JP2009175496A - Developing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To satisfactorily maintain toner electrification property of carrier in two-component developer over a long term while trying miniaturization of a developing device. <P>SOLUTION: In the developing device 34, an amount of toner supplied from a toner storing chamber 68 storing toner to a developer storing chamber 66 storing developer is adjusted in accordance with change of the amount of toner on a developer carrier 54 carrying the developer, and the developer containing charged particles held separably on a surface of the toner is used, and electric field to make the toner in the developer held by the developer carrier 54 move to a toner carrier 48 and separate at least a part of the charged particles held on the surface of the toner in the developer from the toner to hold on a surface of the carrier is formed between the developer carrier 54 and the toner carrier 48. <P>COPYRIGHT: (C)2009,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) adhering to the surface of the carrier increases due to long-term use, and therefore, the ability to charge the toner is reduced, causing the problem of fogging and toner scattering. 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.

  In view of such problems, for example, the developing device disclosed in Patent Document 1 employs so-called hybrid development that combines the advantages of one-component development and the advantages of two-component development as the development method. A developing device adopting hybrid development includes a developer conveying roller and a developing roller, and selectively selects only toner from the developer including toner and carrier held on the outer circumferential surface of the developer conveying roller on the outer circumferential surface of the developing roller. Then, the electrostatic latent image (electrostatic latent image portion) on the photosensitive member is developed using the toner held on the outer peripheral surface of the developing roller.

  In the hybrid development, as in the one-component development, since only the toner is carried on the developing roller and the carrier is not carried, the carrier does not come into contact with the surface of the photoreceptor, and a high-quality image can be obtained. In the hybrid development, as in the two-component development, the toner is charged by frictional contact with the carrier, so that the toner can be charged with a relatively small stress.

Patent Document 2 proposes a technique for reducing the size of a developing device with respect to a developing device employing hybrid development. More specifically, the developing device of Patent Document 2 stores a developer storage chamber that stores a developer (toner and carrier) carried on the developer transport roller, and toner that is supplied to the developer storage chamber. And a toner storage chamber. When toner in the developer storage chamber is consumed during development, the toner is appropriately supplied from the toner storage chamber to the developer storage chamber. The amount of toner replenished from the toner storage chamber to the developer storage chamber is adjusted according to the toner ratio of the developer on the developer transport roller (ratio M / N of the toner amount M to the carrier amount N). Thus, the toner ratio of the developer is stabilized. According to such a configuration, the developer carrier only needs to be accommodated in the developer accommodating chamber, and the amount of the carrier accommodated is small. Therefore, the developing device can be downsized.
JP-A-9-185247 JP 2001-201927 A

  However, since the developing device of Patent Document 2 has a small amount of carrier accommodation, the toner chargeability of the carrier tends to decrease due to adhesion of spent, and the life of the developing device may be shortened.

  Accordingly, an object of the present invention is to maintain the toner chargeability of the carrier of the two-component developer satisfactorily over a long period while reducing the size of the developing device.

In order to achieve this object, a developing device according to the present invention provides:
A developer including a toner and a carrier, wherein the toner and the carrier are charged with the first polarity by frictional contact with each other and the carrier is charged with a second polarity different from the first polarity; ,
A developer carrying member carrying the developer;
A toner carrier that is disposed opposite to the developer carrier through a supply and recovery region and carries toner supplied from the developer carrier in the supply and recovery region;
A developer containing chamber disposed facing a part of the outer peripheral surface of the developer carrying member and containing the developer;
A toner storage chamber for storing the toner for replenishing the developer storage chamber;
The amount of toner replenished from the toner containing chamber to the developer containing chamber through the toner replenishing port facing the outer peripheral surface of the developer carrying member so as to partition the toner containing chamber from the developer containing chamber. A wall portion arranged to be adjusted according to a change in the amount of toner on the developer carrier,
A developing device that visualizes an electrostatic latent image on an electrostatic latent image carrier using the developer,
In addition to the toner and the carrier, the developer includes charged particles that are detachably held on the surface of the toner.
The charged particles are particles that, when separated from the surface of the toner and held on the surface of the carrier, charge the toner to the first polarity by frictional contact with the toner,
A first electric field is formed between the toner carrier and the electrostatic latent image carrier to move the toner held by the toner carrier to the electrostatic latent image of the electrostatic latent image carrier. First electric field forming means to
The toner in the developer held by the developer carrier is moved to the toner carrier, and at least some of the charged particles held on the surface of the toner in the developer are separated from the toner to The apparatus further comprises second electric field forming means for forming a second electric field to be held on the surface of the carrier between the developer carrying member and the toner carrying member.

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

  According to the present invention, the second electric field is formed in the supply / recovery region between the developer carrier and the toner carrier while reducing the size of the developing device by reducing the amount of carriers accommodated. By holding charged particles in the carrier, the toner chargeability of the carrier can be maintained well over a long period of time. Specifically, when the developer on the developer carrying member is transported to the supply and recovery region, it is removably held on the toner surface by the action of the second electric field formed by the second electric field forming means. At least some of the charged particles are separated from the toner and held on the surface of the carrier on the developer carrying member, so that the toner chargeability of the carrier is well maintained over a long period of time. As a result, the toner in the developer storage chamber maintains a stable charge amount by frictional contact with the charged particles held on the carrier. Therefore, a developing device and an image forming apparatus incorporating the present invention can form a high-quality image over a long period of time.

  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, but the portion where the potential is attenuated is the electrostatic latent image non-image portion, A portion that substantially maintains the charged potential may be used as the electrostatic latent 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.

  As a material of the developing roller 48, for example, a metal material such as aluminum is used. When aluminum is used as the material of the developing roller 48, it is preferable to perform a surface treatment. Further, as the material of the developing roller 48, a surface of a conductive base material such as aluminum coated with resin or rubber may be used. In this case, examples of the resin coated on the surface of the conductive substrate include polyester resin, polycarbonate resin, acrylic resin, polyethylene resin, polypropylene resin, urethane resin, polyamide resin, polyimide resin, polysulfone resin, and polyether ketone resin. , Vinyl chloride resin, vinyl acetate resin, silicone resin or fluororesin. On the other hand, examples of the rubber coated on the surface of the conductive substrate include silicone rubber, urethane rubber, nitrile rubber, natural rubber, and isoprene rubber. Moreover, when using the thing which coat | covered resin or rubber | gum on the surface of the electroconductive base material as a material of the developing roller 48, you may add a electrically conductive agent to a coating layer. In this case, as the conductive agent, for example, an electronic conductive agent or an ionic conductive agent is used. Examples of the electronic conductive agent include, but are not limited to, carbon black such as ketjen black, acetylene black or furnace black, metal powder, or metal oxide fine particles. On the other hand, examples of the ionic conductive agent include, but are not limited to, cationic compounds such as quaternary ammonium salts, amphoteric compounds or ionic polymer materials.

  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 that is fixed so as not to rotate, 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 sleeve 60. In the embodiment, the plurality of magnetic poles are a magnetic pole S1 facing the upper inner peripheral surface portion of the sleeve 60 in the vicinity of the regulating plate 62, and a magnetic pole facing the left inner peripheral surface portion of the sleeve 60 in the vicinity of the supply / recovery gap 56. N1, a magnetic pole S2 facing the lower inner peripheral surface portion of the sleeve 60, and a magnetic pole N2 facing the right inner peripheral surface portion of the sleeve 60.

  A developer storage chamber 66 that stores the developer is formed adjacent to the transport roller 54. The developer storage chamber 66 is disposed so as to face a part of the outer peripheral surface of the transport roller 54, specifically, the upper right portion of the outer peripheral surface of the transport roller 54.

  A toner storage chamber 68 for storing developer toner is formed behind the developer storage chamber 66. The toner storage chamber 68 is rotatably provided with a supply member 82 for supplying toner stored in the toner storage chamber 68 to the developer storage chamber 66. When the replenishing member 82 rotates clockwise, the toner in the toner storage chamber 68 is conveyed toward a toner replenishing port 76 described later, and is replenished to the developer storage chamber 66 through the toner replenishing port 76.

  The toner replenishing port 76 is provided in a wall portion 70 disposed so as to partition the toner storage chamber 68 and the developer storage chamber 66. The wall portion 70 includes a vertical portion 72 that hangs down from the ceiling portion of the housing 42, and a horizontal portion 74 that extends substantially horizontally from the lower end portion of the vertical portion 72 toward the transport roller 54. The horizontal portion 74 is disposed at a position facing the magnetic pole N <b> 2 of the transport roller 54. A gap having a predetermined interval is formed between the front end of the horizontal portion 74 and the outer peripheral surface of the conveying roller 54, and this gap constitutes a toner supply port 76. Thus, the toner supply port 76 is formed along the longitudinal direction of the transport roller 54 at a position facing the outer peripheral surface of the transport roller 54.

  At the toner replenishing port 76, the developer carried on the transport roller 54 is present. At the toner supply port 76, the toner supplied from the toner storage chamber 68 to the developer storage chamber 66 passes through the toner gap on the transport roller 54. Therefore, the smaller the amount of developer on the transport roller 54 at the toner replenishing port 76, the larger the amount of toner replenished from the toner storage chamber 68 to the developer storage chamber 66. Since the developer carrier is hardly consumed by the development, and the carrier amount on the transport roller 54 becomes substantially constant, the amount of developer on the transport roller 54 increases as the toner amount of the developer increases. Become. Therefore, the amount of toner replenished from the toner storage chamber 68 to the developer storage chamber 66 increases as the toner amount on the transport roller 54 decreases, and decreases as the toner amount on the transport roller 54 increases. In this way, the amount of toner replenished from the toner storage chamber 68 to the developer storage chamber 66 is adjusted in accordance with the toner amount of the developer on the transport roller 54, so that the developer in the developer storage chamber 66 is adjusted. The toner ratio (the ratio M / N of the toner amount M to the carrier amount N) is maintained substantially constant.

  In this manner, in the developing device 34, the internal space of the housing 42 is divided into the developer storage chamber 66 and the toner storage chamber 68, and the developer carrier is stored only in the developer storage chamber 66. The capacity can be reduced. Therefore, the developing device 34 can be downsized as compared with the configuration in which the carrier is accommodated in the entire housing 42.

  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 replenishment member 82 rotates in the direction of arrow 84. Thus, the toner stored in the toner storage chamber 68 is conveyed toward the toner supply port 76 by the supply member 82, and an appropriate amount of toner is supplied to the developer storage chamber 66. In the developer accommodating chamber 66, the toner and the carrier contained in the developer are brought into frictional contact with each other by the convection of the developer, and are charged to opposite polarities. In the embodiment, it is assumed that the carrier is positively charged and the toner is negatively charged. As shown in FIG. 2, since the carrier 4 is considerably larger than the toner 6, the toner 6 charged to the negative polarity around the carrier 4 charged to the positive polarity mainly based on the electrical attraction force of both. It is attached.

  Returning to FIG. 1, the developer in the developer storage chamber 66 is held on the outer peripheral surface of the sleeve 60 of the transport roller 54 by the magnetic force of the magnet body 58 of the transport roller 54. The developer held on the sleeve 60 forms 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 that is held on the magnetic pole S <b> 1 in the area facing the restriction plate 62 (restriction area 86) is restricted by the restriction plate 62 to a predetermined amount by the restriction plate 64. 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. Thus, the toner 6 adhering to the carrier 4 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 4 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. The developer that has passed through the supply / recovery region 88 is held by the magnetic force of the magnet body 58, and when the sleeve 60 rotates, it passes through the opposing portion of the magnetic pole S2 and the opposing portion of the magnetic pole N2 and reaches the developer containing chamber 66 again. The developer containing an appropriate amount of toner is held in the sleeve 60 again in the developer storage chamber 66. As a result, even when toner is consumed during development, the toner ratio of the developer on the transport roller 54 is maintained substantially constant.

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 6 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 the electrostatic latent image portion. The latent image is visualized as a developer image.

  FIG. 10 shows a developing device 234 according to another embodiment. In the developing device 234 shown in FIG. 10, a compression member (corresponding to a compression unit in claims) 98 that compresses the developer on the conveyance roller 54 is disposed opposite to the outer peripheral surface of the conveyance roller 54. Specifically, the compression member 98 faces a position downstream of the supply / recovery region 88 in the rotation direction of the transport roller 54 and upstream of the toner supply port 76, more specifically, the magnetic pole S 2 of the transport roller 54. It is provided in the position to do.

  The compression member 98 is a belt-like member that extends in the central axis direction of the transport roller 54. One end of the compression member 98 in the width direction (hereinafter referred to as “base end”) is fixed to the inner peripheral surface of the housing 42, and the other end in the width direction (hereinafter referred to as “tip end”) is a free end. The compression member 98 is disposed so as to gradually approach the outer peripheral surface of the transport roller 54 from the proximal end toward the distal end.

  The distance between the inner peripheral surface of the housing portion located below the transport roller 54 and the outer peripheral surface of the transport roller 54 is, for example, 1 mm, and the distance between the tip of the compression member 98 and the outer peripheral surface of the transport roller 54 is, for example, 0. .2 mm. On the other hand, when it is assumed that the compression member 98 is not provided, the layer thickness of the developer carried on the lower outer peripheral surface of the conveyance roller 54 is, for example, 0.4 mm. Therefore, the developer on the transport roller 54 is compressed by the compression member 98 until the layer thickness is reduced to about half when passing through the portion facing the tip of the compression member 98. At this time, the load that the developer on the transport roller 54 receives from the compression member 98 (the load per unit length in the longitudinal direction of the transport roller 54) is, for example, 7 N / m.

  As described above, the developer on the transport roller 54 passes through the supply / recovery region 88 and is then transported to the portion facing the front end of the compression member 98 and compressed by the compression member 98. The charged particles 8 separated from the toner 6 are efficiently held by the carrier 4 at a portion facing the compression member 98. Thereby, the toner chargeability of the carrier 4 is maintained well, and the life of the developer 2 can be extended.

  The other configuration of the developing device 234 shown in FIG. 10 is the same as that of the developing device 34 shown in FIG. Further, in the embodiment shown in FIG. 10, the compression member 98 is configured by a belt-like member as described above, but the shape of the compression member 98 is not particularly limited in the present invention. Furthermore, in the embodiment shown in FIG. 10, the compression member 98 separate from the housing 42 is used as the compression unit that compresses the developer, but a compression unit integral with the housing 42 may be used.

[3. Electric field forming means]
In order to efficiently move the toner from the sleeve 60 of the conveying roller 54 to the developing roller 48 in the supply region 90, the developing roller 48 and the sleeve 60 are electrically connected to the electric field forming device 110. Specific examples of the power source are shown in FIGS.

The electric field forming device 110 shown in FIG. 4A includes a first power source 112 (corresponding to the first electric field forming means in the claims) connected to the developing roller 48 and a second power source 114 (corresponding to the first electric field forming means in the claims). (Corresponding to the second electric field forming means). The first power supply 112 includes a DC power supply 118 connected between the developing roller 48 and the ground 116, and a 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 roller 48. 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 (for example, −400 volts) is applied to the conveyance roller 54. As a result, in the supply region 90, the negatively charged toner 6 is electrically attracted from the sleeve 60 to the developing roller 48 under the action of a DC electric field formed between the developing roller 48 and the sleeve 60. Is done. At this time, the positively charged carrier 4 is not attracted to the developing roller 48 from the sleeve 60. In the developing area 96, the negative toner held on the developing roller 48 is, as shown in FIG. 4B, the developing roller 48 (V _DC1 : −200 volts) and the electrostatic latent image portion (V _L :−). It adheres to the electrostatic latent image portion based on the potential difference of 80 volts). At this time, the negative polarity toner adheres to the electrostatic latent image non-image portion due to a potential difference between the developing roller 48 (V _DC1 : −200 volts) and the electrostatic latent image non-image portion (V _H : −600 volts). There is nothing.

In the electric field forming device 122 shown in FIG. 5A, the first power supply 124 has a DC power supply 128 connected between the developing roller 48 and the ground 126, like the power supply in FIG. The first direct current voltage V _DC1 (for example, −200 volts) having the same polarity as is applied to the developing roller 48. The second power source 130 includes a DC power source 132 and an AC power source 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. 5B, 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 region 90, the negatively charged toner 6 is electrically transferred from the sleeve 60 to the developing roller 48 under the action of a pulsating electric field formed between the developing roller 48 and the sleeve 60. Sucked. 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 roller 48. In the developing region 96, the negative toner held on the developing roller 48 is caused by a potential difference between the developing roller 48 (V _DC1 : −200 volts) and the electrostatic latent image portion (V _L : −80 volts). Based on the electrostatic latent image portion.

In the electric field forming device 136 shown in FIG. 6A, the first power source 138 includes a DC power source 142 and an AC power source 144 between the developing roller 48 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 developing roller 48. 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 developing roller 48 and the ground 140. The second power source 146 includes a DC power source 150 connected between the terminal 148 between the developing roller 48 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, whereby the sleeve 60 is biased to the negative polarity with respect to the developing roller 48. (See FIG. 6B). Accordingly, in the supply region 90, the negatively charged toner 6 is electrically attracted from the sleeve 60 to the developing roller 48 due to the action of the pulsating electric field formed between the developing roller 48 and the sleeve 60. Is done. In the developing region 96, the negative toner on the developing roller 48 is statically charged based on the potential difference between the developing roller 48 (V _DC1 : −200 volts) and the electrostatic latent image portion (V _L : −80 volts). It adheres to the electrostatic latent image portion.

A power source 152 shown in FIG. 7 is obtained by adding AC electric field forming devices 154 and 156 to the first power source 112 and the second power source 114, respectively, in the power source of the embodiment shown in FIG. 4A. The output voltages of the AC electric field forming devices 154 and 156 are V _AC1 and V _AC2 . The voltages V _AC1 and V _AC2 may be the same or different. An electric field forming device 158 shown in FIG. 8 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. 4A. The output voltage of the AC power supply 160 is _{V AC.} Similarly to the power sources 110, 122, and 136, the electric field forming devices 152 and 158 of these forms are also subjected to a pulsating electric field formed between the developing roller 48 and the sleeve 60, and have a negative polarity in the supply region 90. The toner 6 charged in the negative direction is supplied from the sleeve 60 to the developing roller 48, and in the developing region 96, the toner 6 charged negatively is supplied from the developing roller 48 to the electrostatic latent image portion (V _L : −80 volts). Is supplied to the electrostatic latent image portion.

[4. Developer)
In general, in a two-component developer containing toner and carrier as main components, dirt (spent) is generated by the toner adhering to the surface of the carrier, and this reduces the life of the carrier. In order to solve this problem, in the present invention, charged particles (implant particles) are added as a third component to the two-component developer.

  2 and FIG. 3, the image forming apparatus and the developing apparatus according to the present invention use the toner 6 and the carrier 4 in addition to the toner 6 by the frictional contact with the toner 6 with a normal polarity (implementation). It includes charged particles 8 having a diameter smaller than that of the toner 6, which are negatively charged in the form. In the embodiment, the charged particles 8 are accommodated in the toner accommodating chamber 68 while being detachably held on the outer peripheral surface of the toner 6, and are supplied together with the toner 6 from the toner accommodating chamber 68 to the developer accommodating chamber 66.

  At the time of image formation, the charged particles 8 are supplied together with the toner 6 to the developer storage chamber 66, and then held in the sleeve 60 together with the toner 6 and the carrier 4, and move in the regulation area 86 and the supply / recovery area 88. In this conveyance process, the charged particles 8 held on the surface of the toner 6 and charged to the positive polarity are placed in the electric field of the supply / recovery region 88, which is opposite to the electric force acting on the toner 6. The toner 6 is detached from the outer peripheral surface of the toner 6 by receiving the electric force in the direction. The separated charged particles 8 are held or driven on the outer peripheral surface of the carrier 4 by stress acting between the separated charged particles 8 and the carrier 4. As shown in FIG. 3, when a part or the whole of the outer peripheral surface of the carrier 4 is covered with the spent 10, the charged particles 8 are driven into the spent 10. The charged particles 8 held or driven on the outer peripheral surface of the carrier 4 are charged to a polarity opposite to that of the toner 6 by frictional contact with the toner 6. In the embodiment, since the toner 6 is charged to a negative polarity, the charged particles 8 are charged to a positive polarity. As a result, the carrier 4 into which the charged particles 8 are implanted maintains the same chargeability as the state without the spent 10 even if at least a part of the outer peripheral surface thereof is covered with the spent 10, and the toner 6 is preliminarily provided. Charged to the polarity.

  As described above, the charged particles 8 are charged with a polarity opposite to that of the toner 6. Therefore, as shown in FIG. 9, in the supply / recovery region 88, the toner 6 moves from the sleeve 60 to the developing roller 48 based on the electric field formed between the developing roller 48 and the sleeve 60. Further, the charged particles 8 separated from the toner 6 are quickly held on the carrier surface of the developer that is relatively carrier-rich by the toner 6 being taken away in the supply region 90 and supplied to the developing roller 48 together with the toner 6. Even if not supplied or supplied to the developing roller 6, the amount is extremely small.

  By the way, in the developing device 34 configured to accommodate the carrier 4 only in the developer accommodating chamber 66 as described above, the toner chargeability of the carrier 4 is likely to decrease because the amount of the carrier 4 is small. However, since all or part of the charged particles 8 are held on the surface of the carrier 4 in the supply / recovery region 88 during development, the toner chargeability of the carrier 4 can be maintained well, and the life of the developer can be maintained. Can be lengthened.

  In the embodiment, the toner 6 is charged to a negative polarity and the carrier 4 is charged to a positive polarity by frictional contact between the toner 6 and the carrier 4. Further, the charged particles 8 are charged negatively by contact with the toner 6, and the charged particles 8 are charged positively. The chargeability of the toner, carrier, and charged particles used in the present invention is not limited to such a combination. Specifically, the toner 6 is charged positively by the frictional contact between the toner 6 and the carrier 4, the carrier 4 is charged negatively, and the charged particles 8 are charged positively by the contact with the toner 6. A combination in which the charged particles 8 are negatively charged is also conceivable.

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

[Charged particles]
The charged particles suitably used are appropriately selected according to the charging polarity of the toner. The number average particle diameter of the charged particles is, for example, 100 to 1000 nm. When using toner that is negatively charged by frictional contact with the carrier, charged particles are fine particles that are positively charged by contact with the toner. Such fine particles include, for example, inorganic fine particles such as strontium titanate, barium titanate, calcium titanate, and alumina, thermoplastic resins such as acrylic resin, benzoguanamine resin, nylon resin, polyimide resin, and polyamide resin, or thermosetting. Can be made of resin. The resin constituting the fine particles may contain a positive charge control agent that is positively charged by contact with the toner. As the positive charge control agent, for example, nigrosine dye, quaternary ammonium salt and the like can be used. The charged particles may be composed of a copolymer of nitrogen-containing monomers. Examples of the nitrogen-containing monomer include 2-dimethylaminoethyl acrylate, 2-diethylaminoethyl acrylate, 2-dimethylaminoethyl methacrylate, 2-diethylaminoethyl methacrylate, vinyl pyridine, N-vinyl carbazole, and vinyl imidazole. Can be used.

  In the case of a toner that is positively charged by frictional contact with the carrier, fine particles that are negatively charged by contact with the toner are used as the charged particles. Examples of such fine particles include inorganic fine particles such as silica and titanium oxide, and fine particles composed of a thermoplastic resin or a thermosetting resin such as a fluororesin, a polyolefin resin, a silicone resin, and a polyester resin. . A negative charge control agent that is negatively charged by contact with the toner may be contained in the resin constituting the charged particles. Examples of negative charge control agents include salicylic acid-based and naphthol-based chromium complexes, aluminum complexes, iron complexes, and zinc complexes. The charged particles may be a copolymer of a fluorine-containing acrylic monomer or a fluorine-containing methacrylic monomer.

  In order to control the chargeability and hydrophobicity of the charged particles, the surface of the inorganic fine particles may be surface-treated with a silane coupling agent, a titanium coupling agent, silicone oil, or the like. In particular, when imparting positive electrode chargeability to inorganic fine particles, it is preferable to surface-treat with an amino group-containing coupling agent. When imparting negative chargeability to the fine particles, it is preferable to surface-treat with a fluorine coupling agent.

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

  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, alkylsalicylic acid metal compounds, and calixarene 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, silica, titanium oxide, aluminum oxide, or the like 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 10 to 100 nm.

[Carrier]
As the carrier, a known carrier that has been generally used can be used. For example, a binder type carrier or a coat type carrier is 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 by 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. The toner ratio is preferably 3 to 50% by weight, more preferably 6 to 30% by weight based on the total amount of the toner and the carrier. preferable.

[Experiment A]
The effect of charged particles was examined using an image forming apparatus provided with the developing device of FIG. For the experiment, a toner A carrying charged particles and a toner A ′ not carrying charged particles were prepared.

[Toner A ']
The production method of the toner A ′ is as follows. To 100 parts by weight of a toner base material having a volume average particle diameter of about 6.5 μm prepared by a wet granulation method, 0.2 parts by weight of a plurality of additives-first hydrophobic silica and 0.2% of second hydrophobic silica are added. 5 parts by weight and 0.5 parts by weight of hydrophobic titanium oxide were added. Next, using a Henschel mixer manufactured by Mitsui Mining Co., Ltd., the toner base material to which the additive was added was agitated to cause the additive to adhere to the surface of the toner base material to obtain negatively charged toner A ′. The rotating speed of the mixer was 40 m / second, and the stirring time was 3 minutes. The first hydrophobic silica is obtained by surface-treating silica (# 130: manufactured by Nippon Aerosil Co., Ltd.) having a number average primary particle size of 16 nm with a hydrophobizing agent hexamethyldisilazane (HMDS). The second hydrophobic silica is obtained by surface-treating silica (# 90: manufactured by Nippon Aerosil Co., Ltd.) having a solid average primary particle size of 20 nm with HMDS. The hydrophobic titanium oxide is obtained by surface-treating anatase-type titanium oxide having a number average primary particle size of 30 nm with a hydrophobizing agent, isobutyltrimethoxysilane, in an aqueous wet environment.

[Toner A]
The manufacturing method of the toner A is as follows. To toner A ′, strontium titanate having a number average particle diameter of 350 nm was added as charged particles. The amount of charged particles added was 2 parts by weight with respect to 100 parts by weight of toner base material particles contained in toner A ′. Next, the toner A ′ to which charged particles were added was stirred with a Henschel mixer manufactured by Mitsui Mining Co., Ltd., and charged particles were adhered to the surface of the toner to obtain toner A. The rotating speed of the mixer was 40 m / second, and the stirring time was 3 minutes.

[Carrier]
The carrier used for the experiment is a carrier for bizhub C350 manufactured by Konica Minolta Business Technologies. This carrier is a coated carrier in which carrier core particles made of a magnetic material are coated with an acrylic resin.

[Example 1]
As the developing device, a developing device having the form shown in FIG. 1 was used. As the developer, the above-described carrier and toner A were used. The toner ratio in the developer was adjusted to 8%. The toner ratio is a ratio of the total weight of the toner and the additive containing charged particles to the total weight of the developer. The electric field forming apparatus employs the form shown in FIG. 8, and a DC voltage V _{DC2 of} −400 volts is applied to the conveying roller, and an AC voltage of DC voltage V _{DC1 of} −300 volts is applied to the developing roller. AC voltage frequency: 2 kHz, the amplitude _V P-P: 1,400 volts, minus the duty ratio (toner collecting duty ratio): 40%, plus a duty ratio (toner supply duty ratio): was 60% of the rectangular wave (See FIG. 11). Therefore, the supply potential difference (toner supply voltage) for biasing the negatively charged toner from the sleeve to the developing roller is 800 volts, and the recovery voltage difference (toner recovery voltage) for biasing the toner from the developing roller to the sleeve is 600 volts.

As the developing roller, an aluminum roller whose surface was anodized was used. The supply / recovery gap between the developing roller and the sleeve was set to 0.3 mm. As a result, the electric field supplied to the toner formed between the developing roller and the sleeve was 2.7 × 10 ⁶ V / m (= 800 V / 0.3 mm). The regulation gap between the regulation plate and the sleeve was set to 0.35 to 0.5 mm so that the magnetic brush on the sleeve was in contact with the outer peripheral surface of the developing roller. The developing roller and the sleeve rotate in the same direction so that the developer transport direction on the sleeve and the toner on the developing roller move in the opposite directions in the supply and recovery area. The charged potential of the photosensitive member was −550 volts, and the potential of the electrostatic latent image portion formed on the photosensitive member was −60 volts. The developing gap between the photoconductor and the developing roller was set to 0.15 mm.

  The gap between the horizontal portion of the wall portion and the sleeve was set to 0.3 mm. Thereby, when the toner ratio of the developer on the sleeve is 8% or more, the gap between the horizontal portion of the wall portion and the sleeve is sealed by the developer on the sleeve, and the toner storage chamber is transferred to the developer storage chamber. The toner is not replenished. On the other hand, when the toner ratio of the developer is smaller than 8%, a gap is generated in the gap between the horizontal portion of the wall portion and the sleeve because the volume of the developer on the sleeve passing through the gap is reduced. The toner is supplied from the toner storage chamber to the developer storage chamber. When the toner is replenished, the toner ratio of the developer on the sleeve increases, and when the toner ratio reaches 8% again, the toner replenishment is stopped. In this way, the toner ratio of the developer on the sleeve is always maintained at about 8%.

[Comparative example]
As the developer, the above carrier and toner A ′ were used. Other conditions are the same as those in the first embodiment.

[Evaluation]
Using an image forming apparatus modified from the bizhub C350 copier manufactured by Konica Minolta Business Technologies, 100,000 original images with an image area ratio of 5% were printed under a plurality of conditions. The developer in the developing device was sampled every 10,000 printed sheets, and the toner charge amount was measured. The results are shown in FIG. As is apparent from this figure, in Example 1, the toner charge amount was maintained at a substantially constant value regardless of the increase in the number of printed sheets. On the other hand, in the comparative example, the toner charge amount decreased as the number of printed sheets increased.

[Conclusion]
As described above, in the developing device, charged particles that are charged with a polarity opposite to that of the toner adhere to the surface of the carrier, thereby compensating for a decrease in the ability of the carrier to charge the toner and charging the toner for a long time. It was found that the amount was kept at the required value.

[Experiment B]
Using the toner A used in Example 1 and the developing device of FIG. 1, the intensity of the electric field acting on the developer is changed between the sleeve and the developing roller, and an image with an image area ratio of 5% is 50,000. After sheet printing, the amount of decrease in the toner charge amount of the developer carried on the surface of the developing roller was measured. Tables 1 and 2 show the experimental conditions and results.

As can be seen from Table 1, in the case of a weak toner supply electric field of 1 × 10 ⁶ V / m or less (Experiment 1 and 7) in the supply and recovery region, a relatively large reduction in charge amount was observed. However, even under such conditions, an image quality with no practical problem was obtained. Such a decrease in the charge amount is caused by the fact that the electric field for separating charged particles from the toner is weak so that it behaves together with the toner, the charged particle adhesion amount on the carrier surface is small, and sufficient toner charging performance cannot be obtained. It is thought that there is. Therefore, when a DC electric field is adopted, it is preferable to form a toner supply electric field of 1 × 10 ⁶ V / m or more in the supply and recovery area.

As is clear from the comparison between the results of Experiment 1 and Experiment 4, and the results of Experiment 8 and Experiment 9, when an oscillating electric field is applied to the supply and recovery region, even if the average electric field is equal to the DC electric field, It can be seen that high toner charging performance can be obtained. The reason is considered that the urging force in the opposite direction acts alternately on the toner and the charged particles due to the oscillating electric field, thereby effectively separating the charged particles from the toner. Therefore, it can be said that it is more preferable to form an oscillating electric field in the supply and recovery region than a direct current electric field. When using an oscillating electric field, it is considered that the toner supply electric field is preferably about 2.5 × 10 ⁶ V / m or more.

[Experiment C]
A plurality of toners B to F were prepared in addition to the toner A, and changes in the toner charge amount were examined. Toners B to F were obtained by adding charged particles made of strontium titanate having number average particle diameters of 210 nm, 140 nm, 70 nm, 850 nm, and 1,000 nm to toner A ′ and stirring them. The amount of charged particles added was 2 parts by weight with respect to 100 parts by weight of toner base material particles. Stirring was performed using a Henschel mixer for 3 minutes at a stirring speed of 40 m / sec. Other conditions are the same as those in the first embodiment.

  The prepared toners A to G are loaded into the developing device shown in FIG. 1, and 50,000 images with an image area ratio of 5% are printed. The toner held on the outer peripheral surface of the developing roller every 10,000 sheets The amount of charge was measured. The results are shown in the graph of FIG. As shown in this graph, the toners A, B, C, and E had almost no decrease in charge amount, but the toners D and F had a tendency to decrease in toner charge amount as the number of printed sheets increased. From the result, it is considered that when the number average particle diameter is small, the charged particles are difficult to separate from the toner, and as a result, the amount adhering to the carrier decreases. In addition, when the number average particle size is increased, it is considered that the chargeability of charged particles into the carrier is lowered, and the chargeability of the toner cannot be effectively exhibited. From these facts, it is considered that the particle size of the charged particles is preferably in the range of about 100 nm to about 850 nm.

[Experiment D]
A plurality of toners G to J were prepared in addition to the toner A, and changes in the toner charge amount were examined. Toners G to J are charged toner particles each composed of titanium oxide having a number average particle diameter of 150 nm, alumina having a number average particle diameter of 200 nm, barium titanate having a number average particle diameter of 500 nm, and melamine resin beads having a number average particle diameter of 200 nm. It was obtained by adding to and stirring. The amount of charged particles added was 2 parts by weight with respect to 100 parts by weight of toner base material particles. Stirring was performed using a Henschel mixer for 3 minutes at a stirring speed of 40 m / sec. Other conditions are the same as those in the first embodiment.

  The prepared toners A, G to J are loaded into the developing device shown in FIG. 1, and 50,000 images with an image area ratio of 5% are printed. Each 10,000 sheet is held on the outer peripheral surface of the developing roller. The charge amount of the toner was measured. The results are shown in the graph of FIG. As shown in this graph, there was almost no decrease in toner charge amount for toner A to which strontium titanate was added, toner I to which barium titanate was added, and toner G to which titanium oxide was added. For toner H to which alumina was added, the toner charge amount was somewhat reduced. For toner J to which melamine resin beads were added, the toner charge amount decreased most.

  Thus, it is considered that the cause of the difference in the charge amount due to the difference in the materials constituting the charged particles is the saturation charge amount of the material itself. In other words, when the amount of charge that the particle can have is small, the particle is saturated early, and the saturated charge amount is not enough to charge the toner to the required level, but when the particle can have a large amount of charge, It is considered that the particles charged to the saturation state can charge the toner to a necessary level.

The amount of charge that a particle can have is proportional to the relative dielectric constant of the material that makes it up. The relative permittivity of the charged particle material described above is shown in Table 3 below together with the evaluation result of the chargeability obtained in Experiment E. From this table, it can be seen that the relative dielectric constant of the charged particles added to the toner is preferably 8.5 or more.

[Experiment E]
For Example 2 below, the effect of charged particles was examined.

[Example 2]
As the developing device, a developing device having the form shown in FIG. 10 was used. As the developer, the above-described carrier and toner K described later were used. The gap between the inner surface of the housing portion located on the lower side of the sleeve and the outer peripheral surface of the sleeve was 1 mm, and the gap between the tip of the compression member and the outer peripheral surface of the sleeve was 0.2 mm. As a result, the developer (layer thickness 0.4 mm) on the sleeve passing through the portion facing the compression member is compressed by the compression member.

  As in the toner A, the toner K was obtained by adding charged particles made of strontium titanate having a number average particle diameter of 350 nm to the toner A ′ and stirring. However, unlike the toner A, the amount of charged particles added was 1 part by weight with respect to 100 parts by weight of the toner base material particles. Stirring was performed using a Henschel mixer for 3 minutes at a stirring speed of 40 m / sec. Other conditions are the same as those in the first embodiment.

  The prepared toner K is loaded into the developing device shown in FIG. 10, and 50,000 images with an image area ratio of 5% are printed. The amount of charge of toner held on the outer peripheral surface of the developing roller every 10,000 sheets Was measured. The results are shown in the graph of FIG. As shown in this graph, in Example 2, as in Example 1, there was almost no decrease in the charge amount. From this, it has been found that when a compression member for compressing the developer on the sleeve is provided, the toner chargeability of the carrier can be maintained for a long time even if the amount of charged particles added is relatively small. This is considered because the developer on the sleeve that has become carrier-rich due to the consumption of toner in the supply and recovery area is compressed by the compression member, so that charged particles are efficiently attached to the carrier. .

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 typically the state in which the toner which hold | maintained the charged particle has adhered to the surface of a carrier. The figure which shows typically the state by which the charged particle was bombarded on the surface of the carrier to which the spent adhered. 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. 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 the relationship between the voltage supplied to the sleeve and the image development sleeve from the electric field formation apparatus shown to FIG. 6A. The figure which shows other embodiment of an electric field formation apparatus. The figure which shows other embodiment of an electric field formation apparatus. The figure which shows typically the motion of the toner and charged particle in a supply collection area | region. FIG. 3 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 another embodiment. FIG. 3 is a diagram illustrating a waveform of a voltage supplied to a sleeve and a developing roller in Embodiment 1. 6 is a graph showing the relationship between the number of printed sheets and the toner charge amount. 6 is a graph showing the relationship between the number of printed sheets and the toner charge amount. 6 is a graph showing the relationship between the number of printed sheets and the toner charge amount. 6 is a graph showing the relationship between the number of printed sheets and the toner charge amount.

Explanation of symbols

1: image forming apparatus, 2: developer, 4: carrier, 6: toner, 8: charged particles, 10: spent, 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: 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 accommodating chamber, 68: toner accommodating chamber, 70: wall portion, 72: vertical portion, 74: horizontal portion, 76: toner supply port 86: Restriction area, 88: Supply / recovery area, 90: Supply area, 92: Collection area, 98: Compression member, 110: Electric field forming device, 112: First power supply, 114: Second power supply, 116: Ground, 118: DC power supply, 120: DC power supply, 122: Electric field forming device, 124: First power supply, 126: Ground, 128: DC power supply, 130: Second power supply, 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 supply, 152: Electric field forming device, 154: AC power source, 156: AC power source, 158: Electric field forming device, 160: AC power source.

Claims (7)

A developer including a toner and a carrier, wherein the toner and the carrier are charged with the first polarity by frictional contact with each other and the carrier is charged with a second polarity different from the first polarity; ,
A developer carrying member carrying the developer;
A toner carrier that is disposed opposite to the developer carrier through a supply and recovery region and carries toner supplied from the developer carrier in the supply and recovery region;
A developer containing chamber disposed facing a part of the outer peripheral surface of the developer carrying member and containing the developer;
A toner storage chamber for storing the toner for replenishing the developer storage chamber;
The amount of toner replenished from the toner containing chamber to the developer containing chamber through the toner replenishing port facing the outer peripheral surface of the developer carrying member so as to partition the toner containing chamber from the developer containing chamber. A wall portion arranged to be adjusted according to a change in the amount of toner on the developer carrier,
A developing device that visualizes an electrostatic latent image on an electrostatic latent image carrier using the developer,
In addition to the toner and the carrier, the developer includes charged particles that are detachably held on the surface of the toner.
The charged particles are particles that, when separated from the surface of the toner and held on the surface of the carrier, charge the toner to the first polarity by frictional contact with the toner,
A first electric field is formed between the toner carrier and the electrostatic latent image carrier to move the toner held by the toner carrier to the electrostatic latent image of the electrostatic latent image carrier. First electric field forming means to
The toner in the developer held by the developer carrier is moved to the toner carrier, and at least some of the charged particles held on the surface of the toner in the developer are separated from the toner to A developing apparatus, further comprising: a second electric field forming unit that forms a second electric field to be held on the surface of the carrier between the developer carrying member and the toner carrying member.   A compression unit that compresses the developer on the developer carrier at a position downstream of the supply and recovery area and upstream of the toner supply port in the moving direction of the developer on the developer carrier. The developing device according to claim 1, wherein the developing device is disposed so as to face the outer peripheral surface of the developer carrying member.   3. The developing device according to claim 1, wherein the second electric field forming unit forms an oscillating electric field that moves the toner from the developer carrying member toward the toner carrying member. The developing device according to claim 3, wherein the second electric field formed in the supply and recovery region by the second electric field forming unit is 2.5 × 10 ⁶ V / m or more.   5. The developing device according to claim 1, wherein the number average particle diameter of the charged particles is in the range of about 100 nm to about 850 nm.   The developing device according to claim 1, wherein a relative dielectric constant of the charged particles is 8.5 or more.   An image forming apparatus comprising the developing device according to claim 1.

Images