How do they make film?

I assume that the majors extrude their own base, but what's the coating technology?

I've never been closer to a film-making facility than possibly flying over one

unawares, but I've been around roller coating, curtain coating,

cylindrical-screen printing, rotogravure, and spraying as industrial processes

in my checkered career, and I'm curious. I'm assuming that all layers are

applied inline, that is coating 1, dryer, coating 2, dryer, etc. through eight

or ten coatings, and that this all happens in one long line as opposed to coat,

dry, roll up, and then load up and repeat with a change of coating or on a

different machine.

I'm assuming further that the drying is done with high velocity dessicated air,

as the halide layers would probably have problems after infrared, ultraviolet,

or electron-beam curing.

I spent a major part of my adult life attempting to apply even coatings of

various types (mostly acrylics, vinyls, and epoxies) to various surfaces

(acrylic, vinyl, polycarbonate, aluminum), mostly with images but also finish

clear. The more I think about it, the more miraculous it is that anyone can make

a color film that is remotely consistent from batch to batch!

Van

Van;

Film support itself is cast, not extruded onto a large polished wheel. Kodak has placed an old one at the entrance to one part of Kodak Park.

Kodak coats all layers at one time in one pass with a multiple head slide or curtain coater. All of the emulsion layers go onto the support at the same time.

Slow speed coatings are sometimes made using an extrusion hopper.

Drying is done in huge air conditioned cabinets at high speed.

Eastern European companies often use either an offset press type transfer roller or a dip tank with a doctor blade to remove excess. They often use festoon drying.

Ron Mowrey

Thanks, Ron.

I can see casting rather than extrusion, eliminates the striation possibility from flaws in the extruder die. I'm surprised that the coatings are wet-on-wet, although if it works it does eliminate a lot of possible contamination. With all the layers going down at once, and what I expect the speed must be, I would expect the dryers to be huge!

Dip roller and doctor blade wouldn't have occurred to me, but it certainly would work as long as the blade stayed true, and that's probably not much harder to maintain than the blades of a curtain coater.

Van

One of the most amazing parts of the film coating operation is that several layers are coated simultaneously in the same hopper. If the layers have the right flow rates and viscosities you can keep them in the laminar flow region. If the viscosity is too low of the flow rate is too high there will be turbulence that will destroy the pack structure. You also have to get the right surfactants in the layer on the top of the pack. I've seen this operation many times and I never ceased to be amazed.

This multiple layer coating technology was developed at Kodak in the 1950's. It was a key technology in efficient manufacture of multilayer color films.

Kodak first used the dip roller, then the offset roller method, and finally the extrusion hopper.

For multilayers, there were two or more hoppers on the machine to apply the multiple layers, and the coating was built up in twos or multiples in separate passes through the machines.

And yes, the dryers are huge and must be carefully balanced for air flow or you get harmonics. I have seen a harmonic cause paper to stick to the side of the drying cabinet and jam, ripping paper and causing the formation of nearly a mile of confetti. It was a mess.

I've also seen coatings slide off the support onto the bottom of the drying cabinet, due to improper viscosity. I did that once and had to help "B" trick clean the cabinet with a putty knife.

Ron Mowrey

What's the material film slides/negatives made out of? Plastic?

Celluloid? or some industry secret composite?

In general, film base is either cellulose triacetate or polyester. If you cut a notch in the film and can tear it cleanly, it's acetate. If it distorts at the edge, or tears your fingers, it's polyester.

I believe both are considered thermoplastic materials, they both are definitely among the things that the general public calls "plastic".

Van

Some sheet film products used to be coated on cellulose acetate buterate. It is similar to triacetate, but stayed flatter over a range of humidities. Most of these products have converted to Estar (polyethylene teraphthalate or PET) which is the same resin used for plastic soft drink bottles.

APS film (what little of it is still made) uses polyethelyne napthalate (PEN). The PET resin used for other products would take a very tight curl if you left the film in a hot car. PEN can withstand these temperatures.

For a more general article about how film works, go to: http://science.howstuffworks.com/film.htm This article is written by Chuck Woodworth, a former engineer at Kodak.

For an overview of manufacturing, maybe Ron Mowrey will dig out a copy of his cartoon.

HOW DO THEY MAKE FILM?

Here it is again, as requested. Artist unknown.

Ron Mowrey<div></div>

Hey Ron,

Can you invert that cartoon to negative? Then it might look like they're doing it in the dark, like we still do today (sans digital darkroom).

Dan

Dan;

That cartoon was drawn with infra red pens so the room was dark, it just appears light due to the infra red. ;-)

Hope things are going well for you.

All the best.

Ron Mowrey