PHOTOGRAPHIC ELEMENTS WITH STERICALLY HINDERED PHOTOGRAPHIC COUPLER SOLVENTS

Abstract: Photographic coupler solvents comprising aromatic carboxylic esters such as phthalates and isophthalates having bulky or branched ester substituents are described for incorporation in photographic emulsions and elements. The solvents are preferably employed in the cyan layer to protect the cyan dye against ferrous ion reduction. The solvents also provide improvements in yellow dye stability to light, cyan dye stability in the dark and magenta dye stability to heat and light.

Description: This invention relates to silver halide photographic elements employing certain coupler solvents. In a particular aspect, it relates to coupler solvents comprising aromatic carboxylic esters, and particularly phthalates and iso­ phthalates, having bulky or branched ester substituents. Images are commonly obtained in the photographic art by a coupling reaction between the development product of a silver halide color developing agent (i.e., oxidized aromatic primary amino developing agent) and a color forming compound commonly referred to as a coupler. The dyes produced by coupling are indoaniline, azomethine, indamine or indophenol dyes, depending upon the chemical composition of the coupler and the developing agent. The subtractive process of color formation is ordinarily employed in multicolor photographic elements and the resulting image dyes are usually cyan, magenta and yellow dyes which are formed in or adjacent to silver halide layers sensitive to radiation complementary to the radiation absorbed by the image dye; i.e. silver halide emulsions sensitive to red, green and blue radiation. When intended for incorporation in photogra­ phic elements, couplers are commonly dispersed therein with the aid of a high boiling organic solvent, referred to as a coupler solvent. Couplers are rendered nondiffusible in photographic elements, and compatible with coupler solvents, by including in the coupler molecule a group referred to as a ballast group. This group normally is located on the coupler in a position other than the coupling position and imparts to the coupler sufficient bulk to render the coupler nondiffusible in the element as coated and during processing. It will be appreciated that the size and the nature of the ballast group will depend upon the bulk of the unballasted coupler and the presence of other substituents on the coupler. During photofinishing, developing agent sometimes gets carried over and mixed into the bleach solution which results in reduction of ferric ion complexes in the bleach solution to ferrous ion complexes. These ferrous ions then have a tendency to reduce the cyan dye and convert it to a leuco form, causing a loss in dye density. Any alleviation of this problem would be most desirable. These are prior art references which disclose closely related compounds to those of the invention. Research Disclosure , 16744, March 1978, page 13, discloses di- t -butyl phthalate and di-isopropyl phthalate. U.S. Patent 4,407,940 disclosed di- t -octyl phthalate. British Patent 1,274,523 and U.S. Patent 3,779,765 disclose di(2-­ ethylhexyl)phthalate. U.S. Patent 3,475,172 des­ cribes high-boiling solvent esters derived from phthalic, isophthalic or terephthalic acids and alkyl-substitutes cyclohexanols, while those shown in U.S. Patent 3,779,765 are derived from benzenetri­ carboxylic acids and certain branched-alkyl alco­ hols. Japanese Patent Application 59/149348 cites a number of branched and straight-chain alkyl phthalate ester said to be useful for dispersing certain hydroquinone derivatives. U.S. Patents 4,193,802 and 4,327,175 disclose high-boiling solvents in which an aromatic ring is substituted by up to six ester groups comprising cyclic saturated hydrocarbon residues. However, there is a problem with the above compounds since they are not as effective as Applicant's compounds in lessening the ferrous ion reduction of cyan dye problem, as will be shown by comparative tests hereinafter. It is an object of this invention to provide a new class of coupler solvents useful in color photographic materials, particularly those having cyan couplers. It is another object to provide such solvents which markedly reduce the tendency of ferrous ions to reduce cyan dye. Another object of the invention is to provide such coupler solvents which would provide improvement in yellow dye stability to light, cyan dye stability in the dark and magenta dye stability to heat and light. These and other objects are achieved in accordance with the invention which comprises a photographic element comprising a support having thereon at least one silver halide emulsion layer having associated therewith a dye-forming coupler and a coupler solvent therefor having the formula: wherein each X may independently represent a halogen atom, an alkyl group of from 1 to 20 carbon atoms, an alkoxy group of from 1 to 20 carbon atoms, or a carboxylic ester group; m represents an integer of 0 to 5; n represents an integer of 1 to 4; and R₁, R₂, and R₃ each independently represents a substituted or unsubstituted alkyl group having from 1 to 10 carbon atoms such as methyl, trifluoromethyl, ethyl, isopropyl, isohexyl, sec-butyl, sec-heptyl or dodecyl; a substituted or unsubstituted alicyclic group, saturated or partially saturated, having from 3 to 12 carbon atoms such as cyclopropyl, cyclobutyl, cyclohexyl, 4-methyl-cyclohexylene, 4-methyl-­ cyclohexyl, cycloheptyl or decahydro-2-naphthyl; a substituted or unsubstituted aralkyl group having from 7 to 20 carbon atoms such as benzyl, 4-methoxybenzyl or 1-naphthylmethyl; a substituted or unsubstituted aryl group having from 6 to 20 carbon atoms such as phenyl. 4-methoxyphenyl, 2,4-dichlorophenyl or naphthyl; a substituted or unsubstituted heterocyclyl group having from 3 to 10 carbon atoms such as furyl, thienyl, pyridyl, N-methylpyrrolyl, tetrahydrofurfuryl or N-ethyl indolyl; or may be combined together to form one or more rings having from 4 to 10 non-metallic ring atoms such as 3-acetoxy-2,2,4,4-cyclobutyl, 1-methylcyclopentyl, 1-butylcyclohexyl, 1-ethyltetralyl, 2-pinanyl, fenchyl or 3-methyl menthyl; with the proviso that the alpha hydrogens of R₁, R₂ and R₃ total no more than seven; and with the further proviso that R₁ can addition­ ally be hydrogen when a) R₂ and R₃ join together to form a ring substituted by no more than one alpha hydrogen or b) when R₂ and R₃ do not join to form a ring and if at least one of R₂ or R₃ contains an alpha carbon having two different non-hydrogen substituents. In a preferred embodiment of the invention, m in the above formula is 0, n is 2 and the ester groups are located ortho or para to each other as follows: wherein R₁, R₂ and R₃ are defined as above. In another preferred embodiment of the invention, the dye-forming coupler forms a cyan dye upon reaction with oxidized color developing agent, the coupler being a phenol or a naphthol, and the coupler and coupler solvent are located in the silver halide emulsion layer. In still another preferred embodiment of the invention, R₁ is hydrogen or an alkyl group of from 1 to 10 carbon atoms, R₂ is an alkyl group of from 1 to 10 carbon atoms, R₃ is an alkyl or substituted alkyl group of from 2 to 12 carbon atoms, an alicyclic group of from 3 to 12 carbon atoms, a heterocyclyl group of 3 to 10 carbon atoms or an aryl or substituted aryl group of 6 to 20 carbon atoms, or R₂ and R₃ are combined together to form a ring of about 4 to 10 atoms. In yet another preferred embodiment of the invention, R₁ and R₂ are the same or different alkyl or substituted alkyl groups containing from 1 to 10 carbon atoms and R₃ is an alkyl group containing from 2 to 12 carbon atoms. In still yet another preferred embodiment of the invention, R₁ is an alkyl group of from 1 to 10 carbon atoms and R₂ and R₃ are combined together to form a ring of 6 carbon atoms. In another preferred embodiment of the invention, R₁, R₂ and R₃ are each ethyl. In another preferred embodiment of the invention, R₁ is hydrogen or methyl, R₂ is methyl, and R₃ is In another preferred embodiment of the inven­ tion, R₁ and R₂ are each methyl and R₃ is In another preferred embodiment of the inven­ tion, R₁ is ethyl, R₂ is methyl and R₃ is In another preferred embodiment of the invention, R₁ is hydrogen or butyl and R₂-C-R₃ forms the fenchyl group In another preferred embodiment of the inven­ tion, R₁ is methyl and R₂ and R₃ form a cyclohexyl ring. In another preferred embodiment of the inven­ tion R₁ is methyl and R₂-C-R₃ form the menthyl group In another preferred embodiment of the inven­ tion, R₁ is hydrogen, R₂ is methyl and R₃ is phenyl. Preferred compounds included within the scope of the invention include the following: As previously noted in the proviso following the general structural formula for compounds of the invention, the alpha hydrogens of R₁, R₂ and R₃ must total no more than seven. In the following structures representing the alkyl portion of phthalate ester examples, each alpha carbon is designated with an arrow. It can be seen that the hydrogen substituents on these carbons total six and seven, respectively, for Compounds 1 and 3 of this invention but more than seven for comparison solvent CS-5, employed in the examples hereinafter. A similar illustration can be made for the other proviso following the general formula that R₁ can additionally be hydrogen when: a) R₂ and R₃ join together to form a ring substituted by no more than one alpha hydrogen or b) R₂ and R₃ do not join to form a ring and if at least one of R₂ or R₃ contains an alpha carbon having two different non-hydrogen sub­ stituents. In the following structures, R₁ is hydro­ gen (designated *H) and the alpha carbons are marked with arrows. It can be seen for ring compounds that Com­ pound 10 of the invention contains no alpha hydrogen substituents, while two prior art solvents (designated as Compounds 8 and 9, respectively, in U.S. Patent 4,193,802), contains more than one alpha hydrogen. Compound 10 (no H) Prior Art Compound (2H) Prior Art Compound CS-15 (3H) For branched chain structures of Compounds 2 and 13 of the invention, the alpha carbon of R₃, marked by the horizontal arrow, has two different alkyl substituents while a prior art compound (desig­ nated HBS-5 in Japanese Patent Application 59/149,348) is outside the invention because the two non-hydrogen alpha substituents in R₃ are identical. The above compounds may be synthesized by combining bulky and branched alkanols or cycloalkanols with the appropriate aromatic carboxylic acid deriva­ tives, such as derivatives of benzoic, phthalic, iso­ phthalic, terephthalic, benzenetricarboxylic, or benzenetetracarboxylic acids. The coupler solvents of this invention can be used in the ways and for the purposes that coupler solvents are used in the photographic art. They may be used in any concentration which is effective for the intended purpose. Generally, good results can be obtained using concentrations ranging from 0.1 to 1.0 g/m², preferably from 0.2 to 0.4 g/m². Typically, the coupler solvent and coupler are incorporated in a silver halide emulsion and the emulsion coated on a support to form a photographic element. Alternatively, the coupler solvent and coupler can be incorporated in photographic elements adjacent to the silver halide emulsion where, during development, the coupler will be in reactive associa­ tion with development products such as oxidized color developing agent. Thus, as used herein, the term "associated therewith" signifies that the coupler solvent and coupler are in the silver halide emulsion layer or in an adjacent location where, during proces­ sing, they will come into reactive association with silver halide development products. Photographic elements of the invention can be single color elements or multicolor elements. Multi­ color elements contain dye image-forming units sensi­ tive to each of the three primary regions of the visi­ ble spectrum. Each unit can be comprised of a single emulsion layer or of multiple emulsion layers sensi­ tive to a given region of the spectrum. The following examples are included for a further understanding of this invention. Example 1 - Preparation of Bis(1,1-diethylpropyl) Phthalate (Compound 1) To a solution of 23.2 g (0.2 mol) 3-ethyl-­ 3-pentanol in 50 mL tetrahydrofuran, stirred at 0°C under nitrogen, was added dropwise 92 mL of a 2.4M n -butyllithium solution in hexane. Stirring was continued 30 min. as the mixture warmed to room temperature. Then, a solution of 20.3 g (0.1 mol) phthaloyl chloride in 10 mL tetrahydrofuran was added to form lithium chloride as a white precipitate. After addition of 40 mL water, the product was isolated as a viscous liquid to give 32.3 g (89% yield) of Compound 1, confirmed by an nmr spectrum. The same procedure, but replacing the 3-ethyl-3-pentanol with 31 g (0.2 mol) α-terpineol, provided 35 g (79.5% yield) of a very viscous light yellow liquid shown by nmr to be Compound 4. Example 2 - Preparation of Bis(2-n-butylfenchyl) Phthalate (Compound 7) To a solution of 30.5 g (0.2 mol) 1-fenchone in 50 mL tetrahydrofuran, stirred at 0°C under nitrogen, was added dropwise 95 mL of a 2.2M n -butyl-­ lithium solution in hexane. Stirring was continued overnight as the mixture warmed to room temperature. Then a solution of 22.3 g (0.11 mol) phthaloyl chloride in 15 mL tetrahydrofuran was slowly added to form lithium chloride as a white precipitate. Addition of 20 mL water, isolation of product and purification by silica gel chromatography gave, as a first fraction, 2.3 g crystalline Compound 7, m.p. 153-6°C, confirmed by an nmr spectrum. Example 3 - Preparation of Bis(1-ethyl-1,5-dimethyl-­ hexyl) Phthalate (Compound 6) by Hydrogenation of Dilinalyl Phthalate A solution of 10 g (22.8 mmol) dilinalyl phthalate (prepared by the procedure of Example 1) in 100 mL tetrahydrofuran was treated with 2 g palladium on charcoal catalyst and hydrogenated quickly at 40 psi. A small amount of cleavage gave some phthalic acid byproduct, so the mixture was chromatographed on silica gel to give 7.1 g (70% yield) of pure viscous liquid Compound 6, confirmed by its nmr spectrum. Example 4 - Ferrous Ion Stability Tests Photographic elements were prepared by coating a gel-subbed, polyethylene-coated paper support with a photosensitive layer containing a silver bromoiodide emulsion at 0.28 g Ag/m², gelatin at 1.62 g/m², and dispersions containing each of the coupler/solvent combinations described in Table 1. Coupler solvents of the invention were employed along with various comparison solvents (CS) as controls. The cyan coupler coverage was 1.26 milli-­ moles/m² and the weight of coupler solvent was half that of the coupler. The photosensitive layer was overcoated with a layer containing gelatin at 1.08 g/m² and bis­ vinylsulfonylmethyl ether hardener at 2 weight percent based on total gelatin. Cyan Couplers Employed Comparison Coupler Solvents Samples of each element were imagewise exposed through a graduated-density test object, processed at 33°C employing the color developer identified below, then 1.5 minutes in the bleach-fix bath, washed and dried. Color Developer (pH 10.08) Triethanolamine 11 mL Benzyl alcohol 14.2 mL Lithium chloride 2.1 g Potassium bromide 0.6 g Hydroxylamine sulfate 3.2 g Potassium sulfite (45% solution) 2.8 mL 1-Hydroxyethylene-1,1-di­ phosphoric acid (60%) 0.8 mL 4-Amino-3-methyl-N-ethyl-N-β-­ methanesulfonamido)ethyl-­ aniline sulfate hydrate 4.35 g Potassium carbonate (anhydrous) 28 g Stilbene whitening agent 0.6 g Surfactant 1 mL Water to make 1.0 liter Bleach-Fix Bath (pH 6.8) Ammonium thiosulfate 104 g Sodium hydrogen sulfite 13 g Ferric ammonium ethylene-­ diamine tetraacetic acid (EDTA) 65.6 g EDTA 6.56 g Ammonium hydroxide (28%) 27.9 mL Water to make 1 liter Density measurements were then made on a densitometer. Processed strips of each element containing a dye image were then subjected to a 5 minute immersion in the following: 0.1M Ferrous Ion Solution (made under nitrogen purging) Degassed distilled water 750 mL EDTA 32.12 g Ammonium hydroxide (conc. 15 mL solution) Ferrous sulfate·7 H₂O 27.8 g Ammonium hydroxide and water to: 1.0 L (Nitric acid to adjust pH pH 5.0 downward) Density measurements on a densitometer were again made and a density loss was observed for each of the elements as follows: In every case, the coupler solvents of the invention were much more effective in preventing ferrous ion reduction of cyan dye than closely-related comparison coupler solvents. Example 5 - Yellow Dye Light Stability Improvement Photographic elements were prepared and processed as in Example 4 except that the coatings contained 0.40 g Ag/m², 1.09 millimole/m² of a yellow dye-forming coupler, and one-fourth the coupler weight of the coupler solvents listed in Table 2. Densitometric curves were obtained before and after fading for step-wedge exposed strips and density losses were measured. Both shoulder (step 7) and Dmax (step 2) densities of each curve were compared. Fading was accomplished using either a 50 Klux or 5.4 Klux xenon source, the ultraviolet component of which was removed using a Wratten 2B filter. The following results were obtained: The data show that a yellow dye formed from an incorporated coupler dispersed in the coupler solvents of the invention had markedly improved light stability over the same dye formed in the presence of the comparison coupler solvents. Example 6 - Cyan Dye Dark Stability Improvement Photographic elements were prepared and processed as in Example 4. Then, strips containing step images of cyan dyes formed from dispersions of coupler/solvent combinations as indicated in Table 3 were subjected to accelerated tests conducted for the indicated times in dark ovens at either 60°C/70% R.H. or 77°C/5% R.H. Density losses were measured after the keeping tests. The following results were obtained: The data show that a coupler solvent of the invention provided improved cyan dye dark stability in color photographic coatings. Example 7 - Magenta Dye Stability Improvement Photographic elements were prepared and processed as in Example 4, except that the silver bromoiodide emulsion was coated at 0.51 g Ag/m² with 0.66 millimoles/m² of a magenta coupler dispersed in half its weight of coupler solvent as indicated in Table 4 plus 0.39 g/m² chromanol stabilizer (Com­ pound 7 of U.S. Patent 3,432,300). Density changes were measured after light and dark fading tests similar to those described in Examples 5 and 6. The following results were obtained: The data show that a coupler solvent of the invention gave improvements over comparison coupler solvents for magenta dye stability to heat and light while maintaining at least comparable stability to humidity.

Claims: 1. A photographic element comprising a support having thereon at least one silver halide emulsion layer having associated therewith a dye-form­ ing coupler and a coupler solvent therefor, characterized in that said coupler solvent has the formula: wherein each X may independently represent a halogen atom, an alkyl group of from 1 to 20 carbon atoms, an alkoxy group of from 1 to 20 carbon atoms, or a carboxylic ester group; m represents an integer of 0 to 5; n represents an integer of 1 to 4; and R₁, R₂, and R₃ each independently represents a substituted or unsubstituted alkyl group; a substituted or unsubstituted alicyclic group, saturated or partially saturated; a substituted or unsubstituted aralkyl group; a substituted or unsub­ stituted aryl group; a substituted or unsubstituted heterocyclyl group; or may be combined together to form one or more rings; with the proviso that the alpha hydrogens of R₁, R₂, and R₃ total no more than seven; and with the further proviso that R₁ can addition­ ally be hydrogen when a) R₂ and R₃ join together to form a ring substituted by no more than one alpha hydrogen or b) R₂ and R₃ do not join to form a ring and if at least one of R₂ or R₃ contains an alpha carbon having two different non-hydrogen substi­ tuents. 2. The element of Claim 1 characterized in that said coupler solvent has the formula: wherein R₁, R₂ and R₃ are defined as in Claim 1. 3. The element of Claim 1 characterized in that said dye-forming coupler forms a cyan dye upon reaction with oxidized color developing agent. 4. The element of Claim 3 characterized in that said cyan dye-forming coupler is a phenol or a naphthol and said coupler and said coupler solvent are located in said silver halide emulsion layer. 5. The element of Claim 2 characterized in that R₁ is hydrogen or an alkyl group of from 1 to 10 carbon atoms, R₂ is an alkyl group of from 1 to 10 carbon atoms, R₃ is an alkyl or substituted alkyl group of from 2 to 12 carbon atoms or an aryl or substituted aryl group of 6 to 20 carbon atoms, or R₂ and R₃ are combined together to form a ring of 4 to 10 atoms. 6. The element of Claim 2 characterized in that R₁ and R₂ are the same or different alkyl or substituted alkyl groups containing from 1 to 10 carbon atoms and R₃ is an alkyl group containing from 2 to 12 carbon atoms. 7. The element of Claim 2 characterized in that R₁ is an alkyl group of from 1 to 10 carbon atoms and R₂ and R₃ are combined together to form a ring of 6 carbon atoms. 8. The element of Claim 2 characterized in that R₁, R₂ and R₃ are each ethyl. 9. The element of Claim 2 characterized in that R₁ is hydrogen or methyl, R₂ is methyl, and R₃ is 10. The element of Claim 2 characterized in that R₁ and 11. The element of Claim 2 characterized in that R₁ is 12. The element of Claim 2 characterized in that R₁ is hydrogen or butyl and R₂-C-R₃ forms the fenchyl group 13. The element of Claim 2 characterized in that R₁ is methyl and R₂ and R₃ form a cyclohexyl ring. 14. The element of Claim 2 characterized in that R₁ is methyl and R₂-C-R₃ form the menthyl group 15. The element of Claim 2 characterized in that R₁ is hydrogen, R₂ is methyl and R₃ is phenyl.

Inventors: KRISHNAMURTHY, SUNDARAM
Applicants: EASTMAN KODAK COMPANY (A NEW JERSEY CORPORATION)
Application year: 1986
Main classification: G03C7
IPC codes: G03C7, G03C1