JP2005258156A - Pressure roller, fixing device, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pressure roller, a fixing device, and an image forming apparatus that never causes a passing form to wrinkle when heated by a fixing roller. <P>SOLUTION: The pressure roller 1 is arranged while pressed against the fixing roller to fix a toner image on a form, and equipped with a shaft 11, a porous elastic body layer 12 having many voids 13, and a thin film type resin layer 14. The porous elastic body layer 12 has larger void ratio at both the ends of the shaft 11 along the axis than at the center part, and when the layer is heated by the fixing roller, external diameters of both the ends become larger than the external diameter of the center part. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a pressure roller, in particular, a pressure roller disposed in pressure contact with a heat fixing roller for fixing a toner image on a recording material, a fixing device including the pressure roller, and the fixing The present invention relates to an image forming apparatus including the apparatus.

  2. Description of the Related Art Conventionally, in an electrophotographic image forming apparatus such as a copying machine, a printer, or a facsimile, a heated fixing roller and a pressure roller are brought into pressure contact with each other, and a sheet is passed between the two rollers so The toner image transferred to the toner image was fixed.

  FIG. 8 shows a pressure roller 50 conventionally used. The pressure roller 50 is provided with a porous elastic body layer 52 that is substantially uniformly foamed on a shaft 51, and a resin layer 53 is provided on the surface of the porous elastic body layer 52.

  In this type of pressure roller 50, as shown in FIG. 9, the outer diameter A of both end portions of the porous elastic layer 52 is set larger than the outer diameter B of the central portion (FIG. The difference between A and B is exaggerated). This is to prevent the paper from wrinkling by applying an outward pulling force to the paper being passed.

  However, the pressure roller 50 is heated by the fixing roller, and the central portion where the heat storage is large is inevitably heated so that the outer diameter of the central portion is larger than the outer diameters of both end portions. The force that pushes into the area was applied, resulting in wrinkling of the paper.

Various countermeasures have been proposed in the past. Patent Document 1 discloses that the distribution of bubbles in the porous elastic layer constituting the pressure roller is made smaller at both end portions than at the central portion. Patent Document 2 discloses that the foamed cell diameter of the porous elastic layer constituting the pressure roller is smaller at both end portions than at the central portion. Further, Patent Document 3 discloses that the foaming rate of the rubber layer is higher at both end portions than at the central portion so that the outer diameter of the roller during heating is substantially constant between the central portion and both end portions. Yes.
JP-A-9-251252 Japanese Patent Laid-Open No. 11-338224 JP-A-10-307497

  Therefore, an object of the present invention is to add the wrinkles of the passing paper without causing wrinkles when the outer diameter of both end portions expands larger than the outer diameter of the central portion when heated by the fixing roller. To provide a pressure roller, a fixing device, and an image forming apparatus.

  In order to achieve the above object, the present invention provides a pressure roller disposed in pressure contact with a fixing roller heated by a heating means for fixing a toner image on a recording material, the shaft, A porous elastic layer provided on the shaft, and a resin layer provided on the porous elastic layer, wherein the porous elastic layer has a void ratio at the center portion in the axial direction of the shaft. It is larger than the void ratio, and when heated by the fixing roller, the outer diameter of both end portions expands larger than the outer diameter of the central portion.

  The porosity is the ratio of the voids in the unit volume, can be represented by the number of voids and / or the diameter of the voids, and is synonymous with the foaming rate. The porous elastic layer may be made of the same material at both end portions and the central portion, or may be made of different materials. In addition, a plurality of porous elastic layers having different porosity may be connected so that the central portion of the roller is line symmetric.For example, a plurality of porous elastic layers having different porosity may be formed to have a predetermined length. A pressure roller can be obtained by attaching to the shaft.

  According to the pressure roller of the present invention, the porosity of both end portions in the axial direction of the shaft is larger than the porosity of the central portion, and when heated by the fixing roller, the outer diameter of both end portions is the outer diameter of the central portion. Therefore, the pulling force effectively acts on the paper being passed through, and the paper is not wrinkled.

  The fixing device according to the present invention includes the pressure roller, and the image forming apparatus according to the present invention includes the fixing device, both of which have a problem of causing wrinkles on the paper being passed. It can be prevented in advance.

  Embodiments of a pressure roller, a fixing device, and an image forming apparatus according to the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 shows a pressure roller 1 as a first embodiment, FIG. 2 shows a pressure roller 2 as a second embodiment, and FIG. 3 shows a pressure roller 3 as a third embodiment.

  A pressure roller 1 shown in FIG. 1 includes a metal shaft 11, a porous elastic layer 12 provided on the outer peripheral surface of the shaft 11, and a thin resin layer provided on the outer peripheral surface of the elastic layer 12. 14.

  The porous elastic body layer 12 is divided into three segments 12 a, 12 b, 12 c in the axial direction of the shaft 11. The segments 12a and 12c are disposed at both end portions in the axial direction, and the segment 12b is disposed at the central portion in the axial direction. Each segment 12a, 12b, 12c has the same outer diameter at room temperature and the same diameter of the air gap.

  In the porous elastic body layer 12, the number of voids 13 occupying in a unit volume is larger in the segments 12a and 12c than in the segment 12b. That is, the porosity (foaming rate) is set to be larger at both end portions than at the central portion. Further, the porosity is symmetrical left and right with the axial center line C as the center.

  The pressure roller 1 includes, for example, a silicon rubber material as a main component, a foaming agent, a vulcanizing agent, and the like added thereto, and the extruded segments 12a, 12b, and 12c are cut to a predetermined length and bonded / joined to the shaft 11. Then, the porous elastic body layer 12 can be produced by coating the elastic body layer 12 with the resin layer 14. The porosity, that is, the diameter and number of the voids 13 can be adjusted by the amount of foaming agent added, the heating temperature during molding, and the like.

  In the porous elastic layer 12 mainly composed of silicon rubber, the segment 12b is about 1: 0.4 to 1: 0.8 with respect to the segments 12a and 12c with respect to the ratio of the number of voids 13 in the unit volume. Is appropriate.

  The resin layer 14 is preferably made of polytetrafluoroethylene having a heat resistance of 100 μm or less, for example, and is fixed by covering the outer peripheral surface of the porous elastic body layer 12 with an adhesive and heat shrinking. .

  As shown in FIG. 6, the pressure roller 1 having the above configuration is arranged in a state of being pressed against the fixing roller 21 heated from the inside by the heating means 22 to constitute the fixing device 20. A sheet separation claw 23 is attached to the fixing roller 21. FIG. 7 shows an outline of the internal configuration of the electrophotographic copying machine 30 provided with the fixing device 20.

  In FIG. 7, a sheet is fed / conveyed upward along a sheet passing path D from a sheet feeding unit 31, and a toner image formed on a photosensitive drum 32 is transferred by a known electrophotographic method. Thereafter, the sheet passes through the nip portion of the fixing roller 21 and the pressure roller 1 in the fixing device 20 to heat and fix the toner image, and is discharged from the sheet discharge roller pair 33 onto the sheet tray 34.

  Incidentally, the positional relationship between the paper passage position and the pressure roller 1 is such that the conveyance direction center line C ′ of the sheet P coincides with the axial direction center line C of the pressure roller 1, as shown in FIG. The paper is passed.

  When the toner image is heated and fixed, the pressure roller 1 is heated from the fixing roller 21, and the number of voids in the unit volume of the segments 12a and 12c at both ends is larger than the number of voids in the segment 12b at the central portion. Therefore, the outer diameters of the segments 12a and 12c expand larger than the outer diameter of the segment 12b. As a result, an outward pulling force acts on the paper being passed, and wrinkles are prevented from occurring on the paper.

  FIG. 4A shows an example of changes in the outer diameter of the pressure roller 1 when the segments 12a and 12c and the segment 12b are heated. The segments 12a and 12c and the segment 12b have the same outer diameter at 30 ° C., but the outer diameter changes of the segments 12a and 12c increase as the temperature rises. The ratio of the number of voids 13 in the unit volume of the porous elastic layer 12 used in this experiment was segment 12a, 12c: segment 12b = 1: 0.7.

  The pressure roller 2 shown in FIG. 2 has basically the same configuration as the pressure roller 1 and is incorporated in the fixing device 20 in the same manner. Therefore, in FIG. 2, the same members and parts as in FIG.

  In the pressure roller 2, the segments 12a and 12c at both ends are adjusted so that the diameter of the gap 13 is larger than the diameter of the gap 13 of the segment 12b at the center. In the porous elastic body layer 12 containing silicon rubber as a main component, the segment 12b is suitably about 1: 0.6 to 1: 0.9 with respect to the segments 12a and 12c with respect to the diameter ratio of the voids 13.

  When the toner image is heated and fixed, the pressure roller 2 is heated from the fixing roller 21 and the diameter of the gap 13 of the segments 12a and 12c at both ends is larger than the diameter of the gap 13 of the segment 12b at the center. Therefore, the outer diameters of the segments 12a and 12c expand larger than the outer diameter of the segment 12b. As a result, an outward pulling force acts on the paper being passed, and wrinkles are prevented from occurring on the paper.

  FIG. 4B shows an example of changes in the outer diameter of the pressure roller 2 when the segments 12a and 12c and the segment 12b are heated. The segments 12a and 12c and the segment 12b have the same outer diameter at 30 ° C., but the outer diameter changes of the segments 12a and 12c increase as the temperature rises. The ratio of the diameters of the voids 13 in the porous elastic layer 12 used in this experiment was segment 12a, 12c: segment 12b = 1: 0.85.

  The pressure roller 3 shown in FIG. 3 includes a porous elastic body layer 12 composed of segments 12a to 12g, and the other configurations are the same as those of the pressure rollers 1 and 2, and in the same manner, the fixing device. 20 incorporated. Therefore, in FIG. 3, the same members and portions as those in FIGS. 1 and 2 are denoted by the same reference numerals, and the description thereof is omitted.

  In the pressure roller 3, the segment 12d located in the center portion has a smaller diameter of the gap 13 than the diameter of the gap 13 of the segments 12a and 12g located at both end portions, and the number of the gaps 13 is relatively small. The diameter of the gap 13 of the segments 12c and 12e is the same as the diameter of the gap 13 of the segment 12d, but the number of the gaps 13 is adjusted to be larger than that of the segment 12d. The diameters of the gaps 13 of the segments 12b and 12f are the same as the diameters of the gaps 13 of the segments 12c, 12d and 12e, but are adjusted so that the number of the gaps 13 is larger than that of the segments 12c and 12e. The segments 12a and 12g located at both ends are adjusted so that the diameter of the gap 13 is larger than the diameter of the gap 13 of the other segments 12b to 12f.

  In other words, the porosity of the porous elastic layer 12 of the pressure roller 3 gradually increases toward the both ends with respect to the center line C in the axial direction of the shaft 11, and the increasing tendency causes the center line C to increase. Symmetric about the center.

  When the toner image is heated and fixed, the pressure roller 3 is heated from the fixing roller 21, and the outer diameter thereof is the segments 12c and 12e and the segments 12b and 12f in the middle portion than the segment 12d in the central portion, and the segments in both end portions. 12a and 12g expand more greatly. As a result, an outward pulling force acts on the paper being passed, and wrinkles are prevented from occurring on the paper.

  The pressure roller, the fixing device, and the image forming apparatus according to the present invention are not limited to the above-described embodiments, and can be variously modified within the scope of the gist.

It is sectional drawing which shows 1st Example of the pressure roller which concerns on this invention. It is sectional drawing which shows 2nd Example of the pressure roller which concerns on this invention. It is sectional drawing which shows 3rd Example of the pressure roller which concerns on this invention. It is a graph which shows the outer diameter change by the heating in the said 1st and 2nd Example. It is explanatory drawing which shows the positional relationship of the pressure roller which is the said 1st Example, and a paper. 1 is a cross-sectional view illustrating an example of a fixing device according to the present invention. 1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to the present invention. It is sectional drawing which shows the conventional pressure roller. It is explanatory drawing which shows the outer diameter of the conventional pressure roller.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 2, 3 ... Pressure roller 11 ... Shaft 12 ... Porous elastic body layer 12a-12g ... Segment 13 ... Air gap 14 ... Resin layer 20 ... Fixing device 21 ... Fixing roller 22 ... Heating means 30 ... Electrophotographic copying machine

Claims (8)

A pressure roller arranged in pressure contact with a fixing roller heated by a heating means for fixing a toner image on a recording material,
A shaft, a porous elastic layer provided on the shaft, and a resin layer provided on the porous elastic layer;
The porous elastic layer has a void ratio at both end portions in the axial direction of the shaft that is larger than a void ratio at the center portion, and when heated by the fixing roller, the outer diameter of both end portions is larger than the outer diameter of the center portion. Also expand greatly,
A pressure roller characterized by.   2. The pressure roller according to claim 1, wherein the porous elastic layer has a larger number of voids in a unit volume at both end portions than the number of voids in a central portion.   2. The pressure roller according to claim 1, wherein the porous elastic layer has a gap diameter at both end portions larger than a gap diameter at the center portion.   2. The pressure roller according to claim 1, wherein the porous elastic body layer is made of the same material at both end portions and the central portion, and a foaming rate at both end portions is larger than a foaming rate at the central portion.   2. The pressure roller according to claim 1, wherein a plurality of porous elastic layers having different porosity are connected so that a central portion of the roller is axisymmetric.   The pressure roller according to claim 1, wherein a plurality of porous elastic layers having different porosity are attached to a shaft having a predetermined length.   A fixing device comprising the pressure roller according to claim 1.   An image forming apparatus comprising the fixing device according to claim 7.

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