JP4636091B2 - Developing device and image forming apparatus - Google Patents

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 developer and a two-component developing method using toner and a carrier as developers are 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 member and a regulating plate provided by pressing the toner carrying member, 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. Further, since a toner layer having an upper limit of a thickness of several tens of μm is formed on the toner carrier, the toner carrier can be set in a state where a minute gap is maintained between the image carrier and As a result, a strong electric field is formed between the toner carrier and the image carrier to obtain a high toner moving speed, and a high-definition high-quality image can be obtained. However, in the one-component development method, the deterioration of the toner is likely to be promoted by the strong stress received in the restricting portion, the toner charge amount is likely to decrease with durability, and the surface of the restricting plate and the toner carrier surface is not easily removed from the toner and other external surfaces. Contamination with the additive lowers the charge imparting property to the toner, resulting in problems such as fogging, making it difficult to extend the life of the developing device.

  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, the magnetic brush formed by the carrier on the developer conveying roller has a length that is 20 to 50 times the thickness of the toner layer on the toner carrier in the one-component developing system, and is not microscopic. It is formed uniformly. As a result, the electric field between the image carrier and the image carrier must be set to be weaker than in the case of the one-component development method in consideration of leakage prevention and the like, and at least a part of the magnetic brush is in contact with the image carrier. Since it is necessary to set a gap between the image carrier and the image carrier, the toner movement speed to the image carrier is slow, and the toner image on the image carrier is scraped off by the magnetic brush. This is inferior to the one-component development method.

  As a developing method incorporating the advantages of both the one-component developing method and the two-component developing method, Patent Document 1 discloses a magnetic pole body after toner charging in the state of a two-component developer as in the two-component developing method. While the developer is held in a magnetic brush state on the outer peripheral surface by a magnetic force with a supply roller containing the toner, the developer is transported to a region facing the developing roller by rotation, and development on the supply roller is performed by the action of an electric field formed in this region. A toner thin layer is formed on the developing roller by supplying only the toner from the agent to the developing roller, and this toner layer is conveyed to an area (developing area) opposite to the image carrier by the rotation of the developing roller to carry the image. A so-called hybrid development system that performs one-component development for developing an electrostatic latent image on a body has been proposed. According to this developing system, it is possible to achieve both a long life of the developing device and high image quality.

  However, in the hybrid development method, if the toner remaining on the developing roller without being used for development is not sufficiently separated and collected from the developing roller in the developing device, an image memory (or development history phenomenon) occurs. There was a problem. The problem is that the toner on the developing roller after development is scraped off and collected by the magnetic brush on the supply roller while supplying new toner from the supply roller to the development roller in the area where the supply roller and the development roller are opposed to each other. The image memory is particularly prominent when the electric field formed in the opposite area is set closer to the toner supply in order to cope with the increase in the image forming speed. appear.

  As countermeasures against this image memory problem, in Patent Document 2 and Patent Document 3, a magnetic pole is arranged in the developing roller, and development is performed on the magnetic force lines formed by this magnetic pole and the magnetic pole in the supply roller arranged opposite thereto. It has been proposed that the contact area of the developer magnetic brush with the developing roller is increased by constraining the developer magnetic brush, the toner collecting function from the developing roller is improved, and the image memory is eliminated.

JP 2003-15380 A JP 2006-106027 A JP 2006-15380 A

  However, if the magnetic pole is disposed in the developing roller, a magnetic force attracting the magnetic carrier is generated in the developing roller, and carrier transfer (carrier consumption) from the supply roller to the developing roller is likely to occur. In particular, this problem becomes prominent when the speed of the image forming apparatus is increased. In Patent Document 2, a proposal is made to set the magnetization so as to weaken the magnetic force of the circumferential edge of the magnetic pole disposed in the developing roller (the portion corresponding to the developer roller held away from the developing roller surface). However, the difficulty of setting magnetization increases, which also affects productivity.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a developing device capable of suppressing carrier consumption while preventing an image memory, and an image forming apparatus provided with the developing device in the hybrid developing system.

In order to achieve this object, the developing device of the present invention includes a non-magnetic toner and a magnetic carrier, and the toner is charged to the first polarity by mutual frictional contact, and the carrier is the first polarity. A developer charged to a different second polarity;
A conveying roller configured to include a magnetic pole body having a plurality of magnetic pole portions and a cylindrical member whose outer periphery is driven to rotate, while conveying the developer on the outer peripheral surface of the cylindrical member;
A developing roller that opposes the conveying roller through a first region and opposes the image carrier through a second region, and is driven to rotate in the same direction as the conveying roller;
A first electric field forming unit that forms a first electric field between the conveying roller and the developing roller, and moves 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 image carrier, and the toner held by the developing roller is moved to the electrostatic latent image on the image carrier to develop the toner. A second electric field forming unit for forming an image,
A second magnetic pole portion opposite to the first magnetic pole portion corresponding to the first region of the magnetic pole portions of the magnetic pole body and having a different polarity from the first magnetic pole portion is disposed in the developing roller, and the second The magnetic flux density peak position of the magnetic pole portion is located upstream of the straight line connecting the respective centers of the transport roller and the developing roller in the developing roller rotation direction, and the magnetic flux density peak position of the first magnetic pole portion is the second magnetic pole portion. The developer held on the transport roller that is upstream of the magnetic flux density peak position of the section in the transport roller rotation direction and upstream of the straight line in the transport roller rotation direction is in contact with the development roller. It is located in the area | region which is located.

  According to the developing device of the present invention, the conveying roller and the developing roller are driven to rotate in the same direction, and the cylindrical member surface and the developing roller surface of the conveying member move in opposite directions in the first region. However, the first magnetic pole portion in the conveying roller and the second magnetic pole portion in the developing roller are arranged so as to be shifted to the upstream side in the rotation direction of each roller with respect to the straight line connecting the centers of the two rollers. Compared with the case where each magnetic flux density peak position of the second magnetic pole portion is positioned on the straight line, the surface of the developing roller in the first region is a region when the developer roller is separated from the developer held on the conveying roller. The carrier holding force by the first magnetic pole portion of the transport roller is increased, while the carrier attracting force by the second magnetic pole portion of the developing roller is weakened.

  As a result, transfer of the carrier to the developing roller can be suppressed, carrier consumption can be reduced, and white spots on the image and damage to the cleaning blade for the image carrier caused by the dent of the image carrier caused by carrier transfer It is possible to reduce the occurrence of streak noise on the image due to toner remaining after wiping.

  Preferred embodiments of the present invention will be described below 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 photoconductor 12 that is an 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) can 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. In the developer used in the present embodiment, it is assumed that the toner is negatively charged and the carrier is positively charged by 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 4 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 disposed in parallel with the photosensitive member 12 and a predetermined developing gap 50 from the outer peripheral surface of the photosensitive member 12.

  The developing roller 48 includes a cylindrical toner conveying sleeve 45 supported so as to be rotatable in the direction of an arrow 78, and a columnar magnet body 47 fixedly disposed in the sleeve so as not to rotate. The conductive magnet body 47 is electrically connected to an electric field forming device 110 described later, whereby a predetermined developing bias is applied to the developing roller 48. A counter magnetic pole S (second magnetic pole part) is provided on the outer peripheral part of the magnet body 47. The counter magnetic pole S extends along the central axis direction of the developing roller 48. In FIG. 1, the solid line extending from the center 49 of the developing roller 48 toward the counter magnetic pole S indicates the peak position and direction of the magnetic flux density of the counter magnetic pole S. The magnetizing position of the counter magnetic pole S will be described in detail later. In this embodiment, the opposing magnetic pole S provided inside the developing roller 48 is attached to a part of the outer peripheral portion of the columnar magnet body 47 having a diameter substantially equal to the inner diameter of the cylindrical toner conveying sleeve 45. However, the present invention is not limited to this, and a rod-shaped magnet that is thin enough to leave a considerable amount of internal space in the sleeve 45 is fixedly disposed so that the south pole faces the inner peripheral surface of the sleeve. The counter magnetic pole S may be used.

  The developing roller 48 can be formed of a cylindrical member made of a metal such as aluminum that has been subjected to a surface treatment. 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. In addition, 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 conductive agent include, but are not limited to, carbon black particles such as ketjen black, acetylene black, and furnace black, metal powder, and metal oxide fine particles. 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 in an arrow 80 direction that is the same direction as the developing roller 48. 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 transport roller 54 and extending in the direction of the central axis of the transport roller 54. In the embodiment, the plurality of magnetic poles are opposed to the magnetic pole S1 near the upper inner peripheral surface portion of the transport roller 54 near the regulating plate 62 and the left inner peripheral surface portion of the transport roller 54 near the supply and recovery gap 56. Main magnetic pole (first magnetic pole portion) N1, magnetic pole S2 facing the lower inner peripheral surface portion of the transport roller 54, and two adjacent magnetic poles N2, N3 of the same polarity facing the right inner peripheral surface portion of the transport roller 54 including. In FIG. 1, solid lines extending from the center 55 of the transport roller 54 toward the magnetic poles S1, N1, and S2 indicate the peak position and direction of the magnetic flux density of each magnetic pole.

  The main magnetic pole portion N1 of the magnet body 58 is provided corresponding to a supply / recovery region 88 that is a region between the transport roller 54 and the developing roller 48. In particular, as will be described later in the supply / recovery region 88. The toner in the developer held on the conveying roller 54 is opposed to a supply area 90 that is an area where the toner is supplied to the developing roller 48. More specifically, the magnetic flux density peak position of the main magnetic pole portion N1 is a straight line indicated by a one-dot chain line connecting the centers 55 and 49 of the conveyance roller 54 and the developing roller 48 with respect to the rotation direction (arrow 80 direction) of the conveyance roller 54. 59 is slightly shifted to the upstream side. Further, with respect to the rotation direction of the transport roller 54, the magnetic pole S1 adjacent to the upstream side of the main magnetic pole N1 is disposed closer to the magnetic pole S2 adjacent to the downstream side of the main magnetic pole N1, and its magnetic flux density peak value is the same as that of the magnetic pole S1. Is set larger than the magnetic pole S2.

  Here, the opposing magnetic pole S of the magnet body of the developing roller 48 has a different polarity from the main magnetic pole N1 of the conveying roller 54, and the supply / recovery area 88 between the conveying roller 54 and the developing roller 48, particularly the supply. As will be described later, the collecting area 88 is provided to face the collecting area 92 where the toner on the developing roller 48 is separated and collected. More specifically, the peak position of the magnetic flux density of the counter magnetic pole S is slightly relative to the straight line 59 connecting the transport roller 54 and the centers 55 and 49 of the developing roller 48 with respect to the rotation direction of the developing roller 48 (the direction of the arrow 78). It is set to be shifted upstream. As a result, the magnetic flux density peak position of the main magnetic pole N1 of the transport roller 54 is located upstream of the magnetic flux density peak position of the counter magnetic pole S of the developing roller 48 in the rotational direction of the transport roller 54. Further, the magnetic flux density of the main magnetic pole N <b> 1 of the transport roller 54 is set to be larger than the magnetic flux density of the counter magnetic pole of the developing roller 48.

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

  In order to efficiently move the toner from the sleeve 60 of the conveying roller 54 to the sleeve 45 of the developing roller 48 in the supply region 90, the developing roller 48 and the conveying roller 54 are electrically connected to the electric field forming device 110.

  FIG. 2 shows a specific example of the electric field forming device 110. The electric field forming device 110 includes a first power source 112 and a second power source 114. Here, the first and second power sources 112 and 114 constitute a first electric field forming unit, and the first power source 112 constitutes a second electric field forming unit.

The first power source 112 includes a DC power source 118 connected between the developing roller 48 and the ground 116. The DC power supply 118 applies a DC voltage V _DC1 (for example, −300 volts) having the same polarity as the charging polarity of the toner 6 to the developing roller 48. The second power source 114 has a DC power source 120 and an AC power source 122 connected in series between the transport roller 54 and the ground 116. As a result, the conveying roller 54 has a predetermined direct current component V _DC2 (for example, −400 volts) from the direct current power supply 120 and a predetermined alternating current component (the amplitude _VP-P is, for example, 1,500 volts) from the alternating current power supply 122. A superposed vibration voltage is applied.

By applying the voltage V _DC1 to the developing roller 48 as described above, an electric field (second electric field) is formed between the photoconductor 12 and the developing roller 48. By the action of this electric field, the negative polarity toner on the developing roller 48 is electrostatically charged based on the potential difference between the developing roller 48 (V _DC1 : −300 volts) and the electrostatic latent image portion (V _L : −80 volts). It adheres to the latent image portion. 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 : −300 volts) and the electrostatic latent image non-image portion (V _H : −600 volts). There is nothing.

  Further, an oscillating electric field (first electric field) as illustrated in FIG. 3 is formed in the supply / recovery region 88 between the conveying roller 54 and the developing roller 48. As a result, the toner supply action of moving the negative toner from the conveying roller 54 to the developing roller 48 is performed in a time zone region where the electric potential of the conveying roller 54 is negative with respect to the electric potential of the developing roller 48. The toner collects the negative polarity toner from the developing roller 48 side to the conveying roller 54 in a time zone region on the plus side with respect to the potential of the developing roller 48. Further, in the time zone region of the toner collecting action, an electrostatic force in the direction of moving to the developing roller 48 side (carrier supply direction) acts on the positive polarity carrier on the conveyance roller 54, as will be described later. Carrier movement to the developing roller 48 is suppressed.

  In this embodiment, the electric field formed between the conveying roller 54 and the developing roller 48 is an oscillating electric field. However, the electric field is not limited to this. A DC electric field may be used as long as toner supply is possible.

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, it is assumed that the carrier is positively charged and the toner is negatively charged. Carrier particles are considerably larger than toner particles. Therefore, the negatively charged toner adheres around the positively charged carrier mainly based on the electrical attraction force of both.

  The charged developer 2 is supplied to the transport roller 54 while being transported through the front chamber 68 by the front screw 72. The developer 2 supplied from the front screw 72 to the conveyance roller 54 is held on the outer peripheral surface of the sleeve 60 by the magnetic force of the magnetic pole N3 in the vicinity of the magnetic pole N3. The developer 2 held by the sleeve 60 constitutes a magnetic brush along the magnetic field lines formed by the magnet body 58, and is conveyed in the counterclockwise direction based on the rotation of the sleeve 60. The amount of the developer 2 held by the magnetic pole S <b> 1 in the opposed region (restriction region) 86 of the restriction plate 62 is restricted to a predetermined amount by the restriction plate 62. The developer 2 that has passed through the regulation gap 64 moves with the sleeve 60 while being held by the magnetic force of the magnetic pole S1, and is conveyed to a region (supply / recovery region) 88 where the developing roller 48 and the conveying roller 54 face each other.

  In this supply / recovery region 88, the lines of magnetic force are formed at a relatively high density between the main magnetic pole N1 in the transport roller 54 and the opposing magnetic pole S in the developing roller 48 that is different from the main magnetic pole N1. As a result, in the development recovery area 88, the magnetic brush on the transport roller 54 is firmly restrained by the lines of magnetic force, so that the contact area of the developer 2 with the development roller 48 is expanded. As a result, in the supply / recovery region 88, mainly in the upstream supply region 90 with respect to the rotation direction of the sleeve 60, the carrier 4 is affected by the action of the oscillating electric field formed between the transport roller 54 and the developing roller 48. The adhering toner 6 is electrically sufficiently supplied to the sleeve 45 of the developing roller 48. In addition, in the supply / recovery area 88, the toner on the sleeve 45 of the developing roller 48 that has been sent back to the supply / recovery area 88 without being used for development, mainly in the recovery area 92 on the downstream side in the rotational direction of the sleeve 60. However, it is reliably scraped off by the magnetic brush of the developer 2 firmly restrained by the magnetic lines of force and collected by the conveying roller 54, thereby preventing the occurrence of image memory.

  Here, in the developing device 34 of the present embodiment, the sleeves 60 and 45 of the conveying roller 54 and the developing roller 48 are rotationally driven in the same direction, and the surface of the sleeve 60 of the conveying roller 54 and the developing in the supply / recovery region 88. The surface of the sleeve 45 of the roller 48 moves in the opposite direction, but a straight line connecting the main magnetic pole N1 in the transport roller 54 and the opposing magnetic pole S in the developing roller 48 with the centers 55 and 49 of both rollers 54 and 48. As compared with the case where the respective magnetic flux density peak positions of the main magnetic pole N1 and the counter magnetic pole S are located on the straight line 59, respectively, by being shifted to the upstream side in the rotation direction of each roller with respect to 59. In the supply / recovery area 88, the area when the surface of the sleeve 45 of the developing roller 48 is separated from the developer held on the conveying roller 54 (ie, the supply area). 0 in the direction of rotation downstream of the sleeve 45), the carrier attraction force is weakened by the magnetic force of the opposite pole S of the developing roller 48 while the carrier holding force is strong due to the magnetic force of the main magnetic pole N1 of the conveying roller 54. Further, in the present embodiment, the carrier holding force on the transport roller 54 is increased by setting the magnetic flux density peak value of the main magnetic pole N1 to be larger than the magnetic flux density peak value of the counter magnetic pole S. As a result, even if the carrier moves toward the developing roller 48 in the time zone of the toner collecting action that acts in the carrier supply direction in the oscillating electric field, the carrier is pulled back by the magnetic force of the main magnetic pole N1, and the conveying roller By being held at 54, transfer to the developing roller 48 can be suppressed, and carrier consumption can be reduced. As a result, it is possible to reduce the occurrence of streak noises on the image due to white spots on the image due to the dents of the photosensitive member 12 caused by carrier transfer and toner remaining after wiping the photosensitive member cleaning blade 40. .

The toner 6 held on the sleeve 45 of the developing roller 48 in the supply area 90 is conveyed in the counterclockwise direction as the sleeve 45 rotates, and is an area (developing area) 96 where the photosensitive member 12 and the developing roller 48 face each other. It adheres to the electrostatic latent image portion formed on the outer peripheral surface of the photoreceptor 12. 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 is applied to the electrostatic latent image portion by the action of the electric field (second electric field) formed between the photosensitive member 12 and the developing roller 48. The electrostatic latent image is developed as a toner image by flying and adhering. In the development region 96, contact development in which the toner layer on the developing roller 48 is in direct contact with the photoreceptor 12 may be used.

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

[3. Specific materials of developer]
Specific materials of the toner, carrier, charged particles, and other particles included in the developer will be described.

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

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

  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.

  The colorant used in the toner is 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, lei. Key red or the like can be used. 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.

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

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

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

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

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

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

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

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

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

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

[4. Experiment)
Next, an experimental example performed in the image forming apparatus 1 of the present embodiment will be described. In these experiments, the following toner and carrier were used.

  0.2 parts by weight of the first hydrophobic silica and 0.5 parts by weight of the second hydrophobic silica with respect to 100 parts by weight of the toner base material having a volume average particle diameter of about 6.5 μm prepared by the wet granulation method. And 0.5 parts by weight of hydrophobic titanium oxide were subjected to external treatment by surface treatment for 3 minutes at a speed of 40 m / s using a Henschel mixer (Mitsui Metal Mining Co., Ltd.). Toner was used. The first hydrophobic silica used here is a silica (#) 130 (manufactured by Nippon Aerosil Co., Ltd.) having a number average primary particle size of 16 nm and surface-treated with hexamethyldisilazane (HMDS) as a hydrophobizing agent. It is. Hydrophobic titanium oxide is obtained by surface-treating anatase-type titanium oxide having a number average primary particle size of about 30 nm with isobutyltrimethoxysilane which is a hydrophobizing agent in an aqueous wet process.

  Further, as the carrier, a carrier for bizhub C350 manufactured by Konica Minolta Technologies, Inc., which is a coated carrier in which an acrylic resin coat is formed on carrier core particles made of a magnetic material, has an average particle diameter of about 33 μm.

  The developer used in the experimental example has a toner ratio of 8%. The toner ratio is the ratio of the total amount of toner and external additives to the total amount of developer.

Further, an oscillating electric field was formed between the conveying roller 54 and the developing roller 48, and each potential of the conveying roller 54 and the developing roller 48 for forming this oscillating electric field was set as illustrated in FIG. The conveying roller 54, the DC voltage _V DC2 -250 volts, frequency 2 kHz, the amplitude 1500 volts, the toner supply duty ratio 60% alternating obtained by superimposing an AC voltage _{V AC} rectangular wave (toner recovery side duty ratio 40%) A voltage was applied, and a DC voltage V _DC1 -300 volts was applied to the developing roller 48. This potential setting is merely an example, and is changed depending on environmental conditions and image conditions. In addition, it is desirable to set a carrier consumption, which will be described later, such that there is a correlation between the time zone region on the toner collection side, that is, the product of V _min and the collection duty ratio, and this product is 200 v or less.

  Under these conditions, 300,000 durable image charts with an image area ratio of 5% were printed, and the carrier consumption before and after that and the presence or absence of image memory were examined. The results are shown in Table 1. In Table 1, Br represents the magnetic flux density (magnetic flux density peak value), and the image memory ○ represents that no image memory was generated by visual confirmation. Also, in order to prevent the occurrence of image noise such as white spots due to photoconductor dents due to carrier adhesion and streak noise due to wiping residue due to damage to the cleaning blade for the photoconductor, the carrier consumption is reduced to less than 40 g. Experience has shown that it needs to be suppressed.

  As shown in Table 1, the carrier consumption is greatly reduced by setting the magnetic flux density of the main magnetic pole N1 larger than the magnetic flux density of the counter magnetic pole S in the comparison between the experiment numbers 1 and 2-6. I understand that. Further, in the comparison between the experiment number 2 and the experiment numbers 5 and 6 and the comparison between the experiment number 2 and the experiment numbers 3 and 4, the main magnetic pole N1 and the counter magnetic pole S are shifted to the upstream side in the rotation direction of the respective rollers 54 and 48. It can be seen that the carrier consumption is further improved. Furthermore, regarding the magnetic flux density, in the comparison between Experiment No. 4 and Experiment Nos. 5 and 6, the magnetic pole S1 adjacent to the upstream side in the conveyance roller rotation direction with respect to the main magnetic pole N1 is more than the magnetic pole S2 adjacent to the downstream side. It can be seen that carrier consumption is also improved by setting a large magnetic pole position and setting the circumferential angle from the magnetic pole S1 to the magnetic pole N1 smaller than the circumferential angle from the magnetic pole S2 to the magnetic pole N1.

1 is a schematic configuration diagram of an image forming apparatus and a developing device. The figure which shows the specific example of an electric field formation apparatus. The figure which shows the electric potential relationship of a conveyance roller and a developing roller.

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, 45: sleeve, 46: second space, 47: magnet body, 48: developing roller, 49: developing roller center, 50: developing gap, 52: second space, 54: transport roller, 55 : Transport roller center, 56: supply / recovery gap, 58: magnet body, 59: straight line connecting the centers, 60: sleeve, 63: regulating plate, 64: regulating gap, 6: developer stirring chamber, 68: front chamber, 70: rear chamber, 72: front screw, 74: rear screw, 76: partition wall, 86: restriction region, 88: supply / recovery region, 90: supply region, 92: recovery Area 94: discharge area 96: development area 98: toner replenishing section 100: container 102: opening 104: replenishing roller 110: electric field forming device 112: first power source 114: second Power source 116: Ground 118: DC power source 120: DC power source 122: AC power source N1: Main magnetic pole (first magnetic pole part) S: Counter magnetic pole (second magnetic pole part)

Claims (5)

A developer comprising a non-magnetic toner and a magnetic carrier, wherein the toner is charged to a first polarity by mutual frictional contact, and the carrier is charged to a second polarity different from the first polarity;
A conveying roller configured to include a magnetic pole body having a plurality of magnetic pole portions and a cylindrical member whose outer periphery is driven to rotate, while conveying the developer on the outer peripheral surface of the cylindrical member;
A developing roller that opposes the conveying roller through a first region and opposes the image carrier through a second region, and is driven to rotate in the same direction as the conveying roller;
A first electric field forming unit that forms a first electric field between the conveying roller and the developing roller, and moves 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 image carrier, and the toner held by the developing roller is moved to the electrostatic latent image on the image carrier to develop the toner. A second electric field forming unit for forming an image,
A second magnetic pole part opposite to the first magnetic pole part corresponding to the first region of the magnetic pole part of the magnetic pole body and having a different polarity from the first magnetic pole part is disposed in the developing roller, and the second The magnetic flux density peak position of the magnetic pole part is located upstream of the straight line connecting the centers of the transport roller and the developing roller in the developing roller rotation direction, and the magnetic flux density peak position of the first magnetic pole part is the second magnetic pole part. The developer held on the transport roller that is upstream of the magnetic flux density peak position of the section in the transport roller rotation direction and upstream of the straight line in the transport roller rotation direction is in contact with the development roller. A developing device characterized by being located in a region.   The developing device according to claim 1, wherein a magnetic flux density of the first magnetic pole portion is larger than a magnetic flux density of the second magnetic pole portion.   In the magnetic pole body, the magnetic pole part adjacent to the upstream side of the first magnetic pole part is disposed closer to the magnetic pole part adjacent to the downstream side of the first magnetic pole part in the rotation direction of the transport roller. The developing device according to claim 1 or 2.   The developing device according to claim 3, wherein a magnetic flux density peak value of the magnetic pole portion adjacent to the upstream side is set larger than a magnetic flux density peak value of the magnetic pole portion adjacent to the downstream side.   An image forming apparatus comprising the developing device according to claim 1.

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