CA2079512A1

CA2079512A1 - Lubricating oil composition

Info

Publication number: CA2079512A1
Application number: CA002079512A
Authority: CA
Inventors: Mineo Kagaya; Mitsuaki Ishimaru; Hiroaki Ishii
Original assignee: Individual
Current assignee: Eneos Corp
Priority date: 1991-10-04
Filing date: 1992-09-30
Publication date: 1993-04-05
Also published as: EP0535990A1; ATE147096T1; DE69216346D1; EP0535990B1; JPH0598276A; JP2872465B2

Abstract

ABSTRACT OF THE DISCLOSURE
The lubricating oil composition of the present invention 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, the composition having excellent performances such as biodegadability, high-temperature engine cleanliness, lubricity and piston seizure preventiviness which are conductive to enviromental protection.

Description

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TITLE OF TEE INVENTION:
A LUBRICATING OIL COMPOSITION

BACKGROUND OF TllE INVENTION
1. F:Leld of the Invention The present invention relates to a lubricating oil composition and more particularly to a lubricating oil composition which is excellent in biodegradability, high-temperatùre cleanliness and anti-seizure performance and is therefore conductive to environmental protection.

2. Prior Art : Two-cycle engines raise problems as to possible environmental pollution since they discharge an unburned engine oil as an a~companiment 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 unb-urned oil. Chain saws and other -forestry machinery may also cause the polution of forests and rivers due to the unburned oil.
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.

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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 malsers. 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 :L6 - 18 carbon atoms) and a mineral oil-based solvent. They contain an amino amide type ashless dispersant as an additive.
These commercially available oils already passed the TC-WII which is a per-formance standard o-f 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 insu-fficient thermal stability as a lubricating oil.
- Because of this, a biodegradable lubricating oil having better thermal stability and more excellent lubricity has been sought to be developed.

SUMM~R~ OF THE INVENTION
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.

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~ nother object is to provide a method for lublication comprising the use of such a lubricating oil as above.
The present inventors made intensive studies to aim main:Ly 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.
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 (~) 5 - 40 % by weight of a comple~ 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.
In a second aspect of the present invent1on, 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.

DET~ILED EXPLANATION OF T~E INVENTION
The present invention will now be explained hereunder in more detail.
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 satura-ted fatty acid having 8 - 12 carbon atoms, and (B) a complex ester of a hindered aleohol with both a straight-ehain saturated fatty aeid having 8 - 12 carbon atoms and a dibasic acid having 2 - 50 carbon atoms.
In the preparation of this component (A), the hindered alcohol used means one in which the ~ carbon atom of the hydroxyl group is a quarternary carbon_atom.
More specifically, the hindered aleohol preferably used include dihydric to tetrahydric alcohols having 5 - 10 earbon atoms, and a dimer and trimer thereof, and they are exemplified by neopentyl glyeol, 2-methyl-~-propyl-1, 3- propanediol, trimethylol ethane, trimethylol propane (TMP), trimethylol butane, pentaerythritol (PET), di- (trimethylol propane), tri-(trimethylol propane), di- (pentaerythritol) and tri-(pentaerythritol).

- 5 - ~ 2 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 -~orm of a derivative such as an acid anhydride, acid halide and metal salt of the acids. In the preparation o-f 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.
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, _ glu-taric 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.
The component (B) may be exemplified by a complex ester represented by the following general formula tI).

X -C-CH2-OC0-R -C00-CH2-C-X (I) x2 X4 - 6 - 2 ~ ~ ~A ~

wherein X1 to X4 may be identical with or di-~ferent fro~ each other and each represent an alkyl group having 1 - 4 carbon atoms or a group having the follow:ing general formula of -CH2-oCo-R4 (R4 being an alky:L 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.
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 o~ 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 - 7 - 2~

undesirably be insu-fficient in biodegradabilitY-Furthermore, the composition of the present invention shoud have a kinematic viscosity o-f preferably 6 to 15 mm /s at a temperature of 100 C.
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.
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-~-olefin (1-octene oligomer, 1-decene oligomer, etc.); polybutene, alkylbenzenes;

alkylnaphthalenes; polyglycol; diester (ditridecylgultarate, di,2-ethylhexy] adipate);
diisodecyl adipate; di,tridecyl adipate; di,2-ethyl - 8 - ~?~ ~ ~

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 (trime-thylolpropane stearate, trimethylolpropane oleate, pentaerithritol 2-ethylhexanoate, etc.);
polyphenylether; fluorine-based oils; and silicone-based oils.
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.
Moreover, the composition of this invention--may be incorporated with various kinds of known additives 2~ 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 rus-t preventing agent and anti-foaming agent.

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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 speci-fic base oil.
Although the lubricating oil compositions o-f 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 iIl 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.

THE PREFERRED EM~ODIMENTS
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 The biodegradability was measured by the coulometer method using a closed-system oxygen - lo 2~ ~ ~5~ X

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 e-ffected at a temperature of 25C for a period of time of 14 days.
A decomposition degree is represented by the following formula.
Decomposition degree = [(BOD-B)/TOD] X 100 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) ~-5 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).
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 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 t,he glass tube. The oil was degraded by being sub;ected 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 t~beO 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 280C, 16 hrs_as their standard.
The test results thus obtained are shown in Table 1.

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Examples 1 to 6 which show compositions of this invention, exhibited excellent performances in biodegradability and thermal stability as compared wi~h Comparative Examples which show comparative compositions.
(1) Comparative Example 1 is a TMP ester which consists mainly o-f a fatty acid (oleic acid) having 18 carbon atoms. This ester exhibited good biodegradabi]ity, and, however, it was poor in thermal stability as compared the composition of the present invention.
(2) Comparative Example 2 is a PET ester whieh 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 (~-1) and (A-2) of this invention, respectively. Eaeh 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 ~inematic viscosity of less -than 6 mm2/s at lOO~C. This viscosity is too low as a base oil for a two-cycle engine oil, and therefore, these oils are likely to exhibit insuffieient lubrieity and insufficient anti-seizure per-formanee. In addition, Comparative Example 5 used therein an oil alone whieh was the same as the - 15 - 2 ~ J~ ~

component (B) of this invention. Unlike the oils in Comparat:ive Examples 3 and 4, the oil alone in Comparative Example 5 exhibited a kinematic viscosity of higher than 30 mm2/s at 100C, 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 l_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 - 16 ~ 2~5~ ~

a polybutene base oil. Such a mineral base oil is poor in both thermal stability and biodegradability.

(6) As shown i.n the Examples, the composition o~
this invention comprises the components (A) and (B) in the speci~`ied mi~ing rat:lo 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 o-f the composition o-f this invention.
2. Engine test results (1) High-temperature cleanliness teæt on motorcycle engines 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 _nder conditions of an engine speed of 7000rpm, full engi~ne load, a plug gasket temperature of 260C, a fuel:oil mixing ratio of 20:1 and testing time of 3hrs.
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 ~ which were commercially-available biodegradable two-cycle engine oils. This composition of Example 3 was also extremely - 17 - 2 ~ ~ ~ r~ ~

excellent in piston cleanliness without ring sticking after the test.

Table 2 _ _ Test oils Ex. 3 Comp. Comp.
Ex. 7 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 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 200C 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).

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As shown in Table 3, the composition of Example 4 according to this inven-tion was excellent in piston cleanliness without causing ring sticking as compared with Comparative Examp:Le 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.

1~ Table 3 Test oils Ex. 4 Comp. Comp.
Ex. 7 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 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 9000rpm1 full engine load, a plug gasket - 19 - 2~ ~

temperature of 280C, a fuel:oil mixing ratio of 50:1 and testing time of 30 hrs (mixing lubrication).
As shown in Table 4, the composition of Example 4 accordlng to this invention was extremely excellent in rillg 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 plston skart 10 9.0 _ - undercrown 2.4 0.9 -Total: 60 points (full marks) 47.3 34.0 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 o~ this invention has already passed the TC-WII which is a standard of NMMA (National Marine Manufacturers Association) for - 20 - 2~

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 dif~ererlt erom the MITI method of Japan) and wh:Lch indicates that a standard of the biodegradabLlity 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).

Effects of the present invention 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.

Claims

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 o-f 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 o-f 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 o-f 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.