Making a durable discharge screen

[avogel]

We are having trouble with the discharge base screen breaking down after 50 - 100 prints.  We have 13 orders, each one is 600 - 1000 piece run. These are all sim process, so we are using 225S CCI discharge underbase, with Green Galaxy top colors. The Green Galaxy screens are holding up fine. Here is what we are unsuccessfully doing, 225s static screens, Cryocoat coated 2/2. We have Ryonet LED exposing them at 7 seconds. We have been adding extra emulsion around the edges where the edge of the squegee run. Then post exposing for 1 minute. I have ordered some hardener. Will this help? Anything else?

[ericheartsu]

I'd get a stouffer test from Saati to determine if you are exposing correctly. I know that helped us figure out our stencil durability.

[Frog]

I'd get a stouffer test from Saati to determine if you are exposing correctly. I know that helped us figure out our stencil durability.

I'd usually say that as well, and in fact wonder how the 7 seconds was derived, but assuming that this is a photopolymer emulsion, shouldn't the post exposure make up for any initial underexposure? (Unless it's really thin after a lot of unexposed emulsion rinsed away from the inside)

[ericheartsu]

I'm also wondering why you are coating the screen 2/2? especially with the cryocoat, 1/1 should be fine.

So my guess is that the 2/2 is maybe a little to thick, and therefore not exposing all the way?

[avogel]

We changed to 2/2 thinking it might last longer. We normally do them 2/1, but those only lasted about 25 or 30 prints. I will put a test strip on the next one but I don't believe they are extremely underexposed. We tried one at 10 seconds and it was hard to wash out the really low percentage dots. Will the hardener help and when should I apply it?

[brandon]

That should not happen.  To me the exposure sounds wrong for that EOM with a high solids emulsion like that. And are you letting screen "sit" or going straight to press in 15 min?

[ericheartsu]

We changed to 2/2 thinking it might last longer. We normally do them 2/1, but those only lasted about 25 or 30 prints. I will put a test strip on the next one but I don't believe they are extremely underexposed. We tried one at 10 seconds and it was hard to wash out the really low percentage dots. Will the hardener help and when should I apply it?

The Cryocoat is the saati PHU. I'm some one more educated than I can confirm, but I think you are wasting your money putting hardener on that emulsion.

[avogel]

Ok. I will put a test strip on it and take the exposure out longer. The screens have been sitting 8 -12 hours after being made before going to press. How long should I post expose? Really appreciate the help!

[ericheartsu]

saati recommends, I believe 20 mins, in direct sun light.

[avogel]

Thank you. I will try these things and report back how it goes.

[ScreenFoo]

We changed to 2/2 thinking it might last longer. We normally do them 2/1, but those only lasted about 25 or 30 prints. I will put a test strip on the next one but I don't believe they are extremely underexposed. We tried one at 10 seconds and it was hard to wash out the really low percentage dots. Will the hardener help and when should I apply it?

A thicker stencil will make it harder to hold fine dots and details, and harder to properly expose.

If you prefer the sharp edge of the coater, try 1/1, or even try just one stroke with the dull edge.

[zanegun08]

We have similar issues from the screens not being totally cured before imaging.  Before exposing your screens make sure that they have had a good 12+ hours to sit so that more of the water can evaporate out of the emulsion.

Also maybe adding a diazo.  We are currently testing Murakami T9 to see if we get better life out of our screens on water base runs as we've had recent issues with Kiwo Multi-tex

[Nation03]

I think we got a bum batch of Cryocoat. Last time I used it with plasticharge it worked just fine with no break down. Got a quart of it recently and had the same issue. Once we got to around 30 prints in it started to break down. Didn't change my coating method or exposure since last time. Same mesh and everything. I also used less discharge activator then I did the last time so I'm really stumped on this one.

[Doug S]

We use Cryocoat here and always coat 1/1.  With the high solids, it gives more then enough eom.  I agree that 2/2 would make it more difficult to get detail and expose thoroughly with 7 seconds.