JP4770453B2 - Fixing device and image forming apparatus using the same - Google Patents

Description

  The present invention relates to a fixing device that heats and fixes an unfixed toner image formed on a recording material using an electrophotographic method or an electrostatic recording method, and more particularly to a fixing device that uses an endless fixing belt. .

2. Description of the Related Art Conventionally, in a copying machine or printer using an electrophotographic system or the like, a heat and pressure roll is used as a fixing method for making an unfixed toner image formed and supported on a recording material by a transfer system or a direct system into a permanent image. Type fixing devices have been widely used.
In this heating and pressure roll method, the pressure roller pair of the heating roller and the pressure roller is rotated with each other so that the recording material carrying the unfixed toner image passes through the fixing nip region which is the mutual pressure contact portion of the roller pair. By doing so, the toner image is fixed by heat and pressure on the recording material.

In the fixing device using such a heating and pressing roll method, since one or both elastic layers of the heating roll and the pressing roll are distorted to form a fixing nip region, a fixing nip region exceeding a required amount is provided. In order to form, the elastic layer of one or both of a heating roll and a pressure roll must be formed relatively thick, and the pressing force between both rolls must be increased.
This results in an increase in the thickness of the elastic layer and the core (core metal) and an increase in the heat capacity of the heating roll, and the time until the heating roll rises to the fixable temperature, that is, the warm-up time, increases on the contrary. There is a problem.

In order to solve such a problem, a belt fixing method using an endless belt has been proposed (see Patent Document 1).
In this method, a heat-resistant endless belt (fixing belt) is sandwiched between a heating roll (fixing roll) and a fixedly arranged pressing member to form a fixing nip region, and the pressing member is located upstream of the fixing nip region. A pre-nip member and a downstream peeling nip member are used to secure the fixing performance to the recording material and the peeling performance by pressing at two locations (so-called free belt nip method).

Japanese Patent Laying-Open No. 2005-257968 (Embodiment 1, FIG. 2)

At this time, as the peeling nip member, those having the same shape in the longitudinal direction (direction along the axial direction of the fixing roll) are usually used. In general, in the case where the fixing nip component is supported at both ends in the axial direction, the fixing nip pressure at the central portion in the axial direction tends to drop compared to the supported ends due to deflection due to pressure and expansion due to heat. As a result, in the axial direction, generally, the central part has a weak tendency to peel off, and both ends have a tendency to deteriorate the curl. Therefore, if the pressing force is increased in order to prioritize peeling, the surface pressure is more likely to increase at both ends, and curling is likely to occur on both sides of the recording material that has passed through the peeling nip region. If an attempt is made to lower the pressing force in order to prioritize, the surface pressure at the central portion is more likely to decrease, and the peeling performance is lowered.
Also, in order to prioritize the release performance of the recording material, the shape of the release nip member is changed taking into account deflection and thermal expansion, and the convex shape toward the fixing roll side at room temperature and in a single product state (in the axial direction of the fixing roll) If the curved shape of the central part is convex to the fixing roll side), curling of the recording material will be generated, and conversely if the concave curved shape is used, the curling will be improved but the peeling performance will deteriorate. To come. As described above, since the recording material peeling performance and the curl suppressing performance in the peeling nip region are contradictory to each other, it is difficult to realize a peeling nip member that sufficiently satisfies both.

  The present invention has been made to solve the above technical problem, and in a fixing device of a belt fixing system including a fixing roll and a fixing belt, the recording material of the recording material is maintained while maintaining a stable recording material peeling performance. This prevents deformation and maintains high-quality fixing for a wide variety of recording materials over the long term.

  That is, as shown in FIG. 1, the basic configuration of the present invention is a rotatable fixing roll 1 having an elastic layer 1a, a heating source 2 for heating at least the fixing roll 1, and a fixing roll 1 that is in pressure contact with the fixing roll 1. An endless fixing belt 3 that rolls together with the roll 1 to sandwich and convey the recording material 4, and is disposed in contact with the back surface of the fixing belt 3 in the fixing nip region between the fixing roll 1 and the fixing belt 3 and the fixing roll 1. The fixing pad 5 is disposed on the upstream side of the fixing nip region and has a small nip pressure, and the high pressure pad is disposed on the downstream side of the fixing nip region and has a large nip pressure. The high-pressure pad portion 5b is provided at the substantially central portion in the longitudinal direction and the peeling promoting portion 6 for peeling the recording material 4 from the fixing roll 1 and the recording material 4 at both longitudinal ends. Mosquito It is characterized in that it comprises a curl regulating portion 7 to regulate the Le deformation. The peeling promoting part 6 and the curl regulating part 7 are provided continuously on the high-pressure pad part 5b and form a nip surface 8 that presses the fixing roll 1 side.

As an aspect of the reference invention related to the present invention , as shown in FIG. 2A, the nip surface 8 reference line of the high-pressure pad portion 5b and the outer peripheral tangent L0 of the fixing roll 1 at the nip surface 8 inlet position. Is defined as the biting angle θ, the curling angle θ of the peeling promoting portion 6 corresponding to the substantially central portion in the longitudinal direction of the high-pressure pad portion 5b is curl regulation corresponding to both longitudinal ends of the high-pressure pad portion 5b. It is characterized by being set to be larger than the part 7. Here, the nip surface 8 reference line means a line connecting the inlet and the outlet along the recording material conveyance direction in the separation promoting unit 6 and the curl regulating unit 7 with a straight line.

In such technical means, the fixing roll 1 only needs to have an elastic layer 1a and can be elastically deformed. For example, a release layer such as a fluorine-based resin layer may be provided on the surface of the elastic layer 1a.
The fixing belt 3 may have any heat resistance, and resin-based and metal-based materials are used, but a resin-based material is preferable from the viewpoint of improving thermal efficiency at the time of fixing.
Further, the low pressure pad portion 5a constitutes a preheating portion with a low pressure upstream of the fixing nip region, and the high pressure pad portion 5b constitutes a main fixing portion with a high pressure downstream of the fixing nip region. And the low-pressure pad part 5a and the high-pressure pad part 5b may be comprised integrally, and may be a divided | segmented aspect.

Then, by increasing the biting angle (hereinafter abbreviated as an appropriate angle) θ at the peeling promoting portion 6, the entrance side of the nip surface 8 is in the direction of biting into the fixing roll 1 side, and so-called corner hitting occurs. Therefore, the peeling promoting portion 6 having a large angle θ acts to push the recording material 4 toward the fixing roll 1, and the recording material 4 is easily deformed into a convex shape, and the downstream side of the recording material 4 is separated from the fixing roll 1. Head in the direction. As a result, the peeling action at the peeling promoting portion 6 is promoted .

Further, the nip surface 8 is preferably set so as to go from the peeling promoting portion 6 along the curl restricting portion 7 in the direction of the outer peripheral tangent L0 of the fixing roll 1. The curl performance can be further improved.
Furthermore, it is preferable that the difference in angle θ between the peeling promoting portion 6 and the curl regulating portion 7 on the nip surface 8 is set within 6 °. If the difference in the angle θ is larger than this, the difference in load on the recording material 4 between the peeling promoting portion 6 and the curl restricting portion 7 becomes too large, and the peeling performance and the curling performance are deteriorated at least at any part. It becomes like this.
Here, the solid line in FIG. 2A shows the case where the flat nip surface 8 is arranged in parallel with the outer peripheral tangent L0, and the broken line shows the case where the flat nip surface 8 is bitten into the fixing roll 1 side. In this way, the nip surface 8 is digged in, so that the peeling action of the recording material 4 can be strengthened. In the drawing, the fixing belt 3 is omitted, but this is because the nip surface 8 presses the fixing roll 1 via the fixing belt 3, and therefore it is determined that the fixing belt 3 is unnecessary in the description.

As an aspect of the present invention , as shown in FIG. 2B, the nip surface 8 reference line (indicated by L1 in the figure) of the high-pressure pad portion 5b and the outer periphery of the fixing roll 1 at the nip surface 8 inlet position. When the angle formed with the tangent L0 is defined as the biting angle θ and the protruding shape of the nip surface 8 toward the fixing roll 1 is expressed as a curvature , the peeling promoting portion 6 corresponding to the substantially central portion in the longitudinal direction of the high-pressure pad portion 5b . The biting angle θ is equal to or smaller than the biting angle θ of the curl restricting portion 7 corresponding to both longitudinal ends of the high-pressure pad portion 5b, and the curvature of the peeling promoting portion 6 is set larger than that of the curl restricting portion 7.

  In such an embodiment, the nip surface 8 is fixed to the fixing roll when the curvature radius is smaller (larger curvature) as shown by the broken line than when the curvature radius is larger (the curvature is smaller) as shown by the solid line in the figure. The nip surface 8 acts more strongly in the direction of peeling the recording material 4 from the fixing roll 1 side. On the other hand, when the radius of curvature is increased (decreasing the curvature), the peeling action is weakened and the deformation of the recording material 4 can be suppressed. In the figure, the angle θ is assumed to be 0 ° (the same direction as the outer peripheral tangent L0 of the fixing roll 1).

In this embodiment, it is preferable that the nip surface 8 is set so that the curvature continuously changes along the curl regulating portion 7 from the peeling promoting portion 6, and thus continuously changes. By doing so, the load on the recording material 4 is reduced, and the occurrence of curling can be further prevented.
Further, at this time, the difference in angle θ between the peeling promoting portion 6 and the curl regulating portion 7 on the nip surface 8 is within 6 °, the curvature radius of the peeling promoting portion 6 is 3 to 15 mm, and the curvature radius of the curling regulating portion 7 is. Is preferably set to 30 to 110 mm. According to this, both the peeling performance and the curling performance can be maintained satisfactorily. If the difference in the angle θ and the radius of curvature exceed this range, the peeling performance at the peeling accelerating portion 6 is lowered, or the peeling action becomes too strong, resulting in excessive deformation of the recording material 4. It becomes like this. Further, the curl performance at the curl restricting portion 7 is lowered.

In the aspect of the reference invention related to the present invention and the aspect of the present invention , the nip surface 8 has a component along the outer peripheral tangential direction of the fixing roll 1 at the entrance position of the nip surface 8 from the peeling promoting portion 6. It is preferable to set the number to increase toward the curl restricting portion 7, and by increasing the component in the tangential direction from the peeling promoting portion 6 along the curl restricting portion 7, the nip surface 8 moves toward the fixing roll 1. The amount of biting (corresponding to the biting angle θ) is suppressed, the deformation of the recording material 4 in particular on both ends can be prevented, and curling can be suppressed.
In the present invention, it is preferable that the fixing nip width in the fixing nip region is set to be substantially the same from the center portion to both ends, and by making the fixing nip width the same across the entire fixing pad 5. The passing time of the recording material 4 passing through this region is equal in the width direction of the recording material 4, and the fixing performance becomes uniform. This is particularly effective for high gloss images.

Further, it is preferable that the nip surface 8 is set so that the angle θ continuously changes along the curl restricting portion 7 from the peeling promoting portion 6, and the recording material can be changed by continuously changing the angle θ. The load on 4 is reduced, and the occurrence of curling can be further prevented. Note that “continuous” means, for example, that the change may be temporarily stopped in the middle, and may be anything that exhibits a continuous change as a whole.
Furthermore, the nip surface 8 is preferably composed of an elastic body whose hardness is higher than the hardness of the elastic layer 1a and the low-pressure pad portion 5a of the fixing roll 1. Thus, by configuring the nip surface 8 with an elastic body, it is possible to sufficiently cope with changes in the paper thickness and the like, and the followability to the fixing roll 1 in the fixing nip region is improved. Here, the nip surface 8 includes a member constituting the nip surface 8.
The nip surface 8 is preferably composed of a glass-reinforced liquid crystal polymer or a heat-resistant resin, and the liquid crystal polymer has good moldability to an elongated material such as the nip surface 8 and also has heat resistance. There are features. Moreover, as a typical example of a heat resistant resin, as a resin material, tetrafluoroethylene resin and PES with good moldability can be given. Also in this case, the heat radiation from the nip surface 8 can be reduced. Examples of the liquid crystal polymer include DuPont Xenite 3226L, and examples of the resin material include NTN BEAREE FL series.

Further, when the present invention is expressed from the viewpoint of the recording material 4 discharged from the fixing nip region , as shown in FIGS. 3A and 3B, the recording material 4 discharged from the fixing nip region is discharged. As the direction approaches the fixing roll 1 from the central portion of the leading edge of the recording material 4 along both end portions, a component toward the outer peripheral tangential direction of the fixing roll 1 at the entrance position of the nip surface 8 of the high-pressure pad portion 5b increases. It is set to.
As described above, the both end portions of the discharged recording material 4 are directed in the tangential direction, so that curling at both ends can be suppressed.

  Furthermore, the present invention is intended not only for the fixing device described above but also for an image forming apparatus. In this case, an image carrier that carries a toner image and a toner image on the image carrier are recorded on the recording material. 4 and a fixing device for fixing the unfixed toner image transferred onto the recording material 4, and the fixing device described above may be disposed as the fixing device.

  According to the basic configuration of the present invention, a fixing roll having an elastic layer, a fixing belt, and a fixing roller disposed in contact with the back surface of the fixing belt in a fixing nip region between the fixing roll and the fixing belt and pressing the fixing roll. In the so-called free belt nip system having a pad, the fixing pad is disposed on the upstream side of the fixing nip region and has a low nip pressure, and is disposed on the downstream side of the fixing nip region and includes a nip pressure. The high-pressure pad portion is provided at a substantially central portion in the longitudinal direction and is provided with a peeling promoting portion for peeling the recording material from the fixing roll, and is provided at both ends in the longitudinal direction and is subjected to curl deformation of the recording material. The curl restricting section that regulates the image quality ensures a good fixing action in the fixing nip area, and also ensures that the recording material that has passed through the fixing nip area has a peeling performance and curl performance. De become spread, allowing good fixation to a wide variety of recording materials.

In the present invention , the angle formed between the nip surface reference line of the high-pressure pad portion and the outer peripheral tangent of the fixing roll at the nip surface entrance position is defined as the biting angle, and the protruding shape of the nip surface to the fixing roll side Is expressed as the curvature angle of the peeling promoting portion is equal to or less than the biting angle of the curl regulating portion and the curvature of the peeling promoting portion is set larger than that of the curling regulating portion, in particular, the peeling performance is secured and the curling performance is also good. Fixation is made.

  Further, when the present invention is viewed from the discharging direction of the recording material discharged from the fixing nip region, the fixing roller approaches the fixing roll along the both ends from the center of the leading edge of the recording material and at the entrance position of the nip surface. Since the component toward the outer circumferential tangent direction is set to increase, the latitude between the peeling performance and the curling performance of the recording material that has passed through the fixing nip region between the fixing roll and the fixing belt is widened.

  Furthermore, by using such a fixing device as an image forming apparatus, the latitude of the peeling performance and curling performance of various recording materials is widened, and image formation with stable fixing performance over a long period of time is realized. become able to.

Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.
Embodiment 1
FIG. 4 shows a first embodiment of an image forming apparatus to which a reference invention related to the present invention is applied. In the figure, the image forming apparatus of the present embodiment is provided with an apparatus main body 10 having an image forming unit 20 capable of forming a color image, and an image reading unit 11 for reading a document on the upper part of the apparatus main body 10. At the same time, a document feeding device 12 for feeding a document to the image reading unit 11 is disposed above, while a multi-stage feed for supplying paper as a recording material is provided below the image forming unit 20 of the apparatus body 10. The paper cassettes 51 to 53 are arranged so that they can be pulled out.

  The image forming unit 20 used in the present embodiment employs, for example, an electrophotographic system, and includes four colors of yellow (Y color), magenta (M color), cyan (C color), and black (K color). This is a so-called tandem configuration in which the color image forming units 21 (21 a to 21 d) are arranged in parallel on the intermediate transfer belt 30. Therefore, the toner images of the respective colors formed by the respective image forming units 21 (21a to 21d) are sequentially primary-transferred and multiplexed on the intermediate transfer belt 30, and the multiplexed toner images are secondary-transfer device 35. Are collectively transferred onto the sheet conveyed from the sheet feeding cassettes 51 to 53 and guided to the fixing device 40. The color arrangement of the four-color image forming units 21 is not limited to this order, and may be in other orders.

  The image forming unit 21 (21a to 21d) in the present embodiment includes a photosensitive drum 22 that forms and supports each color component toner image, a charging device 23 such as a charging roll that charges the photosensitive drum 22, and a charged photosensitive member. A laser exposure device 24 that forms a latent image on the photosensitive drum 22, a developing device 25 that visualizes the electrostatic latent image on the photosensitive drum 22, and a toner image on the photosensitive drum 22 are primarily transferred onto the intermediate transfer belt 30. For example, a primary transfer device 26 including a primary transfer roll and a cleaning device 27 for cleaning residual toner remaining on the photosensitive drum 22 are configured. In the present embodiment, the laser exposure device 24 exposes the entire four-color image forming unit 21 with one laser exposure device 24.

  Further, the intermediate transfer belt 30 is stretched around a plurality of stretching rolls 31 to 33, and is circulated and conveyed using, for example, the stretching roll 31 as a driving roll. For example, a secondary transfer device 35 including a secondary transfer roll. However, the tension roll 33 is disposed opposite to the backup roll. Further, a belt cleaning device 36 for removing residual toner on the intermediate transfer belt 30 is disposed at a position facing the tension roll 32 of the intermediate transfer belt 30.

Here, the paper transport system in the present embodiment is as follows. A vertical conveyance path 61 extending substantially vertically upward from each of the paper feed cassettes 51 to 53, a main conveyance path 62 extending substantially horizontally on the downstream side of the vertical conveyance path 61, and substantially in the vicinity of the most downstream of the main conveyance path 62. A retreat conveyance path 63 extending downward in a Y shape and a reversal conveyance path 64 extending substantially horizontally from the retreat conveyance path 63 and leading to the vertical conveyance path 61 are configured.
In the main conveyance path 62, a registration roll 54 that regulates the positioning of the paper, a secondary transfer device 35 that collectively transfers the toner images multiplexed on the intermediate transfer belt 30, and a paper on which the toner images are collectively transferred. A conveying belt 55 that conveys the toner, a fixing device 40 that fixes the toner image on the sheet, a discharge roll 56 that discharges the sheet to a discharge tray 57 that is provided on the side of the apparatus main body 10 and stores the discharged sheet are provided. . In these conveyance paths 61 to 64, conveyance members such as a conveyance roll and a conveyance guide for ensuring the conveyance of the paper are appropriately disposed.

In particular, the fixing device 40 of the present embodiment is as shown in FIG. In the drawing, a fixing roll 41 having a heating source 42 such as a halogen lamp inside, an endless belt 43 that rolls with the fixing roll 41 and sandwiches and conveys paper, and a back surface side of the endless belt 43 are arranged in contact with each other. A fixing pad 46 that forms a fixing nip region n is provided between the fixing roll 41 and the endless belt 43. The fixing pad 46 in the present embodiment is configured in a state where it is divided into a pressing pad 46a as a low-pressure pad portion disposed on the upstream side and a fixed pad 46b as a high-pressure pad portion disposed on the downstream side. The fixing nip width is the same from the center of the fixing pad 46 to both ends.
The pressing pad 46 a and the fixed pad 46 b are supported by a rigid support body 44 having a recess, and press the fixing roll 41 from the back side of the endless belt 43 via the endless belt 43.
Further, a belt traveling guide 45 made of, for example, a rigid and low thermal conductive resin is provided below the rigid support 44 to smoothly rotate the endless belt 43.

  A temperature sensor 49 for measuring the surface temperature of the fixing roll 41 is disposed around the fixing roll 41, and the temperature sensor 49 allows the surface temperature of the fixing roll 41 to reach a predetermined temperature. Temperature control is performed. The temperature sensor 49 is not particularly limited as long as it can measure the surface temperature of the fixing roll 41. For example, a temperature sensitive element such as a thermistor or a posistor can be used.

Further, at a position facing the fixing roll 41 on the downstream side of the fixing nip area n, a peeling auxiliary member 48 for preventing the paper discharged from the fixing nip area n from adhering to the fixing roll 41 is provided. The separation assisting member 48 is, for example, a guide 48a fixed to the frame of the fixing device 40 and the guide 48a. The separation assisting member 48 is disposed in the axial direction of the fixing roll 41 so that the front end of the fixing roll 41 is close to the separation roller 48. It consists of an auxiliary sheet 48b. As the peeling assist sheet 48b, a heat resistant resin sheet such as polyimide resin, polyamide resin, or polyamideimide resin, or a metal thin plate such as stainless steel or steel can be used.
Furthermore, the surface of the peeling assist sheet 48b may be covered with a fluorine-based resin such as PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer). By covering with the fluorine-based resin, the frictional force with the paper is also reduced, and the life of the peeling assisting sheet 48b can be extended.

The fixing roll 41 in this embodiment includes a cylindrical core 41a made of metal such as aluminum having excellent mechanical strength and good thermal conductivity, and an elastic layer such as silicone rubber formed on the surface of the core 41a. 41b and a release layer 41c that covers the surface of the elastic layer 41b and is provided to prevent the offset of the unfixed toner image on the paper.
Here, the material of the core 41a is not particularly limited as long as it has mechanical strength and good thermal conductivity, and may be a metal or an alloy such as stainless steel, steel, or brass.
Further, the elastic layer 41b is not limited to silicone rubber, and may be, for example, fluorine rubber as long as it has heat resistance. The method of forming the elastic layer 41b on the surface of the core 41a is not particularly limited, An injection molding method or a coating method can be employed.
Further, the release layer 41c may be any material that has heat resistance and appropriate release properties for the toner. For example, fluorine rubber or fluorine resin is used.
Furthermore, the heating source 42 in the fixing roll 41 is not particularly limited as long as it has a shape and structure that can be accommodated in the core 41a, and may be appropriately selected according to the purpose.

On the other hand, the endless belt 43 may have a single layer structure, but in the present embodiment, a belt having a laminated structure in which a release layer is provided on the surface of the substrate is used.
As the base material of the endless belt 43, if it has heat resistance, for example, a resin base material such as thermosetting polyimide, thermoplastic polyimide, polyamide, polyamide imide, or a metal base material such as stainless steel, nickel, copper alloy is used. It is done. Further, the release layer preferably has good releasability of the toner adhering to the surface, and examples of the material include PTFE (polytetrafluoroethylene) and PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer). ) And FEP (tetrafluoroethylene-hexafluoropropylene copolymer).

Next, the fixing pad 46 in the present embodiment will be described in detail.
The upstream pressure pad 46a is formed of an elastic material such as silicone rubber, and forms a pre-nip region of the fixing nip region between the fixing roll 41 and the endless belt 43, and stably fixes an unfixed toner image on the paper. It is supposed to be. In order to keep the frictional resistance with the endless belt 43 small and to make the rotation of the endless belt 43 smoother on the surface of the pressing pad 46a, for example, a low friction sheet made of a fluorine resin sheet is provided by adhesion or the like. But it doesn't matter. Examples of the low friction sheet include fluorine resin sheets such as PTFE and PFA from the viewpoint of workability and low friction. Further, a glass fiber as a substrate and impregnated with fluorine resin or bonded with a fluorine resin sheet may be used.

  On the other hand, the fixed pad 46b mainly forms a post nip region (peeling nip region) between the fixing roll 41 and the endless belt 43, and has a higher pressure distribution than the pre-nip region. For example, aluminum, stainless steel, Highly rigid materials such as metals, alloys such as steel, copper, brass, and resin materials are mainly used. In this embodiment, a glass-reinforced liquid crystal polymer (Zenite manufactured by DuPont) is used. Therefore, it is possible to realize the fixed pad 46b having a stable and appropriate rigidity along the nip width direction in the peeling nip region.

In particular, the fixed pad 46b has a shape as shown in FIGS. 6A and 6B, and only the angle (corresponding to the biting angle) of the nip surface (pressing surface) 462 of the fixed pad 46b changes. It has become a form. 6A and 6B show the shape from the center portion to the end portion of the fixed pad 46b. FIG. 6A is a view as seen from the sheet conveying direction, and FIG. It is a cross-sectional view. In FIG. 6A, only half of the fixed pad 46b is shown.
In the present embodiment, a straight line L2 extending in the paper conveyance direction from the ridge line 461 at the entrance (upstream side) of the fixed pad 46b along the nip surface 462 of the fixed pad 46b and the outer peripheral tangent line L0 (shown by a virtual line) of the fixing roll. Is set so as to gradually change the angle θ from the longitudinal center portion to the end portion of the fixed pad 46b. That is, in the present embodiment, the fixed pad 46b is attached as shown in FIG. 2A, and the angle θ gradually decreases from the central portion along the end portion. Note that the width of the nip surface 462 is the same from the center to the end.

Next, the operation in the present embodiment will be described first with reference to FIG. 4 focusing on the sheet conveyance system of the image forming apparatus.
The sheet sent out from any of the sheet feeding cassettes 51 to 53 advances along the vertical conveyance path 61, is positioned and regulated by a registration roll 54 provided on the main conveyance path 62, and then proceeds to the secondary transfer device 35. .
On the other hand, the color toner images transferred onto the intermediate transfer belt 30 by the image forming engine 21 (21 a to 21 d) are conveyed on the intermediate transfer belt 30 and reach the secondary transfer device 35.
Then, in the secondary transfer device 35, the multiplexed toner images on the intermediate transfer belt 30 are collectively transferred onto the paper. The sheet on which the toner images are collectively transferred is conveyed by the conveying belt 55 and reaches the fixing device 40. Then, after the toner image is fixed by the fixing device 40, the toner image proceeds on the main conveyance path 62 and is discharged from the discharge roll 56 to the discharge tray 57.

  Here, when performing double-sided recording on a sheet, the sheet that has been fixed by the fixing device 40 is temporarily retreated from the main conveyance path 62 to the retreat conveyance path 63 side. Then, after sufficiently proceeding through the retreat conveyance path 63, when the rear end of the sheet exceeds the entrance of the reversal conveyance path 64, a predetermined conveyance roll in the retreat conveyance path 63 performs a reversing operation, and The sheet is reversed and conveyed to the reverse conveyance path 64 side. The reversely transported sheet is transported again to the main transport path 62 with the front and back sides of the sheet reversed, and a new toner image is formed. Thereafter, the toner is discharged from the fixing device 40 to the discharge tray 57 through the discharge roll 56.

The operation of the fixing device 40 in such a paper transport system will be described with reference to FIGS.
When the sheet onto which the toner images are batch-transferred is inserted into the fixing device 40, the sheet is sufficiently conveyed by the fixing roll 41 while being nipped and conveyed between the fixing roll 41 and the endless belt 43 in the pre-nip region formed by the pressing pad 46a. Stable fixing can be achieved with a sufficient temperature and sufficient pressure.
Further, in the fixed pad 46b of the present embodiment, the function is shared in the longitudinal direction, and the angle θ (corresponding to the biting angle) of the nip surface 462 is increased in the central portion of the fixed pad 46b. As the curling control part suppresses curl deformation of the paper because the angle θ of the nip surface 462 is reduced at the end part (both ends), the peeling action is weakened. Become functional.

  Now, assuming that a normal fixed pad (for example, a nip having a constant angle in the longitudinal direction) is used, the paper shape after the peeling nip is toner at the center as shown in FIG. The sheet is pulled toward the fixing roll 41 due to the adhesive force to the fixing roll 41, and the peeling action is insufficient. On the other hand, at the end portion, the sheet tends to be held down by the peeling action. Therefore, the discharged paper has a large convex portion at the center, and curls at both ends are likely to occur.

In the present embodiment, as shown in FIG. 7A, the sheet immediately after passing through the separation nip area by the fixed pad 46b is peeled from the fixing roll 41 by the shape effect of the fixed pad 46b. The both ends are slightly lifted to the fixing roll 41 side.
Therefore, both ends are directed upward from the central portion of the paper, while the central portion of the paper is pulled toward the fixing roll 41 by the adhesive force of the toner to the fixing roll 41, so that the overall shape approaches a flat shape and is peeled off. Will be done well and curl at both ends will be suppressed.
Further, at this time, if the nip surfaces 462 at both ends of the fixed pad 46b are made substantially parallel to the tangential direction of the fixing roll 41, further curling performance can be secured.

  As described above, in this embodiment, the curling performance of the paper after passing through the fixing nip region can be improved, and the latitude of paper curling and paper peeling is increased, so that various papers can be used. Also, a stable fixing operation can be performed.

In the present embodiment, the pressing pad 46a and the fixed pad 46b are supported by the single rigid support body 44. For example, as shown in FIG. 8, the rigid support body 44 has only the fixed pad 46b. The pressing pad 46a may be supported by a supporting member 47 having a spring 47a between the pressing pad 46a and the rigid support body 44.
Even if it does in this way, while being able to show | play the effect similar to the fixing pad 46 mentioned above, it becomes easier to adjust the pressing force of the press pad 46a.

Embodiment 2
FIG. 9 shows a fixed pad 46b used in the fixing device according to the second embodiment used in the image forming apparatus to which the present invention is applied. Note that other configurations of the image forming apparatus and the fixing apparatus are the same as those in the first embodiment, and thus description thereof is omitted here.

In the figure, the fixing pad 46b in the present embodiment mainly emphasizes the sheet peeling performance, and the angle θ extends from the center to the end of the nip surface 462 of the fixing pad 46b. The curvature (curvature radius) is changed together. Therefore, the radius of curvature gradually increases from the radius of curvature Rc at the center toward the radius of curvature Re at the end, and straight lines L3 and L4 (corresponding to the nip surface reference line) connecting the respective inlet and outlet sides. ) Differs from the outer peripheral tangential direction (L0 direction) of the fixing roll 41, and the angle θ4 at the end is slightly larger than the angle θ3 at the center. That is, the angle θ slightly biting into the fixing roll 41 side from the central portion to the end portion is slightly increased. Needless to say, the difference between the angle θ3 and the angle θ4 is set within 6 °.
In the present embodiment, by changing the angle θ and the curvature (curvature radius) in this way, the nip surface 462 of the fixed pad 46b has more components in the tangential direction (L0 direction) at the end than at the center. ing.

  In this embodiment, since the fixed pad 46b has such a shape, the paper shape after the peeling nip region is substantially the same as that in the first embodiment as shown in FIG. become. This is because the small radius of curvature Rc at the center causes the sheet to move away from the fixing roll 41 in the center after the peeling nip region, and is easily peeled off from the fixing roll 41. On the other hand, at both ends, the paper follows the shape of the edge, and as a result, the paper is discharged from the peeling nip region in a shape with little deformation. Therefore, the curling performance can be ensured together with the paper peeling performance, and the same effect as in the first embodiment can be obtained.

In this example, peeling performance and curl performance in several fixed pad shapes (angle and radius of curvature as shape parameters) were evaluated and confirmed along the above-described embodiment.
As shown in FIG. 10, the shape of the fixed pad was evaluated by expressing the angle of the nip surface as an angle α (unit: °) and the curvature shape as a curvature radius β (unit: mm). The length of the fixed pad was 30 cm, the angle at the center was α (0), the radius of curvature was β (0), the angle at the end was α (15), and the radius of curvature was β (15). Furthermore, α (10) and β (10) are shown at 10 cm from the center. Further, a flat shape having a very large radius of curvature is represented as Flat, and the others are represented by R numerical values (unit: mm).

Each shape parameter was as follows.
In Example 1 and Example 2, the nip surface of the fixed pad is formed in a flat shape as in Embodiment 1, and the angle is changed from the central part to the end part so as to go in the tangential direction. In Example 2, the change in angle was more relaxed.
Moreover, Example 3 and Example 4 change the curvature radius when the change of the angle of a nip surface is made equal similarly to Embodiment 2, and the direction of Example 4 is the end part of Example 3 rather than Example 3. The radius of curvature is increased.
Further, in this example, for comparison, a case where the nip surface is flat and the angle is constant, such as a conventional fixed pad, was also evaluated at the same time.
As for the evaluation method, excluding 5 mm from the four edges of the paper, the peel performance evaluation chart of 100% black toner is fixed, and the trend of the paper after passing through the nip area is visually judged. The paper after fixing was placed on a surface plate, and the curl of the four corners in particular was judged visually. The paper was passed through A4 vertical and horizontal. Further, the evaluation was made into four grades: A: No problem at all, O: No problem, Δ: Slight occurrence was confirmed or the performance stability was slightly inferior, but there was no problem in practical use, x: Problem.

As a result, as shown in FIG. 11, in Example 1 and Example 2, it was confirmed that the curl performance was sufficiently ensured, and that the peel performance was higher than the level at which there was no practical problem. Moreover, in Example 3 and Example 4, it was confirmed that the peeling performance is sufficiently secured, and the curl performance is obtained at a level that is not problematic in practical use. In particular, it was found that Example 1 is preferable when focusing on curl performance, while Example 4 is preferable when focusing on peeling performance.
Furthermore, it was found that the conventional fixed pad as a comparative example could not obtain the peeling performance.
From the above results, the effectiveness of the present invention was confirmed.

FIG. 2 is an explanatory diagram showing an outline of a fixing device according to the present invention. (A) is a situation when the angle of the nip surface of the high pressure pad portion in the reference invention related to the present invention is changed, and (b) is a case where the curvature of the nip surface of the high pressure pad portion is changed in the present invention. Shows the situation. (A) (b) is explanatory drawing which shows the outline | summary at the time of seeing this invention from the recording material discharged | emitted from a fixing nip area. 1 is an explanatory diagram showing Embodiment 1 of an image forming apparatus to which a reference invention related to the present invention is applied. FIG. FIG. 2 is an explanatory diagram illustrating a fixing device according to a first embodiment. (A) (b) is explanatory drawing which shows the outline | summary of the fixed pad of Embodiment 1. FIG. (A) shows the paper shape discharged | emitted after the peeling nip of Embodiment 1, (b) is explanatory drawing which shows the paper shape after the peeling nip by the conventional fixed pad. FIG. 10 is an explanatory diagram illustrating a modification of the fixing device according to the first embodiment. It is explanatory drawing which shows the fixing pad of the fixing device which concerns on Embodiment 2 to which this invention was applied . It is explanatory drawing which shows the shape parameter of the fixed pad used in an Example. It is a table | surface which shows the result of an Example.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Fixing roll, 1a ... Elastic layer, 2 ... Heat source, 3 ... Fixing belt, 4 ... Recording material, 5 ... Fixing pad, 5a ... Low pressure pad part, 5b ... High pressure pad part, 6 ... Peeling promotion part, 7 ... Curling restriction part, 8 ... Nip surface

Claims (10)

A rotatable fixing roll having an elastic layer;
A heating source for heating at least the fixing roll;
An endless fixing belt that is pressed against the fixing roll and rolls together with the fixing roll to sandwich and convey the recording material;
A fixing pad disposed in contact with the back surface of the fixing belt at a fixing nip region between the fixing roll and the fixing belt and pressing the fixing roll;
The fixing pad has a low-pressure pad portion disposed on the upstream side of the fixing nip region and having a small nip pressure, and a high-pressure pad portion disposed on the downstream side of the fixing nip region and having a large nip pressure.
High pressure pad portion defines a nip surface reference line of the high pressure pad portion and the angle of bite angle of the outer peripheral tangent line of the fixing roll in the nip plane entrance position, the protruding shape of the fixing roll side of the nip plane When describing the curvature, the biting angle at the substantially central portion in the longitudinal direction of the high-pressure pad portion is equal to or smaller than the biting angle at both longitudinal end portions of the high-pressure pad portion, and the curvature at the substantially central portion in the longitudinal direction is larger than both longitudinal end portions. a fixing device characterized in that is obtained by setting. The fixing device according to claim 1.
The high-pressure pad portion is characterized in that a substantially central portion in the longitudinal direction is a peeling promoting portion that peels the recording material from the fixing roll, and both end portions in the longitudinal direction are curl regulating portions that restrict curl deformation of the recording material. Fixing device. The fixing device according to claim 1 or 2,
Nip surface of the high pressure pad portion, the component along a direction tangent to an outer circumference of the fixing roll at the entrance position of the nip plane is set from the substantially longitudinal center portion to be larger toward the longitudinal ends A fixing device characterized by the above. The fixing device according to claim 1 or 2,
The fixing nip width of the fixing nip area is set to be substantially the same width from the substantially central portion in the longitudinal direction to both ends in the longitudinal direction of the high-pressure pad portion . The fixing device according to claim 1 or 2,
The fixing device according to claim 1, wherein the nip surface of the high-pressure pad portion is set so that the biting angle continuously changes from the substantially central portion in the longitudinal direction along both end portions in the longitudinal direction . The fixing device according to claim 1 or 2 ,
The fixing device according to claim 1, wherein the nip surface of the high-pressure pad portion is set so that the curvature continuously changes from the substantially central portion in the longitudinal direction along both end portions in the longitudinal direction . The fixing device according to claim 6 .
The difference angle between the nip surface of the pressure pad portion substantially longitudinal center portion and the longitudinal ends is within 6 °, the longitudinal substantially central portion radius of curvature 3~15mm and the longitudinal ends a fixing device of curvature radius of parts is characterized in that it is set to 30～110Mm. The fixing device according to claim 1 or 2,
The fixing device according to claim 1, wherein the nip surface of the high-pressure pad portion is composed of an elastic body having a hardness higher than that of the elastic layer of the fixing roll and the low-pressure nip portion. The fixing device according to claim 1 or 2,
The nip surface of the high pressure pad portion, a fixing device, characterized in that it is constituted by a liquid crystal polymer or heat-resistant resin glass reinforced. An image carrier for carrying a toner image;
A transfer member for transferring the toner image on the image carrier onto a recording material;
An image forming apparatus, comprising a fixing device according to claim 1 or 2, wherein fixing an unfixed toner image transferred on the recording material.

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