Fixing device and image forming apparatus

Abstract

To sufficiently maintain the retentivity of lubricant in a lubricant retaining member even after the lapse of time.SOLUTION: An endless fixing belt 21 is provided, which is heated by a heater 25 (heating means) and rotates in a predetermined rotation direction. A nip forming member 26 is arranged on an inner peripheral surface side of the fixing belt 21, and is in pressure contact with a pressure roller 31 (pressure rotating body) with the fixing belt 21 therebetween to form a nip part N through which a sheet P is conveyed. A soaking member 22 (lubricant retaining member) capable retaining lubricant is interposed between the nip forming member 26 and the fixing belt 21. The soaking member 22 has a non-recessed part W formed in the entire area on the downstream side in the rotation direction on a slide contact surface 22a in slide contact with the inner peripheral surface of the fixing belt 21, and has a plurality of recessed parts 22a1 in at least portions excluding the non-recessed part W.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a fixing device that heats and fixes a toner image carried on the surface of a sheet, and an image forming apparatus equipped with the fixing device, such as a copier, printer, facsimile, or a combination machine thereof. [Background technology]

[0002] Conventionally, in fixing devices installed in image forming devices such as copiers and printers, a device in which a lubricant retaining member such as a heat equalizing member is installed between a fixing belt and a nip forming member has been known (see, for example, Patent Document 1).

[0003] On the other hand, Patent Document 1 discloses a technique for forming a plurality of recesses over the entire sliding surface of a heat spreader, with the aim of improving the retention of lubricant in the heat spreader. Summary of the Invention [Problem to be solved by the invention]

[0004] In the fixing device of Patent Document 1, a plurality of recesses are formed on the sliding surface of the heat equalizing member (lubricant holding member), and therefore, the effect of improving the retention of the lubricant can be expected. However, the lubricant retention capacity was still insufficient, as lubricant leaked from the downstream side of the lubricant retention member over time, which could lead to problems such as an increase in the drive torque of the fixing device over time.

[0005] The present invention has been made to solve the above-mentioned problems, and aims to provide a fixing device and an image forming apparatus in which the lubricant retention ability of the lubricant retention member is sufficiently maintained even over time. [Means for solving the problem]

[0006] The fixing device of this invention comprises an endless fixing belt that is heated by a heating means and rotates in a predetermined rotational direction, a nip forming member that is arranged on the inner surface of the fixing belt and presses against a pressure rotor via the fixing belt to form a nip portion through which a sheet is transported, and a lubricant holding member that is interposed between the nip forming member and the fixing belt and is capable of holding a lubricant, and the lubricant holding member has a sliding surface that slides against the inner surface of the fixing belt, and non-recesses are formed over the entire area downstream in the rotational direction, and a plurality of recesses are formed in at least the portion excluding the non-recesses. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a fixing device and an image forming apparatus in which the lubricant retention ability of the lubricant retention member is sufficiently maintained even over time. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is an overall configuration diagram showing an image forming apparatus according to an embodiment of the present invention; [Figure 2] FIG. 2 is a diagram illustrating a configuration of a fixing device. [Figure 3] FIG. 2 is a side view of the fixing device as viewed in the width direction. [Figure 4] FIG. 4 is an enlarged view showing the vicinity of a nip portion. [Figure 5] FIG. 2 is a schematic diagram showing a fixing belt and a guide member in a width direction. [Figure 6] FIG. 2 is a perspective view showing a lubricant holding member. [Figure 7] 1A and 1B are a side view and a front view, respectively, showing a lubricant holding member; [Figure 8] FIG. 10 is a perspective view showing a lubricant holding member as a first modified example. [Figure 9] FIG. 10 is a perspective view showing a lubricant holding member as a second modified example. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In each drawing, the same or corresponding parts are designated by the same reference numerals, and redundant explanations will be appropriately simplified or omitted.

[0010] First, the overall configuration and operation of an image forming apparatus 1 will be described with reference to FIG. 1, the image forming apparatus 1 in this embodiment is a tandem color printer. Four toner bottles 102Y, 102M, 102C, and 102K corresponding to the respective colors (yellow, magenta, cyan, and black) are detachably (replaceably) installed in a bottle storage section 101 located at the top of the image forming apparatus main body 1. An intermediate transfer unit 85 is disposed below the bottle storage section 101. Opposite to the intermediate transfer belt 78 of the intermediate transfer unit 85, image forming sections 4Y, 4M, 4C, and 4K corresponding to each color (yellow, magenta, cyan, and black) are arranged side by side.

[0011] Each of the image forming units 4Y, 4M, 4C, and 4K is provided with a photosensitive drum 5Y, 5M, 5C, and 5K, respectively. Also, a charging unit 75, a developing unit 76, a cleaning unit 77, a charge removing unit, etc. are provided around each of the photosensitive drums 5Y, 5M, 5C, and 5K. Then, an image forming process (charging process, exposure process, developing process, transfer process, cleaning process) is performed on the surface of each of the photosensitive drums 5Y, 5M, 5C, and 5K, and an image of each color is formed on the surface of each of the photosensitive drums 5Y, 5M, 5C, and 5K.

[0012] The photosensitive drums 5Y, 5M, 5C, and 5K are rotated by a motor in the clockwise direction in Fig. 1. Then, at the position of the charging unit 75, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K are uniformly charged (charging process). Thereafter, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K reach the irradiation position of the laser light L emitted from the exposure unit 3, and an electrostatic latent image corresponding to each color is formed by exposure scanning at this position (this is the exposure process).

[0013] Thereafter, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K reach positions facing the developing unit 76, where the electrostatic latent images are developed to form toner images of the respective colors (developing step). Thereafter, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K reach positions facing the intermediate transfer belt 78 and first transfer bias rollers 79Y, 79M, 79C, and 79K, and at these positions the toner images on the photosensitive drums 5Y, 5M, 5C, and 5K are transferred onto the intermediate transfer belt 78 (this is the primary transfer step). At this time, a small amount of untransferred toner remains on the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K.

[0014] Thereafter, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K reach a position facing the cleaning unit 77, at which point the untransferred toner remaining on the photosensitive drums 5Y, 5M, 5C, and 5K is mechanically collected by the cleaning blade of the cleaning unit 77 (cleaning process). Finally, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K reach positions facing the charge removal units, where the residual potential on the photosensitive drums 5Y, 5M, 5C, and 5K is removed. Thus, a series of image forming processes performed on the photosensitive drums 5Y, 5M, 5C, and 5K is completed.

[0015] Thereafter, the toner images of each color formed on each photosensitive drum through the development process are transferred in a superimposed manner onto the surface of the intermediate transfer belt 78. In this way, a color image is formed on the intermediate transfer belt 78. Here, the intermediate transfer unit 85 is composed of the intermediate transfer belt 78, four primary transfer bias rollers 79Y, 79M, 79C, and 79K, a secondary transfer backup roller 82, a cleaning backup roller 83, a tension roller 84, and an intermediate transfer cleaning section 80. The intermediate transfer belt 78 is stretched and supported by three rollers 82 to 84, and is moved endlessly in the direction of the arrow in FIG. 1 by the rotational drive of one roller 82.

[0016] The four primary transfer bias rollers 79Y, 79M, 79C, and 79K sandwich the intermediate transfer belt 78 between themselves and the photosensitive drums 5Y, 5M, 5C, and 5K, respectively, to form primary transfer nips. A transfer bias opposite in polarity to the toner is applied to the primary transfer bias rollers 79Y, 79M, 79C, and 79K. The intermediate transfer belt 78 then travels in the direction of the arrow and passes through the primary transfer nips of the primary transfer bias rollers 79Y, 79M, 79C, and 79K in sequence. In this way, the toner images of each color on the photosensitive drums 5Y, 5M, 5C, and 5K are primarily transferred onto the intermediate transfer belt 78 in a superimposed manner.

[0017] Thereafter, the intermediate transfer belt 78, onto which the toner images of each color have been transferred and superimposed, reaches a position facing the secondary transfer roller 89. At this position, the secondary transfer backup roller 82 sandwiches the intermediate transfer belt 78 between itself and the secondary transfer roller 89, forming a secondary transfer nip. The four-color toner images formed on the intermediate transfer belt 78 are then transferred onto the sheet P that has been transported to the position of this secondary transfer nip. At this time, untransferred toner that has not been transferred to the sheet P remains on the intermediate transfer belt 78. Thereafter, the intermediate transfer belt 78 reaches the position of the intermediate transfer cleaning unit 80. At this position, untransferred toner on the intermediate transfer belt 78 is collected. Thus, the series of transfer processes performed on the intermediate transfer belt 78 is completed.

[0018] Here, the sheet P transported to the position of the secondary transfer nip is transported from the paper feed section 12 arranged below the device main body 1 via a paper feed roller 97, a pair of registration rollers 98 (a pair of timing rollers), etc. More specifically, a plurality of sheets P such as paper are stacked and stored in the paper feed unit 12. When the paper feed roller 97 is rotated counterclockwise in FIG. 1, the topmost sheet P is fed toward between the pair of registration rollers 98.

[0019] The sheet P conveyed to the registration roller pair 98 stops temporarily at the roller nip position of the registration roller pair 98, which has stopped rotating. Then, the registration roller pair 98 is rotated in synchronization with the color image on the intermediate transfer belt 78, and the sheet P is conveyed toward the secondary transfer nip. In this way, the desired color image is transferred onto the sheet P.

[0020] Thereafter, the sheet P onto which the color image has been transferred at the secondary transfer nip position is conveyed to the position of the fixing device 20. Then, at this position, the color image transferred onto the surface is fixed onto the sheet P by the heat and pressure of the fixing belt 21 and the pressure roller 31 (fixing process). Thereafter, the sheet P is discharged to the outside of the apparatus through the rollers of the discharge roller pair 99. The sheets P discharged to the outside of the apparatus by the discharge roller pair 99 are sequentially stacked on a stack unit 100 as output images. In this way, a series of image forming processes in the image forming apparatus is completed.

[0021] Next, the configuration and operation of the fixing device 20 installed in the image forming apparatus main body 1 will be described in detail with reference to FIGS. 2 to 4, the fixing device 20 is composed of a fixing belt 21 as a belt member, a nip forming member 26, a reinforcing member 23, a heater 25 (heat source) as a heating means, a reflecting plate 27, a pressure roller 31 as a pressure rotating body, a temperature detection sensor 40 as a temperature detection means, a heat equalizing member 22 as a lubricant holding member (lubricant supply member), and the like.

[0022] Here, fixing belt 21 is an endless belt member that contacts pressure roller 31 externally and rotates in accordance with the rotation of pressure roller 31. Fixing belt 21 is a thin, flexible endless belt that rotates (is rotated 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 inner circumferential surface (the surface that comes into contact with heat equalizing member 22 (nip forming member 26)), and the overall thickness is set to 1 mm or less. The base material 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 of the fixing belt 21 has a thickness of 100 to 300 μm and is made of a rubber material such as silicone rubber, foamed silicone rubber, fluororubber, etc. By providing the elastic layer, minute irregularities are prevented from being formed on the surface of the fixing belt 21 at the nip portion, and heat is transferred uniformly to the toner image T on the sheet P, preventing the occurrence of an orange peel image. 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. Providing the release layer ensures releasability (separability) for the toner T (toner image).

[0023] On the inside (inner peripheral surface side) of the fixing belt 21, a heat equalizing member 22 (lubricant holding member), a nip forming member 26, a heater 25 (heating means), a reinforcing member 23, a reflector 27, etc. are provided. Here, 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 nip portion N (fixing nip) through which sheet P is transported. Specifically, nip forming member 26 is installed so as to be in sliding contact with the inner peripheral surface of fixing belt 21 via heat equalizing member 22, which serves as a lubricant holding member. Then, nip forming member 26 is in pressure contact with pressure roller 31 via fixing belt 21, thereby forming nip portion N through which sheet P is transported.

[0024] The fixing belt 21 is directly heated by radiant heat from a heater 25 (heating means) installed inside the fixing belt 21. That is, the heater 25 as a heating means heats the fixing belt 21 in order to heat the sheet 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. More 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. 3). Then, a heating area of ​​fixing belt 21 other than the nip (the area facing heater 25) is mainly heated by radiant heat from heater 25 (heating means) whose output is controlled by control unit 60. Furthermore, heat is applied to toner image T on sheet P from the heated surface of fixing belt 21. The output control of heater 25 is performed based on the detection result of belt surface temperature by temperature detection sensor 40 (temperature detection means), such as a thermopile or thermistor, which faces the surface of fixing belt 21. Furthermore, by controlling the output of heater 25 in this way, the temperature of fixing belt 21 (fixing temperature) can be set to a desired temperature. 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 also be provided on the inner circumferential surface side of the fixing belt 21.

[0025] In this way, in the fixing device 20 of the present embodiment, since fixing belt 21 is heated over a relatively wide area in the circumferential direction rather than only a portion of fixing belt 21 locally, fixing belt 21 is heated sufficiently even when the device is operated at high speed, and the occurrence of fixing defects can be suppressed. In other words, since 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. 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.

[0026] 5, the guide members 29 guide both widthwise ends of the fixing belt 21 from the inner peripheral surface side so that the fixing belt 21 is maintained in a substantially cylindrical position. More specifically, the two guide members 29 are made 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. The guide members 29 are provided with a guide portion 29a 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 widthwise direction (belt deviation), and the like. The guide members 29 are arranged at both ends in the width direction within a circumferential range excluding the nip portion so as not to interfere with the formation of the nip portion by the nip forming member 26.

[0027] In this embodiment, the only members that come into contact with the inner surface of the fixing belt 21 are the guide members 29 that come into loose contact at both ends in the width direction, and the nip forming member 26 (which actually comes through the heat equalizing member 22), and there are no other members (belt guides) that come into contact with the inner surface and guide the rotation of the fixing belt 21. In this way, the fixing device 20 in this embodiment has a configuration in which the pipe-shaped heating element is removed and the fixing belt 21 is heated directly by the heating means (heater 25) without using the pipe-shaped heating element, in order to further improve the heating efficiency of the fixing belt 21 and reduce the cost and size of the device.

[0028] In this embodiment, reinforcing member 23 is installed inside fixing belt 21 so as to contact the roller portion of pressure roller 31 via nip forming member 26, heat equalizing member 22, and fixing belt 21. Reinforcing member 23 reinforces the strength of nip forming member 26 (and heat equalizing member 22) that form the nip portion. Referring to FIG. 3, the reinforcing member 23 is formed so that its length in the width direction is longer than that of the nip forming member 26, and both ends in the width direction are held by the side plates 43 of the fixing device 20. Reinforcing member 23 contacts pressure roller 31 via nip forming member 26, heat equalizing member 22, and fixing belt 21, thereby preventing nip forming member 26 from being significantly deformed by the pressure of pressure roller 31 at nip N. To fulfill the above-mentioned functions, reinforcing member 23 is preferably made of a metal material with high mechanical strength, such as stainless steel or iron. In this embodiment, a reinforcing member 23 having a cross section that is approximately U-shaped is used, but the shape of the reinforcing member 23 is not limited to this, and for example, a reinforcing member having a cross section that is approximately T-shaped can also be used.

[0029] In this embodiment, a reflector 27 is fixed between the reinforcing member 23 and the heater 25. This allows the heat (heat that heats the reinforcing member 23 and is infrared) directed from the heater 25 to the reinforcing member 23 to be reflected by the reflector 27 and used to heat the fixing belt 21, thereby further improving the heating efficiency of the fixing belt 21. The reflector may be made of aluminum, stainless steel, or the like. The same effect can be obtained even if a part or all of the surface of the reinforcing member 23 facing the heater 25 is subjected to a mirror finish or provided with a heat insulating member.

[0030] Referring to Figure 2, the pressure roller 31 has an elastic layer 33 provided on a core metal 32 (shaft portion), and is driven to rotate in a predetermined direction (clockwise in Figure 2) by a drive motor (not shown) as a driving means. The core metal 32 of the pressure roller 31 is a hollow structure made of a metal material. The elastic layer 33 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 33. The pressure roller 31 presses against the fixing belt 21 to form a desired nip N between the two members. Referring to FIG. 3, the pressure roller 31 is provided with a gear 45 that meshes with the drive gear of the drive motor, and the pressure roller 31 is driven to rotate in the direction of the arrow in FIG. 2 (clockwise). Both widthwise ends of the pressure roller 31 are rotatably supported by side plates 43 of the fixing device 20 via bearings 42.

[0031] When elastic layer 33 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, the heat insulation of pressure roller 31 is improved, making it difficult for heat from fixing belt 21 to transfer to pressure roller 31, thereby improving the heating efficiency of fixing belt 21.

[0032] Although resin materials and metal materials can be used as the material for forming nip formation member 26, a resin material (such as liquid crystal polymer (LCP), polyamideimide (PAI), polyethersulfone (PES), polyphenylene sulfide (PPS), polyethernitrile (PEN), polyetheretherketone (PEEK), etc.) that is rigid enough not to bend significantly even when subjected to the pressure of pressure roller 31 and has thermal and heat insulating properties is preferred. In this embodiment, liquid crystal polymer (LCP) is used as the material for nip formation member 26.

[0033] 4 and other figures, heat equalizing member 22 is provided between nip forming member 26 and fixing belt 21, and is a member for equalizing heat in the width direction at contact surface 21a with fixing belt 21. More specifically, heat equalizing member 22 is a plate-like member (with a substantially U-shaped cross section) made of a material with high thermal conductivity, such as copper or aluminum, and is a member for promoting heat transfer in the width direction of fixing belt 21 (the direction perpendicular to the plane of FIG. 4 ). Nip forming member 26 is fitted tightly inside the U-shaped portion of heat equalizing member 22, and its outer surface forms sliding surface 22a that comes into sliding contact with the inner circumferential surface of fixing belt 21. By providing heat equalizing member 22 in this manner, even if sheets P (small-sized paper) with small width dimensions are continuously passed through nip portion N and the temperature of non-paper passing areas of fixing belt 21 is likely to rise excessively, the heat is quickly transferred to the center in the width direction, resulting in a uniform temperature distribution in the width direction. The heat equalizing member 22, together with the nip forming member 26, is held by a side plate 43 of the apparatus via a reinforcing member 23.

[0034] The heat equalizing member 22 interposed between the nip forming member 26 and the fixing belt in this manner also functions as a lubricant retaining member capable of retaining a lubricant. Specifically, a lubricant is applied (retained) in advance on the inner circumferential surface of the fixing belt 21 and the sliding surface 22a of the heat equalizing member 22, and this lubricant is retained (retained) on the sliding surface 22a of the heat equalizing member 22 over time, reducing the sliding resistance between the fixing belt 21 and the heat equalizing member 22. This also reduces the driving torque of the fixing device 20. Furthermore, wear caused by sliding contact between the nip forming member 26 and the fixing belt 21 can be reduced. Here, the lubricant held in the heat equalizing member 22 may be fluorine oil containing a fluorine compound, fluorine grease (including those using fluorine particles as a thickener), silicone grease, or the like. The temperature equalizing member 22 that functions as a lubricant retaining member will be described in more detail later with reference to FIGS. 6 and 7.

[0035] 4, nip forming member 26 (and heat equalizing member 22) that comes into sliding contact with the inner circumferential surface of fixing belt 21 has a flat surface that faces pressure roller 31 (sliding surface). This makes the shape of nip portion N approximately parallel to the image surface of sheet P, increasing the adhesion between fixing belt 21 and sheet P and improving fixability. Furthermore, since the curvature of fixing belt 21 on the exit side of nip portion N is large, sheet P sent out from nip portion N can be easily separated from fixing belt 21. In this embodiment, nip forming member 26 (and heat equalizing member 22) that forms nip portion N is formed in a flat shape, but nip forming member 26 (and heat equalizing member 22) that forms the nip portion can also be formed in a concave shape so as to follow the curvature of pressure roller 31. In this case, sheet P is sent out from nip portion N so as to follow the curvature of pressure roller 31, which can prevent sheet P from being attracted to fixing belt 21 after the fixing process and not being separated.

[0036] The normal operation of the fixing device 20 configured as described above will now be briefly described. When the power switch of the device main body 1 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 with 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. Thereafter, a sheet P is fed from the paper feed unit 12, and an unfixed color image is carried (transferred) onto the sheet P at the position of the secondary transfer roller 89. The sheet P carrying the unfixed image T (toner image) is conveyed in the direction of arrow Y10 in FIG. 2 while being guided by a guide plate, and is sent into the nip portion N between the fixing belt 21 and the pressure roller 31, which are in a pressure-contact state. Then, the toner image T is fixed on the surface of the sheet P by the heating 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 sheet P sent out from the nip portion is transported in the direction of the arrow Y11.

[0037] The characteristic configuration and operation of the fixing device 20 in this embodiment will be described in detail below. As previously described using Figure 4 etc., in the fixing device 20 of this embodiment, a heat equalizing member 22 as a lubricant holding member capable of holding a lubricant is interposed between the nip forming member 26 and the fixing belt 21. 4, 6, and 7, the heat equalizing member 22 (lubricant holding member) has an upstream upright portion 22b that stands up in a direction away from the nip portion N (left side in FIGS. 4 and 7(A)) on the upstream side in the rotation direction (lower in FIGS. 4 and 7, upstream side in the sheet conveying direction indicated by the arrows and white arrows), and a downstream upright portion 22c that stands up in a direction away from the nip portion N on the downstream side in the rotation direction, and the cross section perpendicular to the width direction is formed in an approximately U-shape. The temperature equalizing member 22 is formed such that its range in the rotation direction (sheet conveying direction) is long both on the upstream side and the downstream side with respect to the nip portion N.

[0038] As shown in Figures 6 and 7, the heat equalizing member 22 serving as a lubricant holding member has a sliding surface 22a that is in sliding contact with the inner peripheral surface of the fixing belt 21, and non-recesses W (a smooth surface with no irregularities) are formed over almost the entire area downstream in the rotation direction (upper side in Figure 7), and multiple recesses 22a1 are formed at least in the area excluding the non-recesses W. Specifically, the recesses 22a1 are formed over almost the entire area of ​​the sliding surface 22a (upstream and midstream areas in the rotation direction) excluding the non-recessed area W (downstream area in the rotation direction). Furthermore, a plurality of recesses 22a1 are also formed at the portion where the sliding contact surface 22a and the upstream side standing portion 22b intersect (near the upstream side of the nip portion N).

[0039] These multiple recesses 22a1 are formed in the form of dimples spaced apart from each other on the planar sliding surface 22a, excluding the non-recessed portions W (smooth portions), by applying cutting, pressing, laser processing, etching, blasting, etc. to the planar sliding surface 22a. Each recess 22a1 has a diameter of about 200 to 1000 μm, a depth of about 5 to 20 μm, and an opening in a substantially circular (or rectangular) shape. By forming multiple recesses 22a in the sliding contact surface 22a in this manner, an oil film of lubricant is formed on the sliding contact surface 22a, improving the retention of the lubricant and allowing the lubricant to circulate between the fixing belt 21.

[0040] In this way, the temperature equalizing member 22 (lubricant holding member) in this embodiment does not have a recess 22a1 formed in the downstream portion in the rotational direction (non-recess W), but has multiple recesses 22a1 formed in the upstream and midstream portions in the rotational direction. Therefore, the lubricant does not leak from the downstream side of the heat-equalizing member 22 (lubricant holding member) over time, and the lubricant holding ability of the heat-equalizing member 22 (lubricant holding member) is sufficiently maintained over time. This reduces problems such as a shortage of lubricant over time, which causes an increase in the drive torque of the fixing device 20, and problems such as wear and deterioration of the fixing belt 21 and the heat-equalizing member 22. Specifically, the lubricant adhering to the inner circumferential surface of fixing belt 21 and sliding surface 22a of heat equalizing member 22 moves (flows) in the same direction as fixing belt 21 rotates (moves). At this time, multiple recesses 22a are formed from the intersection between upstream standing portion 22b of heat equalizing member 22 and sliding surface 22a to the upstream side of nip portion N on sliding surface 22a, creating a gap at the contact portion between fixing belt 21 and heat equalizing member 22, making it easier for the lubricant to flow into nip portion N. The lubricant that has flowed into nip portion N then reaches the midstream portion of nip portion N on sliding surface 22a and is held in multiple recesses 22a1 formed from the upstream portion to the midstream portion. On the other hand, the sliding surface 22a of the heat equalizing member 22 has no recess 22a1 formed in the downstream portion (non-recess W) of the nip portion N, making it a smooth surface, so that the lubricant is less likely to flow out of the sliding surface 22a as the fixing belt 21 rotates (moves). Due to this mechanism, the lubricant retention capacity of the temperature equalizing member 22 (lubricant retention member) is maintained sufficiently even over time.

[0041] In this embodiment, in order to further reduce the sliding resistance between the heat equalizing member 22 and the fixing belt 21, a coating layer made of a low-friction material (e.g., containing a solid lubricant such as a fluorine compound or graphite) can be formed on the sliding surface 22a. However, in such a case, the plurality of recesses 22a1 do not need to be coated with a coating layer made of a low-friction material because they are not in direct sliding contact with the fixing belt 21 and are inherently less prone to wear than other parts. This simplifies the process of forming the coating layer, making it possible to reduce the component cost of the heat equalizing member 22 itself.

[0042] <Variation 1> As shown in FIG. 8, in the heat equalizing member 22 serving as the lubricant holding member in the first modified example, a convex portion 22w is formed on the smoothly formed surface in the non-recessed portion W of the downstream portion, protruding toward the nip portion N and extending in the width direction. Specifically, a protrusion 22w protruding from the sliding surface 22a is formed so as to extend over almost the entire width from the non-recessed portion W to its downstream side (downstream side of the nip portion N). By providing such a convex portion 22w downstream of the heat equalizing member 22, the contact pressure between the fixing belt 21 and the heat equalizing member 22 increases, making it less likely that a gap will form, thereby making it even less likely that the lubricant will leak out of the nip portion N along with the movement of the fixing belt 21.

[0043] <Variation 2> As shown in FIG. 9, a temperature equalizing member 22 serving as a lubricant holding member in the second modification also has a convex portion 22w formed in the non-concave portion W in the downstream portion, similar to that in FIG. 9, the protrusion height A2 of the protrusion 22w at both widthwise ends (only one end is shown in FIG. 9) is greater than the protrusion height A1 at the widthwise center (A2>A1), and the thickness B2 in the rotational direction of both widthwise ends (only one end is shown in FIG. 9) is greater than the thickness B1 in the rotational direction at the widthwise center (B2>B1). Note that the protrusion heights A1 and A2 shown in FIG. 9 are based on the position of the bent tip of the downstream standing portion 22c, and the thicknesses B1 and B2 are based on the position of the bent root (downstream end) of the downstream standing portion 22c. Therefore, when viewed from a direction perpendicular to the sliding contact surface 22a, the upstream side of the convex portion 22w in the rotation direction (sheet conveying direction) is V-shaped and recessed downstream from both widthwise ends toward the widthwise center. Also, when viewed in the rotation direction (sheet conveying direction), the convex portion 22w is V-shaped and recessed in a direction away from the nip portion N from both widthwise ends toward the widthwise center. By configuring it in this manner, even if lubricant accumulates in the downstream portion of the nip portion N, the lubricant will move from both widthwise ends to the widthwise center along the V-shaped slope formed in the convex portion 22w (moving in the direction of the white arrow), making it less likely that the lubricant will leak out from both widthwise ends of the nip portion N.

[0044] As described above, fixing device 20 in this embodiment is provided with endless fixing belt 21 that is heated by heater 25 (heating means) and rotates in a predetermined rotation direction. Nip forming member 26, which is in pressure contact with pressure roller 31 (pressure rotating body) via fixing belt 21 to form nip N through which sheet P is conveyed, is disposed on the inner circumferential surface of fixing belt 21. Heat equalizing member 22 (lubricant holding member) capable of holding lubricant is interposed between nip forming member 26 and fixing belt 21. Non-recessed portions W are formed on sliding surface 22a of heat equalizing member 22, which is in sliding contact with the inner circumferential surface of fixing belt 21, over the entire area downstream in the rotation direction, and multiple recessed portions 22a1 are formed at least in the portion excluding non-recessed portions W. This allows the lubricant retention capacity of the temperature equalizing member 22 (lubricant retention member) to be sufficiently maintained even over time.

[0045] In this embodiment, heater 25 is used as the heating means for heating fixing belt 21, but the heating means for heating the fixing belt is not limited to this. For example, an electromagnetic induction coil can be used as the heating means, or a resistance heating element can be used as the heating means. In addition, in this embodiment, the present invention is applied to a fixing device 20 in which a pressure roller 31 is installed as a pressure rotating body, but the present invention can also be applied to a fixing device in which a pressure belt is installed as a pressure rotating body. Furthermore, in this embodiment, the temperature equalizing member 22 also functions as a lubricant holding member, but a member that does not have a temperature equalizing function can also be used as a lubricant holding member. In these cases, the same effect as that of this embodiment can be obtained.

[0046] It is to be noted that the present invention is not limited to the present embodiment, and it is clear that the present embodiment can 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 the number, position, shape, etc. of the components can be any number, position, shape, etc. that is suitable for implementing the present invention.

[0047] In this specification, the term "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. [Explanation of symbols]

[0048] 1 Image forming apparatus (image forming apparatus main body), 20 Fixing device, 21 fixing belt (belt member), 22 Heat equalizing member (lubricant holding member), 22a Sliding surface, 22a1 recess, 22b Upstream upright section, 22c Downstream upright section, 22w convex part, 23 Reinforcing member, 25 heater (heating means), 26 nip forming member, 29 Guide member (flange), 31 pressure roller (pressure rotating body), N nip section (fixing nip), W non-recessed, P sheet (recording medium).

[0049] The present invention can also be embodied in a combination of Supplementary Notes 1 to 9, as follows. (Appendix 1) an endless fixing belt that is heated by a heating means and rotates in a predetermined rotation direction; a nip forming member disposed on an inner peripheral surface side of the fixing belt, the nip forming member being pressed against a pressure rotating body via the fixing belt to form a nip portion through which a sheet is conveyed; a lubricant holding member interposed between the nip forming member and the fixing belt and capable of holding a lubricant; Equipped with The lubricant retaining member has a sliding surface that slides against the inner peripheral surface of the fixing belt, and the sliding surface has non-recessed portions formed over the entire area downstream in the direction of rotation, and a plurality of recessed portions formed at least in the area excluding the non-recessed portions. (Appendix 2) 2. The fixing device according to claim 1, wherein the plurality of recesses are formed over the entire sliding surface excluding the non-recessed portions. (Appendix 3) the lubricant holding member includes an upstream rising portion that rises in a direction away from the nip portion on an upstream side in a rotation direction, 3. The fixing device according to claim 2, wherein the plurality of recesses are also formed at a portion where the sliding surface and the upstream standing portion intersect. (Appendix 4) 4. The fixing device according to claim 1, wherein the non-recessed portion has a smooth surface. (Appendix 5) The fixing device according to any one of Supplementary Note 1 to Supplementary Note 3, characterized in that the non-recessed portion has a convex portion formed on a smoothly formed surface, the convex portion protruding toward the nip portion and extending in the width direction. (Appendix 6) The fixing device described in Appendix 5, characterized in that the protruding height of the convex portion at both ends in the width direction is greater than the protruding height at the center in the width direction, and the thickness in the rotational direction at both ends in the width direction is greater than the thickness in the rotational direction at the center in the width direction. (Appendix 7) 7. The fixing device according to any one of claims 1 to 6, wherein the lubricant holding member is a heat equalizing member that equalizes heat in the width direction on the contact surface. (Appendix 8) a reinforcing member disposed inside the fixing belt so as to contact the pressure roller via the nip forming member, the lubricant holding member, and the fixing belt; guide members that guide both ends of the fixing belt in a width direction so as to maintain the substantially cylindrical posture of the fixing belt; Equipped with The fixing device according to any one of Supplementary Note 1 to Supplementary Note 7, wherein the heating means is configured to heat a circumferential region of the fixing belt different from the nip portion as a heating region. (Appendix 9) An image forming apparatus comprising the fixing device according to any one of Supplementary Notes 1 to 8. [Prior art documents] [Patent documents]

[0050] [Patent Document 1] Japanese Patent Application Publication No. 2020-197669

Claims

1. an endless fixing belt that is heated by a heating means and rotates in a predetermined rotation direction; a nip forming member disposed on an inner peripheral surface side of the fixing belt, the nip forming member being pressed against a pressure rotating body via the fixing belt to form a nip portion through which a sheet is conveyed; a lubricant holding member interposed between the nip forming member and the fixing belt and capable of holding a lubricant; Equipped with The lubricant retaining member has a sliding surface that slides against the inner peripheral surface of the fixing belt, and the sliding surface has non-recessed portions formed over the entire area downstream in the direction of rotation, and a plurality of recessed portions formed at least in the area excluding the non-recessed portions.

2. 2. The fixing device according to claim 1, wherein the plurality of recesses are formed over the entire sliding surface excluding the non-recessed portions.

3. the lubricant holding member includes an upstream rising portion that rises in a direction away from the nip portion on an upstream side in a rotation direction, 3. The fixing device according to claim 2, wherein the plurality of recesses are also formed at a portion where the sliding surface and the upstream side standing portion intersect.

4. 3. The fixing device according to claim 1, wherein the non-recessed portion has a smooth surface.

5. 3. The fixing device according to claim 1, wherein the non-recessed portion has a convex portion formed on a smooth surface thereof, the convex portion protruding toward the nip portion and extending in the width direction.

6. The fixing device according to claim 5, wherein the protruding height of the convex portion at both ends in the width direction is greater than the protruding height of the central portion in the width direction, and the thickness in the rotational direction of the both ends in the width direction is greater than the thickness in the rotational direction of the central portion in the width direction.

7. 3. The fixing device according to claim 1, wherein the lubricant holding member is a heat equalizing member that equalizes heat in the width direction on the contact surface.

8. a reinforcing member disposed inside the fixing belt so as to contact the pressure roller via the nip forming member, the lubricant holding member, and the fixing belt; guide members that guide both ends of the fixing belt in a width direction so as to maintain the substantially cylindrical posture of the fixing belt; Equipped with 3. The fixing device according to claim 1, wherein the heating means heats a circumferential region of the fixing belt different from the nip portion as a heating region.

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

Images