"How much longer can photographic film hold on?"

[Steve Smith]

But, I particularly enjoy and learn from your posts about screen printing technology and materials and how they might cross over to silver gelatin photographic emulsions.

I think screen printing could work for emulsion on paper but probably not for film. When you look closely at printed ink which has been through a screen, you can usually see a witness mark of the mesh. If this was a film it would be enlarged at the printing stage and would be more obvious. However, for a paper, I'm not sure if it would matter - it would be like having a textured paper.

Also I don't know much about viscosity of emulsion at varying temperatures. Is it possible to coat (or print) and then get it to a suitable temperature for it to re-flow?

I'm not really an expert in screen printing as I'm an electronic and mechanical engineer who works for a company which specialises in industrial precision printing. Our products include conductive silver on polyester flexible circuits, membrane switch control panels and medical sensors such as those used to measure blood sugar for diabetes.

However, I have probably subliminally learned many aspects of screen printing over the last 20+ years and I can do it fairly competently myself both by hand and machine as I like to be able to use all of the machinery in our factory rather than just sit at a desk and get other people to do it.

Something else which might be of benefit to emulsion coating is surface treatment. We buy our polyester sometimes as raw material but often with an ink receptive coating or treatment to aid adhesion of the ink. I'm fairly certain that this would translate well to emulsion coating. Do you have materials with similar coatings/treatments?


Steve.

[dwross]

Steve

I agree with you about paper vs. film with screen printing. Strictly a gut feeling, though. I've never personally done any screen printing.

Theoretically, you could reheat the emulsion once it was on the paper. Each heating cycle introduces changes to the sensitivity curve, though, so it would take a new set of trial and error with rigorous controls and observation to standardize things. Practically, it might be a different situation. Paper emulsions are usually hardened in the last step before coating. Chrome alum might give you some re-melt lead time, but glyoxal (my preference) works very fast. Timing would be tricky. Interesting problem, though, with real potential. I hope someone wants to tackle it.

Polyester subbed for inks doesn't seem to work (at least, solvent-based inks.) You need a material subbed for hydrophilic coatings. Besides the material that Photographers' Formulary sells, the only one I've been able to find to work with is Dupont Melinex 535. If push ever came to shove and 535 wasn't available, I'd return to subbing acetate, vis 1920's. I'd have to build a barn far away from the house first. Acetate subbing is on the very, very short list of smells my husband can't stand!

Denise

[Steve Smith]

Whilst our conductive silver inks are solvent based, our dielectrics and graphic colours are now UV cured which needs a different coating so they might be worth trying.


Steve.

[dwross]

Steve,

I always keep my eyes open for new materials. Thanks for the tip! Do you know (if it's not an industrial secret) what the material is?

If you were closer, I'd ask you to snag a small piece to send me, but maybe you can find the time for a quick test there. Make a 10% solution of gelatin and at about 34 degrees make four test patches. 1) just pour a small puddle, 2) smear out a small puddle with a glass rod held at the slightest angle from one end touching the film, 3) and 4) repeat 1 and 2 with a couple of drops PhotoFlo/~250 ml melted gelatin. The two observations you're looking for are how smoothly the gelatin went on, and if it sticks to the film after it's dry. Depending on how well or how dismally the film preforms, you'll probably think of different things to try.

Best of days,
d

[Steve Smith]

Might be easier if I just send you some!

On Monday I will see what we have with coatings for UV cured inks and sort through them. Most will be unsuitable as they will have textures on the non-printed side but we should have some optically clear gloss as well.


Steve.

[dwross]

Thanks! Address sent pm.