pin holes and emulsion?

[whitewater]

Well we recently changed emulsions..now its like pin hole central!

Rarely did we have pinholes with the old emulsion, now they are all over the place. As far as i know our process has been consistent.

Just wondering if anyone else has had this issue? I may go back to the old one, i really had no issues except 2 day ship.

Rob

[mk162]

it might be that you are coating too quickly and ending up not bridging the mesh well.

[Doug S]

Well we recently changed emulsions..now its like pin hole central!

Rarely did we have pinholes with the old emulsion, now they are all over the place. As far as i know our process has been consistent.

Just wondering if anyone else has had this issue? I may go back to the old one, i really had no issues except 2 day ship.

Rob

Just curious as to what emulsion did you switch to?

[3Deep]

Rob, I got the same problem going on now, but I'm thinking its all me with my screen cleaning or dust in the shop getting on screens.  I now take a sticky roller and roll the screens before I coat and I wash my screens better than the last batch...9 times out of 10 it always falls back on us on how we prepare our screens and not the emulsion, at least me anyways LOL.

Darryl

[ScreenFoo]

I'd agree bad prep is one of the easier ways to get a lot of pinholes.

Have you run an exposure calculator with it? 

Different emulsions expose differently... maybe the new stuff takes longer and you're underexposing now?

[Dottonedan]

Also seems to stand to reason that this new emulsion is holding better or finer detail. You prob had the problem all along but your old emulsion may not have held the dust like this new one. That's just a guess. Maybe you will notice being able to hold finer halftone dots now as an added benefit.

[GaryG]

We have found that the higher the solids content, less defects.
From what to what did you switch?

[whitewater]

We went from the Textil PV to QTX...I like the color..LOL

Really prep has stayed the same. maybe we are doing something different, i dont think so..we have been paying attention to it more the last 2 weeks.

With the PV everything was great. Absolutely no trouble burning. I used QTX a few years ago, and sort of remember pinholes then also. They are same price but its easier to get the qtx here in the 1 day, where the PV i remember in the afternoon and then its a 2 day.. I know better preperation on my part.LOL

Well i ordered the PV today and will use that next to see if we still get the holes.


thanks
Rob

[Printficient]

QTX's solids of 28-30% preclude good prep procedures.  Good and thorough rinse with a neutralizing de greaser, drying mesh down in a non "fanned" room with a dehumidifier.  Low dust to dust free environment.  Also a clean glass as QTX exposes quite fast.

[Rockers]

QTX's solids of 28-30% preclude good prep procedures.  Good and thorough rinse with a neutralizing de greaser, drying mesh down in a non "fanned" room with a dehumidifier.  Low dust to dust free environment.  Also a clean glass as QTX exposes quite fast.

You might be confusing the QTX with some other emulsion, but the QTX we used to use  from Ulano got around 46% solids. He should not have these issues, at least not on a whole batch of screens. Once in a while on a single screen and I would put it down to poor screen prep.

[mooseman]

we use QTX and do not get any pin holes. We do however get some thin areas where the emulsion seems to migrate away from a contaminated area. relative to other emulsions we have used I believe QTX is kinda sensitive to any contamination on the screen.
Also due to the viscosity it tends to really hold on to air bubbles.

you might try wiping the screen down (as a test ) with lacquer thinner, alcohol, acetone or similar quick evaporating solvent  just to insure the screen is absolutely clean then coat as usual and evaluate the result relative your norm.

the other test would be to get some of your original emulsion and coat the same screen about 50% with each emulsion. Coat both at the same time or coat half, dry, and then the other half with the other emulsion.

We like QTY but it does seem to have some fussiness .
mooseman
 

[GKitson]

it might be that you are coating too quickly and ending up not bridging the mesh well.

I agree with the coating too quickly analysis, too fast a stroke will fill your coated mesh with little air bubbles that evolve into pinholes.

Hold the coated dried screen up to a light source and check out the 'tiny diamonds in the sky' which are indicative of trapped air bubbles.

~Kitson

[alan802]

We've had a pinhole issue pop up recently so I went into the dark room while my guy was coating and it took one stroke to figure it out.  He had changed from coating around 6"/sec to about 20-25"/sec and that made a huge difference.  Of course my printer thinks he knows everything and told him one day he was coating too slow and to go fast.  I'm constantly having to figure out what one of my guys is learning from the others out there and set them straight, I can't believe there is still that much bad info and techniques lingering around our shop.  Everyone out there knows our way of doing everything yet they think they know a better way and decide to change it without testing or asking me if it's ok.  I don't mind changing anything if it gives us better results but 9 times out of 10, we're already using the best method or practice, that's why we do it that way. 

I'm sure most shops are this way, you get a bunch of guys and one or two think they have all this experience so their knowledge must be great...doesn't really work that way.  I know printers in this town with 20-25 years experience that know less about screen printing than guys that have worked in good shops for a week.

[Orion]

Yep, when it comes to screen coating, speed kills. This will be more noticeable on coarser mesh. You will get the "starry night" pinhole effect, caused by the air bubbles accumulating in the scoop coater. This can be remedied with an additional face coat on the print side of the screen after it is dry from the initial coating.

[ScreenFoo]

Could be worse, Alan.  I still don't think anything tops the phrase "I feel like it works better this way"--and this has been cited as reasoning more than once to me.

Still didn't catch a reply--did you use an exposure calculator to find a proper exposure time on the different emulsion?
PP's are pretty touchy on exposure time...