Image-receiving layer for the dye diffusion transfer process

The invention relates to an image-receiving layer for the color diffusion transfer process which contains a polymer containing cationic groups and a further polymer which contains no cationic groups and is derived from N-vinyl-imidazole or 2-methyl-1-vinyl-imidazole.

As is known, in the color diffusion transfer method, which is particularly important for color immediate image photography, a light-sensitive recording material with several silver halide emulsion layers of different spectral sensitivity and color compounds assigned to them are used. So-called dye developers, for example, are suitable as coloring compounds, which are originally diffusible compounds with a chromophoric residue and a developer function, by means of which the compounds are immobilized during development, or non-diffusing coloring compounds with a chromophoric residue, which is released in image development as a diffusible dye or dye precursor (color releaser).

In order to fix the image dyes formed from the color-providing compounds, which are generally present in anionic form, in the image-receiving layer, this contains cationic compounds as mordants. Polymeric ammonium or phosphonium compounds are mostly used for this. Polymers with a wide variety of cationic structural units, for example, are known for this purpose those which contain the cationic groups in the form of side chains on a polymer backbone, such as those described in US Pat. No. 3,709,690, or those which contain the cationic groups in a polymer chain itself, for example polymers which pass through Quaternization of basic polyurethanes, polyureas or polyurea polyurethanes are derived (DE-A-26 31 521). However, the known cationic mordant polymers are not yet satisfactory in terms of the lightfastness of the anionic image dyes stained on them.

It has been found that the lightfastness of the image dyes pickled on cationic polymers can be considerably improved if the cationic polymer used is one which has been obtained by homopolymerization or copolymerization of ethylenically unsaturated monomeric compounds, and if this cationic polymer has no cationic groups containing homo- or copolymer of N-vinylimidazole or 2-methyl-1-vinylimidazole.

The invention relates to an image-receiving layer for the color diffusion transfer process with a cationic group-containing polymer obtained by homo- or copolymerization of ethylenically unsaturated monomers as a mordant for diffusible anionic dyes, characterized in that it contains a mixture of 5 to 70% by weight of the mordant polymer containing cationic groups and 30 to 95% by weight of a second polymer, which contains no cationic groups and has been obtained by homopolymerization or random copolymerization from N-vinylimidazole or 2-methyl-1-vinylimidazole and, if appropriate, further copolymerizable monomers.

The image-receiving layer according to the invention thus contains a mixture of two mordants, one of which is a polymer containing a conventional cationic group and the other which contains no cationic groups can be represented by the following general formula I:<chemistry id="chem0001" num="0001"><img file="EP0143389A2_D0001.tif" /></chemistry>in what mean<chemistry id="chem0002" num="0002"><img file="EP0143389A2_D0002.tif" /></chemistry><ul id="ul0001" list-style="none"><li>M polymerized units of a monomer copolymerizable with vinylimidazole but which does not contain any cationic groups; and</li><li>x and y are the numerical values ​​characterizing the proportion of the individual comonomers in the polymer, in such a way that</li><li>x for 80 to 100%, and</li><li>y stands for 0 to 20%.</li></ul>

Examples of the comonomers represented by M are approximately (meth) acrylamides such as acrylamide, N, N-dimethylacrylamide; (Meth) acrylates such as ethyl acrylate, methyl methacrylate, chloroethyl methacrylate, hydroxyethyl acrylate, butyl acrylate; vinyl aromatic compounds such as styrene, vinyl toluene; N-vinyl pyrrolidone, vinyl acetate, N-methyl-N-vinyl-acetamide. Instead of a single comonomer copolymerizable with vinylimidazole, the copolymer can also contain two or more such comonomers copolymerizable with vinylimidazole in polymerized form, all of which are represented by M in this case. M can also comprise polymerized units of comonomers which do not exist in the form of ethylenically unsaturated compounds but can be obtained by polymer-analogous reactions, for example vinyl alcohol or vinylamine.

The polyvinylimidazoles used according to the invention can be prepared by customary polymerization processes, for example by emulsion polymerization, solution polymerization or precipitation polymerization of N-vinylimidazole or 2-methyl-1-vinylimidazole, optionally with one or more mono-ethylenically unsaturated comonomers M copolymerizable with vinylimidazole M, in the case of emulsion polymerization, expediently in the presence of an anionic surface-active compound, for example sodium lauryl sulfate or in the presence of the sodium salt of a sulfonated condensate of an alkylphenol-ethylene oxide condensate (for example Alipal, manufacturer General Dyestuff Corp., USA) and expediently in the presence of a radical generator or radical initiator, for example in the presence of a Free radical initiator of the redox type, for example in the presence of potassium persulfate sodium bisulfite; Potassium persulfate Fe; H₂O₂-Fe²⁺. For example, methods such as those described in US-A-3,072,588 can be used.

The use of polyvinylimidazole in image-receiving elements is already known, for example from US Pat. No. 4,282,305, but only in connection with a layer which contains a compound which provides metal ions. Such image-receiving elements are suitable for use in connection with light-sensitive elements which release diffusible chelatable dyes as image dyes. By complexing with the metal ions, the image dyes in the image receiving element are fixed in the form of light-stable dye-metal complexes. The polyvinylimidazole is mainly used to prevent the diffusion of metal ions into the photosensitive element, but in the absence of the metal ions provides only slightly light-stable dye images.

As already mentioned, the polymer containing cationic groups is one which has been obtained by homopolymerization or copolymerization of ethylenically unsaturated monomeric compounds. The cationic groups are preferably quaternary groups of the following formula II<chemistry id="chem0003" num="0003"><img file="EP0143389A2_D0003.tif" /></chemistry>in which mean:<ul id="ul0002" list-style="none"><li>Q is a nitrogen or phosphorus atom;</li><li>R², R, R are each an alkyl radical or a carbocyclic radical, where _R², _R³ and _R⁴ may have the same or different meaning, or two of the said radicals together complete a 5- or 6-membered heterocyclic ring; and</li><li>X^θ an anion.</li></ul>

Alkyl residues by Formula II _R², _R³ and _R⁴_thererg_e- are straight-chain or branched and usually have 1 to 12 carbon atoms. Examples include methyl, ethyl, propyl, isobutyl, pentyl, hexyl, heptyl, dodecyl.

Have in Formula II R², _R³ and or _R⁴ the meaning of carbocyclic radicals, these are optionally substituted cycloalkyl, aralkyl or aryl radicals with preferably 5 to 12 carbon atoms, for example cyclopentyl, cyclohexyl, benzyl, p-methylbenzyl, chlorobenzyl, nitrobenzyl, cyanobenzyl, methoxybenzyl, methoxycarbonylbenzyl, ethylthiobenzyl , Phenyl, tolyl.

Examples of 5- or 6-membered heterocyclic through two of the radicals _R², _R³ and _R⁴ Completed rings include the pyrrolidine, piperidine and morpholine rings.

The polymer containing cationic groups can be obtained by one of the customary addition polymerization techniques, for example by emulsion polymerization, from addition-polymerizable monomers which already contain a quaternary ammonium group or are easily quaternizable, optionally in a mixture with further addition-polymerizable monomers. The quaternization or introduction of quaternary groups can also be carried out after the polymerization, for example by treating tertiary amino groups contained in the polymer with an alkylating quaternizing agent or, for example, by reacting groups contained in the polymer with active halogen atoms with tertiary amines or phosphines.

Suitable cationic polymers are described, for example, in US Pat. No. 3,709,690.

In the image-receiving layer according to the invention, the quantitative ratio between the cationic polymer and the non-cationic polymeric vinylimidazole can vary within the specified limits; excellent results with regard to the lightfastness of the pickled dyes are obtained with higher proportions of polymeric vinylimidazole. The image-receiving layer preferably contains a mixture of 50 to 90% by weight of polyvinylimidazole and 10 to 50% by weight of cationic polymer.

The mixture of non-cationic polymeric vinylimidazole and cationic polymer can be cast as such or optionally with a binder additive to the image-receiving layer.

In addition to gelatin, other hydrophilic film-forming polymers of natural or synthetic origin are also suitable as binders, for example:<ul id="ul0003" list-style="none"><li>Gum arabic, albumin, casein, dextrin, starch ether or cellulose ether, polyvinyl alcohol, succinoylated polyvinyl alcohol, partially phthaloylated polyvinyl alcohol, polyacrylamide, copolymers of acrylic acid, vinyl pyrrolidone, hydroxyethyl acrylamide, vinyl pyridine, maleic acid or maleic anhydride with acrylamide.</li></ul>

The most common known additives can also be incorporated into the image-receiving layer, for example UV absorbers, for example substituted 2-hydroxyphenylbenzotriazoles (Tinuvin) and hydroxybenzophenones, and antioxidants, for example tert. Butylated hydroxyanisole, butylated hydroxytoluene, substituted chromanols. Insofar as such additives are substances which are soluble in organic solvents, they are advantageously used in the form of an emulsifier in an aqueous medium. Furthermore, in the sense of an improvement in dye determination, it can be beneficial if the image-receiving layer contains certain heavy metal ions, in particular Zn^2+-Contains ions.

The mordants used according to the invention can be used to produce a wide variety of photographic materials which have a mordant layer with the aid of which acidic dyes are to be stained.

According to the present invention, the polymers mentioned are mainly used as mordants for diffusible image dyes, ie they form an essential component of image-receiving layers for the color diffusion transfer process. Such image-receiving layers are usually arranged on a transparent or non-transparent layer support and together form the image-receiving element with the latter. This is either not photosensitive as a separate image-receiving sheet or it can form an integral part of a light-sensitive material when the image-receiving layer is in firm contact with the photosensitive silver halide emulsion layer (s).

Suitable supports are, for example, paper, optionally coated with a plastic, glass, metal foils or films made from organic film formers such as cellulose esters, polyethylene terephthalate, polycarbonate or other polymers. By storing opacifying agents such as pigments, opaque carrier layers can also be produced from the materials mentioned last.

In its simplest form, the image-receiving layer according to the invention is arranged on a layer support and, together with it, forms the image-receiving element in the form of an image-receiving sheet. In order to improve the adhesion of the image-receiving layer to the layer support, the latter can be provided with a conventional adhesive layer. In principle, such an image-receiving sheet is suitable for any type of photographic color diffusion transfer process in which acidic diffusible image dyes or also acidic diffusible color formers (image dye precursors) are used or released imagewise and can be transferred to an image-receiving layer. After the transfer has taken place, such a material accordingly has an image-wise distribution of one or more acid dyes in the image-receiving layer.

According to an advantageous embodiment of the invention, in addition to an image-receiving layer with the polymer mixture according to the invention, a photographic material has at least one layer with an acidic dye or a precursor compound for an acidic dye, and at least one light-sensitive layer, in particular a light-sensitive silver halide emulsion layer. The acid dyes mentioned or Precursors for acidic dyes are collectively referred to below as coloring compounds. In addition to the image-receiving layer according to the invention, a photographic recording material can advantageously also contain a plurality of light-sensitive silver halide emulsion layers of different spectral sensitivity as well as further non-light-sensitive layers such as intermediate layers, cover layers and other layers of the most varied functions, as are customary in multi-layer color photographic recording materials for the color diffusion transfer process.

The photographic materials according to the invention, ie an image-receiving sheet with the image-receiving layer according to the invention and in particular color photographic recording materials which contain an image-receiving layer according to the invention as an integral part, can also contain acidic layers and so-called braking or deceleration layers which together form a so-called neutralization system. Such a neutralization system can be arranged in a known manner between the layer support and the image-receiving layer arranged thereon or at another point in the layer structure, for example above the light-sensitive layers, ie viewed beyond the light-sensitive layers from the image-receiving layer. The neutralization system is usually oriented so that the braking or retarding layer is between the acid layer and the location where the alkaline developing liquid or paste is exposed.

The color-imparting compounds assigned to the light-sensitive layers can be colored compounds which are themselves diffusible and which begin to diffuse when the layers are treated with an alkaline processing liquid and are only determined by the development at the exposed areas. However, the coloring compounds can also be diffusion-resistant and release a diffusible dye in the course of development (color releasing agent).

Suitable paint releasing agents are described, for example, in:<ul id="ul0004" list-style="none"><li>US-A-3,227,550, US-A-3,443,939, US-A-3,443,940,</li><li>DE-A- 19 30 215, DE-A- 22 42 762, DE-A- 24 02 900,</li><li>DE-A- 24 06 664, DE-A- 25 05 248, DE-A- 25 43 902,</li><li>DE-A- 26 13 005, DE-A- 26 45 656, DE-A- 28 09 716,</li><li>BE-A-861 241, EP-A- 0 004 399, DE-A- 30 08 588,</li><li>DE-A-30 14 669.</li></ul>

The diffusible dyes released from the dye releasers can belong to the most diverse classes of dyes, for example azo dyes, azomethine dyes, anthraquinone dyes, phthalocyanine dyes, indigoid dyes and triphenylmethane dyes. In connection with the image receiving layer of the present invention, however, those dyes are preferably used which do not form stable dye-metal complexes with metal ions in the image receiving layer.

example 1

Pickling layers of the compositions given below were applied to a paper base coated with polyethylene. The order per m² was 4 g of gelatin and a total of 2 g of pickling polymer (sum of polymer containing cationic groups and polyvinylimidazole). The pickling layers were hardened with 2% 1,3,5-trisacryloylhexahydro-1,3,5-triazine.

The dyes GB 1, PP 1 and BG 1 were bathed in the resulting pickling layers at pH 13.5 until a density of approximately 1.5 was reached. After soaking for 2 minutes, the layers were dried, half covered and irradiated with UV light (4.8.10⁶ lx.h).

The percentage decrease in color density in the irradiated areas was then determined by measuring the color density in the irradiated and non-irradiated areas.<tables id="tabl0001" num="0001"><img file="EP0143389A2_D0004.tif" /></tables>The lightfastness of the pickled dyes is increased by adding polyvinylimidazole.

Example 2

Pickling layers were produced as in Example 1, but using Polymer III and 3.4 g of gelatin per m². The pickling layers were colored with the dyes PP2 and BG2. Otherwise the procedure was as in Example 1.

Polymer III: poly-N, N, N-trimethyl-N-methacryloyloxy-ethyl-ammonium-methyl sulfate according to DE-A-1 000 688.

<tables id="tabl0002" num="0002"><img file="EP0143389A2_D0005.tif" /></tables>

Example 3

A photographic recording material A (not according to the invention) was produced by successively applying the following layers on a transparent layer support made from polyethylene terephthalate. The quantities given relate to 1 m².