Radiation imagery chemistry: process – composition – or product th – Nonradiation sensitive image processing compositions or... – Bleach or intensification
Reexamination Certificate
2000-09-07
2002-04-02
Le, Hoa Van (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Nonradiation sensitive image processing compositions or...
Bleach or intensification
C430S393000, C430S430000
Reexamination Certificate
active
06365332
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to improved photographic bleaching compositions and to methods for their use to provide positive color images in color reversal photographic silver halide elements. Thus, this invention relates to the photographic industry and to photochemical processing in particular.
BACKGROUND OF THE INVENTION
The conventional image-forming process of silver halide photography includes imagewise exposure of a color photographic silver halide recording material to actinic radiation (such as visible light), and the eventual manifestation of a useable image by wet photochemical processing of that exposed material. A fundamental step of photochemical processing is the treatment of the material with one or more developing agents to reduce silver halide to silver metal. A useful color image consists of one or more images in organic dyes produced from an oxidized developing agent formed wherever silver halide is reduced to metallic silver.
To obtain useful color images, it is usually necessary to remove all of the silver from the photographic element after color development. This is sometimes known as “desilvering”. Removal of silver is generally accomplished by oxidizing the metallic silver, and then dissolving it and undeveloped silver halide with a “solvent” or fixing agent in what is known as a fixing step. Oxidation is achieved with an oxidizing agent, commonly known as a bleaching agent.
Color photographic elements can be designed to provide either color negative or color positive images. For example, color negative images can be produced by imaging and appropriate color processing of imagewise exposed color negative films. The typical commercial processing methods for such films generally include color development, bleaching, fixing and final rinsing or stabilizing steps (for example, the conventional Process C-41 method commercialized by Eastman Kodak Company).
A commercially important process intended for providing positive color images can include the following sequence of processing steps: first (or black-and-white) development, reversal reexposure, color development, bleaching, fixing, washing and/or stabilizing. Another useful process has the same steps, but stabilizing (or prebleaching) is carried out between color development and bleaching. Such conventional steps are described, for example, in U.S. Pat. No. 4,921,779 (Cullinan et al), U.S. Pat. No. 4,975,356 (Cullinan et al), U.S. Pat. No. 5,037,725 (Cullinan et al), U.S. Pat. No. 5,523,195 (Darmon et al) and U.S. Pat. No. 5,552,264 (Cullinan et al) for the processing of color reversal films, and are commercialized for example as Process E-6 and Process K-12 by Eastman Kodak Company.
The most common bleaching agents for color photographic processing are complexes of ferric ion and various organic chelating ligands (such as aminopolycarboxylic acids), of which there are hundreds of possibilities, all with varying bleaching activities and biodegradability. Common organic chelating ligands used as part of bleaching agents for color negative film processing include ethylenediaminetetraacetic acid (EDTA), 1,3-propylenediaminetetraacetic acid (PDTA) and nitrilotriacetic acid (NTA).
Ferric complexes with PDTA or its salts are excellent bleaching agents that are commonly used in processing color negative films in the commercial Process C-41 processing method.
Attempts to use these effective and inexpensive bleaching agents to process color reversal films successfully have encountered a problem. The bleaching agents tend to form thick, gelatinous precipitates in the presence of inorganic phosphate ions. Such ions are common in various photoprocessing compositions, notably the color developing and prebleaching compositions that are often used in processing color reversal materials. Phosphate ions in these compositions are apparently carried over into the bleaching solution. If the PDTA-based bleaching agents are present, the undesirable precipitates are formed.
One way to solve this problem is to remove the phosphate ions from the various processing compositions so carryover solutions do not contaminate the bleaching composition. It has not been possible to remove sufficient inorganic phosphate ions from all of those compositions.
Thus, there remains a need for PDTA bleaching compositions that are free of precipitates in the presence of inorganic phosphate ions.
SUMMARY OF THE INVENTION
The problems with known photographic photoprocessing compositions and methods are overcome with the use of a photographic bleaching composition that in aqueous form has a pH of at least 4 and comprises:
a) at least 0.01 mol/l of a bleaching agent that comprises ferric ion chelated with 1,3-propylenediaminetetraacetic acid or a salt thereof, and
b) at least 0.005 mol/l of an organic polyphosphonic acid, an aminopolysuccinic acid, or a polycarboxylic acid containing at least one hydroxy group as a compound to prevent bleaching agent precipitation.
This invention also provides a photographic prebleaching composition that is in aqueous form has a pH of at least 4 and comprises:
c) at least 0.001 mol/l of a photographic prebleaching chemical, and
d) at least 0.01 mol/l of an organic polyphosphonic acid, an aminopolysuccinic acid, or a polycarboxylic acid containing at least one hydroxy group as a compound to prevent bleaching agent precipitation
This invention also provides a method of photographic processing comprising bleaching an imagewise exposed and color developed color reversal photographic silver halide element with the photographic bleaching composition or photographic prebleaching composition described above.
The advantages of this invention are several. The color photographic elements can be processed using a highly effective and inexpensive photographic bleaching agent for color reversal processing without the problem of precipitation if inorganic phosphate ions are present. Because a more effective bleaching agent can be used, less of it is discharged to the environment in effluent. Moreover, other components in the bleaching composition may be lessened, thereby further lowering costs and environmental impact.
The precipitate problem is overcome by having certain bleaching agent precipitation preventing compounds in the bleaching composition. These compounds can be introduced into the bleaching composition of this invention directly (for example during manufacturing or use), or by carryover from prior processing solutions, such as a photographic prebleaching solution. Generally, the bleaching agent precipitation preventing compounds used in the practice of this invention are present in the bleaching composition in an amount of at least 50% of the concentration of the inorganic phosphate ions that can be 0.0005 mol/l or more.
DETAILED DESCRIPTION OF THE INVENTION
The photographic bleaching composition and method of this invention can be used to provide a color positive image in what are known in the art as color reversal photographic elements. After such elements are imagewise exposed and subjected to at least color development, they are bleached and fixed to remove silver, and otherwise processed using conventional steps and compositions (such as using conventional Process E-6 conditions).
Photographic bleaching is carried out in one or more bleaching steps using a particularly desirable bleaching agent that is a ferric complex of 1,3-propylyenediaminetetraacetic acid (PDTA), or a suitable ammonium or alkali metal salt thereof. This is the primary bleaching agent in the bleaching composition meaning that it comprises at least 50 mol % of all ferric complex bleaching agents in the composition. Preferably, the primary bleaching agent comprises at least 70 mol % of the total iron complex bleaching agents, and more preferably, it is the only ferric complex bleaching agent.
Generally, the primary bleaching agent is present in the bleaching compositions of this invention in an amount of at least 0.01 mol/l, and preferably in an amount of from about 0.1 to about 0.4 mol/l.
The bleaching compositions can also inc
Henry William G.
Price Harry J.
Eastman Kodak Company
Le Hoa Van
Tucker J. Lanny
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