Lubricating oil composition

Abstract

To provide a lubricating oil composition capable of achieving both high viscosity and fluidity maintainability at low temperature.SOLUTION: A lubricating oil composition comprising a carboxylic acid ester compound having a structural unit derived from trimethylolpropane, a structural unit derived from adipic acid, and a structural unit derived from caprylic acid, wherein a content of the structural unit derived from trimethylolpropane in all structural units constituting the carboxylic acid ester compound is 28.0 mol% or more and 33.0 mol% or less, and a content of the structural unit derived from caprylic acid in all structural units constituting the carboxylic acid ester compound is 42.4 mol% or more and 48.4 mol% or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a lubricating oil composition. [Background technology]

[0002] Lubricants are used in a variety of fields where friction reduction is required. While natural oils and refined petroleum products have traditionally been used, in recent years synthetic lubricants have been synthesized and used to suit specific applications. In particular, ester compounds such as organic acid esters, phosphate esters, and silicate esters are characterized by their excellent thermal stability. Among these ester compounds, carboxylic acid esters obtained from multi-branched polyhydric alcohols and carboxylic acids have the following characteristics: 1) low pour point, high viscosity index, and wide operating temperature range; 2) high flash point and low evaporation rate; 3) excellent thermal and oxidative stability; and 4) good lubricity.

[0003] Patent Document 1 below discloses that a lubricating base oil made from a synthetic ester having a specific acid value and hydroxyl value, which is obtained by reacting a specific alcohol component with a specific carboxylic acid component in a specific mixing ratio, has excellent seizure resistance, wear resistance, low-temperature fluidity, and oxidation stability. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-102235 Summary of the Invention [Problem to be solved by the invention]

[0005] Lubricating base oils are required to have the ability to maintain fluidity even in cold climates while exhibiting high viscosity, but the lubricating base oils specifically disclosed in Patent Document 1 were not able to achieve both high viscosity and the ability to maintain fluidity at low temperatures when contained in a lubricating oil composition.

[0006] An object of the present invention is to provide a lubricating oil composition that is capable of achieving both high viscosity and maintaining fluidity at low temperatures. [Means for solving the problem]

[0007] The present invention provides A lubricating oil composition containing a carboxylic acid ester compound having a constitutional unit derived from trimethylolpropane and a constitutional unit derived from caprylic acid, the content of the trimethylolpropane-derived structural units in all structural units constituting the carboxylic acid ester compound is 28.0 mol % or more and 33.0 mol % or less; In the lubricating oil composition, the content of the caprylic acid-derived structural units in all structural units constituting the carboxylic acid ester compound is 42.4 mol % or more and 48.4 mol % or less. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a lubricating oil composition that is both highly viscous and maintains fluidity at low temperatures. DETAILED DESCRIPTION OF THE INVENTION

[0009] <Lubricating oil composition> The lubricating oil composition of the present embodiment comprises A lubricating oil composition containing a carboxylic acid ester compound (hereinafter also referred to as component (A)) having a structural unit derived from trimethylolpropane and a structural unit derived from caprylic acid, the content of the trimethylolpropane-derived structural units in all structural units constituting the carboxylic acid ester compound is 28.0 mol % or more and 33.0 mol % or less; The content of the caprylic acid-derived structural units in all structural units constituting the carboxylic acid ester compound is 42.4 mol % or more and 48.4 mol % or less. The lubricating oil composition of this embodiment can achieve both high viscosity and good fluidity retention at low temperatures. The reason why the lubricating oil composition of this embodiment exhibits such effects is partially unknown, but is presumed to be as follows.

[0010] The carboxylic acid ester compound of this embodiment has three hydroxy groups in the molecule and further has structural units derived from trimethylolpropane which have a branched structure, thereby forming a branched structure in the carboxylic acid ester compound, which makes it possible to increase the viscosity of the lubricating oil composition during normal use. Furthermore, by setting the content of structural units of caprylic acid, which has a medium carbon number and a linear structure, to half the amount of the hydroxy groups in trimethylolpropane, it is possible to appropriately adjust the degree of molecular entanglement, which is thought to make it possible to achieve both high viscosity and the ability to maintain fluidity at low temperatures.

[0011] [Component (A)] The component (A) has a structure obtained by dehydration condensation of caprylic acid, a carboxyl group-containing hydrocarbon compound, and trimethylolpropane, an aliphatic polyhydric alcohol, and has structural units derived from trimethylolpropane and structural units derived from caprylic acid.

[0012] The content of trimethylolpropane-derived structural units in all structural units constituting component (A) is 28.0 mol% or more, preferably 28.5 mol% or more, more preferably 29.0 mol% or more, and even more preferably 29.5 mol% or more, from the viewpoint of increasing the viscosity of the lubricating oil composition and ensuring flowability at low temperatures, and from the same viewpoint is 33.0 mol% or less, preferably 32.5 mol% or less, and more preferably 32.0 mol% or less.

[0013] The content of constituent units derived from caprylic acid in all constituent units constituting the component (A) is 42.4 mol% or more, preferably 43.4 mol% or more, more preferably 44.4 mol% or more, and even more preferably 44.9 mol% or more, from the viewpoint of increasing the viscosity of the lubricating oil composition and ensuring flowability at low temperatures, and from the same viewpoint is 48.4 mol% or less, preferably 47.4 mol% or less, more preferably 46.4 mol% or less, and even more preferably 45.9 mol% or less.

[0014] Preferably, component (A) further contains structural units derived from adipic acid. The inclusion of structural units derived from adipic acid allows component (A) to form a polymer structure, further increasing the viscosity of the lubricating oil composition containing component (A). Furthermore, by limiting the proportions of structural units derived from trimethylolpropane, structural units derived from adipic acid, and structural units derived from caprylic acid within specific ranges among all structural units, component (A) is prevented from becoming too network-like, which is believed to improve the low-temperature fluidity of the lubricating oil composition containing component (A).

[0015] The content of structural units derived from adipic acid in all structural units constituting component (A) is preferably 20.2 mol% or more, more preferably 21.2 mol% or more, even more preferably 22.2 mol% or more, and still more preferably 23.3 mol% or more, from the viewpoint of increasing the viscosity of the lubricating oil composition and ensuring flowability at low temperatures, and from the same viewpoint is preferably 26.6 mol% or less, more preferably 25.5 mol% or less, even more preferably 24.4 mol% or less, and still more preferably 23.9 mol% or less.

[0016] From the viewpoint of increasing the viscosity of the lubricating oil composition and ensuring flowability at low temperatures, the acid value of component (A) is preferably 1 mgKOH / g or less, more preferably 0.5 mgKOH / g or less, and even more preferably 0.3 mgKOH / g or less.

[0017] From the viewpoint of increasing the viscosity of the lubricating oil composition and ensuring flowability at low temperatures, the hydroxyl value of component (A) is preferably 20 mgKOH / g or less, more preferably 15 mgKOH / g or less, and even more preferably 11 mgKOH / g or less.

[0018] The lubricating oil composition of this embodiment has a kinematic viscosity at 40°C of preferably 400mm 2 / s or more, preferably 500 mm 2 / s or more, and preferably 800 mm 2 / s or less, preferably 700 mm2 / s or less.

[0019] The lubricating oil composition of this embodiment may contain a component (hereinafter also referred to as component (B)) other than component (A) that is commonly used as a lubricating oil. Examples of component (B) include mineral oils such as paraffinic hydrocarbons, naphthenic hydrocarbons, and aromatic hydrocarbons, synthetic oils such as polyalphaolefins and polybutenes, ether oils such as polyglycols and phenyl ethers, silicone oils such as polydimethylsiloxanes and polyphenylmethylsiloxanes, ester oils other than carboxylic acid esters such as phosphate esters and silicate esters, and oils made of carboxylic acid esters other than component (A).

[0020] In the lubricating oil composition of this embodiment, the content of component (A) relative to the total of components (A) and (B) is preferably 50% by mass or more, more preferably 75% by mass or more, even more preferably 90% by mass or more, still more preferably 99% by mass or more, and even more preferably substantially 100% by mass, from the viewpoint of increasing the viscosity of the lubricating oil composition and ensuring flowability at low temperatures. In this specification, "substantially 100% by mass" refers to a state in which trace amounts of impurities and the like are inevitably contained.

[0021] Furthermore, the lubricating oil composition of this embodiment may contain, in addition to the components (A) and (B), additives generally added to lubricating oils (hereinafter also referred to as component (C)) as needed, provided that the effects of the present invention are not impaired. Examples of component (C) include detergents, dispersants, antioxidants, oiliness improvers, antiwear agents, extreme pressure agents, rust inhibitors, corrosion inhibitors, metal deactivators, viscosity index improvers, pour point depressants, antifoaming agents, emulsifiers, demulsifiers, fungicides, and solid lubricants.

[0022] In the lubricating oil composition of this embodiment, the content of component (C) relative to 100 parts by mass of the total of component (A) and component (B) is preferably 30 parts by mass or less, more preferably 25 parts by mass or less, even more preferably 20 parts by mass or less, and preferably 5 parts by mass or more, more preferably 8 parts by mass or more, even more preferably 10 parts by mass or more.

[0023] The content of component (A) in the lubricating oil composition is preferably 50% by mass or more, more preferably 75% by mass or more, even more preferably 90% by mass or more, still more preferably 99% by mass or more, and even more preferably substantially 100% by mass, from the viewpoint of increasing the viscosity of the lubricating oil composition and ensuring flowability at low temperatures.

[0024] <Method of manufacturing lubricating oil composition> The production method of this embodiment is a production method of the lubricating oil composition of the above embodiment, The method includes a mixture preparation step of preparing a mixture having a trimethylolpropane content of 28.0 mol% or more and 33.0 mol% or less and a caprylic acid content of 42.4 mol% or more and 48.4 mol% or less, and a reaction step of subjecting the trimethylolpropane and caprylic acid in the mixture to an esterification reaction.

[0025] [Mixture adjustment process] When the production method of this embodiment is a production method of a lubricating oil composition of the above embodiment containing component (A) having a structural unit derived from adipic acid, the mixture preparation step is a step of preparing a mixture having a trimethylolpropane content of 28.0 mol % to 33.0 mol % inclusive, an adipic acid content of 20.2 mol % to 26.6 mol % inclusive, and a caprylic acid content of 42.4 mol % to 48.4 mol % inclusive.

[0026] The contents of the trimethylolpropane-derived structural units, the adipic acid-derived structural units, and the caprylic acid-derived structural units in the component (A) contained in the lubricating oil composition of the embodiment can be calculated from the amounts (mol %) of the trimethylolpropane, adipic acid, and caprylic acid in the mixture.

[0027] In the esterification reaction between trimethylolpropane and caprylic acid, the ratio of the total equivalent of carboxy groups in all carboxylic acid components to 1 equivalent of hydroxy groups in trimethylolpropane in the mixture is preferably 0.95 or more and 1 or less, more preferably 0.97 or more and 1 or less. Increasing the proportion of trimethylolpropane in the mixture reduces the probability that trimethylolpropane, which has three reactive sites, will remain unreacted, but it is possible to reduce the amount of carboxylic acid remaining unreacted, and thus it is possible to suppress a decrease in the performance of the lubricating oil composition.

[0028] [Reaction step] The component (A) can be produced by esterifying trimethylolpropane and caprylic acid in the mixture in the reaction step according to a known method. When producing the component (A) having structural units derived from adipic acid, the component (A) having structural units derived from trimethylolpropane, structural units derived from adipic acid, and structural units derived from caprylic acid can be produced by esterifying trimethylolpropane, adipic acid, and caprylic acid in the mixture according to a known method.

[0029] <Grease> The grease of this embodiment contains the lubricating oil composition of the above embodiment.

[0030] From the viewpoint of achieving both high viscosity and maintaining fluidity at low temperatures, the content of component (A) in the grease of this embodiment is preferably 20% by mass or more, more preferably 30% by mass or more, even more preferably 40% by mass or more, still more preferably 50% by mass or more, still more preferably 60% by mass or more, and still more preferably 70% by mass or more.

[0031] The grease of this embodiment preferably contains a thickener. The thickener is not particularly limited, but examples thereof include soap-based thickeners, urea-based thickeners, bentone, and silica gel.

[0032] When a thickener is used in the grease of this embodiment, the blending ratio of the thickener is preferably 1 part by mass or more, more preferably 5 parts by mass or more, and preferably 30 parts by mass or less, more preferably 25 parts by mass or less, per 100 parts by mass of the total content of the components (A) and (B) in the grease of this embodiment.

[0033] The grease of this embodiment may contain additives other than the thickener that are commonly used for greases, as needed, within the scope of not impairing the effects of the present invention. Examples of additives commonly used for greases include detergents, dispersants, antioxidants, oiliness improvers, antiwear agents, extreme pressure agents, rust inhibitors, corrosion inhibitors, metal deactivators, viscosity index improvers, pour point depressants, antifoaming agents, emulsifiers, demulsifiers, fungicides, and solid lubricants.

[0034] The content of the additives generally used for grease is 10 parts by mass or less relative to 100 parts by mass of the total content of the component (A) and the component (B) in the grease of this embodiment.

[0035] The grease of the present embodiment is capable of achieving both high viscosity and maintaining fluidity at low temperatures, and is therefore suitable for use in high and low temperature environments, and is suitable as a grease for use in parts that require maintaining lubrication at high and low temperatures, such as bearings for air conditioner fan motors, automotive bearings, bearings for audio equipment, bearings for computers, and spindle motor bearings. [Example]

[0036] The present invention will be specifically described below based on examples, but the present invention is not limited to these examples. Various measurement and evaluation methods are as follows.

[0037] <Production of lubricating oil composition> Example 1 A 2 L four-neck flask equipped with a stirrer, nitrogen gas inlet, thermometer, and condenser-equipped water separator was charged with 450.0 g (3.35 mol) of trimethylolpropane (Nantong Baichuan New Materials Co., Ltd.), 362.7 g (2.48 mol) of adipic acid (Asahi Kasei Corporation), 689.8 g (4.85 mol) of caprylic acid (Kao Corporation Lunac 8-98), and 1.5 g (0.05 mol% based on the total molar amount of the charged compounds) of tetrapropoxytitanium (Fujifilm Wako Pure Chemical Industries, Ltd.) as a catalyst. Next, the flask was heated with stirring while nitrogen gas (0.2 L / min) was blown into the flask, and the esterification reaction was carried out at 230 °C for 6 hours. Next, 60 g of pure water (4% by mass based on the total mass of the charged compounds) was added to the reaction solution, and the mixture was stirred at 80 °C for 2 hours to hydrolyze the catalyst and then dehydrated. Next, the mixture was subjected to adsorption treatment using diatomaceous earth (Radiolite #2000 manufactured by Showa Chemical Industry Co., Ltd.) and activated carbon (Carborafine-3 manufactured by Osaka Gas Chemicals Co., Ltd.), and then filtered to obtain a carboxylic acid ester compound, which was used as the lubricating oil composition of Example 1.

[0038] Comparative Example 1 In Example 1, the trimethylolpropane, adipic acid, and caprylic acid were charged in the following amounts: 450.0 g (3.35 mol) of trimethylolpropane, 318.7 g (2.19 mol) of adipic acid, and 509.1 g (3.53 mol) of caprylic acid. In addition, 208.9 g (1.22 mol) of capric acid (Lunac 10-98 manufactured by Kao Corporation) and 1.5 g of tetrapropoxytitanium (0.05 mol% relative to the total molar amount of the charged compounds) were added. An ester compound was obtained in the same manner as in Example 1, and a lubricating oil composition according to Comparative Example 1 was prepared.

[0039] <Evaluation method> [Evaluation of kinematic viscosity at 40°C] 40℃ kinematic viscosity (mm 2 / s) was measured in accordance with JIS K2283.

[0040] [Evaluation of low-temperature fluidity] The pour point (°C) was measured according to ASTM D6749 and used as an index of low-temperature fluidity. The lower the pour point, the better the low-temperature fluidity.

[0041] [Measurement of Acid Value] The acid value was measured by neutralization titration in accordance with JIS K0070-1992.

[0042] [Measurement of hydroxyl value] The hydroxyl value was measured by the pyridine-acetyl chloride method in accordance with JIS K0070:1992.

[0043] The evaluation results are shown in Table 1. The numerical values ​​showing the proportions of substance amounts (unit: mol %) in Table 1 indicate the proportions of each structural unit in the component (A) determined from the blending ratios of the raw materials in the mixture.

[0044] [Table 1]

Claims

1. A lubricating oil composition containing a carboxylic acid ester compound having a constitutional unit derived from trimethylolpropane and a constitutional unit derived from caprylic acid, the content of the trimethylolpropane-derived structural units in all structural units constituting the carboxylic acid ester compound is 28.0 mol % or more and 33.0 mol % or less; a lubricating oil composition in which the content of the caprylic acid-derived structural units in all structural units constituting the carboxylic acid ester compound is 42.4 mol % or more and 48.4 mol % or less;

2. the carboxylic acid ester compound has a structural unit derived from adipic acid, 2. The lubricating oil composition according to claim 1, wherein the content of the structural units derived from adipic acid in all structural units constituting the carboxylic acid ester compound is 20.2 mol % or more and 26.6 mol % or less.

3. A grease containing the lubricating oil composition according to claim 1 or 2.

4. A method for producing the lubricating oil composition of claim 1, comprising: a mixture preparation step of preparing a mixture having a trimethylolpropane content of 28.0 mol% or more and 33.0 mol% or less and a caprylic acid content of 42.4 mol% or more and 48.4 mol% or less; A method for producing a lubricating oil composition, comprising a reaction step of esterifying trimethylolpropane and caprylic acid in the mixture.

5. The method for producing a lubricating oil composition according to claim 4, wherein the content of adipic acid in the mixture is 20.2 mol % or more and 26.6 mol % or less.

6. 6. The method for producing a lubricating oil composition according to claim 5, wherein the total equivalent of carboxy groups of all carboxylic acid components in the mixture is 0.95 or more and 1 or less per equivalent of hydroxy groups of trimethylolpropane.

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