JP2007279330A - Developing device, image forming device, carrier used in these, toner - Google Patents

Abstract

[PROBLEMS] To form a magnetic brush with a short head and a high density, which can reduce the pumping amount as compared with a conventional magnetic pole, and the speed of a circulating portion of a one-way circulating developing device without increasing the diameter of a screw. And the life of the developing device can be extended.
A developer carrying member, a supply screw, a collecting screw, and a stirring screw are provided, and a developer obtained by stirring excess developer and collected developer is circulated and opposed to the developer carrying member. And a developer regulating member for regulating the height of the developer layer supplied from the supply path to the developer carrying member, wherein the magnetic brush is rubbed against the latent image carrying member. The attenuation factor of the normal direction magnetic flux density of the main magnetic pole which is the developing magnetic pole in the region is 40% or more.
[Selection] Figure 1

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, and a fax machine, which includes a plurality of developing devices capable of forming a color image and uses an electrophotographic method, a developing device used therefor, and a carrier and a toner used therefor .

  As shown in FIG. 14, the two-axis conveyance type developing device includes an auger 102 and a supply / recovery conveyance path for supplying and collecting the developer to the developing roller 101, a conveyance agitating auger 103 and a stirring and conveyance path after toner replenishment. These two augers and two conveyance paths are arranged horizontally below the developing roller 101.

  Various one-way circulation type (three-axis configuration) developing devices are also disclosed. For example, in Patent Document 1, as shown in FIG. 15, in a vertical developing device, the two-component developer is sufficiently circulated and supplied to the developing roller after being sufficiently stirred, so that the image density is high even in an image with a high printing rate. In order to achieve uniform and non-uniform image quality and to stabilize the density and improve display quality, the surplus developer from the first transport path 110 and the collected developer from the second transport path 111 are merged. A third conveying path 112 that circulates and supplies the first conveying path 110 after the agitating and conveying is provided, and the toner density of the agitated developer that is circulated and supplied to the first conveying path 110 is further increased. An image in which a high-quality image having a constant density and no image unevenness is obtained also in an image having a printing rate is disclosed. In the figure, 116 is a developing device, 117 is a toner supply port, 118 is a developing roller, 120 is a two-component developer, 121 is a photosensitive drum, 123 is a first auger, 124 is a second auger, and 126 is a third. Ogre.

  In Patent Document 2, as shown in FIG. 16, when a developer having a lowered toner density is reused for development, the toner density of the developer becomes non-uniform and the density of an image formed on a sheet is not uniform. As a means to solve the problem, the developer agitated and conveyed by the lower second screw auger is transferred to the third screw through an opening provided outside the width of the image area where the image carrier forms a latent image. The third screw auger moves to the auger and is blocked by a partition that does not mix the developer that is being stirred and transported by the other screw auger so that the third screw auger is transported by stirring and moved to the upper first screw auger that communicates A constituent technology is disclosed. In the drawing, 130 is a developing device, and the developing device 130 includes a developing magnet roller 131, at least three screw augers 132 to 134, and a blade 135. The rotating shaft 136 of each of the screw augers 132 to 134 is parallel to the image carrier 137 and between the upper first screw auger 132 and the lower second screw auger 133 arranged in a vertical relationship. A third screw auger 134 is provided at the height position.

  Further, as shown in FIG. 17, Patent Document 3 has two stirring chambers that are provided substantially in parallel with the width direction of an image to be formed and communicate with each other at both ends, and the developer is circulated in these stirring chambers. As an invention for obtaining a good image free of density unevenness by downsizing the apparatus and making the developer distribution and the toner density distribution uniform in the stirring chamber, the two stirring chambers 140 and 141 are developed. In addition to the auger 142 that conveys the developer, the auger 142 that is above the auger 142 and that conveys the developer in the opposite direction to the auger 142 is placed in the stirring chamber 141 below. 143. Thus, a large amount of developer is prevented from being unevenly deposited in the vicinity of the developer transfer portion from the lower stirring chamber 141 to the upper stirring chamber 140, and a substantially uniform developer distribution is maintained. In the figure, 144 is an electrostatic latent image holder, 145 is a developing device, 146 is a developer carrier, and 147 is a developer regulating member.

Further, there is an invention that defines a layout configuration in a three-axis developing device. In particular, the present invention is characterized in that the position of the apex of the supply screw is 10 to 40 degrees below the center of the developer carrying member, and the recovery, supply, and stirring screws are arranged in a substantially horizontal direction. This is intended to extend the life of the developer and stabilize the image density. However, if the speed of the device is increased, the developer in the supply section will be depleted and the recovery section will not be recovered unless the screw in the circulation section is rotated at a high speed. There is a possibility that the agent overflows, and even if circulation is established at high speed, the developer is rapidly deteriorated, and long-term image density stability cannot be obtained.
Japanese Patent Laid-Open No. 11-167260 JP 2001-249545 A Japanese Patent No. 3127594

  The one-way circulation development method is a configuration in which the developer after development is all collected by the collection unit and is not returned to the supply unit. Therefore, the amount of developer decreases as it goes downstream in the supply unit, so that the amount of developer supplied to the developing sleeve does not become insufficient, and the amount of developer increases as it goes downstream in the recovery unit. In order to prevent the developer from being clogged in the downstream portion and causing the agent to return to the supply portion, it is necessary to ensure a sufficient developer conveyance speed in both the supply portion and the recovery portion.

  For that purpose, it was necessary to rotate the screw at high speed. However, as the rotational speed of the developing sleeve increases with the increase in the linear velocity of the photosensitive member, the developer circulation section further increases in speed. However, circulating the developer at a high speed in the circulation section may cause deterioration of the developer. It will lead to deterioration of developing devices such as screw bearings. On the other hand, it is possible to increase the conveyance amount by increasing the screw diameter, but increasing the diameter of the three screws leads to an increase in the volume of the developing section in terms of layout, and there is a limit. Therefore, it has been difficult to cope with the high speed of the unidirectional circulation development system.

  On the other hand, the amount of change in the developer amount in the supply and recovery unit is determined by the pumping amount that is the developer amount after passing through the doctor, so the developer transport speed can be reduced by reducing the pumping amount. If only the amount is reduced, there is a risk that the image quality is deteriorated due to insufficient development capability or rubbing of the magnetic brush. These problems are largely caused by the shape of the magnetic brush of the developing magnetic pole in the developing area. When the magnetic brush is sparse, the developing ability is lowered, and when the brush chain is long, problems such as rear end scumming are caused.

  Accordingly, it is an object of the present invention to provide a one-way circulation type developing device that can prevent deterioration of the developer and obtain a stable image density and image quality over a long period of time even when the image forming apparatus is speeded up.

  A developing device according to a first aspect of the present invention is a developer carrier comprising a nonmagnetic sleeve that carries and transports a developer composed of toner and a carrier as a magnetic brush, and a magnet roller fixedly disposed in the nonmagnetic sleeve. And a first conveying path having a first screw for agitating and conveying the developer along the axial direction of the developer carrier and supplying the developer to the developer carrier, and the developer A second conveyance path having a second screw for collecting the developer after completion of development from the carrier 5 and conveying the collected developer in parallel and in the same direction as the first screw; The first developer path is supplied with surplus developer that has not been supplied to the developer carrier and the recovered developer from the second transport path via the first transport path, The first agitating and conveying in the opposite direction to the screw A third conveying path that circulates and supplies the developer, in which the surplus developer and the recovered developer are stirred, to the first conveying path 9, and the developer carrying member facing the developer carrying member. A developing device comprising a developer regulating member that regulates the height of the developer layer supplied from the first transport path to the developer carrying member, wherein the magnetic brush rubs against the latent image carrying member. It is characterized in that the attenuation factor of the magnetic flux density in the normal direction of the main magnetic pole as the developing magnetic pole in the developing nip region is 40% or more.

  That is, it is necessary to provide a developing device that can prevent deterioration of the developer and obtain a stable image density and image quality over a long period of time even when the image forming apparatus is increased in speed. In the unidirectional circulation development system, the developer after development is all collected in the collecting unit and is not returned to the supply unit. Therefore, the amount of developer decreases as it goes downstream in the supply unit, so that the amount of developer supplied to the developing sleeve does not become insufficient, and the amount of developer increases as it goes downstream in the recovery unit. In order to prevent the developer from being clogged in the downstream portion and causing the agent to return to the supply portion, it is necessary to ensure a sufficient developer conveyance speed in both the supply portion and the recovery portion. For that purpose, it was necessary to rotate the screw at high speed. However, as the rotation speed of the developing sleeve increases with the increase in the linear velocity of the photosensitive member, the rotation speed of the developer becomes even higher. However, circulating the developer at a high speed in the circulation section may cause deterioration of the developer or screw. This will lead to deterioration of the developing device such as the bearing. On the other hand, it is possible to increase the conveyance amount by increasing the screw diameter, but increasing the diameter of the three screws leads to an increase in the volume of the developing section in terms of layout, and there is a limit. Therefore, it has been difficult to cope with the high speed of the unidirectional circulation development system. On the other hand, the amount of change in the developer amount in the supply and recovery unit is determined by the pumping amount that is the developer amount after passing through the doctor, so that the developer transport speed can be reduced by reducing the pumping amount. However, if the pumping amount is simply reduced, there is a risk of image quality deterioration due to insufficient developing ability or rubbing of the magnetic brush. Therefore, by setting the attenuation rate of the magnetic flux density in the normal direction of the developing main pole to 40% or more, a magnetic brush having a short head and a high density can be formed, so that the pumping amount is reduced as compared with the conventional magnetic pole. be able to. As a result, the speed of the circulating portion of the one-way circulation developing device can be reduced without increasing the diameter of the screw, so that the life of the developing device can be extended. In addition, a stable image density can be obtained over a long period of time, and a high-quality image having no trailing edge can be obtained. If the attenuation rate of the magnetic flux density in the normal direction of the main magnetic pole is less than 40%, a high-density magnetic brush cannot be formed, and image quality may be deteriorated due to insufficient development capability or rubbing.

  According to the second aspect of the present invention, there is provided a non-magnetic sleeve that carries and conveys a developer composed of toner and a carrier as a magnetic brush, a developer carrier composed of a magnet roller fixedly disposed in the sleeve, and the developer A developer is agitated and conveyed along the axial direction of the carrier, and a first conveyance path having a first screw for supplying the developer to the developer carrier, and development from the developer carrier. A second conveyance path having a second screw for collecting the developer after completion and conveying the collected developer in parallel and in the same direction as the first screw; and from the first conveyance path, The excess developer that has not been supplied to the developer carrier and the recovered developer from the second conveyance path via the first conveyance path 9 are received, and in the reverse direction to the first screw Have a third screw A third conveying path that circulates and supplies the developer in which the excess developer and the recovered developer are stirred to the first conveying path, and the developer conveying member facing the first conveying path. A developing device comprising a developer regulating member that regulates the height of the developer layer supplied to the developer carrying member, wherein the magnetic brush is slid against the latent image carrying member in a developing nip region. The half width of the main magnetic pole as the developing magnetic pole is 22 degrees or less. That is, by setting the half width of the developing main magnetic pole to 22 degrees or less, it is possible to form a magnetic brush with short heading and high density, so that the pumping amount can be reduced as compared with the conventional magnetic pole. As a result, the circulation section speed of the unidirectional circulation developing device can be reduced, and the life of the developing device can be extended. In addition, a stable image density can be obtained over a long period of time, and a high-quality image having no trailing edge can be obtained. When the half width of the main magnetic pole is larger than 22 degrees, a high-density magnetic brush cannot be formed, resulting in insufficient development capability and image quality degradation due to rubbing.

  According to a third aspect of the present invention, in the developing device according to the first or second aspect, the magnetic brush is assisted in forming a magnetic force of a main magnetic pole as a developing magnetic pole in a developing nip region where the magnetic brush slides on the latent image carrier. A magnet is provided. That is, by providing the auxiliary magnetic pole for assisting the magnetic formation of the developing main magnetic pole, it is possible to form a magnetic brush having a short head and a high density more stably than using a single developing magnetic pole. The pumping amount can be reduced as compared with the magnetic poles. As a result, the circulation section speed of the unidirectional circulation developing device can be reduced, and the life of the developing device can be extended. In addition, a stable image density can be obtained over a long period of time, and a high-quality image having no trailing edge can be obtained.

  According to a fourth aspect of the present invention, in the developing device of the third aspect, the auxiliary magnets are arranged on the upstream side and the downstream side in the developer transport direction of the main magnet formed by the main magnetic pole. In other words, by arranging the auxiliary magnetic poles upstream and downstream of the main magnetic pole, it is possible to stably form a magnetic brush with short heading and high density, which prevents deterioration of the developer and is stable over a long period of time. It is possible to provide a developing device capable of obtaining the obtained image density and image quality.

  According to a fifth aspect of the present invention, in the developing device of the third or fourth aspect, the main magnetic pole and the auxiliary magnetic pole have different polarities. In other words, by defining the polarity of the auxiliary magnetic pole, the polarity of the auxiliary magnetic pole is different from that of the main magnetic pole, so that it is possible to stably form a magnetic brush having a short head and a high density, preventing deterioration of the developer, A developing device capable of obtaining a stable image density and image quality over a long period of time can be provided.

  According to a sixth aspect of the present invention, in the developing device according to any one of the first to fifth aspects, the magnet forming the main magnetic pole is made of a rare earth metal alloy. In other words, the configuration of the magnet that forms the main magnetic pole is specified, and the magnet that forms the main magnetic pole is made of a rare earth metal alloy, so that it is possible to stably form a magnetic brush with a short head and a high density. It is possible to provide a developing device that can prevent deterioration of the agent and obtain a stable image density and image quality over a long period of time.

  According to a seventh aspect of the present invention, in the developing device according to any one of the first to sixth aspects, the respective transport paths are arranged substantially horizontally. In other words, in the developer conveyance section, the developer is retained by the fact that each conveyance path is arranged almost horizontally in order to reduce the stress during the circulation of the developer as much as possible and achieve a long life of the developer. It is possible to circulate without letting. Therefore, since the developer is not subjected to excessive stress, the life of the developer is extended, and a developing device capable of obtaining a stable image density and image quality over a long period of time can be provided.

  According to the eighth aspect of the present invention, in the developing device according to any one of the first to sixth aspects, the first transport path 9 is provided below the second transport path 7. And That is, in the case of a layout having a recovery unit at the upper part of the supply unit, the space for storing the developer in the supply unit is limited, so that the developer tends to be depleted in the downstream part of the supply unit. By using the invention according to any of the above-mentioned claims in the case of a certain layout, the pumping amount can be reduced without causing insufficient development capability or image quality deterioration, so that stable image density and image quality can be obtained over a long period of time. A developing device can be provided.

  According to the ninth aspect of the present invention, in the developing device according to any one of the first to eighth aspects, the developing bias, which is a voltage waveform applied to the developer carrier, is an AC bias in which an alternating current component is superimposed on a direct current component. It is characterized by that. That is, when the amount of pumping is reduced, further image stability is ensured. Since the developing ability is improved by using an AC bias as the developing bias, there is no fear that the image density is reduced even when developing with a low pumping amount, and a developing device capable of obtaining a stable image density and image quality over a long period of time can be provided.

  An image forming apparatus according to a tenth aspect of the present invention includes a plurality of image carriers on which electrostatic latent images are formed and a developing device according to any one of the first to ninth aspects, and forms a color image on a recording material. It is possible. To provide an image forming apparatus capable of obtaining a high-quality color image having high image density stability and excellent color reproducibility and color balance since a stable toner adhesion amount can be obtained over a long period of time. It becomes possible.

  According to the eleventh aspect, in the color image forming apparatus according to the tenth aspect, the first toner image transferred to the first surface of the recording material is for each color (C, M, Y, K). A first image station comprising a first image forming unit group having at least a developing device and a photoreceptor, and a first toner image carrying belt on which a first toner image formed by the first image forming unit group is transferred and carried The second toner image formed on the recording material and transferred to the second surface of the recording material is a second image forming unit group having at least a developing device and a photoconductor for each color (C, M, Y, K). The second toner image formed by the second image forming unit group is formed by a second image station including a second toner image carrying belt on which the second toner image is transferred and carried. The toner images of Is sequentially transferred to the sheet, characterized in that it is a so-called one-pass double-sided transfer method. By using the developing device of the present invention in an image forming apparatus having a one-pass double-sided configuration, it is possible to obtain a color image having excellent density stability over a long period of time with extremely high productivity. As a result, there is no difference in image quality between the front and back sides, and a color double-sided image with always stable image quality can be obtained.

  A carrier according to a twelfth aspect of the present invention is a carrier used in the developing device according to any one of the first to ninth aspects or the image forming apparatus according to any one of the tenth to twelfth aspects, and has a volume average particle size of 20 to 60 μm. By using a carrier having a small particle diameter, the developing ability can be improved by densifying the magnetic brush, so that the pumping amount can be further reduced. Thereby, the number of screw rotations in the recovery and supply unit can be reduced, which contributes to stress reduction due to the agent circulation. Furthermore, since the magnetic brush in the development area becomes denser, high image quality and stable image quality are achieved. If the average particle size of the carrier is larger than 60 μm, the amount of developer overflowing in the developer circulation portion increases, and stable developer circulation cannot be performed. Furthermore, since the magnetic brush becomes rough, satisfactory image quality cannot be obtained. On the other hand, if it is smaller than 20 μm, the carrier adheres to the photoreceptor or the carrier is likely to be scattered from the developing device.

  A toner according to a thirteenth aspect of the present invention is a toner used in the developing device according to any one of the first to ninth aspects or the image forming apparatus according to any one of the tenth to twelfth aspects, and has a volume average particle size of 3 to 3. The ratio (D4 / D1) of the volume average particle diameter (D4) and the number average particle diameter (D1) is 8 μm and is in the range of 1.00 to 1.40. That is, by using a toner having a small particle size and a sharp particle size distribution, the gap between the toner particles is reduced, so that the required adhesion amount of the toner can be reduced without impairing the color reproducibility. Therefore, density fluctuation in development can be reduced. Further, the stable reproducibility of a minute dot image is improved, and a stable high image quality can be obtained for a long time. When the average particle diameter (D4) is less than 3 μm, problems such as a decrease in transfer efficiency and a decrease in blade cleaning properties are likely to occur. When the average particle diameter (D4) exceeds 8 μm, the fluidity of the developer is deteriorated, and it is difficult to suppress scattering of characters and lines, and it is difficult to stably maintain image quality for a long time.

  According to the fourteenth aspect of the present invention, there is provided toner used in the developing device according to any one of the first to ninth aspects or the image forming apparatus according to any one of the tenth to thirteenth aspects, wherein the shape factor SF-1 is 100 to 180. The shape factor SF-2 is in the range of 100 to 180. When the toner is nearly spherical, the fluidity of the developer is improved, so that the stress in the agent circulation is reduced, and the agent circulation and development can be performed stably for a long period of time.

The toner according to the fifteenth aspect is a toner used in the developing device according to any one of the first to ninth aspects or the image forming apparatus according to any one of the tenth to fourteenth aspects, and has an average primary particle size on the surface of the toner base particles. Is 50 to 500 nm, and fine particles having a bulk density of 0.3 g / cm ³ or more are externally added. That is, since the external additive is hardly buried in the toner and the change in the fluidity and charging characteristics of the developer is small with time, it is possible to perform stable agent circulation and development over the long term.

  In the present invention, the magnetic flux density attenuation rate in the normal direction of the developing main magnetic pole is set to 40% or more, so that a magnetic brush having a short head and a high density can be formed, and the pumping amount is reduced as compared with the conventional magnetic pole. As a result, the speed of the circulating portion of the one-way circulating developing device can be reduced without increasing the diameter of the screw, so that the life of the developing device can be extended. In addition, a stable image density can be obtained over a long period of time, and a high-quality image having no trailing edge can be obtained.

  The best mode for carrying out the present invention will be described below with reference to the embodiments shown in the drawings.

<Explanation about the developer>
A detailed description of the developing device 4 of the present invention will be given below with reference to FIG. In the figure, 1 is a photosensitive drum, 2 is a charging device, L is a laser beam from an exposure device 3 (not shown in FIG. 1), 4 is a developing device, and a developed developer is supplied from a developing roller 5. A collecting screw 6 and a collecting and conveying path 7 for collecting and conveying, and a supplying screw 8 and a supplying and conveying path 9 for supplying and conveying the developer to the developing roller 5 are arranged below the developing roller 5 in parallel. The developer in the collection conveyance path 7 and the supply conveyance path 9 is conveyed in the same direction. Both transport paths communicate with each other on the downstream side in the transport direction, and the recovered developer transported by the recovery screw 6 is transferred to the supply transport path. Further, the collected developer and the developer that has not been supplied to the developing roller 5 conveyed by the supply conveying screw 8 are transferred to the communicating agitating and conveying path 10. The agitating / conveying screw 11 disposed in the agitating / conveying path 10 is configured to collect the collected developer, the developer not supplied to the developing roller, and the replenished developer described later with the developer in the collecting and conveying path 7 and the supply / conveying path 9. The developer is agitated and conveyed in the reverse direction, and the agitated developer is transferred to a supply conveyance path communicating on the downstream side in the conveyance direction.

  The screws 6, 8, 11 and the transport paths 7, 9, 10 are arranged in the lateral direction below the developing roller 5. Each of the transport paths 7, 9, and 10 is formed by a partition plate that is held by an integrated lower casing 12 and an upper casing 13. Here, the transport paths 7 and 9 are partitioned by a partition plate 6a, and the transport paths 9 and 10 are partitioned by a partition plate 6b. In the partition plate 6a, the conveyance paths 7 and 9 are completely blocked in the image output region, that is, the region where the developing roller is present.

  Even if an appropriate amount of developer is supplied, it is desirable that the amount of developer is larger than the amount of developer regulated by the developer regulating member 16, so that the excess developer is discharged on the upstream side 17 of the developer regulating member 16 during operation. It will continue to increase. A surplus developer collecting member 18 is installed to detour and return to the supply conveyance path 9 when the surplus developing developer stays and exceeds a certain amount so as not to cause circulation convection. . Further, the position of the surplus developer collecting member 18 is set so that the reflux developer is not retained due to the magnetic force of the developing roller 5.

  The developer regulating member 16 is tightly fixed to a heat radiating member 19 fixed to the upper casing 13. The developer regulating member 16 transmits heat from the developer to the heat radiating member 19, and fins 20 are formed inside the heat radiating member to dissipate heat by the air flow during operation, thereby reducing the temperature rise of the developer. I am trying. The heat radiating member 19 is provided with a guide portion 21A used as a guide when the developing device or the photosensitive unit (not shown) is attached to or detached from the machine main body (not shown). The lower casing 12 is provided with heat radiating fins 28 so that the temperature rise of the entire developing device can be reduced and cooled by cooling air sent from the front part of the machine to the rear part.

  On the downstream side of the developing roller 5, a developer catching roller 22 </ b> A is installed to catch the developer adhering to the photoreceptor 1 and the developer falling from the developing roller 5, and reversely rotate with the developing roller 5. Or recovered to the recovery conveyance path 7 by the scraper 23A.

  Next, description will be made with reference to FIG. 2 which is a perspective view from the photosensitive drum side of each conveyance path and each auger configured by the lower casing. The lower casing 12 is provided with a recovery screw 6, a supply screw 8, and an agitating and conveying screw 11 from the front of the figure, and each conveying path described above is formed in the lower casing 12 so as to surround each screw. . However, the supply conveyance path and the collection conveyance path are held by an upper casing (not shown) and are separated by a partition plate 6 a that engages with the lower casing 12. The partition plate 6a is installed sufficiently close to the developing roller so that the developer does not enter the collecting section from the collecting section in the image forming area. The developer is transported in the directions of arrows a and b by the collection screw 6 and the supply screw 8, and is transported in the direction of arrow c by the agitation transport screw 11.

  The configuration of the screw will be described using the stirring and conveying screw 11 as an example. For conveying the developer so as not to feed the developer into the conveying screw portion 11a for agitating and conveying the developer toward the developer conveying direction, the transfer paddle 11b for transferring the developer to the adjacent supply screw 8 side, and the bearing portion. A reverse screw 11c having a winding direction opposite to that of the screw 11a is provided. The recovery screw 6 and the supply screw 8 have the same configuration.

In addition, the shape of the screw of a present Example is a stirring screw: outer diameter (phi) 30, pitch 36 (2 items)
Supply screw: outer diameter φ27, pitch 36 (2 items)
Recovery screw: Outer diameter φ25, Pitch 34 (2 items)
It is said. However, the present invention or the embodiment of the present invention is not limited to this value.

  On the downstream side of the developer conveyance direction, each conveyance path is connected, and the developer from the agitation conveyance path is further transferred to the supply screw 8 side by the transfer paddle 11b of the agitation conveyance screw 11 and further to the developing roller (not shown). Along with the developer that has not been sent to, it is transferred to the agitating and conveying screw 11 side by the transfer paddle 11 b of the supply screw 8.

  An output signal from a toner concentration sensor (not shown) provided in the lower casing 12 below the agitating and conveying screw 11 causes a developer replenishing means (not shown) including a control system to supply the supply screw 8. Toner is supplied from the top to the transfer portion position 8a between the agitating and conveying screws 11. By supplying the developer by the paddle 11b, the developer is replenished to a place where the stirring action is large, so that the replenished toner is stirred and mixed in a short time. The toner replenishment position is not limited to between the supply screw 8 and the agitating / conveying screw 11 but may be a transfer unit between the recovery screw 6 and the supply screw 8.

  Details of the developing roller and the developing magnetic pole will be described with reference to FIG. In the developing device 4, a developing roller 41 that is a developer carrying member is disposed so as to be close to the photosensitive drum 1. In the developing roller 41, a developing sleeve 43 formed of a nonmagnetic material such as aluminum, brass, stainless steel, or conductive resin in a cylindrical shape is rotated in a clockwise direction by a rotation driving mechanism (not shown). . A doctor blade 16 for restricting the height of the developer chain spike, that is, the amount of developer on the developing sleeve, is installed on the upstream side of the developing region in the developer transport direction (clockwise as viewed in the figure). ing. A doctor gap, which is a distance between the doctor blade 16 and the developing roller 5 as a developing sleeve, is set to 0.4 mm.

  As a voltage applied to the developing sleeve 5, an AC bias in which an AC component is superimposed on a DC component can be used. By applying an AC bias, the toner in the magnetic brush vibrates due to an electric field in the developing region and easily detaches from the carrier, and the amount of toner contributing to development increases. In this embodiment, a sine wave having a peak-to-peak voltage of 1.2 kV and a frequency of 5 kHz is superimposed on the DC component −500 V as the AC component. The waveform is not limited to this, and may be a rectangular wave or a sawtooth wave.

  In the developing sleeve 5, a magnet roller body (magnet roller) 5 a that forms a magnetic field is provided in a fixed state so as to generate a spike of developer on the peripheral surface of the developing sleeve 5. The developer carrier rises in a chain shape on the developing sleeve 5 so as to follow the normal magnetic field lines emitted from the magnet roller body, and the charged toner adheres to the carrier that has the chain shape. Thus, a magnetic brush is configured. The magnetic brush is transferred in the same direction as the developing sleeve 5 by the rotation of the developing sleeve 5 (clockwise as viewed in the figure). The magnet roller body 5a includes a plurality of magnetic poles (magnets). Specifically, the developing main magnet P1b that generates developer spikes in the development region, main magnetic pole magnetic force formation assisting magnets P1a and P1c that assist the magnetic formation of the main magnetic pole, and the developer sleeve 5 are pumped up. A magnet P3, magnets P4, P5, and P6 that convey the pumped developer to the development area, and a magnetic pole P2 that conveys the developer in the developed area. These magnets P1b, P1a, P1c, P4, P5, P2 and P3 are arranged in the radial direction of the developing sleeve 5. In this example, the magnet roller body 5a is composed of an 8-pole magnet. However, in order to improve the pumping performance and the black solid image followability, the number of magnets (magnetic poles) is further increased between the P3 pole and the doctor blade 16. You may comprise 10 poles or 12 poles.

As shown in FIG. 3, the developing main pole group P1 is composed of magnets having a small cross section arranged in the order of P1a, P1b, and P1c from the upstream side. These magnets having a small cross section are made of a rare earth metal alloy, but samarium alloy magnets, particularly samarium cobalt alloy magnets, can also be used. Among rare earth metal alloy magnets, a typical iron neodymium boron alloy magnet has a maximum energy product of 358 kJ / m ³ , and an iron neodymium boron alloy bonded magnet has a maximum energy product of around 80 kJ / m ³ . Unlike conventional magnets, such a magnet can ensure the required developing roller surface magnetic force even if the size is considerably reduced. In the conventional ordinary ferrite magnets or ferrite bond magnets maximum energy product each 36 kJ / ^{m 3} before and after a 20 kJ / ^{m 3} before and after. When it is acceptable to increase the sleeve diameter, it is possible to reduce the half-value width by increasing the shape using a ferrite magnet or ferrite bonded magnet, or by forming the tip of the magnet facing the sleeve side narrowly. Is possible. Further, in the present embodiment, it is constituted by a magnet having a small cross section, but it may be formed by a magnet roller formed by integral molding, and magnets other than the P1 pole group are integrally molded to individually separate the P1 pole group. They may be formed integrally or simultaneously. You may shape | mold the magnet formed in the fan shape by bonding to a magnet roller axis | shaft.

  In this example, the developing main magnet P1b, the magnet P4 that transports the pumped developer, and the magnet P6 that transports the pumped developer to the developing area form the S pole, and the main magnetic pole assists the formation of the magnetic force of the main pole. Magnetic formation auxiliary magnets P1a and P1c, a magnetic pole P2 for transporting the developer in the developed region, a magnet P3 for pumping the developer onto the developing sleeve 5, and a magnet P5 for transporting the pumped developer are N poles I am doing.

  FIG. 4 is a diagram showing the magnetic force distribution of the developing roller 5 and the magnitude thereof in the developing device. The magnetic flux density in the normal direction is measured and shown as a pie chart graph. As shown in FIG. 4, a magnet having a normal magnetic force of 85 mT or more on the developing roller 5 is used as the main magnet P1b. The magnetic force related to carrier adhesion is tangential magnetic force, and in order to increase this tangential magnetic force, it is necessary to increase the magnetic force of P1b, P1a, and P1c, but suppressing the occurrence of carrier adhesion by increasing any one sufficiently. Can do. The magnet width of the magnets P1b, P1a, and P1c was 3 mm. At this time, the half width of P1b was 16 °.

  Further, an area (development nip) where the photosensitive drum and the magnetic brush are in contact with each other is formed at a portion where the developing roller 5 and the photosensitive drum 1 are opposed to each other. Toner movement occurs between the image carrier and the magnetic brush, and development is performed. In contact development, toner movement mainly occurs in the region. A so-called white spot phenomenon in which the solid rear end part is whitened during development by such toner movement is a problem.

  FIG. 5 is a conceptual diagram of the developing unit for explaining the cause of the trailing edge blank. The image carrier (photosensitive member 1) and developer carrier (developing roller or developing sleeve 5) move in the directions of arrows a and b, respectively. The linear velocity of the developer carrier is higher. Therefore, the magnetic brush always develops while overtaking the electrostatic latent image formed on the image carrier. When the magnetic brush contacts the non-image portion (background portion) on the upstream side of the development area, the toner present at the tip of the magnetic brush receives a force in the developer carrier direction c due to the electric field in the development area, and the image carrier. Move away from the neighborhood. For this reason, the toner concentration in the vicinity of the image carrier decreases as the time during which the magnetic brush contacts the non-image portion is longer. When the magnetic brush moves to the downstream side of the development area as the developer carrier moves and catches up with the image area, the tip of the magnetic brush having a low toner concentration is already developed and attached to the image carrier. Electrostatically attracts in the direction of d. For this reason, the toner after the image decreases, while the toner density at the tip of the magnetic brush increases again. Even if the magnetic brush moves further to the downstream side of the developing region, the toner is not attracted from the image carrier if the toner density is restored. In such a state, there is no problem, but when the contact between the magnetic brush and the image portion is short, the front end of the magnetic brush having a low toner density comes into contact with the end portion (rear end) of the image portion. As a result, an image in which the rear end portion is faint is formed on the image carrier that has passed through the development region.

  This is because when the developing nip is wide, the strength of the electric field strength between the photosensitive member and the developing sleeve in the nip can be different between the central portion of the nip and the nip boundary portion. It is considered that the toner recovery due to the reverse charge on the nearby carrier occurs because the toner adheres more to the photosensitive drum due to the electric field.

  Therefore, by narrowing the developing nip, the electric field strength is not reduced even at the nip boundary as described above, and the carrier is substantially prevented from collecting the toner developed on the photosensitive drum. For this reason, the phenomenon that the rear end is white is eliminated.

  The attenuation factor of the present invention is the difference between the peak value of the normal direction magnetic flux density on the sleeve surface and the peak value of the normal direction magnetic flux density at a distance of 1 mm from the sleeve surface. The ratio divided by the peak value. An increase in the attenuation rate of the magnetic pole means that the spike width between the rising and falling of the magnetic brush is reduced, and as a result, the magnetic brush rises short and densely. The development nip is a region where the latent image carrier and the magnetic brush are in contact with each other, and the development nip boundary is a region end downstream of the closest ground point between the latent image carrier and the developer carrier.

  Increasing the attenuation factor can be realized by selecting a magnet that forms the magnetic pole. Further, as described in the section of the embodiment below, it has been experimentally found that the attenuation factor increases by narrowing the half width of the magnetic pole. The full width at half maximum should be 22 ° or less, preferably 18 ° or less. The half width is a half value of the maximum normal magnetic force (vertex) of the magnetic distribution curve in the normal direction (for example, when the maximum normal magnetic force of a magnet made of N pole is 120 mT (millitesla)) 50% is 60 mT, and there is also an expression of half-value 80%, which in this case is 96 mT). As a measure for narrowing the half-value width of the main magnetic pole, it is conceivable to form an auxiliary magnetic pole that assists the formation of the magnetic force. When the half-value width is narrowed, the position where the magnetic brush is raised approaches the main pole, and the developing nip itself is also narrowed. The auxiliary magnetic pole is formed upstream and / or downstream of the main magnetic pole in the developer conveyance direction. In addition to both the upstream side and the downstream side, it can be formed on either the upstream side or the downstream side, both of which have advantages.

  Next, when considering the decay rate of the magnetic density in the normal direction, the description will be given with reference back to FIG. FIG. 4 shows a normal magnetic force pattern. The solid line is a circle chart graph measuring the magnetic flux density on the surface of the developing sleeve, and the broken line is measuring the magnetic flux density in the normal direction at a distance of 1 mm from the surface of the developing sleeve. Is a pie chart graph. The measurement apparatus used for the measurement was a Gauss meter (HGM-8300) manufactured by ADS and an A1 type axial probe manufactured by ADS, and recorded by a circular chart recorder.

  In the observation with the magnet roller in the first example, the magnetic flux density in the normal direction on the sleeve surface of the main magnetic pole P1b is 95 mT, and the normal direction magnetic flux density at a portion 1 mm away from the sleeve surface is 44.2 mT. There was a magnetic flux difference of 50.8 mT. Attenuation rate of normal direction magnetic flux density at this time (the difference between the normal direction magnetic flux density peak value on the sleeve surface and the normal direction magnetic flux density peak value at a distance of 1 mm from the sleeve surface The ratio divided by the peak value of the magnetic flux density in the linear direction is 53.5%. When the maximum normal magnetic force of the main magnet is 95 mT, the half value is 47.5 mT, and the half value width is 22 °. It was confirmed that an abnormal image was generated when the half width of the main magnetic pole was larger than 22 °.

  The normal magnetic flux density on the sleeve surface of the main magnetic pole magnetic force forming auxiliary magnet P1a located on the upstream side of the main magnetic pole P1b is 93 mT, and the normal magnetic flux density at a portion 1 mm away from the sleeve surface is 49.6 mT. The change in magnetic flux density was a magnetic force difference of 43.4 mT. The attenuation factor of the normal direction magnetic flux density at this time is 46.7%. The normal magnetic flux density on the sleeve surface of the main magnetic pole magnetic force forming auxiliary magnet P1c located downstream of the main magnetic pole P1b is 92 mT, and the normal magnetic flux density at a portion 1 mm away from the sleeve surface is 51.7 mT. The amount of change in magnetic flux density was a magnetic force difference of 40.3 mT. The attenuation factor of the normal direction magnetic flux density at this time is 43.8%. In this example, the magnetic brush formed along the magnetic force lines generated on the magnet roller has only the brush portion formed on the main magnetic pole P1b in contact with the photoconductor, and visualizes the electrostatic latent image on the photoconductor. . At this time, when measured without the photosensitive member being in contact, the length of the magnetic brush at that location is about 1.5 mm, which is shorter than the magnetic brush (about 3 mm) formed by a conventional magnet roller, and has a higher density. It became possible to create a state that became. When the distance between the developer regulating member and the developing sleeve is the same as the conventional one, since the amount of developer passing through the developer regulating member is the same, the magnetic brush in the development area is short and dense. It was confirmed that This phenomenon can be understood from the normal magnetic force pattern shown in FIG. 4, and the normal magnetic flux density at a distance of 1 mm from the developing sleeve surface is greatly reduced, so that the magnetic brush forms a brush chain at a distance from the developing sleeve. Therefore, the magnetic brush is short and densely formed on the surface of the developing sleeve. Incidentally, in the conventional magnet roller, the normal magnetic flux density on the sleeve surface of the main pole is 73 mT, and the normal magnetic flux density at a portion 1 mm away from the sleeve surface is 51.8 mT. The amount was a magnetic difference of 21.2 mT. The attenuation factor of the normal direction magnetic flux density at this time is 29%.

  In experimental values, it has been found that the attenuation rate increases by reducing the half width. Reduction of the half-value width can be achieved by reducing the width of the magnet (width in the sleeve circumferential direction). For example, in the first example, the magnets P1b, P1a, and P1c have a magnet width of 3 mm and the half width of P1b is 16 °, but the 2 mm width magnet has a half width of the main pole of 12 °. By narrowing the half-value width, the dose of magnetic force that wraps around adjacent magnets increases, and the normal magnetic flux density at the part away from the sleeve surface decreases. Between the magnet roller and the developing sleeve, there is a substantial gap based on the space required for the rotation of the developing sleeve with the magnet roller fixed and the developing sleeve, and the tangential magnetic flux density position is substantially developed. Since it concentrates on the sleeve side, the normal magnetic flux density decreases as the distance from the sleeve surface increases.

  When a magnet roller having a high damping rate is used, the magnetic brush is short and densely formed. On the other hand, the magnetic brush is formed long and sparsely in the conventional magnet roller having a low attenuation rate. This is because the magnetic field formed by the magnet having a large attenuation rate is easily attracted to the adjacent magnets (for example, P1a and P1c with respect to P1b), and the contribution of the magnetic flux to the tangential direction is higher than the magnetic flux spreads in the normal direction. Thus, the magnetic flux density in the normal direction becomes small, so that the magnetic brush is hardly formed in the normal direction, and the magnetic brush is formed in a short and dense manner. For example, the magnetic brush formed on the magnet P1b having a high attenuation rate is more stable if it is formed adjacently and shorter than being elongated and individually formed. In a conventional magnet roller having a low damping rate, the magnetic brush is not shortened even if the developer pumping amount is reduced, and the length is almost the same as the magnetic brush described above. Increasing the attenuation factor can also be achieved by bringing the main pole forming auxiliary magnet adjacent to the main pole closer to the main pole position (in the sleeve circumferential direction). By doing so, the lines of magnetic force generated by the main magnetic poles flow into the adjacent main magnetic pole forming auxiliary magnetic poles to increase the damping rate.

<Other configuration of developing device>
Another embodiment of the developing device will be described with reference to FIGS. FIG. 6 is a cross-sectional view of the developing device. The developing roller 5 is opposed to the photosensitive member 1. In the developer circulation path, a recovery path 7 having a recovery screw 6 in the upper part is provided, and a stirring screw 11 is provided in the lower part. A stirring path 10 provided and a supply path 9 provided with a supply screw 8 are respectively arranged. Further, the toner supply means is connected to the developing device via a developer supply port 94. The developer is drawn up from the supply path to the developing roller side by the magnetic pole inside the developing roller, and the developer thinned by the developer regulating member (doctor) 16 is conveyed to the developing region.

  Details of the magnetic pole will be described below. In the present embodiment, the arrangement of the magnet roller body that does not include the auxiliary magnetic pole on the upstream side and the downstream side of the main magnetic pole is shown. The magnet roller body includes a developing main magnet P1 for causing the developer to sprout in the developing area, a magnet P5 for pumping the developer onto the developing sleeve, a magnet P6 for transporting the pumped developer to the developing area, and a post-development magnet. Magnetic poles P2, P3, and P4 are provided for conveying and separating the developer in the region. These magnets are arranged in the radial direction of the developing sleeve. In this embodiment, the magnet roller body is composed of 6-pole magnets. However, in order to improve the pumping performance and black solid image followability, the number of magnets (magnetic poles) is further increased between the P5 pole and the doctor blade 16. You may comprise by 8 or more poles.

  Similar to the example in which auxiliary magnets are provided on the upstream and downstream sides of the main magnet, the main magnet P1 that forms the developing main pole is composed of a magnet having a small cross section. The magnet having a small cross section is made of a rare earth metal alloy, but a samarium alloy magnet, particularly a samarium cobalt alloy magnet, can also be used. When it is permissible to increase the sleeve diameter, it is possible to narrow the half-value central angle by using a ferrite magnet or a ferrite bonded magnet to make the tip of the magnet thin toward the sleeve side.

  Next, the flow of the developer will be described with reference to FIGS. FIG. 6 is a top view of FIG. 6 divided into an upper stage A including the developing roller 5 and the recovery path and a lower stage B including the stirring path and the supply path. The arrow in FIG. 6 represents the flow of the developer, and the size of the arrow schematically represents the flow rate of the developer. The developer after passing through the development area is separated from the development roller by the magnetic pole inside the development roller 5 and collected in the collection path 7. In the recovery path, the developer amount increases toward the downstream portion. In the downstream portion, the developer falls from the agent dropping port 95 to the lower stirring path 10. A toner supply port 94 is disposed directly above or in the vicinity of the agent dropping port 95, and the supplied toner falls into the stirring path 10 together with the developer collected from the agent dropping port 95.

  On the other hand, in the lower part B, the developer circulates in the agitation part and the supply part, and in the upstream part of the agitation part, the recovered agent dropped from above and the surplus agent that was not used for development from the supply part are mixed. The developer is conveyed while being stirred. In the supply unit, the developer is supplied to the developing roller, and the developer amount decreases as the developer goes downstream.

<Detailed description of the entire image forming apparatus>
FIG. 8 is a schematic central sectional view showing the internal configuration of the image forming apparatus to which the present invention is applied.

  In the image forming apparatus main body 100 shown in FIG. 8, the first image carrier unit 20 including the first image carrier belt 21 that moves endlessly in the direction of the arrow with the recording material conveyance path 43 </ b> A as a boundary, A second image carrier unit 30 having a second image carrier belt 31 that moves endlessly in the direction of the arrow is disposed at the bottom. Four first image forming units 80Y, 80C, 80M, and 80K are provided on the upper tension surface of the first image carrier belt 21, and four first image forming units 80Y, 80C, 80M, and 80K are provided on the inclined tension surface of the second image carrier belt 31. Two image forming units 81Y, 81C, 81M and 81K are provided. Y, C, M, and K along the numbers of the first and second image forming units correspond to the colors of the toner to be handled. Y is yellow, C is cyan, M is magenta, and K is black. Means. Y, C, M, and K are also used in the same meaning with respect to the photoreceptor 1 provided in the first and second image forming units and rotating together with the first image carrying belt 21 and the second image carrying belt 31. . The photoreceptors 1Y to 1K are arranged at the same interval, and at least at the time of image formation, are in contact with a part of the stretched portion between the image bearing belts 21 and 31, respectively.

  In FIG. 9, during operation of the image forming apparatus 100, charging means is provided around a cylindrical photosensitive member 1 rotatably supported so as to rotate in the direction of an arrow by a driving source (not shown) according to an electrophotographic process. Image forming members such as the scorotron charger 2, the exposure device 3, the developing device 4, the cleaning device 2, and the light static elimination device Q, the potential sensor S1, and the image sensor S2 are disposed.

  The photoreceptor 1 is obtained by forming an organic photosensitive layer (OPC), which is a photoconductive substance, on an aluminum cylinder surface having a diameter of about 30 to 120 mm, for example. A photoconductor on which an amorphous silicon (a-Si) layer is formed can also be used. A belt-like photoreceptor can also be employed. The cleaning device 85 includes a cleaning brush 85a, a cleaning blade 85b, and a collecting member 85c, and removes and collects foreign matters such as toner remaining on the surface of the photosensitive drum 1.

  An exposure apparatus (not shown) scans light corresponding to image data for each color on the surface of each photosensitive drum 1 that is uniformly charged by the scorotron charger 2 to form an electrostatic latent image. As an exposure apparatus, an exposure apparatus comprising an LED (light emitting diode) array and an imaging element can be used as a light emitting element, but a laser using a light beam modulated according to image data to be formed using a laser light source, a polygon mirror, or the like. A scanning type exposure apparatus can also be employed. In addition to the charger, a type that makes contact with the surface of the photosensitive drum 1, such as a charging roller, can be used as the charging means.

  The development in this embodiment is a development system that employs a two-component developer composed of toner and carrier. The electrostatic latent image for each color formed on the surface of each photosensitive member 1 by a laser beam with respect to the negatively charged photosensitive member 1 is developed with toner of a predetermined color having the same polarity (negative polarity) as the charged polarity of the photosensitive member. And become a visible image. So-called reversal development is performed. The detailed description of the configuration of the developing device is as described above.

  A first image carrier belt 21 as an image carrier that is supported by a plurality of rollers 23, 24, 25, 26 (two), 27, 28, 29 and travels in the direction of the arrow is a first image forming unit 80Y. It is provided below the photoreceptors 1Y, 1C, 1M, and 1K at -80K. The image bearing belt 21 is endless, and is stretched and arranged so that a part of each photoconductor after the developing process comes into contact. In addition, a primary transfer roller 22 is provided on the inner peripheral portion of the first image carrying belt 21 so as to face each of the photoreceptors 1Y, 1C, 1M, and 1K.

  A cleaning device 20 </ b> A is provided on the outer periphery of the first image carrying belt 21 at a position facing the roller 23. The cleaning device 20 </ b> A wipes off unnecessary toner remaining on the surface of the image bearing belt 21 and foreign matters such as paper dust. The members related to the image carrier belt 21 are integrally formed as a first image carrier unit and can be attached to and detached from the image forming apparatus 100.

  A second image carrier belt 31 as an image carrier that is supported by a plurality of rollers 33 to 38 and runs in the direction of the arrow contacts the photoreceptors 1Y, 1C, 1M, and 1K in the second image forming units 81Y to 81K. And it is provided. The image carrying belt 31 is endless and is stretched and arranged so that a part of each photoconductor after the developing process comes into contact. A primary transfer roller 32 is provided on the inner peripheral portion of the image bearing belt 31 so as to face the photoreceptors 1Y, 1C, 1M, and 1K.

  A cleaning device 30 </ b> A is provided on the outer periphery of the second image carrying belt 31 at a position facing the roller 33. The cleaning device 30 </ b> A wipes away unnecessary toner remaining on the surface of the image bearing belt 31 and foreign matters such as paper dust. Members related to the image carrier belt 31 are integrally configured as the second image carrier unit 30 and can be attached to and detached from the image forming apparatus 100.

  Further, a first secondary transfer roller 46 is provided in the vicinity of the support roller 28 on the outer periphery of the first image carrying belt 21. The first image carrying belt 21 is carried by applying a bias to the first secondary transfer roller 46 while passing a recording medium (hereinafter referred to as paper P) between the first image carrying belt 21 and the secondary transfer roller 46. The toner image is transferred onto the paper P.

  A transfer charger 47 as a second secondary transfer unit is provided on the outer periphery of the second image bearing belt 31 and in the vicinity of the support roller 34. The transfer charger 47 is a known type, and a thin wire of tungsten or gold is used as a discharge electrode, held by a casing, and a transfer current is applied to the discharge electrode from a power source (not shown). By applying a transfer current while passing the paper P between the image carrying belt 31 and the transfer charger 47, an image by the toner carried by the second image carrying belt 31 is transferred to the paper P. The polarity of the transfer current applied to the transfer roller 46 and the transfer charger 47 is a positive polarity opposite to the polarity of the toner.

  On the right side of the image forming apparatus 100, a paper feeding device 40 that accommodates paper is provided, and only one sheet is reliably sent to the recording material conveyance paths 43B and 43A by a plurality of conveyance roller pairs 42B. Recording for transporting the sheet that has passed through the second transfer station on the extension of the recording medium conveyance path 43A to the fixing nip of the fixing device 60 provided downstream in the conveyance direction of the recording medium while maintaining a flat state. Body transport means 50 is provided. The recording medium transporting unit 50 has rollers 52, 53, 54, 55, and 56 that support the transport belt 51 that moves endlessly in the direction of the arrow. The cleaning device 50A faces the roller 55 on the outside of the transport belt 51. Further, an adsorption charger 57 for adsorbing the recording medium P facing the roller 56 and a charge eliminating / separating charger 58 facing the roller 54 are provided.

  The conveyance belt 51 that moves together with the recording medium P in contact with the unfixed toner image is negatively charged by the suction charger 57 with the same polarity as the polarity of the toner. As the conveyance belt 51, a metal belt, a polyimide belt, a polyamide belt, or the like can be employed. The surface is provided with releasability from the toner and has a chargeable resistance value. The traveling speed of the belt 51 is matched with the traveling speed of the recording medium in the fixing device.

  A fixing device 60 having a heating unit is provided on the downstream side of the recording material transport unit 50 in the paper transport direction. A type having a heater inside the roller, a belt fixing device that runs a heated belt, a fixing device that employs induction heating as a heating method, and the like can be employed. In order to make the color and glossiness of the images on both sides of the paper the same, the material, hardness, surface properties, etc. of the fixing roller and fixing belt are made equal. Further, the fixing condition is controlled by a full-color and monochrome image, or single-sided or double-sided, or is controlled by a control unit (not shown) so as to obtain an optimal fixing condition according to the type of paper. A cooling roller pair 70 having a cooling function is provided in the conveyance path after fixing in order to cool the sheet after fixing and stabilize the unstable toner state at an early stage. A heat pipe structure roller having a heat radiating portion can be employed. The cooled sheet is discharged and stacked by a discharge roller pair 71 on a discharge stack unit 75 provided on the left side of the image forming apparatus 100. The discharge stacking unit employs a mechanism in which a receiving member moves up and down according to a stack level by an elevator mechanism (not shown) so that a large amount of sheets can be stacked. It is also possible to pass the paper through the paper discharge stack unit 75 and transport the paper toward another post-processing apparatus. Another post-processing apparatus is an apparatus for bookbinding such as punching, cutting, folding, and binding.

  The cartridges 86Y, 86C, 86M, and 86K for each color in which the developer including the unused carrier is stored are detachably stored in the storage space 86. A developer conveying means (not shown) supplies the developer to each developing device as necessary. In the configuration of this embodiment, the cartridge is common to the image forming units 80 and 81 arranged above and below, but they can be separated. The black toner cartridge 86K that is highly consumed can have a particularly large capacity. The storage space 86 is on the back side when viewed from the operation direction on the upper surface of the image forming apparatus, and a plane portion is secured on the front side of the upper surface of the image forming apparatus, so that it can be used as a work table.

The operation will be described below.
<Single-sided recording operation>
The operation at the time of single-sided recording in which a full color image is formed on one side of the paper P in the above configuration will be described. There are basically two types of single-sided recording methods that can be selected. One of the two types is a method of directly transferring an image carried on the first image carrying belt 21 to one side of the paper, and the other method is an image carried on the second image carrying belt 31. Is directly transferred onto one side of the paper. In the present embodiment, because of the configuration of the image forming apparatus 100, when an image carried on the first image carrying belt 21 is directly transferred to one side of the paper, the image is placed on the upper surface of the paper and the second image carrying belt. When the image carried on 31 is directly transferred to one side of the paper, the image is formed on the lower surface of the paper. In the case where the data to be recorded is a plurality of pages, it is convenient to control the image forming order so that the pages are aligned on the paper discharge stack unit 75. An explanation will be given of a method in which an image is carried on the first image carrying belt 21 and then transferred to a sheet so that the pages are arranged in order from the image data of the last page.

  When the image forming apparatus 100 is operated, the photoreceptors 1Y, 1C, 1M, and 1K in the first image carrying belt 21 and the first image forming units 80Y to 80K rotate. At the same time, the second image carrier belt 31 rotates. However, the photoreceptors 1Y, 1C, 1M, and 1K in the second image forming units 81Y to 81K are separated from the second image carrier belt 31 and are not rotated. Is done. First, image formation by the image forming unit 80Y is started. By the operation of the exposure device 4 composed of an LED (light emitting diode) array and an imaging element, light corresponding to image data for yellow emitted from the LED is irradiated onto the surface of the photoreceptor 1Y uniformly charged by the charging device 3. Thus, an electrostatic latent image is formed.

  The electrostatic latent image is developed with yellow toner by the developing roller 5 to become a visible image electrostatically on the first image carrying belt 21 that moves in synchronization with the photoreceptor 1Y by the transfer action of the primary transfer roller 22. Primary transfer is performed. Such latent image formation, development, and primary transfer operations are sequentially performed in the same manner on the photosensitive members 1C, 1M, and 1K.

  As a result, yellow, cyan, magenta, and black toner images are carried on the first image carrying belt 21 as sequentially overlapping full-color toner images, and are moved in the direction of the arrow together with the first image carrying belt 21. .

  At the same time, the paper P used for recording is fed out from the paper feed tray 40a or the paper feed cassettes 40b to 40d in the paper feed device 40 by one of the paper feed / separation means 41A to 41D for feeding the paper P. The pair 42B and 42C are conveyed to the recording material conveyance path 43C. Before the leading edge of the paper is picked up by the registration roller pair 45, the jogger 44 operates to push both sides of the paper from both lateral directions with respect to the paper conveyance direction, and the lateral alignment of the paper is not performed. I can be taken. The registration roller pair 45 is stationary, and the leading edge of the sheet is stationary while entering the nip of the registration roller pair 45, but the timing is set so that the position with the image on the first image carrier belt 21 is normal. Then, the registration roller pair 45 is rotated to convey the sheet to the transfer area.

  The full-color toner image on the first image carrying belt 21 is transferred to the upper surface of the paper P conveyed in synchronization with the first image carrying belt 21 by receiving a transfer action by the secondary transfer roller 46. The bias applied to the secondary transfer roller 46 has a positive polarity opposite to the charging polarity of the toner.

  Thereafter, the surface of the first image carrying belt 21 is cleaned by the belt cleaning device 20A. Further, foreign matters such as toner remaining on the surfaces of the photoreceptors 1Y, 1C, 1M, and 1K in the first image forming units 80Y to 80K that have finished the primary transfer are removed by the cleaning brush 85a and the cleaning blade 85b of the cleaning device 85, respectively. It is removed from the surface of the photoreceptor. The surface of each photoconductor is neutralized by a residual potential by the static eliminator Q to prepare for the next image formation / transfer process. The removed foreign matter such as toner is sent to the collection unit 87 by the collection unit 85c. Sensors S1 and S2 detect whether the surface potential after exposure on the surface of the photoconductor and the concentration of toner attached to the surface of the photoconductor after the development process are appropriate, and appropriately set image forming conditions. Information is sent to a control means (not shown) for control.

  The paper P onto which the toner image that has been superposed and carried on the image carrying belt 21 is transferred is transferred toward the fixing device 60 by the carrying belt 51 of the carrying device 50. The surface of the transfer belt 51 is charged in advance by a sheet suction charger 57 so that the sheet P can be reliably transferred together with the transport belt 51. The neutralization / separation charger 58 operates so that the paper P is separated from the transport belt 51 and is reliably sent to the fixing device 60.

  The toners of the respective colors superimposed on the paper P are subjected to the fixing action by the heat of the fixing device 60, and are melted and mixed to completely form a color image. Since toner is contained only on one side (upper surface) of the paper, less heat energy is required for fixing compared to double-sided recording having toner on both sides. A control means (not shown) optimally controls the power used by the fixing device according to the image. Until the fixed toner is completely fixed on the paper, it is rubbed by a guide member or the like on the conveyance path, and an image is lost or distorted. In order to prevent this problem, the cooling roller pair 70, which is a cooling means, operates to cool the toner and the paper. Thereafter, the paper is discharged by the paper discharge roller 71 onto the paper discharge stack 75 with the image surface facing upward. In the paper discharge stack section 75, the image forming order is programmed so that the recorded matter of the young pages is stacked so as to be sequentially stacked on top, so the page order is aligned. Since the paper discharge stack unit 75 is lowered as the number of discharged paper sheets increases, the paper sheets can be stacked in an orderly and reliable manner, and the page order is not disturbed. Instead of directly stacking the recorded paper on the paper discharge stack section 75, a punching process can be performed, or the paper can be conveyed to a post-processing device such as a sorter, a collator, a binding device, or a folding device.

  In another method of forming an image on one side of the paper P, image formation is performed in order from the image data of young pages in order not to form an image in the first image forming units 80Y to 80K and for page alignment. However, the details are omitted because it is basically the same as the one-side recording process.

<Operation during duplex recording>
Next, the operation at the time of double-sided recording in which images are formed on both sides of the paper P will be described. When a start signal is input to the image forming apparatus, an image for each color sequentially formed by the first image forming units 80Y, 80C, 80M, and 80K described in the single-sided recording operation is displayed on the first image carrying belt 21. The image for each color sequentially formed by the second image forming units 81Y, 81C, 81M, and 81K is applied to the second image carrying belt 31a substantially in parallel with the step of carrying out the primary transfer sequentially and carrying it as the first image. A step of sequentially performing primary transfer and carrying as a second image is performed. Since the configuration shown in FIG. 1 is used, in order for the first image and the second image to coincide with each other at the front end in the sheet conveyance direction, the second image is formed after the start of the first image formation. Is started. Further, since the sheet is stopped and retransmitted by the registration roller pair 45, the sheet is fed in consideration of the time and is aligned by the jogger 44. The registration roller pair 45 transports the sheet to a first transfer station constituted by a transfer roller 46 as a first secondary transfer unit and the first image carrying belt 21 at a timing. A transfer current having a positive polarity is applied to the transfer roller 46, and the image is transferred from the first image carrying belt to one side (upper surface in the drawing) of the paper P.

  Thus, the sheet P having an image on one side is continuously sent to the second transfer station having the transfer charger 47 as the second secondary transfer means by the transfer action of the transfer roller 46. Then, by applying a positive transfer current to the charger, the full-color second image previously carried on the second image carrying belt 31a is transferred to the lower surface of the paper P in a lump.

  The paper P on which the full color toner images are transferred on both sides in this way is transported to the fixing device 60 by the transport belt 51. The surface of the transport belt 51 is charged with the same negative polarity as the polarity of the toner by the suction charger. The unfixed toner on the lower surface of the paper is prevented from transferring to the belt. An alternating current is applied to the charge removal / separation charger 58, and the sheet is separated from the belt 51 and transferred to the fixing device 60. The toner images on both sides of the sheet are melted and mixed in response to a fixing process by heat of the fixing device 60. The sheet subsequently passes through the cooling roller pair and is discharged onto the discharge stack unit 75 by the discharge roller 71.

  When double-sided recording is performed on a plurality of pages of paper, the image formation order is controlled so that the image of a young page becomes the bottom surface and is stacked on the paper discharge stack unit 75. The order of the pages is 1 page in order from the top, 2 pages on the back, 3 pages on the second sheet, and 4 pages on the back. Such control of image forming sequence and control such as increasing the power input to the fixing device compared to the one-side recording are executed by a control means (not shown). As for the single-sided recording and the double-sided recording operation, an example in which full-color recording is executed has been described, but monochrome recording using only black toner is also possible.

  Next, Example 4 is shown in FIG. This is a so-called tandem configuration, which is a color system that forms an image on only one side at a time with respect to FIG. A schematic configuration is shown below.

  The color image forming apparatus shown in FIG. 10 is a so-called tandem system, and has a configuration in which process cartridges PU for each color are arranged in series. The process cartridge PU for each color includes a charging device 2, a developing device 4, a cleaning device 96, and the like centering on the photoreceptor 1. Further, an exposure device 3 and a first image carrier belt 21 of an intermediate transfer device are arranged for the photosensitive member 1 of each process cartridge PU, and in addition, a paper transport unit, a paper transfer device 34a, a fixing device 60, and the like are provided. ing. In the present invention, a plurality of components such as the photosensitive member 1, the charging device 2, the developing device 4, and the cleaning device 96 described above are integrally coupled as a process cartridge PU. The process cartridge PU is configured to be detachable from an image forming apparatus main body such as a copying machine or a printer. Since these image forming operations are merely the absence of image formation on the back surface (second surface) in FIG. 8 described above, description thereof is omitted.

  Next, the characteristics of the developer used in the present invention will be described. The carrier preferably has a volume average particle size of 20 to 60 μm. By using a carrier having a small particle diameter having an average particle diameter of 60 μm or less, the amount of pumping can be reduced without reducing the developing ability, and the amount of developer circulating in the developing device can be reduced. In particular, since the amount of developer passing through the stress-regulating developer regulating member is reduced, it contributes to a longer life. Furthermore, since the magnetic brush in the development area becomes denser, further higher image quality and stability of image quality are achieved. If the average particle size of the carrier is larger than 60 μm, overflow tends to occur in the developer circulation portion, and stable agent circulation cannot be performed. On the other hand, if it is smaller than 20 μm, the carrier adheres to the photoreceptor or the carrier is likely to be scattered from the developing device. The average particle size of the carrier can be measured using a SRA type of a Microtrac particle size analyzer (Nikkiso Co., Ltd.) with a range setting of 0.7 [μm] or more and 125 [μm] or less.

  Next, toner characteristics will be described. Regarding the particle diameter, the volume average particle diameter of the toner is preferably 3 to 8 μm. By using a toner having a small particle size and a sharp particle size distribution, the gap between the toner particles is reduced, so that the necessary amount of toner can be reduced without impairing the color reproducibility. Therefore, density fluctuation in development can be reduced. Further, the stable reproducibility of a minute dot image of 600 dpi or more is improved, and a stable high image quality can be obtained for a long time. On the other hand, when the volume average particle diameter (D4) is less than 3 μm, phenomena such as a decrease in transfer efficiency and a decrease in blade cleaning properties tend to occur. When the volume average particle diameter (D4) exceeds 8 μm, the pile height of the image becomes large and it is difficult to suppress scattering of characters and lines. At the same time, the ratio (D4 / D1) of the weight average particle diameter (D4) to the number average particle diameter (D1) is preferably in the range of 1.00 to 1.30.

  The closer (D4 / D1) is to 1.00, the sharper the particle size distribution. With such a toner having a small particle size and a narrow particle size distribution, the toner charge amount distribution is uniform, a high-quality image with little background fogging can be obtained, and the electrostatic transfer method has a high transfer rate. can do.

  Next, a method for measuring the particle size distribution of toner particles will be described. Examples of the measuring device for the particle size distribution of toner particles by the Coulter counter method include Coulter Counter TA-II and Coulter Multisizer II (both manufactured by Coulter). The measurement method is described below.

  First, 0.1 to 5 ml of a surfactant (preferably alkylbenzene sulfonate) is added as a dispersant to 100 to 150 ml of an aqueous electrolytic solution. Here, the electrolytic solution is prepared by preparing an about 1% NaCl aqueous solution using primary sodium chloride, and for example, ISOTON-II (manufactured by Coulter) can be used. Here, 2 to 20 mg of a measurement sample is further added. The electrolytic solution in which the sample is suspended is subjected to a dispersion treatment with an ultrasonic disperser for about 1 to 3 minutes, and the measuring device is used to measure the volume and number of toner particles or toner using a 100 μm aperture as an aperture. Volume distribution and number distribution are calculated. From the obtained distribution, the weight average particle diameter (D4) and the number average particle diameter (D1) of the toner can be obtained.

  As channels, 2.00 to less than 2.52 μm; 2.52 to less than 3.17 μm; 3.17 to less than 4.00 μm; 4.00 to less than 5.04 μm; 5.04 to less than 6.35 μm; 6 Less than 35 to 8.00 μm; less than 8.00 to less than 10.08 μm; less than 10.08 to less than 12.70 μm; less than 12.70 to less than 16.00 μm; less than 16.00 to less than 20.20 μm; Uses 13 channels of less than 40 μm; 25.40 to less than 32.00 μm; 32.00 to less than 40.30 μm, and targets particles having a particle size of 2.00 μm to less than 40.30 μm.

The toner shape factor SF-1 is preferably in the range of 100 to 180, and the shape factor SF-2 is preferably in the range of 100 to 180. 11 and 12 are diagrams schematically showing the shape of the toner in order to explain the shape factor SF-1 and the shape factor SF-2. The shape factor SF-1 indicates the ratio of the roundness of the toner shape and is represented by the following formula (1). This is a value obtained by dividing the square of the maximum length MXLNG of the shape formed by projecting the toner on a two-dimensional plane by the figure area AREA and multiplying by 100π / 4. That is,
SF-1 = {(MXLNG) ² / AREA} × (100π / 4)
It can be expressed. When the value of SF-1 is 100, the shape of the toner becomes a true sphere, and becomes larger as the value of SF-1 increases.

The shape factor SF-2 indicates the ratio of the unevenness of the toner shape, and is represented by the following formula. A value obtained by dividing the square of the perimeter PERI of the figure formed by projecting the toner onto the two-dimensional plane by the figure area AREA and multiplying by 100 / 4π. That is,
SF-2 = {(PERI) ² / AREA} × (100 / 4π)
It can be expressed. When the value of SF-2 is 100, there is no unevenness on the toner surface, and as the value of SF-2 increases, the unevenness of the toner surface becomes more prominent.

  Specifically, the shape factor is measured by taking a photograph of the toner with a scanning electron microscope (S-800: manufactured by Hitachi, Ltd.), introducing it into an image analyzer (LUSEX 3: manufactured by Nireco) and analyzing it. Can be calculated.

  When the shape of the toner is close to a sphere, the contact state between the toners becomes a point contact, so that the attractive force between the toners is weakened and the fluidity is increased. Therefore, since the circulatory property of the agent is improved, the stress is reduced, and it becomes possible to perform a stable unidirectional circulation for a long time. In addition, since the contact state between the toner and the photoconductor is a point contact, the attractive force between the toner and the photoconductor is weakened, and the transfer rate is increased, contributing to the improvement in image quality. On the other hand, if any of the shape factors SF-1 and SF-2 exceeds 180, the fluidity is deteriorated and the agent circulation property is poor. Further, the transfer rate is lowered, which is not preferable.

In the toner of the present invention, fine particles (hereinafter, simply referred to as fine particles) having an average primary particle diameter of 50 to 500 nm and a bulk density of 0.3 mg / cm ³ or more are adhered to the toner particle surface. In addition, although silica etc. are often used for a normal fluid improvement agent, for example, the average primary particle diameter of this silica is 10-30 nm normally, and a bulk density is 0.1-0.2 mg / cm < ³ >.

  In the present invention, since fine particles having appropriate characteristics are present on the surface of the toner, an appropriate gap is formed between the toner particles and the object. Further, the fine particles have a very small contact area with the toner particles, the photoconductor, and the charge imparting member and are evenly contacted with each other. Moreover, since the fluidity of the developer is increased, it has an effect of reducing stress and contributes to a longer life. Furthermore, since it plays the role of a roller, it is difficult to be buried in toner particles even during cleaning under high stress (high load, high speed, etc.) between the cleaning blade and the photoconductor without wearing or damaging the photoconductor. Or, even if it is buried a little, it can be detached and returned, so that stable characteristics can be obtained over a long period of time. Further, the toner is moderately detached from the surface of the toner and accumulated at the tip of the cleaning blade, and the so-called dam effect has an effect of preventing a phenomenon that the toner passes from the blade. Since these characteristics have an effect of reducing the share received by the toner particles, the filming effect of the toner itself due to the low rheological component contained in the toner is exhibited for high-speed fixing (low energy fixing). In addition, when fine particles having an average primary particle size in the range of 50 to 500 μm are used, the excellent cleaning performance can be fully utilized, and since the particle size is extremely small, the powder fluidity of the toner is improved. There is no reduction. Further, although the details are not clear, even if the surface-treated fine particles are externally added to the toner or the carrier is contaminated, the degree of developer deterioration is small. Accordingly, since the change in toner fluidity and chargeability with time is small, the developer can be circulated stably over a long period of time. Also, the stability of image quality is increased.

  The average primary particle size (hereinafter referred to as the average particle size) of the fine particles is 50 to 500 nm, and particularly preferably 100 to 400 nm. If the thickness is less than 50 nm, the fine particles may be buried in the concave and convex portions on the toner surface to lower the role of the rollers. On the other hand, when the particle size is larger than 500 μm, when the fine particles are located between the blade and the surface of the photosensitive member, the order is the same level as the contact area of the toner itself, and the toner particles to be cleaned pass, that is, defective cleaning occurs. It becomes easy.

When the bulk density is less than 0.3 mg / cm ³ , although there is a contribution to the improvement of fluidity, the scattering property and adhesion of the toner and fine particles become high, so the effect as a toner and a roller, and the accumulation in the cleaning unit. As a result, the so-called dam effect that prevents toner cleaning failure is reduced.

In the fine particles of the present invention, the inorganic compounds include SiO ₂ , TiO ₂ , Al ₂ O ₃ , MgO, CuO, ZnO, SnO ₂ , CeO ₂ , Fe ₂ O ₃ , BaO, CaO, K ₂ O, Na ₂ O. , ZrO ₂ , CaO · SiO ₂ , K ₂ O (TiO ₂ ) n, Al ₂ O ₃ · 2SiO ₂ , CaCO ₃ , MgCO ₃ , BaSO ₄ , MgSO ₄ , SrTiO _{3 and the} like, preferably , SiO ₂ , TiO ₂ , Al ₂ O ₃ . In particular, these inorganic compounds may be hydrophobized with various coupling agents, hexamethyldisilazane, dimethyldichlorosilane, octyltrimethoxysilane, and the like.

  The organic compound fine particles may be a thermoplastic resin or a thermosetting resin. For example, vinyl resin, polyurethane resin, epoxy resin, polyester resin, polyamide resin, polyimide resin, silicon resin, phenol resin, melamine resin, Examples include urea resins, aniline resins, ionomer resins, and polycarbonate resins. As the resin fine particles, two or more of the above resins may be used in combination. Of these, vinyl resins, polyurethane resins, epoxy resins, polyester resins, and combinations thereof are preferred because an aqueous dispersion of fine spherical resin particles is easily obtained.

  Specific examples of vinyl resins include polymers obtained by homopolymerization or copolymerization of vinyl monomers, such as styrene- (meth) acrylic acid ester copolymers, styrene-butadiene copolymers, (meth) acrylic acid. -Acrylic ester copolymer, styrene-acrylonitrile copolymer, styrene-maleic anhydride copolymer, styrene- (meth) acrylic acid copolymer, and the like.

The bulk density of the fine particles was measured by the following method. Using a 100 ml graduated cylinder, fine particles were gradually added to make 100 ml. At that time, no vibration was applied. The bulk density was measured by the difference in weight before and after placing the fine particles of the graduated cylinder.
Bulk density (g / cm ³ ) = fine particle amount (g / 100 ml) ÷ 100

  The fine particles of the present invention can be externally added and adhered to the toner surface by mechanically mixing and adhering the toner base particles and fine particles using various known mixing devices, or in the liquid phase. There is a method in which the base particles and the fine particles are uniformly dispersed with a surfactant or the like, and are dried after the adhesion treatment.

  Here, continuous durability evaluation of 50,000 sheets was performed with an image forming apparatus equipped with a one-way circulation type developing device using a developing roller having a developing magnetic pole as shown in the table of FIG. The photosensitive member linear velocity of this image forming apparatus is 500 mm / s. FIG. 13 shows the results of ranking the initial white background, roughness, background stain, and image density deviation after printing 50,000 sheets as evaluation contents. The best level is 5, level 1 where the abnormality is conspicuous, and 3 in between. In addition, the overall evaluation is represented by ◎ when the sum of the ranks of image blank, roughness, background stain, and image density deviation is 17 or more, ◯ when 12 or more, and × when less than 12.

  In the initial image, as the half width of the main magnetic pole increases, the degree of white spots and roughness tends to deteriorate. In the image after 50,000 sheets, No. At the level of 1, the background dirt and density deviation are also worsened. This is considered to be because the chargeability of the developer is lowered due to the deterioration of the developer.

The figure which shows the image development apparatus of 1st Example of this invention. Perspective view from the photosensitive drum side of each conveyance path and each auger configured by the lower casing Diagram showing development roller and development magnetic pole Diagram showing magnetic distribution and magnitude of developing roller in developing device It is a figure which shows the modification of the Example of FIG. The figure which shows the other implementation structure of a developing device. The figure which shows the other implementation structure of a developing device. 1 is a schematic central sectional view showing an internal configuration of an image forming apparatus to which the present invention is applied; Enlarged view of the charger part of the apparatus of FIG. The figure which shows the image forming apparatus which concerns on the 4th Example of this invention. The figure shown about shape factor SF-1 Diagram showing shape factor SF-2 The figure which shows the result of having performed the durability evaluation of 50,000 sheets continuously in the image forming apparatus equipped with the one-way circulation type developing device using the developing roller of the developing magnetic pole The figure which shows the developing device of a biaxial conveyance type Diagram showing developing device of one-way circulation system (3-axis configuration) The figure which shows the image development apparatus which the 3rd screw auger carries out stirring conveyance by being shielded by the partition which the developer currently carrying out stirring conveyance of the other screw auger does not mix The figure which shows the image development apparatus which has two stirring chambers connected in the width direction of the image formed, and circulates and conveys a developer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging apparatus 3 Exposure apparatus 4 Developing apparatus 5 Developing roller 5a Magnet roller body (magnet roller)
6 Recovery screw 6a, 6b Partition plate 7 Recovery transfer path 8 Supply screw 8a Transfer part position 9 Supply transfer path 10 Stirring transfer path 11 Stirring transfer screw 11a Transfer screw part 11b Transfer paddle 11c Reverse screw 12 Lower casing 13 Upper casing 16 Developer regulating member 18 Surplus developer collecting member 19 Heat radiating member 20 Fin 20A Cleaning device 21 First image carrier belt 21A Guide portion 22A Developer capturing roller 23 to 29 Roller 23A Scraper 28 Heat radiating fin 30 Second image carrier unit 30A Cleaning device 31 Second image carrier belt 31a Second image carrier belt 32 Primary transfer roller 33-38 roller 34a Paper transfer device 40 Paper feed device 40a Paper feed tray 40b-40d Paper feed cassette 41 Developing roller 41A- 41D Paper feeding / separating means 42B, 42C Conveying roller pair 43 Developing sleeves 43A, 43B, 43C Recording member conveying path 44 Jogger 45 Registration roller pair 46 Secondary transfer roller 47 Transfer charger 50 Recording member conveying means 50A Cleaning device 51 Conveying belt 52 ˜56 roller 57 suction charger 58 static elimination / separation charger 60 fixing device 70 cooling roller pair 71 paper discharge roller pair 75 paper discharge stack unit 80Y, 80C, 80M, 80K first image forming unit 81Y, 81C, 81M, 81K second Image forming unit 85 Cleaning device 85a Cleaning brush 85b Cleaning blade 85c Collection member 86 Storage space 86Y, 86C, 86M, 86K Cartridge 94 Developer supply port 95 Agent drop port 96 Cleaning device 1 00 Image forming apparatus body PU Process cartridge Q Photostatic discharger S1 Potential sensor S2 Image sensor P Paper P1b Development main magnet P1a, P1c Main magnetic pole magnetic force forming auxiliary magnet P3-P6 Magnet

Claims (15)

A non-magnetic sleeve that carries and conveys a developer composed of toner and a carrier as a magnetic brush, and a developer carrier comprising a magnet roller fixedly disposed in the non-magnetic sleeve;
A first conveying path having a first screw for agitating and conveying the developer along the axial direction of the developer carrying body and supplying the developer to the developer carrying body;
A second conveyance path having a second screw for collecting the developer after completion of development from the developer carrier and conveying the collected developer in parallel and in the same direction as the first screw;
Received the supply of surplus developer that was not supplied to the developer carrier from the first transport path 9 and the recovered developer from the second transport path via the first transport path, A third screw having a third screw that stirs and conveys the first screw in a direction opposite to the first screw, and that circulates and supplies the developer obtained by stirring the surplus developer and the recovered developer to the first conveyance path; Road,
A developing device comprising a developer regulating member that regulates a height of a developer layer supplied to the developer carrying body from the first transport path so as to face the developer carrying body,
2. A developing apparatus according to claim 1, wherein a decay rate of a magnetic flux density in a normal direction of a main magnetic pole as a developing magnetic pole in a developing nip region in which the magnetic brush is rubbed against the latent image carrier is 40% or more. A non-magnetic sleeve that carries and conveys a developer composed of toner and a carrier as a magnetic brush, and a developer carrier composed of a magnet roller fixedly disposed in the sleeve;
A first conveying path having a first screw for agitating and conveying the developer along the axial direction of the developer carrying body and supplying the developer to the developer carrying body;
A second conveyance path having a second screw for collecting the developer after completion of development from the developer carrier and conveying the collected developer in parallel and in the same direction as the first screw;
The supply of surplus developer that has not been supplied from the first transport path to the developer carrier and the recovered developer from the second transport path via the first transport path, A third conveyance path having a third screw that stirs and conveys the first screw in a direction opposite to the first screw, and that circulates the developer that has agitated the excess developer and the recovered developer into the first conveyance path; When,
A developing device comprising a developer regulating member that regulates a height of a developer layer supplied to the developer carrying body from the first transport path so as to face the developer carrying body,
2. A developing device according to claim 1, wherein a half width of a main magnetic pole as a developing magnetic pole in a developing nip region where the magnetic brush is slid against the latent image carrier is 22 degrees or less. 3. The developing device according to claim 1 or 2, further comprising an auxiliary magnet that assists in forming a magnetic force of a main magnetic pole that is a developing magnetic pole in a developing nip region in which the magnetic brush is rubbed against the latent image carrier. Development device. 4. The developing device according to claim 3, wherein the auxiliary magnets are arranged on the upstream side and the downstream side in the developer transport direction of the main magnet formed by the main magnetic pole. 5. The developing device according to claim 3, wherein the main magnetic pole and the auxiliary magnetic pole have different polarities. 6. The developing device according to claim 1, wherein the magnet forming the main magnetic pole is made of a rare earth metal alloy. 7. The developing device according to claim 1, wherein each of the transport paths is arranged substantially horizontally. 7. The developing device according to claim 1, wherein the first transport path 9 is disposed below the second transport path 7. 7. 9. The developing device according to claim 1, wherein the developing bias, which is a voltage waveform applied to the developer carrying member, is an AC bias in which an alternating current component is superimposed on a direct current component. An image forming apparatus comprising: an image carrier on which an electrostatic latent image is formed; and a plurality of developing devices according to claim 1, wherein a color image can be formed on a recording material. 11. The image forming apparatus according to claim 10, wherein the first toner image transferred to the first surface of the recording material has at least a developing device and a photoconductor for each color (C, M, Y, K). Formed by a first image station comprising an image forming unit group and a first toner image carrying belt on which a first toner image formed by the first image forming unit group is transferred and carried;
The second toner image transferred to the second surface of the recording material includes a second image forming unit group having at least a developing device and a photoreceptor for each color (C, M, Y, K) and the second image. Formed by a second image station comprising a second toner image carrying belt on which a second toner image formed by the forming unit group is transferred and carried;
2. An image forming apparatus according to claim 1, wherein the first toner image and the second toner image are transferred onto a paper sheet simultaneously or sequentially before fixing. A carrier for use in the developing device according to any one of claims 1 to 9 or the image forming device according to any one of claims 10 to 12, wherein the carrier has a volume average particle diameter of 20 to 60 µm. A toner used in the developing device according to any one of claims 1 to 9 or the image forming device according to any one of claims 10 to 12, wherein the volume average particle size is 3 to 8 µm, and the volume average particle size (D4) is A toner having a ratio (D4 / D1) to a number average particle diameter (D1) in the range of 1.00 to 1.40. The toner used in the developing device according to any one of claims 1 to 9 or the image forming device according to any one of claims 10 to 13, wherein the shape factor SF-1 is in the range of 100 to 180, and the shape factor SF- 2 is in the range of 100 to 180. A toner for use in the developing device according to any one of claims 1 to 9 or the image forming device according to any one of claims 10 to 14, wherein an average primary particle size is 50 to 500 nm and a bulk density on the surface of the toner base particles. A toner in which fine particles of 0.3 g / cm ³ or more are externally added.