JP2011253141A - Fixing device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device capable of reducing occurrence of abnormal heating in the fixing device using a resistance heating layer as a heating element.SOLUTION: The fixing device feeds an electric current to a cylindrical heating roller 51 having a resistance heating layer 514 on an insulative peripheral surface to heat the heating roller 51, and heat-fixes an unfixed image on a recording sheet. The resistance heating layer 514 has a configuration where a plurality of elongated resistive thin pieces are arranged in a circumferential direction of the rotor with a gap between the adjacent resistive thin pieces and with both ends of each respective piece connected to feeding electrodes formed on the whole circumference at both ends of the rotor.

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 layer.

  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. Since there is a risk of electric shock if the resistance heating element layer that is energized is touched directly, the resistance heating element layer is generally covered with an insulating layer in order to prevent electric shock.

  Patent Document 1 discloses a fixing device using a resistance heating element layer covered with an insulating layer as a heating layer. 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

  Since the resistance heating element layer is covered with an insulating layer, it is not usually touched directly. However, since the thickness of the insulating layer is as thin as about several hundred μm, the insulating layer is scratched by contact with foreign matter or a recording sheet mixed from the outside, and the scratch extends to the resistance heating layer. The current density locally increases in the vicinity of the part, and the portion where the current density is increased in the resistance heating layer may generate abnormal heat.

  FIG. 6 is a diagram schematically showing a state in which a resistance heating element layer is flawed and a peripheral portion of the flaw is heated in a fixing device using a conventional resistance heating element layer as a heating element. In the figure, reference numeral 600 indicates a fixing device, reference numeral 510 indicates a heating rotator, reference numeral 520 indicates a fixing roller, reference numeral 530 indicates a pressure roller, reference numerals 541 and 542 indicate power supply brushes, and reference numeral 543 indicates. Reference numerals 544 and 545 denote power supply electrodes.

  Reference numerals 601 and 604 indicate scratches generated in the resistance heating element layer, and reference numeral 602 indicates a current flowing around the scratches 601. As shown in FIG. 6, when a scratch is generated in the resistance heating element layer, the progress of the current 602 is interrupted by the scratch, and the current 602 wraps around the edge of the scratch, so that the current density around the edge increases, Abnormal heat is generated as indicated by the white arrow 603. Similarly, abnormal heat is generated around the edge of the scratch 604 as indicated by the white arrow 605.

  In this way, if a person touches a part that has generated abnormal heat, it will cause a serious situation such as a burn, which is extremely dangerous. The present invention has been made in view of the above-described problems, and includes a fixing device capable of reducing abnormal heat generation in a fixing device using a resistance heating element layer as a heat generating layer, and the fixing device. An object is to provide an image forming apparatus.

  In order to achieve the above object, a fixing device according to an embodiment of the present invention supplies a heat to a cylindrical rotating body having a resistance heating element layer on an insulating peripheral surface to generate heat, and an unfixed image on a recording sheet. The resistance heating element layer is a state in which a plurality of elongated thin resistance pieces are connected at their both ends in the longitudinal direction to power supply electrodes formed on the entire circumference of both ends of the rotating body. Thus, the arrangement is arranged at intervals in the circumferential direction of the rotating body.

  The cylindrical rotating body may be an endless belt that is driven to circulate. Further, the interval may be less than 1 cm. The image forming apparatus according to an aspect of the present invention may be an image forming apparatus including the fixing device.

  By providing the above configuration, each of the plurality of resistance thin pieces of the resistance heating element layer is arranged on the insulating peripheral surface at intervals in the circumferential direction of the rotating body. If the size of the resistance thin piece extends over the entire circumferential width of the resistance thin piece, the energization of the resistance thin piece is interrupted by the scratch, and no current flows through the resistance thin piece, and the resistance heating element layer is caused by the scratch. Can prevent abnormal heat generation.

  In addition, even when the scratches generated in the resistance heating element layer are small and do not reach the entire circumferential width of the resistance flakes, the current flowing through the adjacent resistance flakes is insulated from the adjacent resistance flakes. Therefore, it is possible to suppress the flow into the resistance thin piece where the scratch has occurred, and accordingly, the current density flowing into the periphery of the end portion of the scratch can be reduced, and the temperature rise in the vicinity of the end portion 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 structure in a region excluding both ends of a heating rotator 51. FIG. 4 is a cross-sectional view in the direction of the rotation axis around one end of the heating rotator 51 (the end on the side where the electrode 511 is present). 3 is a diagram illustrating a relationship between a configuration of a control unit 60 and main components that are controlled by the control unit 60. FIG. FIG. 6 is a diagram schematically showing a state in which a resistance heating element layer is scratched and heat is generated around the edge of the scratch in a conventional fixing device using the resistance heating element layer as a heating element.

(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 unit 33Y, a primary transfer roller 34Y, and a cleaner 35Y for cleaning 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. 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 image is shifted on the intermediate transfer belt 11 so that the toner image is superimposed on the same position on the intermediate transfer belt 11 by the primary transfer rollers of the image forming units 3Y, 3M, 3C, and 3K. After the primary transfer sequentially, the toner images on the intermediate transfer belt 11 are secondarily transferred onto the recording sheet collectively by the action of electrostatic force by the secondary transfer roller 45. The recording sheet on which the toner image is 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. Thereafter, the paper is discharged onto a paper discharge tray 72 by a 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 sending 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 of the rollers such as the feeding roller 42 and the timing roller 44 is driven to rotate by a conveyance motor (not shown) as a power source through a power transmission mechanism (not shown) such as a gear or a belt. 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 includes a heating rotator 51, a fixing roller 52, and a pressure roller 53. The heating rotator 51 is an endless belt, and power supply electrodes 511 and 512 are provided at both ends thereof. Power is supplied to both electrodes from the power supply unit 500 through power supply brushes 501 and 502. Thereby, an electric current flows between both electrodes, and the heating rotator 51 generates heat. Furthermore, a temperature sensor 54 is disposed at a predetermined position in the vicinity of the outer peripheral surface of the heating rotator 51 (here, in the vicinity of the central portion in the rotation axis direction).

  FIG. 3 is a cross-sectional view showing a detailed structure in a region excluding both ends of the heating rotator 51. As shown in the figure, in the region excluding both ends, the heating rotator 51 is configured by laminating an insulating layer 513, a resistance heating element layer 514, an elastic layer 515, and a release layer 516 in this order. The resistance heating element layer 514 is divided into a plurality of elongated layers in the circumferential direction of the heating rotator 51 (here, equally divided), and is divided into elongated layers (hereinafter referred to as “divided layers”). ) Are arranged so as to circulate on the insulating layer 513 at equal intervals in the circumferential direction. A gap between adjacent divided layers is filled with an insulating elastic layer 515 so that the adjacent divided layers are in an insulating state. In order to prevent temperature unevenness in the fixing temperature in the paper passing region of the heating rotator 51, it is desirable that the distance between adjacent divided layers be as close as possible, and be several mm or less (less than 1 cm). It is desirable.

As described above, the resistance heating element layer 514 is not integrally formed as one layer covering the entire peripheral surface of the insulating layer 513, but is divided into a plurality of divided layers and arranged in the insulating layer 513. When the resistance heating element layer 514 is scratched, the amount of abnormal heat generation around the edge of the scratch can be reduced.
For example, as indicated by reference numeral 201 in FIG. 2, when the circumferential length of the scratch extends over the entire circumferential width of one divided layer of the resistance heating element layer 514, energization is caused by the scratch. Since the current does not flow through the divided layer as indicated by an arrow with a cross with a symbol 202, the temperature of the divided layer does not increase. On the other hand, as shown in FIG. 6, in the fixing device 600 in which the resistance heating element layer is configured as one layer covering the entire peripheral surface of the insulating layer, the scratch 601 generated at the position corresponding to the scratch 201 in FIG. Since the current 602 flows intensively around the end portion and the current density around the end portion increases, the temperature around the end portion suddenly increases and abnormal heat is generated as indicated by the white arrow 603.

  Furthermore, as indicated by reference numeral 203 in FIG. 2, even when the scratch is small and does not reach the entire circumferential width of one divided layer of the resistance heating element layer 514, the adjacent divided layer is insulative. Since it is configured to be insulated by being separated by the elastic layer 515, the current indicated by the arrow marked with × of 204 does not flow from the adjacent divided layer to the periphery of the wound end. Compared to the temperature increase indicated by reference numeral 605 in FIG. 6 (temperature increase in the vicinity of the end of the scratch 604 at a position corresponding to the scratch 203 in FIG. 2) when configured as a single layer covering the entire surface, the end of the scratch As much as the current density flowing into the periphery can be reduced, the temperature increase in the vicinity of the end portion is indicated by reference numeral 205 (in FIGS. 2 and 6, the degree of temperature increase is indicated by the length of the white arrow). To reduce Door can be.

The greater the number of divided layers of the resistance heating element layer 514 that is equally divided, the smaller the circumferential width of the divided layer can be, and even the smaller flaws can be reduced accordingly. The temperature rise in the vicinity can be effectively reduced.
FIG. 4 is a cross-sectional view in the rotation axis direction around one end of the heating rotator 51 (the end on the side where the electrode 511 is present). As shown in the drawing, an insulating layer 513, a resistance heating element layer 514, and an electrode 511 are laminated in this order at the end of the heating rotator 51. The electrode 511 is made of a conductive material. As a material of the electrode 511, for example, a metal such as copper (Cu), aluminum (Al), nickel (Ni), brass, phosphor bronze, or the like can be used. The insulating layer 513 is a layer that reinforces the strength of the heating rotator 51 and insulates the divided layers of the adjacent resistance heating element layer 514. As the insulating layer 513, for example, a polyimide resin is used. be able to.

  The resistance heating element layer 514 is a layer that is electrically connected to the electrodes 511 and 512 and generates Joule heat when supplied with power through the electrodes 511 and 512. The resistance heating element layer 514 is configured by dispersing a conductive material in an insulating material such as a heat resistant resin. The electric resistance value (or volume resistivity) of the resistance heating element layer 514 is adjusted to a predetermined electric resistance value (or volume resistivity) by adjusting the amount of the conductive material.

  Examples of heat-resistant resins include polyimide resins, polyethylene sulfide resins, polyether ether ketone resins, polyaramid resins, polysulfone resins, polyimide amide resins, polyester-imide resins, polyphenylene oxide resins, poly-p-xylylene resins, polybenzimidazole resins, etc. Can be used. As the heat-resistant resin used for the resistance heating element layer 514, it is desirable to use a polyimide resin that exhibits excellent characteristics such as heat resistance, insulation, and mechanical strength.

  As the conductive material, 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 materials (for example, carbon nanomaterial and metal) may be used. In this case, the metal is preferably needle-like or flaky silver (Ag) or nickel (Ni), and the particle size is preferably 0.01 to 10 μm. Thereby, the resistance heating element layer 514 having a uniform electric resistance can be molded by being intertwined with the carbon nanomaterial linearly. When the metal is in the form of particles, powders, or lumps, the resistance heating element layer has a uniform electric resistance because it is not entangled with the carbon nanomaterial mixed in the resistance heating element layer 514 and is in point contact with the carbon nanomaterial. 514 is difficult to obtain.

The thickness of the resistance heating element layer 514 is arbitrary, but is preferably about 5 to 100 μm. The electric resistance value of the resistance heating element layer 514 can be set in a range of about 1.0 × 10 ^{−6 to} 1.0 × 10 ⁻² Ω · m, but the electric resistance value is 1.0 × 10 ^{−5 to} 5.0 ×. It is desirable to be within the range of 10 ⁻³ Ω · m.
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, an insulating rubber material or resin material having heat resistance and elasticity is used. For example, silicone rubber can be used.

  The thickness of the elastic layer 515 is 10 to 800 μm, more preferably 100 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 514 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.

  Returning to the description of FIG. 2, 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 when the driving force from the pressure roller driving motor 56 is transmitted. 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 circumference 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 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 a 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 heating rotator 51 to form a fixing nip having a predetermined width in the circumferential direction between the outer peripheral surface of the heating rotator 51. The metal core 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 515, 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 515. it can.
The temperature sensor 54 detects the surface temperature in the circumferential direction of the outer peripheral surface of the heating rotator 51 that is driven to rotate, and outputs the detection result to the control unit 60. The time interval to be detected is set in advance to a time interval at which the surface temperature in the region on the outer peripheral surface of the heating rotator 51 corresponding to each divided layer of the resistance heating element layer 514 divided in the circumferential direction during the circular drive can be detected. Has been. As the temperature sensor 54, for example, an infrared detection type thermopile can be used. Based on the detection result of the surface temperature, the control unit 60 controls on / off of energization to the heating rotator 51 so that the surface temperature becomes a predetermined temperature (for example, a fixing temperature).

[3] Configuration of Control Unit FIG. 5 is a diagram illustrating a relationship between the configuration of the control unit 60 and main components to be controlled by the control unit 60. The control unit 60 is a so-called computer, and as shown in the figure, a CPU (Central Processing Unit) 601, a communication interface (I / F) unit 602, a ROM (Read Only Memory) 603, a RAM (Random Access Memory). 604, an image data storage unit 605, and the like.

The communication I / F unit 602 is an interface for connecting to a LAN such as a LAN card or a LAN board. The ROM 603 stores a program for controlling the image processing unit 3, the paper feeding unit 4, the fixing device 5, and the operation panel 6.
The RAM 604 is used as a work area when the CPU 601 executes a program.
The image data storage unit 605 stores image data for printing input via the communication I / F unit 602 or an image reading unit (not shown). The CPU 601 controls the image processing unit 3, the paper feeding unit 4, the fixing device 5, and the operation panel 6 by executing various programs stored in the ROM 603.
(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 belt heating type fixing device is used. However, the effect of this embodiment is that the fixing device using the resistance heating element layer is a fixing device other than the belt heating type. Can also be realized. For example, a divided layer of the plurality of resistance heating element layers 514 may be provided directly on the fixing roller, and the fixing device may be configured by a fixing roller and a pressure roller.

(2) In the present embodiment, the resistance heating element layer 514 is equally divided into a plurality of layers at equal intervals in the circumferential direction, but the way of division is not limited to equal division. For example, the widths in the circumferential direction of the respective divided layers may be different lengths, and the circumferential distance between the divided layers may not be equal as long as it does not exceed 1 cm.
(3) In the present embodiment, the shape of each divided layer of the resistance heating element layer 514 is an elongated shape, but the shape of the divided layer is not limited to an elongated shape. The shape may be any shape as long as the peripheral surface of the insulating layer 513 can be covered with an interval close to the circumferential direction (an interval shorter than 1 cm).

  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 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 Feed cassette 42 Feed roller 43 Conveying path 44 Timing roller 45 Secondary transfer roller 46 Secondary transfer position 51 Heating rotary member 52 Fixing roller 53 Pressure roller 54 Temperature sensor 60 Control unit 71 Discharge roller 72 Discharge tray 500 Power supply unit 501 , 502 Power supply brush 511, 512 Electrode 513 Insulating layer 514 Resistance heating element layer 515, 533 Elastic layer 516, 534 Release layer 521, 531 Core metal end 522, 532 Core metal 523 Thermal insulation layer

Claims (4)

A fixing device that heats a cylindrical rotating body having a resistance heating element layer on an insulating peripheral surface to generate heat and heat-fix an unfixed image on a recording sheet,
The resistance heating element layer has a plurality of elongated resistance thin pieces spaced apart in the circumferential direction of the rotating body in a state where both ends in the longitudinal direction are connected to power supply electrodes formed on the entire circumference of both ends of the rotating body. A fixing device characterized by having a configuration arranged in a line. The fixing device according to claim 1, wherein the cylindrical rotating body is an endless belt that is driven to rotate. The fixing device according to claim 1, wherein the interval is less than 1 cm.   An image forming apparatus comprising the fixing device according to claim 1.

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