Screen Printing Problems?

Hi. Me and my friend have just started try to do some screen printing for tee shirts. We have made a few mistakes and it still isn't working properly. We bought a speedball kit and when we coated our first screen with emulation we then realised that we didn't mix the emulation with the sensitizer. So we washed off and then recoated with the now mixed emulation. We have also been using a 200w bulb and exposed our screen for 25 mins. We use transparent projector sheets. We also didn't have any black card so used a black bin bag under our screen when exposing. When we wash off the emulation with a hand held spray gun, too much emulation is coming away and leaving patches of space. Is this because we are not exposing it for long enough, or that the emulation is no good or a combination of all? Also, How long does it take for the emulation to dry and does this have a limited amount of time before exposure? Please help :-)

JUST027 years ago
Hi there. To your exposure problem. To get a screen exposed. You need to expose the screen to a uv light & not a standard 200watt light bulb, a minimum of 2000watts uv will reduce the time & expose your screen correctly. A 5000watt uv system will expose your screen in about 3-4minutes. You can expose your screen in direct sun light (sun light has uv rays), but you will have to experiment with the time & make sure you have vacuum. If not just coat your positive in clear oil (clean standard cooking) & it will stick well to your screen. Make sure to get any air pockets out. Please note that this is a real back-yard way of doing it, but it will work a bit better then a 200watt globe. You should invest in the right equipment, for the best results. Coat your screen once on the inside & twice on the outside. A screen of about 500x700mm should not take more then 15 to 20 min to dry, in warm dry air conditions. Screens that have been coated should be kept in a dark room & will last for weeks, Hope you come right Chow4now Dave
Robb JUST027 years ago
you can certainly use a standard 200w bulb, it just takes longer. do a test where you expose it for 5minutes and then cover up an increment of the screen every 2 minutes for 20 minutes or so. then you'll see what the optimum exposure time is for your bulb and setup.
I used to be a screen printer. 1. If the emulsion is washing off, the exposure time is too short. Only the unexposed areas should wash off. Use a gentle spray of water. 2. The emulsion should be dry in a few hours, depending on humidity and air flow. 3. The unexposed emulsion coated screens have a life of weeks. ~Bob~
siol (author)  ShutterBugger8 years ago
Thanks for your help Bob :-)