Film coating machine (homemade) on Flickr

[tim_walls]

Originally Posted by rmazzullo

What I would like to know is how do the separate emulsion layers stay separate during the coating phase?

Are there additives in each particular emulsion layer that prevent mixing (different specific gravity)?

Or is it that you can just layer one emulsion on top of another, providing you chill the emulsion stack very soon afterwards that the layers remain separate before mixing has a chance to occur?

My guess is it's all about getting the head design and flow rate right so that you achieve laminar flow (i.e. no turbulence.)

[Photo Engineer]

It is a very impressive machine, but is not a cascade (slide) coater. The hopper shown in the photo is indeed an extrusion hopper capable of only one layer at a time, unless two or 3 layers are fed to the hopper at one time. This cannot be determined from the photo, but it surely is not a classic slide hopper.

The coating speed in this design would be limited to about 10 f/m - 100 f/m on average. Did you notice that he is coating on Titanox, and so is making the equivalent of paper negatives but on film support.

PE

[Photo Engineer]

I should add that from the patent shown above and the original Kodak patents, a slide or cascade coater has the emulsion exposed for quite a distance before it meets the film surface, but an X or extrusion hopper has the emulsion meet the film upon extrusion from the hopper itself. This is seen in the photo.

Note also that it is about 4" wide. This is on the scale of a research machine capable of 4x5" sheets. It in no way is meant as a criticism but does point out the limitation to 4" wide coatings. The design of a 10" machine would be just the thing for LF, as is this can supply 35mm (if you can perf it), 120 if you can coat on 5 mil stock and 4x5 on 7 mil stock.

PE

[AgX]

PE,

Before reading your post I was looking at the coating head again. It seems it consists out of two acrylic plates screwd onto each other, with one having been milled out, so that a small volume is made which at the same time forms the slit at one end. Thus the coating, except for base velocity, is mainly controlled by the pressure in that coating head chamber.

[Steve Smith]

I think I see the difference now. A cascade coater has the exit slot on the top surface and the emulsion flows down to meet the film whereas with this one, the exit slot is at the point of (not quite) contact with the film. Presumably at the junction of the two perspex plates.


Steve.

[Photo Engineer]

Originally Posted by AgX

PE,

Before reading your post I was looking at the coating head again. It seems it consists out of two acrylic plates screwd onto each other, with one having been milled out, so that a small volume is made which at the same time forms the slit at one end. Thus the coating, except for base velocity, is mainly controlled by the pressure in that coating head chamber.

You are pretty much correct as is Steve. The cascade coater is the only one that can do multiple layers at the same time. It is called a 'slide hopper' at Kodak. The other hopper is called a 'curtain coater' and is entirely different from either a slide hopper or an extrusion hopper.

What you see in the picture is commonly called an X-hopper or an extrusion hopper at Kodak and functions as you describe.

PE

[Dark Orange]

Hello peoples. I am the guy who uploaded the photos to Flickr, and was contacted (I think) the original poster of this thread as a courtesy. While I am not the builder, I am close to him and can act as a go-between for any any questions you have.

Let me fill in some details on the project...

The builder is a retired chemist from Kodak here in Australia and was high up enough up the food chain so that when the plant finally shut down, he was able to acquire a few useful bits to assist the build.

He is a tinkerer and this project essentially is a means to an end, the end being something I am not entirely not sure of, but no doubt involves researching exotic emulsions. The end result is definately not the sale of large format custom/exotic filmstock, but if there is a demand for the left-overs, I am sure it is an income stream he would consider to offset the cost of building it.

I have been very busy going around the countryside for work over the last couple of months and have been unable to get new photos, but will be spending a lot of time over there the next couple of days so feel free to ask questions, and I will endeavour to get them answered and take more photos of any specific bits if required.

As mentioned, this project has no commercial considerations. The film size chosen was based on price and availability.

The film base is threaded and spliced into a single loop, so each coating run gives a standard length of product.

With regards to multi-coating, the engineering involved for the gains made is not worth it in this case so the machine is set up to do a single layer at a time. Extra layers can be applied straight away, or the coated film can be stored until required.

I have mentioned a TiO2 base, and this is currently just a bit of playing around. When the machine is up and going properly, the end product will be 'normal' negative film.

A cascade coater has the exit slot on the top surface and the emulsion flows down to meet the film whereas with this one, the exit slot is at the point of (not quite) contact with the film. Presumably at the junction of the two perspex plates.

From what I understand (IE: the original builder explained to me a long time ago) the cascade coaters are used for multi-layer coatings, to allow an even surface for the multiple layers to be laid on before application to the base. (I could be wrong on this) The method used for this machine is as described above.

The last year or so has been mainly taken up with trying to remove the problem of uneven layering of the emulsion that shows up as regular 'banding' pattern on the finished product. The problem had been isolated to the drive roller, and was assumed to be gearbox chatter. A *lot* of time and expense was used to track this down, and eventually a high-res stepper motor and drive all but removed the problem. The banding that is left is due to the coating roller by the looks, being a high-speed unit running on low speed the bearings will need to be either replaced or maybe we could get away with repacking them with a light oil rather than grease.

Thank you for the interest, I thought it was far too interesting to be left in the dark in a garage. While the builder uses the net for research rather than "social" uses, I will endeavour to get him into the forum, it looks like it will be one he will enjoy.

[Photo Engineer]

I thought those undercut rollers looked familiar!

All kidding aside, banding can also come from air pump pulsations in the drying cabinets, and pulsations in the emulsion feed pump. These all can cause banding in the final coating.

I have coated Titanox in gelatin on film many times. It is what we at Kodak called a "White Rug". It is very hard to coat uniformly at the level needed to get a good reflection backing for film or paper. I have 2 or 3 1 foot snips from a roll of one of my coatings sitting here in an old box. They sure have streaks in them. Making the TiO2 in gelatin is also not easy. It is tough to do and can require a ball mill.

This technology was used in Kodak Instant materials and in the Kodak Blood Test equipment now made by Johnson and Johnson at Kodak Park on their new updated equipment. They still have some old Kodak equipment running to make stuff for them too. So, the "White Rug" is still a coating staple at Kodak Park but made by J&J.

PE

[Dark Orange]

OK, some more photos for you all. First off, let me apologise for the pretty ordinary photos. The Filminator has now been built into its own room, and there isn't much space to swing a camera.

We'll start with a photo of the finished splicing cabinet. Note that when I said it used a 4" base, I should have said 5". For the record, each loop of finished product is 14m long.





And this is the mission control centre.




And now another view of the chiller unit. The builder is particularly impressed with his effort in designing this. Utilising a built-in container of ice-water, it pumps the water through a condensor from an automotive aircon unit (Ford, I believe) to chill the air.






Now the intereting bit - the "Extrusion slide coating head". Sorry for the crap image, there wasn't much light or contrast.




The Zenith emulsion pump.




Some examples of the finished product.




The builder, not satisfied with merely developing his own Kodachrome, is wanting to develop his OWN Kodchrome.

BTW, Merry Christmas everybody. I hope Santa was generous.

[Emulsion]

Thanks Dark Orange,

Excellent photos and information!

Is it possible to obtain from the maker any suggested emulsion formulas?

Merry Christmas from,
Emulsion.