Ricoh Company, Ltd.

Tomoe Hagiwara

Masami Tomita

Motoi Orihara

Masanori Suzuki

Mitsuo Aoki

Shinichi Kuramoto

Takahisa Kato

Koji Suzuki

Naoki Iwata

Shigekazu Enoki

Tomio Kondou

Koichi Katoh

Hachiro Tosaka

Kohichi Katoh

Hiroshi Tanaka

In an electrophotographic or electrostatic image forming device, the toner concentration of a two-component developer, i.e., a mixture of toner and carrier is measured on the basis of an output of a magnetic bridge type concentration sensor responsive to the magnetic permeability of the developer. The sensor has a surface whose mean roughness along the center line is less than 0.4 .mu.m Ra.

Method and apparatus for measuring a toner concentration of a

A positively-chargeable toner includes a binder resin, a coloring agent, and a quaternary-ammonium-base containing copolymer with a weight-average molecular weight of 5,000 to 25,000, which included a repeat unit of formula (I), and a repeat unit of formula (II): ##STR1## wherein R.sup.1 is a hydrogen atom or a methyl group; R.sup.2 is a hydrogen atom or a methyl group; R.sup.3 is an alkylene group, and R.sup.4, R.sup.5 and R.sup.6 are an alkyl group. The quaternary-ammonium-base containing copolymer may further include a repeat unit of formula (III): ##STR2## wherein R.sup.7 is a hydrogen atom or a methyl group; and R.sup.8 is an alkyl group.

Positively-chargeable toner

A toner comprising a binder resin and a coloring agent, with an aggregation degree of 5 to 60%, and an absolute value of Q/M measured by the suction method of 2 to 30 .mu.C/g for use in (1) an image formation method in which electric charges are selectively held on the surface of a development roller to form a number of closed micro fields near the surface of the development roller, a non-magnetic one-component type developer comprising toner, with addition of an auxiliary agent thereto when necessary, is supplied onto the development roller, the developer is held on the surface of the development roller by the micro fields, and latent electrostatic images are developed to visible toner images, and (2) an image formation method in which the surface of a developer-bearing member having a chargeable and photoconductive surface is charged, the charged surface is selectively exposed to light for form a number of micro fields near the developer-bearing member, a non-magnetic one-component type developer comprising toner, to which auxiliary agents may be added when necessary, is supplied onto the development roller, the developer is held on the surface of the development roller by the micro fields, and latent electrostatic images are developed to visible images by the developer.

Toner and method of developing

An image formation method of developing a latent electrostatic image formed on a latent-electrostatic-image bearing member to a visible toner image by a one-component type developer consisting essentially of a toner is carried out by the steps of forming numerous micro closed electric fields near the surface of a developer-bearing member by causing the developer-bearing member to selectively hold electric charges on the surface thereof; supplying the developer to the surface of the developer-bearing member to hold the toner on the surface of the developer-bearing member by the micro closed electric fields; and developing a latent electrostatic image to a visible toner image by the toner. The toner is composed of a binder resin, a coloring agent and a quaternary ammonium salt serving as a charge controlling agent.

Image formation method

A toner for developing latent electrostatic images which comprises a binder resin comprising a styrene polymer or a copolymer thereof, a releasing agent, dispersed in the above binder resin, comprising a low-molecular-weight polypropylene with a weight-average molecular weight of 3000 to 25000, and a coloring agent, dispersed in the above binder resin, with the styrene polymer or copolymer thereof being contained in a ratio of 10-50% and the low-molecular-weight polypropylene in a ratio of 5-60% at a surface portion of the above toner measured by the electron spectroscopy for chemical analysis (ESCA), and a maximum particle diameter of the low-molecular-weight polypropylene contained in the releasing agent being 5000 .ANG. or less.

Toner for developing latent electrostatic images

In a developing device and a dry color toner for color electrophotography. The developing device is provided with a toner conveying member and a toner layer thickness controlling member which is in contact with the toner conveying member. The color toner for developing electrostatic images used in this developing device has the following relation between the number average particle diameter and the volume average particle diameter: ##EQU1## Even after a continuous copying, the developing device and the color toner provide substantially the same image quality as that in the earlier stages of the continuous copying.

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Shizuoka, Japan

Tomoe Hagiwara