Fixing device

Abstract

To provide a configuration that can achieve both prevention of the occurrence of uneven glossiness and prevention of the occurrence of wrinkles in a recording material.SOLUTION: A slide member 304 slides with an inner peripheral surface of a belt 301 at a nip part N formed by the belt 301 and a pressure roller 305. A pad 303 is arranged inside the belt 301 to sandwich the slide member 304 and the belt 301 with the pressure roller 305, and backs up the slide member 304. When the value of load on the nip part N is defined as W [N], the Young's modulus of the slide member 304 as E [Mpa], the thickness of the slide member 304 as t [mm], the coefficient of friction between the slide member 304 and the belt 301 as μ, and the length of the slide member 304 with respect to the width direction of a recording material as L [mm], the slide member 304 satisfies the following formula.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a fixing device that fixes a toner image carried on a recording material onto the recording material. [Background technology]

[0002] A known fixing device has a nip formed between a belt and a nip-forming member such as a roller, which sandwiches and conveys the recording material, and heats and pressurizes the recording material as it passes through the nip. In this configuration, a sliding member slides on the inner circumferential surface of the belt in the nip, forming the nip between the belt and the nip-forming member.

[0003] In a fixing device, to ensure the quality of an image fixed to a recording material, it is necessary to suppress slippage between the recording material conveyed to the nip portion and the belt, and between the recording material and the nip-forming member. To achieve this, it is necessary to reduce the frictional force between the belt and the sliding member compared to the frictional force between the recording material and the belt and between the recording material and the nip-forming member. In particular, in a configuration having a wide nip in which the width of the nip is widened to increase heating efficiency, it is necessary to reduce the frictional force between the belt and the sliding member.

[0004] For example, Patent Document 1 discloses a configuration in which unevenness is formed on a sliding sheet that slides against the inner circumferential surface of the belt in the nip portion, thereby reducing the frictional force between the sliding sheet and the belt. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-52354 Summary of the Invention [Problem to be solved by the invention]

[0006] In the above-described configuration in which the belt and the sliding member slide against each other, if the frictional force acting on the nip portion becomes large, the sliding member may deform, causing pressure unevenness within the nip portion. Pressure unevenness can result in gloss unevenness in the fixed image. In particular, in a wide nip configuration in which the width of the nip portion is wide, the frictional force acting on the nip portion is likely to be large.

[0007] Increasing the rigidity of the sliding member is one way to suppress deformation of the sliding member, but if the rigidity of the sliding member is too high, it may not be able to follow the shape of the backup member that backs up the sliding member, which may result in localized high pressure within the nip portion. If the pressure within the nip portion becomes locally high, there is a risk of wrinkles occurring on the recording material passing through the nip portion.

[0008] SUMMARY OF THE INVENTION An object of the present invention is to provide a configuration that can simultaneously suppress the occurrence of uneven glossiness and the occurrence of wrinkles on the recording material. [Means for solving the problem]

[0009] The present invention is a fixing device that fixes a toner image carried on a recording material to the recording material, comprising: an endless, rotatable belt; a nip-forming member that contacts the outer peripheral surface of the belt to form a nip portion where the recording material is sandwiched and transported between the belt and the nip-forming member; a sliding member that slides against the inner peripheral surface of the belt at the nip portion; and a backup member that is disposed inside the belt so as to sandwich the sliding member and the belt between the sliding member and the nip-forming member and backs up the sliding member, wherein the sliding member satisfies the following formula:

number

number

[0010] According to the present invention, it is possible to simultaneously suppress the occurrence of uneven glossiness and the occurrence of wrinkles on the recording material. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a cross-sectional view showing a schematic configuration of an image forming apparatus according to an embodiment. [Figure 2] FIG. 2A is a cross-sectional view showing the schematic configuration of a fixing device according to an embodiment, and FIG. 2B is an enlarged schematic view showing a portion A of FIG. [Figure 3] 1A and 1B are a cross-sectional view and a plan view, respectively, schematically illustrating a sliding member according to an embodiment. [Figure 4] FIG. 2 is a plan view schematically showing the relationship between a sliding member and a belt according to the embodiment. [Figure 5] 1A is a cross-sectional view schematically showing the configuration around the nip portion when no pressure is applied, and FIG. 1B is a cross-sectional view schematically showing the configuration around the nip portion when pressure is applied. [Figure 6] 1A is a graph showing pressure distribution in an ideal nip portion in the width direction, and FIG. 1B is a plan view showing a schematic diagram of the relationship between forces when conveying a recording material in an ideal nip portion. [Figure 7] 10A is a graph showing pressure distribution in the width direction of the nip portion in the comparative example, and FIG. 10B is a plan view schematically showing the relationship of forces when conveying a recording material in the nip portion in the comparative example. [Figure 8] 1 is a table showing the conditions of various sliding members used in Verification 1. [Figure 9] Graph showing the results of Verification 1. [Figure 10] Graph showing the results of Verification 2. [Figure 11] Graph showing the results of Verification 3. [Figure 12] Graph showing the results of Verification 4. DETAILED DESCRIPTION OF THE INVENTION

[0012] The embodiment will be described with reference to Figures 1 to 12. First, the schematic configuration of an image forming apparatus according to the present embodiment will be described with reference to Figure 1.

[0013] [Image forming equipment] Image forming apparatus 1 is an electrophotographic full-color printer having four image forming units Pa, Pb, Pc, and Pd corresponding to the four colors of yellow, magenta, cyan, and black. In this embodiment, the image forming units Pa, Pb, Pc, and Pd are arranged in tandem along the rotation direction of an intermediate transfer belt 204 (described later). Image forming apparatus 1 forms a toner image (image) on a recording material in response to an image signal from an image reading unit (document reading device) 2 connected to image forming apparatus main body 3 or from a host device such as a personal computer connected to image forming apparatus main body 3 so as to be able to communicate with the image forming apparatus main body 3. Examples of recording materials include sheet materials such as paper, plastic film, and cloth.

[0014] The image forming apparatus 1 comprises an image reading unit 2 and an image forming apparatus main body 3. The image reading unit 2 reads an original placed on a platen glass 21. Light emitted from a light source 22 is reflected by the original and forms an image on a CCD sensor 24 via optical components 23 such as a lens. This optical unit scans in the direction of the arrow, converting the original into a line-by-line electrical signal data stream. The image signal obtained by the CCD sensor 24 is sent to the image forming apparatus main body 3, where it is subjected to image processing in accordance with each image forming unit (described later) by a control unit 30. The control unit 30 also receives external inputs as image signals from external host devices such as a print server.

[0015] The image forming apparatus main body 3 includes multiple image forming units Pa, Pb, Pc, and Pd, and each image forming unit forms an image based on the image signal. That is, the image signal is converted into a laser beam that is PWM (pulse width modulation) controlled by a control unit 30. A polygon scanner 31 serving as an exposure device scans the laser beam in accordance with the image signal. The laser beam is then irradiated onto photosensitive drums 200a to 200d serving as image carriers of each image forming unit Pa to Pd.

[0016] Note that Pa is a yellow (Y) image forming unit, Pb is a magenta (M) image forming unit, Pc is a cyan (C) image forming unit, and Pd is a black (Bk) image forming unit, each forming an image of the corresponding color. Since the image forming units Pa to Pd are substantially identical, the Y image forming unit Pa will be described in detail below, and descriptions of the other image forming units will be omitted. In the image forming unit Pa, a toner image is formed on the surface of the photosensitive drum 200a based on an image signal, as will be described below.

[0017] A charging roller 201a, which serves as a primary charger, charges the surface of the photosensitive drum 200a to a predetermined potential to prepare for the formation of an electrostatic latent image. A laser beam from a polygon scanner 31 forms an electrostatic latent image on the surface of the photosensitive drum 200a, which has been charged to a predetermined potential. A developing unit 202a develops the electrostatic latent image on the photosensitive drum 200a to form a toner image. A primary transfer roller 203a discharges electricity from the back surface of the intermediate transfer belt 204 and applies a primary transfer bias of opposite polarity to the toner, transferring the toner image on the photosensitive drum 200a onto the intermediate transfer belt 204. After transfer, the surface of the photosensitive drum 200a is cleaned by a cleaner 207a.

[0018] The toner image on intermediate transfer belt 204 is then conveyed to the next image forming station, where the toner images of each color formed at each image forming station are transferred in the order of Y, M, C, and Bk, forming a four-color image on the surface. The toner image that has passed through Bk image forming station Pd, which is located at the most downstream side in the rotation direction of intermediate transfer belt 204, is conveyed to a secondary transfer station made up of a pair of secondary transfer rollers 205 and 206. In the secondary transfer station, a secondary transfer electric field of opposite polarity to the toner image on intermediate transfer belt 204 is applied, thereby secondarily transferring the toner image onto the recording material.

[0019] The recording material is stored in a cassette 9, and the recording material fed from the cassette 9 is transported to a registration unit 208, which is made up of, for example, a pair of registration rollers, and waits at the registration unit 208. Thereafter, the timing of the registration unit 208 is controlled to align the position of the toner image on the intermediate transfer belt 204 with the position of the paper, and the recording material is transported to a secondary transfer unit.

[0020] The recording material onto which the toner image has been transferred in the secondary transfer section is transported to a fixing device 8, where the toner image carried on the recording material is fixed to the recording material by heating and pressing. The recording material that has passed through the fixing device 8 is discharged onto a discharge tray 7. When forming images on both sides of the recording material, after the toner image has been transferred and fixed onto the first side (front side) of the recording material, the recording material is turned over via a reversing conveyance section 10, and the toner image is transferred and fixed onto the second side (rear side) of the recording material, and the recording material is then stacked on the discharge tray 7.

[0021] As described above, the control unit 30 controls the entire image forming apparatus 1. The control unit 30 can also perform various settings based on input from the operation unit 4 of the image forming apparatus 1. The control unit 30 has a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory). The CPU controls each unit by reading a program corresponding to a control procedure stored in the ROM. The RAM stores working data and input data, and the CPU performs control by referring to the data stored in the RAM based on the aforementioned programs.

[0022] [Fixing device] Next, the configuration of the fixing device 8 in this embodiment will be described with reference to Figures 2(a) and (b). In this embodiment, a fixing device of a belt heating type using an endless belt is adopted. In Figure 2(a), the X direction indicates the conveyance direction of the recording material P (not shown in the figure), the Y direction indicates the width direction of the recording material that intersects with the conveyance direction of the recording material (orthogonal in this embodiment), and the Z direction indicates the pressure direction in which the recording material is pressed at the nip portion N. In this embodiment, the X direction, Y direction, and Z direction are each orthogonal to each other.

[0023] The fixing device 8 includes a fixing belt (hereinafter referred to as "belt") 301, a stay 302, a pressure pad (hereinafter referred to as "pad") 303, a sliding member 304, a pressure roller 305, a heating roller 307, and a thermistor 308. The belt 301 is an endless, rotatable heating rotor. The pressure roller 305, which serves as a nip portion forming member, is a pressure rotor that contacts the outer circumferential surface of the belt 301 to form a nip portion N between the belt 301 and the pressure roller 305, which sandwiches and conveys the recording material.

[0024] Sliding member 304 slides against the inner circumferential surface of belt 301 at nip portion N. Pad 303, serving as a backup member, is disposed inside belt 301 so as to sandwich sliding member 304 and belt 301 between it and pressure roller 305, thereby backing up sliding member 304. Sliding member 304 is disposed so as to cover the outer circumferential surface of pad 303 facing belt 301. Stay 302 is disposed inside belt 301, on the opposite side of nip portion N across pad 303, and supports pad 303. Heating roller 307 is disposed inside belt 301 so as to stretch belt 301, and heats belt 301. Thermistor 308, serving as a temperature detection member, detects the temperature of belt 301. Each component will be described in detail below.

[0025] The belt 301 has thermal conductivity, heat resistance, and the like, and is a thin-walled cylindrical shape. In this embodiment, as shown in FIG. 2(b), the belt 301 has a three-layer structure including a base layer 301a, an elastic layer 301b formed around the outer periphery of the base layer 301a, and a release layer 301c formed around the elastic layer 301b. The base layer 301a is, for example, 80 μm thick and made of polyimide resin (PI). The elastic layer 301b is, for example, 300 μm thick and made of silicone rubber. The release layer 301c is, for example, 30 μm thick and made of PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin) as a fluororesin. The belt 301 is stretched by a pad 303 and a heating roller 307. In this embodiment, the outer diameter of the belt 301 is 150 mm.

[0026] The pad 303 is disposed inside the belt 301 so as to face the pressure roller 305 across the belt 301, and forms a nip N between the belt 301 and the pressure roller 305, where the recording material is nipped and conveyed. In this embodiment, the pad 303 is a generally plate-shaped member that is long in the width direction of the belt 301 (the longitudinal direction intersecting the rotation direction of the belt 301, the direction of the rotation axis of the heating roller 307). The pad 303 is pressed against the pressure roller 305 across the belt 301, thereby forming the nip N. The pad 303 is made of LCP (liquid crystal polymer) resin. The pad 303 has a crown shape in a direction perpendicular to the conveyance direction so as to compensate for deformation due to bending of the stay 302 when pressure is applied. A sliding member 304 is interposed between the pad 303 and the belt 301. Details of the sliding member 304 will be described later.

[0027] Pad 303 is supported by stay 302, which serves as a support member and is disposed inside belt 301. That is, stay 302 is disposed on the opposite side of pad 303 from pressure roller 305, and supports pad 303. Such stay 302 is a reinforcing member having long rigidity along the longitudinal direction of belt 301, and contacts pad 303 to back up pad 303. That is, stay 302 provides strength to pad 303 when pad 303 is pressed by pressure roller 305, thereby ensuring the pressure at nip portion N.

[0028] The stay 302 is made of a metal such as stainless steel, and has a substantially rectangular cross section (transverse cross section) perpendicular to the longitudinal direction of the stay 302, which intersects with the rotation direction of the belt 301. For example, the stay 302 is made of a 3 mm thick drawn material of SUS304 (stainless steel), and the transverse cross section is formed into a hollow, substantially square shape to ensure strength. Note that the stay 302 may also be formed into a substantially rectangular cross section by combining multiple metal plates and fixing them together by welding or the like. The material of the stay 302 is not limited to stainless steel as long as strength can be ensured.

[0029] Heating roller 307 is disposed inside belt 301 and stretches belt 301 together with pad 303. Heating roller 307 is formed into a cylindrical shape from a metal such as aluminum or stainless steel, and has a halogen heater 306 disposed inside as a heat source for heating belt 301. Heating roller 307 is heated to a predetermined temperature by halogen heater 306.

[0030] The heating roller 307 has a rotation center at one end or near the center in the longitudinal direction, and rotates relative to the belt 301 to generate a tension difference between the front and rear, thereby also serving as a steering roller that controls the position of the belt 301 in the main scanning direction. The heating roller 307 is also biased by a spring supported by a frame (not shown), and serves as a tension roller that applies a predetermined tension to the belt 301.

[0031] In this embodiment, the heating roller 307 is formed, for example, from a stainless steel pipe having a thickness of 1 mm. Although a single halogen heater 306 is sufficient, it is preferable to have multiple heaters in consideration of controlling the temperature distribution in the longitudinal direction (direction of the rotation axis) of the heating roller 307. The multiple halogen heaters 306 have different light distributions in the longitudinal direction, and the lighting ratio is controlled according to the size of the recording material. In this embodiment, three halogen heaters 306 are provided. Note that the heat source is not limited to a halogen heater, and other heaters capable of heating the heating roller 307, such as a carbon heater, may also be used.

[0032] Belt 301 is heated by heating roller 307 heated by halogen heater 306, and is controlled to a predetermined target temperature according to the type of recording material based on temperature detection by thermistor 308. Thermistor 308 is arranged facing the outer circumferential surface of belt 301 near the center in the width direction of belt 301, through which recording materials of all sizes that can be fixed by fixing device 8 pass. Thermistor 308 detects the temperature of belt 301, and control unit 30 controls the power supplied to halogen heater 306 so that the temperature detected by thermistor 308 becomes the target temperature. Thermistor 308 may be a non-contact sensor arranged in proximity to the outer circumferential surface of belt 301, or a contact sensor arranged in contact with the outer circumferential surface of belt 301.

[0033] The pressure roller 305 rotates in contact with the outer circumferential surface of the belt 301 and also serves as a driving rotor that applies a driving force to the belt 301. In this embodiment, the heat roller 307 is also driven by a drive source (e.g., a drive motor) and applies a driving force to the belt 301. However, the application of a driving force to the heat roller 307 may be omitted. The pressure roller 305 is a roller comprising a core (shaft) 305c, an elastic layer 305b on the outer periphery of the core 305c, and a release layer 305a on the outer periphery of the elastic layer 305b. The core 305c is made of stainless steel, for example, with a diameter of 72 mm. The elastic layer 305b is made of conductive silicone rubber, for example, with a thickness of 8 mm. The release layer 305a is made of a fluororesin, such as PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin), with a thickness of 100 μm. The pressure roller 305 is rotatably supported by a frame (not shown) of the fixing device 8, has a gear fixed to one end, and is connected to a drive source (e.g., a drive motor, not shown) via the gear to be rotated.

[0034] The fixing device 8 sandwiches the recording material P carrying a toner image in a nip portion N formed between the belt 301 and the pressure roller 305, and heats the toner image while transporting the recording material P. In this way, the fixing device 8 fixes the toner image to the recording material P while sandwiching and transporting the recording material P. Therefore, the fixing device 8 must be able to both apply heat and pressure and transport the recording material P. A driving source (not shown) presses the pressure roller 305 against the sliding member 304 via the belt 301. In this embodiment, the pressure force (NF) at the nip portion N during image formation, i.e., the load value applied between the pad 303 and the pressure roller 305, is 1600 N, and the width of the nip portion N in the X direction (the transport direction of the recording material) is set to 24.5 mm, and the width in the Y direction (the width direction of the recording material) is set to 326 mm.

[0035] The length of nip portion N in the conveying direction (X direction) (nip width) is formed by pressing sliding member 304 against pressure roller 305 via belt 301. If the pressure force (NF) at nip portion N falls below 900 N, a non-contact area begins to occur between sliding member 304 and belt 301, making it impossible to maintain the required nip width. For this reason, in this embodiment, the pressure force (NF) applied to nip portion N, i.e., the load value applied between pad 303 and pressure roller 305, is set to be 900 N or greater.

[0036] [Sliding member] The detailed configuration of the sliding member 304 is shown in Figures 3(a) and (b). Figure 3(a) is a cross-sectional view of the sliding member 304 cut in the conveyance direction, and Figure 3(b) is a plan view of the sliding member 304 seen from the contact surface side between the belt 301 and the sliding member 304. The sliding member 304 is fixed to the stay 302 via the pad 303 with screws or the like. The sliding member 304 may be integral with the pad 303. Alternatively, a portion of the sliding member 304 may be fixed to the stay 302 or the pad 303. For example, both ends of the sliding member 304 in the Y direction (width direction) may be fixed to the pad 303 with screws or the like.

[0037] The sliding member 304 is composed of a base layer 304a and a sliding layer 304c. A plurality of protrusions (embossed portions) 304b that protrude toward the inner circumferential surface of the belt 301 are formed on the side of the base layer 304a that slides against the belt 301. The sliding layer 304c is provided so as to cover the surface of the base layer 304a that slides against the belt 301 (including the plurality of protrusions 304b).

[0038] The base layer 304a only needs to have sufficient heat resistance and strength. Materials include stainless steel, copper, aluminum, engineering plastics (PI (polyimide), PEEK (polyether ether ketone), LCP (liquid crystal polymer), etc.), and in this embodiment, metal materials such as stainless steel, copper, and aluminum are desirable. In this embodiment, PI with a thickness of 300 μm is used as the base layer 304a.

[0039] The plurality of protrusions 304b are integrally formed from the same material as the base layer 304a, and are arranged in a plurality of positions across the conveyance direction (X direction) of the recording material in the nip portion N and across the width direction (Y direction) of the recording material that intersects with the conveyance direction. The plurality of protrusions 304b are arranged so that the total area of ​​the tip surfaces of all of the plurality of protrusions 304b is 90% or more of the total area of ​​the inner circumferential surface of the belt 301 and the surface of the sliding member 304 that slides against it.

[0040] The distance (interval) d between the centers of adjacent protrusions 304b in the conveying direction and the distance (interval) d between the centers of adjacent protrusions 304b in the width direction are each 1.25 mm or more, preferably 1.4 mm or more. In this embodiment, to ensure uniform sliding with the belt 301, the intervals between the multiple protrusions 304b are the same in the conveying direction and the width direction, and each interval d is 1.4 mm. However, if the pressure distribution differs between the width direction and the conveying direction, the intervals between the protrusions in each direction may be changed depending on the pressure distribution.

[0041] By providing multiple protrusions 304b on the surface of sliding member 304 that slides against belt 301, the contact area between sliding member 304 and belt 301 is reduced, thereby reducing the sliding resistance between sliding member 304 and belt 301.

[0042] The sliding layer 304c is preferably made of a coating agent such as a fluororesin (PTFE (polytetrafluoroethylene), PFA, etc.) to achieve low friction. In this embodiment, the sliding member 304 is formed by coating the surface of the base layer 304a, which includes a plurality of protrusions 304b, with PTFE having a thickness of 20 μm. In this embodiment, a lubricant is applied to the inner surface of the belt 301. This allows the belt 301 to slide smoothly against the sliding member 304. Silicone oil is used as the lubricant.

[0043] Furthermore, the sliding member 304 of this embodiment is configured to cover the pad 303 regardless of whether it is inside or outside the nip portion N. That is, the entire surface of the pad 303 that faces the belt 301 is covered by the sliding member 304, except for the surface opposite the nip portion N. The sliding member 304 may be disposed only in the nip portion N of the surface of the pad 303. Furthermore, although the multiple protrusions 304b are disposed over the entire area of ​​the sliding member 304, if the sliding member 304 is larger than the nip portion N, the multiple protrusions 304b may be disposed only in the nip portion N.

[0044] [Causes of pressure unevenness due to deformation of sliding components] Next, the principle of the generation of pressure unevenness due to deformation of the sliding member 304 will be explained using Figure 4. Figure 4 is a view of the nip portion N as seen from above in Figure 2, and for the sake of explanation, the stay 302 and pad 303 are not shown. The sliding member 304 is pressed by the pressure roller 305 through the belt 301 toward the pad 303 (Z direction) with a pressure force W. The belt 301 is driven by the heating roller 307 and moves in the belt conveyance direction (X direction). If the coefficient of friction between the belt 301 and the sliding member 304 is μ, then the sliding member 304 is subjected to a friction force μW in the movement direction of the belt 301.

[0045] At this time, if the friction force μW becomes large, depending on the rigidity of the sliding member 304, it may buckle and deform in the conveyance direction (X direction), causing localized pressure unevenness in the nip portion. It was found that if the recording material passes through the nip portion in a state where this localized pressure unevenness occurs, the influence of the pressure unevenness causes gloss unevenness in the image.

[0046] In conventional fixing devices, the pressure applied is relatively small, at around 600 N, so even if the sliding member deforms, it is minimal, resulting in minor gloss unevenness and not a problem. However, in fixing devices with a wide nip to accommodate higher speeds, it has been found that this phenomenon becomes apparent when a high pressure of 900 N or more is applied due to the increased pressure area. That is, in a wide nip configuration such as fixing device 8 of this embodiment, which requires a high pressure of 900 N or more, if the rigidity of sliding member 304 is low, deformation of sliding member 304 may cause pressure unevenness. This pressure unevenness then causes gloss unevenness.

[0047] [Rigidity of sliding components] In order to prevent the occurrence of uneven glossiness as described above, it is conceivable to reduce the amount of deformation by increasing the rigidity of the sliding member 304. However, it has been found that if the rigidity of the sliding member 304 is made too high, the pressure distribution in the width direction (Y direction) becomes unstable, which may result in conveyance problems such as wrinkles in the recording material.

[0048] This phenomenon will be explained using FIGS. 5(a) to 7(b). FIGS. 5(a) and 5(b) are cross-sectional views of the nip portion viewed from the conveyance direction, with each component exaggerated. FIG. 5(a) schematically illustrates the nip portion N when no pressure is applied by the pressure roller 305 (non-pressurized state), and FIG. 5(b) illustrates the nip portion N when pressure is applied (pressurized state). As shown in FIG. 5(a), the pad 303 has a crown shape that is convex downward toward the pressure roller 305 when no pressure is applied. When the pressure roller 305 is applied, the stay 302 flexes due to the high load of the wide nip configuration, resulting in deformation as shown in FIG. 5(b). The crown shape of the pad 303 is optimized so that the desired pressure distribution in the width direction (Y direction) within the nip portion N is achieved when the stay 302 flexes.

[0049] The pressure distribution in the width direction (Y direction) within the nip N and the conveying force of the recording material P will be explained using Figures 6(a) and (b). Figure 6(a) is a graph of the ideal pressure distribution in the width direction when the crown shape of the pad 303 is optimized. Figure 6(b) schematically shows the distribution of the conveying force of the recording material P in the nip N, the force acting on the recording material at the entrance of the nip N, and the rotational moment acting on the recording material P. The length of the arrow in the distribution of the conveying force of the recording material P in the nip N indicates the magnitude of the conveying force.

[0050] In the nip portion N, by setting the pressure higher at the edges in the width direction than at the center, the conveying force of the recording material P increases as it approaches the edges in the width direction, as shown in Figure 6(b). As a result, even when a recording material with low rigidity is conveyed to the nip portion N, it is possible to prevent wrinkles from occurring in the recording material by applying a moment that spreads the recording material at the entrance of the nip portion N.

[0051] On the other hand, as a comparative example, the widthwise pressure distribution and the conveying force of the recording material when wrinkles occur in the recording material when the rigidity of the sliding member 304 is high will be described using Figures 7(a) and (b). Figure 7(a) is a graph of the widthwise pressure distribution in the comparative example. Figure 7(b), like Figure 6(b), schematically shows the distribution of the conveying force of the recording material P in the nip portion N, the force acting on the recording material at the entrance of the nip portion N, and the rotational moment acting on the recording material P in the configuration of the comparative example.

[0052] Unlike the widthwise pressure distribution in Figure 6(a), the widthwise pressure distribution in Figure 7(a) has a locally high pressure area at part α, which results in a conveying force distribution as shown in Figure 7(b), and the rotational moment of this conveying force distribution causes inward forces to interact at the entrance of the nip N, causing wrinkles in the recording material P at part β.

[0053] The reason why the pressure becomes locally high at the portion α in Fig. 7(a) will now be explained. Consider the case in Fig. 5(b) where the pressure roller 305 presses the stay 302 side. If the rigidity of the sliding member 304 is low, the sliding member 304 deforms in accordance with the crown shape optimized by the pad 303, and therefore the sliding member 304 itself has little effect on the pressure distribution in the width direction.

[0054] However, if the sliding member 304 has high rigidity, it will not deform to conform to the crown shape optimized by the pad 303. This means that the sliding member 304 itself may affect the pressure distribution in the width direction, resulting in locally high pressure. This phenomenon is less likely to occur if the sliding member 304 has high rigidity but is not warped and has low flatness. However, variations during mass production and handling during the process can cause some warping, resulting in high flatness. This causes the sliding member 304 to be unable to conform to the shape of the pad 303 in some areas, resulting in locally high pressure as shown in Figure 7(a), which can cause wrinkles in the recording material.

[0055] [Methods for measuring various parameters] Below, methods for measuring various important parameters in this embodiment, namely, Young's modulus E and thickness t of the sliding member, will be described. First, a method for measuring Young's modulus E of the sliding member 304 will be described. When measuring Young's modulus, a tensile tester AG-X manufactured by Shimadzu Corporation was used. The attachment of the tensile tester AG-X was a 500 N load cell and a 500 N mechanical parallel clamping grip. When conducting the tensile test, the temperature of the thermostatic chamber was set to 180°C, the pulling speed was set to 5 mm / min, and the results of a thickness measurement were input in advance.

[0056] The thickness measurement used above was the thickness of the base layer 304a, which had the greatest strength among the layers of the sliding member 304. The elastic modulus was calculated within a load cell test force range of 10 N to 15 N. This measurement began after confirming that the temperature setting of the thermostatic chamber for the tensile test had reached 180°C. The dumbbell shape used in the tensile test was specified in JIS K7139-A24. After 10 measurements were taken in both the longitudinal and lateral directions of the sliding member 304, the average values ​​were calculated to determine the elastic modulus in the longitudinal and lateral directions. The Young's modulus E [MPa] of the sliding member 304 in this measurement was the average value in the longitudinal and lateral directions. If the sliding member 304 has multiple types of sliding layers, all of them are treated as a single layer, and the above procedure is followed.

[0057] Next, a method for measuring the thickness t of the sliding member 304 will be described. When measuring the thickness t, the sliding member 304 was cut into four equal parts in the Y direction (width direction) to create samples. The thickness t of the sliding member 304 was measured using a digital length measuring device CT6001 manufactured by HEIDENHAIN Corporation. The temperature and humidity conditions during the measurement were 23°C and 30%. The thickness of each of the four equal parts was measured in the X direction (transport direction), and the average value of the four equal parts was then taken as the thickness t [mm] of the sliding member 304. In this measurement, if there is a sliding layer 304c, as in the sliding member 304, the thickness of the base layer 304a excluding the sliding layer 304c is measured.

[0058] The method for measuring the friction coefficient μ of the sliding member 304 will be described. When measuring the friction coefficient μ, the sliding portion of the sliding member 304 was cut into a 5 mm square to prepare a sample. The friction coefficient was measured using a friction and wear tester FRP2100 manufactured by Rhesca Co., Ltd. The temperature of the measurement table was adjusted to 180°C to match the actual usage environment, and the belt 301 was cut into a circle with a diameter of 50 mm and attached to it so that the inner surface of the belt 301 would slide against the sample. The lubricant used was a lubricant with a dynamic viscosity of 1000 mm. 2 Silicone oil of 250 mm / s was applied to the sliding surface of the belt 301, and the friction coefficient was measured in a constant rotational speed mode at 250 mm / s and a load of 10 N.

[0059] [Image confirmation verification method] The following describes an evaluation method for determining whether or not an abnormal image is produced in the image forming apparatus 1 shown in Fig. 1. During the verification, a fixing device 8 with necessary parameters (E, t, W) set was installed. W is the load applied to the nip portion N. The method for changing the parameters will be described later in the description of the embodiments.

[0060] The peripheral speed of pressure roller 305 mounted in fixing device 8 was set to 250 mm / sec, and the control unit 30 controlled the temperature detected by a contact thermistor (not shown) in contact with heating roller 307 to be 195°C. At this time, the surface of belt 301 was monitored with an infrared radiation thermometer IT-340 manufactured by HORIBA, and it was confirmed that the surface temperature of belt 301 was 180°C. Then, a black toner image was formed on the recording material, and this toner image was fixed to the recording material in fixing device 8. An examination was performed by visually checking the presence or absence of image defects on the output black sample image.

[0061] The recording material used was OHT film VF-1420N A4 size manufactured by KOKUYO Co., Ltd., to make it easier to see image defects caused by pressure unevenness. A high-density, all-over black toner image was formed on the recording material as a sample image to make it easier to see image defects caused by pressure unevenness. After using the fixing device 8, if uneven gloss or density was observed near the center of the sample image, it was determined that an image defect had occurred due to pressure unevenness caused by deformation of the sliding member 304.

[0062] The gloss unevenness was ranked as follows: no gloss unevenness at all was ranked 5; slight gloss unevenness was ranked 4; gloss unevenness was more visible than rank 4 but not visible when viewed from the back of the OHT film was ranked 3; gloss unevenness was clearly visible from the back of the OHT film was ranked 1; and a level between ranks 3 and 1 was ranked 2.

[0063] In addition, to check for the occurrence of wrinkles in the recording material, a Canon CS-520 A3T (basis weight 52 g / m) recording material with a relatively low stiffness was used.2 A black halftone image was simultaneously output onto the recording material of 10 sheets. Ten sheets were passed through the fixing device 8 in succession, and the rate of wrinkles was checked.

[0064] [Verification procedure and results] The following describes the verification procedure using the configuration of this embodiment, and the results of the verification performed by changing the thickness and Young's modulus E of the sliding member 304. The verification flow for Verifications 1 to 4 will be explained in order. First, various parameters of the fixing device 8 were determined, and the load value W applied to the nip portion N was set accordingly. The sliding member 304 was prepared by measuring its Young's modulus E, thickness t, and friction coefficient μ. Next, the sliding member 304 was attached to the fixing device 8, and an image confirmation verification was performed, and each was judged.

[0065] Figure 8 shows the conditions for the various sliding members used in the verification. Figures 9 to 12 show graphs showing the results of verifications 1 to 4. A circle in the graph plot indicates that no uneven gloss or wrinkles occurred in the image evaluation results, and an × in the graph plot indicates that uneven gloss or wrinkles occurred in the image evaluation results.

[0066] [Verification 1] In Verification 1, as shown in Figure 8, the material and thickness of the base layer 304a of the sliding member 304 were changed to change the rigidity and check the occurrence level of gloss unevenness, a cause of pressure unevenness. All of the sliding members 304 used were coated with PTFE as the sliding layer 304c. The friction coefficient μ was 0.03 due to the PTFE coating. The load value W was set to 1600 N, so the friction force acting on the sliding portion between the sliding member 304 and belt 301 was μW = 48 N. The occurrence rank of gloss unevenness was evaluated according to the criteria described in the image confirmation verification method.

[0067] Pressure unevenness, which causes gloss unevenness, occurs due to the influence of deformation of the sliding member 304. If the rigidity of the sliding member 304 can be ensured against the frictional force acting on it, the sliding member 304 will not deform, and pressure unevenness and gloss unevenness will not occur. In order to investigate the relationship between frictional force and the rigidity of the sliding member 304, a parameter called the allowable frictional force ratio has been defined and is listed in the table of Figure 8. The allowable frictional force ratio is expressed by the following equation (1).

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[0068] The numerator of equation (1) is the friction force associated with the sliding member 304, and the denominator is an index that takes into account the flexural rigidity of the sliding member 304, which is composed of the Young's modulus E [MPa], the thickness t [mm], and the length L [mm] in the width direction perpendicular to the conveying direction of the recording material.

[0069] Figure 9 shows a graph showing the relationship between the allowable friction force ratio and image rank, based on the results in Figure 8. From these results, it can be seen that as the allowable friction force ratio increases, the gloss unevenness rank decreases, and that in order to achieve a gloss unevenness rank of 5, where no gloss unevenness occurs, the allowable friction force ratio must be 1200 or less.

[0070] [Verification 2] In Verification 2, in order to investigate the relationship between the allowable frictional force ratio in more detail, the material of the base material layer 304a of the sliding member 304 was fixed to stainless steel, and the thickness and rigidity were changed to confirm the occurrence level of gloss unevenness, a cause of pressure unevenness. As in Verification 1, all of the sliding members 304 used were coated with PTFE as the sliding layer 304c. The friction coefficient μ was 0.03 due to the PTFE coating. The load value W was set to 1600 N, so the friction force acting on the sliding part was μW = 48 N.

[0071] 10 is a graph showing the relationship between the thickness t of the base material layer 304a of the sliding member 304 and the allowable frictional force ratio. From this result, it can be seen that as the thickness t increases, the allowable frictional force ratio decreases, and gloss unevenness does not occur at an allowable frictional force ratio of 1200 or less. From this result, it can be seen that by changing the thickness and Young's modulus of the sliding member 304 and setting the allowable frictional force ratio to 1200 or less, it is possible to avoid gloss unevenness caused by pressure unevenness.

[0072] [Verification 3] In Verification 3, to investigate the relationship between the load and the allowable frictional force ratio, the material of the base material layer 304a of the sliding member 304 was fixed to stainless steel, the thickness was fixed to 0.04 mm, and the rigidity was changed to confirm the level of gloss unevenness, a cause of pressure unevenness. As in Verification 1, all of the sliding members 304 used were coated with PTFE as the sliding layer 304c. The friction coefficient μ was 0.03 due to the PTFE coating. The load value W applied to the nip portion N was changed from 200 to 2000 N, and the frictional force μW applied to the sliding portion between the sliding member 304 and belt 301 was changed to investigate the relationship between the allowable frictional force ratio and image rank.

[0073] 11 is a graph showing the relationship between the allowable frictional force ratio and image rank. From this result, it can be seen that as the load value W applied to the nip portion N increases, the frictional force of the sliding portion increases, resulting in gloss unevenness. From this result, it can be seen that by changing the thickness t and Young's modulus E of the sliding member 304 according to the load value W applied to the nip portion N and setting them so that the allowable frictional force ratio is 1200 or less, it is possible to avoid gloss unevenness caused by pressure unevenness.

[0074] The results of verifications 1 to 3 showed that gloss unevenness can be prevented by satisfying the following formula (2) regarding the allowable frictional force ratio.

number

[0075] [Verification 4] In verification 4, in order to investigate the effect of wrinkling on the recording material when the rigidity of the sliding member 304 becomes too high, the material of the base layer 304a of the sliding member 304 was fixed to stainless steel, and a verification similar to verification 2 was performed. The thickness t of the sliding member 304 was changed in the range of 0.5 to 3.5 mm, and the level of wrinkling on the recording material was confirmed. As an index of the rigidity of the base layer 304a, the following equation (3) was used, which takes into account the second moment of area and takes into account local deformation in the width direction (Y direction).

number

[0076] The rigidity of the base layer 304a shown in formula (3) is composed of the Young's modulus E [MPa] and thickness t [mm] of the sliding member 304. FIG. 12 shows a graph representing the relationship between the thickness t of the base layer 304a of the sliding member 304 and the rigidity of the base layer 304a. In the plot of the graph, circles represent conditions under which no wrinkles occurred in the recording material, and crosses represent conditions under which wrinkles occurred in the recording material. From these results, it can be seen that if the thickness t of the base layer 304a of the sliding member 304 is thinner than 2.5 mm, wrinkles do not occur in the recording material, but if the thickness t is thicker than 3.0 mm, wrinkles occur in the recording material. Furthermore, from the graph of FIG. 12, the rigidity condition of the base layer 304a that prevents wrinkles from occurring in the recording material is 2.6×10 5 The results of Verification 4 show that the occurrence of wrinkles in the recording material can be suppressed by satisfying the following formula (4).

number

[0077] [Other embodiments] In the above embodiment, the sliding member 304 has been described as having the protrusions 304b to reduce the sliding resistance with the belt 301. However, the present invention is also applicable to a configuration in which the sliding member does not have the protrusions 304b. [Explanation of symbols]

[0078] 8. Fixing device 301 Belt 303 Pad (backup member) 304...Sliding member 304a...Base material layer 304b...Protrusion 304c···Sliding layer 305 Pressure roller (nip forming member)

Claims

1. A fixing device, comprising: an endless belt for heating a recording material; a rotatable pressure rotor that is in contact with an outer circumferential surface of the belt; a sliding member disposed inside the belt, forming a nip portion for sandwiching and conveying the belt between the pressing rotor and the sliding member, the sliding member sliding against an inner peripheral surface of the belt; the pressure rotating body cooperates with the belt to nip and convey the recording material at the nip portion, and fixes the toner image on the recording material to the recording material by applying heat and pressure to the recording material; The sliding member has a base material extending in the width direction of the belt, the base material is made of metal and has a plurality of protrusions protruding toward the pressure rotating body; When the load value applied to the nip portion is W [N], the Young's modulus of the sliding member is E [MPa], the thickness of the sliding member is t [mm], the friction coefficient between the sliding member and the belt is μ, and the length of the sliding member in the width direction is L [mm], the sliding member satisfies the following formula: A fixing device comprising: [0010] [0025]

2. The pressure applied to the nip portion is 900 N or more.

2. The fixing device according to claim 1,

3. The sliding member has a sliding layer on the surface of the base material, the sliding layer being in sliding contact with the inner circumferential surface of the belt.

3. The fixing device according to claim 1, wherein the fixing member is a fixing member having a fixing roller.

4. The sliding layer is made of a fluororesin.

4. The fixing device according to claim 3.

5. Further comprising a holding member for holding the sliding member, The holding member is made of resin.

5. The fixing device according to claim 3, wherein the fixing member is a fixing member having a fixing roller.

6. The retaining member is formed of a resin different from that of the sliding layer.

6. The fixing device according to claim 5,

7. The plurality of protrusions are provided so that the area of ​​the end face on the pressurizing rotor side is 90% or more of the total area of ​​the surface of the sliding member that slides against the inner circumferential surface of the belt.

7. The fixing device according to claim 1, wherein the fixing member is a fixing member having a fixing member.

8. In a cross section perpendicular to a conveying direction of the recording material, the holding member has a first region corresponding to a center portion of the nip portion and a second region corresponding to both ends of the nip portion and adjacent to the first region, The thickness of the first region is greater than the thickness of the second region.

7. The fixing device according to claim 5, wherein the fixing member is a fixing member having a fixing roller.

9. In a cross section perpendicular to a conveying direction of the recording material, the holding member has a crown shape that is convex toward the pressure rotating body.

7. The fixing device according to claim 5, wherein the fixing member is a fixing member having a fixing roller.

Images