Post Exposure

[Prōdigium]

I am curious as to how many printers post expose their screens? Plus if you do post exposure, how do you do it?

A very long time ago we did this for our screens, makes a big difference and we were fortunate to have a rollup door by the washout area so we just sun dried them...and post expose all in one shot.

[ericheartsu]

if they aren't soaking up the sun, then we'll post expose with our richmond solarbeam.

[Homer]

we do with long WB/DC runs only because we use emulsion for block out, no taping. We switched to emulsion because it reclaims so much easier than anything else we tried. We can post expose with the starlight but it gives us a reason to step outside once in a while. However yesterday was windy and I watched 200 clams worth of screens blow over and one popped. 

[jvanick]

since we switched to a Pure Photopolymer emulsion, we post-expose all long run, and ALL discharge/waterbase screens.
we try to do so in the sun, but if the sun isn't available, we use a Saati Multi-300 light for 5 minutes on the screens.  We just have a stack of screens sitting by the light that when people walk by and it's dark, they swap out the next screen.

We've seen no issues with reclaim on non-post exposed screens (or at least those that are properly exposed in the first place)

-J

[Prōdigium]

The sun seems to be the best, and most cost effective method to post expose. Back in the day we also used emulsion for blocking out the edges on the non-squeegee side and taped the well side only. True, it was easier to reclaim then the blockout...course that was 20 years ago, and blockout has come a long way.

We had a wall mounted unit that was a pain to use for post exposure as the light source could not be focused low enough to simply place them against the wall instead of in the unit.

Seams to me that many people in the industry fail to understand how useful it can be to post expose. We actually found that the emulsion was EASIER to reclaim when it was fully exposed....Ulano 925WR was already hard enough to reclaim, post exposing helped.

[jsheridan]

It used to be that a proper exposure was all we needed.

now with SBQ's and using their inefficiency of light absorption, the post exposure has become actually necessary for doing WB/DC  on the same screen used for plastisol inks.

printing a 6 over white base.. shoot normal and go about your day.

same screens for a wb run.. stick em in the light to 'finish' off the remaining SBQ polymer chains.

It's now a win win as you only need one type of emulsion, the exposure is quicker meaning more done in less time with less energy.

[ZooCity]

No post expo here.  All diazo added emulsion, "fully" exposed.

I did a side by side years ago on this and what I found, if you want consistently bulletproof screens, is that you can either post-expo or harden.  You don't need both but you probably "need" one of them if you want the toughest screens that you can still reclaim normally.  We opted to simply harden.  Takes seconds to do the way we have integrated it into the process, product is very cheap and no dragging delicate screens outside and jimmy rigging them around the shop yard full of dangerous pointy things. 

Those exposing at rapid speed with PP emulsions and scanning LED should probably be post exposing with most emulsions.

[screenprintguy]

We now use Murikami T9 SBQ for everything. If we are printing water based/discharge inks, then we will post expose as that is the recipe for a very durable screen for thousands of prints, no hardeners needed. If just plastisol, then a normal exposure, dry, tape and go. This emulsion rocks on all fronts!!!!

[Maxie]

We put them on a shelf next to a big window, I am not sure if this post exposes.
Does the emulsion need direct sun or is sunlight OK?

[screenprintguy]

We put them on a shelf next to a big window, I am not sure if this post exposes.
Does the emulsion need direct sun or is sunlight OK?

I guess if the sun is blaring through and they are there for hours they would get a post expose, but from what I've been told by Murikami, you really want direct mid day sun light, or in the exposure unit if you are trying to achieve the post exposure for a specific reason like with the use of T9 emulsion for waterbased prints.

[JBLUE]

If you use Diazo you only get one shot anyways. Post exposing does not do anything after the initial exposure.

[ScreenFoo]

^^Well, I've seen the yellow of diazo bleach out of underexposed stencils in the sun, so it might do something--not necessarily something that will help you though.  I thought it helped a bit with chemical resistance, but that was back when I dealt with a lot of other stupid crap that will screw everything up at the same time. 

As I understand it, if your screen is dripping wet, you put it out in the sun to dry, and it still has diazo that hasn't crosslinked, it will preferentially crosslink with the water in your stencil, not the solids in your stencil.

There should be at least one Al in this thread by now.   

[3Deep]

Wow thought I was the only one sticking screens outside in the sun, I have to watch them now days being so hot outside if left to long will pop a screen in a heart beat.

[Frog]

Wow thought I was the only one sticking screens outside in the sun, I have to watch them now days being so hot outside if left to long will pop a screen in a heart beat.

Older frames with glued mesh can certainly be susceptible to this.

[Rockers]

For longer runs we post expose the squeegee side of the screen with our LED unit.