Lubricant composition and production method of lubricant composition

Abstract

To provide a lubricant composition that has excellent friction and wear characteristics even in a vacuum environment.SOLUTION: A lubricant composition comprises: an alkyl-cyclopentane oil; and a poly(meth)acrylate copolymer (X). The poly(meth)acrylate copolymer (X) contains the poly(meth)acrylate copolymer (X) comprising: a structural unit (a) derived from a specific alkyl(meth)acrylate (A); a structural unit (b) derived from a specific hydroxyl group-containing (meth)acrylate (B); and a structural unit (c) derived from a specific phosphorus-containing (meth)acrylate (C).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a lubricating oil composition and a method for producing a lubricating oil composition. [Background technology]

[0002] In vacuum environments such as outer space, liquids with high vapor pressure evaporate during use. Therefore, alkylcyclopentane oil, which has extremely low vapor pressure and does not evaporate easily in vacuum environments such as outer space, is mainly used as a lubricant in equipment installed in devices used in outer space, such as artificial satellites, probes, and lunar rovers. In recent years, alkylcyclopentane oil has been proposed for use as a lubricant not only in outer space but also in equipment used in vacuum environments such as semiconductor manufacturing equipment. For example, Patent Document 1 discloses a lubricating oil composition comprising alkylcyclopentane oil, crown ethers, and extreme pressure additives. Patent Document 1 lists zinc dithiophosphate, zinc dithiocarbamate, molybdenum dithiophosphate, molybdenum dithiocarbamate, zinc sulfonate, barium sulfonate, calcium sulfonate, phosphate esters, phosphite esters, hypophosphite esters, and acidic phosphate esters as extreme pressure additives. Furthermore, in Patent Document 1, crown ethers are used as solubilizers to ensure good dissolution of the extreme pressure additives in the alkylcyclopentane oil. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2009-203381 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] However, the lubricating oil composition described in Patent Document 1 is considered to have insufficient friction reduction performance and wear resistance performance (hereinafter collectively referred to as "friction and wear characteristics") when used in a vacuum environment.

[0005] Therefore, the object of the present invention is to provide a lubricating oil composition that exhibits excellent friction and wear characteristics even in a vacuum environment, and a method for producing the lubricating oil composition. [Means for solving the problem]

[0006] According to the present invention, the following [1] to [2] are provided. [1] Contains alkylcyclopentane oil and poly(meth)acrylate copolymer (X), The poly(meth)acrylate copolymer (X) comprises a constituent unit (a) derived from an alkyl(meth)acrylate (A) represented by the following general formula (a-1), a constituent unit (b) derived from a hydroxyl group-containing(meth)acrylate (B) represented by the following general formula (b-1), and a constituent unit (c) derived from a phosphorus-containing(meth)acrylate (C) represented by the following general formula (c-1), in a lubricating oil composition. [ka] [In the above general formula (a-1), R a1 R is a hydrogen atom or a methyl group. a2 This represents an alkyl group with 8 to 20 carbon atoms. [ka] [In the above general formula (b-1), R b1 R is a hydrogen atom or a methyl group. b2 This indicates an alkylene group with 2 to 4 carbon atoms. m1 is an integer from 1 to 10. Multiple R when m1 is an integer of 2 or more. b2 They may be the same or different. [ka] [In the above general formula (c-1), R c1 is a hydrogen atom or a methyl group. R c2 represents an ethylene group. m2 represents an integer of 1 to 6. When m2 is an integer of 2 or more, a plurality of R c2 may be the same or different. n represents an integer of 1 or 2. When n = 1, at least one of the plurality of R c3 represents a hydrogen atom, and one of the plurality of R c3 may be a methyl group or an ethyl group. When n = 2, R c3 is a hydrogen atom.] [2] A method for producing a lubricating oil composition, comprising a step of mixing an alkylcyclopentane oil and a poly(meth)acrylate copolymer (X), wherein the poly(meth)acrylate copolymer (X) comprises a structural unit (a) derived from an alkyl (meth)acrylate (A) represented by the following general formula (a-1), a structural unit (b) derived from a hydroxyl group-containing (meth)acrylate (B) represented by the following general formula (b-1), and a structural unit (c) derived from a phosphorus-containing (meth)acrylate (C) represented by the following general formula (c-1).[[ID=​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​[In the above general formula (c-1), R c1 R is a hydrogen atom or a methyl group. c2 represents an ethylene group. m2 represents an integer from 1 to 6. Multiple R when m2 is an integer of 2 or more. c2 They may be the same or different. n represents an integer of 1 or 2. If n=1, there are multiple R c3 At least one of them represents a hydrogen atom, and multiple R c3 One of them may be a methyl group or an ethyl group. When n=2, R c3 It is a hydrogen atom. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a lubricating oil composition that exhibits excellent friction and wear characteristics even in a vacuum environment, and a method for producing the lubricating oil composition. [Modes for carrying out the invention]

[0008] The upper and lower limits of the numerical ranges described herein can be combined in any way. For example, if the numerical ranges "A to B" and "C to D" are described, the numerical ranges "A to D" and "C to B" are also included within the scope of the present invention. Furthermore, unless otherwise specified, the numerical range "lower limit to upper limit" described herein means that the value is greater than or equal to the lower limit and less than or equal to the upper limit. Furthermore, in this specification, the numerical values ​​in the examples are values ​​that can be used as upper or lower limits. In this specification, "(meth)acrylate" means acrylate or methacrylate, and the same applies to other similar terms.

[0009] [Aspects of lubricating oil composition] The lubricating oil composition of this embodiment contains alkylcyclopentane oil and poly(meth)acrylate copolymer (X). The poly(meth)acrylate copolymer (X) contains a constituent unit (a) derived from an alkyl(meth)acrylate (A) represented by the following general formula (a-1), a constituent unit (b) derived from a hydroxyl group-containing(meth)acrylate (B) represented by the following general formula (b-1), and a constituent unit (c) derived from a phosphorus-containing(meth)acrylate (C) represented by the following general formula (c-1). [ka] [In the above general formula (a-1), R a1 R is a hydrogen atom or a methyl group. a2 This represents an alkyl group with 8 to 20 carbon atoms. [ka] [In the above general formula (b-1), R b1 R is a hydrogen atom or a methyl group. b2 This indicates an alkylene group with 2 to 4 carbon atoms. m1 is an integer from 1 to 10. Multiple R when m1 is an integer of 2 or more. b2 They may be the same or different. [ka] [In the above general formula (c-1), R c1 R is a hydrogen atom or a methyl group. c2 represents an ethylene group. m2 represents an integer from 1 to 6. Multiple R when m2 is an integer of 2 or more. c2 They may be the same or different. n represents an integer of 1 or 2. If n=1, there are multiple R c3 At least one of them represents a hydrogen atom, and multiple R c3 One of them may be a methyl group or an ethyl group. When n=2, R c3 It is a hydrogen atom.

[0010] The inventors of the present invention conducted diligent studies to solve the above problems. As a result, it was found that the lubricating oil composition described in Patent Document 1 has low molecular weights for the crown ethers and extreme pressure additives blended into the alkylcyclopentane oil, so these evaporate in a vacuum environment, resulting in insufficient friction and wear characteristics of the lubricating oil composition. Therefore, the inventors conducted further intensive studies and succeeded in creating a poly(meth)acrylate copolymer (X) as a compound that can impart excellent friction and wear properties to alkylcyclopentane oil. Since poly(meth)acrylate copolymer (X) is a polymer, it does not evaporate easily in a vacuum environment and can maintain its solubility in alkylcyclopentane oil for a long period of time even in a vacuum environment. Accordingly, a lubricating oil composition containing alkylcyclopentane oil and poly(meth)acrylate copolymer (X) can exhibit excellent friction and wear properties for a long period of time even in a vacuum environment.

[0011] Furthermore, it is presumed that the reason why the poly(meth)acrylate copolymer (X) exhibits excellent friction and wear properties is that the inclusion of the above-mentioned structural unit (a) ensures solubility in alkylcyclopentane oil, the inclusion of the above-mentioned structural unit (b) makes it a multi-point adsorption type polymer, and the inclusion of the above-mentioned structural unit (c) introduces phosphate groups or groups derived from acidic phosphate esters into the side chains. More specifically, in the lubricating oil composition, the steric hindrance of the poly(meth)acrylate copolymer (X) protects the phosphate groups or groups derived from acidic phosphate esters introduced into the side chains. On the other hand, in the sliding part, it is presumed that the poly(meth)acrylate copolymer (X) is compressed, exposing the phosphorus of the phosphate groups or groups derived from acidic phosphate esters introduced into the side chains, and that this phosphorus reacts with the metal, improving the friction and wear properties. Furthermore, according to the inventors' studies, the poly(meth)acrylate copolymer (X) also exhibits excellent thermal stability, making it less susceptible to the effects of solar radiation in outer space. It is also less susceptible to the effects of exposure to high temperatures within semiconductor manufacturing equipment.

[0012] The lubricating oil composition of this embodiment may consist only of alkylcyclopentane oil and poly(meth)acrylate copolymer (X). Furthermore, other components of alkylcyclopentane oil and poly(meth)acrylate copolymer (X) may be included, without departing from the spirit of the present invention. In the lubricating oil composition of this embodiment, the total content of alkylcyclopentane oil and poly(meth)acrylate copolymer (X) is preferably 95% to 100% by mass, more preferably 98% to 100% by mass, even more preferably 99% to 100% by mass, and even more preferably 100% by mass, based on the total amount of the lubricating oil composition.

[0013] The alkylcyclopentane oil and poly(meth)acrylate copolymer (X) will be described in detail below.

[0014] <Alkylcyclopentane oil> The lubricating oil composition of this embodiment contains alkylcyclopentane oil. In this embodiment, alkylcyclopentane oil functions as a base oil constituting the lubricating oil composition. Alkylcyclopentane oil, also known as MAC oil (Multiply Alkylated Cyclopentane oil), is a low-evaporation base oil composed of compounds in which multiple alkyl groups are bonded to a cyclopentane ring. The total number of carbon atoms of the alkyl groups bonded to the cyclopentane ring is preferably 48 to 112, and each alkyl group may be the same or different. Specific examples of alkylcyclopentane oils include tris(2-octyldodecyl)cyclopentane and tetra(dodecyl)cyclopentane.

[0015] (Alkylcyclopentane oil content) In the lubricating oil composition of this embodiment, the alkylcyclopentane oil content is preferably 95.0% by mass or more, more preferably 99.0% by mass or more, even more preferably 99.3% by mass or more, even more preferably 99.5% by mass or more, and still more preferably 99.7% by mass or more, based on the total amount of the lubricating oil composition, from the viewpoint of ensuring a sufficient base oil content in the lubricating oil composition. Furthermore, the alkylcyclopentane oil content is preferably 99.99% by mass or less, more preferably 99.95% by mass or less, even more preferably 99.92% by mass or less, and even more preferably 99.90% by mass or less, based on the total amount of the lubricating oil composition, from the viewpoint of ensuring room for the incorporation of poly(meth)acrylate copolymer (X) in the lubricating oil composition. The upper and lower limits of these numerical ranges can be combined in any way. Specifically, preferably 95.0% to 99.99% by mass, more preferably 99.0% to 99.99% by mass, even more preferably 99.3% to 99.95% by mass, even more preferably 99.5% to 99.92% by mass, and still more preferably 99.7% to 99.90% by mass.

[0016] In the following explanation, "alkylcyclopentane oil" will also be referred to as "MAC oil."

[0017] <Poly(meth)acrylate copolymer (X)> The lubricating oil composition of this embodiment contains a poly(meth)acrylate copolymer (X). The lubricating oil composition of this embodiment contains a poly(meth)acrylate copolymer (X), which provides excellent friction and wear characteristics. Alkylcyclopentane oil alone cannot adequately ensure sufficient friction and wear characteristics.

[0018] The poly(meth)acrylate copolymer (X) comprises a constituent unit (a) derived from an alkyl(meth)acrylate (A) represented by the above general formula (a-1), a constituent unit (b) derived from a hydroxyl group-containing(meth)acrylate (B) represented by the above general formula (b-1), and a constituent unit (c) derived from a phosphorus-containing(meth)acrylate (C) represented by the above general formula (c-1).

[0019] Alkyl (meth)acrylate (A), hydroxyl group-containing (meth)acrylate (B), and phosphorus-containing (meth)acrylate (C) will be described in detail below. In the following explanation, alkyl (meth)acrylate (A), hydroxyl group-containing (meth)acrylate (B), and phosphorus-containing (meth)acrylate (C) will also be referred to as "monomer (A)," "monomer (B)," and "monomer (C)," respectively.

[0020] (Alkyl (meth)acrylate (A)) The alkyl (meth)acrylate (A) used in this embodiment is represented by the following general formula (a-1). [ka]

[0021] The constituent unit (a) derived from alkyl(meth)acrylate (A) is primarily responsible for providing solubility in alkylcyclopentane oil (hereinafter also referred to as "oil solubility") in the poly(meth)acrylate copolymer (X). If the poly(meth)acrylate copolymer (X) does not contain constituent units (a) derived from alkyl(meth)acrylate (A), it becomes difficult to ensure the oil solubility of the poly(meth)acrylate copolymer (X). Furthermore, alkyl (meth)acrylate (A) may be used alone or in combination of two or more types. Therefore, the poly(meth)acrylate copolymer (X) may contain one or more constituent units (a) derived from alkyl (meth)acrylate (A).

[0022] In the above general formula (a-1), R a1 This is a hydrogen atom or a methyl group. That is, alkyl(meth)acrylate(A) has an acryloyl group or a methacryloyl group as a polymerizable functional group. R a1 Monomers in which substituents other than hydrogen atoms and methyl groups are difficult to obtain, and because such monomers have low reactivity, polymerization of them is also difficult. Here, in this embodiment, from the viewpoint of making it easier to adjust the molecular weight of the poly(meth)acrylate copolymer (X), R a1 It is preferable that this is a hydrogen atom. That is, it is preferable that alkyl(meth)acrylate(A) has an acryloyl group as a polymerizable functional group.

[0023] In the above general formula (a-1), R a2 This represents an alkyl group having 8 to 20 carbon atoms. If the alkyl group has fewer than 8 carbon atoms, or if the alkyl group has more than 20 carbon atoms, it becomes difficult to ensure the oil solubility of the poly(meth)acrylate copolymer (X).

[0024] R a2 Examples of C8-C20 alkyl groups that can be selected include linear alkyl groups such as octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, and eicosyl groups. These may be linear or branched.

[0025] Here, from the viewpoint of making it easier to ensure the oil solubility of the poly(meth)acrylate copolymer (X), the number of carbon atoms in the alkyl group is preferably 10 to 18, more preferably 10 to 16, and even more preferably 10 to 14.

[0026] (Hydroxyl group-containing (meth)acrylate (B)) The hydroxyl group-containing (meth)acrylate (B) used in this embodiment is represented by the following general formula (b-1). [ka]

[0027] The constituent unit (b) derived from the hydroxyl group-containing (meth)acrylate (B) plays a role in making the poly(meth)acrylate copolymer (X) a multi-point adsorption type polymer, and is presumed to contribute to improving friction and wear properties. If the poly(meth)acrylate copolymer (X) does not contain constituent units (b) derived from hydroxyl group-containing (meth)acrylate (B), it becomes difficult to improve friction and wear properties. Furthermore, the hydroxyl group-containing (meth)acrylate (B) may be used alone or in combination of two or more types. Therefore, the poly(meth)acrylate copolymer (X) may contain one or more constituent units (b) derived from the hydroxyl group-containing (meth)acrylate (B).

[0028] In the above general formula (b-1), R b1 This is a hydrogen atom or a methyl group. That is, hydroxyl group-containing (meth)acrylate (B) has an acryloyl group or a methacryloyl group as a polymerizable functional group. R b1 Monomers in which substituents other than hydrogen atoms and methyl groups are difficult to obtain, and because such monomers have low reactivity, polymerization of them is also difficult. Here, in this embodiment, from the viewpoint of making it easier to adjust the molecular weight of the poly(meth)acrylate copolymer (X), R b1 It is preferable that the atom is a hydrogen atom. That is, the hydroxyl group-containing (meth)acrylate (B) preferably has an acryloyl group as a polymerizable functional group.

[0029] In the above general formula (b-1), R b2 This represents an alkylene group with 2 to 4 carbon atoms. When the alkylene group has only one carbon atom, its polarity increases and its oil solubility decreases. Furthermore, if the alkylene group has 5 or more carbon atoms, its oil solubility increases too much, reducing its adsorption to metals. Here, from the viewpoint of ensuring appropriate oil solubility and appropriate adsorption to metals, the number of carbon atoms in the alkylene group is preferably 2 to 3, more preferably 2.

[0030] m1 represents an integer between 1 and 10. Multiple R when m1 is an integer greater than or equal to 2. b2 They may be the same or different. Also, -(OR b2 ) m1 The bonding configuration between the parts represented by the symbol may be random or block bonding, but from the viewpoint of ease of polymerization, random bonding is preferred. When m1 is 0, the hydroxyl group-containing (meth)acrylate (B) becomes a carboxylic acid, thus reducing its oil solubility. Also, if m1 is an integer greater than or equal to 11, -(OR b2 The influence of the )-part increases polarity and reduces oil solubility. Here, from the viewpoint of easily ensuring appropriate oil solubility, m1 is preferably 1 to 6, more preferably 1 to 4, even more preferably 1 to 2, and even more preferably 1.

[0031] (Phosphorus-containing (meth)acrylate (C)) The phosphorus-containing (meth)acrylate (C) used in the present invention is represented by the following general formula (c-1). [ka]

[0032] It is presumed that the constituent unit (c) derived from phosphorus-containing (meth)acrylate (C) plays a role in improving friction and wear properties by introducing a phosphate group or a group derived from an acidic phosphate ester into the side chain of the poly(meth)acrylate copolymer (X). If the poly(meth)acrylate copolymer (X) does not contain constituent units (c) derived from phosphorus-containing (meth)acrylate (C), it becomes difficult to improve friction and wear properties. Here, phosphorus is an element that reduces thermal stability, and therefore is generally not introduced from the viewpoint of ensuring thermal stability. However, the present inventors, while investigating the introduction of a phosphate group or a group derived from an acidic phosphate ester from the viewpoint of improving friction and wear properties, found that by introducing a phosphorus-containing (meth)acrylate (C) component (c) into a polymer that combines a component (a) derived from alkyl (meth)acrylate (A) and a component (b) derived from a hydroxyl group-containing (meth)acrylate (B), the problem of reduced thermal stability caused by the introduction of phosphorus is mitigated, resulting in a polymer (X) that is excellent in thermal stability as a whole and also excellent in friction and wear properties.

[0033] Furthermore, phosphorus-containing (meth)acrylate (C) may be used alone or in combination of two or more types. Therefore, the poly(meth)acrylate copolymer (X) may contain one or more constituent units (c) derived from phosphorus-containing (meth)acrylate (C).

[0034] In the above general formula (c-1), R c1 This is a hydrogen atom or a methyl group. In other words, phosphorus-containing (meth)acrylate (C) has an acryloyl group or a methacryloyl group as a polymerizable functional group. R c1 Monomers in which substituents other than hydrogen atoms and methyl groups are difficult to obtain, and because such monomers have low reactivity, polymerization of them is also difficult. Here, in this embodiment, from the viewpoint of making it easier to adjust the molecular weight of the poly(meth)acrylate copolymer (X), R c1 It is preferable that this is a hydrogen atom. That is, the phosphorus-containing (meth)acrylate (C) preferably has an acryloyl group as a polymerizable functional group.

[0035] In the above general formula (c-1), R c2 This indicates an ethylene group. When the alkylene group has only one carbon atom, its polarity increases and its oil solubility decreases. Furthermore, if the alkylene group has three or more carbon atoms, its oil solubility increases too much, reducing its adsorption to metals.

[0036] m2 represents an integer from 1 to 6. Multiple R when m2 is an integer greater than or equal to 2. c2 They may be the same or different. Also, -(OR c2 ) m2 The bonding configuration between the parts represented by the symbol may be random or block bonding, but from the viewpoint of ease of polymerization, random bonding is preferred. When m2 is 0, the polarity of the phosphorus-containing (meth)acrylate (C) increases, reducing its oil solubility. Also, if m2 is an integer greater than or equal to 7, -(OR b2 The influence of the )-part increases polarity and reduces oil solubility. Here, from the viewpoint of easily ensuring appropriate oil solubility, m2 is preferably 1 to 4, more preferably 1 to 2, and even more preferably 1.

[0037] n represents an integer of 1 or 2. If n=1, multiple R c3 At least one of them represents a hydrogen atom, and multiple R c3 One of them may be a methyl group or an ethyl group. When n=2, R c3 It is a hydrogen atom. Here, when n=1, from the viewpoint of making it easier to exhibit the effects of the present invention, multiple R c3 Preferably, all of these are hydrogen atoms. Furthermore, from the viewpoint of making it easier to exhibit the effects of the present invention, it is preferable that the phosphorus-containing (meth)acrylate (C) mainly contains phosphorus-containing (meth)acrylate (C1) where n=1. In this specification, "main component" refers to a component whose content exceeds 50% by mass. That is, the content of phosphorus-containing (meth)acrylate (C1) n=1 is preferably more than 50% by mass to 100% by mass, more preferably 60% by mass to 100% by mass, even more preferably 70% by mass to 100% by mass, even more preferably 80% by mass to 100% by mass, and still more preferably 90% by mass to 100% by mass, based on the total amount of phosphorus-containing (meth)acrylate (C). Furthermore, the content of the constituent unit (c1) derived from the phosphorus-containing (meth)acrylate (C1) where n=1 is preferably more than 50% by mass to 100% by mass, more preferably 60% by mass to 100% by mass, even more preferably 70% by mass to 100% by mass, even more preferably 80% by mass to 100% by mass, and still more preferably 90% by mass to 100% by mass, based on the total amount of constituent unit (c) derived from the phosphorus-containing (meth)acrylate (C).

[0038] Furthermore, the phosphorus-containing (meth)acrylate (C) used in this embodiment is more preferably 300 mg KOH / g to 600 mg KOH / g, and even more preferably 350 mg KOH / g to 550 mg KOH / g, from the viewpoint of making it easier to improve friction and wear characteristics. In this specification, the acid value of phosphorus-containing (meth)acrylate (C) refers to the value measured by the potentiometric method specified in JIS K 2501 2003, Section 7.

[0039] (Requirement(α)) The poly(meth)acrylate copolymer (X) preferably satisfies requirement (α). That is, the content ratio of the above constituent unit (a) to the above constituent unit (b) [(a) / (b)] is preferably 50 / 50 to 90 / 10 in molar ratio. When [(a) / (b)] is 50 / 50 or more, it is easier to improve the oil solubility of the poly(meth)acrylate copolymer (X). Furthermore, from the viewpoint of improving the oil solubility of the poly(meth)acrylate copolymer (X), [(a) / (b)] is more preferably 60 / 40 or more, even more preferably 70 / 30 or more, and even more preferably 75 / 25. Furthermore, if [(a) / (b)] is 90 / 10 or less, it is easier to improve the friction and wear properties of the poly(meth)acrylate copolymer (X). The upper and lower limits of these numerical ranges can be combined in any way. Specifically, preferably 60 / 40 to 90 / 10, more preferably 70 / 30 to 90 / 10, and even more preferably 75 / 25 to 90 / 10.

[0040] (Requirements (β)) In this embodiment, the poly(meth)acrylate copolymer (X) preferably satisfies requirement (β) from the viewpoint of making it easier to exhibit the effects of the present invention. That is, the phosphorus content of the poly(meth)acrylate copolymer (X) is preferably 0.05% by mass or more and 1.0% by mass or less on a basis of the total amount of the poly(meth)acrylate copolymer (X). Furthermore, from the viewpoint of making it easier to exhibit the effects of the present invention, it is more preferably 0.10% by mass or more, even more preferably 0.20% by mass or more, on a basis of the total amount of the poly(meth)acrylate copolymer (X). Furthermore, it is more preferably 0.70% by mass or less, even more preferably 0.50% by mass or less, even more preferably 0.40% by mass or less, and still still more preferably 0.30% by mass or less. The upper and lower limits of these numerical ranges can be combined in any way. Specifically, more preferably, they are 0.10% to 0.70% by mass, even more preferably 0.10% to 0.50% by mass, even more preferably 0.20% to 0.40% by mass, and still more preferably 0.20% to 0.30% by mass. The phosphorus content of the poly(meth)acrylate copolymer (X) can be calculated based on the amount of phosphorus in the organic solvent (e.g., lubricating oil base oil) after dissolving a predetermined amount of the poly(meth)acrylate copolymer (X) in an organic solvent (e.g., lubricating oil base oil), measured in accordance with JIS-5S-38-03, and the amount of poly(meth)acrylate copolymer (X) dissolved in the organic solvent.

[0041] (Other monomers) The poly(meth)acrylate copolymer (X) may contain, in addition to the above-mentioned constituent units (a), (b), and (c), other monomer-derived constituent units, to the extent that they do not impede the effects of the present invention. Examples of such other monomers include functional group-containing monomers other than monomers (A), (B), and (C). Examples of such other functional group-containing monomers include functional group-containing (meth)acrylates other than monomers (A), (B), and (C). However, from the viewpoint of making it easier to further improve the effects of the present invention, the total content of the above constituent units (a), (b), and (c) in the poly(meth)acrylate copolymer (X) is preferably more than 50% by mass to 100% by mass, more preferably 60% by mass to 100% by mass, even more preferably 70% by mass to 100% by mass, even more preferably 80% by mass to 100% by mass, and still more preferably 90% by mass to 100% by mass, based on the total constituent units of the poly(meth)acrylate copolymer (X). Furthermore, from the viewpoint of making it easier to exhibit the effects of the present invention, the poly(meth)acrylate copolymer (X) contains, more preferably, less than 50% by mass, more preferably less than 40% by mass, even more preferably less than 30% by mass, even more preferably less than 20% by mass, and still more preferably less than 10% by mass, based on the total constituent units of the poly(meth)acrylate copolymer (X).

[0042] (Physical properties of poly(meth)acrylate copolymer (X)) (Mass average molecular weight (Mw), molecular weight distribution (Mw / Mn)) The mass-average molecular weight (Mw) of the poly(meth)acrylate copolymer (X) in this embodiment is preferably 5,000 or more, more preferably 8,000 or more, and even more preferably 10,000 or more, from the viewpoint of making it easier to suppress evaporation in a vacuum environment and to ensure oil solubility and improve friction and wear characteristics. It is also preferably 100,000 or less, more preferably 50,000 or less, and even more preferably 40,000 or less. The upper and lower limits of these numerical ranges can be combined in any way. Specifically, they are preferably 5,000 to 100,000, more preferably 8,000 to 50,000, and even more preferably 10,000 to 40,000. Furthermore, the molecular weight distribution (Mw / Mn) of the poly(meth)acrylate copolymer (X) in this embodiment is preferably 3.5 or less, more preferably 3.0 or less, and even more preferably 2.8 or less, from the viewpoint of making it easier to further improve the effects of the present invention. The molecular weight distribution (Mw / Mn) of the poly(meth)acrylate copolymer (X) in this embodiment may be 1.01 or more, 1.3 or more, or 1.5 or more. The mass-average molecular weight (Mw) and molecular weight distribution (Mw / Mn) are values ​​measured or calculated by the method described in the examples below.

[0043] (Modulation pattern) The polymerization method of the poly(meth)acrylate copolymer (X) in this embodiment is not particularly limited and may be block copolymerization, random copolymerization, or block / random copolymerization. Among these, random copolymerization is preferred from the viewpoint of ease of polymerization reaction.

[0044] (Method for producing poly(meth)acrylate copolymer (X)) The method for producing the poly(meth)acrylate copolymer (X) is not particularly limited, but for example, it includes a step (S) of polymerizing an alkyl(meth)acrylate (A) represented by the following general formula (a-1), a hydroxyl group-containing(meth)acrylate (B) represented by the following general formula (b-1), and a phosphorus-containing(meth)acrylate (C) represented by the following general formula (c-1) to produce the poly(meth)acrylate copolymer (X). [ka] [In the above general formula (a-1), R a1 R is a hydrogen atom or a methyl group. a2 This represents an alkyl group with 8 to 20 carbon atoms. [ka] [In the above general formula (b-1), R b1 R is a hydrogen atom or a methyl group. b2 This indicates an alkylene group with 2 to 4 carbon atoms. m1 is an integer from 1 to 10. Multiple R when m1 is an integer of 2 or more. b2 They may be the same or different. [ka] [In the above general formula (c-1), R c1 R is a hydrogen atom or a methyl group. c2 represents an ethylene group. m2 represents an integer from 1 to 6. Multiple R when m2 is an integer of 2 or more. c2 They may be the same or different. n represents an integer of 1 or 2. If n=1, there are multiple R c3 At least one of them represents a hydrogen atom, and multiple R c3 One of them may be a methyl group or an ethyl group. When n=2, R c3 It is a hydrogen atom.

[0045] The process (S) for producing the poly(meth)acrylate copolymer (X) will be described in detail below.

[0046] (Process (S) for producing poly(meth)acrylate copolymer (X)) The method for producing the poly(meth)acrylate copolymer (X) (polymerization method) is not particularly limited and can be produced by applying any known method. Examples of such methods include emulsion polymerization, suspension polymerization, and solution polymerization. Here, as a method for producing the poly(meth)acrylate copolymer (X) (polymerization method), it is preferable to employ a solution polymerization method using a solvent that dissolves in alkylcyclopentane oil, which is the base oil, as the solvent.

[0047] (Solution polymerization method) Solution polymerization is carried out, for example, by charging monomers (A), (B), and (C), along with a solvent and an initiator, purging the reactor with nitrogen, and then reacting with stirring at 60°C to 100°C for 2 to 10 hours. Other monomers besides monomers (A), (B), and (C) may also be optionally charged into the reactor.

[0048] Solvents used in solution polymerization include, for example, alcohols such as methanol, ethanol, propanol, 2-propanol, and butanol; hydrocarbons such as benzene, toluene, xylene, and hexane; esters such as ethyl acetate, butyl acetate, and isobutyl acetate; ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; ethers such as methoxybutanol, ethoxybutanol, ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, propylene glycol monobutyl ether, and dioxane; mineral oil; and synthetic oils such as poly-α-olefins, ethylene-α-olefin copolymers, alkylbenzenes, alkylnaphthalenes, polyphenyl ethers, alkyl-substituted diphenyl ethers, polyol esters, dibasic acid esters, hindered esters, monoesters, GTL base oils, and alkylcyclopentane oils. These can be used individually or in combination of two or more types.

[0049] Initiators used in solution polymerization include, for example, azo-based initiators such as 2,2'-azobis(isobutyronitrile), 2,2'-azobis(2-amidinopropane) dihydrochloride, 2,2'-azobis-(N,N-dimethylene isobutylamidine) dihydrochloride, and 1,1'-azobis(cyclohexyl-1-carbonnitrile); hydrogen peroxide; organic peroxides such as benzoyl peroxide, t-butyl hydroperoxide, cumene hydroperoxide, methyl ethyl ketone peroxide, and perbenzoic acid; persulfates such as sodium persulfate, potassium persulfate, and ammonium persulfate; and hydrogen peroxide-Fe 2+ Examples include redox initiators and other existing radical initiators.

[0050] The molecular weight of the poly(meth)acrylate copolymer (X) can be controlled by known methods. For example, the molecular weight of the poly(meth)acrylate copolymer (X) can be controlled by the reaction temperature, reaction time, amount of initiator, amount of each monomer charged, type of solvent, and use of chain transfer agent.

[0051] (Preferred embodiment 1 in process (S)) In step (S), from the viewpoint of producing a poly(meth)acrylate copolymer (X) that satisfies the above requirement (α), it is preferable to adjust the blending ratio [(A) / (B)] of alkyl(meth)acrylate (A) and hydroxyl group-containing(meth)acrylate (B) to 50 / 50 to 90 / 10 in molar ratio. Furthermore, from the viewpoint of further improving the oil solubility of the poly(meth)acrylate copolymer (X), [(A) / (B)] is more preferably 60 / 40 to 90 / 10, even more preferably 70 / 30 to 90 / 10, and even more preferably 75 / 25 to 90 / 10.

[0052] (Preferred embodiment 2 in process (S)) In step (S), from the viewpoint of producing a poly(meth)acrylate copolymer (X) that satisfies the above requirement (β), it is preferable to adjust the blending ratio [(C) / {(A)+(B)}] of phosphorus-containing (meth)acrylate (C) and the total amount of alkyl (meth)acrylate (A) and hydroxyl group-containing (meth)acrylate (B) to 0.1 / 100 to 10 / 100 in molar ratio. Furthermore, from the viewpoint of making it easier to improve the friction and wear characteristics of the poly(meth)acrylate copolymer (X), [(C) / {(A)+(B)}] is more preferably 0.5 / 100 or more, and even more preferably 1.0 / 100 or more. Furthermore, from the viewpoint of making it easier to improve the thermal stability of the poly(meth)acrylate copolymer (X), [(C) / {(A)+(B)}] is more preferably 5.0 / 100 or less, and even more preferably 3.0 / 100 or less. The upper and lower limits of these numerical ranges can be combined in any way. Specifically, more preferably, they are 0.5 / 100 to 5.0 / 100, and even more preferably 1.0 / 100 to 3.0 / 100.

[0053] (Content of poly(meth)acrylate copolymer (X)) In the lubricating oil composition of this embodiment, the content of poly(meth)acrylate copolymer (X) is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, even more preferably 0.08% by mass or more, and even more preferably 0.1% by mass or more, based on the total amount of the lubricating oil composition, from the viewpoint of easily exhibiting the effects of adding poly(meth)acrylate copolymer (X). Furthermore, the content of the poly(meth)acrylate copolymer (X) is preferably 1.0% by mass or less, more preferably 0.7% by mass or less, even more preferably 0.5% by mass or less, and even more preferably 0.3% by mass or less, from the viewpoint of ensuring the oil solubility of the poly(meth)acrylate copolymer (X) while obtaining an effect commensurate with the amount of poly(meth)acrylate copolymer (X) added. The upper and lower limits of these numerical ranges can be combined in any way. Specifically, preferably they are 0.01% to 1.0% by mass, more preferably 0.05% to 0.7% by mass, even more preferably 0.08% to 0.5% by mass, and even more preferably 0.1% to 0.3% by mass.

[0054] <Other additives> The lubricating oil composition of this embodiment may or may not contain other additives other than the poly(meth)acrylate copolymer (X), as long as they do not hinder the effects of the present invention. Other additives include, for example, viscosity index improvers. Examples of viscosity index improvers include polymethacrylates that do not fall under the category of poly(meth)acrylate copolymer (X), dispersed polymethacrylates, olefin copolymers (e.g., ethylene-propylene copolymers, etc.), dispersed olefin copolymers, and styrene copolymers (e.g., styrene-diene hydrogenated copolymers, etc.). Furthermore, the lubricating oil composition of this embodiment may also contain a thickening agent as another additive. In other words, the lubricating oil composition of this embodiment may be in the form of a grease composition containing a thickening agent.

[0055] <Physical properties of lubricating oil compositions> (Kinematic viscosity, viscosity index) The kinematic viscosity of the lubricating oil composition of this embodiment at 100°C is preferably 5.0 mm from the viewpoint of suppressing evaporation. 2 / s or more, more preferably 8.0 mm 2 / s or more, more preferably 10.0 mm 2 It is 25 mm or more. Also, from the viewpoint of suppressing power loss due to viscous resistance, it is preferable to 25 mm. 2 / s or less, more preferably 20mm 2 / s or less, more preferably 18mm 2 It is less than or equal to / s. The viscosity index of the lubricating oil composition of this embodiment is preferably 100 or higher, more preferably 110 or higher, and even more preferably 120 or higher. The kinematic viscosity and viscosity index of the lubricating oil composition are values ​​measured or calculated in accordance with JIS K2283:2000.

[0056] (Coefficient of friction) The lubricating oil composition of this embodiment has a coefficient of friction of 0.065 or less, more preferably 0.060 or less, even more preferably 0.055 or less, and even more preferably 0.050 or less, as determined by the friction and wear test described in the examples described later.

[0057] (Abrasion resistance) The lubricating oil composition of this embodiment has a wear mark diameter of preferably 0.35 mm or less, more preferably 0.30 mm or less, and even more preferably 0.25 mm or less, as determined by the friction and wear test described in the examples below.

[0058] [Method for producing a lubricating oil composition] The method for producing the lubricating oil composition of this embodiment is not particularly limited, but examples include the following methods. In other words, the method for producing the lubricating oil composition of this embodiment includes the step of mixing alkylcyclopentane oil and poly(meth)acrylate copolymer (X). The poly(meth)acrylate copolymer (X) contains a constituent unit (a) derived from an alkyl(meth)acrylate (A) represented by the following general formula (a-1), a constituent unit (b) derived from a hydroxyl group-containing(meth)acrylate (B) represented by the following general formula (b-1), and a constituent unit (c) derived from a phosphorus-containing(meth)acrylate (C) represented by the following general formula (c-1). [ka] [In the above general formula (a-1), R a1 R is a hydrogen atom or a methyl group. a2 This represents an alkyl group with 8 to 20 carbon atoms. [ka] [In the above general formula (b-1), R b1 R is a hydrogen atom or a methyl group. b2 This indicates an alkylene group with 2 to 4 carbon atoms. m1 is an integer from 1 to 10. Multiple R when m1 is an integer of 2 or more. b2 They may be the same or different. [ka] [In the above general formula (c-1), R c1 R is a hydrogen atom or a methyl group. c2 represents an ethylene group. m2 represents an integer from 1 to 6. Multiple R when m2 is an integer of 2 or more. c2 They may be the same or different. n represents an integer of 1 or 2. If n=1, there are multiple R c3At least one of them represents a hydrogen atom, and multiple R c3 One of them may be a methyl group or an ethyl group. When n=2, R c3 It is a hydrogen atom.

[0059] The poly(meth)acrylate copolymer (X) can be produced, for example, by the production method described above. There are no particular limitations on the method for mixing alkylcyclopentane oil and poly(meth)acrylate copolymer (X), but one example is a method that includes a step of blending the alkylcyclopentane oil with the poly(meth)acrylate copolymer (X). Other additives may be blended with the alkylcyclopentane oil at the same time as the blending with the poly(meth)acrylate copolymer (X), or they may be blended separately. Each component may be blended in the form of a solution (dispersion) by adding a diluent oil or the like. After blending each component, it is preferable to stir and disperse them uniformly by a known method.

[0060] [Uses of lubricating oil compositions] In this embodiment, both the alkylcyclopentane oil and the poly(meth)acrylate copolymer (X), which are components of the lubricating oil composition, are less likely to evaporate even in a vacuum environment. Therefore, even in a vacuum environment, the state in which the poly(meth)acrylate copolymer (X) is dissolved in the alkylcyclopentane oil can be maintained for a long period of time, and sufficient friction and wear characteristics are exhibited. Therefore, the lubricating oil composition of this embodiment is suitable as a lubricating oil composition used for lubricating equipment used in a vacuum environment. Examples of equipment used in a vacuum environment include devices mounted on spacecraft such as artificial satellites, probes, and lunar rovers. Also, examples include equipment used in the manufacturing of semiconductors, liquid crystal and organic EL flat panel displays, and solar panels, specifically in spaces where various processes are performed under a vacuum (such as vacuum chambers and vacuum transfer rooms).

[0061] In addition, in this specification, the "vacuum environment" may be a high-vacuum environment of 10 -1 Pa or less, may be an ultra-high-vacuum environment of 10 -5 Pa or less, or may be an extremely-high-vacuum environment of 10 -9 Pa or less.

[0062] [Lubrication method using the lubricating oil composition] As a lubrication method using the lubricating oil composition of the present embodiment, preferably, a method of using the lubricating oil composition for lubricating a device used in a vacuum environment is exemplified. Examples of the device used in a vacuum environment include the various devices described above.

[0063] [One aspect of the present invention provided] According to one aspect of the present invention, the following [1] to [7] are provided. [1] A lubricating oil composition containing an alkylcyclopentane oil and a poly(meth)acrylate copolymer (X), The poly(meth)acrylate copolymer (X) includes a structural unit (a) derived from an alkyl (meth)acrylate (A) represented by the following general formula (a-1), a structural unit (b) derived from a hydroxyl group-containing (meth)acrylate (B) represented by the following general formula (b-1), and a structural unit (c) derived from a phosphorus-containing (meth)acrylate (C) represented by the following general formula (c-1). [Chemical formula] [In the above general formula (a-1), R a1 is a hydrogen atom or a methyl group. R a2 represents an alkyl group having 8 to 20 carbon atoms.] [Chemical formula] [In the above general formula (b-1), R b1 is a hydrogen atom or a methyl group. R b2 represents an alkylene group having 2 to 4 carbon atoms. m1 represents an integer of 1 to 10. When m1 is an integer of 2 or more, a plurality of Rb2 may be the same or different.] [Chemical formula] [In the general formula (c-1), R c1 is a hydrogen atom or a methyl group. R c2 represents an ethylene group. m2 represents an integer from 1 to 6. When m2 is an integer of 2 or more, a plurality of R c2 may be the same or different. n represents an integer of 1 or 2. When n = 1, at least one of the plurality of R c3 represents a hydrogen atom, and one of the plurality of R c3 may be a methyl group or an ethyl group. When n = 2, R c3 is a hydrogen atom.] [2] In the general formula (c-1), when n = 1, all of the plurality of R c3 are hydrogen atoms, and the lubricating oil composition according to [1] above. [3] The poly(meth)acrylate copolymer (X) has a mass average molecular weight (Mw) of 5,000 to 100,000, and the lubricating oil composition according to [1] or [2] above. [4] The poly(meth)acrylate copolymer (X) further satisfies the following requirement (α), and the lubricating oil composition according to any one of [1] to [3] above. <Requirement (α)> The content ratio [(a) / (b)] of the structural unit (a) and the structural unit (b) is 40 / 60 to 90 / 10 in terms of molar ratio. [5] The poly(meth)acrylate copolymer (X) further satisfies the following requirement (β), and the lubricating oil composition according to any one of [1] to [4] above. <Requirement (β)> The phosphorus content in the poly(meth)acrylate copolymer (X) is 0.05% by mass or more and 1.0% by mass or less based on the total amount of the poly(meth)acrylate copolymer (X). [6] The lubricating oil composition according to any one of [1] to [5] above, which is used for lubricating equipment used in a vacuum environment. [7] A step of mixing alkylcyclopentane oil with a poly(meth)acrylate copolymer (X), A method for producing a lubricating oil composition, wherein the poly(meth)acrylate copolymer (X) comprises a constituent unit (a) derived from an alkyl(meth)acrylate (A) represented by the following general formula (a-1), a constituent unit (b) derived from a hydroxyl group-containing(meth)acrylate (B) represented by the following general formula (b-1), and a constituent unit (c) derived from a phosphorus-containing(meth)acrylate (C) represented by the following general formula (c-1). [ka] [In the above general formula (a-1), R a1 R is a hydrogen atom or a methyl group. a2 This represents an alkyl group with 8 to 20 carbon atoms. [ka] [In the above general formula (b-1), R b1 R is a hydrogen atom or a methyl group. b2 This indicates an alkylene group with 2 to 4 carbon atoms. m1 is an integer from 1 to 10. Multiple R when m1 is an integer of 2 or more. b2 They may be the same or different. [ka] [In the above general formula (c-1), R c1 R is a hydrogen atom or a methyl group. c2 represents an ethylene group. m2 represents an integer from 1 to 6. Multiple R when m2 is an integer of 2 or more. c2 They may be the same or different. n represents an integer of 1 or 2. If n=1, there are multiple R c3 At least one of them represents a hydrogen atom, and multiple R c3 One of them may be a methyl group or an ethyl group. When n=2, R c3 It is a hydrogen atom. [Examples]

[0064] The present invention will be specifically described by the following examples, but the present invention is not limited to the following examples.

[0065] [Methods for measuring various physical properties] The properties of each raw material used in each example and comparative example, as well as the properties of each lubricating oil composition in each example and comparative example, were measured according to the following procedure.

[0066] (1)Kinematic viscosity, viscosity index The kinematic viscosity at 40°C, kinematic viscosity at 100°C, and viscosity index of the lubricating oil composition were measured or calculated in accordance with JIS K2283:2000.

[0067] (2) Mass average molecular weight (Mw), molecular weight distribution (Mw / Mn) A Waters 1515 isocratic HPLC pump and a 2414 differential refractive index (RI) detector were used, with one TSKguardcolumn SuperHZ-L and two TSKSuperMultipore HZ-M columns from Tosoh Corporation installed in that order from upstream. Measurements were taken at a temperature of 40°C, with tetrahydrofuran as the mobile phase, a flow rate of 0.35 ml / min, and a sample concentration of 1.0 mg / ml. The results were then calculated in terms of standard polystyrene equivalents.

[0068] [Examples 1-4, Comparative Example 1] Alkylcyclopentane oil and poly(meth)acrylate copolymer (X) were thoroughly mixed in the amounts (mass%) shown in Table 1 to prepare the lubricating oil compositions of Examples 1 to 4. In Comparative Example 1, only alkylcyclopentane oil was used. Details of the alkylcyclopentane oil and poly(meth)acrylate copolymer (X) used in Examples 1-4 and Comparative Example 1 are as follows.

[0069] <Alkylcyclopentane oil> Tris(2-octyldodecyl)cyclopentane was used.

[0070] <Poly(meth)acrylate copolymer (X)> • Poly(meth)acrylate copolymer (X)-1: Produced by the method described in Production Example 1. • Poly(meth)acrylate copolymer (X)-2: Produced by the method described in Production Example 2. • Poly(meth)acrylate copolymer (X)-3: Produced by the method described in Production Example 3.

[0071] <Manufacturing Examples 1-3> (Monomers used in manufacturing examples 1-3) • "Dodecyl acrylate": In the above general formula (a-1), R a1 is a hydrogen atom, and R a2 This compound has a dodecyl group (a C12 alkyl group). It was used as alkyl (meth)acrylate (A). • "2-hydroxyethyl acrylate": In the above general formula (b-1), R b1 is a hydrogen atom, and R b2 This compound has an ethylene group (a C2 alkylene group) and m1=1. It was used as a hydroxyl group-containing (meth)acrylate (B). • "P-1A(N)": Manufactured by Kyoeisha Chemical Co., Ltd., phosphorus content = 14.3% by mass The above general formula (c-1) is a mixture in which the compound with n=1 is the main component, and also contains the compound with n=2. Both compounds are R c1 This is a hydrogen atom, and m2=1. Also, in both compounds, R c3 This is a hydrogen atom. It was used as a phosphorus-containing (meth)acrylate (C). The acid value of P-1A(N) (measured by the potentiometric method specified in JIS K 2501 2003, Section 7) is 420-520 mgKOH / g.

[0072] (Manufacturing Example 1: Manufacturing of poly(meth)acrylate copolymer (X)-1) A 200 mL four-necked flask equipped with a thermometer, nitrogen inlet tube, and stirrer was charged with 53.9 g (224 mmol) of dodecyl acrylate, 2.89 g (24.9 mmol) of 2-hydroxyethyl acrylate, 0.944 g (4.8 mmol) of P-1A(N), and 47.6 g of 2-propanol as the solvent. Next, the flask was purged with nitrogen, and 0.2 g of 2,2'-azobis(isobutyronitrile) was added as an initiator. The mixture was then slowly heated while stirring and reacted under reflux at a temperature of 75-85°C for 4 hours. After the reaction was complete, the solvent was removed by distillation under reduced pressure to obtain poly(meth)acrylate copolymer (X)-1. The poly(meth)acrylate copolymer (X)-1 had a mass-average molecular weight (Mw) of 20,500 and a molecular weight distribution (Mw / Mn) of 2.1. Furthermore, the phosphorus content of poly(meth)acrylate copolymer (X)-1 was 0.28% by mass. Furthermore, the content ratio of constituent unit (a) to constituent unit (b) of poly(meth)acrylate copolymer (X)-1 [(a) / (b)] is 90 / 10 in molar ratio. The obtained poly(meth)acrylate copolymer (X)-1 was mixed with alkylcyclopentane oil in the formulations shown in Table 1 and subjected to the evaluation described later.

[0073] (Manufacturing Example 2: Manufacturing of poly(meth)acrylate copolymer (X)-2) By changing the amount of dodecyl acrylate to 47.9 g (199 mmol) and the amount of 2-hydroxyethyl acrylate to 5.8 g (49.8 mmol), poly(meth)acrylate copolymer (X)-2 was obtained by the same method as in Production Example 1. The poly(meth)acrylate copolymer (X)-2 had a mass-average molecular weight (Mw) of 21,300 and a molecular weight distribution (Mw / Mn) of 2.2. Furthermore, the phosphorus content of poly(meth)acrylate copolymer (X)-2 was 0.28% by mass. Furthermore, the content ratio of constituent unit (a) to constituent unit (b) of the poly(meth)acrylate copolymer (X)-2 [(a) / (b)] is 80 / 20 in molar ratio. The obtained poly(meth)acrylate copolymer (X)-2 was mixed with alkylcyclopentane oil in the formulations shown in Table 1 and subjected to evaluation described later.

[0074] (Manufacturing Example 3: Manufacturing of poly(meth)acrylate copolymer (X)-3) By changing the amount of dodecyl acrylate to 36 g (150 mmol) and the amount of 2-hydroxyethyl acrylate to 11.5 g (99 mmol), poly(meth)acrylate copolymer (X)-3 was obtained by the same method as in Production Example 1. The poly(meth)acrylate copolymer (X)-3 had a mass-average molecular weight (Mw) of 18,200 and a molecular weight distribution (Mw / Mn) of 2.1. Furthermore, the phosphorus content of poly(meth)acrylate copolymer (X)-3 was 0.28% by mass. Furthermore, the content ratio of constituent unit (a) to constituent unit (b) of poly(meth)acrylate copolymer (X)-3 [(a) / (b)] is 60 / 40 in molar ratio. The obtained poly(meth)acrylate copolymer (X)-3 was mixed with alkylcyclopentane oil in the formulations shown in Table 1 and subjected to evaluation described later.

[0075] [Evaluation Method] The friction and wear tests described below were conducted, and the coefficient of friction and the diameter of the wear marks were measured.

[0076] <Friction and wear test> Using a ball-on-disk type high-speed reciprocating friction tester TE77 (manufactured by Phoenix Tribology), a lubricating oil composition was introduced between the test plate and the test ball, and the test was conducted by moving the test ball under the following conditions, and the average coefficient of friction was measured. In addition, the diameter of the wear marks in the longitudinal and transverse directions of the test ball after the test was measured, and the average value of the wear mark diameter was calculated using the following formula. • Test pieces: Upper ball (SUJ2), lower disc (SUJ2) • Amplitude: 10.0 mm • Frequency: 10Hz • Load: 50N ·Temperature: 100℃ • Exam duration: 20 minutes Average wear mark diameter = {(Vertical wear mark diameter) + (Horizontal wear mark diameter)} / 2 The lower the coefficient of friction, the better the lubricating oil composition is in reducing friction. Furthermore, the smaller the value of the wear mark diameter, the better the wear resistance of the lubricating oil composition.

[0077] The results are shown in Table 1.

[0078] [Table 1]

[0079] From Table 1, the following can be seen. The lubricating oil compositions of Examples 1 to 4 exhibit excellent friction and wear characteristics, as evidenced by their low coefficient of friction and small wear mark diameters. As described in Production Examples 1-3, the poly(meth)acrylate copolymers (X)-1, (X)-2, and (X)-3 all have a large mass-average molecular weight and are resistant to evaporation even in a vacuum environment. Therefore, it can be seen that the excellent friction and wear properties of the lubricating oil compositions of Examples 1-4 can be maintained even in a vacuum environment.

[0080] Furthermore, visual inspection of the lubricating oil compositions of Examples 1 to 4 revealed no cloudiness or precipitation in any of them, confirming that the poly(meth)acrylate copolymer (X) has good solubility (oil solubility) in alkylcyclopentane oil.

Claims

1. Contains alkylcyclopentane oil and a poly(meth)acrylate copolymer (X), The poly(meth)acrylate copolymer (X) comprises a structural unit (a) derived from an alkyl (meth)acrylate (A) represented by the following general formula (a-1), a structural unit (b) derived from a hydroxyl group-containing (meth)acrylate (B) represented by the following general formula (b-1), and a structural unit (c) derived from a phosphorus-containing (meth)acrylate (C) represented by the following general formula (c-1): 【Chemistry 1】 [In the above general formula (a-1), R ａ１ is a hydrogen atom or a methyl group. ａ２ represents an alkyl group having 8 to 20 carbon atoms. 【Chemistry 2】 [In the above general formula (b-1), R ｂ１ is a hydrogen atom or a methyl group. ｂ２ represents an alkylene group having 2 to 4 carbon atoms. m1 represents an integer of 1 to 10. When m1 is an integer of 2 or more, a plurality of R ｂ２ may be the same or different. 【Chemistry 3】 [In the above general formula (c-1), R ｃ１ is a hydrogen atom or a methyl group. ｃ２ represents an ethylene group. m2 represents an integer of 1 to 6. When m2 is an integer of 2 or more, ｃ２ may be the same or different. n represents an integer of 1 or 2. When n=1, a plurality of R ｃ３ At least one of R represents a hydrogen atom; ｃ３ may be a methyl or ethyl group. When n=2, R ｃ３ is a hydrogen atom.]

2. In the general formula (c-1), when n=1, a plurality of R ｃ３ The lubricating oil composition of claim 1 , wherein each of

3. The lubricating oil composition according to claim 1 or 2, wherein the poly(meth)acrylate copolymer (X) has a mass average molecular weight (Mw) of 5,000 to 100,000.

4. The lubricating oil composition according to claim 1 or 2, wherein the poly(meth)acrylate copolymer (X) further satisfies the following requirement (α): <Requirements (α)> The content ratio of the structural unit (a) to the structural unit (b) [(a) / (b)] is 50 / 50 to 90 / 10 in terms of molar ratio.

5. The lubricating oil composition according to claim 1 or 2, wherein the poly(meth)acrylate copolymer (X) further satisfies the following requirement (β): <Requirements (β)> The poly(meth)acrylate copolymer (X) has a phosphorus content of 0.05% by mass or more and 1.0% by mass or less based on the total amount of the poly(meth)acrylate copolymer (X).

6. The lubricating oil composition according to claim 1 or 2, which is used for lubricating equipment used in a vacuum environment.

7. The method includes a step of mixing an alkylcyclopentane oil with a poly(meth)acrylate copolymer (X), The poly(meth)acrylate copolymer (X) comprises a structural unit (a) derived from an alkyl (meth)acrylate (A) represented by the following general formula (a-1), a structural unit (b) derived from a hydroxyl group-containing (meth)acrylate (B) represented by the following general formula (b-1), and a structural unit (c) derived from a phosphorus-containing (meth)acrylate (C) represented by the following general formula (c-1). 【Chemistry 4】 [In the above general formula (a-1), R ａ１ is a hydrogen atom or a methyl group. ａ２ represents an alkyl group having 8 to 20 carbon atoms. 【Chemistry 5】 [In the above general formula (b-1), R ｂ１ is a hydrogen atom or a methyl group. ｂ２ represents an alkylene group having 2 to 4 carbon atoms. m1 represents an integer of 1 to 10. When m1 is an integer of 2 or more, a plurality of R ｂ２ may be the same or different. 【Chemistry 6】 [In the above general formula (c-1), R ｃ１ is a hydrogen atom or a methyl group. ｃ２ represents an ethylene group. m2 represents an integer of 1 to 6. When m2 is an integer of 2 or more, ｃ２ may be the same or different. n represents an integer of 1 or 2. When n=1, a plurality of R ｃ３ At least one of R represents a hydrogen atom; ｃ３ may be a methyl or ethyl group. When n=2, R ｃ３ is a hydrogen atom.]

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