Sliding resin composition, and sliding member

Abstract

A resin composition for use in a sliding member, which has higher seizing resistance while maintaining abrasion resistance. The sliding resin composition includes: a resin binder; a solid lubricant; and a protecting and reinforcing agent that is harder and brittler than the resin binder. As the protecting and reinforcing agent, aggregates of particles harder than the resin binder are used. The amount of the protecting and reinforcing agent contained is 1 vol. % or more but 20 vol. % or less of the entire sliding resin composition. The particles harder than the resin binder have an average particle diameter of 10 nm or more but 100 nm or less that is smaller than that of the solid lubricant.

Claims

1. A sliding resin composition, comprising: a resin binder; a solid lubricant; and a protecting and reinforcing agent comprising aggregates of primary particles, said primary particles being harder than said resin binder and having an average particle diameter of 10 nm or more but 100 nm or less, and said aggregates being more brittle than said resin binder, wherein said primary particles have a smaller diameter than that of said solid lubricant, and said protecting and reinforcing agent occupies 10-20 vol. % inclusive of the entire sliding resin composition, wherein, when an average particle diameter of said aggregates is defined as A and a standard deviation of the average particle diameter of said aggregates is defined as , A1 is 60 nm or more and A+1 is 400 nm or less, and wherein the diameter and axes of individual particles and aggregates are determined by use of a particle-equivalent ellipse.

2. A sliding member, comprising a base material layer and a coating layer that is laminated on the base material layer and includes the sliding resin composition according to claim 1, wherein the surface of said coating layer opposite said base material layer is the sliding surface.

3. The sliding member according to claim 2, wherein the average angle between a long axis of said aggregates in said sliding resin composition and the sliding surface is 45 degrees or less.

4. The sliding member according to claim 3, wherein said base material layer has a semi-cylindrical portion.

5. The sliding resin composition according to claim 1, wherein ten percent or more of said aggregates are attached to said solid lubricant or present in the vicinity of said solid lubricant.

6. The sliding resin composition according to claim 1, wherein the average particle diameter of said aggregates is 40% or less of the average particle diameter of said solid lubricant.

7. The sliding member according to claim 3, wherein the average angle between the long axes of the aggregates in said sliding composition and the sliding surface is 22 degrees or less.

8. The sliding resin composition according to claim 1, wherein said aggregates are of smaller diameter than said solid lubricant.

9. The sliding resin composition according to claim 1, wherein the aspect ratio of said aggregate is set to 10 or less.

10. The sliding resin composition according to claim 1, wherein the value of D90/D10 of said primary particles constituting said aggregates is set to 5 or less, wherein D10 is a particle diameter when a cumulative height of particle diameters is 10%, and D90 is a particle diameter when a cumulative height of particle diameters is 90%.

11. The composition of claim 1, wherein said primary particles are formed of silicon dioxide.

12. The sliding resin composition according to claim 1, wherein said solid lubricant occupies 20-70 vol. % inclusive of the entire resin composition.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a schematic view showing the structure of a sliding member according to an embodiment of the present invention.

(2) FIG. 2 is a partially-enlarged view showing the structure of a resin coating layer.

(3) FIG. 3 is an enlarged view of a portion indicated by an arrowed line III in FIG. 2.

(4) FIG. 4 is a schematic view illustrating the separation and breakage of a resin binder when aggregates of protecting and reinforcing particles are absent in a resin composition.

(5) FIG. 5 is a schematic view illustrating partial detachment of aggregates of protecting and reinforcing particles caused by applying the threshold stress of the aggregates to the aggregates.

(6) FIG. 6 is a schematic view illustrating an angle between a long axis of the aggregates of the protecting and reinforcing particles and a sliding surface of the resin composition.

DESCRIPTION OF EMBODIMENTS

(7) FIG. 1 shows a layered structure of a sliding member 1 according to an embodiment of the present invention.

(8) This sliding member 1 has a structure in which a resin coating layer 7 including a sliding resin composition is laminated on a base material layer 2.

(9) In the sliding member 1 including a cylindrical or semi-cylindrical bearing, the base material layer 2 thereof includes a cylindrical or semi-cylindrical steel plate layer 3. If necessary, an alloy layer 5 made of an alloy of Al, Cu, Sn, or the like is provided on the surface (inner peripheral surface) of the steel plate layer 3. Although not shown, the base material layer 2 may be one having, on the surface of the alloy layer 5, a Sn-, Bi-, or Pb-group plating layer or a layer having a resin. The layer having a resin is different from the resin coating layer 7.

(10) In order to improve adhesion between the base material layer 2 and the resin coating layer 7, the inner peripheral surface of the base material layer 2 may be subjected to surface roughening. The surface roughening may be performed by chemical surface treatment such as combination of alkaline etching and pickling or mechanical surface treatment such as shot blasting.

(11) The constituent material of the steel plate layer 3 is not limited to steel, and may be, for example, an alloy of aluminum, copper, and tungsten.

(12) The sliding resin composition constituting the resin coating layer 7 includes a resin binder 10, a solid lubricant 11, and aggregates 20 of protecting and reinforcing primary particles 13.

(13) In the resin composition, the resin binder 10 binds the resin coating layer 7 to the base material layer 2 and fixes the solid lubricant 11. A resin material used for the resin binder 10 may be appropriately selected depending on, for example, the intended use of the sliding member 1. When the sliding member 1 is used for vehicle engines, the resin material may be at least one of polyimide resins, polyamideimide resins, epoxy resins, phenol resins, polyamide resins, fluorine resins, and elastomers, and may be a polymer alloy.

(14) The thickness of the resin coating layer 7 may be arbitrarily designed, and may be, for example, 1 m or more but 20 m or less.

(15) A method for laminating the resin coating layer 7 may also be arbitrarily selected. Examples of the method to be used include pad printing, screen printing, air spray painting, airless spray painting, electrostatic painting, tumbling, squeezing, rolling, and roll coating.

(16) The material of the solid lubricant 11 may also be appropriately selected depending on the intended use of the sliding member. For example, the material of the solid lubricant 11 may be at least one selected from molybdenum disulfide, tungsten disulfide, h-boron nitride, polytetrafluoroethylene, melamine cyanurate, carbon fluoride, phthalocyanine, graphene nanoplatelets, fullerene, ultrahigh molecular weight polyethylene (manufactured by Mitsui Chemicals, Inc. under the trade name of MIPELON), and N-lauroyl-L-lysine (manufactured by Ajinomoto Co., Inc. under the trade name of AMIHOPE).

(17) The amount of the solid lubricant 11 contained in the resin composition may be arbitrarily selected depending on the intended use of the sliding member. For example, when the amount of the entire resin composition constituting the resin coating layer 7 is defined as 100 vol. %, the amount of the solid lubricant 11 contained in the resin composition may be 20 vol. % or more but 70 vol. % or less.

(18) In order to improve the slip properties of the resin coating layer 7, the (0, 0, L) plane orientation intensity ratio of the solid lubricant 11 is preferably 75% or more.

(19) As shown in FIG. 3, the protecting and reinforcing primary particles 13 are provided in the sliding resin composition constituting the resin coating layer 7, and the protecting and reinforcing primary particles 13 are aggregated together to form aggregates 20 as a protecting and reinforcing agent.

(20) The abrasion resistance of the resin coating layer 7 itself is improved by using, as the protecting and reinforcing primary particles 13, ultrafine particles that are harder than the material of the resin binder 10 and have a smaller diameter than the solid lubricant 11, preferably, a nano-order diameter (see Patent Document 2).

(21) In order to directly achieve such a purpose, the protecting and reinforcing primary particles 13 are preferably dispersed more evenly in the resin coating layer. More specifically, it is preferred that the protecting and reinforcing primary particles 13 be dispersed without coupling together as much as possible, that is, the protecting and reinforcing primary particles 13 be dispersed as primary particles.

(22) However, as a result of study by the present inventors, when a heavy load is applied to the resin coating layer 7, as shown in FIG. 4, the resin binder 10 may be deformed beyond its limitation and significantly broken at once. FIGS. 4A and 4B schematically show a situation in which the resin coating layer 7 is separated from the base material layer 2 due to the breakage of the resin binder 10.

(23) On the other hand, according to this invention, as shown in FIG. 3, the protecting and reinforcing primary particles 13 are allowed to be intentionally aggregated to form the aggregates 20. The protecting and reinforcing primary particles 13 constituting the aggregates 20 can be described, from the viewpoint of stress applied to the resin coating layer 7, that the aggregates 20 are not affected at all even when the stress at which deformation of the solid lubricant starts is applied (i.e., the aggregates 20 are not deformed), but are deformed or disintegrated before the start of deformation of the resin binder 10 beyond the threshold stress of the resin binder 10.

(24) Therefore, when a heavy load is applied to the resin coating layer 7, part of stress generated in the resin coating layer 7 is relaxed by deformation or disintegration of the aggregates 20, which prevents the resin coating layer 7 from being significantly broken at once.

(25) At this time, as shown in FIG. 5, when the aggregates 20 are exposed at the sliding surface, some of the protecting and reinforcing primary particles 13 constituting the aggregates 20 are detached. As a result, as shown in FIG. 5B, recesses (micro pods) 30 are formed in the aggregates 20. The recesses 30 can hold lubricant oil supplied to the sliding surface of the sliding member 1. Also from this viewpoint, the aggregates 20 contribute to maintaining an oil film on the sliding surface of the sliding member 1.

(26) From the viewpoint of improving the abrasion resistance of the resin coating layer 7 itself, the constituent material of the protecting and reinforcing primary particles 13 is harder than the resin binder 10 and has a smaller diameter than the solid lubricant. The constituent material of the protecting and reinforcing primary particles 13 may be arbitrarily selected depending on the intended use of the sliding member, and more specifically, may be, for example, microparticles of gold, silver, silicon oxide (silica), aluminum oxide, zinc oxide, tin oxide, or zirconium oxide.

(27) The protecting and reinforcing primary particles 13 may have an average particle diameter of 10 nm or more but 100 nm or less.

(28) The average particle diameter of the protecting and reinforcing primary particles 13 can, of course, be determined from the specifications of raw material particles, but can also be determined in the following manner even in a state where the protecting and reinforcing primary particles 13 are contained in the resin coating layer 7. More specifically, for example, the resin coating layer is cut in an axial direction perpendicular to the sliding surface of the resin coating layer to obtain a cutting surface, and an image of a predetermined range of any portion in the cutting surface of the resin coating layer (hereinafter, sometimes referred to as axial-direction cutting surface) is taken. The thus obtained image is analyzed by image analysis software to approximate the primary particles in the image by ellipses (particle-equivalent ellipses). In this analysis software, an ellipse having the same area and primary and secondary moments as those of a target object (primary particle) is defined as the particle-equivalent ellipse.

(29) Such protecting and reinforcing primary particles can be formed by, for example, a crushing method using a ball mill, a jet mill, or the like, an aggregation method (reductive method) including aggregation caused by reduction using a reducing agent or by electrochemical reduction, a pyrolysis method including thermal decomposition, a physical vapor deposition method such as evaporation in plasma gas, a laser vaporization method including rapid laser vaporization, or a chemical vapor deposition method including a chemical reaction in a vapor phase. A reaction field for production of the protecting and reinforcing primary particles may be either a gas phase or a liquid phase.

(30) When the amount of the entire resin composition constituting the resin coating layer 7 is defined as 100 vol. %, the amount of the protecting and reinforcing primary particles 13 contained in the resin composition, that is, the amount of the aggregates 20 contained in the resin composition may be 1 vol. % or more but 20 vol. % or less.

(31) This makes it possible to allow the resin composition to have sufficient abrasion resistance and to control the viscosity of the resin composition to be suitable for production.

(32) When the average particle diameter of the obtained aggregates is defined as A and the standard deviation of the average particle diameter is defined as , A1 is 60 nm or more and A+1 is 400 nm or less.

(33) The average particle diameter of the aggregates can be determined by the same method as used for the protecting and reinforcing primary particles.

(34) The size of the aggregates can be adjusted by appropriately adjusting the method of surface treatment of the protecting and reinforcing primary particles and the degree of surface treatment, the type of dispersion medium for dispersing the protecting and reinforcing primary particles and the viscosity of the dispersion medium, and the concentration of the primary particles in the dispersion medium, and further homogenizing this dispersion system.

(35) The angle between the long axis of the aggregates 20 and the surface (sliding surface) of the resin coating layer 7 is set to 45 degrees or less. The long axis of the aggregates 20 can be determined by the same method as used for the protecting and reinforcing primary particles.

(36) The angle between the aggregates 20 and the surface of the resin coating layer 7 is adjusted by controlling the viscosity of a raw material of the resin coating layer 7 (containing a solvent added to improve flowability) and the time elapsed until the raw material is cured to form the resin coating layer 7.

(37) At first, the orientations of long axes of the aggregates contained in the resin composition having high flowability are random, but the aggregates are rotated due to the influence of gravity with time so that the long axes thereof are parallel to the sliding surface (hereinafter, sometimes referred to as leveling). This rotation progresses with time, and the progression is accelerated when the viscosity of the raw material is lower.

(38) FIG. 6 is a schematic view showing an angle between the long axis of the aggregate 20 and a sliding surface 7a of the resin coating layer 7. In FIG. 6, a virtual ellipse D of the aggregate 20 is indicated by an alternate long and short dashed line, and the long axis thereof is indicated by an arrow. The angle between the long axis and the sliding surface 7a is set to 45 degrees or less.

(39) From the viewpoint of improving the abrasion resistance of the resin composition constituting the resin coating layer 7, hard particles that form substantially no aggregates may be added to the resin composition.

(40) Such hard particles preferably have a size larger than 100 nm Examples of the material of the hard particles include oxides such as aluminum oxide, chromium oxide, cerium oxide, zirconium oxide, titanium oxide, silicon oxide, and magnesium oxide, nitrides such as silicon nitride and cubic boron nitride, carbides such as silicon carbide, and diamond. When the amount of the entire resin composition constituting the resin coating layer 7 is defined as 100 vol. %, the amount of the hard particles contained in the resin composition may be 1 vol. % or more but 5 vol. % or less. When the material of the hard particles is different from that of the protecting and reinforcing primary particles, the properties of the resin coating layer 7 can be easily controlled. When the hard particles are made of the same material as the protecting and reinforcing primary particles, the sliding member can be inexpensively produced.

(41) When the amount of the entire resin composition is defined as 100 vol. %, metal particles of Sn, Bi, Pb, In, or the like may be added in an amount of 1 vol. % or more but 5 vol. % or less.

(42) Hereinbelow, a method for producing the sliding member 1 will be described.

(43) In this embodiment, a solution obtained by dissolving the resin binder in a solvent and a solution obtained by dispersing the aggregates in the solvent are mixed together, and the resulting mixture is mixed with the solid lubricant and an additive used depending on the intended use to prepare a coating liquid. If necessary, the amount of the solvent is controlled to adjust the viscosity of the coating liquid to be within a preferred range. Then, the coating liquid is applied onto the base material layer 2. Then, the coating liquid is allowed to stand for a predetermined time (leveling step) so that the angle between the long axis of the aggregates and the sliding surface is 45 degrees or less, and is then subjected to a drying step to remove the solvent therefrom by heating so as to be cured to form the resin coating layer 7 including the sliding resin composition.

EXAMPLES

(44) Hereinbelow, the present invention will be described with reference to the following examples suitable for a semi-cylindrical sliding member.

(45) An aluminum bearing alloy layer was pressure-welded to the surface of a back metal layer formed from a semi-cylindrical steel member. Finishing for bearing inner surface is performed on the inner peripheral surface of the alloy layer, and then degreasing and removal of foreign dirt were performed.

(46) Then, surface roughening treatment was performed by shot blasting.

(47) Onto the inner peripheral surface of this intermediate, a previously-prepared coating liquid was applied by spraying so as to have a thickness of about 5 m. Then, the coating liquid was subjected to a leveling step for a predetermined time and a drying step, and was then subjected to a curing step at 200 C. to 300 C. for 30 min to 120 min. In this way, a sliding member (bearing) was produced which had a resin coating layer 7 including a resin composition of each of Examples and Comparative Examples shown in Table 1.

(48) The thus obtained sliding members (bearings) were subjected to a seizing test under the following conditions. Rotation speed: 1500 rpm Lubricant oil: VG22 Oil supply rate: 150 mL/min Material of shaft: S55C

(49) A specific load was increased step by step to determine a specific load for seizing.

(50) The results are shown in Table 1.

(51) TABLE-US-00001 TABLE 1 Resin Protecting and reinforcing agent (aggregates) binder Solid lubricant Size of Tilt angle of Specific load Content Content Content Primary particle aggregates aggregates for seizing Type vol % Type vol % Type vol % diameter nm A 1 A + 1 () (MPa) V Example 1 PAI balance MoS.sub.2 40 SiO.sub.2 10 15 134.9 301.7 15 65.0 Example 2 PAI balance MoS.sub.2 30 SiO.sub.2 10 50 175.1 382.1 7 65.0 Example 3 PAI balance MoS.sub.2 40 SiO.sub.2 20 50 201.4 398.6 44 65.0 Example 4 PAI balance MoS.sub.2 30 SiO.sub.2 1 15 62.1 181.2 21 65.0 IV Example 5 PAI balance MoS.sub.2 31 SiO.sub.2 1 15 63 180 55 62.5 III Example 6 PAI balance MoS.sub.2 40 SiO.sub.2 10 15 134.7 480.1 75 60.0 Example 7 PAI balance MoS.sub.2 30 SiO.sub.2 10 50 141.6 430.3 48 60.0 Example 8 PAI balance MoS.sub.2 70 SiO.sub.2 20 100 252.1 452.8 80 52.5 Example 9 PAI balance MoS.sub.2 50 SiO.sub.2 20 10 121.9 408.1 52 52.5 Example 10 PI balance MoS.sub.2 20 SiO.sub.2 1 100 182.1 490.8 69 50.0 Example 11 PBI balance MoS.sub.2 60 SiO.sub.2 1 10 54.1 148.7 71 50.0 II Example 12 PAI balance WS.sub.2 30 Si.sub.3N.sub.4 15 120 241.9 501.6 68 47.5 Example 13 PI balance PTFE 50 Ag 5 8 49.1 219.0 49 47.5 I Example 14 PAI balance MoS.sub.2 30 SiO.sub.2 0.5 50 62.1 173.6 11 40.0 Example 15 PAI balance MoS.sub.2 30 SiO.sub.2 25 50 210.1 389.1 25 37.5 Comparative PAI balance MoS.sub.2 30 SiO.sub.2 10 15 20.5 Example 1

(52) The content of each component (vol. %), the diameter of protecting and reinforcing primary particles, the size of aggregates, and the angle of long axes of aggregates (tilt angle of aggregates) shown in Table 1 were determined by observing the axial-direction cutting surface of each of the resin coating layers 7. More specifically, an image of an arbitrary portion (with a certain area) in the cutting surface was taken, and the obtained image was analyzed with image analysis software (Image-pro plus ver. 4.5) to calculate each of these values.

(53) The following can be seen from the results shown in Table 1.

(54) In each of the resin coating layers 7 of Examples 1 to 15, aggregates 20 of protecting and reinforcing primary particles were dispersed in a resin binder 10, and some of them were exposed at the sliding surface of the resin coating layer 7. In Comparative Example 1, aggregates 20 were not formed.

(55) Example 14 and Example 15 of Group I do not satisfy the requirement (1) the amount of the protecting and reinforcing primary particles contained in the resin composition is 1 vol. % or more but 20 vol. % or less of the entire resin composition, and therefore the specific loads for seizing thereof are higher than that of Comparative Example 1, but are relatively lower than those of Examples of other groups.

(56) Example 12 and Example 13 of Group II satisfy the requirement (1) the amount of the protecting and reinforcing primary particles contained in the resin composition is 1 vol. % or more but 20 vol. % or less of the entire resin composition, and therefore the specific loads for seizing thereof are higher than those of Examples of Group I.

(57) Examples 6 to 11 of Group III satisfy the requirement (1) the amount of the protecting and reinforcing primary particles contained in the resin composition is 1 vol. % or more but 20 vol. % or less of the entire resin composition and the requirement (2) the average particle diameter of the protecting and reinforcing primary particles is 10 nm or more but 100 nm or less, and therefore the specific loads for seizing thereof are higher than those of Example 12 and Example 13 of Group II.

(58) Example 5 of Group IV satisfies the above requirements (1) and (2) and the requirement (3) the size A1 of the aggregates is 60 nm or more and the size A+1 of the aggregates is 400 nm or less, and therefore the specific load for seizing thereof is higher than those of Examples 6 to 11 of Group III.

(59) Examples 1 to 4 of Group V satisfy the above requirements (1) to (3) and the requirement (4) the aspect ratio of the aggregates is 10 or less, and therefore the specific loads for seizing thereof are higher than that of Example 5 of Group IV.

(60) According to study by the present inventors, one or two or more of the following properties of the resin composition has/have an influence on the seizing resistance of the resin composition.

(61) (1) Aspect Ratio of Aggregates

(62) When aggregates are used as the protecting and reinforcing particles, the aspect ratio of the aggregates is set to 10 or less. The aspect ratio of the aggregates is defined as follows. The aggregates appearing in a measured view in a cutting surface obtained by cutting the sliding resin composition in a direction perpendicular to the sliding surface of the sliding resin composition are approximated by ellipses, and the ratio between the long axis and the short axis of the ellipses is defined as an aspect ratio (long axis/short axis).

(63) When the aspect ratio of the aggregates is 10 or less, in other words, when the shape of the aggregates is closer to a sphere, the area of the aggregates exposed at the sliding surface of the resin composition is stable. A general aggregate is approximated by an ellipse. Therefore, when the aggregates have an aspect ratio of 10 or less, the area of the aggregates appearing in the sliding surface of the resin composition is stable irrespective of the orientation of long axis of the aggregates.

(64) (2) Relationship I between Aggregates and Solid Lubricant

(65) Ten percent or more of the aggregates are closely attached to the solid lubricant or are present in the vicinity of the solid lubricant.

(66) When the aggregates are closely attached to the solid lubricant, the solid lubricant that is first deformed, cleaved, or disintegrated by the application of a load influences the aggregates that are closely attached to the solid lubricant.

(67) For example, when the aggregates are closely attached to the ends of particles of the cleavable solid lubricant so as to cover them, the cleavage of the solid lubricant generates a force that shears the aggregates so that the deformation of the aggregates is induced. That is, the solid lubricant and the aggregates that relax the stress of the resin binder work together so that the solid lubricant having a small threshold stress is first deformed due to an increase in load, and then the aggregates having a relatively large threshold stress are deformed. In this way, stress relaxation follows to load increase without any gap.

(68) Further, also when the aggregates are closely attached to the sides of particles of the solid lubricant, the solid lubricant is first deformed by the application of a load, which influences the resin binder surrounding the solid lubricant so that the resin binder is slightly deformed. That is, a large stress is locally generated in the vicinity of the solid lubricant in the resin binder. At this time, when the aggregates are closely attached to the solid lubricant, the stress locally generated in the resin binder can reliably be relaxed.

(69) As can be seen from the above description, the aggregates may be present in the vicinity of the solid lubricant to relax stress locally generated in the resin composition. In this case, the distance between the solid lubricant and the aggregates is equal to or less than the average particle diameter of the protecting and reinforcing primary particles (10 nm or more but 100 nm or less). When the aggregates are present at such a distance within the above range from the solid lubricant, stress locally generated in the vicinity of the solid lubricant in the resin composition due to the deformation of the solid lubricant can reliably be relaxed.

(70) When 10% or more of the aggregates are closely attached to the solid lubricant or are present in the vicinity of the solid lubricant, deformation of the solid lubricant directly influences the 10% or more of the aggregates. Therefore, even when a load is increased, the solid lubricant and the aggregates work together to continuously relax stress without any gap.

(71) Here, the percentage (%) of the aggregates that are closely attached to the solid lubricant or are present in the vicinity of the solid lubricant is determined in the following manner

(72) The number of the aggregates that are closely attached to the solid lubricant or are present in the vicinity of the solid lubricant is counted and compared with the total number of the aggregates appearing in a predetermined measured view in a cutting surface obtained by cutting the sliding resin composition in a direction perpendicular to the sliding surface of the sliding resin composition.

(73) (3) Relationship II between Aggregates and Solid Lubricant

(74) The amount of the aggregates to which the ends of two or more particles of the solid lubricant are coupled is 5.0% or more.

(75) When the aggregates are closely attached to the tips of particles of the solid lubricant, the solid lubricant that is first deformed, cleaved, or disintegrated by the application of a load influences the aggregates that are closely attached to the tips of particles of the solid lubricant.

(76) For example, when the aggregates are closely attached to the ends of particles of the cleavable solid lubricant so as to cover them, the cleavage of the solid lubricant generates a force that shears the aggregates so that the deformation of the aggregates is induced. That is, the solid lubricant and the aggregates that relax the stress of the resin binder work together so that the solid lubricant having a small threshold stress is first deformed due to an increase in load, and then the aggregates having a relatively large threshold stress are deformed. In this way, stress relaxation follows to load increase without any gap.

(77) Further, when one aggregate is closely attached to the tips of two or more particles of the solid lubricant to couple them, a force generated by deformation of each of the particles of the solid lubricant is concentrated on the one aggregate, and therefore a force applied to the aggregate due to the deformation of the solid lubricant is increased so that the aggregate is more reliably deformed or disintegrated.

(78) Further, an assembly of two or more particles of the solid lubricant coupled by the aggregate functions as one piece of the solid lubricant because, as described above, the aggregate is easily deformed or disintegrated. In other words, the assembly covers a wider range of the resin binder to relax the stress of the resin binder. This makes it possible to more reliably prevent the disintegration or detachment of the resin binder.

(79) The amount of the aggregates coupling the ends of two or more particles of the solid lubricant is set to 5.0% or more of all the aggregates. When the amount of the aggregates coupling the ends of two or more particles of the solid lubricant is set to 5.0% or more, deformation of two or more particles of the solid lubricant directly influences the aggregates, and therefore the aggregates are more reliably deformed or disintegrated to exert the function of stress relaxation. Therefore, even when a load is increased, the solid lubricant and the aggregates work together to continuously relax stress without any gap.

(80) (4) Relationship III between Aggregates and Solid Lubricant

(81) The average particle diameter of the aggregates is 40% or less of the average particle diameter of the solid lubricant.

(82) When the average particle diameter of the aggregates is 40% or less of the average particle diameter of the solid lubricant, the aggregates are sufficiently smaller than the solid lubricant. This makes it possible to promote the dispersion of the aggregates in the resin composition to ensure the effect of the aggregates on relaxing the stress of the resin binder in the entire resin composition.

(83) (5) Relationship between Particles Constituting Aggregates

(84) The value of D90/D10 of the protecting and reinforcing primary particles constituting the aggregates is set to 5 or less, wherein D10 is a particle diameter when a cumulative height of particle diameters is 10%, and D90 is a particle diameter when a cumulative height of particle diameters is 90%.

(85) Here, a cumulative height of particle diameters refers to an integrated quantity in a particle diameter distribution curve, and D10 refers to a particle diameter when a cumulative percentage reaches 10% from the lower side of the distribution curve, and D90 refers to a particle diameter when a cumulative percentage reaches 90% from the lower side of the distribution curve. Therefore, when the value of D90/D 10 is smaller, the particle diameter distribution of the particles is sharper.

(86) When the value of D90/D10 is set to 5 or less, the particles have a sharp particle diameter distribution, that is, have a uniform particle diameter.

(87) The present invention is not limited to the above description of the embodiment according to the present invention. Various modified embodiments are also included in the present invention as long as they are easily conceivable by those skilled in the art and do not depart from the scope of the claims.

(88) The above embodiment has been described with reference to a case where the sliding member is a bearing, but the present invention is applicable also to other sliding members.

REFERENCE SIGNS LIST

(89) 1: Sliding member 2: Base material layer 3: Back metal layer 5: Alloy layer 7: Resin coating layer 10: Resin binder 11: Solid lubricant 13: Protecting and reinforcing primary particle 20: Aggregate 30: Recess