Radiation imagery chemistry: process – composition – or product th – Nonradiation sensitive image processing compositions or... – Developer
Reexamination Certificate
2000-06-06
2001-05-29
Le, Hoa Van (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Nonradiation sensitive image processing compositions or...
Developer
Reexamination Certificate
active
06238854
ABSTRACT:
DESCRIPTION
1. Field of the Invention
The present invention relates to a developer composition having less tendency to sludge formation in the developing step of the processing of light-sensitive silver halide photographic materials.
2. Background of the Invention
Sludge formation in developers used in the processing of light-sensitive silver halide photographic materials is a well-known problem clients are confronted with. In the developer solution a deposit, known as silver sludge on the walls of the developer tank, on the rollers and on the racks are forming an ever lasting problem. In rinsing water microbiological growth is permanently causing dirt. Addition of fungicide-treated water as a solution proposed in U.S. Pat. No. 4,839,273 is however not always desired from an ecological point of view.
The presence of these undesired precipitates gives rise to failures on the processed film surface and, as a consequence thereof, to lowering of the diagnostic value of the obtained images and to the need to stop the machine in order to provide a long cleaning time, which is very expensive: silver sludge formed is not easy to oxidize as silver is a precious metal, requiring strong oxidants. As the well-known potassium bichromate is not desired from a point of view of ecology, weaker alternative oxidants are even taking longer times.
When a light-sensitive photographic silver halide material becomes processed, silver halide at the sites exposed by irradiation is transformed into metallic silver, catalyzed by the presence of latent image centers in the silver halide crystal, by the reducing compounds in the developer solution like hydroquinones, phenidones, ascorbic acid, reductic acid, etc. In order to provide rapid processing it is necessary to get a quick dissolution of the non-exposed silver halide, e.g. by the presence of sulfite in suitable amounts. In the developer however the dissolved silver halide becomes also (slowly) reduced into metallic silver nuclei, acting as a catalytic center stimulating further reduction of silver ions. Growth of those silver nuclei up to larger grey-black particles of more than 1 &mgr;m, together with coalescence and coagulation of smaller particles makes said particles form dirty flocculates, having the undesired effects of sludge formation mentioned hereinbefore.
Hitherto measures have been taken in order to dissolve lower amounts of unexposed silver halide in the developer, especially for crystals rich in silver chloride (see e.g. U.S. Pat. Nos. 5,641,620 and 5,707,793 and EP-A 0 851 282) as the solubility product of silver chloride is about 100 times the one of silver bromide. Use in the developer solution of lower amounts of e.g. sulfite, promoting dissolution of silver halides, is advantageous. This is however opposite to the advantage of rapid processing of film materials coated with light-sensitive layers having emulsion crystals rich in silver chloride and moreover, opposite to the thereby offered advantageous use of lower amounts of developer replenisher. A solution for the problem of sludge formation as has been set forth has e.g. been given in EP-A's 0 136 582, 0 223 883, 0 785 467 and 0 789 272 and in U.S. Pat. No. 5,240,823, wherein thioctic acid, polysulfide compounds having carboxylic acid, sulfonic acid, etc. and aminoalkane thiosulfonic acid or a salt thereof have been used.
Another measure applied in order to reach the same effects can be obtained by making use of a compound inhibiting dissolution by adsorption at the surface of the silver halide crystals. Protection of the said surface by adsorption effectively inhibits the dissolution of silver halide indeed, so that less silver ions are diffusing into the developer solution. A disadvantage however is the simultaneous inhibition of the velocity of the developing reaction so that a strong influence on sensitometry may occur in that speed, maximum density and contrast may be suppressed. Useful agents inhibiting dissolution of silver halide in a developer composition have been proposed as e.g. thioether compounds in U.S. Pat. No. 5,821,040; the mercapto-s-triazines from U.S. Pat. No. 5,300,410 and the mercapto or disulfide compounds in U.S. Pat. No. 5,364,746.
In spite of all measures silver ions may (and will) diffuse into the developer. In order to overcome the disadvantages already mentioned hereinbefore a suitable measure is to provide the presence of complexing agents into the said developer in order to occlude silver ions into a complex, forming a complex ion wherein the silver ions are protected against reduction by reducing developing agents. The said complex ion, opposite to silver metal formed by reduction, remains in the developer solution without causing sludge formation.
When in spite of application of an inhibitor and/or a complexing agent for silver ions no satisfying solution can be offered for the problems situated hereinbefore, addition of products providing (anionic) charges to the particles can be added in order to decrease the velocity of particle growth and flocculation as has e.g. been suggested in EP-A 0 223 883 and in U.S. Pat. Nos. 5,457,011 and 5,840,471 as well as in U.S. Pat. No. 5,824,458 wherein mercapto-alkyl carboxylic acids, mercapto-alkylamides or compounds, combining these two compounds have been proposed, thereby combining inhibition of dissolution and charging dissolved silver ions.
As is evident to anyone skilled-in-the-art of photography in the processing of materials coated with huge amounts of silver halide, problems will become more severe, as e.g. in the processing of radiographic materials used in diagnostic imaging, and still more in the processing of non-destructive film materials as has been set forth in EP-A's 0 620 483, 0 620 484 and 0 621 506.
Another form of sludge formation may occur in the developer and fixer solutions during processing as a consequence of the use of more ecologically interesting developing agents like ascorbic acid known from EP-A's 0 731 381, 0 731 382, 0 732 619 and Research Dislosure No. 371052, p. 185-224, published Mar. 1, 1995, especially when the silver halide materials are containing higher amounts of calcium, e.g. when using gelatin rich in calcium ions: oxidized ascorbic acid developer contains considerable amounts of oxalic acid, thereby forming calcium oxalate precipitate, as has been set forth in U.S. Pat. No. 5,723,267.
As already mentioned hereinbefore solving the problem of sludge formation set forth hereinbefore may lay burden on the desirable use of low replenishing amounts, set forth e.g. more specifically for ascorbic acid developers in EP-A 0 573 700 and in U.S. Pat. No. 5,503,965.
OBJECTS OF THE INVENTION
Therefore it is an object of the present invention to provide a photographic developer composition showing a reduced amount of sludge formation in order to eliminate the problems caused thereby like e.g. staining of the processed photographic material, in particular when low amounts of developer replenisher are used.
It is a further object of the present invention to postpone the formation of a precipitate in a photographic developer during processing of an exposed silver halide photographic material.
Another object of the present invention is to reduce the frequency of cleaning tanks containing developer solution in an automatic processor to at most twice a year.
It is still a further object of the present invention to prevent staining of the processed photographic film material, more particularly when said material is coated from high amounts of silver halide and/or silver halides having a higher solubility and/or when said material is loaded with high amounts of calcium compounds.
More in particular it is an object of the present invention to provide a developer having ascorbic acid as an ecologically interesting developing compound in order to process silver halide photographic film materials having low amounts of calcium compounds without stain or sludge formation, even when low replenishing amounts of developer are used.
Further on it is an object of the present in
Baecke Govert De
Jansen Benny
Loccufier Johan
Michiels Frank
Rutges Ton
AGFA-GEVAERT
Breiner & Breiner
Le Hoa Van
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