JP2012103552A - Fixation device and image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixation device and an image formation device capable improving heat insulation efficiency by energy saving as well as inhibiting a slip phenomenon of a driven member, so that excellent image quality can be obtained.SOLUTION: A fixation device includes: a rotatable fixation member; a pressure roller 31 forming a nip part that presses the fixation member so as to cause unfixed toner on a passing recording medium to be fixed onto the recording medium; and heating means configured to heat the fixation member. The pressure roller 31 is a roller member including a sheet passing portion that serves as a region through which the recording medium passes and a grip part pressure-welded with the fixation member and configured to rotate the fixation member along a rotary drive of the pressure roller 31, in a manner arranged parallel in an axial direction at the nip part. The grip part is composed of a grip member 50 attachable to a roller body 31a of the pressure roller 31.

Description

  The present invention relates to a fixing device for fixing toner on a recording medium by heat and pressure, and image formation such as FAX, printer, copying machine or their combined machine using an electrophotographic system, electrostatic recording system, etc. equipped with the fixing device. It relates to the device.

  Conventionally, various image forming apparatuses using an electrophotographic system have been devised as image forming apparatuses such as copying machines and printers, and are well known in the art. In the image forming process, an electrostatic latent image is formed on the surface of the photosensitive drum as an image carrier, and the electrostatic latent image on the photosensitive drum is developed with a toner as a developer to be visualized and developed. The image is transferred to a recording medium (also referred to as a fixing material, paper, or recording paper) by a transfer device to carry the image, and the toner image on the recording medium is fixed by a fixing device that uses pressure or heat. is doing.

  In this fixing device, a fixing member and a pressing member constituted by opposing rollers or belts or a combination thereof are arranged so as to contact each other to form a nip portion, and a recording medium is sandwiched in the nip portion, Heat and pressure are applied to fix the toner image on the recording medium.

  As an example of the fixing device, a technique using a fixing belt stretched around a plurality of roller members as a fixing member is known (for example, see Patent Document 1). An apparatus using such a fixing belt is provided in a fixing belt (endless belt) as a fixing member, a plurality of roller members that stretch and support the fixing belt, and one of the plurality of roller members. And a heater, a pressure roller (pressure member), and the like. The heater heats the fixing belt via the roller member. Then, the toner image on the recording medium conveyed toward the nip formed between the fixing belt and the pressure roller is fixed on the recording medium by receiving heat and pressure at the nip. Belt fixing method).

  In such a fixing device, either the fixing member or the pressure member is a member that rotates by driving (drive member), and the other is a driven member that rotates with the drive member. Is a driving member, and the fixing member is a driven member.

  Here, the surface of both the fixing member and the pressure member is provided with a high release material such as fluororesin in order to prevent adhesion of toner, paper powder, etc., and its surface friction coefficient is also low. The driving force for rotating the driven member was weak. In particular, when a sheet is passed, a recording medium is inserted into the nip portion, and most of the fixing member and the pressure member are not in contact with each other in the nip portion. There has been a problem that a slip phenomenon occurs in which the drive member (for example, a pressure member) rotates with a delay, and the image quality is deteriorated.

  To solve this problem, the end surface layer in the axial direction of the pressure member is made of a material having a higher friction coefficient than the central portion, or the axial end portion has a higher load on the fixing member than the central portion. For example, there has been proposed a fixing device having a configuration in which the fixing member is reliably rotated with respect to the pressure member.

  For example, in Patent Document 2, a high friction body is provided on a non-sheet passing portion of a pressure belt that is a pressure member and a non-sheet passing portion of a heating roller that is a fixing member, and another member is provided from the inside of the pressure belt. A configuration is disclosed in which a sufficient grip is obtained and driven by being pressed against a heating roller. However, this method requires a separate member for pressing the pressure member against the fixing member, leading to an increase in the number of parts, which is disadvantageous in terms of cost. In addition, increasing the number of parts increases the heat capacity, which also reduces the thermal efficiency.

  In Patent Document 3, the end grip portion of the heating roller, which is a fixing member, is set to have an outer diameter larger than that of the central sheet passing portion, and the end portion of the pressure member and the end portion of the heating roller are connected to each other when the recording medium passes. The structure which can prevent detachment | leave and can transmit motive power with a grip of an edge part reliably is disclosed. In this case, the rotation speed (or speed) of the fixing member is determined by the end portion, but the speed of the recording medium is determined by the central portion serving as the sheet passing portion. For this reason, if the difference in the outer diameter of the heating roller between the sheet passing portion and the end portion becomes large, a difference occurs between the speed of the heating roller and the conveyance speed of the recording medium, resulting in a problem that the image quality deteriorates.

  By the way, in response to the recent trend of power saving and energy saving, the fixing device also efficiently transfers the heat energy from the heat source to the recording medium and the toner, and conversely, wasteful heat energy is transferred to other than the recording medium and the toner. Measures are taken to prevent leakage.

  Here, in the fixing device, the pressure member is configured to press-contact with the fixing member to form a nip, and heat from the fixing member is applied to the recording medium and the toner. The fixing member causes thermal energy to flow out to the pressure member that is in direct contact. Therefore, by making the pressure member a foam, the heat conductivity of the pressure member is lowered or the heat capacity is lowered to enhance the heat insulation effect and prevent the outflow of heat energy.

  However, when the pressure member surface is made of a foam in this way, the driving force for rotating the driven member also decreases due to the low rigidity of the foam itself and the reduced contact area with the fixing member. There was a problem. Further, in order to solve this problem, a forming method by combining the paper passing portion in the axial direction of the pressurizing member with a foam and the grip portion with a non-foam can be considered. However, it was complicated and caused an increase in cost.

  The present invention has been made in view of the above problems in the prior art, and improves the heat insulation efficiency by energy saving, suppresses the slip phenomenon of the driven member, and obtains a good image quality, and the fixing device An object of the present invention is to provide an image forming apparatus using a fixing device.

The present invention provided to solve the above problems is as follows. In addition, the site | part and code | symbol etc. which respond | correspond in the form for implementing this invention in a parenthesis are shown.
[1] A rotating fixing member (fixing belt 21) and a nip portion that fixes unfixed toner (toner image T) on a recording medium (recording medium P) that presses and passes the fixing member to the recording medium. A pressure member (pressure roller 31) to be formed, and heating means (heater 25, induction heating unit 60) for heating the fixing member. The pressure member is formed on the recording medium at the nip portion. A roller member in which a paper passing portion serving as a passing region and a grip portion that is in pressure contact with the fixing member and rotates the fixing member as the pressure member rotates are arranged in parallel in the axial direction; A fixing device (fixing device 20, FIGS. 2 to 12), wherein the grip portion is constituted by a grip member (grip member 50) that can be attached to and detached from a roller main body (roller main body 31a) of the pressure member. .
[2] The fixing according to [1], wherein the grip member is a cylindrical member, and is fixed to a roller body of the pressure member so as to be integrated as a roller member. Apparatus (FIG. 4, FIGS. 7-10).
[3] Screw tightening direction when the roller shaft rotates in the rotational driving direction of the pressure member on the cylindrical inner peripheral portion (base member 51) of the grip member and the roller shaft (roller shaft 35) of the roller body. So that a female screw part (female screw part 51n) and a male screw part (male screw part 35n) are provided, and both are screwed together to fix the grip member to the roller body of the pressure member. The fixing device according to [2] (FIG. 9).
[4] The fixing device (2) according to [2], wherein the grip member is fixed to a roller shaft of the roller body via a one-way clutch (one-way clutch 57).
[5] While the nip portion is formed, the pressure member is rotated in the direction opposite to the driving rotation to slide the sheet passing portion of the pressure member and the fixing member. The fixing device according to [3] or [4], wherein the fixing device has a cleaning mode for cleaning the surface.
[6] In the axial direction of the pressurizing member, a space (gap 58, hole portion 59) for accommodating a foreign substance toward the grip portion by separating the roller portion constituting the paper passing portion from the grip member. The fixing device according to any one of [1] to [5], which is provided (FIG. 9).
[7] Any one of [1] to [6], wherein the roller outer peripheral surface of the paper passing portion and the roller outer peripheral surface of the grip portion of the pressure member are substantially flat in the axial direction. The fixing device according to 1.
[8] An image forming apparatus (image forming apparatus 1, FIG. 1) comprising the fixing device (fixing apparatus 20) according to any one of [1] to [7].

According to the fixing device of the present invention, the pressure member is in contact with the fixing member at a nip portion, which is a region through which the recording medium passes, and the fixing member is rotated with the pressure member. Since the rotating grip part is a roller member that is arranged in parallel in the axial direction, and the grip part is constituted by a grip member that can be attached to and detached from the roller body of the pressure member, the sheet passing of the pressure member It is assumed that only the part has an elastic layer that has a heat insulating effect such as foam, and a grip part that prevents the fixing member from slipping can be provided in the non-sheet passing part, reducing the outflow of heat to the pressure member during sheet passing Thus, power saving can be achieved, and the fixing member can be stably rotated without impairing the gripping force. Furthermore, since the grip member and the roller body can be manufactured separately at the time of manufacture, it is difficult to realize by one-piece manufacture, such as a combination of a roller body having an elastic layer made of foam and a grip member having a solid elastic layer. It is possible to easily configure a pressure member having a complex structure. Further, since only the grip member can be removed and replaced with respect to the deterioration of the grip portion of the pressurizing member, the service cost can be reduced and the resources can be saved.
According to the image forming apparatus of the present invention, since the fixing device of the present invention is provided, it is possible to stably form an image with good image quality over a long period of time.

1 is a cross-sectional view showing an overall configuration of an image forming apparatus according to the present invention. 1 is a cross-sectional view showing a basic configuration (1) of a fixing device according to the present invention. FIG. 3 is a front view of the fixing device in FIG. 2 as viewed from the nip exit side. It is sectional drawing which shows the structural example (1) of the pressure roller used for the fixing apparatus of this invention. It is a perspective view which shows the structure of the pressure roller of FIG. It is a side view which shows the structure of the pressure roller of FIG. It is sectional drawing which shows the modification (1) of the pressure roller of FIG. It is sectional drawing which shows the modification (2) of the pressure roller of FIG. It is sectional drawing which shows the structural example (2) of the pressure roller used for the fixing apparatus of this invention. It is sectional drawing which shows the structural example (3) of the pressure roller used for the fixing apparatus of this invention. FIG. 3 is a cross-sectional view showing a basic configuration (2) of the fixing device according to the present invention. FIG. 3 is a cross-sectional view showing a basic configuration (3) of the fixing device according to the present invention.

The configurations of the fixing device and the image forming apparatus according to the present invention will be described below.
A configuration example of the entire image forming apparatus according to the present invention will be described with reference to FIG.
As shown in FIG. 1, the image forming apparatus 1 is a tandem type color printer. Four bottles 102Y, 102M, 102C, and 102K corresponding to the respective colors (yellow, magenta, cyan, and black) are detachably (replaceable) installed in the bottle housing portion 101 above the image forming apparatus main body 1. ing.
An intermediate transfer unit 85 is disposed below the bottle housing portion 101. Image forming units 4Y, 4M, 4C, and 4K corresponding to the respective colors (yellow, magenta, cyan, and black) are arranged in parallel so as to face the intermediate transfer belt 78 of the intermediate transfer unit 85.

  Photosensitive drums 5Y, 5M, 5C, and 5K are disposed in the image forming units 4Y, 4M, 4C, and 4K, respectively. Further, around each of the photosensitive drums 5Y, 5M, 5C, and 5K, a charging unit 75, a developing unit 76, a cleaning unit 77, a charge eliminating unit (not shown), and the like are disposed. Then, an image forming process (charging process, exposure process, development process, transfer process, cleaning process) is performed on each of the photoconductive drums 5Y, 5M, 5C, and 5K. An image of each color is formed on 5K.

The photosensitive drums 5Y, 5M, 5C, and 5K are rotationally driven in a clockwise direction in FIG. 1 by a drive motor (not shown). Then, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K are uniformly charged at the position of the charging unit 75 (a charging process).
Thereafter, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K reach the irradiation position of the laser light L emitted from the exposure unit 3, and electrostatic latent images corresponding to the respective colors are formed by exposure scanning at this position. (It is an exposure process.)

Thereafter, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K reach a position facing the developing device 76, and the electrostatic latent image is developed at this position to form toner images of each color (developing process). .)
Thereafter, the surfaces of the photoconductive drums 5Y, 5M, 5C, and 5K reach the positions facing the intermediate transfer belt 78 and the first transfer bias rollers 79Y, 79M, 79C, and 79K, and at these positions, the photoconductive drums 5Y, 5M. The toner images on 5C and 5K are transferred onto the intermediate transfer belt 78 (this is a primary transfer process). At this time, a small amount of untransferred toner remains on the photosensitive drums 5Y, 5M, 5C, and 5K.

Thereafter, the surfaces of the photoconductive drums 5Y, 5M, 5C, and 5K reach a position facing the cleaning unit 77, and untransferred toner remaining on the photoconductive drums 5Y, 5M, 5C, and 5K is removed at this position. 77 is mechanically collected by a cleaning blade (cleaning process).
Finally, the surfaces of the photoconductive drums 5Y, 5M, 5C, and 5K reach a position facing a neutralization unit (not shown), and the residual potential on the photoconductive drums 5Y, 5M, 5C, and 5K is removed at this position. The
Thus, a series of image forming processes performed on the photosensitive drums 5Y, 5M, 5C, and 5K is completed.

Thereafter, the toner images of the respective colors formed on the respective photosensitive drums through the developing process are transferred onto the intermediate transfer belt 78 in an overlapping manner. In this way, a color image is formed on the intermediate transfer belt 78.
Here, the intermediate transfer unit 85 includes an intermediate transfer belt 78, four primary transfer bias rollers 79Y, 79M, 79C, and 79K, a secondary transfer backup roller 82, a cleaning backup roller 83, a tension roller 84, and an intermediate transfer cleaning unit 80. , Etc. The intermediate transfer belt 78 is stretched and supported by the three rollers 82 to 84 and is endlessly moved in the direction of the arrow in FIG.

The four primary transfer bias rollers 79Y, 79M, 79C, and 79K sandwich the intermediate transfer belt 78 with the photosensitive drums 5Y, 5M, 5C, and 5K, respectively, thereby forming primary transfer nips. Then, a transfer bias reverse to the polarity of the toner is applied to the primary transfer bias rollers 79Y, 79M, 79C, and 79K.
The intermediate transfer belt 78 travels in the direction of the arrow and sequentially passes through the primary transfer nips of the primary transfer bias rollers 79Y, 79M, 79C, and 79K. In this way, the toner images of the respective colors on the photosensitive drums 5Y, 5M, 5C, and 5K are primarily transferred while being superimposed on the intermediate transfer belt 78.

Thereafter, the intermediate transfer belt 78 onto which the toner images of the respective colors are transferred in an overlapping manner reaches a position facing the secondary transfer roller 89. At this position, the secondary transfer backup roller 82 sandwiches the intermediate transfer belt 78 between the secondary transfer roller 89 and forms a secondary transfer nip. The four color toner images formed on the intermediate transfer belt 78 are transferred onto the recording medium P conveyed to the position of the secondary transfer nip. At this time, untransferred toner that has not been transferred to the recording medium P remains on the intermediate transfer belt 78.
Thereafter, the intermediate transfer belt 78 reaches the position of the intermediate transfer cleaning unit 80. At this position, the untransferred toner on the intermediate transfer belt 78 is collected.
Thus, a series of transfer processes performed on the intermediate transfer belt 78 is completed.

  Here, the recording medium P transported to the position of the secondary transfer nip is transported from the paper feeding unit 12 disposed below the apparatus main body 1 via the paper feeding roller 97 and the registration roller pair 98. It is a thing. Specifically, a plurality of recording media P such as transfer paper are stored in the paper supply unit 12 in an overlapping manner. When the paper feed roller 97 is rotationally driven in the counterclockwise direction in FIG. 1, the uppermost recording medium P is fed between the rollers of the registration roller pair 98.

  The recording medium P conveyed to the registration roller pair 98 is temporarily stopped at the position of the roller nip of the registration roller pair 98 that has stopped rotating. Then, the registration roller pair 98 is rotationally driven in synchronization with the color image on the intermediate transfer belt 78, and the recording medium P is conveyed toward the secondary transfer nip. In this way, a desired color image is transferred onto the recording medium P.

Thereafter, the recording medium P on which the color image is transferred at the position of the secondary transfer nip is conveyed to the position of the fixing device 20. At this position, the color image transferred on the surface is fixed on the recording medium P by heat and pressure generated by the fixing belt 21 and the pressure roller 31.
Thereafter, the recording medium P is discharged out of the apparatus through a pair of paper discharge rollers 99. The transferred P discharged from the apparatus by the discharge roller pair 99 is sequentially stacked on the stack unit 100 as an output image.
Thus, a series of image forming processes in the image forming apparatus is completed.

Next, the fixing device according to the present invention will be described.
FIG. 2 is a cross-sectional view showing the basic configuration of the fixing device according to the present invention. FIG. 2 shows a cross-sectional configuration of the sheet passing portion through which the recording medium P passes at the nip portion. FIG. 3 is a front view of the fixing device 20 as seen from the nip exit side.
First, as shown in FIG. 2, the fixing device 20 includes a fixing belt 21 as a fixing member, a heating member 22, a reinforcing member 23, a heat insulating member 27, a heater 25 as a heat source, a pressure roller 31 as a pressure member, and a temperature. The sensor 40 is configured.

  Here, the fixing belt 21 as a fixing member is a thin and flexible endless belt, and rotates (runs) in an arrow direction (counterclockwise) in FIG. The fixing belt 21 is formed by sequentially laminating an elastic layer and a release layer on a base material, and the entire thickness thereof is set to 1 mm or less.

The base material of the fixing belt 21 has a layer thickness of 30 to 50 μm and is formed of a metal material such as nickel or stainless steel or a resin material such as polyimide.
Further, the elastic layer of the fixing belt 21 has a layer thickness of 100 to 300 μm and is formed of a rubber material such as silicone rubber, foamable silicone rubber, or fluorine rubber. By providing the elastic layer, minute irregularities on the surface of the fixing belt 21 in the nip portion are not formed, and heat is uniformly transmitted to the toner image T on the recording medium P, thereby suppressing the generation of a scum skin image.
The release layer of the fixing belt 21 has a layer thickness of 10 to 50 μm, and includes PFA (tetrafluoroethylene bar fluoroalkyl vinyl ether copolymer resin), PTFE (tetrafluoroethylene resin), polyimide, polyetherimide, It is made of a material such as PES (polyether sulfide). By providing the release layer, the releasability (peelability) for the toner (toner image) is ensured.

Further, the diameter of the fixing belt 21 is set to be 15 to 120 mm. In the present embodiment, the diameter of the fixing belt 21 is set to 30 mm, for example.
Inside the fixing belt 21 (inner peripheral surface side), a heater 25 (heat source), a heating member 22, a reinforcing member 23, a heat insulating member 27, and the like are fixed. Thus, the heating member 22 reinforced by the reinforcing member 23 is pressed to form a nip portion with the pressure roller 31.

  Here, a heat insulating member 27 is provided between the reinforcing member 23 and the heating member 22, whereby the heat of the heating member 22 moves to the reinforcing member 23 side and the heating efficiency of the heating member 22 decreases. Defects are suppressed. In addition, as a material of the heat insulation member 27, it is a heat-resistant and highly heat-insulating material, and rubber, resin, felt, a ceramic sheet, etc. can be used.

  The heating member 22 is a substantially pipe-shaped member formed by bending a thin metal plate, for example, and is formed in a substantially circular shape so as to face the entire inner peripheral surface of the fixing belt 21. Through the pressure roller 31 to form a nip portion. The heating member 22 is heated by the radiant heat of the heater 25 to heat the fixing belt 21 (transmits heat). As a material of the heating member 22, it is preferable to use a metal thermal conductor (a metal having thermal conductivity) such as aluminum, iron, and stainless steel.

The heating member 22 is formed so that the position corresponding to the nip portion and the facing surface of the heating member 22 in the nip portion (surface facing the pressure roller 31) are flat. As a result, the shape of the nip portion is substantially parallel to the image surface of the recording medium P, and the adhesion between the fixing belt 21 and the recording medium P is increased, so that the fixing property is improved. Further, since the curvature of the fixing belt 21 on the exit side of the nip portion is increased, the recording medium P sent from the nip portion can be easily separated from the fixing belt 21.
Referring to FIG. 3, both ends of the heating member 22 in the width direction are fixedly supported by the side plates 43 of the fixing device 20.

  The reinforcing member 23 is a member having a substantially T-shaped cross section, and is formed so that the length in the width direction (axial direction) is at least equal to the length in the axial direction of the fixing belt 21. Both end portions in the width direction are fixedly supported on the side plate 43 of the fixing device 20 on the inner peripheral side of the fixing device 20.

  The heater 25 is a halogen heater or a carbon heater, and both ends thereof are fixed to the side plate 43 of the fixing device 20. The heating member 22 is heated by the radiant heat of the heater 25 whose output is controlled by the power supply unit of the apparatus main body. Further, the fixing belt 21 is entirely heated by the heating member 22, and heat is applied to the toner image T on the recording medium P from the surface of the heated fixing belt 21. The output control of the heater 25 is performed based on the detection result of the belt surface temperature by the temperature sensor 40 such as a thermistor facing the surface of the fixing belt 21. Further, the temperature of the fixing belt 21 (fixing temperature) can be set to a desired temperature by such output control of the heater 25.

  Referring to FIG. 2, the pressure roller 31 has a diameter of 30 mm, and has a basic configuration in which an elastic layer 33 is formed on a hollow cylindrical cored bar 32. The elastic layer 33 of the pressure roller 31 is made of a material such as foamable silicone rubber, silicone rubber, or fluorine rubber. A thin release layer made of PFA, PTFE or the like can be provided on the surface layer of the elastic layer 33.

  Further, both ends of the pressure roller 31 in the width direction are rotatably supported on the side plate 43 of the fixing device 20 via bearings 42 and movably on the heating member 22 (reinforcing member 23) side. The pressure roller 31 is provided with pressure means (not shown) for pressing the roller shafts at both axial ends of the pressure roller 31 toward the heating member 22 (reinforcing member 23). The pressure roller 31 is pressed against the heating member 22 reinforced by the reinforcing member 23 via the fixing belt 21 by the pressing of the means, and a desired nip portion is formed between the two members.

  Referring to FIG. 3, the pressure roller 31 is provided with a gear 45 that meshes with a drive gear of a drive mechanism (not shown), and the pressure roller 31 is in the direction of the arrow (clockwise) in FIG. Driven by rotation. A heat source such as a halogen heater can be provided inside the pressure roller 31.

Note that when the elastic layer 33 of the pressure roller 31 is formed of a sponge-like material such as foamable silicone rubber, the pressure applied to the nip portion can be reduced. Further reduction can be achieved. Furthermore, since the heat insulation of the pressure roller 31 is enhanced and the heat of the fixing belt 21 is difficult to move to the pressure roller 31 side, the heating efficiency of the fixing belt 21 is improved.
In this embodiment, the fixing belt 21 has a diameter equal to that of the pressure roller 31, but the fixing belt 21 has a diameter smaller than the pressure roller 31. You can also. In that case, since the curvature of the fixing belt 21 in the nip portion is smaller than the curvature of the pressure roller 31, the recording medium P sent out from the nip portion is easily separated from the fixing belt 21.

The fixing device 20 configured as described above operates as follows.
First, when the power switch of the apparatus main body is turned on, electric power is supplied to the heater 25 and the pressure roller 31 presses the heating member 22 (reinforcing member 23) through the fixing belt 21 by the pressing means. Then, the rotational drive in the direction of the arrow in FIG. 2 is started. Accordingly, the fixing belt 21 is also driven (rotated) in the direction of the arrow in FIG. 2 by the frictional force with the grip portion (described later) of the pressure roller 31.
Thereafter, the recording medium P is fed from the paper supply unit 12, and an unfixed color image is carried (transferred) on the recording medium P at the position of the secondary transfer roller 89. The recording medium P carrying the unfixed image (toner image T) is conveyed in the direction of the arrow Y10 in FIG. 2 while being guided by a guide plate (not shown), and the fixing belt 21 and the pressure roller 31 in the pressure contact state are conveyed. It is fed into the nip part.
The toner image is formed on the surface of the recording medium P by the heating by the fixing belt 21 heated by the heating member 22 (heater 25) and the pressing force of the heating member 22 reinforced by the reinforcing member 23 and the pressure roller 31. T is fixed. Thereafter, the recording medium P delivered from the nip portion is conveyed in the direction of arrow Y11.

  As described above, in the fixing device 20 according to the present embodiment, the fixing belt 21 is heated almost entirely in the circumferential direction by the heating member 22 without locally heating only a part of the fixing belt 21. Therefore, even when the speed of the apparatus is increased, the fixing belt 21 is sufficiently heated and the occurrence of fixing failure can be suppressed. That is, since the fixing belt 21 can be efficiently heated with a relatively simple configuration, the warm-up time and the first print time are shortened, and the size of the apparatus is reduced.

Here, the fixing belt 21 is nipped by the heating member 22 reinforced by the pressure roller 31 and the reinforcing member 23, and the fixing belt 21 is caused by a reaction force of a frictional force generated when the pressure roller 31 tries to rotate. 21 is configured to rotate, but when the pressure roller 31 surface is made of a foam having a heat insulation effect, the rigidity of the foam itself is low and the contact area with the fixing belt 21 is reduced. The driving force for rotating the fixing belt 21 as the driven member decreases, and the fixing belt 21 slips with respect to the pressure roller 31 as the driving member, thereby deteriorating the image quality. In particular, when a release layer made of a fluororesin is provided on the surfaces of the fixing belt 21 and the pressure roller 31, the surface friction coefficient is low, so that the driving force for rotating the fixing belt 21 is weaker. Further, the recording medium P is inserted into the nip portion when the paper is passed, and the fixing belt 21 and the pressure roller 31 are mostly not in contact with each other at the nip portion, and the frictional force between the two is reduced. Met.
The inventors improve the frictional resistance state between the fixing belt 21 and the pressure roller 31 in the non-sheet passing portion, which is an area other than the sheet passing portion where the recording medium exists in the nip portion, and wears in the pressure roller 31. In order to realize that the non-sheet passing portion that can easily be replaced can be easily studied, the present invention has been achieved. Hereinafter, the configuration of the main part of the present invention will be described.

[Configuration of pressure roller]
In the fixing device 20 of the present invention, the pressure roller 31 is fixed in accordance with the rotational driving of the pressure roller 31 in contact with the fixing belt 21 and the sheet passing portion which is a region through which the recording medium P passes in the nip portion. A roller member in which a grip portion for rotating the belt 21 is arranged in parallel in the axial direction, and the grip portion is constituted by a grip member that can be attached to and detached from the roller body of the pressure roller 31. Is. At this time, it is preferable that the roller outer peripheral surface of the paper passing portion and the roller outer peripheral surface of the grip portion of the pressure roller 31 are substantially flat in the axial direction.

As a result, even when the paper is passing, a strong driving force is applied to the fixing belt 21 as the driven member from the grip portion of the pressure roller 31, and the fixing operation can be performed without slipping. In addition, since the grip portion is constituted by a separate member (grip member) that can be attached to and detached from the roller body of the pressure roller 31, the desired grip portion can be obtained by integrating the grip member and the roller body after being manufactured separately. It is possible to easily obtain the pressure roller 31 having a low cost.
Hereinafter, a specific example of the pressure roller 31 will be described with reference to the drawings.

(First embodiment)
The first embodiment will be described with reference to FIGS.
4 is a cross-sectional view showing a configuration example (1) of a pressure roller used in the fixing device of the present invention, FIG. 5 is a perspective view thereof, and FIG. 6 is a side view thereof.
As shown in FIGS. 4 and 5, the pressure roller 31 has, as an outer peripheral surface of the roller, a paper passing portion in which the central portion in the axial direction passes through the recording medium P in the nip portion, and both axial ends. A grip portion which is a region where the recording medium P does not pass in the nip portion (non-sheet passing portion) and is a region where the fixing belt 21 is rotated by the rotational driving of the pressure roller 31 in pressure contact with the fixing belt 21. , Are arranged side by side.

  Note that the sheet passing portion here is an area where the recording medium P passes through in an ideal state at the nip portion, and is the amount of play in the axial direction of the pressure roller 31 in the actual apparatus mechanism, or the recording medium P being conveyed. At least a region to which a variation in the sheet passing position in the main scanning direction (axial direction) is added. In addition, the grip portion is a region having a width that can secure a grip force enough to prevent the fixing belt 21 from slipping when the grip portion is pressed against the fixing belt 21 and driven to rotate in the non-sheet passing portion. FIG. 4 shows a configuration in which the entire non-sheet passing portion is a grip portion.

  Here, the roller main body 31a is provided by extending at least the sheet passing portion in which the elastic layer 33 and the release layer 34 made of a fluororesin are sequentially laminated on the core metal 32, and both ends of the core metal 32 in the axial direction. And a roller shaft 35 formed. In addition, in the roller main body 31a of this embodiment, as shown in FIG. 4, it has the structure by which a part of elastic layer 33 was extended in the axial direction to the inner peripheral part side of the grip member 50. As shown in FIG.

  The grip member 50 constituting the grip portion is a base member 51 formed into a cylindrical shape at least using a metal such as iron, aluminum, stainless steel or a heat resistant resin such as PPS (polyphenylene sulfide resin) or PET (polyethylene terephthalate resin). And an elastic layer 52 formed using silicone rubber or the like on the outer periphery of the base member 51. In addition, at least cylindrical shape means not only a cylindrical shape but also a cup shape. In the present embodiment, a cup-shaped base member 51 is shown.

  The base member 51 has a cylindrical or cup-shaped inner diameter that is substantially the same as the outer diameter of the non-sheet passing portion of the roller body. The cup-shaped base member 51 is provided with a hole through which the roller shaft 35 passes at the bottom of the cup. When the base member 51 is made of a metal material, the metal plate may be formed into a cup shape or a cylindrical shape by drawing or cutting. However, in the case of a cylindrical shape, care must be taken because the heat capacity increases and it is easy to take heat away from the fixing belt 21.

  Further, the silicone rubber constituting the elastic layer 52 is made of a material having a low elasticity and a high tack property, and the surface is not provided with a release layer, and the surface property is increased so that the friction coefficient is increased, thereby making contact. The driving force can be stably transmitted to the fixing belt 21.

  The grip member 50 is preferably fixed to the roller body of the pressure roller 31 so as to be integrated as a roller member. When the roller shaft 35 is rotationally driven, the grip member 50 is also rotated as a part of the pressure roller 31 so that the driving force can be transmitted to the abutting fixing belt 21. Say.

  In this embodiment, as shown in FIG. 6, the cross-sectional shape of the roller shaft 35 in the pressure roller 31 is an oval shape, and is substantially the same shape as the outer shape of the roller shaft 35 on the cup bottom surface of the base member 51. An oval hole 54 into which the roller shaft 35 is inserted is provided. Alternatively, in the case where the roller shaft 35 has a round bar shape, a hole having substantially the same diameter through which the roller shaft 35 can be inserted is provided on the bottom surface of the cup of the base member 51, and a key groove for preventing rotation is provided on both sides. The rotational drive may be transmitted from the roller shaft 35 to the grip member 50. Further, the roller main body 31a and the grip member 50 are fitted by press-fitting the outer diameter of the portion of the elastic layer 33 that extends to the inner peripheral side of the grip member 50 and the cup inner diameter of the base member 51 as substantially the same diameter (D2). It is good also as a structure. Alternatively, the grip member 50 may be fixed to the roller shaft 35 or a part of the elastic layer 33 so that the grip member 50 can be attached and detached. With these structures, the grip member 50 can also rotate as a part of the pressure roller 31 as the roller shaft 35 rotates.

The roller shaft 35 is provided with a C-ring groove 35a. After the grip member 50 is mounted on the roller body 31a, a C-ring (not shown) is attached to the C-ring groove 35a, thereby preventing the grip member 50 from coming off in the axial direction. It is good to do.
The grip member 50 is attached to both end sides in the axial direction of the pressure roller 31 with the same configuration.

  With the above configuration, only the paper passing portion of the pressure roller 31 has the elastic layer 33 having a heat insulating effect such as a foam, and the grip portion for preventing the fixing belt 21 from slipping is provided in the non-paper passing portion. It is possible to reduce the outflow of heat to the pressure roller 31 during paper feeding and to save power, and to stably rotate the fixing belt 21 without impairing the grip force. Further, since the grip member 50 and the roller main body 31a can be manufactured separately at the time of manufacture, for example, a combination of the roller main body 31a having the elastic layer 33 made of foam and the grip member 50 having the solid elastic layer 52 is used. Thus, it is possible to easily configure the pressure roller 31 having a composite structure that is difficult to realize by integral manufacturing. Further, since only the grip member 50 can be removed and replaced with respect to the deterioration of the grip portion of the pressure roller 31, the service cost can be reduced and the resources can be saved.

7 and 8 show a modification of the present embodiment.
FIG. 7 shows an example in which the grip member 50 is injection molded with an elastomer resin or the like. As a result, the grip member 50 can be formed from a single material, and the strength required to rotate as a part of the pressure roller 31 required for the grip member 50 and the frictional resistance (grip force) against the fixing belt 21 are ensured. Is possible.

FIG. 8 shows a configuration example in which the release layer 34 is omitted at the boundary portion between the grip portion of the grip member 50 on the outer peripheral surface of the pressure roller 31 and the sheet passing portion of the roller body 31a.
That is, on the outer peripheral surface of the pressure roller 31, the elastic layer 52 of the grip member 50 and the release layer 34 in the sheet passing portion of the roller body 31a are adjacent to the grip portion of the roller body 31a. Instead of providing the release layer 34 at the part, the elastic layer 33 is provided with an inclined surface 37 such that the depth from the outer peripheral surface increases toward the grip portion. Thereby, wrinkles and breakage of the end surface of the release layer 34 due to contact between the elastic layer 52 of the grip member 50 and the release layer 34 of the roller body 31a can be prevented.

(Second Embodiment)
FIG. 9 is a sectional view showing a configuration example (2) of the pressure roller used in the fixing device of the present invention.
In the present embodiment, the cylindrical inner periphery of the grip member 50 and the roller shaft 35 of the roller main body 31a are respectively female so that when the roller shaft 35 rotates in the rotational drive rotational direction of the pressure roller 31, the screw tightening direction is obtained. A screw portion 51n and a male screw portion 35n are provided, and both are screwed to fix the grip member 50 to the roller body 31a of the pressure roller 31. As shown in FIG. 9, the grip member 50 includes a cylindrical base member 51 and an elastic layer 52 provided on the outer periphery of the base member 51. A portion 51n is formed.

  Here, a male screw portion 35n is provided at a portion where the grip member 50 is fitted in the roller shaft 35 of the pressure roller 31 so as to serve as a bolt, and the inner peripheral surface of the corresponding grip member 50 A female screw 51n is provided on the side to serve as a nut. At this time, the female screw portion 51n is in the direction of the screw to be tightened in the opposite direction to the rotation direction of the pressure roller 31 (the rotation direction driven during the fixing process in the fixing device 20), thereby forming a nip portion. As the pressure roller 31 is driven to rotate in the state, the grip member 50 moves to the axially central side (paper passing side), and the bolt (roller shaft 35) is tightened to the nut (grip member 50) in relation to the bolt and nut. It has become a relationship. For example, in FIG. 2, when the pressure roller 31 rotates in the clockwise direction, the grip member 50 on the left side in FIG. 3 (the front side in FIG. 2) has a screw tightening direction counterclockwise. In the grip member 50 on the right side in FIG. 3 (the back side of the drawing sheet in FIG. 2 and the pressure driving gear 45 side), a reverse screw is used, which is a positive screw in a direction in which the screw is tightened clockwise.

  As a result, when the pressure roller 31 is driven to rotate, the torque at the time of driving the fixing belt 21 is applied to the pressure roller 31 at the nip portion, so that the grip member 50 is always moved toward the center in the axial direction (paper passing side). As the screw is tightened, it does not loosen. Further, a C-ring groove 35a is provided on the tightening side (right side in FIG. 9) of the roller shaft 35, and a C-ring (not shown) is provided, so that the grip member 50 is not pushed to the end position of the paper passing portion. As described above, the pushing position is regulated. Thus, when the fixing device 20 is driven, the grip member 50 is fixed to an appropriate position without being loosened by the roller body 31a.

As a result, as in the first embodiment, the heat flow to the pressure roller 31 can be reduced during paper feeding to save power, and the fixing belt 21 can be rotated stably without impairing the gripping force. it can.
When the grip member 50 needs to be replaced due to wear or the like, the grip member 50 can be removed and replaced without using a tool or the like by rotating each grip member 50 in the direction in which the screw is loosened. Further, it is not necessary to fasten the roller body 31a and the grip member 50 in the processing step (attachment step), and the manufacturing cost is reduced. Further, when a jam occurs at the nip portion, if the recording medium P is pulled out in the direction opposite to the conveyance direction, the grip member 50 is on the loose side, so that the fixing belt 21 is not rotated and the user operation force for jam processing is increased. It can also be reduced.

(Third embodiment)
FIG. 10 is a cross-sectional view showing a configuration example (3) of the pressure roller used in the fixing device of the present invention.
In the present embodiment, the grip member 50 is fixed to the roller shaft 35 of the roller body 31a via a one-way clutch 57. That is, the grip member 50 includes a cylindrical base member 51 and an elastic layer 52 provided on the outer periphery of the base member 51, as shown in FIG. A one-way clutch 57 is arranged between the outer peripheral portion of 35. At this time, the one-way clutch 57 is arranged so that the direction in which the fixing belt 21 is driven in the pressure roller 31 is the direction in which the rotation of the one-way clutch 57 is locked.

  As a result, when the pressure roller 31 is driven to rotate, the one-way clutch 57 is locked, and the grip member 50 rotates as a part of the pressure roller 31. As a result, as in the first embodiment, the heat flow to the pressure roller 31 can be reduced during paper feeding to save power, and the fixing belt 21 can be rotated stably without impairing the gripping force. it can.

  When the pressure roller 31 rotates in the direction opposite to the driving rotation, the one-way clutch 57 rotates, so that the driving force from the roller shaft 35 is not transmitted to the grip member 50 and the roller shaft 35 rotates idly. It becomes a state. Therefore, when the jam occurs at the nip portion, if the recording medium P is pulled out in the direction opposite to the conveying direction, the grip member 50 becomes loose and the fixing belt 21 is not rotated, so that the user operation force for the jam processing is reduced. Can do.

  Here, in the second and third embodiments, with the nip portion formed, the pressure roller 31 is rotated in the direction opposite to the driving rotation, so that the sheet passing portion of the pressure roller 31 and the fixing belt 21 are moved. By sliding, it is possible to provide a cleaning mode for cleaning both surfaces.

  That is, it is possible to reverse the rotation direction of the drive source (not shown) and rotate the roller body 31a (roller shaft 35) in the direction opposite to the drive rotation in the normal fixing process by driving transmission from the gear 45. The reverse rotation of the roller shaft 35 is the rotation of the grip member 50 in the loosening direction of the screw between the male screw portion 35n and the female screw portion 51n in the second embodiment, and the idling direction of the one-way clutch 57 in the third embodiment. Therefore, the grip member 50 is not rotated, and the grip member 50 does not function to drive the fixing belt 21. Accordingly, only the roller main body 31a rotates. However, since the release layer 34 is provided in the sheet passing portion that is in contact with the fixing belt 21 on the roller main body 31a, the driving force is increased by the fixing belt. However, the fixing belt 21 slips with respect to the rotating paper passing portion. As a result, a linear velocity difference is generated between the pressure roller 31 and the fixing belt 21, and the effect of scraping off the aggregates of toner and paper powder fixed on the surfaces of the fixing belt 21 and the pressure roller 31 from each other is mutually. The agglomerates easily fall off from the surfaces of the fixing belt 21 and the pressure roller 31. Subsequently, the pressure roller 31 is rotated in the forward direction to allow the cleaning paper to pass therethrough, whereby the agglomerates having weakened adhesion can be gradually discharged (self-cleaning). By periodically performing this operation (cleaning mode), the adhesion of the toner adhering matter to the recording medium P is reduced, and agglomerates of toner and paper dust are permanently adhered to the pressure roller 31 and the fixing belt 21. It is possible to prevent sticking and extend the life of the parts.

  By the way, in the image forming apparatus 1, when the printing operation is repeated, paper dust and toner often accumulate on the pressure roller 31, and the amount of paper dust generated from the end surface of the recording medium P is particularly larger than the paper passing surface. There is a possibility that paper dust and toner adhere to the grip portion, which is the outer peripheral surface of the grip member 50 disposed near the end surface of the recording medium P. As for the toner, the toner offset to the fixing belt 21 may go around to the pressure roller 31 side, or the toner floating in the apparatus may be electrostatically adsorbed. When these paper dust and toner adhere to the grip portion, the coefficient of friction with the fixing belt 21 decreases, and it becomes impossible to obtain a grip force stably over time.

  Therefore, in the first to third embodiments described above, in the axial direction of the pressure roller 31, the roller portion constituting the paper passing portion of the roller body 31a and the grip member 50 are separated from each other, and the outer peripheral surface of the grip member 50 is separated. It is preferable to provide a space for accommodating a foreign object toward the grip portion. The configuration will be described with reference to FIG.

  That is, as shown in FIG. 9, a gap 58 with a predetermined interval is provided between the grip member 50 and the roller portion constituting the paper passing portion of the roller body 31a. The gap 58 may be formed by regulating the position of the grip member 50 in the axial direction by a C-ring groove 35 a provided in the roller shaft 35. As a result, foreign matters such as paper dust and toner heading to the grip portion can be stored in the gap 58, and adhesion to the grip portion can be prevented. Further, at this time, it is more preferable to provide a hole portion 59 on the side surface facing the gap 58 of the base member 51 constituting the grip member 50 because the paper dust and toner that have entered can be stored more. The hole portion 59 may be provided on the side surface of the elastic layer 33 of the roller body 31a.

  Although the present invention has been described with the embodiments shown in the drawings, the present invention is not limited to the embodiments shown in the drawings, and other embodiments, additions, modifications, deletions, etc. Can be changed within the range that can be conceived, and any embodiment is included in the scope of the present invention as long as the effects and advantages of the present invention are exhibited.

  For example, the basic configuration of the fixing device 20 is not limited to that shown in FIG. 2, and may be the configuration shown in FIG. 11, for example. Here, like the one shown in FIG. 2, the fixing belt 21, the heating member 22, the reinforcing member 23, the heater 25, the pressure roller 31 and the like are configured.

  Here, in the fixing device 20 shown in FIG. 11, an abutting member 26 (fixed to the inner peripheral surface side of the fixing belt 21 and abutting against the pressure roller 31 via the fixing belt 21 to form a nip portion. A nip portion forming member) is provided separately from the heating member 22. The heating member 22 is formed in a substantially circular shape so as to face the inner peripheral surface of the fixing belt 21 at a position excluding the nip portion, and a concave portion is provided so as to store and hold the contact member 26 at the position of the nip portion. Is formed. The heating member 22 is formed so as to hold the contact member 26 via the heat insulating member 27 at the position of the nip portion.

  The contact member 26 is formed in a concave shape so that the surface facing the pressure roller 31 follows the curvature of the pressure roller 31. Thereby, since the recording medium P is sent out from the nip portion so as to follow the curvature of the pressure roller 31, the problem that the recording medium P after the fixing process is not attracted to the fixing belt 21 and separated is suppressed. be able to.

  Further, as a material for forming the contact member 26, a material having a certain degree of rigidity (for example, a highly rigid metal, ceramic, or the like) is used so that the contact member 26 does not bend greatly even if the pressure applied by the pressure roller 31 is applied. .).

  Here, the contact member 26 is detachably installed on the fixing device 20. Specifically, both end portions in the width direction of the contact member 26 are detachably fixed to the side plate of the fixing device 20 by screws, snap fits, or the like. As a result, even if the wear of the contact member 26 increases due to sliding contact with the fixing belt 21 over a long period of use, only the contact member 26 can be efficiently replaced (maintenance).

  The contact surface of the contact member 26 is formed of a material having a low friction coefficient so that the wear of the fixing belt 21 is reduced even if the contact member 26 and the fixing belt 21 are in sliding contact with each other. It is preferable to apply a lubricant between the belt 26 and the fixing belt 21. Specifically, by applying a surface coating such as Teflon (registered trademark), plating, DLC (diamond-like carbon), glass coating or the like to the sliding contact surface of the contact member 26, the surface roughness of the sliding contact surface is Rz = It is desirable that the thickness be 64 μm or less.

  In the fixing device 20 of FIG. 11 as well, by applying the configuration of the pressure roller 31 described above, it is possible to reduce the outflow of heat to the pressure roller 31 during paper feeding and to save power, and to impair grip force. The fixing belt 21 can be stably rotated. In addition, it is possible to easily configure the pressure roller 31 having a composite structure that is difficult to realize by integral manufacturing, and further, only the grip member 50 can be removed and replaced with respect to the deterioration of the grip portion of the pressure roller 31. Reduction and resource saving.

  Further, instead of the heater 25 in FIG. 11, an induction heating unit 60 of an electromagnetic induction heating method as shown in FIG. 12 is arranged on the outer peripheral side of the heating member 22, and the induction heating unit 60 passes the heating member 22 through the heating member 22. The fixing belt 21 may be heated. The other configuration is the same as that shown in FIG. The reinforcing member 23 may be omitted.

Further, the belt fixing device includes a fixing belt that is wound around a plurality of rollers including a fixing roller and a heating roller, and a heating roller that presses the fixing roller through the fixing belt to form a nip portion. The present invention may be applied to a pressure roller.
Alternatively, the present invention may be applied to a pressure roller in a roller-roller type fixing device in which a fixing roller and a pressure roller are in direct contact with each other to form a nip portion.

  In the above-described embodiment, the configuration based on the premise that the center of the nip portion is the paper passing portion is shown. However, the paper passing method based on one of the end sides in the axial direction of the nip portion (that is, The present invention can also be applied to a case where the end side is a paper passing portion. In this case, the grip member 50 is provided on one end side in the axial direction of the pressure roller 31.

1. Image forming device (device main body)
3 Exposure unit 4Y, 4M, 4C, 4K Image forming unit 5Y, 5M, 5C, 5K Photosensitive drum 12 Paper feed unit 20 Fixing device 21 Fixing belt (fixing member)
22 Heating member 23 Reinforcing member 25 Heater (heat source)
26 Contact member 27 Heat insulation member 31 Pressure roller (pressure member)
31a Roller body 32 Core metal 33 Elastic layer 34 Release layer 35 Roller shaft 35a C ring groove 35n Male thread part 37 Inclined surface 40 Temperature sensor 42 Bearing 43 Side plate 45 Gear 50 Grip member 51 Base member 51n Female thread part 52 Elastic layer 54 Oval hole 57 One-way clutch 58 Clearance 59 Hole part 60 Induction heating part 75 Charging part 76 Developing device 77 Cleaning part 78 Intermediate transfer belt 79Y, 79M, 79C, 79K Primary transfer bias roller 80 Intermediate transfer cleaning part 82 Secondary transfer backup Roller 83 Cleaning backup roller 84 Tension roller 85 Intermediate transfer unit 89 Secondary transfer roller 97 Paper feed roller 98 Registration roller pair 99 Paper discharge roller pair 100 Stack part 101 Bottle storage part 102Y, 102M, 1 2C, 102K toner bottle P recording medium T toner (toner image)

Japanese Patent Laid-Open No. 11-2982 JP 2008-165102 A JP 2009-1004045 A

Claims (8)

A rotating fixing member;
A pressure member that forms a nip portion for fixing the unfixed toner on the recording medium passing through the fixing member to the recording medium;
Heating means for heating the fixing member,
The pressure member includes a paper passing portion that is a region through which the recording medium passes in the nip portion, and a grip portion that presses the fixing member and rotates the fixing member as the pressure member rotates. Is a roller member arranged side by side in the axial direction, and the grip portion is constituted by a grip member that can be attached to and detached from the roller body of the pressure member.   The fixing device according to claim 1, wherein the grip member is a cylindrical member, and is fixed to a roller body of the pressure member so as to be integrated as a roller member.   A female threaded part and a male threaded part are arranged on the inner peripheral part of the cylinder of the grip member and the roller shaft of the roller body so that when the roller shaft is rotated in the rotational direction of the rotational drive of the pressure member, the screw tightening direction is obtained. The fixing device according to claim 2, wherein the grip member is fixed to a roller body of the pressure member by screwing together.   The fixing device according to claim 2, wherein the grip member is fixed to a roller shaft of the roller body via a one-way clutch.   With the nip portion formed, the pressure member is rotated in the direction opposite to the driving rotation, and the sheet passing portion of the pressure member and the fixing member are slid. The fixing device according to claim 3, further comprising a cleaning mode for cleaning.   The axial direction of the said pressurizing member WHEREIN: The roller part which comprises the said paper passing part, and the said grip member are spaced apart, The space which accommodates the foreign material which goes to the said grip part is provided. The fixing device according to any one of the above.   The fixing device according to claim 1, wherein a roller outer peripheral surface of the sheet passing portion and a roller outer peripheral surface of the grip portion of the pressure member are substantially flat in the axial direction.   An image forming apparatus comprising the fixing device according to claim 1.

Images