Image forming apparatus

Abstract

To provide a configuration capable of enhancing carrier recovery capability while suppressing an increase in the size of an apparatus.SOLUTION: An image forming apparatus 100 performs primary transfer of a toner image from a photosensitive drum 10 to the outer peripheral surface of an intermediate transfer belt 50 at a primary transfer part T1 and secondary transfer of the toner image from the intermediate transfer belt 50 to a recording material m at a secondary transfer part T2. A carrier recovery device 7 includes a rotatable recovery sleeve 701 disposed opposite the intermediate transfer belt 50 and a magnet roller 702 non-rotatably disposed inside the recovery sleeve 701 and recovers a carrier on the intermediate transfer belt 50. The carrier recovery device 7 is positioned downstream of the primary transfer part T1 and upstream of the secondary transfer part T2 in a rotation direction of the intermediate transfer belt 50.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] As an image forming apparatus, a configuration in which a toner image is formed using a two-component developer containing a non-magnetic toner and a magnetic carrier has been conventionally known. In this configuration, normally, in the developing process, an electrostatic latent image on a photosensitive drum is developed into a toner image by toner, but a certain percentage of the carrier may also adhere to the photosensitive drum (carrier adhesion). If carrier adhesion occurs, it will affect the output image, so for example, Patent Document 1 discloses a configuration equipped with a carrier recovery device that recovers the carrier that has adhered to the photosensitive drum. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 1-134484 Summary of the Invention [Problem to be solved by the invention]

[0004] Here, various devices used in the image forming process, such as a charging device, a developing device, a transfer device, and a cleaning device, are arranged around the photosensitive drum. Therefore, if an attempt is made to arrange a carrier recovery device around the photosensitive drum, the size of the device will increase. On the other hand, if the carrier recovery device is made small and arranged around the photosensitive drum in order to prevent the device from becoming large, the carrier recovery performance of the carrier recovery device may become insufficient.

[0005] An object of the present invention is to provide a configuration capable of increasing the carrier recovery capability while suppressing an increase in the size of the apparatus. [Means for solving the problem]

[0006] One aspect of the present invention is an image forming apparatus comprising: a rotatable image carrier on which an electrostatic latent image is formed; a developing device that develops the electrostatic latent image formed on the image carrier with a developer containing non-magnetic toner and a magnetic carrier to form a toner image; a rotatable intermediate transfer body to which the toner image carried on the image carrier is transferred; a rotatable sleeve arranged opposite the intermediate transfer body; and a magnet arranged non-rotatingly inside the sleeve; and a carrier recovery device that recovers the carrier on the intermediate transfer body, wherein the carrier recovery device is arranged downstream of a first transfer position where the toner image carried on the image carrier is transferred to the intermediate transfer body, with respect to the rotation direction of the intermediate transfer body, and upstream of a second transfer position where the toner image carried on the intermediate transfer body is transferred to a recording material. Effect of the Invention

[0007] According to the present invention, it is possible to improve the carrier recovery capacity while suppressing an increase in the size of the apparatus. [Brief description of the drawings]

[0008] [Figure 1] 1 is a schematic cross-sectional view of an image forming apparatus according to a first embodiment. [Diagram 2] FIG. 2 is a cross-sectional view showing a schematic configuration of an image forming unit according to the first embodiment. [Diagram 3] FIG. 2 is a plan view showing a schematic configuration of an intermediate transfer belt according to the first embodiment. [Figure 4] FIG. 2 is a cross-sectional view showing a schematic configuration of the periphery of the carrier recovery device according to the first embodiment. [Diagram 5] 1 is a cross-sectional view showing a schematic configuration of a carrier charge eliminating device and its periphery according to a first embodiment. [Figure 6] FIG. 2 is a diagram showing a carrier charge eliminating wire according to the first embodiment. [Figure 7] FIG. 4 is a schematic cross-sectional view of an image forming unit according to a first comparative example. [Figure 8] FIG. 11 is a schematic cross-sectional view of an image forming unit according to Comparative Example 2. [Figure 9] FIG. 11 is a cross-sectional view showing a schematic configuration of a carrier recovery device and its periphery according to a second embodiment. [Figure 10] FIG. 11 is a cross-sectional view showing a schematic configuration of an image forming apparatus according to a third embodiment. [Figure 11] FIG. 13 is a schematic plan view of the periphery of a carrier recovery device according to a fourth embodiment. [Figure 12] FIG. 13 is a cross-sectional view showing a schematic configuration of an image forming apparatus according to a fifth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] <First embodiment> The first embodiment will be described with reference to Figures 1 to 8. First, the schematic configuration of an image forming apparatus according to the present embodiment will be described with reference to Figures 1 to 3.

[0010] [Image forming equipment] The image forming apparatus 100 of this embodiment is an electrophotographic full-color laser beam printer. As shown in FIG. 1, the image forming apparatus 100 includes four image forming units 1Y, 1M, 1C, and 1K, an intermediate transfer belt 50, a belt cleaning device 53, a carrier charge eliminating device 6, and a carrier recovery device 7. The image forming apparatus 100 forms a toner image on a recording material in response to an image signal from a host device such as a document reading device connected to the image forming apparatus main body or a personal computer connected to the image forming apparatus main body so as to be able to communicate with the image forming apparatus main body. Examples of the recording material include sheet materials such as paper, plastic film, and cloth. The four image forming units 1Y, 1M, 1C, and 1K form yellow, magenta, cyan, and black toner images, respectively.

[0011] The four image forming units 1Y, 1M, 1C, and 1K included in the image forming apparatus 100 have substantially the same configuration, except for the different developing colors. Therefore, the image forming unit 1Y will be described as a representative, and descriptions of the other image forming units will be omitted.

[0012] As shown in Fig. 2, the image forming unit 1Y is provided with a cylindrical photosensitive member, i.e., a photosensitive drum 10, as an image carrier capable of carrying an electrostatic latent image on its surface. The photosensitive drum 10 is rotated by a driving force transmitted from a driving unit (not shown) provided in the image forming apparatus main body. In the image forming unit 1Y, a charging roller 12 as a charging device, a developing device 13, a primary transfer roller 4 (Fig. 1) as a primary transfer member, and a drum cleaning device 14 are arranged around the photosensitive drum 10. An exposure device (not shown in the figure, a laser scanner in this embodiment) is arranged above the photosensitive drum 10.

[0013] The photosensitive drum 10 has an outer diameter of, for example, 30 mm and an organic photosensitive layer. The photosensitive drum 10 rotates in the direction of the arrow D10 at a maximum peripheral speed of 330 mm / s during image formation. The charging roller 12 uniformly charges the surface of the photosensitive drum 10. The exposure device exposes the surface of the photosensitive drum 10 charged by the charging roller 12 to light to form an electrostatic latent image. The developing device 13 has a developing container that contains a developer (two-component developer) containing non-magnetic toner and a magnetic carrier, and a developing sleeve as a developer carrier that can carry the developer in the developing container and rotate. The electrostatic latent image formed on the surface of the photosensitive drum 10 is developed into a toner image by the developer carried by the developing sleeve. The primary transfer roller 4 performs primary transfer of the toner image formed on the surface of the photosensitive drum 10 to the intermediate transfer belt 50. The drum cleaning device 14 removes the transfer residual toner remaining on the photosensitive drum 10 after the primary transfer.

[0014] The intermediate transfer belt 50 as an intermediate transfer body is rotatable, and the toner image carried on the photosensitive drum 10 is transferred onto the intermediate transfer belt 50. The intermediate transfer belt 50 contacts the photosensitive drum 10 of the image forming units 1Y, 1M, 1C, and 1K to form a primary transfer portion T1 where the toner image is primarily transferred from the photosensitive drum 10. In addition, downstream of the primary transfer portion T1 with respect to the rotation direction of the intermediate transfer belt 50, a secondary transfer portion T2 is formed where the toner image is secondarily transferred from the intermediate transfer belt 50 to a recording material. In the secondary transfer portion T2, a secondary transfer roller 8e as a secondary transfer member is disposed so as to abut against the outer circumferential surface of the intermediate transfer belt 50. A nip portion for nipping and conveying the recording material is formed between the intermediate transfer belt 50 and the secondary transfer roller 8e.

[0015] The intermediate transfer belt 50 has a volume resistivity of 10 6 ~10 12 The intermediate transfer belt 50 may be made of an elastic material such as urethane resin, fluorine resin, nylon resin, polyimide resin, silicone rubber, or hydrin rubber, or may have carbon or conductive powder dispersed therein to adjust the electrical resistance.

[0016] 1, the intermediate transfer belt 50 is supported by a plurality of tension rollers, namely, a first roller 51, a second roller 52, and a third roller 8i. The magnitude of the tension applied to the first, second, and third rollers 51, 52, and 8i depends on the material of the intermediate transfer belt 50, but it is preferable that the intermediate transfer belt 50 does not break or become permanently distorted. In this embodiment, a polyimide resin-based intermediate transfer belt 50 is used to prevent breakage or permanent distortion.

[0017] The first roller 51 has an elastic layer made of EPDM (ethylene propylene diene rubber) on the outer periphery, and has an outer diameter of 30 mm. The first roller 51 is driven by a motor (not shown) to rotate the intermediate transfer belt 50 in the direction of the arrow D50. That is, the first roller 51 is a drive roller that drives the intermediate transfer belt 50. The second roller 52 is made of a solid non-magnetic metal and has an outer diameter of 30 mm. As shown in FIG. 3, the second roller 52 changes the position of a support member 54 that supports one end 52aef of the rotation shaft in the direction of the arrow D54, thereby controlling the position of the intermediate transfer belt 50 in a direction perpendicular to the moving direction of the intermediate transfer belt 50 (width direction, arrow D50V direction) to an appropriate position. That is, the second roller 52 is a steering roller that controls the position (deviation position) of the intermediate transfer belt 50 in the width direction.

[0018] The first roller 51, the second roller 52, and the third roller 8i are arranged in order in the rotation direction of the intermediate transfer belt 50, and in a first tension region α of the intermediate transfer belt 50 stretched by the first roller 51 and the second roller 52, a toner image is transferred from the photosensitive drum 10 to the intermediate transfer belt 50. That is, in the first tension region α, the photosensitive drums 10 of the image forming units 1Y, 1M, 1C, and 1K are arranged on the outer periphery side of the intermediate transfer belt 50, and the primary transfer roller 4 is arranged on the inner periphery side of the intermediate transfer belt 50, forming the primary transfer portion T1 of each image forming unit 1Y, 1M, 1C, and 1K. In each primary transfer portion T1, the intermediate transfer belt 50 is sandwiched between the primary transfer roller 4 and the photosensitive drum 10. As the primary transfer roller 4, it is preferable to form an elastic layer such as urethane foam on the outer periphery of a metallic rotating shaft. A voltage of 100 to 1000 V of a polarity opposite to the normal charging polarity of the toner is applied to the primary transfer roller 4.

[0019] The third roller 8i is disposed at a position facing the secondary transfer roller 8e with the intermediate transfer belt 50 interposed therebetween. That is, the third roller 8i is a secondary transfer inner roller that stretches the intermediate transfer belt 50 at the secondary transfer portion T2. ​​In this embodiment, the third roller 8i and the secondary transfer roller 8e constitute the secondary transfer device 8.

[0020] The material of the third roller 8i is preferably solid or foamed EPDM, NBR (nitrile rubber), etc., and the material of the secondary transfer roller 8e is preferably NBR, etc. A voltage of 1.0 to 6.0 kV of a polarity opposite to the normal charging polarity of the toner is applied to the secondary transfer roller 8e.

[0021] [Overall operation of the image forming device] The operation of the entire image forming apparatus 100 will be described below, adding an appropriate explanation of the configuration. Based on image information received from a host computer (not shown) or the like, in each image forming unit 1Y, 1M, 1C, 1K, the photosensitive drum 10 is rotated counterclockwise in FIG. 2 by a drive unit (not shown), and the surface is uniformly charged by the charging roller 12. Then, an exposure device (not shown) irradiates the surface of the photosensitive drum 10 with a laser beam modulated based on the image information, and an electrostatic latent image is formed. The intensity and spot diameter of the laser beam are appropriately set according to the resolution of the image forming apparatus 100 and the desired image density. The electrostatic latent image on the photosensitive drum 10 is formed by the portion irradiated with the laser beam (light portion, potential VL) and the portion not irradiated with the laser beam (dark portion, potential VD).

[0022] As the photosensitive drum 10 rotates, the electrostatic latent image reaches a portion facing the developing device 13, where toner charged with the same polarity (negative polarity in this embodiment) adheres to the light portion of the electrostatic latent image to develop it into a toner image. When forming a full-color image, toner images of each color are formed in the image forming units 1Y to 1K corresponding to each color in the same manner. These toner images of each color are sequentially primarily transferred onto the intermediate transfer belt 50 at each primary transfer portion T1 and are superimposed on the intermediate transfer belt 50.

[0023] At each primary transfer portion T1, the toner image is primarily transferred by an electric field formed at the primary transfer portion T1 by a voltage of the opposite polarity to the toner applied to the primary transfer roller 4 in contact with the inner circumference of the intermediate transfer belt 50. When the intermediate transfer belt 50 passes through the primary transfer portion T1 with the photosensitive drum 10 of each color, a full-color toner image is carried on the intermediate transfer belt 50, and the primary transfer process is completed. Meanwhile, the surfaces of the photosensitive drums 10 that have completed the primary transfer of the toner images are cleaned by the drum cleaning devices 14, and then prepared for the next image forming process.

[0024] Next, one sheet of recording material m is taken out from a feeding section (not shown) and conveyed in the direction of secondary transfer section T2. ​​At this time, a voltage of the opposite polarity to that of the toner is applied to secondary transfer roller 8e, whereby the four color toner images are secondarily transferred collectively from intermediate transfer belt 50 onto recording material m. After passing through secondary transfer section T2, recording material m carrying an unfixed toner image reaches a fixing device (not shown) where it is fixed as a permanent image by being heated and pressed. Meanwhile, the surface of intermediate transfer belt 50 after the toner image has been transferred onto recording material m is cleaned by belt cleaning device 53.

[0025] The belt cleaning device 53, for example, brings a cleaning blade made of urethane rubber or the like into contact with the surface (outer circumferential surface) of the intermediate transfer belt 50 to scrape off the secondary transfer residual toner adhering to the surface of the intermediate transfer belt 50. The scraped off secondary transfer residual toner is collected in a waste toner container (not shown). The secondary transfer residual toner refers to the toner that is not secondary transferred to the recording material m during the secondary transfer and remains on the surface of the intermediate transfer belt 50. In addition, the inner circumferential surface of the intermediate transfer belt 50 facing the belt cleaning device 53 is supported by a support roller 539. This allows the cleaning blade to be stably contacted with the outer circumferential surface of the intermediate transfer belt 50, and the secondary transfer residual toner can be more reliably removed. The belt cleaning device 53 may be disposed on the outer circumferential surface of the intermediate transfer belt 50 stretched by the first roller 51. In this case, the first roller 51 functions as a support roller.

[0026] [Carrier recovery device] Next, the carrier recovery device 7 that recovers the carrier adhering to the intermediate transfer belt 50 will be described with reference to Figs. 1 and 4. Fig. 4 is an enlarged view of the carrier recovery device 7. In the configuration described in the above-mentioned Patent Document 1, the carrier recovery device is disposed around the photosensitive drum, but in this embodiment, the carrier recovery device 7 is disposed around the intermediate transfer belt 50, not around the photosensitive drum 10.

[0027] The carrier recovery device 7 is disposed downstream of a primary transfer section (first transfer position) T1 and upstream of a secondary transfer section (second transfer position) T2 in the rotation direction (direction of arrow D50) of the intermediate transfer belt 50 so as to face the outer circumferential surface of the intermediate transfer belt 50 without contacting the outer circumferential surface of the intermediate transfer belt 50. In the present embodiment, since there are four image forming units 1Y to 1K, the carrier recovery device 7 is disposed downstream of the primary transfer section (first transfer position) T1 of the image forming unit 1K which is the most downstream in the rotation direction of the intermediate transfer belt 50 among these image forming units.

[0028] In particular, in this embodiment, as shown in FIG. 1, the carrier recovery device 7 is disposed at a position facing the second tension region β of the intermediate transfer belt 50, which is tensioned by the second roller 52 and the third roller 8i. As described above, the intermediate transfer belt 50 is tensioned by the first roller 51, the second roller 52, and the third roller 8i, and has a substantially triangular cross-sectional shape. Therefore, a relatively large space exists outside the second tension region β of the intermediate transfer belt 50. Therefore, in this embodiment, the carrier recovery device 7 is disposed in this space. Specifically, as shown in FIG. 1, the carrier recovery device 7 is disposed so that the bottom end 7b of the carrier recovery device 7 is above the horizontal line LT2 passing through the position (secondary transfer portion T2) where the secondary transfer roller 8e and the third roller 8i are closest to each other. This makes it possible to prevent the image forming apparatus 100 from becoming large even if the carrier recovery device 7 is disposed in the image forming apparatus 100.

[0029] The carrier recovery device 7 recovers the carrier adhering to the outer peripheral surface of the intermediate transfer belt 50. Particularly in this embodiment, the carrier recovery device 7 recovers the carrier by magnetic force. Specifically, as shown in FIG. 4, the carrier recovery device 7 has a carrier recovery roller 70, a carrier recovery blade 71, a carrier transport screw 72, a carrier recovery container 73, and the like. The carrier recovery container 73 contains the carrier recovery roller 70, the carrier recovery blade 71, and the carrier transport screw 72, and also contains the recovered carrier. The carrier recovery roller 70 has a recovery sleeve 701 as a rotatable sleeve, a magnet roller 702 as a magnetic field generating unit (magnet), and the like.

[0030] The recovery sleeve 701 rotates while facing the outer circumferential surface of the intermediate transfer belt 50 with a predetermined gap therebetween. The recovery sleeve 701 is, for example, a cylindrical member made of non-magnetic metal with an outer diameter of 24.5 mm and a thickness of 0.7 mm. It is made of a material that is not thermally deformed, has excellent abrasion resistance, and is easy to process. The recovery sleeve 701 rotates in the direction of arrow D701 (i.e., counter direction) in which the movement direction of the surface at the position facing the intermediate transfer belt 50 is opposite to the movement direction of the outer circumferential surface of the intermediate transfer belt 50. In addition, the gap between the outer circumferential surface of the recovery sleeve 701 and the outer circumferential surface of the intermediate transfer belt 50 at the closest position is, for example, 100 μm or more and 150 μm or less.

[0031] In order to maintain a constant distance between the collection sleeve 701 and the intermediate transfer belt 50, a support roller 79 is disposed inside the intermediate transfer belt 50 at a position facing the collection sleeve 701 so as to abut against the inner circumferential surface of the intermediate transfer belt 50. The support roller 79 supports the intermediate transfer belt 50 from the inside, and is, for example, a cylindrical member made of a non-magnetic metal and having an outer diameter of 20 mm. The support roller 79 does not have a driving source, and is pressed against the intermediate transfer belt 50 by a pressure spring (not shown) so as to follow the movement of the intermediate transfer belt 50.

[0032] The magnet roller 702 is disposed inside the recovery sleeve 701 in a non-rotating manner, and attracts the carrier to the surface of the recovery sleeve 701 by magnetic force. In this embodiment, the magnet roller 702 has multiple magnetic poles (three in this embodiment) around a rotating shaft made of nonmagnetic metal, has a cylindrical outer circumferential surface, and has an outer diameter of 17 mm. For the magnetic poles, a ferrite magnet such as barium ferrite or strontium ferrite, or a rubber ferrite magnet in which a ferrite magnet is dispersed in rubber can be used.

[0033] The magnet roller 702 has a magnetic pole N1 as a first magnetic pole, a magnetic pole S1 as a second magnetic pole, and a magnetic pole S2 as a third magnetic pole. The magnetic pole N1 is disposed at a position facing the intermediate transfer belt 50 via the collection sleeve 701. The magnetic pole N1 is a magnetic pole for attracting carriers attached to the outer peripheral surface of the intermediate transfer belt 50, and for this reason, the magnetic pole N1 is disposed in the vicinity of the closest position between the intermediate transfer belt 50 and the collection sleeve 701. The magnetic flux density of the magnetic pole N1 in a direction perpendicular to the surface of the collection sleeve 701 is preferably 150 mT or more.

[0034] The magnetic pole S1 is disposed downstream of the magnetic pole N1 in the rotation direction of the recovery sleeve 701, and has a polarity different from that of the magnetic pole N1. The magnetic pole S2 is disposed adjacent to the magnetic pole S1 downstream of the magnetic pole S1 in the rotation direction of the recovery sleeve 701, and has the same polarity as the magnetic pole S1. Such magnetic poles S1 and S2 are a repulsive magnetic pole pair provided on the opposite side of the magnetic pole N1 with respect to the rotation axis of the recovery sleeve 701. At position A in the center between the magnetic poles S1 and S2, the force exerted on the carrier by the repulsive magnetic field formed by the magnetic poles S1 and S2 on the surface of the recovery sleeve 701 is almost zero. At position A, the carrier falls from the recovery sleeve 701 into the carrier recovery container 73, preventing the carrier once recovered from being transported again to the surface of the intermediate transfer belt 50.

[0035] The carrier recovery blade 71 as a blade is disposed so as to face the recovery sleeve 701 with a gap therebetween downstream of the position where the recovery sleeve 701 faces the intermediate transfer belt 50 with respect to the rotation direction of the recovery sleeve 701. This gap is, for example, 100 μm. The carrier recovery blade 71 removes the carrier attached to the recovery sleeve 701. In this embodiment, the carrier recovery blade 71 is disposed at a position facing the magnetic pole S2 across the recovery sleeve 701. Therefore, the carrier that stands up due to the magnetic field of the magnetic pole S2 can be scraped off by the carrier recovery blade 71. As a result, the carrier that does not fall from the recovery sleeve 701 due to the repulsive magnetic field of the magnetic poles S1 and S2 and remains in the recovery sleeve 701 can be scraped off into the carrier recovery container 73 by the carrier recovery blade 71.

[0036] The carrier transport screw 72 as a carrier transport member is disposed below the collection sleeve 701 in the carrier collection container 73. The carrier transport screw 72 has a rotating shaft made of a non-magnetic metal and resin blades formed in a spiral shape around the rotating shaft, and has an outer diameter of, for example, 33 mm. The carrier transport screw 72 transports the carriers that have dropped from the collection sleeve 701 in the direction of the rotation axis by rotating. In this embodiment, the rotation axis direction of the carrier transport screw 72 and the rotation axis direction of the collection sleeve 701 are approximately parallel to each other.

[0037] In this embodiment, the carrier attached to the surface of the intermediate transfer belt 50 is attracted to the surface of the recovery sleeve 701 by the magnetic pole N1 and is transported to the inside of the carrier recovery container 73 as the recovery sleeve 701 rotates. Then, due to the action of the magnetic poles S1 and S2 which repel each other, the magnetic force acting on the carrier becomes almost zero at the position A at the approximate center, so the carrier transported to the position A falls by gravity. The carrier that does not fall at the position A and remains in the recovery sleeve 701 is scraped off by the carrier recovery blade 71. The carrier that falls into the carrier recovery container 73 is transported in the direction along the rotation axis by the carrier transport screw 72 and is stored in a carrier storage container (not shown) provided on the front side of the image forming apparatus main body. The front side is, for example, the side where an operator such as a user operates the image forming apparatus 100, and is, for example, the side where an operation unit such as an operation panel for operating the image forming apparatus 100 is arranged. The back side is the opposite side to the front side, and is the back side of the image forming apparatus 100.

[0038] By transporting the carrier dropped from the collection sleeve 701 by the carrier transport screw 72 in this manner, it is possible to prevent the carrier from accumulating too much below the collection sleeve 701. The carrier transported by the carrier transport screw 72 is stored in the carrier storage container as described above, and the carrier storage container is replaced by a user or a service person during maintenance, for example. In the above description, the magnetic poles S1, S2 and the carrier collection blade 71 that repel each other are used to drop the carrier from the collection sleeve 701, but the configuration for dropping the carrier into the repulsive magnetic field may be omitted. However, having both configurations makes it possible to drop the carrier from the collection sleeve 701 more efficiently.

[0039] Furthermore, in this embodiment, a power supply 74 is provided as a voltage application unit capable of applying a voltage of the same polarity as the charge polarity of the toner to the collection sleeve 701. For this purpose, the power supply 74 is connected to the collection sleeve 701 via a cable 75. By applying a voltage of the same polarity as the charge polarity of the toner to the collection sleeve 701 from the power supply 74, it is possible to prevent the toner carried on the intermediate transfer belt 50 from being collected by the collection sleeve 701. The voltage applied from the power supply 74 to the collection sleeve 701 is, for example, 1000 V or more and 1500 V or less in absolute value.

[0040] In this embodiment, the carrier on the surface of the intermediate transfer belt 50 is collected by the magnetic field of the magnet roller 702 built in the collection sleeve 701, and the power source 74 applies a voltage of the same polarity as the charging polarity of the toner to the collection sleeve 701. As a result, it is possible to prevent a part of the toner of the toner image carried on the intermediate transfer belt 50 from being collected by the collection sleeve 701 while collecting the carrier from the intermediate transfer belt 50. Therefore, even if the carrier collection device 7 is provided downstream of the primary transfer portion T1 and upstream of the secondary transfer portion T2 with respect to the rotation direction of the intermediate transfer belt 50, it is possible to prevent the carrier collection device 7 from affecting the toner image transferred to the intermediate transfer belt 50 at the primary transfer portion T1.

[0041] [Carrier charge elimination device] 1, in this embodiment, a carrier charge eliminating device 6 that reduces the charge amount of the carrier prior to carrier recovery is disposed adjacent to the upstream side of the carrier recovery device 7 in the rotation direction of the intermediate transfer belt 50. That is, the carrier charge eliminating device 6 as a second voltage application unit is disposed downstream of the primary transfer portion T1 and upstream of the carrier recovery device 7 in the rotation direction of the intermediate transfer belt 50. The carrier charge eliminating device 6 is capable of applying a voltage of a polarity opposite to the charge polarity of the carrier to the carrier attached to the outer circumferential surface of the intermediate transfer belt 50.

[0042] Such a carrier charge eliminating device 6 includes a corona charger 61 and a power source 62, as shown in Fig. 5. The corona charger 61 includes a housing 61b made of a non-magnetic metal having an opening 61a facing the intermediate transfer belt 50, and a charge eliminating wire 60 arranged inside the housing 61b. The charge eliminating wire 60 is arranged along the width direction intersecting with the rotation direction of the intermediate transfer belt 50, and as shown in Fig. 6, a power source 62 is connected to a rear end 60er of the charge eliminating wire 60 via an electrode (not shown) arranged on the image forming apparatus main body side and a cable 63. A charge eliminating bias, which is a voltage of a polarity opposite to the charge polarity of the carrier, is applied from the power source 62 to the charge eliminating wire 60.

[0043] As a result, the charge amount of the carrier attached to the intermediate transfer belt 50 by the corona charger 61 can be reduced, and the electrostatic adhesion force of the carrier to the intermediate transfer belt 50 can be reduced. This makes it easier to recover the carrier on the intermediate transfer belt 50 in the carrier recovery device 7 located downstream of the carrier charge removal device 6 in the rotation direction of the intermediate transfer belt 50. In this embodiment, the absolute value of the charge removal bias applied from the power source 62 is 500V or more and 1000V or less.

[0044] According to the configuration of this embodiment, carrier recovery can be sufficiently performed while suppressing the size of the device. That is, in this embodiment, unlike the first embodiment described above, a carrier recovery device is not provided around the photosensitive drum, but a carrier recovery device 7 is provided around the intermediate transfer belt 50. Therefore, the carrier adhered to the photosensitive drum 10 from the developing device 13 adheres to the intermediate transfer belt 50 at the primary transfer portion T1. The carrier adhered to the outer peripheral surface of the intermediate transfer belt 50 is recovered by the carrier recovery device 7 disposed downstream of the primary transfer portion T1 and upstream of the secondary transfer portion T2 before being transferred to the recording material m.

[0045] This prevents carrier from entering between the intermediate transfer belt 50 and the belt cleaning device 53, thereby preventing scratches on the outer periphery of the intermediate transfer belt or disturbance of the toner image formed on the recording material m, thereby improving the durability of the intermediate transfer belt 50 and obtaining a stable output image.

[0046] In addition, since the carrier recovery device 7 in this embodiment is sufficiently small compared to the circumferential length of the intermediate transfer belt 50 (750 mm in this embodiment), even if the carrier recovery device 7 is arranged on the outer periphery side of the intermediate transfer belt 50, the effect on the size increase of the image forming apparatus 100 is small. Furthermore, when attempting to arrange the carrier recovery device around the photosensitive drum while suppressing the size increase of the image forming apparatus 100, it is required to make the carrier recovery device small, but if the carrier recovery device is made small, there is a possibility that sufficient carrier recovery performance cannot be obtained. On the other hand, in this embodiment, since the carrier recovery device 7 is arranged on the outer periphery side of the intermediate transfer belt 50, there is little effect on the size increase of the apparatus even if the carrier recovery device 7 is not made small. As a result, the size increase of the image forming apparatus 100 can be suppressed with a configuration that sufficiently obtains carrier recovery performance.

[0047] [experiment] Here, an experiment conducted to confirm the effect of the first embodiment described above will be described. The experiment was conducted as follows for Example 1, which is the configuration of the first embodiment described above, Example 2, which is the configuration of the second embodiment described below, Example 3, which is the configuration of the third embodiment, Example 4, which is the configuration of the fourth embodiment, Example 5, which is the configuration of the fifth embodiment, and Comparative Examples 1 and 2. That is, in the experiment, in each configuration, a solid black (K) image was formed on an A-size sheet, and the "occurrence rate of image defects due to carrier adhesion" and "occurrence rate of image defects due to scattered toner adhesion" were visually confirmed when 1000 pages were output.

[0048] The "occurrence rate of image defects due to carrier adhesion (%)" is the ratio of the number of pages of output images with image defects due to carrier adhesion to all output image pages, and the "occurrence rate of image defects due to scattered toner adhesion (%)" is the ratio of the number of pages of output images with image defects due to scattered toner adhesion to all output image pages. The charge polarity of most scattered toner is opposite to the polarity of normally charged toner and is the same polarity as the carrier. Therefore, the scattered toner is collected together with the carrier in the carrier recovery device. Therefore, if the carrier recovery performance of the carrier recovery device is high, the scattered toner recovery performance will also be high, and the occurrence rate of image defects due to scattered toner adhesion will also decrease.

[0049] The results of this experiment are shown in Table 1. The "total cost of the carrier recovery device and carrier de-electrification device" shown in Table 1 is a relative value with Example 1 being set at 100. Table 1 also shows the lifespan of the intermediate transfer belt in each configuration and the size of the image forming apparatus 100. The lifespan of the intermediate transfer belt is the same for each configuration. The size of the image forming apparatus is the size in the left-right direction when the image forming apparatus is viewed from the front side. [Table 1]

[0050] [Comparative Example 1] Comparative Example 1 will now be described with reference to Fig. 7. Fig. 7 shows only an image forming unit 1A of Comparative Example 1, which is the same as that of the first embodiment except for the position and number of the carrier recovery devices. In Comparative Example 1, the carrier recovery device 7A is disposed near the outer periphery of the photosensitive drum 10, downstream of the developing device 13 in the rotation direction of the photosensitive drum 10 (the direction of the arrow D10), and upstream of the primary transfer portion T1.

[0051] The basic configuration of the carrier recovery device 7A is the same as that of the carrier recovery device 7 in the first embodiment, but in Comparative Example 1, it is made smaller to fit into a narrow space. Specifically, the outer diameter of the recovery sleeve is set to 10 mm (24.5 mm in Example 1). Therefore, the magnetic force of the magnet roller arranged inside the recovery sleeve is also low, and the carrier recovery performance is low. In addition, since the image forming apparatus has four image forming units, four carrier recovery devices 7A are also required in Comparative Example 1, which increases the cost of the apparatus and the size of the image forming apparatus.

[0052] [Comparative Example 2] Next, Comparative Example 2 will be described with reference to FIG. 8. FIG. 8 shows only the image forming unit 1B of Comparative Example 2, which is the same as that of the first embodiment except for the position and number of the carrier recovery devices. In Comparative Example 2, similar to Comparative Example 1, the carrier recovery device 7B is disposed near the outer periphery of the photosensitive drum 10, downstream of the developing device 13 with respect to the rotation direction of the photosensitive drum 10 (arrow D10 direction), and upstream of the primary transfer portion T1. However, in Comparative Example 2, the carrier recovery device 7B is not excessively miniaturized as in Comparative Example 1, with a priority given to ensuring sufficient performance. In other words, the carrier recovery device 7B is larger than that of Comparative Example 1.

[0053] In Comparative Example 2, in order to arrange a large carrier recovery device 7B around the photosensitive drum 10, the outer diameter of the photosensitive drum 10 is set to 84 mm, thereby expanding the space around the photosensitive drum 10. This makes it possible to arrange a carrier recovery device 7B with sufficient performance, but increases the cost of the photosensitive drum 10 and further increases the size of the image forming apparatus. Furthermore, as in Comparative Example 1, four carrier recovery devices 7B are required, which increases the cost of the apparatus and also increases the size of the image forming apparatus.

[0054] In Table 1, comparing Example 1 and Comparative Example 1, it can be seen that Example 1 has better results than Comparative Example 1 in terms of "Rate of image defects caused by carrier adhesion (%)" and "Rate of image defects caused by scattered toner adhesion (%)". It can also be seen that the cost can be reduced in Example 1 compared to Comparative Example 1.

[0055] Moreover, when comparing Example 1 and Comparative Example 2, it is found that the "image defect occurrence rate (%) due to carrier adhesion" is the same, but the "image defect occurrence rate (%) due to scattered toner adhesion" is better in Example 1 than in Comparative Example 2. It is also found that the image forming apparatus in Comparative Example 2 is larger than that in Example 1, and the cost is significantly higher than that in Example 1. From the above, it is found that by arranging the carrier recovery device 7 on the outer periphery of the intermediate transfer belt 50 as in Example 1, it is possible to achieve carrier recovery performance equal to or better than that in Comparative Examples 1 and 2 in which the carrier recovery device is arranged around the photosensitive drum, while also achieving miniaturization of the apparatus and reduction in the apparatus cost.

[0056] <Second embodiment> The second embodiment will be described with reference to Fig. 9. Unlike the first embodiment, this embodiment does not include a power source 74 as a first voltage application unit capable of applying a voltage of the same polarity as the charge polarity of the toner to the collecting sleeve 701. The other configurations and operations are the same as those of the first embodiment described above.

[0057] In the case of this embodiment, unlike the first embodiment, an electric field that can suppress toner recovery cannot be formed in the carrier recovery device 7. However, since the power source, cable, and electrodes required for the configuration to suppress toner recovery are not provided, the device cost can be reduced compared to the first embodiment.

[0058] In the case of this embodiment, as shown in Example 2 of Table 1 above, the rate of image defects caused by scattered toner adhesion is higher than that of Example 1, but the rate of image defects caused by carrier adhesion is the same as that of Example 1. Therefore, this hardly causes any problems in practice, and the device cost is also low.

[0059] <Third embodiment> The third embodiment will be described with reference to Fig. 10. In this embodiment, unlike the first embodiment, the carrier charge eliminating device 6 is not provided upstream of the carrier recovery device 7 with respect to the rotation direction of the intermediate transfer belt 50. The other configurations and functions are the same as those of the first embodiment.

[0060] In the case of the image forming apparatus 100A of this embodiment, the charge amount of the carrier is not reduced prior to carrier recovery as in the first embodiment. However, since the carrier charge removing device 6 shown in Figs. 5 and 6 can be omitted compared to the first embodiment, the cost of the apparatus can be reduced.

[0061] In the case of this embodiment, as shown in Example 3 of Table 1 above, the carrier recovery efficiency is lower than that of Example 1, so the rate of image defects caused by carrier adhesion increases, but the rate of image defects caused by scattered toner adhesion is the same as that of Example 1. Therefore, this hardly causes any practical problems, and the device cost is also low.

[0062] <Fourth embodiment> The fourth embodiment will be described with reference to Fig. 11. Fig. 11 is a plan view showing a schematic configuration of the periphery of the carrier recovery device 7 of this embodiment (the intermediate transfer belt 50 is not shown).

[0063] In this embodiment, similarly to the first embodiment, the second roller 52 serves as a steering roller that controls the widthwise position (deviation position) of the intermediate transfer belt 50. Meanwhile, in this embodiment, unlike the first embodiment, it is possible to optimize the position of the carrier recovery device 7 with respect to the intermediate transfer belt 50 in conjunction with the control of the widthwise position (deviation position) of the intermediate transfer belt 50 by the second roller 52. The other configurations and operations are the same as those of the first embodiment described above.

[0064] 11, the carrier recovery device 7 is connected to a support member 54 that moves in the direction D54 to control the widthwise position (deviation position) of the intermediate transfer belt 50, and therefore also moves in conjunction with the second roller 52. Furthermore, the carrier recovery device 7 moves in the direction D7 around a fulcrum 7c on the rear side. This allows the carrier recovery device 7 to maintain an optimal relative position with the intermediate transfer belt 50 even when the widthwise position (deviation position) of the intermediate transfer belt 50 is controlled.

[0065] In the case of this embodiment, as shown in Example 4 in Table 1 above, the rate of image defects caused by carrier adhesion is lower than in Example 1. Meanwhile, in Example 1, the carrier recovery device 7 and the steering roller are independent, whereas in Example 4, the carrier recovery device 7 and the steering roller are linked, so that the cost of the device increases by the amount of the mechanism for varying the position of the carrier recovery device 7. Note that in Examples 2, 3, and 5 and Comparative Examples 1 and 2 as well, the carrier recovery device 7 and the steering roller are independent.

[0066] <Fifth embodiment> The fifth embodiment will be described with reference to Fig. 12. Fig. 12 is a cross-sectional view showing a schematic configuration of an image forming apparatus 100' of this embodiment. In this embodiment, in addition to the configuration of the first embodiment, carrier recovery devices 7'Y, 7'M, and 7'C are provided. The other configurations and functions are the same as those of the first embodiment described above.

[0067] As shown in FIG. 12, the image forming apparatus 100' of this embodiment includes four image forming units 1Y, 1M, 1C, and 1K, an intermediate transfer belt 50, a belt cleaning device 53, a carrier charge removing device 6, and a carrier recovery device 7. In the four image forming units 1Y, 1M, 1C, and 1K, the photosensitive drum 10 of the upstream image forming unit among two image forming units adjacent to each other in the rotation direction of the intermediate transfer belt 50 corresponds to the second image carrier, and the developing device 13 corresponds to the second developing device, and the developer used in the second developing device corresponds to the second developer. In addition, the primary transfer portion T1 that transfers a toner image from the photosensitive drum 10 of the upstream image forming unit to the intermediate transfer belt 50 corresponds to the third transfer position, and the primary transfer portion T1 that transfers a toner image from the photosensitive drum 10 located downstream of the photosensitive drum 10 to the intermediate transfer belt 50 corresponds to the first transfer position. In this embodiment, similarly to the first embodiment, the power source 74 for applying a voltage to the recovery sleeve 701 of the carrier recovery device 7 is provided, but like the second embodiment, the power source 74 may be omitted.

[0068] Furthermore, unlike the first embodiment, the image forming apparatus 100' of this embodiment is provided with carrier recovery devices 7'Y, 7'M, and 7'C as second carrier recovery devices immediately downstream of each image forming unit 1Y, 1M, and 1C in terms of the rotation direction of the intermediate transfer belt 50.

[0069] In other words, the carrier recovery device 7'Y is disposed downstream of the image forming unit 1Y and upstream of the image forming unit 1M in terms of the rotation direction of the intermediate transfer belt 50. Also, the carrier recovery device 7'M is disposed downstream of the image forming unit 1M and upstream of the image forming unit 1C in terms of the rotation direction of the intermediate transfer belt 50. Also, the carrier recovery device 7'C is disposed downstream of the image forming unit 1C and upstream of the image forming unit 1K in terms of the rotation direction of the intermediate transfer belt 50.

[0070] The carrier recovery devices 7'Y, 7'M, and 7'C have a different shape from the carrier recovery device 7, but are made of the same material including the components. That is, the carrier recovery devices 7'Y, 7'M, and 7'C have a carrier recovery roller, a carrier recovery blade, a carrier conveying screw, a carrier recovery container, and the like, similar to the carrier recovery device 7 shown in FIG. 4. The carrier recovery roller also has a recovery sleeve as a rotatable second sleeve, a magnet roller as a magnetic field generating unit (second magnet), and the like. The functions and materials of these components are the same as those of the carrier recovery device 7 shown in FIG. 4, but for example, the size of each of these components is different from that of the carrier recovery device 7 shown in FIG. 4. For example, the size of the carrier recovery devices 7'Y, 7'M, and 7'C is made smaller than that of the carrier recovery device 7 shown in FIG. 4.

[0071] Similarly to the carrier recovery device 7 shown in FIG. 4, the carrier recovery devices 7'Y, 7'M, and 7'C may apply a voltage of the same polarity as the charging polarity of the non-magnetic toner to the recovery sleeve serving as the second sleeve from a power source serving as a voltage application unit. This power source may be provided for each of the carrier recovery devices 7'Y, 7'M, and 7'C, or may be common to the carrier recovery devices 7'Y, 7'M, and 7'C. Furthermore, a common power source may be used for the carrier recovery devices 7'Y, 7'M, and 7'C and the carrier recovery device 7 shown in FIG. 4. Note that, similar to the configuration described in FIG. 9, a configuration may be used in which a power source for applying a voltage to the recovery sleeve of the carrier recovery devices 7'Y, 7'M, and 7'C is not provided.

[0072] In the case of this embodiment, as shown in Example 5 in Table 1 above, the image defect occurrence rate due to carrier adhesion is lower than that of Example 1. This is because in Example 5, carrier recovery devices 7'Y, 7'M, and 7'C perform carrier recovery immediately downstream of image forming units 1Y, 1M, and 1C, and therefore the effect of carrier adhesion on image formation in the image forming units immediately downstream of each image forming unit can be reduced. On the other hand, the number of carrier recovery devices is one in Example 1, whereas the number of carrier recovery devices is four in Example 5, and thus the cost of the device increases accordingly.

[0073] <Other embodiments> In the above-described embodiments, the carrier recovery device is configured to recover the carrier by magnetic force. However, the carrier recovery device is not limited to such a configuration, and may be configured to recover the carrier by applying a voltage of opposite polarity to the carrier as disclosed in Patent Document 1. [Explanation of symbols]

[0074] 4. Primary transfer roller (primary transfer member) 7. Carrier recovery device 8e Secondary transfer roller (secondary transfer member) 8i...Third roller 10: Photosensitive drum (image carrier) 13. Developing device 50···Intermediate transfer belt 74...First voltage application section 79... Support roller 100 Image forming apparatus 701 Recovery sleeve 702 Magnetic roller (magnetic field generating part)

Claims

1. a rotatable image carrier on which an electrostatic latent image is formed; a developing device that develops the electrostatic latent image formed on the image carrier into a toner image using a developer containing non-magnetic toner and magnetic carrier; a rotatable intermediate transfer body onto which the toner image carried on the image carrier is transferred; a carrier recovery device that has a rotatable sleeve disposed opposite the intermediate transfer body and a magnet disposed non-rotatably inside the sleeve, and recovers the carrier on the intermediate transfer body; a voltage applying unit that applies a voltage having the same polarity as the charging polarity of the non-magnetic toner to the sleeve; Equipped with The carrier recovery device is disposed downstream of a first transfer position where the toner image carried on the image carrier is transferred to the intermediate transfer body, and upstream of a second transfer position where the toner image carried on the intermediate transfer body is transferred to a recording material, with respect to a rotation direction of the intermediate transfer body. An image forming apparatus characterized by:

2. The lowest end of the carrier recovery device is located above the second transfer position.

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

3. a rotatable steering roller for controlling the position of the intermediate transfer body in a direction perpendicular to the direction of movement of the intermediate transfer body; a support member for supporting an end of the rotation shaft of the steering roller; Further provided with The carrier recovery device is connected to the support member so as to maintain a relative position with the intermediate transfer body.

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

4. a rotatable second image carrier on which an electrostatic latent image is formed; a second developing device for developing the electrostatic latent image formed on the second image carrier into a toner image using a second developer containing non-magnetic toner and a magnetic carrier; a second carrier recovery device that has a rotatable second sleeve disposed opposite the intermediate transfer body and a second magnet non-rotatably disposed inside the second sleeve, and recovers the carrier on the intermediate transfer body; Further provided with The toner image carried on the second image carrier is further transferred onto the intermediate transfer member, The second carrier recovery device is disposed downstream of a third transfer position where the toner image carried on the second image carrier is transferred to the intermediate transfer body and upstream of the first transfer position with respect to the rotation direction of the intermediate transfer body.

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

5. A rotatable image carrier on which an electrostatic latent image is formed; a developing device that develops the electrostatic latent image formed on the image carrier into a toner image using a developer containing non-magnetic toner and magnetic carrier; a rotatable intermediate transfer body onto which the toner image carried on the image carrier is transferred; a carrier recovery device that has a rotatable sleeve disposed opposite the intermediate transfer body and a magnet disposed non-rotatably inside the sleeve, and recovers the carrier on the intermediate transfer body; Equipped with the carrier recovery device is disposed downstream of a first transfer position where the toner image carried on the image carrier is transferred to the intermediate transfer body, and upstream of a second transfer position where the toner image carried on the intermediate transfer body is transferred to a recording material, with respect to a rotation direction of the intermediate transfer body; The lowest end of the carrier recovery device is located above the second transfer position. An image forming apparatus characterized by:

6. Further comprising a voltage application unit that applies a voltage of the same polarity as the charging polarity of the non-magnetic toner to the sleeve.

6. The image forming apparatus according to claim 5,

7. A rotatable steering roller for controlling the position of the intermediate transfer body in a direction perpendicular to the direction of movement of the intermediate transfer body; a support member for supporting an end of the rotation shaft of the steering roller; Further provided with The carrier recovery device is connected to the support member so as to maintain a relative position with the intermediate transfer body.

6. The image forming apparatus according to claim 5,

8. A rotatable second image carrier on which an electrostatic latent image is formed; a second developing device for developing the electrostatic latent image formed on the second image carrier into a toner image using a second developer containing non-magnetic toner and a magnetic carrier; a second carrier recovery device that has a rotatable second sleeve disposed opposite the intermediate transfer body and a second magnet non-rotatably disposed inside the second sleeve, and recovers the carrier on the intermediate transfer body; Further provided with The toner image carried on the second image carrier is further transferred onto the intermediate transfer member, The second carrier recovery device is disposed downstream of a third transfer position where the toner image carried on the second image carrier is transferred to the intermediate transfer body and upstream of the first transfer position with respect to the rotation direction of the intermediate transfer body.

6. The image forming apparatus according to claim 5,

Images