Lubricant for aluminum alloy sliding member

Abstract

To provide a lubricant exhibiting a wear-inhibiting effect for an aluminum alloy sliding member.SOLUTION: A lubricant comprises nanodiamond particles (A), a fatty acid ester-based dispersant (B), and an oil agent (C), wherein the nanodiamond particles (A) are nanodiamond particles having at least one surface modification group selected from the following formulas (a-1) to (a-4).SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a lubricant for application to an aluminum alloy sliding member. [Background technology]

[0002] Many sliding components are composed of iron-based alloys. This makes them heavy and difficult to handle. While efforts are being made to miniaturize them to reduce weight, it is not realistic to reduce their size to, say, one-third of their original size. Furthermore, as sliding components are made smaller, the load pressure applied to the sliding surfaces increases, making it difficult to maintain an oil film even when lubricants are applied. As the sliding surfaces begin to come into direct contact with each other, the coefficient of friction increases and they become more susceptible to wear.

[0003] Therefore, the use of aluminum alloys instead of iron-based alloys has attracted attention. Aluminum alloys have a very small specific gravity, about one-third that of iron-based alloys. Furthermore, aluminum alloy sliding components have the advantage of small inertia even when moving at high speeds.

[0004] However, aluminum alloys are softer and less hard than iron-based alloys. Furthermore, they are prone to adhesion due to frictional heat. Therefore, aluminum alloy sliding components are prone to adhesion and seizure over time on the sliding surfaces, resulting in severe wear.

[0005] Patent Document 1 discloses that a lubricating oil composition containing poly-α-olefin oil, polymethacrylate viscosity index improver, glycerin monooleate ashless friction modifier, and surface-unmodified nanodiamonds exhibits a friction-reducing effect on sliding members synthesized from SUJ2 heat-treated material. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-241443 Summary of the Invention [Problem to be solved by the invention]

[0007] However, when the lubricating oil composition described in Patent Document 1 was applied to an aluminum alloy sliding member, severe adhesion occurred on the sliding surface, and wear progressed. In other words, the lubricating oil composition did not provide an effect of suppressing wear of the aluminum alloy sliding member.

[0008] Therefore, an object of the present disclosure is to provide a lubricant that exhibits a wear suppressing effect on aluminum alloy sliding members. [Means for solving the problem]

[0009] As a result of intensive research to achieve the above object, the present inventors have found that adding nanodiamond particles with improved dispersibility by surface modification to a lubricant causes the nanodiamond particles to intervene on the sliding surface and reduce friction, and that even for sliding members made of materials with low hardness, softness, and susceptibility to adhesion, such as aluminum alloys, by applying a lubricant containing the nanodiamond particles, it is possible to suppress an increase in the coefficient of friction, suppress adhesion on the sliding surface, maintain surface uniformity, and thereby suppress wear of the sliding member. The present disclosure relates to a product completed based on these findings.

[0010] That is, the present disclosure includes nanodiamond particles (A), a fatty acid ester-based dispersant (B), and an oil agent (C), The nanodiamond particles (A) are represented by the following formulas (a-1) to (a-4): [ka] (In the formula, R 1 represents a hydrogen atom or a hydrocarbon group, and R 2 ~R 7 Each independently represents a hydrocarbon group. The bond marked with a wavy line in the formula is bonded to the nanodiamond particle. The present invention provides a lubricant for aluminum alloy sliding members, which is comprised of nanodiamond particles having at least one surface modifying group selected from the group consisting of:

[0011] The present disclosure also provides the lubricant for aluminum alloy sliding members, wherein the content of the nanodiamond particles (A) is more than 0.01 mass % and not more than 5 mass % of the total amount of the lubricant.

[0012] The present disclosure also provides a lubricant for aluminum alloy sliding members, wherein the content of the fatty acid ester-based dispersant (B) is 0.5 to 10 times by mass the content of the nanodiamond particles (A).

[0013] The present disclosure also provides a lubricant for aluminum alloy sliding members, wherein the total content of the nanodiamond particles (A), the fatty acid ester-based dispersant (B), and the oil (C) is 80 mass% or more of the total amount of the lubricant.

[0014] The present disclosure also provides the lubricant for an aluminum alloy sliding member, wherein the oil agent (C) is at least one compound selected from poly-α-olefins, polyol esters, and alkylbenzenes.

[0015] The present disclosure also provides the lubricant for aluminum alloy sliding members, wherein the fatty acid ester-based dispersant (B) is a mono- or polyglycerin fatty acid ester. [Effects of the Invention]

[0016] Use of the lubricant of the present disclosure can suppress an increase in the coefficient of friction of the sliding surface of an aluminum alloy sliding member, suppress the occurrence of adhesive wear and abrasive wear on the sliding surface of the aluminum alloy sliding member, and maintain the surface uniformity of the sliding surface, thereby improving the mechanical life of the aluminum alloy sliding member. The use of the lubricant eliminates the disadvantages of aluminum alloys, such as low hardness, softness, and tendency to adhere, and, thanks to the aluminum alloys' properties of being light and easy to handle, can provide energy-saving effects and reduce environmental impact. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a diagram illustrating a method for calculating the amount of ball wear in a ball-on-disk test. [Figure 2] FIG. 1 is a graph showing the results of measuring the coefficient of friction of an aluminum alloy (A5052) when the lubricant of Example 1 was used. [Figure 3] FIG. 10 is a graph showing the results of measuring the coefficient of friction of an aluminum alloy (A5052) when the lubricant of Example 2 was used. [Figure 4] FIG. 10 is a graph showing the results of measuring the coefficient of friction of an aluminum alloy (A5052) when the lubricant of Example 3 was used. [Figure 5] FIG. 10 is a graph showing the results of measuring the coefficient of friction of an aluminum alloy (A5052) when the lubricant of Example 4 was used. [Figure 6] FIG. 10 is a graph showing the results of measuring the coefficient of friction of an aluminum alloy (A5052) when the lubricant of Example 5 was used. [Figure 7] FIG. 10 is a graph showing the results of measuring the coefficient of friction of an aluminum alloy (A5052) when the lubricant of Example 6 was used. [Figure 8] FIG. 10 is a graph showing the results of measuring the coefficient of friction of an aluminum alloy (A5052) when the lubricant of Example 7 was used. [Figure 9] FIG. 10 is a graph showing the results of measuring the coefficient of friction of an aluminum alloy (A5052) when the lubricant of Example 8 was used. [Figure 10] FIG. 10 is a graph showing the results of measuring the coefficient of friction of an aluminum alloy (A5052) when the lubricant of Example 9 was used. [Figure 11]FIG. 10 is a graph showing the results of measuring the coefficient of friction of an aluminum alloy (A5052) when the lubricant of Example 10 was used. [Figure 12] FIG. 10 is a graph showing the results of measuring the coefficient of friction of an aluminum alloy (A5052) when the lubricant of Example 11 was used. [Figure 13] FIG. 10 is a graph showing the results of measuring the coefficient of friction of an aluminum alloy (A5052) when the lubricant of Example 12 was used. [Figure 14] FIG. 10 is a graph showing the results of measuring the coefficient of friction of an aluminum alloy (A5052) when the lubricant of Example 13 was used. [Figure 15] FIG. 1 is a graph showing the results of measuring the coefficient of friction of an aluminum alloy (A5052) when the lubricant of Comparative Example 1 was used. [Figure 16] FIG. 10 is a graph showing the results of measuring the coefficient of friction of an aluminum alloy (A5052) when the lubricant of Example 14 was used. [Figure 17] FIG. 10 is a graph showing the results of measuring the coefficient of friction of an aluminum alloy (A5052) when the lubricant of Example 15 was used. [Figure 18] FIG. 10 is a graph showing the results of measuring the coefficient of friction of an aluminum alloy (A5052) when the lubricant of Example 16 was used. [Figure 19] FIG. 10 is a graph showing the results of measuring the coefficient of friction of an aluminum alloy (A5052) when the lubricant of Comparative Example 2 was used. [Figure 20] FIG. 10 is a graph showing the results of measuring the coefficient of friction of aluminum alloy (A7075) at a sliding speed of 25 mm / s when the lubricant of Example 6 and the lubricant of Comparative Example 1 were used. [Figure 21] FIG. 10 is a graph showing the results of measuring the coefficient of friction of an aluminum alloy (A7075) at a sliding speed of 50 mm / s when the lubricant of Example 6 and the lubricant of Comparative Example 1 were used. [Figure 22] FIG. 10 is a graph showing the results of measuring the coefficient of friction of an aluminum alloy (A7075) at a sliding speed of 100 mm / s when the lubricant of Example 6 and the lubricant of Comparative Example 1 were used. [Figure 23]FIG. 10 is a graph showing the results of measuring the coefficient of friction of an aluminum alloy (A7075) at a sliding speed of 200 mm / s when the lubricant of Example 6 and the lubricant of Comparative Example 1 were used. [Figure 24] FIG. 10 is a graph showing the results of measuring the coefficient of friction of aluminum alloy (A2024) at a sliding speed of 25 mm / s when the lubricant of Example 6 and the lubricant of Comparative Example 1 were used. [Figure 25] FIG. 10 is a graph showing the results of measuring the coefficient of friction of aluminum alloy (A2024) at a sliding speed of 50 mm / s when the lubricant of Example 6 and the lubricant of Comparative Example 1 were used. [Figure 26] FIG. 10 is a graph showing the results of measuring the coefficient of friction of aluminum alloy (A2024) at a sliding speed of 100 mm / s when the lubricant of Example 6 and the lubricant of Comparative Example 1 were used. [Figure 27] FIG. 10 is a graph showing the results of measuring the coefficient of friction of aluminum alloy (A2024) at a sliding speed of 200 mm / s when the lubricant of Example 6 and the lubricant of Comparative Example 1 were used. [Figure 28] FIG. 1 is a graph showing the viscosity measurement results of the lubricants of Example 6, Example 14, Comparative Example 1, and Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0018] [Lubricant for aluminum alloy sliding parts] The lubricant for aluminum alloy sliding members (hereinafter sometimes referred to as "lubricant") of the present disclosure contains nanodiamond particles (A), a fatty acid ester-based dispersant (B), and an oil agent (C).

[0019] The aluminum alloy is an alloy obtained by adding at least one metal selected from magnesium, copper, zinc, manganese, silicon, nickel, etc. to aluminum, which is the main component. Examples of aluminum alloys include A5052 (Al-Mg type alloy), A2024 (Al-Cu-Mg type alloy), and A7075 (Al-Mg-Zn-Cu type alloy).

[0020] (Nanodiamond particles (A)) The nanodiamond particles (A) are surface-modified ND particles (hereinafter sometimes referred to as "ND particles") having at least one surface-modifying group selected from the following formulas (a-1) to (a-4) on the surface of the nanodiamond particles. [ka] (In the formula, R 1 represents a hydrogen atom or a hydrocarbon group, and R 2 ~R 7 Each independently represents a hydrocarbon group. The bond marked with a wavy line in the formula is bonded to the nanodiamond particle.

[0021] R 1 ~R 7 The hydrocarbon group in includes an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, an aromatic hydrocarbon group, and groups formed by combining these groups.

[0022] The aliphatic hydrocarbon group includes saturated or unsaturated aliphatic hydrocarbon groups. 1-20 An aliphatic hydrocarbon group (saturated or unsaturated aliphatic hydrocarbon group) is preferred. 1-20 Examples of saturated aliphatic hydrocarbon groups include linear or branched alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, s-butyl, t-butyl, pentyl, hexyl, n-octyl, 2-ethylhexyl, nonyl, isononyl, decyl, isodecyl, lauryl, myristyl, isomyristyl, butyloctyl, isocetyl, hexyldecyl, stearyl, isostearyl, octyldecyl, octyldodecyl, and isobehenyl. 1-20 Examples of unsaturated aliphatic hydrocarbon groups include linear or branched alkenyl groups such as vinyl, allyl, 1-butenyl, 7-octenyl, 8-nonenyl, 9-decenyl, 11-dodecenyl, and oleyl; and linear or branched alkynyl groups such as ethynyl, propynyl, decynyl, pentadecynyl, and octadecynyl.

[0023] As the aliphatic hydrocarbon group, from the viewpoint of improving the dispersibility of the nanodiamond particles (A) and improving the wear suppression effect of the aluminum alloy sliding member, C 5-20 Aliphatic hydrocarbon groups are particularly preferred, and C 10-20 Aliphatic hydrocarbon groups are most preferred, with C 15-20 Aliphatic hydrocarbon groups are particularly preferred.

[0024] Alicyclic hydrocarbon groups include C 3-20 Alicyclic hydrocarbon groups are preferred, and examples thereof include cycloalkyl groups having about 3 to 20 members (preferably 3 to 15 members, particularly preferably 5 to 8 members) such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, and cyclooctyl groups; cycloalkenyl groups having about 3 to 20 members (preferably 3 to 15 members, particularly preferably 5 to 8 members) such as cyclopentenyl and cyclohexenyl groups; perhydronaphthalen-1-yl groups, norbornyl groups, adamantyl groups, and tricyclo[5.2.1.0] groups. 2,6 ]decan-8-yl group, tetracyclo[4.4.0.1 2,5 .1 7,10 ] and bridged cyclic hydrocarbon groups such as dodecan-3-yl group.

[0025] The aromatic hydrocarbon group is C 6-14 (Especially C 6-10 Aromatic hydrocarbon groups are preferred, such as phenyl and naphthyl groups.

[0026] R 1 ~R 7 The hydrocarbon group in is preferably an aliphatic hydrocarbon group from the viewpoint of improving the dispersibility of the nanodiamond particles (A) and improving the wear suppression effect of the aluminum alloy sliding member.

[0027] As the surface modification group contained in the nanodiamond particles (A), from the viewpoint of excellent dispersibility and improving excellent wear-inhibiting effect at lower concentrations, the surface modification group represented by the formula (a-1) or (a-2) is preferred, and the surface modification group represented by the formula (a-1) is particularly preferred.

[0028] The average dispersed particle size (D50, median size) of the nanodiamond particles (A) in the lubricant is preferably 2 to 240 nm, more preferably 4 to 200 nm, more preferably 5 to 100 nm, even more preferably 10 to 70 nm, and particularly preferably 12 to 40 nm. The average dispersed particle size can be measured by dynamic light scattering.

[0029] The content of nanodiamond particles (A) in the total amount of lubricant is, for example, more than 0.01% by mass and 5% by mass or less, from the viewpoint of highly dispersing the nanodiamond particles (A) and improving the wear suppression effect of aluminum alloy sliding members. The content of nanodiamond particles (A) is also preferably 0.02 to 5% by mass, particularly preferably 0.05 to 5% by mass, and most preferably 0.1 to 5% by mass, from the viewpoint of suppressing adhesion. Furthermore, from the viewpoint of reducing the amplitude of friction force and suppressing an increase in the friction coefficient, the upper limit of the content of nanodiamond particles (A) is preferably 4% by mass, more preferably 3.5% by mass, more preferably 2% by mass, more preferably 1.5% by mass, even more preferably 1% by mass, particularly preferably 0.5% by mass, most preferably 0.4% by mass, and particularly preferably 0.3% by mass.

[0030] The nanodiamond particles (A) preferably contain primary nanodiamond particles. They may also contain secondary particles formed by the aggregation (adhesion) of multiple primary particles. The surface of the ND particles may also contain one or more types of other surface functional groups (e.g., amino groups, hydroxyl groups, carboxyl groups, etc.) in addition to the surface modification groups.

[0031] The ratio of the mass of the ND particle portion to the mass of the surface modification group portion of the nanodiamond particles (A) [ND particle portion / surface modification group portion] (mass ratio) is not particularly limited, but is preferably 0.5 or more, more preferably 2.5 or more. Furthermore, the mass ratio is preferably 15.0 or less, more preferably 10.0 or less, even more preferably 7.0 or less, and particularly preferably 5.0 or less. When the mass ratio is 0.5 or more, the properties of the nanodiamond material are less likely to be impaired. When the mass ratio is 15.0 or less (particularly 7.0 or less), the degree of modification of the surface modification group is sufficient, allowing for excellent dispersibility. The mass ratio is determined based on the mass loss rate from 200°C to 450°C measured by thermogravimetric analysis, with the lost mass being the mass of the surface modification group.

[0032] (Method for producing nanodiamond particles (A)) Nanodiamond particles (A) can be produced, for example, by subjecting ND particles obtained through the following production process, acid treatment process, oxidation treatment process, crushing treatment process, and drying treatment process to the following modification process.

[0033] (generation process) The formed explosive with an electric detonator attached is placed inside a pressure-resistant container for detonation, and the container is sealed in a state where atmospheric gas and the explosive coexist. The container is made of, for example, iron, and has a volume of, for example, 0.5 to 40 m 3 As the explosive, a mixture of trinitrotoluene (TNT) and cyclotrimethylenetrinitramine, i.e., hexogen (RDX), can be used. The mass ratio of TNT to RDX (TNT / RDX) is, for example, in the range of 40 / 60 to 60 / 40.

[0034] In the production process, an electric detonator is then detonated to detonate the explosive inside the container. Detonation refers to an explosion caused by a chemical reaction in which the flame front of the reaction moves at a speed exceeding the speed of sound. During detonation, the explosive used undergoes partial incomplete combustion, liberating carbon as raw material, and ND particles are generated by the action of the pressure and energy of the shock wave generated by the explosion. The generated ND particles aggregate very firmly between adjacent primary particles or crystallites due to the action of van der Waals forces and the Coulomb interaction between crystal planes, forming an aggregate.

[0035] In the production step, the container is then left to cool at room temperature for about 24 hours, and the temperature of the container and its interior is lowered. After this cooling, the ND particle crude product (including the aggregates of ND particles and soot produced as described above) adhering to the inner wall of the container is collected.

[0036] (Acid treatment process) The nanodiamond crude product obtained by the detonation method contains oxides of metals such as Fe, Co, and Ni that originate from the container used in the detonation method. In the acid treatment step, a strong acid is applied to the ND particle crude product in an aqueous solvent to remove the metal oxides. Examples of the strong acid include hydrochloric acid, hydrofluoric acid, sulfuric acid, nitric acid, and aqua regia. The acid treatment temperature is, for example, 70 to 150°C. The acid treatment time is, for example, 0.1 to 24 hours. After the acid treatment, it is preferable to wash the solid content (including nanodiamond aggregates) with water, for example, by decantation.

[0037] (Oxidation treatment process) The crude ND particle product obtained by the detonation method contains graphite, which is derived from the carbon liberated by the partial incomplete combustion of the explosive used and which did not form ND particle crystals. The oxidation treatment process is a process in which graphite is removed from the crude ND particle product using an oxidizing agent. In addition, the action of an oxidizing agent can introduce functional groups such as carboxyl groups and hydroxyl groups onto the ND particle surface.

[0038] As the oxidizing agent, a mixed acid of sulfuric acid and nitric acid is preferably used, and the mixing ratio of sulfuric acid to nitric acid in the mixed acid (former / latter; mass ratio) is, for example, 60 / 40 to 95 / 5.

[0039] The amount of the oxidizing agent used is, for example, 10 to 50 parts by mass per part by mass of the ND particle crude product.

[0040] When the mixed acid is used as an oxidizing agent, a catalyst may be used together with the mixed acid. The use of a catalyst can further improve the efficiency of graphite removal. Examples of the catalyst include copper (II) carbonate. The amount of catalyst used is, for example, about 0.01 to 10 parts by mass per 100 parts by mass of the crude nanodiamond product.

[0041] The oxidation treatment temperature is, for example, 100 to 200° C. The oxidation treatment time is, for example, 1 to 24 hours.

[0042] After the oxidation treatment step, it is preferable to remove the supernatant liquid by, for example, decantation. During the decantation, it is also preferable to wash the solid content with water.

[0043] (Crushing process) The ND particles may be subjected to a crushing treatment as necessary. For the crushing treatment, for example, a high-shear mixer, a high-shear mixer, a homomixer, a ball mill, a bead mill, a high-pressure homogenizer, an ultrasonic homogenizer, a colloid mill, or the like can be used. The crushing treatment may be carried out wet (for example, crushing treatment in a state of being suspended in water, etc.) or dry. When carried out dry, it is preferable to provide a drying step before the crushing treatment.

[0044] (drying process) Examples of methods for drying ND particles include evaporating the liquid using a spray dryer or an evaporator, and then heating and drying the remaining solid using a drying oven, etc. The heating and drying temperature is, for example, 40 to 150°C.

[0045] (modification process) This is a process for producing nanodiamond particles (A) by reacting (modifying) the surface functional groups (for example, hydroxyl groups, carboxyl groups, etc.) of ND particles with a surface treatment compound.

[0046] The surface treatment compound can be selected depending on the surface modification group to be imparted to the ND particles. For example, when producing ND particles having a surface modification group represented by the formula (a-1), a surface treatment compound represented by the following formula (b-1) is used. When producing ND particles having a surface modification group represented by the formula (a-2), a surface treatment compound represented by the formula (b-2) is used. When producing ND particles having a surface modification group represented by the formula (a-3), a surface treatment compound represented by the following formula (b-3) is used. When producing ND particles having a surface modification group represented by the formula (a-4), a surface treatment compound represented by the following formula (b-4) is used. [ka]

[0047] In the formula, R 1 ~R 7 is the same as above. R 8 represents a hydrogen atom or a hydrocarbon group. The hydrocarbon group includes R 1 ~R 7 Examples of the hydrocarbon group are the same as those in the above.

[0048] The mass ratio (former / latter) of the ND particles to be subjected to the modification reaction to the surface treatment compound is, for example, 1 / 1 to 1 / 25.

[0049] The reaction between the ND particles and the surface treatment compound can be appropriately changed depending on the type of the surface treatment compound.

[0050] For example, when using the surface treatment compound represented by the formula (b-1), it is preferable to react the ND particles with the surface treatment compound in a nano-dispersed state in water. The reaction may be carried out in the presence of an acid catalyst.

[0051] Examples of the acid catalyst include inorganic solid acids, sulfonic acid group-containing compounds, hydrochloric acid, nitric acid, sulfuric acid, sulfuric anhydride, phosphoric acid, boric acid, trihaloacetic acids (trichloroacetic acid, trifluoroacetic acid, etc.), and salts thereof (ammonium salts, etc.), which can be used alone or in combination of two or more.

[0052] As the acid catalyst, a sulfonic acid group-containing compound or an ammonium salt of a sulfonic acid group-containing compound is preferred because of its excellent reaction-accelerating effect.

[0053] Examples of the sulfonic acid group-containing compound include aliphatic sulfonic acids such as methanesulfonic acid, ethanesulfonic acid, propanesulfonic acid, butanesulfonic acid, dodecanesulfonic acid, hexadecanesulfonic acid, trifluoromethanesulfonic acid, and heptadecafluorooctanesulfonic acid; alicyclic sulfonic acids such as 10-camphorsulfonic acid; benzenesulfonic acid, p-toluenesulfonic acid, 2,4,6-trimethylbenzenesulfonic acid, and hexylbenzenesulfonic acid. aromatic sulfonic acids such as octylbenzenesulfonic acid, decylbenzenesulfonic acid, dodecylbenzenesulfonic acid, octadecylbenzenesulfonic acid, 1-naphthalenesulfonic acid, 2-naphthalenesulfonic acid, and butyl-2-naphthalenesulfonic acid; sulfonic acid-type ion exchange resins, 3-[trioctylammonio]propane-1-sulfonic acid-triflimide, and 4-[trioctylammonio]butane-1-sulfonic acid-triflimide.

[0054] The reaction conditions can be appropriately selected within the ranges of, for example, a temperature of 50 to 100° C., a reaction time of 1 to 48 hours, and a pressure of 1 to 5 atm.

[0055] After the reaction is completed, the reaction product obtained may be separated and purified by common methods such as extraction, precipitation, washing, and filtration.

[0056] By the above method, ND particles having a surface modifying group represented by the above formula (a-1) can be obtained.

[0057] For example, when a surface treatment compound represented by the formula (b-2) is used, it is preferable to react the powdered ND particles with the surface treatment compound in the presence of an organic solvent.

[0058] Examples of the organic solvent include aromatic compounds such as toluene and xylene, alkanes such as hexane, ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone, ethers such as dioxane and tetrahydrofuran, alcohols such as n-propanol, isopropanol, hexanol and cyclohexanol, esters such as ethyl acetate and polyol esters, halogenated hydrocarbons such as chloroform, methylene chloride and ethylene dichloride, etc. These can be used alone or in combination of two or more.

[0059] The reaction conditions can be appropriately selected within the ranges of, for example, a temperature of 0 to 30° C., a reaction time of 1 to 48 hours, and a pressure of 1 to 5 atm.

[0060] The reaction may be carried out while crushing or dispersing the ND particles, preferably by ultrasonic treatment in the presence of crushing media (such as zirconia beads).

[0061] The diameter of the crushing media (for example, zirconia beads) is, for example, 15 to 500 μm, preferably 15 to 300 μm, and particularly preferably 15 to 100 μm.

[0062] After the reaction is completed, the reaction product obtained may be separated and purified by common methods such as extraction, precipitation, washing, and filtration.

[0063] By the above method, ND particles having a surface modifying group represented by the above formula (a-2) can be obtained.

[0064] (Fatty acid ester dispersant (B)) The fatty acid ester dispersant (B) is a compound that has the property of improving the dispersibility of the nanodiamond particles (A) in the lubricant. In addition, the fatty acid ester dispersant (B) is a compound that has excellent heat resistance and is resistant to thermal decomposition.

[0065] The lubricant contains a fatty acid ester-based dispersant (B) having the above-mentioned properties together with nanodiamond particles (A), and therefore can suppress the aggregation of nanodiamond particles (A) even under high temperature conditions, thereby exhibiting excellent wear-inhibiting effects.

[0066] The molecular weight of the fatty acid ester dispersant (B) is, for example, 100 to 500, preferably 200 to 400, and particularly preferably 300 to 400, from the viewpoint of obtaining a good wear-inhibiting effect.

[0067] Examples of the fatty acid ester dispersant (B) include esters of polyhydric alcohols and fatty acids, including monoesters, diesters, and triesters.

[0068] Examples of the polyhydric alcohol include aliphatic polyhydric alcohols such as glycerin, polyglycerin, pentaerythritol, ethylene glycol, diethylene glycol, polyethylene glycol, and propylene glycol; and sugar alcohols such as glucose, lactose, maltose, fructose, sorbitol, maltitol, mannitol, xylitol, and trehalose.

[0069] Examples of fatty acids include carboxylic acids and sulfonic acids.

[0070] Examples of the carboxylic acid include aliphatic monocarboxylic acids such as acetic acid, propionic acid, caprylic acid, nonanoic acid, capric acid, octylic acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, isononanoic acid, and arachic acid; and aromatic monocarboxylic acids such as benzoic acid and p-(t-butylbutyl)benzoic acid. Of these, carboxylic acids having 6 or more carbon atoms (for example, 6 to 20 carbon atoms) are preferred.

[0071] The sulfonic acid may, for example, be naphthalenesulfonic acid.

[0072] Examples of glycerin carboxylic acid esters include glycerin monofatty acid esters such as glycerin monopalmitate, glycerin monostearate, glycerin monooleate, glycerin monolinoleate, glycerin monobehenate, and glycerin monolaurate; glycerin difatty acid esters such as glycerin dipalmitate, glycerin distearate, glycerin dioleate, glycerin dilinoleate, and glycerin dibehenate; and glycerin trifatty acid esters such as glycerin tristearate and glycerin trioleate. Of these, glycerin monocarboxylic acid esters are preferred, and glycerin monooleate is most preferred.

[0073] Examples of polyglycerol carboxylic acid esters include polyglycerol monofatty acid esters such as polyglycerol monopalmitate, polyglycerol monostearate, polyglycerol monooleate, polyglycerol monolinoleate, polyglycerol monobehenate, and polyglycerol monolaurate; polyglycerol difatty acid esters such as polyglycerol dipalmitate, polyglycerol distearate, polyglycerol dioleate, polyglycerol dilinoleate, and polyglycerol dibehenate; and polyglycerol trifatty acid esters such as polyglycerol tristearate and polyglycerol trioleate. Among these, polyglycerol monocarboxylic acid esters are preferred, and polyglycerol monooleate is most preferred.

[0074] Examples of sorbitan fatty acid esters include sorbitan laurate, sorbitan palmitate, sorbitan stearate, sorbitan tristearate, sorbitan oleate, sorbitan trioleate, sorbitan behenate, and sorbitan tribehenate.

[0075] Examples of polyglycerol fatty acid esters include diglycerol laurate, diglycerol stearate, diglycerol oleate, diglycerol caprylate, tetraglycerol laurate, tetraglycerol oleate, hexaglycerol oleate, hexaglycerol laurate, decaglycerol laurate, and decaglycerol stearate.

[0076] Examples of propylene glycol fatty acid esters include propylene glycol monolaurate, propylene glycol monopalmitate, propylene glycol monostearate, and propylene glycol monooleate.

[0077] Examples of higher alcohol fatty acid esters include stearyl stearate.

[0078] The fatty acid ester-based dispersant (B) is preferably an ester of an aliphatic polyhydric alcohol and a fatty acid, more preferably a glycerin fatty acid ester or a polyglycerin fatty acid ester, particularly preferably a glycerin fatty acid ester, most preferably a glycerin carboxylic acid ester, and particularly preferably a glycerin carboxylic acid monoester.

[0079] The content of the fatty acid ester-based dispersant (B) in the lubricant is, for example, 0.5 to 10 times by mass (i.e., 0.5 to 10 times by mass) the content of the nanodiamond particles (A), and can be changed appropriately depending on the type of surface modification group of the nanodiamond particles (A). For example, in the case of a lubricant containing ND particles having a surface modification group represented by formula (a-1), the content of the fatty acid ester-based dispersant (B) is 0.5 to 10 times by mass the content of the nanodiamond particles (A), and from the viewpoint of reducing the amplitude of the friction force and suppressing an increase in the friction coefficient, it is preferably 0.5 to 8 times by mass, particularly preferably 0.5 to 5 times by mass, and most preferably 0.5 to 3 times by mass. In the case of a lubricant containing ND particles having a surface modification group represented by formula (a-2), the content of the fatty acid ester-based dispersant (B) is 0.5 to 10 times by mass the content of the nanodiamond particles (A), and from the viewpoint of reducing the amplitude of the friction force and suppressing an increase in the friction coefficient, it is 1 to 10 times by mass, particularly preferably 3 to 10 times by mass, and most preferably 5 to 10 times by mass.

[0080] (Oil (C)) The oil (C) is a dispersion medium for the nanodiamond particles (A) and the fatty acid ester-based dispersant (B). When applied to the contact area of ​​an aluminum alloy sliding component, it forms an oil film, preventing contact between solids and reducing friction and wear.

[0081] Examples of the oil (C) include poly-α-olefins, polyol esters, alkylbenzenes, etc. These can be used alone or in combination of two or more.

[0082] The poly-α-olefin is an oligomer or polymer of an α-olefin or an isomerized α-olefin. The poly-α-olefin may be used singly or in combination of two or more kinds.

[0083] When the poly-α-olefin is an oligomer or polymer obtained by polymerizing two or more different α-olefins, the polymerization method is not particularly limited, and the poly-α-olefin may be any of a block copolymer, a graft copolymer, and a random copolymer.

[0084] Examples of the α-olefins include α-olefins having 8 to 20 carbon atoms, such as 1-octene, 1-nonene, 1-decene, 1-dodecene, 1-tridecene, 1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-nonadecene, 1-eicosene, and 1-docosene. Of these, α-olefins having 10 to 15 carbon atoms are preferred, and α-olefins having 10 to 12 carbon atoms are particularly preferred.

[0085] The polyol ester is an ester of an alcohol and a fatty acid, and one type of polyol ester can be used alone, or two or more types can be used in combination.

[0086] The alcohol is preferably a hindered alcohol such as neopentyl glycol, trimethylolethane, trimethylolpropane, trimethylolbutane, di-(trimethylolpropane), tri-(trimethylolpropane), pentaerythritol, di-(pentaerythritol), or tri-(pentaerythritol).

[0087] The fatty acid is preferably a fatty acid having 4 to 20 carbon atoms, such as isobutyric acid, n-pentanoic acid, n-hexanoic acid, n-heptanoic acid, n-octanoic acid, n-nonanoic acid, isononanoic acid, n-decanoic acid, oleic acid, or 2-methylhexanoic acid.

[0088] Examples of polyol esters include trimethylolpropane caprylate, trimethylolpropane pelargonate, pentaerythritol 2-ethylhexanoate, and pentaerythritol pelargonate.

[0089] Alkylbenzene is a compound in which an alkyl group is bonded to a benzene ring. The number of alkyl groups bonded to the benzene ring is, for example, 1 to 4, and from the viewpoint of excellent stability, it is preferably 1 or 2. That is, the alkylbenzene is preferably a monoalkylbenzene or a dialkylbenzene.

[0090] The alkyl group preferably has a carbon number of 1 to 40. The alkyl group includes linear alkyl groups and branched alkyl groups.

[0091] As the oil (C), from the viewpoints of improving the wear suppression effect of aluminum alloy sliding members, reducing the amplitude of friction force, and suppressing an increase in the coefficient of friction, poly-α-olefins and / or polyol esters are preferred, and poly-α-olefins are particularly preferred.

[0092] The content of the oil (C) in the total amount of the lubricant is, for example, 90 to 99.9 mass% of the total amount of the lubricant. From the viewpoint of improving the wear suppression effect of the aluminum alloy sliding member, the upper limit of the oil (C) content is preferably 99.8 mass%, particularly preferably 99.5 mass%, most preferably 99 mass%, and especially preferably 98.5 mass%. From the viewpoint of reducing the amplitude of the friction force and suppressing an increase in the friction coefficient, the lower limit of the oil (C) content is preferably 93 mass%, more preferably 95 mass%, particularly preferably 96 mass%, most preferably 97 mass%, and especially preferably 98 mass%.

[0093] The content of the oil agent (C) in the total amount of the lubricant is preferably such that the content of the nanodiamond particles (A) falls within the following range. From the viewpoint of highly dispersing the nanodiamond particles (A) and improving the wear suppression effect of aluminum alloy sliding components, it is preferable that the content of the nanodiamond particles (A) relative to the total content of the oil agent (C) and the nanodiamond particles (A) is, for example, in the range of more than 0.01 mass% and not more than 5 mass%. In addition, from the viewpoint of suppressing adhesion of the nanodiamond particles (A), the content of the nanodiamond particles (A) relative to the total content of the oil agent (C) and the nanodiamond particles (A) is preferably 0.02 to 5 mass%, particularly preferably 0.05 to 5 mass%, and most preferably 0.1 to 5 mass%. Furthermore, from the viewpoint of reducing the amplitude of the friction force and suppressing an increase in the coefficient of friction, the upper limit of the content of nanodiamond particles (A) relative to the total content of oil agent (C) and nanodiamond particles (A) is preferably 4 mass%, more preferably 3.5 mass%, more preferably 2 mass%, even more preferably 1.5 mass%, even more preferably 1 mass%, particularly preferably 0.5 mass%, most preferably 0.4 mass%, and especially preferably 0.3 mass%.

[0094] The lubricant has a total content of nanodiamond particles (A), fatty acid ester-based dispersant (B), and oil (C) of, for example, 80 mass% or more (e.g., 80 to 100 mass%), preferably 90 mass% or more, and particularly preferably 95 mass% or more of the total amount of the lubricant.

[0095] (Other (D)) The lubricant may contain an organic solvent (excluding compounds corresponding to oil agent (C)), such as the solvent used in the modification reaction of the ND particles, but the content of the organic solvent is, for example, 10 ppm or less, preferably 5 ppm or less, and particularly preferably 2 ppm or less, of the total amount of the lubricant.

[0096] The proportion of the oil (C) in the total amount of the dispersion medium contained in the lubricant is, for example, 50.0 mass% or more, preferably 60.0 mass% or more, more preferably 70.0 mass% or more, even more preferably 80.0 mass% or more, even more preferably 90.0 mass% or more, even more preferably 95.0 mass% or more, particularly preferably 97.0 mass%, most preferably 98.0 mass%, and particularly preferably 99.0 mass% or more. The upper limit of the proportion of the oil (C) is, for example, 99.9 mass%, preferably 99.8 mass%, and particularly preferably 99.5 mass%. The dispersion medium contained in the lubricant is a component that is liquid at room temperature and normal pressure.

[0097] The lubricant may further contain, as necessary, surfactants, thickeners, coupling agents, rust inhibitors, corrosion inhibitors, freezing point depressants, antifoaming agents, anti-wear additives, preservatives, colorants, etc. The content of these additives is, for example, 30% by mass or less, preferably 20% by mass or less, more preferably 10% by mass or less, even more preferably 5% by mass or less, still more preferably 1% by mass or less, and particularly preferably less than 1% by mass, of the total amount of the lubricant.

[0098] The viscosity of the lubricant at 25°C is preferably 100 mPa·s or less, particularly preferably 70 mPa·s or less, most preferably 50 mPa·s or less, and especially preferably 30 mPa·s, from the viewpoint of forming an oil film, preventing contact between solids at real contact points, and reducing friction and wear.Furthermore, the viscosity of the lubricant at 25°C is preferably 5 mPa·s or more, particularly preferably 10 mPa·s or more, most preferably 15 mPa·s or more, and especially preferably 20 mPa·s or more, from the viewpoint of suppressing oil running out at friction interfaces.

[0099] The viscosity of the lubricant at 100° C. is, for example, 10 mPa·s or less, and preferably 5 mPa·s or less.

[0100] The viscosity of the lubricant can be measured by the method described in the Examples.

[0101] The lubricant can suppress adhesion on the sliding surface of the aluminum alloy sliding member and maintain the surface uniformity of the sliding surface, thereby suppressing wear of the sliding surface. For example, when the hardness of the aluminum alloy is relatively low (such as A5052), adhesion is likely to occur on the sliding surfaces. However, the lubricant covers the sliding surfaces, reducing the frequency of contact between the aluminum alloys, or the presence of the lubricant weakens the adhesive force between the aluminum alloys, thereby preventing adhesion and suppressing adhesive wear (wear while adhering to the mating material). Furthermore, when the hardness of the aluminum alloy is relatively high (for example, in the case of A2024, A7075, etc.), the lubricant coats the sliding surfaces, reducing the frequency of contact between the aluminum alloy members, or the presence of the lubricant weakens the adhesive force between the aluminum alloy members, smoothing the sliding surfaces and forming low-friction surfaces (fitting surfaces). This makes it possible to reduce the size of wear debris (i.e., debris generated by wear), and thereby suppress abrasive wear caused by wear debris. Use of the lubricant can suppress wear and thereby improve the mechanical life of the aluminum alloy sliding member.

[0102] The lubricant can be suitably used as an antifriction agent to be applied to a sliding member made of an aluminum alloy, or as an initial running-in agent to be used to form a low-friction surface (run-in surface) in the initial stage of a machine having the sliding member.

[0103] The above-described configurations and combinations thereof of the present disclosure are merely examples and can be combined with any other features disclosed in this specification. Furthermore, additions, omissions, substitutions, and modifications of configurations are possible as appropriate without departing from the spirit of the present disclosure. Furthermore, the present disclosure is not limited by the embodiments, but is limited only by the claims. [Example]

[0104] Hereinafter, one embodiment of the present disclosure will be described in more detail based on examples.

[0105] Production Example 1 (Production of nanodiamond particles (A)) (generation process) In this process, the formed explosive with an electric detonator attached was first placed inside a pressure-resistant container for detonation, and the container was then sealed. The container was made of iron and had a volume of 15 m 3The explosive used was a mixture of 0.50 kg of TNT and RDX. The mass ratio of TNT to RDX in this explosive (TNT / RDX) was 50 / 50. Next, an electric detonator was detonated to detonate the explosive inside the container (production of nanodiamonds by detonation method). Next, the container and its interior were allowed to cool by leaving it at room temperature for 24 hours. After this cooling, the crude nanodiamond product (including the aggregates of nanodiamond particles and soot produced by the detonation method) adhering to the inner wall of the container was scraped off with a spatula, and the crude nanodiamond product was recovered.

[0106] (Acid treatment process) The crude nanodiamond product obtained by repeating the above-described production process multiple times was then subjected to an acid treatment process. Specifically, 200 g of the crude nanodiamond product was added to 6 L of 10% by mass hydrochloric acid to obtain a slurry, which was then heated under reflux at atmospheric pressure for 1 hour. The heating temperature in this acid treatment was 85 to 100°C. Next, after cooling, the solid matter (including nanodiamond aggregates and soot) was washed with water by decantation. The solid matter was repeatedly washed with water by decantation until the pH of the precipitated liquid reached 2 from the low pH side.

[0107] (Oxidation treatment process) Next, an oxidation treatment step was carried out. Specifically, 6 L of 98% by mass sulfuric acid and 1 L of 69% by mass nitric acid were added to the precipitate liquid (containing nanodiamond aggregates) obtained through decantation after the acid treatment to form a slurry, and this slurry was then heat-treated for 48 hours under reflux at atmospheric pressure. The heating temperature in this oxidation treatment was 140 to 160°C. Next, after cooling, the solid content (containing nanodiamond aggregates) was washed with water by decantation. The supernatant liquid was colored at the start of the washing, so the solid content was repeatedly washed with water by decantation until the supernatant liquid became visually transparent. The supernatant liquid was colored at the start of the washing, so the solid content was repeatedly washed with water by decantation until the supernatant liquid became visually transparent.

[0108] (Crushing process) After the washing, approximately 30 ml of the slurry was adjusted to pH 10 using aqueous ammonia, and then bead milling was carried out using a bead milling device (trade name "Parallel Four-Cylinder Sand Grinder LSG-4U-2L Type", manufactured by Aimex Co., Ltd.). Specifically, 30 ml of the ultrasonically irradiated slurry and 30 μm diameter zirconia beads were placed in a 100 ml mill vessel (manufactured by Aimex Co., Ltd.) and sealed, and the device was operated to carry out bead milling. In this bead milling, the amount of zirconia beads placed was, for example, 33% by volume relative to the volume of the mill vessel, the mill vessel rotation speed was 2570 rpm, and the milling time was 3 hours.

[0109] Next, the slurry that had undergone the above-mentioned disintegration process was centrifuged using a centrifugal separator (classification operation). The centrifugal force in this centrifugation process was 20,000 × g, and the centrifugation time was 30 minutes. Next, 10 ml of the supernatant of the ND-containing solution that had undergone the centrifugal separation process was collected. In this way, an ND aqueous dispersion in which nanodiamonds were dispersed in pure water was obtained. The solid content of this ND aqueous dispersion was 6.0 mass % and the pH was 9.0. The median diameter (particle size D50) of the ND aqueous dispersion obtained as described above was 6.0 nm.

[0110] (modification process) Next, 1.5 mmol of dodecylbenzenesulfonic acid as an acid catalyst and 3 mmol of oleylamine were added to 3.33 g of the ND aqueous dispersion obtained through the above-mentioned disintegration step, and the mixture was reacted for 8 hours with stirring at 80°C. After the reaction was completed, 10 g of toluene was added, and the mixture was cooled to room temperature, followed by washing with water and saturated saline to obtain a toluene dispersion of ND particles (ND-C18B) surface-modified with oleylamino groups.

[0111] Production Example 2 (Production of nanodiamond particles (A)) The production step, acid treatment step, and oxidation treatment step were carried out in the same manner as in Production Example 1.

[0112] (drying process) 1000 mL of the washed slurry obtained through the oxidation treatment process was spray-dried using a spray dryer (trade name "Spray Dryer B-290", manufactured by Nippon Buchi Co., Ltd.) (drying process), thereby obtaining 50 g of nanodiamond powder.

[0113] (modification process) 0.3 g of the obtained nanodiamond particles was weighed into a reaction vessel, and 13.5 g of toluene and 1.2 g of hexadecyltrimethoxysilane as a silane compound were added, followed by stirring for 10 minutes.

[0114] After stirring, 36 g of zirconia beads (Tosoh Corporation, registered trademark "YTZ," diameter 30 μm) were added. After the addition, the mixture was cooled in ice water and sonicated for 20 hours using an ultrasonic disperser (model "UP-400s," Hielscher) with the tip of the ultrasonic disperser's transducer immersed in the solution in the reaction vessel. This allowed the ND particles and the silane compound to react with each other. Initially, the mixture was gray, but the particle size gradually decreased and the dispersion improved, eventually becoming a uniform, black liquid. This is thought to be due to the ND particles gradually being disintegrated (disintegrated) from the ND particle aggregates, the silane compound acting on the dissociated ND particles to bond them, and the ND particles surface-modified by the silane compound becoming dispersed and stabilized in toluene. In this way, a toluene dispersion of ND particles surface-modified with a silane compound (ND-Si-C16) was obtained.

[0115] Example 1 (Production of Lubricant) 60.2 g of the toluene dispersion of surface-modified ND particles (ND-C18B) obtained in Production Example 1 (containing 1 g of the ND particles) was mixed with 0.5 g of GMO, and the toluene was removed using a rotary evaporator. PAO4 was then added to bring the total mass to 25 g. This resulted in Lubricant 1. The ND particle concentration in Lubricant 1 was 4.0 mass%. The nanodiamond particle (A) concentration was determined from the absorbance at 350 nm.

[0116] Examples 2 to 8 (Production of Lubricants) Lubricants obtained in the same manner as in Example 1 were diluted with PAO4 so that the concentrations of surface-modified ND particles (ND-C18B) were as shown in the table below, thereby obtaining lubricants 2 to 8.

[0117] Example 9 (Production of Lubricant) A lubricant was obtained in the same manner as in Example 1, except that the amount of GMO used was changed to 1.0 g, and then the obtained lubricant was diluted with PAO4 so that the concentration of surface-modified ND particles (ND-C18B) became 0.1 mass %. Lubricant 9 was thus obtained.

[0118] Example 10 (Production of Lubricant) A lubricant was obtained in the same manner as in Example 1, except that the amount of GMO used was changed to 5.0 g, and then the obtained lubricant was diluted with PAO4 so that the concentration of surface-modified ND particles (ND-C18B) became 0.1 mass %. Lubricant 10 was thus obtained.

[0119] Example 11 (Production of Lubricant) A lubricant was obtained in the same manner as in Example 1, except that the amount of GMO used was changed to 10.0 g, and then the obtained lubricant was diluted with PAO4 so that the concentration of surface-modified ND particles (ND-C18B) was 0.1 mass %. Lubricant 11 was thus obtained.

[0120] Example 12 (Production of Lubricant) A lubricant was obtained in the same manner as in Example 1, except that 50.0 g of a toluene dispersion of surface-modified ND particles (ND-Si-C16) obtained in Production Example 2 (containing 1 g of the ND particles) was used instead of the toluene dispersion of surface-modified ND particles (ND-C18B) obtained in Production Example 1, and the amount of GMO used was changed to 5.0 g. The obtained lubricant was then diluted with PAO4 so that the ND particle concentration was 0.1 mass %. Lubricant 12 was thereby obtained.

[0121] Example 13 (Production of Lubricant) A lubricant was obtained in the same manner as in Example 12, except that the amount of GMO used was changed to 10.0 g, and then the obtained lubricant was diluted with PAO4 so that the concentration of ND particles (ND-Si-C16) was 0.1 mass %. Lubricant 13 was thus obtained.

[0122] Comparative Example 1 (Production of Lubricant) Only PAO4 was used.

[0123] Example 14 (Production of Lubricant) 6.0 g of the toluene dispersion of the surface-modified ND particles (ND-C18B) obtained in Production Example 1 (containing 0.1 g of the ND particles) was mixed with 0.1 g of AJP-PN411, and after the toluene was distilled off using a rotary evaporator, POE was added to bring the total mass to 100 g. This yielded lubricant 14. The ND particle concentration in lubricant 14 was 0.1 mass%.

[0124] Examples 15 and 16 (Production of lubricant) Lubricants 15 and 16 were obtained by diluting a lubricant obtained in the same manner as in Example 14 with POE so that the concentration of surface-modified ND particles (ND-C18B) was as shown in the table below.

[0125] Comparative Example 2 (Production of Lubricant) Only POE was used.

[0126] For the lubricants obtained in the examples and comparative examples, the wear amount and friction coefficient of the aluminum alloy were determined by the following methods, and the wear suppression effect was evaluated.

[0127] <Wear volume measurement of aluminum alloy> A ball-on-disk test was conducted under the following conditions using an aluminum 5052 disk with 0.1 g of lubricant evenly applied and an aluminum 5052 ball (a polished ball with a radius of 8 mm) under room temperature and atmospheric pressure, and the wear volume (WV) was calculated using the following formula (1). The results are shown in the table below. Aluminum 5052 is an Al-Mg alloy.

[0128] Ball-on-disk test conditions Vertical load: 10N Sliding speed: 100mm / s Slide distance: 150m

[0129]

number

[0130] <Measurement of the friction coefficient of aluminum alloy 1> A ball-on-disk test was carried out under the same conditions as for measuring the wear volume of the aluminum alloy, and the change in the friction coefficient with the change in sliding distance was observed. The results are shown in Figures 2 to 19.

[0131] <Measurement of the friction coefficient of aluminum alloys 2> The same procedure as in Measurement of the Friction Coefficient of Aluminum Alloy 1 was repeated, except that an aluminum 7075 disk was used instead of the aluminum 5052 disk, an aluminum 7075 ball (a polished ball with a radius of 8 mm) was used instead of the aluminum 5052 ball (a polished ball with a radius of 8 mm), and the sliding speed was changed to 25 mm / s, 50 mm / s, 100 mm / s, or 200 mm / s. The aluminum 7075 is an Al-Mg-Zn-Cu alloy (hardness: 190 HV). The results of Example 6 and Comparative Example 1 are shown in Figures 20 to 23.

[0132] <Measurement of the friction coefficient of aluminum alloys 3> The same procedure as in Measurement of the Friction Coefficient of Aluminum Alloy 1 was repeated, except that an aluminum 2024 disc was used instead of the aluminum 5052 disc, an aluminum 2024 ball (a polished ball with a radius of 8 mm) was used instead of the aluminum 5052 ball (a polished ball with a radius of 8 mm), and the sliding speed was changed to 25 mm / s, 50 mm / s, 100 mm / s, or 200 mm / s. Aluminum 2024 is an Al-Cu-Mg alloy. The results of Example 6 and Comparative Example 1 are shown in Figures 24 to 27.

[0133] <d50> The average dispersed particle size of nanodiamond particles (A) in the lubricant was measured by dynamic light scattering (non-contact backscattering method) using a Malvern device (trade name "Zetasizer Nano ZS"). The results are shown in the following table.

[0134] <Viscosity> The viscosity of the lubricant was measured using an EMS viscometer (product name "EMS1000", manufactured by Kyoto Electronics Manufacturing Co., Ltd.) by placing 500 μL of sample and a φ2 mm aluminum ball in a test tube and varying the temperature from 25°C to 120°C at a motor rotation speed of 1000 rpm. The results are shown in Figure 28.

[0135] [Table 1]

[0136] [Table 2]

[0137] The components used in the examples and comparative examples are explained below. <Nanodiamond particles (A)> ND-C18B: ND particles obtained in Production Example 1, surface-modified with oleylamino groups. ND-Si-C16: ND particles obtained in Production Example 2, the surface of which was modified with a silane compound. <Fatty acid ester dispersant (B)> GMO: Glycerin monooleate, molecular weight: 356.5, product name "Leodor MO60", manufactured by Kao Corporation AJP-PN411: Higher fatty acid ester, molecular weight: 9270, manufactured by Ajinomoto Fine-Techno Co., Ltd. <Oil (C)> PAO4: Hydrogenated polydecene, product name "Synfluid PAO4 cSt", manufactured by Matsuwa Sangyo Co., Ltd. POE: Polyol ester, product name "Barrel Process Oil E-32", manufactured by Matsumura Oil Co., Ltd.

[0138] Variations of the invention according to the present disclosure are described below. [1] Nanodiamond particles (A), a fatty acid ester-based dispersant (B), and an oil agent (C), A lubricant for aluminum alloy sliding members, wherein the nanodiamond particles (A) are nanodiamond particles having at least one surface modifying group selected from the formulae (a-1) to (a-4). [2] The lubricant for aluminum alloy sliding members according to [1], wherein the content of the nanodiamond particles (A) is more than 0.01 mass% and not more than 5 mass% of the total amount of the lubricant. [3] The lubricant for aluminum alloy sliding members according to [1] or [2], wherein the content of the fatty acid ester-based dispersant (B) is 0.5 times or more and 10 times or less by mass of the content of the nanodiamond particles (A). [4] A lubricant for aluminum alloy sliding members according to any one of [1] to [3], wherein the total content of the nanodiamond particles (A), the fatty acid ester-based dispersant (B), and the oil (C) is 80 mass% or more of the total amount of the lubricant. [5] The lubricant for aluminum alloy sliding members according to any one of [1] to [4], wherein the oil agent (C) is at least one compound selected from poly-α-olefins, polyol esters, and alkylbenzenes. [6] The lubricant for aluminum alloy sliding members according to any one of [1] to [5], wherein the fatty acid ester-based dispersant (B) is a mono- or polyglycerin fatty acid ester.

Claims

1. The composition comprises nanodiamond particles (A), a fatty acid ester-based dispersant (B), and an oil agent (C), The nanodiamond particles (A) are represented by the following formulas (a-1) to (a-4): 【Chemistry 1】 (In the formula, R 1 represents a hydrogen atom or a hydrocarbon group, and R 2 ~R 7 Each independently represents a hydrocarbon group. The bond marked with a wavy line in the formula is bonded to the nanodiamond particle. A lubricant for an aluminum alloy sliding member, which is nanodiamond particles having at least one surface modifying group selected from the group consisting of:

2. 2. The lubricant for aluminum alloy sliding members according to claim 1, wherein the content of the nanodiamond particles (A) is more than 0.01 mass% and not more than 5 mass% of the total amount of the lubricant.

3. 3. The lubricant for aluminum alloy sliding members according to claim 1 or 2, wherein the content of the fatty acid ester-based dispersant (B) is 0.5 to 10 times by mass the content of the nanodiamond particles (A).

4. 3. The lubricant for aluminum alloy sliding members according to claim 1, wherein the total content of the nanodiamond particles (A), the fatty acid ester-based dispersant (B), and the oil (C) is 80 mass% or more of the total amount of the lubricant.

5. 3. The lubricant for aluminum alloy sliding members according to claim 1, wherein the oil agent (C) is at least one compound selected from the group consisting of poly-α-olefins, polyol esters, and alkylbenzenes.

6. 3. The lubricant for aluminum alloy sliding members according to claim 1, wherein the fatty acid ester-based dispersant (B) is a mono- or polyglycerin fatty acid ester.

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