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 and a resinous surface coated layer coating the magnetic carrier core particles, wherein
• (a) the magnetic carrier core particles has a resistivity of at least 1.times.10.sup.10 ohm.cm, and the magnetic coated carrier has a resistivity of at least 1.times.10.sup.12 ohm.cm,
• (b) the magnetic coated carrier has a number-average particle size of 1-100 .mu.m and has such a particle size distribution that particles having particle sizes of at most a half of the number-average particle size occupy an accumulative percentage of at most 20% by number,
• (c) the magnetic coated carrier has a shape factor SF-1 of 100-130,
• (d) the magnetic coated carrier has a magnetization at 1 kilo-oersted of 40-250 emu/cm.sup.3, and
• (e) the resinous surface coating layer comprises a coating resin composition which in turn comprises a straight silicone resin and a coupling agent, said straight silicone resin comprising trifunctional silicon and difunctional silicon in an atomic ratio of 100:0-40:60.

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 and a resinous surface coated layer coating the magnetic carrier core particles, wherein
• (a) the magnetic carrier core particles has a resistivity of at least 1.times.10.sup.10 ohm.cm, and the magnetic coated carrier has a resistivity of at least 1.times.10.sup.12 ohm.cm,
• (b) the magnetic coated carrier has a number-average particle size of 1-100 .mu.m and has such a particle size distribution that particles having particle sizes of at most a half of the number-average particle size occupy an accumulative percentage of at most 20% by number,
• (c) the magnetic coated carrier has a shape factor SF-1 of 100-130,
• (d) the magnetic coated carrier has a magnetization at 1 kilo-oersted of 40-250 emu/cm.sup.3, and
• (e) the resinous surface coating layer comprises a coating resin composition which in turn comprises a straight silicone resin and a coupling agent, said straight silicone resin comprising trifunctional silicon and difunctional silicon in an atomic ratio of 100:0-40:60.