JP2006243211A - Fixing device, roll member, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device capable of setting the suppress strength between a pressurizing member and a fixing member approximately uniformly in an axial direction when the pressurizing member presses the fixing member at a nip part. <P>SOLUTION: The fixing device is equipped with a fixing belt module 61 and a pressurization belt module 62 which stretches the pressurizing belt and has a pressure roll 65 capable of pressing a fixing roll 610 of the fixing belt module 61. The pressurizing belt module 62 comprises an outer roll 651 formed with the pressure roll 65 in a cylindrical shape and an inner roll 652 disposed on the inner side of the outer roll 651 and formed in a crown shape whose external diameter in the central part of the axial direction is larger than that at both ends. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fixing device used in an image forming apparatus using an electrophotographic system, for example.

  In an image forming apparatus such as a copying machine or a printer using an electrophotographic system, for example, a photosensitive member (photosensitive drum) formed in a drum shape is uniformly charged, and the photosensitive drum is controlled based on image information. A scanning exposure is performed with the exposed light to form an electrostatic latent image on the photosensitive drum. The electrostatic latent image is converted into a visible image (toner image) with toner, and after the toner image is directly transferred from the photosensitive drum to the recording paper, or the toner image is temporarily transferred to the intermediate transfer member. After the secondary transfer from the intermediate transfer member to the recording paper, the toner image is fixed on the recording paper by a fixing device.

  A fixing device used in such an image forming apparatus is, for example, a fixing roll in which a heating source is disposed inside a cylindrical metal core, and a heat-resistant elastic layer and a release layer are laminated on the metal core. And 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 core metal. . Then, the recording paper carrying the unfixed toner image is passed between the fixing roll and the pressure roll, and the toner image is fixed on the recording paper by heating and pressing the unfixed toner image. is doing. Such a fixing device is called a roll nip method and is generally widely used.

By the way, in order to increase the speed in the roll nip type fixing device, in order to supply a sufficient amount of heat to the toner and the recording paper, it is necessary to increase the nip width in proportion to the fixing speed. As a method of increasing the nip width, there are a method of increasing the load between the fixing roll and the pressure roll, a method of increasing the thickness of the elastic body, and a method of increasing the roll diameter.
However, in the method of increasing the load and the method of increasing the thickness of the elastic body, the uneven nip width and paper wrinkle occur because the shape of the nip width due to the deflection of the roll becomes non-uniform along the roll axis. This causes image quality problems such as In addition, the method of increasing the roll diameter causes problems that the apparatus is increased in size and the time (warm-up time) until the roll is raised from room temperature to a fixable temperature is increased.

  Therefore, in order to solve these problems and realize a fixing device corresponding to the speedup of the image forming apparatus, the applicant of the present invention has a tension roll formed by a fixing roll whose surface is covered with an elastic body and a plurality of support rolls. And an endless belt is wound around the fixing roll by a predetermined angle region so as to form a nip region between the endless belt and the fixing roll, and an outlet portion of the nip region (mostly) A technique relating to a fixing device in which a pressure roll for locally applying a pressure larger than that of the other part of the nip region in the downstream portion) is proposed (see, for example, Patent Document 1).

In the fixing device described in Patent Document 1, a nip portion (also referred to as a “belt nip portion”) is formed by bringing an endless belt stretched by a plurality of rolls into contact with the fixing roll. Yes. By adopting such a configuration (this is also referred to as a “belt nip method”), the width of the belt nip formed by the fixing roll and the endless belt is the same as the roll nip portion of the conventional fixing roll and pressure roll. Since it can be easily made larger than the width of the device, it is possible to cope with high speed, and it is easy to reduce the size of the apparatus.
In particular, in the belt nip type fixing device, the heat transmitted from the fixing roll is not easily dissipated because the heat capacity of the endless belt pressed against the fixing roll is small. Therefore, even when the rotation of the fixing roll is started, the amount of heat taken from the fixing roll to the endless belt side is relatively small, and the efficiency of using the heat for melting the toner is increased. It also has the advantage of being able to

Japanese Patent No. 3084692 (pages 5-8)

  By the way, in the belt nip type fixing device described in Patent Document 1 described above, one of the rolls that stretch the endless belt is fixed at the most downstream portion of the nip portion formed by the fixing roll and the endless belt. The roll (fixing member) is configured to come into pressure contact. Thereby, such a roll is set to function as a pressure roll (pressure member), and a pressure larger than that of other portions of the nip portion is locally applied. By adopting such a configuration, a local pressing force is applied to the toner image heated and melted in the nip portion by a pressure roll. Therefore, the fixability of the toner image that has passed through the nip portion is improved, and in particular, the surface of the toner image before solidification is smoothed to give the toner image an appropriate gloss.

However, the pressure roll that presses the fixing roll in the most downstream portion of the nip portion stretches an endless belt on the side circumferential surface in the axial direction. Therefore, in order to set such a pressure roll to be pressed toward the fixing roll, it is necessary to employ a configuration in which the fixing roll is pressed from both ends of the pressure roll. However, in such a configuration in which the pressure roll presses the fixing roll from both ends thereof, the pressure roll (also in the case of the fixing roll in some cases) is bow-shaped, so the axial direction of the pressure roll There is a structural problem in that the pressing force between the fixing roll and the central portion decreases, and the pressing force in the axial direction is likely to be uneven.
For this reason, the fixability tends to deteriorate toward the center of the recording paper, resulting in inconvenience that the image quality is lowered. In addition, since the so-called gloss unevenness in which the glossiness of the toner image decreases particularly in the central portion of the recording paper, there is a disadvantage in that the deterioration of image quality is noticeable in a solid image such as a photographic image.

  Therefore, the present invention has been made to solve the technical problems as described above. The object of the present invention is to provide a pressure member when the pressure member presses the fixing member at the nip portion. It is an object of the present invention to provide a fixing device capable of setting the pressing force between the fixing member and the fixing member substantially uniformly in the axial direction.

  For this purpose, the fixing device of the present invention is a fixing device that fixes a toner image carried on a recording material, and rotates and rotates a rotating member, a pressure belt, and a pressure belt. A pressure belt module having a pressure roll capable of pressing the member and a tension roll that stretches the pressure belt, and the pressure belt module is a first in which the pressure roll is formed in a cylindrical shape. It is characterized by comprising a roll and a second roll disposed inside the first roll and having a crown shape in which the outer diameter of the central portion in the axial direction is larger than both end portions.

Here, the pressure roll of the pressure belt module can be characterized in that the outer diameter of the central portion in the axial direction of the second roll is formed substantially equal to the inner diameter of the first roll. In addition, the pressure roll of the pressure belt module can be configured such that the surface of the second roll is covered with an elastic layer.
Furthermore, the pressurizing belt module can be characterized in that it can be brought into contact with and separated from the rotating member. The pressure roll of the pressure belt module has an axial direction between the inner peripheral surface of the first roll and the outer peripheral surface of the second roll when the pressure belt module is installed apart from the rotating member. The center portion may be configured to contact over the entire area in the circumferential direction. In particular, the pressure roll of the pressure belt module has an inner peripheral surface of the first roll and an outer peripheral surface of the second roll in a region of 1/10 to 1/5 of the length in the axial direction of the first roll. Can also be in contact with each other. Further, when the pressure belt module is installed in pressure contact with the rotating member, the pressure roll of the pressure belt module is in a region opposite to the rotating member with respect to the central axis of the second roll. The inner peripheral surface of the first roll and the outer peripheral surface of the second roll may be configured to be separated from each other.

  The fixing device of the present invention is a fixing device that fixes a toner image carried on a recording material, and is arranged to be able to switch between a rotating member and a pressed state and a separated state with respect to the rotating member. A pressure roll, and a pressure belt that is stretched between the pressure roll and forms a nip portion between the pressure belt and the pressure roll. It is characterized in that it is composed of an inner roll that is disposed on the inner side and can press the outer roll toward the fixing roll.

Here, the inner roll of the pressure roll is formed in a crown shape in which the outer diameter of the axial central portion is larger than both end portions, and the outer diameter of the axial central portion is substantially equal to the inner diameter of the outer roll. be able to. In particular, the inner roll of the pressure roll includes a solid roll formed in a crown shape in which the outer diameter of the central portion in the axial direction is larger than both end portions, and an elastic layer coated on the surface of the roll with a substantially uniform thickness. It can also be characterized by comprising. Further, the inner roll of the pressure roll may be characterized in that a flat portion is formed at the central portion in the axial direction.
Furthermore, the rotating member can include a rotatable fixing roll, a fixing belt stretched around the fixing roll, and a tension roll that stretches the fixing belt. In addition, the outer roll of the pressure roll may be characterized in that an elastic layer is formed on the surface.

Further, the present invention is regarded as a roll member, and the roll member of the present invention is a roll member that is used in a fixing device and can be pressed against a rotating member of the fixing device, and has a cylindrical first roll, A second roll disposed inside the first roll, and before pressing the rotating member, the inner peripheral surface of the first roll and the outer peripheral surface of the second roll are axially centered. When contacting the entire region in the circumferential direction at the portion and pressing the rotating member, the inner peripheral surface of the first roll and the outer peripheral surface of the second roll are related to the central axis of the second roll. It is characterized by being separated in a region opposite to the rotating member.
Here, the second roll can be characterized in that the outer diameter of the central portion in the axial direction is formed in a crown shape larger than both end portions. In addition, the second roll may have a configuration in which an elastic layer is coated on the surface.

Further, the present invention is regarded as an image forming apparatus. The image forming apparatus of the present invention includes a toner image forming unit that forms a toner image, and a transfer unit that transfers a toner image formed by the toner image forming unit onto a recording material. A fixing means for fixing the toner image transferred onto the recording material to the recording material. The fixing means stretches the rotation member, the pressure belt, and the pressure belt, and can press the rotation member. A pressure belt module having a pressure roll and a tension roll that stretches the pressure belt, the pressure belt module including a first roll in which the pressure roll is formed in a cylindrical shape, It is characterized by comprising a second roll disposed inside the first roll and formed in a crown shape having an outer diameter at the central portion in the axial direction larger than both end portions.
Here, the pressure belt module is configured to be able to contact and separate from the rotating member, and the pressure roller of the pressure belt module is installed when the pressure belt module is installed apart from the rotating member. The inner peripheral surface of the first roll and the outer peripheral surface of the second roll may be configured to be in contact with each other over the entire area in the circumferential direction at the central portion in the axial direction.

  As an effect of the present invention, since the pressing member can press the fixing member with a substantially uniform pressing force in the axial direction, a high-quality fixed image having high fixing property and uniform gloss can be formed. Became possible.

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 an image forming apparatus to which the exemplary embodiment is applied. The image forming apparatus shown in FIG. 1 is an intermediate transfer type image forming apparatus generally called a tandem type, and a plurality of image forming units 1Y, 1M, 1C, and 1K on which toner images of respective color components are formed by electrophotography. The primary transfer unit 10 that sequentially transfers (primary transfer) the color component toner images formed by the image forming units 1Y, 1M, 1C, and 1K to the intermediate transfer belt 15, and the superimposed toner image transferred onto the intermediate transfer belt 15. Are provided with a secondary transfer unit 20 that collectively transfers (secondary transfer) to a paper P that is a recording material (recording paper), and a fixing device 60 that fixes the secondary transferred image onto the paper P. Moreover, it has the control part 40 which controls operation | movement of each apparatus (each part).

  In the present embodiment, each of the image forming units 1Y, 1M, 1C, and 1K has a charger 12 that charges the photosensitive drum 11 around the photosensitive drum 11 that rotates in the direction of arrow A, and the photosensitive drum 11. A laser exposure device 13 for writing an electrostatic latent image thereon (exposure beam is indicated by a symbol Bm in the figure), each color component toner is accommodated, and the electrostatic latent image on the photosensitive drum 11 is visualized with toner. A developing unit 14, a primary transfer roll 16 that transfers each color component toner image formed on the photosensitive drum 11 to the intermediate transfer belt 15 in the primary transfer unit 10, and a drum cleaner that removes residual toner on the photosensitive drum 11. 17 and the like are sequentially arranged. These image forming units 1Y, 1M, 1C, and 1K are arranged substantially linearly in the order of yellow (Y), magenta (M), cyan (C), and black (K) from the upstream side of the intermediate transfer belt 15. Has been.

The intermediate transfer belt 15 as an intermediate transfer member is constituted by a film-like endless belt in which an appropriate amount of an antistatic agent such as carbon black is contained in a resin such as polyimide or polyamide. And the volume resistivity is formed so that it may become 10 < ⁶ > -10 < ¹⁴ > (omega | ohm) cm, The thickness is comprised by about 0.1 mm, for example. The intermediate transfer belt 15 is circulated and driven (rotated) at a predetermined speed in the direction B shown in FIG. 1 by various rolls. As these various rolls, a drive roll 31 that is driven by a motor (not shown) having excellent constant speed and rotates the intermediate transfer belt 15, and an intermediate that extends substantially linearly along the arrangement direction of the photosensitive drums 11. A support roll 32 that supports the transfer belt 15, a tension roll 33 that functions as a correction roll that applies a constant tension to the intermediate transfer belt 15 and prevents the intermediate transfer belt 15 from meandering, and a backup provided in the secondary transfer unit 20. A cleaning backup roll 34 provided in a cleaning unit for scraping off residual toner on the roll 25 and the intermediate transfer belt 15 is provided.

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 includes a shaft and a sponge layer as an elastic body layer fixed around the shaft. The shaft is a cylindrical bar made of metal such as iron or SUS. The sponge layer is a sponge-like cylindrical roll formed of a blend rubber of NBR, SBR, and EPDM containing a conductive agent such as carbon black and having a volume resistivity of 10 ⁷ to 10 ⁹ Ωcm. The primary transfer roll 16 is placed in pressure contact with the photosensitive drum 11 with the intermediate transfer belt 15 in between, and the primary transfer roll 16 has a voltage (with negative polarity; the same applies hereinafter) having a polarity opposite to that of the toner. (Primary transfer bias) is applied. As a result, the toner images on the respective photosensitive drums 11 are sequentially electrostatically attracted to the intermediate transfer belt 15 so as to form superimposed toner images 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. The backup roll 25 is composed of a tube of EPDM and NBR blend rubber with carbon dispersed on the surface, and EPDM rubber on the inside. And it forms so that the surface resistivity may be 10 < ⁷ > -10 < ¹⁰ > (omega | ohm) / square, and hardness is set to 70 degrees (Asker C), for example. The backup roll 25 is disposed on the back side of the intermediate transfer belt 15 to form a counter electrode of the secondary transfer roll 22, and a metal power supply roll 26 to which a secondary transfer bias is stably applied is disposed in contact with the backup roll 25. ing.

On the other hand, the secondary transfer roll 22 includes a shaft and a sponge layer as an elastic body layer fixed around the shaft. The shaft is a cylindrical bar made of metal such as iron or SUS. The sponge layer is a sponge-like cylindrical roll formed of a blend rubber of NBR, SBR, and EPDM containing a conductive agent such as carbon black and having a volume resistivity of 10 ⁷ to 10 ⁹ Ωcm. The secondary transfer roll 22 is disposed in pressure contact with the backup roll 25 with the intermediate transfer belt 15 interposed therebetween. Further, the secondary transfer roll 22 is grounded, and a secondary transfer bias is formed between the secondary transfer roll 22 and the backup roll 25. The toner image is secondarily transferred onto the paper P conveyed to the transfer unit 20.

  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 so as to be able to contact and separate. On the other hand, on the upstream side of the yellow image forming unit 1Y, a reference sensor (home position sensor) 42 that generates a reference signal serving as a reference for taking image forming timings in the image forming units 1Y, 1M, 1C, and 1K. It is arranged. Further, an image density sensor 43 for adjusting image quality is disposed on the downstream side of the black image forming unit 1K. The reference sensor 42 recognizes a predetermined mark provided on the back side of the intermediate transfer belt 15 and generates a reference signal. Each image forming unit is instructed by an instruction from the control unit 40 based on the recognition of the reference signal. 1Y, 1M, 1C, and 1K are configured to start image formation.

  Further, in the image forming apparatus according to the present embodiment, as a paper transport system, a paper tray 50 that stores paper P, a pickup roll 51 that picks up and transports the paper P accumulated in the paper tray 50 at a predetermined timing, and a pickup A transport roll 52 that transports the paper P fed by the roll 51, a transport chute 53 that feeds the paper P transported by the transport roll 52 to the secondary transfer unit 20, and transported after being secondarily transferred by the secondary transfer roll 22. A conveyance belt 55 that conveys the paper P to be fixed to the fixing device 60 and a fixing inlet guide 56 that guides the paper P to the fixing device 60 are provided.

  Next, a basic image forming process of the image forming apparatus according to the present embodiment will be described. In the image forming apparatus as shown in FIG. 1, image data output from an image reading device (IIT) not shown or a personal computer (PC) not shown is subjected to predetermined image processing by an image processing device (IPS) not shown. After being applied, the image forming operation is executed by the image forming units 1Y, 1M, 1C, and 1K. In IPS, the input reflectance data is subjected to predetermined image processing such as shading correction, position shift correction, brightness / color space conversion, gamma correction, frame deletion, color editing, moving editing, and other various image editing. Is done. The image data that has undergone image processing is converted into color material gradation data of four colors Y, M, C, and K, and is output to the laser exposure unit 13.

  The laser exposure unit 13 irradiates the photosensitive drums 11 of the image forming units 1Y, 1M, 1C, and 1K, for example, with an exposure beam Bm emitted from a semiconductor laser in accordance with the input color material gradation data. Yes. In each of the photosensitive drums 11 of the image forming units 1Y, 1M, 1C, and 1K, the surface is charged by the charger 12, and then the surface is scanned and exposed by the laser exposure unit 13 to form an electrostatic latent image. The formed electrostatic latent images are developed as toner images of respective colors Y, M, C, and K by the respective image forming units 1Y, 1M, 1C, and 1K.

  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 the primary transfer unit 10 where the photosensitive drums 11 and the intermediate transfer belt 15 come into contact with each other. Transcribed. More specifically, in the primary transfer portion 10, a voltage (primary transfer bias) having a polarity opposite to the toner charging polarity (minus polarity) is applied to the base material of the intermediate transfer belt 15 by the primary transfer roll 16, and the toner image. Are sequentially superimposed on the surface of the intermediate transfer belt 15 to perform primary transfer.

  After the toner images are sequentially primary transferred onto the surface of the intermediate transfer belt 15, the intermediate transfer belt 15 moves and the toner image is conveyed to the secondary transfer unit 20. When the toner image is transported to the secondary transfer unit 20, in the paper transport system, the pick-up roll 51 rotates in accordance with the timing at which the toner image is transported to the secondary transfer unit 20, and the paper of a predetermined size is transferred from the paper tray 50. P is supplied. The paper P supplied by the pickup roll 51 is transported by the transport roll 52 and reaches the secondary transfer unit 20 via the transport chute 53. Before reaching the secondary transfer unit 20, the paper P is temporarily stopped, and a registration roll (not shown) rotates in accordance with the movement timing of the intermediate transfer belt 15 on which the toner image is carried. And the position of the toner image are aligned.

  In the secondary transfer unit 20, the secondary transfer roll 22 is pressed against the backup roll 25 via the intermediate transfer belt 15. At this time, the sheet P conveyed at the same timing is sandwiched between the intermediate transfer belt 15 and the secondary transfer roll 22. At this time, when a voltage (secondary transfer bias) having the same polarity as the toner charging polarity (negative polarity) is applied from the power supply roll 26, a transfer electric field is formed between the secondary transfer roll 22 and the backup roll 25. Is done. The unfixed toner image carried on the intermediate transfer belt 15 is collectively electrostatically transferred onto the paper P in the secondary transfer unit 20 pressed by the secondary transfer roll 22 and the backup roll 25. .

Thereafter, the sheet P on which the toner image has been electrostatically transferred is transported as it is while being peeled off from the intermediate transfer belt 15 by the secondary transfer roll 22, and transported downstream of the secondary transfer roll 22 in the sheet transport direction. It is conveyed to the belt 55. The conveyance belt 55 conveys the paper P to the fixing device 60 in accordance with the optimum conveyance speed in the fixing device 60. The unfixed toner image on the paper P conveyed to the fixing device 60 is fixed on the paper P by being subjected to a fixing process 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 placement unit provided in a discharge unit of the image forming apparatus.
On the other hand, after the transfer onto the paper P is completed, the residual toner remaining on the intermediate transfer belt 15 is conveyed to the cleaning unit as the intermediate transfer belt 15 rotates, and the cleaning backup roll 34 and the intermediate transfer belt cleaner 35 are transferred. Is removed from the intermediate transfer belt 15.

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 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 belt module 62 as an example of a pressure contact member configured to be able to contact and separate from the fixing belt module 61. ing.
The fixing belt module 61 includes a fixing roll 610 that rotates in the direction of arrow A, a tension roll 615 in which a halogen heater 616a as a heating member is disposed, and a halogen heater 616b in the same manner as a heating member. The tension roll 618, the support roll 619 that supports the fixing belt 614 between the fixing roll 610 and the tension roll 615, the tension roll 610, the tension roll 615, the tension roll 618, and further the tension roll 619 The fixing belt 614 is mounted and moves in the direction of arrow D.

The fixing roll 610 is a soft roll having an outer diameter of 65 mmφ and a length of 420 mm, which is formed by coating a surface of a metal core 611 made of aluminum having a thickness of 5 mm with an elastic body layer 612 having a thickness of 1.5 mm. is there. For the elastic layer 612, LSR (Liquid Silicone Rubber) having a rubber hardness of 25 to 45 ° (JIS-A) is used. The fixing roll 610 rotates in the arrow A direction at a surface speed of 400 mm / s.
Also, a halogen heater 613 rated at 1000 W is provided as a heating source inside the fixing roll 610, and the control of the image forming apparatus is performed based on the measured value of the temperature sensor 617a arranged so as to be in contact with the surface of the fixing roll 610. The unit 40 (see FIG. 1) controls the surface temperature of the fixing roll 610 to 160 ° C.
The material of the elastic layer 612 is not limited to silicone rubber, and various conventionally known materials such as fluoro rubber can be used, and a plurality of layers made of silicone rubber and fluoro rubber are laminated. An elastic body layer 612 may be used. Further, a so-called hard roll without the elastic layer 612 can be used as the fixing roll 610. In this case, the heat supply from the fixing roll 610 to the fixing belt 614 is further improved.

The fixing belt 614 is stretched with a tension of 10 kgf by a fixing roll 610, a tension roll 615, a tension roll 618, and further a support roll 619. The fixing belt 614 is formed of a flexible endless belt having a circumferential length of 330 mm and a width of 400 mm.
The fixing belt 614 includes a base layer made of a polyimide resin having a thickness of 75 μm, an elastic layer made of silicone rubber having a thickness of 200 μm laminated on the surface side (outer peripheral surface side) of the base layer, and an elastic layer. And a surface layer made of a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin (PFA) having a thickness of 30 μm as a release layer. Here, the elastic layer is provided to improve the image quality especially for color images, and in this embodiment, a silicone rubber having a rubber hardness of 20 ° (JIS-A) is used. The configuration of the fixing belt 614 can be appropriately selected in terms of material, thickness, hardness, and the like according to the apparatus design conditions such as the purpose of use and conditions of use.

The tension roll 615 is formed of a stainless steel pipe roll having an outer diameter of 23 mmφ, a thickness of 2 mm, and a length of 420 mm. Inside the tension roll 615, a halogen heater 616 rated at 800 W is disposed as a heating source. The surface temperature of the tension roll 615 is set to 200 ° C. by the temperature sensor 617b and the control unit 40 (see FIG. 1). It is controlled. Therefore, the tension roll 615 has both a function of stretching the fixing belt 614 and a function of heating the fixing belt 614.
Further, the tension roll 615 has an outer diameter that is smaller than that of the end portion in order to make the displacement of the fixing belt 614 in the axial direction as small as possible and to make the tension acting on the fixing belt 614 uniform in the width direction. It is formed in a so-called crown shape in which the central portion is enlarged by 100 μm.
Further, a belt edge position detection mechanism (not shown) for detecting the edge position of the fixing belt 614 is disposed in the vicinity of the tension roll 615. The tension roll 615 is provided with an axial displacement mechanism for displacing the contact position in the axial direction of the fixing belt 614 according to the detection result of the belt edge position detection mechanism, and the meandering (belt walk) of the fixing belt 614 is arranged. Configured to control.

  The tension roll 618 has a stainless steel pipe roll having an outer diameter of 23 mm, a wall thickness of 2 mm, and a length of 420 mm as a base, and its surface is coated with PFA having a thickness of 20 μm to form a release layer. This release layer is formed in order to prevent a slight amount of offset toner and paper powder from the outer peripheral surface of the fixing belt 614 from accumulating on the tension roll 618. Further, the tension roll 618 has an outer diameter of 100 μm at the center portion than the end portion in order to make the displacement of the fixing belt 614 in the axial direction as small as possible and to make the tension of the fixing belt 614 uniform. The so-called crown shape is made larger. Note that not only the tension roll 615 and the tension roll 618 are both formed in a crown shape, but only one of the tension roll 615 and the tension roll 618 may be formed in a crown shape.

Inside the tension roll 618, a halogen heater 616b rated as a heating source is disposed, and the surface temperature is controlled to 200 ° C. by the temperature sensor 617c and the control unit 40 (see FIG. 1). . Accordingly, the tension roll 618 has a function of stretching the fixing belt 614 and a function of heating the fixing belt 614 from the outer surface. Accordingly, since the halogen heater 616 as a heating source is also provided inside the tension roll 615, in this embodiment, the fixing belt 614 is auxiliary heated by both the tension roll 615 and the tension roll 618. It is the composition to do.
The tension roll 618 also has a function as a tension roll that applies a tension of 10 kgf to the entire fixing belt 614.

  Further, the tension roll 618 has a cleaning web mechanism 70 for contacting the surface of the tension roll 618 and wiping off offset toner and paper dust adhering to the surface of the tension roll 618 from the outer peripheral surface of the fixing belt 614. It is arranged.

  Next, the pressure belt module 62 will be described. The pressure belt module 62 includes a pressure belt 620 stretched by three rolls of a lead roll 621, a pressure roll 65, and a tension roll 623, and the pressure belt 620 is interposed inside the pressure belt 620. A main part is constituted by a pressure pad (pressing member) 63 arranged in a state of being biased by the fixing roll 610. When the pressure belt module 62 is installed so as to be pressed against the fixing belt module 61, the pressure belt 620 is fixed as the fixing roll 610 of the fixing belt module 61 rotates in the arrow A direction. It follows the roll 610 and rotates in the arrow B direction. The traveling speed is 400 mm / s which is the same as the surface speed of the fixing roll 610.

  When the pressure belt module 62 is installed so as to be pressed against the fixing belt module 61, the fixing belt 614 is wound around the fixing roll 610 around the contact portion between the pressure belt module 62 and the fixing belt module 61. A nip portion N formed so that the pressure belt 620 is in pressure contact with the outer peripheral surface of the fixing belt 614 is formed in a (wrapped) region (hereinafter referred to as a “wrap region”). ing. In the nip portion N, the pressure pad 63 is disposed inside the pressure belt 620 in a state of being urged toward the fixing roll 610 via the pressure belt 620, and the pressure belt 620 is attached to the fixing roll 610. Pressing against the lap area. A pressure roll 65 is disposed at the most downstream portion of the nip portion N. The pressure roll 65 is urged toward the central axis of the fixing roll 610 via the pressure belt 620 and the fixing belt 614, and a local high pressure is applied to the contact portion between the fixing roll 610 and the fixing belt 614. Is caused.

  The paper P carrying the toner image is heated and pressurized when passing through the nip portion N, and the toner image is fixed on the paper P. At that time, the toner image on the paper P is appropriately glossed by the local high pressure by the pressure roll 65 at the most downstream portion of the nip portion N. In the fixing device 60 of the present embodiment, the nip portion N is formed as a band-like region extending over 45 ° as the central angle with respect to the rotation axis of the fixing roll 610 (hereinafter, this central angle is referred to as “wrap angle”). In this case, the nip width is 26 mm.

Here, the pressure belt 620 includes a base layer, a release layer coated on the surface or both surfaces on the fixing roll 610 side, and an elastic body layer formed between the base layer and the release layer. Preferably it is configured. And as a base layer, it is formed with resin with high heat resistance strength, for example, polyimide, polyamide, polyamideimide, etc. are suitable. The thickness of the base layer is, for example, about 50 to 125 μm, more preferably 75 to 100 μm.
Moreover, as a mold release layer, what coated the fluororesin, for example, PFA, etc. with the thickness of 5-20 micrometers is preferable. Further, as the elastic layer, silicone rubber having a thickness of 20 to 500 μm, preferably 50 to 300 μm and a rubber hardness of 8 to 70 ° (JIS-A), preferably 15 to 30 ° (JIS-A) is used. Can be used.
In the fixing device 60 of the present embodiment, as the pressure belt 620, a polyimide film base layer having a thickness of 75 μm, a width of 370 mm, and a peripheral length of 288 mm is coated with silicone having a rubber hardness of 30 ° (JIS-A) and a thickness of 100 μm. An elastic layer made of rubber and a release layer made of fluororesin (PFA) having a thickness of 30 μm are laminated on the outer surface side (fixing belt module 61 side).

The three rolls that stretch the pressure belt 620 include a stainless steel lead roll 621, a pressure roll 65 that will be described in detail later, and a stainless steel tension roll 623. The pressure belt 620 is stretched by tension. The outer diameter of each roll is 25 mmφ, 40 mmφ, and 25 mmφ, and the length is 390 mm. In addition, a halogen heater 625 is disposed inside the lead roll 621 as a heating source. The surface temperature is controlled to 120 ° C. by a temperature sensor and control unit 40 (see FIG. 1) (not shown), and the pressure belt 620 is preheated.
Further, a belt edge position detection mechanism (not shown) for detecting the edge position of the pressure belt 620 is disposed in the vicinity of the tension roll 623. The tension roll 623 is provided with a shaft displacement mechanism that displaces the contact position in the axial direction of the pressure belt 620 according to the detection result of the belt edge position detection mechanism. ) Is configured to control.

  Further, the pressure pad 63 as a pressing member includes an elastic member for securing a wide nip portion N, and a low friction layer provided on a surface where the elastic member contacts the inner peripheral surface of the pressure belt 620. 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 that substantially follows the outer peripheral surface of the fixing roll 610 on the fixing roll 610 side, is pressed against the fixing roll 610, and is disposed in the wrap region of the fixing roll 610. An entrance side region of the formed nip portion N is formed.

As the elastic member of the pressure pad 63, 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 620 and the pressure pad 63, and is a material having a low 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.
The pressure pad 63 may be, for example, a roll-shaped one in addition to the pad-shaped one as in the present embodiment, and may be a fixing roll 610 via a pressure belt 620. The surface may be urged and driven to rotate. However, the pressure pad 63 molded in the shape of a pad as in the present embodiment can apply a nip pressure more widely and uniformly over the entire nip portion N in contact.

  A pressure roll 65 disposed downstream of the pressure pad 63 in the paper P conveyance direction (arrow C direction) is attached toward the central axis of the fixing roll 610 via the pressure belt 620 and the fixing belt 614. Therefore, a local high pressure is generated at the contact portion between the fixing roll 610 and the fixing belt 614. At that time, in order to efficiently apply a local high pressure to the fixing roll 610 and the fixing belt 614 with a low load, the outer diameter of the pressure roll 65 is smaller than that of the fixing roll 610 and the surface thereof is the surface of the fixing roll 610. It is desirable to form it more rigidly.

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 unit 20 (see FIG. 1) of the image forming apparatus is directed toward the nip N of the fixing device 60 by the conveyance belt 55 and the fixing inlet guide 56 ( It is conveyed (in the direction of arrow C). During the image forming operation, the pressure belt module 62 is installed so as to be pressed against the fixing belt module 61, and an unfixed toner image on the surface of the paper P passing through the nip portion N is pressure applied to the nip portion N. It is fixed on the paper P by heat and heat. In the fixing device 60 of the present embodiment, as described above, the nip portion N has a configuration in which the pressure roller 63 is pressed and the fixing roll 610 on which the fixing belt 614 is wrapped and the pressure belt 620 are in contact with each other. Therefore, stable fixing performance can be ensured.

  At this time, in the fixing device 60 of the present embodiment, the heat acting on the nip portion N is mainly supplied by the fixing belt 614. The fixing belt 614 is supplied from the halogen heater 613 disposed inside the fixing roll 610 through the fixing roll 610 and from the halogen heater 616 a disposed inside the stretching roll 615 through the stretching roll 615. It is configured to be heated by heat and heat supplied through the tension roll 618 from the halogen heater 616b disposed inside the tension roll 618. Therefore, even when the heat energy is insufficient with only the fixing roll 610, the heat energy can be appropriately and quickly supplied from the tension roll 615 and the tension roll 618. However, a sufficient amount of heat can be secured even at a high speed of 400 mm / s.

That is, in the fixing device 60 of the present embodiment, the fixing belt 614 that functions as a direct heating member can be formed with a very small heat capacity. In addition, the fixing belt 614 is configured to contact the fixing roll 610 that is a heat supply member, the tension roll 615, and the tension roll 618 with a wide lap area (large wrap angle). Therefore, since a sufficient amount of heat is supplied from the fixing roll 610, the stretching roll 615, and the stretching roll 618 during a short period of one rotation of the fixing belt 614, the fixing belt 614 is returned to the necessary fixing temperature in a short time. It becomes possible to make it. Therefore, at the nip portion N, a predetermined fixing temperature can always be maintained even if the speed of the fixing device 60 is increased.
As a result, in the fixing device 60 of the present embodiment, it is possible to suppress the occurrence of the temperature droop phenomenon in which the fixing temperature is lowered at the start of the high-speed fixing operation. In particular, it is possible to suppress the occurrence of temperature droop even in fixing to thick paper having a large heat capacity. Further, even 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 614 has a small heat capacity, so that the halogen heater 613 and further, By adjusting the outputs of the halogen heater 616a and the halogen heater 616b, it is possible to easily and quickly switch to a desired temperature.

Further, in the fixing device 60 of the present embodiment, in the nip portion N, the pressure belt 620 of the pressure belt module 62 is only in the region (wrap region) where the fixing belt 614 is wound around the surface of the fixing roll 610. The fixing belt 614 is in contact with the outer peripheral surface. That is, in the nip portion N, the fixing roll 610 is located over the entire area on the inner peripheral surface side of the fixing belt 614. Accordingly, the contact between the fixing belt 614 and the pressure belt 620 is performed in a state where the fixing belt 614 is stably supported by the surface of the fixing roll 610, so that both of them can be uniformly adhered in the entire nip portion N. Due to the good adhesion between the fixing belt 614 and the pressure belt 620, heat conduction from the fixing belt 614 to the paper P can be efficiently performed, so that the occurrence of temperature droop is more effectively suppressed. Can do.
Further, due to the configuration of the nip portion N, an area where the fixing belt 614 contacts only the fixing roll 610 is formed upstream of the fixing belt 614 on the inlet side of the nip portion N. Therefore, when the fixing belt 614 passes through this region, wrinkles generated in the fixing belt 614 during rotation are corrected. Accordingly, since the nip portion N can be brought into contact with the unfixed toner image on the paper P in a smooth state, a high-quality fixed image can be obtained.

  In addition, in the fixing device 60 according to the present embodiment, a pressure roll 65 that is urged toward the central axis of the fixing roll 610 is disposed at the most downstream portion of the nip portion N. The pressure roll 65 applies a local high pressure to the melted toner image. As a result, high fixability is ensured and the surface of the toner image is smoothed to give particularly good image gloss to a color image. As described above, the pressure roll 65 is smaller in diameter than the fixing roll 610 and its surface is formed to be harder than the surface of the fixing roll 610, thereby efficiently applying a local high pressure to the toner image with a low load. be able to.

Here, the pressure roll 65 arranged to be urged toward the central axis of the fixing roll 610 at the most downstream portion of the nip portion N will be described.
First, the configuration of the pressure roll 65 will be described. FIG. 3 is a side sectional view showing the configuration of the pressure roll 65. As shown in FIG. 3, the pressure roll 65 includes an outer roll (first roll) 651 disposed on the outer side, and an inner roll (second roll) 652 disposed on the inner side of the outer roll 651. It consists of That is, the pressure roll 65 stretches the pressure belt 620, and the outer roll 651 that presses the fixing roll 610, and the pressure roll 65 is not in pressure contact with the fixing roll 610 inside the outer roll 651. The outer roll 651 and the inner roll 652 disposed coaxially form a double roll structure (roll-in roll structure).
Here, the outer roll 651 is a cylindrical roll member in which an aluminum pipe (cylindrical body) is used as the base material 651b and the outer surface of the base material 651b is covered with the elastic layer 651a. The inner roll 652 is a substantially cylindrical roll member in which a substantially cylindrical body (solid) made of stainless steel is used as the base 652b, and the outer surface of the base 652b is covered with the elastic layer 652a. The base material 652b of the inner roll 652 is formed in a so-called crown shape (crown profile) in which the outer diameter of the central portion in the axial direction is larger than the outer diameters of both end portions. In the fixing device 60 of the present embodiment, the outer roll 651 is made of an aluminum pipe base 651b having an outer diameter of 40 mm, an inner diameter of 33 mm, and a length of 390 mm, and a silicone rubber having a hardness of 35 ° (JIS-A) and a thickness of 5 mm. The elastic layer 651a is covered. Further, the inner roll 652 has a hardness of 50 ° (JIS-) on a solid shaft base material 652b made of stainless steel formed in a crown profile having an outer diameter of 27.5 mm at the center and an outer diameter of 26 mm at both ends. A) An elastic layer 652a of EPDM rubber having a thickness of 2.75 mm is covered.

In addition, the inner roll 652 is provided with support portions 652c at both ends in the axial direction outside the region where the outer roll 651 is disposed. The support portion 652c provided on the inner roll 652 is pressed toward the fixing roll 61 by a spring member (not shown) such as a spring while being rotatably supported by a main body frame (not shown) of the fixing device 60. Yes. Accordingly, when the pressure belt module 62 is installed so as to be pressed against the fixing belt module 61, the inner roll 652 presses the outer roll 651 against the fixing roll 610 via the fixing belt 614 and the pressure belt 620. ing. Further, during the fixing operation, the outer roll 651 and the inner roll 652 rotate integrally with the rotation of the fixing roll 610.
Further, the position restricting plates 631 are disposed in the support portions 652c provided at both end portions in proximity to the side portions at both ends of the outer roll 651. The position restricting plate 631 restricts the outer roll 651 from moving in the axial direction beyond a predetermined range.

Next, functions of the outer roll 651 and the inner roll 652 when the pressure roll 65 is pressed toward the fixing roll 61 will be described.
FIG. 4 is a diagram illustrating a state in which the pressure roll 65 is pressed toward the fixing roll 61 when the pressure belt module 62 is installed so as to be pressed against the fixing belt module 61. As shown in FIG. 4, when the support portions 652 c provided at both ends of the inner roll 652 in the axial direction are pressed toward the fixing roll 610 by the spring member 80, the entire inner roll 652 has the fixing roll 610. An arcuate bend in which the central part becomes concave toward the side occurs. However, as described above, in the inner roll 652, the base material 652b is formed in a crown shape in which the outer diameter of the central portion in the axial direction is larger than the outer diameters of both end portions. Therefore, even if the inner roll 652 is bent, the recess in the central portion in the axial direction is offset by the crown shape of the inner roll 652 itself. Accordingly, in the surface region P where the inner roll 652 presses the outer roll 651 from the inside, the outer surface of the inner roll 652 has a shape that substantially follows the inner peripheral surface of the outer roll 651 having a flat surface shape in the axial direction. Become. As a result, the inner roll 652 can press the outer roll 651 with a substantially uniform force in the axial direction in the surface region P that presses the outer roll 651.

  Therefore, even when the pressure roll 65 is pressed to the fixing roll 610 side, the outer roll 651 hardly bends. As a result, pressure is applied to the contact surface (the surface corresponding to the surface region P where the inner roll 652 presses the outer roll 651) between the pressure roll 65 and the fixing roll 610 via the fixing belt 614 and the pressure belt 620. Since the roll 65 can come into pressure contact with the fixing roll 610 with a substantially uniform pressing force in the axial direction, a substantially uniform local pressing force in the axial direction is applied to the sheet at the most downstream portion of the nip portion N. It can be applied to the toner image on P. As a result, the toner image that has passed through the nip portion N is uniform in the width direction of the paper P, and high fixability can be obtained. Further, since the surface of the toner image before solidification can be uniformly smoothed across the width direction, it is possible to give the toner image uniform and appropriate gloss.

  By the way, when the fixing roll 610 receives a pressing force from the pressure roll 65, a reaction force against the pressing force from the pressure roll 65 is generated in the fixing roll 610. There may be a bow-shaped deflection with a concave central part toward the side. In this case, since the rigidity of the fixing roll 610 is configured to be larger than that of the pressure roll 65, the amount of bending is extremely small as compared with the inner roll 652. Therefore, even if the fixing roll 610 is bent when pressed from the pressure roll 65, the inner roll 652 extends over the outer roll 651 in the axial direction in the surface region P that presses the outer roll 651 as described above. Therefore, the outer roll 651 and the fixing roll 610 can be deformed by following the slight bending of the fixing roll 610 on the surface where the outer roll 651 and the fixing roll 610 are pressed. In addition, even in this state, the inner roll 652 presses the outer roll 651 with a substantially uniform force over the axial direction, so that even if the fixing roll 610 is slightly bent, the pressure roll 65 extends over the axial direction. It is possible to press the fixing roll 610 with a substantially uniform pressing force.

  In the pressure roll 65 of the present embodiment, the inner roll 652 is entirely formed in the crown profile by forming the base 652b of the inner roll 652 in the crown profile. It is also possible to form the entire inner roll 652 in the crown profile by forming the elastic layer 652a that is formed of the actual shaft and covers the base material 652b with the crown profile. That is, as long as the entire inner roll 652 can be formed with a crown profile, any configuration can be adopted.

  Next, in the pressure roll 65 of the present embodiment, the outer roll 651 and the inner roll 652 are arranged coaxially and in the axial direction when the pressure roll 65 is not in pressure contact with the fixing roll 610. In the central portion (region Q in FIG. 3), the outer peripheral surface of the inner roll 652 is formed so as to contact the inner peripheral surface of the outer roll 651. That is, when the pressure roll 65 is not in pressure contact with the fixing roll 610, the outer diameter of the inner roll 652 in the axial central portion is formed to be approximately equal to the inner roll 651 so as to be slightly larger than the inner diameter of the outer roll 651. Due to the elastic compression of the elastic layer 652a, the outer roll 651 is in contact with the inner peripheral surface, and the outer roll 651 is configured to be supported by the inner roll 652.

By the way, in the fixing device 60 of the present embodiment, the fixing belt module 61 and the pressure belt module 62 are configured to be able to contact and separate. That is, during the image forming operation, as shown in FIG. 2, the fixing belt module 61 and the pressure belt module 62 are arranged in pressure contact with each other at the nip portion N. However, when the image forming apparatus receives the instruction signal for the image forming operation and starts the image forming operation, the fixing device 610 is heated to a predetermined temperature so that the fixing device 60 can perform the fixing process in a short time. It needs to be set to an elevated state. Similarly, the pressure belt 620 needs to be heated to a predetermined temperature so as not to unnecessarily remove heat from the fixing belt 614 and reduce the temperature of the fixing belt 614 during the fixing operation. In such a case, the fixing belt module 61 and the pressure belt module 62 are set in a state of being separated (retracted), and the fixing belt module 61 and the pressure belt module 62 are separately rotated while performing a rotation operation. The fixing belt 614 and the pressure belt 620 are heated, respectively.
Therefore, in this case, the pressure belt module 62 is stretched by the lead roll 621, the pressure roll 65, and the tension roll 623 while being retracted from the fixing belt module 61, and the pressure belt 620 is rotated. Let The pressure belt 620 is uniformly heated in the belt circumferential direction by a halogen heater 625 disposed in the lead roll 621.

  As described above, when the pressure belt module 62 rotates while retracted from the fixing belt module 61, the pressure roll 65 rotates without being pressed against the fixing roll 610 side. For this reason, if the outer roll 651 is supported in an unstable state with respect to the inner roll 652 in the pressure roll 65, the outer roll 651 has a large axial swing during the rotation of the pressure belt module 62. Motion occurs. As a result, even if the tension roll 623 is provided with a shaft displacement mechanism for controlling the belt walk, it is difficult to stably rotate the pressure belt 620. Therefore, a large belt walk occurs in the pressure belt 620, and the end of the pressure belt 620 strongly collides with a member such as a main body frame. Specifically, a situation where the entire pressure belt 620 is damaged is also assumed.

  On the other hand, in the pressure roll 65 used in the pressure belt module 62 of the present embodiment, the outer roll 651 and the inner roll 652 are coaxial in a state where the pressure roll 65 is not pressed against the fixing roll 610. In addition, the outer peripheral surface at the axially central portion of the inner roll 652 is configured to come into contact with the inner peripheral surface of the outer roll 651. Therefore, when the pressure roll 65 is not in pressure contact with the fixing roll 610, the outer roll 651 and the inner roll 652 are arranged coaxially, and the outer roll 651 is stabilized by the axial center portion that contacts the inner roll 652. Therefore, the swinging in the axial direction generated in the outer roll 651 can be suppressed to be small. As a result, when the pressure belt module 62 rotates in a retracted state from the fixing belt module 61, the belt walk of the pressure belt 620 caused by the swinging of the outer roll 651 is performed on the shaft provided on the stretch roll 623. The displacement mechanism can be sufficiently controlled, and the pressure belt 620 can be stably rotated. Therefore, the pressure belt 620 is retracted while the pressure belt module 62 is retracted while avoiding a situation in which the end of the pressure belt 620 is cracked or eventually the entire pressure belt 620 is damaged. Can be heated evenly.

  Here, in a state where the outer diameter of the inner roll 652 is substantially equal to the inner diameter of the outer roll 651 and the pressure roll 65 is not pressed against the fixing roll 610, the outer circumference of the inner roll 652 and the inner circumference of the outer roll 651 The area in contact with the surface (contact area: in the vicinity of the area Q shown in FIG. 3) is a length area that is 1/10 to 1/5 the length of the outer roll 651 in the axial direction. This is preferable in order to stably suppress the oscillation of the. That is, when the contact area Q is smaller than 1/10 of the length of the outer roll 651 in the axial direction, the support of the outer roll 651 by the inner roll 652 becomes unstable, and the swing of the outer roll 651 is relatively small. There is a tendency to become large. For this reason, there is a case where the swing of the outer roll 651 cannot be suppressed by the belt walk control by the shaft displacement mechanism provided on the tension roll 623, which is not preferable. When the contact area is larger than 1/5 of the length of the outer roll 651 in the axial direction, the inner roll 652 is bent when the pressure roll 65 is pressed against the fixing roll 610 side. It is not preferable to compensate with the crown profile of 652, and the effect of pressing the pressure roll 65 against the fixing roll 610 with a substantially uniform pressing force in the axial direction is reduced. Therefore, in the pressure roll 65, the inner roll extends over the region of 1/10 to 1/5 of the length of the outer roll 651 in the axial direction symmetrically about the axial center of the outer roll 651. It is preferable that the outer peripheral surface of the roll 652 and the inner peripheral surface of the outer roll 651 come into contact with each other.

  As shown in FIG. 5, a flat portion having a constant outer diameter is formed on the outer peripheral surface of the inner roll 652 in the axially central portion (region Q in FIG. 3), and this flat portion is included. The outer peripheral surface of the inner roll 652 may be configured to contact the inner peripheral surface of the outer roll 651 in the region. When configured in this manner, the inner roll 652 and the outer roll 651 can be supported more stably at the flat portion.

Next, the elastic layer 652a that covers the inner roll 652 of the pressure roll 65 will be described. FIG. 6 is a partial side cross-sectional view showing the central portion in the axial direction of the pressure roll 65 in a state where the pressure roll 65 is in pressure contact with the fixing roll 610. That is, FIG. 6 shows the periphery of a region where the outer diameter of the inner roll 652 is the largest when the pressure roll 65 is pressed against the fixing roll 610.
As shown in FIG. 6, when the pressure roll 65 is pressed against the fixing roll 610, the entire inner roll 652 is bent into an arcuate shape having a concave central portion toward the fixing roll 610. However, in the inner roll 652, since the base material 652b is formed in a crown shape as described above, the dent in the central portion in the axial direction due to the bending is offset by the crown shape. Thereby, in the surface region P where the inner roll 652 presses the outer roll 651 from the inside, the outer surface of the inner roll 652 has a shape that substantially follows the inner peripheral surface of the outer roll 651 having a flat surface shape in the axial direction. . Therefore, the inner roll 652 presses the outer roll 651 with a substantially uniform force in the axial direction in the surface region P that presses the outer roll 651. In the surface region P where the inner roll 652 presses the outer roll 651, the elastic layer 652a of the inner roll 652 is compressed by the pressing force from the inner roll 652, so the thickness of the elastic layer 652a is the original thickness t. The thickness t1 is smaller than that (t1 <t).
Therefore, in the pressure roll 65 of the present embodiment, when the elastic layer 652a is compressed in the surface region P where the inner roll 652 presses the outer roll 651, in the surface region Q opposite to the surface region P, The thickness t and elastic modulus of the elastic layer 652a of the inner roll 652 are set so that a gap (gap) is generated between the outer peripheral surface of the inner roll 652 and the inner peripheral surface of the outer roll 651.

This is because the elastic layer 652a of the inner roll 652 is compressed in the surface region P where the inner roll 652 presses the outer roll 651, so that the surface speed of the inner roll 652 is the same as the surface region P in which the elastic layer 652a is compressed. This is based on the phenomenon that the elastic layer 652a differs from the uncompressed surface region Q. That is, the elastic layer 652a disposed on the surface of the inner roll 652 has a characteristic as an elastic body, so that the surface velocity of the elastic layer 652a in the compressed surface region P is increased, and the elasticity in the uncompressed surface region Q is increased. The surface speed of the layer 652a becomes slow. Therefore, the surface speed of the outer roll 651 that rotates according to the surface speed of the elastic layer 652a in the surface area P is higher than the surface speed of the inner roll 652 in the uncompressed surface area Q. As a result, in the surface region Q, a difference occurs between the surface speed of the outer peripheral surface of the inner roll 652 and the surface speed of the inner peripheral surface of the outer roll 651.
Therefore, when the outer peripheral surface of the inner roll 652 and the inner peripheral surface of the outer roll 651 are in contact with each other in the surface region Q in a state where the pressure roll 65 is in pressure contact with the fixing roll 610, The outer peripheral surface of the roll 652 and the inner peripheral surface of the outer roll 651 are rubbed together. Due to this, abnormal noise occurs between the inner roll 652 and the outer roll 651, or the elastic layer 652a of the inner roll 652 is scraped, and the predetermined crown profile of the inner roll 652 cannot be maintained. There is a fear.

  Therefore, in the pressure roll 65 of the present embodiment, when the elastic layer 652a is compressed in the surface area P where the inner roll 652 presses the outer roll 651, the outer surface of the inner roll 652 and the outer surface of the outer roll 651 are compressed. The thickness t and elastic modulus of the elastic layer 652a of the inner roll 652 are set so that a gap (gap) is formed between the inner peripheral surface of the roll 651. Thereby, even when a difference occurs between the surface speed of the outer peripheral surface of the inner roll 652 and the surface speed of the inner peripheral surface of the outer roll 651 in the surface region Q, it is possible to suppress the occurrence of friction between the two. Further, the generation of abnormal noise is suppressed, and the elastic layer 652a of the inner roll 652 is prevented from being scraped, so that a predetermined crown profile of the inner roll 652 can be maintained.

  As described above, in the fixing device 60 of the present embodiment, the pressure roll 65 that presses the fixing roll 610 at the most downstream portion of the nip portion N includes the outer roll 651 and the outer roll 651 that are disposed on the outer side. A double roll structure (roll-in-roll structure) with an inner roll 652 formed in a crown shape is provided while being disposed inside. The entire pressure roller 65 is pressed toward the fixing roller 610 by pressing the inner roller 652 from both ends on the axially outer side. With such a configuration, the inner roll 652 that presses the entire pressure roll 65 toward the fixing roll 610 bends, but the bending cancels out by the crown shape of the inner roll 652 itself, so that the inner roll 652 becomes the outer roll 651. Can be pressed with a substantially uniform pressure over the axial direction. As a result, the pressure roll 65 can be brought into pressure contact with the fixing roll 610 with a substantially uniform pressing force in the axial direction. Therefore, in the most downstream portion of the nip portion N, it is possible to apply a substantially uniform local pressing force to the toner image on the paper P in the axial direction. As a result, the toner image that has passed through the nip portion N is uniform in the width direction of the paper P, and high fixability can be obtained. Further, since the surface of the toner image before solidification can be uniformly smoothed across the width direction, it is possible to give the toner image uniform and appropriate gloss.

  Further, in the fixing device 60 of the present embodiment, the pressure roll 65 is arranged such that the outer roll 651 and the inner roll 652 are coaxially arranged in a state where the pressure roll 65 is not pressed against the fixing roll 610. The outer peripheral surface in the axially central portion of the inner roll 652 is configured to contact the inner peripheral surface of the outer roll 651. Therefore, even when the pressure roll 65 is not in pressure contact with the fixing roll 610, the outer roll 651 is stably supported by the central portion in the axial direction in contact with the inner roll 652. Accordingly, since it is possible to suppress the swing in the axial direction generated in the outer roll 651, when the pressure belt module 62 rotates in a retracted state from the fixing belt module 61, the outer roll 651 The belt walk of the pressure belt 620 due to the swinging can be sufficiently controlled, and the pressure belt 620 can be stably rotated. As a result, the pressure belt 60 is retracted while avoiding a situation in which the end of the pressure belt 620 is cracked or eventually the entire pressure belt 620 is damaged. 620 can be heated evenly.

  Further, in the fixing device 60 of the present embodiment, the pressure roll 65 is located on the opposite side to the surface area P when the elastic layer 652a is compressed in the surface area P where the inner roll 652 presses the outer roll 651. In the surface region Q, the thickness t and the elastic modulus of the elastic layer 652a of the inner roll 652 are set so that a gap (gap) is generated between the outer peripheral surface of the inner roll 652 and the inner peripheral surface of the outer roll 651. Yes. As a result, even when there is a difference between the surface speed of the outer peripheral surface of the inner roll 652 and the surface speed of the inner peripheral surface of the outer roll 651 in the surface region Q, no friction occurs between the two. It is also possible to maintain the predetermined crown profile of the inner roll 652 by suppressing the occurrence of the cracks and suppressing the occurrence of scraping on the elastic layer 652a of the inner roll 652.

  In addition, in the fixing device 60 of the present embodiment, a tension roll 615 in which a halogen heater 616a is disposed in parallel with the fixing roll 610 and a tension roll 618 in which a halogen heater 616b is disposed. The tension roll 615, the tension roll 618, and the fixing roll 610 are stretched by an endless fixing belt 614. Then, the fixing belt 614 functions as a main heating member for heating the paper P, and the fixing roll 610, the stretching roll 615, and the stretching roll 618 function as a heat supply member that supplies heat to the fixing belt 614. Yes. For this reason, in the nip portion N, even if the fixing device 60 is speeded up, a predetermined fixing temperature can always be maintained, so that occurrence of temperature droop can be suppressed.

[Embodiment 2]
In the first embodiment, the image forming apparatus is equipped with a fixing device 60, and as a heating unit used for the fixing device 60, a tension roll 615 and a tension roll 618 as auxiliary heating members and a fixing roll 610 are used. The configuration using the fixing belt module 61 in which the endless fixing belt 614 is stretched has been described. In the second embodiment, a fixing device 90 mounted on the image forming apparatus shown in FIG. 1 and having only a fixing roll 610 as heating means used in the fixing device 60 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. 7 is a cross-sectional side view illustrating the configuration of the fixing device 90 according to the present exemplary embodiment. The fixing device 90 of the present embodiment is the same as the fixing device 60 of the first embodiment, except that only the fixing roll 610 is provided in place of the fixing belt module 61 of the first embodiment. It is.

  Also in the fixing device 90 of the present embodiment, the pressure roll 65 that presses the fixing roll 610 at the most downstream portion of the nip portion N is disposed on the inner side of the outer roll 651 and the outer roll 651. And a double roll structure (roll-in-roll structure) with an inner roll 652 formed in a crown shape. The entire pressure roller 65 is pressed toward the fixing roller 61 by pressing the inner roller 652 from both ends on the axially outer side. With such a configuration, the inner roll 652 that presses the entire pressure roll 65 toward the fixing roll 610 bends, but the bending cancels out by the crown shape of the inner roll 652 itself, so that the inner roll 652 becomes the outer roll 651. Can be pressed with a substantially uniform pressure over the axial direction. As a result, the pressure roll 65 can be brought into pressure contact with the fixing roll 610 with a substantially uniform pressing force in the axial direction. Therefore, in the most downstream portion of the nip portion N, it is possible to apply a substantially uniform local pressing force to the toner image on the paper P in the axial direction. As a result, the toner image that has passed through the nip portion N is uniform in the width direction of the paper P, and high fixability can be obtained. Further, since the surface of the toner image before solidification can be uniformly smoothed across the width direction, it is possible to give the toner image uniform and appropriate gloss.

  Further, in the fixing device 90 of the present embodiment, the pressure roll 65 is arranged such that the outer roll 651 and the inner roll 652 are coaxially arranged in a state where the pressure roll 65 is not pressed against the fixing roll 610. The outer peripheral surface in the axially central portion of the inner roll 652 is configured to contact the inner peripheral surface of the outer roll 651. Therefore, even when the pressure roll 65 is not in pressure contact with the fixing roll 610, the outer roll 651 is stably supported by the central portion in the axial direction in contact with the inner roll 652. As a result, it is possible to suppress the swing in the axial direction generated in the outer roll 651 to be small. Therefore, when the pressure belt module 62 rotates in the retracted state from the fixing roll 610, the swing of the outer roll 651 is suppressed. The belt walk of the pressure belt 620 due to the movement can be sufficiently controlled, and the pressure belt 620 can be stably rotated. As a result, the pressure belt 60 is retracted while avoiding a situation in which the end of the pressure belt 620 is cracked or eventually the entire pressure belt 620 is damaged. 620 can be heated evenly.

  Further, in the fixing device 90 according to the present embodiment, the pressure roll 65 is located on the side opposite to the surface area P when the elastic layer 652a is compressed in the surface area P where the inner roll 652 presses the outer roll 651. In the surface region Q, the thickness t and the elastic modulus of the elastic layer 652a of the inner roll 652 are set so that a gap (gap) is generated between the outer surface of the inner roll 652 and the inner peripheral surface of the outer roll 651. Yes. As a result, even when there is a difference between the surface speed of the outer peripheral surface of the inner roll 652 and the surface speed of the inner peripheral surface of the outer roll 651 in the surface region Q, no friction occurs between the two. It is also possible to maintain the predetermined crown profile of the inner roll 652 by suppressing the occurrence of the cracks and suppressing the occurrence of scraping on the elastic layer 652a of the inner roll 652.

  As an application example of the present invention, application to an image forming apparatus such as a copying machine or a printer using an electrophotographic system, for example, application to a fixing apparatus that fixes an unfixed toner image carried on recording paper (paper). is there. Further, there is application to an image forming apparatus such as a copying machine or a printer using an ink jet method, for example, a fixing device that dries an undried ink image carried on a recording paper (paper).

1 is a schematic configuration diagram illustrating an image forming apparatus of the present invention. 2 is a side cross-sectional view illustrating a configuration of a fixing device according to Embodiment 1. FIG. It is a sectional side view which shows the structure of a pressure roll. It is a figure which shows the state by which the pressure roll was pressed by the fixing roll side. It is a fragmentary sectional side view which shows an example of a structure of an inner roll. FIG. 4 is a partial side cross-sectional view showing an axially central portion of the pressure roll in a state where the pressure roll is in pressure contact with the fixing roll. FIG. 4 is a side sectional view illustrating a configuration of a fixing device according to a second embodiment.

Explanation of symbols

1Y, 1M, 1C, 1K ... image forming unit, 11 ... photosensitive drum, 12 ... charger, 13 ... laser exposure device, 14 ... developing device, 15 ... intermediate transfer belt, 16 ... primary transfer roll, 17 ... drum cleaner , 20 ... secondary transfer unit, 60, 90 ... fixing device, 61 ... fixing belt module, 62 ... pressure belt module, 63 ... pressure pad, 64 ... peeling pad, 65 ... pressure roll, 70 ... cleaning web mechanism, 80 ... Spring member, 610 ... Fixing roll, 613, 616a, 616b, 625 ... Halogen heater, 614 ... Fixing belt, 615, 618, 623 ... Stretching roll, 620 ... Pressure belt, 621 ... Lead roll, 651 ... Outer Roll, 651a, 652a ... elastic layer, 651b, 652b ... base material, 652 ... inner roll, 652c ... support part

Claims (18)

A fixing device for fixing a toner image carried on a recording material,
A rotating member;
A pressure belt, a pressure roll that stretches the pressure belt and presses the rotating member, and a pressure belt module that includes a tension roll that stretches the pressure belt,
The pressure belt module includes a first roll in which the pressure roll is formed in a cylindrical shape, and a crown that is disposed inside the first roll and has an outer diameter at a central portion in an axial direction larger than both ends. A fixing device comprising a second roll formed in a shape.   2. The fixing device according to claim 1, wherein the pressure roll of the pressure belt module is formed such that an outer diameter of an axially central portion of the second roll is substantially equal to an inner diameter of the first roll. apparatus.   The fixing device according to claim 1, wherein the pressure roll of the pressure belt module has an elastic layer coated on a surface of the second roll.   The fixing device according to claim 1, wherein the pressure belt module is configured to be able to contact and separate from the rotating member.   The pressure roll of the pressure belt module includes an inner circumferential surface of the first roll and an outer circumferential surface of the second roll when the pressure belt module is installed apart from the rotating member. 5. The fixing device according to claim 4, wherein the fixing device is configured to be in contact with the entire area in the circumferential direction at a central portion in the axial direction.   The pressure roll of the pressure belt module includes an inner peripheral surface of the first roll and the second roll in a region of 1/10 to 1/5 of the length in the axial direction of the first roll. The fixing device according to claim 5, wherein the outer peripheral surface of the fixing device is in contact with the fixing device.   The pressure roll of the pressure belt module is opposite to the rotation member with respect to the central axis of the second roll when the pressure belt module is installed in pressure contact with the rotation member. The fixing device according to claim 4, wherein the inner peripheral surface of the first roll and the outer peripheral surface of the second roll are configured to be separated from each other in the region. A fixing device for fixing a toner image carried on a recording material,
A rotating member;
A pressurizing roll disposed so as to be switchable between a pressure contact state and a separation state with respect to the rotating member;
A pressure belt stretched over the pressure roll and forming a nip portion with the fixing belt,
The pressure roll is composed of an outer roll that stretches the pressure belt, and an inner roll that is disposed inside the outer roll and can press the outer roll toward the fixing roll. A fixing device.   The inner roll of the pressure roll is formed in a crown shape in which the outer diameter of the axial central portion is larger than both ends, and the outer diameter of the axial central portion is substantially equal to the inner diameter of the outer roll. The fixing device according to claim 8.   The inner roll of the pressure roll includes a solid roll formed in a crown shape in which the outer diameter of the central portion in the axial direction is larger than both end portions, and an elastic layer coated on the surface of the roll with a substantially uniform thickness The fixing device according to claim 9, comprising:   The fixing device according to claim 9, wherein the inner roll of the pressure roll has a flat portion formed at a central portion in an axial direction.   9. The fixing according to claim 8, wherein the rotating member includes a rotatable fixing roll, a fixing belt stretched around the fixing roll, and a tension roll stretching the fixing belt. apparatus.   The fixing device according to claim 8, wherein an elastic layer is formed on a surface of the outer roll of the pressure roll. A roll member that is used in a fixing device and can be pressed against a rotating member of the fixing device,
A cylindrical first roll;
A second roll disposed inside the first roll,
Before pressing the rotating member, the inner peripheral surface of the first roll and the outer peripheral surface of the second roll are in contact with each other over the entire region in the circumferential direction at the central portion in the axial direction. When pressing the moving member, the inner peripheral surface of the first roll and the outer peripheral surface of the second roll are in a region opposite to the rotating member with respect to the central axis of the second roll. A roll member that is separated.   The roll member according to claim 14, wherein the second roll is formed in a crown shape in which an outer diameter of an axially central portion is larger than both end portions.   The roll member according to claim 14, wherein an elastic layer is coated on a surface of the second roll. 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 material;
Fixing means for fixing the toner image transferred onto the recording material to the recording material,
The fixing means is
A rotating member;
A pressure belt, a pressure roll that stretches the pressure belt and presses the rotating member, and a pressure belt module that includes a tension roll that stretches the pressure belt,
The pressure belt module includes a first roll in which the pressure roll is formed in a cylindrical shape, and a crown that is disposed inside the first roll and has an outer diameter at a central portion in an axial direction larger than both ends. An image forming apparatus comprising: a second roll formed in a shape. The pressure belt module is configured to be able to contact and separate from the rotating member,
The pressure roll of the pressure belt module includes an inner circumferential surface of the first roll and an outer circumferential surface of the second roll when the pressure belt module is installed apart from the rotating member. The image forming apparatus according to claim 17, wherein the two are in contact with each other over the entire area in the circumferential direction at the central portion in the axial direction.

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