JP2007156012A - Developing device, process cartridge and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device in which the stagnation of a developer on an upstream side of a developer regulation member is surely reduced and the stress acting on the developer is reduced to obviate the occurrence of surface staining and toner scattering, and to provide a process cartridge and an image forming apparatus. <P>SOLUTION: The developer regulation member 32d includes a plane 23d at which an angle α with a virtual tangent S2 of a developer carrier 23a passing the nearest point M at the developer carrier 23a most proximate to the developer regulation member 32d attains 120 to 180° in the rotating direction of the developer carrier 23a on the upstream side of the rotating direction. Further, the developer regulation member 32d is so disposed that the virtual normal K1 passing the nearest point M and the center of rotation of the developer carrier 23a is kept within a range from -90 to +45° (=β) in the rotating direction of the developer carrier 23a. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a developing device that develops a latent image formed on an image carrier, and a process cartridge and an image forming device including the developing device, and in particular, a developing device that uses a two-component developer, a process cartridge, and The present invention relates to an image forming apparatus.

  Conventionally, in an image forming apparatus using an electrophotographic system such as a copying machine, a printer, a facsimile, or a composite machine thereof, a two-component developer (added with an external additive or the like) composed of a non-magnetic toner and a magnetic carrier is added. In many cases, a developing device containing a case is used (see, for example, Patent Document 1).

  In Patent Document 1, etc., the developing device includes a developing roller (developer carrier), two transport screws, and the like. Then, according to toner consumption in the developing device, toner is appropriately supplied into the device from a toner supply port provided at one end of the device. The replenished toner is mixed with the developer in the developing device while being circulated in the device in the longitudinal direction (the same direction as the rotation axis of the developing roller) by two transport screws. A part of the mixed developer is supplied to the developing roller by the first conveying screw facing the developing roller. 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 developer is placed on the photosensitive drum at a position facing the photosensitive drum (image carrier). It adheres to the latent image.

  In such a developing device using a two-component developer, the external additive on the toner surface is buried in or detached from the toner or the carrier surface is exposed to stress while the developer is circulated in the device. It is known that a problem that the toner component is fixed (spent) occurs with time. When such a problem occurs, the charging ability of the toner and the carrier is reduced, and background contamination (a phenomenon in which toner adheres to a non-image area on the photosensitive drum or the output image) or toner scattering. Will occur.

  On the other hand, Patent Document 2 and the like describe a doctor blade for the purpose of reducing the stress received when the developer carried on the developing roller (developing sleeve) passes through the position of the doctor blade (regulating blade). Techniques for optimizing the arrangement of the are disclosed. Specifically, in Patent Document 2, etc., the doctor blade is disposed so as to face the developing roller in a range of 90 degrees in the rotation direction from the lowest point of the developing roller.

  In Patent Document 3, etc., the developer roller is opposed to the developer roller for the purpose of uniformly charging the developer carried on the developer roller (developer carrier) and passing through the position of the doctor blade (developer regulating plate). A technique for providing a curvature on the opposite surface of a doctor blade is disclosed.

Japanese Patent Laid-Open No. 10-69155 JP 2000-206792 A JP 2002-236417 A

  In the prior art, the developer stays on the upstream side of the doctor blade (developer regulating member), so that the stress applied to the developer cannot be sufficiently reduced.

  That is, on the upstream side of the doctor blade (the upstream side in the vicinity of the doctor gap), the developer regulated by the doctor blade is held by the magnetic pole formed on the developing roller and stays at that position. It was. When the developer carried on the developing roller (developer carrier) passes through the position of the doctor blade (doctor gap) in a compacted state where the developer stays in the vicinity of the doctor gap in this way, a strong stress is applied to the developer. It was hanging. As a result, the external additive on the toner surface is buried or detached from the toner, or the toner component is fixed (spent) on the carrier surface, resulting in background contamination and toner scattering.

  The technique described in Patent Document 2 described above cannot be expected to have an effect of sufficiently reducing the retention of developer on the upstream side of the doctor blade. In particular, in the technique disclosed in Patent Document 2, the doctor blade is disposed so as to face the developing roller in a range of 90 degrees in the rotation direction from the lowest point of the developing roller, and therefore, a photosensitive drum (image carrier). The degree of freedom in developing roller layout is greatly limited. Specifically, the developing roller is disposed below the photosensitive drum. Therefore, the layout of the image forming unit and the entire image forming apparatus is also greatly restricted.

  In addition, the technique of Patent Document 3 and the like aims to equalize and stabilize the charge amount of the developer passing through the doctor gap by providing a curvature on the opposite surface of the doctor blade. It is not possible to expect the effect of effectively suppressing the retention of the developer generated on the upstream side of the blade over time.

  The phenomenon in which the developer stays on the upstream side of the doctor blade and stresses the developer is particularly noticeable when a small particle size toner is used to improve the image quality. This is because when the toner has a small particle size, the fluidity of the developer is lowered and the developer tends to stay on the upstream side of the doctor blade.

  The present invention has been made to solve the above-described problems, and the retention of the developer on the upstream side of the developer regulating member is surely reduced, the stress applied to the developer is reduced, and background stains and An object of the present invention is to provide a developing device, a process cartridge, and an image forming apparatus in which toner scattering does not occur over time.

  The inventor of the present application has conducted research in order to solve the above-described problems. As a result, the developer on the upstream side of the developer regulating member is not greatly limited without greatly restricting the degree of freedom of the layout of the developer carrier relative to the image carrier. It came to know that there exists a structure and arrangement | positioning of the developer control member which can make a flow smooth.

  The present invention is based on this matter, that is, the developing device according to the first aspect of the present invention accommodates a developer having toner and a carrier and also forms a latent image formed on the image carrier. And a developer carrying body that rotates while carrying the developer, and that faces the developer carrying body, and on the developer carrying body. A developer regulating member that regulates the amount of the carried developer, and the developer regulating member passes through the nearest point in the developer carrying body closest to the developer regulating member. A plane having an angle with the virtual tangent of the body of 120 to 180 degrees in the rotation direction of the developer carrying member on the upstream side in the rotation direction, and passing through the closest point and the rotation center of the developer carrying member. Normal is before In which with respect to a virtual horizontal line passing through the center of rotation is arranged to be in the range of -90 to + 45 degrees in the rotation direction of the developer carrying member.

  According to a second aspect of the present invention, there is provided the developing device according to the first aspect, wherein the toner is formed so that a volume average particle diameter is within a range of 3 to 7 μm and an average circular shape is obtained. The degree is 0.95 or more.

  According to a third aspect of the present invention, in the developing device according to the first or second aspect, the developer carrying member includes a magnet body that forms a magnetic pole in the vicinity of the position of the nearest contact point. It is set.

  According to a fourth aspect of the present invention, there is provided the developing device according to any one of the first to third aspects, wherein the developer regulating member is inclined to the downstream side in the rotation direction of the developer carrier. The planar member is an inclined surface provided on the upstream surface in the rotational direction of the planar member.

  Further, in the developing device according to claim 5, in the invention according to any one of claims 1 to 4, a part or all of the developer regulating member is formed of a magnetic material. 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 carrier is formed so that the particle diameter is in a range of 20 to 60 μm. It is a thing.

  A developing device according to a seventh aspect of the present invention is the developing device according to any one of the first to sixth aspects, wherein the toner is formed to contain inorganic fine particles.

  A process cartridge according to an eighth aspect of the present invention includes the developing device according to any one of the first to seventh aspects and the image carrier.

  An image forming apparatus according to a ninth aspect of the present invention includes the developing device according to any one of the first to seventh aspects and the image carrier.

  In the present application, the “process cartridge” refers to a charging unit that charges the image carrier, a developing device (developing unit) that develops a latent image formed on the image carrier, and a cleaning on the image carrier. It is defined as a unit in which at least one of the cleaning units and the image carrier are integrated and configured to be detachable from the image forming apparatus main body.

  Since the present invention optimizes the configuration and arrangement of the developer regulating member, the retention of the developer on the upstream side of the developer regulating member is reliably reduced, the stress applied to the developer is reduced, and the background stains are reduced. In addition, it is possible to provide a developing device, a process cartridge, and an image forming apparatus in which toner scattering does not occur over time.

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 will be described with reference to FIG.
In FIG. 1, 1 is a main body of a color printer as an image forming apparatus, 2 is a writing unit that emits laser light based on image information, and 20Y, 20M, 20C, and 20BK are colors (yellow, magenta, cyan, and black). The corresponding process cartridge 21 is a photosensitive drum as an image carrier housed in each of the process cartridges 20Y, 20M, 20C, and 20BK, 22 is a charging unit that charges the photosensitive drum 21, 23Y, 23M, 23C, 23BK is a developing device (developing unit) for developing the electrostatic latent image formed on the photosensitive drum 21, 24 is a transfer bias roller for transferring the toner image formed on the photosensitive drum 21 to the intermediate transfer belt 27, Reference numeral 25 denotes a cleaning unit that collects untransferred toner on the photosensitive drum 21.

  In addition, 27 is an intermediate transfer belt on which toner images of respective colors are transferred in an overlapping manner, 28 is a second transfer bias roller for transferring the toner image formed on the intermediate transfer belt 27 to the transfer material P, and 29 is an intermediate transfer belt. 27 is an intermediate transfer belt cleaning unit that collects untransferred toner, 30 is a transfer belt that conveys a transfer material P onto which four color toner images are transferred, and 32Y, 32M, 32C, and 32BK are developing devices 23Y. , 23M, 23C, and 23BK, a toner replenishing unit that replenishes toner of each color, 61 a paper feeding unit that accommodates a transfer material P such as transfer paper, and 66 a fixing that fixes an unfixed image on the transfer material P Indicates the part.

Here, each of the process cartridges 20Y, 20M, 20C, and 20BK is obtained by integrating the photosensitive drum 21, the charging unit 22, and the cleaning unit 25, respectively. The process cartridges 20Y, 20M, 20C, and 20BK are exchanged with respect to the apparatus main body 1 in a predetermined exchange cycle. Similarly, the developing devices 23Y, 23M, 23C, and 23BK are also exchanged with respect to the apparatus main body 1 in a predetermined exchange cycle.
Image formation of each color (yellow, magenta, cyan, black) is performed on the photosensitive drum 21 in each of the process cartridges 20Y, 20M, 20C, and 20BK.

Hereinafter, an operation during normal color image formation in the image forming apparatus will be described.
Each of the four photosensitive drums 21 rotates in the clockwise direction in FIG. First, the surface of the photosensitive drum 21 is uniformly charged at a position facing the charging unit 22 (a charging process). Thereafter, the surface of the charged photosensitive drum 21 reaches the irradiation position of each laser beam.

  On the other hand, in the writing unit 2, laser light corresponding to the image signal is emitted from the light source corresponding to each color. The laser light is incident on the polygon mirror 3 and reflected, and then passes through the lenses 4 and 5. The laser light after passing through the lenses 4 and 5 passes through different optical paths for each of the yellow, magenta, cyan, and black color components (this is an exposure process).

The laser beam corresponding to the yellow component is reflected by the mirrors 6 to 8 and then irradiated onto the surface of the photosensitive drum 21 of the first process cartridge 20Y from the left side of the drawing. At this time, the yellow component laser light is scanned in the rotation axis direction (main scanning direction) of the photosensitive drum 21 by the polygon mirror 3 that rotates at high speed. Thus, an electrostatic latent image corresponding to the yellow component is formed on the photosensitive drum 21 charged by the charging unit 22.
Similarly, the laser beam corresponding to the magenta component is reflected by the mirrors 9 to 11 and then irradiated to the surface of the photosensitive drum 21 of the second process cartridge 20M from the left side of the paper, thereby causing an electrostatic latent image corresponding to the magenta component. An image is formed. The cyan component laser light is reflected by the mirrors 12 to 14 and then irradiated to the surface of the photosensitive drum 12 of the third process cartridge 20C from the left side of the drawing to form a cyan component electrostatic latent image. The black component laser light is reflected by the mirror 15 and then irradiated on the surface of the photosensitive drum 21 of the fourth process cartridge 20BK from the left side of the paper, thereby forming an electrostatic latent image of black component.

Thereafter, the surface of the photosensitive drum 21 on which the electrostatic latent images of the respective colors are formed further rotates to reach positions facing the developing devices 23Y, 23M, 23C, and 23BK, respectively. Then, the respective color toners are supplied from the developing devices 23Y, 23M, 23C, and 23BK onto the photosensitive drum 21, and the latent image on the photosensitive drum 21 is developed (this is a developing step).
Thereafter, the surface of the photosensitive drum 21 after the development process reaches a position facing the intermediate transfer belt 27. Here, the transfer bias roller 24 is installed at each facing position so as to contact the inner peripheral surface of the intermediate transfer belt 27. Then, the image of each color formed on the photosensitive drum 21 is sequentially transferred onto the intermediate transfer belt 27 at the position of the transfer bias roller 24 (first transfer step).

Then, the surface of the photosensitive drum 21 after the first transfer process reaches a position facing the cleaning unit 25. The untransferred toner remaining on the photosensitive drum 21 is collected by the cleaning unit 25 (this is a cleaning process).
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.

On the other hand, the surface of the intermediate transfer belt 27 on which the images of the respective colors on the photosensitive drum 21 are transferred in an overlapping manner travels in the direction of the arrow in the drawing and reaches the position of the second transfer bias roller 28. Then, the full color image on the intermediate transfer belt 27 is secondarily transferred onto the transfer material P at the position of the second transfer bias roller 28 (second transfer step).
Thereafter, the surface of the intermediate transfer belt 27 reaches the position of the intermediate transfer belt cleaning unit 29. Then, the untransferred toner on the intermediate transfer belt 27 is collected by the intermediate transfer belt cleaning unit 29, and a series of transfer processes on the intermediate transfer belt 27 is completed.

Here, the transfer material P is transported from the paper feeding unit 61 to the position of the second transfer bias roller 28 via the transport guide 63, the registration roller 64, and the like.
Specifically, the transfer paper P fed by the paper feed roller 62 from the paper feed unit 61 that stores the transfer material P is guided to the registration roller 64 after passing through the conveyance guide 63. The material P to be transferred that has reached the registration roller 64 is conveyed toward the position of the second transfer bias roller 28 in synchronization with the toner image on the intermediate transfer belt 27.

Thereafter, the transfer material P onto which the full color image has been transferred is guided to the fixing unit 66 by the transfer belt 30. In the fixing unit 66, the color image is fixed on the transfer material P at the nip between the heating roller 67 and the pressure roller 68.
Then, the transfer material P after the fixing process is discharged as an output image outside the apparatus main body 1 by the paper discharge roller 69, and a series of image forming processes is completed.

Next, the image forming unit of the image forming apparatus will be described in detail with reference to FIGS. FIG. 2 is a cross-sectional view showing the image forming unit, and FIG. 3 is a cross-sectional view taken along the line AA showing the developing device.
The four image forming units installed in the apparatus main body 1 have substantially the same structure except that the color of the toner T used in the image forming process is different. Therefore, the alphabet of reference numerals in the process cartridge, the developing device, and the toner supply unit (Y, M, C, BK) is removed for illustration.

  As shown in FIG. 2, the process cartridge 20 mainly contains a photosensitive drum 21 as an image carrier, a charging unit 22, and a cleaning unit 25 integrally in a case 26. The cleaning unit 25 is provided with a cleaning blade 25 a and a cleaning roller 25 b that are in contact with the photosensitive drum 21.

  The developing device 23 (developing unit) mainly includes a developing roller 23a as a developer carrying member facing the photosensitive drum 21, a first conveying screw 23b facing the developing roller 23a, and a first member via a partition member 23e. A second conveying screw 23c facing the conveying screw 23b, a doctor blade 23d as a developer regulating member facing the developing roller 23a, a toner concentration sensor 23g for detecting the toner concentration of the developer G in the developing device 23, Consists of. In the developing device 23, a two-component developer G composed of carrier C and toner T is accommodated. Referring to FIG. 3, developing roller 23a is fixed inside and forms a plurality of magnetic poles (see FIG. 4) on the outer peripheral surface of the roller, and rotates around magnet body 23a1. And a sleeve 23a2. The doctor blade 23d is a plate-like member arranged to be inclined downstream in the rotation direction of the developing roller 23a, and an inclined surface 23d1 is formed on the upstream surface in the rotation direction (see FIG. 5). .

The above-described image forming process will be described in more detail with a focus on the developing process.
The developing roller 23a rotates in the direction of the arrow in FIG. As shown in FIG. 3, the developer G in the developing device 23 is generated by the rotation of the first conveying screw 23 b and the second conveying screw 23 c arranged so as to interpose the partition member 23 e therebetween in the arrow direction. It circulates in the longitudinal direction while being agitated and mixed with the toner T replenished from the replenishing part 32 through the replenishing port 23f (circulation in the direction of the broken arrow in FIG. 3).

  Then, the toner T that is frictionally charged and adsorbed on the carrier C is pumped onto the developing roller 23a together with the carrier C by an agent pumping pole (P3 magnetic pole in FIG. 4) formed on the developing roller 23a. The developer G carried on the developing roller 23a then reaches the position of the doctor blade 23d (the position of the doctor gap). The developer G on the developing roller 23a is adjusted (regulated) to an appropriate amount at the position of the doctor blade 23d, and then reaches a position facing the photosensitive drum 21 (development region).

  Thereafter, in the development area, the toner T in the developer G adheres to the electrostatic latent image formed on the surface of the photosensitive drum 21. Specifically, the toner T is latently exposed by the electric field formed by the potential difference (development potential) between the latent image potential (exposure potential) of the image area irradiated with the laser light L and the development bias applied to the development roller 23a. Adhere to the image.

  Thereafter, most of the toner T adhering to the photosensitive drum 21 in the developing process is transferred onto the intermediate transfer belt 27. The untransferred toner T remaining on the photosensitive drum 21 is collected in the cleaning unit 25 by the cleaning blade 25a and the cleaning roller 25b.

  Here, on the outer peripheral surface of the sleeve 23a2 of the developing roller 23a, a plurality of magnetic poles are formed by the magnet body 23a1. Specifically, with reference to FIG. 4, the magnet body 23a1 includes three N-pole magnet portions and two S-pole magnet portions. With these magnet portions, a developer pumping pole (P3 magnetic pole) for pumping the developer G onto the developing roller 23a, and a transport for transporting the developer G carried on the developing roller 23a to the downstream side of the doctor blade 23d. Developing the pole (P4 magnetic pole), the transport pole (P5 magnetic pole) for transporting the developer G to the development area, the main pole (P1 magnetic pole) formed in the development area, and the developer G after passing through the development area A magnetic distribution including a transport pole (P2 magnetic pole) that transports to the agent separation pole (between the P2 magnetic pole and the P3 magnetic pole) to be separated from the roller 23a is formed on the developing roller 23a. Due to the magnetic force distribution, the developer G moves on the developing roller 23a as the sleeve 23a2 rotates.

  As shown in FIG. 4, the doctor blade 23d is disposed so that its closest point (the position closest to the developing roller 23a) is directly above the P4 magnetic pole. That is, the developing roller 23a is provided with a magnet body 23a1 that forms a P4 magnetic pole in the vicinity of the position of the closest point M (the position closest to the doctor blade 23d). With such a configuration, developer spikes are formed on the P4 magnetic poles in which the magnetic lines of force extend in the normal direction, so that the developer spikes by the tip of the doctor blade 23d can be facilitated. Therefore, the stress applied to the developer whose amount is regulated by the doctor blade 23d can be reduced.

  Here, the toner supply unit 32 provided in the apparatus main body includes a toner bottle 33 configured to be replaceable, a toner hopper unit 34 that holds and rotates the toner bottle 33 and supplies fresh toner T to the developing device 23. , Is composed of. The toner bottle 33 contains toner T (any one of yellow, magenta, cyan, and black). In addition, a spiral protrusion is formed on the inner peripheral surface of the toner bottle 33.

  The toner T in the toner bottle 33 is appropriately replenished into the developing device 23 from the replenishing port 23f as the toner T in the developing device 23 is consumed. The consumption of the toner T in the developing device 23 is detected by a toner concentration sensor 23g that magnetically detects the toner concentration in the device 23. The replenishing port 23f is provided at one end in the longitudinal direction of the second transport screw 23c (the left-right direction in FIG. 3) and above the second transport screw 23c.

  In the toner T (nonmagnetic toner) used in the present embodiment, a binder resin, a wax component, a colorant, and the like are mixed by a mixer or the like (a charge control agent may be further added and mixed), and heat. After kneading using a kneader such as a roll or an extruder, the mixture is cooled and solidified, pulverized with a jet mill or the like, and then classified. The toner has a substantially spherical shape and a small particle size, and a toner having a relatively narrow particle size distribution. Such a toner can be manufactured by using a polymerization method, and the image quality is high and the manufacturing cost can be reduced.

  Further, the toner in the present exemplary embodiment is formed so that its volume average particle diameter is in the range of 3 to 7 μm. Generally, the smaller the toner particle size, the higher the resolution and the higher quality the image can be obtained. If the toner particle diameter exceeds the above range, it will be difficult to obtain a high-resolution image.

Further, the toner in the present exemplary embodiment is formed so that the average circularity is 0.95 or more.
The closer the toner particle shape is to a spherical shape, the more suitable for developing a high-resolution image. Here, the average circularity can be measured by a flow type particle image analyzer “FPIA-1000” (manufactured by Toa Medical Electronics Co., Ltd.).
The specific measurement method is as follows. First, 0.1 to 0.5 ml of a surfactant (preferably an alkylbenzene sulfonate) is added as a dispersant to 100 to 150 ml of water from which impure solids have been removed in advance. About 0.1 to 0.5 g of a measurement sample is added. Then, the suspension in which the sample is dispersed is subjected to a dispersion process for about 1 to 3 minutes with an ultrasonic disperser, and the shape and distribution of the toner are measured by the above-described analyzer with a dispersion concentration of 3000 to 10,000 / μl. To obtain the average circularity.

Here, the toner formed with an average circularity of 0.95 or more is almost spherical, and the toner can move more easily between the carriers than the deformed toner (general pulverized toner). Therefore, the fluidity as the developer is improved, and the retention of the developer near the doctor blade 23d (particularly on the upstream side) is reduced.
Further, if the stress applied to the developer at the position of the doctor blade 23d (the stress at the time of regulation) is reduced, the toner may not be able to hold a sufficient charge amount. In this case, since the toner surface can easily come into contact with the carrier uniformly, a sufficient charge amount can be secured.

  Furthermore, as an external additive for assisting the fluidity, developability and chargeability of the toner, inorganic fine particles such as silica, alumina and titanium oxide can be used. The primary particle diameter of the inorganic fine particles is preferably 5 nm to 2 μm, and particularly preferably 5 nm to 500 nm. Moreover, it is preferable that the specific surface area by BET method is 20-500 m <2> / g. The use ratio of the inorganic fine particles is preferably 0.01 to 5% by weight of the toner, and particularly preferably 0.5 to 3.0% by weight.

  The content ratio of the carrier and the toner in the developer is preferably 1 to 10 parts by weight of the toner with respect to 100 parts by weight of the carrier. As the magnetic carrier, iron powder, ferrite powder, magnetite powder, magnetic resin carrier or the like having a particle diameter of about 20 to 200 μm can be used. As the coating material, amino resins, polyvinyl and polyvinylidene resins, polystyrene resins, silicone resins, and the like can be used.

The carrier particle size is suitably 20-100 μm, more preferably 20-60 μm. By reducing the particle size of the carrier in accordance with the particle size of the toner and increasing the surface area, it becomes possible to make the charging of the toner uniform, and the magnetic brush that rises on the developing roller 23a becomes dense. In addition, it is possible to perform further high-definition development. In addition, the carrier in this Embodiment is formed so that the particle size may be in the range of 20 to 60 μm.
By using the developer (toner and carrier) described above, the retention of the developer is reduced in the vicinity of the doctor blade 23d, and the developer is smoothly circulated in the developing device 23.

Next, a doctor blade 23d as a developer regulating member, which is characteristic in the present embodiment, will be described.
As a result of repeated research, the inventor of the present application has a high degree of freedom in the layout of the developing roller 23a with respect to the photosensitive drum 21, and the flow of the developer on the upstream side of the doctor blade 23d can be made smooth. It came to know that there is composition and arrangement.

  That is, as shown in FIG. 5, the doctor blade 23d as a developer regulating member and the virtual tangent S2 of the developing roller 23a passing through the closest point M (the position closest to the doctor blade 23d) in the developing roller 23a. Is provided on the upstream side in the rotational direction with a plane 23d1 (on the broken line S1) that is 120 to 180 degrees in the rotational direction of the developing roller 23a. The flat surface 23d1 is an inclined surface provided on a surface on the upstream side (on the upstream side in the rotation direction of the developing roller 23a) of the doctor blade 23d (plate-shaped member) formed in a plate shape.

  Further, in the doctor blade 23d, a virtual normal line K1 passing through the closest point M and the rotation center of the developing roller 23a is in a rotation direction (in the rotation direction of the developing roller 23a) with respect to a virtual horizontal line K2 passing through the rotation center of the developing roller 23a. In the range of −90 to +45 degrees (= β). That is, the angle β of the virtual normal line K1 with respect to the virtual horizontal line K2 is set to be within a range of −90 to +45 degrees. Here, with respect to the angle β, the rotation direction of the developing roller 23a is + (plus) and the counter-rotation direction is − (minus) with reference to the position of 0 degree in FIG.

In the present embodiment, as shown in FIG. 5, the angle α is set to about 120 degrees, and the angle β is set to about +45 degrees.
Thus, if the relationship of 120 ≦ α ≦ 180 and −90 ≦ β ≦ + 45 is satisfied, the flow of the developer in the vicinity of the doctor blade 23d can be made smooth as indicated by the broken line arrow in FIG. Therefore, the shape and arrangement of the doctor blade 23d are not limited to those of the present embodiment. For example, as shown in FIG. 6, the angle α is set to about 120 degrees and the angle β is set to about −90 degrees. It can also be set.

  Here, when the angle α is less than 120 degrees, the developer stays on the upstream side of the doctor blade 23d. More specifically, the excessive developer released from the developing roller 23a by the doctor blade 23d stays in a state where it is further pushed up by the developer conveyed thereafter.

  FIG. 6 is a cross-sectional view showing a conventional developing device. In the developing device 23, the angle α of the doctor blade 23d is set to about 90 degrees. As shown in FIG. 6, in the conventional developing device, the developer is trapped by the magnetic force generated from the magnetic poles on the upstream side of the doctor blade 23 d, and the developer retention portion A is formed. The developer in the staying part A becomes compacted by the developer conveyed thereafter, and is attracted by the magnetic force toward the surface of the developing roller 23a, so that a great stress is applied to the developer conveyed to the developing region. End up. As a result, the external additive on the surface of the toner is buried or detached from the toner, or the toner component is fixed (spent) on the surface of the carrier. Toner scattering occurs. Furthermore, the surface of the developing roller 23a may be scraped by applying a great deal of stress to the developer passing through the doctor gap.

In the present embodiment, since the angle α is optimized and the flow of the developer on the upstream side of the doctor blade 23d is made smooth, the above-described problems are eliminated.
The upper limit of the angle α is set to 180 degrees because it is a geometrically necessary condition for the doctor blade 23d to mechanically scrape a part of the developer carried on the developing roller 23a.

  On the other hand, when the angle β exceeds +45 degrees, the developer scraped off by the doctor blade 23d is put on the doctor blade 23d and the circulation of the developer becomes worse. On the other hand, when the angle β is less than −90 degrees, it becomes difficult in terms of layout to provide a part for pumping up the developer and a part for releasing the developer on the developer roller 23a. Therefore, the developer can be circulated without stagnation within the range of the angle β in the present embodiment.

  Further, in the present embodiment, an inclined surface 23d1 (a flat surface serving as a developer contact surface) is provided on the upstream surface of the doctor blade 23d as a plate-like member, and the tip portion (the closest contact M side). It is formed so that the plate thickness becomes thinner as it goes to. As a result, the stress applied to the developer flowing in the vicinity of the doctor blade 23 can be reduced while ensuring the strength required for the doctor blade 23d.

  The doctor blade 23d is preferably partly or entirely formed of a magnetic material. When a part or all of the doctor blade 23d is formed of a magnetic material, the developer carried on the developing roller 23a easily rises at the position of the doctor gap, and the stress applied to the developer is further reduced. The developer amount is optimized.

As described above, in the present embodiment, since the configuration and arrangement of the doctor blade 23d (developer regulating member) are optimized, the developer in the vicinity of the doctor blade 23d (particularly on the upstream side). Retention is reliably reduced. Therefore, the stress applied to the developer is reduced, and the occurrence of background stains and toner scattering is suppressed over time.
In particular, by using a toner having a volume average particle diameter of 3 to 7 μm and an average circularity of 0.95 or more, the retention of the developer near the doctor blade 23d is further reduced while ensuring high image quality. be able to.

  In the present embodiment, the developing device 23 is configured separately from the process cartridge 20. On the other hand, the developing device 23 can be integrated with the process cartridge 20. Further, the developing device 23 is integrated with at least one of the photosensitive drum 21, the charging unit 22, the transfer unit 24, the cleaning unit 25, and the toner replenishing unit 32 to constitute a unit. It can also be detachably installed in the apparatus main body 1. In such a case, the same effect as in the present embodiment can be obtained, and the maintainability of the image forming unit is improved.

  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. In addition, 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 suitable for implementing the present invention can be achieved.

1 is an overall configuration diagram illustrating an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a cross-sectional view illustrating an image forming unit in the image forming apparatus of FIG. 1. FIG. 3 is a cross-sectional view showing an AA cross section of the developing device in the image forming unit of FIG. 2. It is a figure which shows magnetic force distribution formed on a developing roller. FIG. 4 is a partially enlarged view showing the configuration and arrangement of a developer regulating member. FIG. 6 is a partially enlarged view showing another configuration and arrangement of a developer regulating member. It is sectional drawing which shows the conventional image development apparatus.

Explanation of symbols

1 image forming apparatus body (apparatus body),
20, 20Y, 20M, 20C, 20BK Process cartridge,
21 photosensitive drum (image carrier), 22 charging unit,
23, 23Y, 23M, 23C, 23BK Developing device (developing unit),
23a Development roller (developer carrier),
23a1 magnet body, 23a2 sleeve,
23b 1st conveyance screw, 23c 2nd conveyance screw,
23d doctor blade (developer regulating member, plate-like member),
23d1 plane (inclined surface),
25 Cleaning section,
32, 32Y, 32M, 32C, 32BK toner supply unit,
33 Toner bottle, 34 Toner hopper section.

Claims (9)

A developing device for containing a developer having toner and a carrier and developing a latent image formed on an image carrier,
A developer carrying body facing the image carrying body and rotating carrying the developer;
A developer regulating member that faces the developer carrying body and regulates the amount of the developer carried on the developer carrying body,
The developer regulating member has an angle with a virtual tangent of the developer carrying body passing through the closest point in the developer carrying body closest to the developer regulating member in the rotation direction of the developer carrying body. A rotation plane of the developer carrying member with respect to a virtual horizontal line passing through the rotation center, the virtual normal passing through the closest point and the rotation center of the developer carrying member. A developing device arranged in a range of −90 to +45 degrees in the direction. 2. The toner according to claim 1, wherein the toner has a volume average particle diameter of 3 to 7 μm and an average circularity of 0.95 or more. Development device. 3. The developing device according to claim 1, wherein the developer carrying body includes a magnet body that forms a magnetic pole in the vicinity of the position of the nearest contact point. 4. The developer regulating member is a plate-like member arranged to be inclined downstream in the rotation direction of the developer carrier,
The developing device according to claim 1, wherein the flat surface is an inclined surface provided on a surface on the upstream side in the rotation direction of the plate-like member. The developing device according to claim 1, wherein a part or all of the developer regulating member is made of a magnetic material. The developing device according to claim 1, wherein the carrier is formed so as to have a particle diameter in a range of 20 to 60 μm. The developing device according to claim 1, wherein the toner is formed so as to contain inorganic fine particles. 8. A process cartridge comprising the developing device according to claim 1 and the image carrier integrally. An image forming apparatus comprising the developing device according to claim 1 and the image carrier.

Images