JP2007147905A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably separate recording paper from a belt member in a fixing device using the belt member. <P>SOLUTION: A peeling pad 64 for peeling paper P from a fixing belt 610 stretched around a rotatable fixing roll 611 is arranged so that the outer surface of the fixing belt 610 is pressed to a pressure roll 62 in the vicinity of the downstream side of a press-contact part between the fixing roll 611 and the pressure roll 62 and constituted of a plurality of pressing members (an upstream side peeling pad 641 and a downstream side peeling pad 642) capable of forming different nip pressures, respectively. <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 image forming apparatuses are 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, a belt member stretched around the fixing roll, and a belt. A pressure member that presses the fixing roll through the member; and 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 member is composed of a plurality of pressing members capable of forming different nip pressures.

Here, the peeling member includes a first pressing member that presses the outer surface of the belt member against the pressing member in the vicinity of the downstream side of the pressure contact portion between the fixing roll and the pressing member, and a belt member of the first pressing member. The second pressing member that presses the outer surface of the belt member against the pressing member with a pressing force smaller than the pressing force by the first pressing member on the downstream side in the moving direction can be characterized.
In addition, the peeling member is configured by a rigid body in which the pressing member disposed at the most upstream portion in the moving direction of the belt member is formed in a substantially arc shape whose side surface facing the fixing roll side follows the surface shape of the fixing roll. It can also be characterized.

  Further, the peeling member includes a peeling surface that changes the pressing member disposed at the most downstream portion in the moving direction of the belt member so as to bend the moving direction of the fixing belt located on the side opposite to the fixing roll side. It can also be characterized by comprising an elastic body. In particular, the pressure roll includes an elastic layer, and the elastic coefficient of the pressing member disposed at the most downstream portion in the moving direction of the belt member may be configured to be smaller than the elastic coefficient of the pressure roll. . In addition, the peeling member is a spring in which the pressing member disposed at the most downstream portion in the moving direction of the belt member is fixed to one of the plurality of pressing members, and the downstream side in the moving direction of the belt member is formed as a free end. It can also be characterized by comprising a plate-like member having elasticity.

  Further, the peeling member can be characterized in that a plurality of pressing members are integrally formed. Further, the peeling member is a continuous flat surface without a step, or a continuous curved surface without a step following the surface shape of the pressure member, with a plurality of pressing members pressing the outer surface of the belt member against the pressing member. It can also be characterized by being formed.

  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 belt member stretched around the fixing roll, and a belt member stretched. A tension roll, a pressure member that is pressed against the fixing roll via the belt member, and the belt member near the downstream side of the pressure contact portion between the fixing roll and the pressure member. A peeling member that presses the surface against the pressure member, and the peeling member is provided on the upstream side in the moving direction of the belt member with a first nip pressure area and pressed on the downstream side in the moving direction of the belt member. And a second nip pressure region that is pressed by the second nip pressure.

Here, in the first nip pressure region, the first nip pressure Pn is Pn ≧ Po × (Tn / To−1) where the absolute temperature of the belt member is Tn, the absolute temperature of the surrounding environment is To, and the atmospheric pressure is Po. ). Further, the second nip pressure region may be characterized in that the second nip pressure is set to a nip pressure that does not cause deformation on the pressure roll surface. In addition, the peeling member is set to monotonously decrease the first nip pressure and the second nip pressure in the traveling direction of the belt member in the region from the first nip pressure region to the second nip pressure region. It can be characterized by.
Further, the pressing member can 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 peeling member can be characterized in that the upstream end portion in the traveling direction of the belt member is disposed in a wedge-shaped region defined by the fixing roll and the pressure member.
In addition, it is possible to configure that the fixing roll has a heating member disposed therein, and the stretching roll has a heating member disposed therein.

  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 includes a rotatable fixing roll, a belt member stretched around the fixing roll, and a belt member. A pressure member that presses against the fixing roll; and 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. It is characterized by comprising a plurality of pressing members capable of forming a nip pressure.

Here, the peeling member of the fixing unit presses the outer surface of the belt member against the pressure member with a first nip pressure that does not generate bubbles near the downstream side of the pressure contact portion between the fixing roll and the pressure member. A first pressing member and a second pressing member that presses the outer surface of the belt member against the pressing member with a second nip pressure that does not cause deformation of the pressing member on the downstream side of the first pressing member in the moving direction of the belt member. It can be characterized by comprising.
In the fixing unit, Pn ≧ Po × (Tn / To−) where the first nip pressure Pn of the first pressing member is Tn, the absolute temperature of the belt member is Ton, the absolute temperature of the surrounding environment is To, and the atmospheric pressure is Po. It can also be characterized by being set to satisfy 1). Further, in the fixing unit, the nip pressure in the region 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 is directed in the traveling direction of the belt member. It can also be characterized by being set to monotonously decrease.
In addition, 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, a tension roll 612 that stretches the fixing belt 610 from the inside, and a fixing belt 610 from the outside. A tension roll 613 that stretches the belt, a posture correction roll 614 that corrects the posture of the fixing belt 610 between the fixing roll 611 and the tension roll 612, and a region where the fixing belt module 61 and the pressure roll 62 are in pressure contact with each other. A peeling pad 64 as an example of a peeling member that peels off the paper P from the fixing belt 610, and a tension roll 615 that stretches the fixing belt 610 on the downstream side of the nip N. The main part is constituted by.

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. A fluororesin with a thickness of 200 μm is coated as a protective layer for preventing metal wear on the core roll surface. It is a hard roll formed in this way. 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 200 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 wall thickness of 2 mm, and a length of 360 mm. A halogen heater 616b rated at 1500 W is disposed as a heating source inside the tension roll 612. The surface temperature is controlled to 190 ° C. by the temperature sensor 617b and the control unit 10 (see FIG. 1). Yes. Therefore, 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, spring members (not shown) that press the fixing belt 610 outward are disposed at both ends of the tension roll 612, and the tension of the entire fixing belt 610 is set to 15 kgf.

The tension 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 tension 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 stretching roll 613.
Inside the tension roll 613, a halogen heater 616c rated as 1000 W is disposed as a heating source, and the surface temperature is controlled to 190 ° C. by the temperature sensor 617c and the control unit 10 (see FIG. 1). Yes. Accordingly, the tension 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 stretching roll 612, and the stretching roll 613 is employed.

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. A belt edge position detection mechanism (not shown) that detects the edge position of the fixing belt 610 is disposed in the vicinity of the posture correction roll 614. The posture correction roll 614 is provided with an axis displacement mechanism that displaces the contact position in the axial direction of the fixing belt 610 according to the detection result of the belt edge position detection mechanism, and performs meandering (belt walk) of the fixing belt 610. Configured to control.
Such meandering control with respect to the fixing belt 610 may be performed by the tension roll 612 instead of the posture correction roll 614.

The peeling pad 64 is arranged in close contact with the upstream peeling pad 641 on the downstream side in the rotation direction of the fixing belt 614 and the upstream peeling pad 641 arranged in the vicinity of the circumferential surface of the fixing roll 610. It is comprised with the pad 642 (refer FIG. 3 of a back | latter stage). The upstream peeling pad 641 is a block member having a substantially arc-shaped cross section formed of a rigid body such as a metal such as SUS or aluminum or a resin. The downstream peeling pad 642 is a block member having a substantially arc shape in cross section formed of an elastic body such as silicone rubber. Then, the upstream side peeling pad 641 and the downstream side peeling at a position in the vicinity of the downstream side of the region 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). The pad 642 is integrated with the fixing roll 611 over the entire axial direction. Further, the peeling pad 64 causes the pressure roll 62 to pass through a fixing belt 610 over a predetermined width region (in this embodiment, a width of 8 mm along the traveling direction of the fixing belt 610) (for example, 40 kgf) so as to press uniformly, and forms a “peeling nip portion N2” (see FIG. 3 in the subsequent stage) described later.
The tension roll 615 is a cylindrical roll formed of stainless steel having an outer diameter of 12 mm and a length of 360 mm. The fixing belt 610 that has passed through the peeling pad 64 is disposed in the vicinity of the downstream side of the fixing pad 610 in the traveling direction of the fixing belt 610 so that the fixing belt 610 smoothly rotates toward the fixing roll 611.

  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 fixing belt 610 is wound (wrapped) in the region (wrapped region) around the fixing roll 611. , The pressure roll 62 is arranged so as to be in pressure contact with the outer peripheral surface of the fixing belt 610, whereby a roll nip portion (first nip portion) N1 is formed.

Here, in the fixing device 60 of the present embodiment, as described above, the fixing roll 611 that is one of the rolls forming the roll nip portion N1 has a heat-resistant resin (fluororesin) on the surface of an aluminum core metal (core roll). 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, in the vicinity of the downstream side of the roll nip portion N1, a peeling pad 64 in which an upstream peeling pad (first pressing member) 641 and a downstream peeling pad (second pressing member) 642 are integrally formed is disposed. Yes. 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 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 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 tension roll 615 by the peeling pad 64. For this reason, the paper P that has passed through the roll nip portion N1 and the peeling nip portion N2 cannot follow the change in the advancing direction of the fixing belt 610 when it exits the peeling 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 of the peeling nip N2. In the fixing device 60 of the present embodiment, the peeling nip portion N2 is set to a width of 8.5 mm along the traveling direction of the fixing belt 610.

Next, the arrangement position of the peeling pad 64 and the nip pressure distribution (nip pressure profile) of the peeling nip portion N2 formed by the peeling pad 64 will be described.
As described above, the peeling pad 64 is disposed in the vicinity of the downstream side of the roll nip portion N1. As a result, in the nip portion N including the roll nip portion N1 and the peeling nip portion N2, the position where the nip pressure peaks in the roll nip portion N1 (see FIG. 5 in the subsequent stage) reaches the most downstream position of the peeling nip portion N2. 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, in the fixing device 60 of the present embodiment, an operation based on the configuration of the peeling pad 64, which will be described in detail later, is added to achieve stable paper separation, and at the same time, high quality without image defects such as image unevenness. A fixed image can be provided.
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 in which 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, the peeling member that peels the paper P from the fixing belt 610, that is, the peeling pad 64, is rapidly changed in the downstream direction of the nip portion N. It is arranged.

However, when the peeling nip portion N2 is formed continuously with the roll nip portion N1 by disposing the peeling pad 64, the region in the peeling nip portion N2 where the peeling pad 64 is disposed (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 the nip pressure profile of the nip portion N (the roll nip portion N1 and the peeling nip portion N2) when the peeling pad 64 is disposed at a predetermined distance or more away from the downstream end N1E of the roll nip portion N1. FIG. As shown in FIG. 4, in this case, in the peeling nip portion N2, a valley region where the nip pressure Pn 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 nip portion N2 is formed in a low state that is equal to or lower than a predetermined value Pn1, bubbles that have been suppressed in the roll nip portion N1 are generated in the boundary region N2S. 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 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 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 to continuously and monotonously decrease in a region from the position where the nip pressure peaks in the roll nip portion N1 in the nip portion N to the most downstream position of the peeling 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. Furthermore, by setting the nip pressure to continuously decrease 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 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 nip portion N2, and the occurrence of the phenomenon of bubbles moving around as described above is suppressed. 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 configuration of the peeling pad 64 of this embodiment will be described.
FIG. 6 is a schematic cross-sectional view illustrating the configuration of the peeling pad 64. As shown in FIG. 6, the peeling pad 64 is in close contact with the upstream peeling pad 641 disposed in the vicinity of the circumferential surface of the fixing roll 610 and the upstream peeling pad 641 on the downstream side in the rotation direction of the fixing belt 610. The downstream peeling pad 642 arranged in this manner is integrally formed. The upstream peeling pad 641 is formed of a rigid body such as a metal or resin such as SUS or aluminum, and the downstream peeling pad 642 is formed of an elastic body such as silicone rubber. Thereby, in the peeling pad 64 of this Embodiment, it sets so that the pressing force to the pressure roll 62 by the upstream peeling pad 641 and the pressing force to the pressure roll 62 by the downstream peeling pad 642 may differ. be able to. Specifically, the pressing force by the upstream peeling pad 641 formed of a rigid body is set to a higher pressure than the nip pressure Pn1 that can suppress the generation of bubbles represented by the above-described equation (1). On the other hand, the pressing force at the downstream peeling pad 642 formed of an elastic body is set to a low pressure equal to or lower than a predetermined nip pressure so as not to cause deformation (concave portion) on the surface of the pressure roll 62.

First, in the peeling pad 64 of the present embodiment, the inner side surface 64 a of the upstream side peeling pad 641 is formed in a shape that allows the upstream side peeling pad 641 to be disposed close to the peripheral surface of the fixing roll 611. That is, the inner side surface 64a of the upstream peeling pad 641 has the upstream peeling pad 641 as close as possible to the fixing roll 611 side (in this embodiment, the gap between the peeling pad 64 and the fixing roll 611 is 0.5 mm). In order to arrange them, a curved surface that follows the peripheral surface of the fixing roll 611 is formed.
In order to set the boundary region N2S shown in FIG. 6 as narrow as possible, a wedge shape is formed in the vicinity of the downstream side of the roll nip N1 (see also FIG. 3) and defined by the fixing roll 611 and the pressure roll 62. In the region Q, it is necessary to arrange the upstream peeling pad 641 so as to press the surface of the pressure roll 62. Therefore, the upstream end portion (upstream end portion of the pressing surface 641c of the upstream release pad 641) 64p of the inner side surface 64a of the upstream release pad 641 is located near the downstream end portion N1E of the roll nip portion N1, that is, the wedge described above. The inner side surface 64 a is formed in a curved surface following the peripheral surface of the fixing roll 611 so that the inner side surface 64 a can be installed at a position close to the fixing roll 611 in the shaped region Q. In the peeling pad 64 of the present embodiment, the inner side surface 64a of the upstream side peeling pad 641 is formed by a substantially circumferential surface having a curvature radius of 33 mm. In addition, as long as it is a curved surface that follows the peripheral surface of the fixing roll 611, it is not limited to a curved surface such as a substantially circumferential surface, and a plurality of flat surfaces can be bent stepwise.
Further, the upstream end 64p of the inner side surface 64a of the upstream peeling pad 641 can be installed at a position close to the fixing roll 611 in the wedge-shaped region Q, and at the same time, the strength and rigidity of the upstream end 64p portion are increased. In order to ensure, it is preferable that the upstream peeling pad 641 is made of a rigid body, and the angle θ1 formed by the inner surface 64a and the pressing surface 641c is set to 15 to 50 °.

The outer surface 64b of the downstream peeling pad 642 is formed so as to rapidly change the traveling direction of the fixing belt 610 that has passed through the peeling nip N2. That is, the outer surface 64b of the downstream peeling pad 642 guides the fixing belt 610 in cooperation with the stretching roll 615 and the fixing roll 611, and rapidly changes the traveling direction thereof, so that the sheet P is removed from the fixing belt 610. The surface to be peeled off. Therefore, in order to stably peel the paper P from the fixing belt 610, the upstream end region of the outer surface 64b of the downstream peeling pad 642, that is, the region where the fixing belt 610 is separated from the pressure roll 62 (peeling region). In R, the angle θ2 (see FIG. 6) formed by the tangent of the pressure roll 62 and the tangent of the outer surface 64b is set to be 25 ° or more. Further, in the peeling region R, the outer surface 64b of the downstream peeling pad 642 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 surface 64 b of the downstream peeling pad 642 faces the stretching roll 615 so that the fixing belt 610 moves smoothly in the direction of the stretching roll 615 and the fixing roll 611 after the fixing belt 610 is separated from the pressure roll 62. It is formed with an inclined plane. In this case, the outer surface 64b of the downstream peeling pad 642 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 of the downstream peeling pad 642 also rubs against the fixing belt 610, for example, the surface of the fixing belt 610 has a small friction coefficient and excellent wear resistance. (Registered trademark) or the like is preferably used.

Next, the pressing surface on which the peeling pad 64 presses the fixing belt 610 against the pressure roll 62 will be described.
The pressing surface of the peeling pad 64 is formed by a pressing surface 641 c of the upstream peeling pad 641 and a pressing surface 642 c of the downstream peeling pad 642. In order to smoothly move the fixing belt 610 at the peeling nip portion N2 so as not to disturb the image on the paper P, the pressing surface 641c and the pressing surface 642c are formed as a continuous flat surface having no step. Note that the pressing surface 641c and the pressing surface 642c can also be formed of a continuous concave curved surface having no step following the circumferential surface of the pressure roll 62, whereby the pressing force can be made more uniform.
Further, the pressing surface 641c of the upstream side peeling pad 641 and the pressing surface 642c of the downstream side peeling pad 642 rub against the fixing belt 610, so that the fixing belt 610 moves smoothly. For example, it is preferable to have a configuration in which, for example, Teflon (registered trademark) or the like excellent in wear resistance is coated.

First, on the pressing surface 641c of the upstream peeling pad 641, the pressing force for pressing the pressure roll 62 is set to a high pressure that can suppress the generation of bubbles. That is, the nip pressure (first nip pressure) in the region where the pressing surface 641c of the upstream peeling pad 641 presses the pressure roll 62 (upstream pad portion N2T1: first nip pressure) is as described above (1). It is set to a nip pressure Pn1 or higher that can suppress the generation of bubbles shown in the equation. Thereby, it is possible to stably set the nip pressure of the boundary region N2S to Pn1 or more in combination with the inner side surface 64a of the upstream peeling pad 641 being arranged close to the peripheral surface of the fixing roll 611. Generation of bubbles in the boundary region N2S can be suppressed. Further, it can contribute to imparting high gloss to the fixed image. Thus, in order to set the nip pressure at the pressing surface 641c of the upstream peeling pad 641 to be equal to or higher than the nip pressure Pn1, the upstream peeling pad 641 is formed of a rigid body.
Further, the upstream peeling pad 641 gradually releases water vapor or air that is to be thermally expanded in the roll nip portion N1 set to a nip pressure Pn1 or higher, so that the nip pressure peaks in the roll nip portion N1. The nip pressure lower than the nip pressure at the peak position of the roll nip portion N1 is set so that the nip pressure continuously and monotonously decreases from the position (peak position).

On the other hand, also on the pressing surface 642c of the downstream peeling pad 642, similarly, in order to gradually release the water vapor or air to be thermally expanded that has been suppressed in the roll nip portion N1, the peeling nip portion from the upstream pad portion N2T1. The nip pressure is set to continuously and monotonously decrease until reaching the most downstream position of N2. That is, the nip pressure (second nip pressure) in the region where the pressing surface 642c of the downstream peeling pad 642 presses the pressure roll 62 (downstream pad portion N2T2: second nip pressure region) is the upstream pad portion. It is set lower than the nip pressure at N2T1.
In addition, the nip pressure at the downstream pad portion N2T2 is predetermined so that deformation (concave portion) does not occur on the surface of the pressure roll 62 in the region (peeling region) R where the fixing belt 610 is separated from the pressure roll 62. It is set to a low pressure below the nip pressure. That is, by setting the pressing force with which the peeling pad 64 presses the fixing belt 610 against the pressure roll 62 not to be higher than necessary, the surface of the pressure roll 62 is prevented from being deformed (recessed), and the paper P is stably peeled from the fixing belt 610.

  FIG. 7 is a view showing a state in which the nip pressure at the downstream pad portion N2T2 is set higher than necessary, and the downstream peeling pad 642 causes deformation (concave portion) on the pressure roll 62 surface. As described above, the pressure roll 62 that receives the pressing force from the peeling pad 64 functions as a roll (NFPR) that forms a nip (roll nip portion N1), and therefore has an elastic layer 622 made of silicone rubber or the like. It is a roll (soft roll). Therefore, as shown in FIG. 7, if the pressing force from the peeling pad 64 is higher than necessary, the surface of the pressure roll 62 is deformed (recessed) in the peeling region R. In that case, an up curl is formed on the sheet P that has passed through the peeling nip portion N2 due to the deformation (concave portion) of the surface of the pressure roll 62 in the peeling region R. Accordingly, the change in the traveling direction of the fixing belt 610 with respect to the traveling direction of the paper P becomes relatively small, and the separation of the paper P from the fixing belt 610 becomes unstable.

Therefore, in the peeling pad 64 of the present embodiment, the pressing surface 642c of the downstream peeling pad 642 that presses the fixing belt 610 against the pressure roll 62 in the peeling region R causes deformation (concave portion) on the surface of the pressure roll 62. The pressing force is set so that it does not occur. By setting in such a manner, as shown in FIG. 8 (a diagram showing a case where the downstream peeling pad 642 is set with a pressing force that does not cause deformation (concave) on the surface of the pressure roll 62), the peeling region R No deformation (concave portion) occurs on the surface of the pressure roll 62. Therefore, the paper P that has passed through the peeling nip portion N2 advances straight, or advances in a direction in which some down curl is formed along the peripheral surface of the pressure roll 62 at the peeling nip portion N2. Accordingly, the change in the traveling direction of the fixing belt 610 relative to the traveling direction of the paper P becomes relatively large, and the paper P can be stably peeled from the fixing belt 610.
In addition, by setting a low pressing force that does not cause deformation (concave portion) on the surface of the pressure roll 62 in the peeling region R, the adhesive force between the toner on the paper P and the fixing belt 610 is reduced. It also has the effect of stabilizing.
Thus, in order to set the nip pressure at the pressing surface 642c of the downstream peeling pad 642 to a low pressing force that does not cause deformation (concave) on the surface of the pressure roll 62, the downstream peeling pad 642 is made of an elastic body. ing.

  Here, the pressing force that does not cause deformation (concave portion) on the surface of the pressing roll 62 set on the pressing surface 642c of the downstream peeling pad 642 is the rubber hardness and the layer thickness of the elastic layer 622 formed on the pressing roll 62. The thickness and thickness of the release layer 623 coated on the surface of the pressure roll 62 and the hardness and shape of the elastic body constituting the downstream peeling pad 642 are determined. Therefore, it is determined in accordance with the configuration of the pressure roll 62 and the downstream peeling pad 642.

  However, from the viewpoint of stably peeling the paper P, it is necessary to press the paper P to the surface side of the pressure roll 62 in the entire separation nip portion N2. Therefore, the nip pressure at the downstream pad portion N2T2 needs to be a predetermined value or more regardless of the configuration of the pressure roll 62 and the downstream peeling pad 642. In that case, the elastic coefficient of the downstream peeling pad 642 is lower than the elastic coefficient of the pressure roll 62 in order to give a margin to the set value of the pressing force that does not cause deformation (concave portion) on the surface of the pressure roll 62. It is preferable to configure. For example, the elastic layer 622 of the pressure roll 62 is made of silicone rubber having an elastic modulus of 60 Hs (Asker-C), and the downstream peeling pad 642 is made of silicone rubber having an elastic modulus of 22 Hs (Asker-C). By configuring in this way, the elastic coefficient of the downstream peeling pad 642 can be configured to be lower than the elastic coefficient of the pressure roll 62. Accordingly, when the pressing force from the pressing surface 642c is shaken in a high direction, the increased pressing force can be absorbed on the downstream peeling pad 642 side. The deformation (concave portion) can be prevented from occurring.

As described above, in the peeling pad 64 according to the present embodiment, the upstream peeling pad 641 is disposed on the upstream side at the same time that the inner side surface 64a of the upstream peeling pad 641 is disposed close to the peripheral surface of the fixing roll 611. The nip pressure at the pad portion N2T1 is set to a high pressure equal to or higher than the nip pressure Pn1 at which generation of bubbles is suppressed. Thereby, as shown in FIG. 5, the nip pressure in the boundary region N2S is ensured to be equal to or higher than the nip pressure Pn1 that can suppress the generation of bubbles, and the generation of bubbles in the boundary region N2S can be suppressed.
Further, in the downstream peeling pad 642, the nip pressure at the downstream pad portion N2T2 is set to a nip pressure Pn2 or less that does not cause deformation (concave portion) on the surface of the pressure roll 62, as shown in FIG. . Thereby, the paper P can be stably peeled from the fixing belt 610.

In the peeling pad 64 of this embodiment, the upstream side peeling pad 641 and the downstream side peeling pad 642 are configured as separate and independent members, and as described above, the nip pressure at each upstream side pad portion N2T1. And the nip pressure at the downstream pad portion N2T2 can be set independently. Therefore, the nip pressure profile at the peeling nip portion N2 can be set so that the peeling pad 64 functions optimally. Accordingly, it is possible to set a nip pressure profile corresponding to the thermal expansion of the pressure roll 62 and corresponding to the thickness of the paper P to be used.
In this embodiment, the peeling pad 64 is composed of the upstream peeling pad (first pressing member) 641 and the downstream peeling pad (second pressing member) 642. However, the peeling pad 64 functions optimally. In order to set a simple nip pressure profile, the peeling pad 64 can be constituted by a plurality of pressing members of three or more.

  In addition, the upstream side peeling pad 641 and the downstream side peeling pad 642 change the nip pressure in the peeling nip portion N2 from the peak position of the nip pressure in the roll nip portion N1 to the most downstream position (peeling region R). ) Is set to continuously decrease monotonically. As a result, the water vapor or air that is about to expand due to the high nip pressure in the roll nip portion N1 is gradually released along the path until it passes through the peeling nip portion N2, and the bubbles move around. Occurrence 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.

Here, evaluation regarding the sheet separation performance in the fixing device 60 of the present embodiment was performed. In this evaluation test, the process speed was set to 264 mm / s and 50 sheets were passed. As the paper P to be used, relatively thin OK top coat N paper (85 gsm paper) and OK top coat N paper (127.9 gsm paper) manufactured by Oji Paper Co., Ltd. were used. Further, as a toner image formed on the paper P, a solid image (density 100%) with a cyan single color and a leading edge margin width of 3 mm was used. The evaluation conditions in this evaluation test using such a thin paper P having a small basis weight and forming a solid image with a narrow leading edge margin width are adopted because they are severe conditions for paper separation. .
As a comparative example, the same evaluation test was performed using a conventional fixing device in which the peeling pad 64 is not provided, that is, the nip portion N is configured only by the roll nip portion N1.
As a result, in the fixing device 60 of the present embodiment, all 50 sheets were successfully peeled off, and no jamming was observed. On the other hand, in the conventional fixing device, 5 to 10 separation defects occurred in 50 sheets. Thus, the superiority of the sheet separation performance in the fixing device 60 of the present embodiment was confirmed.

  By the way, in the upstream peeling pad 641 of the peeling pad 64, the upstream end 64p of the pressing surface 641c is disposed at a position close to the fixing roll 611 in order to make the width of the boundary region N2S as small as possible. At that time, it is also possible to arrange the upstream end 64 p so as to contact the fixing roll 611. By setting as described above, the boundary region N2S can be almost eliminated, and almost the entire separation nip portion N2 can be formed by the pressure contact portion N2T between the separation pad 64 and the pressure roll 62. In addition, since the upstream end 64p can simultaneously receive the pressing force from the fixing roll 611, the pressing surface 641c can form a sufficient nip pressure in the entire upstream pad portion N2T1.

FIG. 9 is a diagram showing a configuration in which the upstream end 64 p of the pressing surface 641 c of the upstream peeling pad 641 is set to contact the fixing roll 611 and receives the pressing force from the fixing roll 611 at the same time. As shown in FIG. 9, in this case, the upstream end portion 64p of the pressing surface 641c 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 641c 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.
In this configuration, the upstream peeling pad 641 rubs against the fixing belt 610 and the fixing roll 611, so that the fixing belt 610 and the fixing belt 610 move smoothly, and the fixing belt 610 and the fixing roll 611 In order to reduce wear, it is preferable that the surface is coated with, for example, Teflon (registered trademark) having a small friction coefficient and excellent wear resistance.

In addition to the above-described configuration, the following configuration can also be used as the peeling pad 64 that independently sets the nip pressure at the upstream pad portion N2T1 and the nip pressure at the downstream pad portion N2T2.
FIG. 10 is a diagram showing another configuration example of the peeling pad 64. The peeling pad 64 shown in FIG. 10 is formed of a metal block such as SUS or aluminum to form the entire peeling pad 64 as an upstream peeling pad 641, and a notch is formed in a region including the peeling region R of the peeling pad 64. Is formed. A downstream peeling pad 642 made of an elastic material such as silicone rubber having a hardness of 22 Hs (Asker-C) is disposed in the notch. In this case, for example, the width of the pressing surface 641c by the upstream peeling pad 641 is 5 mm, and the width of the pressing surface 642c by the downstream peeling pad 642 is 3 mm.
Furthermore, FIG. 11 is also a diagram illustrating another configuration example of the peeling pad 64. The peeling pad 64 shown in FIG. 11 is formed as an upstream peeling pad 641 by forming the entire peeling pad 64 with a metal block such as SUS or aluminum. Then, a stainless steel spring having a thickness of, for example, 0.1 mm is formed on the pressing surface 641c of the upstream side peeling pad 641 with an outer side surface 64b that rapidly changes the advancing direction of the fixing belt 610 that has passed through the peeling nip portion N2. A plate member having elasticity is fixed to constitute the downstream peeling pad 642. The pressing force to the pressure roll 62 is applied by the upstream peeling pad 641, and the plate-like member presses the pressure roll 62 with spring elasticity. In this case, for example, the width of the pressing surface 641c by the upstream peeling pad 641 is 5 mm, and the width of the pressing surface 642c by the downstream peeling pad 642 is 3 mm.
10 and FIG. 11 also ensures that the nip pressure in the boundary region N2S is equal to or higher than the nip pressure Pn1 at which the generation of bubbles can be suppressed by the upstream side release pad 641. It is possible to suppress the generation of bubbles in the region N2S. Further, the sheet P can be stably peeled from the fixing belt 610 by setting the nip pressure Pn2 or less at which the deformation (concave portion) is not generated on the surface of the pressure roll 62 by the downstream peeling pad 642.

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 is supplied through the tension roll 612 from the heat supplied from the halogen heater 616a disposed inside the fixing roll 611 through the fixing roll 611 and from the halogen heater 616b disposed inside the tension roll 612. It is configured to be heated by heat and heat supplied from the halogen heater 616c disposed inside the tension roll 613 through the tension roll 613. Therefore, since heat energy can be replenished to the fixing belt 610 mainly and appropriately from the tension roll 612 and the tension roll 613, the process speed at the nip portion N is as high as 440 mm / s. 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 stretching roll 612, and the stretching roll 613 with a wide lap area (large wrap angle). Therefore, since a sufficient amount of heat is supplied from the fixing roll 611, the stretching roll 612, and the stretching roll 613 during a short period of one rotation of the fixing belt 610, the fixing belt 610 is returned to the necessary fixing temperature in a short time. It becomes possible to make it. 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, it is possible to easily and quickly switch to a desired temperature.

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 nip portion N2. In the peeling nip portion N <b> 2, the fixing pad 610 is pressed against the pressure roll 62 by pressing the peeling pad 64 in which the upstream side peeling pad 641 and the downstream side peeling pad 642 are integrally formed with the pressure roll 62. Is formed. 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 nip portion N2 is convex upward due to the curvature of the pressure roll 62. It has a certain curved shape.
Therefore, the paper P heated and pressed under the curvature of the fixing roll 611 at the roll nip portion N1 is changed in the traveling direction to a curvature directed in the opposite direction by the pressure roll 62 at the separation 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 nip portion N2 is also positioned in a preparation process for surely peeling in the final peeling process.

  Then, at the exit (peeling region R) of the peeling nip portion N2, the fixing belt 610 is conveyed so as to be wound around the peeling pad 64. Therefore, 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. Therefore, the paper P whose adhesion to the fixing belt 610 is weakened in advance in the peeling nip portion N2 is self-striped from the fixing belt 610 by the stiffness of the paper that the paper P itself has.

  At that time, as described above, the peeling pad 64 is pressurized with the upstream peeling pad 641 that sets a nip pressure higher than the nip pressure Pn1 that can suppress the generation of bubbles represented by the above-described formula (1). It is composed of a downstream peeling pad 642 that sets a nip pressure equal to or lower than a predetermined pressure that does not cause deformation (concave portion) on the surface of the roll 62. Thereby, the nip pressure in the boundary region N2S can be ensured to be equal to or higher than the nip pressure Pn1 that can suppress the generation of bubbles, and the generation of bubbles in the boundary region N2S can be suppressed. In the peeling region R, the sheet P can be stably peeled from the fixing belt 610 by setting the nip pressure Pn2 or less so as not to cause deformation (concave portion) on the surface of the pressure roll 62. Therefore, it becomes possible to improve the peeling performance at the peeling pad 64, and the sheet P is stably separated from the fixing belt 610 by the curvature when the paper P exits the peeling nip portion N2.

  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 nip portion N2. The paper P guided by the peeling guide plate 83 is then discharged out of the apparatus by the paper discharge guide 65 and the paper discharge roll 66 (see FIG. 2), and the fixing process is completed.

  As described above, 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 is composed of a roll nip portion N1 and a peeling 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 nip portion N2 includes an upstream peeling pad 641 that sets a nip pressure higher than the nip pressure Pn1 that can suppress the generation of air bubbles represented by the above formula (1), and a pressure It is composed of a downstream peeling pad 642 that sets a nip pressure equal to or lower than a predetermined pressure that does not cause deformation (concave portion) on the surface of the roll 62. Further, the upstream peeling pad 641 is disposed in the vicinity of the downstream side of the roll nip portion N1. As a result, the nip pressure Pn that satisfies the above equation (1) is set in the boundary region N2S, so that 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 be deterred. Furthermore, it is possible to set so that the nip pressure continuously decreases monotonously 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 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 air that is about to expand due to the air pressure in the path until it passes through the peeling 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.

In addition, the fixing belt 610 that has passed through the peeling pad nip N2 is rapidly changed by the outer side surface 64b of the downstream side peeling pad 642 constituting the peeling pad 64 so that the traveling direction thereof is bent. Therefore, the sheet P that has passed through the roll nip portion N1 and the separation nip portion N2 is separated from the fixing belt 610 at the time of exiting the separation nip portion N2, and the curvature separation from the sheet P can be performed.
At that time, in the peeling region R, a nip pressure equal to or lower than a predetermined pressure that does not cause deformation (concave portion) on the surface of the pressure roll 62 by the downstream side peeling pad 642 is set. As a result, it is possible to improve the peeling performance by the peeling pad 64, and even when the speed of the image forming apparatus is increased, it can be stably applied to thin paper with weak solidity on which a solid image is formed. Paper separation can be performed.

[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 610.

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 via a pressure belt 700 and a fixing belt 610 by a compression coil spring (not shown) as a pressing means. A local high pressure is generated at the contact portion of 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 pressure roll 701, the inlet roll 702, and the stretching roll 703 includes a belt edge position detection mechanism that detects the belt edge position of the pressure belt 700, and a detection result of the belt edge position detection mechanism. Accordingly, an axial displacement mechanism for displacing the contact position in the axial direction of the pressure belt 700 may be disposed 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 610, 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, a 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. Accordingly, a separation nip portion N2 where the fixing belt 610 is wrapped on the pressure roll 701 side is set continuously to the belt nip portion N3.

Further, as with the fixing device 60 of the first embodiment, the peeling pad 64 that forms the peeling nip portion N2 has a nip pressure Pn1 that can suppress the generation of bubbles represented by the formula (1) described in the first embodiment. An upstream side peeling pad 641 that sets a higher nip pressure and a downstream side peeling pad 642 that sets a nip pressure equal to or lower than a predetermined pressure that does not cause deformation (concave portion) on the surface of the pressure roll 62. Further, the upstream peeling pad 641 is disposed in the vicinity of the downstream side of the roll nip portion N1. As a result, the nip pressure Pn that satisfies the above equation (1) is set in the boundary region N2S, so that 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 be deterred. Furthermore, it is possible to set so that the nip pressure continuously decreases monotonously 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 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 air that is about to expand due to the air pressure in the path until it passes through the peeling 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.

In addition, the fixing belt 610 that has passed through the peeling pad nip N2 is rapidly changed by the outer side surface 64b of the downstream side peeling pad 642 constituting the peeling pad 64 so that the traveling direction thereof is bent. Therefore, the sheet P that has passed through the roll nip portion N1 and the separation nip portion N2 is separated from the fixing belt 610 at the time of exiting the separation nip portion N2, and the curvature separation from the sheet P can be performed.
At that time, in the peeling region R, a nip pressure equal to or lower than a predetermined pressure that does not cause deformation (concave portion) on the surface of the pressure roll 62 by the downstream side peeling pad 642 is set. As a result, it is possible to improve the peeling performance by the peeling pad 64, and even when the speed of the image forming apparatus is increased, it can be stably applied to thin paper with weak solidity on which a solid image is formed. Paper separation can be performed.

1 is a schematic configuration diagram illustrating a digital color printer which is an example of an image forming apparatus of 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 profile of the nip part at the time of arrange | positioning the peeling pad spaced apart from the roll nip part more than predetermined distance. It is the figure which showed the outline of the nip pressure profile of the nip part at the time of arrange | positioning the peeling pad of this invention. It is a schematic sectional drawing explaining the structure of a peeling pad. It is the figure which showed the state by which the nip pressure in downstream pad part N2T2 was set more highly than needed, and the deformation | transformation (recessed part) produced in the pressure roll surface by the downstream peeling pad. It is a figure which shows the case where a downstream peeling pad is set with the pressing force which does not produce a deformation | transformation (recessed part) on the pressure roll surface. FIG. 5 is a diagram showing a configuration in which an upstream end of a pressing surface of an upstream peeling pad is set to contact a fixing roll and receives a pressing force from the fixing roll at the same time. It is the figure which showed the other structural example of the peeling pad. It is the figure which showed the other structural example of the peeling pad. FIG. 4 is a side sectional view showing a schematic configuration of a fixing device according to a second embodiment.

Explanation of symbols

26Y, 26M, 26C, 26K ... Image forming unit, 31 ... Photoconductor drum, 32 ... Charging roll, 25Y, 25M, 25C, 25K ... Laser exposure device, 33 ... Developer, 34 ... Drum cleaner, 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, 641 ... Upstream release pad, 642 ... Downstream Side peeling pad, 610... Fixing belt, 611 .. fixing roll, 70... Pressure belt module, 700... Pressure belt, 702.

Claims (20)

A fixing device for fixing a toner image carried on a recording material,
A rotatable fixing roll;
A belt member stretched around the fixing roll;
A pressure member that presses the fixing roll via the belt member;
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 fixing device, wherein the peeling member includes a plurality of pressing members capable of forming different nip pressures.   The peeling member includes a first pressing member that presses the outer surface of the belt member against the pressing member in the vicinity of the downstream side of the press contact portion between the fixing roll and the pressing member, and the first pressing member. The second pressing member that presses the outer surface of the belt member against the pressing member with a pressing force smaller than the pressing force of the first pressing member on the downstream side in the moving direction of the belt member. The fixing device according to claim 1, wherein:   The peeling member is a rigid body in which the pressing member disposed at the most upstream portion in the moving direction of the belt member is formed in a substantially arc shape whose side surface facing the fixing roll side follows the surface shape of the fixing roll. The fixing device according to claim 1, wherein the fixing device is configured.   The peeling member is a peeling surface in which the pressing member disposed at the most downstream portion in the moving direction of the belt member is located on the side opposite to the fixing roll side and changes so that the traveling direction of the fixing belt is bent. The fixing device according to claim 1, wherein the fixing device is formed of an elastic body including   The pressure member includes an elastic layer, and an elastic coefficient of the pressing member disposed at the most downstream portion in the moving direction of the belt member is configured to be smaller than an elastic coefficient of the pressure member. Item 5. The fixing device according to Item 4.   In the peeling member, the pressing member disposed at the most downstream portion in the moving direction of the belt member is fixed to one of the plurality of pressing members, and the downstream side in the moving direction of the belt member is formed as a free end. 5. The fixing device according to claim 4, wherein the fixing device is made of a plate-like member having spring elasticity.   The fixing device according to claim 1, wherein the peeling member is formed by integrally forming the plurality of pressing members.   In the peeling member, the pressing surface by which the plurality of pressing members press the outer surface of the belt member against the pressing member is a continuous flat surface without a step, or has no step following the surface shape of the pressing member. The fixing device according to claim 1, wherein the fixing device is formed of a continuous curved surface. A fixing device for fixing a toner image carried on a recording material,
A rotatable fixing roll;
A belt member stretched around the fixing roll;
A tension roll that stretches the belt member;
A pressure member which is arranged to press against the fixing roll via the belt member and has elasticity;
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 peeling member has a first nip pressure region that is pressed with a first nip pressure on the upstream side in the moving direction of the belt member, and a second nip pressure that is pressed with a second nip pressure on the downstream side in the moving direction of the belt member. And a nip pressure region. In the first nip pressure region, the first nip pressure Pn is defined such that the absolute temperature of the belt member is Tn, the absolute temperature of the surrounding environment is To, and the atmospheric pressure is Po.
Pn ≧ Po × (Tn / To−1)
The fixing device according to claim 9, wherein the fixing device is set so as to satisfy.   The fixing device according to claim 9, wherein the second nip pressure region is set to a nip pressure at which the second nip pressure does not cause deformation of the pressure roll surface.   The peeling member monotonously decreases the first nip pressure and the second nip pressure toward the traveling direction of the belt member in a region from the first nip pressure region to the second nip pressure region. The fixing device according to claim 9, wherein the fixing device is set as follows.   The fixing device according to claim 9, wherein the pressing member has a dent amount at a pressure contact portion with the fixing roll larger than a dent amount of the fixing roll.   The fixing device according to claim 9, wherein the peeling member is disposed in a wedge-shaped region where an upstream end portion in the traveling direction of the belt member is defined by the fixing roll and the pressure member. .   The fixing device according to claim 9, wherein a heating member is disposed in the fixing roll, and a heating member is disposed in the stretching roll. 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 belt member stretched around the fixing roll;
A pressure member that presses against the fixing roll via the belt member;
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 image forming apparatus according to claim 1, wherein the peeling member includes a plurality of pressing members capable of forming different nip pressures.   The peeling member of the fixing unit is applied to the pressure member at a first nip pressure that does not generate bubbles on the outer surface of the belt member near the downstream side of the pressure contact portion between the fixing roll and the pressure member. The first pressing member to be pressed and the pressurizing with the second nip pressure that does not cause the pressing member to deform the outer surface of the belt member on the downstream side of the first pressing member in the moving direction of the belt member. The image forming apparatus according to claim 16, further comprising a second pressing member that presses against the member. In the fixing unit, the first nip pressure Pn of the first pressing member is Tn, the absolute temperature of the belt member is Ton, the absolute temperature of the surrounding environment is To, and the atmospheric pressure is Po.
Pn ≧ Po × (Tn / To−1)
18. The image forming apparatus according to claim 17, wherein the image forming apparatus is set so as to satisfy the following condition.   The fixing unit has a nip pressure in a region 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. The image forming apparatus according to claim 16, wherein the image forming apparatus is set to monotonously decrease in a traveling direction.   The image forming apparatus according to claim 16, wherein the fixing unit is formed of a pressure belt module in which the pressure member is stretched by a plurality of tension rolls.

Images