Photographic light-sensitive material with preserved antistatic properties

Abstract: A photographic silver halide material is disclosed which comprises a support and on one or both sides thereof at least one silver halide emulsion layer and a protective gelatin antistress layer and which comprises in an outermost layer on the side(s) containing at least one emulsion layer a polyoxyalkylene compound as an antistatic agent, characterised in that said antistress layer comprises an ionic or non-ionic polymer or copolymer latex. In addition to the preservation of antistatic properties after processing of the said material an improvement in surface glare as appreciated upon examination of medical X-ray films is obtained. Moreover the occurrence after processing of water spot defects and sticking is avoided.

Description: 1. FIELD OF THE INVENTION The invention is related to a light-sensitive silver halide photographic material having an antistatic layer. 2. BACKGROUND OF THE INVENTION It is well-known that a photographic film coated with hydrophilic colloid layers at one or two sides of the undercoat, e.g. a polyester undercoat, has a low conductivity due to the electric-insulating properties and becomes electrostatically charged by friction with dielectric materials and/or contact with electrostatically chargeable transport means, e.g. rollers. The charging occurs particularly easily in a relatively dry atmospheric environment, and especially with rapidly moving mechanical transport systems. The electrostatical charge that is accumulated may cause various problems due to the fact that it cannot be discharged gradually. As a consequence e.g. partial exposure of the photosensitive silver halide emulsion layers of the photographic material after an abrupt discharge may occur before development. This partial exposure results in the formation of dot-like or branch-like or feather-like spots after development of the photographic material. In praxis the photographic material is subjected to frictional contact with other elements during manufacturing, e.g. during a coating or cutting stage, and during use, e.g. during image-processing. Especially in the reeling-up or unreeling of dry photographic film in a camera high friction may build up, resulting in electrostatic charges that may attract dust or cause sparking. In unprocessed photographic silver halide emulsion materials sparking causes undesirable exposure marks and degrades the image quality. These disturbing phenomena however cannot be observed prior to development. As this phenomenon is very irreproducible, difficulties arise for the quality control department to evaluate said photographic material. In order to reduce electrostatic charging of a photographic material comprising a hydrophobic resin undercoat layer or support and at least one hydrophilic colloid layer on at least one side of said support without impairing its transparency it is known to apply coatings which are formed of or incorporate ionic compounds such as antistatic high molecular weight watersoluble polymeric compounds having ionic groups at frequent intervals in the polymer chain [ref. e.g. Photographic Emulsion Chemistry, by G.F. Duffin, - The Focal Press - London (1966) - Focal Press Limited, p. 168, US-P 4,301,240]. Especially preferred antistatic compositions have been described in US-P 4,610,955. These compositions comprise a hydrophilic binder, a surface active polymer having polymerized oxyalkylene monomers and an inorganic salt of organic tetrafluoroborates, perfluoroalkylcarboxylates, hexafluorophosphates and perfluoroalkyl carboxylates, said fluorinated surfactants leading to a good coating quality of the hydrophylic layers. To minimize the electrostatic charge properties of photographic materials, especially the tribo-electrical charging causing electrostatical discharges and mechanical faults by transporting, it has been proposed according to EP 319 951 to use in the hydrophilic colloid layer a combination of three surfactants viz. an anionic fluorinated surfactant, a nonionic oxyalkyl compound and a nonionic oxyalkyl compound containing fluorine atoms. Nevertheless a remaining problem is the preservation of the antistatic properties during storage of the photographic material for a long time after manufacturing, especially when said storage takes place in severe circumstances as e.g. at high temperature and high relative humidity. A solution for the preservation problem of the antistatic properties may be offered by the coating of a thicker antistress layer with an increased amount of antistatic agents, e.g. polyoxyethylene polymers. Although these increased amounts have the advantage of giving rise to more surface glare after processing, an inadmissable contamination or sludge formation in the coating step and, after exposure and development, may occur in the processing solutions. Moreover a thicker hydrophilic layer may retard the processing and drying velocity. This is obviously contradictory to the trend to develop rapid processing systems characterized by films with thin coating layers. 3. OBJECTS OF THE INVENTION. Therefor it is a first object of this invention to provide a photographic material having antistatic characteristics that are preserved after storage of said photographic material for a long time between manufacturing and processing, with minimum amounts of antistatic agent(s) and other additives coated in order to minimize the contamination of the processing solutions. Further it is another object of this invention to improve the outlook of the film surface after processing of the thin coated gelatin layers, in particular by providing enough glare as appreciated upon examination of medical X-ray films and in addition by avoiding water spot defects and sticking. Other objects will become apparent from the description hereinafter. 4. SUMMARY OF THE INVENTION. It has been found that the objects can be attained by a photographic silver halide material which comprises a support and on one or both sides thereof at least one silver halide emulsion layer and a protective antistress layer of a hydrophilic colloid and which comprises in an outermost layer on the side(s) containing at least one emulsion layer a polyoxyalkylene compound as an antistatic agent, characterised in that said antistress layer comprises an ionic or non-ionic polymer or copolymer latex. 5. DETAILED DESCRIPTION Preferred copolymers used according to the present invention are generally cross-linked and are prepared analogously to the method described in US-P 4,301,240 by emulsion polymerisation of aliphatic esters of acrylic and/or methacrylic acid in water in the presence of polyfunctional cross-linking monomers and an emulsifier, followed by saponification of the obtained copolymer. By said emulsion polymerisation copolymers with a molecular weight well above 500,000 are obtained and the average particle size of the latex is smaller than 150 nm. Examples of the synthesis of ionic cross-linked copolymers in hydrophilic colloid coatings of a recording material according to the present invention can further be found in EP-A 452 568. A preferred latex used in accordance with this invention is a latex of a cross-linked polymer, being a copolymer of an acrylic and/or methacrylic acid ester including 90-99 mole % of acrylate and/or methacrylate units and 1 to 10 mole % of tetraallyloxyethane units as polyfunctional crosslinking monomer, wherein in said copolymer at least 75 % of the ester groups have been transformed into alkali metal carboxylate groups, thus exhibiting ionic characteristics. In a preferred embodiment according to this invention an especially preferred latex of a cross-linked ionic polymer is poly([c.l.]tetraallyloxyethane-co-methyl acrylate/acrylic acid), the formula (I) of which is given with a x/y/z=3/18/79 molar ratio. Moreover according to this invention the following polymers or copolymeric combinations of monomers have been found to be very useful as ionic or nonionic polymers, whether or not in combination with the cross-linked copolymers cited hereinbefore: polyvinylpyrrolidone, polyacrylamide, polyacrylic acid, polyamethylacrylate, polyethylacrylate, polymethylmethacrylate, polyethylmethacrylate as well as styrene-maleïc acid or a styrene-maleïc acid anhydrid type copolymer. In the antistress layer(s) comprising the latex-type polymers or copolymers described hereinbefore, hydrophilic colloid binders that can be homogeneously mixed therewith are e.g. proteinaceous colloids, e.g. gelatin, polysaccharide, and synthetic substitutes for gelatin as e.g. polyvinyl alcohol, poly-N-vinyl pyrrolidone, polyvinyl imidazole, polyvinyl pyrazole, polyacrylamide, polyacrylic acid, and derivatives thereof. Furthermore the use of mixtures of said hydrophilic colloids is not excluded. Among these binders the most preferred is gelatin. Conventional lime-treated or acid treated gelatin can be used. The preparation of such gelatin types has been described in e.g. "The Science and Technology of Gelatin", edited by A.G. Ward and A. Courts, Academic Press 1977, page 295 and next pages. The gelatin can also be an enzyme-treated gelatin as described in Bull. Soc. Sci. Phot. Japan, N° 16, page 30 (1966). To minimize the amount of gelatin, however can be replaced in part or integrally by synthetic polymers as cited hereinbefore or by natural or semi-synthetic polymers. Natural substitutes for gelatin are e.g. other proteins such as zein, albumin and casein, cellulose, saccharides, starch, and alginates. Semi-synthetic substitutes for gelatin are modified natural products as e.g. gelatin derivatives obtained by conversion of gelatin with alkylating or acylating agents or by grafting of polymerizable monomers on gelatin, and cellulose derivatives such as hydroxyalkyl cellulose, carboxymethyl cellulose, phthaloyl cellulose, and cellulose sulphates. According to a preferred embodiment of this invention the cross-linked copolymers as defined above are applied in an amount of at least 10% by weight versus the amount of hydrophilic colloid present in the antistress layer(s). In addition the said latex-type copolymers may be present in an outermost gelatin free coating (if any) applied thereover. A preferred protective antistress layer is made from gelatin hardened up to a degree corresponding with a water absorption of less than 2.5 grams of water per m 2 . The gelatin coverage in the protective layer is preferably not higher than about 1.20 g per m 2 and is more preferably in the range of 1.20 to 0.60 g per m 2 . In a preferred embodiment gelatin in the antistress layer is partially replaced by colloidal silica as it gives rise to a further improvement of the obtained properties according to this invention. Preferably colloidal silica having an average particle size not larger than 10 nm and with a surface area of at least 300 m 2 per gram is used, the colloidal silica being present at a coverage of at least 50 mg per m 2 . Further the coverage of said colloidal silica in the antistress layer is preferably in the range of 50 mg to 500 mg per m 2 . Particularly good results which are fully in accordance with this invention are obtained by using an antistatic layer consisting for at least 50 % by weight of colloidal silica versus the preferred ionic polymer latex described hereinbefore. Especially preferred colloidal silica particles have a surface area of 500 m2 per gram and an average grain size smaller than 7 nm. Such type of silica is sold under the name KIESELSOL 500 (KIESELSOL is a registered trade name of Bayer AG, Leverkusen, West-Germany). In admixture with the hardened gelatin the antistress layer may further contain friction-lowering substance(s) such as dispersed wax particles (carnaubawax or montanwax) or polyethylene particles, fluorinated polymer particles, silicon polymer particles etc. in order to further reduce the sticking tendency of the layer especially in an atmosphere of high relative humidity. The gelatin binder can be forehardened with appropriate hardening agents such as those of the epoxide type, those of the ethylenimine type, those of the vinylsulfone type e.g. 1,3-vinylsulphonyl-2-propanol, chromium salts e.g. chromium acetate and chromium alum, aldehydes e.g. formaldehyde, glyoxal, and glutaraldehyde, N-methylol compounds e.g. dimethylolurea and methyloldimethylhydantoin, dioxan derivatives e.g. 2,3-dihydroxy-dioxan, active vinyl compounds e.g. 1,3,5-triacryloyl-hexahydro-s-triazine, active halogen compounds e.g. 2,4-dichloro-6-hydroxy-s-triazine, and mucohalogenic acids e.g. mucochloric acid and mucophenoxychloric acid. These hardeners can be used alone or in combination. The binder can also be hardened with fast-reacting hardeners such as carbamoylpyridinium salts as disclosed in US Patent 4,063,952 and with the onium compounds as disclosed in EU Patent Application 408,143. The ionic or non-ionic polymers or copolymeric combinations of monomers cited hereinbefore are optionally added in addition to non-ionic surfactant(s) having antistatic characteristics that is (are) present in the outermost layer at side of the support where the emulsion layer(s) has (have) been coated. As non-ionic surfactant(s) having antistatic characteristics any of the generally known polyalkylene oxide polymers is useful as antistatic agent. Suitable examples of alkylene oxides are e.g. polyethylene glycol, polyethylene glycol/polypropylene glycol condensation products, polyethylene glycol alkyl ethers or polyethylene glycol alkylaryl ethers, polyethylene glycol esters, polyethylene glycol sorbitan esters, polyalkylene glycol alkylamines or alkylamides, silicone-polyethylene oxide adducts, glycidol derivatives, fatty acid esters of polyhydric alcohols and alkyl esters of saccharides. Preferred antistatic agents are polyoxyethylene compounds. A more preferred antistatic agent corresponds to formula (II) R-O-(CH 2 CH 2 O) n -H wherein n is an integer of at least 4 preferably between 8 and 30 and R represents a long chain alkyl or alkylaryl group having at least 10 C-atoms as e.g. oleyl. According to this invention in a preferred embodiment said antistatic coating is applied as an outermost coating, e.g. as protective layer at the silver halide emulsion layer side of a photographic silver halide emulsion layer material. In another preferred embodiment the protective antistress layer, optionally comprising antistatic agent(s), is covered with a gelatin free antistatic afterlayer comprising the polyoxyalkylene compound. The coating of the said gelatin free antistatic layer, as well as the coating of the antistress layer may proceed by any coating technique known in the art, e.g. by doctor blade coating, air knife coating, curtain coating, slide hopper coating or meniscus coating, which are coating techniques known from the production of photographic silver emulsion layer materials. Moreover the spray coating technique, known from US-P 4,218,533, may be applied. Any thickening agent may be used so as to regulate the viscosity of the solution used for any of the said coating techniques provided that they do not particularly affect the photographic characteristics of the silver halide light-sensitive photographic material. Preferred thickening agents include aqueous polymers such as polystyrene sulphonic acid, sulphuric acid esters, polysaccharides, polymers having a sulphonic acid group, a carboxylic acid group or a phosphoric acid group, polyacrylamide, polymethacrylic acid or its salt, copolymers from acrylamide and methacrylic acid and salts derived thereof, copolymers from 2-acrylamido-2-methyl-propansulphonic acid, polyvinyl alcohol, alginate, xanthane, carraghenan and the like. Polymeric thickeners well-known from the literature resulting in thickening of the coating solution may be used independently or in combination. Patents concerning thickening agents are U.S. Patent No. 3.167.410, Belgian Patent No. 558.143, JP OPI Nos. 53-18687 and 58-36768 and DE 3,836,945. As a preferred polymeric thickener use can be made of the product characterized by formula (III) with x/y=24/76. The gelatin-free antistatic afterlayer may further comprise spacing agents and coating aids such as wetting agents as e.g. perfluorinated surfactants. Spacing agents which may also be present in the protective antistress layer in generally have an average particle size which is comprised between 0.2 and 10 µm. Spacing agents can be soluble or insoluble in alkali. Alkali-insoluble spacing agents usually remain permanently in the photographic element, whereas alkali-soluble spacing agents usually are removed therefrom in an alkaline processing bath. Suitable spacing agents can be made i.a. of polymethyl methacrylate, of copolymers of acrylic acid and methyl methacrylate, and of hydroxypropylmethyl cellulose hexahydrophthalate. Other suitable spacing agents have been described in US-A 4,614,708. It has now quite unexpectedly been found that according to this invention the presence of at least one ionic or non-ionic polymer or copolymer latex in the protective anti stress coating, and, optionally, in the afterlayer coated thereover, provides the preservation of good antistatic properties of the material. Moreover the absence of water spot defects for the dry film after processing can be observed as well as the appearance of an improved surface glare. Even for thin coated layers for applications in rapid processing conditions the same advantages can be recognized. Furthermore the appearance of sludge in the processing is significantly reduced as well in hardener free as in hardener containing processing solutions. A common support of a photographic silver halide emulsion material is a hydrophobic resin support or hydrophobic resin coated paper support. Hydrophobic resin supports are well known to those skilled in the art and are made e.g. of polyester, polystyrene, polyvinyl chloride, polycarbonate, preference being given to polyethylene terephthalate. The hydrophobic resin support may be provided with one or more subbing layers known to those skilled in the art for adhering thereto a hydrophilic colloid layer. Suitable subbing layers for polyethylene terephthalate supports are described e.g. in US-P 3,397,988, 3,649,336, 4,123,278 and 4,478,907. Photographic silver halide emulsion materials, containing at least one silver halide emulsion layer and as an antistatic outermost layer a protective antistress layer according to this invention and an optionally present afterlayer, may be of any type known to those skilled in the art. For example, the said antistatic outermost layer is useful in materials for continuous tone or halftone photography, microphotography and radiography, in black-and-white as well as colour photographic materials. It is clear that also single side coated materials can be prepared according to this invention. In that case the single side coated photographic material comprises a support and on one side thereof at least one silver halide emulsion layer and a protective gelatin antistress layer containing an ionic or non-ionic polymer or copolymer latex and in an outermost coating on the said side a polyoxyalkylene compound wherein on the other side an outermost layer is present comprising a said ionic or non-ionic polymer and a said polyoxyalkylene compound. In the back coated layer(s) one or more antihalation dyes can be present either in the said outermost coating or in an underlying back coating or in both of them. Antihalation dyes are non-spectrally sensitizing dyes which are widely used in photographic elements to absorb reflected and scattered light. Examples of the said dyes have been described e.g. in US-P 3,560,214; US-P 4,857,446 and in EP-Applications 92.202.767 and 92.202.768. The filter dye(s) can be coated in layers of photographic elements in the form as has been described in EP 0,384,633 A2; EP 0,323,729 A2; EP 0,274,723 B1, EP 0,276,566 B1, EP 0,351,593 A2; in US-Patents 4,900,653; 4,904,565; 4,949,654; 4,940,654; 4,948,717; 4,988,611 and 4,803,150; in Research Disclosure 19551 (July 1980); in EP 0,401,709 A2 and in US-Patent 2,527,583, these examples being not limitative. By using a recording material having a composition according to the present invention problems as preservation of antistatic characteristics before processing, water spot defects, sticking and insufficient glare after processing in automatic processing machines can be avoided or substantially reduced. Such means for example that the formation of static charges by contact of a silver halide emulsion layer side with the rear side of the recording material or caused by friction with substances such as rubber and hydrophobic polymeric binder, e.g. the binder constituent of phosphor screens used as X-ray intensifying screens, can be markedly reduced by employing the present antistatic layer. The building up of static charges and subsequent dust attraction and/or sparking, e.g. during loading of films in cassettes, e.g. X-ray cassettes, or in cameras, or during the taking or projection of a sequence of pictures as occurs in automatic cameras or film projectors is prevented. The following examples illustrate the present invention without however limiting it thereto. 6. EXAMPLES EXAMPLE 1. An X-ray photographic material was provided with an antistatic layer as a gelatin free outermost layer on top of the protective antistress layer covering the silver halide emulsion layer. Use was made of the slide hopper coating technique for simultaneous application of the emulsion layer, the antistress layer and the antistatic coating. The composition of said outermost layer was as follows: an ammoniumperfluorocarbonate compound represented by the formula F 15 C 7 COONH 4 a polyoxyethylene compound represented by the formula (II) R-O-(CH 2 CH 2 O) n -H with n=10 and R=oleyl and a polymeric thickener represented by the formula (III) with x/y=24/76. The three products were added to an aqueous solution containing up to 10% of ethyl alcohol with respect to the finished solution, ready for coating. Said three products were present in an amount of 0.75 g/l, 5.0 g/l and 6.5 g/l respectively and coated in an amount of 6.0 mg/m 2 , 40.0 mg/m 2 and 52.0 mg/m 2 respectively. The amount of ethyl alcohol was evaporated during the coating and drying procedure of the antistatic layer. The antistress layer was coated with the following compounds, expressed in grams per square meter per side: gelatin 1.10 polymethylmethacrylate (average particle diameter : 6 µm) 0.023 1-p-carboxyphenyl-4,4'-dimethyl-3-pyrazolidine-1-one 0.054 C 17 H 15 -CO-NH-(CH 2 -CH 2 -O-) 17 -H 0.0188 formaldehyde 0.1 The resulting material is the comparative coating No. 1 in Table 1. A material according to the present invention was prepared in an analogous way with the difference that an amount of 0.375 g/m 2 of the ionic polymer corresponding to formula (I) was added to the protective antistress layer. The resulting material is the inventive coating No. 2 in Table 1. As an objective evaluation of the antistatic properties the lateral surface resistance was measured before processing. A comparison was made between the lateral surface resistivity of a freshly prepared photographic material and said material after storing for 36 hours in a conditioned atmosphere of 57°C and 34% RH (relative humidity). The lateral surface resistance is indicated as LSR in Table 1, taken as a representive parameter to characterize the antistatic properties of the material, was expressed in ohm/square (ohm/sq.) and was measured by a test proceeding as follows : two conductive copper poles having a length of 10 cm parallel to each other were placed at a distance of 1 cm onto the surface to be tested and the resistance built up between said electrodes was measured with a precision ohm-meter. By multiplying the thus determined ohm value with the factor 10 the surface resistance value expressed as ohm/square (ohm/sq) was obtained. Moreover the presence of water spot defects and of sticking defects after processing was qualitatively evaluated as "good" or "bad", "bad" being indicated as soon as "drip marks" were visually observed after processing in the case of the water spot defect evaluation or as soon as "sticking flecks" were visually observed after processing and piling up a series of films of the same coating material. The processing conditions and the composition of the processing solutions is given hereinafter: the processing of the described photographic materials in accordance with this invention proceeds in the processing machine CURIX HT530 (Agfa-Gevaert trademarked name) with the following time (in seconds) and temperature (in °C) characteristics: loading 0.2 sec. developing 9.3 sec. 35°C in developer I described below cross-over 1.4 sec. rinsing 0.9 sec. cross-over 1.5 sec. fixing 6.6 sec. 35°C in fixer I described below cross-over 2.0 sec. rinsing 4.4 sec. 20°C cross-over 4.6 sec. drying 6.7 sec. total 37.6 sec. Composition of Developer I: -concentrated part : water 200 ml potassium bromide 12 grams potassium sulphite (65% solution) 249 grams ethylenediaminetetraacetic acid, sodium salt,trihydrate 9.6 grams hydroquinone 106 grams 5-methylbenzotriazole 0.076 grams 1-phenyl-5-mercaptotetrazole 0.040 grams sodiumtetraborate (decahydrate) 70 grams potassium carbonate 38 grams potassium hydroxide 49 grams diethylene glycol 11 grams potassium iodide 0.088 grams 4-hydroxymethyl-4methyl-1phenyl-3-pyrazolidinone 12 grams Water to make 1 liter pH adjusted to 11.15 at 25°C with potassium hydroxide. For initiation of the processing one part of the concentrated developer was mixed with 3 parts of water. No starter was added. The pH of this mixture was 10.30 at 25°C. Composition of the fixer: -concentrated part : ammonium thiosulfate (78% solution) 661 grams sodium sulphite 54 grams boric acid 25 grams sodium acetate-trihydrate 70 grams acetic acid 40 grams water to make 1 liter pH adjusted with acetic acid to 5.30 at 25°C To make this fixer ready for use one part of this concentrated part was mixed with 4 parts of water. A pH of 5.25 was measured at 25°C. Lateral Surface Resistance for an X-ray photographic film coated with a protective layer and an outermost gelatin free afterlayer. Coating No. LSR x 10 -10 Ohm/square Fresh LSR x 10 -10 Ohm/square After 36 h Water spot defects Sticking defects 1 (comp.) 100 1300 bad bad 2 (inv.) 17 95 good good As can be seen from Table 1 a remarkable improvement is observed in antistatic properties, for the freshly prepared and for the stored material if the ionic polymer latex having a structure according to formula I is added to the protective layer. Moreover the coating according to this invention shows an improvement in the surface characteristics after processing as water spot defects and sticking defects are no longer observed. The same results concerning water spot defects and sticking are obtained if the processing solutions contain a hardening compound as glutar dialdehyd in the developer solution and aluminum sulphate in the fixer. EXAMPLE 2. The same materials as in Example 1 were coated as coating No. 1 (comparative) and coating No. 2 (invention). In coating No. 1', polyethyl acrylate was added as an alternative polymer latex to the protective layer coating composition, whereas in coating No. 2' a higher amount of 0.56 g/m 2 of the ionic polymer latex of formula (I) was added as compared to coating No. 2. For the 4 coated materials an evaluation of the surface glare characteristics was made quantitatively. Therefor use was made of the measurement technique with a reflectometer as described in ASTM D523, 1985, corresponding with DIN 67530 (01.82) and ISO 2813 (1978) wherein reflections are measured at values of the reflection angles of 20°, 60° and 85°, depending on the glare of the surfaces. Measurement takes place at reflection angles of 20° in the case of high gloss, at 60° for moderate gloss and at 85° for low gloss. The corresponding results are summarized in Table 2. Quantitative evaluation of surface glare after processing for an X-ray photographic film coated with a protective layer and an outermost gelatin free afterlayer. Coating No. Glare (angle: 20°) Glare (angle: 60°) 1 (comparative) 2 23 1' (comparative) 2.6 26 2 (invention) 6 46 2' (invention) 10 56 The difference in effectiveness of both products, polymer latex polyethyl acrylate (coating No. 1') and the ionic polymer latex of formula (I) according to this invention (coatings Nos. 2 and 2') with respect to surface glare after processing as described hereinbefore is quite clear: a remarkable improvement in the surface glare characteristics has been reached and the effect is still more pronounced as the concentration in the protective coating of the polymer latex used according to this invention is enhanced as is illustrated for material No. 4. EXAMPLE 3. In this example the surface glare characteristics are measured and summarized in Table 3 for the following materials. Coating No. 1 is the comparative example, corresponding to the comparative coatings No. 1 in the previous Examples 1 and 2. Said material has a coated amount of gelatin in the protective layer of 1.1 g/m 2 . In coating No. 1'', the amount of gelatin is lowered to 0.8 g/m 2 and additionally 0.26 g/m 2 of Kieselsol 500, trade name product of BAYER AG, Leverkusen, Germany, is added as a silica sol. In coating No. 3, according to this invention, an amount of 0.19 g/m 2 of the ionic polymer latex of formula (I) is added to the protective layer with the same composition as in coating No. 1''. Quantitative evaluation of surface glare after processing for an X-ray photographic film coated with a protective layer and an outermost gelatin free afterlayer. Coating No. Glare (angle: 20°) Glare (angle: 60°) 1 (comparative) 2.9 30 1'' (comparative) 6.4 46 3 (invention) 12 62 As can be seen from Table 3 the surface glare is improved to the level as in Example 2, coating No. 1', by decreasing the amount of gelatin and adding silica to the protective layer, instead of making use of the polymer latex according to this invention. However additionally added to the coating, the ionic polymer latex according to this invention makes the surface glare reach an unexpected level as is illustrated by the figures for coating No. 3! EXAMPLE 4. A set of 12 materials was coated in accordance with the procedure described in Example 1 for coating No. 2 with the difference that the amounts of gelatin in the antistress layer (gel AS) and in the emulsion layer (gel EM) and the amounts of polymer latex of formula (I) (LATEX) and silica sol KIESELSOL 500 (SILICA) in the protective layer were as listed in Table 4. According to the method described in Example 3, the surface glare was measured at respective angles of 20° (GLARE 20°) and 60° (GLARE 60°) for the materials processed in accordance with the processing cycle and the processing baths, represented in Example 1. Quantitative evaluation of surface glare after processing for X-ray films coated with a protective layer and an outermost gelatin free afterlayer. Mat.No gel AS g/m 2 gel EM g/m 2 LATEX g/m 2 SILICA g/m 2 GLARE 20° GLARE 60° 4 0.8 2.2 0 0 3.4 35.7 5 0.8 2.2 0 0.08 8.1 50.7 6 0.8 2.2 0.0835 0.04 6.9 46.7 7 0.8 2.2 0.167 0 14.2 58.8 8 0.8 2.2 0.167 0.08 21.0 64.0 9 1.05 1.95 0.0835 0 5.4 43.9 10 1.05 1.95 0.167 0.04 16.8 60.6 11 1.3 1.7 0 0 5.8 43.8 12 1.3 1.7 0 0.08 10.7 53.6 13 1.3 1.7 0.083 0.04 8.2 49.5 14 1.3 1.7 0.167 0 8.8 53.0 15 1.3 1.7 0.167 0.08 20.8 64.2 As can be seen from Table 4 the highest figures for surface glare can be obtained if the ionic polymer latex according to the invention and/or silica sol are present in the protective layer. Moreover an increase of gelatin in the protective antistress layer makes the glare level to increase, at least when the total amount of gelatin present in the emulsion and the protective layer is held constant. For all 12 materials no water spot defects after processing, nor sticking defects after piling up the processed films were observed. Further the antistatic behaviour was excellent. EXAMPLE 5. The same coating composition as in Example 1, No. 1 was taken as a comparative example. For coatings No. 16 to 21 additions to the protective antistress layer were performed as summarized in Table 5, the amounts of the additives being expressed in mg/m 2 and per side of the support. Figures for the lateral surface resistivity, for the freshly coated (LSR FC) material as well as for the material preserved for 36 hours (LSR 36H), measured as set forth in Example 1 are also given in the said Table 5. Moreover the surface glare (GLARE) was measured at angles of 20° and 60° as described in Example No. 2. Moreover water spot defects were evaluated qualitatively and quantitatively. Therefor the contact angle (C.A, expressed in °) of water drops on the film surface in the processing after the rinsing step, before entering the drying unit of the processor was measured. A lower contact angle was considered to be indicative for a better spreading of the water drops on the surface and a decreasing water spot defect level was expected. Further water spots defects (WSD) were evaluated qualitatively as already mentioned in Example 1, but a more detailed analysis was made: figures were given from "1" to "5", "1" indicating that there were no detectable water spot defects, "5" indicative for an unacceptable level of water spots. As polymers or copolymers, whether or not from the latex-type, the following compounds have been represented in abbreviated form: I: indicating the copolymer according to formula (I) II: indicating the copolymer according to formula (II) PAA: polyacrylic acid (in acid or salt form depending on pH) PVP: polyvinylpyrrolidone STMA: styrene maleic acid anhydride copolymer MMA/MA/EA: copolymer of methylmethacrylate/methacrylic acid/ethylacrylate In Table 5 "POL" has the meaning of "POLYMER" and the lateral surface resistance LSR has been expressed in Ohms/square. The data given in the Table for LSR have already been multiplied by 10 -10 . Mat. No LATEX or POL LATEX g/m 2 SILICA g/m 2 GLARE 20° GLARE 60° LSR LSR 36H CA ° WSD 1 0 0 0 1.8 23.8 280 10 5 62 5 16 I 0.188 0.188 7.7 49.3 140 550 29 0-1 17 PAA 0.050 0 2.4 29.8 37 130 49 3-4 18 PVP 0.075 0 2.6 30.6 35 74 47 3 19 II 0.050 0 2.4 29.2 59 150 46 3-4 20 STMA 0.025 0 4.0 38.7 130 230 52 3 21 MMA/MA/EA 0.250 0 8.3 50.2 350 2600 28 1-2 As can be seen from Table 5 a remarkable improvement of the surface resistance for the freshly coated and preserved material is established if ionic or non-ionic polymer or copolymer latex compounds are present in the protective antistress layer of the material according to this invention, wherein the said protective antistress layer has an antistatic afterlayer composition coated thereover. Moreover an improvement in surface glare for the thin coated layers is observed as well as an improvement in water spot defects after processing. The said improvement is detected by measuring lower contact angles of water drops adsorbed on the film surface after the rinsing step, before going into the drying unit of the film processor.

Claims: A photographic silver halide material which comprises a support and on one or both sides thereof at least one silver halide emulsion layer and a protective antistress layer of a hydrophilic colloid and which comprises in an outermost layer on the side(s) containing at least one emulsion layer a polyoxyalkylene compound as an antistatic agent, characterised in that said antistress layer comprises an ionic or non-ionic polymer or copolymer latex. A photographic material according to claim 1 comprising a support and on one side thereof at least one silver halide emulsion layer and a protective antistress layer of a hydrophilic colloid containing an ionic or non-ionic polymer or copolymer latex and in an outermost coating on the said side a polyoxyalkylene compound wherein on the other side an outermost layer is present comprising a said ionic or non-ionic polymer and a said polyoxyalkylene compound. A photographic material according to claim 2 wherein on the said other side one or more antihalation dyes are coated in the said outermost coating, in an underlying back coating or in both of them. A photographic silver halide material according to any of claims 1 to 3, wherein the said polyoxyalkylene compound is present in a substantially gelatin free surface layer coated over the said antistress layer. A photographic silver halide material according to any of claims 1 to 4, wherein the said polyoxyalkylene compound is a polyoxyethylene compound. A photographic silver halide material according to any of claims 1 to 5 wherein the said latex is a latex of a cross-linked ionic polymer, being a copolymer of an acrylic and/or methacrylic acid ester including 90-99 mole % of acrylate and/or methacrylate units and 1 to 10 mole % of tetraallyloxyethane units as polyfunctional crosslinking monomer, wherein in said copolymer at least 75 % of the ester groups have been transformed into alkali metal carboxylate groups. A photographic silver halide material according to claim 6, wherein the said polymer latex is poly([c.l.]tetraallyloxyethane-co-methyl acrylate/potassium acrylate) that is prsent in a 3/18/79 molar ratio. A photographic silver halide material according to any of claims 1 to 5 wherein the said polymer or copolymer is selected from the group consisting of vinylpyrrolidone, acrylamide, acrylic acid, methylacrylate, ethylacrylate, methylmethacrylate, ethylmethacrylate or a latex of copolymers of styrene and maleïc acid or styrene and maleïc acid anhydride. A photographic silver halide material according to any of claims 1 to 8, wherein the said polymer or copolymer latex is present in an amount of at least 10% by weight versus the amount of hydrophilic colloid present in the antistress layer(s). A photographic silver halide material according to any of claims 1 to 9, wherein in the said antistress layer(s), the amount of hydrophilic colloid coated is less than 1.2 g/m 2 . A photographic silver halide material according to any of claims 1 to 10, wherein colloidal silica particles are present in the antistress layer(s) in an amount of 50 to 500 mg/m 2 . A photographic silver halide material according to claim 11, wherein the colloidal silica particles have a surface area of 500 m2 per gram and an average grain size smaller than 7 nm. A photographic material according to any of claims 1 to 12, wherein said photographic material is a medical X-ray material.

Inventors: VANDENABEELE HUBERT, VANDENABEELE, HUBERT, VANDENABEELE, HUBERT, C/O AGFA-GEVAERT N.V.
Applicants: AGFA GEVAERT NV, AGFA-GEVAERT N.V.
Application year: 1993
Main classification: G03C1
IPC codes: G03C1, G03C5