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Thread: Process C-22

  1. #11
    htmlguru4242's Avatar
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    Thanks for the help, all ...

    Yeash, running C-22 through a C-41 machine does not sound like a good idea. I'd imagine that 100ºF will do quite a job on a 75ºF design emulsion...

    Thinking about it more carefully, maybe C-41 dev. would be a better modification candidate than RA-4?

  2. #12

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    Quote Originally Posted by Photo Engineer
    Gerald, sorry, this is wrong.

    Kodak and Agfa both used side chains from the start. The side chains on Kodak couplers were nonionic but the Agfa side chains were ionic (sulfonic acids or carboxylic acids).

    Kodak couplers were dissolved in organic solvents, while the Agfa couplers were dissolved in mild alkali and then placed directly into the gelatin. As a result, the Agfa couplers tended to thicken the gelatin and make coating more difficult. Therefore, in the mid 70s, Agfa, Fuji and Konishiroku (all users of the Agfa method btw) converted to the Kodak method of long chain non-ionic couplers in organic solvents.

    PE
    Perhaps my choice of the term "resin beads" was not accurate although I have seen this term used before. A text that it consulted refers to "oily droplets".

    "Others though, notably those of the Ektachrome type, have oily droplets in the gelatine which have been used to suspend the color couplers. These droplets have a refractive index different from that of the gelatine when wet and give the film an opalescent appearance: the color balance also looks wrong when the film is wet."

    The Agfa films do not use this method depending on the weight of the coupler molecules to prevent drift in the emulsion.

  3. #13
    htmlguru4242's Avatar
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    I'm pretty sure that some early Kodak films did in fact use resin beads. They were used to hold the couplers in place before a better method was devised.

  4. #14
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    Gerald, Kodak did indeed refer to the droplets as either oily droplets or resin beads. This is related to the form that the dispersed coupler in solvent takes in the coating, ie whether it is 'soft' or 'hard' in nature. But both terms can be used.

    The problem I have with this is that Kodak has never moved to the Agfa method, as you state, but rather that all other companies have moved to the Kodak method.

    The sulfonic and carboxylic acids of the couplers used in the Agfa method are called "Fischer Couplers" after the inventor, and the Kodak couplers are sometimes referred to as "Kodacolor Couplers". The Fischer Couplers interfere with the rheology of gelatin and prevent efficient coating. Kodakcolor couplers do not.

    So, when the companies wishing to coat modern color films found this to be true, and wishing to make their coating the most efficient possible, they were forced to convert to the Kodak method either through license or by waiting until the patents expired.

    I have coated both types of couplers and I must say that the rheology of Fischer Couplers is a royal pain. Sometimes, the gelatin will not even set up. I have had to help clean a coating machine once due to that very problem. I brought my own putty knife.

    As for the opalescence, you may note that modern color products have far less than older films when wet. In fact, color paper has virtually none, whereas the original Type "C" paper of the 50s was very bad in this regard. When wet, that old color paper was just about only cyan in color. You could not see the other layers very well at all. A lot of progress has been made in this regard, and that has contributed to the improvements in grain and sharpness as well as opalescence.

    Essentially, you dissolved the Fischer coupler in base + water, added to gelatin and then neutralized to get a suspension of coupler in gelatin as the free acid or a salt depending on prep. With Kodakcolor couplers, you dissoslve them in a solvent, mix with a liquid 'resin' and then mix that with gelatin. Then you run this through a colloid mill (an industrial blendor with adjustable particle size settings) with the unit set for the size particle you want. You end up with something that looks like milk or cream which you then can go on to coat.

    In the case of the Kodacolor coupler, it is isolated from the silver halide and from the gelatin and so there is little interaction chemically. It makes better coatings.

    More than you ever wanted to know. Right?

    PE

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    Quote Originally Posted by Photo Engineer
    More than you ever wanted to know. Right?
    PE
    Actually not, always interested in new information.

    I was unaware that the side chains were different for Kodak and Agfa. The way it had be explained to me was that for the Kodak C-22 films the couplers had a low molecular weight and had to fixed by the "resin beads". The Agfa couplers had a very long side chain which created drag and prevented drift within the emulsion.

  6. #16
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    They are both basically 'ballasted' couplers. The ballast length may vary from coupler to coupler and from company to company but the Kodak couplers always ended in a nonionic moiety, whereas the Agfa couplers ended in an ionic moiety.

    During WWII there was free exchange between Agfa, Konica (then larger than Fuji) and Fuji which was a tiny company compared to the others. They all shared technology including color methodology. In the 60s, to foster efficient coating, all companies converted to the Kodak method or they just could not coat fast enough with few enough defects.

    Kodak never sold a color product using the Agfa method, but the other companies now all use the Kodak method.

    The ballast is there in all cases to prevent couplers from wandering. The bigger the ballast, the less the wander, but then the lower the ratio of 'dye' to 'inert' material in a coupler, so it is an art to balance off these forces in any design of coupler.

    The ballast also affects dye hue. The 'resin' or 'coupler solvent' also affects the hue of the final dye. Oh, one additional thing. The resin protects the dye from oxygen and other agents that cause fade, and therefore improves dye stability. Early Agfa type prints using similar couplers to Kodacolor couplers faded much more rapidly and it was not until the other companies started using the resin or droplet dispersions that they were able to begin to catch up in that area. Now, of course, it is a see saw battle in dye stability between Fuji and Kodak.

    PE

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