# problem with 925wr emulsion- not resisting water



## lady noir (May 15, 2007)

hey!

i just ordered a gallon of 925wr emulsion and coated some screens with it (one coat on the inside and one on the outside). 

i am printing with water based ink, and near the end of my print run the emulsion wore thin in many spots and then eventually got eaten through entirely- ruining a shirt and my screen 

any advice from some experts would be really helpful. i bought that emulsion thinking that it could withstand the water...?


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## dk8100 (Nov 20, 2008)

lady noir said:


> hey!
> 
> i just ordered a gallon of 925wr emulsion and coated some screens with it (one coat on the inside and one on the outside).
> 
> ...



Did you mix the sensitizer into the emulsion?

make sure your burn time is adequate cause I had a lot of problems with 925WR degrading mid run cause it wasn't curing all of the way through. I also do a post washout cure to make sure that the screen is durable enough for printing.


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## Calibrated (Oct 26, 2006)

The first issue I see here is that your screen coating method is insufficient. Just because the emulsion is water resistant that does not mean that a thin coat will be durable enough for your run of shirts. You need to apply at very least 2 coats to the face side, followed with at least 2 coats on the inside. This emulsion must also dry for much longer than most emulsions before exposure..I would suggest at least overnight.

Secondly 925-WR takes considerably longer to expose than most emulsions as most diazo emulsion do, so you need to make sure that the entire coating of emulsion has been thoroughly exposed. Any slimy residue on the inside, or excessive sudsy foam created from washing out the stencil is a sure sign of an underexposed screen...Which will not hold up for very long with any waterbased inks, but especially discharge inks. 

Lastly, 925-WR has a very short shelf life once sensitized, so if you mixed it up more than 30-45 days ago...toss it out and get a new batch.


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## lady noir (May 15, 2007)

that was really helpful!!! thank you so much!!!!


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## RichardGreaves (Nov 7, 2006)

*Ulano 925WR emulsion- not resisting water-based ink*



lady noir said:


> i am printing with water based ink, and near the end of my print run the emulsion wore thin in many spots and then eventually got eaten through entirely- ruining a shirt and my screen
> 
> any advice from some experts would be really helpful. i bought that emulsion thinking that it could withstand the water...?


925WR is an industrial standard for screen printing water resistance. That gallon you sensitized will be "fresh" for 4-6 weeks and will coat about 90 t-shirt sized screens. Like milk or lettuce, it will not perform consistently as it ages.

I assume you're a beginner, and your print runs are less than 70,000, which would still be a job that could be handled with one - 925WR screen. 

"Wore thin" sounds like the stencil eroded rather than chipped or cracked because it was too thin.

*Under exposure*
It's the job of the screen maker to completely *harden *the stencil so it survives. Plastisol ink is like salad dressing when it comes to attacking a stencil, but water-based ink, (made of 80% water) is made of the stuff that dissolves un-cured stencil like the Wicked Witch of the West.

If your industrial grade stencil broke down during a run of 200 - your problem is not enough exposure to completely cure the entire stencil, not thickness. The proof is that it broke down.

Don't get me wrong - I think your 1x1 coating will barely fill the open holes of the mesh, much less reproduce images well, but it won't break down in 200 images.
Homework: Coating FAQ of Screen Making Products

*UV energy penetration*
Exposure with invisible UV energy cross links the diazo sensitizer in the stencil so it won't absorb water, swell or dissolve anymore.

That UV energy has to move all the way _through the entire stencil_ to cure it, or it will look like a steak or pancake you cook on only one side. The stencil bottom got the most exposure, but the inside of your stencil is still raw - and will _still_ dissolve with water like the image area you covered with a positive.









The under exposed, raw, _inside _of the stencil will still be soluble (_vulnerable / dissolvable_), to the water in your ink - and it will breakdown as you rub it, over and over with your _*eraser like squeegee blade*_.

If the texture of the inside of a stencil feels different from the bottom of your stencil during washout - UV energy didn't completely penetrate and get to the inside where it's needed most.

You are guessing exposure because you are not *measuring stencil hardness* with a US$10 Stouffer 21 step gray scale that simulates 21 different exposures.
Exposure FAQ Screen Making Products how to measure exposure

The core responsibility of the screen maker is to able to judge exposure time with tests. It takes a lot less time to actually test a screen, than for me to actually type up these notes.

If I was at your shop today, I would still have to make a test.

*Diazo sensitizer color change*
You are lucky. When you test different exposures (like any cooking process), stencils with diazo sensitizer will change color during exposure because the yellowish diazo will actually degrade from UV reaction and the stencil will return to the color is was before you sensitized it.

When you don’t see any more color change, all the diazo is used up, the stencil has reached it's saturation point, and more UV energy just doesn't change it any more.

Don’t waste any more time exposing it, if it won't change any more.

Pre-sensitized (non-water resistant), SBQ stencils are harder to judge because they don't change color, so you have focus on hardness and look closely for when fine lines start to close up.

*Develop*
Wash out the stencil with a skin temperature water spray and look for signs of under exposure on the squeegee side of the stencil. It will be sticky and slimy because it didn't get enough UV light to cross-link the molecules so they won't dissolve with water and go down the drain.


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## printing40years (Dec 27, 2008)

There's lots of good information for you above. I would just add that you possible rushed the process. make sure your coated screen is completely dry...that means no water left in the emulsion whatsoever, before you expose the screen. Then make sure it is completely dry in front of a fan after you wash out the image. Exposure time has to match the type of bulb energy to the distance from the screen to the thickness of the emulsion. When in doubt expose it much longer. Better than cutting it close.Get that emulsion hard. Then it won't break down from the water in the ink. 925WR has been around for over twenty years for large and small shops alike...so it does work when used properly.


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## printing40years (Dec 27, 2008)

Did that do the trick for you?


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## ShirlandDesign (Nov 29, 2009)

I started out with 925wr using water based inks doing index seps. To get a good cure the exposures were starting to close the open areas, 190 ppi using 230 mesh screens. I would really have to knock the uncured emultion out with water presure which teneded to thin the stencil. I switched to QT discharge and fell in love. Once I accidentally doubled the exposure time and still the uncured parts just fell out with no real water presure. Water based inks or no I use QT on all my stencils. Also my supplier GSG in Tulsa gave me a sample quart to try. Just love the stuff.


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## printing40years (Dec 27, 2008)

QT is newer more expensive technology and 925WR is old technology used successfully for 25 years or so. Use what works for you and fits your budget.


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## zymerguyer (Feb 15, 2007)

I love my 925wr. I've only used a few other types but with a 2/2 coating and and 3/3 for the auto, the stuff holds up really well and washes out well with Franmar cleaners. Good stuff!

-Travis


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## evo noche (Dec 11, 2008)

ShirlandDesign said:


> I started out with 925wr using water based inks doing index seps. To get a good cure the exposures were starting to close the open areas, 190 ppi using 230 mesh screens. I would really have to knock the uncured emultion out with water presure which teneded to thin the stencil.


This is usually caused by the light source not being strong enough to cure the emulsion quickly. If you expose 925wr too long the light creeps around the dots and pinches them.

What's the light source and the exposure time?


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## ShirlandDesign (Nov 29, 2009)

I've been usin a bank of 8 20 watt florerscent bulbs set about 4" from the screen. Exposing for about 2.75 to 3 minutes. The exposure unit is homemade and of course not point. I just felt lucky to get a wr emulsion to work this well with a low cost system.


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## RichardGreaves (Nov 7, 2006)

ShirlandDesign said:


> I've been usin a bank of 8 20 watt florerscent bulbs set about 4" from the screen. Exposing for about 2.75 to 3 minutes. The exposure unit is homemade and of course not point. I just felt lucky to get a wr emulsion to work this well with a low cost system.


I would suggest using QT-Discharge for much faster exposure than 925WR. I suspect you are under exposing at 3 minutes with 20 watt lamps.


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## ShirlandDesign (Nov 29, 2009)

First of all let me apologize for "beating up" on your product. I'm sure it has specific applications and uses I am unaware of. I have a chromaline exposure calculator to set exposure times. But I'll be the first to admit that technical issues aren't my first love in this craft. If I can find a simple path to repeatable quality output I move on to what I consider to be more pressing issues, like is that design too weird, or just weird enough. Having said that I absolutly love QT dis. Frees up what grey matter I have to focus or unfocus on the grey issues of our craft.


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