JP2007199383A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress a recording medium such as a recording paper from curling in a fixing device etc., equipped with a belt member which rotates. <P>SOLUTION: In the fixing device, a pressure roll module 62 equipped with a pressure belt 620 is arranged while pressed against a fixing belt module 61 equipped with a fixing belt 610 and a nip part N consisting of a roll nip part N1 and a release pad nip part N2 is formed between the both. The pressure belt 620 is tensed between the pressure roll 621 and a pressure tensing roll 622 and arranged along a path extending downstream, and a path after passing the release pad nip part N2 is bent by a curl correcting roll 65 convexly and reversely to the arc of the pressure roll 621. <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 rotating belt member.

  2. Description of the Related Art In image forming apparatuses such as copying machines and printers using an electrophotographic system, a configuration called a two-roll system is widely used as a fixing device that fixes a toner image transferred onto a recording sheet. The two-roll type fixing device is configured such that a pressure roll is pressed against a fixing roll heated by a heating source (heater), and a recording sheet is passed through the pressure contact area (nip portion) of both rolls to perform heating / heating. Pressurize to fix the toner image on the recording paper.

There is also known a fixing device in which a heating member for heating a recording sheet is formed of a film-like belt member (fixing belt) (see, for example, Patent Documents 1 and 2).
In such a fixing device using a fixing belt, the fixing belt is sufficiently heated before entering the nip portion, and the toner image is fixed by applying heat from the fixing belt to the recording paper at the nip portion. The fixing belt has a small heat capacity and can recover to a predetermined fixing temperature in a short time even if the recording paper is deprived of heat by the fixing action, and can cope with a higher image forming speed.

By the way, in the fixing device in which the toner is heated and melted and fixed on the recording paper as described above, the recording paper is hardly peeled off from the fixing roll and the fixing belt by the adhesive force of the toner melted by heat. A configuration in which the recording paper is peeled off from the fixing roll or the fixing belt is required.
In a fixing device using a fixing belt, as a peeling structure for peeling the recording paper from the fixing belt, a peeling member for setting a large curvature of the fixing belt is provided inside the fixing belt at the outlet portion (downstream portion) of the nip portion. A configuration in which the recording paper is peeled off by changing the curvature of the fixing belt has been proposed (see, for example, Patent Document 3).

In a configuration including such a peeling member, it is considered that the fixing belt is pressed against a pressure roll by the peeling member to form a part of the nip portion.
FIG. 7 is an enlarged view of the nip portion of the fixing device having such a configuration. In the figure, 70 is a fixing belt, 71 is a fixing roll, 72 is a pressure roll, and 73 is a peeling member.
In the case of this configuration, a nip portion (roll nip portion N1) formed by the fixing roll 71 and the pressure roll 72, and a nip portion (release member nip portion N2) formed by the peeling member 73 and the pressure roll 72, If there is a gap between the two, there is a possibility that the pressure contact force is reduced at the gap portion and an image defect such as a blister is caused. Therefore, the peeling member 73 is installed as close as possible to the fixing roll 71 around which the fixing belt 70 is wound.

Here, when the fixing roll 71 is made of a metal such as aluminum with high rigidity, and the elastic roll is provided on the surface of the pressure roll 72, as shown in the figure, the roll nip portion N1 and the peeling member The recording paper path (the path of the fixing belt 70) is bent between the nip portion N2.
That is, when the nip portion N where the roll nip portion N1 and the peeling member nip portion N2 are continuous is viewed as a whole, the shape of the recording paper movement path is bent in an S shape in the figure, and at the exit portion, the fixing roll 71 side is formed. A convex shape will be exhibited. A recording sheet that receives a fixing action at such a nip portion N has the highest temperature at the exit of the nip portion N, and when it exits the nip portion N, it is released from pressure and heating and cooled. As a result, the recording paper is curled (curled) along the shape near the exit. That is, it curls in a direction along the peripheral surface of the pressure roll 72.
When such curling occurs on the recording paper, there is a problem in that it cannot be smoothly guided to a conveying roll (not shown) that is wound around the pressure roll 72 after fixing and disposed forward, thereby causing a conveyance failure. In addition, there arises a problem that the recording sheets after discharging are not aligned.

Conventionally, configurations as disclosed in Patent Documents 4 to 5 have been proposed for suppressing curling of recording paper discharged from a fixing device.
That is, Patent Document 4 shows a configuration in which the recording material after the conveyance belt passes through the heating nip portion is conveyed to the heater side from the conveyance surface to the heating nip portion of the recording material.
In Patent Document 5, the contact point of the pressure roller with respect to the fixing roller having a common tangent line between the fixing roller and the downstream roller is disposed in the pressure contact portion on the downstream side in the sheet conveying direction from the straight line connecting the rotation centers of the fixing roller and the pressure roller. The configuration is shown.

Patent Documents 6 to 7 disclose a configuration for correcting a curl generated on a recording sheet.
That is, Patent Document 6 discloses a guide member that guides a sheet separated by a separation member in a state of being separated from the separation member, and a sheet curl that is in contact with a surface opposite to the surface of the sheet on which the guide member abuts. The structure provided with the curl correction member which corrects is shown.
Patent Document 7 discloses a configuration in which a decurler is provided downstream of the belt fixing unit in the recording material conveyance direction so that a bending force opposite to the roller constituting the belt fixing unit is applied to the recording material.

JP-A-3-133871 JP-A-63-193168 Japanese Patent Laid-Open No. 2003-5565 JP 2000-1942 A JP 2001-109293 A JP 2003-179318 A JP 2003-295657 A

However, the configuration disclosed in Patent Document 4 has a problem in that the recording paper cannot be peeled from the conveyance belt satisfactorily.
The configuration disclosed in Patent Document 5 has a problem in that the pressure applied to the recording paper is reduced at a part of the nip formed by the pressure roll being pressed against the fixing belt, and blisters are likely to occur.
Further, in the configuration for correcting the curl generated on the recording paper as disclosed in Patent Documents 6 and 7, the size of the curl varies depending on conditions such as the thickness of the recording paper and the image density to be formed. It is difficult to guide the recording paper to the decurler, and there is a problem that the structure becomes complicated.

  The present invention has been made to solve the technical problems as described above, and an object of the present invention is to occur in a recording medium such as a recording sheet in a fixing device having a rotating belt member. The curling is to be suppressed with a simple configuration.

  For this purpose, the fixing device of the present invention is a fixing device for fixing a toner image carried on a recording medium, and includes a rotatable fixing roll member, and a fixing roller that is stretched and rotated around the fixing roll member. A belt member; heating means for heating the fixing belt member; a rotatable pressure roll member that forms a nip portion by pressing a portion of the fixing roll member around which the fixing belt member is wound; and a downstream side of the nip portion. A separation member that is interposed between the fixing belt member and the fixing roll member and bends the fixing belt member with a large curvature to separate the recording medium from the fixing belt member, and is stretched by the pressure roll member and recorded from the nip portion. A pressure belt member rotatably provided in a path extending downstream in the moving direction of the medium, and a path on the downstream side from the peeling member of the pressure belt member is a convex shape opposite to the circumferential arc of the pressure roll member. Bend Characterized in that it comprises a road bending member.

Here, the pressure roll member can be characterized by including an elastic layer on the surface thereof. The path bending member may be characterized in that the pressure belt member is pressed against the pressure roll member. Further, the path bending member is a roll member, and a release layer made of a fluorine-based resin is formed on the peripheral surface thereof.
Further, in addition to the above-described configuration, a cooling means for cooling the pressure belt member can be provided. The cooling means may be configured to cool the downstream portion of the pressure belt member from the path bending member from the inner peripheral side.
The cooling means can be characterized by including a heat radiation fin disposed in contact with the pressure belt and a cooling fan that blows and cools the heat radiation fin. In addition, the cooling means includes a heat pipe member provided with its heat absorbing portion in contact with the pressure belt, and a cooling fan that blows and cools the heat radiating portion of the heat pipe member. Can do.

  A fixing device according to another aspect of the invention is a fixing device that fixes a toner image carried on a recording medium, and is rotated by a rotatable fixing roll member, a fixing roll member, and a fixing stretching roll member. A fixing belt member for heating, a heating means for heating the fixing belt member, a pressure member for pressing a portion of the fixing roll member around which the fixing belt member is wound to form a nip portion, and a fixing belt downstream of the nip portion. A pressing member is pressed against the pressure member to form a second nip portion. The peeling member is bent over the fixing belt member with a large curvature to peel the recording medium from the fixing belt member. And a pressure belt member rotatably provided in a path extending downstream from the second nip portion in the moving direction of the recording medium, and a path downstream from the peeling member of the pressure belt member. Of the nip Characterized in that it comprises a path bending member for bending the side to correct the curl formed on the medium.

Here, the pressurizing member is a roll member, and has an elastic layer on the surface thereof.
The path bending member may be provided so as to press the pressure belt member against the pressure member, and the path bending member is a roll member having a fluorine-based circumferential surface. A release layer made of resin is formed.
Furthermore, it can be provided with a cooling means for cooling the pressure belt member. The cooling means may be configured to cool the downstream portion of the pressure belt member from the path bending member from the inner peripheral side.

  An image forming apparatus according to the present invention includes a toner image forming unit that forms a toner image, a transfer unit that transfers a toner image formed by the toner image forming unit onto a recording medium, and a toner image that is transferred onto the recording medium. A fixing device that fixes the recording medium. The fixing device includes a rotatable fixing roll member, a fixing belt member that is stretched and rotated by the fixing roll member, and heating that heats the fixing belt member. Means, a rotatable pressure roll member that presses a portion of the fixing roll member around which the fixing belt member is wound to form a nip portion, and an intermediate portion between the fixing belt member and the fixing roll member on the downstream side of the nip portion. A peeling member that bends the fixing belt member with a large curvature to peel the recording medium from the fixing belt member, and is stretched by the pressure roll member and extends downstream from the nip portion in the moving direction of the recording medium. A pressure belt member rotatably provided in the path, a path bending member that defines a path downstream from the peeling member of the pressure belt member in a convex shape opposite to the circumferential arc of the pressure roll member, It is characterized by providing.

  According to the fixing device and the like of the present invention configured as described above, curling that occurs on a recording medium such as recording paper can be suppressed.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a schematic configuration diagram of an image forming apparatus 1 to which the exemplary embodiment is applied.
An image forming apparatus 1 shown in FIG. 1 is an intermediate transfer type image forming apparatus called a so-called tandem type, and a plurality of image forming units 1Y as toner image forming means for forming toner images of respective color components by electrophotography. , 1M, 1C, 1K, and a primary transfer unit 10 that sequentially transfers (primary transfer) the color component toner images formed by the image forming units 1Y, 1M, 1C, 1K to the intermediate transfer belt 15. Further, the image forming apparatus 1 includes a secondary transfer unit 20 as a transfer unit that collectively transfers (secondary transfer) the superimposed toner image transferred onto the intermediate transfer belt 15 onto a recording paper P as a recording medium, and a secondary transfer unit 20. And a fixing device 60 for fixing the transferred image onto the recording paper P. Further, the image forming apparatus 1 includes a recording paper transport mechanism 50 and a control unit 40 that controls the operation of each device (each unit).

  Each of the image forming units 1Y, 1M, 1C, and 1K includes a photosensitive drum 11 that rotates in the direction of arrow A, as representatively shown by the image forming unit 1Y in the drawing. Around the photosensitive drum 11, there are a charger 12 for charging the photosensitive drum 11, and a laser exposure unit 13 for writing an electrostatic latent image on the photosensitive drum 11 (the exposure beam is indicated by Bm in the figure). And a developing device 14 that accommodates each color component toner and visualizes the electrostatic latent image on the photosensitive drum 11 with the toner. Further, a primary transfer roll 16 that transfers each color component toner image formed on the photosensitive drum 11 to the intermediate transfer belt 15 by the primary transfer unit 10, and a drum cleaner 17 that removes residual toner on the photosensitive drum 11, Is arranged. These image forming units 1Y, 1M, 1C, and 1K are arranged in a substantially straight line from the upstream side of the intermediate transfer belt 15 in the order of yellow (Y), magenta (M), cyan (C), and black (K). Has been.

The intermediate transfer belt 15 is stretched by various rolls so as to have a path extending substantially linearly along the arrangement direction of the photosensitive drums 11, and is circulated at a predetermined speed in the direction of arrow B shown in FIG. Be moved).
The primary transfer unit 10 includes a primary transfer roll 16 that is disposed to face the photosensitive drum 11 with the intermediate transfer belt 15 interposed therebetween. The primary transfer roll 16 is configured to press the intermediate transfer belt 15 against the photosensitive drum 11. Further, a voltage (primary transfer bias) having a polarity opposite to the charging polarity of the toner is applied to the primary transfer roll 16. As a result, the toner images on the respective photosensitive drums 11 are electrostatically attracted sequentially to the intermediate transfer belt 15, and the toner images are superimposed on the intermediate transfer belt 15.

The secondary transfer unit 20 includes a secondary transfer roll 22 disposed on the toner image carrying surface side of the intermediate transfer belt 15 and a backup roll 25 disposed opposite to the secondary transfer roll 22 with the intermediate transfer belt 15 interposed therebetween. It is constituted by.
A secondary transfer bias is applied to the backup roll 25, and the secondary transfer roll 22 is grounded, and a secondary transfer bias is formed between the backup roll 25 and the backup roll 25. Then, the toner image carried by the intermediate transfer belt 15 is secondarily transferred onto the recording paper P that is conveyed and supplied.

Further, on the downstream side of the secondary transfer portion 20 of the intermediate transfer belt 15, an intermediate transfer belt that removes residual toner and paper dust on the intermediate transfer belt 15 after the secondary transfer and cleans the surface of the intermediate transfer belt 15. A cleaner 35 is provided.
The recording paper transport mechanism 50 transports the recording paper P from the recording paper tray 51 containing the recording paper P to the secondary transfer unit 20, and the toner image is transferred (secondary transfer) by the secondary transfer unit 20. The recording sheet P is conveyed to the fixing device 60.

The image forming apparatus 1 is controlled by the control unit 40 and forms an image as follows.
That is, based on image data output from an image reading device (not shown) or a personal computer (not shown), toner images of respective colors are respectively formed on the respective photosensitive drums 11 of the image forming units 1Y, 1M, 1C, and 1K. Form. In the image forming units 1Y, 1M, 1C, and 1K, toner images are formed by scanning and exposing the photosensitive drum 11 charged by the charger 12 with the laser exposure unit 13 to form an electrostatic latent image. The electrostatic latent image is developed by the developing device 14 to form a toner image.

Next, the toner images formed on the photosensitive drums 11 of the image forming units 1Y, 1M, 1C, and 1K are transferred onto the intermediate transfer belt 15 in each primary transfer unit 10 and transferred to the secondary transfer unit 20. Electrostatic transfer is collectively performed on the recording paper P conveyed by the recording paper conveyance mechanism 50.
Thereafter, the recording paper P onto which the toner image has been transferred is transported to the fixing device 60 by the recording paper transport mechanism 50, and the toner image is fixed on the recording paper P by heat and pressure by the fixing device 60, and a paper discharge mount (not shown) It is discharged to the mounting part.

Next, the fixing device 60 will be described in detail.
FIG. 2 is a perspective view conceptually showing one end portion of the fixing device 60 according to the embodiment of the present invention. FIG. 3 is a cross-sectional view showing a schematic configuration of the fixing device 60. Further, FIG. 4 is an enlarged cross-sectional view of a region near the nip portion N, and FIG. 5 is a view as seen from an arrow A in FIG.
The fixing device 60 includes a fixing belt module 61 including a fixing belt 610 and a pressure roll module 62 disposed in pressure contact with the fixing belt module 61. A nip portion N for fixing the toner image by pressurizing and heating the recording paper P is formed between the fixing belt module 61 and the pressure roll module 62. The nip portion N includes a roll nip portion N1 and a peeling pad nip portion N2 as a second nip portion.
Further, a peeling guide plate 68 is disposed adjacent to the downstream side of the nip portion N (downstream side of the peeling pad nip portion N2) of the fixing device 60.

  The fixing belt module 61 includes a fixing belt 610 as a fixing belt member, a fixing roll 611 as a fixing roll member that rotates while the fixing belt 610 is stretched, and a tension roll 612 that stretches the fixing belt 610 from the inside. And. In addition, a tension roll 613 that is disposed outside the fixing belt 610 and defines a circulation path thereof, and a posture correction roll 614 that corrects the posture of the fixing belt 610 between the fixing roll 611 and the tension roll 612. I have. Further, a peeling pad 64 as a peeling member disposed in the vicinity of the fixing roll 611 on the downstream side in the nip portion N, which is a region where the fixing belt module 61 and the pressure roll module 62 are pressed against each other, and the nip portion N A tension roll 615 for tensioning the fixing belt 610 is provided on the downstream side.

  The fixing belt 610 is a flexible endless belt having a predetermined width and a predetermined circumference. For example, a base layer formed of polyimide resin having a thickness of 80 μm, an elastic layer made of 200 μm thick silicone rubber laminated on the surface side (outer peripheral surface side) of the base layer, and further coated on the elastic layer And a release layer comprising a 30 μm thick tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin (PFA) tube. 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 roll 611 has, for example, a 200 μm-thick fluororesin film as a protective layer for preventing metal wear on the surface of a cylindrical core roll (core metal) formed of aluminum or the like with a predetermined outer diameter and a predetermined thickness. Hard roll. However, the fixing roll 611 is not limited to this configuration. When the nip portion N is formed with the pressure roll module 62, the fixing roll 611 is almost deformed with respect to the pressing force from the pressure roll module 62. There should be no hard rolls. Fixing roll 611 is driven by a drive motor (not shown) and rotates in the direction of arrow C at a surface speed of, for example, 300 mm / s.
In addition, a halogen heater 616 a is provided as a heating unit inside the fixing roll 611, and the image forming apparatus 1 is based on a measurement value by a temperature sensor (not shown) arranged so as to be in contact with the surface of the fixing roll 611. The controller 40 (see FIG. 1) controls the surface temperature to 150 ° C., for example.

The tension roll 612 is a cylindrical roll formed of aluminum or the like with a predetermined outer diameter and a predetermined thickness. A halogen heater 616b is provided as a heating means inside the tension roll 612, and the surface temperature is set to, for example, 190 ° C. by the control unit 40 (see FIG. 1) based on temperature detection information by a temperature sensor (not shown). Be controlled. That is, 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 surface side.
Further, both ends of the tension roll 612 are urged to move outward by tension springs (not shown), and the tension of the entire fixing belt 610 is set to 15 kgf, for example.

The tension roll 613 is a cylindrical roll formed of aluminum or the like with a predetermined outer diameter and a predetermined thickness. A release layer made of, for example, a fluororesin having a thickness of 20 μm is formed on the surface. 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 tension roll 613.
A halogen heater 616c as a heating unit is provided inside the tension roll 613, and the surface temperature is set to, for example, 190 ° C. by the control unit 40 (see FIG. 1) based on temperature detection information by a temperature sensor (not shown). Be controlled. That is, 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, the fixing belt 610 is heated by the fixing roll 611, the stretching roll 612, and the stretching roll 613.

  The posture correction roll 614 is a cylindrical roll formed of aluminum or the like with a predetermined outer diameter and a predetermined thickness. 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.

  The peeling pad 64 is a block-like member having a length corresponding to the fixing roll 611 and formed of a rigid body such as a metal such as SUS or a resin. The cross-sectional shape of the fixing belt 610 has an inner surface 64a facing the fixing roll 611, a pressing surface 64b that presses the fixing belt 610 against the pressing roll module 62, and a predetermined angle with respect to the pressing surface 64b. It has an arcuate shape surrounded by an outer surface 64c that rapidly changes the traveling direction and an upper surface 64d. Then, as shown in FIG. 2, at both ends thereof, an area where the pressure roll module 62 is pressed against the fixing belt module 61 is supported by the arms 641 that are swingably fitted to the support shaft 611 a of the fixing roll 611. The fixing roll 611 is disposed over the entire axial direction inside the fixing belt 610 on the downstream side of the roll nip portion N1. Further, the peeling pad 64 is oscillated and biased by a biasing means (not shown) such as a spring, and the fixing belt 610 is applied to a pressure roll module 62 (a pressure roll module 620 described later) with a predetermined load by the pressing surface 64c. (For example, 10 kgf) It is provided so that it may press. Thereby, for example, a separation pad nip portion N2 having a width of 5 mm is formed along the traveling direction of the fixing belt 610.

The tension roll 615 is a cylindrical roll formed of aluminum or the like with a predetermined outer diameter and a predetermined thickness. The fixing belt 610 that has passed through the peeling pad 64 is disposed in the vicinity of the downstream side of the peeling pad 64 in the traveling direction of the fixing belt 610 so that the fixing belt 610 smoothly rotates toward the fixing roll 611.
The peeling guide plate 68 disposed at the exit of the nip portion N (exit of the peeling pad nip portion N2) is formed with a sharply tapered tip edge. Then, the tip edge is provided close to a portion where the advancing direction of the fixing belt 610 changes along the outer surface 64c from the pressing surface 64b.

The pressure roll module 62 includes a pressure belt 620 as a pressure belt member, a pressure roll 621 as a pressure roll member that stretches the pressure belt 620 so as to be able to circulate, and a tension belt 620 from the inside. And a pressure tension roll 622 to be mounted. Further, a curl correction roll 65 as a path bending member for bending the path of the pressure belt 620 and a cooling device 66 as a cooling means for cooling the pressure belt 620 are provided.
Similar to the fixing belt 610, the pressure belt 620 is a flexible endless belt having a predetermined width and a predetermined circumference. For example, a release layer made of a fluororesin such as PFA is coated with a thickness of, for example, 30 μm on the outer peripheral surface of a base layer having a thickness of about 80 μm formed of a resin having high heat resistance such as polyimide.

The pressure roll 621 has a thickness made of, for example, silicone rubber having a rubber hardness of 30 ° (JIS-A) on a peripheral surface of a cylindrical roll 621a formed with aluminum or the like and having a predetermined outer diameter and a predetermined thickness. A soft roll formed by laminating a 10 mm elastic layer 621b and a release layer made of a PFA tube having a thickness of 100 μm. The pressure roll 621 is rotatably supported.
The pressure tension roll 622 is a metal roll formed to have a predetermined outer diameter with aluminum or the like. The pressure roll 621 is rotatably arranged on the downstream side in the moving direction of the recording paper P, and both end portions thereof are pressed outward by tension springs (not shown), thereby reducing the tension of the entire pressure belt 620. For example, it is set to 15 kgf.

  The pressure roll module 62 configured in this manner has a posture in which the circulation path of the pressure belt 620 stretched between the pressure roll 621 and the pressure stretch roll 622 protrudes downstream in the moving direction of the recording paper P. Thus, a pressure roll 621 is provided in pressure contact with the fixing belt module 61 by a biasing means such as a spring (not shown) to a portion where the fixing belt 610 winds the fixing roll 611. The pressure belt 620 wound around the pressure roll 621 is pressed against the fixing belt 610 around which the fixing roll 611 is wound to form a roll nip portion N1. As a result, the pressure belt 620 of the pressure roll module 62 is rotated by the pressure belt 620 of the pressure roll module 62 following the rotation of the fixing belt 610 of the fixing belt module 61.

Here, the peeling pad 64 of the above-described fixing belt module 61 presses the fixing belt 610 against the pressure roll module 62 (pressure roll 621) at a position adjacent to the downstream side of the roll nip portion N1, thereby causing the peeling pad nip portion N2 to move. Forming. Thereby, it forms continuously adjacent to peeling pad nip part N2 in the downstream of roll nip part N1, and nip part N is formed by these.
The roll nip portion N1 becomes convex in the figure due to elastic deformation of the pressure roll 621, and the peeling pad nip portion N2 becomes convex in the figure substantially along the peripheral surface of the pressure roll 621. For this reason, the entire shape of the nip portion N has an S-shape in the drawing that is deflected at a portion where the roll nip portion N1 and the peeling pad nip portion N2 are continuous.

The curl correction roll 65 is a metal roll having a predetermined diameter formed of aluminum or the like, and has a length corresponding to the pressure roll 621. The diameter is, for example, about 10 to 20 mm. A fluororesin film such as PFA is formed on the peripheral surface.
The curl correction roll 65 is rotatably supported and is urged by an urging means (not shown) such as a spring so that the pressure belt 620 downstream of the peeling pad nip portion N2 is applied to the pressure roll 621 with a predetermined force. It is provided to press.

With such a curl correction roll 65, the circulation path of the pressure belt 620 moves along the pressure roll 621 even after passing through the peeling pad nip portion N2, as shown in FIGS. After passing through, it is prescribed | regulated that it leaves | separates from the pressure roll 621 and goes to the pressure tension roll 622. That is, the curl correction roll 65 moves the path of the pressure belt 620 after passing through the nip portion N (peeling pad nip portion N2) from the path linearly toward the pressure tension roll 622 to the pressure roll 621 side. It is bent so as to be convex. In other words, the bending direction is reversely convex with the arc of the pressure roll 621, and the chevron formed by the continuous portion of the roll nip portion N1 and the peeling pad nip portion N2 can be said to be reversely convex.
The curl correction roll 65 is disposed to bend the path of the pressure belt 620 in this way. For this reason, it does not necessarily have to be pressed against the pressure roll 621 and may be provided so as to press only the pressure belt 620. However, by disposing the pressure roller 621 so as to press it, the path of the pressure belt 620 can be bent into a more accurate and stable path.

As shown in FIG. 5, the cooling device 66 includes heat radiating fins 661 and a cooling fan 662 that blows air to the heat radiating fins 661. Then, the pressure belt 620 is provided on the inner peripheral side of the circulation path of the pressure belt 620 that is separated from the pressure roll 621 and moves toward the pressure tension roll 622.
The heat dissipating fins 661 are formed by standing a plurality of fins on a substrate having a predetermined area, using a material having good heat conductivity such as aluminum. The back surface of the substrate is disposed so as to coincide with the path of the pressure belt 620. As a result, the pressure belt 620 contacts the back surface of the substrate of the heat radiation fin 661 and moves along the back surface.
The cooling fan 662 is a fan that is rotationally driven by a motor or the like, and is provided to blow air toward the radiation fins 662 and promote heat radiation.

The fixing device 60 configured as described above operates as follows to perform a fixing operation.
That is, the recording paper P is electrostatically transferred to the unfixed toner image in the secondary transfer unit 20 (see FIG. 1) of the image forming apparatus 1 and is conveyed from the left side to the right side in FIG. Is passed through the nip portion N, and the toner image is fixed on the recording paper P mainly by pressure and heat acting on the roll nip portion N1.

  At this time, 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. Heat is applied by heat and heat supplied through the tension roll 613 from the halogen heater 616 c disposed inside 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 300 mm / s, for example. A sufficient amount of heat can be secured.

Here, one fixing roll 611 forming the roll nip portion N1 is a hard roll as described above, and the other pressure roll 621 is a soft roll having an elastic layer 621b on its peripheral surface. For this reason, the roll nip portion N1 of the present embodiment is formed solely by the deformation of the elastic layer 621b of the pressure roll 621.
Thus, since the fixing roll 611 wrapped with the fixing belt 610 is hardly deformed in the roll nip portion N1, the turning radius of the fixing belt 610 that rotates along the surface thereof does not change. For this reason, the fixing belt 610 can pass through the roll nip portion N1 while maintaining its traveling speed constant, and no wrinkles or distortion occurs during the passage. As a result, image disturbance of 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 15 mm (that is, the nip width is 15 mm) in the traveling direction of the fixing belt 610.

  After passing through the roll nip portion N1, the recording paper P moves to the peeling pad nip portion N2. The peeling pad nip portion N2 is formed with a predetermined angle with respect to the roll nip portion N1 having a curved shape convex downward due to the curvature of the fixing roll 611. For this reason, the recording paper P heated and pressed under the curvature of the fixing roll 611 in the roll nip portion N1 changes in the traveling direction at the nip boundary point BP with the peeling pad nip portion N2, thereby the toner image and the fixing belt. Since the adhesive force with 610 is weakened, the recording paper P is easily peeled off from the fixing belt 610.

  At the exit of the peeling pad nip portion N2, the fixing belt 610 rotates so as to wind around the peeling pad 64 from the pressing surface 64b to the outer side surface 64c, and the traveling direction thereof changes abruptly. As a result, the recording paper P is naturally peeled from the fixing belt 610 by the stiffness of the recording paper P itself. That is, the recording paper P is stably separated from the fixing belt 610 when it leaves the peeling pad nip portion N2. Then, the movement toward the fixing belt module 61 is regulated by the peeling guide plate 68 and guided to the pressure roll module 62 side.

Here, the recording paper P that receives the fixing action at the nip portion N curls along the shape near the outlet having the highest temperature (the shape of the peeling pad nip portion N2). The peeling pad nip portion N2 is substantially along the circumferential surface of the pressure roll 621. Therefore, the recording paper P peeled from the fixing belt 610 is moved in the circumferential direction of the pressure roll 621 along the peeling pad nip portion N2. Curl. Due to this curl, the recording paper P tries to move so as to wind around the circumferential surface of the pressure roll 621, but the movement is regulated by the pressure belt 620 and supported by the pressure belt 620, and the curl correction roll 65 reaches the pressure contact portion to the pressure belt 620.
At the portion where the curl correction roll 65 is in contact with the pressure belt 620, the path of the pressure belt 620 is bent by the curl correction roll 65 so as to be opposite to the arc of the pressure roll 621 as described above. That is, the curl in the circumferential direction of the pressure roll 621 attached to the recording paper P is bent oppositely.

When the recording paper P still in a high temperature state passes through the pressure contact portion of the curl correction roll 65 to the pressure roll 621, the recording paper P is bent in a direction opposite to the curl and the curl is corrected. Is done.
The recording paper P with the curl corrected in this way moves together with the pressure belt 620 in a posture along the pressure belt 620 and reaches a cooling position by the cooling device 66. In this cooling position, the recording paper P is cooled by the cooling device 66 via the pressure belt 620, whereby the posture without curling is fixed.
The recording paper P is discharged out of the apparatus by a paper discharge guide and a paper discharge roll (not shown).

  As described above, in the fixing device 60, the recording paper P that has exited the nip portion N is bent by the curl correction roll 65 so as to be opposite to the bent shape near the exit of the nip portion N to correct the curl, and the cooling device 66. Cool with to fix the corrected posture. As a result, the recording paper P can be smoothly transported without causing a transport failure, and the recording paper after discharge can be arranged in an orderly manner.

The cooling means is not limited to the above configuration example, and may have other configurations.
FIG. 6 is a conceptual configuration diagram corresponding to FIG. 5 of another configuration of the cooling means.
The cooling device 67 shown in FIG. 6 includes a heat pipe 671 and a cooling fan 672.
The heat pipe 671 is provided such that the heat absorbing portion 671 a is in contact with the back surface of the pressure belt 620 and the heat radiating portion 671 b at one end is positioned outside the side end of the pressure belt 620.
The cooling fan 672 is a fan that is rotationally driven by a motor, and is provided so as to blow air toward the heat radiating portion 671b and promote heat dissipation.
According to such a configuration, the recording paper can be quickly cooled via the pressure belt 620 that is in contact with the heat absorbing portion 671a.

  Further, the present invention is not limited to the above embodiment. In the above embodiment, the present invention is applied to a so-called tandem color image forming apparatus. For example, the present invention is applied to a color image forming apparatus using a rotary developing device, a monochrome copying machine, or the like. It goes without saying that it is also good.

1 is a schematic configuration diagram of an image forming apparatus to which an exemplary embodiment is applied. FIG. 3 is a perspective view conceptually showing one end of the fixing device. FIG. 2 is a side sectional view illustrating a schematic configuration of a fixing device. It is an expanded sectional view near a nip part. It is A arrow directional view of FIG. It is a conceptual block diagram corresponding to FIG. 5 of the other structure of a cooling means. FIG. 6 is a schematic enlarged cross-sectional view in the vicinity of a nip portion of a fixing device as a conventional example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 60 ... Fixing apparatus, 61 ... Fixing belt module, 62 ... Pressure roll module, 64 ... Peeling pad (peeling member), 65 ... Curl correction roll (path bending member), 610 ... Fixing belt (fixing) Belt member), 611... Fixing roll (fixing roll member), 616a, 616b, 616c... Halogen heater (heating means), 612 .. tension roll (fixing tension roll member), 620. 621 ... Pressure roll, 621b ... Elastic layer, 622 ... Pressure tension roll (pressure tension roll member), 66, 67 ... Cooling device (cooling means), 661 ... Heat radiation fin, 662 ... Cooling fan, 671 ... Heat pipe, 671a ... Heat absorption part, 671b ... Heat dissipation part, 672 ... Cooling fan, N ... Nip part, N2 ... Peeling pad nip part (second nip part)

Claims (15)

A fixing device for fixing a toner image carried on a recording medium,
A rotatable fixing roll member;
A fixing belt member that is stretched and rotated by the fixing roll member;
Heating means for heating the fixing belt member;
A rotatable pressure roll member that presses a portion of the fixing roll member around which the fixing belt member is wound to form a nip portion;
A peeling member interposed between the fixing belt member on the downstream side of the nip portion and the fixing roll member to bend the fixing belt member with a large curvature and peel the recording medium from the fixing belt member;
A pressure belt member provided on the pressure roll member so as to be rotatable in a path extending from the nip portion to the downstream side in the moving direction of the recording medium;
A path bending member that bends the path on the downstream side of the peeling member of the pressure belt member in a convex shape opposite to the circumferential arc of the pressure roll member;
A fixing device comprising:   The fixing device according to claim 1, wherein the pressure roll member includes an elastic layer on a surface thereof.   The fixing device according to claim 2, wherein the path bending member presses the pressure belt member against the pressure roll member.   The fixing device according to claim 3, wherein the path bending member is a roll member, and a release layer made of a fluororesin is formed on a peripheral surface thereof.   The fixing device according to claim 1, further comprising a cooling unit that cools the pressure belt member.   The fixing device according to claim 5, wherein the cooling unit is configured to cool a portion of the pressure belt member downstream of the path bending member from an inner peripheral side thereof. The cooling means is
A heat dissipating fin disposed in contact with the pressure belt;
A cooling fan that blows and cools the radiation fins;
The fixing device according to claim 6, further comprising: The cooling means is
A heat pipe member provided with its heat absorbing portion in contact with the pressure belt;
A cooling fan that blows and cools the heat dissipating part of the heat pipe member;
The fixing device according to claim 6, further comprising: A fixing device for fixing a toner image carried on a recording medium,
A rotatable fixing roll member;
A fixing belt member that is stretched and rotated by the fixing roll member and the fixing tension roll member;
Heating means for heating the fixing belt member;
A pressure member that forms a nip portion by pressing a portion of the fixing roll member around which the fixing belt member is wound;
A second nip portion is formed by pressing the fixing belt member against the pressure member on the downstream side of the nip portion, and the fixing belt member is bent with a large curvature so that the recording medium is moved from the fixing belt member to the recording medium. A peeling member for peeling
A pressure belt member provided on the pressure member so as to be rotatable in a path extending from the second nip portion to the downstream side in the moving direction of the recording medium;
A path bending member that bends a path downstream of the peeling member of the pressure belt member to a side that corrects curl formed on the recording medium by the nip portion and the second nip portion;
A fixing device.   The fixing device according to claim 9, wherein the pressure member is a roll member and includes an elastic layer on a surface thereof.   The fixing device according to claim 10, wherein the path bending member is provided so as to press the pressure belt member against the pressure member.   The fixing device according to claim 11, wherein the path bending member is a roll member, and a release layer made of a fluororesin is formed on a peripheral surface thereof.   The fixing device according to claim 9, further comprising a cooling unit that cools the pressure belt member.   The fixing device according to claim 13, wherein the cooling unit is configured to cool a downstream portion of the pressure belt member from the path bending member from an inner peripheral side thereof. Toner image forming means for forming a toner image;
Transfer means for transferring the toner image formed by the toner image forming means onto a recording medium;
A fixing device for fixing the toner image transferred onto the recording medium to the recording medium,
The fixing device includes:
A rotatable fixing roll member;
A fixing belt member that is stretched and rotated by the fixing roll member;
Heating means for heating the fixing belt member;
A rotatable pressure roll member that presses a portion of the fixing roll member around which the fixing belt member is wound to form a nip portion;
A peeling member interposed between the fixing belt member on the downstream side of the nip portion and the fixing roll member to bend the fixing belt member with a large curvature and peel the recording medium from the fixing belt member;
A pressure belt member provided on the pressure roll member so as to be rotatable in a path extending from the nip portion to the downstream side in the moving direction of the recording medium;
A path bending member that defines a path downstream of the peeling member of the pressure belt member in a convex shape opposite to the circumferential arc of the pressure roll member;
An image forming apparatus comprising:

Images