JP5831064B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a technique of a fixing device and an image forming apparatus.

  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 charged, and the photosensitive drum is controlled by light controlled based on image information. Exposure is performed 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 the toner image is transferred from the photosensitive drum to a recording medium such as recording paper, and then the toner image is fixed on the recording paper by a fixing device. Let Image formation is performed by such a process.

  In a conventional fixing device, a heating source is provided inside a cylindrical metal core, a heat-resistant elastic layer on the metal core, and a fixing roll formed by laminating a release layer on the outer peripheral surface; A pressure roll which is disposed in pressure contact with the fixing roll, and is formed by laminating a heat-resistant elastic body layer on a core metal and a release layer made of a heat-resistant resin film or a heat-resistant rubber film on an outer peripheral surface thereof. Some are configured. Then, a recording medium (recording paper) holding an unfixed toner image is passed between the fixing roll and the pressure roll, and the unfixed toner image is heated and pressed to thereby record the recording paper. The toner image is fixed to the toner image. Such a fixing device is called a roll nip method, a 2ROLL method, or a heating roll method, and is widely used in general.

  Further, for example, in Patent Documents 1 and 2, a rotatable fixing roll, an endless belt that can run while being in contact with the fixing roll, a pressure pad that is arranged in a non-rotating state inside the endless belt, A fixing device is disclosed in which a main portion is constituted by a sheet-like sliding member having a low frictional resistance between a pressure pad and an endless belt. In the fixing devices of Patent Documents 1 and 2, the endless belt is pressed against the fixing roll by the pressure pad, and a nip portion through which the recording medium (paper P) passes is formed between the endless belt and the fixing roll. Further, the nip portion on the exit side of the recording medium passing through the nip portion is locally deformed on the surface of the fixing roll.

  Nowadays, even with an electrophotographic image forming apparatus, it is possible to form an image quality close to printing, and it is required to be adapted to the market for light printing and graphic arts, and also has a high gloss. There is a demand to suppress the occurrence of image density unevenness in a high image density image on coated paper or the like.

Japanese Patent Application Laid-Open No. 11-133776 JP 2001-356625 A

  An object of the present invention is to provide a fixing device that suppresses occurrence of uneven image density in an image on a recording medium, and an image forming apparatus including the fixing device.

The invention according to claim 1 is disposed so as to face a rotatable rotating member, a belt member movable while being in contact with the rotating member, and the belt member facing the rotating member. A nip portion forming member that forms a nip portion through which a recording medium passes between the rotating member and the belt member by pressure contact; and a surface of the nip portion forming member that is opposite to the surface on the belt member side. A pressure member that pressurizes the nip portion forming member in the direction of the rotating member, and the pressure member is a shape changing member whose shape changes at a predetermined temperature or more, and the pressure member is , the belt member side surface of said nip forming member and is provided on the side opposite to a said shape changing member Ru Tei a plurality arranged in a width direction of the nip forming member, the shape-changing member Shape change More, a constant deposition apparatus pressure distribution in the width direction of the nip Ru is adjusted.

According to a second aspect of the present invention, a rotatable rotating member, a belt member movable while contacting the rotating member, and the belt member are arranged so as to face each other, and the belt member is disposed on the rotating member. A nip portion forming member that forms a nip portion through which a recording medium passes between the rotating member and the belt member by pressure contact; and a surface of the nip portion forming member that is opposite to the surface on the belt member side. A pressure member that pressurizes the nip portion forming member in the direction of the rotating member, and the pressure member is provided on the opposite surface side of the nip portion forming member, and the nip portion formation has a first pressing Ru Tei is arranged at the center in the width direction of the member, and a second pressure Ru Tei disposed at the end portion in the width direction of the nip formation member, the second pressure pressure part shape will change at a predetermined temperature or higher A shape changing member, the shape change of the shape-changing member, a constant deposition apparatus pressure Ru is adjusted at the end portion in the width direction of the nip portion.

According to a third aspect of the present invention, there is provided an image carrier, a charging unit for charging the surface of the image carrier, a latent image forming unit for forming a latent image on the charged surface of the image carrier, and developing the latent image. A developing unit that forms a toner image by developing with an agent, a transfer unit that transfers the toner image to a recording medium having an image receiving layer on at least a side in contact with the toner image, and the fixing device according to claim 1 or 2 . An image forming apparatus.

According to the first aspect of the present invention, the occurrence of uneven image density is suppressed in the image on the recording medium as compared with the case without this configuration.

According to the second aspect of the present invention, the occurrence of uneven image density is suppressed in the image on the recording medium as compared with the case without this configuration.

According to the third aspect of the present invention, the occurrence of image density unevenness in the image on the recording medium is suppressed as compared with the case without this configuration.

1 is a schematic configuration diagram illustrating an example of a configuration of an image forming apparatus according to an exemplary embodiment. 2 is a schematic side sectional view illustrating an example of a configuration of a fixing device used in the image forming apparatus according to the exemplary embodiment. FIG. FIG. 6 is a partial cross-sectional schematic diagram of the fixing device for explaining a state where a belt member is supported. 3 is a schematic cross-sectional view of a pressure member of the present embodiment showing a state before a sheet P passes through a nip portion N. FIG. 3 is a schematic cross-sectional view of a pressure member of the present embodiment showing a state in which a sheet P has continuously passed through a nip portion N. FIG. 3 is a schematic cross-sectional view of a normal pressure member showing a state in which a sheet P has passed through a nip portion N continuously. FIG. (A), (B) is a schematic cross section of the pressurization member for demonstrating the modification of a pressure pad pressurization member.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to this embodiment.

  FIG. 1 is a schematic configuration diagram illustrating an example of a configuration of an image forming apparatus according to the present embodiment. FIG. 1 shows an image forming apparatus 100 of an intermediate transfer type generally called a tandem type. The image forming apparatus 100 shown in FIG. 1 includes a plurality of image forming units 1Y, 1M, 1C, and 1K on which toner images of respective color components are formed by electrophotography, and the image forming units 1Y, 1M, 1C, and 1K. The primary transfer unit 10 that sequentially transfers (primary transfer) each color component toner image formed by the above process to the intermediate transfer belt 15 and the superimposed toner image transferred onto the intermediate transfer belt 15 as a recording medium (recording paper) P Are provided with a secondary transfer portion 20 that performs batch transfer (secondary transfer) 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 this embodiment, each of the image forming units 1Y, 1M, 1C, and 1K includes a charger 12 that charges the photosensitive drum 11 around the photosensitive drum 11 that rotates in the direction of arrow A, and a photosensitive drum. A laser exposure unit 13 for writing an electrostatic latent image on the image 11 (in FIG. 1, the exposure beam is indicated by a symbol Bm), and each color component toner is accommodated so that the electrostatic latent image on the photosensitive drum 11 can be transferred with the toner. A developing device 14 for visualizing, a primary transfer roll 16 for transferring each color component toner image formed on the photosensitive drum 11 to the intermediate transfer belt 15 in the primary transfer unit 10, and residual toner on the photosensitive drum 11. An electrophotographic device such as a drum cleaner 17 is removed in order. 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 which is an intermediate transfer member is constituted by a film endless belt (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. The volume resistivity of the intermediate transfer belt 15 is formed to be, for example, 10 ⁶ Ωcm or more and 10 ¹⁴ Ωcm or less, and the thickness thereof is, for example, about 0.1 mm. The intermediate transfer belt 15 is circulated and driven at a predetermined speed in the direction B shown in FIG. 1 by various rolls. In this embodiment, as 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 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 tension to the intermediate transfer belt 15 and prevents meandering of the intermediate transfer belt 15, and a backup provided in the secondary transfer unit 20. A roll 25 and a cleaning backup roll 34 provided in a cleaning unit that scrapes residual toner on the intermediate transfer belt 15 are provided.

In the present embodiment, 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 (not shown) and a sponge layer (not shown) as an elastic layer fixed around the shaft. The shaft is, for example, a cylindrical bar made of a metal such as iron or SUS. The sponge layer is made of, for example, a blend rubber of acrylonitrile-butadiene rubber (NBR), styrene-butadiene rubber (SBR), and ethylene-propylene-diene rubber (EPDM) containing a conductive agent such as carbon black, and has a volume resistivity. Is a sponge-like cylindrical roll of 10 ⁷ Ωcm or more and 10 ⁹ Ωcm or less. The primary transfer roll 16 is disposed in pressure contact with the photosensitive drum 11 with the intermediate transfer belt 15 interposed therebetween. Further, the primary transfer roll 16 has a polarity opposite to the toner charging polarity (negative polarity; the same applies hereinafter). A voltage (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.

In the present embodiment, the secondary transfer unit 20 includes a secondary transfer roll 22 disposed on the toner image holding surface side of the intermediate transfer belt 15 and a backup roll 25. The backup roll 25 includes, for example, an inner layer portion made of EPDM rubber and a tubular surface layer made of a blend rubber of EPDM and NBR in which carbon is dispersed. The surface resistivity is, for example, 10 ⁷ Ω / □ or more and 10 ¹⁰ Ω / □ or less, and the hardness is set to 70 ° (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. Yes.

In the present embodiment, the secondary transfer roll 22 includes a shaft (not shown) and a sponge layer (not shown) as an elastic layer fixed around the shaft. The shaft is, for example, a cylindrical bar made of a 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 blended with a conductive agent such as carbon black and having a volume resistivity of 10 ⁷ Ωcm or more and 10 ⁹ Ωcm or less. The secondary transfer roll 22 is placed 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 next transfer unit 20.

  Further, in this embodiment, residual toner and paper dust on the intermediate transfer belt 15 after the secondary transfer are removed downstream of the secondary transfer portion 20 of the intermediate transfer belt 15, and the surface of the intermediate transfer belt 15 is cleaned. An intermediate transfer belt cleaner 35 is provided so as to be contactable and separable. Further, in the present embodiment, a reference sensor (home position sensor) 42 that generates a reference signal for taking an image forming timing in each of the image forming units 1Y, 1M, 1C, and 1K on the upstream side of the yellow image forming unit 1Y. Is arranged. The reference sensor 42 recognizes a mark provided on the back side of the intermediate transfer belt 15 and generates a reference signal. In response to an instruction from the control unit 40 based on the recognition of the reference signal, each image forming unit 1Y, 1M, 1C, and 1K are configured to start image formation. Further, in the present embodiment, an image density sensor 43 for adjusting image quality is disposed on the downstream side of the black image forming unit 1K.

  Further, in the image forming apparatus 100 of the present embodiment, as a paper transport system, a paper tray 50 that stores the paper P, a pickup roll 51 that takes out and transports the paper P accumulated in the paper tray 50, and a pickup roll 51 A transport roll 52 that transports the paper P fed out by the transport roller 52, 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 100 according to the present embodiment will be described.

  In the image forming apparatus 100 as shown in FIG. 1, image data output from an image reading apparatus (IIT) (not shown), a personal computer (PC) (not shown) or the like is received by an image processing apparatus (IPS) ( After the image processing is performed by the image forming unit 1Y, 1M, 1C, 1K, the image forming operation is performed. Specifically, in the IPS, input reflectance data is subjected to predetermined image editing such as shading correction, position shift correction, brightness / color space conversion, gamma correction, frame deletion, color editing, moving editing, and the like. Image processing is performed. The image data that has been subjected to 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, for example, the photosensitive drum 11 of each of the image forming units 1Y, 1M, 1C, and 1K with an exposure beam Bm emitted from a semiconductor laser in accordance with the input color material gradation data. ing. 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 image is developed as a toner image of each color of Y, M, C, K by each image forming unit 1Y, 1M, 1C, 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 are in contact with each other. Transcribed. More specifically, in the primary transfer unit 10, a voltage (primary transfer bias) having a polarity opposite to the charging polarity (negative polarity) of the toner is applied to the base material of the intermediate transfer belt 15 by the primary transfer roll 16. Primary transfer is performed by sequentially superposing the toner images on the surface of the intermediate transfer belt 15.

  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 the registration roller (not shown) rotates in accordance with the movement timing of the intermediate transfer belt 15 on which the toner image is held. 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 held on the intermediate transfer belt 15 is pressed by the secondary transfer roll 22 and the backup roll 25 and is electrostatically transferred onto the paper P in a lump.

  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 with heat and pressure by the fixing device 60, as will be described later. 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 to 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 is cleaned by the cleaning backup roll 34 and the intermediate transfer belt cleaner 35. It is removed from the intermediate transfer belt 15.

  Next, the fixing device 60 used in the image forming apparatus 100 according to the present embodiment will be described.

  FIG. 2 is a schematic side sectional view showing an example of the configuration of the fixing device used in the image forming apparatus according to the present embodiment. The fixing device 60 includes a fixing roll 61 as an example of a rotating member, a belt member 62, a pressure pad 64 as an example of a nip part forming member that presses the belt member 62 against the fixing roll 61 to form a nip part, Pressure members that pressurize the pressure pad 64 in the direction of the fixing roll 61 from the surface opposite to the belt member 62 side of the pressure pad 64 (specifically, the pressure pad pressing member 641 and the pressure pad support member 642). ) And the main part.

  In the present embodiment, the fixing roll 61 is a cylindrical roll configured by laminating a heat-resistant elastic layer 612 and a release layer 613 around a metal core (cylindrical cored bar) 611 and is rotatable. It is supported and rotates at a predetermined surface speed (for example, 194 mm / sec). In the present embodiment, the fixing roll 61 is a so-called straight roll.

  Inside the fixing roll 61, for example, a halogen heater 66 having a rating of 600 W is disposed as a heat source. A temperature sensor 69 is disposed in contact with the surface of the fixing roll 61. The control unit 40 of the image forming apparatus controls lighting of the halogen heater 66 based on the temperature measurement value by the temperature sensor 69 so that the surface temperature of the fixing roll 61 maintains a predetermined set temperature (for example, 160 ° C.). It is adjusted to.

  In this embodiment, the belt member 62 includes a pressure pad 64 (specifically, an elastic pressure pad 64a and a high-rigidity pad 64b described later), a belt guide member 63, and a belt disposed inside the belt member 62. It is rotatably supported by edge guide members 80 (see FIG. 3 in the subsequent stage) arranged at both ends of the member 62. And it arrange | positions so that it may press-contact with the fixing roll 61 in the nip part N mentioned later, and it rotates (for example, 194 mm / sec) following the fixing roll 61.

  The belt member 62 of the present embodiment is preferably a seamless endless belt (endless belt) whose original shape is formed in a cylindrical shape so that defects due to the seam are not generated as much as possible in the output image. However, the belt may have a seam.

  The belt guide member 63 is attached to a holder 65 disposed inside the belt member 62 along the longitudinal direction. In the present embodiment, the belt guide member 63 is formed with a plurality of ribs (not shown) in the rotational direction of the belt member 62 so that the contact area with the inner peripheral surface of the belt member 62 is minimized. It is configured. Further, the belt guide member 63 is formed of a material having a low coefficient of friction so that the belt member 62 rotates smoothly, and a material having a low thermal conductivity so that it is difficult to remove heat from the belt member 62. . Specifically, a heat resistant resin such as tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) or polyphenylene sulfide (PPS) is used.

  The pressure pad 64 is disposed so as to be pressed against the fixing roll 61 via the belt member 62, and forms a nip portion N with the fixing roll 61. In the present embodiment, the pressure pad 64 includes an elastic pressure pad 64a and a high-rigidity pad 64b. The elastic pressure pad 64a is disposed on the recording medium inlet side of the nip portion N (hereinafter sometimes referred to as the recording medium upstream side), and ensures a wide nip portion N. Further, the high-rigidity pad 64b is disposed on the recording medium outlet side (hereinafter sometimes referred to as the recording medium downstream side) of the nip portion N, and locally presses the surface of the fixing roll 61 so as to contact the surface of the fixing roll 61. A down curl is formed on the paper P by giving distortion (dent).

  In the present embodiment, the pressure member includes a pressure pad pressure member 641 and a pressure pad support member 642. The pressure pad support member 642 is fixed to the surface of the elastic pressure pad 64a opposite to the surface on the belt member 62 side. The elastic pressure pad 64 a is supported by the metal holder 65 via the pressure pad support member 642 inside the belt member 62. Further, one end of the pressure pad pressurizing member 641 is fixed to the pressure pad support member 642 (the side opposite to the surface on the belt member 62 side of the elastic pressure pad 64a), and the other end of the pressure pad pressurizing member 641 is The pressure pad fixing member 643 is fixed. The pressure pad fixing member 643 is fixed to the holder 65.

  In the present embodiment, the pressurizing member is installed on the elastic pressure pad 64a side, but is not limited to this, and may be installed on the high-rigidity pad 64b side. 64b may be installed in both.

  In the present embodiment, the shape formed of the shape-changing material whose shape changes when the pressure pad pressing member 641 constituting the pressing member becomes equal to or higher than a predetermined temperature (hereinafter sometimes referred to as a shape recovery temperature). It is a changing member. However, in the present embodiment, both the pressure pad pressurizing member 641 and the pressure pad support member 642 constituting the pressurizing member may be a shape change member formed of a shape change material, and among the pressurization members The pressure pad support member 642 may be a shape change member formed of a shape change material.

  In the present embodiment, the contact surface of the elastic pressure pad 64a and the high-rigidity pad 64b with the belt member 62 has a low friction sliding in order to reduce the sliding resistance between the inner peripheral surface of the belt member 62 and the pressure pad 64. A sheet 68 may be provided. The form of the sliding member is not limited to a sheet shape, and is not particularly limited to a cylindrical shape.

  The sliding sheet 68 has an upstream end of the nip portion N fixed to the holder 65 by a sliding sheet fixing member 68a. In the present embodiment, the sliding sheet 68 is sandwiched between the pressure pad 64 (the elastic pressure pad 64a and the high-rigidity pad 64b) and the inner peripheral surface of the belt member 62 along the rotation direction of the belt member 62. Thus, the nip portion N is disposed over the entire area. Note that the downstream side of the recording medium at the nip portion N of the sliding sheet 68 is not fixed and is set to a free end (free) state so that the sliding sheet 68 is not distorted as much as possible. The sliding sheet 68 has a sliding resistance between the inner peripheral surface of the belt member 62 and the pressure pad 64 under a state in which a pressing force is applied between the pressure pad 64 and the fixing roll 61 at the nip portion N. (Friction resistance) is reduced.

  A lubricant application member 67 is disposed in the holder 65 along the longitudinal direction of the fixing device 60. The lubricant application member 67 is disposed so as to be in contact with the inner peripheral surface of the belt member 62 and supplies an appropriate amount of lubricant such as amino-modified silicone oil. Accordingly, the lubricant is supplied to the sliding portion between the belt member 62 and the sliding sheet 68, and the sliding resistance between the belt member 62 and the pressure pad 64 via the sliding sheet 68 is further reduced, so that the belt member 62 is smoothly rotated.

  As an auxiliary means for peeling the paper P, a peeling auxiliary member 70 may be provided on the downstream side of the recording medium in the nip portion N of the fixing roll 61. The peeling auxiliary member 70 is held by the holder 72 in a state in which the peeling baffle 71 is close to the fixing roll 61 in a direction (counter direction) opposite to the rotation direction of the fixing roll 61.

  Next, an example of a configuration for supporting the belt member 62 in the fixing device 60 will be described.

  FIG. 3 is a partial cross-sectional schematic diagram of the fixing device for explaining a state in which the belt member is supported. FIG. 3 shows one end region of the fixing device 60 viewed from the downstream side in the transport direction of the paper P. As shown in FIG. 3, edge guide members 80 are disposed at both ends of the holder 65 disposed inside the belt member 62. In the present embodiment, the edge guide member 80 includes a belt travel guide portion 801 having a cylindrical shape in which a notch is formed in a portion corresponding to the nip portion N and its vicinity, that is, a substantially C-shaped cross section, and the belt travel guide portion. A flange portion 802 provided outside the belt member 62 and having an outer diameter larger than the outer diameter of the belt member 62, and further provided outside the flange portion 802, positioning the edge guide member 80 on the fixing device 60 main body. And a holding portion 803 for fixing.

  At both ends of the belt member 62, the inner peripheral surfaces of both ends are supported by the outer peripheral surface of the belt traveling guide portion 801, and the belt member 62 rotates along the outer peripheral surface of the belt traveling guide portion 801. Therefore, the belt traveling guide portion 801 is preferably formed of a material having a small friction coefficient so that the belt member 62 rotates smoothly, and furthermore, the thermal conductivity is low so that heat is not easily taken from the belt member 62. It is preferable to form with a material.

  Further, the flange portion 802 is disposed such that inner surfaces of both flange portions 802 disposed so as to face each other at both end portions of the holder 65 have a distance substantially matching the width of the belt member 62. When the belt member 62 rotates, the end of the belt member 62 comes into contact with the inner surface of the flange portion 802, so that the belt member 62 is restricted from moving in the width direction (belt walk). In this way, the belt member 62 is supported by the edge guide member 80 so that the deviation is regulated.

  In the fixing device 60 having such a configuration, the fixing roll 61 is connected to a drive motor (not shown) and rotates in the direction of arrow C, and the belt member 62 also rotates in the same direction as the fixing roll 61 following this rotation. The sheet P on which the toner image is electrostatically transferred in the secondary transfer unit 20 of the image forming apparatus shown in FIG. 1 is guided by the fixing inlet guide 56 and conveyed to the nip N. When the paper P passes through the nip portion N, the toner image on the paper P is fixed by the pressure acting on the nip portion N and the heat supplied from the fixing roll 61. In the fixing device 60 of the present embodiment, the nip portion N is widened by the concave elastic pressure pad 64a that follows the outer peripheral surface of the fixing roll 61, and thus, for example, stable fixing performance is ensured. The paper P peeled off from the fixing roll 61 by the high-rigidity pad 64b is completely separated from the fixing roll 61 by the peeling auxiliary member 70 disposed on the recording medium downstream side of the nip portion N, and the discharging portion of the image forming apparatus. To the paper discharge path toward

  Next, the operation of the pressure member when the paper P passes through the nip portion N will be described.

  FIG. 4 is a schematic cross-sectional view of the pressure member of the present embodiment showing a state before the paper P passes through the nip portion N. As described above, in the present embodiment, the pressure pad support member 642 and the pressure pad pressurizing member 641 which is a shape changing member are disposed on the surface side of the elastic pressure pad 64a opposite to the surface on the belt member side. Yes. Further, as shown in FIG. 4, a plurality of pressure pad pressing members 641 (shape changing members) are arranged in the width direction of the elastic pressure pad 64a (the width direction of the passing paper P). Here, the pressure pad pressurizing member 641 will be described as a spring-like shape changing member that contracts when it reaches a predetermined temperature (shape recovery temperature) or higher. Further, as shown in FIG. 4, when the paper P passes through the nip portion N, the elastic pressure pad 64a receives heat from the fixing roll via the paper P and the elastic pressure pad 64a (and a belt member (not shown)). ) Transmitted to the elastic pressure pad 64a (and a belt member not shown) without passing through the paper P (hereinafter, sometimes referred to as a paper passing area) (hereinafter referred to as a paper passing area). Sometimes called a non-paper passing area).

  Before the paper P passes through the nip N, or when the plurality of papers P does not pass through the nip N continuously, heat is not supplied from the fixing roll to the elastic pressure pad 64a (via the belt member). Even if heat is supplied, the temperature of the elastic pressure pad 64a is lower than that when the paper P passes through the nip portion N continuously. Further, even if the temperature of the paper passing area of the elastic pressure pad 64a is compared with the temperature of the non-paper passing area of the elastic pressure pad 64a, there is no significant difference. In such a state, the elastic pressure pad 64a hardly expands.

  FIG. 5 is a schematic cross-sectional view of the pressure member of the present embodiment showing a state in which the paper P has passed through the nip portion N continuously. When a plurality of sheets P pass through the nip N continuously, heat from the fixing roll is transmitted to the elastic pressure pad 64a, and the temperature rises before the sheet P passes through the nip N. At this time, heat from the fixing roll is transmitted through the paper P (and the belt member) in the paper passing area of the elastic pressure pad 64a. On the other hand, in the non-sheet passing region of the elastic pressure pad 64a, heat from the fixing roll is transmitted without passing through the sheet P. Accordingly, the temperature of the non-sheet passing region of the elastic pressure pad 64a is higher than the temperature of the sheet passing region of the elastic pressure pad 64a. Therefore, as shown in FIG. It expands more thermally than the sheet passing area of the pad 64a. However, in the present embodiment, a spring-like shape changing member that contracts when the pressure recovery temperature becomes equal to or higher than the shape recovery temperature is used for the pressure pad pressing member 641, so that the heat of the elastic pressure pad 64 a The pressure pad pressurizing member 641 contracts when the temperature becomes equal to or higher than the shape recovery temperature. In other words, if the shape recovery temperature is the temperature of the non-sheet passing region of the elastic pressure pad 64a when the sheet P continuously passes through the nip portion N or around that temperature (for example, ± 10 ° C.), it is not allowed to pass. The spring-like shape changing member (pressure pad pressurizing member 641) disposed under the paper region contracts as the temperature of the non-paper passing region of the elastic pressure pad 64a increases. The elastic pressure pad 64a is deformed by being pulled by the contraction of the shape changing member (pressure pad pressing member 641). As described above, even if the non-sheet passing region of the elastic pressure pad 64a is thermally expanded, the shape changing member disposed below the non-sheet passing region contracts, and therefore the pressure increase in the nip portion N above the non-sheet passing region. Is suppressed. As a result, a decrease in the pressure at the nip portion N above the sheet passing region, in particular, the pressure at the end in the width direction of the nip portion N above the sheet passing region is suppressed. Therefore, in the present embodiment, the pressure difference of the nip portion N above the non-sheet passing area and above the sheet passing area is adjusted so as not to open as much as possible. As described above, even if the paper P is continuously passed, the pressure difference in the nip portion N is adjusted. For example, even when the paper P holding an image with a high image density is passed, image density unevenness occurs. Is suppressed.

  FIG. 6 is a schematic cross-sectional view of a normal pressure member showing a state in which the paper P has passed through the nip portion N continuously. The pressure pad pressurizing member 641a shown in FIG. 6 does not use the shape changing member described above, and is, for example, a metal member that does not shrink even at a predetermined temperature or higher. When a plurality of sheets P pass through the nip N continuously, as described above, the temperature of the non-sheet passing area of the elastic pressure pad 64a becomes higher than the temperature of the sheet passing area of the elastic pressure pad 64a. The non-sheet passing area of the pad 64a is more thermally expanded than the sheet passing area of the elastic pressure pad 64a. However, since the pressure pad pressing member 641a does not contract with the thermal expansion of the elastic pressure pad 64a, the pressure of the nip portion N above the non-sheet passing region is the pressure of the nip portion N above the sheet passing region. Increased compared to Due to the pressure increase at the nip N above the non-sheet passing area, the pressure at the nip N above the sheet passing area, particularly the pressure at the end in the width direction of the nip N above the sheet passing area decreases. Therefore, for example, when the paper P holding an image with a high image density is passed, image density unevenness may occur.

  As described above, in the present embodiment, both the pressure pad pressurizing member 641 and the pressure pad support member 642 constituting the pressurizing member may be a shape change member formed of a shape change material. Among them, the pressure pad support member 642 may be a shape change member formed of a shape change material. That is, since the pressure member formed of the shape change material reaches the shape recovery temperature and the shape of the pressure member changes, the pressure distribution in the nip formed by the pressure pad may be adjusted. For example, the pressure distribution of the nip portion may be adjusted by the pressure pad support member 642 formed of the shape changing member reaching the shape recovery temperature and changing the shape of the shape changing member.

  In the present embodiment, the fixing roll 61 is disposed on the side in contact with the unfixed toner, and the belt member 62 and the nip portion forming member (pressure pad 64) are disposed on the pressure side. It is not limited. For example, a heating source such as the halogen heater 66 is not disposed inside the fixing member such as the fixing roll 61 but may be a so-called external heating unit that heats from the outside, or a heating source is disposed on the belt member 62 side. Also good. Further, the belt member 62 may be disposed on the toner surface side on the recording medium and used as a fixing belt, and the fixing roll 61 may be used as a pressure roll.

  The shape changing member will be described below.

  In the present embodiment, a spring-like shape changing member having a shape recovery temperature set so that the pressure pad pressurizing member 641 contracts in accordance with the thermal expansion of the elastic pressure pad 64a is used. The shape recovery temperature is set according to the thermal expansion coefficient of the elastic pressure pad 64a, the thermal expansion coefficient and shape of the pressure pad support member 642, the temperature of the fixing roll 61, the number of sheets P passing through the nip portion N, and the like. However, it is not limited to the above. In addition, the shape of the shape change member of the present embodiment is described by taking a spring that contracts at a shape recovery temperature or higher as an example, but when the shape recovery temperature is reached, the shape change member changes shape and the nip portion The shape is not limited to the above as long as the pressure distribution of N is adjusted. For example, it may be a rod-like shape change member that bends in a square shape at a temperature higher than the shape change temperature.

  FIGS. 7A and 7B are schematic cross-sectional views of a pressure member for explaining a modification of the pressure pad pressure member. As shown in FIGS. 4 and 5, a plurality of pressure pad pressing members 641 (shape changing members) may be arranged in the width direction of the elastic pressure pad 64a, for example, or the pressure pad pressurizing member shown in FIG. One may be sufficient like the pressure member 641b (shape change member). In addition, as shown in FIGS. 4 and 5, a plurality of the pressure media are arranged along the width direction of the elastic pressure pad 64a in that the pressure in the width direction of the nip portion N is adjusted corresponding to all sizes of the recording medium. It is preferable. The pressure pad pressing member shown in FIG. 7B includes a first pressing unit 641c and a second pressing unit 641d. The first pressurizing unit 641c is disposed at the center in the width direction of the elastic pressure pad 64a. The second pressurizing part 641d is disposed at the end of the elastic pressure pad 64a in the width direction, and uses the shape changing member described above. Generally, since the heat from the fixing roll is transmitted to the elastic pressure pad 64a without passing through the paper P, the end portion in the width direction of the elastic pressure pad 64a is compared with the center portion in the width direction of the elastic pressure pad 64a. The temperature is high and thermal expansion is easy. Therefore, as shown in FIG. 7B, the second pressure member 641d disposed at the end in the width direction of the elastic pressure pad 64a is the above-described shape changing member, whereby the width direction of the elastic pressure pad 64a. Even when the end portion of the elastic pressure pad thermally expands, the second pressurizing portion 641d (shape changing member) contracts, so that an increase in pressure in the nip portion N above the end portion in the width direction of the elastic pressure pad is suppressed. As a result, the pressure drop in the nip portion N above the central portion in the width direction of the elastic pressure pad is suppressed. For example, when a sheet P holding an image with a high image density is passed, image density unevenness occurs. It can be suppressed. Here, the width of the central portion and the width of the end portion in the width direction of the elastic pressure pad are set by, for example, the size of the sheet P passing through, the temperature distribution in the width direction of the elastic pressure pad 64a, and the like.

  Examples of the shape change material for forming the shape change member include a shape memory alloy, a shape memory resin, and the like. In particular, a shape memory alloy is preferable from the viewpoint of strength and the like. Shape memory alloys include non-ferrous alloys such as Ni-Ti alloys, Ni-Al alloys, Cu-Zn-Al alloys, Cu-Al-Ni alloys, and Fe-Ni-Co-Ti alloys. , Fe-Mn-Si alloys, Fe-Ni-C alloys, Fe-Ni-Cr alloys, and other iron alloys. The shape memory material is preferably a two-element shape memory alloy such as a Ni—Ti alloy from the viewpoint of mechanical properties such as shape recovery temperature, strength, and fatigue resistance.

  In the present embodiment, the case where the shape changing member (pressure pad pressing member 641) described above is installed on the elastic pressure pad 64a side is described. However, the shape changing member (pressure pad pressing member 641) is a high-rigidity pad. The image unevenness can also be suppressed by setting the pressure at the nip portion above the high-rigidity pad 64b by installing it at 64b. That is, the shape changing member (pressure pad pressurizing member 641) described above may be installed on the pressure pad 64, and may be installed on at least one of the elastic pressure pad 64a and the high-rigidity pad 64b. That's fine.

  A Ni-Ti alloy (a two-element shape memory alloy) has a crystal structure called an austenite phase at a temperature higher than the shape recovery temperature, and when this is cooled, it transforms into a martensite phase. Since this martensite phase is easily deformed by an external force, the crystal structure changes to a deformed martensite phase if it is deformed in advance. When this is heated to a certain temperature, the structure returns to the crystal structure of the austenite phase, so that the shape of the Ni—Ti alloy returns to the original shape. For example, the shape recovery temperature of the Ni—Ti alloy is set to a temperature at which the pressure pad 64 thermally expands and image unevenness occurs. Then, the length of the Ni—Ti alloy in the martensite phase is elongated from the length of the Ni—Ti alloy in the austenite phase. As a result, the Ni—Ti alloy (pressure pad pressing member 641) contracts when it reaches a temperature at which image unevenness occurs, so that image unevenness is effectively prevented as described above. The shape recovery temperature of the Ni—Ti alloy is generally 20 ° C. or higher and 100 ° C. or lower. The temperature at which image unevenness occurs is approximately 70 ° C. or higher and 100 ° C. or lower. Therefore, by adjusting the shape recovery temperature of the Ni—Ti alloy to about 70 ° C. or more and 100 ° C. or less, the shape memory is adapted to the thermal expansion difference between the non-sheet passing region and the sheet passing region of the pressure pad 64. The alloy is shrunk.

  The manufacturing method of shape memory alloys, such as a Ni-Ti type alloy, is not specifically limited, A well-known method is used. The shape memory temperature of the shape memory alloy is adjusted by changing the ratio of each metal in the alloy.

  Hereinafter, other members constituting the fixing device 60 will be described.

  First, the core 611 of the fixing roll 61 is formed of, for example, a metal or alloy having high thermal conductivity such as iron, aluminum (for example, A-5052 material), SUS, or copper, ceramics, or FRM (fiber reinforced metal). . The outer diameter of the core 611 is, for example, in the range of φ15 mm to 30 mm, and the thickness varies depending on the material of the core 611, but in the case of aluminum, for example, in the range of about 1 mm to 3 mm, and in the case of SUS or iron, for example, 0.4 mm or more The range is about 1.8 mm or less and about 0.4 mm or more and 1.5 mm or less.

  The material of the heat resistant elastic layer 612 of the fixing roll 61 may be any material as long as it is an elastic body having high heat resistance. In particular, it is preferable to use an elastic body such as rubber or elastomer having a rubber hardness of about 15 ° to 45 ° (JIS-A). Specifically, silicone rubber, fluorine rubber or the like is used. Of these, silicone rubber is preferred because it has a low surface tension and is excellent in elasticity. Examples of such silicone rubbers include RTV (room temperature vulcanization type) silicone rubber and HTV (high temperature vulcanization type) silicone rubber. Specific examples include polydimethyl silicone rubber (MQ) and methyl vinyl silicone. Examples thereof include rubber (VMQ), methylphenyl silicone rubber (PMQ), and fluorosilicone rubber (FVMQ). In the fixing device 60 of the present embodiment, for example, an HTV silicone rubber having a rubber hardness of 35 ° (JIS-A) is coated on the core 611 with a thickness of 600 μm. The thickness of the heat resistant elastic layer 612 is, for example, 3 mm or less, preferably in the range of 0.1 mm to 1.5 mm. There is no restriction | limiting in particular as a method to form in the surface of the core 611 of the heat-resistant elastic layer 612, For example, a well-known coating method, shaping | molding, etc. are employ | adopted.

  Any material may be used for the release layer 613 formed on the outer peripheral surface of the heat resistant elastic layer 612 as long as it is a heat resistant resin. For example, a silicone resin, a fluororesin, or the like is used. In particular, a fluororesin is preferable from the viewpoints of releasability of the release layer 613 with respect to the toner, wear resistance, and the like. Examples of the fluororesin include PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), PTFE (polytetrafluoroethylene), FEP (tetrafluoroethylene-hexafluoropropylene copolymer), and composite materials thereof. Also, those obtained by blending such resins with fillers such as carbon, alumina, and barium sulfate are used. The thickness of the release layer 613 is preferably in the range of 5 μm to 50 μm, more preferably 10 μm to 40 μm.

  The belt member 62 is a seamless endless belt (endless belt) that is formed in a cylindrical shape having an original shape in a range of, for example, a diameter of 15 mm or more and 40 mm or less so that defects caused by the seam are not generated in the output image as much as possible. preferable. The belt member includes, for example, a base layer and a release layer coated on the surface or both surfaces of the base layer on the fixing roll 61 side. The material for the base layer is not particularly limited and is usually selected appropriately from various known resin materials and the like. For example, polymers such as polyimide, polyamide, and polyimideamide are used. The thickness of the base layer is, for example, in the range of 30 μm to 200 μm, preferably in the range of 40 μm to 125 μm, and more preferably in the range of 50 μm to 100 μm. As the material for the release layer coated on the surface of the base layer, for example, a fluororesin is used. Examples of the fluororesin include tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and composite materials thereof. Moreover, what mix | blended fillers, such as carbon, an alumina, and barium sulfate, with those resin is mentioned. The thickness of the release layer is, for example, in the range of 5 μm to 100 μm, preferably 10 μm to 40 μm.

  For the elastic pressure pad 64 a constituting the pressure pad 64, for example, an elastic body such as silicone rubber or fluorine rubber, a leaf spring, or the like is used, and the surface on the fixing roll 61 side is a concave shape that substantially follows the outer peripheral surface of the fixing roll 61. It is formed with a curved surface.

  The high-rigidity pad 64b constituting the pressure pad 64 is, for example, PPS (polyphenylene sulfide), polyimide, polyester, polyamide or other heat-resistant resin, a material obtained by adding glass fiber or the like to these resins, or iron, It is made of a highly rigid material such as a metal such as aluminum or SUS. As the shape of the high-rigidity pad 64b, for example, the outer surface shape at the nip portion N is formed as a convex curved surface having a constant radius of curvature.

  The pressure pad support member 642 is preferably made of a material and a shape that can support the elastic pressure pad 64a (and the high-rigidity pad 64b) and that can be deformed to some extent, such as thin PPS (polyphenylene sulfide). Heat-resistant resin or a thin metal material is used.

  The pressure pad fixing member 643 is preferably a material that is assembled to the holder 65 and has enough rigidity to fix the pressure pad pressing member 641. For example, a metal material such as SUS or aluminum, A heat-resistant resin such as thick PPS (polyphenylene sulfide) is used.

  Since the sliding sheet 68 is provided mainly to reduce the sliding resistance (friction resistance) between the inner peripheral surface of the belt member 62 and the pressure pad 64, the sliding surface has a small coefficient of friction, wear resistance and heat resistance. A material excellent in properties is preferred. Examples of the sliding sheet 68 include a sintered molded PTFE resin sheet, a glass fiber sheet impregnated with a fluororesin, and a laminated sheet in which a film sheet made of a fluororesin is heat-fused onto a glass fiber and sandwiched.

  Further, as described above, since the belt guide member 63 is rubbed against the inner peripheral surface of the belt member 62, the belt guide member 63 is made of a material having a low coefficient of friction and a low thermal conductivity that makes it difficult to remove heat from the belt member 62. preferable. Examples of the material of the belt guide member 63 include heat resistant resins such as PFA and PPS.

  DESCRIPTION OF SYMBOLS 10 Primary transfer part, 11 Photosensitive drum, 12 Charging device, 13 Laser exposure device, 14 Developer, 15 Intermediate transfer belt, 16 Primary transfer roll, 17 Drum cleaner, 20 Secondary transfer part, 22 Secondary transfer roll, 25 Backup roll, 26 Power supply roll, 31 Drive roll, 32 Support roll, 33 Tension roll, 34 Cleaning backup roll, 35 Intermediate transfer belt cleaner, 40 Control unit, 42 Reference sensor, 43 Image density sensor, 50 Paper tray, 51 Pickup roll , 52 transport roll, 53 transport chute, 55 transport belt, 56 fixing inlet guide, 60 fixing device, 61 fixing roll, 62 belt member, 63 belt guide member, 64 pressure pad, 64a elastic pressure pad, 64b high rigidity pad, 65 Ho 66, halogen heater, 67 lubricant application member, 68 sliding sheet, 68a sliding sheet fixing member, 69 temperature sensor, 70 peeling auxiliary member, 71 peeling baffle, 72 holder, 80 edge guide member, 100 image forming apparatus, 611 Core, 612 Heat resistant elastic layer, 613 Release layer, 641 Pressure pad pressing member, 641a, 641b Pressure pad pressing member, 641c First pressing portion, 641d Second pressing portion, 642 Pressure pad support member, 643 Pressure pad fixing member, 801 Belt running guide part, 802 flange part, 803 holding part.

Claims (3)

A rotatable rotating member, a belt member movable while contacting the rotating member, and disposed so as to face each other via the belt member, and the rotating member and the rotating member are brought into pressure contact with the rotating member. A nip portion forming member for forming a nip portion through which a recording medium passes between the nip portion forming member and the belt member, and a surface of the nip portion forming member opposite to the belt member side surface in the direction of the rotating member. A pressure member that pressurizes the part forming member,
The pressure member is a shape change member whose shape changes at a predetermined temperature or higher,
The pressing member, the belt member side surface of said nip forming member and is provided on the side opposite to a plurality arranged in a width direction of the nip forming member located in said shape-changing member Ru Tei The fixing device is characterized in that the pressure distribution in the width direction of the nip portion is adjusted by the shape change of the shape change member. A rotatable rotating member, a belt member movable while contacting the rotating member, and disposed so as to face each other via the belt member, and the rotating member and the rotating member are brought into pressure contact with the rotating member. A nip portion forming member for forming a nip portion through which a recording medium passes between the nip portion forming member and the belt member, and a surface of the nip portion forming member opposite to the belt member side surface in the direction of the rotating member. A pressure member that pressurizes the part forming member,
Said pressure member is provided on the side of the opposite side of the nip formation member, a first pressure Ru Tei is arranged at the center in the width direction of the nip forming member, the nip disposed at the end portion in the width direction of the forming member and a second pressing Ru Tei, a,
The second pressurizing part is a shape changing member whose shape changes at a predetermined temperature or higher, and the pressure at the end in the width direction of the nip part is adjusted by the shape change of the shape changing member. A fixing device characterized. An image carrier, a charging unit for charging the surface of the image carrier, a latent image forming unit for forming a latent image on the charged surface of the image carrier, and developing the latent image with a developer to form a toner image 3. An image, comprising: a developing unit that performs transfer; a transfer unit that transfers the toner image to a recording medium having an image receiving layer on at least a side in contact with the toner image; and a fixing device according to claim 1. Forming equipment.