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screen printing => Screen Making => Topic started by: Rockers on January 18, 2016, 08:18:20 PM
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we are encountering much longer exposure times on any of our emulsion we are using. Murakami Aquasol TS and ChromaLime. Times have doubled for screens we have coated in the afternoon and dried and then exposed the next morning. If we don`t double the times then the emulsion washes right of the screen.
Never had this happen before. I assume it`s due to our new screen room which is getting pretty cold over night in winter .
Does this sound like a familiar problem?
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I have had similar issues in the past (Cold shop) but never had to double exposure but definitely had to lengthen it. So it's not unheard of or you got a bad batch of emulsion. Try putting a space heater in your dark room and bring the temp up some then try it again.
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if it's getting that cold at night the screens might not be fully dry if they were coated the day before.
do you have some way to read the moisture on the screens?
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No matter where you are in the world..
Screens LOVE an environment that is 40% or less humidity and 70-90 degrees F.
A simple dehumidifier will keep a small screen room very warm.
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No matter where you are in the world..
A simple dehumidifier will keep a small screen room very warm.
This^^^
Sent from my XT1585 using Tapatalk
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Odd. In the past week (as it has actually gotten cold finally in New England) we noticed this same thing happening. Aquasol HV...I figured it was our bulb. We do 100-200 screens a day, sometimes excessive double post exposure, high density screens coated 300µ-600µ thick with 300 to 600 second exposures. It's been 3 months, figured it was time.
Well, put the new bulb in today and barely dropped our exposure times. I wonder if we might be afflicted by the same thing...never noticed it in the cold before. But perhaps it's the batch of emulsion?
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i do know that if is below freezing our supplier will not ship it out as the emulsion will get too cold in UPS. they wait till the temp at there shop is above freezing
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I had a five freeze once. I opened it and it was partial normal looking and a big globby stringy mess in the rest. Easy to tell.
I'd hate to be the person in my supplier's warehouse that shipped a drum to me on a Friday in below zero weather, instead of shipping the following Monday as I specified. I didn't even have to open it, I just refused it.
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No matter where you are in the world..
A simple dehumidifier will keep a small screen room very warm.
This^^^
Sent from my XT1585 using Tapatalk
yep. thats all i use to keep my room warm and low humidity. And when it is hot I have a small window unit AC that keeps it below 90.
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if it's getting that cold at night the screens might not be fully dry if they were coated the day before.
do you have some way to read the moisture on the screens?
They should be dry. I always turn the heater and dehumidifier on in the screen room once I get to the shop in the morning. Still an hour later the screens don`t expose right. That`s especially noticeable on the high mesh counts.
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I always turn the heater and dehumidifier on in the screen room once I get to the shop in the morning.
Never turn em off in the first place.
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Do you have a fan blowing at the screens?
If not try a fan, because I think the colder temperature is condensing the air thus making it thicker and heavier. This will form a denser boundary layer on the surface of the emulsion like an insulator. get a fan and disrupt that boundary layer so their will be evaporation.
http://kula.geol.wwu.edu/rjmitch/L9_evaporation.pdf (http://kula.geol.wwu.edu/rjmitch/L9_evaporation.pdf)
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Plug in timer on the heater so it starts up a couple hours before open time?
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Yah don't turn them off at all just leave it on until the weather breaks. I also use to use Aquasol HVP before I switched to CCI
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I'm having similar issues here in NY, especially recently since winter finally came around. Our Screen room is pretty cold, but I do keep our coated screens sectioned off with a small space heater and dehumidifier... but it's still pretty cold. I'm about to put in a bigger space heater and keep a closer eye on the temp and humidity. But for some reason it seems to be affecting our S-mesh screens the most....
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i do know that if is below freezing our supplier will not ship it out as the emulsion will get too cold in UPS. they wait till the temp at there shop is above freezing
Hmm. My supplier drops off directly from their warehouse one town away...but some times they are left at the edge of our bay overnight or even an entire weekend. Doors closed, sure...but it's been getting mighty cold out at night.
What symptoms would I get from an emulsion that got too cold and/or frozen? Would it be obvious? Does it have to freeze all the way to ruin it or does getting colder start to cause issues and the colder it gets the worse it gets?
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some emulsions are likely more freeze-stable than others.
I believe that Al from Murakami told me that SP1400 is freeze-stable...
The Saati guys told me that their emulsions were fine to be shipped in freezing conditions... so we actually tested it and put a quart of Saati PHU in the freezer over night, and while it didn't freeze solid, it defintely thickened up... after it warmed back to room temperature, no problems at all.. exposed just like a non-frozen batch.
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So here are my observations. The extended exposure times are rather down to the exposure units. I did a couple of screens this morning. On our Vastex LED exposure unit we did not manage to make a screen that did not wash off even if we doubled the exposure times.
Then we burned the images on our MSP3140. Came out all fine. What I noticed while burning them on the MSP3140 was that at lamp start up the LTU were counting down extremely slow probably 3 sec per LTU. After a 10 sec that changed to around 1 sec per LTU. I assume the lamp needs to reach a certain temperature before max UV output is achieved.
Now on the LED units it seems low temperatures are much more of a problem as the lamps don`t really heat up a lot!?
But maybe I`m just barking up the wrong tree here.