JP2007164025A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably peel recording paper from a belt member in a fixing device using the belt member. <P>SOLUTION: The fixing device includes a fixing roll 611, a pressure roll 62 which is arranged to press the fixing roll 611 across a fixing belt 610 and forms a nip part N, a peeling pad 64 which presses an external surface of the fixing belt 610 against the pressure roll 62 nearby a downstream side of a press-contact part between the fixing roll 611 and pressure roll 62, and an idler roll 615 which is arranged downstream from the peeling pad 64 and upstream from a lap region where the fixing belt 610 is tensed around the fixing roll 611 downstream from the nip part N and then tenses the fixing belt 610. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fixing device used in an image forming apparatus using, for example, an electrophotographic method, and more particularly to a fixing device including a rotatable belt member.

  In an image forming apparatus such as a copying machine or a printer using an electrophotographic method, generally, a surface of a photosensitive drum rotating at a constant speed is uniformly charged by a charger, and then a laser controlled based on image information. Light is scanned and exposed to form an electrostatic latent image. The electrostatic latent image formed on the photosensitive drum is developed by a developing device, and the developed toner image is electrostatically transferred onto the recording paper. Then, the toner image is fixed on the recording paper by the fixing device, and an image is formed.

  As a fixing device used in such an image forming apparatus, a configuration called a two-roll system has been widely used in general. This two-roll type fixing device includes a fixing roll formed by laminating a heat-resistant elastic layer and a release layer on the surface of a cylindrical core bar in which a heating source (heater) is disposed; A pressure roll formed by laminating a heat-resistant elastic layer and a release layer made of a heat-resistant resin film or a heat-resistant rubber film on a metal core is configured to be in pressure contact with each other. Then, the recording paper carrying the unfixed toner image is passed through the pressure contact area (nip portion) between the fixing roll and the pressure roll, and the toner image is heated and pressed against the unfixed toner image. Is firmly established.

By the way, in recent years, as the image forming apparatus is rapidly increasing in productivity and color, many apparatuses having a double-sided printing mechanism have been developed. Furthermore, it is expected that the speeding up of the image forming apparatus will accelerate in the future. For this reason, there is an increasing need to further cope with higher speeds in the fixing device mounted in the image forming apparatus.
However, the conventional two-roll type fixing device has a problem that it is difficult to perform a sufficient fixing process on a large number of recording sheets continuously fed at a high speed. That is, in the two-roll type fixing device, a core metal constituting the fixing roll, an elastic layer made of silicone rubber coated on the core metal, or the like acts as a thermal resistor. Therefore, in the two-roll type fixing device, it is structurally difficult to supply the heat corresponding to the amount of heat taken by the recording paper from the surface of the fixing roll promptly and sufficiently from the heater arranged inside the fixing roll. .
As a result, when the recording paper is continuously fed to the two-roll type fixing device at a high speed, the surface temperature of the fixing roll gradually decreases and the fixing performance gradually decreases. In addition, when the image forming apparatus starts up, a so-called “temperature droop phenomenon” in which the surface temperature of the fixing roll temporarily drops tends to occur. In particular, when thick paper with a large heat capacity is used as recording paper, the amount of heat taken away from the surface of the fixing roll increases, so that the fixing performance decreases and the temperature droop increases, resulting in image quality deterioration due to poor fixing. Will be generated.

Under such circumstances, a technique has been developed that solves the above-described problems that occur when a two-roll type fixing device is used, and realizes a fixing device that can cope with higher speed of the image forming apparatus. For example, there is a technique related to a fixing device in which a heating member that heats recording paper is configured by a film-like belt member (fixing belt) stretched by a plurality of stretching rolls (see, for example, Patent Document 1).
In such a fixing device using a fixing belt, the fixing belt is sufficiently heated by a heater provided in advance in the stretching roll before entering the nip portion, and the fixing belt heated in the nip portion is heated. The toner image is fixed by applying heat to the recording paper and the toner image. Therefore, even if the fixing belt is deprived of heat by the recording paper during the fixing process, since the heat capacity of the fixing belt itself is small, the fixing belt is recovered to a predetermined fixing temperature in a short time by the heater in the stretching roll. It is possible to make it. Accordingly, in the fixing device using the fixing belt as the heating member, it becomes easy to maintain the temperature of the fixing belt when entering the nip portion at a predetermined value, and even if the image forming apparatus is speeded up, It is possible to supply a sufficient amount of heat.

  However, even in a fixing device using a fixing belt, since a toner image is carried on the surface of the recording paper, when the toner image is melted by the heat of the fixing belt, the toner image becomes an adhesive and becomes a recording paper. Adhesive force acts between the toner and the fixing belt. Therefore, it is necessary to provide a mechanism for peeling the recording paper from the surface of the fixing belt as in the conventional two-roll type fixing device. In particular, when the speed of the image forming apparatus is increased, if a separation failure occurs once in the fixing device and a paper jam occurs, the number of subsequent recording papers damaged by the influence increases. For this reason, it is necessary to stably and reliably peel the recording paper that has passed through the nip portion at a high speed from the fixing belt side.

  As a mechanism for separating the recording paper from the surface of the fixing belt, as described in Patent Document 1 described above, a structure in which a separation claw is disposed in contact with the fixing belt on the downstream side of the nip portion is conventionally used. Yes. In a fixing device having a configuration in which a pressure roll is disposed in pressure contact with a fixing belt stretched between a fixing roll and a heating roll, a position corresponding to an outlet portion (the most downstream portion) of the nip portion A fixing member for setting a large curvature of the fixing belt at the outlet is provided inside the fixing belt, and the recording paper is peeled off by changing the curvature of the fixing belt (see, for example, Patent Document 2). .

JP-A-3-133871 (page 4, FIG. 3) Japanese Patent Laying-Open No. 2003-5566 (page 6-8, FIG. 4)

  However, in the fixing device using the fixing belt, when the separation claw is used as a mechanism for separating the recording paper from the surface of the fixing belt, the separation claw is used to stably peel the recording paper from the fixing belt side. It is necessary to be disposed in contact with the. Therefore, the surface of the fixing belt is easily worn by the separation claw. If wear due to the separation claw occurs on the surface of the fixing belt, fixing unevenness corresponding to the wear mark on the surface of the fixing belt may occur on the fixed image, which may deteriorate the image quality. Further, the offset toner may gradually adhere to and accumulate on the wear scar, causing stain on the fixed image. Further, when the surface of the fixing belt progresses, the thin-layer fixing belt eventually breaks, and the function of the fixing device may be impaired.

  Further, as a mechanism for peeling the recording paper from the surface of the fixing belt, when a fixing member for forming a large curvature of the fixing belt is provided at the exit portion of the nip portion, a nip where the fixing roll and the pressure roll are pressed against each other is provided. In the nip intermediate region between the inlet portion of the portion and the outlet portion where the fixing member is disposed, the fixing belt is pressed against the pressure roll only by the tension of the fixing belt. For this reason, the nip pressure in the intermediate nip region is relatively low. When the recording paper or toner is heated in such a low nip pressure region, the water in the recording paper is vaporized to become water vapor, or the air in the toner is thermally expanded. An air gap (bubbles) may be formed between the pressure rolls. When such an air gap occurs, since the toner on the recording paper existing in the nip portion is not completely fixed, the bubbles move around and the unfixed toner is easily disturbed. As a result, an image defect such as unevenness occurs in the fixed image, which causes a serious problem that the image quality is deteriorated.

Accordingly, the present invention has been made to solve the technical problems as described above, and an object of the present invention is to stably separate the recording paper from the belt member in the fixing device using the belt member. There is.
Another object of the present invention is to provide a fixing device that can maintain high fixing performance even when the speed of the image forming apparatus is increased.

For this purpose, the fixing device of the present invention is a fixing device for fixing a toner image carried on a recording material, and includes a rotatable fixing roll and a rotatable belt stretched around the fixing roll. An outer surface of the belt member in the vicinity of the downstream side of the pressure contact portion between the fixing roller and the pressure member, the pressure member disposed to press the fixing roll via the belt member, and forming a nip portion. A separation member that presses the pressure member against the pressure member, and a belt disposed downstream of the separation member and downstream of the nip portion and upstream of a lap region where the belt member is stretched around the fixing roll. A first stretching roll for stretching the member is provided.
Here, “upstream side” and “downstream side” mean “upstream side” and “downstream side” in the rotation direction (movement direction) of the belt member. The same applies hereinafter.

Here, the first stretching roll can be characterized in that the belt member that has passed through the peeling member is guided in a direction away from the peeling member. Further, the first tension roll may be characterized in that a tension adjusting mechanism for adjusting the tension of the belt member is provided. In this case, the tension adjusting mechanism includes a spring member that presses the first tension roll in a direction from the inner peripheral surface side to the outer peripheral surface side of the belt member, a load detection unit that detects a spring load on the spring member, and And the pressing force of the spring member to the first tension roll is adjusted so that the spring load detected by the load detection unit is within a predetermined range.
Further, the belt member is disposed in a region downstream of the nip portion where the belt member is stretched around the fixing roll and downstream of the nip portion and upstream of the nip portion. It is also possible to further include a second tension roll provided with a tension adjusting mechanism for adjusting the tension of the second tension roll. Further, the first tension roll may be characterized in that a drive unit that rotates the first tension roll in the moving direction of the belt member is provided. In this case, the drive unit may be characterized by rotating the first tension roll at a peripheral speed faster than the moving speed of the belt member.

  The fixing device of the present invention is a fixing device for fixing a toner image carried on a recording material, and includes a rotatable fixing roll, a rotatable belt member stretched around the fixing roll, and a belt. A pressure member that is arranged to press the fixing roll through the member and forms a nip portion; and a pressure member on the outer surface of the belt member in the vicinity of the downstream side of the pressure contact portion between the fixing roll and the pressure member. A separation member that presses the belt member, and a belt member that is disposed downstream of the separation member and downstream of the nip portion and upstream of the wrap region where the belt member is stretched around the fixing roll. In addition, the first tension roll that can adjust the tension of the belt member, the downstream side of the lap region where the belt member is stretched on the fixing roll downstream of the nip portion, and the upstream side of the nip portion Placed in a certain area, the belt member While rack is characterized in that a second tension roller capable of adjusting the tension of the belt member.

Here, the first tension roll includes a spring member that presses the first tension roll from the inner peripheral surface side to the outer peripheral surface side of the belt member, and a load detection unit that detects a spring load on the spring member. The second tension roll includes a spring member that presses the second tension roll from the inner peripheral surface side to the outer peripheral surface side of the belt member, and a spring load at the spring member. It is possible to provide a tension adjustment mechanism including a load detection unit that detects the above. In this case, the first tension roll and the second tension roll are the spring load value detected by the tension adjustment mechanism of the first tension roll and the tension adjustment mechanism of the second tension roll. It is also possible to adjust the tension of the belt member based on one or both of the detected spring load values.
Further, the first tension roll and the second tension roll are a support body on which the fixing roll and the pressure member are pivotally supported, and maintain a substantially parallel positional relationship between the fixing roll and the pressure member. However, it can be characterized by being pivotally supported while being movable. In addition, the peeling member may be arranged so as to be swingable with respect to the fixing roll.
Furthermore, a guide member that guides the recording material peeled off from the belt member that has passed through the peeling member is further provided, and the guide member is arranged to be swingable with respect to the fixing roll. Further, the first tension roll may be characterized in that a high friction layer is formed on the surface.

  Further, the present invention is regarded as an image forming apparatus. The image forming apparatus of the present invention includes a toner image forming unit that forms a toner image, and a transfer unit that transfers the toner image formed by the toner image forming unit onto a recording material. A fixing unit that fixes the toner image transferred onto the recording material to the recording material, the fixing unit including a rotatable fixing roll, a rotatable belt member stretched around the fixing roll, and a belt A pressure member that is arranged to press the fixing roll through the member and forms a nip portion; and a pressure member on the outer surface of the belt member in the vicinity of the downstream side of the pressure contact portion between the fixing roll and the pressure member. A separation member that presses the belt member, and a belt member that is disposed downstream of the separation member and downstream of the nip portion and upstream of the wrap region where the belt member is stretched around the fixing roll. Having a first tension roll It is characterized.

  Here, the fixing unit has a nip pressure in a region extending from the most downstream portion of the pressure contact portion between the fixing roll and the pressure member to the most downstream portion of the pressure contact portion between the pressure member and the peeling member in the traveling direction of the belt member. It can be characterized by being set so as to monotonously decrease. Further, the pressing member of the fixing unit may be characterized in that a dent amount at a pressure contact portion with the fixing roll is larger than a dent amount of the fixing roll. Further, the fixing unit may be characterized in that the pressure member is formed of a pressure belt module in which the belt member is stretched by a plurality of tension rolls.

  According to the present invention, the recording paper can be stably peeled from the belt member even when the speed of the image forming apparatus is increased. Further, since high fixing performance can be stably maintained, it is possible to provide a large amount of high-quality images in a short time.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
[Embodiment 1]
FIG. 1 is a schematic configuration diagram illustrating a digital color printer 1 as an example of an image forming apparatus to which the exemplary embodiment is applied. A digital color printer 1 shown in FIG. 1 is a so-called tandem type, and is connected to an image forming process unit 20 that performs image formation corresponding to image data of each color, for example, a personal computer (PC) 3 or an image reading device 4. An image processing unit (IPS: Image Processing System) 22 that performs predetermined image processing on image data received from these units and a control unit 10 that controls the operation of each device (each unit) are provided.

The image forming process unit 20 includes four image forming units 26Y, 26M, 26C, and 26K that are arranged in parallel at a predetermined interval. The image forming units 26Y, 26M, 26C, and 26K include a photosensitive drum 31 that forms an electrostatic latent image and carries a toner image, a charging roll 32 that uniformly charges the surface of the photosensitive drum 31 at a predetermined potential, The image forming apparatus includes a developing unit 33 for developing the electrostatic latent image formed on the body drum 31 and a drum cleaner 34 for cleaning the surface of the photosensitive drum 31 after the transfer. Further, laser exposure devices 25Y, 25M, 25C, and 25K that expose the photosensitive drum 31 are provided corresponding to the image forming units 26Y, 26M, 26C, and 26K, respectively.
Here, the image forming units 26Y, 26M, 26C, and 26K are configured in substantially the same manner except for the toner stored in the developing device 33. The image forming units 26Y, 26M, 26C, and 26K respectively form yellow (Y), magenta (M), cyan (C), and black (K) toner images.

  In addition, the image forming process unit 20 includes an intermediate transfer belt 41 to which the toner images of the respective colors formed on the photosensitive drums 31 of the image forming units 26Y, 26M, 26C, and 26K are transferred, and the image forming units 26Y and 26Y. A primary transfer roller 42 that sequentially transfers (primary transfer) each color toner image of 26M, 26C, and 26K to the intermediate transfer belt 41 at the primary transfer portion T1, and a superimposed toner image transferred onto the intermediate transfer belt 41 is a secondary transfer portion. A secondary transfer roll 50 that performs batch transfer (secondary transfer) onto a sheet P that is a recording material (recording sheet) at T2 and a fixing device 60 that fixes the secondary transferred image onto the sheet P are provided.

  In the digital color printer 1 of the present embodiment, the image forming process unit 20 performs an image forming operation based on a control signal supplied from the control unit 10. At that time, image data input from the PC 3 or the image reading device 4 is subjected to image processing by the IPS 22 and supplied to the laser exposure devices 25Y, 25M, 25C, and 25K. For example, in the yellow (Y) image forming unit 26Y, the surface of the photosensitive drum 31 uniformly charged at a predetermined potential by the charging roll 32 is applied by the laser exposure device 25Y based on the image data obtained from the IPS 22. An electrostatic latent image is formed on the photosensitive drum 31 by scanning exposure. The formed electrostatic latent image is developed by the developing device 33, and a Y toner image is formed on the photosensitive drum 31. Similarly, in the image forming units 26M, 26C, and 26K, M, C, and K color toner images are formed.

The color toner images formed by the image forming units 26Y, 26M, 26C, and 26K are sequentially electrostatically attracted by the primary transfer roll 42 onto the intermediate transfer belt 41 that rotates in the direction of arrow A in FIG. A toner image superimposed on the belt 41 is formed. As the intermediate transfer belt 41 moves, the superimposed toner image is conveyed to the secondary transfer portion T2 where the secondary transfer roll 50 is disposed. When the superimposed toner image is conveyed to the secondary transfer portion T2, the paper P is supplied to the secondary transfer portion T2 in accordance with the timing at which the toner image is conveyed to the secondary transfer portion T2. Then, the superimposed toner images are collectively electrostatically transferred onto the conveyed paper P by the transfer electric field formed by the secondary transfer roll 50 in the secondary transfer portion T2.
Thereafter, the sheet P on which the superimposed toner image has been electrostatically transferred is peeled off from the intermediate transfer belt 41 and conveyed to the fixing device 60 by the conveyance belts 76 and 77. The unfixed toner image on the paper P conveyed to the fixing device 60 is fixed on the paper P by being subjected to fixing processing by heat and pressure by the fixing device 60. Then, the paper P on which the fixed image is formed is conveyed to a paper discharge mounting portion (not shown) provided in the discharge portion of the image forming apparatus.

Next, the fixing device 60 used in the image forming apparatus of the present embodiment will be described.
FIG. 2 is a side sectional view showing a schematic configuration of the fixing device 60 of the present embodiment. The fixing device 60 includes a fixing belt module 61 as an example of a heating member and a pressure roll 62 as an example of a pressure member disposed in pressure contact with the fixing belt module 61. Yes.
The fixing belt module 61 includes a fixing belt 610 as an example of a belt member, a fixing roll 611 that rotates while the fixing belt 610 is stretched, and a tension roll as a second stretching roll that stretches the fixing belt 610 from the inside. 612, an external heating roll 613 that stretches the fixing belt 610 from the outside, an attitude correction roll 614 that corrects the attitude of the fixing belt 610 between the fixing roll 611 and the tension roll 612, a fixing belt module 61, and a pressure roll 62 Is disposed in a downstream region in the nip portion N, which is a region where the sheet is pressed, and is a separation pad 64 as an example of a separation member that separates the paper P from the fixing belt 610. The fixing belt 610 is stretched in a region until the 610 is stretched again on the fixing roll 611. The main portion is constituted by idler roller 615 as the first stretching roll.

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

  The fixing belt 610 is a flexible endless belt having a circumferential length of 314 mm and a width of 340 mm. The fixing belt 610 has a multilayer structure, and is composed of a base layer formed of a polyimide resin having a thickness of 80 μm, and a silicone rubber having a thickness of 50 μm laminated on the surface side (outer peripheral surface side) of the base layer. It is composed of an elastic layer and a release layer made of a 30 μm-thick tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin (PFA) tube coated on the elastic layer. Here, the elastic layer is provided in order to improve the image quality especially for color images. The configuration of the fixing belt 610 can be appropriately selected in terms of material, thickness, hardness, and the like according to device design conditions such as the purpose of use and use conditions. The fixing belt 610 is rotated in the arrow D direction by the fixing roll 611.

The tension roll 612 is a cylindrical roll formed of aluminum having an outer diameter of 30 mm, a thickness of 2 mm, and a length of 360 mm disposed on the upstream side of the nip portion N. A halogen heater 616b rated at 1500 W is disposed as a heating source inside the tension roll 612, and the surface temperature is controlled to 190 ° C. by the temperature sensor 617b and the control unit 10 (see FIG. 1). . Accordingly, the tension roll 612 has a function of stretching the fixing belt 610 and a function of heating the fixing belt 610 from the inner peripheral surface side.
In addition, tension adjusting devices (not shown) including spring members that press the fixing belt 610 outward are disposed at both ends of the tension roll 612. Thereby, the tension roll 612 has a function of adjusting the tension of the fixing belt 610 to a predetermined value (for example, 15 kgf).
Further, a belt edge position detection mechanism (not shown) for detecting the edge position of the fixing belt 610 is disposed in the vicinity of the tension roll 612. The tension roll 612 is provided with an axial displacement mechanism (not shown) that displaces the contact position in the axial direction of the fixing belt 610 according to the detection result of the belt edge position detection mechanism. Thereby, it also functions as a steering roll for controlling meandering (belt walk) of the fixing belt 610.
Note that such meandering control for the fixing belt 610 may be performed by the posture correction roll 614.

The external heating roll 613 is a cylindrical roll formed of aluminum having an outer diameter of 25 mm, a thickness of 2 mm, and a length of 360 mm. Further, a release layer made of PFA having a thickness of 20 μm is formed on the surface of the external heating roll 613. This release layer is formed to prevent slight offset toner and paper powder from the outer peripheral surface of the fixing belt 610 from accumulating on the external heating roll 613.
Inside the external heating roll 613, a halogen heater 616 c rated at 1000 W is disposed as a heating source, and the surface temperature is controlled to 190 ° C. by the temperature sensor 617 c and the control unit 10 (see FIG. 1). Yes. Therefore, the external heating roll 613 has a function of stretching the fixing belt 610 and a function of heating the fixing belt 610 from the outer peripheral surface side. Therefore, in this embodiment, a configuration in which the fixing belt 610 is heated by the fixing roll 611, the tension roll 612, and the external heating roll 613 is adopted.

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

The peeling pad 64 is a block member having a substantially arc-shaped cross section, and is formed of a rigid body such as a metal such as SUS or a highly rigid resin. Then, the entire area in the axial direction of the fixing roll 611 is located in the vicinity of the downstream side of the area where the pressure roll 62 is pressed against the fixing roll 611 via the fixing belt 610 (see “roll nip portion N1”: FIG. 3 in the subsequent stage). Are fixedly arranged. The peeling pad 64 is installed so as to uniformly press the fixing belt 610 against the pressure roll 62 with a predetermined load (for example, 10 kgf), and a “peeling pad nip portion N2” described later (see FIG. 3 in the latter stage). ) Is formed.
Further, the peeling pad 64 is disposed so as to be swingable with respect to the rotation shaft of the fixing roll 611. Thereby, for example, when the pressure roll 62 is configured to be able to contact and separate from the fixing roll 611, when the pressure roll 62 is brought into contact with and separated from the fixing roll 611, the pressing load value of the pressure roll 62 against the fixing roll 611 In addition, when the relative position between the peeling pad 64 and the pressure roll 62 when the cardboard enters the nip portion N is changed, the gap between the peeling pad 64 and the fixing roll 611 is changed. Can be configured not to fluctuate. Therefore, since the interference between the peeling pad 64 and the fixing roll 611 can be suppressed, an area (boundary area N2S (see FIG. 2)) that is pressed against the pressure roll 62 only by the tension of the fixing belt 610 in the nip portion N, which will be described later. 3))) can be maintained at a minimum width (for example, 2 mm or less), so that stable fixing performance and high reliability in the fixing device 60 can be ensured.

The idler roll 615 is a cylindrical roll formed of a cored bar made of stainless steel having an outer diameter of 12 mm and a length of 360 mm and a rubber layer made of, for example, 1 mm thick silicone rubber coated on the surface of the cored bar. The idler roll 615 is near the downstream side of the peeling pad 64 in the direction in which the fixing belt 610 travels, and the fixing belt 610 is stretched around the fixing roll 611 again, and the fixing belt 610 is wound around the fixing roll 611 (wrapping). The fixing belt 610 that has passed through the peeling pad 64 is disposed at a position that guides the separation belt 64 away from the peeling pad 64 in an area upstream of the area (wrapping area).
With the idler roll 615 arranged in this manner, in the fixing device 60 of the present embodiment, it is possible to set a short region where the fixing belt 610 and the peeling pad 64 slide on the downstream side of the peeling pad 64. Become. As a result, it is possible to suppress the occurrence of an extra load on the fixing belt 610, and thus the fixing belt 610 can be smoothly conveyed. Therefore, the conveyance of the fixing belt 610 at the nip portion N is smooth, and a high-quality fixed image can be formed.

Further, the idler roll 615 is driven in the conveyance direction of the fixing belt 610 by a driving unit (not shown) at a speed slightly higher than the conveyance speed of the fixing belt 610. Accordingly, when the sheet P passes through the nip portion N, vibration occurs in the peeling pad 64, and even when the contact state of the peeling pad 64 with the fixing belt 610 changes, the fixing belt 610 that has passed through the peeling pad nip portion N2. In this way, it is possible to suppress the occurrence of wavy distortion and the like, and maintain further smooth conveyance toward the fixing roll 611.
Further, the idler roll 615 is provided with a tension adjusting device 80 (not shown in FIGS. 2 and 3; see FIGS. 8 and 9 in the subsequent stage) for adjusting the tension of the fixing belt 610. . The tension adjusting function of the idler roll 615 by the tension adjusting device 80 will be described in detail later.

  Next, the pressure roll 62 has a cylindrical roll 621 made of aluminum having a diameter of 45 mm and a length of 360 mm as a base, in order from the base side, a 10 mm thick elastic layer 622 made of silicone rubber, and a 100 μm thick PFA. A soft roll formed by laminating a release layer 623 made of a tube. The pressure roll 62 is installed so as to be pressed against the fixing belt module 61. As the fixing roll 611 of the fixing belt module 61 rotates in the direction of arrow C, the pressure roll 62 follows the fixing roll 611 and moves in the direction of arrow E. To turn. The traveling speed is 440 mm / s, which is the same as the surface speed of the fixing roll 611.

Next, the nip portion N where the fixing belt module 61 and the pressure roll 62 are pressed against each other will be described.
FIG. 3 is a schematic cross-sectional view showing the vicinity of the nip N. As shown in FIG. As shown in FIG. 3, in the nip portion N where the fixing belt module 61 and the pressure roll 62 are pressed against each other, the pressure roll 62 is fixed in the lap region where the fixing belt 610 is wrapped by the fixing roll 611. A roll nip portion (first nip portion) N1 is formed by being disposed so as to be in pressure contact with the outer peripheral surface of the belt 610.

In the fixing device 60 of the present embodiment, as described above, the fixing roll 611, which is one of the rolls forming the roll nip portion N1, covers the surface of an aluminum core metal (core roll) with a heat resistant resin (fluororesin). The fixing roll 611 is not covered with an elastic layer. The pressure roll 62, which is the other roll forming the roll nip portion N1, is a soft roll coated with an elastic layer 622.
With such a configuration of the fixing roll 611 and the pressure roll 62, the roll nip portion N1 is formed by the deformation of the elastic layer 622 of the pressure roll 62 in the roll nip portion N1 of the present embodiment. The roll 62 side functions as a roll (NFPR: NIP Forming Pressure Roll) that forms a nip (roll nip portion N1). That is, in the roll nip portion N1, the fixing roll 611 is hardly dented, and only the surface of the pressure roll 62 is largely dented (the amount of depression of the pressure roll 62> the amount of depression of the fixing roll 611). Thus, a nip region having a predetermined width in the traveling direction of the fixing belt 610 is created.
As described above, in the fixing device 60 of the present embodiment, the fixing roll 611 on the side where the fixing belt 610 is wrapped in the roll nip portion N1 is hardly deformed, and the cylindrical shape is maintained. Therefore, the fixing belt 610 rotates along the circumferential surface of the surface of the fixing roll 611, and the rotation radius does not change. Therefore, the fixing belt 610 can pass through the roll nip portion N1 while maintaining a constant traveling speed. it can. As a result, even when the fixing belt 610 passes through the roll nip portion N1, the fixing belt 610 hardly generates wrinkles or distortion. As a result, the occurrence of image disturbance in the fixed image is suppressed, and a high-quality fixed image can be stably provided. In the fixing device 60 of the present embodiment, the roll nip portion N1 is set to a width of 15 mm along the traveling direction of the fixing belt 610.

Further, a peeling pad 64 is disposed in the vicinity of the downstream side of the roll nip portion N1. The peeling pad 64 presses the fixing belt 610 against the surface of the pressure roll 62. Accordingly, a peeling pad nip portion (second nip portion) N2 in which the fixing belt 610 is wrapped on the surface of the pressure roll 62 is formed downstream of the roll nip portion N1.
As shown in FIG. 3, the peeling pad 64 that forms the peeling pad nip portion N2 has a substantially arc-shaped cross section, and is disposed along the axial direction of the fixing roll 611 in the vicinity of the downstream side of the roll nip portion N1. Yes. Then, the fixing belt 610 after passing through the peeling pad nip portion N <b> 2 rotates following the outer surface of the peeling pad 64. Accordingly, the advancing direction of the fixing belt 610 is rapidly changed so as to be bent in the direction of the idler roll 615 by the peeling pad 64. Therefore, the paper P that has passed through the roll nip portion N1 and the peeling pad nip portion N2 cannot follow the change in the advancing direction of the fixing belt 610 at the time of exiting the peeling pad nip portion N2, and the paper P is fixed by its so-called “koshi”. The belt 610 is peeled off. In this way, the curvature separation with respect to the paper P is stably performed at the exit portion of the peeling pad nip portion N2. In the fixing device 60 of the present embodiment, the peeling pad nip portion N2 is set to a width of 8.5 mm along the traveling direction of the fixing belt 610.

Here, the arrangement position of the peeling pad 64 and the nip pressure distribution (nip pressure profile) of the peeling pad nip portion N2 formed by the peeling pad 64 will be described.
As described above, the peeling pad 64 is disposed in the vicinity of the downstream side of the roll nip portion N1. As a result, in the nip portion N including the roll nip portion N1 and the peeling pad nip portion N2, the position where the nip pressure peaks in the roll nip portion N1 (see FIG. 5 in the subsequent stage) reaches the most downstream position of the peeling pad nip portion N2. Thus, the generation of a valley region where the nip pressure drops below a predetermined value is suppressed, and the nip pressure can be set to continuously monotonously decrease. Therefore, the fixing device 60 according to the present embodiment can provide a high-quality fixed image without image defects such as image unevenness as well as realizing stable sheet separation.
Here, first, the peeling pad 64 disposed in the vicinity of the downstream side of the roll nip portion N1 suppresses the generation of a valley region where the nip pressure drops below a predetermined value, and the nip pressure continues in the nip portion N. The points set to monotonously decrease will be described.

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

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

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

By the way, in the fixing process by the fixing device 60 of the present embodiment, the paper P carrying the toner image is heated and pressed in the roll nip portion N1, and the toner is melt-pressed. At that time, the water in the paper P vaporizes from the paper P and the toner that have received heat in the roll nip portion N1 to generate water vapor, or the air in the toner tends to thermally expand. However, since a high nip pressure is applied at the roll nip portion N1, an air gap (bubbles) due to water vapor or expanded air does not occur between the fixing belt 610 and the pressure roll 62.
However, when the nip pressure Pn in the boundary region N2S with the roll nip portion N1 in the peeling pad nip portion N2 is formed in a low state below a predetermined value Pn1, bubbles that have been suppressed in the roll nip portion N1 are generated in the boundary region N2S. Will occur without being suppressed. Then, when the paper P enters the high nip pressure region N2T where the peeling pad 64 is disposed in a state where bubbles are generated, the bubbles generated in the boundary region N2S move around on the surface of the paper P due to the high nip pressure. It will be. As a result, the toner image on the paper P is immediately after passing through the roll nip portion N1, and the melted toner is not yet completely solidified. Arise. As a result, a situation in which an image defect such as image unevenness occurs in the fixed image is caused.

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

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

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

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

  The pressing surface 64 c of the peeling pad 64 is a surface that presses the fixing belt 610 against the pressure roll 62 and presses against the surface of the pressure roll 62. Therefore, the pressing surface 64 c is formed as a flat surface so that the fixing belt 610 is uniformly pressed against the pressure roll 62. Furthermore, the pressing surface 64c can also be formed as a concave curved surface that follows the circumferential surface of the pressure roll 62, whereby the pressing force can be made more uniform.

Further, as described above, the upstream end 64p of the pressing surface 64c is disposed at a position close to the fixing roll 611 in order to reduce the width of the boundary region N2S as much as possible. It is also possible to arrange the portion 64p so as to contact the fixing roll 611. By setting in this way, the boundary region N2S can be almost eliminated, and almost the entire area of the peeling pad nip portion N2 can be formed by the pressure contact portion N2T between the peeling pad 64 and the pressure roll 62. In addition, since the upstream end portion 64p of the pressing surface 64c can simultaneously receive the pressing force from the fixing roll 611, a sufficient nip pressure can be formed in the entire area of the peeling pad nip portion N2.
FIG. 7 is a view showing a configuration in which the upstream end portion 64p of the pressing surface 64c is set in contact with the fixing roll 611 and receives the pressing force from the fixing roll 611 at the same time. As shown in FIG. 7, in this case, the upstream end portion 64p of the pressing surface 64c is formed in a wedge shape so as to fill the deepest portion of the wedge-shaped region Q. Thus, by forming the upstream end portion 64p of the pressing surface 64c in a wedge shape, it is possible to stably receive the pressing force from the fixing roll 611, and at the same time, even if it rubs against the fixing roll 611, Wear is unlikely to occur on the contact surface of the upstream end portion 64p with the fixing roll 611 and the surface of the fixing roll 611. Therefore, it is possible to maintain the function of the peeling pad 64 over a long period of time.
The pressing surface 64c rubs against the fixing belt 610 and the fixing roll 611, so that the fixing belt 610 advances smoothly, and the friction coefficient is applied to the surface of the pressing surface 64c in order to reduce wear on the fixing roll 611. For example, it is preferable to have a structure that is small and excellent in wear resistance, such as Teflon (registered trademark).

The outer side surface 64 b is a surface on which the sheet P is peeled from the fixing belt 610 by guiding the fixing belt 610 in cooperation with the idler roll 615 and the fixing roll 611 and rapidly changing the traveling direction thereof. Therefore, in order to stably peel the paper P from the fixing belt 610, the pressure roll in the upstream end region of the outer surface 64 b, that is, the region (peeling region) R where the fixing belt 610 is separated from the pressure roll 62. The angle θ2 (see FIG. 6) formed by the tangent line 62 and the tangent line of the outer surface 64b is set to be 25 ° or more. Further, in the peeling region R, the outer surface 64b is formed in a curved surface so that the fixing belt 610 can be smoothly moved in the peeling region R that is bent sharply.
Further, the outer side surface 64b is formed as a flat surface inclined toward the idler roll 615 so that the fixing belt 610 moves smoothly in the direction of the idler roll 615 and the fixing roll 611 after being separated from the pressure roll 62. Yes. In this case, the outer surface 64b can be formed as a curved surface that is convexly curved toward the outer side (the fixing belt 610 side). Since the outer surface 64b also rubs against the fixing belt 610 in the same manner as the pressing surface 64c, the surface of the fixing belt 610 has a small friction coefficient and excellent wear resistance. It is preferable that the structure is coated with Teflon (registered trademark) or the like.

Next, the tension adjustment function of the idler roll 615 will be described.
As described above, the idler roll 615 is near the downstream side of the peeling pad 64 in the direction in which the fixing belt 610 travels, and in the area upstream of the lap area where the fixing belt 610 is stretched again on the fixing roll 611. The fixing belt 610 that has passed through the peeling pad 64 is disposed at a position for guiding the fixing belt 610 away from the peeling pad 64. The idler roll 615 includes an example of a tension adjusting mechanism that adjusts the tension (tension) of the fixing belt 610 in a region up to a lap region where the fixing belt 610 passes through the nip portion N and is stretched around the fixing roll 611 again. A tension adjusting device 80 is provided.

FIG. 8 is a side view showing one end of the idler roll 615 where the tension adjusting mechanism 80 is disposed, and FIG. 9 is a diagram for explaining the configuration of the tension adjusting mechanism 80.
As shown in FIGS. 8 and 9, the tension adjusting device 80 applies a pressing force toward the outside from the inner peripheral surface side of the fixing belt 610 at both ends of the idler roll 615 to the fixing belt 615. 610 is configured to adjust the tension.

As shown in FIG. 9, the tension adjusting device 80 is a tensioner frame 801 that is slidably supported in the direction of arrow J (see also FIG. 8) with respect to the main body frame (support: not shown) of the fixing device 60. A tensioner base 802 fixed to the tensioner frame 801, a bearing 805 that rotatably supports the idler roll 615 on the tensioner frame 801, a slider 806 that slidably supports the bearing 805 on the tensioner frame 801 in the arrow J direction, and the tensioner base 802 A load as a load detection unit that is installed in a supported manner and is disposed between the spring member 803 that applies a pressing force to the idler roll 615, the tensioner base 802, and the spring member 803, and detects the pressing force of the spring member 803. Mainly by sensor 804 Part is configured.
The tension adjusting device 80 is provided with a tensioner moving mechanism 810 that slides the tension adjusting device 80 in the direction of arrow J. The tensioner moving mechanism 810 includes two eccentric cams 811, and is configured to slide the entire tension adjusting device 80 in the arrow J direction via the tensioner base 802 by rotating the eccentric cam 811. Yes.

The tension adjusting device 80 presses the idler roll 615 from both ends by the spring member 803. Accordingly, a predetermined tension is applied to the fixing belt 610 stretched on the idler roll 615 in a region between the fixing belt 610 passing through the peeling pad 64 and the wrapping region stretched on the fixing roll 611 again. Is granted.
The idler roll 615 is supported by the tensioner frame 801 via a slider 806. Thereby, when the paper P enters the nip portion N, the relative positions of the fixing roll 611, the pressure roll 62, and the peeling pad 64 change, and the tension of the fixing belt 610 changes. Correspondingly, the idler roll 615 can vibrate in the direction of arrow J. Therefore, it is possible to absorb the fluctuation of the tension of the fixing belt 610 due to the impact when the paper P enters the nip portion N, and to suppress the occurrence of image disturbance.

  Further, in the tension adjusting device 80 of the present embodiment, the pressing force of the spring member 803 is detected by the load sensor 804. Data (spring load value data) related to the pressing force (spring load value) of the spring member 803 detected by the load sensor 804 is transmitted to the control unit 10. The control unit 10 that has received the spring load value data transmits a control signal to the tensioner moving mechanism 810 so that the pressing force of the spring member 803 is within a predetermined range. The tensioner moving mechanism 810 rotates the eccentric cam 811 based on a control signal from the control unit 10 to slide the tension adjusting device 80 (in the arrow J direction), and the pressing force of the spring member 803 is within a predetermined range. Adjust as follows. In this way, the tension adjusting device 80 maintains the tension of the fixing belt 610 within a predetermined range in the region up to the lap region where the fixing belt 610 passes through the nip portion N and is stretched around the fixing roll 611 again. The tension adjustment operation is also performed.

By adjusting the tension of the fixing belt 610 as described above, the fixing belt 610 passes through the nip portion N, and the fixing belt 610 is slackened in the region up to the lap region stretched around the fixing roll 611 again. It becomes possible to suppress.
Here, FIG. 10 is a view showing a case where the fixing belt 610 is loosened on the downstream side of the peeling pad 64. In such a state, since the stiffness of the fixing belt 610 is strong, the fixing belt 610 cannot follow the sudden change in the curvature in the peeling region R of the peeling pad 64 or the fixing belt in a region other than the nip portion N. This occurs, for example, when a slip occurs at 610. In this case, since there is no sudden change in the curvature of the fixing belt 610 in the separation region R, the separation failure of the paper P is likely to occur. Further, since the adhesion between the fixing belt 610 and the paper P is impaired, there is a high possibility that uneven gloss will occur.
FIG. 11 is a diagram showing a case where the fixing belt 610 is slack in the boundary region N2S in the peeling pad nip portion N2. Such a state occurs when the fixing belt 610 is braked when the sliding resistance of the peeling pad 64 is large. In this case, there is a possibility that troubles such as occurrence of gloss unevenness, image unevenness, and buckling of the fixing belt 610 occur.

  On the other hand, in the fixing device 60 of the present embodiment, the idler roll 615 is provided in the region up to the lap region where the fixing belt 610 passes through the nip portion N and is stretched around the fixing roll 611 again, and the idler roll A tension adjusting device 80 for adjusting the tension (tension) of the fixing belt 610 is provided at 615. Accordingly, it is possible to suppress the occurrence of slack in the fixing belt 610 in the region from the fixing belt 610 passing through the nip portion N to the wrap region stretched around the fixing roll 611 again. Therefore, it is possible to realize stable peeling of the paper P, and to prevent occurrence of troubles such as occurrence of gloss unevenness and image unevenness, and buckling of the fixing belt 610.

  In the fixing device 60 of the present embodiment, as described above, the idler roll 615 is driven at a speed slightly higher than the conveyance speed of the fixing belt 610 by a driving mechanism (not shown). Therefore, in the region up to the lap region where the fixing belt 610 passes through the nip portion N and is stretched around the fixing roll 611 again, the slack suppressing effect on the fixing belt 610 can be further enhanced. In this case, since the rubber layer for increasing the surface friction force is formed on the surface of the idler roll 615, the driving force from the idler roll 615 can be effectively transmitted to the idler roll 615. In addition, the structure which has the effect which raises the frictional force of the idler roll 615 surface is not restricted to a rubber layer like this Embodiment, For example, the surface is good also as a rough surface.

Further, in the fixing device 60 of the present embodiment, in addition to the idler roll 615, the fixing belt 610 passes through the nip portion N and is a region downstream of the wrap region stretched around the fixing roll 611 again. In the tension roll 612 disposed in the upstream region of the nip portion N, the same tension adjusting device 80 as that disposed in the idler roll 615 is provided.
For example, in the tension adjusting device 80 with the idler roll 615, when the fixing belt 610 is stretched without slack, a predetermined circumferential length error (for example, ± 0.5 mm) generated when the fixing belt 610 is manufactured can be absorbed. Is set to apply a predetermined tension or more. However, when the driving torque of the fixing belt 610 greatly changes when a thick paper is passed, the belt slip of the fixing belt 610 is likely to occur, and a local slack of several millimeters may occur. In this case, the control range of the tension adjusting device 80 with the idler roll 615 is exceeded, and there is a possibility that the slack that occurs in the fixing belt 610 cannot be sufficiently suppressed.
In contrast, by providing the tension adjusting device 80 also on the tension roll 612, the tension of the fixing belt 610 can be adjusted by either or both of the tension adjusting device 80 in the idler roll 615 and the tension adjusting device 80 in the tension roll 612. Can be detected as a spring load value by the load sensor 804, and the tension of the fixing belt 610 can be adjusted by both the tension roll 612 and the idler roll 615. For this reason, the tension of the fixing belt 610 falls within a predetermined range by cooperating with the tension adjusting device 80 of the tension roll 612 with the slack generated in the fixing belt 610 in a range that cannot be adjusted only by the tension adjusting device 80 of the idler roll 615. As a result, more precise management of the belt tension is possible.

  The tension roll 612 and the idler roll 615 are maintained in a substantially parallel positional relationship with the main body frame (support) of the fixing device 60 on which the fixing roll 611 and the pressure roll 62 are rotatably supported. By supporting the shaft so that it can move as it is, it is possible to prevent the skew (tilt) from occurring in the tension roll 612 and the idler roll 615. For this reason, it is possible to suppress the occurrence of uneven tension in the axial direction.

As described above, in the fixing device 60 of the present embodiment, the nip portion N including the roll nip portion N1 and the peeling pad nip N2 is formed in the region where the fixing belt module 61 and the pressure roll 62 are pressed. The release pad 64 that forms the release pad nip N2 is disposed in the vicinity of the downstream side of the roll nip portion N1, and the release pad 64 is set to press the pressure roll 62. Therefore, it is possible to suppress the generation of a valley region where the nip pressure falls in the nip portion N, and it is possible to form the nip pressure Pn that satisfies the above-described expression (1) also in the boundary region N2S. Accordingly, the nip pressure is set to continuously and monotonously decrease in a region from the position where the nip pressure reaches a peak in the roll nip portion N1 in the nip portion N to the most downstream position of the peeling pad nip portion N2. Is possible.
Therefore, it is possible to suppress the generation of bubbles in the boundary region N2S. Furthermore, by setting the nip pressure so as to continuously decrease monotonously, water vapor or air that is about to expand due to the high nip pressure in the roll nip portion N1 is passed through the peeling pad nip portion N2. It is possible to gradually open the route. As a result, it is possible to suppress the phenomenon that water vapor or thermally expanded air becomes bubbles and move around in the nip, so that the toner image that has not yet been completely solidified is hardly disturbed and fixed. It is possible to suppress the occurrence of image defects such as image unevenness in the image.

  Further, since the cross section of the peeling pad 64 forming the peeling pad nip portion N2 is formed in a substantially arc shape, the fixing belt 610 that has passed through the peeling pad nip N2 is rapidly changed so that the traveling direction thereof is bent. . Therefore, the paper P that has passed through the roll nip portion N1 and the peeling pad nip portion N2 is peeled from the fixing belt 610 at the time of exiting the peeling pad nip portion N2, and the curvature separation from the paper P can be performed.

In addition, in the fixing device 60 according to the present embodiment, in the vicinity of the peeling pad 64 on the downstream side of the fixing belt 610 in the traveling direction, up to the lap region where the fixing belt 610 is stretched again on the fixing roll 611, An idler roll 615 is disposed at a position where the fixing belt 610 that has passed through the peeling pad 64 is guided away from the peeling pad 64.
With the idler roll 615 arranged in this manner, in the fixing device 60 of the present embodiment, it is possible to set a short region where the fixing belt 610 and the peeling pad 64 slide on the downstream side of the peeling pad 64. Become. As a result, it is possible to suppress the occurrence of an extra load on the fixing belt 610, and thus the fixing belt 610 can be smoothly conveyed. Therefore, the conveyance of the fixing belt 610 at the nip portion N is smooth, and a high-quality fixed image can be formed.
The idler roll 615 is provided with a tension adjusting device 80 for adjusting the tension of the fixing belt 610. Accordingly, it is possible to suppress the occurrence of slack in the fixing belt 610 in the region from the fixing belt 610 passing through the nip portion N to the wrap region stretched around the fixing roll 611 again. Therefore, it is possible to realize stable peeling of the paper P, and to prevent occurrence of troubles such as occurrence of gloss unevenness and image unevenness, and buckling of the fixing belt 610.

Next, a fixing operation in the fixing device 60 of the present embodiment will be described.
The sheet P on which the unfixed toner image is electrostatically transferred in the secondary transfer portion T2 (see FIG. 1) of the image forming apparatus is directed toward the nip portion N of the fixing device 60 by the conveyance belts 76 and 77 (see FIG. 2). : Arrow F direction) The unfixed toner image on the surface of the paper P passing through the nip portion N is fixed on the paper P mainly by pressure and heat acting on the roll nip portion N1.

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

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

Further, in the fixing device 60 of the present embodiment, the fixing roll 611 which is one of the rolls forming the roll nip portion N1 is configured by coating the surface of an aluminum core metal (core roll) with a heat resistant resin (fluororesin). The fixing roll 611 is not covered with an elastic layer. The pressure roll 62, which is the other roll forming the roll nip portion N1, is a soft roll coated with an elastic layer 622.
Therefore, in the roll nip portion N1 of the present embodiment, a configuration is realized in which the fixing roll 611 on the side where the fixing belt 610 is wrapped is hardly deformed. Accordingly, when the fixing belt 610 passes through the roll nip portion N1, it is possible to keep the traveling speed constant, and it is possible to prevent the fixing belt 610 from being wrinkled or distorted in the roll nip portion N1. . As a result, when the paper P passes through the roll nip portion N1, occurrence of toner image disturbance due to wrinkles and distortion of the fixing belt 610 can be suppressed, and a high-quality fixed image can be stably provided. .

Subsequently, after passing through the roll nip portion N1, the paper P is conveyed to the peeling pad nip portion N2. The peeling pad nip portion N2 is formed so that the peeling pad 64 is pressed and the fixing belt 610 is in pressure contact with the pressure roll 62. Therefore, as shown in FIG. 3, the roll nip portion N1 has a curved shape that is convex downward due to the curvature of the fixing roll 611, whereas the peeling pad nip portion N2 is convex upward due to the curvature of the pressure roll 62. It has a certain curved shape.
Therefore, the traveling direction of the paper P heated and pressed under the curvature of the fixing roll 611 in the roll nip portion N1 is changed to the curvature directed in the opposite direction by the pressure roll 62 in the peeling pad nip portion N2. At that time, a minute micro slip occurs between the toner image on the paper P and the surface of the fixing belt 610. As a result, the adhesion between the toner image and the fixing belt 610 is weakened, and a state in which the paper P is easily peeled off from the fixing belt 610 is formed. As described above, the peeling pad nip portion N2 is also positioned in a preparation process for surely peeling in the final peeling process.

At the exit (peeling region R) of the peeling pad nip portion N2, the fixing belt 610 is conveyed so as to be wound around the peeling pad 64, so that the conveying direction of the fixing belt 610 changes abruptly there. That is, since the fixing belt 610 moves along the outer surface 64b of the peeling pad 64, the bending of the fixing belt 610 becomes large. For this reason, the paper P whose adhesion to the fixing belt 610 has been weakened in advance in the peeling pad nip portion N2 is self-striped from the fixing belt 610 by the stiffness of the paper that the paper P itself has.
In this way, the sheet P is peeled off from the fixing belt 610 at the time of exiting the peeling pad nip portion N2, and the curvature is stably and reliably separated.

Further, the fixing belt 610 that has passed through the peeling pad 64 is peeled in a region near the downstream side of the peeling pad 64 in the traveling direction of the fixing belt 610 up to a lap region where the fixing belt 610 is stretched again on the fixing roll 611. An idler roll 615 is disposed at a position that leads away from the pad 64. With the idler roll 615 arranged in this way, it is possible to set a short region in which the fixing belt 610 and the peeling pad 64 slide on the downstream side of the peeling pad 64. As a result, it is possible to suppress the occurrence of an extra load on the fixing belt 610, and thus the fixing belt 610 can be smoothly conveyed. Therefore, the conveyance of the fixing belt 610 at the nip portion N is smooth, and a high-quality fixed image can be formed.
The idler roll 615 is provided with a tension adjusting device 80 for adjusting the tension of the fixing belt 610. Accordingly, it is possible to suppress the occurrence of slack in the fixing belt 610 in the region from the fixing belt 610 passing through the nip portion N to the wrap region stretched around the fixing roll 611 again. Therefore, it is possible to realize stable peeling of the paper P, and to prevent occurrence of troubles such as occurrence of gloss unevenness and image unevenness, and buckling of the fixing belt 610.

Then, the paper P separated from the fixing belt 610 is guided in its traveling direction by a peeling guide plate 83 as an example of a peeling auxiliary member disposed on the downstream side of the peeling pad nip portion N2. The paper P guided by the peeling guide plate 83 is then discharged out of the apparatus by the paper discharge guide 65 and the paper discharge roll 66 (see FIG. 2), and the fixing process is completed.
Here, the peeling guide plate 83 can also be disposed so as to be swingable with respect to the rotation shaft of the fixing roll 611. The peeling pad 64 swings according to the thickness and hardness of the paper P to be passed, and the tension (tension) of the fixing belt 610 is adjusted by the tension adjusting device 80 arranged on the idler roll 615 accordingly. When the adjustment is performed, the traveling direction of the fixing belt 610 in the peeling region R may change. At that time, the sheet P separated from the fixing belt 610 can be stably guided to the paper discharge guide 65 by adjusting the position of the peeling guide plate 83 in accordance with the traveling direction of the fixing belt 610. .

  As described above, the fixing device 60 of the present embodiment uses the fixing belt module 61 in which the fixing belt 610 is stretched by a plurality of rolls including the fixing roll 611 as a heating member. Even if the speed of the forming apparatus is increased, a predetermined fixing temperature can always be maintained in the fixing device 60. Furthermore, it is possible to suppress the occurrence of a temperature droop phenomenon in which the fixing temperature drops at the start of the high-speed fixing operation. For this reason, it is possible to provide a large amount of high-quality fixed images in a short time.

At the same time, the nip portion N includes a roll nip portion N1 and a peeling pad nip portion N2 formed downstream of the roll nip portion N1 and continuously to the roll nip portion N1. The peeling pad 64 that forms the peeling pad nip portion N2 is disposed in the vicinity of the downstream side of the roll nip portion N1, and the peeling pad 64 is set to press the pressure roll 62. Accordingly, by setting the nip pressure Pn satisfying the above-described expression (1) in the boundary region N2S, the generation of a valley region where the nip pressure falls is suppressed, and the generation of bubbles in the boundary region N2S is suppressed. can do. Furthermore, it is possible to set the nip pressure to continuously and monotonously decrease in a region from the position where the nip pressure reaches a peak in the roll nip portion N1 to the most downstream position of the peeling pad nip portion N2.
As described above, in the fixing device 60 according to the present embodiment, the generation of bubbles in the boundary region N2S is suppressed, and the nip pressure is set so as to continuously and monotonously decrease, whereby a high nip pressure is obtained in the roll nip portion N1. It is possible to gradually release the water vapor or the air that is about to be thermally expanded that has been held in by the path until it passes through the peeling pad nip portion N2, and the water vapor or the thermally expanded air becomes bubbles and moves around in the nip. Occurrence of the phenomenon can be suppressed. Therefore, the toner image that has not been completely solidified is hardly disturbed, and it is possible to suppress the occurrence of image defects such as image unevenness in the fixed image.

  Further, since the cross section of the peeling pad 64 forming the peeling pad nip portion N2 is formed in a substantially arc shape, the fixing belt 610 that has passed through the peeling pad nip portion N2 is rapidly changed so that the traveling direction thereof is bent. It is done. Therefore, the paper P that has passed through the roll nip portion N1 and the peeling pad nip portion N2 is peeled from the fixing belt 610 at the time of exiting the peeling pad nip portion N2, and the curvature separation from the paper P can be performed.

In addition, in the fixing device 60 according to the present embodiment, in the vicinity of the peeling pad 64 on the downstream side of the fixing belt 610 in the traveling direction, up to the lap region where the fixing belt 610 is stretched again on the fixing roll 611, An idler roll 615 is disposed at a position where the fixing belt 610 that has passed through the peeling pad 64 is guided away from the peeling pad 64.
With the idler roll 615 arranged in this manner, in the fixing device 60 of the present embodiment, it is possible to set a short region where the fixing belt 610 and the peeling pad 64 slide on the downstream side of the peeling pad 64. Become. As a result, it is possible to suppress the occurrence of an extra load on the fixing belt 610, and thus the fixing belt 610 can be smoothly conveyed. Therefore, the conveyance of the fixing belt 610 at the nip portion N is smooth, and a high-quality fixed image can be formed.
The idler roll 615 is provided with a tension adjusting device 80 for adjusting the tension of the fixing belt 610. Accordingly, it is possible to suppress the occurrence of slack in the fixing belt 610 in the region from the fixing belt 610 passing through the nip portion N to the wrap region stretched around the fixing roll 611 again. Therefore, it is possible to realize stable peeling of the paper P, and to prevent occurrence of troubles such as occurrence of gloss unevenness and image unevenness, and buckling of the fixing belt 610.

[Embodiment 2]
In the first embodiment, the configuration in which the pressure roller 62 is used as the pressure member disposed in pressure contact with the fixing belt module 61 in the fixing device 60 mounted on the image forming apparatus has been described. In the second embodiment, a configuration using a pressure belt module 70 in which a pressure belt 700 is stretched by a plurality of rolls as a pressure member will be described. In addition, the same code | symbol is used about the structure similar to Embodiment 1, and the detailed description is abbreviate | omitted here.

  FIG. 12 is a side sectional view showing the configuration of the fixing device 90 according to the present embodiment. The configuration of the fixing device 90 according to the present embodiment is different from the fixing device 60 according to the first embodiment except that a pressure belt module 70 is provided as a pressure member in place of the pressure roll 62. This is the same as the fixing device 60 of the first embodiment.

  The pressure belt module 70 according to the present embodiment includes a pressure belt 700, a pressure belt 700, and a fixing belt 610 that are stretched by three rolls of a pressure roll 701, an inlet roll 702, and a tension roll 703. The pressure pad 704 as a pressure member arranged in a state of being biased by the fixing roll 611 constitutes a main part. The pressure belt module 70 is installed so as to be pressed against the fixing belt module 61, and the pressure belt 700 is driven by the fixing roll 611 as the fixing roll 611 of the fixing belt module 61 rotates in the arrow C direction. And rotate in the direction of arrow G. The traveling speed is 440 mm / s, which is the same as the surface speed of the fixing roll 611.

In the nip portion N where the pressure belt module 70 and the fixing belt module 61 are pressed against each other, the pressure belt 700 is pressed against the outer peripheral surface of the fixing belt 610 in the lap region where the fixing belt 610 is wound around the fixing roll 611. A belt nip portion N3 formed so as to be set is set.
In the fixing device 90 according to the present exemplary embodiment, the pressure pad 704 is disposed inside the pressure belt 700 in a state of being urged toward the fixing roll 611 via the pressure belt 700. The wrap area of the fixing roll 611 is pressed. In the most downstream portion of the belt nip portion N3, the pressure roll 701 is attached to the central axis of the fixing roll 611 via the pressure belt 700 and the fixing belt 610 by a compression coil spring (not shown) as a pressure unit. It is biased toward the surface, and a local high pressure is generated at the contact portion between the fixing roll 611 and the fixing belt 610.
Therefore, since the belt nip portion N3 can be formed widely, further stable fixing performance for the toner image on the paper P can be realized. In addition, since the pressure is efficiently applied to the melted toner image by the local high pressure by the pressure roll 701, high fixability is maintained, and the toner image surface is smoothed to give a good image gloss to the color image. be able to.

  Here, the pressure belt 700 disposed in the pressure belt module 70 is formed of a base layer made of a resin having high heat resistance such as polyimide, polyamide, polyamideimide, or the like. The thickness of the base layer is, for example, about 50 to 125 μm. Further, the pressure belt 700 may have a configuration in which a release layer is coated on the surface or both surfaces of the base layer on the fixing roll 611 side. In this case, the release layer is preferably a fluororesin such as PFA coated with a thickness of 5 to 20 μm. Furthermore, it is possible to adopt a laminated structure in which an elastic layer is formed between the base layer and the release layer as necessary. In that case, a silicone rubber having a thickness of 100 to 200 μm can be used as the elastic layer. In the fixing device 90 of the present embodiment, the pressure belt 700 is composed only of a base layer of a polyimide film having a thickness of 75 μm, a width of 350 mm, and a circumferential length of 240 mm.

  The three rolls that stretch the pressure belt 700 include a pressure roll 701 having a steel core covered with silicone rubber as an elastic layer, a stainless steel inlet roll 702, and a stainless steel tension roll 703. The pressure belt 700 is stretched with a tension of 10 kgf. The outer diameters of the pressure roll 701 are 25 mm, the inlet roll 702 is 22 mm, the tension roll 703 is 20 mm, and the length is 360 mm. A halogen heater 705 is disposed inside the inlet roll 702 as a heating source. The surface temperature is controlled to 120 ° C. by a temperature sensor and control unit 10 (see FIG. 1) (not shown), and the pressure belt 700 is preheated.

The pressure roll 701 is urged toward the central axis of the fixing roll 611 (in the direction of an arrow K) via a pressure belt 700 and a fixing belt 610 by a compression coil spring (not shown) as a pressing means. In addition, a local high pressure is generated at the contact portion between the fixing roll 611 and the fixing belt 610. In that case, the pressure roll 701 has a smaller diameter than the fixing roll 611 in order to efficiently apply a local high pressure to the fixing roll 611 and the fixing belt 610 with a low load.
Note that any one of the inlet roll 702 and the tension roll 703 includes a belt edge position detection mechanism that detects the belt edge position of the pressure belt 700 and a pressure belt according to the detection result of the belt edge position detection mechanism. An axial displacement mechanism for displacing the abutting position in the axial direction of 700 may be provided to control meandering (belt walk) of the pressure belt 700.

The pressure pad 704 as a pressure member includes an elastic member for securing a wide belt nip portion N3, and a low friction layer provided on a surface where the elastic member contacts the inner peripheral surface of the pressure belt 700. And is held by a holder (not shown) made of metal or the like. The elastic member having the low friction layer on the surface is formed in a concave shape in which the fixing roll 611 side substantially follows the outer peripheral surface of the fixing roll 611, is pressed against the fixing roll 611, and is disposed in the wrap region of the fixing roll 611. An entrance side region of the formed belt nip portion N3 is formed.
As the elastic member of the pressure pad 704, a highly heat-resistant elastic body such as silicone rubber or fluororubber, a leaf spring, or the like can be used. The low friction layer formed on the elastic member is provided to reduce the sliding resistance between the inner peripheral surface of the pressure belt 700 and the pressure pad 704, and is a material having a small friction coefficient and wear resistance. It is desirable. Specifically, a glass fiber sheet impregnated with Teflon (registered trademark), a fluororesin sheet, a fluororesin coating film, or the like can be used.

  Further, also in the fixing device 90 of the present embodiment, the peeling pad 64 is disposed in the vicinity of the downstream side of the belt nip portion N3. The peeling pad 64 is installed so as to press the fixing belt 610 against the surface of the pressure roll 701. As a result, a separation pad nip portion N2 in which the fixing belt 610 is wrapped on the pressure roll 701 side is set continuously to the belt nip portion N3.

  In the peeling pad nip portion N2 set by the peeling pad 64, as in the fixing device 60 of the first embodiment, the nip pressure Pn in the boundary region with the belt nip portion N3 in the peeling pad nip portion N2 is equal to or higher than a predetermined value (above (See equation (1)). Accordingly, the generation of a valley region where the nip pressure drops is suppressed, and the generation of bubbles in the region is suppressed. Further, the nip pressure is set to continuously and monotonously decrease in a region from the position where the nip pressure reaches a peak in the belt nip portion N3 to the most downstream position of the peeling pad nip portion N2. Therefore, it is possible to gradually release water vapor or air that is about to be thermally expanded by the high nip pressure in the belt nip portion N3 through a path until it passes through the peeling pad nip portion N2, and the water vapor and the heat expanded. Occurrence of a phenomenon in which air becomes bubbles and moves around in the nip portion N can be suppressed. Therefore, the toner image that has not been completely solidified is hardly disturbed, and it is possible to suppress the problem that image defects such as image unevenness occur in the fixed image.

In addition, in the fixing device 90 of the present embodiment, similarly to the first embodiment, the fixing belt 610 is stretched around the fixing roll 611 again in the vicinity of the peeling pad 64 on the downstream side in the fixing belt 610 traveling direction. An idler roll 615 is disposed at a position that guides the fixing belt 610 that has passed through the peeling pad 64 away from the peeling pad 64 in the area up to the wrapping area.
With the idler roll 615 arranged in this way, even in the fixing device 90 of the present embodiment, it is possible to set a short region where the fixing belt 610 and the peeling pad 64 slide on the downstream side of the peeling pad 64. Become. As a result, it is possible to suppress the occurrence of an extra load on the fixing belt 610, and thus the fixing belt 610 can be smoothly conveyed. Therefore, the conveyance of the fixing belt 610 at the nip portion N is smooth, and a high-quality fixed image can be formed.
In addition, the idler roll 615 is provided with a tension adjusting device 80 for adjusting the tension of the fixing belt 610 as in the first embodiment. Accordingly, it is possible to suppress the occurrence of slack in the fixing belt 610 in the region from the fixing belt 610 passing through the nip portion N to the wrap region stretched around the fixing roll 611 again. Therefore, it is possible to realize stable peeling of the paper P, and to prevent occurrence of troubles such as occurrence of gloss unevenness and image unevenness, and buckling of the fixing belt 610.

1 is a schematic configuration diagram illustrating an image forming apparatus (digital color printer) according to the present invention. 2 is a side cross-sectional view illustrating a schematic configuration of a fixing device according to Embodiment 1. FIG. It is a schematic sectional drawing showing the vicinity area | region of a nip part. It is the figure which showed the outline of the nip pressure distribution of a nip part when a peeling pad is spaced apart and arrange | positioned more than predetermined distance from a roll nip part. It is the figure which showed the outline of nip pressure distribution at the time of arrange | positioning a peeling pad in the downstream vicinity of a roll nip part. It is a schematic sectional drawing showing the periphery of the area | region where the peeling pad is arrange | positioned. It is the figure which showed the structure of the peeling pad set so that the upstream edge part of a press surface might contact a fixing roll. It is a side view which shows one edge part by which the tension adjustment mechanism was arrange | positioned by the idler roll. It is a figure explaining the structure of a tension adjustment mechanism. FIG. 6 is a diagram illustrating a case where the fixing belt is slackened on the downstream side of the peeling pad. FIG. 10 is a diagram illustrating a case where the fixing belt is slack in the boundary region N2S in the peeling pad nip portion N2. FIG. 4 is a side sectional view showing a schematic configuration of a fixing device according to a second embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Control part, 25Y, 25M, 25C, 25K ... Laser exposure apparatus, 26Y, 26M, 26C, 26K ... Image forming unit, 31 ... Photosensitive drum, 32 ... Charging roll, 33 ... Developer, 34 ... Drum cleaner, DESCRIPTION OF SYMBOLS 41 ... Intermediate transfer belt, 42 ... Primary transfer roll, 50 ... Secondary transfer roll, 60, 90 ... Fixing device, 61 ... Fixing belt module, 62, 701 ... Pressure roll, 64 ... Release pad, 70 ... Pressure belt Module, 80 ... tension adjusting device, 83 ... peeling guide plate, 610 ... fixing belt, 611 ... fixing roll, 612 ... tension roll, 615 ... idler roll, 700 ... pressure belt, 702 ... inlet roll, 704 ... pressure pad, 801 ... Tensioner frame, 802 ... Tensioner base, 803 ... Spring member, 804 ... Load sensor, 80 ... bearing, 806 ... sliders, 810 ... tensioner moving mechanism, 811 ... eccentric cam

Claims (18)

A fixing device for fixing a toner image carried on a recording material,
A rotatable fixing roll;
A rotatable belt member stretched around the fixing roll;
A pressure member that is arranged to press the fixing roll via the belt member to form a nip portion;
A peeling member that presses the outer surface of the belt member against the pressure member in the vicinity of the downstream side of the pressure contact portion between the fixing roll and the pressure member;
The belt member is arranged in a region downstream of the peeling member and downstream of the nip portion and upstream of a wrap region stretched around the fixing roll, and stretches the belt member. A fixing device comprising: 1 tension roll.   The fixing device according to claim 1, wherein the first tension roll guides the belt member that has passed through the peeling member in a direction away from the peeling member.   The fixing device according to claim 1, wherein the first tension roll includes a tension adjusting mechanism that adjusts a tension of the belt member.   The tension adjusting mechanism includes a spring member that presses the first tension roll in a direction from the inner peripheral surface side to the outer peripheral surface side of the belt member, and a load detection unit that detects a spring load on the spring member. The pressing force of the spring member to the first tension roll is adjusted so that the spring load detected by the load detector is within a predetermined range. Fixing device.   The belt member is arranged in a region downstream of the nip portion and downstream of a wrap region stretched around the fixing roll and upstream of the nip portion, and stretches the belt member. The fixing device according to claim 1, further comprising a second tension roll provided with a tension adjusting mechanism for adjusting the tension of the belt member.   The fixing device according to claim 1, wherein the first tension roll is provided with a drive unit that rotates the first tension roll in a moving direction of the belt member.   The fixing device according to claim 6, wherein the driving unit rotates the first tension roll at a peripheral speed faster than a moving speed of the belt member. A fixing device for fixing a toner image carried on a recording material,
A rotatable fixing roll;
A rotatable belt member stretched around the fixing roll;
A pressure member that is arranged to press the fixing roll via the belt member to form a nip portion;
A peeling member that presses the outer surface of the belt member against the pressure member in the vicinity of the downstream side of the pressure contact portion between the fixing roll and the pressure member;
The belt member is disposed in a region downstream of the peeling member and downstream of the nip portion and upstream of a wrap region stretched around the fixing roll, and stretches the belt member. A first tension roll capable of adjusting the tension of the belt member;
The belt member is arranged in a region downstream of the nip portion and downstream of a wrap region stretched around the fixing roll and upstream of the nip portion, and stretches the belt member. And a second stretching roll capable of adjusting the tension of the belt member.   The first tension roll includes a spring member that presses the first tension roll from the inner peripheral surface side to the outer peripheral surface side of the belt member, and a load detection that detects a spring load on the spring member. The second tension roll includes a spring member that presses the second tension roll from the inner peripheral surface side to the outer peripheral surface side of the belt member, and the spring. The fixing device according to claim 8, further comprising a tension adjusting mechanism including a load detection unit that detects a spring load on the member.   The first tension roll and the second tension roll include a spring load value detected by the tension adjustment mechanism of the first tension roll and the tension adjustment of the second tension roll. The fixing device according to claim 9, wherein the tension of the belt member is adjusted based on one or both of a spring load value detected by a mechanism.   The first tension roll and the second tension roll are a support on which the fixing roll and the pressure member are pivotally supported, and are substantially parallel to the fixing roll and the pressure member. 9. The fixing device according to claim 8, wherein the fixing device is rotatably supported while maintaining the positional relationship.   The fixing device according to claim 8, wherein the peeling member is disposed to be swingable with respect to the fixing roll.   9. A guide member for guiding a recording material peeled off from the belt member that has passed through the peeling member, and the guide member is disposed so as to be swingable with respect to the fixing roll. The fixing device described.   The fixing device according to claim 8, wherein the first tension roll has a high friction layer formed on a surface thereof. A toner image forming unit for forming a toner image;
A transfer unit that transfers the toner image formed by the toner image forming unit onto a recording material;
A fixing unit for fixing the toner image transferred onto the recording material to the recording material,
The fixing unit is
A rotatable fixing roll;
A rotatable belt member stretched around the fixing roll;
A pressure member that is arranged to press the fixing roll via the belt member to form a nip portion;
A peeling member that presses the outer surface of the belt member against the pressure member in the vicinity of the downstream side of the pressure contact portion between the fixing roll and the pressure member;
The belt member is arranged in a region downstream of the peeling member and downstream of the nip portion and upstream of a wrap region stretched around the fixing roll, and stretches the belt member. An image forming apparatus comprising: 1 tension roll.   The fixing unit has a nip pressure in a region from the most downstream part of the pressure contact part between the fixing roll and the pressure member to the most downstream part of the pressure contact part between the pressure member and the peeling member. The image forming apparatus according to claim 15, wherein the image forming apparatus is set to monotonously decrease in a traveling direction.   The image forming apparatus according to claim 15, wherein the pressing member of the fixing unit has a dent amount at a pressure contact portion with the fixing roll larger than a dent amount of the fixing roll.   The image forming apparatus according to claim 15, wherein the pressure member is formed of a pressure belt module in which a belt member is stretched by a plurality of tension rolls.

Images