How long can you keep coated screens?

[Maxie]

How long can you keep coated screens before exposing?
How much does heat and humidity effect this?

[mimosatexas]

So I just finished my temp and humidity controlled screen room last month, but screens a month old are as good as new, both diazo and non (SP-1400 and HVP)

Before that I had a humidity controlled, but not temp controlled drying cabinet.  In the dead of summer, diazo screens would basically become unusable in a week or less. 

The humidity control seems more important when it comes to drying time after coating and making screens hold up better to discharge in the long run, but doesn't really seem to change the time they remain good.  Heat definitely will ruin a diazo screen in short order.  Honestly though, Aquasol HVP works no matter what though for long periods of time.  I've burned screens 3-4 months after coating with tons of temp changes etc and had no problems with that emulsion.

[Frog]

What emulsion?
When in doubt, read the tech sheet. Though suggested one month, I have kept Photopolymer coated screens for six months in normal conditions (below 80 and in California's generally low humidity) with no noticeable detriment, Obviously, your results may vary.

In fact, this longevity was a great selling point for me.

[alan802]

We've always had a controlled screen room and we've also used many different emulsions over the years, but I've never had a screen that failed due to it being too old or whatever you want to call it.  We've always turned screens around pretty quickly so using screens that have been sitting for months doesn't usually happen but I burned a few 83 mesh screens on Friday that have been coated for 5-6 months, HVP.  We've been predominantly a pure photopolymer shop but the first year we only used dual cure, Kiwo Poly Plus S and some of our higher mesh screens would go 4 months easy between coating and burning them and we never had issues. 

[screenxpress]

I had some coated (QTX) screens in storage for a bit over 2 years in a cardboard box and they exposed fine.  I realize that's probably not the best thing.

[Maxie]

Thanks for the helpful replies.
What is the ideal humidity and temperature?

[Frog]

From the Tech Data Sheet for Murakami Aquasol HV (which I also linked)

Coated screens may be stored for up to
one month when kept under the following
conditions.
• 59° to 77° degrees F (15° to 25° C)
• 30% to 50% relative humidity


http://www.murakamiscreen.com/pdf/dealer_tds/aquasolts_dealer.pdf

[Denis Kolar]

I have had some work after 4-5 weeks.
Using Chromaline CT-R emulsion.

[Sbrem]

Before we had a screen dryer, yes, diazo's would "self-expose" due to too much heat and humidity, in fact, we had it happening overnight. However, coated screens don't hang around here more than a couple of days. I wouldn't coat screens a month in advance, if you don't need them in the next couple of days, I really don't see the point. Though we get pretty sticky in the summer here in New England, it's not like Louisiana or Florida, but still low humidity and temps under 80° will keep them much longer if that's the way you want to go...

Steve

[screenxpress]

Thanks for the helpful replies.
What is the ideal humidity and temperature?

Don't laugh.  Mine were in cardboard boxes in a non-temperature controlled facility in Houston (humidity?, lol) and I'll leave you to your imagination on temperature swings over 2 yrs. 

[ABuffington]

Diazo Emulsion is heat and time sensitive. Once a screen is stored above 80 degrees even for short periods or longer than 4-6 weeks even in optimum conditions the risk of 'dark hardening' occurs.  Basically the image won't wash out when it is dark hardened.  Diazo emulsions should also be used within 4-6 weeks once mixed.  This is for optimum resolution of the halftones and details in an exposure, for solid art you can still get exposure for weeks after this.  Typically not only are dark hardened screens hard to wash out but edge quality may sawtooth.

On the other hand Pure Photopolymer emulsions like HVP can last for 6 months coated or longer depending on storage conditions and over a year pot life.  They are unaffected by heat.  All emulsions are affected by humidity.  It isn't what it does to the emulsion, its what it does to the exposing light.  It interferes with the cross linking process and inhibits good exposures. 

Hopefully everyone is too busy printing to worry about pot life and coated screen life!  When you can't coat screens fast enough to meet demand you are doing something right!

Al

[Prosperi-Tees]

How about this question. With the move to less than 10 second exposures via LED, how long can an imaged/exposed go without being washed out?

[Sbrem]

I think the short exposures are from the intensity and proximity of the lights in the LED units, so I would guess the unexposed emulsion might have pretty much the same life, maybe a little less? But why not just wash it out?

Steve

[Prosperi-Tees]

Just wondering could you expose say 10 screens in a row set them aside and take them all to the washout booth which isn't in a light safe area to wash out instead of going back and forth for each one.

[Sbrem]

In that case, yes; I was thinking you meant letting them hang around for a few days or something.

Steve