JP2008197576A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an external heating type fixing device capable of stably operating support rollers and to provide an image forming apparatus provided with the fixing device. <P>SOLUTION: The fixing device 10 is provided with an external heating member 29, and two support rollers 33a and 33b provided on the external heating member 29 are configured so that the rotational torque T1 of the support roller 33a on the upstream side in the rotational direction of a fixing roller 25 is smaller than the rotational torque T2 of the support roller 33b on the downstream side in the rotational direction of the fixing roller 25, in the two support rollers 33a and 33b. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

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

  Generally, a heat roller fixing method is used as a fixing device used in an electrophotographic image forming apparatus such as a conventional copying machine and printer. The heat roller fixing system includes a pair of rollers that are in pressure contact with each other, specifically, a fixing roller and a pressure roller, and a roller by heating means including a halogen heater or the like disposed in both or one of the roller pairs. The pair is heated to a predetermined fixing temperature. When the recording paper on which the unfixed toner image is formed passes through the pressure contact portion, so-called fixing nip portion, while the roller pair is heated, the toner image is fixed on the recording paper by heat and pressure.

  In particular, in a color fixing device, an elastic roller in which an elastic layer made of silicon rubber or the like is provided on the surface layer of the fixing roller is used. By using an elastic roller as the fixing roller, the surface of the fixing roller is elastically deformed according to the unevenness of the unfixed toner image and comes into contact with the toner image so as to cover the toner image. It is possible to perform heat fixing on an unfixed toner image satisfactorily. As another effect, it is possible to improve the releasability of the color toner that is more likely to be offset than monochrome because of the effect of releasing the distortion of the elastic layer at the fixing nip portion. Furthermore, since the nip shape of the fixing nip is convex outward in the radial direction, in other words, a reverse nip shape, the paper peeling performance is improved, and the paper can be peeled without using a peeling means such as a peeling claw. (Self-strip) and image defects caused by the peeling means can be eliminated.

  However, the fixing roller provided with the elastic layer has a very low thermal conductivity of the elastic layer itself. Therefore, when a heating means is provided inside the fixing roller, the heat transfer efficiency is lowered and the warm-up time is increased. When the speed of the fixing roller is increased, there is a problem that the temperature of the fixing roller does not follow the fixing temperature.

  As a conventional fixing device that solves such a problem, an external heating fixing method is known in which an external heating means is brought into contact with the surface of the fixing roller and the fixing roller is heated from the outside. An external belt heat fixing method using a belt has been proposed. The external heating means of the external belt heating and fixing system includes a driving roller for driving the belt, a belt supporting roller having a heating means inside, and a belt wound between the driving roller and the belt supporting roller. . On the outer peripheral surface of the drive roller, anti-slip means capable of transmitting the driving force without substantially slipping is disposed in a region having a circumferential length that does not temporarily contact during rotation. Examples of the anti-slip means include heat-resistant synthetic rubbers such as silicon rubber and fluororubber, ceramic powder, and metal powder having a higher friction coefficient than that of other regions on the outer peripheral surface of the drive roller. As a result, a required driving force of the driving roller with respect to the belt is secured, and the belt is held at a predetermined axial position (see, for example, Patent Document 1).

JP 2006-11111 A

  In the above-described fixing device of the external belt heating system, a gear is integrally disposed on the driving roller, is engaged with the gear of the fixing roller, and is driven to rotate by the gear. Accordingly, there is a problem that the configuration is complicated, the gear becomes a rotational resistance, and the fixing roller cannot be rotated smoothly. Further, there is no driving means on the belt support roller side, and there is a possibility of slipping because it is configured to follow and rotate with the rotation of the belt, and in the case of slipping, there is a problem that the heating performance of the belt decreases.

  FIG. 5 is an enlarged front view showing a configuration related to the external heating belt 2 provided in the conventional fixing device 1. When the diameters of the support rollers 3a and 3b constituting the external heating belt 2 are made the same, and the external heating belt 2 is in contact with the fixing roller 4 and driven to rotate, as shown by the phantom line in FIG. A phenomenon that the support roller 3a on the upstream side in the rotational direction 4 slips with respect to the external heating belt 2 is observed. This is considered to be due to the occurrence of sagging due to thermal expansion of the heated external heating belt. When sagging occurs, the frictional force between the support roller and the belt decreases, so that the belt slips. When slip occurs on the support roller in this way, heat is transferred to the belt where it is in contact with the belt, but only heat is dissipated into the air where it is not in contact with the belt. At the same time, the heating performance with respect to the belt decreases, which is not preferable.

  Accordingly, an object of the present invention is to provide an external belt heating type fixing device capable of operating a support roller stably without a driving unit, and an image forming apparatus including the fixing device.

The present invention provides a fixing member that is supported so that the outer peripheral surface can circulate, a pressure unit that presses and circulates the outer peripheral surface of the fixing member, and at least one of the outer peripheral surface of the fixing member and the outer peripheral surface of the pressure member. And an external heating member that contacts and heats the recording material. When a recording material carrying a toner image is conveyed to the pressure contact portion between the fixing member and the pressurizing unit, the toner image is thermally melted on the recording material. A fixing device that is worn and fixed,
The external heating member is
A plurality of support rollers;
A heating source provided in at least one of the plurality of support rollers;
A belt stretched rotatably around the plurality of support rollers,
Among the plurality of support rollers, each support roller is configured such that the rotation torque of the upstream support roller is smaller than the rotation torque of the downstream support roller with respect to the rotation direction of the fixing member. And a fixing device.

In the present invention, the external heating member further includes a bearing that supports the plurality of support rollers,
With respect to the rotation direction of the fixing member, the bearing of the upstream support roller is a ball bearing, and the bearing of the downstream support roller is a sliding bearing.

Furthermore, the present invention provides a fixing member that is supported so that the outer peripheral surface can circulate, a pressure unit that presses and circulates the outer peripheral surface of the fixing member, and at least one of the outer peripheral surface of the fixing member and the outer peripheral surface of the pressure member. An external heating member that contacts and heats any one of them, and heats the toner image on the recording material when the recording material carrying the toner image is conveyed to the pressure contact portion between the fixing member and the pressure unit. A fixing device for fusing and fixing,
The external heating member is
A plurality of support rollers;
A heating source provided in at least one of the plurality of support rollers;
A belt stretched rotatably around the plurality of support rollers,
Among the plurality of support rollers, each support roller is configured such that the friction coefficient of the outer peripheral surface of the upstream support roller is larger than the friction coefficient of the outer peripheral surface of the downstream support roller with respect to the rotation direction of the fixing member. The fixing device is characterized by the above.

Further, in the present invention, a rubber coat is applied to the upstream support roller with respect to the rotation direction of the fixing member,
The support roller on the downstream side is provided with a fluororesin coat.

  Further, according to the present invention, the friction coefficient of the outer peripheral surface of the upstream support roller is larger than the friction coefficient of the outer peripheral surface of the downstream support roller with respect to the rotation direction of the fixing member. Each support roller is constituted.

Further, the present invention is characterized in that the external heating member further includes a belt deviation regulating member that regulates relative displacement of the supporting roller and the belt on the downstream side with respect to the rotation direction of the fixing member in the axial direction of the supporting roller. And
Furthermore, the present invention is an image forming apparatus including the fixing device.

  According to the present invention, the external heating member includes a plurality of support rollers, a heating source, and a belt. Since the heat source is provided in at least one of the plurality of support rollers, the support roller can be heated. Since the belt is rotatably stretched around the plurality of support rollers, the belt is heated by the support roller having a heating source. The heated belt can heat the member to be heated by bringing it into contact with at least one of the outer peripheral surface of the fixing member and the outer peripheral surface of the pressure member as the heated member. In addition, among the plurality of support rollers provided in the external heating unit, each support roller is configured such that the rotational torque of the upstream support roller is smaller than the rotational torque of the downstream support roller with respect to the rotation direction of the fixing member. Is done. As a result, it is easy for the belt to sag and the upstream support roller, which is likely to slip, can easily rotate, thereby preventing the support roller from slipping. Accordingly, it is possible to prevent a decrease in heating performance due to slip between the belt and the support roller.

  According to the present invention, a ball bearing is used for the upstream support roller with respect to the rotation direction of the fixing member, and a sliding bearing is used for the downstream support roller. Each support roller is configured such that the rotational torque of the side support roller is reduced. As a result, it is easy for the belt to sag and the upstream support roller, which is likely to slip, can easily rotate, thereby preventing the support roller from slipping. Accordingly, it is possible to prevent a decrease in heating performance due to slip between the belt and the support roller.

  Furthermore, according to the present invention, the external heating member includes a plurality of support rollers, a heat source, and a belt. Since the heat source is provided in at least one of the plurality of support rollers, the support roller can be heated. Since the belt is rotatably stretched around the plurality of support rollers, the belt is heated by the support roller including a heating source. The heated member can be heated by bringing the heated belt into contact with the heated member. Further, among the plurality of support rollers provided in the external heating member, the friction coefficient of the outer peripheral surface of the upstream support roller is larger than the friction coefficient of the outer peripheral surface of the downstream support roller with respect to the rotation direction of the fixing member. Each support roller is configured. As a result, the deflection of the belt can be reduced, and the upstream support roller can be rotated by the frictional force even if the belt is somewhat bent. Accordingly, it is possible to prevent a decrease in heating performance due to slip between the belt and the support roller.

  Further, according to the present invention, with respect to the rotation direction of the fixing member, the support roller on the upstream side is provided with a rubber coat, and the support roller on the downstream side is provided with a fluororesin coat. Since the fluororesin coat has a smaller friction coefficient than the rubber coat, the friction coefficient of the outer peripheral surface of the upstream support roller can be made larger than the friction coefficient of the outer peripheral surface of the downstream support roller. As a result, it is possible to reliably prevent the belt from sagging and slipping upstream as described above.

  Further, according to the present invention, among the plurality of support rollers provided in the external heating member, the friction of the outer peripheral surface of the upstream support roller is determined by the friction coefficient of the outer peripheral surface of the downstream support roller with respect to the rotation direction of the fixing member. Each support roller is configured to have a large coefficient. As a result, the effect based on the magnitude relationship between the rotational torques of the support rollers can be further increased by the effect based on the magnitude relationship between the friction coefficients. Accordingly, it is possible to reliably prevent the belt from sagging and slipping on the upstream side.

  Furthermore, according to the present invention, the external heating member further includes a belt deviation regulating member that regulates relative displacement of the supporting roller and the belt on the downstream side with respect to the rotation direction of the fixing member in the axial direction of the supporting roller. Since the belt does not sag in the vicinity of the downstream support roller, by providing the belt restricting member on the downstream side, the belt restricting member can reliably prevent the belt from being relatively displaced in the axial direction of the support roller. Accordingly, each support roller can prevent the belt from falling off from the support roller and meandering, and can reliably convey the belt.

  Furthermore, according to the present invention, since the image forming apparatus includes the fixing device, it is possible to realize an image forming apparatus that achieves the above-described excellent effects.

  Hereinafter, a plurality of embodiments for carrying out the present invention will be described with reference to the drawings. Portions corresponding to the matters described in the preceding forms in each embodiment are denoted by the same reference numerals, and overlapping description may be omitted. When only a part of the configuration is described, the other parts of the configuration are the same as those described in the preceding section. Not only the combination of the parts specifically described in each embodiment, but also the embodiments can be partially combined as long as the combination does not hinder.

  FIG. 1 is a front view schematically showing a fixing device 10 according to a first embodiment of the present invention. FIG. 2 is a front view schematically showing an image forming apparatus 11 as an application example of the fixing device 10. The image forming apparatus 11 of the present embodiment is realized by a dry electrophotographic color image forming apparatus 11. The image forming apparatus 11 forms a multicolor or single color image on a predetermined recording paper 12 based on image data transmitted from each terminal device on the network, for example. The image forming apparatus 11 includes four visible image forming units 13Y, 13M, 13C, and 13B (hereinafter sometimes collectively referred to as “visible image forming unit 13”), a recording paper transport unit 21, and a fixing device 10. , And a supply tray 14.

  A plurality of recording papers 12 can be placed on the supply tray 14, and the plurality of recording papers 12 placed on the supply tray 14 are separated one by one, and the visible image forming unit 13Y closest to the supply tray 14 is provided. To supply.

  Each visible image forming unit 13 corresponds to four colors of yellow (Y), magenta (M), cyan (C), and black (B), respectively, and four visible image forming units 13Y, 13M, 13C, 13B. Are arranged side by side. The visible image forming unit 13Y forms an image using yellow (Y) toner T, and the visible image forming unit 13M forms an image using magenta (M) toner T to form a visible image. The unit 13C forms an image using cyan (C) toner T, and the visible image forming unit 13B forms an image using black (B) toner T. A specific arrangement is a so-called tandem type in which four visible image forming units 13 are arranged along a conveyance path of the recording paper 12 connecting the supply tray 14 of the recording paper 12 and the fixing device 10.

  Each visible image forming unit 13 has substantially the same configuration, and each includes a photosensitive drum 15, a charger 16, a laser beam irradiation means 17, a developing unit 18, a transfer roller 19, and a cleaner unit 20. , Is provided. Each visible image forming unit 13 multi-transfers each color toner T onto the recording paper 12 conveyed from the supply tray 14.

  The photosensitive drum 15 carries an image to be formed. The charger 16 uniformly charges the surface of the photosensitive drum 15 to a predetermined potential. The laser light irradiation means 17 exposes the surface of the photosensitive drum 15 charged by the charger 5 according to the image data input to the image forming apparatus 11, and an electrostatic latent image is formed on the surface of the photosensitive drum 15. Form. The developing device 52 visualizes the electrostatic latent image formed on the surface of the photosensitive drum 15 with the toner T of each color. The transfer roller 19 is applied with a bias voltage having a polarity opposite to that of the toner T, and transfers the formed toner image onto the recording paper 12 conveyed by the recording paper conveying means 21 described later. The drum cleaner unit 20 removes and collects the toner T remaining on the surface of the photosensitive drum 15 after the developing process in the developing unit 18 and the transfer of the image formed on the photosensitive drum 15. The transfer of the toner image onto the recording paper 12 as described above is repeated four times for four colors.

  The recording paper transport unit 21 includes a driving roller 22, an idling roller 23, and a transport belt 24. The recording paper is supplied from the supply tray 14 so that a toner image is formed on the recording paper 12 by the visible image forming unit 13. The paper 12 is conveyed. The drive roller 22 and the idling roller 23 stretch the endless transport belt 24. The drive roller 22 is rotated at a predetermined peripheral speed to rotate the endless transport belt 24. Yes. The transport belt 24 generates static electricity on the outer surface, and transports the recording paper 12 while electrostatically attracting the recording paper 12.

  In this way, after the toner image is transferred to the recording paper 12 while being transported to the transport belt 24, the recording paper 12 is peeled off from the transport belt 24 by the curvature of the driving roller 22 and transported to the fixing device 10. The fixing device 10 applies a suitable heat and pressure to the recording paper 12 to dissolve the toner T and fix it to the recording paper 12, thereby forming a robust image.

  Next, the fixing device 10 will be described. Referring to FIG. 1, the fixing device 10 according to the present embodiment applies a heat and pressure to a recording paper 12 having an unfixed toner image formed on the surface thereof, and heat-fuses the toner image onto the recording paper 12. It is to fix. An unfixed toner image is a developer (hereinafter referred to as “non-magnetic one-component developer (non-magnetic toner)”, non-magnetic two-component developer (non-magnetic toner and carrier), and magnetic developer (magnetic toner)). (Also called “toner”) T.

  The fixing device 10 includes a fixing roller 25, a pressure roller 26, a fixing roller heater lamp 27 that is a heat source for heating the fixing roller 25, and a pressure roller heater lamp that is a heat source for heating the pressure roller 26. 28. Four thermistors 31a, 31b, 31c as temperature sensors constituting an external heating member 29 for heating the fixing roller 25 from the outside, a cleaning device 30 for cleaning the fixing roller 25, and temperature detecting means for detecting the temperature of each roller. , 31d.

  The fixing roller 25 is a fixing member, and is supported so that its outer peripheral surface can circulate. A fixing roller heater lamp 27 for heating the fixing roller 25 is disposed inside the fixing roller 25. By energizing the fixing roller heater lamp 27 from a control circuit (not shown), the fixing roller heater lamp 27 emits light and radiates infrared rays. As a result, the inner peripheral surface of the fixing roller 25 is heated by absorbing infrared rays, and the entire fixing roller 25 is heated. The fixing roller 25 is heated to a predetermined temperature, for example, 180 ° C., and heats the recording paper 12 on which an unfixed toner image passing through the fixing nip portion 32 is formed.

  The fixing roller 25 has a three-layer structure in which a core metal, an elastic layer, and a release layer are formed in order from the inside. For the metal core, for example, a metal such as iron, stainless steel, aluminum, copper, or an alloy thereof is used. For the elastic layer, for example, silicon rubber is used. For the release layer, for example, a fluororesin such as PFA (copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether) and PTFE (polytetrafluoroethylene) is used.

  The pressure roller 26 is a pressure unit and rotates around the outer peripheral surface of the fixing roller 25. A pressure roller heater lamp 28 for heating the pressure roller 26 is disposed inside the pressure roller 26. By energizing the pressure roller heater lamp 28 from a control circuit (not shown), the pressure roller heater lamp 28 emits light and radiates infrared rays. As a result, the inner peripheral surface of the pressure roller 26 is heated by absorbing infrared rays, and the entire pressure roller 26 is heated. Similar to the fixing roller 25, the pressure roller 26 is heated to a predetermined temperature, for example, 180 ° C., and heats the recording paper 12 on which an unfixed toner image passing through the fixing nip portion 32 is formed.

  Similar to the fixing roller 25, the pressure roller 26 has a three-layer structure in which a metal core, an elastic layer, and a release layer are formed in this order from the inside. For the metal core, for example, a metal such as iron, stainless steel, aluminum, copper, or an alloy thereof is used. For the elastic layer, for example, silicon rubber is used. For the release layer, for example, a fluororesin such as PFA (copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether) and PTFE (polytetrafluoroethylene) is used.

  Thermistors 31a and 31b as temperature detecting means are disposed on the outer peripheral surfaces of the fixing roller 25 and the pressure roller 26, respectively, and detect the surface temperature of each of the rollers 25 and 26. Each thermistor 31a, 31b supplies the detected temperature data to a control circuit (not shown) having a function as temperature control means. The control circuit controls energization of the heater lamps 27 and 28 so that the temperature of the rollers 25 and 26 becomes a predetermined temperature.

  The fixing roller 25 and the pressure roller 26 are brought into pressure contact with each other with a predetermined load, for example, 600 N, and a fixing nip portion 32 that is a pressure contact portion is formed therebetween. The fixing nip portion 32 is a portion where the fixing roller 25 and the pressure roller 26 are in contact with each other, and has a width of 9 mm in the circumferential direction of the rollers 25 and 26, for example. The recording paper 12 passes through the fixing nip portion 32 so that the toner image is fixed. When the recording paper 12 passes through the fixing nip portion 32, the fixing roller 25 contacts the toner image forming surface of the recording paper 12, while the pressure roller 26 contacts the surface of the recording paper 12 opposite to the toner image forming surface. Configured to touch.

  The recording paper 12 on which an unfixed toner image is formed at a predetermined fixing speed and copying speed is conveyed to the fixing nip portion 32 and is fixed by heat and pressure. The fixing speed is a so-called process speed, for example, 355 mm / sec. The copying speed is the number of copies per minute, for example 70 sheets / minute.

  The fixing roller 25 is rotationally driven by a drive motor (not shown) so that the recording paper 12 can pass through the fixing nip portion 32. Further, the pressure roller 26 rotates following the rotation of the fixing roller 25. Accordingly, the fixing roller 25 and the pressure roller 26 rotate in opposite directions as shown in FIG.

  The cleaning device 30 is configured to reliably clean the toner T offset on the fixing roller 25 and prevent the toner T from adhering to the pressure roller 26. The cleaning device 30 is provided on the upstream side of the pressure roller 26 with respect to the rotation direction of the fixing roller 25.

  FIG. 3 is an enlarged plan view showing the external heating member 29. Referring also to FIG. 1, the external heating member 29 is in contact with at least one of the outer peripheral surface of the fixing roller 25 and the outer peripheral surface of the pressure roller 26 to heat the object to be contacted. The external heating member 29 is provided in contact with the fixing roller 25 in the present embodiment. The external heating member 29 includes a plurality of, in the present embodiment, two support rollers 33a and 33b, an external heating belt 34, two external heating heater lamps 35a and 35b, and a belt shift regulating member 36.

  Each of the support rollers 33a and 33b is provided to be rotatable around two axes substantially parallel to the axes of the fixing roller 25 and the pressure roller 26 (the term “substantially parallel” includes parallel). Each of the support rollers 33 a and 33 b is provided in the vicinity of the opposite side of the fixing nip portion 32 with respect to the axis of the fixing roller 25. The outer peripheral surfaces of the support rollers 33a and 33b are spaced apart from the outer peripheral surface of the fixing roller 25, and are arranged at least at an interval at which the external heating belt 34 can be displaced. Each of the support rollers 33a and 33b has a cylindrical shape, and the diameters are set to be equal to each other. Each of the support rollers 33a and 33b is made of a hollow cylindrical metal core material made of, for example, aluminum and an iron-based material.

  Further, of the supporting rollers 33a and 33b, two supporting rollers 33a and 33b are set such that the rotational torque T1 of the upstream supporting roller 33a is smaller than the rotational torque T2 of the downstream supporting roller 33b with respect to the rotational direction of the fixing roller 25. 33a and 33b are configured. In other words, when the rotational torque of the upstream support roller 33a with respect to the rotation direction of the fixing roller 25 is T1, and the rotational torque of the downstream support roller 33b is T2, the relationship of T1 <T2 is established. The In the present embodiment, the support rollers 33a and 33b are rotatably supported by bearings. The bearing of the upstream support roller 33 a is a ball bearing 37, and the bearing of the downstream support roller 33 b is a sliding bearing 38.

  Each of the external heating heater lamps 35a and 35b is a heating source, and is provided on at least one of the plurality of support rollers. In the present embodiment, each of the two support rollers 33a and 33b is provided. Each of the external heating heater lamps 35a and 35b has a function as a heating source for heating the support rollers 33a and 33b. Each of the external heating heater lamps 35a and 35b is disposed inside the two support rollers 33a and 33b, respectively. When the external heating heater lamps 35a and 35b are energized from a control circuit (not shown), the external heating heater lamps 35a and 35b emit light and radiate infrared rays. As a result, the inner peripheral surfaces of the support rollers 33a and 33b are heated, and the external heating belt 34 is heated via the support rollers 33a and 33b.

  The external heating belt 34 is endless and is rotatably stretched between the two support rollers 33a and 33b. In the natural state, the external heating belt 34 is stretched so as to have a tension that does not undesirably displace in the axial direction of the support rollers 33a and 33b. The external heating belt 34 is provided so that the outer surface of the external heating belt 34 faces the fixing roller 25 is in contact with the outer peripheral surface of the fixing roller 25. The external heating belt 34 is provided on the upstream side of the fixing nip portion 32 with respect to the fixing roller 25, and is configured to be pressed against the fixing roller 25 with a predetermined pressing force, for example, 40N. The external heating belt 34 is formed between the fixing roller 25 and a heating nip portion 39, for example, 20 mm in the circumferential direction of the external heating belt 34. The external heating belt 34 is configured to rotate following the fixing roller 25 when the fixing roller 25 rotates, and the support rollers 33a and 33b also rotate according to the rotation of the external heating belt 34. Is done. The outer peripheral surface of the external heating belt 34 is heated from the two support rollers 33 a and 33 b, and the fixing roller 25 is heated via the external heating belt 34.

  The external heating belt 34 is composed of a heat-resistant resin such as polyimide or a surface of a hollow cylindrical base material made of a metal material such as stainless steel and nickel, and a synthetic layer excellent in heat resistance and releasability as a release layer. It has a two-layer structure in which a resin material, for example, a fluororesin such as PFA and PTFE is formed. Further, in order to reduce the offset force of the external heating belt 34, the inner surface of the belt base material may be coated with a fluorine resin or the like.

  Each thermistor 31c, 31d functions as a temperature detection means, and is provided in the vicinity of each support roller 33a, 33b, and the outer peripheral surface of the external heating belt 34 is provided, and detects the surface temperature of the external heating belt 34. To do. Each thermistor 31c, 31d provides the detected temperature data to a control circuit (not shown). The control circuit controls energization to each of the external heating heater lamps 35a and 35b so that the temperature of the external heating belt 34 becomes a predetermined temperature.

  The belt deviation regulating member 36 regulates the relative displacement of the support roller 33b and the external heating belt 34 in the axial direction of the support roller 33b. The belt deviation regulating member 36 is provided on the downstream support roller 33b in the present embodiment. The belt deviation regulating member 36 is a ring-shaped member, and is provided between the slide bearing 38 and the external heating belt 34 so as to protrude outward in the radial direction of the support roller. Therefore, the surface portion of the belt-side regulating member 36 that faces the external heating belt 34 faces the surface portion on the outer side in the width direction of the external heating belt 34 and restricts the external heating belt 34 from being displaced in the axial direction of the support roller.

  As described above, the fixing device 10 included in the image forming apparatus 11 according to the present embodiment includes the external heating member 29 and can heat the outer peripheral surface of the fixing roller 25. Of the two support rollers 33a and 33b provided in the external heating member 29, the rotational torque T1 of the upstream support roller 33a is smaller than the rotational torque T2 of the downstream support roller 33b with respect to the rotational direction of the fixing roller 25. Thus, the support rollers 33a and 33b are configured. As a result, the upstream support roller 33a that easily sags from the external heating belt 34 and easily slips can be easily rotated, so that the upstream support roller 33a can be prevented from slipping. Accordingly, it is possible to prevent the heating performance from being deteriorated due to the slip between the external heating belt 34 and the support roller 33a. Therefore, the fixing roller 25 can be heated without unevenness, and the toner T can be stably fixed on the recording paper 12.

  In the present embodiment, the bearing of the upstream support roller 33 a is the ball bearing 37 and the bearing of the downstream support roller 33 b is the sliding bearing 38 with respect to the rotation direction of the fixing roller 25. Since the ball bearing 37 supports the support roller so that it can rotate smoothly from the slide bearing 38, the rotational torque T1 of the upstream support roller 33a can be made smaller than the rotational torque T2 of the downstream support roller 33b. . As a result, it is possible to reliably prevent the external heating belt 34 from slipping upstream as described above. Further, since the bearing of the support roller 33b on the downstream side is a sliding bearing 38, the configuration is simpler than the ball bearing 37, and the bearing can be realized at low cost. Therefore, a configuration for preventing the external heating belt 34 from slipping can be easily realized.

  Further, in the present embodiment, the external heating member 29 is a belt shift regulation that regulates the relative displacement in the axial direction of the support roller 33 b between the support roller 33 b and the external heating belt 34 on the downstream side with respect to the rotation direction of the fixing roller 25. A member 36 is further provided. In the vicinity of the downstream support roller 33b, the external heating belt 34 is less likely to sag in the vicinity of the upstream support roller 33a. Therefore, by providing the belt shift restriction member 36 on the downstream side, the belt shift restriction member 36 can reliably It is possible to prevent the external heating belt 34 from being relatively displaced in the axial direction of the support roller 33b. As a result, each of the support rollers 33a and 33b can prevent the external heating belt 34 from dropping from the support rollers 33a and 33b and meandering, and can reliably convey the external heating belt 34.

  Next, the fixing device 10 according to the second embodiment of the present invention will be described. FIG. 4 is an enlarged plan view showing the external heating member 29A of the present embodiment. The fixing device 10 of the present embodiment has the same configuration as the fixing device 10 of the first embodiment described above, and a part of the configuration of the external heating member 29A is different. Of the support rollers 33a and 33b constituting the external heating member 29A, the rotational torque T1 of the upstream support roller 33a and the rotational torque T2 of the downstream support roller 33b are equal to each other with respect to the rotational direction of the fixing roller 25. The two support rollers 33a and 33b are configured as described above. Each support roller 33a, 33b is rotatably supported by a bearing. The bearings of the two support rollers 33a and 33b are sliding bearings 38.

  Of the two support rollers 33a and 33b, the friction coefficient μ1 of the outer peripheral surface of the upstream support roller 33a is larger than the friction coefficient μ2 of the outer peripheral surface of the support roller 33b on the downstream side with respect to the rotation direction of the fixing member. Each support roller 33a, 33b is configured. In other words, of the two support rollers 33a and 33b, if the friction coefficient of the upstream support roller 33a with respect to the rotation direction of the fixing roller 25 is μ1, and the friction coefficient of the downstream support roller 33b is μ2, μ1> μ2. It is configured so that the relationship is established.

  The support roller 33a on the upstream side is coated with rubber, and the support roller 33b on the downstream side is coated with fluororesin. Specifically, the upstream support roller 33a is coated on a hollow cylindrical metal core made of, for example, aluminum and iron-based material, such as fluoro rubber and silicon rubber. The downstream support roller 33b is coated with a fluororesin on a hollow cylindrical metal core made of, for example, aluminum and an iron-based material.

  As described above, the friction coefficient μ2 of the outer peripheral surface of the support roller 33b on the downstream side with respect to the rotation direction of the fixing roller 25 among the two support rollers 33a and 33b provided in the external heating member 29A of the present embodiment. The support rollers 33a and 33b are configured such that the friction coefficient μ1 of the outer peripheral surface of the upstream support roller 33a is increased. As a result, the deflection of the external heating belt 34 can be reduced, and even if the external heating belt 34 is somewhat bent, the upstream support roller 33a can be rotated by the frictional force. Accordingly, it is possible to prevent the heating performance from being deteriorated due to the slip between the external heating belt 34 and the support roller 33a. Therefore, the fixing roller 25 can be heated without unevenness, and the toner T can be stably fixed on the recording paper 12.

  Further, in the present embodiment, with respect to the rotation direction of the fixing roller 25, the upstream support roller 33a is coated with rubber, and the downstream support roller 33b is coated with fluororesin. Since the fluororesin coat has a smaller friction coefficient than the rubber coat, the friction coefficient of the outer peripheral surface of the upstream support roller 33a can be made larger than the friction coefficient of the outer peripheral surface of the downstream support roller 33b. As a result, as described above, it is possible to reliably prevent the sag and slip of the external heating belt 34 on the upstream side. In other words, in order to increase the friction coefficient of the support roller 33a where the sagging occurs with respect to the external heating belt 34, slip is effectively prevented by coating the upstream support roller 33a with a rubber-based material having a large friction coefficient. be able to. If the downstream support roller 33b is also coated with a rubber-based material, the offset force of the external heating belt 34 becomes too large, causing a problem in durability of the belt end, and therefore a fluorine-based material having a relatively small friction coefficient. These resins are preferably used.

  In the present embodiment, the belt shift regulating member 36 is provided on the upstream side support roller 33a and the downstream side support roller 33b. In particular, since the downstream support roller 33b has no slack in the external heating belt 34, there is no concern that the external heating belt 34 will run on the belt-side regulating member 36, and the friction coefficient of the downstream support roller 33b is reduced. Further, since the offset force itself is smaller than that of the upstream support roller 33a, the meandering of the belt can be prevented more reliably.

  Next, the fixing device 10 according to the third embodiment of the present invention will be described. The fixing device 10 according to the present embodiment is configured by combining the configurations of the fixing device 10 according to the first embodiment and the fixing device 10 according to the second embodiment. Therefore, of the two support rollers 33a and 33b constituting the external heating member 29 of the fixing device 10 of the first embodiment, the friction coefficient of the outer peripheral surface of the support roller 33b on the downstream side with respect to the rotation direction of the fixing roller 25. The support rollers 33a and 33b are configured so that the friction coefficient μ1 of the outer peripheral surface of the upstream support roller 33a is larger than μ2. As a result, the effect based on the magnitude relationship between the rotational torques of the support rollers 33a and 33b can be further increased by the effect based on the magnitude relationship between the friction coefficients. As a result, it is possible to reliably prevent the external heating belt 34 from sagging on the upstream side.

  In each of the above-described embodiments, the number of support rollers is two, but the number is not limited to two and may be a plurality. When the external heating member includes three or more support rollers, it is preferable that the rotational torque or the friction coefficient is sequentially changed from the upstream side in the rotation direction of the fixing roller 25.

  In each of the embodiments described above, the recording paper 12 is used as the recording material. However, the recording material is not limited to the recording paper 12 and is a recording material that can be conveyed to the fixing nip portion 32 between the fixing roller 25 and the pressure roller 26. I just need it.

  In the first and third embodiments described above, the same effect can be obtained even if the rotational resistance of the support rollers 33a and 33b is configured so that the upstream support roller 33a is smaller than the downstream support roller 33b. And can achieve the effect.

  In the first and third embodiments described above, the same effect can be obtained even if the weights of the support rollers 33a and 33b are configured such that the upstream support roller 33a is smaller than the downstream support roller 33b. And can achieve the effect.

  In the first and third embodiments described above, even if the diameter of each of the support rollers 33a and 33b is configured such that the upstream support roller 33a is smaller than the downstream support roller 33b, The effect can be achieved.

1 is a simplified front view of a fixing device 10 according to a first embodiment. 2 is a front view schematically showing an image forming apparatus 11 as an application example of the fixing device 10. FIG. It is a top view which expands and shows the external heating member 29 of 1st Embodiment. It is a top view which expands and shows the external heating member 29A of 2nd Embodiment. It is a front view which expands and shows the structure relevant to the external heating belt 2 provided in the fixing apparatus 1 of a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Fixing device 11 Image forming device 25 Fixing roller 26 Pressure roller 30 External heating member 33a, 33b Support roller 34 External heating belt 36 Belt deviation regulating member 37 Ball bearing 38 Slide bearing

Claims (7)

A fixing member that is supported so that the outer peripheral surface can circulate, a pressure unit that presses and circulates the outer peripheral surface of the fixing member, and at least one of the outer peripheral surface of the fixing member and the outer peripheral surface of the pressure member. An external heating member that heats in contact with the recording medium, and when a recording material carrying a toner image is conveyed to the pressure contact portion between the fixing member and the pressure unit, the toner image is thermally fused and fixed to the recording material. A fixing device that
The external heating member is
A plurality of support rollers;
A heating source provided in at least one of the plurality of support rollers;
A belt stretched rotatably around the plurality of support rollers,
Among the plurality of support rollers, each support roller is configured such that the rotation torque of the upstream support roller is smaller than the rotation torque of the downstream support roller with respect to the rotation direction of the fixing member. A fixing device. The external heating member further includes a bearing that supports each of the plurality of support rollers,
2. The fixing device according to claim 1, wherein the bearing of the upstream support roller is a ball bearing and the bearing of the downstream support roller is a sliding bearing with respect to the rotation direction of the fixing member. A fixing member that is supported so that the outer peripheral surface can circulate, a pressure unit that presses and circulates the outer peripheral surface of the fixing member, and at least one of the outer peripheral surface of the fixing member and the outer peripheral surface of the pressure member. An external heating member that heats in contact with the recording medium, and when a recording material carrying a toner image is conveyed to the pressure contact portion between the fixing member and the pressure unit, the toner image is thermally fused and fixed to the recording material. A fixing device that
The external heating member is
A plurality of support rollers;
A heating source provided in at least one of the plurality of support rollers;
A belt stretched rotatably around the plurality of support rollers,
Among the plurality of support rollers, each support roller is configured such that the friction coefficient of the outer peripheral surface of the upstream support roller is larger than the friction coefficient of the outer peripheral surface of the downstream support roller with respect to the rotation direction of the fixing member. A fixing device. A rubber coat is applied to the upstream support roller with respect to the rotation direction of the fixing member,
The fixing device according to claim 3, wherein the downstream support roller is coated with a fluorine resin.   Among the plurality of support rollers, each support roller is configured such that the friction coefficient of the outer peripheral surface of the upstream support roller is larger than the friction coefficient of the outer peripheral surface of the downstream support roller with respect to the rotation direction of the fixing member. The fixing device according to claim 1, wherein the fixing device is used.   The external heating member further includes a belt shift regulating member that regulates a relative displacement in the axial direction of the support roller and the belt on the downstream side with respect to the rotation direction of the fixing member. The fixing device according to any one of?   An image forming apparatus comprising the fixing device according to claim 1.

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