JP2009265600A - Developing device, process cartridge, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device, which never causes a void image on an output image by preventing developer supported on a developer carrier and regulated by a developer regulating member from partially staying in a case member or the like, a process cartridge and an image forming apparatus. <P>SOLUTION: The device includes a case member 23r which covers above a developer carrying member 23b1 while holding a developer regulating member 23c. The case member 23r is formed in such a manner that an opposed surface 23r1 opposed to the developer carrying member 23b1 is formed circularly to a predetermined position continuously to an opposed surface 23c1 of the developer regulating member 23c opposed to the developer carrying member 23b1, and the angle θ formed by the opposed surface 23c1 of the developer regulating member 23c opposed to the developer carrying member 23b1 and the opposed surface 23r1 of the case member 23r opposed to the developer carrying member 23b1 is an obtuse angle. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using an electrophotographic system such as a copying machine, a printer, a facsimile, or a complex machine thereof, and a developing device and a process cartridge installed therein, and particularly includes a toner and a carrier. The present invention relates to a developing device, a process cartridge, and an image forming apparatus using a two-component developer.

  2. Description of the Related Art Conventionally, a developing device that performs a developing process using a two-component developer (including an additive and the like) composed of a toner and a carrier in an image forming apparatus such as a copying machine or a printer is known. (For example, see Patent Document 1 and Patent Document 2).

  In a developing device using a two-component developer, toner is appropriately replenished into the developing device from a toner replenishing port provided in a part of the developing device according to toner consumption in the developing device. The replenished toner is agitated and mixed together with the developer in the developing device by a developer conveying member such as a conveying screw (screw auger). Part of the stirred and mixed developer is supplied to the developing roller (developer carrier) by the developer conveying member. The developer carried on the developing roller is regulated to an appropriate amount by a doctor blade (developer regulating member), and then the toner in the two-component developer is located at a position facing the photoreceptor drum (image carrier). A toner image is formed on the latent image on the drum.

JP 2001-249545 A JP 2005-148413 A

  In the conventional developing device described above, a part of the developer carried on the developing roller and regulated by the doctor blade covers the upper side of the developer conveying member without returning to the conveying path by the developer conveying member. The case member (upper case) sometimes accumulated in part. Then, the developer accumulated in a part of the case member is gradually compressed and then dropped onto the developing roller, is again carried on the developing roller and adheres to the photosensitive drum, so that the firefly is displayed on the output image. In some cases, an image (a phenomenon in which, in the image portion, a toner nucleus is generated in the center portion and the periphery thereof is whitened) is generated.

  The present invention has been made to solve the above-described problems, and a part of the developer that is carried on the developer carrying member and regulated by the developer regulating member is accumulated in the case member or the like. It is another object of the present invention to provide a developing device, a process cartridge, and an image forming apparatus in which a firefly image does not occur on an output image.

The inventor of the present application has come to know the following matters as a result of repeated studies to solve the above-mentioned problems.
That is, the developer carried on the developer carrying member and regulated by the developer regulating member is the opposite surface of the developer regulating member facing the developer carrying member or the case member facing the developer carrying member. The fluid flows along the opposite surface of the toner and is returned to the transport path by the developer transport member. Therefore, the shape from the facing surface of the developer regulating member facing the developer transporting member to the facing surface of the case member facing the developer transporting member (from the tip of the developer regulating member to the predetermined position of the case member) If the shape of the facing surface facing the conveying member is not gentle and uneven, the portion becomes a dead space and the developer tends to stay.

  The present invention is based on the matters described above. That is, the developing device according to the first aspect of the present invention accommodates the developer and develops the latent image formed on the image carrier. A developing device that faces the image carrier and carries a developer, and an amount of developer that bears on the developer carrier while facing the developer carrier A developer regulating member that regulates the developer, a developer conveying member that faces the developer carrying member, supplies the developer to the developer carrying member while carrying the developer, and holds the developer regulating member. And a case member that covers an upper portion of the developer conveying member, and the case member faces the developer conveying member subsequent to the facing surface of the developer regulating member facing the developer conveying member. Opposite surface The angle formed between the facing surface of the developer regulating member facing the developer transport member and the facing surface of the case member facing the developer transport member is an obtuse angle. It is formed.

  According to a second aspect of the present invention, there is provided the developing device according to the first aspect, wherein the predetermined position of the case member is a position beyond the uppermost portion of the developer conveying member. .

  According to a third aspect of the present invention, in the developing device according to the first or second aspect, the case member has a cooling fin on its outer surface.

  A developing device according to a fourth aspect of the present invention is the developing device according to any one of the first to third aspects, wherein the developer conveying member is configured to convey the developer in a longitudinal direction. The curvature of the arcuate facing surface of the case member facing the developer transport member is smaller on the downstream side in the transport direction of the developer transport member than on the upstream side in the transport direction of the developer transport member. It is formed.

  A developing device according to a fifth aspect of the present invention is the developing device according to any one of the first to fourth aspects, wherein the developer conveying member is configured to convey the developer in a longitudinal direction. And a second developer conveying member disposed below the developer conveying member and facing the developer carrying member and carrying the developer detached from the developer carrying member. Is.

  The developing device according to a sixth aspect of the present invention is the developing device according to any one of the first to fifth aspects, wherein the developer carrying member has a plurality of magnetic poles formed around the developer carrying member. Are formed such that the magnetic flux density in the normal direction of the magnetic pole formed at a position facing the developer regulating member is 80 to 120 mT.

  A process cartridge according to a seventh aspect of the present invention is a process cartridge which is detachably installed on the main body of the image forming apparatus, and is according to any one of the first to sixth aspects. The developing device and the image carrier are integrated.

  An image forming apparatus according to an eighth aspect of the present invention includes the developing device according to any one of the first to sixth aspects and the image carrier.

  In the present application, the “process cartridge” refers to a charging unit that charges the image carrier, a developing unit (developing device) that develops a latent image formed on the image carrier, and a cleaning on the image carrier. At least one of the cleaning units and the image carrier are defined as a unit that is integrated and detachably installed on the image forming apparatus main body.

  Further, in the present application, the “arc shape” is defined as a curved surface formed in a concave shape when viewed from the developer conveying member (or the inside of the developing device) and includes a substantially arc shape.

  The present invention optimizes the shape of the surface facing the developer conveying member from the front end of the developer regulating member to a predetermined position of the case member, so that the developer regulating member is supported on the developer carrying member. It is possible to provide a developing device, a process cartridge, and an image forming apparatus in which a part of the developer after being regulated by the member does not accumulate in the case member or the like and a firefly image is not generated on the output image. .

Embodiment.
Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified or abbreviate | omitted suitably.

First, the configuration and operation of the entire image forming apparatus in the embodiment will be described with reference to FIG.
The writing units 2A to 2D are devices for writing an electrostatic latent image on the photosensitive drum 21 (image carrier) after the charging process based on image information. The writing units 2A to 2D are optical scanning devices using polygon mirrors 3A to 3D, optical elements 4A to 4D, and the like. An LED array can be used as the writing unit instead of the optical scanning device.
The paper feeding 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 for transferring the toner image formed on the photosensitive drum 21 onto the recording medium P by electrostatically attracting and transporting the recording medium P to the surface thereof. An adsorption roller 64 and a belt cleaner 65 are provided on the outer peripheral surface.
The transfer roller 24 that faces the photosensitive drum 21 via the transfer belt 30 includes a cored bar and a conductive elastic layer that covers the cored bar. The conductive elastic layer of the transfer roller 24 is prepared by blending and dispersing a conductive agent such as carbon black, zinc oxide or tin oxide in an elastic material such as polyurethane rubber or ethylene-propylene-diene polyethylene (EPDM). 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 to the recording medium P by pressure and heat.
The four process cartridges 20Y, 20C, 20M, and 20BK arranged in the vertical direction along the transfer belt 30 are for forming toner images of yellow, cyan, magenta, and black, respectively.

On each of the process cartridges 20Y, 20C, 20M, and 20BK, agent cartridges 28Y, 28C that supply a carrier (magnetic carrier) and toner (toner particles) of each color (yellow, cyan, magenta, black) to the developing device 23, 28M and 28BK are installed.
The process cartridges 20Y, 20C, 20M, and 20BK and the agent cartridges 28Y, 28C, 28M, and 28BK can be attached to and detached from the apparatus main body 1 by opening the transfer belt 30 around the rotation support shaft.

  The image forming apparatus in this embodiment is a composite image forming apparatus that functions as a copying machine and a printer. When functioning as a copying machine, the image information read from the scanner is subjected to various image processing such as A / D conversion, MTF correction, gradation processing, etc., and converted into writing data. In the case of functioning as a printer, image processing is performed on image information in a format such as a page description language or a bitmap transmitted from a computer or the like, and converted into write data.

  At the time of image formation, exposure light corresponding to the image information of black, magenta, cyan, and yellow is irradiated from the writing units 2A to 2D to the process cartridges 20BK, 20M, 20C, and 20Y, respectively. That is, exposure light (laser light) emitted from each light source passes through the polygon mirrors 3 </ b> A to 3 </ b> D, the optical elements 4 </ b> A to 4 </ b> D, and is irradiated onto each photosensitive drum 21. Thus, a toner image corresponding to the exposure light is formed on the photosensitive drum 21 (image carrier) of each process cartridge 20BK, 20M, 20C, 20Y. Then, this toner image is transferred to the recording medium P.

  The recording medium P fed from the paper feeding unit 61 is transported to the position of the transfer belt 30 at the timing of the registration roller 63 and the timing. The suction roller 64 provided at the transfer position of the transfer belt 30 causes the transfer medium 30 to suck the recording medium P that has been transferred by applying a voltage. The recording medium P that moves as the transfer belt 30 travels in the direction of the arrow sequentially passes through the positions of the process cartridges 20Y, 20C, 20M, and 20BK, and the toner images of the respective colors are superimposed and transferred.

  The recording medium P to which the color toner image is transferred is separated from the transfer belt 30 and reaches the fixing unit 66. The toner image on the recording medium P is fixed on the recording medium P by being heated while being sandwiched between the heating roller 68 and the pressure roller 67. On the other hand, the surface of the transfer belt 30 after the recording medium P is separated reaches the position of the belt cleaner 65, and dirt such as toner adhering to the surface is cleaned.

Next, the process cartridge and the agent cartridge in the image forming apparatus will be described in detail.
The process cartridges 20Y, 20C, 20M, and 20BK have substantially the same structure, and the agent cartridges 28Y, 28C, 28M, and 28BK have substantially the same structure. The alphabet (Y, C, M, BK) is removed for illustration. In addition, the writing unit is illustrated by removing the alphabet (A to D).

  FIG. 2 is an enlarged view showing the process cartridge 20 and the agent cartridge 28 installed in the apparatus main body 1. FIG. 3 is an enlarged view showing the developing device 23 installed in the process cartridge 20. 4 is a cross-sectional view of the circulation path in the developing device 23 as viewed from the direction of the arrow X shown in FIG. 3 in the longitudinal direction. FIG. 5 is a cross-sectional view showing a Y1-Y1 cross section of the circulation path in the developing device 23 of FIG. 6 is a cross-sectional view showing a Y2-Y2 cross section of the circulation path in the developing device 23 of FIG.

As shown in FIG. 2, the process cartridge 20 includes a photosensitive drum 21 as an image carrier, a charging unit 22, a developing device 23 (developing unit), and a cleaning unit 25, and is a premix developing unit. System (development system in which carrier is replenished / discharged as appropriate) is adopted.
The photosensitive drum 21 as an image carrier is a negatively charged organic photosensitive member, and is rotationally driven counterclockwise by a rotation driving mechanism (not shown).

The charging unit 22 is a charging roller having elasticity in which a medium-resistance foamed urethane layer in which a urethane resin, carbon black as conductive particles, a sulfurizing agent, a foaming agent, and the like are formed in a roller shape is formed on a cored bar. The material of the middle resistance layer of the charging unit 22 is urethane, ethylene-propylene-diene polyethylene (EPDM), butadiene acrylonitrile rubber (NBR), silicone rubber, isoprene rubber, etc. It is also possible to use a rubber material in which a conductive material such as the above is dispersed or a foamed material of these materials.
The cleaning unit 25 is provided with a cleaning brush (or cleaning blade) that is in sliding contact with the photosensitive drum 21, and mechanically removes and collects untransferred toner on the photosensitive drum 21.

  In the developing device 23, two developing rollers 23a1 and 23a2 as developer carrying members are disposed so as to be close to the photosensitive drum 21, and the photosensitive drum 21 and the magnetic brush are in contact with each other at both opposing portions. A development area is formed. In the developing device 23, a developer G (two-component developer) composed of toner T and carrier C is accommodated. The developing device 23 develops the electrostatic latent image formed on the photosensitive drum 21 (forms a toner image). The configuration and operation of the developing device 23 will be described in detail later.

Here, the developing device 23 in the present embodiment is of a premix developing system, and a new carrier C (developer G) is appropriately supplied from the agent cartridge 28 into the developing device 23 and deteriorated. The developer G thus discharged is discharged toward the agent storage container 70 installed outside the developing device 23.
Referring to FIG. 2, the agent cartridge 28 accommodates developer G (toner T and carrier C) to be supplied into the developing device 23 therein. The agent cartridge 28 functions as a toner cartridge that supplies new toner T to the developing device 23, and also functions as a supply unit that supplies new carrier C to the developing device 23. Specifically, the shutter mechanism 80 is based on the information of the toner density (the ratio of the toner in the developer G) detected by the magnetic sensor 26 (see FIG. 4) installed in the developing device 23. The developer G is appropriately supplied from the agent cartridge 28 into the developing device 23.
In the present embodiment, the mixing ratio (toner concentration) of the toner T with respect to the carrier C in the developer G of the agent cartridge 28 is set to be relatively high.
The supply pipe 29 is for reliably guiding the developer G (toner T and carrier C) supplied from the agent cartridge 28 into the developing device 23. That is, the developer G discharged from the agent cartridge 28 is supplied into the developing device 23 via the supply pipe 29.

Next, an image forming process performed on the photosensitive drum 21 will be described.
Referring to FIG. 2, when the photosensitive drum 21 is driven to rotate counterclockwise, first, the surface of the photosensitive drum 21 is uniformly charged at the position of the charging unit 22. Thereafter, the surface of the charged photosensitive drum 21 reaches the irradiation position of the exposure light L, and an exposure process by the writing unit 2 is performed. That is, by selectively removing the charge on the photosensitive drum 21 in accordance with the image information by irradiation with the exposure light L, a difference (potential contrast) from the potential of the non-image portion that has not been irradiated is generated, and electrostatic latent Form an image. In this exposure step, the charge generation material receives light in the photosensitive layer of the photosensitive drum 21 to generate charges, and among these holes, the holes cancel out the charged charges on the surface of the photosensitive drum 21.

Thereafter, the surface of the photosensitive drum 21 on which the latent image is formed reaches a position facing the developing device 23. The electrostatic latent image on the photosensitive drum 21 comes into contact with the magnetic brush on the developing rollers 23a1 and 23a2, and the negatively charged toner T in the magnetic brush is attached and visualized.
Specifically, the developer G pumped up by the magnetic force generated by the magnetic pole of the upper developing roller 23a1 is made into an appropriate amount by a doctor blade 23c as a developer regulating member, and then the developing region (the developing region (opposite part to the photosensitive drum 21)). This is a region where the two developing rollers 23a1 and 23a2 and the photosensitive drum 21 face each other). The carrier C spiked in the development area rubs the photosensitive drum 21. At this time, the toner T mixed with the carrier C is negatively charged due to friction with the carrier C. On the other hand, the carrier C is positively charged. A predetermined developing bias is applied to the developing rollers 23a1 and 23a2 from a power supply unit (not shown). As a result, an electric field is formed between the developing rollers 23a1 and 23a2 and the photosensitive drum 21, and the negatively charged toner T is selectively attached only to the image portion on the photosensitive drum 21 by the electric field, and the toner image. Form.

Thereafter, the surface of the photosensitive drum 21 on which the toner image is formed reaches a position facing the transfer belt 30 and the transfer roller 24. Then, the toner image on the photosensitive drum 21 is transferred onto the recording medium P conveyed to the facing position in accordance with this timing. At this time, a predetermined voltage is applied to the transfer roller 24.
Thereafter, the recording medium P to which the toner image is transferred passes through the fixing unit 66 and is discharged from the discharge roller 69 to the outside of the apparatus.

On the other hand, toner T (untransferred toner) remaining on the photosensitive drum 21 without being transferred to the recording medium P during the transfer process reaches the portion facing the cleaning unit 25 while adhering to the photosensitive drum 21. The untransferred toner on the photosensitive drum 21 is removed and collected by the cleaning unit 25.
Thereafter, the surface of the photosensitive drum 21 passes through a static elimination unit (not shown), and a series of image forming processes on the photosensitive drum 21 is completed.

Hereinafter, the configuration and operation of the developing device 23 will be described in detail.
Referring to FIG. 3, the developing device 23 includes developing rollers 23a1 and 23a2 as developer carriers, conveying screws 23b1 to 23b3 (auger screws), a doctor blade 23c as a developer regulating member, a carrier collecting roller 23k, It comprises a scraper 23m, a discharge screw 23n, an upper case 23r as a case member, and the like. Further, in the developing device 23, three developer transport portions B1 to B3 that transport the developer G to form a circulation path are formed.

  The developing rollers 23a1 and 23a2 serving as developer carriers are formed by rotating a sleeve formed of a nonmagnetic material such as aluminum, brass, stainless steel, or conductive resin into a cylindrical shape in a clockwise direction by a rotation driving mechanism (not shown). It is configured as follows. In the sleeves of the developing rollers 23a1 and 23a2, a magnet for forming a magnetic field is fixed so as to cause the developer G to rise on the peripheral surface of the sleeve. The carrier C in the developer G rises in a chain shape on the sleeve so as to follow the normal magnetic field lines emitted from the magnet. The charged toner T is attached to the carrier C that is spiked in a chain shape to form a magnetic brush. The magnetic brush is transferred in the same direction (clockwise) as the sleeve by the rotation of the sleeve.

  Specifically, a plurality of magnetic poles are formed around the developing rollers 23a1 and 23a2 by magnets in the sleeve, respectively. Around the first developing roller 23a1, there are a pumping magnetic pole for pumping up the developer contained in the first developer transport unit B1, a doctor-facing magnetic pole formed at a position facing the doctor blade 23c, and a photosensitive member. A main magnetic pole formed in a region facing the drum 21 and a transport magnetic pole for transporting the developer to a position facing the second developing roller 23a2 are formed. Around the second developing roller 23a2, there are a receiving magnetic pole for receiving the developer on the first developing roller 23a1, a main magnetic pole formed in a region facing the photosensitive drum 21, and a carrier collecting roller 23k. A collecting roller facing magnetic pole formed at the facing position, a agent separating magnetic pole (agent separating pole) for separating the developer toward the second developer conveying portion B2, and the like are formed.

  The doctor blade 23c as a developer regulating member is installed on the upstream side of the developing area, and regulates the developer carried on the first developing roller 23a1 to an appropriate amount. The doctor blade 23c in the present embodiment is a plate-like member having a plate thickness of about 2 mm formed of a nonmagnetic metal material such as SUS316 or XM7. Note that a thin plate having a thickness of about 0.3 mm made of a magnetic metal material such as SUS430 can be installed on the opposite surface 23c side of the doctor blade 23c.

Each of the three transport screws 23b1 to 23b3 has a screw portion spirally formed on the shaft portion, and the developer G accommodated in the developing device 23 is in the longitudinal direction (in the direction perpendicular to the plane of FIG. 2). )) While circulating.
The first conveying screw 23b1 as the developer conveying member is disposed at a position facing the developing roller 23a1 in the first developer conveying portion B1, and conveys the developer G in the horizontal direction (see FIG. 4). In addition, the developer 23a is supplied onto the developing roller 23a1. In other words, the first transport screw 23b1 faces the developing roller 23a1 and supplies the developer G to the developing roller 23a1 while transporting the developer G in the longitudinal direction (the rotational axis direction of the developing roller 23a1).

The second transport screw 23b2 as the second developer transport member is installed in the second developer transport section B2. The second transport screw 23b2 is disposed below the first transport screw 23b1 and at a position facing the developing roller 23a2. Then, the developer G separated from the developing roller 23a2 (the developer G forcibly separated from the developing roller 23a2 by the agent separation pole after the developing step) is conveyed in the horizontal direction (indicated by a white arrow in FIG. 4). It is a left-hand conveyance.) In other words, the second conveying screw 23b2 is disposed at a position below the first developer conveying portion B1 and facing the developing roller 23a2, and the developer G detached from the developing roller 23a2 is disposed in the longitudinal direction. Transport.
The first transport screw 23b1 and the second transport screw 23b2 are arranged so that the rotation axis is substantially horizontal, like the developing rollers 23a1 and 23a2 and the photosensitive drum 21.

  The third transport screw 23b3 as the third developer transport member is installed in the third developer transport unit B3. The third conveyance screw 23b3 is disposed obliquely with respect to the horizontal direction so as to linearly connect the downstream side of the conveyance path by the second conveyance screw 23b2 and the upstream side of the conveyance path by the first conveyance screw 23b1. (See FIG. 4). The third transport screw 23b3 transports the developer G transported by the second transport screw 23b2 to the upstream side of the transport path by the first transport screw 23b1, and from the downstream side of the transport path by the first transport screw 23b1. The developer G circulated through the drop path 23f is transported to the upstream side of the transport path by the first transport screw 23b1 (the transport is obliquely upward to the right as indicated by the white arrow in FIG. 4). In other words, the third transport screw 23b3 transports the developer G transported by the second developer transport unit B2 to the upstream side of the first developer transport unit B1, and the downstream side of the first developer transport unit B1. The developer G that has reached 1 is conveyed to the upstream side of the first developer conveyance part B1.

A transport path (first developer transport section B1) by the first transport screw 23b1, a transport path by the second transport screw 23b2 (second developer transport section B2), and a transport path (first transport by the third transport screw 23b3). 3 developer transport section B3) is isolated from the wall.
Referring to FIG. 4, the downstream side of the second developer transport unit B2 and the upstream side of the third developer transport unit B3 communicate with each other via the first relay unit 23g. In addition, the downstream side of the third developer conveyance unit B3 and the upstream side of the first developer conveyance unit B1 are communicated with each other via the second relay unit 23h. In addition, the downstream side of the first developer transport unit B1 and the upstream side of the third developer transport unit B3 communicate with each other via a drop path 23f.

With such a configuration, a circulation path for circulating the developer G in the longitudinal direction in the developing device 23 is formed by the three developer conveying portions B1 to B3 (conveying screws 23b1 to 23b3). Here, when the developing device 23 is operated, the developer accommodated in the device flows in a state as indicated by the oblique lines in FIG. Referring to FIG. 4, in the first developer conveying section B1, the developer surface on the downstream side is lower than the upstream agent surface because part of the developer being conveyed is developed. This is because it is supplied to the roller 23a1. That is, the developer that has not been supplied to the developing roller 23a1 moves to the upstream side of the third developer conveying portion B3 via the dropping path 23f.
Note that a magnetic sensor 26 (toner density sensor) is installed in the third developer conveying section B3. Based on the toner density information detected by the magnetic sensor 26, the developer G having a predetermined toner density is supplied from the agent cartridge 28 into the developing device 23. In the present embodiment, the toner concentration of the developer G in the developing device 23 is controlled to be 4 to 7% by weight.

4 and 5, a part of the developer G accommodated in the developing device 23 is discharged to the outside (agent storage container 70) on the wall portion of the first developer conveying portion B1. A discharge port 23d (discharge means) is provided. Specifically, the discharge port 23d has a predetermined developer surface (upper surface) of the developer that is supplied to the developing device 23 from the agent cartridge 28 into the developing device 23 to increase the amount of developer in the device and is conveyed to that position. When the height is exceeded, the excess developer G is discharged toward the agent storage container 70. That is, the excess developer G exceeds the lower portion of the discharge port 23 d, is discharged from the discharge port 23 d, and gravity falls toward the agent storage container 70 via the discharge path 71. As described above, the carrier deteriorated by being contaminated by the base resin or the external additive of the toner T is automatically discharged to the outside of the developing unit, so that deterioration of the image quality can be suppressed even over time.
Although not shown in FIG. 2, FIG. 4, etc., a discharge screw 23n for conveying the developer discharged from the discharge port 23d in the horizontal direction is installed in the discharge path 71 ( See FIG. 3).

  Further, a bypass for returning a part of the developer G to the upstream side of the circulation path without passing through the position where the discharge port 23d (discharge means) is disposed in the developer circulation path in the developing device 23. A path is formed. Specifically, referring to FIG. 4 and FIG. 6, the opening 23e is the first developer transport unit B1 and upstream of the discharge port 23d (a position relatively close to the discharge port 23d). Is provided. The opening 23e serves as the inlet of the bypass path, and the outlet of the bypass path is disposed in the transport path (near the center in the longitudinal direction) by the third transport screw 23b3.

  As described above, by providing the bypass path in the developer circulation path in the developing device 23, even if the developer in the developing device has a wavy deviation or the like, the amount of developer discharged from the discharge port 23d varies. It is possible to suppress a problem that the developer exceeding the necessary amount is discharged from the developing device 23.

  FIG. 7 is a diagram illustrating a state in which the developer is wavy in the developer circulation path in the developing device 23. As described above, there is a case where a wavy deviation with a large height difference occurs in the developer circulation path. Such a wave-like bias appears remarkably immediately after the operation of the developing device 23 is started (immediately after restarting). When such a wave-like deviation occurs, conventionally, all of the developer (a developer having a height H2 in FIG. 7) located higher than the lower portion of the discharge port 23d is discharged. It was discharged from the outlet 23d. Since the developer discharged in this way is not originally intended to be discharged, if such a phenomenon occurs repeatedly, the amount of developer in the developing device 23 becomes insufficient, and the developer As a result, the deterioration state of the toner becomes unstable or the charge amount of the toner decreases, which causes problems such as a decrease in image density on the output image.

  On the other hand, in the present embodiment, since the opening 23e leading to the bypass path is provided on the upstream side of the discharge port 23d, a part of the developer located at a position higher than the lower portion of the discharge port 23d is discharged. Without being discharged from 23d, it is returned to the transport path in the third transport screw 23b3 through the opening 23e. As a result, it is possible to suppress a problem that the developer is excessively discharged from the discharge port 23d.

Here, the height of the lower portion of the opening 23e in the bypass path is configured to be higher by the height H1 than the height of the lower portion of the discharge port 23d.
As a result, of the developer at a position higher than the lower portion of the discharge port 23d, the developer for the height (H2-H1) is not discharged from the discharge port 23d, and is discharged from the third conveyance screw 23b3 through the opening 23e. It will be returned to the transport path. Accordingly, it is possible to reliably prevent the problem that the developer is excessively discharged from the discharge port 23d while maintaining the original function of the discharge unit. Here, the distance W in the longitudinal direction between the discharge port 23d and the opening 23e is preferably as short as possible.

Here, referring to FIG. 3 (not shown in FIG. 2, FIG. 4, etc.), in the present embodiment, below the second developing roller 23a2 (downstream in the rotational direction), A carrier collecting roller 23k is installed at a position facing the photosensitive drum 21. Further, a scraper 23m is installed at a position where it abuts on the carrier collecting roller 23k.
The carrier collecting roller 23k is a cylindrical body made of stainless steel or the like in which a magnet for forming a predetermined magnetic field is fixed, and the carrier that moves (flys) from the inside of the developing device 23 and adheres to the photosensitive drum 21. It is for collecting. The carrier collecting roller 23k is driven to rotate counterclockwise in FIG. Most of the carriers collected and carried by the carrier collecting roller 23k are transferred onto the developing roller 23a2 at a position facing the second developing roller 23a2, and the agent separating pole (agent separating magnetic pole) of the developing roller 23a2 is obtained. ) And is separated from the developing roller 23a2 and collected in the second developer conveying portion B2. On the other hand, the carrier remaining and carried on the carrier collecting roller 23k without moving onto the developing roller 23a2 is mechanically scraped off by the scraper 23m and collected in the second developer conveying portion B2. In this way, by installing the carrier collecting roller 23k, the carrier adhering to the photosensitive drum 21 can be collected in the developing device 23, so that the occurrence of abnormal images (firefly images, whiteout images) is suppressed. In addition, the shortage of carriers in the developing device 23 is suppressed.

In the present embodiment, the outer diameters of the developing rollers 23a1 and 23a2 are 30 mm, the linear velocity on the outer peripheral surface of the developing rollers 23a1 and 23a2 is 748 mm / second, the outer diameter of the carrier collecting roller 23k is 16 mm, and the carrier collecting The linear velocity on the outer peripheral surface of the roller 23k is 10.6 mm / second, 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 about 440 mm / second. Is set to
The carrier C used in the present embodiment has a particle size of 55 μm and a saturation magnetization of about 96 emu / g. Further, the toner T used in the present embodiment has a particle size of about 6.8 μm.

Hereinafter, the configuration and operation of the developing device 23 which are characteristic in the present embodiment will be described in detail with reference to FIGS.
Referring to FIG. 3, an upper case 23r as a case member that covers the upper side of the first conveying screw 13b1 is configured to hold a doctor blade 23c. Specifically, the doctor blade 23c is formed with a long hole (not shown) penetrating the surface facing the upper case 23r at both ends in the longitudinal direction and at the center in the longitudinal direction. Then, a screw is screwed into the female screw portion formed on the upper case 23r from above the doctor blade 23c through the elongated hole, and the doctor blade 23c is held by the upper case 23r. Here, the long hole described above is for adjusting the doctor gap (the gap between the doctor blade 23c and the developing roller 23a1). In the present embodiment, the upper case 23r is made of aluminum.

Here, the upper case 23r (case member) has a facing surface 23r1 (indicated by a two-dot chain line in FIG. 3) facing the first transport screw 23b1 following the facing surface 23c1 of the doctor blade 23c facing the first transport screw 23b1. Is a circular arc shape up to a predetermined position. Further, an angle θ formed by the opposing surface 23c1 of the doctor blade 23c that opposes the first conveying screw 23b1 and the opposing surface 23r1 of the upper case 23r that opposes the first conveying screw 23b1 (both opposing surfaces 23c1 and 23r1 are in contact with each other). Is an obtuse angle).
As described above, the shape from the facing surface 23c1 of the doctor blade 23c facing the first transport screw 23b1 to the facing surface 23r1 of the upper case 23r facing the first transport screw 23b1 (from the tip of the doctor blade 23c to the predetermined of the upper case 23r). The shape of the facing surfaces 23c1 and 23r1 facing the first conveying screw 23b1 up to the position) is a gentle and uneven shape without a dead space where the developer stays. Therefore, the developer G after being supported on the developing roller 23a1 and regulated by the doctor blade 23c smoothly from the opposing surface 23c1 of the doctor blade 23c along the opposing surface 23r1 of the upper case 23r without staying. The fluid flows and is returned to the first developer conveyance section B1 (the movement in the direction of the thick broken line arrow in FIG. 3 or FIG. 8A). As a result, it is possible to prevent a problem that a firefly image is generated due to the developer staying and compressing in the dead space.

FIG. 9 summarizes the problems of the conventional developing device.
As shown in FIG. 9A, when there is a portion A that prevents the developer from flowing smoothly along the case member 230r from the tip of the doctor blade 23c, the portion A is dead. The developer becomes stagnant as a space. Then, after the developer staying in the dead space A is gradually compressed, it falls onto the developing roller 23a1, and is again carried on the developing roller 23a1 and adheres to the photosensitive drum 21, whereby FIG. ), A firefly image PH (a phenomenon in which toner nuclei are generated in the central portion and the periphery thereof is whitened out) is generated on the output image.
On the other hand, in the present embodiment, since the shape from the tip of the doctor blade 23c to a predetermined position of the upper case 23r is optimized on the facing surface facing the first conveying screw 23b1, the doctor blade 23c Without forming a dead space where a part of the regulated developer G stays, it is possible to suppress a problem that the firefly image PH is generated on the output image.

Further, when the developer conveying member (first conveying screw 23b1) conveys the developer in the longitudinal direction as in the developing device 23 in the present embodiment, the opposing surface 23r1 of the upper case 23r is circular. In addition to being formed in an arc shape, the angle θ formed by the facing surface 23c1 of the doctor blade 23c and the facing surface 23r1 of the upper case 23r is formed as an obtuse angle, so that the developer on the downstream side in the transport direction of the first developer transport unit B1 is formed. The amount of decrease can be reduced.
Specifically, as described above with reference to FIG. 4, the first transport screw 23b1 transports the developer to the developing roller 23a1 while transporting the developer in the longitudinal direction, and transports the first developer transport section B1. The developer amount (agent height) on the downstream side in the direction is smaller than that on the upstream side in the transport direction. Then, as shown in FIG. 9A, when there is a dead space A that hinders the developer from flowing smoothly along the case member 230r from the tip of the doctor blade 23c, that portion. Since the developer stays in A, the developer amount (agent height) on the downstream side in the transport direction of the first developer transport unit B1 is further reduced. In such a case, the amount of developer supplied to the developing roller 23a1 is insufficient on the downstream side in the transport direction of the first developer transport unit B1, and the image density on the output image is lowered, or the output Image density unevenness (pitch unevenness) corresponding to the screw pitch of the first conveying screw 23a1 may occur on the image.
On the other hand, in the present embodiment, since the shape from the tip of the doctor blade 23c to a predetermined position of the upper case 23r is optimized on the facing surface facing the first conveying screw 23b1, the doctor blade 23c Without forming a dead space in which a part of the regulated developer G stays, it is possible to suppress a problem that an image density lowering or image density unevenness occurs on an output image.

  Further, in the present embodiment, since the shape from the tip of the doctor blade 23c to a predetermined position of the upper case 23r is optimized on the facing surface facing the first conveying screw 23b1, it is regulated by the doctor blade 23c. The subsequent developer G does not stay and smoothly flows back toward the first developer transport unit B1. Therefore, damage to the developer G flowing along the facing surfaces 23c1 and 23r1 is reduced, and the developer G is unlikely to deteriorate.

Here, in the present embodiment, the above-described predetermined position of the upper case 23r (the end position of the arcuate facing surface 23r1) is configured to be a position beyond the uppermost portion of the first transport screw 23b1. is doing. That is, with reference to FIGS. 3 and 8, the end of the arc-shaped facing surface 23r1 of the case 23r is disposed on the left side of the drawing (in a direction away from the developing roller 23a1) from the position indicated by the one-dot chain line. Has been.
With such a configuration, the developer G (developer after being regulated by the doctor blade 23c) flowing along the arcuate opposing surface 23r1 of the case 23r is in the back of the first developer transport unit B1. (Which is a direction away from the developing roller 23a1), and then sufficiently stirred and mixed along the rotation direction of the first conveying screw 23b1 (counterclockwise rotation in the figure). However, it is conveyed in the longitudinal direction. Therefore, in addition to the effect of reducing the above-described generation of firefly images and the deterioration of the developer, the effect of reducing the decrease amount of the developer on the downstream side in the transport direction of the first developer transport unit B1 is more reliably exhibited. Will be.

In the present embodiment, referring to FIGS. 3 and 8, a plurality of cooling fins 23r2 are installed on the outer surface of upper case 23r.
Thereby, the heat dissipation of the upper case 23r is enhanced, and the temperature rise of the upper case 23r is reduced, so that the thermal deterioration of the developer G flowing along the facing surface 23r1 of the case 23r can be reduced. .

Further, in the upper case 23r in the present embodiment, the curvature of the arcuate opposing surface 23r1 is smaller on the downstream side in the transport direction of the first developer transport unit B1 than on the upstream side in the transport direction of the first developer transport unit B1. It is formed to become. That is, the curvature of the facing surface 23r1 of the upper case 23r on the upstream side in the transport direction shown in FIG. 8A is larger than the curvature of the facing surface 23r1 of the upper case 23r on the downstream side in the transport direction shown in FIG. Is set. Specifically, the curvature of the facing surface 23r1 of the upper case 23r can be configured to gradually decrease from the upstream side toward the downstream side, or can be configured to gradually decrease.
With such a configuration, the developer flowing along the facing surface 23r1 of the upper case 23r in the longitudinal direction in accordance with the change in the developer amount in the longitudinal direction (conveying direction) of the first developer transport unit B1. It will be controlled in a well-balanced manner. That is, by varying the curvature of the facing surface 23r1 of the upper case 23r between the downstream side where the developer amount is small and the upstream side where the developer amount is large, the facing surface 23r1 of the upper case 23r is changed in the longitudinal direction. The developer is adjusted so that the fluidity of the developer is uniform. Thereby, the effect demonstrated previously is exhibited reliably over a longitudinal direction.

Further, the developing device 23 according to the present embodiment includes a doctor-facing magnetic pole formed at a position facing the doctor blade 23c (developer regulating member) among the plurality of magnetic poles formed around the first developing roller 23a1. Is formed so that the magnetic flux density in the normal direction is 80 to 120 mT.
Thereby, it is possible to sufficiently secure the amount of developer carried (held) on the first developing roller 23a1 on the upstream side of the doctor blade 23c without increasing the driving torque of the developing device 23 so much. it can. That is, a sufficient amount of developer passing through the gap between the doctor blade 23c and the developer blade 23c can be secured without causing a great stress on the developer at the position of the doctor blade 23c and without losing the balance of the developer amount in the developing device 23. Thus, the image quality of the output image can be stabilized.

  FIG. 10 is a graph showing the relationship between the magnetic force of the doctor-facing magnetic pole of the first developing roller 23a1, the saturated developer weight, and the driving torque in the developing device 23 according to the present embodiment. In FIG. 10, the horizontal axis indicates the magnetic force (normal magnetic flux density) of the magnetic pole facing the doctor of the first developing roller 23a1, and the left vertical axis indicates the weight of the saturated developer in the developing device 23 (on the upstream side of the doctor blade 23c). The right vertical axis represents the driving torque of the developing device 23 (the amount of stress applied to the developer at the position of the doctor blade 23c). Is almost proportional to the above). In FIG. 10, the solid line graph shows the relationship between the magnetic force of the doctor counter magnetic pole and the saturated developer weight, and the broken line graph shows the relationship between the magnetic force of the doctor counter magnetic pole and the driving torque. Referring to FIG. 10, when the magnetic flux density in the normal direction of the doctor counter magnetic pole is less than 80 mT, the amount of developer carried on the first developing roller 23a1 is insufficient on the upstream side of the doctor blade 23c. As a result, the image quality of the output image deteriorates. If the magnetic flux density in the normal direction of the doctor-facing magnetic pole is 80 mT or more, the amount of developer held on the first developing roller 23a1 on the upstream side of the doctor blade 23c increases proportionally and sufficiently. When the magnetic flux density exceeds 120 mT, the developer holding amount is saturated. Further, the stress applied to the developer at the position of the doctor blade 23c increases almost proportionally as the magnetic force of the doctor opposing magnetic pole increases even if the magnetic flux density exceeds 120 mT. For these reasons, it is preferable to set the magnetic flux density in the normal direction of the doctor-facing magnetic pole to the above-described range.

  As described above, in the present embodiment, the first conveying screw 23b1 (developer conveying member) from the tip of the doctor blade 23c (developer regulating member) to a predetermined position of the upper case 23r (case member) is opposed. Since the shapes of the opposing surfaces 23c1 and 23r1 are optimized, a part of the developer G after being supported on the developing roller 23a1 (developer carrier) and regulated by the doctor blade 23c is the upper case 23r, etc. Therefore, a problem that a firefly image is generated on the output image is suppressed.

In the present embodiment, the present invention is applied to the developing device 23 in which three developer conveying units B1 to B3 are installed. However, the development in which two or less developer conveying units are installed or four or more developer conveying units are installed. The present invention can also be applied to an apparatus. Even in that case, the same effect as the present embodiment can be obtained.
In the present embodiment, the third transport screw 23b3 is disposed obliquely with respect to the horizontal direction. However, the third transport screw 23b3 can be disposed horizontally.
Further, in the present embodiment, the discharge port 23d is provided in the wall portion of the first developer conveyance portion B1, but the discharge port 23d can also be provided in the wall portions of the other developer conveyance portions B2 and B3.

  In the present embodiment, the developer G (toner T and carrier C) is supplied from the agent cartridge 28 toward the developing device 23. However, only the carrier C can be supplied from the cartridge toward the developing device 23. . In that case, a toner cartridge containing only toner is installed separately from the agent cartridge (carrier cartridge), and the toner contained in the toner cartridge is appropriately directed toward the developing device 23 based on the detection result of the magnetic sensor 26. I will supply it. Furthermore, the present invention can also be applied to a developing device that is not a premix developing system and supplies only toner from a cartridge without supplying a carrier. Even in these cases, the same effects as in the present embodiment can be obtained.

Further, in the present embodiment, the present invention is applied to an image forming apparatus in which a part of the image forming unit is configured by the process cartridge 20. However, the application of the present invention is not limited to this, and the present invention can naturally be applied to an image forming apparatus in which the image forming unit is not formed into a process cartridge. Specifically, the present invention can naturally be applied even when the developing device 23 is configured as a unit that is detachably attached to the image forming apparatus main body.
Further, in the present embodiment, the present invention is applied to the developing device 23 in which two developing rollers 23a1 and 23a2 are installed. However, the present invention is also applied to a developing device in which one or more developing rollers are installed. Of course, the present invention can be applied. Even in that case, the same effect as the present embodiment can be obtained.

  In the present embodiment, the present invention is applied to the developing device in which the conveying screws 23b1 and 23b2 are installed in the vertical direction. However, the developing device in which a plurality of conveying screws are installed in the horizontal direction (Patent Document 2, etc.) And a developing device provided with a paddle-shaped developer conveying member that conveys the developer in the lateral direction instead of the first conveying screw 23b1 that conveys the developer in the longitudinal direction. Can be applied. Even in that case, the same effect as that of the present embodiment can be obtained by using the upper case and the doctor blade configured in the same manner as the present embodiment.

  It should be noted that the present invention is not limited to the present embodiment, and it is obvious that the present embodiment can be modified as appropriate within the scope of the technical idea of the present invention, other than suggested in the present embodiment. is there. Further, the number, position, shape, and the like of the constituent members are not limited to the present embodiment, and the number, position, shape, and the like that are suitable for implementing the present invention can be used.

1 is an overall configuration diagram illustrating an image forming apparatus according to an embodiment of the present invention. FIG. 2 is an enlarged view showing a process cartridge installed in the image forming apparatus of FIG. 1. It is an enlarged view which shows a developing device. It is sectional drawing which looked at the circulation path in a developing device to the longitudinal direction. It is sectional drawing which shows the Y1-Y1 cross section in the circulation path | route of FIG. It is sectional drawing which shows the Y2-Y2 cross section in the circulation path | route of FIG. FIG. 5 is a diagram illustrating a state in which a wavy bias is generated in the developer in the circulation path of FIG. 4. It is an enlarged view which shows the vicinity of a doctor blade and a case member. (A) The enlarged view which shows the principal part of the conventional image development apparatus, (B) The schematic which shows a firefly image. It is a graph which shows the relationship between the magnetic force of a doctor opposing magnetic pole, saturated developer weight, and drive torque.

Explanation of symbols

1 image forming apparatus body (apparatus body),
20, 20Y, 20C, 20M, 20BK Process cartridge,
21 Photosensitive drum (image carrier),
23 Developing device (developing part),
23a1, 23a2 developing roller (developer carrier),
23b1 first conveying screw (developer conveying member),
23b2 second transport screw (second developer transport member),
23b3 third transport screw (third developer transport member),
23c Doctor blade (developer regulating member),
23c1 facing surface,
23r upper case (case member),
23r1 facing surface, 23r2 cooling fin,
23d outlet,
G developer (two-component developer), T toner, C carrier.

Claims (8)

A developing device for containing a developer and developing a latent image formed on an image carrier,
A developer carrying body facing the image carrying body and carrying a developer;
A developer regulating member facing the developer carrying body and regulating the amount of developer carried on the developer carrying body;
A developer conveying member facing the developer carrying member and supplying the developer to the developer carrying member while conveying the developer;
A case member that holds the developer regulating member and covers an upper side of the developer transport member;
With
The case member has an opposing surface facing the developer conveying member formed in an arc shape up to a predetermined position following an opposing surface of the developer regulating member facing the developer conveying member.
The angle formed by the facing surface of the developer regulating member facing the developer transport member and the facing surface of the case member facing the developer transport member is an obtuse angle. Developing device.   The developing device according to claim 1, wherein the predetermined position of the case member is a position beyond an uppermost portion of the developer conveying member.   The developing device according to claim 1, wherein the case member includes a cooling fin on an outer surface thereof. The developer conveying member is configured to convey the developer in the longitudinal direction,
The curvature of the arcuate facing surface of the case member facing the developer transport member is such that the downstream side in the transport direction of the developer transport member is smaller than the upstream side in the transport direction of the developer transport member. The developing device according to claim 1, wherein the developing device is formed. The developer conveying member is configured to convey the developer in the longitudinal direction,
A second developer conveying member disposed below the developer conveying member and facing the developer carrying member, and carrying the developer detached from the developer carrying member; The developing device according to claim 1, wherein:   A plurality of magnetic poles are formed around the developer carrier, and a magnetic flux density in a normal direction of the magnetic poles formed at positions facing the developer regulating member among the plurality of magnetic poles is 80 to 120 mT. The developing device according to claim 1, wherein the developing device is formed as described above. A process cartridge that is detachably installed on the main body of the image forming apparatus,
7. A process cartridge in which the developing device according to claim 1 and the image carrier are integrated.   An image forming apparatus comprising the developing device according to claim 1 and the image carrier.

Images