Powdertech Co., Ltd.

Masahiro Ogata

Yuji Sato

Toshio Honjo

Kanao Kayamoto

Kouichi Shimizu

Masaaki Yamaya

Yuji Yoshikawa

Hiromichi Kobayashi

Takao Sugiura

Kazunori Takagi

Norio Takei

A resin-coated carrier for an electrophotographic developer which comprises a carrier core coated with an acryl-modified silicone resin the silicone resin of which has a methyl group and other organic groups, the molar ratio of the methyl group to the total organic groups inclusive of the methyl group &lsqb;methyl group/(methyl group&plus;other organic groups)&rsqb;being 64 mol % or higher and lower than 70 mol %, and the acrylic resin to silicone resin weight ratio ranging from 2/8 to 4/6.

Carrier for electrophotographic developer and electrophotographic developer containing the same

A ferrite carrier for electrophotographic developers which comprises a Mn-Mg ferrite having the general formula

Ferrite carrier for electrophotographic developer and developer

This invention provides a ferrite carrier for an electrophotographic developer characterized in that a core material is ferrite particle composed of 17.0 to 29.0 mol % of Li.sub.2 O and 71.0 to 83.0 mol % of Fe.sub.2 O.sub.3, exhibits a resistance of 2.5.times.10.sup.8 to 2.5.times.10.sup.9 .OMEGA. when a voltage of 250 V is applied, satisfies the relationship: a.sub.1 -a.sub.2 .ltoreq.1.5 when the resistance (R.sub.1) of the ferrite particle exhibited when a voltage of 250 V is applied thereto is taken as a.sub.1 .times.10.sup.b .OMEGA. and the resistance (R.sub.2) thereof exhibited when a voltage of 1000 V is applied thereto is taken as a.sub.2 .times.10.sup.b .OMEGA. (with the proviso that 1.0.ltoreq.a.sub.1 &lt;10, 0.1.ltoreq.a.sub.2, and b is an integer of 6 to 9), and the carrier prepared by coating the ferrite particle with a resin exhibits a resistance of 1.0.times.10.sup.9 to 1.0.times.10.sup.15 .OMEGA. when a voltage 250 V is applied thereto, and has a true specific gravity of 4.70 or below.

Ferrite carrier for electrophotographic developer and developer using

A ferrite carrier for electrophotographic developers which comprises a lithium-based ferrite having the general formula

An iron carrier for an electrophotographic developer, the carrier having a mean particle diameter of 25 to 40 .mu.m, a magnetization of at least 160 emu/g at 3000 Oe, an apparent density of 3.0 to 4.2 g/cm.sup.3, a percentage sphericity of at least 80%, and a specific surface area of at least 350 cm.sup.2 /g as determined by an air permeation method; a process for preparing the carrier by a plasma method; and an electrophotographic developer comprising the carrier.

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Kashiwa, Japan

Masahiro Ogata