Advanced coating

Discussion in 'Silver Gelatin Based Emulsion Making & Coating' started by Photo Engineer, Aug 29, 2006.

  1. Photo Engineer

    Photo Engineer Subscriber

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    After the last 2 threads, this will be the final one on coating technology as practiced in the photo industry. The next will be on hand coating at home.

    While the extrusion hopper was a great success, it required very complicated machinery and/or many passes through the machine to make a color product. The early type "C" color paper required 3 passes through the coating machine.

    To get around that, Kodak started 2 projects. One was called Mixed Packet technology, and the other was called the Slide Hopper. Mixed Packet was a color material in which all 3 layers were combined into one layer. It was a great success in some ways, but the Slide Hopper got there first.

    When I first joined EK, the Mixed Packet project had just wound down and many color products were already being coated using the Slide Hopper.

    Basically, the Slide Hopper is a set of extrusion hoppers behind what looks like a childs playground slide. The extruded emulsion emerges out of the base of the slide via small slits and slides down the slide to the surface of the support as it moves by.

    Using this technology, I have coated or seen coated anywhere from 2 to over a dozen layers at one time. And, the nice thing is, the higher the coating speed, the better the coating quality. Products became better than ever before. Of course, this required huge drying cabinets for the high speed but that is about the only real change.

    At the present time, another technology is in use called Curtain Coating. It is a step beyond that of Slide coating. This allowed another quantum leap in coating speeds and coating quality. It can be used on Slide coating machines with little change except for drying capacity. I made only one Curtain Coating during its development stage many years ago. We genrally didn't use it in research as it was too fast for us. We did use it for demonstrations of variations of the technique, development of new plant equipment and for the proof of concept for patents.

    PE
     
  2. Mike Wilde

    Mike Wilde Member

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    Great series - please keep the knowledge transfer coming

    This is the stuff that just never makes it into accessible books. I am very pleased that you are pecking this out. If the goal is to entice us into attendance at a workshop, you are heading in the right direction.
     
  3. Photo Engineer

    Photo Engineer Subscriber

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    Mike, this is the stuff you will never see at a workshop! Coating machines are too big to ship. No, that is not my intention at all.

    LoL.

    PE
     
  4. Mike Wilde

    Mike Wilde Member

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    I understand, Ron

    The process machinery you describe simply scales the basic process things up. The basic scheme remains the same. But the scaling up is almost always a non-trivial excercise, as this engineer is well aware of.

    It is always interesting to hear how it has ben done, though. I understand the doctor blade and granite slabs will be the route of choice for most home workers.. This is a bit too big for my present darkroom. I am presently trying to figure out how to take over the adjacent laundry room without having to do all of the laundry. One option is to relocate the laundry to the second floor, but that is not a step I am ready to raise with my wife just yet.
     
  5. Photo Engineer

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    Mike, my wife is all for it, as then the laundry would be on the 1st floor and more convenient for her. The problem is the cost. My darkroom is too small.

    I use a stainless steel plate myself, not a granite slab, but I do have an old table top granite piece under my stainless plate. I think that a plain counter top would do ok if level and flat.

    PE
     
  6. Gatsby1923

    Gatsby1923 Member

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    Granite Plates can be found relatively cheaply from industrial suppliers. Look around for toolmakers granite surface plates. An inexpensive source is www.use-enco.com. The shop I used to work in bought a whole truckload of their grade "B" plates. They will be more than flat for anything youÂ’d need to do, and a 9x12 plate is under $30.00