BACKGROUND OF THE INVENTION
[0001] The present invention relates to a lubricating oil composition or, more particularly,
to a lubricating oil composition having excellent stability against oxidation, performance
at extremely low temperatures, cleanness at high temperatures and friction characteristics
in wet clutches and usable in a wide variety of applications, for example, as an engine
oil in internal combustion engines, ATF oil, lubricating oil in wet clutches for agricultural
tractors and the like, compressor oil, gear oil, bearing oil and so on.
[0002] As is known, poly-α-olefins as a class of synthetic lubricating oils are utilized
as a base oil of high-grade lubricating oils by virtue of their excellent stability
against oxidation and fluidity at low temperatures. In addition to the economical
. disadvantage due to the expensiveness, however, poly-d-olefins have some technical
problems when they are used, for example, as an engine oil in internal combustion
engines or lubricating oil in wet clutches including poor cleanness at high temperatures,
insufficient friction characteristics with wet clutches and others.
[0003] With an object to solve the economical problem, on the other hand, it is proposed
to admix the poly-a-olefin with a mineral oil. This measure, however, never provides
a true technical solution of the problem since admixture of a mineral oil may badly
affect the excellent performance at extremely low temperatures and stability against
oxidation inherent in the poly-
d-olefins.
SUMMARY OF THE INVENTION
[0004] Thus, the present invention has an object to provide a novel poly-α-olefin based
lubricating oil composition of high economical feasibility having excellent cleanness
at high temperatures and friction characteristics with wet clutches without being
affected in respect of the stability against oxidation and performance at extremely
low temperatures. The extensive investigations undertaken with this object have unexpectedly
led to a discovery that the object can be fully achieved by blending a poly-a-olefin
with a mineral oil only when a poly-d-olefin having specific properties is combined
with a mineral oil having specific properties in a specific proportion.
[0005] The lubricating oil composition of the invention formulated on the base of the above
mentioned discovery comprises:
(A) from 15 to 85 parts by weight of a poly-α-olefin having a kinematic viscosity
in the range from 1.5 to 150 centistokes at 100 °C; and
(B) from 85 to 15 parts by weight of a mineral oil having a kinematic viscosity in
the range from 2 to 50 centistokes at 100 °C and a pour point of -35 °C or below.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0006] As is understood from the above given summary of the invention, the inventive lubricating
oil composition is a mixture of a specific poly-a-olefin as the component (A) and
a specific mineral oil as the component (B) in a specific weight proportion. The poly-α-olefin
as the component (A) is a type of synthetic lubricating oil also called an α-olefin
oligomer and represented by the general formula

in which R is an alkyl group having 4 to 12 carbon atoms and the subscript m is zero
or a positive integer not exceeding 30. The poly-α-olefin should have a kinematic
viscosity in the range from 1.5 to 150 centistokes or, preferably, from 2 to 50 centistokes
at 100 °C. The poly-α-olefin should have a relatively low degree of polymerization
and particular examples of preferable poly-α-olefins include dimers to decamers of
1-octene, 1-decene or 1-dodecene, of which dimer, trimer and tetramer of 1-decene
are more preferable.
[0007] Such a poly-α-olefin can be prepared by a known method including the steps of polymerization,
decomposition of the catalyst, distillation and hydrogenation. A means to control
the degree of polymerization of the poly-α-olefin is to control the staying time of
the reactants in the reaction vessel in the step of polymerization.
[0008] The mineral oil as the component (B) to be combined with the above described poly-d-olefin
as the component (A) should have a kinematic viscosity in the range from 2 to 50 centistokes
or, preferably, from 5 to 35 centistokes at 100 °C and a pour point of -35 °C or below
or, preferably, -40 °C or below. The content of aromatic hydrocarbons in the mineral
oil, referred to as % C hereinbelow, should be 20
% or lower or, preferably, 10% or lower. The content of sulfur therein should be 50
ppm or lower or, preferably, 5 ppm or lower. Use of a mineral oil containing more
than 50 ppm of sulfur is undesirable due to the decreased stability of the resultant
lubricating oil composition against oxidation. Mineral oils satisfying such requirements
can be obtained from a paraffinic crude oil or an intermediate base crude oil by distilling
the same to give a distillate having a boiling point of 250 to 450°C under normal
pressure which is then refined by a conventional method followed by a deep dewaxing
treatment.
[0009] The distillate here implied is obtained by subjecting a crude oil to distillation
under normal pressure or by subjecting a residue oil from distillation under normal
pressure to distillation under reduced pressure. Though not particularly limitative,
the distillate can be refined by one of the following five methods including: (1)
hydrogenation treatment of the distillate, optionally, followed by alkali distillation
or scrubbing with sulfuric acid; (2) solvent treatment of the distillate, optionally,
followed by alkali distillation or scrubbing with sulfuric acid; (3) hydrogenation
treament of the distillate in two steps; (4) hydrogenation treatment of the distillate
in three steps; and (5) hydrogenation treatment of the distillate in two steps followed
by alkali distillation or scrubbing with sulfuric acid. Following description is exemplary
of a process for the treatment of the distillate.
[0010] A paraffinic crude oil or an intermediate base crude oil is processed according to
a conventional procedure to give a base material for lubricating oil which is then
subjected to an extensive hydrogenation treatment. By this treatment, certain constituents
in the base material undesirable for the fraction of lubricating oils, such as the
aromatic matter, can be removed or converted into effective constituents along with
removal of the sulfurous and nitrogenous matters almost to completeness.
[0011] The base material-after the hydrogenation treatment is then subjected to fractional
distillation under reduced pressure so as to be imparted with a necessary viscosity.
Thereafter, the oil is subjected to a dewaxing treatment using a solvent according
to a known procedure to such an extent that the oil should have a pour point, which
conventional paraffin-based oils may have, in the range, for example, from -15 °C
to -10 °C.
[0012] If necessary, this dewaxing treatment is followed by a further treatment of hydrogenation
to such an extent that the aromatic compounds contained in the base oil are mostly
hydrogenated and converted into saturated compounds to impart the base oil with increased
thermal and chemical stability. The thus refined base oil is still not suitable as
a component of the inventive lubricating oil composition due to the high pour point.
Accordingly, the above described refining treatment should be followed by a deep dewaxing
treatment. This dewaxing treatment can be performed either by the method of solvent
dewaxing under extensive conditions or by the method of catalytic hydrogenation dewaxing
using a zeolite as the catalyst, in which the paraffin compounds or, mainly, normal
paraffins adsorbed in the pores of the catalyst are preferentially decomposed under
the atmosphere of hydrogen so that the base oil is freed from the constituents responsible
for the formation of waxy materials.
[0013] Although the conditions of the hydrogenation treatment depend on the properties of
the base oil and other factors, the process parameters usually include a reaction
temperature in the range from 200 to 480 °C or, preferably, from 250 to 480 °C, pressure
.of hydrogen in the range from 5 to 300 kg/cm
2 or, preferably, from 30 to 250 kg/cm
2 and volume of the hydrogen gas introduced in the range from 30 to 3000 Nm or, preferably,
from 100 to 2000 Nm per kiloliter of the feed of the distillate. The catalyst suitable
for this catalytic hydrogenation treatment can be prepared by using alumina, silica,
silica-alumina, zeolite, active carbon, bauxite and the like as a carrier on which
a metallic element belonging, for example, to the VIth or VIIIth Group of the Periodic
Table or, preferably, cobalt, nickel, molybdenum, tungsten and the like is supported
as the catalytically effective ingredient according to a known method for catalyst
preparation. The catalyst should preferably be subjected to a preliminary sulfurization
treatment prior to use.
[0014] As is mentioned above, the distillate oil after the hydrogenation treatment is subjected
to one or more of different post-treatments. When the post-treatment includes the
second- step or, further, third-step hydrogenation treatment, in particular, the process
parameters in these subsequent hydrogenation treatments can be selected within the
above described ranges and the conditions in each of the first-step to third-step
hydrogenation treatments can be the same as or different from those in the other steps.
It is usually preferable, however, that the hydrogenation in the second step and in
the third step should be performed more extensively than in the first step and in
the second step, respectively.
[0015] The alkali distillation to follow is undertaken with an object to remove any trace
amount of the acidic substances contained in the hydrogenated oil so as to improve
the stability thereof. This process is performed by the distillation of the distillate
oil with admixture of an alkali such as sodium hydroxide, potassium hydroxide and
the like under reduced pressure.
[0016] The scrubbing of the oil with sulfuric acid, which is alternative to the alkali distillation,
is a treatment conventionally performed as a finishing step of various petroleum products
and undertaken here with an object to improve the properties of the distillate oil
by removing aromatic hydrocarbons or, in particular, polycyclic aromatic hydrocarbons,
olefins, sulfur compounds and so on therefrom. In the preparation of the mineral oil
for the inventive lubricating oil composition, the distillate oil after the hydrogenation
treatment is contacted with concentrated sulfuric acid in an amount of 0.5 to 5% by
weight at a temperature in the range from room temperature to 60°C followed by neutralization
with an alkali such as sodium hydroxide.
[0017] As is described in the above by (1) to (5), the distillate oil is treated in one
of the combinations of the above described unit procedures while the procedures of
(1), (3) and (4) are particularly preferable.
[0018] The distillate oil after the treatment in the above described manner has a kinematic
viscosity of 2 to 50 centistokes at 100°C and a pour point of -35°C or below and the
content of the aromatic hydrocarbons % C
A therein does not exceed 20%.
[0019] The lubricating oil composition of the present invention is composed of the above
described poly-a-olefin and the minerai oil. The composition should be composed of
from 15 to 85% by weight or, preferably, from 20 to 80% by weight of the former component
and from 85 to 15% by weight or, preferably, from 80 to 20% by weight of the latter
component. The above given range is critical in order that the inventive composition
may have excellent cleanness at high temperatures and friction characteristics with
a wet clutch.
[0020] Although the essential ingredients in the inventive lubricating oil composition are
the above described poly-a-olefin and mineral oil, it is optional that the lubricating
oil composition is admixed with various kinds of additives according to need. For
example, the composition can be admixed with an antioxidant such as zinc thiophosphate,
phenolic compounds, e.g. di-tert-butyl p-cresol, amine compounds, e.g. diphenyl amine,
and the like. Other additives to be added to the inventive composition include detergent-dispersants
of the types of sulfonates, phenates, phosphonates, imides and amides, molybdenum
dithiophosphate, molybdenum dithiocarbamate, phosphorus-containing extreme-pressure
additives, sulfur-based extreme-pressure additives, friction modifiers and other extreme-pressure
additives . and oiliness improvers, corrosion inhibitors, anti-foam agents, rust inhibitors
and so on each in a limited amount.
[0021] It is further optional that the inventive lubricating oil composition is admixed
with a viscosity-index improver and pour-point depressor such as polymethacrylates,
copolymers of olefins, polybutenes and the like. It is noteworthy that the low-temperature
viscosity of the composition can be improved by the addition of a smaller amount of
these additives than in the conventional lubricating oil compositions so that the
decrease in the high-temperature cleanness by these additives can be minimized.
[0022] As is understood from the above given description, the lubricating oil composition
of the present invention is imparted with greatly improved high-temperature cleanness
and excellent friction characteristics with wet clutches. Further, the inventive lubricating
oil composition well retains the excellent stability against oxidation and performance
at extremely low temperatures as the inherently advantageous features of the poly-a-olefins
along with still less expensiveness than the poly-a-olefinsperse. Moreover, the inventive
lubricating oil composition does not require addition of a large amount of a pour-point
depressor or-viscosity-index improver, which may have an adverse influence on the
high-temperature cleanness of the lubricating oil, so that the high-temperature cleanness
of the composition can be exhibited so much. Accordingly, the lubricating oil composition
of the invention is very useful in a variety of applications where lubrication is
required.
[0023] In the following, examples are given to illustrate the lubricating oil composition
of the invention in more detail.
Preparation of Compositions 1 to 7.
[0024] Seven different base oils having a kinematic viscosity of 5 centistokes at 100°C
were prepared each by uniformly blending the poly-a-olefin A
l and one of the mineral oils B
1 to B
6 characterized by the property parameters indicated in Table 1 below in the weight
proportion indicated in Table 2 below. The poly-a-olefin was a mixture of the dimer
to tetramer of 1-decene.
[0025] Each of the base oils (kinematic viscosity of 5 centistokes at 100°C) was modified
by the admixture of 7% by weight of a copolymer of ethylene and propylene having an
average molecular weight of about 65,000 so as to be equivalent to an oil of the SAE
viscosity grade IOW/30 and further admixed with 8% by weight of a commercial product
of an additive package for engine oils containing calcium sulfonate as the principal
ingredient. The thus prepared seven lubricating oil compositions are referred to as
the Compositions 1 to 7 hereinbelow.
Preparation of Composition 8.
[0026] The base oil was prepared by uniformly blending the poly-a-olefin A
2, which was also a mixture of the dimer to tetramer . of 1-decene, and the mineral
oil B
5 characterized by the property parameters indicated in Table 1 in a 50:50 by weight
proportion. The base oil was admixed with 15% by weight of the same ethylene-propylene
copolymer as used in the formulation of the Compositions 1 to 7. The thus prepared
lubricating oil composition is referred to as the Composition 8 hereinbelow.

Examples 1 to 4 and Comparative Examples 1 to 4.
[0027] Each of the Compositions 1 to 8 was subjected to the test of the high-temperature
cleanness according to the testing procedure described below to give the results shown
in Table 3 below which also shows the kinematic viscosity at 100°C and the low-temperature
viscosity at -30°C measured according to the procedure specified in ASTM D 2983.
[Test of high-temperature cleanness]
[0028] The sample oil was subjected to the panel-coking test according to the procedure
specified in Federal Test Method Standard No. 79la, Method 3462T with the conditions
of the panel temperature of 320°C, oil temperature of 100°C and testing time of 3
hours and the high-temperature cleanness of the oil was evaluated by the weight increase
of the panel in mg after the test.

Example 5 and Comparative Examples 5 and 6.
[0029] The Compositions 2, 6 and 8 prepared in the above described manner were each subjected
to the test of stability against oxidation according to the procedure specified in
JIS K 2514 to give the results of the increase in the overall acid value shown in
Table 4 below in mg KOH/g together with the viscosity ratio at 100°C.

Preparation of Compositions 9 to 11.
[0030] The Compositions 9 to 11 were each prepared by admixing a base oil composed of the
poly-a-olefin A
2 and one of the mineral oils characterized in Table 1 in the weight proportion indicated
in Table 5 below with 10% by weight of a commercial product of an additive package
for ATF containing an ashless dispersant as the principal ingredient and 5% by weight
of a polymethacrylate having a weight-average molecular weight of about 80,000.

Example 6 and Comparative Examples 7 and 8.
[0031] The Compositions 9 to 11 prepared in the above described manner were each subjected
to the SAE No. 2 friction test under the conditions indicated below to give the results
shown in Table 6 by the values of µ
0/µ
1200, in which µ
1200 is the coefficient of dynamic friction at a velocity of rotation of 1200 rpm and
u
0 is the coefficient of static friction in a static condition.
[SAE No. 2 friction test]
[0032] The friction characteristics of the sample oil were evaluated using an SAE No. 2
testing machine manufactured by Greening Co., U.S.A., under the following experimental
conditions. Discs: 2 paper-based discs for automatic transmission Plates: 3 steel-made
plates for automatic transmission Revolution of motor: 3000 rpm Pressing-down pressure
of piston: 10 kg/cm
2 Temperature of oil: 100°C
