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.