JP2011002590A - Fixing device and image forming apparatus including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a belt fixing type fixing device which achieves shortening of warm-up time, and improvement in durability and fixing performance of a fixing roller without causing an increase in manufacture cost.SOLUTION: A roller member including a cylindrical or columnar core bar 3a, a sponge layer 3b formed on an outer circumferential surface of the core bar 3a and a resin tube 10 covering the sponge layer 3b is used as the fixing roller 3 included in the belt fixing type fixing unit 2.

Description

  The present invention relates to a fixing device that fixes toner on a recording material and an image forming apparatus including the same.

  In general, an electrophotographic image forming apparatus has an advantage that an image having a good image quality can be easily formed, and is widely used in a copying machine, a printer, a facsimile machine, a multifunction machine, and the like. Yes. In this type of image forming apparatus, a charging process for charging the surface of the photoreceptor, an exposure process for forming an electrostatic latent image by exposing the surface of the charged photoreceptor according to image data, An image is formed on the recording material by performing a developing step for developing with toner, a transferring step for transferring the developed toner image to the recording material, and a fixing step for fixing the toner image transferred to the recording material to the recording material. .

  As a fixing device for performing the fixing process, a heat roller fixing type fixing device is frequently used. A heat roller fixing type fixing device includes a pair of a fixing roller and a pressure roller that are in pressure contact with each other, and includes a heat source such as a halogen lamp inside at least one of the fixing roller and the pressure roller.

  In a fixing device of the heat roller fixing method, in a fixing process, after a roller pair is heated to a fixing temperature which is a predetermined temperature necessary for fixing by a heat source, a recording material such as paper on which an unfixed toner image is formed is fixed. The toner is supplied to a fixing nip portion that is a pressure contact portion between the roller and the pressure roller. As a result, the unfixed toner image passing through the fixing nip is fixed to the recording material by the heat and pressure from the roller pair. Although the temperature temporarily decreases in the sheet passing portion where the recording material passes in the fixing nip portion, it is heated again to the fixing temperature by the heat source.

  In such a heat roller fixing type fixing device, an elastic roller having an elastic layer on the surface may be used as the fixing roller. When the elastic roller is used, the elastic layer on the surface of the elastic roller is elastically deformed corresponding to the unevenness of the unfixed toner image at the fixing nip portion. As a result, the elastic roller covers the unfixed toner image so as to contact the unfixed toner image, so that the fixability can be improved even for a color unfixed toner image having a larger amount of toner than a single color image. it can.

  Further, by using the elastic roller, it is possible to improve the releasability of the color toner that is easily offset as compared with the single-color image due to the strain releasing effect of the elastic layer on the surface of the elastic roller. Specifically, an elastic layer that has been compressed and distorted at the fixing nip portion is released from the distortion at the exit of the fixing nip portion. Occurs. As a result, the adhesive force of the elastic layer to the toner image is reduced and the releasability is improved.

  Furthermore, since the nip shape, which is a shape in which the elastic roller and the pressure roller are in pressure contact with each other in the fixing nip portion, is convex toward the elastic roller (reverse nip shape), the separation performance between the elastic roller and the recording material is improved. For this reason, self-stripping that allows the recording material and the elastic roller to be peeled off without using a peeling claw or the like can be realized as a peeling means for peeling the elastic roller and the recording material. It will be resolved. In a fixing device provided in an image forming apparatus capable of full color printing, for example, silicon rubber or the like is used as an elastic layer of an elastic roller.

  By the way, in a fixing device provided in an image forming apparatus that performs full-color printing, in order to increase the process speed (recording material conveyance speed), a fixing nip portion is used to impart an appropriate amount of heat to the toner on the recording material. It is necessary to widen the nip width which is the width in the recording material conveyance direction.

  As a method for widening the nip width, there are two methods: a method of increasing the elastic layer of the elastic roller and a method of increasing the diameter of the elastic roller. However, if the elastic layer of the elastic roller having the heating means is thickened, the heat conductivity of the elastic layer is very low, so that the warm-up time becomes long. Further, if the process speed is increased to increase the number of recording materials printed per predetermined time, it becomes difficult to maintain the temperature of the elastic roller at the fixing temperature. On the other hand, in the method of increasing the diameter of the elastic roller, the heat capacity of the elastic roller increases, so that the power consumption of the heating means increases.

  In order to solve these problems, in Patent Document 1, a fixing belt is suspended from a plurality of rollers including a fixing roller, and a pressure roller is provided in pressure contact with the fixing roller via the fixing belt. A belt fixing type fixing device has been proposed in which a recording material is supplied between a fixing belt and a pressure roller. Japanese Patent Application Laid-Open No. H10-228561 describes using an elastic roller in which a sponge layer and a solid rubber layer are laminated as a fixing roller.

JP 2007-86134 A (published April 5, 2007)

  However, in the technique of the above-mentioned patent document 1, since the elastic roller in which a solid rubber layer having a large heat capacity is laminated on the surface of the sponge layer is used as the fixing roller, the heat of the fixing belt is taken away by the fixing roller. There is a problem that becomes longer.

  Patent Document 1 discloses an elastic roller including a solid rubber layer and a sponge layer. However, since the sponge layer is thinned by providing the solid rubber layer, the strength of the sponge layer is reduced and the sponge layer is reduced. There is a problem that the deterioration of the layer is accelerated.

  In addition, in order to provide a solid rubber layer on the sponge layer, rubber molding must be performed a plurality of times, and there is a problem that the manufacturing cost of the fixing roller increases.

  The present invention has been made in view of the above-described problems, and its object is to reduce the warm-up time, the durability of the fixing roller, without increasing the manufacturing cost, in the belt fixing type fixing device. And to improve the fixing performance.

  In order to solve the above problems, the fixing device of the present invention is an endless belt that is rotatably supported by a fixing roller that is rotatably supported, a belt suspension member, and the fixing roller and the belt suspension member. A recording having an unfixed toner image, comprising: a fixing belt; a heating unit that heats the fixing belt; and a pressure member that is rotatably supported so as to be pressed against the fixing roller via the fixing belt. A fixing device that fixes the unfixed toner image on the recording material by conveying the material while the fixing belt and the pressure member are sandwiched between the fixing belt and the fixing roller. It is characterized by comprising a material, a sponge layer formed on the outer peripheral surface of the base material, and a resin tube covering the sponge layer.

  According to the above configuration, since the sponge layer is provided, the heat capacity of the fixing roller can be reduced compared to a configuration using a fixing roller made of a solid rubber layer, so that the warm-up time and power consumption can be reduced. Reduction can be achieved. In addition, since the fixing roller is deformed according to the shape of the pressure member in the fixing nip portion where the fixing roller and the pressure member are pressed through the fixing belt, the fixing nip width can be widened to improve the fixing performance. it can. Furthermore, since the sponge layer is covered with the resin tube, the fixing roller bulge at the exit of the fixing nip is suppressed by the shrinkage force of the resin tube, and the shape of the fixing roller is quickly restored to the non-pressure contact state. Therefore, the paper peelability can be improved. Further, since the resin tube can be formed thinner than the configuration in which the sponge layer is covered with the solid rubber layer as in Patent Document 1, the sponge layer can be formed thicker than in the case of Patent Document 1. For this reason, durability of a sponge layer can be improved. Furthermore, when a solid rubber layer is formed on the surface of the sponge layer, it is necessary to perform rubber molding a plurality of times, whereas according to the above configuration, it is only necessary to cover the resin tube. This can reduce the manufacturing cost.

  The resin tube may be a heat-shrinkable tube that shrinks so that the diameter is reduced by applying heat. For example, the resin tube may be a PFA tube or a PTFE tube.

  According to the above configuration, the swell of the fixing roller at the exit of the fixing nip portion can be suppressed by the contraction force of the resin tube, and the shape of the fixing roller can be quickly restored to the non-pressing state, so that the paper peelability Can be improved.

  Further, the film thickness of the resin tube may be not less than 40 μm and not more than 70 μm.

  When the tube film thickness is too thin, the swell of the fixing roller at the exit of the fixing nip portion cannot be properly suppressed, and the peelability of the recording material is deteriorated. On the other hand, if the tube film thickness is too thick, the amount of heat applied to the toner will be insufficient due to the narrow width of the fixing nip, etc., and the recording material will easily adhere to the fixing roller and the releasability of the recording material will decrease. To do. On the other hand, according to the above configuration, the recording material can be appropriately separated from the fixing roller at the exit of the fixing nip portion.

  The fixing roller may have an Asker C hardness of 45 degrees to 70 degrees.

  If the hardness of the fixing roller is too low, the pressure acting on the toner and the recording material is insufficient, and the surface layer of the fixing belt 5 cannot follow the irregularities on the surface of the recording material 9 and the temperature on the toner on the recording material is increased. Because of the difference, gloss unevenness occurs in the image after the fixing process, or the fixing strength decreases. On the other hand, when the hardness of the fixing roller is too high, the pressure contact force between the fixing roller and the pressure member becomes excessively large, causing bending along the axial direction of the fixing roller, and the fixing nip width at the central portion of the recording material is narrow. As a result, the fixing strength decreases. On the other hand, according to the above configuration, it is possible to appropriately perform the fixing process without causing a decrease in fixing strength and uneven gloss.

  Further, the thickness of the sponge layer when the fixing roller is not in contact with another member is t1, and the pressure contact portion when the fixing roller and the pressure member are pressed against each other via the fixing belt. When the thickness of the sponge layer is t2, the structure may be 0.2 ≦ t2 / t1 ≦ 0.35.

  If the value of t2 / t1 is too small, the pressure acting on the recording material and the toner at the fixing nip is insufficient, resulting in fixing failure. On the other hand, if the value of t2 / t1 is too large, the load applied to the sponge layer is increased and the durability of the fixing roller is lowered. On the other hand, according to the above-described configuration, it is possible to prevent the durability of the fixing roller from being lowered and perform a stable fixing process over a long period of time.

  The resin tube may contain a conductive material.

  According to the above configuration, charging of the fixing belt can be suppressed, and problems such as electrostatic offset can be suppressed.

  The pressure member includes a pressure roller rotatably supported, a second belt suspension member, and a pressure belt rotatably suspended on the pressure roller and the second belt suspension member. The unfixed toner image is fixed on the recording material by passing the recording material on which the unfixed toner image is formed passing through the pressure contact portion between the fixing belt and the pressure belt. Also good.

  According to the above configuration, it is possible to shorten the warm-up time, improve the durability of the fixing roller, and improve the fixing performance without increasing the manufacturing cost.

  The image forming apparatus of the present invention includes any one of the fixing devices described above. Accordingly, it is possible to shorten the warm-up time, improve the durability of the fixing roller, and improve the fixing performance without increasing the manufacturing cost.

  As described above, the fixing device of the present invention is a belt fixing type fixing device, and the fixing roller includes a cylindrical or columnar base material, a sponge layer formed on the outer peripheral surface of the base material, A resin tube covering the sponge layer.

  Therefore, it is possible to shorten the warm-up time, improve the durability of the fixing roller, and improve the fixing performance without increasing the manufacturing cost.

1 is a cross-sectional view of a fixing device according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of an image forming apparatus including the fixing device illustrated in FIG. 1. FIG. 2 is a block diagram illustrating a configuration of a control unit in the fixing device illustrated in FIG. 1. FIG. 2 is an explanatory diagram illustrating a state during a fixing process in the fixing device illustrated in FIG. 1. FIG. 2 is a cross-sectional view illustrating a configuration of a support mechanism for each member in the fixing device illustrated in FIG. 1. It is sectional drawing of the fixing device which concerns on other embodiment of this invention.

[Embodiment 1]
An embodiment of the present invention will be described. In the present embodiment, the case where the present invention is applied to a color multifunction peripheral will be described. However, the application target of the present invention is not limited to this, and the present invention can be applied to any electrophotographic image forming apparatus.

(1-1. Configuration of color MFP)
FIG. 2 is a cross-sectional view of the color multifunction peripheral (image forming apparatus) 1 according to the present embodiment. As shown in this figure, the color multifunction peripheral 1 includes an optical system (exposure) unit 40, four sets of visible image forming units 50a to 50d, an intermediate transfer unit 64 having an intermediate transfer belt 60, and a secondary transfer unit. 70, a fixing unit (fixing device) 2, an internal paper feeding unit 80, and a manual paper feeding unit 90. The operation of each member provided in the color multifunction device 1 is controlled by a main control unit (not shown) including a CPU and the like.

  The visible image forming units 50a to 50d respectively form black (K), cyan (C), magenta (M), and yellow (Y) toner images, and the intermediate transfer belt 60 so that these toner images overlap each other. It will be transferred to the top.

  The visible image forming unit 50a includes a charging unit 52a, a developing unit 53a, a primary transfer unit 54a, and a cleaning unit 55a around a photosensitive drum (toner image carrier) 51a that is rotatably provided. It is the structure arrange | positioned in this order along the rotation direction of the body drum 51a.

  The charging unit 52a is for uniformly charging the surface of the photosensitive drum 51a to a predetermined potential. In this embodiment, a charging roller type (contact charging type) is used as the charging unit 52a. However, the configuration of the charging unit 52a is not limited to this. For example, a non-contact charger such as a corona discharge method may be used, or a contact charger such as a brush charger may be used.

  The optical system (exposure) unit 40 exposes the surfaces of the photosensitive drums 51a to 51d charged by the charging units 52a to 52d according to the image data, thereby converting the image data onto the surfaces of the photosensitive drums 51a to 51d. It is for forming a corresponding electrostatic latent image. In the optical system (exposure) unit 40, a laser scanning unit (LSU) including a light source 41, a reflection mirror 42, and the like is used. As the optical system (exposure) unit 40, for example, an EL or LED writing head in which light emitting elements are arranged in an array may be used.

  The developing unit 53a performs a developing process for visualizing the electrostatic latent image formed on the photosensitive drum 51a with toner. As the toner, for example, a non-magnetic one-component developer (non-magnetic toner), a non-magnetic two-component developer (non-magnetic toner and carrier), a magnetic developer (magnetic toner) and the like can be used. In this embodiment, as shown in FIG. 2, the developing unit 53a provided in the visible image forming unit 50a that forms a black toner image is replaced with visible image forming units 50b to 50d that form toner images of other colors. The developing units 53b to 53d provided in the apparatus have a larger toner capacity. However, the present invention is not limited to this, and the capacity of each developing unit may be the same.

  The primary transfer units 54a to 54d are respectively positioned via the intermediate transfer belt 60 at positions between the facing portions of the photosensitive drums 51a to 51d facing the developing units 53a to 53d and the facing portions facing the cleaning units 55a to 55d. It arrange | positions so that the photoconductor drums 51a-51d may be opposed. The toner images on the photosensitive drums 51a to 51d are superimposed on the intermediate transfer belt 60 by applying a high voltage (+) opposite to the toner charging polarity (−) to the primary transfer units 54a to 54d. It is designed to be transcribed.

  The cleaning unit 55a is for removing and collecting toner remaining on the surface of the photosensitive drum 51a after the toner image is transferred to the intermediate transfer belt 60.

  The visible image forming units 50b to 50d have substantially the same configuration as the visible image forming unit 50a except that the color of the toner used for the development processing is different. That is, black (B), yellow (Y), magenta (M), and cyan (C) toners are stored in the developing units of the visible image forming units 50a to 50d, respectively.

  The intermediate transfer unit 64 includes an intermediate transfer belt 60, an intermediate transfer belt driving roller (tension roller) 61, an intermediate transfer belt driven roller (tension roller) 62, and an intermediate transfer belt cleaning unit 63.

  The intermediate transfer belt 60 is an endless belt, and is suspended and driven by an intermediate transfer belt driving roller 61 and an intermediate transfer belt driven roller 62. The toner images of the respective colors formed on the photosensitive drums 51a to 51d are transferred so as to sequentially overlap the intermediate transfer belt 60, and a color toner image (multicolor toner image) is formed on the intermediate transfer belt 60. It is like that.

  In addition, the toner image formed on the intermediate transfer belt 60 is conveyed to a facing portion between the intermediate transfer belt driving roller 61 and the secondary transfer unit 70, and onto a recording material such as a recording sheet conveyed to the facing portion. It is designed to be transcribed. The intermediate transfer belt cleaning unit 63 contacts the intermediate transfer belt 60 and removes and collects toner remaining on the intermediate transfer belt 60 after the toner image is transferred onto the recording material.

  The fixing unit 2 is pressed into contact with the fixing roller 3 with a predetermined load via the fixing roller 3, the heating roller 6, the fixing belt 5 suspended between the fixing roller 3 and the heating roller 6, and the fixing belt 5. And a pressure roller (pressure member) 4 that is disposed downstream of the secondary transfer unit 70 in the recording material conveyance direction. Then, the fixing unit 2 feeds the recording material onto which the toner image has been transferred by the secondary transfer unit 70 to the pressure contact portion (fixing nip portion) between the fixing belt 5 and the pressure roller 4 and passes the pressure contact portion. The toner image is fixed on the recording material by heat and pressure. Note that the surface of the recording material on which the unfixed toner image is formed contacts the fixing belt 5, and the surface of the recording material opposite to the surface on which the unfixed toner image is formed contacts the pressure roller 4. Details of the fixing unit 2 will be described later.

  The internal paper feeding unit 80 is for accumulating recording materials used for image formation. The manual paper feed unit 90 is foldably provided on the side wall of the color multifunction peripheral 1 and is for manually feeding a recording material. The paper discharge tray 92 is a tray on which the recording material on which an image has been formed is placed.

  In addition, the color multifunction peripheral 1 performs secondary transfer of a recording material fed from the internal paper feeding unit 80 by the paper feeding roller 81 and a recording material fed from the manual paper feeding unit 90 by the paper feeding roller 91. A sheet conveyance path for sending the sheet to the sheet discharge tray 92 via the unit 70 and the fixing unit 2 is provided. A large number of roller members for conveying the recording material are arranged in the paper conveyance path. Note that the sheet conveyance speed (process speed) in the color multifunction peripheral 1 is 220 mm / sec, and continuous copying processing can be performed at a copying speed of 50 sheets / min (A4 lateral feed).

(1-2. Configuration of Fixing Unit)
Next, the fixing unit 2 will be described in detail. FIG. 1 is a cross-sectional view showing the configuration of the fixing unit 2. As shown in this figure, the fixing unit 2 includes a fixing roller 3, a pressure roller 4, a fixing belt 5, and a heating roller 6.

The fixing roller 3 is a substantially cylindrical roller member. A cored bar (base material) 3a and a sponge layer (elastic layer) 3b are formed in this order from the central axis toward the outer peripheral side. The resin tube 10 is coated on the surface. For the metal core 3a, a metal such as iron, stainless steel, aluminum or copper, or an alloy thereof can be used. As the sponge layer 3b, a foamed rubber material having heat resistance such as silicon rubber or fluorine rubber can be suitably used. The resin tube 10 is not particularly limited as long as it has a contracting force that acts to tighten the sponge layer 3b when attached to the outer peripheral surface of the sponge layer 3b. Therefore, a heat-shrinkable tube that shrinks so that its diameter can be reduced can be suitably used. Specifically, a fluororesin such as PFA (a copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether) or PTFE (polytetrafluoroethylene) can be suitably used. It is more preferable to add a conductive material such as a carbon filler to the resin tube 10 and adjust the surface resistivity to be 10 ⁴ Ω / □ or more and 10 ⁷ Ω / □ or less. By imparting conductivity to the resin tube 10, charging of the fixing belt 5 can be suppressed, and problems such as electrostatic offset can be reduced.

  In this embodiment, stainless steel having a diameter of 20 mm is used for the core metal 3 a, silicon sponge rubber having a thickness of 5 mm is used for the sponge layer 3 b, and a PFA tube having a thickness of 50 μm is used as the resin tube 10. Therefore, the diameter (outer diameter) of the fixing roller 3 is about 30 mm.

  The fixing roller 3 is supported so as to be rotatable about a cylindrical central axis, and is driven to rotate by the pressure roller 4 and the fixing belt 5.

  The pressure roller 4 is a substantially cylindrical roller member, and has a three-layer structure in which a core metal 4a, an elastic layer 4b, and a release layer 4c are formed from the central axis toward the outer peripheral side. For the metal core 4a, a metal such as iron, stainless steel, or aluminum copper, or an alloy thereof can be used. For the elastic layer 4b, a heat-resistant rubber material such as silicon rubber or fluorine rubber can be suitably used. For the release layer 4c, a fluororesin such as PFA (copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether) or PTFE (polytetrafluoroethylene) can be suitably used. In this embodiment, iron (STKM) having an inner diameter of 26 mm and a wall thickness of 1 mm is used as the core metal 4a, silicon solid rubber having a thickness of 1 mm is used as the elastic layer 4b, and a PFA tube having a thickness of 50 μm is used as the release layer 4c. It was. Accordingly, the diameter (outer diameter) of the pressure roller 4 is about 30 mm.

  Note that the pressure roller 4 is rotationally driven by pressure roller driving means M (see FIG. 3) including a motor or the like.

  A heater lamp 7 a for heating the pressure roller 4 is disposed inside the pressure roller 4. When the control unit 95 (see FIG. 3) of the fixing unit 2 supplies (energizes) power to the heater lamp 7a from the power supply circuit unit 96 (see FIG. 3), the heater lamp 7a emits light, and infrared rays are emitted from the heater lamp 7a. Radiated. Thereby, the inner peripheral surface of the pressure roller 4 is heated by absorbing infrared rays emitted from the heater lamp 7a, and the entire pressure roller 4 is heated. In this embodiment, the heater lamp 7a having a rated power of 300 W is used. A thermistor 8 a that detects the temperature of the peripheral surface of the pressure roller 4 is provided on the peripheral surface of the pressure roller 4.

  The fixing belt 5 is an endless belt that is rotatably supported by the fixing roller 3 and the heating roller 6, and has a three-layer configuration including a base material, an elastic layer, and a release layer. As the base material, a heat-resistant resin such as polyimide or a hollow cylindrical material made of a metal material such as stainless steel and nickel can be used. As the elastic layer, an elastomer material having excellent heat resistance and elasticity, such as silicon rubber, can be used. As the release layer, a synthetic resin material that is excellent in heat resistance and release properties, for example, a fluororesin such as PFA or PTFE can be used.

  In this embodiment, polyimide having a thickness of 50 μm is used as the base material of the fixing belt 5, silicon rubber having a thickness of 150 μm is used as the elastic layer, and a PFA tube having a thickness of 30 μm is used as the release layer. Further, a roller having a diameter of 50 mm when the side surface is substantially circular without being suspended from the fixing roller 3 and the heating roller 6 was used. The fixing belt 5 is driven to rotate by the pressure roller 4.

  The heating roller 6 is a substantially cylindrical roller member, and has a three-layer structure in which an infrared absorption layer 6a, a cored bar 6b, and a protective layer 6c are formed from the central axis toward the outer periphery. The infrared absorbing layer 6a is formed by coating and baking a heat-resistant carbon-containing paint on the inner side of the cored bar 6b. For the metal core 6b, for example, a metal such as iron, stainless steel, aluminum, copper, or an alloy thereof can be used. For the protective layer 6c, a fluororesin such as PFA (copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether) or PTFE (polytetrafluoroethylene) can be suitably used. The protective layer 6 c is for preventing the base material of the fixing belt 5 and the heating roller 6 from being worn by contact between the fixing belt 5 and the heating roller 6. In this embodiment, a carbon black paint having a thickness of 100 μm was used as the infrared absorption layer, hollow aluminum having an outer diameter of 28 mm and a thickness of 1 mm was used as the core metal, and a PTFE coating layer having a thickness of 50 μm was used as the protective layer. Therefore, the diameter (outer diameter) of the heating roller 6 is about 28 mm.

  In addition, a heater lamp 7 b for heating the heating roller 6 is disposed inside the heating roller 6. The control unit 95 (see FIG. 3) of the fixing unit 2 supplies (energizes) power to the heater lamp from the power supply circuit unit 96 (see FIG. 3), whereby the heater lamp 7b emits light and infrared radiation is emitted from the heater lamp 7b. Is done. Thereby, the inner peripheral surface of the heating roller 6 is heated by absorbing the infrared rays emitted from the heater lamp 7b, and the entire heating roller 6 is heated. In this embodiment, the heater lamp 7b having a rated power of 900 W is used. A thermistor 8 b that detects the temperature of the peripheral surface of the heating roller 6 is provided on the peripheral surface of the heating roller 6.

  FIG. 3 is a block diagram illustrating a relationship between a control unit that controls the fixing unit 2 and each unit of the fixing unit 2. The controller 95 controls the operation of each part of the fixing unit 2. The control unit 95 may be provided in the main control unit of the color multifunction peripheral 1, or may be provided separately from the main control unit and operate in cooperation with the main control unit.

  As shown in FIG. 3, the thermistors 8 a and 8 b, the pressure roller drive motor M, and the power supply circuit unit 96 are connected to the control unit 95. Further, the power supply circuit unit 96 is connected to the heater lamps 7a and 7b.

  Accordingly, the control unit 95 controls the power supplied from the power supply circuit unit 96 to the heater lamps 7a and 7b based on the temperature detection results of the respective parts input from the thermistors 8a and 8b, and the fixing belt 5 and the pressure roller. The temperature of 4 is controlled so as to approach each set temperature. The control unit 95 controls the rotation state of the pressure roller 4 by controlling the operation of the pressure roller drive motor M.

  FIG. 5 is a cross-sectional view schematically showing a support mechanism for each member in the fixing unit 2. As shown in this figure, the rotation shaft of the fixing roller 3 is rotatably supported by the main frame 13 of the fixing unit 2. The rotating shaft of the pressure roller 4 is rotatably supported by a rectangular pressure roller support frame 14. One end of the pressure roller support frame 14 is rotatably connected to the main frame 13 by a fulcrum Q, and a pressure roller load spring 15 is connected to the other end and is urged toward the fixing roller 3. As a result, the pressure roller 4 is pressed against the fixing roller 3 through the fixing belt 5 with a predetermined load (400 N in this embodiment), and the fixing nip portion 12 is formed as shown in FIG.

  Further, the rotation shaft of the heating roller 6 that is spaced apart from the pressure roller 4 with the fixing roller 3 interposed therebetween is similarly rotatably supported by a rectangular heating roller support frame 16. One end of the heating roller support frame 16 is rotatably connected to the main frame 13 by a fulcrum R, and a heating roller load spring 17 is connected to the other end. As a result, the heating roller 6 is urged in a direction opposite to the fixing roller 3 with a predetermined load (in this embodiment, 50 N), and tension is applied to the fixing belt 5. Therefore, when the pressure roller 4 is driven to rotate, the fixing belt 5 is driven to rotate by the pressure roller 4, and the fixing roller 3 and the heating roller 6 are driven to rotate by the fixing belt 5.

  In this embodiment, the fixing nip width, which is the width of the fixing nip portion 12 in the recording material conveyance direction, is 7 mm. The fixing nip portion 12 is fed with a recording material 9 which is a member to be fixed that carries an unfixed toner image. The recording material fed to the fixing nip portion 12 is rotated by the pressure roller 4 in the direction of the arrow R1, and the fixing belt 5 and the fixing roller 3 are rotated in the direction of the arrow R2. It is conveyed so as to pass through the section 12. When the recording material 9 passes through the fixing nip portion 12, it acts between the heat supplied from the fixing belt 5 heated to a predetermined temperature by the heating roller 6 and between the fixing belt 5 and the pressure roller 4. The unfixed toner image is fixed on the recording material 9 by the pressure applied.

(1-3. Relationship between resin tube 10 and paper peelability)
FIG. 4 is an explanatory diagram schematically showing a state during the fixing process in the fixing unit 2. In FIG. 4, the fixing belt 5 is omitted for convenience of explanation. As shown in FIG. 4, the angle formed by the tangent of the surface of the fixing roller 3 and the tangent of the surface of the pressure roller 4 at the exit of the fixing nip portion 12 (position where the fixing roller 3 and the pressure roller 4 start to separate). Is θ, the larger the angle θ, the higher the sheet peelability.

  For this reason, by reducing the outer diameter of the fixing roller 3 or the pressure roller 4, the angle θ can be increased to improve the sheet peelability. However, in this case, the area of the fixing nip portion is reduced, so that fixing is performed. The nature will decline.

  On the other hand, since the fixing unit 3 uses the fixing roller 3 having the sponge layer 3b, the sponge layer 3b of the fixing roller 3 is brought into contact with the pressure roller 4 at the fixing nip portion 12 as shown in FIG. While being pushed in, the shape of the fixing roller 3 is deformed into a concave shape along the outer periphery of the pressure roller 4, whereas it is deformed so as to swell in a convex shape at the outlet of the fixing nip portion 12. If the bulge at the exit of the fixing nip portion 12 is too large, the angle θ becomes too small, and the sheet peelability is deteriorated. Therefore, in order to improve both the fixing performance and the sheet peelability, it is required to suppress the swelling of the fixing roller 3 at the exit of the fixing nip portion 12 while allowing the fixing roller 3 to be deformed in the fixing nip portion 12. It is done.

  Further, quick restoration from the state in which the fixing roller 3 is pressed in the fixing nip portion 12 into the state before the fixing roller 3 is pressed in at the exit of the fixing nip portion 12 is also related to the improvement of the sheet peelability. . That is, since the fixing belt 5 is deformed according to the shape of the fixing roller 3, the restoration of the fixing roller 3 generates a force by which the fixing belt 5 pushes the recording material 9 downward in the figure, and the sheet peelability is reduced. Increase. For this reason, the higher the restoring force of the fixing roller 3, that is, the resilience of the sponge layer 3b, the more the paper peelability can be improved.

  Therefore, in the fixing unit 2 according to the present embodiment, the surface layer of the sponge layer 3b is covered with the resin tube 10 that is contractible and has high tension. As a result, the hardness of the surface layer portion of the fixing roller 3 is increased, so that the fixing roller 3 at the outlet of the fixing nip portion 12 is allowed to be deformed according to the shape of the pressure roller 4 in the fixing nip portion 12. Therefore, both the fixing performance and the sheet peeling performance can be improved. Further, by covering the sponge layer 3b with the resin tube 10, the shape of the fixing roller 3 can be quickly restored at the exit of the fixing nip portion 12, so that the sheet peeling performance can be further improved.

(1-4. Experimental results)
(1-4-1. Experiment 1)
First, the results of an experiment conducted for examining the relationship between the thickness of the resin tube 10 and the sheet peelability will be described. In addition, the conditions of each member used for experiment are as follows.

  As the fixing roller, a solid iron cored bar having a diameter of 20 mm and a sponge layer made of foamed silicon rubber was formed, and the sponge layer was further covered with a PFA tube. It should be noted that six types of fixing rollers were used in which the thickness of the PFA tube was set to 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, and 80 μm, respectively. The hardness of the sponge layer before coating the PFA tube is 40 degrees in Asker C hardness.

  As the fixing belt, an elastic layer made of silicon rubber having a thickness of 150 μm was formed on a substrate having a thickness of 50 μm made of polyimide, and a release layer made of PFA having a thickness of 30 μm was further formed thereon. The thing of was used.

  As the heating roller, an aluminum cored bar having an outer shape of 28 mm and a wall thickness of 0.7 mm provided with a protective layer having a thickness of 50 μm was used.

  As a pressure roller, an elastic layer made of silicon solid rubber having a thickness of 1 mm is formed on an iron core having an outer diameter of 28 mm and a thickness of 1 mm, and a release layer made of a PFA tube having a thickness of 50 μm is further provided. Was used.

The process speed (paper conveyance speed) was 220 mm / sec. In addition, the lowering of the sheet peelability is more noticeable as the fixing temperature (the surface temperature of the fixing belt 5 during the fixing process) is higher. Therefore, in this experiment, the fixing temperature is set to the upper limit value of the fixable temperature range of the fixing unit 2. It was 200 degreeC near. Further, a paper having a basis weight of 64 g is used as a recording material, and an unfixed toner image in which four colors of cyan, magenta, yellow, and black are laminated on the leading end portion of the paper with a toner amount of 1.0 mg / cm ^2. ) Was supplied to the fixing unit 2. As the toners of the respective colors, those having a WAX content of 1.5 wt% or more and 5.0 wt% or less were used.

  Further, the pressure contact load between the fixing roller 3 and the pressure roller 4 was adjusted so that the pressing rate of the fixing roller 3 was 30%. Here, the pressing rate of the fixing roller is “pressing rate = (radius when the fixing roller 3 is not pressed) + radius when the pressure roller 4 is not pressed + thickness of the fixing belt 5 when not pressed” −when pressing. The distance between the axes of the fixing roller 3 and the pressure roller 4) / the thickness of the sponge layer 3b when not pressed. The deformation of the fixing roller 3 and the pressure roller 4 when the fixing roller 3 and the pressure roller 4 are brought into pressure contact mainly occurs in the sponge layer 3b. Therefore, the above-mentioned push-in rate is such that the thickness of the sponge layer 3b when the fixing roller 3 is not in contact with another member is t1, and the fixing roller 3 and the pressure roller 4 are pressed against each other via the fixing belt 5. When the thickness of the sponge layer 3b at the pressure contact portion is t2, the value is substantially the same as t2 / t1.

  Table 1 shows the experimental results of the above experiment. In addition, as an evaluation method, for each of the cases where the above six types of fixing rollers are used, a fixing process is performed on the above-mentioned paper, and a case where a paper peeling failure occurs is ×, and a case where no paper peeling failure occurs. ○.

  As shown in Table 1, when the thickness of the resin tube 10 was 40 μm to 70 μm, the fixing process could be performed satisfactorily. On the other hand, when the thickness of the resin tube 10 was 30 μm and when it was 80 μm, a paper peeling failure occurred. The reason why the paper peeling failure occurs when the thickness of the resin tube 10 is 30 μm is that the shrinkage force of the resin tube 10 is too small to appropriately suppress the swelling of the sponge layer 3 b at the exit of the fixing nip portion 12. It is thought that. Further, when the thickness of the resin tube 10 is 80 μm, the sheet peeling failure occurs because the hardness of the surface of the fixing roller 3 becomes too high so that the repulsive force of the sponge layer 3b cannot be applied to the recording material. This is probably because of this.

(1-4-2. Experiment 2)
Next, the result of an experiment conducted for examining the relationship between the hardness of the fixing roller 3 and the fixing performance will be described.

  In this experiment, a fixing roller was used in which a 5 mm sponge layer formed by foaming silicon rubber was formed on a solid iron core having a diameter of 20 mm, and the sponge layer was covered with a PFA tube having a thickness of 50 μm. In addition, by changing the foaming rate of the sponge layer, the hardness after covering the PFA tube was set to 35 degrees, 40 degrees, 45 degrees, 50 degrees, 60 degrees, 65 degrees, and 70 degrees in Asker C hardness, respectively. Seven types of fixing rollers were used. Further, since the lowering of the fixing performance is more noticeable as the fixing temperature is lower, the fixing temperature is set to 165 ° C., which is lower than that in Experiment 1. Other conditions are the same as in Experiment 1.

  Table 2 shows the results of this experiment. As for the fixing strength, a bending test was performed in which the image portion of the paper after the fixing process was bent 180 degrees, and the toner peeling width of the folded portion was 80 μm or more was evaluated as x, and the one less than 80 μm was evaluated as ◯. In addition, regarding gloss unevenness, the case where the gloss unevenness was confirmed by visual inspection was rated as x, and the case where the gloss unevenness was not confirmed was rated as ○.

  As shown in Table 2, good fixing strength was obtained when the hardness of the sponge layer was 45 to 65 degrees, but sufficient fixing strength was obtained when it was 40 degrees or less and 70 degrees or more. It was not obtained. This is because the pressure acting on the toner and the recording material is insufficient when the hardness of the sponge layer is too low, and the pressure contact force between the fixing roller 3 and the pressure roller 4 is large when the hardness of the sponge layer is too high. This is considered to be because the fixing nip width becomes narrow at the central portion of the recording material (the central portion in the direction perpendicular to the transport direction) due to excessive deformation and bending along the axial direction of the fixing roller 3.

  Further, when the hardness of the sponge layer was 40 degrees to 70 degrees, no occurrence of uneven gloss was confirmed, but when the hardness of the sponge layer was 35 degrees, uneven gloss was confirmed.

  This is because the fixing belt 5 provided in the fixing unit 2 of the belt fixing system has a thin elastic layer in order to reduce the heat capacity for the purpose of shortening the warm-up time. Is insufficient, the shape of the surface layer of the fixing belt 5 cannot follow the irregularities on the surface of the recording material 9, and the toner temperature varies at the irregularities on the surface of the recording material 9. As a result, the toner melting state changes. This is considered to be because the gloss changes and gloss unevenness occurs. Therefore, in order to make the surface layer of the fixing belt 5 follow the unevenness of the surface of the recording material 9 and prevent the occurrence of uneven gloss, a fixing pressure of a predetermined value or more is required. Increasing the fixing pressure can prevent the occurrence of uneven gloss and the like, and has the advantage that the fixing temperature for performing proper fixing can be lowered.

  In this experiment, the hardness of the fixing roller was changed by changing the foaming rate of the sponge layer. However, the foaming rate of the sponge layer was kept constant, and the hardness of the fixing roller was changed by changing the material of the sponge layer. Alternatively, the hardness of the fixing roller may be varied by changing both the material of the sponge layer and the foaming rate. In either case, substantially the same experimental results are obtained.

(1-4-3. Experiment 3)
Next, an experiment was conducted on the relationship between the indentation rate of the sponge layer, the durability of the fixing roller, and the fixing strength.

  In this experiment, a fixing roller was used in which a 5 mm sponge layer formed by foaming silicon rubber was formed on a solid iron core having a diameter of 20 mm, and the sponge layer was covered with a PFA tube having a thickness of 50 μm. In addition, the hardness of the sponge layer before covering the PFA tube was set to 40 degrees in Asker C hardness. Further, six types of cases in which the pressure contact force between the fixing roller 3 and the pressure roller 4 is adjusted so that the pressing rate of the fixing roller 3 is 15%, 20%, 25%, 30%, 35%, and 40%. The experiment was conducted.

  Table 3 shows the experimental results of this experiment. The fixing strength was evaluated by the same method as in Experiment 2. For durability, the fixing temperature (165 ° C.) was used to evaluate the fixing properties (fixing strength and gloss unevenness) in the same manner as in Experiment 2, and the fixing temperature was 200 ° C. and the paper was peeled off in the same manner as in Experiment 1. The case where the result of evaluating the property did not change before and after the fixing process was performed on 200,000 sheets of recording material at a fixing temperature of 180 ° C. was evaluated as “◯”.

  As shown in Table 3, when the indentation rate was 20% to 35%, sufficient fixing strength was obtained, and there was no problem with durability. On the other hand, when the indentation rate was 15%, sufficient fixing strength could not be obtained in the initial state. This is presumably because if the indentation rate is too low, the fixing nip width becomes narrow and sufficient heat and pressure cannot be applied to the toner. Further, when the indentation rate was 40%, the durability was lowered. This is because when the pressing force is increased by increasing the pressure contact force between the pressure roller 4 and the fixing roller 3 in order to increase the fixing pressure, the hardness of the sponge layer 3b is reduced, the bubbles of the sponge layer 3b are destroyed, and the sponge layer 3b. This is because peeling between the metal core 3a and the sponge layer 3b is liable to occur and the surface pressure (fixing pressure) of the fixing nip portion 12 is lowered, and both the peelability and the fixability are lowered. it is conceivable that.

(1-5. About toner)
The toner immediately after fixing at the exit of the fixing nip portion 12 is sticky at a high temperature, and is therefore difficult to adhere to the fixing belt 5 and leave. For this reason, in addition to the flexibility of the fixing belt 5 and the resilience of the fixing roller 3, the wax added to the toner plays an important role in order to improve the releasability between the fixing belt 5 and the toner. However, when the wax content is high, the toner releasability with respect to the fixing belt 5 is improved, so that the fixable temperature range is expanded. However, since the toner fluidity is lowered, the toner replenishment is delayed and the image quality is likely to deteriorate. . On the other hand, when the wax content is small, the fluidity of the toner is improved, but the releasability of the toner with respect to the fixing belt 5 is lowered, and the fixable temperature range is narrowed.

  Table 4 shows the results of examining the toner fluidity and fixability when toners having different wax contents are used in the color multifunction peripheral 1 according to the present embodiment. Regarding toner fluidity, the case where toner aggregation occurred in the developing units 53a to 53d was evaluated as x, and the case where the toner aggregation did not occur was evaluated as ◯. In addition, regarding the fixability, the case where an offset occurred was indicated as x, and the case where no offset occurred was indicated as ◯. The fixing temperature was 180 ° C.

  As shown in Table 4, when the wax content (the ratio of the wax weight to the total toner weight) is 1.5% by weight to 5.0% by weight, both the fluidity and the fixing property of the toner are good. Results were obtained. On the other hand, when the wax content was 1% by weight, an offset occurred. This is presumably because the fixable temperature range is narrowed. When the wax content was 5.5% by weight, toner aggregation occurred.

  From this experimental result, in this embodiment, a toner having a wax content of 1.5 wt% or more and 5.0 wt% or less is used. When the wax content is within this range, it is possible to prevent problems due to toner aggregation and fixing defects due to a decrease in toner releasability.

  The toner includes at least a binder resin, a colorant, and wax. The binder resin is not particularly limited, and a conventionally known binder resin for black toner or binder resin for color toner can be used. For example, binder resins composed of polyester resins, styrene resins such as polystyrene and styrene-acrylate copolymer resins, acrylic resins such as polymethyl methacrylate, polyolefin resins such as polyethylene, polyurethane, and epoxy resins. Can be used.

  Further, as a binder resin, a resin obtained by mixing a raw material monomer mixture with a release agent and performing a polymerization reaction may be used. In this case, it is preferable to include a polyester resin. By using a binder resin containing a polyester resin, the dispersion state controllability of the release agent is improved, and a toner having even better fixing properties can be obtained. Furthermore, the toner can be provided with excellent durability and transparency. Binder resin may be used individually by 1 type, and may use 2 or more types together.

  Moreover, said polyester resin is not specifically limited, A conventionally well-known thing can be used. For example, a polycondensation product of polybasic acids and polyhydric alcohols may be used. Polybasic acids are polybasic acids and derivatives of polybasic acids, such as acid anhydrides or esterified products of polybasic acids. Polyhydric alcohols are compounds containing two or more hydroxyl groups, and include both alcohols and phenols. In addition, as the polybasic acids, those commonly used as monomers for polyester resins can be used. Examples include aromatic carboxylic acids such as terephthalic acid, isophthalic acid, phthalic anhydride, trimellitic anhydride, pyromellitic acid and naphthalenedicarboxylic acid, and aliphatic carboxylic acids such as maleic anhydride, fumaric acid, succinic acid and adipic acid. used. Polybasic acids can be used alone or in combination of two or more.

  As polyhydric alcohols, those commonly used as monomers for polyester resins can be used. For example, aliphatic polyhydric alcohols such as ethylene glycol, propylene glycol, butanediol, hexanediol, neopentyl glycol and glycerin, alicyclic polyhydric alcohols such as cyclohexanediol, cyclohexanedimethanol and hydrogenated bisphenol A, bisphenol Aromatic diols such as an ethylene oxide adduct of A and a propylene oxide adduct of bisphenol A are exemplified.

  Bisphenol A is 2,2-bis (p-hydroxyphenyl) propane. Examples of the ethylene oxide adduct of bisphenol A include polyoxyethylene-2,2-bis (4-hydroxyphenyl) propane. Examples of the propylene oxide adduct of bisphenol A include polyoxypropylene-2,2-bis (4-hydroxyphenyl) propane. Polyhydric alcohols may be used alone or in combination of two or more.

  The polyester resin can be synthesized by a condensation polymerization reaction. For example, it can be synthesized by polycondensation reaction, specifically dehydration condensation reaction of polybasic acids and polyhydric alcohols in the presence of a catalyst in an organic solvent or without solvent. At this time, a demethanol polycondensation reaction may be performed using a methyl esterified product of a polybasic acid as part of the polybasic acid. The polycondensation reaction between the polybasic acid and the polyhydric alcohol may be terminated when the acid value and softening point of the polyester resin to be produced reach the values in the polyester resin to be synthesized. In this polycondensation reaction, by appropriately changing the reaction conditions such as the mixing ratio of polybasic acids and polyhydric alcohols and the reaction rate, for example, the content of carboxyl groups bonded to the terminal of the resulting polyester resin, and thus The acid value, softening point, and other physical properties of the resulting polyester resin can also be adjusted.

  As described above, the fixing unit 2 according to the present embodiment is a belt fixing type fixing device, and includes the fixing roller 3 having the sponge layer 3b and the resin tube 10 covering the surface of the sponge layer 3b. .

  As a result, the heat capacity of the fixing roller can be reduced as compared with a configuration using a fixing roller made of solid rubber, so that the warm-up time can be shortened and the power consumption can be reduced. Further, since the fixing roller is deformed in accordance with the shape of the pressure roller in the fixing nip portion, the fixing nip width can be widened to improve the fixing performance. Further, since the sponge layer 3b is covered with the resin tube 10, the swelling of the fixing roller 3 at the outlet of the fixing nip portion is effectively suppressed by the contraction force of the resin tube 10, and the shape of the fixing roller 3 is not pressed. Since it is possible to quickly restore the time state, it is possible to improve the paper peelability. Further, since it is only necessary to use the fixing roller 3 having the simple structure as described above, the above-described effects can be obtained without increasing the manufacturing cost.

  Further, since the resin tube can be formed thinner than the conventional solid rubber layer, the sponge layer 3b of the fixing roller 3 can be formed thicker than the conventional one. For this reason, durability of the sponge layer 3b can be improved. Further, since it is not necessary to perform rubber molding a plurality of times as in the conventional configuration in which the solid rubber layer is formed on the surface of the sponge layer, the manufacturing cost of the fixing unit 2 can be reduced.

  In the fixing unit 2 according to the present embodiment, the fixing roller 3 is configured to be rotated by the pressure roller 4, but the present invention is not limited to this. A conventional fixing roller having a sponge layer is generally configured to be driven and rotated by a pressure roller for reasons such as the durability of the sponge layer. In the fixing unit 2 according to this embodiment, the sponge of the fixing roller 3 is used. Since the layer 3b is covered with the resin tube 10, the durability of the sponge layer 3b can be improved. In the present invention, the fixing roller 3 may be directly rotated by a driving unit.

  In the present embodiment, only one heater lamp 7b is provided inside the heating roller 6. However, the present invention is not limited to this, and a plurality of heater lamps 7b may be provided. In this embodiment, the heater lamp 7b as a heating unit for heating the fixing belt 5 is provided inside the heating roller 6. However, the present invention is not limited to this. For example, the fixing belt 5 may be rotatably suspended between the fixing roller 3 and a support roller that does not include a heating unit, and the fixing belt 5 may be heated by a heating unit provided separately from the support roller. . The heating unit may be a contact type heating unit that contacts the fixing belt 5 or may be a non-contact type heating unit that does not contact the fixing belt 5. Further, an induction heating device using induction heating may be used, and a plurality of types of heating means may be used in appropriate combination. Further, the heating means (heating element) itself may function as a belt suspension member for rotatably suspending the fixing belt 5.

  In this embodiment, the fixing belt 5 is suspended from two roller members (the fixing roller 3 and the heating roller 6). However, the present invention is not limited to this, and may be configured to be suspended from three or more roller members. The fixing belt 5 is not limited to a configuration in which the fixing belt 5 is suspended on a plurality of roller members, and any configuration may be used as long as the fixing belt 5 can be suspended so as to be driven and rotated by the fixing roller 3.

[Embodiment 2]
Another embodiment of the present invention will be described. For convenience of explanation, members having the same functions as those described in the first embodiment are denoted by the same reference numerals and description thereof is omitted.

  In the first embodiment, the configuration in which only one belt member is provided in the fixing unit has been described. In the present embodiment, an example in which the present invention is applied to a configuration having a plurality of belt members will be described.

  FIG. 6 is a cross-sectional view of the fixing unit (fixing device) 102 according to the present embodiment. The fixing unit 102 is provided in place of the fixing unit 2 in the color multifunction peripheral 1 shown in the first embodiment.

  As shown in FIG. 6, the fixing unit 102 includes a fixing roller 3, a heating roller 6, a fixing pad 103, a fixing belt 5, a pressure roller 4, a tension roller (second belt suspension member) 114, a pressure pad 104, and This is a twin belt type fixing device including a pressure belt 105.

  The configurations of the fixing roller 3, the heating roller 6, and the fixing belt 5 are substantially the same as those in the first embodiment. However, in this embodiment, the fixing belt 5 is suspended from the fixing pad 103 in addition to the fixing roller 3 and the heating roller 6. The fixing pad 103 is made of PPS (polyphenylene sulfide resin), and both ends thereof are supported by side plates (not shown) of the fixing unit 102. The positions of the fixing roller 3, the heating roller 6, and the fixing pad 103 are adjusted so that when the fixing belt 5 is suspended, the tensile load acting on the fixing belt 5 is 50N.

  The fixing roller 3 is in pressure contact with a pressure roller 4 (described later) with a predetermined load via the fixing belt 5 and the pressure belt 105. Further, the fixing pad 103 is brought into pressure contact with a later-described pressure pad 104 through the fixing belt 5 and the pressure belt 105 with a predetermined load. The fixing belt 5 is driven to rotate by the pressure belt 105, and the fixing roller 3 and the heating roller 6 are driven to rotate by the fixing belt 5. As a result, the toner of the unfixed toner image on the recording material 9 passed between the fixing belt 5 and the pressure belt 105 is heated and melted and fixed on the recording material 9. In the example shown in FIG. 6, two heater lamps 7 b are provided in the heating roller 6, but the number of heater lamps 7 b is not limited to this. Also good.

  The pressure belt 105 is rotatably suspended on the pressure roller 4, the tension roller 114, and the pressure pad 104, and is rotated by the pressure roller 4. As the pressure belt 105, a belt having the same configuration as that of the fixing belt 5 can be used. In the present embodiment, the pressure roller 4, the tension roller 114, and the pressure roller 4, the tension roller 114, and the tension roller 114 so that the tensile load generated on the pressure belt 105 when suspended on the pressure pad 104 is 50 N. And the position of the pressure pad 104 was adjusted. The pressure roller 4 is substantially the same as in the first embodiment.

  The tension roller 114 is a roller-shaped member including a cored bar 114a and an elastic layer 114b, and is rotatably supported on a side plate (not shown) of the fixing unit 102. In this embodiment, an elastic layer 114b made of silicon sponge is applied to the surface of an iron alloy cored bar 114a having an outer diameter of 30 mm and an inner diameter of 26 mm in order to reduce the heat conductivity and reduce the heat conduction from the pressure belt 105. The tension roller 114 having a configuration provided with the above was used.

  As described above, the pressure pad 104 is provided at a position facing the fixing pad 103 via the fixing belt 5 and the pressure belt 105. The pressure pad 104 is made of PPS.

  As described above, the twin belt type fixing device including the fixing belt 5 and the pressure belt 105 can obtain substantially the same effect as that of the first embodiment.

  In this embodiment, in order to obtain a wide fixing nip portion 112 without increasing the size of the fixing unit 102, the fixing pad 103 and the pressure pad are opposed to each other via the fixing belt 5 and the pressure belt 105. 104 is provided, and these two pads are pressed against each other with a predetermined load via the fixing belt 5 and the pressure belt 105. Thus, the fixing nip portion 112 is formed in a wide area from the facing portion between the fixing pad 103 and the pressure pad 104 to the facing portion between the fixing roller 3 and the pressure roller 4, and the heat transfer area to the recording material 9 is increased. can do. Therefore, even when the process speed is increased, it is possible to prevent a defective fixing due to insufficient heat transfer to the recording material 9.

  By the way, when the fixing pad 103 and the pressure pad 104 which are not rotating bodies are provided as in the present embodiment, the inner peripheral surfaces of the fixing belt 5 and the pressure belt 105 slide on the fixing pad 103 and the pressure pad 104, respectively. Will rub. For this reason, when the dynamic friction coefficient between the fixing belt 5 and the fixing pad 103 and the dynamic friction coefficient between the pressure belt 105 and the pressure pad 104 are large, the sliding resistance increases. As a result, problems such as belt scraping, gear breakage, and increased power consumption of the pressure roller driving means M may occur. Therefore, in order to prevent these problems, the fixing pad 103 and the pressure pad 104 are made of a material having a small dynamic friction coefficient with respect to the fixing belt 5 and the pressure belt 105, or the fixing belt 5 and the pressure belt. It is preferable to provide a low friction sheet (not shown) having a low dynamic friction coefficient on the surface in contact with 105.

  In the present embodiment, the configuration including the fixing pad 103 and the pressure pad 104 has been described, but both of these pads are not essential and may be omitted. In this case, the fixing nip portion 112 may be formed only at a portion where the fixing roller 3 and the pressure roller 4 are opposed to each other, and a portion of the pressure belt 105 that is not in contact with the pressure roller 4 and the tension roller 114 is acceptable. A configuration may be adopted in which the fixing roller 3 is pressed against the fixing roller 5 via the fixing belt 5.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and the embodiments can be obtained by appropriately combining technical means disclosed in different embodiments. The form is also included in the technical scope of the present invention.

  INDUSTRIAL APPLICABILITY The present invention can be used for a belt fixing type fixing device used in an electrophotographic image forming apparatus and an image forming apparatus including the fixing device.

1 Color compound machine (image forming device)
2 Fixing unit (fixing device)
3 Fixing roller 3a Core metal (base material)
3b Sponge layer 4 Pressure roller (Pressure member)
5 Fixing belt 6 Heating roller (belt suspension member)
7a, 7b Heater lamp (heating means)
8a, 8b Thermistor 9 Recording material 10 Resin tube 12 Fixing nip 103 Fixing pad 104 Pressure pad 114 Tension roller (second belt suspension member)
M Pressure roller drive motor

Claims (9)

A fixing roller rotatably supported, a belt suspension member, an endless fixing belt rotatably suspended on the fixing roller and the belt suspension member, heating means for heating the fixing belt, and the fixing A pressure member that is rotatably supported so as to be in pressure contact with the fixing roller via a belt, and conveys a recording material on which an unfixed toner image is formed while the fixing belt and the pressure member sandwich the recording material. A fixing device for fixing the unfixed toner image on the recording material,
The fixing roller includes a cylindrical or columnar base material, a sponge layer formed on an outer peripheral surface of the base material, and a resin tube that covers the sponge layer.   The fixing device according to claim 1, wherein the resin tube is a heat-shrinkable tube that shrinks so as to reduce its diameter when heat is applied.   The fixing device according to claim 2, wherein the resin tube is a PFA tube or a PTFE tube.   The fixing device according to claim 3, wherein a film thickness of the resin tube is 40 μm or more and 70 μm or less.   5. The fixing device according to claim 1, wherein the fixing roller has an Asker C hardness of 45 degrees or more and 70 degrees or less. When the fixing roller is not in contact with another member, the thickness of the sponge layer is t1, and the sponge layer at the pressure contact portion when the fixing roller and the pressure member are pressed against each other via the fixing belt. Let t2 be the thickness of
0.2 ≦ t2 / t1 ≦ 0.35
The fixing device according to claim 1, wherein the fixing device is a fixing device.   The fixing device according to claim 1, wherein the resin tube contains a conductive material. The pressure member includes a pressure roller rotatably supported, a second belt suspension member, and a pressure belt rotatably suspended on the pressure roller and the second belt suspension member. And
2. The recording material on which an unfixed toner image is formed passes through a pressure contact portion between the fixing belt and the pressure belt, whereby the unfixed toner image is fixed on the recording material. 8. The fixing device according to any one of items 1 to 7.   An image forming apparatus comprising the fixing device according to claim 1.

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