JP2018081152A - Developing device, process cartridge, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a developing device that prevents adhesion of toner to developer carriers for a long period, and prevents a reduction in the amount of pumped-up developer to prevent the occurrence of abnormal images and scattering of toner, a process cartridge, and an image forming apparatus.SOLUTION: A developing device 50 comprises: a first developer carrier 51A that carries a two-component developer G carried in a first developing area opposing to the surface of an image carrier 21; and a second developer carrier 51B that receives, on its surface, at least part of the developer G after that has passed the first developing area and is carried on the first developer carrier 51A, and carries the two-component developer G carried in a second developing area opposing to the surface of the image carrier 21. The developer carriers 51A and 51B have their respective surfaces roughened with grooves; the grooves formed in the developer carriers 51A and 51B have their respective widths formed larger than their depths; the depths of the grooves formed in the first developer carrier 51A are larger than the depths of the grooves formed in the second developer carrier 51B.SELECTED DRAWING: Figure 2

Description

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

  In a developing device using a two-component developer used in an electrophotographic image forming apparatus, a developer carrying member that carries a developer on an outer peripheral surface by a magnetic force and conveys the developer to a developing region is known. In this developing device, the electrostatic latent image on the latent image carrier is developed by forming an electric field between the developer carrier and the latent image carrier. However, the toner remains attracted to the developer carrying member. The residual toner adheres to the outer peripheral surface of the developer carrier over time.

In a high-speed machine with a large number of image formations per minute, a structure using a plurality of developer carriers has been proposed in order to stabilize the developing ability of the latent image carrier because the developer carrier is moved quickly. However, in this case as well, due to the large number of images formed, toner fixation occurs particularly in the first developer carrying member that conveys the developer in the developing device to the developing region, and the developer is carried to the developing region. The amount (pumped amount) decreases.
In addition, a configuration has been proposed in which the surface of the first developer carrier is roughened and the toner adhesion is suppressed by adopting a configuration in which the average roughness interval of the roughness is increased. If the average interval is simply increased, the amount of developer (pumped amount) carried to the development area is lowered early. That is, since both the toner fixation and the reduction in the pumping amount cannot be improved, there is a problem that the image quality is deteriorated such as a decrease in image density and the toner is scattered over time.

  In order to solve the above-mentioned problems, the surface of the developing member is roughened to prevent the occurrence of two phenomena of contamination and toner image degradation due to toner fusion to the developing member as a developer carrier. A first developing member that has been applied and a second developing member that has been coated after having been similarly roughened. The unevenness average interval of the first developing member is Sm1, and the unevenness of the second developing member A configuration has been proposed that satisfies Sm1> Sm2 and Sm2 <D <Sm1, where Sm2 is the average interval and D is the carrier particle size of the developer (see, for example, “Patent Document 1”).

However, the above-described technique does not improve the problem that the pumping amount of the first developing member is lowered early.
In addition, in the configuration in which the unevenness average interval of the second developing member is smaller than the carrier particle size, only the effect of 10,000 sheets has been confirmed, and high productivity and long-life image formation requiring 5 million sheets or more is required. In the apparatus, the life of about 10,000 sheets is insufficient, and in the image formation of 5 million sheets, there is a problem in that the sleeve sticks at an uneven average interval smaller than the carrier particle size.

  The present invention solves the above-described problems, improves the toner fixing of the developer carrying member over a long period of time, prevents the pumping amount from decreasing, and prevents development of abnormal images and toner scattering. An object is to provide an apparatus, a process cartridge, and an image forming apparatus.

  The present invention comprises a first developer carrying member carrying a two-component developer containing a carrier on the surface thereof and carrying the two-component developer carried on a first development region facing the surface of the image carrier. Two components received on the surface of at least a part of the developer carried by the first developer carrying member after passing through one developing region, and carried on the second developing region facing the surface of the image carrier. A second developer carrying member that conveys the developer, each developer carrying member has its surface roughened by a groove, and each groove formed in each developer carrying member comprises: The respective depths are formed larger than the particle diameter of the carrier and the respective widths are formed larger than the depth, and the depth of the groove formed in the first developer carrier is the first depth. 2 More than the depth of the groove formed on the developer carrier And wherein the door.

  According to the present invention, the surface of each developer carrier is roughened by a groove, and the toner attached to the groove is collected by the carrier by making the groove depth and width larger than the carrier particle diameter of the developer. In addition, since the groove depth is sufficiently deep, the developer transportability can be sufficiently secured, so that the toner adhesion of the developing roller can be improved over a long period of time, and the decrease in the pumping amount is prevented to reduce the image density. The generation of abnormal images and the occurrence of toner scattering can be prevented.

1 is a schematic configuration diagram of an image forming apparatus to which an embodiment of the present invention can be applied. It is a schematic block diagram of the process cartridge used for one Embodiment of this invention. It is a schematic sectional drawing of the image development apparatus used for one Embodiment of this invention. It is the schematic explaining the developer control member used for one Embodiment of this invention. It is the schematic explaining the developing roller used for one Embodiment of this invention. It is the schematic explaining the magnetic pole of the developing roller used for one Embodiment of this invention. It is the schematic explaining the flow of the developer in the developing device used for one embodiment of the present invention. It is the schematic of the measuring apparatus which measures the volume specific resistance value of the magnetic carrier used for one Embodiment of this invention. It is the schematic for demonstrating the surface property of the developing roller used for one Embodiment of this invention. FIG. 6 is a diagram showing a relationship between ten-point average roughness on the surface of the developing roller and sleeve fixing when forming an image of 5 million sheets in one embodiment of the present invention. FIG. 6 is a diagram showing a relationship between an average unevenness on the surface of the developing roller and sleeve fixing when forming 5 million images in an embodiment of the present invention. It is the schematic for demonstrating the measuring method which measures the static friction coefficient of the developing roller used for one Embodiment of this invention. 6 is a graph in which data of a developing roller with a ta-C coat is added to a diagram showing the relationship between the ten-point average roughness on the surface of the developing roller and the fixing of a sleeve when an image of 5 million sheets is formed in an embodiment of the present invention. 4 is a graph in which data of a developing roller with a ta-C coat is added to a diagram showing the relationship between the average unevenness on the surface of the developing roller and the sleeve fixing when a 5 million-sheet image is formed in an embodiment of the present invention. It is a schematic sectional drawing of the image development apparatus used for the modification of each embodiment of this invention. FIG. 6 is a diagram showing a relationship between the number of images formed on a first developing roller and a sleeve fixing rank in a confirmation test for confirming the effect of each embodiment and modification of the present invention. FIG. 6 is a diagram showing a relationship between the number of images formed on a second developing roller and a sleeve fixing rank in a confirmation test for confirming the effects of the embodiments and modifications of the present invention.

FIG. 1 shows a printer 10 as an image forming apparatus to which an embodiment of the present invention can be applied. In the figure, writing units 2A, 2B, 2C, and 2D are devices for writing electrostatic latent images on four photosensitive drums 21 as image carriers after the charging process based on image information. , An optical scanning device using polygon mirrors 3A, 3B, 3C and 3D and optical elements 4A, 4B, 4C and 4D.
As the writing unit, an LED array device can be used instead of the optical scanning device.

The paper supply unit 61 stores a recording medium P such as recording paper or OHP, and feeds the recording medium P toward the transfer belt 30 during image formation. The transfer belt 30 is an endless belt body for transporting the recording medium P while electrostatically attracting to the surface thereof, and transferring the toner image formed on each photosensitive drum 21 to the recording medium P. A suction roller 64 and a belt cleaner 65 are disposed in the vicinity of the transfer belt 30 so as to abut on the outer peripheral surface of the transfer belt 30.
The four transfer rollers 24 facing each photoconductor drum 21 via the transfer belt 30 have a core metal and a conductive elastic layer that covers the core metal. The conductive elastic layer of the transfer roller 24 is prepared by blending and dispersing a conductive agent such as carbon black, zinc oxide, tin oxide in an elastic material such as polyurethane rubber, ethylene-propylene-diene polyethylene (EPDM), etc. It is an elastic body whose volume resistivity is adjusted to medium resistance.
The fixing unit 66 includes a heating roller 68 and a pressure roller 67, and fixes the toner image on the recording medium P onto the recording medium P by heat and pressure.

  The four process cartridges 20Y, 20C, 20M, and 20Bk arranged in the vertical direction in FIG. 1 along the transfer belt 30 form yellow, cyan, magenta, and black toner images, respectively. On each of the process cartridges 20Y, 20C, 20M, and 20Bk, there are agent cartridges 28Y, 28C, 28M, and 28Bk that supply a two-component developer including the magnetic carrier C and the toner T of each color to the developing device 50. . The process cartridges 20Y, 20C, 20M, and 20Bk and the agent cartridges 28Y, 28C, 28M, and 28Bk can be rotated integrally around a rotation shaft (not shown), respectively, and the transfer belt 30 is opened so that the apparatus main body 1 is opened. It is comprised so that attachment or detachment is possible.

  The printer 10 shown in the present embodiment performs image processing on image information such as a page description language or a bitmap format transmitted from a computer or the like, and converts it into write data. At the time of image formation, exposure light corresponding to black, magenta, cyan, and yellow image information is irradiated from the writing units 2A, 2B, 2C, and 2D to the process cartridges 20Y, 20C, 20M, and 20Bk, respectively. In other words, exposure light (laser light) emitted from each light source is irradiated onto each photosensitive drum 21 via each polygon mirror 3A, 3B, 3C, 3D and each optical element 4A, 4B, 4C, 4D. . As a result, electrostatic latent images corresponding to the exposure light are formed on the photosensitive drums 21 of the process cartridges 20Y, 20C, 20M, and 20Bk, respectively. The electrostatic latent image is developed with toner of each color by a developing device 50 arranged to face the surface of each photosensitive drum 21. Each color toner image is formed on each photosensitive drum 21, and each toner image is sequentially transferred onto the recording medium P.

In the paper feeding unit 61, the recording medium P fed by the rotation of the paper feeding roller 62 is temporarily stopped by the registration roller pair 63 and fed onto the transfer belt 30 with timing. The suction roller 64 disposed at the recording medium feed position to the transfer belt 30 causes the transfer medium 30 to suck the recording medium P sent by voltage application. As the transfer belt 30 travels in the direction of the arrow in FIG. 1, the recording medium P adsorbed to the transfer belt 30 sequentially passes through the positions facing the process cartridges 20Y, 20C, 20M, and 20Bk. The toner images are superimposed and transferred so as to overlap each other.
The recording medium P to which the toner of each color is thus transferred is separated from the transfer belt 30 and sent to the fixing unit 66, and the toner image on the recording medium P is heated while being sandwiched between the pressure roller 67 and the heating roller 68. As a result, the image is fixed on the recording medium P. On the other hand, the transfer belt 30 from which the recording medium P has been separated is cleaned of dirt such as toner adhering to the surface thereof by the belt cleaner 65 and is prepared for the next image formation.

Next, each process cartridge 20Y, 20C, 20M, 20Bk and each agent cartridge 28Y, 28C, 28M, 28Bk in the printer 10 will be described. FIG. 2 is a view showing the process cartridge 20 and the agent cartridge 28 arranged in the apparatus main body 1.
Note that the process cartridges 20Y, 20C, 20M, and 20Bk and the agent cartridges 28Y, 28C, 28M, and 28Bk have substantially the same structure, and therefore the suffixes Y, M, C, and Bk are omitted as appropriate.

As shown in FIG. 2, the process cartridge 20 includes a photosensitive drum 21, a charging device 22, a developing device 50, and a cleaning device 25 that are integrally configured.
The photosensitive drum 21 is a negatively charged organic photosensitive member, and is rotationally driven counterclockwise in FIG. 2 by a rotational driving mechanism (not shown).
The charging device 22 is a charging roller having elasticity in which a medium-resistance foamed urethane layer in which urethane resin, carbon black as conductive particles, a sulfurizing agent, a foaming agent, and the like are formed in a roller shape on a core metal. Examples of the medium resistance material of the charging device 22 include a base material such as urethane rubber, ethylene-propylene-diene polyethylene (EPDM), butadiene acrylonitrile rubber (NBR), silicone rubber, isoprene rubber, carbon black for resistance adjustment, A rubber material in which a conductive substance such as a metal oxide is dispersed, or a foamed material of these rubber materials can be used.
The cleaning device 25 has a cleaning brush or a cleaning blade that contacts the surface of the photosensitive drum 21, and mechanically removes and collects the transfer residual toner on the photosensitive drum 21.

FIG. 3 shows the developing device 50 provided in the process cartridge 20. In the figure, the developing device 50 is a so-called multi-stage developing system provided with two developing rollers, a first developing roller 51A as a first developer carrier and a second developing roller 51B as a second developer carrier. It is a developing device.
The developing rollers 51A and 51B are opposed to each other so as to be close to the surface of the photosensitive drum 21, and each facing position is a developing area. In each developing region, a magnetic brush made of a developer spiked on the surface of each developing roller 51A, 51B comes into contact with the surface of the photosensitive drum 21. The developing device 50 contains a two-component developer G containing toner T and magnetic carrier C. The developing device 50 develops an electrostatic latent image formed on the photosensitive drum 21 to produce a toner image. Development processing is performed.
In the present embodiment, the first developing roller 51A is vertically arranged in the gravity direction upper side and the second developing roller 51B is vertically arranged in the gravity direction lower side, thereby reducing the space in the width direction of the developing device 50, and the printer. Space saving in the width direction of the entire 10 is also realized.

Next, an image forming process performed on the photosensitive drum 21 will be described.
When the photosensitive drum 21 is rotationally driven in the counterclockwise direction, the surface of the photosensitive drum 21 is uniformly charged by the charging device 22, and then the charged surface of the photosensitive drum 21 is supplied from the writing unit 2. Exposure is performed with exposure light L shown in FIG. That is, by selectively removing the charge on the photosensitive drum 21 in accordance with image information by irradiation with the exposure light L, a potential difference (potential contrast) from a non-image portion that has not been irradiated with the exposure light L is generated, and static electricity is generated. An electrostatic latent image is formed. In this exposure process, the charge generating material receives light in the photosensitive layer of the photosensitive drum 21 to generate charges, and the positive charges cancel out the charged charges on the surface of the photosensitive drum 21.

The surface of the photosensitive drum 21 on which the electrostatic latent image is formed reaches a position facing the developing device 50 by rotational movement. The electrostatic latent images are visualized by sequentially contacting the magnetic brushes on the developing rollers 51A and 51B and adhering the negatively charged toner T in the magnetic brushes. The developer G pumped up on the first developing roller 51 </ b> A disposed above is appropriately adjusted by the developer regulating member 52.
In the present embodiment, the developer regulating member 52 is screwed to the developing device main body, and more specifically, is fixed at three locations, that is, the central portion and both end portions in the axial direction of the developing roller. The developer G adjusted to an appropriate amount by the developer regulating member 52 is transported to the first development region which is a portion facing the photosensitive drum 21 by the first developing roller 51A.

The gap between the photoconductor and the developing roller (development gap) is becoming narrower due to the recent improvement in image quality (improving dot reproducibility), and the amount of developer on the developing roller is reduced as the developing gap becomes narrower. There is a need. Here, there is only a method of narrowing the regulation gap (doctor gap) only with the developer regulating member made of a non-magnetic material, and by this, the developer is rubbed at the doctor portion between the developer regulating member and the developing roller. The state of sleeve fixing in which the developer adheres to the developing sleeve is deteriorated.
In order to widen the doctor gap, it is necessary to use a magnetic member as the developer regulating member. Accordingly, the developer can be raised by collecting the magnetic field on the developer regulating member, and the doctor gap can be widened. Thereby, the rubbing of the developer at the doctor portion can be reduced, and deterioration of the above-mentioned sleeve fixing state can be suppressed. Moreover, since the torque at the doctor portion is also reduced, the deterioration of the developer can be suppressed.

  FIG. 4 is an enlarged view of the developer regulating member 52 used in the present embodiment. In the figure, a developer regulating member 52 is a non-magnetic doctor blade 52A as a non-magnetic member made of a stainless steel plate having a thickness of 2 mm, and a thickness 0 disposed on the upstream side of the doctor blade 52A in the developing roller rotation direction. And a magnetic body 52B as a magnetic member made of a 3 mm SUS430 plate. The developer regulating member 52 is disposed on the surface facing the first developing roller 51A so that the magnetic body 52B protrudes 0.2 mm from the doctor blade 52A toward the first developing roller 51A.

With the above-described configuration, since the doctor portion has the magnetic member, the doctor gap is widened, whereby the torque of the developing roller 51A can be reduced, and the friction with the developer G at the doctor portion is reduced. Therefore, it is possible to prevent the toner from adhering to the doctor part and to prevent the developer pumping amount from being lowered. Further, since the magnetic body 52B protrudes from the doctor blade 52A toward the first developing roller 51A, the doctor gap can be further widened to reduce the torque of the developing roller 51A, and the magnetic body 52B does not protrude from the doctor blade 52A. Compared to the above, toner adhesion at the doctor portion can be further reduced.
If the decrease in the developer pumping amount over time is acceptable, the doctor blade 52A and the magnetic body 52B are arranged on the same surface, or the doctor blade 52A protrudes from the magnetic body 52B. Alternatively, the doctor blade 52A may be protruded from the magnetic body 52B and the magnetic body 52B may be bent upstream in the developing roller rotation direction.

In the first developing area, the developer G on the first developing roller 51A rises due to the magnetic force of the developing magnetic pole provided in the first developing roller 51A, and the formed magnetic brush slides on the surface of the photosensitive drum 21. Rub. At this time, the toner T in the developer G is applied to the image portion on the photosensitive drum 21 by the action of a developing electric field formed by a predetermined developing bias applied to the first developing roller 51A from a power supply unit (not shown). Only selectively adhere to form a toner image.
The developer G on the first developing roller 51A that has passed through the first developing area is transported to the developer passing area facing the passing magnetic pole disposed inside the second developing roller 51B as the first developing roller 51A rotates. Is done. In the developer transfer area, a part or all of the developer G on the first developing roller 51A moves to the surface of the second developing roller 51B under the magnetic force action of the transfer magnetic pole, and on the surface of the second developing roller 51B. Supported.

As described above, the developer G carried on the second developing roller 51B is conveyed to the second developing region facing the surface of the photosensitive drum 21 by the rotation of the second developing roller 51B. In the second developing area, the developer G on the second developing roller 51B is raised by the magnetic force of the developing magnetic pole provided in the second developing roller 51B, and the formed magnetic brush slides on the surface of the photosensitive drum 21. Rub. At this time, the toner T in the developer G is applied to the image portion on the photosensitive drum 21 by the action of a developing electric field formed by a predetermined developing bias applied to the second developing roller 51B from a power supply unit (not shown). Only selectively adhere to form a toner image.
Thereafter, the developer G on the second developing roller 51B that has passed through the second developing region is separated from the surface of the second developing roller 51B and returned to the developing device 50.

  In this embodiment, a superimposed voltage obtained by superimposing an alternating voltage (AC) on a direct current voltage (DC) is applied as a developing bias. The superimposed voltage has a frequency of 0.99 kHz, a peak-to-peak voltage (Vpp) of 800 V, + A rectangular wave with a side duty of 10% is used. The superimposed voltage and the waveform shape are not limited to this, and for example, a high frequency such as 8 kHz may be used, or another waveform shape such as a sin wave or a triangular wave may be used. It is also possible to use only a DC voltage as the developing bias.

The surface portion of the photosensitive drum 21 on which the toner image is formed by the development processing in the first development area and the second development area reaches a position facing the transfer belt 30 and the transfer roller 24 as the photosensitive drum 21 rotates. To do. At this timing, the recording medium P is conveyed by the operation of the registration roller pair 63, and the toner image on the photosensitive drum 21 is transferred onto the recording medium P. At this time, a predetermined voltage is applied to the transfer roller 24. The recording medium P to which the toner image is transferred passes through the fixing unit 66 and is fixed to the recording medium P, and then is discharged out of the apparatus by a discharge roller 69.
On the other hand, toner (transfer residual toner) T remaining on the photosensitive drum 21 without being transferred to the recording medium P during the transfer process reaches the portion facing the cleaning device 25 while adhering to the photosensitive drum 21. And removed and collected by the cleaning device 25. Thereafter, the surface of the photosensitive drum 21 is neutralized by a neutralizing device (not shown), and a series of image forming processes is completed.

Next, the configuration and operation of the developing device 50 in the present embodiment will be described.
The developing device 50 includes a first developing roller 51A, a second developing roller 51B, a first conveying screw (auger screw) 53A, a second conveying screw 53B, a third conveying screw 53C, a developer regulating member 52, and a carrier collecting roller 54. , Scraper 55, discharge screw 56 and the like. Further, in the developing device 50, there are formed three developer transport paths: a developer supply transport path B1, a developer recovery transport path B2, and a developer circulation transport path B3 that transport the developer G to form a circulation path. Has been.

FIG. 5 is a schematic view of the first developing roller 51A and the second developing roller 51B. Since the developing rollers 51A and 51B have the same configuration, only the first developing roller 51A will be described, and the second developing roller 51B is only given a reference numeral.
In the first developing roller 51A, a sleeve 51A1 in which a non-magnetic material such as stainless steel, aluminum, brass, conductive resin or the like is formed in a cylindrical shape is rotationally driven in a clockwise direction in FIG. In the sleeve 51A1, a magnet 51A2 is disposed that forms a magnetic field for causing the developer G to rise on the peripheral surface of the sleeve 51A1. Then, the carrier C in the developer G rises in a chain shape on the sleeve 51A1 along the magnetic lines of force generated by the magnet 51A2, and the charged toner T adheres to the carrier C to form a magnetic brush. . The formed magnetic brush is conveyed along with the rotation of the sleeve 51A1.
Further, the surface of the sleeve 51 </ b> A <b> 1 is provided with a rough surface portion that has been subjected to uneven processing in order to improve the conveying ability of the developer G. This rough surface portion will be described later.

  On the surface of each developing roller 51A, 51B, the magnetic poles H11, H12, H13, H14, H15, H16 of the magnet 51A2 and the magnetic poles H21, H22, H23, H24 of the magnet 51B2 are indicated by broken lines in FIG. Magnetic flux density distribution is formed. The broken line in the figure indicates the magnitude of the magnetic flux density in the normal direction on the surface of each of the developing rollers 51A and 51B. The farther from the surface, the larger the magnetic flux density in the normal direction is. Is shown.

The magnet 51 </ b> A <b> 2 is formed on the main magnetic pole H <b> 11 where a magnetic line of force is formed at a position facing the photosensitive drum 21, and on the conveying magnetic pole H <b> 12 where the magnetic line of force is formed between the developer regulating member 52 and the main magnetic pole H < The opposing regulating magnetic pole H13, the pumping magnetic pole H14 where magnetic lines of force are formed at positions facing the first conveying screw 53A, the first passing magnetic pole H16 where the magnetic lines of force are formed at positions facing the second developing roller 51B, the first passing magnetic poles A conveyance magnetic pole H15 in which lines of magnetic force are formed between H16 and the pumping magnetic pole H14 is provided.
The magnet 51B2 includes a main magnetic pole H21 where a magnetic line of force is formed at a position facing the photosensitive drum 21, a second transfer magnetic pole H22 where a magnetic line of force is formed at a position facing the first transfer magnetic pole H16, a developer recovery conveyance path B2, and the like. Are provided with an agent separating magnetic pole H23 in which magnetic lines of force are formed, and a conveying magnetic pole H24 in which magnetic lines of force are formed between the main magnetic pole 21 and the agent separating magnetic pole H23.

The magnetic field lines of the pumping magnetic pole H14 act on the carrier C, and the developer G accommodated in the developer supply transport path B1 is carried on the surface of the first developing roller 51A. The developer G carried on the first developing roller 51A is scraped off by the developer regulating member 52 when a part thereof passes through a regulating gap that is an interval between the developer regulating member 52 and the first developing roller 51A. The developer G thus scraped is returned to the developer supply transport path B1.
On the other hand, the developer G on the first developing roller 51A that has passed through the regulation gap where the magnetic force by the regulation magnetic pole H13 acts is conveyed to the first development region by the magnetic force of the conveyance magnetic pole H12, and the first magnetic pole H11 faces the first. In the developing area, the surface of the photosensitive drum 21 is rubbed by rising due to the magnetic force of the main magnetic pole H11.

Thereafter, the developer G that has passed through the first development area is conveyed to the developer delivery area, which is the position of the first delivery magnetic pole H16 (position facing the second delivery magnetic pole H22), and is supplied to the developer on the first development roller 51A. Part or all of the developer G is transferred onto the second developing roller 51B by the magnetic force (transfer magnetic force) of the first transfer magnetic pole H16 and the second transfer magnetic pole H22. The developer G transferred onto the second developing roller 51B then rises by the magnetic force of the main magnetic pole H21 in the second developing region where the main magnetic pole H21 faces, and rubs the surface of the photosensitive drum 21.
Thereafter, the developer G on the second developing roller 51B that has passed through the second developing region passes through the transport magnetic pole H24 and reaches the position of the agent separating magnetic pole H23. Then, the repulsive magnetic field in the agent separating magnetic pole H23 acts on the carrier C, and the developer G after the development processing carried on the second developing roller 51B is detached from the second developing roller 51B. The separated developer G is collected in the developer collection conveyance path B2, and conveyed along the longitudinal direction, which is the axial direction of the developing roller, by the second conveyance screw 53B.

  Each of the transport screws 53A, 53B, and 53C has a spiral screw portion formed on the shaft portion, and transports the developer G accommodated in the developing device 50 along the shaft portion. The first transport screw 53A is disposed in the developer supply transport path B1, and transports the developer G in the developer supply transport path B1 from the front side to the back side in FIG. 3, which is the longitudinal direction. When being transported by the first transport screw 53A, the developer G in the developer supply transport path B1 is sequentially pumped onto the surface of the first developing roller 51A. Therefore, in the developing device 50 shown in the present embodiment, the amount of the developer G decreases as it goes to the downstream side in the developer transport direction of the developer supply transport path B1.

  The second conveyance screw 53B is disposed inside the developer recovery conveyance path B2, and is positioned below the first conveyance screw 53A in the vertical direction. The developed developer G separated from the second developing roller 51B and collected in the developer collection conveyance path B2 is conveyed from the near side to the back side in FIG. 3 in the developer collection conveyance path B2. The transport screws 53A and 53B are arranged so that their shaft portions are substantially parallel to the rotation shafts of the developing rollers 51A and 51B.

The third transport screw 53C is disposed inside the developer agitation transport path B3, and includes a downstream part in the developer transport direction of the developer recovery transport path B2 and an upstream part in the developer transport direction of the developer supply transport path B1. In order to tie them linearly, as shown in FIG. The third transport screw 53C transports the developer G that has been transported in the developer recovery transport path B2 by the second transport screw 53B to the upstream side in the developer transport direction of the developer supply transport path B1.
The third transport screw 53C is also transported to the downstream end portion in the developer transport direction of the developer supply transport path B1 by the first transport screw 53A, and the developer G that has passed through the drop path B4 is also the developer supply transport path B1. The developer is transported upstream in the developer transport direction.

FIG. 7 is a schematic view of the developer G transport path as viewed from the left side of FIG. Note that the conveyance direction of the developer G is indicated by a white arrow in each region.
As shown in FIG. 7, the downstream side of the developer recovery conveyance path B2 in the developer conveyance direction and the upstream side of the developer agitation conveyance path B3 in the developer conveyance direction communicate with each other via the first relay portion B5. Yes. Further, the downstream side in the developer transport direction of the developer agitation transport path B3 and the upstream side in the developer transport direction of the developer supply transport path B1 communicate with each other via the second relay portion B6. Note that the downstream side in the developer conveyance direction of the developer supply conveyance path B1 and the upstream side in the developer conveyance direction of the developer agitation conveyance path B3 communicate with each other via the drop path B4 as described above.

With the above-described configuration, the developer G circulates in the developing device 50 by moving the developer G in the developer transport paths B1, B2, and B3 by the transport force of the transport screws 53A, 53B, and 53C.
In this embodiment, the linear velocity on the outer peripheral surface of each of the developing rollers 51A and 51B is 1136 mm / sec, and the process linear velocity (the linear velocity on the outer peripheral surface of the photosensitive drum 21 and the conveyance speed of the recording medium P) is It is set to about 738 mm / sec.
A magnetic sensor 26 functioning as a toner concentration sensor is disposed inside the developer stirring and conveying path B3, and a predetermined amount of toner is supplied from the agent cartridge 28 to the developing device 50 based on information from the magnetic sensor 26. Is done. The replenishment toner is replenished from a portion indicated by a symbol T which is the left end in FIG. 7 of the developer stirring and conveying path B3, and in this embodiment, the toner concentration of the developer G in the developing device 50 is 4 to 7% by weight. Controlled.

Next, a two-component developer that is preferably used in the present embodiment will be described.
As the magnetic carrier C of the developer G, for example, a magnetic resin carrier in which ferrite, magnetite, or iron powder containing iron oxide as a main component and coated with a resin using iron powder as a core material can be used. Examples of the magnetic carrier coating material (coating material) include amino resins such as urea-formaldehyde resin, melamine resin, benzoguanamine resin, urea resin, and polyamide resin.
Polyvinyl and polyvinylidene resins such as acrylic resins, polymethyl methacrylate resins, polyacrylonitrile resins, polyvinyl acetate resins, polyvinyl alcohol resins, polyvinyl butyral resins, polystyrene resins and styrene acrylic copolymer resins, Halogenated olefin resins such as vinyl chloride, polyester resins such as polyethylene terephthalate resin and polybutylene terephthalate resin, polycarbonate resins, polyethylene resin, polyvinyl fluoride resin, polyvinylidene fluoride resin, polytrifluoroethylene resin, polyhexa Fluoropropylene resin, copolymer of vinylidene fluoride and acrylic monomer, copolymer of vinylidene fluoride and vinyl fluoride, tetrafluoroethylene and fluoride Fluoro terpolymer of terpolymers, etc. of vinylidene and a non-fluorinated monomer, and silicone resins.
The magnetic carrier used in this embodiment is coated with an amino resin.

The volume resistivity of the magnetic carrier C is a fluororesin containing electrodes 82a and 82b having a distance between electrodes of 2 mm and a surface area of 2 × 4 cm, as shown in FIG. 8 which is a schematic perspective view of a volume resistivity measurement device of the magnetic carrier C. Measurement is performed using a cell 81 made of a container. A magnetic carrier 83 is filled between the electrodes 82a and 82b, and a tapping operation is performed for 1 minute at a tapping speed of 30 times / min using a tapping machine PTM-1 manufactured by Sankyo Piotech.
A DC voltage of 1000 V is applied between the electrodes 82a and 82b, and the DC resistance is measured by a high resistance meter 4329A (4329 + LJK5HVLVWDQFH 0HWHU Yokogawa Hewlett-Packard Co., Ltd.) to determine the electrical resistivity RΩ · cm, and the Log R is calculated. In this embodiment, a magnetic carrier of 15 LogΩ · cm was used.

The weight average particle diameter of the magnetic carrier C is preferably 20 to 65 μm, more preferably 20 to 50 μm. When the weight average particle size is less than 20 μm, carrier adhesion to the photoreceptor may occur due to the decrease in the uniformity of the core material. When the weight average particle size exceeds 65 μm, the image details are reproduced. In some cases, the quality deteriorates and a fine image cannot be obtained.
Here, as the measurement of the weight average particle diameter, any instrument capable of measuring the particle size distribution can be measured without particular limitation, and can be appropriately selected according to the purpose. As an example, a Microtrac particle size distribution meter (model HRA9320-X100) can be used.
The weight average particle size of the magnetic carrier C used in this embodiment was set to 35 μm.

The toner T of the developer G is not limited as long as it is a toner used as a two-component developer, and toners including a binder resin, a colorant, a release agent, a charge adjusting agent, an external additive, etc. can also be used. It is.
In this embodiment, a toner manufactured by a pulverization method is used. However, a known method such as a polymerization method can also be used as a toner manufacturing method, and the present invention is not limited to the pulverization method. Absent.
In this embodiment, toner T having a particle size of about 5.3 μm is used.

Next, the developing rollers 51A and 51B will be described with reference to FIG.
In general, the developer slips and stays on the surface of the developing sleeve that rotates at a high speed, and the followability of the developer to the developing sleeve deteriorates, resulting in a problem that the image density is lowered. In order to solve this problem, a configuration in which the developer follow-up property is maintained by roughening the surface of the developing sleeve can be considered.

As a method for roughening the surface of the developing sleeve, a method for roughening the base tube of the developing sleeve by processing such as sand blasting or bead blasting, a small concave portion that exhibits a circular or elliptical shape in a V-groove shape or a plan view. , A method in which a large number is regularly provided at intervals so as not to overlap with each other (a number of intervals may be irregularly provided or may be an interval at which they overlap each other), and a metal material is sprayed on the element tube And the like.
Although it is possible to prevent a decrease in the developer conveyance amount due to changes over time by these surface treatments, the configuration to be taken differs depending on the target life of the developing sleeve.

The developing sleeve is generally configured such that the raw tube is made of aluminum and blasted or a groove shape is formed to roughen the surface, but this may be selected from the viewpoint of the cost and workability of the raw tube. Many. The good workability means that the developing sleeve is easily worn by a carrier of Hv = 180, which is iron powder having a hardness higher than that of aluminum having a Vickers hardness of Hv = 100 or less.
In order to cope with high-speed and large-volume image formation, it is essential to increase the image stability by extending the life of the developing sleeve. For this purpose, stainless steel having a hardness higher than that of the carrier (Hv = 200 or so in SUS304) or the like is selected as the raw tube. However, the high hardness has the problem of poor cutting workability and high production costs. Therefore, in the present embodiment, the surface is roughened by spraying stainless steel onto stainless steel.

The surface of the developing sleeve is roughened by first preparing a hollow tube made of SUS304 with an outer diameter of 30 mm, a wall thickness of 1 mm, and a length of 490 mm as stainless steel for the base tube, and blasting the outer surface of the hollow tube. The surface roughness is Rz 6 μm. Thereafter, a material harder than the carrier is arc sprayed to form irregularities on the surface of the developing sleeve.
At the time of thermal spraying, stainless steel has a smaller coefficient of thermal expansion than aluminum, so that thermal deformation due to temperature rise of the raw tube is small, and since mechanical strength is high, deformation due to impact force during thermal spraying is small. Therefore, by making the base tube stainless, deterioration of the outer diameter fluctuation accuracy of the developing sleeve is suppressed as compared with the case of aluminum, and periodic fluctuations in image density are suppressed.

As the thermal spraying material, various metals such as aluminum and titanium can be selected. However, in the case of a material having a hardness lower than that of the magnetic carrier C such as aluminum, the roughened shape has a high speed and a large amount of image due to wear by the magnetic carrier C. Long-term life corresponding to formation cannot be maintained. Titanium is a high-hardness material and can achieve a lifetime, but production costs are increased. In addition, if the raw tube of the developing sleeve is different from the thermal spray material, there is a problem in that the thermal spray material is easily peeled off during long-term use because of low fusion between the raw tube and the thermal spray material.
Therefore, in the present embodiment, the surface of the developing sleeves 51A1 and 51B1 is made uneven by arc spraying a wire of SUS304, which is the same material as the base tube. Since the base tube and the thermal spray material are the same material, the fusion between the two is high, and the thermal spray material is difficult to peel off even during long-term use, and the durability can be improved. If the base tube and the thermal spray material are made of the same material, a configuration in which both the base tube and the thermal spray material are titanium may be adopted. In this case, the same long life as when stainless steel is used can be expected, but the production cost is greatly increased.

  As described above, the surface of the developing sleeves 51A1 and 51B1 is harder than the magnetic carrier C and is made of the same material as the base tube by thermal spraying to form irregularities, thereby forming the magnetic carrier C in high-speed and large-volume image formation. It is possible to prevent the unevenness of the surface of the developing sleeves 51A1 and 51B1 from being worn for a long time. As a result, the developing rollers 51A and 51B can pump up the developer stably for a long period of time, thereby preventing a decrease in the amount of developer drawn up over time.

  Each of the developing rollers 51A and 51B in the present embodiment uses a stainless steel hollow tube that is surface-treated by arc spraying stainless steel. Then, the ten-point average roughness Rz and the unevenness average interval Sm on the surfaces of the developing rollers 51A and 51B, that is, the surfaces of the developing sleeves 51A1 and 51B1, were measured. A measuring method will not be specifically limited if it is a measuring method based on JISB0601-1994. In this embodiment, the measurement was performed using FORMRACER SV-C500 manufactured by Mitutoyo Corporation.

FIG. 9 is a schematic diagram showing the depth and width of the grooves in the irregularities formed on the outer peripheral surfaces of the developing rollers 51A and 51B, and the magnetic carrier C and the toner T. Based on FIG. 9, the relationship between the particle size of the magnetic carrier C and the groove depth and groove width of the developing rollers 51A and 51B, which is a feature of the present invention, will be described.
First, the groove depth of the developing rollers 51A and 51B will be described. The depth of the grooves of the developing rollers 51A and 51B is such that the magnetic carrier C enters the groove to some extent so that the sleeve can easily convey the magnetic carrier C (developer G), stabilize the pumping amount, and the toner adhering to the grooves There is a function of collecting T with the magnetic carrier C (see FIG. 9A). Therefore, the relationship between the ten-point average roughness Rz corresponding to the groove depth and the carrier particle size D is important.

FIG. 10 shows the relationship between the ten-point average roughness Rz and the sleeve fixing rank when forming an image of 5 million sheets. The target of the sleeve fixing rank, that is, the sleeve fixing level that has no influence on the market is rank 3.5 or higher, and the particle size of the magnetic carrier C used for the evaluation is 35 μm.
As can be seen from FIG. 10, since the ten-point average roughness Rz is about 50 μm, which is about 1.4 times the carrier particle diameter D, the sleeve fixing tends to be improved and is 1.5 times or more larger. When the thickness is 55 μm, the magnetic carrier C sufficiently enters the groove, stabilizes the transport of the developer G, collects the toner T adhering to the groove, and suppresses the sleeve fixing rank to the target level. Therefore, in order to prevent occurrence of sticking of the sleeve, a relationship of 1.5D <Rz is necessary. In addition, the uneven | corrugated average space | interval Sm at this time was 220 micrometers.

Next, the groove width of the developing rollers 51A and 51B will be described.
When the groove width is narrow as shown in FIG. 9B, the toner T adhering to the inside of the groove cannot be collected by the magnetic carrier C, but the groove width as shown in FIG. 9A. Is wide, the toner T adhering to the inside of the groove can be collected by the magnetic carrier C in contact therewith, so that no toner adheres to the groove.
Since the fixing of the sleeve is caused by the toner T adhering to the groove, it is only necessary that the magnetic carrier C enters the groove and collects the adhering toner T. That is, the relationship between the groove width and depth is important. If the average unevenness interval Sm corresponding to the width of the groove is smaller than the carrier particle size D, the magnetic carrier C cannot enter the groove, so that the toner T adhering to the inside of the groove can be collected by the magnetic carrier C. The sleeve will stick. The uneven average interval Sm is required to be larger than the carrier particle diameter D. However, in order to effectively collect the toner T adhering to the groove, the relationship between the uneven average interval Sm and the ten-point average roughness Rz is also included. Necessary.

FIG. 11 shows the relationship between the unevenness average interval Sm and the sleeve fixing rank when forming 5 million images. The target of sleeve fixing, that is, the level of sleeve fixing that does not affect the market is rank 3.5 or higher, and the particle size of the magnetic carrier C used for the evaluation is 35 μm.
As can be seen from FIG. 11, when the uneven average interval Sm exceeds 200 μm, the sleeve fixing tends to be improved, and when the uneven average interval Sm is 220 μm or more, the sleeve fixing can be suppressed to the target level. At this time, the ten-point average roughness Rz was 55 μm. Therefore, in order to prevent the occurrence of sleeve sticking, the unevenness average interval Sm is required to be at least four times the ten-point average roughness Rz, that is, 4 · Rz <Sm.
From the above results, the following relational expression is established among the carrier particle diameter D, the ten-point average roughness Rz, and the uneven average interval Sm.
1.5D <Rz <1/4 · Sm Formula 1

In this embodiment, the measurement direction of the ten-point average roughness Rz and the uneven average interval Sm is the developing roller axial direction.
The relationship between the carrier particle diameter D, the ten-point average roughness Rz, and the uneven average interval Sm needs to be satisfied in either the developing roller axial direction or the developing roller rotating direction, and the other (the developing roller rotating direction in this embodiment). The minimum condition is that the groove depth and the groove interval are larger than the carrier particle diameter D. Of course, the carrier particle diameter D, the ten-point average roughness Rz, and the unevenness average interval Sm may be satisfied in both the developing roller axial direction and the developing roller rotation direction.

In the first embodiment of the present invention, both the first developing roller 51A and the second developing roller 51B adopt the same surface texture configuration, and the ten-point average roughness Rz1 = Rz2 = 70 μm with respect to the carrier particle size D = 35 μm. The average unevenness interval Sm1 = Sm2 = 300 μm (see the upper part of Table 1).
In the first embodiment, the carrier particle diameter D = 35 μm to 1.5D = 52.5 μm, and the unevenness average interval Sm = 300 μm, so that 1/4 Sm1 = 1/4 Sm2 = 75 μm. That is, 1.5D = 52.5 <Rz1 = 70 <1 / 4Sm1 = 75, 1.5D = 52.5 <Rz2 = 70 <1 / 4Sm2 = 75, and the first developing roller 51A and the second developing roller 51B. It was revealed that both of the configurations satisfied Formula 1 (see the lower part of Table 1).

As a result, since the configuration satisfies Expression 1, it is possible to suppress the occurrence of sticking of the sleeve and the reduction of the pumping amount, thereby preventing the occurrence of abnormal images such as a decrease in image density and the occurrence of toner scattering. Can be prevented.
According to the present invention from the above-described configuration, the surface is roughened by forming grooves on the surfaces of the developing rollers 51A and 51B, and the grooves are formed by making the depth and width of the grooves larger than the carrier particle diameter D. The adhering toner T can be collected by the magnetic carrier C, and since the groove depth is sufficiently deep, the developer G can be sufficiently transported, so that the fixing rollers 51A and 51B can adhere to the toner for a long period of time. In addition to being able to improve, it is possible to prevent a decrease in the pumping amount, thereby preventing the occurrence of abnormal images such as a decrease in image density and the occurrence of toner scattering.

Next, a second embodiment of the present invention will be described. In the second embodiment, the first developing roller 51A and the second developing roller 51B have different surface properties, and the first developing roller 51A has a ten-point average roughness Rz1 = as in the first embodiment. 70 μm and uneven average interval Sm1 = 300 μm, the second developing roller 51B is configured to be smaller than the first developing roller 51A by both the ten-point average roughness Rz and the uneven average interval Sm, and the ten-point average roughness Rz2 = 55 μm, the uneven average interval. Sm2 = 240 μm (see the upper part of Table 2).
From the carrier particle diameter D = 35 μm, the first developing roller 51A satisfies the formula 1, as 1.5D = 52.5 <Rz1 = 70 <1 / 4Sm1 = 75, as in the first embodiment. The second developing roller 51B has a carrier particle size D = 35 μm to 1.5D = 52.5 and Sm2 = 240 μm to ¼ Sm2 = 60 μm. Therefore, 1.5D = 52.5 <Rz2 = 55 <1 / 4Sm2 = 60, and it is clear that the configuration satisfies Expression 1 (see the lower part of Table 2).

  As a result, the occurrence of sticking of the sleeve can be suppressed and the reduction of the pumping amount can be suppressed, so that it is possible to prevent the occurrence of abnormal images such as a decrease in image density and the occurrence of toner scattering. Furthermore, since the surface property of the second developing roller 51B is smaller than that of the first developing roller 51A, image quality such as dot reproducibility can be improved.

Next, a third embodiment of the present invention will be described. This third embodiment is different from the first embodiment only in that the surface of each developing roller 51A, 51B is coated with a low friction resistance layer, and the other configurations are the same.
As shown in FIG. 5, low friction resistance layers 51A3 and 51B3 are coated on the surfaces of the developing rollers 51A and 51B. Since this coating has the effect of reducing the toner T adhering to the developing sleeves 51A1 and 51B1, it prevents the formation of density unevenness images and contributes to the suppression of the occurrence of sleeve sticking from the viewpoint of long-term use.
Further, since the surfaces of the developing sleeves 51A1 and 51B1 are protected by the low friction resistance layers 51A3 and 51B3, there is also an effect of suppressing the uneven wear on the surfaces of the developing sleeves 51A1 and 51B1 by the magnetic carrier C, and the developing roller 51A , 51B is a configuration suitable for the purpose of further extending the service life.

  The low friction resistance layers 51A3 and 51B3 are made of a material having a lower friction coefficient than the base material of the developing sleeves 51A1 and 51B1, such as tetrahedral amorphous carbon (ta-C) and titanium nitride (TiN). Stratify. As the low friction resistance layers 51A3 and 51B3, any material may be used as long as it is not contrary to the object of the present invention as long as it is a material having a lower friction coefficient than the base material of the developing sleeves 51A1 and 51B1. Materials other than ta-C and TiN, such as titanium (TiC), titanium carbonitride (TiCN), and molybdic acid may be used. In addition, the friction coefficient in each material is stainless steel, aluminum alloy: 0.5 or more, TiN: 0.3-0.4, ta-C: 0.1 or less grade.

Further, since the toner attached to the developing sleeve facing the non-image portion of the photosensitive member has a charge, when the attached toner is fixed, the developing potential is raised by the amount of the charge of the toner on the developing sleeve when the image is formed, Density unevenness that occurs when the toner development amount increases, that is, a so-called ghost image occurs.
In this embodiment, by forming low friction resistance layers 51A3 and 51B3 having a lower coefficient of friction than the base material on the surface of the developing sleeves 51A1 and 51B1, the toner T adhering to the developing sleeves 51A1 and 51B1 is reduced, and a ghost image is obtained. Can be suppressed, and the occurrence of sticking of the sleeve can also be prevented.
Further, the developing sleeves 51A1 and 51B1 can be made to have higher hardness by coating the low friction resistance layers 51A3 and 51B3. That is, since it is possible to suppress the uneven wear formed on the surfaces of the developing rollers 51A and 51B by the magnetic carrier C, it is also possible to suppress a decrease in the pumping amount due to the uneven wear on the sleeve surface.

Next, a method for measuring the surface frictional resistance of the developing rollers 51A and 51B will be described.
FIG. 12 is a schematic configuration diagram of the static friction coefficient measuring device 70. The surface friction resistance of the developing rollers 51A and 51B described above is measured by obtaining the maximum static friction coefficient μ by the Euler belt method. As shown in the drawing, a medium-quality high-quality paper 71a is used as a belt, and a thread 71b is attached to both ends thereof to form a measurement paper piece 71. The produced measurement paper piece 71 is stretched around the circumference ¼ of the developing roller 72, and a weight 73 of, for example, 0.98 N (100 g) is attached to one thread 71b. Then, the measurement paper piece 71 is pulled by the digital push-pull gauge 74 from the end of the other thread 71b, and the value (load) of the digital push-pull gauge 74 when the measurement paper piece 71 starts to move is read. When this load is F (N), the maximum static friction coefficient μ is obtained by μ = ln (F / 0.98) / (π / 2).

The maximum static friction coefficient μ of the developing roller covered with the fluororesin as described above was measured by this static friction coefficient measuring method and found to be 0.4 or less. In the present embodiment, the low friction resistance layers 51A3 and 51B3 are ta-C films formed on the surfaces of the developing sleeves 51A1 and 51B1 by a filtered cathode vacuum arc method (FCVA) that is widely used. It is formed with.
The outline of the film formation of the ta-C film by the FCVA method will be described. High purity carbon (graphite) is placed as a target in a substantially vacuum chamber, and arc discharge is performed on the target. Then, the plasma generated by the arc discharge is guided to the base material of the developing sleeve which is a deposition target by electromagnetic induction. In this induction process, macro particles, neutral atoms, neutral molecules, etc. that are unnecessary for vapor deposition are removed by an electromagnetic spatial filter, and only ionized carbon is extracted. And the ionized carbon which reached | attained the base material aggregates on the base-material surface, and forms a ta-C film | membrane. As a result, a low frictional resistance layer made of a ta-C film is formed on the surface of the developing sleeve.
Such a low frictional resistance layer made of a ta-C film can be formed with a uniform thickness as compared with a film formed by plating or coating, and can be formed at a relatively low temperature. Strain due to sleeve temperature is less likely to occur. Therefore, the shape accuracy of the developing sleeve can be increased.

The low friction resistance layers 51A3 and 51B3 may be formed of TiN films formed on the surfaces of the developing sleeves 51A1 and 51B1 by a hollow cathode method (HCD) widely used in place of the FCVA method. Good. According to the ion plating method which is one of the physical vapor deposition (PVD) methods, a film having excellent adhesion can be obtained relatively easily. Among the ion plating methods, the HCD method is used to achieve a uniform and film thickness. Can be obtained, and a film can be obtained along the surface roughness of the developing rollers 51A and 51B (the shape after thermal spraying on the hollow tube).
In this embodiment, ta-C is coated as the low friction resistance layers 51A3 and 51B3, and the ten-point average roughness Rz and the unevenness average interval Sm, which are the surface properties of the developing rollers 51A and 51B after coating, are the same as in the first embodiment. (See the upper part of Table 3). The carrier particle diameter D = 35 μm to 1.5D = 52.5 μm, and the concave / convex average interval Sm = 300 μm to 1/4 Sm1 = 1/4 Sm2 = 75 μm. Therefore, 1.5D = 52.5 <Rz1 = 70 <1 / 4Sm1 = 75, 1.5D = 52.5 <Rz2 = 70 <1 / 4Sm2 = 75, and the first developing roller 51A and the second developing roller 51B. It was clarified that the two satisfy the formula 1 (see the lower part of Table 3).
As a result, the occurrence of sticking of the sleeve can be suppressed and the decrease in the pumping amount can be suppressed, so that it is possible to prevent the occurrence of abnormal images such as a decrease in image density and the occurrence of toner scattering.

FIG. 13 is obtained by adding data (■ plot) of the developing rollers 51A and 51B having the ta-C coat to the graph showing the relationship between the ten-point average roughness Rz and the sleeve fixing shown in FIG. FIG. 14 is obtained by adding data (■ plots) of the developing rollers 51A and 51B having the ta-C coat to the graph showing the relationship between the average unevenness interval Sm and the sleeve fixing shown in FIG.
In either case, the sleeve fixing rank is improved by about 1 by performing the ta-C coating. In other words, it becomes clear that the coating of the low friction resistance layers 51A3 and 51B3 can suppress the adhesion of the toner T to the developing sleeves 51A1 and 51B1, and suppress the uneven wear of the developing sleeves 51A1 and 51B1. The life of the developing rollers 51A and 51B can be further extended.

The surface properties of the developing rollers 51A and 51B can be different in the developing rollers 51A and 51B as in the second embodiment. Also in this case, if each of the developing rollers 51A and 51B satisfies the formula 1, an effect of suppressing the occurrence of sleeve sticking can be obtained.
Further, since the first developing roller 51A facing the rubbing member such as the developer regulating member 52 is more likely to stick to the sleeve than the second developing roller 51B, only the first developing roller 51A has a low friction. Even when the resistance layers 51 </ b> A <b> 3 and 51 </ b> B <b> 3 are formed, it is possible to suppress the occurrence of sleeve fixing as long as the structure satisfies Expression 1.

Next, a modified example of the first to third embodiments described above will be described with reference to FIG. The developing device 50A shown in this modification is different from the developing device 50 shown in each of the above-described embodiments only in that it has a developer discharge port 57, and the other configurations are the same. .
In FIG. 15, a developer for discharging a part of the developer G accommodated in the developing device 50 </ b> A to a developer reservoir (not shown) provided outside is provided on the wall of the developer supply transport path B <b> 1. A discharge port 57 is provided. The developer discharge port 57 is supplied with the developer G from the agent cartridge 28 into the developing device 50 </ b> A so that the amount of the developer in the developing device 50 </ b> A increases and is conveyed to a position corresponding to the developer discharge port 57. When the upper surface exceeds the predetermined height, the excess developer G, which is the amount exceeding the predetermined height, is discharged toward a developer storage section (not shown). Excess developer G exceeds the opening height of the developer discharge port 57 and is discharged from the developer discharge port 57 and is conveyed toward the developer storage portion via the discharge path 58.
In this case, by using a replenished toner in which magnetic carrier C and toner T are mixed in advance, a decrease in the developer amount due to discharge can be prevented, and developer G containing deteriorated toner T is automatically developed. It is discharged outside the device 50A. Thereby, the occurrence of sticking of the sleeve can be suppressed over time, and further the deterioration of image quality can be suppressed.

  Next, a comparative example of the present invention will be described. In this comparative example, with respect to the carrier particle size D = 35 μm, the surface properties of the developing rollers 51A and 51B were set to 10-point average roughness Rz1 = Rz2 = 35 μm and uneven average spacing Sm1 = Sm2 = 150 μm (Table 4). (See the top row). The difference between the present comparative example and the first embodiment is only the surface property, and the carrier particle diameter D = 35 μm to 1.5D = 52.5 μm, and the unevenness average interval Sm1 = Sm2 = 150 μm to 1/4 Sm1 = 1 / 4Sm2 = 37.5 μm. Therefore, 1.5D = 52.5> Rz1, Rz2 = 35 <1 / 4Sm1, 1 / 4Sm2 = 37.5, which is a configuration that does not satisfy Formula 1 (see the lower part of Table 4).

  Based on the first to third embodiments and the comparative example described above, a confirmation test was performed under the following conditions. The evaluation machine used RICOH PRO 8100S, and formed 5 million images on an A4 size recording medium with an image area ratio of 5%. Evaluation items are: image density (ID of whole solid image: measured by X-Rite 939), toner fixing of developing sleeve (rank evaluation: 5-level evaluation, 1 (bad fixing state) to 5 (no fixing)), Toner scattering (visual confirmation). The results are shown in Table 5.

In comprehensive judgment, (circle) has shown the pass and x has shown failure. As apparent from Table 5, in each of the first to third embodiments, there was no problem in all items, and the overall judgment was acceptable. In particular, in the third embodiment, the results show that the durability of the developing rollers 51A and 51B is increased by providing the low friction resistance layers 51A3 and 51B3.
On the other hand, in the comparative example, various problems such as a decrease in image density, occurrence of toner sticking to the developing roller, and occurrence of toner scattering occurred, and all the items could not satisfy the judgment criteria and failed in the comprehensive judgment. It was.

16 shows the relationship between the number of images formed by the first developing roller 51A and the sleeve fixing rank in the above-described confirmation test, and FIG. 17 shows the relationship between the number of images formed by the second developing roller 51B and the sleeve fixing rank. .
In the comparative example, the target rank 3.5 of the sleeve fixing is lower than the image formation number of 2 million sheets, but in each of the first to third embodiments, the target rank 3.5 is set up to 5 million image formation numbers. It can be seen that it is maintained. From the above confirmation test, the effect of the present invention could be confirmed.

  In each of the above-described embodiments, the recording medium P is shown as an image to be formed. However, the recording medium S is not limited to recording paper, and is cardboard, postcard, envelope, plain paper, thin paper, coated paper. (Coated paper, art paper, etc.), tracing paper, etc. are also included. As the recording medium other than paper, any material may be used as long as it is a sheet-like material capable of forming an image, such as an OHP sheet, an OHP film, or a resin film.

The printer 10 using the process cartridge 20 has been described above as an example. However, the present invention is not limited to this, and the process cartridge 20 includes the photosensitive drum 21, the developing device 50, and the like as separate units. It is also possible to adopt a configuration. The configuration of the image forming apparatus is also arbitrary, and the arrangement order of the color image forming units in the tandem method is arbitrary. Further, the present invention is not limited to a 4-color machine, and can be applied to a 3-color machine, a full-color machine using five or more color toners, a multi-color machine using two-color toner, or a monochrome machine.
The image forming apparatus is not limited to a printer, and may be a copier, a facsimile machine, a plotter, or a complex machine such as these.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to such specific embodiments, and unless specifically limited by the above description, the present invention described in the claims is not limited. Various modifications and changes are possible within the scope of the gist. The effects described in the embodiments of the present invention are merely examples of the most preferable effects resulting from the present invention, and the effects of the present invention are limited to those described in the embodiments of the present invention. is not.

10 Image forming device (printer)
20 Process cartridge 21 Image carrier (photosensitive drum)
22 Charging device 25 Cleaning device 50 Developing device 51A First developer carrier (first developing roller)
51B Second developer carrier (second developing roller)
51A3, 51B3 Low friction resistance layer 52 Developer regulating member 52A Non-magnetic member (doctor blade)
52B Magnetic member (magnetic material)
57 Developer outlet G Two-component developer

Japanese Patent No. 4732536

Claims (12)

A first developer carrying member carrying a two-component developer containing a carrier on its surface and conveying the two-component developer carried on a first development region facing the surface of the image carrier;
At least a part of the developer carried by the first developer carrying member after passing through the first developing region is received on the surface and carried on the second developing region facing the surface of the image carrier. A second developer carrier for conveying a two-component developer,
Each of the developer carriers has a surface roughened by a groove, and each of the grooves formed in each developer carrier has a depth larger than the particle diameter of the carrier. And the width of each of the grooves formed in the first developer carrier is greater than the depth of the groove formed in the second developer carrier. The developing device. The developing device according to claim 1,
Each of the developer carriers has a low friction resistance layer on the surface thereof. The developing device according to claim 2, wherein
The developing device according to claim 1, wherein the low frictional resistance layer is provided at least on the first developer carrier. The developing device according to any one of claims 1 to 3,
A developing device comprising a non-magnetic member and a magnetic member, and having a developer regulating member disposed opposite to the first developer carrying member. The developing device according to claim 4.
The developing device according to claim 1, wherein the magnetic member protrudes more toward the surface of the first developer carrier than the nonmagnetic member. The developing device according to any one of claims 1 to 5,
A developing device having a developer discharge port. The developing device according to any one of claims 1 to 6,
The developing device according to claim 1, wherein each of the grooves is formed by thermal spraying. The developing device according to claim 7.
The developing device according to claim 1, wherein the grooves and the base material of the developer carrier are made of the same material. The developing device according to any one of claims 1 to 8,
The developing device according to claim 1, wherein the developer carrying members are arranged in the vertical direction.   The developing device according to claim 1 and at least one of the image carrier, the charging device, and the cleaning device are integrally formed, and are configured to be detachable from the image forming apparatus main body. A process cartridge characterized by that.   An image forming apparatus comprising at least one developing device according to claim 1.   An image forming apparatus comprising at least one process cartridge according to claim 10.

Images