Corona discharge polyester subbing

[hrst]

AH!! This explains the mottle in rev.RA4! I've been wondering it so much. Thanks for the explanation.

 

[Hamster]

Don't know if we are talking about the same technology.

I used to print on PET roll material, and before the first ink roller is applied, the substrate undergoes corona treatment.

If we had any problems with the ink not sticking on the substrate, we would have to measure the effectiveness of surface treatment. We use a test solution (most accurate), or test pens (good enough) to test surface tension, measured in dynes/cm. As a rule of thumb, Printing on PET needs a minimum of 42dyne/cm.

My understanding of the corona treatment is that the surface is deformed to increase surface area. But I think there is another school that thinks corona treatment creates microscopic pinhole in the substrate.

There is a lot of information about Corona Treatment from the world of Narrow Web Printing, perhaps some would be useful to you.

Dead Link Removed

 

[Steve Smith]

I used to print on PET roll material, and before the first ink roller is applied, the substrate undergoes corona treatment.

We screen print conductive ink onto polyester sheets. All of our print lines have an 'anti-static bar' to remove the static charge from the sheet prior to printing. This is probably the same as the system you are describing although for us, it is more as a handling aid than for ink adhesion.

Manual handling of polyester sheets can result in a lot of static shocks. Not so much of a problem with a web based process.


Steve.

 

[Photo Engineer]

The corona treatment is not permanent. If it created defects or whatever, this treatment would perhaps be permanent, but the corona discharge treatment dissipates and is gone in about 24 hours. The film or RC must be re-bombarded.

PE

 

[hrst]

Good news; I was able to reduce contact angle to about 30...50 degrees throughout the whole sheet and many times in a row. Water behaved completely differently now on the surface, forming large (~1 cm) puddles instead of small drops. This contact angle should be really enough for coating, but after so many failures I'm not sure yet . I made a test coating again and will report soon.

The key was a new anode electrode made of metal mesh to increase its surface area. And, the surprising part, which I accidentally found, was that no matter what, the wrong side of the sheet seems to get the treatment. So, the side facing the anode (mesh) does not work, but the side facing the dielectric-coated plate (cathode) shows a great hydrophilicity. Changing the polarity didn't change this; the side facing the plate was treated. Oh well, this doesn't matter really, if it just works, but I was surprised. The voltage has still to be very high, 18 kVrms, despite the patents speaking about much lower voltages.

 

[holmburgers]

Just to bridge the gap, this thread is continued here... (there was a url link here which no longer exists)