JP6188840B2 - Developing device, process cartridge, and image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that forms an image on a recording material using an electrophotographic method, and more particularly to a developing device and a process cartridge that are applied to the image forming apparatus.

  In an image forming apparatus such as a printer using an electrophotographic image forming method (electrophotographic process), an electrophotographic photosensitive member (hereinafter referred to as “photosensitive member”) as an image bearing member is uniformly charged, and the charged photosensitive member. An electrostatic image is formed on the photoreceptor by selectively exposing the body. The electrostatic image formed on the photoreceptor is visualized as a toner image with toner as a developer. The toner image formed on the photoconductor is transferred to a recording material such as recording paper or a plastic sheet, and the toner image is applied to the recording material by applying heat or pressure to the toner image transferred onto the recording material. Image recording is performed by fixing.

  Such an image forming apparatus generally requires replenishment of developer and maintenance of various process means. In order to facilitate the replenishment of the developer and maintenance of various process means, the photosensitive member, the charging means, the developing means, the cleaning means, etc. are collectively assembled into a cartridge, and a process that can be attached to and detached from the image forming apparatus main body. A cartridge has been put into practical use. According to the process cartridge system, an image forming apparatus with excellent usability can be provided.

  In recent years, color image forming apparatuses that form color images using a plurality of color developers have become widespread. As a color image forming apparatus, a photoconductor corresponding to each of image forming operations using a plurality of color developers is arranged in a line along the surface movement direction of a transfer target body onto which a toner image is transferred, so-called An in-line image forming apparatus is known. Some in-line color image forming apparatuses have a plurality of photoconductors arranged in a line in a direction (for example, a horizontal direction) intersecting a vertical direction (gravity direction). The in-line method is a preferable image forming method in that it is easy to meet demands such as an increase in image forming speed and development to a multifunction printer.

  Further, as an image forming apparatus, there is an image forming apparatus in which a photosensitive member is disposed below an intermediate transfer member as a transfer member or a recording material carrier that transports a recording material as a transfer member (see Patent Document 3). .

  When the photosensitive member is disposed below the intermediate transfer member or the recording material carrier, the fixing device and the developing device (or the exposure device, for example) are arranged in such a manner that the intermediate transfer member or the recording material carrier is sandwiched in the image forming apparatus main body. ) Can be arranged at remote locations. Therefore, there is an advantage that the developing device (or the exposure device) is hardly affected by the heat of the fixing device.

  On the other hand, when the photosensitive member is disposed below the intermediate transfer member or the recording material carrier as described above, in the developing device, the developer roller (developer carrier) It may be necessary to supply the developer to the supply roller (supply member).

  Therefore, Patent Document 1 discloses a method of bringing a receiving sheet into contact with the lower side of the supply member as means for supplying the developer to the supply member. According to this method, the receiving sheet prevents the developer adhering to the supply member from dropping due to gravity, and prevents the developer that can be supplied to the developer carrier from decreasing, thereby preventing a decrease in the density of the solid image. ing.

  In Patent Document 2, a conveyance member is provided below the supply member in the development chamber located above the developer container, and the developer is conveyed to the lower surface of the supply member by the conveyance member, and toner aggregation in the development chamber is performed. A method of suppressing this is disclosed.

JP 2003-173083 A JP 2009-222931 A

  However, in the developer supply method as in Patent Document 1, when images with a low printing rate are continuously output, the developer stays and aggregates between the supply member and the receiving sheet, resulting in image quality such as density unevenness. A decrease may occur.

  In the configuration as in Patent Document 2, a transport member is required as an additional member in addition to the supply member in the developing chamber, and the apparatus configuration is complicated. In addition, friction with the conveying member in the developing chamber has been a factor of deteriorating the developer.

  The present invention has been made in view of such a problem, and is configured to convey the developer from a developer container disposed below the developing chamber onto a supply member disposed in the developing chamber. An object of the present invention is to provide a developing device, a process cartridge, and an image forming apparatus capable of stably forming a high-quality image with a simple configuration when a developing device is used.

In order to achieve the above object, the invention according to the present application is a developing device used in an electrophotographic image forming apparatus, the developer carrying member for carrying the developer and developing the electrostatic latent image, and the developer A developing chamber provided with a supply member arranged to form a nip portion with the carrier and supplying the developer to the developer carrier;
A developer accommodating portion that is disposed below the developing chamber and accommodates the developer, and a developer accommodated in the developer accommodating portion via the opening provided in the developing chamber. A conveying member that conveys upward,
The developer carrying member and the supply member rotate in a direction in which each surface moves from the upper end to the lower end of the nip portion.

  As described above, according to the present invention, the developing device configured to transport the developer from the developer accommodating portion disposed below the developing chamber onto the supply member disposed in the developing chamber is used. In this case, it is possible to provide a developing device, a process cartridge, and an image forming apparatus capable of stably forming a high-quality image by forming a good circulation of the developer with a simple configuration.

1 is a schematic cross-sectional view of an image forming apparatus according to an embodiment to which the present invention can be applied. 1 is a schematic cross-sectional view of a process cartridge according to an embodiment to which the present invention can be applied. FIG. 6 is a diagram illustrating toner movement in a developing device according to an embodiment to which the invention can be applied. It is a figure showing the example of another composition of the development device concerning the example which can apply the present invention. It is a schematic structure sectional view of a process cartridge of a comparative example.

  Hereinafter, a developing device, a process cartridge, and an image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

[Entire configuration of image forming apparatus]
First, the overall configuration of an electrophotographic image forming apparatus (image forming apparatus) according to the present invention will be described.
FIG. 1 is a schematic cross-sectional view of an image forming apparatus 100 of the present embodiment. The image forming apparatus 100 of this embodiment is a full-color laser printer that employs an inline method and an intermediate transfer method. The image forming apparatus 100 can form a full-color image on a recording material (for example, recording paper, plastic sheet, cloth, etc.) according to the image information. The image information is input to the image forming apparatus main body 100A from an image reading apparatus connected to the image forming apparatus main body 100A or a host device such as a personal computer connected to the image forming apparatus main body 100A so as to be communicable.

  The image forming apparatus 100 includes, as a plurality of image forming units, first, second, and third images for forming yellow (Y), magenta (M), cyan (C), and black (K) images, respectively. And fourth image forming units SY, SM, SC, and SK. In the present embodiment, the first to fourth image forming units SY, SM, SC, and SK are arranged in a line in a direction that intersects the vertical direction.

  In the present embodiment, the configurations and operations of the first to fourth image forming units SY, SM, SC, and SK are substantially the same except that the colors of images to be formed are different. Therefore, in the following, unless there is a particular distinction, the subscripts Y, M, C, and K given to the reference numerals to indicate that they are elements provided for any color are omitted, and generally explain.

  In this embodiment, the image forming apparatus 100 includes four drum-type electrophotographic photoreceptors, that is, the photoreceptor drums 1 arranged in parallel in a direction intersecting the vertical direction as a plurality of image carriers. The photosensitive drum 1 is rotationally driven by a driving means (drive source) (not shown) in the direction indicated by an arrow A (clockwise). Around the photosensitive drum 1, a charging roller 2 as a charging means for uniformly charging the surface of the photosensitive drum 1, a laser is irradiated based on image information, and an electrostatic image (electrostatic) is formed on the photosensitive drum 1. A scanner unit (exposure device) 3 is disposed as exposure means for forming a (latent image). Further, around the photosensitive drum 1, a developing unit (developing device) 4 as developing means for developing an electrostatic image as a toner image, toner remaining on the surface of the photosensitive drum 1 after transfer (transfer residual toner) A cleaning member 6 is disposed as a cleaning means for removing water. Further, an intermediate transfer belt 5 as an intermediate transfer body for transferring the toner image on the photosensitive drum 1 to the recording material 12 is disposed opposite to the four photosensitive drums 1.

  In this embodiment, the developing unit 4 uses a non-magnetic one-component developer toner as the developer. In this embodiment, the developing unit 4 performs reverse development by bringing a developing roller (described later) as a developer carrying member into contact with the photosensitive drum 1. In other words, in this embodiment, the developing unit 4 is a portion where the charge is attenuated due to the exposure of the toner charged to the same polarity as the charging polarity of the photosensitive drum 1 (negative polarity in this embodiment) on the photosensitive drum 1 ( The electrostatic image is developed by being attached to the image portion and the exposure portion).

  In this embodiment, the photosensitive drum 1 and the charging roller 2, the developing unit 4 and the cleaning member 6 as process means acting on the photosensitive drum 1 are integrated, that is, integrated into a cartridge, A process cartridge 7 is formed. The process cartridge 7 can be attached to and detached from the image forming apparatus 100 via mounting means such as a mounting guide and a positioning member provided in the image forming apparatus main body 100A. In this embodiment, the process cartridges 7 for the respective colors all have the same shape, and each of the process cartridges 7 for each color has yellow (Y), magenta (M), cyan (C), and blank ( K) toner of each color is accommodated.

  The intermediate transfer belt 5 formed of an endless belt as an intermediate transfer member abuts on all the photosensitive drums 1 and circulates (rotates) in the direction of arrow B (counterclockwise) in the figure. The intermediate transfer belt 5 is wound around a driving roller 51, a secondary transfer counter roller 52, and a driven roller 53 as a plurality of support members.

  On the inner peripheral surface side of the intermediate transfer belt 5, four primary transfer rollers 8 as primary transfer means are arranged in parallel so as to face the respective photosensitive drums 1. The primary transfer roller 8 presses the intermediate transfer belt 5 toward the photosensitive drum 1 to form a primary transfer portion N1 where the intermediate transfer belt 5 and the photosensitive drum 1 abut. A bias having a polarity opposite to the normal charging polarity of the toner is applied to the primary transfer roller 8 from a primary transfer bias power source (high voltage power source) as a primary transfer bias applying unit (not shown). As a result, the toner image on the photosensitive drum 1 is transferred (primary transfer) onto the intermediate transfer belt 5.

  A secondary transfer roller 9 as a secondary transfer unit is disposed at a position facing the secondary transfer counter roller 52 on the outer peripheral surface side of the intermediate transfer belt 5. The secondary transfer roller 9 is pressed against the secondary transfer counter roller 52 via the intermediate transfer belt 5 to form a secondary transfer portion N2 where the intermediate transfer belt 5 and the secondary transfer roller 9 come into contact. A bias having a polarity opposite to the normal charging polarity of the toner is applied to the secondary transfer roller 9 from a secondary transfer bias power source (high voltage power source) as a secondary transfer bias applying unit (not shown). As a result, the toner image on the intermediate transfer belt 5 is transferred (secondary transfer) to the recording material 12.

  More specifically, at the time of image formation, first, the surface of the photosensitive drum 1 is uniformly charged by the charging roller 2. Next, the surface of the charged photosensitive drum 1 is scanned and exposed by laser light corresponding to the image information emitted from the scanner unit 3, and an electrostatic image according to the image information is formed on the photosensitive drum 1. Next, the electrostatic image formed on the photosensitive drum 1 is developed as a toner image by the developing unit 4. The toner image formed on the photosensitive drum 1 is transferred (primary transfer) onto the intermediate transfer belt 5 by the action of the primary transfer roller 8.

  For example, when forming a full-color image, the above-described process is sequentially performed in the first to fourth image forming units SY, SM, SC, and SK, and the toner images of the respective colors are next superimposed on the intermediate transfer belt 5. The primary transfer.

  Thereafter, the recording material 12 is conveyed to the secondary transfer portion N2 in synchronization with the movement of the intermediate transfer belt 5. The four color toner images on the intermediate transfer belt 5 are secondarily transferred onto the recording material 12 collectively by the action of the secondary transfer roller 9 that is in contact with the intermediate transfer belt 5 via the recording material 12.

  The recording material 12 onto which the toner image has been transferred is conveyed to a fixing device 10 as a fixing unit. The toner image is fixed on the recording material 12 by applying heat and pressure to the recording material 12 in the fixing device 10.

  Further, the primary transfer residual toner remaining on the photosensitive drum 1 after the primary transfer process is removed and collected by the cleaning member 6. The secondary transfer residual toner remaining on the intermediate transfer belt 5 after the secondary transfer process is cleaned by the intermediate transfer belt cleaning device 11.

  Note that the image forming apparatus 100 can form a single-color or multi-color image using only one desired image forming unit or using only some (not all) image forming units. It is like that.

[Process cartridge configuration]
Next, the overall configuration of the process cartridge 7 mounted on the image forming apparatus 100 of the present embodiment will be described. In the present embodiment, the configuration and operation of the process cartridge 7 for each color are substantially the same except for the type (color) of the contained toner.

  FIG. 2 is a schematic cross-sectional view (main cross-sectional view) of the process cartridge 7 of this embodiment viewed along the longitudinal direction (rotational axis direction) of the photosensitive drum 1. The posture of the process cartridge 7 in FIG. 2 is a posture in a state where the process cartridge 7 is mounted on the image forming apparatus main body. When the positional relationship and direction of each member of the process cartridge are described below, the positional relationship and direction in this posture are described below. Etc.

  The process cartridge 7 is configured by integrating a photosensitive unit 13 including the photosensitive drum 1 and the developing unit 4 including a developing roller 17 and the like.

  The photoconductor unit 13 has a cleaning frame 14 as a frame that supports various elements in the photoconductor unit 13. The photosensitive drum 1 is rotatably attached to the cleaning frame 14 via a bearing (not shown). The photosensitive drum 1 is rotationally driven in the direction of the arrow A (clockwise) in accordance with the image forming operation by transmitting the driving force of a driving motor (not shown) as a driving means (driving source) to the photosensitive unit 13. Is done. In this embodiment, the photosensitive drum 1 which is the center of the image forming process is an organic photosensitive drum in which an outer surface of an aluminum cylinder is coated with a functional undercoat layer, a carrier generation layer, and a carrier transfer layer in this order. 1 is used.

  Further, the cleaning unit 6 and the charging roller 2 are disposed in the photosensitive unit 13 so as to come into contact with the peripheral surface of the photosensitive drum 1. The transfer residual toner removed from the surface of the photosensitive drum 1 by the cleaning member 6 falls and is stored in the cleaning frame 14.

  The charging roller 2 as charging means is driven to rotate by bringing the roller portion of conductive rubber into pressure contact with the photosensitive drum 1.

  Here, as a charging process, a predetermined DC voltage is applied to the core of the charging roller 2 with respect to the photosensitive drum 1, whereby a uniform dark portion potential (Vd) is applied to the surface of the photosensitive drum 1. Is formed. The spot pattern of the laser beam emitted in accordance with the image data by the laser beam from the scanner unit 3 described above exposes the photosensitive drum 1, and the exposed portion is charged on the surface by the carrier from the carrier generation layer. Disappears and the potential drops. As a result, an electrostatic latent image is formed on the photosensitive drum 1 with a predetermined light portion potential (Vl) at an exposed portion and a predetermined dark portion potential (Vd) at an unexposed portion. In this embodiment, Vd = −500V and Vl = −100V.

  On the other hand, the developing unit 4 has a developing roller 17 as a developer carrying member for carrying toner 80 and a developing chamber in which a toner supply roller 20 as a supply member for supplying toner to the developing roller 17 is disposed. doing. Further, the developing unit 4 includes a toner storage chamber 18 having a toner storage portion (developer storage portion) 18 a for storing toner below the toner supply roller 20 in the gravity direction. In this embodiment, toner having an aggregation degree of 5 to 40% in the initial state is used. In order to ensure the fluidity of the toner through durability, it is desirable to use a toner having such a degree of aggregation. Further, the degree of aggregation of the toner was measured as follows.

  As a measuring apparatus, a powder tester (manufactured by Hosokawa Micron Corporation) having a digital vibrometer (manufactured by DEGITAL VIBRATION METERMODEL 1332 SHOWA SOKKI CORPORATION) was used.

  As a measurement method, set 390 mesh, 200 mesh, and 100 mesh sieves on a shaking table in the order of narrow opening, that is, 390 mesh, 200 mesh, and 100 mesh sieves so that 100 mesh sieve is at the top. did.

  Add 5 g of accurately weighed sample (toner) to the set 100 mesh sieve, adjust the displacement value of the digital vibrometer to 0.60 mm (peak-to-peak), and apply vibration for 15 seconds. It was. Thereafter, the mass of the sample remaining on each sieve was measured to obtain the degree of aggregation based on the following formula.

  The measurement samples at that time were each left for 24 hours in an environment of 23 ° C. and 60% RH in advance, and the measurement was performed in an environment of 23 ° C. and 60% RH.

Aggregation degree (%) = (residual sample mass on 100 mesh sieve / 5 g) × 100 + (residual sample mass on 200 mesh sieve / 5 g) × 60 + (residual sample mass on 390 mesh sieve / 5 g) × 20
Further, the toner supply roller 20 is rotated by forming a toner nip N (a portion where the toner is sandwiched between the development roller 17 and the toner supply roller 20) between the toner supply roller 20 and the development roller 17.

  A stirring and conveying member 22 is provided in the toner storage chamber 18. The agitating / conveying member 22 agitates the toner accommodated in the toner accommodating chamber 18 and also conveys the toner in the direction of arrow G in the figure toward the top of the toner supply roller 20. In this embodiment, the agitating and conveying member is driven to rotate at 30 rpm.

  The developing blade 21 is disposed below the developing roller 17 and is in contact with the developing roller at a counter, and regulates the coating amount of toner supplied by the toner supply roller 20 and applies a charge. In this embodiment, a SUS thin plate having a thickness of 0.1 mm is used as the developing blade 21, a contact pressure is formed by utilizing the spring elasticity of the thin plate, and the surface thereof is toner and the developing roller 17. Abut. Here, the developing blade is not limited to this, and may be a thin metal plate such as phosphor bronze or aluminum. Alternatively, the surface of the developing blade 21 may be coated with a thin film such as polyamide elastomer, urethane rubber, or urethane resin.

  The toner is triboelectrically charged by rubbing between the developing blade 21 and the developing roller 17 to be charged, and at the same time the layer thickness is regulated. In this embodiment, a predetermined voltage is applied to the developing blade 21 from a blade bias power source (not shown) to stabilize the toner coat. In this example, V = −500 V was applied as the blade bias.

  The developing roller 17 and the photosensitive drum 1 rotate so that the surfaces of the developing roller 17 and the photosensitive drum 1 move in the same direction (in this embodiment, from the bottom to the top).

  In the present embodiment, the developing roller 17 is disposed in contact with the photosensitive drum 1, but the developing roller 17 is disposed close to the photosensitive drum 1 at a predetermined interval. May be.

  In this embodiment, a toner charged negatively by frictional charging with respect to a predetermined DC bias applied to the developing roller 17 has a bright portion potential portion in a developing portion where the toner contacts the photosensitive drum 1 from the potential difference. The electrostatic latent image is visualized by transferring only to. In this embodiment, by applying V = −300 V to the developing roller, a potential difference ΔV = 200 V from the bright portion is formed, and a toner image is formed.

  The toner supply roller 20 and the developing roller rotate in the direction in which the respective surfaces move from the upper end to the lower end of the nip portion N. That is, the toner supply roller 20 rotates in the direction of the arrow E (clockwise) and the developing roller 17 rotates in the direction of arrow D. The toner supply roller 20 is an elastic sponge roller in which a foam layer is formed on the outer periphery of a conductive metal core. The toner supply roller 20 and the developing roller 17 are in contact with each other with a predetermined intrusion amount, that is, in FIG. The toner supply roller 20 and the developing roller 17 rotate with a peripheral speed difference in the same direction at the nip portion N. With this operation, the toner is supplied to the developing roller 17 by the toner supply roller 20. . At this time, the toner supply amount to the developing roller can be adjusted by adjusting the potential difference between the toner supply roller and the developing roller. In this embodiment, the toner supply roller is driven to rotate at 200 rpm and the developing roller is driven to rotate at 100 rpm, and a DC bias is applied to the toner supplying roller so as to have the same potential as the developing roller.

  In the present embodiment, both the developing roller 17 and the toner supply roller 20 have an outer diameter of 15 mm, and the amount of penetration of the toner supply roller 20 into the developing roller 17, that is, the toner supply roller 20 is recessed by the developing roller 17. The dent amount ΔE is set to 1.0 mm. Further, the toner supply roller and the developing roller are arranged so that the center height is the same.

Details of the toner supply roller used in this embodiment will be described below.
The toner supply roller 20 in this embodiment includes a conductive support and a foam layer supported by the conductive support. Specifically, a foamed urethane layer as a foamed layer composed of a cored bar electrode 20a having an outer diameter of φ5 (mm), which is a conductive support, and an open cell body (open cells) in which bubbles are connected to the periphery thereof. 20b is provided and rotates in the direction E in the figure.

A large amount of toner can enter the inside of the toner supply roller 20 by using urethane on the surface layer as an open cell body. Further, the resistance of the toner supply roller 20 in this embodiment is 1 × 10 ⁹ (Ω).

  Here, a method of measuring the resistance of the toner supply roller 20 will be described. The toner supply roller 20 is brought into contact with an aluminum sleeve having a diameter of 30 mm so that an intrusion amount described later becomes 1.5 mm. By rotating the aluminum sleeve, the supply roller 2 is driven to rotate relative to the aluminum sleeve at 30 rpm.

  Next, a DC voltage of −50 V is applied to the developing roller 17. At that time, a resistance of 10 kΩ is provided on the ground side, the current is calculated by measuring the voltage at both ends, and the resistance of the toner supply roller 20 is calculated. In this embodiment, the surface cell diameter of the toner supply roller 20 is set to 50 μm to 1000 μm.

  Here, the cell diameter means the average diameter of the foamed cells having an arbitrary cross section. First, the area of the foamed cell that is the maximum is measured from the enlarged image of the arbitrary cross section, and the maximum cell diameter is converted from this area by converting the equivalent circle diameter. Get. And after deleting the foam cell which is 1/2 or less of this maximum cell diameter as noise, it points out the average value of each cell diameter converted similarly from the remaining individual cell area.

Next, the flow of toner in the developing chamber will be described with reference to FIGS.
In this embodiment, FIG. 3 is an enlarged schematic cross-sectional view of the developing chamber, and shows the movement of the toner conveyed from the stirring and conveying member 22 to the toner supply roller 20.

  The toner is supplied to the developing chamber by the agitating and conveying member 22 mainly toward the upper portion of the toner supply roller 20 (arrow G in FIG. 3), and the supplied toner is supplied to the inside of the toner supply roller and the surface thereof. Retained. Since the toner supply roller 20 rotates in the direction of arrow E, the toner held on the toner supply roller is conveyed toward the nip portion N with the developing roller (arrow F1 in FIG. 3). Here, a part of the toner conveyed by the toner supply roller is discharged by deformation of the toner supply roller at the entrance to the nip portion N, and is accumulated and stored above the nip portion N (arrow in FIG. 3). F2). By storing the toner above the nip portion N in this way, the amount of toner in the supply roller does not decrease between the time when the agitating and conveying member 22 conveys the toner to the developing chamber and the next time it is conveyed. The stored toner can be stably supplied to the toner supply roller and the developing roller.

  Next, the toner transported to the nip portion N is charged by being rubbed and charged in the nip because the toner supply roller and the developing roller are rotated with a difference in peripheral speed. Thereafter, a part of the charged toner is transferred to the developing roller. In this embodiment, since the peripheral speed of the toner supply roller is faster than the peripheral speed of the developing roller, the amount of toner passing over the developing roller per unit time increases, and more toner is transferred to the developing roller. It will be. The toner transferred to the developing roller is regulated and charged by the developing blade at a regulating portion between the developing roller and the developing blade, and a uniform toner coat is formed on the developing roller by the toner passing through the regulating portion.

  On the other hand, the toner regulated by the developing blade is conveyed toward the developing opening (opening portion) provided in the developing chamber by the rotation of the toner supply roller, and is returned to the toner containing chamber through the developing opening. In this embodiment, the bottom of the developing chamber is formed so that the upper end of the wall 30b below the developing opening separating the developing chamber and the toner storage chamber (that is, the lower end of the developing opening) is 1 mm below the center of the toner supply roller. The gap between the frame body and the lower surface of the toner supply roller was arranged to be 1.5 mm.

  As described above, the toner is supplied to the toner supply roller by feeding the toner to the upper portion of the toner supply roller through the developing opening by the agitating and conveying member. Further, the toner returned from the developing chamber to the toner storage chamber by the rotation of the toner supply roller also passes through the developing opening. Therefore, the configuration of the developing opening affects the flow of toner between the developing chamber and the toner storage chamber, and particularly the position of the upper end of the wall 30b below the developing opening (the position of the lower end of the developing opening). . That is, as compared with the case where the position of the upper end of the developing opening wall 30b (the position of the lower end of the developing opening) is made higher than the upper end of the supply roller as shown in FIG. 4, the upper end of the developing opening wall 30b as shown in FIG. By making the position (the position of the lower end of the development opening) lower than the upper end of the toner supply roller, the toner transported in the direction of the development opening by the toner supply roller is likely to exceed the wall, and the toner in the development chamber enters the toner storage chamber. Easy to return. The toner circulates well between the developing chamber and the toner storage chamber, so that the deterioration of the toner is suppressed, and even when images with a low printing rate are output continuously, the occurrence of toner aggregation is suppressed, resulting in high quality. Stable images can be output stably. Further, in the present embodiment, the height of the wall 30b is set lower than the rotation center of the toner supply roller in order to better supply the toner onto the toner supply roller (on the supply member) by the stirring and conveying member.

  In the configuration of this embodiment, the gap between the frame forming the bottom of the developing chamber and the lower surface of the toner supply roller is set to 1.5 mm. The gap is desirably 5.0 mm or less in order to sufficiently convey the toner below the toner supply roller by the rotation of the toner supply roller.

  In this embodiment, there is only one drive input to the developing unit, and the developing roller, the toner supply roller, and the toner conveying member are connected by a gear (not shown) and are simultaneously driven during image formation. As a result, the toner conveying member supplies the toner while the toner supply roller is driven to rotate, and the toner circulation between the developing chamber and the toner storage chamber can be promoted.

  As described above, in the configuration of this embodiment, not only can the toner be stably supplied to the developing roller, but also the toner circulation that does not stagnate from the toner storage chamber to the development chamber and from the development chamber to the toner storage chamber can be realized. Can do.

  As described above, in this embodiment, the toner conveyed from the toner conveying member can be efficiently supplied to the nip portion between the toner supply roller and the developing roller by the driving rotation of the toner supply roller. In addition, toner in a region below the developing roller and the supply roller in the developing chamber (mainly toner that has been regulated and dropped by the developing blade) is returned to the toner storage chamber through the developing opening by the rotation of the toner supply roller. . Therefore, it is possible to provide a developing device, a process cartridge, and an image forming apparatus capable of stabilizing the density of a solid image and supplying a high-quality image while suppressing toner deterioration.

<Comparative Example 1>
In Comparative Example 1, a process cartridge having the configuration shown in FIG. The rotation direction of the toner supply roller shown in FIG. 5A is opposite to that in the first embodiment. The toner supply roller is driven to rotate at 100 rpm. Other configurations of the process cartridge and the entire configuration of the image forming apparatus are the same as those in the first embodiment.

<Comparative example 2>
In Comparative Example 2, a process cartridge having the configuration shown in FIG. In Comparative Example 2, as in the background art (Patent Document 1) described above, the rotation direction of the toner supply roller 20 is opposite to that in Example 1. A toner receiving member 30 is provided below the toner supply roller 20, and one end of a receiving sheet 32 is attached to the toner receiving member 30, and the receiving sheet 32 is brought into contact with the lower side of the supplying member with an appropriate linear pressure.

<Comparative Example 3>
In Comparative Example 3, as in the above-described background art (Patent Document 2), the toner conveying member 16 is disposed below the supply member having the configuration of Comparative Example 1 (see FIG. 5C). The toner conveying member 16 supplies toner to the toner supply roller 20 by rotating at a rotation speed of 200 rpm. Other configurations of the process cartridge and the entire configuration of the image forming apparatus are the same as those in the first comparative example.

<Experiment>
The following two experiments were conducted for the configurations of the above-described Examples and Comparative Examples.

(1) Evaluation of density stability of solid image As an evaluation of density stability of a solid image, a measurement of an image density reduction amount when continuous high-printing printing was performed.
The evaluation was performed after printing the 100 sheets after allowing the image forming apparatus to stand in the evaluation environment at 25.0 ° C. and 50% Rh for one day to adjust to the environment. The printing test for 100 sheets was performed by continuously passing a horizontal line recorded image having an image ratio of 5%. Thereafter, three solid images were continuously output, and evaluation shown below was performed using a spectrodensitometer 500 manufactured by X-Rite based on the density difference between the output leading edge and the trailing edge of the third solid image. The print test and evaluation image were output in a single color (black).
A: In a solid image, the density difference between the leading edge and the trailing edge of the paper is less than 0.2.
B: In solid image, density difference between paper leading edge and paper trailing edge is less than 0.2 to less than 0.3 C: In solid image, density difference between paper leading edge and paper trailing edge is 0.3 or more

(2) Presence / absence of toner aggregation The toner was evaluated by disassembling the image forming apparatus for which the endurance test was completed and investigating whether or not there was toner aggregation in the developing chamber.
A: No toner aggregation B: Toner aggregation occurred As a condition for the endurance test, 10,000 horizontal sheets having an image ratio of 1% were intermittently passed (printed) in an environment of 32.5 ° C. and 80% Rh. Intermittent paper passing means that the next printing is performed after waiting after printing.

  Here, “toner aggregation occurs” indicates a state where toner is pressed and aggregated below the developing roller and the supply roller. When image formation is performed in a state where toner aggregation occurs, image quality such as density unevenness is deteriorated.

(3) Presence / absence of toner fusion to the developing roller Evaluation of toner fusion to the developing roller is made by observing the developing roller of the image forming apparatus that has finished its durability and investigating whether or not toner fusion has occurred. did.
A: No toner fusing B: Some toner fusing (developing roller turns slightly white)
C: Toner fused (colored stain on developing roller)
The durability was the same as in the evaluation of (2) toner aggregation.

<Experimental result>
Table 1 shows the settings of the examples and the evaluation results thereof.

  First, the results of Comparative Example 1 will be described. In Comparative Example 1, the toner supply roller rotates in the counterclockwise direction. In the configuration of Comparative Example 1, much of the toner supplied on the toner supply roller is not supplied near the developing roller, but returns to the toner storage chamber from the developing opening by the rotation of the toner supplying roller. Therefore, it is difficult to ensure the density stability of the solid image.

  Further, as a result of continuing to output an image with a low printing rate, the toner is crushed and aggregated in a region below the toner supply roller and the developing roller in the developing chamber. Further, since the toner in the developing chamber does not return to the toner storage chamber, the toner in the vicinity of the developing blade is locally deteriorated, and toner fusion to the developing roller occurs.

Next, the result of Comparative Example 2 will be described. In the configuration of Comparative Example 2, since the toner receiving member is provided below the toner supply roller, the toner conveyed by the toner supply roller is stably supplied without falling into the toner storage chamber and is regulated by the developing blade. Only the remaining toner falls into the toner storage chamber. Therefore, the density stability of the solid image can be ensured, and the toner fusion to the developing roller does not aggregate near the developing blade. However, since the toner receiving sheet is in contact with the toner supply roller, the toner aggregates between the toner supplying member and the toner receiving sheet, and image density unevenness due to toner aggregation occurs.
Next, the result of Comparative Example 3 will be described. In Comparative Example 3, compared with the configuration of Comparative Example 1, a toner conveying member is disposed below the toner supply roller in the developing chamber. By disposing the toner conveying member, aggregation of the toner in the region below the toner supply roller and the developing roller in the developing chamber is suppressed, and at the same time, the toner below the toner conveying member is returned to the toner containing chamber. Therefore, problems such as density unevenness due to toner aggregation do not occur. However, since toner is contained and deteriorated due to friction between the toner and the toner conveying member, toner fusion to the developing roller was observed when an image with a low printing rate continued. Further, since it is necessary to provide a toner conveying member as an additional member in addition to the supply roller in the developing chamber, the apparatus configuration is complicated.

  Next, the results of this example will be described. In this embodiment, since the toner supply roller rotates in the clockwise direction in FIG. 2, the toner supplied onto the toner supply roller accumulates on the upper portion of the nip portion between the toner supply roller and the developing roller and accumulates toner. Form. As a result, the toner can be stably supplied to the developing roller, and the density stability of the solid image can be ensured. Further, the toner in the developing chamber and the toner in the region below the developing roller are returned to the toner containing chamber by the rotation of the toner supplying roller, so that toner aggregation and local deterioration do not occur. Further, it is not necessary to provide a toner supply member with a conveying member for conveying toner in the developing chamber, and the above evaluation result can be achieved with a simple apparatus configuration. That is, a good circulation of the developer is formed with a simple configuration, and a high-quality image can be stably formed.

  In this embodiment, an image forming apparatus capable of forming a color image is illustrated, but the present invention is not limited to this, and the same effect can be obtained even in an image forming apparatus capable of forming a monochrome image. Can be obtained.

  In the above-described embodiment, the printer is exemplified as the image forming apparatus. However, the present invention is not limited to this, and other image forming apparatuses such as a copying machine and a facsimile apparatus, or their functions are provided. Another image forming apparatus such as a combined machine, or an image forming apparatus that uses a recording material carrier and sequentially superimposes and transfers toner images of each color onto a recording material carried on the recording material carrier. The same effect can be obtained.

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 4 Developing unit 7 Process cartridge 13 Photosensitive unit 15 Developing chamber 17 Developing roller 18 Toner storage chamber 20 Toner supply roller 22 Stirring conveyance member 30 Developing opening 80 Toner 100 Image forming apparatus

Claims (7)

A developing device used in an electrophotographic image forming apparatus,
A developer carrying member for carrying the developer to develop the electrostatic latent image and the developer carrying member are arranged so as to form a nip portion of the developer, and the developer is supplied to the developer carrying member. A developing chamber comprising:
An accommodating portion that is disposed vertically below the developing chamber and accommodates the developer;
A conveying member that conveys the developer accommodated in the accommodating portion onto the supply member via an opening provided in the developing chamber;
Have
The developer carrier and the supply member rotate in a direction in which each surface moves from the upper end to the lower end of the nip portion,
A frame having a bottom of the developing chamber ;
Said bottom, one has a shape which protrudes toward the nip portion, the other a lower end of the opening, distance of the bottom and the supply member is a 5.0mm or less,
A developing device, wherein a lower end of the opening is positioned between an upper end and a lower end of the supply member in a vertical direction.   The developing device according to claim 1, wherein the frame forming the bottom of the developing chamber has a shape along the shape of the supply member.   The developing device according to claim 1, wherein the supply member includes a foam layer on a surface thereof.   The developing device according to claim 1, wherein the developer carrying member rotates in a direction in which a surface moves from an upper end to a lower end of the nip portion.   An image carrier that carries the electrostatic latent image and the developing device according to claim 1, wherein the image carrier is configured to be detachable from the main body of the image forming apparatus. To process cartridge.   An image forming apparatus comprising: an image carrier that carries the electrostatic latent image; and the developing device according to claim 1, and forms an image on a recording material.   An image forming apparatus comprising the process cartridge according to claim 5 and forming an image on a recording material.

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