JP2010223993A - Developing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device that stably charges toner over a long period of time, in a hybrid developing type system. <P>SOLUTION: The developing device includes a first transport member 54, which holds and conveys a developer 2 on the surface thereof; two or more second transport members 48a and 48b, which hold and convey toner on the surface thereof. In a rotational direction of an electrostatic latent image carrier 12, the rotational directions of the second transport members 48a and 48b at the uppermost stream side and the lowermost downstream side, in an opposing section to the electrostatic latent image carrier are each in the same direction as that of the electrostatic latent image carrier, and the rotational direction 54 of the first transport member in an opposing section to the second transport member 48b at the most downstream side is in the opposite direction to the second transport member at the lowermost downstream side. A developer includes 0.1-3 pts.wt. of particles with reverse polarity, which are charged in the polarity reverse to the charge polarity of the toner due to frictional contact with a carrier, based on 100 pts.wt. of a toner base material, and the residual ratio of the particles with reverse polarity remained on a surface of the toner base material when ultrasonic waves are applied for 5 minutes in water is 60-90%. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

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

  As a developing method employed in an electrophotographic image forming apparatus, a one-component developing method using only toner as a main component of a developer and a two-component developing method using toner and a carrier as main components of a developer are known. ing.

  The developing device of the one-component development system includes a toner carrying member that carries and conveys toner, and a friction charging member that contacts the toner carrying surface of the toner carrying member. When the toner carried on the toner carrying member passes through the contact position of the frictional charging member, the toner is brought into frictional contact with the frictional charging member to be thinned and charged to a predetermined polarity. As described above, the one-component developing device has an advantage that the configuration is simple, small, and inexpensive because the toner is charged by frictional contact with the frictional charging member. However, since the toner is subject to strong stress at the contact position of the frictional charging member, the toner is liable to deteriorate, so that the chargeability of the toner is impaired relatively early. In addition, the contact pressure between the toner carrying member and the frictional charging member reduces the ability of the toner to adhere and charge the toner, resulting in a relatively short life of the developing device.

  In the developing device of the two-component developing method, the toner and the carrier are charged to a predetermined polarity by frictional contact between the toner and the carrier, so that the toner receives less stress than the one-component developing device. Since the surface area of the carrier is larger than that of the toner, the toner is less likely to be adhered and soiled. However, dirt (spent) attached to the surface of the carrier increases due to long-term use, and therefore the ability to charge the toner decreases. In order to extend the life of the two-component developing device, it is conceivable to increase the amount of carrier accommodated in the developing device, but this leads to an increase in the size of the developing device.

  Accordingly, a hybrid development system has been proposed that enjoys the advantages of the one-component development system and the two-component development system. For example, in Patent Document 1, as shown in FIG. 8, one magnetic roller 101 and one developing roller 102 are provided, and a toner 104 to a toner 104 including a toner and a carrier held on the outer peripheral surface of the magnetic roller 101 are included. Is selectively supplied to the outer peripheral surface of the developing roller 102, and the electrostatic latent image (electrostatic latent image portion) on the photosensitive member 105 is developed using the toner 104 held on the outer peripheral surface of the developing roller. An image forming apparatus using a hybrid developing system has been proposed. The developer is charged with a polarity opposite to the charged polarity of the toner and contains particles of the opposite polarity, and an electric field for selectively moving the toner is applied between the magnetic roller and the developing roller. In such a hybrid development method, the opposite polarity particles are separated and collected from the toner surface by the electric field, and adhere to the carrier and serve as a carrier charging site, thus ensuring the toner charging performance of the carrier and suppressing carrier deterioration. The

JP 2003-287959 A

  However, in the above-described hybrid development method, there is a problem in that reverse polarity particles (charged particles) are scattered to a place other than the developing tank. If the adhesion strength of the reverse polarity particles to the toner is increased in order to reduce the amount of scattering, the amount of scattering can be reduced. On the other hand, the amount of reverse polarity particles separated from the toner is reduced and collected in the developing tank. Since the amount of the reverse polarity particles to be reduced is reduced, it is difficult to maintain the charging stability for a long time.

  An object of the present invention is to provide a developing device and an image forming apparatus that can stably charge toner for a long period of time in a hybrid developing system.

The present invention is a developing device that visualizes an electrostatic latent image on an electrostatic latent image carrier using a developer,
A developer comprising toner and carrier, wherein the toner and carrier are charged to opposite polarities by frictional contact;
A first conveying member that is disposed in an opening of a developing tank containing the developer and conveys the developer while holding the developer on the surface;
Two or more second transports that face the first transport member via the first region, face the electrostatic latent image carrier via the second region, and transport the toner while holding it on the surface. Element;
A first electric field is formed between the first conveying member and the second conveying member to move and separate the toner from the developer held by the first conveying member to the second conveying member. 1 electric field forming means; and a second electric field formed between the second conveying member and the electrostatic latent image carrier, and the toner held by the second conveying member is transferred to the electrostatic latent image carrier. A second electric field forming means for making the electrostatic latent image visible by moving to the electrostatic latent image of
With respect to the rotation direction of the electrostatic latent image carrier, the rotation direction of the second transport member on the most upstream side and the most downstream side is the same direction as that of the electrostatic latent image carrier at the portion facing the electrostatic latent image carrier. ,
The rotation direction of the first conveying member is opposite to the second conveying member on the most downstream side in the facing portion with the second conveying member on the most downstream side,
The developer further includes 0.1 to 3 parts by weight of reverse polarity particles charged to a polarity opposite to the charged polarity of the toner by frictional contact with the carrier with respect to 100 parts by weight of the toner base material. The present invention relates to a developing device characterized in that the residual ratio of reverse polarity particles remaining on the surface of a toner base material when a sound wave is applied for 5 minutes is 60 to 90%.

  The present invention also relates to an image forming apparatus including the developing device.

  According to the present invention, since the adhesion strength of the reverse polarity particles is increased, scattering of the reverse polarity particles can be suppressed. In the hybrid development system, the rotation direction of the development roller (second conveyance member) and the rotation direction of the conveyance roller (first conveyance member) on the most upstream side and the most downstream side are set to predetermined directions, respectively. The developability between these developing rollers is improved, and each developing roller rotates in the opposite direction to the conveying roller at the portion facing the conveying roller, so that the toner between the developing roller and the conveying roller is removed. Supply and recovery are also improved. Separation / collection of the reverse polarity particles is performed between each developing roller and the conveying roller, that is, performed at two or more locations. As a result, even if the adhesion strength of the reverse polarity particles is relatively strong, the recovery of the reverse polarity particles can be achieved in a sufficient amount, so that the toner can be stably charged over a long period of time.

1 is a diagram illustrating an example of a schematic configuration of an image forming apparatus according to the present invention and a schematic configuration of a developing device according to the present invention. FIG. 3 is a schematic diagram illustrating an arrangement of a developing roller, a photoreceptor, and a first conveying member in an example of a developing device according to the present invention. The figure which shows one Embodiment of an electric field formation apparatus. The figure which shows the relationship between the voltage supplied to the sleeve and the image development sleeve from the electric field formation apparatus shown to FIG. 3A. The figure which shows other embodiment of an electric field formation apparatus. The figure which shows the relationship between the voltage supplied to the sleeve and the image development sleeve from the electric field formation apparatus shown to FIG. 4A. The figure which shows other embodiment of an electric field formation apparatus. The figure which shows the relationship between the voltage supplied to the sleeve and the image development sleeve from the electric field formation apparatus shown to FIG. 5A. The figure which shows other embodiment of an electric field formation apparatus. The figure which shows other embodiment of an electric field formation apparatus. FIG. 10 is a schematic diagram illustrating an arrangement of a developing roller, a photoreceptor, and a first conveying member in a conventional developing device. FIG. 3 is a cross-sectional view of an apparatus for measuring a toner charge amount.

  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. A charging station 16, an exposure station 18, developing stations 20 a and 20 b, a transfer station 22, and a cleaning station 24 are arranged around the photoconductor 12 along the rotation direction of the photoconductor 12.

  The charging station 16 includes a charging device 26 that charges the photosensitive layer, which is the outer peripheral surface of the photoreceptor 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. The charging device 26 may be a non-contact type. 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 stations 20a and 20b have 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. The cleaning device 40 uses a plate-like cleaning blade, but is not limited to this.

  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 is a developing tank (housing) 42 that houses a non-magnetic toner that is first component particles, a two-component developer including a magnetic carrier that is second component particles, and various members described below. It has. In order to facilitate understanding of the invention by simplifying the drawing, a part of the developing tank 42 is omitted. The developing tank 42 includes a series of openings (44, 52) opened toward the photosensitive member 12, and two developing rollers, which are toner conveying members (second conveying members), are provided in the space of the opening 44. 48 a and 48 b are provided side by side along the outer peripheral surface of one photoconductor 12. Each of the developing rollers 48a and 48b is a cylindrical member (second rotating cylindrical body), and is arranged so as to be rotatable in parallel with the photosensitive member 12 and through the outer peripheral surface of the photosensitive member 12 and a predetermined developing gap. Has been. The developing rollers 48a and 48b are not in contact with the photoconductor 12, but may be in contact with each other. In FIG. 1, two second conveying members (developing rollers) 48a and 48b are shown, but two or more may be used. For example, a schematic diagram showing the arrangement of the developing rollers 48a, 48b, and 48c, the photoconductor 12, and the conveying roller (first conveying member) 54 when three developing rollers 48a, 48b, and 48c are used. Is shown in FIG. As described above, even when three or more developing rollers are used, the developing rollers are provided between the photosensitive member 12 and the conveying roller 54 between the photosensitive member 12 and the conveying roller 54. Are provided side by side along the outer peripheral surface of the. When only one developing roller is used, toner supply / collection is not sufficiently performed between the developing roller and the conveying roller. As a result, the reverse polarity particles cannot be sufficiently collected on the conveying roller side, so that the toner charging performance of the carrier is lowered relatively early and the toner cannot be stably charged over a long period of time. Hereinafter, when including two or more developing rollers, the developing roller 48 is used.

  The developing roller rotates so that the rotation direction of the developing roller on the most upstream side and the most downstream side in the rotation direction of the photosensitive member is the same as that of the photosensitive member at a portion facing the photosensitive member. For example, when two developing rollers 48a and 48b are used as shown in FIG. 1, the rotating directions of the developing rollers 48a and 48b are indicated by 78a and 78b, respectively, and the rotating direction of the photoconductor 12 is indicated by 14.

  Further, for example, when three or more developing rollers are used, the rotation directions of the developing rollers are the same as those of the photosensitive member in the rotation direction of the most upstream side and the most downstream side of the developing roller. If it is, it will not restrict | limit in particular, The rotation direction of developing rollers other than the developing roller of the most upstream side and the most downstream side may be the same direction as a photoconductor in the opposing part with a photoconductor, or is different from a photoconductor. It may be a direction. When three or more developing rollers are used, the rotation directions of all the developing rollers are usually the same direction as the photosensitive member at the portion facing the photosensitive member. Specifically, when three developing rollers 48a, 48b, and 48c are used as shown in FIG. 2, the rotation direction of these developing rollers is the rotation of the developing rollers 48a and 48b on the most upstream side and the most downstream side. The direction is not particularly limited as long as the direction of the developing roller 48c is the same as that of the photosensitive member at the portion facing the photosensitive member, and the rotation direction of the developing roller 48c may be the same direction as the photosensitive member at the portion facing the photosensitive member. The direction may be different from that of the photoreceptor. In FIG. 2, the rotation directions of the developing rollers 48 a, 48 b, and 48 c are the same directions as the photoconductors at the portions facing the photoconductors.

  When the rotation direction of the most upstream developing roller and / or the most downstream developing roller is a direction different from the photosensitive member in the portion facing the photosensitive member, the developing roller is in contact with the conveying roller in the portion facing the conveying roller. Since the toner rotates in the same direction, the toner is not sufficiently supplied and collected between the developing roller and the transport roller. As a result, the reverse polarity particles cannot be sufficiently collected on the conveying roller side, so that the toner charging performance of the carrier is lowered relatively early and the toner cannot be stably charged over a long period of time.

  Hereinafter, the case of using two developing rollers will be described in detail, but the same applies to the case of using three or more developing rollers unless otherwise specified.

  The developing rollers 48a and 48b may be conductive rollers made of a metal material such as aluminum or stainless steel, those obtained by subjecting the conductive rollers to oxidation treatment, or surface layers on the conductive roller bases. It may have. As the surface layer, for example, polyester resin, polycarbonate resin, acrylic resin, polyethylene resin, polypropylene resin, urethane resin, polyamide resin, polyimide resin, polysulfone resin, polyether ketone resin, vinyl chloride resin, vinyl acetate resin, silicone resin and Examples thereof include resin coat layers such as fluororesins, and rubber coat layers such as silicone rubber, urethane rubber, nitrile rubber, natural rubber, and isoprene rubber. A conductive agent may be added to the inside or the outermost surface of such a surface layer. Examples of the conductive agent include an electronic conductive agent and an ionic conductive agent. Examples of the electronic conductive agent include, but are not limited to, carbon black such as ketjen black, acetylene black, and furnace black, metal powder, and metal oxide fine particles. Examples of the ionic conductive agent include, but are not limited to, cationic compounds such as quaternary ammonium salts, amphoteric compounds and other ionic polymer materials.

  Another space 52 as an opening is formed behind the developing rollers 48a and 48b. In the space 52, a conveyance roller 54 as a developer conveyance member (first conveyance member) is parallel to the development rollers 48a and 48b and the outer peripheral surfaces of both the development rollers 48a and 48b and a predetermined supply and recovery gap 56a, 56b. The conveyance roller 54 includes a magnet body 58 that is fixed so as not to rotate, and a cylindrical sleeve 60 (first rotating cylinder body) that is rotatably supported around the magnet body 58. Above the sleeve 60, a restricting plate 62 fixed to the developing tank 42 and extending in parallel with the central axis of the sleeve 60 is disposed oppositely with a predetermined restricting gap.

  The rotation direction of the conveying roller 54 is the opposite direction to the most downstream developing roller 48b at the portion facing the most downstream developing roller 48b in the rotation direction of the photosensitive member. When the rotation direction of the conveying roller 54 is the same direction as the developing roller 48b at the portion facing the developing roller 48b, the toner is not sufficiently supplied and collected between the developing roller and the conveying roller. As a result, the reverse polarity particles cannot be sufficiently collected on the conveying roller side, so that the toner charging performance of the carrier is lowered relatively early and the toner cannot be stably charged over a long period of time.

  The magnet body 58 has a plurality of magnetic poles facing the inner surface of the transport roller 54 and extending in the direction of the central axis of the transport roller 54. In the embodiment, the plurality of magnetic poles are provided on the upper left inner peripheral surface portion of the transport roller 54 near the supply recovery gap 56a, the magnetic pole S1 facing the upper inner peripheral surface portion of the transport roller 54 in the vicinity of the regulating plate 62. The opposing magnetic pole N1, the magnetic pole S2 facing the left inner peripheral surface portion of the transport roller 54, the magnetic pole N2 facing the lower left inner peripheral surface portion of the transport roller 54 in the vicinity of the supply and recovery gap 56b, and the lower portion of the transport roller 54 A magnetic pole S3 facing the peripheral surface portion and two adjacent magnetic poles N3 and N4 of the same polarity facing the right inner peripheral surface portion of the transport roller 54 are included.

  A developer stirring chamber 66 is formed behind the transport roller 54. The stirring chamber 66 has 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. A magnetic permeability sensor (not shown) for detecting a toner ratio (weight ratio) in the developer is preferably disposed in the vicinity of the front screw 72.

  The operation of the developing device 34 configured as described above will be described. During image formation, the developing rollers 48a and 48b and the sleeve 60 rotate in directions of arrows 78a, 78b, 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 N4 in the vicinity of the magnetic pole N4. 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 S1 in the area facing the restriction plate 62 (restriction area 86) is restricted by the restriction plate 62 to a predetermined amount. The developer 2 that has passed through the regulation gap is conveyed to a region (supply / recovery region) 88a where the developing roller 48a 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 88a, mainly in the upstream region (supply region) 90a with respect to the rotation direction of the sleeve 60, the presence of an electric field formed between the developing roller 48a and the sleeve 60 exists. Thus, the toner adhering to the carrier is electrically supplied to the developing roller 48a. Further, in the supply / recovery area 88a, mainly in the downstream area (recovery area) 92a with respect to the rotation direction of the sleeve 60, the development sent back to the supply / recovery area 88a without contributing to the development, as will be described later. The toner on the roller 48a is scraped off by a magnetic brush formed along the magnetic field lines of the magnetic pole N1 and collected by 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 48a.

The toner held on the developing roller 48a in the supply area 90a is conveyed in the counterclockwise direction along with the rotation of the developing roller 48a. In the area (developing area) 96a where the photoconductor 12 and the developing roller 48a face each other, the toner 12 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. Therefore, in the developing region 96a, 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 48a. The image is visualized as a developer image. The developing method may be such a reversal developing method or a regular developing method.

  The developer 2 that has passed through the supply / recovery region 88a is held by the magnetic force of the magnet body 58, passes through the opposing portion of the magnetic pole S2 along with the rotation of the sleeve 60, and the magnetic pole N2 faces, and the developing roller 48b and the transport roller 54 face each other. To the area (supply / recovery area) 88b. Of the supply / recovery area 88b, the upstream area (supply area) 90b mainly in the rotational direction of the sleeve 60 is similar to the area 90a due to the presence of an electric field formed between the developing roller 48b and the sleeve 60. The toner adhering to the carrier is electrically supplied to the developing roller 48b. Further, in the supply / recovery area 88b, the downstream area (recovery area) 92b mainly with respect to the rotation direction of the sleeve 60 is sent back to the supply / recovery area 88b without contributing to the development as in the area 92a. The toner on the developing roller 48b is scraped off by the magnetic brush formed along the magnetic field lines of the magnetic pole N2 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 48b.

  The toner held on the developing roller 48b in the supply area 90b is conveyed counterclockwise with the rotation of the developing roller 48b, and the developing area 96a is an area (developing area) 96b where the photosensitive member 12 and the developing roller 48b face each other. In the same manner as in, the toner adheres to the electrostatic latent image portion formed on the outer peripheral surface of the photoreceptor 12 and is sufficiently developed.

  When the developer 2 that has passed through the supply / recovery region 88b is held by the magnetic force of the magnet body 58 and passes through the opposing portion of the magnetic pole S3 along with the rotation of the sleeve 60, it reaches the opposing region (discharge region 94) of the magnetic poles N3 and N4. The repulsive magnetic field formed by the magnetic poles N3 and N4 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.

  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 stored in the developing tank 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 the toner 6. 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 6 drops and replenishes the rear chamber 70.

  The toner 6 to be replenished may have the same composition as the toner in the developer, and in detail, a reverse polarity particle and optionally a fluidizing agent are externally added to a toner base material to be described later. The content of the reverse polarity particles in the replenishment toner 6 may be such that the content with respect to 100 parts by weight of the toner base material is within the range described later.

[3. Electric field forming means]
In order to efficiently move toner from the sleeve 60 to the developing roller 48a in the supply area 90a and efficiently move toner from the sleeve 60 to the developing roller 48b in the supply area 90b, the developing rollers 48a, 48b and the sleeve 60 are The electric field forming device 110 is electrically connected. The electric field forming device 110 forms a first electric field between the conveying roller 54 and the developing rollers 48a and 48b, and moves and separates toner from the developer held by the conveying roller to the developing rollers 48a and 48b. The first electric field forming means, a second electric field is formed between the developing rollers 48a and 48b and the photoconductor 12, and the toner held by the developing rollers 48a and 48b is transferred to the electrostatic latent image on the photoconductor 12. And a second electric field forming means for making the electrostatic latent image visible. Usually, the same voltage is applied to the developing rollers 48a and 48b. When three or more developing rollers are used, the same voltage is normally applied to all the developing rollers.

  Specific examples of the power source constituting the first and second electric field forming means are shown in FIGS.

The electric field forming apparatus 110 according to the first exemplary embodiment illustrated in FIG. 3A includes a first power source 112 (corresponding to a second electric field forming unit) connected to the developing rollers 48a and 48b and a second power source connected to the sleeve 60. 114 (corresponding to first electric field forming means). The first power source 112 includes a DC power source 118 connected between the developing rollers 48 a and 48 b and the ground 116, and a first DC voltage V _DC1 (for example, −200) having the same polarity as the charging polarity of the toner 6. Bolt) is applied to the developing rollers 48a and 48b. The second power supply 114 has a DC power supply 120 connected between the sleeve 60 and the ground 116, and has the same polarity as the charging polarity of the toner 6 and a second DC voltage that is higher than the first DC voltage. V _DC2 (eg, −400 volts) is applied to the sleeve 60. As a result, in the supply regions 90a and 90b, the negatively charged toner 6 is transferred from the sleeve 60 to the developing rollers 48a and 48b by the action of a DC electric field formed between the developing rollers 48a and 48b and the sleeve 60. 48b is electrically attracted. At this time, the positively charged carrier 4 is not sucked from the sleeve 60 to the developing rollers 48a and 48b. In the developing regions 96a and 96b, the negative polarity toner held on the developing rollers 48a and 48b is, as shown in FIG. 3B, the developing rollers 48a and 48b (V _DC1 : −200 volts) and the electrostatic latent image image. It adheres to the electrostatic latent image portion based on the potential difference from the portion (V _L : −80 volts). At this time, the negative toner is transferred to the electrostatic latent image non-image portion due to a potential difference between the developing rollers 48a and 48b (V _DC1 : -200 volts) and the electrostatic latent image non-image portion (V _H : -600 volts). It will not adhere.

In the electric field forming apparatus 122 of FIG. 4A according to the second embodiment, the first power supply 124 (corresponding to the second electric field forming means) is similar to the power supply of the first embodiment in that the developing rollers 48a and 48b, the ground 126, and the like. The first DC voltage V _DC1 (for example, −200 volts) having the same polarity as the charging polarity of the toner 6 is applied to the developing rollers 48a and 48b. The second power supply 130 (corresponding to the first electric field forming means) has a DC power supply 132 and an AC power supply 134 between the sleeve 60 and the ground 126. The DC power supply 132 applies a second DC voltage V _DC2 (for example, −400 volts) having the same polarity as the charging polarity of the toner 6 and higher than the first DC voltage to the sleeve 60. As shown in FIG. 4B, the AC power supply 134 applies an _AC voltage VAC having a peak-to-peak voltage V _PP of, for example, 300 volts between the sleeve 60 and the ground 126. As a result, in the supply regions 90a and 90b, the negatively charged toner 6 is received from the sleeve 60 from the developing roller 48a by the action of the pulsating electric field formed between the developing rollers 48a and 48b and the sleeve 60. , 48b. At this time, the positively charged carrier 4 is held by the sleeve 60 by the magnetic force of the fixed magnet inside the sleeve 60 and is not supplied to the developing rollers 48a and 48b. Further, in the developing regions 96a and 96b, the negative toner held on the developing rollers 48a and 48b is the developing rollers 48a and 48b (V _DC1 : −200 volts) and the electrostatic latent image portion (V _L : −80). And the electrostatic latent image image portion.

In the electric field forming device 136 shown in FIG. 5A, the first power supply 138 (corresponding to the second electric field forming means) has a DC power supply 142 and an AC power supply 144 between the developing rollers 48a and 48b and the ground 140. The DC power supply 142 applies a first DC voltage V _DC1 (for example, −200 volts) having the same polarity as the charging polarity of the toner 6 to the sleeve 60 and the developing rollers 48 a and 48 b. The AC power supply 144 applies an _AC voltage VAC having an amplitude (peak-to-peak voltage) _VP-P of, for example, 1,600 volts between the sleeve 60 and the developing rollers 48a and 48b and the ground 146. The second power source 146 (corresponding to the first electric field forming means) has a DC power source 150 connected between the terminal 148 between the developing rollers 48 a and 48 b and the AC power source 144 and the sleeve 60. The DC power supply 150 can output a predetermined DC voltage V _DC2 , and the anode is connected to the terminal 148 and the cathode is connected to the sleeve 60, so that the sleeve 60 has a negative polarity with respect to the developing rollers 48 a and 48 b. Biased (see FIG. 5B). Therefore, in the supply regions 90a and 90b, the negatively charged toner 6 is received from the sleeve 60 by the action of the pulsating electric field formed between the developing rollers 48a and 48b and the sleeve 60. 48b is electrically attracted. In the developing regions 96a and 96b, the negative toner on the developing rollers 48a and 48b is transferred to the developing rollers 48a and 48b (V _DC1 : −200 volts) and the electrostatic latent image portion (V _L : −80 volts). Is attached to the electrostatic latent image portion based on the potential difference.

The electric field forming device 152 shown in FIG. 6 is obtained by adding AC power sources 154 and 156 to the first power source 112 and the second power source 114, respectively, in the electric field forming device 110 of the first embodiment shown in FIG. 3A. The output voltages of the AC power supplies 154 and 156 are V _AC1 and V _AC2 . The voltages V _AC1 and V _AC2 may be the same or different. The electric field forming device 158 shown in FIG. 7 is obtained by adding an AC power source 160 to the first power source 112 in the power source of the embodiment shown in FIG. 3A. The output voltage of the AC power supply 160 is _{V AC.} Similarly to the electric field forming devices 110, 122, and 136, the electric field forming devices 152 and 158 in these forms also receive the action of the pulsating electric field formed between the developing rollers 48 a and 48 b and the sleeve 60, thereby supplying the supply region. In 90a and 90b, the negatively charged toner 6 is supplied from the sleeve 60 to the developing rollers 48a and 48b, and in the developing regions 96a and 96b, the negatively charged toner 6 is electrostatically supplied from the developing rollers 48a and 48b. Based on the potential difference from the latent image portion (V _L : −80 volts), it is supplied to the electrostatic latent image portion.

[4. Developer)
The developer includes at least toner, a carrier, and reverse polarity particles that are charged to a polarity opposite to the charged polarity of the toner by frictional contact with the carrier.

  In the developing tank 42, the reverse polarity particles are usually held mainly on the toner surface based on electrostatic attraction. At the time of image formation, the reverse polarity particles are transported in the developing tank 42 together with the toner and the carrier, and then are held by the sleeve 60 and move in the regulation area 86, the supply / recovery areas 88a and 88b, and the discharge area 94. In this conveyance process, when the reverse polarity particles held on the toner surface are placed in the first electric field (the electric fields of the supply and recovery areas 88a and 88b), a part of the electric force acts on the toner. Is separated from the surface (outer peripheral surface) of the toner by receiving an electric force in the opposite direction. The separated reverse polarity particles move to the surface (outer peripheral surface) of the carrier and are retained. If part or all of the surface of the carrier is covered with spent, the opposite polarity particles are driven into the spent. The reverse polarity particles held on the surface of the carrier are charged to a polarity opposite to that of the toner by frictional contact with the carrier. In this embodiment, since the toner is charged to a negative polarity, the reverse polarity particles are charged to a positive polarity. For this reason, the carrier holding the reverse polarity particles can maintain the same charging ability as when there is no spent even if at least a part of the surface is covered with the spent, and can charge the toner to a predetermined polarity. Moreover, in the present invention, in particular, the developer has a predetermined reverse polarity particle residual ratio and content, and two or more developing rollers are used, and the most upstream and the most downstream developing rollers thereof, and Since each of the transport rollers rotates in a predetermined direction, the reverse polarity particles can be separated and collected in a sufficient amount while the scattering of the reverse polarity particles is effectively suppressed during durability. As a result, the amount of the reverse polarity particles transferred to the carrier surface by the first electric field is stabilized even in the case of long-term continuous printing, and the deterioration of the toner charging performance of the carrier can be prevented over a long period. Therefore, the toner can be stably charged over a long period of time, and image noise such as fog can be suppressed over a long period of time.

  In the present invention, the residual ratio of reverse polarity particles remaining on the surface of the toner base material when ultrasonic waves are applied for 5 minutes in water is 60 to 90%, preferably 70 to 80%. If the residual ratio is too large, the amount of reverse polarity particles that are separated from the toner by the first electric field is reduced between the transport roller and the developing roller. For this reason, it is impossible to effectively prevent a decrease in chargeability of the carrier, and stable toner charging cannot be performed in the long term. If the residual rate is too small, the number of reverse polar particles separated in the first electric field part will increase and scatter, and the appropriate amount will not return to the developer tank, preventing a decrease in the chargeability of the carrier, and stable toner charging over the long term. I can't.

The residual rate can be measured by the method shown below.
4 g of toner is wetted with 40 g of a 0.2% aqueous solution of polyoxyethyl phenyl ether, and an electric current indicating a vibration instruction value attached to the main unit is obtained using an ultrasonic homogenizer US-1200T (manufactured by Nippon Seiki Co., Ltd .; specification frequency 15 kHz). The ultrasonic energy was adjusted so that the total value indicated 60 μA (50 w) and applied for 5 minutes. This toner and a toner to which no ultrasonic wave has been applied are subjected to fluorescent X-ray analysis. The amount of reverse polarity particles (X) remaining in the toner after the ultrasonic wave application and the reverse polarity adhered to the toner before the ultrasonic wave application. By quantifying the amount (Y) of the particles, the residual ratio of the reverse polarity particles was determined based on the following formula.
Residual ratio of reverse polarity particles (% by weight) = (X / Y) × 100

  The toner base material refers to colored particles containing at least a binder resin and a colorant, and a toner base material having a reverse polarity particle and optionally a fluidizing agent added externally is referred to as a toner. To do.

  The content of the reverse polarity particles is 0.1 to 3 parts by weight with respect to 100 parts by weight of the toner base material, and preferably 0.1 to 2 parts by weight. When the content is too large, the amount of reverse polarity particles released in the developing tank increases, and the charge amount in the developing tank decreases. As a result, stable toner charging cannot be performed in the long term. When the content is too small, the number of reverse polarity particles in the developing tank decreases, and when the carrier spent progresses, the spent portion increases and the chargeability decreases. As a result, stable toner charging cannot be performed in the long term.

  As the reverse polarity particles, those having a blow-off charge amount with respect to iron powder having the opposite sign to the charge polarity of the toner are used, and those having an absolute value in the range of 0.1 to 100 μC / g are preferably used.

In this specification, the blowoff charge amount is a value measured by the following method.
Using a blow-off powder charge measuring device (manufactured by Toshiba Chemical Co., Ltd.), a sample with a concentration of 0.2 wt% added to an iron powder carrier (Z-150 / 250) (manufactured by Powder Tech Co., Ltd.) It is shown by the value when mixed for 1 minute with a mixer. The apparatus conditions are SUS400 mesh, blow pressure 1 kgf / cm ² , and 60 second value.

  Specifically, for example, when using a toner that is negatively charged by frictional contact with the carrier, the reverse polarity particles are particles that are positively charged by frictional contact with the carrier, preferably blow-off to iron powder. Those having a charge amount in the range of +5 to +100 μC / g are used. Such positively chargeable particles include, for example, titanate compounds such as strontium titanate, barium titanate and calcium titanate, inorganic particles such as alumina, and positively chargeable thermoplastic resins such as nitrogen-containing resins and acrylic resins. Alternatively, organic particles composed of a positively chargeable thermosetting resin can be used. Examples of the nitrogen-containing resin include 2-dimethylaminoethyl acrylate, 2-diethylaminoethyl acrylate, 2-dimethylaminoethyl methacrylate, 2-diethylaminoethyl methacrylate, vinylpyridine, N-vinylcarbazole, and vinylimidazole. A polymer containing at least one nitrogen-containing monomer selected from the group as a monomer, a benzoguanamine resin, a nylon resin, a polyimide resin, a polyamide resin, or the like can be used. Moreover, you may use what contained the positive charge control agent which can provide the positive charging property to the said particle | grain by making it contain in the resin particle in the resin particle. As the positive charge control agent, for example, nigrosine dye, quaternary ammonium salt and the like can be used. As the resin containing the positive charge control agent, for example, an acrylic resin, a styrene / acrylic resin, a silicone resin, or the like can be used. Furthermore, what coat | covered the surface of the particle | grain with the positively chargeable surface treating agent which can provide the positive chargeability to the said particle | grain by coating the particle | grain surface may be used. Such particles are not particularly limited, and for example, the above-described inorganic particles and organic particles that can be used as positively charged particles, and inorganic particles and organic particles described later that can be used as negatively charged particles are used. it can. As the positively chargeable surface treatment agent, for example, the above-mentioned positively chargeable thermoplastic resin or positively chargeable thermosetting resin and a known surface treatment agent having an amino group, a nitrile group or an isocyanate group may be used as they are or as desired. It can be used by dissolving in a solvent. Examples of known surface treating agents include synthetic resins such as urethane-modified resins and acrylonitrile resins, γ- (2-aminoethyl) aminopropyltrimethoxysilane, γ- (2-aminoethyl) aminopropylmethyldimethoxysilane, aminosilane, Silane coupling agents such as γ-aminopropyltriethoxysilane, N- (2-aminoethyl) 3-aminopropyltrimethoxysilane and N-β- (N-vinylbenzylaminoethyl) -γ-aminopropyltrimethoxysilane In addition, silicone oils such as amino-modified silicone oils can be used.

  In addition, for example, when using a toner that is positively charged by frictional contact with a carrier, the reverse polarity particles are particles that are negatively charged by frictional contact with the carrier, and preferably have a blow-off charge amount with respect to iron powder. Those in the range of −5 to −100 μC / g are used. Examples of such negatively chargeable particles include inorganic particles such as silica and titanium oxide, and fluorine resins such as polymers containing fluorine-containing acrylic monomers and / or fluorine-containing methacrylic monomers, polyolefin resins such as polyethylene, Organic particles composed of negatively chargeable thermoplastic resins such as silicone resins and polyester resins or negatively chargeable thermosetting resins can be used. Moreover, you may use what contained the negative charge control agent which can provide the negative chargeability to the said particle | grain by making it contain in the resin particle in the resin particle. As the negative charge control agent, for example, salicylic acid-based or naphthol-based chromium complexes, aluminum complexes, iron complexes, zinc complexes, and the like can be used. Examples of the resin containing the negative charge control agent include acrylic resins, styrene / acrylic resins, and silicone resins. Further, a particle surface coated with a negatively chargeable surface treating agent capable of imparting negative chargeability to the particle by coating the particle surface may be used. Such particles are not particularly limited. For example, the above-described inorganic particles and organic particles that can be used as negatively charged particles, and the above-described inorganic particles and organic particles that can be used as positively charged particles are used. it can. As the negatively chargeable surface treating agent, for example, the negatively chargeable thermoplastic resin, the negatively chargeable thermosetting resin, the fluorine-based silicone oil or the like can be used as it is or after being dissolved in a solvent as desired.

  The average primary particle size of the reverse polarity particles further stabilizes the amount of the reverse polarity particles that migrate to the carrier surface by the first electric field, while further preventing the charging ability from being reduced due to the toner spent of the carrier. From a viewpoint, 100-900 nm is preferable, More preferably, it is 100-500 nm.

  The reverse polarity particles are held on the surface of the toner base material and replenished as the toner 6 from the toner replenishing unit 98.

  In the embodiment, the toner is negatively charged and the carrier is positively charged by frictional contact between the toner and the carrier. Further, the reverse polarity particles are positively charged. The chargeability of the toner, carrier, and reverse polarity particles used in the present invention is not limited to such a combination. Specifically, a combination in which the toner is positively charged, the carrier is negatively charged by the frictional contact between the toner and the carrier, and the reverse polarity particles are negatively charged may be used.

[5. Developer production method]
The developer can be produced by once adding and mixing a fluidizing agent, which will be described later, to the toner base material, adding and mixing the reverse polarity particles, and then adding and mixing the carrier.

  Specifically, for example, when mixing immediately after the addition of the reverse polarity particles is performed using a Henschel mixer (manufactured by Mitsui Kinzoku Mining Co., Ltd.), the rotation temperature is 25 to 50 m / s at a coolant temperature of 30 to 40 ° C., preferably Stir at 30-40 m / s for 5-30 minutes, preferably 10-25 minutes. If such agitation is insufficient, the reverse polarity particles are not sufficiently fixed, and the residual rate is too low to achieve the predetermined residual rate. If the agitation is performed excessively, the reverse polarity particles are excessively fixed, so that the residual ratio is too high and the predetermined residual ratio cannot be achieved.

Specifically, at the time of addition of the reverse polarity particles and at the time of mixing immediately after the addition, the amount of the reverse polarity particles is adjusted, and the refrigerant temperature, rotation speed and stirring time of the mixing device are adjusted within an appropriate range. Residual rate can be controlled.
For example, if the rotational speed is increased, the stirring time is increased, or the refrigerant temperature is increased, the remaining rate is increased. On the other hand, when the rotational speed is reduced, the stirring time is shortened, or the refrigerant temperature is lowered, the remaining rate is reduced.
Further, for example, when the amount of the reverse polarity particles added is increased, the remaining rate is decreased. On the other hand, when the addition amount of the reverse polarity particles is reduced, the remaining rate is increased.

[6. Specific materials)
Specific materials of other particles contained in the toner, carrier, and developer will be described.

〔toner〕
As the toner base material, a known toner base material that has been generally used in image forming apparatuses can be used. The toner base material particle size is, for example, about 3 to 15 μm. The toner base material contains at least a colorant in a binder resin, and may contain a charge control agent and a release agent.

  The toner base material 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 base material is not limited. For example, styrene resin (monopolymer or copolymer containing styrene or a styrene-substituted product, such as styrene / acrylic resin), 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 80 to 160 ° C and a glass transition point in the range of 40 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, alkylsalicylic 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.

〔Release agent〕
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]
A fluidizing agent that promotes fluidization of the developer may be externally added to the toner base material. 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 1 to 5 parts by weight with respect to 100 parts by weight of the toner base material. Two or more kinds of particles may be used as the fluidizing agent, and in such a case, the total amount thereof may be within the above range.
The number average primary particle size of the fluidizing agent is preferably 1 to less than 100 nm.

[Carrier]
As the carrier, a known carrier that has been generally used can be used. A binder type carrier or a coat type carrier can be used. The carrier particle size is not limited, but is preferably 15 to 100 μm.

  The binder-type carrier is obtained by dispersing magnetic fine particles in a binder resin, and fine particles that are charged positively or negatively can be fixed on the surface, or a coating layer can be provided. 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.

  Binder resins used in binder-type carriers include thermoplastic resins such as vinyl resins, polyester resins, nylon resins, polyolefin resins such as polystyrene resins, and curable resins such as phenol resins and silicone resins. Illustrated.

  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 magnetic fine particles may be any of granular, spherical and acicular. 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. .

  The charge polarity of each component due to the combination of the toner base, carrier, and reverse polarity particles is easily known from the direction of the electric field for separating the toner or the reverse polarity particles from the developer after mixing and stirring them into the developer. be able to.

<Example 1>
(Carrier A)
A carrier for bizhub C350 manufactured by Konica Minolta Business Technologies, Inc., which is a coat type carrier in which an acrylic resin coat is formed on carrier core particles made of a magnetic material, is used as carrier A.

(Toner base material)
As the toner base material, a toner base material for bizhub C350 manufactured by Konica Minolta Business Technologies, Inc. was used. Specifically, the toner base material was prepared by a wet granulation method and had a volume average particle size of about 6.5 μm.

(toner)
To 100 parts by weight of the toner base material, 0.2 parts by weight of the first hydrophobic silica, 0.5 parts by weight of the second hydrophobic silica, and 0.5 parts by weight of the hydrophobic titanium oxide are added. (Metal Mining Co., Ltd.) was used and mixed for 5 minutes at a mixer rotation speed of 40 m / s for external addition treatment. Next, the temperature of water flowing through the Henschel mixer is set to 35 ° C., and 0.1 part by weight of strontium titanate particles (reverse polarity particles) having a number average particle diameter of 350 nm are added to 100 parts by weight of the toner base material. Using a mixer, the mixture was stirred for 10 minutes at a mixer rotation speed of 40 m / s to obtain a toner.
The blow-off charge amount of the strontium titanate particles to the iron powder was +5 μC / g.

The first hydrophobic silica used here is a silica (# 130: manufactured by Nippon Aerosil Co., Ltd.) having a number average primary particle size of 16 nm and surface-treated with hexamethyldisilazane (HMDS) as a hydrophobizing agent. is there.
The second hydrophobic silica is obtained by surface-treating silica having a number average primary particle size of 20 nm (# 90: manufactured by Nippon Aerosil Co., Ltd.) with HMDS.
Hydrophobic titanium oxide is obtained by surface-treating anatase-type titanium oxide having a number average primary particle size of 30 nm with isobutyltrimethoxysilane as a hydrophobizing agent in an aqueous wet process.

(Evaluation)
An image forming apparatus (bizhub C350; Konica Minolta Business Technologies Co., Ltd.) in which the developer obtained by mixing the toner and carrier A at a weight mixing ratio (toner / carrier) 8/92 is modified to the configuration shown in FIG. Mounted on the company). Using this image forming apparatus, 500,000 image charts having an image area ratio of 5% were printed. The toner was controlled to be replenished based on the toner density detection result of the developer. The printing conditions used were the standard conditions of the above copying machine unless otherwise specified.

・ Developing roller 48A
An aluminum roller with alumite treatment on the surface was used.
・ Development roller 48B
The developing roller 48B was the same as the developing roller 48A.

Development conditions are as follows. The electric field forming apparatus employs the form shown in FIG. 7, and a DC voltage V _DC2 : −500 volts is applied to the conveying roller 54. A DC voltage V _DC1 : -300 volts and an AC voltage were applied to the developing rollers 48a and 48b. AC voltage frequency: 2 kHz, the amplitude _V P-P: 1,600 volt, negative duty ratio: was 40% of the rectangular wave. Accordingly, the potential difference in the direction in which the negatively charged toner is supplied from the conveying roller 54 to the developing rollers 48a and 48b is 1000V, and the potential difference in the direction in which the toner is collected from the developing rollers 48a and 48b to the conveying roller 54 is 600V. It was. The gaps at the closest portions 56a and 56b between the developing rollers 48a and 48b and the conveying roller 54 were set to 0.3 mm. Accordingly, the electric field in the toner supply direction formed between the transport roller 54 and the developing rollers 48a and 48b was 1000 V / 0.3 mm = 3.3 × 10 ⁶ V / m.
The gap (interval) between the regulating member 62 and the conveying roller 54 was set to 0.4 mm. The rotation direction of the sleeve 60 in the conveying roller 54 is the opposite direction to the developing roller 48a at the portion facing the developing roller 48a, and the opposite direction to the developing roller 48b at the portion facing the developing roller 48b. The background potential of the photoreceptor 12 was −550 volts, and the image potential was −60 volts. The gap between the closest portions 96a and 96b between the photoreceptor 1 and the developing rollers 48a and 48b was set to 0.15 mm.

-Charging stability The developer was sampled from the front chamber 68 of the developing device at the initial stage and after printing 500,000 sheets, and the toner charge amount was measured. The charge amount was measured using a measuring apparatus shown in FIG. After the developer composed of the toner containing the reverse polarity particles and the carrier is stirred, 1 g of the developer weighed with a precision balance is placed on the surface of the conductive sleeve 72 so as to be uniform. Next, a voltage of 2 kV is supplied from the bias power supply 78 to the conductive sleeve 72, and the rotation speed of the magnet roller 74 provided in the sleeve 72 is set to 2000 rpm. In this state, the toner is collected on the cylindrical electrode 76 by being left for 30 seconds. After 30 seconds, the potential Vm of the cylindrical electrode 76 was read, the charge amount of the toner was determined, and the mass of the collected toner was measured with a precision balance to determine the average charge amount.

Evaluation was made by the following three ranks according to the difference in charge amount before and after durability.
A: The difference in charge amount is 8 μC / g or less, the chargeability is very stable, and there is no practical problem.
◯: When the difference in charge amount exceeds 8 μC / g and is 15 μC / g or less, the chargeability is stable, and there is no practical problem.
X: The difference in charge amount exceeds 15 μC / g, the chargeability is unstable, and a practical problem arises.

(Residual rate of reverse polarity particles on toner base surface)
Measurement was performed by the method described above.

<Examples 2 to 12 / Comparative Examples 1 to 6>
Example 1 except that the addition amount of the reverse polarity particles and the water temperature, rotation speed and stirring time of the mixing apparatus were changed to the predetermined values described in the table at the time of addition of the reverse polarity particles and at the time of mixing immediately after the addition. A developer was produced and evaluated in the same manner as described above.

  1: image forming apparatus, 2: developer, 6: toner, 12: photoconductor, 16: charging station, 18: exposure station, 20: developing station, 22: transfer station, 24: cleaning station, 26: charging device, 28: Exposure device, 30: Image light, 32: Passage, 34: Development device, 36: Transfer device, 38: Sheet, 40: Cleaning device, 42: Development tank (housing), 44: Opening, 48a: 48b: Developing roller 52: Opening portion (second space) 54: Conveying roller 56: Supply / recovery gap 58: Magnet body 60: Sleeve 62: Restricting plate 66: Developer stirring chamber 68: Front chamber , 70: rear chamber, 72: front screw, 74: rear screw, 76: partition wall, 86: restriction region, 88a: 88b: supply / recovery region, 90a: 90b: supply region, 9 a: 92b: collection area, 94: discharge area, 96: development area, 98: toner replenishment section, 100: container, 102: opening, 104: replenishment roller, 110: electric field forming device, 112: first power supply, 114: Second power source, 116: Ground, 118: DC power source, 120: DC power source, 122: Electric field forming device, 124: First power source, 126: Ground, 128: DC power source, 130: Second power source, 132: DC power supply, 134: AC power supply, 136: Electric field forming device, 138: First power supply, 140: Ground, 142: DC power supply, 144: AC power supply, 146: Second power supply, 148: Terminal, 150: DC power source, 152: electric field forming device, 154: AC power source, 156: AC power source, 158: electric field forming device, 160: AC power source.

Claims (4)

A developing device that visualizes an electrostatic latent image on an electrostatic latent image carrier using a developer,
A developer comprising toner and carrier, wherein the toner and carrier are charged to opposite polarities by frictional contact;
A first conveying member that is disposed in an opening of a developing tank containing the developer and conveys the developer while holding the developer on the surface;
Two or more second transports that face the first transport member via the first region, face the electrostatic latent image carrier via the second region, and transport the toner while holding it on the surface. Element;
A first electric field is formed between the first conveying member and the second conveying member to move and separate the toner from the developer held by the first conveying member to the second conveying member. 1 electric field forming means; and a second electric field formed between the second conveying member and the electrostatic latent image carrier, and the toner held by the second conveying member is transferred to the electrostatic latent image carrier. A second electric field forming means for making the electrostatic latent image visible by moving to the electrostatic latent image of
With respect to the rotation direction of the electrostatic latent image carrier, the rotation direction of the second transport member on the most upstream side and the most downstream side is the same direction as that of the electrostatic latent image carrier at the portion facing the electrostatic latent image carrier. ,
The rotation direction of the first conveying member is opposite to the second conveying member on the most downstream side in the facing portion with the second conveying member on the most downstream side,
The developer further includes 0.1 to 3 parts by weight of reverse polarity particles charged to a polarity opposite to the charged polarity of the toner by frictional contact with the carrier with respect to 100 parts by weight of the toner base material. A developing device, wherein the residual rate of reverse polarity particles remaining on the surface of a toner base material when a sound wave is applied for 5 minutes is 60 to 90%.   The developing device according to claim 1, wherein the reverse polarity particles are titanic acid compound particles.   The developing device according to claim 1, wherein the average primary particle diameter of the reverse polarity particles is 100 to 900 nm.   An image forming apparatus comprising the developing device according to claim 1.

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