Fixing device and image forming apparatus

Abstract

To provide a fixing device that can prevent heat from a fixing member from moving to a holding member through a vapor chamber, and thereby achieves good thermal efficiency.SOLUTION: A fixing device of the present invention comprises: an endless fixing member that is rotatably provided; heating means that applies heat to the fixing member; a pressure rotating body that is provided outside the fixing member and applies pressure to the fixing member; and a nip forming member that is provided inside the fixing member and forms a nip part between the fixing member and the pressure rotating body. The nip forming member includes a vapor chamber to which the heat is transferred from an inner peripheral surface of the fixing member, and a holding member that holds the vapor chamber. The holding member has a plurality of convex parts and is in contact with the vapor chamber at the convex parts. Consequently, the heat from the fixing member is prevented from moving to the holding member through the vapor chamber, and thereby thermal efficiency can be improved.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a fixing device and an image forming apparatus. [Background technology]

[0002] In image forming devices such as copiers and printers, a fixing device is used to fix an image onto a recording material. It is known that when fixing a recording material that is narrower than the heating width of the heating element, a temperature rise of the fixing member occurs in an area where the recording material does not pass (so-called edge temperature rise).

[0003] Patent Document 1, for example, is a technology related to suppressing this temperature rise at the end of the fixing member. This document discloses that a nip forming member disposed inside the fixing member has a heat pipe through which heat is transferred from the inner peripheral surface of the fixing member, and a coating layer of a sliding material formed between the heat pipe and the inner peripheral surface of the fixing member. This configuration can effectively suppress temperature rise at the end of the fixing member due to the high thermal uniformity of the heat pipe.

[0004] Furthermore, in order to address the strength issues of hollow heat pipes, a technology is also known that uses a vapor chamber with a reinforcing columnar member inside the hollow as an alternative to the heat pipe. Summary of the Invention [Problem to be solved by the invention]

[0005] Such a vapor chamber is configured to be held within the fixing device by a holding member, but due to the high thermal conductivity of the vapor chamber, heat from the fixing member can be transferred to the holding member via the vapor chamber, which could result in a decrease in thermal efficiency.

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a fixing device with good thermal efficiency, which prevents heat from being transferred from the fixing member to the holding member via the vapor chamber. [Means for solving the problem]

[0007] The above problem is solved by a fixing device comprising a rotatably arranged endless fixing member, a heating means for heating the fixing member, a pressure rotating body arranged outside the fixing member and applying pressure to the fixing member, and a nip forming member arranged inside the fixing member and forming a nip portion between the fixing member and the pressure rotating body, wherein the nip forming member includes a vapor chamber to which heat is transferred from the inner surface of the fixing member, and a holding member for holding the vapor chamber, and the holding member has a plurality of convex portions that are in contact with the vapor chamber. [Effects of the Invention]

[0008] The fixing device of the present invention can suppress the transfer of heat from the fixing member to the holding member via the vapor chamber, thereby improving thermal efficiency. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic diagram illustrating an overall configuration of an image forming apparatus according to an embodiment of the present invention. [Figure 2] 1 is a cross-sectional view of a fixing device according to an embodiment of the present invention; [Figure 3] FIG. 2 is a cross-sectional view of a fixing belt and a guide member. [Figure 4] FIG. 2 is a diagram illustrating the configuration of a fixing belt, a pressure roller, a reinforcing member, and a nip forming member. [Figure 5] FIG. 2 is a partial cross-sectional view showing an example of the configuration of a nip forming member. [Figure 6] FIG. 2 is a partial cross-sectional view showing an example of the configuration of a vapor chamber. [Figure 7] FIG. 2 is a partial cross-sectional view showing the configuration of a nip forming member according to an embodiment of the present invention. [Figure 8] FIG. 2 is a perspective view showing the arrangement of a holding member and a vapor chamber according to one embodiment of the present invention. [Figure 9]1A and 1B are partial cross-sectional views showing the arrangement of the convex portions and the columnar members, in which (a) shows a matched arrangement and (b) shows a mismatched arrangement. [Figure 10] 1A and 1B are plan views showing the shapes of columnar members arranged inside a vapor chamber according to one embodiment of the present invention, where (a) is a rectangular shape and (b) is an oval or elliptical shape. [Figure 11] FIG. 10 is a partial cross-sectional view showing the configuration of a holding member according to a modified example of the present invention. [Figure 12] 1A is a cross-sectional view of a nip forming member in which the height of a plurality of convex portions gradually decreases along the longitudinal direction of the holding member, and FIG. 1B is a perspective view of the holding member. [Figure 13] 1A is a cross-sectional view of a nip forming member in which the height of a plurality of convex portions gradually increases along the longitudinal direction of the holding member, and FIG. 1B is a perspective view of the holding member. [Figure 14] 1A is a cross-sectional view of a nip forming member in which the height of a plurality of convex portions gradually increases along the conveyance direction of the holding member, and FIG. 1B is a perspective view of the holding member. [Figure 15] 15 is a partial cross-sectional view of a nip forming member using the nip forming member of FIG. 14. FIG. [Figure 16a] 10 is a partial cross-sectional view (part 1) of a nip forming member according to a modified example of the present invention. FIG. [Figure 16b] FIG. 16b is a perspective view of the retaining member of FIG. 16a. [Figure 17] 10 is a partial cross-sectional view (part 2) of a nip forming member according to a modified example of the present invention. FIG. [Figure 18] FIG. 10 is a cross-sectional view (part 1) of a fixing device according to a modified example of the present invention. [Figure 19] FIG. 10 is a cross-sectional view (part 2) of a fixing device according to a modified example of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will be described below with reference to the accompanying drawings. In each drawing for explaining the present invention, components such as members and components having the same function or shape are designated by the same reference numerals as far as they can be distinguished, and descriptions thereof will be omitted once they have been described.

[0011] FIG. 1 is a schematic diagram showing the overall configuration of an image forming apparatus according to one embodiment of the present invention.

[0012] 1 includes four imaging units 1Y, 1M, 1C, and 1Bk that are detachable from the image forming apparatus main body. Each imaging unit 1Y, 1M, 1C, and 1Bk has the same configuration except that it contains a developer of a different color: yellow, magenta, cyan, or black, which corresponds to the color separation components of a color image.

[0013] Specifically, each of the imaging units 1Y, 1M, 1C, and 1Bk includes a drum-shaped photoconductor 2 that is an image carrier, a charging device 3 that charges the surface of the photoconductor 2, and a developing device 4 that supplies toner that is a developer to the surface of the photoconductor 2 to form a toner image. Furthermore, a cleaning device 5 that cleans the surface of the photoconductor 2 is also included.

[0014] The image forming apparatus 100 also includes an exposure device 6 that exposes the surface of each photoconductor 2 to light to form an electrostatic latent image, a paper feed device 7 that supplies paper P as a recording material, and a transfer device 8 that transfers the toner image formed on each photoconductor 2 to the paper P. The image forming apparatus 100 further includes a fixing device 20 that fixes the toner image transferred to the paper P, and a paper discharge device 10 that discharges the paper P to the outside of the apparatus.

[0015] The transfer device 8 has an endless intermediate transfer belt 11 as an intermediate transfer body stretched by multiple rollers, and four primary transfer rollers 12 as primary transfer members that transfer the toner images on the photoreceptors 2 onto the intermediate transfer belt 11. It also has a secondary transfer roller 13 as a secondary transfer member that transfers the toner images transferred onto the intermediate transfer belt 11 onto paper P.

[0016] Each of the multiple primary transfer rollers 12 contacts the photosensitive drum 2 via the intermediate transfer belt 11. This brings the intermediate transfer belt 11 and each photosensitive drum 2 into contact with one another, forming a primary transfer nip therebetween. Meanwhile, the secondary transfer roller 13 contacts one of the rollers that stretch the intermediate transfer belt 11 via the intermediate transfer belt 11. This forms a secondary transfer nip between the secondary transfer roller 13 and the intermediate transfer belt 11.

[0017] Also, a paper transport path 14 is formed inside the image forming apparatus 100, along which paper P sent out from the paper feeder 7 is transported. A pair of timing rollers 15 is provided on the paper transport path 14 midway from the paper feeder 7 to the secondary transfer nip (secondary transfer roller 13).

[0018] Next, the printing operation of the image forming apparatus will be described with reference to FIG.

[0019] When a command to start a printing operation is issued, in each of the imaging units 1Y, 1M, 1C, and 1Bk, the photoconductor 2 is rotated clockwise in FIG. 1, and the surface of the photoconductor 2 is charged to a uniform high potential by the charging device 3. Next, the exposure device 6 exposes the surface of each photoconductor 2 based on the image information of the original document read by the original document reader or the print information instructed to be printed from a terminal, thereby reducing the potential of the exposed area and forming an electrostatic latent image. Then, toner is supplied from the developing device 4 to this electrostatic latent image, and a toner image is formed on each photoconductor 2.

[0020] When the toner images formed on each photoconductor 2 reach the primary transfer nip (position of primary transfer roller 12) as each photoconductor 2 rotates, they are transferred so as to overlap one another onto the intermediate transfer belt 11, which rotates counterclockwise in FIG. 1. The toner images transferred onto the intermediate transfer belt 11 are then transported to the secondary transfer nip (position of secondary transfer roller 13) as the intermediate transfer belt 11 rotates, and are transferred onto the transported paper P at the secondary transfer nip. This paper P is supplied from the paper feeder 7.

[0021] The paper P supplied from the paper feeder 7 is stopped temporarily by a timing roller 15, and then transported to the secondary transfer nip in time with the timing at which the toner image on the intermediate transfer belt 11 reaches the secondary transfer nip. In this way, a full-color toner image is carried on the paper P. After the toner image is transferred, the toner remaining on each photoconductor 2 is removed by each cleaning device 5.

[0022] The paper P onto which the toner image has been transferred is transported to the fixing device 20, which fixes the toner image onto the paper P. The paper P is then discharged outside the device by the paper discharge device 10, completing the series of printing operations.

[0023] Next, the configuration and operation of the fixing device 20 installed in the main body of the image forming apparatus 100 will be described with reference to FIGS.

[0024] The fixing device 20 is a device that heats and conveys the paper P (a sheet carrying unfixed toner). The fixing device 20 includes a fixing belt 21 as a fixing member, a nip forming member 26, a reinforcing member 23, a heater 25 as a heating means (heat source), a reflecting plate 27, a pressure roller 31 as a pressure rotating body, and a temperature detection sensor 40 as a temperature detection means.

[0025] (fixing belt) Fixing belt 21 is an endless belt member that contacts pressure roller 31 and rotates in accordance with the rotation of pressure roller 31. Fixing belt 21 is thin and flexible, and rotates (rotates in accordance with the rotation of pressure roller 31) in the direction of the arrow (counterclockwise) in Fig. 2. Fixing belt 21 has a base material layer, an elastic layer, and a release layer laminated in this order from the side of its inner peripheral surface (the surface that comes into contact with nip forming member 26), and its overall thickness is set to approximately 1 mm or less.

[0026] The base layer of the fixing belt 21 has a thickness of 30 to 50 μm and is made of a metal material such as nickel or stainless steel, or a resin material such as polyimide. The elastic layer has a thickness of 100 to 300 μm and is made of a rubber material such as silicone rubber, foamed silicone rubber, or fluororubber. The provision of the elastic layer prevents minute irregularities from forming on the surface of the fixing belt 21 at the nip portion, allowing heat to be transferred evenly to the toner image T on the paper P, preventing the occurrence of an orange peel image.

[0027] The release layer of the fixing belt 21 has a layer thickness of 5 to 50 μm and is made of a material such as PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), PTFE (polytetrafluoroethylene), polyimide, polyetherimide, PES (polyethersulfone), etc. By providing the release layer, it is possible to ensure releasability (separability) for the toner image T.

[0028] On the inside (inner peripheral surface side) of fixing belt 21, there are provided nip forming member 26, heater 25 (heating means), reinforcing member 23, reflector 27, etc. Nip forming member 26 is in pressure contact with pressure roller 31 via fixing belt 21 on the inside (inner peripheral surface side) of fixing belt 21, forming a nip portion (fixing nip) that sandwiches and transports paper P.

[0029] (Guide member) 3, the guide members 34 guide both widthwise ends of the fixing belt 21 from the inner peripheral surface side so as to maintain the substantially cylindrical posture of the fixing belt 21. More specifically, the two guide members 34 are formed of a heat-resistant resin material or the like, and are fitted into the side plates 43 at both widthwise ends of the fixing device 20, respectively.

[0030] The guide member 34 is provided with a guide portion 34a for holding the fixing belt 21 while maintaining the substantially cylindrical posture of the fixing belt 21, a stopper portion for restricting movement of the fixing belt 21 in the width direction (toward the belt), etc. The guide members 34 are arranged at both ends in the width direction within a circumferential range excluding the nip so as not to interfere with the formation of the nip by the nip forming member 26.

[0031] In this embodiment, the only members that come into contact with the inner surface of the fixing belt 21 are the guide members 34 that come into loose contact at both ends in the width direction, and the nip forming member 26; there are no other members (belt guides) that come into contact with the inner surface and guide the rotation of the fixing belt 21.

[0032] (Pressure roller) As shown in Figure 2, the pressure roller 31 as a heating rotor has an elastic layer 31b provided on a core metal 31a (shaft portion), and is driven to rotate in a predetermined direction (clockwise in Figure 2) by a drive motor (driving means) not shown.

[0033] The core metal 31a of the pressure roller 31 is a hollow structure made of a metal material. The elastic layer 31b of the pressure roller 31 is made of a material such as foamed silicone rubber, silicone rubber, or fluororubber. A thin release layer made of PFA, PTFE, or the like may be provided on the surface of the elastic layer 31b.

[0034] The pressure roller 31 is pressed against the fixing belt 21 to form a desired nip between the two members. As shown in Fig. 4, the pressure roller 31 is provided with a gear 45 that meshes with a drive gear of a drive motor, and both widthwise ends of the pressure roller 31 are rotatably supported by side plates 43 of the fixing device 20 via bearings 42. Therefore, the pressure roller 31 is driven to rotate in the direction of the arrow (clockwise) as shown in Fig. 2.

[0035] When elastic layer 31b of pressure roller 31 is formed from a sponge-like material such as foamed silicone rubber, the pressure acting on the nip portion can be reduced, thereby reducing the load on nip forming member 26. Furthermore, by improving the heat insulation of pressure roller 31, heat from fixing belt 21 is less likely to transfer to pressure roller 31, thereby improving the heating efficiency of fixing belt 21.

[0036] (Nip forming member) 2, nip forming member 26 is installed so as to be in sliding contact with the inner circumferential surface of fixing belt 21. Nip forming member 26 presses against pressure roller 31 via fixing belt 21, thereby forming a nip through which paper P is transported.

[0037] 5, nip forming member 26, which comes into sliding contact with the inner circumferential surface of fixing belt 21, has a flat surface facing pressure roller 31 (sliding contact surface 28a of vapor chamber 28, which will be described later). That is, sliding contact surface 28a of nip forming member 26 (the surface facing pressure roller 31) is formed to have a flat shape. This makes the shape of the nip portion approximately parallel to the image surface of paper P, increasing the adhesion between fixing belt 21 and paper P and improving fixation. Furthermore, because the curvature of fixing belt 21 on the exit side of the nip is large, paper P sent out from the nip can be easily separated from fixing belt 21.

[0038] The nip forming member 26 is provided with a vapor chamber 28 on the nip side, which will be described in detail later.

[0039] (reinforcing member) 2, reinforcing member 23 is provided inside fixing belt 21 and abuts against pressure roller 31 via nip forming member 26 and fixing belt 21. Reinforcing member 23 reinforces the strength of nip forming member 26 that forms the nip, and is integrated with nip forming member 26 by screw fastening or the like.

[0040] 4, reinforcing member 23 is formed so that its length in the width direction is longer than nip forming member 26, and both ends of the reinforcing member in the width direction are movably held by side plates 43 of fixing device 20. Reinforcing member 23 abuts against pressure roller 31 via nip forming member 26 and fixing belt 21, thereby preventing nip forming member 26 from being significantly deformed in the nip portion due to the pressure force of pressure roller 31. In order to fulfill this function, reinforcing member 23 is preferably formed from a metal material with high mechanical strength, such as stainless steel or iron.

[0041] (Heating means) The fixing belt 21 is directly heated by radiant heat from a heater 25 (heating means) installed inside the fixing belt 21. The heater 25 as a heating means heats the fixing belt 21 in order to heat the paper P. The heater 25 (heating means) is configured to heat a circumferential region of the fixing belt 21 that is different from the nip portion as a heating region.

[0042] Specifically, heater 25 as heating means is a halogen heater (or a carbon heater), and both ends thereof are fixed to side plates 43 of fixing device 20 (see FIG. 4). Then, by radiant heat from heater 25 (heating means) whose output is controlled by the control unit, a heating area of ​​fixing belt 21 other than the nip, that is, an area facing heater 25, is mainly heated. Furthermore, heat is applied to toner image T on paper P from the surface of heated fixing belt 21.

[0043] The output control of heater 25 is performed based on the detection result of the belt surface temperature by temperature detection sensor 40 (temperature detection means), such as a thermopile or a thermistor, facing the surface of fixing belt 21. Furthermore, by such output control of heater 25, the temperature (fixing temperature) of fixing belt 21 can be set to a desired temperature.

[0044] (reflector) 2, a reflector 27 is fixed between the reinforcing member 23 and the heater 25. As a result, heat (infrared rays that heat the reinforcing member 23) directed from the heater 25 to the reinforcing member 23 is reflected by the reflector 27 and used to heat the fixing belt 21. This further improves the heating efficiency of the fixing belt 21. The reflector 27 can be made of aluminum, stainless steel, or the like. Note that the same effect can be obtained by providing a mirror finish or a heat insulating member to part or all of the surface of the reinforcing member 23 that faces the heater 25.

[0045] In this way, in the fixing device 20 of this embodiment, since the fixing belt 21 is heated over a relatively wide area in the circumferential direction rather than only a portion of it being locally heated, the fixing belt 21 is sufficiently heated even when the device is operated at high speed, and the occurrence of fixing defects can be suppressed. In other words, since the fixing belt 21 can be heated efficiently with a relatively simple configuration, the warm-up time and the first print time can be shortened, and the device can be made more compact.

[0046] In particular, the fixing device 20 in this embodiment is configured so that the fixing belt 21 is directly heated by the heater 25 (heating means), which further improves the heating efficiency of the fixing belt 21 and enables the fixing device 20 to be further reduced in cost and size.

[0047] In this embodiment, two heaters 25 (heating means) are provided on the inner circumferential surface side of the fixing belt 21, but one or three or more heaters may be provided on the inner circumferential surface side of the fixing belt 21. The position of the heaters 25 and the shape of the reinforcing member 23 (described later) are also not limited to those of this embodiment. For example, the heaters 25 may be disposed so as to face the fixing belt 21 on the upstream side in the rotation direction compared to that shown in FIG. 2, and the shape of the reinforcing member 23 may be set accordingly.

[0048] A brief description will now be given of normal operation of the fixing device 20 configured as described above. When the power switch of the image forming apparatus 100 is turned on, power is supplied to the heater 25, and the pressure roller 31 starts to rotate in the direction of the arrow in Fig. 2. As a result, the frictional force between the fixing belt 21 and the pressure roller 31 at the nip portion causes the fixing belt 21 to rotate (co-rotate) in the direction of the arrow in Fig. 2.

[0049] Thereafter, paper P is fed from the paper feeder 7, and an unfixed color image is carried (transferred) onto the paper P at the position of the secondary transfer roller 13. The paper P carrying the toner image T (unfixed image) is transported in the direction of arrow Y10 in FIG. 2 while being guided by a guide plate, and is sent into the nip portion between the fixing belt 21 and pressure roller 31, which are in a pressure-contact state.

[0050] Then, the toner image T is fixed onto the surface of the paper P by the heat of the fixing belt 21 heated by the heater 25 and the pressing force of the nip forming member 26 reinforced by the reinforcing member 23 and the pressure roller 31. Thereafter, the paper P sent out from the nip portion is transported in the direction of the arrow Y11.

[0051] Next, the holding member 30 and the vapor chamber 28 provided in the nip forming member 26 will be described.

[0052] 5 and the like, in fixing device 20 of this embodiment, nip forming member 26 is provided with vapor chamber 28 that is in sliding contact with the inner circumferential surface of fixing belt 21. More specifically, nip forming member 26 includes holding member 30 (nip forming member main body) and vapor chamber 28.

[0053] The holding member 30 holds the vapor chamber 28 on the side (inside the belt) away from the nip (fixing nip), and has a rigidity sufficient to prevent it from bending significantly even when subjected to the pressure force of the pressure roller 31. The holding member 30 holds the vapor chamber 28 and is held by the reinforcing member 23.

[0054] The material for forming the holding member 30 may be a resin material, such as liquid crystal polymer (LCP), polyamideimide (PAI), polyethersulfone (PES), polyphenylene sulfide (PPS), polyethernitrile (PEN), polyetheretherketone (PEEK), etc.

[0055] Vapor chamber 28 is a metal heat dissipation member, and has a hollow portion 28b filled with a working fluid such as water, and has the function of instantly transferring heat by vaporizing and condensing the working fluid. Referring to Figure 6, vapor chamber 28 has wicks 36 (generally gauze-like members with fine internal shapes) provided on almost the entire surfaces of inner wall surfaces 28c and 28d.

[0056] The working fluid inside vapor chamber 28 evaporates due to heat from the heat source, and the vapor dissipates heat by diffusing inside vapor chamber 28. The vapor that dissipated heat condenses again as a liquid and circulates back to the heat source due to capillary action caused by wick 36. In this way, vapor chamber 28 can achieve high thermal conductivity and uniform heat distribution. Note that vapor chamber 28 differs in configuration from a heat pipe, which is also a metal heat dissipation component, in that wick 36 is provided in hollow portion 28b.

[0057] The substantially rectangular frame that constitutes the vapor chamber 28 is made of a material with high thermal conductivity, such as copper, aluminum, silver, graphite, etc. In this embodiment, the sliding surface 28a of the vapor chamber 28 (i.e., the surface that comes into sliding contact with the inner circumferential surface of the fixing belt 21) is formed in a flat shape.

[0058] Furthermore, sliding surface 28a of vapor chamber 28 is formed of a low-friction material. Specifically, thin-film coating layer 29 made of a low-friction material such as fluororesin is formed on sliding surface 28a.

[0059] With this configuration, the friction resistance between the fixing belt 21 and the sliding contact surface 28a of the vapor chamber 28 can be reduced, and therefore wear deterioration of the fixing belt 21 and the sliding contact surface 28a can be reduced.

[0060] In order to achieve the above-mentioned effect, it is sufficient to form only the sliding contact surface 28a from a low-friction material, but other portions may also be formed from a low-friction material.

[0061] Furthermore, as shown in Figure 6, in the vapor chamber 28 of this embodiment, in the hollow portion 28b in which the working fluid is sealed, multiple columnar members 32 are provided between the inner wall surface 28c on the nip side and the inner wall surface 28d on the reinforcing member side opposite the inner wall surface 28c.

[0062] That is, the hollow portion 28b of the vapor chamber 28 is not only a space through which the working fluid flows, but also has a plurality of pillar-shaped members 32 provided within a range that does not interfere with heat exchange due to the flow of the working fluid. The pillar-shaped members 32 of this embodiment are integrally formed from the same material as the frame of the vapor chamber 28.

[0063] By providing such columnar members 32, the mechanical strength of vapor chamber 28 can be increased, making it less likely to deform even when pressure is applied from pressure roller 31. Nip forming member 26 equipped with such vapor chamber 28 can perform good heat exchange, maintain the desired nip shape, and perform a stable fixing process over a long period of time.

[0064] In this embodiment, the columnar member 32 is formed in a square column shape to emphasize the strength of the vapor chamber 28, but the shape of the columnar member 32 is not limited to this. For example, the columnar member 32 may be formed in a cylindrical shape so as not to impair the fluidity of the working fluid in the hollow portion 28b.

[0065] Next, the problem to be solved by the present invention and the characteristic configuration for solving the problem will be described.

[0066] 5, vapor chamber 28 is held by holding member 30, and its sliding surface 28a is in sliding contact with the inner circumferential surface of fixing belt 21. Vapor chamber 28 quickly equalizes the heat from fixing belt 21 in the longitudinal direction, thereby suppressing temperature deviation (temperature rise at the end portions) of fixing belt 21 in the longitudinal direction.

[0067] On the other hand, the contact surfaces of the vapor chamber 28 and the holding member 30 are flat and in contact over the entire surface. This full-surface contact makes it easier for heat from the fixing belt 21 to be absorbed by the holding member 30 via the vapor chamber 28. In particular, immediately after starting up the device, the fixing belt 21 reaches a high temperature while the temperature of the holding member 30 remains low, resulting in a large temperature difference and making it easier for heat to transfer. If this causes the temperature of the fixing belt 21 to drop, further heating is required, reducing the thermal efficiency of the fixing device. Because the vapor chamber 28 has particularly good thermal conductivity and allows heat to transfer quickly, some kind of countermeasure is desirable.

[0068] 7 is a partial cross-sectional view showing the configuration of a nip forming member according to one embodiment of the present invention. The holding member 30 has multiple convex portions 30a, and these convex portions 30a contact the vapor chamber 28. In other words, the holding member 30 has an uneven shape, and the tips of the multiple convex portions 30a contact the vapor chamber 28, so the contact area between the holding member 30 and the vapor chamber 28 can be made smaller than in the configuration of FIG. 5.

[0069] As a result, it is possible to reduce the rate at which heat transfers from the vapor chamber 28 to the holding member 30, and to minimize the temperature drop in the fixing belt 21. Therefore, in addition to the heat uniformity effect provided by the vapor chamber 28, it is possible to realize a fixing device with good thermal efficiency.

[0070] Fig. 8 is a perspective view showing the arrangement of a holding member and a vapor chamber according to one embodiment of the present invention. In Fig. 8, a plurality of convex portions 30a are provided on the flat surface of the holding member 30 facing the vapor chamber 28. Meanwhile, a plurality of columnar members 32 are provided in the hollow portion 28b of the vapor chamber 28.

[0071] The pillar-shaped members 32 of the vapor chamber 28 serve to maintain the strength of the vapor chamber 28 and prevent it from being crushed and deformed by the pressure of the nip portion. Here, in this embodiment, the multiple convex portions 30a of the holding member 30 and the multiple pillar-shaped members 32 of the vapor chamber 28 are arranged so as to substantially coincide with each other in the longitudinal direction and the conveyance direction of the fixing belt 21.

[0072] That is, the plurality of convex portions 30a are arranged so as to overlap the plurality of columnar members 32 when viewed from the pressure direction of the pressure roller 31.

[0073] 9(a), the pressure force W of the nip portion is received by the plurality of columnar members 32, and the force P1 acting on the plurality of columnar members 32 is received by the plurality of convex portions 30a, respectively. Here, the force P1 acting on the plurality of columnar members 32 and the reaction force P2 from the plurality of columnar members 32 are each on approximately the same line, so that the vapor chamber 28 can be prevented from being crushed and deformed.

[0074] 9(b), if the arrangement of the columnar members 32 does not match the arrangement of the convex portions 30a, the vapor chamber 28 is subjected to bending stress due to the reaction force P2 from the convex portions 30a. Therefore, depending on the pressure of the pressure roller 31, there is a risk of crushing deformation.

[0075] 10A and 10B are plan views showing the shapes of columnar members disposed inside a vapor chamber according to one embodiment of the present invention. The columnar member 32 shown in FIG. 10A has a rectangular shape, while the columnar member 32' shown in FIG. 10B has an oval or elliptical shape. Both have a shape that is elongated in the longitudinal direction of the vapor chamber 28.

[0076] The vapor chamber 28 thermally expands when heated during fixing, and the amount of expansion in the longitudinal direction (axial direction) is greater than the amount of expansion in the transport direction. At this time, the holding member 30 also thermally expands, but the amounts of expansion of the vapor chamber 28 and the holding member 30 differ due to differences in material and / or temperature. As a result, misalignment easily occurs between the columnar member 32 and the convex portion 30a. This is particularly noticeable in the longitudinal direction, where the amount of thermal expansion is greater.

[0077] In contrast, by making the cross-sectional shape of the columnar member 32 rectangular, oval, or elliptical, even if there is some misalignment between the columnar member 32 and the convex portion 30a, it is possible to leave a portion where their positions match.

[0078] Similarly, the convex portion 30a of the holding member 30 is preferably formed to have a cross-sectional shape that is long in the longitudinal direction (rectangular, oval, or elliptical).

[0079] 11 is a partial cross-sectional view showing the configuration of a holding member according to one variation of the present invention. Each of the multiple convex portions 30a of the holding member 30 has a heat insulating member 33 with lower thermal conductivity than the holding member 30 provided at the portion that comes into contact with the vapor chamber 28. The heat insulating member 33 can be a sheet-like material made of woven heat-resistant fibers, a glass wool-like material, a resin foam, or a hollow member. Materials that contain an air layer inside tend to provide good heat insulation.

[0080] This configuration can further reduce the rate at which heat transfers from the vapor chamber 28 to the holding member 30, minimizing the temperature drop in the fixing belt 21. Therefore, in addition to the uniform heat effect provided by the vapor chamber 28, a fixing device with good thermal efficiency can be realized.

[0081] FIG. 12(a) is a cross-sectional view of a nip forming member in which the height of a plurality of convex portions gradually decreases along the longitudinal direction of the holding member, and (b) is a perspective view of the holding member.

[0082] In this embodiment, the height of the convex portions 30a of the holding member 30 is gradually decreased from the center toward both longitudinal ends. Specifically, the height of the convex portion 30a1 in the center is the highest, and decreases toward both ends, with the height of the convex portions 30an at both ends being the lowest.

[0083] During fixing, vapor chamber 28 receives nip pressure from pressure roller 31 across its entire width, causing it to deform into a shape that matches the height of convex portions 30a1-30an. As a result, vapor chamber 28 has a central convex shape, and the longitudinal nip pressure is distributed higher in the center than in a flat shape, which is expected to improve fixability near the center. In addition, because the nip pressure at both ends is equalized, the stability of paper transport can be improved.

[0084] FIG. 13(a) is a cross-sectional view of a nip forming member in which the height of a plurality of convex portions gradually increases along the longitudinal direction of the holding member, and (b) is a perspective view of the holding member.

[0085] In this embodiment, the height of the convex portions 30a of the holding member 30 gradually increases from the center toward both longitudinal ends. Specifically, the height of the convex portion 30a1 in the center is the lowest, and increases toward both ends, with the height of the convex portions 30an at both ends being the highest.

[0086] During fixing, vapor chamber 28 receives nip pressure from pressure roller 31 across its entire width, causing it to deform into a shape that matches the height of convex portions 30a1-30an. As a result, vapor chamber 28 becomes concave in the center, and the longitudinal nip pressure is distributed higher at both ends than in a flat shape, which is expected to improve fixability near the ends. In addition, because the conveying force at the ends is increased, the force that spreads the paper to both ends also increases, improving the effectiveness of preventing paper wrinkles.

[0087] FIG. 14(a) is a cross-sectional view of a nip forming member in which the height of a plurality of convex portions gradually increases along the conveyance direction of the holding member, and (b) is a perspective view of the holding member.

[0088] In this embodiment, the height of the convex portions 30a of the holding member 30 gradually increases from the center toward both ends in the short side direction. Specifically, the height of the convex portion 30a1 in the center is the lowest, and increases toward both ends, with the height of the convex portions 30a2 at both ends being the highest.

[0089] Vapor chamber 28 receives nip pressure from pressure roller 31 across its entire width during fixing, and is deformed into a shape that matches the height of convex portions 30a1-30a3. As a result, vapor chamber 28 becomes concave at the center, and assumes a shape similar to the outer shape of pressure roller 31 (see FIG. 15). This configuration increases the cross-sectional area of ​​vapor chamber 28 in the short side direction, promoting heat diffusion at the nip end.

[0090] Furthermore, compared to a rectangular parallelepiped vapor chamber 28, the vapor chamber 28 can be more easily stably held by the holding member 30. Furthermore, the pressure distribution within the nip becomes uniform, which improves the stability of paper transport.

[0091] The above effect can be obtained even if the contact surface between the holding member 30 and the vapor chamber 28 is convex (i.e., the convex portion 30a is not used), but the amount of heat transferred from the vapor chamber 28 to the holding member 30 increases, resulting in a decrease in thermal efficiency.

[0092] FIG. 16a is a partial cross-sectional view (part 1) of a nip forming member according to a modified example of the present invention, and FIG. 16b is a perspective view of a holding member.

[0093] 16a, the holding member 30′ has a shape (holding portions 30b) that holds both sides of the vapor chamber 28 on the upstream and downstream sides in the transport direction. This allows the vapor chamber 28 to be held and fixed against the sliding torque of the fixing belt 21.

[0094] 16b, the holding member 30' may have a shape (holding portion 30b') at both longitudinal ends that sandwich (surround) and hold both sides of the vapor chamber 28. In this case, the holding member 30' can surround and hold the vapor chamber 28 on all four sides, simplifying the means for holding them together (such as by screws).

[0095] In particular, since the vapor chamber 28 can be made to have a simple configuration such as a flat plate shape, it is possible to improve thermal conductivity and productivity of parts, and reduce manufacturing costs.

[0096] 17 is a partial cross-sectional view (part 2) of a nip forming member according to a modified example of the present invention. As shown in FIG. 17, holding member 30″ has outlet convex shape 30c that is convex toward pressure roller 31 at the nip outlet downstream of the fixing member in the conveyance direction.

[0097] Since the fixing belt 21 at the nip exit faces the pressure roller 31 in accordance with the exit convex shape 30c, the paper P discharged from the nip portion is also discharged toward the pressure roller 31. This prevents the paper P from wrapping around the fixing belt 21 after fixing, and ensures stable separation performance.

[0098] (Variation 1) 18 is a cross-sectional view (part 1) of a fixing device according to a modified example of the present invention. As shown in FIG. 18, fixing device 20′ is configured to heat fixing belt 21 with heating element (resistance heating element) 38, which is a heating means.

[0099] One surface of the heat generating element 38 is in sliding contact with the inner circumferential surface of the fixing belt 21, and the opposite surface is in contact with the vapor chamber 28. The nip forming member 26′ is configured to include the heat generating element 38, the vapor chamber 28, and a holding member 30 that holds the heat generating element 38 and the vapor chamber 28.

[0100] The surface of the heating element 38 that comes into contact with the fixing belt 21 is made of a low-friction material to reduce sliding resistance. The holding member 30 has multiple convex portions 30a that come into contact with the vapor chamber 28.

[0101] In the fixing device 20' configured in this manner, the vapor chamber 28 makes the temperature distribution of the heating element 38 uniform in the width direction, and the fixing temperature of the fixing belt 21 heated by the heating element 38 is also sufficiently uniform across the width direction. In addition, the rate at which heat transfers from the vapor chamber 28 to the holding member 30 can be reduced.

[0102] As a result, the heat of the heating element 38 can be transferred to the fixing belt 21 without waste, and together with the heat uniformity effect of the vapor chamber 28, a fixing device with good thermal efficiency can be realized.

[0103] (Variation 2) 19 is a cross-sectional view (part 2) of a fixing device according to a modified example of the present invention. As shown in FIG. 19, fixing device 20'' is configured to heat fixing belt 21' with electromagnetic induction heating coil 50, which is a heating means. However, nip forming member 26 (vapor chamber 28 and holding member 30), reinforcing member 23, etc. are the same as those of fixing device 20 in FIG. 7.

[0104] In addition to the base layer, elastic layer, and release layer described above with reference to FIG. 2 and other figures, fixing belt 21′ also has a heat-generating layer that is electromagnetically heated by electromagnetic induction heating coil 50. This heat-generating layer can be formed, for example, between the elastic layer and the release layer, or the base layer can be used as the heat-generating layer. Materials that can be used for the heat-generating layer include nickel, stainless steel, iron, copper, cobalt, chromium, aluminum, gold, platinum, silver, tin, palladium, and alloys of two or more of these metals.

[0105] On the other hand, the electromagnetic induction heating coil 50 is composed of an excitation coil, a core, a coil guide, etc. The excitation coil is a Litz wire, which is a bundle of thin wires, extended in the width direction so as to cover a portion of the fixing belt 21'. The core is a semi-cylindrical member made of a ferromagnetic material such as ferrite (relative permeability is approximately 1000 to 3000), and is provided with a center core and side cores to form an efficient magnetic flux toward the heat-generating layer of the fixing belt 21'. The core is disposed so as to face the excitation coil extended in the width direction. The coil guide is made of a highly heat-resistant resin material or the like, and holds the excitation coil and core.

[0106] The fixing device 20 configured as described above operates as follows. When the fixing belt 21' rotates in the direction of the arrow in FIG. 19 (counterclockwise), the fixing belt 21' is heated at a position facing the electromagnetic induction heating coil 50. More specifically, by passing a high-frequency alternating current through the electromagnetic induction heating coil 50, magnetic field lines are formed around the fixing belt 21' so that they alternate in both directions. At this time, eddy currents are generated on the surface of the heat-generating layer of the fixing belt 21', and Joule heat is generated due to the electrical resistance of the heat-generating layer itself. This Joule heat electromagnetically heats the heat-generating layer, thereby heating the fixing belt 21'.

[0107] In the example of FIG. 19, the electromagnetic induction heating coil 50 is disposed so as to face the outer peripheral surface of the fixing belt 21', but the electromagnetic induction heating coil 50 may also be disposed so as to face the inner peripheral surface of the fixing belt 21'.

[0108] In the electromagnetic induction type fixing device 20'' configured in this manner, the fixing temperature of the fixing belt 21' is made sufficiently uniform across the width direction by the vapor chamber 28. Moreover, since the holding member 30 is in contact with the vapor chamber 28 at the convex portion 30a, the rate at which heat transfer from the vapor chamber 28 to the holding member 30 can be reduced.

[0109] The present invention has been described in detail above using the embodiments. This embodiment is merely an example, and various modifications can be made without departing from the spirit and scope of the present invention. For example, in the above embodiment, the present invention is applied to fixing devices 20, 20', and 20'' that use a pressure roller 31 as a pressure rotating body, but the present invention can also be applied to fixing devices that use a pressure belt as a pressure rotating body. Even with such a configuration, the same effects as those of the above embodiments can be obtained.

[0110] Furthermore, it is clear that the present invention is not limited to the present embodiment, and that the present embodiment may be appropriately modified within the scope of the technical concept of the present invention in addition to the modifications suggested in the present embodiment. Furthermore, the number, position, shape, etc. of the components are not limited to the present embodiment, and may be any number, position, shape, etc. suitable for implementing the present invention.

[0111] Furthermore, in this specification and the drawings, the "width direction" is defined as a direction perpendicular to the sheet conveyance direction and the same direction as the rotation axis direction of the fixing belt and pressure roller.

[0112] For example, aspects of the present invention are as follows. (Aspect 1) a rotatable endless fixing member; a heating means for heating the fixing member; a pressure rotating body provided outside the fixing member and pressing the fixing member; a nip forming member provided inside the fixing member and forming a nip portion between the fixing member and the pressure rotating body, The nip forming member includes a vapor chamber (28) to which heat is transferred from the inner circumferential surface of the fixing member, and a holding member that holds the vapor chamber. The fixing device is characterized in that the holding member has a plurality of convex portions, and the convex portions are in contact with the vapor chamber. (Aspect 2) The vapor chamber has a plurality of columnar members in a hollow portion, 2. The fixing device according to claim 1, wherein the plurality of convex portions overlap with the plurality of columnar members, respectively, when viewed from the pressure direction of the pressure rotating body. (Aspect 3) The fixing device according to aspect 2, wherein the cross-sectional shapes of the convex portions and the columnar members are rectangular or elliptical with their long sides in the axial direction of the fixing member. (Aspect 4) A fixing device described in any one of aspects 1 to 3, characterized in that the convex portion of the holding member has an insulating material with lower thermal conductivity than the holding member provided in the portion that comes into contact with the vapor chamber. (Aspect 5) 5. The fixing device according to any one of aspects 1 to 4, wherein the height of the plurality of convex portions gradually increases or decreases from the center of the holding member toward both longitudinal ends thereof. (Aspect 6) 5. The fixing device according to any one of aspects 1 to 4, wherein the height of the plurality of convex portions gradually increases from the center of the holding member toward both ends in the lateral direction. (Aspect 7) 7. The fixing device according to any one of aspects 1 to 6, wherein the holding members hold the vapor chamber by sandwiching both sides of the vapor chamber on the upstream and downstream sides in the transport direction. (Aspect 8) Aspects 8. The fixing device according to any one of aspects 1 to 7, wherein the holding member has an outlet convex shape at an outlet of the nip portion downstream in the conveyance direction of the fixing member. (Aspect 9) The fixing device according to any one of aspects 1 to 8, wherein the vapor chamber has a sliding contact surface with the fixing member formed of a low-friction material. (Aspect 10) 10. The fixing device according to any one of aspects 1 to 9, wherein the heating unit is a heater disposed opposite to the inner circumferential surface of the fixing member. (Aspect 11) 10. The fixing device according to any one of aspects 1 to 9, wherein the heating unit is an electromagnetic induction coil disposed opposite the outer circumferential surface or the inner circumferential surface of the fixing member. (Aspect 12) a rotatable endless fixing member; a heating means for heating the fixing member; a pressure rotating body provided outside the fixing member and pressing the fixing member; a nip forming member provided inside the fixing member and forming a nip portion between the fixing member and the pressure rotating body, the heating means is a heat generating element having one surface in sliding contact with the inner circumferential surface of the fixing member, the nip forming member includes the heating element, a vapor chamber in contact with the opposite side of the one surface, and a holding member that holds the heating element and the vapor chamber; The fixing device is characterized in that the holding member has a plurality of convex portions, and the convex portions are in contact with the vapor chamber. (Aspect 13) An image forming apparatus including the fixing device according to any one of aspects 1 to 12. [Explanation of symbols]

[0113] 1Bk, 1C, 1M, 1Y imaging unit 2 Photoreceptor 3. Charging device 4. Developing device 5 Cleaning Device 6 Exposure equipment 7 Paper feeder 8 Transfer device 10 Paper ejection device 11 Intermediate transfer belt 12 Primary transfer roller 13 Secondary transfer roller 14 Paper transport path 15 Timing roller 20, 20', 20'' fixing device 21, 21' Fuser belt 23 Reinforcement member 25 Heater 26, 26' Nip forming member 27 Reflector 28 Vapor Chamber 28a Sliding surface 28b Hollow part 28c, 28d inner wall 29 Coating Layer 30 Retaining member 30a, 30a1, 30a2, 30an convex part 30', 30'' retaining member 30b, 30b' holding part 30c Exit convex shape 31 Pressure roller 31a Core metal 31b Elastic layer 32, 32' columnar members 33 Heat insulating materials 34 Guide member 34a Guide part 36 Wick 38 Heating element 40 Temperature detection sensor 42 Bearings 43 Side panel 45 gears 50 Electromagnetic induction heating coil 100 Image forming device P Paper [Prior art documents] [Patent documents]

[0114] [Patent Document 1] Japanese Patent Publication No. 2020-086350

Claims

1. a rotatable endless fixing member; a heating means for heating the fixing member; a pressure rotating body provided outside the fixing member and pressing the fixing member; a nip forming member provided inside the fixing member and forming a nip portion between the fixing member and the pressure rotating body, the nip forming member includes a vapor chamber to which heat is transferred from the inner circumferential surface of the fixing member, and a holding member that holds the vapor chamber; The fixing device is characterized in that the holding member has a plurality of convex portions, and the convex portions are in contact with the vapor chamber.

2. The vapor chamber has a plurality of columnar members in a hollow portion, 2. The fixing device according to claim 1, wherein the plurality of convex portions overlap with the plurality of columnar members, respectively, when viewed from the pressure direction of the pressure rotating body.

3. The fixing device according to claim 2 , wherein the cross-sectional shape of the convex portion and the columnar member is a rectangle or an ellipse that is long in the axial direction of the fixing member.

4. The fixing device according to claim 1 , wherein the convex portion of the holding member is provided with a heat insulating member having lower thermal conductivity than the holding member at a portion where the convex portion comes into contact with the vapor chamber.

5. 2. The fixing device according to claim 1, wherein the height of the plurality of convex portions gradually increases or decreases from the center of the holding member toward both ends in the longitudinal direction.

6. 2. The fixing device according to claim 1, wherein the height of the plurality of convex portions gradually increases from the center of the holding member toward both ends in the lateral direction.

7. The fixing device according to claim 1 , wherein the holding members sandwich and hold both sides of the vapor chamber on the upstream and downstream sides in the transport direction.

8. 2. The fixing device according to claim 1, wherein the holding member has an outlet convex shape at an outlet of the nip portion downstream in the conveying direction of the fixing member.

9. 2. The fixing device according to claim 1, wherein the vapor chamber has a sliding contact surface with the fixing member formed of a low-friction material.

10. 2. The fixing device according to claim 1, wherein the heating means is a heater disposed opposite to the inner circumferential surface of the fixing member.

11. 2. The fixing device according to claim 1, wherein the heating means is an electromagnetic induction heating coil disposed opposite to the outer circumferential surface or the inner circumferential surface of the fixing member.

12. a rotatable endless fixing member; a heating means for heating the fixing member; a pressure rotating body provided outside the fixing member and pressing the fixing member; a nip forming member provided inside the fixing member and forming a nip portion between the fixing member and the pressure rotating body, the heating means is a heat generating element having one surface in sliding contact with the inner circumferential surface of the fixing member, the nip forming member includes the heating element, a vapor chamber in contact with the opposite side of the one surface, and a holding member that holds the heating element and the vapor chamber; The fixing device is characterized in that the holding member has a plurality of convex portions, and the convex portions are in contact with the vapor chamber.

13. An image forming apparatus comprising the fixing device according to claim 1 .

Images