Sumitomo Chemical Company, Limited

Iwao Sakaguchi

Yoshiaki Hayashi

Hiroki Inoue

Keisuke Ito

Toshiaki Kishimoto

Katsutoshi Numano

Kunitoshi Takahashi

4,4'-Diamino-1,1'-dianthraquinonyl compounds which are obtained in a known manner and which are easy to agglomerate or aggregate owing mainly to their too fine particle size are conditioned by heating an aqueous suspension consisting essentially of the 4,4'-diamino-1,1'-dianthraquinonyl compound and water in the presence or absence of a mineral acid or an alkali. The thus obtained 4,4'-diamino-1,1'-dianthraquinonyl pigments are used in paints, printing inks, coloring of plastics and the like. The aqueous suspension is preferably prepared by desulfonating a 4,4'-diamino-1,1'-dianthraquinonyl-3,3'-disulfonic acid compound in a mineral acid such as sulfuric acid and then mixing the desulfonation reaction mixture with water or by once isolating the resulting 4,4'-diamino-1,1'-dianthraquinonyl compound and mixing the isolated compound with water.

Process for producing 4,4'-Diamino-1,1'-dianthraquinonyl pigments

Crude 4,4'-diamino-l,l'-dianthraquinonyl-3,3'-disulfonic acids or salts thereof are purified by subjecting an aqueous solution containing the crude products to salting-out using inorganic salts, the aqueous solution being adjusted within a range of from acid to neutral region, whereby a product usable as such for the production of 4,4'-diamino-1,1'-dianthraquinonyl red pigments having excellent pigmentary properties is obtained in high yields with industrial advantages.

Process for purification of crude

A desulfonation reaction mixture of 4,4'-diamino-1,1'-dianthraquinonyl-3,3'-disulfonic acid obtainable in a conventional manner is mixed in the form of an aqueous acid suspension with a surface active agent, followed by filtration, whereby filterability and flowability of the produced 4,4'-diamino-1,1'-dianthraquinonyl pigment are efficiently improved.

Process for producing 4,4'-diamino-1,1,'-dianthraquinonyl pigments

A process for producing stable (.beta.-type) dioxazine violet pigment having superior gloss and tinting strength to the metastable (.alpha.-type or a type analogous thereto) dioxazine violet pigment, by mixing an aqueous suspension of a metastable dioxazine violet pigment with an acetate or ketone compound and then heating the mixture. The metastable dioxazine violet pigment may be that obtained according to the conventional method, and employable in situ.

Process for producing dioxazine violet pigment

Dioxazine violet pigment having a stable crystal form is advantageously produced by heating a mixture containing an aqueous suspension of a metastable dioxazine violet pigment obtainable in a conventional manner and an aromatic compound having a low solubility in water such as benzoic acid. This stable pigment is useful as a paint and excellent in tinting strength, gloss and dispersibility.

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Hyogo, Japan

Iwao Sakaguchi