JP2008197342A - Magnet roller, developer carrier and image forming apparatus - Google Patents

Abstract

Provided is a magnet roller having a narrow half-value width of magnetic flux density without providing an auxiliary magnetic pole close to a developing pole, and a developer carrier comprising the magnet roller is used in an electrophotographic image forming apparatus. By using the toner image, a high-quality toner image that suppresses “blank trailing edge” on the toner image is obtained.
A magnet roller 40 for constituting a developer carrier of a developing device includes a shaft 31 and a plurality of magnets 32a to 32e provided around the shaft. These magnets include a magnet 32a having a groove 33a extending in the axial direction of the shaft 31 on the surface, and a magnet block 33 having the same magnetism as the magnet 32a having the groove is accommodated in the groove 33a. . The magnet block 33 protrudes to the outer peripheral side of the magnet roller 40 from the magnets 32a adjacent to the grooves 33a.
[Selection] Figure 6

Description

The present invention relates to a magnet roller, a developer carrier, a developing device, a process cartridge, and an image forming apparatus that constitute an electrophotographic image forming apparatus.
That is, the present invention relates to a developer carrying member used for forming a magnetic brush in a developing device constituting an image forming apparatus that develops an electrostatic latent image with a two-component developer, such as a copying machine, a facsimile, or a laser printer. Further, the present invention relates to a magnet roller that constitutes the developer carrier, a developing device that includes the developer carrier, a process cartridge that includes the developing device, and an image forming apparatus that includes the process cartridge. It is.

  Patent Document 1 below discloses a magnet roller having a groove (a storage groove for a magnet block) in a magnet roller, and a so-called half-width reduced by attaching a magnet block to the groove, and a manufacturing method thereof. ing.

  In the field of an electrophotographic image forming apparatus that develops an electrostatic latent image with a two-component developer comprising a toner and a carrier, a magnetic brush developing method that has been widely used in the past has not developed a developing carrier (developing roller). A magnetic brush is formed by pumping a developer onto a magnetic cylinder (developing sleeve) and making it stand up. In addition, a plurality of magnetic poles are provided on the magnet roller in the non-magnetic cylindrical body in order to collect the carrier after supplying the toner from the magnetic brush to the image carrier such as a photosensitive drum carrying the electrostatic latent image.

  By the way, the applicant of the present application has reported that the toner once supplied to the image carrier again moves back to the carrier on the non-magnetic cylindrical body, resulting in white spots due to insufficient toner adhesion on the development end side of the image, so-called “after”. Focusing on the fact that the “white-out” appears particularly prominently in the case of a halftone image, a technique useful for preventing the occurrence of such “white-out white” (hereinafter referred to as “SLIC developing device” for convenience). Is proposed in Patent Document 2 below.

  In this SLIC developing device, a magnetic pole portion corresponding to a developing area (area where toner moves relative to the image carrier), that is, an auxiliary magnetic pole is disposed in the vicinity of the developing pole, and the developer on the nonmagnetic cylindrical body is arranged. Therefore, it is necessary to make the magnetic brush formed on the development pole uniformly short, and to form the magnetic brush densely on the nonmagnetic cylindrical body.

  In the invention of the above-mentioned patent document 1, as a manufacturing method of the magnet roller, after forming the magnet roller by injection molding or extrusion molding, the adjacent pole portion sandwiching the developing pole portion is magnetically oriented by the magnetic pole divided into two branches. The development pole portion and the adjacent pole are magnetized, and a high magnetic force magnet block, which is the same polarity as the development pole and is a separate member from the magnet roller, is attached.

Japanese Patent No. 3840415 JP 2000-305360 A

  However, in the manufacturing method of the above-mentioned Patent Document 1, it is necessary to divide the magnetic pole into two parts, and the problem is that the mold structure for manufacturing the magnet roller becomes complicated.

Accordingly, an object of the present invention is to provide a magnet roller with a narrow half-value width of magnetic flux density without providing an auxiliary magnetic pole close to the developing pole, and to provide a developer carrying member comprising this magnet roller for an electrophotographic system. By using it in an image forming apparatus, it is to obtain a high-quality toner image in which “rear edge” on the toner image is suppressed.
That is, the main object of the present invention is to eliminate the complexity of the mold structure, and to provide an auxiliary magnetic pole close to the developing pole, so that the full width at half maximum of the magnetic flux density is small and the “rear end” It is an object of the present invention to provide a magnet roller that is effective in preventing the occurrence of white spots.
Another object of the present invention is to provide a developer carrying member constituted by the magnet roller, a developing device provided with the developer carrying member, and a process cartridge provided with the developing device.
A further object of the present invention is to provide an image forming apparatus provided with the process cartridge, which can obtain a high-quality image.

The object of the present invention will be described according to the claims.
Claims 1 and 2 are simple configurations in which a magnet roller is formed of a plurality of magnets, and a magnet block having the same polarity as the magnet is disposed in the groove of the magnet provided with a groove in the axial direction. An object of the present invention is to provide a magnet roller in which the half-value width of the magnetic flux density is narrowed without providing an auxiliary pole close to the developing pole.

A third object of the present invention is to provide a developer carrier that has a narrow half-value width of magnetic flux density and is advantageous in preventing “rear end white spot” by using the magnet roller according to the first and second aspects. .
A fourth object of the present invention is to provide a developing device that is advantageous in preventing “rear end white spot”.
A fifth object of the present invention is to provide a process cartridge that is advantageous in preventing “rear end white spot” by using the developing device according to the fourth aspect.
A sixth aspect of the present invention provides an image forming apparatus capable of obtaining a high-quality image free of “rear end white spot” by using the developing device according to the fourth aspect.
A seventh object of the present invention is to provide an image forming apparatus that uses the process cartridge according to the fifth aspect to obtain a high-quality image without “blank trailing edge”.

  The invention according to claim 1 is a magnet roller comprising a shaft and a plurality of magnets provided around the shaft, wherein the plurality of magnets include a magnet having a groove extending in the axial direction on a surface thereof. A magnet roller is included, wherein a magnet block having the same magnetic property as the magnet having the groove is disposed in the groove.

  According to a second aspect of the present invention, the distance from the (diameter direction) center of the shaft to the contour line of the magnet adjacent to the groove is the distance from the center of the shaft to the contour line of the magnet not having the groove. It is shorter than this, It is a magnet roller of Claim 1 characterized by the above-mentioned.

  According to a third aspect of the present invention, there is provided a rotatable nonmagnetic cylindrical body on the outer periphery of the magnet roller according to the first or second aspect, a first flange at one end of the nonmagnetic cylindrical body, and a second at the other end. The first flange is for transmitting rotational motion to the non-magnetic cylinder, and the second flange is for supporting the magnet roller. A developer carrier.

According to a fourth aspect of the present invention, in the developing device including at least a developer carrier, a developer supply member, and a developer layer regulating member, the developer carrier according to the third aspect is used as the developer carrier. This is a developing device.
According to a fifth aspect of the present invention, there is provided a process cartridge comprising the developing device according to the fourth aspect.
An invention according to claim 6 is an image forming apparatus comprising the developing device according to claim 4, and an invention according to claim 7 is provided with the process cartridge according to claim 5. An image forming apparatus.

  According to the present invention, without providing an auxiliary magnetic pole close to the developing pole, the half-width of the magnetic flux density is narrow, and the magnet roller, the developing carrier, and the developing device that are effective in preventing “rear end white spot” on the image. A process cartridge and an image forming apparatus can be provided.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[First embodiment]
FIG. 1 is an explanatory diagram showing a schematic configuration of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus denoted by reference numeral 80 in FIG. This is an electrophotographic system that develops with a two-component developer, and includes at least an optical writing unit 103, a transfer member 105, a fixing device 117, and a process cartridge 70 according to an embodiment of the present invention. In FIG. 1, reference numeral 41 denotes a developer supply member, 42 denotes a developer layer regulating member, 43 denotes a developer carrier, 44 denotes a charging roller, and 45 denotes an image carrier. These will be described in detail later. To do.

  The process cartridge 70 includes a charging roller 44, an image carrier 45, and a developing device 60, as shown in FIG.

  As shown in FIG. 3, which is an explanatory diagram of a schematic configuration, the developing device 60 includes a developer carrier 43 disposed opposite to the image carrier 45, the height of the developer, that is, development on a nonmagnetic cylinder. At least a developer layer regulating member 42 that regulates the amount of the developer and a developer supply member 41 that pumps the developer to the developer carrier 43 while stirring the developer.

  In such a configuration (see FIG. 1), the image carrier 45 whose surface is uniformly charged by the charging roller 44 forms an electrostatic latent image by exposure of the optical writing means 103, and a toner image is developed by the developing device 60. Is formed. The toner image is transferred from the surface of the image carrier 45 to a transfer material 106 conveyed from a paper feed tray (not shown) by a transfer member 105 formed of a transfer belt or the like. During this transfer, the transfer material 106 electrostatically attached to the image carrier 45 is separated from the image carrier 45 by a separation claw (not shown). The transfer material carrying the unfixed toner image is subjected to an action such as heat and pressure when passing through the fixing device 117, and the toner image on the transfer material is fixed. On the other hand, the toner remaining on the image carrier 45 without being transferred is removed and collected by the cleaning device. The image carrier 45 from which the residual toner has been removed is initialized by a static elimination lamp (not shown) and used for the next image forming process.

As shown in FIG. 4 which is a sectional view (longitudinal sectional view) in the central axis direction, the developer carrying member 43 includes a magnet roller 40 having a shaft 31 and a non-rotatable roller disposed concentrically on the outer periphery thereof. A magnetic cylindrical body 34, a flange 35 that transmits rotational motion to the end thereof, and a flange 36 that supports the magnet roller are coupled to each other by caulking, press-fitting, adhesion, or the like.
As the nonmagnetic cylindrical body 34, for example, aluminum, SUS (stainless steel), or the like can be used. Aluminum is often used in terms of workability and lightness. In the case of aluminum, A6063, A5056, A3003 and the like can be used, and in the case of SUS, 303, 304, 316 and the like can be used.

  The magnet roller 40 used in the configuration of the developer carrier 43 in this embodiment is provided with a shaft 31 and around the shaft 31 as shown in the schematic perspective view of FIG. 5 and the axial sectional view of FIG. A magnet roller provided with a plurality of magnets 32 (32a to 32e), each having a groove 33a extending in the axial direction of the shaft 31 on the surface, that is, a magnet 32a having a groove for storing a magnet block. In addition, a magnet block 33 having the same magnetic property as the magnet 32 a having the groove is disposed in the groove 33 a (Claim 1).

5 and 6 will be described more specifically.
In the magnet roller 40, a plurality of (five) magnets are provided around the shaft 31. Among these, the four magnets 32b, 32c, 32d, and 32e are columnar magnets surrounded by two straight lines having the same length and two arcs having the same center in the sectional view of FIG. is there.
Further, the magnet 32a corresponding to the developing pole is a columnar magnet having a shape surrounded by two straight lines having the same length and two arcs having the same center in the sectional view of FIG. The groove 33a extending in the axial direction is provided in the arc portion. And the magnet block 33 which has the same polarity is affixed on this groove | channel 33a.
Furthermore, the magnet block 33 protrudes to the outer peripheral side of the magnet roller 40 from the magnets 32a adjacent to the grooves 33a. Thus, since the magnet block 33 protrudes from the outer peripheral surface of the main body portion of the magnet roller 40, the magnetic flux density from the edge portion of the magnet block does not enter the magnet roller main body portion. . Although not shown, the shaft 31 is provided with a predetermined reference surface.

  The plurality of magnets are plastic magnets or rubber magnets in which magnetic powder is dispersed in a polymer material. These magnets use, for example, Sr ferrite or Ba ferrite as magnetic powder, and PA (polyamide) materials such as EEA (ethylene-ethyl copolymer), 6PA or 12PA, and rubbers such as NBR as polymer materials It is obtained by using a material and molding it by extrusion molding or injection molding with a mold having a predetermined shape. At that time, a magnet having a high magnetic force may be molded while applying an orientation magnetic field to the mold.

  The magnets 32a to 32e formed in the shape as described above are attached to a predetermined position around the shaft 31 with an adhesive, and then magnetized so as to have a magnetic flux density distribution shown in FIG. Yes. FIG. 7 is a magnetic flux density distribution diagram of the magnet roller before the magnet block 33 is attached to the groove 33a. In particular, in the magnet 32a having the groove 33a, as shown in FIG. 7, there is a drop in magnetic flux density at the center of the groove, and a magnetic flux density distribution is formed so as to increase at both sides of the groove. FIG. 8 shows the magnetic flux density distribution of the magnet roller after the magnet block 33 is attached to the groove 33a.

  In the present embodiment, the shape of each magnet is a columnar shape surrounded by two straight lines having the same length and two arcs having the same center in the axial cross section of the magnet roller. The present invention is not limited to this, and the arc portion may include a straight line or a curve other than the arc.

  In order to prevent the “rear end white spot” described above, it is desirable to achieve a high magnetic force with a smaller volume than the magnet forming the magnetic pole. In order to achieve this, it has been experimentally found that it is desirable to use a material satisfying the condition of residual magnetic flux density Br> 0.5T (Tesla) as the magnet block 33 disposed in the groove. Examples of satisfying the above conditions include Ne-based (Ne-Fe-B, etc.) or Sm-based (Sm-Co, Sm-Fe-N, etc.) rare earth magnets, or these magnet powders as polymer compounds. There are mixed plastic magnets or rubber magnets. In addition, rare earth magnet powders include isotropic and anisotropic magnet powders. In general, anisotropic magnets are often used because they have higher magnetic force. However, any type may be used as long as it can effectively prevent “rear end white spot”.

Summarizing the effects of the first embodiment, in this embodiment, in the magnet roller in which magnets corresponding to a plurality of magnetic poles are bonded to the shaft, a magnet block having the same polarity is bonded to the pole corresponding to the developing pole. Thus, a magnet roller having a narrow half-width of the magnetic flux density can be obtained, and the “rear end white spot” can be effectively prevented without having an auxiliary magnetic pole close to the developing pole.
In addition, in the developer carrier using such a magnet roller, the developing device using the developer carrier, the process cartridge, and the image forming apparatus using these, there is a problem on the image of “blank rear edge”. Can be prevented.

[Second Embodiment]
In the magnet roller 40 shown in FIG. 9, the distance from the (diameter direction) center of the shaft 31 to the surface of the magnets on both sides of the groove 33a (both magnets 32a) is a magnet that does not have the groove 33a from the center of the shaft 31. It is characterized by being shorter than the distance to the surface (for example, magnet 32e) (Claim 2).
That is, in the magnet roller of FIG. 9, a flat portion (straight portion in the cross-sectional view) is provided on the surface of the magnet 32 a adjacent to both sides of the groove 33 a for adhering the magnet block, and the adjacent side of the groove 33 a from the center of the shaft 31. The distance b to the magnet surface (magnet linear outline) is shorter than the distance a to the magnet surface (magnet arc outline) having no groove. That is, distance a> distance b. As a result, the magnet block 33 protrudes to the outer peripheral side of the magnet roller 40 from both sides of the groove 33a (see the following embodiment).

FIG. 10 is an explanatory sectional view showing an example in which the magnet block 33 is provided in the groove 33a in an undesirable manner. In this example, the magnetic flux density from the edge portion of the magnet block 33 (the right-angle portions of the upper ends of the rectangle indicating the magnet block 33 in FIG. 10) is within the magnet 32a having the groove 33a as indicated by the arrows in the figure. Get in. For this reason, it becomes difficult to narrow the half width. In this example, the distance from the center of the shaft 31 to the magnet surface (magnet arc outline) adjacent to the groove 33a is equal to the distance from the magnet surface (magnet arc outline) having no groove. Yes. That is, the above condition “distance a> distance b” is not satisfied.
On the other hand, in the magnet roller 40 of FIG. 9, the magnetic flux density from the edge portion of the magnet block 33 does not enter the inside of the magnet 32a, so that the half width can be easily narrowed.

  In the present embodiment, as described above, the embodiment has been described in which the distance from the axis center to the magnet surface on both sides of the groove is shorter than the distance to the magnet surface without the groove. The distance from the axis center to the magnet surface on both sides of the groove may be shorter than the distance from the axis center to the magnet surface other than on both sides of the groove.

  In the magnet roller according to the embodiment of the present invention, a 3 mm × 3 mm rare earth magnet block obtained by mixing 12 PA (polyamide) as a binder with anisotropic Nd—Fe—B, and 6 PA (polyamide) on Sr ferrite. Was placed in a groove (reference numeral 33a) of a magnet formed by mixing as a binder. The relationship between the protruding amount of the magnet block at this time and the half-value width of the magnetic flux density is shown in FIG. As is clear from this result, the full width at half maximum can be efficiently narrowed by increasing the protrusion amount.

Specifically, by setting the protrusion amount to 0.2 mm, the full width at half maximum of the magnetic flux density can be reduced by about 8%. A development electrode could be obtained.
That is, by determining in advance the relationship between the magnet protrusion amount and the half-value width (or the half-value width narrowing ratio) as shown in FIG. 11, the magnet protrusion amount is set according to the half-value width of the desired magnetic flux density. Can do.

FIG. 12 shows the magnetic flux density distribution when the protrusion amount of the magnet block is 0 mm and when it is 0.2 mm (the present invention), and it can be seen that the full width at half maximum of the magnetic flux density is narrowed in the present invention.
According to the present invention, the shape from which the distance from the axis center to the magnet surface on both sides of the groove is shorter than the distance to the magnet surface without the groove is flat on the magnet surfaces on both sides of the groove, for example, as shown in FIG. In addition to the provision of the portion, as shown in FIG. 13, the same effect as described above can be obtained even in a shape in which the chamfer 32 </ b> A is provided in the edge portion composed of the groove and the magnet surface.

  In the example of FIG. 13, the magnet block can be projected from the magnet surfaces on both sides of the groove by setting the distance from the axis center to the magnet block to be equal to or less than the distance to the other magnet surface. There is also an advantage that the problem that the magnet roller comes into contact with the inner surface of the cylindrical body and the rotational load of the non-magnetic cylindrical body increases and the problem that abnormal noise occurs is less likely to occur.

As described above, in the second embodiment, the distance from the axial center to the magnet surface on both sides of the groove is shorter than the distance to the magnet surface without the groove, and the magnet block is on the magnet surface on both sides of the groove. Therefore, the full width at half maximum of the magnetic flux density can be effectively narrowed.
In addition, since the half-value width of the magnetic flux density can be reduced by setting the distance from the axis center to the magnet block surface to be equal to or less than the distance from the magnet surface having no groove, Can be prevented from coming into contact with the inner surface of the non-magnetic cylindrical body, increasing the rotational load of the non-magnetic cylindrical body, or generating abnormal noise due to the contact.

1 is a cross-sectional view illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a cross-sectional view showing a schematic configuration of a process cartridge constituting the image forming apparatus of FIG. 1. FIG. 3 is a cross-sectional view showing a schematic configuration of a developing device constituting the process cartridge of FIG. 2. FIG. 4 is a longitudinal sectional view of a developer carrier provided in the developing device of FIG. 3. FIG. 5 is a schematic perspective view of a magnet roller constituting the developer carrier of FIG. 4. It is an axial sectional view (transverse sectional view) of the magnet roller of FIG. It is a magnetic flux density distribution map of the magnet roller before sticking a magnet block (33) to a groove (33a). It is a magnetic flux density distribution figure of a magnet roller after sticking a magnet block (33) on a groove (33a). It is an axial sectional view (transverse sectional view) of a magnet roller according to a second embodiment of the present invention. It is explanatory sectional drawing which shows the example which provided the magnet block (33) in the groove | channel (33a) in the unpreferable aspect. FIG. 6 is a graph relating to an example of the present invention and showing a relationship between a magnet block protrusion amount of a magnet roller and a half-value width and a half-value width narrowing ratio of magnetic flux density. It is a graph which concerns on the Example of this invention, and shows the relationship between the magnet block protrusion amount of a magnet roller, and magnetic flux density distribution. It is an axial sectional view (transverse sectional view) showing a magnet roller provided with a chamfer (32A) at an edge portion composed of a groove and a magnet surface.

Explanation of symbols

31: Shaft 32A: Chamfer 32a: Magnet 32b: Magnet 32c: Magnet 32d: Magnet 32e: Magnet 33: Magnet block 33a: Groove (groove for storing magnet block)
34: Non-magnetic cylinder 35: Flange 36: Flange 40: Magnet roller 41: Developer supply member 42: Developer layer regulating member 43: Developer carrier 44: Charging roller 45: Image carrier 60: Developing device 70: Process cartridge 80: Image forming apparatus 103: Optical writing means 105: Transfer member 106: Transfer material 117: Fixing apparatus

Claims (7)

A magnet roller comprising a shaft and a plurality of magnets provided around the shaft,
The plurality of magnets include magnets having grooves extending in the axial direction on the surface,
A magnet roller characterized in that a magnet block having the same magnetic property as the magnet having the groove is disposed in the groove.   The distance from the center of the shaft to the outline of the magnet on both sides of the groove is shorter than the distance from the center of the axis to the outline of the magnet not having the groove. Magnet roller. The outer periphery of the magnet roller according to claim 1 or 2, comprising a rotatable nonmagnetic cylindrical body, a first flange at one end of the nonmagnetic cylindrical body and a second flange at the other end,
The first flange transmits rotational motion to the nonmagnetic cylindrical body,
The developer carrying member, wherein the second flange supports the magnet roller.   A developing device comprising at least a developer carrying member, a developer supply member, and a developer layer regulating member, wherein the developer carrying member according to claim 3 is used as the developer carrying member.   A process cartridge comprising the developing device according to claim 4.   An image forming apparatus comprising the developing device according to claim 4.   An image forming apparatus comprising the process cartridge according to claim 5.

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