Long Run discharge

[Orion]

Here is a good read on the subject of proper exposure and the benefits of post exposure.

http://www.calibratedsps.com/screenprint/screen-printing-tutorials-/pre-press-shop-tutorials/the-benefits-of-screen-post-exposure.html

[3Deep]

Once I expose my screen I don't put them back on the exposure unit for post exposure, if I think I need to post I take them outside and let the sun hit them for a few seconds...most times I try and get it right the first time.  You'll know right away at wash out if you did your exposure right.

Darryl

[ZooCity]

like Daryl, we have our exposures dialed in. the post expo is done to dry the emulsion block out and expose it primarily and is done in the sun wherever possible.  this takes no more or less time than it would to dry your block out.  in fact, we put regular ol plastisol screens out in the sun to dry in the warm season.  theres no loss of efficiency here if using sunlight. 

but theres validity to post exposing and hardening  photopolymers even if it does add a little prep time. I've seen it make a difference using thin stencils and wb inks more aggressive than the textile inks we use.   Is it absolutely necessary with textile wb screens?  depends on the emulsion, inks, etc.  It could certainly be eliminated with the right setup but you'll still be drying that block out so why not?  it's certainly not weakening the stencil.

[ZooCity]

oh, forgot to add that I think proper drying is of paramount importance with wb screens.

another point for sunlight post exposure

[RICK STEFANICK]

The purpose of post exposure is to ensure that the emulsion blockout is exposed. It's insurance.

ok, thats understood but the earlier posts the argument said nothing about it being to cure the emulsion blockout. i can understaqnd that reason but for any other its crazyland unless u leave them on there for 15 minutes.

[ZooCity]

I think it's both really. My original statement focused on #2 below but Daryl's point was a very good one about it being part of the flow anyhow.

Post exposure:

1. Exposes the emulsion blockout you applied to cover reg marks, block pinholes, build up along blade contact areas, etc.
2. Helps photopolymer (key word!) emulsion crosslink further, strengthening an already properly exposed stencil.

*I actually do set the expo time very long on screens I'm post exposing on the exposure unit and agree that unless it's quite a few times longer than the original expo and done 'backwards' with the squeegee side facing the light, it's probably doing very little that proper exposure isn't getting done already.

If you don't want to do post exposure I'd say use a diazo sensitized emulsion made for WB, a hella wide coater, travel as far as you can to the top/bottom of the screen when coating, use a pre-reg to the point where you eliminate reg marks and use some other non-water soluble blockout instead of emulsion as needed.  I'm sure that's doable but it's not a good fit for everyone. 

The hardener?  I have no idea how or why the hell it works or what it is but it makes a difference when you introduce more aggressive WB inks and thinner stencils.  Murakami's Hardener has helped out my poster screens a ton, keeping them dryer on the print side throughout the run.  They weren't ever breaking down before but they were getting tacky/moist on the print side without the hardener, which keeps them much drier on that side. 

[jsheridan]

When you have a factory that runs 24/7 6-7 days a week where 250+ screens are exposed and recycled daily with screens all over the place being used for WB and plastisol on one of 8 machines.. you don't have time to put screens in the sun, no sun at 2AM, or post expose or use emulsion for blockout. You dry them, put on some hardener and send em to the floor.

you do it right the first time and get busy printing!

[ZooCity]

Hey John, how about something constructive here instead of just implying we're all doing it wrong, like details on your process?  What emulsions are you using to achieve this?  No reg marks then, or do those get blocked out with the nail polish as well?

[ebscreen]

I'll admit that using the sun throws a loop in our screen cycle (literally, taking them out front completely changes the
path they normally take).

So much so that I'm thinking of asking the landlord is I can put a back door in!


If the sun's shining, use it. Cheaper and better than electricity if only to dry and a sun baked screen is indestructible.

[3Deep]

You forget the sun was the first exposure unit and I saw in Imperssions mag a few years back where a shop used both.  They had a vac frame that could be flipped around to use the sun or they light.

Darryl

[ZooCity]

You forget the sun was the first exposure unit and I saw in Imperssions mag a few years back where a shop used both.  They had a vac frame that could be flipped around to use the sun or they light.

Darryl

Yeah that's an awesome concept.  You can use a light integrator to control the exposure.  Trouble is, like eb knows, how often is your darkroom or wash room conveniently setup next to a big open window or door?  Throws off the flow. 

I had this idea for a fiber optic line that runs from a 'light trap' installed on your roof or outside wall.  The cable pipes the light right into a shuttered light unit, like an Olec, that also has a bulb in there for backup or for when sunlight is too low.  So it's always gunning sunshine but the bulb kicks on at the needed intensity as indicated by your settings in the integrator when there's not enough UV from the sun coming in.  This concept lets you train the light to be actnic rather than diffuse.  The would function nearly identically to a standard halide unit with no loss of performance, probably a gain actually, and save a lot of electricity and bulbs. 

I've never had time to explore it further but I think the same concept could be used to light buildings without too much variance in the lighting.  The light fixtures would contain both a bulb and the piped in sunlight from the fiber optic line.  You digitally set how bright you want it and it shutters the sunlight accordingly or adds in the appropriate amount of light from the bulb as needed.  I'm not sure if that would be cost prohibitive with the fiber optic lines and traps and photocells in each fixture though.  It would save large buildings a lot of cash once installed, that's for sure. 

[jsheridan]

Hey John, how about something constructive here instead of just implying we're all doing it wrong, like details on your process?  What emulsions are you using to achieve this?  No reg marks then, or do those get blocked out with the nail polish as well?

Changing my reply to this..
Its not up to me to give you the answers, its my intention to get you looking over the questions again and form your own answers to your own set of problems.
What and how I do things, are shaped around my own set of problems that can never be the same as yours. We may use the same supplies and tools, its how we use them that differs the end result.

I can not stress enough that the way anyone does something will not work for others in the same fashion.

As for your sun idea.. look into what the smithsonian uses.. something along the lines of fiber optic to light the entire building. I remember bringing it up on some board years ago when I first read about it. Fascinating process. They also have skylights that project the sunlight into your house/building as well that could be used for exposure.

[Admiral]

When you have a factory that runs 24/7 6-7 days a week where 250+ screens are exposed and recycled daily with screens all over the place being used for WB and plastisol on one of 8 machines.. you don't have time to put screens in the sun, no sun at 2AM, or post expose or use emulsion for blockout. You dry them, put on some hardener and send em to the floor.

you do it right the first time and get busy printing!

this is just someone looking for advice for first time running this, not a huge shop without 5 min to spare in the process

Good info about post exposure, doesn't really help diazo just dual cure and photopolymer emulsions.

Still use the hardener though.

Check out this way of exposing screens fast(the Sun), I couldn't believe how quick and easily this worked:

CURSO DE SERIGRAFIA GRAVAÇÃO DE TELA NO SOL