Gelatin coating paper by air spray

[jon.oman]

I worked for a number of years at Ford Motor Company, and a few years at an outside vendor as well. I worked in one of the cameras that would take up two rooms. The copy board was six feet high by twenty feet in length. The film board was about six by six feet in size. Both were large vacuum frames. In one process, we would make 'shrink' negatives of engineering drawings. The shrink factor was in thousands of an inch, over the entire twenty feet. The resulting negatives were then stripped together and contact printed on Mylar. This Mylar was then used in a process to create the molds that were used to stamp the parts. The shrink factor allowed for the heat shrinkage of the part after being stamped.

In another process, we sprayed our own emulsions unto Mylar that was 62 inches in width, and twenty or more feet in length. This was done in a huge spray booth with the worker using a respirator. The finished product was used to make secondary originals of the engineering drawings that the draftsmen had drawn by hand. These were then given back to the team that worked on the drafts to be distributed to another worker for changes/additions.

I worked a large contact frame as well, making the secondary originals. This was an additional task as well as the camera work that I did. I did not spray the emulsions, and do not remember all that went into it. The only thing I do remember (I think) is that one of the ingredients was casein, which I think is a milk-based product. I do not know what the sensitizer was. Needless to say, everything was super high contrast, because of the intended output.

Jon

 

[Ray Rogers]

Thats interesting.

Casein can be used in either Gelatin-Silver halide or Gum-bichromate type emulsions.
Do you recall anything about the processing chemistry, the color of the emulsion or how it was exposed?

 

[Sean]

I think the future will be inkjet coating of emulsions. They can already use inkjet technology to coat living cells onto burned skin, or to build organs with different cell types layer by layer. If it can coat something such as a living cell one cell layer thick at a time, then surely it can be modified to coat emulsions? I would also think there would be no visible matrix from the coating as the emulsion would settle out and have perfect uniformity. I don't know of anyone who has tried it yet but as soon as someone does we could have a 'micro brew' explosion of films and papers produced this way. It's all speculation on my part though and I have no idea of the hurdles involved.

 

[hrst]

The point of inkjet printing applications you mention is that they NEED to be heterogenous - they consist of different parts at different locations, and very small parts, so they cannot be coated like film. Thus, "inkjet printing" or spraying is the only way.

OTOH, coating film emulsion is completely opposite. It must NOT be heterogenous. You don't make graphics, you just want one extremely even application. While "inkjet" printing of emulsion can work, currently used methods probably give better results much easier. Well, this is all said in the comments above, because "inkjet printing" IS spraying so the mentioned drawbacks apply. Its advantage of controlling different areas is not needed or even wanted.

IMO I feel that for film industry, curtain coaters are the way to go. They coat multi-layer with single pass (not possible by spraying I guess) and do it perfectly and are already available and in use. On the other hand, for us home enthusiasts, coating blades are super simple to construct and use and produce good results for small batches. So, I cannot see any use for "emulsion inkjet printing" for commercial nor very small scale coating. It would be especially hard to try at home. Think of normal inkjet printer operation with all the clogging problems even with specially designed inks, then think of the cheap "pirate" inks that clog even easier, and then think of gelatin!

 

[jon.oman]

Thats interesting.

Casein can be used in either Gelatin-Silver halide or Gum-bichromate type emulsions.
Do you recall anything about the processing chemistry, the color of the emulsion or how it was exposed?

My involvement with this process is over thirty years ago, so I don't remember too many details. To expose the material, we had a 24 foot horizontal vacuum frame that we rolled it out on, and then placed the negative above it. The huge glass frame was lowered unto the bed, and the vacuum was started. Finally, a frame with a number of UV light tubes was lowered into place, and the material was exposed. I seem to remember that the exposures were in the neighborhood of three to five minutes. The material was then carried to the processing room, where we had a large sink/table. It was rolled out, and the unexposed emulsion was washed away with a spray of tepid water. Some areas would have to be touched up with an ammonia based cleaner. Thinking about it, the areas that were exposed would have hardened, and the unexposed areas would still be soft. The process faithfully reproduced the smallest lines made by the draftsmen.

If I remember correctly, the unexposed Mylar was a light black in color, and after processing, the exposed lines darkened up to a dark black.

 

[Photo Engineer]

This probably was not a Silver Halide emulsion.

PE