JP2009109931A - Fixing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device having stable fixability over the whole region of a roller shaft direction. <P>SOLUTION: The fixing device 9 forms a fixing nip part N between a fixing roller 91 and a fixing belt 92, and includes two pressure pads of a hard pad 921 and a soft pad 922 on an inner peripheral face side of the fixing belt 92. The soft pad 922 is an elastic body, is positioned at the upstream side of a conveying direction of a recording material, and elastically deformed by pressure. The hard pad 921 is positioned at the downstream side of the conveying direction of the recording material, and is composed of a member of higher hardness than the soft pad 922. Furthermore, the surface hardness of the pad face of the soft pad 922 is low in a center part as compared with the end of the roller shaft direction. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fixing device used in an electrophotographic image forming apparatus such as a copying machine, a facsimile, and a printer. More specifically, the present invention relates to a fixing device in which an endless fixing belt is pressed against a fixing roller.

  An electrophotographic image forming apparatus includes a fixing device that fixes a toner image onto a recording sheet. In recent years, a fixing device using an endless belt as a fixing member has been proposed in order to reduce the heat capacity (energy saving, short warm-up) of the device. Further, among fixing devices using an endless belt, as in Patent Document 1, for example, an endless belt is provided on the pressure side, and a pressure pad serving as a pressure member is disposed inside the belt to fix the toner to the paper. A fixing device for forming a nip portion necessary for the above is disclosed.

In addition, the pressure pad of Patent Document 1 includes a soft pad made of a material with low hardness and a hard pad made of a material with high hardness. The hard pad is located on the exit side of the nip, making it easier to peel off the paper after fixing. On the other hand, the soft pad is located on the inlet side of the nip portion, and presses the fixing roller and elastically deforms to secure the width of the nip portion in the circumferential direction of the roller (hereinafter referred to as “nip width”) necessary for fixing. is doing.
Japanese Patent Laid-Open No. 2005-4126

  However, the conventional fixing device described above has the following problems. That is, in the fixing device, in order to maximize the advantage of the low heat capacity, the fixing roller is made thinner and smaller in diameter. When such a fixing roller is used, the fixing roller is bent by the pressing force from the endless belt on the pressure side. As a result, in the vicinity of the central portion in the roller axial direction, the nip width is narrower than that of the end portion, and uneven fixing occurs in the roller axial direction.

  The present invention has been made to solve the problems of the conventional fixing device described above. That is, an object of the present invention is to provide a fixing device having a stable fixing property over the entire roller axial direction.

  In order to solve this problem, a fixing device is provided so that it can be freely rotated by heating the rotating body, and press-contacting the heating rotating body to form a nip portion with the heating rotating body. A first pressure pad made of an elastic body, which is arranged along the axial direction of the heating rotator and presses the heating rotator from the inside of the belt member. And positioned downstream of the first pressure pad in the conveyance direction of the recording material, and arranged along the axial direction of the heating rotator, pressing the heating rotator from the inside of the belt member, and A second pressure pad made of a member having a hardness higher than that of the pressure pad, and the surface hardness of the first pressure pad is lower in the central portion than the end portion in the axial direction of the heating rotator. It is a feature.

  The fixing device of the present invention forms a nip portion between a heating rotator such as a fixing roller and a belt member pressed from the inside, and includes two pressure pads inside the belt member. . One is a first pressure pad that is located upstream in the conveyance direction of the recording material (that is, the inlet side of the nip portion) and elastically deforms when pressed, and the other is in the conveyance direction of the recording material. The second pressure pad is located on the downstream side (that is, on the outlet side of the nip portion) and has higher hardness than the first pressure pad.

  Among these, the first pressure pad forms a nip portion necessary for heat fixing by elastic deformation. Furthermore, the first pressure pad of the present invention has a lower surface hardness at the center than at the axial end of the heating rotator. That is, the central part of the first pressure pad is more easily elastically deformed than the end part. Therefore, even if the pressure on the central portion is reduced due to the curvature of the heating rotator, the nip width of the central portion is ensured. Therefore, the difference in the nip width in the axial direction of the roller is small, and the nip width is made uniform in the axial direction of the roller. As a result, stable fixability can be obtained over the entire roller axial direction.

  The surface hardness of the first pressure pad is preferably increased continuously from the central portion in the axial direction of the heating rotator toward the end portion. That is, by changing the surface hardness continuously, the boundary of the change in surface hardness is eliminated. Therefore, partial differences in gloss and fixing properties and occurrence of streak noise at the boundary of surface hardness are suppressed.

  Further, the surface hardness of the first pressure pad may be increased stepwise from the central portion in the axial direction of the heating rotator toward the end portion. That is, by changing the surface hardness stepwise, a pad having a predetermined surface hardness can be individually manufactured. For this reason, variations in parts can be suppressed in creating the soft pad.

  In the fixing device of the present invention, a concave portion having a concave shape is provided at the center portion in the axial direction of the heating rotator of the pressing surface of the second pressure pad to the heating rotator. Then better. That is, by providing a recess at the center of the second pressure pad, the pressing force is higher at the end than at the center. For this reason, the friction force is greater at the end than at the center, and the transport force near both ends is greater. Accordingly, a pulling force acts in the width direction of the belt member on the recording material passing through the nip portion, and paper wrinkles when passing through the nip portion are suppressed.

  According to the present invention, a fixing device having a stable fixing property over the entire roller axial direction is realized.

  DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments embodying a fixing device according to the present invention will be described below in detail with reference to the accompanying drawings. In this embodiment, the present invention is applied to a fixing device mounted on an electrophotographic image forming apparatus.

  The image forming apparatus 100 of this embodiment is a tandem color printer, and has four image forming units arranged in parallel as shown in FIG. Specifically, the image forming apparatus 100 of the present embodiment includes four color image forming units 1K, 1C, 1M, and 1Y. In addition, an exposure device 7, an intermediate transfer belt 8, a secondary transfer roller 50, and a fixing device 9 are provided. Each image forming unit forms a toner image of each color on the intermediate transfer belt 8. Each image forming unit corresponds to each color of black (K) for the image forming unit 1K, cyan (C) for the image forming unit 1C, magenta (M) for the image forming unit 1M, and yellow (Y) for the image forming unit 1Y. , 1Y, 1M, 1C, and 1K are arranged in this order from the upstream side in the rotation direction of the intermediate transfer belt 8 (the arrow direction in FIG. 1). The arrangement of the image forming units is not limited to the order shown in FIG.

  Further, as shown in FIG. 2, the image forming unit 1K is a rotating drum type electrophotographic photosensitive member, and includes a photosensitive drum 2 which is a negatively chargeable organic photoconductor (OPC). The photosensitive drum 2 rotates at a constant speed in the direction of the arrow in FIG. Further, around the photosensitive drum 2, a charging device 3, a developing device 4, a transfer device 5, and a cleaning device 6 are sequentially arranged along the rotation direction. An exposure area in which a latent image is formed is provided between the charging device 3 and the developing device 4. The other image forming units have the same configuration.

  Next, an image forming operation of the color printer 100 of this embodiment will be described. First, the surface of the photosensitive drum 2 is charged to −600 V by the charging bias of the charging device 3. Next, a latent image of the first page is formed in the exposure area. Next, the developing device 4 performs development with negatively charged toner, and a toner image of the first page is formed on the photosensitive drum 2. Next, the toner image of the first page is transferred onto the intermediate transfer belt 8 by the transfer device 5. That is, the toner on the photosensitive drum 2 is transferred to the intermediate transfer belt 8 by the plus bias of the transfer device 5. At this time, a part of the toner remains on the photosensitive drum 2 without being transferred and becomes a transfer residual toner. Then, the transfer residual toner is scraped and collected by the cleaning device 6.

  Such an operation is repeated for each image forming unit, and the toner images of the respective colors are superimposed on the intermediate transfer belt 8. A color image is formed on the intermediate transfer belt 8 by superimposing the four color toner images. This color image is transferred onto the recording paper by the secondary transfer roller 50. Then, the recording paper is output to the discharge tray via the fixing device 9.

  Next, the configuration of the fixing device 9 of this embodiment will be described with reference to FIG. The fixing device 9 includes a fixing roller 91, a fixing belt 92, a temperature sensor 93, guide members 94 and 94, and a conveyance roller pair 96. The fixing roller 91 has a built-in heater lamp 911 serving as a heat source. The number of heater lamps 911 is not limited to one and may be a plurality. In the fixing device 9, an endless fixing belt 92 is pressed against the fixing roller 91 to form a nip portion N, and the recording material passes through the nip portion N, whereby an unfixed image on the recording material is heated and fixed. The

  The fixing roller 91 has a metal core metal (aluminum, iron, etc.) with a thickness of 0.4 mm provided with an elastic layer such as silicon rubber, and further a coat layer such as PTFE or PFA provided thereon. Yes. The elastic layer is provided to improve the image quality. That is, when the elastic body layer is not provided, the unevenness due to the toner on the recording material (the unevenness is conspicuous in the color image) is crushed, and the image quality is deteriorated. By providing the elastic body, the elastic body layer adapts to the unevenness of the toner on the recording material to some extent, and image quality deterioration is suppressed. The coat layer is provided in order to obtain releasability from the toner.

  The metal core of the fixing roller 91 is radiantly heated by a heater lamp 911 such as a halogen lamp. Note that the heat source is not limited to the halogen lamp, and may be, for example, one that energizes a resistance heating element or one that uses electromagnetic induction.

  The fixing belt 92 is provided with a coating layer such as PTFE or PFA on the surface of a heat-resistant resin base material such as polyimide having a thickness of 200 μm. The coat layer is provided to obtain releasability from the toner.

  Further, in the region surrounded by the fixing belt 92, pressure pads 921 and 922 that are arranged in parallel in the width direction of the fixing roller 91 and are in pressure contact with the fixing roller 91 via the fixing belt 92, and the rotation of the fixing belt 92 The guide members 923A and 923B for guiding the movement, the sliding sheet 924 sandwiched between the fixing belt 92 and the pressure pads 921 and 922, and the pressure pads 921 and 922 are supported and fixed to non-rotation. And a support member 925.

  The support member 925 disposed in the fixing belt 92 is biased toward the fixing roller 91 by a biasing member such as a spring member or a cam mechanism. The pressure pads 921 and 922 press the fixing belt 92 as the support member 925 is biased. As a result, a nip portion N for heating and fixing an unfixed image is formed between the fixing belt 92 and the fixing roller 91. Note that the support member 925 may be provided with a pressure release mechanism and a pressure change mechanism as necessary.

  The pressure pad serving as the pressing member is positioned on the upstream side in the recording material conveyance direction (on the inlet side of the nip portion N) and on the downstream side in the recording material conveyance direction (on the outlet side of the nip portion N). The pressure pad 921 is configured to be configured. The pressure pad 922 is made of an elastic material such as silicon rubber (hereinafter, the pressure pad 922 is referred to as “soft pad 922”). On the other hand, the pressure pad 921 is made of a material harder than the pressure pad 922, such as a metal such as aluminum or SUS, or a heat-resistant resin such as PPS or PBT (hereinafter, the pressure pad 921 is referred to as “hard pad 921”). To do). On the other hand, details of the shape of each pad will be described later.

  FIG. 4 shows a state before the pressure pad is pressed ((a) in FIG. 4) and after the pressure pad ((b) in FIG. 4). In FIG. 4, the sliding sheet 924 is omitted.

  The soft pad 922 is supported by the hard pad 921. In the state before the press contact, as shown in FIG. 4A, the soft pad 922 is disposed so as to protrude toward the fixing roller 91 with respect to the hard pad 921. D1 in FIG. 4 indicates the protruding amount of the soft pad 922.

  In the state after the press contact, as shown in FIG. 4B, the soft pad 922 and the hard pad 921 press the fixing belt 91 with the fixing belt 92 interposed therebetween, whereby the nip portion N is formed. At this time, the protruding portion of the soft pad 922 is deformed and protrudes to the upstream side in the recording material conveyance direction. 4, D2 indicates the amount of protrusion of the soft pad 922, and Dnip indicates the width of the nip portion N (nip width).

  When the pressure pad serving as the pressing member is heavy, distortion of the elastic layer on the fixing roller 91 increases, resulting in durability deterioration such as rubber breakage. On the other hand, if the deformation of the elastic layer on the fixing roller 91 in the vicinity of the exit of the fixing nip N is small, the separation of the recording material from the fixing roller 91 on the image surface side is poor. Therefore, the soft pad 922 reduces the load on the elastic layer on the fixing roller 91, and secures the nip width necessary for fixing while having a low load. On the other hand, the hard pad 921 ensures the amount of deformation of the elastic layer on the fixing roller in the vicinity of the exit of the nip portion N necessary for separating the recording material.

  FIG. 5 shows the nip pressure distribution at the sheet passing center of the fixing belt 92. As shown in FIG. 5, the portion pressed by the soft pad 922 (portion from the entrance to the center of the nip portion N) is at a low pressure. On the other hand, the portion pressurized by the hard pad 921 (portion near the exit of the nip portion N) becomes high pressure.

  The sliding sheet 924 is a sheet member having a smooth surface such as polyimide, and is provided to reduce the frictional resistance between the pressure pad (hard pad 921, soft pad 922) and the fixing belt 92. As means for reducing the frictional resistance, in addition to the sliding sheet 924, a coating layer of heat-resistant resin such as PFA or PTFE is provided inside the fixing belt 92, or a low friction member such as a glass cloth sheet is disposed. You may do it.

  In the fixing device 9 of this embodiment, the fixing roller 91 is rotationally driven by a drive motor (not shown). By rotating the fixing roller 91, the fixing belt 92 also rotates following the fixing roller 91. As the fixing belt 92 rotates, the entire circumference is heated, and the entire circumference is heated to a predetermined temperature. When the recording material is conveyed to the nip portion N, the recording material is conveyed in the conveying direction (the arrow direction in FIG. 3) by the frictional force between the fixing roller 91 and the recording material, and is not fixed on the recording material. The image is heat-fixed.

  Next, details of the soft pad 922 will be described. As shown in FIG. 6, the soft pad 922 has a pad layer 922X that is an elastic body of silicon rubber on a base material 922Y that is a thin plate made of SUS. The surface of the pad layer 922X opposite to the surface in contact with the base material 922Y is a pressing surface (nip surface) to the fixing belt 92. Further, the pad layer 922X has end regions 922A and 922C located at both ends in the width direction of the fixing belt 92 and a center region 922B located at the center, and the surface hardness of the center region 922B is the end region 922A. , 922C is configured to be lower than the surface hardness.

  Specifically, the elastic member in the central region 922B is made of silicon rubber having a hardness of 5 degrees (JIS-A) with a thickness of 4 mm, and the surface hardness is 35 degrees (Asker C). On the other hand, the elastic members in the end regions 922A and 922C are made of silicon rubber having a hardness of 20 degrees (JIS-A) with a thickness of 4 mm, and the surface hardness is 42 degrees (Asker C). Note that the distance from the sheet passing center to the boundary of the surface hardness is set within a range of 50 mm to 90 mm.

  FIG. 7 shows the nip width distribution in the roller axis direction of the nip portion N formed by the soft pad 922. As shown in FIG. 7, in the case of a conventional soft pad (that is, a soft pad whose surface hardness is uniform in the roller axial direction), the load at the central portion in the roller axial direction is reduced due to the curvature of the fixing roller 91. Therefore, the nip width at the center is shorter than the end. On the other hand, in the case of the soft pad 922 of this embodiment, the center region 922B is softer than the end regions 922A and 922C and is easily deformed. Therefore, a decrease in the nip width of the central region 922B is suppressed, and a difference in nip width between the end regions 922A and 922C and the central region 922B is reduced. As a result, the nip width is made uniform in the direction of the roller axis, and the decrease in fixing performance is compensated.

[First application example]
The soft pad of the first application example is configured such that the surface hardness continuously changes from the central region to the end region. This is different from the embodiment in which the surface hardness is changed stepwise between the central region and the end region. The soft pad as in this application example is created, for example, by adjusting the concentration of the filler contained in the rubber material.

  FIG. 8 shows the surface hardness distribution in the roller axis direction of the soft pad of this application example. The soft pad of this application example has no change in surface hardness because the surface hardness continuously changes. That is, when the surface hardness is changed stepwise, as shown in FIG. 7, a step with a nip width occurs at the boundary portion. On the other hand, by continuously changing the surface hardness, the boundary of the surface hardness is eliminated, and the step of the nip width is eliminated. This solves the problem that the gloss and fixing properties are partially different, and the problem that stripe noise occurs at the boundary of the surface hardness.

[Second application example]
The soft pad of the second application example has a large number of regions from the central region to the end region, and the surface hardness thereof is configured to change in a plurality of stages. The surface hardness of each region is higher in the region closer to the edge. In this respect, the present embodiment is different from the embodiment configured by two regions of a central region and an end region. The soft pad as in this application example is created by, for example, creating each region individually and then combining them and arranging them linearly.

  FIG. 9 shows the surface hardness distribution in the roller axis direction of the soft pad of this application example. Since the surface hardness of the soft pad of this application example changes in a plurality of stages, the nip width can be made more uniform as compared with the embodiment in which the surface hardness changes only in one stage. In addition, in the creation of the soft pad, the variation between components can be suppressed as compared with the first application example that is continuously changed. Therefore, the fixing quality can be stabilized. Further, if each region can be removed, maintenance such as surface hardness adjustment can be facilitated.

[Third application example]
In the third application example, an indentation 921A having a concave shape as shown in FIG. 10 is provided on the nip surface of the hard pad 921. Specifically, the hard pad 921 has a pad layer 921X made of a material having a hardness higher than that of the soft pad 922 on the base material 921Y which is a thin plate made of SUS.

  Further, the pad layer 921X of the hard pad 921 is provided with a central recess 921A located at the center of the nip surface in the roller axial direction and a trench 921B engaged with the soft pad 922 and cut in the roller axial direction. ing. The depth of the central recess 921A in this application example is set within a range of 0.1 mm to 0.3 mm.

  The conveying speed of the recording material in the nip portion N is governed by a portion where the frictional force between the fixing roller 91 as a driving roller and the recording material becomes a peak. In this embodiment, the portion where the hard pad 921 abuts becomes the peak of the frictional force. If the peak value distribution of this frictional force is uniform in the axial direction of the roller, paper wrinkles are likely to occur on the recording material in the nip portion N.

  Since the hard pad 921 of this application example is provided with the center recess 921A, the end portion has a higher pressing force than the center portion. For this reason, the friction force is greater at the end than at the center, and the transport force near both ends is greater. Accordingly, a pulling force in the belt width direction acts on the fixing belt 92 or the recording material, and paper wrinkling when the recording material passes through the nip portion N is more positively suppressed.

  In addition, if the concave portion 921A is provided on the hard pad, the peak pressure at the center portion becomes lower than the peak pressure at the end portion, and there is a concern about variation in fixability. However, in this embodiment, the nip width can be widened by deformation of the central portion 922B of the soft pad 922. For this reason, it is possible to compensate for a decrease in the fixing property at the center. That is, the depth of the hollow 921A is adjusted by the balance between the suppression of paper wrinkles and the stabilization of fixing properties.

  As described in detail above, the fixing device 9 of this embodiment forms the nip portion N for fixing between the fixing roller 91 and the fixing belt 92, and the hard disk is formed on the inner peripheral surface side of the fixing belt 92. Two pressure pads, a pad 921 and a soft pad 922, are provided. The soft pad 922 is located on the upstream side in the recording material conveyance direction (that is, the inlet side of the nip portion N) and is elastically deformed by pressing, and the hard pad 921 is downstream in the recording material conveyance direction (that is, the recording material conveyance direction). , Located on the exit side of the nip portion N) and is made of a high hardness member.

  Among these, the soft pad 922 forms a nip portion N necessary for heat fixing by elastic deformation. Furthermore, the soft pad 922 has a surface hardness of the pad surface that is lower in the central portion 922B than in the end portions 922A and 922C in the roller axial direction. That is, the center portion 922B of the soft pad 922 is more easily elastically deformed than the end portions 922A and 922C. Therefore, even if the pressure on the central portion 922B is reduced due to the curvature of the fixing roller 91, the nip width of the central portion 922B is ensured. Therefore, the difference in the nip width in the roller axis direction is small, and the nip width is made uniform in the roller axis direction. As a result, stable fixability can be obtained over the entire roller axial direction. Therefore, a fixing device having a stable fixing property over the entire roller axial direction is realized.

  Note that this embodiment is merely an example, and does not limit the present invention. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof. For example, in the embodiment, the present invention is applied to a printer, but the present invention is not limited to this. That is, even a copying machine, scanner, FAX, word processor, or the like can be applied as long as it has a fixing device. Moreover, it is not limited to color but may be dedicated to monochrome images. Further, a tandem method or a four-cycle method may be used.

  In this embodiment, the fixing roller 91 forming the nip portion N has a built-in heat source and is directly heated. However, the present invention is not limited to this. For example, a configuration may be employed in which a heating roller having a heat source is brought into contact with the outer peripheral surface side of the fixing roller 91 and the fixing roller is heated from the outside. A heating roller having a heat source; a fixing roller opposed to the pressure-side fixing belt; and a heating-side fixing belt wound around the two rollers. Alternatively, the nip portion N may be formed.

1 is a schematic diagram illustrating a configuration of an image forming apparatus according to an embodiment. 1 is a schematic diagram illustrating a configuration of an image forming unit according to an embodiment. 1 is a schematic diagram illustrating a configuration of a fixing device according to an embodiment. It is the schematic which shows the state before pressure contact of a press pad, and after pressure contact. FIG. 6 is a conceptual diagram of a nip pressure distribution in a sheet passing direction at a center portion in a width direction of a fixing belt. It is the schematic which shows the structure of a soft pad. It is a conceptual diagram of nip width distribution of the roller axial direction in the nip part which a soft pad forms. It is a conceptual diagram of the surface hardness distribution of the roller axial direction in the soft pad of the 1st application example. It is a conceptual diagram of the surface hardness distribution of the roller axial direction in the soft pad of the 2nd application example. It is the schematic which shows the structure of the hard pad of the 3rd application example.

Explanation of symbols

9 Fixing device 91 Fixing roller (heated rotating body)
92 Fixing belt (belt member)
921 Hard pad (second pressure pad)
921A Central concave (dent)
922 Soft pad (first pressure pad)
922A end area 922B central area 922C end area 100 image forming apparatus

Claims (4)

A fixing device comprising: a heating rotator that is rotatably arranged; and an endless belt member that is press-contacted to the heating rotator, forms a nip portion with the heating rotator, and is rotatably arranged. In the device,
A first pressure pad that is arranged along the axial direction of the heating rotator, presses the heating rotator from the inside of the belt member, and is made of an elastic body;
It is located downstream of the first pressure pad in the recording material conveyance direction, and is arranged along the axial direction of the heating rotator, pressing the heating rotator from the inside of the belt member, and A second pressure pad made of a member having a hardness higher than that of the first pressure pad,
The fixing device according to claim 1, wherein a surface hardness of the first pressure pad is lower in a central portion than an end portion in an axial direction of the heating rotator. The fixing device according to claim 1,
The fixing device according to claim 1, wherein a surface hardness of the first pressure pad is continuously increased from a central portion in an axial direction of the heating rotator toward an end portion. The fixing device according to claim 1,
The fixing device according to claim 1, wherein the surface hardness of the first pressure pad increases stepwise from a central portion in the axial direction of the heating rotator toward an end portion. In the fixing device according to any one of claims 1 to 3,
A fixing device, wherein a concave portion having a concave shape is provided in a central portion of the pressing surface of the second pressure pad against the heating rotator in the axial direction of the heating rotator.

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