JP2020066682A - Lubricating base oil and lubricating oil composition and method of using lubricating oil composition - Google Patents

Abstract

To provide a lubricating oil composition that can be suitably used for lubricating a traction drive.SOLUTION: A lubricating base oil has a distance between solid surfaces of 1.0 nm or more and a normalized peak intensity ratio of more than 0.2 and not more than 1.0 at a surface pressure of 12.4 MPa measured by using a resonance shear measurement device, and a lubricating oil composition includes the lubricating base oil.SELECTED DRAWING: None

Description

  The present invention relates to a lubricating base oil, a lubricating oil composition containing the lubricating base oil, and a method of using the lubricating oil composition.

In recent years, efforts have been made to improve fuel economy in various industrial fields, and a continuously variable transmission is often used as a power transmission device as a means for improving fuel economy.
A continuously variable transmission is a transmission device that can continuously change the output rotation with respect to a constant input rotation, and uses a friction drive that transmits power using a metal belt or a chain, and such elements. There is no traction drive.
In particular, the traction drive is compact and capable of transmitting a large amount of power, and is being put to practical use in the field of automobiles.

By the way, the lubricating oil used for the traction drive is required to have a high traction coefficient in order to improve power transmission.
For example, Patent Document 1 discloses a naphthene-based synthetic lubricating base oil having a flash point of 180 ° C. or lower as a lubricating base oil composition having improved flash point and low temperature fluidity without impairing the high temperature traction coefficient. , A lubricating base oil composition comprising a paraffin-based synthetic lubricating base oil such as poly α-olefin having a higher flash point than the naphthene-based synthetic lubricating base oil.

JP, 2000-204386, A

  The lubricating base oil composition described in Patent Document 1 can be preferably used for lubrication of a traction drive, but a lubricating oil composition that can be preferably used for lubrication of a traction drive is required.

  The present invention provides a lubricating base oil in which the distance between solid surfaces and the normalized peak strength ratio at a surface pressure of 12.4 MPa measured using a resonance shear measuring device are adjusted to fall within a predetermined range.

More specifically, the present invention provides the following [1] to [3].
[1] The distance between solid surfaces measured using a resonance shear measuring device at a surface pressure of 12.4 MPa is 1.0 nm or more, and the normalized peak intensity ratio at the distance between solid surfaces is 0.2. Lubricating base oil having a super 1.0 or less.
[2] A lubricating oil composition containing the lubricating base oil according to the above [1].
[3] A method of using the lubricating oil composition according to the above [2], which is used for lubricating a traction drive.

  By using the lubricating base oil of the invention, it is possible to prepare a lubricating oil composition that can be more suitably used for lubricating a traction drive.

[Lubricant base oil]
The lubricant base oil of the present invention has a solid-surface distance of 1.0 nm or more measured under the condition of a surface pressure of 12.4 MPa, which is measured by using a resonance shear measuring device. It was prepared so that the normalized peak intensity ratio was more than 0.2 and 1.0 or less.

The "resonance shear measurement device" sandwiches a liquid between two facing solid surfaces and determines the surface force (repulsive force / attractive force) generated in the direction perpendicular to the facing two solid surfaces as the inter-surface distance. It has a function as a surface force device for simultaneous measurement. In addition, the device also has the function of evaluating the properties (structuring behavior, viscosity, friction, lubrication, shear resistance) of the liquid sandwiched between the surfaces by the resonance shear response.
An example of such a "resonance shear measuring device" is a product name "RSM-1" (manufactured by Advance Riko Co., Ltd.).
The liquid sandwiched between solid surfaces shows a property that is significantly different from that of the bulk when the inter-surface distance is reduced to the nanometer unit, which causes the formation of ordered structures and a dramatic increase in viscosity due to the effects of confinement and interface. It is known.

Using this resonance shear measuring device, various lubricating base oils are sandwiched between two opposing solid surfaces, and the opposing two solid surfaces are separated via air (Separation in air; AS). ) To a state in which two opposing solid surfaces are in contact (Solid contact; SC), the distance between the solid surfaces is gradually reduced to the nanometer unit, and the change in the surface pressure value is measured.
As a result, even if the distance between the solid surfaces was gradually decreased in the vicinity of the AS side, the surface pressure was increased at a constant rate for a while, but it was tried to reduce the distance between the solid surfaces to 1 nm. It was confirmed that the lubricating base oil, in which the viscosity was rapidly increased and the surface pressure value was remarkably increased in the course of the process, was observed.
It was also found that the value of the distance between the solid surfaces when the surface pressure remarkably rises varies depending on the type of structure constituting the lubricating base oil, which is the sample oil.

In the process of reducing the distance between the solid surfaces to 1 nm, when the surface pressure value was remarkably increased, the lubricating base oil was rapidly thickened to form and hold a strong oil film. It is believed that Moreover, the oil film has a thickness of 1 nm or more.
The property of the lubricating base oil capable of forming such an oil film can be suitably used for lubrication of various devices, particularly for traction drive lubrication.
In other words, the oil film formed by the traction drive has a high traction coefficient in order to improve the driving force and wear resistance that can prevent the contact of two solid surfaces facing each other in rolling contact and suppress the wear of the solid surfaces. Two properties that are are required.
Since the oil film formed in the above process has a thickness of 1 nm or more, it is considered that the oil film has good retention and can exhibit excellent wear resistance. Further, since the oil film formed and retained by the thickening so that the surface pressure value is remarkably increased is strong, it is considered that the high traction coefficient is achieved and the power transmission is improved. Therefore, it can be said that the lubricating oil composition using such a lubricating base oil is suitable for the lubrication application of the traction drive.

In view of the above matters, the lubricating base oil of the present invention was prepared by focusing on the distance between solid surfaces at a surface pressure of 12.4 MPa and the normalized peak strength ratio at the distance between solid surfaces.
The term "distance between solid surfaces at a surface pressure of 12.4 MPa" means the value of the surface pressure caused by sudden thickening of the lubricating base oil in the process of decreasing the distance between solid surfaces to 1 nm. It defines the distance between the solid surfaces when a significant rise in is observed.
In addition, after the sudden increase in the viscosity of the lubricating base oil was caused and the surface pressure reached 12.4 MPa, the surface pressure was such that it became difficult to reduce the distance between the solid surfaces.

The lubricant base oil of the present invention is prepared to have a solid surface distance of 1 nm or more at a surface pressure of 12.4 MPa.
A lubricating oil composition containing such a lubricating base oil forms a strong oil film with a thickness of 1 nm or more when used for lubrication in a nano space having a facing distance between two surfaces of several nm. It is considered that the oil film can be retained and the lubricating characteristics can be improved. In particular, when the lubricating oil composition is used for the lubrication of a traction drive, the oil film has a thickness of 1 nm or more, so that the retaining property is good and contact between two opposing solid surfaces in rolling contact is prevented, It is possible to exhibit excellent wear resistance which can suppress wear of the solid surface.
In addition, the lubricant base oil, which has a surface pressure of less than 1 nm to reach a surface pressure of 12.4 MPa, or which cannot reach a surface pressure of 12.4 MPa even if the distance between the solid surfaces is reduced to near the SC side, is an oil film. However, it is difficult to use it for lubrication in the above nano space.

  From the above viewpoint, the distance between the solid surfaces at the surface pressure of 12.4 MPa of the lubricating base oil of one embodiment of the present invention is preferably 1.2 nm or more, more preferably 1.5 nm or more, still more preferably 2.0 nm or more. Is more preferably 2.5 nm or more, and is usually 10 nm or less, preferably 9 nm or less, more preferably 8 nm or less, and particularly preferably 7 nm or less.

Further, the lubricating base oil of the present invention is prepared so that the normalized peak intensity ratio at the solid surface distance at a surface pressure of 12.4 MPa is more than 0.2 and 1.0 or less.
Here, the “normalized peak intensity ratio” is the peak intensity I of the resonance frequency at a surface pressure of 12.4 MPa with respect to the peak intensity I _sc of the resonance frequency in a state (SC) where two opposing solid surfaces are in contact with each other. The ratio [I / I _sc ] of

The value of the normalized peak intensity ratio is an index of the hardness of the oil film formed in the nano space.
That is, it is considered that a lubricating base oil having a normalized peak intensity ratio of more than 0.2 has a strong oil film retained in the nano space. It is considered that the property of holding a strong oil film achieves a high traction coefficient and contributes to improvement of power transmission when a lubricating oil composition containing the lubricating base oil is used for lubrication of a traction drive.
On the other hand, a lubricating base oil having a normalized peak strength ratio of 0.2 or less is considered to have insufficient oil film hardness, and when used for traction drive lubrication, the traction coefficient becomes low. , There is a problem in terms of power transmission.

  From the above viewpoint, the normalized peak intensity ratio at the surface pressure of 12.4 MPa of the lubricating base oil of one embodiment of the present invention is preferably 0.22 to 1.00, more preferably 0.25 to 1.00, It is more preferably 0.35 to 1.00, still more preferably 0.50 to 1.00, and particularly preferably 0.70 to 1.00.

In the present specification, the distance between the solid surfaces and the normalized peak intensity ratio at the surface pressure of the lubricating base oil of 12.4 MPa are the resonance shear measurement device (for example, product name “RSM-1” (advanced Riko Co., Ltd.) and the like). As a specific measurement procedure using the resonance shear measurement device, the method described in Reference 1 (A new physical model for resonance shear measurement of confined liquids between solid surfaces, REVIEW OF SCIENTIFIC INSTRUMENTS 79, 113705 2008) can be mentioned. More specifically, it can be measured based on the method described in Examples.
In view of such characteristics, the lubricating base oil of one aspect of the present invention is preferably used in a lubricating oil composition for traction drive.

In the lubricating base oil of one embodiment of the present invention, the viscosity η _{P at} 40 ° C. measured under a surface pressure of 12.4 MPa can be a lubricating base oil that can be prepared into a lubricating oil composition suitable for traction drive lubrication. From the viewpoint of the above, it is preferably 10 to 50 mPa · s, more preferably 12 to 45 mPa · s, further preferably 14 to 40 mPa · s, and still more preferably 16 to 35 mPa · s.

Further, in the lubricating base oil of one embodiment of the present invention, the viscosity η _{0 at} 40 ° C. measured under normal pressure (0.10 MPa) conditions can be adjusted to a lubricating oil composition suitable for traction drive lubrication. From the viewpoint of a lubricating base oil, it is preferably 5 to 50 mPa · s, more preferably 7 to 45 mPa · s, and further preferably 9 to 40 mPa · s.

In the lubricating base oil of one embodiment of the present invention, the viscosity η _{P at} 40 ° C. measured under a surface pressure of 12.4 MPa and the viscosity η _{0 at} 40 ° C. measured under a normal pressure (0.10 MPa) condition. The ratio [η _P / η ₀ ] is preferably 1. from the viewpoint of a lubricating base oil that can be prepared into a lubricating oil composition capable of forming a strong oil film with high power transmission efficiency in nano space. 05 to 2.0, more preferably 1.1 to 1.7, still more preferably 1.15 to 1.5.

In this specification, the viscosity η ₀ can be measured according to the method described in Reference Document 2 below, and the viscosity η _P can be measured according to the method described in Reference Document 3 below in accordance with the falling ball formula. It can be measured using a high-pressure viscometer. More specific measurement procedure is as described in the examples.
・ Reference 2: API Standard 2540 (1980) 'Manual of Measurement Standard Chapter 11.1-Lolume Correction Factors, Volume XIV' Appendix A
・ Reference 3: Tribologist, vol.55, No.9 (2010), p41-52 (Idemitsu Kosan Co., Ltd.)

The kinematic viscosity at 100 ° C. in one embodiment the lubricating base oils of the present invention, preferably 2.0~10.0mm ² / s, more preferably 2.2~8.5mm ² / s, more preferably 2 0.5-7.0 mm < ² > / s, More preferably, it is 2.8-6.5 mm < ² > / s.
The viscosity index of the lubricating base oil of one embodiment of the present invention is usually 45 or more, but from the viewpoint of a lubricating base oil having a small temperature dependence, preferably 70 or more, more preferably 80 or more, More preferably, it is 90 or more.
In the present specification, the kinematic viscosity and viscosity index of the lubricating base oil mean values measured and calculated according to JIS K2283: 2000.

  The lubricating base oil of one aspect of the present invention can be composed of one or more selected from mineral oils and synthetic oils, and the values of the distance between solid surfaces and the value of the normalized peak strength ratio are in the above ranges. From the viewpoint of preparation of the above, it is preferable to contain at least one selected from ester synthetic oils, naphthene synthetic oils, and mineral oils, and it is more preferable to contain at least one selected from ester synthetic oils and naphthene synthetic oils. It is more preferable to include an ester synthetic oil.

By the way, as described above, the values of the distance between the solid surfaces and the normalized peak intensity ratio are likely to change depending on the molecular structure of the lubricating base oil. Therefore, for example, even in the case of ester synthetic oil, the values of the distance between the solid surfaces and the normalized peak intensity ratio change depending on the difference in the molecular structure. In the case of a mixture composed of two or more compounds, these values also change depending on the content ratio of each compound.
In the lubricating base oil of the present invention, by selecting a compound having a specific molecular structure, and by adjusting the content ratio of each compound, the values of the solid surface distance and the normalized peak intensity ratio are described above. The range is set to.

For example, the ester synthetic oil preferably contains an ester compound of an aliphatic polyhydric alcohol from the viewpoint of adjusting the distance between the solid surfaces and the value of the normalized peak intensity ratio to be large. The valence of the aliphatic polyhydric alcohol is preferably 2-6.
The ester compound preferably contains a compound having an alkyl group having 6 to 20 carbon atoms, and more preferably contains a compound having an alkyl group having 8 to 12 carbon atoms.
Further, the ester-based synthetic oil is preferably composed of a compound having at least one type of alkyl group having 8 to 12 carbon atoms, and at least two or three types of alkyl group having 8 to 12 carbon atoms. More preferably, it is a mixture composed of the compound having.

The naphthene-based synthetic oil preferably contains a naphthene compound having 10 to 25 carbon atoms and has 12 to 20 carbon atoms from the viewpoint of adjusting the distance between the solid surfaces and the value of the normalized peak intensity ratio to be large. It is more preferable to include a naphthene compound.
Further, the naphthene compound contains a compound having a ring selected from a bicyclo [2.2.1] heptane ring, a bicyclo [2.2.2] octane ring, and a bicyclo [3.3.0] octane ring. Is more preferable, and it is more preferable to include a dimer having two of these rings.
Further, the naphthene compound preferably contains a compound having an alkyl group having 1 to 3 carbon atoms, and more preferably contains a compound having a plurality of alkyl groups having 1 to 3 carbon atoms.

Examples of the mineral oil include atmospheric residual oil obtained by atmospheric distillation of crude oil such as paraffinic crude oil, intermediate base crude oil, and naphthenic crude oil; distillate oil obtained by vacuum distillation of these atmospheric residual oils. A refined oil obtained by subjecting the distillate oil to one or more purification treatments such as solvent degassing, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, and hydrorefining; natural gas to Fischer Mineral oil (GTL) obtained by isomerizing wax (GTL wax (Gas To Liquids WAX)) manufactured by the Tropsch method etc. is mentioned.
Among these, from the viewpoint of adjusting the distance between the solid surfaces and the value of the normalized peak intensity ratio to be large, the mineral oil is a mineral oil composed of a compound having a hydrocarbon group having 12 to 50 carbon atoms. A paraffinic mineral oil composed of a compound having a hydrocarbon group having 12 to 50 carbon atoms is more preferable. The number of carbon atoms of the hydrocarbon group is preferably 12 to 50, but more preferably 16 to 50, and further preferably 16 to 50, from the viewpoint of adjusting the values of the distance between the solid surfaces and the normalized peak intensity ratio to be large. It is preferably 20 to 50, more preferably 22 to 50.

  The lubricating base oil of one aspect of the present invention may be a mixed base oil containing a plurality of types of base oils. In the case of a mixed base oil, if the mixed base oil has a blending ratio of each base oil such that the solid surface distance and the value of the normalized peak intensity ratio fall within the above range. Good.

In addition, the lubricating base oil of one aspect of the present invention is an olefin-based synthesis such as poly α-olefin, from the viewpoint of adjusting the distance between the solid surfaces and the value of the normalized peak intensity ratio to fall within the above range. The oil content is preferably as low as possible.
From the above viewpoint, in the lubricating base oil of one embodiment of the present invention, the content of the olefinic synthetic oil is preferably less than 10% by mass, more preferably less than 10% by mass, based on the total amount (100% by mass) of the lubricating base oil. It is less than 5% by mass, more preferably less than 1% by mass, even more preferably less than 0.1% by mass, particularly preferably less than 0.01% by mass.
The content of poly α-olefin is also preferably within the above range.

[Lubricant composition]
The lubricating oil composition of the present invention contains the above-mentioned lubricating base oil of the present invention.
In the lubricating oil composition of one aspect of the present invention, the content of the lubricating base oil is preferably 60% by mass or more, more preferably 70% by mass, based on the total amount (100% by mass) of the lubricating oil composition. The amount is more preferably 80% by mass or more, further preferably 85% by mass or more.

Note that the lubricating oil composition of one aspect of the present invention may contain various additives, if necessary.
Examples of such additives include antioxidants, detergent dispersants, pour point depressants, viscosity index improvers, antiwear agents, extreme pressure agents, defoamers, rust inhibitors, and corrosion inhibitors. To be
These lubricating oil additives may be used alone or in combination of two or more.

  The content of each of these additives can be appropriately adjusted depending on the type of the additive, but based on the total amount (100% by mass) of the lubricating oil composition, independently for each additive, It is usually 0.001 to 15% by mass, preferably 0.005 to 10% by mass, and more preferably 0.01 to 5% by mass.

[Uses of lubricating oil composition]
Applications of the lubricating oil composition of one aspect of the present invention include traction drive fluids, transmission fluids, hydraulic fluids, compressor oils, electrical insulating oils and the like.
However, as described above, the lubricating base oil of the present invention is considered to have excellent wear resistance and high power transmission efficiency, as described above, because a strong oil film is formed and retained in the nano space. . Therefore, it is considered that the lubricating oil composition of the present invention containing the lubricating base oil can also exhibit similar characteristics.
Therefore, the lubricating oil composition of one embodiment of the present invention is preferably used as a traction drive fluid for lubrication of a traction drive, and the distance between two surfaces facing each other in the traction drive is 1.0 to 10 nm in a nano space. More preferably used for lubrication.
The distance between two surfaces of the traction drive that opposes corresponds to the distance between the solid surfaces in the above-mentioned resonance shear measuring device.

Further, considering the above-mentioned characteristics of the lubricating oil composition of one aspect of the present invention, the present invention can also provide the following [1] and [2].
[1] A traction drive using the lubricating oil composition of one aspect of the present invention described above.
[2] A method of using a lubricating oil composition, which comprises using the lubricating oil composition according to one embodiment of the present invention for lubricating a traction drive.
In addition, in the above [1] and [2], the lubricating oil composition of one embodiment of the present invention is used for lubrication in a nano space having a distance between two opposing surfaces in a traction drive of 1.0 to 10 nm. preferable.

  Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. The methods for measuring or evaluating various physical properties are as follows.

(1) Measurement and Calculation of Distance between Solid Surfaces and Normalized Peak Strength Ratio Using a resonance shear measuring device (Advance Riko Co., Ltd., product name "RSM-1"), sample oil accompanying changes in the distance between solid surfaces The change in the surface pressure value was measured.
Specifically, based on the method described in Reference Document 1 below, using the above resonance shear measuring device, at room temperature (25 ° C.), between two surfaces facing clean and smooth mica cleavage surface, About 200 μl of any one of the sample oils (α1) to (α7) was dropped, and the samples were brought into contact with each other in an orthogonal cylinder format. The distance between the solid surfaces was calculated by the colorimetric order interference fringe method. Then, the two solid surfaces facing each other are separated from each other via air (AS) to the contact state (SC) of the two solid surfaces facing each other, and the distance between the solid surfaces is gradually reduced. The distance between the solid surfaces when the surface pressure reached 12.4 MPa was measured.
Regarding the resonance shear response, a voltage Uin is applied to the resonance shear unit to generate horizontal vibration, and the amplitude of the vibration is measured by measuring the voltage Uout, and the vibration intensity [Uout / Uin] is measured. Evaluated as. By analyzing the obtained resonance shear response (vibration intensity [Uout / Uin]) by the method described in Reference Document 1 below, the peak intensity I of the resonance frequency when the surface pressure reached 12.4 MPa was obtained. calculates a peak intensity I _SC of the resonance frequency in the SC, the ratio of both [I / I _SC] was normalized peak intensity ratio.
・ Reference 1: A new physical model for resonance shear measurement of confined liquids between solid surfaces, REVIEW OF SCIENTIFIC INSTRUMENTS 79, 113705 2008

(2) Viscosity η _{0 at} 40 ° C. under normal pressure (0.10 MPa) conditions
It was calculated according to the method described in Reference Document 2 below.
The density (dt) at 40 ° C. used when calculating the viscosity η ₀ can be calculated by the following calculation formula.
dt = d15 × exp (−D × Δt × (1 + 0.8 × D × Δt))
(In the above calculation formula, D = 0.6278 / 1000 × d15 (where d15 is the density of the sample oil at 15 ° C. measured according to JIS K2249-4: 2011) and Δt = t-15.)
・ Reference 2: API Standard 2540 (1980) 'Manual of Measurement Standard Chapter 11.1-Lolume Correction Factors, Volume XIV' Appendix A
(3) Viscosity η _{P at} 40 ° C. under surface pressure of 12.4 MPa
In accordance with the method described in Reference Document 3 below, the viscosity η _P of the sample oil at a pressure of 12.4 MPa was calculated using a falling ball high pressure viscometer.
・ Reference 3: Tribologist, vol.55, No.9 (2010), p41-52 (Idemitsu Kosan Co., Ltd.)
(4) Kinematic viscosity and viscosity index Measured and calculated in accordance with JIS K2283: 2000.

・試料油（α３）：１００℃動粘度＝６．０ｍｍ^２／ｓである、炭素数２２〜５０の炭化水素基を有する化合物を含むパラフィン系鉱油。
・試料油（α４）：１００℃動粘度＝３．１ｍｍ^２／ｓである、炭素数１６〜３０の炭化水素基を有する化合物を含むパラフィン系鉱油。
・試料油（α５）：１００℃動粘度＝５．９ｍｍ^２／ｓであるポリα−オレフィン。
・試料油（α６）：１００℃動粘度＝３．９ｍｍ^２／ｓであるポリα−オレフィン。
・試料油（α７）：１００℃動粘度＝１．８ｍｍ^２／ｓであるポリα−オレフィン。 Examples 1-4, Comparative Examples 1-3
With respect to the following sample oils (α1) to (α7) obtained by a predetermined purification method or synthetic method, various physical properties including a distance between solid surfaces and a normalized peak intensity ratio were measured. The measured physical properties are shown in Table 1.
Sample oil (α1): ester-based synthetic oil, a mixture of ester compounds containing trimethylolpropane triester having an alkyl group having 8, 10 or 12 carbon atoms.
-Sample oil (α2): naphthenic synthetic oil, an alicyclic polycyclic compound represented by the following formula.

Sample oil (α3): 100 ° C. kinematic viscosity = 6.0 mm ² / s, a paraffinic mineral oil containing a compound having a hydrocarbon group having 22 to 50 carbon atoms.
Sample oil (α4): 100 ° C. kinematic viscosity = 3.1 mm ² / s, a paraffinic mineral oil containing a compound having a hydrocarbon group having 16 to 30 carbon atoms.
Sample oil (α5): polyα-olefin having a kinematic viscosity at 100 ° C. of 5.9 mm ² / s.
Sample oil (α6): polyα-olefin having a kinematic viscosity at 100 ° C. of 3.9 mm ² / s.
Sample oil (α7): polyα-olefin having a kinematic viscosity at 100 ° C. of 1.8 mm ² / s.

It is considered that the sample oils (α1) to (α4) of Examples 1 to 4 can form and hold a strong oil film in the nano space, based on the values of the solid surface distance and the normalized peak intensity ratio. Therefore, it can be said that these sample oils can be suitably used for the lubrication of the traction drive.
On the other hand, since the sample oils (α5) to (α7) of Comparative Examples 1 to 3 have low values of the normalized peak intensity ratio, it is considered that there is a problem in the hardness of the oil film formed, It is presumed that it is not suitable for traction drive lubrication. Further, since the sample oils (α6) to (α7) of Comparative Examples 2 to 3 have a value of the distance between solid surfaces of less than 1.0 nm, it is considered that the oil film retainability is poor in the nano space.

Claims (10)

  Lubricating base oil having a distance between solid surfaces of 1.0 nm or more and a normalized peak intensity ratio of more than 0.2 and not more than 1.0 at a surface pressure of 12.4 MPa measured using a resonance shear measuring device. . The lubricating base oil according to claim 1, having a viscosity η _{P at} 40 ° C of 10 to 50 mPa · s measured under a surface pressure of 12.4 MPa. The lubricating base oil according to claim 1, wherein the viscosity η _{0 at} 40 ° C. measured under normal pressure conditions is 5 to 50 mPa · s.   The lubricating base oil according to any one of claims 1 to 3, containing at least one selected from ester synthetic oils, naphthene synthetic oils, and mineral oils.   The lubricating base oil according to any one of claims 1 to 4, which is used in a lubricating oil composition for a traction drive.   A lubricating oil composition comprising the lubricating base oil according to any one of claims 1 to 5.   The lubricating oil composition according to claim 6, which is used for lubricating a traction drive.   The lubricating oil composition according to claim 7, which is used for lubrication in a nano space having a distance between two surfaces facing each other of the traction drive of 1.0 to 10 nm.   A method of using the lubricating oil composition according to claim 6 for lubricating a traction drive. The method of using the lubricating oil composition according to claim 9, which is used for lubrication in a nano space having a distance between two surfaces facing each other of the traction drive of 1.0 to 10 nm.