Hitachi Metals, Ltd.

Tsutomu Saitoh

Masumi Asanae

Masahisa Ochiai

Takashi Hayano

A magnetic carrier for a developer used in electrostatically forming a visual image, comprising a magnetic core material, an electrically-conductive particle-containing resin layer and electrically-conductive particles externally added to the electrically-conductive particle-containing resin layer, the magnetic carrier having a magnetization (.sigma..sub.1000) of 61-100 emu/g at 1 kOe magnetic field, a specific volume resistance of 10.sup.6 .OMEGA..multidot.cm or less, and an average particle size of 10-100 .mu.m. The magnetic carrier of low specific volume resistance has a high durability and provides high quality images. In particular, when the magnetic carrier is applied to an image forming process by rear side exposure, the residual toner on the image-bearing member can be effectively removed without using an additional cleaning means, and high quality images free from the background fogging and contamination can be produced.

Carrier for magnetic developer and method of electrophotographically

An Li--Mn type ferrite carrier for use in electrophotographic development comprising ferrite particles having a chemical composition of 3 to 15% of Li.sub.2 O, 5 to 35% of MnO and 60 to 90% of Fe.sub.2 O.sub.3, each in terms of percent by mole. The ferrite particles consisting essentially of crystal grains having an average grain size of 1 to 50 .mu.m. The surface of the crystal grains is provided with a minute roughness or unevenness during the production of the ferrite carrier. The minute roughness on the grain surface enhances the ability of the ferrite carrier to triboelectrically charge the toner and the bonding strength of the resin coating to the carrier surface.

Ferrite carrier for electrophotographic development

An Li--Mn ferrite carrier comprising 2 to 15 mol % of Li.sub.2 O, 5 to 30 mol % of MnO and 60 to 90 mol % of Fe.sub.2 O.sub.3. The carrier may contain at least one sintering aid selected from the group consisting of CaO, Na.sub.2 O, SiO.sub.2, V.sub.2 O.sub.5, Al.sub.2 O.sub.3, As.sub.2 O.sub.3, Bi.sub.2 O.sub.3, Sb.sub.2 O.sub.3 and B.sub.2 O.sub.3 to improve the surface properties thereof. The carrier may be made sensitive to the intensity of electric field by regulating the specific volume resistivities at 200 V/cm and 10 kV/cm within the specific ranges. This carrier is particularly suitable in the reversal developing method, and in the developing method where an A.C. bias voltage is superimposed to a D.C. bias voltage.

Ferrite carrier, two-component developer and electrostatic imaging

A ferrite carrier for use in electrophotographic development of electrostatic latent images, which comprises a ferrite particles having an average particle size of 10 to 100 .mu.m, a specific resistivity of 10.sup.6 .OMEGA..cm or more and a chemical composition represented by the following formula:

A method in which a photoconductive surface is charged to a uniform potential by a charging brush and a two-component magnetic developer is directly attracted on the surfaced of a sleeve-less developing roll formed from a permanent magnet member and transported by the rotation of the permanent magnet member. An electrostatic latent image is developed with the transported magnetic developer in a developing zone to form a visual toner image on the photoconductive drum. The toner image is transferred to a recording sheet by a transfer roll and permanently fixed thereon by a suitable fixing means. The specific volume resistance of the magnetic carrier is restricted to a particular range to prevent the magnetic carrier from adhering to the photoconductive surface.

Method of electrostatically forming visual image

An image forming method includes the steps of charging a surface of a movable image-bearing member uniformly by using a roller charging means, forming an electrostatic latent image on the image-bearing member by carrying out an image exposure, delivering a magnetic developer which is attracted onto a surface of a sleeveless permanent magnetic member to a developing region located opposite to the electrostatic latent image formed on the image-bearing member, the sleeveless permanent magnetic member being formed with a plurality of magnetic poles provided on its surface and having a cylinder shape, developing the electrostatic latent image using the magnetic developer comprising a toner and magnetic carriers, the magnetic carriers having a volume resistivity of 10.sup.10 .OMEGA..cm or more, and transferring a toner image onto a transfer sheet by using a roller transfer means.

Method of forming image using magnetic developer with high volume

A magnetic carrier for a developer for use in electrophotographic recording, comprising a ferromagnetic particle of an average particle size of 100 .mu.m or less, a ratio (T/a) of the minimum outer size (T) and the maximum outer size (a) of the magnetic carrier being 0.02-0.5. Since the magnetic carrier has a large specific surface area, a toner can be sufficiently charged by the magnetic toner. Therefore, a high quality printed image free from defect such as fogging, spreadness, carrier adhesion, streak, etc. can be obtained even in continuous printing of a long period of time.

Magnetic carrier for developer

A binary developer is composed of a carrier and a magnetic toner. The carrier consists of nonspherically formed magnetic particles having an average diameter of 5 to 100 .mu.m, preferably 5 to 50 .mu.m. The magnetic toner is formed to have an average particle diameter of 10 .mu.m or less and a saturated magnetization .sigma..sub.s of 50 emu/g or less.

Binary developer

A carrier for the developer of electrostatic latent images which is designed to reduce the fouling of the photosensitive member in the developer unit and to lower the volume resistivity of the carrier. This object is achieved by covering the resin-coated carrier with carbon black having a pH value lower than 7 and an average particle diameter smaller than 16 nm. The object is also achieved by covering the resin-bonded carrier with carbon black having a pH value higher than 7.5, if the carrier is to be mixed with a negatively charged toner, or having a pH value lower than 7, if the carrier is to be mixed with a positively charged toner, such that the carrier has a volume resistivity in the range of 10.sup.1 to 10.sup.4 .OMEGA.-cm.

Carrier for developer of electrostatic latent images

There is provided an improved carrier for a developer for use in an electrophotographic recording apparatus, which is composed of iron particles having non-spherical shapes and an average size of 10-50 .mu.m, and resin layers formed on surfaces of the iron particles. There is also provided a method of producing a visual toner image, in which a developer containing the above carrier is employed and a magnetic brush of the developer functions to develop an electrostatic latent image and clean a residual toner simultaneously. The toner image obtained exhibits a high toner density and a high image quality.

Growing community of inventors

Kumagaya, Japan

Tsutomu Saitoh