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(11) | EP 0 410 753 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Photographic recording materials with latent image stability |
| (57) Latent image stability is enhanced in photographic recording materials through the
use of long chain N-alkyl- or N-alkenylbenzothiazolium salts. |
[0001] The present invention relates to photographic recording materials and more particularly to photographic recording materials having latent image keeping stability.
[0002] A visible image is formed in silver halide photographic materials by exposure of the material to actinic radiation to form a record of the exposure. This record, which is invisible to the unaided eye, yields a visible image by photographic processing of the exposed material.
[0003] It is generally believed that the latent image comprises minute specks of metallic silver. These specks form in or on individual silver halide grains by interaction between silver ions and photoelectrons generated by absorption of actinic radiation by the silver halide grains.
[0004] Processing of most common silver halide photographic materials includes a development step in which the material is contacted with an aqueous alkaline solution of a developing agent. The developing agent, which is a reducing agent, selectively reduces to metallic silver those silver halide grains containing a latent image.
[0005] It is recognized in the photographic art that a latent image is not permanent and that, with passage of time, silver halide grains which would be developable immediately after exposure become nondevelopable. This phenomenon is termed latent image fading and manifests itself as a loss in image density in the developed-image and a consequent loss in speed in the silver halide photographic material.
[0006] If silver halide materials were developed immediately following imagewise exposure, latent image fading would not be a problem. However, with many silver halide materials, delays between exposure and processing frequently occur. For example, with amateur film materials in which multiple images are formed on a single roll of film there is often a delay of months between the time the first image is exposed and the time the exposed material is processed. With such materials latent image fading can present a significant problem and compounds are added to photographic materials to prevent or reduce this undesirable effect. These compounds are referred to as latent image stabilizers and prevention or reduction of latent image fading is referred to as latent image stabilization.
[0007] Various attempts have been made to solve this problem. One attempt is mentioned in U. S. Patent 3,954,478 where N-2-propenyl-benzothiazolium and N-2-propenyl-naphthothiazolium salts are described as being useful for this purpose.
[0008] Other proposed solutions to latent image instability are described in U. S. Patent 4,374,196 where acyclic compounds, obtained by basic hydrolysis of N-alkenylthiazolium salts, are shown to reduce latent image instability. In U.S. Patent 4,423,140 certain aromatic mercaptide compounds are described as being useful in reducing latent image instability. Published European Application 250,740 discloses 2-unsubstituted N-alkenylthiazolium salts as latent image stabilizers.
[0009] The present invention provides a photographic recording material comprising a support and a silver halide emulsion characterized in that the emulsion has associated therewith a long chain N-alkyl or N-alkenylbenzothia- zolium salt having the structural formula:
wherein:
R¹ is hydrogen, halogen, lower alkyl or lower alkoxy;
R² is -CH=CH₂ or CH₃;
Y is a counterbalancing ion;
m is 0 to 4; and
n is 2 to 6.
[0010] When R¹ is alkyl or alkoxy, the length of the carbon chain which designates "lower" is from 1 to about 5 carbon atoms, preferably from 1 to about 3 carbon atoms. The alkyl or alkoxy group can be straight or branched chain. When R¹ is halogen it is preferably chloro.
[0011] The counterbalancing ion Y can be any anion compatible with the photographic material in which it is coated. Useful ions include inorganic anions such as halides, halophosphates, trifluoromethane sulfonates and the like.
[0012] While n can be an integer as high as 6, it is at least 2 and preferably from 2 to 5. The carbon chain can be straight or branched chain, such as for example n-propyl, s-butyl or t-amyl.
[0013] The alkylene group which is bonded directly to the quaternary nitrogen atom, and which is also linked to the terminal ethylene or methyl group, comprises at least 2 and as many as 6 carbon atoms. Such substitution on the nitrogen atom of the indicated quaternary salts provides latent image stability for the photographic recording materials in which they are coated.
[0014] Specific compounds falling within this invention which can provide latent image stability in an exposed photographic silver halide emulsion include the following:
[0015] Compounds useful in this invention can be prepared for example by treating alcohol with trifluoromethanesulfonic anhydridide in the presence of pyridine and subsequently treating the product with benzothiazole under a nitrogen environment to produce the desired salt.
Example 1 - Preparation of Compound No. 7
[0017] In a flask equipped with a magnetic stirrer, dropping funnel, nitrogen inlet, and reflux condenser were placed pyridine (0.79 g, 0.01 mole) and dichloromethane (20 ml). The flask was chilled in an ice-salt bath at 0°C and a nitrogen atmosphere was maintained inside. Trifluoromethanesulfonic anhydride (2.82 g, 0.01 mole) in dichloromethane (20 ml) was added dropwise. A white precipitate formed; the resulting thick suspension was stirred for 10 minutes. 1-Pentanol (0.88 g, 0.01 mole) in dichloromethane (20 ml) was added dropwise over 30 minutes. The reaction mixture was then stirred at 0°C for 10 more minutes. The reaction mixture was quickly filtered through a pad of sodium sulfate. The filtrate was immediately added to a solution of benzothiazole (1.10 g, 0.008 mole) in dichloromethane (50 ml). The resulting solution was stirred at room temperature under a nitrogen atmosphere for 19 hours. The solvent was removed on a rotary evaporator to give a pink oil. This oil was then dissolved in warm water (50 ml). Sodium hexafluorophosphate (1.5 g) was added with stirring. A white precipitate immediately formed. The aqueous mixture was stirred at room temperature for 30 minutes, and then was filtered. The collected solid was washed first with water and then with ether. The product was dried overnight in a vacuum oven at room temperature. This gave 2.3 g (82%) of a white powder, m.p. 133-135 C.
Anal. Calcd. for C₁₂H₁₆F₆NPS: C, 41.0; H, 4.6; N, 4.0; S, 9.1.
Found: C, 41.2; H, 4.5; N, 3.9; S, 9.7.
Example 2 - Preparation of Compound No. 1
[0018] In a three-necked round bottomed flask equipped with a dropping funnel, mechanical stirrer, pot thermometer, and nitrogen inlet were placed 3-buten-1-ol (12.8 g, 0.177 mole) and dichloromethane (500 ml). The solution was stirred and the flask was chilled until the pot temperature was 0°C. Pyridine (14.3 g, 0.18 mole) was added, and then trifluoromethanesulfonic anhydride (50.0 g, 0.18 mole) was added dropwise at a rate such that the pot temperature was kept below 10°C. After this addition was complete, the resulting mixture was stirred at 10°C for 1/2 hour; the temperature was then allowed to rise to 20°C. The entire reaction mixture was filtered through anhydrous sodium sulfate. Benzothiazole (24.0 g, 0.18 mole) was added to the filtrate and the mixture was stirred overnight at room temperature under a nitrogen atomosphere. The solvent was removed from the resulting solution to give an oil. This oil was dissolved in water (500 ml). Potassium hexafluorophosphate (33.0 g, 0.18 mole) was added and the aqueous mixture was stirred until a crystalline precipitate formed. The mixture was filtered and the collected solid was recrystallized twice from methanol. This gave 13.0 g (22%) of product, m.p. 100°C.
Anal. Calcd. for C₁₁H₁₂F₆NPS: C, 39.4; H, 3.6; N, 4.2; F, 34.0; S, 9.6.
Found: C, 39.3; H, 3.6; N, 4.2; F, 33.8; S, 10.3.
[0019] The benzothiazolium and benzoselenazolium salts described herein can be added to a silver halide emulsion at any point subsequent to precipitation of the silver halide grains. Preferably, the salts are added to an emulsion after chemical and spectral sensitization, but prior to coating. However, the salts can be present during these sensitization procedures.
[0020] The optimum amount of benzothiazolium salt added to an emulsion will depend upon various factors such as the particular salt employed, the particular silver halide emulsion used or the nature of other components of the emulsion. Useful amounts are within the range of from about 0.002 to about 10 millimoles of salt per mole of silver. Preferably, the salt is incorporated in the emulsion in an amount of from about 0.02 to about 0.5 millimole per mole of silver.
[0021] The silver halide emulsions employed in the present invention can be any of the silver halide emulsions known in the art which are desirably protected against latent image instability or fading. The silver halide emulsions can be comprised of silver bromide, silver chloride, silver chlorobromide, silver chloroiodide, silver bromoiodide, silver chlorobromoiodide or mixtures thereof. The emulsions can include coarse, medium or fine grains and can be monodisperse or polydisperse.
[0022] The silver halide emulsions are preferably surface latent image-forming emulsions. They can be chemically sensitized as illustrated by T. H. James, The Theory of the Photographic Process, 4th Ed., Macmillan, 1977, pp. 67-76, or with sulfur, selenium, tellurium, gold, platinum, palladium, iridium, osmium, rhenium or phosphorus sensitizers, or combinations of these sensitizers, as illustrated by Research Disclosure, Vol. 134, June 1975, Item 13452, or in U. S. Patent Nos. 1,623,499; 1,673,522; 2,399,083; 2,642,361; 3,297,447; 3,297,446; 1,315,755; 3,772,031; 3,761,267; 3,857,711; 3,565,633; 3,901,714 and 3,904,415 and U. K. Patent No. 1,396,696.
[0023] Chemical sensitization can optionally be conducted in the presence of thiocyanate derivatives, as described in U. S. Patent Nos. 2,222,264 and 2,642,361; thioether compounds, as disclosed in U. S. Patent Nos. 2,521,926; 3,021,215 and 4,054,457; or azaindenes, azapyridazines and azapyrimidines, as described in U. S. Patent Nos. 3,411,914; 3,554,757; 3,565,631 and 3,901,714. Additionally or alternatively, the emulsions can be reduction sensitized e.g., with hydrogen, as illustrated by U. S. Patent Nos. 3,891,446 and 3,984,249 by low pAg (e.g., less than 5), high pH (e.g., greater than 8) treatment or through the use of reducing agents, such as stannous chloride, thiourea diozide, polyamines and amineboranes, as illustrated by Research Disclosure, Vol. 136, August 1975, Item 13654, or U. S. Patent Nos. 2,518,696; 2,739,060; 2,743,182; 2,743,183; 2,983,609; 3,026,203 and 3,361,564 (Research Disclosure is published by Industrial Opportunities Ltd., Homewell, Havant Hampshire, PO9 IEF, United Kingdom.)
[0024] The silver halide emulsions can be spectrally sensitized with dyes from a variety of classes, including the polymethine dye class, which includes the cyanines, merocyanines, complex cyanines and merocyanines (i.e., tri-, tetra-, and poly-nuclear cyanines and merocyanines), oxonols, hemioxonols, styryls, merostyryls and streptocyanines. Particularly useful dyes are benzoxazole, benzimidazole and benzothiazole carbocyanine dyes.
[0025] The photographic silver halide emulsions can contain various colloids alone or in combination as vehicles. Suitable hydrophilic materials as well as hardeners therefore, are described in Research Disclosure, December 1978, Item 17643, Sections IX and X.
[0026] The photographic silver halide emulsions and elements employing the stabilizing agents of this invention can contain other addenda conventional in the photographic art. Useful addenda are described, for example, in Research Disclosure, December 1978, Item 17643 and include antifoggants, couplers (such as dye forming couplers, masking couplers and DIR couplers) DIR compounds, anti-stain agents, image dye stabilizers, absorbing materials such as filter dyes and UV absorbers, light scattering materials, coating aids, plasticizers and lubricants.
[0027] The photographic recording materials described herein can be black-and-white or monochrome materials or they can be multilayer and/or multicolor elements comprising a support bearing one or more layers of a silver halide emulsion. These materials can be designed for processing in conventional developer solutions. Multicolor elements can contain dye image forming units sensitive to each of the three primary regions of the spectrum. Each unit can be comprised of a single emulsion layer or of multiple emulsion layers sensitive to a given region of the spectrum. The layers of the element, including the layers of the image-forming units, can be arranged in various orders as known in the art. In an alternative format, the emulsion or emulsions can be disposed as one or more segmented layers.
[0028] A preferred color photographic recording material according to this invention comprises a support bearing at least one blue-sensitive silver halide emulsion layer having associated therewith a yellow dye-forming coupler, at least one green-sensitive silver halide emulsion layer having associated therewith a magenta dye-forming coupler and at least one red-sensitive silver halide emulsion layer having associated therewith a cyan dye-forming coupler, at least one of the silver halide emulsion layers containing a latent image stabilizing compound of this invention. In accordance with a particularly preferred aspect of the present invention, the stabilizing compound is contained in a yellow dye-forming blue-sensitive silver halide emulsion.
[0029] The photographic recording materials of the present invention can contain additional layers conventional in photographic elements, such as overcoat layers, spacer layers, filter layers, antihalation layers, scavenger layers and the like. The support can be any suitable support used with photographic elements. Typical supports incude polymeric films, paper (including polymer-coated paper), glass and the like. Details regarding supports and other layers of the photographic elements of this invention are contained in Research Disclosure, December 1978, Item 17643, referred to above.
[0030] As used herein, the term "associated therewith" signifies that the stabilizing compound is in a silver halide emulsion layer or in an adjacent layer so that the materials contained therein are accessible to one another.
Example 3 - Photographic Evaluations
[0032] Benzothiazolium salts as latent image keeping agents, were evaluated in a black-and-white photographic test. This test used sulfur and gold sensitized 0.8 µm octahedral silver bromide emulsion prepared in the presence of 1,10-dithia-18-crown-6 ether and bis(2-amino-5-iodopyridine-dihydroiodide) mercuric iodide. This emulsion was coated in a single layer format. The melt pH was 5.6 and the pAg was 8.5. All the benzothiazolium salts were coated at 0.2 mmole/mole Ag. The latent image keeping (LIK) coatings were exposed for 1/50 sec and were then incubated at 49°C/50% RH for two weeks. The raw stock keeping (RSK) coatings were incubated first, followed by exposure as described above. Both coatings were processed for 6 minutes in KODAK Rapid X-ray Developer.
[0033] The data obtained are given below in Table I. In this table, speed values are given for fresh, raw stock keeping (RSK), and for latent image keeping (LIK). The LIK-RSK difference represents the speed loss due to latent image degradation.
Table I
| Compound | n | Fresh Speed | 2 Week Speed | ||
| RSK | LIK | LIK-RSK | |||
| control | ― | 243 | 255 | 170 | -85 |
| 1 | 2 | 239 | 245 | 222 | -23 |
| 2 | 3 | 239 | 234 | 218 | -16 |
| 3 | 4 | 238 | 232 | 215 | -17 |
[0034] From the data contained in Table I it is apparent that, in the presence of benzothiazolium salts as described herein, reduced loss of film sensitivity during storage prior to processing is obtained.
Example 4 - Photographic Evaluation
1. A photographic recording material comprising a support and a silver halide emulsion
which has associated therewith an N-alkyl or N-alkenylbenzothiazolium salt having
the structural formula:
wherein:
R¹ is hydrogen, halogen, lower alkyl or lower alkoxy;
R² is -CH=CH₂ or CH₃;
Y is a counterbalancing ion;
m is 0 to 4; and
n is 2 to 6.
wherein:
R¹ is hydrogen, halogen, lower alkyl or lower alkoxy;
R² is -CH=CH₂ or CH₃;
Y is a counterbalancing ion;
m is 0 to 4; and
n is 2 to 6.
2. The recording material of claim 1 wherein R¹ is hydrogen or alkyl or alkoxy having
from 1 to about 5 carbon atoms.
3. The recording material of claim 2 wherein n is from 2 to 5.
4. The recording material of claim 1 wherein R² is -CH=CH₂ or -CH₃.
5. The recording material of claim 1 wherein the salt has at least one of the structural
formulae:
