DE69504224T2 - Surfactants and hydrophilic colloidal compositions and materials containing them - Google Patents

Description

Field of the invention

The invention relates to surfactants and their use as dispersing aids in the preparation of hydrophilic colloid compositions having hydrophobic particles dispersed therein. Such compositions can be used for the preparation of multilayer photographic materials.

Background of the invention

A wide variety of surfactants have been described for use in the manufacture of photographic materials.

JP56-19042 describes various diester sulfoitaconates as dispersing aids for photographic additives. The two hydrophobic groups connected by ester groups have a number of substituted or unsubstituted alkyl or aryl groups.

US-A-3,948,663 describes photographic materials containing certain sulfosuccinate-based surfactants and relates to their possible use as dispersing aids and coating aids. A specific example of such a surfactant is sodium dioctyl sulfosuccinate, which is commercially available as Aerosol® OT.

WO93/03420 describes a process for preparing finely divided photographic coupler dispersions which comprises preparing a dispersion of photographic coupler, coupler solvent and auxiliary coupler solvent in an aqueous gelatin medium containing at least about 1% by weight of an anionic surfactant having a hydrophobicity of 2 to 10 log P(OH), and washing the dispersion with water for a period of time sufficient to remove at least to remove at least one quarter of the surfactant. Anionic surfactants of various structures can be used and among many surfactants mentioned is diphenylbutyl sodium sulfosuccinate.

A disadvantage of using surfactants described in JP56-19042 and US-A-3,948,663 is the very low surface tension values that the compounds exhibit at concentrations above their critical micelle concentration (CMC). In simultaneous multilayer coating of hydrophilic colloid layers, it is essential that the surface tension of the top layer is lower than that of the underlying layers if spreading is to be maintained during the coating operation. If one of the underlying layers has a lower surface tension than the top layer, the top layer will be pulled in from the edges to the center of the coating. This is often referred to as "edge retraction." The greater the surface tension imbalance, the more disruptive the effect. Larger differences can cause retraction of the entire coating pack and general layer inversions. The surface tension of layers underlying the top layer in the multilayer coating of photographic materials is often dominated by the surface active dispersing aid used to stabilize the emulsified hydrophobic particles therein, for example, color couplers and their associated solvents.

When such prior art surfactants are used as dispersing aids for emulsified materials introduced into hydrophilic colloid layers underlying the top layer during simultaneous multilayer coating, there is a constraint on the selection of the surfactant or the concentration of the surfactant which is appropriate for the overlying layers. required, ie the coating margin is relatively narrow.

A further disadvantage of using the surfactants described in JP56-19042 and US-A-3 948 663 as dispersing aids for photographic couplers in hydrophilic colloid compositions is that the photographic properties of such compositions, for example the reactivity of the liquid dispersion, may be lower than desired.

A further disadvantage of using the surfactants described in JP56-19042 and US-A-3,948,663 as dispersing aids in photographic materials is that they can contribute to foaming during photographic processing, particularly in the case of spent developers containing surfactants that have leached out of the material and have built up in concentration.

The problem solved by the invention

The invention overcomes the problem of coating latitude associated with prior art dispersing aids.

Limitations in the photographic properties of dispersions of photographic couplers in hydrophilic colloids can be overcome.

The invention can reduce the foaming that can occur during the processing of photographic materials containing the dispersing aids of the prior art.

Summary of the invention

The invention relates to a process for producing a multilayer photographic material comprising

(a) simultaneously coating a support with a plurality of aqueous hydrophilic colloid layers, including at least one light-sensitive silver halide emulsion layer, wherein at least one of the covering or underlying hydrophilic colloid layers contains hydrophobic particles dispersed therein by means of a surfactant and

(b) drying of the applied layers,

characterized in that the surfactant has the structure

wherein

R is H or methyl, provided that when in each case n = 1, each R is methyl;

M is a cation; and

n is a number from 1 to 6.

Furthermore, the invention is directed to the use of a surfactant having the structure I in the process described above as an agent that improves the coating latitude.

According to another aspect, the invention relates to the use of a surfactant having the structure I in a multilayer photographic material comprising a support on which a plurality of hydrophilic colloid layers including at least one light-sensitive silver halide emulsion layer, at least one of the underlying hydrophilic colloid layers containing hydrophobic particles dispersed therein by means of the surfactant; to reduce foaming which may occur during photographic processing of the material.

The invention further relates to a process for preparing a composition comprising a hydrophilic colloid having hydrophobic particles dispersed therein, which comprises dispersing a hydrophobic material with a photographic coupler in an aqueous solution of a hydrophilic colloid in the presence of the surfactant, characterized in that the surfactant has the structure I and that the surfactant is used in an amount of less than 1% by weight, without a washing step to remove at least one quarter of the surfactant.

Advantageous effects of the invention

By providing aqueous hydrophilic colloid melts with high surface tension minima, the invention enables an increased coating latitude.

Improved photographic performance can be achieved with dispersions of a photographic coupler in a hydrophilic colloid. The nature of the improvement depends on the type of coupler dispersion. For example, in the case of a microprecipitated dispersion, the benefits include reduced droplet size, increased reactivity of the liquid dispersion, and increased Dmax in the coated product. In the case of a homogenized dispersion, the benefits include increased reactivity of the liquid dispersion and increased shoulder density and contrast in the coated product.

A further advantage is the reduced foaming during photographic development, especially in the case of a used developer.

Detailed description of the invention

In structure I, the cation M is a positively charged atom or a positively charged group of atoms, preferably selected from alkali metal cations, for example Na+, or ammonium.

Preferred compounds include those in which each n is 2 to 4 and each R is H. In the case of a particularly preferred compound, each n is 3 and each R is H.

The compounds can be water-soluble or water-dispersible.

The compounds can be prepared by esterifying maleic acid with a phenyl alcohol, wherein the alcohol has 3 to 8 carbon atoms. A specific procedure that can be used with respect to all of the compounds is given below in Example 1.

Compositions comprising a hydrophilic colloid having hydrophobic particles dispersed therein can be prepared by a process comprising dispersing a hydrophobic material in an aqueous solution of a hydrophilic colloid in the presence of the surfactant.

In the case of homogenized dispersions, the surfactant is preferably used in an amount of 0.4 to 1.2, more preferably in an amount of 0.6 to 0.9% by weight, based on the weight of the aqueous dispersion.

In the case of microprecipitated dispersions, the surfactant is preferably used in an amount such that the molar ratio of surfactant:hydrophobic material, for example photographic coupler, is 1:4 to 2:1.

Regardless of the particular method of preparation, dispersions can be prepared according to the invention which avoid the coating latitude problems associated with the prior art by using less than about 1% by weight of the surfactant, and without requiring a washing step to remove at least one-quarter of the surfactant, i.e., for example, no washing step is used.

The invention is particularly suitable for the preparation of photographic compositions and materials.

In the following discussion of suitable materials for use in the compositions and materials of this invention, reference is made to Research Disclosure, December 1989, No. 308119, published by Kenneth Mason Publications, Ltd., Dudley Annex, 12a North Street, Emsworth, Hampshire, P010 7DQ, UK. This reference is hereinafter referred to as Research Disclosure.

A number of hydrophobic photographic additives used in light-sensitive photographic materials are oil-soluble and are used by dissolving in a substantially water-insoluble, high boiling point solvent, which is then dispersed in an aqueous hydrophilic colloid solution with the aid of a dispersing aid. Such oil-soluble additives include image-forming color couplers, dye stabilizers, antioxidants and ultraviolet radiation absorbing agents. A typical solvent used to dissolve the additives is aromatic in nature, for example, di-n-butyl phthalate.

Gelatin is the preferred hydrophilic colloid, but other hydrophilic colloids can be used alone or in combination with gelatin.

Suitable methods for preparing photographic dispersions are described in Research Disclosure, Sections XIV A and XIV B. For example, homogenized oil in aqueous gelatin dispersions of photographic couplers can be prepared by dissolving the couplers in a coupler solvent and mechanically dispersing the resulting solution in an aqueous gelatin solution (see U.S. Patent 2,322,027).

Alternatively, microprecipitated dispersions of photographic couplers prepared by solvent and/or pH shift techniques are more widely used (see references: U.K. Patent 1,193,349; Research Disclosure 16468, December 1977, pages 75-80; U.S. Serial No. 288,922 (1988) to K. Chari; U.S. Patents 4,970,139 and 5,089,380 to P. Bagchi; U.S. Patent 5,008,179 to K. Chari, W.A. Bowman and B. Thomas; U.S. Patent 5,104,776 to P. Bagchi and S.J. Sargeant) and these techniques offer advantages in terms of reduced droplet size and often increased reactivity relative to conventional homogenized oil-in-water dispersions.

Multilayer photographic materials according to the invention have one or more overlying or underlying layers formed from such compositions.

Preferred multilayer photographic materials include color materials of the type described in Research Disclosure in Sections VII A through VII K.

Methods for producing multilayer photographic materials by simultaneous application of the layers are known. Special methods are described in Research Dis closure, Sections XV A and XV B. Such methods include extrusion coating and curtain coating. The hydrophobic material dispersed in the hydrophilic colloid may be a photographic coupler.

Couplers which form cyan dyes upon reaction with oxidized color developing agents are described in such representative patents and publications as U.S. Patents 2,772,162; 2,895,826; 3,002,836; 3,034,892; 2,747,293; 2,423,730; 2,367,531; 3,041,236 and 4,333,999; and in Research Disclosure, Section VII D.

Couplers which form magenta dyes upon reaction with oxidized color developing agents are described in such representative patents and publications as: U.S. Patents 2,600,788; 2,369,489; 2,343,703; 2,311,082; 3,152,896; 3,519,429; 3,062,653 and 2,908,573; and Research Disclosure, Section VII D.

Couplers which form yellow dyes upon reaction with oxidized color developing agents are described in such representative patents and publications as U.S. Patents 2,875,057; 2,407,210; 3,265,506; 2,298,443; 3,048,194; and 3,447,928; and in Research Disclosure, Section VII D.

Couplers which form colorless products upon reaction with oxidized color developing agents are described in such representative patents as U.K. Patent No. 861,138; U.S. Patent Nos. 3,632,345; 3,928,041; 3,958,993; and 3,961,959.

The couplers can be dissolved in a solvent and then dispersed in a hydrophilic colloid. Examples of solvents suitable for this process include Organic solvents having a high boiling point such as alkyl esters of phthalic acid (for example, dibutyl phthalate, dioctyl phthalate), phosphoric acid esters (for example, diphenyl phosphate, triphenyl phosphate, tricresyl phosphate, dioctyl butyl phosphate), citric acid esters (for example, tributyl acetyl citrate), benzoic acid esters (for example, octyl benzoate), alkylamides (for example, diethyl laurylamide), esters of fatty acids (for example, dibutoxyethyl succinate, dioctyl acelate), trimesic acid esters (for example, tributyl trimesate), and organic solvents having a boiling point of about 30º to about 150ºC such as short chain alkyl acetates (for example, ethyl acetate, butyl acetate), ethyl propionate, secondary butyl alcohol, methyl isobutyl ketone, b-ethoxyethyl acetate, methyl cellosolve acetate, mixtures of organic solvents having a high boiling point and organic solvents having a low boiling point can also be used.

As the binder or the protective colloid for the photographic emulsion layers or interlayers of the photographic light-sensitive material of the present invention, gelatin is preferably used, but other hydrophilic colloids may also be used alone or together with gelatin.

As gelatin, not only lime-digested gelatin but also acid-digested gelatin can be used in the present invention: The methods for producing gelatin are described in more detail in the book by Ather Veis, The Macromolecular Chemistry of Gelatin, Academic Press (1964).

As the above-described hydrophilic colloids other than gelatin, it is possible to use proteins such as gelatin derivatives, graft polymers of gelatin and other polymers, albumin, casein; saccharides such as cellulose derivatives such as hydroxyethyl cellulose, cellulose sulfate, sodium alginate, starch derivatives; as well as various synthetic hydrophilic high molecular weight substances, such as homopolymers or copolymers, for example polyvinyl alcohol, polyvinyl alcohol semiacetal, poly-N-vinylpyrrolidone, polyacrylic acid, polymethacrylic acid, polyacrylamide, polyvinylimidazole, polyvinylpyrazole.

In the photographic emulsion layers or other hydrophilic colloid layers of the photographic light-sensitive material of the present invention, various surface active compounds may be present as coating aids or for other various purposes, for example, for preventing charging, improving slip properties, accelerating emulsification and dispersion, preventing adhesion and improving photographic characteristics (for example, accelerating development, producing high contrast and sensitization).

Surface-active compounds which may be used are non-ionic surfactants, for example saponin (steroid-based), alkylene oxide derivatives (for example polyethylene glycol, a polyethylene glycol/polypropylene glycol condensate, polyethylene glycol alkyl ethers or polyethylene glycol alkylaryl ethers, polyethylene glycol esters, polyethylene glycol sorbitan esters, polyalkylene glycol alkylamines or polyalkylene glycol alkylamides and silicone/polyethylene oxide adducts and the like), glycidol derivatives (for example alkenyl succinic acid polyglyceride and alkylphenol polyglyceride), fatty acid esters of polyhydric alcohols and alkyl esters of sugar; anionic surfactants having an acidic group, for example a carboxy group, a sulfo group, a phosphorus group, a sulfuric acid ester group and a phosphoric acid ester group, for example alkylcarboxylic acid salts, alkylsulfonic acid salts, alkylbenzenesulfonic acid salts, alkylnaphthalenesulfonic acid salts, alkylsulfuric acid esters, alkylphosphoric acid esters, N-acyl-N-alkyltaurines, sulfosuccinic acid esters, sulfoalkylpolyoxyethylenealkylphe nyl ethers, as well as polyoxyethylene alkyl phosphoric acid esters; amphoteric surfactants, such as amino acids, aminoalkyl sulfonic acids, aminoalkyl sulfuric acid or aminoalkyl phosphoric acid esters, alkyl betaines and amine oxides; and cationic surfactants, such as alkylamine salts, aliphatic or aromatic quaternary ammonium salts, heterocyclic quaternary ammonium salts (for example pyridinium and imidazolium) and aliphatic or heterocyclic phosphonium or sulfonium salts.

In the photographic emulsion layer of the photographic light-sensitive material used in the present invention, any of silver bromide, silver iodobromide, silver iodochlorobromide, silver chlorobromide and silver chloride can be used as the silver halide.

The light-sensitive silver halide contained in the photographic material can be developed after exposure to form a visible image by bringing the silver halide into contact with an aqueous alkaline medium in the presence of a developing agent contained in the medium or material. Suitable types of photographic development are described in Research Disclosure, Sections XIX A to XIX J. Suitable developing agents are described in Research Disclosure, Sections XX A to XX B.

The following examples further illustrate the invention.

A number of compounds referred to in the examples have a structure as follows:

example 1 Synthesis of sodium di(4-phenylbut.-1-yl)sulfosuccinate

All sodium sulfosuccinate surfactants were prepared according to the general method described below: A solution of maleic anhydride (32.6 g, 0.33 mol), 4-phenyl-1-butanol (100.0 g, 0.66 mol), and concentrated sulfuric acid (1.5 cm³) were suspended in toluene (750 cm³) and heated to reflux temperature for 16 hours in a flask equipped with a Dean and Stark trap.

Upon cooling, the toluene solution was reduced to 1/4 volume under reduced pressure on a rotary evaporator, washed with saturated sodium hydrogen carbonate (2 x 200 cm3) and then with water (2 x 200 cm3). The organic layer was dried over magnesium sulfate and the solvent was removed under reduced pressure (15 mmHg, 50 °C) to give an intermediate diester as a clear precipitate (119.5 g, 95%).

A solution of sodium metabisulfite (65.7 g, 0.34 mol) in water (400 cm3) was added to a solution of this diester (119.5 g, 0.31 mol) in ethanol (400 cm3) and the mixture was brought to reflux for 15 minutes. Then, sodium sulfite (36.0 g, 0.28 mol) was added portionwise to the mixture over a period of 40 minutes and the reaction was then allowed to proceed overnight under reflux conditions. The reaction mixture was then evaporated to dryness (15 mmHg, 50 °C) and then extracted into ethyl acetate (1.5 L, hot) and filtered. The ethyl acetate solution was concentrated and allowed to cool to give the product as a white crystalline solid material (139.8 g, step yield 93%, overall yield 87%).

Spectroscopic data and 1 Hnmr data were consistent with the presumed product, sodium di(4-phenylbut.-1-yl)sulfosuccinate.

Example 2

Tables IA and IB compare the surface tension data of the compounds of the invention with commercial examples of dialkyl sulfosuccinate, Aerosol® MA (sodium dihexyl sulfosuccinate), Aerosol® OT (sodium diisooctyl sulfosuccinate) and Aerosol® AY (sodium dipentyl sulfosuccinate). The method used to measure surface tension was the following method.

The surface tension of an aqueous solution containing surfactant was measured over a range of concentrations including the critical micelle concentration using the Wilhelmy technique (Padday, JF, 2nd International Congress on Surface Activity, I, 1, 1957) with a platinum sheet. Dynamic surface tension comparison measurements were also made using the same technique using a circular overflow (ibid.). The mean surface age of the solutions in the overflowing weir was determined to be of the order of 0.1 seconds. TABLE IA: Surface tension (mN/m) of solutions in water at 25ºC TABLE IB: Surface tension (mN/m) of solutions in water at 25ºC (commercial literature)

Tables IA and IB clearly show that as the surfactant concentrations approach or go below their CMC value, where surface tension values tend to plateau, the compounds of this invention exhibit much higher surface tension values than the corresponding dialkyl equivalents. Equivalents mean compounds of similar CMC. When comparing equivalent compounds at such concentrations, the materials of this invention exhibit surface tension values that are 10-14 mN/m higher.

Tables IIA and IIB show similar data to Tables IA and IB, but the measurements were made in solutions containing 7% deionized bone gelatin Type IV in water at 40ºC to simulate a coating melt. TABLE IIA: Surface tension (mN/m) of solutions of 7% deionized bone gelatin Type IV in water at 40ºC (compounds of this invention)

In the following table, the comparison compounds sulfosuccinates with the formula TABLE IIB: Surface tension (mN/m) of solutions of 7% deionized bone gelatin type IV in water at 40ºC (reference compounds)

Tables IIA and IIB further clearly demonstrate that when the surfactant concentrations approach or exceed their CMC value in aqueous gelatin solution, the compounds of this invention still exhibit much higher surface tension values than the corresponding dialkyl equivalents. When comparing equivalent compounds at such concentrations, the materials of this invention again exhibit surface tension values that are 10-14 mN/m higher.

In general, therefore, the materials of this invention exhibit the advantage of relatively high surface tension minima coupled with reasonably low CMC values (up to 0.3 wt.% in 7% gelatin in water) in situations where low values are undesirable, for example in underlying layers during simultaneous multi-layer coating.

Example 3 Increased coating latitude using materials of the invention as dispersing aids in covered layers during simultaneous application of multiple layers:

To demonstrate that the compounds of this invention allow a wider coating latitude when used as disperse To test the use of surfactants in the underlying layers of a two-layer coating produced by simultaneous coating, the following format was produced by coating at 15 m/min at 40ºC with a range of different surfactants:

Lower class:

A dispersion of a color coupler was prepared according to the following recipes:

2 kg dispersion of coupler I:

258 g of coupler I was dissolved in a mixture of 65 g of di-n-butyl phthalate and 65 g of solvent III at 145°C to prepare solution A. 176 g of gelatin was dissolved in 1354 g of water containing 17.6 g of dispersing aid (the surfactant to be tested) and 31 g of propionic acid/sodium propionate preservative to prepare solution B. After heating solution B to 80°C, solution A was added to solution B and the whole mixture was immediately homogenized for 5 minutes at 10,000 rpm with a Kinematica Polytron homogenizer equipped with a 35 mm diameter head.

1.7 kg Dispersion of Coupler II:

149 g of coupler II was dissolved in a mixture of 58.5 g of di-n-butyl phthalate, 22.3 g of solvent III, 79.1 g of stabilizer IV and 14.9 g of scavenger V at 145°C to produce solution C. 149 g of gelatin was dissolved in 1180 g containing 16.4 g of dispersing aid (the surfactant to be tested) and 32.7 g of propionic acid/sodium propionate preservative to produce solution D. After heating solution D to 80°C, solution C was added to solution D and the whole mixture was immediately homogenized for 5 minutes at 10,000 rpm using a Kinematica Polytron homogenizer equipped with a head of 35 mm diameter. mm homogenized.

The coupler dispersion, containing approximately 9 wt% gelatin, was then diluted at 40°C with water containing a red dye marker to a gelatin content of 4 wt%. The resulting mixture was used for the bottom layer of a two-layer funnel coating as illustrated above.

Thus, a range of lower layer coating melts were prepared that differed in the dispersion component, the primary difference being the dispersing aid (surfactant) used. The primary objective was to compare four diarylalkyl sulfosuccinate dispersing aids according to this invention with two commercially available dialkyl sulfosuccinate dispersing aids and the commercially available surfactant Alkanol® XC (sodium triisopropyl naphthalene sulfonate). Two types of couplers, I and II, were used to prepare the coupler dispersions. It should be noted for each coupler used that the surfactant comparisons were between compounds of similar hydrophilic/lipophilic balance, i.e., of similar CMC values.

Upper layer:

Four different surfactants were selected for the top layer coating aid to obtain a range of characteristic values of minimum surface tension, 25.5-37.2 mN/m. A working concentration of 0.3% was selected to ensure that the surfactants were used well beyond their CMC values so that the surface tensions of the corresponding solutions under dynamic conditions were very similar to those under static conditions and, consequently, were essentially at a characteristic plateau value. The procedure used to determine a dynamic value of surface tension is described in Example 2. The materials selected are given in the following table along with representative surface tension data. TABLE III: Surface Tension Data

Triton® X100 is t-octylphenyl polyethylene oxide (9.5 moles).

Texofor® FN15 is nonylphenyl polyethylene oxide (15 moles).

SDS is sodium dodecyl sulfate.

A complete 4 x 7 matrix of two-layer coatings was prepared, with the four types of top layers applied to the seven types of bottom layers. The dried coatings were then to determine if the top coat was successfully applied over the underlying coat. The coating was considered successful (OK) if the blue top coat remained satisfactorily spread over the full width of the coating, and the coating was considered unsuccessful if the bottom coat caused the top coat to pull in from one of the edges or if multiple cratering occurred in the center of the coating as a result of the bottom coat being pressed through the surface. By using the red dye in the bottom coat and the blue dye in the top coat, it was clearly evident when the coating was unsuccessful. Table IV summarizes the coating results of representative strips: TABLE IV: Coating Results - Various Surfactants in the Top Coat Table IV (continued)

The above results from the two-layer coatings clearly demonstrate that a large increase in coating latitude occurs when the surfactants of this invention are used as dispersing aids for dispersions in the cover or bottom layers during multi-layer coating, relative to the comparative compounds. As explained above and illustrated here, this means that the use of the dispersing aids of this invention results in less constraints on the selection of a surfactant as the coating aid required in the top layer to achieve a good coating. Logically, there should also be less constraints on the concentration of the coating aid required to achieve a good coating. This aspect is illustrated in Table V where Aerosol® OT was used as the coating aid in the top layer within a range of concentrations using the same coating conditions as previously described. TABLE V. Coating results - different concentrations of coating aid AOT in the top layer

Example 4 Photographic advantages with microprecipitated dispersions Increased dispersion reactivity

Microprecipitated dispersions of photographic couplers, prepared by solvent and/or pH shift techniques are increasingly used and offer advantages of reduced droplet size and often increased reactivity compared to conventional oil-in-water homogenized dispersions. When microprecipitated dispersions are prepared using the compounds of this invention, these advantages are enhanced.

The microprecipitated dispersions were prepared using the following method:

The coupler (20 g) was dissolved in a mixture of propan-1-ol (40 g) and a 20% sodium hydroxide solution (5 g) at 60°C and poured into a solution of the surfactant (weight equimolar with the coupler) and polyvinylpyrrolidone (10 g) in water (600 g). The resulting micellar solution was reduced to pH 6.0 by the dropwise addition of 15% propanoic acid to produce the crude microprecipitated dispersion, which was then dialyzed through hollow fiber ultrafiltration cartridges of the Amicon type and concentrated to one fifth of its volume.

The measurements of the reactivity of the liquid dispersion were carried out using the following method. The particle size was measured by photon correlation spectroscopy.

The method used is similar to that described by Bagchi in U.S. Patents 4,970,139, 5,089,380 and 5,104,776. A sample of the dispersion was mixed with a developer solution containing sodium sulfite, CD-3 developer and EDTA. This mixture was mixed with an activator solution containing the oxidizing agent sodium persulfate and a buffer of sodium carbonate and sodium bicarbonate which brought the pH of the final solution to 10.1 (close to the pH of the developing solutions). The concentrations of oxidizing agent and coupler are much higher than those of the developer. The resulting effect is that that the oxidizing agent produces oxidized developer which then reacts with the coupler (or with the competing sulfite) to produce image dye and byproducts. The optical density of the dye was then read spectrophotometrically so that, in the case of a known dye extinction coefficient, the concentration of the dye could be deduced.

If the coupling reaction is considered to be a homogeneous, single-phase reaction, the kinetics of the coupling reaction can be calculated. It was assumed that the coupling reaction and the competitive reaction of the sulfite with oxidized developer are both second order reactions. Taking into account that coupler and oxidizer concentrations are greater than that of the developer, the following equation is obtained for the rate constant of the coupling reaction, k₁, which is used as a measure of the reactivity of the liquid dispersion:

k&sub1; = k2 1n[a/(a-x)]/ln[b/(b-c+x)]

where k2 is the sulfonation rate constant (previously calculated), where a is the coupler concentration, b is the sulfite concentration, c is the developer concentration, and x is the dye concentration. TABLE VI. Data from microprecipitated dispersions of coupler VI

The above results clearly demonstrate that the compounds of this invention:

(i) increase the reactivity of the liquid dispersion if the length of the hydrophobic chain increases. (Note: phenylpropyl is the minimum chain length to achieve increased reactivity, which illustrates why shorter chains, such as phenylethyl, are outside the invention);

(ii) increase the reactivity of the liquid dispersion towards the aliphatic sulfosuccinates (i.e. those not terminated with a phenyl group);

(iii) enhance the reactivity of the liquid dispersion relative to other commonly available anionic dispersing aids such as sodium dodecyl sulphate (SDS) and sodium dodecylbenzenesulphonate (SDBS);

(iv) increase the reactivity of the liquid dispersion compared to the three chain phenyl terminated sulfonates such as TPE-STC (tri-2-phenylethyl sulfotricarballylate) and TPME-STC (tri-2-phenyl-2-methylethyl sulfotricarballylate) (U.S. Patent 4,988,610), indicating that the geometry of the two hydrophobic chains of the materials of this invention is critical to their performance;

(v) reduce particle size, particularly in the case of the examples with longer hydrophobic chains according to the invention, compared to other anionic surfactants such as SDS, SDBS, aliphatic sulfosuccinates and phenyl-terminated sulfotricarballylates.

Increased Dmax value

When coatings are prepared from the most reactive microprecipitated dispersions, the examples of the invention show the highest Dmax value.

Monochrome coatings of the microprecipitated dispersions were prepared according to the procedures given.

A monochrome two-layer format was used for the photographic investigation of the coupler dispersions:

The two layers were applied simultaneously.

The coatings were exposed to white light for 0.1 s through a 21-step step tray at 0.15 logE increments and developed using standard RA-4 chemistry. Reflectance Dmax values of each coating were measured using an X-Rite Model 414 reflection densitometer. The results were as follows: TABLE VII. Coatings of Microprecipitated Coupler VI Dispersions

Table VII shows:

(i) The Dmax value increases with increasing hydrophobic chain length in the case of the materials of the invention;

(ii) higher Dmax values are achieved in the case of the longer chain length compounds of this invention as compared to the commonly available anionic dispersing aids such as SDS and SDBS;

(iii) the benefits of the higher Dmax do not occur in the case of the short chain phenyl terminated sulfosuccinates, which are outside the scope of this invention.

Photographic advantages with homogenized oil-in-water gelatin dispersions of color couplers Increased contrast and shoulder density.

Traditionally, color couplers are dissolved in a high boiling water-insoluble solvent and mechanically dispersed in an aqueous gelatin solution containing a surfactant to facilitate dispersion. Mean particle sizes are normally considerably larger (typically 0.2 µm) than those produced by microprecipitation techniques (typically 0.02 µm).

The homogenized dispersions were prepared using the following method:

A dispersion was prepared according to the following general formula:

Coupler VI 11.7%

Di-n-butyl phthalate 3.9%

Gelatin 9.5%

Water and surfactant 74.8%

Coupler VI was dissolved in di-n-butyl phthalate and heated to 140°C until the coupler was completely dissolved. Gelatin was dissolved in water and heated to 70°C. Surfactant was added to the gelatin solution in an amount of 0.1 molar equivalents to the coupler. The coupler solution was then added to the gelatin solution and homogenized for 3 minutes using a Kinematica Polytron set at 10,000 rpm, after which the whole was passed (twice) through a Microfluidics Microfluidiser (Model No. 110E) operating at a pressure of 68.95 MPa (10,000 psi) and a water bath temperature of 75°C.

Coatings were prepared as described above and exposed to white light for 0.1 seconds through a 21-step step tablet with 0.15 logE increments and developed through standard RA-4 chemistry. Contrast, Dmax, Dmin and shoulder densities were measured using an X-Rite Model 414 reflection densitometer and the values are summarized in Table VIII.

In the table below, the types of surfactants used for comparison purposes were as follows:

Type A - Sulfonate

Type B - Sulfosuccinate

Type C - Sulfoitaconate with the formula

Type D - Sulfoglutaconate with the formula TABLE VIII. Measurements of coated dispersions of coupler VI prepared with various surfactants

In the case of homogenized dispersions of coupler VI, the materials of the invention clearly demonstrate:

(i) increased contrast and shoulder density relative to aliphatic non-phenyl-terminated sulfosuccinates such as Aerosol OT; common anionic surfactants such as SDBS ω-arylalkyl phenyl-terminated sulfoitaconates and sulfoglutaconates; and the shorter chain phenyl-terminated sulfosuccinates, which are outside the scope of this invention;

(ii) the shorter chain sulfosuccinates with a phenyl end group, which are outside the scope of this invention, also show a considerably lower Dmax, indicating the importance of chain length for the materials of this invention;

(iii) there is no significant disadvantage for Dmin.

In summary, the phenyl-terminated sulfosuccinate dispersing aids of this invention offer advantages over a wide variety of chemically similar materials when used in the photographic context described.

Increased reactivity of the liquid dispersion

Dispersions of Couplers I and II were prepared by the procedure of Example 3. Measurements on the liquid dispersions were made as described above and the results are shown in Table IX. TABLE IX. Liquid dispersion data for homogenized dispersions of Couplers I and II.

Table IX clearly shows that in the case of dispersions of Coupler I and Coupler II, the materials of the invention enhance the reactivity of the liquid dispersion relative to aliphatic non-phenyl terminated sulfosuccinates such as Aerosol® OT and a conventional anionic surfactant such as Alkanol® XC.

Example 5 Low foaming in the developer

Foaming can cause serious problems during photographic processing, especially in the case of used developers, in which case surfactants have leached out of the photographic product and a concentration of them has built up. This foaming can cause solution spill, solution loss, uneven development and solution carryover to subsequent processing tanks.

To demonstrate that one of the preferred materials of this invention exhibits a lower tendency to foam, tests were conducted on a simulated used developer, namely a developer based on an ECP-2b color developer, using the Ross-Miles foam test.

The test was first developed by Ross and Miles (Ross, J. and G.D. Miles, Am. Soc. for Testing Materials, Method D1173-53, Philadelphia, PA 1953; Oil and Soap 18, 99, 1941). This test is based on placing some solution in both a lower and upper reservoir; the solution passes from the upper reservoir through a special opening (2.9 mm internal diameter), whereby the solution drips freely over a certain distance (initially 90 cm), whereupon the drops splash into the lower reservoir. The foam thus formed is measured immediately after the upper reservoir is empty and again 5 minutes later. The foam stability is then expressed as a percentage of the height remaining after 5 minutes. relative to the initial height of the foam. It is obvious that the lower the percentage, the lower the foam stability.

To simulate a used developer, solutions of ECP-2b were prepared at 37-38ºC such that each solution contained 0.006 wt% gelatin and 0.002 wt% surfactant. Each surfactant was tested independently in this format.

In the following table, foam stability is defined as Foam (5 min)/Foam (0 min) x 100%. TABLE X. Ross-Miles Foam Tests

Olin® 10 G is nonylphenyldecaglycidol

FT248 is tetraethylammonium perfluorooctane sulfonate

Table X illustrates that one of the preferred materials of this invention (n = 3, R = 1) produces significantly less foam in the simulated used developer than the corresponding aliphatic sulfosuccinate, Aerosol® OT, and significantly less foam than examples of other surfactants that can be found in photographic products such as Alkanol® XC, Olin 10 G, and FT248.

Claims (9)

1. A process for producing a multilayer photographic material, comprising: (a) simultaneously applying to a support a plurality of aqueous hydrophilic colloid layers including at least one light-sensitive silver halide emulsion layer, at least one of the underlying hydrophilic colloid layers containing particles dispersed therein by means of a surfactant, and (b) the applied layers dry, characterized in that the surfactant has the structure wherein R is H or methyl, provided that when each n = 1, each R is methyl; M is a cation; and n represents a number from 1 to 6. 2. Use of a surfactant having the structure wherein R is H or methyl, provided that when each n = 1, each R is methyl; M is a cation; and n represents a number from 1 to 6; in the process according to claim 1 as a coating latitude improving agent. 3. Use of a surfactant having the structure wherein R is H or methyl, provided that when each n = 1, each R is methyl; M is a cation; and n represents a number from 1 to 6; in a multilayer photographic material comprising a support having thereon a plurality of hydrophilic colloid layers, including at least one light-sensitive silver halide emulsion layer, at least one of the underlying hydrophilic colloid layers containing hydrophobic particles dispersed therein by means of the surfactant; to reduce foaming that may occur during photographic development of the material. 4. A method or use according to any one of claims 1 to 3, wherein the hydrophobic particles comprise a photographic coupler. 5. A process for preparing a composition comprising a hydrophilic colloid having hydrophobic particles dispersed therein, which comprises dispersing a hydrophobic material with a photographic coupler in an aqueous solution of a hydrophilic colloid in the presence of the surfactant, characterized in that the surfactant has the structure wherein R is H or methyl, provided that when each n = 1, each R is methyl; M is a cation; and n represents a number from 1 to 6; and wherein the surfactant is used in an amount of less than 1% by weight without a washing step to remove at least one quarter of the surfactant. 6. Process or use according to any one of the preceding claims, wherein n is a number from 2 to 4 and R is H. 7. A method or use according to any one of the preceding claims, wherein n is 3 and R is H. 8. A process or use according to any one of the preceding claims, wherein M is an alkali metal ion. 9. A method or use according to any preceding claim, wherein the hydrophilic colloid is gelatin.