JP6426116B2 - Fixing device and image forming apparatus - Google Patents

Description

  The present invention relates to a fixing device and an image forming apparatus provided with the fixing device.

  In an image forming apparatus such as a printer, copier, or facsimile, an unfixed toner image is a recording medium sheet, printing paper, photosensitive by an image transfer method or a direct method by an image forming process such as electrophotographic recording, electrostatic recording, magnetic recording, etc. It is formed on a recording medium such as paper or electrostatic recording paper. As a fixing device for fixing an unfixed toner image, a contact heating type fixing device such as a heat roller method, a film heating method or an electromagnetic induction heating method is widely adopted.

  In these fixing devices, when the fixing member is heated to a predetermined temperature by a heating source, the energy consumption can be significantly reduced if the heating time to the predetermined temperature can be shortened. In order to achieve this, it has been proposed to use a low heat capacity thin belt composed of a metal substrate and an elastic rubber layer as a fixing member (see Patent Document 1).

  As shown in FIG. 8, the fixing device includes an endless belt 100, a pipe-shaped metal heat conductor 200 disposed inside the endless belt 100, and a heat source 300 disposed inside the metal heat conductor 200. The pressure roller 400 is in contact with the metal heat conductor 200 via the endless belt 100 to form the nip portion N. The rotation of the pressure roller 400 causes the endless belt 100 to rotate together, and at this time, the metal heat conductor 200 guides the movement of the endless belt 100. Further, the endless belt 100 is heated by the heat source 300 in the metal heat conductor 200 via the metal heat conductor 200, thereby enabling the entire endless belt 100 to be warmed. As a result, the first print time from the heating standby time can be shortened, and it is possible to eliminate the heat quantity shortage at the time of high speed rotation.

  However, it is necessary to further improve the thermal efficiency to further improve the energy saving performance and the first print time. Then, the structure which heats an endless belt directly (without passing through a metal heat conductor) instead of heating an endless belt indirectly through a metal heat conductor is proposed (refer to patent documents 2).

  In this configuration, as shown in FIG. 9, the pipe-like metal heat conductor is removed from the inside of the endless belt 100, and instead, a plate-like nip forming member 500 is provided at a position facing the pressure roller 400. There is. In the case of this configuration, since the endless belt 100 can be directly heated by the heat source 300 except at the place where the nip forming member 500 is disposed, the heat transfer efficiency is significantly improved and the power consumption is reduced. This makes it possible to further reduce the first print time from the heating standby time. Moreover, the cost reduction by not providing a metal heat conductor is also expectable.

  In a configuration in which the endless belt is directly heated as shown in FIG. 9, various stresses act on the endless belt 100. For example, as shown in FIG. 10A, the belt 100 passing through the nip portion N is sheared by the rotational driving force of the pressure roller 400 and the frictional force generated between the nip forming member 500 (Indicated by the arrow) acts. Also, as shown in FIG. 6B, the rotating belt approaches one of the axial directions, but at that time, the end face of the belt 100 comes into sliding contact with the belt holding member 600 that regulates the deviation of the belt 100. Shear force acts on the Furthermore, as shown in FIG. 6C, in order to improve the separation when the sheet is separated from the belt surface, it is desirable to make the cross-sectional shape of the belt 100 a shape other than a perfect circle. Because of the change in curvature at the X and Y portions, repeated bending forces act on the belt 100.

  In the configuration in which the endless belt is directly heated (FIG. 9), the stresses generated by these forces tend to concentrate at the belt end. Therefore, the end portion of the belt is easily damaged, and there is a problem in the durability of the belt.

  In view of the above, it is an object of the present invention to provide a fixing device in which the durability of the fixing belt is improved, and an image forming apparatus provided with the fixing device.

In order to solve the above problems, a fixing device according to the present invention comprises a rotatable endless fixing belt, a heating member for heating the fixing belt, and a nip forming member disposed inside the fixing belt. An opposing rotating body forming a nip portion with the fixing belt by contacting the nip forming member via the fixing belt, and the fixing belt held at both axial ends thereof, the fixing belt at both axial ends and a belt holding member is not held between parts, said heating member, the fixing device for heating the interior of the fixing belt except that the the fixing belt and the nip forming member is brought into direct contact, the belt holding member, a cylindrical portion which is disposed inside the axial end portion of the fixing belt, and a flange portion protruding on the outer diameter side of the cylindrical portion, the axial end portion of the fixing belt of the belt holding member Between the end face of the flange portion, a fitted protective member on the outer periphery of the tubular portion is provided, the outer periphery of said protective member when viewed from the axial direction, than the surface of the fixing belt abutting nip forming member The opposing rotating body and the belt holding member are disposed in an axially offset state without overlapping in the axial direction, and the protective member is disposed on the flange portion of the belt holding member. It is characterized by being rotatable relative to it.

According to the present invention, when the fixing belt is deviated in the axial direction, the end of the fixing belt can be prevented from coming into direct contact with the end face of the flange of the belt holding member. Damage can be prevented.

FIG. 1 is a cross-sectional view showing a schematic configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a cross-sectional view showing a schematic configuration of a fixing device mounted on the image forming apparatus. FIG. 2A is a perspective view, FIG. 2B is a plan view, and FIG. 2C is a cross-sectional view taken along line A-A of FIG. It is a top view which shows other embodiment of a belt holding member. It is sectional drawing of radial direction which shows the modification of a belt holding member. FIG. 7 is a cross-sectional view showing another embodiment of a fixing device. FIG. 7 is an enlarged cross-sectional view of a nip forming member of the fixing device shown in FIG. 6; FIG. 6 is a cross-sectional view showing a schematic configuration of a conventional fixing device. FIG. 14 is a cross-sectional view showing a schematic configuration of another conventional fixing device. It is a figure explaining the stress which arises on a belt, (a) is a sectional view of the radial direction, (b) is a perspective view, and (c) is a sectional view of a radial direction.

  Hereinafter, an embodiment of the present invention will be described based on the attached drawings. In each of the drawings for describing the embodiments of the present invention, components such as members having the same function or shape and components such as components are described once by attaching the same reference numerals as much as possible. So I will omit the explanation.

First, with reference to FIG. 1, the entire configuration and operation of an image forming apparatus according to an embodiment of the present invention will be described.
The image forming apparatus 1 shown in FIG. 1 is a color laser printer, and four image forming units 4Y, 4M, 4C, and 4K are provided at the center of the apparatus main body. The image forming units 4Y, 4M, 4C and 4K contain developers of different colors of yellow (Y), magenta (M), cyan (C) and black (K) corresponding to color separation components of a color image. Other than the above, the configuration is the same.

  Specifically, each of the image forming units 4Y, 4M, 4C, and 4K includes a drum-shaped photosensitive member 5 as a latent image carrier, a charging device 6 for charging the surface of the photosensitive member 5, and a surface of the photosensitive member 5. The developing device 7 that supplies toner, and a cleaning device 8 that cleans the surface of the photosensitive member 5 are provided. In FIG. 1, only the photosensitive member 5, the charging device 6, the developing device 7, and the cleaning device 8 provided in the black image forming unit 4K are denoted by reference numerals, and in the other image forming units 4Y, 4M, and 4C. The sign is omitted.

  Below each image forming unit 4Y, 4M, 4C, 4K, an exposure device 9 for exposing the surface of the photosensitive member 5 is disposed. The exposure device 9 includes a light source, a polygon mirror, an f-θ lens, a reflection mirror, and the like, and irradiates the surface of each photosensitive member 5 with a laser beam based on image data.

  The transfer device 3 is disposed above the image forming units 4Y, 4M, 4C, and 4K. The transfer device 3 includes an intermediate transfer belt 30 as a transfer body, four primary transfer rollers 31 as primary transfer means, a secondary transfer roller 36 as secondary transfer means, a secondary transfer backup roller 32, and cleaning. A backup roller 33, a tension roller 34, and a belt cleaning device 35 are provided.

  The intermediate transfer belt 30 is an endless belt, and is stretched by a secondary transfer backup roller 32, a cleaning backup roller 33, and a tension roller 34. Here, when the secondary transfer backup roller 32 is rotationally driven, the intermediate transfer belt 30 travels (rotates) in the direction indicated by the arrow in the drawing.

  The four primary transfer rollers 31 respectively sandwich the intermediate transfer belt 30 with the respective photosensitive members 5 to form a primary transfer nip. Further, a power supply (not shown) is connected to each primary transfer roller 31 so that a predetermined DC voltage (DC) and / or an alternating voltage (AC) is applied to each primary transfer roller 31.

  The secondary transfer roller 36 sandwiches the intermediate transfer belt 30 with the secondary transfer backup roller 32 to form a secondary transfer nip. Further, similarly to the primary transfer roller 31, a power supply (not shown) is connected to the secondary transfer roller 36, and a predetermined DC voltage (DC) and / or an AC voltage (AC) is applied to the secondary transfer roller 36. It has become so.

  The belt cleaning device 35 has a cleaning brush and a cleaning blade disposed to abut the intermediate transfer belt 30. A waste toner transfer hose (not shown) extended from the belt cleaning device 35 is connected to an inlet of a waste toner container (not shown).

  In the upper part of the printer main body, a bottle storage portion 2 is provided, and four toner bottles 2Y, 2M, 2C, 2K containing toner for replenishment are detachably mounted in the bottle storage portion 2. Between the respective toner bottles 2Y, 2M, 2C, 2K and the respective developing devices 7 there is provided a supply path (not shown), and development is carried out from each toner bottle 2Y, 2M, 2C, 2K via this supply path. The toner is supplied to the device 7.

  On the other hand, at the lower part of the printer main body, a sheet feeding tray 10 accommodating sheets P as a recording medium, a sheet feeding roller 11 for discharging the sheet P from the sheet feeding tray 10 and the like are provided. Here, the recording medium includes, in addition to the plain paper, thick paper, postcard, envelope, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, OHP sheet, etc. Although not shown, a manual sheet feeding mechanism may be provided.

  In the printer main body, a conveyance path R for discharging the sheet P from the sheet feed tray 10 through the secondary transfer nip and out of the apparatus is disposed. On the conveyance path R, on the upstream side of the position of the secondary transfer roller 36 in the sheet conveyance direction, a pair of registration rollers 12 as conveyance means for conveying the sheet P to the secondary transfer nip is disposed.

  Further, a fixing device 20 for fixing the unfixed image transferred to the sheet P is disposed downstream of the position of the secondary transfer roller 36 in the sheet conveyance direction. Further, on the downstream side of the fixing device 20 in the sheet conveyance direction of the conveyance path R, a pair of sheet discharge rollers 13 for discharging the sheet to the outside of the apparatus is provided. Further, a sheet discharge tray 14 for stocking the sheets discharged to the outside of the apparatus is provided on the upper surface portion of the printer main body.

Subsequently, the basic operation of the printer according to the present embodiment will be described with reference to FIG.
When the image forming operation is started, the photosensitive members 5 in the image forming units 4Y, 4M, 4C, and 4K are rotationally driven clockwise by a driving device (not shown), and the surfaces of the photosensitive members 5 are charged. Is uniformly charged to a predetermined polarity. Laser light is irradiated from the exposure device 9 on the surface of each charged photosensitive member 5 to form an electrostatic latent image on the surface of each photosensitive member 5. At this time, the image information to be exposed on each photosensitive member 5 is monochrome image information obtained by decomposing a desired full color image into yellow, magenta, cyan and black color information. Thus, the electrostatic latent image is visualized (visualized) as a toner image by supplying toner to each electrostatic latent image formed on each photosensitive member 5 by each developing device 7 .

  Further, when the image forming operation is started, the secondary transfer backup roller 32 is rotationally driven counterclockwise in the figure to cause the intermediate transfer belt 30 to run in the direction shown by the arrow in the figure. Then, a constant voltage or a constant current controlled voltage having a reverse polarity to the charging polarity of the toner is applied to each primary transfer roller 31. As a result, a transfer electric field is formed at the primary transfer nip between each primary transfer roller 31 and each photoconductor 5.

  Thereafter, when the toner image of each color on the photosensitive member 5 reaches the primary transfer nip as the photosensitive member 5 rotates, the toner image on each photosensitive member 5 is generated by the transfer electric field formed in the primary transfer nip. Are sequentially superimposed and transferred onto the intermediate transfer belt 30. Thus, a full color toner image is carried on the surface of the intermediate transfer belt 30. Further, the toner on each photosensitive member 5 that can not be transferred to the intermediate transfer belt 30 is removed by the cleaning device 8. Thereafter, the surface of each photosensitive member 5 is neutralized by a static elimination device (not shown) to initialize the surface potential.

  At the lower part of the image forming apparatus, the sheet feeding roller 11 starts rotational driving, and the sheet P is fed from the sheet feeding tray 10 to the conveyance path R. The sheet P fed to the conveyance path R is timed by the registration roller 12 and is sent to the secondary transfer nip between the secondary transfer roller 36 and the secondary transfer backup roller 32. At this time, a transfer voltage having a polarity opposite to that of the toner charging polarity of the toner image on the intermediate transfer belt 30 is applied to the secondary transfer roller 36, whereby a transfer electric field is formed in the secondary transfer nip.

  Thereafter, when the toner image on the intermediate transfer belt 30 reaches the secondary transfer nip as the intermediate transfer belt 30 circulates, the transfer electric field formed in the secondary transfer nip causes the toner image on the intermediate transfer belt 30 to The toner images on the sheet P are collectively transferred onto the sheet P. At this time, the residual toner on the intermediate transfer belt 30 which has not been transferred to the sheet P is removed by the belt cleaning device 35, and the removed toner is conveyed to a waste toner container (not shown) and collected.

  Thereafter, the sheet P is conveyed to the fixing device 20, and the toner image on the sheet P is fixed to the sheet P by the fixing device 20. Then, the sheet P is discharged to the outside of the apparatus by the sheet discharge roller 13 and is stocked on the sheet discharge tray 14.

  The above description is an image forming operation for forming a full color image on a sheet, but a monochrome image can be formed using any one of the four image forming units 4Y, 4M, 4C, 4K, It is also possible to use two or three imaging units to form a two or three color image.

Next, the configuration of the fixing device 20 will be described based on FIG.
As shown in FIG. 2, the fixing device 20 includes a fixing belt 21 as a rotatable fixing rotating body, a pressure roller 22 as an opposing rotating body rotatably provided facing the fixing belt 21, and fixing Radiation from the halogen heater 23 as a heat source for heating the belt 21, the nip forming member 24 disposed inside the fixing belt 21, the stay 25 as a support member for supporting the nip forming member 24, and the halogen heater 23 Of the fixing belt 21, a temperature sensor 27 as temperature detecting means for detecting the temperature of the fixing belt 21, a separating member 28 for separating the sheet from the fixing belt 21, and the fixing belt 21. A belt holding member 40 (see FIGS. 3A to 3C) holding both end portions, and a pressure unit (not shown) for pressing the pressure roller 22 to the fixing belt 21 Eteiru.

  The fixing belt 21 is composed of a thin and flexible endless belt member (including a film). Specifically, the fixing belt 21 is made of an inner peripheral base material made of a metal material such as nickel or SUS or a resin material such as polyimide (PI), and a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) Or it is comprised by the mold release layer of the outer peripheral side formed with polytetrafluoroethylene (PTFE) etc. In addition, an elastic layer formed of a rubber material such as silicone rubber, foamable silicone rubber, or fluororubber may be interposed between the substrate and the release layer.

  The pressure roller 22 includes a cored bar 22a, an elastic layer 22b made of foamable silicone rubber, silicone rubber, fluororubber or the like provided on the surface of the cored bar 22a, and a PFA provided on the surface of the elastic layer 22. Or a release layer 22c made of PTFE or the like. The pressure roller 22 is pressed toward the fixing belt 21 by a pressure unit (not shown) and is in contact with the nip forming member 24 via the fixing belt 21. Where the pressure roller 22 and the fixing belt 21 are in pressure contact with each other, the elastic layer 22 b of the pressure roller 22 is crushed to form a nip portion N having a predetermined width. Further, the pressure roller 22 is configured to be rotationally driven by a drive source such as a motor (not shown) provided on the printer main body. When the pressure roller 22 is rotationally driven, the driving force is transmitted to the fixing belt 21 at the nip portion N, and the fixing belt 21 is driven to rotate.

  In the present embodiment, the pressure roller 22 is a solid roller, but may be a hollow roller. In that case, a heating source such as a halogen heater may be provided inside the pressure roller 22. When the elastic layer is not present, the heat capacity is reduced and the fixing ability is improved. However, when the unfixed toner is crushed and fixed, the minute unevenness of the belt surface is transferred to the image, and the uneven part of the image has uneven gloss. It may occur. In order to prevent this, it is desirable to provide an elastic layer having a thickness of 100 μm or more. By providing the elastic layer having a thickness of 100 μm or more, fine irregularities can be absorbed by the elastic deformation of the elastic layer, so that occurrence of gloss unevenness can be avoided. The elastic layer 22 b may be solid rubber, but if there is no heat source inside the pressure roller 22, sponge rubber may be used. Sponge rubber is more desirable because heat insulation is enhanced and heat of the fixing belt 21 is less likely to be taken away. Further, the fixing belt 21 and the pressure roller 22 are not limited to the case where they are in pressure contact with each other, but may be configured to be merely brought into contact without pressure application.

  Both ends of each of the halogen heaters 23 are fixed to a side plate (not shown) of the fixing device 20. Each halogen heater 23 is configured to be output controlled by a power supply unit provided in the printer body to generate heat, and the output control is based on the detection result of the surface temperature of the fixing belt 21 by the temperature sensor 27. To be done. By such output control of the heater 23, the temperature (fixing temperature) of the fixing belt 21 can be set to a desired temperature. In addition to the halogen heater, an IH, a resistance heating element, a carbon heater or the like may be used as a heating source for heating the fixing belt 21.

  The nip forming member 24 has a base pad 241 and a sliding sheet (low friction sheet) 240 provided on the surface of the base pad 241. The base pad 241 is disposed longitudinally in the axial direction of the fixing belt 21 or in the axial direction of the pressure roller 22, and determines the shape of the nip portion N under the pressure of the pressure roller 22. is there. The base pad 241 is fixed and supported by the stay 25. As a result, it is possible to prevent the nip forming member 24 from being bent due to the pressure by the pressure roller 22 and to obtain a uniform nip width in the axial direction of the pressure roller 22. The stay 25 is preferably formed of a metal material having high mechanical strength, such as stainless steel or iron, in order to satisfy the deflection prevention function of the nip forming member 24. In the present embodiment, the surface of the base pad 241 facing the pressure roller 22 is formed in a flat surface shape, and the nip portion N is thus formed in a straight shape. By forming the nip portion N in a straight shape, the pressing force by the pressing roller 22 can be reduced.

  Further, the base pad 241 is made of a hard material to a certain extent for securing strength, and is made of a heat resistant material having a heat resistant temperature of 200 ° C. or more. As a result, in the toner fixing temperature range, the deformation of the nip forming member 24 due to heat is prevented, the stable state of the nip portion N is secured, and the output image quality is stabilized. Materials for the base pad 241 include polyether sulfone (PES), polyphenylene sulfide (PPS), liquid crystal polymer (LCP), polyether nitrile (PEN), polyamide imide (PAI), polyether ether ketone (PEEK), etc. It is possible to use metal, ceramic, etc. other than general heat resistant resin.

  The sliding sheet 240 is disposed on the surface of the base pad 241 facing at least the fixing belt 21. Thus, the base pad 241 indirectly contacts the fixing belt 21 via the sliding sheet 240. During rotation of the fixing belt 21, the fixing belt 21 slides with respect to the sliding sheet 240, so the frictional force generated on the fixing belt 21 is reduced, and the driving torque of the fixing belt 21 is reduced. In addition, it is also possible to set it as the structure which does not have the sliding sheet 240. FIG.

  The reflection member 26 is disposed between the stay 25 and the halogen heater 23. In the present embodiment, the reflecting member 26 is fixed to the stay 25. As a material of the reflecting member 26, aluminum, stainless steel or the like can be used. By arranging the reflection member 26 in this manner, the light emitted from the halogen heater 23 to the stay 25 side is reflected to the fixing belt 21. As a result, the amount of light emitted to the fixing belt 21 can be increased, and the fixing belt 21 can be efficiently heated. Moreover, since it can suppress that the radiant heat from the halogen heater 23 is transmitted to the stay 25 grade | etc., Energy saving can also be achieved.

  Although not shown, shielding members for shielding the heat from the halogen heater 23 are disposed between the fixing belt 21 and the halogen heater 23 at both axial ends of the fixing belt 21. Thereby, it is possible to suppress an excessive temperature rise particularly in the non-sheet passing area of the fixing belt at the time of continuous sheet passing, and to prevent deterioration and damage of the fixing belt due to heat.

  Further, the fixing device 20 according to the present embodiment is subjected to various contrivances in order to further improve the energy saving property and the first print time.

  Specifically, the fixing belt 21 can be directly heated by the halogen heater 23 at locations other than the nip N (direct heating system). In the present embodiment, nothing is interposed between the halogen heater 23 and the left side portion of the fixing belt 21 in FIG. 2 and radiation heat from the halogen heater 23 is directly applied to the fixing belt 21 at that portion.

  Further, in order to reduce the heat capacity of the fixing belt 21, the fixing belt 21 is made thinner and smaller in diameter. Specifically, the thicknesses of the base material, the elastic layer, and the release layer that constitute the fixing belt 21 are set in the range of 20 to 50 μm, 100 to 300 μm, and 10 to 50 μm, respectively, and the thickness as a whole is set. It is set to 1 mm or less. The diameter of the fixing belt 21 is set to 20 to 40 mm. In order to further reduce the heat capacity, the thickness of the entire fixing belt 21 is preferably 0.2 mm or less, and more preferably 0.16 mm or less. The diameter of the fixing belt 21 is preferably 30 mm or less.

  In the present embodiment, the diameter of the pressure roller 22 is set to 20 to 40 mm, and the diameter of the fixing belt 21 and the diameter of the pressure roller 22 are configured to be equal. However, the present invention is not limited to this configuration. For example, the diameter of the fixing belt 21 may be smaller than the diameter of the pressure roller 22. In that case, the curvature of the fixing belt 21 at the nip portion N is smaller than the curvature of the pressure roller 22, so the sheet P discharged from the nip portion N is easily separated from the fixing belt 21.

  Further, as described above, as a result of reducing the diameter of the fixing belt 21, the space inside the fixing belt 21 becomes smaller, but the stay 25 is formed in a concave shape bent at both end sides, and the inner side of the concave portion formed. By accommodating the halogen heater 23, the stay 25 and the halogen heater 23 can be disposed even in a small space.

  Further, in order to arrange the stay 25 as large as possible even in a small space, the nip forming member 24 is formed to be compact on the contrary. Specifically, the width of the base pad 241 in the sheet conveyance direction is formed smaller than the width of the stay 25 in the sheet conveyance direction. Further, in FIG. 2, the heights of the upstream end 24 a and the downstream end 24 b of the base pad 241 with respect to the nip N or the virtual extension E thereof are h 1 and h 2, respectively. When the maximum height of the portion N of the base pad 241 other than the downstream end 24b with respect to the nip N or the virtual extension E thereof is h3, h1 ≦ h3 and h2 ≦ h3. With this configuration, the upstream end 24 a and the downstream end 24 b of the base pad 241 do not intervene between the respective bent portions on the upstream and downstream sides of the stay 25 in the sheet conveyance direction and the fixing belt 21. Therefore, each bent portion can be disposed close to the inner peripheral surface of the fixing belt 21. As a result, the stay 25 can be disposed as large as possible in the limited space in the fixing belt 21, and the strength of the stay 25 can be secured. As a result, the deflection of the nip forming member 24 by the pressure roller 22 can be prevented, and the fixing property can be improved.

  Further, in order to secure the strength of the stay 25, in the present embodiment, the stay 25 contacts the nip forming member 24 and extends in the sheet conveyance direction (vertical direction in FIG. 2); It is configured to have rising portions 25 b extending in the contact direction (left side in FIG. 2) of the pressure roller 22 from the respective end portions on the upstream side and the downstream side in the sheet conveyance direction. That is, by providing the rising portion 25b in the stay 25, the stay 25 has a horizontally long cross section extending in the pressure direction of the pressure roller 22, the cross section coefficient becomes large, and the mechanical strength of the stay 25 is increased. It is possible to improve the

  If the rising portion 25 b is formed longer in the contact direction of the pressure roller 22, the strength of the stay 25 is improved. Therefore, it is desirable that the front end of the rising portion 25 b be as close as possible to the inner peripheral surface of the fixing belt 21. However, during rotation, the fixing belt 21 shakes (does not move) regardless of whether the fixing belt 21 is too close to the inner peripheral surface of the fixing belt 21. There is a risk of contact with In particular, in the configuration using the thin fixing belt 21 as in the present embodiment, since the swing width of the fixing belt 21 is large, it is necessary to set the position of the tip of the rising portion 25 b with caution.

  Specifically, in the case of the present embodiment, the distance d in the contact direction of the pressure roller 22 between the tip of the rising portion 25b and the inner circumferential surface of the fixing belt 21 is at least 2.0 mm, preferably 3.0 mm or more. It is preferable to set. On the other hand, when the fixing belt 21 has a certain thickness and there is almost no deflection, the distance d can be set to 0.02 mm. When the reflecting member 26 is attached to the tip of the rising portion 25 b as in the present embodiment, the distance d needs to be set so that the reflecting member 26 does not contact the fixing belt 21.

  As described above, the leading end of the rising portion 25 b is disposed as close as possible to the inner peripheral surface of the fixing belt 21, whereby the rising portion 25 b is disposed long in the contact direction of the pressure roller 22. Can. As a result, even in the configuration using the fixing belt 21 with a small diameter, the mechanical strength of the stay 25 can be improved.

The basic operation of the fixing device according to the present embodiment will be described below with reference to FIG.
When the power switch of the printer main body is turned on, electric power is supplied to the halogen heater 23, and the pressure roller 22 starts to rotate clockwise in FIG. Thus, the fixing belt 21 is driven to rotate counterclockwise in FIG. 2 by the frictional force with the pressure roller 22.

  Thereafter, the sheet P carrying the unfixed toner image T in the above-described image forming process is conveyed in the direction of the arrow A1 in FIG. 2 while being guided by the guide plate (not shown), and the fixing belt 21 in pressure contact The sheet is fed to the nip portion N of the pressure roller 22. The fixing roller 21 heats the side on which the unfixed image T of the sheet P is carried, and the heat on the halogen heater 23 and the pressure between the fixing belt 21 and the pressure roller 22 cause toner on the surface of the sheet P. The image T is fixed.

  The sheet P on which the toner image T is fixed is carried out from the nip portion N in the direction of the arrow A2 in FIG. The tip 28a of the separation member 28 disposed near the exit of the nip portion N is not in contact with the surface of the fixing belt 21 and forms a separation gap g with the surface. When the leading end of the sheet P conveyed out of the nip portion N contacts the leading end 28 a of the separating member 28, the sheet P is separated from the fixing belt 21. Thereafter, as described above, the separated sheet P is discharged to the outside of the machine by the discharge roller and is stocked in the discharge tray.

  Next, based on FIGS. 3A to 3C, a support structure for supporting both axial ends of the fixing belt 21 will be described. In this support structure, both ends of the fixing belt 21 are rotatably supported by a belt holding member 40 inserted in the inner periphery thereof. By fixing the belt holding member 40 to a side plate (not shown), the fixing device 20 is incorporated into the image forming apparatus. In FIGS. 3A to 3C, only the belt holding member 40 on one side is illustrated, but since the belt holding member on the other side has the same configuration, the belt on one side will be described below. Only the holding member 40 will be described.

  As shown in FIGS. 3A and 3B, the belt holding member 40 projects to the outer diameter side of the cylindrical portion 40a whose outer peripheral surface is a cylindrical surface and the cylindrical portion 40a, and moves the fixing belt 21 in the axial direction. And a flange portion 40b for regulating. The belt holding member 40 is integrally formed, for example, by injection molding of resin. As shown in FIG. 3C, the cylindrical portion 40a of the belt holding member 40 is formed in a C-shaped cross section having an axial notch at the position of the nip portion N (the position where the nip forming member 24 is disposed). ing. The cylindrical portion 40 a of the belt holding member 40 is loosely fitted to the inner peripheral surface of the fixing belt 21, and the end of the fixing belt 21 is rotatably held by the cylindrical portion 40 a. The end of the stay 25 is fixed to the belt holding member 40 and positioned.

  As shown in FIGS. 3A and 3B, the end of the fixing belt 21 is located between the axial end surface of the fixing belt 21 and the opposing surface of the belt holding member 40 (the end surface 401 of the flange portion 40b). A slip ring 41 is disposed as a protection member for protecting the portion. Thus, when the fixing belt 21 is deviated in the axial direction, the end of the fixing belt 21 can be prevented from coming into direct contact with the end face 401 of the flange portion 40 b of the belt holding member 40. It can prevent wear and breakage. Since the slip ring 41 is fitted on the outer periphery of the cylindrical portion 40 a of the belt holding member 40 with a margin, when the end of the fixing belt 21 contacts the slip ring 41, the slip ring 41 and the fixing belt 21 It is possible to take along. At this time, the slip ring 41 does not necessarily have to be rotated, and the slip ring 41 may be stationary. As a material of the slip ring 41, it is preferable to apply a so-called super engineer plastic excellent in heat resistance, for example, PEEK, PPS, PAI, PTFE and the like.

  In the above supporting structure, only the both end portions of the fixing belt 21 are held by the belt holding member 40, so that the fixing belt 21 is in a freely deformable state except the nip portion N between the both end portions. Further, with the nip portion N having a straight shape, a force always acts on the fixing belt 21 so as to deform in an elliptical shape. Therefore, the fixing belt 21 in rotation has an elliptical shape in which the radial cross section is substantially perfect circular at both ends, and the radial cross section in the region between both ends has the minor axis normal to the nip portion N. Transform to become

  In the fixing device 20 having such a configuration, when the axial length of the pressure roller 22 is substantially the same as that of the fixing belt 21 and the pressure roller 22 is disposed so as to overlap the belt holding member 40 in the axial direction, It was revealed that the end of the fixing belt 21 was broken. Specifically, at the boundary between the portion of the fixing belt 21 in contact with the cylindrical portion 40 a of the belt holding member 40 and the portion not in contact (at the leading edge 403 of the cylindrical portion 40 a except for the outer peripheral chamfer 402) It was found that circumferential cracks and streaks occurred along the surface. As described above, the failure of the fixing belt 21 is deformed into the action of the shear force (FIG. 10 (a)) at the nip N, the action of the shear force (FIG. 10 (b)) at the belt end, and further elliptical. It is considered that stress concentration is generated in the area along the leading edge 403 of the cylindrical portion 40 a of the fixing belt 21 due to the fluctuation of the bending force (FIG. 3C) due to the above.

  On the other hand, in the present invention, as shown in FIG. 3B, the pressure roller 22 and the belt holding member 40 are disposed in the state of being axially shifted without being overlapped in the axial direction. In this case, the axial length of the pressure roller 22 is shorter than the axial length of the fixing belt 21, and the tip of the belt holding member 40 (the tip of the cylindrical portion 40 a) and the end 22 a of the pressure roller 22 are axial Space in the direction. As a result, an axial region L is formed on the fixing belt 21 so as not to be in contact with both the pressure roller 22 and the belt holding member 40 (the cylindrical portion 40 a axially outside the leading edge 403). According to the verification of the present inventors, it has been found that the adoption of such a configuration can prevent the occurrence of cracks and streaks at the end of the fixing belt 21. This is considered to be because stress concentration near the leading edge 403 of the fixing belt 21 can be alleviated. By preventing damage at the end portion of the fixing belt 21 as described above, the durable life of the fixing device 20 and the image forming apparatus can be improved.

  In order to obtain the above effects, it is desirable that the axial separation distance L between the end 22a of the pressure roller 22 and the leading edge 403 of the belt holding member be 3 mm or more, preferably 5 mm or more. .

  FIG. 4 shows another embodiment of the fixing device 20 of the present invention. In the embodiment of FIGS. 3A to 3C, the cylindrical portion 40a of the belt holding member 40 is formed in a C-shaped cross section, and the nip forming member 24 is accommodated in the notch of the cylindrical portion 40a. 24 is disposed over the entire axial length of the fixing belt 21. On the other hand, in the embodiment shown in FIG. 4, the cylindrical portion 40a of the belt holding member 40 has a cylindrical shape without a notch, and the nip forming member 24 is shortened to make the space between the cylindrical portions 40a of the belt holding members 40 on both sides. The nip forming member 24 is disposed. At this time, the end of the nip forming member 24 is axially closer to the center than the end 22 a of the pressure roller 22.

  Also in this embodiment, as in the embodiment shown in FIGS. 3A to 3C, the pressure roller 22 and the belt holding member 40 are disposed in an axially shifted state without overlapping in the axial direction. This makes it possible to prevent the occurrence of cracks and streaks at the end of the fixing belt 21. The axial separation distance L between the end 22 a of the pressure roller 22 and the leading edge 403 of the belt holding member 40 is set to 3 mm or more (preferably 5 mm or more). In this case, the value obtained by subtracting the thickness α of the slip ring 41 from the axial distance W between the end surface 401 of the flange portion 40b of the belt holding member 40 and the end 22a of the pressure roller 22 is 10 mm or more Set

  In this configuration, an axial region L not in contact with any of the pressure roller 22, the nip forming member 24, and the belt holding member 40 is formed in the fixing belt 21. In this region, the shape of the fixing belt 21 is not restrained by the pressure roller 22, the nip forming member 24, or the belt holding member 40, and the fixing belt can be freely deformed. Therefore, stress concentration in the vicinity of the leading edge 403 of the cylindrical portion 40 a of the fixing belt 21 can be alleviated, and the durability of the fixing belt 21 can be improved.

  FIG. 5 shows a modification of the cylindrical portion 40 a of the belt holding member 40. Although the cross-sectional shape of the cylinder part 40a is made substantially circular in embodiment of FIG.3 (a)-(c) and FIG. 4, the cross-sectional shape of the cylinder part 40a is closely approached to a rectangle in FIG. With such a configuration, the curvature of the fixing belt 21 becomes large (curvature radius becomes small) near the exit of the nip portion N, and the separability of the sheet P by the leading end 28 a of the separating member 28 is improved.

  Another embodiment of the fixing device 20 is shown in FIG. The fixing device 20 of this embodiment is provided with three halogen heaters 23 as heat sources. In this case, by making the heat generation region different for each halogen heater 23, it is possible to heat the fixing belt 21 in a range corresponding to the sheet width of various widths. A sheet metal 250 is provided so as to surround the nip forming member 24, and the nip forming member 24 is supported by the stay 25 via the sheet metal 250.

  Also in this embodiment, similarly to the embodiment shown in FIGS. 3A to 3C and FIG. 4, the pressure roller 22 and the belt holding member 40 are shifted in the axial direction without overlapping in the axial direction. By arranging in the above, it is possible to prevent the occurrence of cracks and streaks at the end of the fixing belt 21.

  In the nip forming member 24 shown in FIG. 6, a protrusion 241 a that protrudes toward the pressure roller 22 is provided at the downstream end of the nip portion N. From such a configuration, as shown in FIG. 7, the exit of the nip portion N faces the pressure roller 22 side, so that the separation of the sheet P can be enhanced. The nip forming member 24 can also be used as a nip forming member of the fixing device 20 shown in FIG.

  In the embodiment shown in FIG. 6, the configuration other than the above is basically in common with the configuration of the embodiment shown in FIG.

  The features of the fixing device 20 according to the present invention described above are listed below.

  A rotatable endless fixing belt 21, a belt holding member 40 for holding the fixing belt 21 at both ends in the axial direction, a heating source 23 for heating the fixing belt 40, and a nip disposed inside the fixing belt In the fixing device 20 including the forming member 24 and the opposing rotating body 22 forming the nip portion N with the fixing belt 21 by coming into contact with the nip forming member 24 via the fixing belt 21, the opposing rotating body 22 By arranging the belt holding member 40 in the axial direction without overlapping in the axial direction, stress concentration in the fixing belt 21 is alleviated, and breakage of the end portion of the fixing belt 21 is prevented for a long time It is possible to

  In this configuration, the belt holding member 40 is provided with a cylindrical portion 40a inserted into the inner periphery of the fixing belt 21 and a flange portion 40b protruding to the outer diameter side of the cylindrical portion, and the tip of the cylindrical portion 40a and This can be realized by axially separating the end of the opposing rotating body 22 opposed to the other. At this time, it is desirable that the axial separation distance L be 5 mm or more.

  By providing the fixing belt 21 with an axial region not in contact with both the opposing rotating member 22 and the belt holding member 40 (see FIG. 3B), stress concentration in the fixing belt is alleviated, and the fixing belt is broken. It is possible to prevent for a long time.

  By providing the fixing belt 21 with an axial region not in contact with any of the facing rotating body 22, the belt holding member 40, and the nip forming member 24 (see FIG. 4), stress concentration in the fixing belt is alleviated, and the fixing belt is fixed. Durability can be improved.

  The fixing belt 21 is desirably driven to rotate with respect to the opposing rotating body 22.

  When the outer peripheral surface of the cylindrical portion 40 a of the belt holding member 40 is made into a non-perfect circular shape, the separating property of the sheet P by the separating member 28 is enhanced. The same effect can be obtained by causing the nip forming member 24 to protrude toward the opposing rotary body 22 at the downstream end of the nip portion N.

  The embodiment of the present invention has been described above, but the present invention is not limited to a fixing device in which the fixing belt is made thinner and smaller in diameter for the purpose of improving energy saving and the like as in the above-described embodiment. Further, the fixing device according to the present invention is not limited to the color laser printer shown in FIG. 1, but can be installed in a monochrome image forming apparatus, other printers, copiers, facsimiles, or composite machines of these. . Also, it goes without saying that various modifications can be made without departing from the scope of the present invention.

20 fixing device 21 fixing belt 22 pressure roller (opposite rotating body)
22a end 23 halogen heater (heating source)
24 nip forming member 25 stay (supporting member)
28 Separation member 40 Belt holding member 40a Tube portion 40b Flange portion 403 Tip edge (tip)
N nip P paper (recording medium)
g separation gap

JP 2007-334205 A Unexamined-Japanese-Patent No. 2007-233011 gazette

Claims (14)

A rotatable endless fixing belt,
A heating member for heating the fixing belt;
A nip forming member disposed inside the fixing belt;
An opposing rotating body that forms a nip portion with the fixing belt by coming into contact with the nip forming member via the fixing belt;
And a belt holding member that holds the fixing belt at both axial ends and does not hold the fixing belt between the axial ends.
In the fixing device, the heating member directly heats the inside of the fixing belt except that the fixing belt and the nip forming member abut each other.
The belt holding member has a cylindrical portion disposed inside the axial end portion of the fixing belt, and a flange portion protruding to the outer diameter side of the cylindrical portion.
A protective member fitted to the outer periphery of the cylindrical portion is provided between the axial end of the fixing belt and the end face of the flange portion of the belt holding member, and the outer periphery of the protective member when viewed from the axial direction , Ri the opposed rotary section near than the surface of the fixing belt abutting nip forming member,
The opposing rotating body and the belt holding member are disposed in an axially offset state without overlapping in the axial direction;
The fixing device is characterized in that the protective member is rotatable with respect to a flange portion of the belt holding member . Said flange portion, a fixing device according to claim 1, further comprising a restricting shape capable its axial movement when axial movement of the fixing belt. The fixing device according to claim 1 , wherein the protection member fitted around the outer periphery of the cylindrical portion of the belt holding member is rotatable with the fixing belt .   The fixing device according to any one of claims 1 to 3, wherein an end of the cylindrical portion and an end portion of an opposing rotating body opposed thereto are separated in an axial direction.   The fixing device according to claim 4, wherein the axial separation distance is 5 mm or more. Wherein the fixing belt, the counter rotating body and the belt holding member fixing device according to claim 1 to 5 any one of claims provided with axial region not in contact with both. Wherein the fixing belt, the counter rotating member, said belt holding member, and the fixing device of claims 1 to 5 any one of claims that with any provided an axial region which does not contact the nip forming member. The fixing device according to any one of claims 1 to 7, wherein an end portion of the nip forming member is axially closer to the center than an end portion of the counter rotating body .   The fixing device according to any one of claims 1 to 7, further comprising a support member for supporting the nip forming member, wherein an end of the nip forming member is axially closer to the center than an end of the support member. . The fixing belt, a fixing device according to the driven any one of claims 1 to 9 to rotate relative to the opposing rotor. The fixing device according to claim 1, wherein an outer peripheral surface shape of the cylindrical portion is non-perfect circular. The fixing device according to the nip formation member at the downstream end to any one of claims 1 to 11 which projects in the opposite rotary section of the nip. The fixing device according to any one of claims 1 to 12 minus the thickness of the protective member from the axial distance is 10mm or more between the end of the end face and the opposite rotation of the flange portion .   An image forming apparatus comprising the fixing device according to any one of claims 1 to 13.

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