Discuss the different types of equipment needed for screen printing. Topics include manual screen printing presses, automatic presses, dryers, folding machines, starter kits and high end machines.
I posted this once and it doesn't seem to have made it through. So here goes again...
Here's what's going. Basically the emulsion around the edges of my art are getting really soft and bubbling up as I'm washing out. In some case fine detail (which really isn't FINE just small - like a thin line or dot with NO emulsion around it).
Since I tried to post before I've run a test.
I coated two screens. One was slightly heavier then the other.
Both dried completely. The heavier one I dried a bit longer.
I burned the image on the first screen. 8 mins, about 12 inches above, using 250 watt halogen.
As soon as it was burn I put a little water where the image was until the image started to come through. Let it sit for about 20 seconds. Then washed it out.
BEAUTIFUL! It washed out with almost no pressure.
Now the second SLIGHTLY heavier screen. 8 mins, etc etc. same as before.
Here's the problem. The emulsion didn't come out as easy. I had to use more pressure and lots more water.
I thought it was going to be great. But as I looked closer the edges in the art started to bubble up and peal back.
QUESTION?
Should I have burn heavier coated screens a little longer. Say another minute? I'm kind of at a loss really.
Before this last test I was burning for 11 to 12 mins and the image was not wanting to budge. So by the time it did the fine detail was lifting away. I backed off the burn time...see above. LOL!
How large is your screen? 12 inch placement of your light source may not be high enough. So the edges of the emulsion imay not be getting burned into the screen.
Heavier screen (for me :-) is a heavier coating of emulsion. The first one I did had a much thinner coating (2 on the outside and 1 on the inside). the second was heavier but not by much at all.
My screens are 20x24 my image area is about 8x10 (little more). I'm coating the entire screen though.
I didn't realize that the height mattered THAT much. How would I know if the edges are getting burned enough? It's almost like water is getting trapped and just lifting the image up.
In fact this second (VERY FRUSTRATING) test ended worse than the others! It washed out pretty easily. But longer still then the others...so more water. After it washed out I thought...oh perfect! Then by the time I got inside with it.......see links! GRRR! I don't know...I don't know!
The screen that was heavier was honestly an accident. I tipped over the lamp and the light broke. So in the dark I tried to finish. I ended up having to fix the coating a bit.
This last time. I don't know. It was 2/1. So I don't know what's going on.
Maybe I need to do another test where you burn in one minute intervals, moving a board to uncover the next area?
Yes, a step test will tell you the exact time you need.
Let's just cover some basics to make sure we are laying the correct foundation:
1. Your screen looks new. You are degreasing them before you use them, correct? If not, this will cause emulsion not to stick.
2. You may want to research here on the forum the ideal distance you need the screen to be from the light source. I use a 500 watt halogen and my distance is 24 inches. Even with a 250W, your distance should be about the same, just a longer exposure time. The correct distance allows the light rays to reach all parts of the screen uniformly.
It's important to get the correct distance because even though you may burn a correct screen now with a smaller design, when you go to a bigger design, correct distance will critical to prevent a repeat of emulsion washing away from underexposure.
Yes a heavier caoted screen will require a longer burn time for the light to penetrate the thicker emulsion. I recommend 2 coats on the shirt side though, thats where you want the thicker stencil. But everybody has their own way that works for them. If its just the very edges of your image that is coming out it is possible that you are burning too long. The light may be under cutting the artwork but just not enough to harden the emulsion. After you have one of your "bad burns" dry it off and lay the art on top again. Is the emulsion coming off within the image area? ie.. does the image on the screen seem smaller than the artwork.
What was happening...as you could see from the image I posted...is that the emulsion was pealing away from the open screen.
I THINK...I THINK...it was two reasons.
1) Not getting the screen really good and degreased. I solved that with a new scrub brush and Mean Green (a good suggestion from someone!).
2) I wasn't getting a proper exposure. I did a strip test tonight. Turns out that with a 500 watt light about 18ish inches away with a vellum sheet (actually two back to back) I get a nice burn at 9 mins.
NOW...I realized that 1 min washes out...stepping up the "peal" away starts to happen a lot less the longer the exposure. I actually thought it would be the opposite.
ALSO...I can feel the stencil outline...the roughness to the edge go away the longer the burn went for. The final step area was really smooth.
FINALLY...wash out was really fast. The last few steps took no time to wash out. The bad side to this test was that it took more water then normal because I tried to wash out the other areas. That...I felt...compromised the best exposed areas.
I think you are probably still underexposing. My experience with a 500W halogen was about 18mins @26" with QX-1 emulsion, 2 or 3/1 coating. This gives me a solid 7 step consistently. I frequently burned at ~14-15mins to avoid undercutting, with decent results.
Wet your screen with a spray bottle and let it sit for a min or so before spraying it out.
You will know when you are exposing correctly, because you wont have to worry about the edges blowing out at all. It's either exposed or not. Then you can determine if you have probs with your vellum or contact between the screen and positive.
Also, I would bump up to a 500W halogen, it should only cost a few bucks.
Stencil Blowing Out Around Edges 
