JP2007086530A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device using a belt member, wherein high fixing performance can be maintained for a long time by preventing wear of a fixing roller due to a peeling member that adversely affects the fixing performance, and to provide an image forming apparatus. <P>SOLUTION: The fixing device includes: a fixing belt module having a fixing belt 610; and a pressure roll 62 disposed in press-contact with the fixing belt module. A separation pad 64 is disposed near a fixing roll 611 in the downstream area of a nip section where the fixing belt module and the pressure roll 62 are disposed in press-contact with each other. The separation pad 64 is formed such that a slide contact piece 64B is removably attached to a pad main body 64A and the slide contact face 64a of the slide contact piece 64B is in contact with the fixing roll 611. The slide contact piece 64B is made of a fluorocarbon resin or the like. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fixing device used in an image forming apparatus using, for example, an electrophotographic method, and more particularly to a fixing device including a rotating belt member.

  In an image forming apparatus such as a copying machine or a printer using an electrophotographic system, image formation is performed as follows. First, for example, the surface of a photosensitive member (photosensitive drum) formed in a drum shape is uniformly charged by a charging device. The charged photosensitive drum is scanned and exposed with light controlled based on the image information, and an electrostatic latent image is formed on the surface thereof. Subsequently, the electrostatic latent image formed on the photosensitive drum is made a visible image (toner image) by the developing device, and then the toner image is conveyed to the transfer unit along with the rotation of the photosensitive drum to be recorded. It is electrostatically transferred onto the paper. The toner image carried on the recording paper is subjected to a fixing process by a fixing device to complete the image.

  As a fixing device used in such an image forming apparatus, a configuration called a two-roll system is widely used. This two-roll type fixing device includes a fixing roll formed by laminating a heat-resistant elastic layer and a release layer on the surface of a cylindrical core bar in which a heating source (heater) is disposed; A pressure roll formed by laminating a heat-resistant elastic layer and a release layer made of a heat-resistant resin film or a heat-resistant rubber film on a metal core is configured to be in pressure contact with each other. Then, the recording sheet carrying the unfixed toner image is passed through the pressure contact area (nip portion) between the fixing roll and the pressure roll, and the toner image is heated and pressed against the unfixed toner image. Is firmly established.

By the way, in recent years, high productivity and colorization have rapidly progressed in image forming apparatuses, and many apparatuses having a double-sided printing mechanism have become widespread. Therefore, it is necessary to further cope with the high speed in the fixing device mounted on the image forming apparatus.
However, the conventional two-roll type fixing device has a problem that it is difficult to perform a sufficient fixing process on a large number of recording sheets fed continuously at a high speed. That is, in the two-roll type fixing device, a core metal constituting the fixing roll, an elastic layer made of silicone rubber coated on the core metal, or the like acts as a thermal resistor. Therefore, in the two-roll type fixing device, it is structurally difficult to supply the heat corresponding to the amount of heat taken by the recording paper from the surface of the fixing roll promptly and sufficiently from the heater disposed inside the fixing roll. .

  As a result, when recording paper is continuously fed to the two-roll type fixing device at a high speed, the surface temperature of the fixing roll gradually decreases, and the fixing performance gradually decreases. In addition, when the image forming apparatus starts up, a so-called “temperature droop phenomenon” in which the surface temperature of the fixing roll temporarily drops tends to occur. In particular, when thick paper with a large heat capacity is used as recording paper, the amount of heat taken away from the surface of the fixing roll increases, so that the fixing performance decreases and the temperature droop increases, resulting in image quality deterioration due to poor fixing. Will be generated.

  Under such circumstances, a technique has been developed that solves the above-described problems that occur when a two-roll type fixing device is used, and realizes a fixing device that can cope with higher speed of the image forming apparatus. For example, there is a technique related to a fixing device in which a heating member that heats a recording sheet is configured by a film-like belt member (fixing belt) stretched by a plurality of stretching rolls (see, for example, Patent Document 1).

  In such a fixing device using a fixing belt, the fixing belt is sufficiently heated by a heater provided in advance in the stretching roll before entering the nip portion, and the fixing belt heated in the nip portion is heated. The toner image is fixed by applying heat to the recording paper and the toner image. Therefore, even if the fixing belt is deprived of heat by the recording paper during the fixing process, since the heat capacity of the fixing belt itself is small, the fixing belt is recovered to a predetermined fixing temperature in a short time by the heater in the stretching roll. It is possible to make it. Accordingly, in the fixing device using the fixing belt as the heating member, it becomes easy to maintain the temperature of the fixing belt when entering the nip portion at a predetermined value, and even if the image forming apparatus is speeded up, It is possible to supply a sufficient amount of heat.

  However, even in a fixing device using a fixing belt, since the toner image is carried on the surface of the recording paper, the toner image becomes an adhesive when the toner image is melted by the heat of the fixing belt. Adhesive force acts between the toner and the fixing belt. Therefore, it is necessary to provide a mechanism for peeling the recording paper from the surface of the fixing belt, as in the conventional two-roll type fixing device. In particular, when the speed of the image forming apparatus is increased, once a separation failure occurs in the fixing device and a paper jam occurs, the number of subsequent recording sheets that are damaged by the influence increases. For this reason, it is necessary to stably and reliably peel the recording paper that has passed through the nip portion at a high speed from the fixing belt side.

As a mechanism for peeling the recording paper from the surface of the fixing belt, a configuration in which a separation claw is disposed in contact with the fixing belt on the downstream side of the nip portion as described in Patent Document 1 is generally used. ing.
However, in the configuration in which the recording paper is peeled off from the fixing belt surface by the separation claw in this way, especially when fixing is performed at a high speed, the leading edge of the recording paper collides with the peeling claw and the leading edge is damaged, This could cause paper jams. This tends to occur particularly in the case of a recording sheet having a thin paper thickness.

In order to prevent such a problem and stably peel the recording sheet from the fixing belt side, it is necessary to strongly press the separation claw against the fixing belt. However, in this case, there is a possibility that the surface of the fixing belt is worn by the separation claw. If wear occurs on the surface of the fixing belt, fixing unevenness corresponding to wear marks on the surface of the fixing belt may occur on the fixed image, which may deteriorate the image quality. Further, the offset toner may gradually adhere to and accumulate on the wear scar, causing stain on the fixed image. Further, when the surface of the fixing belt progresses, the thin-layer fixing belt eventually breaks, so that high durability cannot be obtained.
Therefore, the inside of the fixing belt at a position corresponding to the outlet portion (the most downstream portion) of the nip portion can be used to stably peel the recording paper from the fixing belt side without using such a separation claw. In addition, a configuration has been proposed in which a peeling member is provided for setting a large curvature of the fixing belt at the exit portion, and the recording paper is peeled by a change in the curvature of the fixing belt (see, for example, Patent Document 2).

JP-A-3-133871 (page 4, FIG. 3) Japanese Patent Laying-Open No. 2003-5566 (pages 6 to 8, FIG. 4)

  As described above, a release member for increasing the curvature of the fixing belt is provided at the exit portion of the nip portion, and in this configuration, the recording paper is peeled from the surface of the fixing belt. It is conceivable to form part of the part. In that case, if there is a gap between the nip part (roll nip part) formed by the fixing roll and the pressure roll and the nip part (peeling nip part) formed by the peeling member and the pressure roll, There is a possibility that the pressure contact force is reduced at the gap portion and image defects such as blisters are caused. For this reason, the peeling member is provided as close as possible to the fixing roll around which the fixing belt is wound, and preferably in contact with the fixing roll.

However, when the peeling member is provided in contact with the fixing roll, the fixing roll is brought into sliding contact with the fixed peeling member, and the resulting wear affects the fixing performance, so that high fixing performance cannot be maintained for a long time. There is a problem.
For example, the fixing roll is often formed of a light aluminum alloy having a high thermal conductivity, but when the peeling member is formed of a stainless alloy, the peripheral surface of the fixing roll is worn by the peeling member. As a result, if unevenness is formed on the peripheral surface of the fixing roll, the pressure at the roll nip becomes non-uniform, resulting in image defects such as blisters. Further, when wear powder is sandwiched between the fixing belt and the peeling member, the pressure at the peeling nip portion becomes non-uniform, which also causes image defects.

  Accordingly, the present invention has been made to solve the technical problems as described above, and the object of the present invention is to prevent the fixing roll from being worn by a peeling member that adversely affects the fixing performance, and to achieve high fixing performance. An object of the present invention is to provide a fixing device and an image forming apparatus using a belt member that can be maintained for a long period of time.

For this purpose, the fixing device of the present invention is a fixing device for fixing a toner image carried on a recording medium, and includes a rotatable fixing roll member, a rotatable tension roll member, and a fixing roll member. A fixing belt member that is stretched and rotated by the tension roll member, a heating unit that heats the fixing belt member, and a portion of the fixing roll member that is wound around the fixing belt member to form a nip portion. A pressure member; and a peeling member that is interposed between the fixing belt member and the fixing roll member on the downstream side of the nip portion and bends the fixing belt member with a large curvature. The peeling member is a fixing roll member. It is formed of a material having a lower hardness and is provided in contact with the fixing roll member.
Here, the pressure means is a pressure roll member having an elastic layer on the surface thereof.

Another fixing device of the present invention is a fixing device that fixes a toner image carried on a recording medium, and includes a rotatable fixing roll member, a rotatable tension roll member, a fixing roll member, and a tension member. A fixing belt member that is stretched and rotated by a gantry roll member, a heating unit that heats the fixing belt member, and a pressure that presses a portion of the fixing roll member around which the fixing belt member is wound to form a nip portion. And a peeling member that is interposed between the fixing belt member and the fixing roll member on the downstream side of the nip portion and bends the fixing belt member with a large curvature. The peeling member contacts the fixing roll member. And a sliding contact portion having a hardness lower than that of the fixing roll member formed at least on the surface portion in contact with the fixing roll member.
Here, the peeling member is characterized in that the sliding contact member including the sliding contact portion is detachably mounted on the peeling member main body. The sliding contact member is provided so as to cover the periphery of the peeling member in the moving direction of the fixing belt member. Further, the slidable contact portion is a release layer such as a fluororesin layer formed on the surface portion of the slidable contact member that contacts the fixing roll member.

  In addition, the image forming apparatus of the present invention includes a toner image forming unit that forms a toner image, a transfer unit that transfers a toner image formed by the toner image forming unit onto a recording medium, and a toner that is transferred onto the recording medium. A fixing unit configured to fix an image on a recording medium, the fixing unit including a rotatable fixing roll member, a rotatable tension roll member including a heater, a fixing roll member, and a tension roll member; A fixing belt member that is stretched around and rotated, a pressurizing means that includes an elastic layer on a surface that forms a nip portion by pressing against a portion of the fixing roll member around which the fixing belt member is wound, and a downstream portion of the nip portion A separation member interposed between the fixing belt member and the fixing roll member and separating the recording medium from the fixing belt member, and the separation member is provided in contact with the fixing roll member, At least It includes small sliding portion hardness of the fixing roll member formed on the surface portion in contact with the fuser roll member characterized.

According to the fixing device of the present invention, it is possible to suppress the abrasion of the fixing roll due to the peeling member that adversely affects the fixing performance, and it is possible to stably maintain high fixing performance for a long period of time. Therefore, a fixing device having high durability can be obtained.
In addition, according to the image forming apparatus of the present invention, it is possible to suppress the wear of the fixing roll that adversely affects the fixing performance of the fixing device, and to maintain high fixing performance stably for a long period of time. It is possible to configure a highly durable image forming apparatus that can be provided in a large amount in time.

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

  Each of the image forming units 1Y, 1M, 1C, and 1K has an electrostatic latent image on the photosensitive drum 11 around the photosensitive drum 11 that rotates in the direction of arrow A, and a charger 12 that charges the photosensitive drum 11. A laser exposure device 13 (exposure beam is indicated by a symbol Bm in the figure), a developing device 14 that accommodates each color component toner and visualizes the electrostatic latent image on the photosensitive drum 11 with the toner, a photoconductor For electrophotography, such as a primary transfer roll 16 for transferring each color component toner image formed on the drum 11 to the intermediate transfer belt 15 in the primary transfer unit 10 and a drum cleaner 17 for removing residual toner on the photosensitive drum 11. Devices are arranged sequentially. These image forming units 1Y, 1M, 1C, and 1K are arranged in a substantially straight line from the upstream side of the intermediate transfer belt 15 in the order of yellow (Y), magenta (M), cyan (C), and black (K). Has been.

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

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

Further, on the downstream side of the secondary transfer portion 20 of the intermediate transfer belt 15, an intermediate transfer belt that removes residual toner and paper dust on the intermediate transfer belt 15 after the secondary transfer and cleans the surface of the intermediate transfer belt 15. A cleaner 35 is provided.
Further, the image forming apparatus 1 includes a recording paper transport mechanism 50. The recording paper transport mechanism 50 transports the recording paper P from the recording paper tray 51 containing the recording paper P to the secondary transfer unit 20, and the toner image is transferred (secondary transfer) by the secondary transfer unit 20. The recording sheet P is conveyed to the fixing device 60.

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

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 in a superimposed manner.
The toner image formed on the surface of the intermediate transfer belt 15 is moved to the secondary transfer unit 20 by the rotation of the intermediate transfer belt 15, and is transported by the recording paper transport mechanism 50 in the secondary transfer unit 20. The recording sheet P is electrostatically transferred collectively onto the recording sheet P.
The recording paper P to which the toner image has been transferred is transported to the fixing device 60 by the recording paper transport mechanism 50, and the toner image is fixed by receiving a fixing process using heat and pressure by the fixing device 60. Then, the recording paper P on which the image is fixed is discharged to a paper discharge mounting portion (not shown) provided in the discharge portion of the image forming apparatus 1.

Next, the fixing device 60 used in the image forming apparatus 1 of the present embodiment will be described.
FIG. 2 is a perspective view conceptually showing one end portion of the fixing device 60 of the present embodiment, and FIG. 3 is a side sectional view showing a schematic configuration of the fixing device 60. 4 is a schematic cross-sectional view showing a region near the nip portion N, and FIG. 5 is a schematic cross-sectional view showing the periphery of the region where the peeling pad 64 is disposed. Further, FIG. 6 is a sectional view of the peeling pad 64 alone, and FIG. 7 is an exploded perspective view of the peeling pad 64.
The fixing device 60 includes a fixing belt module 61 including a fixing belt 610 and a pressure roll 62 as a pressing unit disposed in pressure contact with the fixing belt module 61.

  The fixing belt module 61 includes a fixing belt 610 as a belt member, a fixing roll 611 as a fixing roll member that rotates while the fixing belt 610 is stretched, and a tension roll member as a tension roll member that stretches the fixing belt 610 from the inside. A stretching roll 612, a stretching roll 613 as a stretching roll member that stretches the fixing belt 610 from the outside, a posture correcting roll 614 that corrects the posture of the fixing belt 610 between the fixing roll 611 and the stretching roll 612, fixing A stripping pad 64 as a stripping member disposed in the vicinity of the fixing roll 611 in the downstream region in the nip N where the belt module 61 and the pressure roll 62 are in pressure contact with each other, downstream of the nip N The main part is composed of a tension roll 615 as a tension roll member for tensioning the fixing belt 610 in FIG. There.

  The fixing belt 610 is a flexible endless belt having a circumferential length of 314 mm and a width of 340 mm. Then, a base layer made of polyimide resin having a thickness of 80 μm, an elastic layer made of 200 μm thick silicone rubber laminated on the surface side (outer peripheral surface side) of the base layer, and further covering the elastic layer And a release layer comprising a 30 μm thick tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin (PFA) tube. Here, the elastic layer is provided in order to improve the image quality especially for color images. The configuration of the fixing belt 610 can be appropriately selected in terms of material, thickness, hardness, and the like according to device design conditions such as the purpose of use and use conditions.

The fixing roll 611 is a cylindrical core roll (core metal) made of aluminum having an outer diameter of 65 mm, a length of 360 mm, and a thickness of 10 mm. A fluororesin with a thickness of 200 μm is coated as a protective layer for preventing metal wear on the core roll surface. It is a hard roll formed in this way. However, the fixing roll 611 is not limited to this configuration. When the nip portion N is formed between the fixing roll 611 and the pressure roll 62, the fixing roll 611 is sufficiently deformed with respect to the pressing force from the pressure roll 62. Any configuration that functions as a hard roll can be used. The fixing roll 611 rotates in the arrow C direction at a surface speed of 440 mm / s in response to a driving force from a driving motor (not shown).
In addition, a halogen heater 616 a rated at 900 W is provided as a heating unit inside the fixing roll 611, and the image forming apparatus 1 is based on the measured value of the temperature sensor 617 a arranged so as to contact the surface of the fixing roll 611. The control unit 40 (see FIG. 1) controls the surface temperature of the fixing roll 611 to 150.degree.

The tension roll 612 is a cylindrical roll formed of aluminum having an outer diameter of 30 mm, a wall thickness of 2 mm, and a length of 360 mm. In addition, a halogen heater 616b rated at 1000 W is provided as a heating source inside the tension roll 612, and the surface temperature is controlled to 190 ° C. by the temperature sensor 617b and the control unit 40 (see FIG. 1). Yes. Therefore, the tension roll 612 has a function of stretching the fixing belt 610 and a function of heating the fixing belt 610 from the inner peripheral surface side.
In addition, spring members (not shown) that press the fixing belt 610 outward are disposed at both ends of the tension roll 612, and the tension of the entire fixing belt 610 is set to 15 kgf. At that time, in order to make the tension of the fixing belt 610 uniform in the width direction and to suppress the displacement of the fixing belt 610 in the axial direction as much as possible, the tension roll 612 has an outer diameter at the center portion rather than the end portion. It is formed in a so-called crown shape that is larger by 100 μm.

  The tension roll 613 is a cylindrical roll formed of aluminum having an outer diameter of 25 mm, a thickness of 2 mm, and a length of 360 mm. Further, a release layer made of a fluororesin having a thickness of 20 μm is formed on the surface of the tension roll 613. This release layer is formed to prevent slight offset toner and paper powder from the outer peripheral surface of the fixing belt 610 from accumulating on the stretching roll 613. Similarly to the tension roll 612, the tension roll 613 has a crown shape in which the outer diameter is larger by 100 μm at the center than at the end. Note that not only the tension roll 612 and the tension roll 613 are both formed in a crown shape, but only one of the tension roll 612 and the tension roll 613 may be formed in a crown shape.

  Inside the tension roll 613, a halogen heater 616c rated as 1000 W is disposed as a heating means. The surface temperature is controlled to 190 ° C. by the temperature sensor 617c and the control unit 40 (see FIG. 1). Yes. Accordingly, the tension roll 613 has a function of stretching the fixing belt 610 and a function of heating the fixing belt 610 from the outer peripheral surface side. Therefore, in this embodiment, a configuration in which the fixing belt 610 is heated by the fixing roll 611, the stretching roll 612, and the stretching roll 613 is employed.

  The posture correction roll 614 is a cylindrical roll formed of aluminum having an outer diameter of 15 mm and a length of 360 mm. A belt edge position detection mechanism (not shown) that detects the edge position of the fixing belt 610 is disposed in the vicinity of the posture correction roll 614. The posture correction roll 614 is provided with an axis displacement mechanism that displaces the contact position in the axial direction of the fixing belt 610 according to the detection result of the belt edge position detection mechanism, and performs meandering (belt walk) of the fixing belt 610. Configured to control.

The peeling pad 64 has a substantially rectangular cross-sectional shape, and a sliding contact surface 64a that contacts the fixing roll 611 around the moving direction of the fixing belt 610, an outer surface 64b that rapidly changes the traveling direction of the fixing belt 610, A pressing surface 64c for pressing the fixing belt 610 against the pressure roll 62 and an upper surface 64d are provided. The sliding surface 64 a is an arcuate curved surface that follows the peripheral surface of the fixing roll 611. The outer surface 64b has an arc shape substantially along the sliding contact surface 64a. The shape of each surface will be described in detail later.
As shown in FIGS. 6 and 7, the peeling pad 64 is slid as a sliding contact member constituting a sliding contact portion on the front surface side (side facing the fixing roll 611) of the pad main body 64A as the peeling member main body. The contact piece 64B is mounted and configured.
The pad main body 64A has a block shape that forms an outer surface 64b and a pressing surface 64c, and is formed of a rigid body such as stainless alloy steel, for example. The surface facing the fixing roll 611 is a mounting surface 64Aa on which the sliding contact piece 64B is mounted. The mounting surface 64Aa has a shape substantially along the sliding contact surface 64a, and a plurality of positioning holes 64Ab are formed at predetermined positions.

The sliding contact piece 64B has a shape in which the surface forming the sliding contact surface 64a follows the peripheral surface of the fixing roll 611, and the back surface is substantially parallel to this surface. Thereby, the schematic cross-sectional shape has a thin plate shape. A positioning projection 64Bb corresponding to the positioning hole 64Ab of the pad main body 64A is projected from the back surface 64Ba.
The sliding contact piece 64B is made of a material having a hardness lower than that of the fixing roll 611 made of aluminum, a low frictional resistance, a good slidability, and excellent wear resistance and heat resistance. For example, the material is preferably a fluororesin such as tetrafluoroethylene. However, the present invention is not limited to this, and any material having the above-described conditions can be used.
The sliding contact piece 64B formed in this manner is detachably mounted on the mounting surface 64Aa of the pad main body 64A by fitting the positioning protrusion 64Bb into the positioning hole 64Ab. The back surface 64Ba and the mounting surface 64Aa of the pad main body 64A may be bonded by an adhesive means such as a double-sided tape. However, if a predetermined mounting strength is obtained only by fitting the positioning projection 64Bb into the positioning hole 64Ab, There is no particular need for it.

  As described above, the peeling pad 64 integrally formed by mounting the sliding contact piece 64B on the pad main body 64A has an outer surface 64b formed by the back surface of the pad main body 64A. The pressing surface 64c is formed by the lower surface of the pad main body 64A and the plate thickness portion of the sliding contact piece 64B, and the sliding contact surface 64a is formed by the surface of the sliding contact piece 64B.

  The peeling pad 64 is supported at both ends in the axial direction of the fixing roll 611 by arms 641 that are swingably fitted to the support shaft 611a of the fixing roll 611, as shown in FIG. A fixing roll 611 is fixedly disposed on the downstream side of the roll nip portion N1 (see FIG. 4) over the entire axial direction of the fixing roll 611. The sliding contact surface 64 a is in contact with the peripheral surface of the fixing roll 611. In addition, the peeling pad 64 allows the pressure roll 62 to pass through the fixing belt 610 with a predetermined load (for example, 10 kgf) over a predetermined width region (for example, a width of 5 mm along the traveling direction of the fixing belt 610). It is installed so as to press uniformly, and forms a “peeling pad nip portion N2” described later.

The sliding contact surface 64 a of the peeling pad 64 is formed in an arcuate curved surface that coincides with the peripheral surface of the fixing roll 611 as described above in order to place the peeling pad 64 in contact with the fixing roll 611. The upstream end of the sliding contact surface 64a is in contact with the fixing roll 611 and has an edge shape.
The pressing surface 64 c of the peeling pad 64 is a surface that presses the fixing belt 610 against the pressure roll 62 and presses against the surface of the pressure roll 62. Therefore, the shape of the fixing belt 610 substantially follows the circumferential surface of the pressure roll 62 so that the fixing belt 610 is uniformly pressed against the pressure roll 62.

The outer surface 64b of the peeling pad 64 is a surface that peels the recording paper P from the fixing belt 610 by guiding the fixing belt 610 in cooperation with the stretching roll 615 and the fixing roll 611 and changing its traveling direction rapidly. It is. Therefore, the tangent line of the pressure roll 62 in the upstream end region (region where the fixing belt 610 is separated from the pressure roll 62) R of the outer surface 64b so that the recording paper P can be stably peeled from the fixing belt 610. The angle θ (see FIG. 5) formed by the tangent to the outer surface 64b is set to be 40 ° or more. Further, in the upstream end region R, the outer side surface 64b is formed as a curved surface so that the fixing belt 610 can be smoothly moved in the upstream end region R that is bent sharply.
Further, the outer surface 64b is formed by a plane inclined toward the stretching roll 615 so that the fixing belt 610 moves smoothly in the direction of the stretching roll 615 and the fixing roll 611 after being separated from the pressure roll 62. Has been. In this case, the outer side surface 64b can be formed as a curved surface that curves toward the outer side (the fixing belt 610 side).

  The tension roll 615 is a cylindrical roll formed of aluminum having an outer diameter of 12 mm and a length of 360 mm. The fixing belt 610 that has passed through the peeling pad 64 is disposed in the vicinity of the downstream side of the fixing pad 610 in the traveling direction of the fixing belt 610 so that the fixing belt 610 smoothly rotates toward the fixing roll 611.

  The pressure roll 62 has a cylindrical roll 621 made of aluminum having a diameter of 45 mm and a length of 360 mm as a base, and an elastic layer 622 having a thickness of 10 mm made of silicone rubber having a rubber hardness of 30 ° (JIS-A) in order from the base. And a release layer 623 made of a PFA tube having a film thickness of 100 μm. The pressure roll 62 is installed so as to be pressed against the fixing belt module 61. As the fixing roll 611 of the fixing belt module 61 rotates in the direction of arrow C, the pressure roll 62 follows the fixing roll 611 and moves in the direction of arrow E. To turn. The traveling speed is 440 mm / s, which is the same as the surface speed of the fixing roll 611.

Next, the nip portion N where the fixing belt module 61 and the pressure roll 62 are pressed against each other will be described.
As shown in FIG. 4, in the nip portion N where the fixing belt module 61 and the pressure roll 62 are pressed against each other, the fixing belt 610 is wound (wrapped) in the area (wrapped area) around the fixing roll 611. , The pressure roll 62 is arranged so as to be in pressure contact with the outer peripheral surface of the fixing belt 610, whereby a roll nip portion (first nip portion) N1 is formed.

Here, in the fixing device 60 of the present embodiment, as described above, the fixing roll 611 that is one of the rolls forming the roll nip portion N1 has a heat-resistant resin (fluororesin) on the surface of an aluminum core metal (core roll). The fixing roll 611 is not covered with an elastic layer. Further, the pressure roll 62 forming the roll nip portion N1 is a soft roll covered with an elastic layer 622.
With such a configuration of the fixing roll 611 and the pressure roll 62, the roll nip portion N1 is formed by the deformation of the elastic layer 622 of the pressure roll 62 in the roll nip portion N1 of the present embodiment. The roll 62 side functions as a roll (NIP Forming Pressure Roll) that forms a nip. That is, in the roll nip portion N1, the fixing roll 611 is hardly dented, and only the surface of the pressure roll 62 is largely dented (the amount of depression of the pressure roll 62> the amount of depression of the fixing roll 611). Thus, a nip region having a predetermined width in the traveling direction of the fixing belt 610 is created.

  As described above, in the fixing device 60 of the present embodiment, the fixing roll 611 on the side where the fixing belt 610 is wrapped in the roll nip portion N1 is hardly deformed, and the cylindrical shape is maintained. Therefore, the fixing belt 610 rotates along the circumferential surface of the surface of the fixing roll 611, and the rotation radius does not change. Therefore, the fixing belt 610 can pass through the roll nip portion N1 while maintaining a constant traveling speed. it can. As a result, even when the fixing belt 610 passes through the roll nip portion N1, the fixing belt 610 hardly generates wrinkles or distortion. As a result, the occurrence of image disturbance in the fixed image is suppressed, and a high-quality fixed image can be stably provided. In the fixing device 60 of the present embodiment, the roll nip portion N1 is set to 15 mm (that is, the nip width is 15 mm) in the traveling direction of the fixing belt 610.

Further, a peeling pad 64 is disposed on the downstream side of the roll nip portion N1, and the peeling pad 64 presses the fixing belt 610 against the surface of the pressure roll 62. Accordingly, a peeling pad nip portion (second nip portion) N2 in which the fixing belt 610 is wrapped on the surface of the pressure roll 62 is formed downstream of the roll nip portion N1.
As shown in FIG. 4, the peeling pad 64 forming the peeling pad nip portion N2 contacts the fixing roll 611 at the sliding contact surface 64a on the downstream side of the roll nip portion N1, and is disposed along the axial direction thereof. Thereby, the peeling pad nip portion N2 is continuously formed without a gap in the roll nip portion N1. Therefore, there is no gap region where the pressure contact force is reduced between the roll nip portion N1 and the peeling pad nip portion N2, and image defects such as blisters due to the reduction of the pressure contact force are not generated.

  Then, the fixing belt 610 after passing through the peeling pad nip portion N <b> 2 rotates along the peripheral surface of the peeling pad 64. Accordingly, the advancing direction of the fixing belt 610 is rapidly changed so as to be bent in the direction of the tension roll 615 by the peeling pad 64. Therefore, the recording paper P that has passed through the roll nip portion N1 and the peeling pad nip portion N2 cannot follow the change in the advancing direction of the fixing belt 610 when the recording paper P exits the peeling pad nip portion N2, and the recording paper P is so-called “koshi” Is peeled off from the fixing belt 610. In this manner, the curvature separation with respect to the recording paper P is stably performed at the exit portion of the peeling pad nip portion N2. In the fixing device 60 of the present embodiment, the peeling pad nip portion N2 is set to 5 mm (that is, nip width 5 mm) in the traveling direction of the fixing belt 610.

Next, a fixing operation in the fixing device 60 of the present embodiment will be described.
The recording paper P on which the unfixed toner image is electrostatically transferred in the secondary transfer unit 20 (see FIG. 1) of the image forming apparatus 1 is transferred to the nip portion N of the fixing device 60 by the recording paper transport mechanism 50 (see FIG. 1). (Refer to FIG. 3: arrow F direction). The unfixed toner image on the surface of the recording paper P passing through the nip portion N is fixed on the recording paper P mainly by pressure and heat acting on the roll nip portion N1.

  At this time, in the fixing device 60 of the present embodiment, heat acting on the nip portion N is mainly supplied by the fixing belt 610. The fixing belt 610 is supplied through the tension roll 612 from the heat supplied from the halogen heater 616a disposed inside the fixing roll 611 through the fixing roll 611 and from the halogen heater 616b disposed inside the tension roll 612. It is configured to be heated by heat and heat supplied from the halogen heater 616c disposed inside the tension roll 613 through the tension roll 613. Therefore, since heat energy can be replenished to the fixing belt 610 mainly and appropriately from the tension roll 612 and the tension roll 613, the process speed at the nip portion N is as high as 440 mm / s. A sufficient amount of heat can be secured.

After passing through the roll nip portion N1, the recording paper P is conveyed to the peeling pad nip portion N2. The peeling pad nip portion N <b> 2 is formed such that the peeling pad 64 is pressed against the pressure roll 62 and the fixing belt 610 comes into pressure contact with the pressure roll 62. Therefore, as shown in FIG. 4, the roll nip portion N1 has a curved shape that is convex downward due to the curvature of the fixing roll 611, whereas the peeling pad nip portion N2 is convex upward due to the curvature of the pressure roll 62. It has a certain curved shape.
Therefore, the recording paper P heated and pressed under the curvature of the fixing roll 611 in the roll nip portion N1 is changed in the traveling direction to the curvature directed in the opposite direction by the pressure roll 62 in the peeling pad nip portion N2. At that time, a minute micro slip occurs between the toner image on the recording paper P and the surface of the fixing belt 610. As a result, the adhesion between the toner image and the fixing belt 610 is weakened, and the recording paper P is easily peeled off from the fixing belt 610. As described above, the peeling pad nip portion N2 is also positioned in a preparation process for surely peeling in the final peeling process.

Since the fixing belt 610 is conveyed so as to be wound around the peeling pad 64 at the exit of the peeling pad nip portion N2, the conveyance direction of the fixing belt 610 changes abruptly there. That is, since the fixing belt 610 moves along the outer surface 64b of the peeling pad 64, the bending of the fixing belt 610 becomes large. Therefore, the recording paper P whose adhesion with the fixing belt 610 has been weakened in advance in the peeling pad nip portion N2 can be self-striped from the fixing belt 610 by the stiffness of the paper possessed by the recording paper P itself. .
In this way, the recording paper P is stably separated from the fixing belt 610 by the curvature when it leaves the peeling pad nip portion N2.
The recording sheet P separated from the fixing belt 610 is discharged out of the apparatus by the discharge guide 65 and the discharge roll 66, and the fixing process is completed.

  Here, as described above, the peeling pad 64 is formed by the sliding contact piece 64B in which the sliding contact surface 64a in contact with the fixing roll 611 is detachably attached to the pad main body 64A. The sliding contact piece 64B is made of a fluororesin or the like having a smaller hardness than the fixing roll 611 that is in sliding contact, a small frictional resistance, a good slidability, and excellent wear resistance and heat resistance. For this reason, even if the peripheral surface of the fixing roll 611 comes into contact with and slides on the sliding contact surface 64a of the fixed peeling pad 64, the peripheral surface of the fixing roll 611 is not worn. Further, the wear of the peeling pad 64 (sliding contact piece 64B) can be suppressed to a very small amount. Thereby, it is possible to suppress the occurrence of defects due to wear on the peripheral surface of the fixing roll 611. That is, it is possible to suppress the occurrence of image defects such as blisters due to non-uniform pressure in the nip portion (roll nip portion N1) due to the unevenness of the peripheral surface of the fixing roll 611. In addition, it is possible to suppress the occurrence of image defects due to non-uniform pressure caused by wear powder sandwiched between the fixing belt 610 forming the nip portion (peeling pad nip portion N2) and the peeling pad 64.

  Furthermore, due to the relationship between the material properties of the fixing roll 611 and the peeling pad 64 described above, the side of the peeling pad 64 is worn out in the long term. If the slidable contact surface 64a is excessively polished due to wear, the pressing force of the peeling pad nip portion N2 may change from the initial setting state. In such a case, it is possible to return to the initial state by removing the worn sliding contact piece 64B from the pad main body 64A and replacing it with a new sliding contact piece 64B.

The configuration in which the sliding contact surface 64a of the peeling pad 64 is formed by another detachable member having a hardness smaller than that of the fixing roll 611, a low frictional resistance, a good slidability, and excellent wear resistance and heat resistance is described above. It is not limited to the embodiment.
For example, the sliding contact piece 64B may be formed of metal, and a peeling layer made of a fluororesin or the like may be formed on the sliding contact surface 64a.

FIG. 8 is a cross-sectional view of a peeling pad 67 of an embodiment different from the above embodiment.
The peeling pad 67 shown in FIG. 8 slidably contacts a sheet 67B as a slidable contact member that forms a slidable contact portion so as to wrap around the body pad 67A as a peeling member body formed slightly smaller than the outer shape of the peelable pad 67. Is installed.
The slidable contact sheet 67B is formed of a thin plate made of a fluororesin or the like having a hardness smaller than that of the fixing roll 611 (see FIG. 3), a small frictional resistance, a good slidability, and excellent wear resistance and heat resistance. Then, a sliding contact surface 67a is formed from the upper surface 67d of the main body pad 67A around the main body pad 67A in the counterclockwise direction in the figure, and the overlapping portions at the front and rear ends are fastened to the upper surface 67d of the main body pad 67A by screws 68. It is worn and worn. The sliding contact sheet 67B is adhered to the outer surface of the main body pad 67A with a double-sided tape or the like as necessary.
In this configuration, the peeling pad 67 includes not only the sliding contact surface 67a that is in sliding contact with the fixing roll 611 but also the outer surface 67b and the pressing surface 67c that are in sliding contact with the fixing belt 610 by the sliding contact sheet 67B. For this reason, there is little sliding resistance of the fixing belt 610, and wear and breakage of the fixing belt 610 can be suppressed.

As described above, the fixing device 60 of the present embodiment uses the fixing belt module 61 in which the fixing belt 610 is stretched by a plurality of rolls including the fixing roll 611 as a heating member. Even if the forming apparatus 1 is speeded up, the fixing device 60 can always maintain a predetermined fixing temperature. Furthermore, it is possible to suppress the occurrence of a temperature droop phenomenon in which the fixing temperature drops at the start of the high-speed fixing operation. For this reason, it is possible to provide a large amount of high-quality fixed images in a short time.
At the same time, even if the peeling pads 64 and 67 are in contact with the fixing roll 611 at the sliding contact surfaces 64a and 67a, the peripheral surface of the fixing roll 611 is not worn and causes a problem. , 67 can be dealt with by replacing the slidable contact piece 64B and the slidable contact sheet 67B forming the slidable contact surfaces 64a, 67a. Thereby, high fixing performance can be maintained for a long time.

The present invention is not limited to the above embodiment. In the above embodiment, the present invention is applied to a so-called tandem color image forming apparatus. For example, the present invention is applied to a color image forming apparatus using a rotary developing device, a monochrome copying machine, or the like. It goes without saying that it is also good.
Further, the configuration using the pressure roll 62 as the pressure means disposed in pressure contact with the fixing belt module 61 has been described, but the pressure belt is stretched by a plurality of rolls as the pressure member. The present invention may be applied to a configuration using a pressure belt module.

1 is a schematic configuration diagram of an image forming apparatus to which an exemplary embodiment is applied. FIG. 3 is a perspective view conceptually showing one end of the fixing device. FIG. 2 is a side sectional view illustrating a schematic configuration of a fixing device. It is a schematic sectional drawing showing the vicinity area | region of a nip part. It is a schematic sectional drawing showing the periphery of the area | region where the peeling pad is arrange | positioned. It is sectional drawing of a peeling pad single-piece | unit. It is a disassembled perspective view of a peeling pad. It is sectional drawing of the peeling pad of different embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 60 ... Fixing device, 61 ... Fixing belt module, 62 ... Pressure roll (pressing means), 64, 67 ... Release pad (release member), 64a, 67a ... Sliding contact surface (fixing roll member) 64A, 67A ... pad main body (peeling member main body), 64B ... sliding contact piece (sliding contact portion, sliding contact member), 67B ... sliding contact sheet (sliding contact portion, sliding contact member), 610 ... fixing belt (fixing belt member), 611 ... fixing roll (fixing roll member), 616a, 616b, 616c ... halogen heater (heating means), 612, 613, 615 ... stretching roll (stretching roll member)

Claims (12)

A fixing device for fixing a toner image carried on a recording medium,
A rotatable fixing roll member;
A rotatable tension roll member;
A fixing belt member that is stretched and rotated by the fixing roll member and the stretching roll member;
Heating means for heating the fixing belt member;
A pressurizing unit that presses a portion of the fixing roll member around which the fixing belt member is wound to form a nip portion;
A peeling member that is interposed between the fixing belt member and the fixing roll member on the downstream side of the nip portion and bends the fixing belt member with a large curvature;
The fixing device, wherein the peeling member is made of a material having a hardness lower than that of the fixing roll member, and is provided in contact with the fixing roll member.   The fixing device according to claim 1, wherein the pressure unit is a pressure roll member having an elastic layer on a surface thereof. A fixing device for fixing a toner image carried on a recording medium,
A rotatable fixing roll member;
A rotatable tension roll member;
A fixing belt member that is stretched and rotated by the fixing roll member and the stretching roll member;
Heating means for heating the fixing belt member;
A pressurizing unit that presses a portion of the fixing roll member around which the fixing belt member is wound to form a nip portion;
A peeling member that is interposed between the fixing belt member and the fixing roll member on the downstream side of the nip portion and bends the fixing belt member with a large curvature;
The peeling member is provided in contact with the fixing roll member, and includes a sliding contact portion having a hardness lower than that of the fixing roll member formed at least on a surface portion in contact with the fixing roll member. Fixing device.   The fixing device according to claim 3, wherein the peeling member is configured such that a sliding contact member including the sliding contact portion is detachably attached to a peeling member main body.   The fixing device according to claim 4, wherein the sliding contact member is provided so as to cover a periphery of the peeling member in a moving direction of the fixing belt member.   The fixing device according to claim 4, wherein the sliding contact portion is a release layer formed on a surface portion of the sliding contact member that contacts the fixing roll member.   The fixing device according to claim 6, wherein the release layer is a fluororesin layer. Toner image forming means for forming a toner image;
Transfer means for transferring the toner image formed by the toner image forming means onto a recording medium;
Fixing means for fixing the toner image transferred on the recording medium to the recording medium,
The fixing means is
A rotatable fixing roll member;
A rotatable tension roll member provided with a heater,
A fixing belt member that is stretched and rotated by the fixing roll member and the stretching roll member;
A pressure unit provided with an elastic layer on a surface that forms a nip portion by pressing against a portion of the fixing roll member around which the fixing belt member is wound;
A peeling member that is interposed between the fixing belt member and the fixing roll member on the downstream side of the nip portion and peels the recording medium from the fixing belt member;
The peeling member is provided in contact with the fixing roll member, and includes at least a sliding contact portion having a lower hardness than the fixing roll member formed on a surface portion in contact with the fixing roll member. Forming equipment.   The image forming apparatus according to claim 8, wherein the peeling member is configured such that a sliding contact member including the sliding contact portion is detachably attached to a peeling member main body.   The image forming apparatus according to claim 9, wherein the sliding contact member is provided so as to cover a periphery of the peeling member in a moving direction of the fixing belt member.   The image forming apparatus according to claim 9, wherein the sliding contact portion is a release layer formed on a surface portion of the sliding contact member that contacts the fixing roll member.   The image forming apparatus according to claim 11, wherein the release layer is a fluororesin layer.

Images