Low-friction structure between sliding surfaces and method for providing same

Abstract

To provide a novel low friction structure for reducing friction between sliding surfaces, and a method of providing the same.SOLUTION: There are provided a low friction structure for reducing friction between sliding surfaces in a moving member that slidably moves relative to the reference surface of a reference member, with its moving surface made to face the reference surface, and a method of providing the same. With a liquid film of a first lubricating liquid being provided to cover at least a portion of the reference surface and a liquid film of a second lubricating liquid immiscible to the first lubricating liquid being provided in a manner of covering the moving surface, the moving member is positioned on the reference member via the first lubricating liquid and the second lubricating liquid in between. The contact angle with respect to the reference surface and the surface tension of the second lubricating liquid are made greater than those of the first lubricating liquid so as to let the moving surface of the moving member slidably move with respect to the reference surface of the reference member, while allowing the liquid film of the second lubricating liquid to move relative to the liquid film of the first lubricating liquid.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a low-friction structure that reduces friction between sliding surfaces and a method for providing the same, and more particularly to a low-friction structure that reduces friction between sliding surfaces of a moving member that slides relative to a reference surface of a reference member with its moving surface facing the reference surface of the reference member, and a method for providing the same. [Background technology]

[0002] The use of environmentally friendly materials such as water and ethanol as lubricants to reduce friction between sliding surfaces has been proposed. Water-based lubricants, in particular, are expected to be used in industrial equipment due to their abundant availability and low cost. However, compared to conventional lubricants such as mineral oil, these lubricants have low viscosity, making them difficult to maintain between sliding surfaces. They also make it difficult to form a liquid film of sufficient thickness, making it difficult to maintain a low-friction structure over long periods of time. Therefore, lubricants have been proposed that combine oil and water to form an emulsion, imparting the lubricating properties of oil to water.

[0003] For example, Patent Document 1 discloses a water-soluble metal surface lubricant in which a paraffin-based hydrocarbon substance is emulsified in water with a surfactant as a lubricant that does not use organic solvents and reduces friction on the metal surfaces of electronic components such as connectors, switches, or chip components. Examples of hydrocarbon substances cited here include paraffin, liquid paraffin, petrolatum, and squalane, which are decomposed into carbon dioxide and water by microorganisms in water or soil in a short period of time. This method of imparting a low-friction structure is said to be able to lower the coefficient of friction compared to conventional solvent-based lubricants without increasing the contact resistance of the electronic components, and also to reduce the impact on the environment. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-212582 Summary of the Invention [Problem to be solved by the invention]

[0005] In the emulsion-based lubricants described above, surfactants are used to stabilize the emulsion, but these surfactants have a significant environmental impact. Special equipment is required to recover the emulsion, and recovery and disposal costs are high, resulting in environmental impacts. Therefore, a new low-friction structure that does not use surfactants and that can reduce friction between sliding surfaces, and a method for applying this structure, were sought.

[0006] The present invention has been made in consideration of the above-mentioned problems, and an object of the present invention is to provide a new low-friction structure for reducing friction between sliding surfaces and a method for providing the same. [Means for solving the problem]

[0007] The low-friction structure according to the present invention is a low-friction structure for reducing friction between sliding surfaces of a moving member that slides relative to a reference surface of a reference member, with its moving surface facing the reference surface of the reference member, and is characterized in that a liquid film of a first lubricating liquid is provided to cover at least a portion of the reference surface, and a liquid film of a second lubricating liquid that is insoluble in the first lubricating liquid is provided to cover the moving surface, so that the moving member is positioned on the reference member with the first lubricating liquid and the second lubricating liquid interposed therebetween, and the contact angle and surface tension of the second lubricating liquid with respect to the reference surface are made larger than those of the first lubricating liquid, so that the liquid film of the second lubricating liquid moves relative to the liquid film of the first lubricating liquid while the moving surface of the moving member slides relative to the reference surface of the reference member.

[0008] Furthermore, a method for imparting a low-friction structure according to the present invention is a method for imparting a low-friction structure to reduce friction between sliding surfaces of a moving member that slides relative to a reference surface of a reference member, with its moving surface facing the reference surface of the reference member, and is characterized in that a liquid film of a first lubricating liquid is provided to cover at least a portion of the reference surface, and a liquid film of a second lubricating liquid that is insoluble in the first lubricating liquid is provided to cover the moving surface, and the moving member is positioned on the reference member with the first lubricating liquid and the second lubricating liquid interposed therebetween, and the contact angle and surface tension of the second lubricating liquid with respect to the reference surface are made larger than those of the first lubricating liquid so that the liquid film of the second lubricating liquid moves relative to the liquid film of the first lubricating liquid while the moving surface of the moving member slides relative to the reference surface of the reference member.

[0009] According to this feature, multiple lubricating liquids are held between the sliding surfaces, creating a fluid lubrication state in which lubricating liquid is always present between the parts that slide relative to one another, and by utilizing the Laplace pressure of the liquid to apply a force in the opposite direction to the load (pressure) direction, direct contact between the parts is prevented, resulting in a stable, low-friction environment.

[0010] In the above-described invention, the contact angle of the first lubricating liquid with respect to the reference surface may be set to 40 degrees or less. The reference surface may be provided with a surface treatment or a surface coating that adjusts the contact angle with the first lubricating liquid. This feature makes it possible to obtain a low-friction environment with a friction coefficient of 0.1 to 0.01, which is similar to that of conventional lubricating oils, or even less.

[0011] In the above invention, the first lubricating liquid and the second lubricating liquid may be hydrocarbon and water, respectively. This feature provides high selectivity for the lubricating liquid, low disposal costs, and excellent maintainability, as the lubricating liquid does not become cloudy like an emulsion, making it easy to observe the sliding surface.

[0012] In the above-described invention, one or more additional liquid films may be included between the liquid film of the first lubricating liquid and the liquid film of the second lubricating liquid, and the additional liquid films may be arranged so that the contact angle and surface tension with respect to the reference surface increase sequentially from the first lubricating liquid side toward the second lubricating liquid side. This feature prevents direct contact between components, thereby achieving a more stable, low-friction environment. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a cross-sectional view showing a low friction structure according to the present invention. [Figure 2] 1 is a cross-sectional view showing a low friction structure according to the present invention. [Figure 3] 1 is a cross-sectional view of a single lubricating liquid film when a load is applied by a moving member, where (b) is an enlarged view of the main part of (a). [Figure 4] 1 is a cross-sectional view of one embodiment when a load is applied to liquid films of two types of lubricating liquid by a moving member, where (b) is an enlarged view of a main part of (a). [Figure 5] 10 is a cross-sectional view of another embodiment when a load is applied to liquid films of two types of lubricating liquid by a moving member, where (b) is an enlarged view of the main part of (a). [Figure 6] 1 is a graph showing the contact angle and surface tension of oleic acid and water on a molecular thin film. [Figure 7] FIG. 2 is a cross-sectional view of a molecular thin film when a first lubricating liquid (oleic acid) and a second lubricating liquid (water) are applied. [Figure 8] FIG. 1 is a cross-sectional view showing a method for a friction test. [Figure 9] 10 is a graph showing the results of a comparative example of a friction test. [Figure 10] 1 is a graph showing the results of an example of a friction test. [Figure 11] The figure shows the height analysis results (top) and surface observation photographs (bottom) of the sliding surfaces observed with a 3D laser microscope during a friction test. [Figure 12]10 is a graph showing the results of a comparative example of a friction test in which the friction speed was changed. [Figure 13] 1 is a graph showing the results of an example of a friction test in which the friction speed was changed. [Figure 14] 1 is a cross-sectional view showing a time series immediately after the start of a friction test in a comparative example, and a corresponding photograph of the lower part of a moving member (glass pin). [Figure 15] 1 shows cross-sectional views illustrating the time series immediately after the start of a friction test in an example, and corresponding photographs of the lower part of a moving member (glass pin). [Figure 16] 1 shows cross-sectional views illustrating the time series immediately after the start of a friction test in an example, and corresponding photographs of the lower part of a moving member (glass pin). [Figure 17] 1 is a graph summarizing the results of friction tests. [Figure 18] 1 is a graph summarizing the results of friction tests. DETAILED DESCRIPTION OF THE INVENTION

[0014] First, we will explain the principle of the low-friction structure for reducing friction between the sliding surfaces of moving members that slide relatively against the reference surface of a reference member according to the present invention. Here, we will effectively retain multiple lubricating liquids between the sliding surfaces to create a fluid lubrication state in which a liquid film of lubricating liquid always exists between the members that slide relatively, and we will also use the Laplace pressure of the liquid to apply a force in the opposite direction to the load (pressure) direction, thereby preventing direct contact between the members and maintaining a stable low-friction environment.

[0015] Two or more types of lubricating liquid films are used between the components that slide against each other. Adjacent lubricating liquids are made of substances that do not dissolve in each other even when stirred, and do not change in properties. The lubricating liquids are selected based on the contact angle with the reference component (substrate, base material) and the surface tension of the liquid itself.

[0016] As shown in FIG. 1 , in the lubricated surface formed by liquid films of a first lubricating liquid 21 and a second lubricating liquid 22, the contact angle of the second lubricating liquid 22 placed on top of the reference surface 10a, which is the sliding surface of the reference member 10, is larger than that of the first lubricating liquid 21. The surface tension of the second lubricating liquid 22 is also larger than that of the first lubricating liquid 21. Although not shown, in the case where an additional liquid film made of three or more types of lubricating liquid is included, the lubricating liquids are similarly arranged in sequence so that the contact angle of the upper lubricating liquid with respect to the reference surface 10a of the reference member 10 is larger than that of the lubricating liquid located below it, and the surface tension of the upper lubricating liquid is also larger than that of the lubricating liquid located below it.

[0017] If the contact angle of the first lubricating liquid 21 with respect to the reference surface 10a is as small as possible, typically 40 degrees or less, preferably 20 degrees or less, and more preferably 10 degrees or less, direct contact between the reference member 10 and the moving member 11, which move relative to each other, is prevented and a stable, low-friction environment is obtained. Also, the contact angle of the second lubricating liquid 22 with respect to the reference surface 10a of the reference member 10 is larger than the contact angle of the first lubricating liquid 21 with respect to the reference member 10, and the larger the difference in contact angles, the more direct contact between the two members 10 and 11 is prevented and the more a stable, low-friction environment is obtained.

[0018] In order to satisfy the above-mentioned contact angle conditions, the reference surface 10a of the reference member 10 may be subjected to a surface treatment or a surface coating, for example, an alkali treatment or a UV / O3 treatment.

[0019] The area where the second lubricating liquid 22 comes into contact with the first lubricating liquid 21 is equal to or smaller than the area where the lubricating liquid 21 comes into contact with the reference member 10. In other words, although not shown, the area where the lubricating liquid 21 covers at least a part of the reference surface 10a is the largest, and as the distance from the reference member 10 increases, the area covered by the lubricating liquid decreases, or becomes the same area as the lubricating liquid on the adjacent reference member 10 side.

[0020] When the second lubricating liquid 22 is in the form of droplets as a form of a liquid film, it is possible to hold a plurality of droplets of lubricating liquid 22 on the lubricating liquid 21, and a low-friction structure is provided as a liquid film by arranging the droplets below the moving surface 11a of the moving member 11. Here again, as described above, the total contact area of ​​the droplets of lubricating liquid 22 with the lubricating liquid 21 does not exceed the contact area of ​​the lubricating liquid 21 with the reference member 10.

[0021] The amount of the first lubricating liquid is 0.01 μL / cm 2 or more, preferably 0.1 μL / cm 2 It is preferable that this is equal to or greater than this.

[0022] As shown in FIG. 2, the reference surface 10a of the reference member 10 or the coating thereon (not shown) should always be covered with the lubricating liquid 21. In other words, even if the surface has uneven portions 12 and recessed portions 13 due to damage caused by friction, wear, etc. or surface roughness, they should be covered with the lubricating liquid 21. Here, if a protrusion 12a with a protruding height exists on the reference surface 10a, which is the surface of the reference member 10 having a low friction structure, the lubricating liquid 21 must cover the protrusion 12a. Also, if a recess 12b due to surface roughness, etc., or a damaged recess 13 due to friction or wear occurs, the interior of the recess should be filled with the lubricating liquid 21 and covered by the lubricating liquid 21. In other words, the maximum film thickness DA of the lubricating liquid 21 is max must be larger than the combined height of the protrusions 12a and the depth of the recesses 13. Even if the protrusions 12a are not completely covered with the lubricating liquid 21, the lubricating liquid 21 can be added to increase the thickness of the film so that the protrusions 12a are covered.

[0023] As shown in FIGS. 3 to 5, a state in which a load is applied by pressing a moving member 15 vertically from above onto the reference surface 10a of the reference member 10 is schematically shown.

[0024] As shown in Figure 3, when a single lubricating liquid 21 is applied to the reference surface 10a of the reference member 10, surface tension causes the lubricating liquid 21 to move to areas other than the bottom of the moving member 15 that are not subjected to load, causing the tip of the moving member 15 to come into contact with the reference member 10.

[0025] On the other hand, as shown in FIG. 4, the lubricating liquid 22 exists together with the lubricating liquid 21, and the maximum film thickness D A·MAX The maximum film thickness of the lubricating liquid is D B·MAX When the force F is small, even if the tip of the moving member 15 appears to be in contact with the reference member 10, the lubricating liquid 22 is interposed between the reference member 10 and the moving member 15. In other words, the lubricating liquid 22 near the tip of the moving member 15 is surrounded by the lubricating liquid 21 due to the difference in surface tension, and Laplace pressure is generated in the lubricating liquid 22, which acts to lift the moving member 15 in the opposite direction to the load direction of the moving member 15, creating a low-friction environment. This reverse force F droplet can be expressed by the following relational expression by assuming droplets of the lubricating liquid 22. F droplet = πγ AB r 2 ·(-cosθ A -cosθ B ) / h - 2πrγ AB sinθ A where γ AB is the interfacial tension between the lubricating liquids 21 and 22, r is the contact radius of the droplet of the lubricating liquid 22 with the moving member 15, and θ A is the contact angle of the droplet of lubricating liquid 22 with the moving member 15, and θ B is the contact angle of the droplet of lubricating liquid 22 on the reference member 10 (or the surface to which a surface treatment or surface coating has been applied), and h is the height of the droplet. Note that even if the tip of the moving member 15 is spherical, it is assumed to be flat when viewed microscopically.

[0026] As shown in FIG. 5, the lubricating liquid 22 exists together with the lubricating liquid 21, and the maximum film thickness D B·MAX is the maximum film thickness D of the lubricating liquid 21 A·MAXIn addition to the above, it is also possible to consider the case where the lubricating liquid 22 is not present directly under the tip of the moving member 15, but is present around the tip of the moving member 15 in a doughnut shape. In this case, too, a force acts to lift the moving member 15 in the opposite direction to the load direction, creating a low-friction environment. In this case, as in the case above, F droplet can be expressed by the following relational expression: F droplet = πγ AB r 2 ·(-cosθ A -cosθ B ) / h - 2πrγ AB sinθ A 2πR Here, R is the radius from the center of gravity of the annular (donut-shaped) lubricating liquid 22 to the center of the slice.

[0027] By selecting the lubricating liquid 21 so that it exhibits intermolecular interactions with the surface of the reference member 10 (or a surface that has been surface-treated or coated), it is possible to achieve a low-friction structure that is stable for a longer period of time. This intermolecular interaction can be achieved as long as the functional groups of each material have a chemical attraction, and it is preferable that one or more of the following interactions exist between the materials: electrostatic interaction (including Coulomb interaction, polarization-dipole moment interaction, ion-dipole interaction, dipole-dipole interaction, and induced dipole interaction), van der Waals interaction, hydrogen bond, interaction between hydrogen atoms and π electrons, interaction between π electrons, interaction via coordinate bonds, charge-transfer interaction, and hydrophobic interaction.

[0028] The lubricating liquid may be selected from mineral oil, synthetic oil, vegetable oil, animal oil, alcohol, aqueous solution, water, and the like.

[0029] Specifically, these include various silicone oils (decamethylcyclotetrasiloxane, octamethylcyclotetrasiloxane, dodecamethylcyclohexasiloxane, methylsilicone, methylphenylsilicone, methylhydroxysilicone, amino-modified silicone oil, epoxy-modified silicone oil, carboxy-modified silicone oil, carbinol-modified silicone oil, methacrylic-modified silicone oil, mercapto-modified silicone oil, phenol-modified silicone oil, polyether-modified silicone oil, methylstyryl-modified silicone oil, alkyl-modified silicone oil, fatty acid ester-modified silicone oil, and partially fluorinated silicone oil).

[0030] Alternatively, the liquid may be a liquid containing lower saturated fatty acids, higher saturated fatty acids, lower unsaturated fatty acids, higher unsaturated fatty acids, higher alcohols, fatty acid compounds (sesame oil, rapeseed oil, almond oil, cottonseed oil, salad oil, etc.), fluoroalkylethoxysilane, fluoroalkylmethoxysilane, alkylethoxysilane, alkylmethoxysilane, DB2-EOS, EF-DB2, P3-EOS, CnHx (n>4 or more) alkanes, alkenes, alkynes, oils and fats (beef tallow, lard, castor oil, palm oil, etc.), polyoxyalkylenated oils and fats (castor oil, hydrogenated castor oil), chlorinated oil, sulfurized oil (soybean oil, lard), polymerized oil (soybean oil, fish oil), or other fatty acid derivatives (fatty acids, soaps, esters, amides, polyoxyalkylene adducts, chlorinated / sulfurized / polymerized fatty acid alkyl esters).

[0031] In addition, examples of lubricating liquids having an aromatic ring include phenyltriethoxysilane, phenyltrimethoxysilane, phenylchlorosilane, phenylmethylchlorosilane, 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-[(hexyl)oxy]-phenol, 1-[2-{3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyloxy}ethyl]-4 ...}-2,2,6,6-tetramethylpiperidine, 4,4'-bis(α,α-dimethyl-benzyl)diphenylamine, 2,4-diamino-phenyl-1,3,5-triazine, tris(nonylphenyl)phosphite, tris(mixed, mono- and dinonylphenyl)phosphite, tris(2,4-di-t-butylphenyl)phosphite, 4,4'-butylidene-bis(3-methyl-6-t-butylphenyl-di-tridecylphosphite), 1 ,1,3-tris(2-methyl-4-di-tridecylphosphite-5-t-butyl-phenyl)butane and diphenyl phosphite mixture, 4,4'-biphenylenediphosphinic acid tetrakis(2,4-di-t-butylphenyl), cyclic neopentanetetraylbis(2,4-di-t-butylphenyl phosphite), tris(cyclohexylphenyl)phosphite, 2-t-butyl-α-(3-t-butyl-4-hydroxyphenyl)-P-chlor Menyl bis(p-nonylphenyl)phosphite, bis-[2-methyl-4,6-bis-(1,1-dimethylethyl)phenyl]ethyl phosphite, 3,9-bis{2,4-bis(1-methyl-1-phenylethyl)phenoxy}-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5,5]undecane, 6-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propoxy-2,4,8,10-tetra-t-butylbenz[d, f] [1,3,2]dioxaphosphepine, n-octadecyl-β-(4'-hydroxy-3',5'-di-t-butylphenyl)propionate, 4,4'-butylidenebis(6-t-butyl-m-cresol) or 1,1-bis(2'-methyl-4'-hydroxy-5'-t-butyl-phenyl)butane, triethylene glycol bis-3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionate, 2,2'-oxamidobis[ethyl 3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane), 2-t-butyl-6-(3-t-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenylacrylate, tetrakis[methylene-3-(3',5)di-t-butyl-4'-hydroxyphenyl]propionate]methane, bis[3,3 -Bis(4'-hydroxy-3'-t-butylphenyl)butanoic acid] glycol ester, 1,4-benzenedicarboxylic acid bis[2-(1,1-dimethylethyl)-6-[[3-(1,dimethylethyl)-2-hydroxy-5-methylphenyl]methyl]-4-methylphenyl] ester, N,N-bis{3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyl}hydrazine, 3,9-bis[2-{3-(3-t-butyl-4-hydroxy-5-methyl phenyl)propionyloxy}-1,1-dimethylethyl]-2,4,8,10-tetraoxaspiro[5,5]undecane, 2-[1-(2-hydroxy-3,5-di-t-pentylphenyl)ethyl]-4,6-di-t-pentylphenyl acrylate, pt-butylphenyl salicylate, 2,4-di-t-butylphenyl-3,5-di-t-butyl-4-hydroxybenzoate, 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 2-(2'-hydroxy (3'-t-butyl-5'-methylphenyl)-5-chlorobenzotriazole, phenyl salicylate or phenyl salicylate, 2-(2H-benzotriazol-2-yl)-4,6-bis(1-methyl-1-phenylethyl)phenol, 2-(2'hydroxy-5'-methacryloxyethylphenyl)-2H-benzotriazole and methyl methacrylate copolymer, 2-cyano-3,3-diphenylacrylate-2-ethylhexyl, poly(oxy-1,2-ethanediyl),α-[4-(3-butoxy-2-cyano-3-oxo-1-propen-1-yl)-2-methoxyphenyl]-ω-hydroxy-2-(2'-hydroxy-3'5'-di)-t-amylphenyl)benzotriazole, polyoxyethylene (4-50 mol) alkyl (C7 or higher) phenyl ether, polyoxyethylene (4-50 mol) alkyl (C7 or higher) phenyl ether sulfate (Na, NH4), polyoxyethylene (5-55 mol) Examples include nonylphenyl phosphate, α(p-nonylphenyl)-ω-hydroxypoly(oxyethylene) dihydrogen phosphate ester, monohydrogen phosphate ester mixture, methylphenylpolysiloxane, polyorgano (C1 to C32 alkyl and / or phenyl) siloxane and polyalkylene (C2 to C3) glycol condensate, benzene-1,2-dimethyl-4,5-bis(1-phenylethyl), benzene-4-(1,3 diphenylbutyl)-1,2 dimethyl, benzene [1-(3,4-dimethylphenyl)ethyl] (1-phenylethyl) mixture, branched polycarbonate, sodium bis(4-t-butylphenyl) phosphate, sodium 2,2'-methylenebis(4,6-di-t-butylphenyl) phosphate, zinc(II) phenylphosphonate, and 7,8,9-trideoxy-3,5:4,6-O-bis-(4-propylphenyl)methylene=D-glycero-L-gulononitol. ,

[0032] The above-mentioned materials may be used alone or in combination of two or more, provided that the above-mentioned conditions of contact angle and surface tension with respect to the reference member 10 are met in order to form a film of the lubricating liquid.

[0033] Known methods can be used to manufacture the reference surface 10a, which is the sliding surface of the reference member 10, and to apply the lubricating liquids 21 and 22. For example, the lubricating liquids can be applied by spin coating, dipping, roll-to-roll coating, squeegee coating, doctor blade coating, coating, casting, or layer-by-layer coating (layer-by-layer adsorption). These methods may be used alone or in combination of two or more. For example, the lubricating liquid 21 may be applied to the surface of the reference member 10 by dipping, and then the lubricating liquid 22 may be sprayed onto it by a spray method. Similarly, known methods can be used to form coatings on substrates. [Example]

[0034] A glass slide (26 x 76 mm) was used as the reference member 10, and a molecular thin film was formed on its surface. A mixed solution of phenyltriethoxysilane, ethanol, hydrochloric acid, and water was prepared as the solution for the molecular thin film. The glass slide was immersed in the solution and left to stand for 24 hours, forming a molecular thin film on the surface. Oleic acid and water, which are hydrocarbons, were selected as the lubricating liquids 21 and 22. The surface tension of oleic acid is 32.8 mN / m, and the surface tension of water is 72.8 mN / m.

[0035] The contact angles of oleic acid and water on the molecular thin film formed as described above are shown in Figure 6. The contact angle of oleic acid was 7.96 degrees, and the contact angle of water was 79.96 degrees.

[0036] Figure 7 shows the cross-sectional configuration of the friction test. From the relationship between the contact angle of the lubricating liquid with the molecular thin film 10b and the surface tension, the lubricating liquid 21 closest to the reference member 10 is oleic acid, and the lubricating liquid 22 above it is water. The thickness of the molecular thin film 10b is 7.5 nm, and the concentration of oleic acid is 0.1 μL / cm 2 A drop of water was placed on the molecular thin film 10b and allowed to wet and spread. Different amounts of water droplets were placed on the oleic acid surface to examine the difference in the coefficient of friction.

[0037] Example 1 As shown in Figure 8, the tip of a moving member 15 made of a glass pin was pressed against a reference member (glass substrate) 10 made of a glass slide, a load P was applied, and the glass pin was moved back and forth to conduct a reciprocating friction test. Here, the load P was 50 mN. The glass pin was made of borosilicate glass and was a rod-shaped object with a tip radius of 3 R and a diameter of 3 mm and a length of 20 mm. Measurements were performed by moving the pin back and forth 1,000 times over a linear distance of 6 mm at an average friction speed of 0.5 Hz. The Hertzian contact angle was 1.8 MPa for the combination of borosilicate glass and glass substrate.

[0038] The results of the friction tests are shown in Figures 9 and 10. First, as a comparative example, as shown in Figure 9(a), measurements were taken on a glass substrate without any coating, i.e., without applying lubricating liquids 21 and 22. The average friction coefficient was 0.64 and the median was 0.63. As shown in Figure 9(b), measurements were taken on a glass substrate with a molecular thin film 10b formed thereon and without applying any lubricating liquid. The average friction coefficient was 0.89 and the median was 0.90. Furthermore, as shown in Figure 9(c), measurements were taken on a molecular thin film 10b with a single lubricating liquid 21 consisting of oleic acid held on top of it. The average friction coefficient was 0.073 and the median was 0.058.

[0039] FIG. 10 shows an example in which multiple lubricating liquids 21 and 22 are placed on a molecular thin film 10b. After stabilizing oleic acid, 1, 10, 30, and 100 μL of water droplets are placed on the oleic acid. The friction coefficients are measured using a 1 μL water droplet, as shown in FIG. 10(a). The average friction coefficient is 0.029 and the median is 0.020. As shown in FIG. 10(b), the average friction coefficient is 0.024 and the median is 0.015. As shown in FIG. 10(c), the average friction coefficient is 0.020 and the median is 0.015. Furthermore, as shown in FIG. 10(d), the average friction coefficient is 0.019 and the median is 0.015. As shown in FIG. 10(d), the average friction coefficient is 0.019 and the median is 0.015. For each amount of water, the friction coefficient showed a similar value after reaching a constant value, but when the amount of water was small, it took longer to reach this constant value. This is thought to be because the load is applied vertically from directly above the center of the water droplet, but this tends to shift, and low friction is achieved after the water droplet moves to the optimal position where it is applying the load during sliding.

[0040] FIG. 11 shows the results of surface observation after the above-described friction test. FIG. 11(a) corresponds to FIG. 9(a), and the surface was damaged by the glass pin, and wear marks and wear debris were observed. FIG. 11(b) corresponds to FIG. 9(b), and similar to FIG. 11(a), wear marks and wear debris were observed on the surface. FIG. 11(c) corresponds to FIG. 9(c), and it was confirmed that no visible large wear marks or debris were formed on the surface in the height evaluation defined as 1 μm or more or within the range of 1 μm to −1 μm. However, lines (streaks) were observed at the sliding points in the image of the surface observed under a microscope. On the other hand, FIG. 11(d) corresponds to the example of FIG. 10(c), and contact between the reference member 10 and the moving member 15 was prevented, and no wear marks or debris were observed on the surface, and no sliding marks were observed in the image observed under a microscope.

[0041] Figures 12 and 13 show the measurement results of friction tests conducted by changing the friction speed of the moving member 15. Figure 12(a) corresponds to Figure 9(a), and shows that the friction coefficient varied regardless of the friction speed due to wear and debris generation. Figure 12(b) corresponds to Figure 9(b), and shows that the variation in the friction coefficient was small when the friction speed was high, but as the friction speed approached 0 mm / sec, the variation increased, reaching a maximum of 1.4. This is thought to be because, when the friction speed was close to 0 mm / sec, the static friction coefficient became dominant and the members came into contact with each other. On the other hand, Figure 13 corresponds to the example shown in Figure 10(c), and the variation in the friction coefficient was a maximum of 0.25, which was smaller than the case shown in Figure 12(c). In addition, even when the friction speed is slow, the friction coefficient can be relatively high. This is thought to be because, as the water droplets slide back and forth, an inertial force acts on them in the direction of the sliding, and at the end of the reciprocating movement where the friction speed becomes 0 mm / sec, a force in the opposite direction is applied to the initial movement.

[0042] 14 to 16 show the results of observing the vicinity of the tip of the moving member 15 from the back surface of the reference member 10 immediately after the start of the friction test described above. Fig. 14 corresponds to Fig. 9(c), and even after the moving member 15 is pressed to start the test, no lubricating liquids 21 and 22 are observed between the reference member 10 and the moving member 15, and no difference is observed between the initial contact image and the image of the contact surface (see the photograph on the right side of Fig. 14; note that oleic acid has been stained for observation). 10(a) and 10(c), respectively, but when the moving member 15 is pressed, water droplets descend into the liquid film of oleic acid along the load direction, and even when the moving member 15 comes into contact with the reference member 10, water droplets remain between the sliding surfaces (see FIG. 15, the water is dyed for observation purposes), or water is present in a ring shape surrounding the moving member (glass pin) 15 (see FIG. 15, the water is dyed for observation purposes). In other words, when water droplets are present between the sliding surfaces of the reference member 10 and the moving member 15 (including when water is present in a ring shape around the moving member 15), a force is generated that lifts the moving member 15 upward due to the Laplace pressure caused by the difference in surface tension between the water droplets and the surrounding oleic acid.

[0043] <Example 2> As in Example 1, a continuous friction test was performed by pressing the tip of a moving member 15 made of a glass pin against a reference member (glass substrate) 10 made of a disk-shaped slide glass, applying a load P, and continuously moving the glass pin. Measurements were performed by rotating a disk-shaped glass substrate with a radius of 5 mm 1,000 times at different friction speeds. Here, the Hertzian contact pressure was 1.8 MPa for the combination of borosilicate glass and glass substrate.

[0044] 17 and 18 show the measurement results of the average friction coefficient versus friction speed.

[0045] In Figure 17, when measurements were taken on a glass substrate without the molecular thin film 10b, i.e., without the lubricating liquids 21 and 22, the average friction coefficient was 0.40 to 0.56 and the median was 0.40 to 0.57. Furthermore, when measurements were taken on a glass substrate with the molecular thin film 10b applied but without the lubricating liquids 21 and 22, the average friction coefficient was 0.10 to 0.18 and the median was 0.10 to 0.18 at friction speeds of 30 rpm or less. However, at friction speeds of 50 rpm or more, the average friction coefficient was equivalent to that of the glass substrate alone. Furthermore, when measurements were taken with only oleic acid applied as the lubricating liquid 21 on the molecular thin film 10b, the average friction coefficient was 0.027 to 0.056 and the median was 0.025 to 0.055. Furthermore, after oleic acid was stably retained on the molecular thin film 10b, a 30 μL droplet of water was placed on the oleic acid, and the friction coefficient was measured. The average value was 0.012 to 0.020, and the median value was 0.0098 to 0.019, indicating a low friction coefficient. In particular, the film exhibited super-lubricity with a friction coefficient of 0.01 or less at a friction speed of 30 rpm.

[0046] As described above, a low-friction structure can be obtained simply by selecting and combining multiple lubricating liquids with different surface tensions and contact angles with the substrate. An ultra-low friction coefficient of 0.01 or less (ultra-lubricity) can be achieved without immersing the friction area in oil, as in the past. Furthermore, environmentally friendly liquids such as water can be used as the lubricating liquid, and by layering multiple lubricating liquids under energetically stable conditions, the problems of conventional emulsions, such as difficulty in recovery, high disposal costs, and cloudiness, can be solved.

[0047] Although the embodiments of the present invention and modifications based thereon have been described above, the present invention is not necessarily limited thereto, and a person skilled in the art will be able to find various alternative embodiments and modifications without departing from the spirit of the present invention or the scope of the appended claims. [Explanation of symbols]

[0048] 10 Reference member (glass substrate) 10a Reference plane 11, 15 Moving parts (glass pins) 12 Uneven part 13 Recess 21 1st lubricating liquid 22 Second lubricating liquid

Claims

1. A low-friction structure for reducing friction between the sliding surfaces of a reference surface and a moving surface of a reference member, in which the moving surface faces a reference surface of a reference member and slides relative to the reference surface, by interposing water between the reference surface and the moving surface and generating Laplace pressure in the water so as to lift the moving member in a direction opposite to a direction in which a load is applied by the moving member toward the reference surface, a liquid film of a first lubricating liquid having a contact angle and surface tension with respect to the reference surface smaller than those of water, being insoluble in water, and not changing its properties when in contact with water, is provided to a predetermined thickness to cover at least a part of the reference surface, and a liquid film of a second lubricating liquid made of water that is insoluble in the first lubricating liquid is provided to a lower part of the moving surface so as to cover the moving surface, and the moving member is positioned above the reference member with the first lubricating liquid and the second lubricating liquid interposed therebetween; A low-friction structure between sliding surfaces, characterized in that the moving surface of the moving member slides against the reference surface of the reference member while pressing and descending a liquid film of the second lubricating liquid against a liquid film of the first lubricating liquid.

2. A low-friction structure between sliding surfaces as described in claim 1, characterized in that the first lubricating liquid consists of a hydrocarbon.

3. The low-friction structure between sliding surfaces according to claim 1, wherein the predetermined thickness is a thickness that allows the amount of the first lubricating liquid to be 0.01 μL / cm 2 or more.

4. 2. The low friction structure between sliding surfaces according to claim 1, wherein the contact angle of the first lubricating liquid with respect to the reference surface is 40 degrees or less.

5. 3. The low-friction structure between sliding surfaces according to claim 1, wherein the reference surface is provided with a surface treatment or a surface coating that adjusts the contact angle with the first lubricating liquid.

6. A method for providing a low-friction structure in a moving member that slides relative to a reference surface of a reference member with its moving surface facing the reference surface of the reference member, by interposing water between the reference surface and the moving surface and generating Laplace pressure in the water so as to lift the moving member in a direction opposite to a direction in which a load is applied by the moving member toward the reference surface, thereby reducing friction between the sliding surfaces of the reference surface and the moving surface, a liquid film of a first lubricating liquid having a contact angle and surface tension with respect to the reference surface smaller than those of water, being insoluble in water, and not changing its properties when in contact with water, is provided to a predetermined thickness to cover at least a part of the reference surface, and a liquid film of a second lubricating liquid made of water that is insoluble in the first lubricating liquid is provided to a lower part of the moving surface so as to cover the moving surface, and the moving member is positioned above the reference member with the first lubricating liquid and the second lubricating liquid interposed therebetween; A method for imparting a low-friction structure, characterized in that the moving surface of the moving member is slid against the reference surface of the reference member while pressing and descending a liquid film of the second lubricating liquid against a liquid film of the first lubricating liquid.

7. A method for imparting a low friction structure as described in Claim 6, characterized in that the first lubricating liquid consists of a hydrocarbon.

8. The method for imparting a low friction structure according to claim 6, wherein the predetermined thickness is a thickness that makes the amount of the first lubricating liquid 0.01 μL / cm 2 or more.

9. 7. The method for imparting a low friction structure according to claim 6, wherein the contact angle of the first lubricating liquid with respect to the reference surface is set to 40 degrees or less.

10. 8. The method for imparting a low-friction structure according to claim 6, wherein the reference surface is provided with a surface treatment or a surface coating that adjusts the contact angle with the first lubricating liquid.

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