Magnetic coated carrier two-component type developer and developing method

A two-component type developer for developing an electrostatic image, comprising:

• a toner and a magnetic coated carrier;
• wherein the magnetic coated carrier comprises magnetic coated carrier particles comprising magnetic carrier core particles each comprising a binder resin and metal oxide particles dispersed in the binder resin, and a coating layer surface-coating each carrier core particle, wherein
• the metal oxide particles consist essentially of (a) ferromagnetic metal oxide particles having been subject to a surface lipophilicity-imparting treatment and (b) non-magnetic metal oxide particles having been subject to a surface lipophilicity-imparting treatment,
• the non-magnetic metal oxide particles have a higher resistivity than the ferromagnetic metal oxide particles,
• the magnetic carrier core particles have a resistivity of at least 1.times.10.sup.10 ohm.cm,
• the magnetic coated carrier has a resistivity of at least 1.times.10.sup.12 ohm.cm, and
• the magnetic coated carrier has a particle size distribution such that (i) it has a number-average particle size Dn of 5-100 .mu.m, (ii) it satisfies a relationship of Dn/.delta..gtoreq.3.5, wherein .delta. denotes a standard deviation of number-basis particle size distribution of the carrier, and (iii) it contains at most 25% by number of particles having particle sizes of at most Dn.times.2/3.

A developing method, comprising:

• carrying a two-component type developer on a developer-carrying member enclosing therein a magnetic field generating means, forming a magnetic brush of the two-component type developer on the developer-carrying member, causing the magnetic brush to contact an image-bearing member, and developing an electrostatic image on the image-bearing member while applying an alternating electric field to the developer-carrying member;
• wherein the two-component type developer comprises a toner and a magnetic coated carrier;
• wherein the magnetic coated carrier comprises magnetic coated carrier particles comprising magnetic carrier core particles each comprising a binder resin and metal oxide particles dispersed in the binder resin, and a coating layer surface-coating each carrier core particle, wherein
• the metal oxide particles consist essentially of (a) ferromagnetic metal oxide particles having been subject to a surface lipophilicity-imparting treatment and (b) non-magnetic metal oxide particles having been subject to a surface lipophilicity-imparting treatment, the non-magnetic metal oxide particles have a higher resistivity than the ferromagnetic metal oxide particles,
• the magnetic carrier core particles have a resistivity of at least 1.times.10.sup.10 ohm.cm,
• the magnetic coated carrier has a resistivity of at least 1.times.10.sup.12 ohm.cm, and
• the magnetic coated carrier has a particle size distribution such that (i) it has a number-average particle size Dn of 5-100 .mu.m, (ii) it satisfies a relationship of Dn/.sigma..gtoreq.3.5, wherein .sigma. denotes a standard deviation of number-basis particle size distribution of the carrier, and (iii) it contains at least 25% by number of particles having particle sizes of at most Dn.times.2/3.