Friday, May 30, 2014

Coatings, and economy of scale

All film-related technology relies upon advanced coating technology.  This week we traveled to the old Kodak Park in Windsor, Colorado to attempt to line up the necessary coating services and know-how needed for New55 FILM production.  The campus is many hundreds of acres/hectares big, and the companies have coaters that can coat materials at rates of up to 500 meters per minute.  That means we could get everything we need in about five minutes!  But not really, as the preparation and setup time can take months. New55 FILM is a tiny customer, but we hope to be a good one for these types of services.

Kodak Park in Colorado
Since we are planning to use an off-the-shelf 4x5 negative emulsion, if possible, the focus is on the even more complex coating of the Receiver Sheet, or just "the receiver".  This is the white shiny paper that the positive print forms on.  But it isn't just paper: This is the special material that was first formulated by Weyde and Rott and then improved by Polaroid over many years.  The function of the receiver is to take a portion of the processing negative and, via diffusion transfer, form a reverse, positive image with tone characteristics that are similar to conventional continuous tone photographic printing.

And, since Polaroid kept much of the receiver design a secret, the only book-form reference we have is the Focal Press book by Andre Rott and Edith Weyde entitled, "Photographic Silver Halide Diffusion Processes", and certain of the early Edwin H. Land essays, such as published by McCann, particularly Volume 1, "Polarizers and Instant Photography".  Then there are several patents, long expired, that hint of certain tips, tricks and practical implementations of "the receiver".  These are, by far, the most valuable to us, and it is good that the companies concentrated on patents, which as you know have a limited lifetime, so anyone, including you, can now use them.

Very small clumped and dispersed nanoparticles
This technology detective story becomes even deeper when we start to analyze the materials used to make the receiver.  For instance, both aqueous and solvent processes are used to coat the receiver and further processing is needed to convert metallic salts put down into a properly distributed network of metallic nanoparticles. The nanoparticles act like seeds, or electrodes/catalysts, which form the various grades of tones from black to gray.  I will post more about this fascinating area of nanotechnology that has been going on in the photographic industries for a long time, unseen.  The importance of having just the right mix of metals, and the right number of particles over a certain area is high, as that sets the tone scale, and there is also a cost per unit area of materials to consider.  Weyde, and Land, both wrote about how each particle ought to be for its intended use.

Aqueous Coatings vs Solvent-Based Coatings

There are thousands of coatings and many techniques for coating sheet products such as paper, plastics, films and fabrics. We need to coat baryta paper - the paper that is normally used for photo prints - with the special materials mentioned previously to form the receiver sheet, and produce the positive print. Aqueous coatings, as the name suggests, are water-based. Water is a good and environmentally safer solvent for paints, for instance, and for things such as gelatin emulsions, candy, food, and printing.  But solvent-based coatings have their own advantages: Oil paints use a solvent (volatile petroleum oils) to maintain a sticky, adhesive and semiliquid state. The solvent evaporates into the atmosphere. Other solvent-based materials contain alcohols, or light oils similar to paint thinner. Oil paints can be stronger, and tougher, and have other chemical advantages, but industrial coatings with solvent-based materials also require additional steps to capture and clean the evaporated solvents. Often this is termed "solvent recovery".

Our detective work tells us that traditional receivers are made of both aqueous (water) and solvent based materials, which have to work together to form the nucleating layer. Sounds complex? Yes it is. We are fortunate to have the experience of coaters, some who were with Kodak, Polaroid and other important firms in the coating business, to help us understand the manufacturing tradeoffs as we near decision points on the processes needed to produce New55 FILM.  Even they, however, find this field of coated nanoparticles something they will have to learn about, too.

Secrecy is needed in industry, this we understand, and trade secrets are essential to keep. But when companies die, the knowledge can, and often does die. Look at the many industries and technologies from the Roman Era until today - medicine, surgery, navigation, pigments, gold plating, and many many more - that were lost because nobody dared write down how to do it out of fear of copying. It was not until the 18th Century when patents allowed inventors to bring forth their ideas for public review in return for 20 years of exclusivity, and look at what happened since then. But not everything to be known is written, and it certainly is not on the internet, or google searchable.

So that was the subject-of-the-week, amid many sourcing and vendor efforts, phone calls, visits, quotations and buying the things we need to finalize the design. Onward.


Sam said...

Photographic Silver Halide Diffusion Processes by Andrea Rott & Edith Weyde (1972) is available in PDF, EPUB and MP3 (audiobook) formats here.

dave said...

Of course, much of the expertise in this field is still alive at Fuji, but presumably they aren't sharing because they are still actively making a DTR product (at least for a little while longer...)

Bob Crowley said...

Fujifilm's last DTR product was discontinued in 2013.

Tutejszy said...

Extremaly interesting to read!

Unknown said...

What's the password Sam? I feel nervous about downloading random files from file storage websites claiming to hold a password to a pdf...

Bob Crowley said...

You have to pay for it. Publications like this aren't copyright free. Another way for you to get the book is from Amazon - have their booksellers alert you to when a copy comes in. These torrent sites are directing you to paid content. Scibd and many others sell downloads of published books and papers and all require payment and a download.

Michael Calvert said...

Why bother with a 'receiver' at all???? cut costs?

Bob Crowley said...

Right - what about just an instant negative? A few people would be OK with that and I think it has to be considered for the future, but right now, the expectation is to have both positive print and a good negative.

What about an instant color negative too? That would be the coolest thing. We could have instant ortho negatives, and instant lith negs too. All could have uses.