JP2004280092A - Development apparatus and tandem type color image forming machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a development apparatus which can make an image forming machine more compact and a tandem type color image forming machine equipped with the development apparatus. <P>SOLUTION: The development apparatus is equipped with a housing 110 in which a two-component developer is housed, a stirring transfer means 120 which stirs and transfers the developer in the housing 110, a magnetic roller 130 which holds and transfers the developer, and a developing roller 140 which is disposed at the magnetic roller 130 apart a gap therefrom. The stirring transfer means 120 is arranged at a I-th quadrant around the center O of rotation of the magnetic roller 130 as an origin and the developing roller 140 is arranged at a III-rd quadrant. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to a developing device provided in an image forming machine such as a copying machine, a printer, and a facsimile using an electrophotographic system. More specifically, a two-component developer having a magnetic carrier and a non-magnetic toner is used. A non-contact type in which a non-magnetic toner is charged using a carrier, only the charged toner is attached to the peripheral surface of the developing roller, and the toner attached to the peripheral surface of the developing roller is caused to fly to develop an electrostatic latent image. The present invention relates to a developing device of a developing system and an image forming machine provided with the developing device, in particular, a tandem type color image forming machine.

A housing accommodating a two-component developer composed of a magnetic carrier and a non-magnetic toner, a stirring / conveying unit for stirring / conveying the developer contained in the housing, and a developer carrying / holding the developer on the peripheral surface and conveying the developer A developing device including a magnetic roller as a body and a developing roller as a toner carrier disposed at a predetermined gap between the magnetic roller and the belt-shaped photoconductor has already been proposed (for example, see Patent Document 1). 1). In the housing, a first developer stirring chamber is provided at a position adjacent to the magnetic roller, and further, a second developer stirring chamber separated from the first developer stirring chamber and a partition is provided. The first and second developer stirring chambers communicate with each other at both axial ends of the magnetic roller. The first and second developer stirring chambers are respectively provided with a first stirring and conveying member (first screw auger) and a second stirring and conveying member (second screw auger). The developer stirred in the first and second developer stirring chambers is supplied to the magnetic roller by the first stirring and conveying member. The toner in the developer held by the magnetic roller is electrostatically attached to the developing roller, and the toner attached to the developing roller flies to the electrostatic latent image formed on the belt-shaped photoconductor to develop. I do.

The developing device can be applied to a plurality of color image forming machines. That is, in the color image forming machine disclosed in Patent Document 1, the belt-shaped photoconductor is formed in an endless shape including a vertical region extending in a vertical direction, that is, a substantially vertical direction. A plurality of the developing devices are arranged along a vertical region of the belt-shaped photoconductor. In each of the developing devices, the developing roller, the magnetic roller, the first stirring and conveying member, and the second stirring and conveying member are arranged in the housing in this order substantially horizontally adjacent to each other, and the peripheral surface of the developing roller is a belt-shaped photosensitive member. Are arranged to face each other with a gap in the vertical region.

Since the belt-shaped photoreceptor in the above color image forming machine is formed endlessly including the vertical region, the height of the entire image forming machine becomes extremely high, and in installation, a vertical space which can be said to be excessive is required. You. Therefore, the above problem can be solved by forming the belt-shaped photoconductor in an endless shape including a horizontal region extending in a horizontal direction, that is, a substantially horizontal direction. However, in the developing device, the developing roller, the magnetic roller, the first stirring and conveying member, and the second stirring and conveying member are arranged in the housing substantially horizontally and horizontally adjacent to each other in this order. Even if the developing roller is disposed below the magnetic roller, the overall length of the image forming apparatus in the lateral direction becomes considerably large. Therefore, in order to reduce the size of the image forming machine, further improvement is required for the developing device. In addition, a configuration in which a photosensitive drum facing a developing roller of each developing device is arranged instead of the belt-shaped photosensitive member is also known.
JP-A-6-67546 (FIGS. 1 and 2)

SUMMARY OF THE INVENTION It is an object of the present invention to provide a novel developing device capable of reducing the vertical and horizontal dimensions of an image forming machine to make the overall configuration compact, and a tandem type color image forming machine equipped with the developing device. To provide.

Another object of the present invention is to provide a novel developing device capable of reliably preventing poor separation of a developer from a magnetic roller and ensuring a uniform image density at all times, and a tandem type color image forming apparatus including the developing device. Is to provide a machine.

Still another object of the present invention is to provide a novel developing device, which can reliably prevent defective separation of a developer from a magnetic roller to ensure uniform image density and prevent leakage of the developer at all times. And a tandem-type color image forming machine provided with the developing device.

According to one aspect of the invention,
A housing accommodating a two-component developer composed of a magnetic carrier and a non-magnetic toner, a stirring and conveying means for stirring and conveying the developer contained in the housing, and a magnetic roller for holding and conveying the developer on the peripheral surface; A magnetic roller, a developing roller disposed with a predetermined gap therebetween, the magnetic roller includes a magnetic sleeve, and a stationary permanent magnet disposed in the magnetic sleeve and having a plurality of magnetic poles arranged in a circumferential direction. Wherein the stirring and conveying means includes a stirring and conveying member extending along the magnetic roller near the magnetic roller, and the toner in the developer held by the magnetic roller is electrostatically attached to the developing roller. At
With the rotation center of the magnetic roller as the origin, the stirring and conveying member is arranged in quadrant I, the developing roller is arranged in quadrant III,
The magnetic poles of the stationary permanent magnet include a pair of magnetic poles that are circumferentially spaced from each other and are the same in polarity, and are formed by a repulsive magnetic force generated between the pair of magnetic poles on a radially outer side of the magnetic sleeve. An area formed between the pair of magnetic poles and having the lowest value of the perpendicular magnetic force is positioned within an angle range of 35 ° to 60 ° in the quadrant I,
A developing device is provided.
It is preferable that the saturation magnetization value of the magnetic carrier is specified to be 35 to 50 emu / g.
It is preferable that the volume resistivity of the magnetic carrier is specified to be 10 ⁸ to 10 ¹² Ω · cm.
It is preferable that the volume average particle size of the magnetic carrier is specified to be 35 to 50 μm.
It is preferable that, of the pair of magnetic poles, a magnetic pole disposed on the upstream side in the rotation direction of the magnetic sleeve has a perpendicular magnetic force of 62 to 76 mT.
It is preferable that, of the pair of magnetic poles, the magnetic pole disposed on the downstream side in the rotation direction of the magnetic sleeve has a perpendicular magnetic force of 34 to 60 mT.

According to another aspect of the present invention,
A tandem-type color image forming machine in which a plurality of image forming means including a photosensitive drum, a charger arranged around the photosensitive drum, an exposure device, a developing device, a transfer device, and a cleaning device are arranged in a substantially horizontal direction. And a developing device in each of the image forming means, a housing for containing a two-component developer including a magnetic carrier and a non-magnetic toner, and a stirring and conveying means for stirring and conveying the developer contained in the housing. A magnetic roller that transports the developer while holding the developer on the peripheral surface; and a developing roller that is disposed at a predetermined gap between the magnetic roller and the photosensitive drum. The toner in the developer held by the magnetic roller is provided. Is a tandem type color image forming machine electrostatically attached to a developing roller,
With the center of rotation of the magnetic roller in each developing device of the image forming means as the origin, the stirring and conveying means is disposed in the first quadrant, and the photosensitive drum, the charger, the exposure device, the developing roller, the transfer device, and the cleaning device are in the third quadrant. Located in the quadrant, below the housing, a spatial area is formed in the fourth quadrant or spans from the fourth quadrant to the third quadrant, which is horizontally adjacent to the spatial area. A photosensitive drum, a charger, an exposure device, a transfer device, and a cleaning device in the image forming unit are arranged.
A tandem type color image forming machine is provided.
In each of the developing devices of the image forming means, the magnetic roller includes a magnetic sleeve, and a stationary permanent magnet disposed in the magnetic sleeve and having a plurality of magnetic poles arranged in a circumferential direction, and the stirring and conveying means includes a magnetic roller. A magnetic agitator carrying member extending in the vicinity along the magnetic roller, wherein the magnetic poles of the stationary permanent magnet comprise a pair of magnetic poles which are circumferentially spaced from each other and are the same in polarity; On the outer side in the radial direction, a region where the value of the perpendicular magnetic force is the lowest formed between the pair of magnetic poles by the repulsive magnetic force generated between the pair of magnetic poles is positioned within an angle range of 35 ° to 60 ° in the quadrant I. Preferably.
It is preferable that the saturation magnetization value of the magnetic carrier is specified to be 35 to 50 emu / g.
It is preferable that the volume resistivity of the magnetic carrier is specified to be 10 ⁸ to 10 ¹² Ω · cm.
It is preferable that the volume average particle size of the magnetic carrier is specified to be 35 to 50 μm.
It is preferable that, of the pair of magnetic poles, a magnetic pole disposed on the upstream side in the rotation direction of the magnetic sleeve has a perpendicular magnetic force of 62 to 76 mT.
It is preferable that, of the pair of magnetic poles, the magnetic pole disposed on the downstream side in the rotation direction of the magnetic sleeve has a perpendicular magnetic force of 34 to 60 mT.

Hereinafter, preferred embodiments of a developing device constituted according to the present invention and a tandem-type color image forming machine provided with the developing device will be described in more detail with reference to the accompanying drawings.

FIG. 1 is a schematic cross-sectional view of a tandem-type color image forming apparatus provided with a developing device configured according to the present invention. The illustrated tandem-type color image forming machine includes an image forming machine main body 2 having a substantially rectangular parallelepiped shape. In the image forming machine main body 2, a black image forming means 3, a cyan image forming means 4, a magenta image forming means 5, and a yellow image forming means 6 are horizontally arranged from left to right in FIG. They are arranged in this order. These image forming means 3, 4, 5 and 6 are respectively a photosensitive drum 10, a charger 12, an exposure device (strictly, a semiconductor laser or LED head which is a part of the exposure device) 14, and will be described later in detail. An image forming element such as a developing device 100, a transfer device 16, and a cleaning device 18 is provided. In FIG. 1, for simplicity of illustration, the reference numerals of the image forming elements are given only in the black image forming means 3. Each of the developing devices 100 of the image forming units 3, 4, 5, and 6 is provided with a toner container 100A for supplying a toner of a corresponding color.

A transport belt mechanism 20 is disposed below the image forming means 3, 4, 5, and 6. The transport belt mechanism 20 includes a drive roller 20A, a driven roller 20B, and an endless transport belt 20C wound between the drive roller 20A and the driven roller 20B. The upper moving surface 20a of the conveyor belt 20C extends substantially horizontally in the horizontal direction through the space between the photosensitive drum 10 and the transfer device 16 in the image forming means 3, 4, 5, and 6, and conveys the recording paper. Forming a surface. The transport belt 20C is rotated counterclockwise in FIG. 1 by the driving roller 20A and the driven roller 20B (see the arrow in FIG. 2). A paper feed cassette 22 is provided below the transport belt mechanism 20. A fixing device 24, a discharge roller 26, a paper discharge tray 28, and the like are disposed downstream of the transport belt mechanism 20. The recording paper sent from the paper feed cassette 22 is transported by the transport belt mechanism 20 between the photosensitive drum 10 and the transfer device 16. Toner of a color corresponding to the color image is sequentially polymerized and transferred onto the recording paper, and is fixed by a fixing device 24, and then discharged to a discharge tray 28 by a discharge roller 26.

Next, the image forming means 3, 4, 5, and 6 including the developing device 100 provided in the tandem type color image forming machine will be described in detail. Since the configurations of the image forming units 3, 4, 5, and 6 are substantially the same as each other, the black image forming unit 3 will be described below as a representative thereof.

2 and 3, as described above, the image forming means 3 includes the photosensitive drum 10, the charger 12, the exposure device 14, the developing device 100, the transfer device 16, the cleaning device 18, and the like. An imaging element is provided. In the tandem type image forming machine, it is important to design compactly the image forming elements such as the charger 12, the exposure device 14, the developing device 100, the transfer device 16, and the cleaning device 18 which are arranged around the photosensitive drum 10. Therefore, in the present invention, the developing device 100 is configured in a substantially vertical layout.

As the photosensitive material of the photosensitive drum 10, a positively charged organic photosensitive body (positive OPC), an a-si photosensitive body, or the like can be used. When the positive OPC is used, the generation of ozone and the like is small and the charging is stable. Particularly, the positive OPC having a single-layer structure has a small change in the photosensitive characteristics even when the film thickness is changed over a long period of use. Since the image quality is stable, it is suitable for a long-life system. When the positive OPC is used in a system having a long life, it is preferable to set the film thickness to about 20 μm to 40 μm. When the film thickness is less than 20 μm, when the film thickness decreases to about 10 μm, black spots are noticeably generated due to dielectric breakdown. When the film thickness is set to exceed 40 μm, the sensitivity is reduced, which causes a reduction in image density.

The exposure device 14 can use a semiconductor laser or an LED head. When positive OPC is used as a photosensitive material, a wavelength around 770 nm is effective, and in the case of an a-si photosensitive member, a wavelength around 685 nm is effective. In the embodiment of the present invention, positive OPC is used as the photosensitive material, and an LED head is used as the exposure device 14.

The developing device 100 includes a housing 110 that can be formed from an appropriate synthetic resin. An end surface of the housing 110 facing the photoconductor drum 10 is opened, and a two-component developer including a magnetic carrier and a non-magnetic toner is accommodated in the housing 110. In the housing 110, a stirring and conveying means 120 for stirring and conveying the accommodated two-component developer, a magnetic roller 130 for conveying the developer by magnetically attracting and holding it on the peripheral surface, a magnetic roller 130 and a photosensitive drum A developing roller 140 which is disposed at a predetermined gap from each of the peripheral surfaces of the developing roller 10 and to which only the toner is attached is rotatably disposed.

The magnetic roller 130 has a cylindrical magnetic sleeve 132 made of a non-magnetic material such as aluminum, and a plurality of magnetic poles N1, S1, N2, N3, and S2 arranged in the circumferential direction in this order. And a stationary permanent magnet 134. The stationary permanent magnet 134 will be further described later. The two-component developer is magnetically attracted and held on the peripheral surface of the magnetic sleeve 132 to form a magnetic brush, and the two-component developer is conveyed by the rotation of the magnetic sleeve 132. A predetermined DC bias voltage is applied to the magnetic roller 130 by a first DC power supply 136. The developing roller 140 is formed of a cylindrical member (sleeve) made of conductive aluminum or the like. The material of the sleeve may be a uniform conductor, such as SUS or one whose peripheral surface is covered with a conductive resin. The gap between the peripheral surface of the developing roller 140 and the peripheral surface of the positive OPC is set to about 250 μm. A predetermined DC bias voltage is applied to the developing roller 140 by the second DC power supply 142, and an AC bias voltage is superimposed and applied by the AC power supply 144.

In the housing 110, a first developer stirring chamber 112 is provided at a position adjacent to the magnetic roller 130, and further a second developer stirring chamber 114 partitioned by the first developer stirring chamber 112 and a partition 113 is provided. Is provided. The first and second developer stirring chambers 112 and 114 are communicated with each other at both axial ends of the magnetic roller 130 to form an endless circulating conveyance path as a whole. This circulating transport path forms a developing chamber in the housing 110. The first developer stirring chamber 112 extends linearly along the magnetic roller 130 in parallel with the magnetic roller 130. The second developer stirring chamber 114 extends linearly in parallel with the first developer stirring chamber 112 with the partition wall 113 interposed therebetween.

The stirring and conveying means 120 includes a first rotating spiral blade member 122 as a first stirring and conveying member, and a second rotating spiral blade member 124 as a second stirring and conveying member. The first rotating spiral blade member 122 is rotatably disposed in the first developer stirring chamber 112 so as to extend linearly along the first developer stirring chamber 112, and has a second rotating spiral. The blade member 124 is rotatably disposed in the second developer stirring chamber 114 so as to extend linearly along the second developer stirring chamber 114. The first rotary spiral blade member 122 constitutes a stirring and conveying member extending along the magnetic roller 130 in the vicinity of the magnetic roller 130. In the housing 110, a layer thickness regulating blade 117 for regulating the layer thickness of the developer held on the peripheral surface of the magnetic roller 130 is provided.

In the developing device 100, the first and second rotation spirals are set with the rotation center O of the magnetic roller 130 (in other words, the rotation center O of the magnetic sleeve 132) as the origin (the intersection of the virtual plane coordinates x-axis and y-axis). The blade members 122 and 124 are arranged in the first quadrant. The developing roller 140 is disposed in the third quadrant. Such a configuration makes it possible to form a space area S below the housing 110 as described below, which greatly contributes to achieving a compact image forming machine. In the housing 110, regions defining the first and second developer stirring chambers 112 and 114 are configured to extend substantially horizontally and laterally from the first quadrant to the second quadrant. The region where the roller 140 is provided is configured to be inclined generally downward from the quadrant I to the quadrant III. Below the housing 110 (between the lower surface of the housing 110 and the upper moving surface 20a of the belt mechanism 20 in the embodiment), the space area S is formed in the IV quadrant, or Although formed from the quadrant to the third quadrant, in the embodiment, it is formed to extend from the fourth quadrant to the third quadrant as illustrated. In the image forming means 3 including the developing device 100, the photosensitive drum 10, the charger 12, the LED head 14, the transfer device 16, and the cleaning device 18 are arranged in the third quadrant.

As shown in FIGS. 1 and 4, in the space area S, the photosensitive drum 10, the charger 12, and the image forming means adjacent in the horizontal and horizontal directions, in the embodiment, the cyan image forming means 4. The LED head 14, the transfer device 16, and the cleaning device 18 are arranged. Similarly, in the space area S formed below the housing 110 of the developing device 100 in the image forming means 4 for cyan, the photosensitive drum 10 and the charger 12 in the image forming means 5 for magenta horizontally adjacent in the horizontal direction. , An LED head 14, a transfer device 16 and a cleaning device 18 are arranged. In the same manner, in the magenta image forming means 5, a space area S formed below the housing 110 of the developing device 100 includes a photosensitive drum 10 and a charger in the yellow image forming means 6 which are horizontally and horizontally adjacent to each other. 12, an LED head 14, a transfer device 16 and a cleaning device 18 are arranged. In this manner, the image forming means 3, 4, 5, and 6 each including the substantially vertical developing device 100 can be arranged in the horizontal and horizontal directions while making use of the useless space as effectively as possible. It is possible to reduce the vertical and horizontal dimensions of the color image forming apparatus, thereby making the overall configuration compact.

In each of the image forming units 3, 4, 5, and 6, the toner container 100A can be disposed above the developing device 100, that is, above the housing 110. The image forming apparatus can be freely dropped, and can be detached from above the image forming apparatus main body 2 at the time of replacement, and can be mounted again from above. Further, similarly to the toner container 100A, the developing device 100 can be detached upward and can be mounted again from above, so that detachment and mounting operations can be easily performed in the event of an abnormality or maintenance. The configuration of the developing device 100 is also simplified as a whole.

Referring to FIG. 3, the magnetic poles of stationary permanent magnet 134 include a pair of magnetic poles that are circumferentially spaced from each other and have the same polarity. In the above-described embodiment, the stationary permanent magnet 134 is configured such that a plurality of magnetic poles N1, S1, N2, N3, and S2 are arranged in the circumferential direction in this order, and a pair of magnetic poles (repulsive poles) having the same polarity are mutually formed. , And magnetic poles N2 and N3. That is, the stationary permanent magnet 134 receives and holds the magnetic pole N <b> 1 located closest to the developing roller 140 and the two-component developer agitated and transported by the first rotating spiral blade member 122, and holds the peripheral surface of the magnetic sleeve 132. Magnetic pole N3 located in the ear-cutting region where the ear-cutting is performed by the layer-thickness regulating blade 117 for controlling the height of the magnetic brush formed on the magnetic pole, and the transport magnetic pole S2 for transporting the magnetic brush cut to the nearest magnetic pole N1. , A transport magnetic pole S1 receiving the magnetic brush from the closest magnetic pole N1, and a transport magnetic pole N2 receiving the magnetic brush from the transport magnetic pole S1 and transporting the magnetic brush into the first developer stirring chamber 112.

In the present invention, on the outer side in the radial direction of the magnetic sleeve 132, a vertical magnetic field formed between the pair of magnetic poles N2 and N3 by a repulsive magnetic force generated between the pair of magnetic poles (repulsive poles) N2 and N3 having the same polarity. A region having the lowest magnetic force value (hereinafter, this region is referred to as a “lowest magnetic force region”) is formed, and the lowest magnetic force region is set within an angle range of θ = 35 ° to 60 ° in the quadrant I. Positioning is important. The reason will be described later. The angle θ in the I-th quadrant means an angle that rotates counterclockwise around the origin O, which is the intersection of the x axis and the y axis, with the angle of the x axis being zero degrees. It goes without saying that the perpendicular magnetic force in the lowest magnetic force region differs depending on the configuration of the developing device 100 (the diameter of the magnetic roller 130, the arrangement of the stationary permanent magnets 134, the magnetic force of the stationary permanent magnets 134, and the like). For example, it may be 1 mT (millitesla) or less, or 3 mT or less, but ideally, it is preferably 0 tesla or a value as close to 0 tesla as possible.

The image forming means 3 in the illustrated embodiment is configured as described above, and its operation will be described below with reference to FIGS.

The photoreceptor drum 10, the developing roller 140, the magnetic roller 130, the first rotary spiral blade member 122, and the second rotary spiral blade member 124 in the developing device 100 are rotated in the directions indicated by arrows in FIG. Driven. The positive OPC, which is an electrostatic latent image carrier, is charged to 400 V by the charger 12. Thereafter, when exposure is performed at a wavelength of 770 nm by the LED head, the potential after exposure (the potential of the photoconductor after maximum exposure) is set to 70V. By rotating and driving the first and second rotary spiral blade members 122 and 124, the developer is stirred to charge the toner to an appropriate level. The two-component developer in the first developer stirring chamber 112 is held on the peripheral surface of the magnetic sleeve 132. The developer held on the peripheral surface of the magnetic sleeve 132 is formed to have a predetermined thickness by passing through the layer thickness regulating blade 117.

The developer held on the peripheral surface of the magnetic sleeve 132 in this way comes into contact with the peripheral surface of the developing roll 140 with a certain thickness. A predetermined DC bias voltage V1 is applied to the magnetic sleeve 132 by the first DC power supply 136, and a predetermined DC bias voltage V2 is applied to the developing roller 140 by the second DC power supply 142. Then, only the toner is attracted to the peripheral surface of the developing roller 140 by the potential difference (V1-V2) between the magnetic sleeve 132 and the developing roller 140, and a thin layer is formed. By setting the DC bias voltage V1 of the magnetic sleeve 132 to 400 V and the DC bias voltage V2 of the developing roller 140 to 100 to 150 V, a toner layer of about 1.0 to 1.5 mg / cm ² is formed on the peripheral surface of the developing roller 140. A thickness is formed. At this time, the appropriate charge amount of the developer is about 10 to 20 μC / g. When the charge amount is less than 10 μC / g, toner scattering is conspicuous, and when the charge amount exceeds 20 μC / g, the toner formed in a thin layer hardly flies to the peripheral surface of the photosensitive drum 10.

The toner attached to the peripheral surface of the developing roller 140 flies to the electrostatic latent image formed on the peripheral surface of the photosensitive drum 10 by applying a bias voltage in which DC and AC are superimposed on the developing roller 140. And can be developed. In order to prevent the toner from scattering, the application of the AC bias voltage to the developing roller 140 is performed immediately before the development. Specifically, a predetermined AC bias voltage is applied to the developing roller 140 by the AC power supply 144 immediately before the development with respect to the developing roller 140 to which the predetermined DC bias voltage V2 is applied by the second DC power supply 142. Superimposed and applied. By setting the AC bias voltage (peak-to-peak voltage) Vp-p = 1.5 KV and the frequency f = 3.0 KHz, it is possible to balance image density, dot reproduction, and fog removal. Further, by setting the duty ratio (DUTY ratio) to 30%, the development ghost can be removed.

When the potential across the surface of the toner layer of the developing roller 140 is measured, it is about 320 V, and it can be said that 320 V-70 V (the potential of the photoconductor after the maximum exposure) = 250 V is a substantial development execution unit.

The gap between the peripheral surface of the magnetic sleeve 132 and the peripheral surface of the developing roller 140 is set to 400 μm. The gap between the layer thickness regulating blade 117 and the peripheral surface of the magnetic sleeve 132 is adjusted according to the particle diameter of the magnetic carrier. The magnetic carrier having a volume average particle diameter of 35 μm and the two-component developer containing 10% of non-magnetic toner are used. Is set to 400 to 500 μm so that the magnetic brush contacts the peripheral surface of the developing roller 140. If the gap between the peripheral surface of the magnetic sleeve 132 and the peripheral surface of the developing roller 140 is too small, the two-component developer cannot pass between the magnetic sleeve 132 and the developing roller 140 and overflows. On the other hand, if the gap is too wide, the two-component developer cannot contact the peripheral surface of the developing roller 140, and it becomes difficult to collect the toner on the developing roller 140. Therefore, when the developing operation is repeated in this state, the toner gradually adheres to the peripheral surface of the developing roller 140, and the toner cannot fly to the photosensitive drum 10. These problems are solved by setting the gap to 400 to 500 μm.

The layer thickness regulating blade 117 made of an appropriate magnetic material is disposed so as to substantially face radially outward with respect to the ear-cut magnetic pole N3 disposed on the stationary permanent magnet 134 of the magnetic roller 130. A magnetic field is formed between the magnetic roller 130 and the thickness regulating blade 117. With such a configuration, the transportability of the magnetic brush formed on the peripheral surface of the magnetic sleeve 132 is reduced, and the transportability is further improved by subjecting the surface of the magnetic sleeve 132 to knurling or blasting. The gap margin between the blade 132 and the thickness regulating blade 117 can be reduced.

The two-component developer in the first developer stirring chamber 112 is adsorbed on the peripheral surface of the rotating magnetic sleeve 132 and is pumped up to form a magnetic brush. The magnetic brush having passed through the gap between the magnetic sleeve 132 and the layer thickness regulating blade 117 supplies only the non-magnetic toner to the developing roller 140 while passing through the gap with the developing roller 140. The magnetic brush in which only the non-magnetic toner is supplied to the developing roller 140 is conveyed to the first developer stirring chamber 112 while being attracted to the peripheral surface of the magnetic sleeve 132, and is peeled off from the peripheral surface of the magnetic sleeve 132. Then, the developer is returned into the first developer stirring chamber 112. The two-component developer returned into the first developer stirring chamber 112 is supplied to the first and second rotary spiral blades along the first developer stirring chamber 112 and the second developer stirring chamber 114, respectively. The components 122 and 124 are agitated and transported together with the other two-component developer. When the amount of toner in the developing chamber becomes insufficient, toner is supplied from the toner container 100A in a known manner. In order to record a color image on many recording sheets, it is necessary to repeat such a process.

By the way, in order to peel off the magnetic brush from the peripheral surface of the magnetic sleeve 132, it is easiest to pull the magnetic brush directly downward (in the direction of gravity). Has a large effect on the body and is not desirable. As described above, in the developing device 100 according to the present invention, the first and second rotary spiral blade members 122 and 124 are disposed in the first quadrant to promote downsizing of the image forming machine. 140 is located in the third quadrant. For this reason, in the magnetic sleeve 132, the magnetic brush that supplies only the toner to the developing roller 140 moves the magnetic brush from the bottom to above the horizontal position on the peripheral surface of the magnetic sleeve 132, specifically, in the third quadrant. And it must be lifted from the IV quadrant to the I quadrant and peeled off.

In order to peel off the magnetic brush from the peripheral surface of the magnetic sleeve 132, permanent magnets having the same polarity are fixed and arranged inside the magnetic sleeve 132 to form the above-described minimum magnetic force region. However, when the magnetic brush is pulled up to the horizontal position, even if there is a minimum magnetic force region due to the repulsive magnetic force, if the minimum magnetic force region is close to the horizontal position, the magnetic brush is moved to the developing chamber (first developer stirring chamber 112). Therefore, the magnetic carrier and / or non-magnetic toner as a part thereof leaks from the developing chamber downward (fourth quadrant). On the other hand, when the lowest magnetic force region is set at a position close to the second quadrant, the magnetic brush passes through the gap between the peripheral surface of the magnetic sleeve 132 and the thickness regulating blade 117 without peeling. As a result, the same magnetic brush continues to be present on the peripheral surface of the magnetic sleeve 132, which is an undesirable state of so-called poor separation. When such separation failure occurs, the image density is extremely reduced only by developing a few sheets of recording paper.

In the present invention, the stationary permanent magnet 134 incorporated in the magnetic roller 130 is provided with a pair of magnetic poles N2 and N3 having the same polarity, and the repulsive magnetic force generated between the magnetic poles N2 and N3 causes the pair of magnetic poles N2 and N3 to move between the magnetic poles N2 and N3. The region where the value of the perpendicular magnetic force is the lowest, that is, the lowest magnetic force region is positioned within the angle range of 35 ° to 60 ° in the quadrant I, so that the poor separation of the developer and the developing This makes it possible to simultaneously eliminate two undesirable phenomena, that is, leakage from the chamber downward (quadrant IV). That is, in the developing process, the magnetic brush in which only the non-magnetic toner is supplied to the developing roller 140 is conveyed to the first developer stirring chamber 112 which is a developing chamber while being attracted to the peripheral surface of the magnetic sleeve 132, In the region where the magnetic field becomes 0 Tesla, the magnetic sleeve 132 is peeled off from the peripheral surface and returned to the first developer stirring chamber 112. Since the minimum magnetic force region is positioned within the angle range of 35 ° to 60 ° in the first quadrant, the magnetic brush can reliably return to the developing chamber (first developer stirring chamber 112), and a part thereof. Is prevented from leaking from the developing chamber downward (quadrant IV). Further, the magnetic brush is peeled off while passing through the angle range of 35 ° to 60 ° in the quadrant I in a state of being attracted to the peripheral surface of the magnetic sleeve 132, so that the peripheral surface of the magnetic sleeve 132 and the layer thickness regulation are controlled. The problem of so-called separation failure, in which the same magnetic brush continues to be present on the peripheral surface of the magnetic sleeve 132 through the gap between the blade 117 and the same, is also solved.

In short, according to the present invention, in the developing process, the magnetic brush in which only the non-magnetic toner has been supplied to the developing roller 140 is in a state where the magnetic brush is attracted to the peripheral surface of the magnetic sleeve 132 and the first developer agitator which is the developing chamber. After being reliably transported to the chamber 112, the developer is peeled off in the developing chamber, so that two problems, that is, leakage of the developer downward and poor separation, are eliminated at the same time. In the illustrated embodiment, the pair of magnetic poles N2 and N3 having the same polarity are arranged in the quadrant I. However, the present invention is not limited to this. In short, it is important to position the minimum magnetic force region formed between the magnetic poles N2 and N3 (between the repulsive magnetic forces) within an angle range of 35 ° to 60 ° in the quadrant I, and a pair having the same polarity mutually is important. The circumferential positions of the magnetic poles N2 and N3 may be set to appropriate positions according to the individual developing devices. A developer having a toner concentration of 10% was prepared using a magnetic carrier having a saturation magnetization of 42 emu / g, a volume average particle diameter of 50 μm, and a volume resistivity of 1.2 × 10 ¹⁰ Ω · cm. investigated. As a result, when the lowest magnetic force region was positioned at 26 °, the developer leaked from the gap between the developing device 100 and the developing roller 140. When the minimum magnetic force region was positioned at 38 ° or 56 °, printing could be continued without any problem. When the minimum magnetic force region is positioned at 64 °, when a high-density image, for example, half of a sheet is printed as a solid image, the image density of the second sheet is extremely reduced, and the image density is not uniform. there were.

The present inventor further suggests that the use of a magnetic carrier having a low saturation magnetization facilitates the separation of the magnetic brush from the peripheral surface of the magnetic sleeve 132, thereby reducing the magnetic carrier binding force, and thus reducing the vertical developing device. It has been found that it is suitable as a magnetic carrier for a two-component developer. Regarding the carrier adhesion, which is the biggest problem of the low magnetic force carrier, once, only the toner is supplied from the magnetic roller 130 to the developing roller 140 to form a thin layer of toner on the peripheral surface of the developing roller 140, Can be solved by using a so-called non-contact development method in which the image flies onto the electrostatic latent image on the photosensitive drum 10. That is, according to such a non-contact developing method, even if a small amount of magnetic carrier is moved from the magnetic roller 130 to the peripheral surface of the developing roller 140 and adheres, the magnetic carrier cannot fly to the photosensitive drum 10. Therefore, the magnetic carrier adhering to the peripheral surface of the developing roller 140 is attracted to the magnetic roller 130 and returned to the developing chamber, and there is no problem that the amount of the magnetic carrier, that is, the amount of the two-component developer is reduced. is there. As a result, we succeeded in making a vertical developing device practical and promoting downsizing of the image forming machine.

In a vertical developing device, the weight of the two-component developer plays an important role in peeling off the magnetic brush from the peripheral surface of the magnetic sleeve 132 due to gravity acting downward. When the amount of the developer in the developing chamber is small, the amount of the magnetic brush formed on the peripheral surface of the magnetic sleeve 132 is small, so that the peeling is not performed well and the separation is poor. On the other hand, if too much developer is put into the developing chamber, the mixing of the non-magnetic toner and the magnetic carrier supplied from the toner container 100A will not be effectively performed. Further, when the developer is excessively charged in the developing chamber, in the developing device in which the developer is circulated in the developing chamber by the stirring and conveying means as in the above-described embodiment, the developer is left and right (first developer). (The longitudinal direction of the stirring chamber 112).

Therefore, it is desired that the separation failure and the bias of the developer do not occur even if the amount of the developer accommodated in the developing chamber is reduced. By setting the content to 50 emu / g, the above requirement was successfully satisfied. In the case of a magnetic carrier having a saturation magnetization value of less than 35 emu / g, the amount of impurities increases and the firing conditions need to be reduced, so that a sufficient ferrite reaction cannot be obtained, and as a result, the carrier surface tends to be uneven. In addition, there is a problem that it becomes unstable in mass productivity due to the surface coating treatment and the volume resistivity varies, so that it is practically difficult to use.

FIG. 5 shows that the saturation magnetization value, the volume average particle diameter, and the volume resistivity of the magnetic carrier are changed to cause poor separation of the developer, the margin of the developer, the image density, and the current leakage between the developing roller and the magnetic roller. 3 is a table showing the results of an experiment in which the state of No. was examined and the practical optimality was examined.
In the table, Comparative Examples 1 to 6 have a saturation magnetization value of 32 to 56 emu / g, a volume average particle diameter of 31 to 58 μm, and a volume resistivity of 2.1 × 10 ^{7 to} 8.1 × 10 of the magnetic carrier. It is an experimental result which changed each within the range of ¹² Ω · cm.
In Examples 1 to 4, the saturation magnetization value of the magnetic carrier was 38 to 47 emu / g, the volume average particle diameter was 39 to 46 μm, and the volume resistivity was 2.4 × 10 ^{8 to} 4.7 × 10 ^11. It is an experimental result which changed each within the range of Ω · cm.
For the saturation magnetization, VSM-P7 manufactured by Toei Kogyo was used as a measuring device, and the applied magnetic field during the measurement was set to 3.95 × 10 ⁵ A / m.
For the volume resistivity, a sample to be measured is filled in a cell having electrodes of 25.4 mm × 5.0 mm arranged vertically, a load of 1 kgf is applied, and a value after one minute is defined as a resistance value. The volume resistivity was determined from the thickness of the sample. As a measuring instrument, an ultra-high resistance / micro ammeter (model number: R8340A) manufactured by Advantest Corporation was used, and the applied voltage was set to 500V.
For the measurement of the volume average particle size, a particle size distribution measuring device (model number: LA500) using a laser diffraction method manufactured by Horiba, Ltd. was used. 300 ml of pure ethanol was used as a dispersion solvent for the carrier particles, and 500 mg of the carrier to be measured and the ethanol were charged into the apparatus. Ethanol and the carrier are automatically mixed inside the device and an automatic measurement is performed.
The image density of each of the examples and the comparative examples was measured using a reflection type image density measurement device (model number: RD918) manufactured by Macbeth.
The experimental conditions of Comparative Examples 1 to 6 and Examples 1 to 4 are as follows.
Angle θ shown in FIG. 3: 45 °
Magnetic force N1: 85mT in the vertical direction of the magnetic pole
S1: 90mT
N2: 67mT
N3: 47mT
S2: 75mT
Diameter of magnetic roller: 16.0 mm
Developing roller diameter: 16.8 mm
Blade gap: 0.525mm
Magnetic roller-developing roller gap: 0.400 mm
Developing roller-photosensitive drum gap: 0.235 mm
Magnetic roller linear velocity: 225.0 mm / sec
Developing roller linear speed: 150.0 mm / sec
Photoreceptor drum linear velocity: 100.0 mm / sec
Toner density: 10%
In the above experimental conditions, the angular position of the N2 pole in FIG. 3 (the angular position when the x-axis is 0 °) is −5 °, and the angular position of the N3 pole in FIG. 3 is 85 °.

Comparative Example 1 shows the results of an experiment using a two-component developer obtained by mixing 10% of a non-magnetic toner with a magnetic carrier having a volume average particle diameter of 41 μm and mixing with a ball mill. The saturation magnetization value of the magnetic carrier was 32 emu / g, and the volume resistivity was 5.1 × 10 ¹⁰ Ω · cm. The gap between the peripheral surface of the magnetic sleeve 132 and the thickness-regulating blade 117 was adjusted to 550 to 650 μm, and the magnetic brush was set to be in contact with the developing roller 140. As a result of the experiment, the toner layer was not sufficiently formed on the developing roller 140, the image density unevenness was severe, and the image density could not be measured. This is presumed to be due to the fact that the saturation magnetization value is as low as 32 emu / g, and the binding force on the magnetic roller 130 is excessively reduced.

In Comparative Example 2, the saturation magnetization value of 32 emu / g of the magnetic carrier in Comparative Example 1 was greatly increased to 56 emu / g. As a result, although the image density was restored to the extent that the measurement was possible, the image density was not sufficient to obtain a sufficient image density in comparison with the experimental result of Comparative Example 1. This is because the saturation magnetization value is considerably high at 56 emu / g, so that poor separation easily occurs. Therefore, it is necessary to set a large amount of the developer, and the stirring and conveying ability of the stirring and conveying means 120 cannot be balanced. It is presumed to be caused by this.

In Comparative Example 3, the volume average particle size of the magnetic carrier of 41 μm in Comparative Example 1 was significantly reduced to 31 μm. As a result, the fluidity of the developer in the developing chamber deteriorated, and the developer could not be sufficiently stirred, and the toner layer on the developing roller 140 was thinned to lower the image density.

In Comparative Example 4, the volume average particle diameter of the magnetic carrier in Comparative Example 1 was 41 μm, which was significantly increased to 58 μm, contrary to that in Comparative Example 3. As a result, although the separation failure was improved, a sufficient image density was not obtained.

In Comparative Example 5, the volume resistivity of the magnetic carrier of Comparative Example 1 was reduced from 5.1 × 10 ¹⁰ Ω · cm to 2.1 × 10 ⁷ Ω · cm. As a result, a current leaked between the developing roller 140 and the magnetic roller 130 and the machine stopped operating, so that the image could not be formed. It is presumed that the reason why the machine stopped operating was that the CPU mounted on the machine stopped operating due to the electrical noise caused by the leak. In general, when a current leaks between the developing roller 140 and the magnetic roller 130, the developing bias is not applied for a certain period of time, and a white band image is frequently output. This is because during development, an AC bias voltage is applied to the developing roller 140 by the AC power supply device 144 in order to cause a thin layer of toner formed on the peripheral surface of the developing roller 140 to fly to the photosensitive drum 10. Since an AC bias voltage is also applied to the magnetic roller 130 via the brush, if the volume resistivity of the magnetic carrier is too low, a current leaks between the developing roller 140 and the magnetic roller 130, and as described above. This is a phenomenon in which a large developing bias is not applied.

In Comparative Example 6, the saturation magnetization value in Comparative Example 1 was increased from 32 emu / g to 40 emu / g, the volume average particle diameter was reduced from 41 μm to 38 μm, and the volume resistivity was increased from 5.1 × 10 ¹⁰ Ω · cm to 8 μm. It is a relatively large increase up to 0.1 × 10 ¹² Ω · cm. As a result, although the separation failure and the margin were improved, a sufficient image density could not be obtained.

Example 1 shows the results of an experiment conducted using a two-component developer obtained by mixing 10% of a non-magnetic toner with a magnetic carrier having a volume average particle diameter of 42 μm and mixing with a ball mill. The saturation magnetization value was 38 emu / g, and the volume resistivity was 1.2 × 10 ¹⁰ Ω · cm. The experimental results show that there is no problem with poor separation, margin, image density and leak.

In Example 2, the saturation magnetization value of 38 emu / g in Comparative Example 1 was changed to 42 emu / g, the volume average particle diameter was changed to 42 μm to 46 μm, and the volume resistivity was changed to 1.2 × 10 ¹⁰ Ω · cm to 7.8 × 10 5. Each was raised to ¹⁰ Ω · cm.
In Example 3, the saturation magnetization value of Comparative Example 1 was increased from 38 emu / g to 47 emu / g, the volume average particle diameter was increased from 42 μm to 45 μm, and the volume resistivity was 1.2 × 10 ¹⁰ Ω · cm. It is reduced to 4 × 10 ⁸ Ω · cm.
In Example 4, the saturation magnetization value of 38 emu / g in Comparative Example 1 was increased to 43 emu / g, the volume average particle diameter was 42 μm to 39 μm, and the volume resistivity was 1.2 × 10 ¹⁰ Ω · cm to 4.7. × 10 ¹¹ Ω · cm.
The experimental results show that there are no problems with the separation failure, the margin, the image density, and the leak, as in the first embodiment.

As is clear from the table shown in FIG. 5 and the above description, the experimental results of Comparative Examples 1 to 6 have problems in developer separation failure, developer margin, and image density. In some cases, current leakage was observed between the magnetic roller and the magnetic roller, and a predetermined uniform image density was not obtained, indicating that practicality was not recognized. On the other hand, the experimental results of Examples 1 to 4 show that there is no problem in the poor separation of the developer, the margin of the developer and the image density, and no leakage of the current between the developing roller and the magnetic roller is recognized. This shows that uniform image density is secured and high practicability is recognized.

In the present invention, the perpendicular magnetic force of the magnetic pole N2 disposed on the upstream side in the rotation direction of the magnetic sleeve 132 among the pair of magnetic poles N2 and N3 having the same polarity is defined as 62 to 76 mT. This makes it possible to simultaneously eliminate two undesirable phenomena, that is, poor separation of the developer and leakage of the developer (carrier) from the developing chamber to the lower side (quadrant IV in FIG. 3). FIG. 6 is a table showing experimental results in which the perpendicular magnetic force of the magnetic pole N2 was changed to check for poor separation and leakage of the developer, and to examine the practical optimality.
The experimental conditions of Comparative Examples 7 and 8 and Examples 5 to 8 are as follows.
Saturation magnetization value of magnetic carrier: 42 emu / g
Volume average particle size: 46 μm
Volume resistivity: 7.8 × 10 ¹⁰
Angle θ shown in FIG. 3: 45 °
Magnetic force N1: 85mT in the vertical direction of the magnetic pole
S1: 90mT
S2: 75mT
Diameter of magnetic roller: 16.0 mm
Developing roller diameter: 16.8 mm
Blade gap: 0.525mm
Magnetic roller-developing roller gap: 0.400 mm
Developing roller-photosensitive drum gap: 0.235 mm
Magnetic roller linear velocity: 225.0 mm / sec
Developing roller linear speed: 150.0 mm / sec
Photoreceptor drum linear velocity: 100.0 mm / sec
Toner density: 10%
In the above experimental conditions, the angular position of the N2 pole in FIG. 3 (the angular position with the x-axis being 0 °) is −5 °, and the angular position of the N3 pole in FIG. 3 is 85 °.

As is clear from the table shown in FIG. 6, the experimental results of Comparative Examples 7 and 8 show that when the perpendicular magnetic force of the N2 pole is too low, the developer leaks and the perpendicular magnetic force of the N2 pole is too high. This indicates that poor separation of the developer occurs. Examples 5 to 7 show that by setting the perpendicular magnetic force of the magnetic pole N2 in the range of approximately 62 to 76 mT, no inconvenience occurs.

In the present invention, furthermore, of the pair of magnetic poles N2 and N3 having the same polarity mutually, the perpendicular magnetic force of the magnetic pole N3 arranged on the downstream side in the rotation direction of the magnetic sleeve 132 is defined as 34 to 60 mT, so that the development is performed. This makes it possible to simultaneously eliminate two undesirable phenomena, ie, poor regulation of the layer thickness of the agent and poor separation. FIG. 7 is a table showing experimental results in which the perpendicular magnetic force of the magnetic pole N3 is changed to investigate the defective regulation of the layer thickness of the developer and the defective separation, and to examine the practical optimality.
The experimental conditions of Comparative Examples 9 and 10 and Examples 8 to 10 are the same as the experimental conditions for obtaining the evaluation results shown in FIG.

As is clear from the table shown in FIG. 7, the experimental results of Comparative Examples 9 and 10 show that when the perpendicular magnetic force of the N3 pole is too low, the layer thickness regulation failure occurs and the perpendicular magnetic force of the N3 pole is too high. This indicates that poor separation of the developer occurs. Examples 8 to 10 show that no inconvenience occurs by defining the perpendicular magnetic force of the magnetic pole N3 in a range of approximately 34 to 60 mT.

1 is a schematic configuration diagram illustrating a preferred embodiment of a tandem-type color image forming machine configured according to the present invention. FIG. 2 is a schematic configuration diagram showing an enlarged image forming unit for black provided in the tandem-type color image forming machine shown in FIG. 1. FIG. 3 is an enlarged schematic diagram illustrating a developing device provided in the black image forming unit illustrated in FIG. 2. FIG. 2 is an enlarged schematic diagram illustrating a black image forming unit and a cyan image forming unit provided in the tandem-type color image forming apparatus illustrated in FIG. 1. By changing the saturation magnetization value, volume average particle diameter and volume resistivity of the magnetic carrier, investigate the poor separation of the developer, the margin of the developer, the image density, and the state of the current leak between the developing roller and the magnetic roller. 4 is a table showing experimental results of examining practical optimality. 9 is a table showing experimental results obtained by examining developer separation failure and leakage by changing the perpendicular magnetic force of the magnetic pole N2, and examining practical practicality. 9 is a table showing experimental results obtained by examining the layer thickness regulation failure and separation failure of the developer by changing the perpendicular magnetic force of the magnetic pole N3, and examining the practicality of optimality.

Explanation of reference numerals

2 Image forming machine main body 3 Black image forming means 4 Cyan image forming means 5 Magenta image forming means 6 Yellow image forming means 10 Photoconductor drum 12 Charger 14 LED head 16 Transfer device 18 Cleaning device 100 Developing device 110 Housing 112 first developer stirring chamber 113 partition 114 second developer stirring chamber 117 layer thickness regulating blade 120 stirring and conveying means 122 first rotating spiral blade member 124 second rotating spiral blade member 130 magnetic roller 132 magnetic sleeve 134 Stationary permanent magnet 140 Developing rollers N1, S1, N2, N3, S2 Magnetic pole S Space area below housing

Claims (13)

A housing accommodating a two-component developer composed of a magnetic carrier and a non-magnetic toner, a stirring and conveying means for stirring and conveying the developer contained in the housing, and a magnetic roller for holding and conveying the developer on the peripheral surface; A magnetic roller, a developing roller disposed with a predetermined gap therebetween, the magnetic roller includes a magnetic sleeve, and a stationary permanent magnet disposed in the magnetic sleeve and having a plurality of magnetic poles arranged in a circumferential direction. Wherein the stirring and conveying means includes a stirring and conveying member extending along the magnetic roller near the magnetic roller, and the toner in the developer held by the magnetic roller is electrostatically attached to the developing roller. At
With the rotation center of the magnetic roller as the origin, the stirring and conveying member is arranged in quadrant I, the developing roller is arranged in quadrant III,
The magnetic poles of the stationary permanent magnet include a pair of magnetic poles that are circumferentially spaced apart from each other and are the same in polarity, and are formed by a repulsive magnetic force generated between the pair of magnetic poles on a radially outer side of the magnetic sleeve. An area formed between the pair of magnetic poles and having the lowest value of the perpendicular magnetic force is positioned within an angle range of 35 ° to 60 ° in the quadrant I,
A developing device, comprising: The developing device according to claim 1, wherein the saturation magnetization value of the magnetic carrier is specified to be 35 to 50 emu / g. The developing device according to claim 1, wherein the volume resistivity of the magnetic carrier is specified to be 10 ⁸ to 10 ¹² Ω · cm. The developing device according to claim 1, wherein a volume average particle size of the magnetic carrier is specified to be 35 to 50 μm. 5. The developing device according to claim 1, wherein a magnetic force in a vertical direction of a magnetic pole disposed on the upstream side in the rotation direction of the magnetic sleeve of the pair of magnetic poles is specified to be 62 to 76 mT. 6. The developing device according to claim 1, wherein a magnetic force in a vertical direction of a magnetic pole of the pair of magnetic poles disposed downstream of the magnetic sleeve in the rotation direction is defined as 34 to 60 mT. 7. A tandem-type color image forming machine in which a plurality of image forming means including a photosensitive drum, a charger arranged around the photosensitive drum, an exposure device, a developing device, a transfer device, and a cleaning device are arranged in a substantially horizontal direction. Wherein the developing device in each of the image forming means includes a housing for containing a two-component developer composed of a magnetic carrier and a non-magnetic toner, and a stirring and conveying means for stirring and conveying the developer contained in the housing. A magnetic roller that transports the developer while holding the developer on the peripheral surface; and a developing roller that is disposed at a predetermined gap between the magnetic roller and the photosensitive drum. The toner in the developer held by the magnetic roller is provided. Is a tandem type color image forming machine electrostatically attached to a developing roller,
With the center of rotation of the magnetic roller in each developing device of the image forming means as the origin, the stirring and conveying means is disposed in the first quadrant, and the photosensitive drum, the charger, the exposure device, the developing roller, the transfer device, and the cleaning device are in the third quadrant. Located in the quadrant, below the housing, a spatial area is formed in the fourth quadrant or spans from the fourth quadrant to the third quadrant, which is horizontally adjacent to the spatial area. A photosensitive drum, a charger, an exposure device, a transfer device, and a cleaning device in the image forming unit are arranged.
A tandem-type color image forming machine, characterized in that: In each of the developing devices of the image forming means, the magnetic roller includes a magnetic sleeve, and a stationary permanent magnet disposed in the magnetic sleeve and having a plurality of magnetic poles arranged in a circumferential direction, and the stirring and conveying means includes a magnetic roller. A magnetic agitator carrying member extending in the vicinity along the magnetic roller, wherein the magnetic poles of the stationary permanent magnet comprise a pair of magnetic poles which are circumferentially spaced from each other and are the same in polarity; On the outer side in the radial direction, a region where the value of the perpendicular magnetic force is the lowest formed between the pair of magnetic poles by the repulsive magnetic force generated between the pair of magnetic poles is positioned within an angle range of 35 ° to 60 ° in the quadrant I. The tandem-type color image forming machine according to claim 7, wherein 9. The tandem-type color image forming apparatus according to claim 8, wherein the saturation magnetization value of the magnetic carrier is specified to be 35 to 50 emu / g. The tandem-type color image forming apparatus according to claim 8 or 9, wherein the volume resistivity of the magnetic carrier is specified to be 10 ⁸ to 10 ¹² Ω · cm. The tandem-type color image forming apparatus according to any one of claims 8 to 10, wherein the volume average particle diameter of the magnetic carrier is specified to be 35 to 50 µm. The tandem-type color image according to any one of claims 8 to 11, wherein, of the pair of magnetic poles, a magnetic pole in a vertical direction of a magnetic pole arranged on the upstream side in the rotation direction of the magnetic sleeve is specified to be 62 to 76 mT. Forming machine. The tandem-type color image according to any one of claims 8 to 12, wherein, of the pair of magnetic poles, a magnetic pole in a vertical direction of a magnetic pole arranged on the downstream side in the rotation direction of the magnetic sleeve is regulated to 34 to 60 mT. Forming machine.

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