Mita Industrial Co., Ltd.

Takahiro Ishihara

Takayuki Itakura

Toyotsune Inoue

Yoshitake Shimizu

Hiroshi Shimoyama

Kenshi Matsui

Kazuya Nagao

Norio Horikami

Takashi Nishino

Kiyofumi Nakatsu

Disclosed are a positive charging color toner comprising a coloring agent and a positive charging electric charge controlling material in a fixing resin, wherein the fixing rein is an urethane-modified polyester resin having an acid value of not more than 5 KOHmg/g, a hydroxyl value of not more than 9 KOHmg/g, a weight-average molecular weight of 8,000 to 120,000 and a number-average molecular weight of 2,000 to 70,000, and the positive charging electric charge controlling material is (a) a quaternary ammonium salt having a melting point of not less than 200&deg; C., or (b) a styrene-acrylate copolymer having a trisubstituted amminio group and a glass transition temperature Tg of not less than 55&deg; C.; and a positive charging one-component non-magnetic color toner comprising a polyester resin having an acid value of not more than 5 KOHmg/g, a hydroxyl value of not more than 9 KOHmg/g, a weight-average molecular weight of 7000 to 20,000 and a number-average molecular weight of 1,000 to 6,000, a polyolefine (releasing agent) having an acid value of not more than 10 KOHmg/g and a weight-average molecular weight of 8,000 to 15,000, a proportion of a polyolefine having a particle diameter of not less than 1.5 &mgr;m among polyolefines dispersed in the toner being within 1% in terms of the number, a coloring agent and a positive charging electric charge controlling resin.

Positive charging color toner

Disclosed are a positive charging color toner comprising a coloring agent and a positive charging electric charge controlling material in a fixing resin, wherein the fixing rein is an urethane-modified polyester resin having an acid value of not more than 5 KOHmg/g, a hydroxyl value of not more than 9 KOHmg/g, a weight-average molecular weight of 8,000 to 120,000 and a number-average molecular weight of 2,000 to 70,000, and the positive charging electric charge controlling material is (a) a quaternary ammonium salt having a melting point of not less than 200.degree. C., or (b) a styrene-acrylate copolymer having a trisubstituted amminio group and a glass transition temperature Tg of not less than 55.degree. C.; and a positive charging one-component non-magnetic color toner comprising a polyester resin having an acid value of not more than 5 KOHmg/g, a hydroxyl value of not more than 9 KOHmg/g, a weight-average molecular weight of 7000 to 20,000 and a number-average molecular weight of 1,000 to 6,000, a polyolefine (releasing agent) having an acid value of not more than 10 KOHmg/g and a weight-average molecular weight of 8,000 to 15,000, a proportion of a polyolefine having a particle diameter of not less than 1.5 .mu.m among polyolefines dispersed in the toner being within 1% in terms of the number, a coloring agent and a positive charging electric charge controlling resin.

The present invention provides an electrophotographic developer comprising a magnetic carrier and a toner, wherein a certain voltage-dependent index Y of the developer and a number proportion X (%) of a certain non-charged toner in the total toner have a relation satisfying the following formula (3):

Electrophotographic developer having a specific voltage-dependant index

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Osaka, Japan

Takahiro Ishihara