Increased photographic activity precipitated coupler dispersions

Abstract

Base and auxiliary solvent solubilized precipitated dispersions of couplers and other photographic materials usually produce very small particle dispersions, and usually such dispersions are extremely highly reactive because of the smallness of the particle size. However, some relatively more hydrophobic couplers, even though they produce small particles when a dispersion is formed by the precipitation technique, lead to extremely unreactive dispersions. The method of this invention constitutes a single step coprecipitation technique where a base deprotonation compound, preferably a liquid carboxylic acid, is incorporated into the precipitated particles to produce photographically highly active coupler dispersions. The invention is performed by providing a first flow of an aqueous surfactant solution and a second flow comprising a basic solution of the coupler and the base deprotonable compound in a water miscible volatile auxiliary solvent and mixing the said first and second streams either simultaneously or immediately following thereof, neutralizing said streams with an acid solution. Such immediate neutralization protects any hydrolizable surfactants that may be utilized in the crude emulsion stream. In a preferred method, the first and the second stream may be brought together immediately prior to neutralization or directly into a mixer with addition of acid directly into the mixer to neutralize the dispersion to form a dispersion of fine particles.