Photographic element having improved sensitometry and...

Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Silver compound sensitizer containing

Reexamination Certificate

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C430S639000, C430S640000, C430S641000, C430S642000

Reexamination Certificate

active

06664038

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a silver halide photographic element. More particularly, the present invention relates to a silver halide photographic element for use in radiography having improved sensitometric results and mechanical resistance comprising a mixture of a gelatin derivative, a dextran and a hydrogenated polysaccharide.
2. Background of the Art
In recent years, there has been a strong demand for high sensitivity, low graininess and low fog in silver halide photographic elements as well as a capability for rapid processing in which development is expedited. Recently, the demands for performance by silver halide photographic light sensitive materials have become severe. In particular, demands for not only basic performance such as high sensitivity, low fog and superior graininess but also other measures of performance such as rapid processing, mechanical resistance and storage stability have become stronger than in the past.
In general, silver halide photographic light sensitive materials are subject to a variety of mechanical stresses that can have adverse effects upon the general performance of the photographic materials. A photographic film is subject to mechanical stresses in the manufacturing process thereof, or may be bent or abraded when being transported in the automatic processor. As well known in the art, when mechanical stresses are applied to the silver halide photographic material, changes in photographic performance are produced, and a technique for enhancing resistance to the effects of these mechanical stresses has been desired. The silver halide emulsions presently employed in photographic elements are more sensitive to mechanical stresses during automatic processing than older emulsions. There is the need to provide a photographic element having increased mechanical resistance without negatively affecting the high quality sensitometric properties provided by modern silver halide emulsions.
Several approaches have been attempted to solve this problem. Hardening of emulsion layers has been the more general approach described in a number of patent and patent applications, such as, for example, in U.S. Pat. Nos. 5,529,892 and 5,302,505. Another approach relates to the introduction of an intermediate gelatin layer interposed between the support and the emulsion layer, as described, for example, in U.S. Pat. No. 3,637,389.
Still another approach relates to the introduction of coating additives. For example, methods in which polymer latexes or plasticizers are included, methods in which the silver halide/gelatin ratio in the silver halide emulsion layer is reduced, and methods in which a lubricant or colloidal silica is added to the protective layer, are well known as means of improving the mechanical resistance of photographic elements. A description of useful coating aids can be found in Research Disclosure No. 38597, September 1996, “Photographic Silver Halide Emulsions, Preparations, Addenda, Systems and Processing”, Item IX.
U.S. Pat. No. 5,374,509 describes a mixture of hydrophilic colloid, a branched polysaccharide, a polyacrylamide, a polyvinylidine chloride and a polyacrylate in a binder.
JP 08-0122956 describes a silver halide emulsion which contains a metal chelating agent (type tartaric acids, ethylene diamine tetraacetates, nitro triacetates, uramil diacetates) and a mono-, di- or poly-saccharide.
JP 55-098745 and JP 55-098746, describes polysaccharides having glucose units as main chain and mannose, fucose and glucoronic acids as side chain in photographic solution preparation for high speed coating and improved physical properties.
U.S. Pat. No. 5,370,986 describes the use of polyhydroxyalkyl stabiliser compounds and a co-stabilising agent in a silver chloride photographic element to prevent fog formation. The polyhydroxyalkyl stabiliser is a non-reducing oligosaccharide or its alkyl-substituted glycoside of formula R—(CHOH)
n
(CHOR
1
)
m
—Z with n═3-7, m═0-7, R═R
1
═H or 1-3C alkyl, Z═COOR′ or CONR′R′ and R′═1-3C alkyl.
WO 95-02614, EP 950,697, and EP 936,201 describe the preparation and use of hydrogenated polysaccharides for the preparation of mixtures with mineral binders, fillers and/or pigments.
EP 965,880 describes the use of hydrogenated polysaccharides in combination with aryl compound having at least two hydroxyl groups to increase the speed to Dmin ratio of a light-sensitive silver halide element.
SUMMARY OF THE INVENTION
A first aspect of the present invention relates to a silver halide emulsion which comprises silver halide grains dispersed in a hydrophilic colloid mixture, the hydrophilic colloid mixture comprising from 5% to 25% by weight of dextran, from 20% to 40% by weight of a hydrogenated polysaccharide having an average molecular weight equal to or lower than 10,000, and from 40% to 60% by weight of gelatin.
In another aspect, the present invention relates to a silver halide photographic element comprising a support, at least one silver halide emulsion layer coated on at least one side of said support, and at least one protective layer coated over said emulsion layer, said emulsion layer comprising silver halide grains dispersed in a hydrophilic colloid mixture, characterized in that said hydrophilic colloid mixture comprises from 5 to 25% by weight of dextran, from 20% to 40% by weight of a hydrogenated polysaccharide having an average molecular weight equal to or lower than 10,000, and from 40% to 60% by weight of gelatin and in that said photographic element is forehardened.
In yet another aspect the present invention relates to the use of a hydrophilic colloid mixture comprising from 5% to 25% by weight of dextran, from 20% to 40% by weight of a hydrogenated polysaccharide having an average molecular weight equal to or lower than 10,000, and from 40% to 60% by weight of gelatin to improve the sensitometry and the mechanical resistance of a silver halide photographic element.
DETAILED DESCRIPTION OF THE INVENTION
Accordingly, in one aspect the present invention relates to a silver halide emulsion which comprises silver halide grains dispersed in a hydrophilic colloid mixture, the hydrophilic colloid mixture comprising from 5% to 25% by weight of dextran, from 20% to 40% by weight of a hydrogenated polysaccharide having an average molecular weight equal to or lower than 10,000, and from 40% to 60% by weight of gelatin.
According to a preferred aspect of the present invention, the hydrophilic colloid mixture comprises from 10% to 20% by weight of dextran, from 25% to 35% by weight of a hydrogenated polysaccharide having an average molecular weight equal to or lower than 10,000, and from 45% to 55% by weight of gelatin.
Dextran is the generic name denoting many high molecular weight glucans predominantly composed of alpha-1→6 bonds as derivatized from sucrose by Leuconostoc mesenteroides and other organisms. Dextran is commercially available in a range of average molecular weight of from 3,000 to 500,000. A preferred range of average molecular weight to be used in the practice of the present invention is comprised between 5,000 and 50,000, more preferably from 10,000 to 25,000. Dextran derivatives include (1) carboxyalkyl dextrans (such as carboxymethyl dextran), (2) dialkyl aminoalkyl dextrans (such as diethyl aminoethyl dextran), and (3) amino dextrans.
For the purposes of the present invention, dextran is typically added in an amount of from 5 to 100 grams per mole of silver, preferably in the range of from 10 to 80 grams per mole of silver, more preferably from 20 to 40 grams per mole of silver. Some photographic elements are provided as ‘two-sided’ photographic elements in which a support has at least one silver halide emulsion layer on each side of the support. Such amounts of ingredients in the hydrophilic colloid mixture can be expressed in terms of grams per square meter per side of the resulting silver halide radiographic element, wherein the amounts above correspond to an amount of from about 0

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