Toda Kogyo Corporation

Naoki Uchida

Koso Aoki

Hiromitsu Misawa

Minoru Kozawa

Kazuo Fujioka

Ryo Iwai

Mamoru Kamigaki

Shinji Uemoto

Yoji Okano

Nobuya Shimo

Sigenori Miyazaki

Suehiko Miura

Eiichi Kurita

Kaori Kinoshita

Kazushi Takama

Hiroshi Akai

Minoru Kouzawa

Kazuya Fujita

Black magnetic iron oxide particles having an average particle diameter of 0.05 to 2.0 &#x3bc;m and an electric resistance value at an applied voltage of 100 V of not less than 1&#xd7;10&#x3a9;&#xb7;cm. Also a magnetic carrier for electrophotographic developer having spherical magnetic composite particles obtained by dispersing black magnetic iron oxide particles in a binder resin. The magnetic carrier has an electric resistance value Rat an applied voltage of 100 V of 1&#xd7;10to 1&#xd7;10&#x3a9;&#xb7;cm, and an electric resistance value Rat an applied voltage of 300 V which satisfies the relationship represented by the formula:0.1&#x2266;300/100&#x2266;1.

Black magnetic iron oxide particles, magnetic carrier for electrophotographic developer and two-component developer

The present invention relates to black magnetic iron oxide particles comprising magnetite as a main component, wherein when the black magnetic iron oxide particles are molded into a tablet shape, an electric resistance value of the tablet in an alternating current electric field is controlled to produce an impedance of not less than 2&#xd7;10&#x3a9;cm as measured in a characteristic frequency range thereof. The black magnetic iron oxide particles according to the present invention can provide a toner capable of exhibiting a good charging performance and a uniform charging property under the high-temperature and high-humidity conditions, so that when developing an electrostatic latent image therewith, it is possible to obtain toner images having a high resolution or definition, and further the use of heavy metal elements in the black magnetic iron oxide particles can be minimized.

Black magnetic iron oxide particles

The present invention relates to a black magnetic iron oxide particles each having a polyhedral shape wherein when a percentage of dissolution of iron element based on a total amount of iron element contained in the black magnetic iron oxide particles is 50%, a percentage of dissolution of sulfur element based on a total amount of sulfur element contained in the black magnetic iron oxide particles is less than 40%.

Black magnetic iron oxide particles having a specific dissolution of sulfur element

The present invention relates to black magnetic iron oxide particles comprising core particles and a surface layer formed on a surface of the respective core particles which is made of a compound of at least one alkali earth metal element selected from the group consisting of Mg, Ca, Sr and Ba and an aluminum element, in which a content of the at least one alkali earth metal element present in the surface layer is from 100 ppm to 1000 ppm on the basis of a whole weight of the black magnetic iron oxide particles; a content of the aluminum element present in the surface layer is from 1000 ppm to 20000 ppm on the basis of a whole weight of the black magnetic iron oxide particles; a ratio [A/B] of the content [A (ppm)] of the aluminum element to the content [B (ppm)] of the at least one alkali earth metal element present in the surface layer is from 1 to 100; and a molded product comprising said black magnetic iron oxide particles has a breakdown voltage of not less than 400 V/cm.

Black magnetic iron oxide particles having high breakdown voltage

There are provided magnetic iron oxide particles having an average particle diameter (Dp) of primary particles of 0.05 to 0.3 &#x3bc;m, an average particle diameter (Da) of secondary particles of 0.055 to 0.9 &#x3bc;m, and a ratio of the average particle diameter (Da) of the secondary particles to the average particle diameter (Dp) of the secondary particles (Da/Dp) of 1.1 to 3.0, as well as a magnetic toner containing the magnetic iron oxide particles. The magnetic iron oxide particles of the present invention are in the form of small agglomerated particles and exhibit an excellent dispersibility, and the magnetic toner using the magnetic iron oxide particles is excellent in electrification stability.

Magnetic iron oxide particles and magnetic toner using the same

Black magnetic iron oxide particles and magnetic toner

Black magnetic iron oxide particles for magnetic toner and process for producing the same

Magnetite particles of the present invention have an average particle diameter of 0.05 to 0.50 .mu.m, each of the magnetite particles having a plurality of mountain-shaped protrusions with unsharpened crests on a surface of each magnetite particle, and the number of the mountain-shaped protrusions formed on the surface of each magnetite particle being in the range of 2 to 30 when viewed in projected plan; magnetic iron oxide particles for magnetic toner comprising not less than 60%, in particle number, of the said magnetite particles; and a magnetic toner comprising the said magnetic iron oxide particles and a binder resin. The magnetite particles of the present invention are free from the falling-off from toner particles. The toner particles of the present invention shows a good fluidity and produces visual images having a higher definition upon development of electrostatic latent images.

Magnetic toner particles comprising magnetite particles containing

Magnetic particles for a magnetic toner comprise:

Magnetic particles for magnetic toner and process for producing the same

Magnetite particles of the present invention have an average particle diameter of 0.05 to 0.50 .mu.m, each of the magnetite particles having a plurality of mountain-shaped protrusions with unsharpened crests on a surface of each magnetite particle, and the number of the mountain-shaped protrusions formed on the surface of each magnetite particle being in the range of 2 to 30 when viewed in projected plan; magnetic iron oxide particles for magnetic toner comprising not less than 60%, in number, of the said magnetite particles; and a magnetic toner comprising the said magnetic iron oxide particles and a binder resin. The magnetite particles of the present invention are free from the falling-off from toner particles. The toner particles of the present invention shows a good fluidity and produces visual images having a higher definition upon development of electrostatic latent images.

Magnetite particles, magnetic iron oxide particles, process for the

A magnetic toner containing 100 parts by weight of magnetic Fe.sup.2+ -containing iron oxide particles having an average particle size of 0.05 to 0.30 .mu.m, containing not less than 0.9 atm % and less than 1.7 atm % of silicon, calculated as Si, based on Fe, having a substantially cubic shape each ridge of which has a curved surface, and having a ratio .phi. represented by the following formula of more than 1.0 and less than 1.4:

Magnetic particles for magentic toner and process for producing the same

Spherical magnetic iron oxide particles for a magnetic toner comprise:

Spherical magnetic particles for magnetic toner and process for

Magnetic toner particles composed of magnetite core particles containing 0.10 to 1.00 wt % silicon and a hydrous coprecipiate of silica and alumina deposited or adhered on the surfaces of the magnetite core particles. The magnetic toner particles have an area-average diameter of 0.05 to 1.0 .mu.m.

Magnetic particles comprising magnetite core and process for producing

Granular magnetite particles useful as coloring pigments assuming a black color and containing elemental aluminum, 3 to 6 wt %, in the magnetite crystal lattice. The magnetite has a spinel structure with a lattice constant of 8.340 to 8.375 .ANG..

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Otake, Japan

Naoki Uchida