Fixing device

Abstract

To provide a fixing device that has projections arranged at an appropriate interval and prevents uneven glossiness.SOLUTION: A fixing device comprises: an endless fixing belt; a heating rotating body that is in contact with an inner peripheral surface of the fixing belt and heats the fixing belt; a pressure roller that applies pressure to the fixing belt; and a slide member that is in contact with the inner peripheral surface of the fixing belt with the heating rotating body, and can slide with the inner peripheral surface of the fixing belt. The slide member forms a fixing nip part with the pressure rotating body with the fixing belt therebetween, and sandwiches and conveys a recording material carrying toner to the fixing nip part to fix a toner image to the recording material. The slide member has a plurality of projections on a surface sliding with the inner peripheral surface of the fixing belt, and the distance between the projections is within a predetermined range.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a fixing device for fixing a toner image on a recording material.

Background Art

[0002] An image forming apparatus has a fixing device for fixing an unfixed toner image on a recording material to the recording material.

[0003] The fixing device includes an endless fixing belt, a heating rotating body that applies heat to the fixing belt, a pressing rotating body that is rotationally driven to form a fixing nip portion between the fixing belt by pressing the fixing belt, and the fixing nip portion is formed by the pressure between a fixing pad and a pressing roller via the fixing belt. When a recording material on which unfixed toner is placed is conveyed to the fixing nip portion, the heat of the heating rotating body and the pressure by the pressing rotating body are applied to the recording material, and the toner image is fixed to the recording material.

[0004] With the increase in the printing speed of the image forming apparatus, a fixing device having a larger fixing nip width in the conveyance direction of the recording material has been proposed. By increasing the fixing nip width, it is advantageous for coping with high-speed printing, but the sliding resistance between the fixing belt and the fixing pad increases. <s

[0005] Therefore, a technique for reducing the sliding resistance with the fixing belt by using a sliding member provided with a plurality of protrusions on the surface contacting the fixing belt has been disclosed (Patent Document 1).

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] When a sliding member with multiple protrusions on the surface that contacts the fixing belt is used, the pressure difference between the area with protrusions and the area without protrusions within the fixing nip becomes large. This pressure difference affects the gloss unevenness of the toner image after fixing. Therefore, a smaller pressure difference is preferable.

[0008] To reduce the pressure difference, it is proposed to reduce the distance between the protrusions. However, if there is a difference in height between the protrusions, and the distance between them is too small, the fixing belt may not be able to follow, potentially leading to a larger pressure difference. Therefore, to suppress uneven gloss, it is necessary to set the distance between the protrusions within a predetermined range.

[0009] Therefore, the fixing device according to the present invention aims to suppress the increase in pressure difference within the fixing nip section and to suppress gloss unevenness that occurs on the image surface. [Means for solving the problem]

[0010] In view of the above problems, the fixing device according to the present invention comprises an endless fixing belt, a heating rotating body that contacts the inner circumferential surface of the fixing belt and heats the fixing belt, a pressure roller that pressurizes the fixing belt, a sliding member that contacts the inner circumferential surface of the fixing belt together with the heating rotating body and is slidable with the inner circumferential surface of the fixing belt, the sliding member together with the pressure rotating body via the fixing belt to form a fixing nip portion, the fixing nip portion to grip and transport a recording material bearing toner and fix the toner image to the recording material, the sliding member having a plurality of protrusions on the surface that slides with the inner circumferential surface of the fixing belt, and when the pressure in the fixing nip portion is P, the Young's modulus of the fixing belt is E, the thickness of the fixing belt is t, and the distance between the protrusions in the paper width direction of the recording material is d,

[0011]

number

[0012] The fixing device according to the present invention can suppress gloss unevenness in a fixing device having a sliding member provided with a plurality of protrusions.

Brief Description of the Drawings

[0013] [Figure 1] It is a schematic diagram of an image forming apparatus. [Figure 2] It is a schematic cross-sectional view of the fixing device in the present embodiment. [Figure 3] It is a detailed view of the sliding member. [Figure 4] It is a schematic diagram for explaining the peak pressure ΔP. [Figure 5] It is a schematic diagram for explaining height pressure unevenness. [Figure 6] It is a cross-sectional shape view of the embossed portion. [Figure 7] It is a schematic diagram for explaining a method of measuring the distance between embosses. [Figure 8] It is a graph showing the examination result of Study 1. [Figure 9] It is a graph showing the examination result of Study 2. [Figure 10] It is a graph showing the examination result in Study 3. [Figure 11] It is a table showing the examination results in Results 1 to 3.

Embodiments for Carrying Out the Invention

[0014] Hereinafter, embodiments of the image forming apparatus in the present embodiment will be described based on the drawings. In the following, an example in which the present invention is applied to a full-color electrophotographic image forming apparatus having a plurality of photosensitive drums will be described, but the present invention is not limited thereto and can also be applied to a monochromatic image forming apparatus or the like.

[0015] <Image Forming Apparatus> The schematic configuration of the image forming apparatus 1 of the present embodiment will be described using FIG. 1.

[0016] Figure 1 shows a full-color image forming apparatus according to this embodiment. The image forming apparatus 1 comprises an image reading unit 2 and an image forming apparatus body 3. The image reading unit 2 reads a document placed on the document glass 21. Light emitted from the light source 22 is reflected by the document and formed on a CCD sensor 24 via an optical system component 23 such as a lens. By scanning in the direction of the white arrows in Figure 1, this optical system unit converts the document into a series of electrical signal data for each line. The image signal obtained by the CCD sensor 24 is sent to the image forming apparatus body 3, where the control unit 30 performs image processing according to each image forming unit, which will be described later. The control unit 30 also accepts external input as an image signal from an external host device such as a print server.

[0017] The main body of the image forming apparatus 3 has four types of image forming units—yellow Pa, magenta Pb, cyan Pc, and black Pd—arranged along the direction of movement of the intermediate transfer belt 204. First, the process of forming a toner image on the intermediate transfer belt 204 will be explained using the yellow image forming unit Pa as an example.

[0018] In Figure 1, the surface of the rotating photosensitive drum 200a is uniformly charged by the charger 201a (charging). Subsequently, the exposure device 31 irradiates the surface of the photosensitive drum 200a with a laser according to the input image data, forming an electrostatic latent image on the surface of the photosensitive drum 200a (exposure). Then, the developing device 202a forms a yellow toner image on the photosensitive drum 200a. The primary transfer roller 203a applies a voltage to the intermediate transfer belt 204 with a polarity opposite to the potential polarity of the yellow toner image. As a result, the yellow toner on the photosensitive drum 200a is transferred to the intermediate transfer belt 204 (primary transfer). Any yellow toner that remains on the surface of the photosensitive drum 200a without being transferred is scraped off by the toner cleaner 207a and removed from the surface of the photosensitive drum 200a. This series of processes is carried out similarly for magenta Pb, cyan Pc, and black Pd. As a result, a full-color toner image is formed on the intermediate transfer belt.

[0019] The toner image on the intermediate transfer belt 204 is transported to the secondary transfer section N2, which is formed by the secondary transfer roller pair 205, 206. In accordance with the timing of the toner image transport, one sheet of recording material S is taken out from the recording material cassettes 8, 9 and fed to the secondary transfer section N2. Then, the toner image on the intermediate transfer belt 204 is transferred to the recording material S (secondary transfer).

[0020] The recording material S onto which the toner image has been transferred is transported to the fuser unit F, where it is fixed by heat and pressure (fixing). The recording material S with the fixed toner image is then discharged into the output tray 7.

[0021] The image forming apparatus 1 can also perform monochrome image formation. When forming a monochrome image, only the black image forming unit Pd among the multiple image forming units is driven.

[0022] When image formation is performed on both sides of the recording material S, once the transfer and fixing of the toner on the first image-forming surface (1st surface) is complete, the recording material S is reversed by passing through a reversal section located inside the image forming apparatus after fixing. Next, the toner on the second image-forming surface (2nd surface) is transferred and fixed, and the material is ejected from the machine and stacked on the output tray 7.

[0023] The process from charging to the discharge of the recording material S, on which the toner image has been fixed, into the output tray 7 is referred to as the image forming process (print job). The period during which image forming is taking place is referred to as the image forming process (print job in progress).

[0024] <Fusing device> Figure 2 shows a schematic diagram of the overall configuration of the belt heating type fixing device F in this embodiment. In the figure, the X direction indicates the transport direction of the recording material S, the Y direction indicates the paper width direction, and the Z direction indicates the pressure direction. The pressure direction is the direction in which the pressure roller 305 comes into contact with the fixing belt by the contact-separation mechanism described later. The area enclosed by the dotted line in Figure 2 represents an enlarged cross-section of the nip section N.

[0025] The fixing device F includes a fixing belt (hereinafter referred to as "belt") 301 as an endless, rotatable heated rotating body, a pad member (hereinafter referred to as "pad") 303 for supporting the fixing member, and a stay 302 for supporting the pad 303. It also includes a sliding member 304 positioned to cover the pad 303, a heating roller 307, and a pressure roller 305 as a pressurizing rotating body that faces the belt and forms a nip portion N together with the belt.

[0026] The belt 301 has thermal conductivity and heat resistance, and is a thin-walled cylindrical shape. In this embodiment, it 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 is 80 μm thick and made of polyimide resin (PI). The elastic layer is 300 μm thick and made of silicone rubber. The release layer is 30 μm thick and uses PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin) as a fluororesin. The belt 301 is stretched by a pad 303 placed on the inner circumference of the belt 301 and a heating roller 307. The outer diameter of the belt 301 in this embodiment is 150 mm.

[0027] The pad 303 is pressed against the pressure roller 305 via the belt 301, thereby forming a fixing nip portion N. The pad 303 is made of LCP (liquid crystal polymer) resin. A sliding member 304 is interposed between the pad 303 and the belt 301.

[0028] In this embodiment, the fixing device F has a pressure of 1600N applied to the fixing nip section N and a nip width of 24.5mm, resulting in high sliding resistance between the pad 303 that tensions the belt 301 and the fixing device F. To reduce this sliding resistance, a sliding member 304 that can slide against the belt 301 is provided on the belt 301 side of the pad 303. Details are described below.

[0029] The detailed configuration of the sliding member 304 is shown in Figure 3. Figure 3a) is a cross-sectional view of the sliding member 304 when the left-right direction on the paper plane is the conveying direction (X direction) and the up-down direction is the pressing direction (Z direction). Figure 3b) is a view of the sliding member 304 from the pressurizing roller 305 side when the left-right direction on the paper plane is the paper width direction (Y direction) and the up-down direction is the conveying direction (X direction). As shown in Figure 3a), the sliding member 304 of this embodiment is composed of a base material portion 304a, an embossed portion which is a projection 304b, and a sliding layer 304c. The base material portion 304a should have sufficient heat resistance and strength. The material should preferably be SUS, copper, aluminum, or engineering plastic (PI, PEEK, LCP, etc.). In this embodiment, the sliding member 304 has projections arranged at equal intervals with a distance d between the projections (distance between protrusions) of 1.4 mm in the paper width direction. By providing the embossed portion 304b, the contact area with the belt 301 is reduced, thereby lowering the sliding resistance. The method for measuring the distance d between the embossed portions will be described later. In this embodiment, the base material portion 304a and the embossed portion 304b are made of SUS, which is a metal. It is preferable to use any metal with excellent heat resistance and durability, not limited to SUS.

[0030] It is preferable to provide a material (such as a fluorine coating, PTFE, or PFA) in the sliding layer 304c to achieve low friction. In this embodiment, a PTFE (polytetrafluoroethylene) coating with a thickness of 20 μm was applied. Since the frictional force between the inner circumferential surface of the belt 301 and the sliding member 304 is very large, applying a lubricant further allows the belt 301 to slide smoothly against the sliding member 304. Silicone oil was used as the lubricant. In addition, it is necessary to reinforce the strength of the pad 303 in order to form the fixing nip portion N. For this reason, a stay 302 was provided.

[0031] In this embodiment, the sliding member 304 is configured to cover the pad 304 both inside and outside the nip portion N. Although not shown here, it is acceptable if only a part of the fixing nip portion N is covered by the sliding member 304. In other words, it is also acceptable to have a configuration in which the sliding member 304 is placed only on the nip portion N.

[0032] In this embodiment, the sliding member embossed portion 304b is provided over the entire sliding member 304. Although not shown here, it is acceptable if a part of the fixing nip portion N is covered by the sliding member embossed portion 304b. In other words, it is also acceptable to have a configuration in which the sliding member embossed portion 304b is provided only on the nip portion N.

[0033] In this embodiment, a configuration is adopted in which the sliding member 304 is fixed to the stay 302. (Not shown) Although not shown here, 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 (paper width direction) may be fixed to the pad 303 with screws or the like.

[0034] The heating roller 307 is a 1 mm thick stainless steel pipe, with a halogen heater 306 disposed inside as a heat source, capable of generating heat up to a predetermined temperature. This embodiment has multiple halogen heaters 306 with different orientation distributions in the paper width direction. This allows the heating area to be changed according to the size of the recording material S, which is advantageous for preventing edge heating, which is particularly noticeable when small-sized paper is continuously fed through. The heating roller 307 is positioned on the inner circumference of the belt 301 and stretches the belt 301 over it. The heating roller 307 can transfer heat to the belt 301 by contacting it. Furthermore, the heating roller 307 is made of a metal pipe such as stainless steel. Therefore, metal rollers have superior thermal conductivity compared to rollers with a rubber layer, and the heat from the halogen heater 306 is quickly transferred to the surface of the heating roller 307.

[0035] The heating roller 307 has a pivot point at one end or near the center, and generates a tension difference by rotating relative to the belt 301. This allows for steering control to control the position of the belt 310 in the width direction. Alternatively, a separate component capable of steering control may be provided. In other words, the belt 301 may be tensioned by three components: the heating roller 307, the pad 303, and the steering roller. Furthermore, the heating roller 307 is biased by a spring supported by the frame of the heating unit 300, and also functions as a tension roller that applies a predetermined tension to the belt 301.

[0036] The pressure roller 305 is a roller with a core metal layer 305c, an elastic layer 305b on the outer circumference of the shaft, and a release layer 305a on the outer circumference of the elastic layer. The shaft is made of a SUS material with a diameter of 72 mm, the elastic layer is made of conductive silicone rubber with a thickness of 8 mm, and the release layer is made of PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin) as a fluororesin with a thickness of 100 μm. Both ends of the pressure roller 305 in the paper width direction are supported by a fixing frame (not shown) of the fixing device F. A gear is fixed to one end and connected to a drive source (not shown) via the gear, thereby rotating the pressure roller 305.

[0037] As the fixing nip section N is formed, the pressure roller 305 is driven to rotate. As a result, the belt 301 rotates in a manner driven by the pressure roller 305. The heating roller 307 is also driven to rotate, so the belt 301 rotates in a manner driven by the heating roller 307 as well. In the nip section N formed between the belt 301 and the pressure roller 305, the recording material S carrying the toner image is held and heated while being transported. In this way, the fixing device F fixes the toner image to the recording material S while holding and transporting the recording material S. In this embodiment, the pressure applied to the fixing nip section N is 1600N, and the width of the fixing nip section N in the X direction (transport direction) is set to 24.5 mm, and the width in the Y direction (paper width direction) is set to 326 mm.

[0038] <Contact / separation mechanism> The contact and separation mechanism of the pressure roller 305 will now be described. The pressure roller 305 can move to a position in contact with or separated from the belt 301 by the contact and separation mechanism. The contact and separation mechanism has a frame 311 and a drive motor. The frame 311 supports the pressure roller 305. The frame 311 rotates with the rotation axis 310 as its axis, driven by the drive motor. When the drive motor rotates the frame 311 clockwise on the plane of the paper with the rotation axis 310 as its axis, the pressure roller 305 moves in the direction of arrow P. As a result, the pressure roller 305 comes into contact with the belt 301 and the pad 303 in a direction perpendicular to the transport direction of the recording material, i.e., in the pressurizing direction (contact state). This forms the fixing nip portion N. When the frame 311 rotates counterclockwise on the plane of the paper with the rotation axis 310 as its axis, the pressure roller 305 becomes separated from the belt 301 (separated state).

[0039] As explained above, the recording material carrying the unfixed toner image is clamped and transported in the fixing nip section N, and heat and pressure are applied to fix it.

[0040] <An embossed portion is provided on the sliding member.> The sliding member 304 is configured with a sliding layer 304c and a lubricant to reduce deterioration due to friction. However, in this embodiment, the width of the fixing nip portion N is 24.5 mm and the applied pressure is 1600 N, resulting in a large frictional force between the belt 301 and the sliding member 304 at the fixing nip portion N. Therefore, deterioration of the inner circumferential surface of the belt 301 and the sliding member 304 is severe. To address this, the sliding member 304 is configured with multiple embossed portions 304b, which are protrusions. By providing multiple embossed portions 304b, the contact area between the belt 301 and the sliding member 304 can be reduced, thereby reducing the frictional force. Thus, deterioration of the belt 301 and the sliding member 304 is suppressed, resulting in a longer lifespan.

[0041] <Causes of uneven pressure distribution due to embossing> As described above, multiple embossed portions 304b are provided on the sliding member 304. This creates a problem where, in the paper width direction (Y direction), the difference between the peak pressure in the area where the embossed portions 304b are provided and the pressure in the area where the embossed portions 304b are not provided becomes large. Pressure unevenness within the fixing nip portion N depends on the distance between the embossed portions. Pressure unevenness affects the gloss unevenness of the toner image after fixing. Therefore, it is preferable to have small pressure unevenness. To reduce pressure unevenness, it is proposed to reduce the distance between the embossed portions.

[0042] However, if there is a difference in height between the embossed portions 304b, and the distance between the embossed portions is too small, the belt 301 may not be able to follow, potentially leading to increased pressure unevenness. Therefore, in order to suppress gloss unevenness, it is necessary to set the distance between the embossed portions within a predetermined range. The details of the pressure unevenness, which is the issue in this case, are described below.

[0043] Using Figures 4 and 5, we will explain the pressure unevenness that occurs when multiple embossed portions 304b are provided on the sliding member 304. In this embodiment, the fixing nip portion N is 24.5 mm and is a wide nip. As a result of examining the wide nip configuration, it was found that two minute pressure unevennesses of different properties originating from the sliding member embossed portion 304b occur in the nip portion, causing image defects during paper feeding.

[0044] The first type of pressure unevenness is the one shown in Figure 4, which is caused by high pressure at the tip of the embossed portion 304b of the sliding member (hereinafter referred to as peak unevenness).

[0045] The second type of pressure unevenness, shown in Figure 5, is caused by the difference in height between adjacent sliding member embossed portions 304b (hereinafter referred to as height-based pressure unevenness). Here, we will explain the details of the verification formula that led to the present invention and the two causes mentioned above.

[0046] "Peak unevenness" will be explained using Figure 4. Figure 4 is a schematic diagram showing the state in which the recording material S on which the toner image T is placed is being conveyed under pressure in the fixing nip section N of the fixing device F, and a diagram showing the pressure distribution on the surface of the toner image T (dotted line in the figure). The recording material S is heated and pressurized through the sliding member 304, belt 301, and pressure roller 305, and the toner image T is fixed to the recording material S. Figure 4a) is a schematic diagram in this embodiment using the embossed portion 304b of the sliding member and a diagram showing the pressure distribution on the surface of the toner image T in the dotted line section. On the other hand, Figure 4b) is a schematic diagram when the distance d between the embossed portions 304b of the sliding member is doubled compared to Figure 4a) and a diagram showing the pressure distribution on the surface of the toner image T in the dotted line section. The pressure distribution on the surface of the recording material S has an upward and downward amplitude (hereafter referred to as peak pressure ΔP) centered on the embossed portion 304b, depending on the shape and distance of the embossed portion 304b of the sliding member. It can be seen that the pressure in the embossed area 304b is high, and the pressure in the area where the embossed area 304b is not formed is low. As shown in Figure 4b), when the distance d between the embossed areas is doubled, the above ΔP increases. When ΔP becomes larger than a predetermined value, uneven gloss occurs when the toner image T is fixed to the recording material S by heating and pressurizing at the fixing nip N. That is, the areas with high pressure in Figure 4 tend to have high gloss because the surface condition of the belt surface layer 301c is transferred well. On the other hand, the areas with low pressure tend to have low gloss because the surface condition of the belt surface layer 301c is not transferred as well as in the areas with high pressure. There is a risk that uneven gloss (image defects) will occur by providing the embossed area 304. As a result of the verification, it was inferred that ΔP [MPa] can be calculated according to the following verification formula.

[0047] For verification, Hertz's contact formula was used. From Hertz's contact formula, the following formula was derived from the shape of the embossed portion 304b in this embodiment and the possible distances between the embossed portions 304b. The possible distances between the embossed portions 304b were set to 0.2 to 2.5 mm.

[0048] The pressure applied per unit area is determined by considering Hertz's contact method and the shape of the embossed portion 304b in this embodiment.

[0049] Let F[N] be the pressure applied to the fixing nip portion N. The contact area S[mm²] between the belt 301 and the embossed portion 304b. 2 The area S of the fixing nip portion N is the contact area a of one embossed portion 304b and the belt 301. 2 And the number of embossed parts 304b per unit d 2 This is calculated by multiplying it by the area Ns of the fixing nip portion N.

[0050]

number

[0051] The shape of the embossed portion 304b in this embodiment, as well as the possible distance d and contact width between the embossed portions 304b, were taken into consideration. Then, rearranging the above equation, the following equation was obtained.

[0052]

number

[0053] The pressure F[N] applied to the fixing nip N is multiplied by the area Ns[mm²] of the fixing nip N. 2 Dividing by ] gives the average pressure P [MPa] of the fixing nip N. Therefore, the formula was rearranged as follows.

[0054]

number

[0055] From Equation 1, the peak pressure ΔP depends on the distance d between the embossings and the average pressure P of the fixing nip N.

[0056] Next, height pressure unevenness will be explained using Figure 5. Figure 5a) is a schematic diagram of this embodiment using the embossed portion 304b of the sliding member, and shows the pressure distribution on the surface of the toner image T in the dotted line area. Figure 5b) is a schematic diagram of the case when an embossed gap eg occurs in a part of the embossed portion 304b of the sliding member, and shows the pressure distribution on the surface of the toner image T in the dotted line area. If the height of the embossed portion 304b is uniform, the pressure distribution on the surface of the recording material S depends on the embossed portion 304b of the sliding member and has a constant ΔP centered on the embossed portion 304b. On the other hand, when an embossed gap eg occurs, the pressure in the part where the embossed gap eg occurs decreases, and the pressure in the embossed portions 304b on both sides increases. As a result of the above, an uneven pressure deviation (ΔPeg) occurs on the surface of the toner image T. If an uneven pressure deviation (ΔPeg) occurs on the surface of the toner image T, there is a risk of uneven gloss occurring when the toner image T is fixed to the recording material P by heating and pressurizing at the fixing nip section N. In other words, in the figure, areas with high ΔPeg pressure tend to have high gloss because the surface condition of the belt surface layer 301c is transferred well. Areas with low ΔPeg pressure tend to have low gloss because the surface condition of the belt surface layer 301c is not transferred as well as in areas with high pressure. Uneven gloss (image defects) occurs when a gap eg occurs in the embossed area. The gap eg in the embossed area occurs due to individual errors in the embossed area. Therefore, it is necessary to design considering the gap eg in the embossed area. To suppress ΔPeg, it is necessary to consider how well the belt 301 follows the sliding embossed area 304b when pressure is applied at the nip section N. If an embossed gap eg occurs and there is an embossed section 304b that is lower in height than the adjacent embossed section 304b, the belt 301 can follow the lowered embossed section 304b by the amount of the lowered section, thereby suppressing ΔPeg. Here, the amount of intrusion into the embossed gap eg of the sliding embossed section 304b is defined as the concave follow amount h [mm]. Numerical verification revealed that whether or not the belt 301 follows the embossed gap eg is determined by the relationship between the embossed gap eg and the concave follow amount h defined above.

[0057] To calculate the amount of concave follow-up h, the formula for a beam with uniformly distributed load and supported at both ends, and the formula for the second moment of area were used. The calculation was performed assuming that the embossed portion 304b supports both ends of the belt 301.

[0058] Using the formula for beams and the formula for the second moment of area, the following equation can be derived.

[0059]

number

[0060] Let P be the average pressure [MPa] of the anchoring nip section N, E be the Young's modulus of belt 301 [MPa], and t be the thickness [mm] of belt 301.

[0061] If we consider δMax on the left side of the above equation as the concave tracking amount h [mm], and rearrange the right side of the equation, we obtain the following equation.

[0062]

number

[0063] As the distance d between embossed sections decreases, the "apparent rigidity" of the belt 301 between the embossed sections 304b of the sliding member increases, thus reducing the amount of concave-following h. Also, as the Young's modulus E of the belt increases, or as the thickness of the belt increases, the belt can no longer follow the embossed gap, thus reducing the amount of concave-following h. Furthermore, as the average pressure of the nip section N increases, the force applied to the belt increases, thus reducing the amount of concave-following h. From the above equations, the range of values ​​for each that can prevent height unevenness can be determined by determining the minimum acceptable amount of concave-following h (i.e., the amount of concave-following h is sufficiently larger than the embossed gap eb).

[0064] Analysis of the verification formulas for peak unevenness and height pressure unevenness revealed that it is necessary to set an appropriate distance d between embossing points depending on the average pressure P of the nip section N, the Young's modulus E of the belt 301, and the thickness t of the belt 301. Peak unevenness should be addressed by reducing the peak pressure ΔP by decreasing the distance d between embossing points. On the other hand, height pressure unevenness should be addressed by increasing the amount of concave-following h by increasing the distance d between embossing points. Therefore, once the average pressure P of the nip section N, the Young's modulus E of the belt 301, and the thickness t of the belt 301 are determined, the usable distance d between embossing points can be determined. Subsequently, by conducting tests on the actual system, the acceptable upper limit of peak pressure ΔP and the lower limit of concave-following h were determined and verified.

[0065] <Methods for measuring various parameters> The measurement methods for various parameters (Young's modulus of the fixing belt (E), thickness of the fixing belt (t), distance between embossings (d), and average pressure of the nip (P)) are explained below using Figures 6 and 7.

[0066] <Method for measuring Young's modulus E> This document describes the method for measuring the Young's modulus (E) of belt 301. A Shimadzu AG-X tensile tester is used for Young's modulus measurement. The AG-X tensile tester attachments are a 500N load cell and a 500N mechanical parallel clamping chuck. When performing the tensile test, the constant temperature chamber temperature is set to 180 degrees Celsius, the pulling speed to 5 mm / min, and the results of the prior thickness measurement are entered. The thickness measurement used above should be the thickness of the belt base layer 301a, which has the greatest strength among the layers of belt 301. The modulus of elasticity is calculated in the range of 10N to 15N for the load cell test force. This measurement should begin after confirming that the constant temperature chamber temperature for the tensile test has reached 180 degrees Celsius. The dumbbell shape used during the tensile test should conform to JIS K7139-A24. After 10 measurements in both the circumferential and longitudinal directions, the average values ​​are taken to determine the modulus of elasticity in both directions. The Young's modulus E [MPa] of the belt measured in this study was the average value in both the circumferential and longitudinal directions. If the belt has multiple layers of different types, as shown in belt 301 in Figure 1, all layers should be treated as a single layer, and the above procedure should be followed.

[0067] <Method for measuring thickness t> Next, the method for measuring the thickness (t) of belt 301 will be explained. When measuring the thickness, belt 301 is cut into four equal parts in the Y direction (paper width direction) to create samples. The belt thickness was measured using a HEIDENHAIN CT6001 digital length 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 (paper feeding direction), and then the average value of these four points was taken as the belt thickness t [mm]. In this measurement, if the belt has multiple layers, as shown in Figure 1, the thickness of the base layer 301a is measured, excluding the belt elastic layer 301b and the surface layer 301c. If there are other layers besides the elastic layer, surface layer, and base layer, the thickness of the other layers and the base layer is defined as the belt thickness, and the measurement is performed.

[0068] <Method for measuring the distance d between embossing marks> A method for measuring the distance d between the embossed areas of the sliding member embossed portion 304b will be explained.

[0069] First, Figure 6 shows a schematic diagram of the cross-sectional shape of the sliding member embossed portion 304b, illustrating the parameters used during measurement. Figure 6a) is a view of the sliding member embossed portion 304b in Figure 3, seen from the pressure roller 305 side (the Z direction, which is the pressure direction). Figure 6b) is a schematic diagram of the vertex of the embossed portion 304b cut in cross-section in the X direction (conveying direction). Figure 6c) is a schematic diagram of two adjacent embossed portions 304b in Figure 3, cut in cross-section in the Y direction (paper width direction) passing through the vertex of each embossed portion. In the figure, Wex represents the width in the X direction of the portion where the sliding member embossed portion 304b contacts the belt 301. In the figure, Wey represents the width in the Y direction of the portion where the sliding member embossed portion 304b contacts the belt 301. In the figure, Web represents the width in the Y direction of the distance between the vertices of adjacent sliding member embossed portions 304b.

[0070] As a modification of the embodiment, we define Wex when the shape of the embossed portion 304b of the sliding member is asymmetric in the X direction (conveying direction) or the Y direction (paper width direction) using Figure 6a). When the shape of the embossed portion 304b of the sliding member is asymmetric in the X and Y axes, first determine the axis CSmax in the XY plane where the portion of the embossed portion 304b that contacts the belt 301 is maximized, and define the contact width Wmax on the CSmax axis. Next, estimate the angle Θ between the Y axis and the CSmax axis in the figure. Finally, calculate Wex = Wmax × sinΘ and Wey = Wmax × cosΘ to use the contact width in the projection on the CSmax axis as the measured value.

[0071] As a modified example, using Figure 6a), we define the distance Web between the vertices of adjacent sliding member embossed portions 304b when the shape of the sliding member embossed portion 304b is asymmetrical in the X direction (conveying direction) or the Y direction (paper width direction). First, a cross section CSya is created passing through the vertex of the first embossed portion, and the distance Weba between the vertices of adjacent sliding member embossed portions 304b is measured. Next, a cross section CSyb in the Y direction is created passing through the vertex of the other embossed portion, and the distance Webb between the vertices of adjacent sliding member embossed portions 304b is measured. The average of Weba and Webb is taken as Web.

[0072] Next, we will explain the methods for measuring each of the parameters (Wex, Wey, Web) mentioned above.

[0073] The contact widths Wex and Wey of the embossed portion 304b of the sliding member with the belt 301 were measured using a 3D shape measuring machine (Keyence VR-3200) and pressure-sensitive paper (Prescale) manufactured by Fujifilm. For the Fujifilm pressure-sensitive paper, ultra-low pressure type (LLW) was used to match the measurement pressure range (2.5 MPa to 10 MPa). In the fixing device F shown in Figure 2, the fixing belt 301 was cut lengthwise, and the Prescale was inserted between the sliding member 304 and the fixing belt 301 in the corresponding area of ​​the fixing nip portion N, and then pressurized. When the pressurized force was divided and the Prescale was observed, only the contact area at the tip of the embossed portion 304b of the sliding member turned red. The contact area of ​​the pressurized Prescale was measured in two dimensions using the 3D shape measuring machine (Keyence VR-3200), and the contact widths Wex and Wey were calculated. The magnification was set to 40x during measurement. Wex was measured over a cross-section perpendicular to the X direction (conveying direction) passing through the center of the red area of ​​the Prescale. Wey was measured over a cross-section perpendicular to the Y direction (conveying direction) passing through the center of the red area of ​​the Prescale. When calculating the contact widths Wex and Wey, at least 10 measurements should be taken of the embossed portion 304b of the sliding member from at least different locations, and the average value should be used. Although not addressed in this implementation, if the shapes of the embossed portion 304b of the sliding member are not all identical, it is desirable to calculate the average value including those with different shapes.

[0074] The distance Web between the vertices of adjacent sliding member embossed portions 304b was measured using a Keyence VR-3200 three-dimensional shape measuring machine. A magnification of 40x or higher is desirable during measurement. The sliding member embossed portion 304b was set on the machine so that the convex portion faced upwards during measurement. After measurement, the cross-sectional shape profile was checked, and the distance in the Y direction (paper width direction) between the vertices was measured in the cross-section connecting the highest vertex positions of the sliding member embossed portion 304b, and this was defined as the distance Web between the vertices.

[0075] Based on the measurement method described above, the procedure for determining the distance d between embossing sections will be explained using Figure 7. First, to estimate the distance between CSy sections at the measurement pitch in the Y direction (conveying direction) (Figure 4b), the contact width, i.e., Wex, where the sliding member embossed section 304b in the CSx direction in Figure 7a) contacts the belt 301 is measured using the procedure described above. Next, the Web is measured in the horizontal cross section in the Y direction (conveying direction). As shown by the dotted line CSy3 in Figure 7b), the profile is measured so as to pass through the tip of the sliding member embossed section 304b. From the profile measurement results, the distance Web between each adjacent sliding member embossed section 304b is calculated (in the figure, measurements are taken at 4 locations). The measured Web values ​​are averaged by the number of measurement locations and recorded, for example, as the measured value Weba3 in the cross section of the dotted line CSy3. The same work is performed on the dotted lines CSy1, CSy2, and CSy4 to obtain Weba for each cross section (i.e., Weba1, 2, and 4). Finally, the average value from Weba1 to Weba4 is calculated and taken as the distance d between embossings. To calculate Weba for each cross section CSy, it is desirable to take between 1 and 10 Webs. Also, although Figure 7b) explains the measurement cross section as CSy1 to Cy4 (four locations), it is desirable to measure the measurement cross section CSy in 5 or more rows and calculate the average value.

[0076] As a point of caution, we will provide a supplementary explanation on how to create the dotted line CSy section when calculating the distance d between the embossing areas. For explanation purposes, Figure 7c) shows (1) the case where only a portion of the sliding member embossed portion 304b is misaligned, and (2) the case where only a portion of the sliding member embossed portion 304b is not misaligned. Focusing on the embossing indicated by the white circle in Figure 7c), when creating the CSy5 and CSy6 sections, the treatment of the CSy5 and CSy6 sections is determined by the magnitude of the X-direction pitch distance Δ between CSy5 and CSy6 as shown in the figure. For example, if the X-direction pitch distance Δ is larger than the CSx-direction contact width Wex calculated above, the two dotted line sections Sy5 and CSy6 are treated separately and calculated. On the other hand, if the X-direction pitch distance Δ is smaller than the CSx-direction contact width Wex calculated above, the two dotted line sections Sy5 and CSy6 are treated as the same and the calculation is performed as one CSy7 section.

[0077] The sliding member embossed shape 304b used in this embodiment was investigated under the condition that the belt contact width Wey of the embossed portion is sufficiently smaller than the distance d between the embossed portions. Sliding members 304 were created by changing the distance d between the embossed portions from 0.2 to 2.5 mm, and the distance d between the embossed portions and the belt contact width Wey of the embossed portion were measured. The distance d between the embossed portions and the belt contact width Wey of the embossed portion were measured in the same manner as described above. As a result of the measurements, it was confirmed that in the range of the distance d between the embossed portions from 0.2 to 2.5 mm, the average value Weva of the belt contact width Wey of the embossed portion was more than twice. Therefore, it was found that the sliding member embossed shape 304b in this embodiment was investigated in a range where the average value Weva of the belt contact width Wey of the embossed portion was more than twice. In other words, in this embodiment, the average contact width Wey between the belt 301 and the sliding member 304 in the paper width direction of the surface where the sliding member 304 is in contact with the belt 301 is smaller than the average non-contact width. Therefore, the configuration reduces the contact width between the belt 301 and the sliding member 304. This reduces friction between the belt 301 and the sliding member 304 and suppresses deterioration.

[0078] As described above, the distance d between embossing areas is measured. The distance d between embossing areas is calculated by averaging the distances between the tips of the embossing areas. The tip of the embossing area 304b refers to the part of the embossing area 304b that protrudes furthest towards the pressure roller 305. Therefore, in a single embossing area 304b, the area with the highest pressure is the tip of the embossing area, and the distance between the tips is used to calculate the distance d between embossing areas.

[0079] <Method for measuring the average pressure P at the fixing nip section> This document explains the method for measuring the load value NF applied to the nip section N and the method for calculating the average pressure P at the fixing nip section. The average pressure P at the fixing nip section was determined by measuring and calculating the load value NF and the nip area S. The load value NF was measured using a NITTA I-SCAN pressure measuring instrument. The sheet portion of the I-SCAN was inserted into the fixing nip section N of the fixing device F, and after applying a load to the fixing nip section N, the load value NF was measured using dedicated software. The nip section area S was measured using Fujifilm's pressure-sensitive paper, Prescale, measuring the nip width and the nip paper feeding direction width L. The low-pressure version (4LW) of Fujifilm's pressure-sensitive paper, Prescale, was used to match the measurement pressure range (0.05 MPa to 0.2 MPa). Prescale was inserted between the fixing belt 301 and the pressure roller 305 in the relevant area of ​​the fixing nip section N of the fixing device F shown in Figure 2, and pressure was applied. When the pressure was divided and the Prescale was observed, only the area of ​​the nip section N turned red. The contact area of ​​the pressurized Prescale was measured evenly at approximately 10 points in the X direction (conveying direction) using a scale, and the average value was defined as the nip width Nx. Similarly, the contact area of ​​the pressurized Prescale was measured evenly at approximately 5 points in the Y direction (paper width direction) using a scale, and the average value was defined as the nip width Ny. From the above measurement results, the average pressure (P) at the nip was calculated as NF / S, i.e., NF / (Nx×Ny).

[0080] <Image Verification Method> The evaluation method for determining the presence or absence of abnormal images on the image forming apparatus shown in Figure 1 is described below. During verification, a fixing device F with the necessary parameters (d, E, t, P) set was installed. (The method for changing the parameters will be explained in the description of the example.) The peripheral speed of the pressure roller 305 mounted on the fixing device F was set to 250 mm / sec, and the temperature control of the heating heater 307 was set to 195 degrees. At that time, the surface of the belt 301 was monitored with a HORIBA infrared thermometer IT-340 and it was confirmed that the belt surface temperature was 180 degrees. An examination was conducted to check for the presence or absence of image defects on the printed black sample. To make image defects easier to see, KOKUYO OHT film VF-1420N A4 size was used. To make image defects caused by uneven pressure easier to see, a sample with a dense, entirely black surface was printed. If gloss unevenness or density unevenness extending horizontally in the transport direction was visible on the paper sample, it was determined that an image defect had occurred. If uniform, comb-like variations in gloss or density occur across the entire surface of the paper sample, it is determined that an image defect has occurred due to uneven embossing peak pressure. If uneven gloss or density occurs on the paper sample, it is determined that an image defect has occurred due to uneven embossing height pressure.

[0081] <Verification Procedure and Verification Results> The verification procedure using this implementation and the results of the verification performed by changing the distance d between the embossed parts of the sliding member embossed portion 304b are described below.

[0082] The verification process in Verification 1 to 3 is explained step by step. First, the various parameters of the fixing device F (nip width Nx in the transport direction, nip width Ny in the paper width direction, load value NF, average pressure P at the nip, belt Young's modulus E, belt thickness t) are set and prepared. Next, the sliding member 304 of the actual system is attached, and image verification is performed to make a judgment. The above procedure was repeated by replacing the sliding member 304 with different distances d between embossed parts 304b (d = 0.2, 0.9, 1.8, 2.1, 2.5 mm) and performing image verification. Finally, the calculated values ​​from the various parameters and the image verification results for the distance d between embossed parts were summarized in tables and graphs. For parameters other than the distance d between embossed parts, the parameter settings described in the example were used for verification unless otherwise specified.

[0083] Figures 8 to 10 show graphs illustrating the results of verifications 1 to 3. Figure 11 shows the parameters used in verifications 1 to 3, the calculated peak pressure ΔP and concave-following amount h of the sliding embossed portion 304b when the distance d between each emboss is changed, and the image evaluation results. The solid line graphs in Figures 8 to 10 were created based on the table in Figure 11. In addition, a circle (○) in the graph plot indicates that no image defects occurred in the image evaluation results, and a cross (×) indicates that image defects occurred in the image evaluation results.

[0084] <Verification 1> First, various parameters were verified under the conditions shown in Figure 11 (the same as in the example), and the upper limit of the peak pressure ΔP and the lower limit of the concave-following amount h of the sliding part embossed section 304b were determined from the threshold for the occurrence of image defects. The base material of the belt 301 was confirmed to be polyimide, with E=5000MPa and t=0.08mm. The graph of the verification results is shown in Figure 8. The left figure shows the relationship between the peak pressure ΔP and the distance d between the emboss, and the right figure shows the relationship between the concave-following amount h and the distance d between the emboss. As shown in the graph on the left of Figure 8, when the peak pressure ΔP of the sliding part embossed section 304b exceeded a certain level, image defects caused by uneven peak pressure of the emboss occurred. From the verification results, it was found that the upper limit of the peak pressure ΔP at which no image defects caused by uneven peak pressure of the emboss occur is 0.08MPa (solid line value in the figure). As shown in the graph in the right-hand figure of Figure 8, when the amount of concave tracking h of the sliding embossed portion 304b falls below a certain level, image defects caused by uneven pressure at the emboss peak occur. It was found that the lower limit of the amount of concave tracking h at which no image defects caused by uneven pressure at the emboss peak occur is 0.01 mm (solid line value in the figure). From the graph in Figure 8 and the table in Figure 11, it can be seen that image defects can be prevented by keeping the distance d between embossings within a predetermined range. From Verification 1, it was found that the range in which image defects (caused by uneven pressure at the emboss peak, caused by uneven pressure at the emboss peak) can be prevented can be expressed by the following formula.

[0085]

number

[0086] <Verification 2> Next, to verify the validity of equations 3 and 4 mentioned above, various parameters were tested under the conditions shown in Figure 11, and the threshold for image defect occurrence was confirmed. The Young's modulus of the pressure roller elastic layer 305b was changed to 1400N for further investigation. The graph of the verification results is shown in Figure 9. The left figure shows the relationship between the peak pressure ΔP and the distance d between the embossed areas, and the right figure shows the relationship between the amount of concave tracking h and the distance d between the embossed areas. As shown in the left figure of Figure 9, it was found that the presence or absence of image defects caused by uneven embossed peak pressure can be determined with respect to the peak pressure threshold of 0.08 MPa (solid line in the figure). Also, as shown in the right figure of Figure 9, it was found that the presence or absence of image defects caused by uneven embossed peak pressure can be determined with respect to the amount of concave tracking threshold of 0.01 (solid line in the figure). From these results, it was confirmed that the two equations mentioned above hold true even when the average pressure P of the fixing nip section N is changed by changing the load value NF.

[0087] Furthermore, the two equations mentioned above still hold true even when the load value NF is changed to something other than 1600N or 1400N.

[0088] <Verification 3> Finally, to verify the validity of equations 3 and 4 mentioned above, various parameters were tested under the conditions shown in Figure 11, and the threshold for the occurrence of image defects (caused by uneven embossing peak pressure) was confirmed. The physical properties of the fixing belt base layer 301a were changed to nickel material, and the test was performed at E=150000MPa and t=0.04mm. The graph of the test results is shown in Figure 9. The left figure shows the relationship between the peak pressure ΔP and the distance d between embossing marks, and the right figure shows the relationship between the amount of concave tracking h and the distance d between embossing marks. As shown in the left figure of Figure 9, it was found that the presence or absence of image defects caused by uneven embossing peak pressure could be determined with the peak pressure threshold of 0.08MPa (solid line in the figure) as the boundary. Also, as shown in the right figure of Figure 9, it was found that the presence or absence of image defects caused by uneven embossing peak pressure could be determined with the amount of concave tracking threshold of 0.01 (solid line in the figure) as the boundary. From these results, it was confirmed that the two equations mentioned above still hold true even when the anchoring belt base layer 301a is changed and the belt Young's modulus E and belt thickness t are changed.

[0089] Furthermore, the two equations mentioned above still hold true even if the Young's modulus of belt 301 is changed to a value other than 5000 MPa or 150000 MPa. Also, the two equations mentioned above still hold true even if the belt thickness t is changed to a value other than 0.08 mm or 0.04 mm.

[0090] <Effects that make Equation 3 true> Equation 3 shows that the peak pressure ΔP is below a predetermined value. By making the distance between embossing areas d small enough to satisfy Equation 3, the distance between embossing areas becomes smaller. Assuming that the pressure on the fixing nip N remains unchanged, the pressure on each embossing area 304b decreases as a result. This lowers the peak pressure, and the value of the peak pressure ΔP decreases. This makes it possible to suppress gloss unevenness that occurs on the image surface.

[0091] <Effects when Equation 4 is made to hold> Equation 4 shows the amount h of the fixing belt 301 to follow within the range in which gloss unevenness can be suppressed. Since multiple embossed sections are provided within the fixing nip section, there are differences in the height of the embossing between individual sections. By making the distance d between embossing sections large enough to satisfy Equation 4, the distance between embossing sections increases. When the distance between embossing sections is large, the amount of follow-up h increases. As a result, the fixing belt 301 can follow according to the height difference of the embossing sections 304b. In other words, the belt can bite into the lower height embossing section 304b, and the pressure on the embossing sections on either side of the lower height embossing section can be reduced. This makes it possible to suppress gloss unevenness that occurs on the image surface.

[0092] <Effects when equations 3 and 4 are made to hold> By using Equation 3, the upper limit of the embossing distance d can be set. Furthermore, by using Equation 4, the lower limit of the embossing distance d can be set. By setting the embossing distance d within the range satisfying Equations 3 and 4, the increase in peak pressure ΔP can be suppressed, thereby reducing gloss unevenness.

[0093] Furthermore, in this embodiment, the distance d between embossings in the paper width direction (Y direction) is 1.4 mm, and they are arranged at equal intervals. By arranging them at equal intervals, it is possible to suppress large differences in the pressure applied to the protrusions 304b in the same row in the paper width direction within the fixing nip section N. Note that if the arrangement of the embossing sections 304b is shifted due to manufacturing errors or other reasons when they are arranged at equal intervals, these shifts are considered to be included in the equal intervals.

[0094] Furthermore, as shown in Figure 7a), if one row of protrusions 304b is used as a reference in the paper width direction, the protrusions 304b of the adjacent row in the transport direction are offset in the paper width direction and arranged at equal intervals. This makes it possible to reduce pressure unevenness in the paper width direction within the fixing nip section N compared to the case where there is no offset in the paper width direction.

[0095] <Effects of using metal in sliding components> In this embodiment, the base material portion 304a and the embossed portion 304b of the sliding member 304 are integrally molded from SUS metal. The sliding member 304 together with the pressure roller 305 forms the fixing nip portion N. In this embodiment, the pressure applied to the fixing nip portion N is 1600N, and the width of the fixing nip portion N in the X direction (conveying direction) is 24.5 mm, so the belt 301 and the sliding member 304 slide under large pressure. If the sliding member that forms the fixing nip portion N is not highly durable, the member forming the fixing nip portion N may deform, potentially causing wrinkles in the paper. Therefore, by using a highly durable and heat-resistant metal (SUS in this embodiment) for the sliding member 304, a highly durable pad can be realized.

[0096] In this embodiment, the shape of the embossed portion 304b that contacts the belt 301 is circular. However, it is not limited to this. The shape of the embossed portion 304b does not have to be circular, as long as the formula holds true when the area of ​​the embossed portion 304b is substituted into the formula. For example, if the shape of the embossed portion 304b is rectangular, the distance d between the embossed portions is the distance between the centroids of the rectangle. Also, the shape of the embossed portion 304b is not limited to circular, as long as the formula holds true when the area that contacts the belt 301 is calculated and substituted into the formula. [Explanation of Symbols]

[0097] F Fixing device N Fixing nip section 1. Image forming apparatus 301 Fixing belt (belt) 302 Stay 303 Pad component (pad) 304 Sliding member 304a Base material part 304b Embossed area (protrusion) 304c sliding layer 305 Pressure Roller 306 Halogen Heater 307 Heating roller

Claims

1. An endless fixing belt; a heating rotator that contacts an inner circumferential surface of the fixing belt and heats the fixing belt; a pressure roller for applying pressure to the fixing belt; a sliding member that is in contact with the inner circumferential surface of the fixing belt together with the heating rotator and is slidable against the inner circumferential surface of the fixing belt; the sliding member forms a fixing nip portion together with the pressure rotating body via the fixing belt, and conveys a recording material carrying toner to the fixing nip portion to fix a toner image on the recording material; the sliding member has a plurality of protrusions on a surface that slides against an inner circumferential surface of the fixing belt, Let P [MPa] be the pressure in the fixing nip, E [MPa] be the Young's modulus of the fixing belt, t [mm] be the thickness of the fixing belt, and d [mm] be the distance between the protrusions in the paper width direction of the recording material. Let a 2 [mm 2 ] be the area where the protrusions in region d 2 come into contact with the belt. [0010] A fixing device characterized in that the above two formulas are satisfied.

2. 2. The fixing device according to claim 1, wherein the sliding member has a base portion on which the protrusions are provided, and the base portion and the protrusions are integrally molded from metal.

3. 3. The fixing device according to claim 1, wherein the distance between the protrusions in the paper width direction is a distance between the tips of adjacent protrusions.

4. 4. The fixing device according to claim 1, wherein the sliding member has a sliding layer, and the sliding layer covers at least the protrusions.

5. 5. The fixing device according to claim 1, wherein a width in the paper width direction within the fixing nip portion where the sliding member contacts the fixing belt is smaller than a width where the sliding member and the fixing belt are not in contact with each other.

6. 6. The fixing device according to claim 1, wherein the protrusions are arranged at equal intervals in the paper width direction.

7. 7. The fixing device according to claim 1, wherein the distance between the protrusions is a value calculated by averaging distances between a plurality of the protrusions.

Images