JP2013235133A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device that reliably separates even thin paper and maintains high fixability to thick paper, while suppressing deterioration of a fixing member without decreasing productivity.SOLUTION: A fixing device forms a fixing nip by a fixing rotation member including heating means and a pressure rotation unit disposed at an opposite position to the fixing rotation member, and applies heat to an unfixed toner on a recording medium while holding and conveying the recording medium to fix a toner image to the recording medium. The pressure rotation unit is configured by having a belt member laid over a plurality of rollers; and the plurality of rollers includes at least a pressure roller that forms the fixing nip and a separation roller that is arranged at a position downstream in a conveyance direction of the recording medium of the fixing nip. The pressure rotation unit has adsorption means attached therealong for causing the recording medium to be adsorbed to the belt member; and the recording medium is separated from the belt member at a position where the separation roller is arranged.

Description

  The present invention relates to a fixing device used in an image forming apparatus such as a so-called electrophotographic printer, copying machine, facsimile, or the like.

  In the fixing process of the fixing device, heat and pressure are applied to a toner image carried on a recording medium such as transfer paper to melt the toner and fix the toner image on the recording medium. Adhesive force due to the viscosity of the molten toner is generated between the roller and the fixing belt. Therefore, the fixing device needs to have a separation function for separating the fixing member and the recording medium.

  The simplest separation means is a method of separating the recording medium with the curvature of the nip portion. The larger the curvature of the nip portion, the easier the recording medium is separated from the fixing member. However, in order to maintain good fixability for various recording media, particularly for thick paper, a predetermined nip time is required under a constant pressing force. In addition to appropriate elasticity of the roller, a certain degree of roller diameter (curvature is reduced) is required. Therefore, the curvature of the roller pair is limited in order to maintain the fixing property. On the other hand, under conditions suitable for thick paper, thin paper adheres more than necessary to the fixing member and is difficult to separate. That is, there are many problems in achieving both separation of thin paper and fixing of thick paper.

  In the past, in order to maintain the fixability of thick paper, it was considered that the process line speed was reduced when the thick paper was passed to secure the fixing nip time. However, the reduction of the process line speed reduced the productivity of image formation. This is a problem.

  As a proposal for stably separating the recording medium from the fixing member while maintaining high fixing performance, for example, from Patent Document 1, a fixing nip is formed on the inner peripheral side of a fixing belt that forms a fixing nip with a counter roller. A separation pad is arranged downstream of the recording medium conveyance direction, and the fixing belt moves in a region passing through the separation pad while drawing a different bent shape at the center and both ends in the width direction. Are known. This can be said to improve the certainty of curvature separation as described above, but it moves while drawing different bent shapes at the center and both ends of the fixing belt in the width direction, so the burden on the fixing belt is very large. In addition to the negative product life of the belt, the deterioration of the belt surface is shifted with time at the center and both ends in the width direction, and the surface smoothness contacting the toner carrying surface of the recording medium is different, and the fixing property But it can be a problem. Further, although the peeling guide plate is disposed on the fixing nip outlet side, the peeling guide plate rubs against the fixing belt, which is not desirable with respect to the durability quality of the fixing belt.

  As another configuration for separating the curvature, a configuration using a small-diameter roller stretched on the downstream side of the fixing nip of the fixing belt is also known (Patent Document 2). However, with such a configuration, there is a risk of causing image degradation between the fixing nip portion and the small diameter roller. This is because, in the low nip pressure region between the fixing nip portion and the separation portion, the recording medium and the toner are heated, the water in the recording medium is vaporized to become water vapor, and the air in the toner is thermally expanded. This is because an air gap (bubble) is generated between the fixing belt and the recording medium, and the unfixed toner is easily disturbed.

  Further, there are Patent Document 3, Patent Document 4, and the like as proposals for a configuration for easily separating the recording medium from the fixing member.

  In view of the above-mentioned problems of the prior art, the problem of the present invention is that the fixing member can be reliably separated even if it is thin paper without deteriorating the productivity and the productivity is lowered, and high fixing property is maintained even for thick paper. It is an object of the present invention to provide a fixing device.

  According to the present invention, the above-described problem is that a fixing nip is formed by a fixing rotating member provided with a heating unit and a pressure rotating unit disposed at an opposing position thereof, and the recording medium is sandwiched and conveyed on the recording medium. In the fixing device for fixing the toner image to the recording medium by applying heat to the unfixed toner, the pressure rotating unit is configured to include a belt member stretched around a plurality of rollers, and the plurality of rollers include at least the following: A pressure roller that forms a fixing nip, and a separation roller that is arranged at a position downstream of the fixing nip in the recording medium conveyance direction. Further, the pressure rotation unit adsorbs the recording medium to the belt member. Means are provided to solve the problem by separating the recording medium from the belt member at the position of the separation roller.

  According to the present invention, the separation function from the respective members of the recording medium can be divided by separating from the fixing rotation member at the fixing nip and separating from the pressure belt at the position of the separation roller. That is, while maintaining high fixability at the fixing nip, the recording medium is surely separated from the fixing rotation member, and then the recording medium is separated from the pressure belt. Since the pressure belt is in contact with the back side of the fixed image, there is an advantage that the recording medium can be conveyed to the separation roller without causing image deterioration.

1 is a schematic configuration diagram of an image forming apparatus. FIG. 2 is a main configuration diagram of a fixing device. FIG. 6 is an enlarged partial view in the vicinity of a separation roller showing a charge removal member that removes charges from a charged belt member.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram showing an example of an image forming apparatus to which the present invention is applied. In the figure, reference numeral 100 denotes a tandem intermediate transfer type image forming apparatus main body as an image forming apparatus, and 200 denotes a paper feeding apparatus on which the image forming apparatus main body 100 is mounted and provided with a plurality of paper feeding trays 44. The image forming apparatus main body 100 includes a plurality of image forming units 1Y, 1M, 1C, and 1K (subscripts Y, M, C, and K indicate yellow, cyan, magenta, and black, respectively. A tandem type intermediate transfer type image forming unit (hereinafter referred to as a tandem type image forming unit) 20 in which subscripts are sometimes omitted) is provided. Below the image forming unit 20, an endless belt-like intermediate transfer member (hereinafter referred to as an intermediate transfer belt) 10 is provided. The intermediate transfer belt 10 is wound around a plurality of support rollers 14, 15, 15 ′, 16 and the like and can be rotated and conveyed clockwise in the drawing.

  In this illustrated example, a cleaning device 17 for the intermediate transfer belt is provided on the downstream side in the belt movement direction of the support roller (secondary transfer counter roller) 16 that wraps around the belt at the lowermost part of the intermediate transfer belt 10. The cleaning device 17 removes residual toner remaining on the intermediate transfer belt 10 after image transfer.

  On the intermediate transfer belt 10 stretched horizontally between the support roller 14 and the support roller 15, four image forming units 1Y, 1M, 1C, and 1K are arranged side by side along the moving direction. A tandem image forming unit 20 is configured. The image forming units 1Y, 1M, 1C, and 1K of the tandem-type image forming unit 20 are photosensitive drums 40Y, 40M, and 40C as image carriers that carry toner images of yellow, cyan, magenta, and black, respectively. 40K.

  Two exposure devices 21 are provided above the tandem image forming unit 20. Each exposure device 21 corresponds to two image forming units (1Y and 1M, 1C and 1K), for example, two light source devices (semiconductor laser, semiconductor laser array or multi-beam light source) and a coupling optical system, This is an optical scanning type exposure device composed of a common optical deflector (polygon mirror, etc.), two scanning imaging optical systems, etc., and each light sensitive to each color image information of yellow, cyan, magenta, and black. The body drums 40Y, 40M, 40C, and 40K are exposed to form an electrostatic latent image.

  In addition, around the photosensitive drum 40 of each image forming unit 1, an electrostatic latent image formed by the charging device and the exposure device 21 that uniformly charges each photosensitive drum prior to the exposure is formed with toner of each color. Developing devices 18Y, 18M, 18C, and 18K for developing, and a photosensitive member cleaning device for removing transfer residual toner on the photosensitive drum are provided. Further, at the primary transfer position where the toner image is transferred from each photosensitive drum to the intermediate transfer belt 10, the primary transfer is performed so as to face each of the photosensitive drums 40Y, 40M, 40C, and 40K with the intermediate transfer belt 10 interposed therebetween. Primary transfer rollers 62Y, 62M, 62C, and 62K are provided as components of the means.

  Of the plurality of support rollers that support the intermediate transfer belt 10, the support roller 14 on the downstream side in the belt movement direction near the image forming unit 1K is a drive roller that rotationally drives the intermediate transfer belt 10, and a drive transmission mechanism (not shown). It is connected to the motor via (gear, pulley, belt, etc.). When a black single color image is formed on the intermediate transfer belt 10, the intermediate transfer is performed by moving the support rollers 15 and 15 ′ on the upstream side in the belt movement direction from the drive roller 14 by a moving mechanism (not shown). The belt 10 can be separated from the photosensitive drums 40Y, 40M, and 40C of yellow, cyan, and magenta.

  A secondary transfer device 22 is provided on the opposite side of the intermediate transfer belt 10 from the tandem image forming unit 20. In the illustrated example, the secondary transfer device 22 presses the secondary transfer roller 16 ′ against the secondary transfer counter roller 16 and applies a transfer electric field to thereby form an image on the intermediate transfer belt 10 as a sheet as a recording medium. The transfer paper S is transferred.

  A fixing device 25 for fixing the transfer image on the transfer paper S is provided on the downstream side of the secondary transfer device 22 in the paper conveyance direction. In the fixing device 25, a pressure roller 27 is pressed against the fixing belt 26 which is an endless belt. The fixing belt 26 is wound around at least two support rollers, and at least one of the rollers is provided with heating means (a heater, a lamp, an electromagnetic induction heating device, or the like). In the illustrated example, a heating roller incorporating such a heating unit, a fixing roller, and a tension roller are shown.

  The transfer sheet S on which the image is transferred by the secondary transfer device 22 is transported to the fixing device 25 by the transport belt 24 supported by the two rollers 23. Of course, the location of the transport belt 24 may be a fixed guide member, or may be replaced by a transport roller, a transport roller, or the like.

  In the illustrated example, the transfer sheet S is inverted under such a secondary transfer device 22 and the fixing device 25 so as to record images on both sides of the transfer sheet S in parallel with the tandem image forming unit 20 described above. A sheet reversing device 28 is provided.

  Next, the fixing device 25 according to the present embodiment will be described. FIG. 2 is a side sectional view showing a schematic configuration of the fixing device 25. The fixing device 25 constitutes a main part of a fixing belt unit as an example of a heating member and a pressure belt unit disposed in pressure contact with the fixing belt unit.

  The fixing belt unit includes an endless fixing belt 30, a fixing roller 31 that rotates while the fixing belt is stretched inside, a heating roller 33 that includes a halogen heater 32 and the like to apply heat to the fixing belt 30, The tension roller 34 stretches the fixing belt 30 from the inside. The fixing belt 30 includes a base layer formed of a polyimide resin having a thickness of about 80 μm, an elastic layer made of silicone rubber having a thickness of about 200 μm laminated on the outer peripheral surface side of the base layer, and further on the elastic layer. And a release layer made of PFA having a thickness of about 20 μm and coated with fluororesin. The release layer is formed to reduce the adhesion between the fixing belt and the toner and to facilitate separation of the transfer paper from the fixing belt.

  On the other hand, the pressure belt unit includes a pressure roller 35 at a position facing the fixing roller 31, a separation roller 36 having a relatively small diameter is disposed at a downstream position in the sheet conveyance direction, and the pressure belt 37 is stretched by these rollers. It has a configuration to hang. The pressure belt 37 is selected from a material having higher tack than the fixing belt 30. For example, a single layer belt made of silicone rubber is used. By adopting such a material configuration, the transfer paper passing through the fixing nip can be actively drawn toward the pressure belt, and the transfer paper can be more reliably separated from the fixing belt 30.

Further, in order to attract the transfer paper to the pressure belt unit, a charging roller 38 that comes in contact with the belt outer peripheral surface upstream of the fixing nip in the belt moving direction is provided. The charging roller 38 is applied to the core metal from a high voltage power supply (not shown), and the outer periphery of the core metal has a resistance value of 10 ⁶ to 10 ⁹ Ωcm by blending silicone rubber with a conductive agent such as carbon black. It is adjusted to the degree. The surface of the pressure belt is charged by applying a high voltage of about 3 kV to the charging roller 38, for example. After the transfer paper passes through the fixing nip, the transfer paper is charged and adsorbed to the pressure belt 38 and is separated from the fixing belt unit, that is, the fixing belt 30, and the curvature is separated from the pressure belt at the separation roller portion on the downstream side in the paper conveyance direction. Is done. The smaller the diameter of the separation roller 36 is, the more reliable the separation is. However, it is preferable that the diameter of the separation roller 36 is about 20 mm in consideration of the rigidity of the roller.

  In order to weaken the electrostatic attraction force of the pressure belt in the separation roller portion, it is also conceivable to dispose a charge eliminating member. Specifically, as shown in FIG. 3, by disposing a static elimination brush 39 made of conductive fibers with excellent heat resistance in the vicinity of the curvature separation position of the separation roller portion, the electrostatic adsorption force can be weakened. it can.

  In the state where the fixing roller 31 and the pressure roller 35 are nipped through the belts 30 and 37, the fixing roller 31 selects the hardness of both rollers so that the nip outlet is bent downward by the pressure of the pressure roller 35. It is also possible to do. For example, the fixing roller 31 is a roller having an outer diameter of φ60 mm in which the outer periphery of an aluminum cylindrical roller is formed of an elastic rubber layer, and the pressure roller 35 is an aluminum cylindrical roller having a thickness of about 2 mm and has an outer diameter of φ65 mm. With such a configuration, the leading edge of the transfer paper passing through the nip is discharged downward (pressure belt side) from the fixing nip, and the fixing belt and the recording paper are more reliably separated at the nip exit.

Instead of electrostatic attraction, it is also possible to form countless holes in the pressure belt 37 and suck the transfer paper by sucking air from the belt inner peripheral side.
In addition, at the separation position of the fixing belt, a separation claw may be brought close to the fixing belt in case the transfer paper cannot be separated from the fixing belt. The charging bias may be controlled so that the output is appropriately output or turned off according to the type of transfer paper (paper thickness, etc.).

25 Fixing Device 30 Fixing Belt 31 Fixing Roller 32 Halogen Heater 33 Heating Roller 34 Tension Roller 35 Pressing Roller 36 Separating Roller 37 Pressing Belt 38 Charging Roller 39 Static Removal Brush

JP 2007-65082 A (Patent No. 4609240) JP 2003-195666 A JP 2010-78747 A JP 2005-241723 A (Patent No. 4304097)

Claims (6)

A fixing rotating member having a heating unit and a pressure rotating unit disposed at the opposite position form a fixing nip, and heat is applied to the unfixed toner on the recording medium while nipping and conveying the recording medium. In a fixing device for fixing a toner image,
The pressure rotation unit includes a belt member stretched around a plurality of rollers, and the plurality of rollers are at least a pressure roller that forms a fixing nip and a downstream position in the recording medium conveyance direction from the fixing nip. The pressure rotating unit is further provided with suction means for sucking the recording medium to the belt member, and the recording medium is separated from the belt member at the position of the separation roller. A fixing device characterized by the above.   The fixing device according to claim 1, further comprising a bias applying unit configured to charge the belt member, and electrostatically adsorbing a recording medium to the belt member.   The fixing device according to claim 2, further comprising a neutralizing member that removes electric charges of the charged belt member in the vicinity of a recording medium separation position of the separation roller.   The fixing device according to claim 1, wherein at least a surface of the pressure belt is made of a material having a higher tackiness against a recording medium than a surface of the fixing rotation member.   The fixing rotating member is a roller composed of at least a cored bar and an elastic body covering the outer periphery thereof, and the surface hardness of the pressure roller is set to be higher than the hardness of the fixing roller. The fixing device according to claim 1, wherein the fixing device is directed toward the pressure roller.   An image forming apparatus comprising the fixing device according to claim 1.

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