[0001] The present invention relates to a lubricating oil composition and more particularly
to a lubricating oil composition which is excellent in biodegradability, high-temperature
cleanliness and anti-seizure performance and is therefore conductive to environmental
protection.
[0002] Two-cycle engines raise problems as to possible environmental pollution since they
discharge an unburned engine oil as an accompaniment of their exhaust gases due to
their lubrication mechanism. For example, outboard engines used in rivers, lakes or
oceans discharge exhaust gases containing unburned oil into the water thereby to raise
problems as to water pollution due to the unburned oil. Chain saws and other forestry
machinery may also cause the polution of forests and rivers due to the unburned oil.
[0003] In Europe, there have been lively activities in attempts to establish laws, regulations
and standards concerning the biodegradability of the two-cycle engine oils from the
standpoint of environmental protection. Because of this, a two-cycle engine oil having
biodegradability has heretofore been tried to be developed and it has already been
sold from several oil makers. These oils, in all cases, comprise, as a specific base
oil an ester compound (based on a mixture of saturated and unsaturated fatty acid
esters each having 16 - 18 carbon atoms) and a mineral oil-based solvent. They contain
an amino amide type ashless dispersant as an additive.
[0004] These commercially available oils already passed the TC-WII which is a performance
standard of oils for outboard engines. However, when these oils are used in recently
manufactured high-performance water-cooled outboard engines and air-cooled engines,
they are considered to raise problems as to ring sticking and piston seizure due to
their insufficient thermal stability as a lubricating oil.
[0005] Because of this, a biodegradable lubricating oil having better thermal stability
and more excellent lubricity has been sought to be developed.
[0006] An object of the present invention is to provide a lubricating oil having excellent
performances in biodegradability, high-temperature cleanliness, lubricity and anti-seizure
performance.
[0007] Another object is to provide a method for lublication comprising the use of such
a lubricating oil as above.
[0008] The present inventors made intensive studies to aim mainly at solving the above problems
and, as the result of their studies, they found out that a lubricating oil comprising
predetermined esters as main components satisfies the above-mentioned requirements,
thus achieving the present invention.
[0009] More particularly, in a first aspect of the present invention, a lubricating oil
composition comprises as the main component an ester mixture consisting of (A) 60
- 95 % by weight of an ester of a hindered alcohol with a straight-chain saturated
fatty acid having 8 - 12 carbon atoms, and (B) 5 - 40 % by weight of a complex ester
of a hindered alcohol with a straight-chain saturated fatty acid having 8 - 12 carbon
atoms and also with a dibasic acid having 2 - 50 carbon atoms.
[0010] In a second aspect of the present invention, a lubricating oil composition comprises
(I) 100 parts by weight of an ester mixture consisting essentially of (A) 60 - 95
% by weight of an ester of a hindered alcohol and a straight-chain saturated fatty
acid having 8 - 12 carbon atoms, and (B) 5 - 40 % by weight of a complex ester of
a hindered alcohol with both a straight-chain saturated fatty acid having 8 - 12 carbon
atoms and a dibasic acid having 2 - 50 carbon atoms, and (II) not more than 30 parts
by weight of a hydrocarbon-based solvent and/or a lubricating base oil.
[0011] The present invention will now be explained hereunder in more detail.
[0012] The ester mixture used in the present invention as the main ingredient is a mixture
of (A) an ester of a hindered alcohol and a straight-chain saturated fatty acid having
8 - 12 carbon atoms, and (B) a complex ester of a hindered alcohol with both a straight-chain
saturated fatty acid having 8 - 12 carbon atoms and a dibasic acid having 2 - 50 carbon
atoms.
[0013] In the preparation of this component (A), the hindered alcohol used means one in
which the β carbon atom of the hydroxyl group is a quarternary carbon atom. More specifically,
the hindered alcohol preferably used include dihydric to tetrahydric alcohols having
5 - 10 carbon atoms, and a dimer and trimer thereof, and they are exemplified by neopentyl
glycol, 2-methyl-2-propyl-1, 3- propanediol, trimethylol ethane, trimethylol propane
(TMP), trimethylol butane, pentaerythritol (PET), di- (trimethylol propane), tri-(trimethylol
propane), di- (pentaerythritol) and tri-(pentaerythritol).
[0014] The straight-chain saturated fatty acid having 8 - 12 carbon atoms used in the present
invention include caprylic acid, pelargonic acid, capric acid and lauric acid. Furthermore,
such fatty acids may be used in the form of a derivative such as an acid anhydride,
acid halide and metal salt of the acids. In the preparation of the component (A),
at least two different acids among these fatty acids may be esterified with the same
hindered alcohol, or the resulting ester may have a hydroxyl group therein which remains
without being esterified.
[0015] In the preparation of the component (B), the same hindered alcohol and the saturated
fatty acid having 8 - 12 carbon atoms as those used in the preparation of the above
component (A) may be employed. The dibasic acids having 2 - 50 carbon atoms used in
said preparation include oxalic acid, malonic acid, succinic acid, glutaric acid,
adipic acid, pimeric acid, suberic acid, azelaic acid and sebacic acid, as well as
other acids having more carbon atoms than the above-mentioned acids. Among these acids,
those having 6 - 40 carbon atoms are desirably used.
[0016] The component (B) may be exemplified by a complex ester represented by the following
general formula (I).
wherein X¹ to X⁴ may be identical with or different from each other and each represent
an alkyl group having 1 - 4 carbon atoms or a group having the following general formula
of -CH₂-OCO-R⁴ (R⁴ being an alkyl group having 7 - 11 carbon atoms). Also, in the
formula (I), R¹ represents an alkylene or alkenylene group having 1 - 48 carbon atoms
with the proviso that when the number of carbon atoms of a dibasic acid is 2, R¹ does
not exist in the formula I. R² to R⁴ may be identical with or different from each
other and each represent a straight-chain alkyl group having 7 - 11 carbon atoms.
In this case, R¹ corresponds to the alkylene group of a dibasic acid having 3 - 50
carbon atoms, R² to R⁴ each correspond to the alkyl group of a straight-chain saturated
fatty acid having 8 - 12 carbon atoms.
[0017] In this invention, the content of the above component (A) is 60 to 95%, preferably
70 to 90%, by weight based on the total weight of the specific base oil. The content
of the above component (B) is 5 to 40%, preferably 10 to 30%, by weight based on the
total weight of the specific base oil. When the contents of the above components (A)
and (B) do not fall respectively within the above ranges, the resulting composition
will not be appropriate in viscosity. In addition, when the content of the above component
(B) exceeds 40% by weight, the resulting composition will undesirably be insufficient
in biodegradability. Furthermore, the composition of the present invention shoud have
a kinematic viscosity of preferably 6 to 15 mm²/s at a temperature of 100 °C.
[0018] The lubricating oil composition of the present invention may contain the above ester
mixture alone, and, however, it may further contain a known hydrocarbon-based solvent
and/or a known lubricating base oil as required. This hydrocarbon-based solvent may
be one which is usually used for two-cycle engine oils, and it is exemplified by a
petroleum-based hydrocarbon solvent and/or a synthesized hydrocarbon solvent each
having a boiling point of 150 to 300 °C at atmospheric pressure. Specifically, these
solvents are illustrated by Stoddard solvent, mineral spirits, kerosene fractions,
n-paraffins, i-paraffins and propylene oligomers.
[0019] The lubricating base oil may be one which is usally used as a base oil for lubricating
oils and it is exemplified by paraffinic and naphthenic mineral oils prepared by refining
lubricating oil fractions which are obtained by distilling crude oils under atmospheric
or a reduced pressure; poly-α-olefin (1-octene oligomer, 1-decene oligomer, etc.);
polybutene, alkylbenzenes; alkylnaphthalenes; polyglycol; diester (ditridecylgultarate,
di,2-ethylhexyl adipate); diisodecyl adipate; di,tridecyl adipate; di,2-ethyl hexyl
cebacate; esters of polyol with a straight-chain chain fatty acid having up to 7 or
at least 13 carbon atoms or with a branched-chain fatty acid (trimethylolpropane stearate,
trimethylolpropane oleate, pentaerithritol 2-ethylhexanoate, etc.); polyphenylether;
fluorine-based oils; and silicone-based oils.
[0020] In a case where the solvent and/or a lubricating base oil other than the above-mentioned
ester mixture (the specific base oil) are/is to be added to the ester mixture, it
is preferable to add the solvent and/or the lubricating base oil in a total amount
of up to 30 parts, preferably up to 20 parts, by weight per 100 parts by weight of
the specific base oil consisting of the ester mixture so as not to deteriorate the
excellent thermal stability, lubricity and also biodegradability which are the features
of this invention.
[0021] Moreover, the composition of this invention may be incorporated with various kinds
of known additives for the purpose of further improving the performance of the composition,
as required. The additives include basic calcium sulfonate, basic calcium phenate,
basic calcium salicylate, alkenyl succinic acid imide, benzyl amine, a detergent such
as a polyalkenyl amine, a pour point depressant such as polymethacrylate, a rust preventing
agent and anti-foaming agent.
[0022] These additives may be added alone or jointly. They may be added in any optional
amount and, usually, they may each be added in an amount of up to 30, preferably 0.5
- 15, parts by weight per 100 parts by weight of the specific base oil.
[0023] Although the lubricating oil compositions of this invention are suited especially
for two-cycle engines such as outboards and chain saws since they are excellent in
biodegradability, they are preferably used in engines for two-wheeled vehicles such
as mopet (motorlike) and motorcycles, and in portable power unit engines for lawnmowers
and power generators. Furthermore, they can be used as a four-cycle engine oil, a
hydraulic oil, a gear oil and a metal processing oil.
[0024] The present invention will be better understood by way of Examples and Comparative
examples, and, however, it is not limited to these Examples. 1. biodegradability and
thermal stability
The biodegradability and thermal stability which are fundamental performances of
this invention were evaluated.
(1) biodegradability
[0025] The biodegradability was measured by the coulometer method using a closed-system
oxygen consumption measurement apparatus, and this method is usually called the MITI
method which is one of the test methods prescribed by the Chemical Substances Control
Law in Japan. This method is the one in which incubation is effected at a temperature
of 25°C for a period of time of 14 days.
[0026] A decomposition degree is represented by the following formula.
BOD: Biological Oxygen Demand of a test substance (Value found, mg)
B: Oxygen consumption of a culture medium into which activated sludge has been
inoculated (Value found, mg)
TOD: Theoretical Oxygen Demand required for complete oxidation of the test substance
(Value calculated, mg). The value for TOD was determined by calculating the molecular
formula obatined from the elemental analysis of the test substance (oil).
[0027] A test substance which showed a decomposition degree of 35 to 40 % in this test is
considered to have undergone almost complete biodegradation, and, therefore, the biodegradability
standard for the compositions of this invention has been determined in conformity
with said decomposition degree.
(2) Thermal stability
[0029] Thermal stability was evaluated by a hot tube test (HTT) (This test is described
in SAE Paper 881619, 1988). This test was carried out by installing a glass tube into
an electric furnace and then pushing a test oil upward with air through the glass
tube. The oil was degraded by being subjected to heat and oxidation when it passed
through the glass tube. In this test, a merit rating is represented by the shade of
lacquer-like color of a deposit to the inner wall of the glass tube. The merit rating
is between 10 points when no deposit is found, and 0 point when a deposit looks black
in color. Because there is comparatively good correlation between piston cleanliness
found by engine tests and HTT merit rating, the HTT is utilized as a screening test
before subjecting to an engine test. The compositions of this invention were produced
so that they would exhibit a HTT merit rating of at least 5 points at 280°C, 16 hrs
as their standard.
[0030] The test results thus obtained are shown in Table 1.
[0031] Examples 1 to 6 which show compositions of this invention, exhibited excellent performances
in biodegradability and thermal stability as compared with Comparative Examples which
show comparative compositions.
(1) Comparative Example 1 is a TMP ester which consists mainly of a fatty acid (oleic
acid) having 18 carbon atoms. This ester exhibited good biodegradability, and, however,
it was poor in thermal stability as compared the composition of the present invention.
(2) Comparative Example 2 is a PET ester which consists of a branched-chain fatty
acid having 8 carbon atoms. This PET ester exhibited low biodegradability although
it exhibited good thermal stability.
(3) Comparative Examples 3 and 4 used therein oils alone which were the same as the
components (A-1) and (A-2) of this invention, respectively. Each of these oils exhibited
good biodegradability and thermal stability. However, in a case where each of said
oils is used alone as a lubricating oil, it exhibits a kinematic viscosity of less
than 6 mm²/s at 100°C. This viscosity is too low as a base oil for a two-cycle engine
oil, and therefore, these oils are likely to exhibit insufficient lubricity and insufficient
anti-seizure performance. In addition, Comparative Example 5 used therein an oil alone
which was the same as the component (B) of this invention. Unlike the oils in Comparative
Examples 3 and 4, the oil alone in Comparative Example 5 exhibited a kinematic viscosity
of higher than 30 mm²/s at 100°C, and raised problems as to its detergency and fluidity.
(4) Comparative Example 6 used therein an oil prepared by mixing the components (A)
and (B) of this invention. The oil so prepared exhibited inferior biodegradability
since the mixing ratio was outside that specified for the composition of this invention.
(5) Comparative Examples 7 and 8 show commercially-available biodegradable two-cycle
engine oils respectively. These oils use therein the same ester as used in Comparative
Example 1 as a main component of the base oil. In contrast with these Comparative
Examples, it is apparent that the compositions of this invention shown in Examples
1 to 6 were remarkably improved in thermal stability. In addition, Comparative Example
9 shows a polybutene base oil for commercially-available low-smoke exhaust gas type
two-cycle engine oil. This polybutene base oil exhibits good thermal stability in
the HTT, but it has low biodegradability. Comparative Example 10 shows a mineral base
oil for two-cycle engine oil, and Comparative Example 11 shows an oil for commercially-available
low-smoke exhaust gas type two-cycle engine oil, in which the base oil has partly
been replaced with a polybutene base oil. Such a mineral base oil is poor in both
thermal stability and biodegradability.
(6) As shown in the Examples, the composition of this invention comprises the components
(A) and (B) in the specified mixing ratio thereby enabling the composition to have
a suitable range of viscosity which is required in two-cycle engine oils, and also
to exhibit excellent lubricity as well as excellent biodegradability and thermal stability
which are important properties of the composition of this invention.
2. Engine test results
(1) High-temperature cleanliness test on motorcycle engines
[0032] Using an air-cooled two-cycle, 1-cylinder engine having a displacement of 123 c.c.
for motorcycles, a high-temperature cleanliness test was carried out under conditions
of an engine speed of 7000rpm, full engine load, a plug gasket temperature of 260°C,
a fuel oil mixing ratio of 20:1 and testing time of 3hrs.
[0033] As shown in Table 2, the composition of this invention in Example 3 was excellent
in anti-seizure performance between the piston and the cylinder as compared with Comparative
Examples 7 and 8 which were commercially-available biodegradable two-cycle engine
oils. This composition of Example 3 was also extremely excellent in piston cleanliness
without ring sticking after the test.
Table 2
Test oils |
Ex. 3 |
Comp. Ex. 7 |
Comp. Ex. 8 |
ring sticking, |
top ring |
10 |
0 |
6 |
|
second ring |
10 |
0 |
6 |
ring land, |
top |
4.1 |
1.5 |
3.8 |
|
second |
5.6 |
0.3 |
4.1 |
piston skart |
9.4 |
5.3 |
9.2 |
undercrown |
2.9 |
0.6 |
2.0 |
Total: 60 points (full marks) |
42.0 |
7.7 |
33.1 |
Note:
Since the piston seizure took place in 2.5 hours in Comparative Example 7, Comparative
Example 7 shows the piston cleanliness at that time. |
(2) Cleanliness test on engine for electric generator
[0034] Using a 1-cylinder engine employed for a generator and having a displacement of 63
cc, an engine cleanliness test was made under conditions of full engine load (800
W) and testing time of 5hrs. A plug gasket temperature was set at 200°C by covering
about 50% of the air intake of a forced cooling fan. The test was carried out at a
fuel:oil mixing ratio of 50 : 1 (mixing lubrication).
[0035] As shown in Table 3, the composition of Example 4 according to this invention was
excellent in piston cleanliness without causing ring sticking as compared with Comparative
Example 7 which was a commercially available biodegradable two-cycle engine oil and
with Comparative Example 8 which has a mineral base oil. The composition of Example
4 was also extremely low in cylinder head deposits.
Table 3
Test oils |
Ex. 4 |
Comp. Ex. 7 |
Comp. Ex.10 |
ring sticking, |
top ring |
10 |
8 |
10 |
|
second ring |
10 |
10 |
10 |
ring land, |
top |
6.7 |
1.0 |
1.6 |
|
second |
8.2 |
5.3 |
4.4 |
piston skart |
10 |
9.3 |
9.2 |
undercrown |
10 |
2.2 |
1.6 |
cylinder head |
10 |
8.9 |
5.7 |
Total: 70 points (full marks) |
64.9 |
44.7 |
42.5 |
(3) Engine cleanliness test on chain saw engine
[0036] An engine cleanliness test was carried out on a 1-cylinder engine used for a chain
saw engine and having a displacement of 45 cc, under conditions of an engine speed
of 9000rpm, full engine load, a plug gasket temperature of 280°C, a fuel oil mixing
ratio of 50:1 and testing time of 30 hrs (mixing lubrication).
[0037] As shown in Table 4, the composition of Example 4 according to this invention was
extremely excellent in ring sticking resistance and piston cleanliness as compared
with Comparative Example 11 which was an oil for a commercially-available low-smoke
type two-cycle engine oil.
Table 4
Test oils |
Ex. 4 |
Comp. Ex. 11 |
ring sticking, |
top ring |
7.0 |
5.0 |
|
second ring |
10 |
10 |
ring land, |
top |
8.4 |
3.9 |
|
second |
9.5 |
5.2 |
piston skart |
10 |
9.0 |
undercrown |
2.4 |
0.9 |
Total: 60 points (full marks) |
47.3 |
34.0 |
[0038] As described above, several points of excellent performances of the composition according
to this invention were illustrated in the tests, and, further, the same results were
obtained even in other engine tests. In addition, the composition of this invention
has already passed the TC-WII which is a standard of NMMA (National Marine Manufacturers
Association) for two-cycle engine oils for use in outboard engines and has also passed
the CEC L-33-T-82 which is a test method of evaluating biodegradability of two-cycle
engine oils for outboard engines (the method of biodegradability test is different
from the MITI method of Japan) and which indicates that a standard of the biodegradability
is at least 67 % (for example, Example 4 exhibited a decomposition degree of 87 %,
and, on the other hand, Comparative Example 7 showed 67 % in this test method).
[0039] As will be understood from the above, the composition according to this invention
is a lubricating oil which can solve the problems as to the piston ring sticking and
piston seizure which have become problems in the market.
1. A lubricating oil composition comprising an ester mixture as the main ingredient consisting
of
(A) 60 - 95 % by weight of an ester of a hindered alcohol with a straight-chain saturated
fatty acid having 8 - 12 carbon atoms, and
(B) 5 - 40 % by weight of a complex ester of a hindered alcohol with a straight-chain
saturated fatty acid having 8 - 12 carbon atoms and also with a dibasic acid having
2 - 50 carbon atoms.
2. A lubricating oil composition comprising
(I) 100 parts by weight of an ester mixture consisting of
(A) 60 - 95 % by weight of an ester of a hindered alcohol with a straight-chain saturated
fatty acid having 8 - 12 carbon atoms, and
(B) 5 - 40 % by weight of a complex ester of a hindered alcohol with a straight-chain
saturated fatty acid having 8 - 12 carbon atoms and also with a dibasic acid having
2 - 50 carbon atoms,
(II) not more than 30 parts by weight of a hydrocarbon based solvent and/or a lubricating
base oil.
3. A lubricating oil composition according to claim 1, which is used as a two-cycle engine
oil.
4. A lubricating oil composition according to claim 2, which is used as a two-cycle engine
oil.
5. A method for lubrication comprising the use of a lubricating oil composition comprising
an ester mixture as the main ingredient consisting of
(A) 60 - 95 % by weight of an ester of a hindered alcohol with a straight-chain saturated
fatty acid having 8 - 12 carbon atoms, and
(B) 5 - 40 % by weight of a complex ester of a hindered alcohol with a straight-chain
saturated fatty acid having 8 - 12 carbon atoms and also with a dibasic acid having
2 - 50 carbon atoms.
6. A method for lubrication comprising the use of a lubricating oil composition comprising
(I) 100 parts by weight of an ester mixture consisting of
(A) 60 - 95 % by weight of an ester of a hindered alcohol with a straight-chain saturated
fatty acid having 8 - 12 carbon atoms and
(B) 5 - 40 % by weight of a complex ester of a hindered alcohol with a straight-chain
saturated fatty acid having 8 - 12 carbon atoms and also with a dibasic acid having
2 - 50 carbon atoms, and
(II) not more than 30 parts by weight of a hydrocarbon based solvent and/or a lubricating
base oil.
7. A method for lubrication according to claim 5 or 6, which is applied to a two-cycle
engine.