Abstract: A developing roller of the present invention is made up of a nonmagnetic sleeve and a magnet roller disposed in the sleeve. The magnet roller includes a cylindrical magnet produced by molding a mixture of magnetic powder and a high polymer, and a single rare-earth magnet block mounted on the magnet at a position corresponding to a main magnetic pole for development. The cylindrical magnet is magnetized such that magnetic poles adjoining the main magnetic pole are opposite in polarity to the main pole. The main pole and each pole adjoining it make an angle of 45° or less therebetween.

Abstract: A developing device for developing a latent image formed on an image carrier of the present invention includes a rotatable, nonmagnetic developer carrier, and a magnetic field generating member for generating a magnetic field in a developing zone where the developer carrier faces the image carrier. The magnetic field generated causes a developer deposited on the developer carrier to rise in the form of a magnet brush. A magnetic pole for development is located upstream of a position where the developer carrier and image carrier are closest to each other in a direction of rotation. A magnetic force, as measured on the surface of the developer carrier, increases from the position of the magnetic pole toward a position where the magnet brush finally leaves the image carrier.

Abstract: An image forming apparatus has a non-magnetic rotatable cylinder having a diameter of 10 mm to 25 mm, a plurality of magnetic field generating means which is inside the non-magnetic cylinder and fixed, a developing container which houses a two component developer containing a magnetic carrier and a non-magnetic toner and has the non-magnetic cylinder rotatably mounted at an opening portion thereof, agitating conveyer means which is inside the developing container and agitates the two component developer and conveys it to the non-magnetic cylinder, and an image bearing member arranged in opposition to the non-magnetic cylinder at intervals. The image forming apparatus is an image forming apparatus which conveys the two component developer by the rotation of the non-magnetic cylinder, and an electrostatic latent image on the image bearing member is magnetic-brush-developed.

Abstract: An image forming apparatus of the present invention includes a developing device of the type causing a developer to form a magnet brush on the surface of a developer carrier having a magnet roller in a developing region or nip for development. The magnet brush contacts and thereby develops a latent image formed on an image carrier. The magnet roller has a main magnetic pole for development wherein the flux density in the tangential direction has a maximum variation ratio of 40 T/m or above in absolute value. The apparatus of the present invention increases image density and faithfully reproduces even low-contrast images with a low-cost configuration. Further, the apparatus reduces image defects, including granularity and the omission of the trailing edge of an image, even if the range over which the magnet brush and image carrier contact is reduced.

Abstract: A developing device including a developer supporter, and a napping unit for napping the developer on the developer supporter by magnetic poles. The napping unit further includes a developing main magnetic pole installed at a location opposite to a latent image supporter, and a developing auxiliary magnetic pole located at a downstream side of the developing main magnetic pole in a rotational direction of the developer supporter. The developing main magnetic pole has a half-value width equal to or less than 22°. The composite magnetic flux density of the developing main magnetic pole and the developing auxiliary magnetic pole is equal to or greater than 80 mT. In this way, the disclosure can prevent voids in a back end from occurring to improve the fine line reproduction, and additionally, the carrier adhesion can be also prevented.

Abstract: In a developing device for an image forming apparatus of the present invention, a main magnetic pole for development has an angle of 60° or below between opposite pole transition points respectively positioned upstream and downstream thereof in a direction of developer conveyance. A flux density between the main magnetic pole and the magnetic pole downstream of the main magnetic pole in the normal direction has a peak value that is 80% of the maximum flux density of the main pole in the normal direction or above. With this configuration, it is possible to reduce various defective images at the same time.

Abstract: A magnetic roll assembly including an roll core made of a first material and having a longitudinal axis; plural locating members formed of the first material on the outside surface for locating strip magnets; and plural strip magnets located on the plural locating members on the outside surface, the plural strip magnets each having at least first and second surfaces, and a mating feature on one of the at least first and second surfaces mirroring one of the plural locating members for locating and attaching each the plural strip magnets to the roll core, thereby resulting in a magnetic roll assembly that is easily and correctly assembled, and that facilitates rework and remanufacturing.

Abstract: A developing method of the present invention develops a latent image formed on an image carrier with a two-ingredient type developer, which consists of toner grains and carrier grains retaining the toner grains thereon, deposited on a developer carrier in the form of brush chains. Assume that the brush chains on the developer carrier has a height of h as measured at a zero field point where the magnetic field formed by a main magnet is zero, and that a gap for development that is the shortest distance between the developer carrier and the image carrier is a, then a and h are equal to each other. Image quality is estimated by varying the combination of an angle &thgr; between the gap and the zero field point, the outside diameter of the image carrier and the outside diameter of the developer carrier and the height h. A desirable or an optimum range of the results of estimation are selected to set various conditions.

Abstract: A position where a transport amount regulation member is opposed to a developing roller is in an area wherein the magnetic flux density in the tangent line direction becomes 95% or less of the maximum value upstream in the developer transport direction from the position at which the magnetic flux density in the normal direction formed by two magnetic poles on both sides of the transfer amount regulation member on the sleeve roller surface of the developing roller becomes 0 gausses and is in an area wherein the magnetic flux density in the normal direction becomes 90% or less of the maximum value of the upstream pole in the developer transport direction.

Abstract: In a developing device of the present invention, in a developing zone where an image carrier and a developer carrier face each other, the developer carrier carrying a developer thereon moves at a linear velocity of 150 mm/sec or above, but below 500 mm/sec. The amount of the developer conveyed to the developing zone by the developer carrier is between 65 mg/cm2 and 95 mg/cm2. A magnetic flux generated on the developer carrier in the developing zone by a magnetic pole has a flux density having an attenuation ratio of 40% in the direction normal to the developer carrier. The flux density in the direction normal to the developer carrier, as measured on the surface, is between 100 mT and 200 mT. Magnetic grains, which constitute the developer together with toner grains, have a saturation magnetization value of 40×10−7×4&pgr; Wb·m/kg or above, but below 50×10−7×4&pgr; Wb·m/kg.

Abstract: An image forming apparatus including a developing device and an image carrier facing the developing device. The developing device includes a main magnetic pole for causing a developer to magnetically deposit on an outer periphery of a developer carrier in a form of a magnet brush. The image carrier has a coefficient of friction of 0.5 or below, and a flux density in a normal direction has an attenuation ratio of 40% or above.

Abstract: A magnetic roll assembly including an roll core made of a first material and having a longitudinal axis; plural locating members formed of the first material on the outside surface for locating strip magnets; and plural strip magnets located on the plural locating members on the outside surface, the plural strip magnets each having at least first and second surfaces, and a mating feature on one of the at least first and second surfaces mirroring one of the plural locating members for locating and attaching each the plural strip magnets to the roll core, thereby resulting in a magnetic roll assembly that is easily and correctly assembled, and that facilitates rework and remanufacturing.

Abstract: A developing device of the present invention uses a developer containing magnetic toner grains and includes a main pole for development disposed in a sleeve. Flux density generated by the magnetic pole in a direction normal to the surface of the sleeve outside of the surface has an attenuation ratio of 50% or above. The toner grains have a weight mean grain size of 6.0 &mgr;m to 8.0 &mgr;m while the toner grains having grain sizes of 5 &mgr;m and below occupy 40 number % to 80 number % of the entire developer. The toner grains have magnetization strength of 10 emu/g to 25 emu/g in a magnetic field of 5 kOe or magnetization strength of 7 emu/g to 20 emu/g in a magnetic field of 1 kOe. The toner grains reduce toner scattering and image defects despite that they are magnetic, thereby implementing ultrahigh resolution, image reproducibility.

Abstract: In a developing device according to the present invention, a developing roller 8 has a fixed shaft 12 and a sleeve 13. The length of a draw-up magnetic pole N3 provided in the fixed shaft 12 is made shorter than the length of a main magnetic pole N1. Accordingly, the amount of a developer adhering to both ends of an outer peripheral surface of the sleeve 13 is reduced, so that the density of the developer at both the ends of the sleeve 13 is maintained in suitable conditions in a state where the developer is over the main magnetic pole N1.

Abstract: An image forming apparatus is provided for obtaining excellent developing properties using toner with small particle diameters and for forming high-quality visual images. In the developing device of the image forming apparatus, a two-component developer is used which satisfies conditions that volume mean particle diameter dt of the toner is 3˜5 &mgr;m (Condition 1), volume mean particle diameter dc of the carrier is 5dt˜10dt (Condition 2), and a weight ratio Rw of the toner and the carrier is 1.6 (dt/dc)×(&rgr;t/&rgr;c)˜2.4 (dt/dc)×(&rgr;t/&rgr;c) (Condition 3, where &rgr;t and &rgr;c are density of the toner and the carrier, respectively). A main magnetic pole of a rotary sleeve is arranged in the vicinity of the closest position of the rotary sleeve and the image forming body, and the closest distance D between the rotary sleeve and the image forming body satisfies a condition that D is 0.5 H˜0.8 H for the free tip height H of a magnetic brush of the main magnetic pole.

Abstract: A developing device for an image forming apparatus of the present invention includes a developing roller made up of a sleeve and a magnet roller and a doctor facing the surface of the sleeve. The edge of the doctor faces the sleeve at a particular position selected to stabilize the amount of a developer to be scooped up, protect the developer from deterioration, and allow an adequate amount of charge to deposit on the developer by friction.

Abstract: A developing device includes a developing container containing a developer having non-magnetic toner and magnetic carriers. A developer carrying member bears and carries the developer contained in the developing container. A magnetic field generating device generates a magnetic field provided in the developer carrying member, wherein an electrostatic latent image formed on an image bearing member is developed with a magnetic brush, which is formed on the developer carrying member by the magnetic field generating device. The image bearing member and the developer carrying member move in opposite directions at a closest portion therebetween. A peak position of a magnetic force Fr generated by the magnetic field generating device in a direction vertical to a surface of the developer carrying member is disposed in the vicinity of the closest portion and downstream in a rotation direction of the developer carrying member from the closest portion.

Abstract: A developing device of the present invention includes a developing roller provided with a plurality of magnetic poles. The magnetic poles include a main pole and two auxiliary poles positioned at both sides of the main pole for helping the main pole form a magnetic force. The auxiliary poles reduce the half width of the main pole. An AC-biased DC bias for development is applied to the developing roller and disturbs carrier grains close to the developing roller. Images free from various defects including granularity and local omission are achievable with the developing device.

Abstract: An image forming apparatus of the present invention includes a developing device including a sleeve and a magnet roller fixedly accommodated in the sleeve. The magnet roller includes a main magnetic pole and an auxiliary magnetic pole adjoining it at a downstream side in the direction of rotation of the sleeve. A magnetic collection pole is positioned on the edge of an opening formed in a casing and facing a photoconductive drum. The collection pole forms a magnetic field that prevents a developer flew away from the sleeve from flying out of the developing device via the opening.

Abstract: A developing device is provided. The developing device comprises a developer supporter; and a napping unit for napping the developer on the developer supporter by magnetic poles. The napping unit further comprises a developing main magnetic pole installed at a location opposite to a latent image supporter, and a developing auxiliary magic pole located at a downstream side of the developing main magnetic pole in a rotational direction of the developer supporter. The developing main magnetic pole has a half-value width equal to or less than 22°. The composite magnetic flux density of the developing main magnetic pole and the developing auxiliary magnetic pole is equal to or greater than 80 mT. In this way, the disclosure can prevent voids in a back end from occurring to improve the fine line reproduction, and additionally, the carrier adhesion can be also prevented.

Abstract: An image forming apparatus of the present invention includes a developing device including two developing rollers arranged in parallel in a direction in which an image carrier moves each for forming a magnet brush thereon. The magnetic poles of the developing rollers for effecting hand-over of a developer between the rollers are provided with the same polarity. An optical writing device optically writes an image on the image carrier in accordance with tonality data of four levels or less for a single dot. The developing device prevents the developer from moving through a gap between the developing rollers and bringing about irregular image density and background contamination. In addition, the optical writing device successfully obviates ghosts, which are likely to appear when a uniform halftone image including solid portions or bold characters is reproduced.

Abstract: The present invention provides a developing apparatus which has a developer carrying member opposed to an image bearing member for bearing a latent image and adapted to carry magnetic developer, a magnet provided within the developer carrying member and having one end secured to a frame of the apparatus, and a bearing fitted on other end of the magnet and adapted to rotatably support the developer carrying member, wherein a fitting portion between the magnet and the bearing has a non-circular shape.

Abstract: In a developing device for an image forming apparatus of the present invention, a main magnetic pole for development has an angle of 60° or below between opposite pole transition points respectively positioned upstream and downstream thereof in a direction of developer conveyance. A flux density between the main magnetic pole and the magnetic pole downstream of the main magnetic pole in the normal direction has a peak value that is 80% of the maximum flux density of the main pole in the normal direction or above. With this configuration, it is possible to reduce various defective images at the same time.

Abstract: A developing apparatus is provided which includes a hollow cylindrical sleeve which is rotationally driven and a magnetic shaft which is rotationally driven inside the sleeve. The magnetic shaft causes magnetic toner to adhere to a peripheral surface of the sleeve by magnetic force. The magnetic toner adhering to the peripheral surface is supplied to a developing position by rotation of the sleeve and adheres to an electrostatic latent image formed on the surface of a photosensitive body. The center of rotation of the magnetic shaft is deviated from the center of rotation of the sleeve nearer to the photosensitive drum, and frontward along the direction of rotation of the sleeve from a line connecting the center of rotation of the sleeve and the center of rotation of the photosensitive body.

Abstract: A magnet roller comprises a magnet body integrally molded out of a resin magnet composition prepared by mixing and dispersing magnetic powders in a resin binder and a shaft portion projecting from both ends or one end in an axial direction of the magnet body and has a magnetization pattern with a zero-gauss zone between a pair of magnetic poles having the same polarity which are adjacent to each other in a circumferential direction, wherein a cut-out portion extending in an axial direction is formed on the side of the magnetic body at the predetermined position of the zero-gauss zone.

Abstract: A magnetic toner with a negative polarity for developing latent electrostatic images is made of toner particles, each toner particle containing a binder resin, a magnetic powder, and a charge control agent, the surface of the magnetic toner satisfying the relationship of 2×10−7≦C/Sw≦10×10−7, provided C≦8×10−3, wherein C is an amount (g/g) of the charge control agent dissolved in a solvent comprising water and methanol, and Sw is a specific surface area (cm2/cm3) of the toner particles determined from a weight-average particle diameter of the toner particles. An image forming apparatus has an electrostatic image bearing member, and a unit for developing the electrostatic image with the above magnetic toner, the unit having a developer holding member provided with a magnet, and a developer container.

Abstract: In a two-component developing unit, by devising the layout of magnetic poles 6 (particularly a pickup magnetic pole 6b and a trimming magnetic pole 6c) of a magnet member 5 arranged inside a developer carrier 3, an excess portion of a developer G picked up onto the surface of the developer carrier 3 is allowed to drop in the vicinity of the height of the rotational center O of the developer carrier 3, and only the developer G restricted to a predetermined layer thickness is carried and transported to a development region m. A charging member 9 is disposed over a periphery of the developer carrier 3, as required. In addition, the layout of the magnetic poles 6 of the magnet member 5 arranged inside the developer carrier 3 is set variably between the time of development and the time of nondevelopment, and the amount of developer carried on the surface of the developer carrier and transported to the development region m is set to substantially zero at the time of nondevelopment.

Abstract: In an image forming apparatus, a magnet brush forming device includes at least a first magnetic pole facing an image carrier carrying a latent image and a second magnetic pole positioned downstream of the first magnetic pole in the direction of rotation of a developer carrier. When a magnet brush formed on a developer carrier by the first magnetic pole forms a nip between it and the image carrier, flux density in the direction normal to the developer carrier has an attenuation ratio of 40% or above. The second magnetic pole has an upstream half-value point located downstream of a point upstream of and angularly spaced from the edge of a developer storing member by 15°. Flux density in the normal direction and flux density in the tangential direction between the first and second magnetic poles have vectors the sum of which is 85 mT or above.

Abstract: A developing device for an image forming apparatus capable of collecting a developer left on an image carrier with a so-called cleanerless process is disclosed. A ratio of a distance between the image carrier and a developer carrier at the boundary of a nip to a development gap at the center of the nip is selected to be 1.5 or less. This obviates the omission of the trailing edge of an image and granularity and enhances faithful reproduction of horizontal lines and dots despite the use of the cleanerless process.

Abstract: An image developing apparatus includes a latent image carrying member and a developer carrying member. The developer carrying member carries developer which forms a magnetic brush on a surface thereof and causes the magnetic brush to brush a surface of the latent image carrying member in the developing region so that the latent image on the latent image carrying member is visualized. In the apparatus, a developing nip is formed relatively small so that a time period in which a toner of the magnetic brush moves to the developer carrying member back from the latent image carrying member is reduced and a density of the magnetic brush is increased. A developing magnetic pole of the developer carrying member has specific half-angle and attenuation rate values.

Abstract: In a two-component developing unit, by devising the layout of magnetic poles 6 (particularly a pickup magnetic pole 6b and a trimming magnetic pole 6c) of a magnet member 5 arranged inside a developer carrier 3, an excess portion of a developer G picked up onto the surface of the developer carrier 3 is allowed to drop in the vicinity of the height of the rotational center O of the developer carrier 3, and only the developer G restricted to a predetermined layer thickness is carried and transported to a development region m. A charging member 9 is disposed over a periphery of the developer carrier 3, as required. In addition, the layout of the magnetic poles 6 of the magnet member 5 arranged inside the developer carrier 3 is set variably between the time of development and the time of nondevelopment, and the amount of developer carried on the surface of the developer carrier and transported to the development region m is set to substantially zero at the time of nondevelopment.

Abstract: An image forming apparatus of the present invention includes a developing roller accommodating a magnet roller therein. The magnet roller includes a main pole forming a magnetic flux whose attenuation ratio is 40% or above in the direction normal to the developing roller. The axis A of the developer carrier, the axis B of the image carrier and the peak C of the magnetic force of the main pole in the above direction are positioned such that an angle between a line AB and a line AC is substantially zero degree.

Abstract: An image forming apparatus in which the flux density of a main magnetic pole for development has an attenuation ratio of 40% or above in the normal direction is disclosed. Assume that a period of time of T1 is necessary for a photoconductive element to move by a single dot at a nip for development. Also, assume that, in a single period of an alternating electric field applied to a developing sleeve as a bias, the duration of an electric field causing toner to move toward the photoconductive element is T2. Further, assume that the duration of an electric field causing the toner to move toward the sleeve is T3. Then, a relation of T1>T2>0 or a relation of T1>T3>0 holds.

Abstract: A developing roller of the present invention is made up of a nonmagnetic sleeve and a magnet roller disposed in the sleeve. The magnet roller includes a cylindrical magnet produced by molding a mixture of magnetic powder and a high polymer, and a single rare-earth magnet block mounted on the magnet at a position corresponding to a main magnetic pole for development. The cylindrical magnet is magnetized such that magnetic poles adjoining the main magnetic pole are opposite in polarity to the main pole. The main pole and each pole adjoining it make an angle of 45° or less therebetween.

Abstract: A magnetic roll, such as for use in a xerographic printing apparatus, is formed from two semicylindrical partial cylinders. The partial cylinders can be molded and attached to each other to form a complete cylinder defining magnetic poles along the circumference thereof.

Abstract: When the structure is arranged such that one of the repulsion poles is used as a developer layer thickness regulation pole, screw pitch-shaped density unevenness occurred at the rear end of a solid black image.

Abstract: A magnet roll has a plurality of magnetic poles on a surface with at least one magnetic pole portion being composed of an anisotropic bonded magnet including magnet powder and binder resin. The anisotropic bonded magnet contains R—T—N magnet powder, wherein R is at least one rare earth element including Y, Sm being indispensable, and T is Fe or Fe and Co. The R—T—N magnet powder may also contain inevitable impurities such as C, O and H. The binder resin constitutes 20-70% of the volume of the anisotropic bonded magnet such that the anisotropic bonded magnet have a maximum energy product (BH)max of 10 MGOe or more and a residual magnetization Br of 2800 G or more.

Abstract: In an image forming apparatus for charging a photosensitive body, changing the light exposure amount in at least three levels at exposure to light, thereby forming an electrostatic image made up of a high-potential part, a low-potential part, and an intermediate-potential part therebetween on the photosensitive body, and normally developing and inversely developing the electrostatic image using toners different in charge polarity for forming two types of toner images on the photosensitive body, a first developer used with a first toner image developing unit has electric resistance changed within 10% in the change range of applied voltage to the developer as the difference between a surface potential of the photosensitive body and a developing bias voltage.

Abstract: In an image forming apparatus, the rise and fall of a short magnet brush are realized and allow a nip for development to be reduced. This, coupled with the fact that the short magnet brush uniformly rises and falls in the axial direction of a developing sleeve, frees the trailing edge of an image from local omission or jaggedness while reducing defective images including a thinned dot image.

Abstract: The invention relates generally to apparatus for electrostatic image development and, in particular, apparatus that implement a magnetic brush with a drum photoconductor. According to an aspect of the invention, a method and apparatus for developing an electrostatic image are provided implementing a drum photoconductor and a magnetic brush contacting the photoconductor. The magnet brush comprises a mixture of toner and hard magnetic carriers.

Abstract: An image forming apparatus of the present invention includes a developing device of the type causing a developer to form a magnet brush on the surface of a developer carrier in a developing region or nip for development. The magnet brush contacts and thereby develops a latent image formed on an image carrier. The apparatus of the present invention increases image density and faithfully reproduces even low-contrast images with a low-cost configuration. Further, the apparatus reduces image defects, including granularity and the omission of the trailing edge of an image, even if the range over which the magnet brush and image carrier contact is reduced.

Abstract: A developing device includes a developing container for containing therein a developer provided with a carrier and a toner, a conveying device for conveying the developer in the developing container, a developer bearing member for bearing thereon the developer conveyed by the conveying device, the developer bearing member conveying the developer to a developing portion for developing a latent image formed on an image bearing member, a magnetic field generating device provided in the developer bearing member for generating a magnetic field, the magnetic field generating device being provided with a first magnetic pole and a second magnetic pole provided so as to be adjacent to the downstream side of the first magnetic pole in the direction of rotation of the developer bearing member and having the same polarity as the first magnetic pole, and a regulating device for regulating the layer thickness of the developer on the developer bearing member at a location substantially opposed to the second magnetic pole.

Abstract: A developing device of the present invention includes an image carrier for forming a latent image thereon, and a developer carrier for depositing a developer thereon in the form of a magnet brush. The magnet brush is caused to contact the latent image to thereby develop it. The developer carrier includes a main magnetic pole for development and an auxiliary magnetic pole adjoining the main pole and helping the main pole exert a magnetic force. The developer carrier and said image carrier are spaced by a gap of 0.3 mm or above, but 0.6 mm or below.

Abstract: A developing apparatus comprises a hollow cylindrical sleeve which is rotationally driven and a magnetic shaft which is rotationally driven inside the sleeve. The magnetic shaft causes the magnetic toner to adhere to the peripheral surface of the sleeve by the magnetic force. The magnetic toner adhering to the peripheral surface is supplied to the developing position by rotation of the sleeve and adheres to the electrostatic latent image formed on the surface of a photosensitive body. The center of rotation of the magnetic shaft is deviated from the center of rotation of the sleeve nearer to the photosensitive drum, and frontward along the direction of rotation of the sleeve from a line connecting the center of rotation of the sleeve and the center of rotation of the photosensitive body.

Abstract: An image forming apparatus has a non-magnetic rotatable cylinder having a diameter of 10 mm to 25 mm, a plurality of magnetic field generating means which is inside the non-magnetic cylinder and fixed, a developing container which houses a two component developer containing a magnetic carrier and a non-magnetic toner and has the non-magnetic cylinder rotatably mounted at an opening portion thereof, agitating conveyer means which is inside the developing container and agitates the two component developer and conveys it to the non-magnetic cylinder, and an image bearing member arranged in opposition to the non-magnetic cylinder at intervals. The image forming apparatus is an image forming apparatus which conveys the two component developer by the rotation of the non-magnetic cylinder, and an electrostatic latent image on the image bearing member is magnetic-brush-developed.

Abstract: A synthetic resin magnet composition that can maintain its good melt flowability without deterioration in moldability or in uniformity of magnetic force even when the amount of magnetic powder being filled is increased, and thus, can accomplish an improvement in magnetic characteristic of the molded-product is provided. Further, the synthetic resin magnet composition is used to provide a synthetic resin magnet molded-product, such as a magnetic roller, that can achieve high-magnetization without causing any variation in surface magnetic force or deterioration in dimensional precision. Such a composition is composed by mixing and dispersing a magnetic powder and at least one type of aromatic polyamine compound to a synthetic resin binder.

Abstract: An image forming apparatus develops a latent image formed on an image carrier with a developer that forms a magnet brush on a developer carrier. The developer carrier is made up of a sleeve and a stationary magnet roller accommodated in the sleeve. The magnet roller includes a main pole for causing the developer to form the magnet brush and auxiliary poles for helping the main pole exert a magnetic force. An electric field including an oscillation component is formed between the image carrier and the developer carrier. A particular ratio is set up between a distance between the image carrier and the developer carrier, as measured at the boundary of a nip, and the shortest distance between them, between the above shortest distance and the shortest distance between the developer carrier and a metering member, or between the shortest distance between the image carrier and the developer carrier and the amount of developer scooped up to the image carrier.

Abstract: A negative conductive silica and an inorganic oxide are added to a negative magnetic toner so as to obtain a developing agent satisfactory in the rise of the charging and in the stability of charging over the entire life of the developing agent and capable of forming an image free from blurring and a defective transference.

Abstract: A disposal cartridge for use in an image forming apparatus includes a sheet and a roller. An area of the sheet is at least equal to an area of the entire circumferential surface of the roller. The sheet is detachably bonded to an entire circumferential surface of the roller. The roller attracts toner and is detachably and rotatably mounted on the disposal cartridge.

Abstract: A developing device which prevents bias of a developer caused by an axial magnetic force of a magnet roller, and which can form an image uniform in the axial direction; and a magnet roller for a developing device which is used in the above developing device and is reduced in axial magnetic force. The developing device includes a rotatable sleeve which carries a developer on the surface thereof, a fixed magnet roller which is provided within the sleeve and has a plurality magnetic poles, and a doctor blade which controls the amount of developer carried on the sleeve. The developing device is constructed so that among the plurality of magnetic poles of the magnet roller, the ratio of the axial magnetic flux density to the radial magnetic flux density of a magnetic pole opposing the doctor blade is 2.5/100 or less in a central portion in the axial direction.