Dyne Levels for UV Digital Printing Success - help!

[theloop]

We supply white gloss PVC laminated to magnetic sheet that is used for a range of printed displays.
The vinyl is purchased as being suitable for Solvent and UV Digital Printing.

We have some issues in that when it is printed using UV Digital machines, we can see various blemishes in the finished print, ranging from 20mm wide parallel lines, blotches in a line running the length of the vinyl (in the direction of calendering), marks that look like a cloth has been wiped over the vinyl and what look like hand prints. However, on many occasions, the vinyl prints perfectly without issue.

We just bought a full set of Dyne Pens from Dyne Technology Ltd (liquid ink pens not the Rapid Test Felt Tipped kind) and can confirm that the vinyl has a surface tension of 34 Dyne/cm.

We also purchased some expensive UV Digital Vinyl from Metamark for some benchmark testing and find this too has a surface tension level of 34 Dyne/cm

I have read that UV Digital inks themselves have surface tension around 50 Dyne/cm and so require substrates to have surface tension above this level in order to achieve satisfactory wetting, then elsewhere I have read that 38 Dyne/cm is more than sufficient.

This just leads to total confusion - not least since the Metamark product (which I am assured runs perfectly and is guaranteed to do so) has a surface tension (as tested) of 34 Dyne/cm. I also understand that Dyne levels can reduce over time on Vinyl and note that none of the material has been Corona treated.

We are trying to understand what has caused the print defects - my belief is that the vinyl has at some stage been contaminated by products unkown or by sweaty human hands, resulting in a lowered surface tension at the point of contact.

At no point has the ink failed to adhere - it can be guillotined after printing and does not chip and neither can it be removed with sticky tape over an area that has been scored.

All of our staff wear gloves when handling the vinyl which are bought as UV Digital Printing compatible gloves and are changed daily!

Anything that people can offer would be most greatly appreciated as we endeavour to understand what is going on here.

Many thanks,

Pete

[rcm355]

Look into Tekra's PVC products. Never had an issue with them.

[REYES1377]

Not certin if the same rules applty to digital, but in offset lithograpphy a dyne level of 37 would be the lowest point for inks to adhere. 34 would be rejected for an offset press.