JP7723934B2 - Lubricating oil additives and lubricating oil compositions - Google Patents

Description

The present invention relates to a lubricating oil additive comprising a methacrylic block copolymer that exhibits friction-reducing effects even at low temperatures, and to a lubricating oil composition containing the copolymer.

In recent years, energy conservation through lubricants has become an important issue from the perspective of protecting the global environment and achieving carbon neutrality. To solve these issues, it is essential to use lubricant additives to improve viscosity index, shear stability, and adjust friction.

In particular, in automotive applications, with the increase in hybrid and plug-in hybrid vehicles, it has become clear that the engine oils and drive oils used in these vehicles have lower oil temperatures than those used in conventional internal combustion engine vehicles. For this reason, lubricants are required to have the ability to improve viscosity index and reduce friction at low temperatures.

Patent Document 1 uses a block copolymer obtained by reversible addition-fragmentation chain transfer polymerization (RAFT) that is composed of a polar block containing amino or hydroxyl groups and a hydrophobic block containing alkyl (meth)acrylate as a lubricating oil composition. However, its shear stability and low-friction effect at low temperatures are unknown.

Patent Document 2 uses a hydroxyl-containing methacrylic polymer obtained by known radical polymerization as a lubricating oil composition. However, the oil film performance is insufficient.

Patent Document 3 uses a commercially available amino group-containing methacrylic viscosity index improver as a lubricating oil additive, but its oil film performance at low temperatures is unknown.

Patent Document 4 uses a hydroxyl-containing acrylic polymer obtained by known radical polymerization as a lubricating oil composition. However, its performance as a viscosity index improver is unknown.

Patent Document 5 uses molybdenum dithiocarbamate (MoDTC) and a hydroxyl-containing acrylic polymer obtained by known radical polymerization as a lubricating oil composition. However, its performance as a viscosity index improver and its effect on reducing friction at low temperatures are unknown.

Patent Document 6 uses an acrylic comb polymer containing amino groups obtained by atom transfer radical polymerization (ATRP) as a lubricating oil composition. However, its low-temperature friction-reducing effect is unclear, and its base oil solubility is insufficient.

Patent 4686444 JP 2009-7562 Patent Publication No. 2012-107143 Patent Publication No. 2013-124266 WO2019/203332A1 Special Table 2020-502344

The present invention provides a lubricating oil additive comprising a methacrylic block copolymer that combines the properties of a viscosity index improver and a friction modifier that is effective even at low temperatures, and a lubricating oil composition containing the copolymer.

As a result of investigations to achieve the above object, the present invention has been completed, including the following aspects.
[1]
A lubricating oil additive comprising a methacrylic block copolymer (C) which comprises a methyl methacrylate polymer block (A) and a methacrylic acid alkyl ester polymer block (B) having an alkyl group having 10 to 36 carbon atoms, and which has a molecular weight distribution (Mw/Mn) of 1.01 to 1.60.
[2]
The lubricating oil additive according to [1], wherein the mass ratio of the methyl methacrylate polymer block (A) in the methacrylic block copolymer (C) is 1 to 50%.
[3]
The lubricating oil additive according to [1] or [2], wherein the weight average molecular weight (Mw) of the methacrylic block copolymer (C) is 5,000 to 500,000.
[4]
The lubricating oil additive according to any one of [1] to [3], wherein the methacrylic block copolymer (C) is a polymer obtained by an anionic polymerization method or an atom transfer radical polymerization method.
[5]
[1] The lubricating oil additive according to any one of [1] to [3], wherein the methacrylic block copolymer (C) is a polymer obtained by (living) anionic polymerization in the presence of organoaluminum.
[6]
A lubricating oil composition comprising the lubricating oil additive according to any one of [1] to [5] and at least one lubricating base oil (D) selected from API Groups III, III+, IV and V.

The present invention makes it possible to reduce friction and improve shear stability of lubricating oils at low temperatures compared to conventional lubricating oil additives. Furthermore, by using a lubricating oil composition containing the lubricating oil additive of the present invention, which has excellent friction-modifying properties, energy savings and extended lubricating oil life can be achieved, reducing the burden on the global environment.

The present invention is described in detail below.

The methacrylic block copolymer (C) used in the present invention is a block copolymer having one or more polymer blocks containing methyl methacrylate units and one or more polymer blocks containing methacrylic acid alkyl ester units having an alkyl group having 10 to 36 carbon atoms.
The lubricating base oil (D) used in the lubricating oil composition of the present invention is API Group III or higher among base oils classified according to the API standards of the American Petroleum Institute (API Groups I to V).
API Group I: Sulfur content 0.03% or more and/or saturated content less than 90%, viscosity index 80-120 (mineral oil)
API Group II: Sulfur content 0.03% or less and saturates 90% or more, viscosity index 80-120 (hydrocracked)
API Group III: Sulfur content 0.03% or less and saturates 90% or more, viscosity index 120 or more (VHVI)
API Group III+: Sulfur content 0.03% or less and saturates 90% or more, viscosity index 135 or more (VHVI)
API Group IV: Polyalphaolefin (synthetic oil)
API Group V: APIs not belonging to API Groups I to IV (vegetable oils, esters, alkylnaphthalenes, PAGs)

The lubricating base oil (D) comprises at least one selected from the group consisting of API Group III, API Group III+, API Group IV, and API Group V. Preferred lubricating base oil (D) is at least one selected from the group consisting of API Group III, API Group III+, and API Group IV, more preferably at least one selected from the group consisting of API Group III and API Group III+, and even more preferably API Group III. API Group III, API Group III+, API Group IV, and API Group V may be represented as GrIII, GrIII+, GrIV, and GrV, respectively, which have the same meaning.
Examples of API Group III to V lubricating base oil (D) products include the following:
API Group III: YUBASE 2, 3, 4, 6, 8 (all manufactured by SK Lubricants), PHAZOL 7, 35 (all manufactured by Exxon Mobil)
API Group III+: YUBASE 4/6 Plus (SK Lubricants Co., Ltd.)
API group IV: SpectraSyn, SpectraSynPlus, SpectraSynUltra (all manufactured by ExxonMobil Corporation)
Furthermore, the Diana Fresia series (Idemitsu Kosan) and the Ultra-S series (S-oil corporation) can also be used.

Examples of the methacrylic acid alkyl ester polymer block unit (B) having an alkyl group with 10 to 36 carbon atoms that constitutes the methacrylic block copolymer (C) together with the methyl methacrylate polymer block unit (A) include n-decyl methacrylate, n-undecyl methacrylate, n-dodecyl methacrylate, n-tridecyl methacrylate, n-tetradecyl methacrylate, n-pentadecyl methacrylate, n-hexadecyl methacrylate, n-heptadecyl methacrylate, n-octadecyl methacrylate (also known as stearyl methacrylate), n-nonadecyl methacrylate, n-eicosyl methacrylate, and n-heneicosyl methacrylate. alkyl methacrylates containing a linear alkyl group having 10 to 36 carbon atoms, such as n-octacosyl, n-docosyl methacrylate, n-tricosyl methacrylate, n-tetracosyl methacrylate, n-pentacosyl methacrylate, n-hexacosyl methacrylate, n-heptacosyl methacrylate, n-octacosyl methacrylate, n-nonacosyl methacrylate, n-triacontyl methacrylate, n-hentriacontyl methacrylate, n-dotriacontyl methacrylate, n-tritriacontyl methacrylate, n-tetratriacontyl methacrylate, n-pentatriacontyl methacrylate, and n-hexatriacontyl methacrylate;
Isodecyl methacrylate, 2,4,6-trimethylheptyl methacrylate, 2-butyloctyl methacrylate, 2-ethyl-n-dodecyl methacrylate, 2-methyl-n-tetradecyl methacrylate, isohexadecyl methacrylate, 2-n-octyl-n-nonyl methacrylate, isooctadecyl methacrylate, 1-n-hexyl-n-tridecyl methacrylate, 2-ethyl-n-heptadecyl methacrylate, isoicosyl methacrylate (also known as 2-n-octyl-n-dodecyl methacrylate), 1-n and units consisting of methacrylic acid alkyl esters containing a branched alkyl group having 10 to 36 carbon atoms, such as 2-n-octyl-n-pentadecyl methacrylate, 2-n-decyl-n-tetradecyl methacrylate, 2-n-dodecyl-n-pentadecyl methacrylate, isotriacontyl methacrylate, 2-n-tetradecyl-n-heptadecyl methacrylate, 2-n-hexadecyl-n-heptadecyl methacrylate, 2-n-hexadecyl-n-icosyl methacrylate, and 2-n-tetradecyl-n-docosyl methacrylate.

Of these methacrylic acid alkyl ester polymer block units (B) having a linear or branched alkyl group having 10 to 36 carbon atoms, from the viewpoint of solubility in API Group III or higher lubricating base oils, methacrylic acid alkyl ester units having an alkyl group having 14 to 30 carbon atoms are preferred, methacrylic acid alkyl ester units having an alkyl group having 16 to 28 carbon atoms are more preferred, and methacrylic acid alkyl ester units having an alkyl group having 16 to 24 carbon atoms are particularly preferred. The methacrylic block copolymer (C) may use only one type of methacrylic acid alkyl ester unit having an alkyl group having 10 to 36 carbon atoms, or two or more types may be contained and mixed and used.
In another preferred embodiment of the present invention, the methacrylic acid alkyl ester polymer block units (B) having a linear or branched alkyl group having 10 to 36 carbon atoms preferably use two or more types of methacrylic acid alkyl ester units, and in this case, the solubility in the lubricating base oil (D) can be improved by using a combination of a methacrylic acid alkyl ester unit having an alkyl group containing 10 to 15 carbon atoms and a methacrylic acid alkyl ester unit having an alkyl group containing 16 to 36 carbon atoms. The mass ratio of the methacrylic acid alkyl ester unit having an alkyl group containing 10 to 15 carbon atoms to the methacrylic acid alkyl ester unit having an alkyl group containing 16 to 36 carbon atoms is preferably 40:60 to 50:50, more preferably 42:58 to 49:51.

The methacrylic copolymer (C) is preferably soluble in a lubricating base oil of API Group III or higher (III, III+, IV) and with a viscosity index of 120 or higher. Here, "soluble" means that when 15 parts by mass of the methacrylic block copolymer (C) is added to 85 parts by mass of the lubricating base oil (D), no insoluble matter of the methacrylic copolymer (C) is found and the appearance is uniform in the temperature range of -20 to 80°C.

The methacrylic block copolymer (C) may contain units derived from (meth)acrylic acid ester monomers other than the above-mentioned alkyl methacrylate esters. Examples of such other (meth)acrylic acid ester monomer units include (meth)acrylic acid esters having an alicyclic alkyl group such as cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, and tricyclododecyl (meth)acrylate; (meth)acrylic acid esters having an aromatic hydrocarbon group such as phenyl (meth)acrylate, benzyl (meth)acrylate, naphthyl (meth)acrylate, and biphenyl (meth)acrylate; methoxymethyl (meth)acrylate, 2-methacrylic acid ester; and (meth)acrylic acid esters having an ether group such as 2-methoxypropyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 2-ethoxypropyl (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, and methoxypolypropylene glycol (meth)acrylate; N,N-dialkyl(meth)acrylamide such as (meth)N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-diisopropyl(meth)acrylamide, and N,N-di-n-butyl(meth)acrylamide; p) acrylamide; (meth)acrylic acid esters having an epoxy group such as glycidyl (meth)acrylate; 1,3-propanediol di(meth)acrylate, 1,3-butanediol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, polyalkylene glycol di(meth)acrylate, bisphenol A Examples include polyfunctional (meth)acrylic acid esters such as Nol A di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, glycerin tri(meth)acrylate, and pentaerythritol tetra(meth)acrylate; (meth)acrylic acid alkyl esters having a linear or branched alkyl group having 2 to 9 carbon atoms; and methyl acrylate; and units consisting of such; acrylic acid alkyl ester units corresponding to the methacrylic acid alkyl ester polymer block unit (B).

There are no particular restrictions on the methacrylic block copolymer (C) as long as it contains methyl methacrylate units and (meth)acrylic acid alkyl ester units having an alkyl group of 10 to 36 carbon atoms. However, from the viewpoint of solubility in the lubricating base oil (D), it preferably contains 5 to 34 mass% methyl methacrylate units and 95 to 66 mass% (meth)acrylic acid alkyl ester units having a linear alkyl group of 10 to 36 carbon atoms. Furthermore, the content of the methyl methacrylate units in the methacrylic block copolymer (C) is more preferably 10 to 32 mass%, and even more preferably 15 to 30 mass%. Furthermore, the content of the (meth)acrylic acid alkyl ester units having a linear alkyl group of 10 to 36 carbon atoms in the methacrylic block copolymer (C) is more preferably 68 to 90 mass%, and even more preferably 70 to 85 mass%.

The weight average molecular weight Mw of the methacrylic block copolymer (C) is preferably 5,000 or more, more preferably 5,000 to 500,000, even more preferably 10,000 to 300,000, and particularly preferably 15,000 to 200,000.
The number average molecular weight Mn of the methacrylic block copolymer (C) is preferably 4,500 or more, more preferably 4,500 to 450,000, even more preferably 9,000 to 270,000, and particularly preferably 13,000 to 180,000.

The methacrylic block copolymer (C) preferably has a ratio of Mw to number-average molecular weight (hereinafter referred to as "Mn") (Mw/Mn, hereinafter referred to as the "molecular weight distribution") of 1.01 to 1.6, more preferably 1.01 to 1.4, even more preferably 1.02 to 1.4, particularly preferably 1.05 to 1.4, and most preferably 1.05 to 1.3. When used as a lubricating oil additive, such as a friction modifier or viscosity index improver, the methacrylic block copolymer (C) is soluble in API Group III, III+, or IV lubricating base oil (D), exhibiting excellent viscosity index improvement when used as a viscosity index improver and excellent shear viscosity stability when used in a lubricating oil composition. The Mw and Mn depend, for example, on the amount of hydroxyl-containing compounds and polymerization inhibitors in the raw materials, including (meth)acrylic acid alkyl ester monomers, used in the production of the methacrylic block copolymer (C). Mw and Mn are polystyrene-equivalent molecular weight values determined by GPC measurement.

Preferred methods for producing the methacrylic block copolymer (C) include atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer polymerization (RAFT), nitroxide-mediated polymerization (NMP), iodine transfer polymerization, polymerization using heavy heteroelements (such as organotellurium, antimony, and bismuth), boron-mediated polymerization, catalyst transfer polymerization (CCT), and controlled radical polymerization (OMRP) using a carbon bond with a metal such as cobalt or titanium as the dormant species, as well as anionic polymerization (typically anionic polymerization with high living properties). Furthermore, anionic polymerization is more preferred because it produces a methacrylic block copolymer (C) with high thermal stability. Examples of such anionic polymerization methods include a method in which an organic alkali metal compound is used as a polymerization initiator to carry out anionic polymerization in the presence of a mineral acid salt such as an alkali metal or alkaline earth metal salt (see JP-B-7-25859), a method in which an organic alkali metal compound is used as a polymerization initiator to carry out anionic polymerization in the presence of an organoaluminum compound (see JP-A-11-335432), and a method in which an organic rare earth metal complex or a metallocene metal complex is used as a polymerization initiator (see JP-A-6-93060). Among these, the method in which an organic alkali metal compound is used as a polymerization initiator to carry out anionic polymerization in the presence of an organoaluminum compound is particularly preferred because it produces polymers with a smaller Mw/Mn ratio, which results in good shear viscosity stability when used as a viscosity index improver, and it produces polymers with high syndiotacticity, which results in a high viscosity index improvement effect when used as a viscosity index improver.

A method of anionic polymerization in the presence of an organoaluminum compound using an organic alkali metal compound as a polymerization initiator, which is preferably employed as a method for producing the methacrylic block copolymer (C), is, for example, a method of anionic polymerization in the presence of an organic alkali metal compound using an organic lithium compound as the organic alkali metal compound and an organoaluminum compound represented by the following general formula (1):
AlR ¹ R ² R ³ (1)
(In general formula (1), R ¹ , R ² and R ³ each independently represent an alkyl group which may have a substituent, a cycloalkyl group which may have a substituent, an aryl group which may have a substituent, an aralkyl group which may have a substituent, an alkoxyl group which may have a substituent, an aryloxy group which may have a substituent or an N,N-disubstituted amino group, or R ¹ represents any of the groups described above, and R ² and R ³ together represent an arylenedioxy group which may have a substituent.)
and, if necessary, in the presence of an organoaluminum compound represented by the formula (I), a (meth)acrylic acid ester is polymerized in the presence of an ether such as dimethyl ether, dimethoxyethane, diethoxyethane, or 12-crown-4; or a nitrogen-containing compound such as triethylamine, N,N,N',N'-tetramethylethylenediamine, N,N,N',N'',N''-pentamethyldiethylenetriamine, 1,1,4,7,10,10-hexamethyltriethylenetetramine, pyridine, or 2,2'-dipyridyl in the reaction system.

Examples of organolithium compounds that can be used in the above-mentioned anionic polymerization method include alkyllithiums and alkyldilithiums such as methyllithium, ethyllithium, n-propyllithium, isopropyllithium, n-butyllithium, sec-butyllithium, isobutyllithium, tert-butyllithium, n-pentyllithium, n-hexyllithium, tetramethylenedilithium, pentamethylenedilithium, and hexamethylenedilithium; aryllithiums and aryldilithiums such as phenyllithium, m-tolyllithium, p-tolyllithium, xylyllithium, and lithium naphthalene; One or more of the following can be used: aralkyllithiums and aralkyldilithiums such as benzyllithium, diphenylmethyllithium, trityllithium, 1,1-diphenyl-3-methylpentyllithium, α-methylstyryllithium, and dilithium produced by the reaction of diisopropenylbenzene with butyllithium; lithium amides such as lithium dimethylamide, lithium diethylamide, and lithium diisopropylamide; and lithium alkoxides such as methoxylithium, ethoxylithium, n-propoxylithium, isopropoxylithium, n-butoxylithium, sec-butoxylithium, tert-butoxylithium, pentyloxylithium, hexyloxylithium, heptyloxylithium, octyloxylithium, phenoxylithium, 4-methylphenoxylithium, benzyloxylithium, and 4-methylbenzyloxylithium.

In addition, examples of organoaluminum compounds represented by the above general formula (1) include trialkylaluminums such as trimethylaluminum, triethylaluminum, triisobutylaluminum, and tri-n-octylaluminum; dialkylphenoxyaluminums such as dimethyl(2,6-di-tert-butyl-4-methylphenoxy)aluminum, dimethyl(2,6-di-tert-butylphenoxy)aluminum, diethyl(2,6-di-tert-butyl-4-methylphenoxy)aluminum, diethyl(2,6-di-tert-butylphenoxy)aluminum, diisobutyl(2,6-di-tert-butyl-4-methylphenoxy)aluminum, and diisobutyl(2,6-di-tert-butylphenoxy)aluminum; methylbis(2,6-di-tert-butyl-4-methylphenoxy)aluminum; aluminum, methylbis(2,6-di-tert-butylphenoxy)aluminum, ethyl[2,2'-methylenebis(4-methyl-6-tert-butylphenoxy)]aluminum, ethylbis(2,6-di-tert-butyl-4-methylphenoxy)aluminum, ethylbis(2,6-di-tert-butylphenoxy)aluminum, ethyl[2,2'-methylenebis(4-methyl-6-tert-butylphenoxy)]aluminum, isobutylbis Alkyldiphenoxyaluminums such as (2,6-di-tert-butyl-4-methylphenoxy)aluminum, isobutylbis(2,6-di-tert-butylphenoxy)aluminum, and isobutyl[2,2'-methylenebis(4-methyl-6-tert-butylphenoxy)]aluminum; methoxybis(2,6-di-tert-butyl-4-methylphenoxy)aluminum, and methoxybis(2,6-di-tert-butylphenoxy)aluminum; aluminum, methoxy[2,2'-methylenebis(4-methyl-6-tert-butylphenoxy)]aluminum, ethoxybis(2,6-di-tert-butyl-4-methylphenoxy)aluminum, ethoxybis(2,6-di-tert-butylphenoxy)aluminum, ethoxy[2,2'-methylenebis(4-methyl-6-tert-butylphenoxy)]aluminum, isopropoxybis(2,6-di-tert-butyl-4-methylphenoxy) One or more of the following can be used: aluminum; alkoxydiphenoxyaluminums such as isopropoxybis(2,6-di-tert-butylphenoxy)aluminum and isopropoxy[2,2'-methylenebis(4-methyl-6-tert-butylphenoxy)]aluminum; and triphenoxyaluminums such as tris(2,6-di-tert-butyl-4-methylphenoxy)aluminum and tris(2,6-diphenylphenoxy)aluminum. Among these, isobutylbis(2,6-di-tert-butyl-4-methylphenoxy)aluminum, isobutylbis(2,6-di-tert-butylphenoxy)aluminum, and isobutyl[2,2'-methylenebis(4-methyl-6-tert-butylphenoxy)]aluminum are particularly preferred because they are easy to handle and can promote polymerization of (meth)acrylic acid esters without deactivation under relatively mild temperature conditions.

Methacrylic block copolymer (C) can be obtained, for example, by adding a polymerization terminator to the polymerization reaction solution to terminate the polymerization reaction. In the case of anionic polymerization, examples of the polymerization terminator include protic compounds such as water, methanol, acetic acid, and hydrochloric acid. The amount of polymerization terminator used is not particularly limited, but is typically in the range of 1 to 100 times the molar amount of the polymerization initiator used.

If aluminum derived from the organoaluminum compound used remains in the solution of methacrylic copolymer (C) after anionic polymerization termination, it may cause a deterioration in the physical properties of methacrylic copolymer (C) and materials using it. Therefore, it is preferable to remove the aluminum derived from the organoaluminum compound after polymerization completion. Effective methods for removing the aluminum include washing the polymerization reaction solution after adding the polymerization terminator with an acidic aqueous solution, subjecting it to adsorption using an adsorbent such as an ion exchange resin, or separating it by precipitation.

The lubricating oil used in this invention is not particularly limited as long as it is a lubricating base oil that meets API standards, but mineral oil or polyalphaolefin-based synthetic oil is preferred, and mineral oil is more preferred. Examples of mineral oils that can be used include SK Oil Lubricants' YUBASE 4 (API Group III, viscosity index 122), YUBASE 4 Plus (API Group III+, viscosity index 136), YUBASE 6 (API Group III, viscosity index 131), YUBASE 6 Plus (API Group III+, viscosity index 145), and YUBASE 8 (API Group III, viscosity index 128). Examples of synthetic oils that can be used include ExxonMobil's Spectrasyn 4 (API Group IV, viscosity index 126), Spectrasyn 5 (API Group IV, viscosity index 138), Spectrasyn 6 (API Group IV, viscosity index 138), Spectrasyn 8 (API Group IV, viscosity index 139), Spectrasyn 10 (API Group IV, viscosity index 147), and Spectrasyn 100 (API Group IV, viscosity index 170), all of which are commercially available lubricating base oils.

The methacrylic block copolymer (C) of the present invention is one in which, when dissolved in lubricating base oil (D) at a mass ratio of 15:85, no insoluble matter is observed after standing at 0°C for 24 hours. From the viewpoint of ease of handling of the resulting lubricating base oil solution, the mass of the methacrylic copolymer (C) in the methacrylic copolymer solution obtained by dissolving the methacrylic copolymer (C) in the lubricating base oil (D) is preferably 10% by mass or more and 50% by mass or less, more preferably 15% by mass or more and 25% by mass or less.

Lubricating oil compositions containing the methacrylic block copolymer (C) of the present invention can be suitably used as engine oils (for gasoline, diesel, etc.), drive system oils [gear oils (manual transmission oils, differential oils, etc.)], automatic transmission oils [ATF (Automatic Transmission Fluid), CVTF (Continuously Variable Transmission Fluid)]], hydraulic oils (power steering oils, shock absorber oils), etc. Among these, engine oils, drive system oils, and hydraulic oils are preferred. Engine oils and drive oils are particularly preferred.

The lubricating oil composition of the present invention may contain other optional components, such as other types of friction modifiers, viscosity index improvers, pour point depressants, oiliness agents, antioxidants, detergents, dispersants, antioxidants, antifoaming agents, demulsifiers, and corrosion inhibitors, as needed.

The lubricating base oil solution containing the methacrylic block copolymer (C) of the present invention may further include a step of adding other additives. Examples of additives include antioxidants, heat degradation inhibitors, light stabilizers, UV absorbers, lubricants, mold release agents, polymer processing aids, antistatic agents, flame retardants, dyes and pigments, light diffusing agents, organic dyes, matting agents, impact resistance modifiers, fluorescent materials, corrosion inhibitors, rust inhibitors, pour point depressants, demulsifiers, metal deactivators, antifoaming agents, and extreme pressure agents.

The block copolymer (C) contained in the polymer solution of the present invention has a narrow molecular weight distribution and excellent mechanical properties such as shear viscosity stability. Therefore, the methacrylic copolymer (C) of the present invention can be used in a variety of applications, including lubricating oil additives including viscosity index improvers, polyolefin modifiers, pressure-sensitive adhesives, adhesives, primers, surface functional coating agents such as hard coats, and tire modifiers.

The present invention will be specifically explained below using examples and comparative examples, but the present invention is not limited to the following examples. Furthermore, the chemicals used in the following examples and comparative examples were dried and purified using conventional methods.

In the following examples and comparative examples, the measuring instruments used to analyze the polymers and the methods for evaluating the polymers as lubricating oil additives are also described.
(1) Measurement of number average molecular weight (Mn), weight average molecular weight (Mw), and molecular weight distribution (Mw/Mn) by gel permeation chromatography (GPC) GPC device: HLC-8320, manufactured by Tosoh Corporation
Detector: differential refractive index detector Column: Two TSKgel SuperMultipore HZM-M columns and a SuperHZ4000 column, both manufactured by Tosoh Corporation, connected in series, were used.
Eluent: tetrahydrofuran Eluent flow rate: 0.35 ml/min Column temperature: 40°C
Calibration curve: Created using data from 10 standard polystyrenes. (2) Measurement of monomer conversion rate by gas chromatography (GC) Equipment: Shimadzu Gas Chromatograph GC-14A
Detector: Flame ionization detector (FID)
Carrier gas: Helium Spirit ratio: 30.0
Flow rate: total flow rate 78.9 mL/min, column flow rate 2.54 mL/min, linear velocity 37.0/sec, purge flow rate 0.3 mL/min. Column: GL Sciences INERTCAP1 (df = 0.4 μm, inner diameter 0.25 mm × length 60 m)
Analysis conditions: injection 240°C, detector 300°C, 50°C (held for 0 minutes) → 10°C/min → 280°C (held for 7 minutes)
(3) Measurement of kinematic viscosity and calculation of viscosity index: Measurement was carried out in accordance with JIS K2283.
(4) Measurement of Shear Viscosity Decrease Rate As an index of shear stability, the shear viscosity decrease rate was calculated in accordance with JPI-5S-29.
(5) Solubility Evaluation The lubricating base oil solution containing the block copolymer was visually observed for the presence or absence of insoluble matter after 24 hours at 20°C, and the case where no insoluble matter was found was evaluated as "○", and the case where insoluble matter was found was evaluated as "×".
(6) Oil Film Thickness Measurement The oil film thickness measurement was carried out under the following conditions.
・Device: Ball-on-disk type EHL tester (oil film thickness measurement mode)
- Slip rate: 0%
- Ball material: JIS SUJ2
-Disc material: Hard glass -Peripheral speed: 0.001 to 0.005 m/s
Load: 14N (average Hertzian pressure 0.24GPa)
・Temperature: Room temperature (20-23℃)
(7) Measurement of Traction Coefficient The traction coefficient measurement was carried out under the following conditions.
・Device: Ball-on-disk type EHL tester (traction measurement mode)
- Slip rate: 5%
- Ball material: JIS SUJ2
-Disc material: Hard glass -Peripheral speed: 0.004 to 0.05 m/s
Load: 14N (average Hertzian pressure 0.24GPa)
・Temperature: Room temperature (20-23℃)
(8) Measurement of Friction Coefficient Measurement of friction coefficient was carried out under the following conditions.
・Device: Ball-on-disk type reciprocating friction and wear tester ・Ball material: JIS SUJ2
-Disc material: JIS SUJ2
Load: 100N (1.45GPa)
・Stroke: 1mm
Frequency: 5Hz
・Temperature: 50℃

(Production Example 1)
A three-way stopcock was attached to a thoroughly dried 1 L three-neck flask, and the inside was purged with nitrogen. Then, at room temperature, 566 g of toluene, 1.39 g (6.0 mmol) of 1,1,4,7,10,10-hexamethyltriethylenetetramine, and 13 g of a 0.45 M toluene solution of isobutylbis(2,6-di-t-butyl-4-methylphenoxy)aluminum were added, followed by 3.5 g of a mixed solution of cyclohexane and n-hexane containing 5.5 mmol of sec-butyllithium. Subsequently, 30 g of methyl methacrylate was added. The reaction solution was initially yellow, but became colorless after stirring for 1 hour. At this point, 0.5 g of the reaction solution was collected in a sampling vessel containing a small amount of methanol for analysis. GC and GPC measurements of the reaction solution showed a 100% conversion of methyl methacrylate, a weight-average molecular weight (Mw) of 8,300, a number-average molecular weight (Mn) of 7,600, and a molecular weight distribution (Mw/Mn) of 1.10. Subsequently, 70 g of a mixture containing 43% by mass of stearyl methacrylate and 57% by mass of lauryl methacrylate was added as a raw material. The reaction solution was initially yellow, but became colorless after stirring for 1 hour. At this point, 0.5 g of the reaction solution was collected in a sampling vessel containing a small amount of methanol for analysis. GC measurements of the reaction solution showed a 100% conversion of stearyl methacrylate, a methacrylic acid alkyl ester monomer, and a 100% conversion of lauryl methacrylate. 3.6 g of 30% aqueous acetic acid was added to the resulting solution at room temperature to terminate the polymerization. The solution was heated at 70°C for 3 hours to precipitate metal salts. The solution was allowed to stand overnight, and the supernatant was collected to obtain a toluene solution with a methacrylic block copolymer concentration of 15% by mass. The resulting reaction solution was poured into a beaker containing 5000 mL of methanol to obtain a precipitate. This was vacuum dried at 80°C for 24 hours to obtain 90 g of a cake-like polymer. GPC measurement of the resulting methacrylic block copolymer revealed a weight-average molecular weight (Mw) of 21,000, a number-average molecular weight (Mn) of 19,300, and a molecular weight distribution (Mw/Mn) of 1.09.

(Production Example 2)
A three-way stopcock was attached to a thoroughly dried 1 L three-neck flask, and the inside was purged with nitrogen. Then, at room temperature, 566 g of toluene, 1.39 g (6.0 mmol) of 1,1,4,7,10,10-hexamethyltriethylenetetramine, and 13 g of a 0.45 M toluene solution of isobutylbis(2,6-di-t-butyl-4-methylphenoxy)aluminum were added, followed by 3.5 g of a mixed solution of cyclohexane and n-hexane containing 5.5 mmol of sec-butyllithium. Subsequently, 100 g of a mixture containing 30% by mass of methyl methacrylate, 30% by mass of stearyl methacrylate, and 40% by mass of lauryl methacrylate was added as a raw material. The reaction solution was initially yellow, but became colorless after stirring for 1 hour. At this point, 0.5 g of the reaction solution was collected in a sampling vessel containing a small amount of methanol for analysis. GC and GPC measurements of the reaction solution showed that the conversion rates of methyl methacrylate, stearyl methacrylate, and lauryl methacrylate were each 100%. 3.6 g of 30% aqueous acetic acid was added to the resulting solution at room temperature to terminate the polymerization. The solution was heated at 70°C for 3 hours to precipitate metal salts. After allowing the solution to stand overnight, the supernatant was collected, yielding a toluene solution with a 15% by mass concentration of methacrylic random copolymer. The resulting reaction solution was poured into a beaker containing 5000 mL of methanol to obtain a precipitate. This was vacuum dried at 80°C for 24 hours to obtain 90 g of a cake-like polymer. GPC measurement of the resulting methacrylic random copolymer revealed a weight-average molecular weight (Mw) of 18,700, a number-average molecular weight (Mn) of 17,000, and a molecular weight distribution (Mw/Mn) of 1.10.

(Production Example 3)
The same procedure as in Production Example 2 was repeated, except that 100 g of methyl methacrylate was added. GC measurement of the reaction solution showed that the conversion of methyl methacrylate was 100%. GPC measurement of the resulting methacrylic copolymer showed that it had a weight average molecular weight (Mw) of 20,000, a number average molecular weight (Mn) of 18,500, and a molecular weight distribution (Mw/Mn) of 1.08.

Example 1
A lubricating oil composition was prepared by mixing the resin obtained in Production Example 1 with an API Class Gr III base oil (YUBASE 4), and the composition was evaluated according to the evaluation methods described above. The results are shown in Table 1.

<Comparative Example 1>
A lubricating oil composition was prepared in the same manner as in Example 1, except that the resin obtained in Production Example 2 was used, and evaluated according to the evaluation methods described above. The results are shown in Table 1.

<Comparative Example 2>
The same procedure as in Example 1 was carried out except that an API Class Gr I base oil (solvent refined mineral oil) was used. The results are shown in Table 1.

<Comparative Example 3>
The same procedure as in Example 1 was carried out except that the resin obtained in Production Example 3 was used. The results are shown in Table 1.

<Comparative reference example>
The API classification Gr III base oil (YUBASE 4) was used as is. The results are shown in Table 1.

Claims (5)

A lubricating oil composition comprising: a lubricating oil additive comprising a methacrylic block copolymer (C) having a molecular weight distribution (Mw/Mn) of 1.01 to 1.60, the methacrylic block copolymer (C) comprising a methyl methacrylate polymer block (A) and a methacrylic acid alkyl ester polymer block (B) in which the mass ratio of methacrylic acid alkyl ester units in the alkyl group having 10 to 15 carbon atoms to methacrylic acid alkyl ester units in the alkyl group having 16 to 36 carbon atoms is 40:60 to 50:50; and at least one lubricating oil base oil (D) selected from the group consisting of API Group III, III+, and IV . 2. The lubricating oil composition according to claim 1, wherein the mass ratio of the methyl methacrylate polymer block (A) in the methacrylic block copolymer (C) is 1 to 50%. 3. The lubricating oil composition according to claim 1, wherein the methacrylic block copolymer (C) has a weight average molecular weight (Mw) of 5,000 to 500,000. The lubricating oil composition according to any one of claims 1 to 3, wherein the methacrylic block copolymer (C) is a polymer obtained by anionic polymerization or atom transfer radical polymerization. The lubricating oil composition according to any one of claims 1 to 3, wherein the methacrylic block copolymer (C) is a polymer obtained by (living) anionic polymerization in the presence of an organoaluminum compound.