IMPROVED PERFORMANCE OF PHOTOGRAPHIC EMULSIONS AT HIGH SILVER ION ACTIVITIES

Abstract: A photographic recording material is described which comprises a chemically sensitized photosensitive silver halide emulsion layer which has a pH value from 2 to 5 and a pAg value from 1 to 4.7. Also disclosed are sensitizing dyes for use with the described photographic recording materials.

Description: IMPROVED PERFORMANCE OF PHOTOGRAPHIC EMULSIONS AT HIGH SILVER ION ACTIVITIES Technical Field This invention relates to a photographic recording material and more particularly to a recording having coated thereon a silver halide emulsion layer which has improved resistance to fog, particularly on storage prior to use, while maintaining desired photographic speed. Background Art It is well known to manufacture silver halide emulsions under acidic conditions. For example, U.S. Patent 3,271,157 describes manufacture and coating of silver halide emulsions at pH values below about 5, for example, at values as low as pH 2.0. Such conventional low pH emulsions contain excess soluble halide ions and have pAg values of at least 8. One of the effects of low pH manufactured and coated silver halide emulsions is greater resistance to fog formation, although this is frequently offset by loss of desirable photographic speed. Little information is available on how pAg variations influence sensitometric properties. In one study by Collier and Gilman (Photogr. Sci . Eng., 16, 413, 1972), silver bromide emulsions which had not been chemically sensitized, were examined at pH 4 over the range pAg 10 to 3, both in the absence and presence of cationic cyanine iodides. As reported in The Theory of the Photographic Process. 4th Ed. , Macmillan Publishing Co., New York, 1977, pp. 25-37, these pAg values cover a range where the chemically non-sensitized silver bromide emulsions contained an excess of either soluble halide ions or soluble silver ions. Collier and Gilman observed an increase in the ratio between spectral sensitivity and sensitivity at 400 nm when pAg was lowered from about pAg 10 to pAg 7, and that this ratio remained essentially constant with further pAg decreases. However, at low pAg values, cyanine deaggregation was noted and fog became apparent. The changed response of the initially chemically non-sensitized silver bromide was ascribed to formation of metallic silver. It is also well established in the photographic literature that for emulsions which were previously chemically sensitized, an exposure to low pAg conditions promotes both instability and fog formation. An example of this behavior is furnished in Research Disclosure No. 15560, March, 1977, Published by Kenneth Mason Publications, Ltd., The Old Harbourmaster's, 8 North Street, Emsworth, Hampshire, P010 7DD, England, the disclosure of which is herein incorporated by reference. This publica¬ tion shows that a chemically sensitized silver bromide emulsion at pH 5.6 and pAg 5.0 exhibited substantial fog whereas the same emulsion at either pH 2 and pAg 5 or pH 5.6 and pAg 8.2, did not undergo this fogging reaction. Disclosure of Invention It is an object of the present invention to provide a photographic recording material which has improved resistance to storage fog, which is capable of providing the desired or increased photographic speed and which displays no stain as a result of spectral dye sensitization. The present invention provides a photo¬ graphic recording material comprising a support and a photosensitive chemically sensitized silver halide emulsion layer which has a pH value between about 2 to about 5 and a pAg value between about 1 to about 4.7. Modes For Carrying Out the Invention The low pH and low pAg silver halide emulsions also yield advantageous sensitivity when they have incorporated therein particular spectral sensitizing dyes. These dyes are oxonols, merocyanines and cyanines and have the structures noted below. The photographic silver halide emulsions may be formed and chemically sensitized by any method known in the prior art. Such emulsions may contain previously described additives such as development modifiers and couplers for dye formation. Adjustment of the final acidity between the values of pH 2 and pH 5 can be made with inorganic or organic acids and bases exemplified by sulfuric, nitric, methanesulfonic, benzenesulfonic or trifluoroacetic acids and by sodium hydroxide, tetramethylammonium hydroxide and the like. Similarly, the adjustments to pAg values between 1 and 4.7 can be made with inorganic or organic silver salt such as silver nitrate, silver perchlorate, silver benzene sulfonate and the like. Preferably, the silver halide emulsions have a pH of from about 2 to about 4 and have pAg values between about 3 to about 4.7. The silver halide emulsions employed in the recording materials of this invention contain an excess of more than 0.01 illimolar (mM) soluble, dissociated acid and more than 0.01 mM soluble, dissociated silver salt. These emulsions can be comprised of silver bromide, silver chloride, silver iodide, silver chlorobromide, silver chloroiodide, silver bromoiodide, silver chlorobromoiodide or other mixed compositions of these halides. The emulsions can include silver halide grains of any conventional shape or size. Specifically, the emulsions can include coarse, medium or fine silver halide grains. High aspect ratio tabular grain emulsions are specifically contemplated, such as those disclosed by Wilgus et al U.S. Patent 4,434,226, Daubendiek et al U.S. Patent 4,414,310, Wey U.S. Patent 4,399,215, Solberg et al U.S. Patent 4,433,048, Mignot U.S. Patent 4,386,156, Evans et al U.S. Patent 4,504,570, Maskasky U.S. Patent 4,400,463, Wey et al U.S. Patent 4.414,306, Maskasky U.S. Patents 4,435,501 and 4,643,966 and Daubendiek et al U.S. patents 4,672,027 and 4,693,964. Also specifically contemplated are those silver bromoiodide grains with a higher molar proportion of iodide in the core of the grain than in the periphery of the grain, such as those described in British Patent 1.027,146; Japanese Published Application 54/48,521; U.S. Patents 4,379,837; 4,444,877; 4,665,012; 4,686,178; 4,565,778; 4,728,602; 4,668,614; 4,636,461 and European Patent 264,954. The silver halide emulsions can be either monodisperse or polydisperse as precipitated. The grain size distribution of the emulsions can be controlled by silver halide grain separation techniques or by blending silver halide emulsions of differing grain sizes. The silver halide emulsions can be chemically sensitized. Noble metals (e.g., gold), Group VIII compounds, middle chalcogens (e.g., sulfur, selenium, or tellurium), copper, thallium, lead, bismuth or cadmium may be used. Reduction sensitization is also specifically contemplated. Typical chemical and spectral sensitizers are listed in Research Disclosure Item 17643, Sections III and IV published by Kenneth Mason Publications, Ltd., The Old Harbourmaster's, 8 North Street, Emsworth, Hampshire, P010 7DD, England, the disclosures of which are incorporated herein by reference. This publication will be identified hereafter by the term "Research Disclosure". The emulsions can be surface-sensitive, i.e., emulsions that form latent images primarily on the surfaces of the silver halide grains, or internal latent image-forming emulsions, i.e., emulsions that form latent images predominantly in the interior of the silver halide grains. The emulsions can be negative-working, such as surface-sensitive emulsions or unfogged internal latent image-forming emulsions, or direct—positive emulsions of the unfogged, internal latent image-forming type, which are positive-working when development is conducted with uniform light exposure or in the presence of a nucleating agent. As noted above, the silver halide emulsions disclosed herein can be spectrally sensitized. Particularly useful are oxonol, merocyanine or cyanine dyes . Such dyes are well known in the art and are often incorporated in conventional silver halide emulsions containing excess soluble halide ions as "bleachable filter dyes" in order to control the spectral distribution of exposure. Examples illustrating that purpose for ' oxonol dyes are British Patent Specifications 506385; for merocyanines; U.S. Patents 2,493,747, 2,493,748, 2,526,632, 2,719,088 and 3,840,375; and for cyanines : U.S. Patent 3,988,155. For this prior art purpose, these dyes must be largely inert as sensitizers, desensitizers or foggants . They also must be readily decolorized during processing, for example, in the development or fixing step. These dyes are generally employed in an amount within the range of about 0.05 to 2.0 mmole/mole silver. Because these molecules, previously known as "bleachable filter dyes", were unexpectedly converted to effective spectral sensitizers in the low pH and low pAg environment of this invention, the dyes offer the particular advantage of yielding spectral sensitization which, after emulsion processing, lead to images without stain from residual sensitizing dye. Antifoggants and stabilizers as described on page 26, in the Research Disclosure noted above, hardeners and coating aids as described on pages 26 and 27, and other layers and components of the photographic elements such as vehicles and extenders which are described on pages 25 to 27 of this Research Disclosure can be incorporated in the photographic elements by the procedures as described therein. The various silver halide emulsion layers of a color film assembly employed in this invention are disposed in the usual order, i.e., the blue—sensitive silver halide emulsion layer first with respect to the exposure side, followed by the green-sensitive and red-sensitive silver halide emulsion layers. If desired, a yellow dye layer or a yellow colloidal silver layer can be present between the blue—sensitive and green—sensitive silver halide emulsion layers for absorbing or filtering blue radiation that is transmitted through the blue-sensitive layer. If desired, the selectively sensitized silver halide emulsion layers can be disposed in a different order, e.g., the blue-sensitive layer first with respect to the exposure side, followed by the red—sensitive and green-sensitive layers. The supports for the photographic materials used in this invention can be any material, as long as it does not deleteriously affect the photographic properties of the material and is dimensionally stable. Typical flexible sheet materials are described on page 28 of the December, 1978 edition of Research Disclosure noted above. The term "nondiffusing" used herein has the meaning commonly applied to the term in photography and denotes materials that for all practical purposes do not migrate or wander through organic colloid layers, such as gelatin, in the photographic elements of the invention in an alkaline medium. The term "associated therewith" is intended to mean that the materials can be in either the same or different layers, so long as the materials are accessible to one another. Table I below shows examples of typical oxonol dyes having the generic structure: where n is 0, 1 or 2; M is hydrogen, an onium cation or an inorganic cation; and the letters Y and Y represent the atoms necessary for completion of a 5 or 6-membered heterocycle. In order to make these spectrally sensitizing oxonol dyes bleachable in photographic processing solutions and thus obtain images without stain from residual sensitizing dye, the heterocyclic residue represented by Y and Y , which can be the same or different, is preferably a rhodanine, thiohydantoin or thiazolidinedione or preferably comprises a pyrazolone, isoxozolone, pyrandione, barbituric or thiobarbituric acid group. These groups are illustrated as "Acidic Heterocycles" in The Theory of the Photographic Process, ed . T. H. James, Fourth Ed. , Macmillon Publishing Co. , New York, 1977, Chapter 8. Dye COTPAUStd _n_ JRi X 1-1 1 C 2 H 5 C 2 H 5 C 2 H 5 C 2 H 5 S I oo 1-2 1 C 4 H 9 CH 2 C0 2 M C 4 H 9 CH 2 C0 2 0 0 I 1-3 1 C 5 H 10 CO 2 C 5 H 10 C0 2 M C 2 H 5 C 5 H 10 C0 2 M 0 S 1-4 1 C 5 H 10 CO 2 M C 5 H 10 C0 2 M C 5 H 10 0 2 M C 5 H 10 CO 2 M S T ble I - ' I σ I Table I - Cont'd _L_ _X_ L I C 6 H 5 C 6 H 5 C 6 H 5 0 0 CH 2 C0 2 M C 4 H 9 CH 2 C0 2 M 0 0 1-11 C 5 H 10 C0 2 M C 5 H 1Q C0 2 C 5 H 10 C0 2 M C 5 H 10 C0 2 M S Table I - Cont'd .8 _R_ _R_ 1-12 (CH 2 ) 3 S0 3 M CH 3 CH 2 3 S0 3 M 1-13 C 6 H 5 CH-, C 6 H 5 rυ I 1-14 C 6 H 5 S0 3 M( ) CH 3 C 6 H 5 S0 3 M(p) 1-15 C 6 H 5 S0 3 ( ) CH 3 C 6 H 5 S0 3 M(p) 1-16 C 6 H 5 S0 3 ) C0 2 C 2 H 5 C 6 H 5 S0 3 ) 1-17 C 6 H 5 S0 3 M(p) C0 2 M C 6 H 5 S0 3 ) 1-18 C 6 H 5 (S0 3 2 CH 3 C 6 H 5 S0 3 2 1-19 0=CCH 3 * 2,5-disubstituted In Table I above R, R 1 , R 2 , R 2 ', R 3 , R , R , R , R , R , R , R , R and R 9' , which may be the same or different, are alkyl groups having from 1 to about 10 carbon atoms which may be unsubstituted or substituted or aryl groups having from 6 to about 10 carbon atoms which may be unsubstituted or substituted. Substituents which may be present on the alkyl or aryl groups include carboxylic, ester, ether, ketone or sulfonate; M is as defined above; X and X' are oxygen or sulfur; A is hydrogen or alkyl having from 1 to 3 carbon atoms ; and L and L' are as defined above for R 1 to R9* The following Tables IIA and IIB illustrate examples of merocyanine dyes suitable for use in this invention. The illustrated examples have the general formula: wherein n and Y are as defined above; Z represents the atoms necessary to form a 5- or a 6-membered heterocycle; X is a divalent link illustrated by Group VI elements, by NHR , or by the groups -CH=CH- or -CH 2 ~, -CR--; and R and R represent hydrogen or a hydrocarbon residue having from 1 to about 18 carbon atoms either of which may be further substituted with oxygen, sulfur or nitrogen-containing functions. In order to make these spectrally sensitizing merocyanine dyes bleachable in photographic processing solutions and thus obtain images without stain from residual sensitizing dye, the preferred divalent link X is oxygen and the heterocyclic residue represented by Y is preferably a pyrazolone, isoxozolone, pyrandione, pyrazolidinedione, barbituric or thiobarbituric acid. Tab e HA ve Compound £ 12 ύl n ,14 ,15 II-l H C 2 H 5 1 CH, C 6 H 5 S0 3 M(p) II-2 H C 2 H 5 2 CH, C 6 H 5 S0 3 M II-3 S0 3 M C 2 H 5 2 CH, C 6 H 5 S0 3 M(p) II-4 H C 2 H 5 2 CH, C 6 H 5 NHS0 2 C 6 H 5 (p II-5 H C 2 H 5 2 CH, C 6 H 5 II-6 H C 2 H 5 2 CH-CO-M C 6 H 5 Tahle HE Dve Compound ,15 ,14 ,13 II-7 1 C 2 H 5 C 2 H 5 (CH 2 ) 3 S0 3 Na II-8 2 C 4 H 9 4 H 9 (CH 2 ) 3 S0 3 Na II-9 2 C 5 H 10 C0 2 H C 5 H 1Q C0 2 H (CH 2 3 S0 3 a wherein: is hydrogen or alkyl or from 1 to about 12 carbon atoms which may be substituted; R12, R13 and R14 represent hydrogen or alkyl of from 1 to about 12 carbon atoms which may be substituted; and R is aryl of from 6 to about 10 carbon atoms which may be substituted. Specific examples of compounds of Tables HA and IIB are shown below. ?2 H 5 11-12 C 2 H 5 C 2 E 5 C 2 H 5 Table HI illustrates cyanine dye molecules of the following structure: where n, R , A, X and Z are as described above; A' is hydrogen or R ; Q is a charged group or ion necessary to provide the molecule with charge neutrality, X', Z' and R 10 respectivel ■ yy., can be the same as or different from X, Z or R ,10 In order to minimize stain after processing from residual cyanine sensitizer, it is preferable that in aqueous solutions of approximately pH 2—7, the cyanine dye exhibit a net negative charge. This condition is met when substituents of A, R and Z contain at least two acidic groups with acid dissociation constants pKa <7. Carboxylic and sulfonic acids are typical examples of such groups. In Table III, M has the definition as noted above. Table III Dve Compound C 3 H 6 S0 3 - C 3 H 6 S0 3 M O cπ cπ The following examples with chemically sensitized emulsions demonstrate the unexpectedly advantageous performance achieved by the combination of high proton and high silver ion concentrations in silver halide environment, both in the absence and presence of spectral sensitizers. Unless otherwise indicated, all parts, percents and ratios are by weight. Example 1 A sulfur-sensitized silver chlorobromide emulsion (88 mole 7. bromide) consisting of cubo—octahedral grains having a mean dimension of 0.35 microns and containing 47β by weight of ossein gelatin (IP 4.9) was used at pH 3.3. The pAg was adjusted to the value indicated below in Parts I and II at 40 C C. For cases where spectral sensitizers were evaluated, they were added after pH/pAg adjustments and then digested in the emulsion for at least 10 minutes at 55 β C before coating at a weight of about 11 kg/mole Ag with coverages of about 1176 2 mg Ag and 4306 mg gelatin per m . The dry coating was exposed either by a spectral sensitometer or by a fixed light source from which spectral regions were selected with a blue filter (Wratten #36B, #38A), a green filter (Wratten #16B, #61), a red filter (Wratten #23A) or, as a Minus Blue source, a yellow filter (Wratten #16). The coated films were processed with development being carried out with KODAK Developer DK-50 or with an Elon-Ascorbic acid formulation. Example 1. Part I Silver Halide Dispersions of Example 1 at pH 3.3 Without Spectral Sensitizer *These speed values as well as those noted in Example 1, Part II and in Examples 2 and 3 are normalized with respect to blue speed of the emulsion of Example 1 in the absence of spectral sensitizer. Example 1. Part II Silver Halide Dispersions of Example 1 at pH 3.3 With 0.4 mmole Oxonol 1-14 Dye/Mole Silver Results of Example I. Part I and II The speeds listed make it apparent that in the chemically sensitized silver chlorobromide emulsion, in the absence of any spectral sensitizer, blue speed is enhanced at pH 3.3 with growing availability of free silver ions. The indicated speed increase approaches a factor of 2 without significant contrast change and without formation of fog. Part II also shows a substantial gain in blue speed with decreasing pAg in the presence of the oxonol dye 1-14. However, the Minus Blue speed response is increased by many decades in the same pH range. Moreover, the sensitizer 1—14 is decolorized during processing. Accordingly, the coatings of Part II exhibited no stain from residual sensitizing dye upon completion of the process cycle. Example 2 One part of the emulsion described above in Example 1 was adjusted at 40°C to a pH of 6 and to a pAg of 7.3 (Condition A). Another part of the same emulsion was similarly adjusted to a pH of 3 and to a pAg of 4.3 (Condition B). These silver halide emulsions were then examined with and without 0.4 mmole of an oxonol dye per mole of silver as indicated in the following table. The indicated oxonol dyes provide no significant spectral response at conventional pH and pAg values. However, under a low pH and low pAg conditions in accordance with this invention, the same dyes yield appreciably improved emulsion response in the Minus Blue spectral region. Example 3 A silver halide dispersion of the emulsion of Example 1 was coated on cellulose acetate support at pH 3.3 with 0.4 mmole of merocyanine dye II-2 per mole of silver. The pAg values of the coatings were varied between 7.3 and 3.7. After processing as described in Example 1 results were as follows: Emulsion Relative Speed* _ Contrast p g Blue Minus Blue Blue Minus Blue I&&. 7.3 100 0 03 6.2 132 0 04 5.6 138 0 04 5.2 145 0, 03 4.7 151 0.04 4.1 159 0.03 3.7 170 0.04 *These speed values are normalized with respect to the blue speed of the emulsion coated at pAg 7.3. The data demonstrate that when excess soluble halide ions (high pAg) is decreased and an excess of soluble silver ions is introduced (low pAg), the emulsion's sensitivity is increased at essentially constant contrast without any fog production. Whereas increasing the silver ion activity in the emulsion containing merocyanine dye II-2 enhances the intrinsic blue sensitivity by a factor smaller than two, in the same pAg range the emulsion's response in the spectrally sensitized (Minus Blue) region is increased more than 10-fold. After processing, the coatings contained no stain from merocyanine dye II-2. Example 4 Silver halide dispersions of the emulsion of Example I were coated with 0.4 mmole/mole Ag of the indicated merocyanine dyes. Emulsion Relative Speed (2) Cond tion (1) Dye Blue Green Minus Blue Fog A 0.04 same 0.04 same 0.04 B 0.04 same 0.04 same 0.04 'Emulsion conditions are described in Example 2. 'These speed values are normalized with respect to blue speed of the emulsion of Condition A in the absence of spectral sensitizer. These data demonstrate that the low pH and low pAg environment of Condition B (Invention) improve the sensitivity of a chemically sensitized emulsion without formation of fog. This effect is particularly obvious with merocyanine II—3. Even merocyanine 11—11, which contains a thione group and which is already a good spectral sensitizer in the conventional environment of Condition A, exhibits improved speeds in the acidic high silver ion environment of Condition B (Invention). Thus it is apparent that the presence of a dye's thione group, which might interact with excess silver ions, does not interfere with the beneficial effects of this invention. Example 5 Silver halide dispersions of the emulsion of Example II were coated with 0.2 mmole/mole Ag of the indicated cyanine dyes. Emulsion Relative Speeds (2) Condition^ Dye Blue Minus Blue Fog (1) Emulsion conditions are described in Example 2 (2)S ( peed values are normalized with respect to blue speed of the emulsion of Condition A in the absence of spectral sensitizer. Sxamplt This example is the same as Example 5, above, except that 0.4 mmole of the indicated cyanine dye was used per mole of silver. Emulsion Relative Speeds* Condition Dye Blue Red Minus Blue *Normalized speed as explained in Example 3. Data from Examples 5 and 6 show that with chemically sensitized emulsions without fog production, cyanine dyes provide superior sensitivity in the blue and in the spectrally sensitized region when the emulsion medium is changed from a conven- tional environment (Condition A) to the acidic high silver ion environment of the invention (Condition B). Furthermore, since 111-16 is a blue—sensitizing cationic dye, III—8 is a green—sensitizing anionic dye and 111-17 represents a red-sensitizing zwitterionic dye, the evidence in these Examples demonstrate that this invention benefits all three cyanine charge—classes and encompasses the whole visible spectrum. The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

Claims: Claims : 1. A photographic recording material comprising a support and a photosensitive chemically sensitized silver halide emulsion layer which has a pH value between about 2 to about 5 and a pAg value between about 1 to about 4.7. 2. The recording material according to claim 1 wherein the pH is from about 2 to about 4 and the pAg is from about 3 to about 4.7. 3. The recording material according to claim 2 wherein the chemical sensitizing agent is sulfur, gold or a mixture thereof. 4. The recording material according to claim 1 which also comprises a natural or synthetic hydrophilic colloid. 5. A photographic recording material according to claim 5 wherein the hydrophilic colloid is gelatin. 6. The photographic recording material according to claim 1 wherein the silver halide is one or more of silver chloride, silver bromide, silver iodide, silver chlorobromide, silver chloroiodide, silver bromoiodide or silver chlorobromoiodide. 7. The recording material of claim 1 which also comprises a sensitizing dye. 8. The recording material of claim 7 wherein the dye is present within the range of about 0.05 to 2.0 mmole/mole silver. 9. The recording material of claim 7 wherein the dye is an oxonol dye. 10. The recording material of claim 7 wherein the dye is a merocyanine dye. 11. The recording material of claim 7 wherein the dye is a cyanine dye. 12. A photographic recording material comprising a support and a photosensitive chemically sensitized silver halide emulsion layer which contains an excess of more than 0.01 millimolar soluble, dissociated acid and more than 0.01 millimolar soluble, dissociated silver salt.

Inventors: EVANS FRANCIS JOHN, HERZ ARTHUR, EVANS, FRANCIS, JOHN, HERZ, ARTHUR
Applicants: EASTMAN KODAK CO, EASTMAN KODAK COMPANY
Application year: 1990
Main classification: G03C1
IPC codes: G03C1