JP6375943B2 - Resistance heating element, fixing device and image forming apparatus - Google Patents

Description

  The present invention relates to a resistance heating element, a fixing device, and an image forming apparatus.

  As a fixing device employed in an image forming apparatus such as a copying machine or a laser beam printer, a thermal film fixing type fixing device is known. The fixing device can shorten the time (warming up time) from power-on to copy start, and is excellent from the viewpoint of energy saving.

  The fixing device includes a heat generating belt (resistance heating element) that generates heat by supplying electricity as a fixing belt that directly contacts the recording medium. Such a fixing belt is a seamless belt having, for example, a film containing a heat-resistant resin such as polyimide and a conductive filler, and a release layer such as a fluororesin covering the outer peripheral surface thereof. In the fixing belt, it is known that a conductive fibrous filler satisfying specific requirements is used for the conductive filler for the purpose of reducing the resistance of the fixing belt or increasing the resistance stability. (For example, see Patent Documents 1 and 2).

JP 2012-8299 A JP2013-25120A

  The fixing belt described in Patent Document 1 can have a sufficiently low initial resistance value. Further, the fixing belt described in Patent Document 2 has higher resistance stability than the conventional one. However, even when these fixing belts are used, the resistance value of the fixing belt may fluctuate over time, and fixing unevenness due to fluctuations in the resistance value of the fixing belt may occur.

A first object of the present invention is to provide a resistance heating element whose resistance value is stable for a long period of time.
A second object of the present invention is to provide an image forming apparatus capable of suppressing fixing unevenness.

  The present invention is a resistance heating element composed of a resin composition containing a heat-resistant resin and conductive fibers, wherein the conductive fibers are dispersed in the resin composition, and stainless steel fibers, Provided is a resistance heating element having a carbon coating layer covering the surface of the stainless steel fiber.

  The present invention also provides an endless fixing belt, a fixing roller disposed inside the fixing belt and contacting a part of an inner peripheral surface of the fixing belt, an outer surface of the fixing belt, and the fixing roller. A fixing device having a pressure roller that presses the outer peripheral surface of the fixing belt toward the surface and a power supply device that supplies electricity to the fixing belt, wherein the fixing belt includes the resistance heating element on the endless belt. A fixing device is provided.

  Furthermore, the present invention provides an image forming apparatus having the above-described fixing device that fixes an unfixed toner image formed on a recording medium by electrophotography on the recording medium by heating and pressing.

  According to the present invention, it is possible to provide a resistance heating element whose resistance value is stable for a long period of time, and to provide an image forming apparatus capable of suppressing fixing unevenness.

It is a figure showing typically an example of a resistance heating element concerning an embodiment of the invention. It is a figure which shows typically the other example of the resistance heating element which concerns on embodiment of this invention. FIG. 3A is a front view of the fixing device schematically showing a configuration of the fixing device as an example of the heating device according to the embodiment of the present invention, and FIG. 3B is a schematic diagram showing the configuration of the fixing device. It is a side view of a fixing device. 1 is a diagram schematically illustrating a configuration of an example of an image forming apparatus according to an embodiment of the present invention.

  Embodiments of the present invention will be described below.

[Resistance heating element]
The resistance heating element according to the present embodiment is constituted by a resin composition containing a heat resistant resin and conductive fibers. The resistance heating element generates heat when energized. The form can be appropriately determined according to the application, for example, a sheet or an endless belt. The calorific value of the resistance heating element can be determined by the energization amount, the content of conductive fibers in the resin composition, and the like. For example, the calorific value can be increased by increasing these. .

  The heat resistant resin may be one kind or more. Examples of the heat resistant resin include polyphenylene sulfide, polyarylate, polysulfone, polyethersulfone, polyetherimide, polyimide, polyamideimide, and polyetheretherketone. Among these, polyimide is preferable from the viewpoint of heat resistance.

  A polyimide can be obtained by advancing a dehydration and cyclization (imidization) reaction of the precursor polyamic acid by heating at 200 ° C. or more, or by using a catalyst. For this reason, when using a polyimide as a heat resistant resin, after mixing a polyamic acid and an electroconductive fiber, it is preferable to heat at the temperature of 200 degreeC or more, for example. The polyamic acid may be produced by dissolving a tetracarboxylic dianhydride and a diamine compound in a solvent and mixing and heating the polycondensation reaction, or a commercially available product may be used. Examples of the diamine compound and tetracarboxylic dianhydride include the compounds described in paragraphs 0123 to 0130 of JP2013-25120A.

  The content of the heat-resistant resin in the resin composition is preferably 40 to 90% by volume from the viewpoint of moldability and the like.

  The said conductive fiber is comprised by the stainless steel fiber and the coating layer made from carbon which covers the surface of the said stainless steel fiber. One or more conductive fibers may be used.

  For example, the conductive fiber has a ratio (l / L) of a short diameter (fiber cross-sectional diameter; l) to a long diameter (fiber length; L) of 0.25 or less. The ratio 1 / L is more preferably 0.025 to 0.25. The major diameter L of the conductive fiber is preferably 5 to 1000 μm, and more preferably 10 to 200 μm. The short diameter l of the conductive fiber is preferably 0.5 to 30 μm, and more preferably 1 to 10 μm. The “fiber cross-sectional diameter” is a long diameter in the fiber cross section, and is a diameter when the fiber cross section is circular. The size of the conductive fiber can be regarded as substantially the same as the size of the following stainless steel fiber.

  The major axis and minor axis of the conductive fiber are average values of values measured from images such as micrographs. For example, the above-mentioned major axis and minor axis are obtained by photographing a stainless steel fiber 500 times with a scanning electron micrograph, taking the obtained image into a scanner, and extracting a conductive fiber sample 500 from the obtained image data. The major axis and the minor axis are measured and calculated from the average value.

  The stainless steel fiber may be one kind or more. Examples of the stainless steel of the stainless steel fiber include various stainless steels such as austenite, martensite, ferrite, austenite / ferrite, and precipitation hardening.

  Examples of austenitic stainless steel include SUS201, SUS202, SUS301, SUS302, SUS303, SUS304, SUS305, SUS316, and SUS317. Examples of martensitic stainless steel include SUS403 and SUS420. Examples of ferritic stainless steel include SUS405, SUS430, and SUS430LX. Examples of austenitic ferritic stainless steel include SUS329J1. Examples of the precipitation hardening stainless steel include SUS630. Among these, austenitic stainless steel and ferritic stainless steel are preferable from the viewpoint of oxidation prevention.

  The stainless steel fiber may be a manufactured product or a commercial product. For example, stainless steel fibers can be obtained by a conventionally known production method. That is, the stainless steel is pulled out from the nozzle into a fiber shape, further stretched as necessary, and heated as necessary to produce a stainless steel element fiber having a desired short diameter, and this is made to a desired length. Obtained by cutting.

  The coating layer is made of carbon. For example, the coating layer is composed mainly of carbon atoms. The said coating layer may contain the other element in the range with the effect of this embodiment mentioned later. The conductive fiber usually exhibits a color including black due to carbon in the coating layer.

  The coating layer can be produced by a known technique. For example, the coating layer can be produced by carbon plating. Carbon plating can be performed by subjecting the stainless steel fiber to electrolytic plating in a molten salt containing a compound serving as a carbon supply source. Examples of the compound serving as the carbon supply source include calcium carbide. Examples of the molten salt include lithium chloride, potassium chloride, and mixtures thereof. The carbon plating is performed at an appropriate temperature for maintaining the molten salt (for example, 300 ° C. or more in the case of the molten salt illustrated above).

  For example, the said coating layer can also be produced by the method using a spray pyrolysis method. In this method, for example, by introducing (spraying) a mixed liquid of a solvent and a metal salt serving as a carbon supply source into a high-temperature reactive group, carbon generated by evaporation, crystallization, and thermal decomposition of the solvent Fine particles covering the metal salt are generated, and the fine particles adhere to and cover the surface of the stainless steel fiber, thereby producing the coating layer.

  If the thickness of the coating layer is too thin, the coating of the surface of the stainless steel fiber with the coating layer may be insufficient. If the thickness is too thick, for example, the effect of the coating layer will reach its peak. From such a viewpoint, the thickness of the coating layer is preferably 400 nm or less, and more preferably 100 nm or more. The thickness of the coating layer can be determined, for example, by TEM observation of the cross section of the conductive fiber, and can be adjusted by the treatment amount in carbon plating, the adhesion amount of carbon fine particles, and the like.

  The stainless steel fiber may further have a coating. The coating is preferably an antioxidant coating having an antioxidant function. For example, the film may be a film formed from at least one oxide of Cr, Mo, Cu, and Si and a complex oxide thereof from the viewpoint of resistance stability of the resistance heating element at a high temperature. Preferably, it is a chromium oxide film. The antioxidant coating may cover substantially the whole of the stainless steel fiber, or may cover a part of the stainless steel fiber, but it is preferable to cover the whole.

  Examples of the antioxidant coating include (1) a method in which stainless steel fibers are immersed in a solution of the material for the antioxidant coating, (2) a method in which the stainless steel fibers are heated at a low temperature in oxygen or clean air, or (3) Stainless steel fibers can be made by a method of anodic polarization in an oxidant solution. From the viewpoint of the uniformity of the produced antioxidation coating, the method (1) is preferable.

  The material of the antioxidant coating is, for example, a general oxidizing agent, and examples thereof include nitric acid, sulfuric acid, phosphoric acid, chromic acid, and dichromic acid. According to the method (1), it is possible to form a coating of various oxides (composite oxides) such as Cr, Ni, Ti, Mo, Al, and Si.

  The content of the conductive fiber in the resin composition is preferably 10 to 60% by volume from the viewpoint of imparting appropriate strength, toughness, conductivity and the like to the resistance heating element, and is 15 to 45% by volume. More preferably.

  The resin composition may further include other components other than the heat-resistant resin and the conductive fibers as long as the effects of the present embodiment are exhibited. Examples of the other configurations include conductive materials other than the stainless steel fibers.

  One or more conductive materials may be used. Examples of the conductive material include pure metals such as gold, silver, iron, and aluminum, alloys such as nichrome, and nonmetals such as carbon and graphite. The form of the conductive material is not particularly limited, and is, for example, a spherical powder, an amorphous powder, a flat powder, or a fiber.

  Moreover, the said resistance heating element may further contain other structures other than the said resin composition in the range with the effect of this Embodiment. Examples of the other configurations include electrodes and other layers such as an elastic layer and a release layer.

  Two or more electrodes are arranged on the resistance heating element, and from the viewpoint of efficiently supplying electricity for the desired heat generation, a pair of electrodes are arranged on opposite ends (both edges) of the resistance heating element. . Examples of the electrode include a thin metal plate, a ring formed by rolling the metal plate, and a solidified product of a conductive paste. The electrode made of a thin metal plate is bonded to the surface of the resistance heating element with, for example, a conductive adhesive. Examples of the material of the electrode include iron, nickel, and stainless steel such as SUS430. Examples of the conductive adhesive include a composition including an adhesive base material such as an epoxy resin and the conductive material described above, and a silane coupling agent. Examples of the silane coupling agent include alkylaminotrialkoxysilane.

  Examples of the other layers include a release layer, an elastic layer, and a reinforcing layer. The release layer is a layer having releasability and is disposed on the surface of the resistance heating element. Examples of the release layer material include polyethylene, polypropylene, polystyrene, polyisobutylene, polyester, polyurethane, polyamide, polyimide, polyamideimide, alcohol-soluble nylon, polycarbonate, polyarylate, phenol, polyoxymethylene, polyetheretherketone. , Polyphosphazenes, polysulfones, polyether sulfides, polyphenylene oxides, polyphenylene ethers, polyparabanic acids, polyallylphenols, fluororesins, polyureas, ionomers, silicones, and mixtures or copolymers thereof. The thickness of the release layer is, for example, 5 to 20 μm.

  The elastic layer is a layer having stronger elasticity than other layers, for example, and is disposed, for example, between the resistance heating element and the release layer. Examples of the material of the elastic layer include silicone rubber, thermoplastic elastomer and rubber material. The thickness of the elastic layer is, for example, 5 to 300 μm from the viewpoint of heat transfer and sufficient expression of elasticity.

  The reinforcing layer is a layer for increasing the mechanical strength of the resistance heating element, and is disposed, for example, on the surface of the resistance heating element opposite to the release layer or the elastic layer. The said reinforcement layer can be comprised with the heat resistant resin mentioned above, The thickness can be determined suitably.

  The resistance heating element can be manufactured using a normal method for manufacturing the fixing belt except that the conductive fiber is used as a conductive material. For example, the resistance heating element includes a step of dispersing the conductive fibers in the heat resistant resin or a precursor thereof, and a step of producing a resin composition (a molded body of heat resistant resin) in which the conductive fibers are dispersed. It is possible to produce by the method containing these. The molded body of the heat resistant resin can be produced by precipitation (drying) from a solution of the heat resistant resin, generation of the heat resistant resin by the reaction of the precursor, or both.

An example of the resistance heating element is shown in FIG.
As shown in FIG. 1, the resistance heating element 10 includes a heating layer 12 and an electrode 14. The heat generating layer 12 is a polyimide film containing the conductive fibers. The shape of the heat generating layer 12 is an endless belt shape. The electrode 14 is a ring formed of a thin metal plate. The electrodes 14 are disposed at both ends of the outer peripheral surface of the heat generating layer 12.

  The resistance heating element 10 is manufactured by the following method. First, the varnish of the polyamic acid containing the said conductive fiber is apply | coated to the surface of a base | substrate not shown, the coating film of the said varnish is produced, the said coating film is dried and solidified. Subsequently, the said coating film is thermoset (imidized) in a 350-450 degreeC heating furnace, and the heat-generating layer 12 is obtained. Next, a conductive adhesive is applied to both ends of the heat generating layer 12, and a ring of a thin metal plate is fitted and bonded to the end of the heat generating layer 12 to obtain the electrode 14.

Another example of the resistance heating element is shown in FIG.
As shown in FIG. 2, the resistance heating element 20 is arranged on the outer peripheral surface of the elastic layer 16 and the elastic layer 16 disposed on the outer peripheral surface of the heat generating layer 12 in addition to the heat generating layer 12 and the electrode 14. And a release layer 18. As described above, the elastic layer 16 is, for example, a silicone rubber layer. The release layer 18 is, for example, a fluororesin layer.

  The resistance heating element 20 includes, for example, a heat generation layer 12 in a fluororesin tube to be the release layer 18, a silicone rubber material paint is applied to the surface of the heat generation layer 12, and the paint is cured to generate heat. A silicone rubber layer (elastic layer 16) for bonding the layer 12 and the tube is prepared. The tube serves as a release layer 18 disposed on the elastic layer 16.

  The resistance heating element has high strength (toughness), and its resistance value is stable for a long time. The reason is considered as follows.

  In general, the adhesion of metal to resin is weaker than that of carbon. Therefore, when the resistance heating element in which the stainless steel fibers are dispersed is deformed, the stainless steel fibers are displaced from the heat resistant resin in the resistance heating element. If the stainless steel fibers are dispersed in the resistance heating element, the toughness of the resistance heating element is improved, but the effect of improving the toughness is weakened by the amount of the deviation.

  However, since the surface of the stainless steel fiber is covered with a coating layer made of carbon, the conductive fiber exhibits stronger adhesion to the heat resistant resin. For this reason, even if a resistance heating element deform | transforms, the shift | offset | difference of the said conductive fiber in a resistance heating element is suppressed. As a result, in the resistance heating element according to the present embodiment, the effect of improving toughness due to the addition of stainless steel fibers is sufficiently expressed as compared to the resistance heating element containing stainless steel fibers that do not have the coating layer. it is conceivable that.

  Further, since the conductive fiber has a carbon coating layer on its surface, an effect of improving dispersibility in the heat resistant resin is also expected. Therefore, it is expected that the resistance heating element will exhibit more uniform and precise electrical characteristics. For the above reasons, according to the resistance heating element, it is considered that the resistance heating element has higher toughness and stable electrical characteristics over a long period of time compared to the resistance heating element in which stainless steel fibers are dispersed. It is done.

  As is clear from the above description, the resistance heating element is composed of a resin composition containing a heat-resistant resin and conductive fibers, and the conductive fibers are dispersed in the resin composition, and are made of stainless steel. It is comprised by the carbon coating layer which covers the surface of the steel fiber and the said stainless steel fiber. Therefore, the effect of improving the toughness of the resistance heating element due to the addition of the conductive fiber (stainless steel fiber) is sufficiently exhibited, and as a result, the resistance value of the resistance heating element is stabilized for a long time.

  Moreover, it is much more effective that the thickness of the said coating layer is 400 nm or less from a viewpoint of expressing sufficient adhesiveness to the heat resistant resin of an electroconductive fiber.

  In addition, the heat-resistant resin is polyimide, and the content of the conductive fiber in the resin composition is 10 to 60% by volume, which realizes suitable mechanical and electrical characteristics of the resistance heating element. It is much more effective from the viewpoint of

  Further, it is more effective that the resistance heating element is an endless belt that is likely to cause periodic deformation of the resistance heating element from the viewpoint of enhancing the superiority of the above effect. For these reasons, the resistance heating element is suitably used in a field that requires an endless heating belt.

[Fixing device]
The fixing device according to the present embodiment is provided with an endless fixing belt, a fixing roller disposed inside the fixing belt and contacting a part of the inner peripheral surface of the fixing belt, and disposed outside the fixing belt. A pressure roller that presses the outer peripheral surface of the fixing belt toward the fixing roller, and a power supply device that supplies electricity to the fixing belt. The fixing belt is the resistance heating element in the form of an endless belt.

  The fixing device according to the present embodiment is suitably used for a fixing device of an electrophotographic image forming apparatus. Hereinafter, an example of the fixing device will be described in more detail.

  The fixing device 70 includes a fixing roller 72, a fixing belt 73, a pressure roller 74, and a power feeding device 75 as shown in FIGS. 3A and 3B. The shape of the fixing belt 73 is an endless belt. The fixing belt 73 is, for example, the resistance heating element 10 or the resistance heating element 20 described above.

  The fixing roller 72 includes a cylindrical cored bar 721 and a resin layer 722 disposed on the peripheral surface thereof. The outer diameter of the resin layer 722 is smaller than the inner diameter of the fixing belt 73. The fixing roller 72 is disposed inside the fixing belt 73. The fixing roller 72 is in contact with the inner peripheral surface of the fixing belt 73 at a part in the circumferential direction of the fixing belt 73.

  The pressure roller 74 includes a cylindrical cored bar 741 and a resin layer 742 disposed on the peripheral surface thereof. The pressure roller 74 is disposed to face the fixing roller 72 with the fixing belt 73 interposed therebetween. The pressure roller 74 is disposed so that the outer peripheral surface of the fixing belt 73 can be pressed toward the fixing roller 72. The pressure roller 74 is normally disposed away from the fixing belt 73.

  The resin layers 722 and 742 are, for example, a known resin layer or a layer formed by foaming a known resin. Examples of the resin include silicone rubber and fluororubber. At least one of the resin layers 722 and 742 has elasticity that deforms when pressed by the pressure roller 74.

  The pressure roller 74 may further have a release layer on the resin layer 742 that has a release property for a recording medium such as plain paper or toner. Examples of the material of the release layer include a fluororesin, and the release layer is constituted by a fluorine tube, a fluorine coating, or the like. The thickness of the release layer is, for example, 5 to 100 μm.

  The power feeding device 75 includes an AC power source 751, a power feeding member 752 that contacts the electrode 14, and a conductive wire 753 that connects the AC power source 751 and the power feeding member 752. The power supply member 752 is biased toward the electrode 14 by an elastic member (not shown) such as a plate spring or a coil spring. The power supply member 752 may be a member that slides with respect to the electrode 14 or a member that rotates. Examples of the power supply member 752 include a carbon brush made of a carbon-based material such as graphite or a copper-graphite composite material.

  The fixing belt 73, the fixing roller 72, and the pressure roller 74 are all rotatable. Each may be independently rotatable, and the other may be rotated according to one that is rotationally driven.

  When the pressure roller 74 presses the outer peripheral surface of the fixing belt 73 toward the fixing roller 72, a contact portion (nip portion) between the fixing belt 73 and the pressure roller 74 is formed. The nip portion may be formed by depression of the fixing roller 72 or may be formed by depression of the pressure roller 74.

  When fixing the toner image, the rotation of each roller and the fixing belt 73, the power supply to the fixing belt 73, and the formation of the nip portion can be performed in the same manner as a known fixing device. The fixing device 70 may further include another configuration of a known fixing device within a range where the effects of the present embodiment can be achieved.

  Since the fixing belt 73 is the resistance heating element 10, the shift of the conductive fibers in the fixing belt 73 is suppressed even by periodic deformation in the nip portion due to the use of the fixing device 70, and the electric power of the fixing belt 73 is reduced. There is virtually no variation in characteristics. For example, when the resistance heating element is energized and heated under the conditions of a fixing device in an electrophotographic image forming apparatus, it is possible to suppress the resistance change rate with time of the resistance heating element to 3% or less. .

[Image forming apparatus]
An image forming apparatus according to the present embodiment includes the above fixing device for fixing an unfixed toner image formed on a recording medium by electrophotography to the recording medium by heating and pressing. The image forming apparatus can be configured in the same manner as a known image forming apparatus except that the fixing device is employed as a fixing device. Hereinafter, an example of the image forming apparatus according to the present embodiment will be described with reference to FIG.

  The image forming apparatus 50 includes an image forming unit, an intermediate transfer unit, a fixing device 70, an image reading unit, and a recording medium transport unit.

  The image forming unit includes, for example, four image forming units corresponding to yellow, magenta, cyan, and black colors. As shown in FIG. 4, the image forming unit includes a photosensitive drum 51, a charging device 52 that charges the photosensitive drum 51, and an exposure device that irradiates the charged photosensitive drum 51 with light to form an electrostatic latent image. 53, a developing device 54 for supplying toner to the photosensitive drum 51 on which the electrostatic latent image is formed to form a toner image corresponding to the electrostatic latent image, and a cleaning device for removing residual toner on the photosensitive drum 51 55.

  The photoreceptor drum 51 is, for example, a negatively charged organic photoreceptor having photoconductivity. The charging device 52 is, for example, a corona charger. The charging device 52 may be a contact charging device that contacts a charging member such as a charging roller, a charging brush, or a charging blade with the photosensitive drum 51 for charging. The exposure device 53 is composed of a semiconductor laser, for example. The developing device 54 is a known developing device in an electrophotographic image forming apparatus, for example. “Toner image” refers to a state where toner is gathered in an image form.

  The intermediate transfer unit includes a primary transfer unit and a secondary transfer unit. The primary transfer unit includes an intermediate transfer belt 61, a primary transfer roller 62, a backup roller 63, a plurality of support rollers 64, and a cleaning device 65. The intermediate transfer belt 61 is an endless belt. The intermediate transfer belt 61 is stretched in a loop shape by a backup roller 63 and a support roller 64. When at least one of the backup roller 63 and the support roller 64 is rotationally driven, the intermediate transfer belt 61 runs on the endless track in one direction at a constant speed.

  The secondary transfer unit includes a secondary transfer belt 66, a secondary transfer roller 67, and a plurality of support rollers 68. The secondary transfer belt 66 is also an endless belt. The secondary transfer belt 66 is stretched in a loop by a secondary transfer roller 67 and a support roller 68.

  The fixing device 70 is, for example, the fixing device 70 shown in FIGS. 3A and 3B. The paper S corresponds to a recording medium.

  The image reading unit includes a paper feeding device 81, a scanner 82, a CCD sensor 83, and an image processing unit 84. The recording medium transport unit includes three paper feed tray units 91 and a plurality of registration roller pairs 92. In the paper feed tray unit 91, paper S (standard paper, special paper) identified based on basis weight, size, or the like is stored for each preset type. The registration roller pair 92 is disposed so as to form an intended conveyance path.

Image formation by the image forming apparatus 50 will be described.
The scanner 82 optically scans and reads the document D on the contact glass sent from the paper feeding device 81. Reflected light from the document D is read by the CCD sensor 83 and becomes input image data. The input image data is subjected to predetermined image processing in the image processing unit 84 and sent to the exposure device 53.

  On the other hand, the photosensitive drum 51 rotates at a constant peripheral speed. The charging device 52 uniformly charges the surface of the photosensitive drum 51 to a negative polarity. The exposure device 53 irradiates the photosensitive drum 51 with a laser beam corresponding to the input image data of each color component. Thus, an electrostatic latent image is formed on the surface of the photosensitive drum 51. The developing device 54 visualizes the electrostatic latent image by attaching toner to the surface of the photosensitive drum 51. Thus, a toner image corresponding to the electrostatic latent image is formed on the surface of the photosensitive drum 51. The toner image on the surface of the photosensitive drum 51 is transferred to the intermediate transfer belt 61. The transfer residual toner on the photosensitive drum 51 is removed by the cleaning device 55. To the intermediate transfer belt 61, the toner images of the respective colors formed on the respective photosensitive drums 51 are transferred so as to sequentially overlap.

  On the other hand, the secondary transfer roller 67 presses the secondary transfer belt 66 toward the backup roller 63 and presses against the intermediate transfer belt 61. Thereby, a secondary transfer nip portion is formed. On the other hand, the paper S is conveyed from the paper feed tray unit 91 to the secondary transfer nip portion via the registration roller pair 92. The registration roller pair 92 corrects the inclination of the paper S and adjusts the conveyance timing.

  When the paper S is conveyed to the secondary transfer nip, a transfer voltage is applied to the secondary transfer roller 67 and the toner image on the intermediate transfer belt 61 is transferred to the paper S. The paper S on which the toner image is transferred is conveyed to the fixing device 70 by the secondary transfer belt 66. The transfer residual toner on the intermediate transfer belt 61 is removed by the cleaning device 65.

  In the fixing device 70, when the paper S is conveyed, for example, the pressure roller 74 is urged toward the fixing roller 72 and the fixing belt 73 to form a fixing nip portion. The paper S is heated and pressed at the fixing nip portion. Thus, the toner image on the paper S is fixed on the paper S. The paper S on which the toner image is formed is discharged out of the apparatus.

  As described above, the image forming apparatus 50 includes the fixing device 70. For this reason, fluctuations in electrical characteristics accompanying deformation of the fixing belt 73 in the fixing device 70 and fixing defects such as fixing unevenness are prevented over a long period of time. Therefore, the image forming apparatus 50 can stably form a high-quality image for a long time.

  The present invention will be described more specifically with reference to the following examples and comparative examples. Hereinafter, unless otherwise specified, each operation is performed at room temperature (25 ° C.). The present invention is not limited to the following examples.

[Example 1]
First, carbon-plated stainless steel fibers are prepared. The stainless steel fibers used as the base material are SUS430 fibers, the minor axis is 8 μm, the major axis is 35 μm, and the aspect ratio (minor axis / major axis) is 0.229. The stainless steel fibers are subjected to acid cleaning (degreasing treatment) for 10 minutes in dilute hydrochloric acid, and subjected to constant current electrolysis at 12 mA / cm ² for 10 minutes in a molten salt of LiCl—KCl—CaCl ₂ at 500 ° C. Is attached to the surface of the stainless steel fiber to obtain a carbon-plated stainless steel fiber whose surface is covered with a carbon plating layer. The thickness of the carbon plating layer in the carbon-plated stainless steel fiber is determined to be about 380 μm by observing the cross section of the stainless fiber with SEM or TEM.

  21.2 g of the above carbon-plated stainless steel fiber was put into 100 g of a polyamic acid solution (U-Vanice S301, solvent: N-methyl-2-pyrrolidone, manufactured by Ube Industries, Ltd.), which is a polyimide resin precursor. A polyamic acid dope solution is prepared by mixing, stirring and defoaming with a disperser.

  A coating film of the dope solution is formed by spirally applying the polyamic acid dope solution on the outer peripheral surface of a cylindrical mold so that the film thickness after firing is 100 μm. The coating film is dried at 120 ° C. for 60 minutes and then baked at 450 ° C. for 20 minutes. In this way, a cylindrical (endless belt-like) heating resistor 1 made of a resin composition containing polyimide and carbon-plated stainless fiber is produced. The content of the carbon-plated stainless steel fiber in the heating resistor 1 is 15% by volume.

  On the outer peripheral surface of the heating resistor 1, a primer (manufactured by Shin-Etsu Chemical Co., Ltd .: KE-1880) is applied, leaving both ends thereof, and dried at room temperature for 30 minutes. Next, the heating resistor 1 is inserted into the fluororesin tube (Gunze Co., Ltd .: GRC) coated with the primer (Momentive Performance Materials: XP-A6361) on the inner peripheral surface, leaving both ends. To do.

  Next, silicone rubber (Momentive Performance Materials, Inc .: XE15-C2038) is injected between the heating resistor 1 and the fluororesin tube, primary vulcanized at 150 ° C. for 30 minutes, and further at 200 ° C. 4 Perform secondary vulcanization for hours. Next, the obtained tubular product is removed from the mold, and a roll of conductive tape CU-35C (manufactured by 3M) having a width of 10 mm and a thickness of 2 mm is attached to the outer peripheral surfaces of both ends. In this way, an endless fixing belt 1 as shown in FIG. 2 is obtained which further has an elastic layer having a thickness of 200 μm and a release layer having a thickness of 30 μm in this order on the outer peripheral surface of the heating resistor 1.

[Examples 2 and 3]
A fixing belt 2 is obtained in the same manner as the fixing belt 1 except that the content of the carbon-plated stainless steel fibers in the resistance heating element 1 is 20% by volume (30 g with respect to 100 g of the polyamide solution). Further, the fixing belt 3 is obtained in the same manner as the fixing belt 1 except that the content of the carbon-plated stainless steel fibers in the resistance heating element 1 is 25% by volume (40 g with respect to 100 g of the polyamide solution).

[Comparative Examples 1-3]
A fixing belt C1 is obtained in the same manner as the fixing belt 1 except that the stainless steel fiber before carbon plating (non-carbon plated stainless steel fiber) is used instead of the carbon plated stainless steel fiber. Also, fixing belts C2 and C3 are obtained in the same manner as the fixing belts 2 and 3, except that the non-carbon plated stainless steel fibers are used instead of the carbon-plated stainless steel fibers.

[Evaluation]
A sample sheet having a length of 44 mm and a width of 10 mm is cut out from each of the resistance heating elements 1 to 3 and C1 to C3, and both ends in the length direction are bonded with a cellophane tape to prepare a sample ring. On the other hand, an openable / closable holding jig is prepared by bonding one end edges of two plastic plates with cellophane tape. Then, the sample ring is sandwiched by the sandwiching jig, one plate of the sandwiching jig sandwiching the sample ring is pushed in, and an indentation load IL (g) when the sample ring is cracked is obtained.

Further, each of the fixing belts 1 to 3 and C1 to C3 is mounted as a fixing belt in the fixing device of the image forming apparatus as shown in FIG. 4, and 500,000 sheets of solid images are formed on the recording medium and subsequently formed. The solid image is observed for fixing unevenness (a portion observed to have poor toner adhesion) and evaluated according to the following evaluation criteria. If “◎”, “◯”, and “Δ”, there is no practical problem.
(Double-circle): The maximum length of the said site | part is 0.2 mm or less.
○: The maximum length of the part is more than 0.2 mm and 0.5 mm or less.
(Triangle | delta): The maximum length of the said site | part is more than 0.5 mm and 1 mm or less.
X: The maximum length of the said site | part exceeds 1 mm.

  Table 1 shows the measurement results (IL) for the resistance heating elements 1 to 3 and C1 to C3, and the evaluation results for the fixing belts 1 to 3 and C1 to C3.

  As is apparent from Table 1, each of the resistance heating elements 1 to 3 having the carbon-plated stainless steel fibers has a high bending strength and can sufficiently exhibit the desired heat generation characteristics over a long period of time. This is presumably because the carbon-plated stainless steel fiber exhibits higher adhesion to polyimide as described above.

  On the other hand, each of the resistance heating elements C1 to C3 has a low bending strength and is insufficient from the viewpoint of exhibiting the desired heat generation characteristics over a long period of time. This is presumably because the adhesiveness of the stainless steel fibers in the resistance heating element to the polyamide is low, the strength imparted to the resistance heating element becomes insufficient, and partial fluctuations in energization and heat generation occur.

  According to the present invention, it is possible to provide an image forming apparatus that has high bending strength and does not cause fixing unevenness in a heat generating belt. Therefore, according to the present invention, further improvement in performance and labor saving are expected in the electrophotographic image forming apparatus, and further spread of the image forming apparatus is expected.

DESCRIPTION OF SYMBOLS 10, 20 Resistance heating element 12 Heat generation layer 14 Electrode 16 Elastic layer 18 Release layer 50 Image forming apparatus 51 Photosensitive drum 52 Charging apparatus 53 Exposure apparatus 54 Developing apparatus 55, 65 Cleaning apparatus 61 Intermediate transfer belt 62 Primary transfer roller 63 Backup Roller 64, 68 Support roller 66 Secondary transfer belt 67 Secondary transfer roller 70 Fixing device 72 Fixing roller 73 Fixing belt 74 Pressure roller 75 Power feeding device 81 Paper feeding device 82 Scanner 83 CCD sensor 84 Image processing unit 91 Paper feeding tray unit 92 Registration roller pair 721, 741 Core metal 722, 742 Resin layer 751 AC power supply 752 Power supply member 753 Conductor D Original S Paper

Claims (7)

A resistance heating element composed of a resin composition containing a heat resistant resin and conductive fibers,
The conductive fibers are dispersed in the resin composition, and are constituted by stainless steel fibers and a coating layer made of carbon that covers the surface of the stainless steel fibers.
Resistance heating element.   The resistance heating element according to claim 1, wherein the coating layer has a thickness of 400 nm or less.   The resistance heating element according to claim 1, wherein the coating layer is a layer formed by carbon plating. The heat resistant resin is polyimide,
The content of the conductive fiber in the resin composition is 10 to 60% by volume.
The resistance heating element according to any one of claims 1 to 3.   The resistance heating element according to any one of claims 1 to 4, which is an endless belt. An endless fixing belt,
A fixing roller disposed inside the fixing belt and contacting a part of an inner peripheral surface of the fixing belt;
A pressure roller disposed outside the fixing belt and pressing an outer peripheral surface of the fixing belt toward the fixing roller;
A fixing device having a power supply device for supplying electricity to the fixing belt,
The fixing device includes the resistance heating element according to claim 5. In an image forming apparatus having a fixing device for fixing an unfixed toner image formed by electrophotography on a recording medium to the recording medium by heating and pressing,
The image forming apparatus according to claim 6, wherein the fixing device is a fixing device according to claim 6.

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