Dyes absorbing light in the extended red and infrared region of the wavelength spectrum

Abstract

 Dyes absorbing light in the extended red and/or infrared region of the wavelength spectrum are incorporated in one or more hydrophilic layer or layers of photographic materials, spectrally sensitized for the same spectral region, characterised in that said dyes are silver salt complexes of pentamethine oxonol dyes. The dyes are in the non-migratory state in said hydrophilic colloid layer or layers of the photographic materials wherefrom they can be rapidly removed in alkaline aqueous liquids used in the processing of said materials. Upon storage they show a high stability.

Description

1. Field of the Invention

[0001] The present invention relates to silver salts of filter dyes and their use as infrared filter and antihalation dyes in photographic elements.

2. Background of the Invention

[0002] Non-spectrally sensitizing dyes are widely used in photographic elements, particularly in photographic elements of the silver halide type. They may be used in a photosensitive silver halide emulsion layer as screening dyes, in an undercoat adjacent to the photosensitive layer and/or in a backing layer on the side of the support opposite to the photosensitive layer to absorb reflected and scattered light thereby serving as antihalation dye or in an overcoat or interlayer to shield a particular photosensitive layer against undesired exposure being therefore referred to as filter or absorber dye.

[0003] Spectrally the dye absorption spectrum should approximately be equal to the sensitivity spectrum of the corresponding silver halide emulsion in the layer of which a sharp image has to be reproduced.

[0004] On the one hand it is very important that filter dyes remain, i.e. that they are non-migratory, in the layer wherein they have been incorporated especially when this layer is in direct contact with the silver halide emulsion layer in order to prevent an undesired desensitizing action on the silver halide. On the other hand the filter dyes may not stain the photographic material after image processing. Therefore preference is given to filter dyes that decolorize or can be removed from the photographic element in the processing stage. This requirement is nowadays becoming more and more stringent as rapid processing times are of increasing interest.

[0005] As described in US-P 3,560,214 dyes comprising a carboxyl and phenyl substituted pyrazoline nucleus linked through a methine group to a dialkylaminophenyl group can be removed relatively easily in alkaline aqueous processing liquids but lack sufficient fastness to diffusion in hydrophilic colloid layers.

[0006] Other filter dyes characterized by the presence of a 2-pyrazolin-5-one nucleus substituted with a carboxyphenyl group and including a methine group or chain linked to a dialkylamino group are described in US-P 4,857,446. The decolorization of said filter dyes proceeds very rapidly in alkaline aqueous processing baths. The monomethine dyes have an absorption spectrum of which the maximum is in the shorter wavelength range of the visible spectrum so that normally a second filter dye is needed to block or absorb green light and even a third one to absorb radiations of longer wavelengths, e.g. radiations in the red or even in the infrared region. The use of exposure light absorbing dyes in a antihalation layer in silver halide emulsion materials that are made spectrally sensitive to extended red and infrared light and of which the exposure proceeds with an extended red or infrared emitting laser is strongly preferred as in the last years there is an increasing interest for extended red (660-700nm) or infrared-sensitive materials due to the entrance in the market of laser-recording systems, making use of extended red or infrared laserdiodes.

[0007] Not only in graphic arts applications but also in medical applications, as e.g. for monitoring films used in medical X-ray diagnostic applications, there has been put a lot of effort in the research for suitable infrared antihalation dyes: infrared-absorbing antihalation dyes are described in e.g. US-Patent Applications 4,933,269; 4,871,656; 4,876,181 and EP 251,282; 101,646; 329,491 and 341,958.

[0008] Once a filter dye has been selected, the problem is how to get the filter dye in a coated layer so that all the requirements mentioned previously are met.

[0009] One of the possibilities is to make use of solid particle dispersions of water insoluble dyes as has been described in EP 0,384,633 A2; EP 0,323,729 A2; EP 0,274,723 B1, EP 0,276,566 B1 and US-Patents 4,900,653; 4,904,565; 4,940,654; 4,948,717; 4,988,611 and 4,803,150.

[0010] Another possibility is offered in Research Disclosure 19551 (July 1980) which describes an approach of associating hydrofobic compounds with latex polymer particles.

[0011] EP 0,401,709 A2 describes the dissolution of hydrophobic dyes into oil droplets being substantially insoluble in water and the preparation of the corresponding oilformer dispersions or loaded polymer latex dispersions.

[0012] To prevent dye wandering, the dye is often coated with a mordant to bind the dye in the layer in which it is coated as is e.g. illustrated in US-Patent 2,527,583. As dye mordants polymers are often used.

[0013] Another possibility is offered by adsorption of dyes at the surface of very fine light-insensitive silver halide crystals with the expectable disadvantages of the coating of more silver halide crystals and possibly fixation difficulties.

[0014] Very few dyes satisfy the above requirements especially when rapid processing is concerned. Moreover, apart from the requirement of non-diffusibility and of decolourizing or removal by processing that the dyes should meet, they should have high stability in the photographic material, not only under the influence of the ingredients present in the emulsion layers prior to coating, but especially under severe storage conditions of the packed material e.g. under circumstances of high temperatures and high degrees of humidity. Especially for the group of organic filter dyes with a high extinction coefficient, that are used in antihalation layers of silver halide materials and that absorb substantially light of the extended-red and/or near infrared wavelength-region, the storage stability is problematic.

3. Objects and Summary of the Invention

[0015] Therefore it is an object of the present invention to provide new filter dyes having an absorption maximum in the extended red and/or infrared wavelength-region that can be incorporated in non-migratory state in hydrophilic colloid layers of photographic materials wherefrom they can be rapidly removed in alkaline aqueous liquids used in the processing of said materials.

[0016] It is a further object of the invention to provide such new filter dyes that have high stability upon storage of the photographic materials in which they are incorporated.

[0017] Another object of the invention is to provide photographic materials comprising said dyes.

[0018] Other objects will become apparent from the description hereinafter.

[0019] In accordance with the present invention silver salts of pentamethine oxonol dyes, are provided, the dyes preferably corresponding to the following general formula (I):


wherein
each of Z₁ and Z₂ represents the members necessary to close a five- or six-membered heterocyclic nitrogen containing nucleus, preferably a pyrazolidinone nucleus,
each of R₁,R₂ and R₃ independently represents hydrogen, substituted or
unsubstituted alkyl, cyclo-alkyl or a bridge-forming alkyl group between (adjacent) C-atoms of the methine chain, substituted or unsubstituted aryl, halogen. NHSO₂R₄ with R₄ being a substituted or unsubstituted alkyl, or a substituted or unsubstituted aryl group.

[0020] Further in accordance with the present invention a photographic element is provided comprising a support and at least one extended-red and/or infrared-sensitive, photo-sensitive silver halide emulsion layer, wherein the said element comprises, dispersed in a hydrophilic waterpermeable colloid binder, at least one metal ion salt, preferably a silver salt of a dye according to the above general formula.

4. Detailed description of the Invention

[0021] As is generally known the presence of one or more anionic, weakly-acidic groups in filter dyes is important to provide sufficient non-migratory character at coating pH values in the range of 4 to 8.

[0022] In the acid pH range the filter dyes according to the present invention can be incorporated in aqueous coating compositions in dispersed form by using commercial mixing devices for making colloidal dispersions.

[0023] At a pH of at least 10 said filter dyes are easily solubilized so that they are removed almost completely from a hydrophilic waterpermeable colloid layer of a photographic silver halide emulsion material by its common alkaline aqueous liquid processing and leave almost no residual stain. The presence of sulfite in the processing solution contributes to a more rapid discoloration of the filter dyes. In its silver salt form the behaviour of the dyes as a function of pH is quite analogous.

[0024] Representative examples of dyes for use in salt form in accordance with the present invention are:








   The silver salts of compounds (II) to (XII) are particularly useful for blocking light in the extended red and infrared spectral regions.

[0025] Quite unexpectedly it has been found that many examples of the filter dyes according to the formula (I), of which specific examples are given in the formulae (II) to (XII) are showing a strong bathochrome shift after treatment with a solution containing transition metal ions, preferably silver ions. It is even possible to reach a bathochromic shift of more than 100 nm under certain conditions as will be illustrated in the Examples.

[0026] Although it has been observed experimentally that these filter or antihalation dyes are forming complexes with most of the ions of the transition metals, like iron, gold, chromium, palladium, zinc, manganese, copper, molybdenum, nickel and tellurium, silver ions are preferred not only because silver salts react to form a soluble complex with thiosulphate ions during the fixation step, offering the possibility to set the dye free again, but also for ecological reasons.

[0027] An important advantage of the invention consists in the very simple preparation of the silver salts of mentioned oxonol dyes. For the formation of a dye in a hydrophilic colloid layer it suffices to mix in the coating composition of the layer a silver salt, e.g. silver nitrate, together with the dispersed dye, to obtain a silver salt complex in situ that is non-diffusing when the hydrophilic colloid composition is coated and that can be decolorized during fixation. The hydrophilic colloidal layer can be a backing layer, an antihalation undercoating layer, a silver halide emulsion layer, containing silver halide crystals with a diameter of at least 0.1 µm, a layer containing very fine silver halide particles with a diameter of 10 to 100 nm known as Lippmann emulsions and a protection layer coated as an outermost layer. In a special embodiment it is possible to obtain the silver salt of a dye in a layer, containing already said dye, by wet-coating said layer with an aqueous composition containing a dilute silver nitrate solution so delivering the equivalent amount of silver ions needed to build up the required silver salt complex of said dye.

[0028] The layers previously mentioned as suitable layers comprising a filter or antihalation silver salt dye may be incorporated in e.g. X-ray materials, graphic materials, diffusion transfer materials, black and white or colour cinematographic materials etc.

[0029] According to a preferred embodiment the silver salt complex of the suitable dye or dyes are incorporated in an antihalation back coating because otherwise when in water permeable relationship with silver halide emulsion layers the silver salt complex(es) may be decomposed due to the interaction of the silver ions of said complex(es) with halide ions from said emulsion layers, said halide ions forming less soluble complexes with these Ag⁺-ions.

[0030] Nevertheless it is possible to put dye silver salts for use according to the present invention in an emulsion layer containing silver halide crystals, provided that the pAg value is low enough so that the excess of halide ions is reduced to a minimum level.

[0031] According to a preferred embodiment said extended red and infrared-light absorbing dyes can be used in an antihalation layer of a photographic silver halide emulsion material in order to improve image sharpness by absorbing exposure light penetrating the emulsion layer(s) into the direction of the support.

[0032] A specific advantage of this invention consists in the stability of the bathochromically shifted transition metal ion complex of filter dyes, said filter dyes having an absorption maximum in the visible wavelength region before treatment with a transition metal ion solution.

[0033] Stabilizers capable of forming complexes with silver ions can be incorporated in a hydrophilic colloid layer together with the silver complex dyes in order to improve the stability of the silver salts of the dyes in an atmosphere of high temperature and/or high relative humidity against reduction of free silver ions to fine silver metal clusters which would act as development centre or development nucleus. As suitable stabilizers the well-known compounds used to stabilize silver halide crystals in a hydrophilic colloidal silver halide emulsion layer of a photographic material can be used.

[0034] Suitable examples are i.a. the heterocyclic nitrogen-containing compounds such as benzothiazolium salts, nitroimidazoles, nitrobenzimidazoles, chlorobenzimidazoles, bromobenzimidazoles, mercaptothiazoles, mercaptobenzothiazoles, mercaptobenzimidazoles, mercaptothiadiazoles, aminotriazoles, benzotriazoles (preferably 5-methyl-benzotriazole), nitrobenzotriazoles, mercaptotetrazoles, in particular 1-phenyl-5-mercapto-tetrazole, mercaptopyrimidines, mercaptotriazines, benzothiazoline-2-thione, oxazoline-thione, triazaindenes, tetrazaindenes and pentazaindenes, especially those described by Birr in Z. Wiss. Phot. 47 (1952), pages 2-58, triazolopyrimidines such as those described in GB-A 1,203,757, GB-A 1,209,146, JA-Appl. 75-39537, and GB-A 1,500,278, and 7-hydroxy-s-triazolo-[1,5-a]-pyrimidines as described in US-A 4,727,017, and other compounds such as benzenethiosulphonic acid, benzenethiosulphinic acid, benzenethiosulphonic acid amide. Other compounds that can be used are the fog-inhibiting compounds described in Research Disclosure N° 17643 (1978), Chapter VI. In a preferred embodiment it has been found that 1-phenyl-5-mercapto-tetrazole and/or 4-hydroxy-6-methyl-1,3,3a-tetrazaindene are particularly suitable.

[0035] The invention is concerned with the use of the dyes in photographic silver halide materials. However, the transition metal complex dyes can also be used for other purposes. For example a hydrophilic colloid layer containing the silver (or any of the previously mentioned transition metal ion) salt of a suitable dye absorbing light in the infrared region of the wavelength spectrum can be used as a particularly sensitive element to detect the presence of halide ions: any contact of this element with halide ions makes the colour of the layer change from colourless to e.g. deep blue, as is the case for dye (II), due to the hypsochromic shift after decomposition of the silver salt complex of the dye.

[0036] In a special embodiment, it is even possible to use the colloidal liquid as a colourless ink so that the text written with it can be made visible after contacting the dried document with a solution of a halide salt.

EXAMPLES

Example 1

Preparation of filter dye layers.

[0037] An amount of 3 g of gelatin was allowed to swell during 1 hour in a vessel containing 50 ml of demineralized water. The gelatin was of a low viscosity (13.6 mPas for a 10% solution at 40°C measured with a Haake Rotavisco RV2 apparatus). The mixture was heated to a temperature of 38°C. 1 mmole of dye (II) was dissolved in 50 ml of demineralized water; the pH-value was increased with sodium hydroxyde until the dye was completely dissolved and the dye solution added under stirring conditions to the gelatinous mixture described above. During 1 minute such equivalent amounts of silver nitrate as listed in the Table 1 hereinafter were added from a 0.1 N solution in demineralized water under vigorously stirring conditions. After the addition of C₁₄H₂₉OSO₃Na as a surface active agent and polystyrene sulphonic acid as a thickener to raise the viscosity to a value of 20 mPas the composition was coated on a substrated polyester with a thickness of 100 microns, the amount of gelatin of the coated layer being about 1 g/m². The coating was allowed to solidify at room temperature and then dried at 35°C in a ventilated oven. Transmission spectrograms of the coated samples were taken versus a reference sample without a dye coating with a Hewlett Packard 8450A UV-VIS spectrophotometer, measuring in the wavelength region from 200 to 800 nm. A reference sample for the tested silver salt dye was made by replacing the diluted silver nitrate solution by an equivalent amount of demineralized water and adjusting the pH to a value of 6.5.

Results

[0038] In Fig. 1 absorption spectra are given for the dye corresponding to formula (II) and its silver salt derivative prepared as described above by addition of 1, 2 and 3 equivalent amounts (mmoles) of silver nitrate for the respective curves 1, 2 and 3.

[0039] In Table I the wavelength at which the absorption of the dye corresponding to formula (II) and of the corresponding silver salt reaches its maximum is listed. For the silver salt of the dye the amount of equivalents of the silver ion added to the dye as described in the procedure hereinbefore is also listed, as well as the maximum density and the density (expressed in %) remaining after rinsing during 30 s with demineralized water and subsequent drying.

TABLE I

Formula	Absorption maximum (in nm)	Density	% Density remaining after rinsing
(II)	668	0.52	0
+ 3 eq. Ag⁺	796	1.14	85

[0040] Table I illustrates that by the reaction of the dye with silver ions a silver salt complex is formed that is characterised in that

• the absorption maximum is shifted toward longer wavelengths
• the extinction is enhanced
• the diffusion is inhibited

Example 2

[0041] Coatings were made as described in Example 1 with dyes (II) to (XII). In Table II the obtained values are given of the optimum amounts of silver nitrate (expressed in equivalents) added to the dye and the value (expressed in nm) of the maximum absorption wavelength of the corresponding silver salt of the dye. A qualitative evaluation of the intensity and the stability of the obtained silver salt dyes is also given: the more + signs are indicating that the intensity (resp. stability) is higher (resp. better).

TABLE II

Formula	Optimal Ag⁺ eq.	Absorption maximum	Intensity Stability
(II)	>1.0	> 800	+++
(III)	>1.25	> 800 (broad)	++
(IV)	>1.0	800	++
(V)	>1.0-1.25	very broad	-
(VI)	>1.0-1.25	600-700	+(+)
(VII)	>1.0	640 (very broad)	+(+)
(VIII)	>1.0	690	+
(IX)	>0.75-1.0	670	-
(X)	>1.25	> 800	+(+)
(XI)	>1.25	> 800	++(+)
(XII)	>3.0	> 800	++(+)

Example 3

[0042] A practical infrared absorbing antihalation back coating on a subbed polyethyleneterephtalate support was made after incorporation of the silver salt dye of formula (II). The back coating was formed with two different layers: an antihalation layer containing the silver salt complex of said dye and a protective layer so as to protect the antihalation layer against chemical (e.g. halide ions) and mechanical influences.

First layer: the antihalation layer.

[0043] The layer was prepared according to the procedure described in Example 1. Before coating this colloidal solution was containing 47.7 g of gelatin in which 3 mmole of the dye with formula (II) and 3 mmole of a silver nitrate solution were mixed together. An antistatic agent (see formula XIII),


with x=0.30 and y=0.70, a matting agent (SiO₂) and a surface active agent (C₁₄H₂₉OSO₃Na) were added after formation of the silver salt of the dye and 1-phenyl-5-mercaptotetrazole (PMT) was added in different amounts as listed in Table III. Before coating the pH-value of the coating composition was adjusted to a value of 6.3. With a total volume of 900 ml after the addition of demineralized water, a coating was made with a wet thickness of 50 µm. This layer formed was quite clear without any turbidity.

Second layer: the protective layer.

[0044] The protective coating composition contained 27 g of gelatin, 32 ml (3.2% by weight in a 10% gelatinous aqeous solution) of a matting agent, 5.4 ml (10% by weight) of MOBILCER Q, trademarked product from MOBIL OIL, as a lubrificating agent, 8.1 ml (5% by weight) of C₇F₁₅COONH₄ (the ammonium salt of perfluorocaprylic acid, trademarked product from 3M) as a surface-active agent and 135 ml (10% by weight) of glutaric dialdehyd as a hardener. Sodium hydroxyde was added to reach a pH value of 6.3 and water added to an amount of 900 ml. The layer had a wet-coated thickness of 17 µm.

[0045] This material was stored for 36 hours at a temperature of 57°C and a relative humidity of 34%. After treatment with a common developing (24 s at 34°C) and fixing solution (24 s at 34°C) of the stored material and a comparative material stored in normal conditions (room temperature and relative humidity of 50%), the density differences after processing between both layers as well as the density at 796 nm before processing were measured as a function of the amount of 1-phenyl-5-mercaptotetrazole (PMT). The results are summarized in Table III. It has to be kept in mind that the dye was completely rinsed out of the layer after processing (development and fixation) and that the differences in density are listed as an increase in fog-density after storing.

TABLE III

mmole of PMT	increase in fog density	density at 796 nm
0.0	+0.031	1.12
0.5	+0.006	0.94
2.5	+0.001	0.02*
5.0	+0.000	0.02*

* density of the supporting layer

[0046] The results in Table III clearly illustrate that it is possible to reduce the increasing amount of fog density during preservation by adding a stabilizer to a certain extent as mentioned before without risking an unacceptable decrease of the density of the silver salt dye before processing, the decrease being obviously due to the strong complex formation between the silver ions in silver salt dye complex and the PMT compound.

Claims

1. A dye absorbing light in the extended red and/or infrared region of the wavelength spectrum characterised in that said dye is a silver salt complex of a pentamethine oxonol dye.

2. A dye according to claim 1 wherein said dye is a silver salt of a pentamethine oxonol dye corresponding to the following general formula:

wherein
each of Z₁ and Z₂ represents the members necessary to close a five- or six-membered heterocyclic nitrogen containing nucleus, preferably a pyrazolidinone nucleus,
each of R₁,R₂ and R₃ independently represents hydrogen, substituted or unsubstituted alkyl , cyclo-alkyl or a bridge-forming alkyl group between (adjacent) C-atoms of the methine chain, substituted or unsubstituted aryl, halogen, NHSO₂R₄ wherein R₄ represents substituted or unsubstituted alkyl, or substituted or unsubstituted aryl.

3. A dye according to any of claims 1 or 2 wherein said dye has an absorption maximum at a wavelength above 750 nm.

4. A photographic material comprising a support and at least one silver halide emulsion layer that has been spectrally sensitized for the extended red and/or infrared region of the spectrum characterised in that it comprises in a hydrophilic colloid layer a dye according to any of claims 1 to 3.

5. A photographic material according to claim 4 wherein said dye is incorporated into an antihalation undercoat layer coated between the support and at least one silver halide emulsion layer.

6. A photographic material according to claim 4 wherein said dye is incorporated into a backing layer.

7. A photographic material according to any of claims 4 to 6 wherein the dye is present in a hydrophilic colloid layer in an amount of 0.01 to 1.0 mmole/m².

8. A photographic material according to any of claims 4 to 6 wherein the layer in which the dye is incorporated comprises a silver ion complexing compound.

9. A photographic material according to claim 8 wherein said silver ion complexing compound is 1-phenyl-5-mercaptotetrazole or 4-hydroxy-6-methyl-1,3,3a-tetrazaindene.

10. A photographic material according to any of claims 4 to 9 wherein said photographic material is an X-ray material.

Drawing