Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Identified radiation sensitive composition with color...
Patent
1990-09-14
1993-01-26
McCamish, Marion E.
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Identified radiation sensitive composition with color...
430569, 430631, 430642, 430935, 252314, G03C 106, G03C 1025
Patent
active
051821907
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method for obtaining photographic compositions for a coating layer.
In the following description, the terms "silver halide photographic emulsion" or "emulsion" refer to an emulsion formed of gelatin, containing silver halides, prepared by precipitation, washing, and spectral and chemical sensitizations. Conventionally, at this step, the emulsion is cold-stored, before melting, finishing and coating. The term "finishing addenda" particularly refers, but is not limited to addenda such as anti-fogging agents, stabilizers, coating additives, coupler dispersions, which are usually added to the melted emulsion before coating. The term "coating composition" refers to the composition ready to be coated, containing the finishing addenda.
A conventional method for preparing a coating composition consists in melting in a kettle a silver halide emulsion which is prepared beforehand and cold-stored, adding therein the finishing addenda and feeding the liquid emulsion into the coating machine.
However, it is difficult to obtain, according to this method, homogeneous and reproducible products, without important losses.
Another method of the prior art consists in continuously liquefying the emulsion.
Thus, French patent Agfa 2,111,176 describes a system for continuously melting the emulsion, which consists in crushing the gelled emulsion, under vacuum, then, in liquefying the resulting small granules, still under vacuum, by means of saturated steam at a temperature not exceeding by more than 10.degree. C. the final temperature desired for coating. The liquid emulsion is then fed to a station where it is separated from steam, then it is discharged by a pump toward coating stations. This system prevents overheating near the vessel walls and also provides the continuous production of emulsions with easily reproducible properties.
However, this method exhibits the following drawback: it is not possible to use, just as they are, standard emulsion formulations, since the formulations must be altered by means of water addition. On the other hand, this patent mentions neither the finishing addenda nor the other steps for manufacturing the coating composition. Regarding this point, it can be assumed that the patent implicitly refers to the known or conventional art, wherein the finishing addenda are added to the melting emulsion, which does not totally eliminate the drawbacks of the conventional method in kettle, and particularly, the necessity to check the liquid product just before feeding it to the coating machine.
French patent Agfa 2,277,360 and its English counterpart 1,501,515 describes a method for processing a gelled photographic emulsion, which consists in liquefying gelled emulsion chunks on a heating grid, and then to let the liquid emulsion flow in a mixing-machine comprising various metering pumps allowing to add the finishing addenda in given order and time, the liquid blend thus prepared being then fed into the coating station. The flow of the mixing-machine is equal to the emulsion liquefaction rate.
The waiting time of the melted emulsion with the addenda decreases, but this method exhibits the following drawback: it only allows low flows for the mixing-machine and the coating station, because the heat transfer from the heating grid is not very efficient. Further, such a metering pumps system for adding the addenda is complicated to carry out, and thereby, it is difficult to obtain a reliable system. The pumps must be very accurate, so as to obtain reproducible results, and the quality must be checked on line prior to coating.
German patent Fuji 3,406,600 describes a method in which the gelled photographic emulsion is milled, the resulting chunks are then fed into a heat exchanger, then in a static mixer. The finishing addenda are added in the static mixer, if desired, hence in the remelted emulsion.
In all these methods, the finishing addenda are added to the liquid blend at the melting step, which does not allow to use predetermined formulations, in spite of the improvements w
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Hervieux Jean-Claude
Le Faou Jacques
Dote Janis L.
Eastman Kodak Company
McCamish Marion E.
Ruoff Carl F.
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