Fixing device

Abstract

To suppress wear of an endless belt and a slide sheet.SOLUTION: A fixing device includes a rotor 120, an endless belt 130, a heater, a slide sheet 150, and a pressure pad. The endless belt 130 is brought into contact with an outer peripheral surface of the rotor 120, and has a base material composed of a heat-resistant resin having a glass transition temperature of 140°C or higher. The heater heats at least one of the rotor 120 and the endless belt 130. The slide sheet 150 is brought into contact with an inner peripheral surface of the endless belt 130, and has a base material composed of a heat-resistant resin having a glass transition temperature of 140°C or higher. The pressure pad sandwiches the endless belt 130 and the slide sheet 150 between the rotor 120 and the pressure pad. Microhardness by a nano-indentation method of the endless belt 130 is larger than microhardness of the slide sheet 150.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a fixing device equipped with an endless belt. [Background technology]

[0002] Conventionally, some fixing devices using a pressure pad have a sliding sheet between the endless belt and the pressure pad (see Patent Document 1). The sliding sheet has a surface hardness equal to or greater than that of the endless belt in order to reduce the sliding resistance between the endless belt and the sliding sheet and to reduce the amount of wear. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2009-014893 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, when the surface hardness of the sliding sheet is set to be equal to or greater than that of the endless belt, the endless belt may wear out quickly. The sliding sheet is in constant contact with the endless belt, whereas each part of the inner peripheral surface of the endless belt alternates between contacting and not contacting the sliding sheet. In such a case, the endless belt, which slides intermittently, wears out faster than the sliding sheet, which slides continuously. For this reason, for example, when the material of both the endless belt and the sliding sheet is a resin with the same surface hardness, the endless belt may wear out faster than the sliding sheet.

[0005] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to suppress wear of the endless belt and the sliding sheet. [Means for solving the problem]

[0006] The fixing device according to the present invention for solving the above-mentioned problems includes a rotating body, a heater, a pressure pad, a sliding sheet, and an endless belt. The endless belt contacts the outer peripheral surface of the rotating body, and its base material is made of a heat-resistant resin having a glass transition temperature of 140°C or higher. The heater heats at least one of the rotating body and the endless belt. The sliding sheet contacts the inner peripheral surface of the endless belt, and its base material is made of a heat-resistant resin having a glass transition temperature of 140°C or higher. The pressure pad sandwiches the endless belt and the sliding sheet between the rotating body and the pressure pad. The microhardness of the endless belt measured by a nanoindentation method is greater than the microhardness of the sliding sheet.

[0007] According to this configuration, wear of the endless belt can be suppressed.

[0008] At least one of the base material of the endless belt and the base material of the sliding sheet may be made of polyimide.

[0009] According to this, since polyimide has high heat resistance, wear of the endless belt or the sliding sheet is suppressed.

[0010] The endless belt and the sliding sheet may each be made of a polyimide material.

[0011] According to this, since polyimide has high heat resistance, wear of the endless belt and the sliding sheet is suppressed.

[0012] In addition, the surface roughness Ra of the inner surface of the endless belt measured along the rotation direction of the endless belt may be smaller than the surface roughness Ra of the opposing surface of the sliding sheet that faces the endless belt measured along the rotation direction.

[0013] According to this, the greater the surface roughness Ra, the more susceptible the wear is, so by making the surface roughness Ra of the endless belt smaller than the surface roughness Ra of the sliding sheet, wear of the endless belt and the sliding sheet can be suppressed.

[0014] Furthermore, grease may be disposed between the endless belt and the sliding sheet, and the grease may contain a base oil containing perfluoropolyether and a thickener containing polytetrafluoroethylene.

[0015] This makes it possible to suppress wear on the endless belt and the sliding sheet.

[0016] The grease may also contain melamine cyanurate as an additive.

[0017] This can further reduce wear on the endless belt and the sliding sheet.

[0018] The opposing surface of the sliding sheet opposing the inner circumferential surface of the endless belt may have a contact portion that contacts the endless belt and a plurality of recesses that are recessed from the contact portion and do not contact the endless belt.

[0019] According to this, the sliding sheet has an uneven shape, and only the contact portion comes into contact with the endless belt, so that the contact area between the sliding sheet and the endless belt can be reduced. Therefore, the friction between the sliding sheet and the endless belt can be reduced. In addition, since grease can be held in the recesses of the sliding sheet, the friction between the sliding sheet and the endless belt can be further reduced.

[0020] In addition, in the sliding sheet, the ratio of the area of ​​the contact portion to the area of ​​the opposing surface of a predetermined area may be 50% or less.

[0021] In addition, in the sliding sheet, the opposing surface may be formed into an uneven shape with a plurality of polygonal sides forming ridges, the contact portions may be located on the sides of the polygons, and the recesses may be surrounded by the contact portions.

[0022] According to this, since the recess is surrounded by the contact portion, it is easy to retain the grease.

[0023] In addition, in the sliding sheet, the polygon may be a square.

[0024] According to this, the concave and convex shape is simple, so that the sliding sheet is easy to manufacture.

[0025] In addition, the contact portion of the sliding sheet may extend obliquely with respect to the direction of rotation of the endless belt.

[0026] According to this, the direction in which the contact portion extends is neither parallel to the rotation direction nor perpendicular to the rotation direction of the endless belt, thereby suppressing unevenness in the nip pressure in the rotation direction that occurs when the endless belt rotates.

[0027] In addition, in the sliding sheet, a groove may be formed in the contact portion so as to extend in a direction in which the contact portion extends.

[0028] According to this, grease can be held in the groove, so that friction between the sliding sheet and the endless belt can be further reduced.

[0029] In the sliding sheet, the depth of the groove may be 0.1 to 0.005 times the depth of the recess.

[0030] In addition, in the sliding sheet, the groove may have a first groove extending in a direction approaching the center of the width of the sliding sheet as it moves in the direction of movement of the endless belt, and a second groove extending in a direction away from the center of the width of the sliding sheet as it moves in the direction of movement of the endless belt, and the first groove may extend continuously and the second groove may be divided by the first groove.

[0031] According to this, when the endless belt moves, the first groove can move the grease to the center in the width direction of the sliding sheet. Since the second groove is divided by the first groove, the grease does not easily move outward.

[0032] The pressure pad may include a first pressure pad and a second pressure pad disposed downstream of the first pressure pad in the rotation direction of the endless belt.

[0033] According to this, since the pressure pad is formed of two pads, a long nip width can be ensured.

[0034] The second pressure pad may have a durometer hardness greater than that of the first pressure pad.

[0035] This allows the soft first pressure pad to secure a long pressing range, and the hard second pressure pad to appropriately adjust image quality, such as gloss, for example.

[0036] In addition, the second pressure pad may be positioned away from the first pressure pad, and the area of ​​the nip portion where the rotating body and the endless belt are in contact, that is not pressed by either the first pressure pad or the second pressure pad, may be configured to be 20 to 50% of the entire area of ​​the nip portion.

[0037] According to this, since there is a gap between the two pads, a long nip width can be ensured, and friction between the endless belt and the sliding sheet in the nip portion can be reduced.

[0038] The pressing range of the second pressure pad may be 10 to 20% of the entire range of the nip portion.

[0039] According to this, by reducing the pressing range of the second pressure pad, which has a high pressing force, it is possible to reduce the friction between the endless belt and the sliding sheet. Effect of the Invention

[0040] According to the present invention, wear of the endless belt and the sliding sheet can be suppressed. [Brief description of the drawings]

[0041] [Figure 1] 1 is a cross-sectional view showing a laser printer according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a cross-sectional view showing the fixing device. [Diagram 3]3 is an enlarged view showing a part of the endless belt and the sliding sheet in FIG. 2. [Figure 4] FIG. 4 is an enlarged perspective view showing an opposing surface of a sliding sheet. [Diagram 5] FIG. 4 is a plan view of the opposing surface of the sliding sheet. [Figure 6] 11A and 11B are perspective views showing another embodiment of the sliding sheet. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0042] Hereinafter, an embodiment of the invention will be described in detail with reference to the drawings as appropriate. 1, a fixing device 8 according to the embodiment is used in an image forming apparatus 1 such as a laser printer. The image forming apparatus 1 includes a main body housing 2, a sheet supply unit 3, an exposure device 4, a developer image forming unit 5, and the fixing device 8.

[0043] The sheet supply unit 3 is provided in the lower part of the main body housing 2, and includes a sheet tray 31 in which sheets S such as paper are stored, and a sheet supply mechanism 32. The sheets S in the sheet tray 31 are supplied to the developer image forming unit 5 by the sheet supply mechanism 32.

[0044] The exposure device 4 is disposed at the upper part inside the main body housing 2, and includes a light source device (not shown), a polygon mirror (shown without reference numerals), a lens, a reflecting mirror, etc. The exposure device 4 exposes the surface of the photoconductor drum 61 by scanning the surface of the photoconductor drum 61 at high speed with a light beam (see dashed line) based on image data emitted from the light source device.

[0045] The developer image forming unit 5 is disposed below the exposure device 4. The developer image forming unit 5 is configured as a process cartridge, and is detachable from the main body housing 2 through an opening formed when a front cover 21 provided at the front of the main body housing 2 is opened. The developer image forming unit 5 includes a photosensitive drum 61, a charger 62, a transfer roller 63, a developing roller 64, a supply roller 65, and a developer storage unit 66 that stores a developer made of dry toner.

[0046] The developer image forming unit 5 uniformly charges the surface of the photoconductor drum 61 using a charger 62. Thereafter, the surface of the photoconductor drum 61 is exposed to a light beam from an exposure device 4, so that an electrostatic latent image based on image data is formed on the surface. In addition, the developer image forming unit 5 supplies the developer in a developer container 66 to a development roller 64 via a supply roller 65.

[0047] Then, the developer image forming unit 5 supplies the developer on the developing roller 64 to the electrostatic latent image formed on the photosensitive drum 61. As a result, the electrostatic latent image is visualized and a developer image is formed on the photosensitive drum 61. Thereafter, the developer image forming unit 5 transfers the developer image on the photosensitive drum 61 to the sheet S by transporting the sheet S supplied from the sheet supply unit 3 between the photosensitive drum 61 and the transfer roller 63.

[0048] The fixing device 8 is disposed behind the developer image forming section 5. The fixing device 8 will be described in detail later. The fixing device 8 thermally fixes the developer image to the sheet S by passing the sheet S onto which the developer image has been transferred. The image forming apparatus 1 discharges the sheet S onto which the developer image has been thermally fixed, by a conveying roller 23 and a discharge roller 24, onto a paper discharge tray 22 outside the main body housing 2.

[0049] 2, the fixing device 8 includes a heating unit 81 and a pressure unit 82. The pressure unit 82 is urged toward the heating unit 81 by a pressing mechanism (not shown). In the following description, the direction in which the pressure unit 82 is urged toward the heating unit 81 is referred to as a "predetermined direction." In this embodiment, the predetermined direction is a direction perpendicular to the width direction and movement direction (described later), and is a direction in which the heating unit 81 and the pressure unit 82 face each other.

[0050] The heating unit 81 includes a heater 110 and a rotating body 120. The pressure unit 82 includes an endless belt 130, a pressure pad P, a holder 140, a sliding sheet 150, an upstream belt guide 160, a downstream belt guide 170, a stay 180, and grease GR. In the following description, the width direction of the endless belt 130 is simply referred to as the "width direction." The width direction is the direction in which the rotation axis X1 of the rotating body 120 extends. The width direction is perpendicular to a predetermined direction.

[0051] The heater 110 heats at least one of the rotating body 120 and the endless belt 130. In this embodiment, the heater 110 is disposed inside the rotating body 120 and heats the rotating body 120.

[0052] The rotating body 120 is a cylindrical roller, and has a base tube 121 and an elastic layer 122. The base tube 121 is a metal pipe. The elastic layer 122 is rotatable about a rotation axis X1. The rotating body 120 is driven to rotate by a motor (not shown) provided in the image forming apparatus 1. The elastic layer 122 is provided on the outer periphery of the base tube 121. In other words, the rotating body 120 has the elastic layer 122 on its surface. The elastic layer 122 has elasticity.

[0053] The endless belt 130 is an endless belt made of metal or the like. The endless belt 130 has a width larger than the width of the largest sheet S transported by the image forming apparatus 1. The endless belt 130 contacts the outer circumferential surface of the rotating body 120. The endless belt 130 transports the sheet S by sandwiching it between the endless belt 130 and the rotating body 120. When the rotating body 120 rotates, the endless belt 130 rotates clockwise in FIG. 2 due to friction with the rotating body 120 or the sheet S.

[0054] The pressure pad P is a member that sandwiches the endless belt 130, the sliding sheet 150, and the sheet S between the pressure pad P and the rotating body 120 to form a nip portion NP. In the following description, the moving direction of the endless belt 130 in the nip portion NP is simply referred to as the "moving direction". In this embodiment, the moving direction is a direction along the outer circumferential surface of the rotating body 120, but since this direction is approximately a direction perpendicular to the predetermined direction and the width direction, it will be illustrated as a direction perpendicular to the predetermined direction and the width direction. The moving direction is the same as the conveying direction of the sheet S in the nip portion NP.

[0055] The pressure pad P has a first pressure pad P1 and a second pressure pad P2. The second pressure pad P2 is located downstream of the first pressure pad P1 in the moving direction. The second pressure pad P2 has a durometer hardness higher than that of the first pressure pad P1.

[0056] Durometer hardness is specified in ISO7619-1. Durometer hardness is a value obtained from the depth of a specified indenter when the indenter is pressed into a test piece under specified conditions. For example, when the durometer hardness of the elastic layer 122 is 5, it is preferable that the durometer hardness of the first pressure pad P1 is 6 to 10, and the durometer hardness of the second pressure pad P2 is 70 to 90.

[0057] The first pressure pad P1 is a rectangular parallelepiped member. The first pressure pad P1 is made of rubber such as silicone rubber. The first pressure pad P1 has elasticity and can be elastically deformed. Since the first pressure pad P1 is thicker than the elastic layer 122, when the rotating body 120 and the first pressure pad P1 are pressed against each other, the deformation amount of the elastic layer 122 is smaller than the deformation amount of the first pressure pad P1. The first pressure pad P1 forms a first nip portion NP1 by sandwiching the endless belt 130 between the first pressure pad P1 and the rotating body 120.

[0058] The second pressure pad P2 is a rectangular parallelepiped member. The second pressure pad P2 is made of rubber such as silicone rubber. The second pressure pad P2 has elasticity and can be elastically deformed. The second pressure pad P2 has a higher durometer hardness than the elastic layer 122, but is thicker than the elastic layer 122. Therefore, when the rotating body 120 and the first pressure pad P1 are pressed against each other, the deformation amount of the elastic layer 122 is smaller than the deformation amount of the first pressure pad P1. The second pressure pad P2 forms a second nip portion NP2 by sandwiching the endless belt 130 between the rotating body 120 and the second pressure pad P2.

[0059] In the moving direction, between the first nip portion NP1 and the second nip portion NP2, there is a third nip portion NP3 where the pressure from the pressure unit 82 does not directly act. In this third nip portion NP3, the endless belt 130 contacts the rotating body 120, but there is no member that sandwiches the endless belt 130 between the rotating body 120 and the third nip portion NP3, so almost no pressure is applied. Therefore, the sheet S passes through the third nip portion NP3 while being heated by the rotating body 120 and almost without being pressurized. In this embodiment, the region from the upstream end of the first nip portion NP1 to the downstream end of the second nip portion NP2, that is, the entire region where the outer circumferential surface of the endless belt 130 and the rotating body 120 contact each other, is referred to as the nip portion NP. In other words, in this embodiment, the nip portion NP includes a portion to which the pressing force from the first pressure pad P1 and the second pressure pad P2 is not applied.

[0060] Of the nip portion NP where the rotating body 120 and the endless belt 130 come into contact, the area not pressed by either the first pressure pad P1 or the second pressure pad P2, i.e., the size in the movement direction of the third nip portion NP3, is 20 to 50% of the size in the movement direction of the entire range of the nip portion NP. The pressing area of ​​the second pressure pad P2, i.e., the size in the movement direction of the second nip portion NP2, is 10 to 20% of the size in the movement direction of the entire range of the nip portion NP.

[0061] The holder 140 is a member that holds the pressure pad N.

[0062] The sliding sheet 150 is disposed by being sandwiched between the inner peripheral surface 131 of the endless belt 130 and the pressure pad P. The sliding sheet 150 contacts the inner peripheral surface 131 of the endless belt 130. When the rotating body 120 rotates, the sliding sheet 150 is always in contact with the endless belt 130. In contrast, when the rotating body 120 rotates, each part of the inner peripheral surface of the endless belt 130 alternates between a state of contact with the sliding sheet 150 and a state of not contacting the sliding sheet 150.

[0063] The sliding sheet 150 is a sheet-like member. The base material of the sliding sheet 150 is made of a heat-resistant resin having a glass transition temperature of 140° C. or higher. In this embodiment, the sliding sheet 150 is made of polyimide. That is, in this embodiment, the base material of the endless belt 130 and the base material of the sliding sheet 150 are both polyimide. Note that the sliding sheet 150 may have various coatings on its surface.

[0064] As shown in Fig. 3, the sliding sheet 150 has an opposing surface 151 that faces the inner circumferential surface 131 of the endless belt 130. As shown in Fig. 4, the opposing surface 151 is formed in an uneven shape with multiple polygonal sides forming ridges. In this embodiment, the opposing surface 151 is formed in an uneven shape with multiple square sides forming ridges. The opposing surface 151 has a contact portion 152 that contacts the endless belt 130 and multiple recesses 153 that do not contact the endless belt 130.

[0065] The ratio of the area of ​​the contact portion 152 to the area of ​​the facing surface 151 having a predetermined area is 50% or less. The contact portion 152 is located on the side of a square formed on the facing surface 151. The contact portion 152 extends obliquely with respect to the rotation direction, i.e., the moving direction, of the endless belt 130. The contact portion 152 has a groove 154 formed therein, which extends in the direction in which the contact portion 152 extends.

[0066] The groove 154 extends obliquely with respect to the moving direction of the endless belt 130. The depth of the groove 154 is 0.1 to 0.005 times the depth of the recess 153. The groove 154 has a first groove 154A and a second groove 154B.

[0067] 5, the first groove 154A extends in a direction approaching the center C in the width direction of the sliding sheet 150 as it moves in the moving direction of the endless belt 130. The first groove 154A extends continuously. The second groove 154B extends in a direction away from the center C in the width direction of the sliding sheet 150 as it moves in the moving direction of the endless belt 130. The second groove 154B extends discontinuously, separated by the first groove 154A.

[0068] The recess 153 is a portion recessed from the contact portion 152 in a direction away from the endless belt 130. The recess 153 is surrounded by the contact portion 152. As shown in Fig. 4, in this embodiment, the contact portion 152 is formed in a square shape, and therefore the recess 153 has a quadrangular pyramid shape with the bottom as the apex.

[0069] The endless belt 130 has a base material made of a heat-resistant resin having a glass transition temperature of 140° C. or higher. Examples of heat-resistant resin having a glass transition temperature of 140° C. or higher include polyimide (glass transition temperature 220° C.), polyether ether ketone (glass transition temperature 143° C.), and polyetherimide (glass transition temperature 216° C.). In this embodiment, the endless belt 130 is made of polyimide. The surface of the endless belt 130 may be coated with a fluororesin or the like.

[0070] The microhardness of the endless belt 130 measured by the nanoindentation method is greater than the microhardness of the sliding sheet 150. The microhardness is measured in accordance with the ultra-microload hardness test method defined in the Japanese Industrial Standard JIS Z2255. The microhardness is the microhardness of the inner circumferential surface 131 of the endless belt 130 and the contact portion 152 on the opposing surface 151 of the sliding sheet 150. For example, the microhardness may be measured using a film material that is the material of the endless belt 130 and the sliding sheet 150.

[0071] The surface roughness Ra of the inner surface 131 of the endless belt 130 measured along the rotation direction of the endless belt 130 is smaller than the surface roughness Ra of the opposing surface 151 of the sliding sheet 150 that faces the endless belt 130 measured along the rotation direction. The surface roughness Ra is measured in accordance with the method specified in Japanese Industrial Standard JIS B0601.

[0072] 2, the upstream belt guide 160 is a member that guides the movement of the endless belt 130 upstream of the nip portion NP in the conveying direction of the sheet S. The upstream belt guide 160 has a curved surface that allows the endless belt 130 to rotate smoothly.

[0073] The downstream belt guide 170 is a member that guides the movement of the endless belt 130 downstream of the nip portion NP in the conveying direction of the sheet S. The upstream belt guide 160 has a curved surface that allows the endless belt 130 to rotate smoothly.

[0074] The stay 180 is a member that supports the holder 140, the upstream belt guide 160, and the downstream belt guide 170. The stay 180 is formed by pressing a metal plate.

[0075] The grease GR is provided between the endless belt 130 and the sliding sheet 150 to reduce friction between the endless belt 130 and the sliding sheet 150. The grease GR is located on the inner circumferential surface 131 of the endless belt 130, the contact portion 152 of the sliding sheet 150, the recessed portion 153, and the groove 154.

[0076] Grease GR contains a base oil, a thickener, and an additive. Grease GR desirably has a consistency of 330 to 385 at 25° C. Grease GR more desirably has a consistency of 335 to 350 at 25° C. Grease GR has a yield stress of 50 to 250 Pa.

[0077] The consistency and yield stress of grease GR can be adjusted by the blending ratio of base oil and thickener.

[0078] Penetration is measured according to the method specified in the Japanese Industrial Standard JIS K2220. The penetration of grease GR is measured at 25°C by dropping a cone attached to a penetration meter into a pot filled with a sample and reading the depth of penetration for 5 seconds (see JIS K2220 7.1).

[0079] The yield stress in this application is the stress value when the storage modulus G' = the loss modulus G". The storage modulus G' and the loss modulus G" are measured using a rheometer (viscoelasticity measuring device) specified in Japanese Industrial Standard JIS K7244-10. In this case, the measurement frequency of the rheometer is 1 Hz. The storage modulus G' and loss modulus G'' can be measured by measuring the stress while gradually increasing the strain, and the strain γ0, phase difference δ, and stress peak σ0 can be measured. The storage modulus G' is the peak value of the elastic component divided by the peak value of strain (G' = σ0 × cosδ ÷ γ0). The loss modulus G″ is the peak value of the viscous component divided by the peak value of strain (G″=σ0×sinδ÷γ0).

[0080] The base oil is made of a fluorine oil. The fluorine oil is, for example, perfluoropolyether (PFPE) or chlorotrifluoroethylene (CTFE). In this embodiment, the base oil contains perfluoropolyether. The viscosity of the base oil in this embodiment is 100 to 400 mm at 40°C. 2 / S.

[0081] The thickener is made of a solid lubricant containing fluorine. In this embodiment, the solid lubricant containing fluorine is polytetrafluoroethylene (PTFE).

[0082] The additive is a solid lubricant having layered crystals and not containing fluorine. Examples of the layered solid lubricant not containing fluorine include melamine cyanurate (MCA), molybdenum disulfide, and graphite. In this embodiment, the solid lubricant is melamine cyanurate (MCA). The particle size of melamine cyanurate is 10 to 20 times larger than that of polytetrafluoroethylene (PTFE).

[0083] As described above, the following effects can be obtained in this embodiment. The sliding sheet 150 is in constant contact with the endless belt 130, whereas each portion of the inner peripheral surface of the endless belt 130 alternates between a state of contact and a state of no contact with the sliding sheet 150. In such a case, the endless belt 130, which slides intermittently, wears out faster than the sliding sheet 150, which slides continuously. In the fixing device 8 of this embodiment, both the endless belt 130 and the sliding sheet 150 are made of polyimide, but the microhardness of the endless belt 130 measured by the nanoindentation method is greater than the microhardness of the sliding sheet 150, so that it is possible to suppress wear of the endless belt 130. As a result, in the fixing device 8, the endless belt 130 does not wear out more quickly than necessary relative to the sliding sheet 150, and wears out in a balanced manner, so that the life of the fixing device 8 is extended.

[0084] Furthermore, the surface roughness Ra of the inner peripheral surface 131 of the endless belt 130 measured along the rotation direction of the endless belt is smaller than the surface roughness Ra of the sliding sheet measured along the rotation direction. Since the larger the surface roughness Ra, the more susceptible the endless belt 130 is to wear, by making the surface roughness Ra of the endless belt 130 smaller than the surface roughness Ra of the sliding sheet 150, wear of the endless belt 130 and the sliding sheet 150 can be suppressed.

[0085] Furthermore, the grease GR placed between the endless belt 130 and the sliding sheet 150 contains a base oil containing perfluoropolyether and polytetrafluoroethylene, so that wear of the endless belt 130 and the sliding sheet 150 can be suppressed.

[0086] Furthermore, since the grease GR further contains, as an additive, melamine cyanurate, which is a fluorine-free solid lubricant having layered crystals, the wear of the endless belt 130 and the sliding sheet 150 can be further suppressed.

[0087] Furthermore, the opposing surface 151 of the sliding sheet 150 has a contact portion 152 that contacts the endless belt 130, and a plurality of recesses 153. Therefore, the sliding sheet 150 can reduce the contact area between the endless belt 130 and the sliding sheet 150, and can reduce friction between the endless belt 130 and the sliding sheet 150. Furthermore, since the recesses 153 of the sliding sheet 150 can hold grease GR, friction between the sliding sheet 150 and the endless belt 130 can be further reduced.

[0088] In addition, since the recessed portion 153 of the sliding sheet 150 is surrounded by the contact portion 152, the grease GR can be easily retained.

[0089] Furthermore, the sliding sheet 150 is formed in an uneven shape with multiple square sides forming ridges. Since the uneven shape of the sliding sheet 150 is simple, the sliding sheet 150 is easy to manufacture.

[0090] Furthermore, the contact portion 152 of the sliding sheet 150 extends obliquely with respect to the rotation direction of the endless belt 130. This makes it possible to suppress unevenness in the nip pressure in the rotation direction that occurs when the endless belt 130 rotates.

[0091] Furthermore, the sliding sheet 150 has a groove 154 formed in the contact portion 152, the groove 154 extending along the extending direction of the contact portion 152. Therefore, the grease GR can be held in the groove 154, and the friction between the sliding sheet 150 and the endless belt 130 can be further reduced.

[0092] 5, the groove 154 of the sliding sheet 150 has a first groove 154A and a second groove 154B. Since the first groove 154A extends in a direction approaching the center C of the sliding sheet 150 in the width direction and extends continuously, when the endless belt 130 moves, the first groove 154A can move the grease GR toward the center C of the sliding sheet 150 in the width direction. On the other hand, since the second groove 154B is divided by the first groove 154A, the grease GR is less likely to move outward.

[0093] The pressure pad P includes a first pressure pad P1 and a second pressure pad P2, which ensures a long nip width.

[0094] Furthermore, since the second pressure pad P2 is harder than the first pressure pad P1, the soft first pressure pad P1 can secure a longer pressing range, and the hard second pressure pad P2 can appropriately adjust image quality such as gloss.

[0095] 2, the area of ​​the nip portion NP that is not pressed by either the first pressure pad P1 or the second pressure pad P2 (third nip portion NP3) is 20 to 50% of the entire area of ​​the nip portion NP. Therefore, by providing a gap between the first pressure pad P1 and the second pressure pad P2, a long nip width can be ensured and friction between the endless belt 130 and the sliding sheet 150 in the nip portion NP can be reduced.

[0096] The pressing range of the second pressure pad P2 is 10 to 20% of the entire range of the nip portion NP. Therefore, by reducing the pressing range of the second pressure pad P2, which has a high pressing force, the friction between the endless belt 130 and the sliding sheet 150 can be reduced.

[0097] The present invention is not limited to the above-described embodiment, but can be used in various forms as exemplified below.

[0098] In the above embodiment, a cylindrical roller incorporating a heater 110 is exemplified as the rotating body, but the present invention is not limited thereto, and may be, for example, an endless belt whose inner circumferential surface is heated by a heater. Alternatively, an external heating method in which a heater is disposed outside the rotating body and the outer circumferential surface of the rotating body is heated, or an induction heating method may be used. Alternatively, a heater may be disposed inside the endless belt and the rotating body in contact with the outer circumferential surface of the endless belt may be indirectly heated. Alternatively, the rotating body and the endless belt may each incorporate a heater.

[0099] In the above embodiment, the base material of the endless belt 130 and the base material of the sliding sheet 150 are both polyimide, but the present invention is not limited to this, and at least one of the base material of the endless belt and the base material of the sliding sheet may be polyimide. For example, the endless belt may have a base material made of polyimide and the sliding sheet may have a base material made of another heat-resistant resin. Also, the endless belt may have a base material made of another heat-resistant resin and the sliding sheet may have a base material made of polyimide.

[0100] Furthermore, both the base material of the endless belt 130 and the base material of the sliding sheet 150 may not be polyimide.

[0101] In the above embodiment, the opposing surface 151 of the sliding sheet 150 is formed in an uneven shape with multiple square sides forming ridges, but the present invention is not limited to this, and may be a polygon other than a rectangle, parallelogram, or quadrangle. For example, as shown in FIG. 6(a), the opposing surface of the sliding sheet 250 is formed in an uneven shape with multiple hexagonal sides forming ridges. Also, as shown in FIG. 6(b), the opposing surface of the sliding sheet 350 is formed in an uneven shape with multiple triangular sides forming ridges. Even with such sliding sheets 250 and 350, the same effect as in the above embodiment can be obtained. Note that, although grooves formed in the contact portion are omitted in FIGS. 6(a) and (b), a configuration in which grooves are formed similarly to the above embodiment can be used.

[0102] The elements described in the above-mentioned embodiment and modified examples may be implemented in any combination. [Explanation of symbols]

[0103] 1. Image forming device 8 Fixing device 110 Heater 120 Rotating Body 121 Plain tube 122 Elastic layer 130 Endless Belt 131 Inner surface 140 Holder 150 Sliding Sheet 151 Opposite Surface 152 Contact part 153 Recess 154 Groove 154A 1st groove 154B 2nd groove GR Grease N Pressure Pad NP Nip

Claims

1. A rotating body; an endless belt in contact with an outer circumferential surface of the rotor, the endless belt having a base material made of a heat-resistant resin having a glass transition temperature of 140° C. or higher; a heater for heating at least one of the rotating body and the endless belt; a sliding sheet in contact with an inner peripheral surface of the endless belt, the sliding sheet having a base material made of a heat-resistant resin having a glass transition temperature of 140° C. or higher; a pressure pad that sandwiches the endless belt and the sliding sheet between the pressure pad and the rotating body, The microhardness of the endless belt measured by a nanoindentation method is greater than the microhardness of the sliding sheet, a surface of the sliding sheet facing the inner circumferential surface of the endless belt has a contact portion that contacts the endless belt and a plurality of recesses that are recessed from the contact portion and do not contact the endless belt, The fixing device, wherein the contact portion has a groove formed therein, the groove extending in a direction in which the contact portion extends.

2. 2. The fixing device according to claim 1, wherein at least one of a base material of the endless belt and a base material of the sliding sheet is made of polyimide.

3. 3. The fixing device according to claim 1, wherein a base material of the endless belt and a base material of the sliding sheet are made of polyimide.

4. 4. The fixing device according to claim 1, wherein a surface roughness Ra of an inner surface of the endless belt measured along a rotation direction of the endless belt is smaller than a surface roughness Ra of an opposing surface of the sliding sheet facing the endless belt measured along the rotation direction.

5. Grease is disposed between the endless belt and the sliding sheet, 5. The fixing device according to claim 1, wherein the grease contains a base oil containing perfluoropolyether and a thickener containing polytetrafluoroethylene.

6. 6. The fixing device according to claim 5, wherein the grease contains melamine cyanurate as an additive.

7. 7. The fixing device according to claim 1, wherein a ratio of an area of ​​the contact portion to a predetermined area of ​​the facing surface is 50% or less.

8. The opposing surface is formed in an uneven shape with a plurality of polygonal sides forming ridges, the contact portion is located on a side of the polygon; The fixing device according to claim 1 , wherein the recess is surrounded by the contact portion.

9. The fixing device according to claim 8 , wherein the polygon is a square.

10. 10. The fixing device according to claim 1, wherein the contact portion extends obliquely with respect to a rotation direction of the endless belt.

11. 11. The fixing device according to claim 1, wherein the depth of the groove is 0.1 to 0.005 times the depth of the recess.

12. The groove is a first groove extending in a direction approaching a center in a width direction of the sliding sheet as the groove advances in a moving direction of the endless belt; a second groove extending in a direction away from the center of the width direction of the sliding sheet as the second groove extends in a direction toward the moving direction of the endless belt, The first groove extends continuously, The fixing device according to claim 1 , wherein the second groove is separated from the first groove.

13. 13. The fixing device according to claim 1, wherein the pressure pad includes a first pressure pad and a second pressure pad disposed downstream of the first pressure pad in the rotation direction of the endless belt.

14. 14. The fixing device according to claim 13, wherein the second pressure pad has a durometer hardness higher than that of the first pressure pad.

15. the second pressure pad is located away from the first pressure pad; The fixing device according to claim 13 or 14, characterized in that the area of ​​the nip portion where the rotating body and the endless belt are in contact and that is not pressed by either the first pressure pad or the second pressure pad is 20 to 50% of the entire area of ​​the nip portion.

16. 16. The fixing device according to claim 15, wherein the pressing range of the second pressure pad is 10 to 20% of the entire range of the nip portion.

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