Manufacturing method for sliding members and bearings

Abstract

The present invention provides a method for manufacturing a sliding member having a sliding layer made of a resin composition that does not use PFAS. [Solution] The method for manufacturing a sliding member includes the steps of: preparing an intermediate material by heating polyimide varnish to reduce the solvent content; impregnating the surface of a porous layer formed on one side of a metal substrate with the intermediate material; and forming a sliding layer made of a resin composition mainly composed of polyimide that covers the porous layer by firing the intermediate material.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a sliding member and a bearing.

Background Art

[0002] In sliding members, durability is required when used in a high-speed environment for application to compressors. In resin-based bearings, fluororesins that are the base resins of resin compositions are well-known as synthetic resins having excellent sliding properties, and sufficient heat resistance is ensured against heat generation due to sliding friction. Therefore, PTFE (polytetrafluoroethylene), PFA (perfluoroalkoxyalkane), FEP (perfluoroethylene propene copolymer), and ETFE (ethylene tetrafluoroethylene copolymer) are often used as the base resins of the resin compositions of sliding members (for example, see Patent Document 1).

[0003] However, in recent years, as part of environmental issues, the use of PFAS (perfluoroalkyl compounds and polyfluoroalkyl compounds) has been regarded as a problem, and the above PTFE, PFA, FEP, and ETFE are all substances classified as PFAS.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The present invention has been made in consideration of the above points. An object of the present invention is to provide a method for manufacturing a sliding member and a bearing having a sliding layer made of a resin composition that does not use PFAS.

Means for Solving the Problems

[0006] A method for manufacturing a sliding member according to a first aspect of the present invention is: The process involves a step of producing an intermediate material by heating polyimide varnish to reduce the solvent content, The steps include impregnating the surface of a porous layer formed on one side of a metal substrate with the intermediate material, The steps include: firing the intermediate material to form a sliding layer made of a resin composition mainly composed of polyimide that covers the porous layer; Includes.

[0007] According to this embodiment, by reducing the solvent content in the polyimide varnish before impregnating the intermediate material into the porous layer, it is possible to suppress the generation of bubbles on the surface of the resin composition due to solvent evaporation when firing the intermediate material impregnated into the porous layer. As a result, it becomes possible to form the sliding layer covering the porous layer with a resin composition mainly composed of polyimide with a uniform structure, thereby realizing the manufacture of a sliding member having a sliding layer that does not use PFAS.

[0008] A method for manufacturing a sliding member according to a second aspect of the present invention is a method for manufacturing a sliding member according to a first aspect, In the step of impregnating the intermediate material, the intermediate material is pressed onto the surface of the porous layer to impregnate it.

[0009] According to this embodiment, even an intermediate material mainly composed of polyimide with reduced solvent content and a clay-like consistency can be sufficiently impregnated into the porous layer by pressing.

[0010] A third aspect of the present invention is a method for manufacturing a sliding member, which is a method for manufacturing a sliding member according to the first or second aspect of the present invention. In the step of producing the intermediate material, the intermediate material is produced by reducing the solvent content of the polyimide varnish until it becomes clay-like.

[0011] In this embodiment, since the solvent content in the intermediate material is sufficiently reduced before impregnation of the intermediate material into the porous layer, it is possible to effectively suppress the generation of bubbles on the surface of the resin composition due to the evaporation of the solvent when the intermediate material impregnated into the porous layer is fired.

[0012] A method for manufacturing a sliding member according to a fourth aspect of the present invention is a method for manufacturing a sliding member according to any one of the first to third aspects, In the step of producing the intermediate material, the solvent content is reduced until no bubbles are generated on the surface of the polyimide varnish due to the evaporation of the solvent during the firing step.

[0013] According to this embodiment, when the intermediate material impregnated in the porous layer is fired, no bubbles are generated on the surface of the resin composition due to the evaporation of the solvent. Therefore, it becomes possible to form the sliding layer covering the porous layer with a resin composition mainly composed of polyimide with a sufficiently uniform structure.

[0014] A fifth aspect of the present invention is a method for manufacturing a sliding member according to any one of the first to fourth aspects, In the step of producing the intermediate material, the solvent content is reduced such that, when the solvent content at the start of the step is 100 wt%, the solvent content at the end of the step is 16 wt% or more and less than 28 wt%.

[0015] According to actual verification by the inventors of this case, it was confirmed that by reducing the solvent content in the intermediate material during the intermediate material preparation step, such that the solvent content at the end of the step is between 16 wt% and 28 wt%, when the solvent content at the start of the step is set to 100 wt%, it is possible to effectively suppress the generation of bubbles on the surface of the resin composition due to solvent evaporation when the intermediate material impregnated in the porous layer is fired.

[0016] A method for manufacturing a sliding member according to the sixth aspect of the present invention is a method for manufacturing a sliding member according to any of the first to fifth aspects, The polyimide varnish further comprises ultra-high molecular weight polyethylene, graphite, and molybdenum disulfide. The total content of ultra-high molecular weight polyethylene, graphite, and molybdenum disulfide in the polyimide varnish, excluding the solvent, is 40 vol% or less.

[0017] Verification by the inventors of this invention confirmed that by limiting the content of additives excluding solvents in the polyimide varnish to 40 vol% or less, it is possible to prevent the homogeneity of the resin composition mainly composed of polyimide from being impaired when the intermediate material impregnated in the porous layer is fired. Furthermore, it was confirmed that the resistance to seizing can be improved by including ultra-high molecular weight polyethylene, graphite, and molybdenum disulfide in the resin composition within a predetermined range.

[0018] A method for manufacturing a sliding member according to the seventh aspect of the present invention is a method for manufacturing a sliding member according to any of the first to sixth aspects, The polyimide varnish further comprises one or more solid lubricants selected from the group consisting of metal oxides, Cu alloys, sulfur compounds (excluding molybdenum disulfide), aramid, carbon fibers, polyether ether ketone (PEEK) resin, and hard particles containing a Laves phase composed of Co, Mo, and Si. The total content of ultra-high molecular weight polyethylene, graphite, molybdenum disulfide, and the solid lubricant in the polyimide varnish, excluding the solvent, is 40 vol% or less.

[0019] Actual verification by the inventors confirmed that by keeping the additive content excluding solvents in the polyimide varnish at 40 vol% or less, it is possible to prevent the homogeneity of the resin composition mainly composed of polyimide from being impaired when the intermediate material impregnated in the porous layer is fired. Furthermore, it was confirmed that the resistance to seizing can be improved by including ultra-high molecular weight polyethylene, graphite, molybdenum disulfide, and a solid lubricant in the resin composition within a predetermined range.

[0020] The manufacturing method of the sliding member according to the eighth aspect of the present invention is the manufacturing method of the sliding member according to any one of the first to seventh aspects, and in the step of producing the intermediate material, the polyimide varnish is heated at 80°C to 150°C.

[0021] According to such an aspect, the content of the solvent can be reduced without curing the polyimide varnish.

[0022] The manufacturing method of the bearing according to the ninth aspect of the present invention is a step of producing an intermediate material by heating a polyimide varnish to reduce the content of the solvent, and a step of impregnating the surface of the porous layer formed on one surface of the plate-shaped metal base material with the intermediate material, and a step of forming a sliding layer made of a resin composition mainly composed of polyimide that covers the porous layer by firing the intermediate material, and including.

[0023] The manufacturing method of the bearing according to the tenth aspect of the present invention is a step of producing an intermediate material by heating a polyimide varnish to reduce the content of the solvent, and a step of impregnating the surface of the porous layer formed on one surface of the metal base material with the intermediate material, and a step of forming a sliding layer made of a resin composition mainly composed of polyimide that covers the porous layer by firing the intermediate material, and a step of processing the metal base material on which the sliding layer covering the porous layer is formed into a scroll bush shape with the sliding layer on the inside, and including.

Effect of the Invention

[0024] According to the present invention, it is possible to provide a manufacturing method of a sliding member and a bearing having a sliding layer made of a resin composition that does not use PFAS.

Brief Description of the Drawings

[0025] [Figure 1] Figure 1 is a cross-sectional diagram of an example of a sliding member according to one embodiment. [Figure 2] Figure 2 is a perspective view showing an example of a bearing according to one embodiment. [Figure 3] Figure 3 is a cross-sectional view showing an example of a bearing according to one embodiment. [Figure 4] Figure 4 is a flowchart showing an example of a manufacturing method for a sliding member according to one embodiment. [Figure 5] Figure 5 is a flowchart showing an example of a bearing manufacturing method according to one embodiment. [Figure 6] Figure 6 is a flowchart showing another example of a bearing manufacturing method according to one embodiment. [Figure 7] Figure 7 is a schematic diagram illustrating the overview of the seizure resistance test. [Figure 8] Figure 8 is a table summarizing the composition and test results of the resin compositions of the sliding members in the examples and comparative examples. [Figure 9] Figure 9 is a graph showing the relationship between the composition of the resin composition and the baking pressure. [Figure 10] Figure 10 is a graph showing the relationship between the content of ultra-high molecular weight polyethylene and the baking surface pressure when the blending ratio of graphite and molybdenum disulfide in the resin composition is kept constant. [Figure 11] Figure 11 is a graph showing the relationship between the content of ultra-high molecular weight polyethylene and the baking surface pressure when the total content of graphite, molybdenum disulfide, and ultra-high molecular weight polyethylene in the resin composition is kept constant. [Figure 12A] Figure 12A shows a cross-sectional view of the fixture used for the viscosity test, in the left-right direction. [Figure 12B] Figure 12B is a plan view of the jig used for the viscosity test, seen from the top opening. [Modes for carrying out the invention]

[0026] Embodiments of the present invention will be described in detail below with reference to the attached drawings. In this specification, "%" in relation to composition means "vol%" unless otherwise specified. Also, in this specification, "○○~△△" (where ○○ and △△ are both numbers) means "○○ or more and △△ or less" unless otherwise specified. Also, in this specification, "main component" means a component that is present in an amount of 50 volume (vol) or more of the total composition.

[0027] <Configuration of sliding members> Figure 1 is a cross-sectional diagram showing an example of a sliding member 1 according to one embodiment. The sliding member 1 according to this embodiment comprises a metal base material 2, a porous layer 3 formed of a single metal or alloy composition on one surface of the metal base material 2, and a sliding layer 5 in which the porous layer 3 is coated with a resin composition 4.

[0028] The material of the metal base material 2 is not particularly limited as long as it has sufficient strength and dimensional stability to be used as a backing plate base material for bearings. For example, it may be low-carbon steel (SPCC, SS400, etc.) or copper-plated steel sheet made of Fe-based sheet material plated with Cu.

[0029] The porous layer 3 is formed by sintering metal powder onto the surface of the metal substrate 2. In this example, the metal substrate 2 is an iron (Fe)-based plate material. The metal powder used to form the porous layer 3 is either pure Cu or an alloy mainly composed of Cu, and in this example, Cu-Sn alloy powder is used. Note that the Cu-Sn alloy powder may contain metals other than Cu and Sn, specifically P, etc.

[0030] The manufacturing method for the porous layer 3 involves scattering Cu-Sn alloy powder onto a steel plate to a predetermined thickness, and then sintering the steel plate with the scattered Cu-Sn alloy powder in a sintering furnace. This forms a porous layer 3 of Cu-Sn alloy on the steel plate to a predetermined thickness.

[0031] The sliding layer 5 is formed by impregnating the porous layer 3 with an intermediate material to a predetermined thickness, and then firing the intermediate material impregnated in the porous layer 3. Here, the intermediate material refers to a polyimide varnish to which additives are added as needed, and then the solvent contained in the polyimide varnish is evaporated. Furthermore, the process of heating the intermediate material applied to and impregnated on the metal substrate 2 and the porous layer 3 at a predetermined temperature to change it into a resin composition 4 and form the sliding layer 5 is called firing.

[0032] In this example, the manufacturing method for the sliding layer 5 involves first adding additives to the polyimide varnish as needed, then heating the container containing the polyimide varnish in a water bath at approximately 100°C for 3 hours using a hot plate, thereby volatilizing the solvent in the polyimide varnish and producing an intermediate material. Any known heating method can be used to volatilize the solvent in the polyimide varnish, and in addition to a hot plate, a heating furnace or the like may also be used. Next, a predetermined amount of the intermediate material is supplied onto the porous layer 3 formed on the surface of the metal substrate 2, and the intermediate material is pressed against the porous layer 3, thereby impregnating the porous layer 3. The amount of intermediate material supplied onto the porous layer 3 is such that, after firing the intermediate material as described later, the porous layer 3 is covered to a thickness that prevents it from being exposed from the surface of the sliding layer 5. After that, the intermediate material impregnated into the porous layer 3 is fired. As an example, using a firing furnace, the intermediate material impregnated in the porous layer 3 is heated at 120°C for 10 minutes as a preliminary drying step, and then heated at 220°C for 60 minutes as a main drying step to harden the intermediate material. In this way, a sliding layer 5 made of a resin composition 4 mainly composed of polyimide is formed.

[0033] In this example, the sliding member 1 can use metal powder in which the total particle size of the metal powder forming the porous layer 3 is in the range of 15 to 180 μm, preferably 25 to 150 μm. Furthermore, the thickness T1 of the porous layer 3 formed by such metal powder can be set to about 0.03 to 0.45 mm. The thickness of the porous layer 3 is such that at least two or more layers of metal powder can be stacked and sintered.

[0034] Furthermore, the sliding member 1 can have a sliding layer 5 thickness T2 of approximately 0.05 to 0.50 mm. Here, the sliding layer 5 thickness T2 is the thickness from the surface of the metal substrate 2. The thickness of the sliding layer 5 is set to be on average thicker than the thickness of the porous layer 3 so that the porous layer 3 is not exposed. In this example, the sliding layer 5 thickness T2 was set to 0.3 mm.

[0035] <Bearing configuration> Figure 2 is a perspective view showing an example of a bearing 7 according to one embodiment, and Figure 3 is a cross-sectional view showing an example of a bearing 7 according to one embodiment, illustrating an example of the use of the sliding member 1 according to this embodiment.

[0036] The bearing 7 according to this embodiment is configured in an annular shape with the sliding member 1, as described with reference to Figure 1, having a sliding layer 5 on the inside. The bearing 7 supports the shaft 8, which is the mating material, with the sliding layer 5 that forms a cylindrical inner circumferential surface. The bearing 7 is configured such that the shaft 8 slides in linear motion or rotational motion.

[0037] As a first modification, the bearing 7 may comprise a cylindrical metal substrate 2 having a seam that divides it in the circumferential direction, a seamless porous layer 3 formed on the inner circumferential surface of the metal substrate 2, and a sliding layer 5 covering the porous layer 3. In this case, since there is no seam in the porous layer 3 of the bearing 7, no seams appear in the sliding layer 5 covering the porous layer 3, reducing friction at the seams and reducing heat generation due to friction. This improves wear resistance and seizure resistance in the high-speed rotation range, and also improves the performance of the bearing 7 itself. Furthermore, since there is no seam in the porous layer 3, no seams appear in the sliding layer 5 covering the porous layer 3, reducing the torque generated during friction at the seams. This contributes to reducing power consumption and energy loss. Therefore, it can contribute to carbon neutrality. In addition, for bearings used in high-speed rotation environments such as EV motors and electric compressors, it becomes possible to replace conventional rolling bearings with the bearing 7 according to this modification, which leads to miniaturization and weight reduction. Furthermore, when conventional bearings with seams on the sliding surface are applied to motors and compressors, an internal diameter cutting process (i.e., surface alignment of the inner surface at the seam) is required. However, with the bearing 7 according to this modified example, since there are no seams in the porous layer 3, no seams appear in the sliding layer 5 covering the porous layer 3, thus eliminating the internal diameter cutting process. In addition, by eliminating this process, the generation of industrial waste (carbon contained in the resin composition) generated during cutting can be suppressed, thus contributing to carbon neutrality.

[0038] An example of a manufacturing method for the bearing 7 according to the first modified example will be described. First, a cylindrical metal substrate 2 having a joint that divides it in the circumferential direction is press-fitted into the inside of a cylindrical housing to make the joint tightly closed. Next, a cylindrical or columnar jig is placed inside the metal substrate 2 in the press-fitted state in the housing, and raw material powder for the porous layer 3 is filled into the gap between the inner circumferential surface of the metal substrate 2 and the outer circumferential surface of the jig. At this time, the raw material powder may be filled into the gap while rotating the jig and / or while applying ultrasonic vibration to the jig. Then, by sintering the raw material powder, a seamless porous layer 3 made of a single metal or alloy composition is formed on the inner circumferential surface of the metal substrate 2. In the step of sintering the raw material powder, the metal substrate 2 together with the jig may be placed in a heating furnace to sinter the raw material powder. Next, the intermediate material described above is impregnated into the surface of the porous layer 3. Then, by firing the intermediate material, a sliding layer 5 made of a resin composition 4 mainly composed of polyimide is formed to cover the porous layer 3. Subsequently, the inner surface of the sliding layer 5 may be burnished to reduce the inner diameter roundness to 50 μm or less by pressing a cylindrical core into the inside of the sliding layer 5 while constraining the outer surface of the metal substrate 2 with a die.

[0039] As a second modification, the bearing 7 comprises a cylindrical metal base material 2, a porous layer 3 formed on the inner circumferential surface of the metal base material 2, and a sliding layer 5 covering the porous layer 3. The bearing 7 may have a region on the inner circumferential surface where the resin composition 4 is absent, and a non-porous layer formed of a single metal or alloy composition is exposed. In this case, the bearing 7 has a region on its inner circumferential surface where the resin composition 4 is absent, and a non-porous layer formed of a single metal or alloy composition is exposed. This region is recessed compared to the surrounding area because the resin composition 4 is absent in the surrounding area, and the non-porous layer does not contain the numerous voids found in the porous layer 3, thus acting as a groove. When the bearing 7 is in use, the inner surface of the groove does not come into contact with the shaft 8, which is the object being slid, thus contributing to a reduction in heat generation due to friction. This suppresses temperature rise in the high-speed rotation region, improving the performance of the bearing 7 itself. In particular, when lubricating oil or grease is present, the oil film formation on the sliding surface is maintained in the groove, so a further reduction in heat generation is expected compared to use in a dry environment. Furthermore, a portion of the inner circumferential surface of the bearing 7 lacks the resin composition 4, and an area is provided where a non-porous layer formed of a single metal or alloy composition is exposed. As a result, no protrusions due to the joint appear on the sliding surface, reducing the torque generated during friction at the joint. This contributes to reducing power consumption and energy loss. Therefore, it can contribute to carbon neutrality. In addition, for bearings used in high-speed environments such as EV motors and electric compressors, it is possible to replace conventional rolling bearings with the bearing 7 according to this modified example, which leads to miniaturization and weight reduction. Moreover, when applying conventional bearings with joints on the sliding surface to motors and compressors, an internal diameter cutting process (i.e., surface alignment of the inner surface at the joint) was required. However, with the bearing 7 according to this modified example, a portion of the inner circumferential surface of the bearing 7 lacks the resin composition, and an area is provided where a non-porous layer formed of a single metal or alloy composition is exposed. As a result, no protrusions due to the joint appear on the sliding surface, thus eliminating the need for the internal diameter cutting process.

[0040] An example of a manufacturing method for the bearing 7 according to the second modified example will be described. First, a porous layer 3 made of a single metal or alloy composition is formed on one surface of a plate-shaped metal substrate 2. Next, the metal substrate 2 is rolled up with the porous layer 3 on the inside to form a cylindrical shape. Next, the joint portion is welded from the outer diameter side of the metal substrate 2. At this time, the porous layer 3 above the joint portion melts, forming a non-porous layer made of a single metal or alloy composition. Next, the intermediate material described above is impregnated into the surface of the porous layer 3, and then the intermediate material is fired to form a sliding layer 5 made of a resin composition 4 mainly composed of polyimide that covers the porous layer 3. At this time, since the surface of the non-porous layer is not impregnated with the intermediate material, the resin composition 4 is not present in a part of the inner circumferential surface of the bearing 7, and an area where the non-porous layer is exposed is formed. After that, the inner circumferential surface of the sliding layer 5 may be burnished by pressing a cylindrical mandrel into the inside of the sliding layer 5 while constraining the outer circumferential surface of the metal substrate 2 with a die.

[0041] Another example of a method for manufacturing the bearing 7 according to the second modified example will be described. First, a porous layer 3 made of a single metal or alloy composition is formed on one surface of a plate-shaped metal substrate 2. Next, the above-mentioned intermediate material is impregnated into the surface of the porous layer 3, and the intermediate material is fired to form a sliding layer 5 made of a resin composition 4 mainly composed of polyimide that covers the porous layer 3. Next, the metal substrate 2 is rolled up with the sliding layer 5 on the inside to form a cylindrical shape. Next, the joint portion is welded from the outer diameter side of the metal substrate 2. At this time, the porous layer 3 above the joint portion melts to form a non-porous layer made of a single metal or alloy composition, and the sliding layer 5 above the joint portion peels off, so that a region is formed on the inner circumferential surface of the bearing 7 where the resin composition 4 is absent and the non-porous layer is exposed. After that, the inner circumferential surface of the sliding layer 5 may be burnished by pressing a cylindrical mandrel into the inside of the sliding layer 5 while constraining the outer circumferential surface of the metal substrate 2 with a die.

[0042] [Resin composition] The resin composition 4 will be described in detail below. Resin composition 4 mainly contains polyimide, and further contains ultra-high molecular weight polyethylene, graphite, and molybdenum disulfide. The content of ultra-high molecular weight polyethylene in resin composition 4 is 1 vol% or more and less than 5 vol%. The total content of ultra-high molecular weight polyethylene, graphite, and molybdenum disulfide in resin composition 4 is 10 vol% or more and 40 vol% or less.

[0043] The content of ultra-high molecular weight polyethylene in resin composition 4 may be less than the total content of graphite and molybdenum disulfide in the resin composition. The content of graphite and molybdenum disulfide in resin composition 4 may both be greater than the content of ultra-high molecular weight polyethylene in resin composition 4.

[0044] The resin composition 4 may further contain one or more solid lubricants selected from the group consisting of metal oxides, Cu alloys, sulfur compounds (excluding molybdenum disulfide), aramid, carbon fibers, PEEK resin, and hard particles containing a Laves phase composed of Co, Mo, and Si. The total content of ultra-high molecular weight polyethylene, graphite, molybdenum disulfide, and solid lubricants in the resin composition 4 may be 40 vol% or less.

[0045] <Polyimide> Polyimide serves as the base resin for resin composition 4. Examples of commercially available polyimide include the Spixeria® series manufactured by Somar Co., Ltd. Polyimide is available in liquid form as polyimide varnish.

[0046] The resin composition 4 contains 40 vol% or less of additives other than polyimide. If the content of additives other than polyimide exceeds 40 vol%, the homogeneity of the resin composition 4 is impaired, making it difficult to form the sliding layer 5 due to surface roughness and impregnation failure. The polyimide content in the resin composition 4 is preferably 50 vol% or more, and more preferably 60 vol% or more.

[0047] <Ultra-high molecular weight polyethylene> Ultra-high molecular weight polyethylene (UMLME) is an essential additive in the resin composition 4 that forms the sliding layer 5. The content of UMLME in the resin composition 4 is 1 vol% or more and less than 5 vol%. The content of UMLME in the resin composition 4 may be 4.5 vol% or less, or 4 vol% or less. The average molecular weight of the UMLME may be 1 million to 7 million particles. The specific gravity of the UMLME may be 0.92 to 0.96. By adding a predetermined amount of UMLME to the resin composition 4, the UMLME forms a film on the sliding surface of the sliding layer 5 and transfers to the mating material, thereby improving the resistance to seizing and slipping. Examples of commercially available UMLME include Mitsui Chemicals' MIPELON (registered trademark) (weight-average molecular weight 500,000 to 7 million), Toyobo's Izanas (registered trademark), and Honeywell's SPECTRA (registered trademark). Ultra-high molecular weight polyethylene can be used in powder form, with particle sizes, for example, 30 μm or less at d50.

[0048] <Graphite> Graphite is an essential additive in the resin composition 4 that forms the sliding layer 5. By adding a predetermined amount of graphite to the resin composition 4, the frictional resistance can be reduced. Commercially available products include the GRAPHITE POWDER series from Nippon Graphite Industries and the AT series from Oriental Sangyo Co., Ltd. Graphite is available in powder form.

[0049] <Molybdenum disulfide> Molybdenum disulfide is an essential additive in the resin composition 4 that forms the sliding layer 5. By adding a predetermined amount of molybdenum disulfide to the resin composition 4, the frictional resistance can be reduced. Commercially available products include H / GMoS2 from Taiyo Kogyo Co., Ltd. and the molybdenum disulfide powder series from Daizo Co., Ltd. Molybdenum disulfide is available in powder form.

[0050] <Metal oxides> The metal oxide is an optional additive in the resin composition 4 that forms the sliding layer 5. As the metal oxide, for example, ferric oxide (Fe2O3), silicon dioxide, ferroferric oxide (Fe3O4), molybdenum oxides (MoO2, MoO3), etc. are used. By including a predetermined amount of the metal oxide in the resin composition 4, the wear resistance can be improved. Examples of commercially available products include the SUNSPHERE series manufactured by AGC Si-Tech Co., Ltd. and the Morishita Color series of Morishita Valve Industry Co., Ltd. The metal oxide can be obtained in powder form.

[0051] <Cu alloy> The Cu alloy is an optional additive in the resin composition 4 that forms the sliding layer 5. As the Cu alloy, for example, copper sulfide is used. By including a predetermined amount of the Cu alloy in the resin composition 4, the heat dissipation characteristics of the sliding layer 5 are improved. Thereby, the temperature rise of the sliding layer 5 due to the sliding of the mating member is suppressed, and the deformation of the sliding layer 5 accompanying the temperature rise is suppressed.

[0052] Also, it is known that when the resin composition 4 that forms the sliding layer 5 contains a filler of carbon fiber, the strength of the resin layer is improved. By improving the strength of the sliding layer 5, the deformation of the sliding layer 5 due to the sliding of the mating member is also suppressed.

[0053] When the deformation amount of the sliding layer 5 increases, the wear amount increases compared to the case where the deformation amount is small. Therefore, by suppressing the deformation of the sliding layer 5, the wear of the sliding layer 5 is suppressed, and the wear resistance characteristics are improved. And by suppressing the wear of the sliding layer 5, the exposure of the porous layer 3 is suppressed, and a dry touch that causes factors such as seizure when the porous layer 3 and the mating member come into direct contact can be suppressed, and the seizure resistance is improved.

[0054] <Sulfur compound (excluding molybdenum disulfide)> Sulfur compounds (excluding molybdenum disulfide) are optional additives in the resin composition 4 that forms the sliding layer 5. As sulfur compounds (excluding molybdenum disulfide), for example, BaSO4, CaSO4, etc. are used. By including a predetermined amount of sulfur compounds (excluding molybdenum disulfide), the resin composition 4 can improve friction characteristics such as frictional resistance and wear.

[0055] <Aramid> Aramid is an optional additive in the resin composition 4 that forms the sliding layer 5. By adding a predetermined amount of aramid, the resin composition 4 can enhance its wear resistance and seizure resistance. Commercially available aramids include Kevlar (registered trademark) manufactured by Toray DuPont and Twaron (registered trademark) manufactured by Teijin. Aramid is usually available in fiber form or powder form.

[0056] <Carbon fiber> Carbon fiber is an optional additive in the resin composition 4 that forms the sliding layer 5. It is known that when the resin composition 4 contains carbon fiber, functionality such as improved strength of the resin layer is imparted. The carbon fiber preferably has a fiber diameter of 5 μm or more and 20 μm or less, a fiber length of 10 μm or more and 150 μm or less, and an aspect ratio of 2 or more and 20 or less.

[0057] <PEEK resin> PEEK resin is an optional additive in the resin composition 4 that forms the sliding layer 5. By adding a predetermined amount of PEEK resin, the resin composition 4 can improve its wear resistance. Commercially available products include VESTAKEEP manufactured by Polyplastics Eponic. PEEK resin is, for example, in powder form and those with an average particle size of about 20 μm are available.

[0058] <Hard particles containing a Laves phase composed of a composition of Co, Mo, and Si> Hard particles containing a Raves phase composed of Co, Mo, and Si are optional additives in the resin composition 4 that forms the sliding layer 5. Hard particles containing a Raves phase composed of Co, Mo, and Si may be dispersed in the resin composition 4 of the sliding layer 5. Here, the Raves phase is an intermetallic compound based on the AB2 type, consisting of elements A and B with an atomic radius ratio of approximately 1.2:1, and has three types of structures: MgZn2(C14), MgCu2(C15), and MgNi2(C36). The Raves phase composed of Co, Mo, and Si (more specifically, Co3Mo2Si) is a Raves phase in which element A is Mo, element B is Co, and 25 at% of Co is substituted with Si, and is a MgZn2 type with a hexagonal crystal structure. The Vickers hardness of the Raves phase composed of Co3Mo2Si is Hv1000~1200. Although the hard particles dispersed in the sliding layer 5 are thought to be subjected to a higher load than the resin composition 4 that forms the sliding layer 5, the hard Laves phase, composed of Co, Mo, and Si, precipitates on the friction surface and supports the load, which can be advantageous in reducing wear of the sliding layer 5.

[0059] Furthermore, a sulfide film of MoS2 can be formed on the friction surface by Mo in the Raves phase and S in the lubricating oil. MoS2 is a material known as a sulfide that replaces the solid lubricity of lead and contributes to improving frictional properties. Because the bonds between sulfur particles are weaker than the bonds between molybdenum particles and between molybdenum and sulfur, lubrication occurs when friction occurs as the bonds between sulfur particles are selectively broken, which can effectively suppress wear. In addition, Mo oxides formed on the friction surface by the oxidation of Mo in the Raves phase during sliding can also exert a lubricating effect and effectively suppress wear.

[0060] According to this embodiment, the resin composition 4 of the sliding layer 5 mainly contains polyimide other than PFAS. Although sliding members using polyimide alone have inferior seizure resistance compared to sliding members mainly composed of PTFE, by further incorporating ultra-high molecular weight polyethylene, graphite, and molybdenum disulfide into the resin composition 4 within a predetermined range, seizure resistance can be improved compared to sliding members mainly composed of PTFE without using PFAS.

[0061] The sliding layer 5 formed from the resin composition 4 has higher strength and heat resistance compared to the sliding layer 5 formed from other materials, making it extremely useful. This embodiment is particularly useful in applications where it was previously considered difficult to apply a sliding layer formed from a resin composition, such as applications where the temperature rise of the sliding layer due to friction exceeds 100°C, or applications where the sliding layer is subjected to a pressure of 10 MPa or more, especially in bearings.

[0062] When this embodiment is adopted for bearings, it is possible to extend the lifespan under normal sliding conditions, and the improved durability provides the exceptional benefit of being applicable in high-speed and harsh sliding conditions with high loads.

[0063] In this embodiment, any shape adopted in the industry can be used for the sliding member 1, such as a plate shape, a cylindrical shape (outer circumference and inner circumference), a curved shape, a spherical shape, and so on.

[0064] <Manufacturing method for sliding members> Next, with reference to Figure 4, an example of a method for manufacturing the sliding member 1 will be described. Figure 4 is a flowchart showing an example of a method for manufacturing the sliding member 1.

[0065] As shown in Figure 4, first, additives are blended into the polyimide varnish that will be the raw material for the resin composition 4 (step S10). As an example, the additives may include ultra-high molecular weight polyethylene, graphite, and molybdenum disulfide. As another example, in addition to ultra-high molecular weight polyethylene, graphite, and molybdenum disulfide, the additives may further include one or more solid lubricants selected from the group consisting of metal oxides, Cu alloys, sulfur compounds (excluding molybdenum disulfide), aramid, carbon fibers, polyether ether ketone (PEEK) resin, and hard particles containing a Laves phase composed of Co, Mo, and Si. By incorporating additives within a predetermined range in the polyimide varnish that will be the raw material for the resin composition 4, the seizure resistance of the sliding layer 5 made of the resin composition 4, which is formed by firing an intermediate material prepared by volatilizing a solvent, can be improved.

[0066] The total content of additives relative to the components excluding the solvent in the polyimide varnish is preferably 40 vol% or less. By keeping the content of additives excluding the solvent in the polyimide varnish at 40 vol% or less, it is possible to prevent the homogeneity of the resin composition 4, which is mainly composed of polyimide, from being impaired when the polyimide varnish impregnated in the porous layer 3 is fired.

[0067] Note that the step of adding additives to the polyimide varnish (step S10) is not mandatory, and the process may be started from the next step S11 without adding additives to the polyimide varnish.

[0068] Next, an intermediate material is prepared by heating the polyimide varnish while stirring to reduce the solvent content in the polyimide varnish (step S11). The solvent is, for example, methyl benzoate. By preparing the intermediate material by reducing the solvent content in the polyimide varnish before the step of impregnating the porous layer 3 with the intermediate material (step S12), it is possible to suppress the generation of bubbles on the surface of the resin composition 4 due to the evaporation of the solvent during the step of firing the intermediate material impregnated in the porous layer 3 (step S13).

[0069] In the process of preparing the intermediate material (step S11), the solvent content may be reduced until the polyimide varnish becomes clay-like. Here, "clay-like" means a state in which it deforms when external pressure is applied, but maintains its original shape unless pressure is applied, and does not spread by its own weight like a liquid. Specifically, "clay-like" means that, as confirmed in the viscosity test described later, after filling the intermediate material into the jig with the shape shown in Figures 12A and 12B through the opening at the top of the jig, when the intermediate material is pressed downwards from the opening at the top of the jig, the extrusion load when the intermediate material is pushed out from the opening at the bottom of the jig (2.5 × 8.3 mm square) is 2.5 kN or more. By reducing the solvent content until the polyimide varnish becomes clay-like, it is possible to effectively suppress the generation of bubbles on the surface of the resin composition 4 due to the evaporation of the solvent in the process of firing the intermediate material impregnated in the porous layer 3 (step S13).

[0070] In the process of preparing the intermediate material (step S11), the solvent content may be reduced until no bubbles are generated on the surface of the resin composition 4 due to solvent evaporation in the firing process (step S13) described later. In this case, since no bubbles are generated on the surface of the resin composition 4 due to solvent evaporation in the firing process (step S13) of the intermediate material impregnated in the porous layer, it becomes possible to form the sliding layer 5 that covers the porous layer 3 with a resin composition 4 mainly composed of polyimide with a sufficiently uniform structure.

[0071] In the process of preparing the intermediate material (step S11), the solvent content may be reduced such that, when the solvent content at the start of step S11 is set to 100 wt%, the solvent content at the end of step S11 is 16 wt% or more and less than 28 wt%.According to actual verification by the inventors, it was confirmed that by reducing the solvent content in step S11 such that, when the solvent content at the start of step S11 is set to 100 wt%, the solvent content at the end of step S11 is 16 wt% or more and less than 28 wt%, the generation of bubbles on the surface of the resin composition 4 due to solvent volatilization in the process of firing the intermediate material impregnated in the porous layer 3 (step S13) can be effectively suppressed.

[0072] In the process of preparing the intermediate material (step S11), the polyimide varnish may be heated to 80°C to 150°C. For example, the polyimide varnish may be heated and stirred at 100°C for 4 hours. By heating within the temperature range of 80°C to 150°C, the solvent content can be reduced without curing the polyimide, and the intermediate material can be prepared.

[0073] Next, the intermediate material is impregnated into the surface of the porous layer 3 formed on one side of the metal substrate 2 (step S12).

[0074] In step S12, the intermediate material may be pressed onto the surface of the porous layer 3 to impregnate it. In this case, even if the intermediate material has a reduced solvent content and has become clay-like, pressing it allows it to be sufficiently impregnated into the porous layer 3 (to a depth where the intermediate material contacts the surface of the metal substrate 2, as shown in Figure 1).

[0075] As an example, the intermediate material supplied to the surface of the porous layer 3 may be passed between a pair of rolls, thereby pressing and impregnating the intermediate material into the porous layer 3. As another example, the intermediate material supplied to the surface of the porous layer 3 may be pressed perpendicularly to the surface of the porous layer 3 by a pressing member, thereby impregnating the porous layer 3.

[0076] Next, the intermediate material impregnated in the porous layer 3 is fired to form a sliding layer 5 made of a resin composition 4 mainly composed of polyimide that covers the porous layer 3 (step S13). For example, using a firing furnace, the intermediate material impregnated in the porous layer 3 is heated at 120°C for 10 minutes as a preliminary drying step, and then heated at 220°C for 60 minutes as a main drying step to harden the intermediate material. In this way, a sliding member 1 having a sliding layer 5 made of a resin composition 4 mainly composed of polyimide can be manufactured.

[0077] Actual verification by the inventors of this case revealed that if the solvent content is not reduced before the step of impregnating the intermediate material into the porous layer 3 (step S12), bubbles will form on the surface of the resin composition 4 during the step of firing the intermediate material (step S13) due to the evaporation of the solvent. As a method to suppress the generation of bubbles, the resin manufacturer proposed extending the heating time during firing, but actual verification by the inventors of this case revealed that the method proposed by the resin manufacturer could not completely suppress the generation of bubbles. When bubbles occur, the sliding layer 5 covering the porous layer 3 cannot be formed with a resin composition with a uniform structure, and the sliding member becomes a defective product.

[0078] In contrast, actual verification by the inventors of this case has confirmed that by performing a step (S11) to prepare the intermediate material by heating the polyimide varnish while stirring to reduce the solvent content before the step (S12) to impregnate the intermediate material into the porous layer 3, it is possible to suppress the generation of bubbles on the surface of the resin composition 4 due to the evaporation of the solvent during the step (S13) in which the intermediate material is fired. As a result, it becomes possible to form the sliding layer 5 that covers the porous layer 3 with a resin composition 4 mainly composed of polyimide with a uniform structure, thereby realizing the manufacture of a sliding member 1 having a sliding layer 5 without using PFAS.

[0079] <Bearing manufacturing method> Next, with reference to Figure 5, an example of a method for manufacturing the bearing 7 will be described. Figure 5 is a flowchart showing an example of a method for manufacturing the bearing 7.

[0080] In one example of a method for manufacturing the bearing 7, the steps of blending additives into the polyimide varnish (step S10) and heating the polyimide varnish while stirring to reduce the solvent content in the polyimide varnish and thereby producing an intermediate material (step S11) are the same as in the example of a method for manufacturing the sliding member 1 shown in Figure 4, and therefore will not be explained further. Note that in one example of a method for manufacturing the bearing 7, the step of blending additives into the polyimide varnish (step S10) is not mandatory, and the process may be started from step S11 without blending additives into the polyimide varnish.

[0081] After the step of reducing the solvent content in the polyimide varnish to produce an intermediate material (step S11), the intermediate material is impregnated into the surface of a porous layer 3 formed on one side of a plate-shaped metal substrate 2, as shown in Figure 5 (step S22).

[0082] In step S22, the intermediate material may be pressed onto the surface of the porous layer 3 and impregnated, similar to step S12. In this case, even if the intermediate material has a reduced solvent content and has become clay-like, pressing it will allow it to be sufficiently impregnated into the porous layer 3 (to a depth where the intermediate material contacts the surface of the metal substrate 2, as shown in Figure 1).

[0083] Next, similar to step S13, the intermediate material impregnated in the porous layer 3 is fired to form a sliding layer 5 made of a resin composition 4 mainly composed of polyimide that covers the porous layer 3 (step S23). By this method, a bearing 7 having a sliding layer 5 made of a resin composition 4 mainly composed of polyimide can be manufactured.

[0084] Next, with reference to Figure 6, another example of a method for manufacturing the bearing 7 will be described. Figure 6 is a flowchart showing another example of a method for manufacturing the bearing 7.

[0085] In another example of the method for manufacturing the bearing 7, the steps from the process of blending additives into the polyimide varnish (step S10) to the process of forming a sliding layer 5 made of a resin composition 4 mainly composed of polyimide that covers the porous layer 3 by firing the intermediate material impregnated in the porous layer 3 (step S13) are the same as the example of the method for manufacturing the sliding member 1 shown in Figure 4, and therefore the explanation is omitted. In this other example of the method for manufacturing the bearing 7, the step of blending additives into the polyimide varnish (step S10) is not essential, and the process may be started from step S11 without blending additives into the polyimide varnish.

[0086] After the step of firing the intermediate material impregnated in the porous layer 3 (step S13), the metal substrate 1 on which the sliding layer 5 covering the porous layer 3 is formed is processed into a rolled bush shape with the sliding layer 5 on the inside, as shown in Figure 6 (step S14). A bearing 7 having a sliding layer 5 made of a resin composition 4 mainly composed of polyimide can also be manufactured by this method.

[0087] <Examples> Next, a specific example of this embodiment will be described.

[0088] (Seizure resistance test) Using the resin compositions of Examples 1 to 14 and Comparative Examples shown in Figure 8, test specimens were prepared using the manufacturing method described above, and the seizure resistance of the test specimens was tested in the following manner.

[0089] A schematic diagram of the test method is shown in Figure 4. A test specimen of the dimensions specified below was fixed to the test stand of the testing machine specified below, and a mating cylindrical ring of the dimensions specified below was pressed against it from above under the test conditions specified below while rotating. The pressing load was gradually increased every 10 minutes, and the load at which the test specimen temperature exceeded 200°C was defined as the seizure load (evaluated by seizure surface pressure (unit: MPa)). Testing machine: High-pressure atmosphere friction and wear testing machine (Shinko Seiki Co., Ltd.) Specimen dimensions: 45mm x 45mm x 1.0~2.5mm Molding material cylindrical ring dimensions: Outer diameter Φ30mm x Inner diameter Φ24mm, Contact area with test piece (254.5mm) 2 ) Base material: Cu-plated steel sheet made of cold-rolled steel sheet (SPCC) Porous layer: formed from CuSn powder (Sn: 10wt%, balance Cu) Sliding layer thickness: 0.3 ± 0.1 mm Mating material cylindrical ring material: Carbon steel S45C Test conditions: Speed ​​(0.25m / s) Rotation speed (177 rpm) Load (50 kgf (490 N) gradually increased every 10 minutes) Atmosphere (dry)

[0090] (Test results and discussion) The test results are shown in Figure 8. Polyimide used was from the product name: Spixeria® NA series. The graphite used was product name CPB. For the molybdenum disulfide used, we used product name: H / GMoS2. For the ultra-high molecular weight polyethylene, we used the product name: Mipelon. In the process of preparing an intermediate material by heating and stirring the polyimide varnish before impregnating the porous layer to reduce the solvent content, the polyimide varnish was heated and stirred at 100°C for 4 hours. In all test specimens of Examples 1 to 14, it was visually confirmed that the sliding layer 5 covering the porous layer 3 was formed of a resin composition 4 with a uniform structure.

[0091] Figure 9 is a graph showing the relationship between the composition of the resin composition and the baking pressure. As shown in Figure 9, the baking pressure of the comparative example test piece, in which the resin composition mainly consisted of fluororesin (PTFE), was 25 MPa, while the baking pressure of the test piece of Example 6, in which the resin composition consisted solely of polyimide, was a low 7.7 MPa. In contrast, the baking pressure of the test piece of Example 9, in which the base resin of the resin composition was polyimide and graphite and molybdenum disulfide were further added, improved to 33.8 MPa. Furthermore, the baking pressure of the test piece of Example 4, in which the base resin of the resin composition was polyimide and graphite, molybdenum disulfide, and ultra-high molecular weight polyethylene were further added, improved to 44.3 MPa. Therefore, it was confirmed that by including graphite, molybdenum disulfide, and ultra-high molecular weight polyethylene in a resin composition whose base resin is polyimide, the baking resistance can be further improved compared to the case in which only graphite and molybdenum disulfide are included.

[0092] Referring to Figure 8, the test pieces of Examples 1 to 5, in which the resin composition mainly contains polyimide and further contains ultra-high molecular weight polyethylene, graphite, and molybdenum disulfide, with an ultra-high molecular weight polyethylene content of 1 vol% or more and less than 5 vol%, showed higher bake-on surface pressure than any of the following: (a) the test piece of Example 6, in which the resin composition consists of polyimide alone; (b) the test pieces of Examples 7 to 9, in which the resin composition mainly contains polyimide and further contains graphite and molybdenum disulfide (but does not contain ultra-high molecular weight polyethylene); (c) the test pieces of Examples 10 to 14, in which the resin composition mainly contains polyimide and further contains ultra-high molecular weight polyethylene, graphite, and molybdenum disulfide, with an ultra-high molecular weight polyethylene content of 5 vol% or more; and (d) the test piece of the comparative example, in which the resin composition consists of fluororesin (PTFE). In other words, it was confirmed that they have excellent bake-on resistance.

[0093] Figure 10 is a graph showing the relationship between the ultra-high molecular weight polyethylene content and the baking pressure when the blending ratio of graphite and molybdenum disulfide in the resin composition is kept constant (15 vol%). Figure 11 is a graph showing the relationship between the ultra-high molecular weight polyethylene content and the baking pressure when the total content of graphite, molybdenum disulfide, and ultra-high molecular weight polyethylene in the resin composition is kept constant (35 vol%). As shown in Figures 10 and 11, the baking pressure decreased as the ultra-high molecular weight polyethylene content increased. Therefore, it was found that the ultra-high molecular weight polyethylene content in the resin composition is preferably less than 5 vol%, more preferably 4.5 vol% or less, and even more preferably 4 vol% or less.

[0094] (Viscosity test) Viscosity tests were conducted on the intermediate material and polyimide varnish using jigs of the shapes shown in Figures 12A and 12B, according to the following procedure. Figure 12A is a cross-sectional view of the jig used for the viscosity test in the left-right direction, and Figure 12B is a plan view of the jig as seen from the opening at the top.

[0095] First, intermediate materials (i.e., polyimide varnish from which the solvent has been evaporated) used to form the resin compositions of Examples 1 to 14 shown in Figure 8 were prepared. Next, the intermediate material was filled into a jig with the shape shown in Figures 12A and 12B through the opening at the top of the jig. Then, the intermediate material was pressed downwards through the opening at the top of the jig, and the extrusion load was measured when the intermediate material was pushed out through the opening at the bottom of the jig. The opening at the bottom of the jig was 2.5 × 8.3 mm square. The other dimensions of the jig were as shown in Figures 12A and 12B.

[0096] Viscosity test results confirmed that the extrusion load was 2.5 kN or higher for all intermediate materials used to form the resin compositions of Examples 1 to 14.

[0097] Furthermore, using the same test method as described above, the polyimide varnish (polyimide varnish before being used as an intermediate material) used to form the resin compositions of Examples 1 to 14 was also subjected to an extrusion load within 10 seconds after being filled into a jig of the shape shown in Figures 12A and 12B. As a result, it was confirmed that the extrusion load for all polyimide varnishes used to form the resin compositions of Examples 1 to 14 was less than 2.5 kN.

[0098] Although embodiments and modifications of the present invention have been described above by example, the scope of the present invention is not limited thereto, and it is possible to modify and transform it according to the purpose within the scope described in the claims. Furthermore, each embodiment and modification can be appropriately combined as long as the processing content is not contradictory. [Explanation of Symbols]

[0099] 1. Sliding member 2 Metal base material 3. Porous layer 4 Resin composition 5. Sliding layer 7 Bearings 8 axes

Claims

1. The process involves a step of producing an intermediate material by heating polyimide varnish to reduce the solvent content, The steps include impregnating the surface of a porous layer formed on one side of a metal substrate with the intermediate material, The steps include: firing the intermediate material to form a sliding layer made of a resin composition mainly composed of polyimide that covers the porous layer; A method for manufacturing a sliding member, characterized by including [a specific component].

2. In the step of impregnating the intermediate material, the intermediate material is pressed onto the surface of the porous layer to impregnate it. A method for manufacturing a sliding member according to claim 1, characterized in that it is as described above.

3. In the step of producing the intermediate material, the intermediate material is produced by reducing the solvent content until the polyimide varnish becomes clay-like. A method for manufacturing a sliding member according to claim 1, characterized in that it is as described above.

4. In the step of producing the intermediate material, the solvent content of the intermediate material is reduced until no bubbles are generated on the surface of the resin composition due to the evaporation of the solvent during the firing step. A method for manufacturing a sliding member according to claim 1, characterized in that it is as described above.

5. In the step of producing the intermediate material, the solvent content is reduced such that, when the solvent content at the start of the step is 100 wt%, the solvent content at the end of the step is 16 wt% or more and less than 28 wt%. A method for manufacturing a sliding member according to claim 1, characterized in that it is as described above.

6. The polyimide varnish further comprises ultra-high molecular weight polyethylene, graphite, and molybdenum disulfide. The total content of ultra-high molecular weight polyethylene, graphite, and molybdenum disulfide relative to the solvent component in the polyimide varnish is 40 vol% or less. A method for manufacturing a sliding member according to claim 1, characterized in that it is as described above.

7. The polyimide varnish further comprises one or more solid lubricants selected from the group consisting of metal oxides, Cu alloys, sulfur compounds (excluding molybdenum disulfide), aramid, carbon fibers, polyetheretherketone (PEEK) resin, and hard particles containing a Laves phase composed of Co, Mo, and Si. The total content of ultra-high molecular weight polyethylene, graphite, molybdenum disulfide, and the solid lubricant in the polyimide varnish, excluding the solvent, is 40 vol% or less. A method for manufacturing a sliding member according to claim 1, characterized in that

8. In the step of producing the intermediate material, the polyimide varnish is heated to 80°C to 150°C. A method for manufacturing a sliding member according to claim 1, characterized in that it is as described above.

9. The process involves a step of producing an intermediate material by heating polyimide varnish to reduce the solvent content, The steps include impregnating the surface of a porous layer formed on one side of a plate-shaped metal substrate with the intermediate material, The steps include: firing the intermediate material to form a sliding layer made of a resin composition mainly composed of polyimide that covers the porous layer; A method for manufacturing a bearing, characterized by including the following:

10. The process involves a step of producing an intermediate material by heating polyimide varnish to reduce the solvent content, The steps include impregnating the surface of a porous layer formed on one side of a metal substrate with the intermediate material, The steps include: firing the intermediate material to form a sliding layer made of a resin composition mainly composed of polyimide that covers the porous layer; The steps include processing the metal substrate on which the sliding layer covering the porous layer is formed into a rolled bush shape with the sliding layer facing inward, A method for manufacturing a bearing, characterized by including the following:

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