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  1. #11
    kb3lms's Avatar
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    Trying one more time with the PVC

    Yesterday afternoon, I spent some time researching solvents for PVC. Kaszuba gives an ascorbic acid subbing formula for PVC in the patent, above, mainly including a lot more acetone and less methanol, but I could not get it to work. Ian makes a good point that there might be some other coating or ingredient from the manufacturer. Grafix doesn't tell you what's in it in the MSDS.

    Turns out PVC is pretty tough stuff but the main solvents are acetone, MEK and tetrahydrofuran. Acetone and MEK are weak solvents; the best, tetrahydrofuran. These solvents are also the ingredients of common PVC pipe glue along with a small amount of PVC resin. So, I tried adding a bit of PVC glue to the subbing formula. Unfortunately, this precipitates the gelatin in the subbing into a hard ball. Next attempt was to mix a solution of the glue with acetone and apply that mix to soften the PVC. If I apply this first dilute glue solution and let it dry, then apply the regular subbing, and then coat gelatin, the gelatin sticks very well and does not pull off the PVC.

    The glue mix can do some nasty things to the PVC support so it appears that a very dilute solution is needed, since we just want to soften and not dissolve. The correct mix will likely be somewhere between 50:1 and 100:1 acetone to glue. The last attempt I made last evening was 30:1 and the PVC base is too optically distorted to be able to print from it. But the gelatin remained stuck firmly to the base.

  2. #12
    kb3lms's Avatar
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    I have one word for you: acetate

    Last evening I had my first try of coating with the new 5 mil acetate. The subbing formula as given above works great and the gelatin "clings tenaciously" (as some of the patents say.) Now, last night I just did a run with practice gelatin (8%) but sometime here in the next few days will be some real emulsion. Here's hoping.

    I am having some trouble getting the support to stay flat and not wrinkle so much. Subbing both sides helped but I'm not sure thats the answer.

  3. #13
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    Well, we usually did not have problems with film support wrinkling, but if we did we used a vacuum hold down plate.

    OTOH, we never had to suffer making our own subbing!

    PE

  4. #14
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    Back to the PVC.. have you considered (stabilised) chloroform?

  5. #15
    Hexavalent's Avatar
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    Quote Originally Posted by kb3lms View Post
    ....
    I am having some trouble getting the support to stay flat and not wrinkle so much. Subbing both sides helped but I'm not sure thats the answer.
    ...
    Is this 'wrinking' occuring during coating, or during/after drying?

    I've found that pinning my film base to a rigid support, or hanging with weighted clips helps keep things flat and smooth.
    - Ian

  6. #16
    kb3lms's Avatar
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    Back to the PVC.. have you considered (stabilised) chloroform?
    No, I didn't bother. I did find that reducing the amount of THF solvent (aka pipe glue) to a ratio in the 100:1 (acetone:glue) range helped to keep the PVC relatively clear. Since the PVC was a mistake by the purchasing department (me) I was anxious to move on when I received the acetate.

    Is this 'wrinking' occuring during coating, or during/after drying?
    The wrinkling was ocurring somewhat during coating the subbing but moreso during coating of the gelatin. Over the last few evenings I did a few more practice gelatin runs with 3 mil acetate rather than 5 mil on Denise's suggestion. There were a few issues I had to work out. I did find that in most cases the wrinkling would reduce as the gelatin dried.

    One was temperature. Pouring out gelatin that was too warm on to room temperate acetate (fastened to the glass) caused wrinkling as the acetate would pull away from the glass.. Now, I was heating gelatin in the microwave and possibly making it too hot. So I switched to warming the gelatin in 15 ml batches a small stainless cup in 40C water. I also started warming the glass with warm air to about the same temperature. This made a big improvement.

    Second was the amount of acetone in the subbing. For the diacetate film, less acetone seemed to do the job just as well without softening the diacetate as much. I had started with the acetone amounts called for by Wall or Kaszuba and reduced this down to about 25% of the original amount and the subbing still appears to work just as well. I haven't put any of this through a complete "processing" cycle but I don't see any difference in adhesion. I can roll it, bend it, twist it and the gelatin stays put. Maybe this is a difference between diacetate and triacetate, IDK.

    Third was attaching the acetate to the glass prior to coating. I had simply been taping the acetate to the glass. That isn't what you want to do. (I did read somewhere about using a "stickyback" and moved in that directly.) What I worked out was to spread subbing on the glass, using a cotton ball or paper towel - either works, and then using a squeegee to work out the air bubbles and "glue" the acetate down to the glass. I start at one end of the acetate and glue down about a third of it and then do the rest, working the bubbles out along the way. My squeegee is a windshield wiper glued to a wood block, but I guess you could use anything.

    Once the acetate is stuck to the glass, sub the top surface and let that dry for a minute or so to let alcohol and acetone evaporate. Then tape down the edges of the actate to keep it in place. The acetone and alcohol in the subbing solution will dissolve the tape (at least the tape I am using) if you try to tape it before applying subbing. It makes a mess.

    One variation on the above I tried to apply the subbing was to spread subbing over the acatate and then use the squeegee to remove any excess. this leaves a really nice looking piece of acetate ready to coat and adhesion seems to be good. Unfortunately the subbing solution attacks the rubber winshield wiper. In the end there didn't seem to be any real difference once coated with gelatin. IDK if I will end up with subbing lines or not.

    After getting this worked out last night, I set up one final piece of acetate and coated some real emulsion. Although I think my coating is too thin (unrelated problem - I had figured this wet coating to be about 8 mils but 12 seems to work better) it adhered nicely to the base. After drying overnight, it remained stuck to the base and looks pretty good. It'll be cut up and go in the camera today or tomorrow.

    Denise also sent me a quantity of the pre-subbed melinex and I will be trying that as well. While I am sure the factory subbed stuff will be very nice, I want to be able to "own the whole process" just for fun.

    Lastly, for what it's worth, the little stainless cups I mentioned above that I am using to heat gelatin, which I also use to hold weighed and measured chemicals, etc, come from the kitchen gadget section of Walmart. They are stainless condiment holders and you can buy a package of 4 IIRC for 88 cents. They hold about 35 ml. Work great!
    Last edited by kb3lms; 02-17-2012 at 10:19 AM. Click to view previous post history. Reason: Added some more information

  7. #17
    kb3lms's Avatar
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    Tried out the film today. Everything worked up through the developing part. Then emulsion floated off the base in one piece by the time I got to the fixer. Starting to feel like Thomas Edison with light bulbs! I now know about 26 ways that don't work.

  8. #18
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    This is an adhesion problem then not a hardening problem.

    It is not clear whether the subbing or the emulsion is separating though. Not enough information.

    Either way, I don't have a clear solution for you except to say try a different hardener in your gelatin.

    PE

  9. #19
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    How could I tell if it is the emulsion or subbing?

    Two things I will try to proceed:
    1) I will restore the acetone back to the original levels now that I have a better coating workflow and make some more practice runs but now include soaking in some water to simulate processing.
    2) Coat some of the pre-subbed melinex and see how that performs.
    Last edited by kb3lms; 02-18-2012 at 01:59 PM. Click to view previous post history.

  10. #20
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    Several thoughs:

    1. What hardener and at what level did you use it.

    2. To see if it is the emulsion + subbing stripping off, you will probably seen a tacky layer on the back side of the emulsion. If there is one, then the emulsion and subbing probably left the support. If there is no tacky layer on the film, then probably both the subbing and emulsion floated away or the subbing stayed in place and the emulsion floated away. Then check the film to see if it has a tacky layer of subbing.

    In the case of emulsion + subbing leaving then there is no real adhesion of the subbing. It is the wrong subbing for the film support. If the subbing stays and the emulsion leaves then there is no adhesion of the two and the subbing is wrong for the emulsion.

    The one common cure is a different hardener as I said earlier, or a much higher level. Or, you are not letting the coating cure long enough!

    PE

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