JP2009198677A - Developing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device capable of improving the recoverability of toner remaining on a developing roller after development, thereby preventing the occurrence of image memory, and to provide an image forming apparatus that has the developing device. <P>SOLUTION: The developing device 34 develops an image in such a manner that developer 2 containing toner and carrier is conveyed while held on the peripheral face of a conveying roller 54, only toner in the developer held on the conveying roller by a first electric field generating means is moved to the developing roller 48, and the toner held on the developing roller by a second electric field generating means is moved to an electrostatic latent image on a photoreceptor 12. The developing device 34 has a conductive brush 47 used as a toner dispersion member that disperses toner remaining on the developing roller after the development. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electrophotographic image forming apparatus such as a copying machine, a printer, a facsimile, or a composite machine thereof, and a developing device used in the image forming apparatus.

  Conventionally, in an image forming apparatus using an electrophotographic method, as a developing method for developing an electrostatic latent image formed on an image carrier, a one-component developing method using only toner as a main component of a developer, and developing A two-component development system using a toner and a carrier as main components of the agent is known.

  In the one-component development method, generally, the toner is frictionally charged by passing the toner through a regulating portion between the toner carrying body and a regulating plate provided by pressing the toner carrying body, and a toner thin layer having a desired thickness is formed. Since it can be held on the outer peripheral surface of the toner carrier, it is advantageous in terms of simplification of the configuration of the developing device, size reduction, and cost reduction. However, in the one-component development method, the deterioration of the toner is promoted by the strong stress received at the regulating portion, the toner charge amount tends to decrease with durability, and the surface of the regulating plate and the surface of the toner carrying member are not covered with the toner or other external additives. Contamination with the agent lowers the charge imparting property to the toner and causes a problem such as fogging, so that the life of the developing device becomes relatively short.

  On the other hand, the two-component development method is advantageous in terms of toner deterioration because the toner is charged by frictional contact by mixing and stirring with the carrier, so that the stress received by the toner is small. In addition, since the carrier, which is a charge imparting member to the toner, has a surface area larger than that of the toner particles, it is relatively resistant to contamination by toner and other external additives, and is advantageous in extending the life of the developer. It is. However, even in the two-component development method, the carrier is gradually contaminated with toner and other external additives due to long-term use, and the charge amount of the toner is lowered, which may cause problems such as fogging.

  As a developing method for solving the above-mentioned problems in the one-component developing method and the two-component developing method, for example, as disclosed in Patent Document 1, a two-component developer composed of a toner and a carrier is charged with toner by frictional contact. The developer is transported to a region facing the developing roller by rotation while being held in a magnetic brush state on the transport roller including the magnetic pole body, and is held by the transport roller by the action of the electric field formed in this region. A toner layer is formed on the developing roller by supplying only the toner from the existing developer to the developing roller, and the toner layer is conveyed to an area facing the image carrier by the rotation of the developing roller, and formed in this area A so-called hybrid development system that develops toner held on a developing roller by the action of an electric field by flying it onto an electrostatic latent image formed on an image carrier. It has been proposed.

According to the above hybrid development system, the toner is charged by frictional contact of the two-component developer, so that the deterioration of the toner is suppressed, a sufficient toner charge amount can be secured, and the toner from the conveying roller to the developing roller can be secured. Since the toner is supplied by an electric field, the toner charged with the reverse polarity is not supplied to the developing roller, so that the toner does not adhere to the non-image portion on the image carrier and the occurrence of fog is prevented. In addition, since only the toner is supplied to the developing roller, adhesion of the carrier to the image carrier is also prevented.
JP 2003-15380 A

  However, in the above hybrid development method, if the toner remaining on the developing roller without being subjected to development is not sufficiently separated and collected, the toner remains on the developing roller after development and the toner on the developing roller. There is a possibility that an image memory (or development history phenomenon) may occur due to a difference in toner amount or toner charge amount from a region where no toner remains. In the above hybrid development method, when toner remaining on the developing roller after development is collected on the transport roller, new toner is supplied from the transport roller to the developing roller in a region facing the developing roller and the transport roller. The occurrence of image memory can be more noticeable due to the difficulty in achieving both conflicting functions of collecting toner remaining on the developing roller after development to the transport roller.

  Accordingly, the present invention provides a developing device capable of improving the recoverability of toner remaining on the developing roller after development and suppressing the generation of an image memory in the hybrid developing device, and image formation provided with the developing device. An object is to provide an apparatus.

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 to a first polarity by frictional contact with each other and the carrier is charged to a second polarity different from the first polarity; ,
A conveyance roller that is driven to rotate and conveys the developer on the outer peripheral surface;
A developing roller which is opposed to the conveying roller via a first area and is opposed to the electrostatic latent image carrier via a second area and is driven to rotate;
A first electric field forming means for forming a first electric field between the conveying roller and the developing roller, and moving only the toner in the developer held by the conveying roller to the developing roller;
A second electric field is formed between the developing roller and the electrostatic latent image carrier, and the toner held on the developing roller is moved to the electrostatic latent image on the electrostatic latent image carrier to move the static electricity. A developing device comprising: a second electric field forming unit that develops the electrostatic latent image; and the toner remaining on the developing roller after the development is collected by the conveying roller.
A toner diffusing member provided to face the developing roller and diffusing the toner remaining on the developing roller;
It is characterized by that.

  According to the present invention, in the so-called hybrid developing device, the toner remaining on the developing roller after development is diffused by the toner diffusing member, so that the adhesive force of the toner remaining on the developing roller is reduced. As a result, the recoverability of the toner remaining on the developing roller can be improved, and the occurrence of image memory can be suppressed.

  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.

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

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

  When the image forming apparatus 1 having such a configuration forms an image, the photosensitive member 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 photoreceptor is exposed to image light 30 at the 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 developer used in the present embodiment is assumed to be charged with negative polarity of the toner and positive polarity of the carrier due to mutual frictional contact. However, the chargeability of the toner and carrier used in the present invention is not limited to such a combination, and a combination in which the toner is positively charged and the carrier is negatively charged by mutual frictional contact is also conceivable.

  The housing 42 includes an opening 44 that is open toward the photosensitive member 12, and a developing roller 48 that is a toner conveying member 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 the developing roller 48, for example, a conductive roller made of a metal such as aluminum or a coating on the outer peripheral surface which is the outermost surface layer portion of the conductive roller is used. Examples of the surface treatment include 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, and silicone resin. A resin coating such as a fluororesin, or a rubber coating such as silicone rubber, urethane rubber, nitrile rubber, natural rubber, or isoprene rubber is used, but is not limited thereto. Moreover, a conductive agent may be added to the inside or the surface of the coating. As the conductive agent, an electronic conductive agent or an ionic conductive agent can be used. Examples of the electronic conductive agent include, but are not limited to, carbon black particles such as ketjen black, acetylene black, and furnace black, metal powder, metal oxide fine particles, and the like. Examples of the ionic conductive agent include cationic compounds such as quaternary ammonium salts, amphoteric compounds, and other ionic polymer materials, but are not limited thereto.

  A separate space 52 is formed behind the developing roller 48. In the space 52, a transport roller 54 as a developer transport 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 transport roller 54. 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 two adjacent magnetic poles N2 and N3 of the same polarity facing the right inner peripheral surface portion of the sleeve 60.

  A developer stirring chamber 66 is formed behind the transport roller 54. The stirring chamber 66 includes a front chamber 68 formed in the vicinity of the transport roller 54 and a rear chamber 70 separated from the transport roller 54. A front screw 72 that is a pre-stirring and conveying member that conveys the developer while stirring the developer from the front surface to the back surface of the drawing is rotatably disposed in the front chamber 68, and the rear chamber 70 is rotated from the back surface to the front surface of the drawing. A rear screw 74 that is a rear stirring and conveying member that conveys 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 toner replenishing portion 98 is provided above the rear chamber 70, and the toner replenishing portion 98 has 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 a means (not shown) for measuring the mixing ratio of the toner 6 and the carrier accommodated in the housing 42, so that the toner 6 The chamber 70 is dropped and replenished.

  Further, the transport roller 54 and the developing roller 48 are electrically connected to the electric field forming device 110, respectively. As will be described later, the electric field forming device 110 has a region (supply region) 90 on the upstream side (supply region) 90 mainly in the rotation direction of the transport roller 54 in a region (supply / recovery region) 88 where the transport roller 54 and the developing roller 48 face each other. Thus, only the toner 6 in the developer 2 held by the conveyance roller 54 is moved to the development roller 48, and the downstream area (collection area) 92 in the supply and collection area 88 mainly in the rotation direction of the conveyance roller 54. Thus, a predetermined electric field is formed between the conveying roller 54 and the developing roller 48 so that the toner 6 remaining on the developing roller 48 after development is collected by the conveying roller 54.

  2 is a diagram illustrating a specific example of the electric field forming device 110, and FIG. 3 is a diagram illustrating a relationship between voltages supplied from the electric field forming device 110 illustrated in FIG. 2 to the transport roller 54 and the developing roller 48. . 2 includes a first power source 112 connected to the developing roller 48 and a second power source 114 connected to the transport roller 54.

The first power supply 112 has a DC power supply 118 and an AC power supply 160 connected in series between the developing roller 48 and the ground 116, and the DC power supply 118 has the same polarity as the charging polarity of the toner 6. 1, a DC voltage V _DC1 (for example, −300 volts) is applied to the developing roller 48, and the AC power supply 160 is connected to the AC voltage V _AC (amplitude V) between the developing roller 48 and the ground 116 as shown in FIG. _P-P is applied, for example, 1,500 volts). The second power source 114 has a DC power source 120 connected between the conveying roller 54 and the ground 116, and the DC power source 120 has the same polarity as the charging polarity of the toner 6 and is based on the first DC voltage. Also, a high-voltage second DC voltage V _DC2 (for example, −500 volts) is applied to the conveying roller 54.

As shown in FIG. 3, the DC voltage _V DC2 to the conveying roller 54: -500 V was applied, the DC voltage _V to the developing roller 48 DC1: applying a -300 V and an AC voltage _{V AC,} the AC voltage _{V AC} , Amplitude V _P−P : 1,500 volts, negative duty ratio (toner recovery duty ratio): 40%, positive duty ratio (toner supply duty ratio): 60%, the transport roller 54 and the developing roller An oscillating electric field (first electric field) is formed between the two and 48. Under the action of this oscillating electric field, in the supply region 90, the negatively charged toner 6 is electrically attracted from the transport roller 54 to the developing roller 48. At this time, the positively charged carrier is held by the conveyance roller 54 by the magnetic force of the fixed magnet body 58 inside the conveyance roller 54 and is not supplied to the developing roller 48. In the developing region 96, the negative toner held by the developing roller 48 is formed between the developing roller 48 (V _DC1 + V _AC ) and the electrostatic latent image portion (V _L : −80 volts). It adheres to the electrostatic latent image portion under the action of the oscillating electric field (second electric field). Here, the first power source 112 constitutes a second electric field forming unit, and the first power source 112 and the second power source 114 constitute a first electric field forming unit.

In the present embodiment, an example has as the oscillating voltage _V DC1 _{+ V AC} obtained by superimposing an AC voltage _{V AC} to a DC voltage _{V DC1} to the developing roller 48 is applied, applying a DC voltage _{V DC2} to the conveying roller 54 However, the present invention is not limited to this. By applying a DC voltage or an oscillating voltage to the developing roller 48 and applying a DC voltage or an oscillating voltage to the conveying roller 54, there are a total of four combinations including the above example. In these combinations, the electric field formed between the conveying roller 54 and the developing roller 48 may be an oscillating electric field and a direct current if the toner can be supplied from the conveying roller 54 to the developing roller 48 in the supply region 90. Any of the boundaries may be used.

  Further, the developing device 34 extends from a facing region (developing region 96) between the developing roller 48 and the photoreceptor 12 in a rotating direction of the developing roller 48 to a facing region (supply / recovery region 88) between the developing roller 48 and the conveying roller 54. A brush 47 serving as a toner diffusing member is provided at a position opposite to the developing roller 48 and diffuses the toner 6 remaining on the developing roller 48 after development. The brush 47 is configured by flocking a linear member made of, for example, Teflon around the cylindrical body, and a conductive brush in which carbon having conductivity is dispersed is used for the linear member, for example. The brush 47 is configured to be rotatable by a rotation drive mechanism (not shown) and to be reciprocated in the axial direction of the developing roller 48 by a reciprocation mechanism (not shown). The brush 47 is connected to a third power source 49 as bias applying means for applying a DC bias to the brush 47, and the third power source 49 can apply a predetermined DC bias to the brush 4. It can be done. The brush 47 is rotationally driven at a peripheral speed of ± 20% of the peripheral speed of the developing roller 48, the linear member has a linearity of 1 to 4 denier, and the linear member has a flocking density of 100 to 800 kF / square inch. Those are preferred. In addition to the Teflon, the linear member may be a negative charge type.

Next, the operation of the developing device 34 configured as described above will be described.
During image formation, the developing roller 48 and the sleeve 60 rotate in the directions of arrows 78 and 80, respectively, based on driving of a motor (not shown). The front screw 72 rotates in the direction of arrow 82 and the rear screw 74 rotates in the direction of arrow 84. Thereby, the developer 2 accommodated in the developer stirring chamber 66 is stirred while being circulated and conveyed through the front chamber 68 and the rear chamber 70. As a result, the toner and the carrier contained in the developer come into frictional contact with each other and are charged with opposite polarities. In the embodiment, the carrier is charged positively and the toner is negatively charged. The carrier particles are larger than the toner particles, and the negatively charged toner adheres to the periphery of the positively charged carrier mainly based on the electrical attractive 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 transport roller 54 is held on the transport roller 54, specifically the outer peripheral surface of the sleeve 60, near the magnetic pole N 3 by the magnetic force of the magnetic pole N 3. The developer 2 held by the sleeve 60 constitutes a magnetic brush along the magnetic field lines formed by the magnet body 58, and is conveyed in the counterclockwise direction based on the rotation of the sleeve 60. The amount of developer 2 held by the magnetic pole S <b> 1 in the area facing the restriction plate 62 (restriction area 86) is regulated by the restriction plate 62 to a predetermined amount. The developer 2 that has passed through the regulation gap 64 is conveyed to a region (supply / recovery region) 88 where the developing roller 48 and the conveying roller 54 are opposed to each other, where the magnetic pole N1 is opposed.

  As described above, in the supply / recovery area 88, the upstream area (supply area) 90 mainly in the rotation direction of the sleeve 60 is due to the presence of an electric field formed between the developing roller 48 and the transport roller 54. Only the toner 6 adhering to the carrier 4 is electrically supplied to the developing roller 48.

The toner 6 held on the developing roller 48 in the supply area 90 is conveyed counterclockwise with the rotation of the developing roller 48, and the electrostatic latent image image formed on the outer peripheral surface of the photoconductor 12 in the developing area 96. Adhere to the part. In the image forming apparatus 1, an electrostatic latent image in which the outer peripheral surface of the photoconductor 12 is given a predetermined negative potential V _H (for example, −600 volts) by the charging device 26 and the image light 30 is projected by the exposure device 28. The image portion is attenuated to a predetermined potential V _L (for example, −90 volts), and the electrostatic latent image non-image portion on which the image light 30 is not projected by the exposure device 28 substantially maintains the charged 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. In the development region 96, contact development in which the toner 6 on the developing roller 48 is in direct contact with the photoreceptor 12 may be used.

  On the other hand, the toner 6 remaining on the developing roller 48 after being developed without being subjected to development is conveyed in the direction indicated by the arrow 78 according to the rotation of the developing roller 48, and the rotation of the sleeve 60 mainly in the supply / recovery region 88. In a region (recovery region) 92 on the downstream side with respect to the direction, it is scraped off by a magnetic brush formed along the magnetic field lines of the magnetic pole N 1 and recovered by the transport roller 54. The developer 2 containing the toner 6 collected on the transport roller 54 is held by the magnetic force of the magnet body 58 and passes through the facing portion of the magnetic pole S2 along with the rotation of the transport roller 54, so that the facing region (release) of the magnetic poles N2 and N3. When the region 94) is reached, the repulsive magnetic field formed by the magnetic poles N2 and N3 is discharged from the outer peripheral surface of the transport roller 54 to the front chamber 68 and mixed with the developer 2 being transported through the front chamber 68.

  In the present embodiment, the toner 6 remaining on the developing roller 48 after development passes through a region where the developing roller 48 and the brush 47 are opposed to each other while being transported to the collecting region 92. When passing through the facing region, the toner 6 remaining on the developing roller 48 is diffused by, for example, a brush 47 that is rotationally driven in a direction indicated by an arrow 51.

  FIG. 4 is a view schematically showing the surface of the developing roller 48 before and after passing through the region facing the brush 47. FIG. 4A shows the region facing the brush 47 after passing through the developing region 96. FIG. The surface of the developing roller 48 before passing is shown, and FIG. 4B shows the state after the surface of the developing roller 48 shown in FIG. As described above, the toner 6 is held on the developing roller 48 at a portion corresponding to the image forming area in the supply area 90, and when the toner 6 held on the developing roller 48 passes the developing area 96, FIG. As shown in FIG. 4, the surface 130 of the developing roller 48 includes an area 131 where the toner 6 on the developing roller 48 is moved to the photosensitive member 12 corresponding to the electrostatic latent image portion of the photosensitive member 12, and the developing roller 48. The toner 6 corresponds to the non-image portion of the electrostatic latent image on the photoconductor 12 and has a region 132 that remains without being moved to the photoconductor 12.

  When the surface 130 of the developing roller 48 shown in FIG. 4A passes through the opposing area between the developing roller 48 and the brush 47 as the developing roller 48 rotates, it remains on the developing roller 48 due to the diffusing action of the brush 47. The toner 6 is diffused, and as shown in FIG. 4B, a region 133 in which the toner 6 remaining on the developing roller 48 is diffused is formed on the surface 130 of the developing roller 48.

  As described above, in the developing device 34 according to the present embodiment, the toner 6 remaining on the developing roller 48 after the development is diffused by the brush 47, and the adhesion force of the toner remaining on the developing roller 48 is reduced. As a result, when the toner 6 remaining on the developing roller is collected by the transport roller 54 in the collection area 92, the collection performance of the toner 6 can be improved, and the occurrence of image memory can be suppressed.

  Further, in the developing device 34, it is not necessary to provide a cleaning device for removing the toner 6 remaining on the developing roller 48 by collecting the toner 6 remaining on the developing roller 48 after the development by the transport roller 54. The developing device 34 can be downsized. When the toner 6 remaining on the developing roller 48 is removed using the cleaning device, and the removed toner 6 is returned to the developer stirring chamber 66 and used, the toner 6 is removed when the toner 6 is removed by the cleaning device. The toner 6 deteriorates due to strong stress. However, in the developing device 34 according to the present embodiment, the toner 6 remaining on the developing roller 48 after the development is collected by the transport roller 54, so that the toner is deteriorated. Can be suppressed.

[3. Developer)
Here, specific materials of the toner and carrier constituting the developer 2 and other particles contained in the developer 2 will be described.

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

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

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

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

  Examples of the binder resin used in the binder-type carrier include thermoplastic resins such as vinyl resins, polyester resins, nylon resins, polyolefin resins, and the like represented by polystyrene resins, and thermosetting resins such as phenol resins. The

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

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

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

[Charged particles]
The charged particles externally added to the toner are added so that the toner is charged to a predetermined polarity even if the chargeability of the carrier is lowered due to dirt (spent) formed by the toner adhering to the surface of the carrier. Fine particles that are charged with a reverse polarity to the toner are used.

  The charged particles preferably 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 are, for example, inorganic fine particles such as strontium titanate, calcium titanate, barium titanate, and alumina, thermoplastic resins such as acrylic resins, benzoguanamine resins, nylon resins, polyimide resins, polyamide resins, or thermosetting resins. 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 nitrogen-containing monomers. Examples of the material constituting the nitrogen-containing monomer include 2-dimethylaminoethyl acrylate, 2-diethylaminoethyl acrylate, 2-dimethylaminoethyl methacrylate, 2-diethylaminoethyl methacrylate, vinylpyridine, N-vinylcarbazole, There is vinylimidazole.

  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 made of thermoplastic resin or thermosetting resin such as fluororesin, polyolefin resin, silicone resin, and 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, silicon 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 group-containing coupling agent.

[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 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]
In addition, a fluidizing agent that promotes fluidization of the developer may be added. As the fluidizing agent, for example, inorganic fine particles such as silica, titanium oxide, and aluminum oxide, and resin fine particles such as acrylic resin, styrene resin, silicone resin, and fluorine resin can be used. In particular, it is preferable to use a material hydrophobized with a silane coupling agent, a titanium coupling agent, silicon oil or the like. The fluidizing agent is preferably added at a ratio of 0.1 to 5 parts by weight with respect to 100 parts by weight of the toner. The number average primary particle size of these additives is preferably 9 to 100 nm.

[4. Experiment)
Next, an experiment performed with the image forming apparatus 1 of the present embodiment will be described. In the experiment, the following toner and carrier were used to evaluate the image memory generation level and the toner deterioration level.

  The toner used in the experiment is composed of 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, 2 parts by weight of hydrophobic silica, 0.5 parts by weight of hydrophobic titanium oxide, and 2 parts by weight of strontium titanate were added. Next, using a Henschel mixer manufactured by Mitsui Kinzoku Mining Co., Ltd., the toner base material to which the additive was added was agitated to adhere the additive to the surface of the toner base material to obtain a negatively charged toner. 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 number 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. As the strontium titanate, one having a number average particle diameter of 350 nm having a polarity opposite to that of the toner was used.

  The carrier used in the experiment was a carrier for bizhub C350 manufactured by Konica Minolta Business Technologies, Inc., and had an average particle size of about 33 μm. This carrier is a coated carrier in which a carrier core particle made of a magnetic material is coated with a silicone resin.

  The developing device 34 shown in FIG. 1 was used, and 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 external additive containing charged particles to the total weight of the developer.

The electric field forming device 110 applies a DC voltage V _DC2 : −500 volts to the conveying roller 54, a DC voltage V _DC1 : −300 volts to the developing roller 48, a frequency: 2 kHz, and an amplitude V _P−P : 1,500. A rectangular wave-like vibration voltage (V _DC1 + V _AC ) on which an alternating voltage V _AC of 40%, plus duty ratio (toner supply duty ratio): 60% was superimposed was applied. Further, the supply / recovery gap at the closest portion between the developing roller 48 and the conveying roller 54 was set to 0.5 mm.

  The brush 47 as a toner diffusing member is a brush having a conductivity in which a linear member made of Teflon is implanted around a cylindrical body, and conductive carbon is dispersed in the linear member. A wire having a diameter of 9 mm, a linear member having a linearity of 2 denier, and a linear member having a flocking density of 240 kF / in 2 was used.

  In this experiment, as shown in Examples 1 to 6 below, the brush 47 is subjected to various conditions, that is, bias applied to the brush 47, reciprocation of the brush 47 with respect to the axial direction of the developing roller 48, brush The occurrence level of the image memory and the deterioration level of the toner were examined by changing the rotation direction of the brush 47 when the brush 47 was rotated.

[Example 1]
The brush 47 is driven to rotate in the opposite direction to the developing roller 54 at the same peripheral speed as the developing roller 54 (in the same direction in the region where the developing roller 48 and the brush 47 are opposed) and in the axial direction of the developing roller 48. 2 mm was reciprocated. Further, a DC bias of −50 V, which is the same polarity as the toner is charged and has a negative polarity in this experiment, was applied to the brush 47.
[Example 2]
The brush 47 was driven to rotate in the reverse direction with respect to the developing roller 54 at the same peripheral speed as the developing roller 54, but was not reciprocated in the axial direction of the developing roller 48. Further, a DC bias of −50 V was applied to the brush 47.
Example 3
The brush 47 is driven to rotate in the forward direction that is the same direction as the developing roller 54 at the same peripheral speed as the developing roller 54 (the reverse direction in the region where the developing roller 48 and the brush 47 face each other). It was not reciprocated in the axial direction. Further, a DC bias of −50 V was applied to the brush 47.
Example 4
The brush 47 was driven to rotate in the forward direction, which is the same direction as the developing roller 54, at the same peripheral speed as the developing roller 54, and was reciprocated 2 mm in the axial direction of the developing roller 48. Further, a DC bias of −50 V was applied to the brush 47.
Example 5
The brush 47 was reciprocated 2 mm in the axial direction of the developing roller 48, but was not driven to rotate. Further, a DC bias of −50 V was applied to the brush 47.
Example 6
The brush 47 was not driven to rotate, nor was it reciprocated in the axial direction of the developing roller 48. Further, no DC bias was applied to the brush 47.

  Further, as a comparative example, the image memory generation level and the toner deterioration are also observed when the brush 47 as the toner diffusing member is not provided [Comparative Example 1] and when the blade is used as the toner diffusing member [Comparative Example 2]. I checked the level. Polyurethane rubber was used as the blade.

  Using an image forming device modified from Konica Minolta Business Technologies Co., Ltd. bizhub C350, image output on paper was executed under the above conditions, and the generation level of image memory on the paper was confirmed. FIG. 5 is a diagram for explaining an image memory evaluation method. FIG. 5A shows an image pattern for image memory evaluation output on paper, and FIG. 5B shows an image. It shows the state where memory is generated. In the evaluation of the image memory, an image pattern having a solid area and a half area is used, and this image pattern is output to the paper 58 to form a solid pattern portion 141 and a half pattern portion 142 on the paper 58 (FIG. 5A )), And after printing 100 sheets of this image pattern, the memory part 143 generated on the half pattern part 142 was visually confirmed (see FIG. 5B). When the occurrence of the memory part 143 was confirmed, the density difference between the half pattern part 142 and the memory part 143 was further examined. As for the generation level of the image memory, the level where the generation of the memory unit 143 does not occur is ◎, the level where there is a problem in practical use as an image although the memory unit 143 where the density difference is less than 0.03 is partially generated, Although the memory unit 143 of 0.03 or more and less than 0.05 is generated, the level that does not cause a practical problem as an image is Δ, and the memory unit 143 that has a density difference of 0.05 or more is generated and the level that causes a practical problem as an image X was evaluated. The results are shown in Table 1 below. It should be noted that the level at which the memory unit 143 is generated but has no practical problem as an image is a level at which it is possible to make it difficult to discriminate the image memory by image processing.

  In addition, after executing image output, the level of toner deterioration is observed with a scanning electron microscope. The state where the toner is almost the same as the initial state is ○, the surface of the toner is almost free of external additives, cracked or distorted. A state where a lot of toner having a different shape was present was evaluated as x. The results are also shown in Table 1 below.

  As shown in Table 1, regarding the image memory, in the first embodiment, the memory unit 143 is not generated, and in the second to fifth examples, the memory unit 143 having a density difference of less than 0.03 is generated, but the image is practically used. There is no upper problem. In Example 6, although the memory unit 143 having a density difference of 0.03 or more and less than 0.05 is generated, the image has a practically no problem level. On the other hand, with respect to the image memory, in Comparative Example 1, the memory unit 143 having a density difference of 0.05 or more is generated, which is a practically problematic level as an image, whereas in Comparative Example 2, the density difference is 0.03. Although the lower memory portion 143 is generated, the image has a practically no problem level.

  From this result, by providing the brush 47 as a toner diffusing member for diffusing the toner 6 remaining on the developing roller 48 after development, the toner 6 is sufficiently collected from the developing roller 48 in the collecting region 92, It was confirmed that the recoverability of the toner 6 was improved. Further, the brush 47 as a toner diffusing member is reciprocated in the axial direction of the developing roller 48, a DC bias having the same polarity as the polarity to which the toner 6 is charged is applied to the brush 47, and the brush 47 is attached to the developing roller 48. It has been found that the diffusion effect of the toner 6 can be enhanced by rotating in the reverse direction or the forward direction with respect to the rotation direction.

  Regarding toner deterioration, in Examples 1 to 6 and Comparative Example 1, the toner is almost unchanged from the initial state, whereas in Comparative Example 2, there is almost no external additive on the surface of the toner. However, there were many toners that were cracked or distorted.

  From this result, when the blade is used as the toner diffusing member, the image memory has a level that causes no problem in practical use as an image although the memory portion 143 having a density difference of less than 0.03 is generated. As for the deterioration, there was a problem in practical use.

  In this embodiment, the conductive brush 47 is used as the toner diffusing member, and the toner remaining on the developing roller 48 after the development is diffused. However, the present invention is not limited to this. It is possible to use other toner diffusing members that diffuse the toner 6 remaining on the top.

  As described above, according to the developing device 34 according to the present embodiment, the toner 6 remaining on the developing roller 48 after the development is diffused by the toner diffusion member, so that the adhesion force of the toner 6 remaining on the developing roller 48 is increased. As a result, the recoverability of the toner 6 remaining on the developing roller 48 can be improved, and the occurrence of image memory can be suppressed.

  Further, by using the conductive brush 47 as the toner diffusing member, it is possible to suppress the deterioration of the toner as compared with the case of using a blade, and the above effect can be more effectively achieved.

  Further, a DC bias having the same polarity as the polarity at which the toner 6 is charged is applied to the toner diffusing member, the toner diffusing member is reciprocated in the axial direction of the developing roller 48, or the toner diffusing member is driven to rotate. By rotating the member in the opposite direction between the member and the developing roller 48 in the opposite direction, the effect of diffusing the toner remaining on the developing roller 48 by the toner diffusing member can be enhanced.

  Note that the present invention is not limited to the illustrated embodiment, and it goes without saying that various improvements and design changes are possible without departing from the scope of the present invention.

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention. It is a figure which shows the specific example of an electric field formation apparatus. FIG. 3 is a diagram illustrating a relationship between voltages supplied from an electric field forming apparatus illustrated in FIG. 2 to a conveying roller and a developing roller. It is the figure which showed typically the surface of the developing roller before and behind the opposing area | region with a brush. It is a figure for demonstrating the evaluation method of an image memory.

Explanation of symbols

1: Image forming device, 2: Developer, 6: Toner, 12: Photoconductor, 34: Developing device, 47: Brush, 49: Third power supply, 48: Developing roller, 54: Conveying roller, 88: Supply / recovery Area 90: supply area 92: collection area 96: development area 110: electric field forming device 112: first power source 114: second power source

Claims (6)

A developer including a toner and a carrier, wherein the toner and the carrier are charged to a first polarity by frictional contact with each other and the carrier is charged to a second polarity different from the first polarity; ,
A conveyance roller that is driven to rotate and conveys the developer on the outer peripheral surface;
A developing roller which is opposed to the conveying roller via a first area and is opposed to the electrostatic latent image carrier via a second area and is driven to rotate;
A first electric field forming means for forming a first electric field between the conveying roller and the developing roller, and moving only the toner in the developer held by the conveying roller to the developing roller;
A second electric field is formed between the developing roller and the electrostatic latent image carrier, and the toner held on the developing roller is moved to the electrostatic latent image on the electrostatic latent image carrier to move the static electricity. A developing device comprising: a second electric field forming unit that develops the electrostatic latent image; and the toner remaining on the developing roller after the development is collected by the conveying roller.
A developing device, comprising: a toner diffusing member provided to face the developing roller and diffusing the toner remaining on the developing roller.   The developing device according to claim 1, wherein the toner diffusing member is a conductive brush.   The developing device according to claim 1, wherein a direct current bias having the same polarity as the first polarity to which the toner is charged is applied to the toner diffusing member.   The developing device according to claim 1, wherein the toner diffusing member is reciprocated in an axial direction of the developing roller. The toner diffusion member is driven to rotate;
5. The developing device according to claim 1, wherein the toner diffusing member and the developing roller are rotationally driven in opposite directions in a region where the toner diffusing member and the developing roller are opposed to each other.   An image forming apparatus comprising the developing device according to claim 1.