodically test these products before putting them into production. In addition to the proper coating, I would also be looking very hard at both the ink, AND the stock. You made no mention of testing a different stock. The reason I point to the stock is the images you posted, look as if there is a definite delimitation of the papers surface. I fear that you will find this to be really challenging because you almost cant fault ANY consumable supplier for not being able to perform under such adverse conditions.
I will say this.... when exploring coating options my GUESS would be, that you would be best served with a coating thats wax free.

 

[DeltaE]

turbotom1052 Thank you!