U.S. patent application number 17/287323 was filed with the patent office on 2021-11-18 for lubricating oil base oil, lubricating oil composition, and method for using lubricating oil composition.
This patent application is currently assigned to Idemitsu Kosan Co.,Ltd.. The applicant listed for this patent is Idemitsu Kosan Co.,Ltd.. Invention is credited to Kazushi TAMURA, Hiroyuki TATSUMI.
Application Number | 20210355404 17/287323 |
Document ID | / |
Family ID | 1000005785477 |
Filed Date | 2021-11-18 |
United States Patent
Application |
20210355404 |
Kind Code |
A1 |
TAMURA; Kazushi ; et
al. |
November 18, 2021 |
LUBRICATING OIL BASE OIL, LUBRICATING OIL COMPOSITION, AND METHOD
FOR USING LUBRICATING OIL COMPOSITION
Abstract
A lubricating oil base oil may include a solid surface distance
of 1.0 nm or more at a surface pressure of 12.4 MPa and a
normalized peak intensity ratio of more than 0.2 to 1.0 measured
using a resonance shear measurement system and a lubricating oil
composition may include the lubricating oil base oil.
Inventors: |
TAMURA; Kazushi; (Chiba,
JP) ; TATSUMI; Hiroyuki; (Chiba, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Idemitsu Kosan Co.,Ltd. |
Chiyoda-ku |
|
JP |
|
|
Assignee: |
Idemitsu Kosan Co.,Ltd.
Chiyoda-ku
JP
|
Family ID: |
1000005785477 |
Appl. No.: |
17/287323 |
Filed: |
October 25, 2019 |
PCT Filed: |
October 25, 2019 |
PCT NO: |
PCT/JP2019/041863 |
371 Date: |
April 21, 2021 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C10M 171/02 20130101;
C10M 105/32 20130101; C10N 2030/54 20200501; C10M 2203/1065
20130101; C10M 101/02 20130101; C10N 2020/02 20130101; C10M
2207/2805 20130101; C10N 2040/045 20200501; C10M 2203/1006
20130101 |
International
Class: |
C10M 105/32 20060101
C10M105/32; C10M 101/02 20060101 C10M101/02; C10M 171/02 20060101
C10M171/02 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 25, 2018 |
JP |
2018-200593 |
Claims
1. A lubricating oil base oil, having a solid surface distance of
1.0 nm or more, measured using a resonance shear measurement system
at a surface pressure of 12.4 MPa, and having a normalized peak
intensity ratio of more than 0.2 to 1.0.
2. The base oil of claim 1, wherein a viscosity .eta..sub.P of the
base oil at 40.degree. C. measured at a surface pressure of 12.4
MPa, is in a range of from 10 to 50 mPas.
3. The base oil to claim 1, wherein a viscosity .eta..sub.P of the
base oil at 40.degree. C., measured at normal pressure, is in a
range of from 5 to 50 mPas.
4. The base oil of claim 1, which comprises an ester synthetic oil,
a naphthenic synthetic oil, and/or a mineral oil.
5. A traction drive, comprising the base oil of claim 1.
6. A lubricating oil composition,. comprising the base oil of claim
1.
7. A traction drive, comprising the composition of claim 6.
8. The traction drive of claim 7, wherein the composition
lubricates in a nanospace in which a distance between two surfaces
of two opposing solids constituting the traction drive is 1.0 to 10
nm.
9. A method of lubricating a traction drive, comprising contacting
the traction drive with the composition of claim 6.
10. The method of claim 9, comprising lubricating in a nanospace in
which a distance between two surfaces of two opposing solids
constituting the traction drive is 1.0 to 10 nm.
Description
TECHNICAL FIELD
[0001] The present invention relates to a lubricating oil base oil,
a lubricating oil composition comprising the lubricating oil base
oil, and a method for using a lubricating oil composition.
BACKGROUND ART
[0002] In recent years, efforts have been made in each industrial
field for the purpose of improving fuel efficiency, and as a means
for improving fuel efficiency, continuously variable transmissions
(CVTs) are often used in power transmission devices.
[0003] CVTs are transmission devices that can continuously change
the output rotation with respect to a constant input rotation, and
use a mechanism such as a friction drive that transmits power using
a metal belt or chain or a traction drive that does not use such an
element.
[0004] In particular, a 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.
[0005] Then, a lubricating oil used for a traction drive is
required to have a high traction coefficient from the viewpoint of
improving power transmission.
[0006] For example, Patent Literature 1 discloses, as a lubricating
oil base oil composition with an improved flash point and low
temperature fluidity without compromising a high temperature
traction coefficient, a lubricating oil base oil composition
consisting of a naphthenic synthetic lubricating oil base oil
having an ignition point of 180.degree. C. or lower and a
paraffiniic synthetic lubricating oil base oil such as polya-olefin
having a higher ignition point than the naphthenic synthetic
lubricating oil base oil.
Citation List
Patent Literature
[0007] Patent Literature 1: JP 2000-204386 A
SUMMARY OF INVENTION
Technical Problem
[0008] The lubricating oil base oil composition described in Patent
Literature 1 can also be suitably used for lubricating a traction
drive, but there is a demand for a lubricating oil composition that
can be more suitably used for lubricating a traction drive.
Solution to Problem
[0009] The present invention provides a lubricating oil base oil
which is prepared such that the solid surface distance and the
normalized peak intensity ratio at a surface pressure of 12.4 MPa
measured using a resonance shear measurement system are each within
a predetermined range.
[0010] More specifically, the invention provides the following [1]
to [10].
[1] A lubricating oil base oil having a solid surface distance of
1.0 nm or more measured using a resonance shear measurement system
at a surface pressure of 12.4 MPa and having a normalized peak
intensity ratio of more than 0.2 to 1.0 at the solid surface
distance. [2] The lubricating oil base oil according to [1],
wherein a viscosity .sub.rlp of the lubricating oil base oil at
40.degree. C. measured at a surface pressure of 12.4 MPa is 10 to
50 mPas. [3] The lubricating oil base oil according to [1] or [2],
wherein a viscosity .eta.P of the lubricating oil base oil at
40.degree. C. measured at normal pressure is 5 to 50 mPas. [4] The
lubricating oil base oil according to any one of [1] to [3],
wherein the lubricating oil base oil comprises one or more selected
from an ester synthetic oil, a naphthenic synthetic oil, and a
mineral oil. [5] The lubricating oil base oil according to any one
of [1] to [4], wherein the lubricating oil base oil is used in a
lubricating oil composition for a traction drive. [6] A lubricating
oil composition comprising the lubricating oil base oil according
to any one of [1] to [5]. [7] The lubricating oil composition
according to [6], wherein the lubricating oil composition is used
for lubricating a traction drive. [8] The lubricating oil
composition according to [7], wherein the lubricating oil
composition is used for lubrication in a nanospace in which a
distance between two surfaces of two opposing solids constituting
the traction drive is 1.0 to 10 nm. [9] A method for using a
lubricating oil composition, comprising using the lubricating oil
composition according to [6] for lubricating a traction drive. [10]
The method for using a lubricating oil composition according to
[9], wherein the method is used for lubrication in a nanospace in
which a distance between two surfaces of two opposing solids
constituting the traction drive is 1.0 to 10 nm.
Advantageous Effects of Invention
[0011] The use of the lubricating oil base oil of the present
invention enables the preparation of a lubricating oil composition
that can be used more preferably for lubricating a traction
drive.
DESCRIPTION OF EMBODIMENTS
[Lubricating Oil Base Oil]
[0012] The lubricating oil base oil of the present invention is
prepared such that it has a solid surface distance of 1.0 nm or
more measured using a resonance shear measurement system at a
surface pressure of 12.4 MPa and a normalized peak intensity ratio
of more than 0.2 to 1.0 at the solid surface distance.
[0013] The "resonance shear measurement system" functions as a
surface forces apparatus by which a liquid is sandwiched between
two solid surfaces facing each other, and the surface force
(repulsive force/attractive force) generated in the direction
perpendicular to the two solid surfaces facing each other is
measured at the same time as the distance between the surfaces. In
addition, the system also functions to evaluate the properties of
the liquid sandwiched between the surfaces (structural behavior,
viscosity, friction, lubrication, shear resistance) by resonance
shear response.
[0014] An example of such "resonance shear measurement system" is
"RSM-1" (trade name; manufactured by ADVANCE RIKO, Inc.)
[0015] It is known that when the distance between surfaces is
reduced to nanometers, the liquid sandwiched between the solid
surfaces causes the formation of an ordered structure, a dramatic
increase in viscosity, and the like due to the effects of
confinement and interface, and thus it exhibits properties that are
significantly different from those in the bulk liquid form.
[0016] Various lubricating base oils are sandwiched between two
opposing solid surfaces, the solid surface distance (distance
between the solid surfaces) was reduced to nanometers with a shift
from a state in which the two solid surfaces faced each other via
air (AS: separation in air) to a state in which the two solid
surfaces facing each other came into contact with each other (SC:
solid contact), thereby measuring the change in the surface
pressure value.
[0017] As a result, in the vicinity of the AS side, even when the
solid surface distance was gradually reduced, the surface pressure
increased at a constant rate for a while; however, in the process
of trying to reduce the solid surface distance to 1 nm, rapid
thickening was induced, and thus the presence of a lubricating oil
base oil with a significant increase in the surface pressure was
confirmed.
[0018] It was also found that the value of the solid surface
distance when the surface pressure rises significantly differs
depending on the type of structure forming the lubricating oil base
oil, which is a sample oil.
[0019] In the process of reducing the solid surface distance to 1
nm in this way, when a significant increase in the surface pressure
value is observed, it is thought that the lubricating oil base oil
forms and retains a strong oil film due to rapid thickening. On top
of this, the oil film has a thickness of at least 1 nm.
[0020] The properties of the lubricating oil base oil capable of
forming such an oil film can be suitably applied for the purpose of
lubricating various apparatuses, in particular, traction
drives.
[0021] In addition, the term "traction drive" used herein means a
power transmission mechanism which transmits torque through an oil
film under elastic fluid lubrication.
[0022] Two properties are required for the oil film formed by a
traction drive, which are: abrasion resistance that can prevent
solid surface contact between two opposing surfaces which roll and
come into contact with each other and can suppress the wear of the
solid surface; and a high traction coefficient for improving
driving force.
[0023] 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 abrasion resistance.
Further, since the oil film, which has been formed and retained by
thickening to such an extent that the surface pressure value is
remarkably increased, is strong, it is considered that a high
traction coefficient is achieved and the power transmission is
improved. Therefore, it can be said that a lubricating oil
composition using such a lubricating oil base oil is suitable for
the purpose of lubricating a traction drive.
[0024] The lubricating oil base oil of the present invention was
prepared with a focus on the solid surface distance at a surface
pressure of 12.4 MPa and the normalized peak intensity ratio at the
solid surface distance.
[0025] The "solid surface distance at a surface pressure of 12.4
MPa" is specified as a solid surface distance when in the process
of trying to reduce the solid surface distance to 1 nm, rapid
thickening is induced, and a significant increase in the surface
pressure is observed.
[0026] After rapid thickening of the lubricating oil base oil is
induced and the surface pressure reached 12.4 MPa, a state in which
surface pressure is applied to make it difficult to reduce the
solid surface distance is achieved.
[0027] The lubricating oil base oil of the present invention is
prepared such that the solid surface distance is 1 nm or more at a
surface pressure of 12.4 MPa.
[0028] In a case in which a lubricating oil composition comprising
such a lubricating oil base oil is used for lubrication in a
nanospace in which the distance between two opposing surfaces is
several nanometers, it is considered that a strong oil film having
a thickness of 1 nm or more is formed such that the oil film can be
retained and the lubrication property can be improved. In
particular, in a case in which the lubricating oil composition is
used for lubricating a traction drive, since the thickness of the
oil film is 1 nm or more, the retention property is favorable, and
excellent abrasion resistance can be exhibited, which can prevent
solid surface contact between two opposing solid surfaces which
roll and come into contact with each other and can suppress the
wear on the solid surface.
[0029] Note that a lubricating oil base oil with which the solid
surface distance with a surface pressure reaching 12.4 MPa is less
than 1 mm or a lubricating oil base with which the surface pressure
cannot reach 12.4 MPa even with a reduction of the solid surface
distance to around the vicinity of the SC side has a problem in oil
film retention and is difficult to use for the above-described
purpose of lubrication in the nanospace.
[0030] From the above perspective, the solid surface distance for
the lubricating oil base oil at a surface pressure of 12.4 MPa in
one aspect 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, even more preferably 2.5 nm or more, and usually 10 nm or
less, but preferably 9 nm or less, more preferably 8 nm or less,
and particularly preferably 7 nm or less.
[0031] Further, the lubricating oil base oil of the present
invention is prepared such that the normalized peak intensity ratio
at the solid surface distance at a surface pressure of 12.4 MPa is
more than 0.2 to 1.0.
[0032] The term "normalized peak intensity ratio" used herein means
the ratio of the peak intensity I of the resonance frequency at a
surface pressure of 12.4 MPa to the peak intensity I.sub.sc of the
resonance frequency in a state in which two opposing solid surfaces
are in contact with each other (SC) [I/I.sub.sc].
[0033] The value of the normalized peak intensity ratio is an index
of the hardness of an oil film formed in the nanospace.
[0034] In other words, it is considered that the lubricating oil
base oil having a normalized peak intensity ratio of more than 0.2
retains a strong oil film in the nanospace. It is considered that
the property of retaining a strong oil film achieves a high
traction coefficient and contributes to the improvement of power
transmission in a case in which a lubricating oil composition
comprising the lubricating oil base oil is used for lubricating a
traction drive.
[0035] Meanwhile, a lubricating oil base oil having a normalized
peak intensity ratio of 0.2 or less is considered to have
insufficient hardness of the oil film. It can be said that when it
is used for lubricating a traction drive, the traction coefficient
becomes low, which is problematic in terms of power
transmission.
[0036] From the above viewpoint, the normalized peak intensity
ratio at a surface pressure of 12.4 MPa of the lubricating oil base
oil in one aspect of the present invention is preferably 0.22 to
1.00, more preferably 0.25 to 1.00, still more preferably 0.35 to
1.00, even more preferably 0.50 to 1.00, and particularly
preferably 0.70 to 1.00.
[0037] The solid surface distances and the normalized peak
intensity ratio at a surface pressure of 12.4 MPa of the
lubricating oil base oil described herein can be measured by a
resonance shear measurement system (e.g., trade name: "RSM-1"
(manufactured by ADVANCE RIKO, Inc.). As specific measurement
procedures using the resonance shear measurement system, 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, and more
specifically, the measurement can be performed based on the method
described in the Examples.
[0038] In view of such properties, the lubricating oil base oil in
one aspect of the present invention is preferably used in a
lubricating oil composition for a traction drive.
[0039] For the lubricating oil base oil in one aspect of the
present invention, from the viewpoint of obtaining a lubricating
oil base oil that can be prepared into a lubricating oil
composition suitable for lubricating a traction drive, the
viscosity .eta..sub.P at 40.degree. C. measured at a surface
pressure of 12.4 MPa is preferably 10 to 50 mPas, more preferably
12 to 45 mPas, still more preferably 14 to 40 mPas, and even more
preferably 16 to 35 mPas.
[0040] In addition, for the lubricating oil base oil in one aspect
of the present invention, from the viewpoint of obtaining a
lubricating oil base oil that can be prepared into a lubricating
oil composition suitable for lubricating a traction drive, the
viscosity .eta..sub.0 at 40.degree. C. measured at normal pressure
(0.10 MPa) is preferably 5 to 50 mPas, more preferably 7 to 45
mPas, and still more preferably 9 to 40 mPas.
[0041] For the lubricating oil base oil in one aspect of the
present invention, the ratio [.eta..sub.P/.eta..sub.0] of the
viscosity .eta..sub.P at 40.degree. C. measured at a surface
pressure of 12.4 MPa and the viscosity .eta..sub.0 at 40.degree. C.
measured at normal pressure (0.10 MPa) is preferably 1.05 to 2.0,
more preferably 1.1 to 1.7, and still more preferably 1.15 to
1.5.
[0042] As specified herein, the viscosity .eta..sub.0 can be
measured according to the method described in Reference 2 below,
and the viscosity Tip can be measured using a rolling-ball
high-pressure viscometer according to the method described in
Reference 3 below. More specific measurement procedures are as
described in the Examples below.
Reference 2: API Standard 2540 (1980) `Manual of Measurement
Standard Chapter11.1--Lolume Correction Factors, Volume XIV`
Appendix A
[0043] Reference 3: Tribologist, vol. 55, No.9 (2010), pp. 41-52
(published by Idemitsu Kosan Co., Ltd.)
[0044] The kinetic viscosity of the lubricating oil base oil in one
embodiment of the present invention at 100.degree. C. is preferably
2.0 to 10.0 mm.sup.2/s, more preferably 2.2 to 8.5 mm.sup.2/s,
still more preferably 2.5 to 7.0 mm.sup.2/s, and even more
preferably 2.8 to 6.5 mm.sup.2/s.
[0045] In addition, the viscosity index of the lubricating oil base
oil in one aspect of the present invention is usually 45 or more,
but from the viewpoint of obtaining a lubricating oil base oil
having a small temperature dependency, it is preferably 70 or more,
more preferably 80 or more, and still more preferably 90 or
more.
[0046] The kinetic viscosity and the viscosity index of the
lubricating oil base oil described herein mean the values measured
and calculated in accordance with JIS K2283:2000.
[0047] The lubricating oil base oil in one aspect of the present
invention can be composed of one or more selected from mineral oils
and synthetic oils. From the viewpoint of preparing the lubricating
oil base oil such that the values of the solid surface distance and
the normalized peak intensity ratio are within the above ranges,
the lubricating oil base oil comprises preferably one or more
selected from an ester synthetic oil, a naphthenic synthetic oil,
and a mineral oil, more preferably one or more selected from an
ester synthetic oil and a naphthenic synthetic oil, and still more
preferably an ester synthetic oil.
[0048] As stated above, the values of the solid surface distance
and the normalized peak intensity ratio are likely to change
depending on the molecular structure of the lubricating oil base
oil. Therefore, for example, even in the case of an ester synthetic
oil, the values of the solid surface distance and the normalized
peak intensity ratio change depending on the difference in the
molecular structure. Further, in the case of a mixture composed of
two or more different compounds, these values also change depending
on the content ratio of each compound.
[0049] For the lubricating oil base oil of the present invention,
by selecting a compound having a specific molecular structure and
adjusting the content ratio of each compound, the values of the
solid surface distance and the normalized peak intensity ratio are
set to be within the above ranges.
[0050] For example, it is preferable for an ester synthetic oil to
comprise an ester compound of aliphatic polyvalent alcohol from the
viewpoint of adjusting the solid surface distance and the
normalized peak intensity ratio to large values. The valence of
aliphatic polyvalent alcohol is preferably 2 to 6.
[0051] In addition, the ester compound includes preferably a
compound having an alkyl group having 6 to 20 carbon atoms, and
more preferably a compound having an alkyl group having 8 to 12
carbon atoms.
[0052] Further, the ester synthetic oil is composed of preferably
at least one compound having an alkyl group having 8 to 12 carbon
atoms, and more preferably a mixture composed of at least two or
more different compounds having an alkyl group having 8 to 12
carbon atoms.
[0053] The naphthenic synthetic oil comprises preferably a
naphthenic compound having 10 to 25 carbon atoms, and more
preferably a naphthenic compound having 12 to 20 carbon atoms from
the viewpoint of adjusting the solid surface distance and the
normalized peak intensity ratio to large values.
[0054] The naphthenic compound includes preferably A compound
having at least one 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,
and more preferably a dimer having two of these rings.
[0055] In addition, the naphthenic compound includes preferably a
compound having an alkyl group having 1 to 3 carbon atoms, and more
preferably a compound having a plurality of alkyl groups having 1
to 3 carbon atoms.
[0056] Examples of mineral oils include: atmospheric pressure
residual oils obtained by distillation of paraffinic crude oil,
intermediate-base crude oil, naphthenic crude oil, and the like;
distillates obtained by distilling these atmospheric pressure
residual oils under reduced pressure; refined oils obtained by
treating these distillates via one or more purification treatments
such as solvent deasphalting, solvent extraction, hydrogenolysis,
solvent dewaxing, catalytic dewaxing, and hydrorefining; and
mineral oils (GTL) obtained by isomerizing wax (gas-to-liquid (GTL)
wax) produced from natural gas by the Fischer-Tropsch method or the
like.
[0057] Of these, the mineral oil is preferably a mineral oil
composed of a compound having a hydrocarbon group having 12 to 50
carbon atoms, and more preferably a paraffinic mineral oil composed
of a compound having a hydrocarbon group having 12 to 50 carbon
atoms from the viewpoint of adjusting the solid surface distance
and the normalized peak intensity ratio to large values. In
addition, the number of carbon atoms of the hydrocarbon group is
preferably 12 to 50, more preferably 16 to 50, still more
preferably 20 to 50, and even more preferably 22 to 50 from the
viewpoint of adjusting the solid surface distance and the
normalized peak intensity ratio to large values.
[0058] The lubricating oil base oil in one aspect of the present
invention may be a mixed base oil comprising a plurality of types
of base oils. In the case of a mixed base oil, the blending ratio
of each base oil may be adjusted such that the values of the solid
surface distance and the normalized peak intensity ratio of the
mixed base oil are within the above ranges.
[0059] The lubricating oil base oil in one aspect of the present
invention preferably comprises an olefin synthetic oil such as
polya-olefin as little as possible from the viewpoint of adjusting
the solid surface distance and the normalized peak intensity ratio
within the above ranges.
[0060] In view of the above, the content of an olefin synthetic oil
in the lubricating oil base oil in one aspect of the present
invention based on the total amount (100% by mass) of the
lubricating oil base oil is preferably less than 10% by mass, more
preferably less than 5% by mass, still more preferably less than 1%
by mass, even more preferably less than 0.1% by mass, and
particularly preferably less than 0.01% by mass.
[0061] The content of polya-olefin is also preferably in the above
range.
[Lubricating Oil Composition]
[0062] The lubricating oil composition of the present invention
comprises the above-described lubricating oil base oil of the
present invention.
[0063] In the lubricating oil composition in one aspect of the
present invention, the content of the lubricating oil base oil
based on the total amount (100% by mass) of the lubricating oil
composition is preferably 60% by mass or more, more preferably 70%
by mass or more, still more preferably 80% by mass or more, and
even more preferably 85% by mass or more.
[0064] The lubricating oil composition in one aspect of the present
invention may comprise various additives, if necessary.
[0065] Examples of such additives include antioxidants, detergent
dispersants, pour point depressants, viscosity index improvers,
anti-wear agents, extreme pressure agents, anti-foam agents, rust
inhibitors, and corrosion inhibitors.
[0066] These additives for lubricating oil may be used singly or in
combination of two or more kinds thereof.
[0067] The content of each of these additives can be adjusted as
appropriate depending on type of the additive. The content of each
additive is usually 0.001% to 15% by mass, preferably 0.005% to 10%
by mass, and more preferably 0.01% to 5% by mass independently
based on the total amount (100% by mass) of the lubricating oil
composition.
[Applications of Lubricating Oil Composition]
[0068] Applications of the lubricating oil composition in one
aspect of the present invention include traction drive fluid,
transmission oil, hydraulic actuation oil, compressor oil,
electrically insulating oil, and the like.
[0069] As described above, the lubricating oil base oil of the
present invention is considered to have excellent abrasion
resistance and high power transmission efficiency because a strong
oil film can be formed and retained in the nanospace. Therefore, it
is considered that the lubricating oil composition of the present
invention comprising the lubricating oil base oil can exhibit the
same properties.
[0070] Accordingly, the lubricating oil composition in one aspect
of the present invention is preferably used as traction drive fluid
for lubricating a traction drive, and it is more preferably used
for lubrication in a nanospace in which the distance between two
surfaces of two opposing solids constituting the traction drive is
1.0 to 10 nm.
[0071] The distance between two surfaces of two opposing solids
constituting the traction drive corresponds to the solid surface
distance in the resonance shear measurement system described
above.
[0072] In addition, given the above-described properties of the
lubricating oil composition of the present invention, the invention
may also provide the following [1] and [2].
[1] A traction drive using the above-described lubricating oil
composition in one aspect of the present invention. [2] A method
for using a lubricating oil composition, the method comprising
using the lubricating oil composition in one aspect of the present
invention for lubricating a traction drive.
[0073] In [1] and [2] above, the lubricating oil composition in one
aspect of the present invention is preferably used for lubrication
in a nanospace in which the distance between two surfaces of two
opposing solids constituting the traction drive is 1.0 to 10
nm.
EXAMPLES
[0074] Next, the present invention will be described in more detail
with reference to the Examples below, but the present invention is
not limited to these examples. The methods of measuring and
evaluating various physical properties are as follows:
(1) Measurement and Calculation of Solid Surface Distance and
Normalized Peak Intensity Ratio
[0075] The change in the surface pressure applied to a sample oil
with the change in the solid surface distance was measured using a
resonance shear measurement system (trade name: RSM-1; ADVANCE
RIKO, Inc.).
[0076] Specifically, based on the method described in Reference 1
mentioned below, about 200 .mu.l of any one of sample oils
(.alpha.1) to (.alpha.7) was added dropwise between two surfaces of
clean and smooth mica cleavage planes facing each other and brought
in direct contact in a perpendicular cylinder mode using the
resonance shear measurement system at room temperature (25.degree.
C.). The solid surface distance was calculated by the fringes of
equal chromatic order (FECO) method. The solid surface distance was
measured when the surface pressure reached 12.4 MPa by gradually
reducing the solid surface distance with a shift from a state in
which the two solid surfaces faced each other via air (AS) to a
state in which the two solid surfaces facing each other came into
contact with each other (SC).
[0077] In addition, for the resonance shear response, a voltage Uin
was applied to a resonance shear unit so as to generate horizontal
vibration, and the amplitude of vibration was measured by a
capacitance meter to determine a voltage Uout, thereby evaluating
the measured value as a vibration intensity (Uout/Uin). By
analyzing the resulting resonant response (vibration intensity
[Uout/Uin]) using the method described in Reference 1 mentioned
below, the peak intensity I of the resonance frequency when the
surface pressure reached 12.4 MPa and the peak intensity I.sub.SC
of the resonance frequency at SC were calculated, and the ratio of
the two [I/I.sub.SC] was designated as the 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 .eta..sub.0 at 40.degree. C. at Normal Pressure (0.10
MPa)
[0078] Calculation was made in accordance with the method described
in Reference 2 mentioned below.
[0079] The density (dt) at 40.degree. C. used in the calculation of
viscosity .eta..sub.0 can be calculated by the following
formula:
dt=d15.times.exp
(-D.times..DELTA.t.times.(1+0.8.times.D.times..DELTA.t))
(in the formula, D=0.6278/1000.times.d15 (note that d15 is the
density of the sample oil at 15.degree. C. measured in accordance
with JIS K2249-4: 2011).
Reference 2: API Standard 2540 (1980) `Manual of Measurement
Standard Chapter11.1--Lolume Correction Factors, Volume XIV`
Appendix A
(3) Viscosity .eta..sub.P at 40.degree. C. at Surface Pressure of
12.4 MPa
[0080] The viscosity .eta..sub.P of the sample oil at a pressure of
12.4 MPa was calculated using a rolling-ball high-pressure
viscometer in accordance with the method described in Reference 3
mentioned below.
Reference 3: Tribologist, vol. 55, No. 9 (2010), pp. 41-52
(published by Idemitsu Kosan Co., Ltd.)
(4) Kinetic Viscosity, Viscosity Index
[0081] Kinetic viscosity and viscosity index were measured and
calculated in accordance with JIS K2283:2000.
Examples 1 to 4, Comparative Examples 1 to 3
[0082] Various physical properties, including the solid surface
distance and the normalized peak intensity ratio, were measured for
the following sample oils (.alpha.1) to (.alpha.7) obtained by a
predetermined purification or synthesis method. The various
physical properties measured are shown in Table 1.
Sample oil (.alpha.1): Ester synthetic oil comprising a mixture of
ester compounds comprising a trimethylolpropane triester having an
alkyl group having 8, 10, or 12 carbon atoms. Sample oil
(.alpha.2): Naphthenic synthetic oil comprising an alicyclic
polycyclic compound represented by the following formula.
##STR00001##
Sample oil (.alpha.3): Paraffinic mineral oil comprising a compound
having a hydrocarbon group having 22 to 50 carbon atoms, which has
a dynamic viscosity at 100.degree. C.=6.0 mm.sup.2/s. Sample oil
(.alpha.4): Paraffinic mineral oil comprising a compound having a
hydrocarbon group having 16 to 30 carbon atoms, which has a dynamic
viscosity at 100.degree. C.=3.1 mm.sup.2/s. Sample oil (.alpha.5):
Polya-olefin, which has a dynamic viscosity at 100.degree. C.=5.9
mm.sup.2/s. Sample oil (.alpha.6): Polya-olefin, which has a
dynamic viscosity at 100.degree. C.=3.9 mm.sup.2/s. Sample oil
(.alpha.7): Polya-olefin, which has a dynamic viscosity at
100.degree. C.=1.8 mm.sup.2/s.
TABLE-US-00001 TABLE 1 Comp. Comp. Comp. Ex. 1 Ex. 2 Ex. 3 Ex. 4
Ex. 1 Ex. 2 Ex. 3 Sample Sample Sample Sample Sample Sample Sample
oil (.alpha.1) oil (.alpha.2) oil (.alpha.3) oil (.alpha.4) oil
(.alpha.5) oil (.alpha.6) oil (.alpha.7) Solid surface distance
[nm] measured at 4.4 4.4 6.5 1.7 3.4 0.3 0.8 25.degree. C., 12.4
MPa Normalized peak intensity ratio [-] 0.81 0.41 0.26 0.22 0.19
0.13 0.11 measured at 25.degree. C., 12.4 MPa Viscosity .eta..sub.0
[mPa s] at 40.degree. C., normal 18.2 20.6 29.0 10.1 24.4 14.1 3.9
pressure (0.10 MPa) Viscosity .eta..sub.P [mPa s] at 40.degree. C.,
surface 22.1 29.0 39.8 12.6 30.4 17.5 4.7 pressure (12.4 MPa)
Viscosity ratio .eta..sub.P/.eta..sub.0 1.2 1.4 1.4 1.3 1.2 1.2 1.2
Kinetic viscosity [mm.sup.2/s] at 100.degree. C. 4.3 4.0 6.0 3.1
5.9 3.9 1.8 Viscosity index 139 51 121 109 132 120 --
[0083] From the values of the solid surface distance and the
normalized peak intensity ratio, it is considered that the sample
oils (.alpha.1) to (.alpha.4) of Examples 1 to 4 can form and
retain a strong oil film in the nanospace. Therefore, it can be
said that these sample oils can be suitably used for lubricating a
traction drive.
[0084] Meanwhile, since any of the sample oils (.alpha.5) to
(.alpha.7) of Comparative Examples 1 to 3 had a low value of the
normalized peak intensity ratio, it is considered that there is a
problem in terms of the hardness of the formed oil film, and thus,
it is presumed that any of them is not suitable for lubricating a
traction drive. Further, since each of the sample oils (.alpha.6)
and (.alpha.7) of Comparative Examples 2 and 3 had a solid surface
distance of less than 1.0 nm, it is considered that the oil film
retention is inferior in the nanospace.
* * * * *