Stripping layers for imaging elements

Abstract: Imaging elements, in particular image transfer assemblages and processes, are described wherein a stripping layer is employed to enable a layer containing a viewable image to be separated from other portions of the element. The stripping layer comprises certain N-alkyl substituted acrylamide copolymers.

Description: This invention relates to imaging elements, particularly to black-and-white and color image transfer assemblages wherein certain N-alkyl acrylamide stripping agents are employed to enable an imaged layer to be separated from other portions of the element. Transparencies or prints which are less bulky can thereby be obtained from integral assemblages. Various formats for color, integral transfer elements are described in the prior art, such as U.S. Patents 3,415,644; 3,415,645; 3,415,646; 3,647,437; 3,635,707; 3,756,815, and Canadian Patents 928,559 and 674,082. In these formats, an image-receiving layer containing a photographic image for viewing remains permanently attached and integral with the image generating and ancillary layers present in the structure when a transparent support is employed on the viewing side of the assemblage. The image is formed by dyes, produced in the image generating units, diffusing through the layers of the structure to the dye image-receiving layer. After exposure of the assemblage, an alkaline processing composition permeates the various layers to initiate development of the exposed photosensitive silver halide emulsion layers. The emulsion layers are developed in proportion to the extent of the respective exposures, and the image dyes which are formed or released in the respective image generating layers begin to diffuse throughout the structure. At least a portion of the imagewise distribution of diffusible dyes diffuse to the dye image-receiving layer to form an image of the original subject. The user does not have to time this process. A problem with the integral assemblages described above is that the silver halide and other imaging layers, the spent pod which originally contained processing fluid, and the trap which retains excess processing fluid remain with the print after processing. The resulting prints are bulky and are somewhat difficult to stock or store in albums. It is an object of this invention to provide a diffusion transfer assemblage in which a print can be obtained without the spent imaging layers, pod and trap. Such a print would comprise the support, dye image-receiving layer and reflecting layers only, and would more closely resemble conventional prints in appearance and handling. These and other objects are achieved in accordance with this invention. Stripping layers have been previously employed in diffusion transfer photography. However, a stripping layer for an integral diffusion transfer assemblage has many requirements. It must be easily coatable. Dye passage to the image receiving layer must not be hindered. The layers of the assemblage must not crack or separate upon bending and handling. The assemblage must maintain integrity during storage, during the high pH of processing and during the time when the pH is lowered by the process control layers, yet there must be easy and clean separation at the stripping layer after transfer of the image. If the assemblage provides a transparency with high magnification projection, additional requirements for retention of image sharpness arise. To maintain sharpness the diffusion path must be as short as possible, thus a thin stripping layer is desired. If a stripping layer is used in a transparency image-transfer format and the stripping layer surface-interface remains visible to the user, clean separation is critical. Random areas that separate upon stripping even if not visible during projection viewing are undesirable if viewable on the surface. It is another object of this invention to provide stripping layers which are coatable from aqueous solutions and which permit clean separation between the stripping layer and an adjacent layer. Materials employed in the stripping layer of this invention have previously been used in photographic elements. In U.S. Patent 4,504,569, N-alkyl substituted acrylamide polymers are shown in temporary barrier layers. In European published Patent Application 121,141 published October 10, 1984 they are described as gelatin extenders. Neither of these publications, however, discloses that certain N-alkyl substituted acrylamide polymers would be useful as stripping agents. In accordance with this invention, there is provided a photographic element for forming a viewable image comprising a support, a silver halide emulsion layer and a stripping layer therebetween, characterized in that the stripping layer comprises an N-alkyl substituted acrylamide copolymer having the following formula: wherein: A represents randomly recurring units of one or more hydrophilic polymerized N-alkyl- or N,N-dialkylacrylamides; B represents randomly recurring units of one or more polymerized nonionic alkyl-, hydroxyalkyl-, or oxaalkyl-acrylate or methacrylate monomers, or a carboxylic acid group containing monomer; C represents randomly recurring units of one or more polymerized cross-linking monomers having two or more polymerizable groups; x, y and z represent the weight percent of the A, B and C recurring units respectively; x represents 30 to 90 weight percent; y represents 0 to 60 weight percent, no more than 5 weight percent being a polymerized carboxylic acid group containing monomer; z represents 0 to 15 weight percent; the sum of y and z represents 10 to 70 weight percent; and the sum of x, y and z represents 100 weight percent, said copolymer being present at a concentration of from 5 to 500 mg/m² of said element, and the ratio of the A, B and C comonomers is adjusted within the ranges specified to give a wet peel separation force of between 0.4 and 4.0 g/cm, said wet peel separation force being that force needed to cleanly separate the stripping layer, present at 0.5 to 1.5 g/m² of copolymer, from an adjacent layer when the element is wetted with developing composition for 10 minutes at 20°C. Further embodiments of the invention are set forth in claims 2 to 10. Stripping layers in general which comprise half amides of vinyl acetate-maleic anhydride copolymers are known from FR-A-1 585 064. In one embodiment of the invention, the viewable image is formed in the silver halide emulsion layer. In another embodiment of the invention, the viewable image is transferred to a mordant layer between the support and the stripping layer. An image transfer assemblage according to the invention comprises: a) a photosensitive element comprising a support having thereon at least one photosensitive silver halide emulsion layer; and b) an image-receiving layer, and wherein the assemblage contains a stripping layer as described above. In forming a black-and-white image in an image transfer assemblage, the exposed photosensitive element is developed. In the unexposed areas, a silver halide complexing agent dissolves the silver halide and transfers it to the image-receiving layer. Silver precipitating nuclei in the image-receiving layer then cause the transferred silver halide complex to be reduced to silver, thereby forming an image pattern corresponding to the original. Details of the process are well known to those skilled in the art as shown, for example, by U.S. Patents 3,220,835 and 3,820,999. In a preferred embodiment of the invention, the silver halide emulsion layer has associated therewith a dye image-providing material. To be optimally useful in this invention, the ratio of the A, B and C comonomers are adjusted within the ranges specified to give a wet peel separation force of between about 0.4 and 4.0 g/cm. Wet peel separation force is that force needed to cleanly separate the stripping layer, present at 0.5 to 1.5 g/m² of copolymer, from an adjacent layer after the element has been wetted with the processing composition used to form an image for 10 minutes at 20°C. By clean separation is meant that the stripping layer separated at one or the other of the interfaces with the adjacent layers, and does not separate internal to the stripping layer. If the force required to provide clean separation is below about 0.4 g/cm, there is the danger of spontaneous delamination of the element. If the force is much above 4.0 g/cm, there may be undue difficulty in separating the layers. Application of this test to identify optimum materials for image transfer assemblages is illustrated in Example 1, infra. Suitable comonomers for use in this invention include: A1 N-Isopropylacrylamide A2 N,N-Dimethylacrylamide A3 N-n-propylacrylamide A4 N-n-butylacrylamide B1 2-Ethoxyethyl acrylate B2 2-Ethoxyethyl methacrylate B3 Methyl acrylate B4 Methyl methacrylate B5 n-Butyl acrylate B6 n-Butyl methacrylate B7 Ethyl acrylate B8 Pentaethyleneglycol methacrylate B9 Decaethyleneglycol methacrylate B10 Didecylethyleneglycol methacrylate B11 2-Hydroxyethyl acrylate B12 2-Hydroxyethyl methacrylate B13 3-Chloro-2-hydroxypropyl methacrylate B14 Hexafluoro-1,1-3-trihydrobutyl acrylate B15 Trifluoroethyl acrylate B16 Acrylamide B17 N-(1,1-dimethyl-3-oxobutyl)acrylamide B18 Acrylic Acid B19 Methacrylic acid C1 Ethyleneglycol dimethacrylate C2 N,N′-Methylenebisacrylamide C3 Polyethyleneglycol diacrylate C4 Polyethyleneglycol dimethylacrylate Preferred A, N-alkyl substitute acrylamide monomers are: A-1 N-Isopropylacrylamide, or A-2 N,N-Dimethylacrylamide. Preferred B, ester comonomers are: B-1 2-Ethoxyethyl acrylate, B-4 Methyl methacrylate, B-6 n-Butyl methacrylate, or B-12 2-Hydroxyethyl methacrylate, any one of which may be used along or with 1 to 2 weight percent of acrylic acid or methacrylic acid to increase hydrophilic properties. Preferred C, cross-linking comonomers are: C-1 Ethyleneglycol dimethacrylate or C-2 N,N′-Methylenebisacrylamide. Preferred polymers are: Poly(N,N-dimethylacrylamide- co -n-butyl methacrylate- co -ethyleneglycol dimethylacrylate) (50:40:10 wt ratio) Poly(N-isopropylacrylamide- co -2-hydroxyethyl methacrylate- co -N,N′-methylenebisacrylamide) (70:20:10 wt ratio) Poly(N-isopropylacrylamide-co-methyl methacrylate-co-N,N′-methylene bisacrylamide) (80/10/10 wt ratio) Poly(N,N-dimethylacrylamide-co-n-butylmethacrylate) (50/50 wt ratio) Poly(N,N-dimethylacrylamide-co-trifluoroethyl acrylate) (60/40 wt ratio) Poly(N,N-dimethylacrylamide-co-2-hydroxyethyl methacrylate-co-ethyleneglycol dimethacrylate) (30/60/10 wt ratio) The copolymer employed in our invention may be employed in any amount which is effective for the intended purpose, i.e., clean separation between the stripping layer and an adjacent layer. In general, good results have been obtained at a concentration of from about 5 to about 500 mg/m² of element. The particular amount to be employed will vary, of course, depending on the particular stripping agent employed and the composition of other layers of the assemblage. Our invention can be used in diffusion transfer assemblages where a reflection print is obtained without the bulkiness of silver halide and other layers, the spent pod and trap. In other words, our invention combines the handling and storage characteristics of conventional photographs with the convenience and benefits of instant photography. In addition, transparency elements can also be obtained with our invention which requires a transparent support and the removal of residual image dye, silver halide and opacifying layers. By removing the silver halide and dye image-providing material layers from the assemblage, there is also provided the option of recovery of these expensive materials from the discarded portion of the assemblage, if it is economically feasible to do so. The preferred location for the stripping layer is adjacent to the mordant or image-receiving layer. It could also be located in other positions in the assemblage, such as between pigmented gelatin vehicle layers, or adjacent the emulsion layer if desired. A process for producing a photographic image in color according to the invention comprises: I) exposing a photosensitive element comprising a support having thereon at least one photosensitive silver halide emulsion layer having associated therewith a dye image-providing material; II) treating the element with an alkaline polymer thickened processing composition in the presence of a silver halide developing agent to effect development of each exposed silver halide emulsion layer, whereby: (a) an imagewise distribution of the dye image-providing material is formed as a function of the development of the silver halide emulsion layer; and (b) at least a portion of the imagewise distribution of the dye image-providing material diffuses to a dye image-receiving layer; and III) separating the dye image-receiving layer from the rest of the photosensitive element by means of a stripping layer as described above, such that the separated dye image-receiving layer will have substantially none of the emulsion layer adhered thereto. The photographic element in the above-described process can be treated with an alkaline processing composition to effect or initiate development in any manner. A preferred method for applying processing composition is by use of a rupturable container or pod which contains the composition. In a preferred embodiment of the invention, the photographic assemblage comprises: a) a photosensitive element comprising a support having thereon at least one silver halide emulsion layer having associated therewith a dye image-providing material; b) a transparent cover sheet located over the layer outermost from the support of the photosensitive element; c) a dye image-receiving layer located either in the photosensitive element or on the transparent cover sheet; and d) an alkaline processing composition and means containing same for discharge between the photosensitive element and the transparent cover sheet; and wherein the assemblage contains a stripping layer as described above. In a preferred embodiment of the invention, the means containing the alkaline processing composition is a rupturable container or pod which is adapted to be positioned during processing of the film unit so that a compressive force applied to the container by pressure-applying members, such as would be found in a camera designed for in-camera processing, will effect a discharge of the container's contents within the film unit. In general, the processing composition employed in this invention contains the developing agent for development, although the composition could also just be an alkaline solution where the developer is incorporated in the photographic element or cover sheet, in which case the alkaline solution serves to activate the incorporated developer. The dye image-providing material useful in this invention is either positive- or negative-working, and is either initially mobile or immobile in the photographic element during processing with an alkaline composition. A format for integral negative-receiver photographic elements in which the present invention is useful is disclosed in Canadian Patent 928,559. Still other useful integral formats in which this invention can be employed are described in U.S. Patents 3,415,644; 3,415,645; 3,415,646; 3,647,437 and 3,635,707. The film unit or assemblage of the present invention is used to produce positive images in single or multicolors. In a three-color system, each silver halide emulsion layer of the film assembly will have associated therewith a dye image-providing material which possesses a predominant spectral absorption within the region of the visible spectrum to which said silver halide emulsion is sensitive. The following examples are provided to further illustrate the invention. Example 1 The following multilayer elements are coated in the order indicated on a clear poly(ethylene terephthalate) support: 7. Overcoat layer: gelatin (6.5 g/m²) 6. Opaque layer: carbon (0.89 g/m²), gelatin (0.57 g/m²) 5. Stripping layer: indicated polymer coated at 1.1 g/m² 4. Interlayer: gelatin (0.54 g/m²) 3. Opaque layer: carbon (1.9 g/m²), gelatin (1.2 g/m²) 2. Reflecting layer: titanium dioxide (19. g/m²) gelatin (3.0 g/m²) 1. Mordant layer: poly(styrene- co -N-dimethyl-N-vinylbenzylammonium chloride- co -divinylbenzene) (99:99:2) weight ratio) (2.3 g/m²), gelatin (2.3 g/m²) Pods containing the following polymer thickened processing composition were prepared: Cover sheets (acid-timing layers) like those of layers 2 and 1 of U.S. 4,353,973 were prepared. The wet stripping performance of each integral imaging receiver was evaluated by laminating an element to a cover sheet by spreading the viscous processing composition in a pod at room temperature of 20°C, using a pair of 75 µm gap undercoat rollers. After 10 minutes lamination time, two strips 2.5 cm x 12.5 cm were cut and the force required to separate the laminated pair was measured as g/cm force using an Instron Universal Testing Machine Model TM-1122. The separation forces required and limitations on the ability to peel are tabulated below. Forces of between 0.4 and 4.0 g/cm are considered acceptable. The following stripping layer polymers within the composition definition of the invention showed peel force within the test criteria: The following stripping layer polymers do not satisfy the composition definition of the invention. They failed to show satisfactory peel performance. The following stripping layer polymers satisfy the composition definition of the invention but do not satisfy the peel force criteria. They failed to show satisfactory peel performance.

Claims: A photographic element for forming a viewable image comprising a support, a silver halide emulsion layer and a stripping layer therebetween, characterized in that said stripping layer comprises an N-alkyl substituted acrylamide copolymer having the following formula: wherein: A represents randomly recurring units of one or more hydrophilic polymerized N-alkyl- or N,N-dialkylacrylamides; B represents randomly recurring units of one or more polymerized nonionic alkyl-, hydroxyalkyl-, or oxaalkyl-acrylate or methacrylate monomers, or a carboxylic acid group containing monomer; C represents randomly recurring units of one or more polymerized cross-linking monomers having two or more polymerizable groups; x, y and z represent the weight percent of the A, B and C recurring units respectively; x represents 30 to 90 weight percent; y represents 0 to 60 weight percent, no more than 5 weight percent being a polymerized carboxylic acid group containing monomer; z represents 0 to 15 weight percent; the sum of y and z represents 10 to 70 weight percent; and the sum of x, y and z represents 100 weight percent, said copolymer being present at a concentration of from 5 to 500 mg/m² of said element, and the ratio of the A, B and C comonomers is adjusted within the ranges specified to give a wet peel separation force of between 0.4 and 4.0 g/cm, said wet peel separation force being that force needed to cleanly separate the stripping layer, present at 0.5 to 1.5 g/m² of copolymer, from an adjacent layer when the element is wetted with developing composition for 10 minutes at 20°C. The photographic element of claim 1 characterized in that the viewable image is formed in the silver halide emulsion layer. The photographic element of claim 1 characterized in that said silver halide emulsion has a diffusible dye image-forming material associated therewith so that a viewable image can be formed in a mordant layer which is between the support and the stripping layer. A photographic assemblage comprising: a) a photosensitive element comprising a support having thereon at least one photosensitive silver halide emulsion layer; and b) an image-receiving layer, characterized in that said assemblage contains a stripping layer comprising an N-alkyl substituted acrylamide copolymer so that said image-receiving layer may be separated, after processing, from the rest of said assemblage, and that said separated image-receiving layer will have substantially none of said emulsion layer adhered thereto, said stripping layer being as defined in claim 1. The assemblage of claim 4 which also contains an alkaline processing composition containing a silver halide developing agent and means containing same for discharge within said assemblage. The assemblage of claim 5 characterized in that said image-receiving layer contains silver precipitating nuclei and said assemblage also contains a silver halide solvent or complexing agent. The assemblage of claim 5 characterized in that said silver halide emulsion layer has associated therewith a dye image-providing material. The element of claim 1 characterized in that comonomer A is N-isopropylacrylamide or N,N-dimethylacrylamide; comonomer B is 2-ethoxyethyl acrylate, methyl methacrylate, n-butyl methacrylate, or 2-hydroxyethyl methacrylate; and comonomer C is ethyleneglycol dimethacrylate or N,N′-methylenebisacrylamide. The element of claim 1 characterized in that the polymer is Poly(N,N-dimethylacrylamide- co -n-butyl methacrylate- co -ethyleneglycol dimethylacrylate) (50:40:10 wt ratio); Poly(N-isopropylacrylamide- co -2-hydroxyethyl methacrylate- co -N,N′-methylenebisacrylamide) (70:20:10 wt ratio); Poly(N-isopropylacrylamide-co-methyl methacrylate-co-N,N′-methylene bisacrylamide) (80/10/10 wt ratio); Poly(N,N-dimethylacrylamide-co-n-butylmethacrylate) (50/50 wt ratio); Poly(N,N-dimethylacrylamide-co-trifluoroethyl acrylate) (60/40 wt ratio); or Poly(N,N-dimethylacrylamide-co-2-hydroxyethyl methacrylate-co-ethyleneglycol dimethacrylate) (30/60/10 wt ratio). A process for producing a photographic image in color comprising: I) exposing a photographic assemblage according to claim 4, the at least one photosensitive silver halide emulsion layer having associated therewith a dye image-providing material; II) treating the element with an alkaline polymer thickened processing composition in the presence of a silver halide developing agent to effect development of each exposed silver halide emulsion layer, whereby: (a) an imagewise distribution of the dye image-providing material is formed as a function of the development of the silver halide emulsion layer; and (b) at least a portion of the imagewise distribution of the dye image-providing material diffuses to a dye image-receiving layer; and III) separating the dye image-receiving layer from the rest of the photographic assemblage.

Inventors: BOWMAN WAYNE ARTHUR C O EASTMA, HARRISON DANIEL JUDE C O EASTM, BOWMAN, WAYNE ARTHUR C/O EASTMAN KODAK COMPANY, HARRISON, DANIEL JUDE C/O EASTMAN KODAK COMPANY
Applicants: EASTMAN KODAK CO, EASTMAN KODAK COMPANY
Application year: 1989
Main classification: G03C1
IPC codes: G03C1, G03C8