Photographic silver halide emulsion

Details Photographic silver halide emulsion Photographic silver halide emulsion

2001-07-24

2002-12-24

Letscher, Geraldine (Department: 1752)

Radiation imagery chemistry: process, composition, or product th

Radiation sensitive product

Silver compound sensitizer containing

C430S566000, C430S567000, C430S570000, C430S572000, C430S607000, C430S613000, C430S614000

Reexamination Certificate

active

06498001

ABSTRACT:

This invention relates to a spectrally sensitised silver halide emulsion, and to a photographic material comprising a support and at least one layer which comprises at least one spectrally sensitised silver halide emulsion.
It is known that spectrally sensitised emulsions can be supersensitised by depositing compounds apart from sensitisers, particularly additional dyes, on the surface of the silver halide crystals, which compounds are capable of increasing the spectrally sensitised sensitivity. Ascorbic acid is a typical example of such compounds. Other suitable compounds are disclosed in U.S. Pat. Nos. 2,945,762, 3,695,888, 3,809,561 and 4,011,083. The supersensitisation of silver halide emulsions with catechol sulphonic acids is also known. The aforementioned compounds do have a supersensitising effect, but result in an unwanted increase in fogging.
U.S. Pat. No. 5,457,022 describes supersensitisation by metallocenes. These are aromatic transition metal complexes of cyclopentadiene and derivatives thereof which have a characteristic “sandwich structure” without a direct metal-carbon &sgr; bond. The best known of these compounds are bis-(cyclopentadienyl)iron (ferrocene) and derivatives thereof. One disadvantage is that supersensitisation with ferrocenes results either in an unsatisfactory increase in sensitivity or is associated with an increase in fogging, during storage at the latest, due to which any increase in sensitivity is lost again.
Moreover, the use of pyrazoline compounds as a measure for increasing the granularity of colour photographic recording materials is known from DE 19,642,532. These are described there as protective additives, but are not necessarily used in layers which contain emulsions. A sensitivity-enhancing effect is not determined.
With these known measures, however, no success has been achieved in obtaining emulsions, such as those which are required nowadays for high-speed photographic materials, which comprise a very high spectral sensitivity together with reduced fogging and a good shelf life, particularly when they are stored under humid climatic conditions.
The underlying object of the present invention is thus to identify spectrally sensitised photographic silver halide emulsions of increased spectral sensitivity which furthermore are distinguished by a high sensitivity/fogging ratio and by a good shelf life, particularly when stored under humid climatic conditions.
It has surprisingly been found that this object can be achieved by the addition of certain pyrazoline compounds, if the latter are added to the light-sensitive emulsion in the interval between the completion of precipitation and the completion of spectral sensitisation.
The present invention therefor relates to a spectrally sensitised photographic silver halide emulsion, characterised in that after precipitation at least one compound of formula
is added to the emulsion, wherein
R
1
denotes alkyl, aryl, aralkyl, alkenyl or heterocyclyl;
R
2
denotes H, alkyl, aryl, heterocyclyl, amino or alkoxy;
R
3
denotes H, alkyl, aryl, aralkyl or heterocyclyl;
D denotes —OH or —NR
4
R
5
;
X denotes O or N—R
6
;
R
4
denotes H, alkyl, aryl, aralkyl, alkenyl or heterocyclyl;
R
5
: denotes H, alkyl, aryl, aralkyl, alkenyl or heterocyclyl;
R
6
: denotes H, alkyl, aryl, aralkyl, alkenyl, Acyl, alkoxycarbonyl, carbamoyl or heterocyclyl,
and any two of the radicals R
1
to R
6
can together form a heterocyclic ring, such as a pyrrolidine, piperidine, perhydroazepine, piperazine, morpholine or thiomorpholine ring.
Of the possible rings formed by the radicals R
1
to R
6
, 5- to 7-membered rings are preferred.
The alkyl, aralkyl and alkenyl radicals in the sense of the present invention can be straight chain, branched or cyclic radicals. The alkyl, aryl, aralkyl, alkenyl, hetero-cyclyl, amino, alkoxy, acyl, alkoxycarbonyl and carbamoyl groups can be substituted, for example, by alkyl, aryl, heterocyclyl, hydroxy, carboxy, halogen, alkoxy, aryloxy, heterocyclyloxy, alkylthio, arylthio, heterocyclylthio, acyl, acyloxy, acylamino, cyano, nitro, or mercapto groups, wherein the term “heterocyclyl” represents a saturated, unsaturated or aromatic heterocycle and the term “acyl” represents the radical of an aliphatic, olefinic or aromatic carboxylic, carbamic, carbonic, sulphonic, amidosulphonic, phosphoric, phosphonic, phosphorous phosphinic or sulphinic acid.
Examples of preferred compounds of formula I are given below:
Compounds I-1 and I-18 are particularly preferred.
The production of compounds of formula (I) has been described many times, for example by Hukki, Pharmazeutica Acta Helvetiae, pages 704-712 (1986), by Hukki, Acta Chem. Scand. 13, pages 174-177 (1959) and by Bockmühl M., Med. u. Chem. Abhandl. med. chem. Forschungsstätten IG Farbenind. 3, page 294 (1936).
Depending on their substituents, the heterocyclic compounds of formula I according to the invention are hydrophobic to a greater or lesser extent, at least in the form in which they are present in the silver halide. However, they can also be hydrophilic, in the presence of anionisable groups for example. Moreover, in one preferred embodiment they can contain specific groups which improve their adsorption on silver halides, e.g. thioether, selenoether, thione, thiol or amine radicals.
The preferred compounds of formula (I) are characterised in that their redox potential in aqueous solution within the pH range between 5 and 7 differs by no more than +/−100 mV from the standard potential of the hydrogen electrode. In photographic materials, compounds with a potential more negative than −100 mV can easily result in an increase in minimum density. Compounds with a potential which is more positive than +100 mV, in combination with special spectral sensitisers, exhibit a loss of efficacy. The redox potential of a compound I can generally readily be determined by cyclic voltammetry, provided that the redox reaction proceeds at least approximately reversibly.
Compounds of formula (I) are preferably used in an amount of 10
−6
to 10
−2
mol per mol silver halide and can be added to the emulsion to be sensitised before, during or after the addition of dyes, either as a solution or as a dispersion of solids. Compounds of the of formula (I) are preferably added after desalination of the emulsion. It is particularly advantageous if at least one compound of formula I is added to the emulsion directly before the addition of at least one spectral sensitiser or together with at least one spectral sensitiser.
In a further, particularly preferred embodiment, a compound of formula (I) is added to the emulsion directly before or during chemical sensitisation.
Spectrally sensitising dyes which can be used in the presence of compounds according to the invention are to be found in the series comprising the polymethine dyes. Examples of these dyes are described by T. H. James in The Theory of the Photographic Process, 4
th
Edition 1977, Macmillan Publishing Co., pages 194 to 234.
These dyes are capable of sensitising silver halide over the entire range of the visible spectrum and furthermore over the infrared-and/or ultraviolet range. Particularly preferred dyes include mono-, tri- and pentamethine cyanines, the chromophore of which comprises two heterocycles which, independently of each other, can be benzoxazole, benzimidazole, benzthiazole, naphthoxazole, naphthiazole or benzo-selenazole, and the phenyl ring of each of these heterocycles can contain further substituents or further conjoined rings or ring systems. The preferred pentamethine cyanines in turn are those in which the methine part is a constituent of a partially unsaturated ring. The dyes can be cationic, can be uncharged in the form of betaines or sulphobetaines, or can be anionic. Compared with the dye concentration which was found to be the optimum for the respective emulsion without compounds of formula (I) according to the invention, the amount of dye can be increased about 1.5- to 2-fold in the presence of compounds according to the invention. The spectrally

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