Hoechst Aktiengesellschaft

Clariant Corporation

Franz Schui

Reinhold Deubel

Hans-Tobias Macholdt

Martin Ulrich Schmidt

Alexander Sieber

Arpad Acs

R&uuml;diger Jung

Norbert Wester

C.I. Pigment Yellow 191 is obtained in new crystal polymorphs (beta, gamma, delta and epsilon phases) if the known alpha phase or another inventive phase of this pigment is treated with certain solvents and reprecipitated.

Crystal polymorphs of C.I. Pigment Yellow 191 and their preparation

Process for specifically influencing the triboelectric effect of azo pigments in electrophotographic toners or developers or in powders for surface coating by adding to the azo pigments at the coupling reaction stage, at the laking stage or in the course of finishing at least one saltlike, cationic compound whose positively charged center is a nitrogen, phosphorus, arsenic or antimony atom or the group ##STR1## and use of such azo pigments for producing toners or developers used for the electrophotographic copying or manifolding of originals or for printing electronically, optically or magnetically stored data or in colorproofing or use of such azo pigments for producing powders or powder coatings used for the surface coating of articles made of metal, wood, plastics, glass, ceramics, concrete, textile material, paper or rubber.

Specifically influencing the triboelectric effect of azo pigments

A novel crystallographic modification (.beta.-modification) of the pigment C. I. Pigment Red 53:1 is described and claimed which has characteristic reflection values in its X-ray diffraction pattern obtained by means of Cu-K.sub..alpha. radiation. This novel pigment form is obtained by reacting an aqueous solution of an alkali metal or ammonium salt of the formula 1 ##STR1## with the equivalent amount of a water-soluble barium salt in the presence of a compound of the formula 2 ##STR2## The modification is distinguished by a more yellowish-red shade as compared to the known .alpha.-modification.

.beta.-modified crystalline red pigment

Growing community of inventors

Frankfurt am Main, Germany

Franz Schui