Patent ID: 6641621
Filing Date: 2003-11-04
Classification: G03C

Abstract:
Method for preparing a co-precipitated microcrystalline dispersion of dyes, 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 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 dye, an amount of water, followed by addition of an aqueous alkaline solution and a surfactant and, after having completely dissolved the said pyrrole dye, adding, while further stirring, to the solution of the pyrrole dye(s), the solution of the pentamethine oxonol barbituric acid dye(s); 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; and adding a binder.