Motion Picture Print Film

The present invention relates to an improved motion picture print film, and more particularly to a motion picture print film that resists tar adsorption and stain absorbtion.

Motion picture photographic films that are used as print films for movie theater projection have long used a carbon black-containing layer on the backside of the film. This backside layer provides both antihalation protection and antistatic properties. The carbon black is applied in an alkali-soluble binder that allows the layer to be removed by a process that involves soaking the film in alkali solution, scrubbing the backside layer, and rinsing with water. This carbon black removal process, which takes place prior to image development, is both tedious and environmentally undesirable since large quantities of water are utilized in this film processing step. In addition, in order to facilitate removal during film processing, the carbon black-containing layer is not highly adherent to the photographic film support and may dislodge during various film manufacturing operations such as film slitting and film perforating. Carbon black debris generated during these operations may become lodged on the photographic emulsion and cause image defects during subsequent exposure and film processing.

After removal of the carbon black-containing layer the film's antistatic properties are lost. Undesired static charge build-up can then occur on processed motion picture print film when transported through projectors or on rewind equipment. Although these high static charges can discharge they cannot cause static marks on the processed photographic film. However, the high static charges can attract dirt particles to the film surface. Once on the film surface, these dirt particles can create abrasion or scratches or, if sufficiently large, the dirt particles may be seen on the projected film image.

In U.S. Ser. No. 08/576,796 filed Dec. 19, 1995, now U.S. Pat. No. 5,679,505, a motion picture print film is described which contains on the backside of the support, an antistatic layer and a protective overcoat. The protective overcoat is comprised of a polyurethane binder and a lubricant. The polyurethane binder has a tensile elongation to break at least 50% and a Young's modulus measured at 2% elongation of at least 50000 lb/in.sup.2.

However, post processing tar deposits and stain have been a problem with protective overcoats in motion picture print film. This tar is derived mostly from polymeric oxidized developer. The present invention relates to eliminating tar pickup during processing by providing a hydrophilic topcoat that can become hydrated in an aqueous environment thereby creating a diffuse and dynamic interface resistant to any tar adsoprtion.

Further, having the non water permeable polyurethane overcoat below the hydrophilic topcoat of this invention, ensures protection of the underlying antistat layer. The problem with adding hydrophilic additives directly to the polyurethane overcoat is that, at the levels at which the polyurethane surface becomes hydrophilic enough to repel tar, the entire coating becomes too permeable to processing solutions, and provides no protection to the antisat layer below. Hence the advantage of using a hydrophilic topcoat over the protective overcoat.

This invention relates to a motion picture print film having a support and having, in order, on one side thereof an antihalation undercoat and at least one silver halide emulsion layer and having, in order, on the opposite side thereof an antistatic layer, a protective overcoat; characterized in that said protective overcoat includes a polyurethane binder, the polyurethane binder has a tensile elongation to break of at least 50% and a Young's modulus measured at a 2% elongation of at least 50000 lb/in.sup.2, and a topcoat farthest from the support which includes a hydrophilic binder at a weight percent of at least 20.

The photographic film support materials used in the practice of this invention are synthetic high molecular weight polymeric materials. These support materials may be comprised of various polymeric films, but polyester and cellulose triacetate film supports, which are well known in the art, are preferred. The thickness of the support is not critical. Support thickness of 2 to 10 mils (0.002-0.010 inches) can be employed, for example, with very satisfactory results. The polyester support typically employs an undercoat or primer layer between the antistatic layer and the polyester support. Such undercoat layers are well known in the art and comprise, for example, a vinylidene chloride/methyl acrylate/itaconic acid terpolymer or vinylidene chloride/acrylonitrile/acrylic acid terpolymer as described in U.S. Pat. Nos. 2,627,088, 2,698,235, 2,698,240, 2,943,937, 3,143,421, 3,201,249, 3,271,178 and 3,501,301.

The antihalation undercoat used in this invention functions to prevent light from being reflected into the silver halide emulsion layer(s) and thereby causing an undesired spreading of the image which is known as halation. Any of the filter dyes known to the photographic art can be used in the present invention as a means of reducing halation. Thus, for example, water-soluble dyes can be used for this purpose. Such dyes should be incorporated in the antihalation undercoat with a mordant to prevent dye diffusion. Alternatively, and preferably, a solid particle filter dye is incorporated in the antihalation undercoat.

Useful water-soluble filter dyes for the purpose of this invention include the pyrazolone oxonol dyes of U.S. Pat. No. 2,274,782, the solubilized diaryl azo dyes of U.S. Pat. No. 2,956,879, the solubilized styryl and butadienyl dyes of U.S. Pat. Nos. 3,423,207 and 3,384,487, the merocyanine dyes of U.S. Pat. No. 2,527,583, the merocyanine and oxonol dyes of U.S. Pat. Nos. 3,486,897, 3,652,284 and 3,718,472, the enamino hemioxonol dyes of U.S. Pat. No. 3,976,661, the cyanomethyl sulfone-derived merocyanines of U.S. Pat. No. 3,723,154, the thiazolidones, benzotriazoles, and thiazolothiazoles of U.S. Pat. Nos. 2,739,888, 3,253,921, 3,250,617, and 2,739,971, the triazoles of U.S. Pat. No. 3,004,896, and the hemioxonols of U.S. Pat. Nos. 34,215,597 and 4,045,229. Useful mordants are described, for example, in U.S. Pat. Nos. 3,282,699, 3,455,693, 3,438,779, and 3,795,519.

Preferred examples of solid particle filter dyes for use in the antihalation underlayer of this invention are those described in U.S. Pat. No. 4,940,654. These solid particle filter dyes are compounds represented by the following formula(I):

where

D is a chromophoric light-absorbing moiety, which, when y is 0, comprises an aromatic ring free of carboxy substituents,

A is an aromatic ring, free of carboxy substituents, bonded directly or indirectly to D,

X is a substituent, other than carboxy, having an ionizable proton, either on A or on an aromatic ring portion of D, having a pKa of about 4 to 11 in a 50/50 mixture (volume basis) of ethanol and water,

y is 0 to 4,

n is 1 to 7, and

the compound has a log partition coefficient of from about 0 to 6 when it is in unionized form.

Examples of filter dyes according to formula (I) include the following: ##STR1##

To promote adhesion of the antihalation underlayer to the support, primer layers as hereinabove described are advantageously employed, especially when the support is a polyester support.

The use of film-forming hydrophilic colloids as binders in photographic elements, including photographic films and photographic papers, is very well known. The most commonly used of these is gelatin and gelatin is a particularly preferred material for use in this invention. It can be used as the binder in the antihalation underlayer and in the silver halide emulsion layer(s). Useful gelatins include alkali-treated gelatin (cattle bone or hide gelatin), acid-treated gelatin (pigskin gelatin) and gelatin derivatives such as acetylated gelatin, phthalated gelatin and the like. Other hydrophilic colloids that can be utilized alone or in combination with gelatin include dextran, gum arabic, zein, casein, pectin, collagen derivatives, collodion, agar-agar, arrowroot, albumin, and the like. Still other useful hydrophilic colloids are water-soluble polyvinyl compounds such as polyvinyl alcohol, polyacrylamide, poly(vinylpyrrolidone), and the like.

The photographic elements of the present invention can be simple black-and-white or monochrome elements or they can be multilayer and/or multicolor elements.

Color photographic elements of this invention typically contain dye image-forming units sensitive to each of the three primary regions of the spectrum. Each unit can be comprised of a single silver halide emulsion layer or of multiple emulsion layers sensitive to a given region of the spectrum. The layers of the element, including the layers of the image-forming units, can be arranged in various orders as is well known in the art.

A preferred photographic element according to this invention comprises at least one blue-sensitive silver halide emulsion layer having associated therewith a yellow image dye-providing material, at least one green-sensitive silver halide emulsion layer having associated therewith a magenta image dye-providing material and at least one red-sensitive silver halide emulsion layer having associated therewith a cyan image dye-providing material.

In addition to an antihalation underlayer and one or more emulsion layers, the elements of the present invention can contain auxiliary layers conventional in photographic elements, such as overcoat layers, spacer layers, filter layers, interlayers, pH lowering layers (sometimes referred to as acid layers and neutralizing layers), timing layers, opaque reflecting layers, opaque light-absorbing layers and the like.

The light-sensitive silver halide emulsions employed in the photographic elements of this invention can include coarse, regular or fine grain silver halide crystals or mixtures thereof and can be comprised of such silver halides as silver chloride, silver bromide, silver bromoiodide, silver chlorobromide, silver chloroiodide, silver chorobromoiodide, and mixtures thereof. The emulsions can be, for example, tabular grain light-sensitive silver halide emulsions. The emulsions can be negative-working or direct positive emulsions. They can form latent images predominantly on the surface of the silver halide grains or in the interior of the silver halide grains. They can be chemically and spectrally sensitized in accordance with usual practices. The emulsions typically will be gelatin emulsions although other hydrophilic colloids can be used in accordance with usual practice. Details regarding the silver halide emulsions are contained in Research Disclosure, Item 36544, September, 1994, and the references listed therein.

The photographic silver halide emulsions utilized in this invention can contain other addenda conventional in the photographic art. Useful addenda are described, for example, in Research Disclosure, Item 36544, September, 1994. Useful addenda include spectral sensitizing dyes, desensitizers, antifoggants, masking couplers, DIR couplers, DIR compounds, antistain agents, image dye stabilizers, absorbing materials such as filter dyes and UV absorbers, light-scattering materials, coating aids, plasticizers and lubricants, and the like.

Depending upon the dye-image-providing material employed in the photographic element, it can be incorporated in the silver halide emulsion layer or in a separate layer associated with the emulsion layer. The dye-image-providing material can be any of a number known in the art, such as dye-forming couplers, bleachable dyes, dye developers and redox dye-releasers, and the particular one employed will depend on the nature of the element, and the type of image desired.

Dye-image-providing materials employed with conventional color materials designed for processing with separate solutions are preferably dye-forming couplers; i.e., compounds which couple with oxidized developing agent to form a dye. Preferred couplers which form cyan dye images are phenols and naphthols. Preferred couplers which form magenta dye images are pyrazolones and pyrazolotriazoles. Preferred couplers which form yellow dye images are benzoylacetanilides and pivalylacetanilides.

Protective overcoats of the present invention may be successfully employed with a variety of antistatic layers well known in the art. The antistatic layer of this invention may include a variety of electrically conductive metal-containing particles, such as metal oxides, dispersed in a binder material. Many of these metal oxide particles do not require chemical barriers to protect them against harsh environments, such as photographic processing solutions. However, since many of these metal oxides require high particle loading in a binder to obtain good conductivity, i.e. antistatic properties, the physical properties are degraded and an abrasion resistant topcoat is required for good physical durability of the layers. Examples of useful electrically conductive metal-containing particles include donor-doped metal oxides, metal oxides containing oxygen deficiencies, and conductive nitrides, carbides, and borides. Specific examples of particularly useful particles include conductive TiO.sub.2, SnO.sub.2, V.sub.2 O.sub.5, Al.sub.2 O.sub.3, ZrO.sub.2, In.sub.2 O.sub.3, ZnO, ZnSb.sub.2 O.sub.6, InSbO.sub.4, TiB.sub.2, ZrB.sub.2, NbB.sub.2, TaB.sub.2, CrB, MoB, WB, LaB.sub.6, ZrN, TiN, WC, HfC, HfN, and ZrC. Examples of the patents describing these electrically conductive particles include; U.S. Pat. Nos. 4,275,103, 4,394,441, 4,416,963, 4,418,141, 4,431,764, 4,495,276, 4,571,361, 4,999,276, 5,122,445 and 5,368,995. Also included are:

Semiconductive metal salts such as cuprous iodide as described in U.S. Pat. Nos. 3,245,833, 3,428,451, and 5,075,171.

Fibrous conductive powders comprising, for example, antimony-doped tin oxide coated onto non-conductive potassium titanate whiskers as described in U.S. Pat. Nos. 4,845,369 and 5,116,666.

Conductive polymers, such as, the cross-linked vinylbenzyl quaternary ammonium polymers of U.S. Pat. No 4,070,189 or the conductive polyanilines of U.S. Pat. No. 4,237,194.

A colloidal gel of vanadium pentoxide or silver-doped vanadium pentoxide as described in U.S. Pat. Nos. 4,203,769, 5,006,451, 5,221,598 and 5,284,714.

However, the preferred antistatic layer contains vanadium pentoxide as described in one of the aforementioned patents. The antistatic layer described in U.S. Pat. No. 4,203,769 is prepared by coating an aqueous colloidal solution of vanadium pentoxide. Preferably, the vanadium pentoxide is doped with silver. A polymer binder, such as a cationic vinylidene-chloride-containing terpolymer latex or a polyesterionomer dispersion, is preferably employed in the antistatic layer to improve the integrity of the layer and to improve adhesion to the undercoat layer. Typically the dried coating weight of the vanadium pentoxide antistatic material is about 0.5 to 30 mg/m.sup.2. The weight ratio of polymer binder to vanadium pentoxide can range from about 1:5 to 500:1, but, preferably 1:1 to 10:1. Typically, the antistatic layer is coated at a dry coverage of from 1 to 400 mg/m.sup.2 based on total dry weight The electrical resistivity of the antistatic layer is preferably from about 7 to about 11 log.OMEGA./sq, and most preferably less than 9 log .OMEGA./sq.

The antistatic coating formulation may also contain a coating aid to improve coatability. The common level of coating aid in the antistatic coating formula is 0.01 to 0.30 weight percent active coating aid based on the total solution weight. However, the preferred level of coating aid is 0.02 to 0.20 weight percent active coating aid based on total solution weight. These coating aids can be either anionic or nonionic coating aids such as paraisononyphenoxy-glycidol ethers, octylphenoxy polyethoxy ethanol, sodium salt of alkylaryl polyether sulfonate, and dioctyl esters of sodium sulfosuccinic acid, which are commonly used in aqueous coatings. The coating may be applied onto the film support using coating methods well known in the art such as hopper coating, skim pan/air knife, gravure coating, and the like.

The antistatic layer of this invention is overcoated with a polyurethane. Preferably, the polyurethane is an aliphatic polyurethane. Aliphatic polyurethanes are preferred due to their excellent thermal and UV stability and freedom from yellowing. The polyurethanes of the present invention are characterized as those having a tensile elongation to break of at least 50% and a Young's modulus measured at an elongation of 2% of at least 50,000 lb/in.sup.2. These physical property requirements insure that the overcoat layer is hard yet tough to simultaneously provide excellent abrasion resistance and outstanding resiliency to allow the topcoat and antistat layer to survive hundreds of cycles through a motion picture projector. The polyurethane overcoat is preferably coated from a coating formula containing from about 0.5 to about 10.0 weight percent of polymer to give a dry coverage of from about 50 to about 3000 mg/m.sup.2. The dry coverage of the overcoat layer is preferably from about 300 to 2000 mg/m.sup.2.

The polyurethane may be either organic solvent soluble or aqueous dispersible. For environmental reasons, aqueous dispersible polyurethanes are preferred. Preparation of aqueous polyurethane dispersions is well-known in the art and involves chain extending an aqueous dispersion of a prepolymer containing terminal isocyanate groups by reaction with a diamine or diol. The prepolymer is prepared by reacting a polyester, polyether, polycarbonate, or polyacrylate having terminal hydroxyl groups with excess polyfunctional isocyanate. This product is then treated with a compound that has functional groups that are reactive with an isocyanate, for example, hydroxyl groups, and a group that is capable of forming an anion, typically this is a carboxylic acid group. The anionic groups are then neutralized with a tertiary amine to form the aqueous prepolymer dispersion. The chemical resistance of the polyurethane overcoat can be improved by adding a crosslinking agent that reacts with functional groups present in the polyurethane, for example, carboxyl groups. Crosslinking agents such as aziridines, carbodiimides, epoxies, and the like are suitable for this purpose. The crosslinking agent can be used at about 0.5 to about 30 weight percent based on the polyurethane. However, a crosslinking agent concentration of about 2 to 12 weight percent based on the polyurethane is preferred.

The present invention includes a topcoat over the polyurethane overcoat to reduce or eliminate tar pickup. The topcoat contains at least 20 percent by weight of a hydrophilic colloid. Examples of hydrophilic colloids include water-soluble polymers, gelatin, gelatin derivatives, dextran and its derivatives, cellulose esters, latex derivatives, casein, agar, sodium alginate, starch, polyvinyl alcohol, poly(ethylene oxide) copolymers, polyacrylic acid copolymers and maleic anhydride copolymers and mixtures thereof. The cellulose esters include hydroxyl propyl cellulose, carboxymethyl cellulose and hydroxyethyl cellulose. The latex polymers include vinyl chloride copolymers, vinylidene chloride copolymers, acrylic ester copolymers, vinyl acetate copolymers and butadiene copolymers, polyethylene oxide containing copolymers and so on. Among them, gelatin is most preferred.

Gelatin may be any of so-called alkali-treated (lime treated) gelatin which was immersed in an alkali bath, prior to extraction thereof, an acid-treated gelatin which was immersed in an alkali bath prior to extraction thereof, an acid-treated gelatin which was immersed in both baths and enzyme-treated gelatin. If necessary, gelatin can be used in combination with colloidal albumin, casein, a cellulose derivative (such as carboxymethyl or hydroxyethyl cellulose), agar, sodium alginate, a saccharide derivative (such as a starch derivative or dextran), a synthetic hydrophilic colloid (such as polyvinyl alcohol, poly-N-vinylpyrolidone, a polyacrylic acid copolymer, polyacrylamide or a derivative or partial hydrolyzate thereof) or a gelatin derivative.

Preferred ranges of the hydrophilic colloid such as gelatin in the topcoat are 20-100%, more preferably 40-100% and most preferably 60-100%. Preferred coating coverages of the hydrophilic topcoat are 50 to 2000 mg/m.sup.2, more preferably 100 to 1000 mg/m.sup.2.

The topcoat may additionally contain crosslinking agents or hardeners, fillers for improving the modulus of the layer, lubricants, and additives such as matte beads for controlling the ferrotyping characteristics of the surface.

Hardeners suitable for hardening the topcoat include, for example, aldeyhde compounds such as formaldehyde and glutaraldehyde; ketone compounds such as diacetyl and cyclopentanedione; compounds having reactive halogens such as bis(2-chloroethylurea), 2-hydroxy-4,6-dichloro-1,3,5-trizine and those described in U.S. Pat. Nos. 3,288,775 and 2,732,303 and British Patent Nos. 974,723 and 1,167,207; divinylsulfone, 5-acetyl-1,3-diacrylolhexahydro-1,3,5-triazine and reactive olefin-containing compounds such as divinylsulfone, 5-acetyl-1,2-diacryloyl-hexahydro-1,3,5-triazine, and the compounds such as divinylsulfone, 5-acetyl-1,3-diacryloyl-hexahydro-1,3,5-triazine, and the compounds disclosed in U.S. Pat. Nos. 3,635,718 and 3,232,763, and British Patent 994,869; N-hydroxymethylothaimide; N-methylol compounds such as N-hydroxymethylphthalimide and those described in U.S. Pat. Nos. 2,732,316 and 2,586,168; isocyanates described in U.S. Pat. No. 3,103,437; the aziridines disclosed in U.S. Pat. Nos. 3,017,280 and 2,983,611; acid derivatives described in U.S. Pat. Nos. 2,725,294 and 2,725,295; epoxy compounds described in U.S. Pat. No. 3,091,537; and halogenated carboxyaldehydes such as mucochloric acid. Examples of inorganic hardeners include chrome alum, zirconium sulfate and the carboxyl group activating hardeners described in Japanese Patent Publication for opposition purpose (herein after referred to as J.P. Kokoku) Nos. 56-12853 and 58-32699, Belgian Patent No. 825,726, J.P. Kokai Nos. 60-225148 and 51-126125, J.P. Kokoku No. 58-50699, J.P. Kokai No. 52-54427 and U.S. Pat. No. 3,321,313.

Examples of reinforcing filler particles include inorganic powders with a Mohs scale hardness of at least 6. Specific examples are metal oxides such as g-aluminum oxide, chromium oxide, (e.g., Cr.sub.2 O.sub.3), iron oxide (e.g., alpha-Fe.sub.2 O.sub.3), tin oxide, doped tin oxide, such as antimony or indium doped tin oxide, silicon dioxide, alumino-silicate and titanium dioxide; carbides such as silicon carbide and titanium carbide; and diamond in fine powder.

A suitable lubricating agent can be included to give the topcoat a coefficient of friction that ensures good transport characteristics during manufacturing and customer handling of the photographic film. Many lubricating agents can be used, including higher alcohol esters of fatty acids, higher fatty acid calcium salts, metal stearates, silicone compounds, paraffins and the like as described in U.S. Pat. Nos. 2,588,756, 3,121,060, 3,295,979, 3,042,522 and 3,489,567. For satisfactory transport characteristics, the lubricated surface should have a coefficient of friction of from 0.10 to 0.40. However, the most preferred range is 0.15 to 0.30. If the topcoat coefficient of friction is below 0.15, there is a significant danger that long, slit rolls of the photographic film will become unstable in storage or shipping and become telescoped or dished, a condition common to unstable film rolls. If the coefficient of friction is above 0.30 at manufacture or becomes greater than 0.30 after photographic film processing, a common condition of non-process surviving topcoat lubricants, the photographic film transport characteristics become poorer, particularly in some types of photographic film projectors.

Aqueous dispersed lubricants are strongly preferred since lubricants, in this form, can be incorporated directly into the aqueous protective topcoat formula, thus avoiding a separately applied lubricant overcoat on the protective topcoat layer. The aqueous dispersed lubricants of carnauba wax, polyethylene oxide, microcrystalline wax, paraffin wax, silicones, stearates and amides work well as incorporated lubricants in the aqueous, protective topcoat. However, the aqueous dispersed lubricants of carnauba wax and stearates are preferred for their effectiveness in controlling friction at low lubricant levels and their excellent compatibility with aqueous binders.

In addition to lubricants, matting agents are important for improving the transport of the film on manufacturing, printing, processing, and projecting equipment. Also, these matting agents can reduce the potential for the protective overcoat to ferrotype when in contact with the emulsion side surface under the pressures that are typical of roll films. The term "ferrotyping" is used to describe the condition in which the backside protective topcoat, when in contact with the emulsion side under pressure, as in a tightly wound roll, adheres to the emulsion side sufficiently strongly that some sticking is noticed between the protective topcoat and the emulsion side surface layer when they are separated. In severe cases of ferrotyping, damage to the emulsion side surface may occur when the protective topcoat and emulsion side surface layer are separated. This severe damage may have an adverse sensitometric effect on the emulsion.

The topcoat of the present invention may contain matte particles. The matting agent may be silica, calcium carbonate, or other mineral oxides, glass spheres, ground polymers and high melting point waxes, and polymeric matte beads. Polymeric matte beads are preferred because of uniformity of shape and uniformity of size distribution. The matte particles should have a mean diameter size of about 0.5 to about 3 micrometers. However, preferably the matte particles have a mean diameter of from about 0.75 to about 2.5 micrometers. The matte particles can be employed at a dry coating weight of about 1 to about 100 mg/m.sup.2. The preferred coating weight of the matte particles is about 15 to about 65 mg/m.sup.2. The surface roughness (Ra, ANSI Standard B46.1, 1985) in microns should be in the range 0.010 to 0.060 to prevent ferrotyping of the emulsion surface. The preferred Ra value range is from 0.025 to 0.045 for best performance. If the Ra value is below 0.025, there is insufficient surface roughness to prevent slight emulsion surface marking from ferrotyping between the backing and emulsion. If the Ra value is above 0.045, there is sufficient surface roughness with these size matte particles to show some low level of emulsion granularity and loss of picture sharpness, especially under the very high magnifications typical of movie theater projection.

The above described additives, including lubricants, matte beads, and fillers can also be present in the underlying polyurethane overcoat.

The present invention is illustrated by the following examples.

The polyurethane overcoats used in the examples were composed of Witcobond 232 (Witco Corporation) or Sancure 898 (B.F. Goodrich Company) and contained 3 percent by weight (based on polymer) of an aziridine crosslinker. The topcoat contained anywhere from 20-100 percent by weight gelatin the remainder being made up of Witcobond 232 or Sancure 898.

Preparation of support containing an antistatic formulation

A subbed polyester support was prepared by first applying a subbing terpolymer of acrylonitrile, vinylidene chloride and acrylic acid to both sides of the support before drafting and tentering so that the final coating weight was about 90 mg/m.sup.2.

An antistatic formulation consisting of the following components was prepared at 0.078% total solids:

The antistatic formulation was coated over the subbed polyester support on the side opposite to the antihalation layer to give a dry coating weight of about 12 mg/m.sup.2.

A protective overcoat formulation was applied over the antistat layer. The overcoat formulation consisted of the following components:

Topcoats were applied over the coating derived from Example 2 the formulations for which are described in Table 1. All coatings contained 2.5 percent by weight based on gelatin of a divinylsulfone crosslinking agent.

Topcoats were applied over the coating derived from Example 2 the formulations for which are described in Table 2 as blends of a polyurethane and gelatin. All coatings contained 6 percent by weight based on the total binder of an aziridine crosslinker.

Tar Test

During routine film development, by-products of oxidized color developer will form brown, oily residue that may be adsorbed by the film surface and may create permanent, brown stained spots, i.e. tar.

A simulated developer tar test was performed on the samples to determine their propensity for tar stain build-up. The test was done at 105.degree. F. and involved smearing tar harvested from a developer tank onto the coating immersed in a developer bath followed by removal of the tar using dilute sulfuric acid. The resultant stain or tar is indicative of the propensity of the coating for tar adsorption. The results are tabulated in Table 3.

As shown in the Example 2, the polyurethane coating has very poor resistance to picking up developer tar. When this polyurethane overcoat is coated with a gelatin topcoat the propensity to pickup up tar is eliminated (Example 3). As one increases the amount of polyurethane in the gelatin topcoat an increase in tar pickup is observed; however, when the topcoat contains at least 20 percent of the hydrophilic colloid (gelatin) improved results are achieved. (Examples 4-10). As one increases the topcoat coverage, improved results are also achieved.

The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.