JP2008152139A - Fixing device and image forming apparatus having the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device designed to heat by an endless belt rotatably extended by a plurality of support rollers at least one of which incorporates a heating source, wherein the fixing device is designed so as to prevent excessive temperature rise of a heat belt. <P>SOLUTION: A heat transfer acceleration material 100 for accelerating heat transfer between each support roller 81, 82 and the endless belt 83 is disposed on the contact faces of each support roller 81, 82 and the endless belt 83. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fixing device used in an electrophotographic image forming apparatus and an electrophotographic image forming apparatus including the same.

  2. Description of the Related Art Conventionally, as a fixing device used in an electrophotographic image forming apparatus such as a copying machine or a printer, the following configuration is generally used. Specifically, the roller includes a fixing roller and a pressure roller that are pressed against each other, and is heated by a heating unit including a fixing roller or a halogen lamp (halogen heater) disposed inside both the fixing roller and the pressure roller. Is heated to a predetermined temperature (fixing temperature). Then, after heating, the recording paper on which the unfixed toner image is formed is passed through a pressure contact portion (fixing nip portion) between the fixing roller and the pressure roller, and the toner image is fixed by heat and pressure (heat roller) Configuration using a fixing method).

  In particular, in a color fixing device, a configuration using an elastic roller provided with an elastic layer made of silicon rubber or the like on the surface of the fixing roller is generally used.

  By using an elastic roller as the fixing roller, the surface of the fixing roller is elastically deformed corresponding to the unevenness of the unfixed toner image, and comes into contact so as to cover the toner image surface. For this reason, it is possible to satisfactorily heat-fix a color unfixed toner image having a larger amount of toner than monochrome. At the same time, due to the strain relief effect of the elastic layer at the fixing nip, it is possible to improve the releasability of the color toner that is more easily offset than the monochrome toner. Furthermore, since the nip shape of the fixing nip is convex upward (on the fixing roller side) (so-called reverse nip shape), the paper peeling performance is improved and the paper can be peeled off without using a peeling means such as a peeling claw. (Self-strip) and image defects due to the peeling means can be eliminated.

  In an image forming apparatus using monochrome toner, a configuration in which an elastic layer is not provided on the fixing roller but an elastic layer is provided only on the pressure roller to secure the fixing nip portion is also used.

  Incidentally, the fixing roller or the pressure roller provided with the elastic layer has a very low thermal conductivity of the elastic layer. For this reason, when the heating means is provided inside the roller, there arises a problem that the warm-up time becomes long and the temperature of the fixing roller is lowered during continuous high-speed paper feeding.

  In order to solve such a problem, a configuration in which an external heating unit is brought into contact with the surface of the fixing roller and the fixing roller is heated from the outside (configuration using an external heating and fixing method) is known.

For example, Patent Document 1 discloses a technique using a heating belt (endless belt) stretched around a belt suspension roller as an external heating unit (a technique using an external belt heating fixing method). In this technique, a heating belt is used as the external heating unit to increase the contact area between the external heating unit and the fixing roller, thereby promoting the heat supply from the external heating unit to the fixing roller.
JP 2004-198559 A (published July 15, 2004)

  However, in the technique of Patent Document 1, the heating belt is heated by heating the belt suspension roller, and heat is supplied to the fixing member via the heating belt. Therefore, it is necessary to set the temperature of the heating belt higher than the surface temperature of the fixing roller, and further set the belt suspension roller to a temperature higher than that of the heating belt. Therefore, when rotation and heating are suddenly stopped while the belt suspension roller is in pressure contact with the fixing roller via the heating belt, heat is transferred from the belt suspension roller to the heating belt for a while, and pressure contact with the suspension roller. The temperature of the heating belt and fixing roller surface to rise locally increases. As a result, there is a problem that the heat resistance temperature of the release layer having the releasability with the toner on the surface of the fixing roller is exceeded. In Patent Document 1, there is no description about the existence of a problem related to the excessive temperature rise in the case where the heating belt stops suddenly, and countermeasures.

  The present invention has been made in view of the above problems, and an object of the present invention is to prevent overheating of the heating belt.

  In order to solve the above-described problems, a fixing device according to the present invention heats a heating belt that is rotatably stretched between a fixing member, a pressure member, and a plurality of support rollers each having a heating source therein. And an external heating device that heats the heated member by contacting at least one peripheral surface of the fixing member and the pressure member that are heated members, and the fixing member and the pressure member are In the fixing device for fixing an unfixed image on the recording material to the recording material by conveying the recording material while pinching the recording material, the support roller and the heating belt are contacted to the contact surface between the supporting roller and the heating belt. It is characterized by comprising heat transfer promoting means for promoting heat transfer.

  According to the above configuration, the heat transfer promoting means provided on the contact surface between the support roller and the heating belt can promote heat transfer from the support roller to the heating belt. The belt temperature difference can be reduced. Therefore, it is possible to prevent the temperature of the heating belt from becoming very high due to heat transfer from the support roller at the time of a sudden stop such as a paper jam or an exterior door open. Therefore, it is possible to prevent the heat resistance temperature of the release layer having the releasability from the toner on the surface of the fixing roller from being exceeded. Therefore, even in long-term use, the release layer can be kept in a good state, and the toner can be fixed well at all times.

  In the fixing device according to the present invention, in addition to the above-described configuration, the heat transfer promoting means may be a heat conduction promoting material disposed on a contact surface between the support roller and the heating belt.

  According to the above configuration, the minute space between the support roller and the belt can be eliminated by disposing the heat conduction promoting material on the contact surface between the support roller and the heating belt. By filling the space with high heat insulation with the heat conduction promoting material, the amount of heat transferred from the support roller to the heating belt can be improved. Therefore, the heating belt can be heated more uniformly, and the toner can be fixed without causing any trouble even in long-term use.

  In the fixing device according to the present invention, in addition to the above-described configuration, the heat conduction promoting material is a powder, and the average particle size thereof is smaller of the surface roughness of the support roller and the surface roughness of the heating belt. It may be less than one quarter.

  According to the said structure, the clearance gap between a support roller and a heating belt can be suitably filled with powder. Therefore, the heating belt can be heated more uniformly.

  In the fixing device according to the present invention, in addition to the above configuration, the width of the heating belt in the axial direction of the support roller may be larger than the width in the same direction of the heated member to be contacted.

  According to the above configuration, since the width of the heating belt in the axial direction of the support roller is larger than the width of the member to be heated in the same direction, the heat conduction promoting material on the contact surface between the support roller and the heating belt protrudes from the belt end. Even in such a case, it is possible to prevent the thermal conductivity promoting material from adhering to the portion (fixing nip portion) where the heated member sandwiches the recording material. Therefore, a uniform and high-quality image can be stably formed.

  In addition, in the fixing device according to the present invention, in addition to the above-described configuration, the heat conduction promoting member moves the heat conduction promoting material from the end of the heating belt toward the center of the heating belt in the axial direction of the support roller. May be provided.

  When the support roller and the heating belt rotate for a long time, the heat conduction promoting material on the contact surface between the support roller and the heating belt may spread and protrude from the belt end. However, by providing the heat conduction promoting material, the heat conduction promoting material can be moved from the end of the heating belt toward the center of the heating belt in the axial direction of the support roller. Therefore, the heat conduction promoting material can be uniformly disposed on the contact surface between the support roller and the heating belt over a long period of time. Therefore, it is possible to fix the toner while maintaining high quality uniformly.

  In the fixing device according to the present invention, in addition to the above configuration, the outermost surface layer of the support roller is harder than the inner peripheral surface of the heating belt, and has a larger surface roughness than the inner peripheral surface of the heating belt. The outermost layer may serve as the heat transfer promoting means.

  According to the above configuration, the support roller surface is harder than the inner peripheral surface of the heating belt and has a larger surface roughness than the inner peripheral surface of the heating belt. Bites into the inner peripheral surface of the heating belt. Thereby, the real contact area of a support roller and a heating belt can be increased. By increasing the real contact area of the heat transfer surface, the amount of heat transfer from the support roller to the heating belt can be improved.

  Here, the surface of the support roller may be subjected to a mechanical roughening process, and the surface roughness may be larger than the inner peripheral surface of the heating belt.

  Further, when the support roller and the heating belt slide, the area of the transmission surface of the support roller becomes smaller than the area of the heat receiving surface of the heating belt, and heat transfer from the support roller to the belt is reduced. Therefore, by roughening the surface of the support roller, slippage between the support roller and the heating belt can be prevented. This also prevents a decrease in heat transfer from the support roller to the belt, and improves the amount of heat transfer from the support roller to the heating belt. Therefore, the heating belt can be heated more uniformly, and the toner can be satisfactorily fixed without causing problems even in long-term use.

  In the fixing device according to the present invention, in addition to the above configuration, the heat conduction promoting means is a pressing means for pressing at least one of the support rollers against the peripheral surface of the member to be heated via the heating belt. There may be.

  According to the above configuration, the contact area between the support roller and the heating belt is increased by pressing the support roller against the peripheral surface of the fixing member or the pressure member that is the member to be heated via the heating belt. be able to. Thus, by increasing the real contact area of the heat transfer surface, the amount of heat transfer from the support roller to the heating belt can be improved. Therefore, the heating belt can be heated more uniformly, and the toner can be satisfactorily fixed without causing problems even in long-term use.

  In order to solve the above problems, an image forming apparatus according to the present invention includes any one of the fixing devices described above. Even in this case, the same effect as described above can be obtained, and a uniform and high-quality image can be formed with uniform fixability.

  As described above, the fixing device of the present invention includes the heat transfer promoting means for promoting the heat transfer from the support roller to the heating belt on the contact surface between the support roller and the heating belt.

  According to the above configuration, the heat transfer promoting means provided on the contact surface between the support roller and the heating belt can promote heat transfer from the support roller to the heating belt. The belt temperature difference can be reduced. Therefore, it is possible to prevent the temperature of the heating belt from becoming very high due to heat transfer from the support roller at the time of a sudden stop such as a paper jam or an exterior door open. Therefore, it is possible to prevent the heat resistance temperature of the release layer having the releasability from the toner on the surface of the fixing roller from being exceeded. Therefore, even in long-term use, the release layer can be kept in a good state, and the toner can be fixed well at all times.

Embodiment 1
An embodiment of the present invention will be described. First, the image forming apparatus 1 provided with the fixing device of the present embodiment will be described with reference to FIG. FIG. 2 is a schematic diagram showing the internal structure of the image forming apparatus 1. The image forming apparatus 1 is a dry electrophotographic color image forming apparatus, and is based on image data transmitted from each terminal device connected via a network or image data read by a scanner (recording material). , Transfer medium, recording paper) P, and a printer that forms a color image or a monochrome image.

  The image forming apparatus 1 is a dry electrophotographic and quadruple tandem color printer, and includes a visible image transfer unit 50, a paper transport unit 30, a fixing device 40, and a supply tray 20.

  The visible image transfer unit 50 includes a yellow image transfer unit 50Y, a magenta image transfer unit 50M, a cyan image transfer unit 50C, and a black image transfer unit 50B. Specifically, the yellow image transfer unit 50Y, the magenta image transfer unit 50M, the cyan image transfer unit 50C, and the black image transfer unit 50B are arranged between the supply tray 20 and the fixing device 40 from the supply tray 20 side. They are attached in order.

  Each of these transfer portions 50Y, 50M, 50C, and 50B has substantially the same configuration, and a yellow image, a magenta image, a cyan image, and a black image are respectively applied to the paper P based on the image data. Transcript.

  Each of the transfer units 50Y, 50M, 50C, and 50B includes a photosensitive drum 51, and further includes a charging roller 52, an LSU (laser beam scanner unit) 53, a developing unit 54, a transfer roller 55, and a cleaning device 56. It is arranged around the drum 51 along the rotation direction of the photosensitive drum 51 (direction F in FIG. 2).

  The photosensitive drums 51 of the transfer units 50Y, 50M, 50C, and 50B are drum-shaped transfer rollers having a photosensitive material on their surfaces, and are driven to rotate in the direction of arrow F. The charging roller 52 is for charging the surface of the photosensitive drum 51 uniformly (uniformly).

  Pixel signals corresponding to a yellow component, a magenta component, a cyan component, and a black component in the image data are input to the LSUs 53 of the transfer units 50Y, 50M, 50C, and 50B, respectively. Each LSU 53 exposes the charged photosensitive drum 51 based on these image signals to generate an electrostatic latent image.

  The developing units 54 of the transfer units 50Y, 50M, 50C, and 50B have yellow, magenta, cyan, and black toner (developer), respectively. The toner has a function of developing the electrostatic latent image generated on the photosensitive drum 51 with these toners to generate a toner image (visualized image). As the developer, for example, a developer such as a non-magnetic one-component developer (non-magnetic toner), a non-magnetic two-component developer (non-magnetic toner and carrier), and a magnetic developer (magnetic toner) is used. be able to.

  The transfer roller 55 of the transfer units 50Y, 50M, 50C, and 50B is applied with a bias voltage having a polarity opposite to that of the toner. By applying this bias voltage to the paper P, the toner image on the photosensitive drum 51 is transferred to the paper P. It is intended for transfer to.

  The cleaning devices 56 of the transfer units 50Y, 50M, 50C, and 50B are for removing toner remaining on the photosensitive drum 51 after image transfer onto the paper P. The transfer of the toner image onto the paper P as described above is repeated four times for four colors.

  The paper transport unit 30 includes a driving roller 31, a driven roller 32, and a transport belt 33, and transports the paper P so that a toner image is formed on the paper P in order by the transfer units 50Y, 50M, 50C, and 50B. It is.

  The driving roller 31 and the driven roller 32 stretch the conveyor belt 33, and the driving roller 31 has a predetermined peripheral speed (in this embodiment, monochrome image formation (monochrome mode) 355 mm / s, color image formation ( The color belt is controlled to rotate at 175 mm / s), so that the conveyor belt 33 rotates.

  The conveyance belt 33 is a belt that is placed between the driving roller 31 and the idling roller 32 so as to come into contact with the photosensitive drums 51 of the transfer units 50Y, 50M, 50C, and 50B. It is friction driven in the direction of the arrow Z. The transport belt 33 electrostatically attracts the paper P sent from the supply tray 20, and sequentially transports the paper P to the transfer units 50Y, 50M, 50C, and 50B.

  Further, the sheet P on which the toner image has been transferred by each of the transfer units 50Y, 50M, 50C, and 50B is peeled off from the transport belt 33 by the curvature of the drive roller 31 and transported to the fixing device 40 (the one-dot chain line in FIG. Shows the transport path). Note that the toner image after being transferred onto the paper P by the transfer units 50Y, 50M, 50C, and 50B is in an unfixed state on the paper P.

  The fixing device 40 heat-compresses the unfixed toner image transferred onto the paper P to the paper P. Specifically, the fixing device 40 includes a fixing roller (fixing member) 60 and a pressure roller (fixing member) 70. Then, a predetermined conveyance speed (process speed; for example, monochrome mode 355 mm / s, color mode 175 mm / s) and copying speed (number of copies per minute; for example, monochrome mode 70 with A4 lateral feed) from the visible image transfer unit 50. Sheet P conveyed in sheet mode / min, color mode 40 sheets / min) is sent to a fixing nip N formed between the fixing roller 60 and the pressure roller 70. Further, the fixing roller 60 and the pressure roller 70 convey the paper P while sandwiching it. At this time, the toner image (unfixed image) on the paper P is melted by the heat of the peripheral surface of the fixing roller 60 and is pressed by the fixing roller 60 and the pressure roller 70 to be fixed on the paper P. Fix as an image.

  Then, the sheet P after the toner image is fixed by the fixing device 40 is discharged to a discharge tray (not shown) outside the image forming apparatus 1. Thereby, the image forming process ends. A specific configuration of the fixing device 40 will be described later in detail.

  The image forming apparatus 1 also includes a color mode (multicolor mode) in which each transfer unit 50Y, 50M, 50C, and 50B performs image transfer on the paper P to form a color image (multicolor image), and the paper P. On the other hand, only the black image transfer unit 50B can execute a monochrome mode (monochrome mode) in which a monochrome image (monochrome image) is formed by transferring an image. More specifically, the control unit (control integrated circuit board or computer, not shown) provided in the image forming apparatus 1 is in either the color mode or the monochrome mode according to an input instruction from the user. Each of the transfer units 50Y, 50M, 50C, and 50B is controlled so as to execute the image formation corresponding to the selected mode.

  Further, the control unit transports the paper P at a transport speed (process speed) of 355 mm / S in the color mode, and transports the paper P at a transport speed of 175 mm / S in the monochrome mode. Paper transport means (paper transport unit 30, fixing roller 60, pressure roller 70, etc.) are controlled.

  Next, the fixing device 40 will be specifically described. FIG. 3 is a schematic diagram illustrating a schematic configuration of the fixing device 40. The fixing device 40 includes an external heating device 80, a control device 90, a rotation driving device 91, and a belt moving device 110 in addition to the fixing roller 60 and the pressure roller 70 described above. If necessary, a web cleaning device for cleaning the surface of the fixing roller 60 may be further provided.

  The rotation driving device 91 rotates the fixing roller 60, and is composed of, for example, a motor. The operation of the rotation drive device 91 is controlled by the control device 90.

  The fixing roller 60 is a roller that rotates in the G direction shown in FIG. 3, and is formed by covering a metal hollow cylindrical cored bar 61, an elastic layer 62 that covers the outer peripheral surface of the cored bar 61, and the elastic layer 62. The release layer 63 is formed.

  The metal core 61 is made of aluminum having an outer diameter of 46 mm, for example, and has a cylindrical shape. However, the material of the cored bar 61 is not limited to aluminum, and may be made of, for example, iron or stainless steel. The elastic layer 62 has a thickness of 3 mm, for example, and is made of heat-resistant silicon rubber (JIS-A hardness 20 degrees). The release layer 63 is made of, for example, a PFA (copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether) tube having a thickness of about 30 μm. The material of the release layer 63 may be any material as long as it has excellent heat resistance and durability and has excellent release properties with respect to the toner. In addition to PFA, fluorine-based materials such as PTFE (polytetrafluoroethylene) can be used. Materials may be used. The fixing roller 60 having such a configuration has an outer diameter of 50 mm, and the surface hardness of the fixing roller 60 is 68 degrees (Asker C hardness). Note that the width of the surface of the fixing roller 60 in the rotation axis direction is 320 mm in the present embodiment.

  A thermistor 65 for detecting the temperature of the peripheral surface is in contact with the peripheral surface of the fixing roller 60, and a halogen lamp (heater lamp) 64 that emits heat when power is supplied to the inside of the cored bar 61. Is installed. The halogen lamp 64 is a heat source for the fixing roller 60. When power is supplied to the halogen lamp 64, the inside of the fixing roller 60 is heated to a predetermined temperature (180 ° C. in this embodiment) by the halogen lamp 64, and the fixing nip portion N The sheet P on which the unfixed toner image passing through the sheet P is formed is heated.

  In the present embodiment, one halogen lamp 64 is incorporated. However, the present invention is not limited to this. For example, the heat generation distribution is distributed in the direction of the rotation axis so that an optimum temperature distribution can be formed according to the paper size. A plurality of halogen lamps may be used. In this embodiment, the thermistor 65 is arranged so as to contact the longitudinal center of the fixing roller 60. However, the present invention is not limited to this, and is installed at the longitudinal end (non-sheet passing region) of the fixing roller 60. May be. In addition, when the amount of heat generation is different between the center portion and the end portion by installing two halogen lamps or the like, it may be installed at both the center portion and the end portion.

  The pressure roller 70 is a roller that rotates in the H direction shown in FIG. 3, and is formed by covering a metal hollow cylindrical cored bar 71, an elastic layer 72 that covers the outer peripheral surface of the cored bar 71, and the elastic layer 72. The release layer 73 is provided.

  The core metal 71 has an outer diameter of 46 mm, for example, and is made of aluminum. However, the material of the cored bar 71 is not limited to aluminum, and may be made of iron or stainless steel. The elastic layer 72 has a thickness of 2 mm, for example, and is made of silicon rubber having heat resistance. The release layer 73 is made of, for example, a PFA tube having a thickness of about 30 μm. The material of the release layer 73 may be any material as long as it has excellent heat resistance and durability and has excellent release properties with respect to the toner. In addition to PFA, a fluorine-based material such as PTFE may be used. The outer diameter of the pressure roller 70 having such a configuration is 50 mm, and the surface hardness of the pressure roller 70 is 75 degrees (Asker C hardness).

  The pressure roller 70 is pressed against the fixing roller 60 with a predetermined load (600 N in this case) by an elastic member (spring) (not shown). As a result, a fixing nip portion N (a portion where the fixing roller 60 and the pressure roller 70 are in contact with each other, here a width of 9 mm in the sheet conveyance direction) is formed between the peripheral surface of the fixing roller 60 and the peripheral surface of the pressure roller 70. The Further, the pressure roller 70 is rotated in the direction opposite to the fixing roller 60 (the movement direction of both roller surfaces in the fixing nip portion is the same) following the rotation of the fixing roller 60. In the present exemplary embodiment, the pressure roller 70 is configured to be driven to rotate by the fixing roller 60, but is not limited thereto, and may be configured to be rotationally driven by a rotational driving unit different from the fixing roller 60.

  A thermistor 75 that detects the temperature of the peripheral surface is in contact with the peripheral surface of the pressure roller 70, and a halogen lamp (heater lamp) 74 that performs heat radiation by supplying power is provided inside the cored bar 71. is set up. The halogen lamp 74 is a heat source for the pressure roller 70. When power is supplied to the halogen lamp 74, the inside of the pressure roller 70 is heated to a predetermined temperature (150 ° C. in this embodiment).

  In this embodiment, the rubber hardness (75 degrees) of the pressure roller 70 is set higher than the rubber hardness (68 degrees) of the fixing roller 60, but this is between the pressure roller 70 and the fixing roller 60. This is because the fixing nip portion N formed in the above is formed in a reverse nip shape (the shape of the pressure roller 70 is almost unchanged and the fixing roller 60 is slightly recessed). The nip width (width along the circumferential direction of the fixing roller 60) of the fixing nip portion N thus obtained is 8.5 mm in this embodiment.

  Here, the reason why the fixing nip portion N between the pressure roller 70 and the fixing roller 60 has a reverse nip shape will be described. When the fixing nip portion N has a reverse nip shape, the paper P that has passed through the fixing nip portion N is discharged in a direction along the circumferential surface of the pressure roller 70, and thus the paper P is discharged from the fixing nip portion N. At this time, it is easy to perform self-peeling (peeling with a paper scraper without requiring forced peeling assisting means such as a peeling nail). When the surface hardness of the pressure roller 70 is lower than the surface hardness of the fixing roller 60, the shape of the fixing roller 60 remains almost unchanged in the fixing nip portion N between the fixing roller 60 and the pressure roller 70. The sheet P having a slightly recessed shape 70 passes through the fixing nip portion N and is discharged in a direction along the peripheral surface of the fixing roller 60. Therefore, it is difficult for self-peeling to occur.

  The external heating device 80 includes a first support roller (first heating roller) 81, a second support roller (second heating roller) 82, an endless belt (heating belt, external heating belt) 83, and a belt moving device 110 (see FIG. 3). Are not shown), and belt regulating members (regulating members) 121 and 122 (not shown in FIG. 3) are provided. In the following description, when the first support roller and the second support roller are not distinguished, they are simply referred to as support rollers.

  The endless belt 83 is stretched around the support rollers 81 and 82 so that the back surface (inner peripheral surface) side is in contact with the peripheral surfaces of the support rollers 81 and 82. The endless belt 83 is provided on the upstream side of the fixing nip portion N with respect to the fixing roller 60. When the support rollers 81 and 82 are in a first position described later, a predetermined pressing force (40N in this embodiment) is provided. Thus, it is pressed against the fixing roller 60. Thus, a heating nip n (a contact portion between the endless belt 83 and the fixing roller 60; a width 20 mm in the circumferential direction of the fixing roller 60) is formed between the fixing roller 60 and the heating roller.

  Further, the endless belt 83 is driven to rotate by the fixing roller 60 by contacting the circumferential surface of the rotating fixing roller 60. As a result, the support rollers 81 and 82 rotate in the direction opposite to the rotation direction of the fixing roller 60 (K direction in FIG. 3). That is, when the control device 90 controls the rotation driving device 91 of the fixing roller 60 to rotationally drive the fixing roller 60, the endless belt 83 is fixed by the frictional force at the portion where the endless belt 83 and the fixing roller 60 are in contact with each other. The support rollers 81 and 82 and the endless belt 83 are rotated by being driven by the roller 60.

  The endless belt 83 is coated with, for example, a fluororesin blended with PTFE and PFA with a thickness of 20 μm on the outermost surface of a base material made of polyimide having a thickness of 100 μm (product name: Upilex S, manufactured by Ube Industries). It is a belt member. However, the configuration of the endless belt 83 is not limited to this, and a belt member made of metal such as nickel, stainless steel, or iron may be used. Further, the inner diameter of the endless belt 83 is not limited to 30 mm. The material of the release layer of the endless belt 83 may be any material as long as it has excellent heat resistance and durability and excellent release properties from the toner. For example, PTFE or PFA may be used alone. The inner diameter of the endless belt 83 at room temperature (20 ° C.) is 30 mm (inner peripheral length 94 mm) in the present embodiment, but is not limited to this value. The width of the endless belt 83 (the axial width of the support rollers 81 and 82) is 320 mm at room temperature in the present embodiment.

  Each of the support rollers 81 and 82 is a roller in which, for example, a fluororesin in which PTFE and PFA are blended as a release layer is coated with a thickness of 20 μm on the surface of an aluminum core having an outer diameter of 15 mm. In addition, as a material of the release layer, it is only necessary to have excellent heat resistance and durability and excellent release property with the toner. For example, a fluorine-based material such as PFA or PTFE (polytetrafluoroethylene) is used. can do. In addition, the inter-axis distance between the support rollers 81 and 82 is 23.0 mm in the present embodiment.

  Further, the support rollers 81 and 82 are pressed against the peripheral surface of the fixing roller 60 by a predetermined load (for example, 20 N) via the endless belt 83 by a belt moving device 110 described later. As a result, the surface of the endless belt 83 contacts the circumferential surface of the fixing roller 60, and a heating nip portion n is formed between the surface of the endless belt 83 and the circumferential surface of the fixing roller 60. The nip width between the surface of the endless belt 83 and the peripheral surface of the fixing roller 60 (the width along the circumferential direction of the fixing roller 60) is 20 mm.

  A thermistor 85 a that detects the surface temperature of the endless belt 83 is in contact with the outer surface of the contact portion of the endless belt 83 with the first support roller 81. In addition, a halogen lamp (heater lamp) 86 a that generates heat by supplying power is provided inside the first support roller 81. The thermistor 85b for detecting the surface temperature of the endless belt 83 is in contact with the outer surface of the endless belt 83 in contact with the second support roller 82, and the second support roller 82 is supplied with power. A halogen lamp (heater lamp) 86b that generates heat is provided. The halogen lamps 86a and 86b are heat sources for the endless belt 83. When power is supplied to the halogen lamps 86a and 86b, heat is radiated from the halogen lamps 86a and 86b, and the endless belt 83 passes through the support rollers 81 and 82. It is heated to a predetermined temperature (220 ° C. in this embodiment). Since the endless belt 83 is in contact with the peripheral surface of the fixing roller 60 from the outside of the fixing roller 60, the peripheral surface of the fixing roller 60 can be heated through the contact portion. In the present embodiment, since the two thin-walled small-diameter support rollers 81 and 82 and the thin endless belt 83 are used as described above, the temperature of the endless belt 83 can be raised quickly.

  Next, the belt moving device 110 and the belt regulating members 121 and 122 provided in the fixing device 40 will be described. 4A shows a state in which the support rollers 81 and 82 are arranged by the belt moving device 110 at positions where the support rollers 81 and 82 are in contact with the fixing roller 60 via the endless belt 83 (first position). FIG. 4B is a cross-sectional view illustrating a state in which the support rollers 81 and 82 are disposed at positions separated from the fixing roller 60 (second position) by the belt moving device 110. 5A is a top view illustrating the configuration of the belt moving device 110, and FIG. 5B is a cross-sectional view illustrating the configurations of the support rollers 81 and 82, the endless belt 83, and the belt regulating members 121 and 122. It is.

  As shown in FIGS. 4A and 4B and FIG. 5A, the belt moving device 110 includes a side frame 111, an arm 112, an eccentric cam 113, a fulcrum (fulcrum member) 114, and a fulcrum (fulcrum member). 115 and a coil spring 116 are provided. In FIG. 5A, only one end of each of the support rollers 81 and 82 is shown. However, one end (not shown) of the support rollers 81 and 82 has the same configuration (that is, the configuration shown in FIG. ).

  The side frames 111 are provided at both ends of the support rollers 81 and 82, respectively, and rotatably support the support rollers 81 and 82 via bearings 117 and 118 as shown in FIG. is there. Note that the bearings 117 and 118 are fixed to the side frame 111 at a predetermined inter-axis distance, so that the parallelism between the first support roller 81 and the second support roller 82 is ensured. In the present embodiment, the parallelism tolerance between the first support roller 81 and the second support roller 82 is 100 μm or less.

  Further, the side frame 111 is pivotally supported at a fulcrum 114 with respect to the arm 112 so as to be rotatable in a direction substantially perpendicular to the axial direction of the support rollers 81 and 82.

  The arm 112 is rotatably supported by a fulcrum 115 fixed to the frame of the fixing device 40 (not shown), and is urged by the coil spring 116 in a direction in contact with the fixing roller 60 with the fulcrum 115 as an axis.

  The eccentric cam 113 is provided in contact with the vicinity of the end of the arm 112. The eccentric cam 113 is rotationally driven by the control device 90 controlling driving means such as a motor (not shown).

  As a result, the control device 90 (movement control unit 90c) controls the driving means to rotate the eccentric cam 113 and move the support rollers 81 and 82 to the first position as shown in FIG. The eccentric cam 113 is rotated 180 degrees therefrom, and the support rollers 81 and 82 can be moved to the second position as shown in FIG. 4B.

  In this embodiment, the distance between the fulcrum 114 at the first position and the peripheral surface of the fixing roller 60 is 28 mm, and the distance between the fulcrum 114 at the second position and the peripheral surface of the fixing roller 60 is 29.5 mm. . That is, when moving from the first position to the second position, the movement amount (separation length) of the fulcrum 114 is 1.5 mm. The distance between the fulcrum 114 and the fulcrum 115 is 15 mm, and the distance between the contact point between the arm 112 and the eccentric cam 113 and the fulcrum 115 is 15 mm (therefore, the lever ratio is 1: 1). Therefore, the moving amount of the contact portion of the arm 112 with the eccentric cam 113 is also 1.5 mm.

  Further, when the rotation of the fixing roller 60 is stopped at the second position, the contact width (heating nip width) between the endless belt 83 and the fixing roller 60 in the rotation direction is about 10 mm. However, this contact width is a value that can change depending on the bending wrinkles and temperature of the endless belt 83. In general, when the belt is heated, the circumference of the belt is extended, so that the contact width increases. In this embodiment, the separation length is set to 1.5 mm. However, when the separation length is set to 4 mm, the endless belt 83 and the fixing roller 60 are brought into contact with each other by moving to the second position. Without being completely separated.

  As shown in FIGS. 5A and 5B, belt regulating members (shift regulating members, regulating members) 121 and 122 are provided between the support rollers 81 and 82 and the bearings 117 and 118, respectively. Yes. When the endless belt 83 meanders, the belt regulating members 121 and 122 rotate in contact with the end of the belt to regulate the endless belt 83 in the axial direction of the support rollers 81 and 82. The end of the endless belt 83 is to prevent wear and cracks due to sliding with the bearings 117 and 118.

  The belt regulating members 121 and 122 are rotatable with respect to the support rollers 81 and 82 (can be rotated independently of the rotation of the support rollers 81 and 82 about the rotation axis of the support rollers 81 and 82). Further, as shown in FIG. 5B, the belt restricting members 121 and 122 have a cross-sectional shape viewed from the axial direction of the support rollers 81 and 82 concentrically with a circle formed by the cross-section of the support rollers 81 and 82. ing.

  As shown in FIG. 3, the control device 90 includes a temperature control unit 90 a, a rotation control unit 90 b, and a movement control unit 90 c, and the surface temperature of the endless belt 83, the surface temperature of the fixing roller 60, and the pressure roller 70. This is an integrated circuit board for control that controls surface temperature, rotational driving of the fixing roller 60, movement of the belt position by the belt moving device 110, and the like.

  The temperature control unit 90 a is connected to the thermistors 65, 75, 85 a, and 85 b and the heating power supply unit 99. The heating power supply unit 99 is connected to the halogen lamps 64, 74, 81, and 82, and supplies power for heating to these halogen lamps. The temperature control unit 90a switches the supply power from the heating power supply unit 99 to each halogen lamp based on the temperature detection results of the thermistors 65, 75, 85a, and 85b, the image forming mode, etc. The endless belt 83, the fixing roller 60, and the pressure roller 70 are controlled to have predetermined temperatures.

  The rotation control unit 90b is connected to a rotation driving device 91 for driving the fixing roller 60 to rotate. The rotation control unit 90 b controls the rotation speed of the fixing roller 60 by controlling the operation of the rotation driving device 91.

  The movement control unit 90 c is connected to the belt moving device 110. The movement control unit 90 controls the relative positions of the support rollers 81 and 82 provided in the external heating device 80 and the fixing roller 60 by controlling the operation of the eccentric cam 113 provided in the belt moving device 110. The movement control unit 90 changes the contact width (heating nip width) between the endless belt 83 and the fixing roller 60 by controlling the relative positions of the support rollers 81 and 82 and the fixing roller 60, and from the external heating device 80. The amount of heat supplied to the fixing roller 60 is controlled.

  The movement control unit 90c also determines the type of paper (transfer medium) P and the image formation mode (in the monochrome image formation mode and the color image formation mode, or in the case of passing one sheet and in the case of continuous sheet passing). ) Etc., the belt moving device 110 is controlled. By controlling the belt moving device 110 and moving the positions of the support rollers 81 and 82 between the first position and the second position, the contact area (heating nip width) of the endless belt 83 is changed, The amount of heat supplied from the heating device 80 to the fixing roller 60 is controlled.

  When the copying speed is decreased, the movement control unit 90c controls the belt moving device 110 to move the support rollers 81 and 82 from the first position to the second position. For example, the sheet conveyance speed in the monochrome mode is set to 355 mm / s, and the color mode is set to 175 mm / s. The fixing roller setting temperature in the monochrome mode and the fixing roller setting temperature in the color mode are the same at 180 ° C. In the case where the heating nip width between the endless belt 83 and the fixing roller 60 is the same at 20 mm, if the set temperature of the endless belt 83 is 220 ° C. in the monochrome mode and 205 ° C. in the color mode, the paper P is deprived. The amount of heat and the amount of heat supplied from the external heating device 80 to the fixing roller 60 are substantially balanced.

  For this reason, when changing from the monochrome mode to the color mode, the temperature of the endless belt 83 is too higher than the set temperature. If the color image is fixed in a state where the temperature of the endless belt 83 is too high, the temperature of the fixing roller 60 becomes too high and the gloss of the color image becomes excessive or uneven gloss occurs, resulting in a reduction in image quality. To do. In order to avoid such a problem, it is conceivable to wait until the temperature of the endless belt 83 drops to a predetermined temperature when shifting from the monochrome mode to the color mode. However, it takes 30 seconds or more for the temperature of the endless belt 83 to decrease from 220 ° C. to 205 ° C., and the transition from the monochrome mode to the color mode cannot be performed smoothly, resulting in a waiting time. End up.

  Therefore, in this embodiment, the movement control unit 90c controls the relative positions of the support rollers 81 and 82 with respect to the fixing roller 60 (for example, by mechanically moving the support rollers 81 and 82 from the first position to the second position). The contact area between the belt 83 and the fixing roller 60 is reduced to suppress the heat supply from the external heating device 80 to the fixing roller 60.

  In addition, the movement control unit 90c makes contact between the endless belt 83 and the fixing roller 60 in order to increase the amount of heat supplied from the external heating device 80 to the fixing roller 60 to compensate for the amount of heat lost to the paper during continuous sheet passing. Increase the area.

  Immediately after the start of the image forming operation, the fixing roller 60 is heated and rotated in order to make the temperature distribution in the circumferential direction of the fixing roller 60 uniform, but the sheet P does not pass through the fixing nip portion N. 60 is not deprived of heat by the paper P. If the support rollers 81 and 82 are in the first position in this state, the heat supply from the endless belt 83 to the fixing roller 60 becomes excessive, and the temperature of the fixing roller 60 becomes higher than the set temperature. Therefore, the movement control unit 90c controls the belt moving device 110 in order to change the amount of heat supplied from the external heating device 80 to the fixing roller 60 in a short time in order to avoid excessive supply of heat to the fixing roller 60. Thus, the contact area between the endless belt 83 and the fixing roller 60 is reduced.

  Further, at the time of standby after the image forming operation ends (when left), the movement control unit 90c moves the support rollers 81 and 82 to the second position in order to prevent uneven temperature in the circumferential direction of the fixing roller 60. . That is, the movement control unit 90c moves the support rollers 81 and 82 to the second position after the image forming operation, and the support rollers 81 and 82 according to the timing when the paper P after the image forming operation starts reaches the fixing nip portion. Is moved to the first position.

  The movement control unit 90c controls the belt moving device 100 according to the temperature state of each member, the type of paper P (transfer medium, recording paper), the image forming mode, and the like, and the fixing rollers of the support rollers 81 and 82. The relative position with respect to 60 may be at an arbitrary position between the first position and the second position.

  Next, heat transfer from the support rollers 81 and 82 of the external heating device 80 to the endless belt 83 will be described. 1A to 1C are cross-sectional views including the central axes of the support rollers 81 and 82 of the endless belt 83. FIG. As shown in FIG. 1 (c), in this embodiment, the support roller has an outer diameter of 15 mm at the center, an outer diameter of 14 mm (step difference 0.5 mm), and an inner diameter of 13 mm (center). Part thickness 1 mm). Here, in FIG.1 (c), although the shape of the belt control members 121 * 122 differs from FIG.5 (a), it has the same function. In FIG. 1C, the bearings 117 and 118 have a structure in which the bearings 117 and 118 and the side frame 111 shown in FIG. 5 are integrated.

  FIG. 1A is an enlarged view of a contact portion between the endless belt 83 and the support rollers 81 and 82. As shown in FIG. 1A, boron nitride (thermal conductivity 25 W / m · K) powder particles are disposed on the contact surfaces of the support rollers 81 and 82 and the endless belt 83 as the heat conduction promoting material 100. Has been. FIG. 1B is an enlarged view of the contact portion between the endless belt 83 and the support rollers 81 and 82 in the absence of the heat conduction promoting material.

Here, as the heat conduction promoting material 100, a material having a heat conductivity higher than that of air and an average particle size smaller than the roughness (Rmax) of the support rollers 81 and 82 and the endless belt 83 is desirable. As the heat conduction promoting material 100, alumina (thermal conductivity 29 W / m · K) and silicon carbide (thermal conductivity 46 W / m · K) can be used in addition to boron nitride as described above. High aluminum nitride (thermal conductivity 170 W / m · K) can also be suitably used. In the case of boron nitride, the amount to be added is, the inner peripheral surface of the endless belt 83, or preferably on the surface of the supporting rollers 81 and 82 is ^{0.05mg / cm 2 ~0.3mg / cm 2} .

  In addition, the relationship of thermal conductivity is thermal conduction promotion material 100> support rollers 81 and 82> endless belt 83> air. Further, it is better not to interpose the heat conduction promoting material 100 at a place where the support rollers 81 and 82 and the endless belt 83 are in real contact.

  Further, as the heat conduction promoting material 100, in addition to the above, heat conduction grease or gel in which the powder of the heat conduction promoting material is dispersed in a non-volatile and heat-resistant liquid such as silicon oil can be used. In the case of these heat conductive grease and gel, the space formed by the irregularities of the support rollers 81 and 82 and the endless belt 83 can be filled more than the powder. Heat transfer can be promoted.

  In this way, by arranging boron nitride as the heat conduction promoting material 100 at the contact portion between the endless belt 83 and the support rollers 81 and 82, the unevenness of the surfaces of the support rollers 81 and 82 shown in FIG. 1 and the surface irregularities of the endless belt 83 can be filled with boron nitride powder having high thermal conductivity, as shown in FIG. Here, if the diameter of the powder particles is larger than the surface roughness (Rmax) of the support rollers 81 and 82 and the endless belt 83, the contact between the support rollers 81 and 82 and the endless belt 83 is hindered, so that the heat conduction decreases. Therefore, the surface roughness (Rmax) smaller than the above is preferable. Furthermore, in order to increase the filling rate of the gap between the support rollers 81 and 82 and the endless belt 83 with fine irregularities on the surface, the diameter of the powder particles is set to the surface roughness of the support rollers 81 and 82. Of the surface roughness of the endless belt 83, it is desirable that it is 1/4 or less of the smaller one.

  By disposing the heat conduction promoting material 100 between the support rollers 81 and 82 and the endless belt 83, the space with high heat insulation is filled with the heat conduction promoting material 100, so that the support rollers 81 and 82 are transferred to the endless belt 83. The amount of heat transfer can be improved. By promoting the heat transfer from the support rollers 81 and 82 to the endless belt 83, the temperature difference between the support rollers 81 and 82 and the endless belt 83 during the image forming operation can be reduced. Therefore, the temperature of the endless belt 83 can be prevented from becoming very high due to such heat transfer. For this reason, it is possible to prevent the heat resistance temperature of the release layer 63 having release properties from the toner on the surface of the fixing roller 60 from being exceeded. Therefore, even in the long-term use of the fixing device 40, the release layer 63 can be kept in a good state, and the toner can be fixed always well.

  Here, the length of the endless belt 83 in the axial direction of the support rollers 81 and 82 is 320 mm. The length in the axial direction of the fixing roller 60 that is a non-heating member with which the endless belt abuts (the length of the cylindrical surface on which the fixing nip portion N is formed) is 315 mm. For this reason, as shown in FIG. 5, the width of the endless belt 83 in the axial direction of the support rollers 81 and 82 is larger than the width of the fixing roller 60 in contact in the same direction (axial direction).

  With this configuration, even when the heat conduction promoting material 100 on the contact surface between the support rollers 81 and 82 and the endless belt 83 protrudes from the end of the endless belt 83, the heat conduction promoting material is applied to the fixing roller 60 with which the endless belt 83 abuts. 100 does not adhere. Therefore, the heat conduction promoting material 100 can be prevented from adhering to the fixing nip shape portion N. Thereby, a uniform and high quality image can be stably formed. When the heat conduction promoting material adheres to the 100 fixing nip portion N, scratches and streaks are generated on the surface of the fixing roller 60, and uneven glossiness and streak defects on the surface of the image are caused.

  6A and 6B show the configuration of the contact surface between the inner peripheral surface of the endless belt 83 and the fixing roller 60. FIG. As shown in FIGS. 6A and 6B, at the center of the endless belt 83 in the axial direction of the support rollers 81 and 82, the promotion material regulation that inclines and contacts the downstream side in the rotational direction of the endless belt 83. The member 101 may be provided. The promotion material regulating member 101 may be, for example, a rubber blade made of a silicon rubber sheet having a thickness of 1 mm. The heat conduction promoting member 100 is urged toward the center of the endless belt 83 by the promoting material regulating member 101 inclined in the axial direction. The accelerating material regulating member 101 does not completely dam and scrape the heat transfer accelerating material 100, but a part of the accelerating material regulating member 101 is attached to the center of the endless belt 83 in the axial direction of the support rollers 81 and 82 while passing most of the accelerating material regulating member 101. It is to move.

  The heat conduction promoting member 100 tends to gradually spread in the axial direction of the support rollers 81 and 82 by being pressed at the contact portion between the support rollers 81 and 82 and the endless belt 83. For this reason, during long-term use, the heat conduction promoting member 100 moves outward from the end of the endless belt, and the contact surface between the support rollers 81 and 82 and the endless belt is reduced. The promotion material regulating member 101 is inclined to contact with the downstream side in the rotational direction of the endless belt 83 at the center of the endless belt 83 in the axial direction of the support rollers 81 and 82, so that it is likely to spread to the end portion of the endless belt 83. The heat conduction promoting material 100 is returned toward the center of the endless belt 83. Thereby, the heat conduction promoting material 100 can be uniformly disposed on the contact surface between the support rollers 81 and 82 and the endless belt 83 over a long period of time. Therefore, a uniform and high-quality image can be stably formed.

  The promotion material regulating member 101 is not limited to the above-described configuration, and may be, for example, a metal thin plate such as stainless steel having a thickness of 30 μm, a resin sheet or a brush, and a contact portion is also an inner surface of the endless belt 83. Instead, it may be the outer peripheral surface of the support rollers 81 and 82.

  As shown in FIG. 7A, it is desirable that the surface of the aluminum support rollers 81 and 82 be subjected to a roughening treatment by sandblasting so that Ra is, for example, 0.8 μm (Rmax; 6 μm). On the other hand, the surface roughness of the inner peripheral surface of the endless belt 83 made of polyimide is Ra 0.2 μm. The surfaces of the support rollers 81 and 82 are harder than the inner peripheral surface of the endless belt 83 made of polyimide, the surface is rough, and sharp irregularities are formed as schematically shown in FIG.

  With such a configuration, since the surfaces of the support rollers 81 and 82 are harder and rougher than the inner peripheral surface of the endless belt 83, as shown schematically in FIG. At the contact surface with the endless belt 83, the minute protrusions on the surfaces of the support rollers 81 and 82 bite into the inner peripheral surface of the endless belt 83. Thereby, the real contact area of the support rollers 81 and 82 and the endless belt 83 can be increased. By increasing the real contact area of the heat transfer surface, the amount of heat transfer from the support rollers 81 and 82 to the endless belt 83 can be improved. Therefore, in this case, the surfaces of the support rollers 81 and 82 subjected to the roughening function function as heat transfer means. When the support rollers 81 and 82 are roughened, they may or may not have the heat conduction promoting member 100.

  Further, when the heat transfer promoting material 100 is present on the contact surface between the support rollers 81 and 82 and the endless belt 83, the heat transfer promoting material 100 may cause a lubricating action, and the support rollers 81 and 82 and the endless belt 83 may slip. is there. In this case, the area of the transmission surface of the support rollers 81 and 82 is smaller than the area of the heat receiving surface of the endless belt 83, and heat transfer from the support rollers 81 and 82 to the endless belt 83 is reduced. Therefore, as shown in FIG. 7C, the surface of the support rollers 81 and 82 is roughened to prevent slipping between the support rollers 81 and 82 and the endless belt 83. Therefore, it is possible to prevent a decrease in heat transfer from the support rollers 81 and 82 to the endless belt 83, and to improve the amount of heat transfer from the support rollers 81 and 82 to the endless belt 83.

  Alternatively, both of the support rollers 81 and 82 may be brought into pressure contact with the fixing roller 60 as a member to be heated through the endless belt 83 under the contact condition of the endless belt 83. In this embodiment, the contact is made with a pressing force of 20N. For this reason, the contact pressure of the pressure contact portion between the support rollers 81 and 82 and the endless belt 83 is increased. As a result, as shown in FIGS. 7B and 7D, the hard support rollers 81 and 82 bite into the endless belt 83 and the soft endless belt 83 is deformed, so that the support rollers 81 and 82 and the endless belt 83 Real contact area increases. 7A and 7C show a situation where the pressing force is small and the real contact area is small.

  Here, if the width of the fixing roller 60 is 32 cm and the pressing force (contact force) is 20 N, a force of 0.625 N per cm is applied. In the present embodiment, since there are two support rollers, 0.313 N per support roller, which is in contact with the fixing roller 60 via the endless belt 83. The contact force with which the support rollers 81 and 82 contact the fixing roller 60 via the endless belt 83 is preferably 0.2 to 1 N per cm for each support roller. Since the contact area between the support rollers 81 and 82 cannot be measured accurately, the contact force is defined by dividing the pressing force by the length in the width direction as the linear pressure.

  Further, since the fixing roller 60 enters the inner side of the outer common tangent line between the support rollers 81 and 82 for suspending the endless belt 83, tension is generated in the endless belt 83, and the endless belt 83 and the support rollers 81 and 82. The pressure on the contact surface increases. By increasing the pressure at the contact surface between the support rollers 81 and 82 and the endless belt 83, the real contact area can be increased. If the real contact area of the heat transfer surface is increased, the amount of heat transfer from the support rollers 81 and 82 to the endless belt can be improved.

  Here, the force with which the support rollers 81 and 82 are pressed against the fixing roller 60 via the endless belt 83 is preferably in the range of 5N to 100N. If it is less than 5N, the heat conduction to the fixing roller 60 is insufficient, and the temperature rise of the endless belt 83 during an emergency stop increases. On the other hand, when the pressure contact force exceeds 100 N, the shift force of the endless belt 83 becomes large, and the contact force to the shift regulation member becomes excessive. For this reason, the end portion of the endless belt 83 is deformed or damaged during continuous use.

  7C, even when the contact pressure between the support rollers 81 and 82 and the endless belt 83 is low, the heat conduction can be promoted by the heat conduction promoting member 100.

  Here, the fixing device 40 is stopped at the time of heat insulation standby, and the fixing roller 60 is heated by the halogen lamp 64 in the fixing roller 60, and the support roller and the endless belt 83 are heated and held by the halogen lamps 86a and 86b in the support rollers 81 and 82. . During operation, the endless belt 83 and the support rollers 81 and 82 are rotated by the rotation of the fixing roller 60. For example, the fixing roller 60 is maintained at a constant temperature of 170 ° C. and the support rollers 81 and 82 are maintained at a constant temperature of 190 ° C., for example, and the endless belt 83 is set at 220 ° C. and the fixing roller 60 is set at 185 ° C., for example. When the temperature rises from the warming standby state to the image forming operation state, the fixing roller 60 rotates and the endless belt 83 also rotates.

  With this configuration, the endless belt 83 can be uniformly heated in the circumferential direction by rotating the endless belt 83 during heating and heating. Even if the endless belt 83 is not heated during standby, the endless belt 83 is thin and has a small heat capacity. Therefore, if only the support rollers 81 and 82 are kept warm, the temperature can be raised to a predetermined temperature in a short time.

  By stopping at the time of standby heat retention, power for rotating the fixing device 40 becomes unnecessary, and power saving and low noise can be realized. Furthermore, since the endless belt 83 is not heated at the time of stopping, heat dissipation from the end of the endless belt 83 can be suppressed, so that a temperature drop at the ends of the support rollers 81 and 82 can be prevented.

  Since there is no heat loss due to paper passing during standby, the heat retaining heating power of the fixing device 40 is reduced. Therefore, the temperature at the end of the endless belt 83 decreases due to heat conduction and heat dissipation from the end of the endless belt 83. For this reason, if the endless belt 83 is kept at the operating temperature, image formation is started while the temperature at the end of the endless belt 83 is lowered, and the first image has an image quality with uneven fixing. The image becomes low.

  In view of this, the temperature at the standby temperature is lower than the temperature at the time of the image forming operation, and by raising the temperature to a predetermined operating temperature at the start of the operation, a large amount of heat can be supplied uniformly in the width direction. As a result, the temperature at the center of the endless belt 83 rises, the temperature at the end of the endless belt 83 rises greatly to eliminate the temperature drop at the end, and the endless belt 83 in the axial direction of the support rollers 81 and 82 The temperature distribution can be made uniform.

  In the present embodiment, two support rollers 81 and 82 are provided, the outer diameters of the support rollers 81 and 82 are the same, and a halogen lamp (heating element) is provided inside the support rollers 81 and 82. Although the configuration provided with 86a and 86b has been described, the present invention is not limited to this, and the present invention can be applied to any type of external belt heating type fixing device. For example, three or more support rollers may be provided. Moreover, the outer diameter of each support roller may be different. Furthermore, a support roller that does not include a heating element may be included. Further, the heating element may be provided at a position different from the inside of each support roller. In addition, any support roller (belt suspension roller) may not be brought into pressure contact with the fixing roller 60 during the fixing operation, and only the endless belt 83 may be in contact with the fixing roller 60.

(Example)
With respect to the fixing device 40 having the configuration described in the first embodiment, the temperature change of each member when the emergency stop was performed from the continuous paper passing state was measured.

In this example, 0.2 mg / cm ^{2 of} heat conduction grease was used as the heat conduction promoting material 100. Further, Ra of the endless belt 83 was 0.5 μm, and Ra of the support rollers 81 and 82 was 0.3 μm. The pressure applied from the support rollers 81 and 82 to the fixing roller 60 via the endless belt 83 was set to 2 kgf (total of two support rollers).

  In addition, as a comparative example, all the conditions were the same, and the measurement was performed for the case where no heat conduction promoting material was used.

  The result of the measurement is schematically shown in FIG. In FIG. 8, temperature ripples and the like due to on / off control of the heating lamp are omitted. In the case of the present embodiment represented by the broken line in FIG. 8, it is possible to suppress an increase in temperature at an emergency time. On the other hand, in the case of the comparative example without the heat conduction promoter material represented by the solid line in FIG. 8, the temperature between the support rollers 81 and 82 and the endless belt 83 increases during continuous operation, and the endless belt during an emergency stop. It can be seen that the temperature of 83 increases rapidly.

[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 as those in the first embodiment, and the description thereof is omitted.

  The present embodiment is different from the first embodiment in that the external heating device 80 for heating the peripheral surface of the fixing roller 60 is not provided, but the external heating device for heating the peripheral surface of the pressure roller 70 is provided. That is, the fixing device according to the present embodiment is in contact with the peripheral surface of the pressure roller 70 that contacts the back surface of the paper P (the surface on which the unfixed image is not formed) in the fixing nip portion N. An external heating device for heating the peripheral surface of 70 is provided.

  FIGS. 9A and 9B are explanatory views showing the configuration of the pressure roller 70 and the external heating device 130 that heats the peripheral surface of the pressure roller 70. 9A shows a case where the second support roller 132 provided in the external heating device 130 is in a first position which will be described later, and FIG. 9B shows a case where the second support roller 132 is in a second position which will be described later. Is shown.

  As shown in these drawings, the external heating device 130 includes a first support roller 131, a second support roller (heating roller) 132, an endless belt 133, and a belt moving device 140. In the following description, when the first support roller and the second support roller are not distinguished, they are simply referred to as support rollers.

  The endless belt 133 is stretched around the support rollers 131 and 132 so that the back side of the endless belt 133 is in contact with the peripheral surfaces of the support rollers 131 and 132. The endless belt 133 is provided on the upstream side in the rotation direction of the pressure roller 70 with respect to the fixing nip portion. When the second support roller 132 is in a first position described later, a predetermined pressing force (in this embodiment, 40N) and is pressed against the pressure roller 70. Thereby, a heating nip portion (a contact portion between the endless belt 133 and the pressure roller 70) is formed between the pressure roller 70 and the heating nip portion. In the present embodiment, the nip width (the width along the circumferential direction of the pressure roller 70) of the heating nib portion is 20 mm.

  Further, the endless belt 133 is driven to rotate by the pressure roller 70 by contacting the circumferential surface of the pressure roller 70 that rotates. As a result, the support rollers 131 and 132 rotate in the direction opposite to the rotation direction of the pressure roller 70. That is, when the control device 90 controls the rotation driving device 91 of the fixing roller 60 to drive the fixing roller 60 to rotate, the pressure roller 70 is driven to rotate by the fixing roller 60. Then, the endless belt 133 is moved following the pressure roller 70 by the frictional force at the portion where the endless belt 133 and the pressure roller 70 are in contact with each other, so that the support rollers 131 and 132 and the endless belt 133 rotate. It has become.

  The endless belt 133 and the support rollers 131 and 132 are the same as the endless belt 83 and the support rollers 81 and 82 provided in the external heating device 80 of the first embodiment. However, the first support roller 131 is not provided with a halogen lamp, and the second support roller 132 is provided with a halogen lamp. A temperature detecting means (not shown) is provided on the outer peripheral surface of the endless belt 133 in contact with the second support roller 132. Based on the detection result of the temperature detecting means, the control device 90 performs a first operation. (2) The power supply amount to the halogen lamp provided inside the support roller 132, the movement positions of the support rollers 131 and 132 by the belt moving device 140, and the like are controlled.

  Further, in the present embodiment, the support rollers 131 and 132 are made of aluminum, and the surface is roughened by sandblasting to Ra of 0.8 μm (Rmax; 6 μm). On the other hand, the endless belt 133 is made of polyimide, and the surface roughness of the inner peripheral surface is Ra 0.2 μm. For this reason, the surfaces of the support rollers 131 and 132 are harder than the inner peripheral surface of the polyimide belt, the surface is rough, and sharp irregularities are formed as schematically shown in FIG.

  Since the surfaces of the support rollers 131 and 132 are harder and rougher than the inner peripheral surface of the endless belt 133, minute protrusions on the surfaces of the support rollers 131 and 132 are formed on the inner periphery of the endless belt 133 at the contact surface between the support rollers 131 and 132 and the endless belt 133. Cut into the surface. Thereby, the real contact area of the support roller 131.132 and the endless belt 133 can be increased. By increasing the real contact area of the heat transfer surface, the amount of heat transfer from the support rollers 131 and 132 to the endless belt 133 can be improved. In the second embodiment, boron nitride is not added to the contact surface between the support rollers 81 and 82 and the endless belt 83.

  Here, when the support rollers 131 and 132 and the endless belt 133 slide, the area of the transmission surface of the support rollers 131 and 132 becomes smaller than the area of the heat receiving surface of the endless belt 133, and the endless belt 131 Heat transfer to the belt 133 is reduced. Therefore, the surface of the support rollers 131 and 132 is roughened to prevent slipping between the support rollers 131 and 132 and the endless belt 133. Therefore, it is possible to prevent a decrease in heat transfer from the support rollers 131 and 132 to the endless belt 133, and to improve the amount of heat transfer from the support rollers 131 and 132 to the endless belt 133.

  The support rollers 131 and 132 are pressed by the belt moving device 140 to the peripheral surface of the pressure roller 70 via the endless belt 133 with a predetermined load. As a result, the surface of the endless belt 133 contacts the circumferential surface of the pressure roller 70, and a nip portion (heating nip portion n) is formed between the surface of the endless belt 133 and the circumferential surface of the pressure roller 70. The heating nip width between the surface of the endless belt 133 and the circumferential surface of the pressure roller 70 (width along the circumferential direction of the pressure roller 70) is 20 mm.

  The belt moving device 140 includes a side frame 141, an arm 142, an eccentric cam 143, a coil spring 144, and a fulcrum (fulcrum member) 145.

  The side frames 141 are provided on both ends of the support rollers 131 and 132, respectively, and support the support rollers 131 and 132 rotatably via bearings (not shown). In addition, this bearing may be fixed in the distance between shafts similarly to the bearings 117 and 118 provided in the external heating device 80 of the first embodiment, and the distance between the shafts may be variable.

  Further, the side frame 141 is fixed to the arm 142. Furthermore, the arm 142 is pivotally supported at a fulcrum 145 with respect to a frame (not shown) of the fixing device according to the present embodiment so as to be rotatable in a direction substantially perpendicular to the axial direction of the support rollers 131 and 132. . The fulcrum 145 is provided at a position that coincides with the rotation axis of the first support roller 131. Therefore, even if the arm 142 is rotated around the fulcrum 145, the position of the first support roller 131 (the distance between the axes of the first support roller 131 and the pressure roller 70) does not change. Here, the distance between the shafts of the first support roller 131 and the pressure roller 70 is set so that both rollers come into pressure contact with each other with a predetermined pressure via the endless belt 133. A coil spring 144 is attached to a position of the arm 142 opposite to the fulcrum 145 across the second support roller 132, and the side frame 141 attached to the arm 142 by the coil spring 144 is attached to the pressure roller 70. Is biased in the direction.

  The eccentric cam 143 is provided in contact with the vicinity of the end of the arm 142. The eccentric cam 143 is rotationally driven by the control device 90 controlling driving means such as a motor (not shown). As a result, the control device 90 controls the driving means to rotate the eccentric cam 143 and move the second support roller 132 to the first position as shown in FIG. Pressing against the pressure roller 70 or rotating the eccentric cam 143 180 degrees therefrom, and moving the second support roller 132 to the second position as shown in FIG. 9B, pressurizes the second support roller 132. It can be separated from the roller 70. Even in the second position, the first support roller 131 is in pressure contact with the pressure roller 70.

  A belt between the support rollers 131 and 132 and the bearings provided at both ends of the support rollers 131 and 132 is the same as the belt regulating members 121 and 122 provided in the external heating device 80 in the first embodiment. A regulating member (not shown) is provided. That is, the height from the peripheral surface of the support rollers 131 and 132 is higher at both axial ends of the support rollers 131 and 132 than the distance between the support rollers 131 and 132 and the pressure roller 70 at the second position. A belt regulating member is provided.

  As described above, in the present embodiment, of the two support rollers 131 and 132, only the second support roller 132 is provided with the halogen lamp, and the belt support device 140 is provided with the halogen lamp. The roller 132 can be brought into contact with or separated from the pressure roller 70 via the endless belt 133.

  Thereby, the movement control part 90c with which the control apparatus 90 was equipped can control the heat supply amount to the pressure roller 70 by changing the position (relative position with respect to the pressure roller 70) of the 2nd support roller 132. FIG. For example, by setting the position of the second support roller 132 to the second position, the surface temperature of the pressure roller 70 can be quickly lowered, and temperature unevenness on the surface of the pressure roller 70 can be reduced. .

  For example, when the movement control unit 90c continuously performs the printing operation on a small number of sheets P of about 1 to 5 sheets, the position of the second support roller 132 is set to the second position. Also good. Thereby, excessive temperature rise of the pressure roller 70 can be prevented, and problems such as deterioration of image quality can be prevented.

  That is, when a printing operation is performed on a small number of sheets P, the ratio of the time during which the sheet P actually passes through the fixing nip is short in the period from the start of the image forming operation to the completion of paper discharge. . For this reason, the temperature of the pressure roller 70 that rotates in pressure contact with the high-temperature fixing roller 60 tends to increase. In this situation, when the external heating device 130 is in contact with the pressure roller 70 with a wide contact area (when the first support roller 131 is set to the first position), the temperature of the pressure roller 70 is fixed. It will rise above the set temperature during operation (for example, it will rise to about 160 ° C.). If such an excessive temperature rise occurs, the glossiness of the image becomes too high, or a fine hot offset occurs, resulting in a reduction in image quality. In particular, in the case of double-sided printing in which a toner image is formed on the first side of the paper P and then the second image is formed on the second side of the back side, the first printed first surface is pressed when the second side is fixed. Contact the roller 70. At this time, if the temperature of the pressure roller 70 is too high, the glossiness of the image on the first surface becomes too high, resulting in a glaring impression, and the image quality is lowered.

  Therefore, the movement control unit 90c increases the contact area between the endless belt 133 and the pressure roller 70 with the second support roller 132 as the first position when, for example, six or more sheets are continuously passed, and when forming images of five or less sheets. By moving the second support roller 132 to the second position, it is possible to prevent the temperature increase of the pressure roller 70 and to prevent the image quality from deteriorating.

  Further, the movement control unit 90c may move the second support roller 132 to the second position during double-sided printing. At the time of fixing on the second surface during double-sided printing, the temperature of the paper P is high due to the fixing process on the first surface. For this reason, the amount of heat transferred from the pressure roller 70 to the paper P during the fixing process to the second surface is smaller than that during the fixing process to the first surface. Therefore, by moving the second support roller 132 to the second position at the time of double-sided printing, the contact area between the endless belt 133 and the pressure roller 70 can be reduced, and an excessive temperature rise of the pressure roller 70 can be prevented. .

  Further, since only the second support roller 132 out of the two support rollers 131 and 132 is separated, the moving distance of the arm 142 can be reduced, the fixing device can be downsized, and the belt moving device (separating mechanism). 110 power saving can be achieved.

  Further, since the first support roller 131 is always in pressure contact with the pressure roller 70 with a predetermined pressure, the endless belt 133 can be reliably rotated by the pressure roller 70 regardless of the position of the arm 142.

  Further, since the first support roller 131 is always in pressure contact with the pressure roller 70 regardless of the position of the arm 142, both ends of the first support roller 131 can be obtained even when the second support roller 132 is moved to the second position. It is possible to prevent the belt regulating member provided on the side from moving to a position where the belt regulating member contacts the peripheral surface of the pressure roller 70.

  The belt regulating member is not necessarily provided corresponding to both of the two support rollers 131 and 132. However, when a belt restricting member is provided on both ends of the second support roller 132, the height of the belt restricting member from the surface of the second support roller 132 is set to the pressure roller 70 and the second support roller 132 at the second position. It is preferable to make it higher than the interval. Thereby, it is possible to reliably prevent the belt regulating member from moving to a position where it is in contact with the peripheral surface of the pressure roller 70.

  In each of the above embodiments, the fixing roller 60 (the roller that contacts the surface of the paper P where the unfixed toner image is formed in the fixing nip portion N) or the pressure roller 70 (the unfixed toner on the paper P in the fixing nip portion). The configuration in which the external heating device is provided on either one of the rollers (abutting the surface on which no image is formed) has been described, but an external heating device may be provided on each of the fixing roller 60 and the pressure roller 70. When an external heating device is provided for each of the fixing roller 60 and the pressure roller 70, the surface temperatures of both the fixing roller 60 and the pressure roller 70 can be accurately controlled during continuous paper feeding and standby. As a result, high-quality images can be stably obtained, and at the same time, high throughput can be obtained continuously.

  Further, the external heating device 80 of the first embodiment may be used instead of the external heating device 130 of the second embodiment, and the external heating device 130 of the second embodiment may be used instead of the external heating device 80 of the first embodiment. Good.

  In this embodiment, the image forming apparatus that transports paper using the transport belt has been described. However, the configuration of the image forming apparatus is not limited to this. The present invention can be applied to any electrophotographic image forming apparatus. For example, an intermediate transfer belt may be used, or a structure in which the image is transferred from the photosensitive member to the paper P may be used. Further, it may be a single color image or a multicolor image.

  In each of the above embodiments, the control device 90 is configured from the control integrated circuit board. However, the present invention is not limited to this, and the function of each control unit provided in the control device 90 using a processor such as a CPU. May be realized by software. In this case, for example, the control device 90 includes a CPU (central processing unit) that executes instructions of a control program that realizes each function, a ROM (read only memory) that stores the program, and a RAM (random access) that expands the program. memory), a storage device (recording medium) such as a memory for storing the program and various data. An object of the present invention is to provide a recording medium in which a program code (execution format program, intermediate code program, source program) of a control program of the control device 90, which is software that realizes the functions described above, is recorded so as to be readable by a computer. The program is supplied to the control device 90, and the computer (or CPU or MPU) reads and executes the program code recorded on the recording medium.

  Examples of the recording medium include tapes such as magnetic tapes and cassette tapes, magnetic disks such as floppy (registered trademark) disks / hard disks, and disks including optical disks such as CD-ROM / MO / MD / DVD / CD-R. Card system such as IC card, IC card (including memory card) / optical card, or semiconductor memory system such as mask ROM / EPROM / EEPROM / flash ROM.

  The control device may be configured to be connectable to a communication network, and the program code may be supplied via the communication network. This communication network is not particularly limited. For example, the Internet, intranet, extranet, LAN, ISDN, VAN, CATV communication network, virtual private network, telephone line network, mobile communication network, A satellite communication network or the like can be used. Further, the transmission medium constituting the communication network is not particularly limited. For example, even in the case of wired such as IEEE 1394, USB, power line carrier, cable TV line, telephone line, ADSL line, infrared rays such as IrDA and remote control, It is also possible to use wireless such as Bluetooth (registered trademark), 802.11 wireless, HDR, mobile phone network, satellite line, terrestrial digital network. The present invention can also be realized in the form of a computer data signal (data signal sequence) embedded in a carrier wave in which the program code is embodied by electronic transmission.

  In each of the above embodiments, a roller-shaped fixing member (fixing roller) and a pressure member (pressure roller) are used. However, the present invention is not limited to this. For example, a belt-shaped member may be used. .

  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 the respective technical means disclosed in the above-described embodiments. The form is also included in the technical scope of the present invention.

  The present invention can be applied to a fixing device provided in an electrophotographic image forming apparatus such as a printer, a copier, a facsimile machine, and an MFP (Multi Function Printer), and also to the image forming apparatus.

(A) is an enlarged view between the support roller and the endless belt when the heat conduction promoting material is disposed between the support roller and the endless belt of the fixing device according to the embodiment of the present invention. ) Is an enlarged view between the support roller and the endless belt when the heat conduction promoting material is not disposed, and (c) is a cross-sectional view near the end of the support roller of the fixing device according to the embodiment of the present invention. is there. 1 is an explanatory diagram illustrating a configuration of an image forming apparatus including a fixing device according to an embodiment of the present invention. 1 is an explanatory diagram illustrating a configuration of a fixing device according to an embodiment of the present invention. FIG. 4A and 4B are explanatory views showing a fixing device according to an embodiment of the present invention, in which FIG. 5A shows a state in which the support roller is arranged at the first position, and FIG. 5B shows a state in which the support roller is arranged at the second position. . (A) is a top view showing a configuration of a belt moving device provided in a fixing device according to an embodiment of the present invention, and (b) is a sectional view thereof. (A), (b) is a figure which shows the structure of the contact surface of an endless belt inner peripheral surface and the fixing roller 60. FIG. (A)-(d) is an enlarged view between the surface-treated support roller and the endless belt, and FIGS. (A) and (c) show a small pressing force between the support roller and the endless belt. When the contact area is small, (b) and (d) are diagrams when the pressing force between the support roller and the endless belt is large and the true contact area is large. It is a figure which shows the measurement result about the temperature change of a support roller and an endless belt at the time of emergency stop from a continuous paper passing state. 4A and 4B are explanatory diagrams illustrating a configuration of a fixing device according to another embodiment of the present invention, in which FIG. 5A illustrates a case where the support roller is disposed at the first position, and FIG. 5B illustrates a case where the support roller is disposed at the second position. Show.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 40 Fixing apparatus 60 Fixing roller (member to be heated)
62 Elastic layer 64/74 / 86a / 86b Halogen lamp 65/75 / 85a / 85b Thermistor 70 Pressure roller (heated member)
72 Elastic layer 80 External heating device 81 First support roller (support roller)
82 Second support roller (support roller)
83 Endless belt (belt)
90 controller 90a temperature controller (temperature control means)
90b Rotation control unit (rotation control means)
90c Movement control unit 91 Rotation driving device 99 Heating power supply unit 110 Belt moving device (moving means)
121/122 Position regulating member (regulating member)
130 External heating device 131 First support roller (support roller)
132 Second support roller (support roller)
133 Endless belt (belt)
140 Belt moving device (moving means)

Claims (8)

At least one of the fixing member and the pressure member that is a member to be heated by heating a fixing belt, a pressure member, and a heating belt that is rotatably stretched on a plurality of support rollers, at least one of which has a heating source therein. An external heating device that heats the member to be heated by being brought into contact with one peripheral surface, and the fixing member and the pressure member are transported while sandwiching the recording material to determine the position on the recording material. In a fixing device for fixing a received image to the recording material,
A fixing device comprising a heat transfer promoting means for promoting heat transfer from the support roller to the heating belt on a contact surface between the support roller and the heating belt.   The fixing device according to claim 1, wherein the heat transfer promoting means is a heat conduction promoting material disposed on a contact surface between the support roller and the heating belt.   The heat conduction promoting material is a powder, and an average particle diameter thereof is one quarter or less of the smaller one of the surface roughness of the support roller and the surface roughness of the heating belt. The fixing device according to claim 2.   4. The fixing device according to claim 2, wherein a width of the heating belt in an axial direction of the support roller is larger than a width of the member to be heated in the same direction.   5. The acceleration material regulating member for moving the heat conduction promoting material from the end of the heating belt toward the center of the heating belt in the axial direction of the support roller. 6. The fixing device according to Item 1. The outermost surface layer of the support roller is harder than the inner peripheral surface of the heating belt, and has a larger surface roughness than the inner peripheral surface of the heating belt,
The fixing device according to claim 1, wherein an outermost layer of the support roller functions as the heat transfer promoting unit.   The fixing device according to claim 6, further comprising a pressing unit that presses at least one of the support rollers against a peripheral surface of the member to be heated via the heating belt.   An image forming apparatus comprising the fixing device according to claim 1.

Images