JP2019113585A - Image heating apparatus and image forming apparatus - Google Patents

Abstract

To provide an image heating apparatus and an image forming apparatus that can improve separability of a recording material from a belt, and that can reduce necessity to use a separation member to separate the recording material from the belt or necessity to close the separation member to the belt.SOLUTION: An image forming apparatus comprises: a pressure member 2; an endless belt 7; a nip forming member 3; a heating member 4; and a supporting member 6 that is inserted into an inner peripheral surface side of an end part of the belt in a rotation axis direction of a pressure member and in which an outer peripheral surface contacts with an inner peripheral surface of the belt to support the belt. An image heating apparatus A that heats a recording material comprises a guide surface 32a that slides to contact with the belt and in which surface a nip forming member is adjacent to a downstream side of a nip part in a conveyance direction X of the recording material at a nip part N and is leaning to be apart from the pressure member while going to a downstream side in the conveyance direction from the nip part, and the supporting member has a projection part 61 in which the outer peripheral surface projects in an opposite side of the guide surface in an area being opposite to the guide surface.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image heating apparatus used in an image forming apparatus using an electrophotographic method, an electrostatic recording method, a magnetic recording method or the like, and an image forming apparatus provided with the same.

  An image forming apparatus using an electrophotographic method or the like has a fixing device as an image heating device for fixing a toner image on a recording material by heating and pressing a recording material carrying an unfixed toner image. As a fixing device, there is the following film heating type fixing device. A fixing device of a film heating type comprises an endless (cylindrical) belt (film), a heating member disposed on the inner peripheral surface side of the belt, and a rotatable pressure that is in pressure contact with the heating member via the belt. And a member. In this fixing device, when the recording material passes through the fixing nip portion where the belt and the pressing member are in contact, the toner image is fixed to the recording material by the heat by the heating member and the pressure by nipping by the fixing nip portion. Let Since the belt is typically made of a thin film having a small thickness and a small heat capacity, it is possible to reduce power consumption by shortening the time required for startup to a desired fixing temperature (on-demand system) .

  In the film heating type fixing device, when the toner is melted for the fixing process, the toner functions as an adhesive and adhesion acts between the recording material and the belt. Then, due to the adhesion, the recording material and the belt become difficult to separate, and paper jam may occur.

  On the other hand, a separation member for separating the recording material from the belt may be disposed on the downstream side of the fixing nip portion in the conveyance direction of the recording material (Japanese Patent Application Laid-Open No. 2001-147118).

JP, 2009-288587, A

  However, the separating member for separating the recording material from the belt needs to be disposed in the vicinity of the belt immediately after passing through the fixing nip portion. In addition, when the separating member is brought close to the belt in order to enhance the separation of the recording material from the belt, the belt may come in contact with the separating member and damage the belt. When the belt is scratched, the fixing performance may vary in the plane of the belt, which may cause uneven fixing such as uneven gloss (glossy spots).

  Therefore, an object of the present invention is to improve the separation of the recording material from the belt, and to reduce the need to use a separation member for separating the recording material from the belt or to reduce the need to bring the separation member close to the belt. A heating device and an image forming apparatus provided with the same.

  The above object is achieved by an image heating apparatus and an image forming apparatus according to the present invention. In summary, according to the present invention, there are provided a rotatable pressure member, an endless belt having an outer peripheral surface in contact with the pressure member and being driven to rotate with the rotation of the pressure member; A nip forming member disposed on the inner circumferential surface side and forming a nip portion in which the belt and the pressing member are in pressure contact, a heating member disposed on the inner circumferential surface side of the belt and heating the belt, A support member inserted on the inner peripheral surface side of the end of the belt in the rotational axis direction of the pressure member, the outer peripheral surface being in contact with the inner peripheral surface of the belt to support the belt; In the image heating apparatus, in which the recording material carrying the toner is heated while being nipped and conveyed by the belt and the pressing member at the nip portion, the nip forming member is the one in the conveyance direction of the recording material at the nip portion. Adjacent to the downstream side of the nip portion, A guide surface which is inclined away from the pressing member as it goes downstream from the pressing portion in the transport direction, and in the cross section substantially orthogonal to the rotation axis direction of the pressing member, the nip portion in the transport direction A straight line passing through the center of the belt and a straight line substantially orthogonal to the transport direction is a vertical line V, a center B is a center between the inner circumferential surfaces of the opposite belts on the vertical line V, and a straight line perpendicular to the vertical line Of the four areas obtained by dividing the area surrounded by the horizontal line H and the inner circumferential surface of the belt by the vertical line V and the horizontal line H, the area to which the guide surface belongs is a first area E1, the four areas. When a region facing the first region E1 across the center B in the region is defined as a second region E2, the support member is configured such that the distance r from the center B to the outer peripheral surface is in the second region E2. In the direction of rotation of the belt An image heating apparatus, comprising a protrusion protruding to take a maximum value at the upstream than the downstream and the horizontal line H from the vertical line V Te.

  According to another aspect of the present invention, there is provided an image forming apparatus comprising an image forming means for forming a toner image on a recording material, and the image heating apparatus of the present invention.

  According to the present invention, the separation property of the recording material from the belt can be improved, and the necessity of using a separation member for separating the recording material from the belt or the necessity of bringing the separation member close to the belt can be reduced.

1 is a schematic cross-sectional view of an image forming apparatus. FIG. 2 is a schematic cross-sectional view of a fixing device. FIG. 6 is a schematic cross-sectional view of the fixing device when the belt support member is not used. FIG. 2 is a schematic cross-sectional view of the fixing device in the longitudinal direction. It is a schematic sectional drawing for demonstrating the structure of a belt support member.

  Hereinafter, the image heating apparatus and the image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

Example 1
1. Image Forming Apparatus First, an image forming apparatus 100 having a fixing device A as an image heating apparatus according to the present invention will be described. FIG. 1 is a cross-sectional view showing a schematic configuration of an image forming apparatus 100 of the present embodiment. The image forming apparatus 100 of the present embodiment is a tandem-type color laser printer adopting an intermediate transfer method capable of forming a full-color image using an electrophotographic method.

  The image forming apparatus 100, as a plurality of image forming units (stations), forms first, second, third, and so on images for yellow (Y), magenta (M), cyan (C), and black (K), respectively. The fourth image forming units SY, SM, SC, and SK are included. For elements having the same or corresponding functions or configurations in the respective image forming units SY, SM, SC, SK, Y, M, C, K at the end of the code indicating that they are elements for any color are omitted. Can be described in a comprehensive way. In this embodiment, the image forming unit S includes a photosensitive drum 101, a charging roller 102, an exposure device 103, a developing device 104, a primary transfer roller 105, a drum cleaning device 106, and the like, which will be described later.

  The image forming apparatus 100 has a photosensitive drum 101 which is a rotatable drum (cylindrical) photosensitive member (electrophotographic photosensitive member) as an image bearing member. The photosensitive drum 101 is rotationally driven in the direction of the arrow R11 in the drawing. The surface of the rotating photosensitive drum 101 is uniformly charged to a predetermined potential of a predetermined polarity (negative in this embodiment) by the charging roller 102 which is a roller type charging member (contact charging member) as charging means. It is processed. At the time of charging step, a charging power source (not shown) applies a charging bias including a negative DC component to the charging roller 102. The charged surface of the photosensitive drum 101 is scanned and exposed by an exposure device (laser scanner) 103 as an exposure unit based on image data, and an electrostatic image (electrostatic latent image) is formed on the photosensitive drum 101. . In the present embodiment, the exposure device 103 is configured as one unit for exposing the photosensitive drums 101 for each color. The electrostatic image formed on the photosensitive drum 101 is supplied with toner as a developer and developed (visualized) by a developing device 104 as developing means, and a toner image is formed on the photosensitive drum 101. The developing device 104 conveys the toner to a portion (developing position) facing the photosensitive drum 101 by a developing roller as a developer bearing member, and adheres the toner to the surface of the photosensitive drum 101 according to the electrostatic image. In this embodiment, in the image area (exposed area) where the absolute value of the potential is decreased by being uniformly charged and then exposed on the photosensitive drum 101, the charging polarity of the photosensitive drum 101 is the same In the embodiment, the negatively charged toner adheres. In this embodiment, the regular charging polarity of the toner, which is the charging polarity of the toner at the time of development, is negative. During the development process, the development roller includes a DC component set to a potential between the charging potential (dark potential) of the photosensitive drum 101 and the exposure portion potential (bright potential) by a developing power supply (not shown). A bias is applied.

  An intermediate transfer belt 107 as an intermediate transfer member is disposed to face the four photosensitive drums 101. The intermediate transfer belt 107 is a flexible endless belt (endless belt) formed using a dielectric. The intermediate transfer belt 107 is wound around a drive roller 171 as a plurality of stretching rollers, a secondary transfer opposite roller 172, and a tension roller 173, and is stretched with a predetermined tension. When the driving roller 171 is rotationally driven, the intermediate transfer belt 107 rotates (rotational movement, circulation movement) at substantially the same speed as the photosensitive drum 101 in the direction of the arrow R12 in the drawing. On the inner peripheral surface side of the intermediate transfer belt 107, primary transfer rollers 105, which are roller type primary transfer members as primary transfer means, are disposed corresponding to the respective photosensitive drums 107. The primary transfer roller 105 is pressed toward the photosensitive drum 101 via the intermediate transfer belt 107, and forms a primary transfer portion (primary transfer nip portion) T1 at which the photosensitive drum 101 and the intermediate transfer belt 107 contact.

  The toner image formed on the photosensitive drum 101 is transferred (primary transfer) onto the rotating intermediate transfer belt 107 at the primary transfer portion T1 by the action of the primary transfer roller 105. During the primary transfer process, a primary transfer bias (a positive polarity in this embodiment) is applied to the primary transfer roller 105 by a primary transfer power source (not shown), which is a reverse polarity (positive in this embodiment) of the toner charging polarity. Be done. For example, when forming a full-color image, toner images of yellow, magenta, cyan and black formed on the photosensitive drums 101 are sequentially transferred onto the intermediate transfer belt 107 in a superimposed manner. The toner (primary transfer residual toner) remaining on the photosensitive drum 101 without being transferred to the intermediate transfer belt 107 at the primary transfer portion T1 is removed from the photosensitive drum 101 by the drum cleaning device 106 as a photosensitive member cleaning unit and collected. Be done. When forming a single-color image, a toner image is formed only at the image forming unit S for the target color.

  A secondary transfer roller 108, which is a roller type secondary transfer member as a secondary transfer unit, is disposed at a position facing the secondary transfer opposing roller 172 on the outer peripheral surface side of the intermediate transfer belt 107. The secondary transfer roller 108 is pressed toward the secondary transfer opposing roller 172 via the intermediate transfer belt 107, and the secondary transfer portion (secondary transfer nip portion) where the intermediate transfer belt 107 and the secondary transfer roller 108 contact with each other. ) Form T2.

  The toner image formed on the intermediate transfer belt 107 is conveyed by being pinched between the intermediate transfer belt 107 and the secondary transfer roller 108 by the action of the secondary transfer roller 108 at the secondary transfer portion T2, such as paper. The image is transferred (secondary transfer) onto a sheet-like recording material (transfer material) P. At the time of the secondary transfer step, the secondary transfer roller 108 is driven by a secondary transfer power source (not shown) to generate a secondary voltage which is a direct current voltage of the reverse polarity (positive polarity in this embodiment) to the regular charging polarity of the toner. A transfer bias is applied. The recording material P is accommodated in the cassette 111 and fed one by one by the feeding roller 112. Then, the registration roller 113 aligns the timing with the toner image on the intermediate transfer belt 107, and the recording material P is conveyed to the secondary transfer portion T2. Is transported. The toner (secondary transfer residual toner) remaining on the intermediate transfer belt 107 without being transferred to the recording material P at the secondary transfer portion T2 is removed from above the intermediate transfer belt 107 by a belt cleaner as an intermediate transfer member cleaning unit (not shown). It is removed and recovered.

  The recording material P to which the toner image has been transferred is conveyed to a fixing device A as a fixing unit. The fixing device A fixes (melts, fixes) the toner image on the recording material P by heating and pressing the recording material P carrying the unfixed toner image while conveying it. The fixing device A will be described in more detail later. The recording material P subjected to the fixing process of the toner image is discharged (outputted) by a discharge roller 114 to a tray 115 provided outside the apparatus main body 110 of the image forming apparatus 100.

  In this embodiment, in each image forming unit S, the photosensitive drum 101 and the charging roller 102 as a process means acting thereon, the developing device 104, and the drum cleaning device 106 are integrally formed into a cartridge and the process cartridge is formed. Configured. Each process cartridge is detachably attached to the apparatus main body 110. In the present embodiment, in the apparatus main body 110, the four process cartridges are arranged substantially horizontally (in-line configuration, tandem type).

  In this embodiment, the image forming unit S, the intermediate transfer belt 107, the secondary transfer roller 108 and the like constitute an image forming unit for forming a toner image on the recording material P.

2. Fixing Device Next, a fixing device A as an image heating device in the present embodiment will be described. FIG. 2 is a cross-sectional view showing a schematic configuration of the fixing device A of this embodiment. FIG. 2 shows a cross section substantially orthogonal to the rotational axis direction of the pressure roller 2 described later. Here, in the cross section (X-Z plane) of FIG. 2, a direction substantially parallel to the conveyance direction of the recording material P in the fixing nip N described later is referred to as the X direction (here, also referred to as “the conveyance direction of the recording material P” And the direction substantially orthogonal to the X direction is the Z direction. Further, a direction substantially orthogonal to the cross section (X-Z plane) shown in FIG. In the present embodiment, the Y direction is substantially parallel to the rotational axis direction of the photosensitive drum 101. The front side in FIG. 2 in the Y direction is the front side, and the rear side in FIG. 2 in the Y direction is the rear side. FIG. 3 is a cross-sectional view showing a schematic configuration of the fixing device A when the belt support member 6 described later is not attached. FIG. 4 is a cross-sectional view showing a schematic configuration of the fixing device A in a cross section substantially parallel to the Y direction.

  The fixing device A of this embodiment is a film heating type fixing device. The fixing device A includes a heating unit 1 and a pressure roller 2 as a rotatable pressure member (pressure rotator). The heating unit 1 includes a belt 7 as a rotatable fixing member (fixing rotating body), a heater 4 as a heating member (heat source), a nip forming member 3, a pressing member 5, and a belt support member 6. Ru. As described later, the heater 4, the nip forming member 3 and the pressing member 6 are disposed on the inner peripheral surface side of the belt 7 along the Y direction. Further, as described later, the belt support members 6 are disposed at both ends of the belt 7 in the Y direction.

  The belt 7 is an endless (cylindrical) belt (film) formed of a flexible member having heat resistance, that is, an endless belt (endless film). The belt 7 has, but is not limited to, a laminated structure in which a plurality of layers are laminated. For example, the belt 7 may have a two-layer structure having a base (base layer) and a release layer (surface layer) laminated on the base. Further, the belt 7 has a three-layer structure having a base (base layer), an elastic layer laminated on the base, and a release layer (surface layer) laminated on the elastic layer. It may be. As the substrate, a substrate made of a heat resistant resin such as polyimide, polyamide imide, PEEK or the like, or a substrate made of metal such as nickel or SUS can be used. When a heat resistant resin is used as a substrate, the thickness of the substrate is preferably 30 μm or more and 200 μm or less. And, in this case, a fluorine-based resin (for example, PTFE, PFA, FEP) or the like can be coated on the outer peripheral surface of the base material as a release layer. The thickness of the release layer is preferably about 5 μm to 50 μm. On the other hand, when using a metal as a base material, it is preferable that the thickness of a base material is 30 micrometers or more and 100 micrometers or less. In this case, a silicone rubber layer or the like may be provided on the outer peripheral surface of the base as an elastic layer, and a fluorine resin tube (for example, PTFE, PFA, FEP) or the like may be coated on the outer peripheral surface of the elastic layer as a release layer. it can. The thickness of the elastic layer is preferably 100 μm or more and 1000 μm or less. The thickness of the release layer is preferably about 5 μm or more and 100 μm or less.

  The heater 4 is disposed on the inner peripheral surface side of the belt 7 and heats the belt 7 (that is, the recording material P is heated via the belt 7). The heater 4 is a thin-plate ceramic substrate having a rectangular shape in a plan view and a rectangular shape having a predetermined length in each of a longitudinal direction substantially parallel to the Y direction and a short direction substantially parallel to the X direction; And a heating resistor formed on the substrate along the longitudinal direction of the substrate. The heater 4 rapidly generates heat and raises its temperature by power supply to the heating resistor, and is controlled to a predetermined temperature by the temperature control system.

  The nip forming member 3 backs up the belt 7 and presses the belt 7 toward the pressure roller 2 to form a fixing nip portion (fixing portion) N in which the belt 7 contacts the pressure roller 2. The nip forming member 3 is disposed such that its longitudinal direction is substantially parallel to the Y direction. The nip forming member 3 is a member having a heat resistance and a heat insulating property, in which the cross section shown in FIG. The nip forming member 3 is formed using a material having good insulation and heat resistance such as phenol resin, polyimide resin, polyamide resin, polyamide imide resin, PEEK resin, PES resin, PPS resin, PFA resin, PFA resin, PTFE resin, LCP resin, etc. can do. The nip forming member 3 plays a role of backup of the belt 7, pressurization of the fixing nip portion N, support of the heater 4, and conveyance stability when the belt 7 rotates.

  Further, the nip forming member 3 has a nip forming portion 31 for pressing the belt 7 toward the pressure roller 2. Further, the nip forming member 3 has a downstream guide portion 32 for guiding the belt 7 on the downstream side of the nip forming portion 31 in the X direction and an upstream guide portion 33 for guiding the belt 7 on the upstream side of the nip forming portion 31 in the X direction. And.

  On a side surface of the nip forming portion 31 on the pressure roller 2 side in the Z direction, a recess 31 a extending along the Y direction is formed. The heater 4 is attached to the recess 31a. Further, the nip forming portion 31 has a downstream convex portion 31b adjacent to the downstream side of the concave portion 31a in the X direction and projecting to the pressure roller 2 side more than the side surface of the heater 4 on the pressure roller 2 side in the Z direction. . Further, the nip forming portion 31 has an upstream convex portion 31c adjacent to the upstream side of the concave portion 31a in the X direction and projecting to the pressure roller 2 side more than the side surface of the heater 4 on the pressure roller 2 side in the Z direction. . The nip forming member 3 presses the belt 7 toward the pressure roller 2 by the nip forming member 3 and the heater 4 attached to the nip forming member 3 between the upstream convex portion 31 c and the downstream convex portion 31 b in the X direction. As a result, the fixing nip portion N is formed.

  The downstream guide portion 32 is provided adjacent to the downstream side of the fixing nip portion N in the X direction, and is separated from the pressure roller 2 in the Z direction as it goes from the fixing nip portion N to the downstream side in the X direction. The cross section shown in FIG. The downstream guide portion 32 is adjacent to the downstream side of the fixing nip portion N in the X direction, and is inclined so as to be away from the pressure roller 2 in the Z direction as going from the fixing nip portion N to the downstream side in the X direction. It has the downstream guide surface 32a which is a side. The downstream guide portion 32 can guide the belt 7 by the belt 7 coming into contact with the downstream guide surface 32 a immediately downstream of the outlet of the fixing nip portion N. The upstream guide portion 33 is provided on the upstream side of the fixing nip portion N in the X direction, and is separated from the pressure roller 2 in the Z direction as going from the fixing nip portion N to the upstream side in the X direction. The cross section shown in FIG. Further, the upstream guide portion 33 is adjacent to the upstream side of the fixing nip portion N in the X direction, and is inclined so as to be away from the pressure roller 2 in the Z direction as going from the fixing nip portion N to the upstream side in the X direction. It has the upstream guide surface 33a which is a side. The upstream guide portion 33 can guide the belt 7 by the belt 7 coming into contact with the upstream guide surface 33 a immediately upstream of the entrance of the fixing nip portion N.

  The pressing member 5 presses the nip forming member 3 toward the pressure roller 2. The pressing member 5 has a predetermined rigidity so as to press the nip forming member 3. The pressing member 5 can be formed using a metal having high strength such as stainless steel, iron or the like. The pressing member 5 is inserted inside the nip forming member 3 so as to press the nip forming member 3 toward the pressure roller 2 via the belt 7. The pressing member 5 is a substantially U-shaped (arch-shaped) member whose cross section shown in FIG. 2 is open on the pressure roller 2 side in the Z direction. The pressing member 5 is disposed along the Y direction, and an end of the pressing portion 51 substantially parallel to each other abuts on a pressed portion 34 formed on the inner side surface of the nip forming member 3. Further, in the pressing portion 51, both end portions in the Y direction respectively protrude outside the both end portions of the nip forming member 3 to form the receiving portion 52. The receiving member 52 is biased toward the pressing roller 2 along the Z direction by a pressing spring (not shown) which is a pressing member as biasing means, whereby the pressing member 5 is The nip forming member 3 is pressed toward the pressure roller 2.

  The pressing member 5 has the following role. One is to support the nip forming member 3 and the heater 4 attached to the nip forming member 3 on both sides of the fixing nip N in the X direction. The other one is to press the heater 4 toward the pressure roller 2 through the belt 7 along the Z direction to form a uniform fixing nip N along the Y direction.

  The belt support members 6 are provided at both ends of the belt 7 in the Y direction, and support the belt 7 from the inner peripheral surface side. The belt support member 6 can be formed of a heat resistant and slidable resin such as PPS, a liquid crystal polymer, or a phenol resin. The belt support member 6 is inserted on the inner peripheral surface side of the end of the belt 7 in the Y direction, the outer peripheral surface contacts the inner peripheral surface of the belt 7 to support the belt 7, and the movement locus of the belt 7 in the rotational direction. Regulate (the shape in the circumferential direction). The belt support member 6 will be described in more detail later.

  In the present embodiment, the belt supporting member 6 is integrally formed with the width direction restricting member 8 which restricts the movement of the belt 7 in the Y direction (width direction) at the end of the belt 7 in the Y direction. It constitutes nine. The width direction restricting member 8 is disposed outside the belt 7 in the Y direction, and abuts on the end surface of the belt 7 in the Y direction to restrict the movement of the belt 7 in the Y direction. The flange 9 supports the nip forming member 3 and the pressing member 5 and is held by side plates (not shown) on the front and back sides of the fixing device A.

  The pressure roller 2 contacts the outer peripheral surface of the belt 7 to rotate the belt 7. The pressure roller 2 has a core metal (core material) 2a, an elastic layer 2b provided on the outer periphery of the core metal 2a, and a release layer 2c provided on the outer periphery of the elastic layer 2b. The metal core 2 a is rotatably held at both ends in the Y direction by bearing members (not shown) provided on side plates (not shown) on the front and back sides of the fixing device 4. In the pressure roller 2, the pressing member 5 of the heating unit 2 is urged toward the pressure roller 2 along the Z direction so that the elastic layer 2 b is elastically deformed and the belt 7 of the belt 7 is stretched over a predetermined width in the X direction. A fixing nip portion N where the surface and the surface of the pressure roller 2 are in contact is formed.

  Next, the fixing process of the toner image on the recording material P by the fixing device A will be described. The pressure roller 2 is set in a direction indicated by an arrow R1 in FIG. 2 by transmitting the driving force of a motor (not shown) as a driving means (driving source) provided in the apparatus main body 110 to the metal core 2a. Rotate at a circumferential speed of The belt 7 is held between the nip forming member 3 and the heater 4 attached to the nip forming member 3 and the pressure roller 2, and the pressure roller 2 is rotationally driven to rotate the pressure roller 2. 2 to rotate in the direction of the arrow R2 in FIG. The belt 7 rotates at a peripheral speed corresponding to the peripheral speed of the pressure roller 2. The belt 7 rotates with its inner circumferential surface in sliding contact with the heater 4 at the fixing nip N. In order to reduce the sliding friction between the heater 4 and the belt 7 at the fixing nip N, lubrication such as heat resistant grease is provided between the side surface of the heater 4 on the belt 7 side and the inner peripheral surface of the belt 7. The agent is intercalated. The CPU (not shown) of the control unit provided in the apparatus main body 110 measures the temperature of the fixing nip N (that is, the heater 4) monitored by using a temperature detection member such as a thermistor to a predetermined fixing temperature (target temperature) The amount of power supplied to the heater 4 is controlled so as to maintain The recording material P carrying the unfixed toner image t is nipped between the heating unit 1 and the pressure roller 2 at the fixing nip portion N and conveyed. In the conveyance process, the heat of the belt 7 and the pressure of the fixing nip N are applied to the recording material P (that is, the toner on the recording material P), and the toner image is fixed (melted and fixed) on the recording material P Be done.

  The fixing device A of this embodiment is configured such that the belt 7 is rotationally driven by the pressure roller 2 in a state where no tension is applied to at least a part of the circumferential length of the belt 7 (tension free). That is, in the cross section shown in FIG. 2, the belt 7 is externally fitted to the nip forming member 3, the heater 4 and the belt supporting member 6. In the cross section shown in FIG. 2, the inner peripheral length of the belt 7 is larger than the outer peripheral length formed by the nip forming member 3, the heater 4 and the belt supporting member 6 disposed on the inner peripheral surface side of the belt 7.

3. Structure for Improving Separability Next, a structure for improving the detachability of the recording material P from the belt 7 in the fixing device A of this embodiment will be described.

  As described above, in the fixing device A, when the toner is melted for fixing processing, the adhesion of the toner makes it difficult for the recording material P and the belt 7 to be separated, and paper jam may occur. is there. On the other hand, it is conceivable to arrange a separation member for separating the recording material P from the belt 7 on the downstream side of the fixing nip portion N in the conveyance direction of the recording material P. However, when the separating member is brought close to the belt 7 in order to enhance the separation of the recording material P from the belt 7, the belt 7 may come in contact with the separating member and damage the belt 7. Then, if the belt 7 is damaged, the fixing performance may vary within the surface of the belt 7 and the fixing unevenness such as gloss unevenness (glossy spots) may occur. Therefore, it is required to improve the separation of the recording material P from the belt 7 and to reduce the necessity of using a separation member for separating the recording material P from the belt 7 or the necessity of bringing the separation member close to the belt 7 There is.

  Here, as shown in FIG. 3, in the state where the belt support member 6 is not used, the belt 7 is loosely fitted to the nip forming member 3, the heater 4 and the pressing member 5 with a margin. In this state, the recording material P is difficult to be separated from the belt 7 by the curvature, and as described above, there is a possibility that the recording material P and the belt 7 are not separated due to the adhesion of toner and paper jam may occur. Further, in this state, since the belt 7 may flutter and may be puffed to the downstream side in the conveyance direction of the recording material P, the recording material can be disposed by bringing the separation member close to the belt 7 for the reasons described above. There is a limit to improving the separation of P from the belt 7.

  Therefore, in the present embodiment, the belt 7 is made to follow the downstream guide surface 32 a of the nip forming member 3 by the shape of the belt supporting member 6. As a result, the recording material P is easily separated from the belt 7 by the curvature, and the separation of the recording material P from the belt 7 is improved. This will be described in more detail below. In the present embodiment, the belt support members 6 respectively disposed at both ends in the Y direction have the same structure and shape (symmetrical with respect to the center of the belt 7 in the Y direction), so one end here Description will be made by focusing attention on the belt support member 6 on the part side (rear side). In the present embodiment, no separating member for separating the recording material P from the belt 7 is provided.

  In the cross section shown in FIG. 2, a vertical line V is a straight line which passes through the center of the fixing nip N in the X direction (the direction substantially parallel to the conveyance direction of the recording material P in the fixing nip N). . Further, the center between the inner circumferential surfaces of the opposing belts 7 on the vertical line V is taken as a center B. Further, a straight line passing through the center B and orthogonal to the vertical line V is taken as a horizontal line H. Further, the area surrounded by the inner peripheral surface of the belt 7 is divided into four areas by the vertical line V and the horizontal line H (the vertical line V and the horizontal line H belong to any adjacent areas) ). Of the four areas, the area to which the downstream guide surface 32a belongs is taken as a first area (nip exit area) E1. Further, among the four areas, an area facing the first area E1 across the center B (that is, an area from the first area E1 to the second area in the rotational direction of the belt 7) Region) E2.

  At this time, the belt supporting member 6 is shaped so as to have a protrusion 61 whose outer peripheral surface protrudes on the opposite side to the downstream guide surface 32 a in a region facing the downstream guide surface 32 a with the center B interposed therebetween. This allows the belt 7 to be along the downstream guide surface 32a. That is, by using this belt support member 6, the cross-sectional shape (the movement trajectory in the rotational direction) of the belt 7 is shown by the solid line in FIG. 2 from the shape shown by the broken line in FIG. It becomes a shape, and the belt 7 comes to follow the downstream guide surface 32a.

  More specifically, the belt support member 6 protrudes in the second region E2 so that the distance r from the center B to the outer peripheral surface has a maximum value downstream of the vertical line V and upstream of the horizontal line H in the rotational direction of the belt 7 It has a shape having a projecting portion 61. In other words, in the second region E2, the outer peripheral surface of the belt support member 6 has a maximum value in which the distance from the center B to the inner peripheral surface of the belt 7 is downstream of the vertical line V and upstream of the horizontal line H in the rotational direction of the belt 7. It has a shape that makes it Furthermore, in other words, the outer peripheral surface of the belt support member 6 has an asymmetrical shape with respect to the vertical line V. The outer peripheral surface of the belt supporting member 6 has a maximum value between the vertical line V and the horizontal line H in the rotational direction of the belt 7 in the second region E2 such that the distance r from the center B to the outer peripheral surface is It has a protruding shape. On the other hand, the outer peripheral surface of the belt support member 6 is substantially arc-shaped in the area E3 sandwiched between the first area E1 and the second area E2. That is, in the area E3 between the first area E1 and the second area E2, the outer peripheral surface of the belt support member 6 has a distance from the center B to the outer peripheral surface substantially the same from the horizontal line H to the vertical line V. It has a shape (or takes a maximum value on the vertical line V or on the horizontal line).

  At this time, the extent to which the belt support member 6 is protruded can be set so that the belt 7 sufficiently follows the downstream guide surface. If this degree of protrusion is too small, the belt 7 may swell to the downstream side in the conveyance direction of the recording material P, and the separability of the recording material P from the belt 7 may be insufficient. On the other hand, if the degree of protrusion is too large, the fixing device 4 will be upsized. For example, the maximum value of the distance r from the center B to the outer peripheral surface of the belt support member 6 in the second region E2 is larger than the distance r on the vertical line V or the horizontal line H in the second region E2. It is preferable to be larger by 5% or more and 15% or less. More preferably, the maximum value of the distance r from the center B to the outer peripheral surface of the belt support member 6 in the second region E2 is the distance r on the vertical line V or the horizontal line H in the second region E2. Make it 8% or more and 10% or less larger than the major one.

  The downstream guide surface 32a is from the position D1 at the downstream end of the fixing nip N in the X direction around the center B to the position D2 at the downstream position of 15 degrees or more in the rotational direction of the belt 7. Preferably, the belt 7 is in sliding contact with the belt 7 in the sliding contact area D. More preferably, the belt 7 is in sliding contact with the sliding area D from the position D1 to the position D2 downstream by 30 degrees or more. The position D2 is often sufficient at a position downstream of the position D1 by 50 degrees or less, typically by 40 degrees or less.

  In addition, although the protrusion 61 may be in the second area E2, typically, in the second area E2, it passes through each of the positions D1 and D2 of both ends of the sliding contact area D and the center B. The distance r is provided so as to take a local maximum between straight lines.

  The cross-sectional shape of the belt 7 achieved by the belt support member 6 as described above can be seen in a state where the fixing device 4 (belt 7 and pressure roller 2) is stopped. Typically, the same shape is achieved even when the fixing device 4 (belt 7 and pressure roller 2) is driven, but for any reason, for example, the belt 7 temporarily passes from the downstream guide surface 32a. There may be a case where they are separated.

  Further, in the cross section shown in FIG. 2, the angle with the X direction of the upstream guide surface 32a is preferably 20 degrees or more and 60 degrees or less, and more preferably 30 degrees or more and 50 degrees or less. If this angle is too small, the separability of the recording material P from the belt 7 may be insufficient. On the other hand, if this angle is too large, the load on the belt 7 due to bending may become too large. Further, the upstream guide surface 32a may be linear or curved (convex outward). When the upstream guide surface 32a is curved, the angle with respect to the X direction of the tangent of the upstream guide surface 32a in the cross section shown in FIG. 2 may be regarded as the angle with respect to the X direction of the upstream guide surface 32a.

  Here, according to the configuration of the present embodiment, the belt 7 can be efficiently made to follow the downstream guide surface 32 a while suppressing the amount of the belt support member 6 to be protruded. On the other hand, the shape of the outer peripheral surface of the belt support member 6 should be such that the distance r from the center B to the outer peripheral surface in the second region E2 has a maximum value on the vertical line V or the horizontal line H. Then, it may be conceivable to make the belt 7 along the downstream guide surface 32a. However, in this case, in order to make the belt 7 sufficiently along the downstream guide surface 32a, the distance r on the vertical line V or the horizontal line H must be made relatively large. It leads to the enlargement.

  Further, as shown in FIG. 5, when the outer peripheral surface 62 of the belt support member 6 protrudes further downstream in the X direction than the outer peripheral surface 35 of the nip forming member 3 downstream of the vertical line V in the X direction. The belt 7 is supported by the outer circumferential surface 62 of the belt support member 6 which has protruded. This may make it difficult for the belt 7 to follow the downstream guide surface 32a. Therefore, as shown in FIG. 2, in the belt support member 6, the outer peripheral surface 62 of the belt support member 6 is downstream of the outer peripheral surface 35 of the nip forming member 3 downstream of the vertical line V in the X direction. It is preferable that the shape does not protrude to the side. As a result, it is easy to make the belt 7 follow the downstream guide surface 32a.

  As described above, according to this embodiment, it is necessary to use a separating member for improving the separation of the recording material P from the belt 7 and separating the recording material P from the belt 7 or to use the separating member as the belt 7. The need to approach can be reduced. Therefore, it is possible to suppress the belt 7 from being scratched by the separation member, and to suppress the occurrence of the uneven fixing due to the belt 7 being scratched.

[Others]
As mentioned above, although this invention was described based on the specific Example, this invention is not limited to the above-mentioned Example.

  An image heating apparatus for heating a recording material carrying a toner image is typically a fixing apparatus for fixing an unfixed toner image to the recording material, but for example, the recording material on which the toner image is fixed is reheated It may be a device that controls gloss.

  Further, in the above-described embodiment, the separating member for separating the recording material from the belt is not provided in the vicinity of the belt of the image heating apparatus, but a separating member may be provided. Also in this case, as described above, according to the present invention, it is possible to reduce the necessity of bringing the separating member close to the belt.

Reference Signs List 1 heating unit 2 pressure roller 3 nip forming member 4 heater 5 pressing member 6 belt supporting member 7 belt 32a downstream guide surface 61 projecting portion 100 image forming apparatus A fixing device

Claims (6)

A rotatable pressure member,
An endless belt which has an outer peripheral surface in contact with the pressure member and is rotated following the rotation of the pressure member;
A nip forming member disposed on an inner circumferential surface side of the belt and forming a nip portion in which the belt and the pressing member are in pressure contact with each other;
A heating member disposed on the inner circumferential surface side of the belt for heating the belt;
A support member inserted on the inner peripheral surface side of the end of the belt in the rotational axis direction of the pressure member, the outer peripheral surface being in contact with the inner peripheral surface of the belt to support the belt;
Have
In the image heating apparatus, the recording material carrying the toner image is heated while being nipped and conveyed by the belt and the pressing member at the nip portion,
The nip forming member is adjacent to the downstream side of the nip portion in the conveyance direction of the recording material at the nip portion, and inclined so as to be away from the pressing member as it goes downstream from the nip portion in the conveyance direction. Have a guiding surface,
In a cross section substantially orthogonal to the rotation axis direction of the pressure member, a straight line substantially perpendicular to the conveyance direction passing through the center of the nip portion in the conveyance direction is a vertical line V and an opposing belt on the vertical line V A straight line perpendicular to the vertical line passing through the center B and a center B between the inner peripheral surfaces is divided by the horizontal line H and a region surrounded by the inner peripheral surface of the belt is divided by the vertical line V and the horizontal line H When the area to which the guide surface belongs among the four areas is the first area E1, and the area facing the first area E1 across the center B among the four areas is the second area E2, The support member protrudes in the second area E2 such that the distance r from the center B to the outer peripheral surface has a maximum value downstream of the vertical line V and upstream of the horizontal line H in the rotational direction of the belt To have a department An image heating apparatus according to symptoms.   The maximum value of the distance r in the second area E2 is larger by 5% or more and 15% or less with respect to the larger one of the distances r on the vertical line V or the horizontal line H in the second area E2. The image heating apparatus according to claim 1,   The guide surface slides from a position D1 which is a downstream end of the nip portion in the transport direction around the center B to a position D2 which is a position downstream by 15 degrees or more in the rotation direction of the belt. The image heating apparatus according to claim 2, wherein the image heating apparatus is in sliding contact with the belt at a contact area D.   The outer circumferential surface of the support member does not project downstream of the outer circumferential surface of the nip forming member downstream of the vertical line V on the downstream side of the conveyance direction with respect to the vertical line V. An image heating apparatus according to any one of the preceding claims.   The image heating apparatus according to any one of claims 1 to 4, which is a fixing device for fixing an unfixed toner image to a recording material at the nip portion.   An image forming apparatus comprising: an image forming unit that forms a toner image on a recording material; and the image heating apparatus according to any one of claims 1 to 5.