Should/Can we coat out in the open shop or use (dark rm environment)?

[mk162]

we get a lot of sunlight in the shop, i personally wouldn't take a chance, but that is me and our situation.  If we didn't have skylights, then maybe, but hte dust is also worse out there.

[GraphicDisorder]

we get a lot of sunlight in the shop, i personally wouldn't take a chance, but that is me and our situation.  If we didn't have skylights, then maybe, but hte dust is also worse out there.

Just often coats with 2 garage doors open.  One of them is massive and letting a lot, and i mean enough light not to have lights on if you want.

[mk162]

that's the way it is here, under one of the skylights it's dang near as bright as it is outside.  It will cure a screen in no time.

is the dust bad in your shop?

[shellyky]

that's the way it is here, under one of the skylights it's dang near as bright as it is outside.  It will cure a screen in no time.

is the dust bad in your shop?

Dust isn't too bad but we also dry our degreased/emulsioned screens in air-filtered, Vastex DRI-VAULTS (35 slots) w/ built in dryers, so that part is never an issue really.

[ZooCity]

OK, I gotta ask, those of you with actual screen/dark rooms- why are you coating on the linty shop floor in daylight and carting the screens back to the screen room? 

Irregardless of whether or not the diffuse, ambient light of your shop screws up the liquid emulsion you are still 'exposing' that screen to all sorts of possible contaminants and then 'exposing' yourself to carting them back to the screen room for no good reason. 

You are of course also literally exposing those screens, it's photosensitive emulsion and yes, it's light sensitive even when wet, just to a lesser degree.  Perhaps much less, so much less that it's not even relevant how much light hits it wet, but I still don't see why you would not just coat in the room where the screens are going.  And those of you who don't have the space for a screen house. our previous shop had no screen room but I made the whole damn shop a light safe room when I coated and handled screens.

[Prosperi-Tees]

My shop has UV sleeves on all the lights and depending on the time of day I will roll the door down when handling screens

[Dottonedan]

I think it's convenience and simply that it doesn't make a visible dent in the everyday quality.

[Dottonedan]

Anyone ever obtain any results as a test from using a fresh bucket (inside the safe light room for a week or two versus coating out in regular light?

[alan802]

Anyone ever obtain any results as a test from using a fresh bucket (inside the safe light room for a week or two versus coating out in regular light?

As soon as things get back to normal around here I am going to do some "spearmintin" and will report my findings. 

[inkman996]

Dan I am about half done doing my test alas we are busier than a bees nest under attack right now.

I have developed the screen with the emulsion coated in the flouro lights already, it is a 260 and I nailed all the details in  the macdermid exposure calculator, also I noticed not one issue with any of the screens that were used with emulsion coated in the flouro lights.

I have a safe light room for coating and developing screens but for this test I purposely went out in the open.

Maybe today or tuesday I will burn the 260 screen that was coated solely in the safe light room.

[RichardGreaves]

DotToneDan wrote me last night asking my opinion.

Hello Richard,

I wanted to send you a link from our forum (Theshirtboard) where we are debating the affects of open light in a shop on wet emulsion while coating.

My theory is that as you get to the end of the gallon or 5 gallon bucket, you could be affecting the fine detail of say a 53-5% in a 60l line screen due to pre-exposure over a long time. 

A few have said that they read where you mention that it's ok and harmless. Can you elaborate on this? 

Is it totally safe in all cases of lets say extreme detail or is it figuratively speaking, about 95% of the time safe on most jobs?

==============

I assume Dan meant 3-5% 60 line dots.

I couldn't deal with this question until 4:30p and 3 1/2 hours later, I've read all 90+ posts. I spent some time trying to figure out who Inkman996 is and was surprised there was a Rick Roth in MIchigan - until I looked read his signature at the bottom of his post. I'm proud to see old contacts Zoo City, Alan802 although Alan didn't bring me the Round Rock Donuts I told him I needed bad, last year when I spoke in Austin at the Printwear Show.

I have more than 60 notes on details in those 90+ posts as discussion was very broad with answers targeted at tenderfoot printers with no money, to state of the art printers that use DotToneDan separations.

A stroke retired me overnight in 2009, so I don't have a screen room to experiment in, but I don't think this is too hard to test.

Every shop has unique ambient work light, so that's a variable stat isn't standardized - but who really cares what works in other shops?

How long do you expose open buckets?

I would pour 2 inches of fresh emulsion in a shallow container and let it sit for the test time - 1 hour? 3 hours? You have to stir, or the surface will skin and spoil your test.

Coat and dry test screens as equally as you can.

Expose one of each with identical positives as the glass & lamp heats up.

Develop at the same time.

You can now judge your areas.

=====================
Can we coat out in the open shop or should use a screen room?
Can we? This is the first mistake. Can I jump out of this window? Can you?

Or..., should I make an effort to protect the tool we reproduce image with from threats that will make it fail?

Alas, this is America and you must do as you wish. Everybody's emulsion instructions explain: "XXXXX  should be handled only under yellow safe light conditions" but some of you are asking how can I skate on this thin ice without failing?

As with all dangerous practices that our mothers & teachers have warned us about - like , not taking your blood pressure medicine, safe sex, pregnancy or driving home from the tavern - sometimes you can get away with shortcuts and doing it your way instead. Strokes, babies and car wrecks are more life altering than a spoiled screen.

No Room?
You have room if you're coating screens now. Build a tent of clear plastic or more expensive welding curtains over a light wooden or PVC pipe frame.


Monitor your exposure
After an exposure mistake I ordered EVERY positive with halftones or fine lines less than 0.020" must have a control guide the screen maker can see to judge if the stencil is correctly exposed. All tonal positives MUST have a halftone dot gray scale which is easy to add these days in Illustrator or CorelDRAW.


As I was raised in a house with a dark room, I don't believe I've ever exposed a stencil without a U$10 21 Step Gray Scale.


It's a 5.5" film positive that is opaque on one end and clear at the other, with 21 measured steps in between.

The 21 steps, simulate 21 different exposures. You get visual feedback so you can make clear judgments about exposure without guessing. Aim for a Solid Step 7.



These test are basically free.

Dinner calls. I will post more tomorrow.

Richard Greaves  646-807-8580

[alan802]

I am certainly satisfied with Richard's opinion of the matter.  I was hoping he would chime in here.  There are only a handful of guys in this industry that when they tell me something, I don't question it, I just do it and never look back, Richard is one of those guys.

I'll get you some of those donuts some how, some way, some day, it's a promise.

[RichardGreaves]

I'll get you some of those donuts some how, some way, some day, it's a promise.

I'm sure those donuts would be stale by now!

[inkman996]

I performed the test following dans conditions exactly. I opened and used a brand new gallon of emulsion thought the week I coated solely in the open lights of our rear shop. Near the end I coated a 260 tpi screen.

At the beginning of this past week I was able to use that screen for a job and I not only exposed the art film but the macdermid calc as well. Thursday I repeated the process with a 260 that was coated in our safe room like always.

Using a loupe I cannot tell the difference between the two screens, both optimal targets on the scale held all the half tones perfectly.

I did take photos using an iPhone resting on the loupe but alas after checking them on the pc one picture was quite fuzzy, I am planning on bringing in my much better digital camera Tuesday to get proper shots to post here and show what my results are.

I truly feel what I did is exactly what is being discussed here, a typical shop that has no safe light and coats out in the open. I know this is still a lesson in futility because there will still be nay Sayers and some how find fault with my testing. Be that as it may I feel good with my test.

Disclaimer.  I do have a safe room with fully protected fluorescents, not only is this room used for coating but also exposing and storing of screens.

[RichardGreaves]

Water interferes with photochemical crosslinking
When a stencil is exposed, the sensitizer molecules absorb invisible 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.

The sensitizer reacted, but wasn't used, like blanks - not bullets. If this happens too much (like when you add too much plasticizer to plastisol ink), the stencil will breakdown with water and fail - too many molecules not doing their job.

This the reason diazo emulsion ages when wet. Manufacturers warn that diazo sensitized emulsion will not react like a fresh sample 4-6 weeks after you sensitize it.

Photopolymer sensitizers work different and aren't effected by water as diazo is.  At the factory, the photopolymer sensitizer is actually grafted to the Poly Vinyl Alcohol (PVOH) molecules in a sophisticated reaction. PVOH is the component that reacts with a sensitizer to "harden" the emulsion, giving it the ability to resist dissolving with water.

When exposed to UV energy, the photopolymer chains begin to seek each other out. They are very fast-acting, but short-lived. If they do not find each other and form a bond very quickly, they to can become completely ineffective, but their nature makes them very easy to react and join up. Longer exposure doesn't encourage more crosslinking of stubborn photopolymer sensitizer like with diazo.

Plastisol vs. Solvent or Water-base Inks
Plastisol ink is like salad dressing and harmless to stencils. This means that the most poorly exposed stencil (if it survives development), will survive a print run.

Using dragon breath solvents to clean up meek little plastisol, is playing with fire that will damage your stencil, especially if it's under exposed.

Water will break down under exposed stencils.  It is the major component of the emulsion itself and if you don't expose it with invisible UV energy, it won't resist the natural desire of water to dissolve your stencil and rinse it down the drain.