US3709689A

US3709689A - Surface development of an imagewise exposed emulsion containing silver halide grains with cores chemically ripened in two stages

Info

Publication number: US3709689A
Application number: US00025091A
Authority: US
Inventors: R Florens; F Claes; F Moisar
Original assignee: Agfa Gevaert AG
Current assignee: Agfa Gevaert NV; Agfa Gevaert AG
Priority date: 1969-04-02
Filing date: 1970-04-02
Publication date: 1973-01-09
Anticipated expiration: 1990-01-09
Also published as: BE748059A; JPS5036569B1; GB1306801A; DE2015070A1

Abstract

Light-sensitive silver halide emulsion adapted for producing either negative or direct positive photographic images and containing composite grains of silver bromide having internal core portions of chemically ripened silver bromide and external shell portions surrounding such core portions of chemically fogged silver bromide, such emulsion on development with a surface developing agent having a characteristic curve which exhibits a knee portion connecting a generally rectilinear portion of positive gradient and a generally rectilinear portion of negative gradient and is preferably of generally symmetrical configuration. By adjustment of the magnitude of the exposure of the emulsion to light either a direct positive or a negative photographic reproduction is obtained.

Description

United States Patent 11 1 Florens et al. 1451 Jan. 9, 1973 s41 SURFACE DEVELOPMENT OF AN 3,294,540 12/1966 Goffe ..96/87 [M AGEWISE EXPOSED EMULSION 3,501,307 3/1970 lllingsworth ..96/107 CONTAINING SILVER HALIDE GRAINS WITH CORES CHEMICALLY RIPENED IN TWO STAGES Raymond Leopold Florens; Frans Henri Claes, both of Edegem, Delgi lnventors:

. Germany Agfa-Gevaert, Mortsel, Belgium April 2, 1970 Assignee:

Filed:

Appl. No.:

[30] Foreign Application Priority Data April 2, 1969 Great Britain ..l7,16l/69 References Cited UNITED STATES PATENTS Berriman ..96/64 um; Frik Moisar, Cologne-Flittard,

OTHER PUBLICATIONS Photolithography, Associated General Publications Pty, Ltd, Sydney, Australia, 1953, p. 45-46 Primary Examiner-J. Travis Brown Assistant Examiner--Won l-l. Louie, Jr. Attorney-William J. Daniel [57] ABSTRACT Light-sensitive silver halide emulsion adapted for producing either negative or direct positive photographic images and containing composite grains of silver bromide having internal core portions of chemically ripened silver bromide and external shell portions surrounding such core portions of chemically fogged silver bromide, such emulsion on development with a surface developing agent having a characteristic curve which exhibits a knee portion connecting a generally rectilinear portion of positive gradient and a generally rectilinear portion of negative gradient and is preferably of generally symmetrical configuration. By adjustment of the magnitude of the exposure of the emulsion to light either a direct positive or a negative photographic reproduction is obtained.

7 Claims, 2 Drawing Figures Pmmmm ems 3.709.689

' sum 1 OF 2 FIG. 1

2.7 3.0 i log! I. f) rel.

SURFACE DEVELOPMENT OF AN IMAGEWISE EXPOSED EMULSION CONTAINING SILVER HALIDE GRAINS WITH CORES CHEMICALLY RIPENED IN TWO STAGES The present invention relates to the production of photographic images by means of a photographic silver halide recording material, which depending on the intensity of the image-wise exposure yields a negative or positive image.

In the U.K. Pat. Specification Nos. 1,011,062, 1,027,146 and 1,151,781 processes for preparing silver halide emulsions containing silver halide grains that are internally chemically modified have been described.

More particularly according to the process described in the United Kingdom Patent Specification 1,027,146 silver halide grains having a different interior and surface structure are prepared by interrupted precipitation and by chemically modifying the interior part of the grains by adding, e.g., hydrazine as reducing agent after a first precipitation stage. Thus, a silver halide emulsion comprising composite silver halide grains, which consist of a chemically modified -core covered with a layer of unripened silver halide, is obtained.

It has now been found that a photographic silver halide emulsion comprising silver halide grains that contain in the interior part ripening nuclei or sensitivity specks can be fogged externally to such an extent that when said grains are incorporated into a photographic colloid layer and are image-wise exposed in a range of rather low exposure intensities, a negative image is formed, whereas by image-wise exposure in a range of higher exposure intensities a positive image is obtained, the developing conditions of both differently exposed photographic materials being the same.

Silver halide emulsions, which are particularly suited for use according to the present invention are obtained by the following steps:

1. the formation of silver bromide grains by mixing in an aqueous gelatin solution a dissolved water-soluble silver salt and a dissolved water-soluble alkali metal bromide,

2. the interruption of the precipitation,

3. the chemical ripening of the already formed silver bromide grains,

4. the further mixing of said silver salt and bromide solution, thus forming a shell of unripened silver bromide around the ripened cores, and

5. the fogging of the internally ripened silver bromide grains at their surface to such an extent that dependent on the exposure (electromagnetic radiation intensity x time) a substantially negative or a substantially positive image of the original is formed in the silver halide emulsion layer in the same development conditions.

In the chemical ripening (sensitization) of the said cores noble metal compounds, e.g., gold compounds, sulphur compounds, reducing compounds, or mixtures of said compounds may be used.

The gold and sulphur sensitization has been described e.g., by C.E.l(. Mees, The Theory of Photographic Process", New York, The Macmillan Company, revised edition, 1954, pages 1 l2 seq.

The interior ripening of the grains is preferably carried out by means of a gold sensitizing agent or a reducing agent or with mixtures of both.

Particularly preferred for that purpose are thiourea dioxide known also as formamidine sulphinic acid and mixtures of water-soluble gold salts and thiocyanates forming complexes with gold and having a solvent action on the silver'halide grains, e.g., alkali thiocyanates and ammonium thiocyanate.

The precipitation of the silver bromide is preferably accomplished by simultaneously adding the bromide solution and silver salt solution to the gelatin solution and keeping the pAg-value during the precipitation as constant as possible.

The emulsions containing ripening nuclei in the interior of the silver halide grains are fogged uniformly at the surface of the grains.

The fogging can be performed with the aid of suitable reducing agents, e.g., hydrazine, tin(lI) salts, ascorbic acid, or formamidine sulphinic acid. The use of formamidine sulphinic acid (thiourea dioxide) and derivatives as sulphur sensitizers with reducing properties is described in the United Kingdom Patent Specification 789,823 and the U.S. Pat. Nos. 2,983,609 and 2,983,610.

The chemical fogging is the very critical step in the preparation of photographic silver halide emulsions suited for use according to the present invention. Different concentrations of fogging agent must be tried be fore it can be decided which concentration is the best for obtaining a negative or a positive image depending on a properly chosen exposure intensity.

The critical character of said fogging is illustrated in the examples, which prove that for a certain silver halide emulsion and fogging agent a suitable concentration has to be found experimentally.

The development of the exposed silver halide emulsion layers is preferably carried out by means of a surface developer, e.g., a lith-developer, which gives a particularly pronounced differentiation between the negative and positive image formation.

A lith-developer is a developing composition for active-radiation-exposed silver halide, which composition contains an addition compound of an aliphatic aldehyde or ketone with a hydrogen sulphite e.g., formaldehyde hydrogen sulphite, and hydroquinone as the sole developing substance.

The following examples illustrate the present invention.

EXAMPLE 1 An aqueous solution of ammonia was added to 650 ml of a 4 percent by weight aqueous gelatin solution at 45C to obtain a pH value of 9.3. In a precipitating flask were introduced ml of 3N aqueous solution of potassium bromide and 75 ml of 3N aqueous solution of silver nitrate, at a rate of 10 ml per minute, the pAg value during precipitation being adjusted to and maintained at a value corresponding to an E.M.F. of mV (Ag/saturated calomel electrode).

Subsequently 3.5 ml of 10' molar solution of formamidine sulphinic acid were added. After a digestion time of 30 minutes at 45C the pH was lowered to 6.5 whereupon 1.5 ml of 0.08 aqueous solution of gold(lIl) chloride and 1.5 ml of 2 aqueous solution of ammonium thiocyanate were added. The digestion was continued for 10 minutes at 45C.

During the second precipitation an aqueous solution of ammonia was added to obtain a pH value of 9.3. Then 665 ml of 3N aqueous solution of potassium bromide and 665 ml of 3N aqueous solution of silver nitrate were introduced at a rate of 19 ml per min., the

pAg value during precipitation being adjusted to a value corresponding to an E.M.F. of +100 mV (Ag/saturated calomel electrode). The emulsion was allowed to gel after the addition of 84 g of gelatin and washed in the usual manner.

After washing, the emulsion was divided in three equal portions A, B, and C, which were fogged respectively in the following way Portion A was treated for 1 hour at 55C with 1.5 ml

of molar aqueous solution of formamidine sulphinic acid per kg emulsion containing 110 g of silver bromide.

Portion B was treated for 1 hour at 55C with 3 ml of 10- molar aqueous solution of formamidine sulphinic acid Portion C was treated for 1 hour at 55C with 4.5 ml

of 10' molar aqueous solution of formamidine sulphinic acid.

After this fogging step gelatin was added and the pAg was adjusted to avalue corresponding to an E.M.F. of 20 mV (Ag/saturated calomel electrode). The emulsion ready for coating contained per kg 110 g of silver halide, 80 g of gelatin and l g of saponine as wetting agent. Just before coating 500 mg of formaldehyde (hardening agent) was added per kg of emulsion. The emulsion was applied to a polyethylene terephthalate support at a ratio of 7.5 g of silver bromide per sq.m and dried.

Test strips were then exposed to incandescent light through a gray test wedge (constant 0.15) and developed for 135 sec at 20C in a developing solution comprising:

anhydrous sodium sulphite 30 g paraformaldehyde 7.5 g potassium metabisulphite 2.5 g crystalline boric acid 7.5 g hydroquinone 22.5 g potassium bromide 1.5 g water to I000 ml The characteristic curves obtained with the portions A, B, and C respectively are shown in FIG. 1. The exposure intensity expressed in log It relative values is given on the abscissa, whereas the corresponding density values (D) are represented on the ordinate.

EXAMPLE 2 An emulsion was prepared, divided in three portions and fogged as described in Example 1.

Test strips were exposed and developed for 135 sec at 20C in the following developer composition:

p-monomethylaminophenol sulphate 1.5 g anhydrous sodium sulphite g hydroquinone 6 g anhydrous sodium carbonate 80 g potassium bromide 2 g water to l000 ml EXAMPLE 3 The preparation of the emulsion was carried out in the way described in Example 1, but the chemical ripening was performed with a mixture of 6 ml of 0.08 aqueous solution of gold(lll) chloride and 6 ml of 2 aqueous solution of ammonium thiocyanate. The second precipitation occurred at a pAg value corresponding to an E.M.F. of +20 mV (Ag/saturated calomel electrode).

An analogous result (like B in example 1) was obtained by external chemical fogging for minutes at 55C with 7 ml of 10" molar solution of formamidine sulphinic acid per kg of emulsion containing g of silver bromide.

We claim:

1. A process of producing negative or direct positive images from the same light-sensitive photographic material which comprises:

1. forming said material from a silver bromide emulsion prepared by the steps of:

a. forming silver bromide cores by mixing in an ammoniacal aqueous gelatin solution a dissolved water-soluble silver salt and a dissolved watersoluble alkali metal bromide to precipitate grains of silver bromide,

. interrupting the precipitation,

the silver bromide cores with a reducing agent in alkaline medium, lowering the pH to stop that reduction sensitization and continuing the chemical ripening by noble metal compounds in acid medium,

admixing further amounts of the silver salt and bromide solutions after making the solution ammoniacal, thus forming a shell of unripened silver bromide around the ripened cores,

e. fogging the resulting internally ripened silver bromide grains at their surface by contacting such grains with an amount of chemical fogging agent sufficient that an emulsion of the thus-treated grains when exposed to light through a grey test wedge covering in graduated steps a range of log E values from about 0 to at least about 3.00, photographically developed for sec. at 20C in a lith developing solution containing hydroquinone as the sole developing agent and a formaldehyde hydrogen sulfite addition compound, and the density values of the thus developed photographic image plotted against the corresponding log E values, produces a characteristic curve having an initial positively inclined generally straight line portion followed by a knee portion and a negatively inclined generally straight line portion, each of said positively and negatively inclined generally straight line portions extending between a minimum density value not greater than about 0.5 and a maximum density value at least equal to about 1.0;

2. imagewise exposing the thus-formed material to light of an intensity and time giving a log E value in that region of the characteristic curve corresponding to the desired image, and

3. photographically developing the exposed material in a lith developing solution containing hydroquinone as the sole developing agent and chemically ripening (chemical sensitization) of i taneously to the gelatin solution while keeping the pAg value during the precipitation as constant as possible.

5. A process according to claim 1, wherein the fogging is carried out by means of a reducing agent.

6. A process according to claim 1, wherein the fogging is effected with formamidine sulphinic acid.

7. A process according to any of the claim 1, wherein the chemical ripening is carried out by means of a mixture of a water-soluble gold salt and a thiocyanate.

UNKTEEE s'm'ms PATENT @FFIQE @ERTEMQA'EE @E @QRREQEEQN Patent No. 3p709 Dated January 9 1973 Inventor(s) Raymond Leopold FLORENS et al It is certified that error appears in the above-identified patent and that said Letters Patent are hereby-corrected as shown below:

In the Heading of the Patent, correct the inventor's name from "Frik Moi'sar" to Erik Moisar Signed and sealed this 10th day of July 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. Rene Tegcmeyer Attesting Officer Acting Commissioner of Patents

Claims

2. The process of claim 1 wherein the characteristic curve of said emulsion is of substantially symmetrical configuration.
2. imagewise exposing the thus-formed material to light of an intensity and time giving a log E value in that region of the characteristic curve corresponding to the desired image, and
3. photographically developing the exposed material in a lith developing solution containing hydroquinone as the sole developing agent and an addition compound of an aliphatic aldehyde or ketone with hydrogen sulfite.
3. A process according to claim 1, wherein the chemical ripening is carried out by means of a noble metal compound, a sulphur compound, a reducing compound, or a mixture of said compounds.
4. A process according to claim 1, wherein the bromide solution and silver salt solution are added simultaneously to the gelatin solution while keeping the pAg value during the precipitation as constant as possible.
5. A process according to claim 1, wherein the fogging is carried out by means of a reducing agent.
6. A process according to claim 1, wherein the fogging is effected with formamidine sulphinic acid.
7. A process according to any of the claim 1, wherein the chemical ripening is carried out by means of a mixture of a water-soluble gold salt and a thiocyanate.