Treatment Of An Imagewise Exposed And Developed Silver Halide Emulsion Layer Containing A Catalase Active Or Peroxide Active Catalyst With Peroxide

Abstract

A process for the production of positive photographic images comprising the steps of imagewise exposing a light-sensitive silver salt emulsion layer, photographically developing to form a negative silver image in the exposed areas, treating the exposed and developed layer with a peroxide compound, the peroxide compound is left to act on the layer until it has been decomposed at the negative silver image, and forming a positive image by decomposition of the undercomposed peroxide compound in the unexposed areas of the layer.

Description

The invention relates to a process for the production of photographic images by imagewise decomposition of peroxide compounds, a visible image being produced either physically by imagewise production of gas bubbles or chemically by a color-producing oxidation reaction with a suitable reaction component.

The production of photographic images by imagewise production of compounds which form gas bubbles, in particular bubbles from hydrogen peroxide, is known per se. A process for the production of photographic images consisting of a silver image and of bubbles superimposed on the silver image is described in British Patent Specification No. 1,196,200. In the said process, a silver image is first produced in the conventional way in a hydrophilic layer, but this silver image has a much lower density than conventional black and white images. The layer is then brought into contact with hydrogen peroxide, and this hydrogen peroxide is decomposed in the areas of the image which contain finely divided silver to form bubbles of oxygen. The gas bubbles are expanded by subsequent heating of the exposed material, and a vesicle image is formed. Since these expanded bubbles scatter the light in the image areas, these areas appear dark in transmitted light but pale when viewed by reflected light. In the unexposed areas of the layer, most of the incident light is transmitted through the layer. The silver image is greatly intensified by this method and deep black images with high contrast are obtained even when layers which have a very low silver content are used. The quality of photographic images obtained by this process is excellent.

It is also known to render the image visible by chemical means which involve a color-producing oxidation reaction. In this chemical process, a light-sensitive layer is exposed imagewise so that nuclei of noble metals of the Groups Ib or VIII of the Periodic Table are produced in the image area, and this layer is then treated with peroxide compounds which undergo catalytic decomposition at the nuclei formed in the presence of reaction compounds for a color-producing reaction.

Instead of using light-sensitive layers which when exposed to light form noble metal nuclei for the decomposition of hydrogen peroxide, the above mentioned process for the production of photographic images may also be carried out with layers which contain substances which on exposure to light form catalase active or peroxidase catalysts. Suitable substances of this kind are e.g., certain complex compounds of heavy metals of Groups VIb, VIIb or VIII of the Periodic Table of elements with a mono-basic or higher basic carboxylic acid. Compounds which split off iodine ions on exposure to light have the same effect.

All these processes give rise to negative images. Positive images may be obtained using peroxides by the following method:

Light-sensitive photographic materials used for this purpose may contain, uniformly distributed in them, catalase-active or peroxidase-active enzymes such as catalase, peroxidase, hemoglobin or hemin which are inactivated in the image areas when exposed to actinic light. The images obtained with these materials are direct positive images.

A disadvantage of this direct positive process is the relatively low light sensitivity of these catalase active enzymes.

The production of direct positive images by the peroxide process may also be achieved by conventional reversal processing. A process of this type comprises the following process steps:

Imagewise exposure of the silver halide emulsion layer, black and white development to produce a negative silver image, bleaching of the silver image, uniform re-exposure of the silver halide in the emulsion layer, reverse second development to produce the positive silver image, and production of a bubble image or of a dye image by decomposition of peroxide compounds on this positive silver image.

Although this process would make further use of the advantages of the above mentioned processes which are generally carried out with layers which have a very low silver content, namely the lower scattering of light on imagewise exposure and relatively high sensitivity, the process is relatively complicated to carry out and due to the large number of steps involved it is time consuming.

In principle, other effects which give rise to photographic reversal of images could be used for the production of positive images by the peroxide processes described above, for example solarisation, the Sabattier effect, the Herschel effect etc. but all these processes have the disadvantage of having relatively low sensitivity to light.

It is among the objects of the present invention to modify the above mentioned processes which are characterised by imagewise decomposition of peroxide compounds so that positive images may be obtained directly by a process which is highly sensitive to light.

We now have found a process for the production of positive photographic images by imagewise exposure of a light-sensitive layer and treatment of the exposed layer with a peroxide compound in which a light-sensitive layer contains a silver salt is exposed imagewise, developed photographically and then treated with a peroxide compound which is left to act on the layer until it has been decomposed at the areas of the negative silver image, and a positive image is then rendered visible in the unexposed areas of the silver salt layer, which areas still contain undecomposed peroxide compounds, the said positive image being rendered visible by the presence of substances which accelerate the decomposition of peroxides either physically resulting in the development of a bubble image or chemically by an oxidation reaction with a color producing reaction component.

The most suitable silver halide emlusion layers for the process of the invention have a low silver content but a high packing density of the silver halide. The silver application of these layers which are preferably used may be about 0.01 - 1 g of silver in the form of silver halides per m.sup.2. The packing density of the silver halide in these layers, i.e., the proportion of silver halide in the layer, should be at least 50 percent, i.e., the layer may contain at least 1 part by weight of silver halide per 1 part by weight of binder. The light-sensitive layers may be covered with protective layers of gelatin or other binders.

The most suitable silver halide in silver bromide although silver chloride layers may of course, also be used, and the silver halides may contain a certain amount of silver iodide, up to about 10 Mols percent.

After exposure, the layer is photographically developed by the usual processes. The usual developing agents are suitable for this purpose. When the layer is subsequently treated with the peroxide compound, e.g., with hydrogen peroxide, the peroxide compound decomposes very rapidly in those areas where a negative silver image has been produced by the photographic development process. This decomposition of peroxide can be recognized by the vigorous evolution of oxygen in those parts of the layer which have a high silver content. In the unexposed areas of the layer, on the other hand, the peroxide compound is absorbed by the layer and remains practically undecomposed. It remains available for the subsequent production of the positive image.

A certain amount of decomposition of peroxide is also required to render the positive image visible. Suitable measures are therefore required to ensure that a certain amount of decomposition of peroxide compound will also take place in the unexposed areas of the layer. This can be achieved in known manner by adding to the light-sensitive layers, in a uniformly distributed form, substances which accelerate the decomposition of peroxide compound. However, despite the presence of these substances the peroxide compound must be decomposed much more rapidly in the exposed areas which contain the negative silver image than in the unexposed areas which do not contain negative silver.

The following are examples of substances which are suitable for this purpose:

1. Finely divided nuclei of noble metals such as silver, gold, palladium and platinum;

2. Sulfides, selenides, hydroxides, hydrated oxides or oxides of heavy metals such as copper, nickel, iron, manganese, cobalt, lead, vanadium, silver, gold or the metals of the platinum group;

3. Complex compounds of iron or copper, chromates, molybdates, tungstates or vanadates;

4. Active charcoal or organic substances such as catalase active or peroxidase active enzymes.

Decomposition catalysts of the type mentioned above have been described e.g., in the following works: Gmelins "Handbuch der Anorganischen Chemie," 8th edition, "Sauerstoffband," system-No. 3, delivery 7, pages 2,289 - 2,292, Verlag Chemie GmbH, Weinheim/Bergstrasse (1966); "Hydrogen peroxide" by W. C. SCHUMB, C. N. SATTERFIELD and P. L. WENTWORTH, pages 467 to 500, Reinhold Publishing Corp. New York (1955).

The most suitable concentration of these decomposition nuclei for any given application can easily be determined by laboratory tests.

The production of these decomposition nuclei for peroxide compounds in the unexposed areas of the layer can be achieved particularly easily by developing the layer photographically to such an extent that even the unexposed areas of the layer contain a fog of developed silver. A silver fog which has a density of about 0.05, which is barely visible with the naked eye, is sufficient for the process according to the invention. When the layer is treated to render the image visible, a fog of this density would given rise to an image having a density of 1 or more.

The light-sensitive silver salts, especially silver halides, are preferably dispersed in a binder in the light-sensitive layers. The usual binders used for photographic silver halide emulsion layers are suitable, especially proteins and particularly gelatin, but gelatin may be partly or completely replaced by natural or synthetic film-forming binders or inorganic structure-forming substances such as silica gel. Suitable organic film-forming polymers are e.g., polyvinyl acetate, partly saponified polyvinyl acetate, polyvinyl alcohol, cellulose esters such as cellulose acetate, carboxymethyl cellulose and alginic acid or its derivatives such as salts, amides, esters or the like.

Inorganic peroxide compounds, e.g., perborates, percarbonates, perphosphates or persulfates are suitable for the process according to the invention but the most suitable peroxide compound is hydrogen peroxide. Organic peroxide compounds may also be used, e.g., benzoyl peroxide, percarbamide and addition compounds of hydrogen peroxide and aliphatic acid amides, polyalcohols, amines acyl-substituted hydrazines etc. Hydrogen peroxide is preferred on account of its high activity and the ease with which it can be handled in the form of aqueous solutions.

The peroxide compound is preferably used in the form of a solution. Hydrogen peroxide for example may be used also in vapour form.

The process of rendering the positive image visible by decomposition of the peroxide may be effected by physical or chemical means. Thus for example the developed oxygen may be rendered visible in the form of a bubble image by the process described in British Patent Specification No. 1,196,200. Alternatively, the peroxide compounds may be decomposed in the presence of reactants for a color producing oxidation reaction. Processes of this type have been described in U.S. Patent Application No. 881,610.

To produce a bubble image, the exposed and developed layer is heated after the treatment with the peroxide compound and the necessary time of decomposition on the image silver. A bubble image is then formed in the areas where the peroxide compound has been left intact.

The intensity of the vesicle image depends on the quantity of hydrogen peroxide used and the quantity of decomposition nuclei. The heat treatment of the material to produce the visible bubbles should be as brief as possible. The temperature employed in this treatment depends on the properties of the binder. Satisfactory results can be achieved at relatively low temperature of about 60.degree. to 70.degree. C but higher temperatures may also be employed if this is necessitated by the softening point of the binder. If gelatin is used, which is the preferred binder, it is advisable to carry out the treatment in the presence of small quantities of water because this promotes swelling of the gelatin and hence bubble formation. The same applies to other binders which swell in the presence of water.

The use of peroxides mixed with hydrazines is very advantageous for the catalytic production of the bubble image because the gas liberated in that case is not O.sub.2 alone but a mixture of O.sub.2 and N.sub.2.

The bubble images obtained may be stabilized against moisture by the processes described in U.S. Patent Application Nos. 885,984 and 887,392 as required.

Rendering the image visible may be achieved also by a chemical method. In this case, the process is performed in the presence of reaction components for a color producing oxidation reaction. Suitable processes are described in U.S. Patent Application Ser. No. 881,610.

The most suitable reagents for the production of dyes by an oxidizing reaction are, of course, those which yield the most deeply colored compounds on oxidation with the catalytically activated peroxide compound.

The reagents may be organic compounds which yield the dye directly when oxidized, e.g., amino compounds, hydroxyl compounds or aminohydroxyl compounds of isocyclic or heterocyclic aromatic compounds.

The following are given as examples: phenol, aniline, pyrocatechol, resorcinol, hydroquinone, o-, m- and p-phenylenediamine, N,N-dimethyl-phenylenediamine, N,N-diethyl-phenylenediamine, N,N-ethyl-methyl-phenylenediamine, o-, m- and p-aminophenyl, p-methyl aminophenol, 2,4-diaminophenol-(1), 1,7-dihydroxy naphthalene, 2,3-dihydroxy naphthalene, 1,6,7-trihydroxy naphthalene, 1,2-deamino naphthalene, 1,8-diamino naphthalene, benzidine, 2,2'-diamino naphthalene, 4,4'-diaminophenyl, 8-hydroxyquinoline, 5-hydroxyquinoline, 2-hydroxycarbazole, 1-phenylpyrazolene-(3), etc.

The amino, hydroxyl or aminohydroxy compounds may be substituted, e.g., with halogen, alkyl, aryl, alkoxy, sulfonic acid, nitro, keto, carboxylic acid or carbonamide groups.

The following are given as examples: 2,5-dichloro-p-phenylenediamine, guiacol, 4-methoxynaphthol-(1), 1-hydroxy-2-amino-benzene-sulfonic acid-(4), 1-amino-2hydroxybenzene-sulfonic acid-(4), 3-amino-5-sulfo-salicyclic acid, 1,6,7-trihydroxy-naphthalene-sulfonic acid-(3), benzidine-2,2'-disulfonic acid, benzidine-3,3'-disulfonic acid, 1,8-dihydroxy naphthalene-disulfonic acid-(3,6), and 4-nitro-pyrocatechol.

In some cases, mixtures of several such compounds will give rise to much more intense dye formation on oxidation than the individual components. Thus for example a mixture of o-phenylenediamine and pyrocatechol produce a more intense dye-forming reaction. Even components which do not yield dyes on oxidation when used alone, e.g., tetrabromohydroquinone or tetrabromopyrocatechol, may intensify the formation of dyes when they are added to other hydroxyl, amino or aminohydroxy compounds.

The oxidation of aromatic amino, hydroxyl and/or aminohydroxy compounds yields monomeric or polymeric dyes which are related to quinone imines and azines. Some examples of these oxidative dye producing reactions are described in "Kunstliche organische Farbstoffe und ihre Zwischenprodukte" by H. R. SCHWEIZER, Springer-Verlag Berlin-Gottingen-Heidelberg (1964) pages 222, 275, 281 and 293; in "Grundlagen der Synthese von Zwischenprodukten und Farbstoffen" by N. I. WOROSHOW, Akademie-Verlag Berlin (1966), pages 703 to 789; "Chemie der Farbstoffe und deren Anwendung" (Technische Fortschrittsberichte, volume 60) by A. SCHAEFFER, Theodor-Steinkopff-Verlag, Dresden-Leipzig (1963), pages 59 et seq.

Apart from dye precursors, leuco dye compounds and vat dyes which may be oxidized to dyes may, of course, also be used. For examples of these see "Kunstliche organische Farbstoffe und Zwischenprodukte" by H. R. SCHWEIZER, Springer-Verlag, Berlin-Gottingen-Heidelberg (1964), pages 250 and 320.

Oxidizable organic compounds of the type which yield the image dye only in a subsequent reaction with other compounds are also suitable for the process of the invention. In principle, any reaction systems which undergo an oxidizing coupling reaction to yield dyes may be used. Reference may be made particularly to the so-called color producing photographic developers of the phenylene diamine or aminopyrazolone series (see e.g., C. E. K. MEES and T. H. JAMES "The Theory of the Photographic Processes," 3rd Edition, MacMillan Co. New York (1966), page 382; H. R. SCHWEIZER "Kunstliche organische Farbstoffe und ihre Zwischenprodukte," Springer-Verlag, Berlin-Gottingen-Heidelberg (1964), page 295). Isocyclic and heterocyclic hydrazines may also be coupled with suitable components to yield dyes by oxidation (see e.g., H. HUNIG et al., Angew, Chem. 70 (1958) 215; S. HUNIG, Chimia 15 (1961) 133 and Angew, Chem. 74 (1962) 818). The color-producing photographic developer substances are oxidized catalytically by the peroxide compounds in the presence of the catalysts which is distributed imagewise. Their oxidation products may then react with known photographic color couplers which are also present to yield dyes. Suitable color couplers for this purpose are e.g., cyan couplers of the phenol or naphthol series, magenta couplers of the indazole series and yellow couplers of the benzoyl acetanilide series.

The reaction time required for the hydrogen peroxide compound i.e., the length of time between the treatment of the developed layer with the peroxide compound and the rendering visible of the positive image, or in other words, the time required for sufficient decomposition of the peroxide compounds in those parts of the layer which contain the negative image silver, depends primarily on the concentration of the peroxide and the catalytic activity of the negative silver image. The times required for any given peroxide compound and silver halide emulsion can easily be determined by simple laboratory tests.

The maximum density and the gradation of the positive image can be modified by altering the length of waiting time between the peroxide treatment and the production of the positive image.

The individual steps of the process may be accelerated by increasing the temperature. This increase in temperature in addition increases the sharpness of the image.

Example 1:

A highly sensitive silver iodobromide gelatin emulsion (6.5 percent Mol of AgI) is cast on a layer support of polymethylene terephthalate. Layer thickness approximately 10 .mu., silver application approximately 2 g of AgNO.sub.3 /m.sup.2. A protective gelatin layer about 8 .mu. in thickness is then cast over the emulsion layer. Hardning is then carried out in the usual manner by the addition of 25 ml of a 3 percent aqueous solution of formaldehyde per litre of emulsion.

After imagewise exposure (0.5 second with X-rays between fluorescence intensifying foils) the layer is immersed in the following developer solution for 10 seconds at 35.degree. C:

Bath I:

2 g of 1-phenyl pyrazolidone-3

25 g of hydroquinone

25 g of anhydrous Na.sub.2 SO.sub.3

1 g of a polyethylene oxide wax made up to 1 litre with H.sub.2 O adjusted to pH 12.5 with NaOH

After brief washing (water spray for 10 seconds) the layer is treated for 10 seconds in the following mixture heated to 35.degree. C:

Bath II:

700 cc of 30 percent aqueous H.sub.2 O.sub.2

300 cc of isopropanol

5 cc of pentane-dione-(2,4)

After the treatment with this bath, the layer is left untreated for 20 seconds and only then treated for 10 seconds at 35.degree. C with

Bath III:

20 g of 2-amino-5-(N-ethyl-N-ethoxy-amino) toluene

16 g of pyrocatechol

10 g of sodium sulfite

10 g of sodium citrate made up to 1 litre with water pH adjusted to 8 with Na.sub.2 CO.sub.3 solution.

To stabilize and bleach the negative silver, the layer is then passed for 10 seconds through the following bath after a brif washing:

Bath IV:

20 g of ZnSO.sub.4.sup.. 7H.sub.2 O

25 g of K.sub.2 Cr.sub.2 O.sub.7 in 1 litre of H.sub.2 O adjusted to pH 5 with acetic acid/acetate buffer.

This process produces a blue-black, positive image of the original.

Example 2

100 ml of a highly sensitive AgBr emulsion are stirred into 500 ml of a 10 percent aqueous solution of the following cyan color coupler: ##SPC1##

For the other emulsion additives see Example 1.

The mixture is cast to form a layer about 15 .mu. in thickness. Silver application approximately 0.6 g of silver in the form of silver halide per m.sup.2. A protective gelatin layer about 5 .mu. in thickness is then cast over this layer.

After drying, the layer is exposed imagewise in a conventional sensitometer for 1/100th second behind a grey step wedge and then developed for 15 seconds at 35.degree. C in the following developer:

Bath I:

10 g o p-methylaminophenol

12 g of hydroquinone

25 g of anhydrous Na.sub.2 SO.sub.3

40 g of K.sub.2 CO.sub.3 made up to 1 litre with H.sub.2 O adjusted to pH 12.5 with NaOH.

After brief washing (water spray for 10 seconds) the layer is dipped for 10 seconds into the following mixture heated to 35.degree. C:

Bath II:

700 cc of 30 percent aqueous H.sub.2 O.sub.2

300 cc of cyclohexanol

5 cc of cyclohexanone

After the treatment with this bath, the layer is left for 20 seconds and only then treated for 10 seconds at 35.degree. C with

Bath III:

3.5 g of N,N-diethyl-p-phenylenediamine sulfate

2.0 g of anhydrous Na.sub.2 SO.sub.3

2.0 g of sodium ethylenediaminotetra-acetate

1.2 g of hydroxylamine sulfate

75.0 g of K.sub.2 CO.sub.3 made up to 1 litre with H.sub. O

After brief washing and bleach fixing the following bath:

Bath IV:

Solution 1: 50 g of Na.sub.2 SO.sub.2 O.sub.3 in 500 cc of H.sub.2 O

Solution 2: 25 g of K.sub.3 Fe(CN).sub.6 in 500 cc of H.sub.2 O (the two solutions are mixed before use) the layer is washed and dried.

A cyan positive image of the original to which the layer has been exposed is obtained.

If other color couplers are used instead of the color coupler mentioned above (naphthol (1)-sulfonic acid (4)-derivative), other dyes may be produced catalytically, e.g., as in U.S. Patent Application Ser. No. 881,610. Thus for example couplers of the indazole series or pyrazolone series are suitable for use as magenta couplers and those of the benzoyl acetanilide series are suitable as yellow couplers.

Example 3

0.5 cc of a colloidal silver sol prepared as described in "The Theory of the Photographic Process" by C. E. K. MEES, 1st Edition, MacMillan Co., New York (1942), page 565 are added to 100 cc of a silver chlorobromide gelatin emulsion which has a steep gradation (60 Mols percent of AgBr). Suitable quantities of Au, Pt, Pd, Os, Ir and other noble metal sols may be added instead of this silver sol. For the other emulsion additives, see Example 1.

The mixture is cast to form a layer of about 15 .mu. in thickness. Total silver application approximately 2.0 g of silver in the form of silver halide per m.sup.2. Over this is cast a protective gelatin layer of about 8 .mu. in thickness.

After drying, the layer is exposed imagewise as in Example 2 and then developed for 15 seconds at 35.degree. C in the following developer:

Bath I:

5 g of p-methylaminophenol

6 g of hydroquinone

40 g of anhydrous Na.sub.2 SO.sub.3 made up to 1 litre with H.sub.2 O adjusted to pH 10.5 with K.sub.2 CO.sub.3

This non-fogging negative developer may be used in this case because the silver sol added to the emulsion is available as decomposition catalyst for the peroxide compound in the unexposed areas of the layer.

After a brief washing (water spray for 10 seconds) the layer is dipped into the following mixture for 15 seconds at 35.degree. C:

Bath II:

25 g of potassium percarbonate and

40 g of sodium acetate made up to 1 litre with H.sub.2 O

After the treatment with this bath, the layer is heated to about 80.degree. C with infrared radiation for 30 seconds and then treated for 15 seconds at 35.degree. C with

Bath III: 20 g of 1.7-dihydroxy naphthalene

40 g of pyrocatechol made up to 1 litre with H.sub.2 O adjusted to pH 12 with NaOH

To stabilize and bleach the negative silver, the layer is finally passed for 10 seconds through the following bath after a brief washing:

Bath IV:

20 g of Al.sub.2 (SO.sub.4).sub.3.sup.. 18H.sub.2 O

20 g of K.sub.3 Fe(CN).sub.6

in 1 litre of H.sub.2 O adjusted to pH 12 with NaOH

This process results in a reddish black, positive image of the original.

Example 4

A photographic layer as described in Example 1 (after imagewise exposure and fogging development as described in Example 1) is dipped for 10 seconds into the following peroxide bath:

30 ml of 30 percent H.sub.2 O.sub.2

70 ml of ethanol

1 ml of glycerol

The layer is then heated by infrared radiation for 8 seconds to 60.degree. - 120.degree. C, not immediately but after a period of 30 seconds. A reversal image consisting of bubbles of oxygen is formed in the photographic layer.

The formation of gas bubbles may be intensified by the addition of hydrazine hydrate to the above mentioned peroxide bath. The gas bubbles in that case consist not only of oxygen but of mixture of oxygen and nitrogen.

The fogging development may be replaced by a non-fogging development if the layer used has been prepared from 1 litre of silver halide emulsion + 5 ml of a 0.1 percent catalase solution (as catalase active catalyst).

Claims

We claim:

1. A process for the production of positive photographic images by imagewise exposing a light sensitive silver halide emulsion layer on a support, developing the exposed emulsion to provide metallic silver, applying to the exposed and developed emulsion a peroxide compound and decomposing the peroxide on the emulsion, wherein the improvement comprises providing in the emulsion a uniformly distributed catalyst selected from the group consisting of catalase active and peroxide active catalyst, which catalyst accelerates the decomposition of the peroxide to release oxygen at a slow rate, decomposing the peroxide in the exposed areas under the catalytic action of the metallic silver at a high rate of decomposition, catalyzing the decomposition of the applied peroxide in the unexposed areas to release oxygen at a slower rate than said decomposition at the metallic silver so that peroxide compound at the negative silver image is decomposed and a positive image is formed by the decomposition of the remaining peroxide compound in the unexposed areas.

2. The process of claim 1, wherein the exposed layer is treated with a fogging photographic developer.

3. The process of claim 1, wherein the silver halide emulsion layer contains at least one part by weight of silver halide per one part by weight of binder.

4. The process of claim 1, wherein the catalase active and/or peroxidase active catalysts are noble metals of Groups Ib or VIII of the Periodic Table.

5. The process of claim 1, wherein the catalase active and/or peroxidase active catalysts are complex compounds of heavy metals of Groups VIb, VIIb or VIII of the Periodic Table.

6. The process of claim 1, wherein the silver halide emulsion layer contains catalase active and/or peroxidase active enzymes.