UV Ink Adhesion

[jteague]

Hi all

I am relatively new to flexographic printing and uv inks. We currently have a problem with making UV ink adhere to a clear PET film. We have tried a variety of things to improve adhesion (corona treatment, different inks, etc) but the only thing that works is coating the PET film with IPA before applying the ink. Can anyone tell me why this works?
The ink person who suggested this idea only referred to it as an old press trick and didn't really have an explanation as to why this is happening.
So far I have been unable to find any really good source material telling me why this is happening. I am thinking that the IPA is somehow removing contaminants on the film, but when we run some IR tests on IPA cleaned vs non-cleaned film, no differences are picked up.
Any info would be appreciated

 

[thaiha]

Hi Jteague,
1/ You will need to ask your supplier about application of UV on clear PET --> they will answer
2/ I have some product applied UV on clear PET and we have the same problem with you --> no solution, because the nature of UV is apply on ink surface.

 

[Sullyjj]

jteague,

Do you know what the Dyne level is of the clear PET is? Inks adhere best when the Dyne is between 38-42.

 

[jteague]

Sullyjj,
When we tried the corona treatment the surface level was at 52 and still did not adhere very well.

 

[HRoss]

Of the various plastic films, PET has always been a challenge for UV Inks or Coatings to adhere. Clearly there is something sitting on the surface that is soluble in IPA since it is removed and allows your ink to stick. Cornoa was a good thought since it makes the surface more receptive to wetting, but you need something to alter the chemistry of the surface. You need a "site" that the ink can grab. It may be extreme, but you might find a company that provided Plasma Discharge equipment and ask them to provide testing to see if that alters the surface enough to get adhesion. I might "burn off" the material that the IPA is removing.