JP2024006117A - Additive composition for lubricating oils, and lubricating oil composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an additive composition for lubricating oils which is suitable as a load-bearing additive, and offers superior wear resistance, extreme pressure resistance, and thermal stability, and a lubricating oil composition that includes the additive composition for lubricating oils.

SOLUTION: An additive composition for lubricating oils includes a copolymer (X) that comprises a constitutional unit (a) derived from a specific alkyl methacrylate (A), a constitutional unit (b) derived from a specific hydroxy group-containing methacrylate (B), and a constitutional unit (c) derived from a specific phosphorus- and sulfur-containing methacrylate (C).

SELECTED DRAWING: None

COPYRIGHT: (C)2024,JPO&INPIT

Description

The present invention relates to a lubricating oil additive composition and a lubricating oil composition containing the lubricating oil additive composition.

Various lubricating oil additives are blended into lubricating oil for the purpose of imparting properties and performance necessary for lubricating oil, or supplementing and enhancing them.
One of the typical additives for lubricating oils is a load-bearing additive that imparts wear resistance and extreme pressure properties to lubricating oils. As load-bearing additives, low-molecular-weight compounds containing sulfur and phosphorus, such as dithiophosphoric acid esters, are widely used (for example, see Patent Document 1).

JP 2021-147517 Publication

However, low molecular weight compounds containing sulfur and phosphorus do not have sufficient wear resistance and extreme pressure properties, and there is room for further improvement. Furthermore, low molecular weight compounds containing sulfur and phosphorus have problems such as poor thermal stability and tend to generate sludge when used at high temperatures for long periods of time.

Therefore, the present invention provides an additive composition for lubricating oil that is suitable as a load-bearing additive and has excellent wear resistance, extreme pressure properties, and thermal stability, and a lubricating oil containing the additive composition for lubricating oil. An object of the present invention is to provide a composition.

The present inventors conducted extensive studies in order to solve the above problems. As a result, it was discovered that a poly(meth)acrylate copolymer containing structural units derived from a plurality of specific monomers could solve the above problems, leading to the completion of the present invention.

That is, the present invention relates to the following [1] to [4].
[1] A structural unit (a) derived from an alkyl (meth)acrylate (A) represented by the following general formula (a-1) and a hydroxyl group-containing (meth) represented by the following general formula (b-1) Contains a polymethacrylate copolymer (X) containing a structural unit (b) derived from an acrylate (B) and a structural unit (c) derived from a phosphorus- and sulfur-containing (meth)acrylate (C),
The phosphorus- and sulfur-containing (meth)acrylate (C) is an additive composition for lubricating oil, which has a (meth)acryloyl group and a monovalent group containing phosphorus and sulfur represented by the following general formula (1). .

[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. ]

[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 from 1 to 10. When m1 is an integer of 2 or more, a plurality of R ^b2 's may be the same or different. ]

[In the above general formula (1), R ¹ and R ² are each independently an alkyl group having 1 to 10 carbon atoms. ]
[2] A method of using the lubricating oil additive composition according to [1] above as a load-bearing additive.
[3] A lubricating oil composition containing the lubricating oil additive composition according to [1] above and a lubricating oil base oil.
[4] A method for producing a lubricating oil composition, comprising a step of mixing the lubricating oil additive composition according to [1] above and a lubricating oil base oil.

According to the present invention, there is provided an additive composition for lubricating oil that is suitable as a load-bearing additive and has excellent wear resistance, extreme pressure properties, and thermal stability, and a lubricating oil containing the additive composition for lubricating oil. It becomes possible to provide a composition.

The upper and lower limits of the numerical ranges described herein can be arbitrarily combined. For example, when "A to B" and "C to D" are described as numerical ranges, the numerical ranges of "A to D" and "C to B" are also included in the scope of the present invention.
Furthermore, the numerical range "lower limit to upper limit" described in this specification means that it is greater than or equal to the lower limit and less than or equal to the upper limit, unless otherwise specified.
Further, in this specification, numerical values in Examples are numerical values that can be used as upper limit values or lower limit values.
In this specification, "(meth)acrylate" means acrylate or methacrylate, and other similar terms have the same meaning.

[Aspects of additive composition for lubricating oil]
The lubricating oil additive composition of the present embodiment comprises a structural unit (a) derived from an alkyl (meth)acrylate (A) represented by the following general formula (a-1), and a structural unit (a) derived from the following general formula (b-1). Poly(meth) containing a structural unit (b) derived from a hydroxyl group-containing (meth)acrylate (B) represented by ) and a structural unit (c) derived from a phosphorus- and sulfur-containing (meth)acrylate (C) Contains an acrylate copolymer (X).
The phosphorus- and sulfur-containing (meth)acrylate (C) has a (meth)acryloyl group and a monovalent group containing phosphorus and sulfur represented by the following general formula (1).

[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. ]

[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 from 1 to 10. When m1 is an integer of 2 or more, a plurality of R ^b2 's may be the same or different. ]

[In the above general formula (1), R ¹ and R ² are each independently an alkyl group having 1 to 10 carbon atoms. ]

The present inventors conducted extensive studies in order to solve the above problems. As a result, the structural unit (a) derived from the alkyl (meth)acrylate (A) represented by the above general formula (a-1) and the hydroxyl group-containing (meth) acrylate represented by the above general formula (b-1) A poly(meth)acrylate copolymer (X) containing a structural unit (b) derived from an acrylate (B) and a structural unit (c) derived from a phosphorus- and sulfur-containing (meth)acrylate (C), It has been discovered that the poly(meth)acrylate copolymer (X) has excellent wear resistance, extreme pressure properties, and thermal stability, and can be suitably used as an additive for lubricating oils (particularly as a load-bearing additive). I came to find out.
The reason why the poly(meth)acrylate copolymer (X) has excellent wear resistance, extreme pressure properties, and thermal stability is because it contains the above-mentioned structural unit (a). Solubility) is ensured, the inclusion of the above structural unit (b) makes it a multi-point adsorption type polymer, and the inclusion of the above structural unit (c) makes it possible to This is presumably due to the monovalent group shown being introduced into the side chain. More specifically, in the lubricating oil composition, the monovalent group represented by the above general formula (1) introduced into the side chain is protected by steric hindrance of the poly(meth)acrylate copolymer (X). thermal stability is improved. On the other hand, in the sliding part, the poly(meth)acrylate copolymer (X) is compressed, and the phosphorus and sulfur monovalent groups represented by the above general formula (1) introduced into the side chains are It is presumed that by being exposed, the phosphorus and sulfur react with the metal, improving wear resistance and extreme pressure properties.

In the following explanation, "alkyl (meth)acrylate (A),""hydroxyl group-containing (meth)acrylate (B)," and "phosphorus- and sulfur-containing (meth)acrylate (C)" are respectively referred to as "monomer ( A),” “monomer (B),” and “monomer (C).”
Furthermore, in the following description, the "poly(meth)acrylate copolymer (X)" is also simply referred to as "copolymer (X)."

In this embodiment, the copolymer (X) includes only the structural unit (a) derived from the monomer (A), the structural unit (b) derived from the monomer (B), and the structural unit (c) derived from the monomer (C). However, other structural units other than structural units (a), (b), and (c) may be included as long as the effects of the present invention are not impaired.
In this embodiment, the total content of the structural units (a), (b), and (c) in the copolymer (X) is preferably 50 mass based on all the structural units of the copolymer (X). % to 100% by weight, more preferably 60% to 100% by weight, even more preferably 70% to 100% by weight, even more preferably 80% to 100% by weight, even more preferably 90% to 100% by weight %.

Hereinafter, the alkyl (meth)acrylate (A), the hydroxyl group-containing (meth)acrylate (B), and the phosphorus-containing (meth)acrylate (C) will be explained in detail.

<Alkyl (meth)acrylate (A)>
The alkyl (meth)acrylate (A) used in this embodiment is represented by the following general formula (a-1).

The structural unit (a) derived from the alkyl (meth)acrylate (A) mainly functions to exhibit oil solubility in the copolymer (X).
In addition, one type of alkyl (meth)acrylate (A) may be used alone, or two or more types may be used in combination. Therefore, the copolymer (X) may contain only one type of structural unit (a) derived from the alkyl (meth)acrylate (A), or may contain two or more types.

In the above general formula (a-1), R ^a1 is a hydrogen atom or a methyl group. That is, the alkyl (meth)acrylate (A) has an acryloyl group or a methacryloyl group as a polymerizable functional group.
Monomers in which R ^a1 is a substituent other than a hydrogen atom or a methyl group are difficult to obtain, and since these monomers have low reactivity, it is also difficult to polymerize them.
Here, in this embodiment, R ^a1 is preferably a hydrogen atom from the viewpoint of making it easier to adjust the molecular weight of the copolymer (X). That is, it is preferable that the alkyl (meth)acrylate (A) has an acryloyl group as a polymerizable functional group.

In the above general formula (a-1), R ^a2 represents an alkyl group having 8 to 20 carbon atoms.
When the number of carbon atoms in the alkyl group is less than 8, and when the number of carbon atoms in the alkyl group is more than 20, it becomes difficult to ensure the oil solubility of the copolymer (X).

Examples of the alkyl group having 8 to 20 carbon atoms that can be selected as R ^a2 include octyl group, nonyl group, decyl group, undecyl group, dodecyl group, tridecyl group, tetradecyl group, pentadecyl group, hexadecyl group, heptadecyl group, Chain alkyl groups such as octadecyl group, nonadecyl group, and icosyl group are mentioned. These may be linear or branched.

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

<Hydroxy 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).

The structural unit (b) derived from the hydroxyl group-containing (meth)acrylate (B) has the function of making the copolymer (X) a multi-point adsorption type polymer, and contributes to improving wear resistance and extreme pressure properties. It is assumed that.
Note that the hydroxyl group-containing (meth)acrylate (B) may be used alone or in combination of two or more. Therefore, the copolymer (X) may contain one type of structural unit (b) derived from the hydroxyl group-containing (meth)acrylate (B), or may contain two or more types.

In the above general formula (b-1), R ^b1 is a hydrogen atom or a methyl group. That is, the hydroxyl group-containing (meth)acrylate (B) has an acryloyl group or a methacryloyl group as a polymerizable functional group.
Monomers in which R ^b1 is a substituent other than a hydrogen atom or a methyl group are difficult to obtain, and since these monomers have low reactivity, it is also difficult to polymerize them.
Here, in this embodiment, R ^b1 is preferably a hydrogen atom from the viewpoint of making it easier to adjust the molecular weight of the copolymer (X). That is, it is preferable that the hydroxyl group-containing (meth)acrylate (B) has an acryloyl group as a polymerizable functional group.

In the above general formula (b-1), R ^b2 represents an alkylene group having 2 to 4 carbon atoms.
When the number of carbon atoms in the alkylene group is 1, the polarity becomes high and the oil solubility decreases.
Moreover, when the number of carbon atoms in the alkylene group is 5 or more, the oil solubility increases too much and the adsorption to metals decreases.
Here, the number of carbon atoms in the alkylene group is preferably 2 to 3, more preferably 2, from the viewpoint of easily ensuring appropriate oil solubility and appropriate adsorption to metal.

m1 represents an integer from 1 to 10. When m1 is an integer of 2 or more, a plurality of R ^b2 's may be the same or different. Further, the bonding mode between the moieties represented by -(OR ^b2 ) _m1 may be random bonding or block bonding, but from the viewpoint of ease of polymerization, random bonding is preferable.
When m1 is 0, the hydroxyl group-containing (meth)acrylate (B) becomes a carboxylic acid, resulting in decreased oil solubility.
Further, when m1 is an integer of 11 or more, the polarity becomes high due to the influence of the -(OR ^b2 )- moiety, and the oil solubility decreases.
Here, from the viewpoint of easily ensuring appropriate oil solubility, m1 is preferably 1 to 6, more preferably 1 to 4, still more preferably 1 to 2, and even more preferably 1.

<Phosphorous and sulfur-containing (meth)acrylate (C)>
The phosphorus-containing (meth)acrylate (C) used in this embodiment has a (meth)acryloyl group and a monovalent group containing phosphorus and sulfur represented by the following general formula (1).

The structural unit (c) derived from the phosphorus- and sulfur-containing (meth)acrylate (C) improves wear resistance and polarity by introducing a monovalent group containing phosphorus and sulfur into the side chain of the copolymer (X). It is presumed that it plays a role in improving pressure resistance.
Here, since phosphorus and sulfur are elements that cause a decrease in thermal stability, they are elements that are generally not introduced from the viewpoint of ensuring thermal stability. However, while considering the introduction of phosphorus and sulfur from the viewpoint of improving wear resistance and extreme pressure properties, the present inventors discovered that the structural unit (a) derived from alkyl (meth)acrylate (A) and the hydroxyl group By introducing the structural unit (c) derived from the phosphorus- and sulfur-containing (meth)acrylate (C) into the polymer in which the structural unit (b) derived from the containing (meth)acrylate (B) is combined, phosphorus and It has been found that the problem of a decrease in thermal stability due to the introduction of sulfur is alleviated, and the copolymer (X) as a whole becomes a polymer with excellent thermal stability, as well as excellent abrasion resistance and extreme pressure properties.

Note that the phosphorus and sulfur-containing (meth)acrylates (C) may be used alone or in combination of two or more. Therefore, the copolymer (X) may contain one type of structural unit (c) derived from the phosphorus- and sulfur-containing (meth)acrylate (C), or may contain two or more types.

The phosphorus-containing (meth)acrylate (C) has a (meth)acryloyl group as a polymerizable functional group. In this embodiment, the polymerizable functional group of the phosphorus-containing (meth)acrylate (C) is preferably an acryloyl group from the viewpoint of easily adjusting the molecular weight of the copolymer (X).

In the above general formula (1), R ¹ and R ² each independently represent an alkyl group having 1 to 10 carbon atoms.
If the alkyl group does not have the alkyl group, or if the alkyl group has more than 10 carbon atoms, it becomes difficult to obtain the effects of the present invention.

Examples of the alkyl group having 1 to 10 carbon atoms that can be selected as R ¹ and R ² include methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, heptyl group, octyl group, nonyl group, and decyl group. Examples include chain alkyl groups such as. The chain alkyl group may be linear or branched. From the viewpoint of improving the effects of the present invention, the alkyl group preferably has 2 to 8 carbon atoms, more preferably 2 to 6 carbon atoms, still more preferably 2 to 4 carbon atoms, and still more preferably 3 carbon atoms.

Specifically, the phosphorus and sulfur-containing (meth)acrylate (C) is preferably a compound represented by the following general formula (c-1).

In the above general formula (c-1), R ^c1 is a hydrogen atom or a methyl group. Monomers in which R ^c1 is a substituent other than a hydrogen atom or a methyl group are difficult to obtain, and since these monomers have low reactivity, it is also difficult to polymerize them.
Here, in this embodiment, R ^c1 is preferably a hydrogen atom from the viewpoint of making it easier to adjust the molecular weight of the copolymer (X).

In the above general formula (c-1), R ^c2 represents an alkylene group having 2 to 4 carbon atoms.
When the number of carbon atoms in the alkylene group is 1, the polarity becomes high and the oil solubility decreases.
Moreover, when the number of carbon atoms in the alkylene group is 5 or more, the oil solubility increases too much and the adsorption to metals decreases.
Here, the number of carbon atoms in the alkylene group is preferably 2 to 3, more preferably 2, from the viewpoint of easily ensuring appropriate oil solubility and appropriate adsorption to metal.

m2 represents an integer from 0 to 10. When m2 is an integer of 2 or more, a plurality of R ^c2 may be the same or different. Further, the bonding mode between the moieties represented by -(OR ^c2 ) _m2 may be random bonding or block bonding, but from the viewpoint of ease of polymerization, random bonding is preferable.
When m2 is an integer of 11 or more, polarity increases due to the influence of the -(OR ^c2 )- moiety, and oil solubility decreases.
Here, from the viewpoint of easily ensuring appropriate oil solubility, m2 is preferably 1 to 4, more preferably 1 to 2, and still more preferably 1.

In the above general formula (c-1), L ¹ represents a linker.
Linkers that can be selected as L ¹ include, for example, divalent aliphatic hydrocarbon groups having 1 to 4 carbon atoms such as methylene group, ethylene group, propylene group, and butylene group; -O-; -OC(O) -;-O-C(O)-R ^C3 - (R ^C3 is an alkylene group having 2 to 4 carbon atoms), and the like. Among these, -OC(O)-R ^C3 - is preferred as the linker that can be selected as L ¹ .
Further, L ¹ may be a direct bond. That is, when m2=0, the carbon atom of the carbonyl group constituting the (meth)acryloyl group and the sulfur atom of the monovalent group represented by the above general formula (1) may be directly bonded. When m2 is 1 or more, -(OR ^c2 ) _m2 - and the sulfur atom of the monovalent group represented by the above general formula (1) may be directly bonded.

In the above general formula (c-1), R ¹ and R ² are as explained in the above general formula (1), and the preferred ranges are also as explained in the above general formula (1).

<Other monomers>
In addition to the above structural units (a), (b), and (c), the copolymer (X) contains structural units derived from other monomers to the extent that the effects of the present invention are not impaired. You can. Examples of the other monomers include functional group-containing monomers other than monomers (A), (B), and (C). Examples of the other functional group-containing monomers include (meth)acrylates containing functional groups other than monomers (A), (B), and (C).
However, from the viewpoint of improving the effects of the present invention, the copolymer (X) has a total content of structural units derived from functional group-containing monomers other than monomers (A), (B), and (C). Preferably it is less than 50% by weight, more preferably less than 40% by weight, even more preferably less than 30% by weight, even more preferably less than 20% by weight, even more preferably less than 10% by weight, on a constitutional unit basis.

<Content of structural unit (a)>
The content of the structural unit (a) in the copolymer (X) is preferably 50 mass based on the total amount of the copolymer (X) from the viewpoint of ensuring oil solubility and improving the effect of the present invention. % or more, more preferably 60% to 95% by weight, even more preferably 70% to 90% by weight.

<Content of structural unit (b)>
From the viewpoint of improving the effects of the present invention, the content of the structural unit (b) in the copolymer (X) is preferably 1% by mass or more, more preferably 3% by mass, based on the total amount of the copolymer (X). The amount is preferably 6% to 25% by weight, preferably 6% to 25% by weight.

<Content of structural unit (c)>
From the viewpoint of improving the effects of the present invention, the content of the structural unit (c) in the copolymer (X) is preferably 0.1% by mass to 10% by mass based on the total amount of the copolymer (X). , more preferably 0.5% by mass to 5% by mass, still more preferably 0.8% by mass to 3.0% by mass.

<Content ratio [(a)/(b)]>
The copolymer (X) of this embodiment has a content ratio of the structural unit (a) and the structural unit (b) [(a)/( b)] is preferably in a molar ratio of 50/50 to 90/10, more preferably 55/45 to 85/15.

<Sulfur content and phosphorus content of copolymer (X)>
The copolymer (X) of this embodiment has the following characteristics: from the viewpoint of easily ensuring sufficient wear resistance and extreme pressure properties, and from the viewpoint of the balance between the sulfur content in the copolymer (X) and the effects of the present invention. The sulfur content of the copolymer (X) is preferably 0.01% by mass to 2.00% by mass, more preferably 0.02% by mass to 1.50% by mass, based on the total amount of the copolymer (X). %, more preferably 0.04% by mass to 1.00% by mass, even more preferably 0.04% by mass to 0.50% by mass.
In the copolymer (X) of this embodiment, the phosphorus content of the copolymer (X) is set so that the phosphorus content of the copolymer (X) is Based on the total amount of polymer (X), preferably 0.01% by mass to 2.00% by mass, more preferably 0.02% by mass to 1.50% by mass, even more preferably 0.04% by mass to 1.0% by mass. 00% by weight, more preferably 0.04% to 0.50% by weight.
The sulfur content and phosphorus content of the copolymer (X) are determined by dissolving a predetermined amount of the copolymer (X) in an organic solvent (for example, lubricant base oil), and then determining the sulfur content and phosphorus content in the organic solvent. It can be calculated based on the results measured in accordance with JIS-5S-38-03 and the amount of copolymer (X) dissolved in the organic solvent.

<Physical properties of copolymer (X), etc.>
(Mass average molecular weight (Mw), molecular weight distribution (Mw/Mn))
The mass average molecular weight (Mw) of the copolymer (X) of this embodiment is preferably 5,000 to 100,000, more preferably 5,000 to 100,000, from the viewpoint of ensuring oil solubility and improving the effects of the present invention. ,000 to 50,000, more preferably 5,000 to 40,000.
In addition, the molecular weight distribution (Mw/Mn) of the copolymer (X) of the present embodiment is preferably 3.5 or less, more preferably 3.0 or less, from the viewpoint of making it easier to exhibit the effects of the present invention. More preferably, it is 2.5 or less. The molecular weight distribution (Mw/Mn) of the copolymer (X) of this embodiment may be 1.01 or more, 1.3 or more, or 1.5 or more. good.
The mass average molecular weight (Mw) and the molecular weight distribution (Mw/Mn) are values measured or calculated by the method described in the Examples below.

(Polymerization mode)
The polymerization mode of the copolymer (X) of this embodiment is not particularly limited, and may be any of block copolymerization, random copolymerization, and block/random copolymerization. Among these, random copolymerization is preferred from the viewpoint of ease of polymerization reaction.

[Method for producing additive composition for lubricating oil]
The method for producing an additive composition for lubricating oil of the present embodiment includes an alkyl (meth)acrylate (A) represented by the following general formula (a-1) and an alkyl (meth)acrylate (A) represented by the following general formula (b-1). It includes a step (S) of manufacturing a copolymer (X) by polymerizing a hydroxyl group-containing (meth)acrylate (B) and a phosphorus- and sulfur-containing (meth)acrylate (C).
The phosphorus- and sulfur-containing (meth)acrylate (C) has a (meth)acryloyl group and a monovalent group containing phosphorus and sulfur represented by the following general formula (1).

[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. ]

[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 from 1 to 10. When m1 is an integer of 2 or more, a plurality of R ^b2 's may be the same or different. ]

[In the above general formula (1), R ¹ and R ² are each independently an alkyl group having 1 to 10 carbon atoms. ]

Hereinafter, the step (S) of producing the copolymer (X) will be explained in detail.

<Step (S) of producing copolymer (X)>
The manufacturing method (polymerization method) of copolymer (X) is not particularly limited, and it can be manufactured by applying any of the known methods. Examples of such methods include emulsion polymerization, suspension polymerization, and solution polymerization.
Here, from the viewpoint of the use of the copolymer (X) in the present invention, that is, the use as an additive composition for lubricating oil, the method for producing the copolymer (X) (polymerization method) is based on a lubricating oil base. It is preferable to employ a solution polymerization method in which a solvent soluble in oil is used as a solvent.

(Solution polymerization method)
In the solution polymerization method, for example, monomers (A), (B), and (C), as well as a solvent and an initiator are charged into a reactor, the inside of the reactor is purged with nitrogen, and then the reaction is carried out at 60°C to 100°C for 2 hours. The reaction is carried out by stirring and reacting for ~10 hours. Optionally, other monomers besides monomers (A), (B), and (C) are also charged to the reactor.

In addition, the content ratio of each structural unit in copolymer (X) usually corresponds to the ratio (preparation ratio) of each monomer which comprises copolymer (X). Therefore, the blending proportions of monomers (A), (B), and (C) are appropriately determined in consideration of the content proportions of structural units (a), (b), and (c) in copolymer (X). be done.

Examples of solvents used in the solution polymerization method include alcohols such as methanol, ethanol, propanol, 2-propanol, and butanol; hydrocarbons such as benzene, toluene, xylene, and hexane; ethyl acetate, butyl acetate, and isobutyl acetate. Ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone; Ethers such as methoxybutanol, ethoxybutanol, ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, propylene glycol monobutyl ether, dioxane; Mineral oil; Poly-α- Examples include synthetic oils such as olefins, ethylene-α-olefin copolymers, alkylbenzenes, alkylnaphthalenes, polyphenyl ethers, alkyl-substituted diphenyl ethers, polyol esters, dibasic acid esters, hindered esters, monoesters, and GTL base oils.
These may be used alone or in combination of two or more.

Examples of initiators used in the solution polymerization method include 2,2'-azobis(isobutyronitrile), 2,2'-azobis(2-amidinopropane) dihydrochloride, 2,2'-azobis- (N,N-dimethyleneisobutyramidine) dihydrochloride, azo initiators such as 1,1'-azobis(cyclohexyl-1-carbonitrile); hydrogen peroxide; benzoyl peroxide, t-butyl hydroperoxide, Organic peroxides such as cumene hydroperoxide, methyl ethyl ketone peroxide, and perbenzoic acid; persulfates such as sodium persulfate, potassium persulfate, and ammonium persulfate; hydrogen peroxide-Fe ²⁺ redox initiators; other existing radicals Initiators may be mentioned.

In addition, the molecular weight of copolymer (X) is controlled by a known method. For example, the molecular weight of the copolymer (X) can be controlled by the reaction temperature, reaction time, amount of initiator, amount of each monomer charged, type of solvent, use of chain transfer agent, etc.

<Content of copolymer (X) in lubricating oil additive composition>
The additive composition for lubricating oil of the present embodiment has a content of copolymer (X) that can be added to Preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, based on the total amount of the agent composition. Preferably it is 95% by mass or more. Considering the purity of copolymer (X), the content of copolymer (X) is usually less than 99% by mass based on the total amount of the lubricating oil additive composition.
The lubricating oil additive composition of this embodiment may be diluted with a diluting solvent from the viewpoint of solubility with the lubricating base oil and ease of handling. The content of the copolymer (X) in the additive composition for lubricating oil means the content based on the total amount of active ingredients in the additive composition for lubricating oil, excluding the dilution solvent.

<Applications of additive composition for lubricating oil>
The lubricating oil additive composition of this embodiment has excellent wear resistance, extreme pressure properties, and thermal stability. Therefore, it is useful as a load-bearing additive.
Therefore, in this embodiment, a method of using the lubricating oil additive composition as a load-bearing additive is provided.

[Lubricating oil composition]
The lubricating oil composition of this embodiment contains a lubricating oil additive composition containing the copolymer (X) and a lubricating oil base oil.
The content of the lubricating oil additive composition is determined such that the content of the resin component of the copolymer (X) is the same as the total amount of the lubricating oil composition, from the viewpoint of exhibiting the additive effect of the lubricating oil additive composition well. Based on the standard, it is adjusted to preferably 0.3% by mass to 10% by mass, more preferably 0.6% by mass to 6.0% by mass, and even more preferably 1.0% by mass to 5.0% by mass. Ru.
In addition, the content of the lubricating oil additive composition is determined from the viewpoint of exhibiting the additive effect of the lubricating oil additive composition well, and the amount of sulfur derived from the copolymer (X) is determined by the total amount of the lubricating oil composition. Based on the standard, it is preferably 10 mass ppm to 300 mass ppm, more preferably 20 mass ppm to 200 mass ppm, and still more preferably 30 mass ppm to 150 mass ppm.
In addition, when the copolymer (X) contains the structural unit (d) derived from the phosphorus-containing (meth)acrylate (D), from the same viewpoint, the amount of phosphorus derived from the copolymer (X) is Based on the total amount of the composition, preferably 5 ppm to 150 ppm by weight, more preferably 10 ppm to 100 ppm by weight, and still more preferably 15 ppm to 75 ppm by weight.

<Lubricant base oil>
As the lubricating base oil, any general base oil used in lubricating oil compositions can be used without particular limitation. Specifically, for example, one or more types selected from the group consisting of mineral oil and synthetic oil may be mentioned.
The kinematic viscosity at 100° C. of the lubricating base oil is preferably in the range of 1 mm ² /s to 50 mm ² /s, more preferably in the range of 2 mm ² /s to 30 mm ² /s, and 3 mm ² /s More preferably, the speed is in the range of 20 mm ² /s. Further, the viscosity index of the lubricating base oil is preferably 80 or more, more preferably 90 or more, and even more preferably 100 or more.
The kinematic viscosity and viscosity index of the lubricating base oil are values measured or calculated according to JIS K2283:2000.

Specific examples of lubricant base oils are listed below.
Mineral oils include, for example, distillate oil obtained by atmospheric distillation and/or vacuum distillation of paraffinic crude oil, intermediate crude oil, or naphthenic crude oil; refined oil obtained by refining the distillate oil according to a conventional method; oil; etc. Examples of the purification method for obtaining refined oil include solvent dewaxing treatment, hydroisomerization treatment, hydrofinishing treatment, clay treatment, and the like.
Examples of synthetic oils include hydrocarbon oils, aromatic oils, ester oils, and ether oils. Further, as the synthetic oil, GTL (Gas To Liquids) obtained by isomerizing wax (GTL wax, Gas To Liquids WAX) produced from natural gas by the Fischer-Tropsch method or the like may be used.

<Other additives>
The lubricating oil composition of the present embodiment contains an antioxidant, an oily agent, a detergent dispersant, a viscosity index improver, a rust preventive agent, and a metal deactivator within a range that does not inhibit the effects of the above-mentioned lubricating oil additive composition. Other additives such as antifoaming agents and antifoaming agents may also be included. These may be used alone or in combination of two or more.
In addition, in this embodiment, in addition to the lubricating oil additive composition containing the copolymer (X), oxidized Addition for lubricating oil compositions containing one or more additives selected from inhibitors, oiliness agents, detergent dispersants, viscosity index improvers, rust inhibitors, metal deactivators, antifoaming agents, etc. A drug package is also provided.

(Antioxidant)
As the antioxidant, amine antioxidants, phenolic antioxidants, etc. used in conventional lubricating oil compositions can be used. These antioxidants may be used alone or in combination of two or more.
Examples of amine antioxidants include monoalkyldiphenylamine compounds such as monooctyldiphenylamine and monononyldiphenylamine; 4,4'-dibutyldiphenylamine, 4,4'-dipentyldiphenylamine, 4,4'-dihexyldiphenylamine, , 4'-diheptyldiphenylamine, 4,4'-dioctyldiphenylamine, and 4,4'-dinonyldiphenylamine; dialkyldiphenylamine compounds such as tetrabutyldiphenylamine, tetrahexyldiphenylamine, tetraoctyldiphenylamine, and tetranonyldiphenylamine; Polyalkyldiphenylamine compounds; α-naphthylamine, phenyl-α-naphthylamine, butylphenyl-α-naphthylamine, pentylphenyl-α-naphthylamine, hexylphenyl-α-naphthylamine, heptylphenyl-α-naphthylamine, octylphenyl-α-naphthylamine , and naphthylamine compounds such as nonylphenyl-α-naphthylamine.
Examples of phenolic antioxidants include monophenolic compounds such as 2,6-di-tert-butyl-4-methylphenol and 2,6-di-tert-butyl-4-ethylphenol; 4,4' -methylenebis(2,6-di-tert-butylphenol) and 2,2'-methylenebis(4-ethyl-6-tert-butylphenol) and other bisphenol compounds.
The content of the antioxidant may be the minimum amount necessary to maintain the oxidative stability of the lubricating oil composition. Specifically, for example, it is preferably 0.01 to 1% by mass based on the total amount of the lubricating oil composition.

(Oil-based agent)
Examples of the oily agent include aliphatic alcohols; fatty acid compounds such as fatty acids and fatty acid metal salts; ester compounds such as polyol esters, sorbitan esters, and glycerides; and amine compounds such as aliphatic amines.
The content of the oily agent is usually 0.1 to 20% by mass, preferably 0.5 to 10% by mass, based on the total amount of the lubricating oil composition, from the viewpoint of the effect of addition.

(Cleaning dispersant)
Examples of detergent-dispersing agents include metal sulfonates, metal salicylates, metal phenates, and succinimides.
The content of the detergent dispersant is usually 0.01 to 10% by mass, preferably 0.1 to 5% by mass, based on the total amount of the lubricating oil composition, from the viewpoint of the effect of addition.

(Viscosity index improver)
Examples of the viscosity index improver include polymethacrylate, dispersed polymethacrylate, olefin copolymer (e.g., ethylene-propylene copolymer, etc.), dispersed olefin copolymer, styrene copolymer (e.g., styrene-diene hydrogenated copolymers, etc.).
The content of the viscosity index improver is preferably 0.3 to 5% by mass, based on the total amount of the lubricating oil composition.

(anti-rust)
Examples of the rust preventive include metal sulfonates, succinic acid esters, and alkanolamines such as alkylamines and monoisopropanolamines.
The content of the rust inhibitor is usually 0.01 to 5% by mass, preferably 0.03 to 3% by mass, based on the total amount of the lubricating oil composition, from the viewpoint of the effect of addition.

(metal deactivator)
Examples of metal deactivators include benzotriazole and thiadiazole.
The preferred content of the metal deactivator is usually 0.01 to 5% by mass, preferably 0.01 to 1% by mass, based on the total amount of the lubricating oil composition, from the viewpoint of the effect of addition.

(antifoaming agent)
Examples of antifoaming agents include methyl silicone oil, fluorosilicone oil, and polyacrylate.
The content of the antifoaming agent is usually 0.0005 to 0.01% by mass based on the total amount of the lubricating oil composition from the viewpoint of the effect of addition.

<Physical properties of lubricating oil composition>
(Kinematic viscosity, viscosity index)
The 100°C kinematic viscosity of the lubricating oil composition of the present embodiment is preferably 1.0 mm ² /s to 50 mm 2 /s, more preferably 2.0 ^{mm 2 /} s to 30 mm ² /s, even more preferably 3.0 mm. ² /s to 20 mm ² /s.
The viscosity index of the lubricating oil composition of this embodiment is preferably 90 or more, more preferably 100 or more, and still more preferably 110 or more.
The kinematic viscosity and viscosity index of the lubricating oil composition are values measured or calculated according to JIS K2283:2000.

(Abrasion resistance (new oil))
The lubricating oil composition (new oil) of the present embodiment has a wear scar diameter of preferably 0.55 mm or less, more preferably 0.53 mm or less, and still more preferably 0. It is 52 mm or less.

(Abrasion resistance (oil after ISOT test))
The lubricating oil composition (oil after ISOT test) of the present embodiment has a wear scar diameter of preferably 0.55 mm or less, more preferably 0.50 mm or less, and even more preferably is 0.45 mm or less.
Note that the oil after the ISOT test means the oil after forced deterioration by the ISOT test performed by the method described in the Examples.

(Extreme pressure (new oil))
The lubricating oil composition (new oil) of this embodiment has a maximum non-seizure load (LNL) of preferably 392N or more, more preferably 490N, as determined by the shell four-ball test load resistance (EP) test described in the Examples below. That's all.
Further, the fusion load (WL) according to the same test is preferably 1236N or more.

(Extreme pressure property (oil after ISOT test))
The lubricating oil composition (oil after ISOT test) of the present embodiment preferably has a maximum non-seizure load (LNL) of 490 N or more as determined by the shell four-ball test load resistance (EP) test described in the Examples below. .
Further, the fusion load (WL) according to the same test is preferably 1236N or more, more preferably 1569N or more.
Note that the oil after the ISOT test means the oil after forced deterioration by the ISOT test performed by the method described in the Examples.

(thermal stability)
The lubricating oil composition of this embodiment has a sludge generation amount of preferably less than 10 mg/100 mL, more preferably less than 7.0 mg/100 mL, even more preferably 5. It is less than 0 mg/100 mL.

[Method for producing lubricating oil composition]
The method for producing the lubricating oil composition of this embodiment is not particularly limited.
For example, the method for producing a lubricating oil composition of the present embodiment includes a step of mixing the above-mentioned lubricating oil additive composition and a lubricating oil base oil.
There are no particular restrictions on the method for mixing the lubricating oil additive composition and the lubricating oil base oil, but for example, a method that includes a step of blending the lubricating oil additive composition with the lubricating oil base oil can be mentioned. At that time, the other additives mentioned above may also be added at the same time. Further, each component may be mixed in the form of a solution (dispersion) by adding diluting oil or the like. After blending each component, it is preferable to stir and disperse uniformly by a known method.

[Applications of lubricating oil composition]
Since the lubricating oil composition of this embodiment contains the copolymer (X), it has excellent wear resistance, extreme pressure properties, and thermal stability.
Therefore, the lubricating oil composition of this embodiment is, for example, gear oil (manual transmission oil, differential oil, etc.), automatic transmission oil (automatic transmission oil, etc.), continuously variable transmission oil (belt CVT oil, toroidal CVT oil, etc.) Drive system oils such as power steering oils, shock absorber oils, and electric motor oils; Oils for internal combustion engines (engines) such as gasoline engines, diesel engines, and gas engines; Hydraulic oils; Turbine oils; Compressor oils ; Fluid bearing oil; Rolling bearing oil; Refrigerating machine oil, etc., as a lubricating oil composition that can be suitably used for various purposes, and is filled into equipment used in each of these applications to lubricate between the various parts of the equipment. It can be suitably used.

[Lubrication method using lubricating oil composition]
Preferably, the lubricating method using the lubricating oil composition of the present embodiment is a method of filling the lubricating oil composition into equipment used in each of the above-mentioned applications and lubricating between each part of each of the equipment. can be mentioned.

[Grease composition]
The lubricating oil additive composition of this embodiment can also be used by being mixed into a grease composition.
That is, in this embodiment, it is also possible to provide a grease composition containing the above lubricating oil additive composition, a thickener, and a lubricating oil base oil.

[One aspect of the provided invention]
According to one aspect of the present invention, the following [1] to [9] are provided.
[1] A structural unit (a) derived from an alkyl (meth)acrylate (A) represented by the following general formula (a-1) and a hydroxyl group-containing (meth) represented by the following general formula (b-1) Contains a polymethacrylate copolymer (X) containing a structural unit (b) derived from an acrylate (B) and a structural unit (c) derived from a phosphorus- and sulfur-containing (meth)acrylate (C),
The phosphorus- and sulfur-containing (meth)acrylate (C) is an additive composition for lubricating oil, which has a (meth)acryloyl group and a monovalent group containing phosphorus and sulfur represented by the following general formula (1). .

[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. ]

[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 from 1 to 10. When m1 is an integer of 2 or more, a plurality of R ^b2 's may be the same or different. ]

[In the above general formula (1), R ¹ and R ² are each independently an alkyl group having 1 to 10 carbon atoms. ]
[2] The lubricating oil additive composition according to [1] above, wherein the polymethacrylate copolymer (X) has a mass average molecular weight of 5,000 to 100,000.
[3] The content of the structural unit (a) is 50% by mass or more based on all structural units of the polymethacrylate copolymer (X), according to [1] or [2] above. Additive composition for lubricating oil.
[4] Any one of [1] to [3] above, wherein the content of the structural unit (b) is 1% by mass or more based on all structural units of the polymethacrylate copolymer (X). 1. The lubricating oil additive composition according to claim 1.
[5] The content of the structural unit (c) is 0.1% by mass to 10% by mass based on all the structural units of the polymethacrylate copolymer (X), [1] to [2] above. 4]. The lubricating oil additive composition according to any one of [4].
[6] The lubricating oil additive composition according to any one of [1] to [5] above, which is used as a load-bearing additive.
[7] A method of using the lubricating oil additive composition according to any one of [1] to [6] above as a load-bearing additive.
[8] A lubricating oil composition containing the lubricating oil additive composition according to any one of [1] to [6] above and a lubricating oil base oil.
[9] A method for producing a lubricating oil composition, comprising the step of mixing the lubricating oil additive composition according to any one of [1] to [6] above and a lubricating oil base oil.

The present invention will be specifically explained with reference to the following examples, but the present invention is not limited to the following examples.

[Methods for measuring various physical property values]
The properties of each raw material used in each Example and each Comparative Example and the lubricating oil composition of each Example and each Comparative Example were measured according to the procedure shown below.

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

(2) Mass average molecular weight (Mw), molecular weight distribution (Mw/Mn)
Waters'"1515 isocratic HPLC pump", "2414 differential refractive index (RI) detector", one Tosoh column "TSKguardcolumn SuperHZ-L", and two "TSKSSuperMultipore HZ-M" The sample was attached in this order from the upstream side, and the measurement temperature was 40°C, the mobile phase was tetrahydrofuran, the flow rate was 0.35 ml/min, and the sample concentration was 1.0 mg/ml, and the measurements were made in terms of standard polystyrene.

(3) Sulfur content and phosphorus content The sulfur content and phosphorus content of copolymer (X) are determined by dissolving a predetermined amount of copolymer (X) in an organic solvent (lubricating oil base oil). It was calculated based on the results of measuring the amount of sulfur and amount of phosphorus in accordance with JIS-5S-38-03 and the amount of copolymer (X) dissolved in the organic solvent.

[Examples 1 to 6, Comparative Example 1]
The lubricating oil base oil and lubricating oil additive composition shown below were thoroughly mixed in the amounts (mass%) shown in Table 2 to prepare lubricating oil compositions of Examples 1 to 6 and Comparative Example 1, respectively. did.
Details of the lubricant base oil and lubricant additive composition used in Examples 1 to 6 and Comparative Example 1 are as shown below.

<Lubricant base oil>
Mineral oil (150N) classified as Group II by API classification

<Additive composition for lubricating oil>
- Copolymer (X)-1: Produced by the method described in Production Example 1.
- Copolymer (X)-2: Produced by the method described in Production Example 2.
- Copolymer (X)-3: Produced by the method described in Production Example 3.
- Copolymer (X)-4: Produced by the method described in Production Example 4.
- Copolymer (X)-5: Produced by the method described in Production Example 5.
- Copolymer (X)-6: Produced by the method described in Production Example 6.
-IRGALUBE 62 (manufactured by BASF Japan Co., Ltd.): A dithiophosphoric acid ester derivative represented by the following structural formula. In Table 2, it is written as "sulfur phosphorus-containing low molecular compound".

<Production Examples 1 to 6>
(Monomer used in Production Examples 1 to 6)
- "Dodecyl acrylate (DOA)": A compound in the above general formula (a-1) in which R ^a1 is a hydrogen atom and R ^a2 is an n-dodecyl group (an alkyl group having 12 carbon atoms). It was used as alkyl (meth)acrylate (A).
・"2-Hydroxyethyl acrylate (HEA)": In the above general formula (b-1), R ^b1 is a hydrogen atom, R ^b2 is an ethylene group (alkylene group having 2 carbon atoms), m1 = 1, It is a certain compound. It was used as a hydroxyl group-containing (meth)acrylate (B).
- "SPM1": A compound represented by the following structural formula was used. In the compound represented by the following structural formula, in the above general formula (c-1), R ^c1 is a hydrogen atom, R ^c2 is an ethylene group (an alkylene group having 2 carbon atoms), and m2 = 1, L ¹ is -O-C(O)-R ^c3 -, R ^c3 is a propylene group (alkylene group having 3 carbon atoms), and R ¹ and R ² are isobutyl groups (alkyl group having 4 carbon atoms). It is a certain compound. The sulfur content is 15.0% by mass, and the phosphorus content is 7.3% by mass. It was used as phosphorus and sulfur-containing (meth)acrylate (C).

- "SPM2": A compound represented by the following structural formula was used. In the compound represented by the following structural formula, in the above general formula (c-1), R ^c1 is a hydrogen atom, R ^c2 is an ethylene group (an alkylene group having 2 carbon atoms), and m2 = 1, L ¹ is -O-C(O)-R ^c3 -, R ^c3 is an ethylene group (alkylene group having 2 carbon atoms), and R ¹ and R ² are isopropyl groups (alkyl group having 3 carbon atoms); It is a certain compound. The sulfur content is 16.7% by mass, and the phosphorus content is 8.1% by mass. It was used as phosphorus and sulfur-containing (meth)acrylate (C).

- "SPM3": A compound represented by the following structural formula was used. In the compound represented by the following structural formula, in the above general formula (c-1), R ^c1 is a hydrogen atom, R ^c2 is an ethylene group (an alkylene group having 2 carbon atoms), and m2 = 1, L ¹ is -O-C(O)-R ^c3 -, R ^c3 is an ethylene group (alkylene group having 2 carbon atoms), and R ¹ and R ² are ethylene groups (alkyl group having 2 carbon atoms); It is a certain compound. The sulfur content is 18.0% by mass, and the phosphorus content is 8.7% by mass. It was used as phosphorus and sulfur-containing (meth)acrylate (C).

(Synthesis method of SPM1)
IRGALUBE353 (manufactured by BASF Japan Co., Ltd., 13.2 g, 40.2 mmol) and toluene (25 mL) were added to a 200 mL eggplant flask and while stirring at room temperature, thionyl chloride (8.75 g, 74.1 mmol) was added dropwise. . The temperature was raised to 60°C in an oil bath, and the mixture was reacted for 4 hours, followed by heating and concentration under reduced pressure. Dichloromethane (90 mL) was added to the obtained concentrate, hydroxyethyl acrylate (7.00 g, 60.3 mmol) was added dropwise under an ice bath, and the mixture was stirred at room temperature for 3 hours. After the reaction was completed, water was added and the dichloromethane extract was dried over anhydrous magnesium sulfate and concentrated under reduced pressure by heating. The obtained concentrate was purified by silica gel column chromatography to obtain SPM1 (6.52 g, 15.3 mmol).
Note that IRGALUBE353 is a compound represented by the following structural formula.

(Synthesis method of SPM2)
IRGALUBE62 (31.4 g, 100 mmol) and methanol (150 mL) were added to a 1 L eggplant flask, and while stirring at 0° C., 5% aqueous sodium hydroxide solution (200 mL) was added dropwise. After the reaction was completed, 2M aqueous hydrochloric acid solution (150 mL) was added, extracted with ethyl acetate, dried over anhydrous magnesium sulfate, and the resulting concentrate was purified by silica gel column chromatography to obtain the carboxylic acid derivative (24. 8 g, 86.7 mmol) was obtained.
The above carboxylic acid derivative and toluene (54 mL) were added to a 500 mL eggplant flask, and while stirring at room temperature, thionyl chloride (18.9 g, 159.8 mmol) was added dropwise. The temperature was raised to 60°C in an oil bath, and the mixture was reacted for 4 hours, followed by heating and concentration under reduced pressure. Dichloromethane (200 mL) was added to the obtained concentrate, hydroxyethyl acrylate (15.1 g, 130 mmol) was added dropwise under an ice bath, and the mixture was stirred at room temperature for 3 hours. After the reaction was completed, water was added and the dichloromethane extract was dried over anhydrous magnesium sulfate and concentrated under reduced pressure by heating. The obtained concentrate was purified by silica gel column chromatography to obtain SPM2 (36.4 g, 94.9 mmol).

(Synthesis method of SPM3)
Potassium hydroxide (11.2 g, 199 mmol), water (40 mL), chloroform (140 mL), O,O'-diethyl dithiophosphate (32.7 g, 175 mmol), 3-chloropropionic acid (20.0 g, 176 mmol) was added thereto, the temperature was raised to 60°C in an oil bath, and the mixture was reacted for 7 hours. After washing the organic layer with water, the organic layer was dried and concentrated over anhydrous magnesium sulfate to obtain a carboxylic acid derivative (21.6 g, 83.6 mmol).
The above carboxylic acid derivative (10 g, 38.7 mmol) and dichloromethane (50 mL) were added to a 100 mL eggplant flask, and while stirring at 0° C., oxalyl chloride (16.0 g, 125.9 mmol) was added dropwise. After reacting at room temperature for 2 hours, dichloromethane (86 mL) was added to the concentrate obtained by heating and concentrating under reduced pressure, and hydroxyethyl acrylate (6.7 g, 58.1 mmol) was added dropwise in an ice bath. Stir for hours. After the reaction was completed, water was added and the dichloromethane extract was dried over anhydrous magnesium sulfate and concentrated under reduced pressure by heating. The obtained concentrate was purified by silica gel column chromatography to obtain SPM3 (4.88 g, 13.7 mmol).

(Production Example 1: Production of copolymer (X)-1)
In a 200 mL four-necked flask equipped with a thermometer, nitrogen inlet tube, and stirrer, add 33.9 g (137 mmol) of dodecyl acrylate, 10.5 g (90.6 mmol) of 2-hydroxyethyl acrylate, and 0 of SPM1. .43 g (1.0 mmol) and 43.9 g of 2-propanol as a solvent were charged.
Next, the inside of the flask was purged with nitrogen, and after adding 0.18 g of 2,2'-azobis(isobutyronitrile) as an initiator, the temperature was slowly raised while stirring, and the mixture was refluxed at a temperature of 75 to 85°C. The reaction was allowed to proceed for 4 hours, and after the reaction was completed, the solvent was distilled off under reduced pressure to obtain copolymer (X)-1.
Copolymer (X)-1 had a mass average molecular weight (Mw) of 19,800 and a molecular weight distribution (Mw/Mn) of 2.0. Further, the phosphorus content of copolymer (X)-1 was 720 mass ppm, and the sulfur content was 1560 mass ppm.
Copolymer (X)-1 was diluted with mineral oil so that the content of copolymer (X)-1 was 50% by mass, and mixed into lubricating base oil.

(Production Example 2: Production of copolymer (X)-2)
Copolymer (X)-2 was obtained by carrying out the same operation as in Production Example 1 except that 0.44 g (1.1 mmol) of SPM2 was charged instead of SPM1.
Copolymer (X)-2 had a mass average molecular weight (Mw) of 19,700 and a molecular weight distribution (Mw/Mn) of 2.0. Further, the phosphorus content of copolymer (X)-2 was 760 mass ppm, and the sulfur content was 1700 mass ppm.
Copolymer (X)-2 was diluted with mineral oil so that the content of copolymer (X)-2 was 50% by mass, and mixed into lubricating base oil.

(Production Example 3: Production of copolymer (X)-3)
Copolymer (X)-3 was obtained by carrying out the same operation as in Production Example 1 except that 0.44 g (1.2 mmol) of SPM3 was charged instead of SPM1.
The mass average molecular weight (Mw) of copolymer (X)-3 was 19,100, and the molecular weight distribution (Mw/Mn) was 2.0. Further, the phosphorus content of copolymer (X)-3 was 840 mass ppm, and the sulfur content was 1760 mass ppm.
Copolymer (X)-3 was diluted with mineral oil so that the content of copolymer (X)-3 was 50% by mass, and mixed into lubricating base oil.

(Production Example 4: Production of copolymer (X)-4)
The same operation as in Production Example 2 was carried out except that 47.9 g (199 mmol) of dodecyl acrylate, 5.8 g (49.8 mmol) of 2-hydroxyethyl acrylate, and 0.52 g (1.0 mmol) of SPM2 were charged. , Copolymer (X)-4 was obtained.
The mass average molecular weight (Mw) of copolymer (X)-4 was 19,700, and the molecular weight distribution (Mw/Mn) was 2.2. Further, the phosphorus content of copolymer (X)-4 was 760 mass ppm, and the sulfur content was 1660 mass ppm.
Copolymer (X)-4 was diluted with mineral oil so that the content of copolymer (X)-4 was 50% by mass, and mixed into lubricating base oil.

(Production Example 5: Production of copolymer (X)-5)
Copolymer (X)-5 was obtained by carrying out the same operation as in Production Example 2 except that 22.0 g of 2-propanol was added as a solvent.
Copolymer (X)-5 had a mass average molecular weight (Mw) of 34,200 and a molecular weight distribution (Mw/Mn) of 2.3. Further, the phosphorus content of copolymer (X)-5 was 800 mass ppm, and the sulfur content was 1700 mass ppm.
Copolymer (X)-5 was diluted with mineral oil so that the content of copolymer (X)-5 was 50% by mass, and mixed into lubricating base oil.

(Production Example 6: Production of copolymer (X)-6)
Copolymer (X)-6 was obtained by carrying out the same operation as in Production Example 2 except that 144.0 g of 2-propanol was charged as a solvent.
The mass average molecular weight (Mw) of copolymer (X)-6 was 8,700, and the molecular weight distribution (Mw/Mn) was 1.6. Further, the phosphorus content of copolymer (X)-6 was 760 mass ppm, and the sulfur content was 1620 mass ppm.
Copolymer (X)-6 was diluted with mineral oil so that the content of copolymer (X)-6 was 50% by mass, and mixed into lubricating base oil.

Composition of copolymer (X)-1 to copolymer (X)-6, sulfur content and phosphorus content, mass average molecular weight (Mw) of copolymer (X)-1 to copolymer (X)-6 , and molecular weight distribution (Mw/Mn) are shown in Table 1.
In addition, the mass average molecular weight (Mw) is shown in two significant digits.

[Evaluation method]
The tests described below were conducted to evaluate wear resistance, extreme pressure properties, and thermal stability.

<Shell wear test>
The wear resistance of the lubricating oil composition was determined using a shell abrasion tester in accordance with ASTM D 4172, setting the test conditions to be a load of 30 kg, a rotation speed of 1,200 rpm, a temperature of 80°C, and a test time of 30 minutes. was evaluated. The results were expressed as the wear scar diameter (mm) of the test hard ball.
In this test, wear resistance was judged to be good if the wear scar diameter was 0.55 mm or less.

<Shell four-ball test load-bearing (EP) test>
In accordance with ASTM D 2783, the maximum non-seizure load (LNL) and fusion load (WL) were measured using a four-ball tester at a rotation speed of 1,800 rpm and an oil temperature (room temperature: 25 ± 5°C). ) was measured. The larger these values are, the better the extreme pressure properties are.
In this test, if the maximum non-seizure load (LNL) was 392N or more and the fusion load (WL) was 1236N or more, it was determined that the extreme pressure property was good.

<ISOT test>
A copper piece and an iron piece were added as catalysts to the test oil (lubricating oil composition), and an ISOT test in accordance with JIS K 2514-1:2013 was conducted to forcefully degrade the test oil. The test temperature (oil temperature) was 150°C. Then, the amount of sludge (mg/100 mL) was measured for the test oil 24 hours after the start of the ISOT test in accordance with JIS B 9931.
And, if the amount of sludge was less than 10 mg/100 mL, it was determined that the thermal stability was good.

In addition, the above-mentioned shell wear test and shell four-ball test load resistance (EP) test were conducted on the test oil 24 hours after the start of the ISOT test. As with the new oil, it was determined that the wear resistance was good if the wear scar diameter was 0.55 mm or less. Further, if the maximum non-seizure load (LNL) was 392N or more and the fusion load (WL) was 1236N or more, it was determined that the extreme pressure property was good.

The results are shown in Table 2. In Table 2, the numerical value in parentheses for the content of the lubricating oil additive composition means the content in terms of resin content.

From Table 2, the following can be seen.
From the results shown in Examples 1 to 6, copolymer (X)-1, copolymer (X)-2, copolymer (X)-3, copolymer (X)-4, copolymer ( It can be seen that the lubricating oil composition containing X)-5 or copolymer (X)-6 has excellent wear resistance, extreme pressure properties, and thermal stability. Furthermore, it can be seen that even after the ISOT test, it has excellent wear resistance and extreme pressure properties.
On the other hand, the results shown in Comparative Example 1 show that a lubricating oil composition containing a low molecular weight sulfur- and phosphorus-containing compound has insufficient wear resistance and extreme pressure properties, and is clearly inferior in thermal stability.

Claims (9)

A structural unit (a) derived from an alkyl (meth)acrylate (A) represented by the following general formula (a-1) and a hydroxyl group-containing (meth)acrylate (B) represented by the following general formula (b-1). ), and a polymethacrylate copolymer (X) containing a structural unit (c) derived from a phosphorus- and sulfur-containing (meth)acrylate (C),
The phosphorus- and sulfur-containing (meth)acrylate (C) is an additive composition for lubricating oil, which has a (meth)acryloyl group and a monovalent group containing phosphorus and sulfur represented by the following general formula (1). .

[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. ]

[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 from 1 to 10. When m1 is an integer of 2 or more, a plurality of R ^b2 's may be the same or different. ]

[In the above general formula (1), R ¹ and R ² are each independently an alkyl group having 1 to 10 carbon atoms. ] The lubricating oil additive composition according to claim 1, wherein the polymethacrylate copolymer (X) has a mass average molecular weight of 5,000 to 100,000. The lubricating oil additive composition according to claim 1 or 2, wherein the content of the structural unit (a) is 50% by mass or more based on all structural units of the polymethacrylate copolymer (X). thing. The lubricant according to any one of claims 1 to 3, wherein the content of the structural unit (b) is 1% by mass or more based on all the structural units of the polymethacrylate copolymer (X). Additive composition for oil. Any one of claims 1 to 4, wherein the content of the structural unit (c) is 0.1% by mass to 10% by mass based on all the structural units of the polymethacrylate copolymer (X). The additive composition for lubricating oils described in Section 1. The lubricating oil additive composition according to any one of claims 1 to 5, which is used as a load-bearing additive. A method of using the lubricating oil additive composition according to any one of claims 1 to 6 as a load-bearing additive. A lubricating oil composition comprising the lubricating oil additive composition according to any one of claims 1 to 6 and a lubricating oil base oil. A method for producing a lubricating oil composition, comprising the step of mixing the lubricating oil additive composition according to any one of claims 1 to 6 and a lubricating oil base oil.