A magnetic core material for electrophotographic developer, satisfying a value of Expression (1): a+b×10+c+d+e+f, being from 200 to 1,400, when an amount of fluorine ion is denoted by a (ppm), an amount of chlorine ion is denoted by b (ppm), an amount of bromide ion is denoted by c (ppm), an amount of nitrite ion is denoted by d (ppm), an amount of nitrate ion is denoted by e (ppm), and an amount of sulfate ion is denoted by f (ppm), which are measured by combustion ion chromatography; and having a pore volume of from 30 to 100 mm.sup.3/g.

To provide a magnetic core material for electrophotographic developer and carrier for electrophotographic developer which have small environmental dependence of the electric resistance, can suppress the carrier scattering, and can stably provide good images; a developer contains the carrier; a method for producing the magnetic core material for electrophotographic developer; a method for producing the carrier for electrophotographic developer, and a method for producing the developer.

The magnetic core material for electrophotographic developer, satisfying a value of Formula (1): a+b10+c+d+e+f, being from 20 to 150, when a fluoride ion amount is denoted by a (ppm), a chloride ion amount is denoted by b (ppm), a bromide ion amount is denoted by c (ppm), a nitrite ion amount is denoted by d (ppm), a nitrate ion amount is denoted by e (ppm), and a sulfate ion amount is denoted by f (ppm), which are measured by a combustion ion chromatography method.

A carrier core material is represented by a composition formula M.sub.XFe.sub.3-XO.sub.4 (where M is at least one type of metal element selected from Mg, Mn, Ca, Ti, Cu, Zn and Ni, 0<X<1), in which part of M and/or Fe is substituted with Sr and formed of ferrite particles, and in the carrier core material, a Sr content is equal to or more than 2500 ppm but equal to or less than 12000 ppm, the amount of Sr eluted with pure water at a temperature of 25 C. is equal to or less than 50 ppm, an apparent density is equal to or more than 1.85 g/cm.sup.3 but equal to or less than 2.25 g/cm.sup.3 and magnetization .sub.1k when a magnetic field of 79.5810.sup.3 A/m (1000 oersteds) is applied is equal to or more than 63 Am.sup.2/kg but equal to or less than 75 Am.sup.2/kg.

A magnetic carrier including a magnetic carrier particle having a magnetic carrier core and a resin coating layer formed on a surface of the magnetic carrier core, wherein the resin coating layer includes a resin component including a resin A and a resin B, the resin A is a copolymer of monomers including (a) a (meth)acrylic acid ester monomer having an alicyclic hydrocarbon group and (b) a specific macromonomer, the resin B is a copolymer of monomers including (c) a styrene-based monomer and (d) a specific (meth)acrylic acid ester monomer, and based on the resin components of the resin coating layer, the amount of the resin A is from 20% by mass to 99% by mass, and the amount of the resin B is from 1% by mass to 80% by mass.

An object of the present invention is to provide ferrite particles having high saturation magnetisation and electrical resistivity, excellent in dispersibility in a resin, a solvent, or a resin composition; a rein composition containing the ferrite particles; and a resin molding composed of the resin composition. A Ni-Zn-Cu ferrite particle is in a single crystalline body having an average particle diameter of 1 to 2000 nm, has a polyhedral particle shape, and comprises 5 to 10 wt % of Ni, 15 to 30 wt % of Zn, 1 to 5 wt % of Cu, and 25 to 50 wt % of Fe.

An object of the present invention is to provide a ferrite carrier core material for an electrophotographic developer having desired resistance properties and charging properties with small environmental variation of resistivity and charge amount while maintaining the advantages of ferrite carriers, a ferrite carrier for an electrophotographic developer, an electrophotographic developer using the ferrite carrier, and a method for manufacturing the ferrite carrier core material for an electrophotographic developer. In order to solve the problem, a ferrite carrier core material comprising ferrite particles containing 15 mass % or more and 25 mass % or less of Mn, 0.5 mass % or more and 5.0 mass % or less of Mg, 0.05 mass % or more and 4.0 mass % of Sr, and 45 mass % or more and 55 mass % or less of Fe, with Si localized in the surface thereof is used.

A magnetic core material for electrophotographic developer, satisfying a value of Expression (1): a+b10+c+d+e+f, being from 300 to 1,300, when an amount of fluorine ion is denoted by a (ppm), an amount of chlorine ion is denoted by b (ppm), an amount of bromide ion is denoted by c (ppm), an amount of nitrite ion is denoted by d (ppm), an amount of nitrate ion is denoted by e (ppm), and an amount of sulfate ion is denoted by f (ppm), which are measured by combustion ion chromatography, and having a BET specific surface area being from 0.06 to 0.25 m.sup.2/g.

The present invention relates to a carrier core material for electrophotographic developer, having a ferrite composition and having a supernatant transmittance of 85.0% or more, a method for producing the carrier core material, a carrier for electrophotographic developer, containing the carrier core material, and a developer containing the carrier.

A carrier core material formed with ferrite particles, the skewness Rsk of the particle is equal to or more than 0.40 but equal to or less than 0.20, and the kurtosis Rku of the particle is equal to or more than 3.20 but equal to or less than 3.50. Here, the maximum height Rz of the particle is equal to or more than 2.20 m but equal to or less than 3.50 m. Moreover, the ferrite particle contains at least either of Mn and Mg elements. In this way, cracking or chipping in a concave-convex portion of a particle surface is unlikely to occur, and moreover, the amount of coating resin used can be reduced without properties such as electrical resistance being lowered.

A carrier for forming an electrophotographic image is provided. The carrier includes a core particle comprising a manganese-based ferrite particle having an apparent density of from 2.0 to 2.2 g/cm.sup.3 and a magnetization of from 44 to 52 emu/g in a magnetic field of 500 Oe; and a coating layer coating a surface of the core particle. The coating layer contains a carbon black, an inorganic particle A, and an inorganic particle B. The inorganic particle A and the carbon black each have a concentration gradient in a thickness direction of the coating layer. A concentration of the inorganic particle A increases toward a surface of the coating layer, and a concentration of the carbon black decreases toward the surface of the coating layer.