Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Silver compound sensitizer containing
Reexamination Certificate
2002-03-25
2004-09-28
Schilling, Richard L. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Silver compound sensitizer containing
C430S568000, C430S569000
Reexamination Certificate
active
06797459
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a light-sensitive silver halide emulsion, particularly to a tabular silver halide grain emulsion for photography.
BACKGROUND OF THE INVENTION
In general, silver halide emulsions containing tabular silver halide grains (referred to as “tabular grains” hereinafter), especially thin tabular grains, have the following advantages in their photographic characteristics:
(1) since the surface area/volume ratios (referred to as “specific surface areas” hereinafter) of tabular grains are great and large quantities of sensitizing dyes can be adsorbed to the tabular grain surfaces, the emulsions have high spectral sensitization sensitivities as compared with their intrinsic sensitivities,
(2) when emulsions containing tabular grains are coated on a support and dried, the grains are aligned in parallel with the support surface, so the coating layers can be made thin and the resulting photographic light-sensitive material is improved in sharpness,
(3) since little scattering of light is caused by tabular grains, images of high resolution is obtained, and
(4) since the tabular grains have low sensitivity to blue light, using them in a green-sensitive or a red-sensitive layer enables removal of an yellow filter from the emulsion layer. Therefore, such emulsions have so far been used in commercially available high-speed light-sensitive materials.
In Japanese Patent Publication Nos. 44132/1994 and 16015/1993 are disclosed the tabular emulsion grains having aspect ratios of at least 8. The term “aspect ratio” as used herein is defined as a diameter/thickness ratio of each individual grain. The diameter of each individual grain refers to the diameter of a circle having the same area as the grain's projected area determined by observation under a microscope or an electron microscope. The thickness of each individual grain refers to the distance between two parallel surfaces forming the tabular grain.
Further, Japanese Patent Publication No. 36374/1992 discloses the color photographic light-sensitive material which contains tabular grains having a thickness of less than 0.3 &mgr;m and a diameter of at least 0.6 &mgr;m in at least either of the green-sensitive and red-sensitive emulsion layers and thereby achieves improvements in sharpness, sensitivity and graininess. In recent years, on the other hand, silver halide light-sensitive materials have advanced in sensitivity increase and format reduction, and color photosensitive materials having higher sensitivities and improved image qualities have been desired strongly. Therefore, silver halide grain emulsions having higher sensitivity and more excellent graininess have been required. However, conventionally known tabular silver halide emulsions are insufficient to meet these requirements, and so stepped-up improvements in photographic characteristics are expected.
Additionally, tabular grains having greater aspect ratios can have the greater specific surface areas, and so they can make good use of the above-described advantages of tabular grains.
However, tabular grains enable adsorption of sensitizing dyes in greater amounts but, at the same time, have a defect of reflecting a greater proportion of light incident thereon. Therefore, it is difficult to obtain an increase in light absorption as expected.
On the other hand, silver iodide exhibits a face centered cubic crystal lattice structure under very high level of pressure (3,000 to 4000 times the atmospheric pressure) alone. The silver halide of this structure is referred to as &sgr;-phase AgI, and irrelevant to silver halide photography. Normally, the most stable crystal structure of silver iodide is a hexagonal wurtzite type, and the silver iodide of this crystal structure is generally referred to as &bgr;-phase AgI. The photographically useful, sufficiently stable, secondary crystal lattice structure of silver iodide is a face centered cubic zinc-blending type crystal structure, and the silver iodide of this structure is generally referred to as &ggr;-phase AgI. Silver halide emulsions containing &bgr;-phase AgI, &ggr;-phase AgI and AgI having a mixture of these phases, respectively, have been made. The fourth crystallographic form of silver iodide is &agr;-phase, namely a body centered cubic structure. According to the description in T. H. James,
The Theory of Photographic Process,
page 1, the formation of this crystal structure requires the temperature of 146° C. And the bright yellow silver iodide reported in U.S. Pat. No. 4,672,026 to Daubendiek is believed to be &agr;-phase AgI. (The descriptions at pages 1 to 5 of the book compiled by James relate to these crystal lattice structures and these studies.)
High-iodide silver halide grains have a marked advantage over silver halide grains of face centered cubic crystal lattice structure in that they have higher intrinsic absorption in the short blue portion (400 to 450 nm) of spectrum. In particular, high-iodide silver halide is generally identified as silver halide that exhibits an absorption peak at 425 nm missing in the absorption spectra of silver chloride and silver bromide, has a crystal lattice structure different from the face-centered cubic crystal structure and contains at least 97 mole % of iodide (high-iodide), based on total silver, namely only a minute amount of bromide and/or iodide. U.S. Pat. No. 4,184,878 to Maternaghan is an example of the high-iodide silver halide emulsion.
However, high-iodide silver halide grains are difficult to sensitize and develop with commercial developers, and these difficulties greatly inhibit their use for latent image formation.
Under these circumstances, it has been proposed from time to time to join a high-iodide phase to the surface of tabular silver halide grains having a face-centered hexagonal crystal lattice structure with the aim of exploiting both the advantages of tabular grains and high absorptivity of silver iodide, and further with the intention of supplementing defects of tabular grains and silver iodide.
U.S. Pat. No. 4,471,050 discloses selective attachment of nonisomorphic silver salts to edges of silver halide host grains without recourse to any additional site director. In these non-isomorphic silver salts are included silver thiocyanate, &bgr;-phase AgI (exhibiting a hexagonal wurtzite type crystal structure), &ggr;-phase AgI (exhibiting a zinc-blending type crystal structure), silver phosphates (including meta- and pyrophosphates) and silver carbonate. None of these non-isomorphic silver salts exhibit the face-centered cubic crystal structure of the type which is observed in photographic silver halides (namely the isomorphic face-centered cubic crystal structure of rock salt type). In fact, the sensitivity increase produced by nonisomorphic silver salt epitaxy was smaller than that attained by comparative isomorphic silver salt epitaxial sensitization.
Japanese Patent Application (Laid-Open) No. 2000-2959 discloses silver halide tabular grains having, on the main surfaces of {111} tablet having a thickness of 0.1 &mgr;m or below, ruffled surfaces formed of minute protrusions containing 10 mole % or less of iodide and having projected area diameters of 0.15 &mgr;m or below. The present invention can provide tabular silver halide grains enabling adsorption of sensitizing dyes in an increased amount and reduced reflection of light since the grains are increased in specific surface area without decrease in thickness. However, the objective for incorporating silver iodide in those protrusions was not to improve absorption of light, but to maintain structural stability of the protrusions. Therefore, it is hard to say that those tabular grains made good use of photographically useful properties of silver iodide, including highly efficient absorption of light.
U.S. Pat. No. 5,604,086 is one illustrative instance of emulsions containing tabular grains of rock salt-type face-centered cubic lattice structure which have epitaxially grown high-iodide silver halide crystals on the main surfaces thereof. Therein, it i
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