JP5353144B2 - Developing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To securely prevent occurrence of image memory in the case of adopting a hybrid development. <P>SOLUTION: The developing device 34 that visualizes an electrostatic latent image on an electrostatic latent image carrier 12 by use of developer containing toner and carrier is equipped with: a developer carrier 54 that bears developer; a toner carrier 48 that is disposed opposite the developer carrier 54 via a supply recovery area 88 and also facing the electrostatic latent image carrier 12 via a development area 96 and that bears toner, which is supplied from the developer carrier 54, in the supply recovery area 88; and an electric field generating means 110 that generates a first alternating electric field between the developer carrier 54 and toner carrier 48 in order to supply and recover toner therebetween, and that also generates a second alternating electric field between the toner carrier 48 and the electrostatic latent image carrier 12 in order to transfer toner from the toner carrier 48 to the electrostatic latent image carrier 12. The frequency of the first alternating electric field is made larger than that of the second alternating electric field. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to an electrophotographic image forming apparatus and a developing device used in the image forming apparatus.

  With respect to an electrophotographic image forming apparatus, a technique that employs a development system called hybrid development has been proposed (see Patent Document 1). An image forming apparatus that employs hybrid development includes a developing device that includes a developer carrier (magnetic roller) and a toner carrier (developing roller). A two-component developer containing a non-magnetic toner and a magnetic carrier is held on the outer peripheral surface of the developer carrier, and only the toner is selectively selected from the developer held on the developer carrier. The toner held on the outer peripheral surface of the toner carrier is used for the development (development) of the electrostatic latent image on the electrostatic latent image carrier.

  In the hybrid development, the developer held on the outer peripheral surface of the developer carrier is arranged along the magnetic lines formed around the developer carrier. The developer disposed around the developer carrying member in such a state is called a magnetic brush. In the proximity area (supply / recovery area) between the developer carrier and the toner carrier, the tip of the magnetic brush contacts the outer peripheral surface of the toner carrier, and only the toner of the developer constituting the magnetic brush is the developer carrier. It moves to the outer peripheral surface of the toner carrier by an electric field formed between the toner carrier and the toner carrier. Part of the toner held on the outer peripheral surface of the toner carrier is formed by an electric field formed between the toner carrier and the electrostatic latent image carrier in a proximity region (development region) with the electrostatic latent image carrier. To move to the electrostatic latent image portion of the electrostatic latent image carrier. When the remaining toner on the toner carrier is conveyed to the supply and recovery region by the rotation of the toner carrier, it is mechanically scraped by the tip of the magnetic brush and removed from the outer peripheral surface of the toner carrier.

  A bias including an AC component is applied to the developer carrier and the toner carrier. As a result, a supply / recovery electric field is formed between the developer carrier and the toner carrier, and a development electric field is formed between the toner carrier and the electrostatic latent image carrier. In the supply / recovery electric field, the potential difference on the supply side for supplying the toner on the developer carrier to the toner carrier and the potential difference on the recovery side for recovering the toner on the toner carrier to the developer carrier are alternately repeated. It is an alternating electric field. On the other hand, the developing electric field includes a potential difference on the developing side that moves the toner on the toner carrying member to the electrostatic latent image carrying portion on the electrostatic latent image carrying member, and an electrostatic latent image forming portion on the electrostatic latent image carrying member. AC electric field formed by alternately repeating the potential difference on the collecting side where the toner is collected from the toner to the toner carrier. The frequency of the developing electric field is set to a magnitude that does not exceed the frequency that adversely affects development, and the frequency of the supply and recovery electric field is the same as the frequency of the developing electric field (see, for example, Patent Document 2 and Patent Document 3).

  Hybrid development has advantages such as low stress on the toner, high quality images, and low toner scattering. However, the hybrid development has a problem that a phenomenon called an image memory is likely to occur. The image memory is a phenomenon in which an image (inverted image) in which the density of a printed image is inverted appears in the immediately subsequent image area. For example, when an image memory of a print image in which a blank page portion and a solid portion are mixed occurs in an entire halftone density image region (halftone image region), the density of the halftone image region is a solid portion. The portion that was a white paper portion is higher than the portion.

The reason why image memory is generated when hybrid development is used is that the toner on the toner carrier cannot be sufficiently collected by the magnetic brush on the developer carrier, and the variation in the amount of toner adhesion on the toner carrier is eliminated. It is thought that it cannot be done.
JP 2006-308687 A JP-A-2005-242281 JP 2003-15380 A

  In the hybrid development system, in order to improve the toner collecting performance from the toner carrier, it is conceivable to provide a collecting member for collecting the toner on the toner carrier separately from the developer carrier. However, if a collecting member is provided separately from the developer carrier, the number of parts increases, resulting in a problem that leads to an increase in the size of the apparatus.

  Accordingly, an object of the present invention is to reliably prevent an image memory without increasing the number of parts when adopting hybrid development.

In order to solve the above problems, a developing device according to one aspect of the present invention provides:
A developing device that visualizes an electrostatic latent image on an electrostatic latent image carrier using a developer containing a non-magnetic toner and a magnetic carrier,
A developer carrying member carrying the developer;
A toner that is disposed so as to face the developer carrier through the supply / recovery area and to face the electrostatic latent image carrier through the development area, and is supplied from the developer carrier in the supply / recovery area A toner carrier for carrying
Forming a first AC electric field for supplying and collecting toner between the developer carrier and the toner carrier between the developer carrier and the toner carrier; An electric field forming means for forming a second AC electric field for moving the toner from the toner carrier to the electrostatic latent image carrier between the electrostatic latent image carrier and the electrostatic latent image carrier,
Frequency of the first alternating electric field is much larger than the frequency of the second alternating electric field,
The first AC electric field is composed of a potential difference between a supply bias applied to the developer carrier and a development bias applied to the toner carrier,
The development bias is an alternating voltage having a period of a high voltage period in which the development bias is higher than a predetermined voltage and a low voltage period in which the development bias is lower than the predetermined voltage.
The supply bias is applied to the developer carrier during the high voltage period and is applied to the developer carrier during the low voltage period and a first AC voltage having a shorter period than the high voltage period. A voltage obtained by alternately repeating a second AC voltage having a shorter period than the low voltage period,
The high voltage period is an integral multiple of the period of the first AC voltage;
The low voltage period is an integral multiple of the period of the second AC voltage .
Further, a developing device according to another aspect of the present invention includes:
A developing device that visualizes an electrostatic latent image on an electrostatic latent image carrier using a developer containing a non-magnetic toner and a magnetic carrier,
A developer carrying member carrying the developer;
A toner that is disposed so as to face the developer carrier through the supply / recovery area and to face the electrostatic latent image carrier through the development area, and is supplied from the developer carrier in the supply / recovery area A toner carrier for carrying
Forming a first AC electric field for supplying and collecting toner between the developer carrier and the toner carrier between the developer carrier and the toner carrier; An electric field forming means for forming a second AC electric field for moving the toner from the toner carrier to the electrostatic latent image carrier between the electrostatic latent image carrier and the electrostatic latent image carrier,
The frequency of the first alternating electric field is greater than the frequency of the second alternating electric field;
The first AC electric field is composed of a potential difference between a supply bias applied to the developer carrier and a development bias applied to the toner carrier,
The development bias is an alternating voltage having a period of a high voltage period in which the development bias is higher than a predetermined voltage and a low voltage period in which the development bias is lower than the predetermined voltage.
The supply bias is applied to the developer carrier during the high voltage period and is applied to the developer carrier during the low voltage period and a first AC voltage having a shorter period than the high voltage period. A voltage obtained by alternately repeating a second AC voltage having a shorter period than the low voltage period,
The first AC voltage and the second AC voltage are voltages obtained by superimposing another bias component on the development bias,
The first AC voltage and / or the second AC voltage has a pause period in which the bias component pauses at the end or / and start of the high voltage period or the low voltage period.
It is characterized by that.

  An image forming apparatus according to the present invention includes the above-described developing device.

  According to the present invention, the frequency of the first AC electric field formed between the developer carrier and the toner carrier is the second frequency formed between the toner carrier and the electrostatic latent image carrier. Since the frequency is higher than the frequency of the AC electric field, the frequency of the first AC electric field can be sufficiently increased as compared with the conventional case where the frequency of the first AC electric field is equal to the frequency of the second AC electric field. . Therefore, by setting the frequency of the second AC electric field to the same level as that of the prior art, it is possible to avoid adverse effects on development, and by setting the frequency of the first AC electric field sufficiently high. The toner can be actively supplied and recovered between the developer carrying member and the toner carrying member. Accordingly, sufficient toner supply and recovery can make the toner adhesion amount uniform on the outer peripheral surface of the toner carrier, thereby reliably preventing the occurrence of image memory without increasing the number of parts. be able to.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the accompanying drawings. In the following description, terms indicating a specific direction (for example, “up”, “down”, “left”, “right”, and other terms including them, “clockwise direction”, “counterclockwise” ”) Is used to facilitate understanding of the invention with reference to the drawings, and the present invention should not be construed as being limited by the meaning of these terms. Further, in the image forming apparatus and the developing apparatus described below, the same reference numerals are used for the same or similar components.

[1. Image forming apparatus]
FIG. 1 shows a portion related to image formation of an electrophotographic image forming apparatus according to the present invention. The image forming apparatus may be any of a copier, a printer, a facsimile machine, and a multi-function machine having a combination of these functions. The image forming apparatus 1 includes a photoreceptor 12 that is an electrostatic latent image carrier. In the embodiment, the photoconductor 12 is formed of a cylindrical body, but the present invention is not limited to such a form, and an endless belt type photoconductor can be used instead. The photoreceptor 12 is drivingly connected to a motor (not shown), and is rotated in the direction of arrow 14 based on the driving of the motor. Around the photoconductor 12, a charging station 16, an exposure station 18, a developing station 20, a transfer station 22, and a cleaning station 24 are arranged along the rotation direction of the photoconductor 12.

  The charging station 16 includes a charging device 26 that charges a photosensitive layer, which is the outer peripheral surface of the photosensitive member 12, to a predetermined potential. In the embodiment, the charging device 26 is represented as a cylindrical roller. However, instead of this, other types of charging devices (for example, a rotary or fixed brush-type charging device or a wire-discharge-type charging device) may be used. Can be used. In the exposure station 18, the image light 30 emitted from the exposure device 28 disposed in the vicinity of the photosensitive member 12 or away from the photosensitive member 12 travels toward the outer peripheral surface of the charged photosensitive member 12. A passage 32 is provided. On the outer peripheral surface of the photoconductor 12 that has passed through the exposure station 18, an electrostatic latent image is formed that includes a portion where the image light is projected and the potential is attenuated and a portion where the charged potential is substantially maintained. In the embodiment, the portion where the potential is attenuated is the electrostatic latent image portion, and the portion where the charged potential is substantially maintained is the electrostatic latent image non-image portion. The developing station 20 includes a developing device 34 that visualizes the electrostatic latent image using a powder developer. Details of the developing device 34 will be described later. The transfer station 22 includes a transfer device 36 that transfers a visible image formed on the outer peripheral surface of the photoreceptor 12 to a sheet 38 such as paper or film. In the embodiment, the transfer device 36 is represented as a cylindrical roller, but other types of transfer devices (for example, wire discharge transfer devices) can also be used. The cleaning station 24 includes a cleaning device 40 that collects untransferred toner remaining on the outer peripheral surface of the photoconductor 12 without being transferred to the sheet 38 at the transfer station 22 from the outer peripheral surface of the photoconductor 12. In the embodiment, the cleaning device 40 is shown as a plate-like blade, but other types of cleaning devices (for example, a rotary type or a fixed type brush type cleaning device) may be used instead.

  When the image forming apparatus 1 having such a configuration forms an image, the photoconductor 12 rotates clockwise based on the driving of a motor (not shown). At this time, the outer peripheral portion of the photoreceptor passing through the charging station 16 is charged to a predetermined potential by the charging device 26. The charged outer periphery of the photoconductor is exposed to image light 30 at an exposure station 18 to form an electrostatic latent image. The electrostatic latent image is conveyed to the developing station 20 along with the rotation of the photosensitive member 12, where it is visualized as a developer image by the developing device 34. The visualized developer image is conveyed to the transfer station 22 along with the rotation of the photosensitive member 12, and is transferred to the sheet 38 by the transfer device 36 there. The sheet 38 to which the developer image has been transferred is conveyed to a fixing station (not shown), where the developer image is fixed to the sheet 38. The outer peripheral portion of the photosensitive member that has passed through the transfer station 22 is conveyed to the cleaning station 24 where the developer remaining on the outer peripheral surface of the photosensitive member 12 without being transferred to the sheet 38 is recovered.

[2. Development device]
The developing device 34 includes a housing 42 that houses a two-component developer including non-magnetic toner as first component particles and a magnetic carrier as second component particles, and various members described below. In order to facilitate understanding of the invention by simplifying the drawings, a part of the housing 42 is omitted. The housing 42 includes an opening 44 that is open toward the photosensitive member 12, and a developing roller 48 that is a toner carrier is provided in a space 46 formed in the vicinity of the opening 44. The developing roller 48 is a cylindrical member, and is disposed in parallel to the photosensitive member 12 and rotatably via the outer peripheral surface of the photosensitive member 12 and a predetermined developing gap 50.

  A separate space 52 is formed behind the developing roller 48. In the space 52, a conveyance roller 54 as a developer carrying member is disposed in parallel with the developing roller 48 and through an outer peripheral surface of the developing roller 48 and a predetermined supply / recovery gap 56. The conveyance roller 54 includes a magnet body 58 and a cylindrical sleeve 60 that is rotatably supported around the magnet body 58. Above the sleeve 60, a restricting plate 62 fixed to the housing 42 and extending in parallel with the central axis of the sleeve 60 is disposed so as to oppose a predetermined restricting gap 64.

  The magnet body 58 has a plurality of magnetic poles facing the inner surface of the sleeve 60 and extending in the central axis direction of the transport roller 54. In the embodiment, the plurality of magnetic poles are opposed to the magnetic pole S <b> 1 facing the upper inner peripheral surface portion of the transport roller 54 near the regulating plate 62 and the left inner peripheral surface portion of the transport roller 54 near the supply and recovery gap 56. Magnetic pole N1, magnetic pole S2 facing the lower inner peripheral surface portion of the transport roller 54, and two adjacent magnetic poles N2, N3 of the same polarity facing the right inner peripheral surface portion of the transport roller 54.

  A developer stirring chamber 66 is formed behind the transport roller 54. The stirring chamber 66 includes a front chamber 68 formed in the vicinity of the transport roller 54 and a rear chamber 70 separated from the transport roller 54. A front screw 72 that is a pre-stirring and conveying member that conveys the developer while stirring the developer from the front surface to the back surface of the drawing is rotatably disposed in the front chamber 68, and the rear chamber 70 is rotated from the back surface to the front surface of the drawing. A rear screw 74 that is a rear stirring member transporting member that transports the developer while stirring is disposed rotatably. As shown in the figure, the front chamber 68 and the rear chamber 70 may be separated by a partition wall 76 provided therebetween. In this case, the partition portions near both ends of the front chamber 68 and the rear chamber 70 are removed to form a communication passage, and the developer that has reached the downstream end of the front chamber 68 passes through the communication passage. The developer that has been fed to 70 and reaches the downstream end of the rear chamber 70 is fed to the front chamber 68 via a communication passage.

  The operation of the developing device 34 configured as described above will be described. During image formation, the developing roller 48 and the sleeve 60 rotate in the directions of arrows 78 and 80, respectively, based on driving of a motor (not shown). The front screw 72 rotates in the direction of arrow 82 and the rear screw 74 rotates in the direction of arrow 84. Thereby, the developer 2 accommodated in the developer stirring chamber 66 is stirred while being circulated and conveyed through the front chamber 68 and the rear chamber 70. As a result, the toner and the carrier contained in the developer come into frictional contact with each other and are charged with opposite polarities. In the embodiment, it is assumed that the carrier is positively charged and the toner is negatively charged. Since the carrier is considerably larger than the toner, the negatively charged toner adheres around the positively charged carrier mainly based on the electrical attraction force of both.

  The charged developer 2 is supplied to the transport roller 54 while being transported through the front chamber 68 by the front screw 72. The developer 2 supplied from the front screw 72 to the conveyance roller 54 is held on the outer peripheral surface of the sleeve 60 by the magnetic force of the magnetic pole N3 in the vicinity of the magnetic pole N3. The developer 2 held by the sleeve 60 constitutes a magnetic brush along the magnetic field lines formed by the magnet body 58, and is conveyed in the counterclockwise direction based on the rotation of the sleeve 60. The amount of developer 2 held by the magnetic pole S <b> 1 in the area facing the restriction plate 62 (restriction area 86) is regulated by the restriction plate 62 to a predetermined amount. The developer 2 that has passed through the regulation gap 64 is conveyed to a region (supply / recovery region) 88 where the developing roller 48 and the conveying roller 54 are opposed to each other, where the magnetic pole N1 is opposed. As will be described in detail later, in the supply / recovery region 88, an upstream region (supply region) 90 mainly in the rotation direction of the sleeve 60, the presence of an electric field formed between the developing roller 48 and the sleeve 60. As a result, the toner adhering to the carrier is electrically supplied to the developing roller 48. Further, in the supply / recovery area 88, a region (collection area) 92 on the downstream side mainly in the rotation direction of the sleeve 60, as will be described later, the development sent back to the supply / recovery area 88 without contributing to the development. The toner on the roller 48 is scraped off by a magnetic brush formed along the magnetic field lines of the magnetic pole N1 and collected in the sleeve 60. The carrier is held on the outer peripheral surface of the sleeve 60 by the magnetic force of the magnet body 58 and does not move from the sleeve 60 to the developing roller 48. When the developer 2 that has passed through the supply / recovery region 88 is held by the magnetic force of the magnet body 58 and passes through the opposing portion of the magnetic pole S2 along with the rotation of the sleeve 60, the developer 2 reaches the opposing region (discharge region 94) of the magnetic poles N2 and N3. The repulsive magnetic field formed by the magnetic poles N2 and N3 is discharged from the outer peripheral surface of the sleeve 60 to the front chamber 68 and mixed with the developer 2 being conveyed through the front chamber 68.

The toner held on the developing roller 48 in the supply area 90 is conveyed counterclockwise with the rotation of the developing roller 48, and is an area (developing area) 96 where the photoconductor 12 and the developing roller 48 face each other. It adheres to the electrostatic latent image portion formed on the outer peripheral surface. In the image forming apparatus according to the embodiment, a predetermined negative potential V _H is applied to the outer peripheral surface of the photoreceptor 12 by the charging device 26, and the electrostatic latent image image portion on which the image light 30 is projected by the exposure device 28 is predetermined. attenuated until the potential V _L, an electrostatic latent image non-image portion of the image light 30 is not projected by the exposing device 28 maintains a substantially charge potential V _H. Accordingly, in the developing region 96, the negatively charged toner adheres to the electrostatic latent image portion due to the action of the electric field formed between the photosensitive member 12 and the developing roller 48, and this electrostatic latent image is displayed. The image is visualized as a developer image.

  When the toner is consumed from the developer 2 in this way, it is preferable that the developer 2 is supplied with an amount of toner commensurate with the consumed amount. For this purpose, the developing device 34 includes means for measuring the mixing ratio of the toner and the carrier accommodated in the housing 42. In addition, a toner replenishment section 98 is provided above the rear chamber 70. The toner supply unit 98 includes a container 100 for storing toner. An opening 102 is formed at the bottom of the container 100, and a supply roller 104 is disposed in the opening 102. The replenishing roller 104 is drivingly connected to a motor (not shown), and the motor is driven based on the output of the means for measuring the mixing ratio of toner and carrier so that the toner drops and replenishes the rear chamber 70.

[3. Developer Material]
Specific materials of other particles contained in the toner, carrier, and developer will be described.

〔toner〕
As the toner, a known toner that has been conventionally used in an image forming apparatus can be used. The toner particle size is, for example, about 3 to 15 μm. A toner containing a colorant in a binder resin, a toner containing a charge control agent or a release agent, and a toner holding an additive on the surface can also be used.

  The toner can be produced by a known method such as a pulverization method, an emulsion polymerization method, or a suspension polymerization method.

[Binder resin]
The binder resin used for the toner is not limited. For example, styrene resin (monopolymer or copolymer containing styrene or styrene-substituted product), polyester resin, epoxy resin, vinyl chloride resin, phenol resin. , Polyethylene resin, polypropylene resin, polyurethane resin, silicone resin, or any mixture of these resins. The binder resin preferably has a softening temperature in the range of about 80 to 160 ° C and a glass transition point in the range of about 50 to 75 ° C.

[Colorant]
For the colorant, a known material such as carbon black, aniline black, activated carbon, magnetite, benzine yellow, permanent yellow, naphthol yellow, phthalocyanine blue, first sky blue, ultramarine blue, rose bengal, lake red, etc. should be used. Can do. In general, the addition amount of the colorant is preferably 2 to 20 parts by weight with respect to 100 parts by weight of the binder resin.

[Charge control agent]
As the charge control agent, materials conventionally known as charge control agents can be used. Specifically, for the positively charged toner, for example, nigrosine dyes, quaternary ammonium salt compounds, triphenylmethane compounds, imidazole compounds, and polyamine resins can be used as charge control agents. For the negatively charged toner, metal-containing azo dyes such as Cr, Co, Al, and Fe, salicylic acid metal compounds, alkyl salicylic acid metal compounds, and curixarene compounds can be used as charge control agents. The charge control agent is preferably used at a ratio of 0.1 to 10 parts by weight with respect to 100 parts by weight of the binder resin.

  As the release agent, a known release agent conventionally used as a release agent can be used. As the material for the release agent, for example, polyethylene, polypropylene, carnauba wax, sazol wax, or a mixture of them as appropriate is used. The release agent is preferably used at a ratio of 0.1 to 10 parts by weight with respect to 100 parts by weight of the binder resin.

[Other additives]
In addition, a fluidizing agent that promotes fluidization of the developer may be added. As the fluidizing agent, for example, inorganic fine particles such as silica, titanium oxide, and aluminum oxide, and resin fine particles such as acrylic resin, styrene resin, silicone resin, and fluorine resin can be used. In particular, it is preferable to use a material hydrophobized with a silane coupling agent, a titanium coupling agent, silicone oil, or the like. The fluidizing agent is preferably added at a ratio of 0.1 to 5 parts by weight with respect to 100 parts by weight of the toner. The number average primary particle size of these additives is preferably 9 to 100 nm.
[Carrier]
As the carrier, a known carrier that has been generally used can be used. Either a binder type carrier or a coat type carrier may be used. The carrier particle size is not limited, but is preferably about 15 to 100 μm.

  The binder type carrier is obtained by dispersing magnetic fine particles in a binder resin, and those having fine particles or a coating layer charged positively or negatively on the surface can be used. The charging characteristics such as the polarity of the binder type carrier can be controlled by the material of the binder resin, the chargeable fine particles, and the type of the surface coating layer.

  Examples of the binder resin used for the binder-type carrier include thermoplastic resins such as vinyl resins, polyester resins, nylon resins, polyolefin resins, and the like typified by polystyrene resins, and curable resins such as phenol resins. .

  Magnetic fine particles of the binder type carrier include spinel ferrite such as magnetite and gamma iron oxide, and magnets such as spinel ferrite and barium ferrite containing one or more metals other than iron (Mn, Ni, Mg, Cu, etc.). Plumbite type ferrite, iron or alloy particles having an oxide layer on the surface can be used. The shape of the carrier may be granular, spherical, or needle-shaped. In particular, when high magnetization is required, it is preferable to use iron-based ferromagnetic fine particles. In consideration of chemical stability, it is preferable to use ferromagnetic fine particles of magnetoplumbite type ferrite such as spinel ferrite and barium ferrite containing magnetite and gamma iron oxide. A magnetic resin carrier having a desired magnetization can be obtained by appropriately selecting the type and content of the ferromagnetic fine particles. The magnetic fine particles are suitably added in an amount of 50 to 90% by weight in the magnetic resin carrier.

  Silicone resin, acrylic resin, epoxy resin, fluorine resin, etc. are used as the surface coating material for the binder type carrier. The charge imparting ability of the carrier can be improved by coating and curing these resins on the carrier surface to form a coat layer.

  For example, the charging fine particles or the conductive fine particles can be fixed to the surface of the binder type carrier by, for example, mixing the magnetic resin carrier and the fine particles uniformly and adhering the fine particles to the surface of the magnetic resin carrier. This is done by driving fine particles into the magnetic resin carrier by applying a strong impact force. In this case, the fine particles are not completely embedded in the magnetic resin carrier, but are fixed so that a part thereof protrudes from the surface of the magnetic resin carrier. Organic and inorganic insulating materials are used for the chargeable fine particles. Specifically, organic insulating materials include polystyrene, styrene-based copolymers, acrylic resins, various acrylic copolymers, nylon, polyethylene, polypropylene, fluororesin, and cross-linked products thereof such as organic insulating fine particles. is there. The charge imparting ability and the charge polarity can be adjusted to the material of the chargeable fine particles, the polymerization catalyst, the surface treatment and the like. As the inorganic insulating material, negatively charged inorganic fine particles such as silica and titanium dioxide, and positively charged inorganic fine particles such as strontium titanate and alumina are used.

  The coat type carrier is a carrier in which carrier core particles made of a magnetic material are coated with a resin, and like the binder type carrier, chargeable fine particles that are charged positively or negatively can be fixed to the surface of the carrier. The charging characteristics such as the polarity of the coated carrier can be adjusted by selecting the type of the surface coating layer and the electrifying fine particles. As the coating resin, the same resin as the binder resin of the binder type carrier can be used.

  The mixing ratio of the toner and the carrier may be adjusted so as to obtain a desired toner charge amount, and the toner ratio is preferably 3 to 50% by weight, preferably 6 to 30% by weight based on the total amount of the toner and the carrier. .

[Charged particles]
In order to extend the life of the carrier, charged particles (implant particles) that charge the toner to a normal polarity by frictional contact with the toner may be added to the two-component developer as a third component. When charged particles are added, even if dirt (spent) is generated on the surface of the carrier, the charged particles are driven into the spent so that stable toner chargeability can be obtained over a long period of time. The charged particles preferably used are appropriately selected according to the charging polarity of the toner. When using a toner that is negatively charged by frictional contact with the carrier, fine particles that are positively charged by contact with the toner are used as the charged particles. Specifically, for example, strontium titanate is used.

[4. Electric field forming means]
A supply / recovery electric field, which is a first AC electric field for supplying and recovering toner, is formed between the transport roller 54 and the developing roller 48, and the transport roller 54 is provided between the developing roller 48 and the photoconductor 12. The developing roller 48 and the transport roller 54 are electrically connected to the electric field forming device 110 in order to form a developing electric field that is a second AC electric field for moving the toner from the toner to the photoconductor 12. The electric field forming apparatus 110 is controlled by a control unit 182 provided at an arbitrary position of the image forming apparatus 1. The configuration of the electric field forming device 110 is not particularly limited, but the electric field forming device 110 is configured as shown in FIG. 2, for example. In the configuration shown in FIG. 2, the electric field forming device 110 includes a coil 114 having one end connected to the developing roller 48, a DC power source 112 connected to the other end of the coil 114, and a coil 116 disposed adjacent to the coil 114. , An amplifier 118 connected to the coil 116, a DC power source 122 connected to one end of the coil 114, a coil 124 connected at one end to the DC power source 122 and connected at the other end to the conveying roller 54, and adjacent to the coil 124. A coil 126 arranged and an amplifier 128 connected to the coil 126 are provided.

  The supply / recovery electric field is composed of a potential difference (Vd−Vs) between the developing bias Vd applied to the developing roller 48 by the electric field forming device 110 and the supplying bias Vs applied to the conveying roller 54 by the electric field forming device 110. Is a potential difference between the potential of the electrostatic latent image portion on the photoreceptor 12 and the developing bias Vd.

<First Embodiment>
The configuration of the developing bias Vd and the supply bias Vs according to the first embodiment will be described with reference to FIGS.

As shown in FIG. 3, the waveform of the developing bias Vd is a rectangular wave in which the maximum value Vdmax and the minimum value Vdmin are alternately repeated, and the effective value of the developing bias Vd is an integrated value per cycle of the developing bias Vd. Vo. The developing bias Vd is configured by superimposing a DC component on an AC component. Period _{T D} of the developing bias Vd is the developing bias Vd is composed of a high-voltage period _{T DH} higher than the effective value Vo, the lower low voltage period _{T DL} than the developing bias Vd is the effective value Vo. The duty ratio (T _DH / T _D ) of the developing bias Vd is set to 50%, for example, but is not limited to this. That is, the length of the high voltage period _{TDH and} the length of the low voltage period _TDL may be the same or different.

Supply bias Vs is a first alternating voltage _{V S1} is applied to the conveying roller 54 during the high voltage period _{T DH} of the developing bias Vd, is applied to the conveying roller 54 during the low voltage period _{T DL} of the developing bias Vd The second alternating voltage V _S2 is a voltage that is alternately repeated.

The first AC voltage V _S1 has a cycle T _S1 shorter than the high voltage period T _DH of the developing bias Vd. Specifically, the first AC voltage V _S1 is a voltage obtained by superimposing the high frequency alternating current component developing bias Vd than the AC component of the developing bias Vd and the DC component in the high-voltage period T _DH. As a result, the waveform of the first AC voltage V _S1 alternately repeats a maximum value V _S1MAX higher than the maximum value _Vdmax of the developing bias Vd and a minimum value V _S1MIN lower than the maximum value Vdmax of the developing bias Vd. It becomes a square wave.

Similarly, the second AC voltage V _S2 has a cycle T _S2 shorter than the low voltage period T _DL of the developing bias Vd. Specifically, the second AC voltage V _S2 is a voltage obtained by superimposing the high frequency alternating current component than the AC component of the developing bias Vd and the DC component in the low voltage period T _DL to the developing bias Vd. AC component is superimposed on the developing bias Vd in the low voltage period T _DL is preferably the same as the AC component is superimposed on the developing bias Vd in the high voltage period T _DH, may be different. Regardless of whether the high voltage period T _DH as or lower voltage period T _DL, if always the same AC component to form a supply bias Vs by superimposing the developing bias Vd, the period of the first AC voltage V _S1 T _S1 and the period _{T S2} of the second AC voltage _{V S2} is equal. The waveform of the second AC voltage V _S2 is a rectangular wave in which a maximum value V _S2MAX higher than the minimum value Vdmin of the developing bias Vd and a minimum value V _S2MIN lower than the minimum value Vdmin of the developing bias Vd are alternately repeated. is there. In the embodiment, the maximum value V _S2MAX of the second AC voltage V _S2 is the same as the minimum value V _{S1MIN of} the first AC voltage V _S1 .

In the present embodiment, the length of the high voltage period _{T DH} of the developing bias Vd is an integer multiple of the period _{T S1} of the first AC voltage _{V S1} of the supply bias Vs (FIG. 3 three times), the developing bias Vd The length of the low voltage period T _DL is an integral multiple (three times in FIG. 3) of the period T _S2 of the second AC voltage V _S2 of the supply bias Vs. As a result, the waveform of the supply / recovery electric field, that is, the potential difference (Vd−Vs) between the developing bias Vd and the supply bias Vs becomes a continuous rectangular wave as shown in FIG. Therefore, it is possible to appropriately supply and collect toner in the supply / recovery area 88. The period of the supply and recovery electric field is equal to the period T _S1 of the first AC voltage V _S1 of the supply bias Vs in the high voltage period T _DH of the development bias Vd, and the supply bias Vs in the low voltage period T _DL of the development bias Vd. _Is equal to the period T _S2 of the second AC voltage V _S2 .

On the other hand, the potential difference between the developing electric field, i.e. the potential of the electrostatic latent image portion on the photoreceptor 12 and the developing bias Vd is a alternating electric field having the same period T _D and the developing bias Vd. Therefore, the period T _S1 or T _S2 of the supply / recovery electric field is significantly smaller than the period T _{D of the} development electric field. That is, the frequency of the supply / recovery electric field is significantly higher than the frequency of the development electric field. For this reason, even if the frequency of the developing electric field is set so small that the sensitivity of the toner in the developing region 96 does not become excessively high, the frequency of the supplying and collecting electric field can be sufficiently increased. Supply and recovery can be sufficiently performed. Therefore, it is possible to suppress the variation in the toner adhesion amount on the developing roller 48, thereby reliably preventing the occurrence of the image memory.

<Second Embodiment>
The configuration of the developing bias Vd and the supply bias Vs according to the second embodiment will be described with reference to FIGS. Second embodiment, the length of the high voltage period T _DH of the developing bias Vd, or to an integral multiple of the period T _S1 of the first AC voltage V _S1 of the supply bias Vs, low voltage period of the developing bias Vd T _This is a preferred embodiment when the length of _DL cannot be made an integral multiple of the period T _S2 of the second AC voltage V _S2 of the supply bias Vs.

As shown in FIG. 5, the developing bias Vd has the same configuration as that of the first embodiment shown in FIG. On the other hand, the supply bias Vs is different from the first embodiment in that the first AC voltage V _S1 and the second AC voltage V _S2 have pause periods T _P1 and T _P2 . The pause periods T _P1 and T _P2 are periods in which the bias component superimposed on the development bias Vd is paused in order to form the first AC voltage V _S1 or the second AC voltage V _S2 . Rest period _{T P1} of the first AC voltage _{V S1} is provided at the end of the high voltage period _{T DH} of the developing bias Vd, rest period _{T P2} of the second AC voltage _{V S2} is low voltage period _{T DL} of the developing bias Vd At the end of the period. However, rest period _{T P1, T P2} is or provided at the beginning of a high-voltage period _{T DH} or low voltage period _{T DL,} and may be provided to both the beginning and end of the high voltage period _{T DH} or low voltage period _{T DL} Also good. Further, the rest periods T _P1 and T _P2 may be provided in one of the first AC voltage V _{S1 and} the second AC voltage V _S2 .

When the pause periods T _P1 and T _P2 are thus provided, when the supply bias Vs switches between the first AC voltage V _S1 and the second AC voltage V _S2 , the amplitude of the supply bias Vs instantaneously The increase in size can be avoided, thereby preventing the occurrence of leaks.

In the second embodiment, the waveform of the supply / recovery electric field, that is, the potential difference (Vd−Vs) between the development bias Vd and the supply bias Vs is as shown in FIG. In the pause periods T _P1 and T _P2 , the supply bias Vs becomes equal to the development bias Vd, so the potential difference (Vd−Vs) becomes zero.

Also in the second embodiment, the period of the supply and recovery electric field is equal to the period T _S1 of the first alternating voltage V _S1 of the supply bias Vs in the high voltage period T _DH of the development bias Vd, and the low voltage of the development bias Vd. In the period _TDL , it becomes equal to the cycle T _S2 of the second AC voltage V _S2 of the supply bias Vs. Therefore, the frequency of the supply / recovery electric field is significantly higher than the frequency of the development electric field. For this reason, the frequency of the developing bias Vd is set in the same manner as in the prior art, and the supply bias Vs is set to be sufficiently large, thereby avoiding an excessive increase in the sensitivity of the toner in the developing region 96 and generating an image memory. It can be surely prevented.

  While the present invention has been described with reference to the above-described embodiments, the present invention is not limited to the above-described embodiments.

  A test was carried out to confirm the influence of the magnitude relationship between the frequency of the supply / recovery electric field and the frequency of the development electric field on the image memory generation state.

  In the test, a first condition that is advantageous for preventing image memory and a second condition that is disadvantageous for preventing image memory are set. For each condition, the frequency of the supply and recovery electric field and the frequency of the developing electric field are changed. The presence or absence of occurrence was confirmed.

(First condition)
Under the first condition, the toner conveyance amount on the developing roller is 3 g / m ² by adjusting the integral value of the supply / recovery electric field (Vd−Vs) so that the toner on the developing roller is easily collected on the conveying roller. The toner charge amount on the roller was set to −20 μC / g. Here, the toner transport amount on the developing roller refers to the transport amount when the toner transport amount on the developing roller increases and reaches a saturated state by continuing image formation of a blank image, and so on. And Further, the amplitude (ΔVpp) of the supply / recovery electric field (Vd−Vs) is set to 2300 V, so that the toner is actively supplied and recovered between the developing roller and the conveyance roller.

(Second condition)
Under the second condition, the toner conveyance amount by the developing roller is 6 g / m ² by adjusting the integral value of the supply / recovery electric field (Vd−Vs) so that the toner on the developing roller is not easily collected by the conveying roller. The toner charge amount on the roller was set to −40 μC / g. Further, the amplitude (ΔVpp) of the supply / recovery electric field (Vd−Vs) was set to 1500 V so that the supply amount and recovery amount of toner between the developing roller and the conveyance roller were relatively small.

  Both the first condition and the second condition were tested using the image forming apparatus according to the above-described embodiment. As the developer, a carrier and toner for bizhub C350 manufactured by Konica Minolta Business Technologies, Inc. were used. The toner concentration in the developer (the ratio of the total amount of toner and external additives to the total amount of developer) was 8%.

Furthermore, as a setting common to the first condition and the second condition, the potential of the electrostatic latent image non-image portion of the photosensitive member is set to −550V, and the potential of the electrostatic latent image image portion of the photosensitive member is set to −60V. . As the developing roller, an aluminum roller having an alumite treatment on the surface was used, and the gap at the closest part between the photosensitive member and the developing roller was set to 0.15 mm. A rectangular wave developing bias Vd as shown in FIGS. 3 and 5 was applied to the developing roller. The amplitude of the developing bias Vd was set to 1.4 kV, the duty ratio of the developing bias Vd was set to 50%, and the DC component of the developing bias Vd was adjusted so that the solid adhesion amount on the photosensitive member was 6 g / m ² . The gap at the closest part between the developing roller and the conveying roller was set to 0.3 mm, and the developer conveying amount on the conveying roller was set to 200 g / m ² .

  For both the first condition and the second condition, the frequency of the developing electric field is set to 1 kHz, 2 kHz, 3 kHz, 4 kHz, 5 kHz, 6 kHz, or 7 kHz, and the frequency of the supply and recovery electric field is 1 kHz, 2 kHz, 3 kHz, 4 kHz. The image memory was evaluated for each combination of frequencies set to 5 kHz, 6 kHz, or 7 kHz (see Tables 1 and 2).

  For the combination in which the frequency of the supply and recovery electric field is larger than the frequency of the development electric field and the frequency of the supply and recovery electric field is an integral multiple of the frequency of the development electric field, the configuration shown in FIG. The developing bias Vd and the supply bias Vs of the first embodiment described above are applied to the developing roller and the transport roller, the supply / recovery electric field is larger than the frequency of the development electric field, and the frequency of the supply / recovery electric field is For combinations that are not integral multiples of the frequency, the developing bias Vd and the supply bias Vs having the configuration shown in FIG. 5 (the second embodiment described above) were applied to the developing roller and the transport roller by the electric field forming device having the configuration shown in FIG. . For other combinations, a high-voltage amplifier 609E-6 manufactured by Trek and a function generator WF1946 manufactured by NF Circuit Design Block Co. were used as the electric field forming device.

  Under the above conditions, a halftone image is printed after printing the memory evaluation chart image (an image in which a solid image portion and a blank image portion are mixed), and it is visually confirmed whether or not image memory is generated in the halftone image. did. The evaluation of the image memory is “○” when no image memory is confirmed, “△” when a slight image memory is confirmed, and “×” when the image memory is confirmed very clearly. (See Tables 1 and 2).

  Table 1 shows the test results for the first condition. When the frequency of the supply / recovery electric field is 1 kHz, the toner conveyance amount on the developing roller does not reach the predetermined amount, and when the frequency of the developing electric field is 7 kHz, the toner adhesion amount on the photoconductor does not reach the predetermined amount. The image memory could not be evaluated.

As shown in Table 1, in the first condition advantageous to the image memory, when the frequency of the developing electric field is smaller than the frequency of the supply / recovery electric field, the image memory is confirmed very clearly, and the developing electric field of When the frequency is equal to the frequency of the supply and recovery electric field, a slight image memory was confirmed. On the other hand, when the frequency of the supply / recovery electric field is larger than the frequency of the developing electric field, no image memory was generated.

  Table 2 shows the test results for the second condition. When the frequency of the supply / recovery electric field is 1 kHz and 2 kHz, the toner conveyance amount on the developing roller does not reach the predetermined amount, and when the frequency of the developing electric field is 7 kHz, the toner adhesion amount on the photosensitive member does not reach the predetermined amount. Therefore, the image memory could not be evaluated.

As shown in Table 2, in the first condition disadvantageous for the image memory, when the frequency of the developing electric field is smaller than the frequency of the supply and recovery electric field, and when the frequency of the developing electric field and the frequency of the supply and recovery electric field are equal as in the conventional case The image memory was confirmed very clearly. On the other hand, when the frequency of the supply / recovery electric field is higher than the frequency of the development electric field, when the frequency of the supply / recovery electric field is 1 kHz higher than the frequency of the development electric field, a slight image memory is confirmed and the supply / recovery electric field is confirmed. When the frequency of the electric field was 2 kHz or more higher than the frequency of the developing electric field, generation of image memory was not confirmed at all.

  From the above test results, it was confirmed that the effect of preventing the occurrence of image memory can be obtained by making the frequency of the supply and recovery electric field larger than the frequency of the development electric field regardless of the conditions related to the presence or absence of the image memory. did it.

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to the present invention and a cross section of a developing device according to the present invention. The figure which shows an example of a structure of an electric field formation apparatus. 6 is a graph showing waveforms of a developing bias and a supply bias according to the first embodiment. The graph which shows the waveform of the supply collection electric field which concerns on 1st Embodiment. 6 is a graph showing waveforms of a developing bias and a supply bias according to the second embodiment. The graph which shows the waveform of the supply collection electric field which concerns on 2nd Embodiment.

Explanation of symbols

1: Image forming apparatus, 12: Photoconductor, 16: Charging station, 18: Exposure station, 20: Development station, 22: Transfer station, 24: Cleaning station, 26: Charging apparatus, 28: Exposure apparatus, 30: Image light 32: passage, 34: developing device, 36: transfer device, 38: sheet, 40: cleaning device, 42: housing, 44: opening, 46: second space, 48: developing roller, 50: developing gap, 52: second space, 54: transport roller, 56: supply / recovery gap, 58: magnet body, 60: sleeve, 63: restriction plate, 64: restriction gap, 66: developer stirring chamber, 68: front chamber, 70 : Rear chamber, 72: front screw, 74: rear screw, 76: partition wall, 86: restriction area, 88: supply recovery area, 90: supply area, 92: recovery area, 9 : Emission region, 96: development region, 98: a toner supply unit, 100: a container, 102: opening, 104: supply roller, 110: electric field forming apparatus.

Claims (4)

A developing device that visualizes an electrostatic latent image on an electrostatic latent image carrier using a developer containing a non-magnetic toner and a magnetic carrier,
A developer carrying member carrying the developer;
A toner that is disposed so as to face the developer carrier through the supply / recovery area and to face the electrostatic latent image carrier through the development area, and is supplied from the developer carrier in the supply / recovery area A toner carrier for carrying
Forming a first AC electric field for supplying and collecting toner between the developer carrier and the toner carrier between the developer carrier and the toner carrier; An electric field forming means for forming a second AC electric field for moving the toner from the toner carrier to the electrostatic latent image carrier between the electrostatic latent image carrier and the electrostatic latent image carrier,
Frequency of the first alternating electric field is much larger than the frequency of the second alternating electric field,
The first AC electric field is composed of a potential difference between a supply bias applied to the developer carrier and a development bias applied to the toner carrier,
The development bias is an alternating voltage having a period of a high voltage period in which the development bias is higher than a predetermined voltage and a low voltage period in which the development bias is lower than the predetermined voltage.
The supply bias is applied to the developer carrier during the high voltage period and is applied to the developer carrier during the low voltage period and a first AC voltage having a shorter period than the high voltage period. A voltage obtained by alternately repeating a second AC voltage having a shorter period than the low voltage period,
The high voltage period is an integral multiple of the period of the first AC voltage;
The developing device according to claim 1, wherein the low voltage period is an integral multiple of a period of the second AC voltage . A developing device that visualizes an electrostatic latent image on an electrostatic latent image carrier using a developer containing a non-magnetic toner and a magnetic carrier,
A developer carrying member carrying the developer;
A toner that is disposed so as to face the developer carrier through the supply / recovery area and to face the electrostatic latent image carrier through the development area, and is supplied from the developer carrier in the supply / recovery area A toner carrier for carrying
Forming a first AC electric field for supplying and collecting toner between the developer carrier and the toner carrier between the developer carrier and the toner carrier; An electric field forming means for forming a second AC electric field for moving the toner from the toner carrier to the electrostatic latent image carrier between the electrostatic latent image carrier and the electrostatic latent image carrier,
Frequency of the first alternating electric field is much larger than the frequency of the second alternating electric field,
The first AC electric field is composed of a potential difference between a supply bias applied to the developer carrier and a development bias applied to the toner carrier,
The development bias is an alternating voltage having a period of a high voltage period in which the development bias is higher than a predetermined voltage and a low voltage period in which the development bias is lower than the predetermined voltage.
The supply bias is applied to the developer carrier during the high voltage period and is applied to the developer carrier during the low voltage period and a first AC voltage having a shorter period than the high voltage period. A voltage obtained by alternately repeating a second AC voltage having a shorter period than the low voltage period,
The first AC voltage and the second AC voltage are voltages obtained by superimposing another bias component on the development bias,
The first AC voltage and / or the second AC voltage has a pause period in which the bias component pauses at the end or / and start of the high voltage period or the low voltage period. Development device. The first AC voltage and / or the second AC voltage is a voltage formed by superimposing another bias component on the development bias,
The bias component superimposed in the developing bias, a developing device according to claim 1 or 2, characterized in that it comprises the developing bias AC component frequency is higher than the AC component of the. An image forming apparatus comprising the developing device according to any one of claims 1 to 3.

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