Vacuum UV exposure unit
Hey, a question from someone just starting out…
Just getting into letterpress, and want to expose my own plates.This is just a hobby for the minute and cost is an important factor in equipment purchase.
I came across this unit
http://www.vevor.fr/vacuum-uv-exposure-unit.html
It is a good price and appears to be reasonably well made with a 2 year warranty.
I know a platemaker would be better, but they are expensive and used don’t come up that often here in Australia.
My question is do you think this type of unit would be ok for me?
Many thanks in advance.
Hi,
The product you’re looking at is a screen printing exposure unit. I’ve been told that those don’t pump out enough UV for photopolymer. I’ve heard of people using black lights for exposing photopolymers but that may take some experimenting.
Hope I helped a little.
Yes, this is similar to what I’m using. I’m a screenprinter whose gotten into letterpress and have needed to use what I already had. The UV bulbs should be 350nm, which will expose a screen in 3 minutes, but take closer to 25 for a photopolymer plate. The built in timer on my unit only went to 6 minutes, so I had to put in a bypass switch and then time it with a kitchen timer. I think the secret is a good vacuum. Since I got a better vacuum pump, my plates have been much crisper.
I have been making photopolymer plates for several years now, with great results. I use a vacuum frame made out of an old Nuarc 26K plate maker and a 350nm exposure unit on a timer.
I agree with what Ray West says above about good vacuum. I have found it absolutely essential for a crisp image. The light configuration in that unit looks similar to what I use, but I am not sure how you can determine if it will give you the tight seal you need.
I used to use the novelty black light units from Canadian Tire. I bought eight of them, for $12 each at the time. Today, they are about 3 times as much! They were 18 inch long bulbs and 15 watt power all assembled in to a fixture. I bolted them together in to a light panel. It served me well for years! Yes, the exposure time was 3 times more than usual, 9 to 10 minutes, and the bulbs were about 1.25” away from the plate surface. Today, the assembly is the same, but the bulbs are replaced with the pro ones and the exposure time is down to 3 minutes and they are about 2” away from the plate surface. The vacuum table with the creen is a separate story. The timer is still a mechanical timer from a microwave or a toaster oven. The mechanical bell announces when the “pizza is ready”.
The black-lights give out only UVA light ( 350nm ) and they are fairly safe to work with. The safety blue coating on these bulbs reduces the output of the bulb by about half. The industrial bulbs have no safety coating and they output the full spectrum of UV-A-B-C rays. Of course the main output is UVA, but you will get some eye damaging UVB and UVC rays too.
You only need a Stouffer Scale if the plate salesman tries to blame you for the exposure problems. Otherwise just adjust the timing till you get the 25 to 30 degree ( eyeball it ) shoulders ALL THE WAY DOWN to the base of the plate. Yes, good vacuum is essential. The car carburettor manifold pressure gauge helps. 15 to 17 IN-Hg
Louie
http://eagleprint.ca
Thanks everyone, i’ve been away for a while so apologies for the late reply.
I ended up going with a simple UV unit with no vacuum, my plates held in vacuum via a Food Saver vacuum unit in mylar pouches. Will be making first plate this week, i’ll post again with results.