JP2013020278A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make pressing force of a transfer member against an image carrier uniform over a longitudinal direction of the transfer member by preventing a dent dented into a bow shape, that is, a bend of a central portion in the longitudinal direction of the transfer member which is a factor of transfer failure, with a simple and inexpensive configuration.SOLUTION: An image forming apparatus comprises: a photoreceptor drum 21 for carrying a toner image; a belt 50 which is rotationally moved while coming in contact with the photoreceptor drum 21; a non-rotational transfer member 54 facing the drum 21 through the belt 50; and a pressing member 62 for pressing the transfer member 54 against the drum 21. The pressing member 62 presses the transfer member 54 in an image forming area L of the drum 21.

Description

  The present invention relates to an image forming apparatus that forms a transfer nip with an image carrier and a transfer member via a belt and transfers a toner image on the image carrier.

  Conventionally, as a color image forming apparatus such as a printer or a copying machine, the toner images formed on the respective photosensitive drums are sequentially transferred onto the intermediate transfer belt, and the toner images stacked on the intermediate transfer belt are collectively transferred onto the recording material. A technique for forming a color image by transferring is disclosed. Alternatively, using a transfer transfer belt that electrostatically attracts and conveys the recording material, a toner image formed on each photosensitive drum is sequentially transferred onto the recording material on the transfer transfer belt to form a color image. Technology is disclosed.

  A transfer member for transferring a toner image on the photosensitive drum is disposed at a position facing each photosensitive drum via the intermediate transfer belt or the conveyance transfer belt. This transfer member is pressed against the photosensitive drum by a pressing member such as a spring to form a transfer nip. The transfer member includes a rotating body such as a roller that rotates following the intermediate transfer belt or the conveyance transfer belt, and a non-rotating body such as a pad or blade that slides on the intermediate transfer belt or the conveyance transfer belt and does not rotate. is there.

  However, since the transfer member, which is a rotating body, is pressed at both ends in the axial direction perpendicular to the rotation direction of the belt by the pressing member, the axial central portion may be bent in a bow shape. is there. As a result, the nip pressure at the central portion of the transfer nip is lower than both ends in the axial direction, and the nip pressure in the image forming region (image carrying region carrying the toner image) is not uniform, resulting in poor transfer. May occur. In order to cope with this problem, a technique is disclosed in which the outer diameter of the roller is made larger at the center than at both ends in the axial direction so that the nip pressure of the transfer nip is uniform even when the shaft is bent. . In addition, for a transfer member that is a non-rotating member, a technique is disclosed in which a strong reinforcing member is provided over the entire longitudinal direction perpendicular to the belt rotation direction (Patent Document 1). In Patent Document 1, a reinforcing member suppresses the above-described deformation of the transfer member so that the nip pressure of the transfer nip is uniform.

JP-A-8-339131

  However, in the case of a transfer member that is a rotating body, the outer diameter of the roller is changed in the axial direction in addition to pressurization from the outside of the image forming area in order to make the nip pressure of the transfer nip uniform. The cost increases and the device cost increases. In addition, the bearing for rotatably supporting the transfer member, which is a rotating body, must be disposed outside the image forming area of the photosensitive drum, and requires that much space. On the other hand, a transfer member that is a non-rotating body also requires a strong reinforcing member that minimizes the amount of deformation in order to suppress the bow deformation of the transfer member due to pressurization from the outside of the image forming area. This leads to an increase in device cost.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to prevent the bending of the central portion in the longitudinal direction of the transfer member, which causes a transfer failure, with a simple and inexpensive configuration, and to prevent the transfer member from being pressed against the image carrier in the longitudinal direction. It is to make uniform over.

  In order to achieve the above object, a representative configuration of the present invention includes an image carrier that carries a toner image, a belt that rotates in contact with the image carrier, and the image carrier via the belt. An image forming apparatus having an opposing non-rotating transfer member and a pressing member that presses the transfer member against the image carrier, wherein the pressing member is within an image carrier area of the image carrier. The transfer member is pressed.

  According to the present invention, with a simple and inexpensive configuration, it is possible to prevent the bending of the central portion in the longitudinal direction of the transfer member, which causes a transfer failure, in an arcuate shape. It can be uniform over the direction.

Main sectional view of an image forming apparatus using an intermediate transfer belt Cross section of transfer section Sectional drawing of the longitudinal direction of the transfer part concerning 1st Embodiment Configuration perspective view of transfer member and support member Sectional drawing of the longitudinal direction of the transfer part concerning 2nd Embodiment The figure showing the relationship between the pressing position by a pressing member, and the displacement amount of the support member by pressing force Main sectional view of an image forming apparatus using a transfer belt

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in the following embodiments should be appropriately changed according to the configuration of the apparatus to which the present invention is applied and various conditions. Therefore, unless specifically stated otherwise, the scope of the present invention is not intended to be limited thereto.

[First Embodiment]
The image forming apparatus according to the first embodiment will be described. First, a schematic configuration of the image forming apparatus will be described with reference to FIG. Here, an image forming apparatus using an intermediate transfer belt will be described as an example. FIG. 1 is a main sectional view of an image forming apparatus using an intermediate transfer belt.

  In the image forming apparatus shown in FIG. 1, an endless intermediate transfer belt 50 that rotates in the direction of the arrow X is disposed. The intermediate transfer belt 50 is a belt that carries a toner image and is made of a resin subjected to a semiconductive process. The intermediate transfer belt 50 is driven by a driving roller 51 whose surface is covered with a material having a high coefficient of friction such as rubber. The driving roller 51 is supplied with a driving force by a motor disposed in the apparatus main body. In addition to the driving roller 51, the intermediate transfer belt 50 is stretched by a driven roller 52 and a tension roller 53 stretched by a tension applying means such as a spring.

  Above the intermediate transfer belt 50, four image forming units 20Bk, 20Y, 20M, and 20C are arranged side by side in the rotational movement direction of the belt. These image forming units are four image forming units of black (hereinafter referred to as Bk), yellow (hereinafter referred to as Y), magenta (hereinafter referred to as M), and cyan (hereinafter referred to as C) having different colors. In each image forming portion, a photosensitive drum 21Bk, 21Y, 21M, 21C as an image carrier and a process cartridge having a charging device, a developing device, and a cleaning device as process means acting on the photosensitive drum 21 are attached and detached. Arranged to be possible. The process cartridge contains a waste toner box for storing the transfer residual toner collected by the cleaning device, and the developing device contains Bk, Y, M, and C color toners.

  The rotatable photosensitive drum 21 is irradiated with laser light by an image signal from the optical unit 10 via a polygon mirror (not shown) or the like, and forms an electrostatic image on the photosensitive drum 21. The electrostatic image is developed by supplying toner from a developing device and visualized as a toner image. When this toner image reaches the primary transfer portion where the photosensitive drum 21 and the intermediate transfer belt 50 come into contact with the rotation of the photosensitive drum 21, the primary transfer bias applied to the transfer member 54 causes the toner image on the photosensitive drum 21. The toner image is transferred onto the intermediate transfer belt 50 (primary transfer).

  Similarly, as the intermediate transfer belt 50 moves, the toner images are sequentially superimposed and transferred onto the intermediate transfer belt 50 in the primary transfer portions of the second, third, and fourth image forming portions. Then, the recording material P conveyed from the feeding cassette reaches the secondary transfer portion through the registration roller 61, and the four-color color toner image on the intermediate transfer belt 50 by the secondary transfer bias applied to the secondary transfer member 55. Are collectively transferred onto the recording material P (secondary transfer).

  The toner remaining on the belt 50 that has passed through the secondary transfer portion is cleaned by the cleaning means 56. The recording material P onto which the toner image has been transferred is peeled off from the intermediate transfer belt 50 and sent to the fixing device 70. In the fixing device 70, heat and pressure are applied to the recording material P by a pair of rollers, and the toner image is fixed on the recording material P.

  Here, the configuration of the primary transfer unit will be described. FIG. 2 is an enlarged cross-sectional view of the main part around the primary transfer part of FIG. Each primary transfer portion has the same configuration. As shown in FIG. 2, the transfer member 54 is supported in a non-rotating state, and is pressed toward the photosensitive drum by a pressing member 62 such as a spring, and is configured to be movable in the direction of the arrow in the figure. The transfer member 54 supported in a non-rotating state is a substantially rectangular parallelepiped that is in contact with the back surface of the transfer belt 50. The material of the transfer member 54 is preferably a low-elasticity member that has been subjected to a semiconductive process, and is preferably about 0.8 MPa or less, such as urethane foam. The transfer member 54 is mainly held by a resin support member 58 and is pressed toward the photosensitive drum by the pressing member 62. The transfer member 54 is fixed to the support member 58 by adhesion or the like. The transfer member 54 is in contact with the pressing member 62 at one location, and a primary transfer bias is supplied through the pressing member 62. The pressing member 62 presses the transfer member 54 against the photosensitive drum 21.

  FIG. 3 is a diagram showing the configuration of the primary transfer portion in FIG. 2 in the longitudinal direction (direction perpendicular to the rotational movement direction of the belt). The pressing member 62 presses the transfer member 54 in the image forming area L (image carrying area carrying a toner image) of the photosensitive drum 21. Here, the pressing member 62 presses one central portion in the direction perpendicular to the moving direction of the belt 50 of the transfer member 54 in the image forming region L of the photosensitive drum 21. The transfer member 54 is supported by a support member 58 so as to maintain the shape. Here, as shown in FIG. 4, the support member 58 has a box shape in which one side into which the transfer member 54 is inserted is opened, and supports the shape of the transfer member 54. Moreover, the support member 58 is a general resin molding member, and Young's modulus is about 22-25 Mpa.

  As described above, according to the above configuration, by using a non-rotating body for the primary transfer member 54, space can be saved in the longitudinal direction by disposing the pressing member 62 in the image forming region L. become. Thereby, the longitudinal dimension of the structure including the intermediate transfer belt 50 can be reduced. Further, by disposing the pressing member 62 of the primary transfer member 54 that is a non-rotating member in the image forming region L, it is possible to effectively prevent the bow-like bending deformation of the transfer member 54 in the longitudinal direction. Alternatively, the degree of bending deformation can be made extremely small. Therefore, even if the support member 58 that supports the primary transfer member 54 does not ensure extremely strong rigidity, the transfer nip portion should have a predetermined nip width and nip pressure that are necessary and sufficient to ensure transfer performance. it can. In addition, the nip width and nip pressure can be made to have a substantially uniform distribution along the longitudinal direction of the transfer nip portion, and transfer defects due to uneven pressing force can be prevented.

  Further, by adopting a configuration in which the primary transfer member 54 is a substantially rectangular parallelepiped and its one side is in surface contact with the back surface of the intermediate transfer belt 50, the nip width can be arbitrarily set, and a transfer portion with good performance can be configured. it can.

  Further, by forming the primary transfer member 54 with an elastic member and supporting it with a support member capable of holding the shape, a substantially uniform nip along the longitudinal direction of the transfer nip portion even if the pressing force by the pressing member 62 is set low. A width can be formed. For this reason, it is possible to configure a transfer unit that achieves both transfer performance and low load.

[Second Embodiment]
An image forming apparatus according to the second embodiment will be described. The overall configuration of the image forming apparatus is the same as that of the above-described embodiment, and the description thereof is incorporated herein. Here, only the configuration of the primary transfer unit having a different configuration will be described. FIG. 5 is a diagram showing the configuration of the primary transfer portion in FIGS. 1 and 2 in the longitudinal direction (direction perpendicular to the rotational movement direction of the belt). In the above-described embodiment, the configuration in which the pressing member presses the transfer member in the image carrying region of the image carrier is exemplified as the configuration in which one central portion in the longitudinal direction is pressed. However, the present invention is not limited to this. Is not to be done.

  In the present embodiment, in order to press the transfer member 54 more uniformly toward the photosensitive drum, two pressing members 62 are installed at a distance E from the end of the transfer member 54 as shown in FIG. ing.

  In this embodiment, as shown in FIG. 5, the pressing member 62 is in the image forming area L (image carrying area carrying the toner image) of the photosensitive drum 21, and the movement of the belt 50 of the transfer member 54 is performed. Two places on the inner side are pressed by an equal distance E from the end of the direction orthogonal to the direction. As a result, the transfer member 54 can be pressed more uniformly toward the photosensitive drum as compared with the above-described embodiment.

  The distance E from the image forming region L, the end where the pressing member 62 is disposed, and the maximum displacement amount (deflection amount) of the support member 58 due to the pressing force (weight value) of the pressing member 62 are as shown in FIG. is there. The maximum displacement amount of the support member 58 at the position where the pressing member 62 is disposed at E = L / 4 is about 1/6 as compared with the case where the pressing member 62 is disposed at E = 0.

  On the other hand, when the pressing member 62 is installed outside the image forming region L using the transfer member 54 supported non-rotatingly, the support member 58 generates a bow-like deflection at the center in the transfer nip. This adversely affects the transfer at the center of the image. In order to avoid this without using a strong and rigid support member (reinforcing member), as described above, the pressing member 62 is located within the image forming region L and has an inner distance E = L / Placed in 2 places near 4. Thereby, in addition to the effects of the above-described embodiment, a more uniform nip pressure can be ensured without specifying a strong reinforcing member, and good transfer can be obtained.

[Other Embodiments]
In the above-described embodiment, the image forming apparatus using the intermediate transfer belt carrying the toner image is illustrated, and the embodiment in which the present invention is applied to the primary transfer portion in the image forming apparatus has been described as an example. It is not limited to this. For example, as shown in FIG. 7, an image forming apparatus using a transfer transfer belt carrying a recording material may be used. FIG. 7 is a main cross-sectional view of an image forming apparatus using a conveyance transfer belt.

  In the image forming apparatus shown in FIG. 7, an endless conveyance transfer belt 59 that rotates in the direction of the arrow X is disposed. The transport transfer belt 59 is a belt that carries a recording material, and is made of a resin subjected to a semiconductive process. The conveyance transfer belt 59 is driven by a driving roller 51 whose surface is covered with a material having a high friction coefficient such as rubber. The driving roller 51 is supplied with a driving force by a motor disposed in the apparatus main body. The conveyance transfer belt 59 is stretched by a tension roller 53 stretched by a tension applying means such as a spring in addition to the driving roller 51.

  Four image forming units 20Bk, 20Y, 20M, and 20C are arranged side by side in the rotational movement direction of the belt at a position in contact with the conveyance transfer belt 59. These image forming units are four image forming units of black (hereinafter referred to as Bk), yellow (hereinafter referred to as Y), magenta (hereinafter referred to as M), and cyan (hereinafter referred to as C) having different colors. In each image forming section, a photosensitive drum 21 as an image carrier and a process cartridge having a charging device, a developing device, and a cleaning device which are process means acting on the photosensitive drum 21 are detachably disposed. . The process cartridge contains a waste toner box for storing the transfer residual toner collected by the cleaning device, and the developing device contains Bk, Y, M, and C color toners.

  The rotatable photosensitive drum 21 is irradiated with laser light by an image signal from the optical unit 10 via a polygon mirror (not shown) or the like, and forms an electrostatic image on the photosensitive drum 21. The electrostatic image is developed by supplying toner from a developing device and visualized as a toner image. When this toner image reaches the transfer portion where the photosensitive drum 21 and the transport transfer belt 59 abut as the photosensitive drum 21 rotates, the toner image on the photosensitive drum 21 is transferred by the transfer bias applied to the transfer member 54. Is transferred onto the recording material P carried on the transfer transfer belt 59.

  Similarly, as the transport transfer belt 59 moves, the toner images are sequentially superimposed and transferred onto the recording material P carried on the transport transfer belt 59 in the transfer units of the second, third, and fourth image forming units. The The recording material P to which all the toner images have been transferred is peeled off from the transport transfer belt 59 and sent to the fixing device 70. In the fixing device 70, heat and pressure are applied to the recording material P by a pair of rollers, and the toner image is fixed on the recording material P.

  Even if the same configuration as that of the transfer unit (see FIGS. 2, 3, and 5) of the above-described embodiment is applied to each transfer unit in the image forming apparatus using such a transfer transfer belt 59, the same effect can be obtained. Can be obtained.

  In the above-described embodiment, the pressing member is configured to press the transfer member in the image holding area of the image carrier, and is configured to press one central portion in the longitudinal direction of the transfer member. The structure which presses two places on the inner side by equal distance from the is illustrated. However, the arrangement and the number of pressing members in the image bearing area of the image bearing member are not limited to these as long as the transfer member is uniformly pressed against the image bearing member in the longitudinal direction.

  In the above-described embodiment, four image forming units are used. However, the number of used image forming units is not limited, and may be set as necessary.

  In the above-described embodiment, as a process cartridge that is detachable from the main body of the image forming apparatus, a process that integrally includes a photosensitive drum and a charging unit, a developing unit, and a cleaning unit as a process unit that acts on the photosensitive drum. A cartridge was illustrated. However, the process cartridge is not limited to this. For example, in addition to the photosensitive drum, a process cartridge that integrally includes any one of a charging unit, a developing unit, and a cleaning unit may be used.

  Further, in the above-described embodiment, the configuration in which the process cartridge including the photosensitive drum is detachable from the main body of the image forming apparatus is exemplified, but the present invention is not limited to this. For example, it may be an image forming apparatus in which each constituent member is incorporated, or an image forming apparatus in which each constituent member is removable. Similar effects can be obtained by applying the present invention to a transfer portion in these image forming apparatuses. Can be obtained.

  In the above-described embodiments, the printer is exemplified as the image forming apparatus. However, the present invention is not limited to this, and other image forming apparatuses such as a copying machine and a facsimile machine, or a combination of these functions. Other image forming apparatuses such as multifunction peripherals may also be used. The same effect can be obtained by applying the present invention to the transfer portion of these image forming apparatuses.

P ... Recording material 10 ... Optical units 20Bk, 20Y, 20M, 20C ... Image forming portions 21Bk, 21Y, 21M, 21C ... Photoconductor drum 50 ... Intermediate transfer belt 51 ... Drive roller 52 ... Drive roller 53 ... Tension roller 54 ... Transfer Member 58 ... Support member 59 ... Conveyance transfer belt 61 ... Registration roller 62 ... Pressing member 70 ... Fixing device

Claims (7)

An image carrier that carries a toner image, a belt that rotates in contact with the image carrier, a non-rotating transfer member that faces the image carrier via the belt, and the image carrier An image forming apparatus having a pressing member that presses the transfer member,
The image forming apparatus according to claim 1, wherein the pressing member presses the transfer member within an image carrying area of the image carrying body.   The image forming apparatus according to claim 1, wherein the transfer member is a substantially rectangular parallelepiped in surface contact with the belt.   The image forming apparatus according to claim 1, wherein the transfer member is an elastic member and is supported by a support member so as to hold a shape.   The image forming apparatus according to claim 1, wherein the pressing member presses one central portion in a direction orthogonal to a moving direction of the belt of the transfer member.   4. The pressing member according to claim 1, wherein the pressing member presses two inner portions at an equal distance from an end portion in a direction orthogonal to the moving direction of the belt of the transfer member. 5. Image forming apparatus.   6. The belt according to claim 1, wherein the belt is a belt that carries a toner image, and the transfer member is a transfer member that transfers a toner image on the image carrier onto the belt. The image forming apparatus described in 1.   2. The belt according to claim 1, wherein the belt is a belt that carries a recording material, and the transfer member is a transfer member that transfers a toner image on the image carrier onto a recording material carried on the belt. 6. The image forming apparatus according to any one of items 1 to 5.

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