JP2013083870A - Fixing device and image formation apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device having a resistance heating element layer as a heating element, the fixing device being capable of reducing heat values associated with abnormal heat generation.SOLUTION: A fixing device 5 for heat fixing an unfixed image on a record sheet includes a resistance heating element layer generating heat by energization, an endless heating rotator 51 heat-fusing, by using the heat generated by the resistance heating element layer, the unfixed image on the record sheet, and a power supply unit 500 energizing the resistance heating element layer by applying voltage. The resistance heating element layer has resistance anisotropy in which a volume resistivity R1 in a direction orthogonal to a voltage application direction is less than volume resistivity R2 in the voltage application direction (R1<R2).

Description

  The present invention relates to a fixing device provided in an image forming apparatus such as a printer or a copying machine, and more particularly to a technique for reducing abnormal heat generation in a fixing device using a resistance heating element layer as a heating element.

In recent years, as a fixing device for an image forming apparatus such as a printer or a copying machine, a fixing device using a resistance heating element layer that generates Joule heat upon energization has been used. This resistance heating element layer is configured by dispersing a conductive material such as a metal in an insulating material such as a heat resistant resin.
For example, Patent Document 1 discloses a fixing device using a resistance heating element layer covered with an insulating layer as a heating element. In the fixing device, since the heating element generates heat by supplying power directly to the resistance heating element layer, the thermal efficiency of the fixing device can be increased and the warm-up time can be shortened.

JP 2009-109997 A

  Although the resistance heating element layer is covered with an insulating layer, the thickness of the insulating layer is as thin as about several hundreds μm, so that the insulating layer may be damaged by contact with foreign matter mixed in from the outside or the recording sheet. is there. If the scratch extends to the resistance heating layer, and the scratch occurs in a direction that is not parallel to the direction in which the current flows (particularly in a direction perpendicular to the direction in which the current flows), the current is around the edge of the scratch so as to avoid the scratch. Since the current density around the edge of the scratch increases locally, the portion where the current density increases locally in the resistance heating layer may generate abnormal heat. If the abnormal heat generation of the resistance heating element layer is left unattended, the heat generation of the abnormally heated portion proceeds to a high temperature, thereby increasing the risk of damage to the fixing device.

  In order to prevent such damage to the fixing device, various methods for detecting abnormal heat generation in the resistance heating element layer have been proposed. However, in terms of detection responsiveness and detection accuracy, it is difficult to achieve perfection, and detection may or may not be possible after abnormal heat generation has progressed considerably. For this reason, it is desired to establish a technique that does not cause abnormal heat generation rather than detecting abnormal heat generation when the resistance heating element layer is damaged.

  The present invention has been proposed to meet such a demand. In a fixing device using a resistance heating element layer as a heating element, a fixing device capable of reducing the amount of heat generated due to abnormal heat generation and the fixing device are provided. An object of the present invention is to provide an image forming apparatus.

  In order to achieve the above object, a fixing device according to an aspect of the present invention is a fixing device that thermally fixes an unfixed image on a recording sheet, and includes a resistance heating element layer that generates heat when energized, and the resistance heating An endless heating belt for thermally fusing an unfixed image on a recording sheet by heat generated by the body layer, and an energizing means for energizing the resistance heating layer by applying a voltage to the resistance heating element. The layer is characterized by having a resistance anisotropy in which the volume resistivity R2 in the voltage application direction is larger (R1 <R2) than the volume resistivity R1 in the direction orthogonal to the voltage application direction.

  Here, the resistance heating element layer may have a configuration in which the conductive filler is oriented in a direction orthogonal to the voltage application direction in the heat resistant resin. The heating belt has power supply electrodes for supplying power to the resistance heating element layer at both ends in the longitudinal direction, and the power supply means applies a voltage in the longitudinal direction through the power supply electrodes. It can be. Furthermore, each said feeding electrode can be formed in the perimeter of the said heating belt.

  The energization means may energize the resistance heating element layer by applying a voltage in a circumferential direction of the heating belt. An image forming apparatus according to an aspect of the invention includes the fixing device.

  Since the resistance heating element layer has the resistance anisotropy in the volume resistivity R2 in the voltage application direction is larger than the volume resistivity R1 in the direction orthogonal to the voltage application direction by including the above configuration, the damaged portion The surroundings can be made less likely to generate abnormal heat, and the amount of heat generated by abnormal heat generation can be reduced.

1 is a diagram illustrating a configuration of a printer. 2 is a perspective view illustrating a configuration of a fixing device 5. FIG. 3 is a cross-sectional view showing a detailed configuration of a heating rotator 51. FIG. The microstructure of the resistance heating element layer 513, the relationship of the magnitude of electrical resistance (volume resistivity) between the voltage application direction (Rx direction) and the direction orthogonal to the voltage application direction (Ry direction), the resistance heating element FIG. 4 is a diagram illustrating the state in which a current bypasses the vicinity of an end portion of a scratch when a scratch occurs in a direction (Ry direction) orthogonal to a current flowing through a layer and a voltage application direction. The ratio of abnormal heat generation when the resistance heating element layer 513 is damaged and the ratio of the volume resistivity (R2) in the Ry direction to the volume resistivity (R1) in the Rx direction of the resistance heating element layer 513 (R2 / R1) The experimental result which investigated the relationship with is shown. FIG. 6 is a schematic diagram of resistance heating element layers and electrodes for supplementarily explaining the experimental conditions of the experiment shown in FIG. 5. It is a figure which shows the specific example of the time change in the warm-up period of the measurement temperature (S) of a damaged part, and the measurement temperature (T) of a normal part. The modification of the heating rotary body which concerns on this Embodiment is shown. Another modification of the heating rotator according to the present embodiment is shown.

(Embodiment)
Hereinafter, an embodiment of an image forming apparatus according to an embodiment of the present invention will be described with reference to an example in which the image forming apparatus is applied to a tandem color digital printer (hereinafter simply referred to as “printer”).
[1] Configuration of Printer First, the configuration of the printer 1 according to the present embodiment will be described. FIG. 1 is a diagram illustrating a configuration of a printer 1 according to the present embodiment. As shown in FIG. 1, the printer 1 includes an image process unit 3, a paper feed unit 4, a fixing device 5, and a control unit 60.

When the printer 1 is connected to a network (for example, a LAN) and receives a print instruction from an external terminal device (not shown) or an operation panel (not shown), toner images of each color of yellow, magenta, cyan, and black are received based on the instruction. , And multiple transfer of these to form a full-color image, thereby executing a printing process on a recording sheet.
Hereinafter, the reproduction colors of yellow, magenta, cyan, and black are expressed as Y, M, C, and K, and Y, M, C, and K are added as subscripts to the numbers of the components related to the reproduction colors.

The image processing unit 3 includes image forming units 3Y, 3M, 3C, and 3K, an exposure unit 10, an intermediate transfer belt 11, a secondary transfer roller 45, and the like.
Since the image forming units 3Y, 3M, 3C, and 3K have the same configuration, the configuration of the image forming unit 3Y will be mainly described below.
The image forming unit 3Y includes a photosensitive drum 31Y, a charger 32Y, a developing device 33Y, a primary transfer roller 34Y, a cleaner 35Y for cleaning the photosensitive drum 31Y, and the like disposed around the photosensitive drum 31Y. A Y-color toner image is formed on the photosensitive drum 31Y. The developing device 33Y faces the photosensitive drum 31Y and conveys charged toner to the photosensitive drum 31Y.

  The intermediate transfer belt 11 is an endless belt, is stretched around a driving roller 12 and a driven roller 13, and is driven to rotate in the direction of arrow C. In addition, a cleaner 14 for removing toner remaining on the intermediate transfer belt is disposed in the vicinity of the driven roller 13. The exposure unit 10 includes a light emitting element such as a laser diode, emits laser light L for forming images of Y to K colors in response to a drive signal from the control unit 60, and each of the image forming units 3Y, 3M, 3C, and 3K. The photosensitive drum is exposed and scanned.

By this exposure scanning, an electrostatic latent image is formed on the photosensitive drum 31Y charged by the charger 32Y. Similarly, electrostatic latent images are formed on the photosensitive drums of the image forming units 3M, 3C, and 3K. The electrostatic latent image formed on each photoconductor drum is developed by each developing unit of the image forming units 3Y, 3M, 3C, and 3K, and a toner image of a corresponding color is formed on each photoconductor drum.
The formed toner images are assigned primary transfer rollers of the image forming units 3Y, 3M, 3C, and 3K (in FIG. 1, only the primary transfer roller corresponding to the image forming unit 3Y is denoted by reference numeral 34Y, and the other primary transfer rollers). With respect to the transfer roller, the reference numerals are omitted.), So that the secondary transfer is performed sequentially on the intermediate transfer belt 11 at different timings so as to be superimposed on the same position on the intermediate transfer belt 11, and then the secondary transfer. The toner images on the intermediate transfer belt 11 are collectively transferred onto the recording sheet by the action of electrostatic force by the transfer roller 45. The recording sheet on which the toner image has been secondarily transferred is further conveyed to the fixing device 5, and the toner image (unfixed image) on the recording sheet is heated and pressed in the fixing device 5 and thermally fixed on the recording sheet. After that, the paper is discharged to the paper discharge tray 72 by the discharge roller 71.

  The paper feed unit 4 includes a paper feed cassette 41 that stores recording sheets (denoted by reference numeral S in FIG. 1), a feed roller 42 that feeds the recording sheets in the paper feed cassette 41 one by one onto the transport path 43, and a feed roller 42. A timing roller 44 and the like for taking the timing of feeding the recorded sheet to the secondary transfer position 46 are provided. The number of paper feed cassettes is not limited to one and may be plural.

As the recording sheet, paper sheets (plain paper, thick paper) having different sizes and thicknesses, and film sheets such as an OHP sheet can be used. When there are a plurality of paper feed cassettes, recording sheets of different sizes, thicknesses or materials may be stored in the paper feed cassettes.
Each roller such as the feeding roller 42 and the timing roller 44 is rotationally driven through a power transmission mechanism (not shown) such as a gear and a belt using a conveyance motor (not shown) as a power source. As this conveyance motor, for example, a stepping motor capable of controlling the rotational speed with high accuracy is used.

The recording sheet is conveyed from the paper feeding unit 4 to the secondary transfer position 46 in accordance with the movement timing of the toner image on the intermediate transfer belt 11, and the toner images on the intermediate transfer belt 11 are collectively collected by the secondary transfer roller 45. Secondary transfer is performed on the recording sheet.
[2] Configuration of Fixing Device FIG. 2 is a perspective view showing the configuration of the fixing device 5. As shown in the figure, the fixing device 5 applies a voltage to both ends of the heating rotator 51, the fixing roller 52, the pressure roller 53, and the heating rotator 51 (a resistance heating element layer 513 described later). And a power supply member 501 and 502 for supplying power to the heating rotator 51 (electrodes 511 and 512 described later).

  The heating rotator 51 is an endless belt, and power supply electrodes 511 and 512 are provided at both ends thereof. A voltage is applied to both electrodes from the power supply unit 500 through power supply members 501 and 502 to supply power. Is done. As the power supply member, for example, a power supply brush or a power supply roller can be used. By supplying power from the power supply member, a current flows between both electrodes, and the heating rotator 51 generates Joule heat.

  Further, a temperature sensor (not shown) is arranged at a predetermined position (here, near the center in the longitudinal direction) near the outer peripheral surface of the heating rotator 51. The temperature sensor detects the surface temperature of the outer peripheral surface of the heating rotator 51, and the control unit 60 controls the power supply from the power supply unit 500 to the heating rotator 51 according to the temperature detected by the temperature sensor. The temperature of 51 is controlled so that the temperature of the outer peripheral surface of the heating rotator 51 becomes the fixing temperature (for example, 150 ° C.).

FIG. 3 is a cross-sectional view showing a detailed configuration of the heating rotator 51. As shown in the figure, in the image area denoted by reference numeral 301, the heating rotator 51 is configured by laminating a resistance heating element layer 513, a reinforcing layer 514, an elastic layer 515, and a release layer 516 in this order. Yes.
Here, the “image area 301” indicates an area in the belt width direction on the heating rotator 51 corresponding to a range in which an image on the recording sheet is passed. The same applies to the image area shown in FIG.

The resistance heating element layer 513 is a layer that generates Joule heat when power is supplied from the power supply unit 500 through the electrodes 511 and 512. The resistance heating element layer 513 is dispersed on the heat-resistant resin or in the heat-resistant resin so that the fibrous, needle-like, or flake-like conductive filler is oriented in the circumferential direction (direction perpendicular to the voltage application direction). It is configured.
FIG. 4A is a diagram conceptually showing the fine structure of the resistance heating element layer 513. In FIG. 6A, reference numeral 513 represents a resistance heating element layer, reference numeral 513a represents a conductive filler, and reference numeral 513b represents a heat resistant resin. FIG. 4B conceptually represents the relationship between the magnitude of electrical resistance (volume resistivity) between the voltage application direction (Rx direction) and the direction orthogonal to the voltage application direction (Ry direction). FIG.

  4 (c) and 4 (d) respectively show the case where a flaw occurs in the direction (Ry direction) perpendicular to the current flowing through the resistance heating element layer and the voltage application direction, and the current is at the end of the flaw. FIG. 4C is a diagram conceptually showing a circumvention of the vicinity, and FIG. 4C shows that the resistance heating element layer has no resistance anisotropy (described later) (voltage application direction (Rx direction) and voltage application direction orthogonal to each other). 4 (d) shows a resistance heating element layer having a resistance anisotropy (described later) (FIG. 4 (d)). The case of the resistance heating element layer 513) is shown.

  4C and 4D, reference numeral 401 indicates a scratch generated in the resistance heating element layer, each solid line indicated by reference numeral 402 indicates a current, and reference numeral 403 indicates a region near the end of the scratch. , Arrow Rx indicates a voltage application direction, and arrow Ry indicates a direction orthogonal to the voltage application direction. In both figures, the description of the current is omitted in the region below the central portion in the Ry direction of the scratch 401, and the current flows from the left side to the right side of the page.

  As shown in FIG. 4A, the conductive filler 513a is dispersed so as to be oriented in the direction (circumferential direction) orthogonal to the longitudinal direction (voltage application direction), and thus in the resistance heating element layer 513. Is higher in conductivity in the direction (circumferential direction) perpendicular to the longitudinal direction (voltage application direction) than in the longitudinal direction (voltage application direction), as indicated by the length of the white arrow in FIG. The voltage application direction (Rx direction) and the direction orthogonal to the voltage application direction (Ry direction) have different electrical anisotropy (volume resistivity) (voltage application). The electric resistance (volume resistivity) is smaller in the direction (Ry direction) perpendicular to the voltage application direction than in the direction (Rx direction).

  As a result, even if damage occurs in the direction orthogonal to the voltage application direction, when the current detours in the orthogonal direction so as to avoid the damaged portion, the direction orthogonal to the voltage application direction as shown in FIG. The current is distributed in the (Ry direction), and the current density in the region near the end portion 403 of the scratch 401 can be made smaller than when the resistance heating element layer has no resistance anisotropy (FIG. 4C). it can. As a result, the amount of Joule heat generated in this part can be reduced as compared with the case where there is no resistance anisotropy. The calorific value can be reduced.

  The ratio of volume resistivity in both the direction perpendicular to the voltage application direction and the voltage application direction is adjusted by adjusting the density of the conductive filler oriented in the direction perpendicular to the voltage application direction and the interval between the conductive filler patterns oriented in the direction. By adjusting the (interval in the voltage application direction), a resistance heating element layer 513 having a desired ratio of volume resistivity in both directions can be obtained, and the volume resistivity in both directions is set to a predetermined volume resistivity. Can be adjusted.

  Examples of the heat resistant resin used for the resistance heating element layer 513 include polyimide resin, polyethylene sulfide resin, polyether ether ketone resin, polyaramid resin, polysulfone resin, polyimide amide resin, polyester-imide resin, polyphenylene oxide resin, and poly-p-xylylenenone. Resins, polybenzimidazole resins, and the like can be used. Among them, it is desirable to use a polyimide resin because the polyimide resin exhibits excellent characteristics such as heat resistance, insulation and mechanical strength.

As the conductive filler, metals such as silver (Ag), copper (Cu), aluminum (Al), magnesium (Mg), nickel (Ni), carbon nanotubes, carbon nanofibers, carbon nanocoils, etc. can be used. Two or more kinds of conductive fillers (for example, carbon nanomaterial and metal) may be used.
The shape of the conductive filler is preferably a fibrous, needle-like or flake-like shape in order to increase the probability of contact because the conductive fillers are entangled linearly with the same content and easily contact each other. Thereby, the resistance heating element layer 513 having a uniform electric resistance can be molded.

The thickness of the resistance heating element layer 513 is arbitrary, but is preferably about 5 to 100 μm. The volume resistivity of the resistance heating element layer 513 can be set in a range of about 1.0 × 10 ^{−6 to} 1.0 × 10 ⁻² Ω · m, but the volume resistivity is 1.0 × It is desirable to be within the range of 10 ^{−5 to} 5.0 × 10 ⁻³ Ω · m.
Returning to the description of FIG. 3, the reinforcing layer 514 is a layer for reinforcing the strength of the resistance heating element layer 513, and for example, a polyimide resin can be used. The thickness of the reinforcing layer 514 is arbitrary, but is preferably about 5 to 100 μm. The elastic layer 515 is a layer for transferring heat uniformly and flexibly to the toner image on the recording sheet. By providing the elastic layer 515, the toner image can be prevented from being crushed or the toner image can be melted non-uniformly, and image noise can be prevented from being generated. As a material of the elastic layer 515, a rubber material or a resin material having heat resistance and elasticity is used. For example, a heat-resistant elastomer such as silicone rubber or fluoro rubber can be used as the material.

  The thickness of the elastic layer 515 is 10 to 800 μm, more preferably 50 to 300 μm. If the thickness of the elastic layer 515 is less than 10 μm, it is difficult to obtain sufficient elasticity in the thickness direction. On the other hand, if the thickness exceeds 800 μm, it is difficult to cause the heat generated in the resistance heating element layer 513 to reach the outer peripheral surface of the heating rotator 51 and the heat transfer efficiency is poor.

  The release layer 516 is an outermost layer of the heating rotator 51 and is a layer for improving the releasability between the heating rotator 51 and the recording sheet. As a material for the release layer 516, a material that can withstand use at a fixing temperature and has excellent release properties with respect to toner can be used. For example, PFA (tetrafluoroethylene / perfluoroalkoxyethylene copolymer), PTFE (tetrafluoroethylene), FEP (tetrafluoroethylene / hexafluoroethylene copolymer), PFEP (tetrafluoroethylene / hexafluoroethylene) A fluororesin such as a propylene fluoride copolymer) can be used. The thickness of the release layer 516 is 5 to 100 μm, desirably 10 to 50 μm.

On the other hand, in the non-image areas at both ends indicated by reference numerals 302a and 302b in FIG. 3, the heating rotator 51 is composed of an exposed area indicated by reference numerals 303a and 303b and an overlapping area indicated by reference numerals 304a and 304b. .
Here, “non-image areas 302a and 302b” indicate areas in the belt width direction on the heating rotator 51 corresponding to a range in which an image on the recording sheet is not passed. The same applies to the non-image area shown in FIG.

  In the exposed regions 303a and 303b, the electrodes 511 and 512 are each exposed as a single layer, and in the overlapping regions 304a and 304b, the electrodes 511 and 512 are respectively covered with the resistance heating element layer 513. The two layers 513 and the electrode 512 and the resistance heating element layer 513 are overlapped with each other. Further, a reinforcing layer 514, an elastic layer 515, and a release layer 516 are laminated in this order on both layers.

  The electrodes 511 and 512 are made of a conductive material. As the material of the electrode, for example, metals such as copper (Cu), aluminum (Al), nickel (Ni), stainless steel (SUS), brass, phosphor bronze can be used, but the electrical resistivity is low and the heat resistance is high. It is desirable to use nickel, stainless steel, aluminum, etc., which are excellent in oxidation resistance. The thicker the electrode, the higher the rigidity and the higher the resistance to breakage, but it becomes difficult to deform at the fixing nip formed by the pressure member, so considering the balance with flexibility, The thickness is preferably 10 to 100 μm, more preferably about 30 to 70 μm.

Returning to the description of FIG. 2, the power supply members 501 and 502 are provided with biasing members 5011 and 5021 for pressing the power supply member in the direction of the inside of the circulation path of the heating rotator 51, respectively. As the biasing member, for example, a compression spring can be used. Due to the pressing force of the urging members 5011 and 5021, the power feeding member is pressed against the electrode in the exposed region.
The fixing roller 52 and the pressure roller 53 are axially supported at both end portions 521 and 531 in the axial direction of the core bars 522 and 532 so as to be rotatable on a bearing portion of a frame (not shown). The pressure roller 53 is rotationally driven in the direction of arrow B by transmitting a driving force from a driving motor (not shown). As the pressure roller 53 rotates, the heating rotator 51 and the fixing roller 52 are driven to rotate in the direction of arrow A.

  The fixing roller 52 is formed by covering the periphery of a long cylindrical cored bar 522 with a heat insulating layer 523, and is disposed inside the circulation path of the heating rotator 51. The axial length of the fixing roller 52 is the heating rotator 51. The electrodes 511 and 512 are configured so as to be longer than the length in the axial direction between the press contact positions where the electrodes 511 and 512 are in pressure contact with the corresponding power supply members in the exposed regions at both ends. The metal core 522 is a member that supports the fixing roller 52 and is made of a material having heat resistance and strength. As a material of the core metal 522, for example, aluminum, iron, stainless steel, or the like can be used.

  The heat insulating layer 523 is a layer for preventing the heat generated by the heating rotator 51 from escaping to the cored bar 522. As a material for the heat insulating layer 523, it is desirable to use a sponge (heat insulating structure) made of a rubber material or a resin material having low thermal conductivity and heat resistance and elasticity. This is because the heating rotator 51 can be bent and the nip width can be widened. The heat insulating layer 523 may have a two-layer structure of a solid body and a sponge body. In the case where a silicon sponge material is used as the heat insulating layer 523, the thickness is desirably 1 to 10 mm. More preferably, it is 2-7 mm.

The pressure roller 53 is formed by laminating a release layer 534 around the cylindrical cored bar 532 via an elastic layer 533, and is disposed outside the circulation path of the heating rotator 51. Then, the fixing roller 52 is pressed through the outer peripheral surface of the heating rotator 51, and a fixing nip region having a predetermined width in the circumferential direction is formed between the outer peripheral surface of the heating rotator 51.
The core metal 532 is a member that supports the pressure roller 53 and is made of a material having heat resistance and strength. As a material of the core metal 532, for example, aluminum, iron, stainless steel, or the like can be used. The elastic layer 533 is an elastic body such as silicone rubber or fluororubber and is made of a material having high heat resistance within a thickness range of 1 to 20 mm. Similar to the release layer 516, the release layer 534 is a layer for improving the release property between the pressure roller 53 and the recording sheet, and may be composed of the same material and thickness as the release layer 516. it can.

[3] Manufacturing Method of Heating Rotator The heating rotator 51 according to the present embodiment is manufactured through the following steps (1) to (11).
(1) Formation process of electrodes 511 and 512 Metals for electrode formation (for example, nickel, stainless steel, and aluminum) are processed to form ring-shaped electrodes (electrodes 511 and 512) having a thickness of 30 to 70 μm. As the processing method, for example, electroforming, spatula drawing, press drawing, or the like can be used. Moreover, it is good also as forming a ring-shaped electrode by laser welding using the metal sheet for electrode formation.
(2) Step of setting electrodes 511 and 512 to cylindrical molds After applying a release agent on the surface of the cylindrical molds to improve mold separation, ring-shaped electrodes 511 formed in (1), Each of the electrodes 511 and 512 is formed into a cylindrical mold by fitting 512 into the cylindrical mold with a predetermined interval in the axial direction (interval corresponding to the length of the image area in the belt width direction). set.
(3) Precursor application process of resistance heating element layer 513 A polyimide precursor solution in which conductive filler is dispersed is prepared, and a region corresponding to the exposed region of electrodes 511 and 512 set in a cylindrical mold is masked. In this state, the adjusted precursor solution is applied to the outer peripheral surface of the cylindrical mold, and the applied polyimide precursor is heated so as to be in a semi-cured state, thereby forming the polyimide precursor. For example, the polyimide precursor can be brought into a semi-cured state by heating in an oven at about 100 ° C. for about 1 hour.

At this time, the conductive filler is oriented in the circumferential direction by applying the polyimide precursor in which the conductive filler is dispersed while rotating the outer peripheral surface of the cylindrical mold. Further, the outer peripheral surface of the cylindrical mold is moved by a predetermined distance in the cylindrical axis direction, and the operation of applying the conductive filler in the circumferential direction as described above is repeated each time the outer peripheral surface is moved by the predetermined distance.
The weight of the conductive filler dispersed in the polyimide precursor solution is adjusted so that the weight of the conductive filler is 50 to 300% by weight with respect to the solid weight of the polyimide precursor in the polyimide precursor solution. . Thereby, the volume resistivity of the resistance heating element layer 513 can be adjusted so that the calorific value of the fixing device 5 is in the range of 500 to 1500 W.

Also, by adjusting the density of the conductive filler applied in the circumferential direction and the moving distance for moving the outer peripheral surface of the cylindrical mold, the volume in both the circumferential direction (direction perpendicular to the voltage application direction) and the voltage application direction is adjusted. A resistance heating element layer 513 having a desired ratio of resistivity can be obtained.
(4) Step of applying the precursor of the reinforcing layer 514 The polyimide precursor solution is applied as a precursor of the reinforcing layer 514 to the outer peripheral surface of the cylindrical mold after applying the conductive filler.
(5) Molding step of reinforcing layer 514 The applied precursor of the reinforcing layer 514 is heated so that the polyimide precursor is in a semi-cured state in the same manner as in (3) to mold the precursor.
(6) Imidization process of polyimide precursor The molded polyimide precursor is heated to complete imidization of the polyimide precursor. The polyimide precursor is heated, for example, by heating at about 350 ° C. for about 1 hour. Thereby, imidization of both layers is completed substantially simultaneously, the resistance heating element layer 513 and the reinforcement layer 514 are formed, and the adhesiveness between both layers can be improved.
(7) Precursor application step of elastic layer 515 After applying and drying a primer on the outer surface of the reinforcing layer 514, a silicone rubber precursor solution is further applied. For example, “XP81-405” manufactured by Momentive Performance Materials may be used as the primer.

As the silicone rubber precursor solution, for example, “XP81-A6361” manufactured by Momentive Performance Materials may be used.
(8) Forming process of elastic layer 515 The applied silicone rubber precursor solution is heated to perform primary vulcanization, and the elastic layer 515 is formed. The primary vulcanization is performed by heating the silicone rubber precursor solution in an oven at about 150 ° C. for about 10 minutes, for example.
(9) Step of covering elastic layer 515 with release layer 516 In order to improve the adhesion to elastic layer 515, after applying addition type liquid silicone rubber of a silicone rubber precursor to the inner surface of release layer 516, the release layer The elastic layer 515 is covered with the layer 516. As the additional silicone rubber, for example, “XE15-B7354-40K × 2S” manufactured by Momentive Performance Materials, Inc. can be used. As the release layer 516, for example, a PFA tube can be used.
(10) Adhesion process The silicone rubber precursor applied to the elastic layer 515 and the release layer 516 is heated to perform secondary vulcanization, and both layers are adhered. The secondary vulcanization is performed by heating the silicone rubber precursor in an oven at about 200 ° C. for about 4 hours, for example. Thereby, the heating rotator 51 is formed.
(11) Mask removal process The masks of the electrodes 511 and 512 set in the cylindrical mold are removed, and the heating rotator 51 formed on the cylindrical mold is removed from the mold.

[4] Relationship between Abnormal Heat Generation Ratio and Volume Resistivity Ratio in Rx Direction and Ry Direction FIG. 5 shows an abnormal heat generation ratio when the resistance heating element layer 513 is damaged, and Rx of the resistance heating element layer 513. The experimental result investigated about the relationship with the ratio (R2 / R1) of the volume resistivity (R2) of the Ry direction with respect to the volume resistivity (R1) of a direction is shown. The experiment was performed under the following experimental conditions.
(1) Resistance heating element layer used in the experiment Each resistance heating element layer 513 having R2 / R1 of 0.001, 0.01, 0.1 and resistance heating element having R2 / R1 of 1 as a resistance heating element layer for comparison A body layer was used.
(2) Size of Damaged Part Each of the resistance heating element layers of (1) was tested by forming four types of damaged parts in the circumferential direction. Specifically, the damage ratio indicating the ratio (percentage) of the circumferential length of the damaged portion to the length (D) of the entire circumference in the circumferential direction is 11%, 32%, 53%, and 74%, respectively. Damaged portions of each length were formed. Damaged portions of each damage ratio were formed in the substantially central portion of the resistance heating element layer 600 as indicated by reference numeral 601 in FIG. Reference numerals 602 and 603 in the figure denote electrodes.
(3) Calculation method of abnormal heating value ratio For the fixing device in which the resistance heating element layer of the heating rotator is each resistance heating element layer of (1), the fixing device is warmed up continuously for 5 seconds by supplying power. After the measurement, the surface temperature of the outer peripheral surface of the heating rotator is measured in a region corresponding to two locations indicated by A and B in FIG. 6, the ratio between the two is calculated, and the calculation result is the resistance heating element layer. The abnormal calorific value ratio in

  Specifically, the measured temperature (S) in the region corresponding to B near the damaged portion 601 is regarded as the temperature of the damaged portion, and the measured temperature (T) in the region corresponding to A near the electrode 602 is normal without damage. The ratio (S / T) of both was regarded as the abnormal heat generation ratio. FIG. 7 is a diagram illustrating a specific example of a time change during the warm-up period of the measured temperature (S) of the damaged part and the measured temperature (T) of the normal part. In the figure, reference numeral 701 indicates a temperature change of the measured temperature (S) of the damaged part, and reference numeral 702 indicates a temperature change of the measured temperature (T) of the normal part.

In the figure, the ratio (S / T) between the two when the warm-up is completed (when the elapsed time is 5 seconds) is calculated as the abnormal heat generation ratio. In the example of the figure, the temperature (S) of the damaged part at the completion of warm-up is about 295 ° C., and the temperature (T) of the normal part is about 170 ° C. Therefore, the abnormal heat generation ratio (S / T) is , About 1.7.
(4) Determination of Abnormal Heat Generation Ratio (hereinafter referred to as “Non-Damage Ratio”) with No Damage in Fixing Device Due to damage to the resistance heating element layer 513, the surface temperature of the outer peripheral surface of the heating rotator 51 is 300 ° C. Since the fixing roller 52 and the pressure roller 53 may be damaged when the temperature exceeds the range, the present inventor has determined that the range in which the abnormal heat generation ratio (S / T) does not exceed (300 / fixing temperature) Determined as damage ratio. Here, the fixing temperature was 150 ° C. and 2 was used as the non-damage ratio.
(5) About Experimental Results In FIG. 5, reference numeral 501 indicates a graph showing the correspondence between the abnormal heat generation ratio and R2 / R1 when the damage ratio is 74%, and reference numeral 502 indicates that the damage ratio is 53%. In this case, a graph showing the correspondence between the abnormal heat generation ratio and R2 / R1 is shown, and reference numeral 503 shows a graph showing the correspondence between the abnormal heat generation ratio and R2 / R1 when the damage ratio is 32%. Reference numeral 504 indicates a graph showing a correspondence relationship between the abnormal heat generation ratio and R2 / R1 when the damage ratio is 11%. Reference numeral 505 indicates a position where the abnormal heat generation amount ratio corresponds to the non-damage ratio.

As shown in FIG. 5, as R2 / R1 becomes smaller (the volume resistivity in the Ry direction becomes smaller than the volume resistivity in the Rx direction), the abnormal heat generation ratio becomes smaller, and the damaged portion in the resistance heating element layer 513 It was confirmed that the calorific value due to abnormal heat generation in the vicinity was reduced.
In the resistance heating element layer 513 having a R2 / R1 value of 0.001, the abnormal heat generation ratio for the damaged portions of all sizes is lower than the non-damage ratio, and the heat generation amount due to abnormal heat generation in the vicinity of the damaged portions is reduced. It was confirmed that the heat generation amount that does not damage the fixing device 5 can be reduced.

  Further, in the resistance heating element layer 513 having the R2 / R1 value of 0.01, the abnormal heat generation ratio for the damaged portion having the damaged portion size of 11% and 32% is set to be 0.2 / R1. In the resistance heating element layer 513 of FIG. 1, the abnormal heat generation ratio for the damaged portion whose damaged portion is 11% is less than the non-damage ratio, and the heat generation amount due to abnormal heat generation in the vicinity of the damaged portion is the fixing device. It was confirmed that the calorific value which does not damage 5 can be reduced.

In this way, by configuring the resistance heating element layer 513 so that R2 / R1 is at least 0.1 or less, the amount of heat generated due to abnormal heat generation in the vicinity of the damaged portion can be reduced to the extent that the fixing device 5 is not damaged. It was confirmed that it can be reduced.
(Modification)
As described above, the present invention has been described based on the embodiment. However, the present invention is not limited to the above-described embodiment, and the following modifications can be implemented.

  (1) In this embodiment, the voltage application direction of the heating rotator 51 to the resistance heating element layer 513 is the longitudinal direction, and the current flows in the resistance heating element layer 513 in the longitudinal direction. The direction may be the circumferential direction of the heating rotator, and a current may flow in the resistance heating element layer of the heating rotator in the circumferential direction. For example, as shown in FIG. 8A, power supply rollers 1001 and 1002 extending in the direction of the rotation axis are arranged so as to be inscribed on the inner peripheral side of the hollow heating rotating body 51B that is driven to rotate, and the power supply unit 1000 The voltage may be applied in the circumferential direction to the resistance heating element layer of the heating rotator 51B via the power supply rollers 1001 and 1002. With the above configuration, a current flows in the circumferential direction between the power supply rollers 1001 and 1002 as indicated by the white arrows in FIG.

  Even in the case of the heating rotator configured as described above, the configuration of the resistance heating element layer of the heating rotator 51B is similar to the resistance heating element layer 513 of the present embodiment in the volume resistivity in the direction orthogonal to the voltage application direction. When the damage occurs in the direction perpendicular to the voltage application direction compared to the case where there is no resistance anisotropy, the damaged portion is formed by making the volume resistivity smaller than the volume resistivity in the voltage application direction. The surroundings can be made less likely to generate abnormal heat, and the amount of heat generated by abnormal heat generation can be reduced.

Although not shown in FIG. 8A, a fixing member for forming a fixing nip with the pressure roller 1003 is provided between the power supply rollers 1002 and 1003 on the inner peripheral side of the heating rotator 51B. It is arranged so as to be inscribed in.
(2) In the heating rotator 51 of the present embodiment, the reinforcing layer 514 is laminated on the resistance heating element layer 513 and a part of the electrodes 511 and 512 is exposed as a single layer. The configuration of the body is not limited to the above configuration, and may be another configuration. For example, the configuration of the heating rotator may be the configuration shown in FIG. In the figure, the elements constituting the heating rotator 51C are the same as the constituent elements of the heating rotator 51. Therefore, the same numbers as the corresponding constituent elements of the heating rotator 51 are assigned to the respective constituent elements. As shown in the figure, in the heating rotator 51C, the resistance heating element layer 513 is laminated on the reinforcing layer 514, and the electrodes 511 and 512 are formed on the resistance heating element layer 513, respectively.

  The present invention relates to a fixing device provided in an image forming apparatus such as a printer or a copying machine, and can be used as a technique for reducing abnormal heat generation particularly in a fixing device using a resistance heating element layer as a heating element.

DESCRIPTION OF SYMBOLS 1 Printer 3 Image process part 3Y-3K Image formation part 4 Paper feed part 5 Fixing device 10 Exposure part 11 Intermediate transfer belt 12 Drive roller 13 Driven roller 31Y Photosensitive drum 32Y Charger 33Y Developer 34Y Primary transfer roller 35Y Cleaner 41 Paper feed cassette 42 Feed roller 43 Transport path 44 Timing roller 45 Secondary transfer roller 46 Secondary transfer position 51 Heating rotator 52 Fixing roller 53 Pressure roller 60 Control unit 71 Discharge roller 72 Discharge tray 500 Power supply unit 501, 502 Power supply Brush 511, 512 Electrode 513 Resistance heating element layer 514 Reinforcement layer 515, 533 Elastic layer 516, 534 Release layer 521, 531 Core metal end 522, 532 Core metal 523 Heat insulation layer

Claims (6)

A fixing device for thermally fixing an unfixed image on a recording sheet,
An endless heating belt having a resistance heating element layer that generates heat when energized, and heat-sealing an unfixed image on the recording sheet by heat generated by the resistance heating element layer;
Energization means for energizing the resistance heating element layer by applying a voltage;
With
The resistance heating element layer has a resistance anisotropy in which the volume resistivity R2 in the voltage application direction is larger than the volume resistivity R1 in the direction orthogonal to the voltage application direction (R1 <R2). Fixing device. The fixing device according to claim 1, wherein the resistance heating element layer has a configuration in which a conductive filler is oriented in a direction orthogonal to a voltage application direction in a heat resistant resin. The heating belt has power supply electrodes for supplying power to the resistance heating element layer at both ends in the longitudinal direction,
The fixing device according to claim 1, wherein the energization unit applies a voltage in the longitudinal direction via each of the power supply electrodes. The fixing device according to claim 3, wherein each of the power supply electrodes is formed on the entire circumference of the heating belt. The fixing device according to claim 1, wherein the energization unit energizes the resistance heating element layer by applying a voltage in a circumferential direction of the heating belt. An image forming apparatus comprising the fixing device according to claim 1.

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