Ricoh Company, Ltd.

Takahisa Kato

Mitsuo Aoki

Masanori Suzuki

Fumihiro Sasaki

Satoshi Mochizuki

Tomoe Hagiwara

Hajime Oyama

Kiyonori Tsuda

Tomio Kondou

Seiji Oka

Tohru Suganuma

Tetsuo Isoda

Susumu Kawakami

Hironori Hata

Hidefumi Gohhara

Norio Yokoyama

Yutaka Sakai

In a developing device for an image forming apparatus and of the type using a developer consisting of toner and magnetic carrier, a toner hopper has an opening for replenishing toner stored therein. The developer is regulated by a doctor blade to form a thin layer on a developing sleeve. The developer scraped off by the doctor blade is introduced into a developer storing chamber and caused to move toward the opening of the hopper due to its own internal pressure and gravity. The developer from the hopper is returned toward the doctor blade along the surface of the sleeve. The developer on the sleeve and regulated by the doctor blade is conveyed to a developing position where the sleeve faces an image carrier. The toner contained in the developer is a magnetic toner. When the toner concentration of the developer has reached an upper limit, a space or gap exists in the developer storing chamber.

Developing device using a toner and carrier mixture

A carrier for a dry two-component developer, includes a core material and a silicone-modified acrylic resin layer coated on the surface of the core material, the silicone-modified acrylic resin layer including a silicone-modified acrylic resin, with the ratio of the percentage transmission of infrared spectrum Si--O stretching vibrations (T.sub.Si) of the silicone-modified acrylic resin layer to the percentage transmission of infrared spectrum C.dbd.O stretching vibrations (T.sub.C) thereof, T.sub.Si /T.sub.C, being at least 1.0. The silicone-modified acrylic resin layer can be made from a water-soluble synthetic resin solution containing a silicone macromonomer (A) with a vinyl group being introduced into one terminal thereof, and a vinyl monomer (B) which is copolymerizable with the silicone macromonomer (A), with the molecular weight of the silicone macromonomer (A) of the silicone-modified acrylic resin being in the range of 1,000 to 10,000. Methods of producing such carriers are provided.

Carrier for dry two-component developer and method of producing the same

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 two-component dry type developer for developing latent electrostatic images comprises (i) toner particles with an average particle diameter of 14 .mu.m or less and (ii) carrier particles with an average particle diameter of 70 .mu.m or less, with the ratio of the average particle diameter of the toner particles to the average particle diameter of the carrier particles being 1/5 or less, with a dynamic resistance of 1.0.times.10.sup.8 .OMEGA. or less, and the specific triboelectric charge quantity generated between the toner particles and the carrier particles per unit weight of the toner particles is 25 .mu.C/g or more.

Two-component dry type developer for developing latent electrostatic

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Numazu, Japan

Takahisa Kato