JP2012058286A - Developing device, process cartridge and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a developing device which can contribute to improving image quality by resolving the problem of rotation with a developer at the end, while taking an advantage of a hollow, in such a system that a large number of hollows are formed on the surface of a developing sleeve.SOLUTION: The angles of the hollows 139 (shown by hatching) only at the end of a hollow forming part on the developing sleeve 132 at the downstream in the conveyance direction of the developer are changed to a direction opposite to that of a group of hollows 139 inward from the end (central side in the axial direction of the sleeve). Thus, the conveyance direction of the developer on the developing sleeve at the end can be reversed so that the amount of the developer supplied to the end can be reduced and the rotation with the developer at the end hardly occurs.

Description

  The present invention relates to a developing device that visualizes a latent image as a toner image, in particular, a developing device using a two-component magnetic brush developing system, a process cartridge having the developing device, a copier having the developing device, a printer, a facsimile, a plotter, The present invention relates to an image forming apparatus such as a multifunction peripheral provided with at least one of them.

2. Description of the Related Art Conventionally, in an image forming apparatus that visualizes a latent image on an image carrier as a toner image, a two-component magnetic brush developing type developing device has been used. In this developing apparatus, a developer (toner is adsorbed to magnetic powder by electrostatic force) is conveyed to a developing area facing the image carrier, and the electrostatic latent image formed on the image carrier is developed to form a toner image. A developer carrying member (developing roller) for visualization is provided.
The developing roller is, for example, a developing sleeve formed in a cylindrical shape, and a magnetic field generating means (for example, a magnet roller) provided in the developing sleeve and configured to generate a magnetic field so as to cause the developer sleeve to rise. ).
When the developer is spiked, the carrier constituting the developer is spiked on the developing sleeve so as to follow the lines of magnetic force generated by the magnet roller, and charged toner is attached to the carrier. . The magnet roller has a plurality of magnetic poles, and the magnets forming the respective magnetic poles are formed in a molded body such as a rod shape, and in particular, a portion corresponding to the development region portion on the surface of the development sleeve is developed. It has a developing main magnetic pole that makes the agent stand up. The developer that has risen can be moved in the circumferential direction by rotating at least one of the developing sleeve and the magnet roller.

In general, in order to facilitate the conveyance of the developer, the surface of the developing sleeve is provided with irregularities formed by grooves, means such as sand blasting and bead blasting. Particularly in color copying machines and printers, blast sleeves are the mainstream because of the superiority of image quality.
Such roughing (roughening) such as grooving or sandblasting is intended to prevent the occurrence of a decrease in image density caused by the developer slipping and stagnation on the surface of the developing sleeve rotating at high speed. To be done.

A conventional developing apparatus is shown in FIG. In this developing apparatus, a two-component developer is conveyed to a developing region of an image carrier 201 facing the developing roller 200 by a developing roller 200 as a developer carrier, and an electrostatic formed on the surface of the image carrier 201. The latent image is developed to form a toner image.
The developing roller 200 includes a developing sleeve 202 formed in a cylindrical shape, and a magnet roller 203 which is accommodated in the developing sleeve 202 and forms a magnetic field so as to cause a developer to rise on the surface of the developing sleeve 202. I have.
In the developing roller 200, when the developer spikes, the magnetic carrier constituting the developer spikes on the developing sleeve so as to follow the lines of magnetic force generated by the magnet roller, and the developer is applied to the spiked magnetic carrier. The toner constituting the toner adheres.

This type of developing device includes a developer containing tank that contains the developer, a screw-shaped stirring and conveying member (hereinafter also referred to as “stirring member”) that stirs the developer in the developer containing tank, and a developer. And a developer regulating member that makes the amount of the developer pumped up to the developer carrying member uniform.
The developing device shown in FIG. 19 includes a developer storage tank (developer storage chamber a + developer storage chamber b) and a pair of stirring members. The developer in this developing device moves in the developer accommodating tank in the axial direction of the stirring member. The toner replenished from one end of the developer storage tank 204b on the side away from the developing roller 200 is conveyed by the stirring member 205b to the other end of the developer storage tank 204b along the axial direction of the stirring member 205b. Stir with developer.

The developer moves from the other end of the developer accommodating tank 204b to the other developer accommodating tank 204a near the developing roller. The developer transferred to the developer storage tank 204a is pumped up to the surface of the developing sleeve by the magnetic force of the magnet roller 203 and adheres to the surface of the developing sleeve.
Thereafter, the developer is made uniform in layer thickness by a doctor blade 206 as a developer regulating member, and then conveyed to a developing area where the image carrier 201 and the developing roller 202 are opposed to each other with a space therebetween. The The developer develops the electrostatic latent image formed on the image carrier to form a toner image.

The magnet roller 203 includes a plurality of fixed magnetic poles such as S1 (developing pole), N1 (developer conveying pole), S2 (agent separating upstream magnetic pole), S3 (pumping pole = agent separating downstream magnetic pole), N2 ( Developer transport poles) are respectively provided. Since the developing sleeve rotates in the direction of the arrow, the developer moves on the surface of the developing sleeve in the order of the fixed magnetic poles S3, N2, S1, N1, S2, and the agent running out.
In the magnet roller 203, the fixed magnetic pole N1 (developer transport pole) and the fixed magnetic pole N2 (developer transport pole) have the same N polarity, and a magnetic pole p having S polarity is provided between the fixed magnetic pole S2 and the fixed magnetic pole S3. When provided, the developed developer having a low toner concentration is dropped into the developer accommodating tank 204a by the repulsive force of the magnetic pole p in addition to the repulsive force of the fixed magnetic pole S1 and the fixed magnetic pole S2. In the present specification, such a magnetic pole p is referred to as “agent separating magnetic pole or pole cutting out magnetic pole”, and the developed developer is dropped into the developer accommodating tank 204a by the repulsive force of the magnetic pole p.

The developed developer having a low toner concentration dropped into the developer storage tank 204a (that is, out of the agent) is sent from the developer agitation tank 204b in the developer agitation tank 204a. After being stirred together with a new developer having a high toner concentration, it is attracted to the fixed magnetic pole S3 (developer pumping pole) as a developer having a high toner concentration (that is, pumped up), and then the fixed magnetic pole N1 ( (Developer transport pole).
The developer having a high toner concentration transferred to the fixed magnetic pole N1 is transferred to the fixed magnetic pole S1 (developing pole) after the layer thickness is made constant by the doctor blade 206.

  Recently, as shown in FIG. 20, a proposal has been made for the purpose of reducing the stress of the developer and ensuring the depletion of the developing roller itself with a single pumping / developing doctor pole configuration (Patent Document 1). reference).

However, the behavior of the developer as described above is within the image forming region, and there are the following problems at the end in the longitudinal direction of the developing roller.
FIG. 21 shows the agent behavior at the agent separation part in the sectional layout of FIG. In the image forming area, the developer separated by the agent-separated upstream magnetic pole (N2) falls to the lower developer container (developer container) and develops as shown in (a) and (b). The developer is stirred and mixed with the developer in the agent container, and is again pumped up to the developing roller by the pumping pole.
However, at the end (outside of the image forming area), as shown in (a) and (c), the developer separated at the upstream side magnetic pole (N2) away from the agent is outside the magnet roller (the part without magnetic force). ) To the downstream magnetic pole (N3) away from the agent.
As shown in (c), the separated developer is hardly separated from the surface of the developing roller (developing sleeve) and is pumped up to the agent-separated downstream magnetic pole (N3). This is a phenomenon called revolving in the development technology.

The difference between the agent separation portion and the other pole is that the same polarity is adjacent to the agent separation portion, whereas the developer conveyance is carried out by the different polarity at the other electrode, so that from S to N, The developer is attracted from N to S and flows without swelling at the end. Since this part has the same polarity at the agent separation part, they repel each other, and the magnetic component toward the outside in the longitudinal direction becomes stronger, and the developer behaves as shown in (c).
If an image is placed on a portion where the developer is rotated, the toner from the developing tank is not replenished, resulting in an abnormal image in which the image becomes thinner in the sheet passing direction.
For this reason, conventionally, the mainstream method has been to accept that the accompanying phenomenon cannot be avoided, lengthen the longitudinal direction of the developing roller, and generate the accompanying device outside the image guarantee area.
As another countermeasure, it is effective to use a magnet roller shaft as a non-magnetic member, but there is a problem that stainless steel is expensive and aluminum is insufficient in strength.

Recently, there has been introduced a sleeve that maintains the developer density on the sleeve similar to the blast sleeve and maintains the developer conveying force similar to the groove sleeve in which a plurality of grooves extending in the circumferential direction of the sleeve are formed at equal intervals in the circumferential direction. (See Patent Document 2). In the groove sleeve, there is a concern that the developer conveyance amount in the groove portion is large and the image density in the groove portion becomes high, so that the groove pitch unevenness occurs in the output image and the image quality is deteriorated. The described sleeve can solve this problem.
The sleeve described in Patent Document 2 forms a fine ellipse-shaped depression densely by a cutting machine according to the number of rotations of the cutting tool, the cutting speed of the cutting tool, and the rotational speed of the sleeve. On the other hand, a developer conveying force is generated (details will be described in the description of the present invention).
By generating a conveying force in the longitudinal direction of the developing roller, energy can be reduced by suppressing the rotation speed of the stirring screw, and if the rotation speed is maintained, an effect of reducing density unevenness is brought about.
The description from the viewpoint of the end rotation of the sleeve will be described with reference to FIG. FIG. 22 is an enlarged view of the surface of the developing sleeve as viewed from the side, and is an enlarged view of approximately 2 to 3 cm ² . As shown in the figure, when the inclination angle of the recess 139 with respect to the longitudinal direction of the developing roller is increased to the left and the developing sleeve is rotated downward, the developer is blown away in the direction of the arrow in the developer separating portion. In this case, the developer is accumulated in the downstream side of the developing roller on the left side, that is, on the downstream side in the developer conveying direction with respect to the longitudinal direction on the so-called developing sleeve.

  The present invention has been made in view of such a situation, and in the method of forming a large number of depressions on the surface of the developing sleeve, while taking advantage of the depressions, it is possible to solve the problem of the edge developer accompanying, and the image quality The main object of the present invention is to provide a developing device that can contribute to the improvement of image quality.

  In order to achieve the above object, the invention according to claim 1 is provided with a developing casing for accommodating a two-component developer composed of a toner and a carrier, and an image bearing member, and is formed by a magnetic force on the surface. A developing roller that rubs the image carrier with a developer brush and visualizes a latent image on the image carrier as a toner image and a surface of the developing roller with a predetermined gap therebetween, and the developing roller Has a developer regulating member that regulates the layer thickness of the developer on the developing roller on the upstream side in the roller rotation direction of the developing area facing the image carrier, and the developing roller is rotatable and is capable of rotating the developer. A developing sleeve carried on the surface; and a magnetic field generating means fixedly disposed in the developing sleeve, wherein the magnetic field generating means applies the developer after developing the latent image on the image carrier. Remove from developing sleeve And an agent separating upstream magnetic pole that generates a magnetic force for generating a magnetic force, and an agent separating downstream magnetic pole that has the same polarity as the agent separating upstream magnetic pole and is adjacent to the downstream in the rotation direction of the developing sleeve. In the developing device in which a plurality of oval or elliptical recesses are arranged in the sleeve circumferential direction and the sleeve longitudinal direction, the recess at the longitudinal end of the developing sleeve is formed in the developer on the developing sleeve. It is formed so as to impart a conveying force inward in the longitudinal direction.

According to a second aspect of the present invention, in the developing device according to the first aspect, the recesses are formed in a regularly arranged manner, and the major axis has an angle with respect to the longitudinal direction of the developing sleeve. The depressions at the end portions are formed such that the developer conveying direction on the developing sleeve is opposite to the inward depressions.
According to a third aspect of the present invention, in the developing device according to the second aspect, an angle of the recess at the end portion with respect to a longitudinal direction of the developing sleeve is larger than an angle of the inward recess. To do.
According to a fourth aspect of the present invention, in the process cartridge, the developing device according to any one of the first to third aspects and the image carrier are integrally provided.

According to a fifth aspect of the present invention, the image forming apparatus includes the developing device according to any one of the first to third aspects.
According to a sixth aspect of the present invention, in the image forming apparatus according to the fifth aspect, the toner used in the developing device has a volume average particle diameter of 3 to 8 μm, a volume average particle diameter (Dv) and a number average particle diameter. The ratio (Dv / Dn) to the diameter (Dn) is in the range of 1.00 to 1.40.
According to a seventh aspect of the present invention, in the image forming apparatus according to the fifth or sixth aspect, the toner used in the developing device has a shape factor SF-1 in the range of 100 to 180, and the shape factor SF-2. Is in the range of 100-180.

  According to the present invention, it is possible to suppress the phenomenon of developer revolving at the end of the developing sleeve without increasing the axial length of the developing roller, that is, without increasing the size of the developing roller, and a large number of depressions are formed on the sleeve surface. The occurrence of abnormal images can be prevented while taking advantage of the forming method.

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention. It is a schematic sectional drawing of a process cartridge. FIG. 3 is a cross-sectional view of the developing roller taken along line AA in FIG. 2. It is a perspective view of a developing sleeve. It is a top view which shows the arrangement pattern of the hollow formed in the surface of a developing sleeve. It is a figure which shows the shape of a hollow, (a) is a top view, (b) is the circumferential sectional view in VIB of (a), (c) is a longitudinal direction sectional view in VIC of (a). It is a top view which shows that a hollow becomes a curved shape by cutting. FIG. 6 is an enlarged view of the surface shape of the end portion of the sleeve recess forming portion when the developing sleeve is viewed from the side. FIG. 10 is an enlarged view of the surface shape of the end portion of the sleeve recess forming portion when the developing sleeve according to the second embodiment is viewed from the side. It is a figure which shows the modification of a developing device. It is a figure which shows the modification of the shape of a hollow, (a) is a top view, (b) is a circumferential sectional view in IXB of (a), (c) is a longitudinal sectional view in IXC of (a). is there. It is a figure for demonstrating the angle which a hollow and the surface of a sleeve make. It is a figure which shows the modification of the cross-sectional shape of a hollow. It is a figure which shows the other modification of the cross-sectional shape of a hollow. It is a top view which shows the modification of the arrangement pattern of a hollow. It is a top view which shows the other modification of the arrangement pattern of a hollow. FIG. 6 is a schematic diagram for explaining a toner shape factor SF-1. FIG. 6 is a schematic diagram for explaining a toner shape factor SF-2. It is a figure which shows the magnetic pole structure of the conventional developing device. It is a figure which shows the other magnetic pole structure of the conventional developing apparatus. It is a figure for demonstrating the development accompanying phenomenon which arises in the edge part of a developing sleeve. It is a figure which shows the conveyance direction of the developer on the conventional sleeve which forms the row | line | column of a hollow so that a long axis may incline on the surface of a developing sleeve.

Embodiments of the present invention will be described below with reference to the drawings.
The first embodiment will be described with reference to FIGS. First, a schematic configuration of a color copying machine as an image forming apparatus according to the present embodiment will be described with reference to FIG.
A color copier (hereinafter also referred to as “image forming apparatus”) 100 uses, as a transfer material, an image of each color of yellow (Y), magenta (M), cyan (C), and black (K). It has a tandem type configuration using an intermediate transfer belt 129 formed on the recording paper 50. Note that units corresponding to yellow, magenta, cyan, and black colors are denoted by Y, M, C, and K at the end of the reference numerals.

The image forming apparatus 100 includes an apparatus main body 102, a paper feed unit 103, a registration roller pair 110, an intermediate transfer unit 104, a secondary transfer roller 126 as a secondary transfer unit, a fixing unit 105, and a laser writing unit. 122 and process cartridges 106Y, 106M, 106C, and 106K that are detachable from the apparatus main body 102 are provided.
The paper feed unit 103 includes a paper feed cassette 123 that accommodates the recording paper 50 in an overlapping manner and can be freely taken in and out of the apparatus main body 102, and a paper feed roller 124. The paper feed roller 124 is pressed against the uppermost recording paper 50 in the paper feed cassette 123, and separates the top paper one by one by cooperation with a separation member (not shown), to the registration roller pair 110. Send it out.
The registration roller pair 110 is provided in the conveyance path of the recording paper 50 conveyed from the paper supply unit 103 to the secondary transfer site, and the recording paper 50 is sandwiched between the rollers to transfer the image on the intermediate transfer belt 129. Send it out when you get it.

  The intermediate transfer unit 104 is provided above the process cartridges 106Y, 106M, 106C, and 106K. The intermediate transfer unit 104 includes a driving roller 128, a driven roller 127, an intermediate transfer belt 129, and primary transfer rollers 130Y, 130M, 130C, and 130K as primary transfer means. The drive roller 128 is disposed at a position opposite to the secondary transfer roller 126 and is rotationally driven by a motor as a drive source. The driven roller 127 is rotatably supported by the apparatus main body 102. The intermediate transfer belt 129 is formed in an endless belt shape and is stretched over both the driving roller 128 and the driven roller 127. The intermediate transfer belt 129 circulates in the counterclockwise direction in the figure when the driving roller 127 is driven to rotate.

The primary transfer rollers 130Y, 130M, 130C, and 130K are disposed so that the intermediate transfer belt is sandwiched between the process cartridges 106Y, 106M, 106C, and 106K at positions facing the photosensitive drum 108, respectively.
In the intermediate transfer unit 104, the color toner images formed by the process cartridges 106Y, 106M, 106C, and 106K are superimposed as color toner images on the intermediate transfer belt 129 by the primary transfer rollers 130Y, 130M, 130C, and 130K. . The color toner image is conveyed to the secondary transfer portion by the movement of the intermediate transfer belt 129, and is transferred to the recording paper 50 by the secondary transfer roller 126 at the secondary transfer portion.
The secondary transfer roller 126 sends the recording paper 50 onto which the toner image is transferred toward the fixing unit 105.
The fixing unit 105 presses and heats the conveyed recording paper 50 to fix the toner image transferred on the recording paper 50 to the recording paper 50.
After the fixing, the recording paper 50 is discharged to the paper discharge tray unit 153 by the paper discharge roller pair 152. Reference numeral 154 denotes an image reading unit.

The laser writing unit 122 is attached to the lower part of the process cartridges 106Y, 106M, 106C, and 106K. The laser writing unit 122 corresponds to each of the process cartridges 106Y, 106M, 106C, and 106K. The laser writing unit 122 irradiates the outer surface of the photosensitive drum 108 uniformly charged by a charging roller 109, which will be described later, with laser light to An electrostatic latent image is formed.
The process cartridges 106Y, 106M, 106C, and 106K are provided between the intermediate transfer unit 104 and the laser writing unit 122, and are arranged in parallel along the conveyance direction of the intermediate transfer belt 129.

As shown in FIG. 2, the process cartridges 106Y, 106M, 106C, and 106K include a cartridge case 111, a charging roller 109 as a charging device, a photosensitive drum 108 as an image carrier, and a cleaning blade 112 as a cleaning device. And a developing device 113.
The charging roller 109 uniformly charges the outer surface of the photosensitive drum 108. The photosensitive drum 108 is disposed at a distance from a later-described developing roller 115 of the developing device 113.
The cleaning blade 112 removes the transfer residual toner remaining on the outer surface of the photosensitive drum 108 after transferring the toner image to the intermediate transfer belt 129.
The developing device 113 includes a developer supply unit 114, a case 125 as a developing casing, a developing roller 115 as a developer carrying member, a doctor blade 116 as a developer regulating member, and the like.

The developer supply unit 114 includes a storage tank 117 and a pair of stirring screws 118 as stirring members. The storage tank 117 is formed in a box shape having a length substantially equal to that of the photosensitive drum 108. A partition wall 119 extending along the longitudinal direction of the storage tank 117 is provided in the storage tank 117. The partition wall 119 partitions the storage tank 117 into a first space 120 and a second space 121. Both ends of the first space 120 and the second space 121 communicate with each other, and the developer circulates in the storage tank 117.
The developer contains toner and a magnetic carrier (also referred to as magnetic powder). The toner is appropriately supplied to one end of the first space 120 on the side away from the developing roller 115 in the first space 120 and the second space 121 by a toner replenishing device 155 (see FIG. 1).
The toner is spherical fine particles produced by an emulsion polymerization method or a suspension polymerization method. A specific configuration of the toner will be described later.

The magnetic carrier is accommodated in both the first space 120 and the second space 121. The average particle size of the magnetic carrier is 20 μm or more and 50 μm or less.
The stirring screw 118 is accommodated in each of the first space 120 and the second space 121. The longitudinal direction of the stirring screw 118 is parallel to the longitudinal directions of the storage tank 117, the developing roller 115, and the photosensitive drum 108. The agitating screw 118 agitates the toner and the magnetic carrier by rotating, and conveys the developer along the axis.
The agitation screw 118 in the first space 120 conveys the developer from one end to the other end. The stirring screw 118 in the second space 121 conveys the developer 156 from the other end toward the one end.
The developer supply unit 114 conveys the toner supplied to one end of the first space 120 to the other end while stirring with the magnetic carrier, and conveys the toner from the other end to the other end of the second space 121. To do. Then, the developer supply unit 114 agitates the toner and the magnetic carrier in the second space 121 and supplies them to the developing roller 115 while transporting them in the axial direction of the screw.
The case 125 is formed in a box shape and is attached to the storage tank 117 and covers the developing roller 115 and the like together with the storage tank 117. An opening 125 a is provided in a portion of the case 125 that faces the photosensitive drum 108.

The developing roller 115 is formed in a cylindrical shape, and is provided between the second space 121 and the photosensitive drum 108 and in the vicinity of the opening 125a described above. The developing roller 115 is parallel to both the photosensitive drum 108 and the storage tank 117. The developing roller 115 is disposed at a distance from the photosensitive drum 108.
A space between the developing roller 115 and the photosensitive drum 108 forms a developing region 131 in which the toner of the developer is attracted to the photosensitive drum 108 to develop the electrostatic latent image and obtain a toner image.
In the developing area 131, the developing roller 115 and the photosensitive drum 108 face each other.

As shown in FIGS. 2 and 3, the developing roller 115 includes a cored bar 134, a cylindrical magnet roller (also referred to as a magnet body) 133 as a magnetic field generating unit, and a cylindrical developing sleeve 132. . The core metal 134 is arranged in parallel with the longitudinal direction of the photosensitive drum 108 in the longitudinal direction, and is fixed to the case 125 without rotating.
The magnet roller 133 is made of a magnetic material, is formed in a cylindrical shape, and is attached with a plurality of fixed magnetic poles (not shown). The magnet roller 133 is fixed to the outer periphery of the core bar 134 without rotating around the axis.
The fixed magnetic pole is a long and rod-shaped magnet, and is attached to the magnet roller 133. The fixed magnetic pole extends along the longitudinal direction of the magnet roller 133, that is, the developing roller 115, and is provided over the entire length of the magnet roller 133.
The magnet roller 133 is accommodated (enclosed) in the developing sleeve 132.

One fixed magnetic pole is opposed to the stirring screw 118 in the second space 121. The one fixed magnetic pole serves as a pumping magnetic pole, and a magnetic force is generated on the outer surface of the developing sleeve 132, that is, the developing roller 115, so that the developer 156 in the second space 121 of the storage tank 117 is transferred to the developing sleeve 132. Adsorb to the outer surface.
The other fixed magnetic pole is opposed to the photosensitive drum 108. The fixed magnetic pole forms a developing magnetic pole, and generates a magnetic force on the outer surface of the developing sleeve 132, that is, the developing roller 115, thereby forming a magnetic field between the developing sleeve 132 and the photosensitive drum 108. The fixed magnetic pole forms a magnetic brush by the magnetic field so that the developer toner adsorbed on the outer surface of the developing sleeve 132 is transferred to the photosensitive drum 108.
At least one fixed magnetic pole is provided between the pumping magnetic pole and the developing magnetic pole. The fixed magnetic pole generates a magnetic force on the outer surface of the developing sleeve 132, that is, the developing roller 115, and conveys the developer before development toward the photosensitive drum 108, and also transfers the developed developer to the photosensitive drum. From 108 to the inside of the storage tank 117.
The magnetic pole configuration of the magnet roller 133 is the same as the conventional configuration described above.

When the developer is adsorbed on the outer surface of the developing sleeve 132, the fixed magnetic poles described above are stacked on the outer surface of the developing sleeve 132 by stacking a plurality of magnetic carriers of the developer along the lines of magnetic force generated by the fixed magnetic pole. Stand)
In this way, a state in which a plurality of magnetic carriers are stacked on the outer surface of the developing sleeve 132 along the lines of magnetic force is standing on the outer surface of the developing sleeve 132.
The toner is adsorbed to the magnetic carrier that stands up. That is, the developing sleeve 132 attracts the developer 156 to the outer surface by the magnetic force of the magnet roller 133.
As shown in FIG. 4, the developing sleeve 132 is formed in a cylindrical shape. The developing sleeve 132 includes (accommodates) a magnet roller 133 and is provided so as to be rotatable around the axis. The developing sleeve 132 is rotated so that the inner peripheral surface thereof is sequentially opposed to the fixed magnetic pole. The developing sleeve 132 is made of a nonmagnetic material such as aluminum alloy, brass, stainless steel (SUS), or conductive resin. The developing sleeve 132 is subjected to a roughening process (depression formation) on the outer surface by a surface treatment device (see FIG. 8 of Patent Document 4) that cuts with an end mill while rotating the developing sleeve.

As a material for the developing sleeve 132, an aluminum alloy is excellent in terms of workability and lightness. When an aluminum alloy is used, it is preferable to use A6063, A5056, and A3003. When using SUS, it is preferable to use SUS303, SUS304, and SUS316. In the illustrated example, the developing sleeve 132 is made of an aluminum alloy.
The outer diameter of the developing sleeve 132 is about 18 mm in this embodiment. The length of the developing sleeve 132 in the axial direction is preferably about 300 mm to 350 mm when the maximum sheet size of the image forming apparatus is A3.
On the outer surface of the developing sleeve 132, as shown in FIGS. 4, 5, 6 (a), and 7, a large number of recesses 139 having an elliptical shape in plan view are formed.
The depressions 139 are formed in a concave shape on the outer surface of the developing sleeve 132, and are regularly (multiple) arranged in the sleeve circumferential direction and the sleeve longitudinal direction so as not to overlap each other. In the present invention, the arrangement in which the distance between the depressions 139 adjacent to each other in the circumferential direction and the longitudinal direction of the developing sleeve 132 is constant is referred to as the regular arrangement of the depressions 139. That is, the interval between the recesses 139 adjacent to each other in the circumferential direction and the longitudinal direction of the developing sleeve 132 is constant.
The recess 139 is formed so that the opening shape is elliptical (including the concept of an oval shape), and the major axis direction thereof is disposed in a state of being inclined along the longitudinal direction of the developing sleeve 132.

As shown in FIG. 5, FIG. 6A and FIG. 7, a plurality of the recesses 139 are arranged along the longitudinal direction of the developing sleeve 132 and are adjacent to each other in the circumferential direction of the developing sleeve 132. They are arranged so as to be displaced in the longitudinal direction by about half of the length of the recess 139. Further, since the recesses 139 are formed on the outer surface of the developing sleeve 132 by the surface treatment apparatus, they are arranged on the outer surface of the developing sleeve 132 in a spiral shape indicated by a one-dot chain line in FIG.
As shown in FIG. 6B, the recess 139 has a V-shaped cross-section in the width direction (that is, the circumferential direction of the developing sleeve 132), and as shown in FIG. The cross-sectional shape in the direction (that is, the longitudinal direction of the developing sleeve 132) is formed as an arcuate curved surface. Further, since the recess 139 is formed on the outer surface of the developing sleeve 132 by the surface treatment apparatus while rotating the sleeve, the longitudinal direction thereof is slightly curved as shown in FIG.
In the present invention, the shape of the recess 139 is generally referred to as long as the length is longer than the width and the outer edge is formed by a curve, whether it is a longitudinal direction, a straight line, or a slight curve. The shape is elliptical.

The length (major axis) in the longitudinal direction of the recess 139 is 1.0 mm or more and 2.3 mm or less, and the width (minor axis) in the width direction is 0.3 mm or more and 0.7 mm or less. ing. The depth is 0.05 mm or more and 0.15 mm or less.
About 50 to 250 recesses 139 are provided per 100 mm ² of the outer surface of the developing sleeve 132. That is, the total capacity of the plurality (large number) of depressions 139 is 0.5 mm ³ or more and 7.0 mm ³ or less per 100 mm ² of the outer surface of the developing sleeve 132.
Furthermore, 1.0 or more and 3.0 or less recesses 139 are provided in the circumferential direction of the photosensitive drum 108 that rotates together with the developing sleeve 132. 5, 6 </ b> A, and 7, the horizontal direction in the drawing is the longitudinal direction of the developing sleeve 132.

In general, the developer conveyance performance improves as the depth of the recess 139 increases, but periodic pitch unevenness is likely to occur as in the case of a conventional developing sleeve having a groove provided on the outer surface.
On the other hand, as the dent 139 is shallower, pitch unevenness is less likely to occur, but the developer transport performance decreases. Particularly in recent years, the image reproducibility has been improved due to the progress of image forming technology for small particle size toner and magnetic carrier and the image forming technology for proximity development.
Therefore, in the developing sleeve 132 according to the present embodiment, the depth of the recesses 139 is set to be shallow, and the distribution density of the recesses 139 is increased to achieve both the developer conveyance performance and the pitch unevenness prevention. Details will be described later.

As shown in FIG. 2, the doctor blade 116 is provided at the end of the developing device 113 near the photosensitive drum 108. The doctor blade 116 is attached to the case 125 described above with a space from the outer surface of the developing sleeve 132.
The doctor blade 116 scrapes the developer on the outer surface of the developing sleeve 132 exceeding the desired thickness into the storage tank 117, and removes the developer layer on the outer surface of the developing sleeve 132 that is conveyed to the developing region 131. Set to desired thickness.

In the developing device 113 configured as described above, the developer and the magnetic carrier are sufficiently agitated by the developer supply unit 114, and the agitated developer 156 is adsorbed to the outer surface of the developing sleeve 132 by the fixed magnetic pole. In the developing device 113, the developing sleeve 132 rotates and transports the developer adsorbed by the plurality of fixed magnetic poles toward the developing region 131. The developing device 113 causes the photosensitive drum 108 to attract the developer having a desired thickness by the doctor blade 116. In this way, the electrostatic latent image on the photosensitive drum 108 is developed to form a toner image.
The developing device 113 releases the developed developer toward the storage tank 117. The developed developer stored in the storage tank 117 is sufficiently stirred again with another developer in the second space 121 and used for developing the electrostatic latent image on the photosensitive drum 108.
When a toner concentration sensor (not shown) detects that the concentration of the toner supplied to the photosensitive drum 108 has been lowered by the developer supply unit 114, the toner supply device 155 operates to supply toner to the developing device 113. It has become.

In the configuration in which the depression 139 is formed on the outer surface of the developing sleeve 132, the depression 139 is less likely to be worn due to secular change because there is no convex portion formed by conventional sandblasting on the sleeve surface. A decrease in the transport amount of the developer due to the change can be suppressed.
Further, since the developing sleeve 132 is regularly arranged so that the depressions 139 formed on the outer surface do not overlap, the developer accumulates in the depressions 139. The locations where the developer accumulates are regularly arranged on the outer surface, and thus it is possible to prevent the occurrence of image unevenness. Further, the pumping amount can be further increased in order to maintain high image quality in future high-speed machines by adjusting the capacity and number of the recesses 139.

Since the recesses 139 are regularly arranged, it is easy to set processing conditions capable of extending the service life while ensuring an optimum amount of developer to be pumped, and the recesses 139 are surely set under the set conditions. Can be formed and has the effect of excellent workability.
Since the recesses 139 adjacent to each other in the circumferential direction of the developing sleeve 132 are displaced in the longitudinal direction of the developing sleeve 132, many portions and recesses 139 are formed on the outer surface of the developing sleeve 132 where the recess 139 is not formed. It is possible to prevent the occurrence of a spot or the like.
Accordingly, the developer adsorbed on the outer surface of the developing sleeve 132 can be adsorbed without causing unevenness, and image unevenness can be prevented.

As described with reference to FIG. 21, with the magnet roller configuration of the developing device of the present invention, the developer is likely to rotate at the end of the developing sleeve as in the conventional case. Furthermore, when the arrangement of the recesses 139 as shown in FIG. 22 is uniform in the longitudinal direction of the sleeve, a developer conveying force in the longitudinal direction of the developing sleeve is generated on the developing sleeve, so that the developer can easily go to the end. The developer is likely to rotate.
In the present embodiment, in order to prevent this, as shown in FIG. 8, the angle of the depression 139 (indicated by hatching) only at the depression forming section end on the developing sleeve 132 downstream in the developer transport direction is set to the center from the end. The side (inward) recess 139 is changed in the opposite direction. In other words, the angle is changed so as to generate a conveying force against the conveying force by the inner depressions 139 group.
In this way, the developer transport direction on the developing sleeve at the end can be changed in the reverse direction, so the amount of developer supplied to the end can also be reduced, and the developer rotation at the end can be reduced. Can be difficult to generate. Further, the developer can be prevented from entering the end seal portion.

FIG. 9 shows a second embodiment. In addition, the same part as the said embodiment is shown with the same code | symbol, and unless it was especially required, the description on the structure and function which were already demonstrated is abbreviate | omitted, and only the principal part is demonstrated.
As shown in FIG. 9, in this embodiment, the angle of the depression 139 only at the end of the sleeve depression forming portion on the developing sleeve downstream in the developer transport direction is set to the inner depression 139 group in the same manner as in the above embodiment. In addition, the angle of the recess 139 at the end is increased so that the degree of canceling the conveying force by the inner recesses 139 is increased.
That is, when the angle of the end recess 139 in the first embodiment is θ1, the angle θ2 of the end recess 139 in the present embodiment has a relationship of θ1 <θ2. In other words, the rising angle of the recess 139 at the end with respect to the axial direction of the developing sleeve 132 is increased.
By doing so, the end portion can increase the agent conveying force in the longitudinal direction on the sleeve, and the end portion developer can be rotated together to more reliably prevent the developer from entering the end seal portion. can do.

In each of the above embodiments, the depression 139 is formed on the surface of the developing sleeve 132 so that the major axis thereof is inclined, and in the configuration in which the conveying force is generated in the sleeve longitudinal direction, the angle of the depression 139 at the sleeve end is set to the inward depression. However, the present invention can be similarly applied to a configuration in which the depression 139 is formed on the surface of the developing sleeve 132 so that the major axis thereof is parallel to the longitudinal direction of the sleeve.
That is, even in this case, the rotation of the end developer can be suppressed by changing the angle of the recess 139 at the end of the sleeve with respect to the inward recess.

FIG. 10 shows a modification of the developing device.
The developing device 160 according to the present embodiment is formed so that the stirring screw 118b in which the case 125 is separated from the developing roller 115 is closer to the developing roller 115 side than the developing device shown in FIG.
The stirring screw 118a supplies the developer to the developing roller 115 while conveying the developer in the longitudinal direction (axial direction).
The developer separated from the developing device 115 is collected by the stirring screw 118b and mixed and stirred with the replenishing toner here. The mixed and stirred developer is delivered to the stirring screw 118a.
With this configuration, the developer circulates in one direction as indicated by an arrow. Thereby, the increase of the conveyance speed which was the problem of the one-way circulation system mentioned above can be suppressed.
In the developing device 160, by forming the depression 139 as described above on the surface of the developing sleeve 132, the developer transport on the developer collecting side can be assisted, and the rotation speed of the stirring screw 118 can be suppressed.

  In each of the embodiments described above, the cross section of the recess 139 in the circumferential direction of the developing sleeve is formed in a V shape, but may be formed in an arc shape as shown in FIG. In the illustrated example, the cross section of both the circumferential direction and the longitudinal direction of the recess 139 is formed in an arc shape.

In this case, as shown in FIG. 12, the angle θ formed between the inner surface of the recess 139 and the outer surface of the developing sleeve 132 in the circumferential cross section of the developing sleeve 132 is the difference in developing density generated due to the influence of the developing magnetic pole described above. In order to avoid it, it is preferable that it is 60 degrees or less.
When both cross sections in the longitudinal direction and the circumferential direction of the developing sleeve 132 of the recess 139 are formed in an arc shape, the amount of developer that can be accommodated in the recess 139 can be increased, and a sufficient amount of developer is conveyed. be able to.
Further, the cross-sectional shape of the recess 139 in the sleeve circumferential direction may be a shape as shown in FIGS. 13 and 14. FIG. 13 shows a case where the bottom of the V-shaped depression 139 is formed flat, and FIG. 14 shows a case where the bottom of the V-shaped depression 139 is formed in an arc shape.

In each of the above embodiments, as shown in FIG. 5, the recesses 139 are spirally arranged on the outer surface of the developing sleeve 132, and each recess 139 is formed to be slightly bowed. As shown in FIGS. 15 and 16, the recesses 139 may be formed linearly along the longitudinal direction of the developing sleeve 132, and the plurality of recesses 139 are arranged linearly along the circumferential direction of the developing sleeve 132. You may do it.
15 and 16, the inclination of the recess 139 is omitted.

The configuration of the toner will be described in detail with reference to FIGS. 17 and 18.
In order to reproduce minute dots of 600 dpi or more, the toner preferably has a volume average particle diameter of 3 to 8 μm. The ratio (Dv / Dn) of the volume average particle diameter (Dv) to the number average particle diameter (Dn) is preferably in the range of 1.00 to 1.40. The closer (Dv / Dn) is to 1.00, the sharper the particle size distribution.
With such a toner having a small particle size and a narrow particle size distribution, the toner charge amount distribution is uniform, a high-quality image with little background fogging can be obtained, and the electrostatic transfer method has a high transfer rate. can do.
The toner shape factor SF-1 is preferably in the range of 100 to 180, and the shape factor SF-2 is preferably in the range of 100 to 180. 17 and 18 are diagrams schematically showing the shape of the toner in order to explain the shape factor SF-1 and the shape factor SF-2.

As shown in FIG. 17, the shape factor SF-1 indicates the ratio of the roundness of the toner shape and is represented by the following formula (1). This is a value obtained by dividing the square of the maximum length MXLNG of the shape formed by projecting the toner on a two-dimensional plane by the figure area AREA and multiplying by 100π / 4.
SF-1 = {(MXLNG) ² / AREA} × (100π / 4) (1)
When the value of SF-1 is 100, the shape of the toner becomes a true sphere, and becomes larger as the value of SF-1 increases.

Further, as shown in FIG. 18, the shape factor SF-2 indicates the ratio of unevenness of the toner shape, and is represented by the following formula (2). A value obtained by dividing the square of the perimeter PERI of the figure formed by projecting the toner on the two-dimensional plane by the figure area AREA and multiplying by 100π / 4.
SF-2 = {(PERI) ² / AREA} × (100π / 4) Expression (2)
When the value of SF-2 is 100, there is no unevenness on the toner surface, and as the value of SF-2 increases, the unevenness of the toner surface becomes more prominent.
Specifically, the shape factor is measured by taking a photograph of the toner with a scanning electron microscope (S-800: manufactured by Hitachi, Ltd.), introducing it into an image analyzer (LUSEX 3: manufactured by Nireco) and analyzing it. Calculated.
When the shape of the toner is close to a spherical shape, the contact state between the toner and the toner or the toner and the photoconductor becomes a point contact, so that the adsorbing force between the toners becomes weak and the fluidity increases, and the toner and the photoconductor The attraction force becomes weaker and the transfer rate becomes higher. If either of the shape factors SF-1 and SF-2 exceeds 180, the transfer rate is lowered, which is not preferable.

DESCRIPTION OF SYMBOLS 106 Process cartridge 108 Photosensitive drum as an image carrier 115 Developing roller 118 Stirring screw as developer conveyance member 125 Case as developing casing 132 Developing sleeve 133 Magnet roller 139 as a magnetic field generating means dent

JP 2007-183533 A JP 2009-80447 A

Claims (7)

A developing casing containing a two-component developer comprising toner and carrier;
A developing roller that is disposed to face the image carrier and rubs the image carrier with a developer brush formed by a magnetic force on the surface, and visualizes a latent image on the image carrier as a toner image;
Development that regulates the layer thickness of the developer on the developing roller on the upstream side in the roller rotation direction of the developing area where the developing roller faces the image bearing member with a predetermined gap between the developing roller and the surface. An agent regulating member,
The developing roller includes a developing sleeve that is rotatable and carries a developer on a surface thereof, and a magnetic field generating unit that is fixedly disposed in the developing sleeve, and the magnetic field generating unit is disposed on the image carrier. An upstream magnetic pole away from the agent that generates a magnetic force for separating the developer after developing the latent image from the developing sleeve, and adjacent to the downstream in the rotation direction of the developing sleeve with the same polarity as the upstream magnetic pole away from the agent With a downstream pole from the agent,
In the developing device, a plurality of oval or elliptical recesses are arranged on the surface of the developing sleeve in the sleeve circumferential direction and the sleeve longitudinal direction.
The developing device according to claim 1, wherein the depression at the longitudinal end portion of the developing sleeve is formed so as to impart a conveying force inward in the longitudinal direction to the developer on the developing sleeve. The developing device according to claim 1,
The depressions are regularly arranged and formed such that the long axis of the developing sleeve has an angle with respect to the longitudinal direction of the developing sleeve, and the depressions at the ends are inward with respect to the inner depressions. 2. A developing device, wherein the developer conveying direction on the developing sleeve is opposite. The developing device according to claim 2,
The developing device according to claim 1, wherein an angle of the recess at the end portion with respect to a longitudinal direction of the developing sleeve is larger than an angle of the inward recess.   A process cartridge comprising the developing device according to claim 1 and the image carrier in an integrated manner.   An image forming apparatus comprising the developing device according to claim 1. The image forming apparatus according to claim 5.
The toner used in the developing device has a volume average particle diameter of 3 to 8 μm and a ratio (Dv / Dn) of the volume average particle diameter (Dv) to the number average particle diameter (Dn) of 1.00 to 1.40. An image forming apparatus characterized by being in the range. The image forming apparatus according to claim 5 or 6,
The image forming apparatus according to claim 1, wherein the toner used in the developing device has a shape factor SF-1 in the range of 100 to 180 and a shape factor SF-2 in the range of 100 to 180.

Images