JP2005128337A - Fixing device and image forming apparatus equipped therewith - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device realizing miniaturization and power saving while securing fixing property and the peeling property of a recording medium, and an image forming apparatus equipped with the fixing device. <P>SOLUTION: The fixing device 10 is provided with a cylindrical heating roller 11 composed of heat conductive material, an endless belt 41 arranged on the outer circumference of the roller 11 and made longer than the outer circumference of the roller 11, a tension roller 31 which is arranged on a downstream side in the transporting direction of the recording medium with reference to the roller 11 and across which the endless belt is laid, and a pressure roller 21 press-contacting with the roller 11 through the belt 41 and forming a nip part with the belt 41 in between. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a fixing device that fixes an unfixed developer on a recording medium and an image forming apparatus including the fixing device.

  In general, the amount of toner used when forming a toner image on a recording sheet in an electrophotographic image forming apparatus is larger in color printing than in monochrome printing. Therefore, in color printing, in order to satisfactorily fix the toner image on the recording paper, the toner releasability from the fixing roller of the fixing device used in the color image forming apparatus and the releasability of the recording paper are improved. Alternatively, it is required to improve the melting performance of the color toner.

  Therefore, conventionally, by arranging an elastic member (rubber layer or the like) inside the fixing roller (heating roller) and the pressure roller, the fixing nip is made parallel to the paper transport direction and the fixing nip width is widened. Designed to be

  Further, in Cited Document 1, the toner is stably heat-fixed by a configuration including an endless belt including a heating roller (fixing roller) and a peeling roller, and a pressure roller pressed against the heating roller via the endless belt. A fixing device is described. Also, after the transfer material (recording paper) is sandwiched and fixed between the pressure roller and the endless belt, it is conveyed in close contact with the endless belt while being cooled by an air-cooling box, and the belt at the peeling roller. A structure that is peeled off is disclosed. As a result, the toner is cooled while being in close contact with the endless belt, and the transfer material and toner are easily peeled off from the belt.

Further, the conventional color printing fixing device uses a fixing roller having a relatively large outer periphery, for example, an outer periphery substantially equal to the length of the maximum paper size to be used. The fixing roller is heated to a set temperature and rotates to convey a recording sheet on which an unfixed toner image is formed and to melt and fix the toner by contacting the recording sheet. Therefore, if the outer circumference of the fixing roller is approximately equal to the length of the maximum paper size used as in the prior art, it takes a relatively long time for the fixing roller to complete a week, so the paper is fixed at the time of fixing. Even if the heat of the roller is taken away, the temperature returns to a temperature necessary for melting the toner by one week before the next fixing is performed. Therefore, good fixability can be maintained.
Japanese Patent No. 2992710 (registered on October 22, 1999)

  Incidentally, in recent years, power saving and downsizing of image forming apparatuses are required, and power saving and downsizing are also required for fixing devices provided in the image forming apparatus. For this reason, it is desirable for the fixing device to achieve power saving and downsizing of the fixing device while ensuring good fixing performance of the toner image on the recording paper. In particular, full-color printing using an image forming apparatus equipped with a fixing device has been actively performed in recent years, and not only monochrome printing but also image forming apparatuses that perform full-color printing have achieved power saving and downsizing. It has been demanded. In order to respond to such a demand, it is considered that there is still room for further improvement.

  For example, in a conventional color printing fixing device, an elastic member made of rubber having poor conductivity is heated to bring the fixing roller surface to a set temperature as described above, and a large-capacity heat source must be used. There wasn't. Therefore, there has been a problem that it takes a lot of time and electric power to warm up the fixing device for operating the image forming apparatus.

  In order to reduce the size, a method using a short fixing roller as the fixing roller is conceivable. However, in this case, after the fixing roller is deprived of the temperature by the fixing, one week is required until the temperature is raised to the set temperature, and the next fixing is performed. As a result, there is a problem that the fixing performance is different between the portion fixed in the first week of the fixing roller and the portion fixed in the second week, resulting in different hues.

  The present invention has been made to solve the above-described conventional problems, and its purpose is to shorten the warm-up time, reduce the amount of power required for the warm-up, and reduce the size of the fixing device. An object of the present invention is to provide a fixing device capable of performing the fixing process suitably and satisfactorily for both full-color printing and monochrome printing, and an image forming apparatus including the same.

  In order to solve the above-described problems, the fixing device of the present invention is a fixing device that fixes a developer on a conveyed recording medium. In the fixing device, a cylindrical heating roller made of a heat conductive material and an outer periphery of the heating roller An endless belt that is longer than the outer periphery of the heating roller, a tension member that is disposed downstream of the heating roller in the recording medium conveyance direction, and on which the endless belt is suspended, and the heating roller via the endless belt And a pressure roller that forms a nip portion with the endless belt.

  The fixing device of the present invention is further characterized in that the thickness of the heating roller is 3 mm or less.

  The fixing device of the present invention is further characterized in that the endless belt is 300 μm or less.

  The fixing device according to the present invention is characterized in that the endless belt has an elastic belt elastic layer.

  The fixing device according to the present invention is characterized in that the tension member applies tension to the endless belt.

  The fixing device according to the present invention is characterized in that the endless belt rotates following the rotation of the heating roller.

  The fixing device according to the present invention is characterized in that the pressure roller rotates following the rotation of the endless belt.

  The fixing device of the present invention is characterized in that the endless belt has a temperature at which the developer can be melted by absorbing heat of the heating roller while contacting the heating roller.

  The fixing device of the present invention is characterized in that the developer on the recording medium is fixed by a portion from the nip portion of the endless belt to the tension member.

  The fixing device according to the present invention is characterized in that the tension member cools the endless belt.

  The fixing device according to the present invention is characterized in that the tension member bends the endless belt so that the diameter of the curvature circle is 15 mm or less.

  In the fixing device of the present invention, the pressure roller and the tension member are arranged so that a portion from the nip portion of the endless belt to the tension member is perpendicular to a line connecting the axes of the heating roller and the pressure roller. It is characterized by being.

  The fixing device according to the present invention is characterized in that the tension member is disposed so as to contact the pressure roller.

  The fixing device according to the present invention is characterized in that the tension member has a roller shape, and a central portion in the axial direction is thick and both end portions are narrow.

  The image forming apparatus according to the present invention includes the above-described fixing device.

  The image forming apparatus of the present invention is characterized in that a monochrome printing mode or a full color printing mode can be selected.

  As described above, the fixing device according to the present invention includes a cylindrical heating roller made of a heat conductive material, an endless belt, a tension member, and a pressure roller.

  Since the heating roller has a cylindrical shape made of a heat conductive material, the heating roller can be quickly heated (has fast heat properties). Therefore, the warm-up time of the fixing device can be shortened, and the power for heating the heating roller can be reduced. In addition, when the temperature of the heating roller is increased quickly, the recording paper can be quickly recovered to a predetermined temperature after the recording paper is deprived of heat. In order to reduce the diameter of the heating roller, it is necessary for the heating roller to be fast enough to return to the set temperature during one round of the heating roller, but this configuration reduces the diameter of the heating roller. it can. This can reduce the size of the fixing device.

  In the fixing device according to the present invention, since the tension member is disposed downstream of the heating roller in the recording medium conveyance direction, the recording medium is endlessly heated by the heating roller after passing through the nip portion. It is conveyed along the belt. Since the fixing is performed while the recording medium is conveyed along the endless belt, a sufficient fixing time for the recording medium can be secured, and a sufficient fixing performance can be secured. Further, by securing the fixing performance as described above, a sufficient fixing property can be obtained with a single-layer cylindrical pressure roller, so that the cost of the heating roller can be suppressed. In addition, since the toner image can be fixed satisfactorily regardless of the amount of toner, good fixing performance can be exhibited in both monochrome printing and color printing.

  Therefore, the fixing device of the present invention has the effects of maintaining good fixing performance while reducing costs with a simple configuration, further shortening the warm-up time of the heating roller, saving power, and reducing the size.

  Further, in the fixing device according to the present invention, when the thickness of the cylinder of the heating roller is set to 3 mm or less, the heating roller has good rapid heat performance, further shortening the warm-up time of the heating roller, saving power, There is an effect that the size can be reduced. In addition, since the cylinder is thinned, the amount of heat radiation can be reduced, and the heating roller warm-up time and the amount of power required for warm-up can be reduced, thereby reducing the power consumption of the fixing device. Play.

  In the fixing device according to the present invention, the heat of the heating roller can be quickly transmitted to the endless belt by setting the thickness of the endless belt to 300 μm or less. Therefore, the temperature setting of the heating roller for raising the temperature of the endless belt to a temperature at which the developer can be melted can be lowered, so that power saving can be achieved. Furthermore, since the rapid heating property of the heating roller is further improved when the set temperature is lowered, the warm-up time of the heating roller can be shortened and the size can be reduced.

  Further, the fixing device according to the present invention can convey the recording medium satisfactorily because the tension member gives tension to the endless belt.

  Furthermore, in the fixing device according to the present invention, the endless belt rotates following the rotation of the heating roller, so that the endless belt is in close contact with the heating roller, and the heat of the heating roller is conducted well to the endless belt. Further, since a driving source for driving the endless belt is not required, the structure can be simplified and the cost can be reduced.

  Further, in the fixing device according to the present invention, since the recording roller is conveyed at the same speed as the endless belt as the pressure roller rotates following the rotation of the endless belt, the recording sheet slips. Absent. Further, since a driving source for driving the pressure roller is not necessary, the structure can be simplified and the cost can be reduced.

  Further, the fixing device according to the present invention is good because the endless belt absorbs the heat of the heating roller while it is in contact with the heating roller to reach a temperature at which the developer can be melted. In addition, the endless belt can be heated, and the developer on the recording medium can be melted.

  In the fixing device according to the present invention, the developer on the recording medium is fixed by the portion of the endless belt from the nip portion to the tension member, and the developer that has not been completely fixed at the nip portion. This also has the effect of being completely fixed while being conveyed in close contact with the endless belt on the downstream side.

  In addition, the “part from the nip portion of the endless belt until it is suspended by the tension member” is an area where the tension member and the endless belt are in contact with each other from the most downstream point in the area where the heating roller and the endless belt are in contact with each other. The part up to the most upstream point.

  In the fixing device according to the present invention, since the tension member cools the endless belt, the toner that has melted and adhered to the endless belt is cooled and easily peeled off, and offset is prevented. In order to cool the endless belt with the tension member, a material having high thermal conductivity, such as aluminum, may be used as the tension member.

  In the fixing device according to the present invention, since the tension member bends the endless belt so that the diameter of the curvature circle is 15 mm or less, when the recording paper that is in close contact with the endless belt passes through the tension member, the endless belt is as large as the endless belt. The recording paper which does not have the flexibility cannot be along the curvature of the endless belt and is peeled off. Therefore, the recording paper can be peeled naturally without providing a separate peeling mechanism, the cost can be reduced, and fixing can be performed without leaving any trace of peeling.

  Further, in the fixing device according to the present invention, the portion of the endless belt from the nip portion to the tension member is perpendicular to the line connecting the axes of the heating roller and the pressure roller. Since the pressure roller and the tension member are arranged, the recording medium is conveyed without being bent by the endless belt on the downstream side of the nip portion, so that the fixing can be performed without bending the recording medium.

  In the fixing device according to the present invention, when the tension member is disposed so as to contact the pressure roller, the recording medium is pressed until it reaches the tension member after passing through the nip portion. Since it is sandwiched between the roller and the endless belt and is further pressed between the tension member and the endless belt, the recording medium can be transported while being in contact with the endless belt, improving the fixing performance of the recording medium. Can be made.

  Further, in the fixing device according to the present invention, the tension member is in the form of a roller, the central portion in the axial direction is thick, and both end portions are narrowed. Therefore, more endless belts are sent in the middle than both ends. The endless belt suspended on the tension member is kept in the axial central portion of the tension member and does not depend on the end.

  In addition, the image forming apparatus of the present invention includes the above fixing device, and thus has an excellent fixing performance, a small size, a shortened heating roller warm-up time, and power saving. Become.

  Further, the image forming apparatus according to the present invention may be capable of further selecting a monochrome printing mode or a full color printing mode. The fixing device of the present invention can fix the developer suitably and satisfactorily in any case where the amount of developer to be fixed on the recording medium is small or large. Therefore, the fixing device can be suitably used for both the monochrome printing mode in which the amount of developer used is small and the full color printing mode in which the amount of developer used is large. Therefore, there is an effect that it can be suitably used for an image forming apparatus that performs image forming processing in both the monochrome printing mode and the full-color printing mode.

  One embodiment of the present invention will be described with reference to FIGS. 1 to 3 as follows.

  FIG. 1 is a schematic cross-sectional view of a fixing device 10 according to the present embodiment. The fixing device 10 is provided in, for example, an electrophotographic printer (image forming apparatus), and melts an unfixed toner image made of unfixed toner (developer) on a recording paper (recording medium) on the recording paper Secure to. That is, the fixing device 10 includes a heating roller 11, a pressure roller 21, a peeling roller (tension member) 31, and an endless belt 41, and sandwiches a recording sheet between the heating roller 11 and the pressure roller 21. Thus, the toner image is heated and pressed and fixed on the recording paper.

  The heating roller 11 is a heat source for melting the toner on the recording paper, and fixes the toner image on the recording paper by applying pressure with the pressure roller 21. The heating roller 11 receives a driving force from a driving source (not shown) and is rotationally driven in the direction of the arrow in FIG.

  The heating roller 11 is a roller having an outer diameter φ of about 30 mm, for example, made of a metal cylinder 12 (hereinafter referred to as a metal cylinder) 12 such as aluminum or iron. The metal cylinder 12 is hollow, and a heater 14 as a heat source is provided inside. The metal cylinder 12 of the heating roller 11 is heated by the heater 14.

  The metal cylinder 12 of the heating roller 11 serves as a heat storage unit for accumulating heat generated from the heater 14. The thickness of the metal cylinder 12 is preferably 3 mm or less in order to reduce the heat capacity and heat dissipation of the metal cylinder 12. Specifically, when the metal cylinder 12 is formed of aluminum, it is formed in a thin shape of about 1 mm to 3 mm, and when the metal cylinder 12 is formed of iron, 0.1 mm to 0.00 mm. It is preferably formed in a thin shape of about 5 mm. In the present embodiment, an iron heating roller having a thickness of 0.25 mm is used.

  Thus, since the said heating roller 11 is equipped with the thin metal cylinder 12, the heat capacity and heat dissipation of a thermal storage part can be made small. As a result, the warm-up time of the heating roller 11 required for heating the heating roller 11 from room temperature to a predetermined fixing temperature can be shortened, and the amount of power required for warm-up can be reduced. In addition, the temperature of the heating roller can be easily kept constant.

  Further, the heater 14 uses a 950 W halogen lamp. However, the heater 14 only needs to be able to heat the metal cylinder 12 of the heating roller 11, and for example, a halogen lamp, a ceramic heater, or the like may be used.

  The pressure roller 21 is pressed against the heating roller 11 and presses the recording paper on which an unfixed toner image formed between the pressure roller 21 and the heating roller 11 is formed, thereby recording the recording paper. The toner image is fixed on the top. The pressure roller 21 is pressed against the heating roller 11 with a predetermined pressing force (pressure load), for example, 6 kgf, by a pressure spring (not shown), and is driven via the endless belt 41 with respect to the rotation of the heating roller 11. In FIG. 1, it rotates in the direction of the arrow. The pressure load of the pressure roller 21 that is in pressure contact with the heating roller 11 is preferably about 6 kg · f to 20 kg · f.

  The pressure roller 21 is made of, for example, a metal such as stainless steel or iron as a cored bar (cylindrical rotating body; hereinafter referred to as a pressure side cored bar) 22, and rubber, sponge, or the like is provided on the surface of the pressure side cored bar 22. The pressure side elastic layer 23 is provided, and the surface of the pressure side elastic layer 23 is covered with a release layer (not shown).

  The elastic layer 23 is formed of, for example, a foaming sponge with a thickness of 6 mm. However, the material of the elastic layer 23 is not limited to this, and a rubber material such as silicon rubber or fluorine-based rubber having a hardness of about 30 (the hardness specified by the ASKER-C type hardness tester) or foamed silicon rubber What is necessary is just to form with foaming sponges, such as a silicon-type sponge and fluorine-type sponge made. Thereby, the nip width | variety with the endless belt 41 of a press-contact part with a heating roller can be expanded. The nip width with the endless belt 41 is preferably 4 mm or more and 8 mm or less.

  Further, the outer diameter of the pressure roller 21 needs to be larger than that of the heating roller 11 so as to ensure a sufficient nip width with the heating roller 11 via the endless belt 41 with a low load. In the present embodiment, when the 6 mm sponge is used for the elastic layer 23, the outer diameter φ of the heating roller 11 is 30 mm, and the outer diameter φ of the pressure roller 21 is 40 mm. Thereby, a nip width of 6 mm can be ensured.

  The endless belt 41 is disposed on the outer periphery of the heating roller 11. Therefore, the endless belt 41 is sandwiched between the heating roller 11 and the pressure roller 21 and the recording paper to which the toner adheres is added between the endless belt 41 and the pressure roller 21 in the nip portion. Pressed. In the nip portion, the recording paper is heated by the endless belt 41 heated by the heating roller 11 and is pressed and fixed by the pressure roller 21 from the opposite side.

  From the viewpoint of fixing performance, the endless belt 41 is preferably provided with a belt elastic layer on the side in contact with the recording paper. The belt elastic layer has a hardness of about 15 (the hardness specified by the ASKER-C type hardness tester), rubber materials such as silicon rubber and fluorine rubber, silicon sponge formed by foaming silicon rubber, fluorine sponge, etc. What is necessary is just to form with an effervescent sponge. In the present embodiment, an endless belt is used in which a PFA layer of 10 to 30 μm is formed on 90 μm or 100 μm of polyimide.

  The thickness of the endless belt 41 is preferably 300 μm or less. If the endless belt 41 is thicker than 300 μm, the temperature for fixing cannot be quickly increased. The upper limit of the thickness of the endless belt 41 is preferably 500 μm or less, more preferably 300 μm or less, and the lower limit is preferably 50 μm.

  Further, the endless belt 41 is provided with a release layer on the side that directly contacts the toner on the recording paper to improve the releasability from the toner and prevent the toner from adhering to the heating roller 11. Preferably it is. The release layer is preferably formed of a material having releasability and heat resistance. For example, fluorine resin such as PFA (perfluoroalkoxytetrafluoroethylene copolymer), polytetrafluoroethylene (PTFE); Silicon resin or the like may be used. The thickness of the release layer is preferably 10 μm to 50 μm in order to improve the release property, durability, and thermal conductivity. In the present embodiment, the heating-side elastic layer 23 is covered with PFA having a thickness of 10 μm.

  The endless belt 41 is heated by the heating roller 11 while in contact with the heating roller 11, so that the developer can be melted. Further, the recording sheet is arranged along the recording sheet even after the recording sheet has advanced from the fixing nip portion toward the sheet conveyance direction. Thereby, even after the recording paper passes through the nip portion, the endless belt 41 can continue to heat the recording paper, that is, the fixing region of the recording paper is not only the nip portion but also the nip portion forming region of the endless belt 41. To a region (a portion indicated by L in FIG. 1) extending from the tension roller to the tension roller. Therefore, a sufficient time for fixing the toner on the recording paper can be secured, so that the fixing performance can be improved.

  Here, especially when the amount of toner on the recording paper is large as in color printing, since it is necessary to transfer heat over a wide range in order to melt the toner, the arrangement of the endless belt 41 as described above is required. Is important. Further, by sufficiently securing the fixing temperature and the fixing time, the gloss of the surface of the recording paper on which the toner image is fixed can be improved.

  The peeling roller 31 applies tension to the endless belt 41. The peeling roller 31 only needs to support the endless belt 41. For example, a roller made of SUS having a diameter of 8 mm can be used. At this time, the center of the peeling roller 31 in the axial direction is thick, and by narrowing the both ends, a large amount of the endless belt 41 can be fed in the middle, and the endless belt 41 is always held in the middle of the peeling roller.

  Further, in order to arrange the endless belt 41 along the recording sheet after the recording sheet has advanced to the sheet conveying direction side from the fixing nip portion as described above, the separation roller 31 is conveyed from the nip portion to the sheet. What is necessary is just to distribute | arrange to the downstream of a direction. At this time, in order not to curl the recording paper at the time of fixing, a portion (a portion indicated by L in FIG. 1) on the downstream side in the recording medium conveyance direction from the nip portion of the endless belt 41 is between the heating roller 11 and the pressure roller 21. It is preferable to be perpendicular to the line connecting the axes.

  In order to more reliably fix the recording paper, the peeling roller 31 may be provided in contact with the pressure roller 21 as shown in FIG. In this case, since the recording paper is transported between the endless belt 41 and the pressure roller 21 even at the downstream side in the recording paper transport direction from the nip portion of the endless belt 41, the endless belt 41 is more reliably brought into contact with the endless belt 41. Further, since the pressure is again applied to the recording paper other than the holding of the peeling roller 31 between the heating roller 11 and the pressure roller 21, the fixing performance is improved.

Furthermore, in order to peel the recording paper from the endless belt 41 satisfactorily, the diameter of the curvature circle of the peeling roller 31 of the endless belt 41 is preferably 15 mm or less, and more preferably 10 mm or less. For this purpose, for example, a diameter of 8 mm may be used as the peeling roller 31. Here, the peeling roller 31 is described as an example that gives tension to the endless belt 41, but it needs to be in a roller shape. Alternatively, tension may be applied by a member that does not rotate following the rotation of the endless belt 41. For example, it may be a fixed curvature member made of a heat-resistant material, that is, a member fixedly installed in the apparatus so as to give tension to the endless belt 41 and to give curvature to the endless belt 41 at the contact portion.

  When the fixing device 10 having the above-described configuration performs heat and pressure fixing of an unfixed toner image on a recording sheet, it is performed as follows. That is, when a recording sheet on which an unfixed toner image is formed is conveyed so that the unfixed toner and the endless belt 41 are in contact with each other via a transfer roller of a printer, which will be described later, a drive source (not shown) The heating roller 11 is rotationally driven in the direction of the arrow in FIG. 1 by the driving force, and the endless belt 41 and the pressure roller 21 are rotated by the rotation, and the peeling roller 31 is also rotated by the rotation. As a result, the recording paper is conveyed through the nip portion, the toner is melted, and after passing through the nip portion, the recording paper is continuously heated by the endless belt 41, and the toner is completely fixed on the recording paper. Thereafter, the recording sheet is peeled off from the endless belt 41 and discharged from the fixing device 10, and the fixing process is completed. Hereinafter, the fixing process will be described in detail.

  That is, when the recording paper on which the unfixed toner image is formed is conveyed, the heating roller 11 is driven to rotate, and the endless belt 41, the pressure roller 21, and the peeling roller 31 are driven to rotate. At this time, the rotation speed (circumferential speed) of the heating roller 11 may be set in accordance with the process speed of the image forming apparatus.

  When the heating roller 11 is rotationally driven at the above rotational speed, the leading end portion of the recording paper fed from the transfer unit reaches the nip portion between the heating roller 11 and the pressure roller 21. At this time, since the pressure roller 21 is formed with an outer diameter of about 20 mm to 40 mm, the leading end portion of the recording paper is suitably captured by the nip portion.

  When the recording paper is captured in the nip portion, the endless belt 41 is rotated by the rotation of the heating roller 11 and the recording paper is conveyed. At this time, the endless belt 41 of the fixing device 10 is heated to the fixing temperature by the heater 14 in the heating roller 11.

  Further, the peelability of the recording paper changes depending on the outer diameter of the peeling roller 31. In the fixing device 10, the recording paper is conveyed on the surface of the endless belt 41 that is passed along the surface of the peeling roller 31. Therefore, as the outer diameter of the peeling roller 31 is smaller, the endless belt 41 is bent in a direction away from the paper transport direction, so that the recording paper that has passed through the nip portion is easily peeled off from the endless belt 41. That is, the smaller the outer diameter of the peeling roller 31, the higher the peelability from the endless belt 41.

  In this way, after the recording paper on which the toner image is fixed is peeled off by the peeling roller 31, the toner melted by natural cooling is completely cured and sent out in the direction of the paper discharge mechanism of the printer described later. Note that the toner adhering to the endless belt 41 is cooled by the peeling roller 31 and is easily peeled off from the endless belt 41. In order to cool the endless belt 41 by the peeling roller 31, a material having high thermal conductivity, such as aluminum, may be used as the peeling roller 31.

  As described above, in the fixing device 10 of this embodiment, the metal cylinder 12 of the heating roller 11 is thinned to reduce the heat capacity of the heating roller 11. In addition, the endless belt 41 is arranged along the recording sheet that has passed through the nip portion, thereby improving the fixing property. Further, by reducing the outer diameter of the peeling roller 31, sufficient peelability can be ensured.

  Next, a printer (image forming apparatus) 40 provided with the fixing device 10 will be described. FIG. 3 is a schematic cross-sectional view of the printer 40 of the present embodiment. The printer 40 forms a multi-color or single-color image on a predetermined recording sheet based on, for example, image data transmitted from each terminal device on the network. Therefore, the printer 40 can select a full color printing mode or a monochrome printing mode.

  The printer 40, together with the fixing device 10 already described, includes an exposure unit 1, an image forming station P (Pa / Pb / Pc / Pd), an intermediate transfer belt unit 7, a transfer roller 6, a paper feed tray 8, a paper discharge tray ( A paper discharge mechanism / discharge mechanism) 9 is provided.

  Since the printer is capable of full-color printing and monochrome printing, the four image stations Pa, Pb, and Black correspond to each color of black (K), cyan (C), magenta (M), and yellow (Y). Pc and Pd are juxtaposed. That is, the image forming station Pa performs image formation using black (K) toner, the image forming station Pb performs image formation using cyan (C) toner, and the image forming station Pc includes magenta ( The image formation is performed using the toner M), and the image formation station Pd performs the image formation using the yellow (Y) toner.

  The image forming stations Pa to Pd have substantially the same configuration, and each includes a developing device 2 (2a, 2b, 2c, and 2d), a photosensitive drum 3 (3a, 3b, 3c, and 3d), and a cleaner unit. 4 (4a, 4b, 4c, 4d) and a charger 5 (5a, 5b, 5c, 5d) are provided. In the above and below, “a” to “d” assigned to each member number correspond to “a” to “d” assigned to each image forming station P.

  The exposure unit 1 exposes the surfaces of the photosensitive drums 3a to 3d charged by the charger 5 from below according to the image data input to the printer 40, and electrostatic latent images are formed on the surfaces of the photosensitive drums 3a to 3d. Form an image. As shown in FIG. 3, the exposure unit 1 is, for example, a laser scanning unit (LSU) including a laser irradiation unit and a reflection mirror. As the exposure unit 1, for example, an EL writing head or an LED writing head in which light emitting elements are arranged in an array can be used instead of the LSU.

  The chargers 5a to 5d provided in the image forming stations Pa to Pd uniformly charge the surfaces of the photosensitive drums 3a to 3d to a predetermined potential. As shown in FIG. 3, the chargers 5 a to 5 d may be, for example, a contact roller type or a brush type, or may be a non-contact charger type. Further, the developing devices 2a to 2d visualize the electrostatic latent images formed on the surfaces of the photosensitive drums 3a to 3d with toners of respective colors. The cleaner units 4a to 4d remove and remove toner remaining on the surfaces of the photosensitive drums 3a to 3d after the development processing in the developing units 2a to 2d and the transfer of the images formed on the photosensitive drums 3a to 3d. to recover.

  The intermediate transfer belt unit 7 includes an intermediate transfer belt 70, an intermediate transfer belt driving roller 71, an intermediate transfer belt driven roller 72, an intermediate transfer belt tension mechanism 73, intermediate transfer rollers 74 (74a, 74b, 74c, 74d), and an intermediate transfer belt. A cleaning unit 75 is provided.

  The intermediate transfer belt 70 is formed endlessly with a film having a thickness of about 100 μm to 150 μm. The intermediate transfer belt 70 is provided so as to be in contact with the photosensitive drums 3a to 3d, and the toner images of the respective colors formed on the photosensitive drums 3a to 3d are sequentially transferred. When the toner images of each color are superimposed on the intermediate transfer belt 70, a color toner image (multicolor toner image) is formed. The toner image formed on the intermediate transfer belt 70 is transferred onto a recording sheet by a transfer roller 6 described later.

  The intermediate transfer belt driving roller 71, the intermediate transfer belt driven roller 72, the intermediate transfer belt tension mechanism 73, and the intermediate transfer rollers 74a to 74d stretch the intermediate transfer belt 70, and in the direction of arrow A in FIG. The belt 70 is driven to rotate.

  The intermediate transfer rollers 74 a to 74 d are provided for each of the image forming stations Pa to Pd, and are rotatably supported by the intermediate transfer roller mounting portion of the intermediate transfer belt tension mechanism 73. The intermediate transfer rollers 74a to 74d are provided so as to face the photosensitive drums 3a to 3d via the intermediate transfer belt 70, and transfer the toner images formed on the surfaces of the photosensitive drums 3a to 3d to the intermediate transfer rollers 70a to 74d. A transfer bias for transferring onto the belt 7 is applied.

  Therefore, the intermediate transfer rollers 74a to 74d are based on a metal shaft such as stainless steel having a diameter of 8 to 10 mm, and the surface of the metal shaft is made of conductive material such as EPDM (ethylene-propylene-methylene copolymer) or urethane foam. It is covered with an elastic material. The transfer bias is applied to the intermediate transfer rollers 74a to 74d by applying a high-voltage transfer bias (a high voltage having a polarity (+) opposite to the toner charge polarity (-)) to transfer the toner image. Is uniformly applied to the intermediate transfer belt 70 by the conductive elastic material. In this embodiment, the roller-shaped intermediate transfer rollers 74a to 74d are used, but the same function can be obtained by using a brush-shaped transfer electrode.

  Further, the intermediate transfer belt cleaning unit 75 removes toner adhered to the intermediate transfer belt 70 by contact with the photosensitive drums 3a to 3d or toner remaining on the intermediate transfer belt 70 without being transferred onto the recording paper. Remove and collect. This prevents toner color mixing in the next printing step. The intermediate transfer belt cleaning unit 75 is provided with, for example, a cleaning blade that contacts the intermediate belt 70. By providing the cleaning blade at a position facing the intermediate transfer belt driven roller 72 with the intermediate transfer belt 70 interposed therebetween, it is possible to suitably remove toner.

  The transfer roller 6 transfers the toner image formed on the intermediate transfer belt 70 onto a recording sheet. The transfer roller 6 is disposed so as to be in pressure contact with the intermediate transfer belt 70 at a position where the recording paper and the intermediate transfer belt 70 are in contact with each other. Further, the transfer roller 6 is provided to face the intermediate transfer belt driving roller 71 with the intermediate transfer belt 70 interposed therebetween. Therefore, one of the transfer roller 6 and the intermediate transfer belt drive roller 71 is formed of a hard material such as metal so that the transfer roller 6 is pressed against the intermediate transfer belt 70 with a predetermined pressure, and the other is elastic rubber. It is preferable that the elastic roller is made of a soft material such as a foaming resin. A voltage for transferring the toner image formed on the intermediate transfer belt 70 onto the recording paper is applied to the transfer roller 6 (a high voltage having a polarity (+) opposite to the toner charging polarity (−)). .

  The paper feed tray 8 is a tray for storing recording paper used for image formation, and is provided below the image forming stations Pa to Pd and the exposure unit 1 of the printer 40.

  Further, the printer 40 is provided with a manual paper feed tray 8 ′ used when the user prints a small number of sheets. One end of the manual paper feed tray 8 ′ is attached to a side portion of the printer 40, and is attached to the side portion so as to be rotatable. Therefore, when the manual paper feed tray 8 ′ is not used, as shown by a broken line in FIG. 3, by placing the recording paper placement surface along the side of the printer 40, the printer 40 A compact design has been achieved. On the other hand, when the recording paper is manually supplied to the printer 40, the manual paper feed tray 8 ′ is moved so that the above-described placement surface is separated from the side portion of the printer 40, and the recording paper is placed on the placement surface. Can be placed.

  The paper discharge tray 9 is provided on the top of the printer 40 and is a tray for placing printed recording paper face down.

  In the printer 40 having the above-described configuration, the print processing operation is performed as follows. That is, when image data is input from the outside to the printer 40, the recording paper stored in the paper feed tray 8 is separated one by one by the pickup roller 81 provided at the end of the paper feed tray 8. The sheet is sent out to the sheet conveyance path S (the chain line in the figure). Thereafter, the recording paper is conveyed to the registration roller 99 by the conveyance roller 91, and the conveyance of the recording paper is temporarily stopped with the leading edge of the recording paper reaching the registration roller 99.

  On the other hand, when the recording paper placed on the manual paper feed tray 8 ′ is transported, the recording paper is separated and fed one by one by the pickup roller 82 and sent to the paper transport path S. . Thereafter, the sheet is conveyed by a plurality of conveyance rollers 96, 95, and 94 and conveyed to the registration roller 99.

  In parallel with the feeding of the recording paper from the paper feed tray 8 or the manual paper feed tray 8 ', the image forming stations Pa to Pd start forming a toner image based on the input image data. That is, when image data is input to the printer 40, the surfaces of the photosensitive drums 3a to 3d are charged by the chargers 5a to 5d. Thereafter, electrostatic latent images are formed on the surfaces of the photosensitive drums 3a to 3d by the exposure unit 1 in accordance with the input image data. In order to develop the electrostatic latent image, toner is supplied from the developing devices 2a to 2d to form a toner image. Subsequently, the toner images formed on the photosensitive drums 3a to 3d are sequentially transferred onto the intermediate transfer belt 70 by the intermediate transfer rollers 74a to 74d, and the toner images of the respective colors are overlapped to form a multicolor toner image. In the case of monochrome printing, only a black (K) toner image is formed on the intermediate transfer belt 70.

  When the toner image is formed on the intermediate transfer belt 70 in this way, the conveyance of the recording paper from the registration roller 99 is started at the timing aligned with the leading end of the toner image. As the recording paper passes between the transfer roller 6 and the intermediate transfer belt 70, the toner image is transferred onto the recording paper. Thereafter, after the toner image on the recording paper is melted and fixed and printed by the fixing device 10, the paper discharge roller (paper discharge mechanism / discharge mechanism) 92 and the paper discharge roller (paper discharge mechanism / discharge mechanism) 93 are printed. As a result, the paper is discharged onto the paper discharge tray 9. In the fixing device 10 of FIG. 3, configurations other than the heating roller 11 and the pressure roller 21 are omitted.

  When double-sided printing is requested, the recording paper on which one side is printed passes through the fixing device 10, and then the rear end of the recording paper is held by the paper discharge roller 93. With the trailing edge of the recording paper held, the paper discharge roller 93 rotates reversely to be guided to the transport rollers 97 and 98 and reach the registration roller 99 again. Thereafter, as described above, in accordance with the rotation timing of the intermediate transfer belt 70 to which the toner image has been transferred, the recording paper is conveyed and printing is performed on the surface opposite to the previously printed surface. .

  In this embodiment, a printer is described as an example. However, an image is formed by an electrophotographic method such as a copier, a fax machine, or a digital multifunction machine having a printer function, a copy function, a fax function, or the like. The fixing device 10 can be similarly applied to various image forming apparatuses.

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

  In addition, the present invention can be configured as follows.

Heating after transferring image information transmitted from each terminal device on the network to which the device is connected or image information read by the document reading unit of the device onto a sheet conveyed using the developer of the printing unit In the fixing mechanism composed of a roller and a pressure roller,
An endless belt longer than the outer periphery of the heating roller is placed on the outer periphery of the heating roller with a predetermined tension, and the unfixed developer on the paper is melted and fixed at a fixing nip formed by the endless belt and the pressure roller. A fixing device characterized by that.

  The fixing device according to claim 1, wherein the predetermined tension of the endless belt is applied by a tension roller disposed upstream in the paper conveyance direction with respect to a position where the heating roller is disposed.

  The fixing device according to claim 1, wherein the rotation of the endless belt is driven rotation with respect to the rotation of the heating roller.

  The surface temperature of the heating roller is thermally transferred to the endless belt while the endless belt rotates and moves from the point of contact with the heating roller to the fixing nip, and is necessary for melting and fixing the unfixed developer on the paper. Fixing device characterized by endless belt surface temperature.

  The fixing device, wherein the endless belt is heat-removed by passing through the tension roller.

  The fixing device according to claim 1, wherein the rotation of the endless belt is driven by the pressure roller.

  The fixing device, wherein the tension roller having the endless belt as a predetermined tension performs a sheet peeling action in the vicinity of a direction inflection point of the transported sheet in the transport direction of the endless belt.

  A fixing device, wherein a bridging straight line of an endless belt formed by the fixing nip and the tension roller is a paper discharge direction of the device.

  The fixing device, wherein the tension roller is in contact with the pressure roller via the endless belt.

  The fixing device according to claim 1, wherein the tension roller has a regular crown shape with a thick center portion and narrow end portions with respect to the entire length of the roller.

  The fixing device is characterized in that the endless belt is at least a thickness of less than 300 μm due to its rapid heat property, and is made of a material excellent in developer releasability.

  An image forming apparatus capable of mode selection between a full color printing mode and a monochrome printing mode, characterized by using the above-described fixing device.

  An embodiment of the present invention will be described below.

  In the fixing device according to the present embodiment, a roller made of iron having a diameter of 30 mm and a thickness of 0.25 mm was used as the heating roller. As a pressure roller, a roller having a diameter of 23 mm in which a core metal made of iron having a diameter of 11 mm, an elastic layer made of silicon rubber having a thickness of 6 mm, and a PFA of 30 μm on the surface layer thereof was used. The pressure roller is pressed against the heating roller using two springs having a spring pressure of 8.2 kgf. At this time, the contact width (nip width) between the heating roller and the pressure roller was 5.8 mm.

  Further, the endless belt disposed on the outer periphery of the heating roller has a 10 μm thick PFA (perfluoroalkoxytetrafluoroethylene copolymer) coated with PI (polyimide) having a thickness of 100 μm as a base (PI + PFA), or A silicon rubber (Si rubber) of 200 μm was formed using NI (nickel) as a substrate, and a PFA with a thickness of 40 μm was applied (NI + Si rubber + PFA).

  The endless belt is tensioned by a peeling roller provided downstream from the nip portion in the recording sheet conveyance direction. The peeling roller is arranged so that one of the tangents common to the heating roller is parallel to the recording paper conveyance direction. For this reason, the endless belt does not change the conveyance direction of the recording paper that has passed through the nip portion. Transport in parallel.

With this fixing device, the toner images formed on various recording papers were fixed while changing the fixing temperature (surface temperature of the endless belt), and the fixing performance was observed. The recording paper is 52 g / m ² (with or without voids (white background area without image information at the front end in the paper conveyance direction)), 64 g / m ² paper, 80 g / m ² , 105 g / m ² , 200 g. / M ² , recording paper was tested. The results are shown in FIGS. Here, FIG. 4 shows an experimental result of an apparatus using an endless belt of PI + PFA, and FIG. 5 shows an experimental result of an apparatus using an endless belt of NI + Si rubber + PFA.

  According to this, in the apparatus using the PI + PFA endless belt of FIG. 4, the optimum fixing temperature differs depending on the type of recording paper at a process speed of 120 mm / s, but 150 ° C. for 52 g to 110 g recording paper. In general, good fixing performance was obtained at a temperature of from 180 to 180 ° C., particularly at a temperature of from 170 to 180 ° C. In some cases, a cold offset occurred from 130 ° C. to 160 ° C., and a hot offset occurred from 190 ° C. to 210 ° C. However, when the fixing temperature exceeded 180 ° C., a scale-like pattern due to poor fixing appeared at the tip. In addition, with a 200 g recording paper, when the process speed was 120 mm / s, fixing was not successful unless the temperature was raised to about 220 ° C. Thus, when 200 g of recording paper was tested at a process speed of 65 mm / s and 50 mm / s, fixing was possible at a fixing temperature of 170 ° C. to 190 ° C. However, even in this case, there is a problem that a scale-like pattern is formed on the printing surface (indicated by “S” in FIG. 4).

  In the apparatus using the endless belt of NI + Si rubber + PFA shown in FIG. 5 as well, the fixing temperature was generally good at 150 ° C. to 180 ° C. on the recording paper of 52 g to 110 g as in FIG. . Further, even with 200 g recording paper, the process speed of 120 mm / s recording paper has to be heated to about 220 ° C., and the fixing speed is increased from 170 ° C. to 190 ° C. when the process speed is 65 mm / s and 50 mm / s. It was possible to settle. On the other hand, for the scale-like pattern, the recording paper was satisfactorily pressed against the pressure roller by the Si rubber portion of the endless belt, and therefore the scale-like pattern did not appear.

  Next, in the apparatus of Example 1, a PI (thickness: 100 μm) coated with PFA is used as an endless belt, and the recording paper from the fixing device is unified to 52.3 g paper and a process speed of 120 mm / s. The peelability of was observed. As fixing conditions, the orientation of the recording paper (horizontal eyes, vertical eyes), whether the recording paper has voids, or whether the toner image forming surface of the recording paper is vertically upward or downward is changed. The experiment was conducted.

  The results are shown in FIG. According to this, at a fixing temperature of about 150 ° C. to 170 ° C., no wrapping occurred and good fixing was performed. However, when the hot offset region is 180 ° C. or higher, the recording paper may not remain attached to the endless belt in some cases and may be caught by the heating roller (shown as “wrapping” in FIG. 6). This winding of the recording paper was prevented when there was a void because there was no toner layer at the leading edge of the paper and the peelability was improved. Further, when the toner image forming surface of the recording paper faced downward, the winding was likely to occur.

  In the above apparatus using a 100 μm thick PI coated with 10 μm PFA as an endless belt, the rapid heat property of each roller was observed. The horizontal axis represents the time since the heater of the heating roller was turned on, and the vertical axis represents the temperatures of the heating roller, the pressure roller, and the peeling roller. The results are shown in FIG. According to this, the time required to reach the fixing temperature of 180 ° C. was as good as about 40 seconds.

  In the fixing device according to this embodiment, a roller made of iron having a diameter of 40 mm and a thickness of 0.25 mm was used as the heating roller. As the pressure roller, a roller having a diameter of 23 mm, in which a core metal made of SUS having a diameter of 11 mm and an elastic layer having a thickness of 6 mm was provided. The pressure roller is pressed against the heating roller using two springs having a spring pressure of 6.5 kgf. The nip width at this time was 4.9 mm. Further, MI paper was used as the recording paper, and the process speed was 125 mm / s.

  In this apparatus, the position of the peeling roller where the endless belt in the downstream portion of the nip advances in the direction parallel to the paper conveyance direction in the nip portion is set to 0, and the peeling roller is connected to the shaft of the heating roller and the pressure roller. In a direction parallel to the line, it was brought close to the pressure roller for a fixed distance (when it was brought closer to xmm, it was set to -xmm), and the bending (curl) of the recording paper after fixing was observed. Curl placed the discharged paper on a horizontal base and measured the floating of the recording paper (distance from the base at the end of the recording paper).

  The results are shown in FIG. According to this, the curling hardly occurred when the position of the peeling roller was 0, -5 mm, regardless of the fixing temperature, but the float of 60 mm-80 mm occurred when the position was -10 mm to -20 mm. Therefore, in order to prevent curling, it is preferable to dispose the peeling roller at a position where the endless belt in the downstream portion of the nip portion advances in a direction parallel to the paper conveyance direction to the nip portion.

  Under the same conditions as in the fixing device of Example 4, only the distance from the nip portion to the peeling roller in the endless belt was changed to 30 mm to 70 mm, and the length of the scale pattern recognized on the toner image after fixing was measured. did. The results are shown in FIG.

  According to this, it can be seen that when the distance is 30 mm, the scale pattern at the front end of the sheet becomes large. That is, this scale pattern is large when the distance to the peeling roller is short and the fixing is insufficient. Therefore, the distance from the nip portion to the peeling roller is preferably larger than 30 mm.

  Note that this gloss unevenness is a phenomenon that occurs due to non-uniform separation of the paper between the nip portion and the separation roller. Therefore, when the peeling roller is brought into contact with the heating roller so that the paper is not peeled between the nip portion and the peeling roller, the contact property between the endless belt and the paper is improved, and the scale pattern can be prevented.

  In the apparatus of Example 1, polyimide + PFA is used as an endless belt, and the width of the nip portion is changed to 4.0 mm, 5.8 mm, and 6. by changing the spring pressure of the pressure roller or the outer diameter of the pressure roller. It was set to 0 mm. To make the width of the nip portion 4.0 mm, the pressure pressure of the pressure roller is 4.7 kgf × 2, and to make the width of the nip portion 6.0 mm, the diameter of the pressure roller is 40 mm. It was. The nip portion having a width of 5.8 mm is the same as that of the first embodiment.

  The results are shown in FIGS. 10 shows the result of the fixing device having a nip width of 4.0 mm, FIG. 11 shows the nip width of 5.8 mm, and FIG. 12 shows the result of the fixing device having a nip width of 6.0 mm. According to this, a suitable fixing temperature is lowered as the nip width is increased. Therefore, by increasing the nip width, the fixing performance is improved and fixing at a low temperature is possible. Therefore, it is possible to reduce the power consumption of the heat source for fixing and shorten the warm-up time.

  The fixing device of the present invention is used in an image forming apparatus such as a printer, a copying machine, a fax machine, or a digital multi-function machine having these functions, which uses toner to form an image by electrophotography. it can. Since the fixing device can sufficiently secure the fixing property of the toner image on the recording paper and the releasability of the recording paper, it can cope with both monochrome printing and color printing. Further, since the heating roller is thinned and the outer diameters of the pressure roller and the peeling roller are reduced, it is possible to achieve downsizing and power saving of the fixing device, and an image forming apparatus including the fixing device. Can be reduced in size and power consumption.

1 is a schematic cross-sectional view illustrating an embodiment of a fixing device according to the present invention. It is a schematic sectional drawing which shows other one Embodiment of the fixing device in this invention. It is a schematic sectional drawing which shows one Embodiment of the printer in this invention provided with the said fixing device. 6 is a drawing showing the results of an experiment in which the fixing temperature, fixing performance and offset of a heating roller were observed when a PI + PFA endless belt of the fixing device according to the present invention was used. 6 is a diagram showing the results of an experiment in which the fixing temperature, fixing performance, and offset of a heating roller were observed when an endless belt of NI + Si rubber + PFA was used in the fixing device of the present invention. 6 is a drawing showing the results of an experiment in which the fixing temperature, fixing performance and offset of a heating roller were observed in the fixing device according to the present invention. 6 is a diagram showing results of an experiment in which temperature changes of the heating roller, the pressure roller, and the peeling roller are observed from the time when the heat source of the heating roller is turned on in the fixing device according to the present invention. 6 is a diagram showing the results of an experiment in which bending of a recording sheet after fixing was observed using an apparatus with a different position of a peeling roller in the fixing device according to the present invention. 6 is a drawing showing the results of an experiment in which the fixing performance of the fixing device according to the present invention was observed using a device in which the distance between the nip portion of the endless belt and the portion of the endless belt suspended from the peeling roller was different. In the fixing device according to the present invention, it is a drawing showing the results of an experiment in which the fixing temperature, fixing performance and offset of a heating roller were observed with a nip width of 4 mm. In the fixing device according to the present invention, it is a drawing showing the results of an experiment in which the fixing temperature, fixing performance and offset of a heating roller were observed with a nip width of 5.8 mm. In the fixing device according to the present invention, it is a drawing showing the results of an experiment in which the fixing temperature, fixing performance and offset of a heating roller were observed with a nip width of 6.0 mm.

Explanation of symbols

10 Fixing Device 11 Heating Roller 12 Cylinder (Metal Cylinder)
14 Heater (heat source)
21 Pressure roller 22 Core 31 Peeling roller (tension member)
40 Printer (image forming device)
41 endless belt

Claims (16)

In a fixing device for fixing a developer on a conveyed recording medium,
A cylindrical heating roller made of a heat conductive material;
An endless belt that is disposed so as to be in contact with at least a part of the outer periphery of the heating roller, and is longer than the outer periphery of the heating roller;
A tension member that is disposed downstream of the heating roller in the conveyance direction of the recording medium, and on which the endless belt is suspended;
And a pressure roller that presses against the heating roller via the endless belt and forms a nip portion with the endless belt.   The fixing device according to claim 1, wherein a thickness of the heating roller is 3 mm or less.   The fixing device according to claim 1, wherein the endless belt has a thickness of 300 μm or less.   The fixing device according to claim 1, wherein the endless belt includes a belt elastic layer having elasticity.   The fixing device according to claim 1, wherein the tension member applies tension to the endless belt.   The fixing device according to claim 1, wherein the endless belt rotates following the rotation of the heating roller.   The fixing device according to claim 1, wherein the pressure roller is driven to rotate with respect to rotation of the endless belt.   8. The temperature at which the developer can be melted by absorbing heat of the heating roller while the endless belt is in contact with the heating roller. The fixing device according to Item 1.   9. The developer according to claim 1, wherein the endless belt fixes the developer on the recording medium by a portion from the nip portion of the endless belt to the suspension on the tension member. The fixing device according to 1.   The fixing device according to claim 1, wherein the tension member cools the endless belt.   The fixing device according to claim 1, wherein the tension member bends the endless belt so that a diameter of a curvature circle is 15 mm or less.   The pressure roller and the tension member are arranged so that a portion from the nip portion of the endless belt to the tension member is perpendicular to a line connecting the axes of the heating roller and the pressure roller. The fixing device according to claim 1, wherein   The fixing device according to claim 1, wherein the tension member is disposed so as to contact the pressure roller.   The fixing device according to claim 1, wherein the tension member has a roller shape, and has a shape in which a central portion in an axial direction is thick and both end portions are narrow.   An image forming apparatus comprising the fixing device according to claim 1.   16. The image forming apparatus according to claim 15, wherein a monochrome printing mode or a full color printing mode can be selected.

Images