EP0660199B1 - Ladesystem und elektrophotographischer Apparat - Google Patents

Ladesystem und elektrophotographischer Apparat Download PDF

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Publication number
EP0660199B1
EP0660199B1 EP19940120222 EP94120222A EP0660199B1 EP 0660199 B1 EP0660199 B1 EP 0660199B1 EP 19940120222 EP19940120222 EP 19940120222 EP 94120222 A EP94120222 A EP 94120222A EP 0660199 B1 EP0660199 B1 EP 0660199B1
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EP
European Patent Office
Prior art keywords
photosensitive body
electrified
particles
contact
toner
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.)
Expired - Lifetime
Application number
EP19940120222
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English (en)
French (fr)
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EP0660199A1 (de
Inventor
Hideyuki C/O Canon K.K. Yano
Akio C/O Canon K.K. Maruyama
Yomishi C/O Canon K.K. Toshida
Noboru C/O Canon K.K. Kashimura
Kazushige C/O Canon K.K. Nakamura
Shoji C/O Canon K.K. Amamiya
Harumi C/O Canon K.K. Ishiyama
Tadashi C/O Canon K.K. Furuya
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Canon Inc
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Canon Inc
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Publication of EP0660199A1 publication Critical patent/EP0660199A1/de
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Publication of EP0660199B1 publication Critical patent/EP0660199B1/de
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G13/00—Electrographic processes using a charge pattern
    • G03G13/02—Sensitising, i.e. laying-down a uniform charge
    • G03G13/025—Sensitising, i.e. laying-down a uniform charge by contact, friction or induction
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G5/00—Recording members for original recording by exposure, e.g. to light, to heat, to electrons; Manufacture thereof; Selection of materials therefor
    • G03G5/14—Inert intermediate or cover layers for charge-receiving layers
    • G03G5/147—Cover layers
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G5/00—Recording members for original recording by exposure, e.g. to light, to heat, to electrons; Manufacture thereof; Selection of materials therefor
    • G03G5/14—Inert intermediate or cover layers for charge-receiving layers
    • G03G5/147—Cover layers
    • G03G5/14704—Cover layers comprising inorganic material
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G5/00—Recording members for original recording by exposure, e.g. to light, to heat, to electrons; Manufacture thereof; Selection of materials therefor
    • G03G5/14—Inert intermediate or cover layers for charge-receiving layers
    • G03G5/147—Cover layers
    • G03G5/14708—Cover layers comprising organic material
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G5/00—Recording members for original recording by exposure, e.g. to light, to heat, to electrons; Manufacture thereof; Selection of materials therefor
    • G03G5/14—Inert intermediate or cover layers for charge-receiving layers
    • G03G5/147—Cover layers
    • G03G5/14708—Cover layers comprising organic material
    • G03G5/14713—Macromolecular material
    • G03G5/14717—Macromolecular material obtained by reactions only involving carbon-to-carbon unsaturated bonds
    • G03G5/14726—Halogenated polymers
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G5/00—Recording members for original recording by exposure, e.g. to light, to heat, to electrons; Manufacture thereof; Selection of materials therefor
    • G03G5/14—Inert intermediate or cover layers for charge-receiving layers
    • G03G5/147—Cover layers
    • G03G5/14708—Cover layers comprising organic material
    • G03G5/14713—Macromolecular material
    • G03G5/14717—Macromolecular material obtained by reactions only involving carbon-to-carbon unsaturated bonds
    • G03G5/14734—Polymers comprising at least one carboxyl radical, e.g. polyacrylic acid, polycrotonic acid, polymaleic acid; Derivatives thereof, e.g. their esters, salts, anhydrides, nitriles, amides
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G5/00—Recording members for original recording by exposure, e.g. to light, to heat, to electrons; Manufacture thereof; Selection of materials therefor
    • G03G5/14—Inert intermediate or cover layers for charge-receiving layers
    • G03G5/147—Cover layers
    • G03G5/14708—Cover layers comprising organic material
    • G03G5/14713—Macromolecular material
    • G03G5/14791—Macromolecular compounds characterised by their structure, e.g. block polymers, reticulated polymers, or by their chemical properties, e.g. by molecular weight or acidity
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G2215/00—Apparatus for electrophotographic processes
    • G03G2215/02—Arrangements for laying down a uniform charge
    • G03G2215/021—Arrangements for laying down a uniform charge by contact, friction or induction
    • G03G2215/022—Arrangements for laying down a uniform charge by contact, friction or induction using a magnetic brush
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G2215/00—Apparatus for electrophotographic processes
    • G03G2215/04—Arrangements for exposing and producing an image
    • G03G2215/0497—Exposure from behind the image carrying surface

Definitions

  • the present invention relates to a charging system for electrifying (including clearing) a body to be electrified, such as a photosensitive body or a dielectric body, by keeping the body to be electrified in contact with a charging member to which voltage can be applied, and to an electrophotography apparatus for performing such electrification.
  • This charging system can be applied to an image forming apparatus and a process cartridge which is detachably mounted on an image forming apparatus.
  • a corona charging device As a means for charging an image supporter such as a photosensitive body, a dielectric body, and so on, and other kind of bodies to be electrified, a corona charging device has been generally used, for example, in an electrophotography apparatus (copying machine, printer, and the like) and an image forming apparatus such as an electrostatic recording apparatus.
  • Such a corona charging device performs electrification by applying high voltage to wire to cause corona discharge and exposing a body to be charged to the corona.
  • Recently, more and more charging devices of contact electrification type have been employed.
  • Such a charging device performs electrification by keeping a charging member in contact with a body to be electrified and applying voltage to the charging member.
  • the contact charging technique has some merits. That is, the voltage applied to give a desired potential to the surface of the body to be electrified can be reduced (low electric power), the amount of ozone generated in the charging process can be reduced (small amount of ozone), and so on.
  • charging devises of contact electrification type those of roller charging type, which are conductive rollers as the charging members, have been widely used because charging process of this kind of devices is stable.
  • a charging device of roller charging type when the charging roller applied with DC voltage is driven, that is, passively rotated by a photosensitive body or the body to be electrified, non-uniformity in the charged body occurs, because irregularity in the surface of the roller causes non-uniformity in contact condition as well as there is non-uniformity in resistance of the roller. Therefore, it is preferable to make a difference between the speed at which the charging member is rotated and that of the body to be electrified so that the body to be electrified is rubbed against the charging member.
  • a magnetic brush provided on the developer sleeve 3b and a photosensitive body 1 positioned in contact with each other form a nip area N.
  • the cleaning process is carried out, wherein the residual toner after transfer process is scraped off. Since the toner employed is magnetic toner and a magnet roll is provided inside the sleeve, the cleaning effect can be increased by the magnetic brush.
  • the charging process is performed, wherein the surface of the photosensitive body is brushed by the conductive magnetic brush in the nip area N to be electrically charged and given a predetermined potential.
  • the photosensitive body has to be made of materials which make it possible to hold electric charge near the surface of the photosensitive body. More specifically, the photosensitive body may be made of amorphous silicon (hereinafter referred as a-Si) while having its surface coated with an inhibiting layer in order to improve the electric charge filling performance, or may be an OPC photosensitive body. Otherwise, a photosensitive body provided with a surface layer in which conductive particles are dispersed may be also employed.
  • a-Si amorphous silicon
  • an exposure beam is given to the back surface of the photosensitive body, the opposite side with respect to the magnetic brush which comes into contact with the photosensitive body.
  • a light source digital light emitting elements such as an LED array is used. A predetermined position in the nip between the developer sleeve and the photosensitive body is exposed to the light beam.
  • the development process is executed in a developing area, which is downstream in the nip area N.
  • conductive toner When conductive toner is used, electric charge is transmitted through the bristles of the toner to the toner at the end portions of the bristles by the electrostatic induction of the latent image formed on the photosensitive body. Then, the toner at the end portions of the bristles is separated from the bristles by the Coulomb force acting between the electric charge of the toner and that of the latent image, carrying out development.
  • the bristles of the conductive carrier serve as closely positioned electrodes.
  • development with the insulative toner can be performed by applying a low voltage.
  • the back surface exposure technique also has its own problems to be solved because many processes are performed within the narrow nip area N between the photosensitive body and the developer sleeve.
  • One of the most serious problems is poor charge. Since it is difficult to give a desired potential to the surface of the photosensitive body, the photosensitive body may sometimes be poorly and non-uniformly charged.
  • reverse development is performed, wherein the charged potential easily becomes the same as or lower than the developing bias potential. Accordingly, even slightly poor charge may cause fogging (a phenomenon in which toner dimly adheres the background of an image) and a ghost image of the previously formed image.
  • poor charge occurs when chances for the conductive carrier to come into direct contact with the photosensitive body to fill the photosensitive body with electric charge become less, or when the length of the contact nip is not uniform, or when the resistance of the developer increases for some reason.
  • the residual toner which was not transferred onto the transfer medium but still remains is cleaned substantially at the same time that the photosensitive body is charged, and in the narrow nip area.
  • the electrification process starts before the residual toner remaining after transfer process has not yet completely cleaned, or that there is not sufficient time to complete the electrification process.
  • the residual toner hinders electrification, the potential of the previously formed image can not be completely erased and poor charge may often cause a positive ghost image.
  • An object of the present invention is to provide a charging system for stably keeping a charging member in contact with a body to be electrified in order to realize uniform electrification, and an electrophotography apparatus for performing such electrification.
  • Another object of the present invention is to provide a charging system which can reduce torque required to drive a charging member, and an electrophotography apparatus employing such a charging system.
  • Another object of the present invention is to provide a charging system which can prevent abrasion of a charging member even after long-term use, and an electrophotography apparatus employing such a charging system.
  • Another object of the present invention is to provide an electrophotography apparatus which can prevent poor charge and a ghost image, stabilize a nip formed between a photosensitive body and a magnetic brush, and realize smooth movement of developer in the nip.
  • An image forming apparatus of this embodiment employing a charging system in which the circumferential speed of a primary charger device for charging an image supporter is different from that of the image supporter. And the image forming apparatus of this embodiment is further characterized as a laser beam printer performing transfer electrophotography processes.
  • a reference numeral 1 designate an electrophotography photosensitive body serving as a image supporter (a body to be electrified).
  • This photosensitive body 1 is a rotating drum made of OPC photosensitive material, and has a diameter of 30 mm.
  • the photosensitive body 1 is rotated at a process speed (circumferential speed) of 100 mm/sec clockwise, as indicated by an arrow in Fig. 1.
  • a charged brush 2 serving as a contact charging member is positioned in contact with the photosensitive body 1 so that the contact area may have a width of 3 mm.
  • the charged brush 2 is rotated in the direction opposite to the photosensitive body 1 in the contact area at 500 rpm (circumferential speed of 314 mm/sec), and is charged with DC charging bias voltage of -700V by a power source S1 for applying charging bias. Accordingly, the outer peripheral surface of the rotating photosensitive body 1 is uniformly charged with voltage of about - 700V.
  • the charged surface of the rotating photosensitive body 1 is subjected to scan exposure L with laser beams whose intensities are modulated on the basis of time-series electric desital signals according to data of a desired image.
  • laser beams are emitted from a laser beam scanner 4 comprising a laser diode polygonal mirror, and so on.
  • a laser beam scanner 4 comprising a laser diode polygonal mirror, and so on.
  • an electrostatic latent image corresponding to the data of a desired image is formed on the peripheral surface of the rotating photosensitive body 1.
  • the electrostatic latent image is developed to an toner image by a reverse developer apparatus 3 using a one-content magnetic insulative toner.
  • a non-magnetic developer sleeve 3a having a diameter of 16 mm which contains a magnet 3b is coated with said negative toner, and fixed close to the surface of the photosensitive body 1 with a distance of 300 ⁇ m. While the photosensitive body 1 and the developer sleeve 3a are rotated at the same speed, the developer sleeve 3a is applied with developing bias voltage by a power source S2 for applying developing bias.
  • the developing bias voltage is obtained by superimposing a rectangular AC voltage having a frequency of 1800Hz and a peak plateau voltage of 1600V on a DC voltage of -500V. With this developing bias voltage, the jumping development is executed between the developer sleeve 3a and the photosensitive body 1.
  • a transfer medium P serving as a recording medium is conveyed from a sheet feed unit (not shown), and inserted, at predetermined timing, in a pressure contact nip (transfer position) T between the rotating photosensitive body 1 and a transfer roller 5 serving as a contact transfer means.
  • the transfer roller 5 has a medium resistance and is pressed against the rotating photosensitive body 1 so as to obtain a predetermined value of contact pressure.
  • a power source S3 for applying transferring bias applies a transferring bias of a predetermined value to the transfer roller 5.
  • the transfer roller 5 has a resistance of 5x10 8 ⁇ , and the transfer process is carried out by applying a DC voltage of +2000V.
  • the transfer medium P inserted into the transfer position T is pinched and carried through the transfer position T, the toner image formed and supported on the surface of the rotating photosensitive body 1 is gradually transferred onto the surface of the transfer medium P by electrostatic attraction and contact pressure.
  • the transfer medium P on which the toner image has been transferred is separated from the surface of the photosensitive body 1 and carried to a fixing device 7 of, for example, thermal fixture type, where the toner image is fixed.
  • the transfer medium P is discharged out of the apparatus as the medium (a print or a copy) on which the desired image has been formed.
  • the residual toner and other unnecessary things on the surface of the photosensitive body 1 are removed by a cleaning device 6, and the cleaned surface of the photosensitive body 1 is repeatedly used for image formation.
  • a cartridge PC comprises four processing device: the photosensitive body 1, the contact electrification member 2, the developer device 3, and the cleaning device 6, all in a cartridge box member 8. And this cartridge is detachably mounted on the apparatus.
  • all these devices need not be designed as a unit. Any modification can be employed as long as the cartridge is provided, at least, with the photosensitive body and the charging member.
  • a reference numeral 9 designates supporting members for supporting the mounted processing cartridge PC.
  • the power sources S1 and S2 are provided in the main body of the image forming apparatus, and are connected with the charging member and the developer sleeve, respectively, when the cartridge is mounted on the main body of the image forming apparatus.
  • Fig. 2 schematically shows the layer structure of the photosensitive body 1.
  • the photosensitive body 1 is a negatively chargeable organic photoconductor (OPC) photosensitive body, which is prepared by coating an aluminum substrate drum 11 having a diameter of 30 mm with the following first to fifth functional layers 12 to 16 in the named order.
  • OPC organic photoconductor
  • the resultant prepared mixture was applied on the electric charge carrying layer 15, and dried, and cured with light having an intensity of 8mW/cm 2 emitted from a high voltage mercury lamp for 20 seconds.
  • the thickness of the surface layer 16 was 3 pm.
  • the prepared mixture for the surface layer 16 was well dispersed, and the surface of the surface layer 16 was uniformly formed.
  • the volume resistivity of the surface layer 16 was in the order of 10 13 ⁇ , which does not allow a blurred image caused by the drift of the electric charge of a latent image in the peripheral directions, but allows electric charge to move in the direction of the thickness of the layer in some degree. Thus, the residual potential after image exposure is minimized.
  • teflon particles b were dispersed in the binder.
  • the specific surface energy of teflon itself is very small, that is, about 0,02 N/cm (20 dyne/cm)
  • the specific surface energy of the photosensitive body could be remarkably reduced by dispersing teflon.
  • the contact angle of the surface of acrylic resin/stannic oxide, in which teflon is not dispersed, for water is 85°
  • the contact angle thereof when teflon is dispersed can be improved to be 95°.
  • the surface layer 16 formed on the photosensitive body 1 is made of resin in which conductive material and lubricating material are dispersed, uniform contact filling of electric charge can be performed.
  • the electric resistance of the surface layer itself, uniformity of dispersion of the conductive material and the lubricating material, transparency and strength of the surface layer have to be carefully controlled.
  • the electric resistance of the surface layer 16 is adjusted in a range from 1x10 9 ⁇ cm, under which the drift of electric charge causes a blurred image, to 1x10 14 ⁇ cm, which is the maximum resistance allowing filling of electric charge.
  • Transparency of the surface layer 16 is determined by the transparency and particle diameters of the conductive material and the lubricating material.
  • diameters are 0.3 ⁇ m or less, for light should not be scattered. Most preferably, the diameters are 0.1 ⁇ m or less.
  • the conductive material preferably used in the present embodiment is selected from conductive polymers such as poly(acetylene), poly(thiophene) and poly(pyrrole), and fine metal particles, and particles of metal oxides. In consideration of transparency, however, metal oxides and more preferable.
  • the conductive particles used in the present invention may also be selected from metals such as Cu, Al, Ni, and so on, zinc oxide, titanium oxide, antimony oxide, indium oxide, bismuth oxide, indium oxide in which stannum is doped, stannic oxide in which antimony is doped, zirconium oxide, and so on, all in the form of ultra fine particles.
  • metals such as Cu, Al, Ni, and so on, zinc oxide, titanium oxide, antimony oxide, indium oxide, bismuth oxide, indium oxide in which stannum is doped, stannic oxide in which antimony is doped, zirconium oxide, and so on, all in the form of ultra fine particles.
  • Each of these metal oxides may be used separately. Otherwise, two or more metal oxides may be combined, wherein they may be solid solution or be fused.
  • the amount of the conductive fine particles contained in the surface layer 16 is determined according to, for example, their diameter. Preferably, the amount is determined in a range from 10 to 70 wt%.
  • the lubricating material is selected from graphite, wax having long chain alkyl group(s), compounds containing fluorine or silicon, and so on. Especially, compounds containing fluorine or silicone are preferable lubricating materials.
  • Examples of the compounds containing fluorine include, in addition to the above-mentioned polytetrafluoroethylene, copolymers such as tetrafluoroethylene, hexafluoropropylene, trifluoroethylene, chlorotrifluoroethylene, vinylidene fluoride, vinyl fluoride perfluoro alkyl-vinyl ether, and copolymers thereof.
  • Other examples are carbon fluoride with fluorine atoms which has graphite structure, oils with fluorine atoms; and so on, wherein fluorine atoms are added by substitution.
  • inorganic fluorides may be used as the lubricating material.
  • Examples of the compounds containing silicone include monomethyl siloxane having third dimensional bridged structure, dimethylsiloxane-monomethyl-siloxane having third dimensional bridged structure, polydimethylsiloxane having a ultrahigh molecular weight, block polymers containing polydimethylsiloxane segments, graft polymers, surface active agents, macro monomer, polydimethylsiloxane with modified end groups, and so on.
  • the diameter of the lubricating material to be dispersed in the surface layer as particles is preferably 0.005 ⁇ m or more in order to exhibit sufficient lubricating effect, and preferably 0.3 ⁇ m or less in order to obtain a clear image without a blur and dimness.
  • the conductive material and the lubricating material are dispersed by a sand mill, a ball mill, a roller mill, a homogenizer, a nanomizer, a paint shaker, with ultrasonic wave, and so on.
  • auxiliary additives such as surface active agents, graft polymer, coupling agents may be added at the time of dispersion.
  • the surface layer 16 is subjected directly to the toner development, the cleaning operation, and other mechanical brushing operation.
  • the surface layer of this embodiment in which the conductive particles are dispersed is formed as a thin film (of 0.5 to 5.0 ⁇ m. Therefore, sufficient strength against scraping and damage is required.
  • the amount of the lubricating material contained in the surface layer should be 5 wt% or more.
  • the amount of the lubricating material is preferably 60 wt% or less.
  • Non-uniformity in dispersion of the conductive particles causes non-uniformity of electrification, which further causes non-uniformity in the obtained image. Accordingly, the conductive particles have to be dispersed uniformly in the resin. In order to realize uniform dispersion, it is very effective to add coupling agents or treat the surfaces of the conductive particles with the coupling agents.
  • the above-mentioned two characteristics, that is, the strength of the surface layer and the uniformity in dispersion of the conductive particles are considerably varied by the resin used for the surface layer.
  • the resin used for the surface layer of the present invention is selected from, in addition to the above-mentioned acrylic resin, polyester, polycarbonate, polyurethane, polystyrene, fluororesin, cellulose, vinyl chloride, epoxy resin, silicone resin, alkyl resin, vinyl chloride-vinyl acetate copolymer, and so on, all available on the market.
  • a surface layer prepared as described below exhibited remarkable improvement of the strength of the layer and the uniformity of the dispersion of the conductive particles. That is, the conductive particles were dispersed in acrylic monomer which has three or more acryloyl groups per molecule and is curable with light. This resin including the conductive particles was applied on the photosensitive layer and cured with light.
  • acrylic monomer which has two or more acryloyl groups per molecule and is curable with light is mixed with the above-mentioned polyester, polycarbonate, polyurethane, acrylic resin, epoxy resin, silicone resin, alkyd resin, vinyl chloride-vinyl acetate copolymer, and so on, sufficient strength of the layer as well as sufficient uniformity in dispersion of the conductive particles can be obtained.
  • the acrylic monomer curable with light serving as the binder in the present embodiment is selected, for example, from the ones shown bellow. However, any well known acrylic monomers curable with light can be used.
  • photo-initiator is added to the prepared mixture used to form the surface layer.
  • the amount of the photo-initiator to be added is 0.1 to 40 wt% of the weight of the acrylic monomer curable with light, preferably 0.5 to 20 wt%. Examples of typical photo-initiators includes those shown below.
  • the surface layer is formed on the photosensitive layers by the above-mentioned beam coating.
  • Other coating technique such as the spray coating technique may be employed.
  • the dip coating can also be used with properly selected solvent.
  • the thickness of the surface layer is determined in consideration of the electric resistance of the layer. Preferably, the thickness of the surface layer is from 0.1 to 10 ⁇ m, most preferably from 0.5 to 5 ⁇ m.
  • photosensitive layers well known layers may be formed, including those containing inorganic photosemiconductors such as Se, As 2 Se 3 a-Si, CdS, ZnO 2 , and so on, and those containing organic layers such as PVK-TNF, phtalocyanine pigment, azo pigment, and so on.
  • inorganic photosemiconductors such as Se, As 2 Se 3 a-Si, CdS, ZnO 2 , and so on
  • organic layers such as PVK-TNF, phtalocyanine pigment, azo pigment, and so on.
  • an intermediate layer may be provided between the photosensitive layers and the surface layers for protecting them.
  • Such an intermediate layer is provided in order to further bind the surface layer and the photosensitive layers, or to serve as a barrier layer for blocking electric charge.
  • the material for the intermediate layer may be selected from the resin materials, for example, resin, polyester resin, polyamide resin, polystyrene resin, acrylic resin, silicone resin, all available on the market.
  • the conductive substrate drum of the photosensitive body may be made of metal such as aluminum, nickel, stainless steel, steel, and so on, and plastic or glass provided with a conductive layer, and paper treated to exhibit conductivity, and so on.
  • the charged brush is employed as the contact charging member 2.
  • the charged brush 2 is a roller brush having an outer diameter of 14 mm, which comprises a metal core bar 2a having a diameter of 6 mm and tap 2b coiled spirally round the metal core bar 2a.
  • the tape 2b is pile fabric of conductive rayon fibre REC-B manufactured by Unichika Ltd. (300 denier/50 filaments, density of 155 filament per square millimeter).
  • the resistance of the brush is 1x10 5 ⁇ while being applied with voltage from 1 to 1000V (Resistance was calculated from the current measured when the brush was kept in contact with a metal drum having a diameter of 30 mm, with a nip having a width of 3 mm and a longitudinal width of 230 mm, and was applied with voltage).
  • the resistance of the charged brush should be 1x10 4 ⁇ or more.
  • the resistance is 1x10 7 ⁇ or less.
  • the material for the charged brush 2 may be selected from REC-B (manufactured by Unichika Ltd.), SA-7 (TORAY), Thunderon (NIHON SANMO CO., LTD.), Belltron (Kanebo Co., Ltd.), CLACARBO (Kuraray Co., Ltd.), rayon in which carbon is dispersed, ROVAL (MITSUBISHI RAYON CO., LTD.), and so on.
  • REC-B manufactured by Unichika Ltd.
  • SA-7 TORAY
  • Thunderon NIHON SANMO CO., LTD.
  • Belltron Kerbo Co., Ltd.
  • CLACARBO Kerray Co., Ltd.
  • rayon in which carbon is dispersed rayon in which carbon is dispersed
  • ROVAL MITSUBISHI RAYON CO., LTD.
  • the charged brush 2 is rotated so as to move in the direction opposite to the direction in which the surface of the photosensitive body 1 moves at the contact area. And the charged brush 2 is rotated at a rotating speed of 500 rpm (ratio of the circumferential speed is -414%, which is calculated as described later).
  • the charged brush 2 may be rotated at different rotating speed. Most preferable rotating speed varies according to the width of the charging nip formed between the charged brush 2 and the photosensitive body 1, the density of the bristles of the brush, the resistance of the layer to be filled with electric charge of the photosensitive body 1, the process speed (circumferential speed of the photosensitive drum), and other conditions.
  • the charged brush 2 may also be rotated so as to move in the same direction in which the surface of the photosensitive body 1 moves at the contact area. In this case, however, since the amount of electric charge given to the photosensitive body 1 increases as the absolute value of the ratio of the circumferential speed of the charged brush 2 to that of the photosensitive body 1 increases, the charged brush 2 has to be rotated at a higher rotating speed to obtain the same absolute value of the ratio of circumferential speeds. Thus, it is preferable to rotate the charged brush 2 and the photosensitive body 1 in the opposite directions at the contact area because the charged brush 2 can be rotated at a low rotating speed.
  • the "charged up" state is defined as a state in which the brush which has already given negative electric charge to the photosensitive body is further charged with positive electric charge accumulated at the tips of the bristles to have a different potential from that of the core bar of the charging brush.
  • Ratio(%) (Speed of Brush) - (Speed of Drum) Speed of Drum x 100 wherein the circumferential speed of the charged brush has a positive value when the brush is moved in the same direction of the surface of the photosensitive body at the contact area, and a negative value when moved in the opposite direction.
  • the contact charging member 2 having a medium resistance gives electric charge directly to the surface of the photosensitive body 1 having a medium resistance without electrical discharge. More specifically, in the present embodiment, electrification is performed by filling a trap potential of the material used for the surface of the photosensitive body with electric charge, or filling the conductive particles a in the surface layer 16 with electric charge.
  • Fig. 3 shows an equivalent circuit, which illustrates the principles of electrification employed by the present embodiment.
  • a small condenser is formed, wherein the electric charge carrying layer 15 of the photosensitive body 1 serves as a dielectric substance, and the substrate drum 11 and the conductive particles (SnO 2 ) a in the surface layer 16 (charge pour-in layer) as electrodes.
  • This condenser is charged by the contact charging member 2.
  • each conductive particle a is electrically independent of the others, and performs as a kind of small float electrode.
  • the surface of the photosensitive body is uniformity charged, but, in fact, the surface of the photosensitive body is covered with innumerable fine charged particles of SnO 2 .
  • the electrostatic latent image can be supported by the electrically independent SnO 2 particles after the image exposure operation L with laser beams.
  • Electrification can be executed when the resistance of the surface layer 16 is in a range from 1x10 9 to 1x10 14 ⁇ cm.
  • the resistance of the surface layer 16 is preferably in a range from 1x10 12 to 1x10 13 ⁇ cm.
  • the volume resistance is calculated from the measured current obtained as follows.
  • a prepared mixture to form the surface layer 16 is poured between two metal electrodes which are separated from each other at a distance of 200 ⁇ m.
  • the mixture is formed into a layer.
  • a voltage of 100V is applied between the electrodes.
  • Excellent characteristics of electrification can be obtained when the resistance of the surface of the body to be electrified is from 1x10 9 to 1x10 14 ⁇ cm and, at the same time, the contact angle of the surface of the body to be electrified is 90° or greater. As long as the above conditions are present, excellent characteristics of electrification can also be obtained by employing any surface layer having other construction.
  • the material for the surface of the photosensitive body 1 which serves as the body to be electrified
  • the material having small surface energy is employed to reduce the coefficient of friction.
  • the bristles of the charged brush 2 can come into uniform contact with the surface of the photosensitive body.
  • the torque required to rotate the charged brush 2 is reduced, non-uniform rotation can be prevented.
  • the present embodiment is characterized in that functional separation type OPC is used for the photosensitive body 1 serving as the body 1 to be electrified and that the photosensitive body 1 is coated with the surface layer 16 having small surface energy.
  • a photosensitive body coated with a surface layer 16 in which teflon particles b are not dispersed was used.
  • the surface energy of the acrylic resin serving as the binder of the surface layer 16 was great, and the coefficient of friction between the surface of the photosensitive body and the developer was also great.
  • non-uniformity of electrification occurs because the part of the surface of the photosensitive body 1 to be electrified which does not come into direct contact with the charged brush 2 serving as the contact charging member is not sufficiently charged while the other part sufficiently charged.
  • large torque to rotate the charged brush 2 causes non-uniform rotation, which causes non-uniformity in the charged surface of the photosensitive body 1 in the sub-scan direction in which the surface is moved.
  • This non-formity in the charged surface has a bad influence on the image to be formed.
  • abrasion of the tips of the bristles 2b of the charged brush 2 hinders uniform electrification of the photosensitive body 1.
  • the present embodiment whose photosensitive body 1 has the surface layer 16 in which the teflon particles b are dispersed, the surface energy of the surface of the photosensitive body 1 and the coefficient of friction could be reduced.
  • the tips of the bristles of the charged brush 2 could come into uniform contact with the surface of the photosensitive body 1, which realized uniform electrification of the photosensitive body 1.
  • the torque required to rotate the charged brush 2 was reduced, non-uniform rotation could be prevented to realize uniform electrification.
  • the tips of the bristles 2b of the charged brush 2 were free from abrasion and still could uniformly charge the surface of the photosensitive body 1.
  • the present invention could form an excellent image.
  • Table 5 shows the results of the experiments on relations between the amount of the teflon particles b dispersed in the surface layer 16 and the electrification characteristics: the contact angles of the surface of the photosensitive body 1 for water; uniformity of electrification; uniformity of electrification in the longitudinal direction; and ⁇ abrasion of the charged brush 2.
  • Amount of Dispersed Teflon (wt%) Contact Angle for Water Uniformity of Electrification Uniformity of Electrification in Longitudinal Direction Abrasion of Brush 0 85° ⁇ ⁇ ⁇ 17.6 88° ⁇ ⁇ ⁇ 26.3 90° ⁇ ⁇ ⁇ 30 92° ⁇ ⁇ ⁇ 39 95° ⁇ ⁇ ⁇ 46 100° ⁇ ⁇ ⁇ ⁇
  • Table 5 shows that if the contact angle for water is 90° or more excellent uniformity of electrification can be obtained even in the sub-scan direction, and that if 95° or more abrasion of the brush can be sufficiently reduced to obtain an excellent image as well as to prevent the charged brush 2 from making a flaw on the surface of the photosensitive body 1.
  • the material to form the surface layer of the photosensitive body has small surface energy. More specifically the outermost layer, the electric charge carrying layer 15 or the surface layer 16 described before, of the photosensitive body 1 is made of, as the binder, fluororesin having small surface energy.
  • the outermost layer of the photosensitive body was actually the electric charge carrying layer 15.
  • amorphous fluororesin SYTOP (trade mark of ASAHI GLASS CO., LTD.) which is transparent and can be coated was used.
  • hydrazone was dispersed.
  • photosensitive body exhibited a contact angle of 120.5° for water.
  • the same printer (Fig. 1) as the first and a charged brush REC-C manufactured by Unichika Ltd. were used with the above-mentioned photosensitive body to form images.
  • Excellent uniformity of electrification could be realized, and non-uniformity of electrification in the sub-scan direction caused by non-uniform rotation of the charged brush could be prevented.
  • Abrasion of the brush after long-term use could be sufficiently reduced, which further ensured excellent image formation.
  • the charged brush could be prevented from making a flaw on the surface of the photosensitive body.
  • a magnetic brush is used as the contact charging member.
  • the object of this embodiment is to reduce the surface energy of the surface of the photosensitive body as well as the coefficient of friction between the surface of the photosensitive body and the magnetic brush, and realize smooth movement of magnetic particles on the surface of the photosensitive body in the charging nip between the magnetic brush and the photosensitive body.
  • the magnetic particles can more often come into contact with the surface of the photosensitive body and charging performance is improved.
  • a conductive magnetic brush 200 serving as the contact charging member is positioned in contact with the photosensitive body 1.
  • the magnetic brush 200 comprises a non-magnetic rotary electrode sleeve 21 having a diameter of 16 mm, a fixed magnet roller 22 having a longitudinal dimension of 230 mm, and magnetic particles 23 attracted by the magnetic roller 22.
  • the electrode sleeve 21 is rotated as indicated by an arrow in Fig. 6 so that the electrode sleeve 21 and the surface of the photosensitive body 1 are moved in the opposite directions at the contact area, that is, in the nip.
  • the circumferential speed of the magnetic brush is 100 mm/sec.
  • the magnetic particles 23 are ferrite carrier (mean diameter 30 ⁇ m, maximum magnetization 60 Am 2 /kg, density 2.2 g/cm 3 , resistance 5x10 6 ⁇ cm).
  • the resistance is calculated from the measured current obtained when 2g of the carrier particles which are put in a metal cell having a base area of 228 mm 2 and which are subjected to a load of 6.6 kg/cm 2 is applied with a voltage of 100V.
  • the electrode sleeve 21 and the photosensitive body 1 are positioned with a distance of 500 ⁇ m in between. 10g of carrier particles 23 are applied on the electrode sleeve 21.
  • the carrier particles 23 form a nip having a width of ca. 2 mm between the electrode sleeve 21 and the photosensitive body 1. Since there is a difference between the circumferential speed of the magnetic brush 200 and that of the photosensitive body 1, carrier particles 23 accumulate with a width of ca. 3 mm on the upstream side, with respect to the direction of rotation of the sleeve 21, of the nip. That is, the entire charging nip has a width of ca. 5 mm.
  • An electric power source S1 for applying charging bias applies a DC charging bias voltage of -700V to the magnetic brush 200. And the outer peripheral surface of the rotating photosensitive body 1 is uniformly charged with about -700V.
  • the photosensitive body 1 of this embodiment is coated with the surface layer 16 in which the teflon particles b were dispersed could reduce its surface energy and the coefficient of friction of its surface. Accordingly, the magnetic particles 23 could smoothly roll and move over the surface of the photosensitive body. Thus chances for the magnetic particles 23 which were not yet charged up to come into contact with the photosensitive body 1 increased. Accordingly, poor charge could be prevented, and excellent images could be obtained. Since the magnetic particles 23 could move smoothly in the charging nip, uniformity in the nip as well as uniformity of electrification in the longitudinal direction of the sleeve could be improved. In addition, torque to rotate the magnetic brush was reduced, and the magnetic brush rotated uniformly.
  • laser scan exposure is executed to write image data on the photosensitive body 1
  • other technique can be used.
  • an LED head having LED element arrayed in the longitudinal direction of the image supporter may be positioned in front of the photosensitive body 1.
  • line recording may be executed, for example, with an optical system consisting of a liquid crystal shorter and a light source, wherein the light source is turned on/off corresponding to signals from a controller.
  • an insulative (or dielectric) body having a surface layer to which electric charge is given may be used as the image supporter.
  • a multi Stylus recording head is used to form the latent image on the charged image supporter.
  • the multi Stylus recording head has pin electrodes facing to the image supporter on the downstream side, with respect to the contact charging member, in the direction to which the image supporter is moved.
  • the pin electrodes are arrayed in the longitudinal direction of the image supporter. Instead of reverse development, normal development may be carried out.
  • a conductive charging roller made of conductive, solid or porous material having low hardness may be used.
  • a conductive charging roller consisting of a core bar and an EPDM sponge layer having a specific volume resistance of 1x10 5 ⁇ cm is used (ASKER C hardness 45°). This conductive charging roller is positioned in contact with the body to be electrified so as to form a nip having a width of 6 mm, applied with voltage, and rotated.
  • the image forming apparatus of this embodiment uses a photosensitive body for back surface exposure process which exhibits a contact angle of 90° or more for water.
  • a two-component developer is used, containing magnetic conductive carrier particles and magnetic insulative toner.
  • the magnetic conductive carrier particles contribute to cleaning of residual toner remaining after the transfer process, electrification of the surface of the photosensitive body, and conveyance of the toner.
  • Carrier particles brush the surface of the photosensitive body and scrape the toner which was not transferred onto the transfer medium at the time of the previous image forming process but remains on the surface of the photosensitive body (hereinafter such toner is referred as 'residual toner'). Simultaneously with this cleaning operation, the carrier particles give electric charge to the surface of the photosensitive body. But, if the developer does not smoothly move, it is packed, and stagnates in the nip between the developer sleeve and the photosensitive body. In this case, even if the developer sleeve is rotated faster, chances for the developer to come direct contact with the surface of the photosensitive body are not increased. As a result, poor cleaning performance and poor charge occur.
  • the present embodiment employs a material having small surface energy.
  • a material having small surface energy such as polypropylene is used for the surface of the photosensitive body and/or particles such as PTFE are dispersed in the surface of the photosensitive body, and so on.
  • a photosensitive body of functional separation type OPC coated with a surface layer having small surface energy is used. Similar effects of the present embodiment can be obtained as long as material having small surface energy is used for the surface of the photosensitive body for the back surface exposure process.
  • the contact angle of the material for water is used as the index of the surface energy of the material.
  • the surface layer is made of insulative resin in which conductive particles are dispersed.
  • the photosensitive layers serve as a dielectric body, while the conductive particles serve as fine float electrode, which forms a condenser. With conductive developer, this condenser is charged.
  • Fig. 7 schematically shows the elecrophotography apparatus, which comprises a photosensitive drum 1, an exposure device 4, a developer device 3, a transfer device 5, a fixing device (not shown), and so on.
  • the photosensitive body 1 is a transparent glass cylinder having a diameter of 30 mm, on which photosensitive layers are to be laminated.
  • a cylinder made of transparent resin having dimensional stability can be used.
  • a cylinder made of polycarbonate resin, PMMA resin, and the like, may be used.
  • an indium-tin oxide (ITO) layer of ca. 1 ⁇ m serving as a transparent conductive layer is formed by coating.
  • the OPC photosensitive body of functional separation type is prepared.
  • the exposure device 4 comprising an LED head and a Selfox lens array is positioned inside the photosensitive body to radiate light to a predetermined position in the charging nip from the back surface of the photosensitive body.
  • the developer unit (developer device) 3 comprises a rotating sleeve 3b having a diameter of 30 mm which is made of aluminum, stainless steel, and so on, and a fixed magnet 3a fixed in the sleeve 3b.
  • the sleeve 3b is rotated at a circumferential speed six times as high as that of the photosensitive body, wherein the sleeve 3b is moved in the same direction as the photosensitive body at this contact area.
  • the process speed (circumferential speed of the photosensitive drum) is 50 mm/sec. Therefore, the circumferential speed of the sleeve 3b is 300 mm/sec.
  • Eight magnetic poles are symmetrically arranged in the magnet roll 3a. Each magnetic pole has its peak position on the straight line between the center of the photosensitive drum and the center of the developer sleeve. When each peak position on the surface of the sleeve 3b has a magnetic flux density of 800 gauss.
  • the magnetic insulative toner employed is negative toner, with a particle diameter of 7 ⁇ m and an electric resistance of 1x10 14 ⁇ cm.
  • the carrier particles have a diameter of 25 ⁇ m and a resistance of 1x10 2 ⁇ cm.
  • the toner and the carrier particles are mixed at a T/D rate of 8 wt% (T; toner, D; total developer).
  • T toner, D; total developer
  • This mixture is put in the developer device 3, in which a metal blade 3b for regulating the thickness of the toner coat on the developer device is arranged to face to the developer sleeve 3b to make the thickness of the toner coat from the sleeve surface about 1 mm.
  • the developer sleeve 3b and the photosensitive drum 1 are supported by contact rollers (not shown) at their end portion, with a distance of 0.5 mm in between. With this construction, when the photosensitive drum and the developer sleeve are rotated at their predetermined speeds, the contact nip N between them has a width of 7 mm.
  • the photosensitive drum 1 is earthed, while the developer sleeve 3b is charged with a DC voltage of -100V. Thus, reverse development is carried out with the negative toner.
  • the swiftly rotating magnetic brush scrapes the residual toner remaining after the transfer process.
  • the conductive carrier particles come into contact with the surface of the photosensitive body to charge the photosensitive body.
  • the insulative toner forms a toner image on the photosensitive body according to the given electric field. Since the conductive carrier particles serve as closely arranged electrodes in this embodiment, a sufficient image density can be obtained even with a small voltage having an absolute value of about 100V.
  • the transfer roller 5 used is the present embodiment has a volume resistance of 5x10 8 ⁇ cm, and is applied with a bias voltage of +2KV.
  • the toner which is not transferred by the transfer device is sufficiently scraped off on the upstream side in the charging nip at the time of next image forming operation. Accordingly, the residual toner does not hinder the next image forming operation.
  • the transferred toner image is fixed by the thermal fixing roller, and the transfer medium having the printed image is discharged out of the apparatus.
  • the surface layer of the photosensitive body characterizing the present embodiment is formed as follows, 60 parts by weight of acrylic resin curable with light, 60 parts by weight of stannic oxide in which antimony is doped to obtain conductivity, 50 parts by weight of PTFE particles having the mean diameter of 0.18 ⁇ m, 2-methyl thioxanthone serving as a photo-initiator, and 400 parts by weight of methanol are used to prepare a dispersion mixture.
  • the photosensitive drum is coated with the prepared mixture by dip coating technique. And the mixture is cured to form the surface layer having a thickness of ca. 3 mm and a volume resistivity in the order of 10 13 ⁇ m.
  • the electric charge of the latent image can not drift in the peripheral directions, thus, a blurred image can be prevented. On the other hand, electric charge can move little in the direction of the thickness of the layer, which minimizes the potential remaining after the image exposure process.
  • teflon particles are dispersed in the binder, in this embodiment, since the surface energy of the teflon itself is very small, that is, about 0,02 N/cm (20 dyne/cm), surface energy of the photosensitive body can be remarkably reduced by dispersing teflon. While the surface of acrylic resin/stannic oxide in which teflon is not dispersed exhibits a contact angle of 85° for water, the contact angle of the surface in which teflon is dispersed can be improved to be 90°.
  • Images were formed by using the above-mentioned photosensitive drum.
  • a photosensitive body in which teflon particles were not dispersed was used.
  • the surface energy of the acrylic resin itself was great and the coefficient of friction between the surface of the photosensitive body and the developer was also great, the developer could not easily move over the surface of the photosensitive body, but was packed in the charging nip, and stagnated in it.
  • the surface energy of the photosensitive body was great, the residual toner after the transfer process strongly adhered to the photosensitive body, which reduced the cleaning performance in the charging nip and caused a ghost image.
  • teflon particles may be dispersed in the CT layer (electric charge carrying layer) of the photosensitive body.
  • the surface layer of the photosensitive body may be made of material having small surface energy.
  • amorphous transparent fluororesin CYTOP (ASAHI GLASS CO., LTD.) which can be formed by coating, and so on may be used.
  • lubricating agent is added to conductive carrier contained in the developer.
  • the carrier and the toner are mixed to perform electrification and development with one developer.
  • fluidity of the developer is reduced and the carrier for electrification can not smoothly move on the surface of the photosensitive body.
  • uniform electrification becomes difficult. This problem does not occur in electrification with carrier only.
  • the developer employed is a two-component developer containing magnetic conductive carrier and magnetic insulative tonner.
  • the magnetic conductive carrier contributes to cleaning of the residual toner after the transfer process, electrification of the surface of the photosensitive body, and conveyance of toner.
  • the carrier brushes the surface of the photosensitive body to scrape the toner (residual toner) which was not transferred onto the transfer medium at the time of the previous image forming operation but still remains on the surface of the photosensitive body. Simultaneously with this cleaning operation, the carrier gives electric charge to the surface of the photosensitive body.
  • the fluidity of the developer is not sufficient, however, the developer is packed, and stagnates in the nip between the developer sleeve and the photosensitive body. In this case, even if the developer sleeve is rotated faster, chances for the developer to come into direct contact with the surface of the photosensitive body can not be increased. As a result, cleaning performance is reduced and reliable electrification becomes difficult.
  • the carrier particles are coated with silicone resin having an adjusted resistance to improve fluidity of the developer itself. More specifically, 40 parts by weight of conductive stannic oxide fine particles (diameter 0.04 ⁇ m) are dispersed in silicone resin to prepare coating material. The carrier particles are coated with thus prepared coating material to have desired resistance (described latter).
  • the core of the carrier particle used in the present embodiment was 25 ⁇ m, and its resistance was 1x10 2 ⁇ cm, and its fluidity was indicated by a value of 50 s/50g.
  • the carrier particles were resin carrier particles made of phenol resin in which magnetite was dispersed and carbon black giving conductivity was also dispersed.
  • the fluidity is indicated by a value measured as follows. 50g of the particles were put in a funnel, and the time required for all the particles to fall from the funnel was measured according to JIS-Z2502. Hereinafter, the fluidity is indicated by the value measured in this way.
  • the core of the carrier prepared as described above was coated with silicone resin.
  • stannic oxide in which antimony was doped to obtain a desired resistance was dispersed.
  • the present embodiment used acrylic silicone resin KR9706 (trade mark of Shinetsu Silicone), in which 10 wt% of stannic oxide was dispersed to obtain a volume resistance of 1x10 4 ⁇ cm.
  • the surfaces of the carrier particles were coated with thus prepared coating resin by using SPIRA COTA (manufactured OKADA SEIKO CO., LTD.).
  • the formed coat had a film thickness of 0.3 ⁇ m.
  • the carrier particles exhibited a volume resistance of 2x10 2 ⁇ cm, and fluidity was improved to 30 sec/50g.
  • silicone resin was used as the coating material
  • lubricant resin such as poly olefin resin, fluororesin, and so on
  • the core of the carrier particles may contain lubricant resin, or PTFE particles.
  • the magnetic insulative toner contained in the developer was negative toner, with a particle diameter of 7 ⁇ m and an electric resistance of 1x10 14 ⁇ cm.
  • the toner and the carrier was mixed at a T/D rate of 8% (weight ratio of the toner to the total developer).
  • the conductive carrier particles in the developer had sufficient lubricity. Accordingly, the developer was not packed nor stopped in the nip. And fluidity was not reduced. In this case, the developer sleeve rotated at a faster circumferential speed than the photosensitive drum could smoothly push the developer over the surface of the photosensitive body. As a result, the residual toner which had not been transferred onto the transfer medium at the previous image forming operation could be quickly cleaned from the photosensitive body and could not hinder the charging process.
  • the carrier core was a magnetic conductive core made of phenol resin serving as the binder in which magnetite and carbon black were dispersed.
  • the fluidity was indicated by a value of 50 sec/50g, which is not sufficient.
  • the correlation between insufficient fluidity and stagnation of the developer partly depends on the type of the photosensitive body, the clearance between the developer sleeve and the photosensitive body, as well as the characteristics of the toner employed. But, since the T/D ratio of the developer used for the back surface exposure technique is in the order of several percent, the main factor which influences the fluidity of the developer is the fluidity of the carrier particles.
  • the developer can move more smoothly over the surface of the photosensitive body, which further improves uniformity of electrification.
  • the toner in the developer is given lubricity.
  • residual toner after the transfer process can be cleaned more easily, and the ghost images can be prevented.
  • electrification characteristics can be improved as in the first embodiment.
  • cleaning of the photosensitive body and electrification thereof are performed in the same charging nip according to the back surface exposure technique. Therefore, if the toner remaining after the transfer process of the previous image forming operation is not completely removed, this residual toner hinders electrification, which causes poor charge on part of the surface of the photosensitive body. Thus, ghost images occur.
  • the toner in the developer is given lubricity to be easily cleared from the photosensitive body.
  • the fluidity of the developer can be improved.
  • the fluidity of the developer mainly depends on the characteristics of the carrier. But, if toner having a smaller diameter than the carrier and excellent lubricity is added, the developer can move more smoothly in the charging nip, even when the amount of the added toner is small, that is, at T/D ratio in the order of several percent. More specifically, wax is contained in the toner particles to give lubricity.
  • the toner of the present invention consists of styrene acrylic resin serving as the binder containing 50 parts by weight of magnetite as the magnetic material, anti-static agent and wax.
  • the toner of the present invention which contained wax
  • the toner itself exhibited lubricity. Accordingly, when the magnetic brush brushed the surface of the photosensitive body in the charging nip, the toner covering the photosensitive body was easily stirred and lifted off. Accordingly, sufficient cleaning performance could be easily obtained. Since the toner had lubricity, the fluidity of the developer was so good that the developer did not stagnate in the charging nip. As a result, ghost images could be prevented.
  • lubricating liquid or resin such as silicone oil, polypropylene, teflon particles, and so on may be added in the toner. Otherwise, in order to improve the fluidity of the toner, the toner may be mixed with silica, preferably silica treated with oil, titanium oxide particles and so on.
  • wax is generally contained in the toner to improve fluidity of the toner, and lubricating fine particles are generally mixed with the toner to give lubricity to the toner.
  • the object of adding these substances to the toner is different from that of the present embodiment. That is, the object of adding these substances according to conventional art is mainly to improve conveyance of the toner at the time of the development process and development characteristics, and to prevent missing or void of the characters in a character image at the time of the transfer process.
  • the present embodiment is effective especially when applied to the apparatus of back surface exposure type which performs cleaning and electrification at the same time, wherein the lubricity and fluidity of the developer not only affect the cleaning performance but also electrification of the image supporter.
  • improvement of fluidity of the developer which is now proposed according to the present embodiment has different object, different mechanism and further different effects from those of the conventional electrophotography technique.
  • the present invention in the contact charging device in which there is a difference between the circumferential speed of the contact charging member and that of the body to be electrified, as well as in the image forming apparatus and the process cartridge which use such a contact charging device, desirable effects can be obtained. That is, the body to be electrified can be uniformly charged, the torque to rotate the contact charging member can be reduced, and abrasion and damage of the contact charging member and the body to be electrified can be prevented for long-term use. Further, in the image forming apparatus and the process cartridge using the contact charging device of the present invention, excellent images can be reliably obtained for a long time without disturbance in the obtained images caused by non-uniformity of electrification.
  • This invention relates to a charging system for charging a body to be electrified, comprising a body to be electrified, and a charging member which can be applied with voltage to brush the surface of said body to be electrified and charge it.
  • a charging member which can be applied with voltage to brush the surface of said body to be electrified and charge it.
  • the surface of the body to be electrified exhibits a contact angle of 90° or more for water.

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  • Chemical Kinetics & Catalysis (AREA)
  • Inorganic Chemistry (AREA)
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  • Electrophotography Using Other Than Carlson'S Method (AREA)
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Claims (24)

  1. Aufladevorrichtung zur Aufladung eines aufzuladenden Körpers mit
    einem aufzuladenden Körper (1) und
    einem Aufladeelement (2), an das Spannung angelegt werden kann und das dazu dient, mit der Oberfläche des erwähnten aufzuladenden Körpers in Gleitkontakt zu kommen und ihn aufzuladen,
    wobei die Oberfläche des aufzuladenden Körpers mit Wasser einen Randwinkel von 90° oder mehr bildet und die äußerste Schicht (16) des erwähnten aufzuladenden Körpers leitfähige Teilchen (a) und Gleitmittel (b) enthält.
  2. Aufladevorrichtung nach Anspruch 1, bei der die Bewegungsrichtung des erwähnten Aufladeelements der Bewegungsrichtung des aufzuladenden Körpers in dem Kontaktbereich zwischen ihnen entgegengesetzt ist.
  3. Aufladevorrichtung nach Anspruch 1, bei der das erwähnte Aufladeelement Borsten (2b) hat, die mit dem erwähnten aufzuladenden Körper in Kontakt kommen.
  4. Aufladevorrichtung nach Anspruch 1, bei der das erwähnte Aufladeelement eine Magnetbürste (200) ist, die magnetische Teilchen (23) hat, die mit dem erwähnten aufzuladenden Körper in Kontakt kommen.
  5. Aufladevorrichtung nach einem der Ansprüche 1 bis 4, bei der die Oberfläche des erwähnten aufzuladenden Körpers in einem Harz leitfähige Teilchen und ein Gleitmittel enthält.
  6. Aufladevorrichtung nach Anspruch 1 oder 5, bei der die erwähnten leitfähigen Teilchen aus Metalloxid bestehen.
  7. Aufladevorrichtung nach Anspruch 1, bei der das erwähnte Gleitmittel aus Fluorpolymer, Siliconpolymer, Fluoroligomer und Siliconoligomer ausgewählt ist.
  8. Aufladevorrichtung nach Anspruch 1, bei der das erwähnte Gleitmittel ein Polymer oder Copolymer von einem oder mehr als einem Material ist, das aus Tetrafluorethylen, Hexafluorpropylen, Trifluorethylen, Chlortrifluorethylen, Vinylidenfluorid, Vinylfluorid und Perfluoralkylvinylether ausgewählt ist.
  9. Aufladevorrichtung nach Anspruch 1, bei der der erwähnte aufzuladende Körper eine Oberflächenschicht (16) hat, die in ihrer Gesamtmasse 5 bis 60 Masse% Gleitmittel enthält.
  10. Aufladevorrichtung nach einem der Ansprüche 1 bis 9, bei der das erwähnte Gleitmittel aus Teilchen mit einem mittleren Durchmesser von 0,005 bis 0,3 µm besteht.
  11. Aufladevorrichtung nach Anspruch 1, bei der der erwähnte aufzuladende Körper eine Oberflächenschicht (16) mit einem spezifischen Widerstand von 1 × 109 bis 1 × 1014 Ω·cm hat.
  12. Aufladevorrichtung nach einem der Ansprüche 1 bis 4, 6 bis 9 und 11, bei der der erwähnte aufzuladende Körper ein elektrophotographischer lichtempfindlicher Körper ist.
  13. Elektrophotographisches Gerät mit
    einem lichtempfindlichen Körper (1), der lichtempfindliche Schichten (12; 13; 14; 15; 16) und ein Substrat (11) umfaßt, das die lichtempfindlichen Schichten trägt und lichtdurchlässig ist; und
    einem Magnetbürstenelement (2), das in Kontakt mit dem lichtempfindlichen Körper angeordnet ist, an das Spannung angelegt werden kann und das dazu dient, den lichtempfindlichen Körper aufzuladen und eine Entwicklung durchzuführen,
    wobei das Magnetbürstenelement einen magnetischen leitfähigen Tonerträger und einen Toner hat und ein Teil der Rückseite des lichtempfindlichen Körpers, der dem Kontaktbereich mit dem Magnetbürstenelement entspricht, belichtet wird und die Fließfähigkeit des Tonerträgers mindestens einen Wert von 45 s/50 g gemäß JIS Z 2502 oder niedriger hat und wobei die Oberfläche des erwähnten lichtempfindlichen Körpers leitfähige Teilchen und Gleitmittel enthält.
  14. Elektrophotographisches Gerät nach Anspruch 13, bei dem die Oberfläche des erwähnten lichtempfindlichen Körpers mit Wasser einen Randwinkel von 90° oder mehr bildet.
  15. Elektrophotographisches Gerät nach Anspruch 13 oder 14, bei dem der erwähnte Tonerträger in Form von Teilchen vorhanden ist, die aus magnetischen Kernen und einem Umhüllungsmaterial, das die Oberflächen der magnetischen Kerne bedeckt, bestehen.
  16. Elektrophotographisches Gerät nach Anspruch 13 oder 14, bei dem der erwähnte Toner ein isolierender Toner ist, der Wachs enthält.
  17. Elektrophotographisches Gerät nach Anspruch 13 oder 14, bei dem der erwähnte Toner ein isolierender Toner ist, mit dem feine Gleitmittelteilchen vermischt sind.
  18. Elektrophotographisches Gerät nach Anspruch 13, bei dem die Oberfläche des erwähnten lichtempfindlichen Körpers in einem Harz leitfähige Teilchen und ein Gleitmittel enthält.
  19. Elektrophotographisches Gerät nach Anspruch 18, bei dem die erwähnten leitfähigen Teilchen aus Metalloxid bestehen.
  20. Elektrophotographisches Gerät nach Anspruch 13, bei dem das erwähnte Gleitmittel Fluorpolymer, Siliconpolymer, Fluoroligomer oder Siliconoligomer ist.
  21. Elektrophotographisches Gerät nach Anspruch 13, bei dem das erwähnte Gleitmittel ein Polymer oder Copolymer ist, das ein oder mehr als ein Material enthält, das aus Tetrafluorethylen, Hexafluorpropylen, Trifluorethylen, Chlortrifluorethylen, Vinylidenfluorid, Vinylfluorid und Perfluoralkylvinylether ausgewählt ist.
  22. Elektrophotographisches Gerät nach Anspruch 13, bei dem der erwähnte lichtempfindliche Körper eine Oberflächenschicht (16) hat, die in ihrer Gesamtmasse 5 bis 60 Masse% Gleitmittel enthält.
  23. Elektrophotographisches Gerät nach Anspruch 13 oder 22, bei dem das erwähnte Gleitmittel aus Teilchen mit einem mittleren Durchmesser von 0,005 bis 0,3 µm besteht.
  24. Elektrophotographisches Gerät nach Anspruch 13, bei dem der erwähnte lichtempfindliche Körper eine Oberflächenschicht (16) mit einem spezifischen Widerstand von 1 × 109 bis 1 × 1014 Ω·cm hat.
EP19940120222 1993-12-20 1994-12-20 Ladesystem und elektrophotographischer Apparat Expired - Lifetime EP0660199B1 (de)

Applications Claiming Priority (8)

Application Number Priority Date Filing Date Title
JP319994/93 1993-12-20
JP31999493 1993-12-20
JP129706/94 1994-05-19
JP12970694 1994-05-19
JP14020794 1994-06-22
JP140207/94 1994-06-22
JP310548/94 1994-12-14
JP06310548A JP3093594B2 (ja) 1993-12-20 1994-12-14 帯電装置及び電子写真装置

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EP0660199A1 EP0660199A1 (de) 1995-06-28
EP0660199B1 true EP0660199B1 (de) 1999-04-07

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JP (1) JP3093594B2 (de)
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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0712048B1 (de) * 1994-11-08 2007-02-21 Canon Kabushiki Kaisha Bilderzeugungsverfahren und -gerät
DE69523119T2 (de) * 1994-11-28 2002-04-18 Canon Kk Bilderzeugungsverfahren
EP0735435B1 (de) * 1995-03-27 2003-08-20 Canon Kabushiki Kaisha Aufladungsvorrichtung
JP3352292B2 (ja) * 1995-08-21 2002-12-03 キヤノン株式会社 画像形成装置
DE69622829T2 (de) * 1995-12-18 2003-04-10 Canon Kk Ladegerät und elektrofotografisches Gerät
DE69721607T2 (de) * 1996-02-20 2004-03-18 Canon K.K. Bildherstellungsverfahren
JP3907303B2 (ja) * 1997-03-11 2007-04-18 キヤノン株式会社 静電荷像現像用トナー及び画像形成方法
JP4092223B2 (ja) * 2003-02-25 2008-05-28 株式会社リコー 現像装置及び画像形成装置
JP2006084543A (ja) * 2004-09-14 2006-03-30 Ricoh Co Ltd 画像形成装置およびプロセスカートリッジ
JP5076668B2 (ja) * 2007-06-19 2012-11-21 コニカミノルタビジネステクノロジーズ株式会社 電子写真用帯電ブラシおよび画像形成装置

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Publication number Priority date Publication date Assignee Title
US4649094A (en) * 1981-12-08 1987-03-10 Canon Kabushiki Kaisha Image formation method and apparatus in which imaging light and conductive toner are applied to opposite surfaces of a photosensitive member
JPS6022145A (ja) * 1983-07-18 1985-02-04 Canon Inc 画像形成法
JPS61148468A (ja) * 1984-12-24 1986-07-07 Oki Electric Ind Co Ltd 電子写真装置
JPH0285863A (ja) * 1988-09-22 1990-03-27 Canon Inc 電子写真感光体
JP3010303B2 (ja) * 1990-08-29 2000-02-21 キヤノン株式会社 静電荷像現像用トナー及びその定着方法
JPH04142566A (ja) * 1990-10-03 1992-05-15 Konica Corp 帯電及びクリーニング装置
JPH05257315A (ja) * 1992-03-10 1993-10-08 Canon Inc 電子写真感光体、該電子写真感光体を備えた電子写真装置並びにファクシミリ

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EP0660199A1 (de) 1995-06-28
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DE69417705T2 (de) 1999-10-28
JP3093594B2 (ja) 2000-10-03
DE69417705D1 (de) 1999-05-12

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