US 3736141 A
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United States Patent O PHOTOSOLUBILIZATION PROCESS USING CHEMI- CALLY SENSITIZED PHOTOSOLUBLE SILVER HALIDE LAYERS Joseph D. Overman, New Shrewsbury, N.J., and Jack F. Strange, Rochester, N.Y., assignors to E. I. du Pont de Nemours and Company, Wilmington, Del.
No Drawing. Continuation of abandoned application Ser.
No. 739,630, June 25, 1968, which is a continuation-inpart of application Ser. No. 689,331, Dec. 11, 1967. This application Aug. 2, 1971, Ser. No. 168,459
Int. Cl. G03c 5/ 24 U.S. CI. 96-64 9 Claims ABSTRACT OF THE DISCLOSURE Process for increasing photographic speed by exposing a chemically or chemically plus dye sensitized photosoluble element and developing the resulting direct positive latent image to a silver halide direct positive image by treating in a silver halide solution in the presence of a reducing agent.
This application is a continuation of application Ser. No. 739,630, filed June 25, 1968, now abandoned, which is a continuation-in-part of application Ser. No. 689,331, filed Dec. 11, 1967, now abandoned.
BACKGROUND OF THE INVENTION Field of the invention This invention relates to a process for forming images from photosoluble silver halide layers. The present invention constitutes an improvement in a silver halide photosolubilization process by employing photosoluble elements which are chemically or chemically-and-dye sensitized.
Description of the prior art Photosolubilization image-forming processes and photosoluble layers and elements useful in the basic process are described in U.S. Pats. 3,155,507 and 3,155,514 to 3,155,519, inclusive, patented Nov. 3, 1964; Blake 3,284,- 206, Nov. 8, 1966; Blake and Fan 3,368,899, Feb. 13, 1968, and assignees U.S. applications, Fan Ser. Nos. 403,631 and 403,632, filed Oct. 13, 1964, U.S. Pats. 3,407,068 and 3,407,067, respectively, Oct. 22, 1968; and Hunt Ser. No. 388,919, filed Aug. 11, 1964, U.S. Pat. 3,418,124, Dec. 24, 1968. In these applications and patents there are described simple and useful layers and processes for obtaining a positive silver halide image in a single processing step. Intensification of the image, e.g., by reduction to a black metallic silver image, is an additional optional step.
In assignees copending application of Blake, U.S. Ser. No. 684,924, filed Nov. 22, 1967, it is disclosed that processing of photosoluble elements is further improved by the presence of one or more reducing agents and a D maintaining agent during development. Such reducing agents are also requiredduring the dissolution development in accordance with the present invention.
In accordance with the present invention, processing of the photographic elements is carried out in the presence of a maximum density maintainer (D maintaining agent) as listed and classified in assignees copending applications, Blake U.S. Ser. Nos. 648,229 and 648,250, U.S. Pats. 3,493,373, Feb. 3, 1970 and 3,495,982, Feb 17, 1970 respectively and Strange U.S. Ser. No. 653,590, filed June 23, 1967, U.S. Pat. 3,495,983, Feb. 17, 1970.
In Blake U.S. Pat. 3,384,485, May 21, 1968, the application of which was copending with Ser. No. 689,331, it is disclosed that improved photosoluble elements may be obtained by the inclusion of spectral sensitizing dyes in the emulsion. However, there is no disclosure in the application of the combination of chemical sensitization with the use of spectral sensitizing dyes.
SUMMARY OF THE INVENTION This invention pertains to an improvement in a photosolubilization process of forming a direct-positive silver halide image which comprises (a) Exposing a photosoluble emulsion layer, image- Wise, to actinic radiation, said layer containing silver halide crystals made relatively less soluble in a silver halide solvent by treatment with an organic compound capable of forming a salt of lower solubility in water than silver chloride, said organic compound being present in such amount, in terms of the ratio of its weight to the surface area of said silver halide crystals, that when admixed in such ratio with an aqueous silver chlorobromide (70/30 mole percent) gelatin dispersion containing 10 g. of gelatin per mole of Ag and .57 mg. of Ag per ml. and said silver chlorobromide dispersion is treated with 10%, by weight, aqueous sodium thiosulfate (so that the resulting mixture contains 0.29 mg. of silver and mg. of sodium thiosulfate), at least three times the amount of silver chlorobromide remains undissolved as compared with a similar dispersion successively treated with 5%, by weight, aqueous sodium hypochlorite and 10%, by weight, aqueous sodium thiosulfate (so that the resulting mixture contains 0.29 mg. of silver, 25 mg. of sodium hypochlorite and 100 mg. of sodium thiosulfate), after vigorous agitation of both dispersions for 30 seconds at 25 C., and
(b) Treating said layer with an aqueous solution of a silver halide solvent, in the presence of a silver halide reducing agent and a D,,,,,,, maintainer so that the dissolution of exposed silver halide in said solvent is substantially greater than the reduction by said reducing agent, thereby eliecting solubilization of the silver halide in the more exposed areas at a rate substantially greater than in the less exposed areas until a positive image comprised of silver halide is produced;
The improvement being characterized in that the silver halide crystals of said photosoluble emulsion layer are chemically sensitized.
In preferred embodiments of the invention, these silver halide crystals are also spectrally sensitized by means of a cyanine type dye such as a simple cyanine, carbocyanine, dicarbocyanine, merocyanine, pseudocyanine, etc.
DESCRIPTION OF THE PREFERRED EMBODIMENTS In practicing the process of the invention, photosoluble silver halide layers similar to those disclosed in Blake, U.S. 3,155,507 are prepared. The preferred layers are silver chloride emulsion layers insolubilized with 2-mercapto-4-phenylthiazole or a related mercaptan as disclosed in said patent. Prior to treatment with the mercaptan, the silver halide crystals are chemically sensitized by a heat treatment in the presence of a labile sulphur or selenium containing compound, e.g., sodium thiosulfate. Chemical sensitization may be further enhanced by having present during the digestion treatment a gold compound such as auric chloride. In particularly preferred emulsions, photographic spectral sensitizing dyes as set forth in Blake, U.S. Ser. No. 390,460 filed Aug. 18, 1964, U.S. Pat. 3,3 84,485, May 21, 1968 are also present.
The sensitized photosoluble layer is exposed, imagewise, to actinic radiation and then treated in an aqueous bath comprising 0.1 to 2 moles per liter of a thiosulfate (e.g., sodium thiosulfate) silver halide solvent and a small amount of a reducing agent such as 1-phenyl-3- pyrazolidone as disclosed in U.S. Pat. 3,589,900, June 29, 1971. In the practical embodiments of the invention a D maintaining organic compound including those disclosed in U.S. 3,493,373, U.S. 3,495,982 and U.S. 3,495,983, (e.g., o-phenylphenol) is present in D maintaining amounts during the treatment in said aqueous bath, i.e. either present in the bath itself or in the photosoluble element. The time and temperature of treatment in the aqueous bath are obviously dependent variables but at a temperature of 70 F. the time should be about 30 seconds to minutes. This treatment removes silver halide from the exposed areas at a much faster rate than from the unexposed areas leaving a positive silver halide image. A useful positive image can be prodnced, particularly for viewing by projection, by this single treatment, although a washing step is generally used. For most purposes, it is desirable to intensify the silver halide image, usually by treating with a photographic silver halide developer solution to reduce the image to one of black metallic silver. Other methods of intensifying the silver halide image, e.g., by toning, color developing, etc., are disclosed in U.S. 3,155,507.
Any of the various photosoluble silver halide layers and elements described in the U.S. patents and the Blake et al. and Fan applications listed above can be used in the process of this invention. These may be modified in the specific ways described in the patents and applications by variations in the silver halide, the binder (if present), the organic compounds for insolubilization of silver halide (whose utility can be established by the simple tests defined therein for determination of useful compounds), the adjuvants generally employed in silver halide systems, the supports, and in relative concentrations of the various components. Various auxiliary layers may be present, such as abrasion over-coating, subbing layers, and antihalation undercoats or backing layers. The elements may include multilayer as well as monolayer structures.
Useful reducing agents are photographic developing agents, preferably N-methyl-p-aminophenol, l-phenyl-3- pyrazolidone, and said compound having a methyl group in the 4- and/ or 5-position.
The various layers, including the support, may include inert ingredients, e.g., pigments, organic polymer latices, and matting agents. As disclosed in U.S. 3,155,507, the silver halide may be insolubilized by treatment with an appropriate organic compound either during emulsion manufacture or by treatment of the coated element with a solution of the organic compound.
Useful chemical sensitizers include any of the compounds containing labile sulfur or selenium, e.g. thiosulfate, thiourea, tetramethyl thiuram monosul-fide, thiocyanates, elemental sulfur, potassium selenocyanate, various mercaptans, etc. A useful class of sulfur sensitizers are disclosed in Belgium Pat. No. 688,064. Increased sensitization can be achieved by the use of salts of heavy metals in conjunction with the labile sulfur or selenium compounds. Gold salts such as gold chloride or thiocyanate (especially ammonium aurothiocyanate) are particularly useful but salts of other heavy metals are known to improve chemical sensitization and/or to restrain fog, e.g., salts of lead, thallium, cadmium, platinum, and palladium. Waller et al., U.S. 2,399,083, disclosed a number of gold compounds which are effective in increasing the sensitivity of emulsions sensitized with compounds containing labile sulfur. Effective chemical sensitization can also be obtained by the use of certain known reduction sensitizers, e.g., reducing agents such as stannous chloride.
The dissolution developer may contain various adjuvants such as shown below in the working examples. Numerous useful silver halide solvents are disclosed in U.S. 3,155,507 but in the present application only the use of preferred silver halide solvents which contain the thiosulfate anion will be described.
Useful photosoluble emulsions which are chemically or chemi a y-andye sensitized accordin to this invention may also contain a small amount of reducing agent, i.e., the reducing agent can be present in inert form in the emulsion rather than in the dissolution developer solution. The reducing agent could be incorporated with the appropriate silver halide emulsion in an inert form which can be activated at a later time.
The invention will be further illustrated by but is not intended to be limited to the following examples.
EXAMPLE I A light-sensitive silver chloride coagulum, made by precipitation, coagulation and washing as taught in Moede, U.S. Pat. 2,772,165, was redispersed in an aqueous Solution of inert (i.e., very low in labile sulfur content) gelatin so as to achieve a gelatin to silver chloride weight ratio of 0.93. The emulsion was then divided into 7 portions with the additions of sodium thiosulfate and auric chloride chemical sensitizers. These portions were given a first digestion as indicated in Table I below. Then Z-mercapto- 4-phenylthiazole (referred to hereinafter as MPT) was added at a concentration of 0.84 g. per mole of silver chloride to each of the 7 emulsions. The merocyanine spectral sensitizing dye described in Example I of Kendall, U.S. Pat 2,342,546, was added to 5 of the 7 emulsions in the concentrations indicated in Table I and all the emulsions were given a second digestion for 30 minutes at F. Normal emulsion adjuvants were then added to each emulsion including gelatin hardening agents and coating aids, and the emulsions were coated on a vinylidene chloride copolymer subbed polyester base prepared as described in Example IV of Alles, U.S. Pat. 2,779,- 684 (and to which a gelatin sub layer had been subsequently applied). The coating weights were approximately 60 mg./dm. calculated as AgBr.
Film strips from the coated emulsions were exposed for 10 seconds through a /2 step wedge spaced 76 cm. from a 500 watt tungsten filament, incandescent lamp fitted with a Wratten No. 79 filter. The exposed strips were processed with all solutions at 68 F, first treating for 5 min. in a dissolution developer of the following composition to give positive silver halide images:
H O ml 500 N32820:; g NaOH, 3 N ml 10 1-phenyl-3-pyrazolidine ....g 0.5 Na SO anhyd. g 10 Ascorbic acid 2 2.5 CH COOK g 19.6
o-Phenylphenol (5% by wt. aqueous solution in 1 N NaOH, also containing 1% by wt. Na SO ml H O to 1 liter.
pH, adjusted with CH COOH to 8.85 $0.05.
The film strips were then washed 50 seconds, uniform, ly (flash) exposed to room lights, and intensified by developing for 1 min. in the following solution which had been diluted with an equal volume of water:
H O ml 750 p-Methylaminophenol sulfate g 3 Na SO anhyd. g 45 Hydroquinone E 12 N3QCO3H2O g KBr g 1.9 H 0 to 1 liter.
The strips were then given a final wash for 5 min. and dried in air. Optical densities were read'in a conventional densitometer and sensitometric curves were drawn from these data. The variations in chemical and spectral sensitization and digestion are summarized in the table below along with their relative speeds.
The relative speed values in Table I are not all calculated on the same basis. Thus the indicated speed for Film 2 is simply a comparison of its speed relative to that of its control, Film #1, arbitrarily set at 100. Like- TABLE IV wise the indicated speed of Film #4 is a comparison of its 1mm No 1 2 speed relative to that of Film #3 while the indicated NMSZO J ole Agcl) 3 1 1o-a 3 1 1oe o 8 8 speeds of Films #6 and #7 are comparisons of their egg g g gggg 33x10 speeds relative to that of their control which is Film #5. $3, 3,15 3g 3g MPT (gJmole A'iiiiI- None 84 The Wratten No 79 filter that is referred to above MDPO (glmole exgol) 1'17 None transmits radiation m the blue and green region of the g g e n ne g e MEX-I (e/ g J18 J18 ec n iges on: spectrum. Other filters that transmit such radiation can Temp.F 170 170 Time (min.) a0 be used in like manner.
TABLE I Film No 1 2 3 4 5 6 7 Neiseoa (gJmole AgCl) 0 4. 5 10- 0 4. 5 1oo 4. 5x10 4. 5 1o AuCle (gJmole AgCl) 0 0 0 0 0 3. 3X10 3. 3x10 First digestion:
Temp, F 140 140 140 145 Time (min.) None 30 None 30 None 35 MPT (g./m01e AgCl) .84 .84 .84 .84 .84. .84 .84 Merocyanine dye (gJmole .AgOl) 0 0 .05 .05 .15 .15 .15 Second digestion:
emp., F 170 170 170 170 170 170 170 Time (mi1'l.) a0 30 a0 30 a0 30 30 Relative speed 100 200 100 280 100 668 850 EXAMPLE II EXAMPLE V Silver chloride emulsions were prepared, processed and evaluated in a manner, similar to that described in Example I. The sulfur sensitizing compound used was tetramethyl thiuram monosulfide which replaced the sodium thiosulfate of Example I. Other changes are recorded in Table II. A significant increase in speed was noted as the chemical sensitization which occurs during the first digestion progressed.
The emulsion preparation, processing, and evaluation of Example II was repeated except potassium selenocyanate was substituted for the tetramethylthiuram monosulfide. Again speed increased with the time of the first digestion (Table III).
TABLE III Film No 1 2 3 Potassium selenocyanate (g./mo1e AgCl) 3. 35Xl0 3. 35X10- 3. 35Xl0 AuCla (gJmole AgCl)- 1. 83X10- 1. 83X10- 1. 83x10- First digestion:
.Temp. F 140 140 140 Time (min. 30 45 60 Merocyanine dye of AgOl) 067 067 067 MPT (g./mole AgCl) 84 84 84 Second digestion:
Temp. F 170 170 170 Time (min.).. 20 20 20 Relative speed 100 200 250 EXAMPLE IV Two emulsions were prepared, processed, and evaluated as described for Film #6 of Example I except that one of the two was treated with 2-mercapto-4,S-diphenyloxazole (MDPO) instead of MPT after the first digestion as indicated in Table IV. These two coatings gave equivalent speeds.
Two emulsions were prepared, processed and evaluated as in Example IV, one being treated with MPT and the other with 2-mercapto quinoline (MQ) after the first digestion. The details are shown in Table V.
TAB LE V Film No 1 2 2. 76 10- 2 76X10- 2. OeiXlll- 2 04X1O 142 142 50 50 None 84 MQ (g. mole AgCl) 1. 09 None Merocyanine dye of Ex. I (gJmole AgOl).. 083 083 Second digestion:
Temp., F 170 170 Time (min.) 20 20 Relative speed 200 EXAMPLE VI A light sensitive, AgCl (70 mole percent) AgBr (30 mole percent) coagulum, made by precipitation, coagulation and washing as in Example I, was redispersed in an aqueous solution of an inert gelatin so as to achieve a gelatin to silver halide weight ratio of: .85. The emulsion was then divided into 2 portions and treated as shown in Table VI. The films were coated, processed, and evalu ated as in Example I.
TABLE VI Film No 1 2 NazSgOa .lmole Ag) 2. 76 10 2. 76X10- AuCla (g. mole Ag) 2. 04X10- 2. 04x10- First digestion:
emulsion was about 0.4
Average size of grains in this micron. An increase in speed occurred as the sensitizing digestion proceeded.
EXAMPLE VII A film was prepared which was similar to that described as Film #7 of Example I, being sensitized with Na S O AuCl and the merocyanine dye of that example. A control film was sensitized with the merocyanine dye but sensitization with Na S O' and AuCl was omitted. Strips of the two films were exposed for 2 seconds through a V2 stepwedge at 20 inches from a high intensity, tungsten filament, incandescent lamp (General Electric Reflector Photoflood lamp, No. PI-I/RFL 2) with the voltage sup plied to the lamp being reduced to 65% of normal (115 volt) line voltage.
The exposed strips were processed for 3 minutes at 68 F. in the following dissolution developer in which it is noted that a nonselective reducing agent, NaBH is used in small quantities. In other examples the reducing agent has been of the selective type suitable for use as a photographic developing agent.
Na S O anhyd g 32 Na SO anhyd. g 10 o-Phenylphenol, 5% by wt. solution in 1 N NaOH rnl 20 NaBH by wt. solution in l N NaOH ml 1 H O to 1 liter. Adjust pH with NaOH to 10.0.
The strips were then washed for one minute in water, given an overall (flash) exposure to white light, and intensified as in Example I. The film sensitized with labile sulfur and gold chloride was substantially faster than the control film.
The present invention has the advantages of the basic process of photosolubilization, especially that of a very simple, single step process of obtaining a positive image. The present invention provides a means of increasing the light sensitivity of photosoluble emulsions so that less light is required to provide adequate exposure for the film elements. The speed increase is sufficient to achieve a camera speed, direct positive film by the processing technique of the present invention. The same film can be used as a contact speed direct positive when processed in an ordinary dissolution developer (containing a silver halide solvent but no reducing agent).
1. A process for forming a direct positive silver halide image which comprises (a) imagewise exposing a photosoluble silver halide emulsion layer to actinic radiation, said emulsion layer containing a sensitizing amount of a chemical sensitizing compound containing labile sulfur or selenium, and
(b) developing the exposed emulsion layer in the presence of a silver halide reducing agent and a D maintainer.
2. A process according to claim 1 wherein the emulsion layer also contains a cyanine sensitizing dye.
3. A process according to claim 1 wherein the emulsion layer also contains a merocyanine dye.
4. A process according to claim 1 wherein the said emulsion layer contains a carbocyanine sensitizing dye.
5. A process according to claim 1 wherein the chemical sensitizing compound is selected from the group consisting of thiosulfates, thioureas, thiocyanates, mercaptans, elemental sulfur, tetramethyl thiuram monosulfide, and potassium selenocyanate.
6. A process according to claim 1 wherein the chemical sensitizing agent is sodium thiosulfate.
7. A process according to claim 1 wherein the Dmax,
maintainer is o-phenylphenol.
. ,8. A process according to claim 1 wherein said photosoluble silver halide emulsion layer is comprised of silver halide crystals made relatively less soluble in a silver halide solvent by treatment with an organic compound capable of forming a salt of lower solubility in water than silver chloride, said organic compound being present in such amount, in terms of the ratio of its weight to the surface area of said silver halide crystals, that when admixed in such ratio with an aqueous silver chlorobromide (/30 mole percent) gelatin dispersion containing 10 g. of gelatin per mole of Ag and .57 mg. of Ag per ml. and said silver chlorobromide dispersion is treated with 10%, by weight, aqueous sodium thiosulfate (so that the resulting mixture contains 0.29 mg. of silver and mg. of sodium thiosulfate), at least three times the amount of silver chlorobromide remains undissolved as 'compared with a similar dispersion successively treated with 5%, by weight, aqueous sodium hypochlorite and 10%, by weight, aqueous sodium thiosulfate (so that the resulting mixture contains 0.29 mg. of sodium hypochlorite and 100 mg. of sodium thiosulfate), after vigorous agitation of both dispersions for 30 seconds at 25 C.
9. A process according to claim 1 wherein developing the exposed emulsion layer comprises treating said layer with an aqueous solution of a silver halide solvent, in the presence of a silver halide reducing agent, and a Dmax, maintainer so that dissolution of exposed silver halide in said solvent is substantially greater than the reduction by said reducing agent, thereby efiecting solubilization of the silver halide in the more exposed areas at a rate substantially greater than in the less exposed areas until a positive image comprised of silver halide is produced.
References Cited UNITED STATES PATENTS 3,589,900 2/1971 Blake 96-64 3,501,313 5/1970 Willems et al. 96107 3,128,184 4/1964 Lowe et al. 96108 3,408,197 6/1968 McVeigh 96107 3,495,982 2/1970 Blake 9664 3,493,373 2/1970 Blake 96-64 3,495,983 2/ 1970 Strange 96-64 NORMAN G. TORCHIN, Primary Examiner E. C. KIMLIN, Assistant Examiner US. Cl. X.R. 96-108