U.S. patent application number 14/002413 was filed with the patent office on 2014-01-09 for lubricating oil composition.
This patent application is currently assigned to JX NIPPON OIL & ENERGY CORPORATION. The applicant listed for this patent is Noriko Abe, Yasushi Onumata. Invention is credited to Noriko Abe, Yasushi Onumata.
Application Number | 20140011724 14/002413 |
Document ID | / |
Family ID | 46929863 |
Filed Date | 2014-01-09 |
United States Patent
Application |
20140011724 |
Kind Code |
A1 |
Onumata; Yasushi ; et
al. |
January 9, 2014 |
LUBRICATING OIL COMPOSITION
Abstract
A lubricating oil composition which exceeds the fuel saving
performance of a conventional low viscosity lubricating oil
composition, contains (A) a lubricating base oil having a % C.sub.A
of 2 or less, adjusted to a 100.degree. C. kinematic viscosity of
1.5 to 4.5 mm.sup.2/s and (B) a viscosity index improver including
(B1) a poly(meth)acrylate having a weight-average molecular weight
of 50,000 or less in an amount of 1 to 10 percent by mass and (B2)
a poly(meth)acrylate having a weight-average molecular weight of
100,000 to 250,000 in an amount of 0.1 to 5 percent by mass of the
total composition. The composition has a 80.degree. C. high-shear
viscosity (Vs: mPas) and a 80.degree. C. kinematic viscosity (Vk:
mm.sup.2/s) ratio (Vs/Vk) of less than 1, a coefficient of traction
of 0.02 or less at 40.degree. C., an average speed of 3.0 m/s, a
slip ratio of 10%, and a contact pressure of 0.4 GPa.
Inventors: |
Onumata; Yasushi;
(Chiyoda-ku, JP) ; Abe; Noriko; (Chiyoda-ku,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Onumata; Yasushi
Abe; Noriko |
Chiyoda-ku
Chiyoda-ku |
|
JP
JP |
|
|
Assignee: |
JX NIPPON OIL & ENERGY
CORPORATION
Chiyoda-ku, Tokyo
JP
|
Family ID: |
46929863 |
Appl. No.: |
14/002413 |
Filed: |
September 13, 2011 |
PCT Filed: |
September 13, 2011 |
PCT NO: |
PCT/JP2011/070813 |
371 Date: |
August 30, 2013 |
Current U.S.
Class: |
508/469 |
Current CPC
Class: |
C10N 2020/017 20200501;
C10N 2030/54 20200501; C10N 2020/02 20130101; C10N 2030/68
20200501; C10M 2223/04 20130101; C10N 2010/04 20130101; C10N
2030/06 20130101; C10N 2040/042 20200501; C10N 2020/04 20130101;
C10M 2203/1025 20130101; C10M 145/14 20130101; C10M 169/041
20130101; C10N 2040/04 20130101; C10M 2229/02 20130101; C10M 169/04
20130101; C10N 2060/14 20130101; C10N 2040/045 20200501; C10N
2040/044 20200501; C10N 2030/02 20130101; C10M 2209/084
20130101 |
Class at
Publication: |
508/469 |
International
Class: |
C10M 169/04 20060101
C10M169/04 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 25, 2011 |
JP |
2011-068069 |
Claims
1. A lubricating oil composition comprising: (A) a lubricating base
oil having a % C.sub.A of 2 or less and adjusted to have a
100.degree. C. kinematic viscosity of 1.5 to 4.5 mm.sup.2/s; and
(B) a viscosity index improver comprising (B1) a poly(meth)acrylate
having a weight-average molecular weight of 50,000 or less in an
amount of 1 to 10 percent by mass and (B2) a poly(meth)acrylate
having a weight-average molecular weight of 100,000 to 250,000 in
an amount of 0.1 to 5 percent by mass on the total composition mass
basis, the composition having a 80.degree. C. high-shear viscosity
(Vs: mPas) and a 80.degree. C. kinematic viscosity (Vk: mm.sup.2/s)
ratio (Vs/Vk) of less than 1 and a coefficient of traction of 0.02
or less at 40.degree. C., an average speed of 3.0 m/s, a slip ratio
of 10%, and a contact pressure of 0.4 GPa.
2. The lubricating oil composition according to claim 1, wherein
the 80.degree. C. viscosity reduction rate 8 hours after a sonic
shear test is 8% or less.
3. The lubricating oil composition according to claim 1, wherein it
is used for a mechanism containing an oil pump as a structural
element.
4. The lubricating oil composition according to claim 1, wherein it
is used for a continuously variable transmission.
5. The lubricating oil composition according to claim 2, wherein it
is used for a mechanism containing an oil pump as a structural
element.
6. The lubricating oil composition according to claim 2, wherein it
is used for a continuously variable transmission.
Description
TECHNICAL FIELD
[0001] The present invention relates to lubricating oil
compositions, more specifically to those having an enhanced fuel
saving performance, suitable for automobile automatic
transmissions, manual transmissions, and continuously variable
transmissions.
BACKGROUND ART
[0002] Recently, energy saving in automobiles and construction or
agricultural machinery, i.e., fuel saving has become an urgent need
in order to deal with environmental issues such as reduction in
carbon dioxide emissions, and units such as engines, transmissions,
final reduction gears, compressors, or hydraulic power units have
been strongly demanded to contribute to energy saving.
Consequently, the lubricating oils used in these units are required
to be reduced in stir resistance and frictional resistance more
than before.
[0003] Reduction of the viscosity of a lubricating oil can be
pointed out as an effective energy saving means. For example, an
automobile automatic transmission or continuously variable
transmission has a torque converter, a wet clutch, a gear bearing
mechanism, an oil pump and a hydraulic control system while a
manual transmission or final reduction gear unit has a gear bearing
mechanism. Reduction of the viscosity of a lubricating oil to be
used in such transmissions can reduce the stir and frictional
resistances in the torque converter, wet clutch, gear bearing
mechanism and oil pump and thus enhance the power transmission
efficiency, resulting in an improvement in the fuel efficiency of
an automobile.
[0004] However, as described above, the lubricating oil used in
these transmissions is also used as a medium for a hydraulic
control system and thus would have problems that it would fail to
generate sufficient hydraulic pressure due to the leakage from the
oil pump or control valve if it is excessively reduced in
viscosity. The lubricating oil used in the above devices until the
working life thereof comes an end is thus required to maintain a
certain viscosity therefor.
[0005] Conventionally, an automatic transmission oil has been
provided, which is low in viscosity as the whole composition to
enhance fuel efficiency but increased in base oil viscosity to
retain shear stability, lubricating oil life and the like and also
increased in high temperature high shear (HTHS) viscosity and thus
also oil film retaining properties to obtain excellent anti-wear
properties, anti-pitching properties, shear stability and low
temperature viscosity characteristics (see, for example, Patent
Literature 1 below). However, the oil has been unable to meet the
recent further fuel saving demand.
CITATION LIST
Patent Literature
[0006] Patent Literature 1: Japanese Patent Application Publication
2009-096925
SUMMARY OF INVENTION
Technical Problem
[0007] The present invention has been made in view of these
circumstances and has an object to provide a lubricating oil
composition accomplishing a further excellent fuel saving
performance while maintaining viscosity with means exceeding the
conventional concept.
Solution to Problem
[0008] The inventors of the present invention have focused on a
lubricating base oil and a polymer in order to solve the above
problems and as the result of study thereof have accomplished the
present invention on the basis of the finding that the above
problems was able to be solved with a lubricating oil composition
comprising a selected specific base oil and a selected specific
poly(meth)acrylate-based additive.
[0009] That is, the present invention relates to a lubricating oil
composition comprising (A) a lubricating base oil having a %
C.sub.A of 2 or less and adjusted to have a 100.degree. C.
kinematic viscosity of 1.5 to 4.5 mm.sup.2/s and (B) a viscosity
index improver comprising (B1) a poly(meth)acrylate having a
weight-average molecular weight of 50,000 or less in an amount of 1
to 10 percent by mass and (B2) a poly(meth)acrylate having a
weight-average molecular weight of 100,000 to 250,000 in an amount
of 0.1 to 5 percent by mass on the total composition mass basis,
the composition having a 80.degree. C. high-shear viscosity (Vs:
mPas) and a 80.degree. C. kinematic viscosity (Vk: mm.sup.2/s)
ratio (Vs/Vk) of less than 1 and a coefficient of traction of 0.02
or less at 40.degree. C., an average speed of 3.0 m/s, a slip ratio
of 10%, and a contact pressure of 0.4 GPa.
[0010] The present invention also relates to the aforesaid
lubricating oil composition wherein the 80.degree. C. viscosity
reduction rate 8 hours after a sonic shear test is 8% or less.
[0011] The present invention also relates to the aforesaid
lubricating oil composition wherein it is used for a mechanism
containing an oil pump as a structural element.
[0012] The present invention also relates to the aforesaid
lubricating oil composition wherein it is used for a continuously
variable transmission.
Advantageous Effects of Invention
[0013] The lubricating oil composition of the present invention can
reduce resistance to lubrication more than the conventional oils
and thus are suitably used in for example automobile manual
transmissions, automatic transmissions, continuously variable
transmissions or final reduction gears, in particularly suitably
continuously variable transmissions so that the composition can
contribute to an enhancement in the fuel efficiency of an
automobile.
DESCRIPTION OF EMBODIMENT
[0014] The present invention will be described in detail below.
[0015] The lubricating base oil referred to as (A) used in the
present invention is a lubricating base oil having a % C.sub.A of 2
or less and adjusted to have a 100.degree. C. kinematic viscosity
of 1.5 to 4.5 mm.sup.2/s and may be a mineral lubricating base oil,
a synthetic lubricating base oil or a mixture thereof.
[0016] Examples of the mineral lubricating base oil which may be
used in the present invention include paraffinic or naphthenic
mineral base oils which can be produced by subjecting a lubricating
oil fraction produced by atmospheric- or vacuum-distillation of a
crude oil, to any one of or any suitable combination of refining
processes selected from solvent deasphalting, solvent extraction,
hydrocracking, solvent dewaxing, catalytic dewaxing, hydrorefining,
sulfuric acid treatment, and clay treatment; n-paraffins; and
iso-paraffins. These base oils may be used alone or in combination
at an arbitrary ratio.
[0017] Examples of preferred mineral lubricating base oils include
the following base oils:
[0018] (1) a distillate oil produced by atmospheric distillation of
a paraffin base crude oil and/or a mixed base crude oil;
[0019] (2) a whole vacuum gas oil (WVGO) produced by vacuum
distillation of the topped crude of a paraffin base crude oil
and/or a mixed base crude oil;
[0020] (3) a wax produced by a lubricating oil dewaxing process
and/or a Fischer-Tropsch wax produced by a GTL process;
[0021] (4) an oil produced by mild-hydrocracking (MHC) one or more
oils selected from oils of (1) to (3) above;
[0022] (5) a mixed oil of two or more oils selected from (1) to (4)
above;
[0023] (6) a deasphalted oil (DAO) produced by deasphalting an oil
of (1), (2) (3), (4) or (5);
[0024] (7) an oil produced by mild-hydrocracking (MHC) an oil of
(6); and
[0025] (8) a lubricating oil produced by subjecting a mixed oil of
two or more oils selected from (1) to (7) used as a feed stock
and/or a lubricating oil fraction recovered therefrom to a normal
refining process and further recovering a lubricating oil fraction
from the refined product.
[0026] No particular limitation is imposed on the normal refining
process used herein. Therefore, there may be used any refining
process having been conventionally used upon production of a
lubricating base oil. Examples of the normal refining process
include (a) hydro-refining processes such as hydrocracking and
hydrofinishing (b) solvent refining such as furfural extraction,
(c) dewaxing such as solvent dewaxing and catalytic dewaxing, (d)
clay refining with acidic clay or active clay and (e) chemical
(acid or alkali) refining such as sulfuric acid treatment and
sodium hydroxide treatment. In the present invention, any one or
more of these refining processes may be used in any combination and
order.
[0027] The mineral lubricating base oil used in the present
invention is particularly preferably a base oil produced by further
subjecting a base oil selected from (1) to (8) described above to
the following treatments.
[0028] That is, preferred are a hydrocracked mineral oil and/or
wax-isomerized isoparaffinic base oil produced by hydrocracking or
wax-isomerizing a base oil selected from (1) to (8) described above
as it is or a lubricating fraction recovered therefrom and
subjecting the resulting product as it is or a lubricating fraction
recovered therefrom to dewaxing such as solvent dewaxing or
catalytic dewaxing, followed by solvent refining or followed by
solvent refining and then dewaxing such as solvent dewaxing or
catalytic dewaxing. The hydrocracked mineral oil and/or
wax-isomerized isoparaffinic base oil are used in an amount of
preferably 30 percent by mass or more, more preferably 50 percent
by mass or more, and particularly preferably 70 percent by mass or
more, on the total base oil mass basis.
[0029] Examples of synthetic lubricating base oils which may be
used in the present invention include poly-.alpha.-olefins and
hydrogenated compounds thereof; isobutene oligomers and
hydrogenated compounds thereof; isoparaffins; alkylbenzenes;
alkylnaphthalenes; diesters such as ditridecyl glutarate,
di-2-ethylhexyl adipate, diisodecyl adipate, ditridecyl adipate and
di-2-ethylhexyl sebacate; polyol esters such as trimethylolpropane
caprylate, trimethylolpropane pelargonate, pentaerythritol
2-ethylhexanoate and pentaerythritol pelargonate; polyoxyalkylene
glycols; dialkyldiphenyl ethers; and polyphenyl ethers.
[0030] Preferred synthetic lubricating base oils are
poly-.alpha.-olefins. Typical examples of poly-.alpha.-olefins
include oligomers or cooligomers of .alpha.-olefins having 2 to 32,
preferably 6 to 16 carbon atoms, such as 1-octene oligomer,
1-decene oligomer, ethylene-propylene cooligomer, and hydrogenated
compounds thereof.
[0031] No particular limitation is imposed on the method of
producing poly-.alpha.-olefins. For example, poly-.alpha.-olefins
may be produced by polymerizing .alpha.-olefins in the presence of
a polymerization catalyst such as a Friedel-Crafts catalyst
containing aluminum trichloride, boron trifluoride or a complex of
boron trifluoride with water, an alcohol such as ethanol, propanol
and butanol, a carboxylic acid or an ester (for example, ethyl
acetate and ethyl propionate).
[0032] Component (A) used in the present invention may be a mixture
of two or more types of mineral base oils or two or more types of
synthetic base oils or a mixture of mineral base oils and synthetic
base oils. The mix ratio of two or more base oils in such mixtures
may be arbitrarily selected.
[0033] The lubricating base oil referred to as Component (A) used
in the transmission lubricating oil composition of the present
invention is a lubricating base oil adjusted so that the
100.degree. C. kinematic viscosity is from 1.5 to 4.5
mm.sup.2/s.
[0034] Component (A) is preferably one or more types selected from
the following (A-a) to (A-c):
[0035] (A-a) a mineral base oil having a 100.degree. C. kinematic
viscosity of 1.5 to lower than 3.5 mm.sup.2/s, preferably 1.9 to
3.2 mm.sup.2/s;
[0036] (A-b) a mineral base oil having a 100.degree. C. kinematic
viscosity of 3.5 to lower than 7 mm.sup.2/s, preferably 3.6 to 4.5
mm.sup.2/s; and
[0037] (A-c) a poly a-olefin base oil having a 100.degree. C.
kinematic viscosity of 1.5 to lower than 7 mm.sup.2/s, preferably
3.8 to 4.5 mm.sup.2/s.
[0038] Lubricating base oils (A-a) to (A-b) have a % C.sub.A of 2
or less, preferably 1 or less, more preferably 0.5 or less,
particularly preferably substantially 0. Lubricating oil (A-c) has
a %.sub.CA of substantially 0. The use of lubricating base oil (A)
having a % C.sub.A of 2 or less renders it possible to produce a
lubricating oil composition with an excellent oxidation stability
and a coefficient of traction of 0.02 or less that is required by
the present invention.
[0039] The % C.sub.A used herein denotes the percentage of the
aromatic carbon number in the total carbon number, determined in
accordance with ASTM D 3238-85.
[0040] No particular limitation is imposed on the viscosity index
of lubricating base oils (A-a) to (A-c), which is, however,
preferably 80 or greater, more preferably 100 or greater,
particularly preferably 120 or greater and usually 200 or less,
preferably 160 or less. The use of a lubricating base oil having a
viscosity index of greater than 80 renders it possible to produce a
composition exhibiting excellent viscosity characteristics from low
temperatures to high temperatures and also having a low coefficient
of traction. The use of a lubricating base oil having a too high
viscosity index results in a too much normal paraffins in the
resulting composition and also deteriorates the low temperature
fluidity thereof.
[0041] No particular limitation is imposed on the sulfur content of
lubricating base oils (A-a) to (A-b) used in the present invention,
which is, however, 0.1 percent by mass or less, more preferably
0.05 percent by mass or less, more preferably 0.02 percent by mass
or less, particularly preferably 0.01 percent by mass or less, most
preferably 0.005 percent by mass or less. The sulfur content of
lubricating base oil (A-c) is substantially 0%. Reduction of the
sulfur content of Component (A) renders it possible to produce a
composition having a more excellent oxidation stability.
[0042] In the present invention, any one or more of the
above-described base oils (A-a) to (A-c) maybe used. Above all,
preferably (A-a) and (A-b)and/or(A-c) are used in combination. When
Component (A-a) and/or Component (A-b) and Component (A-c) are used
in combination, the content of Component (A-c) is preferably 1 to
50 percent by mass, more preferably 3 to 20 percent by mass, more
preferably 3 to 10 percent by mass on the total base oil mass
basis. In particular, blending of Component (A-c) in an amount of
on the order of 3 to 10 percent by mass renders it possible to
produce a composition exhibiting excellent effects in fatigue life,
low temperature characteristics, and oxidation stability at a low
cost.
[0043] Lubricating base oil (A) used in the present invention has a
100.degree. C. kinematic viscosity of 1.5 to 4.5 mm.sup.2/s,
preferably 2.8 to 4.0 mm.sup.2/s, particularly preferably 3.6 to
3.9 mm.sup.2/s. The use of a lubricating base oil with a
100.degree. C. kinematic viscosity of 4.5 mm.sup.2/s or lower
renders it possible to produce a lubricating oil composition with a
smaller frictional resistance at lubricating sites because its
fluid resistance is small and thus with excellent low temperature
viscosity (for example, the -40.degree. C. Brookfield viscosity is
20,000 Pas or less). The use of a lubricating base oil with a
100.degree. C. kinematic viscosity of 1.5 mm.sup.2/s or higher
renders it possible to produce a lubricating oil composition which
is sufficient in oil film formation and thus more excellent in
lubricity and less in evaporation loss of the base oil under
elevated temperature conditions.
[0044] Lubricating base oil (A) used in the present invention has a
% C.sub.A of 2 or less, preferably 1 or less, more preferably 0.5
or less, particularly preferably substantially 0. The use of the
lubricating base oil (A) with a % C.sub.A of 2 or less renders it
possible to produce a composition with more excellent oxidation
stability and a coefficient of traction 0.02 or less, which is
required by the present invention.
[0045] No particular limitation is imposed on the viscosity index
of lubricating base oil (A) used in the present invention, which
is, however, preferably 80 or greater, more preferably 100 or
greater, particularly preferably 120 or greater. The use of a
lubricating base oil with a viscosity index of 80 or greater
renders it possible to produce a composition with excellent
viscosity characteristics from low temperatures to high
temperatures and also a lower coefficient of traction.
[0046] No particular limitation is imposed on the sulfur content of
lubricating base oil (A) used in the present invention, which is,
however, preferably 0.1 percent by mass or less, more preferably
0.05 percent by mass or less, more preferably 0.02 percent by mass
or less, particular preferably 0.01 percent by mass or less, most
preferably 0.005 percent by mass or less. Decrease of the sulfur
content of Component (A) results in a composition with an excellent
oxidation stability.
[0047] Lubricating base oil (A) used in the present invention is as
described above, but when the resulting lubricating oil composition
has a problem in providing fatigue life, this base oil may be mixed
with a solvent-refined base oil having a kinematic viscosity of 20
mm.sup.2/s to 50 mm.sup.2/s to an extent that the mixed lubricating
base oil (A) is adjusted to have a % C.sub.A of 2 or less and a
100.degree. C. kinematic viscosity of 1.5 to 4.5 mm.sup.2/s and the
resulting lubricating oil composition has coefficient of traction
of 0.02 or less at 40.degree. C., an average speed of 3.0 m/s, a
slip ratio of 10%, and a contact pressure of 0.4 GPa.
[0048] The solvent-refined base oil with a kinematic viscosity of
20 mm.sup.2/s to 50 mm.sup.2/s is preferably such an oil with a
sulfur content of 0.3 to 0.7 percent by mass and a % C.sub.A of 5
or greater and 9 or less.
[0049] The viscosity index improver (Component (B)) contained in
the lubricating oil composition of the present invention is
preferably a poly(meth)acrylate-based additive substantially
containing a structural unit derived from a monomer represented by
formula (1) below.
##STR00001##
[0050] In formula (1), R.sup.1 is hydrogen or methyl, preferably
methyl, and R.sup.2 is a hydrocarbon group having 1 to 30 carbon
atoms.
[0051] Specific examples of the hydrocarbon group having 1 to 30
carbon atoms include alkyl groups having 1 to 30 carbon atoms, such
as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl,
sec-butyl, tert-butyl, straight-chain or branched pentyl,
straight-chain or branched hexyl, straight-chain or branched
heptyl, straight-chain or branched octyl, straight-chain or
branched nonyl, straight-chain or branched decyl, straight-chain or
branched undecyl, straight-chain or branched dodecyl,
straight-chain or branched tridecyl, straight-chain or branched
tetradecyl, straight-chain or branched pentadecyl, straight-chain
or branched hexadecyl, straight-chain or branched heptadecyl,
straight-chain or branched octadecyl, straight-chain or branched
nonadecyl, straight-chain or branched eicosyl, straight-chain or
branched heneicosyl, straight-chain or branched docosyl,
straight-chain or branched tricosyl, straight-chain or branched
tetracosyl groups.
[0052] Component (B) used in the present invention may contain a
structural unit derived from a monomer represented by formula (2)
or (3) below.
##STR00002##
[0053] In formula (2), R.sup.3 is hydrogen or methyl, R.sup.4 is an
alkylene group having 1 to 30 carbon atoms, E.sup.l is an amine
residue or heterocyclic residue having 1 or 2 nitrogen atoms and 0
to 2 oxygen atoms, and a is an integer of 0 or 1.
##STR00003##
[0054] In formula (3), R.sup.5 is hydrogen or methyl, and E.sup.2
is an amine residue or heterocyclic residue having 1 or 2 nitrogen
atoms and 0 to 2 oxygen atoms.
[0055] Specific examples of the groups represented by E.sup.1 and
E.sup.2 include dimethylamino, diethylamino, dipropylamino,
dibutylamino, anilino, toluidino, xylidino, acetylamino,
benzoilamino, morpholino, pyrrolyl, pyrrolino, pyridyl,
methylpyridyl, pyrolidinyl, piperidinyl, quinonyl, pyrrolidonyl,
pyrrolidono, imidazolino and pyrazino groups.
[0056] Preferable examples include dimethylaminomethyl
methacrylate, diethylaminomethyl methacrylate, dimethylaminoethyl
methacrylate, diethylaminoethyl methacrylate, 2-methyl-5-vinyl
pyridine, morpholinomethyl methacrylate, morpholinoethyl
methacrylate, N-vinyl pyrrolidone and mixtures thereof.
[0057] Specific examples of Component (B) include copolymers of
monomers (Ba) to (Bd) represented by formula (1) and polar
group-containing monomers (Be) represented by formula (2) and/or
(3) used if necessary:
[0058] (Ba) (meth)acrylates wherein R.sup.2 is an alkyl group of 1
to 4 carbon atoms;
[0059] (Bb) (meth)acrylate wherein R.sup.2 is an alkyl group of 5
to 10 carbon atoms;
[0060] (Bc) (meth)acrylates wherein R.sup.2 is an alkyl group of 12
to 18carbon atoms;
[0061] (Bd) (meth)acrylate wherein R.sup.2 is an alkyl group of 20
or more carbon atoms; and
[0062] (Be) polar group-containing monomers.
[0063] The structural ratio of monomers (Ba) to (Be) are preferably
as follows on the total monomer mass basis:
[0064] Component (Ba): preferably 10 to 60 percent by mass, more
preferably 20 to 50 percent by mass,
[0065] Component (Bb): preferably 0 to 50 percent by mass, more
preferably 0 to 20 percent by mass
[0066] Component (Bc): preferably 10 to 60 percent by mass, more
preferably 20 to 40 percent by mass,
[0067] Component (Bd): preferably 1 to 20 percent by mass, more
preferably 5 to 10 percent by mass
[0068] Component (Be): preferably 0 to 20 percent by mass, more
preferably 0 to 10 percent by mass, particularly preferably 0 to 5
percent by mass.
[0069] Blending of a poly(meth)acrylate-based viscosity index
improver with this formulation can improve the low temperature
viscosity characteristics of the resulting composition and extend
the fatigue life thereof at the same time.
[0070] No particular limitation is imposed on the method for
producing the above-described poly(meth)acrylate. For example, it
can be easily produced by the radical-solution polymerization of a
mixture of monomers (Ba) to (Be) in the presence of a
polymerization initiator such as benzoyl peroxide.
[0071] Component (B) used in the present invention is a viscosity
index improver having two types of weight-average molecular
weights, i.e., comprising (B1) a poly(meth)acrylate having a
weight-average molecular weight of 50,000 or less in an amount of 1
to 10 percent by mass and (B2) a poly(meth)acrylate having a
weight-average molecular weight of 100,000 to 250,000 in an amount
of 0.1 to 5 percent by mass, on the total composition mass
basis.
[0072] The weight-average molecular weight of Component (B1) is
50,000 or less, preferably 40,000 or less, more preferably 30,000
or less and 5,000 or more, preferably 10,000 or more, more
preferably 15,000 or more. Component (B1) with a weight-average
molecular weight of more than 50,000 leads to a too low shear
stability in combination with Component (B2), resulting in a
lubricating oil composition which would fail to maintain the
required viscosity. Component (B1) with a weight-average molecular
weight of less than 5,000 causes the high-shear viscosity to
increase and thus fails to satisfy the 80.degree. C. high-shear
viscosity (Vs: mPas) and 80.degree. C. kinematic viscosity (Vk:
mm.sup.2/s) ratio (Vs/Vk) which is less than 1.
[0073] When the TBS viscometer is used to measure the high-shear
viscosity, the ratio (Vs/Vk) of the high-shear viscosity (Vs: mPas)
measured at a shear speed of 10.sup.-6/s, which is equal to 1 is
the case where the molecular weight exceeds 50,000, and thus the
value of less than 1 referred herein is a theoretical value.
[0074] The weight-average molecular weight of Component (B2) is
250,000 or less, preferably 200,000 or less, more preferably
170,000 or less and 100,000 or more, preferably 120,000 or more,
more preferably 150,000 or more. Component (B2) with a
weight-average molecular weight of more than 250,000 leads to a too
low shear stability in combination with Component (B1), resulting
in a lubricating oil composition which would fail to maintain the
required viscosity. Component (B2) with a weight-average molecular
weight of less than 100,000 is unlikely to reduce the high-shear
viscosity sufficiently, and thus cannot satisfy the 80.degree. C.
high-shear viscosity (Vs: mPas) and 80.degree. C. kinematic
viscosity (Vk: mm.sup.2/s) ratio (Vs/Vk) which is less than 1.
[0075] The weight-average molecular weight used herein denotes a
weight-average molecular weight on polystyrene basis determined
with a differential refractive index detector (RI) at a temperature
of 23.degree. C., a flow rate of 1 mL/min, a sample concentration
of 1 percent by mass, and a sample injection amount of 75 .mu.L,
using 150-C ALC/GPC manufactured by Waters having two columns
GMHHR-M (7.8mm. ID.times.30 cm) equipped in series therein and
tetrahydrofuran as a solvent.
[0076] Component (B1) used in the present invention is added in an
amount of 10 percent by mass or less, preferably 9 percent by mass
or less, more preferably 8 percent by mass or less and 1 percent by
mass or more, preferably 2 percent by mass or more, more preferably
4 percent by mass or more, more preferably 5 percent by mass or
more on the total composition mass basis. Addition of Component
(B1) in an amount of more than 10 percent by mass increases the
high-shear viscosity too much while addition of Component (B1) in
an amount of less than 1 percent by mass fails to obtain a
sufficient composition viscosity.
[0077] Component (B2) used in the present invention is added in an
amount of 5 percent by mass or less, preferably 4 percent by mass
or less, more preferably 3 percent by mass or less and 0.1 percent
by mass or more, preferably 0.5 percent by mass or more, more
preferably 1 percent by mass or more on the total composition mass
basis. Addition of Component (B2) in an amount of more than 5
percent by mass results in a lubricating oil composition which is
reduced in viscosity caused by shear and thus fails to obtain the
necessary viscosity for extending the working life of machines. On
the other hand, addition of Component (B2) in an amount of less
than 0.1 percent by mass fails to obtain a sufficient composition
viscosity.
[0078] The amount of Component (B) that is a
poly(meth)acrylate-based additive in the lubricating oil
composition of the present invention is as described above but is
preferably such an amount that the resulting lubricating oil
composition has a 80.degree. C. kinematic viscosity of 5 to 10
mm.sup.2/s, preferably 6 to 9 mm.sup.2/s and a viscosity index of
120 to 270, preferably 150 to 250, more preferably 170 to 220.
[0079] In the lubricating oil composition of the present invention,
the 80.degree. C. high-shear viscosity (Vs: mPas) and 80.degree. C.
kinematic viscosity (Vk: mm.sup.2/s) ratio (Vs/Vk) is necessarily
less than 1. The high-shear viscosity referred herein is determined
in accordance with ASTM D-4683 and is also referred to as "HTHS
viscosity". In the present invention, the 80.degree. C. shear
viscosity is measured at 1.times.10.sup.6 s.sup.-1.
[0080] A Vs/Vk of less than 1 means that the viscosity of the
composition is reduced when high shear is applied thereto, and this
is a phenomenon that could occur in a lubricating oil composition
having a viscosity increased with a viscosity index improver
because the shear speed is increased under conditions where sliding
occurs through an extremely thin oil film, specifically conditions
of lubrication through an oil film of 100 .mu.m or thinner, for
example conditions of lubricating bearings, clutches or gear tooth
surfaces. The present invention aims at securing a fuel saving
performance by setting the level of reduction in viscosity to less
than 1 so as to decrease the resistance caused by the reduction of
viscosity occurring under high shear conditions. The viscosity when
a high shear is applied only refers to a fluid lubricating state
and thus no contact between individual pieces occurs.
[0081] Therefore, lower this value is, more improved the fuel
saving performance is, but there is a certain limit to this value
because if the value is too low, a problem in lubricity would
arise. The lower limit of the value is 0.7, preferably 0.8 or
greater, more preferably 0.85 or greater.
[0082] The lubricating oil composition of the present invention has
a coefficient of traction of 0.02 or less, an average speed of 3.0
m/s, a slip ratio of 10%, and a contact pressure of 0.4 GPa, at
40.degree. C.
[0083] This coefficient of traction is measured with a steel ball
disk. While a disk with a radius of 13 cm is rotated at 286.7 rpm,
a load of 20 N is applied on a ball with a radius of 1.27 cm placed
on a position 10 cm apart radially from the center of the disk to
measure the rotation torque applied to the ball at 40.degree. C.,
an average speed of 3.0 m/s, a slip ratio of 10%, and a contact
pressure of 0.4 GPa.
[0084] This condition does not reach what is called the complete
elastohydrodynamic lubrication condition and thus is still in an
intermediate region between the fluid lubrication condition and the
elastohydrodynamic lubrication condition. Conventionally, the
coefficient of traction of a lubricating oil composition is
measured at a high contact pressure, specifically a contact
pressure of greater than 1 GPa, and a composition with a higher oil
film formability, i.e., coefficient of traction under such a high
contact pressure condition is likely to form an oil film and has
been evaluated as having an excellent lubricity under sever
conditions.
[0085] However, the condition of measuring the coefficient of
traction in the present invention is that for measuring it under an
intermediate surface pressure condition that is 0.4 GPa as
described above and thus can be regarded as a typical condition for
parts where the coefficient of traction is involved with the
resistance to lubrication among the parts of a machine to be
lubricated except for ball bearings or roller bearings. Therefore,
reduction of the coefficient of traction under the above-described
conditions reduces the resistance relating to the coefficient of
traction under, lubricating conditions in a machine. That is, since
the coefficient of traction at 40.degree. C., an average speed of
3.0 m/s, a slip ratio of 10% and a contact pressure of 0.4 GPa is
set to 0.02 or less, the composition of the present invention can
secure a fuel saving effect.
[0086] Under these conditions, the coefficient of traction is 0.02
or less and is better as it is low but as described above, is
preferably 0.005 or greater to secure the lubricity for ball
bearings or roller bearings under a higher contact pressure
condition.
[0087] The lubricating oil composition of the present invention has
a viscosity reduction rate of preferably 8% or less at 80.degree.
C. 8 hours after a sonic shear stability test. The sonic shear
stability test referred herein is determined by a method prescribed
in JASO M 347.
[0088] As described above, the lubricating oil composition of the
present invention is also used as a medium for a hydraulic system,
and if reduced in viscosity causes the system to have problems such
as failure to produce sufficient pressure, due to leakage of the
oil from the oil pump or control valve. Thus, the lubricating oil
to be used until the working life of a system ends' needs to
maintain the viscosity as required for this purpose.
[0089] The lubricating oil composition of the present invention
needs to maintain a sufficient viscosity even if applied with
repetitive shear force. What is meant by that the lubricating oil
composition of the present invention has a viscosity reduction rate
of 8% or less at 80.degree. C. 8 hours after a sonic shear
stability test is the value to ensure that the composition has such
a viscosity. The viscosity reduction rate is preferably 7% or less,
more preferably 6% or less.
[0090] The lubricating oil composition of the present invention can
be applicable to various devices such as manual transmissions,
automatic transmissions, continuously variable transmissions, final
reduction gears, and engines of automobiles, as well as
agricultural machines and constructing machines. The lubricating
oil composition is most suitably used in a continuously variable
transmission. This is because this transmission has many parts
likely subjected to shear and high contact pressure and the
composition can exhibit its performances most effectively for the
transmission.
[0091] If necessary, the lubricating oil composition of the present
invention may be blended with various additives such as viscosity
index improvers, extreme pressure additives, dispersants, metallic
detergents, friction modifiers, anti-oxidants, corrosion
inhibitors, rust inhibitors, demulsifiers, metal deactivators, pour
point depressants, seal swelling agents, anti-foaming agents, and
dyes, alone or in combination in order to further enhance the
properties of the composition or impart the composition with
properties required for a lubricating oil.
[0092] Examples of the viscosity index improvers include those
other than Component (B) that are the above-described
poly(meth)acrylates, such as non-dispersant or dispersant type
ethylene-.alpha.-olefin copolymers and hydrogenated compounds
thereof; polyisobutylene and hydrogenated compounds thereof;
styrene-diene hydrogenated copolymers; styrene-maleic anhydride
ester copolymers; polyalkylstyrenes; and copolymers of
(meth)acrylate monomers represented by formula (1) and unsaturated
monomers such as ethylene/propylene/styrene/maleic anhydride.
[0093] When the lubricating oil composition of the present
invention is blended with a viscosity index improver (excluding
Component (B)), no particular limitation is imposed on the content
thereof if the resulting composition meets the requirements
regarding the 100.degree. C. kinematic viscosity and viscosity
index. The content is usually from 0.1 to 15 percent by mass,
preferably 0.5 to 5 percent by mass on the total composition mass
basis.
[0094] The extreme pressure additive is preferably blended, which
comprises at least one type of phosphorus extreme pressure additive
selected from phosphorous acid, phosphorus acid monoesters,
phosphorus acid diesters, phosphorus acid triesters, and salts
thereof; at least one type of sulfur extreme pressure additive
selected from sulfurized fats and oils, sulfurized olefins,
dihydrocarbyl polysulfides, dithiocarbamates, thiaziazoles, and
benzothiazoles; and/or at least one type of phosphorus-sulfur
extreme pressure additive selected from thiophosphorus acid,
thiophosphorus acid monoesters, thiophosphorus acid diesters,
thiophosphorus acid triesters, dithiophosphorus acid,
dithiophosphorus acid monoesters, dithiophosphorus acid diesters,
dithiophosphorus acid triesters, trithiophosphorus acid,
trithiophosphorus acid monoesters, trithiophosphorus acid diesters,
trithiophosphorus acid triesters, and salts thereof.
[0095] The dispersant may be an ashless dispersant such as
succinimide, benzylamine, polyamines, each having a hydrocarbon
group having 40 to 400 carbon atoms, and/or a boron compound
derivative thereof.
[0096] Any one or more compounds selected from these dispersants
may be contained in an amount of usually from 0.01 to 15 percent by
mass, preferably from 0.1 to 8 percent by mass on the total
composition mass basis.
[0097] Examples of the metallic detergent include those such as
alkaline earth metal sulfonates, alkaline earth metal phenates, and
alkaline earth metal salicylates.
[0098] Any one or more compounds selected from these metallic
detergents may be contained in an amount of usually 0.01 to 10
percent by mass, preferably 0.1 to 5 percent by mass on the total
composition mass basis.
[0099] The friction modifier may be any compound that has been
generally used as a friction modifiers for lubricating oils.
Specific examples include amine compounds, imide compounds, fatty
acid esters, fatty acid amides, and fatty acid metal salts, each
having per molecule at least one alkyl or alkenyl group having 6 to
30 carbon atoms, particularly a straight-chain alkyl or alkenyl
group having 6 to 30 carbon atoms.
[0100] Any one or more compounds selected from these friction
modifiers may be contained in an amount of usually 0.01 to 5.0
percent by mass, preferably 0.03 to 3.0 percent by mass on the
total composition mass basis.
[0101] The anti-oxidant may be any anti-oxidant that has been
usually used in lubricating oils, such as phenol- or amine-based
compounds.
[0102] Specific examples of the anti-oxidant include alkylphenols
such as 2-6-di-tert-butyl-4-methylphenol; bisphenols such as
methylene-4,4-bisphenol(2,6-di-tert-butyl-4-methylphenol);
naphthylamines such as phenyl-.alpha.-naphthylamine;
dialkyldiphenylamines; zinc dialkyldithiophosphoric acids such as
di-2-ethylhexyldithiophosphoric acid; and esters of
(3,5-di-tert-butyl-4-hydroxyphenyl)fatty acid (propionic acid) or
(3-methyl-5-tert-butyl-4-hydroxyphenyl)fatty acid (propionic acid)
with a monohydric or polyhydric alcohol such as methanol, octanol,
octadecanol, 1,6-hexanediol, neopentyl glycol, thiodiethylene
glycol, triethylene glycol and pentaerythritol.
[0103] Any one or more of compounds selected from these compounds
may be contained in any amount, which is, however, usually from
0.01 to 5 percent by mass, preferably from 0.1 to 3 percent by mass
on the total composition mass basis.
[0104] Examples of the corrosion inhibitor include benzotriazole-,
tolyltriazole-, thiadiazole-, and imidazole-types compounds.
[0105] Examples of the rust inhibitor include petroleum sulfonates,
alkylbenzene sulfonates, dinonylnaphthalene sulfonates, alkenyl
succinic acid esters, and polyhydric alcohol esters.
[0106] Examples of the demulsifier include polyalkylene
glycol-based non-ionic surfactants such as polyoxyethylenealkyl
ethers, polyoxyethylenealkylphenyl ethers, and
polyoxyethylenealkylnaphthyl ethers.
[0107] Examples of the metal deactivator include imidazolines,
pyrimidine derivatives, alkylthiadiazoles, mercaptobenzothiazoles,
benzotriazoles and derivatives thereof,
1,3,4-thiadiazolepolysulfide,
1,3,4-thiadiazolyl-2,5-bisdialkyldithiocarbamate,
2-(alkyldithio)benzoimidazole, and
.beta.-(o-carboxybenzylthio)propionitrile.
[0108] The pour point depressant may be any of the known pour point
depressants selected depending on the type of lubricating base oil
but are preferably poly(meth)acrylates having a weight average
molecular weight of preferably 20,000 to 500,000, more preferably
50,000 to 300,000, particularly preferably 80,000 to 200,000.
[0109] The anti-foaming agent may be any compound that has been
usually used as an anti-foaming agent for lubricating oils.
Examples of such an anti-foaming agent include silicones such as
dimethylsilicone and fluorosilicone. Any one or more of compounds
selected from these compounds may be contained in any amount.
[0110] The seal swelling agent may be any compound that has been
usually used as a seal swelling agent for lubricating oils.
Examples of such a seal swelling agents include ester-, sulfur- and
aromatic-based seal swelling agents.
[0111] The dye may be any compound that has been usually used and
may be blended in any amount. The amount is usually from 0.001 to
1.0 percent by mass on the total composition mass basis.
[0112] When these additives are blended with the lubricating oil
composition of the present invention, the corrosion inhibitor, rust
inhibitor, and anti-foaming agent are each contained in an amount
of 0.005 to 5 percent by mass, the pour point depressant and metal
deactivator are each contained in an amount of 0.005 to 2 percent
by mass, the seal swelling agent is contained in an amount of 0.01
to 5 percent by mass, and the anti-foaming agent is contained in an
amount of 0.0005 to 1 percent by mass, all on the total composition
mass basis.
EXAMPLES
[0113] The present invention will be described more specifically
with reference to the following Examples and Comparative Examples
but not limited thereto.
Examples 1 and 2 and Comparative Examples 1 to 5
[0114] Lubricating oil compositions for transmissions according to
the present invention (Examples 1 and 2) were prepared in
accordance with the formulations set forth in Table 1. The
performances of each composition were evaluated with the following
tests. The results are set forth in Table 1.
[0115] Also, lubricating oil composition for transmissions for
comparison (Comparative Examples 1 to 5) were prepared in
accordance with the formulations set forth in Table 1. The
performances of each composition were also evaluated with the
following tests. The results are also set forth in Table 1.
[0116] [Pump Test Power Consumption Reduction Rate]
[0117] A lubricating oil is circulated in a test apparatus
including a pressure valve and an oil tank at a constant pump
revolution number so as to measure the power consumed by the pump.
The apparatus has a structure in which the lubricating oil is
pumped out from the oil tank and returned through the pressure
valve to the tank. The pressure valve is adjustably loaded during
the circulation, and the oil tank has a heater and thus can adjust
the lubricating oil temperature to any temperature. In these
examples, the lubricating oil compositions were compared in terms
of power consumption where the lubricating oil temperature and load
were set to 80.degree. C. and 13 MPa, respectively.
TABLE-US-00001 TABLE 1 Comparative Comparative Comparative
Comparative Comparative Base Oil Total Base Oil Mass Basis Example
1 Example 2 Example 1 Example 2 Example 3 Example 4 Example 5 O-1
Base Oil 1 in mass % 80 O-2 Base Oil 2 in mass % 65 65 65 65 65 20
O-3 Base Oil 3 in mass % 20 O-4 Base Oil 4 in mass % 35 35 35 35 35
50 O-5 Base Oil 5 in mass % 30 Additives Total Composition Mass
mass % Basis A-1 Viscosity Index Improver 1 mass % 4 4 6.5 4 6.5
A-2 Viscosity Index Improver 2 mass % 6.2 A-3 Viscosity Index
Improver 3 mass % 2 2 6 A-4 Viscosity Index Improver 4 mass % 1.2
B-1 Additive Package mass % 9 9 9 9 9 9 9 Results of Evaluation
Kinematic Viscosity (40.degree. C.) mm.sup.2/s 24.9 23.9 25.0 24.9
24.7 24.9 27.3 Kinematic Viscosity (80.degree. C.) Vk mm.sup.2/s
8.6 8.6 8.6 8.6 8.6 8.6 8.6 Viscosity Index 189 209 185 189 195 189
153 Shear Test (Sonic 8 h) Kinematic Viscosity after Shear Test
mm.sup.2/s 8.2 8.2 8.3 7.8 7.4 7.3 8.3 Viscosity Reduction Rate 5 5
3 9 14 15 3 Density (80.degree. C.) g/cm.sup.2 0.81 0.78 0.81 0.81
0.81 0.81 0.85 HTHS Viscosity (80.degree. C.) mPa s 6.4 6.2 7.0 6.9
5.9 5.7 7.3 Vs (unit coversion form density data) mm.sup.2/s 7.9
7.9 8.6 8.5 7.3 7.0 8.6 Vs/Vk 0.92 0.92 1.00 0.99 0.85 0.81 1.00
Coefficient of traction 0.020 0.010 0.020 0.020 0.020 0.020 0.032
Pump Test Reduction rate of power % 0.8 3.5 0.0 0.0 1.4 1.7 -1.8
consumption 80.degree. C., 13 Mpa, Comparison with Comparative
Exaple 1 Base Oil 1 % CP: 92.5, % CA: 0, Kinematic Viscosity
(100.degree. C.): 3.9 mm.sup.2/s, Viscosity Index: 143, Sulfur
Content: <10 ppm, Coefficient of traction: 0.008. Base Oil 2 %
CP: 78.5, % CA: 0, Kinematic Viscosity (100.degree. C.): 4.2
mm.sup.2/s, Viscosity Index: 124, Sulfur Content: <10 ppm,
Coefficient of traction: 0.015. Base Oil 3 % CP: 92.4, % CA: 0,
Kinematic Viscosity (100.degree. C.): 2.7 mm.sup.2/s, Viscosity
Index: 128, Sulfur Content: <10 ppm, Coefficient of traction:
0.007. Base Oil 4 % CP: 68.7, % CA: 0, Kinematic Viscosity
(100.degree. C.): 2.4 mm.sup.2/s, Viscosity Index: 100, Sulfur
Content: <10 ppm, Coefficient of traction: 0.017. Base Oil 5 %
CP: 45.4, % CA: 9.5, Kinematic Viscosity (100.degree. C.): 5.8
mm.sup.2/s, Viscosity Index: 43, Sulfur Content: <10 ppm,
Coefficient of traction: 0.070. Viscosity Index Improver 1
(Non-dispersant type PMA, Mw30,000), Viscosity Index Improver 2
(Non-dispersant type PMA, Mw80,000) Viscosity Index Improver 3
(Non-dispersant type PMA, Mw150,000), Viscosity Index Improver 4
(Non-dispersant type PMA, Mw400,000) Additive Package: phosphorus
acid ester-based anti-wear agent 0.3 mass %, Ca metallic detergent
0.5 mass %, anti-oxidant 3.0 mass %, ashless dispersant
(non-boron-modified/boronodified mixture) 4.0 mass %, metal
deactivator 0.2 mass %, oil seal swelling agent 1.0 mass %,
silicone-based anti-foaming agent (slight amount) are contained
[0118] As apparent from the results set forth in Table 1, the
lubricating oil compositions of Examples 1 and 2 have a Vs/Vk of
less than 1 and a coefficient of traction of 0.02 or less. The
compositions have a viscosity reduction rate of 8% or less at
80.degree. C. 8 hours after an sonic shear test. Whereas, the
composition of Comparative Example 1 fails to have a Vs/Vk of less
than 1, the compositions of Comparative Examples 2 to 4 have a
viscosity reduction rate of greater than 8%, and the composition of
Comparative Example 5 fails to have a Vs/Vk of less than 1 and have
a greater coefficient of traction that is 0.032.
INDUSTRIAL APPLICABILITY
[0119] The lubricating oil composition of the present invention has
an excellent fuel saving performance and is advantageously used for
manual transmissions, automatic transmissions, continuously
variable transmissions and final reduction gears.
* * * * *