Alkaline black-and-white developer for silver halide photographic material

Abstract: The present invention relates to an alkaline aqueous black-and-white photographic developer composition comprising: (1) at least one black-and-white developing agent, (2) at least one black-and-white auxiliary developing agent, (3) at least one antifoggant, (4) at least one sequestering agent, (5) a sulfite antioxidant, (6) at least one buffering agent, and (7) a tone modifying agent, wherein said tone modifying agent is an alkali metal or ammonium salt of a polythionic acid.

Description: FIELD OF THE INVENTION The present invention relates to an alkaline black-and-white developer for processing a silver halide photographic material and, more particularly, to an alkaline black-and-white developer for processing a silver halide radiographic material in an automatic processor. The developer provides improved color tone, stability to air oxidation and excellent photographic properties. BACKGROUND OF THE ART The color tone of developed silver is a matter of great concern for photographic film makers. The color tone of black and white developed images not only depends on the photographic materials used but also on the grain size, grain thickness, grain structure, grain surface and reflecting power of the developed silver. It is well known that the warmest tones (yellowish, brownish) can give an unfavorable impression to the observer of the resulting picture image. For this reason a trade requirement of photographic films, in particular for medical X-ray films, is a cold tone (blue-black) in order to make diagnoses easier. The idea of changing the color tone of a black-and-white image is almost as old as the process of making a black-and-white print itself. It is known in the art that compounds called toners may be added to emulsion preparations to produce a colder or blacker image after development. References can be found in US Patent Nos. 4,818,675, 4,201,582, 3,695,880, and 2,512,721, in EP Appl. 271,309, in JP Patent Laid-Open 61/170,739. It is also known that other chemical ingredients for blue-black image formation can be used with a separate toning bath and or activator bath. Reference can be found in US Patent Nos. 4,201,582, 3,622,332, 2,192,891 and 2,156,626, Research Disclosure Item 29963, March 1989; Photographic Science & Engineering, Vol 7, No. 2 "Observation on fine structure of developed silver in the presence of added tone modifiers"; C.E.K. Mees, The Theory of the Photographic Process , 1st Edition, p. 568, The Macmillan Co. ,New York; and A. Rott & E. Weide, Photographic silver halide diffusion processes, pp 61-65, 1972. The silver image commonly formed during normal development is black, although some silver grains may appear to have warm tone by reflected light. This difference is principally due to a difference in size and in structure of the developed metallic silver particles. The two pathways to the reduction of silver ions are physical and chemical development. In physical development, which involves a homogeneous chemical reaction, the developing agent reduces a soluble silver salt that is added (or has been make soluble from the silver halide emulsion layer) to the developer, and the formed metallic silver is deposited on the latent image nuclei, resulting in a developed image consisting of compact, rounded particles. In chemical or direct development, which involves a heterogeneous chemical reaction, the silver halide of the grain that has been image-wise exposed is reduced in situ, resulting in a developed image consisting of particles of filamentary structure. The tight packing of chemically developed filamentary silver ensures the spectral neutrality of this type of silver image and the black color thus appears to be due to multiple scattering and absorption of light. James and Vanselow, in Photographic Science & Engineering, Vol. 1 No. 3, January 1958, "The Influence of the Development Mechanism on the Color and Morphology of Developed Silver" showed that the greater the extent of physical development, the less black was the silver image, the color usually passing to a brownish hue. The presence of silver halide solvents can dissolve some of the silver halide of the emulsion with the result that the image is formed partly by physical development and is affected by warm tones. In order to reduce as low as possible this physical development it is known to use these compounds in the lowest quantities. Now, we have surprisingly found that the use of a metal or ammonium salt of a tetrathionic acid in an amount of 0.4 to 5 g per liter dramatically improves the blue-black tone of developed silver and the speed of the black-and-white photographic film. SUMMARY OF THE INVENTION The present invention relates to a developer composition comprising, (1) at least one black-and-white developing agent, (2) at least one black-and-white auxiliary developing agent, (3) at least one antifoggant, (4) at least one sequestering agent, (5) a sulfite antioxidant, (6) at least one buffering agent, and (7) a tone modifying agent, wherein said tone modifying agent is an alkali metal or ammonium salt of a tetrathionic acid, and said tone modifying agent is added to said developer composition in an amount in the range of from 0.4 to 5 grams per liter.. This developer provides an improvement of both the sensitometric characteristics and the silver blackness of the photographic image obtained from a silver halide photographic material. DETAILED DESCRIPTION OF THE INVENTION Accordingly, the present invention relates to a developer composition comprising, (1) at least one black-and-white developing agent, (2) at least one black-and-white auxiliary developing agent, (3) at least one antifoggant, (4) at least one sequestering agent, (5) a sulfite antioxidant, (6) at least one buffering agent, and (7) a tone modifying agent, wherein said tone modifying agent is an alkali metal or ammonium salt of a tetrathionic acid, and said tone modifying agent is added to said developer composition in an amount in the range of from 0.4 to 5 grams per liter.. The components of the alkaline aqueous black-and-white photographic developer to be used in the present invention will hereinafter be explained in detail. The tone modifying agents according to the present invention are tetrathionates of alkali metals or ammonium. Alkali metals are represented, for example, by potassium. Preferably, the tone modifying agent may be added in an amount in the range of from 0.5 to 2.5 grams per liter. The developing agents for silver halide photographic elements suitable for the purposes of the present invention include hydroquinone and substituted hydroquinones (e.g. t-butylhydroquinone, methylhydroquinone, dimethylhydroquinone, chlorohydroquinone, dichlorohydroquinone, bromohydro- quinone, 1,4-dihydroxynaphthalene, methoxyhydroquinone, ethoxyhydroquinone, etc.). Hydroquinone, however, is preferred. Said silver halide developing agents are generally used in an amount from about 2 to 100 grams per liter, preferably 6 to 50 grams per liter of the ready-to-use developer composition. Such developing agents are used in combination with auxiliary developing agents which show a superadditive affect, such as p-aminophenol and substituted p-aminophenol (e.g. N-methyl-p-aminophenol or metol and 2,4-diaminophenol) and pyrazolidones (e.g. 1-phenyl-3-pyrazolidone or phenidone) and substituted pyrazolidones (e.g., 4-methyl-1-phenyl-3-pyrazolidone, 4-hydroxymethyl-4-methyl-1--phenyl-3-pirazolidone, and 4,4'-dimethyl-1-phenyl-3-pyrazolidone or dimezone). These auxiliary developing agents are generally used in an amount from about 0.1 to 20, preferably 0.5 to 5 grams per liter of ready-to-use developer composition. The antifogging agents, known in the art to eliminate fog on the developed photographic silver halide films, useful in the developer composition of this invention include derivatives of benzimidazole, benzotriazole, tetrazole, indazole, thiazole, etc. Preferably, according to the present invention, the developer comprises a combination of benzotriazole-, indazole- and mercaptoazole-type antifoggants, more preferably a combination of 5-methylbenzotriazole, 5-nitroindazole and 1-phenyl-5-mercaptotetrazole. Other examples of mercaptoazoles are described in US Pat. No. 3,576,633, and other examples of indazole type antifoggants are described in US Pat. No. 2,271,229. More preferably, particular mixtures of these antifogging agents are useful to assure low fog levels; such preferred mixtures include mixtures of 5-nitroindazole and benzimidazole nitrate, 5-nitrobenzotriazole and 1-phenyl-1-H-tetrazole-5-thiol and 5-methylbenzotriazole and 1-phenyl-1-H-tetrazole-5-thiol. The most preferred combination is 5-methylbenzotriazole and 1-phenyl-1-H-tetrazole-5-thiol. These mixtures are used in a total amount of from about 0.01 to 5, preferably 0.02 to 3 grams per liter of the ready-to-use developer composition. Of course optimum quantities of each compound and proportion can be found by the skilled in the art to respond to specific technical needs. In particular, 5-methylbenzotriazoles have been found to give the best results when used in mixture with 1-phenyl-1-H-tetrazole-5-thiol, the latter being present in minor amount with respect to the weight of the total mixture, in a percent of less than 20%, preferably less than 10%. The developer, comprising said antifoggant combination, is advantageously used in a continous transport processing machine at high temperature processing (higher than 30°C) for processing of X- ray materials without changes in the sensitometric properties of the material, mainly without a substantial increase of the fog of the developed material. The sequestering agents used in the present invention are sequestering agents known in the art such as, for example, aminopolycarboxylic acids (ethylenediaminotetraacetic acid, diethylenetriaminepentaacetic acid, nitrilotriacetic acid, diaminopropanoltetraacetic acid, etc.), aminopolyphosphonic acids (methylaminophosphonic acid, phosphonic acids described in Research Disclosure 18837 of December 1979, phosphonic acids described in US Pat. No. 4,596,764, etc.), cyclicaminomethane diphosphonic acids (as described in EP Appl. No. 286,874), polyphosphate compounds (sodium hexametaphosphate, etc.), α-hydroxycarboxylic acid compounds (lactic acid, tartaric acid, etc.), dicarboxylic acid compounds (malonic acid, etc.), α-ketocarboxylic acid compounds (pyruvic acid, etc.), alkanolamine compounds (diethanolamine, etc.), etc. In a particular embodiment, said cyclicaminomethane diphosphonic acid compounds correspond to the following formula wherein R 1 , R 2 , and R 3 , equal or different, each represents a hydrogen atom or a PO 3 M'M'' group, wherein M' and M'' represent a hydrogen atom, an alkali metal such as Li, Na or K or a quaternary ammonium group such as ammonium, pyridinium, triethanolammonium or triethylammonium, and Q represents the atoms or chemical bonds necessary to complete a 3- to 6-membered ring such as aziridino, pyrrolidino, imidazolidino, piperidino, isoindolino or morpholino, with the proviso that at least two of R 1 , R 2 , and R 3 substituents represent a PO 3 M'M'' group. Typical examples of sequestering agents within the general formula above are: The above sequestering agents can be used alone or in combination each other. More preferably, particular mixtures of these sequestering agents are useful to assure strong resistence to air oxidation; such preferred mixtures include mixtures of aminopolycarboxylic acids and cyclicaminomethane diphosphonic acids (according to formula (I) above). Said sequestering agents can be advantageously used in a total amounts of from about 1 to about 60 grams per liter, preferably of from about 2 to about 30 grams per liter of ready-to-use developer. Of course optimum quantities of each compound and proportion can be found by the skilled in the art to respond to specific technical needs. The sequestering agents incorporated into the black-and-white developer of the present invention have been found to increase the stability of the developer over a long period of time. The term "sulfite antioxidants", is meant those compounds known in the art as capable of generating sulfite ions (SO 3 -- ) in aqueous solutions and include sulfites, bisulfites, metabisulfites (1 mole of metabisulfite forming 2 moles of bisulfite in aqueous solution) and aldehyde bisulfite adducts. Examples of sulfites, bisulfites, and metabisulfites include sodium sulfite, sodium bisulfite, sodium metabisulfite, potassium sulfite, potassium bisulfite, potassium metabisulfite and ammonium metabisulfite. The amount of the total sulfite ions is preferably not less than 0.05 moles, more preferably 0.1 to 1.25 moles, and most preferably 0.3 to 0.9 moles, per liter of developer. The amount of the sulfite ions with respect to the hydroquinone preferably exceeds a molar ratio of 2.5:1 and, more preferably, is between 2.5:1 to 4:1. The developer in accordance with the present invention further includes a buffer (e.g., carbonic acid salts, phosphoric acid salts, polyphosphates, metaborates, boric acid and boric acid salts). The amount of the buffer with respect to the sulfite preferably exceeds a molar ratio of 0.5:1 and, more preferably, is between 1:1 to 2:1. In the developer composition there are used inorganic alkaline agents to obtain the preferred pH which is usually higher than 10. Said inorganic alkaline agents include KOH, NaOH, LiOH, sodium and potassium carbonate, etc. Other adjuvants well known to the skilled in the art of developer formulation may be added to the developer of the present invention. These include restrainers, such as the soluble halides (e.g., KBr), solvents (e.g., polyethylene glycols and esters thereof), development accelerators (e.g., polyethylene glycols and pyrimidinium compounds), preservatives, surface active agents, and the like. The developer of the invention is prepared by dissolving the ingredients in water and adjusting the pH to the desired value. The pH value of the developer of the present invention is comprised in the range of from 9 to 12, more preferably of from 10 to 11. The developer may also be prepared in a concentrated form and then diluted to a working strength just prior to use. The developer may be prepared in two or more concentrated parts to be combined and diluted with water to the desired strength and placed in the developing tank of the automatic processing machine. The developer of the present invention is particularly useful when processing is carried out in an automatic processing machines. Automatic processing machines may be of the type described in US Pat. No. 3,545,971, such as an "X-OMAT Processor" made by Eastman Kodak Company, of the series of "TRIMATIC" Processors made by 3M Company and of the type of "Model RK" made by Fuji Photo Film Company. The developing temperature and the developing time are in relation to each other and are dependant on the total processing time. In general, they are about 20°C to 50°C, and 10 seconds to 120 seconds, respectively. After development in the developer of the present invention, the silver halide material is fixed, preferably in an acid fixer, and washed and dried in the usual manner. In the automatic processing machine, these steps are determined by the machine. The silver halide photographic materials which can be used in the present invention comprise a support and at least one silver halide emulsion layer coated on the support. The silver halide emulsion layer may be coated on one side of the support or on both sides thereof. The silver halide photographic element can comprise other non light-sensitive layers, such as backing layers, antihalation layers, interlayers, filter layers, protective layers. The silver halide emulsion comprises silver halide grains (such as silver chloride, silver bromide, silver chlorobromide, silver bromoiodide, silver chlorobromoiodide) dispersed in an hydrophilic colloid (such as gelatin, modified gelatins, albumin, casein, sodium alginate, carboxymethyl cellulose, polyvinyl alcohol, polyvinyl pyrrolidone and mixtures thereof). The emulsion can contain cubic, octahedral, spherical and/or tabular silver halide grains. The emulsion can be chemical and optical sensitized and added during its manufacture or before its coating various additives, such as stabilizers, antifoggants, hardeners, coating aids, etc. The silver halide emulsion is coated on a support such as a cellulose acetate film, or a polyester (e.g., polyethylene terephthalate) film using coating, priming, and subbing methods well known in the art, and dried. The following examples illustrate the aqueous alkaline black-and-white developer of this invention more specifically, being understood, however, that the invention is not limited to these examples. EXAMPLE 1 Aqueous alkaline developers 1 to 7, having the composition shown in Table 1, for silver halide black-and-white photographic materials were prepared. Developer 1 2 3 4 5 6 7 Water g 700 700 700 700 700 700 700 Na 2 S 2 O 5 g 30 30 30 30 30 30 30 KOH 35% (w/w) g 50 50 50 50 50 50 80 K 2 CO 3 g 41 41 41 41 41 41 41 Diethanolamine g 6 6 6 6 6 6 12 Ethyleneglycol g 7.5 7.5 7.5 7.5 7.5 7.5 7.5 DTPA.5Na 40% (w/W) g 12.5 12.5 12.5 12.5 12.5 12.5 12.5 K 2 S 4 O 6 mg 150 - - 150 150 - 500 Na 2 S 2 O 3 mg - 190 - 190 - 190 - NaCNS mg - - 100 - 100 100 - 5 Methylbenzotriazole mg - 125 125 125 125 125 80 1-Phenyl-1-H-tetrazole-5-thiol mg 15 15 15 15 15 15 - 4-Hydroxymethyl 4-methyl-1-phenyl 3-pyrazolidone g 1.3 1.3 1.3 1.3 1.3 1.3 1.3 Hydroquinone g 12 12 12 12 12 12 12 Potassiumbromide g 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Water to make l 1 1 1 1 1 1 1 pH at 20°C 10.7 10.7 10.7 10.7 10.7 10.7 10.7 An infrared sensitized photographic emulsion containing silver bromide fine grains was coated on one side of two photographic supports to have two photographic films at different Ag coverage: A: 1.47g/m 2 B: 1.78 g/m 2 exposed at 780 nm by a laser sensitometer, and then processed using developers 1 to 7, for 12 seconds at 35°C, followed by acid stopping for 8 seconds at 35°C, fixing in 3M XAF/3 Fixer (comprising essentially an acid water solution of ammonium tiosulfate and a hardener) for 8 seconds at 35°C, washing in tap water for 20 seconds at 35°C and drying for 22 seconds at 35°C. The results are summarized in the following Table 2. The image tone of the developed silver was determined on a trasmission densitometer at a visual film density of 1.20. The reported yellow densities are the differences between the visual densities and the color densities (determined through a blue filter) multiplied by 1000. Therefore a -110 yellow value would correspond to a yellow density of 0.11 less than the 1.20 visual density (because the density obtained by the blue filter is 1.09). The lower the yellow value, the better the blue-black tone. Reference to this method of evaluation can be found in US Patent No. 4,201,582 and in "The Influence of Development Mechanism on the Color and Morphology of Developed Silver" by T.H.James and W.Vanselow (Phot. Science & Eng. Vol.1, No. 3, page 107 Jan. 1958). Developer Film D.min D.max Speed Average Contrast Image Tone 1 A 0.17 3.34 1.69 3.28 +20 2 A 0.17 3.34 1.73 3.31 +40 3 A 0.17 3.40 1.70 3.33 +40 4 A 0.18 3.29 1.70 3.48 +10 5 A 0.17 3.38 1.66 3.31 +50 6 A 0.18 3.30 1.70 3.20 +30 7 A 0.20 2.98 1.99 3.67 -150 1 B 0.17 3.78 1.78 3.04 -20 2 B 0.17 3.61 1.79 3.16 -30 3 B 0.18 3.93 1.78 3.21 -30 4 B 0.17 3.64 1.82 3.06 -50 5 B 0.17 3.84 1.77 3.04 -20 6 B 0.18 3.60 1.83 3.00 -20 7 B 0.20 3.24 2.05 3.45 -190 These results clearly show that potassium tetrathionate in an amount of 500 mg/l can improve the blue-black tone of the developed silver. Additionally, there is an improvement in speed and average contrast of the developed film.

Claims: An alkaline aqueous black-and-white photographic developer composition comprising: (1) at least one black-and-white developing agent, (2) at least one black-and-white auxiliary developing agent, (3) at least one antifoggant, (4) at least one sequestering agent, (5) a sulfite antioxidant, (6) at least one buffering agent, and (7) a tone modifying agent, wherein said tone modifying agent is an alkali metal or ammonium salt of a tetrathionic acid, and said tone modifying agent is added to said developer composition in an amount in the range of from 0.4 to 5 grams per liter. The alkaline aqueous developer of claim 1, wherein said black-and-white developing agent is hydroquinone or substituted hydroquinones. The alkaline aqueous developer of claim 1, wherein said tone modifying agent is added to said developer composition in an amount in the range of from 0.5 to 2.5 grams per liter. The alkaline aqueous developer of claim 2, wherein the molar ratio of said sulfite antioxidant to said hydroquinone is at least 2.5:1 and the molar ratio of said buffering agent to said sulfite antioxidant is at least 0.5:1. The alkaline aqueous developer of claim 1, wherein said sequestering agent is selected from at least one of aminopolycarboxylic acids, aminopoly-phosphonic acids, cyclicaminomethane diphosphonic acids, α-hydroxycarboxylic acid compounds, dicarboxylic acid compounds, α-ketocarboxylic acid compounds, alkanolamine compounds. The aqueous alkaline developer of claim 1, wherein said sequestering agent consists in a mixture of aminopolycarboxylic acids and cyclicaminomethane diphosphonic acids. The alkaline aqueous developer of claim 6, wherein said cyclicaminomethane diphosphonic acids correspond to the following formula: wherein R 1 , R 2 and R 3 , equal or different, each represent a hydrogen atom or a PO 3 M'M'' group, wherein M' and M" represent a hydrogen atom, an alkali metal or a quaternary ammonium group, and Q represents the atoms or chemical bonds necessary to complete a 3- to 6-membered ring, with the proviso that at least two of R 1 , R 2 and R 3 substituents represent a PO 3 M'M'' group. The alkaline aqueous developer of claim 6, wherein said cyclicaminomethanediphosphonics acid correspond to the formula: The alkaline aqueous developer of claim 6, wherein said mixture of sequestering agents is used in a total amount of from 1 to about 60 grams per liter of ready-to-use developer. The alkaline aqueous developer of claim 1, wherein said black-and-white developing agent is present in the developer in an amount of from 2 to 100 grams per liter and said auxiliary developing agent is present in an amount of from 0.1 to 20 grams per liter of ready-to-use developer. The alkaline aqueous developer of claim 1, wherein said antifoggant consists in a combination of a benzotriazole-type, indazole-type, and a mercaptotetrazole-type antifoggant. The alkaline aqueous developer of claim 1, wherein said antifoggant consists in a combination of 5-methylbenzotriazole and 1-phenyl-1-H-tetrazole-5-thiol. The alkaline aqueous developer of claims 11 or 12, wherein said antifoggant combination is added in an amount of from about 0.01 to 5 grams per liter of the ready-to-use developer composition.

Inventors: BURIANO FRANCO, FARANDA FILIPPO, MARCHESANO CARLO, BURIANO, FRANCO, FARANDA, FILIPPO, MARCHESANO, CARLO
Applicants: EASTMAN KODAK CO, EASTMAN KODAK COMPANY
Application year: 1992
Main classification: G03C5
IPC codes: G03C5