JP2008116599A - Developing device, image forming apparatus and process unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus of a hopping development system, capable of suppressing soiling of a base more than ever. <P>SOLUTION: The image forming apparatus is constituted in such a way that toner is conveyed to a developing area Ar2 by movement of the surface of a toner bearing roller 2 while hopped on the surface of the toner bearing roller 2 by a progressive electric field generated by the application of pulse voltage to the plurality of electrodes of the toner bearing roller 2, and then the toner is attached to a latent image on a photoreceptor 49, thereby a latent image is developed. The image forming apparatus is provide with a pre-development toner recovering means having a pre-development counter electrode 26 and so on for recovering reversely charged toner particles and highly charged toner particles contained in the hopping toner in a pre-development conveyance area Ar1 among the entire surface of the toner bearing roller 2 in the direction of endless movement, the area Ar1 being an area before the entry of the developing area Ar2 after the passage of the area ArO of the supply of toner by the toner supply roll 18. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a developing device that develops a latent image by attaching toner hopping on the surface of a toner carrier having a plurality of electrodes arranged in a predetermined direction to the latent image on the latent image carrier. . The present invention also relates to an image forming apparatus and a process unit using such a developing device.

  Conventionally, as image forming apparatuses such as a copying machine, a facsimile, and a printer, those described in Patent Document 1 and Patent Document 2 are known. These image forming apparatuses convey toner carried on a developer carrying member such as a developing roller that moves on the surface to a developing position that is a region facing the latent image carrying member as the surface moves. Then, at the development position, development is performed by electrostatically moving the toner on the development carrier by the potential difference between the surface of the developer carrier and the electrostatic latent image on the latent image carrier. In such a configuration, the above-described potential difference must be relatively large. This is because the toner must be given a force sufficient to overcome the adhesion force with the developer carrier due to van der Waals force or mirror image force. In addition, so-called background contamination that causes toner particles to adhere to the background portion of the latent image carrier may occur. This background stain is generated when the reversely charged toner particles that are charged in the opposite polarity to the normal charged polarity contained in the toner adhere to the background portion of the latent image carrier.

  On the other hand, as an image forming apparatus, as described in Patent Document 3, an apparatus that uses toner hopped on the surface of a toner carrier for development is known. Specifically, this image forming apparatus has a cylindrical toner carrier having a plurality of electrodes arranged at a predetermined pitch in the circumferential direction. These electrodes are formed by repeatedly arranging electrode pairs composed of two adjacent electrodes. An alternating electric field is formed between the two electrodes in each electrode pair. Then, the toner located on one electrode in the electrode pair floats and landes on the other electrode, or floats on the other electrode and landes on one electrode. Then, while repeating hopping in this manner, the toner is conveyed to the developing position by the surface movement accompanying the rotational driving of the cylindrical toner carrier. At the developing position, the toner that has floated to the vicinity of the latent image on the latent image carrier is attracted to the electric field by the latent image and does not descend toward the electrode of the toner carrier, and adheres to the latent image. In such a configuration, not the toner adsorbed on the developing roller or the magnetic carrier, but the toner that does not exhibit the adsorbing power due to hopping is used for development. As a result, it is possible to realize low-potential development that cannot be realized by the conventional one-component development method or two-component development method. For example, toner can be selectively attached to an electrostatic latent image having a potential difference of only a few tens [V] with respect to surrounding non-image portions.

JP-A-9-197781 JP-A-9-329947 JP-A-3-21967

  However, even in the image forming apparatus having such a configuration, the reversely charged toner particles hopped on the toner carrier may adhere to the background portion of the latent image carrier and cause background staining. Furthermore, unlike the image forming apparatuses described in Patent Document 1 and Patent Document 2, high charge amount toner particles contained in the toner may cause background staining. Specifically, at the development position where the latent image carrier and the toner carrier face each other, the toner particles hopped from the surface of the toner carrier eventually reach the vicinity of the latent image carrier. Under the toner particles, a toner cloud is formed of countless toner particles that have started hopping around the toner particles. The toner particles that have reached the vicinity of the latent image carrier are repelled by the charges of countless toner particles in the toner cloud and are pushed toward the latent image carrier. Of the infinite number of toner particles contained in the toner, the majority of toner particles having an average charge amount have a relatively low moving speed in the direction toward the latent image carrier. For this reason, even if it is pushed from the toner cloud, it is pushed back by the repulsive force due to the electric field of the background portion of the latent image carrier and starts to descend toward the toner carrier. However, the high charge amount toner particles that are charged to the normal polarity side more than the average value may be attached to the background portion by overcoming the repulsive force with the background portion when pressed from the toner cloud. In this way, scumming due to high charge amount toner particles occurs.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above background, and an object of the present invention is to provide a hopping developing device capable of suppressing the occurrence of background contamination as compared with the conventional one, and an image forming apparatus and a process unit using the same. Is to provide.

In order to achieve the above object, the invention of claim 1 comprises a toner carrier having a plurality of electrodes arranged in a predetermined direction, and a toner supply means for supplying toner to the endlessly moving surface of the toner carrier. Then, the toner supplied onto the surface of the toner carrier by the toner supply means is hopped on the surface by an electric field formed by applying a voltage to the plurality of electrodes, and the toner carrier In the developing device for developing the latent image by attaching the latent image on the latent image carrier at a development position where the latent image carrier and the latent image carrier of the image forming apparatus face each other, hopping is performed on the surface of the toner carrier. At least one of the reversely charged toner particles and the high charge amount toner particles contained in the toner that is included in the toner in the endless movement direction of the surface of the toner carrier is determined by the toner supply means. After passing through the toner supply position, at least one of the reversely charged toner particles and the high charge amount toner particles contained in the toner hopped in the pre-development conveyance area, which is an area before entering the development position, is collected. In this case, a pre-development toner collecting means is provided.
The invention of claim 2 uses the developing device of claim 1 in which the pre-development toner collection means collects both the reversely charged toner particles and the high charge amount toner particles. It is a feature.
According to a third aspect of the present invention, in the developing device of the second aspect, as the pre-development toner collecting means, a pre-development counter electrode facing the pre-development transport area of the toner carrier via a predetermined gap. And having the reversely charged toner particles and the high charge amount toner particles hopping on the surface of the transport area before development adhered to the counter electrode before development and collected. It is characterized by.
According to a fourth aspect of the present invention, in the developing device according to any one of the first to third aspects, the toner supply position after passing through the development position in the entire region in the endless movement direction of the surface of the toner carrier. A post-development facing member is provided to face the post-development transport region, which is a region before entering the space, with a predetermined gap therebetween.
According to a fifth aspect of the present invention, there is provided an image forming apparatus comprising: a latent image carrier that carries a latent image; and a developing unit that develops the latent image carried on the latent image carrier with toner. The developing device according to any one of claims 1 to 4 is used.
According to a sixth aspect of the present invention, in the image forming apparatus of the fifth aspect, the developing device according to the third aspect is used as the developing device, and the latent image with respect to the pre-development counter electrode is used as the pre-development toner collecting means. By supplying a separation bias having the same value as the background potential of the image carrier, reversely charged toner particles and high charge amount toner particles are developed from the toner hopping on the surface of the transport area before development. What is attached to the front counter electrode and separated is used.
According to a seventh aspect of the present invention, in the image forming apparatus of the sixth aspect, the length in the direction orthogonal to the endless movement direction on the surface facing the toner carrier is set as the counter electrode before development. It is characterized in that a material having a length in the same direction as the surface facing the counter electrode before development in the body is used.
The invention according to claim 8 is the image forming apparatus according to claim 6 or 7, wherein the length of the endless moving direction on the surface facing the toner carrier as the counter electrode before development is the development position. It is characterized by using one having a length longer than the endless moving direction.
According to a ninth aspect of the present invention, in the image forming apparatus according to any one of the sixth to eighth aspects, as the pre-development toner collecting means, a bias supplied to the pre-development counter electrode is discharged from the separation bias at a different value. By switching to the bias at a predetermined timing, the reversely charged toner particles and the high charge amount toner particles adhering to the counter electrode before development are returned to the surface of the toner carrier at the predetermined timing. It is characterized by.
According to a tenth aspect of the present invention, in the image forming apparatus according to the ninth aspect, the pre-development toner collecting means is configured to supply the discharge bias consisting of only a DC voltage to the predevelopment counter electrode. It is characterized by this.
The invention of claim 11 is the pre-development toner collecting means in the image forming apparatus of claim 9, wherein the discharge bias is supplied with a DC voltage superimposed with an AC voltage on the counter electrode before development. It is characterized by comprising.
According to a twelfth aspect of the present invention, in the image forming apparatus according to any one of the sixth to eleventh aspects, the gap between the toner carrier and the pre-development counter electrode is separated from the latent image carrier at the development position. The size is the same as the gap with the toner carrier.
The invention according to claim 13 is the image forming apparatus according to any one of claims 6 to 12, wherein the toner hopping condition in the recovery area before development where the toner carrier and the counter electrode before development face each other is defined as the development position. The toner hopping conditions are the same as those in FIG.
According to a fourteenth aspect of the present invention, in the image forming apparatus according to any one of the sixth to thirteenth aspects, the developing device having a post-development counter electrode as the post-development counter member in the developing device of the fourth aspect is used. In addition, a bias supply means for supplying a bias having a polarity opposite to the normal charging polarity of the toner to the counter electrode after the development is provided.
The invention according to claim 15 is a latent image carrier for carrying a latent image, a charging means for uniformly charging the latent image carrier, a cleaning means for cleaning the surface of the latent image carrier, and the latent image carrier. In an image forming apparatus including a developing unit that develops a latent image carried on a body with toner, the developing unit and at least one of the latent image carrier, the charging unit, and the cleaning unit are 1 In a process unit that is held on a common holding body as a single unit and can be integrally attached to and detached from the image forming apparatus main body, the developing device according to any one of claims 1 to 4 is used as the developing means. It is a feature.
According to a sixteenth aspect of the present invention, in the image forming apparatus for forming a toner image on the latent image carrier using the process unit, the process unit according to the fifteenth aspect is used as the process unit. It is.
According to a seventeenth aspect of the present invention, in the image forming apparatus of the sixteenth aspect, a plurality of the process units having at least the developing device and the latent image carrier are provided, and the latent images of the respective process units are provided. The present invention is characterized in that there is provided transfer means for transferring the toner image formed on the carrier in a superimposed manner on the transfer body.

  In these inventions, among the innumerable toner particles hopped in the pre-development conveyance area of the toner carrier, the reversely charged toner particles or the high charge amount toner particles are separated by the pre-development toner collection means before the development of the toner carrier. Collect from the transport area. As a result, by reducing the amount of the reversely charged toner particles or the high charge amount toner particles conveyed to the area entering the developing position, it is possible to suppress the occurrence of background staining as compared with the conventional case.

Hereinafter, an embodiment of an image forming apparatus to which the present invention is applied will be described.
FIG. 1 is a schematic configuration diagram illustrating an image forming apparatus according to the present embodiment. In the figure, a drum-shaped photoconductor 49 as a latent image carrier is rotated in the clockwise direction in the figure.

  When an operator places a document (not shown) on the contact glass 90 and presses a print start switch (not shown), a first scanning optical system 93 including a document illumination light source 91 and a mirror 92 and first mirrors 94 and 95 are provided. The two-scanning optical system 96 moves to read the original image.

  The scanned original image is read as an image signal by an image reading element 98 disposed behind the lens 97, and the read image signal is digitized and image-processed. Then, a laser diode (LD) is driven by the processed signal, and after the laser light from the laser diode is reflected by the polygon mirror 99, the photoconductor 49 is scanned through the mirror 80. Prior to this scanning, the photosensitive member 49 is uniformly charged by the charging device 50, and an electrostatic latent image is formed on the surface of the photosensitive member 49 by scanning with a laser beam.

  The electrostatic latent image is developed into a toner image with toner attached thereto by the developing device 1, and then conveyed to a transfer position that is a position facing the transfer charger 60 as the photosensitive member 49 rotates. With respect to this transfer position, the first paper supply unit 70 having the first paper supply roller 70a or the second paper supply having the second paper supply roller 71a is synchronized with the toner image on the photoconductor 49. The recording paper P is fed from the paper section 71. The toner image on the photoreceptor 49 is transferred onto the recording paper P by corona discharge of the transfer charger 60.

  The recording paper P onto which the toner image has been transferred in this way is separated from the surface of the photoreceptor 49 by corona discharge of the separation charger 61, and then conveyed toward the fixing device 76 by the conveyance belt 75. In the fixing device 76, the fixing roller 76a is sandwiched between fixing rollers 76a including a heat source such as a halogen lamp (not shown) and a pressure roller 76b pressed against the fixing roller 76a. Thereafter, the toner image is fixed on the surface by pressurization or heating in the fixing nip, and then discharged toward a discharge tray 77 outside the apparatus.

  The transfer residual toner adhering to the surface of the photoconductor 49 that has passed the transfer position is removed from the surface of the photoconductor 49 by the cleaning device 45. The surface of the photoreceptor 49 that has been subjected to the cleaning process in this way is discharged by the charge removing lamp 44 and is prepared for the next latent image formation.

  FIG. 2 is a schematic configuration diagram showing the photoreceptor 49 and the developing device 1 in the image forming apparatus according to the present embodiment. In the figure, a drum-shaped photoconductor 49 serving as a latent image carrier is rotationally driven in a clockwise direction in the drawing by a driving means (not shown). A developing device 1 having a cylindrical toner carrier 2 is disposed on the right side of the photoconductor 49 in the drawing.

  The developing device 1 accommodates a first accommodating portion 13 that accommodates a first conveying screw 12 that is driven to rotate clockwise in the drawing, and a second accommodating portion that accommodates a second conveying screw 14 that is driven to rotate counterclockwise in the drawing. The housing portion 15 is separated from each other by a partition wall 16. Each of these accommodating portions accommodates a mixed agent in which a magnetic carrier (not shown) and a negatively chargeable toner are mixed.

  The first conveying screw 12 conveys the mixture in the first accommodating portion 13 from the near side to the far side in the direction orthogonal to the drawing sheet while rotating and stirring the mixture in the first accommodating portion 13 by its rotational drive. At this time, the toner concentration of the mixture being conveyed is detected by the toner concentration sensor 17 fixed to the bottom of the first storage unit 13. Then, the mixed agent conveyed to the vicinity of the end on the back side in the drawing enters the second accommodating portion 15 through a first communication port (not shown) provided near the end on the back side of the partition wall 16.

  The second storage unit 15 communicates with a magnetic brush forming unit 21 that stores a toner supply roll 18 to be described later, and the second conveying screw 14 and the toner supply roll 18 are parallel to each other in the axial direction through a predetermined gap. It is facing in a posture to make. The 2nd conveyance screw 14 in the 2nd accommodating part 15 conveys the mixing agent in the 2nd accommodating part 15 to the near side from the back in the figure, rotating and stirring by the rotational drive. In this process, a part of the mixture conveyed by the second conveying screw 14 is pumped up by the toner supply sleeve 19 of the toner supply roll 18. Then, as the toner supply sleeve 19 rotates in the counterclockwise direction in the drawing, after passing through a toner supply position, which will be described later, the toner supply sleeve 19 is detached from the surface of the toner supply sleeve 19 and returned to the second storage portion 15 again. It is. Thereafter, the mixture conveyed to the vicinity of the front end in the drawing by the second transfer screw 14 is first accommodated through a second communication port (not shown) provided in the vicinity of the front end in the drawing of the partition wall 16. Returned to section 13.

  The toner density sensor 17 described above is a magnetic permeability sensor. The detection result of the magnetic permeability of the mixture by the toner concentration sensor 17 is sent to a control unit (not shown) as a voltage signal. Since the magnetic permeability of the mixed agent has a correlation with the K toner concentration of the mixed agent, the toner concentration sensor 17 outputs a voltage having a value corresponding to the toner concentration.

  A control unit (not shown) of the printer includes a RAM (Random Access Memory), in which Vtref that is a target value of the output voltage from the toner density sensor 17 is stored. Then, the output voltage value from the toner density sensor 17 is compared with Vtref in the RAM, and a toner supply device (not shown) is driven for a time corresponding to the comparison result. By this driving, an appropriate amount of toner is supplied into the first storage unit 13 with respect to the mixture whose toner density is reduced by the consumption of toner accompanying development. For this reason, the toner concentration of the mixture in the second container 15 is maintained within a predetermined range.

  The toner supply roll 18 includes a cylindrical toner supply sleeve 19 made of a non-magnetic material that is driven to rotate counterclockwise in the figure, and a magnet roller 20 that is included so as not to rotate. . The cylindrical toner supply sleeve 19 is formed by forming a nonmagnetic material such as aluminum, brass, stainless steel, or conductive resin into a cylindrical shape. As shown in the figure, the magnet roller 20 includes a plurality of magnetic poles arranged in the rotation direction (N pole, S pole, N pole, S pole, N pole, S pole in order from the 12 o'clock position in the counterclockwise direction). )have. By these magnetic poles, the admixture is adsorbed on the peripheral surface of the toner supply sleeve 19, and a magnetic brush that rises along the lines of magnetic force is obtained.

  The mixture pumped up by the surface of the toner supply sleeve 19 rotates in the counterclockwise direction in the drawing as the toner supply sleeve 19 rotates. Then, it enters the carrying amount regulating position, which is a position facing the regulating member 22 whose front end is opposed to the surface of the toner supply sleeve 19 via a predetermined gap. At this time, the carrying amount on the sleeve surface is regulated by passing through the gap between the regulating member 22 and the sleeve surface.

  On the left side of the toner supply sleeve 19 in the figure, the toner carrying roller 2 as a toner carrying body faces the surface of the toner supply sleeve 19 with a predetermined gap and is driven to rotate counterclockwise in the figure by a driving means (not shown). Has been.

  As the toner supply sleeve 19 rotates, the admixture that has passed the above-described carrying amount regulation position enters the toner supply position that is in contact with the toner carrying roller 2 and moves while rubbing the tip of the magnetic brush. . The toner in the magnetic brush is supplied onto the surface of the toner carrying roller 2 due to this rubbing or the potential difference between the toner supply sleeve 19 and the toner carrying roller 2. A supply bias is applied to the toner supply sleeve 19 by a supply bias power source 24. The supply bias may be a DC voltage having the same polarity as the charging polarity of the toner, or may be an AC voltage superimposed on the DC voltage.

  The magnetic brush (mixture) on the toner supply sleeve 19 that has passed through the toner supply position is conveyed to a position facing the second storage portion 15 as the sleeve rotates. In the vicinity of the facing position, the magnetic roller 20 is not provided with a magnetic pole, and no magnetic force attracts the mixture to the sleeve surface, so that the mixture separates from the sleeve surface and is contained in the second container 15. Return to.

  In this printer, the magnet roller 20 has six magnetic poles, but the number of magnetic poles is not limited to this. It may be 8 poles, 12 poles, or the like.

  The toner carrying roller 2 that carries the toner supplied from the toner supply roll 18 exposes a part of the peripheral surface from an opening provided in the casing 11 of the developing device 1. This exposed portion is opposed to the photoreceptor 49 with a gap of several tens to several hundreds [μm]. Thus, the position where the toner carrying roller 2 and the photosensitive member 49 are opposed to each other is the developing position in the printer.

  The toner supplied on the surface of the toner carrying roller 2 is hopped on the surface of the toner carrying roller 2 from the toner supply position toward the developing position with the rotation of the toner carrying roller 2 for the reason described later. Be transported. At the development position, the toner adheres to the electrostatic latent image on the photoreceptor 49 and develops it into a toner image.

  FIG. 3 is a perspective view showing the toner carrying roller 2. The toner carrying roller 2 includes a plurality of electrodes that extend in the roller axial direction and are arranged at a predetermined pitch in the roller circumferential direction on the circumferential surface of the roller portion. More specifically, as shown in FIG. 4, the plurality of electrodes are formed by alternately arranging the A-phase electrodes 3a and the B-phase electrodes 3b in the roller circumferential direction.

  In FIG. 3, the A-phase common electrode 4a is provided at one end in the axial direction of the roller portion of the toner carrying roller 2 so as to extend over the entire circumference of the roller portion. Is connected to one end of each of the plurality of A-phase electrodes 3a. Further, a B-phase common electrode 4b is provided at the other end in the axial direction of the roller portion so as to extend over the entire circumference of the roller portion, and this includes the other ends of the plurality of B-phase electrodes 3b. Each part is connected.

  Although not shown in FIGS. 3 and 4 for convenience, a surface layer 5 made of a non-conductive material is coated on the plurality of A-phase electrodes 3a and B-phase electrodes 3b as shown in FIG. The surface layer 5 avoids contact between the electrodes and the toner. However, no surface layer is provided on the A-phase common electrode 3a and the B-phase common electrode 3b shown in FIG. 3, and these common electrodes are exposed. Then, an A-phase brush contact member (not shown) fixed to the casing (11) rubs against the A-phase common electrode 4a that moves endlessly as the toner carrying roller 2 rotates. The A-phase pulse voltage Va output from the pulse power supply 25 is applied to each A-phase electrode 3a via the A-phase brush contact member and the A-phase common electrode 4a. A B-phase brush contact member (not shown) fixed to the casing rubs against the B-phase common electrode 4b that moves endlessly as the toner carrying roller 2 rotates. The B-phase pulse voltage Vb output from the pulse power supply 25 is applied to each B-phase electrode 3b via the B-phase brush contact member and the B-phase common electrode 4b.

  Hereinafter, a set of a plurality of A-phase electrodes 3a to which the A-phase pulse voltage Va is applied is referred to as an A-phase electrode group. A set of a plurality of B-phase electrodes 3b to which a B-phase pulse voltage is applied is referred to as a B-phase electrode group. Since the A-phase electrodes 3a and the B-phase electrodes 3b are alternately arranged, the order of arrangement of the plurality of A-phase electrodes 3a from the predetermined position in the roller circumferential direction is odd or even. The arrangement order of the plurality of B-phase electrodes 3b is even when the arrangement order of the A-phase electrodes 3a is odd, and is even when the arrangement order of the A-phase electrodes 3a is even. .

  For example, as shown in FIG. 6, the A-phase pulse voltage Va applied to the A-phase electrode group has a rectangular wave characteristic that repeats rising and falling at a predetermined cycle with a predetermined potential as a center. On the other hand, the B-phase pulse voltage Vb applied to the B-phase electrode group has a rectangular wave characteristic in which the rising and falling phases are opposite to the A-phase pulse voltage Va as shown in FIG. is doing. When such a pulse voltage is applied, the toner on the toner-carrying roller (2) floats from directly above the A-phase electrode 3a and lands on the adjacent B-phase electrode 3b so as to draw a parabola. After that, the reciprocating movement by hopping is repeated such that it floats right above the B-phase electrode 3b and returns to the adjacent A-phase electrode 3a so as to draw a parabola.

  In this way, the toner that repeats reciprocating movement by hopping is conveyed to the developing position by the rotational drive of the toner carrying roller (2). At the development position, when the vicinity of the electrostatic latent image of the photoconductor (3) reaches the vicinity of the apex of the parabolic hopping locus, the electrostatic latent image deviates from the hopping locus while being pulled by the electrostatic force. Adhere to the electrostatic latent image. On the other hand, when it reaches the vicinity of the background portion of the photoreceptor (3) near the apex of the parabolic hopping locus, it descends without departing from the hopping locus and lands on the surface of the toner carrying roller (2).

  In such a configuration, the toner in which the adsorbing force with the toner carrying roller (2) is released by hopping is used for the development, so that the conventional one-component development method and the two-component development method could not be realized. Low potential development can be realized. Hereinafter, as in the present image forming apparatus, flare development is a method in which development is performed by transporting toner to the development position by moving the surface of the toner carrier while reciprocating the toner between the electrodes of the toner carrier by hopping. It is called a method.

  In the printer according to the present embodiment, the peak-to-peak voltage Vpp is 200 to 1000 [V] as the A-phase pulse voltage Va and the B-phase pulse voltage Vb, and the frequency f is 0.5 to 5 [V]. [kHz]. The A-phase pulse voltage Va and the B-phase pulse voltage have the same values of the peak-to-peak voltage Vpp, the center potential of the amplitude, and the frequency f. The center potential of the amplitude is set to a value between the latent image potential of the photoreceptor 49 and the background portion potential.

  The pulse voltage applied to the A-phase electrode group and the B-phase electrode group includes an A-phase pulse voltage Va composed of a rectangular wave as shown in FIG. 7 and a DC voltage Vb or 0 [V] that is the center value of the amplitude of the A-phase pulse voltage Va. ] May be adopted. Further, the relationship between the A phase and the B phase in this combination may be reversed. Further, as the waveform of the pulse voltage, other than a rectangular wave, for example, a sine wave, a triangular wave having a time constant, a sine wave corresponding to the time constant, or the like may be employed.

  In FIG. 2 described above, the toner that has not contributed to the development at the development position returns into the casing 11 as the toner carrying roller 2 rotates, and then enters the toner supply position. Even at this toner supply position, since the toner does not exhibit the adhesive force with the roller surface by hopping, it is easily scraped or leveled by the magnetic brush that rubs against the toner carrying roller 2 in the counter direction. . At the same time, new toner is supplied from the magnetic brush on the toner supply sleeve 19. Due to the synergistic action of scraping, collecting, leveling and supply, a uniform amount of toner hops on the surface of the toner carrying roller 12 after passing through the toner supply position.

In FIG. 5 shown above, the A-phase electrode 3a and the B-phase electrode 3b are formed by processing a conductive layer made of a conductive material formed on an insulating support substrate 6 into a required electrode shape by a photolithography method or the like. It has been done. As the support substrate 6, a substrate made of an insulating material such as a glass substrate, a resin substrate, a ceramic substrate, a polyimide substrate, or a substrate made of a conductive material such as SUS, SiO ₂ , BaTiO ₂ , TiO ₂ , TiO ₄ , SiON It is possible to use a substrate on which an insulating film made of BN, TiN, Ta ₂ O ₅ or the like is formed.

  In the drawing, R indicates a gap between the A-phase electrode 3a and the B-phase electrode 17B. Moreover, L has shown the width | variety which is the length of the transversal direction of these electrodes. The electrode arrangement pitch P can be represented by a gap R + width L. On the roller surface, M toner (not shown) located between the electrodes moves along the electric lines of force extending in the direction in which the electrodes are arranged so as to lick the roller surface. On the other hand, the M toner positioned on the electrodes (3a, 3b) hops along the electric lines of force formed so as to draw a parabola between the electrodes, so that it contacts and separates from the roller surface. . In addition, the M toner located near the end in the width direction of the electrode may hop so as to jump over the adjacent electrode. For this reason, when the width L is relatively large, the number of M toner particles on the vicinity of the electrode end portion is relatively large, so that the toner having a large moving distance is relatively large. However, if the width L is too large, the electric field strength in the vicinity of the center of the electrode becomes relatively weak, resulting in poor hopping efficiency. There is an appropriate width L value for efficiently hopping toner at a low voltage.

  The gap R is an element that affects the electric field strength between the electrodes. When the magnitude (amplitude) of the pulse voltage applied to the electrodes is constant, the electric field strength between the electrodes increases as the gap R decreases. Hopping speed increases. However, with the M toner that hops from right above the electrode to right above the adjacent electrode, the moving distance per hopping is relatively short. For this reason, if the frequency f of the pulse voltage is not set high, the landing time becomes longer than the floating time, resulting in poor efficiency. Therefore, there is also an appropriate gap R value for efficiently hopping toner at a low voltage.

  Further, the thickness of the surface layer 5 is one factor that influences the electric field strength on the roller surface. In particular, the influence of the vertical component on the electric field lines is large, which greatly affects the efficiency of hopping. That is, setting the width L, the gap R, and the surface layer thickness appropriately is an important factor for performing efficient hopping at a low voltage.

  In the image forming apparatus according to the present exemplary embodiment, a negatively chargeable toner is used as the toner, but a positively chargeable toner may be used.

Next, a characteristic configuration of the image forming apparatus according to the present embodiment will be described.
Generally, when toner powder is rubbed, the triboelectric charge amount of individual toner particles in the toner powder is not constant, and the charge amount shows a normal distribution curve. In addition, there are not a few negatively charged toner particles that are not reflected in the normal distribution curve and are frictionally charged to a polarity opposite to the normal polarity.

  FIG. 8 is an enlarged configuration diagram illustrating the toner carrying roller 2 and the surrounding configuration of the image forming apparatus according to the present embodiment. In the figure, a region denoted by Ar0 is a toner supply position where the toner carrying roller 2 and a magnetic brush (not shown) formed on the surface of the toner supply sleeve 19 of the toner supply roll 18 serving as the toner supply means rub. Is shown. An area denoted by Ar2 indicates a development position. An area denoted by Ar1 is an area before passing the toner supply position Ar0 and before entering the developing position Ar2 out of all areas in the rotation direction (endless movement direction) of the surface of the toner carrying roller 2. The pre-development transport area is shown. An area denoted by Ar3 indicates a post-development conveyance area as an area before passing through the development position Ar2 and before entering the toner supply position Ar0.

  The developing area Ar2 is an area where the photoconductor 49 and the toner carrying roller 2 face each other, and the photoconductor 49 is very close to the toner carrying roller 2 due to its curvature. The length in the roller rotation direction at the developing position Ar2 can be measured as follows. That is, the solid image formed on the photoconductor 49 is developed while photographing the behavior of the toner at the development position Ar2 and its vicinity in the vicinity of the high-speed and high-speed camera. The toner particles adhering to the upstream end of the solid image in the photosensitive member rotation direction are finally hopped on the surface of the toner carrying roller 2 and the toner particles adhering to the downstream end of the solid image in the photosensitive member rotation direction are the toner. The distance from the last hopped position on the surface of the carrier roller 2 is measured. This distance is the length of the developing area Ar2 in the roller rotation direction.

  The individual toner particles hopped in the pre-development transport area Ar1 gradually approach the development position Ar2 as the toner carrying roller 2 rotates, and include reversely charged toner particles. Further, reversely charged toner particles that are larger than the average toner charge amount on the normal polarity side are also included. When these reversely charged toner particles and high charge amount toner particles are conveyed to the developing position Ar2, they adhere to the non-image area (background area) of the photoreceptor 49 and cause background stains.

  Therefore, in the image forming apparatus according to the present embodiment, the development for collecting the reversely charged toner particles and the high charge amount toner particles out of the toner particles hopping on the surface of the toner carrying roller 2 in the pre-development conveyance area Ar1. Pre-toner collecting means is provided. This pre-development toner collecting means has a pre-development counter electrode 26 that faces the pre-development transport area Ar1 in a rotational direction on the surface of the toner carrying roller 2 via a predetermined gap. . Further, it has a pre-development recovery bias power source 27 as voltage supply means for supplying a pre-development recovery bias to the pre-development counter electrode 26.

  The pre-development counter electrode 26 has at least a surface facing the toner carrying roller 2 so that a gap between the toner carrying roller 2 and the toner carrying roller 2 is uniform from the upstream end to the downstream end in the rotation direction. It is curved. This gap is set to the same value as the developing gap which is the minimum gap between the photosensitive member 49 and the toner carrying roller 2 at the developing position Ar2.

  The pre-development recovery bias power supply 27 outputs a pre-development counter bias composed of a DC voltage having the same polarity and value for the background portion (uniform charging potential) of the photoreceptor 49. That is, by applying the pre-development counter bias, the potential of the pre-development counter electrode 26 has the same polarity and the same value as the background portion potential on the photoconductor 49.

  The above-mentioned pre-development toner collection means has a control unit (not shown) for controlling on / off of the pre-development collection bias output from this power supply, in addition to the pre-development counter electrode 26 and the pre-development collection bias power supply 27. During the developing operation (a state in which toner that can contribute to the development of the electrostatic latent image is being conveyed in the pre-development conveyance area Ar1 and the development position Ar2), the pre-development recovery bias with respect to the predevelopment counter electrode 26. Is applied. In such a configuration, among the infinite number of toner particles hopped in the pre-development transport area Ar1, a scumming toner that adheres to the background of the photoreceptor 49 at the development position Ar2 and causes scumming, that is, reverse charging. The toner particles and the high charge amount toner particles are selectively attached to the counter electrode 26 before development. Thus, the background toner is selectively separated from the toner conveyed in the pre-development conveyance area Ar1.

  When the developing operation (continuous developing operation at the time of continuous printing) is completed, the control unit uses the control signal to change the output voltage from the pre-development recovery bias power supply 27 from the above-described separation bias to the charging polarity side of the toner. To a large discharge bias (large in the negative side in this example). Further, the charging device (50) is controlled so that the uniform charging potential of the photosensitive member 49 is increased to the charging polarity side of the toner as compared with normal printing. As a result, the reversely charged toner particles and the high charge amount toner particles adhering to the pre-development counter electrode 26 are detached from the pre-development counter electrode 26 and discharged onto the surface of the toner carrying roller 2. Then, after passing through the development position Ar2 and the post-development transport area Ar3, the toner is collected in the magnetic brush at the toner supply position Ar0.

  The high charge amount toner particles conveyed on the pre-development conveyance area Ar1 have a larger charge amount than other toner particles, and therefore hop higher than the other toner particles. Then, when the maximum level is reached by hopping, a toner cloud composed of a large amount of toner particles is positioned below itself, and due to the repulsive force, the toner cloud is scattered to the extent that the restraining force due to the electric field on the toner carrying roller 2 does not reach. is there. By providing the pre-development counter electrode 26, it is possible to prevent such scattering of the high charge amount toner particles.

  As the pre-development counter electrode 26, it is desirable to use a surface of an electrode layer made of a conductive material such as a metal (a surface facing the toner carrying roller 2) covered with an insulating layer made of an insulating material. According to such a configuration, it is possible to avoid charge injection to the toner particles and leakage of the charge of the toner particles to the electrode layer by directly contacting the toner particles with the conductive solid surface of the counter electrode 26 before development. it can.

  Further, as the counter electrode 26 before development, the length in the direction orthogonal to the roller rotation direction on the surface facing the toner carrying roller 2 is the length in the same direction of the surface facing the counter electrode 26 before development in the toner carrying roller 2. More than that is used. In such a configuration, the toner that has been hopped in the pre-development conveyance area Ar1 can be subjected to separation processing of the reversely charged toner particles and the high charge amount toner particles in the entire area in the orthogonal direction.

  As the pre-development counter electrode 26, an electrode in which the length in the roller rotation direction on the surface facing the toner carrying roller 26 is longer than the length in the roller rotation direction at the development position Ar2 is used. In such a configuration, unlike the case where the length of the developing position Ar2 is less than the length in the roller rotation direction, the toner is transported immediately below the counter electrode 26 before development for a time longer than the developing position passing time, so that the developing position Ar2 is grounded. Reversely charged toner particles and high charge amount toner particles that become dirty toner can be reliably separated.

  Regarding the toner hopping condition in the area where the toner carrying roller 2 and the pre-development counter electrode 26 face each other (hereinafter, this area is referred to as a pre-development collection area) in the pre-development transport area Ar1, the toner hopping condition in the development position Ar2 Set the same. With such a configuration, it is possible to avoid the deterioration of the separation / collection accuracy of the reversely charged toner particles and the high charge amount toner particles caused by making the toner hopping condition in the pre-development collection area different from the development position Ar2. The toner hopping conditions mentioned here are a combination of the width of the electrodes (3a, 3b), the arrangement pitch of the electrodes, the characteristics of the pulse voltage applied to each electrode, and the thickness of the surface layer (5).

  FIG. 9 is an enlarged configuration diagram showing the developing device 1 in the first modified example of the image forming apparatus according to the embodiment together with the photoreceptor 49. In the developing device 1, the nonmagnetic toner accommodated in the toner accommodating portion in the casing 11 is conveyed toward the toner supply roller 30 described later by the rotation of the two agitation paddles 31.

  The toner supply roller 30 is driven to rotate counterclockwise in the drawing by a driving unit (not shown) while carrying the non-magnetic toner sent from the stirring paddle 31 on the surface. When the non-magnetic toner carried on the surface of the toner supply roller 30 enters the contact position between the roller and the regulating member 22 as the roller rotates, frictional charging is promoted and the non-magnetic toner on the toner supply roller 30 is Layer thickness is regulated.

  The nonmagnetic toner whose layer thickness is regulated in this way enters the toner supply position where the toner carrying roller 2 and the toner supply roller 30 face each other as the toner supply roller 30 rotates. Then, due to the potential difference between the toner supply roller 30 to which the supply bias is applied by the supply bias power supply 24 and the toner carrying roller 2, the toner is transferred from the toner supply roller 30 to the toner carrying roller 2. Thereafter, in the process of being conveyed along with the rotation of the toner carrying roller 2, the reversely charged toner particles and the high charge amount toner particles are collected on the pre-development counter electrode 26 in the pre-development conveyance area (Ar1).

  FIG. 10 is an enlarged configuration diagram showing the developing device 1 together with the photoconductor 49 in the second modified example of the image forming apparatus according to the embodiment. The developing device 1 moves the surface of the roller portion in the opposite direction to the toner carrying roller 2 at the contact portion while the roller portion made of an elastic material such as sponge in the toner supply roller 30 is in contact with the toner carrying roller 2. The toner supply roller 30 is rotated. The toner on the toner supply roller 30 is rubbed at the contact portion between the toner carrying roller 2 and the toner supply roller 30 and is transferred to the toner carrying roller 2 while frictional charging is promoted. Thereafter, in the process of being conveyed along with the rotation of the toner carrying roller 2, the reversely charged toner particles and the high charge amount toner particles are collected on the pre-development counter electrode 26 in the pre-development conveyance area (Ar1).

  FIG. 11 is an enlarged cross-sectional view showing the toner carrying roller 2 in the third modified example of the image forming apparatus according to the embodiment. In the toner carrying roller 2, an intermediate layer 7 made of an insulating material is formed between the support substrate 6 and the surface layer 5. An A-phase electrode 3 a and a B-phase electrode 3 b are formed on the surface of the support substrate 6, and the intermediate layer 7 is laminated on these electrodes and on the non-electrode formation surface of the support substrate 6. Has been.

  A C-phase electrode 3 c is formed on the intermediate layer 7. And the surface layer 5 is coat | covered on this C-phase electrode 3c and the non-electrode formation surface of the intermediate | middle layer 7. FIG.

  In the surface movement direction (arrow direction in the figure) of the toner carrying roller 2, the A-phase electrode 3a, the B-phase electrode 3b, and the C-phase electrode 3c are arranged in order at a predetermined pitch. And each electrode is arrange | positioned so that three rows may be repeated.

  As shown in FIG. 12, one end of each A-phase electrode 3a is connected to an A-phase common electrode 4a extending over the entire circumference of the roller. Further, one end of each B-phase electrode 3b is connected to a B-phase common electrode 4b extending over the entire circumference of the roller in a non-contact manner with respect to the A-phase common electrode 4a adjacent to the A-phase common electrode 4a. Has been. Further, the other end of each C-phase electrode 3c is connected to a C-phase common electrode 4c extending over the entire circumference of the roller at the other end of the roller portion.

  A phase pulse voltage Va, B phase pulse voltage Vb, and C phase pulse voltage Vc as shown in FIG. 13 are applied to the A phase electrode group, the B phase electrode group, and the C phase electrode group. These pulse voltages have the same peak-to-peak voltage Vpp, center potential of amplitude, and frequency f. However, the phases are shifted from each other. When such a pulse voltage is applied, the toner on the surface of the toner-carrying roller 2 performs hopping that moves sequentially in the direction of the arrow in the figure, not hopping that reciprocates. Thus, the toner is transported toward the developing position not only by the surface movement of the toner carrying roller 2 but also by its own hopping. In this conveyance process, reversely charged toner particles and high charge amount toner particles are collected in the pre-development conveyance area in the same manner as in the image forming apparatus according to the embodiment.

Next, the image forming apparatus of each example in which a more characteristic configuration is added to the image forming apparatus according to the embodiment will be described. Note that the configuration of the image forming apparatus according to each example is the same as that of the embodiment unless otherwise specified.
[First embodiment]
FIG. 14 is an enlarged configuration diagram illustrating the toner carrying roller 2 and its peripheral configuration in the developing device (1) of the image forming apparatus according to the first embodiment. In the figure, the post-development counter electrode 28, which is a post-development counter member, faces the post-development transport area Ar3 out of the entire area of the surface of the toner carrying roller 2 in the rotational direction. . Similarly to the pre-development counter electrode 26, the post-development counter electrode 28 is at least a toner carrying roller so that the gap with the toner carrying roller 2 is uniform from the upstream end to the downstream end in the roller rotation direction. The surface facing 2 is curved.

  In such a configuration, the post-development counter electrode 28 can prevent the toner particles hopping in the post-development transport area Ar3 from scattering. Note that a post-development bias power source 29 is connected to the post-development counter electrode 28 through a conductive line. The post-development bias power supply 29 outputs a post-development bias having the same polarity as the toner charging polarity to the post-development counter electrode 28. In this configuration, the counter electrode 28 after development and the toner hopped on the toner carrying roller 2 are electrostatically repelled by a bias after development, so that the counter electrode 28 after development and the hopped toner particles are in contact with each other. Can be suppressed. Thereby, adhesion of toner particles to the counter electrode 28 after development can be suppressed.

  As the counter electrode 28 after development, for the same reason as the counter electrode 26 before development, the surface of an electrode layer made of a conductive material such as metal is coated with an insulating layer made of an insulating material. desirable. In addition, it is desirable to use a surface of the surface facing the toner carrying roller 2 that has a length in the direction orthogonal to the roller rotation direction that is equal to or greater than the length of the toner carrying roller 2 in the same direction. Furthermore, it is desirable to use a roller in which the length in the roller rotation direction on the surface facing the toner carrying roller 2 is greater than or equal to the length in the roller rotation direction at the development position Ar2.

  Further, if the value of the post-development bias is too large, the hopping electric field on the surface of the toner carrying member 2 is crushed and the toner is prevented from being conveyed well. Therefore, the size is set so as not to crush the hopping electric field.

[Second Embodiment]
FIG. 15 is a schematic configuration diagram illustrating an image forming apparatus according to the second embodiment. This image forming apparatus can form a full-color image by superimposing magenta, cyan, yellow, and black (hereinafter referred to as M, C, Y, and K) toner images. The belt unit 81, four process units individually corresponding to four colors, four optical writing units 100M, C, Y, and K, a registration roller pair 79, a transfer roller 87, a fixing device 76, and a paper feed cassette 78 Etc.

  The belt unit 81 endlessly moves an endless belt-like photoreceptor 49 serving as a latent image carrier in a counterclockwise direction in the drawing while stretching in a vertically long posture that takes a space in the vertical direction rather than the horizontal direction. More specifically, the photosensitive member 49 on the endless belt is stretched while being supported from the back side by a driving roller 83, a tension roller 84, a transfer backup roller 85, and four developing counter rollers 86M, C, Y, and K. . Then, the photosensitive member 49 is moved endlessly by the rotation of the driving roller 83 that is driven to rotate counterclockwise in the drawing by a driving means (not shown). The left extending surface in the drawing (hereinafter referred to as the left extending surface) of the photoconductor 49 is in a posture extending substantially in the vertical direction.

  Process units for M, C, Y, and K are arranged in the vertical direction on the left side of the left-side stretched surface of the photoconductor 49, and are arranged on the left-side stretched surface of the photoconductor 49, respectively. Opposite. Each of these four process units includes a developing device (1M, C, Y, K) and a charging device (50M, C, Y, K) for uniformly charging the photoreceptor 49 as one unit, not shown. Is held on the holder. As shown in FIG. 16, the developing device and the charging device are integrally attached to and detached from the printer housing.

  In FIG. 15 shown above, among the four developing devices 1M, C, Y, and K, the K charging device 50K is exposed above the K developing device 1K positioned at the lowest in the vertical direction. The body 49 is disposed so as to face the left-side stretched surface. Further, a Y charging device 50Y is disposed above the Y developing device 1Y disposed immediately above the K developing device 1K so as to face the left-side stretched surface of the photoconductor 49. ing. Further, a C charging device 50C is disposed above the C developing device 1C disposed immediately above the Y developing device 1Y so as to face the left-side stretched surface of the photoreceptor 49. ing. Further, an M charging device 50M is disposed above the M developing device 1M disposed immediately above the Y developing device 1Y so as to face the left-side stretched surface of the photoreceptor 49. ing.

  Four optical writing units 100M, C, Y, and K are arranged in the vertical direction on the left side of the four developing devices 1M, C, Y, and K arranged in the vertical direction. These optical writing units 100M, C, Y, and K drive M, C, Y, and K by driving four semiconductor lasers (not shown) based on image information sent from an external personal computer or scanner (not shown). Writing light Lm, Lc, Ly, and Lk is emitted. Then, while deflecting them by a polygon mirror (not shown), they are reflected by a reflection mirror (not shown) or passed through an optical lens to perform optical scanning on the photoconductor 49. Instead of such a configuration, an LED array that performs optical scanning may be used. The optical scanning is performed in the dark.

  Among the plurality of stretching rollers that stretch the photosensitive member 49, the photosensitive member 49 is directed from the upper side to the lower side in the vertical direction between the driving roller 83 positioned at the lowermost position and the tension roller 84 positioned at the uppermost position. And move almost straight. In this process, first, when passing through a position facing the M charging device 50M, for example, the negative charge is uniformly charged. Then, after carrying the electrostatic latent image for M by optical scanning with the M writing light Lm, it passes through a position facing the developing device 1M for M. At this time, the electrostatic latent image for M written on the photosensitive member 49 is developed by the developing device 1M for M to become an M toner image.

  The photosensitive member 49 on which the M toner image is formed is uniformly charged again by the C charging device 50C in accordance with the movement from the upper side to the lower side in the vertical direction, and then is written by the C writing light Lc. An electrostatic latent image for C is carried by optical scanning. The C electrostatic latent image is developed by the C developing device 1C to become a C toner image. At this time, the entire region or a partial region of the C toner image is developed while being superimposed on the M toner image already formed on the photoreceptor 49. Then, the overlapping portion becomes a secondary color portion by M and C.

  The photosensitive member 49 on which the C toner image is formed is uniformly charged again by the Y charging device 50Y in accordance with the movement from the upper side to the lower side in the vertical direction, and then is written by the Y writing light Ly. An electrostatic latent image for Y is carried by optical scanning. The Y electrostatic latent image is developed by the Y developing device 1Y to become a Y toner image. At this time, the entire area or a partial area of the Y toner image is developed in a state of being superimposed on the M toner image, the C toner image, or the MC secondary color portion already formed on the photoreceptor 49. Then, the overlapping portion becomes a MY secondary color portion, a CY secondary color portion, or an MCY tertiary color portion.

  The photosensitive member 49 on which the Y toner image is formed is uniformly charged again by the K charging device 50K as it moves from the upper side to the lower side in the vertical direction, and then is written by the K writing light Lk. An electrostatic latent image for K is carried by optical scanning. The K electrostatic latent image is developed by the K developing device 1K to become a K toner image.

  By superimposing and developing the M, C, Y, and K toner images as described above, a four-color superimposed toner image is formed on the front surface (loop outer surface) of the photoreceptor 49. As the charging devices 50M, C, Y, and K for M, C, Y, and K, those that uniformly charge the photosensitive member 49 by corona discharge are used.

  The photosensitive member 49 that has passed through the K developing position, which is the position facing the K developing device 1K, moves relative to the vertical direction from the lower side to the upper side when the photosensitive member 49 passes around the driving roller 83. Will come to do. Then, it enters the place where the transfer backup roller 85 is wound. A transfer roller 87 is in contact with the part of the hung portion from the front surface side to form a transfer nip. While the transfer backup roller 85 is grounded, a transfer bias is applied to the conductive transfer roller 87 by a bias applying means (not shown). Thus, a transfer electric field for electrostatically moving the toner image on the photosensitive member 49 from the transfer backup roller 85 side to the transfer roller 87 side between the transfer backup roller 85 and the transfer roller 87 sandwiching the transfer nip therebetween. Is formed.

  On the other hand, the paper feed cassette 78 feeds the recording paper P stored in the cassette toward the paper feed path by rotating the paper feed roller 78a at a predetermined timing. The fed recording paper P is sandwiched between rollers of a registration roller pair 79 disposed below the transfer nip in the drawing. As soon as the registration roller pair 79 sandwiches the leading end portion of the recording paper P, the rotational driving is temporarily stopped. Then, the rotational driving is resumed at a timing at which the recording paper P can be synchronized with the four-color superimposed toner image on the photoconductor 49, and the recording paper P is sent to the transfer nip.

  The four-color superimposed toner image brought into intimate contact with the recording paper P at the transfer nip is collectively transferred from the belt to the recording paper P by the action of the nip pressure and the transfer electric field, and becomes a full color image combined with the white color of the recording paper P. The recording paper P on which a full-color image has been formed in this manner is sent from the transfer nip to the fixing device 76 and then discharged outside the apparatus.

  FIG. 17 is an enlarged configuration diagram showing the K process unit together with the photoreceptor 49. In the developing device 1K shown in the figure, the post-development counter electrode 28K facing the post-development transport region of the toner carrying roller 2K is cantilevered by the vibrator 32K, and its free end is opposed to the toner carrying roller 2K. ing.

  K toner that has not contributed to development at the development position (Ar2) travels to the post-development conveyance area (Ar3) of the toner carrying roller 2K, and then transfers to the surface of the post-development counter electrode 28K to which a post-development bias is applied. . By this transition, K toner is collected from the post-development conveyance area (Ar3) of the toner carrying roller 2K.

  When the timing at which the development operation is not performed, such as after a print job, is reached, the application of the post-development bias is stopped. Thereafter, the operation of a relay switch (not shown) connected to the post-development counter electrode 28K causes the vibrator 32K serving as a vibration means to operate in a state where the post-development counter electrode 28K is grounded, and the post-development counter electrode 28K K toner is shaken off from the surface. Then, it falls to the contact position with the magnetic brush on the toner supply sleeve 19K by its own weight, and is taken into the magnetic brush.

  Note that the counter electrode 28K after development is desirably arranged in a posture in which the toner adhesion surface is inclined as shown in the drawing in order to promote slipping of the K toner from the surface.

  Further, at a timing after a print job, the bias applied to the counter electrode 28K after development is switched to the same polarity as the K toner, and the K toner is transferred again from the counter electrode 28KK to the toner carrying roller 2K after development. It may be used.

  Although the developing device 1K for K has been described in detail, the developing devices for other colors (1M, C, Y) have the same configuration as that for K, and thus the description thereof is omitted. In addition to the charging device or in addition to the charging device, a cleaning unit, a photosensitive member, and the like may be integrated to form a process unit.

[Third embodiment]
FIG. 18 is an enlarged configuration diagram showing the K process unit together with the photoreceptor 49 in the image forming apparatus according to the third embodiment. This image forming apparatus is different from the image forming apparatus according to the second embodiment in the configuration of each color developing device (1M, C, Y, K), but the other points are the image forming apparatus according to the second embodiment. It has become the same.

  In the figure, the developing device 1K has a post-development facing roller 33K as a post-development counter electrode. The post-development opposing roller 33K is rotationally driven in a counterclockwise direction in the figure by a driving means (not shown) while a post-development bias having a polarity opposite to that of the K toner is applied by a post-development bias power source 29K.

  K toner that has not contributed to development at the development position is transferred from the surface of the toner carrying roller 2K to the surface of the counter roller 33K after development in the post-development conveyance area (Ar3). When the counter roller 33K after development reaches the contact portion between the counter roller 33K after development and the cleaning blade 34K as a separating unit, the cleaning blade 34K scrapes off the surface of the counter roller 33K after development. . After that, it falls to the contact position with the magnetic brush on the surface of the toner supply sleeve 2K by its own weight, and is taken into the magnetic brush.

  As shown in the figure, the post-development facing roller 33K is preferably rotated at a position facing the toner carrying roller 2K in such a direction as to move in the same direction as the surface of the toner carrying roller 2K. Further, it is desirable that the linear speed (surface movement speed) of the counter roller 33K after development is higher than the linear speed of the toner carrying roller 2K. By doing this, the solid surface without toner adhesion on the counter roller 33K after development is made to face the K toner on the toner carrying roller 2K that has entered the position facing the counter roller 33K after development. This is because the toner can be satisfactorily transferred to a solid surface.

[Fourth embodiment]
FIG. 19 is an enlarged configuration diagram showing the K process unit together with the photoreceptor 49 in the image forming apparatus according to the fourth embodiment. This image forming apparatus also differs from the image forming apparatus according to the second embodiment in the configuration of each color developing device (1M, C, Y, K), but the other points are the image forming apparatus according to the second embodiment. It has become the same.

  In the figure, the developing device 1K has a collection brush roller 35K instead of the counter electrode after development. The recovery brush roller 35K includes a metal rotary shaft member that is rotatably supported by a bearing, and a brush portion that is formed of a plurality of conductive raised brushes erected on the peripheral surface thereof. Yes.

  The recovery brush roller 35K to which a bias having a polarity opposite to that of the K toner is applied to the rotary shaft member by the post-development bias power supply 29K is arranged such that the tip of the brush portion formed of a plurality of raised portions is conveyed to the post-development conveyance area (Ar3) of the toner carrying roller 2K. ) Is rotated in a direction in which the brush portion is moved in the direction opposite to the surface moving direction of the toner carrying roller 2K. As a result, at the position where the brush portion and the toner carrying roller 2K are in contact with each other, the K toner on the toner carrying roller 2K is scraped off by the brush portion and is transferred and captured in the brush by the action of the bias.

  The K toner trapped in the brush part is shaken from the brush part due to the impact when the fluffed rod 36K, which is a separating means arranged so as to contact the brush part while extending in the brush rotation axis direction, is bounced. Be dropped. A bias roller may be brought into contact with the brush tip instead of the flicker bar 36K. The K toner shaken off from the brush portion by the flicker bar 36K falls to the contact position with the magnetic brush on the surface of the toner supply sleeve 2K by its own weight, and is taken into the magnetic brush.

[Fifth embodiment]
FIG. 20 is an enlarged configuration diagram showing the K process unit together with the photoreceptor 49 in the image forming apparatus according to the fifth embodiment. This image forming apparatus also differs from the image forming apparatus according to the second embodiment in the configuration of each color developing device (1M, C, Y, K), but the other points are the image forming apparatus according to the second embodiment. It has become the same.

  In the figure, the developing device 1K has a suction nozzle 37K as a suction member in place of the counter electrode after development.

  A suction part of a suction pump 39K is connected to the suction nozzle 37K via a relay pipe. An exhaust pipe is connected to the discharge part of the suction pump 39K, and the end of the exhaust pipe is connected to the first housing part 13K of the developing device 1K.

  When the suction pump 39K is operated, air in the vicinity of the suction port of the suction nozzle 37K is sucked into the suction port. At this time, the K toner hopped in the vicinity of the suction port on the toner carrying roller 2K on the post-development conveyance area is sucked into the suction port together with air and collected from the toner carrying roller 2K. Then, after sequentially passing through the relay pipe, the suction pump 39K, and the discharge pipe, it is returned to the first housing portion 13K of the developing device 1K.

  A seal member 38K is cantilevered on the downstream side in the toner transport direction around the suction port of the suction nozzle 37K, and the free end thereof is in contact with the toner carrying roller 2K. This avoids a situation in which the air around the toner supply sleeve 19KK is sucked together with the K toner in the magnetic brush. Further, the K toner rotating together with the toner supply sleeve 2K while hopping is blocked by abutting against the seal member 38K, and is restrained at a position facing the suction port.

  The tip of the suction nozzle 37K. The gap with the surface of the toner carrying roller 2K is preferably several tens to several hundreds [μm] and smaller than the hopping height of K toner on the surface of the toner carrying roller 2K.

  As the suction pump 39K, a pump capable of sucking powder such as K toner, such as a diaphragm pump and a Mono pump, is employed.

  Note that the present invention can also be applied to a color image forming apparatus, a monochrome image forming apparatus, and the like using an intermediate transfer belt, a transfer drum, an intermediate transfer drum, and the like.

  As described above, in the image forming apparatus according to the embodiment, each modified apparatus, and the image forming apparatus according to each example, as the pre-development toner collecting unit, both the reversely charged toner particles and the high charge amount toner particles are collected. , Is used. In such a configuration, it is possible to suppress the occurrence of background contamination as compared with the case of collecting only one of the toner particles.

  Further, in the image forming apparatus according to the embodiment, each modified apparatus, and the image forming apparatus according to each example, a pre-development toner collecting unit has a predetermined pre-development conveyance area of a toner-carrying roller as a toner-carrying member. A reversely charged toner particle and a high charge amount toner particle hopping on the surface of the pre-development conveyance area having a pre-development counter electrode facing each other through a gap are attached to the pre-development counter electrode. The one to be collected is used. In such a configuration, reversely charged toner particles and high charge amount toner particles out of the toner hopped in the recovery area before development can be attached to the counter electrode before development and separated from other toner particles.

  In the image forming apparatuses according to the first, second, and third embodiments, after passing through the developing position and before entering the toner supply position in all the areas in the endless movement direction of the surface of the toner carrying roller. A post-development facing member is provided to face the post-development transport area, which is an area, with a predetermined gap therebetween. In such a configuration, scattering of toner particles conveyed in the post-development conveyance region can be prevented by the counter member after development.

  In the image forming apparatus according to the embodiment, each modified apparatus, and the image forming apparatus according to each example, the background of the photosensitive member 49 serving as a latent image carrier with respect to the pre-development counter electrode is used as a pre-development toner collecting unit. By supplying a separation bias having the same value as the partial potential, reversely charged toner particles and high charge amount toner particles are opposed to each other from the toner hopping on the surface of the toner carrying roller before development. What is attached to the electrode and separated is used. In such a configuration, the reversely charged toner particles and the high charge amount toner particles can be separated from the other toner particles due to a difference in charge polarity and charge amount from the toner particles.

  Further, in the image forming apparatus according to the embodiment, each modified apparatus, and the image forming apparatus according to each example, the counter electrode before development is orthogonal to the endless moving direction (rotation direction) on the surface facing the toner carrying roller. The length of the direction is equal to or longer than the length in the same direction of the surface of the toner carrying roller facing the counter electrode before development. In such a configuration, the reversely charged toner particles and the high charge amount toner particles are separated in the entire region in the direction perpendicular to the endless movement direction of the roller surface with respect to the toner hopping on the surface of the toner carrying roller before the development. Processing can be performed.

  Further, in the image forming apparatus according to the embodiment, each modified apparatus, and the image forming apparatus according to each example, the length of the roller surface on the surface facing the toner carrying roller in the endless moving direction is the counter electrode before development. In this case, the developing position is longer than the endless moving direction. In such a configuration, the toner is transported for a time longer than the developing position passing time immediately under the counter electrode before development, thereby reliably separating the reversely charged toner particles and the high charge amount toner particles that become scumming toner at the developing position. can do.

  Further, in the image forming apparatus according to the embodiment, each modified apparatus, and the image forming apparatus according to each example, the bias supplied to the pre-development counter electrode is different from the separation bias as the pre-development toner collecting unit. By switching to the discharge bias at a predetermined timing, the reversely charged toner particles and the high charge amount toner particles adhering to the counter electrode before development are returned to the surface of the toner carrying roller. In such a configuration, due to excessive accumulation of reversely charged toner particles or high charge amount toner particles on the counter electrode before development, the toner particles are reversely transferred from the counter electrode before development to the toner carrying roller during the developing operation. Can be avoided.

  When the pre-development toner collecting means is configured to supply only the DC voltage as the discharge bias to the pre-development counter electrode, the toner is re-transferred straight from the pre-development counter electrode toward the toner carrying roller. Can be made. On the other hand, as a discharge bias, a pre-development toner collecting means configured to supply the pre-development counter electrode with a DC voltage superimposed on an AC voltage, between the pre-development counter electrode and the toner carrying roller. Thus, the toner can be re-transferred to the toner carrying roller finally while reciprocating.

  Further, in the image forming apparatus according to the embodiment, each modified example apparatus, and each image forming apparatus according to each example, the gap between the toner carrying roller and the counter electrode before development is defined by the photosensitive member 49 and the toner carrying roller at the development position. The same size as the gap. In such a configuration, it is possible to avoid the deterioration of the collection accuracy of the reversely charged toner particles and the high charge amount toner particles caused by the former gap being different from the latter gap.

  In the image forming apparatus according to the embodiment, each modified apparatus, and the image forming apparatus according to each example, the toner hopping condition in the recovery area before development where the toner carrying roller and the counter electrode before development face each other is set as the development position. The toner hopping conditions in FIG. With such a configuration, it is possible to avoid the deterioration of the recovery accuracy of the reversely charged toner particles and the high charge amount toner particles due to the difference in toner hopping conditions.

  When a bias supply means that supplies a bias having a polarity opposite to the normal charging polarity of the toner to the counter electrode after development is used as a recovery bias power supply before development as a bias supply means, toner hopped in the post-development transport area It is possible to suppress adhesion of the particles to the counter electrode after development.

1 is a schematic configuration diagram illustrating an image forming apparatus according to an embodiment. FIG. 2 is a schematic configuration diagram showing a photoreceptor 49 and a developing device 1 in the image forming apparatus. FIG. 3 is a perspective view showing a toner carrying roller in the developing device. FIG. 3 is a schematic plan view showing an electrode configuration of the toner carrying roller. FIG. 3 is a partial cross-sectional view showing the toner carrying roller. The graph which shows the characteristic of the pulse voltage applied to the electrode of the toner carrying roller. The graph which shows the characteristic in the other example of the same pulse voltage. FIG. 3 is an enlarged configuration diagram showing the toner carrying roller and its surrounding configuration. FIG. 6 is an enlarged configuration diagram illustrating a developing device together with a photosensitive member in a first modification device of the image forming apparatus. FIG. 9 is an enlarged configuration diagram illustrating a developing device together with a photosensitive member in a second modification device of the image forming apparatus. FIG. 10 is an enlarged cross-sectional view illustrating a toner carrying roller in a third modification of the image forming apparatus according to the embodiment. FIG. 3 is a schematic plan view showing an electrode configuration of the toner carrying roller. The graph which shows the characteristic of the A, B, C phase pulse voltage applied to the A, B, C phase electrode of the toner carrying roller. FIG. 3 is an enlarged configuration diagram illustrating, in an enlarged manner, a toner carrying roller and its surrounding configuration in the developing device of the image forming apparatus according to the first embodiment. FIG. 6 is a schematic configuration diagram illustrating an image forming apparatus according to a second embodiment. FIG. 2 is a schematic configuration diagram showing the image forming apparatus with a process unit attached / detached. FIG. 3 is an enlarged configuration diagram showing a K process unit of the image forming apparatus together with a photoreceptor. FIG. 9 is an enlarged configuration diagram showing a K process unit together with a photoreceptor in an image forming apparatus according to a third embodiment. FIG. 10 is an enlarged configuration diagram illustrating a K process unit together with a photoreceptor in an image forming apparatus according to a fourth embodiment. FIG. 10 is an enlarged configuration diagram showing a K process unit together with a photoreceptor in an image forming apparatus according to a fifth embodiment.

Explanation of symbols

2: Toner carrying roller (toner carrier)
3a: Phase A electrode 3b: Phase B electrode 3c: Phase C electrode 18: Toner supply roll (toner supply means)
26: Counter electrode before development 27: Recovery bias power source before development 28: Counter electrode after development 29: Bias power source after development (bias supply means)
49: Photoconductor (latent image carrier)
50: Charging device (charging means)
Ar0: toner supply position Ar1: transport area before development Ar2: development position Ar3: transport area after development

Claims (17)

A toner carrier having a plurality of electrodes arranged in a predetermined direction; and a toner supply means for supplying toner to the endlessly moving surface of the toner carrier, on the surface of the toner carrier by the toner supply means. A developing position in which the toner carrier and the latent image carrier of the image forming apparatus face each other while the supplied toner is hopped on the surface by an electric field formed by applying a voltage to the plurality of electrodes. In the developing device for developing the latent image by attaching to the latent image on the latent image carrier,
At least one of the reversely charged toner particles and the high charge amount toner particles contained in the toner hopping on the surface of the toner carrier is transferred to the entire region in the endless movement direction of the surface of the toner carrier. Among them, the reversely charged toner particles and the high charge amount toner particles contained in the toner hopped in the pre-development conveyance area, which is an area before entering the development position after passing the toner supply position by the toner supply means A developing device comprising a pre-development toner collecting means for collecting at least one of the above. The developing device according to claim 1.
A developing device using, as the pre-development toner collecting means, a unit that collects both the reversely charged toner particles and the highly charged toner particles. The developing device according to claim 2.
The pre-development toner collecting means has a pre-development counter electrode facing the pre-development transport area of the toner carrier via a predetermined gap, and on the surface of the pre-development transport area A developing device using the reversely charged toner particles and the high charge amount toner particles that are hopped in step 1 and attached to the counter electrode before development. The developing device according to any one of claims 1 to 3,
Of all the areas in the endless movement direction of the surface of the toner carrier, after passing through the development position and before entering the toner supply position, a post-development transport area is passed through a predetermined gap. A developing apparatus comprising a facing member facing after development. In an image forming apparatus comprising: a latent image carrier that carries a latent image; and a developing unit that develops the latent image carried on the latent image carrier with toner.
An image forming apparatus using the developing device according to claim 1 as the developing means. The image forming apparatus according to claim 5.
While using the developing device of claim 3 as the developing device,
As the pre-development toner collecting means, a separation bias having the same value as the ground portion potential of the latent image carrier is supplied to the pre-development counter electrode, thereby hopping on the surface of the pre-development conveyance area. An image forming apparatus using a toner in which reversely charged toner particles and high charge amount toner particles are attached to and separated from the counter electrode before development. The image forming apparatus according to claim 6.
As the counter electrode before development, the length in the direction orthogonal to the endless movement direction on the surface facing the toner carrier is equal to or longer than the length in the same direction of the surface facing the counter electrode before development on the toner carrier. An image forming apparatus using the apparatus. The image forming apparatus according to claim 6 or 7,
Image formation characterized in that, as the pre-development counter electrode, a length in the endless moving direction on the surface facing the toner carrier is equal to or longer than the length of the developing position in the endless moving direction. apparatus. The image forming apparatus according to any one of claims 6 to 8,
The reversely charged toner particles attached to the pre-development counter electrode by switching the bias supplied to the pre-development counter electrode from the separation bias to another discharge bias at a predetermined timing as the pre-development toner collecting means And an image forming apparatus that returns high-charge toner particles onto the surface of the toner carrier at the predetermined timing. The image forming apparatus according to claim 9.
An image forming apparatus according to claim 1, wherein the pre-development toner collecting means is configured to supply the discharge bias only with a DC voltage to the pre-development counter electrode. The image forming apparatus according to claim 9.
An image forming apparatus according to claim 1, wherein the pre-development toner collecting means is configured to supply the discharge bias with a DC voltage superimposed on an AC voltage to the counter electrode before development. The image forming apparatus according to any one of claims 6 to 11,
An image forming apparatus, wherein the gap between the toner carrier and the pre-development counter electrode is the same as the gap between the latent image carrier and the toner carrier at the development position. The image forming apparatus according to any one of claims 6 to 12,
An image forming apparatus, wherein a toner hopping condition in a pre-development recovery region where the toner carrier and the counter electrode before development face each other is the same as the toner hopping condition in the development position. The image forming apparatus according to any one of claims 6 to 13,
The developing device having a post-development counter electrode as the post-development counter member in the development device of claim 4 and supplying a bias having a polarity opposite to the normal charging polarity of the toner to the post-development counter electrode An image forming apparatus comprising a bias supply unit for performing the above operation. A latent image carrier that carries a latent image; a charging unit that uniformly charges the latent image carrier; a cleaning unit that cleans the surface of the latent image carrier; and a latent image carried on the latent image carrier. In the image forming apparatus including the developing unit that develops the toner, the developing unit and at least one of the latent image carrier, the charging unit, and the cleaning unit are held as a unit on a common holder. In the process unit that can be integrally attached to and detached from the image forming apparatus main body,
5. A process unit using the developing device according to claim 1 as the developing means. In an image forming apparatus that forms a toner image on a latent image carrier using a process unit,
An image forming apparatus using the process unit according to claim 15 as the process unit. The image forming apparatus according to claim 16.
A plurality of process units having at least the developing device and the latent image carrier are provided as the process units, and the toner images formed on the latent image carriers of the respective process units are transferred onto the transfer body in a superimposed manner. An image forming apparatus comprising a transfer unit.

Images