Toyo Soda Manufacturing Co., Ltd.

Eiji Iwamoto

Takeshi Uotani

Osamu Fujii

Katusya Shibata

Motohiro Hamada

Yasukazu Yokoyama

Misao Takano

Finely divided gamma crystal phase quinacridone pigments are prepared by a process wherein a crude quinacridone of an arbitrary crystal phase is dissolved in dimethyl sulfoxide in the presence of a caustic alkali and water and then a mineral acid or a mixture of a mineral acid with at least one diluent selected from water, dimethyl sulfoxide and a monohydric alcohol having 1 to 3 carbon atoms is incorporated into the so-formed solution, thereby neutralizing the caustic alkali present in the solution to precipitate a finely divided gamma phase quinacridone.

Process for preparing gamma phase quinacridone

Isoindolinone pigments of an extremely high purity, which are represented by the following general formula: ##STR1## wherein R represents a carbocyclic bridge member such as:

Process for purifying crude isoindolinone series pigments

6,7,14,15-Tetrahydropyrido[2,1-b]pyrido[1',2':1,2]pyrimido[4,5-g]quinazolin e-7,15-dione is oxidized with a quinone as an oxidizing agent to produce 7,15-dihydropyrido[2,1-b]pyrido[1',2':1,2]pyrimido[4,5-g]quinazoline-7,15- dione.

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Yamato, Japan

Eiji Iwamoto