JP4673050B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

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

  In an image forming apparatus such as an electrophotographic apparatus or an electrostatic recording apparatus, an image is formed by transferring a toner image onto a sheet and fixing it. As a fixing device for fixing an unfixed toner image by heating and melting, a roller fixing system is generally used in which a pressure roller is pressed against a fixing roller having a heater therein to form a nip, and fixing is performed.

  By the way, in order to output a highly glossy image, it is necessary to lengthen the sheet nip passing time and sufficiently melt the toner. At this time, in the roller fixing method, if the nip is to be widened, the roller diameter must be increased, and the apparatus becomes large. Further, the toner can be sufficiently melted by reducing the roller rotation speed, but it is difficult to increase the speed.

  In view of this, an upper and lower belt fixing method that can achieve a sufficient width (length in the conveying direction) of the press contact portion while achieving a reduction in the size and speed of the apparatus with respect to the roller fixing method is disclosed in Japanese Patent Application Laid-Open No. 11-151867. -174878) and Patent Document 2 (Japanese Patent Laid-Open No. 05-072926). In these proposals, the fixing device includes two opposing belt members, and a large width of the press contact portion is obtained by sandwiching and conveying these belt members.

Japanese Patent Laid-Open No. 11-174878 JP 05-072926 A

  However, in the fixing device disclosed in Patent Document 1 and Patent Document 2, the high pressure portion that is pressed between the support members and the pressure that is not supported from both sides of the belt are released in the press contact portion. There is a part. For this reason, when an unfixed toner image is to be fixed, a difference in conveyance speed occurs between the high pressure portion and the missing portion. Since the belt member has a certain degree of flexibility, there arises a problem that the belt expands and contracts due to a difference in conveyance speed, and an image on the sheet shifts. In addition, since air and water vapor in the toner layer cannot be suppressed at the pressure-removal portion, image disturbance is likely to occur particularly in a sheet having low air permeability such as coated paper.

  SUMMARY OF THE INVENTION Accordingly, the present invention provides a fixing device capable of high-speed fixing and preventing image misalignment, and an image forming apparatus provided with the fixing device, by improving the pressure distribution in the pressure contact portion of the fixing device. It is an object.

In order to solve the above-described problems, a typical configuration of the fixing device according to the present invention includes a first belt, a second belt that contacts the first belt, and a second belt from the inner surface of the first belt. A first pressure member that pressurizes the belt toward the belt, a second pressure member that pressurizes the inner surface of the second belt toward the first pressure member, and the first pressure member in the sheet conveying direction. A first roller that is disposed on the downstream side of the first belt and stretches the first belt, and is disposed on the downstream side of the second pressure member in the sheet conveying direction, and is disposed via the first and second belts. A first pressure member, comprising: a second roller that presses the first roller and stretches the second belt; and a driving means that transmits a driving force to at least the first or second roller. The second pressure member, the first roller, and the second roller form a nip portion that conveys the sheet. In a fixing device that heats an image on a sheet at a nip portion, the first pressure member is arranged so as to be shifted in the sheet conveyance direction with respect to the second pressure member, and the first roller is a second roller. The nip portion is continuously formed by the first pressure member, the second pressure member, the first roller, and the second roller, and the pressure in the nip portion is The pressure between the first roller and the second roller is maximum.

  According to the present invention, when a belt is used in the fixing device, the pressure is applied from the pressure unit facing the gap between the two or more support members. Accordingly, the use of the belt can dramatically increase the width of the press contact portion, and a high gloss image can be output even when the speed is increased. At the same time, there is no pressure loss portion, and the occurrence of image misalignment can be prevented.

  Hereinafter, the present invention will be described more specifically with reference to examples. Although these examples are examples of the best mode of the present invention, the present invention is not limited to these examples.

{First Example}
A first embodiment of a fixing device and an image forming apparatus according to the present invention will be described. First, the overall configuration of the image forming apparatus will be described with reference to FIG.

  The image forming apparatus shown in FIG. 6 is an image forming apparatus (so-called printer) that employs an electrophotographic system.

  The image forming apparatus 1 includes a photosensitive drum 2 as an example of an image carrier that carries a latent image. The photosensitive drum 2 is uniformly charged by the charger 3, and a latent image is formed by irradiating light 5 from the optical device 4. The latent image is developed by a developing device 6 as an example of developing means for developing the latent image to form a toner image. The toner image is transferred onto a sheet by a transfer roller 7 as an example of a transfer unit, and the toner remaining on the photosensitive drum 2 is removed by a cleaning device 8.

  The sheet S is provided in a feeding cassette 9 at the lower part of the apparatus, and is fed by a feeding roller 10. The sheet is conveyed in synchronism with the image on the photosensitive drum 2 by a registration roller pair 11 as an example of conveying means, and after the toner image is transferred, the sheet is conveyed to the fixing device A. The sheet S is heated and pressed in the fixing device A to fix the toner image, and is discharged and stacked on the discharge tray 13 at the top of the device by the discharge roller pair 12.

  FIG. 1 is a cross-sectional view of a fixing device A according to this embodiment, and FIG. 2 is a cross-sectional view illustrating a comparative example. As shown in the figure, the fixing device A includes a fixing belt 20 as an example of a first belt and a pressure belt 21 as an example of a second belt. The fixing belt 20 has a polyimide base layer having an inner diameter of 34 mm and a thickness of 75 μm, and a heat-resistant silicone rubber layer having a thickness of 300 μm is provided as an elastic layer on the outer periphery of the base layer. This silicone rubber has a hardness of JIS-A 20 degrees and a thermal conductivity of 0.8 W / mK. Further, on the outer periphery of the elastic layer, a fluororesin layer (for example, PFA or PTFE) is provided with a thickness of 30 μm as a surface release layer. The pressure belt 21 has an inner diameter of 34 mm and a polyimide layer with a thickness of 75 μm as a base layer, and a PFA tube made of a fluororesin with a thickness of 30 μm as a release layer.

  The fixing belt 20 is stretched by a fixing roller 22 and a pressure roller 23 (first roller). The fixing roller 22 is an iron hollow roller having an outer diameter of 20 mm and an inner diameter of 18 mm and a thickness of 1 mm, and a halogen heater 22a as an example of a heating unit is disposed therein. The pressure roller 23 is provided with a silicone rubber sponge layer on an iron alloy core bar having an outer diameter of 20 mm and a diameter of 16 mm in order to reduce heat conductivity and reduce heat conduction from the fixing belt 20. It is. The hardness of the pressure roller 23 at the center in the longitudinal direction is about 60 degrees with an ASK-C hardness meter. The rotation of the fixing belt 20 is driven by a friction between the surface of the silicone rubber sponge of the pressure roller 23 and the inner surface polyimide layer of the fixing belt 20 by driving the pressure roller 23 by a motor (not shown).

  Between the fixing roller 22 and the pressure roller 23, a pressure pad 24 as an example of a first pressure member that supports the fixing belt 20 is arranged close to each other at a distance of about 1 mm from these rollers. Has been. The pressure pad 24 is an elastic body made of a heat-resistant silicone rubber having a thickness of 3 mm and a width of 8 mm, and is fixedly disposed so as to be slidable with respect to the fixing belt 20.

  The pressure belt 21 is stretched by a pressure roller 25 disposed on the upstream side of the pressure contact portion and a pressure roller 26 (second roller) disposed on the downstream side. The pressure roller 25 disposed on the upstream side of the pressure contact portion is the same as the pressure roller 23 disposed in the fixing belt 20, and is an iron alloy cored bar having an outer diameter of 20 mm and a diameter of 16 mm. In addition, a silicone rubber sponge layer is provided in order to reduce the heat conductivity and reduce the heat conduction from the fixing belt 20. The pressure roller 26 disposed on the downstream side of the press contact portion is provided with a core rubber made of an iron alloy having an outer diameter of 20 mm and a thickness of 1.0 mm, and a silicone rubber layer having a thickness of 0.3 mm. That is, the pressure roller 26 is configured to have higher rigidity than the pressure roller 23 facing the pressure roller 26.

  Between the pressure roller 25 and the pressure roller 26, a pressure pad 27 as an example of a second pressure member that supports the pressure belt 21 is disposed close to the rollers at a distance of about 1 mm. Has been. The pressure pad 27 is an elastic body like the pressure pad 24, and is made of a heat-resistant silicone rubber having a thickness of 3 mm and a width of 8 mm. The pressure pad 27 is slidably fixed to the pressure belt 21. Yes.

  The fixing belt 20 is rotationally driven in the direction of the arrow X in FIG. 1 by rotating the pressure roller 23 by a driving unit (not shown) at least during execution of image formation. The circumferential speed of the fixing belt 20 is substantially the same as the conveyance speed of the sheet S conveyed from the image transfer unit side. The pressure belt 21 is rotated in the arrow Y direction by being driven by the fixing belt 20 or by driving the pressure roller 26 so as to have the same peripheral speed. In the case of this embodiment, the surface rotation speed of the fixing belt 20 is rotated at 300 mm / sec, and 70 A4 size full-color images can be fixed per minute.

  In a state where the fixing belt 20 rises to a predetermined fixing temperature and is temperature-controlled, the sheet S having the unfixed toner image T is conveyed between the fixing belt 20 and the pressure belt 21 (pressure contact portion) in the pressure contact portion. The The sheet S is introduced with the surface carrying the unfixed toner image facing the fixing belt 20 side. Then, the unfixed toner image side of the sheet S is in close contact with the outer peripheral surface of the fixing belt 20, and the pressure contact portion is nipped and conveyed together with the fixing belt 20, so that heat of the fixing belt 20 is mainly applied and the pressure contact portion. The unfixed toner image T is fixed to the surface of the sheet S by heat and pressure.

  Further, since the pressure roller 26 located downstream in the pressure belt 21 has higher rigidity than the pressure roller 23 in the fixing belt 20, the pressure contact portion outlet between the fixing belt 20 and the pressure belt 21 has a higher rigidity. As a result, the deformation of the pressure roller 23 is increased, and as a result, the fixing belt 20 is also largely deformed, and the toner image is separated from the fixing belt 20 and the sheet can be separated and conveyed satisfactorily.

  Here, as the support member inside the pressure belt 21, the fixing roller 22, the pressure roller 23, and the pressure pad 24 correspond. Further, the pressure roller 25, the pressure roller 26, and the pressure pad 27 correspond to the support members inside the fixing roller 22. Although these are arranged close to each other, if they are arranged with their gaps facing each other, a pressure release portion will be generated.

  Therefore, in the present embodiment, the fixing belt 20 and the pressure belt 21 that are substantially target support member arrangements are arranged so as to be shifted by a predetermined amount in the conveyance direction. As a result, the pressure roller 26 on the downstream side of the pressure belt 21 faces the gap between the pressure roller 23 and the pressure pad 24 of the fixing belt 20 and is arranged so as to pressurize it. In this embodiment, the pressure roller 26 is arranged so as to press both the pressure roller 23 and the pressure pad 24.

  Similarly, the pressure pad 24 on the upstream side of the fixing belt 20 is disposed so as to press the gap between the pressure roller 26 and the pressure pad 27 of the pressure belt 21. That is, the pressure pad 24 is arranged so as to press both the pressure roller 26 and the pressure pad 27.

  Further, the pressure pad 27 of the pressure belt 21 is disposed so as to press the gap between the fixing roller 22 and the pressure pad 24 of the fixing belt 20. That is, the pressure pad 27 is arranged so as to press both the fixing roller 22 and the pressure pad 24.

  Further, the fixing roller 22 of the fixing belt 20 is disposed so as to press the gap between the pressure roller 25 of the pressure belt 21 and the pressure pad 27. That is, the fixing roller 22 is arranged so as to press both the pressure roller 25 and the pressure pad 27.

  In the fixing device A configured as described above, the width in the belt rotation direction (length in the transport direction) of the pressure contact portion between the fixing belt 20 and the pressure belt 21 is about 25 mm. Since this width is wide, sufficient fixing can be performed even if the sheet is conveyed at high speed.

  Further, since the other supporting member is pressed against the gap between the supporting members inside one of the fixing belt 20 and the pressure belt 21, no pressure loss occurs. Therefore, although it is a wide pressure contact portion, there is no conveyance speed difference, and no image displacement occurs. In the configuration of this example, it was confirmed whether or not the image deviation occurred on the coated paper having low air permeability. As a result, no image deviation occurred.

  Further, since the pressure pads 24 and 27 are made of an elastic body, the pressure in the nip is maximized at a portion where the fixing roller 23 and the pressure roller 26 face each other. Thereby, if each belt is driven by the upper and lower rollers, both belts can be stably rotated without slipping.

  On the other hand, FIG. 2 shows a comparative example in which the fixing roller 22 and the pressure roller 25, the pressure pad 24 and the pressure pad 27, and the pressure roller 23 and the pressure roller 26 are opposed to each other. Accordingly, in the configuration of the fixing device A ′ shown in FIG. 2, the gaps of the support members are opposed to each other, and a pressure relief portion exists in this portion. In this comparative example, when coated paper was passed, occurrence of image misalignment was confirmed.

  In the present embodiment, the fixing belt 20 is described as being shifted downstream in the conveying direction with respect to the pressure belt 21, so that the pressure pad 27, the pressure pad 24, the pressure roller 26, and the pressure roller 23 are sequentially arranged. The nip is formed continuously. However, the fixing belt 20 may be shifted to the upstream side in the conveying direction. In this case, the nip is continuously formed in the order of the pressure pad 24, the pressure pad 27, the pressure roller 23, and the pressure roller 26.

{Second Example}
A second embodiment of the fixing device and the image forming apparatus according to the present invention will be described. FIG. 3 is a diagram illustrating a fixing device B according to the present embodiment, and FIG. 4 is a diagram illustrating a comparative example. The same parts as those in the first embodiment are denoted by the same reference numerals and the description thereof is omitted. In this embodiment, the image forming apparatus 1 is provided with a fixing device B described below instead of the fixing device A described above.

  The fixing belt 30 as an example of the first belt in the fixing device B has an inner diameter of 34 mm and has a base layer made of nickel manufactured by an electroforming method, and the base layer has a thickness of 50 μm. A heat-resistant silicone rubber layer having a thickness of 300 μm is provided on the outer periphery of the base layer as an elastic layer. This silicone rubber has a hardness of JIS-A 20 degrees and a thermal conductivity of 0.8 W / mK. Further, on the outer periphery of the elastic layer, a fluororesin layer (for example, PFA or PTFE) is provided with a thickness of 30 μm as a surface release layer. On the inner surface of the base layer, a resin layer such as fluororesin or polyimide may be provided in an amount of 10 to 50 μm in order to reduce sliding friction with the belt guide member 32 described later. In this example, 20 μm of polyimide was provided. When the inclusion that the inner surface of the fixing belt 30 is in contact with is conductive, it is desirable that the inner surface of the fixing belt 30 has an electrical insulating layer in order to cause an induced current to flow effectively through the fixing belt base metal layer. In addition to nickel, the fixing belt 30 can be appropriately selected from iron alloy, copper, silver, and the like. Moreover, the structure of laminating | stacking these metals on a resin base layer may be sufficient. The thickness of the metal layer may be adjusted according to the frequency of the high-frequency current flowing through the induction heating coil, which will be described later, and the magnetic permeability and conductivity of the metal layer, and is set between about 5 and 200 μm.

  The pressure belt 31 as an example of the second belt in the fixing device B has an inner diameter of 34 mm and a thickness of 75 μm as a base layer, and the surface is provided with a PFA tube made of fluororesin as a release layer with a thickness of 30 μm. It was. In order to reduce sliding friction with the belt guide member 33 described later, it is preferable to disperse fine particles of fluororesin in polyimide as a base layer.

  The fixing belt 30 is supported by a belt guide member 32 and a pressure roller 34.

  The belt guide member 32 is made of a resin having elasticity, and in this embodiment is made of PPS (polyphenylene sulfide resin). The belt guide member 32 applies a tension of about 49 N to the fixing belt 30, and a rib is provided at a portion in contact with the inner surface of the fixing belt 30. The ribs are provided to reduce the frictional resistance by reducing the area where the belt guide member 32 contacts the inner surface of the fixing belt 30. Another reason for this is to reduce the area of contact with the inner surface of the fixing belt 30 and reduce the conduction of heat from the heated fixing belt 30 to efficiently keep only the fixing belt 30 at a high temperature. However, since the pressure is applied by the belt guide member 32 at the pressure contact portion between the fixing belt 30 and the pressure belt, the pressure contact portion of the belt guide member 32 has no rib.

  By using the belt guide member 32 that is a fixed member, the amount of heat transferred from the inner surface of the belt can be reduced as compared with the case of a rotating roller, and the warm-up time is shortened. This is because, in the case of a rotating roller, compared to a fixed guide member, heat is absorbed from the inner surface of the belt to the roller surface when in contact with the inner surface of the belt. This is because heat transfer from the belt inner surface increases because the cycle of heat absorption from the belt inner surface is repeated.

  In addition, by using the belt guide member 32, the two members of the roller and the pad can be arranged continuously, so that no pressure release portion is generated.

  The pressure roller 34 has an outer diameter of 20 mm, a diameter of the central portion in the longitudinal direction of 16 mm, and a diameter of both ends of the iron alloy cored bar made of iron alloy. A silicone rubber sponge layer is provided to reduce conduction. The hardness of the pressure roller 34 in the central portion in the longitudinal direction is about 60 degrees with an ASK-C hardness meter. The reason why the mandrel is tapered is to make the width of the pressure contact portion with the pressure roller 35 uniform in the longitudinal direction even if the pressure roller 34 is bent when being pressed. The belt guide member 32 and the pressure roller 34 are arranged close to each other with a distance of about 1 mm. The fixing belt 30 is rotated by driving the pressure roller 34 by a motor (not shown), and the fixing belt 30 rotates by friction between the silicone rubber sponge surface of the pressure roller 34 and the inner surface polyimide layer of the fixing belt 30.

  The pressure belt 31 is supported by a belt guide member 33 and a pressure roller 35.

  The belt guide member 33 is made of an elastic resin and is made of PPS in this embodiment. The belt guide member 33 applies a tension of about 49 N to the pressure belt 31, and a rib is provided at a portion in contact with the inner surface of the pressure belt 31. The ribs are provided to reduce the frictional resistance by reducing the area where the belt guide member 33 contacts the inner surface of the pressure belt 31. However, since the belt guide member 33 is pressurized at the pressure contact portion between the fixing belt 30 and the pressure belt 31, the belt guide member 33 at the pressure contact portion has no rib.

  By using the belt guide member 33 which is a fixing member, the two members of the roller and the pad can be continuously arranged, so that no pressure loss portion is generated.

  In the pressure roller 35, a core rubber made of an iron alloy having an outer diameter of 20 mm and a thickness of 1.0 mm is provided with a silicone rubber layer having a thickness of 0.3 mm. The belt guide member 33 and the pressure roller 35 are arranged close to each other with a distance of about 1 mm. The pressure belt 31 is rotated by driving the pressure roller 35 by a motor (not shown), and the pressure belt 31 is rotated by friction between the silicone rubber surface of the pressure roller 35 and the polyimide layer of the pressure belt 31.

  In the fixing device B configured as described above, the width in the belt rotation direction (length in the conveying direction) of the pressure contact portion between the fixing belt 30 and the pressure belt 31 is about 25 mm. Since this width is wide, sufficient fixing can be performed even if the sheet is conveyed at high speed.

  The belt guide member 33 is pressed toward the belt guide member 32 by about 98 N, and the pressure roller 35 is pressed toward the pressure roller 34 by about 294 N. At this time, since the pressure per unit area is higher at the positions of the roller pairs 34 and 35 than at the pair of belt guide members 32 and 33 in the press contact portion, if each belt is driven by the upper and lower rollers, both belts It can be rotated stably without slipping.

  Further, since the pressure roller 35 is harder than the pressure roller 34, the pressure roller 34 is greatly deformed at the exit of the pressure contact portion between the fixing belt 30 and the pressure belt 31, and as a result, the fixing belt 30 is also large. The toner image is deformed and the toner image is self-separated, and the sheet can be well separated from the fixing belt 30 and conveyed.

  The induction heating coil 36 as a heating source for the fixing belt 30 is covered with a magnetic core 37 so that the magnetic field generated by the induction heating coil 36 does not leak to any part other than the metal layer of the fixing belt 30, and is further electrically insulating. The induction heating coil 36 and the magnetic core 37 are integrally molded with resin. The fixing belt 30 and the induction heating coil 36 are electrically insulated by a 0.5 mm mold, and the distance between the fixing belt 30 and the induction heating coil 36 is constant at 1.5 mm (the distance between the mold surface and the fixing belt surface is 1.0 mm). The fixing belt 30 is uniformly heated. The length of the induction heating coil 36 along the sheet passing width direction of the sheet S (the direction perpendicular to the conveying direction of the sheet S) is longer than the sheet passing width of the maximum sheet passing width used for image formation. It is formed to become. A high frequency current of 20 to 50 kHz is passed through the induction heating coil described above, and the metal layer of the fixing belt 30 generates heat by induction, so that the temperature of the temperature sensor is constant at 170 ° C. which is the target temperature of the fixing belt 30. The temperature is adjusted by changing the frequency of the high-frequency current based on the detected value to control the power input to the induction heating coil. Since the silicone rubber sponge layer of the pressure roller 34 is 2 mm even at the thinnest point and the cored bar hardly generates heat by the induction heating coil 36, only the fixing belt 30 can be efficiently heated in this embodiment. The temperature sensor is attached to the belt guide member 32, and is in contact with a position where the amount of heat generated by the induction heating coil 36 on the inner surface of the fixing belt 30 is the highest, and detects the temperature of that portion.

  The fixing belt 30 is rotationally driven in the arrow X direction by rotating the pressure roller 34 by a driving unit (not shown) at least during execution of image formation. Similarly, the pressure belt 31 is rotationally driven in the direction of the arrow Y when the pressure roller 35 is rotationally driven by a driving unit (not shown). These peripheral speeds are substantially the same as the conveyance speed of the sheet S conveyed from the image transfer unit side. In the case of this embodiment, the surface rotation speed of the fixing belt 30 and the pressure belt 31 rotates at 300 mm / sec, and 70 A4 size full-color images can be fixed per minute.

  Further, in a state where the fixing belt 30 rises to a predetermined fixing temperature and is temperature-controlled, the sheet S having the unfixed toner image T is interposed between the fixing belt 30 and the pressure belt 31 (pressure contact portion) in the pressure contact portion. Be transported. The sheet S is introduced with the surface carrying the unfixed toner image facing the fixing belt 30 side. The unfixed toner image side of the sheet S is in close contact with the outer peripheral surface of the fixing belt 30, and the pressure contact portion is nipped and conveyed together with the fixing belt 30, so that heat of the fixing belt 30 is mainly applied, and the pressure contact portion. The unfixed toner image T is fixed to the surface of the sheet S by heat and pressure.

  The pressure belt 31 is movable so as to be in contact with the fixing belt 30 by a cam (not shown). By this mechanism, the pressure belt 31 is separated from the fixing belt 30 except during the fixing operation. As a result, the heat of the fixing belt 30 is not conducted to the pressure belt 31, so that the warm-up time of the fixing device B is, for example, in the induction heating coil 36 when the pressure belt 31 is separated from the fixing belt 30. When 1200 W is input, the target temperature of 170 ° C. can be reached in about 18 seconds.

  Here, the belt guide member 32 and the pressure roller 34 correspond to the support members inside the fixing belt 30. Further, the belt guide member 33 and the pressure roller 35 correspond to the support members inside the pressure belt 31. Although these are arranged close to each other, if they are arranged with their gaps facing each other, a pressure release portion will be generated.

  In this embodiment, the fixing belt 30 and the pressure belt 31 that are substantially the target support member arrangement are shifted by a predetermined amount in the transport direction. As a result, the pressure roller 35 of the pressure belt 31 faces the gap between the belt guide member 32 and the pressure roller 34 of the fixing belt 30 and is arranged to pressurize the gap. In this embodiment, the pressure roller 35 is disposed so as to press both the belt guide member 32 and the pressure roller 34.

  At the same time, the belt guide member 32 of the fixing belt 30 is disposed so as to press the gap between the belt guide member 33 and the pressure roller 35. That is, the belt guide member 32 is arranged so as to press both the belt guide member 33 and the pressure roller 35.

  As described above, since the support member in the other side pressurizes the gap between the support members in one side of the fixing belt 30 or the pressure belt 31, no pressure loss occurs. FIG. 3B shows the pressure distribution at the pressure contact portion in the configuration of this example, and it can be seen that there is no large pressure loss portion and the pressure gradually increases from the upstream side. Therefore, although it is a wide pressure contact portion, there is no conveyance speed difference, and no image displacement occurs. In the configuration of this example, it was confirmed whether or not the image deviation occurred on the coated paper having low air permeability. As a result, no image deviation occurred.

  On the other hand, FIG. 4A shows a comparative example in which the belt guide members 32 and 33 and the pressure rollers 34 and 35 are opposed to each other. Accordingly, in the configuration of the fixing device B ′ illustrated in FIG. 4A, the gaps of the support members are opposed to each other. FIG. 4B shows the pressure distribution at the press contact portion in the configuration of this comparative example, and it can be seen that there is a large pressure release portion at the portion where the gap of the support member is opposed. In this comparative example, when coated paper with low air permeability was passed, occurrence of image misalignment was confirmed.

  As described above, in this embodiment, the fixing belt and the pressure belt are supported by the pressure roller and the belt guide, so that the fixing belt having a small diameter and a small heat capacity can be heated with less wasteful heat conduction, The warm-up time can be shortened. In addition, since the relatively high pressure portion downstream of the press contact portion is conveyed with the pair of rollers sandwiching the fixing belt and the pressure belt, it is possible to prevent the belt from slipping. Furthermore, the two support members that form the nip inside one belt are arranged so as to be pressurized by the support member inside the other belt, thereby making it possible to prevent image misalignment.

{Other embodiments}
Even if the fixing device according to the present invention has a configuration other than the configuration described in the above-described embodiment, the pressing unit pressurizes two or more support members forming a nip inside one belt with the support members inside the other belt. As long as it has. This is because the pressure contact portion can obtain a width in the belt rotation direction (length in the conveyance direction) to increase the speed of fixing, and can prevent pressure loss and prevent image displacement.

  FIG. 5 is a diagram schematically illustrating another example of the configuration of the fixing device according to the present invention. The fixing device C shown in FIG. 5A does not include the pressure pads 24 and 27 as compared with the configuration of the first embodiment. Instead, the distance between the shafts of the fixing roller 22 and the pressure roller 23, and the pressure roller 25 and the pressure roller 26 is short, and the pressure roller 23 presses and presses the gap between the pressure roller 25 and the pressure roller 26. The roller 25 presses the gap between the fixing roller 22 and the pressure roller 23.

  In the fixing device D shown in FIG. 5B, the pressure roller 34a is larger and the pressure roller 35a is smaller than the configuration of the second embodiment. Since the pressure roller 35a is small, the belt guide member 33a adjacent to the pressure roller 35a is closer to the pressure roller 34a than in the second embodiment. The pressure roller 34a is easily deformed due to its low hardness, and as a result, the pressure roller 34a presses the gap between the belt guide member 33a and the pressure roller 35a.

  The present invention can be used in a fixing device that fixes a toner image on a sheet and an image forming apparatus including the fixing device.

1 is a cross-sectional view of a fixing device according to a first embodiment. It is sectional drawing explaining the comparative example of a 1st Example. It is a figure explaining the fixing device which concerns on a 2nd Example. It is a figure explaining the comparative example of a 2nd Example. FIG. 10 is a diagram simply illustrating an example of another configuration of a fixing device. 1 is a diagram illustrating an overall configuration of an image forming apparatus.

Explanation of symbols

A to E: fixing device S ... sheet 1 ... image forming device 2 ... photosensitive drum 3 ... charger 4 ... optical device 5 ... light 6 ... developing device 7 ... transfer roller 8 ... cleaning device 9 ... feed cassette
10 ... Feed roller
11… Registration roller pair
12… discharge roller pair
13… discharge tray
20, 30 ... fixing belt
21, 31… Pressure belt
22… Fixing roller
22a… Halogen heater
23… Pressure roller
24… Pressure pad
25, 26, 34, 35… pressure roller
27… Pressure pad
32, 33 ... Belt guide member
36… induction heating coil
37… Magnetic core

Claims (4)

From the first belt, the second belt that comes into contact with the first belt, the first pressure member that pressurizes the inner surface of the first belt toward the second belt, and the inner surface of the second belt A second pressure member that pressurizes the first pressure member; a first roller that is disposed on the downstream side of the first pressure member in the sheet conveying direction and stretches the first belt; A second roller that is disposed downstream of the second pressure member in the sheet conveying direction, presses the first roller via the first and second belts, and stretches the second belt; Driving means for transmitting a driving force to at least the first or second roller, and the sheet is conveyed by the first pressure member, the second pressure member, the first roller, and the second roller. In a fixing device that forms a nip portion and heats an image on a sheet at the nip portion,
By disposing the first pressure member in the sheet conveyance direction with respect to the second pressure member and disposing the first roller in the sheet conveyance direction with respect to the second roller , The nip portion is continuously formed by the one pressure member, the second pressure member, the first roller, and the second roller, and the pressure between the first roller and the second roller in the pressure in the nip portion. A fixing device having a maximum pressure.   The first pressure member and the first roller, the second pressure member and the second roller are arranged apart from each other, the second pressure member, the first pressure member, The fixing device according to claim 1, wherein the nip is continuously formed in the order of the second roller and the first roller.   The fixing according to claim 2, wherein the first pressure member and the second pressure member are slidably fixedly arranged with respect to the first belt and the second belt. apparatus. Conveying means for conveying the sheet;
An image carrier for carrying a latent image;
Developing means for developing the latent image;
Transfer means for transferring the developed image on the image carrier to a sheet;
An image forming apparatus comprising: the fixing device according to claim 1.

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