US2497917A

US2497917A - Method of producing direct positive photographs having increased density

Info

Publication number: US2497917A
Application number: US780569A
Authority: US
Inventors: Stauffer Robert Eliot
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1947-10-17
Filing date: 1947-10-17
Publication date: 1950-02-21
Anticipated expiration: 1967-02-21
Also published as: DE884150C

Description

. R. E. STAUFFER 2,497,917. METHOD OF PRODUCING DIRECT POSITIVE PHOTOGRAPHS Feb. 21, 1950 HAVING INCREASED DENSITY Filed Oct. 17, 1947 FIG. 2.

INVENTOR ATTORNEYS RQBFERT ESTAUFFER Patented Feb. 21, 1950 UNITED STATE METHOD OF PRODUCING DIRECT POSI- TIVE PHOTOGRAPHS GREASE!) DENSITY HAVING IN- Robert Eliot Stauffer, Rochester, N. Y., assignor to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application October 1'7, 1947, Serial No. 780,569 4 Claims. (01. 9588) This invention relates to photography and particularly to a method of making direct positive photographs.

Direct positive effects may be produced by solarizing the developable latent image by overexposure, by using a second exposure to obtain the Sabattier or the Clayden effect or by redeveloping a developed negative image. Solarizable sensitized products require very intense exposures to obtain the desired direct positive photograph. The use of a second exposure has obvious disadvantages from the point of view of practical technique. Redevelopment adds at least two operations to the usual and normal developing procedure.

Fallesen U. S. patent application, Serial No. 780,405, filed concurrently herewith describes forming a direct positive image in a suitable silver halide emulsion by exposing the emulsion in the usual way and developing it in a developer which is capable of giving aerial fog. The emulsion is preferably of the internal latent image type such as described in Davey and Knott U. S. patent application, Serial No. 790,232, filed December 6, 1947, now abandoned.

I have discovered that certain compounds which have been used as photographic antifoggants or emulsion addenda may be added to the developers used in the process of Fallesen patent application, Serial No. 780,405, and that increased aerial fog, that is, higher maximum density of the reversal image, results from this use of the compound. The compounds which I propose to use are heterocyclic nitrogen-containing ring compounds having 5 or 6 atoms in the heterocyclic ring and so constituted as to increase the maximum density of the positive image obtained in developing solutions capable of producing aerial fog.

I have found that in the development of certain emulsions, such as the "internal latent image emulsions, the use of certain anti-foggants or other compounds in the developing solutions increases the density. in the unexposed areas by intensifying the aerial fog in the low exposure regions, At the same time, the ordinary anti-foggant property is exhibited in the toe portion of the reversal curves, that is, the areas of maximum exposure. I believe that this enhancement of aerialfog in unexposed areas is a new phenomenonwhich. offers considerable value for direct positive photographic materials.

In the accompanying drawing, the two figures res a a eri iis ve ei ho gt nh mu.-

sions illustrating results obtained according to my invention.

The photographic emulsion used in the process of my invention is a gelatino-silver halide emulsion such as a silver bromide emulsion, a silver bromoiodide emulsion, or a silver chloro-iodide emulsion. It need not contain optical sensitizing dyes, although certain sensitizing dyes may be added to it for the purpose of inducing aerial fog, as explained more fully in Fallesen application, Serial No. 780,405. A suitable emulsion is that known as Burtons emulsion, described in Wall, Photographic Emulsions, 1929, pages 52 and 53. Burtons emulsion is made asfollows:

A. Silver nitrate grams 100 Water cubic centimeters 500" Ammonia-to form clear solution 7 l B. Potassium bromide grams '80 Potassium iodide do 50 Soft gelatin do 20 Water cubic centimeters 1000 0. Dry gelatin grams 250 B is heated to C. and A, cold, added to B with constant shaking, digested for 20 minutes at 50 C., and allowed to cool slowly. C is added after being allowed to swell for 20 minutes in water, drained, and melted. The emulsion is then set and washed.

An internal latent image emulsion, that is, one which forms the latent image mostly inside the silver halide grains, as described on pages 296 and 297 of Mees, The Theory of the Photographic Process, 1942, is especiallyuseful for the process of my invention.

Most of the internal latent image emulsions are silver bromo-iodide emulsions of high iodide content, preferably containing at least 10 %-20% of iodide. Burtons emulsion is an emulsion of this type, having a silver iodide contentof approximately 40% of the content of silver halide. It is not absolutely essential, however, for the emulsion .to contain silver iodide.

An internal latent image emulsion made as.

described in Davey and Knott U, S. application,

Serial No. 790,232, filed December 6, 194,7, may, also be used according to my invention. This.-

emulsion is prepared by first forming in the ab-. sence of ammonia and in one or more stages silver salt grains consisting at least partly of a silver salt which is more soluble in water than silver bromide, subsequently converting the grainsto silver bromide or silver bromoiodide, and if thesilver iodide content of the emulsion is less than 6% ira a d .0 et il swarms .i a nssrse.

Solution No. l:

Inert gelatine... 20 grams KC] 20 grams at 40 0. Water 560 cubic centimeters sow ng; No. 2: 100

grams Water. 520 cubic centimeters} 45 Solutio rgo. 3: 195

l 3 grams Q w ater 520 cubic ccntimeters} 45 Solution No. 4:

KBr l... 160 grams Kl .l. 40 grams }at 45 0. Water 500 cubic centimeters Run Solutions Nos. 2 and 3 simultaneously into Solution No. l in a vessel, taking 90 seconds to do this. Then ripen for 1 minute at 45 C. Next add Solution No. 4 then ripen for 20 minutes at 45 C. Next add 235 grams of inert gelatine (dry). Then ripen at 45 C. for 15 minutes during which time the gelatine dissolves. Set and shred the emulsion and then wash until free from all soluble bromide and then add about 150 cc. of 10% solution of KCl (by weight), and then add water to make 3 /2 liters.

An internal latent image type of silver halide emulsion may be defined as one which, when a test portion is exposed to a light intensity scale for a fixed time between /100 and 1 second, and

developed for 4 minutes at 20 C. in the ordinary,

surface developer (Example 1), exhibits a maximum density not greater than /5 the maximum density obtained when the same emulsion is equally exposed and developed for 3 minutes at 20 C. in an internal type developer (Example 2). Preferably the maximum density obtained with the surface developer is not greater than fn' the maximum density obtained when the same emulsion is developed in the internal type developer. Stated conversely, an internal latent image emulsion, when developed in an "internal type developer (Example 2) exhibits a maximum density at least 5, and preferably at least 10, times the maximum density obtained when the same emulsion is exposed in the same way and developed in a surface developer (Example 1).

The developer used in the method of my invention should be one which produces oxidation fog or aerial fog. Such developers have been described by Dundon and Crabtree in American Photography, 1924, vol. 18, page 742. An example of such a developer is a hydroquinone developer containing little or no sulfite, and is illustrated in Example 3.

The aerial fog may be produced in the developer in various ways and may be accelerated or intensified by resorting to various expedients. The developer used should preferably have low sulfite ion content and should preferably contain no silver halide solvent more powerful (as a silver halide solvent) than sulfite. Aerial fog may also be increased by bubbling air vigorously through the developer in such manner that the air comes frequently into contact with the emulsion surface of the photograph during development. Certain chemical agents such as copper sulfate incorporated either in the developer or in the emulsion itself may be used to produce or encourage the production of aerial fog. Hydrogen Amount per Compound liter of developer Grams Benzotriazole 0. 4 Methyl benzoti'iazole l 0. 05-0. 2 Ethyl bcnzotriazole 0. 05-0. l l-Ethyl oxiudole. 0.10 5-Nitroindazole. 05-0. 1 (i-Nitrobenzimiclazole 0. 050. 1 Histidinc 0. 10-0. 2 Ethyl benzo. :azole O. 10 N-etliyl pyrrole 0. 1-0. 2 2,5Dimethylpyrrole 0. 05-0. 2 2,4Dimethyl-fi-carbcthoxypyrrole. 0. 05-0. 2 2,3-Dirncthyl quinoxaline. 0.050. 10 2-Thio'2,4(3,5)-thiazolediono 0. 050. 20 2,4,6-Tri-isopropylamino-S-triozi 0. l(). 2 2,4-Dimethylamino-(i-chloro-S-triazine.. 0. l-0. 2 2,4-Di- (B-mcthoxyethylamino)-6-chloro-S-triazinc. 0. 2 2,4,G-Tri-u-butylamino-S-triazine 0. 2 l-Garboxymcthyl-3-phenyl-2-thiohydantoin 0. l-0. 5 l,4-diphcnyl-3-anilino-5-phenylimiuo.

l,2,4triazoline 0.05 to 0.50

An ordinary surface type developer, that is, one which develops an image only on the surface of the grains of internal latent image emulsions, is the following:

Example 1 p-Hydroxyphenylglycine "grams" '10 Sodium carbonate (crystals) sdo Water to liter 1 Development time, 4 min. at 20 C.

An internal type developer, that is, one which develops an image inside the grains of an internal latent image emulsion is the following:

Development time, 3 min. at 20 C.

My invention will be described by reference to the following specific examples.

Example 3 An emulsion such as the Davey and Knott emulsion described above was coated on a support, dried, and exposed on an Eastman IIB Sensitometer (Journal Society Motion Picture Engineers, 17, 1931, page 536). The exposed emulsion was then developed for 12 minutes at 68 F. in the following developing solution:

Hydroquinone grams 22.5 Sodium sulfite do 30 p-Formaldehyde do 7.5 Potassium metabisulfite do 2.6 Boric acid crystals do 7.5 Potassium bromide do 1.6 Water to liter 1 The developer was agitated during the development by forcing air through a sintered glass bubble tube completely submerged in the developer tank. A similar emulsion exposed in the same way was developed for the same length of time in the same solution containing 0.4 g. of benzotriazole per liter of developing solution. Direct positive images were obtained in each case and were plotted as shown in Fig. 1 of the accompanying drawing. Curve A was obtained from the developer containing no benzotriazole and curve B was obtained from the developer containing benzotriazole. The curves show that a higher maximum density was obtained with the developer containing benzotriazole.

Example 4 The same emulsion as that used in Example 3 was exposed in the same way and portions were developed in a developer of the following composition:

Water to 1 liter containing 0, 0.05, 0.1 and 0.4 g. of methylbenzotriazole per liter of developing solution. Sensitometric curves were obtained from these exposures as shown in Fig. 2 and these display the effect of a range of concentrations of anti-foggant. Curve A was obtained from the development containing no anti-foggant, curve B from the development containing 0.05 gm. per liter of methyl benzotriazole, curve C from the development containing 0.1 gm. per liter of methyl henzotriazole and curve D from the development containing 0.4 gm. per liter of methylbenzotriazole. These curves show that at concentrations of from 0.05 to 0.1 gm. of. methyl benzotriazole per liter of developer, the maximum density and gamma are increased, but at higher concentrations, maximum density and gamma are decreased and at a concentration of 0.4 gm. per liter, they are lower than they were with the developer containing no methylbenzotriazole.

Example Additional strips of the film used in Example 3 were exposed in the same way and developed in the developer of Example 4, with various concentrations of G-nitro-benzimidazole nitrate added to the developer. The development then was 5 minutes and the developer was aerated as in Examples 3 and 4. The concentration of the order of 0.05 g. per liter of developer G-nitrobenzimidazole nitrate was found to be effective in increasing maximum density and decreasing minimum density. At higher concentrations maximum density was decreased although at a concentration of 0.1 g. per liter of developer, the maximum density was higher and the minimum density lower than in the case of the developer containing no anti-foggant. The table indicates the maximum and minim-um densities obtained from The following examples illustrate developer formulas used to obtain an increase in maximum density over that obtained with the same developer containing no anti-foggant.

Example 6 Grams Hydroquinone 10 Sodium sulfite 16 p-Formaldehyde 4 Sodium carbonate 25 Benzotriazole 0.1 Water to 1 liter Example 7 Grams Hydroquinone 20 Sodium sulfite 32 p-Formaldehyde 8 Sodium carbonate 50 Benzotriazole 0.8 Water to 1 liter Example 8 Grams Hydroquinone 30 Sodium sulfite 48 p-Formaldehyde 12 Sodium carbonate .75 Benzotriazole 1.2 Water to 1 liter Example 9 Grams Hydroquinone 30 Sodium sulfite 48 p-Formaldehyde 12 Benzotriazole 2.4 Water to 1 liter Example 10 v Grams Hydroquinone 30 Sodium sulfite e- 24 p-Formaldehyde 6 Benzotriazole 2.5 Water to 1 liter Example 11 Grams Hydroquinone -1 30 Monomethyl p-amino phenol sulfate 0.25 Sodium sulfite 50 p-Formaldehyde 12.5 Sodium hydroxide 6 Benzotriazole 2.5

Water to 1 liter When alkalis such as sodium hydroxide or sodium carbonate in large amounts are added to these developers in order to increase the pH for the purpose of decreasing development time, the developers exhibit a tendency to produce lower maximum density. and higher minimum density. This tendency may be overcome by incorporating small amounts of agents such as p-phenylenedi amine or N-methyl-p-amino phenol sulfate, hydroxy hydroquinone or hydrox hydroquinone acetate, in the developers. Example 11 illustrates a developing solution of this type to which sodium hydroxide and N-methyl-p-amino phenol sulfate have been added. A disadvantage of the developers compounded with small amounts of diamino phenylenes or amino phenols is that the amino groups of these compounds apparently react slowly with the formaldehyde of the developer, yielding Schifis bases; therefore these developers are most effective when used within a few hours after preparation. a

The amounts of the diamino 'phenylenes and amino phenols which have proved most satisfactory for incorporation in the developers are of the order of 0.12 to 0.5 g. per liter of developing solution. In the case of hydroxy hydroquinone and hydroxy hydroquinone triacetate, amounts which have proved most efiicacious are of the order of 0.12 to 0.4 g. per liter of developer.

Not all compounds which ma exhibit antifoggant properties are useful in increasing the maximum density of the reversal image obtained with internal latent image emulsions. For example, fi-phenylindole, 1,3-dimethylindole, phenyl mercapto tetrazole, 2-methylbenzoxazole ethiodide, Z-methylbenzothiazole, metho-p-toluene sulfonate, thiobarbituric acid, 2,6-dimethylquinoline, 2,6-dimethyl quinolinium ethiodide and sulfonamidobenzotriazole decreased the maximum density over that obtained with developers not containing these agents. Other compounds such as 3,5-dimethyl pyrazole, barbituric acid and 2-fl-acetanilido vinyl benzoxazole ethiodide produced no effect on either the maximum or the minimum densities obtained.

From the foregoing examples and description, it will be seen that the novel and useful features of my invention consist in the discovery and application of certain anti-foggant or heterocyclic nitrogen compounds in developers for the production of direct positive photographic images of improved contrast and extended density scale (increased shoulder density) by development in low sulfite or formaldehyde bisulfite type developers. It is to be understood that the scope of my invention is not to be limited by the specific concentrations or formulations given in .the above examples.

Observation of the developing solution containing benzotriazole before and after development revealed the fact that it was greatly discolored during development. It is thought that intermediate oxidation products of hydroquinone increased the production of aerial fog. In the developer containing benzotriazole, it appears from this observation that the rate of production of intermediate oxidation products from hydroquinone is increased and that this results in an increase in aerial fog production. This property of the compounds described herein would seem to be quite independent of their normal anti-foggant properties which ma exist simultaneouslywith the accelerating action on the aerial fog as the toe characteristics of the above examples reveal.

I claim:

1. The method of obtaining a direct positive image in a silver halide emulsion layer, which comprises exposing to light rays to which the emulsion is sensitive, a silver halide emulsion layer a test portion of which upon exposure to a light intensity scale for a fixed time between /100 and 1 second and development for 3 minutes at C. in the following internal type developer:

Water to 1 liter gives a maximum density at least 5 times the maximum density obtained when the equally exposed silver halide emulsion is developed for 4 minutes at 20 C. in the following surface developer (I):

Water to 1 liter and developing the unexposed portion of said emulsion layer in an aerial fogging developer with access of oxygen, and containing a heterocyclic, nitrogen-containing ring compound which increases the maximum density of the positive image obtained in said aerial fogging developer, said heterocyclic compound being selected from the group consisting of benzotriazole, methyl benzotriazole, ethyl benzotriazole, l-ethyl oxindole, 5-nitroindazole, 6-nitrobenzimidazole, histidine, ethyl benzoxazole, N-ethyl pyrrole, 2,5-dimethylpyrrole, 2,4-dimethyl 5 carbethoxypyrrole, 2,3-dimethyl quinoxaline, 2-thio-2,4(3,5)- thiazoledione, 2,4,6-tri-isopropylamino S triazine, 2,4-dimethylamino-6-chloro S triazine, 2,4-di (5 methoxyethylamino) 6 chloro S- triazine, 2,4,6-tri-n-butylamino S triazine, 1- carboxymethyl-3-phenyl-2 thiohydantoin, 1,4- diphenyl-3-anilino-5-phenylimino, and 1,2,4-triazoline.

2. The method of obtaining a directpositive image in a silver halide emulsion layer, which comprises exposing to light rays to which the emulsion is sensitive, a silver halide emulsion layer a test portion of which upon exposure to a light intensity scale for a fixed time between and 1 second and development for 3 minutes at 20 C. in the following internal type developer:

Grams p-Hydroxyphenylglycine 10 Sodium carbonate 100 Water to 1 liter and developing the unexposed portion of said emulsion layer in an aerial fogging developer with access of oxygen, and containing benzotriazole, which increases the maximum density of the positive image obtained in said aerial fogging developer.

3. The method of obtaining a direct positive image in a silver halide emulsion layer, which comprises exposing to light rays to which the emulsion is Sensitive, a silver halide emulsion layer a test portion of which upon exposure to a light intensity scale for a fixed time between /100 and 1 second and development for 3 minutes at 20 C. in the following internal type developer:

Grams Hydroquinone 15 Monomethyl-p-aminophenol sulfate 15 Anhydrous sodium sulfite 50 Potassium bromide 10 Sodium hydroxide 25 Sodium thiosulfate 20 Water to 1 liter gives a maximum density at least times the maximum density obtained when the equally exposed silver halide emulsion is developed for 4 minutes at 20 C. in the following surface developer (I):

Grams p-Hydroxyphenylglycine Sodium carbonate 100 Water to 1 liter and developing the unexposed portion of said emulsion layer in an aerial fogging developer with access of oxygen, and containing 5-nitroindazole, which increases the maximum density of the positive image obtained in said aerial fogging developer.

4. The method'of obtaining a direct positive image in a silver halide emulsion layer, which comprises exposing to light rays to which the emulsion is sensitive, a silver halide emulsion layer a test portion of which upon exposure to a light intensity scale for a fixed time between /100 and 1 second and development for 3 minutes at 20 C. in the following internal type developer;

Grams Hydroquinone Monomethyl-p-aminophenol sulfate 15 Anhydrous sodium sulfite 50 Potassium bromide 10 Sodium hydroxide 25 Sodium thiosulfate Water to 1 liter 10 gives a maximum density at least 5 times the maximum density obtained when the equally exposed silver halide emulsion is developed for 4 minutes at 20 C. in the following surface developer (I):

Grams p-Hydroxyphenylglycine 10 Sodium carbonate 100 Water to 1 liter and developing the unexposed portion of said emulsion layer in an aerial fogging developer with access of oxygen, and containing S-nitrobenzimidazole, which increases the maximum density of the positive image obtained in said aerial fogging developer.

ROBERT ELIOT STAUFFER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,271,229 Peterson et al Jan. 27, 1942 2,384,593 Bean Sept. 11, 1945 2,401,051 Crouse et a1. May 28, 1946 OTHER REFERENCES Wall: Photographic Emulsions, publ. 1929 by Amer. Phot. Publ. 00., Boston: pages 52 and 53.

Claims

1. THE METHOD OF OBTAINING A DIRECT POSITIVE IMAGE IN A SILVER HALIDE EMULSION LAYER, WHICH THE COMPRISES EXPOSING TO LIGHT RAYS TO WHICH THE EMULSION IS SENSITIVE, A SILVER HALIDE EMULSION LAYER A TEST PORTION OF WHICH UPON EXPOSURE TO A LIGHT INTENSITY SCALE FOR A FIXED TIME BETWEEN 1/100 AND 1 SECOND AND DEVELOPMENT FOR 3 MINUTES AT 20*C. IN THE FOLLOWING INTERNAL TYPE DEVELOPER: