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More emulsion/exposure issues.

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More emulsion/exposure issues.

Postby Mat Pringle » Thu Apr 15, 2010 2:03 pm

Hi all,

Apologies for using my first post to beg for help - I shall introduce myself properly when I get a moment and I'm not in a seedy internet cafe!

I've been spoilt with a fancy screen-printing studio for the last two years but in order to cut costs I decided to set up from home. I attempted to expose my first screen last week - the results were poor. The image could be seen but the emulsion quickly turned to a nasty condom-like substance and broke away as I washed it out.

I tried again last week using pretty much the same technique but using a different screen and got the perfect image exposure but for the fact the acetate I used to embed the image was actually a bit poor but I was happy because I relaised it was possible to print from home.

Fast forward to today and I went to spray the emulsion off - first of all I got the perfect image but the more I sprayed the emulsion gradually gave way to the condom-like mess again.

Frustrating.

I am using Speedball photo-emuslion. I coat the screen and tuck it away in a dry dark cupboard over night. I expose using acetate under a 200w bulb for 1.5 hours. I wash off the emulsion by spraying luke warm water over the back then the front and gently rubbing away at the screen with my hand.

Any ideas? All help gratefully appreciated.

Oh and the only thing I can think is it's the screen - the screen that went wrong the first time was the srceen that went wrong today. The time it was successful was with a dfifferent screen. Also I wondered if I coated the emulsion on too thickly?

Mat
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Re: More emulsion/exposure issues.

Postby tompaine » Fri Apr 16, 2010 3:09 pm

It's either under-exposed do this: http://www.t-shirtforums.com/t-shirt-ar ... 06506.html or get a stouffer strip or:
You haven't degreased the mesh properly or it's not been abraded.
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Re: More emulsion/exposure issues.

Postby Calibrated S.P.S. » Thu May 20, 2010 11:44 am

There are a couple of problems...most notably your light source. If you have to burn a screen for more than 10 minutes than you seriously need to change the light. I am willing to be that if you took the same screen outside and used the sun, it would expose in 7-10 minutes TOPS!!!

Here is why. Emulsion is exposed by UV (Ultra Violet) light.....a home bulb, or shop lamp will not be a sufficient source of UV for obvious reasons. The next issue may have to do with the temperature of the water you use to rinse the screen. NEVER use hot water, luke warm at best leaning towards cold as the warmer the water the faster the emulsion will want to dissolve.
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Re: More emulsion/exposure issues.

Postby nativesonjls » Mon Jun 21, 2010 6:29 pm

First of all I'm new to the printing end myself, I've sent hundreds of graphics out to the printers but I finally decided to do the printing to. I started with a starter kit from rayonet. They sent a diazo based emulsion and 110 screens. Boy if I only knew what I know now. I've been reclaiming screens for a week to get it right.
1) No warm water, if the emulsion will not wash out with cold you have not done something right
2) If the stencil is dark and the light is strong and you have the stencil tight to the screen, and the time is correct you should have no problem with the wash out with just cold.


a) a 8 dollar 500 watt halogen work light will do the trick, go to home depot or lowes, get two if you can afford it, the more uv light and overlapping cover the better the graphic. But one will do the job in a pinch.
b) use a dual cure emulsion (like EX1) if you have a 110 screen it seems to hold better graphic detail with the low end halogen light (metal halide is better for a point light) point lights cut better edges in the exposed screen than some florescents but if you get to that point you have done some homework.
c) if the size of your graphic it 10 inchs, 15 inchs, etc. multiply this by 1.5 to get the distance to the surface of the screen/stencil from the surface of the light. (take the glass cover off of the light it has a uv filter)
d) place stencil on the screen and tape it down, now point the light up and use that old glass top table from the seventies to set over the light to the distance you need for this graphic, use blocks of wood, kids toys, etc. to raise the table to the correct height. You could just get a light stand with the halogen light (15 dollars) and point it down at the screen and set the glass on top but where is the fun in doing it the easy way.
e) set the screen facing down toward the light which is under the table then place a black cloth over the screen if you have some foam to place on the back of the screen this will allow you to put some objects on the foam this will push the graphic tight to the emulsion the tighter the stencil to the emulsion the crisper the image, not to much, you are on a glass top table.
f) I found no difference in the times for exposure from the diazo to the dual cure emulsions but I've never used your brand. But the cure times for 1 500 watt light with a 1 coat front 1 coat back of screen with 110 mesh was 12min:30sec with two lights this should and could be half that. But a wedge test would zero your time in exactly, I am doing some fine detail so I did several wedge tests with both types and the emulsion just melts away with cold water. With dual cure you need to re-expose the screen or set it in the sun to cure a second time to finish the process, diazo emulsion which is probably similar to the type you are using just needs to be dried. Below is the final adjustments and details on my setup. Eight screens with very detailed graphics and text.

Final results on the wedge test i did for the dual cure emulsion
1) (2) 500 watt halogen work lights at 20 inches below the glass/screen, (1.5 x graphic size to set distance) lights on thirds spacing for max overlap of light for uv increase
2) dual cure EX1, 1 inner 2 outer coats
3) 110 mesh screens, foam with black cloth and weight on it to press graphic to glass for better detail
4) (2) stencils overlay-ed from a lexmark x3350 all in one printer, will refill with dye based ink into their dye based 35 cartridge and run dual black no color cartridge, adjust print options as needed if needed.
5) vellum paper for stencils doubled, settings are black graphic, high quality and coated paper which allowed transfer of ink with time to dry so ink didn't saturate the paper, very fine detail with dark print, best setting of any tried.

final time was 9min 30 seconds,
had time at 10 minutes 30 seconds but had to reclaim one screen with fine detail because it was slightly over cured and several outer letters would not clear, I adjusted my time and also light spacing from side by side to thirds to even light across the stencils and all graphics came out nice on my most detailed graphic, lots of fine small letters.

1) The new emulsion allowed the detail I needed on the 110 mesh, I will increase to 230 mesh later for water base inks and detail, will do wedge test then to confirm time.
2) 2 lights cut my cure time by 10 minutes, will switch to metal halide lights later for better cure times.
3) Had to set the screens in the sun for a time to do the final cure, will coat them with the 3 stage curing agent if the shirts are popular and sell, will need to preserve the screens as long as possible.
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