Ink rubbing off Scitex corrugated plastic prints

[Lindquist]

Periodically, I encounter corrugated plastic prints from our Scitex FB700 where the ink rubs off very easily or is scratched easily. However, most of the time, it's not a problem. Yesterday, I took a sign that was printed 24 hours earlier and tried to scratch the ink off in various ways with little success. Even a key didn't scratch the ink.

But now, we are assembling signs on stakes and pulled some inventory off the shelf (signs printed months ago, stored indoors, but not climate controlled) and the ink is just rubbing off with little effort.

Any ideas what causes this? My first thought was the storage environment. The newly printed sign was stored in an air conditioned office for 24 hours whereas the older sign was stored in a warehouse for months. I don't store all signs, many go out immediately, but I've also had reports from customers in the field of ink coming off. It doesn't seem to be a wide spread problem, and it has affected signs printed at various times throughout the past two years.

 

[Hotspur]

"i corona"

Hi

This effect is caused by the corrugated plastic you are using.

When it is manufactured the supplier applies a corona treatment to the surface using high voltage electricity which changes the energy level of the plastic and allows the ink to flow and stick properly.

This corona treatment fades with time - thus when you have no problems you are using fresh correx & when the ink flakes off you have printed using old / poorly stored correx.

You can use primers to help adhesion with correx known to be old but it's not a great alternative to having fresh correx.

Really this comes down to your supplier having good stock rotation.

If you want to check the surface energy for yourself (or prove to a doubting supplier that their correx is old) buy yourself a dyne pen ($20)

This will show you the level of energy stored on your material - most UVs need a dyne energy level of at least 30+ for the ink to stick so you can get pens rated at different dyne levels to check a batch is OK before using.

The HP UV ink is one of the best for adhesion and so a dyne level of 30ish is all that is required for it to stick OK - other UV ink that struggles with adhesion (e.g. Arizona) needs a higher dyne level to guarantee adhesion - around 42 I think (but worth confirming first)

Either way fresh correx at the time of printing is the key to good adhesion with this substrate.

 

[Robert Gruner]

Thank you Hotspur...
Your posts are always very informative!