Image forming apparatus

Abstract

The objective is to propose an image forming apparatus that can suppress leakage of the secondary transfer voltage to the backsheet holding member, even when the backup member is placed close to the secondary transfer section. [Solution] The system includes a backup member 70 that contacts the inner surface of the intermediate transfer belt upstream of the secondary transfer section, a backup member holding member 71 that holds the backup member, and an insulating sheet 72 that covers the downstream end of the backup member holding member in the intermediate transfer belt conveying direction.

Description

Technical Field

[0001] The present invention relates to an image forming apparatus using an intermediate transfer system.

Background Art

[0002] In order to transfer a toner image formed on an intermediate transfer belt to a recording medium with high accuracy, the contact length between the intermediate transfer belt and the recording medium upstream of the secondary transfer unit is important. If the contact length is long, image defects may occur due to rubbing between the toner and the recording medium caused by the speed difference between the belt and the recording medium. If the contact length is short, image defects may occur due to abnormal discharge caused by the gap between the recording medium and the belt. Therefore, in view of the contact position of the recording medium with the belt upstream of the secondary transfer unit, the conveyance posture of the recording medium and the tension layout of the intermediate transfer belt are determined.

[0003] In Patent Document 1, a configuration is proposed in which a planar correction member (so-called backup member) composed of a flexible plate is provided on the inner surface of the belt upstream of the tacking position between the intermediate transfer belt and the recording medium. According to this, it is possible to suppress the undulation of the belt generated upstream of the secondary transfer unit, suppress the discharge due to the gap between the intermediate transfer belt and the recording medium, and provide a high-quality product.

[0004] In Patent Document 2, regarding the rotation direction of the intermediate transfer belt, the length L along the belt surface between the downstream end of the portion of the backup member in contact with the intermediate transfer belt and the upstream end of the transfer nip portion is defined. That is, a configuration is proposed in which the length L is shorter than the margin length outside the image formation area at the upstream end of the surface of the recording medium. According to this, even when a recording medium with high bending rigidity such as thick paper or coated paper is used, it is possible to prevent image defects from appearing on the recording medium. That is, it is possible to suppress image defects caused by abnormal discharge that may occur due to the separation between the recording medium and the intermediate transfer belt due to the pressing by the recording medium.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Application Publication No. 9-80926 [Patent Document 2] Japanese Patent Publication No. 2015-210313 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] A high voltage for secondary transfer is applied to the secondary transfer section. In recent years, there has been a demand for improved productivity of recording media with high bending rigidity, such as cardboard and coated paper. To maintain transferability even when the transport speed is increased, it has become necessary to increase the high voltage capacity applied to the secondary transfer section. As described in the background technology, the backup member needs to be placed in close proximity to the secondary transfer section to prevent image defects caused by friction between the toner and the recording media, and image defects caused by abnormal discharge due to the gap between the recording media and the intermediate transfer belt.

[0007] The backup member itself is made of a flexible insulating resin material, but the backup member holder that holds the backup member is made of metal to ensure the rigidity of the backup member. Furthermore, the metallic backup member holder is grounded to suppress the generation of noise. As a result, when attempting to place the backup member close to the secondary transfer section, the creepage distance between the secondary transfer section and the backup member holder cannot be sufficiently secured, leading to a problem where the secondary transfer voltage leaks into the backsheet holder. [Means for solving the problem]

[0008] The present invention aims to suppress leakage of the secondary transfer voltage from the secondary transfer section to the backup member holding member.

[0009] The present invention is characterized by comprising: an intermediate transfer belt on which a toner image is transferred; an inner roller for tensioning the intermediate transfer belt; an outer roller that clamps the intermediate transfer belt between itself and the inner roller and forms a transfer nip for transferring the toner image formed on the intermediate transfer belt to a recording medium; a backup member that contacts the inner surface of the intermediate transfer belt upstream of the transfer nip in the transport direction of the intermediate transfer belt; a holding member that holds the backup member such that its downstream end in the transport direction of the intermediate transfer belt contacts the intermediate transfer belt; and an insulating member that covers at least the downstream end of the holding member in the transport direction of the intermediate transfer belt, wherein the insulating member is configured to be longer than the holding member in the width direction of the intermediate transfer belt perpendicular to the transport direction of the intermediate transfer belt and has a first insulating portion that covers a first surface of the holding member; and the insulating member is configured to be longer than the holding member in the width direction of the intermediate transfer belt and has a second insulating portion that covers a second surface of the holding member. [Effects of the Invention]

[0010] According to the present invention, it is possible to suppress leakage of the secondary transfer voltage from the secondary transfer section to the backup member holding member. [Brief explanation of the drawing]

[0011] [Figure 1] Schematic cross-sectional view of an image forming apparatus [Figure 2a] Schematic cross-sectional view of the state before the recording medium P moves to the secondary transfer section. [Figure 2b] Schematic cross-sectional view of the state after the recording medium P has moved to the secondary transfer section. [Figure 2c] Enlarged view of the secondary transfer area in Figure 2b. [Figure 3a] Schematic cross-sectional view of the secondary transfer section including the insulating member 72 according to this embodiment. [Figure 3b] Schematic cross-sectional view of a conventional secondary transfer section. [Figure 4a] A schematic longitudinal view of the secondary transfer section including the insulating member 72 according to this embodiment. [Figure 4b]Schematic cross-sectional view of a conventional secondary transfer section. [Modes for carrying out the invention]

[0012] [Example 1] The following describes embodiments of the present invention with reference to the drawings, but the present invention is not limited to the following embodiments.

[0013] [Image forming apparatus configuration] Figure 1 is a schematic cross-sectional view of an image forming apparatus. This image forming apparatus 100 is a tandem-type intermediate transfer image forming apparatus in which image forming units 1Y, 1M, 1C, and 1K are arranged in series on the horizontal part of the intermediate transfer belt 31. This image forming apparatus 100 forms a full-color image on a recording medium P using an electrophotographic method in response to an image signal transmitted from an external device.

[0014] Image forming units 1Y, 1M, 1C, and 1K form yellow, magenta, cyan, and black toner images on the photosensitive drums 11Y, 11M, 11C, and 11K, and perform primary transfer to the same image position on the intermediate transfer belt 31. The intermediate transfer belt 31 is tautened by a drive roller 33, a tension roller 34, and a secondary transfer inner roller 32 for performing secondary transfer, and rotates in a clockwise direction R1. Primary transfer rollers 35Y, 35M, 35C, and 35K for performing primary transfer are positioned on the inner circumferential surface of the intermediate transfer belt 31, opposite the photosensitive drums 11Y, 11M, 11C, and 11K.

[0015] Around the photosensitive drum 11Y, which forms a yellow toner image, are a charger 12Y that uniformly charges the surface of the photosensitive drum 11Y, and an exposure device 13Y that irradiates the photosensitive drum 11Y with image light to form a latent image on its surface. Also arranged are a developer 14Y that transfers toner to the latent image on the photosensitive drum 11Y to form a toner image, and a cleaning device 15Y that removes toner remaining on the photosensitive drum 11Y after the primary transfer of the toner image. The configuration for forming magenta, cyan, and black toner images can be understood by replacing the subscript Y with M, C, and K in the above description.

[0016] On the other hand, the recording media P stored in the paper supply cassettes 61, 62, and 63 are conveyed to the paper supply conveyance path 67 by the rotation of any one of the paper supply rollers 64, 65, and 66. The registration roller 21 feeds the recording media P to the secondary transfer unit in synchronization with the toner image on the intermediate transfer belt 31. The secondary transfer unit is formed by being sandwiched between the secondary transfer outer roller 41 and the secondary transfer inner roller 32, and the toner image is secondarily transferred onto the recording media P in the secondary transfer unit.

[0017] The transfer residual toner remaining on the intermediate transfer belt 31 after secondary transfer is removed by the cleaning device 36.

[0018] Next, the recording media P onto which the toner image has been transferred is conveyed to the heat fixing device 5 by the conveyance belt 60, and the toner image is fixed on the surface of the recording media P by heating and pressure bonding in the heat fixing device 5. Thereby, the full-color image is fixed on the recording media P and sent out to the paper discharge tray 69 through the paper discharge conveyance path 68.

[0019] [Secondary transfer unit] FIG. 2a is a schematic cross-sectional view of the state before the recording media P moves to the secondary transfer unit, FIG. 2b is a schematic cross-sectional view of the state after the recording media P moves to the secondary transfer unit, and FIG. 2c is an enlarged view of the secondary transfer unit in FIG. 2b.

[0020] As shown in Figure 2, the shape of the intermediate transfer belt 31 is formed by tensioning the secondary transfer inner roller 32 and the secondary transfer pre-roller 37, and the secondary transfer outer roller 41 is elastically biased toward the secondary transfer inner roller 32 by an elastic spring. As a result, the intermediate transfer belt 31 is sandwiched between the secondary transfer inner roller 32 and the secondary transfer outer roller 41, forming the secondary transfer section. Upstream of the secondary transfer section in the rotation direction R1 of the intermediate transfer belt 31, a backup member 70 is positioned close to the secondary transfer inner roller 32 via a backup member holding member 71. The inner surface of the intermediate transfer belt 31 and the tip of the backup member 70 are in contact. That is, the backup member 70 is held by the backup member holding member 71 such that its downstream end abuts against the inner surface of the intermediate transfer belt 31 in the conveying direction of the intermediate transfer belt 31. In this embodiment, the backup member 70 is composed of a PET material 70a with a thickness of 0.5 [mm] and an insulating resin material PET material 70b with a thickness of 0.25 [mm], and the backup member 70 elastically biases the intermediate transfer belt 31 by utilizing its flexural elasticity. Therefore, the backup member 70 settles at a position where the biasing force applied by the backup member 70 to the intermediate transfer belt 31 balances out with the resistance force generated by the tension of the intermediate transfer belt 31. The shape of the intermediate transfer belt 31 upstream of the secondary transfer section is formed by this settled position of the backup member 70. The secondary transfer inner roller 32 is subjected to a bias of the same polarity as the charge polarity of the toner constituting the toner image on the intermediate transfer belt 31 by the secondary transfer high-voltage power supply 38, and the secondary transfer outer roller 41 is grounded, thereby forming a transfer electric field in the secondary transfer section. The recording medium P is sent to the secondary transfer section where the transfer electric field has been formed, guided by a secondary transfer pre-guide (not shown). At this time, the intermediate transfer belt 31 upstream of the secondary transfer section comes into contact with the recording medium P, and the recording medium P is then transported toward the secondary transfer section with the toner image formed on the surface of the intermediate transfer belt 31 in contact with the recording medium P. The recording medium P is then transported to the secondary transfer section, where the toner image is transferred from the intermediate transfer belt 31 to the recording medium P by the pressurizing action between the secondary transfer inner roller 32 and the secondary transfer outer roller 41 and the electrical action of the transfer electric field.When the recording medium P is transported to the secondary transfer section, if the length of contact between the intermediate transfer belt 31 upstream of the secondary transfer section and the recording medium P is short, the gap G between the intermediate transfer belt 31 and the recording medium P becomes large, causing image defects due to discharge phenomena. On the other hand, if the length of contact between the intermediate transfer belt 31 and the recording medium P is long, image defects occur due to friction between the toner image formed on the surface of the intermediate transfer belt 31 and the recording medium P. By optimizing the length of contact between the intermediate transfer belt 31 and the recording medium P, the toner image can be stably transferred to the recording medium P in the secondary transfer.

[0021] The image forming apparatus 100 in this embodiment is a device that achieves high productivity, with the intermediate transfer belt 31 being transported at a speed of 600 [mm / s] and the toner having negative polarity. In order to ensure transfer performance even at this speed, a high-voltage bias of -14 [kV] is applied to the secondary transfer roller 32, but the toner polarity and voltage values ​​are not limited to these.

[0022] In this embodiment, the backup member 70 is made of PET material with a thickness of 0.5 [mm] and PET material with a thickness of 0.25 [mm], but it is not limited to this configuration, and any material that can elastically bias the intermediate transfer belt 31 is acceptable. For example, it may have a thickness of 1.0 [mm], or the material may be PEEK, PPS, etc.

[0023] [Insulating material composition] Figure 3a is a schematic cross-sectional view of a secondary transfer section including the insulating member 72 according to the present invention, Figure 3b is a schematic cross-sectional view of a conventional secondary transfer section, Figure 4a is a schematic longitudinal view of a secondary transfer section including the insulating member 72 according to the present invention, and Figure 4b is a schematic cross-sectional view of a conventional secondary transfer section.

[0024] Next, the configuration of the insulating member 72 will be described. In this embodiment, as shown in Figure 3a, the insulating member 72 is positioned between the backup member 70 and the backup holding member 71, which serves as a holding member. The backup holding member 71 is made of a metallic material. The insulating member 72 is configured to cover the downstream end of the backup holding member 71 in the conveying direction of the intermediate transfer belt 31. That is, the insulating member 72 is an insulating member (first insulating part) that covers the first surface of the holding member 71 at least at the downstream end of the holding member 71 in the conveying direction of the intermediate transfer belt 31. Furthermore, the insulating member 72 is an insulating sheet that includes an insulating member (second insulating part) that is folded back from the first surface downstream of the holding member 71 in the conveying direction of the intermediate transfer belt 31 and covers the second surface of the holding member 71. In this embodiment, the insulating member 72 is made of a polyimide material with a thickness of 0.05 [mm]. In this embodiment, when a secondary transfer high pressure is applied, the creepage distance between the secondary transfer section and the backup member holding member 71 was L1 = 28 [mm] (2V [mm] when the high-pressure capacity is V [kV]), as shown in Figure 3a. Even under the condition that the secondary transfer high pressure in this embodiment is 14 [kV], it is possible to prevent the secondary transfer high pressure from leaking into the backup member holding member 71. In the conventional configuration, the creepage distance between the secondary transfer section and the backup member holding member 71 was L2 < 28 [mm], as shown in Figure 3b. Therefore, under the condition that the secondary transfer high pressure is greater than 11 [kV], there was a risk that the secondary transfer high pressure would leak into the backup member holding member 71.

[0025] Furthermore, in this embodiment, as shown in Figure 4a, the insulating member 72 is positioned to extend beyond both ends of the backup holding member 71 in the direction perpendicular to the transfer belt transport direction. That is, in the width direction of the intermediate transfer belt perpendicular to the transport direction of the intermediate transfer belt 31, the insulating member 72 is longer than the holding member. And, in the width direction of the intermediate transfer belt perpendicular to the transport direction of the intermediate transfer belt 31, both ends of the insulating member 72 are positioned further out than both ends of the holding member 71. When the secondary transfer high voltage is applied, in this embodiment, the creepage distance between the secondary transfer section and the backup member holding member 71 is L4 = 28 [mm], as shown in Figure 4a. That is, when the maximum applied voltage of the secondary transfer high voltage is V [kV], the creepage distance is 2V [mm] or more. In other words, even under the condition that the secondary transfer high voltage in this embodiment is 14 [kV], it is possible to prevent the secondary transfer high voltage from leaking to the backup member holding member 71. In the conventional configuration, the creepage distance between the secondary transfer portion and the backup member holding member 71 in the longitudinal direction of the two-transfer member was L3 < 28 [mm], as shown in Figure 4b. Therefore, under the condition that the secondary transfer high voltage was 14 [kV], there was a risk that the secondary transfer high voltage would leak into the backup member holding member 71.

[0026] In this embodiment, the insulating member 72 is made of polyimide material with a thickness of 0.05 [mm], but it is not limited to this configuration; any material that has insulating properties is acceptable. Also, in this embodiment, the creepage distance between the secondary transfer section and the backup member holding member is set to 28 [mm] (2V [mm] when the high voltage capacity is V [kV]), but the creepage distance is not limited to this length.

[0027] In this embodiment, the secondary transfer inner roller 32 is subjected to a bias of the same polarity as the charge polarity of the toner constituting the toner image on the intermediate transfer belt 31 by the secondary transfer high-voltage power supply 38. The secondary transfer outer roller 41 is then grounded to create a transfer electric field in the secondary transfer section. However, the secondary transfer outer roller 41 may also be subjected to a bias of the opposite polarity to the charge polarity of the toner constituting the toner image on the intermediate transfer belt 31 by the secondary transfer high-voltage power supply 38. The secondary transfer inner roller 31 may then be grounded to create a transfer electric field in the secondary transfer section.

[0028] As described above, according to the present invention, by arranging the insulating member to cover the downstream end of the backup member holding member in the intermediate transfer belt transport direction, it is possible to prevent leakage of the secondary transfer voltage from the secondary transfer section to the backup member holding member. Furthermore, by arranging the insulating member to extend beyond both ends of the backup member holding member in the direction perpendicular to the intermediate transfer belt transport direction, it is also possible to prevent leakage of the secondary transfer voltage to both ends in the direction perpendicular to the intermediate transfer belt transport direction. [Explanation of Symbols]

[0029] 30 Tension springs 31 Intermediate transfer belt 32 Secondary transfer inner roller 33 Drive rollers 34 Tension Roller 35 Primary transfer roller 37 Secondary transfer roller 38 Secondary Transfer High-Voltage Power Supply 41 Secondary transfer outer roller 70 Backup components 71 Backup member holding member 72 Insulating material 100 Image forming apparatus P recording medium G void

Claims

1. An intermediate transfer belt onto which the toner image is transferred, An internal roller that tensions the aforementioned intermediate transfer belt, An outer roller that sandwiches the intermediate transfer belt between itself and the inner roller and forms a transfer nip that transfers the toner image formed on the intermediate transfer belt to a recording medium, A backup member that contacts the inner surface of the intermediate transfer belt upstream of the transfer nip in the conveying direction of the intermediate transfer belt, A holding member that holds the backup member such that the downstream end of the backup member in the conveying direction of the intermediate transfer belt contacts the intermediate transfer belt, An image forming apparatus comprising an insulating member that covers at least the downstream end of the holding member in the conveying direction of the intermediate transfer belt, wherein the insulating member is configured to be longer than the holding member in the width direction of the intermediate transfer belt perpendicular to the conveying direction of the intermediate transfer belt and has a first insulating portion that covers a first surface of the holding member, and a second insulating portion that is configured to be longer than the holding member in the width direction of the intermediate transfer belt and covers a second surface of the holding member.

2. The image forming apparatus according to claim 1, characterized in that the backup member is an insulating resin member and the holding member is a metallic member.

3. The image forming apparatus according to claim 1 or 2, characterized in that both ends of the insulating member are positioned outside of both ends of the holding member.

4. The image forming apparatus according to any one of claims 1 to 3, characterized in that it comprises an application means for applying a transfer voltage to the inner roller, and the outer roller is grounded.

5. The image forming apparatus according to any one of claims 1 to 4, characterized in that the creepage distance between the internal roller and the holding member is 2V [mm] or more when the maximum applied voltage of the applying means is V [kV].

Images