I have a home made exposure unit from the 80's or so. It has three 4' grow tubes from home depot in it which are about 5" away from the glass with the space to expose two screens at once. Problem is its taking well over a half hour for proper exposure (which took me a while to get to). Point is thats a rediculous amount of time. Any advice?
Get a metal-halide stadium light with ballast from an online supplier or a local electrical or lighting supplier. I paid less than 150.00. It would be worth 300.00 for the quality and speed. I never have burned any emulsion for more than 60 seconds and have gone as little as 10 sec with photopolymer emulsion. You can build a unit with a shop vac rubber blanket hold-down for less than 300.00.
I don't know if me using UV output is the right verbage. The light loses it's intensity after hours of use. If you use a step wedge kit and are getting 5 minute exposure times and find out in a couple of months it's now taking 7-8 minutes, it's most likely your bulb. You should try getting into the habit of doing Step Wedge Tests every so often to make sure your exposure times are staying consistent.
"Grow" lights are designed for an exposure time of 8 weeks to 4 months for tomatoes, flowers and marijuana. They are usually 20 watt full spectrum lamps that duplicate daylight.
The kind of UV energy stencils want, (if you want to expose faster), is to use a lamp with more invisible UV-A energy. All other energy is wasted.
F40 BL lamps have a narrow range and emit some visible light, and are designed to last for 20,000 hours. At 5 hours of exposure per day that's 4,000 days. At 245 work days per year, that's 16 years. Light Bulbs from Topbulb
F40 BLB lamps have a wider UV-A range and hardly any visible light. This is the best UV-A fluorescent lamp for screen exposure but it costs twice as much money for that wider UV-A range, so you should seriously consider BL lamps. Light Bulbs from Topbulb
Use this info to start shopping.
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How are you measuring? retired Ulano Technical Support Screen printing since 1979 - SGIA Academy Member
Last edited by RichardGreaves; September 11th, 2008 at 06:52 PM.
yeah dude. I just had to do an oversized run and re-factor my burn time and light layout. Ended up actually just really rigging some halogen work lights together ( 3 with the glass off as they sometimes are UV filters) Its an experiment. On the smaller screens I'm getting 12 minutes with duel cure and 22 minutes on oversized. I simply lined the lights up over the screen and used an old sliding glass door for the glass to keep the pressure on.
I'm sure even if you have an older unit you can modify it for under 50.00 and get optimal results.
Not all emulsions are created equal. Some are faster and some are slower. The thickness of the coating will also effect exposure times.
With the exposure unit i have, the difference in exposure time might be the difference of 30 seconds to 1 minute, but it could also equate to 17 minutes instead of 35. Since i've never worried about speed, i can't recommend which is fastest.
fred
Agreed, my 50 micron cap film takes 6 minutes, while my 30 micron cap film takes 30. This being from a single point light source, 500W bulb
Ive actually upped the exposure time to 45 minutes and things are better than 35. I cant wait until i can afford a real unit (not that I'm not thankful for being able to do it at all).
Hi JB, you can buy a flood light that stand up, it yellow with two lights on it that as 500watt on each size this is a UV light. You can buy it from home depot are a hardware store, it cost about
$35.00 to $40.00 dollars. I have beign exposure my screens this way for 8 years and it only take 3 mins,to exposure a screen.
LaTonya
35 Minute exposures!? 
Re: 35 Minute exposures!? 
