| 摘要 |
PROBLEM TO BE SOLVED: To prevent deterioration of charge controllability for a long period by coating the surfaces of the carrier grains with a polyester resin having urethane bonds in a binder type carrier comprising at least a magnetic powder and a resin in the binder. SOLUTION: The surfaces of the nucleous grains comprising at least a resin and fine magnetic grains are coated with a polyester resin having urethane bonds (a urethane modified polyester resin). This polyester resin is formed by reaction of a polyvalent carboxylic acid, such as malonic acid, with a polyvalent alcohol, such as ethylene glycol in a use ratio of 1.0-1.4. It is preferred that these nucleous grains are prepard by reacting phenols with aldehydes in an aqueous medium in the presence of fine magnetic particles and fine nonmagnetic particles and a suspension stabilizer and a basic catalyst and hardening them, and preferrably incorporating the fine magnetic particles and the nonmagnetic particles in the binder. |
