Eastman-kodak Company

Ming Jye Lin

Joseph C Deaton

Kenneth James Lushington

Roger H Piggin

Frederick Charles Derks

Philip J Zola

The invention relates to an emulsion comprising tabular grains of greater than or equal to about 3.7 .mu.m area weighted mean equivalent circular diameter and thiourea sensitizer having the structural formula: ##STR1## wherein each of R.sub.1, R.sub.2, R.sub.3, and R.sub.4 independently can represent an alkylene, cycloalkylene, carbocyclic arylene or heterocyclic arylene, alarylene or aralkylene group; or taken together with the nitrogen atom to which they are attached, R.sub.1 and R.sub.2 or R.sub.3 and R.sub.4 can complete a 5- to 7-member heterocyclic ring; and

Chemical sensitization of large tabular grain emulsions

A process is disclosed for the preparation of a tabular grain silver bromoiodide emulsion in which silver bromoiodide laminae are formed on the major faces of the tabular grains. The sensitivity of the emulsion as a function of pressure applied is rendered more nearly constant by forming the silver bromoiodide laminae on the major faces of the tabular grains within a pAg and temperature range defined by Curve A in FIG. 1. The laminae are formed by first precipitating iodide as a silver salt at peripheral sites on the tabular grains and then precipitating silver bromoiodide onto the major faces of the host tabular grains with the primary source of iodide being the previously deposited iodide. The emulsions produced exhibit high sensitivity to exposing radiation and reduced sensitivity to localized pressure.

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Penfield, NY, United States of America

Ming Jye Lin