| 摘要 |
<p>A light-sensitive emulsion layer comprising a dispersing medium and silver halide grains, wherein at least 10% of the total projected area of the silver halide grains is formed by silver bromo-iodide grains bounded by at least one substantially concave-shaped major crystal face, having a diameter of at least 0.6 mu m and the half of their thickness, in the deepest point of said concavity, of less than 80% of the half of their border thickness. Photographic elements comprising a support base and at least one such emulsion layer are shown. Multi-step process for preparing an emulsion of light-sensitive silver halide grains dispersed in a hydrophilic dispersing medium which comprises a first double-jet precipitation step for the formation of silver halide growing nuclei, a second double-jet precipitation step of first diameter growth of said nuclei and a third step of grain second growth by means of single-jet solution of silver salts, characterized by the fact that a) said first precipitation step for the formation of growing nuclei occurs at a constsnt pBr ranging from 0.6 to 1.2 in the presence of a soluble chloride to form thick silver halide nuclei, b) said second step of first growth occurs by adding a first jet of a soluble silver salt water solution at constant concentration and accelerated flow rate and a second jet of a bromide and iodide soluble salt water solution at increasing concentrations of bromide and iodide and constant flow rate at a pBr decreasing from about 1.2 to about 0.6, and c) said third step of second growth is performed till increasing pBr above 1.2. For at least 10% of their total projected area the silver halide grains, thus formed, result to be silver bromo-iodide grains bounded by at least one substantially concave-shaped major crystal face, said grains having a diameter of at least 0.6 mu m and the half of their thickness, in the deepest point of said concavity, of less than 80% of the half of their border thickness.</p> |
