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3of4clothing · October 27th, 2009

We're having trouble with emulsion coming off the screen during a print run. Usually the first 4 prints are fine and then print by print small specks of emulsion come off the screen and stick to the t-shirt. It gets to the point where, when you wash the ink off the screen the emulsion just washes out in parts.

We've been screen printing in our flat for about 6mths now and we've never had this problem before. We haven't changed anything regarding our coating or exposing of screens in this time and we have just opened a fresh pot of photo-emulsion. We have started using a heat gun to dry prints though and the weather has gotten colder and wetter here... could it be a moisture issue? Has anyone dealt with this before?

scottyjr · October 27th, 2009

Water based inks? - Scotty

3of4clothing · October 27th, 2009

yep - waterbased inks

jim.goodwin · October 27th, 2009

Make sure you are using an emulsion that is designed to work with waterbased ink. Many aren't made to stand up to that much moisture. Sometimes you get a bad batch of emulsion that just doesn't work right. I've had a couple. Swap out your emulsion for new stuff and I'll bet you are back in business.

You might also try exposing the screen again after you get it all washed out (and dried). I've found this to help.

3of4clothing · October 27th, 2009

Thanks Jim,
We have thought that maybe it was a bad batch or emulsion. It is the same kind as we have used earlier (and printed fine with waterbased inks). However I think the problems might have started when we opened this new container of emulsion.

Guess we'll order another tub of emulsion and give that a go.

jim.goodwin · October 27th, 2009

Your supplier may stand behind their product and take back the bad stuff... it is worth a try. My reasoning is that what they sold you didn't work.

moe_szys1ak · October 27th, 2009

It sounds to me like you're using emulsion that is not made for waterbased ink. What kind of emulsion is it?

RichardGreaves · October 27th, 2009

The best water resistant emulsion uses diazo sensitizer. You can judge exposure by paying attention to the color change of the stencil as the diazo loses color as it is exposed to UV energy.

Adhesion is one of the simplest indicators of stencil failure. Exposed areas are physically adhered to the mesh or they would dissolve and rinse down the drain.

Under Exposure is the #1 waterbased ink problem
Exposure with UV energy cross links the stencil and it won't absorb water, swell or dissolve. UV energy has to move all the way through the stencil to cure it or it will look like a steak or pancake you cook only on one side.

The unexposed inside of the stencil will still be vulnerable to water in your ink - and start to breakdown as you rub it with your eraser like squeegee blade.

If the inside of your screen feels different from the bottom of your screen during washout - UV energy didn't completely penetrate.

http://www.ulano.com/FAQ/FAQexposure.htm#Q1

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Emulsion sticking to t-shirt and coming off the screen