Dowa Electronics Materials Co., Ltd.

Dowa IP Creation Co., Ltd.

Yuto Kamai

Shinya Sasaki

Takeshi Kawauchi

A carrier core material is provided that is formed with ferrite particles which can uniformly adhere a coupling agent to the entire surface. A carrier core material is formed with ferrite particles, and the powder pH of the ferrite particles is equal to or more than 9. Here, the ferrite particles are preferably formed of Mn ferrite or Mn&#x2014;Mg ferrite. The ferrite particles preferably contain 45 wt % or more but 65 wt % or less of Fe, 15 wt % or more but 30 wt % or less of Mn and 5 wt % or less of Mg.

Carrier core material

A carrier core material includes, a main component, a material represented by a composition formula MnMFeO(where M is selected from Mg, Ti, Cu, Zn and Ni, 0&#x3c;X, 0&#x2264;Y, 0&#x3c;X+Y&#x3c;1), in which 0.1 to 1.0 mol % of at least one of Sr element and Ca element is contained as the total amount by conversion to SrO or CaO and in which the frequency of a grain whose length RSm is equal or more than 8.0 &#x3bc;m among grains appearing on the surface of particles of the carrier core material is equal to or less than 2.0 number percent. In this way, the degradation of a carrier caused by long-term use such as the separation of a coating resin is significantly reduced, stable charging performance is maintained and the cracking or chipping of the particles is reduced.

Growing community of inventors

Okayama, Japan

Yuto Kamai