JP2012255894A - Fixing device and image forming device including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device that prevents secular change of a fixed pressure member, and a resultant fixing failure, or a conveyance failure of a recording material.SOLUTION: A fixing device 18 includes a cylindrical fixing roller 21 rotatably arranged, and a pressure member 22 that is fixed in pressure contract with the fixing roller 21 to form a nip with the fixing roller 21. The fixing device 18 is configured to fix a toner image on a recording material by allowing the recording material with the toner image transferred thereon to pass through the nip formed between the fixing roller 21 and the pressure member 22. The pressure member 22 includes: a surface layer member 24 in contact with the fixing roller 21; a pressing member 25 for pressing the surface layer member 24 to the fixing roller 21; and a support member 26 for supporting the pressing member 25. The resilient force for restoring the pressing member 25 deformed toward the downstream in a fixing roller rotation direction when the fixing roller 21 rotates, is applied to the pressing member 25.

Description

  The present invention relates to a fixing device including a rotating fixing roller and a fixed pressure member pressed against the fixing roller, and an image forming apparatus such as a copying machine and a printer including the fixing device.

  In an image forming apparatus such as a copying machine or a printer that forms an image on a recording material such as paper by an electrophotographic method, a toner is developed by developing an electrostatic latent image formed on an image carrier such as a photosensitive drum by a developing device. An image is visualized and the toner image is transferred onto a recording material. Then, the recording material onto which the toner image has been transferred is conveyed to a fixing device, heated and pressurized by the fixing device, fixed on the toner image, and then discharged to the outside of the machine, thereby performing a series of image forming operations. Complete.

  By the way, as a fixing device in such an image forming apparatus, conventionally, a fixing device adopting a heating roller system shown in FIG. 10 has been exclusively used.

  That is, FIG. 10 is a cross-sectional view of a conventional fixing device that employs a heating roller system. The illustrated fixing device 118 includes a fixing roller 121 and a pressure roller 122 that are in contact with each other and rotate in the direction indicated by the arrow. A fixing heater 123 is disposed inside the cylindrical fixing roller 121. Here, the pressure roller 122 forms, for example, a silicon rubber layer 122b on the outer surface of a cored bar 122a having an outer diameter of φ12 mm so that the outer diameter becomes φ25 mm, and an FPA having a thickness of 50 μm as a release layer on the outer surface. The tube 122c is covered so that the overall hardness is 42 ° (Asker-C, 1 kgf). When the pressure roller 122 is pressed against the fixing roller 121 with a load of 7 kgf, the width of the nip formed between the fixing roller 121 and the pressure roller 122 is relatively narrow, about 5 mm.

  The fixing device 118 that employs such a heating roller system has a problem that since the heat capacity of the pressure roller 122 is large, the warm-up time (the time required to reach a fixable temperature) is long and the component cost is high. .

  Therefore, a fixing device 218 as shown in the cross-sectional view of FIG. The illustrated fixing device 218 uses a fixed pressure member 222 instead of the conventional pressure roller 122 (see FIG. 10), and the pressure member 222 is a surface layer member that contacts the fixing roller 221. 224, a pressing member 225 that presses the surface layer member 224 against the fixing roller 221, and a supporting member 226 that supports the pressing member 225 and the surface layer member 224.

  In such a fixing device 218, the recording material is passed through a nip formed between the fixing roller 221 and the pressure member 222, whereby the toner image transferred onto the recording material is heated and pressurized to be fixed. Can be made. According to such a fixing method, while ensuring a required nip width, it is possible to reduce the heat capacity of the pressure member 222 to shorten the warm-up time, and to reduce the cost and size of the fixing device 218. Can be planned.

  In the fixing device 118 adopting the heating roller system shown in FIG. 10, the pressure roller 122 rotates together with the fixing roller 121, so that the pressure contact position of the pressure roller 122 with the fixing roller 121 always fluctuates. In the fixing device 218 using the fixed pressure member 222 shown in FIG. 11A, a force that is pulled downstream in the rotation direction of the fixing roller 221 is applied to the pressure member 222. . This will be described below with reference to FIGS.

  11A to 11D are cross-sectional views showing how the pressure member 222 is deformed. From the state shown in FIG. 11A in which the fixing roller 221 is not rotated to FIG. 11B. As shown, when the fixing roller 221 rotates in the direction indicated by the arrow, the surface layer member 224 and the pressing member 225 of the pressure member 222 are pulled downstream in the rotation direction of the fixing roller 221 by the frictional force generated between the fixing roller 221. As shown in the figure, the adhesive surface to the support member 226 is deformed as a base point, and a restoring force (shearing force) in the reverse direction acts on the pressing member 225. In this case, as the pressure member 222 is pulled toward the downstream side in the rotation direction of the fixing roller 221, the nip entrance is shifted from the initial position in the downstream direction. Further, since the nip inlet side of the pressure member 222 is deformed in a direction away from the fixing roller 221, the contact between the fixing roller 221 and the recording material at the nip inlet becomes insufficient, and the fixing property is deteriorated. For this reason, it is desirable that the pressing member 225 of the pressing member 222 has a surface with low friction so that it can easily return to the initial position, and it is necessary to provide means for preventing the pressing member 225 from being deformed.

  As shown in FIG. 11C, even if the rotation of the fixing roller 221 is stopped, a state in which pressure is applied to the fixing roller 221 and the pressure member 222 is maintained. The state where the member 224 and the pressing member 225 are deformed downstream in the rotation direction of the fixing roller 221 is maintained. If the surface layer member 224 and the pressing member 225 continue to be left in a state of being deformed downstream in the rotation direction of the fixing roller 221, the pressing member 225 formed of an elastic member is plastically deformed, as shown in FIG. As described above, the pressure release portion 225 a is generated in the pressing member 225, and the pressing member 225 is separated from the fixing roller 221 on the nip entrance side. As a result, there arises a problem that the nip width is reduced, resulting in fixing failure and the like.

  By the way, Patent Document 1 proposes a fixing device in which an elastic body of a fixed pressure member is provided with a mechanism for preventing deformation to the downstream side in the sheet material movement direction.

  In Patent Document 2, a fixed pressure member is composed of a support body, an elastic body, and a tube covering them, and the outermost tube is a support body even if a load is generated on the pressure member when paper passes. In addition, a fixing device configured to prevent peeling from an elastic body has been proposed.

  In Patent Document 3, a pressure member is constrained by a heat-resistant sheet by disposing a heat-resistant sheet based on glass fiber between the fixing roller and the pressure member without adhering each other. There has been proposed a fixing device that can suppress deformation of the pressure member.

JP 2002-072718 A JP 2002-123120 A JP-A-8-241000

  According to the fixing device proposed in Patent Document 1, the overall deformation of the elastic body and the position change of the nip outlet can be suppressed, but the position change of the nip inlet and the deformation of the elastic body itself cannot be suppressed. For this reason, when the nip entrance side of the elastic body is deformed, there arises a problem that the nip width is reduced and the fixing property is deteriorated. In addition, since a mechanism for returning the deformed portion of the elastic body on the nip entrance side to the initial state is not provided, the fixability is steadily deteriorated as the durability progresses.

  In the fixing device proposed in Patent Document 2, since the pressure member employs a structure in which the support and the elastic body are covered with the tube, the elastic body and the tube are not separated even when subjected to a load due to paper passing. However, there is a problem that deformation of the elastic body itself cannot be prevented.

  According to the fixing device proposed in Patent Document 3, since the pressure member is not restrained by the heat-resistant sheet, the influence of the deformation of the heat-resistant sheet is suppressed, but the most deformed by the pressure is not the heat-resistant sheet but the pressure. As long as there is no slippage between the pressure member and the heat-resistant sheet even when the heat-resistant sheet is no longer restricted, the pressure member will be held in a deformed state. There is a problem that deterioration cannot be prevented.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and a purpose of the present invention is to fix a fixing pressure member that can prevent a change with time of a fixed pressure member and a fixing failure and a conveyance failure of a recording material. And providing an image forming apparatus including the same.

  In order to achieve the above object, according to the first aspect of the present invention, a cylindrical fixing roller is rotatably arranged, and a pressure member that is pressed against the fixing roller and forms a nip with the fixing roller is fixedly arranged. In the fixing device for fixing the toner image on the recording material by passing the recording material on which the toner image is transferred through the nip formed between the fixing roller and the pressing member, A fixing member that is formed by a surface layer member that contacts the fixing roller, a pressing member that presses the surface layer member against the fixing roller, and a supporting member that supports the pressing member, and is generated in the pressing member when the fixing roller rotates. The present invention is characterized in that a restoring force that restores deformation toward the downstream side in the rotational direction is applied to the pressing member.

  A second aspect of the invention is characterized in that, in the first aspect of the invention, the pressing member is curved in a circular arc shape whose central portion in the longitudinal direction is convex toward the upstream side in the fixing roller rotation direction.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, the pressure member is disposed such that the central pressure direction is upstream of the fixing roller rotation direction with respect to the rotation axis of the fixing roller. It is characterized by that.

  The invention according to claim 4 is characterized in that, in the invention according to any one of claims 1 to 3, the foaming rate at the upstream portion of the pressing member in the rotation direction of the fixing roller is set lower than the foaming rate at the downstream portion. To do.

  The invention according to claim 5 is the invention according to any one of claims 1 to 3, wherein the hardness of the upstream and downstream portions of the pressing member in the fixing roller rotation direction is set higher than the hardness of the intermediate portion. And

  A sixth aspect of the invention is characterized in that, in the invention according to any one of the first to fifth aspects, the pressing member and the support member are concavo-convexly fitted in the upstream portion in the fixing roller rotation direction.

  A seventh aspect of the invention is characterized in that, in the invention according to any one of the first to sixth aspects, a convex portion is provided on the contact surface of the pressing member upstream of the fixing roller in the rotation direction.

  An image forming apparatus according to an eighth aspect includes the fixing device according to any one of the first to seventh aspects.

  According to the first aspect of the present invention, even if the pressing member is deformed to the downstream side in the fixing roller rotation direction due to the rotation of the fixing roller, the pressing member is provided with a restoring force for restoring the deformation. Therefore, when the rotation of the fixing roller stops, the pressing member can return to the initial state. For this reason, it is possible to prevent the occurrence of skewing and wrinkling of the recording material due to the plastic deformation of the pressing member due to durability, the accompanying pressure drop at the nip portion inlet and the fixing failure due to the reduction of the nip width, and the change in timing of applying the recording material conveying force. it can.

  According to the second aspect of the present invention, the pressing member is curved in an arc shape in which the central portion in the longitudinal direction is convex toward the upstream side in the fixing roller rotation direction, thereby causing the pressing member to move downstream in the fixing roller rotation direction. Since the restoring force for restoring the deformation of the fixing roller is applied, the pressing member can be returned to the initial state when the rotation of the fixing roller is stopped, and the occurrence of the fixing failure and the conveyance failure of the recording material can be prevented.

  According to the third aspect of the present invention, since the pressing member is arranged so that the pressing direction at the center is on the upstream side of the rotation direction of the fixing roller with respect to the rotation axis of the fixing roller, the pressing member is positioned with respect to the fixing roller. Therefore, the force that deforms the pressing member in the contact direction is greater than when it is contacted vertically, and the restoring force to return the pressing member to the shape of the job is increased, which effectively causes the occurrence of fixing failure and conveyance failure of the recording material. Is prevented.

  According to the fourth aspect of the present invention, the hardness of the upstream portion of the pressing member in the rotation direction of the fixing roller is set downstream by setting the foaming rate of the upstream portion of the pressing member in the rotation direction of the fixing roller lower than the foaming rate of the downstream portion. It becomes higher than the hardness of the part and the restoring force of the upstream part is strengthened, and a sufficient nip width can be secured between the fixing part and the downstream part of low hardness, so that fixing failure and recording material conveyance failure Is effectively prevented.

  According to the invention of claim 5, since the hardness of the upstream portion and the downstream portion of the pressing member in the rotation direction of the fixing roller is set higher than the hardness of the intermediate portion, the restoring force of the upstream portion having a high hardness of the pressing member is increased. The low-hardness intermediate part is supported by the high-hardness downstream part and deformation is suppressed, so that a sufficient nip width can be secured between the fixing roller and the occurrence of poor fixing and poor conveyance of the recording material. Is effectively prevented.

  According to the sixth aspect of the present invention, since the upstream portion of the pressing member in the fixing roller rotation direction is supported by the support member, a force (restoring force) for deforming the pressing member toward the upstream side in the fixing roller rotation direction is obtained. Strengthening effectively prevents the occurrence of fixing failure and conveyance failure of the recording material.

  According to the seventh aspect of the present invention, the convex portion projecting from the contact surface of the pressing member at the upstream portion in the rotation direction of the fixing roller is pressed by the fixing roller, whereby the upstream portion of the pressing member is deformed in the downstream direction. Therefore, the restoring force of the pressing member is increased, and the occurrence of fixing failure and recording material conveyance failure can be effectively prevented.

  According to the eighth aspect of the present invention, it is possible to stably obtain a high-quality image as a result of preventing the fixing failure and the recording material conveyance failure in the fixing device.

1 is a cross-sectional view of an image forming apparatus according to the present invention. 1 is a cross-sectional view of a fixing device according to Embodiment 1 of the present invention. FIG. 3 is a perspective view of a pressure member of the fixing device according to Embodiment 1 of the present invention. (A)-(d) is sectional drawing which shows the mode of a deformation | transformation of the press member of the fixing device which concerns on Embodiment 1 of this invention. It is sectional drawing of the fixing device which concerns on Embodiment 2 of this invention. It is sectional drawing of the fixing device which concerns on Embodiment 3 of this invention. It is sectional drawing of the fixing device which concerns on Embodiment 4 of this invention. FIG. 9 is a cross-sectional view of a fixing device according to Embodiment 5 of the present invention. It is sectional drawing of the fixing device which concerns on Embodiment 6 of this invention. It is sectional drawing of the conventional fixing device which employ | adopts a heating roller system. (A)-(d) is sectional drawing which shows the mode of a deformation | transformation of the pressure member of the conventional fixing device which has a fixed pressure member.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

[Image forming apparatus]
FIG. 1 is a cross-sectional view of an image forming apparatus according to the present invention. The illustrated image forming apparatus 1 is a laser printer, and an image forming unit 2 is disposed above the inside of the apparatus main body 1A. A sheet storage unit 3 is disposed in the lower half of the sheet.

  The image forming unit 2 forms an image by an electrophotographic method. The image forming unit 2 is a photosensitive drum 4 as a rotatable image carrier, a charger 5 disposed around the photosensitive drum 4, a developing device 6, and the like. In addition to the transfer roller 7 and the cleaning device 8, the developing device 6 is provided with a toner hopper 9 for supplying toner as a developer. A laser scanner unit (LSU) 10 that is an optical scanning device is disposed beside the image forming unit 2.

The paper storage unit 3 includes detachable upper and lower two-stage paper feed cassettes 11 and 12 in which a plurality of paper sheets as recording materials are stacked and accommodated, and in the vicinity of each of the paper feed cassettes 11 and 12, A pick roller 13 for sequentially taking out the paper in each of the paper feed cassettes 11 and 12 from the upper one, a feed roller 14 for feeding out the taken paper one by one and a retard roller 15 are provided. In the apparatus main body 1A, a first transport path S1 from the paper storage unit 3 to the image forming unit 2 and a second transport path S2 from the image forming unit 2 to the paper discharge tray 16 are disposed. A registration roller pair 17 and the transfer roller 7 are provided in the path S1, and a fixing device 18, a conveyance roller pair 9, and a discharge roller pair 20 according to the present invention are provided in the second conveyance path S2. Details of the configuration of the fixing device 18 will be described later.

  Next, an image forming operation of the image forming apparatus 1 configured as described above will be described.

  When the image forming operation is started, in the image forming unit 2, the photosensitive drum 4 is rotationally driven in a direction indicated by an arrow (clockwise) in FIG. Uniformly charged. When a laser beam based on an electrical signal transmitted from a personal computer or the like is output from the laser scanner unit 10 and the surface of the photosensitive drum 4 is exposed and scanned, an electrostatic latent image corresponding to image information is formed on the photosensitive drum 4. Is formed. The electrostatic latent image formed on the photosensitive drum 4 is developed by the developing device 6 using toner as a developer to be visualized as a toner image.

  By the way, when cassette feeding is performed, the paper stored in, for example, the upper paper feeding cassette 11 of the paper storage unit 3 is picked up from the uppermost one by the pick roller 13 and is fed by the feed roller 14 and the retard roller 15. The sheets are separated one by one and conveyed along the first conveyance path S1 to the registration roller pair 17. In the registration roller pair 17, the paper is temporarily put into a standby state and then supplied to the image forming unit 2 at a predetermined timing synchronized with the toner image on the photosensitive drum 4.

  In the image forming unit 2, the sheet supplied to the nip between the photosensitive drum 4 and the transfer roller 7 is conveyed while being pressed against the photosensitive drum 4 by the transfer roller 7, so that the surface of the photosensitive drum 4 is conveyed. The upper toner image is transferred. Then, the sheet on which the toner image is transferred is conveyed to the fixing device 18 and is heated and pressurized in the process of passing through the nip of the fixing device 18 to receive the fixing of the toner image. The toner remaining on the surface of the photosensitive drum 4 (transfer residual toner) after the transfer of the toner image onto the paper is removed by the cleaning device 8, and the photosensitive drum 4 whose surface has been cleaned is prepared for the next image forming operation.

  Thus, the sheet on which the toner image is fixed on the surface by the fixing device 18 is conveyed along the second conveyance path S2 by the conveyance roller pair 19 toward the sheet discharge roller pair 20, and is discharged by the sheet discharge roller pair 20. The paper is discharged to the tray 16, thereby completing a series of image forming operations.

[Fixing device]
Next, an embodiment of the fixing device 18 according to the present invention will be described.

<Embodiment 1>
2 is a cross-sectional view of the fixing device according to the first embodiment of the present invention, FIG. 3 is a perspective view of a pressure member of the identification attachment device, and FIGS. 4A to 4D are deformations of the pressing member of the identification attachment device. It is sectional drawing which shows the mode.

  In the fixing device 18 according to the present invention, a cylindrical fixing roller 21 is rotatably disposed, and a pressure member 22 that is pressed against the fixing roller 21 from below and forms a nip with the fixing roller 21 is fixedly disposed. The fixing heater 23 is disposed at the center of the fixing roller 21.

  In the present embodiment, the fixing roller 21 is made of a fluororesin such as PFA or PTFE in which an outer surface of an aluminum core bar having an outer diameter of φ23 mm and a wall thickness of 0.65 mm is filled with a conductive material or a wear-resistant material. It is constituted by coating with a thickness of 25 μm including the primer layer. The fixing heater 23 disposed inside the fixing roller 21 is composed of a halogen lamp having a voltage of 100 V and an output of 800 W, and the fixing roller 21 is heated to a predetermined fixing temperature by the fixing heater 23. The surface temperature of the fixing roller 21 is always detected by a temperature sensor (not shown), and the detection signal is fed back to a controller (not shown) to control the surface temperature of the fixing roller 21 to a predetermined fixing temperature.

  The pressure member 22 includes a surface layer member 24 that contacts the fixing roller 21, a pressing member 25 that presses the surface layer member 24 against the fixing roller 21, and a support member 26 that supports the surface layer member 24 and the pressing member 25. Has been. In the present embodiment, the support member 26 is composed of a metal member having a width of 15 mm and a thickness of 6 mm, and the pressing member 25 is 10 mm in width, 6 mm in thickness, and a hardness of 10 ° to 45 ° (Asker-C, 1 kgf). ), And is bonded to the upper surface of the support member 26. The surface layer member 24 is composed of a sheet or endless film of PFA, PTFE, PI, Kapton or the like having a thickness of 10 μm to 300 μm.

  Thus, in the fixing device 18 according to the present invention, the pressing member 25 of the pressing member 22 has a central portion in the longitudinal direction convex toward the upstream side in the rotation direction of the fixing roller 21 as shown in FIG. It is curved in an arc shape.

  In the fixing device 18 configured as described above, when the pressing member 22 is pressed against the fixing roller 21 with a predetermined force from below as shown in FIG. 2, the surface layer member 24 and the pressing member of the pressing member 22 are pressed. 25 is deformed into a concave shape along the outer peripheral surface of the fixing roller 21, and a nip having a width of 8 mm is formed between the fixing roller 21 and the pressure member 22.

  Here, the deformation state of the pressing member 25 in the fixing device 18 according to the present invention will be described below with reference to FIGS.

  That is, FIGS. 4A to 4D are cross-sectional views showing how the pressing member 25 is deformed, and shown in FIG. 4B from the state shown in FIG. 4A where the fixing roller 21 is not rotating. Thus, when the fixing roller 21 rotates in the direction of the arrow a (clockwise), the surface layer member 24 and the pressing member 25 of the pressing member 22 rotate in the direction of rotation of the fixing roller 21 due to the frictional force generated between the fixing roller 21. It is pulled downstream and deformed with the adhesive surface to the support member 26 as a base point as shown in the figure, and a restoring force (shearing force) in the reverse direction (arrow b direction) acts on the pressing member 25.

  As described above, when the fixing roller 21 is rotationally driven in the direction of arrow a (clockwise) in FIG. 4B at a predetermined speed, a process in which the sheet on which the toner image is transferred passes through the nip portion as described above. And the toner image is fixed on the paper. At this time, the surface layer member 24 of the pressure member 22 functions to reduce the frictional force generated between the pressure member 22 and the sheet and to prevent the dirt from adhering to the pressing member 25.

  Then, as shown in FIG. 4C, even if the rotation of the fixing roller 21 is stopped, the state where pressure is applied to the fixing roller 21 and the pressure member 22 is maintained. The pressing member 25 is curved in an arc shape so that the central portion in the longitudinal direction is convex toward the upstream side in the rotation direction of the fixing roller 21 as shown in FIG. A restoring force in the direction of the arrow b shown in the figure that restores deformation to the downstream side in the rotational direction is applied. For this reason, the surface layer member 24 and the pressing member 25 that have been deformed downstream in the rotation direction of the fixing roller 21 are initialized as shown in FIG. 4D by the restoring force (shearing force) applied to the pressing member 25. It is possible to return to the shape (the shape shown in FIG. 4A).

  Therefore, according to the fixing device 18 according to the present embodiment, it is possible to suppress the plastic deformation of the pressing member 25 due to durability, the pressure drop of the nip portion inlet and the positional deformation of the nip portion inlet portion, and the fixing failure or In addition to preventing paper conveyance failure, it is possible to prevent sheet skew and wrinkles from occurring when the paper conveyance force is applied.

  As described above, as a result of preventing the fixing failure and the paper conveyance failure in the fixing device 18, a high-quality image can be stably obtained in the image forming apparatus (laser printer) 1 shown in FIG.

<Embodiment 2>
Next, a second embodiment of the present invention will be described with reference to FIG.

  FIG. 5 is a cross-sectional view of the fixing device according to the second embodiment of the present invention. In this embodiment, the fixing member 22 is fixed with respect to the rotation axis of the fixing roller 21. It is characterized by being arranged to be on the upstream side in the rotation direction of the roller 21, and the other configuration is the same as that of the first embodiment.

  Thus, according to the fixing device 18 according to the present embodiment, the pressing direction of the center of the pressing member 22 is upstream of the rotation direction of the fixing roller 21 with respect to the rotation axis of the fixing roller 21. Therefore, the pressing member 25 is more deformed in the contact direction than the first embodiment in which the pressing member 22 is brought into perpendicular contact with the fixing roller 21, and the pressing member 25 has an initial shape. The restoring force to return is enhanced, and the occurrence of fixing failure and paper conveyance failure can be effectively prevented as in the first embodiment.

<Embodiment 3>
Next, Embodiment 3 of the present invention will be described below with reference to FIG.

  FIG. 6 is a cross-sectional view of a fixing device according to Embodiment 3 of the present invention. In this embodiment, the foaming rate of the upstream portion 25A in the fixing roller rotation direction of the pressing member 25 is lower than the foaming rate of the downstream portion 25B. The other configuration is the same as that of the first embodiment.

  Thus, according to the fixing device 18 according to the present embodiment, the pressing member 25 is set by setting the foaming rate of the upstream portion 25A of the pressing member 25 in the fixing roller rotation direction lower than the foaming rate of the downstream portion 25B. The upstream portion 25A has a higher hardness than the downstream portion 25B, thereby increasing the restoring force of the upstream portion 25A, and ensuring a sufficient nip width with the fixing roller 21 in the downstream portion 25B having a low hardness. Therefore, it is possible to effectively prevent the occurrence of fixing failure and paper conveyance failure.

<Embodiment 4>
Next, a fourth embodiment of the present invention will be described with reference to FIG.

  FIG. 7 is a cross-sectional view of a fixing device according to Embodiment 4 of the present invention. In this embodiment, the hardness of the upstream portion 25A and downstream portion 25B in the fixing roller rotation direction of the pressing member 25 is determined from the hardness of the intermediate portion 25C. The other configuration is the same as that of the first embodiment.

  Thus, according to the fixing device 18 according to the present embodiment, the hardness of the upstream portion 25A and the downstream portion 25B in the fixing roller rotation direction of the pressing member 25 is set higher than the hardness of the intermediate portion 25C. Since the restoring force of the upstream portion 25A having a high hardness increases, and the intermediate portion 25C having a low hardness is supported by the downstream portion 25B having a high hardness and the deformation is suppressed, a sufficient nip width between the fixing roller 21 and the intermediate portion 25C is ensured. Therefore, it is possible to effectively prevent the occurrence of fixing failure and paper conveyance failure.

<Embodiment 5>
Next, a fifth embodiment of the present invention will be described with reference to FIG.

  FIG. 8 is a cross-sectional view of a fixing device according to Embodiment 5 of the present invention. In this embodiment, a recess 25a is formed in the upstream portion 25A of the pressing member in the rotation direction of the fixing roller, and a support member 26 is formed in the recess 25a. The projecting portion 26a projecting from the projection 26a is fitted, and the other configuration is the same as that of the first embodiment.

  Thus, according to the fixing device 18 according to the present embodiment, since the upstream portion 25A of the pressing member 25 is supported by the convex portion 26a of the supporting member 26, the pressing member 25 faces the upstream side in the fixing roller rotation direction. Therefore, the force (restoring force) that tends to deform is increased, and the occurrence of fixing failure and paper conveyance failure can be effectively prevented. In the present embodiment, the depression 25a is formed on the pressing member 25 and the projection 26a is formed on the support member 26. On the contrary, the projection 25 is formed on the pressing member 25 and the depression is formed on the support member 26. You may do it.

<Embodiment 6>
Next, a sixth embodiment of the present invention will be described with reference to FIG.

  FIG. 9 is a cross-sectional view of the fixing device according to Embodiment 5 of the present invention. In this embodiment, the convex portion 25b is integrally projected on the contact surface of the pressing member 25 upstream of the fixing roller rotation direction. The other structure is the same as that of the first embodiment.

  Thus, according to the fixing device 18 according to the present embodiment, the pressing portion 25 is pressed by the fixing roller 21 by pressing the convex portion 25 b protruding from the contact surface upstream of the pressing member 25 in the rotation direction of the fixing roller. Since the deformation of the upstream portion of the member 25 in the downstream direction is suppressed, the restoring force of the pressing member 25 is increased, and the effect of preventing the occurrence of fixing failure and paper conveyance failure is obtained.

  Although the present invention has been described with respect to a mode in which the present invention is applied to a monochrome laser printer and a fixing device provided therein, the present invention is not limited to a color leather printer or a monochrome / color printer, and may be a copier or a multifunction machine. Needless to say, the present invention can be similarly applied to other arbitrary image forming apparatuses and the like and a fixing device provided in the image forming apparatus.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 1A Image forming apparatus main body 2 Image forming part 3 Paper storage part 4 Photosensitive drum 5 Charging device 6 Developing device 7 Transfer roller 8 Cleaning device 9 Toner hopper 10 Laser scanner unit (LSU)
DESCRIPTION OF SYMBOLS 11, 12 Paper feed cassette 13 Pick roller 14 Feed roller 15 Retard roller 16 Paper discharge tray 17 Registration roller pair 18 Fixing device 19 Carrying roller pair 20 Paper discharge roller pair 21 Fixing roller 22 Pressure member 23 Fixing heater 24 Surface layer member 25 Press Member 25A Upstream part of the pressing member 25B Downstream part of the pressing member 25C Intermediate part of the pressing member 25a Concave part of the pressing member 25b Convex part of the pressing member 26 Support member 26a Convex part of the supporting member S1 First transport path S2 Second transport path

Claims (8)

A cylindrical fixing roller is rotatably arranged, a pressure member that is pressed against the fixing roller and forms a nip with the fixing roller is fixedly arranged, and the recording material onto which the toner image is transferred is connected to the fixing roller. In a fixing device for fixing a toner image on a recording material by passing through the nip formed between the pressure member,
The pressure member includes a surface layer member that contacts the fixing roller, a pressing member that presses the surface layer member against the fixing roller, and a support member that supports the pressing member, and the pressing member is rotated when the fixing roller rotates. The fixing device is configured to apply a restoring force to the pressing member to restore the deformation of the fixing roller to the downstream side in the rotation direction of the fixing roller.   The fixing device according to claim 1, wherein the pressing member is curved in an arc shape in which a central portion in the longitudinal direction is convex toward the upstream side in the fixing roller rotation direction.   3. The fixing device according to claim 1, wherein the pressing member is arranged such that a pressing direction at a center thereof is upstream of a rotation axis of the fixing roller with respect to a rotation direction of the fixing roller.   The fixing device according to claim 1, wherein a foaming rate at an upstream portion of the pressing member in a rotation direction of the fixing roller is set lower than a foaming rate at a downstream portion.   The fixing device according to claim 1, wherein the hardness of the upstream portion and the downstream portion in the rotation direction of the fixing roller of the pressing member is set higher than the hardness of the intermediate portion.   The fixing device according to claim 1, wherein the pressing member and the support member are concavo-convexly fitted in an upstream portion in the fixing roller rotation direction.   The fixing device according to claim 1, wherein a protrusion is provided on a contact surface of the pressing member upstream of the fixing roller in the rotation direction. An image forming apparatus comprising the fixing device according to claim 1.

Images