Shelf Life on Emulsion

[screenxpress]

I'm not a high volume printer and stuff does sit around a while.   Sometimes too long.

Had some problems this week with an emulsion I've used with no problems before.  But this time, during washout, some edges outside the image (washing out like normal) were lifting up (using a hose sprayer only) as if not bonded to the screen as I tried to made sure the image had completely washed out.  Screens were prepped like normal and happened on several attempts.  I could wet my fingers and come real close to repositioning some of the finer detail and once dry, was stuck again. 

I'm thinking old emulsion....as it didn't do that before (a while before) and all other variables are about the same.

I was going to get some new emulsion...this time in a quart size.

Opinions?  Oh, I know there are opinions out there 

[mooseman]

 Heat or warm storage will cross link emulsion but you will see this as small clumpy nodules in the emulsion.
Mort likely if your storage was OK and it sat for a looooong time the emulsion became somewhat concentrated (lost water content) especially if the container was more empty than full. When this happens the normal coating process will actually give you a heavier EOM. If you have a heavier than normal  screen EOM the full exposure time will go up.
Try same stuff but kick up your exposure time @ 20%.
Also what is your light source, if black light tubes they may be losing some giddy -up.

BTW...someone once said "opinions are like butt holes...everybody has one..."    there is more to the quote butt I will end it here.
mooseman   

[Doug B]

  I say it's old emulsion. lengthening the exposure can help but you will
find that it will still break down sooner than normal. Get a new can.

[Denis Kolar]

Chromaline ChromaBlue or ImageMate PC701 both have 2 year shelf life.
Small printer here too. I have PC701 for a year now and no issues.

[Gilligan]

Our ChromaBlue has recently gotten kind of rank smelling.  Less than a year old and stored in 75-82 (weekends).  Our exposure times definitely seem to be getting longer and it smells up the shop.  I was ready to throw it out but my guy thinks he's still got a few more good screens left in the bucket.

[Admiral]

I'm thinking it might be the screens aren't as dry as normal.  If your humidity is higher than normal there could be more moisture in the stencil prior to washout making it not cross link together as well. 

[screenxpress]

Ok, here's the whole story. 

Emulsion was Chromaline CTR and over 2 years old.  Stored in house closet so not too hot.  Bucket was about 1/2 (gallon) full.  Used a wand and drill to stir it all up and let it set before using to get rid of air bubbles.  No lumps.  I just did the wand stir to get any settled emulsion off the bottom and stirred into the rest.

Screens were dry and this happened with coated screens from last weekend as well as screens coated months ago.  Admiral, your description of emulsion not cross-linked (to hold it together) is an excellent description of what I see happening.  However, the lifting seems to only be on the shirt side emulsion and I coat 1 + 1.

6 light black light exposure and the image washed out just fine.  Just some of the edges around the image lifted up and fluttered.  Like when you hose wash the drive and dirt rides up at the point of contact allowing the water to get underneath. 

I'll try one more shot lengthening the exposure time tomorrow (+20% per Mike)and if continues, I'll switch back to QTX which I used for years until I balked at the cost.  But honestly, as much (infrequent) as I use, I probably should not have been totally motivated by cost.

Thanks guys.

[screenxpress]

Update. 

I don't print much so the mind can play tricks on past numbers.  I would have sworn that I was exposing the CTR at 22 seconds on my Lumitron (QTX was like 18).  Following through with what I said I would do, I upped the time to 30 seconds and did not experience the problem and the image still was not a problem to wash out.  Would not be surprised that I could probably extend that time some for possibly better results. 

So for now, we'll call it busted.  Well, actually we'll call it underexposed. 

I would expect that if I put in new bulbs (still the original) and bought brand new emulsion, I could probably reduce the exposure time.  There are so many variables, there is no single answer, imo.  If I was doing a lot of jobs, I'd probably call upon "step wedge man" once I changed any one of the variables (bulbs, emulsion, etc), but for now I'll coast along with the knowledge that 30+ will get-er-done.

Thanks

[Gilligan]

I bought a bunch of Ted's stuff that he had left over when he hung up his squeegee and one of the things that we use every time is the little exposure strip.

My guy puts that on every strip and is now logging it.  I had to kind of beat him up about it when this problem started raising it's head and we didn't have any real data to go back and look at when we should have!  He was supposed to be keeping notes before but I think now he gets why I was saying we need notes.  Chasing your tail isn't as fun as most dogs (and my cat) make it seems.

One question about that.  The 7 should be a solid exposed emulsion with no disturbances?

[ScreenPrinter123]

I bought a bunch of Ted's stuff that he had left over when he hung up his squeegee and one of the things that we use every time is the little exposure strip.

My guy puts that on every strip and is now logging it.  I had to kind of beat him up about it when this problem started raising it's head and we didn't have any real data to go back and look at when we should have!  He was supposed to be keeping notes before but I think now he gets why I was saying we need notes.  Chasing your tail isn't as fun as most dogs (and my cat) make it seems.

One question about that.  The 7 should be a solid exposed emulsion with no disturbances?

You should have bought Ted's press ; )

[Gilligan]

He wouldn't make me the same deal he made on his supplies.

[Mark @ Hurricane Printing]

Does keeping it in the refrigerator prolong the life of emulsion? I have a quart of some sample emlusion ..it is orange, pre mixed...(dont know the name and i am not home to look at it at this very moment)....and ive been keeping it in the fridge since i opened it and thus far I have not had any issues....going on 3 months now BUT i have not used it in over 2 months...I will be burning 7 screens this week coming up..I will post results.

[screenxpress]

I'll be awaiting your update.  Sounds like you're talking about the new Ulano Orange premix which has had some mixed review here.

[whitewater]

I'm thinking it might be the screens aren't as dry as normal.  If your humidity is higher than normal there could be more moisture in the stencil prior to washout making it not cross link together as well.

i can agree with this..this happened the last 2 weeks because our dehimudifier went kaput.. even screens we had coated before seemed to take in some moisture..