JP5114983B2 - 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 main component of a developer and a two-component developing method using toner and a carrier as main components of a developer are known. ing.

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

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

  In order to solve the above-mentioned problem related to the two-component developing device, Patent Document 1 discloses that a carrier or carrier and toner are replenished to the developer little by little, and the developer whose charging performance is lowered is gradually discharged. A developing device that suppresses an increase in deteriorated carriers is disclosed. According to this technique, it is possible to extend the life of the developer without increasing the size of the developing device. However, a mechanism for collecting the discharged carrier is necessary. In addition, the consumption of the carrier is large, which includes cost and environmental problems. Further, it is necessary to perform a predetermined amount of printing until the ratio of the undegraded carrier and the deteriorated carrier is stabilized.

  Patent Document 2 discloses a carrier in which a resin coating layer containing resin fine particles and conductive fine powder dispersed in a matrix resin is provided on a core material, and an image forming method using the carrier. When the surface of this carrier is partially scraped by contact with other particles (carrier particles, toner particles) or members (rollers, screws), new resin fine particles are exposed on the surface, which comes into contact with the toner. The toner is charged to the required level. However, the thickness of the resin coating layer is limited, and when this resin coating layer is consumed, the carrier reaches the end of its life.

  Patent Document 3 proposes a two-component developer composed of a carrier and a toner carrying charged particles on the surface, and a developing method using the developer. The charged particles are added as an abrasive for removing dirt (spent) mainly caused by toner adhering to the surface of the carrier and extending the life of the carrier. Patent Document 3 also describes that charged particles exhibit a function of polishing the surface of the electrostatic latent image carrier in the cleaning region of the electrostatic latent image carrier. However, since charged particles have a property of being charged to a polarity opposite to the charging polarity of the toner, there is a problem that the charged particles adhere to non-image portions of the electrostatic latent image and are consumed at an early stage. In particular, when an image having a small area (for example, a character image) is created, there is a problem that a large amount of charged particles is consumed, and the ability to polish and regenerate the carrier is not sufficiently exhibited.

  Patent Document 4 has a developing device including a magnetic roller and a developing roller, and selectively selects only toner from the developer including toner and carrier held on the outer peripheral surface of the magnetic roller on the outer peripheral surface of the developing roller. There has been proposed an image forming apparatus that supplies and develops an electrostatic latent image (electrostatic latent image portion) on a photosensitive member using toner held on the outer peripheral surface of the developing roller. As a feature, the invention of Patent Document 4 is interposed between the toner and the carrier without being held on either surface of the toner and the carrier, and the pulverized fine powder of the toner adheres to the surface of the carrier to form a spent. The developer contains charged particles that prevent this. The charged particles are charged with a polarity opposite to the charged polarity of the toner and are contained only in the developer initially introduced into the developing device. However, in the image forming apparatus, the charged particles are charged with a polarity opposite to the charging polarity of the toner, and an electric field for selectively moving the toner is applied between the magnetic roller and the developing roller. Therefore, the charged particles are not sufficiently supplied to the developing roller. Therefore, a static layer is not formed in the gap between the cleaning blade and the photoconductor arranged in contact with the photoconductor, so that the photoconductor is poorly cleaned, and as a result, it is left on the image as a black spot (BS) and There has been a new problem that noise such as filming occurs.

On the other hand, there has been reported a technique in which an external additive such as silica or titanium oxide having a particle size of 0.1 to 1.5 μm is added to a toner in a developing device including a magnetic roller and a developing roller (Patent Document 5).
JP 59-1000047 A JP-A-9-269614 JP 2003-215855 A JP 2006-308687 A JP 2002-365914 A

  SUMMARY OF THE INVENTION An object of the present invention is to provide a developing device and an image forming apparatus that can suppress poor cleaning and suppress poor cleaning and can stably obtain a high-quality image over a long period of time. To do.

The present invention is a developing device that visualizes an electrostatic latent image on an electrostatic latent image carrier using a developer containing toner and a carrier,
A developer including a toner and a carrier, wherein the toner is charged to a first polarity by frictional contact between the toner and the carrier, and the carrier is charged to a second polarity different from the first polarity; ,
A first conveying member disposed in an opening of a developing tank that contains the developer;
A second conveying member facing the first conveying member via a first region and facing the electrostatic latent image carrier via a second region;
A first electric field is formed between the first conveying member and the second conveying member, and toner is moved from the developer held by the first conveying member to the second conveying member. First electric field forming means to be separated;
A second electric field is formed between the second transport member and the electrostatic latent image carrier, and the toner held by the second transport member is transferred to the electrostatic latent image carrier by static electricity. A second electric field forming means for making the electrostatic latent image visible by moving it to an electrostatic latent image;
The developer further includes a large particle A having an average primary particle size of 100 to 850 nm that acts together with the toner and a large particle B having an average primary particle size of 100 to 850 nm that acts together with the carrier. And an image forming apparatus including the developing device.

  According to the present invention, the developer uses not only the large particle B that acts together with the carrier but also the large particle A that acts together with the toner. Since the large-diameter particles A act together with the toner, the large-diameter particles A are supplied to the gap between the cleaning blade and the photoconductor to effectively form a stationary layer. On the other hand, since the large particle B acts together with the carrier, toner spent on the carrier can be effectively prevented. Even if toner spent on the carrier occurs, the large-diameter particles B are held on the surface of the carrier to promote toner charging of the carrier. Therefore, it is possible to suppress a decrease in the toner charging ability of the carrier, and to perform stable toner charging for a long period of time. As a result, it is possible to suppress poor cleaning while suppressing a decrease in the toner charging ability of the carrier, and to provide a high-quality image stably over the long term.

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

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

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

  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 developing tank (housing) 42 that houses a two-component developer containing non-magnetic toner as first component particles and a magnetic carrier as second component particles, and various members described below. ing. In order to facilitate understanding of the invention by simplifying the drawing, a part of the developing tank 42 is omitted. The developing tank 42 includes a series of openings (44, 52) opened toward the photosensitive member 12, and a toner conveying member (second conveying member) is formed in a space 46 formed in the vicinity of the opening 44. A developing roller 48 is provided. The developing roller 48 is a cylindrical member (second rotating cylindrical body), and is arranged 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. .

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

  Behind the developing roller 48, another space 52 is formed as an opening. In the space 52, a transport roller 54 that is a developer transport member (first 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 (first rotating cylinder body) that is rotatably supported around the magnet body 58. Above the sleeve 60, a restricting plate 62 fixed to the developing tank 42 and extending in parallel with the central axis of the sleeve 60 is disposed 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 S <b> 1 facing the upper inner peripheral surface portion of the transport roller 54 near the regulating plate 62 and the left inner peripheral surface portion of the transport roller 54 near the supply and recovery gap 56. Magnetic pole N1, magnetic pole S2 facing the lower inner peripheral surface portion of the transport roller 54, and two adjacent magnetic poles N2, N3 of the same polarity facing the right inner peripheral surface portion of the transport roller 54.

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

  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. As shown in FIG. 2, the carrier 4 is considerably larger than the toner 6. For this reason, the negatively charged toner 6 adheres around the carrier 4 charged to the positive polarity mainly based on the electrical attraction force of both.

  Returning to FIG. 1, the charged developer 2 is supplied to the transport roller 54 in the process of being transported through the front chamber 68 by the front screw 72. The developer 2 supplied from the front screw 72 to the conveyance roller 54 is held on the outer peripheral surface of the sleeve 60 by the magnetic force of the magnetic pole N3 in the vicinity of the magnetic pole N3. The developer 2 held by the sleeve 60 constitutes a magnetic brush along the magnetic field lines formed by the magnet body 58, and is conveyed in the counterclockwise direction based on the rotation of the sleeve 60. The amount of developer 2 held by the magnetic pole S <b> 1 in the area facing the restriction plate 62 (restriction area 86) is regulated by the restriction plate 62 to a predetermined amount. The developer 2 that has passed through the regulation gap 64 is conveyed to a region (supply / recovery region) 88 where the developing roller 48 and the conveying roller 54 are opposed to each other, where the magnetic pole N1 faces. As will be described in detail later, in the supply / recovery region 88, an upstream region (supply region) 90 mainly in the rotation direction of the sleeve 60, the presence of an electric field formed between the developing roller 48 and the sleeve 60. Thus, the toner 6 adhering to the carrier 4 is electrically supplied to the developing roller 48. Further, in the supply / recovery area 88, a region (collection area) 92 on the downstream side mainly in the rotation direction of the sleeve 60, as will be described later, the development sent back to the supply / recovery area 88 without contributing to the development. The toner on the roller 48 is scraped off by a magnetic brush formed along the magnetic field lines of the magnetic pole N1 and collected in the sleeve 60. The carrier 4 is held on the outer peripheral surface of the sleeve 60 by the magnetic force of the magnet body 58 and does not move from the sleeve 60 to the developing roller 48. When the developer 2 that has passed through the supply / recovery region 88 is held by the magnetic force of the magnet body 58 and passes through the opposing portion of the magnetic pole S2 along with the rotation of the sleeve 60, it reaches the opposing region of the magnetic poles N2 and N3 (release region 94). The repulsive magnetic field formed by the magnetic poles N2 and N3 is discharged from the outer peripheral surface of the sleeve 60 to the front chamber 68 and mixed with the developer 2 being conveyed through the front chamber 68.

The toner 6 held on the developing roller 48 in the supply area 90 is conveyed in the counterclockwise direction along with the rotation of the developing roller 48, and is an area (developing area) 96 where the photosensitive body 12 and the developing roller 48 face each other. It adheres to the electrostatic latent image portion formed on the outer peripheral surface. In the image forming apparatus according to the embodiment, a predetermined negative potential V _H is applied to the outer peripheral surface of the photoreceptor 12 by the charging device 26, and the electrostatic latent image image portion on which the image light 30 is projected by the exposure device 28 is predetermined. attenuated until the potential V _L, an electrostatic latent image non-image portion of the image light 30 is not projected by the exposing device 28 maintains a substantially charge potential V _H. Accordingly, in the developing region 96, the negatively charged toner 6 adheres to the electrostatic latent image portion due to the action of the electric field formed between the photosensitive member 12 and the developing roller 48, and the electrostatic latent image portion. The latent image is visualized as a developer image.

  When the toner 6 is consumed from the developer 2 in this way, it is preferable to supply the developer 2 with an amount of toner corresponding to the consumed amount. For this purpose, the developing device 34 includes means for measuring the mixing ratio of the toner and the carrier stored in the developing tank 42. In addition, a toner replenishment section 98 is provided above the rear chamber 70. The toner supply unit 98 includes a container 100 for storing 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. Electric field forming means]
In order to efficiently move the toner 6 from the sleeve 60 to the developing roller 48 in the supply region 90, the developing roller 48 and the sleeve 60 are electrically connected to the electric field forming device 110. The electric field forming device 110 includes a first electric field forming unit that forms a first electric field between the transport roller and the developing roller, and moves and separates the toner from the developer held by the transport roller to the developing roller. Then, a second electric field is formed between the developing roller and the photosensitive member, and the above-mentioned holding by the developing roller is moved to the electrostatic latent image on the photosensitive member to visualize the electrostatic latent image. 2 electric field forming means. Specific examples of the power source constituting the first and second electric field forming means are shown in FIGS.

The electric field forming apparatus 110 according to the first exemplary embodiment illustrated in FIG. 3A includes a first power source 112 (corresponding to a second electric field forming unit) connected to the developing roller 48 and a second power source 114 (corresponding to the second electric field forming unit). Corresponding to first electric field forming means). The first power supply 112 includes a DC power supply 118 connected between the developing roller 48 and the ground 116, and a first DC voltage V _DC1 (for example, −200 volts) having the same polarity as the charging polarity of the toner 6. Is applied to the developing roller 48. The second power supply 114 has a DC power supply 120 connected between the sleeve 60 and the ground 116, and has the same polarity as the charging polarity of the toner 6 and a second DC voltage that is higher than the first DC voltage. V _DC2 (eg, −400 volts) is applied to the sleeve 60. As a result, in the supply region 90, the negatively charged toner 6 is electrically attracted from the sleeve 60 to the developing roller 48 under the action of a DC electric field formed between the developing roller 48 and the sleeve 60. Is done. At this time, the positively charged carrier 4 is not attracted to the developing roller 48 from the sleeve 60. In the developing region 96, the negative toner held on the developing roller 48 is, as shown in FIG. 3B, the developing roller 48 (V _DC1 : −200 volts) and the electrostatic latent image portion (V _L :−). It adheres to the electrostatic latent image portion based on the potential difference of 80 volts). At this time, the negative polarity toner adheres to the electrostatic latent image non-image portion due to a potential difference between the developing roller 48 (V _DC1 : −200 volts) and the electrostatic latent image non-image portion (V _H : −600 volts). There is nothing.

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

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

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

[4. Developer)
In the present invention, the developer is a two-component developer mainly composed of a toner and a carrier, and further includes specific large-diameter particles A and large-diameter particles B.

[Large particle]
The large particle A is a particle that acts together with the toner and has an average primary particle size of 100 to 850 nm. To act together with the toner means that when the toner is moved / separated from the developer held by the conveying roller to the developing roller by the first electric field forming unit, the toner is moved / separated together with the toner to the developing roller. . Such large-diameter particles A are then moved together with the toner from the developing roller to the photosensitive member by the second electric field forming unit and supplied to the gap between the cleaning blade and the photosensitive member, so that a static layer is effectively formed. , Cleaning defects can be suppressed. Not all the large-diameter particles A must act together with the toner, but more than 50% of the large-diameter particles A contained in the developer may act together with the toner. If the large-diameter particles A are too small, the cleaning blade and the photosensitive member are easily slipped through, so that the cleaning effect is insufficient and image noise occurs. On the other hand, if it is too large, it becomes easy to scratch the photoconductor during blade cleaning or press transfer when repeated image formation is performed, so that the cleaning blade is also scratched and defective cleaning such as unwiping occurs. To do.

  Such large-diameter particles A are charged with the same polarity as the charging polarity of the toner, and are collected on the developing roller on the downstream side of the supply area 90 and on the upstream side of the developing area 96 in the rotation direction of the developing roller. Particles whose content in the toner mixture is larger than the content in the initial developer. Here, the content ratio is a ratio with respect to all large-diameter particles in the same average primary particle diameter range as that of the large-diameter particles A.

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

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

  The large particle B is a particle that acts together with a carrier and has an average primary particle size of 100 to 850 nm. Cooperating with the carrier means that when the toner is moved / separated from the developer held by the conveying roller to the developing roller by the first electric field forming unit, the toner remains with the carrier on the conveying roller side. Therefore, the large particle B can effectively prevent toner spent on the carrier, and even if toner spent on the carrier occurs, the large particle B is held on the carrier surface and promotes toner charging of the carrier. As a result, it is possible to suppress a decrease in the toner charging ability of the carrier and to perform stable toner charging for a long period of time. Not all the large-sized particles B must act with the carrier, but more than 50% of the large-sized particles B contained in the developer may act with the carrier. If the large particle B is too small, it is difficult to detach from the toner, and the amount of the large particle B adhering to the carrier is small, so that a decrease in the toner charging ability of the carrier cannot be sufficiently suppressed. On the other hand, if it is too large, the large-diameter particles are difficult to adhere to the carrier, and the effect of suppressing a decrease in the toner charging ability of the carrier cannot be obtained sufficiently.

  Such large-diameter particles B are charged with a polarity opposite to the charging polarity of the toner, and are collected on the developing roller on the downstream side of the supply region 90 and on the upstream side of the developing region 96 in the rotation direction of the developing roller. Particles whose content in the toner mixture is smaller than that in the initial developer. Here, the content ratio is a ratio with respect to all large-diameter particles in the same average primary particle diameter range as that of the large-diameter particles B.

The large-diameter particles B are usually particles that are charged to the opposite polarity to the charging polarity of the toner by frictional contact with the carrier. In the present invention, the blow-off charge amount with respect to the iron powder is opposite to the charging polarity of the toner. And what has an absolute value within the range of 5-100microC / g can be used.
Specifically, for example, when using a toner that is negatively charged by frictional contact with a carrier, the large particle B is usually a particle that is positively charged by frictional contact with the carrier. Those having a blow-off charge amount with respect to the range of +5 to +100 μC / g can be used. As such positively chargeable large diameter particles B, the same particles exemplified as the positively chargeable large diameter particles A can be used.

  In addition, for example, when using toner that is charged to positive polarity by frictional contact with a carrier, the large particle B is usually particles that are negatively charged by frictional contact with the carrier, for example, blow-off charging to iron powder. Those having an amount in the range of -5 to -100 μC / g can be used. As such negatively chargeable large diameter particles B, the same particles exemplified as the negatively chargeable large diameter particles A can be used.

  The contents of the large particle A and the large particle B are not particularly limited as long as the object of the present invention is achieved, and the total content thereof is 1 to 5% by weight, particularly 1 to 4% by weight based on the toner. % Is preferred. The content ratio (A: B) of the large particle A and the large particle B is usually from 4: 6 to 6: 4.

  Specifically, with reference to FIG. 2, the developer 2 used in the image forming apparatus and the developing apparatus of the present invention is not limited to the toner 6 and the carrier 4, but the large particle A ( 7) and large particles B (8) that act together with the carrier. In the embodiment, the large particle A (7) and the large particle B (8) are held on the outer peripheral surface of the toner 6 and are replenished together with the toner 6 from the toner replenishing unit 98.

  At the time of image formation, the large-diameter particles A (7) and the large-diameter particles B (8) are transported through the developing tank 42 together with the toner 6 and the carrier 4 and then held by the sleeve 60 to be regulated and supplied and recovered. The region 88 and the discharge region 94 are moved. In this conveyance process, when the large-diameter particles B (8) held on the surface of the toner 6 are placed in the electric field of the supply / recovery region 88, the electric force acting on the toner 6 is in the opposite direction. The toner 6 is detached from the outer peripheral surface of the toner 6 by receiving an electric force. The detached large-diameter particles B (8) are held or driven on the outer peripheral surface of the carrier 4 by the stress acting between the separated large-diameter particles B (8) and the carrier 4. When a part or the whole of the outer peripheral surface of the carrier 4 is covered with spent, the large-diameter particles B (8) are driven into the spent. The large-diameter particles B (8) held or driven on the outer peripheral surface of the carrier 4 are charged with a polarity opposite to that of the toner 6 by frictional contact with the toner 6. In the embodiment, since the toner 6 is charged to a negative polarity, the large particle B (8) is charged to a positive polarity. As a result, the carrier 4 in which the large-diameter particles B (8) have been implanted maintains the same chargeability as in the absence of spent, even if at least part of the outer peripheral surface thereof is covered with the spent. Is charged to a predetermined polarity.

  As described above, the large-diameter particle B (8) is charged with a polarity opposite to that of the toner 6. Therefore, in the supply / recovery area 88, the toner 6 moves from the sleeve 60 to the developing roller 48 based on the electric field formed between the developing roller 48 and the sleeve 60. Further, the large particle B (8) separated from the toner 6 is quickly held on the carrier surface of the developer which is relatively carrier-rich by the toner 6 being taken away in the supply region 90, and developed together with the toner 6. Even if it is not supplied to the roller 48 or supplied to the developing roller 6, the amount is very small.

  On the other hand, when the large-diameter particle A (7) held on the surface of the toner 6 is placed in the electric field of the supply / recovery region 88, the electric force acting in the same direction as the electric force acting on the toner 6 is applied. Then, the toner 6 moves from the sleeve 60 to the developing roller 48 together with the toner 6. Thereafter, when the large-diameter particles A (7) are held on the developing roller 48 together with the toner 6 and conveyed to the developing area 96, the electric field formed between the photoconductor 12 and the developing roller 48 in the developing area 96. As a result, the negatively charged toner 6 adheres to the electrostatic latent image portion, and the electrostatic latent image is visualized. At this time, since the large-diameter particles A (7) reach the photoconductor, they are supplied to the gap between the cleaning blade and the photoconductor to effectively form a stationary layer.

  In the embodiment, the toner 6 is charged to a negative polarity and the carrier 4 is charged to a positive polarity by frictional contact between the toner 6 and the carrier 4. The large particle A (7) is negatively charged, and the large particle B (8) is positively charged. The chargeability of the toner, carrier, large particle A (7) and large particle B (8) used in the present invention is not limited to such a combination. Specifically, the toner 6 is charged positively and the carrier 4 is negatively charged by the frictional contact between the toner 6 and the carrier 4, the large particle A (7) is positive, and the large particle B (8) is negative. Combinations that are electrically charged are also conceivable.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

  The charging polarity of the toner, carrier, toner by the combination of the large particle A and the large particle B, the large particle A and the large particle B is determined by mixing and stirring them into a developer. It can be easily known from the direction of the electric field for separating the particles A or the large-diameter particles B.

(Carrier A)
A carrier for a bizhub C350 manufactured by Konica Minolta Business Technologies, Inc., which is a coat type carrier in which a carrier core particle made of a magnetic material is coated with a silicone resin and having an average particle diameter of about 33 μm, was used.

(Large particle x1)
A fluorinated silicone oil was surface-treated with 0.2 wt% of strontium titanate particles having a number average particle size of 350 nm to obtain large-diameter particles x1. The large particles had a blow-off charge amount of -5 μc / g.

(Large diameter particles x2 to x5)
Large-sized particles x2 to x5 were obtained in the same manner as the large-sized particle x1 except that strontium titanate particles having a number average particle size of 50, 100, 850, and 1000 nm were used. The blow-off charge amount of these large diameter particles was −5 μc / g.

(Large particle x6)
A fluorinated silicone oil was surface-treated with 1 wt% of strontium titanate particles having a number average particle diameter of 350 nm to obtain large-diameter particles x6. The large particles had a blow-off charge amount of −99 μc / g.

(Large particle y1)
The strontium titanate particles having a number average particle diameter of 350 nm were used as the large particle y1 without being subjected to surface treatment. The large particles had a blow-off charge amount of +5 μc / g.

(Large diameter particles y2 to y5)
The strontium titanate particles having a number average particle size of 50, 100, 850 and 1000 nm were used as large particles y2 to y5 without any surface treatment. The blow-off charge amount of these large diameter particles was +5 μc / g.

(Large particle y6)
The strontium titanate particles having a number average particle diameter of 350 nm were surface-treated with 1% by weight of N- (2-aminoethyl) 3-aminopropyltrimethoxysilane based on the strontium titanate particles to obtain large-diameter particles y6. The large particles have a blow-off charge amount of +98 μc / g.

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

(Toner particles)
As toner particles, toner particles for bizhub C350 manufactured by Konica Minolta Business Technologies, Inc. were used.

Example 1
For 100 parts by weight of toner particles having a volume average particle diameter of about 6.5 μm prepared by the wet granulation method, 0.2 part by weight of the first hydrophobic silica, 0.5 part by weight of the second hydrophobic silica, Surface of 0.5 parts by weight of titanium oxide, 2 parts by weight of large-diameter particles x1, and 2 parts by weight of large-diameter particles y1 at a speed of 40 m / s for 3 minutes using a Henschel mixer (Mitsui Metal Mining Co., Ltd.) After the treatment, external addition treatment was performed to obtain a negatively chargeable toner.

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

(Evaluation)
An image forming apparatus (bizhub C350; Konica) in which a developer obtained by mixing the negatively chargeable toner and carrier A at a weight mixing ratio (toner / carrier) of 8/92 is incorporated with a developing device of the form shown in FIG. Installed in Minolta Business Technologies). Using this image forming apparatus, 100,000 original images with an image area ratio of 5% were printed. The toner is controlled to be replenished based on the toner density detection result of the developer.

Development conditions are as follows. The electric field forming apparatus employs the form shown in FIG. 7, and a DC voltage V _{DC2 of} −500 volts is applied to the conveying roller, and an AC voltage of DC voltage V _{DC1 of} −300 volts is applied to the developing roller. AC voltage frequency: 2 kHz, the amplitude _V P-P: 1,500 volts, minus the duty ratio (toner collecting duty ratio): 40%, plus a duty ratio (toner supply duty ratio): was 60% of the rectangular wave . The development gap 50 was set to 0.3 mm, the supply / recovery gap 56 was set to 0.6 mm, and the regulating portion was set so that the developer conveyance amount of the conveyance roller was 50 mg / cm ² . The charged potential (non-image portion) of the photoreceptor was −550 volts, and the potential of the electrostatic latent image (image portion) formed on the photoreceptor was −60 volts.

-Charging property Charging property is measured by measuring the charge amount of toner on the developing roller with a blow-off powder charge amount measuring device (manufactured by Toshiba Chemical Co., Ltd.) and evaluating the charge amount reduction rate (Rc) after printing 100,000 sheets with respect to the initial stage. did.
○; Rc was less than 5%;
Δ: Rc was 5% or more and less than 10%, but there was no practical problem;
X: Rc was 10% or more.

-Cleaning property The cleaning property was evaluated on the image after printing 100,000 sheets and the surface of the photoreceptor on the basis of image noise caused by cleaning (uncleaned due to defective cleaning, BS, filming).
○: The surface of the photoreceptor was not wiped, and no filming and BS were generated;
Δ: left unwiped, filming and occurrence of BS on the photoreceptor surface;
×: Unwiped, filming and occurrence of BS were present on the surface of the photoreceptor, and could be confirmed on the image.

Large particle ratio Immediately after printing 50,000 sheets and 100,000 sheets, large particle A contained in the developer acts with toner at a ratio exceeding 50% and is moved and separated by the developing roller 48. It was. On the other hand, the large-sized particles B acted with the carrier at a ratio exceeding 50%.
It was clear from the following measurements that the large-diameter particles A acted with the toner in a proportion exceeding 50%. The ratio Xa (% by weight) of the large particle A (x1) to the toner particles contained in the initial developer was calculated. The toner mixture on the developing roller is sampled downstream from the supply area 90 and upstream from the developing area 96 in the rotation direction of the developing roller, and the ratio Xb (% by weight) of the large particle A (x1) to the toner particles is measured. did. It was confirmed that Xb / Xa exceeded 0.5.
It was clear from the following measurements that the large particles B acted with the carrier in a proportion exceeding 50%. The ratio Ya (% by weight) of the large-diameter particles B (y1) to the toner particles contained in the initial developer was calculated. The toner mixture on the developing roller on the downstream side of the supply area 90 and the upstream side of the developing area 96 in the rotation direction of the developing roller is collected, and the ratio Yb (% by weight) of the large-diameter particles B (y1) to the toner particles is measured. did. It was confirmed that 1-Yb / Ya exceeded 0.5.
The ratios Xb and Yb of the large diameter particles A and B can be obtained by carrying out the following method for the large diameter particles A and B, respectively. A large standard particle is dissolved in a solvent, and a calibration curve showing the relationship between the concentration and the absorbance is prepared. Similarly, the toner is dissolved in a solvent and a calibration curve showing the relationship between the concentration and the absorbance is prepared. The sampled toner is dissolved, the absorbance of the solution is measured, and the content ratio of large-diameter particles is derived from the calibration curve. A general absorptiometer can be used for measuring the absorbance.

The content ratio [Xb / (Xb + Yb)] of the large particle A in the toner mixture collected on the developing roller was larger than the content ratio [Xa / (Xa + Ya)] of the large particle A in the initial developer. .
The content ratio [Yb / (Xb + Yb)] of the large particle B in the toner mixture collected on the developing roller was smaller than the content ratio [Ya / (Xa + Ya)] of the large particle B in the initial developer. .

(Examples 2 to 10 / Comparative Examples 1 to 5)
A toner was produced and evaluated in the same manner as in Example 1 except that the large-diameter particles shown in the table were used in the addition amount shown in the table.
In Examples 2 to 10, immediately after printing 50,000 sheets and immediately after 100,000 sheets, the large-diameter particles A contained in the developer act together with the toner in a ratio exceeding 50% and move / separate to the developing roller 48. It had been. On the other hand, the large-sized particles B acted with the carrier at a ratio exceeding 50%. In Examples 2 to 10, the content ratio [Xb / (Xb + Yb)] of the large particle A in the toner mixture collected on the developing roller is equal to the content ratio [Xa / ( Xa + Ya)]. The content ratio [Yb / (Xb + Yb)] of the large particle B in the toner mixture collected on the developing roller was smaller than the content ratio [Ya / (Xa + Ya)] of the large particle B in the initial developer. .

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to the present invention and a cross section of a developing device according to the present invention. The figure which illustrates the composition of a developer typically. The figure which shows one Embodiment of an electric field formation apparatus. The figure which shows the relationship between the voltage supplied to the sleeve and the image development sleeve from the electric field formation apparatus shown to FIG. 3A. The figure which shows other embodiment of an electric field formation apparatus. The figure which shows the relationship between the voltage supplied to the sleeve and the image development sleeve from the electric field formation apparatus shown to FIG. 4A. The figure which shows other embodiment of an electric field formation apparatus. The figure which shows the relationship between the voltage supplied to the sleeve and the image development sleeve from the electric field formation apparatus shown to FIG. 5A. The figure which shows other embodiment of an electric field formation apparatus. The figure which shows other embodiment of an electric field formation apparatus.

Explanation of symbols

  1: image forming apparatus, 2: developer, 4: carrier, 6: toner, 7: large particle A, 8: large particle B, 10: spent, 12: photoconductor, 16: charging station, 18: exposure Station: 20: Development station, 22: Transfer station, 24: Cleaning station, 26: Charging device, 28: Exposure device, 30: Image light, 32: Path, 34: Development device, 36: Transfer device, 38: Sheet, 40: cleaning device, 42: developing tank (housing), 44: opening, 46: second space, 48: developing roller, 50: developing gap, 52: opening (second space), 54: transport roller , 56: supply / recovery gap, 58: magnet body, 60: sleeve, 62: restriction plate, 64: restriction gap, 66: developer stirring chamber, 68: front chamber, 70: rear chamber, 72: front screw 74: Rear screw, 76: Partition, 86: Restriction area, 88: Supply / recovery area, 90: Supply area, 92: Collection area, 94: Release area, 96: Development area, 98: Toner replenishing section, 100: Container , 102: opening, 104: supply roller, 110: electric field forming device, 112: first power supply, 114: second power supply, 116: ground, 118: DC power supply, 120: DC power supply, 122: electric field forming device , 124: first power supply, 126: ground, 128: DC power supply, 130: second power supply, 132: DC power supply, 134: AC power supply, 136: electric field forming device, 138: first power supply, 140: ground 142: DC power supply, 144: AC power supply, 146: second power supply, 148: terminal, 150: DC power supply, 152: electric field forming device, 154: AC power supply, 156: AC power supply, 15 : Electric field forming apparatus, 160: AC power source.

Claims (2)

A developing device that visualizes an electrostatic latent image on an electrostatic latent image carrier using a developer including toner and a carrier,
A toner and a carrier, wherein the carrier contains a magnetic material, and the toner is charged to a first polarity by frictional contact between the toner and the carrier, and the carrier is different from the first polarity. A developer charged to a polarity of
A first conveying member disposed in an opening of a developing tank containing the developer and containing a magnet body ;
A second conveying member facing the first conveying member via a first region and facing the electrostatic latent image carrier via a second region;
A first electric field is formed between the first conveying member and the second conveying member, and toner is moved from the developer held by the first conveying member to the second conveying member. First electric field forming means to be separated;
A second electric field is formed between the second transport member and the electrostatic latent image carrier, and the toner held by the second transport member is transferred to the electrostatic latent image carrier by static electricity. A second electric field forming means for making the electrostatic latent image visible by moving it to an electrostatic latent image;
The developer has the same charging polarity as the charging polarity of the toner, the large-diameter particle A having an average primary particle size of 100 to 850 nm that acts together with the toner, and the charging polarity is opposite to the charging polarity of the toner. there are, developing device, further comprising the larger particles B having an average primary particle size 100~850nm which act together with the carrier. An image forming apparatus comprising the developing device according to claim 1 .

Images