GB2138158A - Process for the preparation of light-sensitive silver halide emulsions - Google Patents

Abstract

According to the invention to the emulsion a cyclodextrin polymer having a cyclodextrin content of from 30 to 70 %, an average molecular mass of from 2,000 to 15,000 and containing structural units of formula (I> <IMAGE> is added in an amount of from 2 to 80% calculated on the weight of the gelatin. In the general Formula I the substituents have the following meanings: CD stands for a group obtained from alpha , beta - or gamma -cyclo-dextrin by cleaving p+s or l+r+t hydroxy group; the remaining substituents are as defined in the specification. m and n stand independently for an integer from 1 to 10, r stands for an integer from 0 to 23, p stands for an integer from 1 to 24, s and t stand independently for an integer from 0 to 7, with the proviso, that when CD stands for a group obtained from alpha -cyclo-dextrin, then p+s </= 18, r+t </= 18, when CD stands for a group obtained from beta -cyclo-dextrin, then p+s </= 21, r+t </= 21, when CD stands for a group obtained from gamma -cyclo-dextrin, then p+s </= 24, r+t </= 24.

Description

SPECIFICATION Process for the preparation of light-sensitive silver halide emulsions The invention relates to a process for the preparation of light-sensitive silver halide emulsions having improved physicochemical and photographic characteristics by using water soluble cyclodextrin polymers.

For improving the physicochemical and photographic characteristics of light-sensitive silver halide emulsions, polymers of high molecular mass are often used. These are applied as additives orforthe partial replacement of gelatin and are aqueous polymer dispersions or water soluble polymers.

According to GB-PS 1,406,752 water soluble acrylic acid or methacrylic acid ester polymers are used for improving the physical and photographic characteristics of the emulsion. According to DOS 2,218,218 acrylate latices are used for improving the dimensional stability. For increasing the covering power, FR-PS 1,518,085 describes the use of acrylic amide/styrene copolymer, and US-PS 3,063,838 and 3,137,575 that of dextrane or polyfructose. The light-sensitivity is increased according to the US-PS 3,006,762 by adding polyvinyl oxazolidone.

Many patent specifications describe the use of polyacrylic amide, acrylic amide/acrylic acid copolymer or polyvinylpyridinefor partial replacement of gelatine. From among these substances only a few were used in the industry (G. F. Duffin: Photographic Emulsion Chemistry, Focal Press, London, 1966, p.30).

The use of latices in the light-sensitive layer in greater amount is restricted owing to compatibility problems and inhibition of the diffusion of the components of the processing solution. Most of the water soluble polymers, which were offered till this time, are also restricted due to their strong interaction with gelatin. According to the known solutions one substance is used only for one function.

The invention is based on the recognition that in case of using a cyclodextrin polymer having suitable chemical structure and relatively low average molecular mass in the photographic emulsion several characteristics will be improved without the disadvantages mentioned above.

The cyclodextrins are cyclic, non reducible oligosaccharides containing 6, 7 or 8 glucopyranose units. They may be produced by enzymatic decomposition of starch. In practice they are mainly used as a consequence of their ability to form inclusion complexes (Szejtli J.: Cyclodextrins and their Inclusion Complexes, Akademiai Kiad6, Budapest 1982). The reactivity of the primary and secondary alcoholic hydroxy groups on the rings of the six-member a-, the seven-member ss- and the eight-member y-cyclodextrin renders the preparation of derivatives having great molecular mass (cyclodextrin polymers) possible.

According to the literature cyclodextrin polymers, which are water soluble, and those, which are water insoluble but swell in water, are known. Due to the greater molecular mass and cross-linked structure the latter are not soluble in any solvent.

Water soluble cyclodextrin polymer may be obtained in two way: unsaturated monomer is prepared from cyclodextrin and this will be polimerized (J. Polym. Sci.Lett. 13,357 (1975)) or the cylcodextrin is cross-linked with a suitable bifunctional reagent, preferably diepoxy derivative or epichlorohydrin (GB-PS 1,244,990 and HU-PS 1961/80).

By both processes products having medium molecular mass may be obtained which may be dissolved in water well and form inclusion complexes. The stability of their complexes is generally greater than that of the monomer cyclodextrins. This may be explained by the advantageous steric position of the rings connected each other and in the case of ss-cyclodextrin by the greater solubility of the polymer (Macromolecules 2,705 (1976), Proceedings of I. Int. Symp, on Cyclodextrins (1981)345).

The water soluble cyclodextrins (generally marked with sCDP) may be neutral or ionic substances.

In the water soluble cyclodextrin polymers according to the invention, which are substituted by ionic groups and contain a structural unit of formula (I)

and are produced by connecting 2 to 10 cyclodextrin rings, the ionic groups may be on the cyclodextrin rings and/or on the bridges or side-chains connected thereto.

In formula (I) the substituents have the following meanings: CD stands for a group obtained from of - or y-cyclodextrin by cleaving p+s or l+r+t hydroxy group, R and R' stand independently for -CH2-, -CH(OH)-CH2-, -CH2-O-/CH2/2-O-CH2-CH(OH)-CH2-, -CH2-O-CH2 CH(OH)-CH2-, -CH2-O-/CH2/4-O-CH2-CH(OH)-CH2-, R1 stands for hydrogen or when r is other than 0, a group obtained from a-, (3for y-cyclodextrin by cleaving a hydroxy group, as well as alkyl, alkylaryl, alkenyl or alkynyl groups bearing acidic functional group(s), e.g. -(CH2)mCOOH, -CH(COOH)2, -CH-CH2(COOH)2, -C(CH2)2(COOH)3 group or an alkylamino, arylamino, alkylarylamino or arylalkylamino group of formula RxRvN#, wherein Rx stands for alkyl, aryl, alkylaryl, arylalkyl or hydrogen, Ry stands for alkyl, aryl, alkylaryl or arylalkyl, R2, R2 and R2 stand independently for acidic aliphatic or aromatic polycarboxylic acid ester group of formula -R3COOH or-R3SO3H, e.g. the group of formula

HOOC-CH2-CO-, further an acidic phosphate ester group of formula -PO3H2, an acidic sulfuric acid ester group of formula -SO3H, a group of formula -R3NH2or-(R3)2NH, R3 stands for a straight or branched chain alkylene having 1 to 5 carbon atoms, m and n stand independently for an integer from 1 to 10, r stands for an integer from 0 to 23, p stands for an integer from 1 to 24, s s and t stand independently for an integer from 0 to 7, with the proviso, that when CD stands for a group obtained from o-cyclodextrin, then p+s #18, r+t #18, when CD stands for a group obtained from ss-cyclodextrin, then p+s #21, r+t #21, when CD stands for a group obtained from y-cyclodextrin, then p+s #24, r+t #24.

The cyclodextrin polymer products mentioned above are solid and soluble in water and in certain organic solvents, e.g. in dimethyl formamide, pyridine, may form not only inclusion complexes but also salts, have a cyclodextrin content of from 30 to 70% and an average molecular mass of from 2,000 to 15,000. The photographic emulsion according to the invention is prepared thereby that the silver halide is precipitated in the aqueous solution of gelatin and water soluble cyclodextrin polymer, the crystals obtained are physically, then after adding the ripening gelatin chemically, digested, thereafter the additives usually employed in photographic emulsions are added to the solution obtained.

The emulsion according to the invention may also be prepared in such way that the silver halide crystals, which were precipitated in the presence of gelatin and water soluble cyclodextrin polymer, are physically digested, then the superfluous ions are removed by flocculation, thereafter the crystals are redispersed with gelatin solution, the emulsion is chemically digested and the usual additives are added.

According to the invention the water soluble cyclodextrin polymer may be added into the emulsion during or after digestion or while adding the other additives.

According to the process of the invention the gelatin may be omitted from the emulsion in the amount corresponding to the amount of the water soluble cyclodextrin polymer or also in a smaller amount The emulsion of the invention may be chemically sensibilized by known methods, e.g. with labile sulfur compound or gold complexes (T. H. James: The Theory of the Photographic Process, IV. Edition, MacMillan, New York, 1977, p. 152-5).

In the emulsion according to the invention the additives usually employed in photographic emulsions may be used. Such additives are the colour sensiting substances, stabilizers, tanning agents, wetting agents, etc.

The colour sensiting substances may be, e.g. 1-ethyl-3'-phenyl-2-quino-5'-rhodanine (dyestuff 1), 3,3'-diethyl-1 '-phenyl-benzoxazolidene-(ethylidene-2'4hiohydanthion) (dyestuff II), 3,3'-diethyl-6,6'dinaphthyl-9-phenyl-thiocarbocyanine (dyestuff Ill), benzthiazole-phenyl-2-thiohydanthion-tetramethylmerocyanine (dyestuff IV) (P. Glafkides: Photographic Chemistry, Volume II, p. 832-856, Fountain Press, London,1960).

The stabilizers may be e.g. 4-hydroxy-6-methyl-1,3,3a,74etraazaindole (TAl), 1-phenyl-5-mercapto- tetrazole FMT), mercaptobenzthiazole (MBT), mercaptobenzoxazole, 2-mercapto-pyrimidines (G. F. Duffin: Photographic Emulsion Chemistry, p. 138-141, Focal Press, London, 1966).

The tanning agents may be e.g. formalin, glutaraldehyde, glyoxal, 2,4-dichloro-6-oxy-S4riazine (T. H.

James: The Theory of the Photographic process, IV. Edition, Mac Millan, New York, 1977, p.82).

The wetting agents may be e.g. alkenylsuccinicacid polyglycerides, dodecylphenolpolyglycolether, saponine (B. M.Derjagin: S. M. Levi: Film Coating Theory, p. 162, Focal Press, London, 1966).

When the emulsions of the invention are used for producing colour photographic layers, yellow and/or magenta and/or cyan hydrophylic or oil soluble colour forming substances may be added. The yellow colour forming agents are e.g. the diketomethylene derivatives, the purple ones the 5-pyrazolone derivatives and the blue-green ones the naphthol or phenol derivatives (G. F. Duffin: Photographic Emulsion Chemistry, Focal Press, London, 1965, p 197-200).

According to the process of the invention the water soluble cyclodextrin polymer is used in an amount of 2 to 80%, preferably 5 to 50% calculated on the amount of the gelatin, in form of its aqueous solution or as a solid product.

The main advantages of the process according to the invention are as follows: 1. By using one polymer several characteristics of the photographic emulsion may be improved atthe same time, i.e.

a) the covering power may be increased, so silver may be saved, b) the sensitivity may be increased, c) the setting ability of the emulsion may be improved.

2. By using the polymer the gelatin may be partially replaced.

3. The tone stability of photographic papers of warm tone may be improved.

4. The polymer used in the process may be prepared cheaply from domestic raw materials.

The invention is further shown by the Examples.

Example 1 In 400 ml of water 10 9 of gelatin are swollen, after complete dissolution 0.065 moles of potassium bromide and 0.095 moles of sodium chloride are added. After the dissolution of the salts silver halide is precipitated with 60 ml of 2 M silver nitrate solution at 62 C. After a heat treatment of 15 minutes 40 g of ripening gelatin are added and the heat treatment is continued for further 65 minutes. The emulsion obtained is cooled to 400C and to an aliquot part thereof the usual additives are added (calculated on one mole of the silver halide 75 ml of 0.05% dyestuff ll solution, 100 ml of 50% gycerol solution, 40 ml of 4% saponine solution, 20 ml of 5% formalin, 35 ml of 1% FMT solution).The emulsion is then applied on a paper base so as to give a metal silver content of 10-2 g/dm2 (A).

An emulsion is prepared as emulsion (A) except that 10 g of gelatin are swollen in 400 ml of 2.5% poly(carboxymethyl-ss-cyclodextrin) solution (compound 1) (B).

A further emulsion is prepared as emulsion (B) except that 30 g of the suitable ripening gelatin composition are used (C).

Emulsion is also prepared as emulsion (A) except that 30 g of the suitable ripening gelatin composition are used and after finishing the heat treatment 100 ml of 10% poly(dimethylaminomethyl-(3-cyclodextrin) solution (compound 2) are added (D).

The photographic characteristics of the light-sensitive layers obtained with emulsions (A) to (D) are shown in Table 1. The sensitograms were exposed by an incandescent lamp having a colour temperature of 28000K and developed for 2 minutes at 180C in a solution having the following composition: 1 g of methol, 4 g of hydroquinone, 20 g of anhydrous sodium sulfite, 9 of anhydrous sodium carbonate, 1 g of potassium bromide in 1 liter water.

TABLE 1 Emul Addition Way of Relative Average Dmax Fog sion of water treat- sensiti- gradient 180C 30 C soluble ing vity 2 10 cyclodext- min min rin polymer (A) no F 100 2.20 1.99 0.05 0.33 110 2.17 1.98 0.05 0.29 (B) during F 126 2.18 2.00 0.05 0.28 precipi- I 131 2.20 1.98 0.04 0.27 tation (C) during F 122 2.24 1.96 0.05 0.27 precipi- I 129 2.21 1.98 0.06 0.28 tation (D) afterfi- F 105 2.15 2.04 0.04 0.26 nishing 1 102 2.12 2.00 0.05 0.25 the diges tion Remarks:F = fresh, untreated sample after incubation for 5 days at 50 C From the above data it can be seen that the cyclodextrin polymer while adding during the precipitation (B) has a sensitivity increasing effect and this effect will be maintained also when the cyclodextrin polymer is applied for the replacement of the gelatin, i.e. the gelatin is omitted from the emulsion in an amount corresponding to the amount of the cyclodextrin polymer (C). When the cyclodextrin polymer is added to the system for the replacement of the gelatin afterfinishing the digestion (D), the same results as in case of the control emulsion are obtained.

Example 2 In 300 ml 1.5% phthaloylgelatin solution 0.25 moles of potassium bromide and 0.01 mole of potassium iodide are dissolved, then 150 ml of 0.5 M silver nitrate solution are added during 2 minutes at 650C under stirring and after 2 minutes stirring 320 ml 0.5 M silver nitrate solution are added during 20 minutes. The emulsion is cooled to 40 C, the pH thereof is adjusted to 3.8 by adding 2 N sulfuric acid dropwise. The precipitate obtained is allowed to settle and the aqueous phase is decanted. To the precipitate 800 ml of cold water are added, the pH is adjusted to 10.0 by adding sodium hydroxide solution dropwise, thereafter the flocculation and decantation are repeated.To the precipitate obtained 400 ml of 12% inert gelatin solution of 600C are added, thereafter goldthiosulfate complex are added and chemical digestion is performed at 60 C.

After finishing the digestion the emulsion is cooled to 400C and to an aliquot part thereof the usual additives are added (calculated on one mole of silver halide 200 ml of 0.1% dyestuff IV solution, 160 ml of 50% glycerol solution, 80 ml of 4% saponine solution, 40 ml of 5% formalin, 300 ml of 1% TAI solution). The emulsion is then applied on a cellulosetriacetate base so as to give a metal silver content of 3.8 x 10-2 g/dm2 (E) An emulsion is prepared as emulsion (E) except that during the precipitation also 6 g of compound 1 are added (F).

Emulsion (E) is also prepared except that to the gelatin solution 2.5 g compound 1 are added and this compound is used also as additive in an amount of 15% calculated on the weight of the gelatin (G).

Light-sensitive layer is also prepared using an emulsion prepared according to emulsion (E) except that after adding the light-sensitive substances the following water soluble cyclodextrin polymers are added in an amount of 20% calculated on the weight of the gelatine: compound 1, poli(sulfobutyl-,-cyclodextrin) (compound 3), poly(aminoethyl-,-cyclodextrin) (compound 4), poly(carbethoxymethyl-(3-cyclodextrin) (compound 5) (H).

Thereafter emulsion (E) is prepared except that for redispersion 300 ml of 14% inert gelatin solution are used and after finishing the digestion 100 ml of 10% solution of compound 1 are added to the emulsion so 11 % of the gelatin was replaced (J).

The photographic characteristics of the light-sensitive layers obtained with emulsions (E) to (J) are shown in Table 2. The sensitograms were exposed by an incandescent lamp having a colour temperature of 5500 K and developed for 8 minutes at 20 C in Kodak D-76 developer.

TABLE 2 Emul- Addition Way of Relative Average Dmax sion of water treat- sensiti- gradient soluble ing vity cyclodext rin polymer (E) no F 100 0.65 0.06 95 0.62 0.06 (F) compound 1 F 115 0.83 0.07 118 0.84 0.07 (H) compound 1 F 130 0.79 0.08 I 136 0.75 0.08 compound3 F 115 0.75 0.07 I 110 0.75 0.08 compound 4 F 110 0.70 0.07 105 0.70 0.08 compound 5 F 125 0.86 0.06 130 0.84 0.07 (G) compound 1 F 125 0.86 0.08 128 0.85 0.08 (J) compound 1 F 123 0.84 0.08 120 0.80 0.07 Remarks: F = fresh, untreated sample I = after incubation for 5 days at 50 C From the data of the Table it can be seen that the water soluble cyclodextrin polymer - similarly as by adding at precipitation - increases the covering power and the sensitivity. When the cyclodextrin polymers are used for replacement of the gelatin, they have the same effect (J).

Claims (9)

1. Process for the preparation of light-sensitive silver halide emulsions having improved physicochemical and photographic characteristics by precipitating the silver halide, optionally removing the superfluous ions with a suitable method, such a flocculation, washing, physical and chemical digestion of the precipitate so obtained and adding known additives, such as colour sensitizing substances, plasticizers, wetting agents, tanning agents and stabilizers, which comprises adding to the emulsion in an amount of from 2 to 80% calculated on the weight of the gelatin a cyclodextrin polymer having a cyclodextrin content of from 30 to 70%, an average molecular mass of from 2,000 to 15,000 and containing structural units of formula (I),

wherein CD stands for a group obtained from a-, (3for ey-cyclodextrin by cleaving p+s or l+r+t hydroxy group, R and R' stand independently for -CH2-, -CH(OH)-CH2-, -CH2-O-/CH2/2-O-CH2-CH(OH)-CH2-, -CH2-O-CH2 CH(OH)-CH2-, -CHrO-/CH2/4-O-CH2-CH(OH)-CH2-, R1 stands for hydrogen or when r is other than 0, a group obtained from a (3for #cyclodextrin by cleaving a hydroxy group, as well as alkyl, alkylaryl, alkenyl or alkynyl groups bearing acidic functional group(s), e.g. #(CH2)mCOOH, -CH(COOH)2, -CH-CH2(COOH)2, -C(CH2)2(COOH)3 group or an alkylamino, arylamino, alkylarylamino or arylalkylamino group of formula RXRyN-, wherein Rx stands for alkyl, aryl, alkylaryl, arylalkyl or hydrogen, Ry stands for alkyl, aryl, alkylaryl or arylalkyl, R2, R2, and R2 stand independently for an acidic aliphatic or aromatic polycarboxylic acid group or a carbonyl aliphatic or aromatic carboxylic acid group containing one or more carboxylic acid groups, e.g.

or HOOC-CH2-CO-, a group of the general formula -R3COOH or R3SO3H, further an acidic phosphate ester group of formula -P03H2, an acidic sulfuric acid ester group of formula -SO3H, a group of formula -R3NH2 or -(R3)2N H, R3 stands for a straight or branched chain alkylene having 1 to 5 carbon atoms or for an optionally substituted phenylene group, m and n stand independently for an integerfrom 1 to 10, r stands for an integer from 0 to 23, p stands for an integerfrom 1 to 24, s and t stand independently for an integer from 0 to 7, with the proviso, that when CD stands for a group obtained from a-cyclodextrin, then p+s #18, r+t 618, when CD stands for a group obtained from ss-cyclodextrin, then p+s #21, r+t #21, when CD stands for a group obtained from y-cyclodextrin, then p+s #24, r+t #24.

2. Process according to claim 1 which comprises adding the cyclodextrin polymer before precipitation on to the gelatin solution.

3. Process according to claim 1 which comprises adding the cylcodextrin polymer during or after digestion to the emulsion.

4. Process according to claim 1, which comprises adding the cyclodextrin polymer as pouring additives.

5. Process for the preparation of a light-sensitive silver halide emulsion, which process comprises adding to a silver halide emulsion a cyclodextrin polymer of the general formula I where CD, R, R', Ra, Rx, Ry, R2 R2, R2,,, Rs, m, n, p, r, sand rare as defined in claim 1.

6. A process according to claim 1 substantially as hereinbefore described in Example 1 or Example 2.

7. A light-sensitive emulsion produced by a process as claimed in any one of claims 1 to 6.

8. A light-sensitive emulsion containing silver halide particles in, preferably digested in, a polymeric substance, which polymeric substance comprises a cyclodextrin polymer as defined in claim 1.

9. Photographic paper or film comprising an emulsion as claimed in claim 7 or 8 coated on a carrier.