This invention relates to photographic silver chloride emulsions having improved keeping properties.

Photographic silver chloride emulsions are now widely used in the manufacture of photographic colour negative paper materials. As such materials age their sensitometric performance changes such that the speed and minimum density (D . ) increase while their contrast decreases. Known techniques for countering these defects in silver halide emulsions in general include the method described in British Specification 1 262 127 which comprises the addition of small quantities of reducing agents such as amino- hexose-reductones. Control of the emulsion pH and pAg can also be beneficial.

There is, however, a need to improve the keeping properties (shelf life) of silver chloride emulsions still further.

Blocked bis—phenols have been described as photographic dye image stabilisers in European Patent specification 0 246 766 (US Patent 4 782 Oil). Specifically the compounds were incorporated into silver chlorobromide emulsions.

According to the present invention there is provided a photosensitive silver chloride emulsion comprising at least 90% silver chloride whose keeping properties have been improved by the incorporation therein of a bisphenol derivative having two linked phenol rings wherein the hydrogen atom of one of the phenolic hydroxy groups is replaced by a blocking group which is a substituent other than hydrogen and at least one of the phenol rings is substituted.

The blocking group may be any group which does not affect the desired properties of the stabilizer.

The two phenol rings of the stabilizer may be linked directly by a single bond or indirectly by a linking group. Preferably, the link between the phenol rings is ortho relative to the phenolic hydroxy group of one ring and the blocked phenolic hydroxy group of the other ring.

Preferably, each phenol ring independently is substituted in a position ortho or para relative to the unblocked or blocked phenolic hydroxy groups. It is further preferred that substituents are present in both ortho and para positions.

The bis—phenol compound preferably has the general formula:

HO OR

. ^■ X- ^N II— R ^κ1 —.I'X-H R2 (I)

/ /

wherein

R is alkyl, cycloalkyl, alkenyl, aryl, acyl, alkylsuphonyl or arylsulphonyl,

R is a single bond or a linking group selected from alkylene, alkylidene, a heteroatom or sulphonyl, and

2 each R independently represents one or more substituents each selected from alkyl, alkoxy, alkenyl, cycloalkyl, aryl or aryloxy or, each R independently represents the atoms necessary to complete with the benzene ring to which it is attached, a fused polycyclic aromatic ring structure. all of said alkyl, alkoxy, cycloalkyl, alkylene, alkenyl, aryl, aryloxy and acyl groups being optionally substituted.

Examples of blocking group R are methyl, ethyl, propyl or butyl, cyclohexyl, phenyl, acetyl or benzoyl.

Examples of linking group R are methylene, butylidene, 3,5,5,-trimethylhexylidene, oxygen, sulphur or sulphonyl. An especially preferred group of bis-phenol compounds has the general formula:

wherein R and R are as defined above, and R , R , R and R are each independently a substituted or unsubstituted alkyl, alkenyl, cycloalkyl or aryl group. Preferably, R ₃ and Λ are identical and Re and R, are identical. Specific examples of bis-phenols suitable for use in the present invention are as follows:

CH, CH,

^C 6 ^H 5

CH,

?6 ^H 5

CH.

-C ₄ H ₉ -C H ₉

CH ₃ CH ₂ -C H ₉ -t

?°2-\ )- ^CH 3

CH.,

t-C ₄ H _g

COCH-.

I ^J

t— C^-Hg t— C^Hg,

CH. CH,

CH ₂ C ₆ H ₅

t— C^Hg ~C H ₉

CH, CH,—C^H _Q —t

?2 ^H 5

OH

CH ₃ CH ₃

The blocked bisphenol derivatives are readily prepared from their unblocked counterparts, many of which are commercially available. For example, a blocking group may be introduced into the unblocked

parent bisphenol by reaction with an appropriate reactive halogen—containing compound e.g. an alkyl bromide, acyl chloride, sulphonyl chloride or a dialkyl sulphate e.g. diethyl sulphate.

Examples of unblocked parent bisphenols from which the stabilizers of the present invention may be prepared are as follows:

CH ₃ CH ₃

i ⁱ 5 ^:) 1 - 18

CH ₃ CH ₂ -C H ₉ -t 5

0

5

CH ₃ CH ₃

The present invention also provides a method for improving the keeping properties of a silver chloride emulsion comprising the incorporation therein of a bisphenol derivative having two linked phenol rings wherein the hydrogen atom of one of the phenolic hydroxy groups is .replaced by a blocking group which is a substituent other than hydrogen and at least one of the phenol rings is substituted.

The present invention further provides a photographic material comprising a support bearing a layer of a photosensitive silver chloride emulsion said material having incorporated therein a bisphenol derivative having two linked phenol rings wherein the hydrogen atom of one of the phenolic hydroxy groups is replaced by a blocking group which is a substituent other than hydrogen and at least one of the phenol rings is substituted in order to improve its keeping properties.

The silver chloride emulsions used in the present invention contain more than 90 mole %, silver chloride preferably the emulsions are substantially pure silver chloride.

The bis—phenol compounds may be incorporated in the silver chloride emulsions as a dispersion of droplets of a high boiling coupler solvent containing the bis—phenol. Such droplets may also contain a colour coupler. Alternatively they may be incorporated as solutions in an alcohol, for example, methanol.

The colour coupler may be of any class of couplers useful in colour photographic materials. Examples of such coupler classes include phenolic and naphtholic cyan couplers, pyrazolidone and pyrazolotriazole magenta couplers and acylacetanilide yellow couplers.

Particularly good results are obtained with the pivaloylacetanilide couplers and especially those with aryloxy coupling-off groups. Such couplers preferably have the general formula:

7

wherein R represents one or more substituents of the type found in such couplers, and gg RR iiss aa ccoouupplliiing-off group, preferably an aryloxy group.

Suitable emulsions, emulsion additives and couplers for use in the emulsions and elements of this invention are described in Research Disclosure, December 1978, Item 17643, published by Kenneth Mason Publications Ltd., 12a North Street, Emsworth, Hants PO10 7DQ, U.K. In particular, information on couplers and on methods for their dispersions are given in Sections VII and XIV, respectively, of this article.

The following examples are included for a better understanding of the invention.

EXAMPLE 1

Four separate dispersions of the following coupler were prepared:

(n)

Coupler (A)

dissolved in one quarter its weight of dibutyl phthalate and 2-(2—butoxyethoxy)ethyl acetate. Two of the dispersions also contained a blocked bis—phenol as indicated below at concentrations equal to half that of the coupler, by weight. The fourth dispersion contained a comparison material the bis-phosphate ester of the formula:

(PhO) ₂ PO.O(CH ₂ ) ₁₀ O.PO(OPh) ₂

at the same concentration.

Each dispersion was mixed with a blue—sensitive silver chloride emulsion and coated on a resin-coated paper support, such that the silver and coupler cc<overages were, respectively, 0.18 g/m and

Strips of the fresh coatings sere exposed and processed through RA4 chemistry to assess sensitometric performance. Further strips were incubated in the dark for 1 week at 50 °C and 50% RH before being similarly exposed and processed.

The Table below shows figures for the D , and contrast of the freshly coated and incubated strips from each coating. The columns labelled "Δ" show the difference between the fresh and incubated samples. Taking the coating without any addendum as a reference, the two blocked bis-phenols reduced the extent of Dmi.n increase and the loss in contrast due to incubation. A contrary effect was show by the comparison bis—phosphate ester.

TABLE 1

'min Contrast

Additive Fresh Inc. Fresh Inc.

None 1-11 1-15 Bis—phos

EXAMPLE 2

Dispersions were prepared containing Compound I—11 with the colour couplers below:

(t) Coupler (B)

Cl

Cl Dispersions of each coupler alone were also made. In each dispersion the coupler was dissolved in its own weight of ethyl acetate and one half its weight of dibutyl phthalate. When present the

10 bisphenol was included at half the weight of the coupler. The oil solutions were dispersed in aqueous gelatin using ultrasonic agitation as in Example 1. Each dispersion containing Coupler (B) was mixed with a red—sensitised silver chloride emulsion ^ and coated on a resin—coated paper support, such that the silver and coupler coverages were, respectively,

239 mg/m 2 and 425 mg/m2. A second pair of coatings was made from the dispersions at the same component coverages but utilising a blue—sensitised 0 emulsion (as used in Example 1) in place of the red sensitised emulsion.

Similarly the dispersions of Coupler (C) were coated together with a green sensitised silver chloride emulsion at silver and coupler coverages of ^J . 285 mg/m2 and 447 mg/m2 respectively.

Sample strips of the fresh coatings were exposed and processed through RA4 chemistry to assess sensitometric performance. Another strip from each coating was incubated in the dark for 8 days at 50°C 0 and 50% RH before being exposed and processed.

The following table shows figures for the D . of the freshly coated and incubated strips.

5

The column labelled "Δ" highlights the differences between the two sets, associated with the incubation treatment. All the coatings show an increase in

Dmi.n on incubation and the magnitude of this increase is always reduced by the presence of the bisphenol.

The beneficial effect of the invention is thus shown not to be dependent on the colour sensitiviy of the emulsion or the coupler it contains

TABLE 2

Emulsion Dmm