Hitachi Metals, Ltd.

Toshihiko Noshiro

Masumi Asanae

Masahisa Ochiai

Koji Noguchi

Fumio Kimura

Akihiko Funakawa

An image forming method for developing an electrostatic latent image on a moving image-bearing member with a magnetic developer and for removing the residual toner after transfer of a developed toner image onto a transfer member is described. The method includes providing a rotatable, cylindrical permanent magnet having a plurality of magnetic poles on the surface for supporting and conveying the magnetic developer directly on the magnet surface; forming an electrostatic latent image into a toner image by attracting and conveying a magnetic developer including a nonspherical magnetic toner obtained by a polymerization or a nonspherical magnetic or non-magnetic toner obtained by a polymerization and magnetic carriers; and removing the residual toner remaining on the image-bearing member after transferring this toner image by a cleaning blade. The method also includes a surface magnetic flux density ranging from 50 to 1200 G, and a value of h, defined as .pi.D.multidot.Vp/(M.multidot.Vm), of 2 or less wherein Vp (mm/s) is the moving speed of the image-bearer, and D (mm), M, and Vm (mm/s) are the outer diameter, the number of magnetic poles, and the peripheral speed of the permanent magnet, respectively.

Image forming developing method

An image forming method for operating a moving image-bearing member bearing an electrostatic latent image and a plurality of developing units disposed near the image-bearing member and being selectively operable is described. The color image forming method develops the electrostatic latent image by using a magnetic developer brush formed on the surface of a developer support and conveyance means, and includes the steps of: providing a rotating cylinder for supporting and conveying the magnetic developer, the cylinder including a permanent magnet with a plurality of magnetic poles on the cylinder surface; supplying a magnetic developer containing non-magnetic color toner for color image formation; attracting and conveying a layer of magnetic developer having a smaller thickness than the gap between the image-bearing member and the developer support and conveyance cylinder on the cylinder surface; and applying in the developing region an alternate electric field with an AC bias superimposed on a DC bias between the image-bearing member and the magnetic developer for the developing of an electrostatic latent image on the image-bearing member. The method also includes a surface magnetic flux density ranging from 50 to 1200 G, and a value of h, defined as .pi.D.multidot.V.sub.p /(M.multidot.V.sub.m), of 2 or less wherein V.sub.p (mm/s) is the moving speed of the image-bearer, and D (mm), M, and V.sub.m (mm/s) are the outer diameter, the number of magnetic poles, and the peripheral speed of the permanent magnet, respectively.

An image forming method for developing an electrostatic latent image on an image-bearing member that moves bearing electrostatic latent images formed of a two-component magnetic developer is described. The method includes the steps of providing a rotatable cylinder for supporting and conveying said magnetic developer, the cylinder including a permanent magnet with a plurality of magnetic poles provided on the surface. Magnetic carriers in the magnetic developer are attracted and conveyed on the surface of the permanent magnet, the magnetic carriers having an average particle size of 5 to 20 .mu.m and opposite to toner in polarity of charge. A carrier particle magnetization .sigma..sub.1000 in a magnetic field of 1000 Oe so as to amount to 50 emu/g or less is also used. The method also includes a surface magnetic flux density ranging from 50 to 1200 G, and a value of h, defined as .pi.D.multidot.Vp/(M.multidot.Vm), of 2 or less wherein Vp (mm/s) is the moving speed of the image-bearer, and D (mm), M, and Vm (mm/s) are the outer diameter, the number of magnetic poles, and peripheral speed of the permanent magnet, respectively.

In an image forming method for developing an electrostatic latent image on an image bearing member by using a two-component magnetic developer includes the steps of supporting and conveying a magnetic developer directly on the surface of a permanent magnet with a plurality of magnetic poles provided on the surface and performing both the removal of the residual toner remaining on the surface of the image-bearing member and the development of the electrostatic latent image while rubbing said surface with said magnetic brush. The magnetic carriers in the magnetic developer have average particle sizes of 5 to 20 .mu.m and opposite to toner in polarity of charge, the magnetization .sigma..sub.1000 in a magnetic field of 1000 Oe is 50 emu/g or less. Nonspherical magnetic toner or non-magnetic toner made by a polymerization process and magnetic carriers may be used.

Simultaneous developing/cleaning method using magnetic support member

A sleeveless magnet roller is formed of at least magnetic powder and resin. It is so arranged that, letting a developing gap Ds be the gap between an image-bearing member for holding an electrostatic latent image and a developer conveying member and a doctor gap Dg be the gap between the developer conveying member and a developer's thickness regulating member, one obtains Ds-Dg=0.1 to 0.3 (mm) and Dg=0 to 0.4 (mm). For image formation, one- or two-component magnetic developer is used and a bias voltage, formed by superimposing AC bias voltage to DC bias voltage, is applied to the developing region.

Image forming method for setting a developing gap

A magnetic toner includes at least binding resin (for instance, a styrene-acryl resin) and magnetic powder (for instance, Mn--Zn ferrite or Ni--Zn ferrite) having a saturation magnetization of at least 50 emu/g and a coercive force as measured under the magnetic field of 10 kOe not exceeding 50 Oe. An image formed by using this magnetic toner has high quality and is free of tailing.

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Kumagaya, Japan

Toshihiko Noshiro