Annealable imaging support containing a gelatin subbing layer and an antistatic layer

Abstract

 An imaging support comprising : a polyester base having a first and a second side; a gelatin subbing layer on the first side; and on the second side an antistatic layer comprising electrically-conductive metal-containing fine particles dispersed in gelatin.

Description

[0001] This invention relates to light sensitive imaging elements in general and in particular to annealable supports with an antistat layer with electrically conductive particles.

[0002] In photographic film manufacture, an imaging layer which typically consists of silver halide grains dispersed in gelatin is deposited onto a polymeric film support which provides support and mechanical integrity to the final product. Cellulosic or polyester supports, such as poly(ethylene terephthalate) (PET) and poly(ethylene naphthalate)(PEN), are typically employed. Polyester supports are considered to be advantageous to cellulose triacetate supports for many imaging applications because they have excellent mechanical strength, dimensional stability and resistance to attack by many chemicals. Furthermore, polyester supports can be manufactured efficiently and at a reduced cost compared to cellulose triacetate supports. However, the chemical inertness of polyester supports also results in difficulty in obtaining acceptable adhesion of polar materials, such as gelatin-based photographic emulsions, to PET and PEN substrates.

[0003] To obtain acceptable adhesion of a silver-halide emulsion layer or a backing layer to a polyester support a variety of methods have been used including, surface treatment of the support or application of adhesion promoting or subbing layers either prior to orientation and crystallization of the support or post-orientation. Adhesion of the anchoring, or subbing layer is promoted by a variety of methods, including the use of chlorine-containing copolymers, as described in US Pat. Nos. 2,627,088; and 3,143,421. The application of the adhesive layer prior to the orientation and heat setting or crystallization of the polyester, and the addition of organic solvents which attack the polyester film surface is described in US Patent No. 3,501,301. In addition, a subsequent gelatin-containing layer is often required on the emulsion side of the support, prior to photographic emulsion coating, for adequate adhesion.

[0004] Similarly, surface treatment or a subbing system is used on the back side of a polyester support, to promote adhesion of electrically-conductive antistatic layers, abrasion resistant layers, magnetic layers, anti-halation layers, curl-control layers, lubricant layers, or other auxiliary layers. A particularly effective subbing system for use on both the emulsion side and back side of polyester supports is a vinylidene chloride containing polymer.

[0005] Despite the above-described advantages of polyester films, there is a drawback that when used in a roll format, a persistently remaining core set curl can occur which may result in poor handling properties. An increasing trend for smaller cameras requires a reduction in the thickness of photographic imaging elements to maintain a similar number of exposures in a smaller film cartridge. Reducing the thickness of the film support has the most impact on the thickness of the photographic element. However, this results in increased demands on core set, dimensional stability and mechanical strength which require the use of polyester supports; particularly for small format films. In order to satisfy these increasing demands a polyester support comprising a poly(alkylene aromatic dicarboxylate) whose glass transition point is from 50 °C to 200 °C such as polyethylene terephtalate or polyethylene naphthalate has increasingly been used in photographic elements. Furthermore, it is well-known that heat-treatment of the polyester support at a temperature of from 40 °C up to the glass transition temperature for a period of from 0.1 hr to 1500 hrs significantly reduces the core set curl.

[0006] In addition to a polymeric support, image forming layer and adhesion promoting layers, it is well known to include in various imaging elements various auxiliary layers including antistatic layers, lubricant or transport-controlling layers, hydrophobic barrier layers, antihalation layers, abrasion and scratch protection layers, transparent magnetic recording layers and other special function layers. The inclusion and use of such transparent magnetic recording layers in light-sensitive silver halide photographic elements has been described in U.S. Pat. Nos. 3,782,947; 4,279,945; 4,302,523; 5,217,804; 5,229,259; 5,395,743; 5,413,900; 5,427,900; 5,498,512; and others. Such elements are advantageous because images can be recorded by customary photographic processes while information can be recorded simultaneously into or read from the magnetic recording layer by techniques similar to those employed for traditional magnetic recording art.

[0007] Problems associated with the generation and discharge of electrostatic charge have been recognized for many years by the photographic industry. The accumulation of charge leads to the attraction of dust, which can produce physical defects. The discharge of accumulated charge can produce irregular fog patterns or static marks in the sensitized emulsion. The presence of dust not only can result in the introduction of physical defects and the degradation of the image quality of the photographic element but also can result in the introduction of noise and the degradation of magnetic recording performance (e.g., S/N ratio, "drop-outs", etc.) for an imaging element containing a magnetic recording layer. In order to prevent these problems arising from electrostatic charging, there are various well known methods by which an electrically-conductive or antistatic layer can be introduced into the photographic element to dissipate electrostatic charge. Typically, in photographic elements comprising a transparent magnetic recording layer, the antistatic layer is present as a backing layer underlying the magnetic recording layer.

[0008] As indicated above, it is desirable to heat-treat or anneal the polyester support to impart the required physical properties, particularly to reduce core set to an acceptable level for recent applications such as small format films for use in smaller cameras. In addition, annealing the support with subbing or backing layers is advantageous for manufacturing efficiency. Annealing of polyester supports having coated thereon an antistatic layer has been disclosed in U.S. Pat. Nos. 5,629,141; 5,582,963; 5,585,229; 5,739,309 and 5,766,835. The process taught in the above patents consists of surface treatment of the polyester support followed by application of an antistatic layer having tin oxide dispersed in gelatin. In the case of '309 and '963 the antistatic layer is applied directly to the surface treated support. In the remaining patents a gelatin undercoat layer is applied prior to the antistatic layer. The support having an antistatic layer is subjected to heat treatment. After heat treatment, a gelatin subbing layer is applied on the photographic emulsion side and additional backing layers may be applied. As an additional backing layer, a protective overcoat layer consisting of cellulose diacetate and a crosslinking agent is taught in the '141, '963, '229, and '309 patents. A magnetic layer having Co-γ-Fe₂O₃ and abrasive particles dispersed in cellulose diacetate which is further crosslinked is applied after heat-treatment of the support as an additional backing layer in '835. The above indicated patents also disclose that the specific heat-treatment conditions are important to control so as to avoid self-adhesion or blocking of the support. U.S. Patent No. 5,629,141 indicates self-adhesion may occur if the winding tension or humidity are too high or the knurl height too low during heat treatment. It is further disclosed that electrification of the support accelerates self-adhesion and it is therefore desirable to include electrically-conductive particles to avoid electrification. U.S. Pat. No. 5,585,229 discloses that in addition to winding tension, temperature, and knurl height, the differences in roll diameter must be kept small to reduce the tendency for sticking or blocking during heat-treatment. It is also disclosed that heat-treatment is preferably conducted before providing a subbing layer for the photographic emulsion side since such subbing layers typically contain gelatin and therefore the layer easily adheres on heating. Examples 1-26, 2-21, and 3-26 of '229 indicate a greatly increased tendency for self-adhesion or blocking and larger regions of poor planeness for samples where the antistatic layer is annealed against a gelatin subbing layer than for similar samples prepared in which the subbing layer is applied after heat-treatment. U.S. Pat. No. 5,739,309 claims heat-treatment of the support is carried out in vacuo or in a current of an inactive gas and additionally discloses it is preferable to carry out the heat-treatment prior to application of the subbing layer.

[0009] Heat-treatment of a backing layer against a gelatin containing subbing layer is taught in U.S. Pat. Nos. 5,580,707; 5,597,682; and 5,719,015. A polyester support is surface treated by corona discharge treatment on both sides, followed by application of a gelatin containing subbing layer on the emulsion side. The opposite side of the support has an antistatic layer consisting of tin oxide particles dispersed in gelatin and coated out of a methanol and water mixture. The antistatic layer is then overcoated with a protective layer containing cellulose triacetate. The support having a subbing layer, antistatic layer, and protective layer is then heat-treated before application of the photographic emulsion layers.

[0010] A silver halide photographic material having a support, a silver halide emulsion layer, a magnetic recording layer and a layer containing metal oxide particles having a crystallite size, on the average, of 1 to 20 nm is claimed in U.S. Pat. No. 5,459,021. A photographic imaging element is taught in which both sides of a polyester support are surface treated by corona discharge, followed by application of subbing layers using various latex polymers consisting of butyl acrylate, styrene, and additional acrylates. The subbing layer on the emulsion side is overcoated with a gelatin subbing layer, while the subbing layer on the opposite side is coated with an antistatic layer consisting of conductive metal oxide particles dispersed in a mixture of a copolymer latex and gelatin. A magnetic layer consisting of Co-γ-Fe₃O₃ dispersed in cellulose nitrate is also taught. Heat-treatment of polyethylene terephthalate or polyethylene naphthalate supports having a subbing layer and a backing layer at a temperature of 60 °C or 80 °C, respectively, for 24 hrs is also indicated. The curl or core set for a film sample prepared in the above manner was evaluated by winding on a 10 mm diameter core and left for 3 days at 55 °C and 20 % relative humidity. For a sample on polyethylene naphthalate which was heat-treated at 80 °C a curl removal of 60 to 70 percent was determined, somewhat improved over a similar sample which was not heat-treated and had a curl removal of 50-60 percent. The core set improvements demonstrated in '021 are advantageous for 35 mm film applications and simulate long term storage at room temperature. However, the core set results demonstrated are not sufficient for photographic elements intended for small format films in which a core diameter of less than 10 mm, typically 6-7 mm, is used in which core set requirements are more stringent. Furthermore, cellulose nitrate is not preferred as a binder for the magnetic layer due to flammability concerns which pose a significant safety risk during manufacturing.

[0011] An object of the present invention is to provide an imaging support having as outermost layers, a gelatin-containing subbing layer on the imaging side of the support, and an antistatic layer on the opposite side which is subsequently annealed at temperatures in excess of 80 °C prior to emulsion coating without causing blocking or self-adhesion of the support or requiring an additional protective or intermediate layer prior to annealing. It is a further objective of the present invention that excellent adhesion of a transparent magnetic recording layer or other auxiliary layers to the annealed support be achieved.

[0012] The present invention is an imaging support which includes a polyester base having a glass transition temperature (T_g) of from 90 to 200 °C, a gelatin-containing subbing layer on one side of the support, and an antistatic layer on the opposite side of the support comprising electrically-conductive metal-containing fine particles dispersed in a gelatin containing layer, and wherein the electrically-conductive fine particles are present at between 45 and 80 volume percent. The imaging support is annealed at a temperature of from 80 °C to the T_g of the polyester base, for 0.1 h to 1500 h. In a further embodiment, a transparent magnetic recording layer is applied to the annealed imaging support.

[0013] The present invention discloses: an imaging support comprising:

a polyester base having a first and a second side;

a gelatin subbing layer on the first side; and

on the second side an antistatic layer comprising electrically-conductive metal-containing fine particles dispersed in gelatin.

[0014] Annealable supports of the invention, having a gelatin subbing layer on the emulsion side and an antistatic layer comprising electrically-conductive metal-containing fine particles dispersed in gelatin on the backing side, does not block during annealing. Furthermore, excellent adhesion of an overlying magnetic layer is obtained for an antistatic layer continuing between 45 and 80 volume percent conductive particle.

[0015] The invention provides an annealable support which does not block against a gelatin subbing layer and yet provides good adhesion of a magnetic layer. In particular, excellent adhesion of the magnetic layer is maintained after annealing and after photographic processing, which has so far been difficult to achieve. The present annealable package does not require an additional protective layer over the antistatic layer. Furthermore, it requires no further magnetic or lubricant development.

[0016] The present invention is an imaging support which includes a polyester base coated with a gelatin-containing subbing layer on the imaging side of the support, and an antistatic layer on the opposite side of the support having electrically-conductive metal-containing fine particles dispersed in a gelatin containing layer, and wherein the electrically-conductive fine particles are present at between 45 and 75 volume percent. The polyester base has a glass transition temperature (T_g) of from 90 to 200 °C. The imaging support having a gelatin subbing layer and a gelatin containing antistatic layer as outermost layers is heat-treated at a temperature of from 80 °C to the T_g of the polyester base, for 0.1 h to 1500 h. In a preferred embodiment, the heat-treated imaging support is subsequently coated with a transparent magnetic recording layer superposed on the antistatic layer and an imaging layer is superposed on the gelatin containing subbing layer. The specified volume percentage of electrically-conductive fine particles in the antistatic layer was found to prevent self-adhesion or blocking between the gelatin subbing layer and antistatic layer during heat-treatment without the requirement of an intermediate protective layer. Furthermore, excellent adhesion of a transparent magnetic recording layer to the imaging support of the present invention is obtained for the specified volume percentages of conductive particles.

[0017] The composite imaging support of this invention is suitable for use in various imaging elements including, for example, photographic, electrostatographic, photothermographic, migration, electrothermographic, dielectric recording, and thermal-dye-transfer imaging elements. Details with respect to the composition and function of this wide variety of imaging elements are provided in U.S. Patent No. 5,719,016. Imaging elements that can be provided with a composite support in accordance with this invention can differ widely in structure and composition. For example, they can vary in regard to the type of support, the number and composition of the image forming layers, and the number and kinds of auxiliary layers included in the elements. The image forming layer(s) of a typical photographic imaging element includes a radiation-sensitive agent (e.g., silver halide) dispersed in a hydrophilic water-permeable colloid. Suitable hydophilic colloids include both naturally-occurring substances such as proteins, for example, gelatin, gelatin derivatives, cellulose derivatives, polysaccharides such as dextran, gum arabic, and the like; as well as synthetic polymers, for example, water-soluble polyvinyl compounds such as poly(vinylpyrrolidone), acrylamide polymers, and the like. A common example of an image-forming photographic layer is a gelatin-silver halide emulsion layer. In particular, the photographic elements can be still films, motion picture films, x-ray films, graphic arts films or microfiche. They can be black-and-white elements, color elements adapted for use in negative-positive process or color elements adapted for use in a reversal process.

[0018] Polymer film supports which are useful for the present invention have a glass transition temperature of from 90 °C to 200 °C and include polyester supports such as poly-1,4-cyclohexanedimethylene terephthalate, polyethylene 1,2-diphenoxyethane-4,4'-dicarboxylate, polybutylene terephthalate, and polyethylene naphthalate and the like; and blends or laminates thereof. Particularly preferred are polyethylene naphthalate and blends of polyethylene naphthalate with polyethylene terephthalate. Additional suitable polyester supports, polyester copolymers and polyester blends are disclosed in detail in U.S. Pat. No. 5,580,707. A laminated support may be prepared by co-extrusion, in-line lamination, or off-line lamination methods. A feedblock or a multi-manifold can be used for coextrusion of polyester supports according to the present invention. A biaxially stretched laminate support is obtained by laminating unstretched or uniaxially stretched film, and then subjecting the laminate film to additional stretching (orientation). In an off-line lamination method, biaxially stretched films are laminated by heat or various adhesives, to give a biaxially stretched laminated support. The supports can either be colorless or colored by the addition of a dye or pigment. Addition of a dye or pigment is particularly desirable for high refractive index polyester supports to reduce the tendency of light-piping or edge-fogging. An ultraviolet absorbent may also be added for anti-fluorescence. The thickness of the support is not particularly critical. Support thicknesses of 2 to 10 mils (50 µm to 254 µm) are suitable for photographic elements in accordance with this invention.

[0019] Film supports can be surface-treated on either or both sides prior to application of the gelatin subbing layer or gelatin-containing antistatic layer by various processes including corona discharge, glow discharge, UV exposure, flame treatment, electron-beam treatment or treatment with adhesion-promoting agents including dichloroacetic acid and trichloroacetic acid, phenol derivatives such as resorcinol and p-chloro-m-cresol, solvent washing prior to overcoating with a subbing layer of the present invention. In addition to surface treatment or treatment with adhesion promoting agents, additional adhesion promoting primer or tie layers containing polymers such as vinylidene chloride-containing copolymers, butadiene-based copolymers, glycidyl acrylate or methacrylate-containing copolymers, maleic anhydride-containing copolymers, condensation polymers such as polyesters, polyamides, polyurethanes, polycarbonates, mixtures and blends thereof, and the like may be applied to the polyester support. Particularly preferred primer or tie layers comprise a chlorine containing latex or solvent coatable chlorine containing polymeric layer. Vinyl chloride and vinylidene chloride containing polymers are preferred as primer or subbing layers of the present invention. Typically the primer compositions of this invention are composed of, by weight, from about 1 to 20 parts of latex polymer solids, and from 0.1 to 5 parts by weight of an adhesion promoter such as resorcinol, chlorophenol or chloromethylphenol in an aqueous system. A stable latex polymer is prepared by emulsion polymerization as described in U.S. Pat. Nos. 2,627,088 and 3,501,301. Suitable chloride containing polymers are composed of from about 70 to 100 percent by weight of vinyl chloride monomer or vinylidene chloride monomer. Acid containing monomers are desirably included to promote adhesion of overlying layers. Additional monomers may be incorporated in the polymer to adjust the glass transition temperature. Suitable acid containing monomers include acrylic acid, methacrylic acid, itaconic acid and maleic acid. Suitable monomers for adjusting the glass transition temperature include acrylonitrile, styrene, methacrylonitrile, glycidyl acrylates and alkyl acrylates. Preferred chlorine containing polymers are composed of a mixture of (1) from about 70 to 90 percent by weight of vinylidene chloride monomer (2) of from about 0.5 to 15 weight percent of an acid containing monomer and (3) from about 5 to 30 weight percent of a T_g modifying monomer. Particularly preferred polymers as a subbing layer are disclosed in U.S. Pat. Appl. No. 09/106,623.

[0020] The subbing or primer composition may be applied to the polyester base using an in-line process during the base manufacture or by an off-line process. When applied in an in-line process, the layer may be coated on the polyester base prior to orientation, after orientation, or after uniaxial orientation but before biaxial orientation. The primer composition described is typically applied in accordance with U.S. Pat. Nos. 2,627,088 and 3,143,421. The coating formulation is coated onto the amorphous support material, dried, and then the resulting film is oriented by stretching and other steps applied to the film such as heat setting, as described in detail in U.S. Pat. No. 2,779,684. Accordingly, the particular support film used, the procedure and apparatus for the coating thereof and the orientation of the film are not limitations of the present invention. Any of the usual coating apparatus and processing steps employed in the art may be employed in treating the film product of the present invention.

[0021] For the imaging side of the support, a hydrophilic subbing layer containing gelatin, gelatin derivatives, a combination of gelatin and polymeric film-forming binder, or a combination of gelatin and non-film-forming polymer latex particles, and the like, is applied to the polyester film base prior to heat-treatment. The subbing layer may be applied to a polyester support which has been surface treated or be superposed on any suitable primer layer. A preferred subbing layer for the imaging side of the support is described in USSN 09/067,306. The gelatin subbing layer is typically used in an amount of from 0.25 to 5 weight percent, preferably 0.5 to 1 weight percent. The subbing layer may include addenda such as dispersants, surface active agents, plasticizers, coalescing aids, solvents, co-binders, soluble dyes, solid particle dyes, haze reducing agents, adhesion promoting agents, hardeners, antistatic agents, matting agents, etc. For altering the coating and drying characteristics it is a common practice in the art to use surface active agents (coating aids) or to include a water miscible solvent in an aqueous dispersion. Suitable solvents include ketones such as acetone or methyl ethyl ketone, and alcohols such as ethanol, methanol, isopropanol, n-propanol, and butanol. Underlying subbing, primer or tie layers may also be surface treated, for example by corona discharge treatment, to aid wetting by the gelatin subbing formulation.

[0022] The electrically conductive antistatic layer of the present invention is coated on the opposite side of the support from the gelatin-containing subbing layer. The antistatic layer consists of electrically conductive metal-containing particles dispersed in a polymeric film-forming binder which includes gelatin or a gelatin-derivative. The electrically conductive particles are present at between 45 and 75 volume percent. Below 45 volume percent conductive particles, an effective antistatic layer can be obtained, however, adhesion of a magnetic recording layer is difficult to achieve, particularly without the presence of a crosslinking agent. Furthermore, significantly below 45 volume percent conductive particles blocking between the antistatic layer and the gelatin subbing layer occurs during heat-treatment. Significantly above 75 volume percent conductive particles, cohesive failure of the antistatic layer, dusting, and increased optical density or haze occurs. Between 45 and 75 volume percent conductive particles, the support can be heat-treated without causing adhesion or blocking, and a subsequent transparent magnetic recording layer or other auxiliary layers can be applied after heat-treatment and exhibit excellent adhesion without the presence of a crosslinking agent. Additional materials in the antistatic layer may include ionically conducting materials, electronically conductive polymers, non-conductive particles, magnetic particles, abrasive particles, matte particles, dispersants, surface active agents, dyes, lubricants, haze reducing agents, adhesion promoting agents, hardeners, etc. The polymeric binder of the antistatic layer contains gelatin or a gelatin derivative and could also include, latex polymers or hydrophilic polymers.

[0023] Electrically conductive metal-containing particles which may be used in the electrically conductive antistatic layer include, e.g., conductive crystalline inorganic oxides, conductive metal antimonates, and conductive inorganic non-oxides or combinations thereof. Crystalline inorganic oxides may be chosen from ZnO, TiO₂, SnO₂, Al₂O₃, In₂O₃, SiO₂, MgO, BaO, MoO₃, WO₃, and V₂O₅ or composite oxides thereof, as described in, e.g., 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 and 5,122,445. The use of antimony-doped tin oxide at an antimony doping level of at least 8 atom percent and haying an X-ray crystallite size less than 100 Å and an average equivalent spherical diameter less than 15 nm but no less than the X-ray crystallite size as taught in U.S. Pat. No. 5,484,694 is the preferred granular conductive oxide. Conductive metal antimonates suitable for use in the antistatic layer include those as disclosed in, e.g., U.S. Pat. Nos. 5,368,995 and 5,457,013. Zinc antimonate is the preferred metal antimonate. Conductive inorganic non-oxides suitable for use as conductive particles in the antistatic layer include: TiN, TiB₂, TiC, NbB₂, WC, LaB₆, ZrB₂, MoB, and the like, as described, e.g., in Japanese Kokai No. 4/55492, published February 24, 1992. The conductive particles present in the electrically conductive antistatic layer are not specifically limited in particle size or shape. The particle shape may range from roughly spherical or equiaxed particles to high aspect ratio particles such as fibers, whiskers or ribbons. In addition conductive acicular metal-containing particles as described in US Patent Nos. 5,719,016 and 5,831,119 are also preferred as antistatic agents. Additionally, the conductive materials described above may be coated on a variety of other particles, also not particularly limited in shape or composition. For example the conductive inorganic material may be coated on non-conductive SiO₂, Al₂O₃ or TiO₂ particles, whiskers or fibers. For the preferred electrically-conductive particles of zinc antimonate and antimony-doped tin oxide the volume percentage of 45 to 75 percent corresponds to about a ratio of 85/15 to 95/5 conductive particles to gelatin.

[0024] Any gelatin, gelatin derivative, or combination of gelatin with a polymeric co-binder may be used for the gelatin-containing subbing layer and as the binder for the antistatic layer. Preferred gelatins include alkali-treated (i.e., lime treated), acid-treated, and enzyme-treated gelatins. The gelatin may be hardened using any of a variety of means known to one skilled in the art. Useful hardening agents include aldehyde 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-triazine, and those described in U.S. Patent Nos. 3,288,775 and 2,732,303 and British Patent No. 994,869; N-methylol compounds such as N-hydroxymethylolphthalimide and those described in U.S. Patent Nos. 2,732,316 and 2,586,168; isocyanates described in U.S. Patent No. 3,103,437; aziridine compounds disclosed in U.S. Patent Nos. 3,017,280 and 2,983,611; acid derivatives described in U.S. Patent Nos. 2,725,294 and 2,725,295; epoxy compounds described in U.S. Patent No. 3,091,537; halogenated carboxyaldehydes such as mucochloric acid; inorganic compounds such as chrome alum, zirconium sulfate, and the carboxyl group activating compounds described in Japanese Patent Publication Nos. 56-12853, 58-32699, 60-225148, 51-126125, 58-50699, 52-54427 and U.S. Patent No. 3,321,313; and the like. The gelatin containing layers may additionally serve as an acid scavenger, neutralizing HCl which may result from thermal degradation of a chlorine containing primer layer.

[0025] Optional polymeric film-forming cobinders suitable for use in conductive layers of this invention include: water-soluble, hydrophilic polymers such as maleic acid anhydride copolymers such as sulfonated styrene/maleic acid anhydride; cellulose derivatives such as carboxymethyl cellulose, hydroxyethyl cellulose, cellulose acetate butyrate, diacetyl cellulose or triacetyl cellulose; synthetic hydrophilic polymers such as polyvinyl alcohol, poly-N-vinylpyrrolidone, acrylic acid copolymers, polyacrylamide, their derivatives and partially hydrolyzed products, vinyl polymers and copolymers such as polyvinyl acetate and polyacrylate acid ester; derivatives of the above polymers; and other synthetic resins. Other suitable cobinders include aqueous emulsions of addition-type polymers and interpolymers prepared from ethylenically unsaturated monomers such as acrylates including acrylic acid, methacrylates including methacrylic acid, acrylamides and methacrylamides, itaconic acid and its half-esters and diesters, styrenes including substituted styrenes, acrylonitrile and methacrylonitrile, vinyl acetates, vinyl ethers, vinyl and vinylidene halides, and olefins and aqueous dispersions of polyurethanes or polyesterionomers. Polyurethanes, polyesterionomers, and aqueous emulsions of vinylidene halide interpolymers are the preferred cobinders.

[0026] Coated supports in accordance with the present invention having as outermost layers a gelatin-containing subbing layer and an antistatic layer, containing gelatin and electrically-conductive particles present at between 45 and 75 volume percent, are subjected to an extended heat treatment or annealing step after conventional support film manufacturing heat treatment to reduce core-set curling tendencies of the support. Such "post manufacture" heat tempering or annealing includes heating the coated film support at a temperature in the range of from about 80 °C (more preferably about 90 °C) up to about the glass transition temperature (Tg) of the polymer support for about 0.1 to 1500 hours (more preferably 0.25 to 500 hours) as described in US Patent Nos. 4,141,735 and 5,326,689. The heat tempering or annealing step for reducing core-set curling tendencies is distinguishable from typical support manufacturing heat treatment in that it is performed after the support is wound on a roll rather than as part of the primary support manufacturing process. In a preferred embodiment of the present invention, the imaging support consists of a polyethylene-2,6-naphthalate film base which is coated on both sides with vinylidene chloride primer layers. A gelatin subbing layer is applied on one side of the support and an aqueous antistatic coating composition having tin oxide or zinc antimonate particles dispersed in gelatin is coated on the opposite side of the support. The support is annealed at a temperature from about from 90 °C to 4 °C below the T_g of the polyester base for between 0.25 and 500 hours. With respect to polyethylene-2,6-naphthalate, the Tg is about 140° C., and the heat treatment temperature is from 90° C. to 120° C., preferably from 100° C. to 115° C., and more preferably from 105° C. to 115° C.

[0027] As indicated in the prior art, the winding tension, winding speed, knurl height, humidity, roll diameter, roll uniformity, core material, and core diameter are also important considerations during the heat treatment process. A preferred winding tension is from 3 to 75 kg/m, more preferably from 5 to 40 kg/m, and most preferably from 10 to 35 kg/m. When the winding tension is too high, self-adhesion of the support may occur, particularly for a gelatin subbing on the imaging side and a gelatin containing antistatic layer having between 45 and about 55 volume percent conductive particles. On the other hand, when the tension is less than 3 kg/m, slippage may occur which results in poor handling characteristics. The winding may be conducted at a constant tension, or while gradually increasing or decreasing the tension. A preferred method is to conduct the winding while decreasing the tension. The winding procedure may be conducted at any temperature ranging from room temperature to the Tg of the support. It is preferred to wind the support at a temperature of greater than 80 °C to reduce the time required at elevated temperature to achieve the appropriate core set reduction while in the rolled format. It is generally preferred to control the humidity during the heat-treatment. The preferred relative humidity is from 0% to 85%, more preferably from 0% to 80%, and most preferably from 0% to 75%.

[0028] After heat-treatment of the support, the antistatic layer of the present invention may optionally be overcoated with a wide variety of additional functional or auxiliary layers such as a transparent magnetic recording layer, abrasion resistant layers, protective layers, curl control layers, transport control layers, lubricant layers, image recording layers, adhesion promoting layers, layers to control water or solvent permeability. In preferred embodiments of the invention, the imaging element further comprises a transparent magnetic recording layer superposed on the antistatic layer, and an image forming layer comprising a silver halide emulsion layer is superposed on the gelatin subbing layer. The transparent magnetic recording layer and the image forming layer are applied after heat-treatment of the support.

[0029] Transparent magnetic layers suitable for use in the composite supports and imaging elements in accordance with the invention include those as described, e.g., in Research Disclosure, November 1992, Item 34390. Research Disclosure is published by Kenneth Mason Publications, Ltd., Dudley House, 12 North Street, Emsworth, Hampshire P010 7DQ, ENGLAND. The magnetic layer may contain optional additional components for improved manufacturing or performance such as crosslinking agents or hardeners, catalysts, coating aids, dispersants, surfactants, including fluorinated surfactants, charge control agents, lubricants, abrasive particles, filler particles and the like. The magnetic particles of the present invention can comprise ferromagnetic or ferromagnetic oxides, complex oxides including other metals, metallic alloy particles with protective coatings, ferrites, hexaferrites, etc. and can exhibit a variety of particulate shapes, sizes, and aspect ratios. Ferromagnetic oxides useful for transparent magnetic coatings include γ-Fe₂O₃, Fe₃O₄, and CrO₂. The magnetic particles optionally can be in solid solution with other metals and/or contain a variety of dopants and can be overcoated with a shell of particulate or polymeric materials. Preferred additional metals as dopants, solid solution components or overcoats are Co and Zn for iron oxides; and Li, Na, Sn, Pb, Fe, Co, Ni, and Zn for chromium dioxide. Surface-treatments of the magnetic particle can be used to aid in chemical stability or to improve dispersibility as is commonly practiced in conventional magnetic recording. Additionally, magnetic oxide particles may contain a thicker layer of a lower refractive index oxide or other material having a low optical scattering cross-section as taught in U.S. Pat. Nos. 5,217,804 and 5,252,441. Cobalt surface-treated γ-iron oxide is a preferred magnetic particle. Ferromagnetic particles of this type are available commercially, for example, from Toda Kogyo Corp. under the tradenames CSF 4085V2, CSF 4565V, CSF 4585V, and CND 865V, and also from ISK Magnetics, Inc. under the tradenames RPX-4392, RPX-5003, RPX-5026, and RPX-5012.

[0030] Suitable polymeric binders for the transparent magnetic recording layer, antistatic layer, or auxiliary layers coated over the subbing layer of the present invention include: gelatin; cellulose compounds such as cellulose nitrate, cellulose acetate, cellulose diacetate, cellulose triacetate, carboxymethyl cellulose, hydroxyethyl cellulose, cellulose acetate butyrate, cellulose acetate propionate, cellulose acetate phthalate and the like; vinyl chloride or vinylidene chloride-based copolymers such as, vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinyl acetate-vinyl alcohol copolymers, vinyl chloride-vinyl acetate-maleic acid copolymers, vinyl chloride-vinylidene chloride copolymers, vinyl chloride-acrylonitrile copolymers, acrylic ester-vinylidene chloride copolymers, methacrylic ester-vinylidene chloride copolymers, vinylidene chloride-acrylonitrile copolymers, acrylic ester-acrylonitrile copolymers, methacrylic ester-styrene copolymers, thermoplastic polyurethane resins, thermosetting polyurethane resins, phenoxy resins, phenolic resins, epoxy resins, polycarbonate or polyester resins, urea resins, melamine resins, alkyl resins, urea-formaldehyde resins, and the like; polyvinyl fluoride, butadiene-acrylonitrile copolymers, acrylonitrile-butadiene-acrylic acid copolymers, acrylonitrile-butadiene-methacrylic acid copolymers, polyvinyl alcohol, polyvinyl butyral, polyvinyl acetal, styrene-butadiene copolymers, acrylic acid copolymers, polyacrylamide, their derivatives and partially hydrolyzed products; and other synthetic resins. Other suitable binders include aqueous emulsions of addition-type polymers and interpolymers prepared from ethylenically unsaturated monomers such as acrylates including acrylic acid, methacrylates including methacrylic acid, acrylamides and methacrylamides, itaconic acid and its half-esters and diesters, styrenes including substituted styrenes, acrylonitrile and methacrylonitrile, vinyl acetates, vinyl ethers, vinyl and vinylidene halides, and olefins and aqueous dispersions of polyurethanes or polyesterionomers. Preferred binders for the transparent magnetic recording layer include polyurethanes, polyesters, vinyl chloride based copolymers, and cellulose esters, particularly cellulose diacetate and cellulose triacetate. Cellulose diacetate is the most commonly used polymeric binder for a transparent magnetic recording layer for application in a small format photographic imaging element and is frequently crosslinked by any suitable crosslinking or hardening agent, though crosslinking is not required according the present invention. Common crosslinking agents which may be used include isocyanates, aziridines, and melamine resins, such as melamine-formaldehyde resins. However, one significant advantage of the present invention is that acceptable adhesion can be obtained without crosslinking of an overlying magnetic recording layer.

[0031] Photographic elements in accordance with the preferred embodiment of the invention can be single color elements or multicolor elements. Multicolor elements contain image dye-forming units sensitive to each of the three primary regions of the spectrum. Each unit can comprise a single emulsion layer or 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 known in the art. In an alternative format, the emulsions sensitive to each of the three primary regions of the spectrum can be disposed as a single segmented layer.

[0032] A typical multicolor photographic element comprises a support bearing a cyan dye image-forming unit comprised of at least one red-sensitive silver halide emulsion layer having associated therewith at least one cyan dye-forming coupler, a magenta dye image-forming unit comprising at least one green-sensitive silver halide emulsion layer having associated therewith at least one magenta dye-forming coupler, and a yellow dye image-forming unit comprising at least one blue-sensitive silver halide emulsion layer having associated therewith at least one yellow dye-forming coupler. The element can contain additional layers, such as filter layers, interlayers, antihalation layers, overcoat layers, subbing layers, and the like.

[0033] Photographic elements in accordance with one embodiment of the invention are preferably used in conjunction with an applied magnetic layer as described in Research Disclosure, November 1992, Item 34390. It is also specifically contemplated to use composite supports according to the invention in combination with technology useful in small format film as described in Research Disclosure, June 1994, Item 36230. Research Disclosure is published by Kenneth Mason Publications, Ltd., Dudley House, 12 North Street, Emsworth, Hampshire P010 7DQ, ENGLAND.

[0034] In the following discussion of suitable materials for use in the photographic emulsions and elements that can be used in conjunction with the composite supports of the invention, reference will be made to Research Disclosure, September 1994, Item 36544, available as described above, which will be identified hereafter by the term "Research Disclosure." The Sections hereafter referred to are Sections of the Research Disclosure, Item 36544.

[0035] The silver halide emulsions employed in the image-forming layers of photographic elements can be either negative-working or positive-working. Suitable emulsions and their preparation as well as methods of chemical and spectral sensitization are described in Sections I, and III-IV. Vehicles and vehicle related addenda are described in Section II. Dye image formers and modifiers are described in Section X. Various additives such as UV dyes, brighteners, luminescent dyes, antifoggants, stabilizers, light absorbing and scattering materials, coating aids, plasticizers, lubricants, antistats and matting agents are described, for example, in Sections VI-IX. Layers and layer arrangements, color negative and color positive features, scan facilitating features, supports, exposure and processing can be found in Sections XI-XX.

[0036] In addition to silver halide emulsion image-forming layers, the image-forming layer of imaging elements in accordance with the invention may comprise, e.g., any of the other image forming layers described in. U.S. Pat. 5,457,013.

[0037] The method of the present invention is illustrated by the following detailed examples of its practice. However, the scope of this invention is by no means limited to these illustrative examples.

EXAMPLES

Support A

[0038] Subbed supports were prepared by first coating a solution of the subbing materials onto both sides of a cast poly(ethylene naphthalate), PEN, support. The solution contained 7% of a poly(acylonitrile-co-vinylidene chloride-co-acrylic acid) latex, 1% resorcinol and 0.2% saponin in water. After drying, the subbed PEN was stretched and tentered at elevated temperatures resulting in an adhesion layer that is approximately 100 nm thick and a PEN layer which is about 95 um thick. To this support, a solution of 1% gelatin and 0.01% saponin in water was applied onto the imaging side of the support to give a dried gel thickness of about 100 nm. The support was then dried at 110 °C and heat relaxed at about 140°C.

[0039] An aqueous antistatic coating formulation containing colloidal conductive zinc antimonate particles dispersed in gelatin and containing various other additives as described below was prepared at nominally 2.3 percent solids by weight. The weight ratio of colloidal zinc antimonate to gelatin was nominally 90/10, and the zinc antimonate was present at nominally 58 volume percent of the coated layer.

Component   Weight % (wet)
Colloidal zinc antimonate1	2.077
Gelatin0.231
Hardener2   0.005
Wetting aid3   0.030
Water 97.657

1 Celnax CX-Z, Nissan Chemical America, Inc.

22,3-dihydroxy-1,4-dioxane

3 Olin 10 G, Olin Mathieson Chemical Co.

[0040] The above coating formulation was applied to vinylidene chloride subbed polyethylene naphthalate support using a coating hopper so as to provide a nominal total dry coverage of 0.30 g/m².

[0041] The support having coated thereon vinylidene chloride primer layers on both sides, a gelatin containing subbing layer on the emulsion side, and an antistatic layer on the opposite side from the gelatin subbing layer was subsequently knurled to provide a nominal knurl height of between 10 and 20 micrometers between 5 and 15 mm width. The knurled support was wound on a cylindrical core with the antistatic layer facing inwards. The cylidrical core consisted of fiberglass and had an outer diameter of 6 inches (15 cm). The wound support was heat-treated at conditions to give 100 °C for 48 hrs throughout the roll.

Support B

[0042] A heat-treated support having a subbing layer on the emulsion side and an antistatic layer on the opposite side was prepared in a similar manner to Support A, except for the composition of the antistatic layer. An aqueous antistatic coating formulation containing colloidal conductive zinc antimonate particles dispersed in gelatin and having various other additives as described below was prepared at nominally 4.6 percent solids by weight. The weight ratio of colloidal zinc antimonate to gelatin was nominally 90/10, and the zinc antimonate was present at nominally 60 volume percent of the coated layer.

Component   Weight % (wet)
Colloidal zinc antimonate1	4.154
Gelatin0.461
Hardener2   0.018
Wetting aid3   0.030
Water 95.337

1 Celnax CX-Z, Nissan Chemical America, Inc.

22,3 -dihydroxy-1,4-dioxane

3 Olin 10 G, Olin Mathieson Chemical Co.

[0043] The above coating formulation was applied to a vinylidene chloride subbed polyethylene naphthalate support using a coating hopper so as to provide a nominal total dry coverage of 0.60 g/m². The support having an antistatic coating was dried and subsequently heat-treated according to the conditions for Support A.

Support C

[0044] A heat-treated support having a subbing layer on the emulsion side and an antistatic layer on the opposite side was prepared in a similar manner to Support A, except for the composition of the antistatic layer. An aqueous antistatic coating formulation containing colloidal conductive zinc antimonate particles dispersed in gelatin and having various other additives as described below was prepared at nominally 4.3 percent solids by weight. The weight ratio of colloidal zinc antimonate to gelatin was nominally 90/10, and the zinc antimonate was present at nominally 60 volume percent of the coated layer.

Component   Weight % (wet)
Colloidal zinc antimonate1	3.807
Gelatin0.423
Hardener2   0.011
Wetting aid3   0.033
Water 95.726

1 Celnax CX-Z, Nissan Chemical America, Inc.

22,3-dihydroxy-1,4-dioxane

3 Olin 10 G, Olin Mathieson Chemical Co.

[0045] The above coating formulation was applied to a vinylidene chloride subbed polyethylene naphthalate support using a coating hopper so as to provide a nominal total dry coverage of 0.55 g/m². The support having an antistatic coating was dried and subsequently heat-treated according to the conditions for Support A.

Support D

[0046] A heat-treated support having a subbing layer on the emulsion side and an antistatic layer on the opposite side was prepared in a similar manner to Support A, except for the composition of the antistatic layer. An aqueous antistatic coating formulation containing colloidal conductive zinc antimonate particles dispersed in gelatin and having various other additives as described below was prepared at nominally 2.3 percent solids by weight. The weight ratio of colloidal zinc antimonate to gelatin was nominally 93/7, corresponding to about 65 volume percent zinc antimonate in the coated layer.

Component   Weight % (wet)
Colloidal zinc antimonate1	2.146
Gelatin0.162
Wetting aid2   0.030
Water 97.662

1 Celnax CX-Z, Nissan Chemical America, Inc.

2 Olin 10 G, Olin Mathieson Chemical Co.

[0047] The above coating formulation was applied to a vinylidene chloride subbed polyethylene naphthalate support using a coating hopper so as to provide a nominal total dry coverage of 0.30 g/m². The support having an antistatic coating was dried and subsequently heat-treated according to the conditions for Support A.

Support E

[0048] A heat-treated support having a subbing layer on the emulsion side and an antistatic layer on the opposite side was prepared in a similar manner to Support A, except for the composition of the antistatic layer. An aqueous antistatic coating formulation containing colloidal conductive zinc antimonate particles dispersed in gelatin and having various other additives as described below was prepared at nominally 4.5 percent solids by weight. The weight ratio of colloidal zinc antimonate to gelatin was nominally 93/7, and the zinc antimonate was present at nominally 68 volume percent of the coated layer.

Component   Weight % (wet)
Colloidal zinc antimonate1	4.292
Gelatin0.323
Hardener2   0.006
Wetting aid3   0.030
Water 95.349

1 Celnax CX-Z, Nissan Chemical America, Inc.

22,3-dihydroxy-1,4-dioxane

3 Olin 10 G, Olin Mathieson Chemical Co.

[0049] The above coating formulation was applied to a vinylidene chloride subbed polyethylene naphthalate support using a coating hopper so as to provide a nominal total dry coverage of 0.60 g/m². The support having an antistatic coating was dried and subsequently heat-treated according to the conditions for Support A.

Support F

[0050] A heat-treated support having a subbing layer on the emulsion side and an antistatic layer on the opposite side was prepared in a similar manner to Support A, except for the composition of the antistatic layer. An aqueous antistatic coating formulation containing colloidal conductive zinc antimonate particles dispersed in gelatin and having various other additives as described below was prepared at nominally 2.4 percent solids by weight. The weight ratio of colloidal zinc antimonate to gelatin was nominally 80/20, and the zinc antimonate was present at nominally 40 volume percent of the coated layer.

Component   Weight % (wet)
Colloidal zinc antimonate1	1.846
Gelatin0.462
Hardener2   0.018
Wetting aid3   0.030
Water 97.644

1 Celnax CX-Z, Nissan Chemical America, Inc.

22,3-dihydroxy-1,4-dioxane

3 Olin 10 G, Olin Mathieson Chemical Co.

[0051] The above coating formulation was applied to a vinylidene chloride subbed polyethylene naphthalate support using a coating hopper so as to provide a nominal total dry coverage of 0.30 g/m². The support having an antistatic coating was dried and subsequently heat-treated according to the conditions for Support A.

Support G

[0052] A heat-treated support having a subbing layer on the emulsion side and an antistatic layer on the opposite side was prepared in a similar manner to Support A, except for the composition of the antistatic layer. An aqueous antistatic coating formulation containing colloidal conductive zinc antimonate particles dispersed in gelatin and having various other additives as described below was prepared at nominally 7.0 percent solids by weight. The weight ratio of colloidal zinc antimonate to gelatin was nominally 80/20, and the zinc antimonate was present at nominally 42 volume percent of the coated layer.

Component   Weight % (wet)
Colloidal zinc antimonate1	5.538%
Gelatin 1.385
Wetting aid2   0.030
Water 93.047

1 Celnax CX-Z, Nissan Chemical America, Inc.

2 Olin 10 G, Olin Mathieson Chemical Co.

[0053] The above coating formulation was applied to vinylidene chloride subbed polyethylene naphthalate support using a coating hopper so as to provide a nominal total dry coverage of 0.90 g/m². The support having an antistatic coating was dried and subsequently heat-treated according to the conditions for Support A.

Support H

[0054] A support was prepared according to Support A without the application of an antistatic layer. Vinylidene chloride containing primer layers were applied to the front and back surfaces of the support. A gelatin containing subbing layer was applied to one surface. The support having coated thereon as outermost layers, a gelatin-subbing layer and a vinylidene chloride primer layer was heat-treated. The support exhibited severe blocking and could not be unwound for subsequent coatings.

Support I

[0055] A heat-treated support having a subbing layer on the emulsion side and an antistatic layer on the opposite side was prepared in a similar manner to Support A, except for the composition of the antistatic layer. An aqueous antistatic coating formulation containing colloidal conductive zinc antimonate particles dispersed in a terpolymer latex consisting of vinylidene chloride, acrylonitrile and acrylic acid and having various other additives as described below was prepared at nominally 2.0 percent solids by weight. The weight ratio of colloidal zinc antimonate to terpolymer was nominally 75/25, and the zinc antimonate was present at nominally 34 volume percent of the coated layer.

Component   Weight % (wet)
Colloidal zinc antimonate1	1.441%
Terpolymer   0.481
Wetting aid2   0.033
Dispersing aid3	0.036
Water 98.009

1 Celnax CX-Z, Nissan Chemical America, Inc.

2 Triton X-100, Rohm & Haas

3 Dequest 2006, Monsanto Co.

[0056] The above coating formulation was applied to vinylidene chloride subbed polyethylene naphthalate support using a coating hopper so as to provide a nominal total dry coverage of 0.60 g/m². The support having an antistatic coating was dried and subsequently heat-treated according to the conditions for Support A. The support exhibited severe blocking and could not be unwound for subsequent coatings.

Support J

[0057] A support was prepared according to Support A without the application of an antistatic layer. Vinylidene chloride containing primer layers were applied to the front and back surfaces of the support. A gelatin containing subbing layer was applied to one surface. The remaining surface had a gelatin containing layer without the addition of an electrically-conductive metal-containing material. The support was annealed against a similar support such that the gelatin subbing layers contacted each other. The support exhibited moderate blocking and was not used for subsequent coatings.

Examples 1-17

[0058] The resultant heat-treated supports, having a gelatin subbing layer and an antistatic layer were subsequently overcoated with one of several transparent magnetic recording layers MC-1 through MC-6. The transparent magnetic recording layers contained cobalt surface-modified γ-Fe₂O₃ particles in a polymeric binder which optionally may be cross-linked and contains suitable abrasive particles. The formulations for the magnetic layers are given below. Total dry coverage for all of the magnetic layers was nominally 1.5 g/m². An optional lubricant-containing topcoat layer containing carnauba wax and a fluorinated surfactant as a wetting aid was applied over the transparent magnetic recording layer to provide a nominal dry coverage of about 0.02 g/m². The resultant multilayer structure including a support having an electrically-conductive antistatic layer and a gelatin subbing layer which has been heat-treated and then subsequently overcoated with a transparent magnetic recording layer, an optional lubricant layer, and other optional layers is referred to herein as a "magnetic backing package."

Magnetic Coating 1 (MC-1) CTA

[0059] A magnetic coating formulation comprising Co-γ-Fe₂O₃ magnetic particles, alumina abrasive particles, cellulose triacetate, cellulose diacetate and various other additives was prepared according to the formulation indicated below.

Cellulose diacetate	2.440 g
Cellulose triacetate	0.180 g
Magnetic oxide Toda CSF-4085V2	0.113
Surfactant Rhodafac PE510	0.006 g
Alumina Norton E-600	0.076 g
Dispersing aid, Zeneca Solsperse 24000	0.004 g
3M FC431	0.015
Dichloromethane	67.919
Acetone	24.257 g
Methyl acetoacetate	4.851 g

Magnetic Coating MC-2

[0060] A magnetic coating formulation was prepared in a similar manner to MC-1 except the binder was predominatly cellulose diacetate rather than cellulose triacetate. The coating formulation is given below.

Cellulose diacetate	2.51 g
Cellulose triacetate	0.115 g
Magnetic oxide Toda CSF-4085V2	0.113 g
Surfactant Rhodafac PE510	0.006 g
Alumina Norton E-600	0.076 g
Dispersing aid, Zeneca Solsperse 24000	0.004 g
3M FC431	0.015 g
Dichloromethane	67.919 g
Acetone	24.257 g
Methyl acetoacetate	4.851 g

Magnetic Coating MC-3, MC-4, and MC-5

[0061] Magnetic coating formulations were prepared in a similar manner to MC-2 however a crosslinking agent was included. MC-3 and MC-4, respectively, had 5 and 10 weight percent based on the weight of cellulose diacetate of Cymel 303 (Cytec Industries, Inc.) a melamine-formaldehyde resin as a crosslinking agent. In addition, 3 % of paratoluene sulfonic acid based on the weight of Cymel 303 was added as a catalyst for the crosslinking reaction. An isocyanate crosslinking agent, Desmodur N3300 (Bayer Corporation ), was added at 7.5 weight percent based on the weight of cellulose diacetate for magnetic coating formulation MC-5.

Magnetic Coating Formulation MC-6 (MmE)

[0062] A magnetic coating formulation was prepared having Co-γ-Fe₂O₃ magnetic particles and alumina abrasive particles dispersed in a polymeric binder consisting of a copolymer of methylmethacrylate-methacrylic acid. The coating solvents used were methylene chloride, ethyl acetate and ethyl alcohol.

[0063] The magnetic backing packages prepared in accordance with this invention and the comparative examples were evaluated for antistatic layer performance, dry adhesion and wet adhesion. Antistatic performance was evaluated by measuring the internal electrical resistivity using a salt bridge wet electrode resistivity (WER) measurement technique (as described, for example, in "Resistivity Measurements on Buried Conductive Layers" by R.A. Elder, pages 251-254, 1990 EOS/ESD Symposium Proceedings). Typically, antistatic layers with WER values greater than about 1x10¹² ohm/square are considered to be ineffective at providing static protection for photographic imaging elements

[0064] Dry adhesion of the magnetic backing package was evaluated by scribing a small region of the coating with a razor blade. A piece of high-tack adhesive tape was placed over the scribed region and quickly removed multiple times. The number of times the adhesive tape could be removed without any coating removal is a qualitative measure of the dry adhesion. Dry adhesion was evaluated both before and after photographic processing by the standard C-41 process. Wet adhesion was evaluated using a procedure which simulates wet processing of silver halide photographic elements. A one millimeter wide line was scribed into a sample of the magnetic backings package. The sample was then immersed in KODAK Flexicolor developer solution at 38 °C and allowed to soak for 3 minutes and 15 seconds. The test sample was removed from the heated developer solution and then immersed in another bath containing Flexicolor developer at about 25 °C and a rubber pad (approximately 3.5 cm dia.) loaded with a 900 g weight was rubbed 100 times back and forth across the sample in the direction perpendicular to the scribe line. The relative amount of additional material removed is a qualitative measure of the wet adhesion of the various layers. Blocking results, WER values and adhesion results are given in Table 1.

[0065] The above results indicate that an imaging support having a gelatin subbing layer on one side of the support and an electrically-conductive layer containing between 45 and 75 volume percent of electrically-conductive metal-containing particles dispersed in gelatin on the opposite side of the support can be annealed at a temperature greater than 80 °C without blocking and provide acceptable adhesion when overcoated with a transparent magnetic recording layer. Example 17 shows that a annealing of a gelatin subbing layer against another gelatin containing layer results in blocking. Similarly, Examples 15 and 16 demonstrate severe blocking when a gelatin subbing layer is in contact with a vinylidene chloride containing primer layer or antistatic layer during annealing of the support. Examples 11-14 demonstrate unacceptable wet adhesion of a transparent magnetic recording layer to an annealed support for an antistatic layer containing less than 45 volume percent conductive particles, even when the magnetic layer contains a crosslinking agent. In addition, the SER and WER results indicate conductivity of the antistatic layer is essentially unaltered by annealing the support and overcoating with a magnetic layer.

Claims

1. An imaging support comprising

a polyester base having a first and a second side;

a gelatin subbing layer on the first side; and

on the second side an antistatic layer comprising electrically-conductive metal-containing fine particles dispersed in gelatin.

2. An imaging support comprising:

a polyester base having a glass transition temperature (T_g) of from 90 to 200 °C;

a gelatin containing subbing layer superposed on a surface of the base;

an electrically conductive layer superposed on the opposite surface of the base wherein the electrically conductive layer comprises electrically-conductive metal-containing fine particles dispersed in a gelatin containing layer, wherein the metal-containing fine particles comprise from between 45 and 75 volume percent of the electrically conductive layer;

   wherein said support has been annealed at a temperature of from 80 °C to the T_g of the polyester base, for 0.1 h to 1500 h.

3. The imaging support of claim 1 wherein the polyester base comprises polyethylene terephthalate, poly-1,4-cyclohexanedimethylene terephthalate, polyethylene 1,2-diphenoxyethane-4,4'-dicarboxylate, polybutylene terephthalate or polyethylene naphthalate.

4. The imaging support of claim 1 further comprising an adhesion promoting layer superposed on a side of the polyester base.

5. The imaging support of claim 1 wherein electrically-conductive metal-containing fine particles comprise antimony-doped tin oxide.

6. The imaging support of claim 1 further comprising an auxiliary layer superposed on the electrically conductive layer side of the polyester base.

7. The imaging support of claim 1 further comprising a transparent magnetic recording layer superposed on the electrically conductive layer.

8. The imaging support of claim 8 wherein the transparent magnetic recording layer comprises magnetic particles dispersed in cellulose acetate.

9. The imaging support of claim 1 wherein the polyester base comprises polyethylene naphthalate.

10. A photographic element comprising:

a polyester base having a first and second side;

a gelatin subbing layer on the first side;

on the second side an antistatic layer comprising electrically-conductive metal-containing fine particles dispersed in gelatin; and

an image-forming layer on the polyester base.