# Can I wash exposed screens outdoors @ night?



## RaiderFred1 (Nov 14, 2011)

I will be getting my 1st silk screening setup tomorrow. I don't have a place to wash out my exposed screens other than the bathroom, which is nowhere near a water hose.

Can I wash out my screens (after exposure) in my back yard at night?


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## Celtic (Feb 19, 2008)

You can do it during the daytime. Just put your exposed screen into a black garbage bag (or double up a bag to be sure it's blocking out all UV light...go quickly outside, pull it out and immediately rinse both sides to side the exposure. Let it sit for 30 seconds to a minute or two, then thoroughly rinse clear.
Blot with newspaper.
dry.
Harden with your UV exposure unit for 5 minutes and you're good to go.


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## kirkmansigns (Jun 22, 2007)

You should be able to get away with it. Ever considered using your bath tub with a hose adapter on the spigot... like one would us to wash a dog ? If you plan on screen printing at any quantity, I'd highly suggest some type of dark room set up because cleaning screens can be VERY messy. Also, just washing the emulsion from a freshly exposed screen can make a mess too.


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## Celtic (Feb 19, 2008)

Get a diptank.
Great tool for your shop.


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## xcelr8hard (Jan 27, 2011)

I used to expose my screens in a spare bedroom. After exposure I would use a spray bottle and spray the screen that was sitting in a cooler, and then take them outside for spraying out. That way it did not matter day or night. Spraying the screens with the spray bottle "stops" the photosensitivity of the emulsion.
Butch


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## selanac (Jan 8, 2007)

Butch, put it in a large cooler? Sounds like a great idea. Someone could probably pick one up at a garage sale. 

If you're exposing at home, I'd recommend buying Capillary film. It's emulsion on a sheet. Just attach it to your screen, squeege the water out and let dry. Once dry, you're ready to go. You don't even need a scoop coater. 

RJennings just posted something about it today. Little more expensive, but saves time.


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## RaiderFred1 (Nov 14, 2011)

xcelr8hard said:


> Spraying the screens with the spray bottle "stops" the photosensitivity of the emulsion.


Butch, 
Just spray them with water?


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## printpromo (Mar 30, 2011)

I also use a spray bottle but I spritz both sides of the screen. I then have to go thru 2 doors to get outside to rinse my screens. I also clean and reclaim my screens outside and haven't had any problems. 

The only problem I have had is when I did not spritz the entire image evenly and some fine detail wouldn't wash out. If you hold the screen parallel to the ground, then by the time you get to your outdoor "rinsing station" and rewet the screen you shouldn't have any problems. I've used this technique on both capillary film and emulsion.

The nice thing about rinsing outside during the day, is it is much easier to make sure you have rinsed out small/fine details.

For the few times a year we agree to do small quantities, rinsing, cleaning, reclaiming outside works for us!


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## xcelr8hard (Jan 27, 2011)

I spray just enough water to wet the emulsion. I use a cooler because some water will run off of the screen, and the cooler I use holds a screen just perfect when I put it in there diagonally. It is snug enough to carry it outside by the screen and the cooler hanging from the bottom.
Butch


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## trdmrkcanada (Nov 17, 2011)

It doo-able for sure.


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## westmama (Feb 22, 2010)

xcelr8hard said:


> I used to expose my screens in a spare bedroom. After exposure I would use a spray bottle and spray the screen that was sitting in a cooler, and then take them outside for spraying out. That way it did not matter day or night. Spraying the screens with the spray bottle "stops" the photosensitivity of the emulsion.
> Butch


This is what I do. I spray my screens then take them out side and use my garden hose. Rinses out wonderfully.


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## cataHMN1 (Nov 2, 2011)

RaiderFred1 said:


> I will be getting my 1st silk screening setup tomorrow. I don't have a place to wash out my exposed screens other than the bathroom, which is nowhere near a water hose.
> 
> Can I wash out my screens (after exposure) in my back yard at night?


Doesn't have to be nightime Don't even have to hurry during the day. You won't have any problems. Your only problems is that you loose time with this trips outside


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## RichardGreaves (Nov 7, 2006)

xcelr8hard said:


> Spraying the screens with the spray bottle "stops" the photosensitivity of the emulsion.


Ah.. no.

Water may block or prevent some UV energy from curing the sensitizer in your stencil, but it doesn't "stop" the sensitizer you didn't cross-link from being sensitive to UV energy. 

This fact doesn't mean you might get away with spraying your screen with water before you step into the UV rich sunlight and getting a workable screen.

Night is certainly safer.


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## RichardGreaves (Nov 7, 2006)

*What's left to expose?*



Celtic said:


> You can do it during the daytime. Just put your exposed screen into a black garbage bag (or double up a bag to be sure it's blocking out all UV light...go quickly outside, pull it out and immediately rinse both sides to side the exposure. Let it sit for 30 seconds to a minute or two, then thoroughly rinse clear.
> Blot with newspaper.
> dry.
> 
> ...


If you have dissolved all the stencil that didn't get cured with UV energy, what un-reacted sensitizer is left to cure with another 5 minutes of UV exposure?


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## TYGERON (Apr 26, 2009)

*Re: What's left to expose?*



RichardGreaves said:


> If you have dissolved all the stencil that didn't get cured with UV energy, what un-reacted sensitizer is left to cure with another 5 minutes of UV exposure?


And also letting it sit wet before thoroughly rinsing risks exposing unwashed emulsion.
I'm not knocking whatever works for folk. *If you're successful with how you're doing it, then carry on.*
But my suggestion would be to avoid unecessary UV period. During the day (even cloudy) there's ambient UV bouncing around enough to expose uncured emulsion (yes, in shadowed areas too), particularly when using a faster cure type.
I also *don't* knock the use of capillary film (well I do...LOL!). Many use it successfully and for some applications it is required for optimum results and consistency. But I don't understand stories I've heard of "liquid type" scoop coater applied emulsions being such a mess, slower or inconvenient. I guess, just like issues encountered with printing, it's about proper technique with both.


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## ScreenFoo (Aug 9, 2011)

Thanks Richard-- As I understand the polymer reactions, (in diazo or DC, at least) if you get the screen wet, your sensitizer is still active--it just cross links preferentially with the water instead of your emulsion solids--Which is why when you expose a screen that was stored in a very high relative humidity, you get a weak stencil.

LOL @ Tygeron-- I'm in the same boat. I used indirect film twenty odd years ago, and the only reason I'll semi-revisit it with cap film is if I ever decide to get all fancy-pants doing process.

I definitely empathize with anyone who is struggling with a lack of equipment or space, but I don't know if that feeling ever goes away. It's tough when you look back and realize how much easier things would have been if you had taken the time to really figure out the process before you jumped right into the "it ain't broke" mentality.
You'll never know what you don't know about what you could be doing better, until you start really thinking about why you have the printing issues you do, and asking yourself tough questions.


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## RichardGreaves (Nov 7, 2006)

*Water is our friend and our enemy in the exposure process*



ScreenFoo said:


> As I understand the polymer reactions, (in diazo or DC, at least) if you get the screen wet, your sensitizer is still active--it just cross links preferentially with the water instead of your emulsion solids--Which is why when you expose a screen that was stored in a very high relative humidity, you get a weak stencil.


Yes, IF it ain't broke, it will work, but that doesn't explain what's happening invisibly. 

Water dilutes the chemical reaction caused by invisible UV energy. It refracts and slows UV energy penetration.

Penetration is hard for low energy sources. The Inverse Square Law that defines energy states if you double stencil thickness, you require 4 times the energy to cure it.

Water also acts as a barrier to the invisible cross-linking reaction so the stencil is still water soluble and it will dissolve and rinse down the drain. 

*Non water ink*
Plastisol ink doesn't attack under cured stencils like water does, so it's not a problem, BUT the problem shows itself when you try to break cross-links with stencil remover that aren't there. The chemical stencil remover makes an adhesive soup that fuses the stencil to the mesh and you have to use the super power washer or a knife to remove the mesh.

*Exposure is easy*
If the stencil breaks down, you didn't expose/cure/harden the stencil completely. The proof is in the stencil failure. Failure o reclaim is also the symptom that signals that you didn't use enough exposure for a trouble free process.


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## ScreenFoo (Aug 9, 2011)

Thanks again for the accurate and useful information.

I'm curious though--when you say water acts as a barrier to the reaction, is the science involved well understood, and if so, do you have any info on what is it that the water does chemically to inhibit full cross-linking, or "cure"?

I only ask because it seems there are more than a few people that believe a humid stencil can be properly exposed by throwing more UV energy at it, which I can only disagree with in experience, seeing stencils start to break down after one or two thousand prints, when it should have lasted ten--at least.

I never even thought about the possibility of molecules of water destroying the directional property of the light you're trying to expose a screen with, but it definitely makes sense.


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## TYGERON (Apr 26, 2009)

And difficulty reclaiming _undercured_ emulsion really seems illogical and confuses people when it occurs.

I also see recommendations for power washers and statements that one is necessary. If an emulsion is properly cured, wet, sit, wash with an insistent spray is all needed. Same with reclaiming.

Power washers are fun though...LOL! Played with one at a show a while back that had quite a kick back. Blew out emulsion with no reclaimer. Could've easily ripped the mesh. Or broken skin. Or put someone's eye out.


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## GraphicGuy (Dec 8, 2008)

I used to set up a mop sink (plastic one from home depot about $30) on a stand (made from 2 x 4s) that was tall enough to put a 5 gallon bucket (from a local restaurant a pickle bucket) underneath to catch the water. That way I could set up anywhere in my building and run a hose to that location. I would use a bug light (yellow light on a cheap drop light hookup) to light the area so I could see. The bug light won't hurt the screen. I used to put one behind the screen so I could see through it while I was washing it out. I made walls for the washout area out of some coroplast (it's like plastic cardboard you can get this from a sign shop) or something else cheap and waterproof. I put the sides in the wash sink to funnel the water into the sink from splash over. Just check the bucket so it doesn't overflow. when it's full just dump it out in the toilet.
There you have a portable washout station.
Also, I use a power washer (the cheapest one from Home Depot) You can use this to reclaim your screens and I use it to wash out my screens after I expose them. DON'T TURN THE POWER ON.... It gives me a nice fan spray that is hard enough to clean out the design and not blow out the screen. I have been doing this for years.
I hope this helps.


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## RichardGreaves (Nov 7, 2006)

*How does water inhibit the exposure reaction*



ScreenFoo said:


> I'm curious though--when you say water acts as a barrier to the reaction, is the science involved well understood, and if so, do you have any info on what is it that the water does chemically to inhibit full cross-linking, or "cure"?
> 
> I only ask because it seems there are more than a few people that believe a humid stencil can be properly exposed by throwing more UV energy at it,
> 
> ...


Water doesn't *destroy *anything, it interferes with the "*joining*".

Sensitizers decompose when they react with UV energy and create photochemicals that "*join*" polyvinyl alcohol, three-dimensionally. 

Water can absorb and block those photochemicals from connecting polyvinyl alcohol molecules and that mens *incomplete polymerization*, and your stencil can still be dissolved by water.


You can't expose the water out of the coating. UV doesn't work that way - but the heat byproduct generated by hot lamps might.


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## RichardGreaves (Nov 7, 2006)

*Re: How does water inhibit the exposure reaction*

I thought about this question over the weekend.


*Photochemical crosslinking*

When a stencil is exposed, the sensitizer molecules absorb UV energy and causes the atomic bonds to lengthen and split apart and bond to the atomic groups in the stencil polymer called hydroxyl groups.

All water molecules contain the equivalent of one hydroxyl group. During exposure the sensitizer molecule will bond to the nearest hydroxyl group and if that group is part of a water molecule the polymer cross-linking is wasted because cross-linking to water won't make the stencil water insoluble.


If I explain this at parties, the girls feint with excitement.


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## TYGERON (Apr 26, 2009)

*Re: How does water inhibit the exposure reaction*



RichardGreaves said:


> If I explain this at parties, the girls feint with excitement.


Potent stuff.

I once explained plastisol curing process to my _then _girlfriend.

We've been married 21 years.


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## ScreenFoo (Aug 9, 2011)

OK, I knew I had read/heard that whole water snagging bonds that were meant for the solids content. I'm glad that I'm not any dumber than I already know I am.

LOL. Obviously I'm going to the wrong parties.


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## smeared ink (Jun 13, 2011)

putting them in a cooler? I am having so much trouble I have a dark room set up and a wash out station. But im not exposing right. My light table will not fit into my make shift dark room, so I have to take the screens out and to the lights table this is all in my garage and then expose, then i wash out but i keep loosing screens. Im spraying out right away, should i jst get the screen wet and let it sit for a min?


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## mimic (Nov 28, 2011)

I am using both a slower dual cure and saati pv which exposes about 3 times faster.

I dont have a dark room and I have not had any problems that werent related to something dumb I did like use old emulsion.

The slower curing stuff is great to work with because you can take it out of your drying box, get the artwork set up, burn and wash @ night/early morning without fear.

I do move quickly, but have not had an issue with screens getting overexposed.


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