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 for fixing a toner image carried on a recording material to the recording material.

Background Art

[0002] As a fixing device, a configuration is conventionally known in which a nip portion for sandwiching and conveying is formed by nip portion forming members such as a belt and a roller, and the recording material passing through the nip portion is heated and pressurized. Further, in this configuration, a nip portion is formed between the belt and the nip portion forming member by sliding a sliding member on the inner peripheral surface of the belt in the nip portion.

[0003] In a fixing device, in order to ensure the quality of an image to be fixed on a recording material, it is required to suppress slip between the recording material conveyed to the nip portion and the belt, and slip between the recording material and the nip portion forming member. For this purpose, it is required to make the frictional force between the belt and the sliding member smaller than the frictional forces between the recording material and the belt and between the recording material and the nip portion forming member. In particular, in a configuration having a wide nip in which the width of the nip portion is widened to improve the heating efficiency, it is required to make the frictional force between the belt and the sliding member smaller.

[0004] For example, Patent Document 1 discloses a configuration in which irregularities are formed on a sliding sheet that slides on the inner peripheral surface of a belt in a nip portion to reduce the frictional force between the sliding sheet and the belt.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] As described above, in a configuration where the belt and sliding member slide against each other, if the frictional force acting on the nip portion becomes large, the sliding member may deform, potentially causing uneven pressure within the nip portion. Uneven pressure can result in uneven gloss in the fixed image. In particular, in a wide-nip configuration where the width of the nip portion is increased, the frictional force acting on the nip portion tends to become larger.

[0007] To suppress deformation of the sliding member, one might consider increasing its rigidity. However, 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 it up, potentially leading to localized pressure increases within the nip. When localized pressure increases within the nip, wrinkles may form in the recording material passing through the nip.

[0008] The present invention aims to provide a configuration that can achieve both the suppression of uneven gloss and the suppression of wrinkle formation in the recording material. [Means for solving the problem]

[0009] One aspect of the present invention is a fixing device comprising: an endless belt for heating a recording material; a rotatable pressurizing rotating body that contacts the outer circumferential surface of the belt; and a sliding member disposed inside the belt, forming a nip portion that grips and conveys the belt between itself and the pressurizing rotating body, and sliding against the inner circumferential surface of the belt. A retaining member that holds the sliding member, The pressurized rotating body cooperates with the belt to grip and transport 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, and 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 projecting toward the pressurized rotating body, In a cross-section of the holding member perpendicular to the direction of transport of the recording material, the holding member has a convex crown shape toward the pressurizing rotating body. When the load 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 coefficient of friction 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 equation: Furthermore, the pressure applied to the nip portion is 900N or more. This fixing device is characterized by the following features.

number

[0010] According to the present invention, it is possible to achieve both suppression of the occurrence of gloss unevenness and suppression of the occurrence of wrinkles in the recording material. [Brief Description of the Drawings]

[0011] [Figure 1] Schematic cross-sectional view of the schematic configuration of the image forming apparatus according to the embodiment. <The [Figure 2] (a) Schematic cross-sectional view of the schematic configuration of the fixing device according to the embodiment, (b) Schematic view showing an enlarged view of part A in (a). [Figure 3] [[ID=The 27]]Schematic view showing the sliding member according to the embodiment, (a) Cross-sectional view, (b) Plan view. [Figure 4] Plan view schematically showing the relationship between the sliding member and the belt according to the embodiment. [Figure 5] (a) Cross-sectional view schematically showing the configuration around the nip portion when not pressurized, (b) Cross-sectional view schematically showing the configuration around the nip portion when pressurized. [[ID=The 34]] [Figure 6] (a) Graph showing the pressure distribution in the width direction of an ideal nip portion, (b) Plan view schematically showing the force relationship during conveyance of the recording material in an ideal nip portion. [Figure 7] (a) Graph showing the pressure distribution in the width direction of the nip portion in the comparative example, (b) Plan view schematically showing the force relationship during conveyance of the recording material in the nip portion in the comparative example. [Figure 8] 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. [Mode for Carrying Out the Invention]

[0012] Embodiments will be described with reference to FIGS. 1 to 12. First, the schematic configuration of the image forming apparatus according to the present embodiment will be described with reference to FIG. 1.

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

[0014] The image forming apparatus 1 includes an image reading unit 2 and an image forming apparatus main body 3. The image reading unit 2 reads a document placed on a document table glass 21, and light irradiated from a light source 22 is reflected by the document and imaged on a CCD sensor 24 via an optical system member 23 such as a lens. Such an optical system unit scans in the direction of the arrow to convert the document into an electric signal data string for each line. The image signal obtained by the CCD sensor 24 is sent to the image forming apparatus main body 3, and image processing is performed by a control unit 30 in accordance with each image forming unit described later. Further, the control unit 30 also receives an external input from an external host device such as a print server as an image signal.

[0015] The main body of the image forming apparatus 3 is equipped with multiple image forming units Pa, Pb, Pc, and Pd, and each image forming unit performs image formation based on the image signal described above. That is, the image signal is converted into a laser beam controlled by PWM (pulse width modulation) by the control unit 30. The polygon scanner 31, which acts as an exposure device, scans the laser beam according to the image signal. The laser beam is then irradiated onto the photosensitive drums 200a to 200d, which serve as image carriers for each of the image forming units Pa to Pd.

[0016] Pa is the image forming unit for yellow (Y), Pb is for magenta (M), Pc is for cyan (C), and Pd is for black (Bk), each forming an image of the corresponding color. Since the image forming units Pa to Pd are substantially the same, the details of the Y image forming unit Pa will be explained below, and the explanations 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 the image signal, as described below.

[0017] The charging roller 201a, acting as a primary charger, charges the surface of the photosensitive drum 200a to a predetermined potential, preparing it for electrostatic latent image formation. An electrostatic latent image is formed on the surface of the photosensitive drum 200a, which has been charged to the predetermined potential, by a laser beam from the polygon scanner 31. The developer 202a develops the electrostatic latent image on the photosensitive drum 200a to form a toner image. The primary transfer roller 203a discharges from the back of the intermediate transfer belt 204, applying a primary transfer bias with the opposite polarity to the toner, and transfers the toner image on the photosensitive drum 200a onto the intermediate transfer belt 204. After the transfer, the surface of the photosensitive drum 200a is cleaned by the cleaner 207a.

[0018] Furthermore, the toner image on the intermediate transfer belt 204 is transported to the next image forming section, and the toner images of each color formed in the respective image forming sections are transferred sequentially in the order of Y, M, C, and Bk, forming a four-color image on its surface. The toner image that has passed through the Bk image forming section Pd, which is the furthest downstream in the rotational direction of the intermediate transfer belt 204, is transported to a secondary transfer section consisting of a pair of secondary transfer rollers 205 and 206. In the secondary transfer section, a secondary transfer electric field with the opposite polarity to the toner image on the intermediate transfer belt 204 is applied, and the image is secondary transferred to the recording material.

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

[0020] The recording material onto which the toner image has been transferred in the secondary transfer unit is transported to the fuser unit 8, where it is heated and pressurized to fix the toner image onto the recording material. The recording material that has passed through the fuser unit 8 is discharged to the discharge tray 7. When image formation is performed on both sides of the recording material, once the transfer and fixing of the toner image to the first side (front) of the recording material is complete, the front and back sides of the recording material are reversed via the inversion transport unit 10, and the toner image is transferred and fixed to the second side (back) of the recording material, which is then loaded onto the discharge tray 7.

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

[0022] [Fusing device] Next, the configuration of the fixing device 8 in this embodiment will be described using Figures 2(a) and 2(b). In this embodiment, a belt heating type fixing device using an endless belt is employed. In Figure 2(a), the X direction is the transport direction of the recording material P (not shown in the figure), the Y direction is the width direction of the recording material which intersects (orthogonal in this embodiment) the transport direction of the recording material, and the Z direction is the pressurizing direction in which the recording material is pressurized at the nip portion N. In this embodiment, the X, Y, and Z directions are all orthogonal to each other.

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

[0024] The sliding member 304 slides against the inner circumferential surface of the belt 301 at the nip portion N. The pad 303, acting as a backup member, is positioned inside the belt 301 so as to sandwich the sliding member 304 and the belt 301 between itself and the pressure roller 305, thereby backing up the sliding member 304. The sliding member 304 is positioned so as to cover the outer circumferential surface of the pad 303 on the belt 301 side. The stay 302 is positioned inside the belt 301, on the opposite side of the nip portion N, sandwiching the pad 303, and supports the pad 303. The heating roller 307 is positioned inside the belt 301 so as to tension the belt 301 and heats the belt 301. The thermistor 308, acting as a temperature sensing member, detects the temperature of the belt 301. Each component will be described in detail below.

[0025] The belt 301 has thermal conductivity and heat resistance, and is a thin-walled cylindrical shape. In this embodiment, as shown in Figure 2(b), the belt 301 has a three-layer structure with a base layer 301a, an elastic layer 301b on the outer circumference of the base layer 301a, and a release layer 301c on the outer circumference of the release layer. 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. The outer diameter of the belt 301 is 150 mm in this embodiment.

[0026] The pad 303 is positioned inside the belt 301, facing the pressure roller 305 with the belt 301 in between, and forms a nip portion N that grips and conveys the recording material between the belt 301 and the pressure roller 305. In this embodiment, the pad 303 is a roughly plate-shaped member that is long along the width direction of the belt 301 (the longitudinal direction intersecting the rotation direction of the belt 301, and the rotation axis direction of the heating roller 307). The nip portion N is formed when the pad 303 is pressed against the pressure roller 305 with the belt 301 in between. The material of the pad 303 is LCP (liquid crystal polymer) resin. The pad 303 also has a crown shape in a direction perpendicular to the conveying direction in order to compensate for deformation due to the deflection of the stay 302 when pressurized. 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] The pad 303 is supported by a stay 302, which acts as a support member positioned inside the belt 301. That is, the stay 302 is positioned on the opposite side of the pad 303 from the pressure roller 305 and supports the pad 303. Such a stay 302 is a rigid reinforcing member that is long along the longitudinal direction of the belt 301, and it contacts the pad 303 to back it up. In other words, when the pad 303 is pressed by the pressure roller 305, the stay 302 provides strength to the pad 303 and ensures the applied pressure at the nip portion N.

[0028] The stay 302 is made of metal such as stainless steel, and its cross-section (transverse plane), perpendicular to the longitudinal direction of the stay 302 and intersecting the rotational direction of the belt 301, is approximately rectangular. For example, the stay 302 is made of 3mm thick extruded SUS304 (stainless steel), and its strength is ensured by forming the cross-section into a roughly square hollow shape. The stay 302 may also be formed into a roughly rectangular cross-section by combining multiple sheet metal pieces and fixing them to each other by welding or other means. Furthermore, the material of the stay 302 is not limited to stainless steel as long as strength can be ensured.

[0029] The heating roller 307 is positioned inside the belt 301 and, together with the pad 303, tensions the belt 301. The heating roller 307 is formed in a cylindrical shape from a metal such as aluminum or stainless steel, and a halogen heater 306 is disposed inside it as a heat source for heating the belt 301. The heating roller 307 is then heated to a predetermined temperature by the halogen heater 306.

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

[0031] In this embodiment, the heating roller 307 is formed from, for example, a stainless steel pipe with a thickness of 1 mm. While one halogen heater 306 may suffice, it is desirable to have multiple halogen heaters to control the temperature distribution along the longitudinal direction (rotation axis direction) of the heating roller 307. Multiple halogen heaters 306 have different light distributions along their longitudinal direction, and the lighting ratio is controlled according to the size of the recording material. In this embodiment, three halogen heaters 306 are arranged. Note that the heating source is not limited to halogen heaters; other heaters capable of heating the heating roller 307, such as carbon heaters, may also be used.

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

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

[0034] The fixing device 8 grips the recording material P, which carries the toner image, in a nip section N formed between the belt 301 and the pressure roller 305, and heats the toner image while transporting it. In this way, the fixing device 8 fixes the toner image to the recording material P while gripping and transporting it. Therefore, it is necessary to balance the function of applying heat and pressure with the function of transporting the recording material P. The pressure roller 305 is pressed against the sliding member 304 via the belt 301 by a drive source (not shown). In this embodiment, the applied pressure (NF) in the nip section N during image formation, i.e., the load value applied to the pad 303 and the pressure roller 305, is 1600N, and the width of the nip section N in the X direction (direction of transport of the recording material) is set to 24.5 mm, and the width in the Y direction (width direction of the recording material) is set to 326 mm.

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

[0036] [Sliding member] The detailed configuration of the sliding member 304 is shown in Figures 3(a) and 3(b). Figure 3(a) is a cross-sectional view of the sliding member 304 when cut in the conveying direction, and Figure 3(b) is a plan view of the sliding member 304 as seen from the contact surface side between the belt 301 and the sliding member 304. The sliding member 304 is, as a retaining member The sliding member 304 is fixed to the stay 302 via the pad 303 using screws or the like. The sliding member 304 may be integrated with the pad 303. Alternatively, the sliding member 304 may be partially 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. On the side of the base layer 304a that slides against the belt 301, a plurality of protrusions (embossed portions) 304b are formed that project toward the inner circumferential surface of 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. Examples of materials include stainless steel, copper, aluminum, and engineering plastics (PI (polyimide), PEEK (polyetheretherketone), LCP (liquid crystal polymer), etc.), and in this embodiment, metallic materials such as stainless steel, copper, and aluminum are preferred. In this embodiment, a PI layer with a thickness of 300 μm was used as the base layer 304a.

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

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

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

[0042] The sliding layer 304c is preferably a coating agent such as a fluororesin (PTFE (polytetrafluoroethylene), PFA, etc.) to achieve low friction. In this embodiment, the sliding member 304 was formed by coating the surface of a base layer 304a containing a plurality of protrusions 304b with PTFE that is 20 μm thick. In this embodiment, a lubricant is applied to the inner surface of the belt 301. As a result, the belt 301 slides smoothly against the sliding member 304. Silicone oil was used as the lubricant.

[0043] Furthermore, the sliding member 304 in this embodiment is configured to cover the pad 303 both inside and outside the nip portion N. That is, the entire surface of the pad 303 facing the belt 301 is covered by the sliding member 304, except for the surface of the pad 303 opposite to the nip portion N. The sliding member 304 may also be placed only on the surface of the pad 303 that is on the nip portion N. In addition, although the multiple protrusions 304b are placed over the entire surface of the sliding member 304, if the sliding member 304 is larger than the nip portion N, the multiple protrusions 304b may be placed only on the nip portion N.

[0044] [Factors causing pressure unevenness due to deformation of sliding members] Next, the principle 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 from above in Figure 2, and the stay 302 and pad 303 are not shown for explanatory purposes. The sliding member 304 is pressurized by the pressure roller 305 with a pressure W in the direction of the pad 303 (Z direction) via the belt 301. The belt 301 is driven by the heating roller 307 and moves in the belt transport direction (X direction). If the coefficient of friction between the belt 301 and the sliding member 304 is μ, the sliding member 304 will be subjected to a frictional force μW in the direction of movement of the belt 301.

[0045] At this time, if the frictional force μW becomes large, depending on the rigidity of the sliding member 304, it may buckle and deform in the transport direction (X direction), causing localized pressure unevenness in the nip section. It was found that when the recording material passes through the nip section with this localized pressure unevenness present, the gloss unevenness in the image is caused by the effect of the pressure unevenness.

[0046] In conventional fixing devices, the pressing force is relatively small, around 600N, so even if the sliding member deforms, it is only slight and does not cause significant gloss unevenness. 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 900N or more is applied due to the increased pressurized area. In other words, in a wide nip configuration requiring a high pressing force of 900N or more, such as fixing device 8 in this embodiment, if the rigidity of the sliding member 304 is low, there is a risk of pressure unevenness occurring due to deformation of the sliding member 304. This pressure unevenness then becomes the cause of gloss unevenness.

[0047] [Regarding the rigidity of sliding members] To prevent the gloss unevenness described above, it is conceivable to increase the rigidity of the sliding member 304 and reduce the amount of deformation. 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 cause transport defects such as wrinkles in the recording material.

[0048] This phenomenon will be explained using Figures 5(a) to 7(b). Figures 5(a) and 5(b) are cross-sectional views of the nip section as seen from the conveying direction, with each component exaggerated. Figure 5(a) schematically shows the case when the nip section N is not pressurized by the pressure roller 305 (unpressurized), and Figure 5(b) schematically shows the case when the nip section N is pressurized (pressurized). As shown in Figure 5(a), the pad 303 has a crown shape that is convex downwards toward the pressure roller 305 side when unpressurized. When the pressure roller 305 is pressed, the stay 302 deforms as shown in Figure 5(b) due to deflection caused by the high load in the wide nip configuration. When the stay 302 deflects, the crown shape of the pad 303 is optimized so that the desired pressure distribution is achieved in the width direction (Y direction) within the nip section N.

[0049] The pressure distribution in the width direction (Y direction) within the nip section N and the transport 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 transport force distribution of the recording material P in the nip section N, the force acting on the recording material at the entrance of the nip section N, and the rotational moment acting on the recording material P. The length of the arrow in the transport force distribution of the recording material P in the nip section N indicates the magnitude of the transport force.

[0050] In the nip section N, the pressure at the ends is set higher than that at the center in the width direction, resulting in a configuration that increases the transport force of the recording material P as it approaches the ends in the width direction, as shown in Figure 6(b). This makes it possible to suppress the occurrence of wrinkles in the recording material by applying a moment to spread the recording material at the entrance of the nip section N, even when a recording material with low rigidity is transported to the nip section N.

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

[0052] Unlike the pressure distribution in the width direction in Figure 6(a), the pressure distribution in the width direction in Figure 7(a) shows a localized area of ​​high pressure at α. This results in a transport force distribution as shown in Figure 7(b), and the rotational moment of this transport force distribution causes internal forces to be exerted at the entrance of the nip section N, causing wrinkles to form in the recording material P at β.

[0053] Now, let's explain the reason why the pressure is locally high at point α in Figure 7(a). Consider the case in Figure 5(b) when the pressure roller 305 is pressurized towards the stay 302. If the rigidity of the sliding member 304 is low, the sliding member 304 deforms according to the crown shape optimized by the pad 303, so the influence of the sliding member 304 itself on the pressure distribution in the width direction is small.

[0054] However, if the rigidity of the sliding member 304 is high, the sliding member 304 does not deform to conform to the crown shape optimized by the pad 303, and the sliding member 304 itself may affect the pressure distribution in the width direction, causing localized pressure increases. This phenomenon has little effect even when the rigidity of the sliding member 304 is high, as long as there is no "warping" in the sliding member 304 and the flatness is low. However, due to variations in mass production and handling during the process, some "warping" inevitably occurs, resulting in high flatness. As a result, the sliding member 304 may not be able to partially conform to the shape of the pad 303, causing localized pressure increases as shown in Figure 7(a), which can lead to wrinkles in the recording material.

[0055] [Methods for measuring various parameters] The following describes the measurement methods for various parameters that are important in this embodiment, namely the Young's modulus E of the sliding member and the thickness t of the sliding member. First, the measurement method for the Young's modulus E of the sliding member 304 will be described. When measuring the Young's modulus, a Shimadzu AG-X tensile tester was used. The attachments for the AG-X tensile tester were a 500N load cell and a 500N mechanical parallel clamping chuck. When performing the tensile test, the constant temperature bath temperature was set to 180°C and the pulling speed to 5 mm / min, and the results of the thickness measurement were entered in advance.

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

[0057] Next, the method for measuring the thickness t of the sliding member 304 will be explained. 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 HEIDENHAIN CT6001 digital measuring instrument. The temperature and humidity conditions during measurement were 23 degrees Celsius and 30% humidity. For each of the four divided samples, the thickness was measured at four points in the X direction (conveying direction), and then the average value of these four points was 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] This section describes the method for measuring the friction coefficient μ of the sliding member 304. For the measurement of the friction coefficient μ, a sample was prepared by cutting a 5mm square section of the sliding portion of the sliding member 304. The friction coefficient was measured using a friction and wear testing machine FRP2100 manufactured by Resca Co., Ltd. To match the actual operating environment, the temperature of the testing platform was adjusted to 180°C. A belt 301 was cut into a Φ50mm circle and attached to the platform so that its inner surface slid against the sample. The kinematic viscosity of the lubricant used was 1000 mm². 2 A silicone oil with a viscosity of / s was applied to the sliding surface of belt 301, and the coefficient of friction was measured in constant rotational speed mode at 250 mm / s and under a load of 10 N.

[0059] [Image Verification Method] The evaluation method for determining the presence or absence of abnormal images in the image forming apparatus 1 shown in Figure 1 will be explained. During verification, a fixing device 8 with the necessary parameters (E, t, W) set was attached. W is the load applied to the nip portion N. The method for changing the parameters will be explained in the description of the embodiment below.

[0060] The peripheral speed of the pressure roller 305 mounted on the fixing device 8 was set to 250 mm / sec, and the control unit 30 controlled the contact thermistor (not shown) in contact with the heating roller 307 so that its detected temperature was 195°C. At that time, the surface of the belt 301 was monitored with a HORIBA IT-340 infrared thermometer, and it was confirmed that the surface temperature of the 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 the fixing device 8. A visual inspection was conducted to check for any image defects on the outputted black sample image.

[0061] To make image defects easier to see, KOKUYO's OHT film VF-1420N A4 size was used as the recording material. To make image defects caused by pressure unevenness easier to see, a sample image of a dense, entirely black toner image was formed on the recording material. After using the fixing device 8, if uneven gloss or density unevenness occurred 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] In terms of gloss unevenness, rank 5 was assigned to those with no unevenness at all, rank 4 to those with slight unevenness, rank 3 to those with more visible unevenness than rank 4 but not visible when checked from the back of the OHT film, rank 1 to those clearly visible from the back of the OHT film, and rank 2 to those between rank 3 and rank 1.

[0063] Furthermore, in order to check for wrinkle formation in the recording material, Canon Inc.'s CS-520 A3T (basis weight 52g / m²), which has relatively low rigidity, was used as the recording material. 2 A black halftone image was simultaneously printed onto the recording material. Ten images were passed through the fixing device 8 in succession, and the rate of wrinkle formation was checked.

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

[0065] Figure 8 shows the conditions for the various sliding members used in the verification. Figures 9 to 12 show graphs illustrating the results of verifications 1 to 4. A circle (○) in the graph plot indicates that no gloss unevenness or wrinkles occurred in the image evaluation results, while an "x" (×) indicates that gloss unevenness 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 alter its rigidity, thereby confirming the level of gloss unevenness caused by pressure unevenness. All sliding members 304 used were coated with PTFE as the sliding layer 304c. The coefficient of friction μ was 0.03 due to the PTFE coating. Since the load value W was set to 1600N, the frictional force applied to the sliding part between the sliding member 304 and the belt 301 was μW = 48N. The rank of gloss unevenness was evaluated according to the criteria described in the image verification method.

[0067] The pressure unevenness that causes the gloss unevenness is caused by the deformation of the sliding member 304. If the rigidity of the sliding member 304 can be ensured against the frictional force applied to the sliding member 304, the sliding member 304 will not deform, and therefore pressure unevenness and gloss unevenness will not occur. To investigate the relationship between the frictional force and the rigidity of the sliding member 304, a parameter called the allowable friction force ratio was defined and is shown in the table in Figure 8. The allowable friction force ratio is given by the following equation (1).

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[0068] The numerator of equation (1) is the frictional force applied to the sliding member 304, and the denominator is an index that takes into account the deflection stiffness of the sliding member 304, consisting of Young's modulus E [MPa], thickness t [mm], and length L [mm] in the width direction perpendicular to the transport direction of the recording material.

[0069] Figure 9 shows a graph illustrating the relationship between the allowable friction force ratio and the 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 in order to satisfy gloss unevenness rank 5, where no gloss unevenness occurs, the allowable friction force ratio must be 1200 or less.

[0070] [Verification 2] In Verification 2, to investigate the relationship of the allowable friction force ratio in more detail, the material of the base layer 304a of the sliding member 304 was fixed to stainless steel, and the thickness was changed to alter the rigidity, thereby confirming the level of gloss unevenness caused by pressure unevenness. As in Verification 1, all 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. Since the load value W was set to 1600N, the friction force applied to the sliding part was μW = 48N.

[0071] Figure 10 shows a graph illustrating the relationship between the thickness t of the base layer 304a of the sliding member 304 and the allowable friction force ratio. From this result, it can be seen that as the thickness t increases, the allowable friction force ratio decreases, and gloss unevenness does not occur when the allowable friction force ratio is 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 friction force ratio to 1200 or less, the occurrence of gloss unevenness due to pressure unevenness can be avoided.

[0072] [Verification 3] In Verification 3, to investigate the relationship between the allowable friction force ratio and the load, the material of the base layer 304a of the sliding member 304 was fixed to stainless steel, the thickness was fixed to 0.04 mm, and the level of gloss unevenness caused by pressure unevenness was confirmed by changing the rigidity. The sliding member 304 used in the same manner as in Verification 1 was all 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 to 200 to 2000 N, and the relationship between the allowable friction force ratio and the image rank was investigated while changing the friction force μW applied to the sliding part between the sliding member 304 and the belt 301.

[0073] Figure 11 shows a graph illustrating the relationship between the allowable friction force ratio and the image rank. From this result, it can be seen that as the load value W applied to the nip portion N increases, the friction force of the sliding portion increases, causing uneven gloss. 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 friction force ratio is 1200 or less, the occurrence of uneven gloss due to pressure unevenness can be avoided.

[0074] The results of verifications 1-3 showed that the occurrence of uneven gloss can be prevented by satisfying the following equation (2) regarding the allowable friction force ratio.

number

[0075] [Verification 4] In Verification 4, to investigate the effect of wrinkles in 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 the same verification as in Verification 2 was performed. The thickness t of the sliding member 304 was changed within the range of 0.5 to 3.5 mm, and the level of wrinkle formation in the recording material was checked. As an indicator of the rigidity of the base layer 304a, the following equation (3), which takes into account the second moment of area and local deformation in the width direction (Y direction), was used.

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[0076] The stiffness of the base layer 304a shown in equation (3) is determined by the Young's modulus E [MPa] and thickness t [mm] of the sliding member 304. Figure 12 shows a graph illustrating the relationship between the thickness t of the base layer 304a of the sliding member 304 and the stiffness of the base layer 304a. In the graph, circles indicate conditions in which no wrinkles occurred in the recording material, and crosses indicate conditions in 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 less than 2.5 mm, no wrinkles occur in the recording material, but if the thickness t is greater than 3.0 mm, wrinkles will occur in the recording material. Furthermore, the condition for the stiffness of the base layer 304a that prevents the occurrence of wrinkles in the recording material can be found in the graph of Figure 12 to be 2.6 × 10⁻⁶. 5 [N · It can be seen that it is less than or equal to [mm]. From the results of Verification 4, it was shown that the occurrence of wrinkles in the recording material can be suppressed by satisfying the following equation (4).

number

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

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

Claims

1. Fixing device, An endless belt for heating the recording material, A rotatable pressurizing rotating body that contacts the outer surface of the belt, A sliding member is provided which is positioned inside the belt, forms a nip portion that grips and conveys the belt between itself and the pressurizing rotating body, and slides against the inner circumferential surface of the belt, The system comprises a holding member for holding the sliding member, The pressurized rotating body, in cooperation with the belt, grips and conveys 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. The sliding member has a base material that extends in the width direction of the belt, The base material is made of metal and has a plurality of protrusions that project toward the pressurized rotating body. In a cross-section of the holding member perpendicular to the direction of transport of the recording material, the holding member has a convex crown shape toward the pressurizing rotating body. When the load 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 coefficient of friction 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 equation, and the applied pressure on the nip portion is 900 N or more. A fixing device characterized by the following features. [Math 1] [Math 2]

2. The sliding member has a sliding layer on the surface of the base material that slides against the inner circumferential surface of the belt. The fixing device according to feature 1.

3. The sliding layer is made of fluororesin. The fixing device according to feature 2.

4. The retaining member is made of resin. The fixing device according to feature 1.

5. The retaining member is formed of a resin different from the sliding layer. The fixing device according to claim 2 or 3.

6. The plurality of protrusions are provided such that the area of ​​the end face on the pressurizing rotating body 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. A fixing device according to any one of claims 1 to 5, characterized by the features described herein.

7. In a cross-section perpendicular to the transport direction of the recording material, the holding member has a first region corresponding to the central part of the nip portion and a second region adjacent to the first region, corresponding to both ends of the nip portion. The thickness of the first region is greater than the thickness of the second region. A fixing device according to any one of claims 1 to 6.

8. The thickness of the sliding member is 3.0 mm or less. The fixing device according to feature 1.

9. A lubricant is applied to the inner surface of the belt. The fixing device according to feature 1.

Images