JP5483138B2 - Developing device, process cartridge, and image forming apparatus - Google Patents

Description

The present invention is a copying machine, a facsimile, an image forming apparatus such as a printer, it relates to a developing device and a process cartridge employed in this.

  Conventionally, a developing device using a two-component developer composed of a toner and a magnetic carrier is known. In this developing apparatus, a developer is carried on a developer carrying member as a so-called magnetic brush, and a predetermined amount is set by a developer regulating member arranged with a certain gap (hereinafter referred to as a doctor gap) with respect to the developer carrying member. The electrostatic latent image on the latent image carrier such as a photoconductor is developed by the formed developer thin layer with the layer thickness limited. As the developer carrying member, for example, a cylindrical developing sleeve that is rotatably arranged and carries and conveys a two-component developer, and a magnet roller that is fixedly arranged in the developing sleeve and has a plurality of magnetic poles arranged around it. The one with is used.

  In the developer restricting portion, the developer restricted without being able to pass through the doctor gap is restricted by the magnetic field formed by the magnet roller and stays upstream of the developer restricting member, except for the developer that does not contact the developing sleeve. To do. The staying developer becomes a packing state over time, and continuously deteriorates due to stress. As developer deterioration progresses, the developer transport amount tends to fluctuate, and there is a problem that the developer thin layer formation becomes unstable.

  In order to suppress deterioration of the developer staying on the upstream side of the developer regulating member in Patent Document 1, the inventor has a surface facing the developer on the upstream side in the developer transport direction of the developer regulating member. A developing device is proposed which is formed in parallel with the magnetic field vector direction of the magnetic field formed by a magnet roller located at a position facing the developer regulating member. In this developing device, by defining the shape of the upstream surface of the developer regulating member, the developer conveying property on the upstream side of the developer regulating member is improved, and the magnetic field of the magnet roller at the site facing the developer regulating member is improved. The amount of developer held by is adjusted to be not more than twice the amount of developer passing through the developer regulating member. As a result, the relative amount of the developer that receives a force from the developer regulating member out of the total developer amount on the upstream side of the developer regulating member is reduced to suppress the developer deterioration.

JP 2005-275069 A

  However, in order to achieve high image quality and high durability, it is desired to suppress the deterioration of the developer that has been regulated by the developer regulating member and stayed on the upstream side more effectively than Patent Document 1.

The present invention has been made in view of the above background, and an object of the present invention is to prevent developer deterioration in a developer regulating unit that regulates the layer thickness of a two-component developer carried on a developer carrying member. suppressing, developing device a developer capable of forming a stable thin layer is to provide a process cartridge及 beauty image forming apparatus.

In order to achieve the above object, the invention of claim 1 includes a developer carrier that contains a magnetic field generating means having a plurality of magnetic poles and carries and conveys a two-component developer composed of toner and a magnetic carrier, In a developing device including a developer regulating member that is disposed with a certain gap with respect to the surface of the developer carrying body and regulates a layer thickness of the developer carried on the surface of the developer carrying body.
Of the plurality of magnetic poles of the magnetic field generating means, the magnetic pole facing the developer regulating member is a first pole, and the magnetic poles adjacent to the first pole from the magnetic pole adjacent to the downstream side of the developer carrying direction of the developer carrier When the second pole and the third pole are used, the second pole is different in polarity from the first pole and the third pole, and a part of the magnetic force lines of the third pole exceeds the second pole and the developer. Passing through the vicinity of the downstream side of the downstream side of the regulating member and leaving the surface of the developer carrying member, and part of the magnetic force line of the first pole is located near the downstream side of the downstream side of the developer regulating member. A magnetic field is formed so as to pass opposite to the magnetic field lines of the third pole, and the developer has a component force in a direction from the vicinity of the downstream side of the downstream side of the developer regulating member toward the upstream side of the developer regulating member. Configure the magnetic field generating means so that a magnetic force acts ,
Position where a part and the opposing part and the first pole of magnetic field lines above Symbol third pole magnetic field lines, with respect to the normal direction of the surface of the developer carrying member, said developer regulating than developer carrying member surface It is characterized in that it is more than the above-mentioned fixed gap where the member is disposed and is closer to the root end of the developer regulating member.
According to a second aspect of the present invention, in the developing device of the first or second aspect, the maximum value of the normal direction magnetic flux density formed on the developer carrier by the second pole is 30 mT or more. It is what.
According to a third aspect of the present invention, in the developing device according to the first or second aspect , the first electrode is a pumping electrode that pumps the developer onto the developer carrier. is there.
According to a fourth aspect of the present invention, in the developing device according to any one of the first, second, and third aspects, the first agitating unit is provided with a developer agitating / conveying member disposed therein for agitating and conveying the toner and magnetic carrier. And a second agitation unit, wherein the developer on the developer carrier is collected into the first agitation unit, and the developer is supplied from the second agitation unit to the developer carrier. To do.
According to a fifth aspect of the present invention, there is provided a latent image carrier that carries a latent image, a charging unit that charges the latent image carrier, and a cleaning unit that cleans transfer residual toner remaining on the latent image carrier. In the process cartridge in which at least one selected from the above and a developing means for developing the latent image on the latent image carrier are integrally formed and detachable from the image forming apparatus main body, the developing means The developing device according to any one of claims 1, 2, 3 and 4 is used.
According to a sixth aspect of the present invention, there is provided a latent image carrier that carries a latent image, a charging unit that charges the latent image carrier, a developing unit that develops a latent image on the latent image carrier, and the latent image carrier. An image forming apparatus comprising a cleaning unit that cleans transfer residual toner remaining on the image carrier, wherein the developing unit according to any one of claims 1, 2, 3, and 4 is used. Is.

In the present invention, the magnetic force in the direction toward the developer carrying member is applied to the developer in the vicinity of the developer regulating member by the first pole disposed so as to face the developer regulating member. Further, a part of the magnetic field lines of the third pole having the same polarity pass in the vicinity of the downstream side surface of the developer regulating member, and a part of the magnetic field lines of the first pole pass so as to face the developer regulating member. A magnetic field is formed in the vicinity of the downstream side surface (see FIG. 4). By this magnetic field, a radial magnetic force is generated in the developer, that is, a magnetic force having a component force in the direction from the vicinity of the downstream side surface of the developer regulating member to the upstream is generated in the developer (see FIG. 5). This component force is away from the developer regulating member in the developer upstream of the developer regulating member. Therefore, the developer that is regulated by the developer regulating member and stays on the upstream side moves away from the upstream side wall surface of the developer regulating member. By creating such a developer flow, the developer is prevented from being in a packing state, and the deterioration of the developer is suppressed.
As a comparative example, in a conventional general developing device, the magnetic lines of force formed from the third pole flow into the second pole, and are opposed to the magnetic lines of force of the first pole as described above near the downstream side surface of the developer regulating member. Absent. For this reason, only the magnetic force in the direction toward the sleeve acts on the developer near the developer regulating member (see FIG. 12). Therefore, it is difficult to eliminate the stagnation of the developer in the upstream portion of the developer regulating member, and the packing state becomes over time.

  As described above, according to the present invention, the deterioration of the developer in the developer restricting portion that restricts the layer thickness of the two-component developer carried on the developer carrying member is suppressed, and the developer is stably formed into a thin layer. There is an excellent effect of being able to.

  Embodiments in which the present invention is applied to an image forming apparatus will be described below. FIG. 1 is a schematic configuration diagram of an image forming apparatus according to the present embodiment. This image forming apparatus is a color image forming apparatus that can form a full-color image by adopting a tandem method, and each color toner image of yellow, cyan, magenta, and black (hereinafter referred to as Y, C, M, and K) is used. Image forming devices 17Y, C, M, and K are provided. Below these image forming devices 17Y, 17C, 17M, and 17K, the image forming devices 17Y, 17C, 17M, and 17K are wound around a plurality of rollers 18 and 19 and carry and transport the recording paper 8 on the surface. A transfer conveyance belt 15 that moves while facing K is disposed. In addition, transfer bias rollers 5Y, 5C, 5M, and 5K that face the image forming devices 17Y, 17C, 17M, and 17K with the transfer conveyance belt 15 interposed therebetween are provided. Further, on the downstream side of the transfer bias rollers 5Y, C, M, and K in the recording paper conveyance direction of the transfer conveyance belt 15, a fixing device 24 that fixes unfixed toner on the recording paper 8 separated from the transfer conveyance belt 15 is fixed. It has. Further, an upper portion of the image forming apparatus main body is provided with a paper discharge tray 25 for stacking the recording paper 8 that has passed through the fixing device 24 and has the toner image fixed thereon.

  A plurality of paper feed cassettes 20, 21, and 22 that store the recording paper 8 are provided below the transfer conveyance belt 15. In addition, a paper feeding / conveying device as a recording paper supplying unit that feeds the recording paper 8 from each of the paper feeding cassettes 20, 21, 22 to a transfer region where the transfer / conveying belt 15 and the image forming devices 17 Y, C, M, K are opposed to each other. 26, and a registration roller 23 for supplying the recording paper conveyed from each of the paper feeding cassettes 20, 21, and 22 in accordance with the timing of image formation by the image forming apparatuses 17Y, 17C, 17M, and 17K.

  In FIG. 1, the transfer conveyance belt 15 is disposed in an oblique direction so that the image forming apparatus is small in the horizontal direction in the drawing, and the recording paper conveyance direction indicated by an arrow is an oblique direction. Thus, in the image forming apparatus, the width of the housing in the left-right direction in the figure is slightly longer than the length in the longitudinal direction of the A3 size recording paper. That is, the image forming apparatus is greatly reduced in size by being the minimum size required to accommodate the recording paper inside.

  Each of the image forming devices 17Y, 17C, 17M, and 17K includes drum-shaped photoreceptors 1Y, 1C, 1M, and 1K as latent image carriers. With respect to the rotation directions of the photoreceptors 1Y, 1C, 1M, and 1K, there are charging devices 2Y, C, M, and K, developing devices 3Y, C, M, and K, cleaning devices 6Y, C, M, and K, respectively. doing. In addition, it is a known configuration in which the writing light L is irradiated from the exposure devices 16Y, 16C, M, and K between the charging devices 2Y, C, M, and K and the developing devices 3Y, C, M, and K. The photoreceptors 1Y, 1C, 1M, and 1K may be belt-shaped instead of drum-shaped.

  Further, as shown in FIG. 11, each image forming device 17 integrally forms the photosensitive member 1 and the respective process means of the charging device 2, the developing device 3, and the cleaning device 6 in a frame (not shown). The process cartridge 10 may be configured to be detachable from the main body of the image forming apparatus. Thereby, maintainability and exchangeability can be improved even for long-term use of the printer.

  In the image forming apparatus having such a configuration, each color toner image is formed by each of the image forming apparatuses 17Y, 17C, 17M, and 17K at the start of image formation. In each of the image forming devices 17Y, 17C, 17M, and 17K, the photoreceptors 1Y, 1C, 1M, and 1K are rotationally driven by a main motor (not shown) and are uniformly charged by the charging devices 2Y, 2C, 2M, and 2K. The exposure device 16Y, 16C, M, or K emits the writing light L in accordance with the image information for each color obtained by color separation of the image, and an electrostatic latent image is formed. The electrostatic latent images formed on the photoconductors 1Y, 1C, 1M, and 1K are developed by the developing devices 3Y, 3C, 3M, and 3K to form respective color toner images. On the other hand, the recording paper 8 fed and transported from the paper feed cassette is carried by the transfer transport belt 15 and transported to the transfer area in accordance with the image forming timing by the image forming devices 17Y, 17C, 17M, and 17K. Is done. The toner images formed on the photoconductors 1Y, 1C, 1M, and 1K are transferred by transfer bias means 5Y, 5C, 5M, and 5K at the facing portions of the photoconductors 1Y, 1C, 1M, and 1K and the transfer conveyance belt 15. The images are sequentially transferred onto the recording paper 8 carried on the conveying belt 15. In this way, the toner images formed on the photoreceptors 1Y, 1C, 1M, and 1K are transferred in the order of Y (yellow), C (cyan), M (magenta), and K (black), and the superimposed colors are transferred. A toner image is formed. The recording paper 8 to which the toner image has been transferred is separated from the transfer conveyance belt 15, conveyed to the fixing device 24, fixed, and discharged as a copy image to a discharge tray 25 outside the apparatus. On the other hand, after the transfer onto the recording paper 8, the photoreceptors 1Y, 1C, 1M, and 1K remove the transfer residual toner by the cleaning devices 6Y, 6C, 6M, and 6K, and if necessary, use a static elimination lamp (not shown). After the charge removal, the operation of being uniformly charged by the charging devices 2Y, 2C, 2M, and 2K is repeated again.

  Next, the developing device will be described in detail. The developing devices 3Y, 3C, 3M, and 3K of the image forming apparatus of the present embodiment use toners of different colors (Y, C, M, and K) as image forming materials, but the other configurations are the same. ing. For this reason, hereinafter, the subscripts Y, C, M, and K are omitted, and the developing device 3 will be described.

  FIG. 2 is a schematic configuration diagram of the developing device 3. The developing device 3 is a two-component developing device using a two-component developer composed of toner and carrier. As shown in FIG. 2, the developing device 3 includes a developing roller 30 as a developer carrying member provided so as to face the photosensitive member 1, and a direction parallel to the axis of the developing roller, that is, in one direction of the axis, that is, on the front side of the sheet. A first developer agitating and conveying member 34 that conveys the developer to the side, and a second developer agitating and conveying member 35 that is arranged in parallel and conveys the developer in the other direction of the shaft, that is, the back side of the sheet. Yes. Further, in the rotation direction of the developing roller 30 that rotates counterclockwise in FIG. 2, the developer pumped up by the developing roller 30 on the downstream side of the facing region between the developing roller 30 and the first developer stirring and conveying member 34. The developer regulating member 33 is disposed with a doctor gap with respect to the developing roller 30 so as to regulate the above.

  The developing roller 30 includes a magnet roller having a plurality of magnets arranged in the circumferential direction, and a cylindrical sleeve rotates around the magnet roller. The sleeve is made of a nonmagnetic metal such as aluminum. The magnet roller is fixed so that each magnet faces a predetermined direction, and a sleeve rotates around the magnet roller to convey the developer attracted by the magnet. In a typical developing device, the developer on the sleeve is formed into a magnetic brush on the chain by using magnetic poles with alternating polarities. When the sleeve is rotated, the magnetic brush is conveyed while being rolled over.

  FIG. 3 shows the direction of the magnetic flux density vector formed on the sleeve 31 by the magnet roller 32 included in the conventional general developing apparatus. In the magnet roller 32 of FIG. 3, the magnetic pole disposed opposite to the developer regulating member 33 is a first pole, and the magnetic pole sequentially disposed on the downstream side in the developer transport direction is a second pole and a third pole. The first and third poles have the same polarity, and the second pole has a different polarity from the first and third poles. The magnetic field lines of each magnetic pole flow into the adjacent magnetic pole. When a carrier made of a magnetic material passes through such a magnetic field, magnetization of the carrier occurs along the magnetic flux density, and a magnetic brush is formed along the magnetic line. At this time, when the sleeve 31 is rotated, the sleeve 31 is conveyed while changing its shape following the magnetic lines of force generated by the magnetic field. Here, in the developer restricting portion, among the developers restricted so as not to pass through the doctor gap with the developer restricting member 33, those other than those that come into contact with the sleeve 31 are restrained by the formed magnetic field, and the developer is restricted. It stays on the upstream side of the restricting member 33 and enters a packing state when used over time. The developer in the packing state deteriorates due to continuous stress. When the developer deteriorates, the developer conveyance amount decreases, and the thin layer formation of the developer becomes unstable.

  FIG. 4 illustrates the direction of the magnetic flux density vector formed by the magnet roller 32 of the developing device 3 employed in the image forming apparatus of the present embodiment. The magnetic field lines of the first pole arranged opposite to the developer regulating member 33 flow into the second pole of different polarity adjacent downstream, and the developer passes through the developer regulating member 33 and is conveyed downstream. To form a magnetic field. Further, the magnetic field lines of the third pole, which have the same polarity as the first pole and are arranged downstream of the second pole, flow into the second pole, and part of the magnetic flux density peak position of the second pole (in the figure) A) is exceeded, passes through the vicinity of the downstream side surface of the developer regulating member 33, and is separated from the surface of the sleeve 31. Further, a part of the magnetic field lines of the first pole having the same polarity pass through the vicinity of the downstream side surface of the developer regulating member 33 so as to oppose the magnetic field lines of the third pole (hereinafter, referred to as a facing part), thereby controlling the developer. A magnetic field shown in FIG. 4 is formed in the vicinity of the downstream side surface of the member 33. Since the polarity of the magnetic pole is not related to S or N, the same applies even if the direction of the magnetic field lines is reversed.

  FIG. 5 shows the magnetic force acting on the developer near the developer regulating member. In this developing device, the magnetic force acting on the developer in the vicinity of the developer regulating member has a direction toward the sleeve 31 due to the first pole arranged to face the developer regulating member 33. Further, a radial magnetic force acts from the opposing portion by the magnetic field formed by the opposing portion of the magnetic lines of force of the first and third poles. This is because a magnetic force having a component force in a direction toward the upstream side of the developer regulating member 33 acts on the developer on the upstream side of the developer regulating member 33 (see FIG. 5). The developer that is regulated by the developer regulating member 33 and stays on the upstream side moves away from the upstream side surface of the developer regulating member 33 by the magnetic force. Thus, by creating the developer flow by the magnetic pole of the magnet roller, it is possible to prevent the developer from being packed and to suppress the deterioration of the developer.

  Further, as the magnetic force approaches the sleeve 31, a normal component toward the surface of the sleeve 31 increases. Further, the normal component increases as the distance from the developer regulating member 33 increases. For this reason, the developer upstream of the developer regulating member 33 is subjected to a force that flows away from the developer regulating member 33 toward the upstream side and flows between the developer regulating member 33 and the sleeve 31. become. By this force, the developer stably flows through the gap with the developer regulating member 33. As described above, the developer flow that flows between the magnetic force generated by the magnetic force of the magnet roller 32 and the developer regulating member 33 is created. Compared with the developing device, the change in developer transport amount due to the change in developer characteristics is small, and the formation of the developer thin layer is stable.

  Further, the circumferential range in which the magnetic lines of the third pole and the first pole face each other is formed in the vicinity of the downstream side surface of the developer regulating member 33 and up to the magnetic flux density peak angle in the normal direction of the second magnet. There is a need. If it is located on the downstream side beyond the peak angle of the pole normal flux density of the second pole, the magnetic force flows to the second pole, and an opposing portion cannot be formed on the upstream side of the developer regulating member 33.

  Further, the range in the normal direction in which the magnetic lines of force of the third pole and the first pole face each other is a position farther from the sleeve 31 than the size of the doctor gap and closer to the root end of the developer regulating member 33, That is, it is preferable to be present at a position facing the downstream side surface of the developer regulating member 33. This is not preferable because when the opposing portion is formed at a position closer to the doctor gap, that is, in the region where the developer flows, the normal force is applied and the developer moves away from the sleeve 31. On the other hand, even if it is formed beyond the root portion of the developer regulating member 33, the component force in the direction toward the upstream side from the developer regulating member is reduced, which makes it difficult to produce the developer flow described above.

  Such a magnetic flux density can be created by appropriately setting the balance of the magnetic pole strength of the magnet roller 32. As a specific setting method, first, the strengths of the first pole, the third pole, and the fourth pole downstream thereof are adjusted. When it is desired to form the facing portion in the vicinity of the first pole, the fourth pole is made stronger than the third pole, and the first pole is made weaker than the third pole. Thereby, the magnetic field lines that have flowed out of the first pole are biased toward the first pole. In this case, since the opposing part of the said magnetic force line is formed in the sleeve 31 vicinity, after that, the normal line position of the opposing part of the said magnetic force line can be set by adjusting the intensity | strength of a 2nd pole.

ここで、表面磁化分布σ、σn ：σの第n次フーリエ係数、δn ：第n次フーリエ係数の位相、θ：基準線から任意の位置までの角度である。
磁石表面における境界条件を考慮すると，磁界Ｈは、次式のように，法線方向成分Ｈrと接線方向成分Ｈθで表すことができる。

ここで、ｉ、ｊは、それぞれ法線方向と接線方向の単位ベクトル、An：磁界のフーリエ係数、μ0：真空の透磁率、a：磁石ローラの半径、r：磁石ローラの軸からの距離である。 In order to determine these magnetic poles, it is necessary to grasp and measure the magnetic field distribution on the sleeve 31. In order to grasp the density of the space, there is a method in which a magnetic probe or the like is arranged in the normal direction and the tangential direction, and the probe is arranged in a necessary space to perform measurement. It is also possible to obtain the magnetic field distribution in space with high accuracy by applying the following equation.

Here, the surface magnetization distribution σ, σn: the nth-order Fourier coefficient of σ, Δn: the phase of the nth-order Fourier coefficient, and θ: the angle from the reference line to an arbitrary position.
Considering the boundary conditions on the magnet surface, the magnetic field H can be expressed by a normal direction component Hr and a tangential direction component Hθ as shown in the following equation.

Here, i and j are unit vectors in the normal direction and tangential direction, respectively, An: Fourier coefficient of magnetic field, μ0: permeability of vacuum, a: radius of magnet roller, r: distance from the axis of magnet roller. is there.

  Further, when the magnetic force is low due to the magnetic field formed in the vicinity of the downstream side surface of the developer regulating member 33, the conveyance is likely to be uneven. Therefore, by setting the size of the second pole on the downstream side to 30 Tm or more, the developer can be stably conveyed to the development area.

  Hereinafter, the developing device 3 according to the present embodiment will be specifically described based on experimental results. In this experiment, a developing roller having a magnetic flux density direction of FIG. 6A and a normal direction magnetic flux density distribution on the sleeve 31 of FIG. 6B was prepared and mounted on the developing device 3 of FIG. , Examples). In the developing device of the embodiment, the opposing portion of the magnetic lines of the third pole and the first pole exists between the developer regulating member 33 and the peak angle of the normal magnetic flux density of the magnetic field generated by the second pole. . In addition, a developing roller having a general magnetic flux density direction as shown in FIG. 7A and a normal direction magnetic flux density distribution on the sleeve 31 as shown in FIG. 3 (hereinafter referred to as a comparative example). In the developing device of the comparative example, the magnetic field lines of the third pole flow into the second pole, and there is no portion facing the first pole.

  In both the developing devices of the example and the comparative example, the doctor gap is set so that the amount of developer passing through the developer regulating member 32 is 50 [mg / cm 2]. Then, with the linear velocity of the developing sleeve 31 set to 200 [mm / sec], only the developing device 3 was driven for 120 minutes, and the amount of developer passing through the developer regulating member 32 was measured every 10 minutes. FIG. 8 shows the measurement results. As shown in FIG. 8, it can be seen that the developing device 3 of the present embodiment has less change in the amount of passage than the conventional developing device.

  As described above, the developing device 3 of the present embodiment controls the movement of the developer by using the magnetic force acting on the developer upstream of the developer regulating member by the magnet roller 32. Therefore, the larger the space where no developer exists on the upstream side and the more easily the developer moves, the higher the effect. As a configuration of such a developing device, the first electrode is a developer pumping electrode. Specifically, the sleeve 31 is disposed away from the developer stirring unit, and the developer is pulled from the developer stirring unit by the magnetic force of the magnet roller 32 included therein and supplied to the sleeve 31. In the process of moving from the developer stirring section to the sleeve 31, there is a gap between the carriers, so the influence of other carriers is small and the influence of the magnetic field is relatively large. Therefore, when the first pole is used as a pumping pole, the effect of creating a developer flow is further increased.

  FIG. 9 is a schematic configuration diagram of a modified example of the developing device. The developing device of FIG. 9 includes a first agitation unit in which a first developer agitating and conveying member and a second developer agitating and conveying member for agitating and conveying the two-component developer in opposite directions with a partition plate interposed therebetween, respectively. And a second stirring unit. The first developer agitating / conveying member is connected to the developing sleeve 31 in parallel to the axial direction on the downstream side of the developing area where the developing sleeve 31 faces the photoconductor, and the second developer agitating / conveying member is located upstream of the developing area. It arrange | positions so that it may oppose. In this developing device, the developer stirred and conveyed by the second developer agitating / conveying member is supplied from the second agitating unit to the developing roller 30, and the developer on the developing roller 30 that has passed through the developing region is fed to the first developer agitating member. It is circulated in one direction so as to be recovered to the first stirring unit by the conveying member. In this way, all the developer that has passed through the development area is returned to the first developer agitating and conveying member side, so that all the developer on the first developer agitating and conveying member side is not used for development (reset). The toner concentration is not lowered. Accordingly, the toner concentration on the second developer agitating / conveying member side is always constant from the upstream side to the downstream side, and there is no difference in the toner concentration on the developing sleeve 31. Therefore, there is no density difference and the density followability is uniform. An image can be obtained. Further, the developer conveyed to the development area is a developer that has been sufficiently agitated and pumped up from the second developer agitating / conveying member side and has passed through the area facing the developer regulating member only once. The charging conditions are equal and the variation in charge amount is reduced. Therefore, since the toner is uniformly charged, it is possible to form a high-quality image free from toner scattering and background stains and free from variations in image details. On the other hand, since the developer is easily depleted on the downstream side of the developing roller 30, it is necessary to increase the number of rotations of the agitating and conveying member, which is problematic in that durability is lowered.

  Therefore, the developing device of FIG. 9 uses the developing roller 30 in which the opposing portion of the magnetic field lines of the third pole and the first pole is in the above-described range and includes the magnet roller 32 having the first pole as a pumping pole. FIG. 10A shows the direction of the magnetic flux density of the magnet roller used, and FIG. 10B shows the normal direction magnetic flux density distribution on the sleeve 31. By using such a magnet roller 32, the developer supplied from the second stirring unit is smoothly taken in. Therefore, it is difficult for the developer to be exhausted downstream of the developing roller 30 as compared with the conventional case.

  The embodiment of the image forming apparatus to which the present invention is applied has been described above. However, the image forming apparatus is a known one such as a copying machine, a facsimile machine, a printer, etc., and can perform image formation using the above developing device. Any form may be used. Further, the image forming apparatus of the above embodiment forms a color image, but may form a single color image.

As described above, according to the present embodiment, in the developing device 3 that uses the developer carrying member including the developing sleeve 31 that includes the magnet roller 32 as a magnetic field generating unit having a plurality of magnetic poles, in the vicinity of the downstream side surface of the developer regulating member 33. In addition, a magnet roller 32 is used that has the same polarity as the first pole and passes through the third pole downstream of the second pole and the magnetic lines of force opposite to the first pole. Due to the influence of the opposing portion of the magnetic force lines, the developer on the upstream side of the developer regulating member 33 has a magnetic force having a component force in the direction toward the upstream side from the developer regulating member in addition to the direction toward the developer carrying member. Acts (see FIG. 5). The developer that is regulated by the developer regulating member and stays on the upstream side moves away from the upstream side surface of the developer regulating member by the magnetic force. By creating such a developer flow with the magnetic field generating means, it is possible to avoid the developer from being packed and to suppress the deterioration of the developer.
Further, the range of the opposing portion in the normal direction is a position farther from the sleeve 31 than the size of the doctor gap and closer to the root end of the developer regulating member 33, that is, at the downstream rear surface of the developer regulating member. What exists in the position which opposes is preferable. This is not preferable because when the facing portion is formed at a position closer to the doctor gap, that is, in a region where the developer flows, a normal force is applied and the developer moves away from the sleeve 31. On the other hand, even if it is formed beyond the root portion of the developer regulating member 33, the component force in the direction toward the upstream side from the developer regulating member is reduced, which makes it difficult to produce the developer flow described above.
Further, when the magnetic field in the vicinity of the facing portion is low, unevenness in conveyance is likely to occur. Therefore, by setting the size of the second pole on the downstream side of the facing portion to 30 Tm or more, the developer can be stably conveyed to the development area.
In the developing device 3, the first pole is used as a pumping pole. The developing device 3 controls the movement of the developer using the magnetic force of the developing roller 30 on the upstream side of the developer regulating member 33. Therefore, the larger the space where no developer exists on the upstream side and the more easily the developer moves, the higher the effect. As a configuration of such a developing device, the first electrode is a developer pumping electrode. In the process in which the developer moves from the stirrer to the sleeve 31 when the developer is pumped up, there is a gap between the carriers, so the influence of other carriers is small and the influence of the magnetic field is relatively large. Therefore, when the first pole is used as a pumping pole, the effect of creating a developer flow is further increased.
In addition, the first agitation unit and the second agitation unit, each having a developer agitating / conveying member disposed therein, are collected, and the developer on the developing roller 30 is collected into the first agitation unit, and the developing roller from the second agitation unit The above-described magnet roller is used in a developing device that supplies developer to 30. In this developing device, the developer tends to be exhausted on the downstream side of the developing roller 30. Therefore, the developing roller 30 including the magnet roller 32 having the third magnetic pole and the first magnetic pole facing each other in the above-described range and having the first pole as a pumping pole is used. As a result, the developer supplied from the second stirring unit is smoothly taken in. Therefore, it is difficult for the developer to be exhausted downstream of the developing roller 30 as compared with the conventional case.
In addition, a process cartridge 100 in which the photosensitive member 1, the charging device 2, the developing device 3, and the cleaning device 6 are integrally formed in a frame (not shown) and can be attached to and detached from the image forming apparatus main body. May be made. Thereby, maintainability and exchangeability can be improved even for long-term use of the printer.

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a schematic configuration diagram of a developing device. Explanatory drawing of the magnetic force line formed with the magnet roller in the conventional developing device. Explanatory drawing of the magnetic force line formed with the magnet roller in the image development apparatus of this invention. FIG. 6 is an explanatory diagram of magnetic force acting on a developer in the vicinity of a developer regulating member in the developing device of the present invention. (A) of the magnetic roller in the image development apparatus of an Example is a direction of magnetic flux density, (b) is a figure which shows normal direction magnetic flux density distribution on a sleeve. (A) of the magnetic roller in the developing device of a comparative example, (b) is a figure which shows the normal direction magnetic flux density distribution on a sleeve, (b). 6 is a graph showing changes with time in the amount of developer passing through a developer regulating member in the developing devices of Examples and Comparative Examples. FIG. 9 is a schematic configuration diagram of a developing device according to a modification. (A) of the magnetic roller in the developing device of a modification, (b) is a figure which shows the normal direction magnetic flux density distribution on a sleeve, (b). FIG. 2 is a schematic configuration diagram of a process cartridge. Explanatory drawing of the magnetic force which acts on the developing agent of the developer control member vicinity in the developing device of a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Charging device 3 Developing device 5 Transfer bias roller 6 Cleaning device 15 Transfer conveyance belt 16 Exposure device 17 Image forming device 20, 21, 22 Paper feed cassette 24 Fixing device 30 Developing roller 31 Sleeve 32 Magnet roller 33 Developer regulation Member 34 First developer stirring and conveying member 35 Second developer stirring and conveying member

Claims (6)

A developer carrier that contains a magnetic field generating means having a plurality of magnetic poles and carries and conveys a two-component developer composed of toner and a magnetic carrier, and a fixed gap with respect to the surface of the developer carrier. In a developing device comprising a developer regulating member that regulates the layer thickness of the developer carried on the surface of the developer carrying body,
Of the plurality of magnetic poles of the magnetic field generating means, the magnetic pole facing the developer regulating member is a first pole, and the magnetic poles adjacent to the first pole from the magnetic pole adjacent to the downstream side of the developer carrying direction of the developer carrier When the second pole and the third pole are used, the second pole is different in polarity from the first pole and the third pole, and a part of the magnetic force lines of the third pole exceeds the second pole and the developer. Passing through the vicinity of the downstream side of the downstream side of the regulating member and leaving the surface of the developer carrying member, and part of the magnetic force line of the first pole is located near the downstream side of the downstream side of the developer regulating member. A magnetic field is formed so as to pass opposite to the magnetic field lines of the third pole, and the developer has a component force in a direction from the vicinity of the downstream side of the downstream side of the developer regulating member toward the upstream side of the developer regulating member. Configure the magnetic field generating means so that a magnetic force acts ,
A position where a part of the magnetic field lines of the third pole and a part of the magnetic field lines of the first pole are opposed to each other from the surface of the developer carrier with respect to the normal direction of the surface of the developer carrier. A developing device characterized in that it is more than the above-mentioned fixed gap where it is disposed and closer to the root end of the developer regulating member . The developing device 請 Motomeko 1, a developing device which is characterized in that the maximum value of the normal flux density formed on the developer carrying member by the second pole and more 30 mT. 3. The developing device according to claim 1, wherein the first electrode is a pumping electrode that pumps up the developer onto the developer carrying member. In any of the developing apparatus according to claim 1, 2 or 3, and a first agitating part and a second agitating part disposed respectively inside the developer stirring and conveying member for agitating and conveying a toner and a magnetic carrier And a developer that collects the developer on the developer carrying member to the first stirring unit, and supplies the developer to the developer carrying member from the second stirring unit. At least one selected from a latent image carrier that carries a latent image, a charging unit that charges the latent image carrier, and a cleaning unit that cleans transfer residual toner remaining on the latent image carrier, A process cartridge that is integrally formed with a developing unit that develops a latent image on the latent image carrier and is configured to be detachable from the main body of the image forming apparatus. Or a process cartridge using any one of the developing devices 4 ; A latent image carrier that carries a latent image, a charging unit that charges the latent image carrier, a developing unit that develops a latent image on the latent image carrier, and a transfer residual toner remaining on the latent image carrier 5. An image forming apparatus comprising: a cleaning unit that cleans the image forming apparatus, wherein the developing unit according to claim 1, 2, 3, or 4 is used as the developing unit.

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