Additional information from R. Shanebrook concerning differences in coating methods
I've just got an Email from Robert Shanebrook (thanks a lot Robert!) with additional information concerning differences between the coating method shown here at InovisCoat, and the film coating methods used by Kodak.
I quote what Robert Shanebrook has written:
"There is a major difference between the current Kodak film coating and the Impossible Project’s (and Polaroid) coating process. Impossible Project uses a multi-slot slide hopper and bead coater. Bead coating means the distance between the end of the slide and the support is crossed by a bead of liquid, the distance is a few millimeters.
Kodak began using “curtain coating” in the 1970’s and now uses only curtain coating for film manufacturing. With curtain coating the distance between the end of the slide hopper and the support is large, perhaps 250 mm. The result is a “curtain” of liquid that falls by gravity to the moving film support. Maintaining the curtain’s integrity is technically complex and is the “trick” of the process. Exactly how this is done remains proprietary to Kodak. If you know how to do it there is no reason to bead coat. Curtain coating has revolutionary advantages:
Coating Speed: The speed of the impossible project machine in the video looked like it is less than 100 ft per minute. C coating can easily run at 1000 ft/minute.
Uniformity: The falling curtain further smooths the individual layers so the uniformity of each is better than can be provided by bead coating
Lines: Particles can form and lodge in the bead causing a streak. With C coating the distance between hopper and substrate is great so particles don’t form. This may seem like a small advantage but can be a major cause of waste. Remember they have to discard all the film with a streak and all the film that MIGHT have a streak. The second category is usually several times larger than the actual defective film.
Splices: C coating doesn't require the hopper to be retracted when a splice goes by every few thousand feet of substrate. Retraction of the hopper causes a lot of waste. Many times the operator has to use a "pick” to re-establish the flow onto the support. The technique used at the bead is very similar to what is shown in the video to start the flow on the slide to disturb the liquid’s surface so the liquid wets the surfaces uniformly. In bead coating if a splice hits the hopper lip it will ruin the hopper.
Number of layers: Kodak’s c-coater can coat many more layers at once than is shown in the bead coating video."
Just some additional info from me:
- the coating presented in the video is from a small scale machine used for tests; it is not the one used for the production;
- due to the information given by InovisCoat on their website, they can coat up to 9 layers simultaneously .