Photographic silver halide element

Abstract: A photographic colour element comprising a support bearing a photosensitive silver halide emulsion layer containing a coupler capable of releasing a development accelerator or fogging agent on colour development (DARC) characterised in that the emulsion has added thereto photosensitive silver halide grains which are more developable than the grains of said silver halide layer whereby the speed of the emulsion is increased without unduly increasing fog.

Description: The invention relates to photographic silver halide elements and, in particular to such elements having increased photographic speed. Couplers which release a development accelerator or fogging agent (DARCs) have been described in US Patent 3,214,377. They are added to silver halide emulsions in order to achieve an increase in speed brought about by the increased image development caused by the imagewise release of the development accelerator. Too much DARC will cause fogging and this limits the extent to which speed can be increased. In US Patent 4,656,123 it is said that in colour materials the migration of developer accelerators released by DARCs in one colour unit to another colour unit causes development producing image dye of the wrong colour. This leads to the undesirable effect of colour mixing. The solution disclosed is the use, betweeen dye image forming layers of a different colour, of a non-developable silver halide layer which acts as a scavenger layer deactivating any unused developer accelerator. The present invention relates to a silver halide element containing a DARC showing improved speed increase without undue fog formation. According to the present invention there is provided a photographic colour element comprising a support bearing a photosensitive silver halide emulsion layer containing a coupler capable of releasing a development accelerator or fogging agent on colour development (DARC) characterised in that the emulsion has added thereto photosensitive silver halide grains which are more developable than the grains of said silver halide layer whereby the speed of the emulsion is increased without unduly increasing fog. The elements of the present invention show higher photographic speeds and improved mid-scale granularity compared to elements without the added slow emulsion without undue increase in fog levels. As is well known, silver halide grains can be made more developable in a number of ways. The halide content is significant and the rate of development reduces as the halide changes, ie. Cl > Br > I. Thus having silver chloride at the grain surface gives the highest rate of development. Another way to increase developability is to increase the surface area of the grains and this can be achieved by using smaller sized grains which, of course, will usually be of slower photographic speed. A comparison of developability can be made by determining the time taken for comparable imagewise exposed coatings of different emulsions to reach a particular density in the same developer solution. For the emulsions employed in Example 2 below, the more developable silver chloride emulsion will develop to completion in 45 secs while the less developable bromoiodide emulsion takes 2.5 mins to only partially develop. Preferably the more developable grains have a speed of at least 0.15, preferably at least 0.3, logE slower than that of the emulsion layer. The added grains are preferably of small size and high specific surface area, preferably their size is from 0.01 to 1.0, especially from 0.125 to 0.15, of the mean grain size of the original emulsion layer. The emulsion layer itself (before addition of the slower grains) may contain grains of a different size and indeed usually will. Its speed is to be taken as the speed of the emulsion when coated and tested. Typically a plot of the size distribution of grains in the original emulsion layer will show a single peak whereas after addition of the slower/smaller grains there will be two peaks. As is usual, the term "size" in connection with grains means diameter if circular, or the diameter of a circle having the same area if not. The granularity, although improved in the mid-scale, is increased in the toe region. Granularity can be improved by the inclusion of a DIR (developer inhibitor releasing) coupler or an anti-foggant. The emulsion layer may also have, associated therewith, an image-dye providing coupler in addition to the DARC. Typically the element will have two or usually three emulsion layer units each sensitised to a different region of the visible spectrum. The DARC compounds can be any of the types known in the art. These include the compounds described in US Patents 3,124,377; 3,253,924; 4,390,618; 4,656,123; in Japanese published, unexamined application 17,437/76, or in British patent specification 2,097,140. This latter publication describes a hydrazine moiety-containing compounds having the formula: wherein: A is a coupler residue, X is a divalent linking group, R¹ is formyl, sulphonyl, alkoxycarbonyl, carbamoyl or sulphamoyl group, R² is hydrogen, or an acetyl, ethoxycarbonyl or a methanesulphonyl group, and R³ and R⁴ are hydrogen, halogen or an alkyl or alkoxy group having from 1 to 4 carbon atoms. As used herein, the term "associated with" signifies that the coupler is incorporated in the silver halide emulsion layer or in a layer adjacent thereto where, during processing, it is capable of reacting with silver halide development products. Such multicolour elements 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. A typical multicolour photographic element comprises a support bearing yellow, magenta and cyan dye image-forming units comprising at least one blue-, green- or red-sensitive silver halide emulsion layer having associated therewith at least one yellow, magenta or cyan dye-forming coupler respectively. The element can contain additional layers, such as filter and barrier layers. In the following discussion of suitable materials for use in the emulsions and elements of this invention, reference will be made to Research Disclosure, December 1978, Item 17643, published by Industrial Opportunities Ltd., The Old Harbourmaster's, 8 North Street, Emsworth, Hants P010 7DD, U.K. This publication will be identified hereafter as "Research Disclosure". The silver halide emulsion employed in the elements of this invention can be either negative-working or positive-working. They may contain grains of any shape, eg. cubic, octahedral or tubular or mixtures thereof. Suitable emulsions and their preparation are described in the literature, eg. in Research Disclosure Sections I and II and the publications cited therein. Suitable vehicles for the emulsion layers and other layers of elements of this invention are described in Research Disclosure Section IX and the publications cited therein. In addition to the DAR-couplers useful in this invention, the elements of the invention can include additional couplers as described in Research Disclosure Section VII, paragraphs D, E, F and G and the publications cited therein. The DAR-couplers useful in this invention and any additional couplers can be incorporated in the elements and emulsions as described in Research Disclosures of Section VII, paragraph C and the publications cited therein. The photographic elements of this invention or individual layers thereof, can contain brighteners (see Research Disclosure Section V), antifoggants and stabilisers (see Research Disclosure Section VI), antistain agents and image dye stabiliser (see Research Disclosure Section VII, paragraphs I and J), light absorbing and scattering materials (see Research Disclosure Section VIII), hardeners (see Research Disclosure Section XI), plasticisers and lubricants (see Research Disclosure Section XII), antistatic agents (see Research Disclosure Section XIII), matting agents (see Research Disclosure Section XVI) and development modifiers (see Research Disclosure Section XXI). The photographic elements can be coated on a variety of supports as described in Research Disclosure Section XVII and the references described therein. Photographic elements can be exposed to actinic radiation, typically in the visible region of the spectrum, to form a latent image as described in Research Disclosure Section XVIII and then processed to form a visible dye image as described in Research Disclosure Section XIX. Processing to form a visible dye image includes the step of contacting the element with a colour developing agent to reduce developable silver halide and oxidise the colour developing agent. Oxidized colour developing agent in turn reacts with the coupler to yield a dye. Preferred colour developing agents are p-phenylene diamines. Especially preferred are 4-amino-3-methyl-N,N-diethylaniline hydrochloride, 4-amino-3-methyl-N-ethyl-N-β-(methanesulphonamido)-ethylaniline sulphate hydrate, 4-amino-3-methyl-N-ethyl-N-β-hydroxyethylaniline sulphate, 4-amino-3-β-(methanesulphonamido)ethyl-N,N-diethylaniline hydrochloride and 4-amino-N-ethyl-N-(2-methoxy-ethyl)-m-toluidine di-p-toluene sulphonate. With negative-working silver halide emulsions this processing step leads to a negative image. To obtain a positive (or reversal) image, this step can be preceded by development with a non-chromogenic developing agent to develop exposed silver halide, but not form dye, and then uniform fogging of the element to render unexposed silver halide developable. Alternatively, a direct positive emulsion can be employed to obtain a positive image. Development is followed by the conventional steps of bleaching, fixing, or bleach-fixing, to remove silver and silver halide, washing and drying. The following Examples are given for a better understanding of the invention. All temperatures are in °C. Example 1 A set of coatings of the structure described below was made with a range of blends of fast and slow emulsions in which the total silver coating weight was 1.0 g/m². All units are in g/m². A yellow image coupler of the formula: was included and three levels of the DARC of the formula: in each emulsion combination. The fast emulsion was an ISO400 speed bromo-iodide (6% iodide) T-grain emulsion of 1.14 µm grain size and the slow was IS0 100 speed bromoiodide (4.8% iodide) three dimensional grain emulsion of 0.32 µm grain size. Both emulsions were chemically sensitised. All figures are coating weights in g/m². Details of coatings are as follows: All emulsion layers contained gelatin (2.2) and coupler (0.6) and had a supercoat of gelatin (1.0) above. These coatings were processed in a cycle described below: Develop 2.5 minutes Fix 4.0 minutes Wash 3.0 minutes The developer and fixer were standard C-41 solutions at 37.8°C. The customary bleach bath was omitted in order to leave the silver image in place for diagnostic purposes. Exposures were made on a graduated 21-step test object with a 0.2 logE exposure increment for 0.01 seconds to simulated daylight. The sensitometric response curves showing dye + silver density are shown in Figure 1. It can be seen that the DARC increases the speed of the fast emulsion by about 0.15 logE whereas with 25% of slow emulsion blended in the speed increase is about 0.3 logE with increased contrast. The slow emulsion by itself is approximately 0.8 logE slower than the fast emulsion. Further increases in speed (0.4 logE total) occur with 50% slow emulsion and 50% fast but now a noticeable fog increase (+ 0.1) occurs.Increase in DARC level to 0.1 g/m² gives a 0.4 logE speed increase for25% slow with a 0.04 fog increase. Photomicrographs of the processed layers show a large number of fine grains of the slow emulsion contributing to the image in addition to the larger grains of the fast component. In the toe region of the characteristic curve there are more fine grains than large grains and this is responsible for the large speed increase associated with this phenomenon. Example 2 To illustrate the general nature of this phenomomeon, a second set of coatings was made as described in Example I but now with a chemically sensitised silver chloride 0.44 µm cubic grain paper emulsion as slow component. The result is shown in Figure 2. Here a smaller level of DARC (0.02 g/m²) and a 12% level of chloride emulsion give a 0.2 logE speed increase but with increased fog. This is because the chloride emulsion is overdeveloped in the processing cycle described above and is running into fog. Further experimentation with different processing cycles is likely to improve on this result. Example 3 Granularity Measurements Further strips of coatings 1, 2 and 4 were exposed as in Example 1 and processed through the following cycle: develop 2.5 min bleach 4.5 min wash 2.0 min fix 3.0 min wash 3.0 min Gamma normalised granularity (σ/γ) measurements for coatings 1, 2 and 4 of Example 1 show that granularity curves have been shifted parallel to the relative exposure axis so that the speed points are superimposed. With thismode of analysis, a comparison of (σ/γ) values at a given relative exposure level in Figure 3, will reflectrelative differences in final print granularity. Although there is a substantial increase in toe (σ/γ) with (4) compared with the fast emulsion alone (1) this is to be expected since (1) is 0.3 logE slower (see Figure 1). In the mid-scale, however the (σ/γ) response with (4) is comparable to (1). Thus mid-scale print granularity equivalent to that of a much slower coating (-0.3 logE) can be achieved by means of the present invention.

Claims: A photographic colour element comprising a support bearing a photosensitive silver halide emulsion layer containing a coupler capable of releasing a development accelerator or fogging agent on colour development (DARC) characterised in that the emulsion has added thereto photosensitive silver halide grains which are more developable than the grains of said silver halide layer whereby the speed of the emulsion is increased without unduly increasing fog. A photographic element as claimed in claim 1 in which the more developable grains have a size which is from 0.01 to 1.0, preferably 0.125 to 0.15, of the mean grain size of said emulsion layer. A photographic element as claimed in claim 1 or 2 in which the more developable grains have a speed of at least 0.15 preferably at least 0.3 logE slower than that of said emulsion layer. A photographic element as claimed in any of claims 1 to 3 in which the more developable grains comprise a higher proportion of silver chloride and/or a lower proportion of silver iodide than in the less developable grains.

Inventors: JARVIS JOHN R, TWIST PETER J, JARVIS, JOHN R., TWIST, PETER J.
Applicants: EASTMAN KODAK CO, KODAK LTD, EASTMAN KODAK COMPANY, KODAK LIMITED
Application year: 1989
Main classification: G03C7
IPC codes: G03C7, G03C1