US 5,670,288 AGranted

Carrier for electrophotography, two-component type developer, and image forming method

AssigneeCanon Kabushiki Kaisha

InventorsKenji Okado, Toshiyuki Ugai, Ryoichi Fujita, Makoto Kanbayashi, Tsuyoshi Takiguchi, Yasuhiro Ichikawa, Wakashi Iida

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Abstract

A carrier for electrophotography has carrier particles. The carrier has a 50% average particle diameter (D.sub.50) of from 15 .mu.m to 45 .mu.m and contains from 1% to 20% of carrier particles with a size smaller than 22 .mu.m, not more than 3% of carrier particles with a size smaller than 16 .mu.m, from 2% to 15% of carrier particles with a size of 62 .mu.m or larger, and not more than 2% of carrier particles with a size of 88 .mu.m or larger. The carrier has a specific surface area S.sub.1 as measured by an air-permeability method and a specific surface area S.sub.2 as calculated by the following expression: S.sub.2 =(6/.rho..multidot.D.sub.50).times.10.sup.4 wherein .rho. is a specific gravity of carrier; satisfying the following condition: 1.2 .ltoreq.S.sub.1 /S.sub.2 .ltoreq.2.0.

Claims75

Dependent claims

An image forming method comprising:

developing in a developing zone defined by a latent image bearing member and a developer carrying member provided opposingly thereto, a latent image beared on the latent image bearing member, using a toner of a two-component type developer carried on the developer carrying member and comprising a toner and a carrier, by applying to the developer carrying member developing voltage having a discontinuous alternating current component to form a developing electric field between the latent image bearing member and the developer carrying member;
said toner comprising toner particles and an external additive, and said carrier comprising carrier particles, wherein;
said carrier has a 50% average particle diameter (D.sub.50) from 15 .mu.m to 45 .mu.m;
said carrier contains from 1% to 20% of carrier particles with a size smaller than 22 .mu.m, not more than 3% of carrier particles with a size smaller than 16 .mu.m, from 2% to 15% of carrier particles with a size of 62 .mu.m or larger, and not more than 2% of carrier particles with a size of 88 .mu.m or larger;
and said carrier has a specific surface area S.sub.1 as measured by an air-permeability method and a specific surface area S.sub.2 as calculated by the following expression:
S.sub.2 =(6.sub./p.D.sub.50).times.10.sup.4
wherein .rho. is a specific gravity of carrier;
satisfying the following condition:
1.2.ltoreq.S.sub.1 /S.sub.2 .ltoreq.2.0.
2.

7 more elements

An image forming method comprising:

developing in a developing zone defined by a latent image bearing member and a developer carrying member provided opposingly thereto, a latent image beared on the latent image bearing member, using a toner of a two-component type developer carried an the developer carrying member and comprising a toner and a carrier;
said toner comprising toner particles and an external additive, and said carrier comprising carrier particles, wherein;
said toner has a weight average particle diameter of from 3 .mu.m to 7 .mu.m and contains more than 40% by number of toner particles with a particle diameter of 5.04 .mu.m or smaller, from 10% to 70% by number of toner particles with a particle diameter of 4 .mu.m or smaller, and from 2% to 20% by volume of toner particles with a particle diameter of 8 .mu.m or larger, and
said carrier has a 50% average particle diameter (D.sub.50) of from 15 .mu.m to 45 .mu.m;
said carrier contains from 1% to 20% of carrier particles with a size smaller than 22 .mu.m, not more than 3% of carrier particles with a size smaller than 16 .mu.m, from 2% to 15% of carrier particles with a size of 62 .mu.m or larger, and not more than 2% of carrier particles with a size of 88 .mu.m or larger;
and said carrier has a specific surface area S.sub.1 as measured by an air-permeability method and a specific surface area S.sub.2 as calculated by the following expression:
S.sub.2 =(6/p.D.sub.50).times.10.sup.4
wherein p in a specific gravity of carrier;
satisfying the following condition:
1. 2.ltoreq.S.sub.1 /S.sub.2 .ltoreq.2.0.

7 more elements

Dependencies are inferred from the claim text.