Mitsui Chemicals, Inc.

Koichi Ogawa

Kazuo Hisamatsu

Hiroshi Maekawa

Yuji Emura

Katsuhiko Mizushima

Urethane-modified polyester resin which has a total acid value not greater than 10 KOH mg/g and is obtained by kneading, in a molten state, a base polyester resin (A) having an acid value of 5 to 20 KOH mg/g and a hydroxyl value of 40 to 70 KOH mg/g, a low-molecular-weight polyester resin (B) having an acid value not greater than 5 KOH mg/g, a hydroxyl value not greater than 10 KOH mg/g and a weight-average molecular weight of 3,000 to 5,000 and a polyisocyanate compound, wherein components (A) and (B) are at a weight ratio of 3 to 5:7 to 5 and the polyisocyanate compound is in an amount of 0.2 to 1.2 equivalent, in terms of an isocyanate group per equivalent, of the total hydroxyl groups of all the resins.

Electrostatic image developing toner

Urethane modified polyester resin which has a total acid value not greater than 10 KOH mg/g and has been obtained by kneading, in a molten state, a base polyester resin (A) having an acid value of 5 to 20 KOH mg/g and a hydroxyl value of 40 to 70 KOH mg/g, a low-molecular-weight polyester resin (B) having an acid value not greater than 5 KOH mg/g, a hydroxyl value not greater than 10 KOH mg/g and a weight-average molecular weight of 3,000 to 5,000 and a polyisocyanate compound, by using the components (A) and (B) at a weight ratio of 3 to 5:7 to 5 and the polyisocyanate compound in an amount of 0.2 to 1.2 equivalent, in terms of an isocyanate group per equivalent, of the total hydroxyl groups of all the resins. This novel urethane-modified polyester resin (C) is used as a binder resin for the toner. For the preparation of the toner, the resin is mixed and kneaded with a colorant, magnetic powders, charge control agent and the like under a molten state, followed by cooling and pulverization.

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Saitama, Japan

Koichi Ogawa