JP5086593B2 - Developing device, process cartridge, and image forming apparatus - Google Patents

Description

The present invention relates to a developing device having a developing roller, a process cartridge, and an image forming apparatus.

In an image forming apparatus such as an electrophotographic copying machine, a laser beam printer, a facsimile, or a complex machine having at least two functions thereof, it is formed on a latent image carrier such as a photosensitive drum or a photosensitive belt. A visible image is obtained by developing the electrostatic latent image with a developing device. In such a developing device, a so-called two-component developing system using a developer in which a non-magnetic toner and a magnetic carrier are mixed is well known and widely used.
In the two-component development method, a developer is magnetically attracted to the outer peripheral surface of the developing roller to form a magnetic brush, and an electrostatic latent image is developed in a developing area where a developable electric field is secured between the developing roller and the latent image carrier. By selectively supplying and adhering toner from the magnetic brush to the latent image surface of the opposing latent image carrier by the electric field between the latent image carrier formed with the sleeve to which an electrical bias is applied, The electrostatic latent image is developed.
The developing roller generally has a cylindrical developing sleeve made of a non-magnetic material, and is provided with a magnet roll that forms a magnetic field on the sleeve surface so as to generate a spike of developer on the sleeve surface. At the time of spike, the carrier spikes on the sleeve so as to follow the lines of magnetic force generated by the magnet roll, and charged toner is attached to the carrier related to the spike. The magnet roll has a plurality of magnetic poles formed of magnets or the like, and includes a developing magnetic pole for starting up the developer, particularly in the developing region portion of the sleeve surface. When at least one of the developing sleeve and the magnet roll moves, the developer having raised the sleeve surface moves, and the developer conveyed to the developing area follows the magnetic lines generated from the developing main pole. The developer chain spike comes into contact with the surface of the latent image carrier so as to bend, and the developer chain spike that comes into contact with the electrostatic latent image is rubbed based on the relative linear velocity difference from the latent image carrier. Supply toner while matching.

In recent years, there has been a growing need for high image quality, compactness, and low cost in electrophotographic image forming apparatuses. As a means for achieving this, the diameter of carriers and toners used in developers and the gap between latent image carriers and developing rollers have been reduced. It has been proved that measures such as narrowing are adopted and it is effective in improving the image quality. Moreover, because of compactness, the space in the unit is reduced and the amount of developer is also reduced. However, as a side effect, the accompanying developer is likely to occur.
This rotation of the developer does not occur if the developer used is separated from the developing sleeve and the fresh developer is pumped up to the developing sleeve, but the distance between the developer peeling electrode and the pumping electrode is reduced in order to make the unit compact. By reducing the diameter of the carrier and toner, the fluidity of the developer will drop, and the developer will be peeled off from the developing sleeve more slowly. Is likely to occur. For this reason, an image with nonuniform image density is generated.
In addition, the magnetic flux density distribution between the development peeling pole and the pumping magnetic pole downstream from it contributes, and by separating the distance between the magnetic poles, the developer peeling position and the pumping position tend to improve, Considering matching with the developing device configuration, the degree of freedom in designing magnetic characteristics is not high, and improvement is difficult.

Patent Document 1 includes a developer carrying member including a non-magnetic developing sleeve that has a magnetic field generating means fixed therein, and carries a two-component developer comprising a magnetic carrier and a toner on the surface and rotates. Image formation for forming an electrostatic latent image on an image carrier into a toner image using a developing device including a developer amount regulating member made of a rigid body for regulating the amount of developer carried on the developer carrier. In the apparatus, the gap between the developing sleeve and the image carrier is 0.4 mm or less, and the magnetic carrier has at least a coating film having a binding resin and particles, and the particle diameter D and the binding An image forming apparatus is disclosed in which the resin film thickness h is 1 <[D / h] <10. As a result, in an image forming apparatus using a two-component developer, the developing ability is enhanced to improve the image quality, and the developer is stably conveyed to the development area while suppressing fluctuations in the pumping amount, thereby producing a high-quality image. I was able to get it for a long time.
Patent Document 2 discloses a developing roller including a nonmagnetic cylinder that can rotate and a magnetic field generating unit that is fixedly installed with magnets for forming a plurality of magnetic poles inside the nonmagnetic cylinder, and a magnetic carrier. And a developer container containing a two-component developer made of non-magnetic toner, an agitating / conveying means for agitating and conveying the two-component developer in the developer container, and a case member surrounding the developing roller, In a two-component developing device that conveys developer by rotating the non-magnetic cylinder and develops an electrostatic latent image on an image carrier by magnetic brush development, the developer passes through the developing position in the magnetic poles constituting the magnetic field generating means. A normal vector standing on the peripheral surface of the developing roller at the lowest repulsive magnetic field formed between the poles of two same-polarity magnetic poles that separate the developer from the developing roller is reflected by the inner wall surface of the case member. Made The direction of the normal reflection vector is set to 0 to 70 degrees with respect to the horizontal line on the side away from the developing position, and the magnetic pole located on the downstream side in the rotation direction of the developing roller among the two same-polarity magnetic poles. A developing device is disclosed in which the peak magnetic force in the normal direction is 35 mT or more and 55 mT or less. Thus, the developing roller 51 provided with a magnetic field generating means, an agitating / conveying means for agitating and conveying the developer in a developing container containing a two-component developer, and a case member surrounding the developing roller, the developer In the two-component developing device that conveys the toner by rotating the developing roller 51 and magnetic brush develops the electrostatic latent image on the photosensitive drum 20, the abnormal image such as uneven image density is suppressed while saving space and increasing the speed. I was able to.
However, both methods have been problematic because they cannot sufficiently suppress the occurrence of follow-up and pumping unevenness from the developer circulation section.

JP 2003-233255 A JP 2005-266366 A

  Accordingly, the present invention has been made in view of the above-mentioned problems, and the problem is that a developing roller in which non-uniform image density and image unevenness are eliminated, a developing device having the developing roller, a process cartridge, and an image forming apparatus. Is to provide.

The features of the present invention, which is a means for solving the above problems, are listed below.
The developing device of the present invention includes a developing roller that draws up the developer, forms a magnetic brush, and slides the developer on the latent image carrier, and the developing roller includes a non-magnetic sleeve and the non-magnetic sleeve. and a magnet roll which is fixedly disposed in the magnetic sleeve, the magnet roll, to the radial direction, and the magnetic pole scooping developer, a first current image agent transport poles, the main for developer bristle a magnetic pole, and a second current image agent transport poles, with at least 5 poles and the developer peeling pole, the half-value width of the magnetic flux density with respect to the normal direction of the developer peeling poles, 15 ° or more with respect to the radial direction The developer regulating member is disposed below the developer conveying magnetic pole in the developing roller at 25 ° or less. Here, the half-value width, Ru der that the angular width of the portion refers to a half value of the maximum normal force in the normal direction of the magnetic force distribution curve.
Also, the developing device of the present invention, further, the developer peeling pole, characterized in that facing the said non-magnetic sleeve rotation upstream side with respect to the radial direction.
The developing device of the present invention is further characterized in that the developer peeling magnetic pole is disposed above the center of the developing roller.

The process cartridge of the present invention is a process cartridge that integrally supports at least a latent image carrier and a developing device, wherein the process cartridge includes any one of the developing devices described above .
An image forming apparatus according to the present invention includes at least a latent image carrier and a developing device that develops a latent image formed on the latent image carrier . It has a developing device.
The image forming apparatus of the present invention, further, the image forming apparatus is characterized by comprising a process cartridge of the upper Symbol detachably.

According to the present invention, it is possible to provide a developing device, a process cartridge, and an image forming apparatus having a developing roller in which uneven image density and image unevenness are eliminated by the means for solving the problems.

  The best mode for carrying out the present invention will be described below with reference to the drawings. Note that it is easy for a person skilled in the art to make other embodiments by changing or correcting the present invention within the scope of the claims, and these changes and modifications are included in the scope of the claims. The following description is an example of the best mode of the present invention, and does not limit the scope of the claims.

Embodiments in which the present invention is applied to an image forming apparatus will be described below.
FIG. 1 shows an electrophotographic full-color printer as an image forming apparatus according to this embodiment. An image unit 10 of the printer includes an intermediate transfer belt 11 as an image carrier that moves endlessly in the direction of an arrow. Four image forming units, which are toner image forming means, are provided on a lower stretched surface of the intermediate transfer belt 11. 12Y, 12C, 12M, and 12K are arranged. Y, C, M, and K along the number of the image forming unit correspond to the color of the toner to be handled, Y means yellow, C means cyan, M means magenta, and K means black. Similarly, Y, C, M, and K are provided along a latent image carrier (hereinafter referred to as a photoreceptor) 40 that is provided in the image forming unit and rotates together with the intermediate transfer belt 11. The photoconductors 40Y to 40K are arranged at equal intervals so as to be in contact with a part of a stretched portion with the intermediate transfer belt 11 at least during image formation.

  FIG. 2 is a diagram illustrating the image forming unit. Although the toner colors to be handled are different, the image forming units 12Y, 12C, 12M, and 12K have the same configuration, and the configuration will be described as the image forming unit 12 with reference to FIG. In FIG. 2, a cylindrical photosensitive member 40 supported to rotate in the direction of the arrow by a drive source (not shown) during operation of the printer is disposed. In addition, an image forming member such as a charging device 41, an exposure device, a developing device 1, a cleaning device 42, and a photostatic device, an electric potential sensor, and an image sensor are arranged around the photoconductor 40 in accordance with an electrophotographic process. Since their configuration and operation are basically known, for the sake of simplification of description, portions particularly related to the present invention will be described here.

An electrostatic latent image is formed on the surface of the uniformly charged photoreceptor 40 by exposure based on image information. This electrostatic latent image is developed by the developing device 1 to form a toner image on the surface of the photoreceptor. The toner image is transferred to the intermediate transfer belt 11 (FIG. 1) by the transfer charger 13. The yellow (Y), cyan (C), magenta (M), and black (K) color toner images transferred to the intermediate transfer belt 11 are superimposed and fed from the paper feed unit 14 (FIG. 1) to the paper feed rollers and registration rollers. The image is transferred using a secondary transfer roller 15 onto the sheet conveyed through the pair. After the transfer, the toner image is fixed by the fixing unit 16 and is discharged out of the apparatus as it is in the case of single-sided image formation. In the case of double-sided image formation, a reversing path (not shown) is known. Through the double-sided portion (not shown), and again sent to the secondary transfer unit.
In this embodiment, at least the photosensitive member 40 and the developing device 1 constitute a cartridge unit, and a process cartridge can be constituted by further including a charging device 41, a cleaning device 42, and a charge eliminating device. When referred to as a process cartridge, the developing device 1 and other process means are integrated and detachable, and the cartridge unit alone can be a process cartridge, or the developing device 1, the photoreceptor 40, and the charging device 41. Various variations such as the developing device 1, the photoreceptor 40, the charging device 41, and the cleaning device 42 may exist.

  Next, the image forming unit will be described with reference to FIG. 2 is a process cartridge in which the photosensitive member 40, the developing device 1, the charging device 41 (charging roller in this embodiment), and the cleaning device 42 (cleaning blade in this embodiment) are integrated. The developing device 1 includes a developing roller 2 that forms a toner visualized image on a latent image on the photoconductor 40 optically formed by a writing unit 43 on the photoconductor 40, and upstream of the developing roller development area. On the side, there is a regulating member 4 (hereinafter referred to as a developing doctor 4) that regulates the amount of developer on the developing roller 2 to a certain amount. A developing tank portion in the developing device 1 contains a two-component developer in which toner particles and magnetic particles (carriers) are mixed. The developer includes two conveying screws, a first conveying screw 5a and a second conveying screw. It is circulated by the screw 5b. Further, a toner concentration sensor 6 is disposed below the second conveying screw 5b, and the toner concentration in the developing tank is measured at any time and controlled so as to be within an appropriate value. In addition, an inlet seal 7 for preventing toner scattering from the developing nip portion is disposed on the right side of the developing doctor 4.

The developing roller 2 includes a developing sleeve 21 and a magnet roll 22 which are nonmagnetic sleeves, and the magnet rolls have different magnetization widths and magnetic flux densities depending on their roles.
When the attenuation rate of the magnetic flux density in the normal direction of the developer peeling magnetic pole 23 is 40% or more, the magnetic flux density decreases rapidly as the distance from the roller surface increases, so the magnetic brush formed by the developer is short and dense. Therefore, the developer can be smoothly peeled off from the developer peeling magnetic pole 23 from the developing sleeve 21, and the developing roller 2 that is difficult to rotate can be obtained.
In order to obtain a high magnetic flux density, it can be achieved by using materials having high magnetic properties for the magnet roll 22, but since these materials are generally expensive, the roller cost increases when used for the entire roller. There is a problem that. Therefore, by using a material containing rare earth metal for the developer peeling magnetic pole 23, it is possible to provide the developing roller 2 having a high magnetic flux density at low cost. As a rare earth magnet material, it is generally desirable in terms of processing and cost to use a plastic magnet in which Nd—Fe—B magnet powder or Sm—Fe—N magnet powder is mixed and kneaded with a polymer compound. In this case, it is desirable that the maximum energy product (BHmax) is 8 MGOe or more as a magnetic characteristic, and as a material, a material having magnetic anisotropy is molded while applying a magnetic field at the time of magnet molding, and the material is anisotropic. High magnetic properties can be obtained by using the same. Further, by having magnetic anisotropy, the normal direction of the magnetic flux density of the developer peeling magnetic pole 23 can be directed to the upstream side of the developing sleeve rotation with respect to the radial direction (see FIG. 3).
By using a material having high magnetic properties for the developer peeling magnetic pole 23, the volume necessary for obtaining the normal direction magnetic flux density as the developer peeling magnetic pole 23 can be made smaller than that of the conventional magnet. The magnetization width can also be reduced. Therefore, the gap between the developer peeling magnetic pole 23 and the developer pumping magnetic pole 24 can be widened, and the effect of facilitating the developer peeling can be obtained.

  As materials other than rare earth magnets, plastic magnets or rubber magnets, in which polymer compounds are mixed with magnetic powder, are often used. Sr ferrite or Ba ferrite is used as the magnetic powder, and PA-based materials such as 6PA or 12PA are used as the polymer compound, and ethylene-based materials such as EEA (ethylene / ethyl copolymer) / EVA (ethylene / vinyl copolymer). Compounds, chlorine-based materials such as CPE (chlorinated polyethylene), and rubber materials such as NBR can be used. In particular, ethylene ethyl acrylate having an EA component of 25% to 35% is suitable for extrusion molding with excellent productivity, and can provide a low-cost developing roller.

  In addition, when the developing roller 2 shown above uses a carrier having a particle diameter of 50 μm or less and a polymerized toner having a particle diameter of 10 μm or less, it is possible to expect a more remarkable effect of increasing the margin for carrying the developer. That is, by using a small particle size carrier / polymerized toner, the latent image on the photoreceptor 40 can be faithfully reproduced, a high-quality image can be obtained, and a developing device with excellent developer rotation performance can be obtained. Because. Further, if the developing roller 2 of the present invention is used in the form of a process cartridge in an image forming apparatus, the developing roller 2 can be easily replaced and can always provide a high-quality image.

  FIG. 4 is a diagram showing a magnetic flux density distribution of a conventional magnet roller. 5 is a diagram showing the magnetic flux density distribution of the magnet roller of the first embodiment, FIG. 6 is a diagram showing the magnetic flux density distribution of the magnet roller of the second embodiment, and FIG. 7 is the diagram of the magnet roller of the third embodiment. It is a figure which shows magnetic flux density distribution. In the conventional example, the half width of the developer peeling magnetic pole 23 is 35 °. In the first embodiment, the half width of the developer peeling magnetic pole 23 is 25 °, in the second embodiment, 15 °, and in the third embodiment, the half width is the same as that of the first embodiment, and the magnetization direction is toward the upstream side of the developing sleeve rotation with respect to the radial direction. It is a thing.

  Using these developing rollers 2, images were confirmed using carriers having an average particle diameter of 55 μm and 35 μm. Evaluation was made on a five-point scale, with 5 being the best, and the granularity, which is image unevenness, image uniformity, and image smoothness, was evaluated.

  As a result, as shown in Table 1, the effect of improving the image quality with respect to the conventional example was obtained. By setting the half width of the developer peeling magnetic pole 23 to 25 ° or less, image unevenness and image density uniformity due to the rotation of the developer are improved. A higher improvement effect was confirmed when the magnetization direction was directed to the upstream side of the developing sleeve rotation with respect to the radial direction.

In the present invention, since the spread of the magnetic flux density in the normal direction of the developer peeling pole can be suppressed small, the developing roller can be separated from the developer pumping pole and has a high margin of developer revolving. it can. In addition, it is possible to provide a developing roller that can shorten the rise of the developer at the developer peeling electrode and can smoothly remove the developer.
In the present invention, when a magnet block containing a rare earth element having high magnetic properties is used for the development peeling pole, a magnetic roller with a narrow half-value width of magnetic flux density and a high attenuation rate can be configured, and development with a high degree of margin of developer follow-up is possible. A roller can be provided. In addition, it is possible to provide a developing roller that has a high degree of freedom in the direction of magnetic flux density and has a high margin with which the developer can move. Furthermore, the direction of the magnetic flux density can be further away from the developer pumping magnetic pole, and a developing roller having a high margin for the developer rotation can be provided.
In the present invention, since extrusion molding with excellent productivity is possible, a low-cost developing roller can be provided. In addition, since a material having high orientation in extrusion molding is used, it is possible to provide a developing roller having a high margin for carrying the developer at a low cost. Furthermore, it is possible to provide a developing roller having a high margin of developer rotation with respect to the developing device in which the developer regulating member is disposed substantially below the developing roller.
In the present invention, since a carrier having a particle size of 50 μm or less is used, it is possible to obtain a developing device having a good image characteristic with a high margin of developer rotation. In addition, since a polymerized toner having an average particle size of 10 μm or less is used, a developing device having good image characteristics with a high margin for the rotation of the developer can be obtained.
In the present invention, by using a process cartridge, replacement is easy, and a high-quality image can always be provided. In addition, it is possible to provide an image forming apparatus that always provides high-quality images.

1 is a diagram illustrating an electrophotographic full-color printer as an image forming apparatus according to an exemplary embodiment. It is a figure which shows an image forming unit. FIG. 6 is a diagram in which the normal direction of the magnetic flux density of the developer peeling magnetic pole is directed to the upstream side of the developing sleeve rotation with respect to the radial direction. It is a figure which shows magnetic flux density distribution of the magnet roller of a prior art example. It is a figure which shows magnetic flux density distribution of the magnet roller of Example 1. FIG. It is a figure which shows magnetic flux density distribution of the magnet roller of Example 2. FIG. It is a figure which shows magnetic flux density distribution of the magnet roller of Example 3.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Developing apparatus 2 Developing roller 4 Restriction member (Development doctor)
5a First conveying screw 5b Second conveying screw 6 Toner density sensor 7 Entrance seal 10 Image unit 11 Intermediate transfer belt 12 Image forming unit 13 Transfer charger 14 Paper feeding unit 15 Secondary transfer roller 16 Fixing unit 21 Developing sleeve (nonmagnetic) sleeve)
22 Magnet roll 23 Developer peeling magnetic pole 24 Developer pumping magnetic pole 40 Photoconductor (latent image carrier)
41 Charging device 42 Cleaning device 43 Writing means

Claims (6)

In a developing device including a developing roller that draws up the developer, forms a magnetic brush, and rubs the developer against the latent image carrier,
The developing roller has a non-magnetic sleeve and a magnet roll fixedly disposed in the non-magnetic sleeve,
The magnet roll, to the radial direction, and the magnetic pole scooping developer, a first current image agent transport poles, a main magnetic pole and the second current image agent transport poles for the developer bristles, developer It has at least 5 poles with peeled magnetic poles,
The full width at half maximum of the magnetic flux density with respect to the normal direction of the developer peeling magnetic pole is 15 ° or more and 25 ° or less with respect to the radial direction,
A developing device, wherein a developer regulating member is disposed below the developer conveying magnetic pole in the developing roller. The developing device according to claim 1,
The developing device according to claim 1, wherein the developer peeling magnetic pole is directed to the upstream side of the rotation of the nonmagnetic sleeve with respect to a radial direction . The developing device according to claim 1 or 2 ,
The developing device, wherein the developer peeling magnetic pole is disposed above a center of the developing roller . In a process cartridge that integrally supports at least the latent image carrier and the developing device,
The process cartridge includes the developing device according to claim 1.
A process cartridge characterized by that. At least a latent image carrier;
An image forming apparatus comprising: a developing device that develops the latent image formed on the latent image carrier;
The image forming apparatus includes the developing device according to claim 1.
An image forming apparatus. The image forming apparatus according to claim 5.
The image forming apparatus includes a process cartridge according to claim 4 detachably.
An image forming apparatus.

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