Testing a Few Emulsions

[ZooCity]

Is anyone out there using a non-diazo emulsion for high eom with thin thread mesh and not having delamination issues?  Just trying to troubleshoot.

I have been working with Saati on this... we still have random delamination issues on thin-thread... thick thread is nearly bullet proof, but throw thin thread into the mix, and EOM from 12% up to 50% fail (they all will fail at the higher end, above 30%)...

We've tried:  starlight, saati multi-300, even sun exposures, everything post exposed for a LONG time in the sun or on the multi 300....

Different emulsions, (even sp1400 sometimes had delam issues -- although less than ANY of the photopolymers we've tried)... Murakami, Kiwo, Chromaline, Ulano, Saati  ... we thought we had the problem solved with mesh abrasion, but it wasn't

and before you ask, the Saati screens have been imaged and checked out by their pros, so it's not an under-exposure issue.. if anything, we're OVER exposed.

The issue seems to be made worse by more pressure, and higher off-contact, along with sharp/hard squeegees.

Have you tried some HD emulsions?  My thinking is that all the screens for this printing technique have always been more or less thin thread so the emulsion must have been engineered to work with it right?  HD printing is also high off contact I believe so it should be flexible enough as well.

I would like to see a revamp of emulsion chemistry for higher eom screens when using thin thread, something with more adhesion and more bridging to compensate for the lack of surface area when using thin thread v. standard.   We do use SP-1400W with good results on 150/48 but still experience delam sometimes and long expo times + high eom coats are not the best combination for holding details.

Last off, eom is kind of an "empty" metric in that it only talks about how thick the dried emulsion layer is relative to the mesh thicnkess.  It doesn't provide information on where that emulsion resides relative to the mesh.  For the purposes of this discussion, we might be just as concerned with the emulsion on the ink side as the substrate side.  My point is that a face coat may work wonders if you are having delam issues.

[jvanick]

Last off, eom is kind of an "empty" metric in that it only talks about how thick the dried emulsion layer is relative to the mesh thicnkess.  It doesn't provide information on where that emulsion resides relative to the mesh.  For the purposes of this discussion, we might be just as concerned with the emulsion on the ink side as the substrate side.  My point is that a face coat may work wonders if you are having delam issues.

this is interesting, as I've been wondering if RZ of the squeegee side could be playing into the issues... maybe time to get an RZ meter in here to find out.

I can tell you that it's nearly impossible to get a perfectly smooth surface on the top of thin-thread mesh.. all the emulsions I've tested 'flow through' to the shirt side when drying. -- doing a face coat is not in my run book as it would add a bunch of extra labor/time to screen prep.

[mimosatexas]

Last 3 comments have been dead on based on what I just experienced. I believe the HS is supposed to be an HD emulsion, but honestly this is new territory for me so I could be completely wrong. You absolutely can feel the mesh on the squeegee side, so gravity is definitely pulling the emulsion through to the shirt side. I may try a face coat, but would prefer not to. The SP1400 has really been pretty bulletproof all around for me, and really the only issues I have are exposure time and getting higher eom on these low thin thread meshes due to it being so runny. I can get decent eom, but it ends up being messy with drip and thickness issues on the screen due to the edge of the coater. I'm wondering if maybe adding diazo to one of these thicker emulsions would help at least by getting me the higher eom without the desalination, but still the longer exposure times...

[ZooCity]

I know, nobody wants to add a step but how else can you get some emulsion on the blade side?

I think Sonny put it best when he made the analogy to hanging onto a pull up bar by your finger tips v. having both your arms wrapped around it.   How long could you stay on that bar in either scenario?  Toss in somebody poking at you from above and pulling down from below and you can see it's a pretty good analogy. 

This is what our emulsions are going through with thin thread mesh- all the weight of the film thickness is on the substrate side with precious little real estate for the tiny bit of emulsion that is on the squeegee side to hold on to. 

Toss in off contact and/or co-solvent inks like HSA and it's a recipe for delamination.

And yes, low rz on the blade side is beneficial.  Imagine hanging on that pull up bar and a giant squeegee slaps into your face or knuckles v. just skimming over your hair.

[abchung]

It could be a bad batch, but it is absolutely like peanut butter. Had to card it toward the mesh while in the trough. It just wasn't moving with gravity...

Good to know about the exposure vs post exposure. I know with sp1400 a hard 7 is fine, but the screen only gets more durable the longer I leave it under the light.

I would not use bad batch emulsion. I had old emulsion that turned into jelly texture.  I thought i was Smart by adding water.  Exposed great. No problem with fine details.
Then came the reclaiming. Took us a few days trying to save 7 new mesh.
N.B: old emulsion can't expose properly. Thus will under expose. This Wil lead to reclaiming issues.

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[Colin]

If you are not getting enough emulsion to stay on top of your screen (low rz value):

Change your coating technique.

Example:

Saati phu is notorious for flowing like honey. 

If you slowly scrape up honey - it will have time to flow through openings and scrape clean:

I.e. you will leave little to nothing on top of your thread.

If you scrape it up fast - The honey can not flow through as fast as you are scraping it up and you will end up hydroplaning over the threads:

I.e. you will end up with more emulsion on top of your thread - and not through it.

TLDR:  coat faster with emulsion that flow like honey.  Coat slower with emulsions that flow like water.

I use the PHU and the Graphic HU at work.  The Graphic HU is a high resolution dual cure.  I HAVE to coat slowly - very slowly - with the dual cure in order to coat my screens properly.  To ensure full encapsulation of my threads and a high rz value.  I use 225S/270/330 panels from ShureLock.

Opposite with the PHU.  I have found better oem and rz value with a slow coat on the t shirt side and a fast coat - sometimes 2 - on the squeegee side.  The variable is how much your scoop coater is angled back/scraping during your coat.

Hope this helps

[mimosatexas]

Definitely things to consider. I'll have time to do more testing next week hopefully.

Abchung: no clue if it is bad, just a guess. This was a sample from my local supplier. I have no idea what it is supposed to be like, but the peanut better consistency struck me as odd...

[abchung]

my one suppose to be nice and smooth (Autotype plus 5000). I kept it on the shelf for about a month after activation. it was lumpy(NOT like honey).

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