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stencils wont wash out, experienced screenprinter confused!

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stencils wont wash out, experienced screenprinter confused!

Postby animalsleep » Fri Feb 26, 2010 10:06 pm

I'd appreciate advice from anyone with some consistant experience using either ulano 925 WR or ulano LX 660. I've been buring my own screens for about 8 years with a very lo-tech set up and usually have consistent results good enough to hold detail and last through at least one print session, which is all I need.
BUT... I just moved to the west coast and have had a terrible time burning screens with my new set up, and I can't figure out why! same exposure lamp, new hose, new closet, new emulsion, same brand (tried both ulano lx 660 and 925 wr as well as saati dw).

Here is what is happening, I mixed the activator into the emulsion and coated the screens in extremely low light, but some stray sunlight was around (tried both coating in the garage where a little light came in from the crack around the garage door and also in my closet which is fairly dark but not lightproof). small amounts of light have never been a problem for me in the past (i've burned hundreds of screens in sunny rooms and even coated some screens in the bathroom in sunlight with no problems, but always dry screens in a relatively dark closet) but no matter how much i under expose my screens now the image refuses to come loose and wash out. i'm used to under exposed screens falling appart when i wash them but these are solid as a rock! not tacky at all in the image area, some emulsion loosens with scrubbing but the mesh doesn't clear out enough for printing. It seems like the screen has been pre-exposed but the emulsion hasn't changed color the way it does when you expose it which leads me to think it hasn't been exposed to ambiant light enough to cause this problem.
i am wondering if it could be heat from exposure lamp cooking the emulsion? (500 watt halogen) or a chemical in the water here? (am i crazy?) i use doubled photocopied transparencies, which have always worked for me in the past so its not that they aren't opaque enough. and they are pressed firmly onto the screen so light isn't creeping under my transperancies.
help me!
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Re: stencils wont wash out, experienced screenprinter confused!

Postby d fleming » Mon Mar 01, 2010 10:49 am

Try calling ulano and checking the product # on bucket to see how old it is. You may have a bucket that has already died on your suppliers' shelf.
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Re: stencils wont wash out, experienced screenprinter confused!

Postby geneh » Mon Mar 01, 2010 2:19 pm

What is temp in your drying room? I have found with some direct emulsions if they see a temp of over 90F for more than 2 hours they will start to develope and become useless. If you think this maybe your issue try drying your screen for an hour then expose and see if that helps.
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Re: stencils wont wash out, experienced screenprinter confused!

Postby tompaine » Wed Mar 03, 2010 3:24 am

Just coat a screen, dry it and see if it washes out.
Sounds like a dead emulsion to me.
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Re: stencils wont wash out, experienced screenprinter confused!

Postby Jiminscreen » Mon Mar 08, 2010 8:31 am

How old is your bulb, how old is your emulsion?

What else is the screen doing when you wash it? Fuzy dots? Some image washing out? Can you see the positive outline in your emulsion.

Here's a trick. Do a step test. Place a piece of cardboard on your screen. burn 10% at a time and move the cardboard over. It will let you know of your already exsposed and give you a correct exsposure.
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