Development device

Abstract

To suppress the occurrence of an image defect in a developing device provided with a sheet part abutting on a developer in a region where the developer on a developing rotary body is napped.SOLUTION: Provided is a development device including: a cover portion provided facing a developing rotor in a non-contact state and configured to cover the developing rotor; a first sheet portion provided fixed to the cover portion and arranged to contact the developing rotor; and a second sheet portion provided fixed to the cover portion and arranged to overlap a surface of the first sheet portion on a side opposite to a surface that contacts the developing rotor, wherein a free end of the first sheet portion is located downstream of a position where a regulating portion faces the developing rotor in a rotation direction of the developing rotor and upstream of the closest portion between the developing rotor and an image carrier, a free end of the second sheet portion is located downstream of an upstream half position of a first magnetic pole in the rotation direction of the developing rotor and at a position where it does not contact the image carrier, and the rigidity of the second sheet portion is greater than the rigidity of the first sheet portion.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a developing device that develops an electrostatic latent image formed on an image carrier with a developer containing toner and a carrier.

Background Art

[0002] In an image forming apparatus using an electrophotographic method or the like, an electrostatic latent image formed on a photoreceptor drum (image carrier) is developed into a toner image by a developing device. As such a developing device, one using a two-component developer containing toner and a carrier has been conventionally used.

[0003] The developing device includes a developing container that houses a developer containing toner and a carrier, a rotatable developing sleeve (developing rotator) that holds the developer to develop the electrostatic latent image formed on the photoreceptor drum, and a regulating blade that regulates the amount of the developer held on the developing sleeve.

[0004] The developer conveyed to the developing area where the electrostatic latent image is developed by the developing sleeve forms a magnetic brush by standing up in the developing area. Then, the toner in the developer supplied from the magnetic brush in the developing area is supplied to the electrostatic latent image, and the electrostatic latent image is developed into a toner image. On the other hand, a part of the toner in the developer supplied from the magnetic brush in the developing area may scatter from the developing area without adhering to the electrostatic latent image in the developing area.

[0005] Patent Document 1 describes a developing device in which a flexible member is provided so as to contact the developer on the developing sleeve in a first area where the developer on the developing sleeve stands up, and so as to be close to the developing sleeve in a second area where the developer on the developing sleeve does not stand up.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] In the configuration of Patent Document 1, since a flexible member is brought into contact with the developer in the first region where the developer on the developing sleeve stands up, even if toner adheres to the opposing surface of the flexible member facing the developing sleeve, the toner adhering to the opposing surface can be removed by the standing-up developer.

[0008] However, when a flexible member is brought into contact with the developer in the first region where the developer on the developing sleeve stands up as in the configuration of Patent Document 1, there is a risk that the flexible member is lifted by the standing-up developer and the tip of the flexible member floats from the developing sleeve.

[0009] If the operation of the developing device is continued with the tip of the flexible member floating from the developing sleeve, the scattered toner accumulates on the tip of the flexible member. And when the toner accumulated on the tip of the flexible member collapses due to its own weight and falls onto the photosensitive drum, there is a risk of image defects such as toner stains called toner dropout occurring on the image.

[0010] The present invention has been made in view of the above problems. An object of the present invention is to provide a configuration capable of suppressing the occurrence of image defects in a developing device provided with a sheet portion that contacts the developer in a region where the developer on the developing rotator stands up.

Means for Solving the Problems

[0011] To achieve the above object, a developing device according to one aspect of the present invention has the following configuration. That is, a developing container that stores a developer containing toner and a carrier, a developing rotator that carries and conveys the developer to develop an electrostatic latent image formed on an image carrier, a first magnetic pole that is non-rotatably fixed inside the developing rotator and is disposed at the closest portion between the developing rotator and the image carrier, and a second magnetic pole that is disposed adjacent to the first magnetic pole upstream of the first magnetic pole with respect to the rotation direction of the developing rotator and has a different polarity from the first magnetic pole. A magnet having the second magnetic pole, a regulating unit that is provided to face the developing rotator non-contactingly and regulates the amount of the developer carried by the developing rotator, a cover unit that is provided to face the developing rotator non-contactingly and covers the developing rotator, a first sheet unit that is fixedly provided on the cover unit and is disposed to contact the developing rotator, and a second sheet unit that is fixedly provided on the cover unit and is disposed to overlap with a surface opposite to the surface of the first sheet unit on the side where the first sheet unit contacts the developing rotator. The free end of the first sheet unit is downstream of the position where the regulating unit faces the developing rotator with respect to the rotation direction of the developing rotator and upstream of the closest portion between the developing rotator and the image carrier. The free end of the second sheet unit is downstream of the upstream half-value position of the first magnetic pole with respect to the rotation direction of the developing rotator and is at a position where it does not contact the image carrier. The stiffness of the second sheet unit is greater than the stiffness of the first sheet unit.

[0012] In addition, a developing device according to another aspect of the present invention for achieving the above object has the following configuration. That is, a developing container that houses a developer containing toner and a carrier, a developing rotator that carries and conveys the developer to develop an electrostatic latent image formed on an image carrier, a first magnetic pole that is non-rotatably fixed inside the developing rotator and is disposed at the closest part between the developing rotator and the image carrier, and a second magnetic pole that is disposed adjacent to the first magnetic pole upstream of the first magnetic pole with respect to the rotation direction of the developing rotator and has a different polarity from the first magnetic pole, a regulating unit that is provided to face the developing rotator in a non-contact manner and regulates the amount of the developer carried on the developing rotator, a cover unit that is provided to face the developing rotator in a non-contact manner and covers the developing rotator, and a sheet unit that is fixedly provided to the cover unit and is disposed so as to contact the developing rotator. The free end of the sheet unit is located downstream of the position where the regulating unit faces the developing rotator with respect to the rotation direction of the developing rotator and upstream of the closest part between the developing rotator and the image carrier, and the stiffness of the sheet unit in a region from the fixed end of the sheet unit to the upstream half-value position of the first magnetic pole with respect to the rotation direction of the developing rotator is greater than the stiffness of the sheet unit at the free end of the sheet unit.

Advantages of the Invention

[0013] According to the present invention, in a developing device including a sheet unit that contacts a developer in a region where the developer stands up on a developing rotator, the occurrence of image defects can be suppressed.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Embodiments for Carrying Out the Invention

[0015] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the present invention according to the claims, and not all combinations of the features described in the first embodiment are essential for the solution means of the present invention. The present invention can be implemented in various applications such as printers, various printing machines, copiers, FAX machines, and multifunction devices.

[0016] [First Embodiment] (Configuration of the Image Forming Apparatus) First, the configuration and operation of the entire image forming apparatus will be described with reference to FIG. 1. FIG. 1 is a cross-sectional view showing the configuration of the image forming apparatus 100 according to the first embodiment.

[0017] The image forming apparatus 100 is a full-color image forming apparatus, and in the case of the first embodiment, for example, it is an MFP (Multi-Function Peripheral) having a copy function, a printer function, and a scan function.

[0018] As shown in FIG. 1, the image forming apparatus 100 is provided with image forming units PY, PM, PC, and PK that perform image forming processes for toner images of four colors, yellow (Y), magenta (M), cyan (C), and black (K), in parallel. Each of the color image forming units PY, PM, PC, and PK includes chargers 21Y, 21M, 21C, and 21K, and developing devices 1Y, 1M, 1C, and 1K. Each of the color image forming units PY, PM, PC, and PK also includes exposure devices 22Y, 22M, 22C, and 22K, photosensitive drums 2Y, 2M, 2C, and 2K, and cleaning devices 26Y, 26M, 26C, and 26K. The image forming apparatus 100 also includes a transfer device 3 and a fixing device 4.

[0019] Since the configurations of the color image forming units PY, PM, PC, and PK are the same, hereinafter, an image forming apparatus will be used for explanation in which symbols obtained by omitting the Y, M, C, and K at the end of the symbols representing the distinctions between the image forming apparatuses Y, M, C, and K are attached to the constituent members.

[0020] The photosensitive drum 2 (image carrier) is rotatably provided and rotates in the direction of arrow a at a process speed of 630 mm / sec. The surface of the photosensitive drum 2 is uniformly charged by the charger 21 and exposed to light modulated according to an information signal by an exposure device 22 (light writing unit) such as a laser, and a latent image (electrostatic latent image) is formed.

[0021] The electrostatic latent image formed on the surface of the photosensitive drum 2 is visualized as a toner image in a process as described later by the developing device 1. The visualized toner image is transferred to a transfer belt 30 that constitutes the transfer device 3 at a primary transfer unit 31 provided at each station. The toner image transferred onto the transfer belt 30 is conveyed to a secondary transfer unit 32.

[0022] Thereafter, the toner conveyed to the secondary transfer unit 32 is transferred onto a sheet P which is a recording material, and then the toner image is fixed onto the sheet P by the fixing device 4 to obtain an image.

[0023] The transfer residual toner on the photoreceptor drum 2 and the toner remaining on the transfer belt 30 after fixing are removed by the cleaning devices 26 and 33. Also, the toner in the developer consumed in image formation is replenished together with the carrier from the toner cartridge.

[0024] (Configuration of the developing device) Subsequently, the configuration and operation of the developing device according to the first embodiment will be described with reference to FIG. 2. FIG. 2 is a cross-sectional view showing the configuration of the developing device 1 according to the first embodiment.

[0025] The developing device 1 includes a developing container 110 that houses a two-component developer (hereinafter simply referred to as the developer) containing toner and a carrier.

[0026] In the first embodiment, as the developer, non-magnetic toner particles (toner) and magnetic carrier particles (carrier) are used. The non-magnetic toner particles are colored resin particles containing a binder resin, a colorant, and, if necessary, other additives, and an external additive such as colloidal silica fine powder is externally added to the surface thereof.

[0027] The non-magnetic toner particles used in the first embodiment are negatively charged polyester-based resins, and the volume average particle diameter is about 4 μm to 8 μm. The magnetic carrier particles are composed of magnetic metal particles such as iron, nickel, cobalt, etc. whose surfaces have been oxidized, for example, and the volume average particle diameter is about 40 μm.

[0028] The inside of the developing container 110 is vertically partitioned into a developing chamber 118 and a stirring chamber 119 by a partition wall 117 extending in a direction perpendicular to the paper surface at a substantially central portion inside the developing container 110, and the developer in which the toner and the magnetic carrier are mixed is accommodated in the developing chamber 118 and the stirring chamber 119.

[0029] In the developing chamber 118 and the stirring chamber 119, a first conveying screw 114 and a second conveying screw 115, which are circulation means for stirring and conveying the developer and circulating the developer in the developing container 110, are respectively arranged.

[0030] The first transfer screw 114 is disposed substantially parallel to the axial direction of rotation of a rotatable developing sleeve (developing rotating body) at the bottom of the developing chamber 118. When the first transfer screw 114 is rotationally driven, the developer in the developing chamber 118 is conveyed in one direction along the axial direction of the rotation axis of the first transfer screw 114. Further, the second transfer screw 115 is disposed substantially parallel to the first transfer screw 114 at the bottom in the stirring chamber 119. When the second transfer screw 115 is rotationally driven, the developer in the stirring chamber 119 is conveyed in a direction opposite to that of the first transfer screw 114.

[0031] In this way, the developer conveyed by the rotation of the first transfer screw 114 and the second transfer screw 115 circulates between the developing chamber 118 and the stirring chamber 119 through the openings (communication portions) at both ends of the partition wall 117.

[0032] The developer in the developing chamber 118 is configured to supply the developer from the regulating blade (regulating portion) 113 and the opening of the partition wall 117 by the rotational drive of the first transfer screw 114. The first transfer screw 114 and the second transfer screw 115 have a screw structure in which stirring blades made of a non-magnetic material are provided spirally around the rotation axis. Each screw diameter is φ20 mm, the screw pitch is 30 mm, and the rotation speed is set to 630 rpm.

[0033] An opening is provided at a portion of the developing container 110 close to the photosensitive drum 2. The developing container 110 is provided with two upstream developing sleeves 111 (first developer carriers) and downstream developing sleeves 112 (second developer carriers) as developer carriers. The upstream developing sleeve 111 and the downstream developing sleeve 112 each have a thickness of 1 mm, an outer diameter of 25 mm, and a length in the thrust direction of 350 mm. The gap (SD gap) between the upstream developing sleeve 111 and the photosensitive drum 2 is set to about 270 μm, and the gap (SD gap) between the downstream developing sleeve 112 and the photosensitive drum 2 is set to about 450 μm.

[0034] Inside the upstream developing sleeve 111, a roller-shaped first tuna roller 131 (a first magnet as a first magnetic field generating member) is disposed in a non-rotating and fixed manner. The upstream developing sleeve 111 rotates at a peripheral speed ratio of 140% with respect to the photosensitive drum 2 in the direction of arrow b, and carries and conveys the developer. In the facing portion between the upstream developing sleeve 111 and the photosensitive drum 2 (hereinafter referred to as the first developing region A1), the rotation direction of the upstream developing sleeve 111 (the direction of arrow b) is the same as the rotation direction of the photosensitive drum 2 (the direction of arrow a).

[0035] On the upstream side of the first developing region A1 with respect to the rotation direction of the upstream developing sleeve 111 (the direction of arrow b), a regulating blade 113 is disposed above the upstream developing sleeve 111 and facing it in a non-contact manner. With this configuration, the developer in the developing chamber 118, which is the developer supplied from the first conveying screw 114 to the upstream developing sleeve 111, has its layer thickness regulated by the regulating blade 113. In the first embodiment, the amount of developer coating per unit area on the upstream developing sleeve 111 is regulated to 30 mg / cm 2 by the regulating blade 113.

[0036] Inside the first tuna roller 131 in the vicinity of the regulating blade 113, a magnetic pole N1 (suction pole) is disposed. The developer accumulated under the restraint of the magnetic force lines (magnetic force, magnetic field) generated by the magnetic pole N1 is regulated to an appropriate layer thickness by the regulating blade 113. Then, the developer with the regulated layer thickness is carried and conveyed to the first developing region A1.

[0037] Further, the first tuna roller 131 has a magnetic pole S2 (developing pole) facing the first developing region A1. The magnetic pole S2 (developing pole) is a magnetic pole disposed at the closest portion between the upstream developing sleeve 111 and the photosensitive drum 2.

[0038] Due to the magnetic field formed by the magnetic pole S2 in the first developing region A1, a magnetic brush (magnetic brush) of the developer is formed on the first tuna roller 131. This magnetic brush contacts the photosensitive drum 2 rotating in the direction of arrow a in the first developing region A1.

[0039] As a result, the electrostatic latent image on the photoreceptor drum 2 is developed in the first development region A1 to form a toner image. This is the first development by the developing device 1. At this time, the toner adhering to the magnetic brush and the toner adhering to the surface of the upstream developing sleeve 111 are transferred to the image region of the electrostatic latent image on the photoreceptor drum 2 to develop the electrostatic latent image.

[0040] In the first embodiment, the first roller 131 has five poles, namely, a magnetic pole S1 (conveying pole), a magnetic pole N2 (conveying pole), and a magnetic pole N3 (delivery pole) in addition to the magnetic pole S2 (developing pole) and the magnetic pole N1 (lifting pole). Among the plurality of magnetic poles of the first roller 131, the magnetic pole N1 and the magnetic pole N3 are adjacent to each other with the same polarity, and a low magnetic field region (first repulsive magnetic field region RF1) where the magnetic flux density is 5 mT or less is formed therebetween. The first repulsive magnetic field region RF1 is a region where a barrier is formed for the developer.

[0041] A downstream developing sleeve 112 is disposed in a region below the upstream developing sleeve 111 and facing both the upstream developing sleeve 111 and the photoreceptor drum 2. The downstream developing sleeve 112 is rotatably disposed at a circumferential speed ratio of 140% with respect to the photoreceptor drum 2 in the direction of arrow c. The downstream developing sleeve 112 is made of a non-magnetic material in the same manner as the upstream developing sleeve 111.

[0042] Inside the downstream developing sleeve 112, a roller-shaped second roller 132 (second magnet as a second magnetic field generating member) is fixedly disposed non-rotatably. The second roller 132 has five poles, namely, a magnetic pole S3 (receiving pole), a magnetic pole N4 (developing pole), a magnetic pole S4 (conveying pole), a magnetic pole N5 (conveying pole), and a magnetic pole S5 (stripping pole).

[0043] Among these, the magnetic brush on the magnetic pole N4 is in contact with the photoreceptor drum 2 at the facing portion between the downstream developing sleeve 112 and the photoreceptor drum 2 (hereinafter referred to as the second development region A2). Therefore, in the second development region A2, the photoreceptor drum 2 after passing through the first development region A1 is further developed a second time. The developer used for the second development by the downstream developing sleeve 112 is returned to the agitation chamber 119.

[0044] Among the plurality of magnetic poles of the second mag roller 132, the magnetic pole S3 and the magnetic pole S5 are of the same polarity. For this reason, a low magnetic field region (second repulsive magnetic field region RF2) where the magnetic flux density is 5 mT or less is formed between the magnetic pole S3 and the magnetic pole S4. The second repulsive magnetic field region RF2 is a region where a barrier is formed for the developer.

[0045] Also, the magnetic pole S3 (receiving pole) of the second mag roller 132 faces the magnetic pole N3 (transfer pole) of the first mag roller 131 in the vicinity of the position where the upstream developing sleeve 111 and the downstream developing sleeve 112 are closest to each other. Also, the magnetic pole S3 of the second mag roller 132 is of a different polarity from the magnetic pole N3 of the first mag roller 131. Thereby, magnetic lines of force are formed between the magnetic pole N3 of the first mag roller 131 and the magnetic pole S3 of the second mag roller 132, and the developer is transferred from the first mag roller 131 to the second mag roller 132 by the magnetic lines of force.

[0046] Note that at the position where the upstream developing sleeve 111 and the downstream developing sleeve 112 are closest to each other, the rotation direction (direction of arrow c) of the downstream developing sleeve 112 is opposite to the rotation direction (direction of arrow b) of the upstream developing sleeve 111.

[0047] The developing bias used in the first embodiment applies a developing bias in which an AC component and a DC component are superimposed to the upstream developing sleeve 111 and the downstream developing sleeve 112 by developing bias applying means. In the first embodiment, a blank pulse of a DC component from which the AC component is intermittently thinned out is provided. The AC component is a rectangular wave of 12 kHz, and the number of pulses is 8 when the blank part is one pulse with a half cycle of the rectangular wave. Also, the ratio (hereinafter, Duty) of the electric field on the developing side to the electric field on the recovery side is 50%.

[0048] (Flow of developer) The flow of the developer performed by the above-described configuration will be described with reference to FIG. 3. FIG. 3 is a cross-sectional view (enlarged view) showing the configuration around the developing sleeve according to the first embodiment.

[0049] Since the developer D has a magnetic carrier mixed with the non-magnetic toner, it is constrained by the magnetic pole N1 of the first mag roller 131. Next, as the upstream developing sleeve 111 rotates, the developer D passes through the magnetic pole N1 facing the regulating blade 113, and the amount of the developer D is regulated to a predetermined amount. The developer D regulated by the regulating blade 113 passes through the magnetic poles S1 and N2 of the first mag roller 131, and the developer D is supplied to the magnetic pole S2 facing the photosensitive drum 2. Passing through the first developing region A1, toner is supplied to the electrostatic latent image formed on the surface of the photosensitive drum 2, and the developer D from which the toner has been consumed is conveyed to the magnetic pole N3 of the first mag roller 131. Here, a first repulsive magnetic field region RF1 is formed between the magnetic poles N1 and N3 of the first mag roller 131. Also, in the downstream developing sleeve 112, a second repulsive magnetic field region RF2 is formed between the magnetic poles S3 and S5 of the second mag roller 132.

[0050] Therefore, as described above, the developer D conveyed on the upstream developing sleeve 111 and passing through the first developing region A1 reaches the magnetic pole N3 of the first mag roller 131. On the other hand, the developer D that has passed through the first developing region A1 cannot pass through the closest position between the upstream developing sleeve 111 and the downstream developing sleeve 112 due to the first repulsive magnetic field region RF1 and the second repulsive magnetic field region RF2.

[0051] Then, the developer D on the upstream developing sleeve 111 moves toward the downstream developing sleeve 112 along the magnetic force lines extending from the magnetic pole N3 of the first mag roller 131 in the direction of the magnetic pole S3 of the second mag roller 132 as indicated by the arrow d. Thereafter, the developer D is conveyed on the downstream developing sleeve 112, passes through the second developing region A2, and reaches the magnetic pole S5 of the second mag roller 132. The developer D is peeled off from the downstream developing sleeve 112 by the second repulsive magnetic field region RF2 at the magnetic pole S5 and is conveyed to the second conveying screw 115 in the agitation chamber 119.

[0052] Note that in a configuration where the poles between the magnetic poles N1 and S2 of the first mag roller 131 (magnetic poles N2 and S1 in the first embodiment) are omitted with respect to the rotation direction of the upstream developing sleeve 111, the conveyance of the developer may become unstable, which may cause density unevenness. Therefore, in the first embodiment, in the first mag roller 131, the magnetic poles S1 and N2, which are conveyance poles, are provided between the magnetic poles N1 and S2.

[0053] Also, in a configuration where the poles between the magnetic poles N4 and S5 of the second mag roller 132 (magnetic poles S4 and N5 in the first embodiment) are omitted with respect to the rotation direction of the downstream developing sleeve 112, the conveyance of the developer may become unstable, which may cause density unevenness. Therefore, in the first embodiment, in the second mag roller 132, the magnetic poles S4 and N5, which are conveyance poles, are provided between the magnetic poles N4 and S5.

[0054] (Toner detachment) The developer D on the developing sleeve is conveyed while the magnetic spikes alternately repeat standing up and falling down according to the magnetic force lines extending from each magnetic pole to the adjacent magnetic pole in the conveyance direction. Due to the centrifugal force when the developer D on the developing sleeve is conveyed, the impact caused by the magnetic spikes of the developer D fluctuating following the magnetic force lines, and the impact when the magnetic spikes fall down, the toner detaches. This phenomenon becomes more prominent as the rotation speed of the upstream developing sleeve 111 increases.

[0055] (Developing sleeve cover and anti-scattering sheet) As shown in FIG. 2, in the developing device 1 according to the first embodiment, a developing sleeve cover 120 (cover portion) is provided facing the upstream developing sleeve 111 in a non-contact manner with respect to the developing container 110. Further, the developing sleeve cover 120 is provided so as to cover the upper side of the developing container 110 from the regulating blade 113.

[0056] Here, the details of the developing sleeve cover 120 will be described with reference to FIG. 4. FIG. 4 is a cross-sectional view (enlarged view) showing the configuration around the developing sleeve cover according to the first embodiment.

[0057] The developer D regulated by the regulating blade 113 passes through the magnetic poles S1 and N2 of the first mag roller 131 and is conveyed to the magnetic pole S2 facing the photosensitive drum 2.

[0058] As shown in FIG. 4, the first scattering prevention sheet 121 (first sheet portion) is fixed to the developing sleeve cover 120 with an adhesive or double-sided tape so as to contact the developer D standing up at the magnetic pole N2.

[0059] Also, the tip (free end 121a) of the first scattering prevention sheet 121 is provided at a position that contacts the photosensitive drum 2 and does not enter the first development region A1. The first scattering prevention sheet 121 is provided over the entire length from one end to the other end in the longitudinal direction of the developer coating region (region where the developer conveying ability exists) of the upstream developing sleeve 111. When the outer surface of the developing sleeve is subjected to blasting or grooving, the region where these processes are performed becomes the region where the developer conveying ability of the developing sleeve exists.

[0060] The first scattering prevention sheet 121 is preferably a sheet with a small Young's modulus in order to contact the developer on the upstream developing sleeve 111. In the first embodiment, the first scattering prevention sheet 121 is composed of a urethane sheet with a thickness of about 100 μm.

[0061] In the first embodiment, by bringing the first scattering prevention sheet 121 into contact with the developer D on the upstream developing sleeve 111, the variation of the developer is reduced and the release of the toner is suppressed.

[0062] Also, toner that has separated from the first development region A1 downstream of the first scattering prevention sheet 121 with respect to the rotation direction of the upstream development sleeve 111 may scatter above the developing container 110, and it is necessary to prevent the contamination of other parts. Therefore, in the first embodiment, a gap of about 2 to 3 mm is provided between the first scattering prevention sheet 121, and a second scattering prevention sheet 122 (third sheet portion) is provided on the developing sleeve cover 120 so as to contact the photosensitive drum 2. The second scattering prevention sheet 122 is composed of a urethane sheet with a thickness of about 100 μm, similar to the first scattering prevention sheet 121.

[0063] (Conventional Example) FIG. 6 is a cross-sectional view showing the configuration of the developing device 10 in the conventional example. FIGS. 7 and 8 are cross-sectional views (enlarged views) showing the configuration around the developing sleeve cover in the conventional example. In particular, FIG. 8 schematically shows the periphery of the developing sleeve cover when the phenomenon of toner dropping occurs in the conventional example.

[0064] As in the conventional example shown in FIGS. 6 and 7, it is assumed that the first scattering prevention sheet 121 is arranged so as to contact the magnetic spike of the developer D on the upstream developing sleeve 111. In such a case, as the upstream developing sleeve 111 is rotationally driven, the first scattering prevention sheet 121 is lifted by the magnetic spike whose contact portion with the magnetic spike stands up.

[0065] When the tip (free end 121a) of the first scattering prevention sheet 121 floats from the upstream developing sleeve 111 due to the standing-up magnetic spike, the first scattering prevention sheet 121 and the developer D on the upstream developing sleeve 111 cannot come into contact at the spike-falling portion.

[0066] As a result, the released toner accumulates on the first anti-scattering sheet 121 in a region that is not in contact with the developer D on the upstream developing sleeve 111. In particular, as shown in FIG. 8, when a certain amount of toner accumulates at the tip (free end 121a) of the first anti-scattering sheet 121 due to the self-weight of the toner itself, the mass of the accumulated toner that loses to gravity rather than the adhesive force between the toners collapses, and the toner falls onto the photosensitive drum 2. For this reason, there is a risk of generating a defective image of toner stain called "dot dropout" on the image.

[0067] Therefore, in the first embodiment, in order to suppress the deformation of the first anti-scattering sheet 121 by the standing magnetic spikes, a backup sheet 123 (second sheet portion) for backing up the first anti-scattering sheet 121 is provided on the developing sleeve cover 120. Thereby, in the developing device provided with the sheet portion that abuts on the developer in the region where the developer on the developing sleeve stands up, the occurrence of image defects is suppressed. The details will be described below.

[0068] (Backup Sheet) First, the configuration of the developing sleeve cover 120 according to the first embodiment will be described with reference to FIG. 4. FIG. 4 is a cross-sectional view (enlarged view) showing the configuration around the developing sleeve cover according to the first embodiment.

[0069] Since the developer D on the upstream developing sleeve 111 is pulled by the magnetic force of the first tuna roller 131 when the upstream developing sleeve 111 is stationary, it is attracted and supported in a form that is concentrated on the surface of the upstream developing sleeve 111. On the other hand, when the upstream developing sleeve 111 is rotationally driven, centrifugal force is applied. Therefore, the magnetic spike of the magnetic pole N2 of the first tuna roller 131 lifts the first anti-scattering sheet 121 when the upstream developing sleeve 111 is rotationally driven.

[0070] On the one hand, in the first embodiment, as shown in FIG. 4, a backup sheet 123 for backing up the first scattering prevention sheet 121 is fixedly provided on the developing sleeve cover 120 so as to cover the magnetic fringe of the magnetic pole N2 of the first roller 131. As means for fixing the backup sheet 123 to the developing sleeve cover 120, for example, an adhesive, a double-sided tape, or the like can be mentioned.

[0071] Also, as shown in FIG. 4, the backup sheet 123 is arranged so as to overlap with the surface on the side opposite to the surface (contact surface of the first scattering prevention sheet 121) where the first scattering prevention sheet 121 contacts the upstream developing sleeve 111 (the back surface of the first scattering prevention sheet 121). Thereby, the first scattering prevention sheet 121 is prevented from being lifted when the upstream developing sleeve 111 is rotationally driven.

[0072] As described above, the first scattering prevention sheet 121 is provided over the entire region from one end to the other end in the longitudinal direction of the developer coating region (the region where the developer conveying ability exists) of the upstream developing sleeve 111. Therefore, the backup sheet 123 is also provided over the entire region from one end to the other end in the longitudinal direction of the developer coating region (the region where the developer conveying ability exists) of the upstream developing sleeve 111 in the same manner as the first scattering prevention sheet 121.

[0073] The position of the tip (free end 123a) of the backup sheet 123 is preferably arranged on the downstream side in the rotational direction of the upstream developing sleeve 111 with respect to the upstream half-value position of the magnetic pole N2. More preferably, the position of the tip (free end 123a) of the backup sheet 123 is arranged on the downstream side in the rotational direction of the upstream developing sleeve 111 with respect to the peak position of the magnetic pole N2. Even more preferably, the position of the tip (free end 123a) of the backup sheet 123 is arranged on the downstream side in the rotational direction of the upstream developing sleeve 111 with respect to the downstream half-value position of the magnetic pole N2.

[0074] Note that the peak position of the magnetic pole N2 refers to the position where the magnetic flux density Br of the magnetic pole N2 in the normal direction with respect to the outer peripheral surface of the upstream developing sleeve 111 reaches the peak value. Further, the upstream half-value position of the magnetic pole N2 refers to the position on the upstream side in the rotation direction of the upstream developing sleeve 111 among the positions where the value of the magnetic flux density Br of the magnetic pole N2 in the normal direction with respect to the outer peripheral surface of the upstream developing sleeve 111 becomes half of the peak value. Further, the downstream half-value position of the magnetic pole N2 refers to the position on the downstream side in the rotation direction of the upstream developing sleeve 111 among the positions where the magnetic flux density Br of the magnetic pole N2 in the normal direction with respect to the outer peripheral surface of the upstream developing sleeve 111 becomes half of the peak value.

[0075] In the first embodiment, the position of the tip (free end 123a) of the backup sheet 123 is arranged on the downstream side in the rotation direction of the upstream developing sleeve 111 from the downstream half-value position of the magnetic pole N2 and does not contact the photoreceptor drum 2. Thereby, the first scattering prevention sheet 121 can be suppressed from being lifted by the magnetic toner, and the magnetic toner of the developer D can contact the tip (free end 121a) of the first scattering prevention sheet 121 without a gap along the developer D on the upstream developing sleeve 111.

[0076] Note that, in order to suppress the deformation of the first scattering prevention sheet 121, it is preferable to adopt a sheet having a higher stiffness than the tip (free end 121a) of the first scattering prevention sheet 121 for the backup sheet 123. In this specification, the stiffness refers to, for example, measured values according to various test standards such as Clark stiffness (JIS P8143), Gurley stiffness (JIS L1085, JIS L1096), and Taber stiffness (JIS P 8125-2). Further, in this specification, the stiffness may refer to, for example, measured values obtained by various experiments such as Young's modulus (ASTM D882), tensile elastic modulus (JIS K7162), and flexural elastic modulus (JIS K7171).

[0077] In the first embodiment, the backup sheet 123 is composed of a PET sheet having a thickness of about 100 μm.

[0078] Suppose that, in order to suppress deformation of the first anti-scattering sheet 121, the first anti-scattering sheet 121 is made of a sheet with high rigidity, for example, a PET sheet with a thickness of about 100 μm. In this case, deformation of the sheet due to the magnetic fringe of the magnetic pole N2 of the first mag roller 131 can be suppressed, but because the rigidity of the sheet is high, it cannot be aligned along the developer D on the upstream developing sleeve 111. As a result, a region that does not come into contact with the developer D is formed at the tip (free end 121a) of the first anti-scattering sheet 121, so there is a risk that the toner that has peeled off and scattered at the tip (free end 121a) of the first anti-scattering sheet 121 will accumulate.

[0079] Therefore, in order to solve such problems, it is preferable to use a sheet with low rigidity for the first anti-scattering sheet 121 so that the magnetic fringe of the developer D can contact the tip (free end 121a) of the first anti-scattering sheet 121 without a gap along the developer D on the upstream developing sleeve 111. On the other hand, in order to suppress deformation of the first anti-scattering sheet 121 due to the fringing of the magnetic pole N2 of the first mag roller 131, it is preferable to use a sheet with high rigidity for the backup sheet 123 for backing up the first anti-scattering sheet 121.

[0080] Therefore, in the first embodiment, the backup sheet 123 is made of a PET sheet with a thickness of about 100 μm, but for example, a PET sheet with a thickness of about 50 μm may be used, preferably with a thickness of about 75 μm or more, more preferably with a thickness of about 100 μm or more.

[0081] Further, in the first embodiment, in order to suppress deformation of the first anti-scattering sheet 121 due to the magnetic fringe, a sheet with high rigidity is used for the backup sheet 123, but the means for increasing the rigidity is not limited to this. For example, a plurality of urethane sheets with the same thickness of about 100 μm as the first anti-scattering sheet 121 are combined. This may be a modified example in which the first anti-scattering sheet 121 is provided with a function of backing it up and the rigidity at the fringing portion of the magnetic pole N2 of the first mag roller 131 is increased.

[0082] As described above, according to the first embodiment, in the developing device including the sheet portion (the first scattering prevention sheet 121) that contacts the developer in the region where the developer on the developing sleeve forms a spike, the occurrence of image defects can be suppressed.

[0083] [Second Embodiment] In the first embodiment described above, an example in which a sheet having a higher rigidity than the first scattering prevention sheet 121 is used for the backup sheet 123 to suppress deformation of the first scattering prevention sheet 121 due to the magnetic spike has been described.

[0084] On the other hand, in the second embodiment, instead of providing the backup sheet 123 on the developing sleeve cover 120, the configuration of the first scattering prevention sheet is different from that of the first embodiment. Since the other configurations and operations are the same as those of the first embodiment described above, the same reference numerals are given to the same configurations, and the description and illustration are omitted or simplified. Hereinafter, the differences from the first embodiment will be mainly described.

[0085] Details of the configuration of the first scattering prevention sheet according to the second embodiment will be described with reference to FIG. 5. FIG. 5 is a cross-sectional view (enlarged view) showing the configuration around the developing sleeve cover according to the second embodiment.

[0086] As shown in FIG. 5, in the second embodiment, the backup sheet 123 is not provided on the developing sleeve cover 120. Instead, in the second embodiment, in order to suppress deformation of the first scattering prevention sheet 221, the rigidity of the first scattering prevention sheet 221 is changed between the free end 221a side and the fixed end 221b side of the first scattering prevention sheet 221. Specifically, the thickness of the sheet is increased to increase the rigidity of the fixed end 221b side of the first scattering prevention sheet 221 with respect to the tip of the first scattering prevention sheet 221, which is the free end 221a side of the first scattering prevention sheet 221.

[0087] In the second embodiment, the tip of the first scattering prevention sheet 221 (on the free end 221a side) is made of a urethane sheet with a thickness of 100 μm, while the thickness of the sheet on the fixed end 221b side is made of a urethane sheet with a thickness of 300 μm. As a result, in the second embodiment, even if the backup sheet 123 is not provided on the developing sleeve cover 120, the deformation of the first scattering prevention sheet 221 due to the magnetic fringe of the magnetic pole N2 of the first roller 131 can be suppressed.

[0088] In the second embodiment as well, in the same manner as in the first embodiment, the first scattering prevention sheet 121 is provided over the entire area from one end to the other end in the longitudinal direction of the developer coating area (the area where the developer conveying ability exists) of the upstream developing sleeve 111.

[0089] In the second embodiment, the region where the stiffness of the first scattering prevention sheet 221 is increased is at least the region from the fixed end 221b of the first scattering prevention sheet 221 to the upstream half-value position of the magnetic pole N2. More preferably, the region where the stiffness of the first scattering prevention sheet 221 is increased is the region from the fixed end 221b of the first scattering prevention sheet 221 to the peak position of the magnetic pole N2. Even more preferably, the region where the stiffness of the first scattering prevention sheet 221 is increased is the region from the fixed end 221b of the first scattering prevention sheet 221 to the downstream half-value position of the magnetic pole N2. The definitions of the peak position, upstream half-value position, and downstream half-value position of the magnetic pole N2 are as described above in the first embodiment.

[0090] In the second embodiment, the region where the stiffness of the first scattering prevention sheet 221 is increased is the region from the fixed end 221b of the first scattering prevention sheet 221 to the downstream half-value position of the magnetic pole N2. That is, the stiffness of the first scattering prevention sheet 221 in the region from the fixed end 221b of the first scattering prevention sheet 221 to the downstream half-value position of the magnetic pole N2 is made greater than the stiffness of the first scattering prevention sheet 221 at the free end 221a of the first scattering prevention sheet 221. As a result, the first scattering prevention sheet 221 can be suppressed from being lifted by the magnetic fringe.

[0091] Also, in the second embodiment, the stiffness from the downstream half-value position of the magnetic pole N2 to the tip (free end 221a) of the first scattering prevention sheet 221 is reduced. Therefore, the magnetic spikes of the developer D can contact the tip (free end 221a) of the first scattering prevention sheet 221 without a gap along the developer D on the upstream developing sleeve 111.

[0092] As described above, according to the second embodiment, in a developing device including a sheet portion (first scattering prevention sheet 221) that contacts the developer in a region where the developer on the developing sleeve forms spikes, the occurrence of image defects can be suppressed.

[0093] (Other Embodiments) The present invention is not limited to the above-described embodiments, and various modifications (including organic combinations of the respective embodiments) are possible based on the gist of the present invention, and they are not excluded from the scope of the present invention.

[0094] In the above-described embodiment, as shown in FIG. 2, the developing device 1 has two upstream developing sleeve 111 and downstream developing sleeve 112 as developer carriers, and an example in which the first scattering prevention sheet 121 contacts the upstream developing sleeve 111 has been described. However, the present invention is not limited to this. The present invention can also be applied to a developing device having one developing sleeve as a developer carrier. In a modified example thereof, the first scattering prevention sheet 121 is brought into contact with one developing sleeve included in the developing device.

[0095] Also, in the above-described embodiment, an example in which a gap of about 2 to 3 mm is provided between the first scattering prevention sheet 121 and the second scattering prevention sheet 122 is provided on the developing sleeve cover 120 so as to contact the photosensitive drum 2 has been described. However, the present invention is not limited to this. A modified example may be such that the first scattering prevention sheet 121 (221) is provided on the developing sleeve cover 120 while the second scattering prevention sheet 122 is not provided. Whether to provide the second scattering prevention sheet 122 on the developing sleeve cover 120 may be appropriately designed according to the degree to which toner scatters from the first developing region A1.

[0096] Also, in the above embodiment, as shown in FIG. 1, the image forming apparatus 100 primarily transfers the toner images carried on the respective photoreceptor drums 2 (2Y, 2M, 2C, 2K) to the transfer belt 30. Thereafter, the image forming apparatus 100 brings the sheet P into contact with the transfer belt 30 and secondarily transfers the toner image carried on the transfer belt 30 to the sheet P. In the above embodiment, the image forming apparatus 100 having such a configuration has been described as an example, but the present invention is not limited thereto. The present invention can also be applied to an image forming apparatus configured to directly transfer the toner images carried on the respective photoreceptor drums 2 (2Y, 2M, 2C, 2K) to the sheet P by bringing the sheet P into direct contact with the photoreceptor drums 2 (2Y, 2M, 2C, 2K).

Explanation of Reference Numerals

[0097] 1 Developing device 110 Developing container 111 Upstream developing sleeve 113 Regulation blade 120 Developing sleeve cover 121 First scattering prevention sheet 123 Backup sheet 131 First mag roller

Claims

1. A developing container that houses a developer containing toner and a carrier, A developing rotator that supports and conveys the developer to develop an electrostatic latent image formed on an image carrier, A first magnetic pole that is fixedly arranged non-rotatably inside the developing rotator and is arranged at the closest part between the developing rotator and the image carrier, and a second magnetic pole that is arranged adjacent to the first magnetic pole upstream of the first magnetic pole with respect to the rotation direction of the developing rotator and has a different polarity from the first magnetic pole, and a magnet having the second magnetic pole, A regulating unit that is provided facing the developing rotator in a non-contact manner and regulates the amount of the developer carried on the developing rotator, A cover unit that is provided facing the developing rotator in a non-contact manner and covers the developing rotator, A first sheet part that is fixedly provided on the cover unit and is arranged to contact the developing rotator, A second sheet part that is fixedly provided on the cover unit and is arranged to overlap with the surface of the first sheet part on the side opposite to the surface that contacts the developing rotator, Comprising, The free end of the first sheet part is downstream of the position where the regulating unit faces the developing rotator with respect to the rotation direction of the developing rotator and upstream of the closest part between the developing rotator and the image carrier, The free end of the second sheet part is downstream of the upstream half-value position of the first magnetic pole with respect to the rotation direction of the developing rotator and is at a position where it does not contact the image carrier, The rigidity of the second sheet part is greater than the rigidity of the first sheet part A developing device characterized by this.

2. The free end of the second sheet part is downstream of the peak position of the first magnetic pole with respect to the rotation direction of the developing rotator and is at a position where it does not contact the image carrier The developing device according to claim 1, characterized by this.

3. The free end of the second sheet part is downstream of the downstream half-value position of the first magnetic pole with respect to the rotation direction of the developing rotator and is at a position where it does not contact the image carrier The developing device according to claim 1, characterized by this.

4. The first sheet part is provided over the entire length of one end and the other end in the longitudinal direction of the region where the developing rotator has the developer conveying ability, The second sheet part is provided over the entire length of one end and the other end in the longitudinal direction of the region where the developing rotator has the developer conveying ability The developing device according to claim 1, characterized by this.

5. The first sheet portion is a urethane sheet, The second sheet portion is a PET sheet The developing device according to claim 1, characterized in that.

6. Further provided with a third sheet portion that is fixedly provided to the cover portion and is arranged to contact the image carrier downstream of the closest portion between the developing rotator and the image carrier with respect to the rotation direction of the developing rotator The developing device according to claim 1, characterized in that.

7. A developing container that houses a developer containing toner and a carrier, A developing rotator that carries and conveys the developer in order to develop an electrostatic latent image formed on an image carrier, A first magnetic pole that is fixedly arranged non-rotatably inside the developing rotator and is arranged at the closest portion between the developing rotator and the image carrier, and a second magnetic pole that is arranged adjacent to the first magnetic pole upstream of the first magnetic pole with respect to the rotation direction of the developing rotator and has a different polarity from the first magnetic pole, a magnet having, A regulating portion that is provided to face the developing rotator non-contactingly and regulates the amount of developer carried on the developing rotator, A cover portion that is provided to face the developing rotator non-contactingly and covers the developing rotator, A sheet portion that is fixedly provided to the cover portion and is arranged to contact the developing rotator, Comprising, The free end of the sheet portion is downstream of the position where the regulating portion faces the developing rotator with respect to the rotation direction of the developing rotator and upstream of the closest portion between the developing rotator and the image carrier, The stiffness of the sheet portion in the region from the fixed end of the sheet portion to the upstream half-value position of the first magnetic pole is greater than the stiffness of the sheet portion at the free end of the sheet portion The developing device characterized by that.

8. The stiffness of the sheet portion in the region from the fixed end of the sheet portion to the peak position of the first magnetic pole is greater than the stiffness of the sheet portion at the free end of the sheet portion The developing device according to claim 7, characterized in that.

9. The stiffness of the sheet portion in the region from the fixed end of the sheet portion to the downstream half-value position of the first magnetic pole is greater than the stiffness of the sheet portion at the free end of the sheet portion The developing device according to claim 7, characterized in that.

10. The sheet portion is provided over the entire length of one end and the other end in the longitudinal direction of the region where the developing rotator has the developer conveying ability The developing device according to claim 7, characterized in that...

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