| 摘要 |
PURPOSE:To obtain a magnetic developing agent having excellent shelf life, fixability and environmental stability by contg. toner particle and gamma-fe2O3 having specific pH and grain size. CONSTITUTION:A developing agent contg. toner particle and gamma-Fe2O3 of <=8.0pH and <=0.1mu grain size. More particularly preferable form is to add gamma-Fe2O3 or <=200 oersted (Oe) coercive force and <=30emu/g residual magnetization at about 0.01-10.0wt% based on the weight of the toner externally onto the surface of a magnetic toner. If the residual magnetization and coercive force of the externally added material are too large in the relation with the magnetic material in the toner, the magnetic force of the toner increases too much and gives adverse influence such as decrease in the density of pictures. If the residual alkali components are contained much in the magnetic material, the rate of moisture absorption of the externally added material in the stage of high humidity increases, thus degrading the electrostatic chargeability of the toner and decreasing the density of pictures. Therefore the preferably pH of the gamma-Fe2O3 is <=8.0. |
