Grease composition and method for producing grease composition

Abstract

Provided is a grease composition, including: a base oil (A); and a thickener (B), wherein the base oil (A) contains one or more kinds selected from the group consisting of: the following component (A1); and the following component (A2): ·component (A1): an ester of a polyol (A11) having 3 to 6 hydroxy groups and a branched fatty acid (A12) having 14 to 20 carbon atoms; and ·component (A2): such an alkyl naphthalene that a temperature at which a mass thereof reduces by 3% in gas chromatography distillation in conformity with ASTM D7500 is 450°C or more, and wherein the thickener (B) contains one or more kinds selected from the group consisting of: the following component (B1); and the following component (B2): ·component (B1): melamine cyanurate; and ·component (B2): a premade urea.

Description

Technical Field

[0001] The present invention relates to a grease composition and a method of producing a grease composition.Background Art

[0002] For example, a fluorine grease composition using a perfluoropolyether (PFPE) as a base oil and using a polytetrafluoroethylene (PTFE) as a thickener has been known as a grease composition to be used in a semiconductor-producing apparatus or the like. In addition, in PTL 1, there is a proposal of a grease composition including: a base oil containing an ester oil or a fluorine-free ether oil; and a thickener containing at least a urea compound and a thickener having self-lubricity.Citation ListPatent Literature

[0003] PTL 1: JP 2011-202061 ASummary of InventionTechnical Problem

[0004] However, a fluorine grease composition using a fluorine oil such as a perfluoropolyether (PFPE) as a base oil may have insufficient lubricity, and hence its improvement has been required.

[0005] In addition, in a semiconductor-producing apparatus, for example, some kinds of treatment, such as film formation and etching, are performed under a temperature as high as 200°C or more. Under such high temperature, a grease composition is required to have thermal stability as well.

[0006] The present invention has been made in view of such requirements, and an object of the present invention is to provide a grease composition excellent in lubricity and thermal stability.Solution to Problem

[0007] According to the present invention, there are provided the following items [1] and [2]. [1] A grease composition, including: a base oil (A); and a thickener (B), wherein the base oil (A) contains one or more kinds selected from the group consisting of: the following component (A1); and the following component (A2): ˙component (A1): an ester of a polyol (A11) having 3 to 6 hydroxy groups and a branched fatty acid (A12) having 14 to 20 carbon atoms; and ˙component (A2): such an alkyl naphthalene that a temperature at which a mass thereof reduces by 3% in gas chromatography distillation in conformity with ASTM D7500 is 450°C or more, and wherein the thickener (B) contains one or more kinds selected from the group consisting of: the following component (B1); and the following component (B2): ˙component (B1): melamine cyanurate; and ˙component (B2): a premade urea. [2] A method of producing a grease composition, including a step (S) of mixing a base oil (A) and a thickener (B), wherein the step (S) includes blending one or more kinds selected from the group consisting of: the following component (A1); and the following component (A2) as the base oil (A): ˙component (A1): an ester of a polyol (A11) having 3 to 6 hydroxy groups and a branched fatty acid (A12) having 14 to 20 carbon atoms; and ˙component (A2): such an alkyl naphthalene that a temperature at which a mass thereof reduces by 3% in gas chromatography distillation in conformity with ASTM D7500 is 450°C or more, and blending one or more kinds selected from the group consisting of: the following component (B1); and the following component (B2) as the thickener (B): ˙component (B1): melamine cyanurate; and ˙component (B2): a premade urea. Advantageous Effects of Invention

[0008] According to the present invention, the grease composition excellent in lubricity and thermal stability can be provided.Description of Embodiments

[0009] The upper limit values and lower limit values of numerical ranges described herein may be arbitrarily combined. For example, when the range of "from A to B" and the range of "from C to D" are described as numerical ranges, the numerical range of "from A to D" and the numerical range of "from C to B" are also included in the scope of the present invention.

[0010] In addition, the numerical range of "from a lower limit value to an upper limit value" described herein means that a physical property value is the lower limit value or more and the upper limit value or less unless otherwise stated.

[0011] In addition, in this description, the numerical values of Examples are numerical values that may each be used as an upper limit value or a lower limit value.[Aspect of Grease Composition]

[0012] A grease composition according to an embodiment of the present invention includes a base oil (A) and a thickener (B).

[0013] The base oil (A) contains one or more kinds selected from the group consisting of: the following component (A1); and the following component (A2): ˙component (A1): an ester of a polyol (A11) having 3 to 6 hydroxy groups and a branched fatty acid (A12) having 14 to 20 carbon atoms; and ˙component (A2): such an alkyl naphthalene that a temperature at which a mass thereof reduces by 3% in gas chromatography distillation in conformity with ASTM D7500 is 450°C or more.

[0014] In addition, the thickener (B) contains one or more kinds selected from the group consisting of: the following component (B1); and the following component (B2): ˙component (B1): melamine cyanurate; and ˙component (B2): a premade urea.

[0015] The inventors of the present invention have made extensive investigations with a view to solving the above-mentioned problems.

[0016] As a result, the inventors have found that the grease composition including the above-mentioned base oil (A) and the above-mentioned thickener (B) is excellent in lubricity and thermal stability.

[0017] The inventors of the present invention have further made various investigations on the basis of the above-mentioned finding, and have completed the present invention.

[0018] Although the grease composition of this embodiment may include only the base oil (A) and the thickener (B), the composition may further include any other component except the base oil (A) and the thickener (B).

[0019] In the grease composition of this embodiment, the total content of the base oil (A) and the thickener (B) is preferably from 90 mass% to 100 mass%, more preferably from 95 mass% to 100 mass% with respect to the total amount of the grease composition.

[0020] The respective components to be incorporated into the grease composition of this embodiment are described in detail below.<Base Oil (A)>

[0021] The grease composition of this embodiment includes the base oil (A).

[0022] In addition, the base oil (A) contains one or more kinds selected from the group consisting of: the following component (A1); and the following component (A2): ˙component (A1): an ester of a polyol (A11) having 3 to 6 hydroxy groups and a branched fatty acid (A12) having 14 to 20 carbon atoms; and ˙component (A2): such an alkyl naphthalene that the temperature at which a mass thereof reduces by 3% in gas chromatography distillation in conformity with ASTM D7500 is 450°C or more.

[0023] When the base oil (A) containing one or more kinds selected from the group consisting of: the component (A1); and the component (A2) is used together with the thickener (B), a grease composition excellent in lubricity and thermal stability can be obtained.

[0024] The phrase "one or more kinds selected from the group consisting of: the component (A1); and the component (A2)" means "one or more kinds selected from the components (A1)," "one or more kinds selected from the components (A2)," or a "combination of one or more kinds selected from the components (A1) and one or more kinds selected from the components (A2)."

[0025] In the grease composition of this embodiment, from the viewpoint of, for example, improving the effect of the present invention, the "one or more kinds selected from the group consisting of: the component (A1); and the component (A2)" are preferably "one or more kinds selected from the components (A1)," or "one or more kinds selected from the components (A2)."

[0026] In addition, from the viewpoint of providing a grease composition excellent in low dust generation property while improving the effect of the present invention, the "one or more kinds selected from the group consisting of: the component (A1); and the component (A2)" are preferably "one or more kinds selected from the components (A2)."

[0027] Herein, from the viewpoint of improving the effect of the present invention, the content of the "one or more kinds selected from the group consisting of: the component (A1); and the component (A2)" is preferably from 50 mass% to 100 mass%, more preferably from 60 mass% to 100 mass%, still more preferably from 70 mass% to 100 mass%, still further more preferably from 80 mass% to 100 mass%, yet still further more preferably from 90 mass% to 100 mass%, even more preferably from 95 mass% to 100 mass%, still even more preferably from 99 mass% to 100 mass%, yet still even more preferably 100 mass% with respect to the total amount of the base oil (A).

[0028] In addition, from the viewpoint of providing a grease composition excellent in low dust generation property while improving the effect of the present invention, the content of the "one or more kinds selected from the components (A2)" is preferably from 50 mass% to 100 mass%, more preferably from 60 mass% to 100 mass%, still more preferably from 70 mass% to 100 mass%, still further more preferably from 80 mass% to 100 mass%, yet still further more preferably from 90 mass% to 100 mass%, even more preferably from 95 mass% to 100 mass%, still even more preferably from 99 mass% to 100 mass%, yet still even more preferably 100 mass% with respect to the total amount of the base oil (A).

[0029] In addition, the content of the base oil (A) is preferably from 40 mass% to 90 mass%, more preferably from 45 mass% to 85 mass% with respect to the total amount of the grease composition.

[0030] The component (A1) and the component (A2) are described in detail below.<<Component (A1)>>

[0031] The component (A1) is an ester of a polyol (A11) having 3 to 6 hydroxy groups and a branched fatty acid (A12) having 14 to 20 carbon atoms.

[0032] When the base oil (A) contains the component (A1), a grease composition excellent in thermal stability can be obtained. In addition, a grease composition that hardly volatilizes (hereinafter also referred to as "low volatility") even under a high vacuum can be obtained.

[0033] Although the component (A1) may be a partial ester or may be a full ester, from the viewpoint of providing a grease composition that is more excellent in thermal stability and low volatility, the component preferably contains a full ester. The content of the full ester in the component (A1) is preferably 90 mass% or more, more preferably 95 mass% or more, still more preferably 97 mass% or more with respect to the total amount of the component (A1).

[0034] The polyol (A11) and the branched fatty acid (A12) are described in detail below.(Polyol (A11))

[0035] The polyol (A11) is a polyol having 3 to 6 hydroxy groups.

[0036] When the polyol having 3 to 6 hydroxy groups is used as an alcohol component for forming the ester, the thermal stability and low volatility of the component (A1) can be made excellent.

[0037] Specific examples of the polyol having 3 to 6 hydroxy groups include: trihydric alcohols (polyols each having 3 hydroxy groups), such as glycerin, trimethylolethane, trimethylolpropane, and trimethylolnonane; and tetrahydric to hexahydric alcohols (polyols each having 4 to 6 hydroxy groups), such as pentaerythritol, ditrimethylolpropane, dipentaerythritol, sorbitol, and mannitol.

[0038] Among them, a tetrahydric to hexahydric alcohol is preferred from the viewpoint of increasing the molecular weight of the component (A1) to facilitate an improvement in low volatility thereof. In addition, among the tetrahydric to hexahydric alcohols, pentaerythritol is preferred from the viewpoint of improving the thermal stability and the low volatility. That is, the polyol (A11) preferably contains pentaerythritol. When the polyol (A11) contains pentaerythritol, the thermal stability of the component (A1) is assumed to be easily improved because of, for example, suppression of the molecular cleavage of an ester, which includes pentaerythritol and the branched fatty acid (A12), resulting from its intramolecular condensation reaction, and effective protection of an ester group by the alkyl group of the branched fatty acid (A12).

[0039] The content of pentaerythritol is preferably from 50 mass% to 100 mass%, more preferably from 60 mass% to 100 mass%, still more preferably from 70 mass% to 100 mass%, still further more preferably from 80 mass% to 100 mass%, yet still further more preferably from 90 mass% to 100 mass%, even more preferably from 95 mass% to 100 mass%, still even more preferably from 99 mass% to 100 mass%, yet still even more preferably 100 mass% with respect to the total amount of the polyol (A11).(Branched Fatty Acid (A12))

[0040] The branched fatty acid (A12) is a branched fatty acid having 14 to 20 carbon atoms.

[0041] When the branched fatty acid having 14 to 20 carbon atoms is used as a fatty acid component for forming the ester, the thermal stability and low volatility of the component (A1) can be made excellent. In addition, the fluidity of the component (A1) can be improved, and the viscosity index thereof can be increased.

[0042] In addition, the number of the branches of the branched fatty acid having 14 to 20 carbon atoms is preferably 1 from the viewpoint of improving the thermal stability and the viewpoint of increasing the viscosity index.

[0043] Preferred specific examples of the branched fatty acid having 14 to 20 carbon atoms and having 1 branch include branched saturated fatty acids, such as butyloctanoic acid, hexyldecanoic acid, and octyldodecanoic acid.

[0044] Among them, hexyldecanoic acid is preferred from the viewpoint of improving, for example, the thermal stability and fluidity of the ester. In addition, among the hexyldecanoic acids, hexyldecanoic acid having a branch at its α-position (carbon atom adjacent to a carboxy group) is preferred from the viewpoint of further improving, for example, the thermal stability and the fluidity. That is, the branched fatty acid (A12) preferably contains a branched fatty acid, which has 14 to 20 carbon atoms, has 1 branch, and has the branch at its α-position.

[0045] The content of the branched fatty acid, which has 14 to 20 carbon atoms, has 1 branch, and has the branch at its α-position, is preferably from 50 mass% to 100 mass%, more preferably from 60 mass% to 100 mass%, still more preferably from 70 mass% to 100 mass%, still further more preferably from 80 mass% to 100 mass%, yet still further more preferably from 90 mass% to 100 mass%, even more preferably from 95 mass% to 100 mass%, still even more preferably from 99 mass% to 100 mass%, yet still even more preferably 100 mass% with respect to the total amount of the branched fatty acid (A12).<<Component (A2)>>

[0046] The component (A2) is such an alkyl naphthalene that the temperature at which a mass thereof reduces by 3% in gas chromatography distillation in conformity with ASTM D7500 is 450°C or more.

[0047] When the base oil (A) contains the component (A2), a grease composition excellent in thermal stability can be obtained. In addition, a grease composition having low volatility can be obtained.

[0048] The alkyl naphthalene is a compound obtained by substituting at least one hydrogen atom of a naphthalene ring with an alkyl group. In addition, when such alkyl naphthalene that the temperature at which a mass thereof reduces by 3% in gas chromatography distillation in conformity with ASTM D7500 is 450°C or more is used, a grease composition excellent in thermal stability (and low volatility) can be obtained.

[0049] The temperature at which the mass of the alkyl naphthalene reduces by 3% is preferably 455°C or more, more preferably 460°C or more, still more preferably 470°C or more from the viewpoint of further improving the thermal stability (and the low volatility).

[0050] The 40°C kinematic viscosity of the alkyl naphthalene is preferably from 75 mm 2< / s to 400 mm 2< / s, more preferably from 100 mm 2< / s to 350 mm 2< / s, still more preferably from 150 mm 2< / s to 300 mm 2< / s from the viewpoint of further improving the thermal stability (and the low volatility).

[0051] The term "40°C kinematic viscosity" as used herein means a value measured in conformity with JIS K 2283:2000.<Thickener (B)>

[0052] The grease composition of this embodiment includes the thickener (B).

[0053] In addition, the thickener (B) contains one or more kinds selected from the group consisting of: the following component (B1); and the following component (B2): ˙component (B1): melamine cyanurate; and ˙component (B2): a premade urea.

[0054] When the thickener (B) containing one or more kinds selected from the group consisting of: the component (B1); and the component (B2) is used together with the base oil (A), a grease composition, which is excellent in thermal stability, has low volatility, and is excellent in lubricity, can be obtained.

[0055] The phrase "one or more kinds selected from the group consisting of: the component (B1); and the component (B2)" means "one or more kinds selected from the components (B1)," "one or more kinds selected from the components (B2)," or a "combination of one or more kinds selected from the components (B1) and one or more kinds selected from the components (B2)."

[0056] In the grease composition of this embodiment, from the viewpoint of, for example, improving the effect of the present invention, the "one or more kinds selected from the group consisting of: the component (B1); and the component (B2)" are preferably "one or more kinds selected from the components (B1)," or "one or more kinds selected from the components (B2)."

[0057] In addition, from the viewpoint of providing a grease composition excellent in low dust generation property while improving the effect of the present invention, the "one or more kinds selected from the group consisting of: the component (B1); and the component (B2)" are preferably "one or more kinds selected from the components (B1)."

[0058] Herein, from the viewpoint of improving the effect of the present invention, the content of the "one or more kinds selected from the group consisting of: the component (B1); and the component (B2)" is preferably from 50 mass% to 100 mass%, more preferably from 60 mass% to 100 mass%, still more preferably from 70 mass% to 100 mass%, still further more preferably from 80 mass% to 100 mass%, yet still further more preferably from 90 mass% to 100 mass%, even more preferably from 95 mass% to 100 mass%, still even more preferably from 99 mass% to 100 mass%, yet still even more preferably 100 mass% with respect to the total amount of the thickener (B).

[0059] In addition, from the viewpoint of providing a grease composition excellent in low dust generation property while improving the effect of the present invention, the content of the "one or more kinds selected from the components (B1)" is preferably from 50 mass% to 100 mass%, more preferably from 60 mass% to 100 mass%, still more preferably from 70 mass% to 100 mass%, still further more preferably from 80 mass% to 100 mass%, yet still further more preferably from 90 mass% to 100 mass%, even more preferably from 95 mass% to 100 mass%, still even more preferably from 99 mass% to 100 mass%, yet still even more preferably 100 mass% with respect to the total amount of the thickener (B).

[0060] In addition, the content of the thickener (B) is preferably from 5 mass% to 60 mass%, more preferably from 10 mass% to 55 mass% with respect to the total amount of the grease composition.

[0061] The component (B1) and the component (B2) are described in detail below.<<Component (B1)>>

[0062] The component (B1) is melamine cyanurate.

[0063] When melamine cyanurate is mixed with the base oil (A), melamine cyanurate functions as a thickener, and a grease composition is prepared. In addition, melamine cyanurate is extremely suitable as a thickener for preparing a grease composition to be used in a semiconductor-producing apparatus because melamine cyanurate is free of any metal content. In addition, melamine cyanurate is excellent in thermal stability, and can improve the lubricity of the grease composition.

[0064] Melamine cyanurate is an organic salt formed of melamine and cyanuric acid, and has a graphite structure.

[0065] With regard to the particle diameter of melamine cyanurate, its average particle diameter is preferably 5.0 µm or less, more preferably 4.0 µm or less, still more preferably 3.0 µm or less, still further more preferably 2.5 µm or less, yet still further more preferably 2.0 µm or less. In addition, although the lower limit value of the particle diameter of melamine cyanurate is not particularly limited, the particle diameter is typically 0.005 µm or more.

[0066] The term "particle diameter of melamine cyanurate" as used herein means a 50% particle diameter (volume median particle diameter, D 50 ) on a scattering intensity basis calculated from a dispersed particle diameter distribution, which is measured by a dynamic light scattering method (photon correlation method) at 25°C and analyzed by a CONTIN method.

[0067] When the component (B1) is used alone as the thickener (B), the content of the component (B1) is preferably from 20 mass% to 60 mass%, more preferably from 25 mass% to 55 mass% with respect to the total amount of the grease composition.<<Component (B2)>>

[0068] The component (B2) is a premade urea.

[0069] At the time of the production of a grease composition, the following has been generally performed: an amine and an isocyanate are loaded into a base oil, and the materials are caused to react with each other to synthesize a urea compound functioning as a thickener in the base oil. In other words, the urea compound serving as a thickener is synthesized in the base oil for forming the grease composition in a production process for the grease composition.

[0070] However, in the case of such method, an unreacted amine and / or an unreacted isocyanate may remain in the grease composition. An investigation made by the inventors of the present invention has revealed that such low-molecular weight compound is responsible for a reduction in thermal stability of the grease composition.

[0071] In view of the foregoing, in this embodiment, an attempt is made to prepare the grease composition by using a urea compound synthesized in advance instead of synthesizing a urea compound in a production process for the grease composition, and mixing the urea compound into the base oil. Such urea compound is referred to as "premade urea."

[0072] Although the urea compound for forming the premade urea only needs to be a compound having a urea bond, a diurea compound having two urea bonds is preferred, and a diurea compound represented by the following general formula (b2-1) is more preferred.         R 1< -NHCONH-R 3< -NHCONH-R 2<      (b2-1)

[0073] In the general formula (b2-1), R 1< and R 2< each independently represent a monovalent hydrocarbon group having 6 to 24 carbon atoms. R 1< and R 2< may be identical to or different from each other. R 3< represents a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms.

[0074] Although the number of the carbon atoms of the monovalent hydrocarbon group that may be selected as each of R 1< and R 2< in the general formula (b2-1) is from 6 to 24, the number is preferably from 6 to 20, more preferably from 6 to 18.

[0075] In addition, examples of the monovalent hydrocarbon group that may be selected as each of R 1< and R 2< include a saturated or unsaturated, monovalent chain hydrocarbon group, a saturated or unsaturated, monovalent alicyclic hydrocarbon group, and a monovalent aromatic hydrocarbon group.

[0076] Examples of the monovalent saturated chain hydrocarbon group include linear or branched alkyl groups each having 6 to 24 carbon atoms, and specific examples thereof include a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, an octadecyl group, an octadecenyl group, a nonadecyl group, and an icosyl group.

[0077] Examples of the monovalent unsaturated chain hydrocarbon group include linear or branched alkenyl groups each having 6 to 24 carbon atoms, and specific examples thereof include a hexenyl group, a heptenyl group, an octenyl group, a nonenyl group, a decenyl group, an undecenyl group, a dodecenyl group, a tridecenyl group, a tetradecenyl group, a pentadecenyl group, a hexadecenyl group, a heptadecenyl group, an octadecenyl group, a nonadecenyl group, an icosenyl group, an oleyl group, a geranyl group, a farnesyl group, and a linoleyl group.

[0078] The monovalent saturated chain hydrocarbon groups and the monovalent unsaturated chain hydrocarbon groups may be linear or branched.

[0079] Examples of the monovalent saturated alicyclic hydrocarbon group include: cycloalkyl groups, such as a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, and a cyclononyl group; and cycloalkyl groups each substituted with an alkyl group having 1 to 6 carbon atoms (preferably a cyclohexyl group substituted with an alkyl group having 1 to 6 carbon atoms), such as a methylcyclohexyl group, a dimethylcyclohexyl group, an ethylcyclohexyl group, a diethylcyclohexyl group, a propylcyclohexyl group, an isopropylcyclohexyl group, a 1-methyl-propylcyclohexyl group, a butylcyclohexyl group, a pentylcyclohexyl group, a pentyl-methylcyclohexyl group, and a hexylcyclohexyl group.

[0080] Examples of the monovalent unsaturated alicyclic hydrocarbon group include: cycloalkenyl groups, such as a cyclohexenyl group, a cycloheptenyl group, and a cyclooctenyl group; and cycloalkenyl groups each substituted with an alkyl group having 1 to 6 carbon atoms (preferably a cyclohexenyl group substituted with an alkyl group having 1 to 6 carbon atoms), such as a methylcyclohexenyl group, a dimethylcyclohexenyl group, an ethylcyclohexenyl group, a diethylcyclohexenyl group, and a propylcyclohexenyl group.

[0081] Examples of the monovalent aromatic hydrocarbon group include a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a diphenylmethyl group, a diphenylethyl group, a diphenylpropyl group, a methylphenyl group, a dimethylphenyl group, an ethylphenyl group, and a propylphenyl group.

[0082] Although the number of the carbon atoms of the divalent aromatic hydrocarbon group that may be selected as R 3< in the general formula (b2-1) is from 6 to 18, the number is preferably from 6 to 15, more preferably from 6 to 13.

[0083] Examples of the divalent aromatic hydrocarbon group that may be selected as R 3< include a phenylene group, a diphenylmethylene group, a diphenylethylene group, a diphenylpropylene group, a methylphenylene group, a dimethylphenylene group, and an ethylphenylene group.

[0084] Among them, a phenylene group, a diphenylmethylene group, a diphenylethylene group, or a diphenylpropylene group is preferred, and a diphenylmethylene group is more preferred.

[0085] With regard to the particle diameter of the premade urea, its average particle diameter is preferably 5.0 µm or less, more preferably 4.0 µm or less, still more preferably 3.0 µm or less, still further more preferably 2.5 µm or less, yet still further more preferably 2.0 µm or less. In addition, although the lower limit value of the particle diameter of the premade urea is not particularly limited, the particle diameter is typically 0.005 µm or more.

[0086] The term "particle diameter of the premade urea" as used herein means a 50% particle diameter (volume median particle diameter, D 50 ) on a scattering intensity basis calculated from a dispersed particle diameter distribution, which is measured by a dynamic light scattering method (photon correlation method) at 25°C and analyzed by a CONTIN method.

[0087] When the component (B2) is used alone as the thickener (B), the content of the component (B2) is preferably from 5 mass% to 45 mass%, more preferably from 10 mass% to 40 mass%, still more preferably from 15 mass% to 35 mass% with respect to the total amount of the grease composition.

[0088] The urea compound for forming the premade urea may be typically obtained by causing a diisocyanate and a monoamine to react with each other in an appropriate solvent.

[0089] Examples of the diisocyanate include diphenylene diisocyanate, 4,4'-diphenylmethane diisocyanate, and tolylene diisocyanate.

[0090] The monoamine is, for example, an amine corresponding to a saturated or unsaturated, monovalent chain hydrocarbon group, a saturated or unsaturated, monovalent alicyclic hydrocarbon group, or a monovalent aromatic hydrocarbon group represented by each of R 1< and R 2< in the general formula (b2-1), and examples thereof include: chain hydrocarbon amines, such as octylamine, dodecylamine, octadecylamine, and octadecenylamine; alicyclic hydrocarbon amines such as cyclohexylamine; aromatic hydrocarbon amines, such as aniline and toluidine; and mixed amines obtained by mixing those amines.

[0091] Examples of the solvent for synthesizing the urea compound include various organic solvents, such as dichloromethane and toluene.

[0092] The urea compound obtained by the above-mentioned synthesis process may be provided as the component (B2) by: washing the compound with the solvent once or more to remove an unreacted raw material; removing the solvent after the removal of the unreacted raw material; and then appropriately subjecting the washed product to fine pulverization treatment by a usual method.<Other Component>

[0093] The grease composition of this embodiment may further include any other component except the base oil (A) and the thickener (B) to the extent that the incorporation of such component does not deviate from the gist of the present invention.

[0094] Examples of the other component include: a base oil that does not correspond to the base oil (A); an antioxidant; and a viscosity index improver.

[0095] The other components may be used alone or in combination thereof.

[0096] The total content of the other component in the grease composition of this embodiment is preferably from 0 mass% to 10 mass%, more preferably from 0 mass% to 5.0 mass%, still more preferably from 0 mass% to 2.0 mass% with respect to the total amount of the grease composition.

[0097] The content of the base oil that does not correspond to the base oil (A) is preferably as small as possible from the viewpoint of improving the effect of the present invention. Specifically, the content of the base oil that does not correspond to the base oil (A) is preferably less than 10 parts by mass, more preferably less than 1 part by mass, still more preferably less than 0.1 part by mass with respect to 100 parts by mass of the base oil (A).

[0098] Examples of the base oil that does not correspond to the base oil (A) include a mineral oil and a diester.

[0099] That is, the content of one or more kinds of base oils selected from the group consisting of: the mineral oil; and the diester is preferably as small as possible, and a specific content thereof preferably falls within the above-mentioned ranges.(Metal Atom-containing Compound)

[0100] In the grease composition of this embodiment, the content of a metal atom-containing compound is preferably adjusted to as small a value as possible.

[0101] This is because of the following reason: when the grease composition including the metal atom-containing compound scatters in a semiconductor-producing apparatus to adhere to a semiconductor product in the semiconductor-producing apparatus, an operational failure resulting from a metal atom incorporated into the metal atom-containing compound occurs to significantly affect the yield of the semiconductor product.

[0102] From such viewpoint, the content of the metal atom derived from the metal atom-containing compound in the grease composition of this embodiment is preferably less than 1.0 mass%, more preferably less than 0.1 mass%, still more preferably less than 0.01 mass%, still further more preferably less than 0.001 mass% with respect to the total amount of the grease composition.

[0103] The content of the metal atom derived from the metal atom-containing compound described above may also be referred to as "content of the metal atom in the grease composition" because the base oil (A) and the thickener (B) are each substantially free of any metal atom.

[0104] Examples of the metal atom include: alkali metal atoms, such as a lithium atom and a sodium atom; alkaline earth metal atoms, such as a calcium atom and a magnesium atom; and transition metal atoms, such as a zinc atom and a molybdenum atom.

[0105] Examples of the metal atom-containing compound include: a metal-based soap and a metal-based complex soap such as a lithium complex soap to be blended as thickeners, the soaps being each obtained by saponifying a carboxylic acid or an ester thereof with a hydroxide of an alkali metal, an alkaline earth metal, or aluminum; and a metal salt and a metal oxide to be blended as a metal-based dispersant, a metal-based detergent, a metal-based extreme pressure agent, and a metal-based rust inhibitor.

[0106] That is, the content of metal atoms derived from one or more kinds of metal atom-containing compounds selected from the group consisting of the above-mentioned components is preferably as small as possible, and a specific content thereof preferably falls within the above-mentioned ranges.(Fluorine Atom-containing Compound)

[0107] In the grease composition of this embodiment, the content of a fluorine atom-containing compound is preferably adjusted to as small a value as possible from, for example, the viewpoint of improving the lubricity of the composition and the viewpoint of complying with PFAS regulations.

[0108] From such viewpoint, the content of a fluorine atom derived from the fluorine atom-containing compound in the grease composition of this embodiment is preferably less than 1.0 mass%, more preferably less than 0.1 mass%, still more preferably less than 0.01 mass%, still further more preferably less than 0.001 mass% with respect to the total amount of the grease composition.

[0109] The content of the fluorine atom derived from the fluorine atom-containing compound described above may also be referred to as "content of the fluorine atom in the grease composition" because the base oil (A) and the thickener (B) are each substantially free of any fluorine atom.

[0110] Specific examples of the fluorine atom-containing compound include: a perfluoropolyether (PEPE) to be blended as a base oil; a polytetrafluoroethylene (PTFE) to be blended as a thickener; and a fluorinated silicone-based compound to be blended as an antifoaming agent.

[0111] That is, the content of fluorine atoms derived from one or more kinds of fluorine atom-containing compounds selected from the group consisting of the above-mentioned components is preferably as small as possible, and a specific content thereof preferably falls within the above-mentioned ranges.[Physical Property of Grease Composition]

[0112] The grease composition of this embodiment preferably satisfies the following physical properties.<Thermal Stability>

[0113] The thermal stability of the grease composition of this embodiment (temperature at which a mass thereof reduces by 1%) measured by a method described in Examples to be described later is preferably 250°C or more.<Lubricity>

[0114] The wear mark diameter of the grease composition of this embodiment measured by a method described in Examples to be described later is preferably 600 µm or less, more preferably 500 µm or less, still more preferably 450 µm or less.<Low Dust Generation Property>

[0115] The number of dust particles generated by the grease composition of this embodiment, which is measured by a method described in Examples to be described later, is preferably 1,200 or less, more preferably 1,000 or less, still more preferably 800 or less, still further more preferably 500 or less, yet still further more preferably 300 or less.[Method of producing Grease Composition]

[0116] A method of producing a grease composition according to an embodiment of the present invention is not particularly limited.

[0117] For example, the method of producing a grease composition of this embodiment includes a step (S) of mixing a base oil (A) and a thickener (B).

[0118] In addition, the step (S) includes blending one or more kinds selected from the group consisting of: the following component (A1); and the following component (A2) as the base oil (A): ˙component (A1): an ester of a polyol (A11) having 3 to 6 hydroxy groups and a branched fatty acid (A12) having 14 to 20 carbon atoms; and ˙component (A2): such an alkyl naphthalene that a temperature at which a mass thereof reduces by 3% in gas chromatography distillation in conformity with ASTM D7500 is 450°C or more, and blending one or more kinds selected from the group consisting of: the following component (B1); and the following component (B2) as the thickener (B): ˙component (B1): melamine cyanurate; and ˙component (B2): a premade urea.

[0119] A method of mixing (kneading) the base oil (A) and the thickener (B) is, for example, a method including using a roll mill.[Application of Grease Composition]

[0120] The grease composition of this embodiment is excellent in lubricity and thermal stability.

[0121] Accordingly, the lubricating oil composition of this embodiment may be used in a wide range of applications where lubricity and thermal stability are required. The composition may be suitably used in a semiconductor-producing apparatus among them. More specifically, the grease composition of this embodiment may be suitably used for lubricating a driving portion under a high-vacuum and high-temperature environment such as a vacuum chamber in the semiconductor-producing apparatus. Examples of the driving portion include, but not necessarily limited to, a linear motion mechanism, and a speed reducer and a speed increaser.

[0122] Examples of the semiconductor-producing apparatus include: an apparatus that performs physical vapor deposition (PVD); and an apparatus that performs chemical vapor deposition (CVD).

[0123] Examples of the physical vapor deposition include: vacuum vapor deposition; sputtering; ion plating; and ion implantation including using any one of various ion guns. Examples of the vacuum vapor deposition include electron beam vapor deposition, ion-assisted electron beam vapor deposition, and arc vapor deposition in addition to general resistance heating-type vapor deposition. Those kinds of physical vapor deposition may be used in combination as appropriate.

[0124] Examples of the chemical vapor deposition include thermal CVD, plasma CVD, photo-CVD, epitaxial CVD, and atomic layer CVD. Those kinds of chemical vapor deposition may be used in combination as appropriate, or may each be used in combination with the physical vapor deposition as appropriate.

[0125] In addition, the grease composition of this embodiment may be suitably used in each of, for example, devices mounted on apparatus to be used in outer space serving as a high-vacuum environment, such as an artificial satellite, a probe, and a moon rover.[One Aspect of the Present Invention to be provided]

[0126] According to one aspect of the present invention, there are provided the following items [1] to [8]. [1] A grease composition, including: a base oil (A); and a thickener (B), wherein the base oil (A) contains one or more kinds selected from the group consisting of: the following component (A1); and the following component (A2): ˙component (A1): an ester of a polyol (A11) having 3 to 6 hydroxy groups and a branched fatty acid (A12) having 14 to 20 carbon atoms; and ˙component (A2): such an alkyl naphthalene that a temperature at which a mass thereof reduces by 3% in gas chromatography distillation in conformity with ASTM D7500 is 450°C or more, and wherein the thickener (B) contains one or more kinds selected from the group consisting of: the following component (B1); and the following component (B2): ˙component (B1): melamine cyanurate; and ˙component (B2): a premade urea. [2] The grease composition according to the above-mentioned item [1], wherein the polyol (A11) contains pentaerythritol. [3] The grease composition according to the above-mentioned item [1] or [2], wherein the branched fatty acid (A12) contains a branched fatty acid, which has 1 branch and has the branch at α-position thereof. [4] The grease composition according to any one of the above-mentioned items [1] to [3], wherein a total content of the base oil (A) and the thickener (B) is from 90 mass% to 100 mass% with respect to a total amount of the grease composition. [5] The grease composition according to any one of the above-mentioned items [1] to [4], wherein the base oil (A) contains one or more kinds selected from the components (A2), and wherein the thickener (B) contains one or more kinds selected from the components (B1). [6] The grease composition according to any one of the above-mentioned items [1] to [5], wherein a content of the thickener (B) is from 5.0 mass% to 60 mass% with respect to a total amount of the grease composition. [7] The grease composition according to any one of the above-mentioned items [1] to [6], wherein the grease composition is used in a semiconductor-producing apparatus. [8] A method of producing a grease composition, including a step (S) of mixing a base oil (A) and a thickener (B), wherein the step (S) includes blending one or more kinds selected from the group consisting of: the following component (A1); and the following component (A2) as the base oil (A): ˙component (A1): an ester of a polyol (A11) having 3 to 6 hydroxy groups and a branched fatty acid (A12) having 14 to 20 carbon atoms; and ˙component (A2): such an alkyl naphthalene that a temperature at which a mass thereof reduces by 3% in gas chromatography distillation in conformity with ASTM D7500 is 450°C or more, and blending one or more kinds selected from the group consisting of: the following component (B1); and the following component (B2) as the thickener (B): ˙component (B1): melamine cyanurate; and ˙component (B2): a premade urea. Examples

[0127] The present invention is specifically described by way of Examples below. However, the present invention is not limited to Examples below.[Methods of measuring various Physical Property Values]

[0128] The respective properties of raw materials used in Examples and Comparative Examples were measured in accordance with the following procedures.(1) Physical Property of Alkyl Naphthalene

[0129] The temperature at which the mass of an alkyl naphthalene reduced by 3% in gas chromatography distillation in conformity with ASTM D7500 was measured.(2) Average Particle Diameter of Melamine Cyanurate

[0130] A 50% particle diameter (volume median particle diameter, D 50 ) on a scattering intensity basis calculated from a dispersed particle diameter distribution, which was measured by a dynamic light scattering method (photon correlation method) at 25°C and analyzed by a CONTIN method, was used.(3) Average Particle Diameter of Premade Urea

[0131] A 50% particle diameter (volume median particle diameter, D 50 ) on a scattering intensity basis calculated from a dispersed particle diameter distribution, which was measured by a dynamic light scattering method (photon correlation method) at 25°C and analyzed by a CONTIN method, was used.(4) 40°C Viscosity

[0132] A 40°C viscosity was measured in conformity with JIS K 2283:2000.[Raw Material and the Like]

[0133] Raw materials and the like used for preparing a grease composition in this Example are described below.<Base Oil (A)>

[0134] ·"Component (A1)": a full ester (pentaerythritol tetra(2-hexyldecanoate), ISOCARB Ester 1605, manufactured by Sasol Ltd.) of pentaerythritol and 2-hexyldecanoic acid (number of carbon atoms: 16, branching position: α-position, number of branches: 1) represented by the following structural formula ·"Component (A2)": an alkyl naphthalene (KR-023, manufactured by King Industries, Inc., 40°C kinematic viscosity: 206 mm 2< / s)

[0135] The temperature at which the mass of the alkyl naphthalene reduced by 3% in gas chromatography distillation in conformity with ASTM D7500 was 486°C.

[0136] ·"Base oil (A')-1": a full ester (tris-(2-octyldodecyl)trimellitic acid ester) of trimellitic acid (manufactured by Wako Pure Chemical Industries, Ltd.) and 2-octyl-1-dodecanol (manufactured by Wako Pure Chemical Industries, Ltd., number of carbon atoms: 20, branching position: α-position, number of branches: 1) represented by the following structural formula ·"Base oil (A')-2": a fluorine oil (perfluoropolyether (PFPE), manufactured by Solvay S.A., product name: Fomblin M30)<Thickener (B)>

[0137] ·"Component (B1)": melamine cyanurate (manufactured by Nissan Chemical Corporation, product name: MC-6000, average particle diameter: 2 µm) ·"Component (B2)": a premade urea (urea structure: aromatic diurea, average particle diameter: 2 µm) 100 Milliliters of dichloromethane and 10.8 g of 4,4'-diphenylmethane diisocyanate (MDI) were loaded into a 500-milliliter separable four-necked flask including a temperature gauge, a stirring blade, and a reflux condenser, and MDI was dissolved in dichloromethane by stirring at room temperature (25°C). Thus, a solution of MDI in dichloromethane was prepared. 25 Milliliters of dichloromethane and 9.2 g of toluidine were loaded into another 200-milliliter beaker, and toluidine was dissolved in dichloromethane by stirring at room temperature. Thus, a solution of toluidine in dichloromethane was prepared. The solution of toluidine in dichloromethane was dropped into the solution of MDI in dichloromethane over 10 minutes to synthesize a diurea compound. After heat generation at the time of the dropping had subsided, the reaction was completed by heating the entirety to 45°C with an oil bath.

[0138] The resultant paste-like mixture of the diurea compound and dichloromethane was removed, and was washed with 50 mL of dichloromethane three times while being subjected to suction filtration. Thus, an unreacted raw material was removed. The resultant solid was dried well by drying under reduced pressure. It was recognized by NMR that the solid was a target diurea compound.

[0139] The resultant diurea compound is an aromatic diurea compound represented by the general formula (b2-1) in which R 1< and R 2< each represent a methyl phenyl group, and R 3< represents a diphenylmethylene group.

[0140] Then, the resultant white solid was pulverized with a mortar to provide 8.4 g of a premade urea in the form of fine powder.<Thickener (B')>

[0141] ·"Non-premade urea": a diurea compound produced by using 4,4'-diphenylmethane diisocyanate and toluidine as raw materials, the compound being produced (synthesized) in a preparation process for a grease composition in Comparative Example 1 to be described later

[0142] In Table 1, the compound was described as "Urea (ordinary method)." ·"Polytetrafluoroethylene (PTFE)": TF 9207Z manufactured by 3M Company[Example 1]

[0143] 32 Grams of the alkyl naphthalene (the above-mentioned component (A2)) and 18 g of melamine cyanurate were kneaded with a triple roll mill to provide a grease composition of Example 1.[Example 2]

[0144] 32 Grams of pentaerythritol tetra(2-hexyldecanoate) (the above-mentioned component (A1)) and 18 g of melamine cyanurate were kneaded with a triple roll mill to provide a grease composition of Example 2.[Example 3]

[0145] 35 Grams of the alkyl naphthalene (the above-mentioned component (A2)) and 15 g of the premade urea were kneaded with a triple roll mill to provide a grease composition of Example 3.[Comparative Example 1]

[0146] 46 Grams of the alkyl naphthalene (the above-mentioned component (A2)) and 11 g of 4,4'-diphenylmethane diisocyanate (MDI) were loaded into a separable flask, and MDI was dissolved in the alkyl naphthalene by heating the mixture to 80°C. Thus, a solution of MDI in the alkyl naphthalene was prepared. 13 Grams of toluidine and 50 g of the alkyl naphthalene (the above-mentioned component (A2)) were loaded into another beaker, and toluidine was similarly dissolved in the alkyl naphthalene by heating. Thus, a solution of toluidine in the alkyl naphthalene was prepared. The solution of toluidine in the alkyl naphthalene was dropped into the solution of MDI in the alkyl naphthalene, which was being stirred, to perform a urea-forming reaction. The reaction was completed by increasing the temperature of the mixture to 160°C while stirring the mixture.

[0147] The resultant diurea compound is an aromatic diurea compound represented by the general formula (b2-1) in which R 1< and R 2< each represent a methyl phenyl group, and R 3< represents a diphenylmethylene group.

[0148] After the completion of the reaction, the resultant was cooled to room temperature, and was then subjected to a roll mill to provide a grease composition of Comparative Example 1.[Comparative Example 2]

[0149] The tris-(2-octyldodecyl)trimellitic acid ester (the above-mentioned base oil (A')-1) and melamine cyanurate were blended at a blending ratio shown in Table 1, and a grease composition of Comparative Example 2 was obtained from the blend by the same method as that of Example 1.[Comparative Example 3]

[0150] The fluorine oil (the above-mentioned base oil (A')-2) and PTFE were blended at a blending ratio shown in Table 1, and a grease composition of Comparative Example 3 was obtained from the blend by the same method as that of Example 1.[Evaluation]

[0151] The grease compositions of Examples 1 to 3 and Comparative Examples 1 to 3 were each subjected to the following evaluations 1 and 2.<Evaluation 1: Evaluation of Thermal Stability>

[0152] The thermogravimetric differential thermal analysis of each of the grease compositions was performed with a thermogravimetric differential thermal analysis apparatus (TG-DTA apparatus, manufactured by Seiko Instruments Inc., product name: TG / DTA 6200).

[0153] Specifically, 0.5 g of the grease composition was loaded into an aluminum pan, and a weight change of the grease composition when its temperature was increased from 50°C to 500°C at a temperature increase rate of 10°C / min under a nitrogen atmosphere was measured.

[0154] Then, the temperature at which the mass of the grease composition reduced by 1% was determined.

[0155] In this evaluation, a case in which the temperature at which the mass of the grease composition reduced by 1% was 250°C or more was regarded as acceptable (A), and a case in which the temperature was less than 250°C was regarded as unacceptable (B).<Evaluation 2: Evaluation of Lubricity>

[0156] Each of the grease compositions was introduced into a space between a test plate and a test ball with a high-speed reciprocating friction tester TE 77 (manufactured by Phoenix Tribology Ltd), and a test was performed by moving the test ball under the following conditions. A wear mark diameter in the longitudinal direction of the test ball after the test, and a wear mark diameter in the lateral direction thereof were measured, and the average of the wear mark diameters was calculated from the following equation. ·Test plate: material: SUJ2, shape: 58 mm long by 38 mm wide by 3.9 mm thick ·Test ball: material: SUJ2, diameter: 10 mm ·Greasing conditions: a grease bath, grease amount: 3 mL ·Load: 200 N (300 seconds) ·Temperature: 100°C ·Amplitude: 10 mm ·Frequency: 10 Hz Average of wear mark diameters={(wear mark diameter in longitudinal direction)+(wear mark diameter in lateral direction)} / 2

[0157] A smaller wear mark diameter means that the grease composition is more excellent in lubricity.

[0158] In this evaluation, a grease composition having a wear mark diameter of 600 µm or less was regarded as acceptable (A), and a grease composition having a wear mark diameter of more than 600 µm was regarded as unacceptable (B).

[0159] The results of the evaluation 1 and the evaluation 2 are shown in Table 1.

[0160] The following is found from Table 1.

[0161] It is found that the grease compositions of Examples 1 to 3 are each a grease composition excellent in thermal stability and lubricity.

[0162] In contrast, it is found that the grease compositions of Comparative Examples 1 to 3 are each poor in thermal stability or lubricity.

[0163] Next, the grease compositions of Examples 1 to 3 and Comparative Examples 1 to 3 were each subjected to the following evaluation 3.<Evaluation 3: Evaluation of Low Dust Generation Property>

[0164] The number of dust particles generated by each of the grease compositions was evaluated with a linear guide placed in a clean room (class 2 specified in ISO 14644-1).

[0165] Specifically, 3 g of the grease composition was loaded into the entire rail surface of the linear guide, and the guide was operated for 50 hours under the conditions of an acceleration of 1.0 mm / s 2< and a stroke of 200 mm. Air was collected (suction rate: 3 L / min) from a suction port placed at a position nearest to a screw in a central portion of the reciprocation of the guide, and a particle counter (apparatus name: Airborne Particle Counter KC-03B, manufactured by RION Co., Ltd.) was activated for 10 minutes every 30 minutes to measure the number of dust particles generated. In a time period of from 40 hours to 50 hours in which the friction state of the guide was brought into a steady state, the average number of the dust particles generated in a 10-minute period was determined.

[0166] The results of the evaluation 3 are shown in Table 2.

[0167] It is found from Table 2 that the grease composition of Example 1 is particularly excellent in low dust generation property.

Claims

1. A grease composition, comprising: a base oil (A); and a thickener (B), wherein the base oil (A) comprises one or more kinds selected from the group consisting of: the following component (A1); and the following component (A2): ˙component (A1): an ester of a polyol (A11) having 3 to 6 hydroxy groups and a branched fatty acid (A12) having 14 to 20 carbon atoms; and ˙component (A2): such an alkyl naphthalene that a temperature at which a mass thereof reduces by 3% in gas chromatography distillation in conformity with ASTM D7500 is 450°C or more, and wherein the thickener (B) comprises one or more kinds selected from the group consisting of: the following component (B1); and the following component (B2): ˙component (B1): melamine cyanurate; and ˙component (B2): a premade urea.

2. The grease composition according to claim 1, wherein the polyol (A11) comprises pentaerythritol.

3. The grease composition according to claim 1 or 2, wherein the branched fatty acid (A12) comprises a branched fatty acid, which has 1 branch and has the branch at α-position thereof.

4. The grease composition according to any one of claims 1 to 3, wherein a total content of the base oil (A) and the thickener (B) is from 90 mass% to 100 mass% with respect to a total amount of the grease composition.

5. The grease composition according to any one of claims 1 to 4, wherein the base oil (A) comprises one or more kinds selected from the components (A2), and wherein the thickener (B) comprises one or more kinds selected from the components (B1).

6. The grease composition according to any one of claims 1 to 5, wherein a content of the thickener (B) is from 5.0 mass% to 60 mass% with respect to a total amount of the grease composition.

7. The grease composition according to any one of claims 1 to 6, wherein the grease composition is used in a semiconductor-producing apparatus.

8. A method of producing a grease composition, comprising a step (S) of mixing a base oil (A) and a thickener (B), wherein the step (S) comprises blending one or more kinds selected from the group consisting of: the following component (A1); and the following component (A2) as the base oil (A): ˙component (A1): an ester of a polyol (A11) having 3 to 6 hydroxy groups and a branched fatty acid (A12) having 14 to 20 carbon atoms; and ˙component (A2): such an alkyl naphthalene that a temperature at which a mass thereof reduces by 3% in gas chromatography distillation in conformity with ASTM D7500 is 450°C or more, and blending one or more kinds selected from the group consisting of: the following component (B1); and the following component (B2) as the thickener (B): ˙component (B1): melamine cyanurate; and ˙component (B2): a premade urea.

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