Mita Industrial Co., Ltd.

Noriaki Tsubota

Masahiko Kubo

Kazuo Fuji

Akihiro Watanabe

Yoshihisa Kuramae

Kazuhisa Edahiro

Akira Nakakuma

Naruo Yabe

Mitsushi Kuroki

Toshiro Tokuno

Katsumi Oyama

Toshio Nishio

Disclosed is a toner having an excellent transparency for full color development, which comprises a binder resin and a magenta coloring dispersed therein wherein (i) said magenta coloring agent is a quinacridone pigment, (ii) said pigment is dispersed in the binder resin in the form of fine particles and that when the toner is formed into a layer having a thickness of 0.9 .mu.m, the area occupied by the dispersed pigment in 780,000 .mu.m.sup.2 of the area of the formed surface is such that the number of dispersed pigment particles having a size of 10 to 12.5 .mu.m.sup.2 is smaller than 40 and the number of dispersed pigment particles having a size of 12.5 to 15.0 .mu.m.sup.2 is smaller than 20, and (iii) the binder resin has an electroconductivity of 1.0.times.10.sup.-9 to 5.0.times.10.sup.-9 (s/cm). The critical quantities of these dispersed particles having the above sizes differ among magenta, cyan and yellow toners. Each of these color toners has an excellent light-transmitting property, and therefore, these toners can be valuably used for the full color development where these toners are developed in the overlapped state on a transfer material to form a full color image.

Method and toner for full color development

The present invention provides a magnetic brush developing method using a two-component developer, characterized in that the development is carried out under such conditions that at the position where the sliding contact of the magnetic brush with the surface of the photosensitive material drum terminates, the following requirement is satisfied:

Magnetic brush development process

The electrophotographic toner for negative charging according to the present invention is characterized in that a metal compound of an aromatic hydroxycarboxylic acid is used as a charge-controlling agent for negative charging and a quaternary ammonium salt having an oxyacid anion is used as a charge-controlling assistant in combination with the charge-controlling agent. This quaternary ammonium salt used as the assistant is incompatible with a fixing resin but dispersible therein. Therefore, the toner of the present invention provides a sharp distribution of the charge quantity, and formation of a highly charged toner having no contribution to development or a lowly charged toner causing scattering of the toner can be effectively prevented.

Electrophotographic toner for negative charging

The electrophotographic toner for negative charging according to the present invention is characterized in that a polyester resin is used as a fixing resin and a quaternary ammonium salt having an oxyacid anion is used as a charge-controlling assistant in combination with a charge-controlling agent for negative charging. This quaternary ammonium salt used as the assistant is incompatible with a fixing resin but dispersible therein. Therefore, the toner of the present invention provides a sharp distribution of the charge quantity, and formation of a highly charged toner having no contribution to development or a lowly charged toner causing scattering of the toner can be effectively prevented.

Disclosed are a two-component type developer for use in the electrophotography or electrostatic printing, which comprises a magnetic carrier and a toner, and a process for the preparation thereof. This developer has a dynamic resistivity (Rd) lower than the dynamic resistivity (Rc) of the magnetic carrier. This developer is prepared by mixing a toner with a magnetic carrier so that the dynamic resistivity (Rd) of the formed developer is lower than the dynamic resistivity (Rc) of the magnetic carrier. This developer is capable of realizing an excellent reproducibility of a fine line image and a high density of a solid image area simultaneously.

Developer and process for preparation thereof

The electrophotographic toner for negative charging according to the present invention is characterized in that an acrylamide copolymer-containing sulfonic acid group is used as a charge-controlling agent for negative charging and a quaternary ammonium salt having an oxyacid anion is used as a charge-controlling assistant in combination with the charge-controlling agent. This quaternary ammonium salt used as the assistant is incompatible with a fixing resin but dispersible therein. Therefore, the toner of the present invention provides a sharp distribution of the charge quantity, and formation of a highly charged toner having no contribution to development or a lowly charged toner causing scattering of the toner can be effectively prevented.

The electrophotographic toner for negative charging according to the present invention is characterized in that a quaternary ammonium salt having an oxyacid anion is used as a charge-controlling assistant in combination with a charge-controlling agent for negative charging. This quaternary ammonium salt used as the assistant is incompatible with a fixing resin but dispersible therein. Therefore, the toner of the present invention provides a sharp distribution of the charge quantity, and formation of a highly charged toner having no contribution to development or a lowly charged toner causing scattering of the toner can be effectively prevented.

Electrophotographic tower for negative charging

Disclosed is a developing process using a two-component type magnetic developer, where the main pole of developing magnetic poles in the developing sleeve is arranged upstream of the position, where a photosensitive drum becomes closest to the developing sleeve, in the rotation direction of the developing sleeve, this closest position between the drum and the developing sleeve is included in a region where the flux density in the magnetic force distribution of the main pole decreases toward the downstream side in the rotation direction of the sleeve, an alternating current voltage is applied between the developing sleeve and the drum to form an alternating electric field between the highest voltage and lowest voltage of the electrostatic latent image and in this state the development is carried out. According to this process, the conditions required for the supply of the developer are considerably moderated and an image having a high quality can be advantageously obtained.

Developing process using two-component type magnetic developer

A process for producing an electrophotographic toner in one step by suspension polymerization of monomers capable of forming a fixing resin. In a first embodiment, the suspension polymerization is carried out in the presence of a specific suspension stabilizer and a radical polymerization initiator. In a second embodiment, the suspension polymerization is carried out while applying ultrasonic radiation of a fixed frequency. The process gives a toner having a uniform particle size distribution.

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Himeji, Japan

Noriaki Tsubota