Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Silver compound sensitizer containing
Reexamination Certificate
2000-12-07
2002-05-07
Huff, Mark F. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Silver compound sensitizer containing
C430S567000, C430S641000
Reexamination Certificate
active
06383730
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to silver halide photography. More specifically, the invention relates to radiation-sensitive high chloride emulsions prepared in the presence of starch peptizer and photographic elements employing such emulsions.
BACKGROUND OF THE INVENTION
The most widely used forms of photographic elements are those that contain one or more silver halide emulsions. Silver halide emulsions are usually prepared by precipitating silver halide in the form of discrete grains (microcrystals) in an aqueous medium. An organic peptizer is incorporated in the aqueous medium to disperse the grains. Varied forms of hydrophilic colloids are known to be useful as peptizers, but the overwhelming majority of silver halide emulsions employ gelatino-peptizers. A summary of conventional peptizers, including gelatino-peptizers, is provided by
Research Disclosure
, Vol. 389, September 1996, Item 38957, II. Vehicles, vehicle extenders, vehicle-like addenda and vehicle related addenda, A. Gelatin and hydrophilic colloid peptizers.
Research Disclosure
is published by Kenneth Mason Publications, Ltd., Dudley House, 12 North St., Emsworth, Hampshire P010 7DQ, England. The term “vehicle” includes both the peptizer used to disperse silver halide grains as they are being formed and the binder used in coating emulsion and processing solution penetrable layers of photographic elements. Gelatin and gelatin derivatives are commonly employed to perform the functions of both peptizer and binder.
Silver halide emulsions having high chloride contents, i.e., greater than 50 mole percent chloride based on silver, are known to be very desirable in image-forming systems due to the high solubility of silver chloride which permits short processing times and provides less environmentally polluting effluents. It is also known that high chloride emulsions are easily fogged during their precipitation and subsequent handling, as their greater reducibility and developability relative to high bromide emulsions make them highly susceptible to fog formation. The control of fog formation during the formation of light-sensitive silver halide emulsions, as well as during the spectral/chemical sensitization of those emulsions, during the preparation of silver halide compositions prior to coating on an appropriate support, and during the aging of such coated silver halide compositions, has been attempted by a variety of means. Mercury-containing compounds, such as those described in U.S. Pat. Nos. 2,728,663, 2,728,664, and 2,728,665, have been used as additives to control fog. Thiosulfonates and thiosulfonate esters, such as those described in U.S. Pat. Nos. 2,440,206, 2,934,198, 3,047,393, and 4,960,689, have also been employed. Organic dichalcogenides, for examples the disulfide compounds described in U.S. Pat. Nos. 1,962,133, 2,465,149, 2,756,145, 2,935,404, 3,184,313, 3,318,701, 3,409,437, 3,447,925, 4,243,748, 4,463,082, and 4,788,132 have been used not only to prevent formation of fog but also as desensitizers and as agents in processing baths and as additives in diffusion transfer systems. Unfortunately, such fog reducing compounds are not without drawbacks. Mercury-containing compounds, while generally thought to be the most effective antifoggants, can diminish the sensitivity of silver halide emulsions, can cause a deterioration in the stability of the latent image, and are environmentally harmful even at relatively low concentrations. The elimination of mercury-containing compounds from photographic compositions is highly desirable. Thiosulfonate salts can cause large sensitivity losses if not used with an excess of sulfinate salt. Many of the organic disulfide compounds need to be added to silver halide compositions from typical organic solvents because of their high water insolubility. While many mild oxidizing agents have been reported to be beneficial in controlling fog, none appear to perform as well as mercury.
While gelatin is by far the most widely used peptizer in the photographic emulsion arts, it has been shown that water dispersable starches may also be used as a peptizer to make silver halide emulsion grains (U.S. Pat. No. 5,284,744), and in particular high bromide {111} (U.S. Pat. Nos. 5,604,085, 5,620,840, 5,667,955, 5,691,131, and 5,733,718) and high chloride {100} (U.S. Pat. No. 5,607,828) tabular grains. It has also been observed, however, that employing a starch peptizer for emulsion grain precipitation may result in somewhat higher minimum densities (i.e., fog) than when a gelatino-peptizer is substituted, even when conventional antifoggants and stabilizers are present in the emulsion. It is likely a result of silver reduction by the starch aldehyde groups. This type of reduction is well known and is the basis for a test for aldehyde groups at ammonium hydroxide pH known as the Tollens' test or “silver mirror” test:
R—CHO+2Ag(NH
3
)
2
+
+3OH
−
⇄2Ag+R—COO
−
+4NH
3
+2H
2
O
Starch aldehyde groups can come about from three sources: (1) starch, being a polymer of glucose, a reducing sugar, has a natural aldehyde group at one end of each polymer strand, (2) hydrolysis of a polymer strand would make a new terminal aldehyde group in addition to the previous aldehyde group, and (3) partial oxidation of a C—C bond in the glucopyranose ring can create two new aldehyde groups at the carbon bond scission point.
Fog may be reduced in starch precipitated emulsions by treating the emulsion (either during or after precipitation) with an oxidizing agent as disclosed, e.g., in U.S. Pat. Nos. 6,027,869 and 6,090,536, where the oxidizing agent establishes an oxidation potential capable of oxidizing metallic silver. Specifically preferred oxidizing agents employed during the preparation of high bromide emulsions precipitated with starch peptizers are halogens, e.g., bromine (Br
2
) or iodine (I
2
), and bromine or iodine generating agents. Elemental bromine and bromine-generating agents (such as an acidified solution of sodium hypochlorite containing sodium bromide) have been found to be particularly effective oxidants. When bromine or iodine is used as an oxidizing agent, the bromine or iodine is reduced to Br
−
or I
−
. These halide ions can simply remain with other excess halide ions in the dispersing medium of the emulsion or be incorporated within the high bromide grains without adversely influencing photographic performance.
The reaction of starch and oxidizing agents such as bromine at typical pH values conventionally used for gelatin peptized emulsions, however, can rapidly deplete the oxidizing agent, requiring the frequent addition of relatively high levels of oxidant to maintain desired high oxidation potentials sufficient for bleaching internal grain fog centers. Health concerns have arisen concerning the handling and generation of significant amounts of volatile halides during emulsion grain manufacture. Further, high chloride emulsions create a more difficult challenge compared to high bromide emulsions in that using bromine to control fog would limit possible emulsion compositions to those containing some bromide throughout the grain structure. The alternative use of chlorine would be impractical and very dangerous.
Accordingly, to enjoy the advantages of starch as a peptizing agent for high chloride emulsions, it would be desirable to provide a high chloride emulsion grain precipitation process employing starch peptizer which would enable a reduction in the amount of fog generation in the precipitated emulsion grains without the need for the use of strong oxidants or environmentally undesirable antifoggants such as mecury-containing compounds.
SUMMARY OF THE INVENTION
In one aspect, this invention is directed to a process for precipitating a high chloride silver halide emulsion in an aqueous medium comprising growing nucleated silver halide grains in a reaction vessel in the presence of a peptizer comprising a water dispersable starch to form high chloride radiation-sensitive silver halide
Maskasky Joe E.
Scaccia Victor P.
Anderson Andrew J.
Eastman Kodak Company
Huff Mark F.
Walke Amanda C.
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