EP0011645B1

EP0011645B1 - Photosensitive elements for use in a diffusion transfer film unit

Info

Publication number: EP0011645B1
Application number: EP19790900514
Authority: EP
Inventors: Peter O. Kliem
Original assignee: Polaroid Corp
Current assignee: Polaroid Corp
Priority date: 1978-05-02
Filing date: 1979-12-04
Publication date: 1983-05-25
Also published as: EP0011645A4; EP0011645A1; WO1979001020A1; DE2965489D1; JPS55500266A; JPS5936253B2

Abstract

Photosensitive elements particularly suitable for use in diffusion transfer photographic film units which include a plurality of essential layers including at least one photosensitive silver halide layer having associated therewith a dye image-forming material which is diffusible during processing as a function of the point-to-point degree of silver halide exposure to actinic radiation and a layer adapted to receive image-forming material diffusing thereto and means for applying an aqueous processing composition. The silver halide layer comprises gelatin and inert particles which are compatible with gelatin, non-swelling in alkali and substantially non-film forming, wherein said inert particles are equal to or less than the silver halide grains in average diameter and wherein the silver halide grains are 2.5 microns or less in average diameter. Preferably, the inert particles are derived from a polymeric latex. In a particularly preferred embodiment, the photosensitive silver halide layer comprises a first and second photosensitive silver halide layer in contiguous relationship.

Description

Diffusion transfer photographic products and processes are known to the art and details relating thereto can be found in U.S. Patents Nos. 2,983,206; 3,415,644; 3,415,645; 3,415,646; 3,473,925; 3,482,972; 3,551,406; 3,573,042; 3,573,043; 3,573,044; 3,576,625; 3,576,626; 3,578,540; 3,569,333; 3,579,333; 3,594,164; 3,594,165; 3,597,200; 3,647,437; 3,672,486; 3,672,890; 3,705,184; 3,752,836 and 3,857,865. Essentially, diffusion transfer photographic products and processes involve film units having a photosensitive system including at least one silver halide layer, usually integrated with an image-providing material. After photoexposure, the photosensitive system is developed to establish an imagewise distribution of a diffusible image-providing material, at least a portion of which is transferred by diffusion to an image-receiving layer capable of mordanting or otherwise fixing the transferred image-providing material. In some diffusion transfer products the transfer image is viewed by reflection after separation of the image-receiving element from the photosensitive system. In other products, however, such separation is not required and instead the transfer image-receiving layer is viewed against a reflecting background usually provided by a dispersion of a white reflecting pigment, such as, for example, titanium dioxide. The latter type of film unit is generally referred to in the art as integral negative-positive film units and are described, for example, in the above-mentioned U.S. Patents Nos. 3,415,644 and 3,594,165.
It is known in the art to incorporate polymeric latices into gelatin silver halide emulsion layers to increase the flexibility of the silver halide layer, thus eliminating the occurrence of fog due to stresses set up in the film unit containing the aforementioned silver halide layer.
U.S. Patent No. 2,772,166 discloses gelatin silver halide emulsions which also contain a hydrosol resulting from the emulsion polymerization of a mixture of styrene, acrylonitrile or a vinylidene chloride with an alkyl acrylate or alkyl methacrylate and acrylic acid. The described hydrosol is used in the range of 1 to 10% of the gelatin.
U.S. Patent No. 2,835,582 is directed to mixtures of gelatin and polymeric hydrosols in silver halide layers wherein the hydrosol is prepared by polymerizing at least one monoethylenically unsaturated monomer in the presence of an ampholytic surface active agent. Among the suitable monomeric materials are mentioned methylmethacrylate and styrene. It is a requirement that the polymeric materials be film formers and the essence of the invention resides in the presence of the ampholytic surface active material to provide its enhanced compatibility with gelatin.
U.S. Patent No. 3,157,510 is directed to gelatin silver halide emulsions which also include a dispersion of minute particles of a water insoluble soft acrylate polymer resin at a level of about 5 to 40% by weight of gelatin.
U.S. Patent No. 3,325,286 is directed to gelatin silver halide emulsions which include an aqueous dispersion of a polymeric vinyl compound and at least one anionic dispersing agent specified in the patent. The emulsion layer also requires a polyoxyethylene compound as defined in the patent. One of the polymeric materials recited is a homopolymer of an a-hydrocarbon substituted acrylic acid ester.
U.S. Patent No. 3,547,650 is directed to gelatin-silver halide emulsions which include an aqueous dispersion of a polymeric vinyl compound dispersed with a mixture of specified organic phosphates. One of the polymerized vinyl compounds recited comprises a homopolymer of an α-hydrocarbon substituted acrylic acid ester.
U.S. Patent No. 3,772,032 is directed to a gelatin silver halide emulsion which includes a polymeric latex prepared by emulsion polymerization in the presence of at least 5% by weight of an emulsifying agent to reduce the stress sensitivity of the emulsion. This patent states that employing the specified emulsifying agent at a level of at least 5% by weight, no fog is found in emulsions employing large amounts of methylmethacrylate in the latex whereas normally the presence of even 50% of methylmethacrylate in the latex results in intolerable increases in fog.
U.S. Patent No. 3,773,517 is directed to a gelatin-silver halide emulsion which includes a polymer latex prepared by copolymerization of a monomer yielding a water insoluble homopolymer and a monomer yielding a water soluble polymer. The patent requires the polymerization to occur in the presence of a specified alkylaryl polyether phosphate surface active agent. One of the monomers which would produce a water insoluble homopolymer is an alkylmethacrylate.
U.S. Patent No. 3,418,132 is directed to a photographic film unit which, in one embodiment, is particularly suited for rapid access processing by virtue of the incorporation of inert particles into at least one layer of the photographic element. The inert particles include starch, barium sulfate, calcium carbonate, synthetic resins etc. The inert particles are in the range of 7 to 15 pm.
Film units containing contiguous silver halide emulsion layers sensitive to the same spectral region are known to the art as shown by the following representative patents.
U.S. Patent No. 3,505,068 is directed to a photographic element which contains overlying silver halide emulsions wherein the first emulsion is a regular silver haloiodide emulsion and the second contains grains which have an iodide-free shell and a silver iodide core.
U.S. Patent No. 3,663,228 is directed to a photographic film unit having a plurality of silver halide emulsion layers divided into sets with each set of a different speed while the layers in each set have the same speed but are responsive to different spectral regions. Color filters are disposed between the layers.
U.S. Patent No. 3,695,882, is directed to a photosensitive element comprising a support carrying two emulsions, each containing a non-diffusing color coupler. Each emulsion has a different speed and different silver halide-coupler molar ratio.
U.S. Patent No. 3,846,135 is directed to a synergistic increase in the sensitivity of two superposed silver halide layers when the lower layer is less sensitive than the upper layer and has a maximum density of at least 1.5 compared to a maximum density of at least 0.9 for the upper layer. The lower layer is about 5 to 15 pm thick. '
U.S. Patents Nos. 3,960,558 and 4,003,744 disclose diffusion transfer film units which employ split silver halide emulsions having dye image-forming material associated therewith and which, in fact, contain dye image-forming material in one of said contiguous layers.
U.S. Patent No. 3,632,342 is directed to a photographic element comprising a support carrying at least one layer containing a high contrast silver halide emulsion layer containing an acrylic latex material and an additional silver halide layer containing a hydrophilic colloid which is free of latex micelles. It is stated that discrete micelles are preferred but that coalescing may occur. Copolymers of hydrophilic and hydrophobic monomers are disclosed.
A photosensitive element according to the invention for use in a diffusion transfer film unit comprises a support carrying at least one photosensitive silver halide layer that has a dye image-forming material associated therewith and that comprises silver halide grains having an average diameter of 2.5 µm or less and gelatin and is characterised in that the said silver halide layer, or at least one of the said silver halide layers, includes inert particles which have an average diameter that is not less than 0.075 jMm but that is less than or equal to the average diameter of the silver halide grains and which are compatible with gelatin, substantially non-swelling in aqueous alkaline processing composition and substantially non-light scattering and which, before and during processing with the aqueous alkaline processing composition, are substantially non-film forming and substantially non-coalescing. The provision of the particles results in bulking of the gelatin layer and by choosing particles that are substantially non-swelling in aqueous alkali they provide a non-swelling, sizeable mass to bulk the gelatin layer. The particles must be substantially non-film forming and substantially non-coalescing in order that they are sufficiently hard to retain their physical' identity as individual particles in the presence of aqueous alkaline processing composition. If the particles were to coalesce or film form to any significant extent this would inhibit dye transfer and also would reduce the bulking effect of the particles. The particles must be substantially non-light scattering in order that the layer containing gelatin and the particles does not cause sufficient light scattering to impair significantly the photographic results obtained with the product. In practice this means that the particles must have a refractive index which is sufficiently close to the refractive index of gelatin to avoid detrimental light scattering. The particles must be compatible with gelatin so as to avoid coagulation within the layer.
The term "photosensitive silver halide layer" as used herein is intended to include a first and second photosensitive silver halide layer sensitive to the same portion of the spectrum and in contiguous relationship, i.e. the so-called "split emulsions". These are described in more detail below.
The dye image-forming material is preferably a dye developer which is soluble and diffusable in alkali as a function of the exposure and development of the silver halide emulsion layer and the present invention will be described with respect to dye developers as the dye image-forming materials although it will be understood that other dye image-forming materials may be employed in the present invention.
Dye developers are well known in the art. A dye developer is a compound which contains a silver halide developing moiety and the chromophoric system of a dye. In multicolor processes, a dye developer providing an image dye of appropriate color is associated with each silver halide emulsion layer; for example, a cyan dye developer with a red sensitive silver halide layer; a magenta dye developer with a green sensitive silver halide emulsion layer; and a yellow dye developer with a blue sensitive silver halide emulsion layer. Unoxidized dye developer is insoluble in water but soluble and mobile in aqueous alkali. Oxidation of the dye developer as a result of development of exposed silver halide results in its immobilization, while unoxidized dye developer can diffuse to the dyeable image-receiving layer producing a positive image therein.
To provide rapid transfer of the unoxidized dye developer and to avoid any unwanted interactions in the negative, it is preferred that the unoxidized dye developer pass through the associated silver halide emulsion layer as rapidly as possible consistent with development thereof. Since gelatin swells to a considerable degree upon contact with the photographic processing composition and thus would be a factor in slowing dye developer transfer, it is desirable to form the silver halide emulsion layer with a minimum of gelatin. The minimum quantity of gelatin employed, however, is controlled to a great degree by the size of the silver halide grains. Thus, it is desirable to employ sufficient gelatin to retain the silver halide grains within the layer, that is, to prevent any projection of the grains or portion of the grains through the gelatin layer at the interface into contact with adjacent layers.
Thus, it will be seen that larger size grains, as commonly employed for high speed emulsions, would require more gelatin than smaller grains at the same unit weight coverage to form a continuous layer without any projection of the grains into contact with adjacent layers.
By means of the present invention it has now been found that the transfer of image-forming materials through gelatin-silver halide emulsion layers can be accelerated, while at the same time completely retaining the silver halide grains within the layer and without adversely affecting the photographic properties of the film unit. In fact, unexpected photographic advantages are achieved as evidenced by H & D curves showing a reduction in slope, increased toe extent and enhanced dynamic range.
Inert particles suitable for use in the present invention include starch, barium sulfate, calcium carbonatq, cellulose esters such as cellulose acetate propionate, cellulose ethers such as ethyl cellulose, glass, synthetic resins such as polyvinyl acetate, polycarbonates, homo and copolymers of styrene, inorganic oxides such as zinc oxide, silica, titanium dioxide, magnesium oxide and aluminium oxide, as well as hardened gelatin grains, calcium sulfate, barium carbonate and the like.
The preferred inert particles for use in the present invention are polymethylmethacrylate and polystyrene and are provided for the film unit by dispersing polymethylmethacrylate latex or polystyrene latex in the emulsion.
The film forming and hardness characteristics of polymers are properties associated with the glass transition temperature of the polymer. Thus, the Tg of the polymer should be above the temperature at which the polymer is dried. Preferably, the Tg is above 35°C, more preferably, above 60°C. In a particularly preferred embodiment, the Tg is above 100°C.
It should be understood that the polymer latex may be a homopolymer or a copolymer provided that the comonomers do not modify the copolymer to the extent that the required properties are not retained. A preferred copolymer is methyl methacrylate/hydroxypropyl methacrylate copolymer.
The inert particles should be no larger than the silver halide grains with which they are associated. In the present invention the maximum average diameter of the silver halide grains is 2.5 pm or less and preferably less than 2.0 ,am. Thus, the maximum average diameter of the inert particles is 2.5 pm. The lower limit of the particles is determined by the fact that one should avoid packing of the particles such as would impede dye transfer. The inert particles must be not less than 0,075 µm in diameter.
In a particularly preferred embodiment the inert particles have an average diameter which is 10-15%, of the average diameter of the silver halide grains associated therewith.
The quantity of polymer latex to be employed may be readily determined for any given silver halide emulsion. For a given silver halide grain size, as the quantity of gelatin decreases, the polymer gelatin ratio goes up to keep the layer dimensions the same. Sufficient gelatin must be present to keep the layer intact and prevent dusting of the polymer particles. Preferably, a ratio (weight basis) of 0.5 to 1 to 10 to 1 polymer latex (solids) to gelatin is employed. Particularly preferred is a 1 to 1 ratio for fine grains (less than about 1 µm) and 6 to 1 for coarse grains (greater than about 1.3 µm). Thus, in a preferred embodiment, the average mean diameter of the fine grains is less than about 1 µm and the large grains, greater than 1.3 µm.
As stated above at least one of the photosensitive silver halide layers that includes the inert particles may be in the form of a split emulsion. Thus, it may comprise a first photosensitive silver halide layer distal to the exposure surface of the element and comprising silver halide grains possessing a first mean particle size, and a second photosensitive silver halide layer having a second mean particle size, the second photosensitive layer having a higher intrinsic speed than the first photosensitive silver halide layer, the first and second photosensitive silver halide layers being in contiguous relationship and the inert particles being in at least the second silver halide layer. The first and second silver halide layers will generally be free of dye image-forming material but will have associated therewith a dye image-forming material which is diffusible as a function of the point-to-point degree of silver halide exposure to actinic radiation. Inert particles may be employed in both layers of the split emulsion.
As stated, the intrinsic speed of the second silver halide emulsion layer is greater than that of the first layer. The speed difference between the first and second layers generally ranges from about 2 to about 8 stops, preferably about 5 stops. In a preferred split emulsion, the average mean diameter of the silver halide grains in the first photosensitive silver halide layer is less than about 1 µm and the average mean diameter of the grains in the second photosensitive layer is greater than about 1.3 µm.
However, when the thickness of the gelatin associated with the layers falls to about 50% or less of the mean volume diameter of the grains, the coated layers do not retain their integrity but rather combine, inter-mixing the grain sizes, so that the resulting combined silver halide layer functions as if a single layer of blended grain sizes were coated, thus losing all the benefits achieved in a layered structure and introducing the drawbacks of the single layered, low gelatin system.
It is believed that the advantages of this invention result, at least in part, by maintaining better separation of the development process of the individual grains as well as separation of the by-products of development by virtue of incorporating the above-described inert particles. By employing such inert .particles in the layers, the layers retain their integrity with the differently sized silver halide particles retained in their own separate and distinct layer.
The photosensitive element of the invention preferably comprises a support carrying a red sensitive silver halide unit having associated therewith a cyan dye developer, a green sensitive silver halide unit having associated therewith a magenta dye developer and a blue sensitive silver halide unit having associated therewith a yellow dye developer. At least one of these units will comprise gelatin and inert particles as defined above and in particular it is preferred for the green sensitive silver halide unit to include the polymeric latex or other inert particles.
The invention includes not only the photosensitive element described above but also diffusion transfer film units comprising a support carrying at least one photosensitive element as defined above and an image receiving element comprising a dyeable receiving layer to receive a dye image diffusing thereto after photoexposure and processing of the photosensitive element. Thus the receiving layer, which can also be called a polymeric layer, is in superposed relationship with the photosensitive eiement at least after exposure of the element and during processing of the exposed photosensitive silver halide emulsion or emulsions, that is during contact of the emulsion with the aqueous alkali processing composition.
Preferably the image receiving element is affixed to at least one edge of the photosensitive element. The film unit may include a rupturable container of processing composition positioned to discharge its contents between a predetermined pair of layers of the film unit.
The dyeable receiving layer may be capable of being superposed over the silver halide emulsion layer or layers subsequent to photoexposure and may be capable of being separated therefrom after processing. Preferably however the film unit is a permanent laminate wherein the image is viewable in the receiving layer without separation of the receiving layer from the film unit. Thus the film unit may be a composite structure comprising the photosensitive element and the image receiving element permanently affixed to each other in superposed relationship, the support layers of each of the elements being outermost. Reference should be made to US Patents Nos. 3415644 and 3647437 for description of suitable integral negative/positive film units.
The support layer of the image receiving element is preferably transparent.
The polymeric latices preferred for employment in the present invention may be prepared by known techniques. The following non-limiting example illustrates the preparation of a latex preferred for use in the present invention.

Example A

A reactor was charge with 102 I of demineralized water and the Dowfax 2A1 and heated under nitrogen to 83°C whereupon 7.65 kg. of methyl methacrylate was added and mixed until the temperature returned to 83°C. After 5 min. at 83°C, 4.93 kg. of initiator solution (0.15 kg. of potassium persulfate and 14.79 kg. water) was added. After the exotherm, the temperature was reduced to 85°C and the remaining methyl methacrylate was added at a rate of about 361 g/min. and the remaining initiator solution at a rate of about 111 g/min. At the end of the monomer and initiator addition, the temperature was maintained at 85°C for 10 min. and then the ascorbic acid was added. The resulting latex had a 30% solids and the latex particles had an average diameter of about a 0.125 IIm.
The following non-limiting examples illustrate the present invention:

Example 1 (Control)

A photosensitive element was prepared by coating, in succession, on a gelatin subbed, opaque polyethylene terephthalate film base, the following layers.

1. a layer comprising the cyan dye developer
dispersed in gelatin and coated at a coverage of about 747 mg/m2 of dye, about 1554 mg/m² of gelatin, about 270 mg/m² of 4'-methylphenylhydroquinone, and about 270 mg/m² of 2-phenyl benzimidazole;
2. a red-sensitive gelatino silver iodobromide emulsion layer comprising a 50/50 blend of 1.05 µm and 1.5 µm grains coated at a coverage of about 1280 mg/m² of silver and about 768 mg/m² of gelatin;
3. an interlayer coated at a coverage of about 2500 mg/m² of a 60-30-4-6 tetrapolymer of butylacrylate, diacetone acrylamide, styrene and methacrylic acid, and about 77 mg/m² of polyacrylamide;
4. a layer comprising the magenta dye developer
dispersed in gelatin and coated at a coverage of about 646 mg/m² of dye and about 426 mg/m² of gelatin and about 229 mg/m² of 2-phenylbenzimidazole;
5. a green-sensitive gelatino silver iodobromide emulsion layer coated at a coverage of about 753 mg/m² of silver and about 347 mg/m² of gelatin;
6. an interlayer containing the tetrapolymer referred to above in layer 3 at a coverage of about 1369 mg/m², about 24 mg/m² of polyacrylamide, and about 75 mg/m² succindialdehyde;
7. a layer comprising the yellow dye developer
dispersed in gelatin and coated at a coverage of about 968 mg/m² of dye and about 450 mg/m² of gelatin and about 208 mg/m² of 2-phenyl benzimidazole;
8. a blue-sensitive gelatino silver iodobromide emulsion layer coated at a coverage of about 1280 mg/m² of silver, about 743 mg/m² of gelatin, and about 204 mg/m² of 4'-methylphenylhydroquinone;
9. an overcoat layer coated at a coverage of about 484 mg/m² gelatin and 43 mg/m² of carbon black.

An image-receiving element was prepared by coating the following layers in succession on a 0.01 mm (4 mil) polyethylene terephthalate film base, said layers respectively comprising:

1. as a polymeric acid layer, the partial butyl ester of polyethylene/maleic anhydride copolymer at a coverage of about 28,000 mg/m²;
2. a timing layer containing about 75:1 ratio of 60-30-4-6 copolymer of butylacrylate, diacetone acrylamide, styrene and methacrylic acid and polyvinyl alcohol at a coverage of about 5600 mg/m²; and
3. a polymeric image-receiving layer containing a 2:1 mixture, by weight, of polyvinyl alcohol and poly-4-vinylpyridine, at a coverage of about 3300 mg/m².

An aqueous alkaline solution was prepared comprising:

Example 2

A second film unit was prepared as described above except that layer 2, the green-sensitive silver halide emulsion layer additionally contained 1292 mg/m² (120 mg/ft²) (solids) of a polymethylmethacrylate latex having an average particle size of about 0.125 Mm and layer 6 was reduced in coverage by 40%..
The film units were processed in the following manner:

The film unit was exposed with white light to a multicolor target and the processing composition was spread between the two elements in a layer approximately 0.07 mm (0.0028") thick in the dark.

The following sensitometer data (green light reflection data in neutral column) was obtained in the resulting multicolor reflection prints:
From the foregoing it can be seen that a 30 unit reduction in slope is achieved; an increase in toe extent of about 14 units as well as an increase in dynamic range of more than 5 units. The loss incidated in the other properties is not considered significant; i.e., the advantages far outweigh the slight decrease recorded in D_max and speed which, in fact, may be within experimental error. It should be understood that these enhanced photographic results are obtained at the same time the magenta dye transfer is accelerated.

Example 3

To illustrate the rapid dye transfer achieved by the novel invention the following structures were prepared:

A. On a polyester base was coated 269 mg/m² (25 mg/ft²) of the cyan dye of Example 1; 538 mg/m² (50 mg/ft²) of gelatin and 21.5 mg/m² (2 mg/ft²) of succinaldehyde.
B. Structure A was overcoated with 1938 mg/m² (180 mg/ft²) of derivatized gelatin.
C. Structure A was overcoated with 1938 mg/m² (180 mg/ft²) of inert gelatin.
D. Structure A was overcoated with a mixture of gelatin 431 mg/m² (40 mg/ft²) and polymethylmethacrylate latex 1722 mg/m² (160 mg/ft2) (0.125 pm average diameter). The processing composition described above was spread between the above structures and the superposed dye- image-receiving sheet described in Example 1 in a thickness of 0.07 mm (28 mils). The density of dye deposited in the receiving sheet was measured as a function of time. The resulting data are set forth below:

The above table illustrates the adverse effect gelatin has on dye transfer. The table also shows that a layer with a greater coverage than the gelatin layer but composed of gelatin and latex particles provides transfer rates approaching that obtained with no overcoat at all, especially in the initial time period.
The following non-limiting example illustrates a particularly preferred film unit of the present invention:

Example 4 (Control)

A photosensitive element was prepared by coating, in succession, on a gelatin subbed, opaque polyethylene terephthalate film base, the following layers:

1. a layer comprising the cyan dye developer
dispersed in gelatin and coated at a coverage of about 747 mg/m² of dye, about 1554 mg/m² of gelatin, about 270 mg/m² of 4'-methylphenylhydroquinone, and about 270 mg/m² of 2-phenyl benzimidazole;
2. a red-sensitive gelatino silver iodobromide emulsion layer coated at a coverage of about 1280 mg/m² of silver and about 768 mg/m² of gelatin;
3. an interlayer coated at a coverage of about 2500 mg/m² of 60-30-4-6 tetrapolymer of butylacrylate, diacetone acrylamide, styrene and methacrylic acid, and about 77 mg/m² of polyacrylamide;
4. a layer comprising the magenta dye developer
dispersed in gelatin and coated at a coverage of about 646 mg/m² of dye and about 426 mg/m² of gelatin and about 229 mg/m² of 2-phenylbenzimidazole;
5. a green-sensitive silver halide emulsion unit consisting of a first layer of 0.6 µm average mean diameter grains coated at a level of about 366 mg/m² of silver and about 161 mg/m² of gelatin and a second layer of 1.42 µm average mean diameter grains coated at a level of about 387 mg/m² silver and about 186 mg/m² of gelatin with a speed difference between said first and second layer of about 5 stops;
6. an interlayer layer containing the tetrapolymer referred to above in layer 3 at a coverage of about 1369 mg/m², about 24 mg/m² of polyacrylamide, and about 75 mg/m² succindialdehyde;
7. a layer comprising the yellow dye developer
dispersed in gelatin and coated at a coverage of about 968 mg/m² of dye and about 450 mg/m² of gelatin and about 208 mg/m² of 2-phenyl benzimidazole;
8. a blue-sensitive gelatino silver iodobromide emulsion layer coated at a coverage of about 1280 mg/m² of silver, about 743 mg/m2 of gelatin, and about 204 mg/m² of 4'-methylphenylhydroquinone;
9. an overcoat layer coated at a coverage of about 484 mg/m² of gelatin and 43 mg/m² of carbon black.

Example 5

A second film unit was prepared as described in Example 4 except that in layer 5 each green-sensitive silver halide emulsion layer additionally contained 4 times the coverage of gelatin of a polymethylmethacrylate latex having an average particle size of about 0.125 pm and layer 6 was reduced in coverage by 40%.
The film units of Examples 4 and 5 were processed in the following manner, using the image-receiving element and processing composition described in Example 1.
The film unit was exposed to white light and the processing composition was spread between the two elements in a layer approximately 0.07 mm (0.0028") thick in the dark.
The following sensitometer data (green light reflection data in neutral column) was obtained in the resulting multicolor reflection prints:
From the foregoing it can be seen that a slight increase in D_max, a 51 unit reduction in slope, an increase in toe extent of about 14 units as well as an increase in dynamic range of almost 12 units are achieved. The loss indicated in the other properties is not considered significant; i.e., the advantages far outweigh the slight decreases recorded in speed. It should be understood that these enhanced photographic results are obtained at the same time the dye transfer is accelerated and silver halide layer integrity maintained.
It should be noted that the interlayer (layer 6) adjacent the silver halide emulsion layer containing the inert particles were reduced in coverage by 40%. This is an additional and unexpected advantage of the present invention which further enhances dye transfer.
A film unit similar to Example 5 was prepared except that the polymer latex employed was a 90/10 methylmethacrylate/hydroxypropyl acrylate copolymer. Upon exposure and processing similar advantageous results were obtained.

Claims

1. A photosensitive element for use in a diffusion transfer film unit and which comprises a support carrying at least one photosensitive silver halide layer that has a dye image-forming material associated therewith and that comprises silver halide grains having an average diameter of 2.5 µm or less and gelatin, characterised in that the said silver halide layer, or at least one of the said silver halide layers, includes inert particles which have an average diameter that is not less than 0.075 11m but that is less than or equal to the average diameter of the silver halide grains and which are compatible with gelatin, substantially non-swelling in aqueous alkaline processing composition and substantially non-light scattering and which, before and during processing with aqueous alkaline processing composition, are substantially non-film forming and substantially non-coalescing.

2. An element according to claim 1 characterised in that the inert particles are derived from a polymer latex.

3. An element according to claim 2 in which the polymer is polystyrene, polymethyl methacrylate or a methylmethacrylate/hydroxypropyl methacrylate copolymer.

4. An element according to any preceding claim in which the weight ratio of inert particles:gelatin is 0.5:1 to 10:1.

5. An element according to claim 4 in which the ratio is 1:1 to 6:1.

6. An element according to any preceding claim characterised in that at least one said photosensitive silver halide layer including the inert particles comprises a first photosensitive silver halide layer distal to the exposure surface of the element and comprising silver halide grains possessing a first mean particle size, and a second photosensitive silver halide layer comprising silver halide grains possessing a second mean particle size, and the second photosensitive silver halide layer has a higher intrinsic speed than the first, the first and second photosensitive silver halide layers are in contiguous relationship, and the inert particles are in at least the second silver halide layer.

7. An element according to claim 6 in which the average mean diameter of the silver halide grains in the first photosensitive silver halide layer is less than about 1 µm and the average mean diameter of the silver halide grains in the second photosensitive layer is greater than 1.3 pm.

8. An element according to claim 6 or claim 7 characterised in that the speed difference between the first and second photosensitive silver halide layers is between 2 and 8 stops.

9. An element according to claim 8 characterised in that the speed difference is about 5 stops.

10. An element according to any preceding claim in which the support carries a red sensitive silver halide unit having associated therewith a cyan dye developer, a green sensitive silver halide unit having associated therewith a magenta dye developer and a blue sensitive silver halide unit having associated therewith a yellow dye developer and in which the green sensitive silver halide unit includes the said inert particles.

11. A diffusion transfer film unit comprising a support carrying at least one photosensitive element and an image receiving element comprising a dyeable receiving layer for receiving a dye image diffusing thereto after photoexposure and processing of the photosensitive element and characterised in that the photosensitive element is an element according to any of claims 1 to 10.