Patent ID: 8475988

Claim:
A resin-filled ferrite carrier core material for an electrophotographic developer, comprising a porous ferrite particle, wherein the composition of the porous ferrite particle is represented by the following formula (1), and part of (MgO) and/or (Fe 2 O 3 ) in the following formula (1) is replaced with SrO: ( MgO ) ⁢ x ⁡ ( Fe 2 ⁢ O 3 ) ⁢ y ⁢ ( x = 10 ⁢ ⁢ mol ⁢ ⁢ % ⁢ ⁢ or ⁢ ⁢ more ⁢ ⁢ and ⁢ ⁢ less ⁢ ⁢ than ⁢ ⁢ 25 ⁢ ⁢ mol ⁢ ⁢ % y = exceeding ⁢ ⁢ 75 ⁢ ⁢ mol ⁢ ⁢ % ⁢ ⁢ and ⁢ ⁢ 90 ⁢ ⁢ mol ⁢ ⁢ % ⁢ ⁢ or ⁢ ⁢ less x + y = 100 ⁢ ⁢ mol ⁢ ⁢ % ) ( 1 ) wherein the pore volume of the porous ferrite particle is 40 to 160 mm 3 /g, the peak pore size of the porous ferrite particle is 0.3 to 2.0 μm, and the pore size variation dv, in the pore size distribution, represented by the following formula (2) is 1.5 or less: dv=|d 84 −d 16 |/2 (2) d 16 : Pore size calculated from the pressure applied to mercury when the amount of the intruded mercury reaches 16% in relation to the total amount of the intruded mercury in the high pressure region, defined as 100% d 84 : Pore size calculated from the pressure applied to mercury when the amount of the intruded mercury reaches 84% in relation to the total amount of the intruded mercury in the high pressure region, defined as 100%.