JP2013134452A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem in which: it has been difficult to provide an image forming apparatus that employs a guide member as an opposing member, and capable of improving separation performance of a transfer material with low rigidity such as thin paper.SOLUTION: A support member is a guide member that comes into rubbing contact with an intermediate transfer belt at a position opposing to a secondary transfer member with the intermediate transfer belt interposed therebetween to regulate a direction of movement of the intermediate transfer belt. The guide member regulates a direction of a leading edge of a transfer material that has passed through a secondary transfer part so that the transfer material that has passed the secondary transfer part comes closer to the secondary transfer member than the intermediate transfer belt.

Description

  The present invention relates to an image forming apparatus such as a copying machine or a laser printer.

  In an electrophotographic color image forming apparatus, in order to print at high speed, each color image forming unit for forming yellow, magenta, cyan, and black images is independently provided. A configuration is known in which an image is transferred to an intermediate transfer member, and further, the image is transferred collectively from the intermediate transfer member to a transfer material.

  Patent Document 1 discloses an image forming apparatus that uses an endless intermediate transfer belt as an intermediate transfer member. A secondary transfer roller is used as the secondary transfer member, and one of the support rollers that supports the inner peripheral surface of the intermediate transfer belt is used as the opposing member of the secondary transfer roller. The secondary transfer roller is brought into pressure contact with the opposing member (opposing roller) via the intermediate transfer belt, thereby forming a secondary transfer portion where the secondary transfer roller and the intermediate transfer belt are in contact with each other.

  A potential difference is generated between the secondary transfer roller to which a voltage is applied and a grounded opposing member on the transfer material conveyed to the secondary transfer unit, and the toner image on the intermediate transfer belt is electrostatically transferred. Transcript to.

  Patent Document 2 discloses a configuration in which a fixing member that slides on the intermediate transfer belt is employed as the facing member instead of the facing roller that is driven by the rotation of the intermediate transfer belt of Patent Document 1. The separation property of the transfer material from the intermediate transfer belt is improved by increasing the curvature on the downstream side of the fixing member.

JP 2004-29057 A JP 2008-46382 A

  However, since a transfer material such as thin paper has low rigidity, the transfer material may be wound around the intermediate transfer belt without being separated from the intermediate transfer belt after the secondary transfer. As the traveling direction of the transfer material tip after passing through the secondary transfer portion is closer to the intermediate transfer belt side, the electrostatic attracting force generated between the intermediate transfer belt and the transfer material increases. When the electrostatic attraction force exceeds the bending stress generated by the curvature of the transfer material, a winding phenomenon of the transfer material around the intermediate transfer belt occurs.

  In view of the above situation, the present invention provides an image forming apparatus that uses a guide member as a counter member, and that can improve the separation performance of a transfer material having a low rigidity such as thin paper with a simple configuration. An object is to provide an apparatus.

In order to solve the above-described problems, the present invention provides an image carrier that carries a toner image, an endless intermediate transfer belt on which a toner image is primarily transferred from the image carrier, and an inner circumference of the intermediate transfer belt. A driving member for supporting the surface and moving the intermediate transfer belt; a support member for supporting the inner peripheral surface of the intermediate transfer belt; and the intermediate transfer belt and the secondary transfer portion contacting the outer peripheral surface of the intermediate transfer belt. A secondary transfer member to be formed, and an image forming apparatus that secondarily transfers a toner image from the intermediate transfer belt to a transfer material conveyed to the secondary transfer unit.
The support member is a guide member that regulates a moving direction of the intermediate transfer belt while rubbing against the intermediate transfer belt at a position facing the secondary transfer member via the intermediate transfer belt, and the guide member is The direction of the leading edge of the transfer material when passing through the secondary transfer portion is regulated so that the transfer material that has passed through the secondary transfer portion approaches the secondary transfer member from the intermediate transfer belt. .

  According to the present invention, by controlling the moving direction of the transfer material after passing through the secondary transfer portion to be on the secondary transfer member side by the shape of the guide member, the electrostatic force generated between the transfer material and the intermediate transfer belt is generated. It becomes possible to weaken the attracting force, and to suppress the occurrence of a winding phenomenon of the transfer material around the intermediate transfer belt.

Schematic illustrating an image forming apparatus according to an embodiment of the present invention. The figure explaining the guide member used in Example 1 The figure explaining the secondary transfer part of the image forming apparatus of a comparative example (A) The figure explaining the secondary transfer part shape and transfer material separation direction in Example 1, (b) The figure explaining the secondary transfer part shape and transfer material separation direction in a comparative example (A) The figure explaining the secondary transfer part in Example 2, (b) The figure explaining the separation direction of the secondary transfer part shape and transfer material in Example 2. The figure explaining the curvature radius in each part of a secondary transfer part

Example 1
In the following, preferred embodiments of the present invention will be described in detail with reference to the drawings. However, the components described in this embodiment are merely examples, and are not intended to limit the scope of the present invention.

  FIG. 1 is a configuration diagram of a color image forming apparatus of an inline type (4-drum system). The image forming apparatus forms an image forming unit a that forms a yellow image, an image forming unit b that forms a magenta image, an image forming unit c that forms a cyan image, and a black image. The image forming unit d includes four image forming units. These four image forming units are arranged in a line at regular intervals.

  Since the configuration of each image forming unit is the same except for the color of the image to be formed, the image forming unit will be described using the image forming unit a. The image forming unit a includes a drum-shaped electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) 1a, a charging member 1b, a developing unit 4a, and a cleaning unit 5c. The image forming unit a of this embodiment is a process cartridge that integrates them and is detachable from the apparatus main body.

  The photosensitive drum 1a, which is an electrophotographic photosensitive member, is rotationally driven at a predetermined peripheral speed (process speed) in the arrow direction R1. The photosensitive drum 1a is uniformly charged to a predetermined polarity and potential by a charging roller 2a, which is a charging member, during this rotation process. In this embodiment, the photosensitive drum 1a is negatively charged by the charging roller 2a. Next, image exposure is performed by the exposure means 3a which is an exposure unit. Thereby, an electrostatic latent image corresponding to the yellow component image of the target color image is formed.

  Next, the electrostatic latent image is developed by the first developing unit (yellow developing device) 4a at the developing position and visualized as a yellow toner image. The yellow developer 4a contains yellow toner charged to a negative polarity, and is developed on the photosensitive drum 1a by a developing roller provided in the yellow developer 4a. The photosensitive drum 1a is an image carrier that carries a toner image.

  The yellow toner image on the photosensitive drum 1a is primarily transferred to the opposing intermediate transfer member. The intermediate transfer belt 10, which is an intermediate transfer body, is an endless belt, is supported by a plurality of support members, and has a photosensitive drum in an arrow direction R <b> 3 that moves in the same direction at a facing portion in contact with the photosensitive drum 1. 1 is rotated at the same peripheral speed as 1. A primary transfer member is provided at a position facing the photosensitive drum 1 a via the intermediate transfer belt 10. The yellow toner image formed on the photosensitive drum 1a is primarily transferred onto the intermediate transfer belt 10 in the process of passing through the primary transfer nip where the photosensitive drum 1a and the intermediate transfer belt 10 abut. At that time, a primary transfer voltage is applied from a primary transfer power supply 15a to a primary transfer roller 14a that is a primary transfer member that forms a primary transfer nip portion.

  The primary transfer residual toner remaining on the surface of the photosensitive drum 1a is cleaned and removed by the cleaning unit 5a.

  Similarly, in each of the image forming units (b) to (d), a second color magenta toner image, a third color cyan toner image, and a fourth color black toner image are formed and are formed on the intermediate transfer belt 10. The combined color image corresponding to the target color image is obtained by sequentially transferring the images. Respective exposure units 3b to 3d and primary transfer rollers 14b to 14d are provided in the image forming portions b to d, respectively.

The four color toner images on the intermediate transfer belt 10 are fed from the sheet feeding means 50 in the process of passing through the secondary transfer portion formed by the intermediate transfer belt 10 and the secondary transfer roller 20 as a secondary transfer member. Secondary transfer is performed on the surface of the transfer material P. At that time, a secondary transfer voltage is applied to the secondary transfer roller 20 from a secondary transfer power source 21. The secondary transfer roller 20 as a secondary transfer member has an outer diameter covered with a nickel-plated steel rod having an outer diameter of 8 mm and a foam sponge of NBR (nitrile rubber) adjusted to a resistance value of 10 ⁸ Ω · cm and a thickness of 5 mm. An 18 mm roller is used. The secondary transfer roller 20 is brought into contact with the outer peripheral surface of the intermediate transfer belt 10 with a pressurizing force of 50 N, and is driven to rotate with respect to the intermediate transfer belt 10.

  Thereafter, the transfer material P carrying the four-color toner images is introduced into the fixing device 30 where the four color toners are melted and mixed and fixed to the transfer material P by being heated and pressurized. Then, the transfer material P is discharged out of the apparatus.

  With the above operation, a full-color print image is formed on the transfer material P. Further, the secondary transfer residual toner remaining on the surface of the intermediate transfer belt 10 is cleaned and removed by the intermediate transfer belt cleaning unit 16.

  Next, the intermediate transfer belt 10 and the plurality of support members 11, 12, and 13 that support the inner peripheral surface of the intermediate transfer belt 10 will be described. The intermediate transfer belt 10 and the support members 11, 12, and 13 are integrated as an intermediate transfer unit and can be attached to and detached from the apparatus main body.

It is desirable that the intermediate transfer belt 10 has little charge remaining after transfer and does not require a static elimination mechanism. In this embodiment, it is preferable that the volume resistivity is made of a material of about 10 ⁸ to 10 ¹¹ Ω · cm because the residual charge after transfer is small and the neutralization mechanism can be made unnecessary. The intermediate transfer belt 10 of this embodiment is made of a material mainly composed of polyvinylidene fluoride (PVdF) having a thickness of 100 μm and a volume resistivity of 10 ⁹ Ω · cm. The intermediate transfer belt 10 may be made of other materials such as polyamide (PI), polyether ether ketone (PEEK).

  The support member 11 is a drive roller that is a drive member that supports the intermediate transfer belt 10 while driving it, and rotates in the arrow direction R2 to rotate and move the intermediate transfer belt 10 in the arrow direction R3. In this embodiment, as the support member 11, a roller in which an aluminum shaft having an outer diameter of 20 mm is coated with an elastic rubber (ethylene propylene rubber) having a thickness of 0.5 mm is used.

  The support member 12 is a tension roller that applies tension to the inner peripheral surface of the intermediate transfer belt 10 from the inner peripheral surface side toward the outer peripheral surface side. In this embodiment, a hollow aluminum shaft having an outer diameter of 20 mm is used as the support member 12. The support member 12 presses the intermediate transfer belt 10 with a total pressure of 39.2N by the spring 12h, and applies tension to the intermediate transfer belt 10.

  The support member 13 is a guide member that faces the secondary transfer roller 20 with the intermediate transfer belt 10 interposed therebetween. The guide member 13 regulates the moving direction of the intermediate transfer belt 10 while sliding on the intermediate transfer belt 10 at a position facing the secondary transfer roller 20 via the intermediate transfer belt 10. The guide member 13 is not configured to rotate with the intermediate transfer belt 10 like other support members, but is configured to be fixed to the intermediate transfer unit. The configuration related to the guide member 13 will be described later.

  The intermediate transfer belt 10, the support members 11, 12, 13 and the primary transfer rollers 14a to 14d are integrated as an intermediate transfer unit. The driving roller 11, the tension roller 12, and the primary transfer rollers 14a to 14d, which are rollers, are supported by the respective bearings and are rotatable. On the other hand, the guide member 13 is fixed to a frame constituting the intermediate transfer unit.

  Below, the structure of the guide member 13 is demonstrated. The guide member 13 of this embodiment is a fixed member that keeps sliding with the rotating intermediate transfer belt 10 and does not follow the rotation of the intermediate transfer belt 10 like an opposed roller.

  FIG. 2 is an enlarged schematic cross-sectional view of the vicinity of the secondary transfer portion of the image forming apparatus according to the present exemplary embodiment. The guide member has a substantially semicircular shape with a longitudinal width of 250 mm and a curvature radius of 10 mm, which is a direction orthogonal to the moving direction of the intermediate transfer belt 10. The rubbing surface of the guide member 13 with the intermediate transfer belt 10 is formed by a plurality of continuous rubbing portions. Specifically, the region is divided into a guide upstream portion Ga1, a secondary transfer portion N, and a guide downstream portion Gb1.

  The guide upstream portion Ga1 (upstream regulating portion) has a function of a bent portion that changes (bends) the rotation angle of the intermediate transfer belt 10, and the surface on the side where the guide member 13 and the intermediate transfer belt 10 are in contact has a curvature radius of 50 mm. It is composed of curved surfaces. The radius of curvature is preferably 8 mm or more (predetermined value or more) in the intermediate transfer belt of this embodiment from the viewpoint of curling. The predetermined value of the radius of curvature required for suppressing curling can be appropriately changed depending on the material constituting the intermediate transfer belt.

  The secondary transfer portion N (second rubbing portion) is located at a portion facing the secondary transfer roller 20 and is formed in a substantially planar shape, and forms a contact portion with the secondary transfer roller 20. The guide downstream portion Gb1 (downstream regulating portion) has a function of separating the intermediate transfer belt 10 and the transfer material P and a function of a bending portion that changes the traveling angle of the intermediate transfer belt 10, and the guide member 13 and the intermediate transfer belt 10 are The surface on the contact side is a curved surface having a curvature radius of 12 mm. The guide downstream portion Gb1 has a function of securing an area for disposing the transfer belt cleaning member 16, and from the viewpoint of securing an area for disposing the belt cleaning member 16, a plane or a larger radius of curvature is provided. Is preferred. Further, the guide downstream portion Gb1 may be a facing portion of a detection unit that detects the density control toner and the registration toner on the intermediate transfer belt 10.

  The transfer material P starts to be separated from the intermediate transfer belt 10 in the tangential direction at the most downstream position of the secondary transfer portion N. The electrostatic attraction force generated between the transfer material P after the secondary transfer process and the intermediate transfer belt 10 varies greatly depending on the separation direction of the leading end portion of the transfer material P, greatly affecting the separation performance of the transfer material P. ing.

  If the traveling direction of the leading edge of the transfer material P after passing through the secondary transfer portion is close to the secondary transfer roller with respect to the imaginary line connecting the upstream and downstream of the secondary transfer portion, the transfer material P and the intermediate transfer belt 10 may The electrostatic attraction force that is generated can be made smaller than the bending stress of the transfer material P even when a sheet of low rigidity such as thin paper is used as the transfer material P. The electrostatic force generated between the transfer material P and the intermediate transfer belt 10 is inversely proportional to the square of the distance between the transfer material P and the intermediate transfer belt 10. When the above-described electrostatic attraction force exceeds the bending stress due to the rigidity of the transfer material P, the transfer material P is attracted to the intermediate transfer belt 10 and is completely adsorbed to the intermediate transfer belt 10. Since it is not separated from 10 and is not conveyed to the fixing device for the next process, problems such as jams occur.

  In order to describe the specific operation of the present embodiment, an image forming apparatus having the configuration of the comparative example shown in FIG. 3 will be described. The image forming apparatus according to the comparative example has a configuration in which a driven roller 130 is employed as a facing member of the secondary transfer unit as shown in FIG. Other configurations are the same as those of the image forming apparatus shown in FIG.

  FIG. 4A is an enlarged schematic view of the vicinity of the secondary transfer portion according to the first embodiment. FIG. 4B is an enlarged schematic view of the vicinity of the secondary transfer portion of the comparative example. 4 (a) and 4 (b), the secondary transfer roller 20 is an elastic body, and the secondary transfer roller 20 is crushed by the applied pressure F to form a secondary transfer portion. FIG. 6 is a diagram showing a relationship between the intrusion amounts of the secondary transfer roller 20 when forming the same width.

  As shown in FIG. 4B, in the configuration of the comparative example, the curved surfaces of the secondary transfer roller 20 and the guide member 13 face each other. Therefore, the secondary transfer portion shape Na3 has a convex shape with respect to the pressing direction F of the secondary transfer roller 20. Therefore, the leading edge traveling direction S of the transfer material P at the separation start position is closer to the intermediate transfer belt 20 with respect to the straight line X connecting the most upstream position and the most downstream position of the secondary transfer portion. The distance d3 between the transfer material P and the intermediate transfer belt 10 is reduced, and the electrostatic attracting force generated between the two is increased. The guide member 13 regulates the direction of the leading edge of the transfer material when it passes through the secondary transfer portion so that the transfer material that has passed through the secondary transfer portion approaches the secondary transfer roller from the intermediate transfer belt.

  As shown in FIG. 4A, in the configuration of this embodiment, the guide member 13 has a substantially planar shape, and the secondary transfer portion shape Na1 has a substantially planar shape. Therefore, the leading edge traveling direction S of the transfer material P at the separation start position is on a straight line X connecting the most upstream position and the most downstream position of the secondary transfer portion, and the movement locus of the intermediate transfer belt 10 is a straight line. The distance d1 between the transfer material P and the intermediate transfer belt 10 is larger than the distance d2. As a result, the electrostatic attraction force generated between the two can be reduced as compared with the comparative example. As the radius of curvature of the guide member shape Gb1 after the secondary transfer portion increases, the distance between the transfer material P and the intermediate transfer belt 10 decreases even when the paper leading edge advance direction S of the transfer material P is the same. As a result, the electrostatic attraction force generated between the two increases and the transfer material P separation performance deteriorates. Therefore, it is preferable to reduce the curvature radius of Gb1.

  Table 1 shows the results of evaluating the separability of the transfer material P in the image forming apparatuses of the comparative example and this example. The separability was evaluated based on the ratio of 100 sheets of A4-size thin paper (basis weight 47 g / cm 2) passed in a high-temperature and high-humidity environment with a temperature of 30 ° C. and a humidity of 80%, and causing separation failure. In the configuration of the comparative example, a separation failure of 5% occurred, but in the configuration of the present example, no separation failure occurred.

  As described above, according to the present invention, the guide member 13 corresponding to the secondary transfer portion has a substantially flat shape so that the separation start direction of the transfer material P is generated with respect to the intermediate transfer belt 10. It is possible to improve the separation performance of the image forming apparatus by reducing the electroadsorption force.

(Example 2)
In the configuration of the image forming apparatus applied in this embodiment, the same members as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted. In the present embodiment, only the shape of the guide member is different, and the other configuration is the same as that of the first embodiment.

  FIG. 5A is a cross-sectional view illustrating the secondary transfer portion of this embodiment, and FIG. 5B is a schematic diagram illustrating the separation direction of the transfer material. As shown in FIG. 5, the guide member 23 of the present embodiment is characterized by having a concave portion with respect to the pressing direction F of the secondary transfer roller 20. FIG. 6 is a diagram for explaining the radius of curvature at each part of the secondary transfer part. As shown in FIG. 6, the concave portion of the guide member is configured such that the curvature radius r <b> 1 is larger than the radius r <b> 2 of the secondary transfer roller 20. Further, the inflection points A and B of the radius of curvature that become the joint between the guide member shape Na2 and the guide member shape Ga2 or Gb2 are not included in the nip width of the secondary transfer roller.

  Specifically, the guide member shape that does not correspond to the secondary transfer portion is an arc shape with Ga2 on the upstream side and Gb2 on the downstream side with respect to the transfer nip, the radius of curvature of Ga2 is 50 mm, and the radius of curvature of Gb2 is 12 mm. Consists of. The guide member shape Na2 is a circular arc shape having a curvature radius of 10 mm, and is recessed in the direction in which the secondary transfer roller 20 is pressed, and the curvature radius is larger than the radius 9 mm of the secondary transfer roller. Yes. Further, the inflection point portion of a certain radius of curvature and the joint between the guide member shape Na2 and the guide member shape Gb2 is configured to have an appropriate roundness.

  As shown in FIG. 5B, in the configuration of this embodiment, the shape Na <b> 2 of the secondary transfer portion is a concave shape with respect to the pressing direction F of the secondary transfer roller 20. Therefore, the leading edge traveling direction S of the transfer material P at the separation start position is closer to the secondary transfer roller 20 with respect to the straight line X connecting the most upstream position and the most downstream position of the secondary transfer portion, and is intermediate from the transfer material P. The distance d2 between the transfer belts 10 is increased. As a result, the electrostatic attraction force generated between the two can be reduced as compared with the comparative example.

  Regarding the separation of the transfer material to the secondary transfer roller 20 side, the radius of curvature of the secondary transfer roller 20 is smaller than the radius of curvature of the guide member, and the material of the secondary transfer roller 20 itself is adsorbed in a sponge shape. Therefore, there is no problem with the transfer material P being wound around the secondary transfer roller 20. Since the inflection points A and B of the radius of curvature that serve as a joint between the guide member shapes Ga2 and Gb2 and the guide member shape Na2 are located outside the secondary transfer portion Na2, the traveling direction of the paper leading edge of the transfer material P Can be reliably controlled to be on the secondary transfer roller 20 side.

  Further, as a feature of the second embodiment, the leading edge traveling direction S of the transfer material P is a direction further away from the intermediate transfer belt 10 as compared with the first embodiment. Therefore, in the configuration of the second embodiment, the transfer material P can be separated even when the curvature radius of Gb2 is larger than the curvature radius Gb1 of the first embodiment.

  As described above, according to the present invention, the guide member 13 corresponding to the secondary transfer portion has a substantially flat shape so that the separation start direction of the transfer material P is generated with respect to the intermediate transfer belt 10. It is possible to improve the separation performance of the image forming apparatus by reducing the electroadsorption force.

DESCRIPTION OF SYMBOLS 10 Intermediate transfer belt 11 Drive roller 12 Tension roller 13 Guide member 20 Secondary transfer member 21 Secondary transfer power supply

Claims (4)

An image carrier that carries a toner image, an endless intermediate transfer belt on which a toner image is primarily transferred from the image carrier, and a driving member that supports the inner peripheral surface of the intermediate transfer belt and moves the intermediate transfer belt A support member that supports an inner peripheral surface of the intermediate transfer belt, and a secondary transfer member that contacts the outer peripheral surface of the intermediate transfer belt and forms a secondary transfer portion with the intermediate transfer belt, In an image forming apparatus that secondarily transfers a toner image from the intermediate transfer belt to a transfer material conveyed to a secondary transfer unit,
The support member is a guide member that regulates a moving direction of the intermediate transfer belt while rubbing against the intermediate transfer belt at a position facing the secondary transfer member via the intermediate transfer belt, and the guide member is The direction of the leading edge of the transfer material when passing through the secondary transfer portion is regulated so that the transfer material that has passed through the secondary transfer portion approaches the secondary transfer member from the intermediate transfer belt. Image forming apparatus.   The guide member has a secondary transfer portion shape for forming the secondary transfer portion in a moving direction of the intermediate transfer belt, and a moving direction of the intermediate transfer belt upstream of the secondary transfer portion shape. The image forming apparatus according to claim 1, further comprising: an upstream restricting portion that restricts; and a downstream restricting portion that restricts a moving direction of the intermediate transfer belt on a downstream side of the shape of the secondary transfer portion.   The image forming apparatus according to claim 2, wherein the secondary transfer portion shape has a straight line as a movement locus of the intermediate transfer belt in the secondary transfer portion. The image forming apparatus according to claim 2, wherein the shape of the secondary transfer portion is a shape that is recessed from the secondary transfer member toward the guide member.

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