Silver Halide Photographic Material Having Improved Antistatic Properties

The present invention relates to a silver halide photographic material, more particularly to a silver halide photographic material having improved antistatic property and improved coating ability.

Silver halide photographic materials are generally composed of an electrically insulating support and photographic layers coated thereon. Such a structure promotes the formation and accumulation of static charges when subjecting the photographic materials to friction or separation, caused by contact with the surface of the same or different materials during steps for manufacturing of the photographic materials or when using them for photographic purposes. These accumulated static charges cause several drawbacks. The most serious drawback is discharge of accumulated charges prior to development processing, by which the light-sensitive silver halide emulsion layer is exposed to light to form dot spots or branched or feathery linear specks when development of the photographic film is carried out. This is the phenomenon of the so-called "static marks". Such static marks cause a reduction of the commercial value of photographic films, which sometimes become completely useless. For example, the formation of static marks in medical or industrial X-ray films may result in a very dangerous judgment or erroneous diagnosis. Static marks are a particular problem because it becomes evident for the first time by carrying out development. Further, these static charges are also the origin of secondary problems such as adhesion of dusts to the surface of films, uneven coating, and the like.

As mentioned above, such static charge are frequently accumulated when manufacturing and/or using silver halide photographic materials. For example, during production, they are generated by friction of the photographic film contacting a roller or by separation of the emulsion surface from the support surface during a rolling or unrolling step. Further, they are generated on X-ray films in an automatic apparatus by contact with or separating from mechanical pads or fluorescent screens, or they are generated by contact with or separation from rollers and bars made of rubber, metal, or plastics in a bonding machine or an automatic developing machine or an automatic developing apparatus or in a camera in the case of using color negative films or color reversal films. In addition they can be generated by contacting with packing materials, and the like.

Silver halide photographic materials having high sensitivity and handling speed are subject to an increase of static mark appearance. In particular, static marks are easily generated because of high sensitization of the photographic material and severe handling conditions such as high speed coating, high speed exposure, and high speed automatic processing.

In order to prevent problems caused by static charges, it is suitable to add an antistatic agent to the silver halide photographic materials. However, antistatic agent conventionally used in other fields cannot be used freely for silver halide photographic materials, because they are subjected to various specific restrictions due to the nature of the photographic materials. More specifically, the antistatic agents which can be used in silver halide photographic materials must have excellent antistatic abilities while not having adverse influences upon photographic properties of the photographic materials, such as sensitivity, fog, granularity, sharpness. Further, such antistatic agents must not have adverse influences upon the film strength and upon antiadhesion properties. Furthermore, the antistatic agents must not accelerate exhaustion of processing solutions and not deteriorate adhesive strength between layers composing the silver halide photographic material.

In the art of silver halide photographic materials a wide number of solutions to the above described problems have been suggested in patent and literature references, mainly based on charge control agents and electrically conductive compounds coated on the silver halide emulsion layer together with a binder as an antistatic layer.

The most useful charge control agents known in the art are ionic and non-ionic surfactant as well as ionic salts. Fluorinated surfactants are often mentioned as good antistatic agents in silver halide photographic materials.

Electrically conductive compounds are mainly focused on conductive polymers such as ionic polymers and electronically conductive polymers.

The use of ionic and non-ionic surfactant as well as fluorinated surfactants is widely disclosed in many patents, such as, for example, U.S. Pat. Nos. 2,600,831, 2,719,087, 2,982,651, 3,026,202, 3,428,456, 3,457,076, 3,454,625, 3,552,972, 3,655,387, 3,850,640, 3,850,642, 4,192,683, 4,267,265, 4,304,852, 4,330,618, 4,367,283, 4,474,873, 4,510,233, 4,518,354, 4,596,766, 4,649,102, 4,703,000, 4,847,186, 4,891,307, 4,916,054, EP 245,090, 300,259, 319,951,370,404, and the like.

The use of conductive polymers is widely disclosed in many other patents, such as, for example, U.S. Pat. Nos. 2,882,157, 2,972,535, 3,062,785, 3,262,807, 3,514,291, 3,615,531, 3,753,716, 3,769,020, 3,791,831, 3,861,924, 3,938,999, 4,147,550, 4,225,665, 4,363,872, 4,388,402, 4,460,679, 4,582,783, 4,585,730, 4,590,151, 4,701,403, 4,891,308, 4,960,687, EP 35,614, 36,702, 87,688, 391,176, 391,402, 424,010, GB 815,662, 1,222,595, 1,539,866, 2,001,078, 2,109,705.

In particular U.S. Pat. No. 4,649,102 discloses the combination of a non-ionic surfactant and an anionic surfactant having a polyoxyethylene group therein, U.S. Pat. No. 4,847,186 discloses the use of a fluorinated ionic or non-ionic compound, EP 245,090 discloses the combination of an organic fluoro compound and a polyoxyethylene non-ionic surfactant, U.S. Pat. No. 3,850,640 discloses the combination of a first layer comprising an anionic surfactant and a second layer comprising cationic and non-ionic surfactants, U.S. Pat. No. 4,596,766 discloses the combination of a polyoxyethylene non-ionic surfactant and a fluorine-containing compound, U.S. Pat. No. 4,367,283 discloses the combination of a polyoxyethylene non-ionic surfactant, a sulfonated surfactant, and a fluorine-containing phosphate surfactant, GB 2,246,870 discloses the combination of a polyoxyalkylene compound and a polystyrenesulfonate compound.

The use of copolymers of styrenesulfonic acid and maleic acid in antistatic layers different from silver halide emulsion layers is specifically disclosed in U.S. Pat. Nos. 4,460,679, 4,585,730, 4,891,308, 4,960,687 wherein a cross-linking agent is used in combination therewith, and in EP 391,402 and EP 391 176.

However, many of these substances and combinations thereof exhibit great specificity, depending upon the kind of film support or the photographic composition. Although some substances produce good results on certain specific film supports, photographic emulsions or other photographic elements, they are not only useless for preventing generation of static marks when using different film supports and photographic elements, but also have an adverse influence upon photographic properties.

On the other hand, there are many cases wherein, although they have excellent antistatic effects, they cannot be used due to their adverse influence upon photographic properties such as sensitivity, fog, granularity, sharpness, and the like.

For example, it has been well known that polyethylene oxide compounds have antistatic effects, but they often have an adverse influence upon photographic properties, such as an increase in fog, desensitization, and deterioration of granularity, in particular in silver halide photographic materials in which both sides of the support are coated with silver halide emulsions, such as medical X-ray photographic materials.

The use of fluorinated surfactants for controlling the electricity generation caused by friction or contacting with different materials, such as, for example, rollers, increases the charging in negative polarity. Accordingly, although it is possible to adapt the electric characteristics of the silver halide photographic material for each roller, such as, for example, rubber rollers, Delrin.TM. rollers, and nylon rollers by suitably combining the fluorinated surfactants with surfactants, charging in positive polarity problems still occur, because a general solution for all kind of rollers cannot be obtained.

Moreover, the market requirement of silver halide photographic material having a reduced processing time has increased the problems of static charges due to the higher speed to which silver halide photographic materials go trough the automatic processors.

Furthermore, the increasing demand of the radiographic market of medical X-ray silver halide photographic material, due to the increase in the worldwide consumption and diffusion of apparatus for X-ray diagnosis, requires an increase in productivity of medical X-ray photographic material that can be obtained with an increase of coating speed. Higher coating speed increases the appearance of static charges, if conventional antistatic agents are used.

The present invention relates to a silver halide photographic material comprising a support and at least one silver halide emulsion layer coated thereon, wherein said silver halide emulsion layer comprises from 5 to 15% by weight of a water-soluble, electrically conductive copolymer containing carboxylic groups and sulfonic groups and wherein a hydrophilic colloid layer comprising a combination of a fluorinated surfactant, a non-ionic polyoxyethylene surfactant and an anionic polyoxyethylene surfactant is coated on said at least one silver halide emulsion layer.

The present invention relates to a silver halide photographic material comprising a support and at least one silver halide emulsion layer coated thereon, wherein said silver halide emulsion layer comprises from 5 to 15% by weight of a water-soluble, electrically conductive copolymer (1) containing carboxylic groups and sulfonic groups and wherein a hydrophilic colloid layer comprising a combination of a fluorinated surfactant (2), a non-ionic polyoxyethylene surfactant (3) and an anionic polyoxyethylene surfactant (4) is coated on said at least one silver halide emulsion layer.

The copolymer (1) useful in the antistatic combination of the present invention is preferably a water soluble (e.g., soluble in water at room temperature for at least 5% by weight, preferably for at least 10%) electrically conductive hydrophilic copolymer having monomer units comprising:

(a) a sulfonate substituted ethylenically unsaturated monomer, and

(b) an ethylenically Unsaturated comonomer containing carboxylic groups, the molar ratio of (a) to (b) preferably being 1:1 to 5:1.

The copolymer (1) can be represented by the following formula: ##STR1## wherein R and R', independently, represent a hydrogen atom, a halogen atom, or an alkyl group, L and L', independently, represent a single chemical bond or a divalent connecting group, such as, for example, hydrocarbon groups, including specifically alkylene groups, arylene groups, and the like, Q represents a hydrogen atom or a carboxylic group, M and M', independently, represent a hydrogen atom, an ammonium ion, or an alkali metal ion, x represents from 50% to 80% mol and y represents from 50% to 20% mol.

According to the scope of the present invention when the term "group" is used to describe a chemical compound or substituent, the described chemical material includes the basic group and that group with conventional substitution. Where the term "moiety" is used to describe a chemical compound or substituent only an unsubstituted chemical material is intended to be included.

For example, monomer (a) may be styrene sulfonic acid, vinyltoluene sulfonic acid, alpha-methyl-styrene sulfonic acid, 2-ethyl-styrene sulfonic acid, 3-acryloyloxypropane-1-sulfonic acid, 3-methacryloyloxypropane-1-sulfonic acid, -acrylamido-2-methylpropane-sulfonic acid, 3-methacryloyloxy-propane-1-methyl-1-sulfonic acid, acryloylmethane-sulfonic acid, 4-acryloyloxybutane-1-sulfonic acid, 2-acryloyloxyethane-1-sulfonic acid, 2-acrylamidopropane-1-sulfonic acid, 2-methacrylamido-2-methylpropane-1-sulfonic acid, 3-methacrylamido-3-methylbutane-1-sulfonic acid in the form of alkali metal salts thereof, preferably Na or K, or ammonium salts.

Monomer (b) may be maleic acid, acrylic acid, methacrylic acid, 2-butenoic acid, as well as their alkali metal or ammonium salts.

More preferably, the component (a) is an alkali metal styrene sulfonate and the component (b) is maleic acid. Most preferably, the copolymer comprises sodium styrene sulfonate and maleic acid in a 2:1 to 4:1 mole ratio, with a number average molecular weight higher than 3000, preferably higher than 4000. The electrically conductive copolymer can comprises, in addition to the above mentioned main components (a) and (b), minor amount of monomers of different chemical structure. Accordingly, the term "copolymer" must not be intended to comprise only two ingredients. By the term "minor amount" is intended an amount of from 0 to 15%, preferably from 5 to 10% by weight.

Examples of electrically;conductive copolymers (1) are poly(sodium styrene sulfonate-maleic acid), poly(sodium styrene sulfonate-methacrylic acid), poly(sodium styrene sulfonate-butylacrylate-methacrylic acid), poly-(sodium2-acrylamido-2-methyl-propanesulfonate-maleic acid) and the like. Poly(sodium styrene sulfonate--maleic acid) represents the preferred copolymer. These copolymers may be purchased commercially or synthesized by copolymerizing the monomers as known in the art.

According to an embodiment of the present invention the fluorinated surfactant (2) useful in the antistatic combination of the present invention is a fluorinated organic salt represented by the reaction product of a polyoxyalkyleneamine compound with a fluorinated organic acid compound.

In the present invention, polyoxyalkyleneamine compounds, used to obtain the fluorinated organic compounds, contain amino groups, preferably primary amino groups, attached to the end of a polyoxyalkylene chain. The polyoxyalkylene chain is based either on propylene oxide, ethylene oxide or mixed ethylene/propylene oxide. The polyoxyalkyleneamine compounds comprise monoamine, diamine and triamine compounds with molecular weights ranging from about 200 to about 6,000. Particularly representative polyoxyalkyleneamine compounds are those represented by the following general formulas from (I) to (V): ##STR2## wherein R represents an alkoxy group, preferably a lower alkoxy group having 1 to 5 carbon atoms, such as methoxy, ethoxy, propoxy, 2-methoxy-ethoxy, etc., R.sub.1 represents a hydrogen atom or a methyl group, n represents an integer of 1 to 50, b represents an integer of 5 to 150, a and c, the same or different, each represent an integer from 0 to 5, such that a+c represents an integer from 2 to 5, A represents a CH.tbd., CH.sub.3 --C.tbd., CH.sub.3 --CH.sub.2 --C.tbd. or a ##STR3## group and x, y and z, equal or different, represent integers of 1 to 30.

Examples of polyoxyalkyleneamine compounds useful to obtain fluorinated organic compounds according to this invention are illustrated below. ##STR4## wherein b is about 8.5 and a+c is about 2.5 ##STR5## wherein b is about 15.5 and a+c is about 2.5 ##STR6## wherein x+y+z is about 5.6 ##STR7## wherein x+y+z is about 30 ##STR8##

Polyoxyalkyleneamine compounds are commercially available with the name of Jeffamine.TM. Polyoxyalkyleneamines manufactured by Texaco Chemical Company.

Preferably, fluorinated organic acid compounds, suitable to react with polyoxyalkyleneamine compounds, are perfluoroalkylsulfonic acid compounds. Suitable perfluoroalkylsulfonic acid compounds are represented by the following general formula:

wherein R.sub.f represents an alkyl group having 2 to 18 carbon atoms, preferably 5 to 10 carbon atoms, or an alkenyl group having 2 to 15 carbon atoms, preferably 4 to 8 carbon atoms in which the hydrogen atoms are partially or completely substituted with fluorine atoms, R.sub.f including at least 3 fluorine atoms, B represents a divalent organic group, o represents 0 or 1 and p represents 1 or 2. B preferably represents a carbonyl, a sulfonyl, an amino, an alkylene group preferably having 1 to 3 carbon atoms, an arylene group (such as phenylene or naphthylene), an oxygen atom or groups consisting of two or more of the above-mentioned groups, such as for instance carbonylamino, sulfonylamino, aminocarbonyl, aminosulfonyl, ester or polyoxyalkylene groups preferably containing 2 to 40 oxyalkylene unities.

Examples of perfluoroalkylsulfonic acids are illustrated below. ##STR9##

The above listed perfluoroalkylsulfonic acid compounds can be found on the market or prepared in a conventional way.

The fluorinated organic salt compounds according to the present invention can be prepared by direct reaction of the above described polyoxyalkyleneamine compounds with the above described fluorinated organic acid compounds, preferably in the presence of a low-boiling organic solvent, e.g. methanol, ethanol, acetone, and the like, and separating the fluorinated organic salt compound with techniques known in the art.

Examples of fluorinated organic salt compounds suitable to the purpose of the present invention are illustrated below. ##STR10## (wherein b=8.5 and a+c=2.5) ##STR11## (wherein b=15.5 and a+c=2.5) ##STR12## (wherein b=40.5 and a+c=2.5) ##STR13## (wherein x+y+z is about 5-6) ##STR14## (wherein x+y+z is about 30).

According to another embodiment of the present invention the fluorinated surfactant (2) useful in the antistatic combination of the present invention is a fluorinated cationic surfactant represented by the following formula: ##STR15## wherein R'f represents an alkyl group having from 3 to 25 carbon, atoms in which the hydrogen atoms are partly or totally replaced by fluorine atoms, A is an alkylene group, an arylene group, or an aralkylene group, L a divalent linking atom or group, such as, for example, sulfonamido group, amido group, oxygen, sulfur, and the like, R.sub.1, R.sub.2, and R.sub.3 are, independently, an alkyl group having from 1 to 10 carbon atoms, X is an anionic atom or group, such as, for example, chloride, bromide, sulfate group, and the like, and m and p are, independently, 0 or 1.

Specific examples of fluorinated cationic surfactants suitable to the purpose of the present invention are illustrated below. ##STR16##

Non-ionic surface active agents (3), for use in the present invention in combination with fluorinated surfactants, are described, for example in British Patent 861,134, in U.S. Pat. Nos. 2,982,651, 3,428,456, 3,457,076, 3,454,625, 3,552,927, 3,655,387, 3,850,641, 4,367,283, 4,518,354, 4,596,766 and in Japanese Patent Publication 208,743/83.

In the present invention, non-ionic surface active agents having a polyoxyalkylene chain represented by the following general formulas are particularly effective as non-ionic surface active agents: ##STR17## wherein R.sub.2 represents an alkyl group having 1 to 30 carbon atoms, an alkenyl group having 1 to 30 carbon atoms or an aryl group (such as phenyl or naphthyl), R.sub.3 represents a hydrogen atom or a methyl group, D represents a group --O--, --S--, --COO--,--NR.sub.4 --,--CO--NR.sub.4 --, or --SO.sub.2 --NR.sub.4 --, wherein R.sub.4 represents a hydrogen atom or an alkyl group having 1 to 12 carbon atoms, q represents 0 or 1 and r represents an integer of 2 to 50.

Examples of non-ionic polyoxyalkylene surface active agents are illustrated below. ##STR18##

Anionic polyoxyethylene surfactants (4), normally used in photography, are surfactants of the type including a polyoxyethylene group linked to an anionic hydrophilic group and to a hydrocarbon residue directly or by means of a bridge consisting of a divalent organic residue, as expressed by the following formula: ##STR19## wherein R is an aliphatic, aromatic or a mixed hydrocarbon residue and preferably a linear or branched alkyl group having from 4 to 18 carbon atoms or an aryl group substituted with one or more alkyl groups altogether having from 4 to 18 carbon atoms,

A is a divalent organic residue, preferably a carbonyl, a sulfonyl, an amino or an alkylene group preferably having from 1 to 3 carbon atoms, an oxygen atom or groups consisting of two or more of the above-mentioned groups, such as for example carbonylamino, sulfonylamino, aminocarbonyl, aminosulfonyl, or ester,

X is an anionic group of the sulfonate, carboxylate, phosphate and sulfate type, and

m is 0 or 1 and n is an integer of from 1 to 25.

Anionic surface active agents of this type are described for example in Schwarz et al. "Surface Active Agents and Detergents", Vol. I and II, Interscience Publ., in the U.S. Pat. Nos. 2,992,108, 3,068,101, 3,201,152 and 3,165,409, in the French Pat. Nos. 1,556,240 and 1,497,930 and in the British Pat. Nos. 580,504 and 985,483. Examples of anionic polyoxyethylene surfactants are illustrated below. ##STR20##

Preferably, the hydrophilic colloid layer comprising the surfactant combination of the present invention comprises an amount of fluorinated surfactant (2) of from 5 to 50 mg/m.sup.2, more preferably from 10 to 30 mg/m.sup.2, an amount of non-ionic polyoxyethylene surfactant (3) of from 50 to 200 mg/m.sup.2, more preferably from 75 to 150 mg/m.sup.2, and an amount of anionic polyoxyethylene surfactant (4) of from 25 to 150 mg/m.sup.2, more preferably from 50 to 100 mg/m.sup.2.

Photographic materials according to the invention generally comprise at least one light sensitive layer, such as a silver halide emulsion layer, coated on at least one side of a support.

Silver halide emulsions typically comprise silver halide grains which may have different crystal forms and sizes, such as, for example, cubic grains, octahedral grains, tabular grains, spherical grains and the like. Tabular grains are preferred. The tabular silver halide grains contained in the silver halide emulsion layers of this invention have an average diameter:thickness ratio (often referred to in the art as aspect ratio) of at least 3:1, preferably 3:1 to 20:1, more preferably 3:1 to 14:1, and most preferably 3:1 to 8:1. Average diameters of the tabular silver halide grains suitable for use in this invention range from about 0.3 to about 5 micrometeres, preferably 0.5 to 3 micrometers, more preferably 0.8 to 1.5 micrometers. The tabular silver halide grains suitable for use in this invention have a thickness of less than 0.4 micrometers, preferably less than 0.3 micrometers and more preferably less than 0.2 micrometers.

The tabular silver halide grain characteristics described above can be readily ascertained by procedures well known to those skilled in the art. The term "diameter" is defined as the diameter of a circle having an area equal to the projected area of the grain. The term "thickness" means the distance between two substantially parallel main planes constituting the tabular silver halide grains. From the measure of diameter and thickness of each grain the diameter:thickness ratio of each grain can be calculated, and the diameter:thickness ratios of all tabular grains can be averaged to obtain their average diameter:thickness ratio. By this definition the average diameter:thickness ratio is the average of individual tabular grain diameter:thickness ratios. In practice, it is simpler to obtain an average diameter and an average thickness of the tabular grains and to calculate the average diameter:thickness ratio as the ratio of these two averages. Whatever the used method may be, the average diameter:thickness ratios obtained do not greatly differ.

In the silver halide emulsion layer containing tabular silver halide grains of the invention, at least 15%, preferably at least 25%, and, more preferably, at least 50% of the silver halide grains are tabular grains having an average diameter:thickness ratio of not less than 3:1. Each of the above proportions, "15%", "25%" and "50%" means the proportion of the total projected area of the tabular grains having a diameter:thickness ratio of at least 3:1 and a thickness lower than 0.4 micrometers, as compared to the projected area of all of the silver halide grains in the layer. Other conventional silver halide grain structures such as cubic, orthorhombic, tetrahedral, etc. may make up the remainder of the grains.

In the present invention, commonly employed halogen compositions of the silver halide grains can be used. Typical silver halides include silver chloride, silver bromide, silver iodide, silver chloroiodide, silver bromoiodide, silver chlorobromoiodide and the like. However, silver bromide and silver bromoiodide are preferred silver halide compositions for tabular silver halide grains with silver bromoiodide compositions containing from 0 to 10 mol % silver iodide, preferably from 0.2 to 5 mol % silver iodide, and more preferably from 0.5 to 1.5% mol silver iodide. The halogen composition of individual grains may be homogeneous or heterogeneous.

Silver halide emulsions containing tabular silver halide grains can be prepared by various processes known for the preparation of photographic materials. Silver halide emulsions can be prepared by the acid process, neutral process or ammonia process. In the stage for the preparation, a soluble silver salt and a halogen salt can be reacted in accordance with the single jet process, double jet process, reverse mixing process or a combination process by adjusting the conditions in the grain formation, such as pH, pAg, temperature, form and scale of the reaction vessel, and the reaction method. A silver halide solvent, such as ammonia, thioethers, thioureas, etc., may be used, if desired, for controlling grain size, form of the grains, particle size distribution of the grains, and the grain-growth rate.

Preparation of silver halide emulsions containing tabular silver halide grains is described, for example, in de Cugnac and Chateau, "Evolution of the Morphology of Silver Bromide Crystals During Physical Ripening", Science and Industries Photographiques, Vol. 33, No.2 (1962), pp. 121-125, in Gutoff, "Nucleation and Growth Rates During the Precipitation of Silver Halide Photographic Emulsions", Photographic Science and Engineering, Vol. 14, No. 4 (1970), pp. 248-257, in Berry et al., "Effects of Environment on the Growth of Silver Bromide Microcrystals", Vol.5, No.6 (1961), pp. 332-336, in U.S. Pat. Nos. 4,063,951, 4,067,739, 4,184,878, 4,434,226, 4,414,310, 4,386,156, 4,414,306 and in EP Pat. Appl. No. 263,508.

As a binder for silver halide emulsions, gelatin is preferred, but other hydrophilic colloids can be used, alone or in combination, such as, for example, dextran, cellulose derivatives (e.g.,hydroxyethylcellulose, carboxymethyl cellulose), collagen derivatives, colloidal albumin or casein, polysaccharides, synthetic hydrophilic polymers (e.g., polyvinylpyrrolidone, polyacrylamide, polyvinylalcohol, polyvinylpyrazole) and the like. Gelatin derivatives, such as, for example, highly deionized gelatin, acetylated gelatin and phthalated gelatin can also be used. Highly deionized gelatin is characterized by a higher deionization with respect to the commonly used photographic gelatins. Preferably, highly deionized gelatin is almost completely deionized which is defined as meaning that it presents less than 50 ppm (parts per million) of Ca.sup.++ ions and is practically free (less than 5 parts per million) of other ions such as chlorides, phosphates, sulfates and nitrates, compared with commonly used photographic gelatins having up to 5,000 ppm of Ca.sup.++ ions and the significant presence of other ions.

The highly deionized gelatin can be employed not only in the silver halide emulsion layers containing tabular silver halide grains, but also in other component layers of the photographic element, such as silver halide emulsion layers containing other than tabular silver halide grains, overcoat layers, interlayers and layers positioned beneath the emulsion layers. In the present invention, preferably at least 50%, more preferably at least 70% of the total hydrophilic colloid of the photographic element comprises highly deionized gelatin. The amount of gelatin employed in the light-sensitive photographic material of the present invention is such as to provide a total silver to gelatin ratio lower than 1 (expressed as grams of Ag/grams of gelatin). In particular the silver to gelatin ratio of the silver halide emulsion layers is in the range of from 1 to 1.5.

Silver halide emulsion layers can be sensitized to a particular range of wavelengths with a sensitizing dye. Typical sensitizing dyes include cyanine, hemicyanine, merocyanine, oxonols, hemioxonols, styryls, merostyryls and streptocyanines. The silver halide photographic material of the present invention can have one or more silver halide emulsion layers sensitized to the same or different regions of the electromagnetic spectrum. The silver halide emulsion layers can be coated on one side or on both side of a support base.

Examples of materials Suitable for the preparation of the support include glass, paper, polyethylene-coated paper, metals, polymeric film such as cellulose nitrate, cellulose acetate, polystyrene, polyethylene terephthalate, polyethylene, polypropylene and the like.

Specific photographic materials according to the invention are black-and-white light-sensitive photographic materials, in particular X-ray light-sensitive materials.

Preferred light-sensitive silver halide photographic materials according to this invention are radiographic light-sensitive materials employed in X-ray imaging comprising a silver halide emulsion layer(s) coated on one surface, preferably on both surfaces of a support, preferably a polyethylene terephthalate support. Preferably, the silver halide emulsions are coated on the support at a total silver coverage in the range of 3 to 6 grams per square meter. Usually, the radiographic light-sensitive materials are associated with intensifying screens so as to be exposed to radiation emitted by said screens. The screens are made of relatively thick phosphor layers which transform the X-rays into more imaging-effective radiation such as light (e.g., visible light). The screens absorb a much larger portion of X-rays than the light-sensitive materials do and are used to reduce the X-ray dose necessary to obtain a useful image. According to their chemical composition, the phosphors can emit radiation in the ultraviolet, blue, green or red region of the visible spectrum and the silver halide emulsions are sensitized to the wavelength region of the radiation emitted by the screens. Sensitization is performed by using spectral sensitizing dyes absorbed on the surface of the silver halide grains as known in the art.

More preferred light-sensitive silver halide photographic materials according to this invention are radiographic light-sensitive materials which employ intermediate diameter:thickness ratio tabular grain silver halide emulsions, as disclosed in U.S. Pat. No. 4,425,426 and in EP Pat. Appl. 84,637.

However other black-and-white photographic materials, such as lithographic light-sensitive materials, black-and-white photographic printing papers, black-and-white negative films, as well as light-sensitive photographic color materials such as color negative films, color reversal films, color papers, etc. can benefit of the use of the present invention.

The light sensitive layers intended for use in color photographic material contain or have associated therewith dye-forming compounds or couplers. For example, a red-sensitive emulsion would generally have a cyan coupler associated therewith, a green-sensitive emulsion would generally have a magenta coupler associated therewith, and a blue-sensitive emulsion would generally have a yellow coupler associated therewith.

The silver halide photographic materials of the present invention are fore-hardened. Typical examples of organic or inorganic hardeners include chrome salts (e.g., chrome alum, chromium acetate), aldehydes (e.g., formaldehyde and glutaraldehyde), isocyanate compounds (hexamethylene diisocyanate), active halogen compounds (e.g., 2,4-dichloro-6-hydroxy-s-triazine), epoxy compounds (e.g., tetramethylene glycol diglycidylether), N-methylol derivatives (e.g., dimethylolurea, methyloldimethyl hydantoin), aziridines, mucohalogeno acids (e.g., mucochloric acid), active vinyl derivatives (e.g., vinylsulfonyl and hydroxy substituted vinylsulfonyl derivatives) and the like. Other references to well known hardeners can be found in Research Disclosure, December 1989, Vol. 308, Item 308119, Section X.

Other layers and additives, such as subbing layers, surfactants, filter dyes, intermediate layers, protective layers, anti-halation layers, barrier layers, development inhibiting compounds, speed-increasing agent, stabilizers, plasticizer, chemical sensitizer, UV absorbers and the like can be present in the photographic element.

A detailed description of photographic elements and of various layers and additives can be found in Research Disclosure 17643 December 1978, 18431 August 1979, 18716 November 1979, 22534 January 1983, and 308119 December 1989.

The silver halide photographic material of the present invention can be exposed and processed by any conventional processing technique. Any known developing agent can be used into the developer, such as, for example, dihydroxybenzenes (e.g., hydroquinone), pyrazolidones (1-phenyl-3-pyrazolidone, 4,4-dimethyl-1-phenyl-3-pyrazolidone), and aminophenols (e.g., N.;methyl-p-aminophenol), alone or in combinations thereof. Preferably the silver halide photographic materials are developed in a developer comprising dihydroxybenzenes as the main developing agent, and pyrazolidones and p-aminophenols as auxiliary developing agents.

Other well known additives can be present in the developer, such as, for example, antifoggants (e.g., benzotriazoles, indazoles, tetrazoles), silver halide solvents (e.g., thiosulfates, thiocyanates), sequestering agents (e.g., aminopolycarboxylic acids, aminopolyphosphonic acids), sulfite antioxidants, buffers, restrainers, hardeners, contrast promoting agents, surfactants, and the like. Inorganic alkaline agents, such as KOH, NaOH, and LiOH are added to the developer composition to obtain the desired pH which is usually higher than 10.

The silver halide photographic material of the present invention can be processed with a fixer of typical composition. The fixing agents include thiosulfates, thiocyanates, sulfites, ammonium salts, and the like. The fixer composition can comprise other well known additives, such as, for example, acid compounds (e.g., metabisulfates), buffers (e.g., carbonic acid, acetic acid), hardeners (e.g., aluminum salts), tone improving agents, and the like.

The present invention is particularly intended and effective for high temperature, accelerated processing with automatic processors where the photographic element is transported automatically and at constant speed from one processing unit to another by means of roller. Typical examples of said automatic processors are 3M TRIMATIC.TM. XP515 and KODAK RP X-OMAT.TM.. The processing temperature ranges from 20.degree. to 60.degree. C., preferably from 30.degree. to 50.degree. C. and the processing time is lower than 90 seconds, preferably lower than 45 seconds. The good antistatic and surface characteristics of the silver halide photographic material of the present invention allow the rapid processing of the material without having the undesirable appearance of static marks or scratches on the surface of the film.

The invention will be described hereinafter by reference to the following example.

A tabular grain silver bromide emulsion (having an average diameter:thickness ratio of 8:1, prepared in the presence of a deionized gelatin having a viscosity at 60.degree. C. in water at 6.67% w/w of 4.6 mPas, a conducibility at 40.degree. C. in water at 6.67% w/w of less than 150 .mu.s/cm and less than 50 ppm of Ca.sup.++) was optically sensitized to green light with a cyanine dye and chemically sensitized with sodium p-toluenethiosulfonate, sodium p-toluenesulfinate and benzothiazoleiodoethylate. At the end of the chemical digestion, non-deionized gelatin (having a viscosity at 60.degree. C. in water at 6.67% w/w of 5.5 mPas, a conducibility at 40.degree. C. in water at 6.67% w/w of 1,100 .mu.s/cm and 4,500 ppm of Ca.sup.++) was added to the emulsion in an amount to have 83% by weight of deionized gelatin and 17% by weight of non-deionized gelatin. The emulsion, containing 5-methyl-7-hydroxytriazaindolizine stabilizer and a hardener, was divided into four portions. The four portions were each added with the compounds indicated in Table 1. Each portion was coated on each side of a blue polyester film support at a silver coverage of 2 g/m.sup.2 and a gelatin coverage of 1.6 g/m.sup.2 per side. A non-deionized gelatin protective supercoat containing 1.1 g/m.sup.2 of gelatin per side and the compounds indicated in Table 1 was applied on each coating so obtaining four different double-side radiographic films A to D.

Hostapur.TM. is the trade name of an anionic surfactant of the alkane sulfonate sodium salt type, manufactured by Hoechst AG, Niaproof.TM. is the trade name of an anionic surfactant of the alkane sulfate type, Tegobetain.TM. is the trade name of an anphoteric surfactant of the betaine type, having the following formula: ##STR21## wherein R is an alkyl chain having from 12 to 17 carbon atoms, manufactured by Th. Goldschmidt AG, Tergitol.TM. NPX is the trade name of a non-ionic surfactant of the nonylphenylpolyethyleneglycolether type, manufactured by Union Carbide Co., Triton.TM. X-200 is the trade name of an anionic surfactant of the alkylaryl sulfonate sodium salt type, L1028 is a cationic fluorinated compound of formula: ##STR22## manufactured by 3M Company, L9342 is a fluorinated salt of formula: ##STR23## wherein b=8.5 and a+c=2.5, manufactured by 3M Company, and Compound A is an electrically conductive copolymer containing carboxylic groups and sulfonic groups having the following formula: ##STR24## having a number average molecular weight of about 3500.

The four samples A to D were conditioned for 15 hours at 25% of relative humidity. After conditioning the samples were exposed and developed. After that they were subjected to the evaluation of the coating quality by technical people. The samples were then evaluated according to the "Charge Decay Time Test" and the "Surface Resistivity Test".

According to this test the static charge dissipation of each of the films was measured. The films were cut into 45.times.54 mm samples and conditioned at 25% relative humidity and T=21.degree. C. for 15 hours. The charge decay time was measured with a Charge Decay Test Unit JCI 155 (manufactured by John Chubb Ltd., London). This apparatus deposits a charge on the surface of the film by a high voltage corona discharge and a fieldmeter allows observation of the decay time of the surface voltage. The lower the time, the better the antistatic properties of the film. To prevent the charge decay behavior of the tested surface from being influenced by the opposite surface, this surface was grounded by contacting it with a metallic back surface.

According to this test the resistivity of the sample surface was measured using the Hewlett Packard model 4329A high resistance meter.

The results of the above mentioned tests are summarized in the following Table 2.

The evaluation of coating quality of Table 2 was expressed by scholastic score as an average of the evaluation of three technical people: 4 means unacceptable, 5 means insufficient, 6 means sufficient and 7 means good.

Sample B, in spite of having good antistatic property, was contaminated by mottles, more visible on processed film, and a large number of repellencies.

Sample D, according to the present invention, showed the best performance either in terms of antistatic properties and of coating quality.

The same tabular grain silver bromide emulsion of example 1 was employed to prepare nine films comprising the compounds indicated in the following Table 3. The emulsion was coated on each side of a blue polyester film support at a silver coverage of 2 g/m.sup.2 per side. A non-deionized gelatin protective supercoat containing 1.1 g/m.sup.2 and the compounds indicated in Table 3 was applied on each coating so obtaining 9 different double-side radiographic films E to O.

Tensagex.TM. DLM 990 is the trade name of a triethoxyalkylsulfonate manufactured by Hichkon-Manro and having the following formula: ##STR25##

Daclor.TM. 70L is the trade name of a triethoxyalkylsulfonate manufactured by D.I.S. and having the following formula: ##STR26##

Tensuccin.TM. HM 935 is the trade name of an alkoxyalkylsulfonate manufactured by Hickon-Manro.

Disponil.TM. FES-92 is the trade name of a dodecaethoxyalkylsulfonate manufactured by Stephan Europe and having the following formula: ##STR27##

Triton.TM. X-100 is the trade name of a non-ionic surfactant of the octylphenylpolyethyleneglycolether type, manufactured by Union Carbide Co. Symperonic 91-10 is the trade name of a non-ionic surfactant of the alkylethyleneglycolether type, manufactured by I.C.I. and having the following formula: ##STR28##

Atlas.TM. G 4848 is the trade name of an alkylpolyoxyethylenemethylether manufactured by I.C.I.

Surfactant.TM. G-10 is the trade name of an alkylpolyoxyethyleneglycol manufactured by Olin Chemicals.

L1028 is a cationic fluorinated compound of formula: ##STR29## manufactured by 3M Company. Tergitol.TM. NPX is the trade name of a non-ionic surfactant of the nonylphenylpolyethyleneglycolether type, manufactured by Union Carbide Co. Triton.TM. X-200 is the trade name of an anionic surfactant of the alkylaryl sulfonate sodium salt type.

Compound A is an electrically conductive copolymer containing carboxylic groups and sulfonic groups having the following formula: ##STR30## and having a number average molecular weight of about 3500.

The nine samples E to O were conditioned for 15 hours at 25% of relative humidity. After conditioning the samples were exposed and developed. The coating quality was evaluated by technical people according the method of Example 1.

After that, the samples were evaluated according to the "Charge Decay Time Test" and the "Surface Resistivity Test" described in Example 1.

The results are summarized in the following Table 4.

All the samples E to O according to the present invention showed a good result both in terms of antistatic properties and of coating quality.