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  1. #21

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    Jim - thanks for your reply. It's great to be able to get info from the author of the original.

  2. #22
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    Kirk;

    Imagine a dodecyl group or two attached to PMT. That is the direction to go. These are not available commercially AFAIK. All the ones I used were custom made in the EK labs or scale up facilities.

    PE

  3. #23

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    Kirk,

    Ballast substitution is very common among cyanine dyes. Substituton with bulky groups on the heterocyclic groups enhances stability of the dye against oxidation, although ethyl group is often sufficient for blue/green dyes. Red and particularly infrared dyes could use more effort in this area. Infrared dyes are usually very susceptible to oxidation and have very short shelf life. Methyl, ethyl, nitro or other substitution on some emulsion stabilizers is used, but the main purpose of such modification is to increase the adsorption of the stabilizer on AgX crystal surface. 5-methylated benzotriazole is a prime example of this. Nitro substitution is also effective on effective desensitizing dyes, because nitro group is more electron withdrawing while alkyl would do the reverse.

    PMT and MBI have very strong adsorption property on AgX crystals and they can displace many other molecules. That is always a possibility to keep in mind in emulsion design. Even weaker adsorber like adenine is known to prevent adsorption of spectral sensitizer. However, in B&W emulsion making, this is not a major problem, since there are always dyes that work well without the need of keeping intricate balancing of competitive adsorption. It is also not something you need to worry about your short term goal of making a usable negative plate emulsions of good speed and low fog.

    One area where this may become a big issue is when you want to make a chloride emulsion using spectral sensitization. Color papers are a prime example of this. This is because chloride emulsions can take quite a lot of PMT without decreasing speed (compared to bromide emulsion).

    Speaking of competitive adsorption of spectral sensitizer dyes, color couplers (in oil-in-water emulsion system) are also a big concern in desorbing sensitizing dyes. Improvements are made in many aspects of this problem, but this is far more tricky issue than PMT displacement. Again, we need not worry about this problem.

  4. #24

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    Quote Originally Posted by Photo Engineer View Post
    Imagine a dodecyl group or two attached to PMT.
    Now that I've read the book a little - and I know what to look for, I see in Chart 3.19 on page 17, they list for TAI "homologs having medium-long alkyls groups, for instance 2-heptyl or 5-hexyl" along with a list of other groups that can be added like phenyl or cyano groups.

    It does look like a good book.

  5. #25
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    Quote Originally Posted by Kirk Keyes View Post
    Now that I've read the book a little - and I know what to look for, I see in Chart 3.19 on page 17, they list for TAI "homologs having medium-long alkyls groups, for instance 2-heptyl or 5-hexyl" along with a list of other groups that can be added like phenyl or cyano groups.

    It does look like a good book.
    Kirk;

    You are now at the heart of the matter as far as sensitized emulsions, mixed emulsions and color systems are concerned. PMT is not used, BTAZ is not used (BenzoTriAZole), and most others mentioned. TAI is used because it has generic beneficial effects. I have used it in many color products with no bad effects, but generally, none of the other compunds mentioned have been used for years.

    PE

  6. #26

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    Quote Originally Posted by dyetransfer View Post
    As far as the Manganous Sulfate, since it was mentioned in the Duffin book, I used it from the beginning. I don't know if it has any effect on the emulsion, and can probably be omitted.
    Jim,

    Do you think that manganese (II) giving extra stability to your emulsion?

    The book in question, the book by Fischer, does mention manganous salt as well as mercury and cadmium (the usual stabilizers used in old days). Now there are quite some old patents specifically mentioning manganese, although those other two are also mentioned, as a stabilizer, and I wonder it may be useful, though perhaps not nearly so as the modern synthetic agents.

  7. #27

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    Ryuji - Does Fischer mention the mechanism that cadmium or mercury used when these species were used as stabilizers? And when he says stabilizer, does he mean that it keeps the product from fogging - ie. it stops the action of sulfur speed enhancement?

  8. #28

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    [QUOTE=Ryuji;621440]Jim,

    Do you think that manganese (II) giving extra stability to your emulsion?

    QUOTE]

    Hi Ryuji, I can't answer this question, because I have always made this addition. I got this from Duffin. I would have to remove the component, and do a stability test with and without. It may have no effect whatsoever, without testing, who knows?

    Regards - Jim Browning

  9. #29

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    Quote Originally Posted by Kirk Keyes View Post
    Ryuji - Does Fischer mention the mechanism that cadmium or mercury used when these species were used as stabilizers? And when he says stabilizer, does he mean that it keeps the product from fogging - ie. it stops the action of sulfur speed enhancement?
    The mechanism is where problem begins. Fischer lumps divalent metals in one short section on p. 138, where he gives reference to James 4th edition for the mechanism, but then James 4th edition gives reference to Mueller and Spracklen for mercury and Ranter for Au, Pt, Ir salts. They all point toward oxidation of metallic silver specks, and while that may be true in some cases, I have rather difficult time believing that is the mechanism, at least for manganese.

    First of all, if the oxidizing power is so significant, why gelatin doesn't interact with the metal salt much faster? Gelatin contains some reducing components, such as sugars, methionine, cystine, aldehydes, etc. Since 1980s oxidized gelatin was introduced to emulsion making, but adding manganese to the kettle is a lot cheaper solution if that was adequate. (Caveat: one main motivation of using oxidized gelatin was tabular grain, and for that matter, adding manganese in the kettle can be a bad idea, as it may affect the crystal habit.)

    Also, if the oxidizing power is significant enough to bleach the reduction fog centers, why isn't manganese used often in gold sensitized emulsions? (Gold sensitized emulsions are very sensitive to reduction fog centers and that's probably one of the three most probable reasons for why gold sensitization can be difficult.) In reality, use of a mild but rapid acting oxidizing agents is frequently contemplated and probably used in practice to produce very low fog emulsions.

    Well, I'll have to read what Mueller and Spracklen found before making my opinion on this matter.

    Generally, the behavior of metal salt/complex dopants/sensitizers/stabilizers is not very straight forward because there are many mechanisms in action. For one thing, they can adsorb on AgX surface and affect the ripening rate (can accelerate or retard, sometime one agent can do both), influence on the interstitial silver ion level, influence on the electron lifetime via electron trap mechanisms, influence on the crystal habit and/or lattice defects, incorporation into sensitivity centers, redox reaction, etc. For example, look at iron or ruthenium. It can kill the sensitivity, it can fog emulsion, and it can improve speed by reducing high intensity reciprocity failure, all depending on how, how much and where they are used. Iron is Fuji's favorite, and ruthenium, Eastman Kodak. Cadmium generally reduces sensitivity but when used in a very small quantity, it can enhance speed (I think Atwell of Eastman Kodak had a patent dated in 50s or 60s on this... I reproduced his results with more eco-friendly metal salts and some of them were similarly useful, tho the effect was less than what Atwell claimed.) Cadmium salts have strong ripening inhibition and I can see that the resulting emulsion is a bit more stable. But at the same time, if this is the effect being sought, organics (like PMT or MBI) can do better.

    Fischer also mentions this, but among the metal salts, I think the most useful and widely used as emulsion stabilizer was mercury compounds, either organic or inorganic. Mueller had a good patent on this subject, but his patents are not as informative as his academic publications. Large grain emulsions with S+Au sensitization, like those used for direct (non-screen) x-ray applications are very difficult to stabilize and mercury compounds are very very popular in those patents, but what replaced mercury compounds is a good question.

    If manganese provides a unique stabilizing property not obtainable with common organic stabilizers, I think it is a great news to us. At the same time, if the same effect can be had by slightly increasing the amount of common organic stabilizers/antifoggants/restrainers, I don't see why we should bother with manganese...
    Last edited by Ryuji; 04-26-2008 at 06:18 AM. Click to view previous post history.

  10. #30

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    Not that these patents have any information you can't get elsewhere, see US Pats 2839405 and 3720516.

    Mueller also said that manganese salt was more commonly used in chloride emulsions.

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