US 3650760 A
Alkoxy mercaptophenols are used in photographic silver halide elements and emulsions in order to stabilize said elements and emulsions against fog.
Description (OCR text may contain errors)
United States Patent Gates, Jr. et al.
[ 51 Mar. 21, 1972  ALKOXY MERCAPTOPHENOLS AS PHOTOGRAPHIC ADDENDA FOR PHOTOGRAPHIC ELEMENTS  Inventors: John W. Gates, Jr.; Dorothy J. Beavers, both of Rochester, NY.
Eastman Kodak Company, Rochester,
 Filed: Sept. 17, 1969 211 Appl. No.: 858,857
 US. Cl ..96/109, 96/66.4, 260/609, 260/619  Int. Cl ..G03c l/34  Field of Search ..96/109, 66, 66.4, 66.5; 260/609, 619, 624, 625
Primary Examiner-John T. Goolkasian Assistant Examiner-M. E. McCamish Att0rneyWilliam H. J. Kline, Bernard D. Wiese and Herbert W. Mylius  ABSTRACT Alkoxy mercaptophenols are used in photographic silver halide elements and emulsions in order to stabilize said elements and emulsions against fog.
15 Claims, No Drawings ALKOXY MERCAPTOPHENOLS AS PHOTOGRAPHIC ADDENDA FOR PHOTOGRAPHIC ELEMENTS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention is related to photography. In one aspect, this invention relates to the stabilization of photographic silver halide elements and emulsions and the reduction of spontaneous fog without adversely affecting the photographic sensitivity of said silver halide elements and emulsions.
2. Description of the Prior Art It is well-known that photographic silver halide on storage tends to lose sensitivity and to become spontaneously developable without exposure to light. The detectable amount of silver salt reduced during development of those areas where there is no exposure is commonly referred to as fog, and more specifically chemical fog where it is desirable to distinguish between it and the effects of accidental exposure to radiation.
Fog depends upon both the particular emulsion and the condition of development. For a given emulsion, fog increases with the degree of development. At constant development conditions, fog generally increases with the temperature, time and relative humidity of storage conditions.
It is known that certain mercaptans, particularly those compounds having mercapto substitution on a heterocyclic ring, have an antifoggant and stabilizing effect when incorporated in photographic silver halide emulsions. For example, U.S. Pat. No. 2,819,965 describes the use of s-triazines having a carboxymethylmercapto substituent, and British Pat. No. 819,370 describes mercapto-l,2,4-triazines. Thiohydroquim ones such as those disclosed in U.S. Pat. No. 3,379,529 issued Apr. 23, 1968, are known to release mercaptan fragmentary elements, thereby inhibiting incubation fog.
Many of the prior art compounds are objectionable either because they are not effective antifoggants unless used in combination with other materials, while others, such as the thiohydroquinones, have a desensitizing effect at concentrations wherein said compounds are most effective as antifoggants. It is therefore desirable to obtain compounds which are effective antifoggants for photographic silver halides without substantially reducing sensitivity.
SUMMARY Q EINV TIQ ZLW.
In accordance with this invention, it has been found that significantly enhanced stability against chemical fog in photographic silver halides can be obtained while not seriously effecting a decrease in their photographic sensitivity. The enhanced stability and control over chemical fog is obtained through the use of compounds not known, heretofore, to have antifoggant properties.
Hence, it is the object, according to one aspect of this invention, to provide stabilized photographic silver halides.
It is another aspect of this invention to provide a method for stabilizing silver halides.
It is yet a further object to stabilize silver halide emulsions and elements without adversely affecting, to any substantial degree, their photographic sensitivity.
It is a further object of this invention to provide photographic silver halide layers which are stabilized with a particular group of phenol derivatives.
Other objects will become apparent from examination and consideration of the specification and claims.
DESCRIPTION OF THE PREFERRED EMBODIMENTS It has been discovered that alkoxy thiophenols are excellent stabilizers and fog inhibitors of photographic silver halides and that the desirable antifoggant properties are not accompanied by the undesirable effect of causing a serious reduction in photographic sensitivity. The alkoxy phenols employed in the practice of this invention have the general formula:
wherein each R is alkyl such as methyl, ethyl and propyl, aryl such as phenyl, halide such as chlorine, bromine and iodine, nitro, carboxy, alkoxycarbonyl such as methoxycarbonyl, ethoxy-carbonyl and propoxycarbonyl, or alkoxy such as methoxy, ethoxy, propoxy and butoxy, and at least one R is alkoxy, n is 1-4 and X is H, alkyl or heterocyclic such as 5- and 6-membered nitrogen, nitrogen and sulfur or nitrogen and oxygen containing heterocyclic rings, preferably nitrogen or sulfur containing rings. Illustrative of the R groups which can be substituted on the phenolic ring are those containing from one to 10 carbon atoms or more, and preferably one to six carbon atoms. Typical of the heterocyclic radicals are tetraazaindenes, tetrazoles, benzothiazoles and benzoxazoles; however, the heterocyclics are not limited to this list since any heterocyclic, such as the 5- and 6-membered rings containing nitrogen, sulfur or oxygen, which does not adversely affect the silver halide emulsion can be substituted for X. (R), should not be understood to represent a polymeric radical but should be understood to represent the number of sites of the phenolic ring which can be substituted. It should further be understood that when n is greater than 1 the radicals represented by R need not be identical.
Examples of the alkoxy mercaptophenols employed in this invention are:
2-mercapto-3,6-dimethyl-4-methoxyphenol, 2-mercapto-3,5,6-trimethyl-4-methoxyphenol, 2-methyl-4-methoxy-6-[ l-phenyl-5-tetrazolythio]phenol, 2-phenyl-4-methoxy-5-[ l-phenyl-5-tetrazolylthio]phenol, 4-methoxy-2-[2-benzothiozolylthio]phenol, and 2-[2-benzoxazolylthio]-4-methoxyphenol.
The preparation of these compounds are well-known in the art and can conveniently be prepared by methods described in Chapman et al., J.,Org. Chem., 30, L520 (1965).
The concentration of the stabilizing compounds can vary considerably depending on various factors such as: the effect desired, silver content of a layer, the nature of the particular silver halide, the degree of ripening, the location of the stabilizer in relation to the silver halide, the particular stabilizer, etc. In general, a concentration in the range of about 0.001 gram to about 10 grams of stabilizer per mole of silver halide is useful. A preferred range is from about 0.0] gram to about 0.5 gram of stabilizer per mole of silver halide. In accordance with the invention, one may use the higher concentrations without including a reduction in sensitivity of the photographic silver halide emulsion. The optimum concentration of stabilizer for a particular photographic system can easily be determined by techniques well-known in the art.
The stabilizing addenda can be added in a variety of stages in the preparation of the photographic system. The stabilizers may be incorporated directly into silver halide elements and emulsions, preferably before the final digestion operation in the case of emulsions and after the silver halide grains are substantially in their final size and shape. The addenda may be added to a layer adjacent to the silver halide layer. The solvents in which the stabilizers may be dissolved are restricted to those that are not harmful to the silver halide and in accordance with the general practice organic solvents and their diluents are preferred.
The light-sensitive silver halide photographic element comprising the antifoggants of this invention can contain addenda such as gelatin plasticizers, coating aids and hardeners such as the aldehyde-type hardeners, e.g., formaldehyde, mucochloric acid, glutaraldehyde bis(sodium bisulfite), maleic dialdehyde and aziridines, dioxane derivatives, vinylsulfonylethers and oxypolysaccharides. Sensitizing dyes useful in sensitizing such emulsions are described, for example, in U.S. Pats. Nos. 2,526,632 of Brooker and White issued Oct. 24, 1950, and 2,503,776 of Sprague issued Apr. 11, 1950. Spectral sensitizers which can be used are the cyanines, merocyanincs, complex (trinuclear) cyanines, complex (trinuclear) merocyanines, styrls and hemicyanines. Developing agents can also be incorporated into the emulsion if desired or can be contained in a separate underlayer.
The stabilizing addenda employed in the practice of this invention can be used in various kinds of photographic emulsions. In addition to being useful in orthochromatic, panchromatic and infrared emulsions, they are also useful in X-ray and other non-spectrally sensitized emulsions. They can be added to the emulsions before, simultaneously or after any spectrally sensitizing dyes that may be used. They are particularly effective in sulfur and gold sensitized silver halide emulsions. Various silver salts can be used as sensitive salts including, for example, silver bromide, silver iodide, silver chloride, silver chlorobromide, silver bromoiodide or silver chloroiodide, and the like. The silver halides can be those which form latent images predominantly on the surface of the silver halide grams or those which form latent images inside the silver halide crystals such as described in U.S. Pat. No. 2,592,250 of Davey and Knott issued Apr. 8, 1952. The subject addenda can be used in emulsions intended for color photography, for example, emulsions containing color-forming couplers or emulsions to be developed by solutions containing couplers or other color-generating materials; emulsions of the mixed-packet type such as described in U.S. Pat. No. 2,698,794 of Godowsky issued Jan. 4, 1955; in silver dye-bleach systems; and emulsions of the mixed-grain type such as described in U.S. Pat. No. 2,592,243 of Carrol and Hanson issued Apr. 8, 1952.
in the preparation of the silver halide dispersions employed for preparing silver halide emulsions, there can be employed as the dispersing agent, or binders as they are known in the art, for the silver halide in its preparation, gelatin or some other colloidal material such as modified gelatin, colloidal albumin, cellulose derivative, a polyvinyl compound, acrylamide polymer, etc., although gelatin is preferred. Mixtures of these binding agents can also be used. The binding agents for the emulsion layer of the photographic element can also contain dispersed polymerized vinyl compounds. Such compounds are disclosed, for example, in U.S. Pats. Nos. 3,142,568 of Nottorf issued July 28, 1964; 3,193,386 ofWhite issued July 6, 1955; 3,062,674 of Houck, Smith and Yudelson issued Nov. 6, 1962; and 3,220,844 of Youck, Smith and Yudelson issued Nov. 30,1965; and include the water-insoluble polymers of alkyl acrylates and methacrylates, acrylic acid, sulfoalkyl acrylates or methacrylates and the like.
The photographic emulsions stabilized according to this invention can be coated on a wide variety of supports. Typical supports include those generally employed for photographic elements, as exemplified by cellulose nitrate film, cellulose ester film, poly(vinyl acetal) film, polystyrene film, poly( ethylene terephthalate) film and related films of resinous materials as well as glass, paper, metal, wood and the like. Supports, such as paper, that are coated with alpha-olefin polymers, particularly polymers of alpha-olefins containing two or more carbon atoms as, for example, polyethylene, polypropylene, ethylene-butene copolymers and the like, can be employed.
Photographic layers comprising the antifoggants can also contain speed-increasing compounds such as quaternary ammonium compounds, polyethylene glycols or thioethers. Frequently, useful effects can be obtained by adding the aforementioned speed-increasing compounds to the photographic developer solutions instead of, or in addition to, the photographic layer.
Silver halide emulsions containing the antifoggants of the instant invention can be sensitized using any of the wellknown techniques in emulsion making, for example, by digesting with naturally active gelatin or various sulfur, selenium, tellurium compounds and/or gold compounds. The emulsions can also be sensitized with salts of noble metals of Group VIII of the Periodic Table which have an atomic weight greater than 100.
Silver halide emulsions containing the antifoggants of the invention can be used in diffusion transfer processes which utilize the undeveloped silver halide in nonimage areas of the negative to form a positive by dissolving the undeveloped silver halide and precipitating it on a receiving layer in close proximity to the original silver halide emulsion layer. Such processes are described in U.S. Pats. Nos. 2,352,014 of Rott issued June 20, 1944; 2,543,181 of Land issued Feb. 27, 1951; and 3,020,155 of Yackel, Yutzy, Foster and Rasch issued Feb. 6, 1962. The emulsions can also be used in diffusion transfer color processes which utilize a diffusion transfer of an imagewise distribution of developer, coupler or dye from a light-sensitive layer to a second layer while the two layers are in close proximity to one another.
The following examples are included for a further understanding of the invention EXAMPLES l-lX Compounds employed in this invention, listed in Table l, are incorporated, at concentrations listed in said Table, into separate samples of high-speed gelatino photographic silver bromoiodide emulsion. Each of the emulsions are coated on a cellulose acetate film support at a coverage of 459 mg. of silver and 1,040 mg. of gelatin per square foot. A sample of each film coating is exposed on an Eastman 1B sensitometer, processed for 5 minutes in Kodak DK-SO Developer, fixed, washed and dried. Separate samples of the film coating are incubated for 2 weeks at 120 F. and 50 percent relative humidity before exposure and development. The results of the sensitometric tests on the fresh and incubated samples are summarized in Table l.
TABLE I 2-week incubation at 120 F. and 50% Fresh test relative humidity Stabilizing Rela- Relaaddenda, (g./mole tive tlve of Ag) speed Gamma Fog speed Gamma Fog (1) A (0.009) 87 1.37 .14 91 1.30 .20 (2) B (0.009) 69 1.37 .15 76 1.27 .21 (3) C (0.03)... 100 1.33 .14 83 1.28 .24 (4) D (0.15). 1.23 .23 76 1.17 .33 (5) E (0.15). 73 1.17 .14 74 1.15 .19 (6) F (0.09). 100 1. 45 .16 89 1.25 .31 (7) G (0.03). 1.15 .16 82 1.00 .29 (8) H (0.009).-
82 1.40 .14 63 1.12 .29 (9) None 1.30 .16 57 .90 .68
C: 2-Inercapt0-3,6-dlmethyl-4-meth0xypheno D: 2-methyl4-methoxy-6-[i-phenyl-5-tetrazolylthio]phenol.
The table shows that the compounds employed in this invention are highly useful as fog inhibitors with respect to silver halide layers. The stabilization and fog inhibition is accomplished without seriously afi'ecting the photographic sensitivity of the emulsion. 1n the case of the incubated samples which incorporate a compound employed in this invention; it should be noted that gamma and speed are superior to that sample which does not contain a fog inhibitor.
Similar results are obtained as in Examples l-lll upon adding the stabilizers of this invention to orthochromatically sensitized gelatino silver bromoiodide emulsions and emulsions sensitized with sulfur and gold.
EXAMPLES X-Xll Film strips are prepared as in Examples l-lX; however, sulfur-containing hydroquinones are substituted for the antifoggants employed in this invention. The strips are exposed and processed as in Examples I-lX. The results are summarized in Table II.
TABLE II 2-week incubation at 120 F. and 50% Fresh test relative humidity Rela- Rela- Stabilizer, gJmole tlve tlve of Ag speed Gamma Fog speed Gamma Fog None 100 1.29 .16 57 .91 .68 (11) I (0.0009) 16 1.25 .31 26 1.15 .30 (12) J (0.3) 46 1.27 .07 73 1.08 .12
I: Z-mercaptohydroquinone. J: 2,5-dlmethyl-3-[1-pheny1-5-tetrazolylthlolhydroqulnone.
Examples 11 and 12 show that, although one may obtain excellent results with respect to fog inhibition when incorporating mercaptohydroquinones in silver halide emulsions, such results are accompanied by a serious reduction in the sensitivity of the film.
This invention, it is seen, provides photographic silver halide emulsions, stabilized with mercapto alkoxyphenols, said stabilizers not causing any deleterious efi'ect upon speed or sensitivity of the film. The mercapto heterocyclic derivatives such as those of Examples 4-6 should also be valuable as development restrainers when treated with alkali.
The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.
1. A photographic element comprising a support, a silver halide layer and a compound having the formula:
(Rln 0 wherein R is alkyl, aryl, halide, nitro, carboxy, alkoxycarbonyl or alkoxy, n is 1-4 and X is H, alkyl or heterocyclic and wherein at least one R is alkoxy.
2. A photographic element as in claim 1 wherein said heterocyclic radical is a nitrogen-containing radical.
3. A photographic element as in claim 2 wherein said heterocyclic contains nitrogen and oxygen.
4. A photographic element as in claim 2 wherein said heterocyclic contains nitrogen and sulfur.
5. A photographic element as in claim 1 wherein said alkoxy mercaptophenol is present at a stabilizing concentration of from about 0.001 to about 10 grams per mole of silver halide.
6. A photographic silver halide emulsion comprising a stabilizing compound having the formula:
wherein R is alkyl, halide, nitro, carboxy, alkoxycarbonyl or alkoxy, n is 14 and X is H, alkyl or heterocyclic and wherein at least one R is alkoxy.
7. A photographic emulsion as in claim 6 wherein said stabilizer is present at a concentration of from about 0.01 to about 0.5 gram per mole of silver halide.
8. A photographic emulsion as in claim 6 wherein each R contains from 1 to 10 carbon atoms.
9. A photographic emulsion as in claim 6 wherein said stabilizer is 2-hydroxy-4-methoxythiophenol.
10. A photographic emulsion as in claim 6 wherein said stabilizer is 2-mercapto-3,6-dimethyl-4-methoxyphenol.
11. A photographic emulsion as in claim 6 wherein said stabilizer is l-phenyl-3-methoxy-5-[l-phenyl-5-tetrazolylthio]- phenol.
12. A photographic emulsion as in claim 6 wherein said stabilizer is 4-methoxy-2-[ 2-benzothiozolylthiolphenol.
13. A photographic emulsion as in claim 6 wherein said stabilizer is 2-methyl-4-methoxy-6-[l-phenyl-5-tetrazolylthio1- henol. p 14. A photographic emulsion as in claim 6 wherein said silver halide emulsion is a high-speed gelatino silver bromoiodide emulsion.
15. A method for stabilizing photographic silver halide against fog which comprises contacting said silver halide with a stabilizing compound having a formula according to claim 6.