JP2012255870A - Fixing device and image forming device including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device that effectively prevents slip between a fixing belt and a pressure member in a nip part between the fixing belt and the pressure member, and to provide an image forming device including the same.SOLUTION: A fixing device 13 includes: an endless fixing belt 21; a belt support member 22 in internal contact with the fixing belt 21; a pair of pressing rollers 31 disposed at both ends of the belt support member 22 so as to be rotatable; a pressure roller 23 to be brought into pressure contact with the belt support member 22 and the pressing roller 31 via the fixing belt 21; and an induction heating part 25 arranged opposite the pressure roller 23 across the fixing belt 21. The outer periphery 31a of the pressing roller 31 protrudes toward the pressure roller 23 more than a surface 22b of the belt support member 22 facing the fixing belt 21. In a part S where the pressing roller 31 faces the pressure roller 23, a pressing force is generated which is larger than that in the part (fixing nip part N) between the belt support member 22 and the pressure roller 23.

Description

  The present invention relates to a belt-fixing type fixing device that inserts a sheet carrying an unfixed toner image into a nip between a heated fixing belt and a pressure member, heats and melts the unfixed toner, and fixes the sheet to the sheet, and The present invention relates to an image forming apparatus using an electrophotographic system including the same.

  In a conventional image forming apparatus using an electrophotographic system, a heat source is built in at least one roller of a pair of fixing rollers forming a nip to form a heating roller, and an unfixed toner image is carried on the nip portion of the roller pair. A heat roller fixing system in which toner is fixed to a sheet by inserting the sheet is widely used.

  In such a heat roller fixing method, the efficiency of heat transfer from a heat source such as a halogen lamp built in the heating roller to the roller surface is low, and heat loss is large. In addition, it takes a long time for heat to be transferred to the roller surface. As a result, there is a problem in that the heating efficiency is low and the power consumption is large, and the warm-up time until the roller surface reaches a fixable temperature becomes long.

  Also, when a hard roller with a fluorocarbon resin coating is used as the heating roller and a rubber roller is used as the pressure roller, the cross-sectional shape of the nip part of the roller pair is a convex arc shape on the pressure roller side. It becomes. Therefore, moisture evaporates by heating, and the paper curled to the heating roller side is further curled by the nip shape and becomes cylindrical. Conversely, if a rubber roller is used on the heating roller side and a hard roller is used on the pressure roller side, the paper may wrap around the pressure roller side and jam may occur during double-sided printing where toner is present on the back side of the paper. was there. On the other hand, in the configuration using rubber rollers on both the heating roller side and the pressure roller side, the cross-sectional shape of the nip portion is a straight line and curling of the paper is difficult to occur, but two or more sheets of paper such as envelopes and invoices. There is a problem that papers that are overlapped cause misalignment.

  In order to improve these problems, the heating member for heating the paper is an endless fixing belt that absorbs radiation light from the heat source instead of the heating roller and generates heat. A belt fixing system has been developed in which a sheet carrying an unfixed toner image is inserted into a nip portion with a pressure member to be fixed, thereby fixing toner on the sheet. This belt fixing method can reduce the heat capacity by reducing the heat capacity compared to the heat roller fixing method, and can reduce power consumption.

  As a driving method of the fixing belt, for example, in Patent Document 1, a flange-shaped end cap member is fixed to both ends in the rotation axis direction of an endless fixing belt, and the fixing belt is connected via a gear formed on the end cap member. A configuration for driving is disclosed. Patent Document 2 discloses a configuration in which the fixing belt is driven by a tension roller disposed at a position downstream of the nip portion inside the endless fixing belt. Further, in Patent Document 3, a belt-driving first roller is provided inside an endless fixing belt, and is fitted tightly (inscribed) in at least a part of a non-sheet passing region of the fixing belt. A configuration in which the outer diameter is changed in the axial direction of the first roller so as to be loosely fitted in the region is disclosed.

JP 2006-227106 A JP 2004-286922 A JP 2010-139934 A

  In the image forming apparatus using the belt fixing system as described above, particularly in the case of a color machine, the amount of toner attached to the recording medium is larger than that of a monochrome machine. It is necessary to take a long time (nip time) in contact with the fixing belt. In order to increase the nip time, it is necessary to ensure a sufficient area (nip width) of the nip portion between the fixing belt and the pressure member.

  However, in the method of directly driving the fixing belt as in Patent Documents 1 to 3, it is necessary to rotate a pressing member such as an end cap member, a stretching roller, or a first roller arranged inside the fixing belt. It was difficult to freely set the shape and width of the part.

  In general, as a method of widening the nip width, a method using a large-diameter pressure roller, a method of increasing the rubber thickness of the pressure roller surface or decreasing the rubber hardness, a pressing force of the pressure roller There are known methods for increasing the value. However, increasing the diameter of the pressure roller increases the size and cost of the fixing device, and increasing the rubber thickness may increase the warm-up time. In addition, a decrease in rubber hardness causes a large change in outer diameter due to temperature, leading to a decrease in transportability and a decrease in durability. Furthermore, an increase in the pressing force of the pressure roller leads to a decrease in transportability due to excessive deflection of the roller surface and an increase in cost due to fixing frame reinforcement.

  Therefore, a belt support member is disposed inside the fixing belt, and a pressure roller is pressed against the belt support member from the outside of the fixing belt, and the belt support member and the fixing belt are caused by frictional force between the pressure roller and the outer surface of the fixing belt. A sliding belt fixing method has been devised in which the fixing belt is driven to rotate by sliding the inner surface of the fixing belt. In the sliding belt system, a wide nip width can be obtained with a low pressing force by setting the shape of the belt support member to a flat shape or an R shape having a small curvature.

  By the way, in the sliding belt system, while the sheet is passing through the nip portion, the fixing belt and the pressure roller are in contact with each other only outside the sheet passing area, and the frictional force for driving the fixing belt is reduced. In addition, the surface layer of the fixing belt uses a fluorine-based resin to improve the releasability with respect to the toner, so the friction coefficient is originally low, and the contact area is reduced due to adhesion of paper powder and toner, and the friction coefficient is further reduced. . As a result, slipping occurs between the fixing belt and the pressure roller, and slipping also occurs between the fixing belt and the melted unfixed toner image carried on the paper. However, there is a problem in that image disturbance such as white spots occurs due to local dropout.

  In view of the above problems, the present invention provides a fixing device capable of effectively suppressing slippage between the fixing belt and the pressure member at the nip portion between the fixing belt and the pressure member, and an image forming apparatus including the same. The purpose is to provide.

  In order to achieve the above object, the present invention provides an endless fixing belt that can be rotated at substantially the same speed as the conveyance speed of a recording medium, a heating unit that heats the fixing belt, and inscribed in the fixing belt. A belt support member that slidably supports the fixing belt, and a pressure member that contacts the belt support member with a predetermined pressure via the fixing belt and applies a rotational driving force to the fixing belt, In a fixing device for fixing a non-fixed toner image carried on a recording medium by inserting a recording medium through a fixing nip formed by the fixing belt and the pressure member, on the outer side in the width direction of the belt support member, A pair of driven rotators for pressing the fixing belt against the pressure member with a pressure larger than that of the belt support member are provided.

  According to the present invention, in the fixing device configured as described above, the driven rotator is disposed outside an insertion region of the recording medium.

  According to the present invention, in the fixing device configured as described above, the distance between the pair of driven rotating bodies is such that the distance on the upstream side in the traveling direction of the fixing belt is shorter than the distance on the downstream side in the traveling direction.

  According to the present invention, in the fixing device configured as described above, the driven rotator is disposed so as to overlap an edge in a width direction of the fixing belt, and is in contact with both the fixing belt and the pressure member. Yes.

  According to the present invention, in the fixing device configured as described above, the driven rotor includes an inner diameter portion that contacts the fixing belt and an outer diameter portion that has a larger diameter than the inner diameter portion that contacts the pressure member. The difference in diameter between the outer diameter portion and the inner diameter portion is not more than twice the thickness of the fixing belt.

  According to the present invention, in the fixing device configured as described above, the outer peripheral surface of the driven rotating body has a tapered shape in which a diameter increases from the inner side in the width direction to the outer side of the fixing belt.

  According to the present invention, in the fixing device configured as described above, a lubricant is applied to the inner surface of the fixing belt.

  The present invention is also an image forming apparatus equipped with the fixing device having the above-described configuration.

  According to the first configuration of the present invention, the fixing belt is brought into pressure contact with the pressure member at the opposed portion of the driven rotor at a pressure higher than that of the opposed portion of the belt support member. As a result, a large frictional force is maintained between the fixing belt and the pressure member even when the recording medium is passed through the fixing nip portion opposed to the belt support member. Sliding with the member can be effectively suppressed.

  According to the second configuration of the present invention, in the fixing device having the first configuration, the driven rotator is disposed outside the insertion region of the recording medium, so that the fixing belt or The surface of the pressure member is not damaged by the insertion of the recording medium, and there is no possibility that the frictional force will decrease with time. Therefore, slipping between the fixing belt and the pressure member can be suppressed over a long period of time.

  According to the third configuration of the present invention, in the fixing device having the first or second configuration, the distance between the pair of driven rotating bodies on the upstream side in the traveling direction of the fixing belt is set to the distance on the downstream side in the traveling direction. By making the length shorter, each driven rotating body tends to be directed inward in the width direction of the fixing belt by rotation, so that it is possible to effectively suppress the meandering of the fixing belt due to component tolerances. Further, since the driven rotating body sends the fixing belt to the downstream side in the traveling direction so as to spread the fixing belt outward in the width direction, it is possible to prevent the fixing belt from being wrinkled.

  According to the fourth configuration of the present invention, in the fixing device of the second configuration, the driven rotator is disposed so as to overlap the edge in the width direction of the fixing belt, and the driven rotator is pressed against the fixing belt. Since both the members are in contact with each other, a driving force is directly applied from the pressure member to the driven rotator, so that slippage at the boundary surface between the fixing belt and the driven rotator can be more effectively suppressed. .

  Further, according to the fifth configuration of the present invention, in the fixing device of the fourth configuration, the driven rotating body has a larger diameter than the inner diameter portion that contacts the fixing belt and the inner diameter portion that contacts the pressure member. Since the outer diameter portion and the difference in diameter between the outer diameter portion and the inner diameter portion are not more than twice the thickness of the fixing belt, the pressing force acting on the fixing belt from the driven rotating body is secured. The slip of the body and the fixing belt can be prevented. Further, since the step formed at the boundary between the outer diameter portion and the inner diameter portion also serves as a detent for suppressing the meandering of the fixing belt, it is not necessary to separately provide a meandering prevention mechanism for the fixing belt.

  According to the sixth configuration of the present invention, in the fixing device having any one of the first to third configurations, the outer peripheral surface of the driven rotating body has a diameter from the inner side to the outer side in the width direction of the fixing belt. By making the taper shape larger, the pressing force gradually increases from the inside to the outside in the thickness direction of the driven rotor, so the fixing belt is sent downstream in the traveling direction so as to spread outward in the width direction and fixed. Generation of wrinkles on the belt can be prevented.

  Further, according to the seventh configuration of the present invention, in the fixing device having the sixth configuration, the sliding load between the fixing belt and the belt support member is further reduced by applying the lubricant to the inner surface of the fixing belt. In addition, the leakage of the lubricant from the end portion in the width direction of the fixing belt can be suppressed by the tapered shape of the driven rotor.

  Also, according to the eighth configuration of the present invention, by mounting the fixing device having any one of the first to seventh configurations, image defects such as image roughness and white spots caused by slipping of the fixing belt. Can be effectively suppressed, a high-quality image can be formed, and a belt-fixing type image forming apparatus having excellent durability can be obtained.

Schematic sectional view of an image forming apparatus equipped with the fixing device of the present invention Side surface sectional drawing of the fixing device 16 which concerns on 1st Embodiment of this invention. The top view which looked at the fixing device 16 of 1st Embodiment from the upper direction of FIG. Perspective view of belt support member 22 and pressing roller 31 An enlarged cross-sectional view of the central portion in the longitudinal direction of the pressure roller 23 to which the belt support member 22 is pressed against the fixing belt 21. Cross-sectional enlarged view of the longitudinal end of the pressure roller 23 to which the pressing roller 31 is pressed through the fixing belt 21. FIG. 9 is a partial plan view of the periphery of the pressing roller 31 of the fixing device according to the second embodiment of the present invention when viewed from the inside of the fixing belt 21. The top view of the fixing device which concerns on 3rd Embodiment of this invention. FIG. 9 is a partial plan view of the periphery of a pressing roller 31 of a fixing device according to a fourth embodiment of the present invention when viewed from the inside of a fixing belt 21.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing a configuration of an image forming apparatus equipped with a fixing device of the present invention. Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view of an image forming apparatus equipped with the developing device of the present invention. Here, a tandem color image forming apparatus is shown. In the main body of the color printer 100, four image forming portions Pa, Pb, Pc, and Pd are sequentially arranged from the upstream side in the transport direction (the right side in FIG. 1). These image forming portions Pa to Pd are provided corresponding to images of four different colors (magenta, cyan, yellow, and black), and magenta, cyan, and yellow are respectively subjected to charging, exposure, development, and transfer processes. And a black image are sequentially formed.

  These image forming portions Pa to Pd are provided with photosensitive drums 1a, 1b, 1c and 1d which carry visible images (toner images) of the respective colors, and are further illustrated by a driving means (not shown). In FIG. 1, an intermediate transfer belt 8 that rotates clockwise is provided adjacent to each of the image forming portions Pa to Pd. The toner images formed on the photosensitive drums 1a to 1d are sequentially primary-transferred and superimposed on the intermediate transfer belt 8 that moves while contacting the photosensitive drums 1a to 1d, and then the secondary transfer roller. 9 is secondarily transferred onto a transfer paper P as an example of a recording medium, and further fixed on the transfer paper P by the fixing device 13 and then discharged from the apparatus main body. An image forming process for each of the photosensitive drums 1a to 1d is executed while rotating the photosensitive drums 1a to 1d counterclockwise in FIG.

  The transfer paper P onto which the toner image is transferred is accommodated in a paper cassette 16 disposed at the lower part of the main body of the color printer 100, and is connected to the secondary transfer roller 9 and a later-described roller via a paper feed roller 12a and a registration roller pair 12b. The intermediate transfer belt 8 is conveyed to a nip portion with the driving roller 11. A sheet made of dielectric resin is used for the intermediate transfer belt 8, and a (seamless) belt having no seam is mainly used. Further, a blade-like belt cleaner 19 for removing toner remaining on the surface of the intermediate transfer belt 8 is disposed on the downstream side of the secondary transfer roller 9.

  Next, the image forming units Pa to Pd will be described. There are chargers 2a, 2b, 2c, and 2d for charging the photosensitive drums 1a to 1d and image information on the photosensitive drums 1a to 1d around and below the photosensitive drums 1a to 1d that are rotatably arranged. The exposure device 5 for exposing the toner, the developing devices 3a, 3b, 3c and 3d for forming toner images on the photosensitive drums 1a to 1d, and the developer (toner) remaining on the photosensitive drums 1a to 1d are removed. Cleaning parts 7a, 7b, 7c and 7d are provided.

  When image data is input from a host device such as a personal computer, first, the surfaces of the photosensitive drums 1a to 1d are uniformly charged by the chargers 2a to 2d, and then light is irradiated according to the image data by the exposure device 5. The electrostatic latent images corresponding to the image data are formed on the respective photosensitive drums 1a to 1d. Each of the developing devices 3a to 3d is filled with a predetermined amount of a two-component developer containing toner of each color of magenta, cyan, yellow, and black. In addition, when the ratio of the toner in the two-component developer filled in each developing device 3a to 3d falls below a specified value due to the formation of a toner image described later, each developing device 3a to 3d is transferred from the toner container 4a to 4d. Toner is replenished. The toner in the developer is supplied onto the photosensitive drums 1a to 1d by the developing devices 3a to 3d and electrostatically adheres to the electrostatic latent image formed by the exposure from the exposure device 5. A toner image is formed.

  The primary transfer rollers 6a to 6d apply an electric field at a predetermined transfer voltage between the primary transfer rollers 6a to 6d and the photosensitive drums 1a to 1d, and magenta, cyan, yellow, and yellow on the photosensitive drums 1a to 1d. A black toner image is primarily transferred onto the intermediate transfer belt 8. These four color images are formed with a predetermined positional relationship predetermined for forming a predetermined full-color image. Thereafter, in preparation for the subsequent formation of a new electrostatic latent image, the toner remaining on the surfaces of the photosensitive drums 1a to 1d after the primary transfer is removed by the cleaning units 7a to 7d.

  The intermediate transfer belt 8 is stretched over an upstream driven roller 10 and a downstream drive roller 11, and the intermediate transfer belt 8 rotates clockwise as the drive roller 11 is rotated by a drive motor (not shown). When the rotation starts, the transfer paper P is conveyed from the registration roller pair 12b to the nip portion (secondary transfer nip portion) between the drive roller 11 and the secondary transfer roller 9 provided adjacent thereto at a predetermined timing. The full color image on the intermediate transfer belt 8 is transferred onto the transfer paper P. The transfer paper P onto which the toner image is transferred is conveyed to the fixing device 13.

  The transfer paper P conveyed to the fixing device 13 is heated and pressed by the fixing belt 21 and the pressure roller 23 (see FIG. 2), and the toner image is fixed on the surface of the transfer paper P, thereby forming a predetermined full-color image. Is done. The transfer paper P on which the full-color image is formed is distributed in the transport direction by the branching portion 14 that branches in a plurality of directions. When an image is formed on only one side of the transfer paper P, it is discharged as it is onto the discharge tray 17 by the discharge roller pair 15.

  On the other hand, when images are formed on both sides of the transfer paper P, the transfer paper P that has passed through the fixing device 13 is once transported in the direction of the discharge roller pair 15 and discharged after the trailing edge of the transfer paper P has passed through the branch portion 14. By rotating the roller pair 15 in the reverse direction and switching the conveyance direction of the branching portion 14, the transfer paper P is distributed from the rear end of the transfer paper P to the reverse conveyance path 18 and re-conveyed to the secondary transfer nip portion with the image surface reversed. Is done. Then, after the next image formed on the intermediate transfer belt 8 is transferred by the secondary transfer roller 9 to the surface of the transfer paper P where the image is not formed and conveyed to the fixing device 13 to fix the toner image. , And discharged to the discharge tray 17.

  FIG. 2 is a side sectional view of the fixing device according to the first embodiment of the present invention, and FIG. 3 is a plan view of the fixing device as viewed from above in FIG. As shown in FIGS. 2 and 3, the fixing device 13 includes an endless fixing belt 21 that rotates counterclockwise in FIG. 2, a belt support member 22 that is inscribed in the fixing belt 21, and a belt support member 22. A pair of pressing rollers 31 rotatably attached to both ends, a pressure roller 23 which is pressed against the belt support member 22 and the pressing roller 31 via the fixing belt 21 and rotates clockwise in FIG. And an induction heating unit 25 disposed on the opposite side of the pressure roller 23 with the belt 21 interposed therebetween. In addition, description of the induction heating part 25 is abbreviate | omitted in FIG.

  The fixing belt 21 is an endless shape formed by laminating a plurality of layers including an induction heating layer provided on the innermost side in contact with the belt support member 22 and a release layer provided on the outermost side in contact with the pressure roller 23. It is a belt. The fixing belt 21 is wound around an arc-shaped flange portion 24 that protrudes from the inner surface of the belt support member 22, the pressing roller 31, and the fixing housing (not shown) and is inscribed at both ends in the width direction of the fixing belt 21. A predetermined tension is applied, and a portion not in contact with the belt support member 22 and the pressing roller 31 is held in an arc shape with a predetermined distance from the induction heating unit 25. Instead of the flange portion 24, a support member having a cross-sectional arch shape inscribed in the fixing belt 21 may be disposed on the opposite side of the belt support member 22 (the side facing the induction heating unit 25).

  As the induction heating layer of the fixing belt 21, a metal layer obtained by plating or rolling a metal such as nickel is used. The release layer is made of a fluorine resin such as PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), and is formed by applying a paint or covering the tube. The release layer has a thickness of about 10 to 50 μm for a PFA tube and about 10 to 30 μm for a fluororesin paint.

  Further, a silicon rubber layer having a thickness of about 100 to 1000 μm may be provided as an elastic layer between the induction heating layer and the release layer. According to this configuration, the elastic layer wraps the unfixed toner image on the paper and can be fixed softly. As a result, the image quality can be improved and the high-performance fixing device 13 can be obtained.

  In addition, a heat storage layer may be provided between the induction heating layer and the release layer so that heat generated in the induction heating layer is not released, and the temperature of the surface of the fixing belt 21 can be kept uniform. As a result, higher heating efficiency can be obtained, and the effects of shortening the warm-up time and reducing power consumption can be enhanced.

  The heat storage layer is composed of silicon rubber having a high thermal conductivity, such as silica, alumina, magnesium oxide powder or the like, and a metal having a high thermal conductivity, such as aluminum, copper, nickel, etc. These are formed by covering or plating a tube-shaped product. The heat storage layer may be made of an elastic material such as silicon rubber. However, when it is made of metal, if the wall thickness is made too thick, the belt hardness increases, and the nip amount necessary to melt the toner is obtained. It will not be possible. Therefore, the thickness of the heat storage layer is 10 to 1000 μm, desirably 50 to 500 μm.

  As the configuration of the fixing belt 21 used in the present embodiment, for example, a 200 μm-thick silicon rubber layer (elastic layer) is laminated on a 35 μm-thick nickel layer (induction heating layer), and a 30 μm-thick PFA tube ( And a belt having an outer diameter of 40 mm and a width of 360 mm coated with a release layer.

  A thermistor (not shown) is provided so as to contact the surface of the fixing belt 21. The temperature of the fixing belt 21 is detected by this thermistor, and the fixing temperature is controlled by turning on / off the current flowing through the induction heating unit 25.

  Also, the dimension in the width direction of the fixing belt 21 (perpendicular to the paper surface in FIG. 2) is set smaller than the dimension in the width direction of the induction heating unit 25 and wider than the maximum sheet width passing through the fixing nip N. Has been. As a result, the induction heating unit 25 uniformly heats the entire fixing belt 21 to prevent the occurrence of uneven fixing, and the fixing belt 21 can cover the entire surface of the paper regardless of the paper size. Unfixed toner can be prevented from adhering to the pressing roller 31.

  The belt support member 22 is in contact with the pressure roller 23 via the fixing belt 21 to form a fixing nip portion N through which a sheet is inserted. As a material of the belt support member 22, a metal such as aluminum, a heat resistant resin, or the like is used. Further, a silicon rubber layer having a thickness of about 100 to 1000 μm is provided as an elastic layer on the contact surface with the fixing belt 21, and a PTFE (polytetrafluoroethylene) sheet is provided as a release layer on the surface of the silicon rubber layer. It is pasted.

  As a configuration of the belt support member 22 used in the present embodiment, for example, a silicon plate having a thickness of 500 μm is formed on a surface of a rectangular parallelepiped stainless steel (SUS) plate member having a width of 11 mm and a length of 300 mm facing the fixing belt 21. A rubber layer (elastic layer) is laminated, and a PTFE sheet (release layer) is further adhered to the rising portion of the opposing surface. A hollow belt support member 22 formed by bending a thin metal plate may be used.

  The pressure roller 23 is provided with an elastic layer 23b on the outer side of the cored bar 23a, for example. A pressure adjusting mechanism (not shown) for adjusting the pressure of the pressure roller 23 is disposed on the cored bar 23a. In the present embodiment, a pressure roller 23 having an outer diameter of 35 mm, in which a silicon rubber layer 23b having a thickness of 7.5 mm constituting an elastic layer is provided on the outer side of an aluminum core 23a having a diameter of 20 mm, is used. The pressure roller 23 is driven to rotate clockwise by a drive motor (not shown). The surface of the pressure roller 23 may be covered with a release layer such as a PFA tube.

  The induction heating unit 25 heats the fixing belt 21 by electromagnetic induction, and is configured by a coil bobbin 27, a coil 29, a core portion including a center core 30a, an arch core 30b, and a side core 30c. It arrange | positions facing so that a part of outer surface of this may be enclosed.

  The coil bobbin 27 is formed in a circular arc shape along the outer surface of the fixing belt 21. The material of the coil bobbin 27 is preferably a heat-resistant resin (for example, PPS: polyphenylene sulfide resin, PET: polyethylene terephthalate resin, LCP: liquid crystal polymer resin).

  On the coil bobbin 27, a coil 29 in which a litz wire bundled with thin wires is wound a plurality of times (here, 8 times) in the longitudinal direction of the induction heating unit 25 (perpendicular to the paper surface of FIG. 2) is arranged. The coil 29 is connected to a power source (not shown). The coil 29 is fixed to the coil bobbin 27 using, for example, a heat resistant adhesive (for example, a silicon-based adhesive).

  The center core 30 a is a ferrite core having a rectangular cross section disposed in the center of the coil 29. A pair of arch cores 30b and side cores 30c are disposed on both sides of the center core 30a. The arch cores 30b on both sides are ferrite cores having symmetrical shapes with respect to the center core 30a and having a cross-sectional shape formed into an arch shape. The total length of each arch core 30b is longer than the area where the coil 29 is disposed. The side cores 30c on both sides are ferrite cores formed in a block shape. The side core 30c is connected to one end (upper and lower ends in FIG. 2) of each arch core 30b. Each side core 30c covers the outside of the region where the coil 29 is disposed.

  The arch core 30b is arrange | positioned in multiple places at intervals in the longitudinal direction of the induction heating part 25, for example. In the present embodiment, the interval between adjacent arch cores 30b is about 10 mm. Further, the higher the arrangement density of the arch cores 30b, the better the magnetic flux induction performance. However, even if the arrangement density of the arch cores 30b is reduced to some extent, the decrease in magnetic flux induction performance is small. Therefore, it is preferable to set the arrangement density of the arch cores 30b so that high cost performance can be obtained within a range where sufficient performance can be exhibited. Further, when adjusting the temperature distribution in the width direction of the fixing belt 21, it can be dealt with by adjusting the arrangement density of the arch cores 30 b.

  Moreover, the side core 30c is divided | segmented into plurality in the longitudinal direction of the induction heating part 25, The length of one is about 30-60 mm. The plurality of side cores 30c are continuously arranged in the longitudinal direction of the induction heating unit 25 without being spaced apart. The total length of the range in which the side core 30c is disposed corresponds to the length of the region in which the coil 29 is disposed. Thus, by arranging a plurality of side cores 30c continuously, there is an effect of equalizing the fluctuation width of the temperature distribution due to the arrangement of the arch core 30b. The arrangement of each arch core 30b and side core 30c is determined in accordance with, for example, the magnetic flux density (magnetic field strength) distribution of the coil 29. Since the arch core 30b is arranged at a certain distance, the side core 30c compensates for the effect of converging the magnetic flux at the location where the arch core 30b is removed, and leveles the magnetic flux density distribution (temperature distribution) in the longitudinal direction.

  The induction heating unit 25 generates a magnetic flux through the center core 30a, the arch cores 30b and the side cores 30c on both sides by supplying a high frequency current to the coil 29. The magnetic flux generated from the induction heating unit 25 acts on the induction heating layer of the fixing belt 21. As a result, an eddy current is generated around the magnetic flux of the induction heat generation layer, so that Joule heat is generated by the electric resistance in the induction heat generation layer, and the fixing belt 21 generates heat.

  The current flowing through the coil 29 is controlled by the thermistor so that the fixing belt 21 has a predetermined temperature. When the fixing belt 21 is heated by the induction heating unit 25 and the temperature is raised to a predetermined temperature, the transfer paper P (see FIG. 1) sandwiched by the fixing nip N is heated and the pressure roller 23 By being pressurized, the toner in the powder state on the transfer paper P is melted and fixed.

  A separation plate 35 that separates the sheet from the fixing belt 21 and a separation plate holder 37 that supports the separation plate 35 are disposed on the downstream side of the fixing nip N with respect to the sheet conveyance direction (from the bottom to the top in FIG. 2). Has been. In the present embodiment, a separation plate 35 having a length of 336 mm and having a fluororesin coating on the surface of a stainless plate having a thickness of 0.1 mm is attached to a separation plate holder 37 made of stainless steel having a thickness of 1.2 mm.

  FIG. 4 is a perspective view of the belt support member 22 and the pressing roller 31. The configurations of the belt support member 22 and the pressing roller 31 used in the fixing device of the present invention will be described in detail with reference to FIGS. In FIG. 4, the arm portion 22a of the belt support member 22 is not shown.

  As shown in FIG. 3, arm portions 22 a protrude from both longitudinal ends of the belt support member 22, and the arm portions 22 a are urged in the direction of arrow A by a coil spring 33. Further, as shown in FIG. 4, the pressing roller 31 is rotatably attached to a support shaft 32 fixed to both end surfaces in the longitudinal direction of the belt support member 22. That is, the belt support member 22 and the pressing roller 31 are pressed against the pressure roller 23 with a predetermined pressure with the fixing belt 21 interposed therebetween. Further, the pressing roller 31 presses the fixing belt 21 against the pressure roller 23 outside the sheet passing region R (non-sheet passing region). As a configuration of the pressing roller 31, for example, a disk-shaped PPS (polyphenylene sulfide) resin having a diameter of 16 mm and a width of 5 mm may be coated with a silicon resin.

  FIG. 5 is an enlarged cross-sectional view of the central portion in the longitudinal direction of the pressure roller 23 to which the belt support member 22 is pressed against the fixing belt 21, and FIG. 6 illustrates the pressing roller 31 being pressed against the fixing belt 21. It is a cross-sectional enlarged view of the longitudinal direction edge part of the pressure roller 23 which is. The outer peripheral surface 31 a of the pressing roller 31 shown in FIG. 4 protrudes closer to the pressure roller 23 than the surface 22 b of the belt support member 22 facing the fixing belt 21. As a result, a higher pressing force is generated in the facing portion S between the pressing roller 31 and the pressure roller 23 than in the facing portion (fixing nip portion N) between the belt support member 22 and the pressing roller 23.

  In the fixing device 16 of this embodiment, the fixing belt 21 is pressed against the pressure roller 23 at a pressure higher than that of the fixing nip portion N at the facing portion S of the pressing roller 31. Thereby, even when the sheet is passed through the fixing nip portion N, a large frictional force is maintained between the fixing belt 21 and the pressure roller 23. Thus, image defects such as image roughness and white spots due to the slip of the fixing belt 21 can be effectively suppressed.

  In addition, since the pressing roller 31 presses the non-sheet passing region of the fixing belt 21, the surface of the fixing belt 21 and the pressure roller 23 is not damaged by the sheet passing at the opposing portion S of the pressing roller 31, and the friction with time. There is no risk of power loss. Accordingly, slipping between the fixing belt 21 and the pressure roller 23 can be suppressed over a long period of time.

  In order to maintain stable fixing performance even in a color image with a large amount of toner adhesion, it is necessary to secure a wide nip width in the fixing nip portion N. Therefore, as shown in FIG. 5, in the fixing nip portion N, the fixing belt 21 has a flat shape along the facing surface 22 b of the belt support member 22. On the other hand, at the facing portion S of the pressing roller 31, as shown in FIG. 6, the circular pressing roller 31 bites into the surface of the pressure roller 23, so that the fixing belt 21 is deformed into an arc shape in cross section. If the deformation of the fixing belt 21 at the facing portion S of the pressing roller 31 becomes large, the fixing belt 21 may be bent between the fixing nip portion N and the facing portion S to be damaged.

  Therefore, the facing portion S of the pressing roller 31 needs to be configured so that the degree of deformation of the fixing belt 21 is reduced. Specifically, the dent amount on the surface of the pressure roller 23 at the facing portion S of the pressing roller 31 is about 1 mm larger than the dent amount on the surface of the pressure roller 23 at the facing portion (fixing nip portion N) of the belt support member 22. It is preferable to set so that Other methods for reducing the bending of the fixing belt 21 include, for example, a method of securing the distance from the belt support member 22 to the pressing roller 31 by increasing the support shaft 32 and a method of increasing the diameter of the pressing roller 31. Can be mentioned.

  FIG. 7 is a partial plan view of the periphery of the pressing roller 31 of the fixing device according to the second embodiment of the present invention as viewed from the inside of the fixing belt 21. In FIG. 7, only one of the pair of pressing rollers 31 is shown, but the other is exactly the same. In the present embodiment, the rear of each pressing roller 31 is inclined inward by an angle θ with respect to the traveling direction of the fixing belt 21 (the direction of arrow B). That is, the pair of pressing rollers 31 are provided with a toe-in so that the distance between the pressing rollers 31 on the upstream side in the traveling direction of the fixing belt 21 is shorter than the distance between the pressing rollers 31 on the downstream side in the traveling direction. Since the configuration of other parts is the same as that of the first embodiment, description thereof is omitted.

  Note that “toe-in” generally means that in the front wheels of an automobile, the distance between the left and right front wheels on the front side in the traveling direction is set shorter than the distance between the left and right front wheels on the rear side in the traveling direction.

  According to the configuration of the present embodiment, by attaching a toe-in to the pair of pressing rollers 31, each pressing roller 31 tends to face the inside of the fixing belt 21 by rotation. Meandering of the fixing belt 21 in the opposite portion S of the pressing roller 31 caused by misalignment of the core metal 23a (roller rotating shaft) or variation in the urging force of the coil spring 33, and the fixing belt 21 goes straight as a result. Can be made.

  In addition, since it is not necessary to apply a pulley or the like to the end face of the fixing belt 21 to prevent the fixing belt 21 from meandering, the configuration of the fixing device 16 is simplified. Furthermore, since the fixing belt 21 is sent to the downstream side in the traveling direction so as to be spread outward in the width direction by the respective pressing rollers 31, wrinkles of the fixing belt 21 can be prevented. Note that the angle θ of the pressing roller 31 needs to be decreased as the moving speed of the fixing belt 21 increases. For example, when the moving speed (system linear velocity) of the fixing belt 21 is 250 mm / sec to 400 mm / sec, the angle θ (toe-in angle) is preferably about 2 °.

  FIG. 8 is a plan view of a fixing device according to a third embodiment of the present invention. In this embodiment, the pressing roller 31 is disposed at a position overlapping the side edge 21 a of the fixing belt 21, and the pressing roller 31 has an inner diameter portion 38 that contacts the fixing belt 21 and an outer surface that contacts the pressure roller 23. It is comprised with the diameter part 39. FIG. Further, the diameter of the outer diameter portion 39 is larger than that of the inner diameter portion 38. Since the configuration of other parts is the same as that of FIG. 3 of the first embodiment, the description thereof is omitted.

  According to the configuration of the present embodiment, a driving force is applied from the pressure roller 23 to the pressing roller 31 by the outer diameter portion 39 that is in direct contact with the pressing roller 23, and therefore the boundary between the fixing belt 21 and the pressing roller 31. Slip on the surface can be more effectively suppressed. Further, by making the diameter of the outer diameter portion 39 larger than that of the inner diameter portion 38, excessive pressing force is applied from the pressing roller 31 to the fixing belt 21, or the pressing force applied from the pressing roller 31 to the pressure roller 23 is insufficient. You do n’t have to. Further, since the step formed at the boundary between the outer diameter portion 39 and the inner diameter portion 38 also serves as a detent for suppressing the meandering of the fixing belt 21, a meandering prevention mechanism for the fixing belt 21 as in the second embodiment. Need not be provided separately.

  On the other hand, when the step between the outer diameter portion 39 and the inner diameter portion 38 is larger than the thickness of the fixing belt 21, the pressing force acting on the fixing belt 21 from the pressing roller 31 is insufficient, and the fixing belt 21 may slip. is there. Therefore, the step formed at the boundary between the outer diameter portion 39 and the inner diameter portion 38 is equal to or less than the thickness of the fixing belt 21, that is, the difference in diameter between the outer diameter portion 39 and the inner diameter portion 38 is determined. Therefore, the pressing force acting on the fixing belt 21 from the pressing roller 31 can be made equal to or higher than the pressing force acting on the pressing roller 23 from the pressing roller 31.

  If the elastic layer 23 b of the pressure roller 23 has sufficient elasticity, the pressing roller 31 having the flat outer peripheral surface 31 a without the inner diameter portion 38 and the outer diameter portion 39 is inserted into the fixing belt 21. You may arrange | position in the position which overlaps with the side edge 21a. In this configuration, the gap corresponding to the thickness of the fixing belt 21 is absorbed by the deformation of the elastic layer 23 b, and the outer peripheral surface 31 a of the pressing roller 31 is reliably in contact with the pressure roller 23.

  FIG. 9 is a partial plan view of the periphery of the pressing roller 31 of the fixing device according to the fourth embodiment of the present invention as viewed from the inside of the fixing belt 21. In FIG. 9, only one of the pair of pressing rollers 31 is shown, but the other is exactly the same. In the present embodiment, the silicon oil 40 is supplied to the back surface of the fixing belt 21 using a roller-like or pad-like application member (not shown), and is generated between the fixing belt 21 and the belt support member 22. Reduces sliding load. The pressing roller 31 has a shape in which the outer peripheral surface 31a is tapered so that the diameter r1 of the outer edge portion is larger than the diameter r2 of the inner edge portion. Since the configuration of other parts is the same as that of the first embodiment, description thereof is omitted.

  Silicone oil 40 has a small change in viscosity due to a change in temperature and is suitable as a lubricant for a sliding belt fixing system used from room temperature to about 200 ° C. However, since the viscosity is relatively low, the end of fixing belt 21 is fixed. It may leak out from the part. Therefore, there is a problem that the slidability between the fixing belt 21 and the belt support member 22 cannot be maintained, or the image quality is deteriorated due to adhesion to the outer peripheral surface of the fixing belt 21.

  Therefore, in the present embodiment, the outer peripheral surface 31a of the pressing roller 31 is tapered to make the outer edge diameter r1 larger than the inner edge diameter r2, thereby increasing the pressing force at the outer edge of the pressing roller 31. Yes. Thereby, the leakage of the silicon oil 40 from the gap between the fixing belt 21 and the pressing roller 31 can be suppressed. In place of the silicon oil 40, fluorine oil, paraffin oil or the like may be used as a lubricant.

  Note that the pressing roller 31 used in the fixing device 13 of the present embodiment can also be used in a configuration in which the silicon oil 40 is not supplied to the back surface of the fixing belt 21. In this case, since the pressing force gradually increases from the inner side in the thickness direction toward the outer side of the pressing roller 31, the fixing belt 21 is sent downstream in the traveling direction so as to be spread outward in the width direction. Thereby, the occurrence of wrinkles on the fixing belt 21 can be prevented.

  In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, in each of the above embodiments, the pair of pressing rollers 31 are supported on both end surfaces of the belt support member 22, but the pressing rollers 31 are provided separately from the belt support member 22, and the belt support member 22 is a dedicated spring member. The non-sheet passing region of the fixing belt 21 may be brought into contact with a stronger pressing force.

  Further, the configuration of the fixing belt 21 and the pressure roller 23 shown in the above embodiment is a preferable example, and other configurations capable of achieving the object of the present invention can also be adopted. Further, instead of the induction heating unit 25, other heating means such as a halogen lamp may be provided.

  The fixing device of the present invention is not limited to the tandem type color printer shown in FIG. 1, but uses an electrophotographic process such as a digital multifunction machine, a color copying machine, an analog type monochrome copying machine, a monochrome printer, or a facsimile. The present invention can be applied to various image forming apparatuses.

  The present invention relates to a belt fixing for fixing an unfixed toner image carried on a recording medium by inserting the recording medium into a fixing nip formed by a fixing belt and a pressure roller that contacts the fixing belt with a predetermined pressure. It can be used for a fixing device of the type. By utilizing the present invention, a sufficient area of the nip portion between the fixing belt and the pressure roller is ensured, and slippage between the fixing belt and the pressure roller at the nip portion is effectively prevented to prevent image defects. A fixing device that can be provided can be provided.

DESCRIPTION OF SYMBOLS 13 Fixing device 21 Fixing belt 22 Belt support member 22a Arm part 23 Pressure roller (pressure member)
25 Induction heating section (heating means)
31 Press roller (driven rotor)
31a Outer peripheral surface 32 Support shaft 33 Coil spring (biasing member)
35 Separating plate 37 Separating plate holder 38 Inner diameter 39 Outer diameter 40 Silicon oil (lubricant)
100 Color printer N Fixing nip P Transfer paper (recording medium)

Claims (8)

An endless fixing belt that can be rotated at substantially the same speed as the conveyance speed of the recording medium;
Heating means for heating the fixing belt;
A belt support member that is inscribed in the fixing belt and slidably supports the fixing belt;
A pressure member that contacts the belt support member with a predetermined pressure via the fixing belt and applies a rotational driving force to the fixing belt;
A fixing device for fixing the unfixed toner image carried on the recording medium by inserting the recording medium through a fixing nip formed by the fixing belt and the pressure member,
A fixing device comprising a pair of driven rotating bodies that press the fixing belt against the pressing member with a pressure larger than that of the belt supporting member, on the outer side in the width direction of the belt supporting member.   The fixing device according to claim 1, wherein the driven rotator is arranged outside an insertion region of the recording medium.   3. The fixing device according to claim 1, wherein the distance between the pair of driven rotating bodies is such that the distance on the upstream side in the traveling direction of the fixing belt is shorter than the distance on the downstream side in the traveling direction.   The fixing device according to claim 2, wherein the driven rotating body is disposed so as to overlap an edge in a width direction of the fixing belt, and contacts both the fixing belt and the pressure member.   The driven rotator has an inner diameter part that contacts the fixing belt and an outer diameter part that is larger in diameter than the inner diameter part that contacts the pressure member, and a difference in diameter between the outer diameter part and the inner diameter part. The fixing device according to claim 4, wherein is less than twice the thickness of the fixing belt.   4. The fixing device according to claim 1, wherein an outer peripheral surface of the driven rotating body has a tapered shape whose diameter increases from the inner side to the outer side in the width direction of the fixing belt.   The fixing device according to claim 6, wherein a lubricant is applied to an inner surface of the fixing belt.   An image forming apparatus comprising the fixing device according to claim 1.

Images