EP0429684A1 - Appareil revelateur - Google Patents

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Publication number
EP0429684A1
EP0429684A1 EP19900909488 EP90909488A EP0429684A1 EP 0429684 A1 EP0429684 A1 EP 0429684A1 EP 19900909488 EP19900909488 EP 19900909488 EP 90909488 A EP90909488 A EP 90909488A EP 0429684 A1 EP0429684 A1 EP 0429684A1
Authority
EP
European Patent Office
Prior art keywords
magnetic roller
developing device
magnetic
developer
developing
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP19900909488
Other languages
German (de)
English (en)
Inventor
Yoshiro Koga
Tahei Ishiwatari
Takashi Hama
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Seiko Epson Corp
Original Assignee
Seiko Epson Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from JP15891989A external-priority patent/JPH0324574A/ja
Priority claimed from JP17233589A external-priority patent/JPH0336571A/ja
Priority claimed from JP17233889A external-priority patent/JPH0337690A/ja
Priority claimed from JP17233489A external-priority patent/JPH0336575A/ja
Priority claimed from JP17233689A external-priority patent/JPH0336572A/ja
Priority claimed from JP17233389A external-priority patent/JPH0336574A/ja
Priority claimed from JP17233789A external-priority patent/JPH0336573A/ja
Priority claimed from JP17233989A external-priority patent/JPH0337689A/ja
Priority claimed from JP17950789A external-priority patent/JPH0343766A/ja
Priority claimed from JP17952189A external-priority patent/JPH0344673A/ja
Priority claimed from JP17952289A external-priority patent/JPH0344674A/ja
Application filed by Seiko Epson Corp filed Critical Seiko Epson Corp
Publication of EP0429684A1 publication Critical patent/EP0429684A1/fr
Withdrawn legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G15/00—Apparatus for electrographic processes using a charge pattern
    • G03G15/06—Apparatus for electrographic processes using a charge pattern for developing
    • G03G15/08—Apparatus for electrographic processes using a charge pattern for developing using a solid developer, e.g. powder developer
    • G03G15/09—Apparatus for electrographic processes using a charge pattern for developing using a solid developer, e.g. powder developer using magnetic brush
    • G03G15/0921—Details concerning the magnetic brush roller structure, e.g. magnet configuration
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F7/00—Magnets
    • H01F7/02—Permanent magnets [PM]
    • H01F7/0231—Magnetic circuits with PM for power or force generation
    • H01F7/0252—PM holding devices
    • H01F7/0268—Magnetic cylinders

Definitions

  • This invention relates to image recording devices which use an electrophotographic process, and more particularly it relates to developing devices for developing electrostatic latent images formed on a latent image carrier.
  • a cylindrical magnetic roller magnetized with a plurality of magnetic poles is positioned inside a rotating, non-magnetic, conductive, cylindrical developer transport member (also called a developer sleeve) typically made from stainless steel, aluminum or brass.
  • a developer sleeve typically made from stainless steel, aluminum or brass.
  • This invention is intended to solve these kind of problems, and its purpose is to offer a low-cost developing device that is easy to manufacture from production to assembly by employing a developing device structure which carries the developer directly on the surface of the magnetic roller. Another purpose is to offer a compact, lightweight developing device. Another purpose is to offer a developing device capable of obtaining a high developer density by transporting a sufficient amount of developer through effective utilization of the magnetic field generated by the magnetic roller. Another purpose is to offer a developing device that will yield high print quality with reduced uneven developing caused by the magnetic roller.
  • the developing device of this invention is a developing device for developing electrostatic latent image patterns formed on a latent image carrier in image recording devices employing an electrophotographic process, wherein the developing device comprises a cylindrical magnetic roller on which a plurality of magnetic poles are formed, the developer is supplied directly to the magnetic roller, the developer is held on the surface of the magnetic roller by the magnetic field generated by the magnetic roller, and the developer being held is transported by rotating the magnetic roller.
  • a developing device can be configured with a simple structure by eliminating the prior art developer transport member (sleeve) positioned around the outside of the magnetic roller. Further, since the developer is transported directly by the magnetic roller, the magnetic field generated by the magnetic roller (magnet) can be utilized most efficiently. Also, the magnetic roller can be configured to be compact and lightweight by forming it from a rare earth magnet with a high magnetic characteristic, and the magnetic roller can be configured to have excellent dimensional accuracy without the need for final machining by forming the magnet by injection molding, compression molding or extraction molding. The mechanical strength and magnetic characteristic, in particular, can be improved by including a yoke, which is made from a soft magnetic material and constitutes the magnetic circuit, in the magnetic roller. Other features of the invention will be made clear in the following explanations.
  • FIG. 1 is a generalized cross section of an image formation device including the developing device in a specific application of the invention.
  • the latent image carrier 1 is formed from a photosensitive layer 3 made up of an organic or inorganic photoconductive material on top of a conductive support member 2.
  • the charger 4 which can be a corona charger or other type of charger, the light emitted from the light source 5 passes through the imaging optical system 6 and is selectively irradiated on the photosensitive layer 3 according to the image, whereby potential contrasts are obtained on the photosensitive layer 3 and the desired electrostatic latent image pattern is formed.
  • the developing device 7 charges the developer 8 which is the image formation material, transports it via the cylindrical magnetic roller 9, and develops the developer 8 according to the potential of the electrostatic latent image on the latent image carrier 1 and the bias voltage from the means for impressing the developing bias voltage in the developing gap where the latent image carrier 1 and the magnetic roller 9 come near each other. In this way, the electrostatic latent image on the latent image carrier 1 is manifested as an image by the developer 8.
  • the developer 8 which has manifest the electrostatic latent image is transferred to the recording paper 15 by the transfer unit 14 using corona discharging, an electric field, pressure or adhesion, and the developer 8 is fixed to the recording paper 15 by a pressurizing or heating means, whereby the desired image is formed from developer 8 on the recording paper.
  • the magnetic roller 9 transports the developer 8 regulated to an appropriate amount by the transport regulating member 11.
  • the magnetic roller 9 can comprise a magnetic circuit made up of a cylindrical magnet 12 with a plurality of magnetic poles around its circumference and a cylindrical yoke 13 made from a soft magnetic material.
  • the magnetic roller 9 is rotated with the developer 8 held directly on its surface by the leakage flux on the outside circumference of the magnet 12, thus facilitating direct transport of the developer 8.
  • the magnetic flux is used to full advantage. Therefore, a magnetic restraint greater than in the prior art can be obtained with even a thin magnet.
  • the arrows indicate the direction of rotation of the respective members, but this invention is not limited to this configuration.
  • the installation and removal of the magnetic roller becomes extremely easy and the moment of inertia of the magnet is small when the magnetic roller is rotated, thus speeding up the start of rotation, nearly eliminating uneven rotation during both low-speed and high-speed rotation and only requiring a small torque for rotation. That is, since the inside of the magnetic roller 9 is open and its moment of inertial is small, the magnetic roller 9 can be quickly rotated, it demonstrates almost no uneven rotation during either low-speed or high-speed rotation, it requires little torque for rotation, and developer can be supplied in consistently appropriate amounts, thus making it possible to reduce uneven developing density and obtain high printing quality.
  • FIG. 2 is a generalized cross section of the magnetic roller being used in a developing device in another specific example of the invention.
  • Developer is held and transported according to the magnetic distribution on the outside surface of the cylindrical magnet 12 which is made from a rare earth magnet and has a plurality of magnetic poles formed radially on its circumference, and the magnetic roller 9 has fitted on the inside of the magnet 12 by adhesion or other means the yoke 13 which makes up the magnetic circuit and is made from a soft magnetic material having iron, etc., as its main component.
  • the magnet 22 By forming the magnet 22 from a rare earth magnet in the invention, the weight of the magnet can be reduced to half of that of the prior art, and it also becomes possible to have more than 10 magnetic poles on the magnet 12 and decrease the weight of the yoke 13.
  • the magnet 12 and yoke 13 can be formed as a unit in the formation of the magnetic roller 9 by first positioning the yoke 13 made from a soft magnetic material in the mold when forming the magnet and injecting a magnetic material containing a magnetic powder or resin around the outside of the yoke.
  • they can be easily formed as a unit by injection molding of plastic, and sufficient mechanical strength can be obtained even when the thickness of the magnet is only 0.5 to 2.0 mm.
  • the deviation in the outside diameter of the magnetic roller 9 can be reduced to less than 25 ⁇ m, whereby fluctuations in the amount of developer transported and in the developing gap can be reduced.
  • All of the commonly known single-component magnetic brush developers and two-component magnetic brush developers can be used as the developer in the invention.
  • such commonly known magnetic materials as ferrite magnet, Alnico magnet, manganese-aluminum magnet or rare earth magnet can be used as the magnetic material for the magnetic roller employed in this invention.
  • a rare earth magnet made up of a 3d transition metal such as iron, nickel or cobalt added to one of the 14 rare earth elements ranging from cerium, atomic number 58, to lutetium, atomic number 71, i.e., neodymium, praseodymium and samarium, as the magnet 22, a strong magnetic field can be achieved with even a thin magnet, and therefore a compact, lightweight magnetic roller can be configured.
  • a magnet formed by compression molding, injection molding or extraction molding can be used, in which case, greater freedom can be taken in the shape and magnetic field distribution of the magnetic roller in addition to making it lightweight and compact.
  • the yoke, etc. can be formed as a unit when configuring the magnetic circuit, and dimensional accuracy can be improved such as reducing the deviation in the outside diameter to less than 25 ⁇ m without final machining. Also, since complex measures such as adhesion, etc., are not employed, fluctuations in the magnetic resistance of the magnetic circuit can be made smaller and the magnetic flux density at the magnet surface can be made uniform, whereby fluctuations in the amount of developer transported and in the amount of developing due to deviations in the magnetic flux can be reduced. Since the magnet can be made thin, a magnetizing yoke can be easily positioned inside or outside to form 10 or more magnetic poles even in a magnet with an outside diameter of only 20 mm. Therefore, by forming a plurality of magnetic poles at a pitch nearly equivalent to the thickness of the magnet, fluctuations in the amount of developer transported and in the amount of developing can be reduced.
  • the magnetic roller was configured from a 4-mm-thick ferrite magnet with an outside diameter of 20 mm and a 2-mm-thick yoke with an outside diameter of 12 mm which made up the magnetic circuit inside the magnet, and the magnet was divided up into 16 magnetic poles which yielded a flux density of more than 1000 gauss on the magnet surface, whereby sufficient developer supply and transport amount were obtained. Also, the magnetic roller could be made lighter by the amount of weight of the metal sleeve used as the developer transport member in the prior art.
  • the magnetic roller was configured from a 1.5-mm-thick samarium-cobalt compression-molded magnet with an outside diameter of 20 mm and a 1-mm-thick yoke with an outside diameter of 17 mm which made up the magnetic circuit inside the magnet, and the magnet was divided up into 40 magnetic poles which yielded a flux density of more than 1000 gauss on the magnet surface, whereby sufficient developer supply and transport amount were obtained.
  • the magnetic roller could be made less than half as light as prior art units employing a ferrite magnet and metal sleeve.
  • the magnetic roller was configured from a 1-mm-thick samarium-cobalt injection-molded magnet with an outside diameter of 12 mm and a 1-mm-thick yoke with an outside diameter of 10 mm which made up the magnetic circuit inside the magnet, and the magnet was divided up into 40 magnetic poles which yielded a flux density of more than 1000 gauss on the magnet surface, whereby sufficient developer supply and transport amount were obtained.
  • the magnetic roller could be made less than one-fourth as light as prior art units employing a ferrite magnet and metal sleeve.
  • the magnetic roller was configured from a 1-mm-thick praseodymium extraction-molded magnet with an outside diameter of 20 mm and a 1-mm-thick yoke with an outside diameter of 18 mm which made up the magnetic circuit inside the magnet, and the magnet was divided up into 60 magnetic poles which yielded a flux density of more than 1000 gauss on the magnet surface, whereby a sufficient developer thin layer and transport amount were obtained.
  • the magnetic roller could be made less than half as light as prior art units employing a ferrite magnet and metal sleeve.
  • the magnetic roller was configured from a 1-mm-thick resin-bonded ferrite magnet with an outside diameter of 20 mm and a 1-mm-thick yoke with an outside diameter of 18 mm which made up the magnetic circuit inside the magnet, and the magnet was divided up into 60 magnetic poles which yielded a flux density of more than 200 gauss on the magnet surface, whereby a sufficient developer thin layer and transport amount were obtained.
  • the magnetic roller could be made less than half as light as prior art units employing a ferrite magnet and metal sleeve.
  • a developer transport member non-magnetic metal sleeve
  • the magnetic roller positioned inside the developing device was configured from a sintered ferrite magnet machined to an outside diameter of 18 mm and a thickness of 2 mm.
  • a flux density of only 500 gauss could be obtained on the surface of the developer transport member, thus preventing sufficient supply and transport of the developer.
  • this developing device was used to form images, only low-contrast images with insufficient developer density could be obtained.
  • a developer transport member with an outside diameter of 20 mm was used, and the magnetic roller positioned inside the developing device was configured from a sintered ferrite magnet machined to an outside diameter of 18 mm and a thickness of 5 mm.
  • the magnetic roller was divided up into eight or less magnetic poles, a flux density of greater than 500 gauss could be obtained on the surface of the developer transport member, thus providing sufficient supply and transport of developer.
  • the weight of the magnetic roller was greater than 0.4 kg at a length of 220 mm, so the unit could not be made lightweight.
  • this invention can be applied to a wide range of electrophotographic and other types of developing devices, and it is particularly suited to printers, copiers, facsimile machines and displays.
  • a low-cost developing device can be produced with fewer processes through to assembly by holding and transporting the developer directly on the cylindrical magnetic roller with a plurality of magnetic poles. Further, since the structure is simplified, a compact, lightweight developing device can be offered. Also, since the developer is transported by the leakage flux, a developing device can be offered which effective utilizes the magnetic field generated by the magnetic roller to yield sufficient transport of developer and a high developing density. Moreover, even if the magnet is divided up into numerous magnetic poles, a sufficient magnetic characteristic can be obtained for holding and transporting the developer, whereby a developing device is realized which reduces uneven developing density caused by the magnetic roller and offers high printing quality.
  • a developing device By employing a rare earth magnet as the magnet for the magnetic roller, a developing device can be realized which yields a sufficient magnetic field for holding and transporting the developer even if the magnet is made thin, whereby the magnetic powder content of the developer can be reduced. Further, a superior fixing characteristic can be obtained at a lower fixing temperature, and images with a superior glossiness can be formed.
  • an efficient magnetic circuit can be configured, and a magnetic flux sufficient for holding and transporting the developer can be obtained on the surface of the magnetic roller.
  • a compression-molded magnet By employing a compression-molded magnet, an injection-molded magnet or an extraction-molded magnet as the magnet of the magnetic roller, machining and assembly processes are reduced and a magnetic roller is obtained with good dimensional accuracy and excellent moldability even when made thin, and sufficient magnetic flux for holding and transporting the developer can be obtained on the surface of the magnetic roller.
  • a developing device By dividing the magnet of the magnetic roller up into 10 or more magnetic poles, a developing device can be offered which reduces uneven developing density caused by the magnetic roller and yields high print quality.
  • a developing device can be offered which is compact and lightweight and forms high quality images.
  • crests and troughs are formed into the outside surface of the magnet 12 of the magnetic roller 9 in this embodiment.
  • the outside diameter of the magnetic brush formed by the developer 8 can be made uniform regardless of the position of the poles.
  • the height of the crest in the crest-and-trough shape should be about one-half the thickness of the layer formed by the developer, whereby a good, uniform effect can be obtained.
  • the above crest-and-trough shape should have the following relationship to the magnetic poles as viewed from the axial direction and the circumferential direction of the magnetic roller.
  • the same number of crests and troughs should be formed in the circumferential direction as the number of magnetic poles.
  • about the same number of crests and troughs should be formed in the axial direction as the number magnetic poles.
  • about the same number of crests and troughs should be formed as the number of magnetic poles according to the position of the magnetic poles.
  • the shape of the crests and troughs depends on the number of magnetic waves, but by making them arc shaped or sine wave shaped, the outside diameter of the magnetic brush can be made uniform.
  • the rotational radius of the end of the developer becomes fixed regardless of the position of the magnetic poles, and in the case of contact developing, the developing nip width can be maintained constant and a consistent image density can be obtained with a fixed developing time and demagnetizing force.
  • consistent image density can be obtained by maintaining a fixed developing electric field.
  • the prescribed crests and troughs can be easily formed on the surface of the magnetic roller by using the compression molding, injection molding or extraction molding described above.
  • a magnetic roller was configured from a resin-bonded ferrite magnet which had an outside diameter of 20 mm, was 1 mm thick at the crests and 0.85 mm thick at the troughs, and had 60 troughs and crests each, and a 1-mm-thick yoke which had an outside diameter of 18 mm and made up the magnetic circuit inside the magnet, whereby a magnetic roller was realized in which a flux density greater than 200 gauss was obtained on the surface of the magnet when the magnet was divided up into 60 magnetic poles and a thin layer of developer with a uniform outside diameter was formed on the surface of the magnet.
  • this magnetic roller could be made less than half as heavy as prior art magnetic rollers which used a ferrite magnet and a metal sleeve. Using this developing device to form images, we were able to consistently form high-density, high-contrast images in which almost no unevenness in developing density could be visually detected.
  • a magnetic roller was configured from a samarium-cobalt compression-molded magnet which had an outside diameter of 20 mm, was 1.5 mm thick at the crests and 1.35 mm thick at the troughs, and had 40 troughs and crests each, and a 1-mm-thick yoke which had an outside diameter of 17 mm and made up the magnetic circuit inside the magnet, whereby a magnetic roller was realized in which a flux density greater than 1000 gauss was obtained on the surface of the magnet when the magnet was divided up into 40 poles and a thin layer of developer with a uniform outside diameter was formed on the surface of the magnet.
  • this magnetic roller could be made less than half as heavy as prior art magnetic rollers which used a ferrite magnet and a metal sleeve. Using this developing device to form images, we were able to consistently form high-density, high-contrast images in which almost no unevenness in developing density could be visually detected.
  • a magnetic roller was configured from a samarium-cobalt injection-molded magnet which had an outside diameter of 12 mm, was 1 mm thick at the crests and 0.9 mm thick at the troughs, and had 40 troughs and crests each, and a 1-mm-thick yoke which had an outside diameter of 10 mm and made up the magnetic circuit inside the magnet, whereby a magnetic roller was realized in which a flux density greater than 1000 gauss was obtained on the surface of the magnet when the magnet was divided up into 40 poles and a thin layer of developer with a uniform outside diameter was formed on the surface of the magnet.
  • this magnetic roller could be made less than one-fourth as heavy as prior art magnetic rollers which used a ferrite magnet and a metal sleeve. Using this developing device to form images, we were able to consistently form high-density, high-contrast images in which almost no unevenness in developing density could be visually detected.
  • a developer transport member non-magnetic metal sleeve
  • the magnetic roller positioned inside the developing device was configured from a sintered ferrite magnet machined to an outside diameter of 18 mm and a thickness of 2 mm.
  • a flux density of only 500 gauss could be obtained on the surface of the developer transport member, thus preventing sufficient supply and transport of the developer.
  • this developing device was used to form images, only low-contrast images with insufficient developer density could be obtained.
  • a developer transport member with an outside diameter of 20 mm was used, and the magnetic roller positioned inside the developing device was configured from a sintered ferrite magnet machined to an outside diameter of 18 mm and a thickness of 5 mm.
  • the magnetic roller was divided up into eight or less magnetic poles, a flux density greater than 500 gauss could be obtained on the surface of the developer transport member, thus providing a sufficient supply and transport of developer.
  • the weight of the magnetic roller was greater than 0.4 kg at a length of 220 mm, so the unit could not be made lightweight, and uneven density accompanying fluctuations in the magnetic field were marked.
  • the surface roughness of the magnetic roller is controlled so that it is less than 40% of the volumetric mean particle diameter of the toner, which is a component of the developer, based on the average roughness measured at 10 points as per the JIS standard (JIS-B0601), whereby the above problem can be effectively solved.
  • a one-component developer made up of a magnetic toner having a volumetric mean particle diameter of 10 ⁇ m and comprising carbon black, Fe3O4 and a polyester resin as its principal components was used.
  • volumetric mean particle diameter of the toner used in this embodiment was 10 ⁇ m
  • good images were obtained when the JIS 10-point average roughness of the magnetic roller 9 was less than 4 ⁇ m; i.e., when the surface roughness of the magnetic roller 9 according to the JIS 10-point average roughness standard was less than 40% of the volumetric mean particle diameter of the toner.
  • a two-component developer which combined a toner having a volumetric mean particle diameter of 12 ⁇ m and comprising carbon black and a polyester resin as its principal components and soft magnetic particles with a particle diameter of 100 ⁇ m as the carrier.
  • volumetric mean particle diameter of the toner used in this embodiment was 12 ⁇ m, good images were obtained when the JIS 10-point average roughness of the magnetic roller 9 was less than 4.8 ⁇ m; i.e., when the surface roughness of the magnetic roller 9 according to the JIS 10-point average roughness standard was less than 40% of the volumetric mean particle diameter of the toner.
  • a one-component developer made up of a magnetic toner having a volumetric mean particle diameter of 9 ⁇ m and comprising particles of carbon black, wax and Fe3O4 as their principal components and covered with styrene acrylic resin was used
  • volumetric mean particle diameter of the toner used in this embodiment was 9 ⁇ m, good images were obtained when the JIS 10-point average roughness of the magnetic roller 9 was less than 3.6 ⁇ m; i.e., when the surface roughness of the magnetic roller 9 according to the JIS 10-point average roughness standard was less than 40% of the volumetric mean particle diameter of the toner.
  • rare earth magnets and other known magnetic materials can be used as the magnetic material for the magnetic roller, but it is particularly desirable to use a rare earth magnetic made up of at least one rare earth element such as neodymium, praseodymium and samarium from among the 14 rare earth elements with atomic numbers ranging from 58 to 71 (symbols Ce to Lu) to which has been added at least one 3d transition metal such as iron, nickel and cobalt.
  • rare earth element such as neodymium, praseodymium and samarium from among the 14 rare earth elements with atomic numbers ranging from 58 to 71 (symbols Ce to Lu) to which has been added at least one 3d transition metal such as iron, nickel and cobalt.
  • the surface of the magnetic roller is provided with a covering layer (at least the developer transport surface of the magnetic roller is covered so the magnet is not exposed), whereby corrosion of the magnetic roller surface due to oxidation caused by oxygen or moisture in the air does not occur, and therefore consistently high quality images can be formed over long periods.
  • any material capable of covering the magnetic roller 9 surface so the magnet 12 is not exposed can be used as the covering layer (not shown in figure) in the invention.
  • the covering layer should be at least 1 ⁇ m thick to prevent the occurrence of pinholes in the formation of the covering layer and deterioration of the covering layer over long periods of use.
  • a sintered neodymium-iron magnet was used as the magnetic roller 9, and the surface of the magnetic roller 9 was covered with an epoxy resin as the covering layer.
  • images equivalent to 50 000 regular A4-size sheets were formed continuously under the ambient conditions 30°C and 60% relative humidity, but no deterioration of the image was observed, and images were obtained with the same high quality and high resolution as the first sheet. Further, no corrosion due to oxidation was observed on the surface of the magnetic roller 9, and a consistently uniform developer layer was formed on the magnetic roller 9.
  • images equivalent to 50 000 regular A4-size sheets were formed continuously under the same conditions as in embodiment D1.
  • the images showed deterioration such as streaking and appearance of background, and corrosion due to oxidation was observed on the surface of the magnetic roller 9.
  • a sintered neodymium-iron magnet was used as the magnetic roller 9, and the surface of the magnetic roller 9 was covered with nickel (nickel plating) as the covering layer.
  • images equivalent to 50 000 regular A4-size sheets were formed continuously under the same conditions as in embodiment D1.
  • the images showed deterioration such as streaking and appearance of background, and corrosion due to oxidation was observed on the surface of the magnetic roller 9.
  • a sintered neodymium-iron magnet was used as the magnetic roller 9, and the surface of the magnetic roller 9 was covered with SiO2 as the covering layer.
  • images equivalent to 50 000 regular A4-size sheets were formed continuously under the same conditions as in embodiment D1.
  • the images showed deterioration such as streaking and appearance of background, and corrosion due to oxidation was observed on the surface of the magnetic roller 9.
  • a sintered neodymium-iron magnet was used as the magnetic roller 9, and the surface of the magnetic roller 9 was covered with TiO2 as the covering layer.
  • images equivalent to 50 000 regular A4-size sheets were formed continuously under the same conditions as in embodiment D1.
  • the images showed deterioration such as streaking and appearance of background, and corrosion due to oxidation was observed on the surface of the magnetic roller 9.
  • a cast praseodymium-iron magnet was used as the magnetic roller 9, and the surface of the magnetic roller 9 was covered with SiC as the covering layer.
  • images equivalent to 50 000 regular A4-size sheets were formed continuously under the same conditions as in embodiment D1.
  • the images showed deterioration such as streaking and appearance of background, and corrosion due to oxidation was observed on the surface of the magnetic roller 9.
  • a cast praseodymium-iron magnet was used as the magnetic roller 9, and the surface of the magnetic roller 9 was covered with Al2O3 as the covering layer.
  • images equivalent to 50 000 regular A4-size sheets were formed continuously under the same conditions as in embodiment D1.
  • the images showed deterioration such as streaking and appearance of background, and corrosion due to oxidation was observed on the surface of the magnetic roller 9.
  • a cast praseodymium-iron magnet was used as the magnetic roller 9, and the surface of the magnetic roller 9 was covered with ZnO as the covering layer.
  • images equivalent to 50 000 regular A4-size sheets were formed continuously under the same conditions as in embodiment D1.
  • the images showed deterioration such as streaking and appearance of background, and corrosion due to oxidation was observed on the surface of the magnetic roller 9.
  • an extraction-molded praseodymium-iron magnet was used as the magnetic roller 9, and the surface of the magnetic roller 9 was covered with aluminum as the covering layer.
  • images equivalent to 50 000 regular A4-size sheets were formed continuously under the same conditions as in embodiment D1.
  • the images showed deterioration such as streaking and appearance of background, and corrosion due to oxidation was observed on the surface of the magnetic roller 9.
  • an extraction-molded samarium-cobalt magnet was used as the magnetic roller 9, and the surface of the magnetic roller 9 was covered with nickel as the covering layer.
  • images equivalent to 50 000 regular A4-size sheets were formed continuously under the same conditions as in embodiment D1.
  • the images showed deterioration such as streaking and appearance of background, and corrosion due to oxidation was observed on the surface of the magnetic roller 9.
  • a compression-molded samarium-cobalt magnet was used as the magnetic roller 9, and the surface of the magnetic roller 9 was covered with TiO2 as the covering layer.
  • images equivalent to 50 000 regular A4-size sheets were formed continuously under the same conditions as in embodiment D1.
  • the images showed deterioration such as streaking and appearance of background, and corrosion due to oxidation was observed on the surface of the magnetic roller 9.
  • the charge held by the various developers varies greatly due to various charging mechanisms such frictional electrification between the surface of the magnetic roller and the developer, between developer and developer, and between the developer and components of the developing device such as the developer transport regulating member. Differences in these kind of charging mechanisms cause developers with a broad charge distribution to be transported on the magnetic roller, thus resulting in extremely poor image quality.
  • the above problem can be solved by providing a covering layer made from at least one type of resin on the surface of the magnetic roller. That is, the resin layer covered on the magnetic roller acts as a carrier, which is a component of a two-component developer, for the developer transported on the magnetic roller, thus controlling charging of the developer due to frictional electrification, whereby the distribution of the charge of the developer becomes uniform and in turn makes it possible to consistently form high quality images.
  • the covering layer (resin layer) was covered completely or uniformly on the surface of the magnetic roller 9, but this invention is not limited to this, in that the covering layer need not be formed on the surface of the magnetic roller 9 in a uniform thickness, it may be incomplete and leave the magnet (surface of magnetic roller) exposed, and it may be formed in a plurality of non-continuous independent resin islands.
  • any known developer can be used as a one-component magnetic brush developer or a two-component magnetic brush developer in this invention, and by appropriately selecting the resin that makes up the covering layer, the charged polarity of the developer 8 can be controlled to the desired polarity, either positive or negative.
  • selection of the resin that makes up the covering layer is extremely important, but when the charge control agent is mixed with the developer 8 in a process which uses a one-component developer as the developer 8, it is desirable to use a resin of the same charge ranking as the resin that makes up the developer 8 in order to maximize the charging effect of the charge control agent.
  • a sintered ferrite magnet was used as the magnetic roller 9, and island-like (multiple independent) coverings made from a polyester resin were formed as the covering layer (resin layer).
  • an extraction-molded samarium-cobalt magnet was used as the magnetic roller 9, and island-like (multiple independent) coverings made from a polycarbonate resin were formed as the covering layer.
  • a sintered neodymium-iron magnet was used as the magnetic roller 9, and a uniform (magnet not exposed) covering made from a polyamide resin was formed as the covering layer.
  • a sintered neodymium-iron magnet was used as the magnetic roller 9, and a uniform (magnet not exposed) covering made from a silicon resin (organic silane resin) was formed as the covering layer.
  • a cast praseodymium-iron magnet was used as the magnetic roller 9, and a uniform (magnet not exposed) covering made from a polyurethane resin was formed as the covering layer.
  • a sintered neodymium-iron magnet was used as the magnetic roller 9, and a uniform (magnet not exposed) covering made from a polyurethane resin diffused with tetrafluoroethylene resin particles was formed as the covering layer.
  • ferrite, Alnico, manganese-aluminum, rare earth magnet and other known magnet materials can be used as the magnet material for the magnetic roller.
  • so-called "developing electrodes” must be provided separately to impress the developing bias voltage on the developer transported on the magnetic roller during developing or to enhance the electric field formed by the potential making up the electrostatic latent image on the latent image carrier, or the yoke or shaft inside the magnetic roller or other conductive material must be used as the developing electrode.
  • the structure becomes complicated, and in the case of the latter, resolution is reduced because the developer electrode is positioned away from the latent image carrier and the power consumption is increased by the increased output of the power source to compensate for the reduced effective developing bias.
  • the magnetic part can be used as the developing electrode, but since corrosion due to oxidation occurs on the surface of the magnetic roller, consistently high quality images cannot be formed over long periods.
  • the above problems can be prevented by providing a covering layer made from at least one type of conductive material on the surface of the magnetic roller. That is, since the conductive material layer functions as the developing electrode, consistently high quality images can be formed over long periods.
  • the developing device 7 charges the developer 8 which is a component of the developer and transports the developer 8 on the rotating cylindrical roller 9.
  • the developer held by magnetic force on the magnetic roller 9 is regulated to an appropriate amount by the developer transport regulating member 10 after which it is carried to the developing gap where the latent image carrier 1 and magnetic roller 9 come near each other.
  • the surface of the magnetic roller 9 is covered with a covering layer (not shown) made from at least one type of conductive material, and particularly in cases in which ferrite magnet or other high resistance material or rare earth magnet with a surface corrosion prevention layer is used as the magnetic roller, the covering layer functions as the developing electrode, whereby the bias voltage is impressed on the developer 8 by the means 10 for impressing the developing bias voltage and the electrostatic latent image on the latent image carrier is manifested by the developer 8 adhering to the electrostatic latent image on the latent image carrier according to the potential of the electrostatic latent image on the latent image carrier 1.
  • the desired image can be obtained by transferring the developer 8 (develops the electrostatic latent image) on the latent image carrier 1 to the recording paper 15 by the transfer device 14 and fixing it to the recording paper 15 by a pressurizing and heating means.
  • one end (end not electrically connected to the support member which makes up the latent image carrier 1) of the bias application means 10 is shown electrically connected to the covering layer, but this invention is not limited to this, and as can be seen, the one end of the bias application means can be electrically connected to at least one of the magnet 12 which makes up the magnetic roller 9, the yoke 13 or other conductive support member electrically connected to the magnet 12, and the covering layer.
  • the covering layer in this invention demonstrates such developing electrode effects as enhancement of the electric field generated by the potential which makes up the latent image on the latent image carrier, but in order to obtain a sufficient developing electrode effect and from the standpoint of the output efficiency of the developing bias application means 10, it is desirable to connect the application means 10 to the covering layer so that the covering layer functions as the developing electrode, particularly in cases in which the magnetic roller 9 is a magnet made from ferrite or other high resistance material or is a rare earth magnet with an extremely thick, high-resistance surface corrosion prevention layer.
  • an adequate developer electrode effect can be achieved by connecting to at least one of the magnet 12 which makes up the magnetic roller 9, the yoke 13 or other conductive support member electrically connected to the magnet 12, and the covering layer.
  • a sintered ferrite magnet was used as the magnetic roller 9, and nickel was used as the covering layer (covered with nickel plating).
  • an injection-molded samarium-cobalt magnet was used as the magnetic roller 9, and the configuration was the same as that in embodiment F1 except that aluminum was used as the covering layer (covered with aluminum plating).
  • This embodiment had the same configuration as that in embodiment F3 except that an extraction-molded samarium-cobalt magnet was used as the magnetic roller 9.
  • This embodiment had the same configuration as that in embodiment F4 except that a polyester resin diffused with carbon black was used as the covering layer.
  • a sintered neodymium-iron magnet was used as the magnetic roller 9, and the configuration was the same as that in embodiment F1 except that aluminum was used as the covering layer (covered with aluminum plating).
  • This embodiment had the same configuration as that in embodiment F6 except that a polycarbonate resin diffused with carbon black was used as the covering layer.
  • the conductive material acts as a developing electrode, whereby consistently high quality images can be formed over long periods.
  • the pressure applied to the developer on the magnetic roller increases, thus forming the developer transported by the magnetic roller into a thin layer.
  • a uniform pressure is applied to the contact surface, whereby a consistently uniform developer layer can be formed which in turn makes it possible to form consistently high quality images.
  • FIG. 4 is a generalized cross section of an image formation device including the developing device of an embodiment of this invention.
  • the latent image carrier which rotates in the direction indicated by A in the figure comprises the conductive support member 2 on which has been applied a photosensitive layer 3 having photoconductivity, and after the photosensitive layer 3 has been charged to the prescribed potential by the charger 4, the light emitted from the light source 5 is irradiated on the photosensitive layer 3 by the imaging optical system 6 according to the image, whereby potential contrasts are obtained and the electrostatic latent image is formed on the latent image carrier 1.
  • the developing device 7 charges the developer 8 which is a component of the developer and transports the developer 8 on the cylindrical magnetic roller 9 which rotates in the direction indicated by B in the figure.
  • the developer 8 held by magnetic force on the magnetic roller 9 is regulated to an appropriate amount by the developer transport regulating member 11, after which it is transported to the developing gap where the latent image carrier 1 and the magnetic roller 9 come near each other and the electrostatic latent image on the latent image carrier 1 is manifested by the developer 8 adhering to the electrostatic latent image on the latent image carrier 1 according to the potential of the electrostatic latent image on the latent image carrier 1 and the bias voltage from the power source 10 which is the developing bias voltage application means.
  • the developer transport regulating member 11 is formed from phosphor bronze, stainless steel or other metal with elasticity or from an elastomer such as polyurethane rubber, and its surface is pressed against the magnetic roller 9 so it makes surface contact without the free end of the developer transport regulating member; i.e., edge positioned downstream as seen from the flow of the developer 8, coming in contact with the magnetic roller 9.
  • the developer 8 follows the rotation of the magnetic roller 9 and is transported along the magnetic roller 9 to where it is subjected to the pressure of the developer transport regulating member.
  • the developer transport regulating member 11 makes surface contact with the magnetic roller 9 so that the free end of the developer transport regulating member 11 does not come in contact with the magnetic roller 9. Therefore, the pressure the developer transport regulating member exerts on the magnetic roller 9 is uniform, and even under extremely high pressure; i.e., under a wide range of pressures, and when a developer is used that is susceptible to plastic deformation or is strongly self-cohesive, a uniform thin layer can be consistently formed.
  • the desired image can be obtained by transferring the developer 8 (which has developed the electrostatic latent image) on the latent image carrier 1 to the recording paper 15 by the transfer device 14 and fixing it to the recording paper 15 by a pressurizing or heating means.
  • the latent image carrier 1 and magnetic roller 9 rotate in the directions indicated by A and B as shown in FIG. 4, but this invention is not limited to this configuration. Also, all known developers can be used in this invention as either a one-component magnetic brush developer or a two-component magnetic brush developer.
  • the image quality is further improved by setting the direction of rotation of the magnetic roller opposite the direction of rotation of the latent image carrier and setting the circumferential speed of the magnetic roller faster than the circumferential speed of the latent image carrier.
  • the developing preventing force by the magnetic roller is sufficiently large to reduce the adherence of developer to the background. Further, by making the direction of rotation of the magnetic roller opposite the direction of rotation of the latent image carrier and the circumferential speed of the magnetic roller faster than the circumferential speed of the latent image carrier, excess supply of developer by the magnetic brush at the leading end of the printing area can be prevented, whereby unnecessary accumulation of developer at the leading end edge is prevented and image quality can be improved.
  • the direction of rotation (counterclockwise) of the magnetic roller 9 is opposite the direction of rotation (clockwise) of the latent image carrier 1, and at the developing gap both are moving in the forward direction, excess supply and accumulation of the developer 8 at the leading end of the printing area are prevented and tailing is reduced, whereby resolution is improved.
  • the arrows indicate the direction of rotation of the respective members.
  • the magnetic roller was configured from a 1-mm-thick ferrite magnet with an outside diameter of 20 mm and divided up into 60 magnetic poles and a 1-mm-thick yoke with an outside diameter of 18 mm which made up the magnetic circuit inside the magnet, and images were formed by rotating the magnetic roller counterclockwise at 200 rpm and rotating the latent image carrier with an outside diameter of 30 mm at 30 rpm in the opposite direction (clockwise) of the magnetic roller, whereby high contrast images with high density and no uneven density could be formed consistently with no tailing of the leading end of the printing area. Further, the weight could be reduced by more than half compared to prior art devices employing a ferrite magnet and metal sleeve.
  • the magnetic roller was configured from a 1.5-mm-thick compression-molded samarium-cobalt magnet with an outside diameter of 20 mm and divided up into 40 magnetic poles and a 1-mm-thick yoke with an outside diameter of 17 mm which made up the magnetic circuit inside the magnet, and images were formed by rotating the magnetic roller counterclockwise at 200 rpm and rotating the latent image carrier with an outside diameter of 30 mm at 30 rpm in the opposite direction (clockwise) of the magnetic roller, whereby high contrast images with high density could be formed consistently with no tailing of the leading end of the printing area. Further, the weight could be reduced by more than half compared to prior art devices employing a ferrite magnet and metal sleeve.
  • the magnetic roller was configured from a 1-mm-thick injection-molded samarium-cobalt magnet with an outside diameter of 12 mm and divided up into 40 magnetic poles and a 1-mm-thick yoke with an outside diameter of 10 mm which made up the magnetic circuit inside the magnet, and images were formed by rotating the magnetic roller counterclockwise at 200 rpm and rotating the latent image carrier with an outside diameter of 20 mm at 30 rpm in the opposite direction (clockwise) of the magnetic roller, whereby high contrast images with high density could be formed consistently with no tailing of the leading end of the printing area. Further, the weight could be reduced to less than one-fourth the weight of prior art devices employing a ferrite magnet and metal sleeve.
  • the magnetic roller was configured from a 1-mm-thick ferrite magnet with an outside diameter of 20 mm and divided up into 60 magnetic poles and a 1-mm-thick yoke with an outside diameter of 18 mm which made up the magnetic circuit inside the magnet, and images were formed by rotating the magnetic roller counterclockwise at 200 rpm and rotating the latent image carrier with an outside diameter of 30 mm at 30 rpm in the same direction (counterclockwise) as the magnetic roller, whereby only low contrast images could be formed with developer remaining in the leading end of the printing area and tailing of the leading end of the printing area.
  • a developer transport member non-magnetic metal sleeve
  • the magnetic roller inside the sleeve was configured from a 5-mm-thick sintered ferrite magnet with an outside diameter of 18 mm and divided up into 8 magnetic poles.
  • Images were formed by rotating the latent image carrier with an outside diameter of 30 mm clockwise at 30 rpm, rotating the developer transport member in the same direction (clockwise) as the latent image carrier at 200 rpm and rotating the magnetic roller in the same direction (clockwise) as the latent image carrier at 1 000 rpm, but only low-contrast, low-resolution images could be formed with tailing of the leading end of the printing area. Also, the magnetic roller could not be made lighter.
  • a developer transport member non-magnetic metal sleeve
  • the magnetic roller inside the sleeve was configured from a 5-mm-thick sintered ferrite magnet with an outside diameter of 18 mm and divided up into 8 magnetic poles.
  • Images were formed by rotating the latent image carrier with an outside diameter of 30 mm clockwise at 30 rpm, rotating the developer transport member in the opposite direction (counterclockwise) as the latent image carrier at 200 rpm and rotating the magnetic roller in the same direction (clockwise) as the latent image carrier at 1 000 rpm, but only low-contrast, low-resolution images could be formed with tailing of the leading end of the printing area. Also, the magnetic roller could not be made lighter.
  • image quality is further improved by making the direction of rotation of the magnetic roller and the direction of rotation of the latent image carrier the same and the setting the interval at the developing gap (location where the magnetic roller and the latent image carrier come nearest each other) so that the height of the developer held on the magnetic roller is larger than the minimum value.
  • the developing stopping force by the magnetic roller can be made sufficiently large to reduce adherence of developer to the background. Further, by using a configuration in which the developer has indirect contact or no contact with the latent image carrier, the adherence of unnecessary developer is reduced and image quality is improved.
  • the magnetic roller was configured from a 1-mm-thick ferrite magnet with an outside diameter of 20 mm and divided up into 60 magnetic poles and a 1-mm-thick yoke with an outside diameter of 18 mm which made up the magnetic circuit in the magnet.
  • the magnetic roller was rotated clockwise at 200 rpm, the latent image carrier with an outside diameter of 30 mm was rotated at 30 rpm in the same direction as the magnetic roller (clockwise), and the developing gap was set so that the developer did not come in contact with the latent image carrier.
  • the images formed using this configuration showed consistently high density and high contrast without tailing in the leading end of the printing area. Also, the weight could be reduced to less than half that of prior art devices which used a ferrite magnet and metal sleeve.
  • the magnetic roller was configured from a 1.5-mm-thick compression-molded samarium-cobalt magnet with an outside diameter of 20 mm and divided up into 40 magnetic poles and a 1-mm-thick yoke with an outside diameter of 17 mm which made up the magnetic circuit in the magnet.
  • the magnetic roller was rotated clockwise at 50 rpm and the latent image carrier with an outside diameter of 30 mm was rotated at 30 rpm in the same direction as the magnetic roller (clockwise).
  • the images formed using this configuration showed consistently high density and high contrast without tailing in the leading end of the printing area. Also, the weight could be reduced to less than half that of prior art devices which used a ferrite magnet and metal sleeve.
  • the magnetic roller was configured as a single unit from a 1-mm-thick injection-molded samarium-cobalt magnet with an outside diameter of 12 mm and divided up into 40 magnetic poles and a 1-mm-thick yoke with an outside diameter of 10 mm which made up the magnetic circuit in the magnet.
  • the magnetic roller was rotated clockwise at 50 rpm and the latent image carrier with an outside diameter of 20 mm was rotated at 20 rpm in the same direction as the magnetic roller (clockwise).
  • the images formed using this configuration showed consistently high density and high contrast without tailing in the leading end of the printing area.
  • the weight of the magnetic roller could be reduced to less than one-fourth that of prior art devices which used a ferrite magnet and metal sleeve.
  • a developer transport member non-magnetic metal sleeve
  • the magnetic roller inside the transport member was configured from a 5-mm-thick sintered ferrite magnet with an outside diameter of 18 mm and divided up into 8 magnetic poles.
  • Images were formed by rotating the latent image carrier with an outside diameter of 30 mm clockwise at 30 rpm, rotating the developer transport member at 200 rpm in the same direction (clockwise) as the latent image carrier and rotating the magnetic roller at 1 000 rpm in the same direction (clockwise) as the latent image carrier, but only low-contrast, low-density images with tailing in the leading end of the printing area could be formed. Also, the magnetic roller could not be made lighter.
  • a developer transport member non-magnetic metal sleeve
  • the magnetic roller inside the transport member was configured from a 5-mm-thick sintered ferrite magnet with an outside diameter of 18 mm and divided up into 8 magnetic poles.
  • Images were formed by rotating the latent image carrier with an outside diameter of 30 mm clockwise at 30 rpm, rotating the developer transport member at 200 rpm in the opposite direction (counterclockwise) as the latent image carrier and rotating the magnetic roller at 1 000 rpm in the same direction (clockwise) as the latent image carrier, but only low-contrast, low-density images with tailing in the leading end of the printing area could be formed. Also, the magnetic roller could not be made lighter. Control of Bias Voltage
  • the above problem is solved by providing a magnetic field detection means for detecting the magnetic field of the magnetic roller and a developing bias voltage fluctuation means for fluctuating the developing bias voltage in sync with the alternating magnetic fields detected by the magnetic field detection means.
  • the magnetic field generated by the magnet can be utilized with the greatest efficiency since the developer is transported directly on the magnet and a developing bias voltage in sync with the alternating magnetic fields can be impressed between the magnet and latent image carrier.
  • FIG. 5 is a generalized cross section of an image formation device including a developing device of an embodiment of this invention.
  • the latent image carrier 1 comprises a conductive support member 2 on which has been applied an organic or inorganic photosensitive layer 3 having photoconductivity. After the photosensitive layer 3 has been charged with a corona charger or other type of charger 4, the light emitted from the light source passes through the imaging optical system 6 and is selectively irradiated on the photosensitive layer 3 according to the image, whereby potential contrasts are obtained and the electrostatic latent image is formed.
  • the developing device 7 charges the developer 8 which is the image-forming material and transports it on the cylindrical magnet roller 9, develops the developer 8 at the developing gap where the latent image carrier 1 and the magnetic roller 9 come near each other according to the potential of the electrostatic latent image on the latent image carrier 1 and the bias voltage of the developing bias voltage application means 10 and manifests the electrostatic latent image on the latent image carrier 1 via the developer 8.
  • the developer 8 which manifests the electrostatic latent image is transferred to the recording paper 15 by the transfer device 14 using corona discharge, an electric field, pressure or adhesive force, and the developer 8 is fixed to the recording paper 15 by a pressurizing or heating means, whereby the desired image formed from the developer 8 is obtained on the recording paper 15.
  • the magnetic roller 9 uses magnetic force to hold the developer supplied to it and transports the developer 8 after it has been regulated to an appropriate amount by the developer transport regulating member 11.
  • the magnetic roller 9 forms a magnetic circuit by means of the cylindrical magnet 12 having a plurality of poles on its outside circumference and the soft, magnetic cylindrical yoke (not shown) positioned inside the magnet 12, and it transports the magnetic developer 8 by forming a magnetic field on the cylindrical, non-magnetic developer transport member 13 positioned inside the magnet 12 with a space between them. As shown in FIG.
  • a magnetic field detection means 16 is positioned adjacent to the magnetic roller 9 to detect the magnetic field generated by the magnet 12 at the developing gap, and the alternating voltage superimposing means 17 superimposes an alternating voltage on the developing bias application means according to the fluctuations in the developing preventing force caused by the magnetic field at the developing gap, whereby the difference between the developing force (Coulomb force) due to the electric field and the developing preventing force due to the magnetic field is maintained constant and fluctuations in the force acting on the developer 8 are reduced, and therefore uneven developing density accompanying rotation of the magnet 12 is reduced and images can be formed with high printing quality.
  • the magnetic field detection means 16 may be mounted anywhere near the magnetic roller 9, any alternating voltage can be superimposed that maintains the developing force constant by converting to a magnetic field at the developing gap, and the waveform of the alternating voltage can be a sine wave, a rectangular wave or a saw-tooth wave.
  • FIG. 6A and FIG. 6B depict the impressed condition of the alternating voltage in an embodiment of this invention.
  • the alternating voltage is impressed in periods one-half the period of the reversal of magnetization, and by superimposing the alternating voltage so that the developing electric field is small when the center of the magnetic poles where the height of the magnetic brush is high passes through the developing gap and the developing electric field is large when the interval between magnetic poles where the height of the magnetic brush is low passes through the developing gap, the difference between the developing force due to the developing electric field and the developing preventing force due to the magnetic force is maintained constant, whereby uneven developing density due to fluctuations in the magnetic field can be reduced.
  • a Hall-effect element, a magnetoresistance element, a coil, etc. can be used as the magnetic field detection means, or an optical encoder, mechanical switch or other device which detects the rotational position of the magnet can be used to indirectly detect the magnetic field (rotational position of magnet) and facilitate superimposition of the alternating voltage in the same manner.
  • the developer was transported on a magnetic roller employing a magnet with eight magnetic poles and having a magnetic flux of 800 gauss on the developer transport member, an organic photoconductor was employed as the latent image carrier, and the magnetic field detection means was located near the developing gap.
  • images were formed with reverse developing by superimposing an alternating voltage to impose a ⁇ 200-V AC component on the -550-V DC component so that the absolute value of the developing bias voltage was small when the center of the magnetic pole passed the center of the developing gap at a frequency twice the frequency of the change in the magnetic field, high quality images were obtained with no uneven developing density in solid images and little change in the width of fine lines.
  • the developing device of the present invention can be widely used in image recording means employing an electrophotographic process, and more, particularly it is widely applicable to developing devices for printers, copiers and facsimile machines.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Magnetic Brush Developing In Electrophotography (AREA)
  • Dry Development In Electrophotography (AREA)

Abstract

Un appareil révélateur d'une image latente électrostatique formée sur un substrat d'images latentes dans un appareil d'enregistrement d'images électrophotographiques comprend un rouleau magnétique cylindrique (9) ayant une pluralité de pôles magnétiques et composé d'aimants métalliques en terres rares. Un révélateur (8) est directement appliqué sur le rouleau magnétique (9), maintenu à la surface du rouleau magnétique par le champ magnétique généré par le rouleau magnétique et transféré par la rotation du rouleau magnétique. On peut ainsi simplifier la structure de l'appareil et améliorer la qualité de l'image.
EP19900909488 1989-06-21 1990-06-20 Appareil revelateur Withdrawn EP0429684A1 (fr)

Applications Claiming Priority (22)

Application Number Priority Date Filing Date Title
JP158919/89 1989-06-21
JP15891989A JPH0324574A (ja) 1989-06-21 1989-06-21 現像装置
JP172334/89 1989-07-04
JP172336/89 1989-07-04
JP17233889A JPH0337690A (ja) 1989-07-04 1989-07-04 現像装置
JP172333/89 1989-07-04
JP172335/89 1989-07-04
JP17233489A JPH0336575A (ja) 1989-07-04 1989-07-04 現像装置
JP172339/89 1989-07-04
JP172338/89 1989-07-04
JP17233689A JPH0336572A (ja) 1989-07-04 1989-07-04 現像装置
JP17233589A JPH0336571A (ja) 1989-07-04 1989-07-04 現像装置
JP17233389A JPH0336574A (ja) 1989-07-04 1989-07-04 現像装置
JP17233789A JPH0336573A (ja) 1989-07-04 1989-07-04 現像装置
JP172337/89 1989-07-04
JP17233989A JPH0337689A (ja) 1989-07-04 1989-07-04 現像装置
JP17950789A JPH0343766A (ja) 1989-07-12 1989-07-12 現像装置
JP17952189A JPH0344673A (ja) 1989-07-12 1989-07-12 現像装置
JP179521/89 1989-07-12
JP179507/89 1989-07-12
JP17952289A JPH0344674A (ja) 1989-07-12 1989-07-12 現像装置
JP179522/89 1989-07-12

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EP0429684A1 true EP0429684A1 (fr) 1991-06-05

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WO (1) WO1990016017A1 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0507324A2 (fr) * 1991-04-05 1992-10-07 Kanegafuchi Kagaku Kogyo Kabushiki Kaisha Moulage composite d'un aimant à liant résineux pour des éléments de machine et procédé de production de ceux-ci
CN1051452C (zh) * 1994-07-26 2000-04-19 中国医学科学院血液学研究所 3-取代芳基氧化吲哚类化合物的应用

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US3863603A (en) * 1974-01-07 1975-02-04 Ibm Magnetic brush roll having resilient polymeric surface
JPS52140334A (en) * 1976-05-19 1977-11-22 Hitachi Metals Ltd Electrostatic image developing apparatus
JPS56113172A (en) * 1980-02-12 1981-09-05 Canon Inc Development device
JPH07111924B2 (ja) * 1984-04-12 1995-11-29 セイコーエプソン株式会社 磁気ロール及び磁気ロール用円筒状磁石の製造方法
JP2648139B2 (ja) * 1986-02-28 1997-08-27 日立金属株式会社 現像方法
JPH05152831A (ja) * 1991-11-29 1993-06-18 Toko Inc マイクロストリツプアンテナの共振周波数調整方法

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Title
See references of WO9016017A1 *

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0507324A2 (fr) * 1991-04-05 1992-10-07 Kanegafuchi Kagaku Kogyo Kabushiki Kaisha Moulage composite d'un aimant à liant résineux pour des éléments de machine et procédé de production de ceux-ci
EP0507324A3 (en) * 1991-04-05 1993-07-28 Kanegafuchi Kagaku Kogyo Kabushiki Kaisha Composite molding of resin-bonded magnet for machine parts and process for producing the same
US5319337A (en) * 1991-04-05 1994-06-07 Kanegafuchi Kagaku Kogyo Kabushiki Kaisha Composite molding of resin-bonded magnet for machine parts and process for producing the same
CN1051452C (zh) * 1994-07-26 2000-04-19 中国医学科学院血液学研究所 3-取代芳基氧化吲哚类化合物的应用

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