Lubricating oil composition

Abstract

To provide a lubricant composition which can excel in extreme pressure performance based on seizure resistance and wear preventive properties and low-temperature fluidity, can have a high viscosity index and can improve fuel-saving performance, gear pitching resistance performance and bearing fatigue life.SOLUTION: There is provided a lubricant composition which comprises a lubricant base oil containing a base oil (A): a specific mineral oil-based base oil, a base oil (B): a specific wax isomerized base oil and a base oil (C): a specific dibasic acid ester base oil, wherein the content of the base oil (A) in the lubricant base oil is 45 mass% or more, the content of the base oil (B) in the lubricant base oil is 10 to 40 mass% and the content of the base oil (C) in the lubricant base oil is 15 to 40 mass% and the kinematic viscosity of the lubricant oil base oil at 100°C is 7.00 mm2 / s or more.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] Lubricating oil compositions are used in a variety of fields, for example, in internal combustion engines such as gasoline engines and diesel engines, gear devices, etc. Research into various types of lubricating oil compositions has been conducted in order to achieve performance suited to these applications.

[0003] For example, Japanese Patent Application Laid-Open No. 2017-171768 (Patent Document 1) discloses a lubricating oil composition that contains (A) a base oil, (B) an olefin polymer having a number average molecular weight of 1,000 to 12,000, and (C) a sulfur compound having a specific structural unit, and that has a total sulfur atom content of 1.2 to 2.5% by mass based on the total amount of the composition.

[0004] Furthermore, Japanese Patent Publication No. 2009-533497 (Patent Document 2) discloses technology related to gear lubricants, and in Example 7 thereof, discloses a 75W-90 grade lubricant oil composition containing 39.9% by mass of a base oil having a viscosity of 7.597 cSt at 100°C, which is prepared by hydrogenating, isomerizing, and dewaxing a mixture of two specific types of wax, and 52.05% by mass of bright stock (Citgo 150 Bright Stock).

[0005] However, conventional lubricating oil compositions such as those described in Patent Documents 1 and 2 have high extreme pressure performance, a high viscosity index, and excellent low-temperature fluidity, but are not sufficient in terms of improving fuel economy, gear pitting resistance, and bearing fatigue life.

[0006] Prior to 2005, the SAE J306 Standard (automotive gear oils) viscosity specification did not specify the kinematic viscosity (minimum viscosity) after shear stress. Therefore, when producing lubricating oil compositions (e.g., gear oil compositions) of 75W-90 grade or higher, the base oil viscosity was set low to meet the 75W low-temperature viscosity specification (BF viscosity at -40°C: 150,000 mPa·s or less). However, if the 75W low-temperature viscosity specification was met by setting the base oil viscosity low, there was concern that the low viscosity would significantly reduce gear fatigue durability. Therefore, conventional lubricating oil compositions (e.g., gear oil compositions) of 75W-90 grade or higher that met the 75W low-temperature viscosity specification by setting the base oil viscosity low are not currently used in large freight vehicles or passenger cars for the purpose of fuel economy. While gear oils using only synthetic oils (e.g., PAO) as the base oil are available on the market, they are not widely used due to cost and durability / reliability considerations. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2017-171768 [Patent Document 2] Special Publication No. 2009-533497 Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention has been made in view of the problems associated with the prior art described above, and has as its object the provision of a lubricating oil composition which is capable of exhibiting excellent extreme-pressure performance, based on anti-seizure properties and anti-wear properties, and excellent low-temperature fluidity, as well as having a high viscosity index, and which is capable of improving fuel economy, gear pitching resistance, and bearing fatigue life. [Means for solving the problem]

[0009] As a result of intensive research conducted by the present inventors to achieve the above object, it has been found that the lubricating oil composition contains a lubricating base oil (base oil composition: mixed base oil) containing the following base oils (A) to (C), and that the content of the base oil (A) in the lubricating base oil is 45% by mass or more, the content of the base oil (B) in the lubricating base oil is 10 to 40% by mass, and the content of the base oil (C) in the lubricating base oil is 15 to 40% by mass, and further, the kinematic viscosity at 100°C of the lubricating base oil is 7.00 mm 2 / s or more, the resulting lubricating oil composition exhibits excellent extreme-pressure performance in terms of anti-seizure properties and anti-wear properties, as well as excellent low-temperature fluidity, and also has a high viscosity index, making it possible to improve fuel economy, gear pitting resistance, and bearing fatigue life, and has thus completed the present invention.

[0010] That is, the lubricating oil composition of the present invention comprises the following base oils (A) to (C): (A) Kinematic viscosity at 100°C is 10 to 40 mm 2 / s and a mineral base oil having a sulfur content of 0.3 to 2.0 mass%; (B) Kinematic viscosity at 100°C is 1.5 to 3.0 mm 2 / s, a wax isomerized base oil having a viscosity index of 120 or more and a pour point of -30°C or less; (C) Kinematic viscosity at 100°C is 1.5 to 3.5 mm 2 / s, a dibasic acid ester base oil having a viscosity index of 120 or more and a pour point of -50°C or less; The lubricating oil base oil comprises The content of the base oil (A) in the lubricating base oil is 45% by mass or more, The content of the base oil (B) in the lubricating base oil is 10 to 40 mass %, The content of the base oil (C) in the lubricating base oil is 15 to 40 mass%, and The kinematic viscosity of the lubricating base oil at 100°C is 7.00 mm 2 / s or more, The present invention is characterized by the following. In this specification, the "content" of each base oil in the descriptions "the content of the base oil (A) in the lubricating base oil," "the content of the base oil (B) in the lubricating base oil," and "the content of the base oil (B) in the lubricating base oil" all refer to the mass ratio (mass content ratio) of each base oil determined based on the total mass of the lubricating base oil (base oil composition) (total amount of lubricating base oil). In addition, in this specification, for base oils (A) to (C), the "sulfur content" in each base oil refers to the mass ratio of sulfur (S) contained in that base oil (mass ratio in terms of sulfur atoms (unit: mass%)) based on the total mass of that base oil, and this value can be measured in accordance with ASTM D4951. Furthermore, in this specification, the "kinematic viscosity at 100 ° C" refers to the kinematic viscosity at 100 ° C specified in JIS K 2283-2000. In this specification, the term "viscosity index" refers to a viscosity index measured in accordance with JIS K 2283-2000. In this specification, the term "pour point" refers to a pour point measured in accordance with JIS K 2269-1987.

[0011] In the lubricating oil composition of the present invention, the mass-based phosphorus content in the lubricating oil composition is preferably 0.05 mass% or more, and the ratio of the mass-based sulfur content in the lubricating oil base oil to the mass-based phosphorus content in the lubricating oil composition ([the sulfur content] / [the phosphorus content]) is preferably 2.0 to 8.0. In this specification, the "mass-based phosphorus content in the lubricating oil composition" refers to the mass ratio of phosphorus (P) contained in the lubricating oil composition (mass ratio in terms of phosphorus atoms (unit: mass%)) determined based on the total mass of the lubricating oil composition (total amount of the lubricating oil composition), and the "mass-based sulfur content in the lubricating oil base oil" refers to the mass ratio of sulfur (S) contained in the lubricating oil base oil (mass ratio in terms of sulfur atoms (unit: mass%)) determined based on the total mass of the lubricating oil base oil (total amount of the lubricating oil base oil). Both the "phosphorus content" and the "sulfur content" can be measured in accordance with ASTM D4951. In addition, the "sulfur content by mass in the lubricating base oil" may be determined by measuring each base oil contained in the lubricating base oil in accordance with ASTM D4951 and calculating from the amount of sulfur in each base oil contained and the content of each base oil.

[0012] Furthermore, in the lubricating oil composition of the present invention, when a shear stability test is conducted in accordance with JPI-5S-29-88 in which ultrasonic waves are irradiated under conditions of a frequency of 10 kHz, an oscillator amplitude of 28 μm, and an irradiation time of 10 hours, and the kinematic viscosity of the lubricating oil composition at 100°C is measured and compared before and after the ultrasonic irradiation, it is preferable that the rate of decrease in the kinematic viscosity of the lubricating oil composition at 100°C due to the ultrasonic irradiation is 10% or less. Furthermore, in the lubricating oil composition of the present invention, it is preferable that the Brookfield viscosity of the lubricating oil composition at -40°C is 150,000 mPa·s or less. Furthermore, in the lubricating oil composition of the present invention, it is preferable that the lubricating oil composition is a gear oil composition. Note that such a lubricating oil composition of the present invention may also comply with the viscosity grade 75W-90 of the SAE J306 Standard revised in 2019. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a lubricating oil composition that is excellent in extreme pressure performance based on anti-seizure properties and anti-wear properties, and in low temperature fluidity, and that has a high viscosity index, and that is capable of improving fuel economy performance, gear pitting resistance, and bearing fatigue life. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will be described in detail below with reference to preferred embodiments. In this specification, unless otherwise specified, the expression "X to Y" for numerical values ​​X and Y means "X or more and Y or less." In addition, when a unit is assigned only to the numerical value Y in such an expression, the unit also applies to the numerical value X.

[0015] The lubricating oil composition of the present invention comprises a lubricating base oil (base oil composition) containing the base oils (A) to (C), wherein the content of the base oil (A) in the lubricating base oil is 45% by mass or more, the content of the base oil (B) in the lubricating base oil is 10 to 40% by mass, the content of the base oil (C) in the lubricating base oil is 15 to 40% by mass, and the kinematic viscosity of the lubricating base oil at 100°C is 7.00 mm 2 / s or more.

[0016] <Base oil (A)> The base oil (A) contained in the lubricating base oil (base oil composition) has a kinematic viscosity at 100°C of 10 to 40 mm 2 The mineral base oil has a sulfur content of 0.3 to 2.0 mass % and a viscosity of 1000 MPa / s. By using such a mineral base oil, it is possible to improve the durability and reliability (seizure resistance and wear prevention) of the lubricating base oil.

[0017] Such base oil (A) has a kinematic viscosity at 100°C of 10 to 40 mm 2 The kinematic viscosity of base oil (A) at 100°C is 10mm / s. 2 / s or more, 10 mm2 Compared with a lubrication rate of less than 40 mm / s, the oil film formation performance at lubrication points is improved, which makes it possible to improve gear pitting resistance and bearing fatigue life, as well as improve seizure resistance. 2 / s or less, 40 mm 2 Compared with a kinematic viscosity exceeding 150 / s, the viscosity temperature characteristics and low-temperature viscosity characteristics are further improved, making it possible to reduce churning loss at low temperatures. The kinematic viscosity of base oil (A) at 100°C is set to 15 to 35 mm / s from the viewpoint of obtaining a greater effect in terms of improving durability and reliability due to oil film forming performance and improving fuel economy performance due to low-temperature fluidity. 2 / s (more preferably 25 to 35 mm 2 / s) is more preferable.

[0018] The base oil (A) is a mineral base oil having a sulfur content (sulfur content) of 0.3 to 2.0% by mass. By setting the sulfur content to 0.3% by mass or more, it is possible to improve seizure resistance and anti-wear properties and improve durability and reliability compared to when the sulfur content is less than 0.3% by mass. On the other hand, by setting the sulfur content to 2.0% by mass or less, it is possible to improve oxidation stability compared to when the sulfur content exceeds 2.0% by mass. The sulfur content of the base oil (A) is more preferably 0.4 to 1.6% by mass (more preferably 0.5 to 1.5% by mass) because this is more effective in improving durability and oxidation stability.

[0019] In addition, as such a mineral oil-based base oil (base oil (A)), a base oil having a kinematic viscosity at 40°C of 70 to 700 mm 2 / s is preferable, 150 to 600 mm 2 / s is more preferable, 250 to 500 mm 2 / s is even more preferred. When the kinematic viscosity at 40°C is equal to or greater than the lower limit, compared to when it is below the lower limit, it is possible to further improve the oil film forming ability at lubricated points, thereby providing better lubrication, and it also tends to be possible to further reduce evaporation loss of the lubricating oil composition and further reduce the amount of lubricating oil consumed. On the other hand, when it is equal to or less than the upper limit, it tends to be possible to obtain higher performance (effect) in terms of low-temperature viscosity characteristics and fuel-saving performance of the lubricating oil composition, compared to when it exceeds the upper limit. In this specification, "kinematic viscosity at 40°C" means the kinematic viscosity at 40°C specified in JIS K 2283-2000.

[0020] Furthermore, the mineral oil base oil (base oil (A)) preferably has a pour point of -5°C or lower (more preferably -7.5°C or lower, even more preferably -10°C or lower, and particularly preferably -12.5°C or lower). When the pour point is below the upper limit, it becomes possible to improve the low-temperature fluidity of the entire lubricating oil composition compared to when the pour point exceeds the upper limit, and a greater effect tends to be obtained in terms of improving the low-temperature fluidity of the composition. Furthermore, although there is no particular restriction on the lower limit of the pour point, from the viewpoint of enabling a higher viscosity index, it is more preferable that the pour point be -17.5°C or higher.

[0021] Furthermore, the mineral oil-based base oil (base oil (A)) preferably has a viscosity index of 80 or more (more preferably 85 or more, even more preferably 90 or more, and particularly preferably 95 or more). By making the viscosity index equal to or higher than the lower limit, a higher effect in terms of fuel economy performance can be obtained.

[0022] Furthermore, the mineral oil-based base oil (base oil (A)) preferably has a flash point of 250°C or higher (more preferably 260°C or higher, even more preferably 280°C or higher, and particularly preferably 300°C or higher). By setting the flash point at or above the lower limit, safety during high-temperature use tends to be improved compared to when the flash point is below the lower limit. In the present invention, the "flash point" of the base oil means the flash point measured in accordance with JIS K 2265-4-2007 (Cleveland Open Method).

[0023] Examples of the mineral base oil (base oil (A)) include paraffinic and naphthenic mineral base oils, normal paraffins, and isoparaffins, which are obtained by refining lubricating oil fractions obtained by atmospheric and vacuum distillation of crude oil through a single or a combination of two or more refining processes such as solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, hydrorefining, sulfuric acid washing, and clay treatment. The mineral base oil (base oil (A)) is preferably a base oil produced by subjecting the feedstock oils (1) to (8) described below to one or two or more of a solvent refining process such as furfural solvent extraction, a dewaxing process such as solvent dewaxing or catalytic dewaxing, and a hydrorefining process such as hydrofinishing. [Feedstock oil (1)~(8)] (1) Distillates obtained by atmospheric distillation of paraffinic and / or mixed crude oils; (2) Vacuum distillates (WVGO) of atmospheric residues of paraffinic and / or mixed crude oils; (3) wax obtained by lubricant dewaxing process and / or Fischer-Tropsch wax produced by GTL process, etc.; (4) Mild hydrocracking oil (MHC) of one or a mixture of two or more oils selected from (1) to (3) above; (5) A mixed oil of two or more oils selected from (1) to (4) above; (6) Deasphalted oil (DAO) of (1), (2), (3), (4), or (5) above; (7) Mild hydrocracked oil (MHC) as described in (6) above; (8) A mixed oil of two or more oils selected from the above (1) to (7).

[0024] As the mineral base oil (base oil (A)), a base oil of Group I in the base oil classification by the American Petroleum Institute (API) can be suitably used (hereinafter, the API base oil classification group will be simply referred to as "API Group"). API Group I base oils are mineral base oils having a sulfur content of more than 0.03 mass% (>0.03 mass%), a saturates content of less than 90 mass% (<90 mass%), and a viscosity index of 80 or more and less than 120. As the mineral base oil (base oil (A)), so-called bright stock (150BS, etc.) can be suitably used. The mineral base oil used as such base oil (A) may consist of one type of mineral base oil or may consist of a mixture of two or more types of mineral base oils.

[0025] <Base oil (B)> The base oil (B) contained in the lubricating base oil (base oil composition) has a kinematic viscosity at 100°C of 1.5 to 3.0 mm 2 / s, a viscosity index of 120 or more, and a pour point of -30°C or less. The use of such wax isomerized base oil makes it possible to improve low-temperature fluidity (fuel economy) and pitting performance (fatigue life) in gears and bearings.

[0026] Such base oil (B) has a kinematic viscosity at 100°C of 1.5 to 3.0 mm 2 The kinematic viscosity of base oil (B) at 100°C is 1.5mm / s. 2 / s or more, 1.5 mm 2 Compared with the case where the kinematic viscosity of the base oil (B) at 100°C is less than 3.0 mm / s, the oil film formation performance at the lubricated portion is improved, and the pitting resistance performance (fatigue life) can be improved. 2 / s or less, 3.0 mm 2In comparison with the case where the kinematic viscosity exceeds 1.9 to 2.9 mm / s, the traction coefficient of the base oil is lowered, and fuel economy performance can be improved. In addition, the kinematic viscosity at 100°C of the base oil (B) is preferably 1.9 to 2.9 mm / s, since a greater effect can be obtained in terms of improving pitting resistance and fuel economy performance. 2 / s (more preferably 2.0 to 2.8 mm 2 / s) is more preferable.

[0027] Furthermore, the base oil (B) is a wax isomerized base oil having a viscosity index of 120 or more. By making the viscosity index of the base oil (B) 120 or more, it is possible to further improve the lubricating effect at low temperatures and also improve fuel economy performance compared to when the viscosity index is less than 120. The viscosity index of the base oil (B) is more preferably 121 or more (more preferably 123 or more, particularly preferably 125 or more). By making the viscosity index equal to or greater than the lower limit, greater effects in terms of fuel economy performance tend to be obtained.

[0028] Furthermore, the base oil (B) is a wax isomerized base oil having a pour point of -30°C or lower. When the pour point of the base oil (B) is -30°C or lower, the low-temperature performance (fluidity at low temperatures and lubrication performance at low temperatures) is superior compared to when the pour point exceeds -30°C. The pour point of the base oil (B) is more preferably -31°C or lower (more preferably -33°C or lower, and particularly preferably -35°C or lower). When the pour point is below the upper limit, the low-temperature fluidity of the entire lubricating oil composition can be improved compared to when the pour point exceeds the upper limit, and a greater effect in improving the low-temperature fluidity of the composition tends to be obtained. Note that the lower limit of the pour point is not particularly limited, but from the viewpoint of achieving a higher viscosity index, the pour point is more preferably -45°C or higher.

[0029] In addition, as such a wax isomerized base oil (base oil (B)), a kinematic viscosity at 40°C of 3.0 to 15.0 mm 2 / s (more preferably 5.0 to 10.0 mm 2When the kinematic viscosity at 40°C is equal to or greater than the lower limit, the oil film forming ability is improved and the lubricity is more excellent than when the kinematic viscosity is less than the lower limit, and on the other hand, when the kinematic viscosity is equal to or less than the upper limit, the low-temperature fluidity is better and the fluid resistance is smaller than when the kinematic viscosity is greater than the upper limit, so that the rotational resistance is smaller and fuel economy is further improved.

[0030] Furthermore, the wax isomerized base oil (base oil (B)) preferably has a flash point of 175°C or higher (more preferably 180°C or higher, even more preferably 185°C or higher, and particularly preferably 190°C or higher). By setting the flash point at or above the lower limit, safety during high-temperature use tends to be further improved compared to when the flash point is below the lower limit.

[0031] From the viewpoint of oxidation stability, the wax isomerized base oil (base oil (B)) preferably has a sulfur content (sulfur content) of 30 ppm by mass or less (more preferably 20 ppm by mass or less, even more preferably 15 ppm by mass or less, and particularly preferably 10 ppm by mass or less). When the sulfur content is equal to or less than the upper limit, a greater effect in terms of improving oxidation stability tends to be obtained compared to when the sulfur content exceeds the upper limit.

[0032] %C of the wax isomerized base oil (base oil (B)) P is preferably 85 or more (more preferably 85 to 95, even more preferably 87 to 95, and particularly preferably 90 to 95). P By making the %C of the base oil (B) equal to or greater than the lower limit, it is possible to improve the viscosity-temperature characteristics and further improve fuel economy performance. In addition, when an additive is blended into the lubricating base oil, it is possible to further enhance the effect of the additive. In addition, the %C of the base oil (B) P When the content is equal to or less than the upper limit, the solubility of the additive can be further increased.

[0033] %C of the wax isomerized base oil (base oil (B))A is preferably 3 or less (more preferably 2.5 to 0, even more preferably 2 to 0, particularly preferably 1 to 0). A By making the %C of the base oil (B) equal to or less than the upper limit, it is possible to further improve the viscosity-temperature characteristics and also to further improve the fuel economy performance. A By making the viscosity index equal to or greater than the lower limit, it is possible to obtain greater effects in terms of improving fuel economy by increasing the viscosity index, and improving safety by increasing the flash point.

[0034] %C of the wax isomerized base oil (base oil (B)) N is preferably 2 to 15 (more preferably 3 to 12, even more preferably 4 to 10, and particularly preferably 5 to 9). N When the %C of the base oil (B) is equal to or less than the upper limit, it is possible to further improve the viscosity-temperature characteristics and also to further improve the fuel economy performance. N When the solubility of the additive is equal to or greater than the lower limit, the solubility of the additive can be further increased.

[0035] In addition, the wax isomerized base oil (base oil (B)) has a %C P、 %C N and %C A More preferably, the wax isomerized base oil (base oil (B)) satisfies the above conditions simultaneously. P is 85 or more, and %C N is 2 to 15 and %C A It is particularly preferred that the wax isomerized base oil satisfies the condition that the β-glucan content is 3 or less.

[0036] In this specification, %C P , %C N and %C AThe percentages of the paraffin carbon number relative to the total carbon number, the percentage of the naphthenic carbon number relative to the total carbon number, and the percentage of the aromatic carbon number relative to the total carbon number, respectively, are determined by a method (ndM ring analysis) in accordance with ASTM D 3238-85.

[0037] The wax isomerized base oil (base oil (B)) is a base oil obtained by isomerizing wax such as petroleum wax or GTL (Gas to Liquid) wax (e.g., Fischer-Tropsch synthetic oil). For example, wax obtained by a lubricant dewaxing process and / or Fischer-Tropsch wax produced by a GTL process or the like, or waxes such as mild hydrocracking oil (MHC) or deasphalted oil (EAO) thereof, is isomerized, and the product is used directly or a lubricant fraction is recovered from it, followed by dewaxing treatment such as solvent dewaxing or catalytic dewaxing, and then solvent refining, or solvent refining followed by dewaxing treatment such as solvent dewaxing or catalytic dewaxing, etc., can be appropriately used. The wax isomerization method is not particularly limited, and known methods used in the field of lubricants can be appropriately used.

[0038] As the wax isomerized base oil (base oil (B)), an API Group III base oil can be suitably used. API Group III base oils have a sulfur content of 0.03 mass% or less, a saturates content of 90 mass% or more, and a viscosity index of 120 or more. The wax isomerized base oil used as base oil (B) may consist of one type of wax isomerized base oil, or may consist of a mixture of two or more types of wax isomerized base oils.

[0039] <Base oil (C)> The base oil (C) contained in the lubricating base oil (base oil composition) has a kinematic viscosity at 100°C of 1.5 to 3.5 mm 2 / s, a viscosity index of 120 or more, and a pour point of -50°C or less. The use of such a dibasic acid ester base oil makes it possible to improve low-temperature fluidity (fuel economy) and pitting performance (fatigue life) in gears and bearings.

[0040] Such base oil (C) has a kinematic viscosity at 100°C of 1.5 to 3.5 mm 2 The kinematic viscosity of base oil (C) at 100°C is 1.5mm / s. 2 / s or more, 1.5 mm 2 Compared with the case where the kinematic viscosity of the base oil (C) at 100°C is less than 3.5mm / s, the oil film formation performance at the lubricated parts is improved, and the pitting resistance performance (fatigue life) can be improved. 2 / s or less, 3.5 mm 2 The kinematic viscosity at 100°C of the base oil (C) is preferably 2.0 to 3.2 mm / s, since a greater effect can be obtained in terms of improving pitting resistance and fuel economy performance. 2 / s (more preferably 2.5 to 3.0 mm 2 / s) is more preferable.

[0041] Furthermore, the base oil (C) is a dibasic acid ester base oil having a viscosity index of 120 or more. By making the viscosity index of the base oil (C) 120 or more, it is possible to further improve the lubricating effect at low temperatures compared to when the viscosity index is less than 120, and it is possible to improve fuel economy performance. The viscosity index of the base oil (C) is more preferably 125 or more (more preferably 130 or more). By making the viscosity index equal to or greater than the lower limit, there is a tendency to obtain a higher effect in terms of fuel economy performance.

[0042] Furthermore, the base oil (C) is a dibasic acid ester base oil having a pour point of -50°C or lower. When the pour point of the base oil (C) is -50°C or lower, the low-temperature performance (fluidity at low temperatures and lubrication performance at low temperatures) is superior compared to when the pour point exceeds -50°C. The pour point of the base oil (C) is more preferably -60°C or lower (more preferably -65°C or lower, and particularly preferably -70°C or lower). When the pour point is below the upper limit, it is possible to improve the low-temperature fluidity of the entire lubricating oil composition compared to when the pour point exceeds the upper limit, and a greater effect tends to be obtained in terms of improving the low-temperature fluidity of the composition.

[0043] In addition, such a dibasic acid ester base oil (base oil (C)) has a kinematic viscosity at 40°C of 3.0 to 15.0 mm 2 / s (more preferably 5.0 to 12.0 mm 2 When the kinematic viscosity at 40°C is equal to or greater than the lower limit, the oil film forming ability is improved and the lubricating properties are more excellent than when the kinematic viscosity is below the lower limit, and on the other hand, when the kinematic viscosity is equal to or less than the upper limit, the lubricating oil composition tends to have better performance (effects) in terms of low-temperature viscosity characteristics and fuel economy performance than when the kinematic viscosity is above the upper limit.

[0044] Furthermore, the dibasic acid ester base oil (base oil (C)) preferably has a flash point of 180°C or higher (more preferably 190°C or higher, even more preferably 200°C or higher, and particularly preferably 210°C or higher). By setting the flash point at or above the lower limit, safety during high-temperature use tends to be further improved compared to when the flash point is below the lower limit.

[0045] Such a dibasic acid ester base oil (base oil (C)) is a base oil made of a dibasic acid ester, which is an ester of a dibasic acid and an alcohol consisting of a monohydric alcohol and / or a polyhydric alcohol. Thus, the dibasic acid ester base oil is a chemically synthesized oil synthesized from an alcohol and a dibasic acid, and basically does not contain sulfur.

[0046] Such dibasic acids preferably have 2 to 16 carbon atoms (more preferably 2 to 12). These dibasic acids may be linear or branched, saturated or unsaturated. Examples of such dibasic acids include ethanedioic acid, propanedioic acid, linear or branched butanedioic acid, linear or branched pentanedioic acid, linear or branched hexanedioic acid, linear or branched heptanedioic acid, linear or branched octanedioic acid, linear or branched nonanedioic acid, linear or branched decanedioic acid, linear or branched undecanedioic acid, linear or branched dodecanedioic acid, linear or branched tridecanedioic acid, linear or branched tetradecanedioic acid, linear or branched tetradecanedioic acid, and linear or branched tetradecanedioic acid. Examples of dibasic acids include heptadecanedioic acid, linear or branched hexadecanedioic acid, linear or branched hexenedioic acid, linear or branched heptene dioic acid, linear or branched octenedioic acid, linear or branched nonenedioic acid, linear or branched decenedioic acid, linear or branched undecenedioic acid, linear or branched dodecenedioic acid, linear or branched tridecenedioic acid, linear or branched tetradecenedioic acid, linear or branched heptadecenedioic acid, and linear or branched hexadecenedioic acid. These dibasic acids may be used alone or in combination of two or more.

[0047] The alcohol forming the ester may be a monohydric alcohol, a polyhydric alcohol (polyol), or a mixture thereof. Thus, the alcohol may be used alone or in combination of two or more.

[0048] The monohydric alcohol preferably has 1 to 24 carbon atoms (more preferably 1 to 12, and even more preferably 1 to 8). Such monohydric alcohols may be linear or branched, and may be saturated or unsaturated. Examples of such monohydric alcohols include methanol, ethanol, linear or branched propanol, linear or branched butanol, linear or branched pentanol, linear or branched hexanol, linear or branched heptanol, linear or branched octanol, linear or branched nonanol, linear or branched decanol, linear or branched undecanol, linear or branched dodecanol, linear or branched octan ... Examples of the polyol include tridecanol, linear or branched tetradecanol, linear or branched pentadecanol, linear or branched hexadecanol, linear or branched heptadecanol, linear or branched octadecanol, linear or branched nonadecanol, linear or branched eicosanol, linear or branched henicosanol, linear or branched tricosanol, linear or branched tetracosanol, and mixtures thereof. The polyol preferably has a hydricity of 2 to 10 (more preferably 2 to 6, and even more preferably 2 to 3).

[0049] Examples of such polyhydric alcohols include dihydric alcohols such as ethylene glycol, diethylene glycol, polyethylene glycol (trimer to 15-mer of ethylene glycol), propylene glycol, dipropylene glycol, polypropylene glycol (trimer to 15-mer of propylene glycol), 1,3-propanediol, 1,2-propanediol, 1,3-butanediol, 1,4-butanediol, 2-methyl-1,2-propanediol, 2-methyl-1,3-propanediol, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, 1,5-pentanediol, and neopentyl glycol; and polyglycerin (dimer to octamer of glycerin, such as diglycerin and triglycerin). polyhydric alcohols such as cellulose, cellulose acetate, cellulose esters, cellulose esters, cellulose gum, cellulose esters, cellulose gums ...

[0050] Among the alcohols used in the production of dibasic acid esters, monohydric alcohols are more preferred from the viewpoints of low-temperature fluidity and flash point.

[0051] The dibasic acid ester base oil (base oil (C)) can suitably be a base oil of API Group V. The dibasic acid ester base oil used as base oil (C) may consist of one type of dibasic acid ester or may consist of a mixture of two or more types of dibasic acid esters.

[0052] <Lubricant base oil> The lubricating base oil contained in the lubricating oil composition of the present invention comprises the base oils (A) to (C) described above, i.e., the lubricating base oil is a base oil composition (mixed base oil) containing the base oils (A) to (C).

[0053] Such a lubricating base oil needs to have a content of the base oil (A) in the lubricating base oil of 45% by mass or more (more preferably 48% by mass or more). By making the content of the base oil (A) in the lubricating base oil 45% by mass or more, the lubricating base oil can have particularly excellent anti-seizure properties and further improve extreme-pressure performance compared to when the content is less than 45% by mass. There is no particular upper limit for the content of the base oil (A), but from the viewpoint of obtaining a greater effect in terms of improving extreme-pressure performance and low-temperature fluidity, it is preferably 60% by mass or less, and more preferably 55% by mass or less.

[0054] The lubricating base oil must have a content of base oil (B) of 10 to 40% by mass. By making the content of base oil (B) in the lubricating base oil 10% by mass or more, it is possible to improve gear pitting resistance and bearing fatigue life compared to when the content is less than 10% by mass, while by making the content 40% by mass or less, it is possible to improve oxidation stability compared to when the content exceeds 40% by mass. The content of base oil (B) in the lubricating base oil is more preferably 15 to 35% by mass, as this provides a greater effect in improving gear and bearing fatigue life (pitting life) and oxidation stability.

[0055] Furthermore, the lubricating base oil must have a content of the base oil (C) of 15 to 40% by mass. By making the content of base oil (C) in the lubricating base oil 15% by mass or more, it is possible to improve the gear / bearing fatigue life (pitting life), while by making the content of base oil (C) 40% by mass or less, it is possible to improve the low-temperature fluidity (BF viscosity) compared to when the content exceeds 40% by mass. The content of base oil (C) is more preferably 15 to 35% by mass, since this provides a greater effect in improving the gear / bearing fatigue life (pitting life) and low-temperature fluidity.

[0056] It is preferable that the lubricating base oil consists essentially of the base oils (A) to (C), but it may contain base oil components other than the base oils (A) to (C) as long as the effects of the present invention are not impaired. Even when the lubricating base oil contains base oil components other than the base oils (A) to (C), it is preferable that the content of such other base oil components is 10 mass % or less based on the total amount of the lubricating base oil.

[0057] The lubricating base oil has a kinematic viscosity of 7.00 mm at 100°C. 2 The kinematic viscosity of the lubricating base oil at 100°C must be 7.00 mm / s or more. 2 / s or more, 7.00 mm 2 Compared with a lubricating base oil having a kinematic viscosity of less than 7.10 to 7.50 mm / s, it is possible to improve gear pitting resistance and bearing fatigue life. In addition, the kinematic viscosity at 100°C of the lubricating base oil is preferably 7.10 to 7.50 mm / s, because it is more effective in improving gear and bearing fatigue life (pitting life) and low-temperature fluidity. 2 / s (more preferably 7.20 to 7.50 mm 2 / s, particularly preferably 7.23 to 7.50 mm 2 / s) is more preferable.

[0058] The lubricating base oil has a kinematic viscosity of 40.0 to 50.0 mm at 40°C. 2 / s (more preferably 43.0 to 46.0 mm 2 When the kinematic viscosity at 40°C is equal to or greater than the lower limit, compared to when it is below the lower limit, it is possible to improve the oil film forming ability at lubricated points and achieve better lubrication, and it is also possible to reduce evaporation loss of the lubricating oil composition and reduce the amount of lubricating oil consumed, and on the other hand, when the kinematic viscosity is equal to or less than the upper limit, it is likely that better performance (effect) can be obtained in terms of low-temperature viscosity characteristics and fuel economy performance of the lubricating oil composition, compared to when it exceeds the upper limit.

[0059] The lubricating base oil preferably has a viscosity index of 120 or more (more preferably 122 or more, even more preferably 124 or more, and particularly preferably 125 or more). By making the viscosity index equal to or higher than the lower limit, greater effects in terms of fuel economy performance tend to be obtained.

[0060] Preferably, the lubricating base oil has a sulfur content of 0.20 to 1.5 mass % (more preferably 0.22 to 1.0 mass %, and even more preferably 0.25 to 0.80 mass %) based on the mass of the lubricating base oil. By setting the sulfur content in such a lubricating base oil at or above the lower limit, a greater effect in terms of improving extreme pressure performance tends to be obtained compared to when the sulfur content is below the lower limit, while when the sulfur content is below the upper limit, a greater effect in terms of improving oxidation stability tends to be obtained compared to when the sulfur content exceeds the upper limit.

[0061] <Lubricating oil composition> The lubricating oil composition of the present invention comprises the lubricating base oil (base oil composition: mixed base oil). In the lubricating oil composition of the present invention, the content of the lubricating base oil is not particularly limited, but is preferably 70% by mass or more (more preferably 75% by mass or more, and even more preferably 80% by mass or more) based on the total amount of the lubricating oil composition, since this provides greater effects in terms of extreme pressure properties (seizure resistance and anti-wear properties), gear and bearing fatigue life (pitting life), low temperature fluidity (high viscosity index and BF viscosity), oxidation stability (thermal stability), and safety (high flash point).

[0062] In addition, the lubricating oil composition of the present invention can contain additives as appropriate within the range that does not impair the effects of the present invention. Such additives are not particularly limited, and known additives used in the field of lubricating oils (for example, those described in JP 2016-3258 A, WO 2015 / 056783 A, JP 2016-160312 A, JP 2003-155492 A, WO 2017 / 073748 A, JP 2020-76004 A, etc.) can be appropriately used depending on the application of the lubricating oil composition.

[0063] Such additives are not particularly limited, but suitable examples include viscosity index improvers, pour point depressants, so-called performance additives, and the like.

[0064] Such viscosity index improvers are not particularly limited, and known viscosity index improvers can be used as appropriate. From the viewpoint of the effect of increasing the viscosity index and improving shear stability, poly(meth)acrylate-based viscosity index improvers (viscosity index improvers made of poly(meth)acrylate) can be suitably used as such viscosity index improvers. In this specification, "(meth)acrylate" refers to acrylate and / or methacrylate. Such poly(meth)acrylate-based viscosity index improvers may be of the so-called non-dispersion type or dispersion type. Furthermore, the poly(meth)acrylate used in the viscosity index improver preferably has a weight-average molecular weight of 10,000 to 100,000 (more preferably 20,000 to 80,000, and even more preferably 30,000 to 60,000). When such a poly(meth)acrylate viscosity index improver is used, its content is preferably 0.1 to 15.0 mass %, more preferably 0.1 to 10.0 mass %, even more preferably 0.5 to 8.0 mass %, particularly preferably 1.0 to 7.0 mass %, and most preferably 2.0 to 6.0 mass %, based on the total amount of the lubricating oil composition.

[0065] Furthermore, from the viewpoint of thickening properties and shear stability, at least one of ethylene and α-olefin copolymers and their hydrogenated products can be suitably used as the viscosity index improver. Such copolymers and their hydrogenated products may be either non-dispersant or dispersant. Furthermore, the copolymers and their hydrogenated products used in the viscosity index improver preferably have a number average molecular weight of 2,000 to 10,000. The "weight average molecular weight" and "number average molecular weight" of the components used in the viscosity index improver refer to values ​​determined by gel permeation chromatography (GPC) (molecular weights obtained in terms of standard polystyrene).

[0066] The viscosity index improvers may be used alone or in combination of two or more. From the viewpoints of improving the viscosity index, low-temperature fluidity, and shear stability, it is more preferable to use a poly(meth)acrylate viscosity index improver in combination with a viscosity index improver made from an ethylene / α-olefin copolymer. When such a viscosity index improver is used, its content is preferably 0.1 to 15.0 mass%, more preferably 1.0 to 12.0 mass%, and even more preferably 2.0 to 10.0 mass%, based on the total amount of the lubricating oil composition.

[0067] The pour point depressant is not particularly limited, and known pour point depressants can be used as appropriate. Examples include poly(meth)acrylate, alkylated aromatic compounds, ethylene-propylene copolymers, fumarate-vinyl acetate copolymers, and ethylene-vinyl acetate copolymers. When the base oil contains an isomerized wax base oil, poly(meth)acrylate pour point depressants (those composed of poly(meth)acrylate) are more preferred from the viewpoint of pour point depressant activity. The pour point depressants may be used alone or in combination of two or more. When a pour point depressant is used, its content is preferably 0.01 to 1.0 mass% (more preferably 0.03 to 0.6 mass%) based on the total amount of the lubricating oil composition from the viewpoint of improving pour point depressant activity and shear stability.

[0068] The performance additive is not particularly limited, and known additives can be used as appropriate, and so-called additive packages (combinations of multiple components) can also be used. Commercially available products (such as the "Anglamol series" manufactured by Lubrizol Corporation and the "Hitec series" manufactured by Afton Chemical Company) can also be used as appropriate.

[0069] From the viewpoint of extreme pressure properties, such performance additives preferably contain sulfur in an amount of 15 to 35 mass % (more preferably 20 to 30 mass %). From the viewpoint of oxidation stability, such performance additives preferably contain boron in an amount of 0.05 to 1.00 mass % (more preferably 0.05 to 0.50 mass %). Furthermore, from the viewpoint of anti-wear properties, such performance additives more preferably contain phosphorus in an amount of 1.0 to 3.0 mass % (more preferably 1.2 to 2.0 mass %).

[0070] Furthermore, from the viewpoint of extreme pressure properties (seizure resistance) and anti-wear properties, it is more preferable that such performance additives have a ratio of sulfur content to phosphorus content by mass in the additive (mass ratio: S / P) of 10 to 20 (more preferably 12 to 18).

[0071] Furthermore, when such performance additives are used, their content may be appropriately set depending on the intended use, etc., and is not particularly limited, but is preferably 2.0 to 14.0 mass%. Here, in one embodiment, for example, from the viewpoint of obtaining a lubricating oil composition that meets API GL standard "GL-4 certification," the content of the performance additive is more preferably 2.0 to 7.0 mass% (more preferably 3.0 to 5.0 mass%) based on the total amount of the lubricating oil composition. In another embodiment, for example, from the viewpoint of obtaining a lubricating oil composition that meets API GL standard "GL-5 ​​certification," the content of the performance additive is more preferably 4.0 to 14.0 mass% (more preferably 5.0 to 12.0 mass%) based on the total amount of the lubricating oil composition.

[0072] Although viscosity index improvers, pour point depressants, and performance additives have been cited as examples of additives that can be suitably used in the lubricating oil composition of the present invention, the additives that can be used in the lubricating oil composition of the present invention are not limited to these, and known additives such as ashless dispersants, metal-based detergents, antioxidants, antiwear agents, metal deactivators, rubber swelling agents, friction modifiers, antifoaming agents, viscosity modifiers, diluent oils, etc. may also be used as appropriate. Furthermore, such additives may be used alone or in combination of two or more, depending on the intended use of the lubricating oil composition.

[0073] Furthermore, in the lubricating oil composition of the present invention, the mass-based phosphorus content in the lubricating oil composition may be appropriately set depending on the intended use, etc., and is not particularly limited, but is preferably 0.02 mass% or more (more preferably 0.02 to 0.25 mass%). Here, in one embodiment, from the viewpoint of obtaining a lubricating oil composition that meets API GL standard "GL-4 certification," for example, the mass-based phosphorus content in the lubricating oil composition is preferably 0.02 mass% or more (more preferably 0.02 to 0.10 mass%, even more preferably 0.03 to 0.08 mass%). In another embodiment, from the viewpoint of obtaining a lubricating oil composition that meets API GL standard "GL-5 ​​certification," for example, the mass-based phosphorus content in the lubricating oil composition is preferably 0.05 mass% or more (more preferably 0.05 to 0.25 mass%, even more preferably 0.08 to 0.20 mass%). By setting the phosphorus content in such a lubricating oil composition at or above the lower limit, it is possible to further improve anti-seizure and anti-wear properties compared to when the content is below the lower limit. Furthermore, when the phosphorus content is below the upper limit, there is a tendency for greater effects to be obtained in terms of gear and bearing fatigue life (pitting life) and oxidation stability compared to when the content exceeds the upper limit.

[0074] Furthermore, in the lubricating oil composition of the present invention, the sulfur content by mass in the lubricating oil composition may be appropriately set depending on the intended use, etc., and is not particularly limited, but is preferably 0.50 to 3.50 mass%. Here, in one embodiment, for example, from the viewpoint of obtaining a lubricating oil composition that meets API GL standard "GL-4 certification," the sulfur content by mass in the lubricating oil composition is preferably 0.50 to 2.50 mass% (more preferably 0.70 to 2.00 mass%, even more preferably 0.80 to 1.50 mass%). In another embodiment, for example, from the viewpoint of obtaining a lubricating oil composition that meets API GL standard "GL-5 ​​certification," the sulfur content by mass in the lubricating oil composition is preferably 1.00 to 3.50 mass% (more preferably 1.50 to 3.40 mass%, even more preferably 1.80 to 3.30 mass%). By setting the sulfur content in such a lubricating oil composition within the above range, it is possible to further improve seizure resistance. The mass-based sulfur content in the lubricating oil composition can be measured in accordance with ASTM D4951.

[0075] The lubricating oil composition of the present invention more preferably satisfies the condition that the ratio of the mass-based sulfur content in the lubricating base oil to the mass-based phosphorus content in the lubricating oil composition ([the sulfur content] / [the phosphorus content]) is 2.0 to 8.0 (more preferably 2.5 to 7.0, and even more preferably 2.5 to 4.0). By setting the ratio of the mass-based sulfur content in the lubricating base oil to the mass-based phosphorus content in the lubricating oil composition to be equal to or greater than the lower limit, better anti-seizure properties and anti-wear properties tend to be obtained compared to when the ratio is below the lower limit. On the other hand, by setting the ratio to the upper limit or less, better oxidation stability and low-temperature fluidity tend to be obtained compared to when the ratio exceeds the upper limit. When these conditions are satisfied, it is preferable that the mass-based phosphorus content in the lubricating oil composition also satisfies the aforementioned preferred conditions for the phosphorus content (for example, as described above, the preferred conditions in one embodiment are preferably 0.02 mass% or more, more preferably 0.02 to 0.10 mass%, and even more preferably 0.03 to 0.08 mass%, and the preferred conditions in another embodiment are preferably 0.05 mass% or more, more preferably 0.05 to 0.25 mass%, and even more preferably 0.08 to 0.20 mass%). Therefore, in one preferred embodiment of the present invention, for example, a lubricating oil composition that satisfies the conditions that the mass-based phosphorus content in the lubricating oil composition is 0.05 mass% or more and the ratio of the mass-based sulfur content in the lubricating base oil to the mass-based phosphorus content in the lubricating oil composition ([the sulfur content] / [the phosphorus content]) is 2.0 to 8.0 can be cited as one preferred embodiment.

[0076] The lubricating oil composition of the present invention has a kinematic viscosity at 100°C of 13.5 to 18.5 mm 2 / s (more preferably 13.5 to 15.5 mm 2 The kinematic viscosity of the lubricating oil composition of the present invention at 40°C is preferably 80 to 150 mm 2 / s, and more preferably 80 to 100 mm 2 / s, and more preferably 80 to 92 mm 2 / s. When these kinematic viscosities are equal to or less than the upper limit, it is possible to further improve fuel economy performance compared to when they exceed the upper limit. On the other hand, when these kinematic viscosities are equal to or greater than the lower limit, it is possible to further improve oil film retention performance and wear resistance, etc., compared to when they are less than the lower limit.

[0077] The lubricating oil composition of the present invention preferably has a viscosity index of at least 155 (more preferably at least 158, and even more preferably at least 160). When the viscosity index is at least the above lower limit, the viscosity-temperature characteristics and anti-wear properties of the lubricating oil composition can be further improved, and fuel economy performance can be further improved, compared to when the viscosity index is below the above lower limit.

[0078] The lubricating oil composition of the present invention is preferably one in which, when a shear stability test is conducted in accordance with JPI-5S-29-88 in which ultrasonic waves are irradiated under conditions of a frequency of 10 kHz, an oscillator amplitude of 28 μm, and an irradiation time of 10 hours, and the kinematic viscosity of the lubricating oil composition at 100°C is measured and compared before and after the ultrasonic irradiation, the rate of decrease in the kinematic viscosity of the lubricating oil composition at 100°C due to the ultrasonic irradiation is 10% or less (more preferably 7.0% or less, and even more preferably 6.0% or less). The "rate of decrease in the kinematic viscosity of the lubricating oil composition at 100°C due to ultrasonic irradiation" referred to here is calculated by the following formula (I): [Decrease rate (unit: %)] = {(ν0-ν1) / ν0} × 100 (I) (wherein v0 represents the kinematic viscosity at 100°C of the lubricating oil composition before ultrasonic irradiation, and v1 represents the kinematic viscosity at 100°C of the lubricating oil composition after ultrasonic irradiation.) When the rate of decrease in kinematic viscosity at 100°C of the lubricating oil composition due to ultrasonic irradiation is equal to or less than the upper limit, there tends to be a greater effect in improving extreme pressure performance and gear / bearing fatigue life (pitting life) than when the rate of decrease exceeds the upper limit.

[0079] The lubricating oil composition of the present invention preferably has a Brookfield viscosity (BF viscosity) at -40°C of 150,000 mPa·s or less (more preferably 130,000 mPa·s or less, even more preferably 120,000 mPa·s or less, and particularly preferably 100,000 mPa·s or less). By setting the BF viscosity at or below the upper limit, it is possible to further improve low-temperature fluidity. Such a Brookfield viscosity (BF viscosity) can be measured in accordance with ASTM D2983.

[0080] Furthermore, the lubricating oil composition of the present invention preferably has a pour point of −40° C. or less (more preferably −42.5° C. or less, and even more preferably −45° C. or less). When the pour point is below the above upper limit, it becomes possible to exhibit better viscosity characteristics over a range from low to high temperatures, and it becomes possible to obtain a lubricating oil composition with better oxidation stability.

[0081] The lubricating oil composition of the present invention preferably has a flash point of 200° C. or higher (more preferably 205° C. or higher, even more preferably 207° C. or higher, and particularly preferably 210° C. or higher). By setting the flash point at or above the lower limit, safety during use at high temperatures tends to be improved compared to when the flash point is below the lower limit.

[0082] The method for producing the lubricating oil composition of the present invention is not particularly limited, and the lubricating oil composition may be prepared by appropriately selecting and mixing the components to be contained so as to obtain the lubricating oil composition of the present invention (so as to satisfy the above-mentioned conditions).

[0083] The lubricating oil composition of the present invention can have excellent extreme-pressure performance based on anti-seizure and anti-wear properties, excellent low-temperature fluidity, and a high viscosity index. It can also improve fuel economy, gear pitching resistance, and bearing fatigue life, making it applicable to a variety of applications. It is particularly preferred to use it as a gear oil (gear oil composition). For example, it can be used as a gear oil for manual transmissions and final reduction gears in large freight and passenger vehicles, or as a gear oil for electric vehicles. Thus, the lubricating oil composition of the present invention is preferably used as a gear oil composition. When the lubricating oil composition of the present invention is used as a gear oil composition, it can meet the extreme-pressure performance and gear durability (fatigue life) levels required for gear oils for large freight and passenger vehicles, while also achieving excellent fuel economy. [Example]

[0084] The present invention will be described in more detail below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0085] (Ingredients used in each example) First, the base oils and additives used in the examples are shown below.

[0086] [Base oil used as the base oil (A) (the "mineral oil-based base oil" according to the present invention)] <Base oil (A-1)> Solvent refined mineral oil [API Group I, 150BS (bright stock), kinematic viscosity at 40°C: 474.9 mm 2 / s, kinematic viscosity at 100°C: 31.92mm 2 / s, viscosity index: 98, sulfur content in base oil (sulfur content in base oil): 0.69 mass%, pour point: -10.0°C, flash point: 322°C] <Base oil (A-2)> Solvent refined mineral oil [API Group I, 150BS (bright stock), kinematic viscosity at 40°C: 467.4 mm 2 / s, kinematic viscosity at 100°C: 31.29mm 2 / s, viscosity index: 97, sulfur content in base oil: 0.48 mass%, pour point: -12.5°C, flash point: 319°C] <Base oil (A-3)> Solvent refined mineral oil [API Group I, 150BS (bright stock), kinematic viscosity at 40°C: 481.8 mm 2 / s, kinematic viscosity at 100°C: 31.76mm 2 / s, viscosity index: 97, sulfur content in base oil: 0.51 mass%, pour point: -10.0°C, flash point: 316°C].

[0087] [Base oil used as the base oil (B) (the "wax isomerized base oil" according to the present invention)] <Base oil (B-1)> Wax isomerized base oil [API Group III, kinematic viscosity at 40°C: 9.072 mm 2 / s, kinematic viscosity at 100°C: 2.621mm 2 / s, viscosity index: 127, sulfur content in base oil: less than 10 mass ppm, pour point: -37.5°C, flash point: 200°C, %C P :91.8, %C N :8.2, %C A :0].

[0088] [Base oil used as the base oil (C) (the "dibasic acid ester base oil" according to the present invention)] <Base oil (C-1)> Dibasic acid ester [API Group V, 2-ethylhexyl ester of azelaic acid, kinematic viscosity at 40°C: 10.3 mm 2 / s, kinematic viscosity at 100°C: 2.9mm 2 / s, viscosity index: 138, pour point: -70.0℃, flash point: 220℃, sulfur: free].

[0089] [Base oil (D): a base oil other than the base oils (A) to (C)] <Base oil (D-1)> Poly-α-olefin (API Group IV, kinematic viscosity at 40°C: 396 mm 2 / s, kinematic viscosity at 100°C: 39mm2 / s, viscosity index: 147, pour point: -35.0℃, flash point: 281℃, sulfur: free].

[0090] <Base oil (D-2)> Solvent refined mineral oil [API Group I, 500N (neutral), kinematic viscosity at 40°C: 93.31 mm 2 / s, kinematic viscosity at 100°C: 10.63mm 2 / s, viscosity index: 96, sulfur content in base oil: 0.21 mass%, pour point: -12.5°C, flash point: 266] [Additives] Viscosity index improver (E-1) Poly(meth)acrylate: [Evonik: Viscoplex 12-151, weight average molecular weight: 50,000] Viscosity index improver (E-2) Ethylene and α-olefin copolymer [Mitsui Chemicals, product name "HC2000", number average molecular weight: 7400] <Performance Additive (F-1)> Additive package [manufactured by Lubrizol, product name "Anglamol 6043Z", phosphorus (P) content: 1.40 mass%, sulfur (S) content: 22.9 mass%, boron (B) content: 0.24 mass%, nitrogen content: 0.9 mass%, phosphorus to sulfur mass ratio (S / P): 16.4] <Performance Additive (F-2)> Additive package [manufactured by Afton Chemical, product name "HiTEC 1536", phosphorus (P) content: 1.90 mass%, sulfur (S) content: 26 mass%, boron (B) content: 0.09 mass%, nitrogen content: 0.55 mass%, phosphorus to sulfur mass ratio (S / P): 13.7] Pour Point Depressant (G-1) Poly(meth)acrylate [manufactured by Sanyo Chemical Industry, product name "Aclub 132"]

[0091] (Examples 1 to 10 and Comparative Examples 1 to 6) The lubricating oil compositions of Examples 1 to 10 and Comparative Examples 1 to 6 were prepared using the aforementioned components so as to have the compositions shown in Tables 1 to 3. In the "Composition" column in Tables 1 to 3, "-" indicates that the component was not used. In the "Composition" column in Tables 1 to 3, "in mass%" indicates the mass content (mass%) relative to the total amount of the lubricating base oil (mixed base oil), and "mass%" indicates the mass content (mass%) relative to the total amount of the lubricating oil composition. The sulfur and phosphorus contents in the composition were measured in accordance with ASTM D4951. The term "sulfur in base oil / phosphorus in composition (S / P)" in Tables 1 to 3 indicates the ratio of the mass content of sulfur in the lubricating base oil to the mass content of phosphorus in the lubricating oil composition ([the sulfur content] / [the phosphorus content]).

[0092] [Method for evaluating the properties of the lubricating oil compositions obtained in each example] <Brookfield viscosity (BF viscosity) measurement> The BF viscosity at -40°C of the lubricating oil compositions obtained in each example was measured in accordance with ASTM D 2983 using a Brookfield viscosity thermostatic bath / Brookfield viscometer as the measuring device, at a temperature of -40°C. The results are shown in Tables 1 to 3. Note that a BF viscosity value of 150,000 mPa s or less satisfies the requirements of "SAE J306 Standard Viscosity Grade 75W," and can be evaluated as having a high level of fluidity at low temperatures.

[0093] <Shear stability test> For each of the lubricating oil compositions obtained in the examples, ultrasonic waves were irradiated for 10 hours using a vibrator at a frequency of 10 kHz and an amplitude of 28 μm in accordance with the shear stability test in accordance with JPI-5S-29-88. The kinematic viscosity of the lubricating oil composition at 100°C after ultrasonic irradiation (kinematic viscosity after test) was determined, and the rate of decrease in the kinematic viscosity of the lubricating oil composition at 100°C due to ultrasonic irradiation was then calculated based on the above calculation formula (I). The results are shown in Tables 1 to 3. A rate of decrease in kinematic viscosity of 10% or less can be said to be more stable against shearing caused by ultrasonic waves, and can be evaluated as having excellent shear stability. Although the test conditions (10 hours) for the shear stability test in accordance with the above JPI-5S-29-88 and the test conditions (CEC L-45 Method C (20 hours)) for the minimum kinematic viscosity (100 ° C) of the SAE J306 Standard (automotive gear oils) are different, the two tests are considered to be interchangeable. Therefore, the kinematic viscosity (100 ° C) after the shear stability test is 13.5 mm. 2 / s or more, it is deemed to have passed the test specified in the minimum kinematic viscosity (100°C) of the 2019 revised SAE J306 Standard (automotive gear oils).

[0094] <Wear resistance test> Measurement of welding load (high-speed four-ball test) For each of the lubricating oil compositions obtained in the examples, the weld load (WL, unit: N) was measured at a rotation speed of 1800 rpm using a high-speed four-ball tester in accordance with ASTM D 2596. The results obtained are shown in Tables 1 to 3. Measurement of wear scar diameter (wear test) For each of the lubricating oil compositions obtained in each Example, a Shell four-ball test (ASTM D4172) was performed under the conditions of a load of 392 N, a rotation speed of 1200 rpm, a temperature of 80°C, and a test time of 1 hour, and the wear scar diameter (mm) was measured. The results are shown in Tables 1 to 3. - Evaluation of abrasion resistance A lubricating oil composition can be evaluated as having excellent wear resistance when the welding load is 3000 N or more and the wear scar diameter is less than 0.60 mm (the larger the welding load, the higher the wear resistance can be evaluated. On the other hand, the smaller the wear scar diameter, the higher the wear resistance can be evaluated. Therefore, in this application, a lubricating oil composition is evaluated as having excellent wear resistance when both of the above conditions are satisfied).

[0095] <Falex seizure resistance test> Using a Falex testing machine specified in ASTM D3233, the seizure load (unit: N) was measured under test conditions of a temperature of 110°C and a rotation speed of 290 rpm. The results are shown in Tables 1 to 3. When the seizure load is 4000 N or more, it can be evaluated as having excellent seizure resistance (extreme pressure resistance between steels).

[0096] <Unisteel rolling fatigue test> For each of the lubricating oil compositions obtained in the examples, a Unisteel rolling fatigue test was conducted in accordance with the IP305 standard of the Institute of Petroleum, to evaluate the rolling fatigue life of a thrust needle bearing. This evaluation was carried out by using a Unisteel rolling fatigue tester conforming to the IP305 standard, with the test specimen being a thrust needle bearing (TP), the rotation speed being 1450 rpm, the surface pressure being 1 GPa, and the oil temperature being 120°C, and determining the time until fatigue damage occurred in either the rolling element (roller) or the raceway. The vibration acceleration measured at the test section by a vibration accelerometer attached to the Unisteel rolling fatigue tester was 1.5 m / s. 2When it reached [a certain value], it was determined that fatigue damage had occurred. Then, a test was repeated 10 times, and from the time until the fatigue damage measured in each test, the fatigue life was calculated as the 50% life (bearing fatigue life L50: the time when the cumulative probability becomes 50%: 50% fracture probability) by Weibull plotting. The obtained results are shown in Tables 1 to 3 (however, regarding this test, for Comparative Example 3 and Comparative Example 6, since they were not carried out, they are indicated as "―" in Table 3). When such a fatigue life (L50) is 1500 minutes or more, it can be evaluated that the bearing fatigue life is more improved (enhanced) by the lubricating oil composition.

[0097] <FZG Gear Test> For each of the lubricating oil compositions obtained in each Example, etc., using an FZG test machine, in accordance with the FVA 2 / IV standard, with the gear: C gear, load stage: 12, oil temperature: 120 °C, rotation speed: 620 rpm, the operation was carried out under the test conditions, and the time when pitching occurred in the gear was measured as the fatigue life of the gear. The obtained results are shown in Tables 1 to 3 (however, regarding this test, for Comparative Example 3 and Comparative Examples 5 to 6, since they were not carried out, they are indicated as "―" in Table 3). When such a fatigue life (the time until pitching occurs in the gear) is 17 hours or more, it can be evaluated that the gear fatigue life is long and the gear pitching resistance performance is high.

[0098] <Measurement of Pour Point> For each of the lubricating oil compositions obtained in each Example, etc., the pour point was measured in accordance with JIS K 2269 - 1987. The obtained results are shown in Tables 1 to 3. When such a pour point is -40 °C or lower, it can be evaluated that the low-temperature fluidity is at a high level. In addition, when the pour point is -40 °C or lower and the BF viscosity is 150,000 mPa·s or less, it can be evaluated that it is more excellent in terms of low-temperature fluidity.

[0099] <Measurement of Flash Point> The flash point of each of the lubricating oil compositions obtained in each example was measured in accordance with JIS K 2265-4-2007 (Cleveland Open Method). The results are shown in Tables 1 to 3. A flash point of 200°C or higher can be evaluated as being safer when used at high temperatures.

[0100] <Oxidation stability test> The oxidation stability of each of the lubricating oil compositions obtained in each example was evaluated by the ISOT test in accordance with JIS K 2514-1. The test was carried out at a temperature of 135°C for 96 hours, and the acid values ​​of the lubricating oil compositions before and after the test were compared to measure the increase in acid value (mgKOH / g) after the test. The results are shown in Tables 1 to 3. If the increase in acid value is 2.5 mgKOH / g or less, the lubricating oil composition can be evaluated as having excellent oxidation stability.

[0101] <Evaluation of fuel economy> For each of the lubricating oil compositions obtained in the examples, the kinematic viscosity at 25°C, the soak temperature and test start temperature in the WLTC mode fuel economy test, was measured in accordance with JIS K 2283-2000, and fuel economy was evaluated from the kinematic viscosity value at 25°C. The results are shown in Tables 1 to 3. 2 If the fuel consumption rate is 1 / s or less, the resistance (agitation loss) caused by stirring of the lubricating oil by rotating bodies such as gears at the start of the fuel consumption test is reduced, and the engine can be evaluated as having excellent fuel economy.

[0102] [Table 1]

[0103] [Table 2]

[0104] [Table 3]

[0105] As is clear from the results shown in Tables 1 to 3, all of the lubricating oil compositions obtained in Examples 1 to 10 were compositions containing a lubricating base oil containing the base oils (A) to (C), wherein the content of the base oil (A) in the lubricating base oil was 45 mass% or more, the content of the base oil (B) in the lubricating base oil was 10 to 40 mass%, the content of the base oil (C) in the lubricating base oil was 15 to 40 mass%, and the kinematic viscosity of the lubricating base oil at 100°C was 7.00 mm 2 For all of the lubricating oil compositions obtained in Examples 1 to 10, the results of the wear resistance test (measurement results of welding load and wear scar diameter) confirmed that the welding load was 3000 N or more and the wear scar diameter was less than 0.60 mm, confirming excellent wear resistance, and the results of the Falex anti-seizure test confirmed that the compositions had excellent seizure resistance, demonstrating that they had excellent extreme-pressure performance based on seizure resistance and wear resistance.

[0106] Furthermore, from the results shown in Tables 1 to 3, it was found that the lubricating oil compositions obtained in Examples 1 to 10 all had a BF viscosity of 150,000 mPa·s or less, satisfying the requirements of the "SAE J306 Standard Viscosity Grade 75W" and exhibiting a high level of low-temperature fluidity based on the BF viscosity. Furthermore, the lubricating oil compositions obtained in Examples 1 to 10 all had pour points below −45°C (<−45°C), demonstrating a high level of low-temperature fluidity based on the pour point. Thus, the lubricating oil compositions obtained in Examples 1 to 10 all had pour points of −40°C or less and BF viscosities of 150,000 mPa·s or less, demonstrating excellent low-temperature fluidity. Furthermore, it was found that the lubricating oil compositions obtained in Examples 1 to 10 all had viscosity indices of 155 or more, demonstrating excellent extreme-pressure performance and low-temperature fluidity while also possessing a high viscosity index.

[0107] Furthermore, from the results shown in Tables 1 to 3, it was found that all of the lubricating oil compositions obtained in Examples 1 to 10 had a fatigue life (L50) of 1,500 minutes or more in the Unisteel rolling fatigue test, and that they are capable of improving the bearing fatigue life. Also, all of the lubricating oil compositions obtained in Examples 1 to 10 had a fatigue life of 17 hours or more in the FZG gear test, and that they also had excellent gear pitting resistance. Furthermore, all of the lubricating oil compositions obtained in Examples 1 to 10 had a kinematic viscosity at 25°C of 190mm 2 / g or less, demonstrating excellent fuel economy. 2 / g or less, and the BF viscosity is 150,000 mPa s or less, which means that the low-temperature fluidity is high. Taking this into consideration, it can be seen that the lubricating oil compositions obtained in Examples 1 to 10 have high fuel economy properties.

[0108] As is clear from the results shown in Tables 1 to 3, all of the lubricating oil compositions obtained in Examples 1 to 10 had a kinematic viscosity at 100°C of 13.5 mm 2 / s or more 18.5mm 2 / s or less, which satisfied the requirements of "SAE J306 Standard Viscosity Grade 90." Note that the kinematic viscosity after shearing by ultrasonic irradiation of all the lubricating oil compositions obtained in Examples 1 to 10 was also 13.5 mm 2 / s or more. From these results, it can be evaluated that all of the lubricating oil compositions obtained in Examples 1 to 10 are compatible with the 2019 revised SAE J306 Standard viscosity grade 75W-90.

[0109] In contrast, the lubricating oil composition of Comparative Example 1, in which the base oil (D-1) consisting of a poly-α-olefin synthetic oil (PAO) was used instead of the base oil (A), had a fatigue life (L50) of 1232 minutes in the Unisteel rolling fatigue test, and was unable to improve the bearing fatigue life to the desired level.

[0110] The lubricating oil composition of Comparative Example 2, in which the content of base oil (A) in the lubricating base oil was less than 45% by mass, exhibited a seizure load of less than 4000 N in the seizure resistance test, indicating that the extreme pressure properties were insufficient from the viewpoint of seizure resistance. The lubricating oil composition of Comparative Example 2 also exhibited a fatigue life of 16 hours in the FZG gear test, indicating that the gear pitting resistance was also insufficient.

[0111] Furthermore, the lubricating oil composition of Comparative Example 3, which used a base oil (D-2) consisting of a mineral oil (a mineral base oil other than base oil (A)) containing less than 0.3% by mass of sulfur instead of base oil (A) and contained less than 10% by mass of base oil (B), had a BF viscosity exceeding 150,000 mPa·s and a pour point of −37.5°C, indicating insufficient low-temperature fluidity. Furthermore, the lubricating oil composition of Comparative Example 3 showed a wear scar diameter of 0.60 mm or more in a wear resistance test, indicating that it was not sufficient in terms of extreme-pressure properties. Furthermore, the lubricating oil composition of Comparative Example 3 also did not provide sufficient fuel economy.

[0112] The lubricating oil composition of Comparative Example 4, which did not use base oil (B), had a wear scar diameter of 0.60 mm in the wear resistance test, which was insufficient from the viewpoint of extreme pressure properties. Furthermore, the lubricating oil composition of Comparative Example 4 had a fatigue life (L50) of 1,354 minutes in the Unisteel rolling fatigue test, which meant that the bearing fatigue life could not be improved to the desired level. Furthermore, the lubricating oil composition of Comparative Example 4 had a fatigue life of 16 hours in the FZG gear test, which meant that the gear pitting resistance was also insufficient.

[0113] Furthermore, the lubricating oil composition of Comparative Example 5, which contains base oils (A) to (C) but has a base oil (B) content of less than 10 mass %, had a fatigue life (L50) of 1421 minutes in the Unisteel rolling fatigue test, and was unable to improve the bearing fatigue life to the desired level.

[0114] Furthermore, the lubricating oil composition of Comparative Example 6, which contained base oils (A) to (C) but had a content of base oil (C) of less than 15 mass %, had a BF viscosity exceeding 150,000 mPa s, and was not sufficient in terms of low-temperature fluidity.

[0115] From these results, it was confirmed that the lubricating oil compositions obtained in Examples 1 to 10 have excellent extreme pressure performance based on anti-seizure performance and anti-wear performance, excellent low-temperature fluidity, and have a low viscosity index, and it was also found that it is possible to improve all of fuel economy performance, gear pitting resistance, and bearing fatigue life. Furthermore, from the results of the lubricating oil compositions obtained in Examples 1 to 10, it was found that a lubricating oil composition comprising a lubricating base oil containing the base oils (A) to (C), wherein the content of the base oil (A) in the lubricating base oil is 45 mass% or more, the content of the base oil (B) in the lubricating base oil is 10 to 40 mass%, the content of the base oil (C) in the lubricating base oil is 15 to 40 mass%, and the kinematic viscosity at 100°C of the lubricating base oil is 7.00 mm 2 / s or more, the lubricating oil composition can be made compliant with the 2019 revised SAE J306 Standard viscosity grade 75W-90, and it is clear that it can be made to have high levels of extreme pressure properties and gear durability (fatigue life), as well as excellent fuel economy, which are required when used as a gear oil for large freight vehicles and passenger cars. [Industrial Applicability]

[0116] As explained above, according to the present invention, it is possible to provide a lubricating oil composition that is excellent in extreme pressure performance based on anti-seizure and anti-wear properties, and in low temperature fluidity, and that has a high viscosity index, and that is capable of improving fuel economy performance, gear pitting resistance, and bearing fatigue life. Due to its properties, the lubricating oil composition of the present invention is particularly useful as a gear oil (composition for gear oil) and the like.

Claims

1. The following base oils (A) to (C): (A) Kinematic viscosity at 100°C is 10 to 40 mm ２ / s and a mineral oil-based base oil having a sulfur content of 0.3 to 2.0 mass%; (B) kinematic viscosity at 100°C of 1.5 to 3.0 mm ２ / s, a wax isomerized base oil having a viscosity index of 120 or more and a pour point of -30°C or less; (C) Kinematic viscosity at 100°C is 1.5 to 3.5 mm ２ / s, a dibasic acid ester base oil having a viscosity index of 120 or more and a pour point of -50°C or less; The lubricating oil base oil comprises The content of the base oil (A) in the lubricating base oil is 45% by mass or more, The content of the base oil (B) in the lubricating base oil is 10 to 40% by mass, The content of the base oil (C) in the lubricating base oil is 15 to 40% by mass, and The kinematic viscosity of the lubricating base oil at 100°C is 7.00 mm ２ / s or more, A lubricating oil composition characterized by:

2. The lubricating oil composition has a phosphorus content of 0.05% by mass or more, and The lubricating oil composition according to claim 1, wherein the ratio of the mass-based sulfur content in the lubricating base oil to the mass-based phosphorus content in the lubricating oil composition ([the sulfur content] / [the phosphorus content]) is 2.0 to 8.

0.

3. 3. The lubricating oil composition according to claim 1, wherein a shear stability test is conducted in accordance with JPI-5S-29-88 in which ultrasonic waves are irradiated under conditions of a frequency of 10 kHz, an oscillator amplitude of 28 μm, and an irradiation time of 10 hours, and when the kinematic viscosity of the lubricating oil composition at 100°C is measured and compared before and after the ultrasonic irradiation, the rate of decrease in the kinematic viscosity of the lubricating oil composition at 100°C due to the ultrasonic irradiation is 10% or less.

4. 4. The lubricating oil composition according to claim 1, wherein the lubricating oil composition has a Brookfield viscosity at −40° C. of 150,000 mPa·s or less.

5. 5. The lubricating oil composition according to claim 1, wherein the lubricating oil composition is a gear oil composition.

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