JP2012208339A - Developing device, image formation apparatus and developing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a developing method and a developing device that can prevent such factors detrimental to electric charge balancing as an increase in the electrostatic charge of the developer in a developer tank of an image formation apparatus while preventing faulty printing due to electrostatic charging of or leaks from a stirring/carrying member in the tank.SOLUTION: A developing device comprises a developer tank accommodating in it a developer containing at least toner; a feed toner tank for accommodating the toner to be fed to the developer tank; a toner feeding member that feeds the toner from the feed toner tank to the developer tank; and a stirring/carrying member that stirs and carries the developer in and from the developer tank. Part of the stirring/carrying member with which the toner supplied by the toner feeding member to the developer tank at least first comes into contact in the developer tank is formed of an electroconductive material, and this electroconductive material is grounded via a varistor.

Description

  The present invention relates to a developing device and a developing method for an electrophotographic image forming apparatus.

  In an image forming apparatus using an electrophotographic system, an electrostatic latent image formed on an electrostatic latent image carrier is developed by a developing device, and the developed toner image is transferred to a recording medium such as paper and transferred. Usually, the toner image is fixed to form an image.

  Development methods are roughly classified into two types: a one-component development method using a one-component developer mainly composed of toner and a two-component development method using a two-component developer in which a toner and a carrier are mainly mixed.

  The structure of the developing device is roughly as follows. There is a developer tank for containing the developer, and a developer carrier such as a developing roller is disposed in an opening of the developer tank provided on the side facing the electrostatic latent image carrier, and the developer carrier The electrostatic latent image on the electrostatic latent image carrier is developed with the developer carried and transported thereon.

  In many cases, a developer agitating and conveying member for agitating and conveying the developer is disposed in the developer tank. There are various shapes of developer agitating and conveying members, which are called by various names such as screws, augers, paddles, and blades. The developer contained in the developer tank is agitated, conveyed, circulated and mixed. And the like.

  With development, the toner in the developer tank is consumed, but in the one-component development method, an amount of toner corresponding to the amount of print data is replenished from the replenishment toner tank into the developer tank or provided separately. By detecting the amount of developer in the developer tank with the developer amount sensor and replenishing the developer tank with an appropriate amount of toner, the developer amount in the developer tank can be maintained within the appropriate range. Is called.

  In the two-component development method, the toner concentration is monitored by a separately provided toner concentration sensor (toner concentration: mass ratio of toner in the developer), and the toner is stored in the developer tank so that the toner concentration is within an appropriate range. Replenishment is performed.

  The developer agitating / conveying member has a structure in which a screw, an auger, a paddle, etc. are arranged around the longitudinal axis in terms of shape, and is composed of metal, plastic (resin), or a composite of these materials. Various productions are possible. However, since it is often used by rotating around the longitudinal axis, at least the shaft portion is often made of a metal material such as steel, aluminum alloy, stainless steel or the like.

  On the other hand, as a material constituting the developer tank, plastic (resin) is frequently used because of its excellent moldability, suitable for mass production, light weight, and low cost, and all the components of the developer tank are made of sheet metal or the like. It is very rare to use a metal member.

  For this reason, when the developing device is designed without particularly being aware of the grounding of the agitating / conveying member, the agitating / conveying member is pivotally supported by a developer tank mainly composed of an insulating material, thereby constituting the agitating / conveying member. Metal members such as shafts are often in a so-called float state that is insulated from the ground.

  In this specification, the ground, the frame ground, and the like are referred to as ground, and the potential is referred to as ground potential.

  In such a stirrer / conveyor member in a float state, it is considered that the frictional charge with the developer is the main cause. It is known to have a large charging potential.

  Even if the agitating / conveying member is charged, there may be no particular problem depending on the potential amount and polarity. However, when the charging potential is extremely high, etc., the charged charge leaks to the adjacent conductive member and spike-like electric noise is generated, and the electric noise is mixed into the image signal, resulting in poor printing. May occur.

  This is because, in many cases, electrical noise is mixed into an image signal, which is a digital signal, so that a signal that is originally 1 becomes 0, or a signal that is 0 becomes 1 on the contrary. This is a phenomenon in which black spots and black lines are generated in the areas, and white spots (white dots and white lines) are generated in the print section (black characters). In addition, there may be a printing failure such as misalignment, duplication, or omission of an image on printing.

  For this reason, when printing failure due to such a leak occurs, in order to prevent charging of the agitating / conveying member, the metal portion of the agitating / conveying member is dropped to the ground via an appropriate terminal or the like, or the developer In many cases, measures are taken such as changing the portion of the tank that supports the agitating / conveying member to a metal material and dropping it to ground.

Japanese Patent Laid-Open No. 2001-22175

  However, when measures were taken to drop the stirring / conveying member to the ground to prevent defective printing due to leakage, it became clear that the following problems may occur.

  FIG. 7 is a schematic diagram of a developing unit 80 according to the prior art. Since the developing unit 5 according to the embodiment of the present invention shown in FIG. 2 and the like has almost the same configuration, common members are given common part numbers.

  In FIG. 7, the two agitating and conveying screws 52 and 53 and the agitating paddle 61, which are agitating and conveying members, are pivotally supported by the developer side plates 57 and 58 made of insulating ABS resin. It becomes an isolated float state. The agitating and conveying screws 52 and 53 have a structure in which a plurality of screw pieces, which are molded products of ABS resin, are inserted into a stainless steel shaft portion. Also, as shown in FIG. 4, the stirring paddle 61 has a structure in which two paddles 61b made of a SECC steel plate having a thickness of 1.0 mm are screwed to a stainless steel shaft portion 61a, and both the shaft portion 61a and the paddle 61b are painted. They are all conductive, including their surfaces.

  The two agitating and conveying screws 52 and 53 are for agitating and conveying the developer (not shown) in the order of arrows D, E, F, and G shown in FIG. Arranged to be embedded in the developer more than half. On the other hand, the stirring paddle 61 is replenished in order to prevent replenishment toner (not shown) replenished from the replenishment toner tank 62 located above the stirring paddle 61 from being mixed into the developer as a lump (chunk). It has a function of extruding the toner in the direction of the developer while crushing the toner and mixing it into the developer. Accordingly, the stirring paddle 61 is such that the tip of the paddle 61b is slightly embedded in the developer, and most of the stirring paddle 61 is located above the developer head. That is, the toner replenished from the replenishing toner tank 62 first comes into contact with the stirring paddle 61 in the developer tank 60.

  The developer stored in the developer tank 60 is a two-component developer whose toner is negatively charged.

  FIG. 5 shows the transition of the charging potential of the shaft portion 61a of the stirring paddle 61 accompanying the printing operation, that is, the stirring and transporting operation of the stirring and transporting member in the developing unit 80 according to the prior art. The charging potential rises with the agitating and transporting operation, reaching a maximum of -3000V. When the potential reaches about -3000V, an instantaneous potential drop from about -1000V to -2000V occurs (indicated by the arrow in the figure), and it can be seen that leakage of charged charges has occurred. Further, at the timing of this leak, as shown in FIG. 10, printing failure of black stripes or white stripes occurs on printing.

  The charging potential of the shaft portion 61a of the stirring paddle 61 can be measured with a commercially available surface potential meter. In the present embodiment, the end portion of the shaft portion 61a is measured with a Monro company MODEL244 surface potential meter.

  In order to prevent this printing failure, the contact pad 70 is provided on the shaft of the stirring paddle 61 and the stirring paddle 61 is dropped to the ground as shown in FIG. The potential remained at 0 V, and charging and leakage did not occur and printing failure was prevented. However, as shown in FIG. 11, the phenomenon that the charge amount of the toner in the developer increases with the printing occurs, and as a result, the problem that the printing density decreases (in FIG. 11 ( B)). The toner charge amount is the charge amount of the toner in the developer contained in the developer tank, and can be measured by various known charge amount measuring devices.

  The cause and mechanism of the increase in the charge amount is not clear, but it is generally grounded (that is, the potential is 0) or a potential opposite to the polarity of the toner in the developer stirred and conveyed in the developer tank. It is presumed that due to the presence of the conductive member having, the charge balance between the toner and the carrier in the two-component developer is lost.

  Further, in the developing device 5 and the developer shown in the embodiments described later, a part of the other conductive member in contact with the developer, that is, the stainless steel shaft of the agitating and conveying screws 52 and 53, and the bottom of the developer tank. Even if the exposed bottom plate member 59 (made of stainless steel) is grounded, such an increase in charge amount is not observed, so the toner supplied to the developer tank is grounded before being mixed with the carrier. It is presumed that the contact with the conductive member is more strongly related to the increase in the charge amount.

  Accordingly, an object of the present invention is to provide a developing method and a developing apparatus capable of preventing the occurrence of printing defects due to charging and leakage of the agitating / conveying member and preventing the charging balance from being lost such as an increase in the charging amount of the developer. Is to provide.

  In order to solve the above-mentioned problems, in the present invention, a developer tank that contains at least a developer containing toner, a toner tank that contains toner to be replenished in the developer tank, and the toner from the toner tank. A developing device having at least a toner replenishing member that replenishes the developer tank and a stirring and conveying member that stirs and conveys the developer in the developer tank, wherein the toner replenished to the developer tank by the toner replenishing member A developing device characterized in that a part of the agitating and conveying member that contacts at least first in the developer tank is formed of a conductive material, and the conductive material and ground are connected via a varistor. Provided.

  In another aspect of the present invention, a developer tank that contains at least a developer containing toner, a toner tank that contains toner to be replenished in the developer tank, and the toner that is contained in the toner tank A developing device having at least a toner replenishing member that replenishes the developer tank, and a stirring and conveying member that stirs and conveys the developer in the developer tank, and is replenished to the developer tank by the toner replenishing member. A part of the agitating / conveying member that the toner contacts at least first in the developer tank is formed of a conductive material, and a bias potential having the same polarity as the charging polarity of the toner is applied to the conductive material. A developing device is provided.

  Furthermore, in another aspect of the present invention, an image forming apparatus having the developing device is provided.

  In another aspect of the present invention, a developer tank containing at least a developer containing toner is supplied from a toner tank containing toner supplied to the developer tank to a toner supply member. The toner is replenished, and the toner replenished in the developer tank forms a part of the agitating and conveying member that contacts at least first in the developer tank with a conductive material. There is provided a developing method characterized by connecting through a varistor.

  In yet another aspect of the present invention, a developer tank containing at least a developer containing toner is supplied from a toner tank containing toner to be supplied to the developer tank to a toner supply member. The toner replenished, and the toner replenished to the developer tank is formed of a conductive material at least part of the agitating and conveying member that contacts at least first in the developer tank. A developing method is provided, wherein a bias potential having the same polarity as the charging polarity of the toner is applied.

  According to the present invention, charging failure of the agitating / conveying member in the developer tank in the image forming apparatus and occurrence of printing failure due to leakage can be prevented, and also the charging balance can be prevented from being lost due to an increase in the charging amount of the developer. be able to.

1 is a diagram illustrating a schematic configuration of an electrophotographic printer that is an embodiment of the present invention. FIG. 1 is a schematic perspective view of a developing device according to an embodiment of the present invention. 1 is an internal external view of a developing device according to an embodiment of the present invention. It is a perspective view of a stirring paddle. It is a figure which shows the electrical potential transition of the stirring paddle accompanying printing operation by the developing device of a prior art. It is a figure which shows the electrical potential transition of the stirring paddle accompanying printing operation by the developing device of this invention. It is a schematic perspective view of the developing device by a prior art. It is a schematic perspective view of the developing device by a prior art. It is a schematic perspective view of the developing device which is another embodiment of the present invention. It is a figure which shows an example of the printing defect at the time of using the developing device by a prior art. It is a figure which compares the electrical potential transition of the stirring paddle accompanying printing operation.

  Hereinafter, an image forming apparatus having a developing device according to an embodiment of the present invention will be described in detail with reference to FIG.

  An electrophotographic printer 1 as an image forming apparatus has side plates 1a and 1d. Around the photosensitive drum 2 serving as an image carrier, the main charger 3, LED print head 4, developing unit 5, transfer charger 6, separation charger 7, pre-cleaning charger 8, carrier recovery unit 9, cleaning unit 10 and static elimination A lamp 11 is disposed (the above corresponds to the image forming unit), and a fixing unit 20 that is a flash fixing device is disposed on the downstream side of the photosensitive drum 2 as viewed along the conveyance path of the recording medium MRC. In the electrophotographic printer 1, the guide plate 13 that is a conveyance unit for the recording medium MRC and the tractor 14 that is also a conveyance unit are positioned at the upstream side of the photosensitive drum 2 in the conveyance path at a position facing the fixing unit 20 in the conveyance path. A transport unit 15 which is another transport means is provided.

  The photosensitive drum 2 is driven by a drive motor and a speed reduction mechanism (not shown).

  Here, in the electrophotographic printer 1, the recording medium MRC uses continuous paper having feed holes (not shown) at both ends thereof. As shown in the figure, the recording medium MRC is introduced from the right inlet 1b of the electrophotographic printer 1 and discharged from the left outlet 1c.

  The tractor 14 serving as a transport unit includes a tractor belt 14b serving as a transport member including a tractor pin 14a that fits into a feed hole of the recording medium MRC. The tractor belt 14b is driven by a drive motor (not shown) and conveys the recording medium MRC. The conveyance speed of the recording medium MRC is set to 424.39 mm / s.

  In the photosensitive drum 2, a photosensitive layer made of a negatively charged organic photosensitive material is formed on the surface of a cylindrical drum, and an electrostatic latent image is formed on the surface by light irradiated from the LED print head 4. Prior to the formation of the latent image on the photosensitive drum 2 by the LED print head 4, the main charger 3 uniformly charges the surface of the photosensitive drum 2 with ions generated by discharge. The LED print head 4 exposes the surface of the photosensitive drum 2 with a light beam to form an electrostatic latent image corresponding to the recorded information.

  The developing unit 5 as a developing device accommodates a developer (not shown) inside, and the developing roller 51 develops the electrostatic latent image on the photosensitive drum 2 to form a toner image.

  The toner is a minus toner mainly composed of a polyester resin having an average particle diameter of 8 μm. The carrier is a coated carrier in which Mn-Mg-St ferrite particles are used as base material particles and 10% by weight of acrylic resin is coated. The average particle size of the carrier is 70 μm. A developer in which the toner and the carrier were mixed at a toner concentration of 5.5 weight percent was used.

  The transfer charger 6 transfers the unfixed toner image developed on the photosensitive drum 2 to the recording medium MRC using ions generated by the discharge. The separation charger 7 is a charger that electrically separates the recording medium MRC from the photosensitive drum 2. For example, a corotron charger to which an alternating voltage is applied is used. The transfer charger 6 and the separation charger 7 are integrally configured with a common shield plate member S.

  Here, a separation claw 12 for mechanically separating the recording medium MRC from the photosensitive drum 2 is provided between the separation charger 7 on the outer periphery of the photosensitive drum 2 and the pre-cleaning charger 8.

  In this embodiment, in addition to the main charger 3 and the transfer charger 6, the pre-cleaning charger 8 is charged. The pre-cleaning charger 8 charges the surface of the photosensitive drum 2 prior to cleaning, The toner particles remaining on the surface of the photosensitive drum 2 without being transferred to the recording medium MRC are used for the purpose of facilitating recovery by the cleaning unit 10.

  The carrier recovery unit 9 is provided between the transfer charger 6 and the cleaning unit 10 when viewed in the rotation direction of the photosensitive drum 2, and is not transferred to the recording medium MRC and remains on the surface of the photosensitive drum 2. The carrier scraped off from the surface of the photosensitive drum 2 due to the brush roller 10b described later is collected. In the carrier recovery unit 9, the recovery roller 9b, which is a magnetic roller, is magnetically attracted and recovered in the housing 9a.

  The cleaning unit 10 mainly removes toner particles remaining on the surface of the photosensitive drum 2 without being transferred to the recording medium MRC. A brush roller 10b and a recovery roller 10c are provided in the housing 10a. The brush roller 10b is applied with a bias voltage having a polarity opposite to that of the toner particles, scrapes the toner particles remaining on the surface of the photosensitive drum 2 with a brush, and electrostatically adsorbs the toner particles for cleaning. The recovery roller 10c is applied with a bias voltage having an absolute value greater than that of the brush roller 10b, and electrostatically recovers the toner particles adsorbed on the brush roller 10b. The collected toner particles are scraped off from the collection roller 10c by a blade (not shown), and are transferred by a transfer roller 10d to a collection unit (not shown) provided in one direction on both sides of the paper surface.

  The charge removal lamp 11 is a small light bulb, and removes residual charges from the surface of the photosensitive drum 2 by light irradiation. A light emitting element such as an LED can be used instead of the light bulb. In the transport unit 15, a transport belt 15b is stretched between two transport rollers 15a, and the two transport rollers 15a are supported by a casing 15c made of a ferromagnetic material. The transport roller 15a is driven to rotate in the direction of the arrow in the drawing by a drive motor (not shown), thereby transporting the recording medium MRC placed on the transport belt 15b.

  A scarfola pair 16 exists behind the transport unit 15. Of the two rollers constituting the pair of scat flora 16, only the roller positioned below the recording medium MRC is rotationally driven by a drive motor (not shown). The other roller is urged downward by its own weight with the recording medium MRC interposed therebetween, and is driven to rotate.

  As shown in FIG. 1, in the electrophotographic printer 1, the toner image is fixed by the fixing unit 20 from the transfer position where the unfixed toner image developed on the photosensitive drum 2 is transferred by the transfer charger 6. The conveyance path through which the recording medium MRC is conveyed, including the period up to the fixing position, is configured to be substantially linear and substantially horizontal. Thus, if the conveyance path of the recording medium MRC is substantially linear, the recording medium is not bent when conveying the recording medium, and special paper such as thick paper, thin paper, synthetic paper, and resin film medium can be easily conveyed. I can do it.

  The fixing unit 20 is provided with a fixing lamp 21 serving as a radiant heat source, a reflection plate 22, and a radiation fin 23 for cooling the reflection plate 22 in the housing 20 a, and a protective glass 24 is provided on the front surface of the housing 20 a facing the transport unit 15. Has been placed. A suction duct 26 for sucking air is provided on the downstream side of the fixing unit 20.

  The suction duct 26 is arranged in the front and back direction of the electrophotographic printer 1 in FIG. 1, has an opening on the transport unit 15 side, and is provided with suction means such as a filter for deodorization and smoke removal and a blower. Yes. The suction duct 26 sucks air around the fixing unit 20 and discharges it to the outside of the electrophotographic printer 1, so that unpleasant odors and smoke of a toner component mainly generated by fixing of an unfixed toner image in the fixing unit 20 are generated. Remove.

  The electrophotographic printer 1 is configured as described above, and performs a desired print by fixing an unfixed toner image on the recording medium MRC by the electrophotographic method described below.

  First, the surface of the photosensitive drum 2 whose surface is cleaned by the cleaning unit 10 and rotated at a constant speed in the direction of the arrow is charged by the main charger 3 after the residual charge on the surface is removed by the charge eliminating lamp 11.

  Next, the LED print head 4 irradiates the photosensitive drum 2 with a light beam to form an electrostatic latent image corresponding to the recording information on the surface of the photosensitive drum 2. The electrostatic latent image is developed by the developing unit 5 by the rotation of the photosensitive drum 2 and becomes an unfixed toner image (visible image).

  The unfixed toner image developed on the photosensitive drum 2 is transferred by the transfer charger 6 onto the recording medium MRC conveyed along the conveyance path indicated by the arrow. The recording medium MRC to which the unfixed toner image is transferred is separated from the photosensitive drum 2 by the separation charger 7 and conveyed to the fixing unit 20 by the conveyance unit 15. In the fixing unit 20, the fixing lamp 21 emits light, and the unfixed toner image is melted by the generated heat and fixed on the recording medium MRC.

  In the electrophotographic printer 1, as described above, an image corresponding to the recording information is formed on the recording medium MRC, charged by the pre-cleaning charger 8, the carrier recovery by the carrier recovery unit 9, and the cleaning unit 10. After the surface cleaning of the photosensitive drum 2, the residual latent image on the photosensitive drum 2 is erased by the charge eliminating lamp 11 and is used for the next subsequent image formation.

  Next, FIG. 2 and FIG. 3 are schematic configuration diagrams of the developing unit 5 as a developing device according to the present invention.

  In the developing unit 5, a developing roller 51 is disposed in an opening facing the photosensitive drum 2, and in parallel with the developing roller 51, two toner stirring and conveying screws are disposed in a horizontal plane. Here, the side near the developing roller 51 is referred to as a first toner stirring and conveying screw 53, and the side far from the developing roller 51 is referred to as a second toner stirring and conveying screw 52. A partition plate 54 is provided between the two agitating and conveying screws except for both end portions thereof, and communication between the first and second toner agitating and conveying screws 52 is established on the outside of both ends of the partition plate. Mouth. Both toner agitating and conveying screws are driven and rotated by drive motors (not shown) in opposite directions (arrows B and C in the figure), and in the developer tank 60 as indicated by arrows D, E, F, and G in FIG. Circulate the developer.

  As shown in FIG. 2, the developing roller 51 is rotationally driven in the direction of arrow A in the drawing, carries the circulating developer on the surface thereof, and conveys it to a region facing the photosensitive drum 2 (developing region). The electrostatic latent image on the photosensitive drum 2 is developed with toner in the development area. The developer that has been subjected to development and has a reduced toner concentration is again collected in the developer tank 60 as the developing roller 51 rotates.

  As seen in the horizontal plane, a stirring paddle 61 is provided on the opposite side of the developing roller 51 of both the stirring and conveying screws 52 and 53, and is rotationally driven in the direction of arrow H in the figure by a driving mechanism (not shown). A replenishment toner tank 62 is disposed above the agitation paddle 61, and an appropriate amount of replenishment toner is replenished by being naturally dropped into the developer tank 60 by a toner replenishment roller 64 serving as a toner replenishment member disposed therein. It has become. In the present embodiment, both the stirring and conveying screws 52 and 53 and the stirring paddle 61 correspond to the stirring and conveying member.

  The toner supply roller 64 includes a screw portion 64a and a sponge roller portion 64b as viewed in the longitudinal axis direction. A partition partitioning the replenishment toner tank 62 and the developer tank 60 (that is, the bottom plate of the replenishment toner tank 62 and the top plate of the developer tank 60) is provided with a replenishment toner opening (not shown). A sponge roller portion 64b is disposed so as to close the opening. When the toner replenishing roller is rotated by a predetermined amount around the longitudinal axis by a rotation driving mechanism (not shown), a replenishment toner carried on the sponge of the sponge roller portion 64b is replenished by a predetermined amount. That is, an arbitrary amount of toner can be replenished by controlling the rotation amount (rotation speed and rotation time) of the replenishment toner roller.

  A stirring paddle 61 is shown in FIG. As described above, the agitation paddle 61 pulverizes the replenishment toner with the paddle 61b so that the replenishment toner replenished by the natural fall from the replenishment toner tank 62 is not mixed into the developer as a lump, and at the same time the second It has a function of pushing out in the direction of the agitating and conveying screw 52 so that the replenishing toner is easily mixed in the developer. As shown in FIG. 4, the stirring paddle 61 has a structure in which two 1.0-mm SECC steel paddles 61b are screwed to a stainless steel shaft 61a, and the stirring paddle 61 as a whole is electrically conductive. Have. This is pivotally supported on both side plates 57 and 58 of the insulating developing unit 5 made of an ABS resin material via a rolling bearing.

  The side plate 58 is provided with a contact terminal 70 that contacts one end portion of the shaft portion 61a. The contact terminal 70 is connected to the main body side plate 1a of the printer via a varistor 71 having a varistor potential of 1000V. Since the figure becomes complicated, the varistor 71 and subsequent parts are simply drawn as circuit diagrams. The main body side plate 1a is connected to the ground by a ground terminal (not shown), and the stirring paddle 61 is connected to the ground via the varistor 71. Note that the connection destination of one end of the varistor 71 is not limited to the main body side plate 1a, and may be any conductive member having a ground potential.

  The effect of the present invention can be achieved by electrically connecting the agitation paddle 61 and the ground via the varistor 71, such as the shape and position of the contact terminal, the mounting position of the varistor, the connection portion with the ground, etc. However, it is not limited to this embodiment.

  FIG. 6 shows changes in the charging potential of the stirring paddle 61 accompanying the printing operation. Unlike FIG. 5 in the prior art, due to the effect of the varistor 71, the charging potential does not reach 1000 V even with an absolute value although there is a slight fluctuation, and no leakage occurs. For this reason, the occurrence of printing failure due to leakage does not occur, and the toner charge amount does not increase as shown in FIG.

  As the varistor 71, a varistor having a varistor voltage in the vicinity of a potential where no leakage occurs and a charging potential does not increase may be used. In this embodiment, the potential leaks from -3000 V to slightly above -1000 V from FIG. 5. If the varistor with a varistor voltage of 1000 V is used so that the potential of the stirring paddle does not exceed 1000 V, the charging potential becomes 1000 V or less. It is suppressed and no leak occurs.

  The varistor suppresses the charging of the stirring paddle 61 that is excessively charged in the float state, and maintains it to the extent that no leakage occurs, thereby preventing the occurrence of leakage and suppressing the increase in the charge amount of the developer. It is effective.

  In this embodiment, the potential of the stirring paddle shaft is controlled using a varistor. However, as another embodiment, it is possible to positively apply and control the potential to the stirring paddle shaft using an external power source. An example is shown in FIG.

  FIG. 11 also shows the relationship between the potential polarity applied to the stirring paddle 61 and the toner charge amount increase ((D) and (E)). When a negative potential is applied to the stirring paddle 61 that first contacts the toner in the developer tank 60, no increase in charge amount is observed, but when a positive potential of opposite polarity is applied, the charge amount is the same as in the case of ground. An increase was seen. In addition to the increase in the charge amount, it was confirmed that a large amount of toner adhered and accumulated on the surface of the stirring paddle 61. This is presumably because a bias reverse to the charging polarity of the toner is applied to the stirring paddle 61. It was also confirmed that the toner deposited and peeled off as a toner lump and mixed in the developer. Such a lump of toner causes printing defects and is not preferable.

  Furthermore, in this embodiment, when the stirring paddle 61 is in a float state, the stirring paddle 61 is negatively charged with the same polarity as the toner. However, depending on the characteristics of the carrier and toner, or in some cases, other constituent materials of the developer tank, it is conceivable that the stirring paddle is charged to a polarity opposite to that of the toner in the float state. In this case, as shown in FIG. 9, it is preferable to positively control the potential of the stirring paddle 61 to a preferred polarity and absolute value using an external power source.

1. Electrophotographic printers 1a, 1d. Side plates 1e, 1f. Stay 1g, 1h. Shield plate 2. 2. Photosensitive drum Main charger 4. LED print head 4a. 4. LED print head cooling fin Developing unit 5a. Toner cartridge 5b. Toner tank 5c. Developing roller 6. Transfer charger 7. Separation charger 8. 8. Pre-cleaning charger Carrier recovery unit 9a. Carrier collection roller 10. Cleaning unit 10a. Cleaning unit top plate 10b. Brush roller 10c. Collection roller 11. Static elimination lamp 12. Separation claw 13. Guide plate 14. Tractor 10b. Brush roller 14. Tractor 15. Transport unit 15a. Conveying roller 15b. Conveying belt 16. Scaffa flora vs. 20. Fixing unit 20a. Housing 21. Flash lamp 22. Reflector 23. Radiating fin 24. Protective glass 26. Suction duct 51. Developing roller 52. Second agitating and conveying screw 53. First stirring and conveying screw 54. Partition plates 57, 58. Development unit side plate 59. Bottom plate member 60. Developer tank 61. Stir paddle 61a. Stir paddle shaft 61b. Paddle 62. Replenishment toner tank 64. Toner supply roller 64a. Screw part 64b. Sponge roller section 70. Contact terminal 71. Varistor 80. Development unit 81. Development unit 82. Development unit

Claims (5)

A developer tank that contains at least a developer containing toner, a replenishment toner tank that contains the toner replenished in the developer tank, and a toner replenishment that replenishes the toner from the replenishment toner tank to the developer tank A developing device having at least a member and an agitating and conveying member for agitating and conveying the developer in the developer tank, wherein the toner replenished to the developer tank by the toner replenishing member is contained in the developer tank. A developing device characterized in that at least a part of the agitating / conveying member that comes into contact first is formed of a conductive material, and the conductive material and the ground are connected via a varistor. A developer tank that contains at least a developer containing toner, a replenishment toner tank that contains the toner replenished in the developer tank, and a toner replenishment that replenishes the toner from the replenishment toner tank to the developer tank A developing device having at least a member and an agitating and conveying member for agitating and conveying the developer in the developer tank, wherein the toner replenished to the developer tank by the toner replenishing member is contained in the developer tank. A developing device characterized in that at least a part of the agitating / conveying member that is initially contacted is formed of a conductive material, and a bias potential having the same polarity as the charging polarity of the toner is applied to the conductive material. An image forming apparatus comprising the developing device according to claim 1. At least a developer containing toner is stored in the developer tank, and the toner is supplied from a supply toner tank containing the toner supplied to the developer tank to the developer tank by a toner supply member. A part of the agitating / conveying member with which the replenished toner contacts at least first in the developer tank is formed of a conductive material, and the conductive material and the ground are connected via a varistor. Developing method. At least a developer containing toner is stored in the developer tank, and the toner is supplied from a supply toner tank containing the toner supplied to the developer tank to the developer tank by a toner supply member. The replenished toner forms at least a part of the agitating / conveying member with which the toner comes into contact first in the developer tank with a conductive material, and a bias potential having the same polarity as the charged polarity of the toner is applied to the conductive material. A developing method characterized by applying.

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