Note: Descriptions are shown in the official language in which they were submitted.
1280403
TRACTION FLUID
FIELD OF THE INVENTION
This invention relates to a traction fluid. More
particularly, the present invention is concerned with a
traction fluid comprising a mixture or blend of a diester
having two cyclohexyl rings and a branched poly-alpha-
olefin as the base oil.
BACKGROUND OF THE INVENTION
Traction drive power transmissions, which transmit
power to a driven part through a traction drive mechanism,
have recently attracted attention in the field of auto-
mobiles and industrial machinery. The traction drive
mechanism is a power transmitting mechanism using a rolling
friction. Unlike conventional drive mechanisms it does not
use any gears, which enables reduction of vibration and
noise as well as a smooth speed change in high-speed
rotation. An important goal in the automobile industry is
improvement in the fuel consumption of automobiles. It has
been suggested that if the traction drive is applied to the
transmission of automobiles to convert the transmission to
the continuous variable-speed transmission fuel consumption
can be reduced by at least 20% compared to conventional
transmission systems since the drive can always be in the
optimum speed ratio. Recent studies have resulted in the
development of materials having high fatigue resistance as
well as in theoretical analysis of traction mechanisms. AS
regards the traction fluid, the correlation of traction
coefficients is gradually being understood on a level of
the molecular structure of the components. The term
"traction coefficient" as used herein is defined as the
ratio of the tractional force which is caused by slipping
at the contact points between rotators which are in contact
with each other in a power transmission of the rolling
friction type to the normal load.
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The traction fluid is required to be comprised of
a lubricating oil having a high traction coefficient. It
has been confirmed in this connection that a traction fluid
possessing a molecular structure having a naphthene ring
exhibits a high performance: "Santotrack(~)" manufactured by
the Monsanto Chemical Company is widely known as a com-
mercially available traction fluid. Japanese Patent
Publication No. 35763/1972 discloses di(cyclohexyl)alkane
and dicyclohexane as traction fluids having a naphthene
ring. This patent publication discloses that a fluid
obtained by incorporating the above-mentioned alkane
compound in perhydrogenated (alpha-methyl)styrene polymer,
hydrindane compound or the like has a high traction
coefficient. Further, Japanese Patent Laid-Open No.
191797/1984 discloses a traction fluid containing an ester
compound having a naphthene ring. It discloses that an
ester obtained by the hydrogenation of the aromatic nucleus
of dicyclohexyl cyclohexanedicarboxylate or dicyclohexyl
phthalate is preferred.
As mentioned above, in recent years the development
of continuous variable-speed transmissions has advanced.
The higher the traction coefficient of the lubricating
fluid the larger the transmission force in the same device.
This allows a reduction in size of the entire device
as well as a reduction in polluting exhaust gases.
Therefore, there is a strong demand for a fluid having a
traction coefficient as high as possible. However, even
the use of Santotrack(~), which is a traction fluid having
the highest performance of all the currently commercially
available fluids, in such a traction drive device provides
unsatisfactory performance with respect to the traction
coefficient, and is expensive. The traction fluid which
has been proposed in Japanese Patent Publication No.
lZ80403
35763/1971 contains Santotrack ~ orits analogue as a
component and, therefore, is also unsatisfactory with
respect to performance and cost.
The present inventors have made extensive and
intensive studies with a view to developing a traction
fluid which not only exhibits a high traction coefficient
but is also inexpensive. AS a result, the inventors have
found that the addition of a specific amount of a branched
poly-alpha-olefin to a diester or its derivative having two
cyclohexyl rings can economically provide a high-performance
base oil fluid. The present invention has been based
on this finding.
SUMMARY OF THE INVENTION
A traction fluid exhibiting a high traction
coefficient comprising (i) fr~m 0.1 to 70 wt. ~ of a
branched poly-alpha-olefin, and (ii) a diester or its
derivative containing two cyclohexyl or alkyl substituted
cyclohexyl moieties connected by ester bonds to an acyclic
hydrocarbyl radical.
DETAILED DESCRIPTION OF THE INVENTION
According to the present invention there is
provided a traction fluid comprising a mixture or blend of
(i) a diester or its derivative represented by the
following general formula:
1 ~ 12 ~ R
and (ii) from 0.1 to 70 % by weight of a branched
poly-alpha-olefin. In the above formula A' is an ester
linkage of -COO- or -OOC-, n is an integer of 1 to 6, R
is independently selected from hydrogen and alkyl groups
having 1 to 8 carbon atoms, and R2 is independently
selected from alkyl groups having 1 to 3 carbon atoms.
~ 4 ~ 1~ 80 40 3
A first object of the present invention is to
provide a high-performance traction fluid having a high
traction coefficient. A second object of the present
invention is to provide a traction fluid which is not only
economical but also readily available and easily applicable
to transmissions.
The traction fluid of the present invention
comprises a base oil comprised of two components, i.e.,
component A comprised of a diester or its derivative and a
specific amount of component s comprised of a branched
poly-alpha-olefin.
In the present invention the component A is a
diester or its derivative having two cyclohexyl rings which
is represented by the above-mentioned structural formula.
A' of the ester linkage is -COo- or -OOC-, and the number,
n, of the repeating units of gemdialkyl structure is 1 to
6, preferably 1 to 3. When n is zero the traction coef-
ficient is low, while when n is 7 or more the viscosity is
unfavourably high. This diester or derivative thereof has a
viscosity of 20 to 50 cst, preferably 24 to 30 cst at 40C,
and 4 to 10 cst, preferably 4 to 6 cst at 100C. Further,
the viscosity index is preferably in the range of 40 to
100, particularly preferably in the range of 50 to 80.
The component A can be prepared by the following
method. Specifically, the component A can be obtained by
the esterification reaction of a glycol compound with a
cyclohexanecarboxylic acid compound. The glycol compound
to be used has 1 to 6 gem-dialkyl structural units. A
preferred glycol compound is neopentyl glycol. Examples of
the cyclohexanecarboxylic acid compound include, besides
cyclohexanecarboxylic acid, those having an alkyl group
with 1 to 8 carbon atoms, e.g., methylcyclohexanecarboxylic
acid, ethylcyclohexanecarboxylic acid, etc. Cyclohexane-
carboxylic acid is particularly preferred. The esteri-
fication reaction is conducted using substantially
stoichiometric amounts of the reactants or in the presence
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of an excess amount of the acid. The former method
requires the use of a catalyst and further has the problem
that a monoalcohol is produced as the by-product. There-
fore, it is preferred that the esterification reaction be
conducted in the presence of an excess amount of the acid.
Specifically, 1 mol of the glycol compound is reacted with
the acid in 2 to 5-fold by mol excess (particularly
preferably in 2.5 to 4-fold by mol excess). The reaction
temperature is about 150 to 250C, preferably 170 to 230C,
and the reaction time is 10 to 40 hr, preferably 15 to 25
hrs. Although the esterification reaction may be conducted
under either elevated or reduced pressures, it is preferred
that the reaction be conducted at atmospheric pressure from
the standpoint of ease of reaction operation. Under this
condition, the excess acid serves as a catalyst. An
alkylbenzene such as xylene or toluene can be added in a
suitable amount as a solvent. The addition of the solvent
enables the reaction temperature to be easily controlled.
As the reaction proceeds water formed during the reaction
evaporates. The reaction is terminated when the amount of
water reaches twice by mol that of the alcohol. The excess
acid is neutralized with an aqueous alkaline solution and
removed by washing with water. When an acid which is
difficult to extract with an alkali washing is used the
reaction is conducted using the acid in an amount of 2 to
2.5-fold mol excess over the alcohol in the presence of a
catalyst. Examples of the catalyst include phosphoric
acid, p-toluenesulfonic acid and sulfuric acid. The most
preferred catalyst is phosphoric acid because it enhances
the reaction rate and increases the yield of the ester.
The reaction product is finally distilled under reduced
pressure to remove water and the solvent, thereby obtaining
the diester compound of the present invention.
The component A of the present invention can also
be prepared by the esterification reaction of a
cyclohexanol compound with a dicarboxylic acid having a
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quaternary carbon atom. In this case, cyclohexanol,
methylcyclohexanol or the like is used as the cyclohexanol
compound, while neopentyldicarboxylic acid or the like is
used as the dicarboxylic acid.
The poly-alpha-olefin component B has a quaternary
carbon atom or a tertiary carbon atom in its main chain and
is a polymer of an alpha-olefin having 3 to 5 carbon atoms
or the hydrogenation product thereof. Examples of the
poly-alpha-olefins include polypropylene, polybutene,
polyisobutylene, polypentene and the hydrogenation products
thereof. Particularly preferred are polybutene and
polyisobutylene and the hydrogenation products thereof.
The polyisobutylene is represented by the following
structural formula:
f H 3 f H3 Cl H 3
3 f ~ c H 2- Cl ~n C H 2 - C = C H 2
C H3 C H 3
The hydrogenation product of the polyisobutylene is
represented by the following structural formula:
F H 3 f H 3 IC H 3
3 1 ~ 2 1 ~n 2 C H C H 3
C H 3 C H3
In the above-mentioned formula the degree of poly-
merization, n, is 6 to 200.
Although the polybutene and polyisobutylene are
generally commercially available, they may be produced by
conventional polymerization methods. The hydrogenation
product thereof is produced by reacting polyisobutylene or
the like in the presence of hydrogen. The molecular weight
of the poly-alpha-olefin is preferably in the range of 500
to 10,000, more preferably in the range of 900 to 5,000.
The molecular weight can be adjusted by suitable methods
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such as decomposition of a poly-alpha-olefin having a high
molecular weight and mixing of poly-alpha-olefins having
different molecular weights. Although an alpha-olefin
copolymer (OCP) is a type of a poly-alpha-olefin, it is
unsuited for use as component B in the present invention.
This is because OCP is obtained by polymerization of two or
more alpha-olefins and such a structure wherein these
alpha-olefins are irregularly linked, as opposed to the
polybutene, etc. of the present invention which have a
regular gemdialkyl structure.
Component A of the present invention, e.g.,
neopentyl glycol cyclohexanecarboxylic acid diester,
exhibits a traction coefficient of 0.100 to 0.104, while
component B, e.g., polybutene, exhibits a traction
coefficient of 0.075 to 0.085.
Since component A of the present invention
exhibits a high traction coefficient, its use alone in a
traction drive device results in a high performance.
However, a further improved traction fluid can be obtained
by blending component A with 0.1 to 70~ by weight,
particularly 10 to 70% by weight, of component B.
Specifically, although component B has a lower traction
coefficient than component A, the gem-dimethylgroup in
component B cooperates with the cyclohexyl ring in
component A to exhibit a synergistic effect (with respect
to improvement of traction coefficient). Further, since
component B is inexpensive and exhibits excellent viscosity
characteristics, a traction fluid can be economically
obtained by blending component A with 0.1 to 70% by weight
of component B without lowering the traction coefficient.
Various additives may also be added to the
traction fluid of the present invention depending upon the
applications thereof. Specifically, when the traction
device undergoes high temperatures and large loads, at
least one additive selected from among an antioxidant, a
wear inhibitor and a corrosion inhibitor may be added in an
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amount of 0.01 to 5% by weight. Similarly, when a high
viscosity index is required a known viscosity index
improver is added in an amount of 1 to 10% by weight.
However, since the use of polymethacrylate and olefin
copolymer unfavorably lowers the traction coefficient, it
is preferred that, if they are present, they be used in an
amount of 4% by weight or less.
The term "traction fluid" as used in the present
invention is intended to mean a fluid for use in devices
which transmit a rotational torque through point contact or
line contact, or for use in transmissions having a similar
structure. The traction fluid of the present invention
exhibits a traction coefficient higher than those of
conventionally known fluids, i.e., exhibits a traction
coefficient 1 to 5% higher than those of the conventional
fluids, although the value varies depending on the
viscosity. Therefore, the traction fluid of the present
invention can be advantageously used for relatively low
power drive transmissions including internal combustion
engines of small passenger cars, spinning machines and food
producing machines, as well as large power drive
transmissions such as industrial machines, etc.
The traction fluid of the present invention
exhibits a remarkably superior traction coefficient
relative to the conventional fluids. The reason why the
traction fluid of the present invention exhibits a high
traction coefficient is not yet fully understood. However,
basically, the reason is believed to reside in the unique
molecular structure of the traction fluid of the present
invention.
The traction fluid of the present invention
comprises a diester. The diester has two cyclohexyl rings
in its molecule which are bonded to each other through two
ester linkages. The two ester linkages bring about an
interdipolar force between the molecules. It is believed
that the interdipolar force serves to bring the fluid into
~'
~280403
a stable glassy state under high load conditions, thereby
increasing the shearing force. Further, the traction fluid
of the present invention has a quaternary carbon atom of
the gem-dialkyl type which is bonded to the two cyclohexyl
rings through a methoxycarbonyl linkage. This suppresses
the internal rotation. Therefore, when the traction device
is under high load conditions the cyclohexyl rings are
firmly engaged, like gears, with the gem-dialkyl portion of
the quaternary carbon atom, while when the device is
released from the load, the engagement is quickly detached,
thereby causing fluidization.
The following Examples are provided for
illustrative purposes only and are not to be construed as
limiting the invention described herein.
EXAMPLES 1 - 9
Diester of neopentyl glycol cyclohexane carboxylic
acid compound of the present invention was synthesized
using the following materials.
First, 1 mol of neopentyl glycol is mixed with 3
mols of cyclohexane carboxylic acid and reacted for 20
hours at a reaction temperature of 200C under atmospheric
pressure. Since the acid is in excess in the mixture
during the reaction, no catalyst is used and xylene is
added as a solvent. The reaction is terminated when the
water which has vaporized as the reaction proceeds has
reached 2 mols of alcohols. The reaction product is washed
with an alkaline solution (caustic soda) to remove the
excess acid, and is further washed with water until it
becomes neutral, followed by vacuum distillation so as to
remove water and xylene, thereby isolating the diester of
the present invention.
The diester thus produced was blended with
different amounts of polybutene having an average molecular
weight of 420 to 2350, as set forth in Table I, followed by
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measurement of traction coefficient. The conditions of
measurement of the traction coefficient were as follows:
measuring equipment: Soda-type four-roller
traction testing machine
test conditions: a fluid temperature of
20C; a roller temperature
of 30C; a mean Hertzian
pressure of 1.2 GPa; a
rolling velocity of 3.6 m/s;
and a slipping ratio of
3.0%.
The traction fluid of the present invention was
found to be remarkably superior in traction performance to
conventional traction fluids as shown in Table 1.
COMPARATIVE EXAMPLES 1 - 7
The traction coefficients were measured under the
same conditions as those used in the above examples with
respect to a traction fluid consisting of 100% by weight of
component B, a traction fluid obtained by blending 10% by
weight of component A with 90% by weight of B component, a
traction fluid obtained by blending component A with OCP or
PMA, and a commercially available traction fluid "Santotrack ~ ".
The results are shown in Table 1. As can be seen from
the data in Table 1, all the comparative samples exhibited
traction coefficients 1 to 5~ smaller than these of the
diester compound of the present invention. It is noted in
this connection that an olefin copolymer, i.e., copolymer
(having an average molecular weight of 150,000 to 300,000)
of ethylene with propylene was used as OCP, while
polymethacrylate having an average molecular weight of
50,000 to 300,000 was used as PMA.
The traction fluid of the present invention com-
prises at least one component A having two cyclohexyl rings
and linear-chain hydrocarbons as the skeleton and a
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specific amount of a component B comprised of a branched
poly-alpha-olefin. Such a traction fluid not only exhibits
an extremely high traction coefficient but is also
inexpensive and exhibits excellent viscosity character-
istics.
Therefore, the use of the traction fluid of the
present invention in a power transmission, particularly a
traction drive device, results in a remarkable increase in
shearing force under a high load. This enables a reduction
in size of the device which leads to lower costs of the
device.
12- 128~)403
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