US 3756822 A
Description (OCR text may contain errors)
United'states Patent Oce 3,756,822 Patented Sept. 4, 1973 Int. Cl. G03c 7/00 US. CI. 96-55 13 Claims ABSTRACT OF THE DISCLOSURE An aqueous photographic color processing monobath which includes a color developer and a fixing agent, the bath having a pH of above about 13.2 and being capable 2f color developing and fixing an exposed photographic This invention relates to photographic color processing solutions and more particularly relates to monobath processing solutions containing both developing and fixing agents.
In ordinary black-and-white silver halide photographic processing, a photographic element bearing a latent image is treated with a developer to cause reduction of silver halide to visible metallic silver in light-exposed areas of the element. Development is then arrested by treating the photographic element with a stop solution, and the photosensitive silver halide which remains in the element is subsequently removed by treating with a fixing solution. For reasons associated with processing time and expense, reduction in the number of processing steps is desired, and to this end, processing baths (monobaths) capable of performing both developing and fixing functions have been developed for black-and-white photography. Representative monobaths are described in G. Haist, Monobath Manual, Morgan and Morgan, Inc., Hastings on Hudson, N.Y., 1966.
Silver halide color photographic processing involves development of a latent image on a silver halide photographic element by treatment with a color developing solution employing a primary aromatic amine developer. The developer is oxidized in latent image areas of the photographic element, and the oxidation production of the developer couples (i.e., reacts) with a photographic color coupler compound to form a dye in such image areas. The metallic silver which is formed in these areas by reduction of silver halide, however, obscures the dye image and hence must be removed. After removal from the photographic element of the remaining silver halide in a fixing bath, the metallic silver is bleached from the film by a solution capable of reoxidizing the reduced silver to form a soluble, easily removed silver salt.
Attempts to prepare a monobath for color photographic processing which would permit color development, bleaching and fixing have generally been unsuccessful. For example, H. Genda and S. Kubo, J. Soc. Sci, Phot. Japan, 21, 133 (1958) described an attempt to prepare a solution capable of developing, fixing and bleaching a color photographic element. The resulting solution reportedly was highly unstable and caused reduction in photographic sensitivity. A monobath for photographic color processing (avoiding separate development, fixing and bleaching steps) is greatly to be desired.
It is an object of the present invention to provide a stable efficient monobath for rapid photographic color processing.
Another object of the invention is to provide a photographic color processing monobath to avoid the necessity of separately removing a visible silver image.
Another object of the invention is to provide a photographic color processing monobath capable of operation at elevated temperatures.
Yet another object of the invention is to provide a method for rapid photographic color monobath processing which enables a stable photographic color reproduction to be produced without the necessity of performing separate developing, bleaching and fixing steps.
Briefly, the present invention relates to an aqueous monobath for color processing of silver halide photographic elements, said monobath having a pH of above about 13.2. The monobath includes a primary aromatic amine developer and a fixing agent L. The fixing agent is capable of reacting with the silver halide in said element to form a water-soluble silver complex which is stable and at the pH of the monobath with the proviso that when said fixing agent is an alkali metal thiosulfate, the amount thereof is not greater than that satisfying the formula wherein pH is the pH of the monobath, K is the dissociation constant of the silver complex in (moles) (liter) and [L] is the concentration of fixing agent in moles per liter.
The invention, in another embodiment, relates to a method for rapid-access color development of an exposed silver halide photographic element which comprises treating the element in an aqueous solution having a pH of at least 13.2 and which includes a primary aromatic amine photographic developer and a fixing agent capable of reacting With the silver halide in said element to form a water-soluble silver complex which is stable at said pH.
The method of the invention is preferably used with monochromatic silver halide radiographic film, and is preferably carried out at temperatures above room temperature (e.g.up to about 50 C.).
The developing agents which are utilized in the present invention are of the primary aromatic amine type common to photographic color processing. Examples of such compounds include p-diethylamino aniline, 4-diethylarnino-o-toluidine,
4- [N-ethyl-N- fi-methanesulfonamidoethyl) -aminoo-toluidine, p- N-ethyl-N-B-hydroxyethyl) -aminoaniline, and the like, which compounds are usually provided in a stable salt form such as the hydrochloride, sesquisulfate, etc. Such developing agents are capable of reducing silver halide to metallic silver in latent image areas of silver halide photographic emulsion, with concurrent oxidation of the developer. The oxidation product of the developer is capable of reacting with a color coupler to form a dye. The concentration of developer in the aqueous monobaths of the invention may fluctuate widely. It has been found convenient, however, from the standpoint of developer solubility and rapidity of development, to employ from about 0.01 to about 0.1 mole of developer per liter of monobath.
Fixing agents utilized in monobaths of the present invention include certain of the ordinary fixing agents known to the art. Alkali metal thiosulfates, such as sodium, potassium and ammonium thiosulfates, are preferred, but other fixing agents, such as those of the organic thiol type (e.g., alkali metal thiocyanates, mercaptoalkanoic acids such as mercaptosuccinic acid and mercaptoacetic acid) may also be utilized. Such fixing agents complex with silver halide to form compounds which are soluble in the aqueous monobaths of the invention, and the complex compounds which are formed are believed to provide a ready source of silver ion for physical development, as will be more fully explained below. The fixing agents utilized in monobaths of the invention are selected by quantity and type so that the complex produced by reaction with silver halide is water-soluble and stable at the pH of the monobath (e.g., above about pH 13.2). The amount of fixing agent employed (fixing amount) is the amount necessary to react with the silver halide in a silver halide photographic color element in order to form soluble complex salts therewith which can be removed readily from the emulsion, leaving the element light-insensitive. See Mees et al., The Theory of the Photographic Process, 3rd ed., Macmillan, New York, 1966, chap. 18. It will be understood that mixtures of fixing agents (e.g., sodium thiosulfate and sodium thiocyanate) may be employed, and the use of mixtures of fixing agents may be desirable to enhance the rate of fixing.
Three processes are believed to occur during development of a silver halide photographic element in a monobath of the present invention. Silver halide is reduced to metallic silver by the conventional action of the primary aromatic amine developer, but this is a comparatively slow reaction. Concurrently, silver halide reacts with the fixing agent to form a soluble silver halide complex which serves as a convenient source of silver ion. Thirdly, physical development raidly occurs; i.e., metallic silver derived from the silver ions of the soluble silver halide complex are deposited on the latent image by electroless deposition. Silver which is thus deposited by physical development appears to be considerably less visible than is silver which is formed by conventional silver halide development, and the dye image which is formed by reaction of oxidized developer with color coupler is hence substantially unobscured by the formation of visible silver deposits (i.e., is transparent).
The rate of physical development in monobaths of the invention is believed to depend, inter alia, upon the pH of the monobath and also upon the concentration therein of silver ions; and the relationship bethween physical development, silver ion concentration, and pH may be approximated by the formula wherein f is a measure of the relative rate of physical development, K is the dissociation constant of the silver complex which results from reaction of the fixing agent with silver halide (expressed in (moles) /(liter) and [L] is the concentration of fixing agent in moles per liter. The variable x" represents the number of ions derived from the fixing agent which are associated with a single silver ion in the complex. For an alkali metal thiosulfate fixing agent, for example, x is 2.
It will be understood that the silver ion concentration is dependent in part upon the concentration of fixing agent in the monobtah. A great excess of fixing agent in the monobath will tend to depress the silver ion concentration, as will too low a concentration of fixing agent. The upper concentration of alkali metal thiosulfate fixing agents in monobaths of the invention, for example, may be derived from the above equation wherein 1 must be greater than 1.0.
The pH of the bath is normally maintained at a value above about 13.2 by addition of e.g., an alkali metal hydroxide such as sodium hydroxide. The success of the monobath of the present invention is dependent upon the pH of the bath, which must be maintained at a value of above about 13.2. Monobaths of reduced pH tend to provide images having significant visible metallic silver. The high pH monobaths of the present invention provide photographic reproductions characterized by substantially invisible silver deposits (thereby obviating bleaching) and further generally promote efficient utilization of dye. It is further desired that the pH be below about 14.8, since exceedingly alkaline developing solutions may damage colloidal binder materials (e.g., gelatin, synthetic polymers, etc.) commonly used in silver halide technology.
Best results from the standpoint of the rate of dye formation and invisibility of the developed silver are generally obtained at a pH of from about 13.5 to 14.2, and this pH range is accordingly preferred.
The photographic color processing monobaths of the present invention may contain, of course, numerous other materials common to photographic processing solutions. For example, the monobaths of the invention may include inert salts of the type ordinarily utilized to reduce the swelling of gelatin in highly alkaline solutions such as sodium sulfate; oxidation inhibitors such as sulfite-producing compounds (e.g., sodium sulfite); Wetting aids such as sodium carboxymethyl-cellulose; color couplers (i.e., compounds capable of reacting with the oxidation product of primary aromatic amine developers to form dyes); fog restrainers such as benzotriazole, potassium bromide, etc.; gelatin hardeners such as formaldehyde, glutaraldehyde and the like; organic solvents such as ethylene glycol, benzyl alcohol, etc.; natural and synthetic polymers such as polyvinylpyrrolidone, polyvinylalcohol, etc., and auxiliary developers such as hydrogen peroxide and l-phenyl- 3-pyrazolidones.
The monobaths of the present invention have been found capable of greatly reducing the time required for color photographic processing. For example, utilizing a color tripack film (i.e., a film containing red-, green-, and blue-sensitive layers) the total processing time can be reduced from about 10 minutes to about 2 /2 minutes. The exposed film need only be treated in a monobath of the invention to cause development of a colored image and fixation of unreduced silver halide, and washed to remove the processing chemicals from the film.
In a preferred embodiment, monobaths of the invention are utilized to develop and fix monochromatic (couplercontaining) radiographic film to provide a radiographic record having a colored image. The eye is apparently able to detect more readily small differences in image intensity in radiographic films containing color images than in conventional radiographic films. In another embodiments, the monobath of the invention may contain one or more color couplers capable of forming e.g., blue dyes. Radiographic film (preferably lightly tinted yellow) may be developed in this monobath to yield a radiographic reproduction having a bluish image upon a yellow background. The present invention thus provides a very valuable method for rapid processing of radiographic films to provide color radiographic reproductions.
Generally it has been found desirable to employ the monobath of the present invention at temperatures exceeding 23 C. Although room-temperature processing yields good results, elevated temperatures have been found to advantageously increase the rate of development and fixation without diminishing the quality of the dye image, thereby further reducing processing time. Bath temperatures of up to 47 C. and above can be employed, although temperatures from about 30 C. to about 40 C. are preferred since this range contributes to rapid processing and yet avoids the problems associated with photographic processing at higher temperatures (gelatin degradation, excessive fog, etc.).
The invention may be more clearly understood by reference to the following illustrative examples wherein the densities referred to are dye densities.
EXAMPLEI A solution of:
G. p- ('N-ethyl-N-thhydroxyethyl)amino aniline (as sulfate salt) 4 Sodium sulfite 10 Sodium sulfate 60 Sodium thiocyanate 1 Potassium bromide 2.9 Sodium thiosulfate 19 Water to 800 ml.
TABLE I (NaOH) g./
800 m1. pH 7 mnx EXAMPLE 2 An image-wise exposed photographic element bearing on a transparent support a silver iodobromide radiographic emulsion containing 1-hydroxy-2-N-(n-octadecylcarbonamido)naphthalene-4-sulfonic acid cyan forming coupler was processed for 7 min. at ambient temperature in a bath of the following composition p (N-ethyl-N-fl-hydroxyethyl)aminoaniline (as the sulfate) 4 Potassium bromide 2.9 Sodium sulfite 10 Sodium sulfate 60 Sodium hydroxide 18.4 Sodium thiosulfate 13 Water to 800 ml.
Bath pH 13.6.
After washing with water, analysis of the imaged element showed a D of 0.16, a D of 2.30, and a 'y of 1.0. The cyan image was transparent.
EXAMPLE 3 To 200 ml. of a stock solution of 2-methyl 4 [N-ethyl N (B-sulfonamidoethyh] aminoaniline (as sesquisulfate) 16 Sodium sulfite Sodium sulfate a 50 Potassium bromide 0.6 Sodium thiocyanate 1 Sodium hydroxide 3 Water to 800 m].
To another 200 m1. portion of the stock solution of Example 3 was added 2 g. sodium hydroxide and 5 g. sodium thiosulfate to yield a pH of 13.5. A sample of the film described in Example 3 was processed therein for 2 min. at room temperature and then washed. Thereafter, 0.1 g. of 1-phenyl-3-pyrazolidone was added as an auxiliary developer to the 200 ml. of monobath, and another sample of film was identically processed therein and washed. The following table lists the photographic results:
TABLE 11 Speed) Dmlu Din" 7 (re].)
Control with 1-pl1enyl-3-pyrazolidone. EXAMPLE 5 The following color developing solution was prepared:
2-methyl-4-[N-ethyl N (B sulfonamidoethyD] aminoaniline (as sesquisulfate) g 16 Sodium sulfite g 5 Sodium sulfate g 50 Potassium bromide g 0.6 Sodium thiocyanate g 1 Sodium hydroxide g 19 Ethylene glycol ml 25 1-(2,4,6-trichlorophenyl)-3-(4-nitroanilino) 2 pyrazoline-S-one (magenta-forming coupler) g.. 1.7
Water to 800 ml.
A sample of the photographic element of Example 3 was exposed through a sensitornetric wedge and was developed in the bath for 2 min. at room temperature. After development, processing was completed according to conventional procedures (bleaching, fixing). The developer was then converted to a monobath of the invention by addition of 13 g. of sodium thiosulfate. Another film sample was processed in this monobath for 6 min. at ambient temperature, and washed. The following results were A silver halide color tripack film was prepared by coating consecutively onto a subbed triacetate film base.
(a) A magenta-forming silver chlorobromide emulsion sensitized to green light and containing 1-(2,4,6-trichlorophenyl)-3-(N'-p-dodecylphenylureido) 2 pyrazoline5- one.
(b) A magenta-forming silver iodobromide emulsion naturally sensitive to blue light and containing N'-(abenzoylacetyl) p aminophenylsulfon (0' cyclohexylanilide, and
(c) A cyan-forming silver chlorobromide emulsion sensitized to red light and containing (1-hydroxy-4-chloro- N-tetradecyl-2-naphthamide.
Each coating contained 10 milligrams of silver per square decimeter.
The resulting film was exposed to light through color separation filters in a sensitometer and thereafter was treated for three minutes at 21 C. in a monobath hav- Water to 1 liter.
After washing and drying, the following results were obtained:
Water to 200 ml.
A photographic element having coated on a transparent film base a gelatino silver iodobromide emulsion containing an oil-dispersed cyan-forming coupler (1-hydroxy-4- chloro-N-tetradecyl-Z-napthamide) was divided into three parts which were respectively processed in the bath at 23 C., 35 C. and 47 C., followed by washing in 1% aqueous formaldehyde solution. The following photographic data were obtained:
8 EXAMPLE 9 A silver chlorobromide emulsion containing an excess of a dibutylphthalatetriphenylphosphate dispersed cyanforming coupler (l-hydroxy-4-chloro N tetradecyl-Z- naphthamide) was dispersed in gelatin and coated on a subbed polyester base. The resulting photographic element was divided into sections, and each section was exposed to 190 meter-candle-seconds of illumination and was then processed for 3 minutes at ambient temperature in a monobath of the following composition, the pH of the monobath being varied by addition of sodium hydroxide as given in Table VII below.
p-(N-ethyl N 9 hydroxyethyl)-amino aniline (as the sulfate) Sodium sulfite 10 Sodium sulfate 60 Potassium bromide 2.9 Benzotriazole 1 Sodium thiosulate (1) Water to 1 liter.
1 See Table VII.
Table VII gives the resulting dye densities as a function of thiosulfate concentration, and further gives the value of fin the equation TABLE v wherein pH is the pH of the solution, K is the dissocia- ReL Processing tion constant (3.5 Xl0 of the silver halide complex e n rature,C. Dmin. Dim. 7 speed time of 25 C. in (molesY /(liter) and [L] is the concentra- 23 0,1 82 0 5 6 1 mm non of fixing agent U1 moles per liter. 0.08 0.86 0.5 2.7 30sec. 47 0.00 1.50 0 0 5.8 30sec. 35 TABLE v11 Sodium thiosultate,gramslliter pH f D EXAMPLE 8 14.2 3.2 Coating failed A photographic element bearing, on a subbed polyester 14- 2 2 33 5 to clear. base, a silver iodobromide emulsion to which had been 1 m 1 added an excess amount of an oil-dispersion of the yellowforming coupler N'-(a-benzoylacetyl)-p-aminophenylsul- 14,2 j fon-(o-cyclohexyloxy)-anilide was prepared and was out 3 23 imageinto four sections, each of which was then exposed to 30 13.2 1122 0I7I meter-candle-seconds of illumination through a continu- Nolmageous wedge. One section was processed at room temperature for 4 minutes in a monobath of the following composition:
Sodium thiosulfate 49 Sodium sulfate 60 Sodium sulfitc 10 Potassium bromide 3 Sodium thiocyanate 1 Sodium hydroxide 92 p-(N-ethyl N 18 hydroxyethyl)-amino aniline (as the sulfate) Water to 800 ml.
TABLE VI D (above fog-monsured through Wratten #47 filter) Additional developing agent added I claim:
1. An aqueous color processing monobath for color processing of silver halide photographic elements, said monobath having a pH of at least 13.2 and including a primary aromatic amine color developer and a fixing agent L capable of reacting with said silver halide in said element to form a water-soluble silver complex which is stable at said pH with the proviso that when said fixing agent is an alkali metal thiosulfate, the amount thereof is not greater than that satisfying the formula pH +1og 1.0
wherein pH is the pH of said monobath, K is the dissociation constant of said silver complex in (moles) (liter) and [L] is the concentration of fixing agent in moles/ liter.
2. The monobath of claim 1 wherein the pH of said monobath is from about 13.5 to about 14.2.
3. The monobath of claim 1 which additionally includes a photographic color coupler.
4. The monobath of claim 1 wherein said fixing agent is sodium thiosulfate.
5. The monobath of claim 1 wherein said fixing agent is a mercaptoalkanoic acid.
6. An aqueous photographic color processing monobath of pH 13.2-14.8 comprising (a) a primary aromatic amine developer; and
(b) sodium thiosulfate in an amount not greater than that satisfying the formula pH+log (%).0
wherein pH is the pH of said monobath, K is the dissociation constant of the silver complex resulting from the reaction between silver halide and said sodium thiosulfate in (molesV/(liter) and [L] is the concentration of fixing agent in moles/liter.
7. A method of developing and fixing a color silver halide photographic element which comprises treating said element in the monobath of claim 1.
8. A method of developing and fixing a color silver halide photographic element which comprises treating said element in the monobath of claim 3.
9. A silver halide photographic element bearing a color image produced by the method of claim 7.
10. A method for rapid color processing of an exposed photographic silver halide element which comprises developing and fixing said element in a single color processing monobath of pH 13.2 to 14.8 and which includes a primary aromatic amine developing agent and a fixing agent capable of reacting with silver halide in said element to form a water-soluble silver complex stable at said pH, and washing said developed and fixed element.
11. The method of claim 10 wherein said fixing agent is sodium thiosulfate.
12. The method of claim 10 wherein said developing and fixing is accomplished at a temperature of from above 23 C. to about 50 C.
13. A method for rapid color processing of an exposed photographic silver halide element which comprises developing and fixing said element at a temperature of from 40 C. in a color processing monobath of pH 13.2 to 14.8 and which includes a primary aromatic amine developing agent and an alkali metal thiosulfate, and washing said developed and fixed element.
References Cited UNITED STATES PATENTS 2,626,215 1/ 1953 Schwerin 96-61 M 2,857,274 10/1958 Land et al. 96-61 M 3,512,980 5/ 1970 Lucas 96-61 M 3,615,509 10/1971 Klein 96-61 M 3,255,008 6/1966 Tefft 96-61 M NORMAN G. TORCHIN, Primary Examiner R. L. SCHILLING, Assistant Examiner US. Cl. X.R. 96-61