JP5343344B2 - Fixing apparatus and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device using a belt member and capable of preventing reduction of tensile force of the belt member in a region where it passes through a nip region and releasing a recording material from the belt member stably. <P>SOLUTION: This fixing device having a fixing belt 610, a fixing roll 611, and a pressurizing roll 62 includes a release member 64 for pressing the fixing belt 610 against the fixing roll 611 in a region on the downstream side in the direction of travel of the fixing belt 610 in the nip region where the pressurizing roll 62 pressurizes the fixing roll 611 and on the upstream side of a region where the fixing belt 610 comes into contact with the fixing roll 611 and a tensile force providing member 641 being a tensile force providing means for giving tensile force to the fixing belt 610 and a pressing member 642 in a region on the downstream side in the direction of travel of the fixing belt 610 in a region where the release member 64 presses the fixing belt 610 against the pressurizing roll 62 and on the upstream side of a region where the fixing belt 610 comes into contact with the fixing roll 611. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

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

In an image forming apparatus such as a copying machine or a printer using an electrophotographic system, there is a high demand for speeding up copying processing and printing processing. Therefore, in a fixing device that fixes a toner image on a recording material, a belt member having a smaller heat capacity than a roll member such as a fixing roll is used as a heating member for heating the toner image, and the time required to reach the fixing possible temperature is shortened. What has been developed has been developed.
In such a fixing device using a belt member, if a member that peels the recording material from the surface of the belt member is placed in contact with the belt member, the thin film-like belt member may break due to wear. As a method corresponding to this, there is known a method of peeling the recording material by making use of a change in the curvature of the belt member without bringing the peeling member into contact with the belt member.
For example, Patent Document 1 includes a fixing belt having a stretched surface that faces the front and back surfaces of a recording material, and a roll that stretches the outlet portion of the recording material of the fixing belt is configured to have a small diameter so that the recording material is separated in curvature. A technique relating to a fixing device is described.

JP 2006-71921 A

Here, in general, the belt member is configured to move while being stretched around a plurality of members including a roll member. For this reason, when the frictional force with the member that stretches the belt member fluctuates, the belt member in the region where the recording material is peeled loosens and sufficient curvature is not formed, and the recording material is not peeled off from the belt member. There is.
SUMMARY OF THE INVENTION An object of the present invention is to suppress a decrease in tension of a belt member in a region that has passed through a nip region in a fixing device using the belt member, and to stably peel the recording material from the belt member.

According to the first aspect of the present invention, a belt member that is formed in a belt shape and moves while being heated, a fixing roll that is formed in a roll shape and stretches the belt member, and the belt member is in contact with the fixing roller. A pressure roll that is arranged so as to press the fixing roll in an area to form a nip area, and passes a recording material holding a toner image through the nip area to fix the toner image; and the nip area A pressing portion having a pressing portion that presses the belt member against the pressure roll in a region downstream of the belt member in the moving direction and upstream of a region where the belt member contacts the fixing roll. A member and the pressing portion of the pressing member are on the downstream side in the moving direction of the belt member in a region where the belt member is pressed against the pressure roll, and the belt member is fixed to the fixing member. Tension applying means for applying tension to the belt member in a region upstream of the region in contact with the tool, and the tension applying means presses the belt member against the pressure roll. A belt support portion disposed on a side surface portion of the pressing member that is in contact with the belt member after passing through a contact area and having a support surface that supports an inner peripheral surface of the belt member; and the belt support portion is connected to the belt member. And a pressing portion that presses toward the fixing device.

According to a second aspect of the present invention, a belt member that is formed in a belt shape and moves while being heated, a fixing roll that is formed in a roll shape and stretches the belt member, and the belt member is in contact with the fixing roll. A pressure roll that is arranged so as to press the fixing roll in an area to form a nip area, and passes a recording material holding a toner image through the nip area to fix the toner image; and the nip area A pressing member that presses the belt member against the pressure roll in a region downstream of the belt member in the moving direction and upstream of a region where the belt member contacts the fixing roll; and the pressing member The region where the member presses the belt member against the pressure roll is downstream in the moving direction of the belt member, and upstream of the region where the belt member contacts the fixing roll. Tension applying means for applying tension to the belt member in a region where the tension applying means is a roll-like tension roll that stretches the belt member, and the tension roll is attached to the belt member. And a pressing portion that presses the pressing member toward the belt member. The fixing device presses the pressing member toward the belt member.
According to a third aspect of the present invention, in the fixing device according to the second aspect, the tension applying means includes a plurality of the pressing portions having different spring constants along a longitudinal direction of the stretching roll. It is.

According to a fourth aspect of the present invention, there is provided a toner image forming unit that forms a toner image, a transfer unit that transfers a toner image formed by the toner image forming unit onto a recording material, and the toner image that is transferred onto the recording material. A fixing unit that fixes the toner image to the recording material, and the fixing unit is formed in a belt shape and is moved while being heated; and a fixing member that is formed in a roll shape and stretches the belt member. A roll and a belt member are arranged to press the fixing roll in an area where the belt member contacts the fixing roll to form a nip area, and a recording material holding a toner image is passed through the nip area to pass the toner. A pressure roll for fixing an image; and a region that is downstream of the nip region in the moving direction of the belt member and upstream of a region where the belt member is in contact with the fixing roller. A pressing member having a pressing portion that presses the belt member against the pressure roll; and a moving direction downstream of the belt member in a region where the pressing portion of the pressing member presses the belt member against the pressure roll. Tension applying means for applying tension to the belt member in a region that is on the upstream side of the region where the belt member is in contact with the fixing roll, and the tension applying unit of the fixing unit includes: A supporting surface that is disposed on a side surface portion of the pressing member that is in contact with the belt member after passing through a region where the pressing member presses the belt member against the pressure roll and supports an inner peripheral surface of the belt member. An image forming apparatus comprising: a belt support portion having a pressing portion that presses the belt support portion toward the belt member .

According to a fifth aspect of the present invention, a toner image forming unit that forms a toner image, a transfer unit that transfers the toner image formed by the toner image forming unit onto a recording material, and the toner image that has been transferred onto the recording material A fixing unit that fixes the toner image to the recording material, and the fixing unit is formed in a belt shape and is moved while being heated; and a fixing member that is formed in a roll shape and stretches the belt member. A roll and a belt member are arranged to press the fixing roll in an area where the belt member contacts the fixing roll to form a nip area, and a recording material holding a toner image is passed through the nip area to pass the toner. A pressure roll for fixing an image; and a region that is downstream of the nip region in the moving direction of the belt member and upstream of a region where the belt member is in contact with the fixing roller. A pressing member that presses the belt member against the pressure roll; and a downstream side of the belt member in the moving direction of the region where the pressing member presses the belt member against the pressure roll; A tension applying unit that applies tension to the belt member in a region upstream of the region in contact with the fixing roll, and the tension applying unit of the fixing unit is a roll-shaped tension member that stretches the belt member. An image forming apparatus comprising: a gantry roll; and a pressing portion that presses the tension roll toward the belt member, and the pressing portion presses the pressing member toward the belt member. .
The invention according to claim 6, wherein the tensioning means of the fixing means, according to claim 5, wherein a plurality of the pressing portions having different spring constants along the longitudinal direction of the tension roll is provided The image forming apparatus described.

According to the first aspect of the present invention, in the fixing device using the belt member, compared with the case where the present invention is not adopted, it is possible to suppress a decrease in the tension of the belt member in the region passing through the nip region, and It can be stably peeled from the belt member .

According to the second aspect of the present invention, in the fixing device using the belt member, as compared with the case where the present invention is not adopted, the tension of the belt member is suppressed from decreasing in the region passing through the nip region, and the recording material is It can be stably peeled from the belt member.
According to the third aspect of the present invention, the deviation of the belt member can be suppressed as compared with the case where the present invention is not adopted.

According to the fourth aspect of the present invention, in the image forming apparatus equipped with the fixing device using the belt member, the tension of the belt member is reduced in the region passing through the nip region as compared with the case where the present invention is not adopted. And the recording material can be stably peeled from the belt member.
According to the fifth aspect of the present invention, in the image forming apparatus equipped with the fixing device using the belt member, the tension of the belt member is reduced in the region passing through the nip region as compared with the case where the present invention is not adopted. And the recording material can be stably peeled from the belt member.
According to the sixth aspect of the present invention, it is possible to suppress the deviation of the belt member as compared with the case where the present invention is not adopted.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
[Embodiment 1]
FIG. 1 is a diagram illustrating an overall configuration of an image forming apparatus 1 to which the exemplary embodiment is applied. An image forming apparatus 1 shown in FIG. 1 is a so-called tandem color printer, and an image forming process unit 10 that forms an image corresponding to image data of each color, and a control unit 30 that controls the operation of the entire image forming apparatus 1. An image processing unit 35 that is connected to an external device such as a personal computer (PC) 3 or an image reading device 4 and performs predetermined image processing on image data received therefrom, and a main power source that supplies power to each unit 50.

The image forming process unit 10 includes four image forming units 11Y, 11M, 11C, and 11K (also collectively referred to as “image forming unit 11”), which are examples of toner image forming units arranged in parallel at regular intervals. ) Is provided. Each of the image forming units 11 is a photosensitive drum 12 as an example of an image carrier that forms an electrostatic latent image and holds a toner image, and a charger 13 that uniformly charges the surface of the photosensitive drum 12 with a predetermined potential. A developing unit 14 for developing the electrostatic latent image formed on the photosensitive drum 12 and a cleaner 15 for cleaning the surface of the photosensitive drum 12 after transfer are provided.
Each image forming unit 11 is configured in substantially the same manner except for the toner stored in the developing device 14. Each image forming unit 11 forms yellow (Y), magenta (M), cyan (C), and black (K) toner images.

  Further, the image forming process unit 10 exposes the photosensitive drums 12 disposed in the respective image forming units 11, and the respective color toner images formed on the photosensitive drums 12 of the respective image forming units 11. Are superimposed on the intermediate transfer belt 20 and the intermediate transfer belt 20 that sequentially transfer (primary transfer) each color toner image formed by each image forming unit 11 to the intermediate transfer belt 20. A secondary transfer roll 22 that batch-transfers (secondary transfer) the transferred color toner images onto a sheet P that is a recording material (recording sheet), and a fixing unit that fixes the secondary-transferred color toner images on the sheet P ( The fixing device 60 is an example of the fixing device). In the image forming apparatus 1 of the present embodiment, the intermediate transfer belt 20, the primary transfer roll 21, and the secondary transfer roll 22 constitute a transfer unit.

  In the image forming apparatus 1 according to the present embodiment, the image data input from the PC 3 or the image reading apparatus 4 is subjected to predetermined image processing by the image processing unit 35 and then each image is formed via an interface (not shown). Sent to unit 11. For example, in the image forming unit 11Y that forms a yellow (Y) color toner image, the photosensitive drum 12 is uniformly charged at a predetermined potential by the charger 13 while rotating in the direction of arrow A, and the laser exposure unit 40 Scanning exposure is performed with laser light whose lighting is controlled based on the image data transmitted from the image processing unit 35. Thereby, an electrostatic latent image related to a yellow (Y) color image is formed on the photosensitive drum 12. The electrostatic latent image formed on the photosensitive drum 12 is developed by the developing device 14, and a yellow (Y) color toner image is formed on the photosensitive drum 12. Similarly, magenta (M), cyan (C), and black (K) toner images are formed in the image forming units 11M, 11C, and 11K, respectively.

  Each color toner image formed by each image forming unit 11 is sequentially electrostatically attracted by the primary transfer roll 21 onto the intermediate transfer belt 20 moving in the direction of arrow B, thereby forming a superimposed toner image in which the respective color toners are superimposed. Is done. The superimposed toner image on the intermediate transfer belt 20 is conveyed to a region (secondary transfer portion T) where the secondary transfer roll 22 is disposed as the intermediate transfer belt 20 moves. When the superimposed toner image is conveyed to the secondary transfer unit T, the sheet P is transferred from one of the selected sheet holding units 71a and 71b in accordance with the timing at which the superimposed toner image is conveyed to the secondary transfer unit T. It is supplied to the next transfer portion T. Then, the superimposed toner image is collectively electrostatically transferred onto the conveyed paper P by the action of the transfer electric field formed by the secondary transfer roll 22 in the secondary transfer portion T.

Thereafter, the sheet P on which the superimposed toner image is electrostatically transferred is peeled off from the intermediate transfer belt 20 and conveyed to the fixing device 60 by the conveying belts 76 and 77. The toner image on the paper P conveyed to the fixing device 60 is fixed on the paper P by receiving a fixing process using heat and pressure by the fixing device 60. Then, the paper P on which the fixed image is formed is conveyed to a paper discharge stacking unit (not shown) provided in the discharge unit of the image forming apparatus 1.
In this way, image formation in the image forming apparatus 1 is repeatedly executed for the number of printed sheets.

Next, the fixing device 60 used in the image forming apparatus 1 of the present embodiment will be described.
FIG. 2 is a side sectional view showing a configuration of the fixing device 60 of the present embodiment. The fixing device 60 includes a fixing belt module 61 and a pressure roll 62 disposed in pressure contact with the fixing belt module 61.
The fixing belt module 61 includes a fixing belt 610 as an example of a belt member, a fixing roll 611 that rotates while the fixing belt 610 is stretched, a tension roll 612 that stretches the fixing belt 610 from the inside, and a fixing belt 610 from the outside. An external heating roll 613 that stretches, a posture correction roll 614 that corrects the posture of the fixing belt 610 between the fixing roll 611 and the tension roll 612, and a nip that is a region where the fixing belt module 61 and the pressure roll 62 are pressed against each other. A separation pad 64 for separating the paper P from the fixing belt 610 and a downstream side of the nip portion N, and the fixing belt 610 is stretched around the fixing roll 611 again. An idler roll 615 that stretches the fixing belt 610 in the area up to .

The fixing roll 611 is made of, for example, a cylindrical core roll (core metal) made of aluminum having an outer diameter of 65 mm, a length of 360 mm, and a thickness of 10 mm, and a fluorine resin having a thickness of 200 μm as a protective layer for preventing metal wear on the core roll surface. It is a hard roll formed by coating. However, the fixing roll 611 is not limited to this configuration. When the nip portion N is formed between the fixing roll 611 and the pressure roll 62, the fixing roll 611 is sufficiently deformed with respect to the pressing force from the pressure roll 62. Any configuration that functions as a hard roll can be used. The fixing roll 611 receives a driving force from a driving motor (not shown) and rotates in the direction of arrow C at a surface speed of 440 mm / s, for example.
In addition, a halogen heater 616 a rated at 900 W is disposed as a heating source inside the fixing roll 611, and the image forming apparatus 1 is based on a measurement value of a temperature sensor 617 a disposed so as to contact the surface of the fixing roll 611. The controller 30 (see FIG. 1) controls the surface temperature of the fixing roll 611 to 150 ° C.

  The fixing belt 610 is a deformable endless belt having a circumferential length of 314 mm and a width of 340 mm, for example. The fixing belt 610 has a multilayer structure, for example, a base layer formed of a polyimide resin having a thickness of 80 μm and a silicone rubber having a thickness of 200 μm laminated on the surface side (outer peripheral surface side) of the base layer. And a release layer made of a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin (PFA) tube having a thickness of, for example, 30 μm and coated on the elastic layer. The elastic layer here is used to improve the image quality of the color image by deforming the surface of the fixing belt 610 following the unevenness of the toner image on the paper P and supplying heat uniformly to the entire toner image. Provided. Note that the material, thickness, hardness, and the like of the configuration of the fixing belt 610 are appropriately selected according to the apparatus design conditions such as the purpose of use and the use conditions. The fixing belt 610 is moved in the direction of arrow D by the fixing roll 611.

The tension roll 612 is a cylindrical roll formed of aluminum having an outer diameter of 30 mm, a thickness of 2 mm, and a length of 360 mm, for example. A halogen heater 616b rated at 1500 W is provided as a heating source inside the tension roll 612, and the surface temperature is controlled to 190 ° C. by the temperature sensor 617b and the control unit 30 (see FIG. 1). . Therefore, the tension roll 612 has both a function of stretching the fixing belt 610 and a function of heating the fixing belt 610 from the inner peripheral surface side.
Further, spring members (not shown) that press the fixing belt 610 outward are disposed at both ends of the tension roll 612. Thereby, the tension roll 612 has a function of adjusting the tension of the fixing belt 610 to a predetermined value (for example, 15 kgf).
Further, a belt edge position detection mechanism (not shown) for detecting the edge position of the fixing belt 610 is disposed in the vicinity of the tension roll 612. The tension roll 612 is provided with an axial displacement mechanism that displaces the contact position in the axial direction of the fixing belt 610 according to the detection result of the belt edge position detection mechanism, and controls the meandering (belt walk) of the fixing belt 610. It also functions as a meandering control roll (steering roll).
Such meandering control for the fixing belt 610 may be performed, for example, by the posture correction roll 614.

The external heating roll 613 is a cylindrical roll formed of aluminum having an outer diameter of 25 mm, a thickness of 2 mm, and a length of 360 mm, for example. Further, a release layer made of PFA having a thickness of 20 μm, for example, is formed on the surface of the external heating roll 613. This release layer is formed to suppress a slight amount of offset toner and paper powder from the outer peripheral surface of the fixing belt 610 from accumulating on the external heating roll 613.
Inside the external heating roll 613, a halogen heater 616 c rated at 1000 W is disposed as a heating source, and the surface temperature is controlled to 190 ° C. by the temperature sensor 617 c and the control unit 30 (see FIG. 1). . Therefore, the external heating roll 613 has both a function of stretching the fixing belt 610 and a function of heating the fixing belt 610 from the outer peripheral surface side.
As described above, the present embodiment employs a configuration in which the fixing belt 610 is heated by the fixing roll 611, the tension roll 612, and the external heating roll 613.

  The posture correction roll 614 is a cylindrical roll formed of aluminum having an outer diameter of 15 mm and a length of 360 mm, for example. The posture correction roll 614 has a function of correcting the posture of the fixing belt 610 that enters the nip portion N.

The peeling pad 64 is a block member having a substantially arc-shaped cross section, and is made of a rigid body such as a metal such as SUS or a highly rigid resin. Then, the entire area in the axial direction of the fixing roll 611 is located in the vicinity of the downstream side of the area where the pressure roll 62 is pressed against the fixing roll 611 via the fixing belt 610 (see “roll nip portion N1”: FIG. 3 in the subsequent stage). Fixedly arranged. Further, the peeling pad 64 is installed so as to uniformly press the fixing belt 610 toward the pressure roll 62 with a predetermined load (for example, 10 kgf), and the “peeling nip portion N2” described later (see FIG. 3 in the latter stage). ). That is, the peeling pad 64 is an example of a pressing member.
The idler roll 615 is an example of a stretch roll, and is a cylindrical roll formed of stainless steel having an outer diameter of 12 mm and a length of 360 mm, for example. Then, the fixing belt 610 that has passed through the peeling nip portion N2 is disposed near the downstream side in the moving direction of the fixing belt 610 of the peeling pad 64 so that the fixing belt 610 smoothly moves toward the fixing roll 611.

  Next, the pressure roll 62 includes, for example, a cylindrical roll 621 made of aluminum having a diameter of 45 mm and a length of 360 mm as a base, and an elastic layer 622 having a thickness of 10 mm made of silicone rubber and a film thickness of 100 μm in this order from the base. And a release layer 623 made of a PFA tube. The pressure roll 62 is installed so as to be pressed against the fixing belt module 61. As the fixing roll 611 of the fixing belt module 61 rotates in the direction of arrow C, the pressure roll 62 follows the fixing roll 611 and moves in the direction of arrow E. Rotate to. The moving speed is 440 mm / s, which is the same as the surface speed of the fixing roll 611.

Next, the nip portion N where the fixing belt module 61 and the pressure roll 62 are pressed against each other will be described.
FIG. 3 is a schematic cross-sectional view illustrating the configuration of the fixing device 60 in the vicinity of the nip portion N. As shown in FIG. 3, in the nip portion N where the fixing belt module 61 and the pressure roll 62 are pressed against each other, the fixing belt 610 is wound (wrapped) in the region (wrapped region) around the fixing roll 611. The pressure roll 62 is disposed so as to be in pressure contact with the outer peripheral surface of the fixing belt 610. Thereby, the roll nip portion N1 is formed.

Here, in the fixing device 60 of the present embodiment, as described above, the fixing roll 611 that is one of the rolls forming the roll nip portion N1 has a heat-resistant resin (fluororesin) on the surface of an aluminum core metal (core roll). ), And the fixing roll 611 is not provided with an elastic layer. The other pressure roll 62 that forms the roll nip portion N1 is a soft roll covered with an elastic layer 622.
With such a configuration of the fixing roll 611 and the pressure roll 62, the elastic layer 622 of the pressure roll 62 is deformed to form the roll nip portion N1. That is, in the roll nip portion N1, the fixing roll 611 is hardly depressed, and only the surface of the pressure roll 62 is depressed (the amount of depression of the pressure roll 62> the amount of depression of the fixing roll 611). A roll nip portion N1 having a predetermined width in the moving direction of the fixing belt 610 is created.
Thereby, in the roll nip portion N1, the fixing belt 610 rotates and moves along the circumferential surface of the surface of the fixing roll 611, and the rotation radius does not change. Therefore, the fixing belt 610 passes through the roll nip portion N1 while keeping the moving speed constant. Accordingly, when the fixing belt 610 passes through the roll nip portion N1, the fixing belt 610 is unlikely to be wrinkled or distorted. In the fixing device 60 of the present embodiment, the roll nip portion N1 is set to a width of about 15 mm along the moving direction of the fixing belt 610.

Further, a peeling pad 64 is disposed in the vicinity of the downstream side of the roll nip portion N1. Then, the peeling pad 64 presses the fixing belt 610 toward the surface of the pressure roll 62. As a result, a separation nip portion N2 in which the fixing belt 610 is wrapped on the surface of the pressure roll 62 is formed downstream of the roll nip portion N1.
As shown in FIG. 3, the peeling pad 64 forming the peeling nip portion N2 has a substantially arc-shaped cross section and is arranged along the axial direction of the fixing roll 611 in the vicinity of the downstream side of the roll nip portion N1. . Then, the fixing belt 610 after passing through the peeling nip portion N <b> 2 moves following the outer surface of the peeling pad 64. Accordingly, the moving direction of the fixing belt 610 is rapidly changed so as to be bent in the direction of the idler roll 615 by the peeling pad 64. Therefore, the sheet P that has passed through the roll nip portion N1 and the separation nip portion N2 cannot follow the change in the moving direction of the fixing belt 610 at the time of exiting the separation nip portion N2, and the sheet P has its own rigidity (so-called “koshi”). ) From the fixing belt 610. In this way, separation from the paper P (so-called “curvature separation”) is performed at the exit of the separation nip N2. In the fixing device 60 of the present embodiment, the peeling nip portion N2 is set to a width of about 8.5 mm along the moving direction of the fixing belt 610.

Next, the arrangement position of the peeling pad 64 and the nip pressure distribution (nip pressure profile) of the peeling nip portion N2 formed by the peeling pad 64 will be described.
As described above, the peeling pad 64 is disposed in the vicinity of the downstream side of the roll nip portion N1. As a result, in the nip portion N composed of the roll nip portion N1 and the peeling nip portion N2, the position where the nip pressure peaks in the roll nip portion N1 (see FIG. 5 in the subsequent stage) reaches the most downstream position of the peeling nip portion N2. In such a region, the generation of a valley region in which the nip pressure drops below a predetermined value is suppressed, and the nip pressure is set to continuously and monotonously decrease.
Here, first, the peeling pad 64 disposed in the vicinity of the downstream side of the roll nip portion N1 suppresses the generation of a valley region where the nip pressure drops below a predetermined value, and the nip pressure continues in the nip portion N. The points set to monotonously decrease will be described.

In the fixing device 60 of the present embodiment, a fixing belt module 61 is used in which a fixing belt 610 as a heating member is stretched by a plurality of rolls including a fixing roll 611. Such a configuration using the fixing belt module 61 maintains a predetermined fixing temperature in the fixing device 60 even when the speed of the image forming apparatus 1 is increased as described later. The occurrence of a so-called “temperature droop phenomenon” in which the fixing temperature drops at the start of operation is suppressed.
However, even in the fixing device 60 using the fixing belt module 61, since the toner image is held on the surface of the paper P, when the toner image is melted by the heat of the fixing belt 610, the toner image is bonded to the adhesive. Thus, an adhesive force acts between the paper P and the fixing belt 610. For this reason, it is necessary to provide a mechanism for peeling the paper P from the surface of the fixing belt 610 as in the conventional fixing device. In particular, when the speed of the image forming apparatus 1 is increased, if a separation failure occurs once in the fixing device 60 and a paper jam occurs, the number of subsequent sheets P damaged due to the influence increases. . For this reason, it is necessary to stably and reliably peel the sheet P that has passed through the nip N at a high speed from the fixing belt 610 side.

At this time, if a conventional separation claw is used as a mechanism for separating the paper P from the surface of the fixing belt 610, the separation claw is applied to the fixing belt 610 in order to stably peel the paper P from the fixing belt 610 side. It must be placed in contact. Therefore, when the separation claw is used, the surface of the fixing belt 610 is easily worn by the separation claw, and the following problems are likely to occur. In other words, wear marks due to the separation claws are generated on the surface of the fixing belt 610, and fixing unevenness corresponding to the wear marks on the surface of the fixing belt 610 may occur on the fixed image, thereby reducing the image quality. Further, the offset toner may gradually adhere to and accumulate on the wear scar, causing stain on the fixed image. Furthermore, when the surface of the fixing belt 610 having a thin film progresses, the fixing belt 610 eventually breaks, and the function of the fixing device 60 may be impaired. Therefore, in order to perform sheet separation in the fixing belt module 61 using the fixing belt 610, as described above, a peeling mechanism by curvature separation that does not require a contact member such as a separation claw is suitable.
Therefore, in the fixing belt module 61 of the present embodiment, the peeling member, that is, the peeling pad 64 that peels the paper P from the fixing belt 610 by changing the moving direction of the fixing belt 610 abruptly downstream of the nip portion N is provided. Provided.

However, when the peeling nip portion N2 is formed continuously with the roll nip portion N1 by providing the peeling pad 64, the region where the peeling pad 64 is disposed in the peeling nip portion N2 (the peeling pad 64 and the pressure roll 62). In the boundary region N2S (see FIG. 3) located closer to the roll nip portion N1 than the N2T, there is no member that directly presses the fixing belt 610 to either the fixing roll 611 or the pressure roll 62. Therefore, the boundary region N2S is pressed against the pressure roll 62 only by the tension of the fixing belt 610, and the nip pressure in the boundary region N2S (hereinafter, the nip pressure in the boundary region N2S is referred to as Pn). It is formed only by the tension of the fixing belt 610. For this purpose, when the separation pad 64 is arranged at a predetermined distance or more from the downstream end N1E (see FIG. 3) of the roll nip N1, the nip pressure Pn in the boundary region N2S is equal to the nip pressure of the roll nip N1. A gap between the nip pressure in the region N2T in which the peeling pad 64 is disposed is formed as a valley region where the nip pressure Pn falls below a predetermined value (referred to as Pn1). The nip pressure Pn in the boundary region N2S is relatively lower than the nip pressure in the roll nip portion N1 and the nip pressure in the region N2T in which the peeling pad 64 is disposed.
Here, FIG. 4 shows the nip pressure profile of the nip portion N (the roll nip portion N1 and the peeling nip portion N2) when the peeling pad 64 is disposed at a predetermined distance or more away from the downstream end N1E of the roll nip portion N1. FIG. As shown in FIG. 4, in this case, in the peeling nip portion N2, a valley region where the nip pressure Pn drops below a predetermined value Pn1 is formed in the boundary region N2S with the roll nip portion N1.

By the way, in the fixing process by the fixing device 60 of the present embodiment, the paper P holding the toner image is heated and pressed in the roll nip portion N1, and the toner is melt-pressed. At that time, the water in the paper P vaporizes from the paper P and the toner that have received heat in the roll nip portion N1 to generate water vapor, or the air in the toner tends to thermally expand. However, since a high nip pressure is applied at the roll nip portion N <b> 1, an air gap (bubble) due to water vapor or expanded air hardly occurs between the fixing belt 610 and the pressure roll 62.
However, when the nip pressure Pn in the boundary region N2S with the roll nip portion N1 in the peeling nip portion N2 is formed in a low state that is equal to or lower than a predetermined value Pn1, bubbles that have been suppressed in the roll nip portion N1 are generated in the boundary region N2S. Occurs without being suppressed. Then, when the paper P enters the high nip pressure region N2T where the peeling pad 64 is disposed in a state where bubbles are generated, the bubbles generated in the boundary region N2S move around on the surface of the paper P due to the high nip pressure. . As a result, the toner image on the paper P is immediately after passing through the roll nip portion N1, and the melted toner is not yet completely solidified. Arise.

Therefore, in the fixing device 60 of the present embodiment, the peeling pad 64 is disposed in the vicinity of the downstream side of the roll nip portion N1. By disposing the peeling pad 64 in this way, the width of the boundary region N2S between the roll nip portion N1 and the region N2T where the peeling pad 64 is disposed in the peeling nip portion N2 is set as narrow as possible. As a result, the area pressed against the pressure roll 62 only by the tension of the fixing belt 610 is narrowed. Therefore, as shown in FIG. 5 (a diagram showing an outline of the nip pressure profile of the nip portion N when the peeling pad 64 of the present embodiment is disposed), the nip pressure Pn is a predetermined value Pn1 in the boundary region N2S. It is possible to suppress the generation of a valley region that falls more than that. Accordingly, the nip pressure is set so as to continuously and monotonously decrease in a region from the position where the nip pressure reaches a peak in the roll nip portion N1 in the nip portion N to the most downstream position of the peeling nip portion N2.
Thus, since the nip pressure Pn of the boundary region N2S is set higher than the predetermined Pn1, the generation of bubbles in the boundary region N2S is suppressed. Furthermore, the nip pressure in the roll nip portion N1 is set so as to continuously and monotonically decrease from the peak position to the most downstream position of the peeling nip portion N2, thereby suppressing the nip pressure in the roll nip portion N1. The water vapor or air that is about to expand is gradually released along the path until it passes through the peeling nip portion N2, and the phenomenon of bubbles moving around as described above is suppressed. Therefore, the disturbance of the toner image that has not been completely solidified is suppressed.

Here, in order to suppress the generation of bubbles in the boundary region N2S, the pressure (nip pressure) Pn in the boundary region N2S needs to satisfy the following expression (1).
Pn ≧ Po × (Tn / To−1) (1)
That is, the predetermined value Pn1 of the nip pressure Pn in the boundary region N2S described above is
Pn1 = Po × (Tn / To−1)
It becomes.
Tn is the absolute temperature of the fixing belt 610, To is the absolute temperature of air (environment temperature) at a position sufficiently away from the fixing roll 611, and Po is atmospheric pressure.

Equation (1) is derived as follows. First, the equation of state of the ideal gas is expressed by the following equation (2).
PV = nRT (2)
In addition, P is a pressure, V is a volume, n is the number of moles, R is a gas constant, and T is an absolute temperature.
Therefore, the following equations (3) and (4) are derived.
(Po + Pn) × Vn = nRTn (3)
PoVo = nRTo (4)
Vn is the volume of bubbles in the boundary region N2S, and Vo is the volume of bubbles under atmospheric pressure. In order to suppress the generation of bubbles in the boundary region N2S, the condition Vn ≦ Vo may be satisfied. Therefore, the following equation (5) is derived from the equations (3) and (4).
Tn / (Po + Pn) ≦ To / Po (5)
Further, when the equation (5) is modified, the above equation (1) is derived.
And the peeling pad 64 is arrange | positioned in the downstream vicinity position of the roll nip part N1 so that the sufficiently narrow boundary area | region N2S used as the nip pressure Pn which satisfy | fills Formula (1) may be formed.

Next, the configuration of the peeling pad 64 disposed in the vicinity of the downstream side of the roll nip portion N1 will be described.
FIG. 6 is a schematic cross-sectional view showing the periphery of a region where the peeling pad 64 is disposed. As shown in FIG. 6, the peeling pad 64 includes an inner side surface 64a facing the fixing roll 611 side, an outer side surface 64b that rapidly changes the moving direction of the fixing belt 610 that has passed through the peeling nip portion N2, and a fixing belt 610. A pressing surface 64 c that presses toward the pressing roll 62 is formed.
The inner surface 64a of the peeling pad 64 is arranged around the fixing roll 611 in order to place the peeling pad 64 as close as possible to the fixing roll 611 side (for example, the gap between the peeling pad 64 and the fixing roll 611 is 0.5 mm). It is formed with a curved surface following the surface. That is, in order to set the boundary region N2S shown in FIG. 6 as narrow as possible, it is defined by the fixing roll 611 and the pressure roll 62 in the vicinity of the downstream side of the roll nip portion N1 (see also FIG. 3). In the wedge-shaped region Q, it is necessary to arrange the peeling pad 64 so as to press the surface of the pressure roll 62. Therefore, the upstream end portion (upstream end portion of the pressing surface 64c) 64p of the inner surface 64a is located near the downstream end portion N1E of the roll nip portion N1, that is, the position close to the fixing roll 611 in the wedge-shaped region Q described above. The inner side surface 64 a is formed in a curved surface that follows the peripheral surface of the fixing roll 611. In the peeling pad 64 of the present embodiment, the inner side surface 64a is formed by a substantially circumferential surface having a curvature radius of 33 mm. The inner side surface 64a is not limited to a curved surface such as a substantially circumferential surface as long as it is a curved surface that follows the peripheral surface of the fixing roll 611, and may be formed by bending a plurality of flat surfaces in stages.
In addition, the upstream end portion 64p of the inner side surface 64a is installed at a position close to the fixing roll 611 in the wedge-shaped region Q, and in order to ensure the strength and rigidity of the upstream end portion 64p portion, The angle θ1 formed between the side surface 64a and the pressing surface 64c is preferably set to 20 to 50 °.

  The pressing surface 64 c of the peeling pad 64 is a surface that presses the fixing belt 610 against the pressure roll 62 and presses against the surface of the pressure roll 62. Therefore, the pressing surface 64 c is formed as a flat surface so that the fixing belt 610 is uniformly pressed against the pressure roll 62. Furthermore, the pressing surface 64c may be formed as a concave curved surface that follows the circumferential surface of the pressure roll 62, thereby increasing the uniformity of the pressing force.

  The outer surface (side surface portion) 64b of the peeling pad 64 guides the fixing belt 610 in cooperation with the idler roll 615 and the fixing roll 611, and peels the paper P from the fixing belt 610 by changing the moving direction rapidly. It is a surface to do. Therefore, in the upstream end region of the outer surface 64 b, that is, in the region (peeling region) R where the fixing belt 610 is separated from the pressure roll 62 so that the paper P is peeled from the fixing belt 610, The angle θ2 (see FIG. 6) formed by the tangent line and the tangent line of the outer surface 64b is set to be 25 ° or more. In addition, in the peeling region R, the outer surface 64b is formed as a curved surface so that the fixing belt 610 smoothly moves in the peeling region R that is bent sharply.

  Further, the outer surface 64 b of the peeling pad 64 is a plane inclined toward the idler roll 615 so that the fixing belt 610 moves smoothly in the direction of the idler roll 615 and the fixing roll 611 after the fixing belt 610 is separated from the pressure roll 62. Formed with. The outer side surface 64 b constitutes a part of the outer side surface 64 b (that is, a support surface that supports the inner peripheral surface of the fixing belt 610) and is an example of a belt support unit that applies tension to the fixing belt 610. The tension applying member 641 and a pressing member 642 as an example of a pressing portion that presses the tension applying member 641 toward the fixing belt 610 are provided. The tension applying member 641 and the pressing member 642 constitute tension applying means.

The tension applying member 641 is formed of a rigid body such as a metal such as SUS or a highly rigid resin. The side surface of the tension applying member 641 facing the fixing belt 610 constitutes a part of the outer side surface 64 b of the peeling pad 64. Therefore, the side surface of the tension applying member 641 facing the fixing belt 610 is formed by a plane inclined toward the continuous idler roll 615 from the outer surface 64b on the peeling region R side. For this reason, the side surface facing the fixing belt 610 is rubbed against the inner peripheral surface of the fixing belt 610, so that the fixing belt 610 moves smoothly. For example, Teflon having a small friction coefficient and excellent wear resistance is provided. (Registered trademark) or the like may be covered.
On the other hand, the side surface of the tension applying member 641 on the fixing roll 611 side is supported by the pressing member 642 and is pressed to the fixing belt 610 side by the pressing member 642.

  The pressing member 642 is configured by a plate-like member made of an elastic body such as foamed urethane rubber having a predetermined thickness and a predetermined elastic modulus. As shown in FIG. 6, one surface is supported by the peeling pad 64, and the other surface supports the tension applying member 641. Then, the tension applying member 641 is pressed to the fixing belt 610 side with a predetermined pressing force, and the fixing belt 610 moves away from the pressure roll 62 toward the idler roll 615 as described later. In the region, tension is applied to the fixing belt 610. As a result, the fixing belt 610 is restrained from being slackened in the region between the pressure roll 62 and the idler roll 615, and the fixing belt 610 is separated from the outer surface 64b in the peeling region R (the state where it is lifted). ).

  By the way, in a region between the pressure roll 62 and the idler roll 615, a peeling nip portion N2 which is a high nip pressure region is formed on the upstream side. Further, on the downstream side, there are a region where the fixing belt 610 contacts the outer surface 64 b of the peeling pad 64 and a region where the fixing belt 610 receives a frictional force from the idler roll 615. Then, a frictional force acts on the fixing belt 610 in each of the regions. Therefore, in the region between the pressure roll 62 and the idler roll 615, the tension of the fixing belt 610 is likely to be influenced by the fluctuation of the frictional force between any of these and the fixing belt 610. For example, when the frictional force between the idler roll 615 and the fixing belt 610 is relatively increased, the driving force from the idler roll 615 is increased and the tension of the fixing belt 610 is increased. On the other hand, when the frictional force between the peeling nip portion N2 and the fixing belt 610 is relatively increased, the driving force acting on the fixing belt 610 from the peeling nip portion N2 is increased, and the tension of the fixing belt 610 is reduced. Similarly, if the frictional force between the outer surface 64b of the peeling pad 64 and the fixing belt 610 becomes relatively large, the tension of the fixing belt 610 in the peeling region R decreases.

As described above, when the frictional force between the peeling nip portion N2 and the fixing belt 610 or the frictional force between the outer surface 64b of the peeling pad 64 and the fixing belt 610 becomes relatively large, the fixing belt in the peeling region R is obtained. The tension at 610 decreases.
FIG. 7 is a view showing a state in which the tension of the fixing belt 610 in the peeling region R is lowered in a configuration in which the tension applying member 641 and the pressing member 642 are not provided on the outer side surface 64b of the peeling pad 64. In this case, as shown in FIG. 7, the fixing belt 610 is loosened in the peeling region R. When the fixing belt 610 is loosened in the peeling region R, the angle θ3 formed between the tangent of the pressure roll 62 and the fixing belt 610 in the peeling region R is formed by the tangent of the pressure roll 62 and the tangent of the outer surface 64b. It becomes smaller than the angle θ2 (see also FIG. 6). That is, the angle θ3 <angle θ2. For this reason, the fixing belt 610 cannot be bent sharply in the peeling region R, and the paper P cannot be peeled by the curvature separation in the peeling region R.

On the other hand, in the fixing device 60 of the present embodiment, the tension applying member 641 that applies tension to the fixing belt 610 and the tension applying member 641 are pressed against the outer surface 64b of the peeling pad 64 toward the fixing belt 610. A pressing member 642 is provided. The pressing member 642 expands and contracts according to the force that the tension applying member 641 receives from the tension of the fixing belt 610. Therefore, when the tension of the fixing belt 610 decreases, the tension applying member 641 is pushed out to the fixing belt 610 side, and the extension is stopped at a position where the tension applying member 641 balances the force received from the tension of the fixing belt 610. . As a result, in the region between the pressure roll 62 and the idler roll 615, the tension of the fixing belt 610 is suppressed from decreasing below a predetermined value.
FIG. 8 illustrates the fixing device 60 according to the present embodiment in which the tension applying member 641 and the pressing member 642 are provided on the outer side surface 64b of the peeling pad 64, and the tension of the fixing belt 610 in the peeling region R decreases to a predetermined value or less. It is the figure which showed the state in which this is suppressed. As shown in FIG. 8, when the tension of the fixing belt 610 decreases, the pressing member 642 pushes the tension applying member 641 toward the fixing belt 610, whereby tension is applied to the fixing belt 610. Accordingly, the angle θ2 ′ formed between the tangent line of the pressure roll 62 and the fixing belt 610 in the peeling region R is equal to the tangent line of the pressure roll 62 and the fixing belt 610 in a configuration in which the tension applying member 641 and the pressing member 642 are not provided. Is corrected to a state substantially the same as the angle θ2 (see FIG. 6) formed by the tangent line of the pressure roll 62 and the tangent line of the outer surface 64b. That is, the angle θ2′≈the angle θ2 (the angle formed by the tangent line of the pressure roll 62 and the tangent line of the outer surface 64b). As a result, the abrupt bent shape of the fixing belt 610 is maintained in the peeling region R, and the paper P is peeled off by the curvature separation in the peeling region R.

Here, the thickness and elastic modulus of the pressing member 642 correspond to the amount of fluctuation in the tension of the fixing belt 610 in the region between the pressure roll 62 and the idler roll 615, and at least the fixing belt 610 in the peeling region R. The tension is set so as to be kept substantially constant.
Further, although the pressing member 642 of the present embodiment has been illustrated as a plate-shaped member made of an elastic body such as foamed urethane rubber, it may be configured using an elastic member such as a spring member. Good.

  As described above, in the fixing device 60 of the present embodiment, as an example of a tension applying unit, the tension applying member 641 that applies tension to the fixing belt 610 and the tension applying member 641 are applied to the outer surface 64b of the peeling pad 64. And a pressing member 642 that presses the fixing belt 610 toward the fixing belt 610 side. Accordingly, when the tension of the fixing belt 610 decreases, the pressing member 642 pushes the tension applying member 641 toward the fixing belt 610 to add tension to the fixing belt 610, and the tension of the fixing belt 610 becomes a predetermined value or less. Decrease is suppressed. Therefore, in the peeling region R where the fixing belt 610 is separated from the pressure roll 62, the angle θ2 ′ formed between the tangent to the pressure roll 62 and the fixing belt 610 is maintained to be equal to or greater than the angle at which the sheet P is subjected to curvature separation.

Next, a fixing operation in the fixing device 60 of the present embodiment will be described.
The sheet P on which the unfixed toner image is electrostatically transferred in the secondary transfer portion T (see FIG. 1) of the image forming apparatus 1 is transferred to the nip of the fixing device 60 by the conveyance belts 76 and 77 and the inlet guide 78 of the fixing device 60. It is conveyed toward the portion N (see FIG. 2: arrow F direction). The unfixed toner image on the surface of the paper P passing through the nip portion N is fixed on the paper P mainly by pressure and heat acting on the roll nip portion N1.

  At this time, in the fixing device 60 of the present embodiment, heat acting on the nip portion N is mainly supplied by the fixing belt 610. The fixing belt 610 includes heat supplied from the halogen heater 616a disposed inside the fixing roll 611 through the fixing roll 611, and heat supplied from the halogen heater 616b disposed inside the tension roll 612 through the tension roll 612. The heater is configured to be heated by heat supplied through the external heating roll 613 from the halogen heater 616c disposed inside the external heating roll 613. Therefore, heat energy is replenished to the fixing belt 610 promptly mainly from the tension roll 612 and the external heating roll 613, so that a sufficient amount of heat is secured at the nip portion N even at a high process speed of 440 mm / s. Is done.

That is, in the fixing device 60 of the present embodiment, the fixing belt 610 that functions as a direct heating member has a small heat capacity. In addition, the fixing belt 610 is configured to contact the fixing roll 611 that is a heat supply member, the tension roll 612, and the external heating roll 613 with a wide lap area (large wrap angle). Therefore, since a sufficient amount of heat is supplied from the fixing roll 611, the tension roll 612, and the external heating roll 613 within a short period of one rotation of the fixing belt 610, the fixing belt 610 returns to the necessary fixing temperature in a short time. . Thereby, in the nip portion N, a predetermined fixing temperature is maintained even if the fixing device 60 is speeded up.
As a result, the fixing temperature is maintained substantially constant even during continuous paper feeding. Further, the occurrence of a temperature droop phenomenon in which the fixing temperature drops at the start of the high-speed fixing operation is suppressed. In particular, maintenance of the fixing temperature and occurrence of temperature droop are suppressed even when fixing on thick paper having a large heat capacity. Further, when it is necessary to switch the fixing temperature in the middle (including both fixing temperature up and down) corresponding to the paper type, the fixing belt 610 has a small heat capacity, so the halogen heater 616a, By adjusting the outputs of the halogen heater 616b and the halogen heater 616c, switching to a desired temperature is easily and quickly performed.

Subsequently, after passing through the roll nip portion N1, the paper P is conveyed to the peeling nip portion N2. In the peeling nip portion N <b> 2, the peeling pad 64 is pressed against the pressure roll 62, and the fixing belt 610 is pressed against the pressure roll 62. Therefore, as shown in FIG. 3, the roll nip portion N1 forms a curved shape that is convex downward due to the curvature of the fixing roll 611, whereas the peeling nip portion N2 is convex upward due to the curvature of the pressure roll 62. To form a curved shape.
For this reason, the sheet P heated and pressed under the curvature of the fixing roll 611 at the roll nip portion N1 changes the moving direction to a curvature directed in the opposite direction by the pressure roll 62 at the peeling nip portion N2. At that time, a minute micro slip occurs between the toner image on the paper P and the surface of the fixing belt 610. As a result, the adhesion between the toner image and the fixing belt 610 is weakened, and a state is formed in which the paper P is easily peeled off from the fixing belt 610. Therefore, the peeling nip portion N2 is also positioned in a preparation process for surely peeling in the final peeling process.

At the exit (peeling region R) of the peeling nip portion N2, the fixing belt 610 is conveyed so as to be wound around the peeling pad 64, so that the moving direction of the fixing belt 610 changes abruptly there. That is, since the fixing belt 610 moves along the outer surface 64b of the peeling pad 64, the bending of the fixing belt 610 becomes large. Therefore, the paper P whose adhesion to the fixing belt 610 is weakened in advance in the peeling nip portion N2 is peeled from the fixing belt 610 by the stiffness of the paper that the paper P itself has.
In particular, in the region between the pressure roll 62 and the idler roll 615, for example, the frictional force between the idler roll 615 and the fixing belt 610, the frictional force between the peeling nip portion N2 and the fixing belt 610, and the outer surface of the peeling pad 64 Even when one or more of the frictional forces between 64b and the fixing belt 610 vary, the large bent shape of the fixing belt 610 in the peeling region R is maintained.
The moving direction of the paper P separated from the fixing belt 610 is guided by a peeling guide plate 83 as an example of a peeling auxiliary member disposed on the downstream side of the peeling nip portion N2. The paper P guided by the peeling guide plate 83 is then discharged out of the apparatus by the paper discharge guide 65 and the paper discharge roll 66 (see FIG. 2), and the fixing process is completed.

  As described above, in the fixing device 60 of the present embodiment, the tension applying member 641 that applies tension to the fixing belt 610 as an example of the tension applying unit on the outer surface 64b of the peeling pad 64, and the tension applying A pressing member 642 that presses the member 641 toward the fixing belt 610 is provided. Accordingly, when the tension of the fixing belt 610 decreases, the pressing member 642 pushes the tension applying member 641 toward the fixing belt 610 to add tension to the fixing belt 610, and the tension of the fixing belt 610 becomes a predetermined value or less. Decrease is suppressed. Therefore, in the peeling region R where the fixing belt 610 is separated from the pressure roll 62, the angle θ2 ′ formed between the tangent to the pressure roll 62 and the fixing belt 610 is maintained to be equal to or greater than the angle at which the sheet P is subjected to curvature separation. As a result, the occurrence of slack in the fixing belt 610 that has passed through the peeling nip portion N2 is suppressed, and the peeling performance in the peeling region R is improved.

[Embodiment 2]
In the first embodiment, a configuration in which a tension applying member 641 and a pressing member 642 are provided as an example of a tension applying unit that applies tension to the fixing belt 610 on the outer surface 64b of the peeling pad 64 in the fixing device 60 will be described. did. In the present embodiment, a configuration in which the idler roll 615 also functions as a tension applying unit will be described. In addition, the same code | symbol is used about the structure similar to Embodiment 1, and the detailed description is abbreviate | omitted here.

  FIG. 9 is a side cross-sectional view showing a mechanism for suppressing the loosening of the fixing belt 610 in the peeling region R in the fixing device 60 of the present embodiment. FIG. 10 is a diagram showing a configuration in the longitudinal direction of a mechanism for suppressing the loosening of the fixing belt 610 in the peeling region R. As shown in FIG. 9, the fixing device 60 of the present embodiment includes a support frame 100 that rotatably supports a rotation shaft 615 a of an idler roll 615 as an example of a tension roll that constitutes a part of a tension applying unit. A spring as an example of a pressing portion that is disposed between the support frame 100 and the peeling pad 64 and constitutes a part of tension applying means that presses the idler roll 615 toward the fixing belt 610 via the support frame 100. A member 110 is provided. That is, one end of the spring member 110 is supported by the support frame 100 and the other end is supported by the peeling pad 64.

  Further, as shown in FIG. 10, a plurality of spring members 110 are arranged in the longitudinal direction of the idler roll 615. Further, the idler roll 615 is set so as to be in contact with a low friction sheet member 115 made of, for example, Teflon (registered trademark) having a small friction coefficient and excellent wear resistance disposed on the inner surface of the support frame 100. Is done. As a result, the entire longitudinal direction of the idler roll 615 is pressed toward the fixing belt 610 with an equal pressing force by the spring members 110 arranged in the longitudinal direction via the support frame 100 and the low friction sheet member 115. At that time, the idler roll 615 rotates smoothly by contact with the low friction sheet member 115.

With such a configuration, when the tension of the fixing belt 610 decreases, the spring member 110 pushes the idler roll 615 to the fixing belt 610 side. As a result, tension is applied to the fixing belt 610, and the tension of the fixing belt 610 is suppressed from decreasing below a predetermined value. Therefore, in the peeling region R where the fixing belt 610 is separated from the pressure roll 62, the angle θ2 ′ formed between the tangent to the pressure roll 62 and the fixing belt 610 is maintained to be equal to or greater than the angle at which the sheet P is subjected to curvature separation.
Further, since one end of the spring member 110 is supported by the support frame 100 and the other end is supported by the peeling pad 64, a pressing force is applied so that the peeling pad 64 presses the pressure roll 62. As a result, the amount of the peeling pad 64 entering the surface of the pressure roll 62, that is, the amount of depression of the surface of the pressure roll 62 by the peeling pad 64 increases, and the bending angle of the fixing belt 610 in the peeling region R (the angle shown in FIG. 6). Increase θ2).

  Here, a plurality of spring members 110 arranged in the longitudinal direction of the idler roll 615 may have different spring coefficients so that, for example, the fixing belt 610 is less likely to meander. For example, the spring coefficient of the spring member 110 disposed at the center in the longitudinal direction of the idler roll 615 may be configured to be large, and the spring coefficient of the spring member 110 disposed on both ends may be configured to be small.

[Embodiment 3]
In the second embodiment, the configuration in which the idler roll 615 also functions as a tension applying unit has been described. In this embodiment, another configuration that allows the idler roll 615 to function as a tension applying unit will be described. Note that the same reference numerals are used for the same configurations as those in the first embodiment, and the detailed description thereof is omitted here. .

FIG. 11 is a side cross-sectional view showing a mechanism for suppressing the loosening of the fixing belt 610 in the peeling region R in the fixing device 60 of the present embodiment. As shown in FIG. 11, the fixing device 60 according to the present embodiment includes a support frame 101 that rotatably supports a rotating shaft 615a of an idler roll 615 as an example of a tension roll that constitutes a part of a tension applying unit. A pressing portion that is disposed between the support frame 101 and the body-side support member 118 of the fixing device 60 and constitutes part of a tension applying unit that presses the idler roll 615 toward the fixing belt 610 via the support frame 101. As an example, a spring member 111 is provided.
With such a configuration, when the tension of the fixing belt 610 decreases, the spring member 111 pulls the idler roll 615 to the fixing belt 610 side. As a result, tension is applied to the fixing belt 610, and the tension of the fixing belt 610 is suppressed from decreasing below a predetermined value. Therefore, in the peeling region R where the fixing belt 610 is separated from the pressure roll 62, the angle θ2 ′ formed between the tangent to the pressure roll 62 and the fixing belt 610 is maintained to be equal to or greater than the angle at which the sheet P is subjected to curvature separation.

1 is a diagram illustrating an overall configuration of an image forming apparatus to which Embodiment 1 is applied. FIG. 3 is a side cross-sectional view illustrating a configuration of the fixing device according to the first embodiment. 2 is a schematic cross-sectional view illustrating a configuration of a fixing device in a region near a nip portion. FIG. It is the figure which showed the outline of the nip pressure distribution of a nip part when a peeling pad is spaced apart and arrange | positioned more than predetermined distance from a roll nip part. It is the figure which showed the outline of nip pressure distribution at the time of arrange | positioning a peeling pad in the downstream vicinity of a roll nip part. It is a schematic sectional drawing showing the periphery of the area | region where the peeling pad is arrange | positioned. FIG. 6 is a view showing a state in which the tension of the fixing belt in the peeling region is lowered in a configuration in which a tension applying member and a pressing member are not provided on the outer surface of the peeling pad. In the fixing device according to the first embodiment in which a tension applying member and a pressing member are provided on the outer surface of the peeling pad, a diagram illustrating a state in which the tension of the fixing belt in the peeling region is suppressed from being reduced to a predetermined value or less. is there. FIG. 10 is a side cross-sectional view showing a mechanism that suppresses the occurrence of slack in the fixing belt in the peeling region in the fixing device according to the second embodiment. FIG. 5 is a diagram illustrating a configuration in a longitudinal direction of a mechanism that suppresses occurrence of loosening of a fixing belt in a peeling region. FIG. 10 is a side cross-sectional view illustrating a mechanism that suppresses the occurrence of loosening of the fixing belt in the peeling region in the fixing device according to the third embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 11 (11Y, 11M, 11C, 11K) ... Image forming unit, 20 ... Intermediate transfer belt, 60 ... Fixing device, 61 ... Fixing belt module, 62 ... Pressure roll, 64 ... Release pad, 100 , 101 ... Support frame, 110, 111 ... Spring member, 610 ... Fixing belt, 611 ... Fixing roll, 615 ... Idler roll, 641 ... Tension applying member, 642 ... Pressing member

Claims (6)

A belt member that is formed in a belt shape and moves while being heated;
A fixing roll formed in a roll shape and stretching the belt member;
The belt member is arranged to press the fixing roll in an area where the belt member is in contact with the fixing roll to form a nip area, and a recording material holding a toner image is passed through the nip area to fix the toner image. A pressure roll to
A pressing unit that presses the belt member against the pressure roll in a region downstream of the nip region in the moving direction of the belt member and upstream of a region where the belt member contacts the fixing roll; A pressing member having,
On the downstream side in the moving direction of the belt member in the region where the pressing portion of the pressing member presses the belt member against the pressure roll, and on the upstream side in the region where the belt member contacts the fixing roll. Tension applying means for applying tension to the belt member in a certain region,
It said tensioning means, said pressing portion is disposed on the side surface of the pressing member in contact with the belt member after passing through an area for pressing said belt member to the pressurizing roll, an inner periphery of the belt member A fixing device comprising: a belt support portion having a support surface that supports the surface; and a pressing portion that presses the belt support portion toward the belt member . A belt member that is formed in a belt shape and moves while being heated;
A fixing roll formed in a roll shape and stretching the belt member;
The belt member is arranged to press the fixing roll in an area where the belt member is in contact with the fixing roll to form a nip area, and a recording material holding a toner image is passed through the nip area to fix the toner image. A pressure roll to
A pressing member that presses the belt member against the pressure roll in a region downstream of the nip region in the moving direction of the belt member and upstream of a region where the belt member contacts the fixing roll; ,
In the region where the pressing member is on the downstream side in the moving direction of the belt member in the region where the belt member is pressed against the pressure roll, and on the upstream side in the region where the belt member is in contact with the fixing roll A tension applying means for applying tension to the belt member;
The tension applying means includes a roll-shaped tension roll that stretches the belt member, and a pressing portion that presses the tension roll toward the belt member, and the pressing portion presses the pressing member. A fixing device that presses against a belt member. The fixing device according to claim 2 , wherein the tension applying unit includes a plurality of the pressing portions having different spring constants along a longitudinal direction of the stretching roll. Toner image forming means for forming a toner image;
Transfer means for transferring the toner image formed by the toner image forming means onto a recording material;
Fixing means for fixing the toner image transferred onto the recording material to the recording material;
The fixing means is
A belt member that is formed in a belt shape and moves while being heated;
A fixing roll formed in a roll shape and stretching the belt member;
The belt member is arranged to press the fixing roll in an area where the belt member is in contact with the fixing roll to form a nip area, and a recording material holding a toner image is passed through the nip area to fix the toner image. A pressure roll to
A pressing unit that presses the belt member against the pressure roll in a region downstream of the nip region in the moving direction of the belt member and upstream of a region where the belt member contacts the fixing roll; A pressing member having,
On the downstream side in the moving direction of the belt member in the region where the pressing portion of the pressing member presses the belt member against the pressure roll, and on the upstream side in the region where the belt member contacts the fixing roll. Tension applying means for applying tension to the belt member in a certain region,
Wherein the tensioning means of the fixing means is arranged on the side surface of the pressing member in contact with the belt member after the pressing portion has passed through an area for pressing said belt member to the pressurizing roll, the belt An image forming apparatus comprising: a belt support portion having a support surface that supports an inner peripheral surface of a member; and a pressing portion that presses the belt support portion toward the belt member . Toner image forming means for forming a toner image;
Transfer means for transferring the toner image formed by the toner image forming means onto a recording material;
Fixing means for fixing the toner image transferred onto the recording material to the recording material;
The fixing means is
A belt member that is formed in a belt shape and moves while being heated;
A fixing roll formed in a roll shape and stretching the belt member;
The belt member is arranged to press the fixing roll in an area where the belt member is in contact with the fixing roll to form a nip area, and a recording material holding a toner image is passed through the nip area to fix the toner image. A pressure roll to
A pressing member that presses the belt member against the pressure roll in a region downstream of the nip region in the moving direction of the belt member and upstream of a region where the belt member contacts the fixing roll; ,
In the region where the pressing member is on the downstream side in the moving direction of the belt member in the region where the belt member is pressed against the pressure roll, and on the upstream side in the region where the belt member is in contact with the fixing roll A tension applying means for applying tension to the belt member;
The tension applying unit of the fixing unit includes a roll-shaped stretching roll that stretches the belt member, and a pressing portion that presses the stretching roll toward the belt member. An image forming apparatus, wherein the member is pressed toward the belt member. The image forming apparatus according to claim 5 , wherein the tension applying unit of the fixing unit includes a plurality of the pressing portions having different spring constants along a longitudinal direction of the stretching roll.

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