JP2021184003A - Fixing device and image forming apparatus - Google Patents

Abstract

To provide a fixing device that can obtain satisfactory fixing performance.SOLUTION: A fixing device comprises an annular belt, a contact member, a support member, and a pressure member. The annular belt can rotate in a conveying direction for conveying a medium. The contact member is in contact with an inner peripheral surface of the annular belt. The support member extends in a direction orthogonal to the medium conveying direction, has a positive crown portion projecting toward the inner peripheral surface of the annular belt, and supports the contact member. The pressure member has a surface opposite to an outer peripheral surface of the annular belt, and can form a nip area where the medium is sandwiched between the surface and the outer peripheral surface of the annular belt. The nip area includes, in an extension direction in which the support member extends, a first end, a second end, and an intermediate part placed between the first end and the second end. A first end conveying force to convey the medium in the conveying direction at the first end and a second end conveying force to convey the medium in the conveying direction at the second end are stronger than an intermediate part conveying force to convey the medium in the conveying direction in the intermediate part.SELECTED DRAWING: Figure 9

Description

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

Some image forming devices fix an image formed on a recording medium by a thermal fixing device. For example, Patent Document 1 discloses a technique of diffusing the heat generated by a heater to a fixing belt by a heat diffusion member in a fixing device.

Japanese Unexamined Patent Publication No. 2019-128507

By the way, in the fixing device, it is expected that the heat generated by the heater is transferred to the fixing belt (annular belt) as evenly as possible, and the image formed on the recording medium is satisfactorily fixed. At that time, it is also required that the recording medium is not wrinkled.

It is desirable to provide a fixing device and an image forming device that can obtain good fixing performance.

The fixing device as one embodiment of the present invention includes an annular belt, a contact member, a support member, and a pressure member. The annular belt is rotatable. The contact member comes into contact with the inner peripheral surface of the annular belt. The support member extends in a direction orthogonal to the transport direction of the medium and has a positive crown portion protruding toward the inner peripheral surface of the annular belt to support the contact member. The pressurizing member has a surface facing the outer peripheral surface of the annular belt, and can form a nip region in which the medium is sandwiched between the surface and the outer peripheral surface of the annular belt. The nip region includes a first end portion, a second end portion, and an intermediate portion sandwiched between the first end portion and the second end portion in the extending direction of the support member. The first end transport force for transporting the medium in the transport direction at the first end and the second end transport force for transporting the medium in the transport direction at the second end are intermediate for transporting the medium in the transport direction at the intermediate portion. Stronger than the unit carrying capacity.

The image forming apparatus according to the embodiment of the present invention includes the fixing apparatus.

According to the fixing device and the image forming apparatus according to the embodiment of the present invention, the first-end transport force and the second-end transport force at the first end and the second end of the nip region are set to the middle of the nip region. Since the force is made stronger than the transport force of the intermediate portion in the portion, it is possible to apply the nip pressure with little variation over the entire nip region. Therefore, good fixing performance can be obtained.
The effect of the present invention is not limited to this, and may be any of the effects described below.

It is a schematic diagram which shows the whole structure example of the image forming apparatus which concerns on one Embodiment. It is a perspective view which shows one structural example of the main part of the fixing apparatus shown in FIG. It is a front view which shows the structural example of the main part of the fixing apparatus shown in FIG. It is sectional drawing which shows one structural example of the main part of the fixing apparatus shown in FIG. FIG. 3 is an enlarged cross-sectional view showing a part of a configuration example of a main part of the fixing device shown in FIG. 4 in an enlarged manner. It is an exploded perspective view which shows the annular belt unit shown in FIG. It is a perspective view which shows the appearance of the stay shown in FIG. FIG. 5 is a cross-sectional view showing a cross section of the stay and the holding member shown in FIG. 5 orthogonal to the longitudinal direction. It is a schematic diagram showing the appearance of the vicinity of the nip region N in the fixing device shown in FIG. 1 as viewed from the downstream in the transport direction. It is a schematic cross-sectional view for demonstrating the outline of the heat transfer member shown in FIG. It is a schematic cross-sectional view for demonstrating the outline of the annular belt shown in FIG. It is explanatory drawing for demonstrating the outline of the pressure roller shown in FIG. It is the schematic sectional drawing for demonstrating the outline of the pressure roller shown in FIG. It is explanatory drawing for demonstrating the deformation rate of the recording medium passing through the nip area shown in FIG. It is a schematic explanatory drawing for demonstrating the measuring method of the transport force in an experimental example. It is a characteristic diagram which shows the relationship between the medium deformation rate and the feed force end center difference rate in an experimental example.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The following description is a specific example of the present invention, and the present invention is not limited to the following aspects. Further, the present invention is not limited to the arrangement, dimensions, dimensional ratio, etc. of each component shown in each figure. The explanation will be given in the following order.
1. 1. Embodiment 2. Experimental example 3. Modification example

<1. Embodiment>
[Rough configuration of image forming apparatus 1]
FIG. 1 is a schematic diagram showing an overall configuration example of an image forming apparatus 1 provided with a fixing apparatus according to an embodiment of the present invention. The image forming apparatus 1 is, for example, a printer using an electrophotographic method, and forms a black-and-white image or a color image on a recording medium PM such as paper by performing an image forming operation using a developer such as toner. It is composed. In the present specification, the position close to the paper feed tray 3 or the direction toward the paper feed tray 3 when viewed from an arbitrary position on the transport path on which the recording medium PM is conveyed is referred to as upstream. Further, when viewed from an arbitrary position on the transport path, a position close to the stacker 9 from which the recording medium PM is discharged and loaded, or a direction toward the stacker 9 is referred to as downstream. The direction from the upstream to the downstream is called the transport direction F.

The image forming apparatus 1 is, for example, inside a main body frame 2 which is a housing of the apparatus main body, for example, a paper feed tray 3, a hopping roller 4, a resist roller pair 5, an image forming unit 10, a fixing device 30, and discharge. It has a roller vs. 6 and.

The paper feed tray 3 is an accommodating unit for accommodating the recording medium PM. A plurality of recording media PMs are loaded on the paper feed tray 3. A hopping roller 4 is provided downstream of the paper feed tray 3.

The hopping roller 4 is a rotating member that presses against the surface of the recording medium PM and feeds the recording medium PM downstream along a guide 7 which is a transport path. The hopping roller 4 is rotated by a power transmitted from a hopping motor (not shown) with the central axis of the hopping roller 4 as a rotation axis. A resist roller pair 5 is provided downstream of the hopping roller 4.

The resist roller pair 5 is configured to convey the recording medium PM toward the image forming unit 10. The resist roller pair 5 is adapted to correct the skew of the recording medium PM by abutting the tip portion of the recording medium PM when the recording medium PM is conveyed. An image forming portion 10 is provided downstream of the resist roller pair 5.

(Image forming unit 10)
The image forming unit 10 is a mechanism for forming an image (toner image) and transferring the image to the recording medium PM. The image forming unit 10 has four developing units 11 (development units 11K, 11Y, 11M, 11C), four exposure units 17 (exposure units 17K, 17Y, 17M, 17C), and a transfer belt unit 18. ing.

The four developing units 11 (development units 11K, 11Y, 11M, 11C) are mechanisms for forming an image using toner, which is a developing agent, based on print data transmitted from a host device such as a personal computer. The four developing units 11 are detachably configured from the image forming apparatus 1. Specifically, the developing unit 11K forms a black image, the developing unit 11Y forms a yellow image, the developing unit 11M forms a magenta color image, and the developing unit 11C is a cyan color. It is designed to form an image. In this example, the developing units 11K, 11Y, 11M, 11C are arranged in this order in the transport direction F of the recording medium PM. The developing units 11K, 11Y, 11M, and 11C have the same configuration except that an image is formed by using toners of different colors as described above. As shown in FIG. 1, each developing unit 11 has, for example, a photosensitive drum 12, a charging roller 13, a developing roller 14, a cleaning blade 15, and a toner accommodating portion 16.

The photosensitive drum 12 is a columnar member that supports an electrostatic latent image on a surface (surface layer portion), and is configured by using a photosensitive member (for example, an organic photosensitive member). The photosensitive drum 12 rotates clockwise in this example by the power transmitted from the photoconductor motor (not shown). The photosensitive drum 12 is charged by the charging roller 13 and exposed by the corresponding exposure unit 17. As a result, an electrostatic latent image is formed on the surface of the photosensitive drum 12. Then, by supplying toner by the developing roller 14, an image corresponding to the electrostatic latent image is formed (developed) on the photosensitive drum 12.

The charging roller 13 is configured to charge the surface (surface layer portion) of the photosensitive drum 12. The charging roller 13 is arranged so as to be in contact with the surface (peripheral surface) of the photosensitive drum 12, and is also arranged so as to be pressed against the photosensitive drum 12 with a predetermined pressing amount. The charging roller 13 rotates counterclockwise in this example in response to the rotation of the photosensitive drum 12. A predetermined charging voltage is applied to the charging roller 13.

The developing roller 14 is configured to support the charged toner on the surface. The developing roller 14 is arranged so as to be in contact with the surface (peripheral surface) of the photosensitive drum 12, and is also arranged so as to be pressed against the photosensitive drum 12 by a predetermined pressing amount. The developing roller 14 rotates counterclockwise in this example due to the power transmitted from the photoconductor motor (not shown). A predetermined developing voltage is applied to the developing roller 14.

The cleaning blade 15 is a member that scrapes and cleans the toner remaining on the surface of the photosensitive drum 12. The cleaning blade 15 is arranged so as to come into contact with the surface of the photosensitive drum 12 with a counter, and is arranged so as to be pressed against the photosensitive drum 12 with a predetermined pressing amount.

The toner accommodating portion 16 is configured to accommodate toner. Specifically, for example, the toner accommodating portion 16 of the developing unit 11K accommodates black toner, the toner accommodating portion 16 of the developing unit 11Y accommodates yellow toner, and the toner accommodating portion 16 of the developing unit 11M is magenta. Toner is accommodated, and the toner accommodating portion 16 of the development unit 11C is adapted to accommodate cyan-colored toner.

The four exposure units 17 (exposure units 17K, 17Y, 17M, 17C) are mechanisms for irradiating the photosensitive drums 12 of the four development units 11 with light, and for example, an LED (Light Emitting Diode) head is used. It is composed of. Specifically, the exposure unit 17K irradiates the photosensitive drum 12 of the developing unit 11K with light, the exposure unit 17Y irradiates the photosensitive drum 12 of the developing unit 11Y with light, and the exposure unit 17M emits light. The photosensitive drum 12 of the developing unit 11M is irradiated with light, and the exposure unit 17C irradiates the photosensitive drum 12 of the developing unit 11C with light. As a result, an electrostatic latent image is formed on the surface of these photosensitive drums 12. Then, an image corresponding to the electrostatic latent image is formed on the photosensitive drum 12.

The transfer belt unit 18 is a mechanism for transferring an image formed on the surface of the photosensitive drum 12 to the surface of the recording medium PM by Coulomb force and transporting the recording medium PM in the transport direction F. The transfer belt unit 18 is adapted to convey the recording medium PM on which the image is transferred toward the fixing device 30. The transfer belt unit 18 includes a transfer belt 19, a drive roller 20, a driven roller 21, four transfer rollers 22 (transfer rollers 22K, 22Y, 22M, 22C), and a cleaning blade 23. The transfer belt 19 is a seamlessly formed annular belt capable of supporting the recording medium PM. The transfer belt 19 is stretched by a drive roller 20 and a driven roller 21. The drive roller 20 is a rotating member that rotates so as to convey the recording medium PM toward the fixing device 30 by the power transmitted from the belt motor (not shown), and causes the transfer belt 19 to circulate and rotate. There is. The driven roller 21 is a member that adjusts the tension applied to the transfer belt 19 while tensioning the transfer belt 19 together with the drive roller 20. The four transfer rollers 22 are rotating members that transfer an image formed on the surface of the photosensitive drum 12 of the corresponding developing unit 11 onto the surface to be transferred of the recording medium PM. The transfer roller 22K is arranged to face the photosensitive drum 12 of the developing unit 11K via the transfer belt 19, and the transfer roller 22Y is arranged to face the photosensitive drum 12 of the developing unit 11Y via the transfer belt 19. The transfer roller 22M is arranged to face the photosensitive drum 12 of the developing unit 11M via the transfer belt 19, and the transfer roller 22C is arranged to face the photosensitive drum 12 of the developing unit 11C via the transfer belt 19. By applying a predetermined transfer voltage to each of the transfer rollers 22K, 22Y, 22M, and 22C, in the image forming apparatus 1, the image formed on the photosensitive drum 12 by the developing unit 11 is covered by the recording medium PM. It is designed to be transferred on the transfer surface. The cleaning blade 23 is a member for scraping and cleaning the waste toner remaining on the surface of the transfer belt 19. A fixing device 30 is provided downstream of the image forming unit 10.

(Fixing device 30)
The fixing device 30 is a mechanism for fixing the image on the recording medium PM by applying heat and pressure to the image transferred on the recording medium PM conveyed from the transfer belt unit 18. In the image forming apparatus 1, the fixing device 30 fixes the image on the recording medium PM and conveys the recording medium PM toward the discharge roller pair 6 along the guide 8 which is a conveying path. A discharge roller pair 6 is provided downstream of the fixing device 30.

The discharge roller pair 6 is configured to convey the recording medium PM toward the stacker 9. With this configuration, the image forming apparatus 1 discharges the recording medium PM to the stacker 9. The stacker 9 is provided on the outside of the main body frame 2 and is a portion on which the recording medium PM on which the image is fixed is loaded.

[Detailed configuration of fixing device 30]
Hereinafter, the detailed configuration of the fixing device 30 will be described with reference to FIGS. 2 to 6. The fixing device 30 corresponds to a specific example of the "fixing device" in the present invention. FIG. 2 is a perspective view showing the main components of the fixing device 30. FIG. 3 is a front view showing the main components of the fixing device 30 when viewed from the Z-axis direction. FIG. 4 is a cross-sectional view showing the main components of the fixing device 30 along the IV-IV line shown in FIG. FIG. 5 is an enlarged cross-sectional view showing the region V shown in FIG. 4 in an enlarged manner. FIG. 6 is an exploded perspective view showing the annular belt unit 40 (described later). FIG. 6 also shows levers 33L and 33R (described later) in addition to the annular belt unit 40.

As shown in FIG. 2, the fixing device 30 includes side frames 31L, 31R, springs 32L, 32R, levers 33L, 33R, a drive gear 35, an annular belt unit 40, and a pressure roller 60. doing.

The side frames 31L and 31R are members fixed to the main body frame 2 of the image forming apparatus 1 by using screws or the like. As shown in FIGS. 2 and 4, the spring 32L is an elastic member such as a spring, and is configured to apply an urging force to the lever 33L. One end of the spring 32L is fixed to the side frame 31L, and the other end of the spring 32L is fixed to the lever 33L. Like the spring 32L, the spring 32R is an elastic member such as a spring, and is configured to apply an urging force to the lever 33R. The lever 33L is configured to rotate in the D1 direction with the rotation fulcrum 34L as the rotation axis in the XZ plane by the urging force applied from the spring 32L. The lever 33L is attached to the side frame 31L. Like the lever 33L, the lever 33R is configured to rotate in the D1 direction with the rotation fulcrum 34R as the rotation axis in the XZ plane by the urging force applied from the spring 32R. When the fixing device 30 does not perform the fixing operation, the levers 33L and 33R are pressed to a predetermined position by a lever fixing member (not shown). That is, since the spring 32L is pressed by the lever fixing member via the lever 33L, urging force can be applied to the lever 33L when the lever 33L is released from the lever fixing member. The same applies to the spring 32R. The drive gear 35 is configured to transmit power from an annular belt motor (not shown) to the pressurizing roller 60.

When the fixing device 30 performs the fixing operation, the drive gear 35 transmits the power from the annular belt motor to the pressurizing roller 60. Further, the levers 33L and 33R are released from the lever fixing member according to the operation of the drive gear 35, so that the levers 33L and 33R rotate in the D1 direction with the rotation fulcrums 34L and 34R as rotation axes. Therefore, the annular belt unit 40 attached to the levers 33L and 33R is pressed against the pressure roller 60, so that the nip region N is formed in the annular belt unit 40 and the pressure roller 60. FIG. 4 shows a state in which the nip region N is formed in the annular belt unit 40 and the pressure roller 60. By transporting the recording medium PM downstream while being sandwiched by the annular belt 53 and the pressure roller 60, that is, by passing the recording medium PM through the nip region N, heat is transferred to the image transferred onto the recording medium PM. And pressure is applied so that the image is fixed on the recording medium PM. In the width direction (Y-axis direction) orthogonal to the transport direction F, the nip region N includes the first end portion NL, the second end portion NR, and the first thereof, as shown in FIG. 7 and the like described later. It has an intermediate portion NC sandwiched between the end portion NL and the second end portion NR.

(Annular belt unit 40)
The annular belt unit 40 is configured to apply heat to the image on the recording medium PM. As shown in FIGS. 4 to 6, the annular belt unit 40 has a stay 41, a holding member 43, a heater 44, a heat retaining plate 48, a heat transfer member 50, and an annular belt 53. There is.

The stay 41 is a specific example corresponding to the "support member" of the present invention. The holding member 43 and the heat transfer member 50 are specific examples corresponding to the "contact member" of the present invention. Further, the annular belt 53 is a specific example corresponding to the "annular belt" of the present invention.

The stay 41 is a member that supports the annular belt 53. The stay 41 is fixed to the lever 33L by the screw 42L and is fixed to the lever 33R by the screw 42R. The holding member 43 is a member that holds the heater 44, the heat retaining plate 48, and the heat transfer member 50. The holding member 43 is fixed to the stay 41. As shown in FIGS. 5 and 6, the heat retaining plate 48, the heater 44, the heat transfer member 50, and the annular belt 53 are arranged in this order along the substantially X-axis direction. That is, the heat retaining plate 48 faces the heater 44, the heater 44 faces the heat transfer member 50, and the heat transfer member 50 faces the annular belt 53. The heater 44 is a plate-shaped member extending in the Y-axis direction, and is a heat source for heating the annular belt 53. Consists of a resistance heating element. The resistance heating element is composed of, for example, a nickel-chromium alloy (NiCr) or a silver-palladium alloy (AgPd).

FIG. 7 is a perspective view showing the appearance of the stay 41. FIG. 8 is a cross-sectional view showing an XZ cross section of the stay 41 and the holding member 43 orthogonal to the longitudinal direction (Y-axis direction). As shown in FIG. 7, the stay 41 has a pair of positive crown portions 41P extending in the width direction (Y-axis direction) and projecting toward the inner peripheral surface 56S of the annular belt 53. The stay 41 has a base portion 411 and a pair of wall portions 421 and 413 erected toward the holding member 43 at both ends of the base portion 411. The base portion 411 is, for example, a plate-shaped member extending in the width direction. The regular crown portion 41P is provided at each of the tip portions of the pair of wall portions 421 and 413, and includes, for example, the tip edge 41E provided in a curved shape. Therefore, the pair of wall portions 421 and 413 have the maximum dimension at the midpoint CP41 in the width direction (Y-axis direction) in the direction (X-axis direction) orthogonal to the inner peripheral surface 56S of the annular belt 53, and have a width. It has the smallest dimensions at the ends 41L, 41R in the direction. That is, the stay 41 has a larger cross-sectional area of the XZ cross section of the central portion in the width direction than the cross-sectional area of the XZ cross sections of the end portions 41L and 41R in the width direction. In the example shown in FIG. 7, the tip edge 41E curved over the entire nip region N in the width direction (Y-axis direction) is provided. That is, the regular crown portion 41P including the tip edge 41E extends from the first end portion NL to the second end portion NR via the intermediate portion NC. However, in the fixing device 30 of the present embodiment, the regular crown portion 41P including the tip edge 41E may be provided only in a part of the nip region N. For example, the positive crown portion 41P in the stay 41 may be provided only at a position corresponding to the intermediate portion NC in the nip region N. That is, in the fixing device 30, it is preferable to provide the positive crown portion 41P at a position corresponding to at least the intermediate portion NC. However, it is desirable that the cross-sectional area of the XZ cross section of the stay 41 is maximum in the positive crown portion 41P.

FIG. 9 is a schematic view showing a state in which the vicinity of the nip region N is viewed from the downstream in the transport direction F. However, in FIG. 10, only the stay 41, the holding member 43, the heat transfer member 50, the annular belt 53, and the pressure roller 60 are described, and the description of other members such as the heater 44 and the heat retaining plate 48 is omitted. As shown in FIG. 9, the stay 41 supports the holding member 43 in a state where the heat transfer member 50 is in contact with the inner peripheral surface 56S of the annular belt 53. The tip edge 41E of the regular crown portion 41P is in contact with the holding member 43, and both the holding member 43 and the heat transfer member 50 follow the shape of the regular crown portion 41P of the stay 41 and are the inner peripheral surfaces of the annular belt 53. It is curved so as to protrude toward 56S. The heater 44 and the heat retaining plate 48 are also curved in the same manner as the holding member 43 and the heat transfer member 50.

The protrusion amount A of the positive crown portion 41P is the maximum at the position corresponding to the intermediate portion NC of the nip region N. As shown in FIG. 7, the maximum value Amax of the protrusion amount A of the positive crown portion 41P is, for example, from the base portion 411 of the tip edge 41E in the direction orthogonal to the inner peripheral surface 56S of the annular belt 53 (X-axis direction). It can be defined as the difference (L41M-L41S) between the distance L41M of the farthest portion and the distance L41S of the portion of the tip edge 41E closest to the base 411.

The stay 41 has a rigidity higher than that of the holding member 43, for example. The stay 41 may be made of a highly rigid material containing a metal as a main component, such as an electrogalvanized steel sheet (SECC). The main component here means a component that occupies 50% by weight of the entire stay 41. On the other hand, as the holding member 43, which is processed into a more complicated shape than the stay 41, a material containing a heat-resistant resin such as a liquid crystal polymer (LCP) as a main component is preferably used. The main component here means a component that occupies 50% by weight of the entire holding member 43. The Young's modulus of the electrogalvanized steel sheet is, for example, 205 GPa, and the Young's modulus of the liquid crystal polymer is, for example, 15.1 GPa. The "rigidity" referred to in this application can be defined by, for example, the value of Young's modulus. That is, it can be said that the higher the Young's modulus value, the higher the rigidity.

The heat retaining plate 48 is a member that stores heat generated by the heater 44. In this example, the heat insulating plate 48 is a plate-shaped member extending in the Y-axis direction along the heater 44. The heat retaining plate 48 makes it difficult to transfer the heat generated by the heater 44 to the side of the heat retaining plate 48 opposite to the surface facing the heater 44.

Heat conductive grease is applied between the heater 44 and the heat retaining plate 48 in order to efficiently transfer the heat generated by the heater 44. Similarly, heat conductive grease is applied between the heater 44 and the heat transfer member 50. The heater 44 and the heat retaining plate 48 are arranged so as to be sandwiched between the holding member 43 and the heat transfer member 50, and are fixed by the holding member 43. In this example, the heat conductive grease is applied between the heater 44 and the heat retaining plate 48, but the present invention is not limited to this, and the heat conductive grease may not be applied.

The heat transfer member 50 is a member having a substantially flat plate shape extending in the Y-axis direction along the heater 44, and is configured to transfer the heat generated by the heater 44 to the annular belt 53. The heat transfer member 50 has a shape in which both ends of the heat transfer member 50 are bent in the thickness direction when viewed from the XZ plane. That is, the heat transfer member 50 has a recess facing the heater 44 in the XZ cross section. As shown in FIG. 5, the convex portion of the heat transfer member 50 in the XZ cross section is inserted into the holding grooves 49L and 49R provided in the holding member 43. Since the holding grooves 49L and 49R have a wider space than the convex portion of the heat transfer member 50, the heat transfer member 50 inserted into the holding grooves 49L and 49R is caused by the annular belt unit 40 being pressed against the pressure roller 60. It can be moved in the thickness direction (approximately the X-axis direction). That is, when the fixing device 30 performs the fixing operation, the heat transfer member 50 is pressed against the heater 44. At this time, the heat transfer member 50 transfers the heat generated by the heater 44 to the annular belt 53.

FIG. 10 is a schematic cross-sectional view for explaining the outline of the heat transfer member 50. As shown in FIG. 10, the heat transfer member 50 includes a heat diffusion member 51 having a first surface 51A facing the heater 44, a second surface 51B opposite to the first surface 51A, and the facing member 52. have. That is, the heat diffusion member 51 is formed with an opposing member 52 provided on the second surface 51B of the heat diffusion member 51. The facing member 52 has a facing surface SF facing the inner peripheral surface 56S of the annular belt 53. In the present specification, the fact that the facing surface SF of the facing member 52 "opposes" the inner peripheral surface 56S of the annular belt 53 means that the facing surface SF is in an arrangement relationship facing the inner peripheral surface 56S. .. In this case, "opposing" means that the facing surface SF is in contact with the inner peripheral surface 56S and has a facing arrangement relationship, or the facing surface SF is inside via another member such as a sliding grease GR described later. It also means that the arrangement is facing the peripheral surface 56S. The heater 44 is located on the side of the heat diffusion member 51 opposite to the facing surface SF.

The heat diffusion member 51 is configured to contain, for example, a metal having a large thermal diffusivity, which represents the speed at which heat is transferred. The thickness Ta of the heat diffusion member 51 is, for example, 0.485 mm. The thermal diffusivity Da in the in-plane direction along the first surface 51A in the heat diffusion member 51 is, for example, 60.4 mm ² / s. In this example, the main component of the heat diffusion member 51 is aluminum (Al). Here, the main component means a component that occupies 50% by weight of the whole of the heat diffusion member 51. That is, the Al content in the heat diffusion member 51 is higher than that of other materials. In this example, the heat diffusion member 51 contains Al, but the heat diffusion member 51 is not limited to this, and may include other metals having a large thermal diffusivity. The heat diffusion member 51 may contain, for example, stainless steel (SUS), copper, or zinc (Zn). The thickness Ta of the heat diffusion member 51 is not limited to the illustrated thickness.

The facing member 52 is configured to contain, for example, a resin having good slidability with the inner peripheral surface 56S of the annular belt 53. The thickness Tb of the facing member 52 is 0.005 mm or more, preferably 0.015 mm or less, and is, for example, 0.015 mm. The thermal diffusivity Db in the plane direction along the facing surface SF in the facing member 52 is, for example, 1.53 mm ² / s.

The annular belt 53 is an annular belt stretched by a stay 41 with a predetermined tension, and is configured to be rotatably held. It has an inner peripheral surface 56S facing the facing surface SF, and is provided so as to slide on the facing surface SF on the inner peripheral surface 56S. The annular belt 53 is adapted to form a nip portion N (FIG. 5) with the pressure roller 60.

FIG. 11 is a schematic cross-sectional view for explaining the outline of the annular belt 53. The annular belt 53 has a surface layer 54, an elastic layer 55, and a base material layer 56. That is, the elastic layer 55 is formed on the base material layer 56, and the surface layer 54 is formed on the elastic layer 55.

The surface layer 54, in this example, comprises a copolymer (PFA) of tetrafluoroethylene and perfluoroalkyl vinyl ether. The surface of the surface layer 54 opposite to the elastic layer 55 is the outer peripheral surface 54S facing the pressure roller 60. The thickness of the surface layer 54 is, for example, 20 μm. It is desired that the thickness of the surface layer 54 is large enough to follow the deformation of the elastic layer 55. On the other hand, if the thickness of the surface layer 54 is too small, the surface layer 54 is wrinkled due to sliding with the pressure roller 60 and sliding with the recording medium PM, so that the thickness of the surface layer 54 is 10 μm to 50 μm. Is preferable. Further, it is desired that the surface layer 54 has heat resistance that can withstand the fixing temperature and has a mold releasability that makes it difficult for the toner remaining on the annular belt 53 and the paper dust derived from the recording medium PM to stick to the surface layer 54, and is substituted with fluorine. It is preferably made of a new material. The material of the surface layer 54 is not limited to the exemplified material, and the thickness of the surface layer 54 is not limited to the exemplified thickness.

In this example, the elastic layer 55 is composed of a silicone rubber having heat resistance that can withstand the fixing temperature. The rubber hardness of the elastic layer 55 is, for example, 12 degrees, and the thickness of the elastic layer 55 is, for example, 300 μm. The elastic layer 55 is desired to have a rubber hardness and a thickness capable of forming the nip portion N. On the other hand, it is desired that the elastic layer 55 suppresses the heat loss of the heat generated from the heater 44 and efficiently transfers the heat generated from the heater 44 to the outer peripheral surface (toner contact surface) of the annular belt 53. .. If the thickness of the elastic layer 55 is large, a uniform nip portion N is likely to be formed, but this is not preferable because the heat capacity becomes large and the heat loss becomes large. The thickness of the elastic layer 55 is preferably 50 to 500 μm. Further, the rubber hardness of the elastic layer 55 is preferably 10 to 60 degrees in order to improve the uniformity of the nip portion N. In this example, the elastic layer 55 contains silicone rubber, but the elastic layer 55 is not limited to this, and may include other materials having heat resistance that can withstand the fixing temperature. The elastic layer 55 may include, for example, fluororubber. The thickness of the elastic layer 55 is not limited to the illustrated thickness.

In this example, the base material layer 56 is configured to contain polyimide (PI), and the main component of the base material layer 56 is PI. Here, the main component means a component that occupies 50% by weight of the entire base material layer 56. That is, the content of PI in the base material layer 56 is higher than that of other materials. The inner diameter of the base material layer 56 is, for example, 30 mm, and the thickness of the base material layer 56 is, for example, 80 μm. The base material layer 56 develops durability and mechanical strength in the annular belt 53, and is excellent in mechanical strength, repeated bending resistance, and buckling resistance. That is, since the base material layer 56 has a large Young's modulus and a high buckling strength, the annular belt 53 is unlikely to break. In this example, the base material layer 56 is designed to contain PI, but is not limited to this, and instead has, for example, high heat resistance, high Young's modulus, and high buckling strength. Other materials may be included. The base material layer 56 may include, for example, stainless steel or a polyetheretherketone (PEEK) material. In particular, a resin material having excellent heat resistance is preferable, and for example, polytetrafluoroethylene (PTFE) is preferable. Further, the base material layer 56 may include a material to which a conductive filler containing a metal element such as carbon black or zinc is added. In this case, the base material layer 56 can exhibit conductivity. Further, the base material layer 56 may contain PTFE to which a filler such as ticker boron is added, and in this case, the slidability and thermal conductivity of the base material layer 56 can be improved. The thickness of the base material layer 56 is not limited to the illustrated thickness.

(Pressurized roller 60)
FIG. 12 is an explanatory diagram for explaining a schematic configuration of the pressure roller 60. FIG. 13 is a schematic cross-sectional view of the pressure roller 60 in the direction of the arrow along the line XIII-XIII shown in FIG. The pressurizing roller 60 is a specific example corresponding to the "pressurizing member" in the present invention. The pressure roller 60 is rotatably provided while facing the outer peripheral surface 54S of the annular belt 53 with the recording medium PM interposed therebetween so that the nip region N is formed between the pressure roller 60 and the annular belt unit 40. That is, the pressurizing roller 60 is a rotating member that applies pressure to the image on the recording medium PM. The outer diameter of the pressure roller 60 is preferably 40 mm, and the hardness of the pressure roller 60 is preferably 50 to 65 degrees. The pressure roller 60 has a surface layer 61, an adhesive layer 62, an elastic layer 63, and a shaft 64. That is, the elastic layer 63 is formed on the shaft 64, the adhesive layer 62 is formed on the elastic layer 63, and the surface layer 61 is formed on the adhesive layer 62. An adhesive layer may be provided between the shaft 64 and the elastic layer 63. The surface of the surface layer 61 is the outer peripheral surface 60S of the pressure roller 60 facing the outer peripheral surface 54S of the annular belt 53.

The surface layer 61 is configured to include PFA in this example. The thickness of the surface layer 61 is, for example, 30 μm. The surface layer 61 is adapted to slide with the recording medium PM and the annular belt 53. It is desirable that the thickness of the surface layer 61 is such that it can follow the deformation of the elastic layer 63, similarly to the surface layer 54 of the annular belt 53. On the other hand, if the thickness of the surface layer 61 is too small, wrinkles are likely to occur on the surface layer 61 due to sliding with the annular belt 53 or sliding with the recording medium PM, so that the thickness of the surface layer 61 is 15 μm to 50 μm. Is preferable. Further, it is desired that the surface layer 61 has a heat resistance that can withstand the fixing temperature and a mold release property that makes it difficult for the toner remaining on the annular belt 53 and the paper dust derived from the recording medium PM to stick to the surface layer 61, and is substituted with fluorine. It is preferably made of a new material. The material of the surface layer 61 is not limited to the exemplified material, and the thickness of the surface layer 61 is not limited to the exemplified thickness.

In this example, the adhesive layer 62 is configured to contain a silicone adhesive that has sufficient adhesive strength and is added with a conductive material and can withstand the fixing temperature. The adhesive layer 62 adheres the elastic layer 63 and the surface layer 61 in order to suppress the peeling of the surface layer 61 from the elastic layer 63 and the occurrence of wrinkles. Since the adhesive layer 62 has conductivity, for example, in continuous printing, the electric charge charged on the pressure roller 60 is accumulated to prevent electrostatic adhesion of paper dust and the like. In this example, the adhesive layer 62 is provided with a conductive material, but the present invention is not limited to this, and the conductive material may not be added. The material of the adhesive layer 62 is not limited to the exemplified material.

In this example, the elastic layer 63 is configured to include a silicone sponge having a foam cell to which a conductive material is added. The thickness of the elastic layer 63 is, for example, 4 mm. Since the elastic layer 63 has conductivity, for example, in continuous printing, the electric charge charged on the pressure roller 60 is accumulated to prevent electrostatic adhesion of paper dust and the like. The elastic layer 63 is desired to have a rubber hardness and a thickness capable of forming the nip portion N. Further, it is desired that the elastic layer 63 has a heat storage property so as not to lose the amount of heat transferred from the annular belt 53 to the image and the recording medium PM. Further, it is preferable that the cell diameter of the foam cell is small so that no nip mark remains in the pressurized nip portion N, and specifically, the average cell diameter of the foam cell is preferably 20 to 250 μm. In this example, the average cell diameter is 100 μm. To measure the average cell diameter, cut the silicone sponge with a razor, observe it with a CCD (Charged-coupled devices) microscope, measure 10 cell diameters within the observation viewing angle, and measure the average value of these. And said. In this example, the conductive material is added to the elastic layer 63, but the present invention is not limited to this, and the conductive material may not be added to the elastic layer 63. Further, although the elastic layer 63 includes a silicone sponge, the elastic layer 63 is not limited to this, and may include other materials. The elastic layer 63 may include, for example, solid rubber. The thickness of the elastic layer 63 is not limited to the illustrated thickness.

The shaft 64 is a member having pressure resistance that is not deformed by the fixing pressure, and is configured to include, for example, solid stainless steel (SUS304). In this example, the shaft 64 includes SUS304, but the shaft 64 is not limited to this, and may include other materials instead. Further, in this example, a solid shaft is used, but the present invention is not limited to this, and a hollow shaft may be used instead.

The outer peripheral surface 60S of the pressure roller 60 may have an inverted crown portion 60U recessed in a direction away from the outer peripheral surface 54S of the annular belt 53. The inverted crown portion 60U may have a curved shape so as to correspond to the shape of the tip edge 41E of the positive crown portion 41P in the stay 41. The pressure roller 60 has a maximum diameter L60M at an intermediate point CP60 in the width direction (Y-axis direction) and a minimum diameter L60S at the end portions 60L and 60R in the width direction. That is, the pressure roller 60 has a smaller cross-sectional area of the XZ cross section of the central portion in the width direction than the cross-sectional area of the XZ cross sections of the end portions 60L and 60R in the width direction. In the example shown in FIG. 12, an inverted crown portion 60U curved over the entire nip region N in the width direction (Y-axis direction) is provided. That is, the inverted crown portion 60U extends from the first end portion NL to the second end portion NR via the intermediate portion NC. However, in the fixing device 30 of the present embodiment, the inverted crown portion 60U may be provided only in a part of the nip region N. For example, the inverted crown portion 60U may be provided only at a position corresponding to the intermediate portion NC in the nip region N. That is, in the fixing device 30, the inverted crown portion 60U may be provided at a position corresponding to at least the intermediate portion NC. However, it is desirable that the cross-sectional area of the XZ cross section of the pressure roller 60 is the minimum in the inverted crown portion 60U.

The recess amount B of the inverted crown portion 60U is the maximum at the position corresponding to the intermediate portion NC of the nip region N. As shown in FIG. 12, the maximum value Bmax of the dent amount B of the inverted crown portion 60U is half the value of the difference between the maximum diameter L60M of the pressure roller 60 and the minimum diameter L60S of the pressure roller 60 (L41M-). It can be defined as L41S) × 0.5. Here, it is desirable that the maximum value Amax of the protrusion amount A of the positive crown portion 41P in the stay 41 is larger than the maximum value Bmax of the dent amount B of the reverse crown portion 60U. This is because an appropriate distribution of the transport force in the transport direction in the width direction is formed.

The fixing device 30 is further configured to satisfy all of the following conditional expressions (1) to (3).
0 <Amax ≦ 0.35 …… (1)
0 <Bmax ≦ 0.30 …… (2)
-0.16 <(Amax-Bmax) ≤ 0.15 ... (3)
However, Amax is the maximum value [mm] of the protrusion amount A of the positive crown portion 40P, and Bmax is the maximum value [mm] of the dent amount B of the reverse crown portion 60U.

In the fixing device 30, the length of the nip region N in the transport direction F is preferably, for example, 8 mm or more and 15 mm or less. Further, the total pressure applied to the nip region N by the stay 41 is preferably, for example, 30 kg or more and 36 kg or less. The total pressure applied to the nip region N can be measured by sandwiching a sheet-shaped pressure sensor over the entire nip region N. Specifically, the total pressure applied to the nip region N is measured by the inter-roller pressure distribution measurement system PINCH (manufactured by Nitta Corporation) using a sensor sheet (PINCH A4-40 NS-SET-PA4-40). can do.

Since the fixing device 30 includes the positive crown portion 41P, in the first end transport force F1 and the second end NR that transport the recording medium PM in the transport direction F in the first end NL of the nip region N. The second end transport force F2 that transports the recording medium PM in the transport direction F is stronger than the intermediate transport force F3 that transports the recording medium PM in the transport direction in the intermediate portion NC.

[Action / Effect]
(A. Basic operation)
In the image forming apparatus 1, the image is transferred to the recording medium PM as follows.

First, the overall operation of the image forming apparatus 1 will be described with reference to FIG. When the image forming apparatus 1 receives print data from the host apparatus, the developing unit 11 rotates the photosensitive drum 12 to perform an image forming process.

In the image forming apparatus 1, the exposure unit 17 selectively irradiates the photosensitive drum 12 whose surface is charged in the developing unit 11 with light, so that an electrostatic latent image is formed on the surface of the photosensitive drum 12. NS. Then, an image is formed on the photosensitive drum 12 according to the electrostatic latent image.

When the image forming apparatus 1 transfers an image to the recording medium PM loaded on the paper feed tray 3, the hopping roller 4 resists the recording medium PM by the power transmitted from the hopping motor (not shown). Go out toward 5 vs. 5. The resist roller pair 5 conveys the recording medium PM toward the image forming unit 10. At that time, the skew of the recording medium PM is corrected by abutting the front edge of the recording medium PM against the resist roller pair 5.

After that, in the image forming unit 10, the transfer belt 19 circulates and rotates to convey the recording medium PM toward the fixing device 30. At that time, the recording medium PM passes between the photosensitive drum 12 and the transfer roller 22.

In the image forming apparatus 1, when an image is formed on the surface of the photosensitive drum 12, the transfer belt unit 18 performs a transfer process. At that time, in the transfer belt unit 18, the transfer roller 22 attracts the image formed on the surface of the photosensitive drum 12 while the transfer belt 19 conveys the recording medium PM. As a result, the image is transferred from the photosensitive drum 12 to the recording medium PM.

When the image is transferred from the photosensitive drum 12 to the recording medium PM, the image forming apparatus 1 conveys the recording medium PM to the fixing device 30. When the recording medium PM is conveyed, the fixing device 30 performs a fixing process. At that time, the fixing device 30 heats and pressurizes the image transferred to the surface of the recording medium PM, melts the image, and fixes the image on the recording medium PM.

When the image is fixed on the recording medium PM, the image forming apparatus 1 conveys the recording medium PM toward the stacker 9 and discharges the recording medium PM onto the stacker 9.

The overall operation of the image forming apparatus 1 is as described above.

(B. Behavior of the fixing device 30 in the fixing operation)
Next, the behavior of the fixing device 30 when the recording medium PM on which the image is transferred passes through the nip region N of the fixing device 30 will be described.

In the fixing device 30, the presence of the positive crown portion 41P forms the nip region N in a state where the annular belt 53 is curved so as to project toward the pressure roller 60 as shown in FIG. 9, and the annular belt 53 is formed. It is designed to rotate in the transport direction F. Therefore, in the recording medium PM passing through the nip region N, the first end transfer force F1 and the second end transfer force F2, which are higher than the intermediate transfer force F3 applied in the intermediate NC, are applied to the first end. It is given in the portion NL and the second end portion NR, respectively. As a result, the deformation rate of the recording medium PM (hereinafter referred to as “medium deformation rate”) is reduced. As shown in FIG. 14, for example, the medium deformation rate is determined by setting the width dimension of the tip portion of the recording medium PM that first passes through the nip region N as a, and after passing through the nip region N behind the tip portion. When the width dimension of the end portion is b, it is defined as (ab) / a × 100 (%). Therefore, the smaller the difference between the width dimension a of the front end portion and the width dimension b of the rear end portion, the smaller the medium deformation rate can be. Note that FIG. 14 is an explanatory diagram for explaining the medium deformation rate of the recording medium PM passing through the nip region N.

(C. Effect)
As described above, in the fixing device 30 of the present embodiment, the positive crown portion 41P is provided so that the first end transport force F1 and the second end transport force F2 are stronger than the intermediate transport force F3 (F1>). Since F3, F2> F3), the medium deformation rate can be reduced. As a result, it is possible to suppress the occurrence of wrinkles in the recording medium PM regardless of the strength of the nip pressure applied to the recording medium PM during the fixing process. Therefore, good fixing processing can be performed even when the recording medium PM is thick paper, and wrinkles can be suppressed even when the recording medium PM is thin paper.

Further, the stay 41 has a positive crown portion 41P at a position corresponding to the intermediate portion NC in the nip region N, and the protrusion amount A of the positive crown portion 41P is at a position corresponding to the intermediate portion NC of the nip region N. I tried to maximize it. Therefore, the symmetry of the distribution of the nip pressure in the width direction is improved, and the first end transfer force F1 and the second end transfer force F2 can be brought close to each other. As a result, the occurrence of wrinkles on the recording medium PM can be further suppressed. Further, the rigidity of the central portion in the width direction of the stay 41 can be increased as compared with the case where the stay 41 does not have the positive crown portion 41P, and the fixing process of the recording medium PM that needs to apply a particularly strong nip pressure can be performed. Even if this is done, the bending of the stay 41 can be suppressed. Therefore, in the fixing device 30, an appropriate distribution of the nip pressure in the width direction is maintained regardless of the strength of the nip pressure, and deterioration of the fixing performance can be prevented.

In particular, in the stay 41, when the cross-sectional area of the XZ cross section of the central portion is larger than the cross-sectional area of the XZ cross section of the end portions 41L and 41R, the amount of bending of the stay 41 during the fixing process can be further reduced. Further, when the cross-sectional area of the XZ cross section of the stay 41 is set to the maximum in the positive crown portion 41P, the amount of bending of the stay 41 during the fixing process can be further reduced. As a result, it is possible to maintain a predetermined transport force distribution, stably maintain the fixing performance and suppress the generation of wrinkles regardless of the nip condition.

Further, in the fixing device 30, the stay 41 has a rigidity higher than that of the holding member 43. Therefore, for example, when the fixing device 30 is exposed to a high temperature and high pressure environment, the positive crown portion 40P is deformed. It is possible to maintain an appropriate protrusion amount A regardless of the strength of the nip pressure. Therefore, for example, it is possible to further improve the fixing performance when the thick paper is fixed as the recording medium PM, and to further suppress the occurrence of wrinkles of the thin paper when the thin paper is fixed as the recording medium PM.

Further, in the fixing device 30, the pressure roller 60 is provided with a reverse crown portion 60U so that the maximum value Amax of the protrusion amount A and the maximum value Bmax of the dent amount B are appropriately set, so that the fixing performance is further improved. , It is possible to achieve both the further suppression of the occurrence of wrinkles in the recording medium PM.

<2. Experimental example>
(Experimental Example 1)
The fixing process was performed in the fixing device 30 described in the above embodiment, the wrinkle generation state of the recording medium PM was confirmed, and the fixing performance was evaluated. At that time, the first end transfer force F1, the second end transfer force F2, and the intermediate transfer force F3 were measured.

In this experimental example, a sample of five types of stays 41 in which the maximum value Amax of the protrusion amount A in the positive crown portion 41P is 0.14, 0.30, 0.35, 0.40, 0.50 was used. Further, samples of four types of pressure rollers 60 having a maximum value Bmax of the dent amount B of the inverted crown portion 60U of 0.10, 0.20, 0.25, 0.30 were used. Table 1 summarizes the values of AB when the samples of the five types of stays 41 having different maximum values Amax and the samples of the four types of pressure rollers 60 having different maximum values Bmax are combined.

FIG. 15 is a schematic diagram illustrating a method for measuring the first end transport force F1, the second end transport force F2, and the intermediate transport force F3 with respect to the recording medium PM. A force gauge (Digital Force Gauge ZP-100N manufactured by Imada Co., Ltd.) was used to measure the transport force. Here, as the recording medium PM, a strip-shaped sample obtained by cutting A4 size plain paper (“Excellent White 80 g / m2” manufactured by Oki Data Corporation) in the lateral direction with a width of WS = 30 mm was used. As shown in FIG. 15, the first end portion of the sample S of the strip-shaped recording medium PM is sandwiched between the position PCs in the nip region N of the fixing device 30, and the second end portion of the sample S is externally held. It was held by the force gauge FG fixed to. In that state, the transport belt 53 was rotated, the transport force was measured at 10 points at 0.5 second intervals, and the average value was calculated. The average value was taken as the carrying force at the position PC. At that time, in the nip region N, the annular belt 53 was made to idle in the medium transport direction F so as to slide on the surface of the sample S. The medium transfer speed by the annular belt 53 was set to 230 mm / s. Similar measurements were performed at the other four positions PL1, PL2, PR2, PR1 in the nip region N, respectively, and the transport forces FL1, FL2, FR2, FR1 at each position were obtained.

In this experimental example, the transport force FL1 measured at the position PL1 is defined as the first end transport force F1, the transport force FR1 measured at the position PR1 is defined as the second end transport force F2, and the transport force FL2 at the position PL2. The sum of the transfer force FC at the position PC and the transfer force FR2 at the position PR2 is defined as the intermediate transfer force F3 (= FL2 + FC + FR2). Then, the feed force end center difference ratio = {[(F1 + F2) / 2]-[, which is a parameter based on the difference between the first end transfer force F1 and the second end transfer force F2 and the intermediate transfer force F3. (F3) / 3]} / [(F3) / 3] * 100 was obtained. The results are shown in Table 2. The center difference ratio at the end of the feed force is determined by how strong the difference between the first end transfer force F1 and the second end transfer force F2 and the intermediate transfer force F3 is with respect to the intermediate transfer force F3. Is a parameter that means.

Further, the fixing process of the A4 size recording medium PM is performed in the fixing device 30 in which the samples of the five types of stays 41 and the samples of the four types of pressure rollers 60 shown in Table 1 are combined, respectively, to deform the medium. I checked each rate. Table 3 and FIG. 16 show the relationship between the center difference rate at the end of the feed force, the deformation rate of the medium, the presence or absence of wrinkles, and the evaluation of the fixing performance.

As shown in Table 3 and FIG. 16, when the center difference ratio at the feed end was positive, the medium deformation rate was 0.5% or less, and the occurrence of wrinkles in the recording medium PM could be prevented. However, the data of the feed force end center difference ratio of 82% corresponds to the case where the protrusion amount A in the positive crown portion 41P is 0, and in this case, the fixing performance is insufficient. This is because the nip pressure is sufficiently applied to the recording medium PM at the first end NL and the second end NR, but the nip pressure applied to the recording medium PM at the intermediate NC is insufficient, and the recording medium is insufficient. It is considered that the fixing process of the portion corresponding to the intermediate portion NC of PM is not sufficiently performed.

<3. Modification example>
Although the present invention has been described above with reference to embodiments, the present invention is not limited to the above embodiments and can be modified in various ways. For example, in the above-described embodiment and the like, an image forming apparatus capable of forming a color image using four colors of toner has been described, but the present invention is not limited to this, and for example, a color image of five or more colors is formed. It may be an image forming apparatus.

Further, in the above-described embodiment, the present invention has been described by exemplifying a direct transfer type image forming apparatus, but the present invention can also be applied to a secondary transfer type image forming apparatus provided with an intermediate transfer belt.

Further, in the above embodiment, a printer having a printing function has been described as a specific example of the "image forming apparatus" in the present invention, but the present invention is not limited to this. That is, in addition to such a printing function, the present invention can be applied to, for example, an image forming apparatus that functions as a multifunction device having a scanning function and a fax function.

1 ... image forming device, 2 ... main body frame, 3 ... paper feed tray, 4 ... hopping roller, 5 ... resist roller pair, 6 ... discharging roller pair, 7, 8 ... guide, 9 ... stacker, 10 ... image forming unit, 11, 11C, 11K, 11M, 11Y ... Development unit, 12 ... Photosensitive drum, 13 ... Charging roller, 14 ... Development roller, 15 ... Cleaning blade, 16 ... Toner container, 17, 17C, 17K, 17M, 17Y ... Exposure Unit, 18 ... Transfer belt unit, 19 ... Transfer belt, 20 ... Drive roller, 21 ... Driven roller, 22, 22C, 22K, 22M, 22Y ... Transfer roller, 23 ... Cleaning blade, 30 ... Fixing device, 31L, 31R ... Side frame, 32L, 32R ... spring, 33L, 33R ... lever, 34L, 34R ... rotation fulcrum, 35 ... drive gear, 40 ... annular belt unit, 41 ... stay, 42L, 42R ... screw, 43 ... holding member, 44 ... Heater, 48 ... Heat retaining plate, 49L, 49R ... Holding groove, 50 ... Heat transfer member, 51 ... Heat diffusion member, 52 ... Opposing member, 53 ... Circular belt, 54, 61 ... Surface layer, 55, 63 ... Elastic layer , 56 ... Base material layer, 56S ... Inner peripheral surface, 54S ... Outer peripheral surface,
60 ... Pressurized roller, 60S ... Outer peripheral surface, 60U ... Reverse crown portion, 62 ... Adhesive layer, 64 ... Shaft, GR ... Sliding grease, SF ... Facing surface.

Claims (14)

With a rotatable annular belt,
With the contact member in contact with the inner peripheral surface of the annular belt,
A support member extending in a direction orthogonal to the transport direction of the medium, having a positive crown portion protruding toward the inner peripheral surface, and supporting the contact member, and a support member.
A pressure member having a surface facing the outer peripheral surface of the annular belt and capable of forming a nip region in which the medium is sandwiched between the surface and the outer peripheral surface is provided.
The nip region includes a first end portion, a second end portion, and an intermediate portion sandwiched between the first end portion and the second end portion in the extending direction in which the support member extends. Including
The first-end transport force for transporting the medium in the transport direction at the first end portion and the second-end transport force for transporting the medium in the transport direction at the second end portion are the same in the intermediate portion. A fixing device that is stronger than the intermediate transfer force that conveys the medium in the transfer direction. The fixing device according to claim 1, wherein the positive crown portion of the support member is provided at a position corresponding to the nip region between the first end portion and the second end portion. The fixing device according to claim 1 or 2, wherein the protrusion amount of the positive crown portion is the maximum in the intermediate portion. The fixing device according to any one of claims 1 to 3, wherein the support member has a larger cross-sectional area of the central portion in the extending direction than the cross-sectional area of both ends in the extending direction. The fixing device according to any one of claims 1 to 4, wherein the cross-sectional area of the support member in a cross section orthogonal to the extending direction is the maximum in the positive crown portion. The fixing device according to any one of claims 1 to 5, wherein the support member has a rigidity higher than that of the contact member. The fixing device according to claim 6, wherein the support member is made of a highly rigid material containing metal as a main component. The fixing device according to any one of claims 1 to 7, wherein the surface of the pressurizing member has an inverted crown portion recessed in a direction away from the outer peripheral surface of the annular belt. The fixing device according to claim 8, wherein the maximum value of the protrusion amount of the positive crown portion is larger than the maximum value of the dent amount of the reverse crown portion. The fixing device according to claim 8 or 9, which satisfies all of the following conditional expressions (1) to (3).
0 <Amax ≦ 0.35 …… (1)
0 <Bmax ≦ 0.30 …… (2)
-0.16 <(Amax-Bmax) ≤ 0.15 ... (3)
However,
Amax: Maximum value of protrusion of positive crown [mm]
Bmax: Maximum value of the amount of dent in the inverted crown [mm]
Is. The fixing device according to any one of claims 1 to 10, wherein the contact member comes into contact with the inner peripheral surface in a state of being curved along the shape of the positive crown portion of the support member. The fixing device according to any one of claims 1 to 11, wherein the length of the nip region in the transport direction is 8 mm or more and 15 mm or less. The fixing device according to any one of claims 1 to 12, wherein the total pressure applied to the nip region by the support member is 30 kg or more and 36 kg or less. An image forming apparatus comprising the fixing apparatus according to any one of claims 1 to 13.

Images