JP2017129617A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain the curvature shape of and pressure condition for the exit of a nip to achieve stable, good separation performance and image quality.SOLUTION: A fixing device 100 comprises a fixing belt 12 that is laid over a fixing roller 11 and a heating roller 14 with a constant tension, and includes a pressure roller 13 that is rotatably in pressure contact therewith on a lower side to form a nip part N. A curvature forming member 16 that reduces the radius of curvature of the fixing belt 12 immediately after the nip part N is provided inside the fixing belt 12. The fixing device 100 further includes separation means 19 that is attached on a sheet ejection side of the nip part N to have its leading end maintaining a minute gap M with the fixing belt 12. The curvature forming member 16 has a projection 16 colliding with a bearing 13a and maintains the substantially constant positional relationship with the pressure roller 13 even when the amount of pressure contact is changed with a cam 21, and thereby the substantially constant curvature of the fixing belt 12 formed by the curvature forming member 16 can be maintained.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a fixing device and an image forming apparatus including the fixing device, such as a copier, a printer, a facsimile machine, or a complex machine thereof.

  An image forming apparatus such as a copying machine is generally provided with a fixing device for fixing the toner image on a sheet-like medium on which a toner image as a non-fixed image is formed. This type of fixing device includes a first rotating member that is a pair of rollers or an endless belt heated by a heating unit such as a heater, and the rotating member in contact with the rotating member and at a position facing the fixed point member. It is common to have a second rotating member (which is usually provided with heating means) on a roller that rotates in the same direction as the member.

  In such a fixing device, the sheet-like medium carrying the toner image is passed through the nip portion due to the opposing contact between the first rotating member and the second rotating member, and heating and pressing are performed at this time ( By nip fixing, the toner image is heated and melted and fixed on the sheet-like medium.

  As a conventional example of a fixing device using a fixing belt, for example, Patent Document 1 is known. This document discloses a technique for setting the hardness of the elastic body of the pressure roller to be 20 to 30 degrees larger than the hardness of the elastic body of the fixing roller by a JIS-A hardness meter. In this technique, since the nip shape is convex, the peeling angle of the transfer material from the heating roller can be increased, and the separation performance is improved. In the technique disclosed in Patent Document 2, a fixing separation claw for separating a recording medium is disposed in a non-contact manner with the surface of the fixing roller. Further, Patent Document 3 discloses a pressure member that performs fixing by forming a nip by pressure contact with a fixing roller via a pressure belt. In this technique, a part of the pressure member (the pressure member is fixed) bites into the fixing roller via the belt at the nip outlet separation portion to form a distortion, and the distortion is caused between the belt and the fixing roller. The aim is to improve separability by the micro slip effect. The belt is referred to as a free belt nip system in which the belt is freely set on the pressure fixing member and there is no belt tension means.

  Further, Patent Document 4 discloses a belt fixing device using a curvature forming member. This technique is provided with a fixed curvature forming member inside the fixing belt, and improves the separation of the transfer paper from the fixing belt.

All the above prior arts still have problems.
In the technique of Patent Document 1, it is difficult to reliably separate the toner due to the effect of the nip shape under the condition that the amount of toner adhering to each color toner in the color image forming apparatus is large. In particular, it is difficult to separate the transfer material without separation means that abuts against a heating roller such as a separation claw under severe conditions such as oilless and high linear velocity.

  In the technique of Patent Document 2, since the fixing roller and the pressure roller have the same configuration, the nip shape is flat and the peeling angle with respect to the fixing roller is small. Therefore, it is necessary to accurately adjust the distance between the separation claw and the fixing roller. . That is, since an adjustment mechanism for the interval is required, the number of parts of the separation claw is increased and the cost is increased. Also in this method, it is difficult to ensure separation performance corresponding to each paper type without applying oil as described above.

  Further, the technique of Patent Document 3 also has a problem that it causes a cost increase because a separation means for assisting the separation performance is provided since the separation performance cannot be obtained sufficiently. Furthermore, the technique of Patent Document 4 has a problem that the separation of the fixing belt is deteriorated because the contribution of the curvature of the fixing belt is reduced particularly when the pressure roller is used in a state where the pressure contact position is located below. Further, there is a problem that the amount of heat received by the sheet from the fixing belt changes in the section from the fixing nip exit to the curvature forming member due to the difference in the pressure contact position of the pressure roller, and the gloss of the toner image varies.

  The present invention eliminates the disadvantages of the conventional belt fixing device, reduces the radius of curvature of the separation portion to improve the separation performance, and performs self-separation of recording paper after single-sided and double-sided fixing, that is, self-separation. It is an object of the present invention to provide a belt fixing device and an image forming apparatus that enable stripping. It is another object of the present invention to reliably separate recording materials without significantly reducing the durability of a fixing belt or a pressure roller.

  The fixing device according to the present invention includes a fixing roller, a heating roller, a fixing belt stretched between both rollers, and a pressure contact that contacts the outer peripheral surface of the fixing belt and forms a nip portion with the fixing belt. In the fixing device including the pressure roller that can be separated, the inner side of the fixing belt on the outlet side of the portion of the nip portion formed by the fixing roller and the pressure roller via the fixing belt. A curvature forming member that forms an outlet separation portion of the nip portion by being pressed against the pressure roller via the fixing belt, and the fixing belt is guided in contact with the curvature formation member at the outlet separation portion, An end portion of the curvature forming member is biased by an end support portion of the pressure roller.

  According to the present invention, in the separation device, it is possible to provide a fixing device that maintains the curvature shape and pressure condition of the nip outlet and achieves stable and good separation performance and image quality. Further, the image forming apparatus can improve the image quality, and both the image forming apparatus and the fixing apparatus have the effects of stabilizing and improving the reliability of the apparatus.

1 is a schematic configuration diagram of a fixing device that can be an object of the present invention. FIG. 2 is a schematic configuration diagram illustrating an operation state of the fixing device in FIG. 1. FIG. 10 is a schematic configuration diagram illustrating an operation state of a conventional fixing device. 1 is a diagram illustrating a configuration of a tandem type color copier that is an image forming apparatus according to the present invention. FIG.

  The present invention relates to a fixing device provided with a curvature forming member for assisting separation of a sheet-like medium (recording paper) after fixing, and an image forming apparatus including the fixing device. Specifically, a fixing device that heats and fixes toner on a sheet to be conveyed and a copying machine, a printer, a facsimile device that forms an image by transferring a toner image formed using an electrophotographic method after being transferred onto the sheet, or these The present invention relates to an image forming apparatus provided with a fixing device, such as a multifunction peripheral.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of a fixing device that can be an object of the present invention. The illustrated fixing device 100 includes a fixing member (fixing belt 12) that is a first nip forming member that is stretched around the fixing roller 11 and the heating roller 14 with a constant tension. A pressure member (pressure roller 13), which is a second nip forming member that forms a fixing pressure contact portion (hereinafter referred to as a nip portion N) by pressing the fixing belt 12 in a rotatable manner on the lower side. Further, inside the fixing belt 12, the surface of the metal base is covered with a fluorine-based coating or a fluorine-based sheet-like material, and immediately after the nip portion N, the radius of curvature of the fixing belt 12 is reduced. A curvature forming member 16 is provided. In addition, a separation unit 19 is provided on the sheet discharge side of the nip portion N and attached to the front end so as to hold a minute gap M with the fixing belt 12. Further, a separation claw 18 for preventing the sheet P from being wrapped around the pressure member (the pressure roller 13) is provided.

  The fixing belt 12 is an endless belt, and has a two-layer structure in which an elastic layer such as a silicon rubber layer is formed on a base material such as nickel, stainless steel, or polyimide. The fixing roller 11 has a metal core and silicon rubber. In order to shorten the warm-up time, foamed silicon rubber may be used so that the heat of the fixing belt 12 is not easily absorbed. The heating roller 14 is an aluminum or iron hollow roller and has a heat source including a heater 14h such as a halogen heater inside. The heat source may be an induction heating mechanism (IH).

  When the fixing device 100 is driven, for example, the fixing belt 12 is rotated in the clockwise direction in the drawing, and the fixing belt 12 discharges the sheet P in a state where an appropriate tension is applied by pressing the tension roller 15 ( It rotates in the clockwise direction in FIG. Note that the pressure roller is pressed to form a nip portion N during paper passing, and the pressure roller is separated from the fixing belt during standby. Further, at the time of fixing, the fixing belt 12 is heated to a predetermined temperature (for example, a temperature suitable for toner fixing) detected by a thermistor (not shown) due to heat generated by a heater 14 h disposed inside the heating roller 14. Is done.

  The pressure roller 13 is a cylindrical roller in which an elastic layer such as silicon rubber is usually provided on a core metal such as aluminum or iron. Further, it is possible to apply pressure by moving the pressure roller 13 toward the fixing belt 12 by a pressure / pressure releasing means (not shown), and to release pressure by moving the pressure roller 13 away from the fixing belt 12. When the fixing device 100 is driven, the pressing and depressurizing means presses the pressure roller 13 against the fixing belt 12 by pressing it toward the fixing belt 12 with a constant pressure.

  Here, a protrusion 16 a is provided at the outer end of the curvature forming member 16 in the width direction of the fixing belt 12 (perpendicular to the paper surface in FIGS. 1 to 3). The curvature forming member 16 is pressed and urged against the pressure roller 13 with the center of the fixing roller 11 as a fulcrum. In other words, the torsion coil spring 20 is urged counterclockwise in the figure, and the protrusion 16 a comes into contact with the bearings 13 a provided at both ends of the pressure roller 13. The pressure contact amount of the pressure roller 13 can be varied to optimize the amount of heat applied to the transfer paper according to the paper type and paper thickness. When the cam 21 further rotates counterclockwise as shown in FIG. 2, the cam follower 23 a attached to the inner arm 23 is pushed up, and the outer arm 25 is pushed up by the load of the spring 24. A bearing 13a of a pressure roller rides on the bearing support portion 25a of the outer arm. When the outer arm 25 is pushed up, the pressure roller 13 bites into the fixing roller 11.

  The curvature forming member 16 has a protrusion 16 a that abuts against the bearing 13 a and is separated from the surface of the fixing roller 11. Therefore, even if the amount of press contact is changed by the cam 21, the positional relationship with respect to the pressure roller 13 is substantially constant. Therefore, the curvature of the fixing belt 12 formed by the curvature forming member 16 can be kept substantially constant. Further, the nip portion between the fixing roller 11 and the pressure roller 13 and the nip portion between the curvature forming member 16 and the pressure roller 13 are physically separated. As a result, a pressure valley is formed between the nip portion formed by the fixing roller 11 and the pressure roller 13 and the nip portion formed by the curvature forming member 16 and the pressure roller 13. The curvature shape and the pressure condition can be maintained with an easy configuration.

  In the illustrated fixing device 100, the surface of the fixing belt 12 is heated to a predetermined temperature while the fixing belt 12 and the pressure roller 13 are rotationally driven. When the sheet P on which the unfixed toner T is formed passes through the nip portion N, fixing is performed by thermally fusing the unfixed toner on the sheet P by pressurization and heating in the nip portion N. In the figure, the paper is passed from the right side to the left side. Next, the sheet P on which the toner has been fixed is discharged from the fixing nip portion N. The sheet P is removed from the fixing belt 12 due to the curvature radius of the fixing belt formed by the curvature forming member 16 disposed inside the fixing belt 12. To be separated.

Next, an image forming apparatus that can be an object of the present invention will be described.
FIG. 4 shows the configuration of a tandem type color copying machine which is an image forming apparatus according to the present invention. The color copying machine 200 includes an image forming unit 200A positioned at the center of the apparatus main body, a paper feeding unit 200B positioned below the image forming unit 200A, and an image reading unit (not shown) positioned above the image forming unit 200A. It has a high-speed machine. The fixing device 100 described above is incorporated in the image forming unit 200A. The image forming unit 200A is provided with a fixing belt 210 having a transfer surface extending in the horizontal direction. A configuration for forming an image of a color complementary to the color separation color on the upper surface of the fixing belt 210. Is provided.

  That is, photoconductors 205Y, 205M, 205C, and 205K as image carriers capable of carrying images of complementary color toners (yellow, magenta, cyan, and black) are juxtaposed along the transfer surface of the fixing belt 210. ing. Each of the photoconductors 205Y, 205M, 205C, and 205K includes a drum that can rotate in the same direction (counterclockwise direction). In addition, there are an optical writing device 201 that performs image forming processing in the rotation process, charging devices 202Y, 202M, 202C, and 202K, developing devices 203Y, 203M, 203C, and 203K, primary transfer devices 204Y, 204M, and 204C, 204K and a cleaning device are arranged.

  Each developing device 203Y, 203M, 203C, 203K contains a respective color toner. The transfer belt 210 is configured to be able to move in the same direction at a position facing the photoconductors 205Y, 205M, 205C, and 205K by being wound around a driving roller and a driven roller. Further, a transfer roller 212 is provided at a position facing a roller 211 that is one of the driven rollers. Further, the conveyance path of the sheet P from the transfer roller 212 to the fixing device 100 is a horizontal path.

  The sheet feeding unit 200B separates the sheet P in the sheet feeding tray 220 one by one from the top in order from the top to the position of the transfer roller 212. It has a transport mechanism for transporting.

  When forming an image in the illustrated image forming apparatus 200, the surface of the photoreceptor 205Y is uniformly charged by the charging device 202Y, and an electrostatic latent image is formed on the photoreceptor 205Y based on the image information from the image reading unit. The The electrostatic latent image is visualized as a toner image by a developing device 203Y containing yellow toner, and the toner image is primarily transferred onto the transfer belt 210 by a primary transfer device 204Y to which a predetermined bias is applied. Is done. The other photoconductors 205M, 205C, and 205K also form similar images only with different toner colors, and the toner images of the respective colors are sequentially transferred and superimposed on the fixing belt 210 by electrostatic force.

Next, the toner image T primarily transferred from the photoconductors 205Y, 205M, 205C, and 205K onto the fixing belt 210 is transferred to the sheet P conveyed by the roller 211 and the transfer roller 212. The sheet P to which the toner image T has been transferred is further conveyed to the fixing device 100 and is fixed at a fixing nip N between the fixing belt 12 and the pressure roller 13. Appropriate amounts of oil are applied to the fixing belt 12 and the pressure roller 13 by an oil application device 22, and a separation device (located on the exit side of the fixing nip portion N as required).
Since the separation claw 18) functions, the sheet P is discharged to the exit side of the fixing nip N without being wound around the fixing belt 12 and the pressure roller 13. Next, the sheet P discharged from the fixing nip N is sent out to the stacker 215 along the discharge path.

As described above, in the image forming apparatus according to the present embodiment, a more advanced fixing / separating function can be obtained, and various paper types and images can be handled.
That is, the separation device according to the present invention can provide a fixing device that maintains the curvature shape and pressure condition of the nip outlet and achieves stable and good separation performance and image quality. Further, it is possible to provide a fixing device with a lower load torque that maintains the curvature shape and pressure condition of the nip outlet with an easy configuration. Further, it is possible to provide a fixing device having high wear resistance and low load torque. Furthermore, an image forming apparatus that achieves good separation performance and image quality can be provided. In addition, image quality can be improved and stabilized, and device reliability can be improved.

  Note that the present invention is not limited to the embodiments shown in the drawings, and other embodiments, additions, modifications, deletions, and the like can be modified within a range that can be conceived by those skilled in the art. The embodiment is also included in the scope of the present invention as long as the operations and effects of the present invention are exhibited.

11: Fixing roller 12: Fixing belt 13: Pressure roller 13a: Bearing 14: Heating roller 14h: Heater 15: Tension roller 16: Curvature forming member 16a: Protrusion 18: Separation claw 19: Separating means 20: Torsion coil spring 21: Cam 22: Oil application device 23: Inner arm 23a: Cam follower 24: Spring 25: Outer arm 25a: Bearing support portion 100: Fixing device 200: Color copier (image forming device)
200A: Image forming unit 200B: Paper feeding unit 201: Optical writing device 202: Charging device 203: Developing device 204: Primary transfer device 205: Photoconductor 210: Fixing belt 211: Roller 212: Transfer roller 215: Stacker 220: Feeding Paper tray M: Micro gap N: Nip part P: Sheet

JP 2000-338811 A JP-A-8-166738 Japanese Patent Application Laid-Open No. 11-133776 JP 2014-178563 A

Claims (6)

A fixing roller, a heating roller, a fixing belt stretched between both rollers, and a pressure roller capable of being in contact with and being separated from the fixing belt so as to contact the outer peripheral surface of the fixing belt and form a nip portion with the fixing belt; In the fixing device provided with
In the nip portion, on the exit side of the portion formed by the fixing roller and the pressure roller via the fixing belt, the pressure roller is pressed against the pressure roller via the fixing belt inside the fixing belt. A curvature forming member that forms an outlet separation portion of the nip portion;
The fixing belt is guided in contact with the curvature forming member in the outlet separation portion, and an end portion of the curvature forming member is urged by an end support portion of the pressure roller.
A fixing device. The belt fixing device according to claim 1.
The curvature forming member is separated without contacting the fixing roller.
A fixing device. The fixing device according to claim 1 or 2,
The fixing device, wherein the curvature forming member is pressed and urged against the pressure roller with the center of the fixing roller as a fulcrum. The fixing device according to any one of claims 1 to 3,
A fluorine-based sheet-like member is wound around the curvature forming member,
A fixing device. In the fixing device according to any one of claims 1 to 4,
A roller for applying tension to the fixing belt from the inside is disposed downstream of the curvature forming member in the forward rotation of the fixing belt and upstream of the heating roller.
A fixing device. An image forming apparatus comprising the fixing device according to claim 1.