JP2016045422A - Developing device and image forming apparatus including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent, when recovering to reuse residual substances such as toner remaining on the surface of a photoreceptor drum with a cleaning device after transfer, image fogging and image defects due to the residual substances.SOLUTION: There is provided a developing device 4 that develops an electrostatic latent image formed on an electrostatic latent image carrier 1 by using a developer including toner to form a toner image, the developing device 4 including a toner returning part 10 that returns the toner remaining on the electrostatic latent image carrier 1 after transfer to a developing tank 41, a developer carrier 44 that carries the developer, and a foreign substance recovery member 46 that is arranged in the vicinity of the developer carrier 44; the foreign substance recovery member 46 is applied with voltage.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an electrophotographic developing device that forms a toner image by developing an electrostatic latent image formed on an electrostatic latent image carrier using a developer containing toner, and an image including the same. The present invention relates to a forming apparatus.

  FIG. 10 is a schematic cross-sectional view showing a main part of an image forming apparatus provided with a conventional developing device.

  Conventionally, when an image is formed in an image forming apparatus such as a copying machine or a printer, as shown in FIG. 10, a drum-shaped electrostatic latent image carrier having a photosensitive layer formed on its surface (hereinafter referred to as a photosensitive drum). 1) is rotated to charge the surface of the photosensitive drum 1 by the charger 2, and then the surface of the charged photosensitive drum 1 is exposed according to the image information by the exposure device 3, and the photosensitive drum 1 is exposed. After forming an electrostatic latent image on the surface of the photosensitive drum 1, toner is supplied from the developing device 4 to the photosensitive drum 1 to form a toner image on the surface of the photosensitive drum 1.

  Then, after the toner image formed on the surface of the photosensitive drum 1 is transferred to the transfer medium P such as paper by the transfer device 5, the transfer medium P on which the toner image is transferred is separated from the photosensitive drum 1. An image is formed by performing a fixing operation with heat or pressure in a subsequent fixing device (not shown).

  Thereafter, a series of operations such as collecting a residue such as toner remaining on the surface of the photoconductive drum 1 by the cleaning device 7 and returning the photoconductive drum 1 to an initial state is repeated, whereby the image is continuously displayed. It was possible to perform the formation.

  By the way, as described above, after the residue such as the toner remaining on the surface of the photosensitive drum 1 is collected by the cleaning device 7, the collected residue such as the toner is generally generally stored in the waste toner box 9 or the like. It was discharged and discarded.

  For this reason, a fixed amount of toner is discarded without being used for image formation, which causes a reduction in the number of output sheets (number of printed sheets) per toner cartridge.

  In addition, if the residue such as toner is discarded as it is, problems such as environmental pollution occur. Therefore, it is necessary to dispose it by special treatment, but it cannot be processed by ordinary users. There was also a problem that it took time and cost.

  Therefore, as shown in FIG. 11, an image forming apparatus has been proposed in which a residue such as toner collected by the cleaning device 7 is returned to the developing device 4 by the toner returning unit 10 and the collected toner is used again for development.

  However, when a residue such as toner remaining on the surface of the photosensitive drum 1 after the transfer is recovered by the cleaning device 7 and reused, the recovered residue includes a transfer medium such as paper in addition to the toner. Since foreign matter such as paper dust and filler generated from 6 is included, the foreign matter enters the developing device 4. The invading foreign matter combines with the toner to generate poorly charged toner with low chargeability or reversely charged toner with a reverse polarity, so that the image quality gradually increases as fog occurs on the image or the foreign matter adheres to the image. There was a problem that it decreased.

Therefore, conventionally, an image forming apparatus for solving this problem has been proposed (for example, see Patent Document 1).
12 and 13 show a configuration example of the image forming apparatus described in Patent Document 1. FIG.

  In the image forming apparatus described in Patent Document 1, the defect contained in the developer while the developer is guided from the regulating member 143 of the developing device 140 to the developing region T where the image carrier 101 and the developer carrier 142 face each other. A collecting means 150 is provided for collecting unnecessary items such as charged toner and foreign matter. Incidentally, reference numeral 102 in the figure denotes a charger, 103 denotes an exposure device, 105 denotes a transfer device, 107 denotes a cleaning device, 108 denotes a residue returning means, 144 denotes a developing power source, and 153 denotes a power source.

  In this prior art, a collecting unit 150 is provided mainly for collecting defective charged toner, or a wire 152 to which a voltage is applied is disposed in the vicinity of the collecting unit 150 (see FIG. 13) to collect defective charged toner. A developing device that can be used is disclosed.

JP 2001-142300 A

  However, in the first place, since the charge amount of the defectively charged toner is small, it is difficult to efficiently recover the defectively charged toner only by applying a voltage to the wire as in the prior art.

  Further, as a result of investigations by the present inventors, when a residue such as toner remaining on the surface of the photosensitive drum 1 is returned to the developing device 4 (or toner cartridge) and used, a large amount of white is printed on the print sample. A large number of black fibrous dots (fogging) were printed, which proved to be a big problem.

  This fogging occurred by the following mechanisms (1) to (4).

  (1) In general, in an image forming apparatus using a negatively charged toner, a positive voltage is applied to attract toner in the transfer portion, but the paper dust adhering to the photosensitive drum is positively charged by the discharge in the transfer portion. The

  (2) The residual toner collected by the cleaning device and the positively charged paper powder are mixed with each other, whereby the paper powder attracts the toner, and paper dust and toner cluster-like foreign matters are formed.

  (3) The cluster-like foreign matter of paper dust and toner is positively charged and moves from the developer carrying member to the electrostatic latent image carrying member by an electric field while being developed in the developing region.

  (4) Thereafter, the toner image is fixed on paper through a transfer process and a fixing process.

  In particular, since the size of the cluster-like foreign matter is 100 to 500 μm, the foreign matter fixed on the white background of the paper in the transfer / fixing process is likely to jump into human eyes.

  The present invention was devised to solve such problems. The purpose of the present invention is to recover toner remaining on the surface of the electrostatic latent image carrier after transfer by a cleaning device and reuse it. Another object of the present invention is to provide a developing device capable of reliably preventing image fogging and image defects due to residues, and an image forming apparatus provided with the developing device.

  In order to solve the above problems, a developing device of the present invention develops an electrostatic latent image formed on an electrostatic latent image carrier using a developer containing toner to form a toner image. A toner return portion for returning the transferred toner remaining on the electrostatic latent image carrier to the developing container, a developer carrier for carrying the developer, and a portion near the developer carrier. And a voltage is applied to the foreign matter collecting member.

  As described above, paper dust and toner are charged in the transfer area with the same polarity (usually plus) as the transfer bias and attract the residual toner (usually minus) charged with the opposite polarity to the transfer bias. Cluster-like foreign matters (hereinafter also simply referred to as clusters). The entire cluster is charged with the same polarity as the transfer bias. When image formation is performed using a developer containing a large number of clusters, the paper dust cluster conveyed to the development area adheres to a white background (background), resulting in an image defect. This paper dust cluster is a big problem because it is easily recognized as 100 to 400 μm. According to the present invention, by applying a voltage to the foreign material collecting member, the paper dust and toner clusters can be collected, and image defects can be suppressed.

  The developing device of the present invention further includes a developer restricting member disposed in the vicinity of the developer carrying member, and the foreign matter collecting member is disposed downstream of the developer restricting member in the developer transport direction. The configuration is made.

  According to this configuration, the developer regulated by the developer regulating member is regulated to have a constant layer thickness, and the clusters in the developer can be collected to the foreign material collecting member stably and uniformly. Therefore, the paper dust cluster can be collected by providing the developer regulating member on the upstream side of the foreign material collecting member in the developer conveying direction.

  In the developing device of the present invention, the polarity of the voltage applied to the foreign matter collecting member is opposite to the charge polarity of the foreign matter.

  According to this configuration, by setting the polarity of the voltage applied to the foreign matter collecting member to be opposite to the charge polarity of the foreign matter, paper dust and toner clusters can be electrically attracted to the foreign matter collecting member.

  In the developing device of the present invention, the polarity of the voltage applied to the foreign matter collecting member is opposite to the transfer voltage.

  According to this configuration, paper dust is positively charged in the transfer area, and a cluster is formed by collecting the negatively charged waste toner. Therefore, in order to attract the paper dust and toner cluster to the foreign matter collecting member, What is necessary is just to apply the voltage of a reverse polarity to a voltage to a foreign material collection | recovery member. In this way, by setting the polarity of the voltage applied to the foreign matter collecting member to a polarity opposite to the transfer voltage, paper dust and toner clusters can be collected by the foreign matter collecting member.

  In the developing device of the present invention, a voltage having an absolute value larger than that of the developer carrier is applied to the foreign matter collecting member.

  According to this configuration, an electric field is formed in which the paper dust and toner clusters fly from the developer carrying member toward the foreign matter collecting member, and the foreign matter collecting member removes the paper dust and toner clusters by causing the clusters to fly. be able to.

  In the developing device of the present invention, the voltage applied to the foreign matter collecting member may be changed as the voltage applied to the developer carrier is changed.

  In general, in an image forming apparatus, at the start of operation, in order to prevent the carrier from flying from the developer carrier to the electrostatic latent image carrier, the bias applied to the developer carrier may be changed stepwise. At that time, as the polarity of the voltage applied to the developer carrier is changed so that the carrier does not fly to the foreign material collection member due to the electric field between the developer carrier and the foreign material collection member, Change the applied voltage. Thereby, flight of a carrier can be prevented.

  In the developing device of the present invention, the voltage applied to the foreign material collecting member may be changed in the polarity of the voltage applied to the developer carrier.

  In general, in an image forming apparatus, a reverse bias may be applied to a developer carrier for cleaning the developing device. In this case, if a reverse bias is applied to the developer carrying member of the developing device while the voltage for collecting the foreign matter is applied to the foreign matter collecting member, there is a problem that the carrier jumps to the foreign matter collecting member. Therefore, the flying of the carrier can be prevented by changing the voltage applied to the foreign material collecting member as the polarity of the voltage applied to the developer carrying member is changed.

  In the developing device of the present invention, the voltage supply source to be applied to the foreign material recovery member may be configured in common with the voltage supply sources of other members.

  According to this configuration, it is possible to reduce the component cost by sharing the supply source of the voltage applied to the foreign material recovery member with other members such as a charger and a developing device.

  In the developing device of the present invention, the voltage supply source to be applied to the foreign material recovery member may be configured in common with the voltage supply source of the developer carrier.

  According to this configuration, it is possible to reduce the component cost by sharing the voltage supply source applied to the foreign material recovery member with the voltage supply source of the developer carrier. In addition, since the developer carrying member and the foreign material collecting member are close to each other, there are advantages such as a short path from the power source and a common unit, which facilitates design support.

  In the developing device of the present invention, a constant voltage rectifier may be disposed between the developer carrier and the voltage supply source.

  According to this configuration, an appropriate potential difference is created between the foreign matter collecting member and the developer carrying member, and in the cleaning mode, the potential difference between the foreign matter collecting member and the developer carrying member is set to 0, whereby the paper dust and the toner cluster are formed. Can be prevented from flying again from the foreign material collecting member to the developer carrying member.

  In the developing device of the present invention, the foreign matter is paper dust. That is, the paper dust cluster conveyed to the development area is adsorbed by the foreign material collecting member as foreign material.

  In the developing device of the present invention, the foreign matter collecting member is arranged in contact with the tip of the developer carried on the developer carrying member, or arranged near the tip of the developer. Also good.

  According to this configuration, by placing the foreign matter collection member in contact with the tip of the developer or in the vicinity of the tip, the electric field between the carrier tip and the foreign matter collection member can be strengthened, and the paper dust and toner clusters are separated. It can be recovered efficiently.

  In the developing device of the present invention, the foreign matter collecting member has a blade shape.

  According to this configuration, by making the shape of the foreign material recovery member into a blade shape, first, paper dust is recovered at the position of the shortest distance between the developer and the recovery member. Paper dust can be collected at the part. Thereby, the collection amount of paper dust can be increased.

  The image forming apparatus according to the present invention includes the developing device having the above-described configurations.

  According to this configuration, in the image forming apparatus configured to return the transferred toner remaining on the electrostatic latent image carrier to the developing container, it is possible to more reliably collect paper dust and toner cluster-like foreign matters. It is possible to provide an image forming apparatus in which image fog and image defects are suppressed.

  According to the present invention, in the configuration in which the transferred toner remaining on the electrostatic latent image carrier is returned to the developing container, a voltage is applied to the foreign matter collecting member that collects the transferred toner remaining on the developer carrier. By doing so, it is possible to more reliably collect paper dust and toner cluster-like foreign matters, so that image fogging and image defects can be suppressed.

FIG. 2 is a schematic cross-sectional view illustrating a configuration of an image forming portion of an image forming apparatus including the developing device of the present invention. FIG. 2 is a schematic cross-sectional view illustrating a configuration of a fixing device. FIG. 6 is a diagram schematically showing a state in which a cluster of paper dust existing in the vicinity of a developer tip on the surface of a developer carrying member is collected by a foreign matter collecting member. It is a schematic sectional drawing which shows the structure of the developing device which concerns on Embodiment 2 shared with the power supply of another member. It is a schematic sectional drawing which shows the structure of the developing device which concerns on Embodiment 3 shared with the power supply of another member. 6 is a timing chart showing a state in which a voltage for recovering a cluster remains applied to a foreign material recovery member when a reverse bias is applied to the developer carrying member at the time of pre-rotation or post-rotation for cleaning. 6 is a timing chart showing the timing at which a foreign matter collecting member is dropped to ground when a reverse bias is applied to the developer carrying member at the time of pre-rotation or post-rotation for cleaning. 6 is a timing chart showing the timing of applying a positive bias to the foreign material collecting member when a reverse bias is applied to the developer carrying member at the time of pre-rotation or post-rotation for cleaning. 6 is a timing chart showing the timing of applying a reverse bias synchronized with a foreign matter collecting member when a reverse bias is applied to the developer carrying member at the time of pre-rotation or post-rotation for cleaning. It is a schematic sectional drawing which shows the principal part of the image forming apparatus provided with the conventional developing device. It is a schematic sectional drawing which shows the principal part of the image forming apparatus provided with the conventional developing device. 10 is a schematic cross-sectional view of a main part showing a configuration example of an image forming apparatus described in Patent Document 1. FIG. 10 is a schematic cross-sectional view of a main part showing a configuration example of an image forming apparatus described in Patent Document 1. FIG.

  Embodiments of the present invention will be described below with reference to the drawings.

<Embodiment 1>
(Description of image forming unit)
FIG. 1 is a schematic cross-sectional view showing a configuration of a visible image forming unit which is an image forming unit in an image forming apparatus equipped with a developing device according to Embodiment 1 of the present invention.

  The visible image forming unit includes a photosensitive drum 1, a sawtooth charger 2, an optical scanning unit 3, a developing device 4, a transfer device 5, a fixing device 6 (see FIG. 2), and a cleaning device 7. .

  The photosensitive drum 1 is an image carrier on which a toner image is formed. The photosensitive drum 1 is supported so as to be rotatable around an axis, and has a cylindrical shape, a cylindrical shape, or a thin film sheet shape (preferably a cylindrical shape) not shown. It includes a substrate and a photosensitive layer formed on the surface of the conductive substrate.

  As the photosensitive drum 1, those commonly used in this field can be used. For example, the photosensitive drum 1 includes an aluminum base tube which is a conductive substrate and an organic photosensitive layer which is a photosensitive layer formed on the surface of the aluminum base tube. A photosensitive drum connected to a GND (ground) potential can be used.

  The organic photosensitive layer may be formed by laminating a charge generation layer containing a charge generation material and a charge transport layer containing a charge transport material, and includes one charge generation material and a charge transport material. It may be formed by layers. The layer thickness of the organic photosensitive layer is not particularly limited, but is 20 μm, for example. Further, an underlayer may be provided between the organic photosensitive layer and the conductive substrate. Further, a protective layer may be provided on the surface of the organic photosensitive layer.

  The photosensitive drum 1 is rotated in a counterclockwise direction toward the paper surface of FIG. 1, for example, at a peripheral speed of 163 mm / s by driving means (not shown in FIG. 1). The driving unit of the photosensitive drum 1 is controlled by a control unit of an image forming unit described later. That is, the rotation speed of the photosensitive drum 1 is controlled by the control unit of the image forming unit.

  The sawtooth charger 2 is a charging means for charging the surface of the photosensitive drum 1 to a predetermined polarity potential, and a sawtooth electrode 22 is fixed in the case 21, and the exposed surface of the case 21 facing the photosensitive drum 1. A grid electrode 23 is disposed on the surface. The sawtooth electrode 22 and the grid electrode 23 are connected to a high voltage circuit (not shown), and a predetermined voltage is applied between the sawtooth electrode 22 and the grid electrode 23 by the high voltage circuit. The sawtooth electrode 22 is discharged, the photosensitive drum 1 is charged with a negative polarity, and a predetermined potential is applied to the photosensitive drum 1. Note that the charging means is not limited to the saw-tooth charger 2 described above, and a roller charger, a brush-type charger, a charger-type charger, or the like can also be used.

  The optical scanning unit 3 irradiates the surface of the photosensitive drum 1 in a charged state with laser light corresponding to image information, and forms a latent image corresponding to the image information on the surface of the photosensitive drum 1. Forming means. A semiconductor laser element or the like is used as the laser light source.

  The developing device 4 is a developing means provided facing the photoconductive drum 1, and in the developing tank (developing container) 41 constituting the internal space, two agitating and conveying members 42 for agitating and conveying the internal developer. 43, a developer carrier 44, a developer regulating member 45, and a foreign matter collecting member 46 to be described later. The developing device 4 carries a two-component developer on the surface of the developer carrier 44, is regulated to a predetermined amount by a developer regulating member 45, and is transported to the surface of the photosensitive drum 1. The electrostatic latent image formed on the surface is developed and visualized. As the developer, a one-component developer not containing a carrier can also be used.

  The developer carrier 44 is rotationally driven in the same direction as the rotational driving direction of the photosensitive drum 1 in the developing nip portion (developing region T) close to the photosensitive drum 1.

  The cleaning device 7 removes and collects the toner remaining on the surface of the photosensitive drum 1 without being transferred after the toner image on the surface of the photosensitive drum 1 is transferred to the paper.

  According to the visible image forming unit having such a configuration, a current of −620 μA, for example, is passed through the sawtooth electrode 22 by a power source (not shown) while the photosensitive drum 1 is driven to rotate about its axis. The surface of the photosensitive drum 1 is charged by applying, for example, a voltage of −600 V to the grid electrode 23 and discharging it. Next, the surface of the photosensitive drum 1 in a charged state is irradiated with laser light corresponding to the image information from the optical scanning unit 3 to form an electrostatic latent image having an exposure potential of −70 V corresponding to the image information.

  Next, the surface of the photosensitive drum 1 and the toner carried on the surface of the developer carrying member 44 are brought close to each other. A DC voltage of −450 V is applied as a developing potential to the developer carrier 44, and toner adheres to the electrostatic latent image due to a potential difference between the developer carrier 44 and the photosensitive drum 1, and the photosensitive drum 1. A toner image is formed on the surface. As will be described later, the toner image is pressed against the surface of the photosensitive drum 1 and transferred to a recording medium P that is conveyed in a direction indicated by an arrow Y in FIG.

The toner remaining on the surface of the photosensitive drum 1 is removed and collected by the cleaning device 7. The residual toner removed and collected is transported to a developing tank 41 (or a toner cartridge (not shown)) of the developing device 4 by a toner transport paddle (toner return portion) 10 and returned to each. The returned toner is agitated with the carrier in the same manner as the newly replenished toner in the developing tank 41, is carried to the developing region T, and is reused.
Thereafter, the toner image forming operation is repeatedly executed in the same manner.

  Next, the two-component developer used in the image forming apparatus of the present embodiment will be described in detail. The two-component developer includes a toner and a carrier.

  The toner is composed of toner particles containing a binder resin, a colorant, and a release agent. As the binder resin, those commonly used in this field can be used. For example, polystyrene, styrene-substituted homopolymer, styrene copolymer, polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, polyester, polyurethane Etc. Binder resin can be used individually by 1 type, or can use 2 or more types together.

  As the colorant, pigments for toners and dyes conventionally used in electrophotographic image forming techniques can be used. Examples of the toner pigment include carbon black and titanium oxide. Toner pigments can be used alone or in combination of two or more.

  As the release agent, for example, wax can be used. As the wax, those commonly used in this field can be used, and examples thereof include polyethylene wax, polypropylene wax, and paraffin wax.

  In addition to the binder resin, the colorant, and the release agent, the toner contains one or more general toner additives such as a charge control agent, a fluidity improver, a fixing accelerator, and a conductive agent. May be.

  The toner can be produced by a known method such as a pulverization method, a suspension polymerization method, or an emulsion aggregation method. In the pulverization method, a toner is obtained by melting and kneading a colorant, a release agent and the like with a binder resin. In the suspension polymerization method, monomers such as a binder resin, a colorant, and a release agent are uniformly dispersed, and then these monomers are polymerized to obtain a toner. In the emulsion aggregation method, a toner is obtained by aggregating a binder resin, a colorant, a release agent, and the like with an aggregating agent, and heating fine particles of the obtained aggregate.

  The volume average particle diameter of the toner is not particularly limited, but is preferably 2 μm or more and 7 μm or less. Further, when the volume average particle diameter of the toner is appropriately small as described above, the coverage with respect to the recording medium P becomes high, so that it is possible to achieve high image quality with a low adhesion amount and reduction in toner consumption.

  When the volume average particle diameter of the toner is less than 2 μm, the fluidity of the toner is lowered, and the toner supply, stirring and charging become insufficient during the developing operation. Therefore, the amount of toner supplied to the photosensitive drum 1 is reduced. There may be a shortage or an increase in reverse toner, and a high-quality image may not be obtained. When the volume average particle diameter of the toner exceeds 7 μm, toner particles having a large particle diameter that is difficult to soften to the central portion at the time of fixing increase, so that the fixability of the toner image on the recording medium P is lowered and the color of the image is reduced. In particular, in the case of fixing to an OHP sheet, the image becomes dark.

The toner used in the image forming apparatus of the present embodiment is a negatively chargeable insulating nonmagnetic toner having a glass transition point of 60 ° C., a softening point of 120 ° C., and a volume average particle diameter of 6 μm. In order to obtain an image density having a reflection density measurement value of 1.4 by X-Rite 310 using this toner, a toner amount of 5 g / m ² is required on the surface of the recording medium P.

  The toner contains polyester having a glass transition point of 60 ° C. and a softening point of 120 ° C. as a binder resin, 12% by weight of each color pigment as a colorant, and a glass transition point as a release agent. A low molecular weight polyethylene wax having a softening point of 70 ° C. at 50 ° C. is contained by 7% by weight of the total amount of the toner. The low molecular weight polyethylene wax used as a release agent for this toner is a wax having a lower glass transition point and softening point than polyester used as a binder resin.

  As the carrier, magnetic particles can be used. Examples of the magnetic particles include metals such as iron, ferrite and magnetite, and alloys of these metals with metals such as aluminum or lead. Among these, ferrite is preferable.

  Further, a resin-coated carrier in which magnetic particles are coated with a resin, or a resin-dispersed carrier in which magnetic particles are dispersed in a resin may be used as the carrier. The resin that coats the magnetic particles is not particularly limited, and examples thereof include olefin resins, styrene resins, styrene acrylic resins, silicone resins, ester resins, and fluorine-containing polymer resins. The resin used for the resin-dispersed carrier is not particularly limited, and examples thereof include styrene acrylic resin, polyester resin, fluorine-based resin, and phenol resin.

The volume average particle diameter of the carrier is not particularly limited, but is preferably 30 μm or more and 50 μm or less in consideration of high image quality. Furthermore, the resistivity of the carrier is preferably 10 ⁸ Ω · cm or more, more preferably 10 ¹² Ω · cm or more.

The carrier resistivity is determined by placing the carrier in a container having a cross-sectional area of 0.50 cm ² and tapping it, then applying a load of 1 kg / cm ² with the weight packed in the container, It is a value obtained by reading a current value when a voltage generating an electric field of 1000 V / cm is applied between them. When the resistivity of the carrier is low, when a bias voltage is applied to the developer carrier 44, charges are injected into the carrier, and carrier particles easily adhere to the photosensitive drum 1. Further, breakdown of the bias voltage is likely to occur.

  The magnetization strength (maximum magnetization) of the carrier is preferably 10 emu / g or more and 60 emu / g or less, more preferably 15 emu / g or more and 40 emu / g or less. Although the magnetization strength depends on the magnetic flux density of the developer carrier 44, under the general magnetic flux density conditions of the developer carrier 44, the magnetic binding force does not work if it is less than 10 emu / g. May cause carrier scattering. On the other hand, if the magnetization strength exceeds 60 emu / g, it becomes difficult to maintain the non-contact state with the photosensitive drum 1 in the non-contact development in which the carrier spikes become too high. Further, in the contact development, there is a risk that a sweep is likely to appear in the toner image.

  The shape of the carrier is preferably a spherical shape or a flat shape.

  The mixing ratio of the toner and the carrier in the two-component developer is not particularly limited, and may be appropriately selected according to the types of the toner and the carrier.

(Description of transfer section)
The transfer device 5 includes a transfer roller 51. The transfer roller 51 is a roller-like member that is in pressure contact with the photosensitive drum 1 and is rotatably driven in the axial direction.

  The transfer roller 51 includes, for example, a metal shaft body and a conductive layer formed on the surface of the metal shaft body. The metal shaft body is formed of a metal such as stainless steel. The conductive layer is formed of a conductive elastic body or the like.

  As the conductive elastic body, those commonly used in this field can be used, and examples thereof include EPDM, foamed EPDM, and foamed urethane containing a conductive material such as carbon black. A power supply (not shown) is connected to the transfer roller 51, and a high voltage having a polarity opposite to the charging polarity of the toner is applied uniformly.

  In the transfer device 5, the recording medium P is conveyed to the transfer nip N in synchronization with the toner image on the photosensitive drum 1 being conveyed to the transfer nip N. Then, the toner image and the recording medium P are overlapped at the transfer nip portion N, and a high voltage having a polarity opposite to the charging polarity of the toner is uniformly applied to the transfer roller 51, whereby an unfixed toner image is recorded on the recording medium. Transferred to P. Then, the recording medium P carrying the unfixed toner image is conveyed to the fixing device 6.

(Description of fixing unit)
FIG. 2 is a schematic cross-sectional view showing the configuration of the fixing device 6.

  The fixing device 6 as a fixing unit includes a fixing roller 61, a pressure roller 62, and a driving unit (not shown in FIG. 2).

  The fixing roller 61 serving as a heating unit includes a cored bar 63 and a surface layer 64. The fixing roller 61 is a roller-like member that is rotatably supported by a support unit (not shown) and is driven to rotate at a predetermined speed in the direction of arrow R1 in FIG. The toner constituting the unfixed toner image is heated and melted and fixed on the recording medium P.

  As the metal forming the cored bar 63, a metal having high thermal conductivity can be used, and examples thereof include aluminum and iron. Examples of the shape of the cored bar 63 include a cylindrical shape or a columnar shape, but a cylindrical shape with a small amount of heat released from the cored bar 63 is preferable in consideration of the amount of heat released.

  The surface layer 64 is a layer formed on the outer peripheral surface of the cored bar 63. The material constituting the surface layer 64 is not particularly limited as long as it is excellent in heat resistance and durability and has weak adhesion to the toner. For example, PFA (copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether), A fluorine resin material such as PTFE (polytetrafluoroethylene) can be used. The thickness of the surface layer 64 is preferably 5 μm or more and 50 μm or less.

  A heat source 65 is disposed inside the fixing roller 61. Specifically, the heat source 65 is disposed in an internal space formed radially inward of the cored bar 63 formed in a cylindrical shape, and generates heat when energized. In the present embodiment, a halogen lamp is used as the heat source 65.

  In the fixing roller 61, heat generated by the heat source 65 is transmitted in the order of the cored bar 63 and the surface layer 64, and this heat is carried on the recording medium P that contacts the surface of the fixing roller 61, that is, the outer peripheral surface of the surface layer 64. The unfixed toner image is heated. Further, a part of the heat generated by the heat source 65 is radiated from the surface of the fixing roller 61, but is stored in the fixing roller 61.

  On the other hand, the pressure roller 62 which is a pressure unit includes a cored bar 66, an elastic body layer 67, and a surface layer 68. The pressure roller 62 is a roller-like member that is rotatably provided in a state in which the pressure roller 62 is in pressure contact with the fixing roller 61 by a pressure mechanism (not shown) on the downstream side of the fixing roller 61 in the rotation direction with respect to the vertical lowest point. It is. A pressure contact portion between the fixing roller 61 and the pressure roller 62 is a fixing nip portion 69. The pressure roller 62 rotates following the rotation of the fixing roller 61. The pressure roller 62 promotes fixing of the toner image onto the recording medium P by pressing the toner in a molten state against the recording medium P when the fixing roller 61 heat-fixes the toner image onto the recording medium P. To do.

  As a material for forming the cored bar 66, the elastic body layer 67, and the surface layer 68 of the pressure roller 62, the same metal or material as the cored bar 63 and the surface layer 64 of the fixing roller 61 can be used.

(Description of foreign material recovery member)
As described above, in the present invention, the toner remaining on the surface of the photosensitive drum 1 after passing through the transfer portion is removed and collected by the cleaning device 7. The residual toner removed and collected is transported to the developing device 4 or a toner cartridge (not shown) by the toner transport paddle 10 and returned to each. The returned toner is replenished into the developing device 4 and is agitated with the carrier in the same manner as the replenished new toner, is carried to the developing region T, and is reused. Since the residual toner contains paper powder, filler, talc, and the like in addition to the toner, the amount of foreign matter in the developing device 4 increases as the number of image formation increases. In order to remove these foreign matters, a foreign matter collecting member 46 is provided in the present invention. Hereinafter, the foreign substance recovery member 46 will be described together with its operation.

  The developing device 4 carries a two-component developer on the surface of the developer carrying member 44, is regulated to a predetermined amount of thickness by a developer regulating member 45, and then moves to the developing region T and moves to the photosensitive drum 1. Develop toner on the surface. Accordingly, the foreign matter collecting member 46 is provided between the developer regulating member 45 and the developing region T.

  The foreign material recovery member 46 is a plate-like member having a metal plate and an insulating layer. The metal plate only needs to be conductive, and aluminum, SUS, phosphor bronze, or the like can be used. As for the insulating layer, it is sufficient if leakage between the carrier and the metal plate can be prevented, and PET, PFA resin, or the like can be used.

  Here, the distance between the tip of the toner (developer) carried on the surface of the developer carrying member 44 and the foreign matter collecting member 46 may be set such that the paper dust cluster can move to the foreign matter collecting member 46. When the distance between the tip of the developer and the foreign material collecting member 46 is large, it is necessary to increase the voltage applied to the foreign material collecting member 46. In addition, when the distance is too short, a new problem arises that the toner (developer) collides with the foreign material collecting member 46 and the toner scatters. Therefore, in this embodiment, considering both of these, the distance (gap) between the tip of the developer and the foreign material recovery member 46 is adjusted to be 1 mm or less.

  Further, the arrangement position of the foreign matter collecting member 46 is not particularly limited as long as it is a position where a cluster of paper dust can be collected. In the present embodiment, considering the ease of management of the gap between the developer front end and the foreign material recovery member 46 in the longitudinal direction (developer transport direction), on the downstream side of the developer regulating member 45 in the developer transport direction. In addition, a foreign matter collecting member 46 is disposed on the upstream side of the developing region T.

  A voltage of −600 V is applied to the foreign material recovery member 46 having such an arrangement by a power source (not shown). After the developer is regulated by the developer regulating member 45, a voltage of −450 V is applied to the developer carrying member 44 when the paper dust cluster existing near the tip of the developer passes through the foreign material collecting member 46. Therefore, the paper dust cluster having a positive polarity is recovered by the foreign material recovery member 46 due to a potential difference of −150V. FIG. 3 is a diagram schematically showing how the foreign matter collecting member 46 collects the paper powder cluster K existing in the vicinity of the tip of the developer on the surface of the developer carrying member 44.

  It is preferable that the potential difference at which the paper dust cluster can be collected by the foreign material collecting member 46 is large. However, if the potential difference is too large, the carrier will fly to the foreign material collecting member 46, so it is necessary to make it smaller. Therefore, in the present embodiment, the voltage applied to the foreign material recovery member 46 is set to −600V. By setting the voltage to −600 V, it is possible to collect the paper dust cluster on the foreign material collecting member 46 and to suppress the flying of the carrier.

  As a result, the developer on the developer carrier 44 is uniformly layer-regulated in the longitudinal direction (developer transport direction) by the developer regulating member 45 and then passes through the foreign matter collecting member 46 in a state where the developer spikes occur. Thus, the collection of paper dust clusters is performed well.

<Embodiment 2>
The foreign material recovery member 46 needs to be applied with a voltage from a power source. As for this power source, there is no problem with the dedicated power source, but it can be shared with the power sources of other members.

  FIG. 4 shows the configuration of the developing device according to the second embodiment shared with the power supply of other members.

  That is, in the second embodiment, the power source of the foreign material recovery member 46 is shared with the power source of the grid electrode 23 of the sawtooth charger 2.

  According to this structure, the cost concerning a power supply can be suppressed. That is, in the case where the power source of the foreign material collecting member 46 and the power source of the sawtooth charger 2 are made common, the location where the foreign material collecting member 46 and the sawtooth charger 2 are arranged is close, so the wiring is short, the wiring is performed, etc. Is advantageous.

<Embodiment 3>
FIG. 5 shows the configuration of the developing apparatus according to the third embodiment shared with the power supply of other members.

  In other words, the third embodiment shows a case where the power source of the foreign material collecting member 46 is shared with the power source of the developer carrier 44. In this case, since it is necessary to provide a potential difference from the developer carrier 44 in order to collect the paper dust cluster in the foreign matter collecting member 46, the constant voltage rectifier (zener diode) 48 or the like is used to A potential difference (−150 V in the above embodiment) sufficient for the paper dust cluster to fly between the developer carrier 44 and the developer carrier 44 is generated.

<Embodiment 4>
By the way, it is necessary to change the state of the voltage applied to the foreign material collection member 46 according to the state of the voltage applied to the sawtooth charger 2.

  For example, as shown in the timing chart of FIG. 6, there is a case where a reverse bias is applied to the developer carrier during the pre-rotation or post-rotation for cleaning. In the case of an image forming apparatus that performs such control, when a reverse bias (plus bias) is applied to the developer carrier 44, a voltage for collecting the paper dust cluster is applied to the foreign material collecting member 46. In some cases, the potential difference between the foreign material recovery member 46 and the developer carrier 44 becomes too large, causing a problem that the carrier moves toward the foreign material recovery member 46. Therefore, when a positive bias is applied to the developer carrying member 44, the foreign material collecting member 46 is dropped to the ground as shown in the timing chart of FIG. 7, or the foreign material collecting member 46 is used as shown in the timing chart of FIG. It is necessary to perform control to apply a positive bias to.

  When the constant voltage rectifier 48 is used to share the power supply with the developer carrier 44 (in the case of the third embodiment shown in FIG. 5), the developer carrier is as shown in the timing chart of FIG. Since a bias synchronized with the foreign matter collecting member 46 is applied to 44, it is not necessary to cope with switching the voltage by software or the like. Therefore, labor saving can be achieved.

  Next, the inventors conducted an experiment in which the effect of the foreign matter collecting member 46 is verified by performing aging in the system in which a voltage is applied from the outside to the foreign matter collecting member 46 having the above configuration.

  This time, in order to verify the effect of the foreign material collecting member 46, the weight of the paper dust collected by the foreign material collecting member 46 was measured every 500 sheets. After printing 10,000 sheets from the start of aging, the weight was measured every 500 sheets. The weight was 13.6 mg for the 10,000th sheet and 15.7 mg for the 10500th sheet. As a result of continuously measuring the weight of the paper after that, it was confirmed that the paper dust was successfully recovered.

  Next, the effect on image defects, which was a problem, was compared at the “fogging level” described below.

  First, a document with a printing rate of 5% is copied. Every time 10,000 copies of a document with a printing rate of 5% are copied, the document is replaced with a sheet on which a circle with a radius of 2 cm is printed at the center of the sheet, and set on the document table of the machine and copied. Next, the output sample is placed at a distance of 40 cm, and a circle with a radius of 2 cm is visually observed to count the number of large crushing stains present in the circle. Then, using the correspondence table shown in Table 1 and FIG. 2, the fogging level of the sample was obtained from the number of crushed dirt. Here, Table 1 is a correspondence table of the fogging level with respect to the number of crushed dirt existing in the circle, and Table 2 is a correspondence table of the evaluation level with respect to the fogging level.

  As a result, as shown in Table 3 showing the fogging evaluation result, in the case of the image forming apparatus without the foreign matter collecting member 46, the fogging level increases as the number of printed sheets increases, and the NG level (fogging level 3). In the case of the image forming apparatus of the present invention in which the foreign matter collecting member 46 is disposed, a good image without fogging with a fogging level of 3.0 or less can be maintained. did it.

  In each of the above-described embodiments, the developing device and the image forming apparatus are described as devices of the toner reuse mechanism. However, the present invention is applicable to any image forming apparatus in which foreign matter such as paper dust enters the developing device. The cleanerless type image forming apparatus is also included in the technical scope of the present invention.

  In addition, the embodiment disclosed herein is an example in all respects and does not serve as a basis for limited interpretation. Therefore, the technical scope of the present invention is not interpreted only by the above-described embodiment, but is defined based on the description of the scope of claims. Moreover, all the changes within the meaning and range equivalent to a claim are included.

1 Photosensitive drum (electrostatic latent image carrier)
2 Saw-tooth charger 3 Optical scanning unit 4 Developing device 5 Transfer device 6 Fixing device 7 Cleaning device 10 Toner transport paddle (toner return portion)
41 Developing tank (developing container)
44 Developer carrier 45 Developer regulating member 46 Foreign material collecting member

Claims (14)

A developing device that forms a toner image by developing an electrostatic latent image formed on an electrostatic latent image carrier using a developer containing toner,
A toner return portion for returning the toner after transfer remaining on the electrostatic latent image carrier to a developing container;
A developer carrying member carrying the developer;
A foreign matter collecting member disposed in the vicinity of the developer carrier,
A developing device, wherein a voltage is applied to the foreign matter collecting member. The developing device according to claim 1,
A developer regulating member disposed in the vicinity of the developer carrier,
The developing device according to claim 1, wherein the foreign matter collecting member is disposed downstream of the developer regulating member in a developer transport direction. The developing device according to claim 1 or 2,
The developing device according to claim 1, wherein the polarity of the voltage applied to the foreign matter collecting member is opposite to the charge polarity of the foreign matter. The developing device according to any one of claims 1 to 3, wherein
The developing device according to claim 1, wherein the polarity of the voltage applied to the foreign matter collecting member is opposite to the transfer voltage. A developing device according to any one of claims 1 to 4, wherein
A developing device, wherein a voltage having an absolute value larger than that of the developer carrying member is applied to the foreign matter collecting member. A developing device according to any one of claims 1 to 5, wherein
The developing device according to claim 1, wherein the voltage applied to the foreign material collecting member is changed as the voltage applied to the developer carrying member is changed. The developing device according to claim 6,
The developing device according to claim 1, wherein the change in the voltage applied to the foreign matter collecting member is a change in the polarity of the voltage applied to the developer carrier. A developing device according to any one of claims 1 to 7,
2. A developing apparatus according to claim 1, wherein a supply source of a voltage applied to the foreign material recovery member is common to a supply source of a voltage of another member. The developing device according to claim 8, wherein
2. A developing device according to claim 1, wherein a supply source of a voltage applied to the foreign matter collecting member is common to a supply source of a voltage of the developer carrier. The developing device according to claim 9, wherein
A developing device comprising a constant voltage rectifier disposed between the developer carrier and the voltage supply source. A developing device according to any one of claims 1 to 10, wherein
The developing device according to claim 1, wherein the foreign matter is paper dust. The developing device according to any one of claims 1 to 11, wherein
The developing device according to claim 1, wherein the foreign matter collecting member is disposed in contact with a tip of the developer carried on the developer carrying member, or disposed in the vicinity of the tip of the developer. A developing device according to any one of claims 1 to 12,
The developing device according to claim 1, wherein the foreign matter collecting member has a blade shape.   An image forming apparatus comprising the developing device according to any one of claims 1 to 13.

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