Image forming apparatus

Abstract

The toner deposited on the collection roller 52 can be prevented from adhering to the photosensitive drum, thereby preventing image contamination.SOLUTION: The carrier recovery device 5 includes a rotatable recovery roller disposed to face the photosensitive drum and a non-rotatable magnet roller disposed inside the recovery roller, and recovers the carrier on the photosensitive drum. A plurality of grooves 71 are formed on the outer peripheral surface of the collection roller 52 along the rotation axis direction of the collection roller. The plurality of grooves 71 are formed such that θ 1 and θ 2 are different from each other in a cross section orthogonal to the rotational axis direction of the collecting roller 52, where θ 1 is the smallest angle among angles formed by the downstream side wall surface 71a and a first imaginary line α 1 orthogonal to the rotational axis of the collecting roller and passing through the downstream side wall surface 71a, and θ 2 is the smallest angle among angles formed by the upstream side wall surface 71b and a second imaginary line α 2 orthogonal to the rotational axis of the collecting roller and passing through the upstream side wall surface 71b.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus such as a copier, printer, facsimile, or a multifunction machine having multiple functions of these. [Background technology]

[0002] Conventionally, image forming apparatuses have been known that form toner images using a two-component developer containing non-magnetic toner and magnetic carrier. In this configuration, an electrostatic latent image on a photosensitive drum (image carrier) is typically developed into a toner image using toner during the development process. However, a certain percentage of the carrier may also adhere to the photosensitive drum (carrier adhesion). Since carrier adhesion can affect the output image, for example, Patent Document 1 discloses a configuration that includes a carrier recovery device that recovers carrier that has adhered to the photosensitive drum.

[0003] The carrier recovery device includes a recovery roller and a magnet installed within the recovery roller. The magnetic force of the magnet and the electric field formed between the photosensitive drum and the recovery roller cause the carrier adhering to the photosensitive drum to adhere to the recovery roller, thereby recovering the carrier. During this carrier recovery, toner also adheres to the recovery roller. If the toner that has adhered to the recovery roller accumulates, it will adhere to the photosensitive drum again, causing image contamination.

[0004] In Patent Document 1, multiple U-shaped inclined grooves are formed in the collection roller along the rotational axis of the collection roller. The multiple inclined grooves are inclined so that the center of the rotational axis of the collection roller is located downstream of both ends in the rotational direction of the collection roller. Carrier adhering to the collection roller enters the multiple inclined grooves, and the toner accumulated in the inclined grooves rubs against the carrier, causing the toner accumulated in the inclined grooves to be collected onto the carrier. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-101596 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the case of Patent Document 1, the toner accumulated in the inclined grooves and the carrier do not rub sufficiently, and the toner accumulated on the recovery roller may adhere to the photosensitive drum, causing image contamination. Specifically, the carrier adhered to the recovery roller is drawn into the U-shaped inclined grooves formed on the surface of the recovery roller by the magnetic field generated by the magnet inside the recovery roller. However, if the side walls of the inclined grooves are steep, the carrier adhered to the recovery roller may not come into contact with the side walls of the inclined grooves and may be collected at the bottom of the inclined grooves. In this case, the toner accumulated on the side walls of the inclined grooves accumulates without being collected by the carrier, eventually adhering to the photosensitive drum and causing image contamination.

[0007] SUMMARY OF THE INVENTION An object of the present invention is to provide a configuration capable of suppressing image contamination caused by toner accumulated on a collection roller adhering to an image carrier. [Means for solving the problem]

[0008] One aspect of the present invention provides a developing device including a rotatable image carrier on which an electrostatic latent image is formed, a developer container containing a developer including toner and a carrier, and a developer carrier that carries the developer to develop the electrostatic latent image formed on the image carrier into a toner image; and a carrier recovery device that recovers the carrier on the image carrier, the carrier recovery device having a transfer member to which the toner image carried on the image carrier is transferred, a rotatable recovery roller disposed opposite the image carrier, and a magnet non-rotatably disposed inside the recovery roller, the recovery roller being located downstream of a development position where the electrostatic latent image formed on the image carrier is developed in terms of the rotation direction of the image carrier, and the toner image carried on the image carrier is transferred to a transfer unit. an image forming apparatus in which the image is transferred onto a material, the recovery roller has a plurality of grooves formed on its outer surface along the direction of the rotational axis of the recovery roller, and the plurality of grooves are formed so that, in a cross section perpendicular to the direction of the rotational axis of the recovery roller, θ1 is the smallest angle between a first wall surface downstream of the deepest position of the groove in the direction of rotation of the recovery roller and a first imaginary line perpendicular to the rotational axis of the recovery roller and passing through the first wall surface, and θ2 is the smallest angle between a second wall surface upstream of the deepest position of the groove in the direction of rotation of the recovery roller and a second imaginary line perpendicular to the rotational axis of the recovery roller and passing through the second wall surface, where θ1 is the smallest angle. [Effects of the Invention]

[0009] According to the present invention, it is possible to prevent the toner accumulated on the recovery roller from adhering to the image carrier, thereby preventing image contamination. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view showing a schematic configuration of an image forming apparatus according to a first embodiment. [Figure 2] FIG. 1 is a cross-sectional view showing a schematic configuration of a carrier recovery device according to a first embodiment. [Figure 3] FIG. 2 is a perspective view of a collection roller according to the first embodiment. [Figure 4] FIG. 3 is a schematic cross-sectional view of a groove of the collection roller according to the first embodiment. [Figure 5] FIG. 3 is a schematic diagram showing the direction of magnetic lines of force formed by a magnet roller inside the collection roller according to the first embodiment. [Figure 6] 5A and 5B are schematic diagrams showing the strength and direction of magnetic lines of force acting on the carrier collected by the collection roller in the vicinity of the closest position between the collection roller and the photosensitive drum according to the first embodiment; [Figure 7] Schematic cross-sectional views showing (a) the carrier positioned downstream of the downstream wall surface of the groove, (b) the carrier entering the groove, and (c) the carrier reaching the upstream wall surface of the groove in the recovery roller of the first embodiment. [Figure 8] 10A and 10B are schematic cross-sectional views showing a state in which the carrier is positioned downstream of the downstream wall surface of the groove, and a state in which the carrier enters the groove, in the collection roller according to Comparative Example 1; [Figure 9] (a), (b), and (c) are schematic diagrams illustrating the angle of the downstream wall of the groove. [Figure 10] FIG. 4 is a schematic diagram illustrating the angle of the upstream wall surface of the collection roller according to the first embodiment. [Figure 11] 10A and 10B are schematic cross-sectional views showing a state in which the carrier reaches the upstream wall surface of the groove and a state in which the carrier climbs over the upstream wall surface in the collection roller according to Comparative Example 2. FIG. [Figure 12] Schematic diagram for explaining the experimental parameters. [Figure 13] FIG. 10 is a schematic cross-sectional view of a groove of a collection roller according to a second embodiment. [Figure 14] FIG. 11 is a schematic cross-sectional view of a groove of a collection roller according to a third embodiment. [Figure 15] FIG. 11 is a schematic cross-sectional view of a groove of a collection roller according to Comparative Example 3. [Figure 16] FIG. 10 is a perspective view of a collection roller according to a fourth embodiment. [Figure 17] 10A and 10B are schematic diagrams illustrating the direction of a force acting on a carrier in a groove in a collection roller according to a fourth embodiment. [Figure 18] FIG. 13 is a perspective view of a collection roller according to another first example of the fourth embodiment. [Figure 19] FIG. 13 is a perspective view of a collection roller according to another second example of the fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] First Embodiment The first embodiment will be described with reference to Figures 1 to 12. First, the schematic configuration of an image forming apparatus 100 of this embodiment will be described with reference to Figure 1.

[0012] [Image forming equipment] The image forming apparatus 100 of this embodiment is a full-color electrophotographic image forming apparatus 100 and includes four image forming units Pa, Pb, Pc, and Pd. The configuration of each image forming unit is essentially the same except for the different developing colors. Therefore, unless a distinction is required, the image forming unit Pa will be described below as a representative. The other image forming units will be designated by the subscripts b, c, and d to indicate the configuration of the image forming unit, and detailed descriptions will be omitted.

[0013] The image forming unit Pa includes a photosensitive drum 1a as a rotatable image carrier carrying an electrostatic latent image on its surface. The photosensitive drum 1a is an example of a photosensitive member for electrophotography and is formed in a cylindrical shape. The photosensitive drum 1a rotates in the direction of the arrow (counterclockwise) in FIG. 1. Around the photosensitive drum 1a, there are arranged a charger 2a as a charging unit, a laser beam scanner 3a as a latent image forming unit, a developing device 4a, a primary transfer roller 6a, a cleaning device 8a, a carrier recovery device 5a, and the like.

[0014] Next, we will explain the overall image formation sequence of the image forming apparatus 100 configured as described above. First, the surface of the photosensitive drum 1a is uniformly charged to a predetermined charging potential by the charger 2a. The photosensitive drum 1a charged by the charger 2a is then scanned and exposed by a laser beam scanner 3a, which is an example of an exposure device, with laser light modulated by an image signal.

[0015] The laser beam scanner 3a is controlled based on input image data, and the image data for emitting the laser beam is input from an external terminal such as a document reader or a personal computer (PC). The laser beam from the laser beam scanner 3a changes the surface potential of the photosensitive drum 1a, which has been charged by the charger 2a, in the image area, and an electrostatic latent image is formed on the photosensitive drum 1a (image carrier).

[0016] The electrostatic latent image formed on the photosensitive drum 1a is reverse-developed with toner by the developing device 4a to form a visible image, i.e., a toner image. In this embodiment, the developing device 4a uses a two-component development method using a developer containing non-magnetic toner and a magnetic carrier. That is, each of the developing devices 4a, 4b, 4c, and 4d contains a two-component developer containing a corresponding color toner. Specifically, the developing device 4a contains yellow (Y) toner, the developing device 4b contains magenta (M) toner, the developing device 4c contains cyan (C) toner, and the developing device 4d contains black (K) toner. Therefore, by performing the above-described process for each image forming station Pa, Pb, Pc, and Pd, four color toner images (yellow, magenta, cyan, and black) are formed on the photosensitive drums 1a, 1b, 1c, and 1d, respectively.

[0017] An intermediate transfer belt 60, which serves as a transfer member and intermediate transfer body, is disposed below each of the image forming stations Pa, Pb, Pc, and Pd. The intermediate transfer belt 60 is suspended around rollers 61, 62, and 63 and is movable in the direction of the arrow. A secondary transfer roller 64 is disposed on the outer side of the intermediate transfer belt 24, which is suspended around the roller 63. The secondary transfer roller 64 is configured so that a recording material can pass between it and the intermediate transfer belt 24. The recording material is, for example, a sheet such as paper or a plastic sheet.

[0018] The toner images on the photosensitive drums 1a, 1b, 1c, and 1d are sequentially transferred (primary transfer) to the intermediate transfer belt 60 at primary transfer sections T1a, T1b, T1c, and T1d, which serve as transfer sections, by primary transfer rollers 6a, 6b, 6c, and 6d, which serve as primary transfer members. As a result, toner images of four colors, yellow, magenta, cyan, and black, are superimposed on the intermediate transfer belt 60 to form a full-color image. Furthermore, toner remaining on the photosensitive drum 1a without being transferred to the intermediate transfer belt 60 is collected by a cleaning device 8a.

[0019] This full-color image on the intermediate transfer belt 60 is secondarily transferred onto a recording material fed from a feeding unit (not shown) at a secondary transfer unit T2 formed by the secondary transfer roller 64 and the intermediate transfer belt 60 by the action of the secondary transfer roller 64. Toner that is not transferred to the recording material and remains on the surface of the intermediate transfer belt 60 is collected by an intermediate transfer belt cleaning device 65. Meanwhile, the recording material onto which the toner image has been transferred is sent to a fixing unit 7, where the image is fixed, and then the recording material is discharged outside the apparatus.

[0020] In this embodiment, the developer contained in the developing device 4a is a two-component developer made of a mixture of negatively charged non-magnetic toner and magnetic carrier. The non-magnetic toner (hereinafter referred to as "toner") is a powder made by incorporating colorants, wax components, etc. into a resin such as polyester or styrene, and then pulverizing or polymerizing it. The magnetic carrier (hereinafter referred to as "carrier") is a core made of resin particles kneaded with ferrite particles or magnetic powder, with a resin coating on the surface.

[0021] The process of developing toner onto the photosensitive drum 1a by the developing device 4a will be described. The developing device 4a has a developer container 40 that contains a developer containing toner and a carrier, and a developing sleeve 41 as a developer carrier. The developing sleeve 41 develops the electrostatic latent image on the photosensitive drum 1a with toner at a developing section (developing position) D facing the photosensitive drum 1a, to form a toner image. More specifically, the photosensitive drum 1a is uniformly charged to a charging potential by a DC voltage applied to the charger 2a, or a voltage obtained by superimposing an AC voltage on a DC voltage. The image area is then exposed to laser light from the laser beam scanner 3a, and the potential at the exposed position becomes the exposure potential, forming an electrostatic latent image on the photosensitive drum 1a.

[0022] The developing device 4a transports the developer to the developing section D by the developing sleeve 41. A DC voltage or a voltage obtained by superimposing an AC voltage on a DC voltage is applied to the developing sleeve 41. The negative polarity toner present in the developer is transported to the electrostatic latent image on the photosensitive drum 1a, which is at the exposure potential, by an electric field created by the charging potential and exposure potential of the developing sleeve 41 and the photosensitive drum 1a, and developed.

[0023] [Carrier recovery device] Next, the carrier recovery devices 5a, 5b, 5c, and 5d will be described using FIG. 2 while referring to FIG. 1. Because the carrier recovery devices 5a, 5b, 5c, and 5d have the same configuration, the following description will focus on the carrier recovery device 5a. As shown in FIG. 1, the carrier recovery device 5a recovers carrier adhering to the photosensitive drum 1a downstream of the development unit D (the area where the developing device 4a and the photosensitive drum 1a are adjacent) and upstream of the primary transfer unit T1a (the area where the primary transfer roller 6a and the photosensitive drum 1a are adjacent, i.e., the transfer position) in the rotation direction of the photosensitive drum 1a. As shown in FIG. 2, the carrier recovery device 5a includes a rotatable recovery roller 52 disposed opposite the photosensitive drum 1a, a magnet roller 51 that is non-rotatingly disposed inside the recovery roller 52 and serves as a magnet for attracting the carrier to the surface of the recovery roller 52 by magnetic force, a recovery chamber 53, and a conveying screw 54 that conveys the carrier collected in the recovery chamber 53. These components are disposed in a recovery container 55.

[0024] The collection roller 52 is disposed downstream of the development unit D (development position) and upstream of the primary transfer unit T1a (transfer position) in the rotation direction of the photosensitive drum 1a so as to face the photosensitive drum 1a. The magnet roller 51 has multiple (three in this embodiment) magnetic poles (magnet pieces) 51a, 51b, and 51c. The magnetic pole 51a is disposed at a position facing the photosensitive drum 28Y with the collection roller 52 interposed therebetween. The magnetic pole 51a is a magnetic pole (in this embodiment, an S pole, hereinafter also referred to as magnetic pole S1) for attracting carrier adhering to the outer peripheral surface of the photosensitive drum 1a. For this reason, the magnetic pole 51a is disposed near the closest position P1 between the photosensitive drum 1a and the collection roller 52. The magnetic pole 51b is a magnetic pole (in this embodiment, an N pole, hereinafter also referred to as magnetic pole N1) disposed downstream of the magnetic pole 51a in the rotation direction of the collection roller 52 and is the opposite polarity to the magnetic pole 51a. The magnetic pole 51c is a magnetic pole (N pole in this embodiment, hereinafter also referred to as magnetic pole N2) disposed adjacent to the magnetic pole 51b on the downstream side of the magnetic pole 51b in the rotation direction of the collection roller 52, and has the same polarity as the magnetic pole 51b.

[0025] 2, the magnetic field created by the magnetic pole 51a arranged around the photosensitive drum 1a in close proximity causes the carrier adhering to the surface of the recovery roller 52 to be attracted to the surface of the recovery roller 52. The attracted carrier is transported as the recovery roller 52 rotates, and is peeled off into the recovery chamber 53 by the repulsive magnetic field created by the magnetic poles 51b and 51c.

[0026] Note that instead of the configuration of the repulsive magnetic field created by the magnetic poles 51b and 51c, or in addition to the configuration of the repulsive magnetic field created by the magnetic poles 51b and 51c, a blade may be disposed opposite the collection roller 52 to strip the carrier from the collection roller 52. For example, the blade may be disposed so as to face the collection roller 52 across a gap, downstream of the position where the collection roller 52 faces the photosensitive drum 28Y in the rotation direction of the collection roller 52.

[0027] The conveying screw 54, which serves as a carrier conveying member, has a rotating shaft made of non-magnetic metal and resin blades spirally formed around the rotating shaft. The conveying screw 54 conveys the carrier that has fallen from the collection roller 52 in the direction of its rotation axis by rotating. In this embodiment, the rotation axis of the conveying screw 54 and the rotation axis of the collection roller 52 are substantially parallel to each other.

[0028] Furthermore, a voltage obtained by superimposing an AC voltage on a DC voltage is applied to the recovery roller 52 from a recovery high-voltage board 130 serving as a voltage application unit. This recovery high-voltage board 130 is controlled by the control unit 101, and can apply an AC voltage superimposed on a DC voltage in accordance with the operation of the carrier recovery device 5a. The carrier recovery devices 5a to 5d recover the carrier adhering to the photosensitive drums 1a to 1d by the force of the magnetic field formed by the magnet roller 51 and the force of the electric field formed between the recovery roller 52 and the photosensitive drums 1a to 1d by the voltage applied to the recovery roller 52.

[0029] [Recovery roller groove] In this embodiment, as shown in Fig. 3, a plurality of grooves 71 are formed on the outer peripheral surface of the collection roller 52 along the rotational axis direction (longitudinal direction) of the collection roller 52. The plurality of grooves 71 are formed substantially parallel to the rotational axis direction of the collection roller 52. However, depending on the shape of the grooves formed on the collection roller, there is a risk that the toner adhering to the collection roller may not be sufficiently collected by the carrier. Therefore, in this embodiment, as shown in Fig. 4, the inclination angle of the wall surface 71a on the downstream side in the rotational direction of the collection roller 52 (hereinafter referred to as the downstream wall surface) is different from the inclination angle of the wall surface 71b on the upstream side in the rotational direction of the collection roller 52 (hereinafter referred to as the upstream wall surface). This will be described in detail below.

[0030] 4 is a schematic diagram of groove 71 in a cross section perpendicular to the rotational axis direction of collection roller 52. The rotation direction of collection roller 52 is the direction of the arrow in FIG. 4. Groove 71 has a downstream wall surface (first wall surface) 71a, which is a wall surface downstream in the rotation direction of collection roller 52 from the deepest position of groove 71 (point X in FIG. 4), and an upstream wall surface (second wall surface) 71b, which is a wall surface upstream in the rotation direction of collection roller 52 from the deepest position of groove 71. As is clear from FIG. 4, in this embodiment, the inclination angles of downstream wall surface 71a and upstream wall surface 71b are different.

[0031] The inclination angles of the downstream wall surface 71a and the upstream wall surface 71b are represented by angles θ1 and θ2. θ1 is the smallest angle between the downstream wall surface 71a (as the first wall surface) and a first imaginary line α1 that is perpendicular to the rotation axis of the collection roller 52 and passes through the downstream wall surface 71a. θ2 is the smallest angle between the upstream wall surface 71b (as the second wall surface) and a second imaginary line α2 that is perpendicular to the rotation axis of the collection roller 52 and passes through the upstream wall surface 71b. In this case, in this embodiment, θ1 and θ2 are made different. In this embodiment, θ1 is made larger than θ2. As a result, as will be described in detail later, a configuration is obtained in which θ1 is made larger than angle θ3 (described later) while angle Φ (described later) is easily made an obtuse angle.

[0032] The reason for making the inclination angles of the downstream wall surface 71a and the upstream wall surface 71b different will be explained below. Fig. 5 shows the direction of the magnetic field lines formed by the magnet roller 51 inside the collection roller 52, and Fig. 6 shows the strength and direction of the magnetic force that is exerted on the carrier collected on the surface of the collection roller 52 by the magnetic field formed by the magnet roller 51 near the closest position between the collection roller 52 and the photosensitive drum 1a. The direction, strength, etc. of the magnetic force can be calculated using, for example, JSOL Corporation's electromagnetic field analysis software JMAG.

[0033] 5, the magnetic flux lines formed by the magnetic poles S1 (magnetic pole 51a in FIG. 2), N1 (magnetic pole 51b in FIG. 2), and N2 (magnetic pole 51c in FIG. 2) of the magnet roller 51 arranged inside the collection roller 52 intersect perpendicularly with the collection roller 52 near the magnetic pole S1, and are parallel to the circumferential direction of the collection roller 52 at the midpoint between the magnetic poles S1 and N1. The force acting on the carrier on the collection roller 52 is directed in the direction along these magnetic flux lines.

[0034] In Figure 6, the strength of the magnetic force is indicated by the size of the arrow in the figure. Looking at Figure 6, although the magnetic force is strong near magnetic pole S1, the magnetic flux lines intersect perpendicularly with the collection roller 52, so the force moving the carrier in the circumferential direction of the collection roller 52 is weak. On the other hand, as the distance from magnetic pole S1 increases, the magnetic flux lines are horizontal relative to the surface of the collection roller 52, so the proportion of the force moving the carrier in the circumferential direction of the collection roller 52 increases. However, as the distance from magnetic pole S1 increases, the magnetic force acting on the carrier weakens, so the force moving the carrier in the circumferential direction of the collection roller 52 also weakens. The position where the carrier is most likely to be collected in groove 71 is considered to be the position where the force moving the carrier in the circumferential direction of the collection roller 52 is strongest. In Figure 6, for example, the force moving the carrier in the circumferential direction of the collection roller 52 is strongest in region A in the figure. In other words, in region A of Figure 6, in a cross section perpendicular to the rotational axis direction of the recovery roller 52, there is a position downstream in the rotational direction of the recovery roller 52 from the closest position between the recovery roller 52 and the photosensitive drum 1a, where the force of the rotational direction component of the recovery roller 52 acting on the carrier on the recovery roller 52 due to the magnetic force of the magnet roller 51 first becomes maximum.

[0035] [Inclination angle of downstream wall] The inclination angle of the downstream wall surface 71a will now be described. FIGS. 7(a) to 7(c) show the behavior of the carrier 72 when it is collected in the groove 71. The carrier 72 collected outside the groove 71 is collected in the groove 71 by a force that moves the carrier 72 in the circumferential direction of the collection roller 52. In the case of the magnetic pole configuration as shown in FIG. 5, the carrier 72 is collected onto the collection roller 52 near the position where the photosensitive drum 1a and the collection roller 52 are closest to each other, so the carrier 72 moves in a direction away from the magnetic pole S1 as the collection roller 52 rotates, and a magnetic force in the direction opposite to the rotation direction of the collection roller 52 acts on the carrier 72. For this reason, as shown in FIG. 7(a), the carrier 72 is collected into the groove 71 from the downstream wall surface 71a side of the collection roller 52 of the groove 71.

[0036] Here, the angle formed by the direction of the magnetic force acting on the carrier 72 in the state shown in Fig. 7(a) and a third imaginary line α3 that is perpendicular to the rotation axis of the collection roller 52 and passes through the position Y where the carrier 72 contacts the collection roller 52 is defined as θ3. In this case, if θ3 is smaller than θ1, which is the inclination angle of the downstream wall surface 71a, the carrier 72 enters the inside of the groove 71 while making contact with the downstream wall surface 71a of the collection roller 52 in the groove 71, as shown in Fig. 7(b), and is collected at the bottom of the groove 71 as shown in Fig. 7(c). That is, the carrier 72 moves along the downstream wall surface 71a toward the bottom of the groove 71 and hits the upstream wall surface 71b.

[0037] The carrier 72 is most likely to be collected in the groove 71 at a position downstream in the rotational direction of the collection roller 52 from the closest position between the collection roller 52 and the photosensitive drum 1a, where the force component of the rotational direction of the collection roller 52 acting on the carrier 72 on the collection roller 52 due to the magnetic force of the magnet roller 51 first becomes maximum, that is, the position where the force moving the carrier 72 in the circumferential direction of the collection roller 52 is strongest, as described above. Therefore, when θ3 is the angle between the direction of the magnetic force acting on the carrier 72 on the collection roller 52 at this position and the third imaginary line α3, if θ1 is greater than θ3, the carrier 72 is likely to be collected at the bottom of the groove 71 while contacting the downstream wall surface 71a of the groove 71, as described above. As a result, the carrier can scrape off the toner accumulated on the wall surface of the groove 71, thereby suppressing toner accumulation on the collection roller 52.

[0038] On the other hand, as shown in Comparative Example 1 in Fig. 8(a), if θ3, which is the angle between the direction of the magnetic force acting on the carrier 72 and the third imaginary line α3, is larger than θ1, which is the angle between the downstream wall surface 71a and the first imaginary line α1, when the carrier 72 is collected in the groove 71, the carrier 72 does not come into contact with the downstream wall surface 71a of the groove 71 and is instead collected directly at the bottom of the groove 71, as shown in Fig. 8(b). In this case, the toner accumulated on the wall surface of the groove 71 cannot be scraped off by the carrier, and the toner that continues to accumulate on the wall surface of the groove 71 eventually adheres to the photosensitive drum 1a, making it more likely that image contamination will occur.

[0039] As described above, θ1 is the smallest angle formed between the first virtual line α1 and the downstream wall surface 71a. Furthermore, if the downstream wall surface 71a that forms an angle θ1 with the first virtual line α1 is a curved surface, θ1 is the smallest angle between the tangent of the curved surface and the first virtual line α1. For example, as shown in FIG. 9(a), if the angle between the first virtual line α1 and the top of the downstream wall surface 71a is smallest, the angle at the top is θ1. In the case of FIG. 9(a), θ1 is approximately 0°. Furthermore, as shown in FIG. 9(b), if the angle between the first virtual line α1 and the middle of the downstream wall surface 71a is smallest, the angle at this position is θ1. Furthermore, as shown in FIG. 9(c), if the downstream wall surface 71a is composed of multiple inclined surfaces, θ1 is the angle between the inclined surface that forms the smallest angle with the first virtual line α1 and the first virtual line α1. The same applies to the angle θ2 formed between the upstream wall surface 71b and the second virtual line α2. In this embodiment, the downstream wall surface 71a and the upstream wall surface 71b are flat surfaces.

[0040] [Upstream wall inclination angle] Next, the inclination angle of the upstream wall surface 71b will be described. FIG. 10 shows the behavior of the carrier 72 after it has been collected in the groove 71. Here, the wall surface of the upstream wall surface 71b at which the angle between the upstream wall surface 71b and the second imaginary line α2 is smallest is defined as the reference wall surface. That is, the reference wall surface is the wall surface that forms an angle θ2 with the second imaginary line α2. In this embodiment, since the upstream wall surface 71b is a flat surface, the reference wall surface is the entire upstream wall surface 71b. Also, the rotation direction of the collection roller 52 when viewed from the direction of the rotation axis of the collection roller 52 is defined as the counterclockwise direction. That is, the collection roller 52 rotates in the direction of the arrow in FIGS. 2 and 10.

[0041] In this case, in a cross section perpendicular to the rotation axis direction of the collection roller 52, the angle formed between the direction of the magnetic force acting on the carrier 72 on the collection roller 52 at the position where the force moving the carrier 72 in the circumferential direction of the collection roller 52 is strongest and the reference wall surface (upstream wall surface 71b) is defined as Φ, where the angle is the angle extending counterclockwise from the direction of the magnetic force toward the reference wall surface. In this embodiment, the upstream wall surface 71b is formed so that the angle Φ is an obtuse angle. As described above, the position where the force moving the carrier 72 in the circumferential direction of the collection roller 52 is strongest is downstream in the rotation direction of the collection roller 52 from the position where the collection roller 52 and the photosensitive drum 1a are closest to each other, and where the force component in the rotation direction of the collection roller 52 acting on the carrier 72 on the collection roller 52 due to the magnetic force of the magnet roller 51 first becomes maximum.

[0042] When the angle Φ formed by the direction of the magnetic force acting on the upstream wall surface 71b and the carrier 72 is an obtuse angle, the carrier 72 receives a force that presses it toward the bottom of the groove 71 when it comes into contact with the upstream wall surface 71b. As a result, the carrier 72 is collected inside the groove 71, transported as the recovery roller 52 rotates, and stripped into the recovery chamber 53 by the repulsive magnetic field created by the magnetic poles 51b and 51c.

[0043] On the other hand, as shown in Comparative Example 2 in FIG. 11(a), when the angle Φ formed by the direction of the magnetic force acting on the upstream wall surface 71b and the carrier 72 is acute, the carrier 72 receives a force that transports it toward the upper part of the groove 71 when it contacts the upstream wall surface 71b. As a result, the collected carrier 72 re-enters the groove 71, as shown in FIG. 11(b). Therefore, in Comparative Example 2, the carrier 72 accumulates near the magnetic pole S1 against the rotation of the recovery roller 52. Eventually, the carrier 72 is no longer retained by the recovery roller 52 and re-adheres to the photosensitive drum 1a. The carrier adhering to the photosensitive drum 1a then inhibits toner transfer to the intermediate transfer belt 60, resulting in an abnormal image with white gaps in the areas where transfer is inhibited. Such an abnormal image is called image noise.

[0044] Therefore, it is desirable that the angle Φ formed by the direction of the magnetic force acting on the upstream wall surface 71b and the carrier 72 be an obtuse angle. The shapes of the downstream wall surface 71a and the upstream wall surface 71b can be measured using, for example, a laser microscope VK-8710 manufactured by Keyence Corporation.

[0045] [experiment] An experiment evaluating the relationship between the shape of the grooves 71 and the amount of toner accumulated on the collection roller 52 will be described below. In the experiment, toner accumulation on the collection roller and image noise were evaluated. Five types of collection rollers 52 were prepared for the experiment: Examples 1-1 and 1-2, and Comparative Examples 1-1, 1-2, and 1-3. The various parameters of the image forming apparatus used in the experiment are as follows: Outer diameter of photosensitive drum 1a: 30 mm Outer diameter of collection roller 52: 15 mm The peripheral speed ratio between the recovery roller 52 and the photosensitive drum 1a: 0.5 The closest distance between the photosensitive drum 1a and the collection roller 52: 0.3 mm Non-printing area potential of photosensitive drum 1a (charge potential): -500V Printing area potential of photosensitive drum 1a (exposure potential): -150V DC voltage applied to collection roller 52: -600V AC voltage applied to the collection roller 52: duty ratio 50%, peak-to-peak voltage 1500V, frequency 5kHz Average toner particle size: 6 μm Carrier average particle size: 50 μm Carrier particle size distribution standard deviation: 10 μm

[0046] The distribution of the magnetic field near the collection roller 52 used in the experiment is shown in Table 1. The angles shown in Table 1 are set such that the position (opposing portion) where the collection roller 52 faces the photosensitive drum 1a is 0°, and the counterclockwise angle in FIG. 2 is a positive angle. The distribution of the magnetic field near the collection roller 52 is common to Examples 1-1 and 1-2 and Comparative Examples 1-1, 1-2, and 1-3. [Table 1]

[0047] Table 2 shows parameters of the groove shape of the collection roller 52 used in the experiment. Five types of collection rollers 52 were prepared in the experiment: Examples 1-1 and 1-2, and Comparative Examples 1-1, 1-2, and 1-3. The parameters in Table 2 are explained in FIG. 12. D in FIG. 12 is the formation period of grooves 71 on the collection roller 52. h is the depth of groove 71. The depth of groove 71 is the distance between the bottom of groove 71 (point X in FIG. 12) and a line H3 connecting the upstream vertex H1 and downstream vertex H2 of groove 71 in the rotation direction of the collection roller 52, in a cross section perpendicular to the rotation axis direction of the collection roller 52. [Table 2]

[0048] In the experiment, the toner accumulation on the recovery roller was evaluated by continuously printing 100,000 sheets of a horizontal band chart with a 5% coverage rate. The toner accumulated on the surface of the recovery roller 52 was then collected with transparent tape and the reflection density of the tape was measured using an X-Rite eXactBasic densitometer. Image noise was evaluated by continuously printing 100,000 sheets, collecting the last five sheets, and visually inspecting them for image noise. The results are shown in Table 3. A "x" in the toner accumulation evaluation indicates a reflection density of 0.6 or higher, indicating a poor evaluation. A "good" in the toner accumulation evaluation indicates a reflection density of less than 0.6, indicating a good evaluation. A "x" in the image noise evaluation indicates the occurrence of image noise, indicating a poor evaluation. A "good" in the image noise evaluation indicates that almost no image noise occurred, indicating a good evaluation. [Table 3]

[0049] In the configuration of this experiment, the angle θ3 (see FIG. 7A) between the direction of the magnetic force acting on the carrier and the third imaginary line α3 at the position where the force moving the carrier in the rotational direction of the collection roller 52 is strongest was 33° in the example and comparative examples. In comparative examples 1-1 and 1-2, θ3 was larger than the angle θ1 (see FIG. 7A) between the downstream wall surface 71a and the first imaginary line α1. In other words, the value of "θ1 - θ3" was a negative value. As a result, the carrier was unable to sufficiently collect the toner adhering to the collection roller 52, and the toner accumulated on the collection roller 52.

[0050] On the other hand, in comparison example 1-3, the toner adhering to the recovery roller 52 was sufficiently recovered, but because the angle Φ formed by the upstream wall surface 71b and the direction of the magnetic force acting on the carrier was an acute angle, the carrier remained near the magnetic pole S1, and eventually the carrier could no longer be held by the recovery roller 52, so it re-adhered to the photosensitive drum 1a, resulting in image noise.

[0051] In contrast, in Examples 1-1 and 1-2, the angle θ1 between the downstream wall surface 71a and the first virtual line α1 was larger than the angle θ3 between the direction of the magnetic force applied to the carrier and the third virtual line α3, so it was possible to prevent toner from accumulating on the collection roller 52. If it is possible to prevent toner from accumulating on the collection roller 52, it is possible to prevent image contamination caused by toner accumulated on the collection roller 52 adhering to the photosensitive drum 1a. In addition, the angle Φ formed between the upstream wall surface 71b and the direction of the magnetic force applied to the carrier was an obtuse angle, so it was possible to suppress image noise.

[0052] Note that the above-described Examples 1-1 and 1-2 are preferred configurations. By varying θ1 and θ2, the behavior of the carrier inside and around the groove 71 can be made different between the entrance side and the exit side of the groove 71, compared to when θ1 and θ2 are the same, i.e., when the downstream wall surface 71a and the upstream wall surface 71b are symmetrical. As a result, the toner accumulated on the wall surface of the groove 71 can be easily scraped off by the carrier, thereby suppressing toner accumulation on the collection roller 52. Furthermore, by making θ1 larger than θ2, the carrier 72 can be easily collected at the bottom of the groove 71, thereby further suppressing toner accumulation on the collection roller 52. As a result, the occurrence of image contamination due to toner accumulated on the collection roller 52 adhering to the photosensitive drum 1a can be suppressed.

[0053] <Second embodiment> The second embodiment will be described with reference to Fig. 13. In this embodiment, the bottom surface 71c of the groove 710 is curved and has a radius of curvature equal to or greater than the radius that includes 20% of the cumulative radius distribution of the carrier 72. Since the other configurations and functions are the same as those of the first embodiment described above, the same reference numerals are used for the same configurations, and explanations and illustrations are omitted or simplified. The following description will focus on the points that are different from the first embodiment.

[0054] FIG. 13 is a schematic diagram of a groove 710 in a cross section perpendicular to the rotational axis of the collection roller 52A of this embodiment. In this embodiment, the groove 710 has a bottom surface 71c formed between a downstream wall surface 71a and an upstream wall surface 71b in the rotational direction of the collection roller 52A. The bottom surface 71c of the groove 710 is curved so as to be recessed toward the rotation center of the collection roller 52A. In other words, the downstream wall surface 71a and the upstream wall surface 71b are connected by the curved bottom surface 71c. The radius of curvature of the bottom surface 71c is set to a radius that includes 20% of the cumulative radius distribution of the carrier 72 or more. The cumulative radius distribution of the carrier can be measured using, for example, an LA-950V2 manufactured by Horiba, Ltd.

[0055] In this embodiment, the radius of curvature of the bottom surface 71c is set to be equal to or greater than the radius that includes 20% of the cumulative radius distribution of the carrier 72, so that the carrier 72 can also come into contact with the bottom surface 71c of the groove 710, making it easier for the carrier to scrape off the toner accumulated on the wall surface of the groove 71. This makes it possible to further suppress toner accumulation on the collection roller 52.

[0056] <Third embodiment> The third embodiment will be described with reference to Figures 14 and 15. In this embodiment, the depth h of the groove 711 is set to a radius equal to or greater than the radius that includes 80% of the cumulative radius distribution of the carrier 72. Since the other configurations and functions are the same as those of the first embodiment described above, the same reference numerals are used for the same configurations, and explanations and illustrations are omitted or simplified. The following description will focus on the points that are different from the first embodiment.

[0057] FIG. 14 is a schematic diagram of the groove 711 in a cross section perpendicular to the rotation axis direction of the collection roller 52B of this embodiment. The depth h of the groove 711 is as described above in FIG. 12. In this embodiment, by setting the depth h of the groove 711 to a length equal to or greater than the radius that includes 80% of the cumulative radius distribution of the carrier 72, it is possible to prevent the carrier 72 from climbing over the groove 71 and accumulating near the magnetic pole S1 against the rotation of the collection roller 52. On the other hand, as shown in Comparative Example 3 of FIG. 15, when the depth h of the groove 711A is less than the radius that includes 80% of the cumulative radius distribution of the carrier 72, carriers on the larger particle size side of the carrier particle size distribution are more likely to climb over the groove 711A. This may make the carrier 72 more likely to accumulate near the magnetic pole S1.

[0058] <Fourth embodiment> The fourth embodiment will be described with reference to Figures 16 to 19. In this embodiment, multiple grooves 712, 713, and 714 are inclined with respect to the rotational axis direction of collection rollers 52C, 52D, and 52E. Since the other configurations and functions are the same as those of the first embodiment described above, the same reference numerals are used for similar configurations, and explanations and illustrations will be omitted or simplified. The following description will focus on the differences from the first embodiment.

[0059] Figure 16 is a perspective view of the collection roller 52C of this embodiment. In this embodiment, the multiple grooves 712 are inclined with respect to the rotational axis direction of the collection roller 52 so that the front side is located downstream in the rotation direction of the collection roller 52C relative to the back side in Figure 16. Figure 17 shows the movement of the carrier 72 at the point where the force moving the carrier 72 in the grooves 712 of the collection roller 52C in the rotation direction of the collection roller 52C is strongest, as viewed obliquely from above the collection roller 52C.

[0060] A force acts on the carrier 72 from the magnet roller 51 inside the collection roller 52C in the direction opposite to the rotation direction of the collection roller 52C. In this embodiment, since the grooves 712 are inclined from the front side to the back side in FIG. 16 , the carrier 72 collected in the grooves 712 moves along the grooves 712 in the direction indicated by arrow B in FIGS. 16 and 17 (from the front side to the back side in FIG. 16 ) due to the magnetic force acting on the carrier 72. This movement enables the carrier 72 to collect toner from a wider range on the collection roller 52C. In other words, the carrier can more easily scrape off toner accumulated on the wall surfaces of the grooves 712, thereby further suppressing toner accumulation on the collection roller 52C.

[0061] In the configuration shown in FIG. 16, the grooves are formed so that the front side is located downstream in the rotation direction of the collection roller 52C relative to the back side of the figure, but the inclination direction of the grooves is not limited to this. For example, they may be formed as in another first example of this embodiment shown in FIG. 18. In the collection roller 52D of this example, the multiple grooves 713 are inclined with respect to the rotation axis direction of the collection roller 52D so that the back side is located downstream in the rotation direction of the collection roller 52D relative to the front side of the figure. In this case, the carrier moves in the direction of arrow C in the figure.

[0062] 19 shows a second example of this embodiment. In the collection roller 52E of this example, the grooves 714 are inclined so that the center of the collection roller 52E in the rotational axis direction is located downstream of both ends in the rotational direction of the collection roller 52E. In this case, the carrier moves in the direction of arrow E in the figure. [Explanation of symbols]

[0063] 1a, 1b, 1c, 1d... Photosensitive drum (image carrier) 4a, 4b, 4c, 4d...developing device 5a, 5b, 5c, 5d: Carrier recovery device 40 Developer container 41 Developing sleeve (developer carrier) 51 Magnetic roller (magnet) 52, 52A, 52B, 52C, 52D... Collection rollers 60... Intermediate transfer belt (transfer member) 71, 710, 711, 712, 713, 714...Groove 71a: Downstream wall (first wall) 71b: Upstream wall (second wall) 71c...Bottom surface 100 Image forming device

Claims

1. a rotatable image carrier on which an electrostatic latent image is formed; a developing device including a developer container that contains a developer containing toner and a carrier, and a developer carrier that carries the developer to develop the electrostatic latent image formed on the image carrier into a toner image; a transfer member onto which the toner image carried on the image carrier is transferred; a carrier recovery device that has a rotatable recovery roller disposed opposite the image carrier and a magnet non-rotatably disposed inside the recovery roller, and recovers carrier on the image carrier; the collection roller is disposed downstream of a development position where the electrostatic latent image formed on the image carrier is developed, and upstream of a transfer position where the toner image carried on the image carrier is transferred to the transfer member, with respect to a rotation direction of the image carrier; The collection roller has a plurality of grooves formed on its outer circumferential surface along the rotation axis of the collection roller, The plurality of grooves, in a cross section perpendicular to the rotation axis direction of the collection roller, θ1 is the smallest angle among the angles formed by a first wall surface downstream of the deepest position of the groove in the rotation direction of the collection roller and a first virtual line perpendicular to the rotation axis of the collection roller and passing through the first wall surface, When the smallest angle among the angles formed by a second wall surface on the upstream side of the deepest position of the groove in the rotation direction of the collection roller and a second virtual line that is perpendicular to the rotation axis of the collection roller and passes through the second wall surface is defined as θ2, The θ1 and θ2 are formed to be different from each other. An image forming apparatus characterized by:

2. The θ1 is greater than the θ2 2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

3. In a cross section perpendicular to the rotation axis direction of the collection roller, downstream in the rotation direction of the collection roller from the position where the collection roller and the image carrier are closest to each other, the angle formed by the direction of the magnetic force acting on the carrier on the collection roller at a position where the force of the rotation direction component of the collection roller acting on the carrier on the collection roller by the magnetic force of the magnet first becomes maximum is defined as θ3, and a third imaginary line that is perpendicular to the rotation axis of the collection roller and passes through the position where the force becomes maximum and the carrier comes into contact with the collection roller, The θ1 is greater than the θ3 2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

4. a wall surface among the second wall surfaces at which an angle formed between the second wall surface and the second virtual line is smallest is defined as a reference wall surface; When the rotation direction of the recovery roller is counterclockwise as viewed from the rotation axis direction of the recovery roller, In a cross section perpendicular to the rotation axis direction of the collection roller, at a position downstream in the rotation direction of the collection roller from the position where the collection roller and the image carrier are closest to each other, where a force component in the rotation direction of the collection roller acting on the carrier on the collection roller due to the magnetic force of the magnet first becomes maximum, the angle formed by the direction of the magnetic force acting on the carrier on the collection roller and the reference wall surface along the counterclockwise direction from the direction of the magnetic force is an obtuse angle.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

5. In a cross section perpendicular to the rotation axis direction of the collection roller, the bottom surface of the groove is curved so as to be recessed toward the rotation center of the collection roller, and has a radius of curvature equal to or larger than a radius that includes 20% of the cumulative radius distribution of the carrier.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

6. The groove has a bottom surface formed between the first wall surface and the second wall surface in the rotation direction of the collection roller.

6. The image forming apparatus according to claim 5,

7. In a cross section perpendicular to the rotation axis direction of the collection roller, the distance between a line connecting the upstream vertex and the downstream vertex of the groove in the rotation direction of the collection roller and the bottom surface of the groove is equal to or greater than a radius that includes 80% of the cumulative radius distribution of the carrier.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

8. The plurality of grooves are inclined with respect to the rotation axis direction of the collection roller.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

9. The plurality of grooves are inclined so that the center in the rotation axis direction of the collection roller is located downstream of both ends in the rotation direction of the collection roller.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

10. The first wall surface and the second wall surface are flat surfaces.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

Images