I have built a homemade exposure unit. It is 25" x 25" and the glass sets 6" off of the lights. I have 4 bulbs which are 14W each. I burn my image for 12 minutes. When I get done exposing, I take it over to my washout sink and spray it and leave it for 30 seconds. After that, I give it a good amount of pressure, about 4-6 inches away, and the image begins to spray out. My problem is, is that when it sprays out, either it sprays out and then the emulsion around it starts peeling away, or in some spots, I have to give it a lot of pressure an order to get the emulsion removed. I have an exposure calculator thing, and that even sprays completely out when i rinse it. I made one good print my first time, and ever since then, I can't get the detail that I want. I figured it might be:
A) my exposure time(tried it at 9 and 12 and appeared to do the same thing.)
B) the time I let my emulsion sit(the last time was overnight, but I do it in my basement, which gets a little cold, probably about 40 deg. down there last night.)
C) the way I'm spraying out the image.( apply a good amount of pressure, but not sure why in some spots it sprays out easy( a little too easy) and some spots doesnt even spray out at all.
Any help would be appreciated. Just looking to get some insight on those fine detail prints.
The first thing I would look at is your films. Make sure they are dark throughout the entire design.
Second, since you are doing this in your basement, make sure that there is not a lot of humidity. Humidity can reek havoc on your emulsion. Go buy a small dehumidifier for where you dry and store your screens.
Lastly, it sound like you are under exposing. Run a step wedge test. This will help narrow down the exposure time.
Good luck and keep trying!!
I am fairly new to screenprinting, have only been doing it for about a year, but I went through the same things you are going through. I also have a homemade exposure unit but now I can get all my images to wash crisp and clean. What my problems were 1. My images weren't dark enough on my transparencys. The darker the better. If you need to, print 2 transparencys and double them up to make it as dark as possible. Another thing I did was to order some toner aid and sprayed it on my transparencys. Spray it on and let it dry for a couple of min and you will be amazed how much darker it makes your image. 2. I was using to much pressure and my images were washing out. Reduce the pressure and move back a little further with your spray nozzle. If exposed correctly the image shouldn't need much pressure at all. You can almost remove the unexposed emulsion with a garden hose nozzle.
Exposure times really depend on what type of emulsion you are using, that is probably the biggest factor. You should have received the exposure times when you got your emulsion, if not you should be able to get it offline. Also, make sure that after you are applying the emulsion to your screens that you are allowing enough time for them to completely dry. I usually let mine dry at least overnight.
Hope this helps some. I know I probably forget something but one of the pros will probably catch it and let you know.
Thanks guys, I think I need to buy a dehumidifier for sure. The basement isn't finished, and kind of stuffy. Also, now that I think about it, the first good print I did was with a different printer on professional transparencies. The second was on my little HP officejet with some 8x11 transparencies I got from school.
Duh...hopefully all of this works with your advice.
I'll have to agree with what everyone else is saying. Up your exposure time and make sure your screens are completely dry. Also make sure your coat of emulsion isn't too thick. Space heaters and dehumidifiers do wonders for drying out screens.
I had the same problem today!!!! It was my first time using a self made unit (500 watt halogen). I underexposed. While the emulsion changed color on shirt side (facing light), the light didn't have enough time to cure the squeegee side so when I washed it out with pressure, the edges of the image began to break and the emulsion on the cure side began to bleed. Before I was using the sun to expose and it only took 2 minutes to cure the entire screen with no problem. With the halogen I only placed it for about 15 minutes and I should have left it for 5-10 more minutes.
Yeah, I feel your pain. I hassled with worrying about edges blowing out, etc. until I finally bought a step gauge and realized I needed to almost double my time with a 500W halogen..to 18 minutes.
CCI DCM Dual Cure Graphic Emulsion this is the emulsion that I am using. I do have the lights pretty spaced out in my light box. Probably 3-4 inches apart from each other. They are the real skinny bulbs. About 20 inches long. Do they make black light bulbs for those?
Are you saying that I need to add more lights, or just replace the 4 bulbs with blacklight bulbs?
CCI DCM Dual Cure Graphic Emulsionthis is the emulsion that I am using.
I do have the lights pretty spaced out in my light box. Probably 3-4 inches apart from each other. They are the real skinny bulbs. About 20 inches long.
Do they make black light bulbs for those?
Are you saying that I need to add more lights, or just replace the 4 bulbs with blacklight bulbs?
You are using a fine diazo sensitized dual-cure emulsion, but, all the chemical resistance qualities you get from the diazo also make react slower to UV energy. You also have about as low output lamps that will still expose stencils. CCI has faster pre-sensitized emulsions.
More lamps would be used if you want to increase the surface area you are exposing. Closer will provide a more even coverage. 40 watt BL lamps will have more penetration power.
Probably an exposure problem but..... 
Re: Probably an exposure problem but..... 
