Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Silver compound sensitizer containing
Reexamination Certificate
1998-03-23
2001-12-11
Baxter, Janet (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Silver compound sensitizer containing
C430S569000
Reexamination Certificate
active
06329131
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a silver halide emulsion and, more particularly, to a tabular silver halide emulsion which contains iodide ions at a high concentration in an outer peripheral portion of a grain and has an average projected area diameter of 0.08 &mgr;m to 0.5 &mgr;m and an aspect ratio of 2 to 30.
The roughness (graininess) of images of color photographic light-sensitive materials, particularly, color reversal photographic light-sensitive materials often used by professional photographers is especially conspicuous in a bright portion (highlight portion) of an image. This portion is formed by relatively small silver halide emulsion grains contained in the lowest-speed one of sensitive layers of each color. To improve the graininess brought about by a silver halide emulsion containing grains in a small-size region, it is necessary to minimize the silver halide grain size required to obtain the same sensitivity. That is, a sensitivity increasing technique which compensates for a decrease in the sensitivity caused by a decrease in the grain size is necessary. U.S. Pat. Nos. (to be also referred to as US hereinafter) 4,434,226, 4,439,520, 4,414,310, 4,433,048, 4,414,306, and 4,459,353 have disclosed a sensitivity increasing technique which improves the color sensitization ratio by spectral sensitizing dyes by increasing the surface of a grain for receiving light by using a tabular silver halide grain. U.S. Pat. Nos. 4,672,027 and 4,693,964 have disclosed tabular grains having an aspect ratio of 8 or more and an average diameter of 0.2 to 0.55 &mgr;m. Jpn. Pat. Appln. KOKAI Publication No. (hereinafter referred to as JP-A-)62-18555 has disclosed that a photographic light-sensitive material that is excellent in sharpness can be obtained by an emulsion containing silver halide grains having a thickness of less than 0.12 &mgr;m, an average diameter of less than 0.6 &mgr;m, and an aspect ratio of 5 or more. The present inventors have studied grains having an average projected area diameter in the range of 0.5 &mgr;m or less and an aspect ratio of 2 or more and confirmed that as the aspect ratio is increased, it is possible to use a larger amount of sensitizing dyes and raise the spectral sensitivity. On the other hand, it is found that the graininess deteriorates as the aspect ratio is increased, and as a consequence the total performance (sensitivity/graininess ratio) cannot be improved. Accordingly, a technique which improves the sensitivity/graininess ratio of tabular silver halide grains in a small-size region has been desired.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to find a technique which increases the sensitivity without causing the drawback that the graininess deteriorates when the aspect ratio is raised in a tabular silver halide whose average projected area diameter is 0.5 &mgr;m or less and aspect ratio is 2 or more, and provide a silver halide photographic emulsion with a high sensitivity/graininess ratio and a silver halide photographic light-sensitive material containing the emulsion.
DETAILED DESCRIPTION OF THE INVENTION
The present inventors have made extensive studies to obtain a tabular photographic emulsion having a high sensitivity/graininess ratio, an average projected area diameter of 0.5 &mgr;m or less, and an aspect ratio of 2 or more. Consequently, it is found that when the grain thickness of a tabular grain is decreased by increasing the aspect ratio, the grain becomes easier to dissolve in the grain preparation step or the development step, especially when a developer contains a solvent, and this strongly correlates with deterioration of the graininess. To raise the sensitivity without deteriorating the graininess, it is only necessary to form a grain composition and a grain structure by which a grain itself is hard to dissolve, and it turns out that it is extremely effective to make the surface region of a grain contain iodide at a high concentration. It is surprising that this effect is notable when the average projected area diameter of grains is 0.5 &mgr;m or less. Also, the method is very effective when the average grain thickness is 0.2 &mgr;m or less, particularly, 0.1 &mgr;m or less. It is also found that to increase the sensitivity in this grain structure, it is effective to form an epitaxial portion containing silver chloride, form a reduction-sensitized region, and use one or both of selenium sensitization and tellurium sensitization.
The present invention provides a silver halide photographic emulsion described below.
(1) A silver halide emulsion, wherein a sum of projected areas of tabular silver halide grains, in which an outer shell region that is 40% in volume from a grain surface contains 5 mol % to 20 mol % of iodide ions with respect to a silver halide in the outer shell region, and which have a projected area diameter of 0.08 &mgr;m to 0.5 &mgr;m and an aspect ratio of 2 to 30, accounts for 80% or more of the total projected area of all grains.
(2) The silver halide emulsion described in item (1), wherein assuming each tabular silver halide grain described in item (1) as a host grain and at least one epitaxially grown portion containing 10 mol % or more of silver chloride is further formed on the host grain.
(3) The silver halide emulsion described in item (1) above, wherein one or both of an interior and a surface of the tabular silver halide grain have at least one reduction-sensitized region.
(4) The silver halide emulsion described in item (1) above, wherein either a surface of the tabular silver halide grain or both an interior and a surface of the tabular silver halide grain are subjected to selenium sensitization, tellurium sensitization, or selenium-tellurium sensitization.
(5) The silver halide emulsion described in item (1) above, wherein either one or both of an interior and a surface of the tabular silver halide grain are subjected to reduction sensitization and selenium sensitization, reduction sensitization and tellurium sensitization, or reduction sensitization and selenium-tellurium sensitization.
(6) The silver halide emulsion described in any one of items (1), (2), (3), (4), and (5) above, wherein an average grain thickness of the tabular silver halide grains is 0.2 &mgr;m or less.
(7) A silver halide photographic light-sensitive material containing the silver halide emulsion described in item (1) above in at least one layer thereof.
The present invention will be described in detail below.
The halogen composition of the emulsion grain is preferably silver iodobromide or silver bromochloroiodide. Silver iodobromochloride containing 40 mol % or less of silver iodide is more preferable.
In the emulsion of the present invention, the sum of the projected areas of the tabular grains having a projected area diameter of 0.08 &mgr;m to 0.5 &mgr;m and an aspect ratio of 2 to 30 accounts for 80% or more of the total projected area of all grains. The production suitability of the emulsion is lowered if the projected area diameter of the grains is less than 0.08 &mgr;m or the aspect ratio exceeds 30. Most preferably, the sum of the projected areas of tabular grains having a projected area diameter of 0.08 &mgr;m to 0.4 &mgr;m and an aspect ratio of 3 to 25 accounts for 80% or more of the total projected area of all grains.
The projected area and the aspect ratio of a tabular grain can be measured from an electron micrograph shadowed together with a reference latex sphere by a carbon replica method. That is, the projected area diameter is represented by the diameter of a circle having the same area as the projected area. The major surface of the tabular grain commonly has a hexagonal, triangular, or circular shape when viewed in a direction perpendicular to the major surfaces, to be described below in detail. The aspect ratio is a value obtained by dividing the projected area diameter by the thickness. The higher the degree of a hexagon as the shape of the major surfaces of a tabular grain, the more preferable the tabular grain is. Also, the ratio of the leng
Baxter Janet
Birch & Stewart Kolasch & Birch, LLP
Fuji Photo Film Co. , Ltd.
Walker Amanda C.
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