Lubricating oil composition

Abstract

A lubricating oil composition comprising a lubricant base oil, the lubricating oil composition containing a base oil (A) which is a specific hydrocarbon-based base oil and a base oil (B) which is a specific silicone oil; wherein the content of the base oil (B) is 2 mass% or more relative to the total amount of the lubricant base oil; the lubricating oil composition is in a state of liquid-liquid phase separation into two phases, namely an upper phase and a lower phase at 25°C; and the kinematic viscosity of the lubricating oil composition at 100°C is 3.5 mm2 / s or more.

Description

lubricating oil composition

[0001] This invention relates to a lubricating oil composition.

[0002] Lubricating oil compositions generally have relatively high viscosity at low temperatures and low viscosity at high temperatures. Therefore, for example, a lubricating oil composition designed to have a viscosity suitable for oil film formation, especially under low-temperature conditions, will generally have a lower viscosity under high-temperature conditions, making it prone to oil film breakdown and potentially causing durability problems. On the other hand, a lubricating oil composition designed to have a viscosity suitable for oil film formation, especially under high-temperature conditions, will generally have a higher viscosity under low-temperature conditions, potentially leading to increased resistance at sliding parts and reduced lubrication performance. Taking an internal combustion engine as an example, the operating environment is low at startup but becomes high during continued operation. Therefore, lubricating oil compositions for use in internal combustion engines require their viscosity design to be appropriately optimized for effective use under both high and low temperature conditions.

[0003] Thus, for applications where the operating environment includes both low and high temperatures (for example, internal combustion engines as described above), lubricating oil compositions have traditionally been required to have an appropriate viscosity in each temperature range so that they can be used at both low and high temperatures. Various lubricating oil compositions have been researched to meet such requirements.

[0004] For example, Japanese Patent Publication No. 2013-023596 (Patent Document 1) discloses a lubricating oil composition comprising: (A) a hydrocarbon as a low viscosity component; (B) a polyalkylene glycol (PAG) with an oxygen / carbon weight ratio of 0.450 to 0.580 as a high viscosity component; and (C) a compound with an oxygen / carbon weight ratio of 0.080 to 0.350 as a control component. Also, Japanese Patent Publication No. 2024-515783 (Patent Document 2) discloses (a) 3.5 to 7.0 mm ２A lubricating oil composition is disclosed comprising: (a) a specific amount of a first base oil component having a kinematic viscosity at 100°C in the range of 1 / second; (b) a specific amount of a second base oil component having a kinematic viscosity in the range of polyalkylene glycol; and (c) an antifoaming additive which is a nonionic surfactant. Furthermore, Japanese Patent Application Publication No. 2003-253281 (Patent Document 3) discloses a lubricating oil composition for nonferrous metal plastic processing comprising alkyl-modified silicone oil and / or alkylaralkyl-modified silicone oil and mineral oil.

[0005] Japanese Patent Publication No. 2013-023596, Japanese Patent Publication No. 2024-515783, Japanese Patent Publication No. 2003-253281

[0006] However, conventional lubricating oil compositions, such as those described in Patent Documents 1 to 3, were not sufficient in terms of minimizing viscosity changes with temperature. Therefore, from the viewpoint of exhibiting a more advanced effect compared to conventional lubricating oil compositions, such as maintaining fluidity at low temperatures while suppressing the reduction in durability due to oil film breakdown at high temperatures, there is a desire for the emergence of lubricating oil compositions with less temperature dependence of viscosity.

[0007] The present invention has been made in view of the problems of the prior art, and aims to provide a two-phase separation type lubricating oil composition that exhibits a liquid-liquid phase separation into two phases under low temperature conditions and a single-phase state under high temperature conditions, while also being able to reduce the temperature dependence of viscosity and have a larger viscosity index (apparent viscosity index).

[0008] The present inventors, through diligent research to achieve the above objective, have determined a lubricating oil composition comprising a lubricating oil base oil, wherein the lubricating oil base oil contains the following base oil (A) and base oil (B), the content of base oil (B) is 2% by mass or more based on the total amount of the lubricating oil base oil, the state of the lubricating oil composition at 25°C is a liquid-liquid phase separation into an upper phase and a lower phase, and the kinematic viscosity of the lubricating oil composition at 100°C is 3.5 mm². ２By setting the temperature to 0 / s or higher, it becomes possible to create a two-phase separation type lubricating oil composition that exhibits a liquid-liquid phase separation into two phases under low-temperature conditions and a single-phase state under high-temperature conditions. Furthermore, it becomes possible to reduce the temperature dependence of the viscosity of the composition and increase the viscosity index (apparent viscosity index) of the composition. We have found this to be the basis for the completion of the present invention.

[0009] In other words, the present invention provides the following embodiments.

[0010] [1] A lubricating oil composition comprising a lubricating oil base oil, wherein the lubricating oil base oil is the following base oils (A) and (B): (A) having a kinematic viscosity of 4.1 mm at 40°C ２ / s or more 9.0mm ２ Hydrocarbon base oils with a kinematic viscosity of 1000 mm² or less at 25°C (B) ２ / s or more 1000000mm ２ The lubricating oil composition contains silicone oil with a viscosity of 0.5 / s or less, the content of the base oil (B) is 2% by mass or more based on the total amount of the lubricating oil base oil, the state of the lubricating oil composition at 25°C is a liquid-liquid phase separation into an upper phase and a lower phase, and the kinematic viscosity of the lubricating oil composition at 100°C is 3.5 mm². ２ A lubricating oil composition having a ratio of / s or higher.

[0011] [2] The kinematic viscosity of the upper phase at 40°C is determined to be 4.1 mm² by taking the supernatant liquid from the upper phase of the lubricating oil composition, which is in a liquid-liquid separated state at 25°C, and using it as a measurement sample. ２ The lubricating oil composition according to [1], wherein the ratio is 1 / s or greater.

[0012] [3] The lubricating oil composition according to [1] or [2], wherein the content of the base oil (B) is 2% by mass or more and 23% by mass or less based on the total amount of the lubricating oil base oil.

[0013] [4] The lubricating oil composition according to any one of [1] to [3], wherein the state of the lubricating oil composition at 100°C is a single-phase liquid state.

[0014] According to the present invention, there is provided a lubricating oil composition which shows a liquid-liquid separated state in two phases under low temperature conditions and a single phase state under high temperature conditions, and which can have a smaller temperature dependence of viscosity and a larger viscosity index (apparent viscosity index).

[0015] Hereinafter, the present invention will be described in detail with reference to its preferred embodiments. In this specification, unless otherwise specified, the notation "X to Y" for numerical values X and Y means "X or more and Y or less". When a unit is attached only to the numerical value Y in such notation, the unit is also applied to the numerical value X.

[0016] The lubricating oil composition of the present invention is a lubricating oil composition containing a lubricating base oil, wherein the lubricating base oil comprises the following base oils (A) and (B): (A) a hydrocarbon base oil having a kinematic viscosity at 40 °C of 4.1 mm ２ / s or more and 9.0 mm ２ / s or less, and (B) a silicone oil having a kinematic viscosity at 25 °C of 1000 mm ２ / s or more and 1000000 mm ２ / s or less, the content of the base oil (B) is 2% by mass or more based on the total amount of the lubricating base oil, the state of the lubricating oil composition at 25 °C is in a liquid-liquid separated state of an upper phase and a lower phase, and the kinematic viscosity of the lubricating oil composition at 100 °C is 3.5 mm ２ / s or more.

[0017] <Base oil (A)> The base oil (A) according to the present invention is a hydrocarbon base oil having a kinematic viscosity at 40 °C of 4.1 mm ２ / s or more and 9.0 mm ２ / s or less. Thus, in the present invention, as an essential component of the lubricating base oil, a hydrocarbon base oil (base oil (A)) having a kinematic viscosity at 40 °C of 4.1 mm ２ / s or more and 9.0 mm ２ / s or less is used.

[0018] Such a hydrocarbon base oil (base oil (A)) has a kinematic viscosity at 40 °C of 4.1 mm ２ / s or more 9.0mm ２ It must be less than or equal to / s. By setting the kinematic viscosity of such hydrocarbon base oil (base oil (A)) at 40°C to be below the upper limit and above the lower limit, it is possible to ensure proper compatibility with silicone oil (B). Furthermore, from the same viewpoint, a higher effect can be obtained, so the kinematic viscosity of hydrocarbon base oil (base oil (A)) at 40°C should be 4.3 mm. ２ / s or more 8.8mm ２ / s or less (more preferably 4.5 mm) ２ / s or more 8.6mm ２ / s or less, particularly preferably 4.7 mm ２ / s or more 8.4mm ２ It is preferable that the value is less than or equal to / s.

[0019] Furthermore, the kinematic viscosity of the hydrocarbon base oil (base oil (A)) at 100°C is 1.3 mm. ２ / s or more 2.8mm ２ It is preferable that the kinematic viscosity of the hydrocarbon base oil (base oil (A)) at 100°C is within the above range (above the lower limit and below the upper limit), which further enhances the effect of ensuring appropriate compatibility with silicone oil (B).

[0020] In this specification, the "kinematic viscosity at 25°C," "kinematic viscosity at 40°C," and "kinematic viscosity at 100°C" for base oils (A) and (B) refer to the values ​​measured at each temperature (25°C, 40°C, and 100°C), respectively, in accordance with ASTM D-445. In the following, the "kinematic viscosity at 25°C" of a base oil may be simply referred to as "25°C kinematic viscosity," the "kinematic viscosity at 40°C" of a base oil or composition may be simply referred to as "40°C kinematic viscosity," and the "kinematic viscosity at 100°C" of a base oil or composition may be simply referred to as "100°C kinematic viscosity." In this specification, the "viscosity index" for base oils (A) and (B) refers to the viscosity index measured in accordance with JIS K 2283-2000.

[0021] Furthermore, the hydrocarbon base oil used as base oil (A) is not particularly limited as long as its kinematic viscosity at 40°C is within the aforementioned range, and any hydrocarbon base oil known in the field of lubricating oils can be used as appropriate. Examples of such hydrocarbon base oils include mineral oil-based hydrocarbon oils, synthetic hydrocarbon oils, or mixtures thereof.

[0022] Suitable examples of mineral-based hydrocarbon oils include mineral oils obtained by refining lubricating oil fractions, which are obtained by atmospheric and vacuum distillation of paraffinic and naphthenic crude oils, using methods such as solvent delamination, solvent refining, hydrorefining, hydrocracking, solvent dewaxing, hydrodewaxing, clay treatment, and sulfuric acid washing. The refining method used in producing such refined oils may be a single method or a combination of two or more methods.

[0023] Furthermore, as mineral oil-based hydrocarbon oils, Group I base oils of the API base oil classification (hereinafter referred to as "API Group I base oil" as may be used), Group II base oils (hereinafter referred to as "API Group II base oil" as may be used), or Group III base oils (hereinafter referred to as "API Group III base oil" as may be used), or mixed base oils obtained by combining them, can be suitably used. Here, API Group I base oil is a mineral oil-based base oil having a sulfur content of more than 0.03% by mass and / or a saturation content of less than 90% by mass, and a viscosity index of 80 or more and less than 120. API Group II base oil is a mineral oil-based base oil having a sulfur content of 0.03% by mass or less, a saturation content of 90% by mass or more, and a viscosity index of 80 or more and less than 120. Furthermore, API Group III base oil is a mineral oil-based base oil having a sulfur content of 0.03% by mass or less, a saturation content of 90% by mass or more, and a viscosity index of 120 or more. API Group I base oils are typically produced through a solvent refining process, while API Group II and Group III base oils are typically produced through a hydrocracking process. In this specification, "sulfur content in lubricating oil base oil" refers to the value measured in accordance with JIS K 2541-2003. In this specification, "saturation content in lubricating oil base oil" refers to the value measured in accordance with ASTM D 2007-93.

[0024] Furthermore, examples of synthetic hydrocarbon oils include alkylbenzene, alkylnaphthalene, poly-α-olefin (PAO), polybutene, and ethylene-α-olefin copolymer. Among such synthetic hydrocarbon oils, API base oil classification group IV base oils are particularly preferred.

[0025] Furthermore, such hydrocarbon base oil (base oil (A)) may consist of only one type of hydrocarbon base oil, or it may consist of a mixture of two or more types of hydrocarbon base oils. In this invention, if base oil (A) consists of a mixture of two or more types of hydrocarbon base oils, then such mixture becomes base oil (A), and the kinematic viscosity of the mixture at 40°C is 4.1 mm². ２ / s or more 9.0mm ２It must be less than or equal to / s.

[0026] <Base oil (B)> The base oil (B) according to the present invention has a kinematic viscosity of 1000 mm at 25°C. ２ / s or more 1000000mm ２ This is a silicone oil with a kinematic viscosity of 1000 mm² / s or less. Thus, in this invention, as an essential component of the lubricating oil base oil, the kinematic viscosity at 25°C is 1000 mm². ２ / s or more 1000000mm ２ A silicone oil (base oil (B)) with a viscosity of / s or less is used.

[0027] Such silicone oil (base oil (B)) has a kinematic viscosity of 1000 mm at 25°C. ２ / s or more 1000000mm ２ It must be less than or equal to / s. By keeping the kinematic viscosity of such silicone oil (base oil (B)) at 25°C within the above range, it is possible to ensure proper compatibility with hydrocarbon base oil (A) and to provide a lubricating oil composition with a higher viscosity index (apparent viscosity index). Furthermore, from the same viewpoint, a higher effect can be obtained, so the kinematic viscosity of silicone oil (base oil (B)) at 25°C is preferably 1000 mm. ２ / s or more, and more preferably 10,000 mm ２ The value is 20,000 mm or more, and is particularly preferred. ２ It is greater than or equal to / s.

[0028] Furthermore, the silicone oil used as the base oil (B) is not particularly limited as long as its kinematic viscosity at 25°C is within the aforementioned range, and any silicone oil known in the field of lubricants can be used as appropriate. Examples of such silicone oils (base oil (B)) include organopolysiloxanes represented by the following general formula (1).

[0029]

[0030] In formula (1), R represents a hydrocarbon group having 1 to 18 carbon atoms, and these may be the same or different. The hydrocarbon groups referred to here include alkyl groups, alkenyl groups, aryl groups, alkylaryl groups, and arylalkyl groups, which may contain fluorine. R is preferably an alkyl group having 1 to 10 carbon atoms, more preferably an alkyl group having 1 to 4 carbon atoms, even more preferably an alkyl group having 1 or 2 carbon atoms, and particularly preferably a methyl group.

[0031] Furthermore, suitable examples of such silicone oils (base oil (B)) include dimethyl silicone, dimethyl silicate, and trifluoropropyl methyl silicone. Among these, from the viewpoint of appropriate compatibility with hydrocarbon base oil (A), it is particularly preferable that such silicone oils (base oil (B)) be oils made of dimethyl silicone (dimethyl silicone oil).

[0032] The silicone oil (base oil (B)) may consist of only one type of silicone oil, or it may consist of a mixture of two or more types of silicone oils. In this invention, if the base oil (B) consists of a mixture of two or more types of silicone oils, then the mixture becomes the base oil (B), and the kinematic viscosity of the mixture at 25°C is 1000 mmHg. ２ / s or more 1000000mm ２ It must be less than or equal to / s.

[0033] <Lubricating Oil Base Oil> The lubricating oil base oil according to the present invention must contain the base oils (A) and (B). In such a lubricating oil base oil according to the present invention, the content of base oil (B) must be 2% by mass or more based on the total amount of the lubricating oil base oil. By setting the content of base oil (B) above the lower limit, it is possible to make the viscosity index (apparent viscosity index) of the composition a larger value. Furthermore, the content of base oil (B) is preferably 2% by mass or more and 23% by mass or less (more preferably 2% by mass or more and 20% by mass or less, and particularly preferably 2% by mass or more and 17% by mass or less) based on the total amount of the lubricating oil base oil. The lower limit of the numerical range for the content of base oil (B) is more preferably 3% by mass, even more preferably 4% by mass, and particularly preferably 5% by mass. By setting the content of base oil (B) below the upper limit, it is possible to suppress the reduction in the amount of oil in the upper phase used as a lubricating component when liquid-liquid phase separation occurs in two phases under low temperature conditions. Furthermore, by setting the base oil (B) content above the aforementioned lower limit, a higher effect can be obtained in terms of the viscosity index (apparent viscosity index) of the composition.

[0034] Furthermore, in the lubricating oil base oil according to the present invention, the content of base oil (A) is preferably 98% by mass or less (more preferably 77% by mass or more and 97% by mass or less, even more preferably 80% by mass or more and 96% by mass or less, and particularly preferably 83% by mass or more and 95% by mass or less) based on the total amount of lubricating oil base oil. By setting the content of base oil (A) in the lubricating oil base oil to be above the lower limit, it is possible to suppress the reduction in the amount of oil in the upper phase used as a lubricating component when liquid-liquid phase separation occurs in two phases under low temperature conditions. In addition, by setting the content of base oil (A) in the lubricating oil base oil to be below the upper limit, an even higher effect can be obtained in terms of the viscosity index (apparent viscosity index) of the composition.

[0035] Furthermore, the lubricating oil base oil according to the present invention may contain other base oils besides base oil (A) and base oil (B) as long as it does not impair the effects of the present invention. Such other base oils are not particularly limited, and known ones used in lubricating oil compositions (e.g., ester compounds, polyalkylene glycols, etc.) can be used as appropriate. In the lubricating oil base oil according to the present invention, the total amount of base oil (A) and base oil (B) is preferably 80% by mass or more and 100% by mass or less (more preferably 85% by mass or more and 100% by mass or less, and particularly preferably 90% by mass or more and 100% by mass or less) of the total amount of lubricating oil base oil. By setting the total amount of base oil (A) and base oil (B) in such a lubricating oil base oil to be above the lower limit, it is possible to ensure appropriate compatibility with other base oils and increase the viscosity index (apparent viscosity index) of the composition.

[0036] Furthermore, the lubricating oil base oil according to the present invention is more preferably a mixture of base oil (A) and base oil (B) (where the total amount of base oil (A) and base oil (B) is 100% by mass based on the total amount of lubricating oil base oil). Thus, the lubricating oil base oil according to the present invention is more preferably a mixture of base oil (A) and base oil (B).

[0037] <Lubricating Oil Composition> The lubricating oil composition of the present invention contains the lubricating oil base oil. Thus, the lubricating oil composition of the present invention only needs to contain the lubricating oil base oil as a component. For this reason, the lubricating oil composition of the present invention may consist only of the lubricating oil base oil, or it may consist of a mixture of the lubricating oil base oil and other additives. Thus, the lubricating oil composition of the present invention may appropriately contain known additives used in the field of lubricating oil compositions, depending on its application, etc., as long as the effects of the present invention are not impaired.

[0038] Examples of such additives include ashless dispersants, metal-based detergents, friction modifiers, anti-wear agents, extreme pressure agents, viscosity index improvers, pour point depressants, corrosion inhibitors, rust inhibitors, metal deactivators, anti-emulsifiers, defoamers, antioxidants, and colorants. Various additives described in publications such as International Publication No. 2013 / 147162, International Publication No. 2017 / 073748, Japanese Patent Publication No. 2018-177875, Japanese Patent Publication No. 2020-76004, International Publication No. 2020 / 095969, International Publication No. 2020 / 095970, Japanese Patent Publication No. 2022-158121, Japanese Patent Publication No. 2022-158124, and Japanese Patent Publication No. 2022-090378 can be used as appropriate. Furthermore, such additives may be used individually or in combination of two or more types in any proportion.

[0039] Furthermore, in the lubricating oil composition of the present invention, the content of the lubricating oil base oil is not particularly limited, but it is preferably 80% by mass or more (more preferably 85% by mass or more and 100% by mass or less, and even more preferably 90% by mass or more and 100% by mass or less) based on the total amount of the lubricating oil composition. If the content of the lubricating oil base oil in such a composition is above the lower limit, then, compared to the case where it is below the lower limit, an even better effect in terms of the solubility stability of the additive can be obtained when the additive is used.

[0040] Furthermore, in the present invention, the state of the lubricating oil composition at 25°C must be in a state of liquid-liquid phase separation into an upper phase and a lower phase. When phase separation into two phases occurs in this manner, the upper phase is basically composed mainly of low-viscosity components, and the lower phase is basically composed mainly of high-viscosity components. Therefore, when the state of the lubricating oil composition at 25°C is in a state of liquid-liquid phase separation into two phases, the upper phase is basically a phase mainly composed of low-viscosity base oil (A), and the lower phase is basically a phase mainly composed of high-viscosity base oil (B). From this viewpoint, in the low-temperature region around 25°C, it is basically possible to use the components constituting the upper phase as lubricating components, and the apparent viscosity of the composition in the low-temperature region (components that substantially function as lubricating components) is basically close to the viscosity of base oil (A) (because some of the base oil (B) may dissolve in the upper phase, the viscosity of the upper phase may not necessarily match the viscosity of base oil (A)). Therefore, by satisfying the condition that the lubricating oil composition is in a liquid-liquid phase separation state of an upper phase and a lower phase at 25°C, it becomes possible to achieve high lubrication performance in the low-temperature range by basically utilizing the components of the upper phase without causing oil film breakdown or the like.

[0041] In this invention, whether or not the condition that the state of the lubricating oil composition at 25°C is in a liquid-liquid phase separation state into an upper phase and a lower phase is met is determined as follows. First, 50 g of the lubricating oil composition to be measured (measurement sample) is prepared and introduced into a 100 mL screw tube together with a stirring bar. Next, the screw tube is placed on the plate (hot plate) of a hot stirrer (for example, the product name "HSH-4D" manufactured by AS ONE Corporation may be used). Then, a thermocouple type oil temperature measuring instrument is installed so that the temperature of the lubricating oil composition in the screw tube can be measured (a thermocouple is placed in the lubricating oil composition to enable measurement of the temperature of the lubricating oil composition). Next, the stirring speed of the hot stirrer is set to 1000 rpm and the mixture is stirred until the temperature of the lubricating oil composition reaches 105°C. When the temperature of the lubricating oil composition reaches 105°C, the heating is stopped and the lubricating oil composition is cooled to 25°C (room temperature), and then left to stand for 12 hours. Then, the state of the sample after standing for 12 hours at a temperature of 25°C (room temperature) is visually inspected to determine whether or not it has separated into two phases.

[0042] Furthermore, the lubricating oil composition according to the present invention requires a combination of base oils (A) and (B) so that it can exhibit a two-phase liquid-liquid separation state under low-temperature conditions. Thus, from the viewpoint of achieving a two-phase liquid-liquid separation state under low-temperature conditions, when combining base oils (A) and (B), it is desirable to appropriately select the kinematic viscosity of the other base oil from the range of kinematic viscosity of each base oil as described above, according to the kinematic viscosity of one of them. This cannot be said in general terms, but even when combining base oils (A) and (B) that satisfy the above conditions, for example, if the kinematic viscosity of base oil (A) at 40°C is 4.1 mmHg ２ / s or more 9.0mm ２ If the value is relatively low within the range of / s or less (for example, 5.8 mm) ２ In cases where the ratio is less than or equal to / s, etc., the kinematic viscosity of the base oil (B) used in combination with this at 25°C should be 1000 mm². ２ / s or more 1000000mm ２ If we choose a relatively low value within the range of / s or less (for example, 3000 mm),２ This is because, in cases such as when the kinematic viscosity is less than 1 / s, if base oil (A) and base oil (B) are combined, and these have relatively low kinematic viscosities, the compatibility between the two becomes high, and it may occur that the mixture does not separate into two liquid-liquid phases under low temperature conditions, but instead remains a single phase. However, it is clear to a person skilled in the art that, once the structural conditions for liquid-liquid phase separation into two phases at 25°C and the types of constituent components to be used are clear, it is possible to easily produce a desired composition that separates into two liquid-liquid phases at 25°C by appropriately designing the necessary combination of base oils (selecting the kinematic viscosity of each base oil appropriately) from among hydrocarbon base oils that satisfy the conditions for base oil (A) and silicone oils that satisfy the conditions for base oil (B), taking into account their compatibility, etc., and by knowing the description in this specification (including the values ​​demonstrated in the Examples section). Here, from the viewpoint of more efficiently separating the liquid-liquid phase into two phases at 25°C, for example, the kinematic viscosity of the hydrocarbon base oil (A) at 40°C is 5.8 mm. ２ If the value is less than or equal to the kinematic viscosity, the kinematic viscosity of the silicone oil (base oil (B)) at 25°C should be 1000 mm². ２ A value exceeding / s (more preferably 3000 mm) ２ A value exceeding / s, more preferably 10,000 mm ２ A value exceeding / s, particularly preferably 20,000 mm ２ It is preferable to select the silicone oil (base oil (B)) to be combined so that the kinematic viscosity of each base oil is greater than the value of / s. Note that the preferred conditions for the combination of kinematic viscosities of each base oil described herein (preferred conditions for selecting kinematic viscosity) are merely preferred examples, and for example, the kinematic viscosity of hydrocarbon base oil (A) at 40°C is a lower value of 4.5 mm. ２ If the value is less than / s, the kinematic viscosity of the silicone oil (base oil (B)) at 25°C should be set to the higher value of 10,000 mm². ２By appropriately selecting the kinematic viscosity of one component, such as setting it to a value exceeding / s, and combining base oils in such a way that the composition undergoes liquid-liquid phase separation into two phases at 25°C, a desired composition that exhibits liquid-liquid phase separation into two phases at 25°C can be produced.

[0043] Furthermore, in the present invention, it is preferable that the state of the lubricating oil composition at 100°C is a single-phase liquid state. When the state is a single-phase liquid state at a temperature of 100°C, it is considered that, under high temperature conditions (temperature conditions higher than 100°C), the lubricating oil base oil is basically a state in which base oil (A) and base oil (B) are uniformly mixed. This makes it possible to efficiently utilize the viscosity characteristics of the mixture of base oil (A) and base oil (B) in the composition, and it is possible to make a composition with less temperature dependence of viscosity without the viscosity of the composition decreasing significantly at high temperatures. The state of the lubricating oil composition at 100°C can be determined by using the same method as for determining whether the state of the lubricating oil composition at 25°C is a liquid-liquid phase separation of upper and lower phases. This is done by visually checking whether it is a single phase when it reaches 100°C during the heating process (heating up) to 105°C.

[0044] Furthermore, in this invention, the kinematic viscosity of the upper phase at 40°C, which is determined by taking the supernatant liquid from the upper phase of the lubricating oil composition, which is in a liquid-liquid separated state into upper and lower phases at 25°C, and using it as a measurement sample, is 4.1 mm². ２ / s or more (more preferably 4.1 mm) ２ / s or more 50mm ２ / s or less, more preferably 4.1 mm ２ / s or more 35mm ２ It is preferable that the kinematic viscosity of the upper phase at 40°C is obtained by taking the supernatant liquid from the upper phase of the lubricating oil composition in a state of liquid-liquid phase separation at 25°C and using it as the measurement sample, or by adopting a measurement method in accordance with ASTM D-445.

[0045] The kinematic viscosity of the upper phase measured in this manner is considered to be close to the kinematic viscosity of the constituent components that are thought to function as lubricating components (components that form an oil film or the like to lubricate when used) at the temperature (around 40°C) when the composition is actually used. Therefore, in this invention, the kinematic viscosity of the upper phase at 40°C is considered to be the kinematic viscosity of the lubricating oil composition at 40°C, and the viscosity index (apparent viscosity index) of the composition is discussed below.

[0046] Furthermore, in the present invention, it is preferable that the lubricating oil composition is in a state of liquid-liquid phase separation into an upper phase and a lower phase at 40°C. When the composition is in a state of liquid-liquid phase separation into an upper phase and a lower phase even at 40°C, the components constituting the upper phase can be used as substantial lubricating components, at least up to 40°C. This state can be determined by visually inspecting the appearance of the lubricating oil composition after heating it to 40°C.

[0047] Furthermore, in the present invention, the kinematic viscosity of the lubricating oil composition at 100°C (100°C kinematic viscosity) is 3.5 mm. ２ It must be 1 / s or higher. By making the kinematic viscosity of the lubricating oil composition at 100°C 100°C 100°C or higher than the lower limit, it becomes less likely for the oil film to break down at high temperatures, and durability can be maintained. Here, the kinematic viscosity of the lubricating oil composition at 100°C is the value obtained by the following measurement method. As a method for measuring the kinematic viscosity of such a lubricating oil composition at 100°C, the lubricating oil composition at 100°C is heated, introduced into the capillary tube of a capillary viscometer (glass capillary viscometer) conforming to ASTM D-445, and the measurement is performed before the temperature drops from 100°C (while maintaining the temperature at 100°C), and the value obtained is adopted. The kinematic viscosity measured in this way is basically considered to be the kinematic viscosity of a single-phase composition that is thought to function as a lubricating component (a component that forms an oil film etc. to lubricate when used) at that temperature (around 100°C) when the composition is actually used. Therefore, in the present invention, the kinematic viscosity of the lubricating oil composition at 100°C is the value obtained by the above method.

[0048] Furthermore, the kinematic viscosity of the lubricating oil composition at 100°C is 3.5 mm. ２ / s or more 35mm ２ / s or less (more preferably 3.5 mm) ２ / s or more 34mm ２ / s or less, more preferably 3.5 mm ２ / s or more 33mm ２ It is preferable that the kinematic viscosity of such a lubricating oil composition at 100°C is above the lower limit, which further enhances the ability to maintain durability at high temperatures, while setting it below the upper limit further enhances the ability to reduce friction loss.

[0049] Furthermore, the kinematic viscosity of base oil (A) at 40°C is 4.1 mm². ２ / s or more 9.0mm ２ A relatively high value within the range of / s or less (for example, 5.8 mm) ２ If the value exceeds / s, the kinematic viscosity of the silicone oil (base oil (B)) at 25°C is also 1000 mm². ２ / s or more 1000000mm ２ Among the values ​​within the range of / s or less, the higher value in the comparative example (for example, 50,000 mm) ２ When these are combined (for example, when the viscosity is greater than or equal to / s), depending on the type of hydrocarbon oil or silicone oil, the resulting composition may become cloudy (non-uniform phase) at 100°C, making it impossible to measure the kinematic viscosity at 100°C. Thus, it is clear that a lubricating oil composition that becomes cloudy at 100°C and whose kinematic viscosity at 100°C cannot be measured will not function as a desired lubricating component at 100°C. Therefore, a lubricating oil composition whose kinematic viscosity at 100°C cannot be measured by the method specified herein is defined as having a kinematic viscosity of 3.5 mm² at 100°C. ２ It is considered that the condition of being greater than or equal to / s is not met. Furthermore, using base oils (A) and (B), the kinematic viscosity of the lubricating oil composition at 100°C is 3.5 mm². ２From the perspective of setting it to 3.5 mm² or higher (while ensuring that the kinematic viscosity can be measured as a single-phase substance without clouding at 100°C, and that the kinematic viscosity is 3.5 mm² or higher) ２ From the perspective of setting it to be 1 / s or more, for example, if the kinematic viscosity of the hydrocarbon base oil (A) at 40°C is relatively high within the aforementioned numerical range (for example, 6.6 mm) ２ In cases where the kinematic viscosity exceeds 1 / s, depending on the magnitude of the kinematic viscosity, a silicone oil with a relatively low kinematic viscosity at 25°C (for example, a kinematic viscosity of 100,000 mm² at 25°C) ２ Less than / s, more preferably 50,000 mm ２ It is preferable to combine it with a base oil (B) with a kinematic viscosity of 3.5 mm² / s or less. While preferred combinations of base oil (A) and base oil (B) have been described here, the combinations described herein result in a kinematic viscosity of 3.5 mm² at 100°C for the lubricating oil composition. ２ This is a suitable example for achieving a viscosity of 5.8 mm² or higher, and depending on the type of base oil actually used, for example, a hydrocarbon base oil (A) with a kinematic viscosity of 5.8 mm² at 40°C. ２ If it exceeds / s, the kinematic viscosity of the silicone oil (base oil (B)) at 25°C should be set to 800,000 mm², depending on the magnitude. ２ / s or less (more preferably 500,000 mm) ２ / s or less, particularly preferably 100,000 mm ２ / s or less, more preferably 50,000 mm ２ From among those with a kinematic viscosity of 3.5 mm² at 100°C (less than or equal to / s), ２ The values ​​should be appropriately selected and combined to achieve the optimal value for a ratio of / s or higher. Furthermore, a person skilled in the art would know that the kinematic viscosity of the lubricating oil composition at 100°C is 3.5 mm². ２ The kinematic viscosity should be 3.5 mm² or higher (while ensuring that the kinematic viscosity can be measured as a single-phase substance without clouding at 100°C). ２Once the structural conditions, such as (to be greater than or equal to / s), and the types of constituent components to be used are clarified, it is clear that, considering the description in this specification (including the values ​​demonstrated in the Examples section), it is possible to appropriately design the necessary combination of base oils from among hydrocarbon base oils that satisfy the conditions of base oil (A) and silicone oils that satisfy the conditions of base oil (B), taking into account compatibility at 100°C, etc. (appropriately selecting the kinematic viscosity of each base oil), and thereby easily produce a desired composition that satisfies such structural conditions.

[0050] Furthermore, in the lubricating oil composition of the present invention, it is preferable that the viscosity index (the viscosity index of the lubricating oil composition thus obtained is sometimes referred to as the "apparent viscosity index" in this specification for convenience) obtained by employing a method similar to the method (calculation method) described in JIS K 2283-2000, is 600 or more (more preferably 800 or more, and even more preferably 1000 or more), which is determined by taking the supernatant liquid from the upper phase of the lubricating oil composition, which is in a liquid-liquid separated state into upper and lower phases at 25°C, and using it as a measurement sample, and considering the kinematic viscosity of the upper phase at 40°C as the kinematic viscosity of the lubricating oil composition at 40°C, and the kinematic viscosity of the lubricating oil composition at 100°C obtained as described above as is, is 600 or more (more preferably 800 or more, and even more preferably 1000 or more). When such a viscosity index (apparent viscosity index) is above the aforementioned lower limit, the change in viscosity due to temperature becomes extremely small. As a result, while oil film formation and fluidity are at a high level at low temperatures, the reduction in durability due to oil film breakdown is suppressed to a high degree even at high temperatures.

[0051] Furthermore, the lubricating oil composition of the present invention can be designed to have a desired kinematic viscosity at 40°C or 100°C by changing the type and content of base oil (A) and base oil (B) depending on the application. For example, when used for lubricating an internal combustion engine of an automobile, the kinematic viscosity of the upper phase at 40°C and the kinematic viscosity of the lubricating oil composition at 100°C, as determined above, can both be 3.5 mm. ２ / s or more 15mm ２ / s or less (more preferably 5 mm) ２12 mm or more and 12 mm or less per second ２ The composition may be formed by appropriately changing the types and contents of base oil (A) and base oil (B) so that it is (12 mm or more and 12 mm or less per second). Thus, according to the application, the types and contents of base oil (A) and base oil (B) can be appropriately changed to design the specific values of the kinematic viscosity at 40 °C and 100 °C to desired values. Therefore, the application of the lubricating oil composition of the present invention is not particularly limited. However, since the temperature dependence of the viscosity of the composition is extremely small, among various applications, it is particularly preferable to use it as a lubricating oil composition for internal combustion engines and transmissions of automobiles, and for EVs, where the difference between the starting temperature and the operating temperature is large.

[0052] In addition, as a method for producing the lubricating oil composition of the present invention, there is no particular limitation, and a method of mixing appropriately selected base oils (A) and (B) (and other additives if necessary) so as to satisfy the above-mentioned conditions can be adopted. The kinematic viscosity of the lubricating oil composition at 100 °C and the state of the appearance at 25 °C can basically be easily adjusted by those skilled in the art from the respective kinematic viscosities of base oils (A) and (B) and the usage amounts of each base oil at the time of combination.

[0053] Hereinafter, the present invention will be described more specifically based on examples and comparative examples, but the present invention is not limited to the following examples.

[0054] <Regarding the base oils used in each example and comparative example> First, the abbreviations (abbreviations such as A-1 to A-5, etc.) of the base oils used in each example and comparative example and their characteristics are described below. In Tables 1 to 3, the types of base oils are indicated by abbreviations.

[0055] <A: Hydrocarbon base oil> A-1: Coal liquefaction base oil (manufactured by Inner Mongolia Yitai Coal Co., Ltd., trade name "IP95", kinematic viscosity at 40 °C: 2.2 mm ２ / s, kinematic viscosity at 100 °C: 1.0 mm ２ / s) A-2: Poly-α-olefin base oil (PAO) (manufactured by ExxonMobil, trade name "Spectrasyn 2", API Group IV base oil, kinematic viscosity at 40 °C: 5.0 mm ２ / s, kinematic viscosity at 100 °C: 1.7 mm ２ / s) A-3: PAO (manufactured by ExxonMobil, trade name "Spectrasyn 4", API Group IV base oil, kinematic viscosity at 40°C: 18.4 mm ２ / s, kinematic viscosity at 100°C: 4.1 mm ２ / s, viscosity index: 125) A-4: Mineral oil (manufactured by SK Lubricants, trade name "YUBASE2", API Group II base oil, kinematic viscosity at 40°C: 8.9 mm ２ / s, kinematic viscosity at 100°C: 2.5 mm ２ / s, viscosity index: 100) A-5: Mineral oil (manufactured by ENEOS, trade name "WBASE07", API Group III base oil, kinematic viscosity at 40°C: 9.2 mm ２ / s, kinematic viscosity at 100°C: 2.6 mm ２ / s, viscosity index: 126).

[0056] <B: Silicone oil> B-1: Silicone oil (manufactured by Shin-Etsu Silicone Co., Ltd., trade name "KF-96-100CS", kinematic viscosity at 25°C: 100 mm ２ / s) B-2: Silicone oil (manufactured by Shin-Etsu Silicone Co., Ltd., trade name "KF-96-1000CS", kinematic viscosity at 25°C: 1000 mm ２ / s) B-3: Silicone oil (manufactured by Shin-Etsu Silicone Co., Ltd., trade name "KF-96-3000CS", kinematic viscosity at 25°C: 3000 mm ２ / s) B-4: Silicone oil (manufactured by Shin-Etsu Silicone Co., Ltd., trade name "KF-96-10,000CS", kinematic viscosity at 25°C: 10,000 mm ２ / s) B-5: Silicone oil (manufactured by Shin-Etsu Silicone Co., Ltd., trade name "KF-96-50,000CS", kinematic viscosity at 25°C: 50,000 mm ２ / s) B-6: Silicone oil (manufactured by Shin-Etsu Silicone Co., Ltd., trade name "KF-96-100,000CS", kinematic viscosity at 25°C: 100,000 mm ２ / s) B-7: Silicone oil (manufactured by Shin-Etsu Silicone Co., Ltd., trade name "KF-96-300,000CS", kinematic viscosity at 25°C: 300,000 mm ２ / s) B-8: Silicone oil (manufactured by Shin-Etsu Silicone Co., Ltd., trade name "KF-96-1,000,000CS", kinematic viscosity at 25°C: 1,000,000 mm ２ / s).

[0057] <C: Polyalkylene glycol> C-1: Polyalkylene glycol (manufactured by NOF Corporation, product name "Unilube MB-700", kinematic viscosity at 40°C: 616 mm) ２ / s, 100℃ kinematic viscosity: 96.7mm ２ / s, viscosity index: 250).

[0058] (Examples 1-13 and Comparative Examples 1-20) Compositions obtained by selecting and mixing base oils to satisfy the compositional conditions described in Tables 1-3 were used as the lubricating oil compositions for each example and comparative example. In Tables 1-3, the "Kinematic viscosity of hydrocarbon base oil" column indicates the kinematic viscosity at 40°C of the hydrocarbon base oil itself used in the composition. If the hydrocarbon base oil consists of a mixture of multiple base oils (for example, the hydrocarbon base oil used in Example 9 is a mixture of two base oils, base oil A-2 and base oil A-4), the kinematic viscosity at 40°C of that mixture is indicated. The "Kinematic viscosity of hydrocarbon base oil" is measured in accordance with ASTM D-445, using a temperature condition of 40°C.

[0059] [Evaluation of the properties of the lubricating oil composition] <Confirmation test of appearance at 25°C> The appearance at 25°C was confirmed using the lubricating oil compositions obtained in each example, as follows. First, 50 g of the lubricating oil composition to be measured (measurement sample) was prepared and introduced into a 100 mL screw tube together with a stirring bar. Next, the screw tube was placed on the plate (hot plate) of a hot stirrer (product name "HSH-4D" manufactured by AS ONE Corporation). Then, a thermocouple type oil temperature measuring instrument was installed so that the temperature of the lubricating oil composition in the screw tube could be measured. When installing such an oil temperature measuring instrument, the thermocouple was placed in the lubricating oil composition to make it possible to measure the temperature of the lubricating oil composition. Next, the stirring speed of the hot stirrer was set to 1000 rpm and the mixture was stirred, and while continuing to stir, the lubricating oil composition was heated until its temperature reached 105°C. Subsequently, heating was stopped when the temperature of the lubricating oil composition reached 105°C, and the lubricating oil composition was allowed to cool to 25°C (room temperature) (natural cooling), and then left to stand for 12 hours. Next, the state of the measurement sample after standing at 25°C (room temperature) for 12 hours was visually checked to confirm whether or not it had separated into two phases. The results are shown in Tables 1 to 3. In Tables 1 to 3, if the observed state was a uniform single phase, it is written as "single phase (homogeneous phase)," and if the observed state was liquid-liquid phase separation into two phases, it is written as "two-phase separation."

[0060] <Confirmation Test of Appearance at 100°C> Using the lubricating oil compositions obtained in each example, the appearance at 100°C was confirmed as follows. Specifically, in the aforementioned "Confirmation Test of Appearance at 25°C," when the lubricating oil composition was heated to 105°C, the state of the lubricating oil composition at 100°C was visually confirmed to check whether it was single-phase or not. The results are shown in Tables 1 to 3. In Tables 1 to 3, those that were observed to be a uniform single-phase liquid state are described as "Single-phase (Hypoallergenic Phase)," and those that were not single-phase (Hypoallergenic Phase) but cloudy are described as "Cloudy (Heterogeneous Phase)." It can be understood that in all cases of "Cloudy (Heterogeneous Phase)," the high-viscosity silicone oil did not dissolve in the low-viscosity hydrocarbon base oil, resulting in a cloudy, heterogeneous state (heterogeneous phase) when the composition was mixed.

[0061] <Measurement of Kinematic Viscosity of Compositions at 100°C> The kinematic viscosity of the lubricating oil compositions obtained in each example was measured as follows. First, the lubricating oil composition was heated to 100°C. Then, the lubricating oil composition at 100°C was introduced into the capillary tube of a capillary viscometer (glass capillary viscometer: Cannon Instruments Company product name "CAV-2000") conforming to ASTM D-445. The kinematic viscosity of the composition at 100°C was measured by measuring the viscosity before the temperature dropped from 100°C (while maintaining the temperature at 100°C). The results obtained from this measurement are shown in Tables 1 to 3. Note that in all cases where the result of the "Confirmation Test of Appearance at 100°C" was cloudy (non-uniform phase), it was not possible to measure the kinematic viscosity using the above method because the high-viscosity silicone oil did not dissolve in the low-viscosity hydrocarbon base oil, and the mixed state became cloudy. As described above, lubricating oil compositions for which the kinematic viscosity at 100°C could not be measured are indicated as "unmeasurable" in the table. Furthermore, in this specification, the kinematic viscosity at 100°C measured as described above is considered to be the kinematic viscosity at 100°C of the lubricating oil composition.

[0062] <Measurement of Kinematic Viscosity of Compositions at 40°C> The kinematic viscosity of the lubricating oil compositions obtained in each example was measured as follows. Specifically, for the lubricating oil compositions that are in a liquid-liquid phase separation state (two-phase separation state) at 25°C, the kinematic viscosity of the upper phase at 40°C was determined by taking the supernatant liquid of the upper phase as the measurement sample, and otherwise employing a measurement method in accordance with ASTM D-445. On the other hand, for the lubricating oil compositions that are in a single-phase state at 25°C, the kinematic viscosity of the composition at 40°C was determined by using the composition as is and employing a measurement method in accordance with ASTM D-445. In this application, the kinematic viscosity at 40°C determined in this way is considered to be the kinematic viscosity of the lubricating oil composition at 40°C, and the results obtained are shown in Tables 1 to 3.

[0063] In this context, for compositions whose kinematic viscosity at 100°C was "unmeasurable" (Comparative Example 2, Comparative Examples 6-9, Comparative Example 12, and Comparative Example 20), the kinematic viscosity at 40°C was not specifically measured for reasons such as the inability to determine the viscosity index described later.

[0064] <Viscosity Index> The viscosity index (apparent viscosity index) of the lubricating oil compositions obtained in each example was determined by adopting the same method (calculation method) as described in JIS K 2283-2000, except that the kinematic viscosity of the composition at 100°C, obtained as described above, was considered to be the kinematic viscosity of the lubricating oil composition at 100°C, and the kinematic viscosity of the composition at 40°C (the kinematic viscosity of the upper phase at 40°C, etc.), obtained as described above, was considered to be the kinematic viscosity of the lubricating oil composition at 40°C. The results are shown in Tables 1 to 3.

[0065]

[0066]

[0067]

[0068] As is clear from the results shown in Table 1, the kinematic viscosity of the hydrocarbon base oil at 40°C was 4.1 mm². ２ / s or more 9.0mm ２The value is less than or equal to / s, and the kinematic viscosity of the silicone oil at 40°C is 1000 mm². ２ / s or more 1000000mm ２ The viscosity is less than or equal to / s, the silicone oil content is 2% by mass or more relative to the total amount of hydrocarbon base oil and silicone oil (total amount of base oil), the composition is in a liquid-liquid phase separation state of upper and lower phases at 25°C, and the kinematic viscosity of the composition at 100°C is 3.5 mm². ２ The lubricating oil compositions obtained in Examples 1 to 12, which were above / s, all had an apparent viscosity index of 600 or higher, and exhibited extremely low temperature dependence of viscosity.

[0069] On the other hand, as is clear from the results shown in Tables 2 and 3, the lubricating oil composition obtained in Comparative Example 1 had a kinematic viscosity of 4.1 mm² at 40°C for the hydrocarbon base oil. ２ / s or more 9.0mm ２ The value is less than or equal to / s, and the kinematic viscosity of the silicone oil at 40°C is 1000 mm². ２ / s or more 1000000mm ２ The viscosity is less than or equal to / s, the silicone oil content is 2% by mass or more relative to the total amount of hydrocarbon base oil and silicone oil (total amount of base oil), and the kinematic viscosity of the composition at 100°C is 3.5 mm². ２ Although it was above / s, it was single-phase at 25°C, with a viscosity index less than 600 and a large temperature dependence of viscosity. In Comparative Example 1, the kinematic viscosity of hydrocarbon base oil (A) at 40°C was 5.8 mm². ２ 4.1 mm such that the result is less than or equal to / s ２ / s or more 9.0mm ２ Based on a numerical range of less than or equal to / s, this is a relatively low value (actually 5.0 mm). ２ While it is given as / s, the kinematic viscosity of silicone oil (base oil (B)) at 25°C is also 1000 mm ２ / s or more 1000000mm ２ Based on a numerical range of less than or equal to / s, this is a relatively low value (actually 1000 mm) ２Because of the condition ( / s), the compatibility between the hydrocarbon base oil and the silicone oil is high, and it is clear that it became a single-phase mixture at 25°C and could not be separated into two phases. Furthermore, in Comparative Example 1, the mixture did not separate into two phases at 25°C, and the lubricating oil composition was formed as a mixed liquid from 25°C. Therefore, there was no change in the phase state due to the rise in temperature, and the viscosity increased with the rise in temperature, similar to a typical lubricating oil composition. For this reason, it is understood that the viscosity index could not be increased to a large value of 600 or more.

[0070] Furthermore, the kinematic viscosity of the hydrocarbon base oil used in the production of the lubricating oil composition was 9.0 mm at 40°C. ２ In Comparative Examples 2, 6-7, and 12, where the values ​​were greater than / s, even though the composition was in a two-phase separation state at 25°C, it became a cloudy, non-uniform state at 100°C, making it impossible to measure the kinematic viscosity at 100°C. Therefore, the lubricating oil compositions obtained in these comparative examples did not meet the criteria for "kinematic viscosity at 100°C of 3.5 mm²" as defined herein. ２ The condition "greater than or equal to / s" was not met. In Comparative Example 2, Comparative Examples 6-7 and Comparative Example 12, the kinematic viscosity of the hydrocarbon base oil at 40°C was 9.0 mm². ２ It can be understood that the low compatibility with silicone, resulting in a cloudy state at 100°C, was caused by a value greater than / s.

[0071] Furthermore, the kinematic viscosity of the hydrocarbon base oil used in the production of the lubricating oil composition was 4.1 mm at 40°C. ２ In Comparative Examples 3-5, 13-14, and 16, where the values ​​were smaller than / s, the compositions were in a single-phase state at 25°C, and it was not possible to achieve a viscosity index of 600 or higher. Furthermore, in Comparative Examples 3-5, 13-14, and 16, the kinematic viscosity of the hydrocarbon base oil at 40°C was 4.1 mm². ２ The fact that the value is smaller than / s suggests that the compatibility with silicone is higher, and the composition is in a single-phase state at 25°C.

[0072] Furthermore, the lubricating oil compositions obtained in Comparative Examples 8 and 9, even though they were in a two-phase separation state at 25°C, became cloudy and non-uniform at 100°C, making it impossible to measure their kinematic viscosity at 100°C. Therefore, the lubricating oil compositions obtained in these comparative examples did not meet the criteria for "kinematic viscosity at 100°C of 3.5 mm" as defined herein. ２ The condition "is greater than or equal to / s" was not met. In comparative examples 8 and 9, the kinematic viscosity of the hydrocarbon base oil (A) at 40°C was 5.8 mm. ２ 4.1 mm, exceeding / s ２ / s or more 9.0mm ２ Based on a numerical range of less than or equal to / s, this is a relatively high value (actually 8.9 mm). ２ While it is given as / s, the kinematic viscosity of silicone oil (base oil (B)) at 25°C is also 50,000 mm ２ 1000mm such that the result is / s or more ２ / s or more 1000000mm ２ It is clear that the relatively high value compared to the standard range of less than or equal to / s resulted in low compatibility between the hydrocarbon base oil and the silicone oil, causing the mixture to become cloudy at 100°C.

[0073] Furthermore, the lubricating oil compositions obtained in Comparative Examples 10 to 11 had a silicone oil content of 1% by mass (less than 2% by mass) relative to the total amount of hydrocarbon base oil and silicone oil (total amount of base oil), and as a result, the kinematic viscosity of the compositions at 100°C was 3.5 mm. ２ The value was smaller than / s, making it impossible to achieve a viscosity index of 600 or higher.

[0074] Furthermore, the lubricating oil compositions obtained in Comparative Examples 15 to 17 had a kinematic viscosity of 100 mmHg at 40°C of the silicone oil used. ２ The value is small at / s, and consequently, the kinematic viscosity of the composition at 100°C is 3.5 mm². ２ The value was smaller than / s, making it impossible to achieve a viscosity index of 600 or higher.

[0075] Furthermore, the lubricating oil composition obtained in Comparative Example 18, which used polyalkylene glycol instead of silicone oil, had a kinematic viscosity of 3.5 mm at 100°C. ２ It was not possible to achieve a value greater than / s, and therefore the viscosity index could not be set to a large value of 600 or higher.

[0076] Furthermore, the lubricating oil composition obtained in Comparative Example 19 was single-phase at 25°C, exhibiting a large temperature dependence of viscosity, and it was not possible to achieve a viscosity index of 600 or higher. In Comparative Example 19, the kinematic viscosity of the hydrocarbon base oil (A) at 40°C was 5.8 mm². ２ A relatively low value such as / s or less (actually 4.5 mm) ２ In contrast to the above, the kinematic viscosity of silicone oil (base oil (B)) at 25°C is also relatively low for a silicone oil (10,000 mm²). ２ It is clear that the high compatibility between the two phases ( / s) resulted in the inability to achieve a two-phase separation state at 25°C.

[0077] Furthermore, the lubricating oil composition obtained in Comparative Example 20, even though the composition was in a two-phase separation state at 25°C, became cloudy at 100°C, making it impossible to measure the kinematic viscosity at 100°C. Therefore, the lubricating oil compositions obtained in these comparative examples do not meet the criteria for "kinematic viscosity at 100°C of 3.5 mm" as defined herein. ２ The condition "is greater than or equal to / s" was not met. In comparative example 20, the kinematic viscosity of the hydrocarbon base oil (A) at 40°C was 5.8 mm². ２ A value exceeding / s, which is relatively high for a hydrocarbon base oil (actually 6.6 mm) ２ While it is ( / s), the kinematic viscosity of silicone oil (base oil (B)) at 25°C is 50,000 mm². ２ A value of 100,000 mm² or more is relatively high for a silicone oil (actually 100,000 mm²). ２ It is clear that the low compatibility between the two substances (due to the s) resulted in a cloudy state at 100°C.

[0078] Furthermore, from the results of Examples 8-10, Comparative Examples 8-9, and Comparative Example 20, in order to prevent the resulting lubricating oil composition from becoming cloudy at 100°C, for example, the kinematic viscosity of the base oil (A) at 40°C should be 4.1 mm. ２ / s or more 9.0mm ２ When using a numerical range of / s or less as a reference, 5.8 mm ２ When the kinematic viscosity is relatively high, exceeding 1 / s, the kinematic viscosity of the silicone oil (base oil (B)) at 25°C is set to a relatively low kinematic viscosity for a silicone oil (preferably 800,000 mm²) according to the magnitude of that kinematic viscosity. ２ / s or less, more preferably 500,000 mm ２ / s or less, more preferably 100,000 mm ２ / s or less, particularly preferably 50,000 mm ２ It is necessary to combine base oil (A) and base oil (B) such that the kinematic viscosity is less than or equal to 3.5 mm² (see Examples 9-10 and Comparative Example 20), and it is understood that the kinematic viscosity of the hydrocarbon base oil used (or the kinematic viscosity of each base oil if it is a mixture of base oils) and the kinematic viscosity of the silicone oil should be appropriately designed (selected) according to the value of one, taking into consideration the intended design. Furthermore, the composition should not become cloudy at 100°C, and the kinematic viscosity of the composition at 100°C should be 3.5 mm². ２ Adjusting the components used to achieve a viscosity of / s or higher can be easily achieved by a person skilled in the art, provided that the target design is clearly stated to be the design described in claim 1 of this application. This can be done by appropriately designing the necessary combination of base oils from among hydrocarbon base oils that satisfy the conditions for base oil (A) specified in claim 1, or silicone oils that satisfy the conditions for base oil (B) specified in claim 1, while also considering the results of the examples and comparative examples described in this application (by appropriately selecting the kinematic viscosity of each base oil).

[0079] Furthermore, from the results of Examples 1-5, Examples 11-12, Comparative Example 1, and Comparative Example 19, in order for the composition to be in a two-phase separation state at 25°C, the kinematic viscosity of the hydrocarbon base oil (A) at 40°C must be 4.1 mm. ２ / s or more 9.0mm ２When using a numerical range of / s or less as a reference, 5.8 mm ２ When the kinematic viscosity is relatively low, such as less than or equal to / s, the kinematic viscosity of the silicone oil (base oil (B)) at 25°C is set to a relatively large value for a silicone oil (preferably 1000 mm²) depending on the magnitude of the kinematic viscosity at 40°C. ２ A value exceeding / s, more preferably 3000 mm ２ A value exceeding / s, more preferably 10,000 mm ２ A value exceeding / s, particularly preferably 20,000 mm ２ It is necessary to set the kinematic viscosity to be greater than / s (see Examples 11-12 and Comparative Example 19), and it is understood that the kinematic viscosity of the hydrocarbon base oil used (or the kinematic viscosity of each base oil if it is a mixture of base oils) and the kinematic viscosity of the silicone oil must be appropriately designed (selected) according to the value of one kinematic viscosity. It should be noted that adjusting the components used so that the composition becomes a two-phase separation state at 25°C can be easily achieved by a person skilled in the art, provided that the target design is clearly stated to be the design described in Claim 1 of this application, by appropriately designing the necessary combination of base oils from among hydrocarbon base oils that satisfy the conditions of base oil (A) specified in Claim 1 and silicone oils that satisfy the conditions of base oil (B) specified in Claim 1 (by appropriately selecting the kinematic viscosity of each base oil), taking into consideration the results of the examples and comparative examples described in this application.

[0080] As described above, the present invention provides a two-phase separation type lubricating oil composition that exhibits a liquid-liquid phase separation into two phases under low-temperature conditions and a single-phase state under high-temperature conditions, while also being able to reduce the temperature dependence of its viscosity and have a larger viscosity index (apparent viscosity index). Thus, because the lubricating oil composition of the present invention has a small temperature dependence of viscosity, it is particularly useful as a lubricating oil composition for use in applications such as internal combustion engines, transmissions, gear systems, bearings, hydraulic systems, and compressors of automobiles.

Claims

1. A lubricating oil composition comprising a lubricating oil base oil, wherein the lubricating oil base oil is the following base oils (A) and (B): (A) having a kinematic viscosity of 4.1 mm at 40°C ２ / s or more 9.0mm ２ Hydrocarbon base oils with a kinematic viscosity of 1000 mm² or less at 25°C (B) ２ / s or more 1000000mm ２ The lubricating oil composition contains silicone oil with a viscosity of 0.5 / s or less, the content of the base oil (B) is 2% by mass or more based on the total amount of the lubricating oil base oil, the state of the lubricating oil composition at 25°C is a liquid-liquid phase separation into an upper phase and a lower phase, and the kinematic viscosity of the lubricating oil composition at 100°C is 3.5 mm². ２ A lubricating oil composition having a ratio of / s or higher.

2. The kinematic viscosity of the upper phase at 40°C is determined to be 4.1 mm² by taking the supernatant liquid from the upper phase of the lubricating oil composition, which is in a liquid-liquid separated state at 25°C, and using it as a measurement sample. ２ The lubricating oil composition according to claim 1, wherein the ratio is 1 / s or more.

3. The lubricating oil composition according to claim 1, wherein the content of the base oil (B) is 2% by mass or more and 23% by mass or less based on the total amount of the lubricating oil base oil.

4. The lubricating oil composition according to claim 1, wherein the state of the lubricating oil composition at 100°C is a single-phase liquid state.

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