GB1570551A - Silver diffusion transfer image receiving elements - Google Patents

Description

(54) SILVER DIFFUSION TRANSFER IMAGE RECEIVING ELEMENTS (71) We, POLAROID CORPORATION, a corporation organised under the laws of the state of Delaware, United States of America, of 549 Technology Square, Cambridge, Massachusetts 02139, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us and the method by which it is to be performed to be particularly described in and by the following statement:- Procedures for preparing photographic images in silver by diffusion transfer principles are well known in the art. For the formation of the positive silver images, a latent image contained in an exposed photosensitive silver halide emulsion is developed and almost concurrently therewith, a soluble silver complex is obtained by reaction of a silver halide solvent with the unexposed and undeveloped silver halide of said emulsion. Preferably, the photosensitive silver halide emulsion is developed with a processing composition in a viscous condition which is spread between the photosensitive element comprising the silver halide emulsion and a print-receiving element comprising, preferably, a suitable silver precipitating layer.

The processing composition effects development of the latent image in the emulsion and, substantially contemporaneously therewith, forms a soluble silver complex, for example, a thiosulfate or thiocyanate, with undeveloped silver halide.

This soluble silver complex is, at least in part, transported in the direction of the print-receiving element and the silver thereof is largely precipitated in the silver precipitating element to form a positive image thereon. Procedures of this description are disclosed, for example, in U. S. Patent No. 2,543,181 issued to Edwin H. Land, See, also, Edwin H. Land, One Step Photography, Photographic Journal, Section A, pp. 7-15, January 1950.

Additive color reproduction may be produced by exposing a photosensitive silver halide emulsion through an additive color screen having filter media or screen elements each of an individual additive color, such as red or green or blue, and by viewing the reversed or positive silver image formed by transfer to a transparent print-receiving element through the same or a similar screen which is suitably registered with the reversed positive image carried by the print-receiving layer.

As examples of suitable film structures for employment in additive color photography, mention may be made of U. S. Patent Nos. 2,861,885; 2,726,154; 2,944,894: 3,536,488; 3,615,427; 3,615,428; 3,615,429; 3,615,426; and 3,894,871.

The image-receiving elements of the present invention are particularly suited for use in diffusion transfer film units wherein there is contained a positive transfer image and a negative silver image, the two images being in separate layers on a common, transparent support and viewed as a single, positive image. Such positive images may be referred to for convenience as "integral positive-negative images", and more particularly as "integral postive-negative transparencies." Examples of film units which provide such integral postive-negative transparencies are set forth, for example, in the above-indicated U.S. Patents Nos. 3,536,488; 3,894,871.

3.615,426; 3,615,427: 3.615,428; and 3,615,429.

In general, silver precipitating nuclei comprise a specific class of adjuncts well known in the art as adapted to effect catalytic reduction of solubilized silver halide specifically including heavy metals and heavy metal compounds such as the metals of Groups IB, IIB, IVA, VIA and VIII and the reaction products of Groups IB, IIB, IVA and VIII metals with elements of Group VIA.

Widely used as silver precipitating agents have been those disclosed in U.S.

Patent No. 2,698,237 and specifically the metallic sulfides and selenides, there detailed, these terms being understood to include the selenosulfides, the polysulfides, and the polyselenides. It has been preferred to employ sulfides whose solubility products in an aqueous medium at approximately 20"C. vary between 10-23 and 10-49, and especially the salts of zinc. Also particularly suitable as precipitating agents heavy metals such as silver, gold, platinum or palladium, and in this category the noble metals illustrated are preferred and are generally provided in a silica matrix as colloidal particles.

The necleation layers in the art have generally had a thickness in excess of the 1 micron range (about 93 mgs/ft2). See, for example, U.S. Patents Nos. 3,220,837 and 3,709,687.

U.S. Patent No. 3,647,440 discloses receiving layers comprising finely divided non-silver noble metal nuclei obtained by reducing a noble metal salt in the presence of a colloid or binder material with a reducing agent having a standard potential more negative than -0.30. It is the thrust of the patent that a reducing agent having a standard potential more negative than -0.30 must be used in order to obtain nuclei of a specific, usable size range. It is further illustrated that stannous chloride, which does not fall within the standard potential range, does not produce useful nuclei. The binder materials disclosed include gelatin, polyvinyl pyrrolidone, polymeric latices such a copoly (2-chloroethylmethacrylate-acrylic acid), a mixture of polyvinyl alcohol and the interpolymer of n-butyl acrylate, 3-acryloyloxypropane I-sulfonic acid, sodium salt and 2-acetoacetoxyethyl methacrylate, polyethylene latex, and colloidal silica. The amount of colloid binder employed ranges from about 5 to 500 mgs/ft2 with the nuclei ranging from 1 to 200 micrograms/ft2.

A novel silver precipitating nuclei system has now been found which possesses advantages not found in the prior art, which system has particular value in silver transfer color images.

The present invention is directed to a receiving element for use in an additive color diffusion transfer process and comprises a transparent support carrying an additive color screen and a layer of noble metal nuclei and a polymer. The nuclei are present at 0.07 to 0.3 mgs/ft2 and the polymer is present at 0.5 to 5 times the coverage of the nuclei. Thus, the total of the nuclei and polymer together is not greater than about 2 mgs/ft2.

In a preferred embodiment, the noble metal nuclei comprise palladium nuclei.

In a particularly preferred embodiment the noble metal nuclei are prepared by reducing a noble metal salt or complex; and, more preferably, reducing with a metal capable of two valence states.

The silver precipitating layers employed in the novel receiving element provide positive silver transfer images at coverages heretofore not employed or taught by the prior art. The relatively thin nucleating layer as well as the small amount of nuclei and the relatively low polymer level is not only unexpected but also unobvious in view of the art. Generally, large excesses of polymer or other binder compared to nuclei are employed.

The noble metals employed in the Present invention include silver, gold, palladium and platinum. However, particularly superior results are achieved at the specified coverages with palladium and, for convenience, the invention will be described primarily in terms of this preferred embodiment.

Superior photographic results are obtained employing the palladium metal nuclei in a gelatin or hydroxyethyl cellulose polymer, particularly with respect to silver image tone and density.

While the amount of noble metal nuclei may range over the range indicated, particularly advantageous results are obtained at 0.15 to 0.25 mgs/ft2, and more particularly, at about 0.2 mgs/ft2.

The polymer is employed at 0.5 to 5 times the coverage of the noble metal nuclei. It is surprising that such a relatively small amount of polymer can be employed without precipitation or settling of the noble metal, while at the same time obtaining the sensitometric properties desired, particularly silver image tone.

In addition, a more neutral image tone is achieved as gelatin at the lower level of the polymer range is employed.

The noble metal muclei are preferably obtained by the reduction of a noble salt or complex. In a preferred embodiment, the reduction is carried out by a first (or reducing) metal capable of existing in two valence states. While it is not intended that we be bound by the theory, it is believed in the art that the noble metal ion is reduced to the metallic state where it can function as a catalytic site for silver deposition in a diffusion transfer process. Thus, the term "noble metal nuclei" is intended to include the metallic noble metal in colloidal form as well as alloyed with other materials such as the aforementioned first metal and the terms "reduce" and "reduction" are intended to refer to the chemical reaction by which the colloidal or alloyed form of the noble metal is obtained. While the noble metal nuclei are substantially in the metallic or alloyed form, it should be understood that minor amounts of noble metal complexes may be present. As examples of suitable materials for use as the first or (or reducing) metal ion, mention may be made of iron, cobalt, nickel, bismuth, lead, titanium, vanadium, chromium, copper, molvbdenum, antimony, tungsten and preferably tin.

Noble metal nuclei prepared by the procedure set forth in U.S. Patent Specification No. 4025343 and British Patent Application 1441/77 Serial No.

1570222 may also be employed in the receiving elements of the present invention.

The term "polymer" as used therein is intended to include natural and synthetic polymers and includes gelatin methyl cellulose sodium salt of carboxymethyl cellulose hydroxymethyl cellulose hydroxyethyl cellulose hydroxypropyl cellulose carboxymethyl hydroxyethyl cellulose alginic acid, sodium salt agarose polyvinyl alcohol deacetylated chitin Successive coatings of the noble metal nucleating layers may be employed, in some cases, separated by layers of a suitable polymeric binder such as deacetylated chitin or gelatin. In a preferred embodiment, however, a single layer of the noble metal/polymer silver precipitating layer is coated.

The novel image-receiving element of the present invention as employed in silver diffusion transfer processing forms a positive silver image therein which is frequently characterized by a uniform mirror deposit of image silver believed to be a result of the relatively thin nuclei layer employed. The positive silver is more dense than that generally found in prior art image-receiving elements and is similar in properties to that obtained by vacuum deposited silver, which is believed to be the most compact form possible. The above-mentioned mirror effect is particularly desirable in photographic transparencies since it tends to increase the Dmax in projection images when the mirror is on the side of the support next to the projection light. The absorption spectrum of the solver transfer image is relatively neutral, i.e., similar to vacuum deposited silver. Thus, by means of the present invention, a thin, tightly packed matrix of nuclei can be prepared so that the image silver deposited therein is similar to vacuum deposited silver.

Combinations of noble metals may be used as well as single noble metals. In a preferred embodiment, a noble metal salt or complex may be reacted in aqueous solution with a salt of the first or reducing metal. Suitable compounds for providing the noble metal include the following: K2PdCl4 PdCI2 H2PtCIe AgNO3 HAUL4 The ratio of first metal salt to noble metal salt or complex may range from 1:1 to 4:1, and preferably 3:1, said ratios based on the weight of the metals.

The following preparations examples illustrate the present invention. In these "Daxad" II is a polymerised sodium salt of alkyl naphthalene sulphonic acid manufactured by W. R. Grace & Co. of Cambridge, Mass. USA. "Daxad" is a trade mark.

Preparation I The following solutions were prepared: Solution A 165 cc water 0.65 g K2PdCI4 85 cc 1% hydroxyethylcellulose 250 cc 0.lav0 alkyl phenoxypolyoxyethylene ethanol surfactant (sold under the trade name PE-120 by NOPCO Chem.

Div. of 'Diamond Shamrock Company) The K2PdCI4 is dissolved in the water and to this solution is added the hydroxyethylcellulose and surfactant.

Solution B 165 cc water 1.0 g SnCl2 85 cc 1% hydroxyethylcellulose 250 cc 0.1% alkylphenoxypolyoxyethylene ethanol surfactant The SnCI, is added to the water and to this mixture is added the hydroxyethylcellulose and surfactant.

Solutions A and B are quickly mixed together, stirred for 30 to 60 minutes and can then be coated on suitable supports for use as silver precipitating layers in accordance with the invention.

The utility of such nuclei layers is described below.

Example 1.

A film unit was prepared comprising transparent polyester film base carrying on one surface an additive color screen of approximately 1000 triplets per inch of red, blue and green filter screen elements in repetitive side-by-side relationship; a 4 micron polyvinylidine chloride-polyvinyl formal protective overcoat layer; nucleating material prepared according to the procedure of Preparation 1 was slot coated over said protective layer; a gel coat (50 mgs/ft2) prepared by adding 26 g. of a 10% inert gel solution to 72 cc of water, heating to 390 C. and mixing until homogeneous and then adding 3 cc of a 1% solution of octylphenoxy polyethoxy ethanol surfactant; a hardened gelatino silver iodochloro emulsion coated at a coverage of about 115 mgs/ft2 of gelatin and about 100 mgs/ft2 of silver with about 7.18 mgs/ft2 propylene glycol alginate and about 0.45 mgs/ft2 of sodium dioctyl sulfosuccinate panchromatically sensitized with 5,5'-dimethyl-9-ethyl-/3,3 '-bis-(3 sulfopropyl) thiacarbocyanine triethyl-ammonium salt and 5,5'-diphenyl-9-ethyl3,3'-bis-(4-sulfobutyl) oxacarbocyanine; and 100 mgs/ft2 of one of the following antihalo top coats. The antihalo top coats referred to below are disclosed and claimed in British Patent Specification No. 1482156.

Top Coat A Wt. % Sodium bis- 1,5 [3-carboxy- 1 -(p-N-n-pentyl sulfonamido-phenyl)-2-pyrazolin-5-one] pentamethine oxonol 0.13 Distilled Water 65.18 4-(2-chloro-4-dimethylaminobenzaldehyde) 1 (p-phenyl carboxylic acid)3-methyl pyrazalone-5 0.01 Gelatin (15% solution) 34.59 "Daxad"-ll 0.007 Top Coat B Gelatin 0.02 Benzimidazole thiol gold complex 0.35 Distilled water 6.66 Pyridinium bis- 1,5(1 ,3-diethyl-2-thiol-5 barbituric acid) Pentamethine oxanol 0.22 4-(2-chloro-4-dimethylamino benzaldehyde)-l- (p-phenyl carboxylic acid)-3-methyl pyrazolone-5 0.28 Gelatin (10% solution) 92.46 "Daxad"-ll 0.01 The procedure was repeated at various coating weights and as described in Table 1.

The above-described film units were given an 8 mcs exposure and was processed through mechanical lab rollers at a 3.0 mil gap disposing one of the processing compositions set forth below between the top coat and a gelatin coated cover sheet. The film units were held in the dark for 1 minute and the neutral column was read to white, red, green and blue light in an automatically recording densitometer.

Processing Composition A Wt. % Water 79.02 Sodium hydroxide 6.97 Hydroxyethyl cellulose 2.70 Sodium sulfite 2.44 2-methylthiomethyl-4.6-dihydroxypyrimidine 4.06 Tetramethyl reductic acid 3.26 Processing Composition A -- Continued Wt % 1,1 2-dodecamethylene-bis-(pyridinium) bromide 1.70 4-amino-pyrazalo[3,4-d]-pyrimidine 0.015 5-bromo-6-methyl azabenzimidazole 0.015 Thiazolidine thione 0.034 Processing Composition B Wt. % Water 75.89 Sodium hydroxide 0.87 Potassium hydroxide 8.61 Hydroxyethyl cellulose 0.95 Tetramethyl reductic acid 3.86 Potassium sulfite 3.79 2-methylthiomethyl-4,6-dihydroxypyrimidine 5.75 1,12-dodecamethylene-bis-(pyridinium) bromide 0.82 4-amino-pyrazolo-[3,4-d]-pyrimidine 0.061 In Table 1 are shown the intended coverage, Dmax, Dmin and the slope as defined on page 266 of Photography by C.B. Neblette, 6th Edition, published by Yon Nostrand.

TABLE 1

Aim Coverage mgs/ft Dmax Hydroxyethyl Dmin Experiment No. Pd Cellulose Gelatin Sn White Light Red Green Blue (White Light) Slope 1 0.25 1.02 - 0.75 2.74 2.74 2.75 2.74 0.13 3.4 2 0.25 0.72 - 0.75 2.42 2.34 2.55 2.60 0.38 1.7 3 0.25 - 1.02 0.75 2.26 2.16 2.56 2.70 0.21 2.5 4 0.25 0.51 - 0.75 1.45 1.36 1.52 1.49 0.21 5 0.25 0.36 - 0.46 2.17 2.16 2.23 2.14 0.60 1.3 Experiments 1 and 3 employed Top Coat A and Processing Composition B.

Experiments 2 and 5 employed Top Coat B and Processing CompositionA.

Experiment 4 employed Top Coat B and Processing Composition B.

The nuclei solution in Experiments 4 and 5 were deaerated before coating.

Preparation 2.

The following solutions were prepared: Solution A 0.5 g. SnCl,.2H2O 100 g. 1.0 acetic acid Water to make 100.5 g. total Solution B 10 g. 1% gelatin solution Solution C 0.286 g. PdCl2 100 g. 2.0% acetic acid Dissolution carried out with stirring at about 40"C.

The nuclei were formed by bringing 145 g. of water to the boil in a flask with a magnetic stirrer. 20 g. of Solution A was added and, after one-half minute, 5 g. of Solution B. The mixture was allowed to come to a boil again and stirred vigorously while 20 g. of Solution C was added. After stirring for another one-half minute, the mixture was cooled to room temperature within five minutes. Sufficient water was then added to make up a total of 190 g. As a coating aid, 20 mls. of 0.1% alkyl phenoxypolyoxy-ethylene ethanol surfactant (sold under the trade name PE120 by NOPCO Chem. Div. of Diamond Shamrock Company) was added.

In an alternative procedure rhe nuclei are formed at room temperature. To differentiate the variations in the procedures the nuclei formed at elevated temperature will be designated "HOT" and the nuclei formed at room temperature designated "Room Temperature".

Example 2.

Film units were prepared according to the procedure of Example I except that the gel layer between the receiving layer and the emulsion layer was replaced with a copper-chitin layer prepared as follows: To a solution comprising: 3300 g. distilled water 3.316 g. copper acetate 0.914 g. sodium acetate was added a solution comprising: 279.413 g. distilled water 9.065 g. acetic acid 11.522 g. deacetylated chitin The thus-formed solution was coated to provide a layer of 7 mgs/ft2.

The above-described copper-chitin layer is described in U.S. Patent Specification No. 4056392.

Film units within the scope of the present invention were prepared using the methods of preparation 2 and Example 2 and processed according to the procedure of Example 1 with the ratios of components, top coats and processing compositions set out below, including in Table 2, and the results are shown in Table 2.

Processing Composition C Wt. % Water 66.2 Sodium hydroxide 7.1 Hydroxyethyl cellulose 0.9 Tetramethyl reductic acid 11.1 Sodium sulfite 0.8 Sodium thiosulfate 12.4 N-benzyl-a-picolinium bromide 1.4 (50% solution) Processing Composition D Wt. % Water 70.6 Sodium hydroxide 7.5 Hydroxyethyl cellulose 0.9 Tetramethyl reductic acid 11.7 Sodium sulfite 2.2 Sodium thiosulfate 5.3 N-benzyl-picolinium bromide 1.7 (50% solution) 4-amino-pyrazolo-[3,4-d]-pyrimidine 0.02 Bromomethyl azcbenzimidazoie 0.03 Processing Composition E Wt % Water 70.4 Sodium hydroxide 7.3 Hydroxyethyl cellulose 0.6 Tetramethyl reductic acid 7.5 Potassium sulfite 3.6 2-methylthiomethyl-4,6-dihydroxy-pyrimidine 7.5 N-benzyl-α-picolinium bromide 3.0 (50 io solution) Top Coat C Wt. % Gelatin 0.03 Benzimidazole thiol gold complex 0.41 Distilled water 44.84 Pyridinium bis-1,5(1 ,3-diethyl-2-thiol-5- barbituric acid) pentamethine oxanol 4-(2-chloro-4-dimethylamino benzaldehyde)-l (p-phenyl carboxylic acid)-3-methyl pyrazolone-5 0.16 Gelatin (10% solution) 54.41 Daxad-l 1 0.01 Top Coat D Wt. % Gelatin 0.03 Benzimidazole thiol gold complex 0.41 Distilled water 45.35 Pyridinium bis- 1,5(1 ,3-diethyl-2-thiol-5- barbituric acid) pentamethine oxanol 0.13 4-(2-chloro-4-dimethylamino benzaldehyde)-l (p-phenyl carboxylic acid)-3-methyl pyrazolone-5 0.16 Gelatin (10% solution) 53.92 Daxad-l 1 0.01 Top Coat E Wt. % Gelatin 0.03 B enzimidazole thiol gold complex 0.02 Distilled water 27.45 Pyridinium bis- 1,5(1 ,3-diethyl-2-thiol-5- barbituric acid) pentamethine oxanol 0.13 4-(2-chloro-4-dimethylamino benzaldehyde)-1- (p-phenyl carboxylic acid)-3-methyl pyrazolone-5 0.16 Gelatin (10% solution) 72.02 Daxad-l 1 0.01 TABLE 2

Aim Coverage (mgs/ft3 Dmax Experiment No. Pd Gelatin Red Green Blue Dmin (white light) 6 0.20 0.10 2.68 2.7 2.68 0.34 7 0.20 0.20 2.80 '.88 '.83 0.32 8 0.20 0.40 2.60 '.80 2.76 0.36 9 0.20 0.10 2.82 2.83 2.80 0.36 10 0.20 0.20 2.80 2.74 2.71 0.33 11 0.20 0.40 2.80 2.90 2.84 0.30 The nuclei of Experiments 6. 7 and 8 were prepared by the "HOT" method of Preparation 2.

The nuclei of Experiments 9, 10 and 11 were prepared by the "Room Temperature" method of Preparation 2. The film units of Experiments 6-11 employed Processing Composition C and Top Coat C.

The following table shows the photographic results obtained with nuclei prepared according to Preparation 2 and incorporated with film units prepared and processed according to the procedure of Example 2 with varying levels of noble metal nuclei.

TABLE 3

Aim Coverage mgs/ft2 Dmax/Dmin Example Pd Gelatin Red Green Blue 3 0.2 0.2 3.20/0.41 3.10/0.42 2.93/0.46 4 0.07 0.07 3.11/0.41 3.09/0.39 2.94/0.41 In Examples 3 and 4 Processing Composition D and Top Coat D were employed.

Example 5.

Nuclei was prepared according to the procedure of Preparation 2 and incorporated into a film unit according to the procedure of Example 2, except that a copper-gelatin layer was substituted for the copper-chitin layer with the same quantity of materials employed. At a 0.2 mgs/ft2 palladium coverage and a 1:1 gelatin-palladium ratio and the following transmission densities were obtained on the film units.

Red Green Blue Dmax 2.95 2.75 2.65 Dmin 0.42 0.36 0.44 Processing Composition D and Top Coat D were employed.

Example 6.

Nuclei were prepared according to the procedure of Preparation 2 except that potassium palladous tetra chloride was substituted for palladium chloride. The nuclei were incorporated into a film unit according to the procedure of Example 2.

At a 0.2 mgs/ft2 palladium coverage and a 1:1 gelatin/palladium ratio the following transmission densities were obtained.

Red Green Blue Dmax 3.33 3.15 3.00 Dmin 0.43 0.39 0.42 Processing Composition D and Top Coat D were employed.

Preparation 3.

The procedure of Preparation 2 was modified by the substitution of 0.235 g. of sodium hypophosphite in 100 g. of water for the stannous chloride reducing agent.

Preparation 4.

The procedure of Preparation 2 was modified by the substitution of 0.084 g. of sodium borohydride in 100 g. of water for the stannous chloride reducing agent.

Example 7.

Nuclei prepared using the reducing agents of Preparation 3 and 4 were incorporated in film units described in Example 2 and processed with the following results obtained: TABLE 4

Aim Coverage mgs/ft2 Dmax Nuclei of Preparation Pd Gelatin Red Green Blue Green Dmin 3 0.0 0.20 3.37 3.06 2.79 0.38 4 0.20 0.20 3.28 3.12 2.78 0.33 Processing Compositions E and Top Coat E were employed.

As stated above, the preferred polymer employed in the receiving layers of the present invention comprises gelatin. Gelatin at the low end of the nuclei-binder ratio can be employed to provide good density, neutral tone positive images in the receiving layer whereas the preferred levels of other polymers, such as hydroxyethyl cellulose are at the higher portions of the nuclei-binder range.

In an alternative embodiment, the colloid formed by the reduction of the noble metal salt or complex is dialyzed before coating. The effect of the dialysis is to provide enhanced stability to the coating composition. While not intending to be bound by theory, it is believed that this enhanced stability is a result of the pH being raised and/or the removal of certain ions, such as H+, K+ and Cl-.

In still a further embodiment, the pH of the above-mentioned colloid is changed from acid to alkaline resulting in the precipitation of the noble metal, which can then be separated, washed and redispersed in a polymer and coated. Any unwanted by-products or starting materials are thereby removed.

The particle size of the silver precipitating nuclei of the present invention may vary over a relatively wide range. In a preferred embodiment, the nuclei range from about 15A" to about 65An. For example, nuclei prepared according to the procedure of Preparation 1, on a 1000 particle count, have a mean diameter of about 20A" with 80% of the particles having a diameter between 17A" and 40An.

Nuclei prepared according to Preparation 2 on a 1000 particle count, have a mean diameter of about 31A" with 80or/ of the particles having a diameter between 19A" and 46An.

The support employed in the present invention is not critical. The support of film base employed may comprise any of the various types of transparent rigid or flexible supports, for example, glass, polymeric films of both the synthetic type and those derived from naturally occurring products. Especially suitable materials, However, comprise flexible transparent synthetic polymers such as polymethacrylic acid, methyl and ethyl esters; vinyl chloride polymers; polyvinyl acetals; polyamides such as nylon; polyesters such as the polymeric films derived from ethylene glycol terephthalic acid; polymer cellulose derivatives such as cellulose acetate, triacetate, nitrate, propionate, butyrate, acetate-butyrate; or acetate propionate; polycarbonates; and polystyrenes.

The additive color screen employed in the present invention may be formed by techniques well known in the art, e.g., by sequentially printing the requisite filter patterns by photomechanical methods. An additive color screen comprises an array of sets of colored areas or filter elements, usually from two to four different colors, each of said sets of colored areas being capable of transmitting visible light within a predetermined wavelength range. In the most common situations the additive color sc

Claims (14)

WHAT WE CLAIM IS:

1. An image receiving element suitable for use in an additive colour photographic diffusion transfer process which comprises a transparent support carrying an additive colour screen and a layer comprising noble metal silver precipitating nuclei and a polymer, and in which the said nuclei are present at 0.07 to 0.3 mgs/ft2; and the said polymer is present at 0.5 to 5 times the coverage of the nuclei.

2. An element according to claim 1 in which the nuclei have been obtained by the reduction of a noble metal salt or complex.

3. An element according to claim 2 in which the reduction was effected by a first metal capable of two valences.

4. An element according to any preceding claim in which the polymer is gelatin.

5. An element according to any of claims 1 to 3 in which the polymer is hydroxyethyl cellulose.

6. An element according to any preceding claim in which the polymer is present at substantially the same level as that of the nuclei.

7. An element according to any preceding claim in which the nuclei are present at about 0.2 mgs/ft2.

8. An element according to any preceding claim in which the noble metal is palladium.

9. An element according to claim 3 in which the said first metal is tin.

10. An element according to claim 9 in which the noble metal salt is palladous chloride and the first metal is provided by stannous chloride.

11. An element according to claim 1 in which the said layer comprises palladium metal silver precipitating nuclei and gelatin, and the said nuclei are present at 0.2 mgs/ft2 and the gelatin is present at 0.2 mgs/ft2; and the palladium nuclei have been formed by the reduction of palladous chloride with stannous chloride.

12. An element according to any preceding claim comprising the support, the screen, the layer comprising the nuclei, a photosensitive emulsion layer and an antihalation layer.

13. An element according to claim 1 substantially as herein described with reference to any one of the Examples.

14. A method of preparing an image-receiving element according to claim 1 which comprises the steps of reducing a noble metal salt or complex in a solution of a polymer; and coating the noble metal and polymer on a transparent support carrying an additive colour screen; wherein the noble metal is present at 0.07 to 0.3 mgs/ft2 and the polymer is present at 0.5 to 5 times the coverage of said noble metal.