Fixing device and image forming apparatus

Abstract

To provide a fixing device that can prevent the occurrence of dirt on the back, while preventing lubricant leaking out from a nip forming member from permeating into a paper feed area.SOLUTION: A fixing device 150 comprises: an endless fixing belt 80; a pressure member 84 that is in contact with an outer peripheral surface of the fixing belt 80; a nip forming member 88 that is arranged inside the fixing belt 80, is in contact with the pressure member 84 with the fixing belt 80 therebetween to form a nip part N, and supplies lubricant to reduce the frictional resistance with the fixing belt 80; and a separation member 32 that separates a recording target medium S passing through the nip part N from the fixing belt 80. The separation member 32 has contact parts 34 that are each formed to project and in contact with the fixing belt 80, near both ends of the fixing belt 80 located axially outside a position where the pressure member 84 is in contact with the fixing belt 80. The pressure member 84 has absorption parts 83 each absorb the lubricant at both ends thereof.SELECTED DRAWING: Figure 3

Description

[Technical Field]

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

[0002] Electrophotographic image forming apparatuses have been widely known, and the image forming process in these image forming apparatuses is as follows: an electrostatic latent image is formed on the surface of a photosensitive drum, which is an image carrier, and the formed electrostatic latent image is visualized and developed with toner, the developed image is transferred to a recording medium by a transfer device, and the transferred image on the recording medium is heated and pressurized by a fixing device to fix the toner image onto the recording medium, thereby obtaining an image. The fixing device that performs the fixing is equipped with a rotating body composed of opposing rollers or a belt, and heats and presses the recording medium while sandwiching it in the nip portion of the rotating body, thereby fixing the toner image onto the recording medium. One example of this type of fixing device is a configuration known as a belt fixing system.

[0003] The basic configuration of a belt fixing type fixing device includes a fixing rotor consisting of a heating roller having a heater as a heating member, a fixing roller with a rubber layer on its surface, an endless fixing belt stretched between the rollers, and a pressure roller in contact with the fixing belt. In this type of fixing device, when a recording medium having an unfixed toner image on its surface is conveyed, the unfixed toner image is heated and pressurized as it passes through the nip between the fixing belt and the pressure roller, and the toner image is fixed to the recording medium.

[0004] Among the fixing devices mentioned above, there is known a fixing device that includes a pressure roller, a fixing belt as a fixing member, and a metal pipe as a holding member disposed adjacent to the inner surface of the fixing belt. The metal pipe is heated by a heating member such as a halogen heater, thereby heating the fixing belt through the metal pipe. In this configuration, a lubricant such as silicone oil or fluorine grease is applied to the sliding surface of the metal pipe. As the fixing belt moves, a circulation path for the lubricant is formed in the gap between the fixing belt and the metal pipe, reducing the sliding resistance between the metal pipe and the fixing belt and reducing wear on both members.

[0005] However, in reality, due to the influence of factors such as the unavoidable shape deviations of each component and uneven expansion of materials due to temperature deviations, and pressure deviations inside the nip portion, a shift occurs in the relative positions of the fixing belt and the metal pipe in the width direction, resulting in the problem of lubricant leaking from the gap between the fixing belt and the metal pipe at both ends in the width direction. To prevent this problem from occurring, a configuration has been proposed that includes sliding contact members that come into sliding contact with both ends of the fixing member in the width direction to stabilize the running performance of the fixing member and suppress deformation of the fixing member near the recording medium outlet in the nip portion (see, for example, Patent Document 1).

[0006] The configuration disclosed in Patent Document 1 involves scraping off the lubricant from the surface of the fixing member with a sliding contact member, but depending on the position at which the sliding contact member contacts the fixing member, the lubricant may penetrate into the pressure roller. Specifically, the lubricant applied to the nip forming member leaks over time from both axial ends of the fixing member, travels from the axial ends to the center of the fixing member, and reaches the separation member that contacts the surface of the fixing member. As a result, the leaked lubricant penetrates into the pressure roller via the separation member, causing a problem of backside contamination of the recording medium. Therefore, a configuration has been proposed in which a separation member contact portion contacts the fixing member, the contact position of the separation member contact portion is located outside the pressure roller in the axial direction, the separation member contact portion contacts the fixing member at a constant width, and the contact position is positioned downstream in the rotation direction of the fixing member as it moves further outward in the axial direction (see, for example, Patent Document 2). Summary of the Invention [Problem to be solved by the invention]

[0007] However, the technology disclosed in Patent Document 2 has the problem that the lubricant that comes into contact with the separating member contact area flows toward the axial center, making it impossible to improve backside contamination. Also, the separating member contact area does not match the shape of the fixing member, which increases contact pressure due to localized contact and exacerbates wear on the surface of the fixing member. SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to provide a fixing device that can prevent the occurrence of back stains while preventing the lubricant leaking from the nip forming member from penetrating into the paper passing area. [Means for solving the problem]

[0008] The invention described in claim 1 comprises an endless fixing belt, a pressure member that contacts the outer peripheral surface of the fixing belt, a nip forming member that is arranged inside the fixing belt and contacts the pressure member via the fixing belt to form a nip portion, and supplies a lubricant that reduces frictional resistance with the fixing belt, and a separation member that separates the recording medium that has passed through the nip portion from the fixing belt, wherein the separation member has protruding contact portions that contact the fixing belt near both ends of the fixing belt that are located axially outer than the position where the pressure member contacts the fixing belt, and the pressure member has absorption portions at both ends that absorb the lubricant. [Effects of the Invention]

[0009] According to the present invention, the lubricant leaked from the end of the fixing belt can be absorbed by the absorbing portion, and therefore, it is possible to provide a fixing device that can suppress the occurrence of backside staining. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic front view of an image forming apparatus to which an embodiment of the present invention can be applied; [Figure 2] 1 is a schematic front view of a main part of a fixing device used in a first embodiment of the present invention. [Figure 3] 1 is a schematic plan view of a fixing device used in a first embodiment of the present invention. [Figure 4] FIG. 2 is a cross-sectional view of a main part of a pressure member used in the first embodiment of the present invention. [Figure 5] 1A is a cross-sectional view of a fixing belt used in a first embodiment of the present invention, taken in the vicinity of an end portion in the axial direction, and FIG. 1B is a cross-sectional view of a fixing belt used in the first embodiment of the present invention, taken in the vicinity of a central portion in the axial direction. [Figure 6] FIG. 1 is a schematic front view of a conventional fixing device. [Figure 7] 1A is a schematic diagram of a fixing belt used in one embodiment of the present invention; FIG. 1B is a schematic diagram of a fixing belt and a separating member; [Figure 8] FIG. 4 is a schematic front view of a main part of a fixing device used in a second embodiment of the present invention. [Figure 9] FIG. 10 is a schematic front view of a main part of a fixing device used in a third embodiment of the present invention. [Figure 10] FIG. 10 is a schematic diagram of a light blocking member used in a third embodiment of the present invention. [Figure 11] 10A and 10B are schematic diagrams showing a displacement state of a light blocking member in the third embodiment of the present invention. [Figure 12] FIG. 10 is a schematic exploded perspective view illustrating a nip forming member used in a fourth embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] Figure 1 shows an image forming apparatus according to one embodiment of the present invention. In this figure, image forming apparatus 100 is a tandem color printer in which image forming units that form images of multiple colors are arranged side by side along the direction of movement of an intermediate transfer belt. Image forming apparatus 100 has photosensitive drums 20Y, 20M, 20C, and 20K, which are image carriers capable of forming images corresponding to the colors yellow (Y), cyan (C), magenta (M), and black (K), respectively. Toner images, which are visible images formed on each photosensitive drum 20, are primarily transferred in a superimposed state onto intermediate transfer belt 11, which is an intermediate transfer body that can travel in the direction of arrow A1 while facing each photosensitive drum 20. Then, in a secondary transfer process, the images are collectively transferred onto transfer sheet S, which is a recording medium.

[0012] Various devices that perform image formation processing in accordance with the rotation of each photosensitive drum 20 are arranged around each photosensitive drum 20. The various devices that perform image formation processing will be described using photosensitive drum 20K, which forms a black image, as a representative example. Around photosensitive drum 20K, a charging device 30K, a developing device 40K, a primary transfer roller 12K, and a cleaning device 50K are arranged in this order along the rotation direction of photosensitive drum 20K. After the photosensitive drum 20K is charged by the charging device 30K, the optical writing device 8 performs optical writing based on image information onto the surface of the photosensitive drum 20K, and an electrostatic latent image is formed on the outer circumferential surface of the photosensitive drum 20K. The formed electrostatic latent image is made visible by the developing device 40K, and a toner image is formed on the outer circumferential surface of the photosensitive drum 20K.

[0013] The toner images formed on each photosensitive drum 20 are primarily transferred onto the intermediate transfer belt 11 in a superimposed manner at the same position on the intermediate transfer belt 11 as the intermediate transfer belt 11 travels in the A1 direction. This primary transfer is performed with staggered timing from the upstream side to the downstream side in the A1 direction by applying a voltage from each primary transfer roller 12 disposed opposite each photosensitive drum 20 via the intermediate transfer belt 11. The photosensitive drums 20Y, 20C, 20M, and 20K are arranged side by side in this order from the upstream side in the A1 direction. Each photosensitive drum 20 is provided in an image station for forming a yellow, cyan, magenta, or black image, respectively.

[0014] The image forming device 100 has four image stations that perform image formation processing for each color, and an intermediate transfer belt unit 10 that is arranged above and opposite each photosensitive drum 20 and is equipped with an intermediate transfer belt 11 and primary transfer rollers 12Y, 12C, 12M, and 12K. The image forming apparatus 100 also has a secondary transfer roller 5 that is disposed opposite the intermediate transfer belt 11 and rotates in response to the movement of the intermediate transfer belt 11. The image forming apparatus 100 also has an intermediate transfer belt cleaning device 13 that is disposed opposite the intermediate transfer belt 11 and cleans the surface of the intermediate transfer belt 11.

[0015] An optical writing device 8 is disposed below each image station, facing the image station. The optical writing device 8 is equipped with a semiconductor laser as a light source, a coupling lens, an Fθ lens, a toroidal lens, a folding mirror, a polygon mirror, etc. The optical writing device 8 irradiates each photoconductor drum 20 with writing light Lb corresponding to each color, and forms an electrostatic latent image on each photoconductor drum 20.

[0016] A sheet feeding device 61 is provided below the image forming apparatus 100, on which transfer sheets S are stacked and transported toward between each photosensitive drum 20 and the intermediate transfer belt 11. The transfer sheets S are fed from the sheet feeding device 61 toward the secondary transfer portion between the intermediate transfer belt 11 and the secondary transfer roller 5 at a predetermined timing that matches the timing of the formation of toner images by the image stations through the registration roller pair 4. A sensor (not shown) detects that the leading edge of the transfer sheet S has reached the registration roller pair 4.

[0017] The transfer sheet S onto which the toner image has been transferred is sent to a fixing device 150 where heat and pressure are applied, thereby fixing the toner image onto the transfer sheet S. The fixing device 150 will be described later. The fixed transfer sheet S is discharged onto a discharge tray 6 formed on the top surface of the image forming apparatus main body by a pair of discharge rollers 7. Inside the image forming apparatus main body located below the discharge tray 6, toner bottles 9Y, 9C, 9M, and 9K filled with yellow, cyan, magenta, and black toner are provided.

[0018] The intermediate transfer belt unit 10 has the intermediate transfer belt 11, each primary transfer roller 12, as well as a drive roller 72 and a driven roller 73 around which the intermediate transfer belt 11 is stretched. The driven roller 73 also functions as a means for applying tension to the intermediate transfer belt 11, and is provided with a biasing means such as a spring. The intermediate transfer belt unit 10, the secondary transfer roller 5, and the intermediate transfer belt cleaning device 13 form a transfer device 71.

[0019] The sheet feeding device 61 has a feeding roller 3 that contacts the uppermost transfer sheet S, and the uppermost transfer sheet S is fed toward a pair of registration rollers 4 by rotating the feeding roller 3 counterclockwise. The intermediate transfer belt cleaning device 13 has a cleaning brush and a cleaning blade arranged to face and contact the intermediate transfer belt 11, and scrapes off and removes foreign matter such as toner remaining on the intermediate transfer belt 11 with the cleaning brush and cleaning blade. The intermediate transfer belt cleaning device 13 also has a discharge means (not shown) for carrying out and discarding the foreign matter removed from the intermediate transfer belt 11.

[0020] 2, the fixing device 150 used in the first embodiment has a fixing belt 80, which is a thin, flexible, endless belt member, and a pressure roller 84 as a pressure member disposed opposite the fixing belt 80. A nip forming unit 86 is provided inside the fixing belt 80 to form a nip N between the fixing belt 80 and the pressure roller 84, where a transfer sheet S, which is a recording medium, is sandwiched and transported. The nip forming unit 86 has a nip forming member 88 disposed inside the fixing belt 80 opposite the pressure roller 84, and a stay member 90 that holds the nip forming member 88 against the pressure from the pressure roller 84.

[0021] The stay member 90 has a box-like shape that is open on the side opposite the nip portion N, and a halogen heater 82 serving as a heat source is disposed inside the stay member 90. The fixing belt 80 is directly heated by radiant heat from the inner surface of the halogen heater 82 at the open side of the stay member 90. To improve the heating efficiency of the halogen heater 82, a reflective member 94 is provided on the inner surface of the stay member 90 to reflect light emitted from the halogen heater 82 toward the fixing belt 80. The reflective member 94 serves to reduce unnecessary energy consumption that would otherwise occur if the stay member 90 were heated by radiant heat from the halogen heater 82. Similar effects can be achieved by applying a heat insulating or mirror-finishing treatment to the inner surface of the stay member 90 instead of the reflective member 94.

[0022] As shown in Fig. 2, pressure roller 84 is configured by providing an elastic silicone rubber layer 84b on the outer periphery of hollow metal roller 84a. To ensure releasability, a release layer of approximately 5 to 50 µm thickness made of PFA (perfluoroalkoxy fluororesin) or PTFE (polytetrafluoroethylene) is provided on the surface of rubber layer 84b. Pressure roller 84 is driven to rotate by motor 85 (see Fig. 3), which is a driving means provided in image forming apparatus 100, and is pressed against fixing belt 80 by a biasing member such as a spring, and a predetermined nip width is formed by rubber layer 84b being crushed and deformed.

[0023] The pressure roller 84 may be solid, but hollow is more preferable because it reduces heat capacity. The pressure roller 84 may also have a heat source such as a halogen heater inside. The rubber layer 84b may be solid rubber, but if the pressure roller 84 does not have a heater inside, sponge rubber may be used. For the rubber layer 84b, sponge rubber is more preferable than solid rubber because it improves heat insulation and makes it more difficult for heat to be lost from the fixing belt 80.

[0024] The fixing belt 80 is a metal belt made of nickel, stainless steel, or the like, or an endless belt or film made of a resin material such as polyimide, with a layer thickness of approximately 30 to 50 μm. The belt surface has a release layer made of PFA, PTFE, or the like to prevent toner adhesion. An elastic layer made of silicone rubber or the like may be provided between the belt substrate and the release layer. If the belt does not have an elastic layer, the heat capacity is reduced and fixing performance is improved, but when an unfixed image is crushed and fixed, subtle irregularities on the belt surface are transferred to the image, resulting in the problem of uneven fixing (uneven gloss) remaining in solid parts of the image.

[0025] To alleviate the above-mentioned problems, the elastic layer should be provided with a thickness of 100 μm or more. This allows the elastic layer to deform, absorbing subtle irregularities and improving the occurrence of uneven fixing. The fixing belt 80 rotates while being sandwiched in the nip portion N, but both ends of the fixing belt 80 remain cylindrical in areas other than the nip portion N, so that the cross-sectional shape of the fixing belt 80 is stably maintained in a circular shape. Also, as shown in FIG. 3, a separating member 32 that separates the transfer sheet S from the fixing belt 80 is provided downstream of the nip portion N in the sheet conveyance direction.

[0026] Nip forming member 88, which is arranged on the inner surface side of fixing belt 80, contacts the inner surface of fixing belt 80 at nip portion N either directly or via a sliding sheet (not shown), and fixing belt 80 slides across this contact area. A lubricant supplied from a supply device (not shown) is applied to the sliding surface of nip forming member 88 that slides against fixing belt 80, reducing frictional resistance caused by the sliding of fixing belt 80 as it travels. In this embodiment, the nip forming member 88 that forms the nip portion N is flat, but it may be concave or have another shape. When the nip forming member 88 is concave, the discharge direction of the leading edge of the sheet is closer to the pressure roller 84, improving separation and suppressing jams.

[0027] The stay member 90 has an axial length that extends over the entire axial length of the fixing belt 80, and both ends thereof are positioned and fixed to side plates (not shown) of the image forming apparatus main body. The stay member 90, which holds the nip forming member 88, prevents the nip forming member 88 from bending when pressure is applied from the pressure roller 84, thereby achieving a uniform nip width in the axial direction. The stay member 90 has sufficient bending strength, and examples of materials that can be used include metal materials such as stainless steel and iron, and metal oxides such as ceramic. In this embodiment, an example is shown in which a halogen heater 82 is used as the heat source, but other heat sources such as an IH, a resistance heating element, or a carbon heater may also be used as the heat source.

[0028] The fixing belt 80 is rotatably supported at both axial ends by flanges 36 that protrude axially from side plates (not shown) of the image forming apparatus main body. The flanges 36 have an outer diameter approximately equal to the inner diameter of the fixing belt 80 and a length that extends approximately 5 to 10 mm inward from both ends of the fixing belt 80. The fixing belt 80 is guided by the flanges 36, so that its cross-sectional shape remains circular even while it is moving. The flanges 36 have an opening at a location corresponding to the nip portion N so that a nip forming unit 86 can be positioned at a predetermined position. The fixing belt 80 rotates when the pressure roller 84 is driven to rotate.

[0029] 3 shows a plan view of the fixing device 150 according to the first embodiment. In the figure, a nip forming member 88 disposed inside a cylindrical fixing belt 80 contacts a pressure roller 84 via the fixing belt 80 to form a nip N. The fixing belt 80 is held at both ends by flanges 36, and moves as the pressure roller 84 rotates. A separating member 32 that separates the transfer sheet S from the fixing belt 80 during the fixing operation is disposed on the side of the fixing belt 80 opposite the portion that the pressure roller 84 abuts against. The separating member 32 has contact portions 34 provided at both ends thereof that abut against the fixing belt 80, thereby suppressing variation in the separation gap. The contact portions 34 are provided at two locations on the outer side of both ends of the pressure roller 84 in the axial direction of the pressure roller 84. Each contact portion 34 is formed to protrude from both ends of the separating member 32 toward the fixing belt 80.

[0030] If there is no gap (they overlap) in the axial direction between the contact position of the contact portion 34 against the fixing belt 80 and the contact position of the pressure roller 84, the lubricant supplied from the nip forming member 88 to the inner circumferential surface of the fixing belt 80 may leak from the end of the fixing belt 80 and transfer to the pressure roller 84 using the contact portion 34 as a flow path. In this case, the lubricant that reaches the paper passing area will stain the transfer sheet S, so a gap is provided between the contact position of the contact portion 34 and the contact position of the pressure roller 84 to prevent the lubricant from penetrating into the paper passing area.

[0031] In the above-described configuration, increasing the gap between each contact portion 34 and both ends of the pressure roller 84 increases the effect of suppressing the penetration of the lubricant into the paper passing area, but it also requires shifting other parts outward in the axial direction to prevent interference, which increases the size of the unit and parts and increases costs. Also, the technology disclosed in Patent Document 2 has the problem that the lubricant that comes into contact with the separating member contact portion flows toward the axial center, making it impossible to improve backside contamination.

[0032] Therefore, in the configuration of the present invention, absorbing sections 83 that absorb lubricant are provided at both ends of the pressure roller 84. By providing the absorbing sections 83, the lubricant that leaks from the ends of the fixing belt 80 can be absorbed by the absorbing sections 83, thereby suppressing the occurrence of backside staining. Furthermore, since the provision of the absorbing sections 83 improves the function of suppressing the penetration of the lubricant, the gaps between each contact section 34 and both ends of the pressure roller 84 can be reduced, thereby achieving cost reduction through miniaturization. The absorbing portion 83 may be a separate member from the pressure roller 84, but in this embodiment, to prevent costs from increasing, the rubber layer 84b, which is an elastic layer, functions as the absorbing portion 83. This configuration simplifies the configuration by providing both the function of forming the nip portion N with the elasticity of the rubber layer 84b and the function of absorbing the lubricant, thereby achieving cost reduction. Here, the rubber material containing the foaming agent is in a sponge-like state, so it has high lubricant absorption efficiency. It is also desirable to appropriately optimize the rubber layer 84b, for example by increasing the foaming rate only in the portion that functions as the absorbing portion 83 to increase absorption efficiency.

[0033] 4 shows a cross-sectional view of a main part of the pressure roller 84 in the first embodiment. As described above, the pressure roller 84 has a rubber layer 84b on the outer periphery of the metal roller 84a, and on the outer periphery of the rubber layer 84b, a release layer 84c that separates the transfer sheet S and an adhesive layer 84d that bonds the rubber layer and the release layer 84c are provided. In this embodiment, the rubber layer 84b functions as the absorbing section 83, and the surface layer of the absorbing section 83 is configured as an adhesive layer 84d to improve frictional force with the fixing belt 80, which rotates drivenly. As shown in Fig. 4, the adhesive layer 84d that protrudes from the release layer 84c is formed so that its thickness decreases toward the outside in the axial direction. This increases the efficiency of absorbing the lubricant toward the outside in the axial direction, and prevents the lubricant from penetrating toward the inside in the axial direction.

[0034] If the adhesive layer 84d is thick, the frictional force with the fixing belt 80 increases, but the rubber layer 84b functioning as the absorbing portion 83 is covered, reducing the lubricant absorption capacity. In this embodiment, the lubricant supplied from the nip forming member 88 leaks from the axial outside of the fixing belt 80, so the lubricant absorption capacity is increased toward the axial outside and the penetration of the lubricant toward the axial inside is suppressed. Also, as shown in FIG. 4, by providing thickness variations in the axial direction, the penetration of the lubricant is mechanically suppressed. It is desirable to appropriately optimize the thickness of the adhesive layer 84d not only in the axial direction but also in the circumferential direction.

[0035] FIG. 5 shows a cross-sectional view of the fixing belt 80, where (a) shows a portion at an end in the axial direction and (b) shows a portion at the center in the axial direction. As described above, the fixing belt 80 is held by the flanges 36 at both axial ends, and the portions near both ends maintain a shape that conforms to the shape of the flanges 36, as shown in FIG. 5(a). Because the fixing belt 80 is thin and prone to breakage from an energy-saving perspective, the flanges 36 are often nearly perfectly circular. Meanwhile, the holding force of the flanges 36 does not reach the center in the axial direction, so the fixing belt 80 is prone to deformation. The dashed line in FIG. 5(b) shows the fixing belt 80 without deformation, but when pressure is applied to form the nip N, the fixing belt 80 deforms to conform to the shape of the nip forming member 88.

[0036] 6 is a schematic diagram of a fixing device 140 disclosed in the aforementioned "Patent Document 2" (Japanese Patent No. 7110783). Fixing device 140 differs from fixing device 150 in that it uses a nip forming member 87, which has a different shape, instead of nip forming member 88, and in that it uses a separating member 33 instead of separating member 32. Separating member 33 has contact portions 35 that contact the circumferential surface of fixing belt 80 at two locations, similar to contact portions 34 in separating member 32, on the outer side of both ends of pressure roller 84 in the axial direction of pressure roller 84. Contact portions 35 have a fixed contact width with fixing belt 80, and are formed so that the more outward in the axial direction they contact, the more downstream in the rotational direction of fixing belt 80 they contact.

[0037] As shown in Fig. 5, the cross-section of the fixing belt 80 changes depending on the axial position, so the shape of the fixing belt 80 that the contact portion 34 contacts is not linear but arc-shaped in the axial direction, as shown in Fig. 7(a). The conventional contact portion 35 did not take into consideration that the fixing belt 80 has an arc-shaped axial direction, so the contact portion 35 does not make linear contact with the fixing belt 80, and the contact pressure of the contact portion 35 against the fixing belt 80 increases. This causes wear on the surface of the fixing belt 80, and the generated wear powder is transferred to the pressure roller 84, reducing the frictional force and causing the fixing belt 80 to slip, resulting in various problems such as abnormal images, sheet conveyance problems, and even breakage due to a decrease in the strength of the fixing belt 80.

[0038] In this embodiment, as shown in FIG. 7(b), the shape of each contact portion 34 is formed so that the amount of protrusion increases toward the outside in the axial direction. This configuration allows each contact portion 34 to be in line contact with the fixing belt 80, suppressing an increase in the contact pressure of the contact portion 34 against the fixing belt 80 and suppressing surface wear of the fixing belt 80. The absorption portion 83 provided on the pressure roller 84 is responsible for suppressing penetration of the lubricant, thereby improving quality over time while maintaining functionality. Because the shape of the fixing belt 80 changes depending on the linear speed, load, and the shape of other components, it is desirable to appropriately optimize the shape of each contact portion 34.

[0039] To reduce costs, the fixing device 150 employs a one-sided drive system in which the motor 85 is located on one side of the pressure roller 84 in the axial direction, as shown in FIG. 3 . In the one-sided drive system, the temperature on the drive side in the axial direction where the motor 85 is located increases due to the effects of frictional heat, etc., which may soften the fixing belt 80 and accelerate wear of the fixing belt 80. Therefore, in this embodiment, the contact pressure of the contact portion 34 on the fixing belt 80, which is on the left side in FIG. 3 where the motor 85 is located, is set to be smaller than the contact pressure of the contact portion 34 on the fixing belt 80 on the right side in FIG. 3 . This configuration reduces surface wear of the fixing belt 80.

[0040] 8 shows a fixing device used in a second embodiment of the present invention. In the figure, fixing device 151 differs from fixing device 150 in that it uses heat source 21 equipped with three halogen heaters instead of halogen heater 82 as a heat source, and in that, in addition to using heat source 21, it uses nip forming member 22, stay member 23, and reflecting member 24 instead of nip forming member 88, stay member 90, and reflecting member 94. In this embodiment, the heat source 21 is equipped with three halogen heaters corresponding to the paper width, so that by heating according to the paper width, excessive heat supply can be suppressed, and in addition to the effects shown in the first embodiment, energy saving can be improved compared to the first embodiment.

[0041] 9 shows a fixing device used in a third embodiment of the present invention. In the figure, fixing device 152 differs from fixing device 150 in that it uses heat source 41 equipped with two halogen heaters instead of halogen heater 82 as the heat source. In addition, fixing device 152 differs from fixing device 150 in that, in addition to using heat source 41, it uses nip forming member 42, stay member 43, reflective member 44, and flange 45 instead of nip forming member 88, stay member 90, reflective member 94, and flange 36, and in that it uses light-shielding member 46.

[0042] 10, the light blocking member 46 has a stepped shape with a light blocking area corresponding to each sheet width (postcard size, B4 size, and A3 size in this embodiment), and is configured to be displaceable along the inner periphery of the fixing belt 80 in a non-contact state relative to the fixing belt 80. As shown in Fig. 11, the light blocking member 46 moves to a position corresponding to each sheet width (Fig. 11(a) corresponds to A3 size, and Fig. 11(b) corresponds to postcard size), and blocks light from areas of the transfer sheet S that are not required for heating. With this configuration, even when narrow transfer sheets S are continuously fed through, the non-paper-feeding areas do not become overheated, and there is no need to take control measures such as reducing productivity to cancel out overheated areas, allowing productivity to be maintained.In addition, with the above configuration, the number of halogen heaters can be reduced from three to two, resulting in cost reduction.

[0043] 12 is a perspective view illustrating a nip forming member used in a fourth embodiment of the present invention. The nip forming member 62 used in the fourth embodiment aims to reduce excessive temperature rise in the non-sheet passing area described above, and has a function as a substitute for the light blocking member 46 while reducing the number of halogen heaters to two. Nip forming member 62 has a heat equalizing member 64 with a sliding sheet 63 on its surface. When fixing belt 80 runs, the friction load is reduced by sliding sheet 63, which has low friction characteristics, and the drive torque of fixing belt 80 is reduced. Heat equalizing member 64, made of a material with high thermal conductivity, such as copper, is formed along the axial direction of fixing belt 80, and absorbs excess heat that accumulates in fixing belt 80 when no paper is passing through and transfers it in the axial direction.

[0044] The heat equalizing member 64 has bent portions 64a and 64b, and the tip of the bent portion 64a, which is located upstream of the nip portion N in the sheet conveying direction, has a sharp tip. When the fixing belt 80 runs, the sliding sheet 63 is pulled in the sheet conveying direction, but the tip of the bent portion 64a, which has a sharp shape, catches on the sliding sheet 63, thereby firmly holding the sliding sheet 63. Note that when the fixing belt 80 rotates in the reverse direction, it is effective to also make the tip of the bent portion 64b sharp. At both widthwise ends and the center of the heat equalizing member 64, first heat insulating members 65 made of a member with lower thermal conductivity than the heat equalizing member 64, for example, made of resin, are arranged. In addition, second heat insulating members 66 made of resin are arranged in the areas located between the first heat insulating members 65. A second heat absorbing member 68 is provided on the upper surface of each second heat insulating member 66, and a single first heat absorbing member 67 covering the upper surfaces of all of the first heat insulating members 65 is provided on the upper surface of each first heat insulating member 65.

[0045] Each first heat insulating member 65 prevents the first heat absorbing member 67 from absorbing excessive heat from the fixing belt 80, thereby preventing a drop in temperature in the paper passing area and suppressing problems such as poor fixing, extended warm-up time, and increased power consumption. The second heat insulating member 66 adjusts the amount of heat transferred from the heat equalizing member 64 to the first heat absorbing member 67 via the second heat absorbing member 68, and the thickness and length of the second heat insulating member 66 are optimized according to the magnitude of the temperature rise that occurs in the non-paper passing area. The first heat absorbing member 67 and the second heat absorbing member 68 are made of materials with high thermal conductivity, and the second heat absorbing member 68 is positioned at a position where a temperature rise occurs in the non-paper passing area. Similar to the second heat insulating member 66, the thickness and length of the second heat absorbing member 68 are optimized according to the magnitude of the temperature rise. With this configuration, in addition to the effects of the third embodiment, the light blocking member 46 and the displacement mechanism for displacing the light blocking member 46 can be omitted, and a significant cost reduction can be achieved.

[0046] In the above embodiment, an example was shown in which a full-color printer was used as an image forming apparatus to which the present invention can be applied, but the image forming apparatus to which the present invention can be applied is not limited to this, and the present invention can also be applied to copying machines, facsimiles, multifunction machines, etc. In addition, in the above embodiment, a configuration is shown in which a transfer sheet S is used as the sheet, which is the recording medium on which an image is formed, but this transfer sheet S is not limited to recording paper, but also includes cardboard, postcards, roll paper, envelopes, plain paper, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, OHP sheets, OHP film, resin film, etc., and any sheet-like material on which an image can be formed may be used.

[0047] The aspects of the present invention are as follows, for example. [1] A fixing device comprising: an endless fixing belt; a pressure member that contacts the outer peripheral surface of the fixing belt; a nip forming member that is disposed inside the fixing belt and contacts the pressure member via the fixing belt to form a nip portion, and supplies a lubricant that reduces frictional resistance with the fixing belt; and a separation member that separates the recording medium that has passed through the nip portion from the fixing belt, wherein the separation member has protruding contact portions that contact the fixing belt near both ends of the fixing belt that are located axially outward from the position where the pressure member contacts the fixing belt, and the pressure member has absorption portions at both ends that absorb the lubricant. [2] The fixing device according to [1], wherein the pressure member has an elastic layer that forms the nip portion, and the elastic layer functions as the absorbing portion. [3] The fixing device described in [2] is characterized in that the pressure member has a release layer on the outer periphery of the elastic layer via an adhesive layer, the adhesive layer and the elastic layer that are not covered with the release layer function as the absorbing section, and the adhesive layer that functions as the absorbing section is formed so that its thickness becomes thinner as it goes outward in the axial direction. [4] The fixing device according to any one of [1] to [3], wherein each of the contact portions is formed so that the amount of protrusion increases as it goes outward in the axial direction. [5] The fixing device described in any one of [1] to [4] is characterized in that the pressure member is rotationally driven by a driving means provided on one side in the axial direction, and the contact pressure at which each contact portion contacts the fixing belt is set smaller on the side where the driving means is provided than on the other side. [6] An image forming apparatus including the fixing device according to any one of [1] to [5].

[0048] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to such specific embodiments, and unless otherwise specifically limited in the above description, various modifications and changes are possible within the scope of the spirit of the present invention as described in the claims. The effects described in the embodiments of the present invention are merely examples of the most preferable effects resulting from the present invention, and the effects of the present invention are not limited to those described in the embodiments of the present invention. [Explanation of symbols]

[0049] 32 Separation member 34 Contact part 80 Fixing belt 83 Absorption section 84 Pressure member (pressure roller) 84b Elastic layer (rubber layer) 84c Release layer 84d adhesive layer 85 Driving means (motor) 88 Nip forming member 100 Image forming device 150 Fixing device N Nip S Recording medium (transfer sheet) [Prior art documents] [Patent documents]

[0050] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-43666 [Patent Document 2] Patent No. 7110783

Claims

1. an endless fixing belt; a pressure member that contacts the outer peripheral surface of the fixing belt; a nip forming member that is disposed inside the fixing belt and contacts the pressure member via the fixing belt to form a nip portion, and that supplies a lubricant that reduces frictional resistance with the fixing belt; a separating member that separates the recording medium that has passed through the nip portion from the fixing belt; Equipped with the separating member has protruding contact portions that contact the fixing belt near both ends of the fixing belt, the protruding contact portions being located axially outward from the positions where the pressing member contacts the fixing belt, The pressure member has absorbing portions at both ends thereof for absorbing the lubricant.

2. 2. The fixing device according to claim 1, The fixing device is characterized in that the pressure member has an elastic layer that forms the nip portion, and the elastic layer functions as the absorbing portion.

3. 3. The fixing device according to claim 2, The pressure member has a release layer on the outer periphery of the elastic layer via an adhesive layer, the adhesive layer and the elastic layer that are not covered with the release layer function as the absorption section, and the adhesive layer that functions as the absorption section is formed so that its thickness becomes thinner as it goes outward in the axial direction.

4. 2. The fixing device according to claim 1, The fixing device is characterized in that each of the contact portions is formed so that the amount of protrusion increases as it goes outward in the axial direction.

5. 2. The fixing device according to claim 1, The pressure member is rotationally driven by a driving means provided on one side in the axial direction, and the contact pressure at which each contact portion contacts the fixing belt is set smaller on the side where the driving means is provided than on the other side.

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

Images