EP0025441B1

EP0025441B1 - Protecting photographic images against microspot attack

Info

Publication number: EP0025441B1
Application number: EP19800900467
Authority: EP
Inventors: Roy King; Philip J. Bly
Original assignee: Kodak Ltd; Eastman Kodak Co
Current assignee: Kodak Ltd; Eastman Kodak Co
Priority date: 1979-03-14
Filing date: 1980-09-24
Publication date: 1982-11-03
Also published as: WO1980001962A1; EP0025441A1; DE3061021D1

Abstract

A method of protecting silver images formed in a photographic material, especially microfilm, against attack by peroxides comprising contacting the material with a catalyst for the decomposition of hydrogen peroxide or a precursor of such a catalyst. The contacting may take place after image formation using a solution of a precursor, e.g. a manganese (11) salt or a catalyst e.g. colloidal manganese dioxide, may be incorporated during manufacture in a layer of the material adjacent a silver halide layer.

Description

This invention relates to the protection of photographic silver images against the action of peroxides.
It is known that processed silver halide emulsion photographic materials and especially microfilms are susceptible to the formation of microscopic spot blemishes when stored under adverse conditions. The defect is described in an article entitled 'Microscopic Spots in Processed Microfilm. Their Nature and Prevention' published in Photographic Science and Engineering, Vol 7, no. 5, P 253, (1963). Oxidation-reduction reactions between silver and peroxides are believed to be the cause of the defects.
Various methods have been described for the prevention or reduction of microscopic ageing defects. Conditions for the processing and storage of microfilm are given in the British Standards Institution Recommendations BS1153, February 1975 'The Processing and Storage of silver-gelatin type Microfilm' and in the American National Standard ANSI PH1.43-1976 'Practice for the Storage of Processed Safety Photographic Film'.
Photographic Science and Engineering 9, 378-384 (1965) describes a protective treatment for microfilm silver images against chemical attack in which the image is treated with a solution of a gold compound. The surface of the filamentary image silver is thus coated with gold by exchange of silver for gold by electrochemical substitution. The method is effective because gold is chemically inert compared to silver.
In U.S. Patent 2,839,405 inorganic metal salts, inter alia manganese (II) salts, are added to photographic silver halide emulsions as antifoggants. Since the photographic materials so formed are processed in conventional acid fixing baths, the manganese (II) will be completely removed during normal processing. There is however a slight chance that colloidal manganese dioxide might be formed by oxidation during storage of the material before use. This form of manganese would also be removed during processing.
The present invention ensures that sufficient catalyst for the decomposition of hydrogen peroxide, inter alia colloidal gold or colloidal manganese dioxide, remains in the fully processed, image-bearing photographic material. When colloidal manganese dioxide, which is coloured, is incorporated in the photographic material during manufacture, it can reduce the photographic speed if it is coated in or over the silver halide emulsion.
The present invention provides a solution to the problem of peroxide microspots which is simple, of low cost, and does not reduce photographic speed.
Accordingly, the present invention provides a method of protecting silver images formed in a photographic material against attack by peroxides characterised in that the material is contacted with colloidal particles of a catalyst for the decomposition of hydrogen peroxide either by

(a) contacting the photographic material with the colloidal catalyst particles or a precursor of colloidal manganese dioxide after the formation of the silver image, or
(b) incorporating the colloidal catalyst particles in the photographic material during manufacture in a layer located between the silver halide layer and the support and, after imagewise exposure, processing the exposed material using only alkaline processing solutions.

In one embodiment of the present invention finely divided, preferably colloidal, particles of the catalyst are incorporated into the photographic material during manufacture in a layer on the same side of the support as a photosensitive silver halide layer. The catalyst may be incorporated in any layer in an amount which does not interfere with the sensitometric properties of the material.
Preferably the catalyst is incorporated in a layer or layers adjacent the silver halide emulsion layer. For example, the catalyst may be incorporated in a sub-layer between the emulsion layer and the support and/or in an overlayer on the other side of the emulsion layer.
The catalyst may comprise gold, palladium or platinum but is preferably manganese dioxide. Colloidal manganese dioxide may be incorporated into a photographic silver halide material in amounts of from 50 to 500 mg/m², preferably from 100 to 300 mg/m^2. As indicated above it may be located in a sub-layer and/or overlay and the amounts used are preferably from 50 to 250 mg/m² in the sublayer and from 5 to 50 mg/m² in the overlayer.
As mentioned above the catalyst particles are colloidal. The size of colloidal particles may vary widely, e.g. 10-^7-10-³ cm, as is known but sizes up to 50 nm or even 100 nm are possible with the preferred particles being no larger than 15 nm.
The thickness of such layers may vary widely but thicknesses in the range 0.5 to 3.0,um for the overlayer and 0.5 to 5.0 um for the sub- layer are preferred.
In an alternative embodiment, the catalyst can be coated in a hydrophilic binder over a layer already containing a silver image.
In the above embodiment the catalyst is present in a layer containing hydrophilic binder which is preferably gelatin, an acylated gelatin, polyvinyl alcohol or mixtures thereof.
Photographic materials containing manganese dioxide catalyst should not be subjected to prolonged contact with acid fixer solutions containing sulphite ions as this can dissolve the catalyst and remove it from the material. The use of an alkaline fixer, e.g. an alkaline thiosulphate solution is therefore preferred.
In another embodiment of the present invention the silver image is treated with an aqueous solution of a catalyst precursor. The precursor is then converted to the catalyst either by a comparatively slow oxidative process involving atmospheric oxygen and/or peroxides or by a further processing step. The treatment with the catalyst precursor solution may, for example, take place as a final processing step or at any time after processing has otherwise been completed. Since the catalyst precursor is water-soluble any processing after its application to the photographic material will normally be avoided as this would tend to remove it.
The preferred catalyst precursor is a water-soluble manganese (II) salt, e.g. manganese (II) sulphate, nitrate or chloride. The solution preferably contains from 0.02 to 0.25, more preferably 0.025 to 0.1, moles manganese (II) salt per litre and optionally contains non- phosphate buffers to maintain the solution between pH 6.5 and 7.5.
The time of treatment may vary widely between, for example, 1 second up to several minutes preferably from 5 to 30 seconds. The temperature of the treatment may also vary widely and, apart from its usual relationship with the time of treatment, is not considered critical.
The catalyst precursor solution preferably contains a wetting agent to provide an even distribution of catalyst precursor in the photographic material and to avoid the formation of salt spots on drying. Any wetting agent may be used, e.g. an anionic, cationic or non-ionic wetting agent.
Water-soluble compounds known to absorb strongly and stabilize filamentary silver images may also be included in the solution, for example nitrogen-containing heterocyclic compounds and thiols, e.g. imidazole and 1-phenyl-5-mercaptotetrazole.
The present invention further provides a photosensitive photographic material comprising a support bearing at least one silver halide emulsion layer which has incorporated in a layer adjacent thereto finely divided, preferably, colloidal, particles of a catalyst for the decomposition of hydrogen peroxide.
The photographic materials protected from peroxide attack by the present invention are preferably microfilm materials but may be any photographic material, for example as described in Research Disclosure, December 1971, Item 9232 published by Industrial Opportunities Ltd., Havant, Hampshire, U.K.
The following Examples are included for a better understanding of the invention.

Example 1

To a stirred solution of 1 g potassium permanganate in 90 ml of demineralised water at pH 7.5 was rapidly added a solution of 15 ml of 20 volume (6%) hydrogen peroxide in 90 ml of demineralised water adjusted to pH 7.5. The reaction mixture was stirred for 30 minutes and then 20 ml of a 10% gelatin solution added. After dialysis for 3 days in semi-permeable membrane tubing the colloidal manganese dioxide content of the solution was found to be 0.15%.
50 ml of the above colloidal manganese dioxide solution were added to 450 ml of a 10% gelatin solution adjusted to pH 6.5. The gelatin solution was then coated over a silver-containing gelatin layer on a polyethylene terephthalate film at the rate of 14 ml/m² to give a Mn0₂ laydown of 2.10 mg/m².
Acceleration tests using hydrogen peroxide as described in Henn and Wiest - Photographic Science and Engineering, Vol. 7, Number 5, September-October 1963, page 253, failed to induce spotwise attack on such coatings whereas similar control coating without manganese dioxide showed the expected spotwise attack.

Example 2

20 ml of 0.15% colloidal manganese dioxide solution were added to 80 ml of a 6% polyvinyl alcohol solution and this solution was coated at a rate of 21.5 ml/m² over an existing layer of silver-containing polyvinyl alcohol coated on polyethylene terephthalate film base to give a final laydown of 6.46 mg Mn0₂ per m2.
Such layers showed increased resistance to oxidation and no tendency to undergo spotwise attack when compared with coatings not containing Mno₂ in the accelerated tests described in Example 1.

Example 3

A photographic microfilm material was prepared by coating on a polyethylene terephthalate film base, a dye-containing anti-halation underlayer containing colloidal manganese dioxide coated at 151 mg/m² and gelatin at 1.90 g/m², a fine grain negative emulsion layer and a gelatin supercoat containing colloidal manganese dioxide coated at 9 mg/m² and gelatin at 0.89 g/_m2.
Another photographic microfilm material was prepared by coating on a polyethylene terephthalate film base, a dye-containing anti-halation underlayer containing colloidal manganese dioxide coated at 176 mg/m² and gelatin at 1.90 g/m², a fine grain negative emulsion layer coated at 1.77 g Ag/m² and a gelatin supercoat at 0.89 g/m².
Samples of the experimental films were exposed either to a uniform neutral density of about 2.0 or a standard test image. These were then processed in a RECORDAK "PROSTAR" (trade mark) processor, model HDVR, under the following conditions:

(i) 75 s development at 30°C in a developer of the formula:
(ii) 37 s wash at 28°C.
(iii) 75 s fix at 28°C in a solution containing:
(iv) 37 s wash at 28°C.
(v) Dry at 50°C.

The processed films were incubated at 49°C, 84% RH in an atmosphere containing 150 ppm hydrogen peroxide for 64 hours.
The control experimental film showed severe microspot attack whilst all samples of the experimental films containing colloidal manganese dioxide in the underlayer and supercoat were unaffected.
At higher peroxide concentrations (600 ppm) none of the samples showed microspot attack but the control film showed a significant loss of density after 3 days. The film containing manganese dioxide was unaffected.

Example 4

The following treatment baths were prepared:

Formulation 1
Formulation 2
Formulation 3

Accelerated tests using acid peroxide as described in Example 1 on processed photographic films treated with the stabilising solutions described above, showed a marked resistance to microspot formation.

Claims

1. A method of protecting silver images formed in a photographic material against attack by peroxides characterised in that the material is contacted with colloidal particles of a catalyst for the decomposition of hydrogen peroxide either by

(a) contacting the photographic material with the colloidal catalyst particles or a precursor of colloidal manganese dioxide after the formation of the silver image, or

(b) incorporating the colloidal catalyst particles in the photographic material during manufacture in a layer located between the silver halide layer and the support and, after imagewise exposure, processing the exposed material using only alkaline processing solutions.

2. A method as claimed in claim 1 (a) in which the photographic material is treated with an aqueous solution of a colloidal manganese dioxide precursor.

3. A method as claimed in claim 2 in which the precursor is manganese (II) sulphate, nitrate or chloride.

4. A method as claimed in claim 3 in which the aqueous solution contains 0.02 to 0.25 moles manganese (II) salt and, optionally, non- phosphate buffers to maintain the solution at pH 6.5-7.5.

5. A method as claimed in any of claims 2-4 in which the solution also contains a nitrogen-containing heterocyclic silver image stabiliser.

6. A method as claimed in claim 1 (b) in which the catalyst is colloidal manganese dioxide and is present in a total amount of from 50 to 500, preferably 100 to 300 mg/m² of support.

7. A photosensitive photographic material comprising a support bearing at least one silver halide emulsion layer characterised in that it has incorporated in a layer located between the silver halide emulsion layer and the support, colloidal particles of a catalyst for the decomposition of hydrogen peroxide.

8. A photographic material as claimed in claim 7 in which the colloidal particles have a mean size of up to 500 nm.

9. A photographic material as claimed in claim 7 or 8 in which the catalyst particles are also present in a layer over the silver halide emulsion layer.

10. A photographic material as claimed in any of claims 7-9 in which the catalyst is colloidal manganese dioxide.

11. A photographic material as claimed in claim 10 in which the manganese dioxide is present in a total amount of from 50 to 500, preferably 100-300, mg/m² of support.