Clear haze in screens? See pic.

[Dottonedan]

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?

[DannyGruninger]

Scum

The emulsion is not fully exposed

[inkman996]

Bad exposure

[mk162]

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.

[inkman996]

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.

[Admiral]

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.

[Frog]

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.

[Prince Art]

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.

[Stinkhorn Press]

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)

[Sbrem]

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

[Croft]

I had an air hose plumbed to the rinse area , it helps with drying , the scum sounds like underexposing

[mooseman]

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

[Frog]

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?

[ebscreen]

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?

[GKitson]

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.