JP2013164633A - Fixing device, and image forming apparatus comprising the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device which reliably separates a recording medium from a heating member with a simple configuration, and to provide an image forming apparatus comprising the same.SOLUTION: A fixing device 5 comprises: a rotatable, endless heating belt 218; a rotatable pressure roller 219 which comes into press contact with the heating belt 218; a heat source 233 which heats the heating belt 218; and a holding member 240 which is fixed in the heating belt 218 to the device body and has a guide surface 244a which guides motion of the heating belt 218 and brings one part of the heating belt 218 in press contact with the pressure roller 219. The guide surface 244a is an arcuate surface being in contact with the heating belt 218 and is arranged so as to face the pressure roller 219 via the heating belt 218, while being inclined to the side of the pressure roller 219 towards a downstream direction of conveyance of a sheet. At the downstream side end of the guide surface 244a, the heating belt 218 and the pressure roller 219 are separated.

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device used in an image forming apparatus such as a copying machine, a printer, a facsimile, or a composite machine using an electrophotographic method, and an image forming apparatus including the fixing device, and more particularly, a sheet conveyed from a fixing nip region. The present invention relates to a fixing device that separates the toner from a heating member and an image forming apparatus including the same.

  In an image forming apparatus using an electrophotographic system, a sheet on which a toner image is transferred is passed through a nip region of a pair of rollers including a heating roller and a pressure roller, and heating by the heating roller and pressure between the rollers are performed. Therefore, a fixing device that melts and fixes a toner image on a sheet is widely used. In this fixing device, when the toner image on the paper is melted and fixed, the toner comes into contact with the heating roller. Therefore, the heating roller is used with a fluorine-based resin having good releasability formed on the surface. However, even when such a heating roller is used, the melted toner is soft and has a high viscosity, so that it easily adheres to the surface of the heating roller and the paper may be wound around the heating roller. Therefore, in order to peel the wound paper from the heating roller, a separation claw is provided on the downstream side in the rotation direction of the nip region of the heating roller.

  However, in the separation structure using the separation claw, scratches such as claw marks are easily attached to the outer peripheral surface of the heating roller, which not only deteriorates the durability of the heating roller, but also causes a problem of image bleeding due to this scratch. It was.

  Therefore, in Patent Document 1, a heat source, a heating member heated by the heat source and provided rotatably, a holder on which the heating member slides, and a holder and the heating member facing each other via a paper conveyance path The heating member is driven to rotate with the rotation of the pressure roller. The sheet is fed into the nip area between the heating member and the pressure roller, and the unfixed toner image on the sheet is melted and fixed in this nip area. The holder slidably holds the heating member on a cylindrical outer periphery, and a separation portion is formed at a position on the downstream end in the conveyance direction of the nip region. The separation part has an arc shape in cross section, and the curvature radius of the separation part is set smaller than the curvature radius of the holder. By separating the paper from the nip region in the separation unit, the separation claw is unnecessary, the device configuration is simplified, and the device is downsized.

  However, in the above-described prior art, when a stiff sheet such as thick paper is conveyed to the nip region, the sheet may be caught at the boundary between the outer peripheral portion of the holder and the arc-shaped portion of the separation portion. Furthermore, when a high-density image is formed on the leading end side of the conveyed paper, the leading end of the paper may not be separated from the surface of the heating member, and the paper may be wound around the heating member.

JP-A-9-152804 (paragraphs [0020], [0021], [0028] to [0030], FIG. 1)

  SUMMARY An advantage of some aspects of the invention is that it provides a fixing device that reliably separates a sheet from a heating member with a simple configuration and an image forming apparatus including the fixing device. And

  In order to achieve the above object, the present invention provides a rotatable endless heating belt, a pressure roller that is able to press and rotate against the heating belt, a heat source that heats the heating belt, the heating belt, and the heating belt. A nip region where the pressure roller comes into pressure contact with the apparatus main body inside the heating belt and is pressed by the pressure roller, and guides the heating belt to move along a predetermined path in the nip region. And a holding member having a guide surface for conveying and fixing the unfixed toner image on the paper by conveying the paper while sandwiching the paper in the nip region. The guide surface is located in the nip region. It is characterized in that it is formed so as to incline toward the pressure roller as it goes to the downstream side in the sheet conveyance direction.

  According to this configuration, when the pressure roller rotates, in the nip region, the heating belt is guided by the guide surface and moves so as to incline toward the pressure roller side toward the downstream side in the paper transport direction, and the paper is It is conveyed along the same path as the heating belt. As a result, the unfixed toner image is melted and fixed on the paper in the nip region, and the front end of the paper faces the direction near the pressure roller at the downstream end in the paper conveyance direction of the nip region. To separate.

  According to a second aspect of the present invention, the guide surface is formed so as to be inclined in an arc shape. According to this configuration, when the pressure roller rotates, in the nip region, the heating belt is guided by the guide surface and moves in an arc shape so as to be inclined toward the pressure roller side toward the downstream side in the paper conveyance direction. The paper is conveyed along the same path as the heating belt. As a result, the unfixed toner image is melted and fixed on the sheet in the nip region, and the sheet is conveyed along the path of the arc-shaped nip region. The paper is directed in a direction close to the pressure roller, and the paper becomes an arc shape and is separated from the surface of the heating belt.

  The invention according to claim 3 is characterized in that the nip pressure in the nip region increases as it goes downstream in the sheet conveyance direction. According to this configuration, since the nip pressure is large on the downstream side of the nip region in the paper conveyance direction, the molten toner image on the paper has a gloss when passing the downstream side of the nip region in the paper conveyance direction.

  According to a fourth aspect of the present invention, the guide surface has a portion located in an extension region extending downstream from the nip region in the paper conveyance direction, and a portion located in the extension region is downstream in the paper conveyance direction. It is characterized in that it is formed on the pressure roller side so as to be further inclined from the nip region as it goes to. According to this configuration, after the sheet passes through the nip region, the sheet is heated for a longer time by being conveyed while being in contact with the surface of the heating belt. Further, the leading edge of the paper faces the direction close to the pressure roller at the downstream end of the extension region in the paper conveyance direction, and the paper is separated from the surface of the heating belt.

  In the invention according to claim 5, the heat source is provided inside the heating belt, the holding member includes a guide plate that forms the guide surface, a holding main body portion fixed to the apparatus main body, And a heat insulating portion disposed between the guide plate and the holding main body. According to this configuration, the heat insulating part suppresses heat transfer from the heat source to the guide plate via the holding main body part, and prevents heat storage of the heat from the heat source to the holding member.

  According to a sixth aspect of the present invention, there is provided an image forming apparatus equipped with the fixing device having the above configuration.

  According to the first aspect of the present invention, when the pressure roller rotates, in the nip region, the heating belt is guided by the guide surface so as to incline toward the pressure roller toward the downstream side in the paper conveyance direction. The paper moves and is conveyed along the same path as the heating belt. As a result, the unfixed toner image is melted and fixed on the paper in the nip region, and the front end of the paper faces the direction near the pressure roller at the downstream end in the paper conveyance direction of the nip region. To separate. Therefore, the sheet can be reliably separated from the heating belt with a simple configuration without using a separation claw, and there is no possibility that the sheet is wound around the heating belt.

  According to the second aspect of the present invention, when the pressure roller rotates, the heating belt is guided by the guide surface in the nip region and is inclined toward the pressure roller side toward the downstream side in the paper transport direction. The sheet is conveyed in the same path as the heating belt. As a result, the unfixed toner image is melted and fixed on the sheet in the nip region, and the sheet is conveyed along the path of the arc-shaped nip region. The paper is directed in a direction close to the pressure roller, and the paper becomes an arc shape and is separated from the surface of the heating belt. Therefore, the paper can be reliably separated from the heating belt with a simple configuration without using a separation claw, and there is no possibility that the paper will wrap around the heating belt.

  According to the third aspect of the present invention, since the nip pressure is large on the downstream side of the nip region in the paper conveyance direction, the molten toner image on the paper is glossy when passing the downstream side of the nip region in the paper conveyance direction. A good image can be obtained.

  According to the fourth aspect of the present invention, after the paper passes through the nip region and is conveyed while being in contact with the surface of the heating belt, the paper is heated for a longer time and the fixability is further improved. The toner image is glossy and a good image can be obtained. Further, the front end of the paper is directed toward the pressure roller side at the downstream end of the extension region in the paper conveyance direction, so that the paper can be reliably separated from the surface of the heating belt.

  According to the invention described in claim 5, the nip shape can be easily formed by the guide plate made of a plate material or the like, and heat is transferred from the heat source to the guide plate through the holding body portion by the heat insulating portion. Therefore, the heat source can efficiently heat the heating belt.

  According to a sixth aspect of the present invention, the image forming apparatus includes a fixing device that reliably separates the paper from the heating belt with a simple configuration.

FIG. 1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a cross-sectional view showing a schematic configuration of a fixing device used in the image forming apparatus according to the first embodiment of the present invention. FIG. 3 is a diagram schematically showing a configuration of a nip region of the fixing device according to the first embodiment of the present invention. FIG. 3 is a diagram showing a schematic configuration of a fixing device used in an image forming apparatus according to a second embodiment of the present invention. FIG. 4 is a diagram schematically showing a configuration of a nip region of a fixing device according to a second embodiment of the present invention.

  Embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited to these embodiments. Further, the use of the invention and the terms shown here are not limited thereto.

(First embodiment)
FIG. 1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention. As shown in FIG. 1, the image forming apparatus 1 includes a sheet feeding unit 2 disposed in a lower portion thereof, a sheet conveying unit 3 disposed on a side of the sheet feeding unit 2, and the sheet conveying unit 3. An image forming unit 4 disposed above the image forming unit 3, a manual feed tray 25 disposed on the right side of the image forming unit 3, and a fixing device 5 disposed on the discharge side of the image forming unit 4. The image reading unit 6 is provided above the image forming unit 4 and the fixing device 5.

  The paper feed unit 2 includes a plurality of paper feed cassettes 7 that store recording materials 9 that are plain paper, and a paper feed cassette selected from among the plurality of paper feed cassettes 7 by the rotation operation of the paper feed roller 8. 7, the recording material 9 is surely sent out one by one to the paper transport unit 3.

  The manual feed tray 25 is loaded with plain paper of a different size from the recording material 9 accommodated in the paper feed cassette 7 or recording material such as an OHP sheet or envelope, and transports the recording material 9 such as an OHP sheet or envelope. Send to part 3.

  The recording material 9 sent to the paper transport unit 3 is transported toward the image forming unit 4 via the paper supply path 10. The image forming unit 4 forms a toner image on the recording material 9 by an electrophotographic process. The photosensitive member 11 is rotatably supported in a predetermined direction (the arrow direction in the figure), and the photosensitive member. A charging device 12, an exposure device 13, a developing device 14, a transfer device 15, a cleaning device 16, and a charge eliminating device 17 are provided around the rotation device 11 along the rotation direction.

  The charging device 12 includes a charging wire to which a high voltage is applied. When a predetermined potential is applied to the surface of the photoconductor 11 by corona discharge from the charging wire, the surface of the photoconductor 11 is uniformly charged. Then, laser light based on the image data of the original read by the image reading unit 6 is irradiated to the photoconductor 11 by the exposure device 13. The surface potential of the photoconductor 11 is selectively attenuated by the irradiated laser light, and an electrostatic latent image is formed on the surface of the photoconductor 11. Next, the developing device 14 develops the electrostatic latent image on the surface of the photoconductor 11, and a toner image is formed on the surface of the photoconductor 11. The toner image is transferred to the recording material 9 supplied between the photosensitive member 11 and the transfer device 15 by the transfer device 15.

  The recording material 9 onto which the toner image has been transferred is conveyed toward the fixing device 5 disposed downstream of the image forming unit 4 in the sheet conveying direction. In the fixing device 5, the recording material 9 is heated and pressed by the heating belt 18 and the pressure roller 19, and the toner image is melted and fixed on the recording material 9. Next, the recording material 9 on which the toner image is fixed is discharged onto the discharge tray 21 by the discharge roller pair 20.

  After the transfer by the transfer device 15, the toner remaining on the surface of the photoconductor 11 is removed by the cleaning device 16, and the residual charge on the surface of the photoconductor 11 is removed by the charge eliminating device 17. Then, the photoreceptor 11 is charged again by the charging device 12, and image formation is performed in the same manner.

  The fixing device 5 will be described in detail with reference to FIG. FIG. 2 is a cross-sectional view showing a schematic configuration of the fixing device 5 used in the image forming apparatus 1 described above.

  As shown in FIG. 2, the fixing device 5 includes a heating belt 18, a pressure roller 19, a heat source 33 including a pair of heater lamps, a holding member 40, and the like.

  The heating belt 18 is formed of an endless metal thin plate such as aluminum or iron having excellent thermal conductivity, and imparts flexibility to the belt. An elastic layer such as silicon rubber is formed on the outer surface of the metal thin plate to impart elasticity to the belt, and a release layer such as a fluororesin is laminated to release the unfixed toner image when it is fused. Improves sex.

  The heat source 33 is fixed to the main body of the fixing device 5 inside the heating belt 18 and heats the heating belt 18.

  The pressure roller 19 includes a cylindrical base material 19a made of synthetic resin, metal or other material, and an elastic layer 19b formed of silicon rubber or the like on the outer periphery of the base material 19a. The surface is covered with a resin having excellent releasability such as a fluororesin. When the pressure roller 19 presses a holding member 40 to be described later via the heating belt 18, the pressure roller 19 comes into pressure contact with the heating belt 18, and a nip region N is formed in this pressure contact portion. In the nip region N, the elastic layer 19b is elastically deformed, and a nip pressure due to the pressure of this elastic deformation acts.

  Further, the pressure roller 19 is connected to a drive source such as a motor and a gear (not shown), and is rotated in the arrow direction (counterclockwise direction) in FIG. 2 by this drive source. When the pressure roller 19 rotates counterclockwise, the heating belt 18 that is in pressure contact with the pressure roller 19 rotates following the direction of the arrow (clockwise direction) shown in FIG. When the heating belt 18 and the pressure roller 19 rotate in the opposite directions, the recording material 9 onto which the toner image has been transferred is nipped and conveyed to the nip region N. Further, in the nip region N, the toner in the powder state on the recording material 9 is pressurized and melted and fixed by being heated and pressed by the heating belt 18 and the pressure roller 19. When the heating belt 18 and the pressure roller 19 are further rotated, the recording material 9 is separated from the heating belt 18 and conveyed to the left side in FIG.

  The holding member 40 is pressed by the pressure roller 19 through the heating belt 18 and guides the heating belt 18 to move along a predetermined path in the nip region N. It has a main body part 45 and a heat insulating part 46.

  The holding main body 45 has a length equal to or greater than that of the heating belt 18 in the width direction of the recording material 9 (paper surface direction in FIG. 2), and is fixed to the fixing device 5 main body. The holding main body 45 has an inverted T-shaped cross section and is disposed between the pair of heat sources 33, and has a holding surface 45a extending below the paper conveying direction. The holding surface 45a is formed as a flat surface inclined toward the pressure roller 19 as it goes downstream in the paper conveyance direction.

  The heat insulating unit 46 blocks heat transmitted from the heat source 33 to the holding unit main body 45 from being further transmitted to the guide plate 44, and suppresses accumulation of heat from the heat source 33 in the holding member 40. The heat insulating portion 46 is made of felt of an alumina silica material, is formed in a rectangular flat plate shape that extends in the width direction of the recording material 9 and the paper conveyance direction, and is attached to the holding surface 45a.

  The guide plate 44 is made of a heat-resistant plate material such as stainless steel having a small friction coefficient. The guide plate 44 includes a flat surface portion that has a guide surface 44a and faces the heat insulating portion 46 on the opposite side of the guide surface 44a, and bent portions 44b and 44c formed at both ends of the flat surface portion in the sheet conveyance direction. . The bent portions 44b and 44c are bent toward the holding main body 45 side. When the guide plate 44 is affixed to the heat insulating portion 46, the guide surface 44a is disposed so as to be inclined toward the pressure roller 19 side as it goes downstream in the paper transport direction, following the holding surface 45a of the holding main body 45. Instead of the configuration of the holding member 40 in which the guide plate 44 is provided separately from the holding main body 45, the holding member 40 is configured only by the holding main body, and the guide surface having the above-described shape is formed on the holding main body. You may do it.

  The guide surface 44 a faces the heating belt 18 and is pressed by the pressure roller 19, whereby the nip region N is deformed following the shape of the guide surface 44 a, and the guide surface 44 a is heated in the nip region N. 18 movement paths are formed. When the pressure roller 19 rotates, the heating belt 18 is guided by the guide surface 44a and moves along the path of the nip region N 1.

  The moving path of the heating belt 18 will be described in detail with reference to FIG. FIG. 3 is a diagram showing a nip region N formed by the guide surface 44a, and the recording material is conveyed from the right side of FIG.

  In FIG. 3, N1, N0, and N2 indicate the entrance, center, and exit of the nip region, respectively, and the recording material is conveyed in the order of the nip portions N1, N0, and N2. Since the guide surface 44a is arranged to be inclined toward the pressure roller 19 as it goes downstream in the paper conveyance direction, the nip portion N1 is formed at a position L1 above the rotation center O of the pressure roller 19, Similar to the nip portion N1, the nip portion N0 is formed at a position L0 from the rotation center O, and the nip portion N2 is formed at a position L2 from the rotation center O. The nip portion N0 is located below the nip portion L1 (on the rotation center side of the pressure roller 19), and the nip portion N2 is located below the nip portion L0 (on the rotation center side of the pressure roller 19).

  Accordingly, the recording material to which the toner has been transferred enters the nip portion N1, is nipped and conveyed along the path of the nip region N, and an unfixed toner image is pressurized and melted on the recording material, and further the toner image is fixed. The leading end of the recording material is conveyed toward the direction near the pressure roller 19 at the nip portion N2, and the recording material is separated from the surface of the heating belt 18.

  The pressure applied to the nip region N of the pressure roller 19 increases as the recording material is conveyed to the nip portions N1, N0, N2, and the recording material has a large nip in the vicinity of the exit (nip portion N2) of the nip region N. Since the pressure is applied, the molten toner image on the recording material is glossy.

  In the first embodiment, the heat source 33 is constituted by a heater lamp disposed inside the heating belt 18, but the present invention is not limited to this, and the heat source 33 is induced by magnetic flux generated from the exciting coil. An electromagnetic induction heating type heat source to be heated may be used, or an electromagnetic induction heating type heat source may be disposed outside the heating belt.

  According to the first embodiment, the fixing device 5 includes the rotatable endless heating belt 18, the pressure roller 19 that can be pressed against the heating belt 18 and rotated, and the heat source 33 that heats the heating belt 18. The nip region N where the heating belt 18 and the pressure roller 19 are in pressure contact with each other, and is fixed to the apparatus main body inside the heating belt 18, is pressed by the pressure roller 19, and the heating belt 18 is predetermined in the nip region N. And a holding member 40 having a guide surface 44a for guiding the movement along the path. The fixing device 5 melts and fixes the unfixed toner image on the recording material 9 by conveying the recording material 9 (paper) while being nipped in the nip region N. The guide surface 44a is formed so as to incline toward the pressure roller 19 side toward the downstream side in the sheet conveyance direction at a portion located in the nip region N.

  According to this configuration, when the pressure roller 19 rotates, in the nip region N, the heating belt 18 is guided by the guide surface 44a and moves so as to incline toward the pressure roller 19 toward the downstream side in the paper transport direction. The recording material 9 is conveyed along the same path as the heating belt 18. As a result, the unfixed toner image is melted and fixed on the recording material 9 in the nip region N, and at the nip portion N2 (the downstream end in the sheet conveyance direction of the nip region N), the front end portion of the recording material 9 is the pressure roller 19. The recording material 9 is separated from the surface of the heating belt 18. Therefore, the recording material can be reliably separated from the heating belt 18 with a simple configuration without using a separation claw, and there is no possibility that the recording material is wound around the heating belt 18.

  Further, according to the first embodiment, the nip pressure in the nip region N increases toward the downstream side in the paper conveyance direction, so that when the recording material 9 passes through the nip region N on the downstream side in the paper conveyance direction. The melted toner image is glossy and a good image can be obtained.

  Further, according to the first embodiment, the heat source 33 is provided inside the heating belt 18, and the holding member 40 includes the guide plate 44 that forms the guide surface 44 a and the holding main body portion fixed to the fixing device 5 main body. 45, and a heat insulating portion 46 disposed between the guide plate 44 and the holding main body portion 45. As a result, the path of the nip region N can be easily formed by the guide plate 44 made of a plate material or the like, and heat is transferred from the heat source 33 to the guide plate 44 through the holding main body portion 45 by the heat insulating portion 46. And the heat storage of the heat source 33 to the holding member 40 is prevented, so that the heat source 33 can heat the heating belt 18 efficiently.

(Second Embodiment)
FIG. 4 is a cross-sectional view showing a schematic configuration of a fixing device used in the image forming apparatus according to the second embodiment of the present invention. The path of the nip region, which is different from the first embodiment, will be mainly described, and the description of the same part as that of the first embodiment will be omitted hereinafter.

  The holding member 240 is pressed against the pressure roller 219 via the heating belt 218 and guides the heating belt 218 to move along a predetermined path in the nip region N. It has a main body portion 245 and a heat insulating portion 246.

  The holding main body 245 has a length equal to or greater than that of the heating belt 218 in the width direction of the recording material 9 (paper surface direction in FIG. 4), and is fixed to the fixing device 5 main body. The holding main body 245 has an inverted T-shaped cross section, is disposed between the pair of heat sources 233, and has a holding surface 245a extending in the paper conveyance direction below the holding main body 245. The holding surface 245a is formed as an arc surface inclined toward the pressure roller 219 as it goes downstream in the sheet conveyance direction. The radius of curvature R2 of the arc surface is set larger than the radius R1 of the outer periphery of the pressure roller 219 (the outer diameter not in contact with the heating belt 218).

  The heat insulating part 246 blocks the heat transmitted from the heat source 233 to the holding part main body 245 from being further transmitted to the guide plate 244 and suppresses the heat from the heat source 233 from being accumulated in the holding member 240. The heat insulating portion 246 is made of an alumina-silica felt, is formed in a rectangular flat plate shape that extends in the width direction of the recording material 9 and the paper conveyance direction, and is attached to the holding surface 245a.

  The guide plate 244 is made of a heat-resistant plate material such as stainless steel having a small friction coefficient. The guide plate 244 has a flat surface portion having a guide surface 244a and facing the heat insulating portion 246 on the opposite side of the guide surface 244a, and bent portions 244b and 244c formed at both ends of the flat surface portion in the paper transport direction. . The bent portions 244b and 244c are bent toward the holding main body portion 245 side. Similar to the holding surface 245a, the guide surface 244a is formed in an arc shape having a radius of curvature R2 that inclines toward the pressure roller 219 toward the downstream side in the paper conveyance direction. The guide plate 244 is attached by being attached to the heat insulating portion 246. In place of the configuration of the holding member 240 in which the guide plate 244 is separately provided on the holding main body 245, the holding member 240 is configured only by the holding main body, and the guide surface having the above-described shape is formed on the holding main body. You may do it.

  The guide surface 244a faces the heating belt 218 and is pressed by the pressure roller 219, whereby the nip region N is deformed following the shape of the guide surface 244a, and the guide surface 244a is heated in the nip region N. 218 movement paths are formed. Further, the guide surface 244a forms a moving path of the heating belt 218 in the extended region M extending from the nip region N to the downstream side in the paper transport direction. When the pressure roller 219 rotates, the heating belt 218 is guided by the guide surface 244a and moves along the path between the nip region N and the extension region M.

  The moving path of the heating belt 218 will be described in detail with reference to FIG. FIG. 5 is a diagram showing a nip region N and an extended region M formed by the guide surface 244a, and the recording material is conveyed from the right side of FIG.

  N21, N20, and N22 in FIG. 5 indicate the inlet, center, and outlet of the nip region, respectively, and the recording material is conveyed in the order of the nip portions N21, N20, and N22. Further, an extension region M is shown between N22 and M23 in FIG. 5. When the recording material passes through the nip portion N22, the recording material is conveyed in close contact with the heating belt 218 between the nip portion N22 and the extension portion M23. Since the guide surface 244a is disposed to be inclined in an arc shape toward the pressure roller 219 toward the downstream side in the sheet conveyance direction, the nip portion N21 is located at a position L21 above the rotation center O of the pressure roller 219. As with the nip portion N21, the nip portion N20 is formed at the position from the rotation center O to L20, the nip portion N22 is formed at the position from the rotation center O to L22, and the extension portion M23 is from the rotation center O to L23. Formed in position. The nip portion N22 is positioned below the nip portion L20 (on the rotation center side of the pressure roller 219), and the extension portion M23 is positioned below the nip portion L22 (on the rotation center side of the pressure roller 219). .

  Accordingly, the recording material onto which the toner has been transferred enters the nip portion N21 and is nipped and conveyed in the nip region N, whereby the unfixed toner image is pressurized and melted on the recording material. The pressure applied to the nip region N by the pressure roller 219 increases as the recording material is conveyed to the nip portions N21, N20, and N22, and the recording material exerts a large nip pressure near the exit (nip portion N22) of the nip region N. As a result, the melted toner image on the recording material is glossy. Further, the recording material on which the toner image is fixed is conveyed in close contact with the heating belt 218 between the nip portion N22 and the extension portion M23, and the leading end portion of the recording material is in a direction close to the pressure roller 219 by the extension portion M23. The recording material is separated from the surface of the heating belt 218 in an arc shape following the path of the extended region M. The recording material is also heated in the extended region M, and the fixing property is further improved.

  In the second embodiment, the guide surface 244a of the holding member 240 is configured to form the path of the nip area N and the path of the extension area M in an arc shape. However, the present invention is not limited to this, and the guide is provided. The surface 244a may be configured to form only the path of the nip region N in an arc shape.

  In the second embodiment, the heat source 233 is composed of a heater lamp disposed inside the heating belt 218. However, the present invention is not limited to this, and the heat source 233 is induced by magnetic flux generated from the excitation coil. An electromagnetic induction heating type heat source to be heated may be used, or an electromagnetic induction heating type heat source may be disposed outside the heating belt.

  According to the second embodiment, the fixing device 5 includes an endless heating belt 218 that can rotate, a pressure roller 219 that can press and rotate against the heating belt 218, and a heat source 233 that heats the heating belt 218. The nip region N where the heating belt 218 and the pressure roller 219 are in pressure contact with each other is fixed to the apparatus main body inside the heating belt 218 and is pressed by the pressure roller 219, and the heating belt 218 is predetermined in the nip region N. And a holding member 240 having a guide surface 244a for guiding the movement along the path. The fixing device 5 melts and fixes the unfixed toner image on the recording material 9 by conveying the recording material 9 (paper) while being nipped in the nip region N. The guide surface 244a is formed in an arc shape that inclines toward the pressure roller 219 toward the downstream side in the sheet conveyance direction at a portion located in the nip region N.

  According to this configuration, when the pressure roller 219 rotates, in the nip region N, the heating belt 218 is guided by the guide surface 244a and is inclined so as to incline toward the pressure roller 219 toward the downstream side in the paper transport direction. The recording material 9 is conveyed in the same path as the heating belt 218. As a result, the unfixed toner image is melted and fixed on the recording material 9 in the nip region N, and the recording material 9 is conveyed along the path of the arc-shaped nip region N, and the downstream end of the nip region N in the sheet conveying direction. Thus, the leading end of the recording material 9 faces the direction close to the pressure roller 219, and the recording material 9 is separated from the surface of the heating belt 218 in an arc shape following the path of the nip region N. Therefore, the recording material can be reliably separated from the heating belt 218 with a simple configuration without using a separation claw, and there is no possibility that the recording material is wound around the heating belt 218.

  Further, according to the second embodiment, the guide surface 244a has the portion located in the extension region M extending from the nip region N to the downstream side in the paper conveyance direction, and the portion located in the extension region M in the paper conveyance direction. It is formed on the pressure roller 219 side so as to be further inclined from the nip region N as it goes downstream. Thus, after passing through the nip region N, the recording material 9 is conveyed while being in contact with the surface of the heating belt 218, so that the recording material 9 is heated for a longer time and the fixability is further improved. Further, the front end portion of the recording material 9 faces the direction close to the pressure roller 219 side at the downstream end (extension portion M23) in the paper conveyance direction of the extension region M, so that the paper can be reliably separated from the surface of the heating belt 218. .

  INDUSTRIAL APPLICABILITY The present invention can be used for a fixing device used in an image forming apparatus such as a copying machine, a printer, a facsimile, and a composite machine using the electrophotographic method, and an image forming apparatus including the fixing device. It can be used for a fixing device that separates the recording material conveyed from the heating member from the heating member and an image forming apparatus including the fixing device.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 5 Fixing device 18, 218 Heating belt 19, 219 Pressure roller 33, 233 Heat source 40, 240 Holding member 44, 244 Guide plate 44a, 244a Guide surface 44b, 44c, 244b, 244c Bending part 45, 245 Holding Main body 46, 246 Thermal insulation M Extension area N Nip area

Claims (4)

A rotatable endless heating belt;
A pressure roller that is in pressure contact with the heating belt and is rotatable;
A heat source for heating the heating belt;
A holding member that is fixed to the apparatus main body inside the heating belt and has a guide surface that guides the movement of the heating belt and presses a part of the heating belt against the pressure roller;
The guide surface is an arcuate surface that abuts the heating belt, and is disposed so as to face the pressure roller via the heating belt, and toward the pressure roller side toward the downstream side in the paper conveyance direction. Tilt,
The fixing device, wherein the heating belt and the pressure roller are separated from each other at an end portion of the guide surface on the downstream side in the sheet conveyance direction.   The fixing device according to claim 1, wherein a radius of curvature of the guide surface is larger than a radius of curvature of an outer periphery of the pressure roller.   The heat source is provided inside the heating belt, and the holding member includes a guide plate that forms the guide surface, a holding main body portion fixed to the apparatus main body, and between the guide plate and the holding main body portion. The fixing device according to claim 1, further comprising a heat insulating portion disposed.   An image forming apparatus on which the fixing device according to claim 1 is mounted.