JP6287425B2 - Fixing device, image forming apparatus - Google Patents

Description

  The present invention relates to a fixing device and an image forming apparatus.

  Patent Document 1 includes a pressing member that presses the fixing belt against the heating roll from the back surface of the fixing belt, and the nip pressure at both ends in the axial direction of the fixing nip region is set higher than the nip pressure at the central portion in the axial direction. The distance between the back surface of the fixing belt and the pressing surface of the pressing member on the upstream side of the fixing nip region is such that the distortion in the conveying direction of the fixing member upstream of the fixing nip region is constant in the axial direction. A fixing device is disclosed in which the shape of the pressing member is set so as to gradually increase from the axial center to both ends.

  In the fixing device disclosed in Patent Document 2, the fixing belt is constrained by the cap member so that the cross-sectional shape of the end portion is circular, is sandwiched between the pressure roll and the pressing pad, and is transmitted from the cap member. It is driven around by the circumferential driving force. The cross-sectional shape of the pressing pad is such that the fixing belt is bent with a large curvature in the sheet passing area. Furthermore, the cross-sectional shape of the pressing pad gradually changes from the sheet passing area toward both ends into a shape having substantially the same curvature as the contact surface between the cap member and the fixing belt.

JP 2009-222810 A JP 2005-221719 A

  An object of the present invention is to suppress wrinkling of a recording medium on which an image is fixed.

According to the first aspect of the present invention, an annular heating belt that heats the recording medium, and pressurizing the recording medium between the heating belt, pressurizing and rotating the heating belt to convey the recording medium. A member and a nip surface that is disposed on the inner peripheral side of the heating belt and sandwiches the heating belt with the pressure member, and the recording medium passes between the heating belt and the pressure member In the region, the nip surface is inclined so as to project outward in the radial direction of the heating belt as it goes downstream in the rotation direction of the heating belt, and the position of the apex on the radially outer side is the pressure member and the heating belt. And a nip member projecting outward in the radial direction from the axial center of the heating belt toward one end and the other end in the passage region.

  According to a second aspect of the present invention, the position of the apex is shifted inward in the radial direction from the center in the axial direction toward the one end and the other end in a non-nip state between the pressure member and the heating belt. Go.

  In the invention of claim 3, the position of the apex is shifted to the upstream side in the rotational direction from the center in the axial direction toward the one end and the other end in the nip state between the pressure member and the heating belt. Go.

  According to a fourth aspect of the present invention, the position of the apex is a non-passing region where the recording medium does not pass between the heating belt and the pressure member in a nip state between the pressure member and the heating belt. It shifts inward in the radial direction toward one end and the other end in the axial direction.

  The invention according to claim 5 is the passage region, and at least in the nip region between the pressure member and the heating belt, the upstream side in the rotational direction is formed flat from the position of the apex of the nip surface. .

  According to a sixth aspect of the present invention, in any one of the first to fifth aspects, the image forming unit that forms an image on a recording medium, and the image formed on the recording medium by the image forming unit are fixed to the recording medium. And the fixing device described.

  According to the configuration of the first aspect of the present invention, the wrinkles of the recording medium on which the image is fixed can be suppressed as compared with the case where the nip member in the present configuration is not provided.

  According to the configuration of the second aspect of the present invention, it is possible to reduce the variation in fixability in the axial direction as compared with the case where the position of the apex does not change from the center in the axial direction toward each of the one end and the other end.

  According to the structure of Claim 3 of this invention, compared with the case where the position of a vertex does not change toward each of an end and an other end from an axial direction center, the axial direction both ends of a heating belt can be hold | maintained at a cylindrical shape.

  According to the configuration of the fourth aspect of the present invention, both ends in the axial direction of the heating belt can be held in a cylindrical shape as compared with the case where the position of the apex does not change from the center in the axial direction toward each of the one end and the other end.

  According to the configuration of claim 5 of the present invention, in the nip region in the passage region, wrinkles generated in the envelope when the envelope is passed are suppressed as compared with the case where the upstream side in the rotational direction from the apex is not formed flat. it can.

  According to the configuration of the sixth aspect of the present invention, the wrinkles of the recording medium on which the image is fixed can be suppressed as compared with the case where the fixing device in the configuration is not provided.

1 is a schematic diagram illustrating a configuration of an image forming apparatus according to an exemplary embodiment. FIG. 2 is a side sectional view showing a configuration of a fixing device according to the present embodiment. It is explanatory drawing of the support structure and drive system of a heating belt and a pressure roll. It is a schematic diagram which shows typically the bending of the pad in the nip state of a heating belt and a pressure roll. It is a graph which shows the position of the vertex of a contact pad in the non-nip state of a heating belt and a pressure roll. It is the figure which showed the cross-sectional shape of the pad. It is a graph which shows the Y direction position of the vertex of the contact pad in the nip state of a heating belt and a pressure roll. It is a graph which shows the position of the vertex of the pad in the nip state of a heating belt and a pressure roll.

  Below, an example of an embodiment concerning the present invention is described based on a drawing.

(Configuration of image forming apparatus 10)
First, the configuration of the image forming apparatus 10 will be described. FIG. 1 is a schematic diagram illustrating a configuration of the image forming apparatus 10.

  As shown in FIG. 1, the image forming apparatus 10 includes an image forming apparatus main body 11 (housing) in which each component is housed. Inside the image forming apparatus main body 11, a plurality of storage units 12 that store recording media P such as paper, an image forming unit 14 that forms images on the recording media P, and images formed on the recording media P are stored. And a fixing device 60 for fixing the recording medium P. In the image forming apparatus main body 11, a transport unit 16 that transports the recording medium P from the storage unit 12 to the image forming unit 14 and a control unit 20 that controls the operation of each unit of the image forming apparatus 10 are further provided. It has been. Further, a discharge unit 18 for discharging the recording medium P on which the image is fixed by the fixing device 60 is provided on the upper portion of the image forming apparatus main body 11.

  The image forming unit 14 includes image forming units 22Y, 22M, 22C, and 22K (hereinafter referred to as 22Y to 22K) that form toner images of colors of yellow (Y), magenta (M), cyan (C), and black (K). And an intermediate transfer belt 24 to which the toner images formed by the image forming units 22Y to 22K are transferred. Further, the image forming unit 14 transfers the toner images formed by the image forming units 22 </ b> Y to 22 </ b> K to the intermediate transfer belt 24 and transferred to the intermediate transfer belt 24 by the first transfer roll 26. And a second transfer roll 28 for transferring the toner image from the intermediate transfer belt 24 to the recording medium P. The image forming unit 14 is not limited to the above-described configuration, and may be another configuration as long as it forms an image on the recording medium P.

  The image forming units 22 </ b> Y to 22 </ b> K are disposed inside the image forming apparatus main body 11 while being inclined with respect to the horizontal direction. Each of the image forming units 22Y to 22K has a photoreceptor 32 that rotates in one direction (for example, the counterclockwise direction in FIG. 1). Since the image forming units 22Y to 22K are configured in the same manner, the reference numerals of the respective portions in the image forming units 22M, 22C, and 22K are omitted in FIG.

  Around each photoconductor 32, a charging roll 23 as a charging device for charging the photoconductor 32 and the photoconductor 32 charged by the charge roll 23 are exposed in order from the upstream side in the rotation direction of the photoconductor 32. An exposure device 36 that forms an electrostatic latent image on 32 and a developing device 38 that develops the electrostatic latent image formed on the photoreceptor 32 by the exposure device 36 to form a toner image are provided.

  The exposure device 36 is configured to form an electrostatic latent image based on the image signal sent from the control unit 20. Examples of the image signal sent from the control unit 20 include an image signal acquired by the control unit 20 from an external device.

  The developing device 38 includes a developer supply body 38A that supplies the developer to the photoconductor 32, and a plurality of transport members 38B that transport the developer applied to the developer supply body 38A while stirring.

  The intermediate transfer belt 24 is formed in an annular shape and is disposed on the upper side of the image forming units 22Y to 22K. On the inner peripheral side of the intermediate transfer belt 24, winding rolls 42, 43, and 44 around which the intermediate transfer belt 24 is wound are provided. The intermediate transfer belt 24 circulates (rotates) in one direction (for example, the clockwise direction in FIG. 1) while being in contact with the photoreceptor 32, for example, when the winding roll 44 is rotationally driven. . The winding roll 42 is an opposing roll that faces the second transfer roll 28.

  The first transfer roll 26 faces the photoconductor 32 with the intermediate transfer belt 24 interposed therebetween. A space between the first transfer roll 26 and the photoconductor 32 is a first transfer position where the toner image formed on the photoconductor 32 is transferred to the intermediate transfer belt 24.

  The second transfer roll 28 faces the winding roll 42 with the intermediate transfer belt 24 interposed therebetween. A space between the second transfer roll 28 and the winding roll 42 is a second transfer position where the toner image transferred to the intermediate transfer belt 24 is transferred to the recording medium P.

  The transport unit 16 is disposed along the transport path 48 and is transported along a transport roll 48 for transporting the recording medium P stored in the storage section 12, a transport path 48 for transporting the recording medium P transported to the transport roll 46. And a plurality of transport rolls 50 for transporting the recording medium P fed by the roll 46 to the second transfer position.

  A fixing device 60 that fixes the toner image transferred to the recording medium P by the second transfer roll 28 to the recording medium P is provided on the downstream side in the transport direction from the second transfer position. On the downstream side of the fixing device 60 in the transport direction, a plurality of transport rolls 52 are provided for transporting the recording medium P on which the toner image is fixed toward the discharge unit 18. A specific configuration of the fixing device 60 will be described later.

  Next, an image forming operation for forming an image on the recording medium P in the image forming apparatus 10 according to the present embodiment will be described.

  In the image forming apparatus 10 according to the present embodiment, the recording medium P sent out from the storage unit 12 by the sending roll 46 is sent to the second transfer position by the plurality of conveying rolls 50.

  On the other hand, in the image forming units 22 </ b> Y to 22 </ b> K, the photosensitive member 32 charged by the charging roll 23 is exposed by the exposure device 36 to form an electrostatic latent image on the photosensitive member 32. The electrostatic latent image is developed by the developing device 38 to form a toner image on the photoreceptor 32. The color toner images formed by the image forming units 22Y to 22K are superimposed on the intermediate transfer belt 24 at the first transfer position to form a color image. Then, the color image formed on the intermediate transfer belt 24 is transferred to the recording medium P at the second transfer position.

  The recording medium P to which the toner image has been transferred is conveyed to the fixing device 60, and the transferred toner image is fixed by the fixing device 60. The recording medium P on which the toner image is fixed is discharged to the discharge unit 18 by the transport roll 52. As described above, a series of image forming operations are performed.

(Configuration of Fixing Device 60)
Next, the configuration of the fixing device 60 according to the present embodiment will be described. FIG. 2 is a cross-sectional side view showing the configuration of the fixing device 60 according to the present embodiment.

  As shown in FIG. 2, the fixing device 60 includes a heating belt 64, a pressure roll 66 (an example of a pressure member), and a heating device 70 that heats the heating belt 64 by electromagnetic induction. In the fixing device 60, the recording medium P introduced between the heating belt 64 and the pressure roll 66 is pressed by the pressure roll 66 and heated by the heating belt 64, thereby fixing the toner image on the recording medium P. Let

  The heating device 70 includes an electromagnetic induction coil 72 that generates a magnetic field, a holding member 74 that holds the electromagnetic induction coil 72, and a magnetic body 76. The holding member 74 is disposed on the side opposite to the pressure roll 66 side with respect to the heating belt 64 (the right side in FIG. 2). The holding member 74 is formed in a substantially arc shape along the outer peripheral surface of the heating belt 64. The holding member 74 has a shaft portion 74 </ b> A protruding toward the side opposite to the heating belt 64 (the right side in FIG. 2).

  The electromagnetic induction coil 72 is wound around the shaft portion 74A a plurality of times. The electromagnetic induction coil 72 is held by the holding member 74 while being wound around the shaft portion 74A. One end in the axial direction of the electromagnetic induction coil 72 held by the holding member 74 is opposed to the outer peripheral surface of the heating belt 64 with the holding member 74 interposed therebetween.

  The magnetic body 76 is disposed on the opposite side of the holding member 74 from the heating belt 64 (on the right side in FIG. 2). The magnetic body 76 is formed in a substantially arc shape along the outer peripheral surface of the holding member 74.

  Further, the heating device 70 includes a heat generating plate 77 that generates heat by electromagnetic induction of the electromagnetic induction coil 72, and a contact plate 78 that contacts the heat generating plate 77. The heat generating plate 77 and the contact plate 78 are disposed on the inner periphery of the heating belt 64.

  The heat generating plate 77 faces the electromagnetic induction coil 72 with the heating belt 64 interposed therebetween, and has a length along the rotation axis direction of the heating belt 64. The heat generating plate 77 is curved in an arc along the inner peripheral surface of the heating belt 64, and is in contact with the inner peripheral surface of the heating belt 64 along the circumferential direction of the heating belt 64.

  The heat generating plate 77 generates heat by electromagnetic induction caused by a magnetic field generated when a current flows through the electromagnetic induction coil 72. In the present embodiment, the heating belt 64 itself also generates heat due to the electromagnetic induction.

  Similar to the heat generating plate 77, the contact plate 78 has a length along the rotation axis direction of the heating belt 64. The contact plate 78 is in contact with the inner peripheral surface of the heat generating plate 77. Thereby, the contact plate 78 moves heat in the length direction of the heat generating plate 77 (the axial direction of the heating belt 64), and suppresses variation in temperature distribution in the length direction of the heat generating plate 77. The contact plate 78 has a function of increasing the heat capacity of the contact plate 78 and the heat generating plate 77 as a whole by contacting and overlapping the heat generating plate 77.

  Further, the fixing device 60 includes a pad 90 (an example of a nip member) that sandwiches the heating belt 64 with the pressure roll 66, and a support member 80 that supports the pad 90, the heat generating plate 77, and the contact plate 78. I have. The pad 90 and the support member 80 are disposed on the inner peripheral side of the heating belt 64. The specific configuration of the pad 90 will be described later.

  As shown in FIG. 3, the support member 80 has a length along the axial direction of the heating belt 64. The support member 80 is fixed to the casing 62 of the fixing device 60 at both longitudinal ends 80A thereof. The support member 80 is provided with belt support portions 81 and 82 that support both ends of the heating belt 64 in the axial direction.

  The belt support portion 81 is formed in a disc shape, and is inserted into one end portion in the longitudinal direction of the heating belt 64 (left end portion in FIG. 3). The heating belt 64 slides in the circumferential direction with respect to the belt support portion 81. That is, the heating belt 64 rotates with respect to the belt support portion 81.

  On the left side of FIG. 3 with respect to the belt support portion 81, an overhang portion 83 (flange portion) that protrudes radially outward from the belt support portion 81 is provided. The overhang portion 83 is in contact with the side end of the heating belt 64 and restricts the movement of the heating belt 64 to the side (left direction in FIG. 3).

  Note that one end portion in the longitudinal direction of the support member 80 (left end portion in FIG. 3) passes through the belt support portion 81 and the overhang portion 83 and is fixed to the casing 62 of the fixing device 60. The belt support portion 81 and the overhang portion 83 are fixed with respect to the support member 80.

  The belt support portion 82 is also formed in a disk shape like the belt support portion 81, and is inserted into the other longitudinal end portion (the right end portion in FIG. 3) of the heating belt 64. The belt support portion 82 is fixed to the inner peripheral surface of the heating belt 64 by adhesion or the like.

  On the right side of FIG. 3 with respect to the belt support portion 82, a gear portion 84 is provided that protrudes radially outward from the belt support portion 82. A driving force is transmitted to the gear portion 84 from a motor 86 (driving portion).

  Note that the other end portion in the longitudinal direction of the support member 80 (the right end portion in FIG. 3) passes through the belt support portion 82 and the gear portion 84 and is fixed to the casing 62 of the fixing device 60. The belt support portion 82 and the gear portion 84 are rotatably supported by the support member 80.

Both ends of the pressure roll 66 are rotatably supported by the moving mechanism 88. The moving mechanism 88 is fixed to the casing 62 of the fixing device 60. The moving mechanism 88 moves the pressure roll 66 in a direction in which the pressure roll 66 comes into contact with and separates from the heating belt 64 (arrow EF direction), presses the pressure roll 66 against the heating belt 64, and heats the heating roll 64. Separate from the belt 64.
By pressing the pressure roll 66 against the heating belt 64, the heating belt 64 and the pressure roll 66 are in a nip state. Further, by separating the pressure roll 66 from the heating belt 64, the heating belt 64 and the pressure roll 66 are in a non-nip state. The gear 66B is also fixed to the rotary shaft 66A of the pressure roll 66, and the driving force from the motor 86 is transmitted to the gear 66B.

  A driving force from a motor 86 is transmitted to a gear portion 84 fixed to the heating belt 64 via a driving force transmission mechanism such as a gear train (not shown) and further via a one-way clutch 87. The On the other hand, the driving force from the motor 86 is also transmitted to the gear 66B fixed to the rotating shaft 66A of the pressure roll 66, but is transmitted without passing through the one-way clutch 87.

  The gear ratio and the like are adjusted so that the surface speed of the pressure roll 66 is slightly higher than the moving speed of the heating belt 64. For this reason, when the pressure roll 66 rotates in contact with the heating belt 64, the one-way clutch 87 is actuated, and the transmission of the driving force from the motor 86 to the gear portion 84 of the heating belt 64 is disconnected. Is driven to rotate by the rotation of the pressure roll 66. On the other hand, when the pressure roll 66 is separated from the heating belt 64, the heating belt 64 rotates with the driving force transmitted via the one-way clutch 87.

(Pad 90)
As shown in FIGS. 4A and 4B, the pad 90 has a length along the axial direction of the heating belt 64 (A direction in the figure). 4A and 4B schematically show the support member 80, the pad 90, and the pressure roll 66, and the heating belt 64 is not shown.

  As shown in FIG. 2, the pad 90 has a nip surface 90 </ b> A that forms a nip portion N (nip region) by sandwiching the heating belt 64 with the pressure roll 66. That is, the nip surface 90 </ b> A is a facing surface that faces the pressure roll 66 through the heating belt 64. Further, the nip surface 90 </ b> A only needs to sandwich the heating belt 64 with the pressure roll 66 at the center side in the axial direction of the heating belt 64, and pressurization is performed at the end in the axial direction (non-passage region described later). The heating belt 64 may not be sandwiched between the rolls 66.

  As shown in FIG. 4A, the nip surface 90 </ b> A protrudes toward the pressure roll 66 toward the center in the longitudinal direction of the pad 90 in a non-nip state between the heating belt 64 and the pressure roll 66. It is formed into a shape. That is, the position of the apex B on the nip surface 90A of the pad 90 (see FIG. 5A) is as shown in FIG. 5B in the non-nip state between the heating belt 64 and the pressure roll 66. The heating belt 64 shifts inward in the radial direction from the center in the longitudinal direction of 90 toward one end and the other end. In addition, as shown in FIG. 5B, it is desirable that the position of the apex B gradually shifts inward in the radial direction of the heating belt 64.

  The apex B on the nip surface 90A of the pad 90 is a point on the nip surface 90A that is the outermost side in the radial direction of the heating belt 64 (most point on the pressure roll 66 side). The more the apex B is located on the lower side in FIG. 5A, the more radially outside the heating belt 64, and the more on the upper side in FIG. Will be located.

  FIG. 5B is a plot of the position of the apex B from the center in the longitudinal direction to one end of the nip surface 90A of the pad 90. That is, the ridge line on the nip surface 90A constituted by connecting the apexes B is shown. The nip surface 90A of the pad 90 has the same (symmetric) shape from the center in the longitudinal direction to the other end. Further, the “passing area” shown in FIG. 5B is a passing area when the maximum width recording medium P that can be used for image formation in the image forming apparatus 10 (see FIG. 1) passes through the nip portion N. is there. The “non-passing area” is an area that is out of the passing area and does not pass through the recording medium P.

  On the other hand, FIG. 6 shows the shape of the nip surface 90 </ b> A in the nip state between the heating belt 64 and the pressure roll 66. Specifically, FIG. 6A is a plan view of the pad 90, and FIGS. 6B, 6C, and 6D are diagrams showing cross-sectional shapes at respective points in the longitudinal direction of the pad 90. FIG.

  As shown in FIGS. 6C and 6D, the nip surface 90A is radially outward of the heating belt 64 (see FIG. 6) as the nip surface 90A goes downstream in the transport direction (left side in the drawing). It is inclined so as to project to the lower side. Therefore, in the passage region, the nip surface 90A has a vertex B (a point on the outermost radial direction) on the downstream side in the transport direction (the downstream side in the rotation direction of the heating belt 64 (the exit side of the nip portion)). In the passing region, the surface upstream of the apex B in the transport direction (upstream in the rotation direction of the heating belt 64 (inlet side of the nip portion)) is a flat flat surface (plane). That is, in the passage region, the upstream side in the transport direction with respect to the apex B on the nip surface 90A is linearly formed in a side view.

  In the nip state between the heating belt 64 and the pressure roll 66, the position of the apex B on the radially outer side of the nip surface 90A is the heating belt in the passing region as shown in FIGS. 6C and 6D and FIG. From the axial center of 64, the same or radially outwardly protrudes (shifts) toward one end and the other end. Note that the position of the apex B is set by the outer peripheral shape of the pressure roll 66, the thickness of the pad 90 (the vertical dimension in FIGS. 6C and 6D), and the like.

  Further, the position of the radially outer apex B on the nip surface 90A is from the axial center of the heating belt 64 in the non-passing region in the nip state between the heating belt 64 and the pressure roll 66 as shown in FIG. It is shifted inward in the radial direction toward one end and the other end.

  The position of the apex B on the radially outer side of the nip surface 90A is, in the nip state between the heating belt 64 and the pressure roll 66, as shown in FIG. Toward the upstream side in the transport direction (upstream in the rotation direction of the heating belt 64 (on the inlet side of the nip portion)). As the apex B is located on the right side in FIG. 8A, it is located on the upstream side in the transport direction (upstream in the rotation direction of the heating belt 64 (inlet side of the nip portion)), and in FIG. The closer to the left, the more downstream in the transport direction (downstream in the rotation direction of the heating belt 64 (exit side of the nip portion)).

(Operation of this embodiment)
Next, the operation of this embodiment will be described.

  In the configuration of the present embodiment, the recording medium P on which the toner image is transferred is introduced into the nip portion N of the fixing device 60. The recording medium P introduced into the nip portion N is conveyed while being sandwiched between the pressure roll 66 and the heating belt 64, and the toner image is applied to the recording medium P by the pressure by the pressure roll 66 and the heating by the heating belt 64. It is fixed.

  In the configuration of the present embodiment, as shown in FIGS. 6C and 6D, the nip surface 90A has a heating belt as the nip surface 90A moves toward the downstream side in the conveyance direction (left side in the drawing) in the passage region. It inclines so that it may protrude to 64 radial direction outer side (lower side in a figure). Thereby, the direction of the heating belt 64 changes in the direction away from the pressure roll 66 at the exit of the nip portion N. For this reason, the recording medium P is easily peeled off from the heating belt 64.

  In the configuration of the present embodiment, the position of the radially outer apex B on the nip surface 90 </ b> A is the heating belt in the passing region as shown in FIG. 7 in the nip state between the heating belt 64 and the pressure roll 66. From the center in the axial direction of 64, the same or radially outwardly protrudes (shifts) toward one end and the other end. For this reason, the diameter of the heating belt 64 in the nip portion N is larger at one end and the other end than the center in the axial direction, and the peripheral speed (conveying speed of the recording medium P) of the heating belt 64 is one end and the other from the center in the axial direction. Get faster at the edge. Thereby, the force by which the recording medium P is pulled outward in the width direction (the direction along the axial direction of the heating belt 64) acts, and wrinkles of the recording medium P are suppressed.

  Further, in the present embodiment, the position of the apex B of the nip surface 90A is the center of the heating belt 64 in the axial direction in the non-nip state between the heating belt 64 and the pressure roll 66, as shown in FIG. Gradually moves inward in the radial direction of the heating belt 64 toward one end and the other end.

  Here, in the present embodiment, the pad 90 is provided on the support member 80 having both longitudinal ends 80 </ b> A fixed to the casing 62 of the fixing device 60. For this reason, when the pressure roll 66 is pressed against the heating belt 64, the pressing force is transmitted to the pad 90 and the support member 80 via the heating belt 64, and as shown in FIG. Bend. Since the support member 80 is supported by the longitudinal end portions 80A, the amount of bending at that time is large at the center in the longitudinal direction of the pad 90 and is smaller at both ends in the longitudinal direction.

  Since the nip surface 90 </ b> A of the pad 90 protrudes at a portion where the deflection amount is large, the nip load variation in the longitudinal direction of the pad 90 is reduced. Thereby, the variation in the longitudinal direction of the pad 90 in the fixability (for example, fixing strength, glossiness) for fixing the toner image on the recording medium P is reduced. The fixing strength is an adhesive strength at which the toner adheres to the recording medium P.

  Furthermore, in the present embodiment, the position of the apex B gradually shifts inward in the radial direction of the heating belt 64, so even if the nip load varies in the longitudinal direction of the pad 90, the change in the nip load does not occur. The heating belt 64 becomes gentle from the axial center to one end and the other end. For this reason, variation in fixability for fixing the toner image on the recording medium P is reduced.

  Further, as shown in FIG. 8B, the position of the radially outer apex B on the nip surface 90A is the upstream side in the transport direction (of the heating belt 64) from the center in the axial direction toward one end and the other end. It shifts to the upstream side in the rotation direction (inlet side of the nip part).

  For this reason, the nip surface 90A of the pad 90 has a shape closer to a circular arc shape at one end and the other end in the axial direction than the center in the axial direction. Thereby, compared with the case where the position of the vertex B does not change from the center in the axial direction toward each of the one end and the other end, both ends in the axial direction of the heating belt 64 are held in a cylindrical shape.

  Further, in the configuration of the present embodiment, in the non-passing region, the heating belt 64 is displaced radially inward from the axial center to one end and the other end.

  For this reason, the nip surface 90A of the pad 90 has a shape closer to a circular arc shape at one end and the other end in the axial direction than the center in the axial direction. Thereby, compared with the case where the position of the vertex B does not change from the center in the axial direction toward each of the one end and the other end, both ends in the axial direction of the heating belt 64 are held in a cylindrical shape.

  Furthermore, in the configuration of the present embodiment, in the nip portion N in the passage region, the nip surface 90A is flat on the upstream side in the transport direction from the apex B (the upstream side in the rotation direction of the heating belt 64 (the inlet side of the nip portion)). It is configured. For this reason, even if an envelope or the like is passed as the recording medium P, a difference in the sheet conveyance speed between the front surface and the back surface hardly occurs, and the generation of wrinkles in the envelope is suppressed.

  The present invention is not limited to the above-described embodiment, and various modifications, changes, and improvements can be made without departing from the spirit of the present invention. For example, the modification examples described above may be appropriately combined.

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 14 Image forming part 60 Fixing apparatus 64 Heating belt 66 Pressure roll (an example of a pressure member)
90 pad (example of nip member)
90A Nip surface P Recording medium

Claims (6)

An annular heating belt for heating the recording medium;
A pressure member that presses the recording medium between the heating belt and conveys the recording medium by rotating together with the heating belt;
The nip surface is disposed on the inner peripheral side of the heating belt and sandwiches the heating belt with the pressure member, and in the passage region where the recording medium passes between the heating belt and the pressure member. The nip surface is inclined so as to protrude outward in the radial direction of the heating belt as it goes downstream in the rotation direction of the heating belt, and the position of the apex outside the radial direction is the nip between the pressure member and the heating belt. In the state, a nip member projecting outward in the radial direction from the axial center of the heating belt toward one end and the other end in the passage region,
A fixing device. The position of the apex is shifted inward in the radial direction from the center in the axial direction toward one end and the other end in a non-nip state between the pressure member and the heating belt. Fixing device. The position of the apex is shifted to the upstream side in the rotation direction from the center in the axial direction toward one end and the other end in a nip state between the pressure member and the heating belt. The fixing device described. The position of the apex is a non-passing region where the recording medium does not pass between the heating belt and the pressure member in the nip state between the pressure member and the heating belt, and is located at one end and the other end in the axial direction. The fixing device according to any one of claims 1 to 3, wherein the fixing device is displaced inward in the radial direction toward the respective sides. 5. The upstream side in the rotation direction from the position of the apex of the nip surface is flat in at least the nip region between the pressure member and the heating belt in the passage region. The fixing device according to claim 1. An image forming unit for forming an image on a recording medium;
The fixing device according to claim 1, wherein an image formed on the recording medium by the image forming unit is fixed to the recording medium.
An image forming apparatus comprising:

Images