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screen printing => Screen Making => Topic started by: Dottonedan on March 21, 2017, 10:52:42 AM
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I overhear that the printers have "stat started" getting this issue over the last year.
I want to help get it resolved.
I asked them if they rinse off the inside one last time after washing out the front. They said yes. So, assuming they are doing that and doing it well enough, what other areas of the process might cause this? Not a good reclaim process/scrubbing actions?
It's not totally blocked. They can print a few times and push through it to get the print to clear.
Thoughts?
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Scum
The emulsion is not fully exposed
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Bad exposure
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yup, you can dissolve it with spit before ink goes into the screen. It'll work to fix the screens that are wrong, but you are best off increasing exposure times to eliminate that.
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If you have a screen with a lot of scum in it take it to the wash out both and quickly rinse it with water to get rid of it and then blow dry before the emulsion softens. Quick fix but exposire times should be adjusted.
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Hard water.
Try using an air hose after washing the stencil out to clear water out (and water near that might move into the open stencil) before drying it and see if that fixes it.
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Like others have said, a by-product of slightly underexposed emulsion, usually on the squeegee side.
It's the highly diluted unexposed emulsion running into open areas of the stencil.
I've been in places that for years avoided the issue, and may well have not realized they were underexposing, with the blotting on newsprint of both sides of the screen after development.
Underexposed or not, no extra water flowing, no issue, just pink or blue newsprint as a record of what happened.
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Hard water.
Try using an air hose after washing the stencil out to clear water out (and water near that might move into the open stencil) before drying it and see if that fixes it.
Could be scum or could be this. Water definitely poses a problem in my area. Last shop I was at used an air hose, with "blowing out" after washout being standard procedure. Bonus: screens dried faster, could be used shortly after exposure.
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echoing all. scum.
what exposure system are you using?
how thick is your emulsion coating/what mesh counts?
we never got rid of it until we got a decent MH system.
a bank of tubes, and "glisten" method coating on low mesh screens will never have enough oomph to expose the far side of the emulsion
though - in a pinch light scum usually washes out with a little bit of water and friction (paper towel, finger)
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Yeah, that's scum. It's been so long since I've seen it I had to really think about for a minute. When it would happen, we would blot the screens and inspect to be sure they were clear before sending them to dry, then changed to compressed air to blow them out, then, finally, found the proper exposure, and use a vacuum with the "screen" attachment...
Steve
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I had an air hose plumbed to the rinse area , it helps with drying , the scum sounds like underexposing
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we have this commonly, result of air drying the screens and the water minerals hanging on / remaining on the mesh.
I never see it that severe looks like an exposure problem. the minerals you will see more collecting more in the corners and in small tight areas of a design especially in the direction of gravity. We hardly ever see this in wide open areas.
We solve our situations with a wipe down with the stuff below
mooseman
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I do have to say that, though a problem in some areas, I'm sure, I have never seen the minerals in any particular water leave the rainbow sheen that is the characteristic visual of scum.Minerals leave more of an actual powder-like residue, don't they?
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I do have to say that, though a problem in some areas, I'm sure, I have never seen the minerals in any particular water leave the rainbow sheen that is the characteristic visual of scum.Minerals leave more of an actual powder-like residue, don't they?
I was just about to post that. Yeah, more of a crust on the screen with minerals. I'm surprised you haven't seen it, we have.
Are you CCWD or EBMUD?
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I overhear that the printers have "stat started" getting this issue over the last year.
I want to help get it resolved.
I asked them if they rinse off the inside one last time after washing out the front. They said yes. So, assuming they are doing that and doing it well enough, what other areas of the process might cause this? Not a good reclaim process/scrubbing actions?
It's not totally blocked. They can print a few times and push through it to get the print to clear.
Thoughts?
Scumming comes from underexposure. Quick underexposure test for screen guys. Any color on the cloth-- DOUBLE exposure and test again. No Expensive testing equipment required.
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I do have to say that, though a problem in some areas, I'm sure, I have never seen the minerals in any particular water leave the rainbow sheen that is the characteristic visual of scum.Minerals leave more of an actual powder-like residue, don't they?
I was just about to post that. Yeah, more of a crust on the screen with minerals. I'm surprised you haven't seen it, we have.
Are you CCWD or EBMUD?
Walnut Creek is EDMUD, while Pleasant Hill and Concord are Contra Costa water. That made a big difference with fish too. My pH right out of the tap was real close to what we wanted.
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On the other hand, our water is A little soft to be perfect for beer.
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On the other hand, our water is A little soft to be perfect for beer.
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Easily fixed with some gypsum :D
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I couldn't recall the boundaries, I have a buddy that works for mud, he's described where one
pipe stops and the other begins. He's also described lead pipes and eternal leaks under roads.
I'd take mud any day having lived under both.
Dark beers are fine with soft water, and if you can see through it, it isn't beer anyways.
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On the other hand, our water is A little soft to be perfect for beer.
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Easily fixed with some gypsum :D
Yep, a standard fix. Loosens up soil too I believe
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Another vote for underexposed.
Murphy
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Another vote for more beer talk.
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I'm now pretty sure it's the exposure unit it'self. It's the flo bulbs in a NuArc First Light. We are coating 2:1 (round) using SAATI emulsion.
I'm told we are getting a solid 7 in the stouffer's step test. If that is the case, then I still think we are a little under...and just enough to leave this residual behind.
Alan Howe came by the other day and will be sending me some samples of other emulsion they sell that might be a good fit for us. What we have right now, is not (as good) for halftone work. We haven't tested all mesh on the exp test yet...and I wasn't around to be there when they did test, so I don't know for sure how accurate the initial test were.
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I'm now pretty sure it's the exposure unit it'self. It's the flo bulbs in a NuArc First Light. We are coating 2:1 (round) using SAATI emulsion.
I'm told we are getting a solid 7 in the stouffer's step test. If that is the case, then I still think we are a little under...and just enough to leave this residual behind.
Alan Howe came by the other day and will be sending me some samples of other emulsion they sell that might be a good fit for us. What we have right now, is not (as good) for halftone work. We haven't tested all mesh on the exp test yet...and I wasn't around to be there when they did test, so I don't know for sure how accurate the initial test were.
solid 7 is a good plan, but it's not a perfect system. depends quite a bit on soak time, washout time, speed, pressure, human. and if you aren't burning all the way through (you aren't) that 7 might be reading from the light-source side of the emulsion only...
which emulsion? flo tubes and 2:1 round is probably a bad combination for all but the easiest to expose emulsions out there, my guess.
is reclaim difficult? is the image left on the screen after reclaim with any consistency?
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I had this with diazo emulsions for a long time. We were underexposing. We solved the problem by blowing the water off with air before drying.
I now use Saati PHU and a Saati led, great screens, 7 on the scale and nothing like this.