Method of preparing co-precipitated microcrystalline dye dispersions and layers coated therewith in materials

Abstract

A method has been disclosed for preparing a co-precipitated microcrystalline dye dispersion, the absorption spectrum of which exceeds the summoned spectra of individually dispersed dyes, which comprises, as consecutive preparation steps: adding to one vessel, an amount of at least one pentamethine oxonol-type barbituric acid filter dye having ionizable sites in its molecular structure; adding thereto an aqueous alkaline solution in an amount sufficient to completely dissolve the said filter dye while stirring the solution thus formed; adding in another vessel, to an amount of at least one pyrrole type filter dye, an amount of water, followed by adding of an aqueous alkaline solution and a surfactant; followed, after having completely dissolved (under stirring conditions) the said pyrrole type filter dye, by adding to the solution thus formed in the other vessel, the solution formed in the one vessel; adding an aqueous acidic solution up to a pH of less than 3.0; adding an aqueous alkaline solution up to a pH in the range from 4.0 up to 5.5; followed by adding a binder in order to make the dispersion thus obtained ready-for-coating in a filter dye layer on a support, suitable for use as antihalation undercoat layer between said support and a light-sensitive layer or as a backing layer of said material, or as layer covering the light-sensitive layer, thus providing safelight protection.