JP2014164223A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent discoloration and deformation of a support member and a reflection member due to an increase in temperature, and prevent deflection of a nip forming member associated with the discoloration and deformation.SOLUTION: A fixing device 20 includes an endless, rotatable fixing belt 21, a nip forming member 24 that is disposed inside the fixing belt, an opposing rotating body 22 that is brought into contact with the nip forming member with the fixing belt therebetween to form a nip part between the fixing belt and the opposing rotating body, a heat source 23 that heats the fixing belt, and a support member 25 that supports the nip forming member. The support member includes a base part 25a that is brought into contact with the nip forming member, and at least one rising part 25b that rises from the base part in a pressing direction; and a light shielding film 23a shielding light from the heat source is disposed over the entire range or a part of the surface or the vicinity of the surface of the heat source 23 opposing to the support member 25.

Description

  The present invention includes a fixing device used in an image forming apparatus such as a facsimile, a printer, a copying machine, a multifunction machine having at least two functions of these, using an electrophotographic method, an electrostatic recording method, and the like, and the fixing device. The present invention relates to an image forming apparatus.

In recent years, market demands for energy saving and high speed have been increasing for image forming apparatuses such as printers, copiers, and facsimiles.
In an image forming apparatus, an unfixed toner image is transferred to a recording material sheet, printing paper, photosensitive paper, electrostatic recording paper, etc. by an image transfer method or a direct method by an image forming process such as electrophotographic recording, electrostatic recording, and magnetic recording. Formed on the recording material. As a fixing device for fixing an unfixed toner image, a contact heating method fixing device such as a heat roller method, a film heating method, and an electromagnetic induction heating method is widely used.

  As an example of such a fixing device, a belt-type fixing device (for example, Patent Document 1) and a surf fixing (film fixing) fixing device (for example, Patent Document 2) using a ceramic heater are known.

  In recent years, belt-type fixing devices have undergone warm-up time, which is the time required to reach a predetermined printable temperature (reload temperature) when the power is turned on, etc. There is a demand for further shortening of the first print time, which is the time from the printing operation to the completion of paper discharge (Problem 1). Further, as the speed of the image forming apparatus increases, the number of sheets passed per unit time increases and the required heat amount increases, so that a so-called temperature drop, in which the heat amount is insufficient particularly at the beginning of continuous printing, is also a problem ( Problem 2).

  As a method for solving the problem of the problem 1, surf fixing using a ceramic heater has been proposed. With this method, it is possible to reduce the heat capacity and reduce the size as compared with a belt-type fixing device. However, since only the nip portion is locally heated, the other portions are not heated, and the belt is in the coldest state at the entrance of the paper or the like of the nip, so that fixing failure is likely to occur. In particular, in a high-speed machine, there is a problem that fixing failure is more likely to occur because the belt rotates fast and the heat radiation of the belt outside the nip increases (problem 3).

  In order to solve the above problems 1 to 3, in the configuration using an endless belt, the entire belt can be heated, the first print time from the heating standby time can be shortened, and at the time of high-speed rotation There has been proposed a fixing device that can solve the shortage of heat and obtain good fixing properties even when mounted on a high-production image forming apparatus (for example, Patent Document 3).

  This fixing device warms the entire endless belt through heating of a pipe-shaped metal heat conductor disposed inside the endless belt. However, a fixing device that directly heats an endless belt is known for further energy saving and first print time improvement (Patent Document 4).

  In this configuration, as shown in FIG. 13, a plate-like nip forming member 500 is provided at a position facing the pressure roller 400, and the endless belt 100 is directly heated by the heat source 300 except where the nip forming member 500 is disposed. Therefore, the heat transfer efficiency is greatly improved and the power consumption is reduced. This makes it possible to further shorten the first print time from the heating standby time. In this fixing device, the nip forming member 500 is supported by a support member 600 such as stainless steel, and the strength of the nip forming member 500 against the pressure applied by the pressure roller 400 is increased.

  In the fixing device shown in FIG. 13, a small-diameter belt having a diameter of about 30 mm is used for the endless belt 100 in order to improve thermal efficiency. With such a configuration, the support member 600 disposed in the endless belt 100 is used. There is also a tendency for the size of to become smaller. As a result, sufficient strength of the nip forming member 500 cannot be obtained, and when the nip forming member 500 is bent due to the pressure applied by the pressure roller 400, the surface pressure distribution and the nip width of the nip portion N vary, thereby fixing. Defects may occur.

  Accordingly, a fixing device has been proposed that can improve the strength of the support member and prevent the nip forming member from being bent (FIG. 2).

  However, as will be described in detail later, in the fixing device shown in FIG. 2, the gap between the support member 25 and the reflection member 26 and the halogen heater 23 that is a heating source must be very narrow as the fixing device is downsized. I do not get. If the distance between the support member 25 or the reflection member 26 and the halogen heater 23 is short, the temperature of the support member 25 or the reflection member 26 increases, and this may cause discoloration or deformation. If the support member 25 or the reflection member 26 is discolored or deformed, the reflection efficiency is lowered, heat is absorbed, and energy saving performance is lowered. In addition, as the temperature of the support member 25 rises, the temperature of the nip forming member 24 supported by the support member 25 rises and the nip forming member 24 is deformed, thereby causing variations in the surface pressure distribution and nip width of the nip portion N. This may cause a fixing failure.

  SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a fixing device and an image forming apparatus that can prevent discoloration and deformation due to a temperature rise of a support member and a reflection member, and can prevent a nip forming member from being bent due thereto. To do.

  In order to solve this problem, a fixing device according to the present invention includes a rotatable endless fixing belt, a nip forming member disposed inside the fixing belt, and the nip forming member via the fixing belt. A counter rotating body that forms a nip portion with the fixing belt by contacting the fixing belt, a heat source that heats the fixing belt, and a support member that supports the nip forming member, and the counter belt faces the fixing belt. A recording medium carrying an unfixed image is conveyed to a nip portion between the rotating body and an unfixed image is fixed on the recording medium. The support member is a base that contacts the nip forming member. And a light-shielding film that blocks light from the heating source, or the surface of the heating source facing the support member or in the vicinity of the surface. Characterized in that it is arranged in the entire range or part.

  According to the present invention, it is possible to suppress the excessive temperature rise of the support member and the reflection member due to the proximity of the support member and the reflection member and the heating source due to the downsizing of the fixing device, and without impairing energy saving and fixing properties. The fixing device and the image forming apparatus can be downsized.

1 is a schematic configuration diagram illustrating an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a schematic configuration diagram of a conventional fixing device mounted on the image forming apparatus. It is explanatory drawing about a reflective surface. 1 is a schematic configuration diagram illustrating an embodiment of a fixing device. FIG. 9 is a schematic configuration diagram illustrating a modified example of the fixing device. FIG. 9 is a schematic configuration diagram illustrating a modified example of the fixing device. FIG. 9 is a schematic configuration diagram illustrating a modified example of the fixing device. FIG. 9 is a schematic configuration diagram illustrating a modified example of the fixing device. FIG. 9 is a schematic configuration diagram illustrating a modified example of the fixing device. FIG. 9 is a schematic configuration diagram illustrating a modified example of the fixing device. FIG. 9 is a schematic configuration diagram illustrating a modified example of the fixing device. It is a schematic block diagram of a halogen heater (heating source) and a light shielding film. It is a schematic block diagram of the conventional fixing device.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In each of the drawings for explaining the embodiments of the present invention, constituent elements such as members and components having the same function or shape are described once by giving the same reference numerals as much as possible. Then, the explanation is omitted.

First, an overall configuration and operation of an image forming apparatus according to an embodiment of the present invention will be described with reference to FIG.
An 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 in the center of the apparatus main body. Each of the image forming units 4Y, 4M, 4C, and 4K contains developers of different colors of yellow (Y), magenta (M), cyan (C), and black (K) corresponding to the color separation components of the color image. The configuration is the same except that.

  Specifically, each of the image forming units 4Y, 4M, 4C, and 4K has a drum-shaped photoconductor 5 as a latent image carrier, a charging device 6 that charges the surface of the photoconductor 5, and a surface of the photoconductor 5. A developing device 7 that supplies toner and a cleaning device 8 that cleans the surface of the photoreceptor 5 are provided. In FIG. 1, only the photoconductor 5, the charging device 6, the developing device 7, and the cleaning device 8 included in the black image forming unit 4 </ b> K are denoted by reference numerals. In the other image forming units 4 </ b> Y, 4 </ b> M, and 4 </ b> C, The reference numerals are omitted.

  Under the image forming units 4Y, 4M, 4C, and 4K, an exposure device 9 that exposes the surface of the photoreceptor 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 photoconductor 5 with laser light based on image data.

  A 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 member, 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 a cleaning device. 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 driven to rotate, the intermediate transfer belt 30 runs (rotates) in the direction indicated by the arrow in the figure.

  Each of the four primary transfer rollers 31 sandwiches the intermediate transfer belt 30 with each photoconductor 5 to form a primary transfer nip. Further, a power source (not shown) is connected to each primary transfer roller 31 so that a predetermined DC voltage (DC) and / or AC 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. Similarly to the primary transfer roller 31, a power source (not shown) is also connected to the secondary transfer roller 36, and a predetermined DC voltage (DC) and / or AC voltage (AC) is applied to the secondary transfer roller 36. It has become so.

  The belt cleaning device 35 includes a cleaning brush and a cleaning blade disposed so as to contact the intermediate transfer belt 30. A waste toner transfer hose (not shown) extending from the belt cleaning device 35 is connected to an entrance of a waste toner container (not shown).

  A bottle container 2 is provided in the upper part of the printer main body, and four toner bottles 2Y, 2M, 2C, and 2K containing replenishing toner are detachably attached to the bottle container 2. A replenishment path (not shown) is provided between each toner bottle 2Y, 2M, 2C, 2K and each developing device 7, and each development from each toner bottle 2Y, 2M, 2C, 2K is performed via this replenishment path. The toner is supplied to the device 7.

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

  In the printer main body, a transport path R is provided for discharging the paper P from the paper feed tray 10 through the secondary transfer nip to the outside of the apparatus. In the transport path R, a pair of registration rollers 12 serving as transport means for transporting the paper P to the secondary transfer nip is disposed upstream of the position of the secondary transfer roller 36 in the paper transport direction.

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

Next, a 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 respective photoconductors 5 in the respective image forming units 4Y, 4M, 4C, and 4K are rotationally driven clockwise by a driving device (not shown), and the surface of each photoconductor 5 is charged by the charging device 6. Are uniformly charged to a predetermined polarity. The surface of each charged photoconductor 5 is irradiated with laser light from the exposure device 9 to form an electrostatic latent image on the surface of each photoconductor 5. At this time, the image information to be exposed on each photoconductor 5 is single-color image information obtained by separating a desired full-color image into color information of yellow, magenta, cyan, and black. In this way, toner is supplied to each electrostatic latent image formed on each photoconductor 5 by each developing device 7, whereby the electrostatic latent image is visualized (visualized) as a toner image. .

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

  Thereafter, when each color toner image on the photoconductor 5 reaches the primary transfer nip as each photoconductor 5 rotates, the toner image on each photoconductor 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 photoconductor 5 that could not be transferred to the intermediate transfer belt 30 is removed by the cleaning device 8. Thereafter, the surface of each photoconductor 5 is neutralized by a neutralizing device (not shown), and the surface potential is initialized.

  In the lower part of the image forming apparatus, the paper feed roller 11 starts to rotate, and the paper P is sent out from the paper feed tray 10 to the transport path R. The sheet P sent to the transport path R is timed by the registration roller 12 and 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 the toner charge polarity of the toner image on the intermediate transfer belt 30 is applied to the secondary transfer roller 36, thereby forming a transfer electric field 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 rotates, the transfer electric field formed in the secondary transfer nip causes a transfer on the intermediate transfer belt 30. The toner images are transferred onto the paper P all at once. At this time, the residual toner on the intermediate transfer belt 30 that could not be transferred onto the paper 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 paper P is conveyed to the fixing device 20, and the toner image on the paper P is fixed to the paper P by the fixing device 20. Then, the paper P is discharged out of the apparatus by the paper discharge roller 13 and stocked on the paper discharge tray 14.

  The above description is an image forming operation when a full-color image is formed on a sheet. A single color image can be formed using any one of the four image forming units 4Y, 4M, 4C, and 4K. Two or three image forming units can be used to form a two-color or three-color image.

Next, the configuration of the fixing device 20 serving as a base of the present invention will be described with reference to FIG.
As shown in the figure, the fixing device 20 includes a fixing belt 21 as a rotatable fixing rotator, a pressure roller 22 as an opposing rotator provided so as to be rotatable facing the fixing belt 21, and a fixing belt 21. Radiated from the halogen heater 23 as a heat source for heating the nip, a nip forming member 24 disposed inside the fixing belt 21, a stay 25 as a support member for supporting the nip forming member 24, and the halogen heater 23. Fixing a reflecting member 26 that reflects light to 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 that separates paper from the fixing belt 21, and the pressure roller 22. A pressing means (not shown) for pressing the belt 21 is provided.

  The fixing belt 21 is composed of a thin and flexible endless belt member (including a film). Specifically, the fixing belt 21 includes a base material on the inner peripheral side formed 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. Further, an elastic layer formed of a rubber material such as silicone rubber, foamable silicone rubber, or fluorine rubber may be interposed between the base material and the release layer.

  The pressure roller 22 includes a cored bar 22a, an elastic layer 22b made of foamable silicone rubber, silicone rubber, or fluorine rubber provided on the surface of the cored bar 22a, and a PFA provided on the surface of the elastic layer 22. Alternatively, it is constituted by 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. At the place where the pressure roller 22 and the fixing belt 21 are in pressure contact, the elastic layer 22b of the pressure roller 22 is crushed to form a nip portion N having a predetermined width. The pressure roller 22 is configured to be rotationally driven by a drive source such as a motor (not shown) provided in 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 disposed inside the pressure roller 22. In addition, when there is no elastic layer, the heat capacity is reduced and the fixability is improved, but when undetermined toner is crushed and fixed, minute irregularities on the belt surface are transferred to the image, resulting in uneven gloss on the solid portion of the image. there is a possibility. In order to prevent this, it is desirable to provide an elastic layer having a thickness of 100 μm or more. By providing an elastic layer having a thickness of 100 μm or more, minute unevenness can be absorbed by elastic deformation of the elastic layer, so that occurrence of uneven gloss can be avoided. The elastic layer 22b 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 preferable because heat insulation is enhanced and heat of the fixing belt 21 is less likely to be taken away. Further, the fixing rotator and the counter rotator are not limited to being brought into pressure contact with each other, and may be configured to simply contact each other without applying pressure.

  Both ends of the halogen heater 23 are fixed to a side plate (not shown) of the fixing device 20. Each halogen heater 23 is configured to generate heat by being output controlled by a power supply unit provided in the printer main body, and the output control is based on the detection result of the surface temperature of the fixing belt 21 by the temperature sensor 27. Done. By such output control of the heater 23, the temperature of the fixing belt 21 (fixing temperature) can be set to a desired temperature.

  The nip forming member 24 is disposed in a longitudinal shape over the axial direction of the fixing belt 21 or the axial direction of the pressure roller 22, and is fixedly supported by a stay 25. Thus, the nip forming member 24 is prevented from being bent by the pressure of the pressure roller 22, and a uniform nip width is obtained 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 bending prevention function of the nip forming member 24. However, the stay 25 may be made of resin. It is.

  The nip forming member 24 is composed of a heat resistant member having a heat resistant temperature of 200 ° C. or higher. This prevents the nip forming member 24 from being deformed by heat in the toner fixing temperature range and ensures a stable state of the nip portion N, thereby stabilizing the output image quality. For the nip forming member 24, 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 a typical heat resistant resin.

  The nip forming member 24 has a low friction sheet (not shown) on its surface. When the fixing belt 21 rotates, the fixing belt 21 slides with respect to the low friction sheet, so that the driving torque generated in the fixing belt 21 is reduced and the load due to the frictional force on the fixing belt 21 is reduced.

  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. Moreover, since the reflecting member 26 is directly heated by the halogen heater 23, it is desirable that the reflecting member 26 be formed of a high melting point metal material or the like. By arranging the reflection member 26 in this way, the light emitted from the halogen heater 23 toward the stay 25 is reflected to the fixing belt 21. As a result, the amount of light applied to the fixing belt 21 can be increased, and the fixing belt 21 can be efficiently heated. Further, since it is possible to suppress the radiant heat from the halogen heater 23 from being transmitted to the stay 25 and the like, energy saving can be achieved.

  Further, the reflective surface may be formed by mirror finishing such as polishing or painting the surface of the stay 25 on the side of the halogen heater 23 without providing the reflective member 26 as in the present embodiment. The reflectance of the reflecting surface of the reflecting member 26 or the stay 25 is desirably 90% or more.

  However, since the shape and material of the stay 25 cannot be freely selected in order to ensure the strength, the separate provision of the reflecting member 26 as in this embodiment increases the degree of freedom in selecting the shape and material, and the reflection. The member 26 and the stay 25 can be specialized for each function. Further, since the reflecting member 26 is provided between the halogen heater 23 and the stay 25, the position of the reflecting member 26 with respect to the halogen heater 23 is reduced, so that the fixing belt 21 can be efficiently heated.

  In addition, the fixing device 20 according to the present embodiment is devised in various configurations in order to further save energy and improve the first print time.

    Specifically, the fixing belt 21 can be directly heated at a place other than the nip portion N by the halogen heater 23 (direct heating method). In this embodiment, nothing is interposed between the halogen heater 23 and the left portion of the fixing belt 21 in FIG.

  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 constituting the fixing belt 21 are set in a range of 20 to 50 μm, 100 to 300 μm, and 10 to 50 μm, and the overall thickness 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 desirably 0.2 mm or less, and more desirably 0.16 mm or less. The diameter of the fixing belt 21 is desirably 30 mm or less.

  In this 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, it is not limited to this configuration. For example, the fixing belt 21 may be formed so that the diameter thereof is smaller than the diameter of the pressure roller 22. In that case, since the curvature of the fixing belt 21 at the nip portion N is smaller than the curvature of the pressure roller 22, the recording medium discharged from the nip portion N is easily separated from the fixing belt 21.

  Further, in order to further improve the heating efficiency of the fixing belt 21 by light reflection, it is necessary to examine the direction of the reflecting surface of the reflecting member 26 or the stay 25. For example, as shown in FIG. 3A, when the reflecting surfaces 70 are arranged concentrically with the halogen heater 23 as the center, light is reflected toward the halogen heater 23, so that the heating efficiency is increased accordingly. It will decline. On the other hand, in FIG. 3B, a part or all of the reflecting surface 70 is arranged so that the reflected light from the reflecting surface is directed to the fixing belt side instead of the halogen heater 23. As a result, the amount of light reflected in the direction of the halogen heater 23 is reduced, so that the heating efficiency by the reflected light can be improved.

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

  Thereafter, the paper 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 a guide plate (not shown), and the fixing belt 21 in the pressure contact state and It is fed into the nip N of the pressure roller 22. Then, the toner image T is fixed on the surface of the paper P by heat from the fixing belt 21 heated by the halogen heater 23 and pressure applied between the fixing belt 21 and the pressure roller 22.

  The paper 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. At this time, the paper P is separated from the fixing belt 21 by the leading edge of the paper P coming into contact with the leading edge of the separation member 28. Thereafter, the separated paper P is discharged out of the apparatus by the paper discharge roller as described above, and stocked on the paper discharge tray.

  However, the configuration shown in FIG. 2 alone cannot prevent discoloration or deformation due to temperature rise of the stay 25 or the reflection member 26, or bending of the nip forming member.

FIG. 4 is a cross-sectional view showing an embodiment of a fixing device according to the present invention. First, the structure of the stay will be described in more detail.
As shown in FIG. 4, the stay 25 is in contact with the nip forming member 24 and extends in the paper conveyance direction, and is pressurized from the upstream and downstream ends of the base portion 25a in the paper conveyance direction. And a pair of rising portions 25b extending in the pressing direction of the roller 22 (left side in the figure). The pair of rising portions 25b are arranged at a distance from each other in the sheet conveyance direction, and are respectively disposed outside both ends of the nip portion N in the sheet conveyance direction (positions indicated by dotted lines). In other words, the rising portion 25b on the upstream side in the paper conveyance direction (downward in the drawing) is disposed upstream of the upstream end portion of the nip portion N, and the rising portion 25b on the downstream side in the paper conveyance direction (upward in the drawing). Is disposed on the downstream side of the downstream end portion of the nip portion N.

  As described above, in this embodiment, by providing the pair of rising portions 25 b extending in the pressing direction of the pressure roller 22, the horizontally long cross section in which the stay 25 extends in the pressing direction of the pressure roller 22 is provided. As a result, the section modulus is increased, and the mechanical strength of the stay 25 is improved. Furthermore, by arranging the pair of rising portions 25b outside the both ends of the nip portion N, the base portion 25a is supported outside the range where the pressing force of the pressure roller 22 is generated. In particular, in the present embodiment, since the rising portions 25b are provided at both ends of the base portion 25a, the strength at both ends of the base portion 25a is improved.

  Thereby, in this embodiment, even if the base part 25a receives the pressing force from the pressure roller 22, the end part of the base part 25a does not bend unlike the conventional case. Further, since the strength of the base portion 25a between the two rising portions 25b is also improved, the strength of the stay 25 as a whole is improved. As a result, the nip forming member 24 can be firmly supported by the stay 25, and the nip forming member 24 can be prevented from bending.

  Each rising portion 25b only needs to be disposed at a position corresponding to at least both ends of the nip portion N or on the outer side. In other words, the strength of the base portion 25a with respect to the pressing force can be improved by disposing the rising portion 25b at both ends of the range where the pressing force from the pressure roller 22 is received or outside thereof. It is also possible to provide three or more rising portions 25b.

  Furthermore, in this embodiment, in order to further improve the strength of the stay 25, the tip of the rising portion 25b is disposed as close as possible to the inner peripheral surface of the fixing belt 21. However, during rotation, the fixing belt 21 may be shaken (disturbance in behavior) regardless of whether it is large or small. Therefore, if the leading end of the rising portion 25b is too close to the inner peripheral surface of the fixing belt 21, the fixing belt 21 is moved to the leading end of the rising portion 25b. There is a risk of contact. In particular, in the configuration using the thin fixing belt 21 as in the present embodiment, since the swinging width of the fixing belt 21 is large, care must be taken in setting the position of the leading end of the rising portion 25b.

  Specifically, in the case of this embodiment, the distance d in the contact direction of the pressure roller 22 between the tip of the rising portion 25b shown in FIG. 4 and the inner peripheral surface of the fixing belt 21 is at least 2.0 mm, preferably 3 It is preferable to set it to 0.0 mm or more. On the other hand, when the fixing belt 21 has a certain thickness and almost no vibration, the distance d can be set to 0.02 mm. When the reflecting member 26 is attached to the tip of the rising portion 25b as in the present embodiment, it is necessary to set the distance d so that the reflecting member 26 does not contact the fixing belt 21.

  In this way, the rising portion 25b is disposed long in the contact direction of the pressure roller 22 by disposing the leading end of the rising portion 25b as close as possible to the inner peripheral surface of the fixing belt 21. Can do. Accordingly, the mechanical strength of the stay 25 can be improved even in the configuration using the small-diameter fixing belt 21.

  As shown in FIG. 4, the halogen heater 23 is disposed between the two rising portions 25b or inside the inner surface extension line L of the both rising portions 25b. By arranging the halogen heater 23 in this way, the halogen heater 23 and the stay 25 can be accommodated in the fixing belt 21 in a compact manner. Further, in the present embodiment, the halogen heater 23 is disposed so as to correspond to the substantially central position of the nip portion N in the sheet conveyance direction.

  By accommodating a part (or all) of the halogen heater 23 inside the stay 25 as in this embodiment, the light irradiation range from the halogen heater 23 to the fixing belt 21 can be narrowed down to a predetermined range. . Generally, in the circumferential direction of the fixing belt 21, the heating temperature is high at a portion near the halogen heater 23, and conversely, the heating temperature is low at a portion far from the halogen heater 23. Therefore, as in this embodiment, the halogen heater 23 is accommodated inside the stay 25, and the irradiation range of the light to the fixing belt 21 is narrowed down to a range in which the distance variation is relatively small. Therefore, it is possible to improve image quality.

Next, a light shielding film that blocks light from the halogen heater will be described.
In the fixing device shown in FIG. 4, a light shielding film 23 a that partially blocks light from the halogen heater is formed on the surface of the halogen heater 23 compared to the fixing device shown in FIG. 2. Specifically, the light-shielding film 23a is disposed inside the both rising portions 25b or inside the inner surface extension line L1 of both rising portions 25b. Furthermore, the light shielding film 23 a is disposed inside the reflecting plate 26 provided on both rising portions 25 b or on the inner side of the inner surface extension line L <b> 2 of the reflecting plate 26. The reflection plate 26 having a reflection surface is provided between both rising portions 25 b and the halogen heater 23.

  As the material of the light shielding film 23a, molybdenum alloy, aluminum foil, or the like can be used. Silver vapor deposition may also be used. As a method of fixing the light shielding film 23a to the halogen heater 23, various methods such as vapor deposition, adhesion, and application can be adopted, and any method can be adopted as long as the temperature of the stay 25 and the reflecting member 26 can be reduced. Good. If the surface of the light shielding film 23a on the side of the halogen heater 23 is configured to reflect infrared rays, the heat generation efficiency is improved, and it is possible to shorten the warm-up time and save energy.

  In the illustrated example, the light shielding film 23a is formed on the glass tube surface of the halogen heater 23. However, a light shielding film may be formed in the vicinity of the surface by providing a gap with the surface of the halogen heater 23. This is also because the heat radiation from the halogen heater 23 has directivity, and the temperature of the stay 25 and the reflecting member 26 can be reduced.

  In the configuration of FIG. 2 that does not have the light shielding film 23a, when the lighting rate of the halogen heater 23 is high and continuous so that the paper P is continuously passed, the surface temperature of the reflecting member 26 on the halogen heater 23 side is 300. It was over ℃. At this time, the mirror surface treatment on the surface of the reflecting member 26 was discolored, or the surface layer was peeled off when the mirror surface treatment was performed by vapor deposition.

  In particular, when the reflecting member 26 is shaped as shown in FIG. 3B in order to improve the heating efficiency by reflected light, this tendency becomes prominent in the proximity portion 70 a closest to the halogen heater 23.

  On the other hand, in the structure of FIG. 4 in which the light shielding film 23a is formed on the glass tube surface of the halogen heater 23, even when the lighting rate of the halogen heater 23 is high and continuous so that the paper P is continuously passed, The surface temperature of the member 26 on the halogen heater 23 side was less than 250 ° C. Accordingly, it is possible to prevent discoloration of the mirror surface treatment on the surface of the reflecting member 26 and peeling of the surface layer when the mirror surface treatment is performed by vapor deposition. In addition, it is possible to achieve both reduction in size of the fixing device and suppression of excessive temperature rise of the support member and the reflection member due to the proximity of the support member and the reflection member to the heating source, which impairs energy saving and fixability. Therefore, the fixing device and the image forming apparatus can be downsized.

5 and 6 are schematic configuration diagrams showing modifications of the fixing device according to the present invention.
In order to improve the heating efficiency by reflected light, the reflecting member 26b has a shape as shown in FIG. The other configuration is the same as that of the fixing device 20 shown in FIG. 4, and the same effect can be obtained even with the configuration of FIG. In the fixing device 20, a light shielding film 23 a is disposed over the entire range of the halogen heater 23 that faces the support member 25 and the reflection member 26 b. Specifically, the light-shielding film 23a is disposed inside the both rising portions 25b or inside the inner surface extension line L1 of both rising portions 25b. Further, the light shielding film 23a is disposed on the inner side of the reflection plate 26b provided on both rising portions 25b or on the inner side of the inner surface extension line L2 of the reflection plate 26b. However, depending on the layout of the apparatus and the like, the light shielding film 23b may be disposed only in a partial range of the halogen heater 23 close to the reflecting member 26b as in the fixing device 20 shown in FIG.

FIG. 7 is a schematic configuration diagram showing a modification of the fixing device according to the present invention.
As shown in the figure, a reflecting surface 29 may be provided on the surface of the stay 25 facing the halogen heater 23 instead of the reflecting members 26 and 26b. The reflection surface 29 is formed by performing a mirror surface treatment such as polishing or painting on the surface of the stay 25 on the halogen heater 23 side. The light shielding film 23a is disposed on the inner side of both the rising parts 25b or on the inner side of the inner surface extension line L1 of the both rising parts 25b. In particular, since the amount of heat reaching the nip forming member 24 can be reduced by providing the light-shielding film 23a in the portion facing the nip forming member 24, it is possible to prevent thermal deformation of the nip forming member 24. Also in this case, depending on the layout of the fixing device, the light shielding film 23a may be provided over the entire range of the halogen heater 23 facing the stay 25, or only in a partial range of the halogen heater 23 adjacent to the reflecting surface 29. May be provided.

FIG. 8 is a schematic configuration diagram showing a fixing device provided with different stays 25.
As shown in the figure, the stay 25 of the present embodiment includes a base portion 25a that contacts the nip forming member 24 and extends in the paper transport direction, and a pressure roller 22 from an end of the base portion 25a on the downstream side in the paper transport direction. And one hollow rising portion 25b extending in the pressing direction (left side in the figure). In the present embodiment, the light shielding film 23 a is disposed over the entire range of the halogen heater 23 facing the stay 25. Specifically, the light shielding film 23a is disposed between the inner surface extension line L3 of the rising portion 25b on the downstream side in the recording medium conveyance direction and the inner surface extension line L4 of the base portion 25a on the upstream side in the recording medium conveyance direction. Yes. Furthermore, the light shielding film 23 a is disposed inside the reflecting plate 26 provided on the rising portion 25 b or inside the inner surface extension line L <b> 2 of the reflecting plate 26.

  Here, one hollow rising portion may extend from the end portion of the base portion 25a on the upstream side in the sheet conveyance direction toward the pressing direction of the pressure roller 22 (left side in the figure). At this time, the light shielding film is disposed between the inner surface extension line of the rising portion on the upstream side in the recording medium conveyance direction and the inner surface extension line of the base portion on the downstream side in the recording medium conveyance direction. Further, as shown in FIG. 9, depending on the layout of the fixing device, the light shielding film 23 b may be disposed only in a partial range of the halogen heater 23 close to the reflecting member 26.

  Further, as shown in FIG. 10, a reflective surface 29 may be provided on the surface of the stay 25 on the side of the halogen heater 23 instead of the reflective member 26. In particular, by providing the light-shielding film 23 a in a portion facing the nip forming member 24, the nip forming member 24 is not directly heated, so that it is possible to prevent the nip forming member 24 from being thermally deformed. In the present embodiment, the light shielding film 23 a is disposed over the entire range of the halogen heater 23 facing the stay 25. However, as shown in FIG. 11, depending on the layout of the fixing device, the light shielding film 23 b may be provided only in a partial range of the halogen heater 23 close to the stay 25.

Next, the configuration of the halogen heater 23 will be specifically described with reference to FIG.
As shown in FIG. 12A, a light shielding film 23a is uniformly formed in the heater axial direction of the heater on the heater portion 23b of the halogen heater 23. However, when the heat distribution of the heater is not uniform across the entire heat generation range of the heater, the light shielding range in the heater circumferential direction of the light shielding film 23a may be partially changed as shown in FIG. In this example, the light shielding range of the light shielding film 23a is large at the heater end and small at the center. Further, as shown in FIG. 12C, the light shielding film 23a may be provided partially, that is, only at the heater end. In this example, the light shielding range of the light shielding film 23a gradually decreases from the heater end toward the center.

  Of course, the light shielding film 23a may adopt a shape other than the shape shown in the figure, and may be changed in a step shape or an arc shape so that the change in the angle of the light shielding range does not become linear.

  Note that the present invention is not limited to the above-described embodiment, and it is obvious that the configuration of the above-described embodiment can be appropriately changed within the scope of the technical idea of the present invention. For example, a plurality of heating sources may be used, and an IH other than the halogen heater, a resistance heating element, a carbon heater, or the like may be used as the heating source. In addition, a member that blocks heat may be disposed between the heat source and the support member or the reflection member.

20 Fixing device 21 Fixing belt 22 Pressure roller (opposite rotating body)
23 Halogen heater (heating source)
23a Light-shielding film 23b Heater part of halogen heater (heating source) 24 Nip forming member 25 Stay (supporting member)
25a Base part 25b Rising part 26 Reflective member, reflector (reflective surface)
29 Reflecting surface N Nip part P Paper (recording medium)

JP 2004-286922 A Japanese Patent No. 2861280 JP 2007-334205 A Japanese Patent Laid-Open No. 2007-233011

Claims (10)

A nip portion is formed between the rotatable endless fixing belt, a nip forming member disposed inside the fixing belt, and the fixing belt by contacting the nip forming member via the fixing belt. An opposite rotating body, a heating source for heating the fixing belt, and a support member for supporting the nip forming member, and an unfixed image is carried on a nip portion between the fixing belt and the opposite rotating body. In a fixing device that conveys a recording medium and fixes an unfixed image on the recording medium,
The support member has a base portion that comes into contact with the nip forming member, and at least one rising portion that rises in the pressing direction from the base portion,
A fixing device, wherein a light-shielding film that blocks light from the heating source is disposed on the entire surface or a part of the surface of the heating source facing the support member or in the vicinity thereof. The rising portion is formed at each of the upstream and downstream ends of the support member in the recording medium conveyance direction,
The fixing device according to claim 1, wherein the light-shielding film is disposed inside the both rising portions or inside an inner surface extension line of the both rising portions. A reflector having a reflecting surface for reflecting light emitted from the heating source is provided between the rising portion and the heating source;
3. The fixing device according to claim 1, wherein the light shielding film is disposed on the inner side of the reflection plate or on the inner side of the inner surface extension line of the reflection plate. The rising portion is formed on either the upstream side or the downstream side in the recording medium conveyance direction of the support member,
The light shielding film is disposed between an inner surface extension line of the rising portion on the downstream side or upstream side in the recording medium conveyance direction and an inner surface extension line of the base portion on the upstream side or downstream side in the recording medium conveyance direction. The fixing device according to claim 1. A reflector having a reflecting surface for reflecting light emitted from the heating source is provided between the rising portion and the heating source;
The fixing device according to claim 4, wherein the light shielding film is disposed on the inner side of the reflection plate or on the inner side of the inner surface extension line of the reflection plate.   5. The fixing device according to claim 1, wherein a reflection surface that reflects light emitted from the heating source is formed by mirror finishing on a surface of the support member on the heating source side.   The fixing device according to claim 3, wherein a reflectance of the reflecting surface is 90% or more.   The part or all of the reflective surface is formed so that the reflected light from the reflective surface is directed to the fixing belt rather than the heating source. Fixing device.   The fixing device according to claim 1, wherein the light shielding film is formed according to a heat distribution of the heating source.   An image forming apparatus comprising the fixing device according to claim 1.

Images