THE STABILIZATION OF DYE IMAGES PRODUCED IN PHOTOGRAPHIC MATERIALS

Abstract: A photographic material comprising a support having thereon at least one silver halide emulsion layer having associated therewith a yellow or cyan dye-forming coupler and a dye stabilizer comprising a phosphate ester compound having the formula: (ArO)₂ - O - X - O - (OAr)₂ wherein each Ar independently represents a substituted or substituted or unsubstituted aryl group, and X is a linking group.

Description: The invention relates to the stabilization of dye images in photographic materials. More particularly, it relates to the use of certain phosphate ester compounds as stabilizers for improving the stability of dye images obtained by colour developing coupler-incorporated photographic silver halide materials. A common form of colour photographic material comprises red-, green- and blue-sensitive silver halide emulsion layers in or adjacent to which are incorporated cyan-, magenta- and yellow-dye forming couplers, respectively. On development of such a material with a developer containing p -phenylenediamine colour developing agent, the oxidation product produced on reduction of the silver halide by the developing agent reacts with the appropriate coupler to give image dye. The dye image obtained by colour development can deteriorate as a result of the action of light, heat and/or humidity and various measures are known for reducing such deterioration. U.S. Patent No. 4,326,022 describes the use of high boiling organophosphorus coupler solvents which are said to improve the resistance of developed dye images to such deterioration. While dye stabilization can be achieved in this way, it is desirable to be able to improve dye stability without putting any restriction on the coupler solvent employed. The present invention provides phosphate ester compounds which can be incorporated in a colour photographic material to improve yellow and cyan dye stability independently of the coupler solvent used. The compounds confer improved stability on image dyes without causing adverse effects such as fogging, deterioration in colour hue and poor dispersion or crystal formation. The compounds used in the present invention are either viscous, colourless liquids which may be employed as or as part of the coupler solvent or crystalline, colourless solids which are employed as addenda. An advantage of the solids is that they may be readily obtained in pure form. An additional advantage of the phosphate ester compounds is that they can be prepared easily and at low cost. A satisfactory level of dye stability in a photographic material may require, singly or in combination, the use of an excess of coupler above the level necessary for image formation and the use of a low level of coupler solvent. Such undesirable measures may be overcome by using a stabilizer compound employed in the present invention which permits the use of less coupler and an increase in the ratio of coupler solvent to coupler. According to the present invention there is provided a photographic material comprising a support bearing at least one developable silver halide emulsion layer and, incorporated in that layer or a water-permeable layer adjacent thereto, a yellow or cyan dye-forming coupler, said material also containing, incorporated in the coupler-containing layer or a water-permeable layer adjacent thereto, as a dye stabilizer, a phosphate ester compound having the formula wherein each Ar independently is substituted or unsubstituted aryl; and, X is a linking group. Examples of suitable aryl groups include phenyl and naphthyl groups. Preferred substituted aryl groups include 4-substituted phenyl groups e.g. 4-alkyl substituted phenyl. The linking group X may contain from 2 to 40 carbon atoms. In one preferred embodiment, X is the residue of a polyhydroxy compound. Optionally, the linking group bears one or more diaryl phosphate groups in addition to those shown in the general formula. Preferred linking groups include alkylene (e.g. methylene, hexamethylene), alkylidene, arylene, alkylenebisarylene, alkylidenebisarylene, sulphonylbisarylene and cycloalkylenebisalkylene, said groups being optionally substituted. With reference to the general formula, specific examples of compounds suitable for use in the present invention are as follows: In the formulae above, i-Pr represents isopropyl and Ph represents phenyl. The phosphate ester compounds are readily prepared by reacting an appropriate diaryl chlorophosphate with an appropriate polyhydroxy compound. Many suitable starting materials are commercially available. For example, the preparation of compound I-3 may be represented as follows: The phosphate ester compounds are used in an amount sufficient to stabilize the photographic image dyes and their precursors e.g. in an amount from 0.1 to 2.0 moles per mole coupler, more preferably from 0.5 to 1.0 mole per mole coupler. Because the compound is used as a dye stabilizer, it is incorporated in the coupler-containing layer or a layer adjacent thereto. It can be incorporated as a separate dispersion, but is preferably incorporated in admixture with the coupler. Both coupler and stabilizer may be dissolved in a conventional coupler solvent, such as dibutyl phthalate. As in the production of ordinary coupler dispersions, a volatile and/or water-miscible auxiliary solvent, such as ethyl acetate, may be used to aid the dispersion process and then removed by evaporation or by washing the set dispersion. Also, the dispersion process can be assisted by the presence of a surface active compound, as usual in the manufacture of coupler dispersions. In the following discussion of suitable materials for use in the emulsions and elements of this invention, reference will be made to Research Disclosure, December 1978, Item 17643, published by Industrial Opportunities Ltd., The Old Marbourmaster's, 8 North Street, Emsworth, Mants P010 7DD, U.K. This publication will be identified hereafter as "Research Disclosure". References giving information on couplers and on methods for their dispersions are given in Sections VII and XIV, respectively, of Research Disclosure. The couplers commonly employed in photographic materials are water-insoluble compounds often containing ballast groups, phenolic (including naphtholic) couplers being used for producing cyan dyes and compounds containing an activated methylene group, including both heterocyclic and open-chain compounds, being used for producing yellow and magenta dyes. Important yellow couplers are benzoylacetanilides and important magenta couplers are pyrazolones. Patents describing couplers include the following United States Patents: An account of dye-forming development is given in ′Modern Photographic Processing′, Vol. 2, Grant Haist, Wiley, New York, 1978, Chapter 9. The stabilizers are useful in any coupler-incorporated silver halide photographic materials, including monochrome materials, false-colour materials and colour transparency, negative and print materials, to stabilize the image dye obtained on development with a solution including a p -phenylenediamine colour developing agent. Such developing agents are well-known, being described in,for example Photographic Processing Chemistry, L.F.A. Mason, Focal Press, London, 2nd edition (1975) pp 229-235 and Modern Photographic Processing, , Grant Haist, Wiley, New York (1979), Volume 2 pp 463-8. The silver halide emulsion employed in the elements of this invention can be either negative-working or positive-working. Suitable emulsions and their preparation are described in Research Disclosure Sections I and II and the publications cited therein. Suitable vehicles for the emulsion layers and other layers of elements of this invention are described in Research Disclosure Section IX and the publications cited therein. The photographicelements of this invention or individual layers thereof, can contain brighteners (see Research Disclosure Section V), antifoggants and stabilizers (see Research Disclosure Section VI), antistain agents and image dye stabilizer (see Research Disclosure Section VII, paragraphs I and J),light absorbing and scattering materials (see research Disclosure Section VIII), hardeners (see Research Disclosure Section XI), plasticizers and lubricants (see Research Disclosure Section XII), antistatic agents (see Research Disclosure Section XIII), matting agents (see Research Disclosure Section XVI) and development modifiers (see Research Disclosure Section XXI). The photographicelements can be coated on a variety of supports as described in Research Disclosure Section XVII and the references described therein. Photographicelements can be exposed to actinic radiation, typically in the visible region of the spectrum, to form a latent image as described in Research Disclosure Section XVIII and then processed to form a visible dye image as described in Research Disclosure Section XIX. Processing to form a visible dye image includes the step of contacting the element with a colour developing agent to reduce developable silver halide and oxidize the colour developing agent. Oxidized colour developing agent in turn reacts with the coupler to yield a dye. With negative working silver halide emulsions this processing step leads to a negative image. To obtain a positive (or reversal) image, this step can be preceded by development with a non-chromogenic developing agent to develop exposed silver halide, but not form dye, and then uniform fogging of the element to render unexposed silver halide developable. Alternatively, a direct positive emulsion can be employed to obtain a positive image. Development is followed by the conventional steps of bleaching, fixing, or bleach-fixing, to remove silver and silver halide, washing and drying. Examples of the preparation of a stabilizer compound used in the present invention are as follows: Preparation of 4,4′-Isopropylidenebisphenylbis[bis(4-3 methylphenyl)phosphate] Bis(4-methylphenyl)phosphorochloridate (29.7 g, 0.1 mole) was added dropwise to a solution of 4,4′-isopropylidenebisphenol (11.4 g, 0.05 mole) in pyridine (200 ml) with stirring at room temperature. The mixture was stirred for 3 hours as pyridinium hydrochloride was precipitated. The reaction mixture was poured into ice/water (1.5ℓ) and neutralized with concentrated hydrochloric acid. The mixture was extracted into ethyl acetate, dried (MgSO₄) and evaporated to dryness under vacuum. The resulting viscous oil was dissolved in dichloromethane and filtered through a bed of silica. Evaporation of the solvent under vacuum afforded the product as a viscous, colourless oil (86% yield). C₄₃H₄₂O₈P₂ requires: C,69.0; H,5.7; P,8.3. found: C,69.4; H,5.4; P,7.5% The structure and purity of the compound were further confirmed by mass spectrum, n.m.r., high performance liquid chromatography (h.p.l.c.) and thin layer chromatography (t.l.c.). Preparation of Hexamethylenebis[bis(4-isopropylphenyl)-phosphate] Bis(4-isopropylphenyl)phosphorochloridate (70.6 g, 0.2 mole) was added dropwise with stirring to a solution of hexane-1,6-diol (11.8 g, 0.1 mole) in dry pyridine (350 ml). The mixture was stirred for 5 hours then poured into ice/water (2ℓ) and neutralized with concentrated hydrochloric acid. The aqueous layer was decanted from the viscous product which was then dissolved in dichloromethane, dried (MgSO₄) and filtered through a bed of silica. Evaporation of the solvent under vacuum afforded the product as a viscous, colourless oil (78% yield). C₄₂H₅₆O₈P₂ requires: C,67.2; H,7.5; P,8.3 found: C,66.8; H,7.3; P,8.0% The structure and purity of the compound were further confirmed by mass spectrum, n.m.r., h.p.l.c. and t.l.c Preparation of Tetramethylenebis(diphenylphosphate) Diphenylphosphorochloridate (53.6 g, 0.2 mole) was added dropwise to a stirred solution of 1,4-butanediol (9.0 g, 0.1 mole) in dry pyridine (400 ml). After 3 hours stirring the mixture was poured into ice/water (2ℓ) and neutralized with concentrated hydrochloric acid. The solid product was filtered off, dried under vacuum and recrystallized from ethyl acetate to give a colourless, pure solid, m.p. 105°C (80% yield). C₂₈H₂₈O₈P₂ requires: C,60.7; H,5.1; P,11.2 found: C,60.7; H,5.1; P,10.9% The structure and purity of the compound were further confirmed by mass spectrum, n.m.r., h.p.l.c. and t.l.c. The invention is further illustrated in the following Examples. Examples 1 to 7 A number of phosphate ester compounds were tested as addenda in a photosensitive layer containing a yellow dye-forming coupler. Strips were prepared by coating corona treated polyethylene coated paper supports with a photosensitive layer containing a silver bromoiodide emulsion at 0.38 g silver m⁻², gelatin at 1.36 g m⁻² and dispersions of Coupler I in dibutyl phthalate as the coupler solvent (1.5 moles per mole of coupler) and the phosphate ester (0.5 mole per mole of coupler). The coupler coverage was 0.83 millimole m⁻². The photosensitive layer was overcoated with a layer containing gelatin at 3.0 g m⁻² and bisvinylsulphonylmethyl ether hardener at 1.0 weight percent based on total gelatin. Samples were exposed through a graduated-density test object and developed with 4-amino-3-methyl-N-ethyl-N-β-(methanesulphonamido)ethylaniline in a standard Ektaprint-2 process (see British Journal of Photography Annual 1986, pages 37 and 38). The samples so obtained were faded for six weeks using a 5.4 Klux xenon source, the ultraviolet component of which was removed using a coating of Tinuvin 328 (Ciba-Geigy) in a gelatin dispersion at a coverage of 750 mg m⁻². Fade was monitored by status A reflection densitometry measurements. The results are given in Table 1 below. The results show that the presence of the stabilizer compounds considerably improved the stability of the yellow image dye. Examples 8 to 11 A number of phosphate ester compounds were tested as coupler solvents. Strips were prepared and tested as in the Examples above except that the phosphate ester being tested replaced the dibutyl phthalate and the weight of the phosphate ester used was 0.46 that of the coupler. A control strip was prepared and tested in which dibutyl phthalate was the coupler solvent. The results are given in Table 2 below. The phosphate ester compounds markedly improved the dye stability. Examples 12 to 15 Strips were prepared in accordance with Examples 8 to 11 except that the photosensitive layer was coated on polyethylene terephthalate supports instead of paper. The strips were exposed, developed and faded in accordance with Examples 8 to 11 except that the fade time was 360 hours. Fade was assessed by U.V./visible spectrophotometry using the loss in absorption density at the wavelength of maximum absorption as a measure of the fade. The results are given in Table 3 below. The stabilizer compounds are shown to improve the stability of the dye image. Example 16 Compound I-9 was tested as an addendum in a photosensitive layer containing a cyan dye-forming coupler. A monochrome control strip was prepared by coating a corona treated polyethylene coated paper support with a photosensitive layer containing a silver bromoiodide emulsion at 0.27 g Ag m⁻², gelatin at 1.52 g m⁻² and Coupler II at 0.66 g m⁻² dispersed in dibutyl phthalate coupler solvent at 0.33 g m⁻². The photosensitive layer was overcoated with a layer containing gelatin at 3.0 g m⁻² and bisvinylsulphonylmethyl ether hardener at 1.5 weight percent based on total gelatin. A second coating was prepared as above except that an amount of the test compound I-9 equimolar to the coupler was also incorporated into the coupler dispersion. Samples were exposed through a graduated density test object and processed through a standard Ektaprint-2 process. Separate samples of both the processed coatings were incubated for 3 weeks in a wet oven (60°C, 70% relative humidity) and a dry oven (75°C). The following table clearly shows improvements in the stability of the cyan image dye when the stabilizer is incorporated:

Claims: 1. A photographic material comprising a support bearing at least one developable silver halide emulsion layer and, incorporated in that layer or a water-permeable layer adjacent thereto, a yellow or cyan dye-forming coupler, said material also containing, incorporated in the coupler-containing layer or a water-permeable layer adjacent thereto, a dye stabilizer, in a amount sufficient to stabilize the dye characterised in that the dye stabilizer is a phosphate ester compound having the formula wherein each Ar independently is substituted or unsubstituted aryl; and, X is a linking group. 2. A material according to claim 1, wherein Ar is phenyl or naphthyl. 3. A material according to claim 1 or claim 2, wherein the linking group X contains from 2 to 40 carbon atoms. 4. A material according to any one of the preceding claims, wherein the linking group X is the residue of a polyhydroxy compound. 5. A material according to any one of the preceding claims, wherein the linking group X is a substituted or unsubstituted alkylene, alkylidene, arylene, alkylenebisarylene, alkylidenebisarylene, sulphonylbisarylene or cycloalkylenebisalkylene group. 6. A material according to any one of the preceding claims, wherein the phosphate ester compound is present in an amount from 0.1 to 2.0 moles per mole coupler. 7. A material according to any one of the preceding claims, wherein the phosphate ester compound is a liquid which is present as or as part of a coupler solvent. 8. A material according to any one of claims 1 to 6, wherein the phosphate ester compound is a solid which is dissolved in a coupler solvent. 9. A material according to claim 7 or claim 8, wherein the coupler solvent comprises dibutyl phthalate.

Inventors: GODDARD, JOHN DEMITA
Applicants: EASTMAN KODAK COMPANY, KODAK LIMITED
Application year: 1988
Main classification: G03C7
IPC codes: G03C7, C07F9