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exposure with 500 watt work light

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exposure with 500 watt work light

Postby nativesonjls » Sun Jun 06, 2010 6:57 pm

I have worked in the graphics end for over 15 years ( Adobe, Corel, Office, 3ds Max, AutoCad, Rhino, Pagemaker, etc.) so I'm not new to the industry but the shop is another matter. I'm setting up my own screen printing shop and I'm starting with a simple single color press and a home made exposure unit. But I'm getting mixed info on line, most every one is recommending 12-15 minutes with 16 to 18 inches above the unit, but a few have said they are only exposing for 4-6 minute with the same set up. Is this with the uv glass on or off, I need to do a wedge test soon. I'm using 110 mesh 20x24 screens and the light sets 16 inches from the top face of the screen to the glass face if needed and 18 to bulb if not. the two times are hugely different so my wedge test could go very badly. Any help would be great.
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Re: exposure with 500 watt work light

Postby nativesonjls » Tue Jun 08, 2010 9:32 am

ran wedge test:
Results were as follows,

1) 1 and 1 coat, with Procem WR-6 water resist photoemulsion which has a diazo catalyst activater and must be premixed
2) Started at 12 min. and moved the block every minute for a total of 18 min., 13 min was the best time, used pdf file with mesh and line segments, wedge sheet is on line with instructions, http://www.smrsoftware.com/vellumexposure.php
3) Didn't use the lens, and the distance from the face of the screen to the face of the unit where the lens was is exactly 16 1/2 inches
4) 500 watt halogen light on a pvc stand. casting light down on the screen. Foam covered in black cloth under the screen and a sheet of glass on top
5) detail is extremely fine for a 110 mesh which is good considering by graphics are very detailed, I used vellum paper to save some money and some graphics are tiled so I have overlap and I needed to use 2 sheets to produce the density needed for the black, so I also set a 1 inch four layer velum strip to the side of my wedge sheet to test the effect of the extra vellum and the test showed no significant difference on the final screen quality.
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Re: exposure with 500 watt work light

Postby tompaine » Tue Jun 08, 2010 3:33 pm

I have an exposure for dummies guide: http://www.positivityltd.co.uk/Tutorial ... ation.html
Do not use any glass that isn't uv clear, it will mess things up.
Your exposure distance should be roughly equal to the diagonal of your screen, it helps keep the exposure even across the area without being too long.
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Re: exposure with 500 watt work light

Postby nativesonjls » Tue Jun 08, 2010 7:10 pm

Thanks, I read it now, I was just following the one on vellum paper I found. Maybe I just got lucky. Which in my case doesn't happen often.
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