Grease composition and method for producing grease composition

Abstract

Disclosed is a grease composition which contains a base oil (A) and a thickening agent (B), wherein: the base oil (A) includes one or more components selected from the group consisting of the component (A1) and the component (A2) described below; and the thickening agent (B) includes one or more components selected from the group consisting of the component (B1) and the component (B2) described below. Component (A1): an ester of a polyol (A11) having 3 to 6 hydroxyl groups and a branched fatty acid (A12) having 14 to 20 carbon atoms Component (A2): an alkylnaphthalene that has a 3% mass loss temperature of 450°C or higher in gas chromatography distillation in accordance with ASTM-D7500 Component (B1): melamine cyanurate Component (B2): pre-made urea

Description

Grease composition and method for producing grease composition

[0001] The present invention relates to a grease composition and a method for producing the grease composition.

[0002] Known grease compositions used in semiconductor manufacturing equipment, etc., include fluorine grease compositions that use perfluoropolyether (PFPE) as a base oil and polytetrafluoroethylene (PTFE) as a thickener. Patent Document 1 also proposes a grease composition containing a base oil containing an ester oil or a fluorine-free ether oil, and a thickener containing at least a urea compound and a self-lubricating thickener.

[0003] Japanese Patent Application Laid-Open No. 2011-202061

[0004] However, fluorine grease compositions using fluorine oils such as perfluoropolyether (PFPE) as base oils sometimes have insufficient lubrication properties, and this is a need for improvement. In addition, in semiconductor manufacturing equipment, processes such as film formation and etching are sometimes performed at high temperatures of 200°C or higher. Under such high temperatures, the grease composition is also required to have thermal stability.

[0005] The present invention has been made in view of such demands, and an object of the present invention is to provide a grease composition that is excellent in lubricity and thermal stability.

[0006] According to the present invention, the following [1] and [2] are provided: [1] A grease composition containing a base oil (A) and a thickener (B), wherein the base oil (A) contains one or more selected from the group consisting of the following components (A1) and (A2): - component (A1): an ester of a polyol (A11) having 3 to 6 hydroxyl groups and a branched fatty acid (A12) having 14 to 20 carbon atoms - component (A2): an alkylnaphthalene having a temperature of 450°C or higher at which a 3% mass loss occurs in gas chromatography distillation in accordance with ASTM-D7500 The thickener (B) contains one or more selected from the group consisting of the following components (B1) and (B2): Component (B1): melamine cyanurate Component (B2): premade urea [2] A method for producing a grease composition, comprising: a step (S) of mixing a base oil (A) with a thickener (B), wherein in the step (S), one or more selected from the group consisting of the following components (A1) and (A2) are blended as the base oil (A), and Component (A1): an ester of a polyol (A11) having 3 to 6 hydroxyl groups and a branched fatty acid (A12) having 14 to 20 carbon atoms Component (A2): an alkylnaphthalene having a temperature of 450°C or higher at which a 3% mass loss occurs in gas chromatography distillation in accordance with ASTM-D7500 A method for producing a grease composition, comprising blending as the thickener (B) one or more selected from the group consisting of the following components (B1) and (B2): Component (B1): melamine cyanurate Component (B2): premade urea

[0007] According to the present invention, it is possible to provide a grease composition that is excellent in lubricity and thermal stability.

[0008] The upper and lower limit values ​​of the numerical ranges described in this specification can be combined in any way. For example, when "A to B" and "C to D" are described as numerical ranges, the numerical ranges "A to D" and "C to B" are also included in the scope of the present invention. Furthermore, the numerical range "lower limit to upper limit" described in this specification means that the range is equal to or greater than the lower limit and equal to or less than the upper limit, unless otherwise specified. Furthermore, in this specification, the numerical values ​​in the examples are numerical values ​​that can be used as upper or lower limit values.

[0009] [Aspects of Grease Composition] The grease composition of this embodiment contains a base oil (A) and a thickener (B). The base oil (A) contains one or more selected from the group consisting of the following components (A1) and (A2): - Component (A1): an ester of a polyol (A11) having 3 to 6 hydroxyl groups and a branched fatty acid (A12) having 14 to 20 carbon atoms - Component (A2): an alkylnaphthalene having a temperature of 450°C or higher at which a 3% mass loss occurs in gas chromatography distillation in accordance with ASTM-D7500 And the thickener (B) contains one or more selected from the group consisting of the following components (B1) and (B2): - Component (B1): melamine cyanurate - Component (B2): premade urea

[0010] The present inventors have conducted extensive research to solve the above problems. As a result, they have discovered that a grease composition containing the base oil (A) and the thickener (B) has excellent lubricity and thermal stability. Based on this discovery, the present inventors have conducted further research and have completed the present invention.

[0011] The grease composition of this embodiment may be composed only of the base oil (A) and the thickener (B), or may further contain other components in addition to the base oil (A) and the thickener (B). In the grease composition of this embodiment, the total content of the base oil (A) and the thickener (B) is preferably 90% by mass to 100% by mass, and more preferably 95% by mass to 100% by mass, based on the total amount of the grease composition.

[0012] Each component contained in the grease composition of the present embodiment will be described in detail below.

[0013] <Base Oil (A)> The grease composition of this embodiment contains a base oil (A). The base oil (A) contains one or more selected from the group consisting of the following components (A1) and (A2): Component (A1): an ester of a polyol (A11) having 3 to 6 hydroxyl groups and a branched fatty acid (A12) having 14 to 20 carbon atoms; Component (A2): an alkylnaphthalene having a temperature of 450°C or higher at which a 3% mass loss occurs in gas chromatography distillation according to ASTM-D7500.

[0014] By using a base oil (A) containing one or more selected from the group consisting of component (A1) and component (A2) together with a thickener (B), a grease composition with excellent lubricity and thermal stability can be obtained. Note that "one or more selected from the group consisting of component (A1) and component (A2)" means "one or more selected from component (A1)," "one or more selected from component (A2)," or "a combination of one or more selected from component (A1) and one or more selected from component (A2)." In the grease composition of this embodiment, from the viewpoint of improving the effects of the present invention, "one or more selected from the group consisting of component (A1) and component (A2)" is preferably "one or more selected from component (A1)" or "one or more selected from component (A2)." Furthermore, from the viewpoint of improving the effects of the present invention while providing a grease composition with excellent low dust generation, "one or more selected from the group consisting of component (A1) and component (A2)" is preferably "one or more selected from component (A2)."

[0015] From the viewpoint of improving the effects of the present invention, the content of "one or more selected from the group consisting of component (A1) and component (A2)" is preferably 50% by mass to 100% by mass, more preferably 60% by mass to 100% by mass, even more preferably 70% by mass to 100% by mass, still more preferably 80% by mass to 100% by mass, even more preferably 90% by mass to 100% by mass, still more preferably 95% by mass to 100% by mass, even more preferably 99% by mass to 100% by mass, and still more preferably 100% by mass, based on the total amount of base oil (A). Furthermore, from the viewpoint of improving the effects of the present invention while providing a grease composition that exhibits excellent low dust generation, the content of "one or more types selected from component (A2)" is preferably 50% by mass to 100% by mass, more preferably 60% by mass to 100% by mass, even more preferably 70% by mass to 100% by mass, still more preferably 80% by mass to 100% by mass, even more preferably 90% by mass to 100% by mass, still more preferably 95% by mass to 100% by mass, even more preferably 99% by mass to 100% by mass, and still more preferably 100% by mass, based on the total amount of base oil (A).

[0016] The content of the base oil (A) is preferably 40 to 90% by mass, more preferably 45 to 85% by mass, based on the total amount of the grease composition.

[0017] The components (A1) and (A2) will be described in detail below.

[0018] <<Component (A1)>> Component (A1) is an ester of a polyol (A11) having 3 to 6 hydroxyl groups and a branched fatty acid (A12) having 14 to 20 carbon atoms. By including component (A1) in base oil (A), a grease composition with excellent thermal stability can be obtained. Furthermore, a grease composition that is unlikely to volatilize even under high vacuum (hereinafter also referred to as "low volatility") can be obtained. While component (A1) may be a partial ester or a full ester, it is preferable to include a full ester from the viewpoint of obtaining a grease composition with excellent thermal stability and low volatility. The content of the full ester in component (A1) is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 97% by mass or more, based on the total amount of component (A1). The polyol (A11) and the branched fatty acid (A12) are described in detail below.

[0019] (Polyol (A11)) The polyol (A11) is a polyol having 3 to 6 hydroxyl groups. By using a polyol having 3 to 6 hydroxyl groups as the alcohol component constituting the ester, the thermal stability and low volatility of component (A1) can be improved. Specific examples of polyols having 3 to 6 hydroxyl groups include trihydric alcohols (polyols having 3 hydroxyl groups) such as glycerin, trimethylolethane, trimethylolpropane, and trimethylolnonane; and tetrahydric to hexahydric alcohols (polyols having 4 to 6 hydroxyl groups) such as pentaerythritol, ditrimethylolpropane, dipentaerythritol, sorbitol, and mannitol. Of these, tetrahydric to hexahydric alcohols are preferred from the viewpoint of increasing the molecular weight of component (A1) and making it easier to improve low volatility. Furthermore, among tetrahydric to hexahydric alcohols, pentaerythritol is preferred from the viewpoint of improving thermal stability and low volatility. That is, it is preferable that polyol (A11) contains pentaerythritol. It is presumed that the inclusion of pentaerythritol in the polyol (A11) facilitates improving the thermal stability of component (A1) by suppressing molecular cleavage due to an intramolecular condensation reaction of the ester formed from pentaerythritol and the branched fatty acid (A12), and by effective protection of the ester group by the alkyl group of the branched fatty acid (A12). The content of pentaerythritol, based on the total amount of polyol (A11), is preferably 50% to 100% by mass, more preferably 60% to 100% by mass, even more preferably 70% to 100% by mass, still more preferably 80% to 100% by mass, even more preferably 90% to 100% by mass, still more preferably 95% to 100% by mass, even more preferably 99% to 100% by mass, and still more preferably 100% by mass.

[0020] (Branched Fatty Acid (A12)) The branched fatty acid (A12) is a branched fatty acid having 14 to 20 carbon atoms. By using a branched fatty acid having 14 to 20 carbon atoms as the fatty acid component constituting the ester, the thermal stability and low volatility of component (A1) can be improved. Furthermore, the fluidity of component (A1) can be improved and the viscosity index can be improved. Furthermore, from the viewpoint of improving the thermal stability and the viscosity index, the branched fatty acid having 14 to 20 carbon atoms preferably has one branch. Specific examples of branched fatty acids having 14 to 20 carbon atoms and one branch include branched saturated fatty acids such as butyloctanoic acid, hexyldecanoic acid, and octyldodecanoic acid. Of these, hexyldecanoic acid is preferred from the viewpoint of improving the thermal stability, fluidity, etc. of the ester. Furthermore, among hexyldecanoic acids, it is preferred to have a branch at the α-position (the carbon atom adjacent to the carboxy group) from the viewpoint of further improving the thermal stability, fluidity, etc. That is, the branched fatty acid (A12) preferably contains a branched fatty acid having 14 to 20 carbon atoms, one branch, and a branch at the α-position. The content of the branched fatty acid having 14 to 20 carbon atoms, one branch, and a branch at the α-position is preferably 50% by mass to 100% by mass, more preferably 60% by mass to 100% by mass, even more preferably 70% by mass to 100% by mass, still more preferably 80% by mass to 100% by mass, even more preferably 90% by mass to 100% by mass, still more preferably 95% by mass to 100% by mass, even more preferably 99% by mass to 100% by mass, and still more preferably 100% by mass, based on the total amount of the branched fatty acid (A12).

[0021] <<Component (A2)>> Component (A2) is an alkylnaphthalene that exhibits a 3% mass loss temperature of 450°C or higher when distilled by gas chromatography in accordance with ASTM-D7500. By including component (A2) in base oil (A), a grease composition with excellent thermal stability can be obtained. In addition, a grease composition with low volatility can be obtained.

[0022] Alkylnaphthalenes are compounds in which at least one hydrogen atom on the naphthalene ring is substituted with an alkyl group. By using alkylnaphthalenes whose temperature at which they lose 3% by mass in gas chromatography distillation according to ASTM-D7500 is 450°C or higher, a grease composition with excellent thermal stability (and low volatility) can be obtained. From the viewpoint of further improving thermal stability (and low volatility), the temperature at which the alkylnaphthalene loses 3% by mass is preferably 455°C or higher, more preferably 460°C or higher, and even more preferably 470°C or higher.

[0023] The kinematic viscosity of the alkylnaphthalene at 40°C is preferably 75 mm from the viewpoint of further improving the thermal stability (and further reducing the volatility). ２ / s ~ 400 mm ２ / s, more preferably 100 mm ２ / s~350m ２ / s, more preferably 150 mm ２ / s ~ 300 mm ２ In this specification, the kinematic viscosity at 40°C means a value measured in accordance with JIS K2283:2000.

[0024] <Thickener (B)> The grease composition of this embodiment contains a thickener (B). The thickener (B) contains one or more components selected from the group consisting of the following component (B1) and the following component (B2): Component (B1): melamine cyanurate Component (B2): premade urea

[0025] By using a thickener (B) containing one or more selected from the group consisting of component (B1) and component (B2) together with base oil (A), a grease composition can be obtained that exhibits excellent thermal stability, low volatility, and lubricity. Note that "one or more selected from the group consisting of component (B1) and component (B2)" means "one or more selected from component (B1)," "one or more selected from component (B2)," or "a combination of one or more selected from component (B1) and one or more selected from component (B2)." In the grease composition of this embodiment, from the viewpoint of improving the effects of the present invention, "one or more selected from the group consisting of component (B1) and component (B2)" is preferably "one or more selected from component (B1)" or "one or more selected from component (B2)." Furthermore, from the viewpoint of improving the effects of the present invention while providing a grease composition that exhibits excellent low dust generation, "one or more selected from the group consisting of component (B1) and component (B2)" is preferably "one or more selected from component (B1)."

[0026] Here, from the viewpoint of improving the effects of the present invention, the content of "one or more selected from the group consisting of component (B1) and component (B2)" is preferably 50% by mass to 100% by mass, more preferably 60% by mass to 100% by mass, even more preferably 70% by mass to 100% by mass, still more preferably 80% by mass to 100% by mass, even more preferably 90% by mass to 100% by mass, still more preferably 95% by mass to 100% by mass, even more preferably 99% by mass to 100% by mass, and still more preferably 100% by mass, based on the total amount of thickener (B). Furthermore, from the viewpoint of improving the effects of the present invention while providing a grease composition that is excellent in low dust generation, the content of "one or more types selected from component (B1)" is preferably 50% by mass to 100% by mass, more preferably 60% by mass to 100% by mass, even more preferably 70% by mass to 100% by mass, still more preferably 80% by mass to 100% by mass, even more preferably 90% by mass to 100% by mass, still more preferably 95% by mass to 100% by mass, even more preferably 99% by mass to 100% by mass, and still more preferably 100% by mass, based on the total amount of thickener (B).

[0027] The content of the thickener (B) is preferably 5 to 60% by mass, more preferably 10 to 55% by mass, based on the total amount of the grease composition.

[0028] The components (B1) and (B2) will be described in detail below.

[0029] <<Component (B1)>> Component (B1) is melamine cyanurate. By mixing melamine cyanurate with base oil (A), the melamine cyanurate functions as a thickener, thereby preparing a grease composition. Furthermore, because melamine cyanurate does not contain any metal components, it is extremely suitable as a thickener for preparing grease compositions used in semiconductor device manufacturing. Furthermore, melamine cyanurate has excellent thermal stability and can improve the lubricity of the grease composition. Melamine cyanurate is an organic salt composed of melamine and cyanuric acid and has a graphite structure. The average particle size of the melamine cyanurate is preferably 5.0 μm or less, more preferably 4.0 μm or less, even more preferably 3.0 μm or less, even more preferably 2.5 μm or less, and even more preferably 2.0 μm or less. There is no particular lower limit for the particle size of melamine cyanurate, but it is typically 0.005 μm or more. In this specification, the particle size of melamine cyanurate is measured at 25°C by dynamic light scattering (photon correlation method) and calculated from the dispersed particle size distribution analyzed by the CONTIN method, as the 50% particle size based on scattering intensity (volume median particle size, D ５０ When component (B1) is used alone as the thickener (B), the content of component (B1) is preferably 20% by mass to 60% by mass, and more preferably 25% by mass to 55% by mass, based on the total amount of the grease composition.

[0030] <<Component (B2)>> Component (B2) is a pre-formed urea. Generally, when producing a grease composition, amines and isocyanates are added to a base oil and reacted to synthesize a urea compound that functions as a thickener in the base oil. In other words, the urea compound serving as a thickener is synthesized in the base oil that constitutes the grease composition during the production process of the grease composition. However, in this method, unreacted amines and / or isocyanates may remain in the grease composition. The inventors' investigations have revealed that such low-molecular-weight compounds can cause a decrease in the thermal stability of the grease composition. Therefore, in this embodiment, a pre-formed urea compound is used and mixed with a base oil to prepare the grease composition, rather than synthesizing the urea compound during the production process of the grease composition. This urea compound is called a "pre-formed urea."

[0031] The urea compound constituting the premade urea may be any compound having a urea bond, but a diurea compound having two urea bonds is preferred, and a diurea compound represented by the following general formula (b2-1) is more preferred. １ -NHCONH-R ３ -NHCONH-R ２ (b2-1)

[0032] In the above general formula (b2-1), R １ and R ２ R each independently represents a monovalent hydrocarbon group having 6 to 24 carbon atoms. １ and R ２ may be the same or different from each other. ３ represents a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms. １ and R ２ The number of carbon atoms of the monovalent hydrocarbon group that can be selected as R is 6 to 24, preferably 6 to 20, and more preferably 6 to 18. １ and R ２Examples of the monovalent hydrocarbon group that can be selected as include a saturated or unsaturated monovalent chain hydrocarbon group, a saturated or unsaturated monovalent alicyclic hydrocarbon group, and a monovalent aromatic hydrocarbon group.

[0033] Examples of the monovalent saturated chain hydrocarbon group include linear or branched alkyl groups 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. Examples of monovalent unsaturated chain hydrocarbon groups include straight-chain or branched-chain alkenyl groups having 6 to 24 carbon atoms, and specific examples 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, a linoleyl group, etc. The monovalent saturated chain hydrocarbon groups and the monovalent unsaturated chain hydrocarbon groups may be straight-chain or branched.

[0034] 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 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 (preferably a cyclohexyl group substituted with an alkyl group having 1 to 6 carbon atoms).

[0035] 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 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 (preferably a cyclohexenyl group substituted with an alkyl group having 1 to 6 carbon atoms).

[0036] 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.

[0037] R in the above general formula (b2-1) ３ The carbon number of the divalent aromatic hydrocarbon group that can be selected as R is 6 to 18, preferably 6 to 15, and more preferably 6 to 13. ３ Examples of the divalent aromatic hydrocarbon group that can be selected as aryl include a phenylene group, a diphenylmethylene group, a diphenylethylene group, a diphenylpropylene group, a methylphenylene group, a dimethylphenylene group, an ethylphenylene group, etc. Among these, a phenylene group, a diphenylmethylene group, a diphenylethylene group, or a diphenylpropylene group is preferred, and a diphenylmethylene group is more preferred.

[0038] The particle size of the premade urea is preferably 5.0 μm or less, more preferably 4.0 μm or less, even more preferably 3.0 μm or less, even more preferably 2.5 μm or less, and even more preferably 2.0 μm or less, as an average particle size. The particle size of the premade urea is not particularly limited to a lower limit, but is usually 0.005 μm or more. In this specification, the particle size of the premade urea refers to the 50% particle size (volume median particle size, D) based on scattering intensity, measured at 25° C. by dynamic light scattering (photon correlation method) and calculated from the dispersed particle size distribution analyzed by the CONTIN method. ５０When component (B2) is used alone as the thickener (B), the content of component (B2) is preferably 5 to 45% by mass, more preferably 10 to 40% by mass, and even more preferably 15 to 35% by mass, based on the total amount of the grease composition.

[0039] The urea compound constituting the premade urea can usually be obtained by reacting a diisocyanate with a monoamine in an appropriate solvent. Examples of the diisocyanate include diphenylene diisocyanate, 4,4'-diphenylmethane diisocyanate, and tolylene diisocyanate. Examples of the monoamine include the urea compound represented by R 1 and R ２ Examples of the amines include amines corresponding to saturated or unsaturated monovalent chain hydrocarbon groups, saturated or unsaturated monovalent alicyclic hydrocarbon groups, and monovalent aromatic hydrocarbon groups, as represented by the formula (I), such as 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 of these. Examples of the solvent used to synthesize the urea compound include various organic solvents such as dichloromethane and toluene. The urea compound obtained by the above synthesis process is washed with a solvent at least once to remove unreacted raw materials, and then the solvent is removed. The urea compound can then be appropriately pulverized by a conventional method and used as component (B2).

[0040] <Other Components> The grease composition of this embodiment may further contain other components in addition to the base oil (A) and the thickener (B) within the scope of the present invention. Examples of other components include a base oil other than the base oil (A), an antioxidant, and a viscosity index improver. One type of other component may be used alone, or two or more types may be used in combination. The total content of the other components in the grease composition of this embodiment is preferably 0% by mass to 10% by mass, more preferably 0% by mass to 5.0% by mass, and even more preferably 0% by mass to 2.0% by mass, based on the total amount of the grease composition.

[0041] From the viewpoint of improving the effects of the present invention, it is preferable that the content of base oils other than base oil (A) is small. Specifically, the content of base oils other than base oil (A) is preferably less than 10 parts by mass, more preferably less than 1 part by mass, and even more preferably less than 0.1 parts by mass, per 100 parts by mass of base oil (A). Examples of base oils other than base oil (A) include mineral oils and diesters. That is, it is preferable that the content of one or more base oils selected from the group consisting of mineral oils and diesters is small, and the specific content is preferably within the above range.

[0042] (Metal Atom-Containing Compound) In the grease composition of this embodiment, it is preferable to adjust the content of the metal atom-containing compound to a low level. This is because if a grease composition containing a metal atom-containing compound were to scatter within semiconductor manufacturing equipment and adhere to semiconductor products within the equipment, malfunctions would occur due to the metal atoms contained in the metal atom-containing compound, significantly affecting the yield of the semiconductor products. From this perspective, the content of metal atoms 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%, even more preferably less than 0.01 mass%, and even more preferably less than 0.001 mass%, based on the total amount of the grease composition. Note that since the base oil (A) and the thickener (B) do not substantially contain metal atoms, the content of metal atoms derived from the metal atom-containing compound can also be said to be the content of metal atoms in the grease composition.

[0043] Examples of metal atoms include alkali metal atoms such as lithium and sodium atoms, alkaline earth metal atoms such as calcium and magnesium atoms, and transition metal atoms such as zinc and molybdenum. Examples of metal atom-containing compounds include metal complex soaps such as lithium complex soaps, which are prepared by saponifying carboxylic acids or their esters with hydroxides of alkali metals, alkaline earth metals, aluminum, etc., and are used as thickeners, as well as metal salts and metal oxides which are used as metal dispersants, metal detergents, metal extreme pressure agents, and metal rust inhibitors. That is, the content of metal atoms derived from one or more metal atom-containing compounds selected from the group consisting of the above components is preferably low, and the specific content is preferably within the above range.

[0044] (Fluorine atom-containing compound) In the grease composition of this embodiment, from the viewpoint of improving lubricity and from the viewpoint of PFAS regulations, it is preferable to adjust the content of the fluorine atom-containing compound to be low. From such viewpoints, the content of fluorine atoms 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%, even more preferably less than 0.01 mass%, and still more preferably less than 0.001 mass%, based on the total amount of the grease composition. Note that since the base oil (A) and the thickener (B) do not substantially contain fluorine atoms, the content of fluorine atoms derived from the fluorine atom-containing compound can also be said to be the fluorine atom content in the grease composition.

[0045] Specific examples of fluorine atom-containing compounds include perfluoropolyether (PEPE) blended as a base oil, polytetrafluoroethylene (PTFE) blended as a thickener, and fluorinated silicone compounds blended as antifoaming agents. That is, the content of fluorine atoms derived from one or more fluorine atom-containing compounds selected from the group consisting of the above components is preferably low, and the specific content thereof is preferably within the above range.

[0046] [Physical Properties of Grease Composition] The grease composition of the present embodiment preferably satisfies the following physical properties.

[0047] <Thermal Stability> The grease composition of this embodiment preferably has a thermal stability (temperature at which 1% by mass is lost) of 250°C or higher, as measured by the method described in the Examples section below.

[0048] <Lubricity> The grease composition of this embodiment preferably has a wear scar diameter of 600 μm or less, more preferably 500 μm or less, and even more preferably 450 μm or less, as measured by the method described in the Examples below.

[0049] <Low Dust Generation> The grease composition of the present embodiment has a dust generation count measured by the method described in the examples below of preferably 1,200 or less, more preferably 1,000 or less, even more preferably 800 or less, still more preferably 500 or less, and even more preferably 300 or less.

[0050] [Method for Producing Grease Composition] The method for producing the grease composition of this embodiment is not particularly limited. For example, the method for producing the grease composition of this embodiment includes a step (S) of mixing a base oil (A) and a thickener (B). In step (S), the base oil (A) is blended with one or more components selected from the group consisting of the following components (A1) and (A2): Component (A1): an ester of a polyol (A11) having 3 to 6 hydroxyl groups and a branched fatty acid (A12) having 14 to 20 carbon atoms; Component (A2): an alkylnaphthalene having a temperature of 450°C or higher at which a 3% mass loss occurs in gas chromatography distillation according to ASTM-D7500. The thickener (B) is blended with one or more components selected from the group consisting of the following components (B1) and (B2). Component (B1): melamine cyanurate Component (B2): premade urea Examples of a method for mixing (kneading) the base oil (A) and the thickener (B) include a method using a roll mill.

[0051] [Uses of Grease Composition] The grease composition of this embodiment has excellent lubricity and thermal stability. Therefore, the lubricating oil composition of this embodiment can be used in a wide range of applications requiring lubricity and thermal stability, and is particularly suitable for use in semiconductor manufacturing equipment. In particular, the grease composition of this embodiment can be suitably used to lubricate moving parts in high-vacuum, high-temperature environments, such as vacuum chambers in semiconductor manufacturing equipment. Examples of such moving parts include, but are not limited to, linear motion mechanisms, reducers, and speed-up gears. Examples of semiconductor manufacturing equipment include physical vapor deposition (PVD) equipment and chemical vapor deposition (CVD) equipment. Examples of physical vapor deposition include vacuum deposition, sputtering, ion plating, and ion bombardment using various ion guns. Examples of vacuum deposition include general resistance heating deposition, electron beam deposition, ion-assisted electron beam deposition, and arc deposition. These physical vapor deposition methods may be used in appropriate combination. Examples of chemical vapor deposition include thermal CVD, plasma CVD, photo CVD, epitaxial CVD, and atomic layer CVD. These chemical vapor deposition methods may be used in appropriate combination, or may be used in appropriate combination with physical vapor deposition.

[0052] The grease composition of the present embodiment can also be suitably used in devices mounted on devices used in outer space, which is a high-vacuum environment, such as artificial satellites, probes, and lunar vehicles.

[0053] [One Aspect of the Present Invention Provided] In one aspect of the present invention, the following [1] to [8] are provided. [1] A grease composition containing a base oil (A) and a thickener (B), wherein the base oil (A) contains one or more selected from the group consisting of the following components (A1) and (A2): - component (A1): an ester of a polyol (A11) having 3 to 6 hydroxyl groups and a branched fatty acid (A12) having 14 to 20 carbon atoms - component (A2): an alkylnaphthalene having a temperature of 450°C or higher at which a 3% mass loss occurs in gas chromatography distillation in accordance with ASTM-D7500 The thickener (B) contains one or more selected from the group consisting of the following components (B1) and (B2): - component (B1): melamine cyanurate - component (B2): premade urea [2] The grease composition according to the above [1], wherein the polyol (A11) contains pentaerythritol. [3] The grease composition according to [1] or [2] above, wherein the branched fatty acid (A12) comprises a branched fatty acid having one branch and a branch at the α-position. [4] The grease composition according to any one of [1] to [3] above, wherein the total content of the base oil (A) and the thickener (B) is 90% by mass to 100% by mass, based on the total amount of the grease composition. [5] The grease composition according to any one of [1] to [4] above, wherein the base oil (A) comprises one or more components selected from the component (A2), and the thickener (B) comprises one or more components selected from the component (B1). [6] The grease composition according to any one of [1] to [5] above, wherein the content of the thickener (B) is 5.0% by mass to 60% by mass, based on the total amount of the grease composition. [7] The grease composition according to any one of [1] to [6] above, which is used in semiconductor manufacturing equipment.[8] A method for producing a grease composition, comprising a step (S) of mixing a base oil (A) with a thickener (B), wherein in the step (S), one or more components selected from the group consisting of the following components (A1) and (A2) are blended as the base oil (A), component (A1): an ester of a polyol (A11) having 3 to 6 hydroxyl groups and a branched fatty acid (A12) having 14 to 20 carbon atoms, component (A2): an alkylnaphthalene having a temperature of 450°C or higher at which a 3% mass loss occurs in gas chromatography distillation in accordance with ASTM-D7500, and the thickener (B) is one or more components selected from the group consisting of the following components (B1) and (B2): component (B1): melamine cyanurate, and component (B2): premade urea.

[0054] The present invention will be specifically described with reference to the following examples, although the present invention is not limited to the following examples.

[0055] [Methods for measuring various physical properties] The properties of the raw materials used in each example and each comparative example were measured according to the procedures shown below. (1) Physical properties of alkylnaphthalene The temperature at which the concentration decreased by 3% by mass was measured in gas chromatography distillation according to ASTM-D7500. (2) Average particle size of melamine cyanurate The mean particle size of melamine cyanurate was measured at 25°C by dynamic light scattering (photon correlation method) and calculated from the dispersed particle size distribution analyzed by the CONTIN method, as the 50% particle size (volume median particle size, D) based on scattering intensity. ５０ (3) Average particle size of premade urea The average particle size of premade urea was measured at 25°C by dynamic light scattering (photon correlation method) and calculated from the dispersed particle size distribution analyzed by the CONTIN method. The 50% particle size based on scattering intensity (volume median particle size, D ５０ (4) Kinematic Viscosity at 40°C: Measured in accordance with JIS K2283:2000.

[0056] [Raw Materials, etc.] The raw materials, etc. used to prepare the grease compositions in the examples are shown below.

[0057] <Base oil (A)> "Component (A1)": a full ester of pentaerythritol and 2-hexyldecanoic acid (number of carbon atoms: 16, branch position: α-position, number of branches: 1) represented by the following structural formula (pentaerythritol tetra(2-hexyldecanoate), ISOCARBESTER 1605, manufactured by SASOL) "Component (A2)": alkylnaphthalene (KR-023, manufactured by King Industries, kinematic viscosity at 40°C: 206 mm ２ / s) When this alkylnaphthalene was distilled by gas chromatography in accordance with ASTM-D7500, the temperature at which it was reduced by 3 mass % was 486°C.

[0058] "Base oil (A')-1": a full ester (tris-(2-octyldodecyl)trimellitic acid ester) of trimellitic acid (manufactured by Wako Pure Chemical Industries, Ltd.) represented by the following structural formula and 2-octyl-1-dodecanol (manufactured by Wako Pure Chemical Industries, Ltd.; carbon number: 20, branch position: α-position, number of branches: 1) represented by the following structural formula: "Base oil (A')-2": Fluorinated oil (perfluoropolyether (PFPE), manufactured by Solvay, product name: Fomblin M30)

[0059] <Thickener (B)> - "Component (B1)": Melamine cyanurate (manufactured by Nissan Chemical Industries, Ltd., product name: MC-6000, average particle size: 2 μm) - "Component (B2)": Premade urea (urea structure: aromatic diurea, average particle size: 2 μm) In a 500 mL separable four-neck flask equipped with a thermometer, a stirring blade, and a cooling reflux tube, 100 mL of dichloromethane and 10.8 g of 4,4'-diphenylmethane diisocyanate (MDI) were added and dissolved by stirring at room temperature (25°C) to prepare an MDI / dichloromethane solution. In a separate 200 mL beaker, 25 mL of dichloromethane and 9.2 g of toluidine were placed and dissolved by stirring at room temperature to prepare a toluidine / dichloromethane solution. The toluidine / dichloromethane solution was added dropwise to the MDI / dichloromethane solution over 10 minutes to synthesize a diurea compound. After the heat generated during the dropwise addition subsided, the whole was heated to 45°C using an oil bath to complete the reaction. The obtained paste-like diurea compound / dichloromethane was taken out and washed three times with 50 mL of dichloromethane while performing suction filtration to remove unreacted raw materials. The obtained solid was thoroughly dried under reduced pressure and confirmed to be the target diurea compound by NMR. The obtained diurea compound was a compound represented by the general formula (b2-1) above, where R １ and R ２ is a methylphenyl group, and R ３ is a diphenylmethylene group, and the resulting white solid was pulverized in a mortar to obtain 8.4 g of fine powder premade urea.

[0060] <Thickener (B')> "Non-premade urea": ​​A diurea compound produced (synthesized) in the process of preparing the grease composition in Comparative Example 1 described later, which is produced using 4,4'-diphenylmethane diisocyanate and toluidine as raw materials. In Table 1, this is shown as "Urea (conventional method)." "Polytetrafluoroethylene (PTFE)": TF9207Z, manufactured by 3M Company.

[0061] Example 1 The grease composition of Example 1 was obtained by kneading 32 g of alkylnaphthalene (component (A2) above) and 18 g of melamine cyanurate using a three-roll mill.

[0062] Example 2 A grease composition of Example 2 was obtained by kneading 32 g of pentaerythritol tetra(2-hexyldecanoate) (component (A1) above) and 18 g of melamine cyanurate using a three-roll mill.

[0063] Example 3 The grease composition of Example 3 was obtained by kneading 35 g of alkylnaphthalene (component (A2) above) and 15 g of premade urea using a three-roll mill.

[0064] Comparative Example 1 46 g of alkylnaphthalene (component (A2) above) and 11 g of MDI (4,4'-diphenylmethane diisocyanate) were placed in a separable flask, heated to 80°C, and dissolved to prepare an MDI / alkylnaphthalene solution. 13 g of toluidine and 50 g of alkylnaphthalene (component (A2) above) were placed in a separate beaker, and similarly heated and dissolved to prepare a toluidine / alkylnaphthalene solution. The toluidine / alkylnaphthalene solution was added dropwise to the stirred MDI / alkylnaphthalene solution, and a urea reaction was carried out. The reaction was completed by raising the temperature to 160°C while stirring. The obtained diurea compound was a compound represented by the general formula (b2-1) above, where R １ and R ２ is a methylphenyl group, and R ３ is a diphenylmethylene group. After the reaction was completed, the mixture was cooled to room temperature and then subjected to a roll mill to obtain the grease composition of Comparative Example 1.

[0065] Comparative Example 2 Tris-(2-octyldodecyl)trimellitic acid ester (the above base oil (A')-1) and melamine cyanurate were blended in the blending ratio shown in Table 1, and the grease composition of Comparative Example 2 was obtained in the same manner as in Example 1.

[0066] Comparative Example 3 A fluorinated oil (the above base oil (A')-2) and PTFE were blended in the blending ratio shown in Table 1, and the grease composition of Comparative Example 3 was obtained in the same manner as in Example 1.

[0067] [Evaluation] The grease compositions of Examples 1 to 3 and Comparative Examples 1 to 3 were subjected to the following evaluations 1 and 2.

[0068] <Evaluation 1: Evaluation of Thermal Stability> A thermogravimetric differential thermal analysis of the grease composition was performed using a thermogravimetric differential thermal analyzer (TG-DTA device, manufactured by Seiko Instruments, product name: TG / DTA6200). Specifically, 0.5 g of the grease composition was filled into an aluminum pan, and the weight change was measured when the temperature was raised from 50°C to 500°C at a heating rate of 10°C / min in a nitrogen atmosphere. The temperature at which the grease composition lost 1% by mass was then determined. In this example, a temperature of 250°C or higher at which the grease composition lost 1% by mass was determined as pass (A), and a temperature of less than 250°C was determined as fail (B).

[0069] <Evaluation 2: Evaluation of Lubricity> Using a TE77 high-speed reciprocating friction tester (Phoenix Tribology), a grease composition was introduced between a test plate and a test ball, and the test ball was moved under the following conditions to perform a test. After the test, the longitudinal and lateral wear scar diameters of the test ball were measured, and the average wear scar diameter was calculated using the following formula: Test plate: Material: SUJ2, Shape: Length 58 mm x Width 38 mm x Thickness 3.9 mm Test ball: Material: SUJ2, Diameter 10 mm Greasing conditions: Grease bath, Amount of grease: 3 mL Load: 200 N (300 seconds) Temperature: 100°C Amplitude: 10 mm Frequency: 10 Hz Average wear scar diameter = {(longitudinal wear scar diameter) + (lateral wear scar diameter)} / 2 The smaller the wear scar diameter, the more excellent the lubricity of the grease composition. In this example, grease compositions with a wear scar diameter of 600 μm or less were rated as pass (A), and grease compositions with a wear scar diameter of more than 600 μm were rated as fail (B).

[0070] The results of evaluations 1 and 2 are shown in Table 1.

[0071] From Table 1, the following can be seen: The grease compositions of Examples 1 to 3 are excellent in thermal stability and lubricity. In contrast, the grease compositions of Comparative Examples 1 to 3 are inferior in thermal stability or lubricity.

[0072] Next, the grease compositions of Examples 1 to 3 and Comparative Examples 1 to 3 were subjected to the following evaluation 3.

[0073] <Evaluation 3: Evaluation of low dust generation> The number of particles generated by the grease composition was evaluated using a linear guide installed in a clean room (class 2 as specified in ISO 14644-1). Specifically, 3 g of the grease composition was filled onto the entire rail surface of the linear guide, and the acceleration was 1.0 mm / s. ２ The test was carried out for 50 hours under the conditions of a stroke of 200 mm. Air was sampled (suction speed: 3 L / min) from an intake port installed immediately adjacent to the screw at the center of the reciprocating motion, and a particle counter (device name: Airborne Particle Counter KC-03B, manufactured by Rion Co., Ltd.) was started for 10 minutes every 30 minutes to measure the number of particles generated. The average number of particles generated over 10 minutes was calculated from 40 to 50 hours, when the friction state reached a steady state.

[0074] The results of Evaluation 3 are shown in Table 2.

[0075] From Table 2, it can be seen that the grease composition of Example 1 is particularly excellent in terms of low dust generation.

Claims

1. A grease composition containing a base oil (A) and a thickener (B), wherein the base oil (A) comprises one or more selected from the group consisting of the following components (A1) and (A2): - Component (A1): an ester of a polyol (A11) having 3 to 6 hydroxyl groups and a branched fatty acid (A12) having 14 to 20 carbon atoms - Component (A2): an alkylnaphthalene having a temperature of 450°C or higher at which a 3% mass loss occurs in gas chromatography distillation in accordance with ASTM-D7500, and the thickener (B) comprises one or more selected from the group consisting of the following components (B1) and (B2): - Component (B1): melamine cyanurate - Component (B2): premade urea 2. The grease composition according to claim 1, wherein the polyol (A11) comprises pentaerythritol.

3. A grease composition according to claim 1 or 2, wherein the branched fatty acid (A12) comprises a branched fatty acid having one branch and a branch at the α-position.

4. A grease composition according to any one of claims 1 to 3, wherein the total content of the base oil (A) and the thickener (B) is 90 mass % to 100 mass % based on the 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 types selected from the component (A2), and the thickener (B) comprises one or more types selected from the component (B1).

6. A grease composition according to any one of claims 1 to 5, wherein the content of the thickener (B) is 5.0 mass % to 60 mass % based on the total amount of the grease composition.

7. The grease composition according to any one of claims 1 to 6, which is used in semiconductor manufacturing equipment.

8. A method for producing a grease composition, comprising a step (S) of mixing a base oil (A) with a thickener (B), wherein in the step (S), one or more selected from the group consisting of the following components (A1) and (A2) are blended as the base oil (A), and ・Component (A1): Ester of a polyol (A11) having 3 to 6 hydroxyl groups and a branched fatty acid (A12) having 14 to 20 carbon atoms ・Component (A2): An alkylnaphthalene having a temperature of 450°C or higher at which a loss of 3% by mass occurs in gas chromatography distillation in accordance with ASTM-D7500, and wherein one or more selected from the group consisting of the following components (B1) and (B2) are blended as the thickener (B). ・Component (B1): Melamine cyanurate ・Component (B2): Primed urea

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