JP2005121774A - Development apparatus and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a development apparatus in which developer subjected to development is replaced with fresh developer on the peripheral face of a small-diameter developing sleeve incorporating a plurality of magnetic poles and uniform development is carried out. <P>SOLUTION: In the vicinity of the developing sleeve 41, the leading end of a developer conveyance paddle 44 rotates in a direction opposite to the developing sleeve 41. Between adjacent magnetic poles having the same polarity, the range AB of a magnetic field, where the lowest value of magnetic attraction force in the direction of a normal relative to the outer peripheral face of the developing sleeve 41 is 0.25N or below, is 120°≥∠AOB≥50°. In addition, the position where a line connecting the center O' of the developer conveyance paddle 44 and the center O of the developing sleeve 41 intersects the peripheral face of the developing sleeve 41 is within an arc AB in downstream of the center of the arc AB in the direction of the rotation. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a developing device used for developing and visualizing an electrostatic latent image on an image carrier using electrophotography, and an image forming apparatus provided with the developing device.

  In order to develop an electrostatic latent image formed on an image carrier using a two-component developer composed of toner and a magnetic carrier, a magnet roller having a plurality of rod-shaped magnetic poles is fixed inside as a magnetic field generating means. A developing sleeve which is a cylindrical and rotating developer carrier is used.

  The developer with toner attached to the magnetic carrier attracted by the internal magnetic poles adheres to the developing sleeve in a rising state, and the layer thickness of the developer is regulated by the layer thickness regulating member, and is conveyed along with the rotation of the developing sleeve. Then, the image is brought into contact with the surface of the image carrier in the development region, and the toner is attached to the portion of the electrostatic latent image formed on the image carrier, and development is performed.

  The developer that has been developed in the development area is returned to the developing container as the developing sleeve rotates, and is peeled off from the developing sleeve by the repulsive magnetic field that is disposed adjacent to the magnetic pole of the same polarity, and collected in the developing container. The On the other hand, after the developer is peeled off, a new developer adheres, and the developer is exchanged and conveyed to the development area.

In developing, since the magnetic flux density due to the magnetic pole inside the developing sleeve greatly affects the developing conditions, the internal magnetic pole has been studied. In order to reduce the edge effect and suppress the occurrence of abnormal images such as graininess and white-out at the rear end of the formed image, and to improve the image quality, the magnetic attraction force on the developing sleeve near the developing area entrance has a predetermined value. Proposals have been made that the conditions must be met. (See Patent Document 1.)
In addition, in order to obtain a uniform image without unevenness by using one pole of the repulsive magnetic pole as the developer layer thickness regulating pole, the magnetic field strength in the vertical direction is between the adjacent magnetic poles in the circumferential direction of the same polarity. A proposal has been made that it is necessary to define a lower limit value (absolute value). (See Patent Document 2)
Japanese Patent Laid-Open No. 2003-21969 JP 2001-194911 A

  When the developer developed in the development region is developed again without being peeled off from the developing sleeve, or when the developer in the developed state adheres again to the developing sleeve without being sufficiently stirred and is used for development. In the developed image on the image bearing member, image quality deterioration and image density decrease due to uneven development are recognized, and the durability of the developer is reduced.

  When the developer is forcibly peeled off by rubbing a blade or the like from the developing sleeve, or when a strong pressure or rubbing force is applied to the developer, deterioration of the developer is accelerated.

  The first object of the present invention is that the developer is hardly deteriorated, and the developer once used for development is sufficiently peeled off from the developing sleeve and newly stirred on the developing sleeve by the configuration of the repulsive magnetic pole. An object of the present invention is to provide a developing device that supplies a developer and performs good development, and an image forming apparatus including the developing device.

  In addition, the developer potential decreases due to long-term use, developer wrinkles decrease, the amount of developer supplied from the developer transport paddle to the developing sleeve decreases, and uneven pitch during development due to poor transport of the developer on the image. Such a defect occurs.

  The second object of the present invention is to form an image in which good development is carried out by stirring and conveying the developer so that the same charged state of the developer as in the initial stage is maintained even after long-term use of the developer. To provide an apparatus.

  In order to achieve the first object of the present invention, the present invention (Claims 1 to 5) is configured as follows.

The invention according to claim 1 is described as follows: “A developer container containing a two-component developer containing a magnetic carrier and toner, a rotatable cylindrical developer carrier installed in the developer container, and the developer carrier A magnetic field generating means having a plurality of magnetic poles arranged non-rotatingly inside the body, and a developer transport paddle for stirring and supplying the developer to the developer carrying member, and adjacent to the plurality of magnetic poles In the developing device provided with the same polarity magnetic pole,
The developer transport paddle tip rotates in opposite directions to each other at a position close to the developer carrier,
The range AB of the magnetic field where the minimum value of the normal magnetic attractive force standing on the outer peripheral surface of the developer carrier between the adjacent magnetic poles of the same polarity is 0.25 N or less is 120 ° ≧ ∠AOB ≧ 50 ° (O is the center of the developer carrier),
The position where the line connecting the center of the developer transport paddle and the center of the developer carrier intersects with the peripheral surface of the developer carrier is an arc on the downstream side in the rotation direction from the center position of the arc AB on the developer carrier. A developing device in the AB. It is.

  The invention according to claim 2 is the “developing device according to claim 1, wherein the developer carrying member comprises a cylindrical body having an outer diameter of 8 mm or more and 40 mm or less”.

  A third aspect of the present invention is the “developing device according to the first or second aspect, wherein the magnetic carrier is a carrier having a volume average particle diameter of 30 μm or more and 80 μm or less”.

  The invention according to claim 4 is the “developing device according to claim 1, wherein the toner is a polymerized toner having a volume average particle diameter of 3 μm or more and 8 μm or less”. is there.

  The invention according to claim 5 is “an image forming apparatus comprising the developing device according to claims 1 to 4”.

  In order to achieve the second object of the present invention, the present invention (Claim 6) is configured as follows.

The invention according to claim 6 is the following: "The developing device for developing the electrostatic latent image on the image carrier is
A developer container containing a two-component developer containing a magnetic carrier and toner, a rotatable cylindrical developer carrier installed in the developer container, and a non-rotating arrangement inside the developer carrier. A magnetic field generating means having a plurality of magnetic poles, and a developer transport paddle that stirs and supplies the developer to the developer carrying member, and a magnetic pole of the same polarity that forms a repulsive magnetic field among the plurality of magnetic poles. Arranged adjacent to each other, the developer transport paddle tip is configured to rotate in the opposite direction at a position close to the repulsive magnetic field region of the developer carrier,
The image forming apparatus according to claim 1, wherein the control unit performs control so as to increase a rotation speed of the developer transport paddle in accordance with a usage time of the developer in the developer container. It is.

  According to the first aspect of the present invention, since the developer on the rotating developing sleeve has been developed, the developer is agitated by the developer transport paddle and is smoothly replaced with a new developer having toner adhered to the carrier by frictional charging. Thus, uniform and high-quality development without uneven development is performed.

  According to the second aspect of the present invention, even with a compact developing device having a small diameter developing sleeve, uniform and high-quality development without uneven development is performed.

  According to the third and fourth aspects of the invention, uniform and high-quality development is performed using a small particle size toner, and high-quality development with high resolution is performed.

  According to the invention of claim 5, uniform and high-quality development is performed by a small and compact image forming apparatus, and an effect of recording a high-quality image with high resolution is produced.

  According to the sixth aspect of the present invention, conventionally, the developer is deteriorated in charging characteristics due to long-term use, and the developer is poorly conveyed to the electrostatic latent image portion of the image carrier. Thus, an image forming apparatus that can perform good development without fluctuation over a long period of time regardless of the fatigue deterioration of the developer is provided.

  The image forming apparatus of the present invention will be described with reference to the drawings.

  (1) The image forming apparatus shown in the cross-sectional configuration diagram of FIG. 1 illustrates an image forming unit of a copying machine using an electrophotographic process for forming a monochrome image to which the present invention is applied. However, the present invention is not limited to the configuration shown in FIG.

  Reference numeral 1 denotes a drum-shaped photosensitive member of a latent image carrier, which is a negatively charged organic semiconductor layer coated with a phthalocyanine pigment dispersed in polycarbonate on a grounded metal cylindrical substrate. The photosensitive layer including the charge transport layer has a film thickness of 30 μm, and is driven to rotate at a peripheral speed (vp) of 230 mm / s or higher in the direction of the arrow with a drum diameter of 60 mm.

  Reference numeral 2 denotes a scorotron charging means for uniformly charging the periphery of the rotating photosensitive member 1 to a predetermined polarity and potential. The grid applied voltage is set to -730 V, and a bias voltage is applied with a charging current value of -800 μA. Is set to −750V.

  Reference numeral 3 denotes an image exposure means using a laser scanning system, which uses a semiconductor laser (LD) having a laser wavelength of 780 nm and has an output power of 300 μW. The image exposure means 3 emits a laser beam and scans and exposes the uniformly charged surface of the photoreceptor 1 to form an electrostatic latent image.

  As will be described in detail later, the developing device 4 develops the electrostatic latent image on the photoreceptor 1 as a toner image by a developing sleeve 41 that rotates to face the photoreceptor 1. Development by contact or non-contact is performed using a two-component developer in combination with image exposure and reversal development. The developing sleeve 41 is a cylindrical member having a roller diameter of φ8 mm or more and 40 mm or less that rotates around a magnet roll 42 that is a magnetic member. In this embodiment, the developing sleeve 41 has a roller diameter of φ25 mm and a linear velocity (vs) of 500 mm / s or more. It rotates with a linear velocity, and the linear velocity ratio (vs / vp) with respect to the photoreceptor 1 is set between 1.5 and 2.8. Development is performed on the developing sleeve 41 with a developing bias of a DC component, and reverse developing is performed by applying a developing bias of −600 V as the DC component.

  As the toner of the two-component developer containing a nonmagnetic toner and a magnetic carrier, a polymerized toner having a volume average particle diameter of 3 to 8 μm is preferable. By using the polymerized toner, an image forming apparatus having a high resolving power and a stable density and a very small occurrence of fog can be realized.

  The polymerized toner is manufactured by the following manufacturing method.

  The formation of the binder resin for toner and the toner shape are obtained by polymerization of the raw material monomer or prepolymer of the binder resin and subsequent chemical treatment. More specifically, it is obtained through a polymerization reaction such as suspension polymerization or emulsion polymerization and, if necessary, a step of fusing particles between them, and in the polymerization toner, the raw material monomer or prepolymer is uniformly dispersed in an aqueous system. Since the toner is subsequently polymerized, a spherical toner having a uniform toner particle size distribution and shape can be obtained.

  If the toner has a volume average particle size of less than 3 μm, fogging and toner scattering are likely to occur. The upper limit of 8 μm is the upper limit of the particle size that can form the high image quality targeted by this embodiment.

  As the carrier, a ferrite core carrier made of magnetic particles having a volume average particle size of 30 to 80 μm and a magnetization of 20 to 70 emu / g is preferable. Carrier adhesion tends to occur with a carrier having a particle size smaller than 30 μm. In addition, in the case of a carrier having a particle diameter larger than 80 μm, an image having a uniform density may not be formed.

  The developer sleeve 41, which has a magnet roll 42 as a magnetic field generating means and rotates in the direction of the arrow, is charged by the mutual friction and the developer in which the toner is attached around the carrier is attached by a magnetic force. The layer thickness of the developer is regulated by the layer thickness regulating member 45, and the developer is transported to the development area facing the photoreceptor 1 for development.

  In the developing container 46, there is a pair of agitating and conveying screws 43A and 43B and a developer conveying paddle 44, and a developing sleeve while mixing and stirring newly supplied toner and recycled toner with the developer in the developing container 46 Transport to 41. The agitating and conveying screws 43A and 43B are both rod-shaped screw members, one of which conveys the developer from the front side of the paper surface to the rear side and the other of the developer from the rear side of the paper surface to the front side while stirring the developer. The toner falls on the developer circulating by the stirring and conveying screws 43A and 43B, is mixed and stirred, and is discharged in the direction of the rotating paddle 44. The developer mixed and agitated with the discharged toner is further agitated by a water wheel-like developer conveyance paddle 44 described later and supplied to the repulsive magnetic field region of the developing sleeve 41. The electrostatic latent image portion is developed.

  Reference numeral 5 denotes a pre-transfer exposure light source for irradiating in order to improve the transferability of the toner image.

  Reference numeral 6 denotes a corotron transfer pole, which transfers the toner image on the photosensitive member 1 onto the transfer paper by constant current control with a transfer current of 200 μA.

  Reference numeral 7 denotes a corotron separation pole, which promotes separation of the transfer paper from the photosensitive member 1 by a separation current of an AC component of 100 μA and a DC component of −200 μA.

  The transfer paper P fed from the paper feed unit is fed in synchronism with the toner image formed on the photosensitive member 1 by the registration roller 21, and the toner image is transferred by the transfer pole 6 at the transfer nip portion. . The transfer paper P that has passed through the transfer nip is separated from the surface of the photosensitive member 1 by the separation pole 7 and is transported to the fixing device 23 by the transport belt 22.

  The fixing device 23 includes a heating roller 23a and a pressure roller 23b in which a heater is disposed. The transfer paper P holding a toner image is heated and pressed between the heating roller 23a and the pressure roller 23b. The transfer paper P, to which the toner image has been fixed, is discharged onto a discharge tray outside the apparatus by a discharge roller 24.

  On the other hand, the transfer residual toner is cleaned by a cleaning device 8 using a cleaning blade that is in sliding contact with the surface of the photoreceptor 1 after the transfer of the toner image onto the transfer paper P. The peripheral surface of the photosensitive member 1 whose surface has been cleaned by passing through the cleaning device 8 is irradiated by a pre-charge exposure (PCL) means 9 using a light wavelength of 700 nm and a light output of 10 lux light source, and the residual potential is lowered to the next. Shift to the image forming cycle.

  (2) FIG. 2 shows an enlarged view of a main part of the developing device 4. In the present embodiment, a developing magnetic pole having a five-pole magnet roll 42, N1, N2 as N poles, S1, S2, S3 as S poles and the magnetic pole N1 facing the photosensitive member 1 is used. . In the present invention, adjacent magnets S1 and S2 of the same polarity are provided to form a repulsive magnetic field, and the developer developed in the developing region is peeled off from the peripheral surface of the developing sleeve 41 rotating in the repelling magnetic field and developed. A new developer supplied from the agent transport paddle 44 is attached to the peripheral surface of the developing sleeve 41, and the attached developer is exchanged and transported to the development region.

  In the present invention, the magnetic field range AB where the minimum value of the normal magnetic attractive force Fr standing on the outer peripheral surface of the developing sleeve 41 between the magnetic poles S1 and S2 is 0.25 N or less is 120 ° ≧ ∠AOB ≧ 50. ° (O is the center of the developing sleeve).

When the magnetic attraction force Fr is represented by a normal magnetic flux density Br and a tangential magnetic flux density Bθ, and expressed in an axisymmetric cylindrical coordinate system (r, θ),
Fr = m × {Br (δBr / δr) + (Bθ / r) (δBr / δθ)}
Although the calculation is performed by the above equation, since a numerical calculation error is likely to occur, the magnetic attractive force Fr is measured by the measuring device shown in FIG.

  A magnet roll 42 having magnetic poles S1 and S2 in FIG. 2 is attached horizontally to the drive unit 31 and the support arm 32 as an object to be measured. A holding member 34 that holds the suction member 40 is set on the electronic balance 33 so that a perpendicular line passing through the rotation axis of the magnet roll 42 is parallel to the rotation axis of the magnet roller 30.

  The attracting member 40 made of a magnetic iron rod is held by a holding member 34 as shown in FIG. 5A, and has a height of 10 ± 0.1 mm and a width of 10 ± as shown in FIG. 5B. It is a rod made of an iron material having a relative permeability of 5000, 0.1 mm, a length of 35 ± 0.5 mm, and chamfered with 2 × 2 mm on both sides of the bottom. The distance between the magnet roll 42 and the suction member 40 is set by the suction gap setting unit 35.

  The magnet roll 42 is rotated by the drive unit 31, and the magnetic attraction force Fr at each rotational position of the magnet roll 42 is measured by the electronic balance 33.

  The measurement result is calculated by the controller 36 and recorded in the recorder 37.

  The magnetic attraction force Fr is a measured value under the condition that the upper surface of the attraction member 40 in FIG. 5 is set at a position corresponding to a position 0.1 mm above the outer peripheral surface of the developing sleeve 20 by the attraction gap setting unit 35. is there.

  FIG. 3 shows the magnetic attractive force Fr in the repulsive magnetic field recorded by the recorder 37. When the magnetic attractive force Fr is larger than 0.25 N, the developer that has been developed tends to maintain adhesion to the developing sleeve 41, and the developer is not sufficiently replaced.

  Further, the range of the replacement of the developer having a magnetic attraction force Fr of 0.25 N or less in which the developer is replaced is 40 mm or less to which the present invention is applied. In this embodiment, the developing sleeve 41 having a small diameter of 25 mm is used. In this case, it is necessary to have an included angle of 50 ° or more. In the developing sleeve 41 having an outer diameter of φ8 mm, a three-pole magnet roll 42 is used, and the magnetic attractive force Fr is 0.25 N or less. The range needs to be set close to 120 °.

  The developer agitated by the agitating and conveying screws 43A and 43B in the developing container 46 is supplied to the repulsive magnetic field of the developing sleeve 41 by the developer conveying paddle 44. And is conveyed to the development area. Next, the developer transport paddle 44 will be described.

  The developer transport paddle 44 having four blades or six blades in a water wheel shape has a diameter of about 25 mm, which is close to the outer diameter of the developer sleeve 41, and the tip of the developer transport paddle 44 is the circumference of the developer sleeve 41. At a position close to the repulsive magnetic field area of the surface and having a gap of 1 to 4 mm, the peripheral speed is slightly slower than the peripheral speed of the developing sleeve 41 in the opposite direction to the developing sleeve 41 (in this embodiment, 5/8 of the developing sleeve 41). (Peripheral speed).

  In the present invention, the position Q where the line connecting the center O ′ of the developer transport paddle 44 and the center O of the developing sleeve 41 intersects the peripheral surface of the developing sleeve 41 is the magnetic attraction force of the peripheral surface of the developing sleeve 41. The Fr is arranged so as to be within the arc AB on the downstream side in the rotation direction of the developing sleeve 41 with respect to the center position M of the magnetic field range AB of 0.25 N or less. By constructing such a positional relationship, after the developer that has been developed is peeled off from the developing sleeve 41, a new developer is supplied and adhered, and within a range that is sufficiently allowed by vision without pitch unevenness and the like. Development is performed under uniform conditions.

  When the position Q where the line connecting the center O ′ of the developer transport paddle 44 and the center O of the developing sleeve 41 intersects the peripheral surface of the developing sleeve 41 is upstream of the center position M of the arc AB, development is performed. Since the finished developer is supplied with a new developer in an insufficient state on the state in which the developer is not sufficiently peeled off from the developing sleeve 41, the occurrence of uneven development in pitch unevenness is recognized.

  According to the tests of the present inventors, the position Q where the line connecting the center O ′ of the developer transport paddle 44 and the center O of the developing sleeve 41 intersects with the peripheral surface of the developing sleeve 41 is the position Q of the peripheral surface of the developing sleeve 41. Make sure that the magnetic attractive force Fr is in a position close to (2/3) from the upstream side in the rotation direction of the magnetic field range AB of 0.25 N or less, so that there is a stable arrangement relationship in which development unevenness does not occur most. ing.

  (3) In the developing device described above, mechanical stress between the developers in the developer container 46 is small, and the deterioration of the developer is slow compared to the conventional case even after long-term use. However, the developer is deteriorated by development in the development region, the charge potential of the carrier is lowered, the amount of toner adhering to the carrier due to frictional charging is reduced, the developer bulk is lowered, and the developer is not conveyed by the developing sleeve 41. Will occur, and uneven development is likely to occur.

  In the present invention, control is performed so as to increase the rotational speed of the developer transport paddle 44 in accordance with the usage time of the developer in the developer container 46, and even if the developer deteriorates, the same good as before deterioration Control is performed so that proper development is performed.

  6 and 7 show an outline of an electric control system related to developing device driving.

  Reference numeral 101 denotes a CPU that performs arithmetic control processing, and is connected to a ROM 102 that stores an image forming program and other data processing programs, a RAM 103 that stores the total driving time of the development driving unit, and the like. Connected to the device. The development drive unit 111A or 111B and the development bias power source 112 are connected to the interface 110 on the output side in relation to development device drive.

  At the time of image formation, the CPU 101 calls an image forming program recorded in the ROM 102 to drive the development drive unit 111A or 111B via the interface 110, and a bias voltage is applied to the development bias power source. Development is performed on the formed electrostatic latent image portion.

  In the present invention, the CPU 101 measures the driving time of the development driving unit 11A or 111B, inputs the measured driving time to the RAM 103, and loads the new developer into the developing container 46 to determine the development driving time after that. The total is memorized.

  FIG. 8 shows a table showing the relationship between the total development drive time and the rotation speed of the developer transport paddle 44. The CPU 101 calls this table from the ROM 102 storing this table, and the developer transport time is up to 100H. The paddle 44 is controlled to rotate at 240 rpm, and if it exceeds 100H, the developer transport paddle 44 is switched to a rotational speed of 270 rpm to increase the speed during development.

  By controlling the number of rotations of the developer transport paddle 44 based on the cumulative development drive time of the CPU 101, when the developer has deteriorated, the rotational speed of the developer transport paddle 44 is increased, and the carrier and toner The development and the development in the same state as the initial stage of development are continued by increasing the agitation and friction between them and increasing the charge of the carrier. In this embodiment, when the total development drive time exceeds 200H, the rotation speed of the developer transport paddle 44 is increased to 330 rpm, and the developer replacement time is reached on the display unit of the image forming apparatus. A display is made.

  In the above description, it has been described that only the developer conveyance paddle 44 is accelerated according to the total development drive time, but the agitating and conveying screws 43A and 43B are simultaneously accelerated together with the developer conveyance paddle 44. It is desirable.

  Regarding the development drive described above, in the development drive unit 111A shown in FIG. 6, the drive motor for driving the development sleeve 41 and the drive motor for driving the developer transport paddle 44 are separate drive motors. The circuit example which CPU101 controls so that the rotational speed of the drive motor which drives the paddle 44 is increased according to development drive accumulation time is shown.

  Further, in the development drive unit 111B shown in FIG. 7, the developing sleeve 41 and the developer transport paddle 44 are rotated by the same drive motor, and the drive transmission unit between the developer transport paddle 44 and the drive motor has a speed. A transmission is provided that is switched. The embodiment shown here is an example of a circuit in which the CPU 101 performs control so that the speed of the transmission is increased according to the development drive cumulative time.

1 is a cross-sectional configuration diagram of an image forming apparatus. The principal part enlarged view of a developing device. Magnetic attraction force recorded by the recorder. A measuring device that measures magnetic attraction. Dimensional shape of suction member. FIG. 3 is a schematic diagram of an electric control system related to developing device driving. FIG. 3 is a schematic diagram of an electric control system related to developing device driving. A table showing the relationship between the total development drive time and the rotation speed of the developer transport paddle.

Explanation of symbols

4 Developing Device 41 Developing Sleeve 42 Magnet Roll 43A, 43B Agitating and Conveying Screw 44 Developer Conveying Paddle 46 Developing Container 100 Control Unit 101 CPU
110 Interface 111A, 111B Development drive unit

Claims (6)

A developer container containing a two-component developer containing a magnetic carrier and toner, a rotatable cylindrical developer carrier installed in the developer container, and a non-rotating arrangement inside the developer carrier. A magnetic field generating means having a plurality of magnetic poles, and a developer transport paddle for stirring and supplying the developer to the developer carrying member, and a developing having a magnetic pole of the same polarity adjacent to the plurality of magnetic poles. In the device
The developer transport paddle tip rotates in opposite directions to each other at a position close to the developer carrier,
The range AB of the magnetic field where the minimum value of the normal magnetic attractive force standing on the outer peripheral surface of the developer carrier between the adjacent magnetic poles of the same polarity is 0.25 N or less is 120 ° ≧ ∠AOB ≧ 50 ° (O is the center of the developer carrier),
The position where the line connecting the center of the developer transport paddle and the center of the developer carrier intersects with the peripheral surface of the developer carrier is an arc on the downstream side in the rotation direction from the center position of the arc AB on the developer carrier. A developing device in the AB. The developing device according to claim 1, wherein an outer diameter of the developer carrying member is a cylindrical body having a diameter of 8 mm or more and 40 mm or less. The developing device according to claim 1, wherein the magnetic carrier is a carrier having a volume average particle diameter of 30 μm or more and 80 μm or less. The developing device according to claim 1, wherein the toner is a polymerized toner having a volume average particle diameter of 3 μm or more and 8 μm or less. An image forming apparatus comprising the developing device according to claim 1. The developing device for developing the electrostatic latent image on the image carrier is
A developer container containing a two-component developer containing a magnetic carrier and toner, a rotatable cylindrical developer carrier installed in the developer container, and a non-rotating arrangement inside the developer carrier. A magnetic field generating means having a plurality of magnetic poles, and a developer transport paddle that stirs and supplies the developer to the developer carrying member, and a magnetic pole of the same polarity that forms a repulsive magnetic field among the plurality of magnetic poles. Arranged adjacent to each other, the developer transport paddle tip is configured to rotate in the opposite direction at a position close to the repulsive magnetic field region of the developer carrier,
The image forming apparatus according to claim 1, wherein the control unit performs control so as to increase a rotation speed of the developer transport paddle in accordance with a usage time of the developer in the developer container.

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