Sliding member

Abstract

A sliding member of the present invention includes a resin overlay layer containing an additive, in which the additive contains an oleophobic resin made of a fluorine resin and/or a silicon resin, and an appropriate amount of the oleophobic resin is uniformly dispersed on a sliding surface of the resin overlay layer. According to the sliding member, oil repellency can be imparted to the sliding surface of the resin overlay layer.

Claims

1. A sliding member comprising a resin overlay layer containing an additive, wherein the additive contains an oleophobic resin made of a fluorine resin and/or a silicon resin, and the oleophobic resin is uniformly dispersed on a sliding surface of the resin overlay layer under the following conditions:
U=s/(S*0.2)1(1) where 6%S30%, s is a standard deviation of areas of Voronoi polygons on a portion of a surface of the overlay layer, wherein the Voronoi polygons are based on the centers of the exposed oleophobic resin, and S is an area ratio calculated as the portion of an area occupied by the resin to the total area of an area of the overlay layer where the oleophobic resin is exposed.

2. The sliding member according to claim 1, wherein the oleophobic resin has a particle size of 1.0 m or less and an aspect ratio of 1.0 to 1.4.

3. The sliding member according to claim 1, wherein an amount of the additive to be added in the resin overlay layer is 30 vol % or more.

4. The sliding member according to claim 3, wherein an amount of the oleophobic resin in the additive contained in the resin overlay layer is 20 vol % or more.

5. The sliding member according to claim 1, wherein a ratio Rp/Rv of a maximum peak height Rp to a maximum valley depth Rv on the sliding surface of the resin overlay layer is from 0.7 to 1.8.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a cross-sectional view showing a configuration of a sliding member according to an embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(2) Hereinafter, the present invention will be described in more detail based on embodiments.

(3) A base material layer 2 constituting a sliding member 1 is generally made of a metal material.

(4) In the bearing as an example of the sliding member, the base material layer 2 has a configuration in which an aluminum-based bearing alloy layer 4 is laminated on a back metal layer 3 made of a steel material.

(5) A resin overlay layer 5 is laminated on the base material layer 2.

(6) The resin overlay layer 5 is made of a composition prepared by adding various additives to a binder resin.

(7) The binder resin can be appropriately selected depending on the intended use of the sliding member 1. For example, one or more of a polyimide resin, a polyamide imide resin, an epoxy resin, a phenol resin, a polyamide resin, and an elastomer can be employed, and a polymer alloy may be used.

(8) An oleophobic resin can be used as the additive.

(9) The material of the oleophobic resin can be appropriately selected depending on the intended use of the sliding member 1.

(10) In the present invention, attention is paid to an oleophobic resin made of a fluorine resin and an oleophobic resin made of a silicon resin.

(11) Examples of the oleophobic resin made of a fluorine resin include PTFE, PFA, FEP, ETFE, and PVDF.

(12) Examples of the oleophobic resin made of a silicon resin include silicone powder and silicone rubber powder.

(13) It is preferable that an appropriate amount of these oleophobic resins is uniformly dispersed on the sliding surface of the resin overlay layer. It is more preferable that the oleophobic resins are also uniformly dispersed in the thickness direction.

(14) In the present invention, the dispersion of the oleophobic resin on the sliding surface of the resin overlay layer is defined as follows:
U=s/(S*0.2)1(1) where 6%S30% holds, s is a standard deviation of areas of Voronoi polygons, and S is an area ratio of an area where the oleophobic resin is exposed.

(15) In order to uniformly disperse the oleophobic resins on the resin overlay layer, the particle size of the oleophobic resins, the selection of the binder resin, the stirring method, and the like are appropriately adjusted.

(16) The ratio of the fluorine resin and the silicon resin is not particularly limited. The fluorine resin may be used singly, the silicon resin may be used singly, or a mixture of the fluorine resin and the silicon resin may be used.

(17) A particle size of the oleophobic resin is 1.0 m or less and an aspect ratio of the oleophobic resin is from 1.0 to 1.4. The particle size is more preferably 0.8 m or less, and the aspect ratio is more preferably from 1.0 to 1.1. The lower limit of the particle size is not particularly limited, and the lower limit of the particle size of an industrially available oleophobic resin is considered to be 0.2 m.

(18) The method for measuring the particle size and the aspect ratio is as described above.

(19) In addition to the oleophobic resins described above, a versatile solid lubricant, hard particles, or the like can be used as the additive.

(20) Examples of the solid lubricant include molybdenum disulfide, tungsten disulfide, h-BN (h-boron nitride), graphite, melamine cyanurate, carbon fluoride, phthalocyanine, graphene nanoplatelets, fullerene, ultra-high molecular weight polyethylene (trade name MIPELON, manufactured by Mitsui Chemicals, Inc.), and N-Lauroyl-L-lysine (AMIHOPE (trade name), manufactured by Ajinomoto Co., Inc.).

(21) Examples of the hard particles include metal particles, metal oxide particles, metal nitride particles, and carbides. Addition of the hard particles enables the wear resistance of the resin overlay layer to be maintained.

(22) Moreover, a pigment can be added as the additive.

(23) The lower limit of the amount of the additive to be added is not particularly limited, and the amount of the additive to be added to the resin overlay layer is preferably 30 vol % or more. The amount of the additive to be added is more preferably 40 vol % or more. The upper limit of the amount of the additive to be added is not particularly limited, and can be set to 60 vol % from the viewpoint of ensuring other characteristics (wear resistance and the like) of the resin overlay layer.

(24) The method for specifying the amount of the additive to be added is as described above.

(25) In all the additives added to the resin overlay layer, the lower limit of the amount of the oleophobic resin is not particularly limited, and this amount is preferably 20% or more. The amount of the oleophobic resin is more preferably 30% or more. The upper limit of the amount of the oleophobic resin is not particularly limited, and can be set to 50% from the viewpoint of ensuring other characteristics (seizure resistance and the like) of the resin overlay layer. The upper limit of the amount of the oleophobic resin is more preferably 40%.

(26) The method for specifying this amount is as described above.

(27) The additive is selected such that the ratio Rp/Rv of the maximum peak height Rp to the maximum valley depth Rv on the sliding surface of the resin overlay layer is from 0.7 to 1.8. The ratio Rp/Rv is more preferably in a range of 0.8 to 1.6.

(28) Here, the Rp and Rv are based on the standard of JIS B 0601.

(29) The resin overlay layer 5 is formed as described below.

(30) In order to dissolve a resin material used for the binder resin, a specific solvent such as NMP (N-methyl-2-pyrrolidone), isophorone, GBL (-butyrolactone), DMSO (dimethylsulfoxide), or DAM (dimethylacetamide) is used. Such a solvent generally has a high boiling point (boiling point: higher than 150 C.) and is expensive. It is necessary to cause a solid lubricant to be dispersed in the solvent. Thus, the binder resin is dissolved in a first solvent such as NMP, and then a second solvent is added to the mixture to adjust the viscosity of the binder resin, resulting in a state in which dispersion is facilitated. Various additives including an oleophobic resin are sequentially added to the mixture and stirred. As the second solvent, a solvent having a boiling point (boiling point: 150 C. or lower) lower than that of the first solvent, such as ethanol, butyl acetate, cyclohexane, methyl ethyl ketone, MIBK (methyl isobutyl ketone), toluene, xylene, or ethylbenzene, can be employed.

(31) The surface of the bearing alloy layer 4 is coated with the liquid composition thus prepared, dried to volatilize the solvent, and then thermally cured. As the coating method, a known method such as a spray coating method, a roll coating method, a padding method, or a screen printing method can be employed.

Examples

(32) Hereinafter, Examples of the present invention will be described.

(33) The sliding member 1 in each of the Examples was formed to have, for example, a cross-sectional structure shown in FIG. 1. More specifically, the aluminum-based bearing alloy layer 4 was lined on the back metal layer 3 made of steel to produce a bimetal, and the bimetal was shaped into a semi-cylindrical shape. Thereafter, the surface of the bearing alloy layer 4 was subjected to boring processing for surface finishing. As a result, the base material layer 2 (thickness: 1.5 mm) was formed. Next, the surface of the semi-cylindrical molded product was washed (washed to give a roughened surface).

(34) The resin overlay layer 5 (3 to 10 m) containing an oleophobic resin was laminated on the upper surface of the base material layer 2 thus formed. The lamination conditions are as follows. (1) Mixing method Solvent 1: NMP Solvent 2: Xylene (2) Coating method: coating by spraying at preheating temperature (80 to 100 C.) (3) Drying conditions: drying in a furnace (at 140 to 180 C.) for about 5 minutes

(35) The resultant sliding members of the Examples and Comparative Examples were subjected to a friction test in a room temperature environment under the following conditions.

(36) TABLE-US-00001 Item Conditions Unit Bearing dimension 56 L15 t1.5 mm Rotation speed 2000 rpm Load 5 Kgf Lubricating oil VG22 Shaft material S55C Time 1 Time

(37) The area ratio S and the standard deviation s were calculated by performing image processing on the cross section of the resin overlay layer.

(38) An electron microanalyzer JXA-8530F was used as a photographing device.

(39) Standard image processing software (WinROOF2021) was used to calculate the areas of the oleophobic resin and the like and to specify the areas of Voronoi polygons and the standard deviation s.

(40) The compositions and measurement results of Examples 1 to 3 and Comparative Examples 1 to 6 are shown in Table 1.

(41) TABLE-US-00002 TABLE 1 Composition (2) Volume ratio Measured value (1) (2) Silicone (3) (3) (2) + (3)/ (2)/ S U Friction PAI PTFE resin MoS.sub.2 Gr (1) + (2) + (3) (2) + (3) Example 1 29.6 0.86 0.09 55 30 15 45% 67% Example 2 16.1 0.9 0.1 64 16 20 36% 44% Example 3 8.2 0.79 0.11 69 7 24 31% 23% Example 4 6.7 0.83 0.11 70 6 24 30% 20% Comparative 5.2 0.96 0.26 65 5 30 35% 14% Example 1 Comparative 32.4 1.00 0.23 62 33 5 38% 87% Example 2 Comparative 4.5 1.90 0.38 56 4 40 44% 9% Example 3 Comparative 40.3 1.24 0.32 57 40 3 43% 93% Example 4 Comparative 13.7 1.06 0.16 71 14 15 29% 48% Example 5 Comparative 25.9 1.12 0.18 64 26 10 36% 72% Example 6

(42) A product, manufactured by Solvay S.A., was used as PAI (polyamide imide) in each of the Examples and Comparative Examples. A product, manufactured by Chemours-Mitsui Fluoroproducts Co., Ltd., was used as PTFE (polytetrafluoroethylene) in each of the Examples and Comparative Examples. The particle size of the oleophobic resin was 1 m or less. The aspect ratio of the oleophobic resin was from 1.0 to 1.4. A product, manufactured by Shin-Etsu Chemical Co., Ltd., was used as the silicone resin of Example 4. The particle size of the oleophobic resin was 1 m or less. The aspect ratio of the oleophobic resin was from 1.0 to 1.4.

(43) From the friction values in the Examples and Comparative Examples in Table 1, it is found that the value of U defined by Formula (1) is preferably less than 1.

(44) Here, it is found that the amount of the additives ((2)+(3)/(1)+(2)+(3)) in the total composition is preferably 30 vol % or more.

(45) Further, it is found that the amount ((2)/(2)+(3)) of the oleophobic resin (PTFE or silicone resin) in the additives is preferably 20 vol % or more.

(46) Next, Table 2 shows a relationship between the roughness of the sliding surface of the resin overlay layer and the friction value under the condition of U<1 in Formula (1).

(47) TABLE-US-00003 TABLE 2 Composition Volume ratio Measured value (1) (2) (3) (2) + (3)/ (2)/ S U Rp/Rv Friction PAI PTFE MoS.sub.2 (1) + (2) + (3) (2) + (3) Example 5 16.1 0.90 1.8 0.10 64 16 20 36% 44% Example 6 15.9 0.88 1.6 0.09 64 16 20 36% 44% Example 7 16.0 0.89 0.8 0.08 64 16 20 36% 44% Example 8 16.3 0.91 0.7 0.10 64 16 20 36% 44%

(48) In Table 2, the particle size of the oleophobic resin (PTEF) was 1 m or less. The aspect ratio of the oleophobic resin was from 1.0 to 1.4.

(49) The results of Table 2 show that a ratio Rp/Rv of a maximum peak height Rp to a maximum valley depth Rv on the sliding surface of the resin overlay layer is preferably set to a range of 0.7 to 1.8. The ratio Rp/Rv is more preferably in a range of 0.8 to 1.6.

(50) Here, the Rp and Rv are based on the standard of JIS B 0601. The surface was measured using Surfcorder SE3500.

(51) The surface roughness was adjusted by blasting.

(52) The sliding surface of the resin overlay layer was subjected to a dropping test in the following manner.

(53) In a room temperature environment, a microsyringe is used to drop 10 L of oil (specific name: HONDA ULTRA NEXT) while a needle of the microsyringe is brought into contact with, or slightly spaced apart from, a sliding surface of a resin overlay layer of each sliding member left to stand.

(54) The state of the sliding surface 2 seconds after the dropping of the droplet is photographed from vertically above while the state of the sliding member left to stand is maintained. The resulting image is processed to obtain the area of the oil. The diameter (spread value) of a circle having the same area as the obtained area is calculated.

(55) A microscope VHX-6000 was used to capture the image. Standard image processing software (microscope VHX-6000) was used for area calculation through image processing.

(56) The results of the dropping test for Examples and Comparative Examples are shown in Table 3.

(57) TABLE-US-00004 TABLE 3 Measured value Composition Volume ratio Spread (1) (2) (3) (2) + (3)/ (2)/ diameter Friction PAI PTFE MoS.sub.2 (1) + (2) + (3) (2) + (3) Example 9 10.0 0.11 60 10 30 40% 25% Example 10 9.0 0.10 60 20 20 40% 50% Example 11 8.6 0.09 60 30 10 40% 75% Comparative 12.0 0.40 60 0 40 40% 0% Example 7

(58) The results of Table 3 show that the diameter of the spread oil droplet is preferably 10.0 mm or less.

(59) The present invention is not limited to the above description of the embodiments of the 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 claims. A device using a bearing mechanism, such as an internal combustion engine, using the sliding member of the present invention exhibits excellent sliding characteristics.