DE69331321T2 - Spectral-sensitized silver halide photographic elements - Google Patents

Description

FIELD OF INVENTION

The present invention relates to spectrally sensitized silver halide photographic elements having broad sensitivity in the red region of the spectrum.

BACKGROUND OF THE INVENTION

Silver halide photography involves the exposure of silver halides to radiation to produce a latent image which is developed into a visible image during photographic processing. Silver halides are inherently sensitive only to light in the blue and ultraviolet regions of the spectrum. Therefore, if silver halides are to be exposed to other wavelengths of radiation, such as green or red light in a multi-color element, a spectral sensitizing dye is required.

A helium-neon laser is a typical light source emitting in the red region of the spectrum (632.8 nm). The advent of solid-state diodes emitting red radiation at wavelengths in the range of 650 to 750 nm has expanded the useful applications of red-sensitive photographic elements. Because of the large number of emission wavelengths, it would be desirable for a red-sensitive photographic element to have broad sensitivity in the red region of the spectrum. This would enable a single element to be used with light sources, such as lasers and diodes, having a variety of emission wavelengths. Such broad sensitivity can generally be provided either by using a single sensitizing dye, which provides broad sensitivity, or by using a combination of sensitizing dyes (usually two), which alone would provide more limited sensitivity. Many dye combinations have disadvantages, such as low sensitivity, e.g. due to Desensitization, or poor storage stability, e.g. formation of turbidity during storage.

U.S. Patent No. 5,116,722 discloses a process for producing a silver image by irradiating a silver halide emulsion spectrally sensitized with a trinuclear merocyanine dye containing at least two water-solubilizing groups with light of 600-690 nm, the trinuclear merocyanine having a benzothiazole or benzoselenazole group. Swiss Patent Application No. 677,409 describes spectrally sensitizing merocyanine dyes containing at least two acid residues for high-contrast silver halide emulsions; a benzothiazole nucleus is preferably present in the structure of the spectrally sensitizing dyes.

U.S. Patent No. 4,717,650 describes a silver halide photographic emulsion having high spectral sensitivity in the red wavelength region, specifically within a wavelength range of 600 to 690 nm, using a benzimidazole pentacarbocyanine spectral sensitizing dye.

U.S. Patent No. 4,336,323 describes a light-insensitive imaging layer comprising a synthetic polymeric binder, a dye containing a quinoline group, a nitrate salt and an acid to obtain a decolorizable image system.

Research publication 346, February 1993, p. 135, No. 34685, discloses methine dyes useful in imaging applications. However, it has been shown that such dyes do not give good results in terms of sensitometric properties and/or residual staining.

Many of the dyes known to spectrally sensitize silver halide photographic emulsions to the red wavelengths of 600 to 690 nm have the disadvantage of having low solubility in water, so that they usually have to be dispersed in the emulsion or added to it in the form of an alcoholic solution. Consequently, they are not adequately removed during processing. As a result, a considerable residual magenta to blue tint remains in the dried element.

It is an object of the present invention to provide photographic silver halide elements with broad sensitivity in the red region of the spectrum which have good photographic properties in terms of light sensitivity and contrast and show minimal residual discoloration after processing.

SUMMARY OF THE INVENTION

The present invention relates to a silver halide photographic element comprising a support having applied thereto at least one silver halide emulsion layer which is spectrally sensitized with a sensitizing dye of the formula (I):

where Z represents the atoms required to complete a 6-membered nitrogen-containing heterocyclic ring, which optionally contains substituents and/or fused rings; at least 2 representatives of R₁, R₂, R₃ and R₄ - but not R₁ and R₂ together - represent an organic radical which carries a water-solubilizing group in the form of free acid, in salt form or in latent form and are the same or different; R₅ and the representatives of R₁, R₂, R₃ and R₄ which are not an organic radical with a water-solubilizing group represent a hydrogen atom, an alkyl radical, an alkenyl radical or an aryl radical; and n is 0 or 1.

The dye described above provides broad sensitivity in the red region of the spectrum with good photosensitivity, good contrast and minimal residual discoloration after processing.

DETAILED DESCRIPTION OF THE INVENTION

In the formula (I) of the present invention, Z represents the atoms required to complete a 6-membered nitrogen-containing heterocyclic ring, such as those from the series of 2-quinolines (e.g. quinoline, 3-methylquinoline, 5-methylquinoline, 7-methylquinoline, 8-methylquinoline, 6-chloroquinoline, 8-chloroquinoline, 6-methoxyquinoline, 6-ethoxyquinoline, 6-hydroxyquinoline, 8-hydroxyquinoline), from the series of 4-quinolines (e.g. quinoline, 6-methoxyquinoline, 7-methoxyquinoline, 8-methylquinoline) and the like, optionally containing substituents and/or fused rings. These nuclei can be substituted with any of several radicals which are known as substituents for such rings. These include sulfo groups, halogen atoms (e.g. chlorine, fluorine), alkyl radicals with 1 to 12 carbon atoms (preferably with about 1 to 4 carbon atoms, e.g. methyl, ethyl, butyl, which themselves can be substituted with known units such as hydroxyl group, halogen atom or sulfo group), alkoxy radicals with 1 to 12 carbon atoms (preferably with about 1 to 4 carbon atoms, e.g. methoxy, ethoxy, butoxy), carboxy radicals, carboxylate radicals with 1 to 4 carbon atoms (e.g. methyl ester, ethyl ester group), sulfonamide radicals or carbonamide radicals.

When the term "group" or "nucleus"/"ring" is used in this invention to describe a chemical compound or substituent, the chemical material described includes the basic group or nucleus as well as that group or nucleus with usual substitution. When the term "moiety" is used to describe a chemical compound or substituent, only an unsubstituted chemical material is intended to be included. For example, "alkyl group" includes not only such alkyl moieties as methyl, ethyl, octyl, stearyl, etc., but also such moieties bearing substitution groups such as halogen, cyano, hydroxy, nitro, amine, carboxylate, etc. On the other hand, "alkyl moiety" or "alkyl" includes only methyl, ethyl, octyl, stearyl, cyclohexyl, etc.

By the term "water-solubilizing group" as used in the present invention is meant a group which imparts to the dye sufficient solubility in water, i.e. soluble to at least 0.5 g in 1 liter of water at room temperature and pH > 7. If the water-solubilizing group is in latent form, sufficient solubility is obtained during alkaline processing.

According to the present invention, at least 2 of the representatives of R₁ to R₄ are organic radicals, e.g. an alkyl radical such as methyl or ethyl, an aryl radical such as phenyl, which carry a water-solubilizing group in the form of free acid, in salt form or in latent form, e.g.:

-(CH2 )m-COOM, -C6 H4 -COOM, -CH2 C6 H4 -COOM, -(CH2 )m-SO3 M, -C6 H4 -SO3 M,

- CH2 -C6 H4 -SO3 M, -CH2 -COO-CH2 -COO-R5 , -CH2 -COO-CH2 -CO-R5 ,

wherein m is an integer preferably from 1 to 4, M is a hydrogen atom, an ammonium group, an alkali metal atom, e.g. sodium, potassium and lithium, or an organic amine salt, e.g. a triethylamine salt, ethyldiisopropylamine salt, pyridine salt, and R₆ is an alkyl radical, e.g. methyl.

Examples of water-solubilizing groups in latent form are:

-CH2 -COO-CH2 -COO-CH3 and -CH2 -COO-CH2 -CO-CH3 .

R₅ and the representatives of R₁ to R₄ which do not represent an organic radical carrying a water-solubilizing group can be selected from a hydrogen atom, an alkyl radical having 1 to 18 carbon atoms (preferably having 1 to 12 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, octyl, etc.), an alkenyl radical having 1 to 18 carbon atoms (preferably having 1 to 12 carbon atoms, such as allyl) and an aryl radical having 6 to 10 carbon atoms (such as phenyl, carboxyphenyl).

Preferably, the present invention relates to a silver halide photographic element comprising a support having applied thereto at least one silver halide emulsion layer which is spectrally sensitized with a sensitizing dye according to the formula (I) wherein Z represents the atoms required to complete a substituted or unsubstituted 6-membered nitrogen-containing heterocyclic radical optionally containing substituents and/or fused rings; R3 and R4 represent an organic radical carrying a water-solubilizing group in free acid, salt or latent form and are the same or different; R1, R2 and R5 are selected from a hydrogen atom, an alkyl radical, an alkenyl radical and an aryl radical; and n is 0 or 1.

More preferably, the present invention relates to a silver halide photographic element comprising a support having applied thereto at least one silver halide emulsion layer which is spectrally sensitized with a sensitizing dye of formula (II):

wherein R₃ and R₄ each represent an organic radical which carries a water-solubilizing group in the form of free acid, in salt form or in latent form and are the same or different; R₁, R₂ and R₅ represent a hydrogen atom, an alkyl radical, an alkenyl radical or an aryl radical; R represents a sulfo group, a halogen atom, an alkyl radical, an alkoxy radical, a sulfonamide or carbonamide group and p is an integer from 0 to 4, with the proviso that the R radicals can be the same or different if p is 2 or more.

Examples of the sensitizing dyes of the present invention include the following exemplary compounds. However, the scope of the invention is not limited to these compounds alone.

Synthesis of compound S1

Compound A: 14.3 g of 2-methylquinoline and ethyl p-toluenesulfonate were heated at 120°C for 2 hours. After cooling, a volume of 100 ml of acetone was added. The precipitate was filtered off and dried at 60°C under reduced pressure.

Compound B: 29.4 g of 5-anilinomethylene-N-ethoxycarbonylmethylrhodanine was dissolved in 100 ml of acetic anhydride and the mixture was refluxed for 2 hours and then allowed to cool to room temperature. The precipitate was filtered off, washed with ethyl acetate and dried at 60°C under reduced pressure.

Compound C: 6.86 g of compound A and 6.72 g of compound B were dissolved in 15 mL of DMF. A volume of 5.4 mL of triethylamine was added to the mixture, which was stirred at room temperature until a blue compound separated. The mixture was diluted with ethanol and filtered. The ethanol-washed solid was used as such in the reaction below.

Compound D: 7.45 g of compound C and an excess of methyl-p-toluenesulfonate were heated at 120°C for 40 minutes. After cooling, a volume of 100 ml of ethyl acetate was added: a green solid separated. It was filtered off and dried at 40°C under reduced pressure.

Compound E: 5.6 g of compound D and 1.9 g of 4-oxo-2-thioxo-3-thiazolidinedineacetic acid were dissolved in 20 ml of methanol and a volume of 4.5 ml of triethylamine was added and the mixture was refluxed for 50 minutes. After cooling to room temperature, 1.3 g of 30% NaOH was added to the solution and the separated solid was filtered off, washed with ethanol and dried.

5.6 g of compound E was dissolved in 20 mL of methanol and 1.3 g of 30% NaOH was added to the solution. The mixture was refluxed for 1 hour and after cooling, the deposited solid was filtered, washed with ethanol and acetone and dried at 55°C under vacuum.

The structure of the product was confirmed by NMR.

The present invention also relates to a process for producing a silver image, comprising imagewise exposing a photographic material by means of a light source which emits light in the wavelength range from 600 to 690 nm, the photographic material comprising a support on which at least one silver halide emulsion layer is applied which is spectrally sensitized with a sensitizing dye of the formula (I):

where Z represents the atoms required to complete a 6-membered nitrogen-containing heterocyclic ring, which optionally contains substituents and/or fused rings; at least 2 representatives of R₁, R₂, R₃ and R₄ - but not R₁ and R together - represent an organic radical which carries a water-solubilizing group in the form of free acid, in salt form or in latent form and are the same or different; R₅ and the representatives of R₁, R₂, R₃ and R₄ which are not an organic radical with a water-solubilizing group represent a hydrogen atom, an alkyl radical, an alkenyl radical or an aryl radical; and n is 0 or 1.

The spectral sensitizing dyes of the present invention can be prepared according to methods known in the art, such as those described in 'James, The Theory of Photographie Processes, MacMillan, 4th ed. (1977)'.

The spectral sensitizing dyes of the present invention spectrally sensitize silver halide emulsions to radiation in the wavelength range of 600 to 700 nm, particularly 620 to 680 nm, to provide photoelements that are particularly suitable with a variety of commercially available laser diodes. Another important advantage resulting from the use of the spectral sensitizing dyes of the present invention is that the photoelement containing the sensitizing dyes exhibits increased contrast and reduced residual discoloration after processing.

The spectral sensitizing dyes according to the invention are integrated in the photographic silver halide emulsion with a content of 0.01 to 0.20 grams / mole of silver, preferably from 0.02 to 0.16 grams / mole of silver.

The spectral sensitizing dyes of the present invention can be dispersed directly in the emulsion. Alternatively, they can be first dissolved in a suitable solvent, such as methyl alcohol, ethyl alcohol, methyl cellosolve, acetone, water, pyridine, or a mixture thereof, to be added to the emulsion as a solution. Methods for adding the sensitizing dyes to the photographic emulsion are described, for example, in U.S. Patent Nos. 3,469,987, 3,676,147, 3,822,135, 4,199,360, and U.S. Patent Nos. 2,912,343, 3,342,605, 2,996,287, and 3,429,835. The above-mentioned sensitizing dyes can be uniformly dispersed in the silver halide emulsion before coating it on a suitable support. Of course, this dispersing process can be carried out in any suitable step in the preparation of the silver halide emulsion.

Any of the various types of silver halide photographic emulsions may be used in the practice of the present invention. For example, silver chloride, silver bromide, silver iodobromide, silver chlorobromide, silver chloroiodobromide, and mixtures thereof may be used dispersed in a hydrophilic colloid or carrier. Any grain structure, cubic, orthorhombic, hexagonal, epitaxial, or tabular (high aspect ratio) grains, may be used. The colloid may be partially or fully hardened with any of the various known photographic hardeners. Such hardeners are free aldehydes, aldehyde releasing compounds, triazines and diazines, aziridines, vinyl sulfones, carbodiimides, and the like, and may be prepared as described, for example, in U.S. Pat. Nos. 3,232,764, 2,870,013, 3,819,608, 3,325,287, 3,992,366, 3,271,175 and 3,490,911.

The silver halide emulsions can be chemically sensitized using the usual sensitizing agents. Sulfur-containing compounds, gold and precious metal compounds, polyoxyalkylene compounds are particularly suitable. Methods for chemically sensitizing silver halide emulsions are described, for example, in Research Disclosure 17643, Section III (1978).

Other conventional photographic additives such as coating aids, antistatic agents, contour dyes, antihalation dyes and layers, antifoggants, latent image stabilizers, supersensitizers, anti-buckling agents, high intensity Schwarzschild effect reducers, plasticizers, matting agents, developers, color couplers, absorbing and scattering materials that can be added to the silver halide emulsion are described in Research Disclosure 17643 (1978).

Gelatin is generally used as the hydrophilic colloid for the silver halide photographic elements of the present invention. In addition to or instead of gelatin, there can be used as the hydrophilic colloids gelatin derivatives, natural substances such as albumin, casein, agar-agar, alginic acid and the like, and hydrophilic polymers such as polyvinyl alcohol, polyvinyl pyrrolidone, cellulose ether, partially hydrolyzed polyvinyl acetate and the like. Furthermore, gelatin can be partially substituted with polymer latexes obtained by emulsion polymerization of vinyl monomers, such as polyethyl acrylate latexes, to improve the physical characteristics of the photographic layers.

The support substrate used in the silver halide photographic elements of the present invention can be any of the conventionally used support substrates such as glass, cloth, metal, film including, for example, cellulose acetate, cellulose acetate butyrate, cellulose nitrate, polyester, polyamine, polystyrene and the like, paper including baryta paper, coated paper, resin coated paper and the like.

The silver halide emulsions according to the invention can be used as photosensitive emulsions for various photoelements, such as negative emulsions with high surface sensitivity or high internal sensitivity, surface-fogged or non-fogged direct positive emulsions, print-out emulsions, Reversal emulsions, emulsions for black and white materials, for color materials, radiographic materials, transfer color materials and the like.

The photographic elements of the invention can be processed to form a visible image upon combination of the silver halides with an alkaline aqueous medium in the presence of a developer contained in the medium or material, as is known in the art. In the case of color photographic elements, processing includes at least a color development bath and optionally a pre-hardening bath, a neutralizing bath, a first (black and white) development bath, etc. These and other baths which complete the photographic processing (e.g., bleach, fix, bleach-fix, intensify, stabilize and wash baths) are known in the art and are described, for example, in Research Disclosure 17643 (1978).

The present invention will now be illustrated with reference to the following example.

EXAMPLE

A cubic monodisperse silver chlorobromide (40 mol% bromide) with a grain size of 0.32 micrometers was prepared as in Example N. 2 of European Patent Application No. 423,538. The resulting emulsion was sensitized with gold and sulfur, then divided into several parts and each part was optically sensitized according to the scheme below:

The resulting emulsion samples were coated on a polyethylene terephthalate support in an amount of 4.1 g/m² as silver. The gelatin content in an emulsion layer thus produced was 2.6 g/m². A protective layer of gelatin (0.7 g/m²) was placed over the emulsion layer. The samples were irradiated in a first case at 60 ergs/cm² with a Toshiba Told 9215 laser diode emitting a laser beam at 670 nm and in a second case with a helium-neon laser source emitting a laser beam at 632.8 nm. The samples were then examined sensitometrically. The photosensitivity was measured in Log E, where E is expressed in lux s at a density of 1.0 above Dmin. The contrast corresponds to the absolute value of the slope of the sensitometric curve measured at densities 0.07 and 0.17 above Dmin. The results are shown in Table 1 below, where Photosensitivity 1 and Contrast 1 respectively refer to the values of photosensitivity and contrast obtained when the samples were irradiated at 670 nm, and Photosensitivity 2 and Contrast 2 respectively refer to the values of photosensitivity and contrast obtained when the samples were irradiated at 632.8 nm. Table 1

Table 1 shows that comparative sample 1, sensitized with reference compound A, which contains a benzothiazole nucleus with only one water-solubilizing group, has a deep blue residual discoloration. Comparative sample 2, sensitized with reference compound B, which contains a quinoline nucleus with only one water-solubilizing group, also shows a deep blue residual discoloration. Comparative sample 3, sensitized with reference compound C, which contains a benzothiazole nucleus with two water-solubilizing groups, still has a slight residual discoloration, low photosensitivity and unacceptable contrast values when irradiated at 670 nm. The inventive sample 4, which is sensitized with the sensitizing dye 53, shows no residual discoloration, while still maintaining the good sensitometric properties in the Sense of contrast and photosensitivity are retained upon irradiation with both different wavelengths 632.8 nm and 670 nm. This fact shows that the sensitizing dyes according to the invention which contain a quinoline nucleus give better results, in particular with regard to the absence of residual discoloration, compared with the same sensitizing dyes which contain a benzothiazole residue.

Claims (7)

1. A silver halide photographic element comprising a support having applied thereto at least one silver halide emulsion layer which is spectrally sensitized with a sensitizing dye of the formula (I): where Z represents the atoms required to complete a 6-membered nitrogen-containing heterocyclic ring; at least 2 representatives of R₁, R₂, R₃ and R₄ - but not R₁ and R₂ together - represent an organic radical which carries a water-solubilizing group in the form of free acid, in salt form or in latent form and are the same or different; R₅ and the representatives of R₁, R₂, R₃ and R₄ which are not an organic radical with a water-solubilizing group represent a hydrogen atom, an alkyl radical, an alkenyl radical or an aryl radical; and n is 0 or 1. 2. A silver halide photographic element as described in claim 1, wherein R₃ and R₄ represent an organic radical bearing a water-solubilizing group in free acid, salt or latent form and are the same or different, and wherein R₁, R₂ and R₅ represent a hydrogen atom, an alkyl radical, an alkenyl radical or an aryl radical. 3. A silver halide photographic element as described in claim 1, wherein Z represents the atoms necessary to complete a quinoline ring. 4. A silver halide photographic element as described in claim 1, wherein the spectral sensitizing dye corresponds to formula (II): wherein R₃ and R₄ each represent an organic radical which carries a water-solubilizing group in the form of free acid, in salt form or in latent form and are the same or different; R₁, R₂ and R₅ represent a hydrogen atom, an alkyl radical, an alkenyl radical or an aryl radical; R represents a sulfo group, a halogen atom, an alkyl radical, an alkoxy radical, a sulfamido or carbonamido group and p is an integer from 0 to 4, with the proviso that the R radicals can be the same or different if p is 2 or more. 5. A silver halide photographic element as described in claim 1, wherein R₃ and R₄ each represents CH₂-COOH. 6. A process for producing a silver image, comprising imagewise exposing a photographic material to a light source which emits light in the wavelength range from 600 to 690 nm, the photographic material comprising a support on which at least one silver halide emulsion layer is applied which is spectrally sensitized with a sensitizing dye of the formula (I): where Z represents the atoms required to complete a 6-membered nitrogen-containing heterocyclic ring; at least 2 representatives of R₁, R₂, R₃ and R₄ - but not R₁ and R₂ together - represent an organic radical which carries a water-solubilizing group in the form of free acid, in salt form or in latent form and are the same or different; R₅ and the representatives of R₁, R₂, R₃ and R₄ which are not an organic radical with a water-solubilizing group represent a hydrogen atom, an alkyl radical, an alkenyl radical or an aryl radical; and n is 0 or 1. 7. A process for forming a silver image as described in claim 6, wherein Z represents the atoms necessary to complete a quinoline ring.