| 摘要 |
An object of the present invention is to provide an electrostatic image developing toner having good charge properties, low-temperature fixing properties, offset resistance and blocking resistance as well as good resistance against sticking to a heated roll and wax dispersibility and a novel urethane-modified polyester resin used for the toner. Provided in the present invention is a novel 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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