JP2011170000A - Fixing device and image forming device - Google Patents

Abstract

A fixing device in which the fixing belt does not cause a slack in the fixing belt on the downstream side of a nip portion, even when the warm-up time or the first print time is short and the device is speeded up, without causing defective fixing or the like. And an image forming apparatus.
A fixing member that is fixed to an inner peripheral surface side of a fixing belt and presses against a pressure rotating body to form a nip portion, and an inner peripheral surface of the fixing belt at a position excluding the nip portion. A pipe-shaped metal member 22 which is fixed so as to be opposed to heat the fixing belt 21. A pressing member 24 that presses the fixing belt 21 from the inner peripheral surface side is provided between the fixing belt 21 and the metal member 22 so that the fixing belt 21 is not slackened on the downstream side of the nip portion.
[Selection] Figure 2

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, or a complex machine thereof, and a fixing device installed therein.

  2. Description of the Related Art Conventionally, in image forming apparatuses such as copiers and printers, fixing apparatuses that have a short warm-up time and first print time and are less likely to cause poor fixing even when the apparatus is speeded up are known (for example, (See Patent Documents 1 and 2).

Specifically, the fixing device of Patent Document 1 or the like heats a fixing belt as a fixing member, a substantially pipe-shaped metal member (opposing member) fixed so as to face the inner peripheral surface of the fixing belt, and the metal member. For this purpose, a heater (heating means) provided in the metal member, a pressure roller as a pressure rotating body that presses against the fixing belt to form a nip portion, and the like are configured.
The fixing belt is heated by the metal member heated by the heater, and the toner image on the recording medium conveyed toward the nip portion is fixed on the recording medium by receiving heat and pressure at the nip portion. It will be.

  In the above-described fixing device disclosed in Patent Document 1, the upstream side of the nip portion becomes the tension side of the fixing belt, and the fixing belt is loosened on the downstream side of the nip portion. When the looseness of the fixing belt generated on the downstream side of the nip portion becomes large in this way, there is a problem that an abnormal image such as gloss unevenness is generated on the fixed image on the recording medium sent from the nip portion, or the nip portion sends the fixing belt. This causes a problem that the separability of the recorded recording medium is lowered.

  The present invention has been made in order to solve the above-described problems. Even if the warm-up time or first print time is short and the apparatus is speeded up, fixing failure or the like does not occur. It is an object of the present invention to provide a fixing device and an image forming apparatus in which the fixing belt is not loosened downstream.

  According to a first aspect of the present invention, there is provided a fixing device that travels in a predetermined direction to heat and melt a toner image, and has an endless fixing belt having flexibility, and an inner peripheral surface of the fixing belt. A fixing member that is fixed on the side and forms a nip portion that is pressed against the pressure rotator through the fixing belt and transports the recording medium, and an inner peripheral surface of the fixing belt at a position excluding the nip portion And a pipe-shaped metal member that is heated by the heating means and is fixed to the nip portion on the downstream side in the running direction of the fixing belt. A pressing member for pressing the fixing belt from the inner peripheral surface side is provided between the fixing belt and the metal member so that the belt is not slackened.

  A fixing device according to a second aspect of the present invention is the fixing device according to the first aspect, wherein the pressing member is moved in the same direction as the traveling direction of the fixing belt at a contact position with the fixing belt. Thus, the roller member is rotationally driven by the driving means.

  According to a third aspect of the present invention, there is provided the fixing device according to the first or second aspect, wherein the center of the metal member and the pressure rotator when viewed in a cross section perpendicular to the width direction. The heating means is arranged in one area divided by a straight line passing through the rotation center of the lens, and the pressing member is arranged in the other area.

  The fixing device according to a fourth aspect of the present invention is the fixing device according to any one of the first to third aspects, wherein the pressing member is downstream in the running direction of the fixing belt with respect to the nip portion. It is arrange | positioned in this position.

  A fixing device according to a fifth aspect of the present invention is the fixing device according to any one of the first to fourth aspects, wherein the pressing member is a heat pipe.

  According to a sixth aspect of the present invention, in the fixing device according to the fifth aspect, the heating means heats the metal member by electromagnetic induction.

  According to a seventh aspect of the present invention, in the fixing device according to the fifth or sixth aspect, the metal member includes a concave portion for avoiding contact with the pressing member. The pressing member is configured to be movable between a position facing the concave portion and a contact position contacting the metal member in the width direction.

  The fixing device according to an eighth aspect of the present invention is the fixing device according to the seventh aspect, wherein the pressing member contacts the contact member when a recording medium having a small size in the width direction is continuously fed. It is controlled to move to a position.

  A fixing device according to a ninth aspect of the present invention is the fixing device according to any one of the first to eighth aspects, wherein the fixing device is fixed to an inner peripheral surface side of the metal member and abuts on the fixing member. And a reinforcing member for reinforcing the fixing member.

  An image forming apparatus according to a tenth aspect of the present invention includes the fixing device according to any one of the first to ninth aspects.

In the present application, the state in which the fixing member is “fixed” is defined as a state in which the fixing member is held in a non-rotating manner without being driven to rotate. Therefore, for example, even when the fixing member is biased toward the nip portion by a biasing member such as a spring, the fixing member is “fixed” if the fixing member is held non-rotating. It becomes a state.
Further, in the present application, the “width direction” is defined as a direction orthogonal to the paper passing direction of the recording medium.

  In the present invention, a pressing member that presses the fixing belt from the inner peripheral surface side is provided between the fixing belt and the metal member. Thereby, even when the warm-up time or the first print time is short and the apparatus is speeded up, fixing failure or the like does not occur, and the fixing belt does not loosen at the downstream side of the nip portion. In addition, an image forming apparatus can be provided.

1 is an overall configuration diagram illustrating an image forming apparatus according to Embodiment 1 of the present invention. FIG. 2 is a configuration diagram illustrating a fixing device installed in the image forming apparatus of FIG. 1. FIG. 3 is a diagram in which the fixing device of FIG. 2 is viewed in the width direction. It is an enlarged view which shows the vicinity of a nip part. FIG. 3 is an enlarged view showing the vicinity of a fixing belt and a metal member. It is an enlarged view showing a part of another fixing device. It is a block diagram which shows the fixing device in Embodiment 2 of this invention. It is an enlarged view which shows a part of fixing device in Embodiment 3 of this invention.

  Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified or abbreviate | omitted suitably.

Embodiment 1 FIG.
The first embodiment of the present invention will be described in detail with reference to FIGS.
First, the configuration and operation of the entire image forming apparatus will be described with reference to FIG.
As shown in FIG. 1, the image forming apparatus 1 according to the first embodiment 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 unit 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 configuration and operation of the fixing device 20 installed in the image forming apparatus main body 1 will be described in detail with reference to FIGS.
2 to 5, the fixing device 20 includes a fixing belt 21 (belt member) as a fixing member, a fixing member 26, a metal member 22 (heating member), a reinforcing member 23, a pressing member 24, and a heating unit. Heater 25 (heat source), pressure roller 31 as a pressure rotating body, temperature sensor 40, heat insulating member 27, stay member 28, and the like.

Here, the fixing belt 21 is a thin and flexible endless belt, and rotates (runs) in an arrow direction (counterclockwise) in FIG. The fixing belt 21 has a base material layer, an elastic layer, and a release layer sequentially laminated from the inner peripheral surface 21a (sliding contact surface with the fixing member 26) side, and its total thickness is 1 mm or less. Is set to
The base material layer 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.
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 fluororubber. 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. In the first embodiment, silicone rubber having a layer thickness of 200 μm is used as the elastic layer of the fixing belt 21.
The release layer of the fixing belt 21 has a layer thickness of 10 to 50 μm, and includes PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), PTFE (polytetrafluoroethylene), polyimide, polyetherimide, PES ( Polyether sulfide) and the like. By providing the release layer, the releasability (peelability) for the toner T (toner image) is secured.

Further, the diameter of the fixing belt 21 is set to be 15 to 120 mm. In the first embodiment, the inner diameter of the fixing belt 21 is set to 30 mm.
A fixing member 26, a heater (heating means), a metal member 22, a reinforcing member 23, a heat insulating member 27, a stay member 28, and the like are fixedly provided inside the fixing belt 21 (inner peripheral surface side). Although not shown, a lubricant is interposed (applied) between the fixing belt 21 and the metal member 22.
Here, the fixing member 26 is fixed so as to be in sliding contact with the inner peripheral surface 21 a of the fixing belt 21. The fixing member 26 is pressed against the pressure roller 31 via the fixing belt 21 to form a nip portion where the recording medium P is conveyed. Referring to FIG. 3, both ends of the fixing member 26 in the width direction are fixedly supported by the side plates 43 of the fixing device 20. The configuration of the fixing member 26 will be described in detail later.

Referring to FIG. 2, the metal member 22 (heating member) is formed so as to face the inner peripheral surface of the fixing belt 21 at a position excluding the nip portion, and the fixing member is interposed via the heat insulating member 27 at the position of the nip portion. 26 is a substantially cylindrical body formed so as to hold 26. Referring to FIG. 3, both ends of the metal member 22 in the width direction are fixedly supported by the side plates 43 of the fixing device 20. In addition, flanges 29 are provided at both ends of the metal member 22 to limit the displacement of the fixing belt 21 (movement in the width direction).
The metal member 22 formed in a substantially pipe shape is heated by the radiant heat of the heater 25 to heat the fixing belt 21 (transmits heat). That is, the metal member 22 is directly heated by the heater 25, and the fixing belt 21 is indirectly heated by the heater 25 through the metal member 22. In order to maintain the heating efficiency of the fixing belt 21 favorably, the thickness of the metal member 22 is preferably set to 0.1 mm or less.
As a material of the metal member 22, a metal heat conductor (a metal having heat conductivity) such as stainless steel, nickel, aluminum, and iron can be used. X Ferrite stainless steel having a relatively small specific heat) is preferred. In the first embodiment, SUS430 that is ferritic stainless steel is used as the material of the metal member 22. Further, the thickness of the metal member 22 is set to 0.1 mm.

  The heater 25 as a heating means is a halogen heater (or carbon heater), and both ends thereof are fixed to the side plate 43 of the fixing device 20 (see FIG. 3). The metal member 22 is heated by the radiant heat of the heater 25 (heating means) whose output is controlled by the power supply unit of the apparatus body 1. Further, the fixing belt 21 is entirely heated by the metal member 22 at a position excluding the nip portion, 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.

  As described above, in the fixing device 20 according to the first embodiment, not only a part of the fixing belt 21 is locally heated, but the fixing belt 21 is almost entirely heated in the circumferential direction by the metal member 22. 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 substantially pipe-shaped metal member 22 is fixed so as to face the inner peripheral surface (the position excluding the nip portion) of the fixing belt 21 with a clearance. A clearance amount δ (a gap at a position excluding the nip portion) between the fixing belt 21 and the metal member 22 is set to be larger than 0 mm and not larger than 1 mm (0 mm <δ ≦ 1 mm). As a result, the area in which the metal member 22 and the fixing belt 21 are in sliding contact with each other is increased, and the problem that the wear of the fixing belt 21 is accelerated is suppressed, and the metal member 22 and the fixing belt 21 are separated too much and the fixing belt 21 is heated. Inconveniences that reduce efficiency can be suppressed. Furthermore, since the metal member 22 is provided close to the fixing belt 21, the circular posture of the flexible fixing belt 21 is maintained to some extent, so that deterioration and breakage due to deformation of the fixing belt 21 can be reduced. . Further, in order to reduce the wear of the fixing belt 21 even if the metal member 22 and the fixing belt 21 are in sliding contact with each other, the inner circumferential surface of the fixing belt 21 has fluorine grease or the like between both members 21 and 22. A lubricant such as silicone oil is applied.
Here, in the first embodiment, a pressing member 24 (roller member) for applying tension to the fixing belt 21 is installed between the fixing belt 21 and the metal member 22. explain in detail.
In the first embodiment, the metal member 22 is formed to have a substantially circular cross-sectional shape, but the metal member 22 may be formed to have a polygonal cross-sectional shape.

  Here, in the first embodiment, the reinforcing member 23 that reinforces the strength of the fixing member 26 that forms the nip portion is fixed to the inner peripheral surface side of the fixing belt 21. Referring to FIG. 3, the reinforcing member 23 is formed so that the length in the width direction is equal to that of the fixing member 26, and both end portions in the width direction are fixedly supported by the side plates 43 of the fixing device 20. . The reinforcing member 23 abuts against the pressure roller 31 via the fixing member 26 and the fixing belt 21, thereby preventing a problem that the fixing member 26 is greatly deformed by the pressure applied by the pressure roller 31 in the nip portion. ing. In the first embodiment, the reinforcing member 23 is a plate-like member disposed so as to divide the inside of the metal member 22 into two spaces.

In order to satisfy the above-described function, the reinforcing member 23 is preferably formed of a metal material having high mechanical strength such as stainless steel or iron. In Embodiment 1, SUS304 (or SUS430) having a plate thickness of about 1.5 to 2 mm is used as the material of the reinforcing member 23.
In addition, a heat insulating member can be provided on a part or all of the surface of the reinforcing member 23 facing the heater 25, or a mirror surface treatment can be performed. As a result, the heat from the heater 25 toward the reinforcing member 23 (heat for heating the reinforcing member 23) is used for heating the metal member 22, so that the heating efficiency of the fixing belt 21 (metal member 22) is further improved. Will do.

  Referring to FIG. 2, a pressure roller 31 as a pressure rotator that contacts the outer peripheral surface of the fixing belt 21 at the position of the nip portion has an outer diameter of 30 mm and is elastic on a hollow core metal 32. Layer 33 (layer thickness is about 3 mm) is formed. The elastic layer 33 of the pressure roller 31 (pressure rotator) is formed of a material such as foamable silicone rubber, silicone rubber, or fluororubber. A thin release layer made of PFA, PTFE or the like can be provided on the surface layer of the elastic layer 33. The pressure roller 31 is pressed against the fixing belt 21 to form a desired nip portion between both members. 3, the pressure roller 31 is provided with a gear 45 that meshes with a drive gear (not shown) of the drive unit 51, and the pressure roller 31 is in the direction of the arrow in FIG. It is rotationally driven (clockwise). Further, both ends of the pressure roller 31 in the width direction are rotatably supported by the side plates 43 of the fixing device 20 via bearings 42. 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 the first embodiment, the diameter of the fixing belt 21 is formed so as to be approximately equal to the diameter of the pressure roller 31, but the diameter of the fixing belt 21 is smaller than the diameter of the pressure roller 31. It can also be formed. 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.

Referring to FIG. 4, the fixing member 26 that is in sliding contact with the inner peripheral surface 21a of the fixing belt 21 has a surface layer 26a formed on a base layer 26b. The fixed member 26 is formed in a concave shape so that the surface (sliding contact 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.
In the first embodiment, the shape of the fixing member 26 that forms the nip portion is formed in a concave shape, but the shape of the fixing member 26 that forms the nip portion can also be formed in a flat shape. That is, the sliding contact surface of the fixing member 26 (the surface facing the pressure roller 31) can be formed in a planar shape. 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.

Further, the material for forming the base layer 26b of the fixing member 26 is made of a material having a certain degree of rigidity so that it does not bend greatly even if it receives pressure applied by the pressure roller 31. In the first embodiment, aluminum having a thickness of about 1.5 mm is used as the material of the base layer 26b.
Since the thickness of the substantially pipe-shaped metal member 22 formed by bending a metal plate can be reduced, the warm-up time can be shortened. However, since the rigidity of the metal member 22 itself is small, the metal member 22 may bend or deform without resisting the pressure applied by the pressure roller 31. If the pipe-shaped metal member 22 is deformed, a desired nip width cannot be obtained and the fixing property is deteriorated. On the other hand, in the first embodiment, since the high-rigidity fixing member 26 is installed separately from the thin metal member 22 to form the nip portion, such a problem is caused in advance. Can be prevented.

Further, the surface layer 26a of the fixing member 26 is formed of a low friction elastic material such as fluoro rubber. By providing such a surface layer 26 a, the problem that both the members 21 and 26 wear due to the sliding contact between the fixing member 26 and the fixing belt 21 is reduced, and a desired gap is provided between the both members 21 and 26. A nip portion is formed. In the first embodiment, the thickness of the surface layer 26a is set to about 1.5 to 2 mm.
In addition, the surface layer 26 a of the fixing member 26 can be impregnated with a lubricant in advance. As a result, the fixing member 26 is in a state where the lubricant is held on the surface in contact with the fixing belt 21, and the problem that both the members 21 and 26 are worn is further reduced.

In the first embodiment, the heat insulating member 27 is installed between the fixing member 26 and the heater 25 (heating means). Specifically, the heat insulating member 27 is installed between the fixing member 26 and the metal member 22 so as to cover the surface of the fixing member 26 excluding the sliding contact surface. As a material of the heat insulating member 27, sponge rubber having excellent heat insulating properties, ceramic having an empty package, or the like can be used.
In the first embodiment, since the fixing belt 21 and the metal member 22 are close to each other over almost the entire circumference, the fixing belt 21 can be heated in the circumferential direction without temperature unevenness even when waiting for heating (when waiting for a printing operation). Therefore, after receiving a print request, a print operation can be performed promptly. At this time, in a conventional on-demand type fixing device (see, for example, Japanese Patent No. 2884714), if heat is applied while the pressure roller is deformed during heating standby at the nip portion, the rubber of the pressure roller Depending on the material, heat deterioration may cause the life of the pressure roller to be shortened or compression set to be generated on the pressure roller. Increased by joining.) When compression set is generated in the pressure roller, a part of the pressure roller is indented, and a desired nip width cannot be obtained. Therefore, fixing failure occurs or abnormal noise occurs during rotation. To do.
On the other hand, in the first embodiment, since the heat insulating member 27 is installed between the fixing member 26 and the metal member 22, the heat of the metal member 22 does not easily reach the fixing member 26 during heating standby. . Therefore, the problem of being heated at a high temperature in a state where the pressure roller 31 is deformed at the time of heating standby can be reduced, and the above-described problems can be prevented from occurring.

Further, the lubricant applied between the two members in order to reduce the frictional resistance between the fixing member 26 and the fixing belt 21 is deteriorated by use under a high temperature condition in addition to the high pressure condition in the nip portion. There is a possibility that problems such as slippage may occur.
On the other hand, in Embodiment 1, since the heat insulating member 27 is installed between the fixing member 26 and the metal member 22, the heat of the metal member 22 does not easily reach the lubricant in the nip portion. Therefore, deterioration due to high temperature of the lubricant is reduced, and the above-described problems can be prevented from occurring.

  In the first embodiment, since the heat insulating member 27 is installed between the fixing member 26 and the metal member 22, the fixing member 26 is thermally insulated and the fixing belt 21 is actively heated in the nip portion. Will not be. For this reason, the temperature of the recording medium P fed into the nip portion is lowered when it is sent out from the nip portion. That is, at the exit of the nip portion, the temperature of the toner image fixed on the recording medium P is lowered, the viscosity of the toner is lowered, and the toner adhesive force to the fixing belt 21 is reduced. Separated from the fixing belt 21. Therefore, the problem that the recording medium P immediately after the fixing process is wound around the fixing belt 21 and jamming is prevented, and toner adhesion to the fixing belt 21 is also suppressed.

In the first embodiment, referring to FIG. 4, a stay member 28 that holds the concave portion 22a of the metal member 22 in which the fixing member 26 is inserted from the inner peripheral surface side is provided.
The substantially pipe-shaped metal member 22 is formed by bending a flat plate made of stainless steel having a thickness of 0.1 mm. Therefore, even if it is going to process a stainless steel plate into a desired pipe shape by bending, it will open in the direction where a diameter becomes large with a spring back, and a desired pipe shape cannot be formed. If the metal member 22 is opened by the spring back, it contacts the inner peripheral surface of the fixing belt 21 and damages the fixing belt 21 or causes uneven heating of the fixing belt 21 due to uneven contact with the fixing belt 21. Resulting in. In the first embodiment, in order to prevent such a problem from occurring, the recess 22a (bent portion) in which the opening of the metal member 22 is formed is fixed by the stay member 28, whereby the metal member 22 Deformation due to springback is suppressed. Specifically, the stay member 28 is press-fitted into the recess 22a from the inner peripheral surface side of the metal member 22 while maintaining the shape of the metal member 22 that has been bent so as to resist the springback force.

Here, in order to increase the heating efficiency of the metal member 22, the thickness of the metal member 22 is preferably set to 0.2 mm or less.
As described above, since the thickness of the substantially pipe-shaped metal member 22 formed by bending a metal plate can be reduced, the warm-up time can be shortened. However, since the rigidity of the metal member 22 itself is small, when the pressing force of the pressure roller 31 acts on the metal member 22, the metal member 22 cannot be fully resisted and is bent or deformed. When the pipe-shaped metal member 22 is deformed, a desired nip width cannot be obtained, and a problem that the fixing property is deteriorated occurs. On the other hand, in the first embodiment, the thin metal member 22 is provided with a recess 22a (a portion where the fixing member 26 is inserted) so as to be separated from the nip portion. Since the pressurizing force is configured not to act directly on the metal member 22, it is possible to prevent such a problem from occurring.

The normal operation of the fixing device 20 configured as described above will be briefly described below.
When the power switch of the apparatus main body 1 is turned on, power is supplied to the heater 25, and the drive unit 51 starts to rotate the pressure roller 31 in the direction of the arrow in FIG. Accordingly, the fixing belt 21 is also driven (rotated) in the direction of the arrow in FIG. 2 by the frictional force with the pressure roller 31 in the nip portion.
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 T (toner image) is conveyed in the direction of arrow Y10 in FIG. 2 while being guided by a guide plate (not shown), and the fixing belt 21 and the pressure roller 31 that are in a pressure contact state. 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 metal member 22 (heater 25) and the pressing force of the fixing member 26 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.

Hereinafter, a characteristic configuration and operation of the fixing device 20 according to the first embodiment will be described in detail.
Referring to FIGS. 2 and 5, in fixing device 20 in the first embodiment, pressing member 24 that presses fixing belt 21 from the inner peripheral surface side is provided between fixing belt 21 and metal member 22. It has been. The pressing member 24 is for preventing the fixing belt 21 from slackening on the downstream side of the nip portion (the downstream side in the running direction of the fixing belt 21 with respect to the nip portion).

Referring to FIG. 4, the fixing belt 21 travels in the direction of the arrow (counterclockwise) due to frictional resistance with the pressure roller 31 at the position of the nip portion. Is the tension side of the fixing belt 21 (the side on which the belt tension is increased). Accordingly, the fixing belt 21 is likely to be slack (the belt trajectory A indicated by a one-dot chain line in the drawing) on the downstream side of the nip portion. When the slackness of the fixing belt 21 increases, the apparent nip width at the nip portion increases, and an excessive amount of heat is supplied to the recording medium P sent from the nip portion, so that glossiness unevenness or offset is caused in the fixed image. An abnormal image such as this occurs. Further, the slack of the fixing belt 21 makes it difficult for the recording medium P sent out from the nip portion to come into close contact with the fixing belt 21 and be separated.
On the other hand, in the first embodiment, since the pressing member 24 that presses the fixing belt 21 from the inner peripheral surface side is provided, a tension is applied to the fixing belt 21 and the fixing belt on the downstream side of the nip portion. 21 slack is reduced. Therefore, a good fixed image without gloss unevenness and offset is output, and the occurrence of poor separation of the recording medium P after the fixing process is also suppressed.

Here, the pressing member 24 in the first embodiment is rotated so as to move in the same direction as the traveling direction of the fixing belt 21 at the contact position with the fixing belt 21 (rotation in the counterclockwise direction in FIG. 5). ). The pressing member 24 (roller member) has an outer diameter of about 2 to 5 mm and is configured to contact the fixing belt 21 over the entire width direction. Further, as shown in FIG. 2, a drive motor 52 as a drive unit that rotationally drives the pressing member 24 (roller member) is provided separately from the drive unit 51 that rotationally drives the pressure roller 31.
In this way, the pressing member 24 is not driven by the frictional resistance with the fixing belt 21, but the pressing member 24 is independently rotated by the drive motor 52 (driving means), and the pressing member 24 is connected to the fixing belt 21. By using the roller member that is in substantially line contact, the problem that the load torque to the fixing belt 21 increases by installing the pressing member 24 can be reduced.
The pressing member 24 has a function of driving the fixing belt 21 in an auxiliary manner by rotationally driving the linear velocity of the pressing member 24 at the contact position with the fixing belt 21 to be equal to the traveling speed of the fixing belt 21. Can also be given. In such a case, it is preferable to use a high friction material that increases the frictional resistance with the fixing belt 21 as the material (surface material) of the pressing member 24. With such a configuration, the slip of the fixing belt 21 can be reliably reduced.

The pressing member 24 is preferably formed of a heat insulating material so as not to take heat away from the fixing belt 21 or the metal member 22 and reduce the heating efficiency of both the members 21 and 22.
Further, in the first embodiment, the pressing member 24 is configured to contact the metal member 22 in consideration of installing the pressing member 24 in a minute clearance between the metal member 22 and the fixing belt 21. However, the pressing member 24 may be configured not to contact the metal member 22.
In the first embodiment, the driving motor 51 (driving means) that rotationally drives the pressing member 24 is provided separately from the driving unit 51 that rotationally drives the pressure roller 31. On the other hand, the pressing member 24 can also be configured to be rotationally driven by the driving unit 51 that rotationally drives the pressure roller 31.

Here, in the first embodiment, as shown in FIG. 5, when viewed in a cross section perpendicular to the width direction (the direction perpendicular to the paper surface of FIG. 5), the center of the metal member 22 and the pressure roller 31. A heater 25 (heating means) is arranged in one area (below the alternate long and short dash line) divided by a straight line passing through the center of rotation (the straight line shown by the alternate long and short dash line in FIG. 5). The pressing member 24 is disposed in the other region (above the alternate long and short dash line).
With this configuration, the region B of the metal member 22 that is directly heated by the heater 25 (the region that is close to and faces the heater 25) can be brought into close contact with the fixing belt 21. Therefore, the heating efficiency of the fixing belt 21 is further improved. That is, as shown in FIG. 6, it is a straight line passing through the center of the metal member 22 and the rotation center of the pressure roller 31 when viewed in a cross section perpendicular to the width direction (a straight line indicated by a one-dot chain line in FIG. 5). When the heater 25 (heating means) and the pressing member 24 are disposed in one area (below the alternate long and short dash line), the metal member 22 heated directly by the heater 25 is divided. Area B becomes difficult to adhere to the fixing belt 21 (it becomes difficult to secure a minute clearance between the fixing belt 21 and the metal member 22).

Moreover, in this Embodiment 1, as shown in FIG. 5, the press member 24 is arrange | positioned in the position of the nip part downstream side (above a dashed-dotted line).
Accordingly, it is possible to effectively apply tension to the fixing belt 21 on the downstream side of the nip portion, and to effectively eliminate the slack of the fixing belt 21 at that position. Further, even when the pressing member 24 takes heat from the fixing belt 21 and the metal member 22, the region B (the region where the metal member 22 is directly heated by the heater 25) is used thereafter. Since the metal member 22 and the fixing belt 21 are positively heated by the heater 25, the problem that the heating failure of the metal member 22 and the fixing belt 21 occurs is suppressed.

  In the first embodiment, the pressing member 24 may be a heat pipe. Thereby, the temperature distribution in the width direction of the fixing belt 21 and the metal member 22 can be made uniform. Therefore, uneven fixing is less likely to occur in the fixed image formed on the recording medium P.

  As described above, in the first embodiment, the pressing member 24 that presses the fixing belt 21 from the inner peripheral surface side is provided between the fixing belt 21 and the metal member 22. Thereby, even when the warm-up time and the first print time are short and the fixing device 20 (image forming apparatus 1) is speeded up, fixing failure or the like does not occur, and the fixing belt 21 is large downstream of the nip portion. It is possible to suppress defects that cause slack.

Embodiment 2. FIG.
A second embodiment of the present invention will be described in detail with reference to FIG.
FIG. 7 is a configuration diagram illustrating the fixing device according to the second embodiment, and corresponds to FIG. 2 according to the first embodiment. The fixing device according to the second embodiment is different from that according to the first embodiment in that the metal member 22 is heated by electromagnetic induction.

  As shown in FIG. 7, the fixing device 20 according to the second embodiment also has a fixing belt 21 (belt member), a fixing member 26, a substantially pipe-shaped metal member 22, and a reinforcement, as in the first embodiment. The member 23, the pressing member 24, the heat insulating member 27, the pressure roller 31 (heating rotator), the temperature sensor 40, and the like are included. Although not shown in the drawings, the fixing device 20 according to the second embodiment also applies a pressing member 24 (roller member) so as to press the fixing belt 21 from the inner peripheral surface side as in the first embodiment. ) Is installed.

  Here, in the fixing device 20 according to the second embodiment, an induction heating unit 50 is installed as a heating unit instead of the heater 25. And unlike the said Embodiment 1 heated by the radiant heat of the heater 25, the metal member 22 in this Embodiment 2 is heated by the electromagnetic induction by the induction heating part 50. FIG.

  The induction heating unit 50 includes an exciting coil, a core, a coil guide, and the like. The exciting coil is formed by extending a litz wire, which is a bundle of thin wires, in the width direction (in the direction perpendicular to the paper in FIG. 7) so as to cover a part of the fixing belt 21. The coil guide is made of a resin material having high heat resistance and holds the exciting coil and the core. The core is a semi-cylindrical member made of a ferromagnetic material such as ferrite (having a relative permeability of about 1000 to 3000), and in order to form an efficient magnetic flux toward the metal member 22, A side core is provided. The core is installed so as to face the exciting coil extending in the width direction.

The fixing device 20 configured as described above operates as follows.
When the fixing belt 21 is rotationally driven in the arrow direction in FIG. 7, the fixing belt 21 is heated at a position facing the induction heating unit 50. Specifically, the magnetic lines of force are formed alternately around the metal member 22 by flowing a high-frequency alternating current through the exciting coil. At this time, an eddy current is generated on the surface of the metal member 22, and Joule heat is generated by the electric resistance of the metal member 22 itself. Due to this Joule heat, the metal member 22 is heated by electromagnetic induction, and the fixing belt 21 is heated by the heated metal member 22.

In order to efficiently perform electromagnetic induction heating of the metal member 22, it is preferable that the induction heating unit 50 is configured to face the entire circumferential direction of the metal member 22. Moreover, as a material of the metal member 22, nickel, stainless steel, iron, copper, cobalt, chromium, aluminum, gold, platinum, silver, tin, palladium, an alloy composed of a plurality of these metals, or the like can be used. .
In addition, the fixing belt 21 is provided with a metal layer made of nickel, stainless steel, iron, copper, cobalt, chromium, aluminum, gold, platinum, silver, tin, palladium, an alloy made of a plurality of these metals, etc. The fixing belt 21 can also be heated by electromagnetic induction by the heating unit 50.

Here, in the second embodiment, the pressing member 24 is preferably a heat pipe. Thereby, the temperature distribution in the width direction of the fixing belt 21 and the metal member 22 can be made uniform. Therefore, uneven fixing is less likely to occur in the fixed image formed on the recording medium P.
In particular, when electromagnetic induction is used as the heating unit as in the fixing device 20 according to the second embodiment, the heating time of the metal member 22 and the fixing belt 21 is higher than when the heater is used as the heating unit. Although greatly shortened, since the temperature distribution in the width direction tends to be non-uniform, it is useful to use the pressing member 24 as a heat pipe.

  As described above, also in the second embodiment, as in the first embodiment, the pressing member 24 that presses the fixing belt 21 from the inner peripheral surface side is provided between the fixing belt 21 and the metal member 22. Provided. Thereby, even when the warm-up time and the first print time are short and the fixing device 20 (image forming apparatus 1) is speeded up, fixing failure or the like does not occur, and the fixing belt 21 is large downstream of the nip portion. It is possible to suppress defects that cause slack.

In the second embodiment, the metal member 22 is heated by electromagnetic induction heating, but the metal member 22 can also be heated by the heat of the resistance heating element. Specifically, the resistance heating element is brought into contact with part or all of the inner peripheral surface of the metal member 22. The resistance heating element is a planar heating element such as a ceramic heater, and a power supply unit is connected to both ends thereof. When a current is passed through the resistance heating element, the resistance heating element is heated by the electric resistance of the resistance heating element itself, and heats the metal member 22 in contact therewith. Further, the fixing belt 21 is heated by the heated metal member 22.
Even in such a case, by providing the pressing member 24, the same effect as in the second embodiment can be obtained.

Embodiment 3 FIG.
A third embodiment of the present invention will be described in detail with reference to FIG.
FIG. 8 is an enlarged view showing a part of the fixing device in the third embodiment, and corresponds to FIG. 5 in the first embodiment. The fixing device according to the third embodiment is different from that according to the second embodiment in that the pressing member 24 is configured to be movable.

  As shown in FIG. 8A, the fixing device 20 according to the third embodiment also has a fixing belt 21 (belt member), a fixing member 26, and a substantially pipe-shaped metal member, as in the second embodiment. 22, a reinforcing member 23, a pressing member 24, a heat insulating member 27, a pressure roller 31 (heating rotator), a temperature sensor 40, and the like. Although not shown, the fixing device 20 according to the third embodiment also has an induction heating unit 50 as a heating unit at a position facing the outer peripheral surface of the fixing belt 21 as in the second embodiment. Is installed. A pressing member 24 (roller member) is installed so as to press the fixing belt 21 from the inner peripheral surface side. The pressing member 24 is a heat pipe.

  Here, the metal member 22 according to the third embodiment is formed with a concave portion 22a for avoiding contact with the pressing member 24 (heat pipe). And it is comprised by the moving mechanism not shown so that the press member 24 can move between the position which opposes the recessed part 22a, and the contact position which contacts the metal member 22 over the width direction. That is, the pressing member 24 has a position shown in FIG. 8A (a position in contact with the metal member 22) and a position shown in FIG. 8B (a position not in contact with the metal member 22). Can move. As such a moving mechanism, for example, a cam mechanism can be used.

Then, during normal paper feeding (fixing process), the pressing member 24 is controlled so as to be in the position of FIG. 8B, and a small size paper (a recording medium P having a small size in the width direction) is used. When the sheets are continuously fed, the pressing member 24 is controlled so as to be in the position of FIG.
With this configuration, when small-size paper is continuously passed, even if the non-sheet passing region (both ends in the width direction) of the metal member 22 is likely to overheat, FIG. As shown, since the heat pipe as the pressing member 24 is in contact with the metal member 22, the heat in the non-sheet passing region can be dispersed in the width direction. On the other hand, since the pressing member 24 is spaced apart from the metal member 22 as shown in FIG. 8B at normal times when no excessive temperature rise occurs at both ends in the width direction, the heat of the metal member 22 is pressed. The fixing belt 21 can be efficiently heated without being taken away by the member 24.

  As described above, also in the third embodiment, the pressing member 24 that presses the fixing belt 21 from the inner peripheral surface side is provided between the fixing belt 21 and the metal member 22 in the same manner as each of the above embodiments. Provided. Thereby, even when the warm-up time and the first print time are short and the fixing device 20 (image forming apparatus 1) is speeded up, fixing failure or the like does not occur, and the fixing belt 21 is large downstream of the nip portion. It is possible to suppress defects that cause slack.

  In each of the above embodiments, the fixing belt 21 having a multilayer structure is used as the fixing belt. However, an endless fixing film made of polyimide, polyamide, fluororesin, metal, or the like may be used as the fixing belt. In this case, the same effects as those of the above embodiments can be obtained.

  It should be noted that the present invention is not limited to the above-described embodiments, and within the scope of the technical idea of the present invention, the embodiments can be modified as appropriate in addition to those suggested in the embodiments. Is clear. In addition, the number, position, shape, and the like of the constituent members are not limited to the above embodiments, and can be set to a number, position, shape, and the like that are suitable for carrying out the present invention.

1 image forming apparatus body (apparatus body),
20 fixing device,
21 fixing belt (fixing member),
22 metal member (heating member),
22a concave part,
23 reinforcing members,
24 pressing member (roller member),
25 heater (heating means),
26 fixing member,
31 Pressure roller (pressure rotating body),
50 induction heating unit (heating means),
52 Drive motor (drive means), P recording medium.

Japanese Patent No. 2008-158482 Japanese Patent No. 2007-334205

Claims (10)

An endless fixing belt having flexibility and running in a predetermined direction to heat and melt the toner image;
A fixing member fixed on the inner peripheral surface side of the fixing belt and forming a nip portion for conveying a recording medium in pressure contact with the pressure rotator via the fixing belt;
A pipe-shaped metal member fixed to be opposed to the inner peripheral surface of the fixing belt at a position excluding the nip portion and heating the fixing belt, and heated by a heating unit;
With
A pressing member that presses the fixing belt from the inner peripheral surface side so that the fixing belt is not loosened downstream of the nip portion in the running direction of the fixing belt is provided between the fixing belt and the metal member. A fixing device provided in the above.   2. The roller member according to claim 1, wherein the pressing member is a roller member that is rotationally driven by a driving unit so as to move in the same direction as the traveling direction of the fixing belt at a contact position with the fixing belt. Fixing device.   When viewed in a cross-section perpendicular to the width direction, the heating means is disposed in one region divided by a straight line passing through the center of the metal member and the rotation center of the pressurizing rotating body, and the other region is The fixing device according to claim 1, wherein a pressing member is provided.   The fixing device according to claim 1, wherein the pressing member is disposed at a position downstream of the nip portion in the traveling direction of the fixing belt.   The fixing device according to claim 1, wherein the pressing member is a heat pipe.   The fixing device according to claim 5, wherein the heating unit heats the metal member by electromagnetic induction. The metal member includes a concave portion for avoiding contact with the pressing member,
7. The fixing according to claim 5, wherein the pressing member is configured to be movable between a position facing the concave portion and a contact position contacting the metal member in the width direction. apparatus.   The fixing device according to claim 7, wherein the pressing member is controlled to move to the contact position when a recording medium having a small size in the width direction is continuously fed.   The reinforcing member according to any one of claims 1 to 8, further comprising a reinforcing member that is fixed to an inner peripheral surface side of the metal member and abuts on the fixing member to reinforce the fixing member. Fixing device.   An image forming apparatus comprising the fixing device according to claim 1.

Images