Magnetic dry developer for electrostatic photography and process for preparation thereof

摘要

A magnetic toner for electrostatic photography consisting essentially of spherical particles of a composition comprising a fine powder of a magnetic material having an average particle size not exceeding 1000 m mu and being dispersed in a binder resin, said powdery magnetic material being present in an amount of 25 to 75% by weight based on the composition, spherical particles of said composition having such a particle size distribution that particles having a particle size larger than 44 mu occupy up to 10% of the total particles and particles having a particle size smaller than 2 mu occupy up to 10% of the total particles, wherein said fine powder of the magnetic material is distributed predominantly in the surface layer portion of each spherical particle and said spherical particles have a volume resistivity not higher than 1 x 1011 OMEGA -cm as measured in a magnetic field of about 680 gauss under a voltage of 1000 V.