Hi guys, this is my first time posting a question after receiving so much awesome help reading other threads. Here is the deal - I recently switched from diazo emulsion to pre-sensitized Ulano QTX emulsion and am finding my old burn times no longer apply. I checked the QTX packaging for guidelines but there were no directions or guidelines.
So, for this job I am using a 200mesh yellow screen, ulano QTX emulsion and a fairly new exposure unit that has "8 unfiltered high UV 30 Watt spectrum blacklight lamps, 240 Watts of Power".
Using the info above, can anyone recommend a good burn time to use as a starting point for trial and error?
I burnt a number of QTX coated screens using my old burn time of 5 minutes and I feel like they were over-exposed and I hope to avoid wasting too many more screens taking stabs in the dark.
Also; as per the thread title, does anyone have a general formula for figuring out the burn time for various screen / light source / emulsion compositions?
Thanks in advance to all the awesome people on this forum!
no one can give you a really good time since all setups are different and there are so many variables.
have you ever done a step test? if not, read up on this. they have a test guide which is free. How to Determine correct screen exposure times using Vellum
Thanks for all the help guys - I wish that spec sheet had come with the emulsion.
So using that spec sheet, my formula looks something like this
240 watts of unfiltered blacklight = 12 seconds burn, add in the yellow mesh multiplier (1.75) and I end up with 21 seconds as the burn time.
This seems to match some of what I have heard said here by others. I will attempt to burn this screen tonight and report back just in case this thread can help someone else down the line!
So I burnt 3 more 200mesh yellow QTX coated screens using a timing of 30 seconds, 1 minute and 2 minutes. The 30 second and 1 minute screens washed out (a big hole blew out in the emulsion and it peeled off) and the 2 minute screen washed out OK, but took a little bit longer than I expected and ultimately the screen began to peel as well. This weekend I am going to try timed intervals of 2:30, 3 and 3:30 minutes to see if we get warmer.
I am a bit confused though, using the formula attached by the ryonet rep, I feel like the burn time should be significantly shorter than it is coming out at.
Assuming you already know how to degrease, coat and dry screens properly based on your previous experience with CCI, I have to wonder if you don't have an old batch of QTX.
If the number you came up with was 21 secs, and your exposure unit is what it says it is, that screen test should have been conclusive.
I'll beat Greaves to the point here and ask "Have you used a step exposure gauge?"
I ordered my very own stouffer 21 step last night :]
The last 3 screens I used were degreased and re-coated. To be totally honest, I messed up the coating on one of the screens which caused it to drip down onto the 2 others - all 3 had drip marks in the middle of the screens. I did my tests on the lower 1/3d where the emulsion was still smooth.
I wonder if I am miss-reading the QTX specs, my lightbox has 8 30watt unfiltered uv bulbs but the spec only lists "40watts" under UV. I assumed that since my total wattage was 240 watts, I could divide the spec sheet time by 6-8 to arrive at my appropriate curing time. Maybe UV light is not multiplicitive?
I wonder if I am miss-reading the QTX specs, my lightbox has 8 30watt unfiltered uv bulbs but the spec only lists "40watts" under UV.
I assumed that since my total wattage was 240 watts, I could divide the spec sheet time by 6-8 to arrive at my appropriate curing time. Maybe UV light is not multiplicitive?
Sorry. You can't use the total wattage. The lower right corner of your stencil will only get whatever UV energy that emits from your 30 watt lamp. It gets no help from the upper left side.
2 exposures with the Stouffer scale and you will never guess again.
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How are you measuring? retired Ulano Technical Support Screen printing since 1979 - SGIA Academy Member
Well, I have 8 screens coated, a pencil and notepad, a stouffer scale in the mail, and some doubled up transparency's to make sure everything is opaque.
I wonder if my semi opaque transparencies that were burning out on the dual cure diazo stopped cutting it with the new QTX emulsion due to the fast curing nature.
Anyhow, I am going to do my best to be scientific and hit the allmighty solid 7 :]
Hi Everyone, after converting to Ulano QTX and running into issues, I finally have 2 beautiful screens.
Here are my findings here in case they can help someone else.
First off, everyone who has problems judging screen exposure really should get a Stouffer 21 step as Richard Greaves and others have suggested! Using this tool I was able to calibrate the proper screen exposure time in 3 attempts. I was surprised at how big a difference as little as 10 seconds burn time made with the QTX and I suspect this was a big part of my earlier problems.
Second, I believe that due to the fast exposing nature of QTX, it is much more important to have Opaque transparencies than the previous emulsion I was using. I have no factual evidence to back up this claim but it is the feeling I get after 10 screens of trial and error. I just doubled up my transparencies and it worked out fine.
Using the Ryonet 25x36" Auto UV Exposure Unit with QTX Emulsion I arrived at the following exposure times - 1:35 for white 110 mesh and 1:50 for yellow 200 mesh.
Thanks again everyone for your advice. This may be the only forum I've ever been involved with where people are genuinely helpful to each other, even to novice printers like myself.
Exposure Time Advice / formula? 
