JP2013114150A - Developing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide means capable of improving a recovery efficiency when recovering a carrier attached to an image carrier by a carrier recovery roller.SOLUTION: A first developer carrier 5 in an uppermost stream side in a rotating direction G of an image carrier 1, which has multistage developer carriers disposed facing the image carrier 1 includes rotatable first developer support means 81, and first magnetic field generating means 82 included in the first developer support means. A second developer carrier 91 in a downmost stream side includes rotatable second developer support means 90 and fixed second magnetic field generating means 93 that is included in the second developer support means 90. The second magnetic field generating means 93 has magnetic poles at positions where the image carrier 1 and the second developer carrier 91 are contiguous, and ears of the developer come into contact with a latent image carrier 1.

Description

  The present invention relates to a developing device and an image forming apparatus such as a copying machine, a facsimile, a printer, a plotter, and a multifunction machine using the developing device.

  In an image forming apparatus such as a developing device and a copying machine, a facsimile, a printer, a plotter, and a multifunction machine using the developing device, an electrostatic latent image formed on a photosensitive member as a latent image carrier is developed by the developing device. A recording output can be obtained by visualizing the image and transferring the visible image to a sheet or the like.

  As a developer used for development, there is a two-component developer obtained by mixing a toner and a carrier in addition to a one-component developer containing only magnetic or non-magnetic toner. The two-component developer is composed of a toner and a carrier that carries the toner, and the toner can be electrostatically attracted to the electrostatic latent image on the photosensitive member by charging the toner by a frictional charging effect that occurs during stirring and mixing. To be.

  In the developing device, a developing sleeve as a developer carrying member for supplying developer toward the electrostatic latent image on the photosensitive member by causing the developer to rise on the peripheral surface by magnetic force, and agitating and mixing the developing sleeve A configuration including a stirring member such as a screw auger for supplying a developer is known.

<Prior Art 1>
In Patent Document 1, as a developing device, a developing roller is provided with a magnet roller, and the developing roller is rotated at high speed to convey the developer while stirring, and development is performed multiple times in the developing region. Have been proposed that also improve the charging efficiency.

  In the developing device disclosed in Patent Document 1, an even number of magnetic poles having different polarities are arranged on a magnet roller, and the magnet roller decenters its cross-sectional center in a direction approaching the photosensitive member with respect to the cross-sectional center of the developing roller. Are arranged. For this reason, since the developer once developed is separated, it is transported again to the development area, so that there is no shortage of image density. However, in this type of developing device, the magnetic brush rotates strongly on the developing roller due to the rotation of the magnet roller, the carrier is scattered by the centrifugal force, and the carrier adhering to the photosensitive member becomes a more serious problem.

  As a countermeasure, for example, as a means for recovering the carrier, when the conventional carrier recovery roller is arranged in the vicinity of the photosensitive member and the developing roller, the alternating magnetic field of the magnet roller interferes with the magnetic field of the carrier recovery roller, and suction and repulsion occur. Repeatedly generates a lot of vibration. This vibration propagates to the photoreceptor and the exposure apparatus, and generates a banding image. In addition, noise may be generated, the life of the developing device may be shortened, and the developer may overflow due to magnetic field interference.

  Although these problems can be improved by reducing the magnetic field of the carrier recovery roller, if the magnetic field of the carrier recovery roller is reduced, the carrier recovery efficiency is lowered.

  a: Therefore, when the carrier recovery roller is arranged at a position sufficiently away from the developing roller without reducing the magnetic field of the carrier recovery roller, the problem of the carrier recovery efficiency is improved, but the image forming apparatus is enlarged, A complicated mechanism is required to return the collected carrier to the developing device. When the collected carriers are not collected in the carrier reservoir and returned to the developing device, the number of carriers in the developing device gradually decreases.

  b: If the electrostatic force is increased to recover the carrier by the carrier recovery roller, the toner image on the photoreceptor is disturbed.

  c: The carrier can be recovered by sufficiently increasing the magnetic force of the carrier recovery magnetic pole. However, the carrier collected on the carrier collecting roller cannot be conveyed and a rubbing image is generated. This rubbing image is generated because the carrier slips and accumulates when the surface of the carrier recovery roller is smooth and the magnetic force of the carrier recovery magnetic pole is high. In order to avoid this, it is only necessary to bring the tip of a thin scraper having elasticity into contact with the carrier recovery roller and to peel the carrier from the carrier recovery roller. For this purpose, it is necessary to smooth the surface of the carrier recovery roller. Yes, increase manufacturing costs.

  d: On the other hand, a carrier recovery roller has also been proposed in which a groove is formed on the surface of the carrier recovery roller to improve carrier transportability. However, as described above, it is difficult to completely remove the carrier due to the restriction that the use of the scraper is accompanied by the smoothing of the surface of the carrier recovery roller, and as a result, the carrier rotates with the rotation of the carrier recovery roller, and again When reaching the vicinity of the carrier recovery magnetic pole, spikes may occur, and a rubbing image may be generated by rubbing the toner image on the photoreceptor.

<Conventional technology 2>
In Patent Document 2, as a developing device, in the developing device that rotates the developing sleeve (71) and the magnetic roller (72), a carrier recovery roller (76) is provided in the vicinity of the developing sleeve (71) in order to remove the adverse effects caused by carrier adhesion. ), A rotatable magnetic roller (77) is housed inside the carrier recovery roller (76), and the developing device is disclosed in which the magnetic roller (77) rotates synchronously with the magnetic force of the magnetic roller (72).

  However, in this configuration, a great amount of vibration is generated by the magnetic field interference between the magnetic roller (77) and the magnetic roller (72), and various problems due to the magnetic field interference (vibration propagates to the photoconductor and the exposure apparatus to form a banding image. Noise generated, the life of the developing device decreased, the developer overflowed, etc.) cannot be solved.

  The tip of the scraper (78) is in pressure contact with the outer peripheral surface of the carrier recovery roller (76) disposed adjacent to the developing sleeve (71). The carrier captured on the outer peripheral surface of the carrier recovery roller (76) is conveyed by the synchronous rotation of the magnetic roller (77) and scraped off by the scraper (78). However, if the magnetic force of the collecting roller is sufficiently increased, it becomes difficult to scrape the carrier with the scraper (78), and the carrier rolls with the rotation of the carrier collecting roller, and the spikes appear when it reaches the vicinity of the carrier collecting magnetic pole again. There is a risk of generating a rubbing image by rubbing the toner image on the photosensitive member.

  The present invention has been made in view of the above problems in the prior art, and it is an object of the present invention to provide means capable of increasing the collection efficiency when a carrier attached to an image carrier is collected by a carrier collection roller.

In order to achieve the object, the present invention has the following configuration.
(1): The first means of the present invention is a development provided with a developer carrier for supplying a two-component developer containing toner and carrier to the electrostatic latent image formed on the image carrier. A device,
A plurality of developer carriers disposed opposite to the image carrier;
Of the plurality of stages of developer carriers, the first developer carrier on the most upstream side in the rotational direction of the image carrier includes a rotatable first developer support means, and the first developer support means. A first magnetic field generating means capable of rotating provided with a magnetic pole for raising and transporting the developer;
Of the plurality of stages of developer carriers, a second developer carrier located on the most downstream side in the rotation direction of the image carrier is provided with a rotatable second developer support means and a second developer support means. A second magnetic field generating means included and fixed;
The second magnetic field generating means includes a magnetic pole at a position close to the image carrier and the second developer carrier, and the developer ears are in contact with the latent image carrier.
Since the magnetic brush of the downstream developing roller (collection roller) as the second developer carrier is in contact with the photoconductor as the image carrier, the image is carried by the developing roller as the upstream first developer carrier. The carrier adhering to the photoconductor (photosensitive member) can be collected without omission from the collecting roller to increase the collecting rate. In the embodiment, a two-stage developing roller is shown. However, the invention is not limited to this, and a multi-stage developing roller may be used. If the lowermost roller is a collecting roller, the same technical advantage can be obtained. to go into.
(2): The second means of the present invention is the developing device according to (1),
The second magnetic field generating means does not have a magnetic pole at a position facing the first developer carrier,
The second developer support means is rotated in a direction that is opposite to the image carrier. Since the second developer support means and the image carrier rotate in the same direction, they pass each other on the opposing surface.
By making the downstream developing roller (collecting roller) counter-rotate, there is no need to place a magnetic pole in the vicinity of the so-called mag-sleeve rotating roller that is the upstream first developer carrier (developing roller 5), and vibration due to magnetic field interference. It is possible to adhere and collect the carrier adhering to the photosensitive member again without causing any trouble.
(3): The third means of the present invention is the developing device according to (1) or (2),
The first magnetic field generating means is rotatable in the direction opposite to the first developer carrier.
By rotating the developer supporting means and the magnetic field generating means in the relative direction, the developer is agitated during conveyance, and development efficiency and charging efficiency are further increased.
(4): The fourth means of the present invention is the developing device according to any one of (1) to (3),
The first magnetic field generating means is disposed with its own cross-sectional center decentered in a direction approaching the image carrier relative to the cross-sectional center of the first developer carrier.
The eccentric arrangement facilitates separation of the developer from the upstream first developer carrier (mag sleeve double-rotating roller). In addition, since vibrations due to magnetic field interference between the upper and lower rollers can be further reduced, there is a margin in the magnetic field waveform of the lower roller.
(5): A fifth means of the present invention is that the image forming apparatus includes the developing device according to any one of (1) to (4).
(6): The sixth means of the present invention is the image forming apparatus according to (5), wherein at least the developing device and the image carrier are collectively contained in a process cartridge.

  In the present invention, when the carrier adhering to the image carrier is collected by the carrier collection roller as the second developer carrier, the collection efficiency can be increased as compared with the prior art.

1 is a diagram illustrating a schematic configuration of an image forming apparatus. FIG. 2 is an enlarged view of a cross section at a substantially central portion in a longitudinal direction of a developing device and a photosensitive member constituting a process cartridge. FIG. 10 is a partial perspective view illustrating a developer conveyance path in the developing device. 1 is an external perspective view of a developing device. FIG. 4 is an enlarged view illustrating a developer conveyance path around a photosensitive member, a developing roller, a carrier recovery roller, and a supply screw in FIG. 3. FIG. 6 is a diagram illustrating a state of a developer around a photoconductor, a developing roller, and a carrier recovery roller in FIG. 5.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified thru | or abbreviate | omitted suitably.

The configuration and operation of the present invention will be described with reference to examples.
In addition, the following description is an example and does not limit a claim.
It is easy for those skilled in the art to make other embodiments by making changes and modifications within the scope of the claims of the present invention, but these changes and modifications are naturally included in the scope of the claims.

[Image forming equipment]
In FIG. 1, a copying machine 500 as an image forming apparatus is roughly divided into a printer unit 100 in the middle in the vertical direction, a paper feeding device 200 below the printer unit 100, a scanner 300 and the like above the printer unit 100. Each has a fixed configuration. An automatic document feeder 400 is fixed on the scanner 300.

  The printer unit 100 includes an image forming unit including four sets of process cartridges 18Y, 18M, 18C, and 18K for forming images of each color of yellow (Y), magenta (M), cyan (C), and black (K). It has.

  Y, M, C, and K added after the numerals of the process cartridges 18Y, 18M, 18C, and 18K indicate members for yellow, magenta, cyan, and black (the same applies hereinafter). In addition to the process cartridges 18Y, 18M, 18C, and 18K, an optical writing unit 21, an intermediate transfer unit 17, a secondary transfer device 22, a resist roller pair 49, a belt fixing type fixing device 25, and the like are disposed. .

  The optical writing unit 21 has a light source (not shown), a polygon mirror, an f-θ lens, a reflecting mirror, and the like, and irradiates a laser beam Lb on the surface of a photoconductor described later based on image data. Each of the process cartridges 18Y, 18M, 18C, and 18K is configured as an integrated unit including devices necessary for image formation.

The yellow process cartridge 18Y will be described below.
The yellow process cartridge 18Y has a drum-shaped photoreceptor 1Y as an image carrier for carrying an electrostatic latent image and a toner image, a charger 2Y, a developing device 4Y, a drum cleaning device 28Y, a static eliminator, etc. The unit is configured to be detachable from the copying machine body as an integral unit. Similarly, the other process cartridges 18M, 18C, and 18K have photosensitive members 1M, 1C, and 1K, chargers 2M, 2C, and K, developing devices 4M, 4C, and 4K, drum cleaning devices 28M, 28C, and 28K, and the like. Yes.

  As a process cartridge, if it is a unit configuration including at least a developing device and a photosensitive member, the process cartridge can be attached to and detached from the copying machine main body, which is convenient for maintenance.

  The surface of the photoreceptor 1Y is uniformly charged by the charger 2Y serving as a charging means. The surface of the photoreceptor 1Y that has been subjected to the charging process is irradiated with a laser beam Lb that has been modulated and deflected by the optical writing unit 21. Thereby, the potential of the surface of the photoreceptor 1Y of the irradiation part (exposure part) is attenuated. Due to the attenuation of the surface potential, an electrostatic latent image for Y is formed on the surface of the photoreceptor 1Y. The formed electrostatic latent image for Y is developed by the developing device 4Y as developing means to become a Y toner image.

  The Y toner image formed on the Y photoconductor 1Y is primarily transferred to an intermediate transfer belt 110 described later. The surface of the photoreceptor 1Y after the primary transfer is cleaned of the transfer residual toner by a drum cleaning device.

  In the Y process cartridge 18Y, the photoreceptor 1Y cleaned by the drum cleaning device 28Y is discharged by the charge eliminator and returned to the initial state. The series of processes as described above is the same for the other process cartridges 18M, 18C, and 18K.

Next, the intermediate transfer unit 17 will be described.
The intermediate transfer unit 17 includes an intermediate transfer belt 110, a belt cleaning device 97, and the like. Further, it also includes a tension roller 14, a driving roller 15, a secondary transfer backup roller 16, four primary transfer bias rollers 62Y, 62M, 62C, and 62K.

  The intermediate transfer belt 110 is stretched by a plurality of rollers including the stretching roller 14. Then, it is rotated and moved endlessly in the clockwise direction in the figure by the rotation of the drive roller 15 driven by a belt drive motor (not shown).

  The four primary transfer bias rollers 62Y, 62M, 62C, and 62K are arranged so as to be in contact with the inner peripheral surface side of the intermediate transfer belt 110, respectively, and receive a primary transfer bias from a power source (not shown). Further, the intermediate transfer belt 110 is pressed toward the photoreceptors 1Y, 1M, 1C, and 1K from the inner peripheral surface side to form primary transfer nips. In each primary transfer nip, a primary transfer electric field is formed between the photoreceptor 1 and the primary transfer bias roller 62 due to the influence of the primary transfer bias.

  The above-described Y toner image formed on the Y photoreceptor 1Y is primarily transferred onto the intermediate transfer belt 110 by the action of the primary transfer electric field and nip pressure. On this Y toner image, the M, C, K toner images formed on the M, C, K photoconductors 1M, 1C, 1K are sequentially superimposed and primarily transferred. By this primary transfer of superposition, a four-color superposed toner image (hereinafter referred to as a four-color toner image) that is a multiple toner image is formed on the intermediate transfer belt 110.

  The four-color toner image superimposed and transferred on the intermediate transfer belt 110 is secondarily transferred to a transfer sheet (not shown) as a recording medium at a secondary transfer nip 22NP described later. Transfer residual toner remaining on the surface of the intermediate transfer belt 110 after passing through the secondary transfer nip 22NP is cleaned by a belt cleaning device 97 that sandwiches the belt with the driving roller 15 on the left side in the drawing.

The secondary transfer device 22 will be described.
In FIG. 1, a paper transport belt 24 is stretched by two stretch rollers 23 below the intermediate transfer unit 17. The paper conveying belt 24 is moved endlessly in the counterclockwise direction in the drawing in accordance with the rotational drive of at least one of the left and right stretching rollers 23 that stretch the paper conveying belt 24.

  Of the two stretching rollers 23, one stretching roller 23 arranged on the right side in the drawing is between the intermediate transfer belt 110 and the paper transport belt between the secondary transfer backup roller 16 of the intermediate transfer unit 17. A secondary transfer device 22 is configured with 24 interposed therebetween. By this sandwiching, a secondary transfer nip 22NP is formed in which the intermediate transfer belt 110 of the intermediate transfer unit 17 and the paper transport belt 24 of the secondary transfer device 22 come into contact with each other.

  Here, of the two stretching rollers 23 that support the paper conveying belt 24, one stretching roller, in this example, the right stretching roller 23 has a secondary transfer bias having a polarity opposite to that of the toner. Applied. By applying the secondary transfer bias, the four-color toner image on the intermediate transfer belt 110 of the intermediate transfer unit 17 is electrostatically moved from the belt side toward the one stretching roller 23 side in the secondary transfer nip 22NP. A secondary transfer electric field is formed.

  On the other hand, the transfer sheet fed toward the secondary transfer nip 22NP from the registration roller pair 49 in synchronization with the four-color toner image on the intermediate transfer belt 110 is affected by the electric field and nip pressure due to the secondary transfer bias. The received four-color toner image is secondarily transferred. Instead of the secondary transfer method in which the secondary transfer bias is applied to the stretching roller 23 as in the above example, a charger for charging the transfer paper in a non-contact manner may be provided.

  In the paper feeding device 200 provided at the lower part of the copying machine 500 main body, a plurality of paper feeding cassettes 44 in which a plurality of transfer sheets can be stacked and stored in a bundle of sheets are arranged so as to overlap each other in the vertical direction. It is installed. Each paper feed cassette 44 presses the paper feed roller 42 against the uppermost transfer paper in the paper bundle. Then, by rotating the paper feed roller 42, the uppermost transfer paper is sent out toward the paper feed path 48.

  The paper feed path 48 that receives the transfer paper fed from the paper feed cassette 44 has a plurality of conveying roller pairs 47 and a registration roller pair 49 provided near the end in the paper feed path 46. Then, the transfer paper is conveyed toward the registration roller pair 49. The transfer sheet conveyed toward the registration roller pair 49 is sandwiched between the rollers of the registration roller pair 49. On the other hand, in the intermediate transfer unit 17, the four-color toner image formed on the intermediate transfer belt 110 enters the secondary transfer nip 22NP along with the endless movement of the belt. The registration roller pair 49 sends out the transfer paper sandwiched between the rollers at a timing at which the transfer paper can be brought into close contact with the four-color toner image at the secondary transfer nip 22NP.

  Thereby, in the secondary transfer nip 22NP, the four-color toner image on the intermediate transfer belt 110 is in close contact with the transfer paper. Then, it is secondarily transferred onto the transfer paper and becomes a full color image on the white transfer paper. The transfer paper carrying the full-color image in this manner exits the secondary transfer nip 22NP as the paper transport belt 24 moves endlessly, and then is sent from the paper transport belt 24 to the fixing device 25.

  The fixing device 25 includes a belt unit that moves the fixing belt 26 endlessly while being stretched by two rollers, and a pressure roller 27 that is pressed toward one roller of the belt unit. The fixing belt 26 and the pressure roller 27 are in contact with each other to form a fixing nip, and the transfer paper received from the paper transport belt 24 is sandwiched therebetween. Of the two rollers in the belt unit, the roller that is pressed from the pressure roller 27 has a heat source (not shown) inside, and heats the fixing belt 26 by the generated heat. The heated fixing belt 26 heats the transfer paper sandwiched in the fixing nip. The full color image is fixed on the transfer paper by the influence of the heating and the nip pressure.

  The transfer paper subjected to the fixing process in the fixing device 25 is stacked on the stack portion 57 provided on the outer side of the left side plate in the drawing of the printer casing constituting the exterior of the copying machine 500, or the other side. In addition, in order to form a toner image, any one of the conveyance forms to be returned to the above-described secondary transfer nip 22NP is selected.

  When copying from a bundle of sheet documents (not shown), the bundle of sheet documents is set on the document table 30 of the automatic document feeder 400. However, when the original is a one-sided original that is bound in a main form, the original is set on the contact glass 32. Prior to this setting, the automatic document feeder 400 is opened upward with respect to the copying machine main body, and the contact glass 32 of the scanner 300 is exposed. Thereafter, as the automatic document feeder 400 is closed, the one-sided original is pressed.

  When a copy start switch (not shown) is pressed after the document is set in this way, the document reading operation by the scanner 300 starts. However, when a sheet document is set on the automatic document feeder 400, the automatic document feeder 400 automatically moves the sheet document to the contact glass 32 prior to the document reading operation.

  In the document reading operation, first, the first traveling body 33 and the second traveling body 34 start traveling together, and light is emitted from a light source provided in the first traveling body 33. Then, the reflected light from the document surface is reflected by a mirror provided in the second traveling body 34, passes through the imaging lens 35, and then enters the reading sensor 36. Upon receiving the incident light, the reading sensor 36 constructs image information based on the incident light.

  In parallel with such document reading operation, each device in each of the process cartridges 18Y, 18M, 18C, and 18K, the intermediate transfer unit 17, the secondary transfer device 22, and the fixing device 25 start driving. Then, based on the image information constructed by the reading sensor 36, the optical writing unit 21 is driven and controlled, and Y, M, C, and K toner images are formed on the respective photoreceptors 1Y, 1M, 1C, and 1K. Is done. These toner images become four-color toner images superimposed and transferred on the intermediate transfer belt 110.

  Further, almost simultaneously with the start of the document reading operation, the paper feeding operation is started in the paper feeding device 200. In this paper feeding operation, one of a plurality of paper feeding rollers 42 is selectively rotated, and transfer paper is sent out from one of paper feeding cassettes 44 accommodated in multiple stages in the paper bank 43.

  The transferred transfer sheets are separated one by one by the separation roller 45 and conveyed toward the secondary transfer nip 22NP by the conveyance roller pair 47. In some cases, paper is fed from the manual feed tray 51 instead of such paper feeding from the paper feeding cassette 44. In this case, after the manual feed roller 50 selectively rotates and feeds the transfer paper on the manual tray 51, the separation roller 52 separates the transfer paper one by one and feeds it to the manual feed path 53 of the printer unit 100. To do.

  In the case of forming a multi-color image composed of two or more toners in the copying machine 500, the intermediate transfer belt 110 is stretched so that the upper stretched surface thereof is substantially horizontal, Photoconductors 1Y, 1M, 1C, and 1K.

  On the other hand, when forming a monochrome image composed of only K toner, the intermediate transfer belt 110 is moved by a mechanism (not shown) while keeping the upper stretched surface of the intermediate transfer belt 110 in contact with the K photoconductor 1K. In the posture inclined to the lower left in the figure, the upper stretched surface is separated from the Y, M, and C photoconductors 1Y, 1M, and 1C. Of the four photoconductors 1Y, 1M, 1C, and 1K, only the K photoconductor 1K is rotated counterclockwise in the drawing to form only the K toner image. At this time, for the photoreceptors 1Y, 1M, and 1C, the driving of not only the photoreceptor 1 but also the developing device 4 is stopped, and the members of the photoreceptor 1 and the developing device 4 and the developer in the developing device 4 are unnecessary. To prevent excessive wear.

  The copier 500 includes a control unit (not shown) composed of a CPU and the like that controls each device in the copier 500, and an operation display unit (not shown) composed of a liquid crystal display, various key buttons, and the like. Yes. The operator sends a command to the control unit by a key input operation on the operation display unit, so that one of the three modes is selected from the three-sided print mode, which is a mode for forming an image only on one side of the transfer paper. You can choose one. The three single-sided printing modes include a direct discharge mode, a reverse discharge mode, and a reverse decal discharge mode.

[Developing device and photoreceptor]
FIG. 2 shows the developing device 4 and the photoconductor 1 taken out of the four process cartridges 18Y, 18M, 18C, and 18K from the printer unit 100 shown in FIG.

  In FIG. 2, the four process cartridges 18Y, 18M, 18C, and 18K have substantially the same configuration except that they handle different colors of toner. Therefore, in FIG. The suffixes “Y”, “M”, “C”, and “K” attached to the symbol “1” indicating the body are omitted.

  As shown in FIG. 2, the surface of the photosensitive member 1 is charged by a charging device (not shown) while rotating in the direction of arrow G in the drawing. An electrostatic latent image is formed on the surface of the charged photoreceptor 1 by the laser light Lb irradiated from the optical writing unit 21 which is the exposure unit shown in FIG. Toner is supplied to the electrostatic latent image from the developing device 4 to form a toner image.

  The developing device 4 has a developing roller 5 as a developer carrier. The developing roller 5 rotates the developing sleeve 81 in the arrow H direction, which is a clockwise direction in the drawing, and conveys the developer, while the toner and the carrier are applied to the electrostatic latent image formed on the surface of the photoreceptor 1. So-called development is performed in which the electrostatic latent image is visualized.

  The developing roller 5 is disposed on the most upstream side of a plurality (two in this example) of developer carriers disposed on the upstream side and the downstream side in the rotation direction G of the photoconductor 1 disposed facing each other. This is a first developer carrier provided on the first stage.

  The developing roller 5 includes a developing sleeve 81 as a first developer supporting means that can rotate in the arrow H direction, which is a clockwise direction, on the outer peripheral portion. The developing sleeve 81 includes a magnet roller 82 as first magnetic field generating means. In contrast to the developing sleeve 81, the magnet roller 82 can rotate in the direction of the arrow A in the counterclockwise direction in the drawing, and has an even number of magnetic poles as magnetism generating means.

  The developing roller 5 and the photosensitive member 1 are located on the downstream side of the facing portion between the developing roller 5 and the photosensitive member 1 in the counterclockwise direction G indicating the traveling direction (rotating direction) of the photosensitive member 1. A carrier recovery roller 13 which is another developer carrier is provided at a position close to.

  The carrier recovery roller 13 is a second-stage second developer carrier disposed on the most downstream side of the plurality (two in this example) of developer carriers. Similarly to the developing roller 5, the carrier recovery roller 13 also includes a carrier recovery sleeve 90 as a second developer support means that can rotate on the outer periphery. The carrier recovery sleeve 90 includes a carrier recovery magnet roller 91 as a second magnetic field generating unit including a composite magnet 93 (see FIGS. 5 and 6) composed of a plurality of fixed magnetic poles. As described above, the carrier recovery roller 13 includes the carrier recovery sleeve 90 and the carrier recovery magnet roller 91 inside thereof. 5 and 6, the carrier recovery sleeve 90 is rotated in the direction of arrow J (counterclockwise direction) in a direction (counter direction) in which the portion facing the photoconductor 1 passes the photoconductor 1.

  A doctor blade 111 is provided on the upstream side of the facing proximity to the photosensitive member 1 in the direction of arrow J, which is the rotation direction of the carrier recovery sleeve 90, and the carrier recovered from the photosensitive member 1 is recovered by the recovery screw 6. ing.

  The carrier adhering to the photoreceptor 1 is collected by the carrier collection roller 13. The carrier recovered by the carrier recovery roller 13 is returned into the developing device 4 by the magnetic force of the carrier recovery magnet roller 91 and the rotation of the carrier recovery sleeve 90. The developing roller 5 and the carrier recovery roller 13 are features of the present invention and will be described in detail later.

  The developing device 4 has a supply screw 8. The supply screw 8 supplies the developer to the developing roller 5 along the axial direction of the developing roller 5 (referred to as the back side in the drawing or the back side in FIG. 2 for convenience). In some cases, a supply transport path 9 for transporting the developer is formed.

  A downstream side in the developer transport direction H from a portion of the developing roller 5 facing the supply screw 8 is partitioned by a second partition wall 134. The second partition wall 134 constitutes a side wall of a flange 9 'that allows the supply conveyance path 9 to communicate with the peripheral surface of the developing roller.

  At a position (a downstream side in the developer conveying direction H) that advances in the clockwise direction along the developing sleeve 81 with respect to the developing region that is the portion of the developing roller 5 facing the photoconductor 1, the recovery screw 6 is located on the developing roller 5. Are arranged opposite to each other. The developed developer that has passed through the developing region and has separated from the surface of the developing roller 5 is collected along a collecting conveyance path 7 formed along the collecting screw 6.

  As shown also in FIG. 3, the collection screw 6 that forms the collection conveyance path 7 functions as a collection conveyance member that conveys the collected developer collected in the same direction as the supply screw 8 along the axial direction of the developing roller 5. In addition, a spiral screw arranged parallel to the axial direction of the supply screw 8 is provided. A supply conveyance path 9 formed along the supply screw 8 is arranged above the developing roller 5, and a collection conveyance path 7 along the collection screw 6 is arranged below the development roller 5.

  In the developing device 4, a stirring conveyance path 10 is provided in parallel with a supply conveyance path 9 and a collection conveyance path 7 along the collection screw 6 provided in parallel with the depth direction of the paper surface of FIG. The stirring conveyance path 10 is the same height as the collection conveyance path 7 whose height position is relatively low on the back side in the depth direction of FIG. 2 and the same as the supply conveyance path 9 whose height position is relatively high on the front side. It is configured to be high. Therefore, as shown in FIG. 3, the agitating and conveying path 10 forms an inclined path that connects the depth side in the depth direction (low) to the near side in the depth direction (high).

  The agitation conveyance path 10 is a conveyance path along the agitation screw 11. The agitation screw 11 is in the opposite direction to the supply screw 8 while agitating the developer along the axial direction of the developing roller 5 (hereinafter referred to as the front side in the drawing for convenience). There is also an agitating and conveying member that conveys toward The agitation screw 11 includes a spiral screw arranged in an inclined manner in the axial direction, and conveys the developer from the back side to the near side while agitating the developer in FIGS.

  In FIG. 2, the supply conveyance path 9 and the agitation conveyance path 10 are partitioned by a first partition wall 133 as a partition member, but at the front end in the figure, the supply conveyance path 9 and the agitation conveyance path An opening called a supply opening is formed so as to communicate with 10. On the near side in the figure, the supply conveyance path 9 and the agitation conveyance path 10 communicate with each other through the opening, and the developer is transferred from the agitation conveyance path 10 to the supply conveyance path 9. This delivery path is indicated by an arrow D in FIG.

  In FIG. 2, the supply conveyance path 9 and the collection conveyance path 7 are partitioned in the longitudinal direction by a second partition wall 134 as a partition member. An opening called a surplus opening is formed so that 9 and the collection conveyance path 7 communicate with each other. On the back side in the figure, the supply conveyance path 9 and the collection conveyance path 7 communicate with each other through the opening, and the developer is transferred from the supply conveyance path 9 to the collection conveyance path 7. This delivery path is indicated by an arrow E in FIG.

  In FIG. 2, the agitating and conveying path 10 and the recovery conveying path 7 are partitioned in the longitudinal direction by a third partition wall 135 as a partition member. An opening called a recovery opening is formed so as to communicate with the path 10 and the recovery transport path 7. On the back side in the figure, the agitation conveyance path 10 and the collection conveyance path 7 communicate with each other through the opening, and the developer is transferred from the collection conveyance path 7 to the agitation conveyance path 10. This delivery path is indicated by arrow F in FIG.

  The supply screw 8, the recovery screw 6 and the stirring screw 11 which are developer conveying members are made of resin or metal screws, and the diameter of each screw is the supply screw 8, the recovery screw 6 is φ26 (mm), and the stirring screw 11 is φ30. (Mm), the screw pitch is 2 (winding) with a supply screw of 54 (mm), the recovery screw 6 is 2 (winding) with 36 (mm), and the stirring screw 11 is 2 (winding) with a rotation of about 54 (mm). It is set to 600 (rpm).

  The developer carried on the developing roller 5 is thinned by a doctor blade 12 made of stainless steel, and is then transported to a developing area which is a portion facing the photoreceptor 1 for development.

  The diameter of the developing roller 5 is φ40 (mm), and the gap between the doctor blade 12 and the photoreceptor 1 is about 0.3 (mm).

  The developed developer is collected in the collection conveyance path 7 and conveyed to the back side in FIGS. 2 and 3, and the developer is provided in a non-image area portion located at the end in the longitudinal direction of these conveyance paths. At the opening of the three partition walls 135, the developer is transferred to the stirring and conveying path 10 along the path indicated by the arrow F.

  In FIG. 3, the toner T is supplied from above to a portion of the supply conveyance path 9 located near the opening of the second partition wall 134 on the back side in the supply conveyance path 9 and on the downstream side in the developer conveyance direction. It has become. In FIG. 4, the supplied toner T is supplied from a toner replenishing port 96 located above the portion of the supply conveyance path 9. The toner supply port 96 will be described later.

  FIG. 3 is a partial perspective cross-sectional view of the developing device 4 and shows the developer transport path and the developer flow in the developing device 4. On the front side, in the supply conveyance path 9 that receives the supply of the developer from the agitation conveyance path 10 through the transfer path indicated by the arrow D, the developing roller 5 moves while the developer moves toward the back side of the supply conveyance path 9. Supplied in contact with

  In this supply process, excess developer that has not been supplied to the developing roller 5 and has moved to the downstream end in the conveyance direction of the supply conveyance path 9 passes through the excessive opening of the second partition wall 134 to the collection conveyance path 7 in the direction of arrow E. Supplied.

  On the other hand, the developer supplied to the developing roller 5 is used for development in the developing region, and then separated from the developing roller 5 and separated from the developing roller 5, and is transferred to the collection conveyance path 7 through a path indicated by an arrow R. The transferred developer is transported to the downstream end (back side) in the transport direction of the recovery transport path 7 by the recovery screw 6, and the recovered developer is stirred and transported in the direction of arrow F through the recovery opening of the third partition wall 135. Supplied to the path 10.

  In the agitation transport path 10, the surplus developer supplied from the supply transport path 9, the recovered developer recovered in the recovery transport path 7, and the toner T replenished from a toner replenishment port 96 (see FIG. 4) described later are agitated. The agitated developer is conveyed downstream (front side) in the conveying direction of the agitating screw 11 and upstream in the conveying direction of the supply screw 8, and the supply opening of the first partition wall 133 is indicated by an arrow. It is supplied to the supply conveyance path 9 in the direction D.

  In FIG. 2, a toner concentration sensor (not shown) including a magnetic permeability sensor is provided below the agitation transport path 10, and a toner supply control device (not shown) is operated by the sensor output of the toner concentration sensor. Toner is replenished from the illustrated toner container through a toner replenishing port 95.

  In the developing device 4, the supply conveyance path 9 and the collection conveyance path 7 in FIG. 2 and FIG. 3 are partitioned by a second partition wall 134 as a partition member at a middle portion in the longitudinal direction from the back side to the near side. Thus, since the supply and recovery of the developer are performed in different developer transport paths, the developed developer is not mixed into the supply transport path 9. For this reason, it is possible to suppress a decrease in the toner concentration of the developer supplied to the developing roller 5 toward the downstream side of the supply conveyance path 9 in the conveyance direction.

  Further, between the recovery conveyance path 7 and the agitation conveyance path 10, a longitudinal intermediate portion from the back side to the near side is partitioned by a third partition wall 135 as a partition member, and the developer recovery and stirring are performed. Are performed in different developer transport paths, so that the developed developer does not fall in the middle of stirring. Thereby, since the sufficiently stirred developer is supplied to the supply conveyance path 9, it is possible to suppress the developer supplied to the supply conveyance path 9 from being insufficiently stirred.

  In this way, the toner density of the developer in the supply conveyance path 9 can be prevented from decreasing, and the developer in the supply conveyance path 9 can be prevented from being insufficiently stirred, so that the image density during development can be kept constant. can do.

  The toner supply position will be described with reference to FIG. The toner replenishing port 96 for replenishing toner is provided above the downstream (back side) end of the supply conveyance path 9 including the supply screw 8 in the conveyance direction. Since the toner supply port 95 is above the excessive opening (arrow E in FIG. 3) of the second partition wall 134, the toner T is likely to be mixed with the excessive developer and the recovered developer. Therefore, toner is supplied at a position above the downstream (back side) end in the transport direction of the supply transport path 9 including the supply screw 8. Thereby, the developer can be efficiently stirred.

  With reference to FIG. 5, the developer path around the developing roller 5 and the carrier recovery roller 13, which is a characteristic part of the present embodiment, will be described. The developing roller 5 includes a cylindrical developing sleeve 81 that carries a developer and a magnet roller 82 that is included in the developing sleeve 81 and serves as a magnetic field generating unit that attracts the developer by magnetic force.

  The developing sleeve 81 is made of a nonmagnetic and conductive material such as aluminum, austenitic stainless steel or magnesium. The surface may be smooth, but the high-speed machine may be subjected to the following roughening treatment and processing in order to suppress developer slip.

Roughening treatment / processing type of the developing sleeve 81 (type A): by groove extrusion processing such as V-groove or U-groove, machining of various concave shapes, laser processing or edging processing.
(Type B): By blasting.
(Type C): By thermal spraying treatment of metal or ceramic.

  The magnet roller 82 is rotatably provided in the direction of arrow A opposite to the arrow H along the rotation direction of the developing sleeve 81 which is the developer conveying direction, and an even number of magnets 83 are arranged at equal intervals. . In the example shown in FIG. 5, 16 magnets are arranged. The polarities of these magnets 83 are opposite to each other so as to attract each other between adjacent magnets.

  In this example, the driving direction of the magnet roller 82 and the developing sleeve 81 can be selected from either the same or relative rotational direction, and the rotational relationship is carried on the surface of the developing sleeve 81. The developer is set on the condition that the number of facings between the developer and the magnet 83 on the magnet roller 82 side is increased.

  Due to the increase in the number of times the developer is opposed to the magnet of the magnet roller 82 obtained by setting the driving direction described above, a spike is formed when the developer is opposed to the magnetic pole, and the spike is broken when the developer is separated from the magnetic pole. The number of repetitions of the phenomenon is increased, and the charging property of the toner can be improved by increasing the chance of frictional contact between the toner and the carrier.

  In this case, the increase in the number of facings can be obtained by setting the rotational direction of the magnet roller 83 and the developing sleeve 81, setting the speed difference, or the like as described above. That is, when both rotate in the same direction, the number of times the developer faces the magnet 83 can be increased by setting a speed difference between them, and the opposite direction without setting the speed difference. In this case, the number of times the developer faces the magnet 83 can be increased in the same manner.

  For the above-described magnet 83, a conventional inexpensive ferrite magnet can be used, but a stronger rare earth magnet such as a samarium cobalt magnet or a neodymium magnet can also be used for downsizing and speeding up. The magnet 83 may be supported on the magnet holder 84 by adhesion, and the outer periphery thereof may be protected by a heat shrinkable tube or the like (not shown).

  If the magnet holder 84 is made of a magnetic material, the magnetic force of the magnet 83 can be slightly improved. However, since the cost is high and magnetic materials mainly composed of iron are generally high in specific gravity, the moment of inertia increases at the time of high-speed rotation, which may cause a problem in the durability of the drive unit. Therefore, although the magnetic force of the magnet 83 is slightly lowered, nonmagnetic and light specific gravity aluminum or magnesium may be used as a material.

  In FIG. 5, the rotation center P 'of the magnet roller 82 in this example is eccentrically positioned at a position separated from the rotation center P of the developing sleeve 81 by a distance (Q).

  The direction of eccentricity is set to an orientation that allows the developer carried on the surface of the developing roller 5 to be closest to the inner surface of the developing roller 81 at a position in the vicinity of transfer to the photoreceptor 1, and is indicated by the symbol Q above. The amount of eccentricity corresponding to the distance is an amount that can suppress the carrier from moving to the photosensitive member 1 in the developing region by the magnetic force from the magnetic pole. As a result, the developer transferred to the photosensitive member 1 can be contacted in a state in which rising is ensured upon contact with the photosensitive member 1, and carrier transfer is prevented by the magnetic force from the approaching magnetic pole so that only the toner is exposed. It will move to supply the latent image of the body.

  On the other hand, the magnetic force can be kept low on the side opposite to the eccentric direction. For this reason, the developer carried on the surface of the developing sleeve 81 can be easily peeled off. With only such an eccentric configuration, the developer can be easily peeled off without using external mechanical external force.

Next, the transfer of the developer in the present embodiment will be described with reference to FIG.
The developer that follows the supply conveyance path 9 along the supply screw 8 is supplied to the developing roller 5 through the conveyance path by the flange 9 '. The developer supplied to the developing roller 5 is attracted onto the developing sleeve 81 by the magnetic force of the magnet roller 82, conveyed by the rotation of the developing sleeve 81, and the amount of the developer is regulated to be constant when passing through the doctor blade 12. The The developer that has passed through the doctor blade 12 is arranged along the magnetic field lines. That is, a magnetic brush is generated on the magnet 83 as indicated by reference numeral B1, and the magnetic brush falls between the magnets 83 as indicated by reference numeral B2.

  When the rotation direction of the magnet roller 82 is a direction opposite to the rotation direction H of the developing sleeve 81 as indicated by an arrow A, the magnetic brush rotates in a so-called flip flap shape while the magnet roller 82 rotates. Then, it proceeds in the direction of the arrow Fm opposite to the direction indicated by the arrow A which is the rotation direction of the magnet roller 82. At this time, the developing sleeve 81 may be supplementarily rotated in the direction of arrow H at a relatively low speed.

  As the developer that passes through the doctor blade 12 continues to rotate, the magnetic roller 82 is decentered to gradually increase the attracting force to the developing sleeve 81 and suppress the carrier from moving to the photosensitive member 1 over the developing region. As the magnet roller 82 rotates at a higher speed, the developer is vigorously agitated at the portion facing the photoconductor 1, so that the toner can be transferred efficiently according to the electrostatic latent image on the photoconductor 1. Since the centrifugal force due to the rotation increases in proportion to the square of the rotation speed, the carrier adhesion also increases. A method for removing carrier adhesion will be described later.

  In FIG. 6, the developer continues to rotate, but passes through the developing region. As a result, the attracting force on the developing sleeve 81 is gradually reduced due to the eccentricity of the magnet roller 82, and is indicated by the arrows K and L by the self-weight in the collection conveyance path 7. As described above, the developing sleeve 81 is detached.

The carrier recovery roller 13 will be described with reference to FIGS. 5 and 6.
The carrier recovery sleeve 90 that constitutes the outer periphery of the carrier recovery roller 13 has a portion facing the photoconductor 1 with respect to the rotation direction of the photoconductor 1 indicated by an arrow G (counterclockwise in FIGS. 5 and 6). It rotates in the counter direction (the direction of arrow J in FIGS. 5 and 6).

A gap between the carrier recovery roller 13 and the photosensitive member 1 (hereinafter referred to as a development gap) is close to 0.3 mm. The developer is pumped up by the magnetic pole P23 of the carrier recovery magnet roller 91, and is regulated by a doctor blade 111 installed downstream of the pumping portion in the rotation direction of the carrier recovery magnet roller 91, so that the developer pumping amount is increased. Be regulated. In this example, the pumping amount of the collection roller was 30 mg / cm ² . The doctor blade 111 is in contact with the P23 pole and the P24 pole with a gap of 0.2 mm.

  The developer regulated by the doctor blade 111 is conveyed along a path winding the outer periphery of the carrier recovery roller 13 to the left, that is, a path indicated by a broken line NR in FIG. 5, and the magnetic pole disposed in the development gap portion of the development area. It is conveyed to the development area of P21. At the magnetic pole P21, the magnetic brush B3 rises on the carrier recovery sleeve 90 and the developer ears are in contact with the photoreceptor 1, so that not only the carrier recovery but also the development is performed.

  The developer that has collected and developed the attached carrier at the magnetic pole P21 (N pole) is conveyed to the magnetic pole P22 adjacent to the magnetic pole P21. Since the magnetic pole P22 and the magnetic pole P23 have the same polarity, the developer is separated from the carrier recovery sleeve 90 of the carrier recovery roller 13 at the magnetic pole P22. Most of the separated developer is attracted to the developing roller 5 and conveyed.

  The linear velocity ratio Vs / Vp between the linear velocity (Vs) of the carrier recovery sleeve 90 and the linear velocity (Vp) of the photosensitive member 1 was Vs / Vp = 1.5. This is because when the linear velocity ratio is set to 1.7 or more, the horizontal line is blurred, and when it is set to 1.3 or less, scuffing of the background dirt is deteriorated.

The configuration of the carrier recovery roller 13 will be described with reference to FIG.
The carrier recovery roller 13 includes a rotatable carrier recovery sleeve 90, includes a plurality of fixed magnetic poles, and includes a carrier recovery magnet roller 91.

  The carrier recovery magnet roller 91 is formed by affixing a composite magnet 93 and a block magnet 94 on a shaft 92 made of a nonmagnetic material such as aluminum, austenitic stainless steel, magnesium, or various resin materials.

  The composite magnet 93 uses Sr ferrite or Ba ferrite as magnet powder, and PA (polyamide) material such as 6PA or 12PA as a polymer compound, EEA (ethylene / ethyl copolymer) or EVA (ethylene / vinyl copolymer). An ethylene compound such as coalescence), a chlorine material such as CPE (chlorinated polyethylene), and a rubber material such as NBR can be used.

  The composite magnet 93 formed on the carrier recovery magnet roller 91 is molded in a half moon shape, has four magnetic poles by magnetization, and has a notch disposed on the developing roller 5 side, on the side facing the developing roller 5. Does not have a magnetic pole.

  A block magnet 94 corresponding to the magnetic pole P21 is disposed in the vicinity of the photosensitive member 1 and the carrier recovery magnet roller 91 (carrier recovery sleeve 90) in order to recover the carrier attached to the photosensitive member 1. The block magnet 94 is smaller in volume than the composite magnet 93 and requires a high magnetic force, and it is desirable to use a material of Br> 0.5T, and most of them are Ne (Ne—Fe—B, etc.) or Sm (Sm—). Co, Sm—Fe—N, etc.) rare earth sintered magnets or rare earth bonded magnets in which these magnet powders are mixed with a polymer compound.

  There are isotropic and anisotropic magnet powders in rare earth magnet powders, and anisotropic magnet powders can provide higher magnetic force, but either type can be used depending on the desired magnetic properties. .

  The block magnet 94 has a width of 3 (mm) and a thickness of 3 (mm) by sintering, extrusion molding, injection molding, or in-mold compression molding of magnetic powder and a binder. The length is 346 (mm), which is about 10 (mm) longer than the magnet roller 82 so that the carrier can be reliably recovered to the end.

  In this example, the block magnet 94 is a rare earth bonded magnet. The magnetic pole P21 has a high magnetic flux density of 150 (mT). For the other transport poles, the magnetic pole P22 was (70 mT), the magnetic pole P23 was (100 mT), the magnetic pole P24 was (80 mT), and the magnetic pole P25 was (80 mT).

  The carrier recovery sleeve 90 is made of a nonmagnetic and conductive material such as aluminum, austenitic stainless steel, or magnesium. Further, in order to transport the developer, it is necessary to subject the surface to the following roughening treatment / processing.

Types of roughening and processing of the carrier recovery sleeve 90 (type A1): by groove extrusion processing such as V-groove or U-groove, machining by various concave shapes, laser processing or edging processing.
(Type B1): By blasting.
(Type C1): By thermal spraying treatment of metal or ceramic.

  As for the above (A1), the depth of the groove / concave is about 0.05 (mm) to 0.5 (mm), and a known technique such as shape and number can be used. About (B1), the roughness is in a range in which Rz7 μm to Rz50 μm can be manufactured and carrier slip can be prevented. About (C1), the roughness is within a range that can be manufactured with Rz 40 μm to Rz 90 μm and can prevent carrier slip. The groove on the sleeve surface of the carrier recovery roller 13 of this example is a V-groove, and the groove depth is 0.1 mm.

  The gap between the carrier recovery roller 13 and the photosensitive member 1 is set to be as narrow as 0.3 (mm), thereby increasing the developing ability of the recovery roller. The gap between the carrier recovery roller 13 and the developing roller 5 is set to be as narrow as 2 (mm) so that the head of the developing roller 5 is brought into contact with the carrier recovery roller 13 and separated from the magnetic pole P22 of the carrier recovery roller 13. Can be recovered.

By bringing the magnetic brush into contact with the portion without the magnetic pole of the carrier recovery roller 13, the agent separated from the recovery roller can be recovered while suppressing vibration due to magnetic field interference.
A casing 98 is provided on the opposite side of the carrier recovery roller 13 from the developing roller 5 in the circumferential direction, and the gap between the carrier recovery roller 13 and the casing 98 is set to be as narrow as 1.5 (mm). The stand can be brought into contact with the casing 98 to increase the collection efficiency.

  The doctor blade 111 abutted between the poles P23 and P24 is made of aluminum. In order to narrow the doctor gap, the doctor blade 111 is brought into contact with the magnetic pole instead of between the poles. As another example, it is also effective to attach a magnetic plate in the vicinity of the carrier recovery sleeve 90.

The carrier recovery rate was carried out under the following experimental conditions that facilitate carrier adhesion.
<Experimental conditions>
・ Carrier: 35μm ferrite carrier for Ricoh Co., Ltd. imagio MP C7500 ・ Toner: PxP polymerization toner for Ricoh Co., Ltd. imagio MP C7500 ・ Toner concentration: 4 [wt%]
-Charge amount: -24 [μC / g]
・ Development potential: 114 [V]
・ Skin potential: 150 [V]
-Photoconductor linear velocity: 700 (mm / s)
・ Mag sleeve double rotation sleeve linear velocity: 880 (mm / s)
-Photoconductor gap of the Magsleeve rotating roller: 0.4 (mm)
・ Magnet sleeve rotation speed of magnet sleeve rotation roller: 3500 (rpm)
-Carrier recovery roller sleeve linear velocity: 1050mm / s

<Comparative example>
The carrier recovery magnetic roller in the carrier recovery roller is fixedly arranged, and the magnetic pole of the carrier recovery magnetic roller is installed only at the position facing the photosensitive member and on the opposite side of the circumference of the development roller, and only at the development roller side at the opposite portion. Arrange the magnetic poles. Also, the rotation direction of the carrier recovery roller is the same as the rotation direction of the developing roller, and the developing roller and the carrier recovery roller are brought close to each other.

  In the comparative example, the carrier recovery rate is 100% when the magnet roller rotation speed of the mag sleeve rotating roller is 3000 rpm, and the recovery rate of the adhered carrier is 100%. As a result, the recovery rate decreased to 90%. On the other hand, in the experimental result according to the above <Experimental conditions> according to this example, the recovery rate was 100% even at the sleeve linear velocity of the recovery roller.

  This difference is due to the fact that the magnetic permeability of the ferrite that is the core of the developer constituting the magnetic brush is high, and the magnetic attraction force on the surface of the photoreceptor is high, and the carrier at the tip of the magnetic brush directly contacts the adhered carrier. For this reason (because the distance = 0), the magnetic brush collides with the photoconductor-adhered carrier, which is considered to reduce the adhesion force between the photoconductor 1 and the adhering carrier.

  In addition, vibration due to magnetic field interference was measured by attaching an acceleration pickup to the upper part of the doctor 12 of the mag-sleeve rotating roller (acceptable level is within 10 m / ses2). In the experimental example of this example, the vibration was within the allowable range of 7 to 8 m / s2.

  This is considered to be because the collection roller is counter-rotated with respect to the photosensitive member 1 so that no magnetic pole is provided in the vicinity of both rotations of the mag sleeve and the agent separated is adsorbed by the magnetic brush of the mag sleeve rotation roller. .

The developer composition used in this experimental example is as follows.
The toner contains at least a binder resin and a colorant, and if necessary, a release agent, a charge control agent, and other components. In addition to the above-mentioned additives, a fluidity improver and other components are added as necessary. For these materials, all known materials are possible. Examples of the binder resin include styrene, parachlorostyrene, vinyl toluene, vinyl chloride, vinyl acetate, vinyl propionate, methyl (meth) acrylate, ethyl (meth) tacrylate, propyl (meth) acrylate, (meth ) N-butyl acrylate, isobutyl (meth) acrylate, dodecyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, (meth) Hydroxypropyl acrylate, 2-chloroethyl (meth) acrylate, (meth) acrylonitrile acid, (meth) acrylamide, (meth) acrylic acid, vinyl methyl ether, vinyl ethyl ether, vinyl isobutyl ether. Examples include a weight body of monomers such as vinyl methyl ketone, N-vinyl pyrrolidone, N-vinyl pyridine and butadiene, a copolymer composed of two or more of these monomers, or a mixture thereof. In addition, polyester resin, polyol resin, polyurethane resin, polyamide resin, epoxy resin, rosin, modified rosin, terbene resin, phenol resin, hydrogenated petroleum resin, ionomer resin, silicone resin, ketone resin, xylene resin, etc. alone or in combination Can be used.

  As the colorant, all known dyes and pigments can be used. For example, carbon black, nigrosine dye, iron black, naphthol yellow S, Hansa yellow (10G, 5G, G), cadmium yellow, yellow iron oxide, ocher, Yellow lead, Titanium yellow, Polyazo yellow, Oil yellow, Hansa yellow (GR, A, RN, R), Pigment yellow L, Benzidine yellow (G, GR), Permanent yellow (NCG), Vulcan fast yellow (5G, R) ), Tartrazine Lake, Quinoline Yellow Lake, Anthrazan Yellow BGL, Isoindolinone Yellow, Bengala, Red Dan, Lead Zhu, Cadmium Red, Cadmium Mercury Red, Antimon Zhu, Permanent Red 4R, Para Red, Phi Se Red, Parachlor Ortonito Aniline Red, Resol Fast Scarlet G, Brilliant Fast Scarlet, Brilliant Carmin Min BS, Permanent Red (F2R, F4R, FRL, FRLL, F4RH), Fast Scarlet VD, Belkan Fast Rubin B, Brilliant Scarlet G, Resol Rubin GX, Permanent Red F5R, Brilliant Carmine 6B, Pigment Scarlet 3B, Bordeaux 5B, Tolujing Maroon, Permanent Bordeaux F2K, Helio Bordeaux BL, Bordeaux 10B, Bon Maroon Light, Bon Maroon Medium, Eosin Lake, Rhodamine Lake B, Rhodamine Lake Y, Alizarin Lake , Thioindigo red B, thioindigo maroon, oil red, quinacridone red, pyrazolone red, Riazo Red, Chrome Vermillion, Benzidine Orange, Perinone Orange, Oil Orange, Cobalt Blue, Cerulean Blue, Alkaline Blue Lake, Peacock Blue Lake, Victoria Blue Lake, Metal Free Phthalocyanine Blue, Phthalocyanine Blue, Fast Sky Blue, Indanthrene Blue (RS, BC), indigo, ultramarine blue, bitumen, anthraquinone blue, fast violet B, methyl violet lake, cobalt purple, manganese purple, dioxane violet, anthraquinone violet, chrome green, zinc green, chromium oxide, pyridian, emerald green, pigment Green B, Naphthol Green B, Green Gold, Acid Green Lake, Malachite Green Lake, Phthalo Cyanine green, anthraquinone green, titanium oxide, zinc white, litbon and mixtures thereof can be used. The amount used is generally 0.1 to 50 parts by weight per 100 parts by weight of the binder resin.

  Examples of the charge control agent include nigrosine dyes, triphenylmethane dyes, chromium-containing metal complex dyes, molybdate chelate pigments, rhodamine dyes, alkoxy amines, quaternary ammonium salts (including fluorine-modified quaternary ammonium salts). .), Alkylamide, phosphorus simple substance or compound, tungsten simple substance or compound, fluorine-based activator, salicylic acid metal salt, metal salt of salicylic acid derivative, and the like. The amount of charge control agent used is determined by the type of binder resin, the presence or absence of additives used as necessary, and the toner production method including the dispersion method, and is not uniquely limited. Preferably, it is used in the range of 0.1 to 10 parts by weight with respect to 100 parts by weight of the binder resin. The range of 2 to 5 parts by weight is preferable. If the amount is less than 0.1 parts by weight, the toner is not practically negatively charged. When the amount exceeds 10 parts by weight, the chargeability of the toner is too high, and the electrostatic attraction force with the carrier increases, leading to a decrease in developer fluidity and a decrease in image density.

  Examples of release agents include low molecular weight polyolefin waxes such as low molecular weight polyethylene and low molecular weight polypropylene, synthetic hydrocarbon waxes such as Fischer-Tropsch wax, beeswax, carnauba wax, candelilla wax, rice wax, and montan wax. Natural waxes such as paraffin wax, petroleum wax such as microcrystalline wax, higher fatty acids such as stearic acid, palmitic acid, myristic acid, metal salts of higher fatty acids, higher fatty acid amides, and various modified waxes thereof. can give.

  These may be used alone or in combination of two or more, but it is preferable to use those having a melting point in the range of 70 to 125 ° C. By setting the melting point to 70 ° C. or more, a toner having excellent transferability and durability can be obtained, and by setting the melting point to 125 ° C. or less, the toner can be melted quickly at the time of fixing and a reliable release effect can be exhibited. The amount of these release agents used is preferably 1 to 15% by weight based on the toner. If it is less than 1% by weight, the effect of preventing offset is insufficient, and if it is 15% by weight or more, transferability and durability are deteriorated.

  As the additive (external additive), at least fine particles having a volume average particle size of 50 to 500 nm and a bulk density of 0.3 g / cm 3 or more are added. The amount of external addition is preferably 0.2 to 3% by weight based on the toner base. If the amount is less than this range, the effect of forming an appropriate gap between the toners or between the toner and the others is not exhibited. On the contrary, if the amount is large, the fluidity is inhibited, and the amount of desorption increases, so that an aggregate of external additives is formed, and the image quality is deteriorated. In addition to the above-mentioned additives, additives outside this range can be added, and it is preferable to add fine particles having a small volume average particle diameter for the purpose of improving fluidity.

  Regarding the additives, inorganic compounds include SiO2, TiO2, Al2O3, MgO, CuO, ZnO, SnO2, CeO2, Fe2O3, BaO, CaO, K2O, Na2O, ZrO2, CaO.SiO2, K2O (TiO2) n, Al2O3.2SO2. , CaCO3, MgCO3, BaSO4, MgSO4, SrTiO3, and the like, preferably SiO2, TiO2 and Al2O3. In particular, these inorganic compounds may be hydrophobized with various coupling agents, hexamethyldisilazane, dimethyldichlorosilane, octyltrimethoxysilane, and the like. Further, the organic compound additive 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. , Urea resin, aniline resin, ionomer resin, polycarbonate resin and the like. 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 additive (fine particles) used in the experiment is excellent as a toner for the developer in the developing device. That is, the contact area with the toner particles, the photoconductor drum, and the charge imparting member is very small and contacts evenly, so the effect of reducing adhesion is great and effective in improving development / transfer efficiency. Furthermore, since it acts as a roller, it is buried in the toner particles even when cleaning the cleaning drum and the photosensitive drum under high stress (high load, high speed, etc.) without wearing or damaging the photosensitive drum. It is difficult to remove or return even after being buried a little, 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.

  As a method for producing the toner used in the experiment of this example, a method obtained by melting and kneading toner constituent materials and then pulverizing and classifying is generally used as a conventional method. However, the present invention is not limited to this method, and includes a polymerization method and the like. Various methods are possible.

  As the polymerization method, a suspension polymerization method, an emulsion polymerization method, a dispersion polymerization method, and the like are possible. Although different from the polymerization method, in addition to a dissolution suspension method, a polymer suspension method, etc., an extension reaction method or the like can be used. .

  Other than the conventional method is preferable in that the toner having the above-described particle size range and circularity can be easily obtained. Further, the circularity may be adjusted by subjecting the toner after pulverization and classification to heat treatment.

  The addition method of the additive in the experiment of this example is not particularly limited, and the toner base particles and the additive can be mechanically mixed and adhered using various known mixing devices, or the toner in the liquid phase. There is a method in which the base particles and additives are uniformly dispersed with a surfactant or the like, and after the adhesion treatment, dried.

  The particle size distribution of the toner described above can be measured by using a toner particle size distribution measuring apparatus by the Coulter counter method. As these apparatuses, there are a Coulter Counter TA-II and a 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 a solution prepared by preparing a 1% NaCl aqueous solution using primary sodium chloride. 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 for about 1 to 3 minutes with an ultrasonic disperser, and the weight and number of toner particles or toner are measured with the above-described measuring apparatus using a 100 μm aperture as the aperture. Calculate weight distribution and number distribution. 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 circularity of the toner described above is a value obtained by the following equation. Circularity = (peripheral length of a circle having the same area as the projected area of the particle) / (peripheral length of the projected particle image) This circularity is an index of the degree of unevenness of the toner particles. When the toner is a perfect sphere 1 .00, and the more complicated the surface shape, the smaller the circularity.

  Circularity can be measured using a flow type particle image analyzer FPIA-1000 manufactured by Toa Medical Electronics. As a specific measuring method, 0.1 to 0.5 ml of a surfactant, preferably alkylbenzene sulfonate, is added as a dispersant to 100 to 150 ml of water from which impure solids have been previously removed, and further measurement is performed. Add about 0.1-0.5g of sample. The suspension in which the sample is dispersed is subjected to dispersion treatment with an ultrasonic disperser for about 1 to 3 minutes, and the shape of the toner is measured with the above-mentioned apparatus with the dispersion concentration being 3000 to 10000 / μl.

  Hereinafter, the carrier used in this example will be described supplementarily. The carrier is formed so that the weight average particle diameter is 20 to 60 μm (preferably 20 to 45 μm). This particle size range is also excellent as a carrier for the developer in the developing device.

  When the average particle diameter of the carrier is less than 20 μm, fine powder is increased in the distribution of the carrier particles, and the magnetization per particle may be lowered to cause carrier scattering. On the other hand, if the average particle size of the carrier exceeds 45 μm, the carrier spikes during the development process become rough, and the uniformity of solid and halftone may be inferior (particularly, the average particle size exceeds 60 μm). And become prominent.) In addition, since the specific surface area is reduced, toner scattering may occur in a small particle size toner.

  The carrier is not particularly limited except for the particle diameter, and can be appropriately selected according to the purpose. However, a carrier having a core material and a resin layer covering the core material is preferable.

  There is no restriction | limiting in particular as a material of a core material, It can select suitably from well-known things, for example, 50-90 emu / g manganese-strontium (Mn-Sr) type material, manganese-magnesium (Mn-Mg) ) Based materials are preferred, and in terms of securing image density, highly magnetized materials such as iron powder (100 emu / g or more), magnetite (75 to 120 emu / g) are preferred. In addition, weak magnetization such as copper-zinc (Cu-Zn) (30 to 80 emu / g) is advantageous in that it can weaken the contact with the photosensitive drum in which the toner is in a spiked state and is advantageous in improving the image quality. Material is preferred. These may be used alone or in combination of two or more.

  The material for the resin layer of the carrier is not particularly limited and can be appropriately selected from known resins according to the purpose. Examples thereof include amino resins, polyvinyl resins, polystyrene resins, and halogenated olefin resins. Polyester resin, polycarbonate resin, polyethylene resin, polyvinyl fluoride resin, polyvinylidene fluoride resin, polytrifluoroethylene resin, polyhexafluoropropylene resin, copolymer of vinylidene fluoride and acrylic monomer, fluoride Examples thereof include a copolymer of vinylidene and vinyl fluoride, a fluoroterpolymer such as a terpolymer of tetrafluoroethylene, vinylidene fluoride, and a non-fluorinated monomer, and a silicone resin. These may be used individually by 1 type and may use 2 or more types together.

  The resin layer may contain conductive powder or the like as necessary. Examples of the conductive powder include metal powder, carbon black, titanium oxide, tin oxide, and zinc oxide. The average particle diameter of these conductive powders is preferably 1 μm or less. When the average particle diameter exceeds 1 μm, it may be difficult to control the electric resistance.

  The carrier resin layer is prepared, for example, by dissolving the silicone resin in a solvent to prepare a coating solution, and then uniformly coating the coating solution on the surface of the core by a known coating method, drying, and baking. It can form by performing. Examples of the application method include an immersion method, a spray method, and a brush coating method.

  The amount of the resin layer in the carrier is preferably 0.01 to 5.0% by mass. If the amount of the resin layer is less than 0.01% by mass, a uniform resin layer may not be formed on the surface of the core material. If the amount exceeds 5.0% by mass, the resin layer becomes too thick. As a result, granulation of carriers occurs, and uniform carrier particles may not be obtained.

  The developer (initial agent) stored in advance in the developing device is also a mixture of the above-described toner and carrier. There is no restriction | limiting in particular as content (carrier density | concentration) of the carrier in a developing agent, According to the objective, it can select suitably. For example, 90-98 mass% is preferable and 93-97 mass% is more preferable.

1M, 1C, 1K, 1Y Photoconductors 2M, 2C, 2K, 2Y Chargers 4M, 4C, 4K, 4Y Developing device 5 Developing roller (first developer carrier)
6 Recovery screw 7 Recovery conveyance path 8 Supply screw 9 Supply conveyance path 9 '樋 10 Stirring conveyance path 11 Stirring screw 12 Doctor blade 13 Carrier recovery roller (second developer carrier)
15 driving roller 16 secondary transfer backup roller 17 intermediate transfer unit 18Y, 18M, 18C, 18K process cartridge 21 optical writing unit 22 secondary transfer device 22NP secondary transfer nip 22NP secondary transfer nip 23 stretching roller 25 fixing device 26 Fixing belt 27 Pressure rollers 28M, 28C, 28K, 28Y Drum cleaning device 30 Document table 32 Contact glass 33 First traveling body 34 Second traveling body 35 Imaging lens 36 Reading sensor 42 Paper feeding roller 43 Paper bank 44 Paper feeding cassette 45 Separating roller 47 Conveying roller pair 48 Feeding path 49 Registration roller pair 51 Manual tray 52 Separating roller 53 Manual feeding path 57 Stack section 62Y, 62M, 62C, 62K Primary transfer bias roller 81 Developing sleeve (first developer supporting means) )
82 Magnet roller (first magnetic field generating means)
83 Magnet 90 Carrier recovery sleeve (second developer support means)
91 Carrier recovery magnet roller (second magnetic field generating means)
92 Shaft 93 Composite magnet 94 Block magnet 95 Belt cleaning device 96 Toner supply port 97 Belt cleaning device 98 Casing 100 Printer unit 110 Intermediate transfer belt 111 Doctor blade 133 First partition wall 134 Second partition wall 135 Third partition wall 200 Apparatus 300 Scanner 400 Automatic document feeder 500 Copiers A, D, E, F, Fm, G, J, H, K, L, R Arrows B1, B2, B3 Magnetic brush Lb Laser light NR Broken lines P21, P22, P23 , P24 Magnetic pole P, P 'Rotation center Q Distance T Toner

JP 2010-282065 A JP-A-62-83767

Claims (6)

A developing device including a developer carrier for supplying a two-component developer containing toner and a carrier to an electrostatic latent image formed on the image carrier,
A plurality of developer carriers disposed opposite to the image carrier;
Of the plurality of stages of developer carriers, the first developer carrier on the most upstream side in the rotational direction of the image carrier includes a rotatable first developer support means, and the first developer support means. A first magnetic field generating means capable of rotating provided with a magnetic pole for raising and transporting the developer;
Of the plurality of stages of developer carriers, a second developer carrier located on the most downstream side in the rotation direction of the image carrier is provided with a rotatable second developer support means and a second developer support means. A second magnetic field generating means included and fixed;
The second magnetic field generating means includes a magnetic pole at a position close to the image carrier and the second developer carrier, and the developer ears are in contact with the latent image carrier. apparatus. The developing device according to claim 1,
The second magnetic field generating means does not have a magnetic pole at a position facing the first developer carrier,
The developing device, wherein the second developer support means rotates in a direction in which the rotation direction of the image carrier and a portion facing the image carrier are different from each other. The developing device according to claim 1 or 2,
The developing device according to claim 1, wherein the first magnetic field generating means is rotatable in a direction opposite to the first developer carrier. The developing device according to any one of claims 1 to 3,
The first magnetic field generating means is disposed with its own cross-sectional center decentered in a direction approaching the image carrier relative to the cross-sectional center of the first developer carrier. apparatus.   An image forming apparatus comprising the developing device according to claim 1.   6. The image forming apparatus according to claim 5, further comprising a process cartridge in which at least the developing device and the image carrier are accommodated together.

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