Oil; Azo is good because it is simple. It is basically a silver chloride emulsion. It does seem to keep well but has other problems that are not readily apparent.
Lee; AFAIK Kodachrome may use formaldehyde, as the formula is so ancient. The orignal 'new' Kodachromes used a prehardener and there was contemplation of increasing the hardener and eliminating this step. IDK how it finally ended up, but that might have given rise to the rumor as the aging on formalin hardened coatings is more critical but only from a hardness standpoint. I've explained the impossibility of making film which requires time to age in. There is no easy way to test for the product to be acceptable then unless one waits. This is extremely difficult.
Imagine if Ford or Chevrolet had to wait 6 months to a year before they were sure if a car was ok to be sold, otherwise it had to be scrapped?
Chrome alum hardening can be greatly accelerated by heat (at say 50 – 60°C).
Originally Posted by Photo Engineer
And regarding formaldehyde, there's a 1930 French patent (Kodak-Pathé) which seems to have gone to oblivion. It stated that adding phenolic compounds like resorcine to aldehyde had some benefits:
1) the amount of formaldehyde could be significantly reduced;
2) there was no after hardening effect.
The quantities involved were 0.1% formaldehyde and 0.25% resorcine (by weight of gelatin).
Not sure about formaldehyde but chrome alum hardening definitely goes back at least as far as 1880.
Originally Posted by Photo Engineer
You are right in all cases.
However, heating many coated emulsions to that temperature for the amount of time necessary to harden with chrome alum was certainly bad for the film or paper.
As for the rescorcinol or the like, it was not very good either. The additive actually put into use, as I noted, was muchochloric acid. That was put into use sometime in the mid 1900s. It was totally abandoned, afaik, in about 1970 - 1980. The only holdout at that time was Kodachrome and it may still use that method. IDK.
Formalin was very detrimental at levels needed for processes above 85 deg F. It reacted badly with both the emulsion and couplers in color products.
Thanks for your reply.
Originally Posted by Photo Engineer
US patent application 20020058215 summarizes a great many hardening agents:
In the method of crosslinking gelatin using a crosslinking agent, all crosslinking agents heretofore known as a hardening agent for gelatin can be used. Representative compounds thereof are described below.
A. Inorganic Crosslinking Agent (Inorganic Hardening Agent)
Cationic chromium complexes (examples of the ligand for the complex include hydroxyl group, oxalic acid group, citric acid group, malonic acid group, lactate, tartrate, succinate, acetate, formate, sulfate, chloride and nitrate);
Aluminum salts (particularly sulfate, potassium alum and aluminum alum; these compounds crosslink the carboxyl group of gelatin);
B. Organic Crosslinking Agent (Organic Hardening Agent)
1. Aldehyde-type Crosslinking Agents:
Formaldehyde is most commonly used. Dialdehyde can also form an effective crosslinking and examples thereof include glyoxal and succinaldehyde with glutaraldehyde being more effective. Various aromatic dialdehydes of diglycoaldehyde, dialdehyde starch, and dialdehyde derivatives of plant gum may also be used for the crosslinking in the present invention.
2. N-Methylol Compounds and Other Protected Aldehyde Crosslinking Agents:
N-methylol compounds obtained by the condensation of formaldehyde with aliphatic linear or cyclic amide of various types, urea or a nitrogen-containing heterocyclic ring. Specific examples thereof include 2,3-dihydroxydioxane, acetic acid esters of dialdehyde and hemiacetal thereof, and 2,5-methoxytetrahydrofuran.
3. Ketone Crosslinking Agents:
Diketone and quinone compounds. Examples of well-known diketones include 2,3-butadione and CH.sub.3COCOCH.sub.3, and examples of well-known quinones include p-benzoquinone.
4. Sulfonic Acid Esters and Sulfonyl Halides:
Representative examples of these compounds include bis(sulfonyl chlorides) and bis(sulfonyl fluorides).
5. Active Halogen Compounds:
Compounds having two or more active halogen atoms. Representative examples of the compound include simple bis-.alpha.-chloro or bis-.alpha.-bromo derivatives, bis(2-chloroethylurea), bis(2-chloroethyl)sulfone and phosphoramidic halide.
Representative examples of this compound include butadiene dioxide.
7. Active Olefins:
A large number of compounds having two or more double bonds, particularly unsubstituted vinyl groups activated by adjacent electron-withdrawing groups are effective as a crosslinking agent of gelatin. Examples of this compound include divinyl ketone, resorcinol bis(vinyl sulfonate), 4,6-bis(vinyl sulfonate), 4,6-bis(vinylsulfonyl)-m-- xylene, bis(vinylsulfonylalkyl) ether or amine, 1,3,5-triacryloylhexahydro- -s-triazine, diacrylamide and 1,3-bis(acryloyl)urea.
8. s-Triazine Type Compounds:
With respect to the compounds of this type, JP-B-47-6151, JP-B-47-33380, JP-B-54-25411 and JP-A-56-130740 describe cyanur chloride-type hardening agents in detail. Also, the compounds having a structure analogous to the cyanur chloride-type hardening agent described in JP-B-53-2726, JP-A-50-61219 and JP-A-56-27135 are useful.
9. Vinyl Sulfone-type Compounds:
The vinyl sulfone-type hardening agent is described in detail, for example, in JP-B-47-24259, JP-B-50-35807, JP-A-49-24435, JP-A-53-41221 and JP-A-59-18944.
10. Carbamoyl Ammonium Salts:
The carbamoyl ammonium salt hardening agent is described in detail in JP-B-56-12853, JP-B-58-32699, JP-A-49-51945, JP-A-51-59625 and JP-A-61-9641.
11. Compounds Described in Belgian Patent 825,726.
12. Amidinium Salt-type Compounds:
The amidinium salt-type hardening agent is described in detail in JP-A-60-225148.
13. Carbodiimide-type Compounds:
The carbodiimide-type hardening agent is described in detail in JP-A-51-126125 and JP-A-52-48311.
14. Pyridinium Base-type Compounds:
The pyridinium base-type hardening agent is described in detail in JP-B-58-50699, JP-A-57-44140 and JP-A-57-46538.
15. Pyridinium Salt-type Compounds:
The pyridinium salt-type hardening agent is described in detail in JP-A-52-54427.
In addition to these compounds, the compounds described in JP-A-50-38540, JP-A-52-93470, JP-A-56-43353, JP-A-58-113929 and U.S. Pat. No. 3,321,313 can also be used as the hardening agent for use in the present invention...
I am familiar with most all of the hardening agents described above. I have tested several of them as a matter of course in my work.
The active chloro compounds require, in many cases, re-application of an activating agent and they released chloride ion, the chloride and some of the epoxides cause side effects with the emulsion. Some react instantly with gelatin and cannot be coated except by extreme methods, and others harden and then are reversed in their action during processing.
It is like any medication, there are side effects. Each company can live with a different set of side effects and have developed work around solutions to them or they don't appear in their coating trials. Kodak's chosen hardener has a series of side effects which we engineers have learned to work around just so we have a hard coating almost instantly when coated.
Fuji, last I heard, used a method entirely different than Kodak used. I have met and discussed this topic with several Fuji and Konica engineers. However, it was done with great care and very obliquely.
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