Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03C—PHOTOSENSITIVE MATERIALS FOR PHOTOGRAPHIC PURPOSES; PHOTOGRAPHIC PROCESSES, e.g. CINE, X-RAY, COLOUR, STEREO-PHOTOGRAPHIC PROCESSES; AUXILIARY PROCESSES IN PHOTOGRAPHY
  • G03C8/00—Diffusion transfer processes or agents therefor; Photosensitive materials for such processes
  • G03C8/02—Photosensitive materials characterised by the image-forming section
  • G03C8/08—Photosensitive materials characterised by the image-forming section the substances transferred by diffusion consisting of organic compounds
  • G03C8/10—Photosensitive materials characterised by the image-forming section the substances transferred by diffusion consisting of organic compounds of dyes or their precursors

Definitions

• the invention relates to a process for producing color photographic images by the dye diffusion transfer process and to a photographic material suitable therefor which contains new diffusion-resistant, oxidizable coloring compounds which release diffusing dyes in a non-oxidized form.
• the color-providing compounds suitable for this purpose include, for example, the non-diffusing color couplers described in DE-PS 1 095 115, which are used in the Development as a result of a reaction with the oxidation product of a color developer compound consisting of a primary aromatic amine releases a pre-formed or diffused form of dye produced in the color coupling.
• the selection of the developer compound required is naturally limited to color developers.
• non-diffusing coloring compounds described in DE-OS 1 930 215, which contain a preformed latent diffusible dye residue linked to a diffusion-proofing residue via a cleavable hydrazone group.
• These compounds are not to be called color couplers, and it has also been found that the choice of developer compounds which are required to release the diffusing dye residue is in no way limited to the usual color developers, but that black and white developers, e.g. Catechins are very useful.
• DE-OS 1 772 929 also describes non-diffusing colored compounds with a special grouping which undergo an oxidative ring closure reaction during development and thereby release a pre-formed dye residue in diffusing form.
• the connections presented there can be divided into two groups.
• the compounds of the one group require a customary color developer compound for development, with whose oxidation product they couple and in a subsequent ring closure reaction release the pre-formed dye residue in diffusing form.
• the compounds of the other group are themselves slip halide developing agents and are therefore able, in the absence of further developer compounds in the oxidustan form, to undergo the above-mentioned ring closure reaction with fralse tion of the diffusing dyes.
• non-diffusing coloring compounds of DE-OS 2 242 762 should also be mentioned at this point.
• These are sulfonamidophenols and sulfonamidoanilines, which after development have undergone oxidation under the influence of the developer alkali with the release of diffusing dyes with a free sulfamoyl group will.
• the above-mentioned coloring compounds work invariably negative, i.e. the image-wise distribution of the diffusing dye set arises when conventional (negative working) silver halide emulsions are used in accordance with the negative silver image produced during development.
• conventional (negative working) silver halide emulsions are used in accordance with the negative silver image produced during development.
• To produce positive finished fabric images it is therefore necessary to use direct-positive silver halide emulsions or otherwise to use a suitable reversal process.
• Non-diffusing coloring compounds are also known from German Offenlegungsschriften 2 402 900 and 2 543 902, which, in non-oxidized form, are capable of a cleavage reaction under alkaline development conditions, a diffusing color step being set free, and in which, on the other hand, in the oxidized form the one mentioned above Cleavage reaction is difficult or prevented.
• Such compounds are suitable in combination with conventional negative emulsions for producing positive transfer color images
• positions 2 and 4 of the above formula contain neither a hydrogen atom nor a substituent which can be exchanged for OH ions.
• the present invention furthermore relates to a material for carrying out the above method, which accordingly, in association with at least one light-sensitive silver halide emulsion layer, contains a non-diffusing oxidizable compound of the type described above.
• the residues of dyes of all classes of dyes are suitable as dye residues insofar as they are sufficiently diffusible to be able to diffuse through the layers of the light-sensitive material into the image-receiving layer.
• the dye residues can be provided with one or more water-solubilizing groups. Suitable water-solubilizing groups include carboxyl groups, sulfo groups, sulfonamide groups and aliphatic or aromatic hydroxyl groups. The sulfinic acid group remaining in the dye after the cleavage can already give the dye molecule a considerable tendency to diffuse in the alkaline Medium, so that the presence of additional water-solubilizing groups is not absolutely necessary.
• the residues of dye precursors are to be understood as the residues of those compounds which, in the course of photographic processing, are subject to conventional or additional processing steps, be it by oxidation, by coupling or by exposure of an auxochromic group in a chromophoric system, for example by saponification Dyes are transferred.
• Dye precursors in this sense can be leuco dyes, couplers or dyes that are converted into other dyes during processing. Unless a distinction between dye residues and the residues of dye precursors is of essential importance, the latter are also to be understood below as dye residues.
• the bivalent link X shown in the general formula can, for example, be a radical of one of the following formulas: Y 1 and Y 2 are preferably hydroxyl. If Y 1 and / or Y 2 is an -NH-S02R8 group, R 8 has the meaning of a photographically inert radical, for example an unsubstituted alkyl or phenyl radical.
• the redox potential of the oxidizable compound can easily be influenced by varying the substituent R 3 and can thus be adapted to practical requirements.
• the selection of the substituents R 4 and R 5 is subject to certain restrictions, insofar as hydrogen or other substituents which can be exchanged for OH - ions are out of the question.
• this does not apply to R 3 to the same extent, so that a larger selection of substituents is available here for setting the desired redox potential.
• another important function of the compounds according to the invention is the easy hydrolyzability in the unoxidized form.
• the hydrolytic cleavage should proceed as quickly as possible in the alkaline developer medium so that the photographically active group is quickly released. On the other hand, the onset of hydrolytic cleavage should be delayed until the imagewise oxidation of the oxidizable compounds by developer oxidation products has essentially been completed.
• the coloring compounds according to the invention should not diffuse as intact molecules in the layers of the photographic material.
• they contain a radical which makes them resistant to diffusion, for example in one of the substituents R to R or in a substituent present on the fused ring completed by R together with R 4.
• Adequate diffusion resistance of the coloring compounds can already exist even if the substituents mentioned do not contain any longer alkyl residues, since the molecule can then also have a sufficient size, depending on the dye residue. Otherwise it is possible to make the coloring compounds sufficiently diffusion-resistant by selecting residues of a suitable size.
• Residues which make it resistant to diffusion are those which make it possible to store the compounds according to the invention in a diffusion-resistant manner in the hydrophilic colloids which are usually used in photographic materials.
• Organic radicals which generally contain straight-chain or branched aliphatic groups and optionally also isocyclic or heterocyclic or aromatic groups with generally 8-22 C atoms are preferably suitable for this purpose.
• residues are connected to the rest of the molecule either directly or indirectly, for example via one of the following groups: -NHCO-, NHSO 2 , -NR-, where R is hydrogen or alkyl, -O-, -S- or -SO 2 , such groups containing such hetero atoms expediently by at least two carbon atoms or methylene groups of the aromatic ring of the general formula ( R 3 , R 4 , R 5 ) or from the carbon atom (R 1 ) bearing the cleavable group -SO 2 - (X) m -A).
• the diffusion-proofing radical can also contain water-solubilizing groups, such as sulfo groups or carboxyl groups, which can also be in anionic form. Since the diffusion properties depend on the molecular size of the total compound used, it is sufficient in certain cases, for example if the total molecule used is large enough, to use shorter-chain residues as "diffusion-proofing residues".
• non-diffusing oxidizable compounds suitable according to the invention are listed below:
• Step 2 4-hydroxy-2,3-dimethyl-6-tetradecanoylphenyl allyl ether
• Step 6 dye sulfinic acid 4- (4-hydroxy-3-N, N-diethylsulfamoyl-8-methylsulfonamido-1-naphthylazo) -benzenesulfinic acid
• a solution was added to a solution of 4 g of the carbinol compound from stage 5 in 300 ml of glacial acetic acid heated to 60 ° C. of 7 g of dye sulfinic acid from stage 6 1.5 g of Na acetate anhydrous 120 ml of glacial acetic acid and 40 ml of water.
• the mixture was heated to 90 ° C. for 2 hours while stirring in a nitrogen atmosphere. After a short time, the dye compound begins to fail. After cooling to 60 ° C, the resulting precipitate was filtered off and washed with glacial acetic acid.
• the dye was purified by stirring with methanol.
• Step 2 4-Hydroxy-2-methyl-5-hexadecanoylphenyl allyl ether
• Step 6 dye sulfinic acid 4- ⁇ 3- [8- (4-nitro-2-methylsulfonylphenylazo) -5-hydroxy-1-naphthyl] sulfamoylbenzene ⁇ sulfionamido benzene sulfinic acid
• the main aspect of the present invention relates to the case where the oxidizable compound is a coloring compound and the photographically active group is a diffusing dye.
• the following mainly refers to coloring compounds, but this should not be understood as a limitation.
• the oxidizable compounds can be used for a wide variety of other purposes, with other photographically active groups being possible.
• the coloring compounds according to the invention are incorporated into the casting solutions for the layers of the photographic material by one of the customary methods.
• the amount of coloring compound used per liter of casting solution varies within relatively wide limits, the most favorable concentration being determined on the basis of simple experiments. For example, 5-80 g, preferably 20-40 g, of coloring compound are used per liter of casting solution.
• the association between diffusion-resistant coloring compound and silver halide required to achieve the desired effect can be produced, for example, by introducing the diffusion-resistant compounds from the aqueous solution into the casting solutions using existing acidic water-solubilizing groups.
• the non-diffusing coloring compounds can, however, also be introduced into the layers by one of the known emulsification processes. Such methods are described, for example, in British Patents 791,219 and 1,099,414 to 1,099,417. It is also possible to prepare aqueous dispersions or coloring compounds and add them to the respective casting solutions. For this purpose, aqueous slurries of the coloring compounds are finely ground, for example by intensive stirring with the addition of sharp-edged sand or by using Ulese.
• the coloring compounds may be desirable, for example, to store the coloring compounds together with silver halide and, if appropriate, developer substances in the form of so-called microcapsules, two or more differently sensitized light-sensitive silver halide emulsions and the corresponding diffusion-resistant compounds in a single layer in the manner of the so-called Mixed grain emulsions are combined, as described, for example, in US Pat. No. 2,698,794.
• the non-diffusing coloring compounds can be accommodated in a light-sensitive layer itself or in a neighboring layer.
• the red-sensitive layer is associated with a compound which cleaves off a cyan dye
• the green-sensitive layer with a compound which cleaves off a purple dye
• the blue-sensitive layer with a compound which cleaves off a yellow dye.
• developer substances in the process according to the invention is not limited to color developers, but that conventional black-and-white developers are preferably also used, which is to be regarded as an advantage because of the lower tendency to discoloration of the latter.
• the developers can already be contained in the layers of the color photographic material, where they are activated by the alkaline activator liquid, or in the alkaline processing liquid or paste. Since the coloring compounds according to the invention themselves have developer properties, the use of auxiliary developer compounds can be dispensed with under certain conditions. In this case, the coloring compound is immediately oxidized by developable silver halide.
• the emulsions can be chemically sensitized, e.g. by adding sulfur-containing compounds during chemical ripening, for example allyl isothiocyanate, allyl thiourea, sodium thiosulfate and the like.
• Reducing agents e.g. the tin compounds described in Belgian patents 493,464 and 568,687, also polyamines such as diethylenetriamine, or aminomethanesulfinic acid derivatives, e.g. according to Belgian patent 547 323 can be used.
• Precious metals or noble metal compounds such as gold, platinum, palladium, iridium, ruthenium or rhodium are also suitable as chemical sensitizers. This method of chemical sensitization is described in the article by R. KOSLOWSKY, Z.Wiss.Phot. 45, 65-72 (1951).
• polyalkylene oxide derivatives e.g. with polyethylene oxide with a molecular weight between 1000 and 20,000
• condensation products of alkylene oxides and aliphatic alcohols, glycols, cyclic dehydration products of hexitols, with alkyl-substituted phenols, aliphatic carboxylic acids, aliphatic amines, aliphatic diamines and amides The condensation products have a molecular weight of at least 700, preferably more than 1000.
• these sensitizers can of course be used in combination, as described in BE-PS 537 278 and in GB-PS 727 982.
• the emulsions can also be spectrally sensitized, for example by the usual mono- or polymethine dyes such as acidic or basic cyanines, hemicyanines, streptocyanm merocyanines, oxonols, hemioxonols, styryl dyes or other, also trinuclear or polynuclear methine dyes for example rhodacyanine or neocyanine.
• mono- or polymethine dyes such as acidic or basic cyanines, hemicyanines, streptocyanm merocyanines, oxonols, hemioxonols, styryl dyes or other, also trinuclear or polynuclear methine dyes for example rhodacyanine or neocyanine.
• sensitizers are described for example in the work of FM HAMER "The Cyanine Dyes and Related Compounds" (19
• the emulsions can contain the usual stabilizers, e.g. homeopolar or salt-like compounds of mercury with aromatic or heterocyclic rings such as mercaptotriazoles, simple mercury salts, sulfonium mercury double salts and other mercury compounds.
• stabilizers e.g. homeopolar or salt-like compounds of mercury with aromatic or heterocyclic rings such as mercaptotriazoles, simple mercury salts, sulfonium mercury double salts and other mercury compounds.
• azaindenes preferably tetra- or penta-azaindenes, in particular those which are substituted by hydroxyl or amino groups. Such compounds are described in the article by BIRR, Z.Wiss.Phot. 47, 2-27 (1952).
• Other suitable stabilizers include heterocyclic mercapto compounds, e.g. Phenyl mercaptotetrazole, quaternary benzothiazole derivatives, benzotriazole and the like.
• Gelatin is preferably used as a binder for the photographic layers. However, this can be replaced in whole or in part by other natural or synthetic binders.
• natural binders e.g. Alginic acid and its derivatives such as salts, esters or amides, cellulose derivatives such as carboxymethyl cellulose, alkyl cellulose such as hydroxyethyl cellulose, starch or their derivatives such as ethers or esters, or caragenates.
• Synthetic binders include polyvinyl alcohol, partially saponified polyvinyl acetate, polyvinyl pyrrolidone and the like.
• the layers can be cured in the customary manner, for example using formaldehyde or halogen-substituted aldehydes which contain a carboxyl group, such as mucobromic acid, diketones, methanesulfonic acid esters, dialdehydes.
• a light-emitting element which contains one or more silver halide emulsion layers and the associated non-diffusing coloring compounds and an image-receiving element in which the desired color image is generated by the imagewise transferred diffusing dyes.
• the mono-sheet material can be composed in such a way that two different parts are produced separately from one another, namely the light-sensitive part (layer elements 1 - 4) and the cover sheet (layer elements 5 - 7), which are then placed on top of one another on the layer and connected to one another, optionally under Use of spacer strips so that a space is formed between the two parts for receiving a precisely measured amount of processing liquid.
• the layer elements 5 and 6, which together form the neutralization system, can also be arranged - albeit in the opposite order - between the layer support and the image-receiving layer of the light-sensitive part.
• Means may be provided to introduce a processing liquid between the photosensitive member and the cover sheet, e.g. in the form of a laterally arranged splitable container which pours its contents between two adjacent layers of the mono-sheet material when subjected to mechanical forces.
• An essential part of the photographic material according to the present invention is the photosensitive member which is used in the case of a single dye transfer process a photosensitive silver halide emulsion layer and associated with this contains a non-diffusing coloring compound.
• the non-diffusing compound can be in a silver halide emulsion schioma. adjacent layer or in the silver halide emulsion layer itself, in the latter case the color of the image dye is preferably selected so that the predominant absorption range of the coloring compound does not match the predominant sensitivity range of the silver halide emulsion layer.
• the light-sensitive element contains three such assignments of coloring compound and light-sensitive silver halide emulsion layer, the absorption range of the coloring compound generally matching the range of spectral sensitivity of the assigned silver halide emulsion layer substantially.
• a prerequisite for the highest possible sensitivity is, however, that the color-providing combination is arranged in a separate binder layer (seen in the direction of the light incident during the exposure) behind the silver halide emulsion layer.
• the developer oxidation products formed during the development of a silver halide emulsion may of course only have an effect on the assigned coloring compound. Separating layers are therefore generally present in the photosensitive element, which effectively prevent the diffusion of the developer oxidation products into other unassigned layers.
• the silver halide emulsion layers can also be arranged in a different order, but the assigned layers must also be interchanged with the coloring systems so that the assignment is retained.
• the opaque layer arranged under the photosensitive element is permeable to aqueous alkaline treatment solutions and thus to the diffusing dyes. It essentially has two functions: firstly, it serves to cover the image silver remaining in the originally light-sensitive element after development, as well as the color-providing compounds remaining as color negatives, so that when viewed through the transparent substrate of the light-sensitive part, only the positive color transfer image is visible ; second, it closes the photosensitive Element from the side of the image receiving layer (downward) from light-tight.
• the latter is particularly important if, after exposure, the mono-sheet material is still brought into contact with the alkaline processing composition in the camera, then is to be pulled out of the camera and developed outside the camera.
• Layers with sufficient opacity but sufficient permeability for diffusing dyes can be produced, for example, with suspensions of inorganic or organic dark, preferably black pigments, for example with suspensions of carbon black, in suitable binders, for example in gelatin solutions.
• black pigments for example with suspensions of carbon black
• suitable binders for example in gelatin solutions.
• 0.5-2 / u thick layers containing 10-90% by weight (based on the total dry weight) of carbon black in gelatin are sufficient in order to ensure sufficient exclusion of light during development.
• the particle size of the pigments used is relatively uncritical as long as it does not significantly exceed 0.5 / u.
• the opaque layer preferably also comprises a white pigment layer arranged underneath.
• a white pigment layer arranged underneath. This has the task of covering the black layer and creating a white background for the picture. All white pigments are suitable for this, provided that their opacity is sufficiently high for layers that are not too large. Examples include barium sulfate, oxides of zinc, titanium, silicon, aluminum and zircon, and also barium stearate or kaolin. Titanium dioxide is preferred as the white pigment. The same information applies to the binder, the concentration and the particle size as for the black pigments.
• the thickness of the white pigment layer can be varied depending on the desired whiteness of the substrate. Thicknesses between 5 and 20 ⁇ are preferably used.
• means for producing such an opaque layer can also be arranged in the monosheet material according to the present invention between the photosensitive element and the image-receiving layer, e.g. in the form of a laterally arranged container with a processing liquid containing an opacifying agent (pigment) which, when subjected to mechanical forces, pours its contents between the layers mentioned, so that such a pigment layer forms there.
• an opacifying agent pigment
• the image-receiving layer essentially consists of a binder which contains dye mordants for fixing the diffusing dyes.
• the dye mordants are dispersed in the receiving layer in one of the usual hydrophilic binders, e.g. in gelatin, polyvinylpyrrolidone, wholly or partially hydrolyzed cellulose esters and the like. Of course, some binders can also act as mordants, e.g.
• Copolymers or polymer mixtures of vinyl alcohol and N-vinylpyrrolidone as described, for example, in DE-AS 1 130 284, and also those which are polymers of nitrogen-containing quaternary bases, e.g. Polymers of N-methyl-2-vinylpyridine, as described, for example, in US Pat. No. 2,484,430.
• the transparent support materials used for the monosheet material according to the invention can be the customary transparent support materials used in photographic practice, for example films of cellulose esters, polyethylene terephthalate, polycarbonate or other film-forming polymers.
• the alkaline processing composition sets a relatively high pH waiting (about 11 to 14) in the light-sensitive material, which triggers the development and the imagewise dye diffusion. It has been shown that at this high pH the dyes and thus the images obtained are not particularly stable. It is therefore necessary that the material is made almost neutral or slightly acidic after development is complete. This can be achieved in a known manner in that the material additionally contains an acidic polymer layer which is only gradually accessible to the alkaline processing composition in the course of development.
• An acidic polymer layer is understood to mean a binder layer which contains polymeric compounds with acid groups, preferably sulfo or carboxyl groups. These acidic groups react with the cations of the processing mass with salt formation and lower the pH value of the mass. Of course, the polymeric compounds and thus the acidic groups are embedded in the layer mentioned in a diffusion-resistant manner.
• the acidic polymers are derivatives of cellulose or derivatives of polyvinyl compounds;
• there may be other polymeric compounds using consequently as usable acidic polymers may be mentioned, for example: cellulose derivatives having a free carboxyl group, for example Cellulosedicarbonklareschreibester with a free carboxyl group such as cellulose acetate hydrogen phthalate, Celluloseacetathydrogenglutarat, Ethylcelluloseacetathydrogensuccinat, Celluloseacetathydrogensuccinathydrogenphthalat, ethers and esters of cellulose with other dicarboxylic acid anhydrides or with Sulphonic acid anhydrides, for example modified with o-sulphobenzoic anhydride, carboxymethyl cellulose, also polystyrene sulphonic acid, polyvinyl hydrogen phthalate, polyvinyl acetate hydrogen phthalate, polyacrylic acid, acetals of polyvinyl alcohol with aldehydes which are
• Suitable acidic polymers are described for example in DE-OS 2 652 464.
• the acidic polymer layer must contain enough acid groups to lower the pH of the processing mass from the beginning 11 to 14 to such an extent that the material is almost neutral or weakly acidic at the end (pH 5-8).
• the time delay of the pE value reduction is achieved in a known manner in that the acidic polymer layer is coated with a so-called delay layer.
• This delay layer is an alkali-impermeable layer, which preferably consists of an alkali inert polymers, for example made of polyvinyl alcohol or a partially acetalized polyvinyl alcohol.
• the time delay of the pH reduction can be adjusted in the desired manner.
• a brake layer with polymers of a novel permeability behavior is described, for example, in DE-OS 2 455 762.
• Neutralization systems which are combinations of an acidic polymer layer and a delay layer, are described, for example, in DE-FS 1 285 310.
• Such layer combinations can be present in the material according to the invention, for example in the light-sensitive part between the transparent layer support and the image-receiving layer.
• Another possibility is to arrange the neutralization system from the acidic polymer layer and a delay layer on the cover sheet.
• these two layers must be arranged in such a sequence that the alkali of the processing composition must first penetrate the retardation layer in order to get into the acidic polymer layer.
• the dye diffusion transfer method according to the invention can advantageously be carried out in or by means of a suitable self-developing camera.
• a suitable self-developing camera This can be provided, for example, with devices which, after exposure of the photosensitive element, make it possible to distribute a working solution between the latter and the cover sheet and to cover the photosensitive material in an opaque manner.
• Such a camera is preferably with two provided against each other nip rollers, between which the mono-sheet material is pulled out, the laterally arranged containers are split and release their contents between the layers of the mono-sheet material. Since the light-sensitive element is protected against unwanted exposure by opaque layers on both sides after passing through the nip rollers, the exposed material can be pulled out of the camera immediately after the development has been started.
• the photosensitive element is brought into contact with the aqueous alkaline working solution.
• the imagewise exposed silver halide emulsion layers are developed in the presence of the developer compound, an imagewise distribution of oxidation products of the developer compound being generated in accordance with the silver image thus formed, which oxidizes the assigned coloring compound, followed by the imagewise distribution of unoxidized coloring compound under the action of the activator or developer alkali the diffusing dye is split off.
• the aqueous alkaline working solution can contain viscosity-increasing additives, e.g. Hydroxyethyl cellulose. Development accelerators, stabilizers, silver salt solvents, fogging agents, antioxidants and other additives can also be contained in the working solution in a known manner.
• viscosity-increasing additives e.g. Hydroxyethyl cellulose.
• Development accelerators, stabilizers, silver salt solvents, fogging agents, antioxidants and other additives can also be contained in the working solution in a known manner.
• the compounds according to the invention are essentially only subjected to hydrolytic cleavage in the reduced state with the release of the photographically active group, but are stable after oxidation, it is obvious to incorporate them into the layers in the oxidized form, but care must be taken must be converted into the hydrolyzable reduced form during development. This can be accomplished by the simultaneous use of so-called electron donor compounds (ED compounds), which are reducing substances which are converted into the oxidized form by reaction with developer oxidation products or with the developable silver halide and thus the reaction with the oxidized Form of the compounds of the invention are withdrawn.
• ED compounds electron donor compounds
• the ED compound remains in its active form only at those points where there is no development of silver halide, which can react with the oxidized form of the coloring compound to form the hydrolyzable reduced form, from which, under the conditions of photographic development, the diffusing dyes are released imagewise.
• the photographically active group is a diffusing dye or diffusing dye precursor.
• the photographically active group is, for example, an antifoggant, a development inhibitor, a hardening agent, a developing agent or a development accelerating agent.
• the photographically active group is released imagewise, i.e. in accordance with imagewise distribution of undeveloped silver halide when using negative emulsions. This opens up a wide range of possibilities for image generation.

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• 1978
  • 1978-12-20 DE DE19782854946 patent/DE2854946A1/de not_active Withdrawn
• 1979
  • 1979-12-01 EP EP79105047A patent/EP0012908A3/fr not_active Withdrawn
  • 1979-12-18 JP JP16367179A patent/JPS5588054A/ja active Pending

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