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Description  |
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BACKGROUND OF THE INVENTION
(i) Field of the Invention
This invention relates to a novel type of lubricating oil compositions and
more particularly, to lubricating oil compositions which comprise esters
constituted with glycerol, fatty acid and boric acid having specific
ratios of carboxylic acid residue, glycerol residue, and boric acid
residue.
(ii) Description of the Prior Art
In recent years, there is an increasing tendency toward the saving of
energy. The energy saving such as in automobiles or ships has become one
of great concerns. For the purpose, improvements have been steadily made
on so-called hardwares such as materials and structures.
On the other hand, attention has been paid to a frictional energy loss in
lubrication. Extensive studies have been made on improvements of
lubricating oils in order to reduce the loss and thus to decrease energy
or fuel consumption.
One of methods of reducing the frictional energy loss is to add friction
reducing additives to lubricating oils.
For instance, Japanese Laid-open Application (Japan kokai) No. 55-66996
discloses fatty acid amides of diethanolamine or mixtures thereof with
fatty acid esters of diethanolamine as friction reducing additive. In
Japanese Laid-open Application (Japan kokai) No. 55-84394, there is
described an improvement of fuel economy of internal combusion engines by
addition of fatty acid glycerol esters to lubricating oils. Although these
additives added to lubricating oils are found to show an improvement of
fuel economy over lubricating oils containing friction reducing additives,
most of them have a difficulty in practical applications because they
allow a degree of corrosion in bearings at the inside of an engine
mechanism to become greater than the tolerance limit of corrosion.
Japanese Laid-open Application (Japan kokai) No. 56-141398 discloses
sorbitan boric esters as friction reducing additive. It is described that
lubricating oil compositions comprising an effective amount of the esters
can not only reduce the consumption of fuel, but also reduce a degree of
corrosion at bearing portions to a minimum. However, when sorbitan boric
esters are allowed to stand in air, they tend to form a thick solid film
deposit on portions where exposed. Once formed, the solid deposit does no
longer dissolve in lubricating oils.
As for other boric esters, boric esters of glycerol fatty acid monoesters
are known in this field and are referred to in U.S. Pat. No. 2,795,548 as
a corrosion inhibitor being incorporated in lubricating oils, in U.S. Pat.
No. 3,117,089 as an anti-rust agent being incorporated in fuels and
lubricating oils, and in Japanese Laid-open Application (Japan kokai) No.
56-150097 (European Patent Application No. 0036708) as friction reducing
additives being incorporated in lubricating oils. However, in such
incorporation of boric esters of glycerol fatty acid monoesters in
lubricating oils, when the proportion of boric acid to glycerol fatty acid
monoester is small, a degree of corrosion in bearings is allowed to become
greater than the tolerance limit, on the other hand, the greater the
proportion is set, the more they tend to form a thick solid film under the
conditions of air-contact. Thus, it is difficult to obtain a lubricating
oil which can satisfy both non-corrosive and friction reducing properties
at the same time.
SUMMARY OF THE INVENTION
Accordingly, we have made intensive studies to develop lubricating oil
additives which show the friction-reducing effect but have almost no
corrosion property in bearing portions and which do not form any solid
film on themselves when allowed to stand in the air in order to ensure the
above-mentioned performance. As a result, it was found that lubricating
oil compositions comprising esters constituted with glycerol, fatty acid
boric acid (hereinafter referred to simply as boric esters), said boric
esters having specific ratios of carboxylic acid residue, glycerol
residue, and boric acid residue, satisfy the above requirement and are
excellent as a lubricating oil.
DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS
The boric esters useful in the present invention may cover a variety of
compounds which vary in structure depending on the types of reactants, the
charge ratios, and the reaction conditions. They may be used singly or in
combination provided that a moiety derived from fatty acids (i.e.
carboxylic acid residues) is contained in the range of 0 to 2.0 mols, and
a moiety derived from glycerol (i.e. glycerol residue) is in the range of
1.5 to 2.0 mols per unit mole of a moiety, derived from boric acid (i.e.
boric acid residue) and further, molar ratio of glycerol residue to
carboxylic acid residue is more than 1.2 on average of a single compound
or a mixture of these compounds. Typical of the boric esters are compounds
represented by the following formulas (I) and (II) or mixtures thereof.
##STR1##
in which X, Y, and Z independently represent an OH group or a
##STR2##
group, and R represents a saturated or unsaturated alkyl group having 7 to
23 carbon atoms.
Of these, more preferable boric esters are those compounds which comprise,
based on unit mol of the boric residue, 1.0 to 1.5 mols of carboxylic acid
residue, and 1.8 to 2.0 mols of the glycerol residue. Most preferably, the
boric esters comprise about 1 mol of carboxylic acid residue, and about 2
mols of the glycerol residue per unit mol of the boric acid residue.
The boric esters of the present invention which meet the above-described
requirements can be prepared, for example, by the following methods.
(a) Method of reacting carboxylic acid monoglyceride, glycerol, and boric
acid at a temperature of 100.degree. to 230.degree. C.
(b) Method of reacting glycerol and boric acid and further reacting the
resulting compound with carboxylic acid, lower alcohol esters of
carboxylic acids, or carboxylic acid halides.
(c) Method of reacting mixtures of carboxylic acid triglycerides, glycerol,
and boric acid at a temperature of about 240.degree. to 280.degree. C.
In these methods, it is necessary that the respective starting materials be
used in amounts satisfying the aforedefined ratios of the boric acid
residue, carboxylic acid residue, and glycerol residue in the final
product. For instance, it is preferable to use 1 to 2 mols of carboxylic
acid monoglycerides and 1 to 0 mol of glycerol per unit mol of boric acid
in the method (a), 2 mols of glycerol and 1 to 2 moles of carboxylic acids
or their esters or halides per unit mol of boric acid in the method (b),
and 1 to 2 mols of carboxylic acid triglycerides and 4 to 5 mols of
glycerol per 3 mols of boric acid in the method (c).
Carboxylic acid triglycerides used as one of the starting materials are
those compounds which contain a saturated or unsaturated long-chain fatty
acid residue having 8 to 22 carbon atoms. Preferable triglycerides are,
for example, animal and vegetable fats such as rape seed oil, cotton seed
oil, soybean oil, lard oil, beef tallow, and the like. Carboxylic acid
monoglycerides may contain small amounts of di- and tri-carboxylic acid
esters. Carboxylic acids useful for the purpose of the invention are
preferably those acids derived from the above-indicated oils or fats, of
which oleic acid or derivatives thereof are most preferable.
The lubricating oil compositions according to the invention are prepared by
adding one or more boric acid esters to lubricating base oils. If desired,
various known additives for lubricating oils may be further added
including, for example, metallic detergents, ashless dispersants,
antioxidants, extreme pressure additives, viscosity index improvers, and
the like in order to attain intended performances.
The lubricating base oils which occupy a major proportion of the
lubricating oil composition of the invention may be mineral lubricating
oils, synthetic lubricating oils, or mixtures thereof.
Phenate and/or sulfonate are usually used as metallic neutralized
detergents. The phenates are alkaline earth metal salts of alkylphenol
sulfides having an alkyl group containing 8 to 30 carbon atoms. Their
calcium, magnesium, or barium salts are preferably used. The sulfonates
are alkaline earth metal salts of sulforic acids derived from lubricating
oils having a molecular weight of about 400 to 600 or aromatic compounds
having alkyl groups synthetically substituted. Their calcium, magnesium or
barium salts are preferably used. Alternatively, alkaline earth metal
salts of salicylates or phosphonates may also be used.
These metallic detergents may be of the neutral type or of the so-called
"over-based" type having a total base number of 300 or higher. The
detergents are added in an amount of 0.5 to 20% by weight of the
composition.
The ashless dispersants are succinimides, succinic esters, or benzylamines
having an alkyl or alkenyl group with a molecular weight of about 700 to
3000. These compounds may be further reacted with boric acid. The ashless
dispersants are used in an amount of 0.5 to 15% by weight of the
composition.
The antioxidants, extreme pressure additives, or antiwear agents are
preferably polyfunctional zinc dihydrocarbyl dithiophosphates having an
alkyl or aryl group having 3 to 18 carbon atoms. The additives are added
in an amount of 0.1 to 3% by weight of the composition. Phenolic or orango
sulfur compounds well-known in this field are often used as antioxidants.
The lubricating oil composition according to the invention may further
comprise, in a so-called multigrade oil, viscosity index improvers such as
polyalkylmethacrylates, ethylene-propylene copolymers, styrene-butadiene
copolymers, and the like. As a matter of course, active viscosity index
improvers which are obtained by imparting dispersability to viscosity
index improvers may also be used.
Aside from the additives described above, the lubricating oil composition
of the invention may still further comprise other additives which are
generally used such as anti-wear agents, antirust agents, corrosion
inhibitors, metal deactivators, antifoam agents, and the lile. These
additives are used within ranges of amounts ordinarily employed for these
purposes.
The boric esters compounded in the lubricating oil composition of the
invention show their effect when added in an amount exceeding about 0.05%.
Larger dosage, lead to an increasing effect with an attendant rise of
cost. Accordingly, the dosage should be determined taking into account the
balance between the saving of fuel and the cost. In general, the esters
are used in an amount of 0.05 to 5 wt%, preferably 0.2 to 1.5 wt%.
Preparatory examples of boric esters and examples of the invention are
described hereinbelow.
PREPARATORY EXAMPLE 1
35.4 g (0.57 mol) of boric acid was charged into a mixture of 200 g (0.57
mol) of commercially available glycerol monooleate and 52.6 g (0.57 mol)
of glycerol, followed by reaction at a temperature of 210.degree. to
220.degree. C. while blowing nitrogen gas thereinto. 26.5 g of the water
produced by the reaction was removed from the reaction system. As a
result, a milky white paste product having an acid value of 124 was
obtained. The analysis revealed that the product had a composition of a
mixture of boric esters of the general formulas (I) and (II), a small
amount of oleic acid glyceride, and a very small amount of glycerol. A
major proportion of the composition was found to be boric esters of the
general formulas (I) and (II) in which one of X, Y, and Z was RCO.sub.2
group (oleic acid residue) and the other two substituents were both a
hydroxyl group.
PREPARATORY EXAMPLE 2
15.5 g (0.25 mol) of boric acid was charged into 46 g (0.5 mol) of
glycerol, followed by reaction at a temperature of 200.degree. to
210.degree. C. while blowing nitrogen gas thereinto and removing 13 g of
produced water. To the reaction product was added 69.1 g (0.25 mol) of
commercially available oleic acid, followed by reaction in a stream of
nitrogen gas at a temperature of 210.degree. to 220.degree. C. for 3 hours
and then removing 4.5 g of produced water. As a result, a light brown,
transparent, liquid product having an acid value of 129 was obtained. The
analysis revealed that the product had a composition comprising a mixture,
based on the rough molar ratio, of about 50% of boric esters of the
general formulas (I) and (II) in wich one of X, Y, and Z is an RCO.sub.2
group and the other two are independently hydroxy group, about 25% of
boric esters of the formulas in which two of X, Y, and Z are independently
RCO.sub.2 groups, and the other is a hydroxyl group, about 25% of boric
esters of the formulas in which X, Y and Z are all hydroxy groups and a
small amount of boric esters of the formulas in which X, Y, and Z are all
RCO.sub.2 groups.
PREPARATORY EXAMPLE 3
20.1 g (0.32 mol) of boric acid was charged into a mixture of 97 g (0.11
mol) of rape seed oil (iodine value=120) and 50 g (0.54 mol) of glycerol,
followed by reaction at a temperature of 255.degree. to 265.degree. C. for
5 hours while blowing nitrogen gas thereinto and removing 17.5 g of
produced water from the system. As a result, there was obtained a yellow,
transparent, liquid product having an acid value of 126.
The analysis revealed that the product had the fatty acid residue derived
from the rape seed oil and had a composition similar to the product of
Preparatory Example 2.
PREPARATORY EXAMPLE 4
24.1 g (0.39 mol) of boric acid was charged into a mixture of 116.4 g (0.13
mol) of lightly hydrogenated rape seed oil (iodine value=77) and 60 g
(0.65 mol) of glycerol, followed by reaction at a temperature of
255.degree. to 265.degree. C. for 5 hours while blowing nitrogen gas
thereinto and removing 23 g of produced water. As a result, there was
obtained a light yellow paste product having an acid value of 129. The
analysis revealed that the product had the fatty acid residue derived from
the lightly hydrogenated rape seed oil whose saturation was relatively
high, and had a composition similar to the product of Preparatory Example
2.
COMPARATIVE PREPARATORY EXAMPLE 1
19.5 g (0.32 mol) of boric acid and 70 g of commercially available
n-butanol were charged into 135 g (0.32 mol) of a commercially available
mixture of sorbitan monooleate and sorbitan dioleate, followed by
azeotropically removing produced water under reflux. Thereafter, the
xylene was removed by distillation under reduced pressure, thereby
obtaining a light brown liquid product.
COMPARATIVE PREPARATORY EXAMPLE 2
32.3 g (0.52 mol) or boric acid and 100 g of commercially available
n-butanol were charged into 135 g (0.32 mol) of a commercially available
mixture of sorbitan monooleate and sorbitan dioleate, followed by treating
in the same manner as in Comparative Preparatory Example 1, thereby
obtaining a light brown liquid product.
COMPARATIVE PREPARATORY EXAMPLE 3
150 g (0.43 mol) of commercially sold glycerol monooleate and 26.5 g (0.43
mol) or boric acid were charged and reacted at a temperature of
170.degree. to 180.degree. C. while blowing nitrogen gas thereinto and
removing of 18.6 g of produced water, thereby obtaining a milky white
paste product having an acid value of 154.
Lubricating oil compositions admixed with various additives were prepared
and subjected to a number of tests. This is particularly described in the
following examples.
COMPARATIVE PREPARATORY EXAMPLE 4
250 g (0.70 mol) of commercial glycerol monooleate and 22.1 g (0.35 mol) of
boric acid were charged and reacted at a temperature of 200.degree. to
210.degree. C. while belowing nitrogen gas thereinto and 18.6 g of water
was removed. A milky white paste product having an acid value of 85 was
obtained.
EXAMPLE 1
A lubricating base line oil having the following composition (hereinafter
referred to as base line) was prepared, to which boric esters of the
present invention or other additives were added to give lubricating oil
compositions. Coefficients of friction on these compositions were
measured.
Base Line
Mineral oil: 87 (%)
Alkenyl succinimide: 6
Over based phenate and sulfonate: 2
Zinc dialkyldithiophosphate: 1
Viscosity index improver: 4 (%)
Apparatus: Soda pendulum tester
The test results are shown in Table 1.
TABLE 1
______________________________________
Coefficient of Friction
Dosage Temp.
Tested Additives
(wt %) 60.degree. C.
90.degree. C.
120.degree. C.
150.degree. C.
______________________________________
-- 0 0.142 0.139 0.134 0.127
(base line)
Preparatory Ex. 1
0.5 0.123 0.122 0.120 0.117
Preparatory Ex. 2
0.5 0.125 0.123 0.120 0.119
Preparatory Ex. 3
0.25 0.129 0.127 0.126 0.124
0.5 0.125 0.121 0.119 0.117
1.0 0.118 0.118 0.116 0.116
Preparatory Ex. 4
0.5 0.123 0.123 0.121 0.114
Com. Prep. Ex. 1
0.5 0.132 0.132 0.129 0.125
Com. Prep. Ex. 3
0.5 0.128 0.125 0.127 0.123
Commercially
-- 0.140 0.140 0.135 0.131
available product
______________________________________
As is shown in Table 1, the lubricating oil compositions of the present
invention which comprise the boric esters have lower friction
coefficients, from which it will become apparent that the boric esters
show an excellent effect as friction-reducing agent.
EXAMPLE 2
As an easy method of measuring the friction reduction performance in actual
engines there was effected a motoring engine test by which torques of the
lubricating oil compositions were measured.
A torque of a lubricating oil composition was measured by a torque meter
which was connected, through a torque converter, to a rotary shaft of a
gasoline engine (4 cylinders, 1968 ml) made in Japan and rotated at a
given number of revolutions by electric power. A lubricating oil being
tested was charged as usual and an oil temperature was maintained at a
constant level on measurement of the torque.
A base line of the same as in Example 1 was used, and the base line was
admixed with additives being tested to obtain lubricating oil
compositions. The base line and the lubricating oil compositions were each
subjected to the torque measurement according to the above-described
method. The friction reduction effect was determined as a torque reduction
rate relative to a torque of the base oil. The torque reduction rate (%)
is calculated according to the following equation.
##EQU1##
In order to prevent carry-over effect, the apparatus was sufficiently
washed after each test and reference test of the base line was conducted
alternatively among series of the test in order to carefully obtain the
data. The rest results are shown in Table 2.
TABLE 2
______________________________________
Torque Reduction Rate Based on
Dos- Base Line (%)
age Number of Revolutions of Engine
Tested (wt 500 1000 1500 2000 2500
Additives %) rpm rpm rpm rpm rpm
______________________________________
-- 0 0 0 0 0 0
(base
line)
Preparatory
0.5 18.7 3.8 1.4 2.0 1.8
Example 1
Preparatory
0.5 16.8 10.8 5.2 3.9 4.0
Example 2
Preparatory
0.5 21.5 12.2 6.6 5.1 4.8
Example 3
Preparatory
0.5 16.8 9.7 4.9 3.3 1.4
Example 4
Commercially
0 -1.7 -2.0 -1.5 -1.8 -1.7
available
product
Comparative
0.5 9.8 7.7 5.6 4.9 4.5
Preparatory
Example 1
Comparative
0.5 16.4 10.4 4.7 3.5 1.9
Preparatory
Example 3
______________________________________
From the results of Table 2, it will be seen that the lubricating oil
compositions of the present invention comprising the boric esters show the
remarkable torque reduction effect. The greater effect of the additives is
produced at the smaller number of revolutions. This is considered as
follows: boundary lubrication takes place more frequently at low speeds
than at high speeds, so that the friction reduction effect becomes more
pronounced at low speeds.
The test results give evidence that the boric ester-containing lubricating
compositions of the present invention have the remarkable function as a
friction-reducing agent.
EXAMPLE 3
In order to prove a fuel-saving effect in an actual engine, a bench test of
an engine was effected at a given level of load while keeping a constant
cooling water outlet temperature, oil temperature, oil pressure, fuel
temperature, fuel feed pressure, air inlet temperature and the like in
order to determine a fuel consumption. The engine used was made in U.S.A.
and had a displacement of 5.7 liters.
As described in Example 2, the test was carefully conducted so that no
influence of an oil being tested in a preceding test was carried over a
subsequent test and a test of a base oil was inserted between series of
the test. Average values of fuel consumptions from repeated data were
calculated. The base line was the same as used in Examples 1 and 2. The
test results are shown in Table 3.
TABLE 3
______________________________________
Saving rate of fuel
Tested Additives
Dosage (wt %)
consumption* (%)
______________________________________
-- 0 (base line)
0
Preparatory Ex. 2
0.5 3.4
Preparatory Ex. 3
0.5 3.1
______________________________________
<Note>
*Average values of 4 measurements
As is apparent from the results of Table 3, the lubricating compositions of
the invention comprising the ester mixtures show a remarkable fuel-saving
effect when applied to the actual engine.
EXAMPLE 4
It is sometimes experienced that when friction-reducing agents showing a
remarkable friction reduction effect are contained in lubricating
compositions, they act to corrode bearings of internal combustion engines
to such an extent as not to be tolerable, thus being not practicable. In
order to check the corrosiveness, the CRC L-38 engine test well-known in
this field as one of standard engine test was conducted. The test results
are shown in Table 4.
TABLE 4
______________________________________
Weight loss of bearings*
Tested Additives
Dosage (wt %)
(mg)
______________________________________
0 (base line)
31.2
Preparatory Ex. 2
0.5 24.5
Preparatory Ex. 3
0.5 23.0
Preparatory Ex. 4
0.5 44.7
Commercially
0.5 45.8
available
diethanolamine
oleic acid amide
Commercially
0.5 86.2
available
glycerol
monooleate
______________________________________
Test time: 40 hours
Base line: Same as indicated in Table 1 of Example 1.
*: The pass limit is below 40 mg.
As can be seen from the results of Table 4, the lubricating compositions of
the present invention comprising the boric ester additives result in a
smaller weight loss of the bearings than the base line. It was found that
little or no corrosion took place on the bearings but a
corrosion-inhibiting characteristic appeared.
On the other hand, the lubricating compositions which were admixed with the
commercially available diethanolamine oleic acid amide or the commercially
available glycerol monooleate in the same amount as in the present
invention did not pass the test, i.e. these additives apparently acted to
corrode the bearings.
Further, lubricating oil composition formulated with the boric esters
obtained in Comparative Preparatory Example 4 did not pass the test and
showed corrosiveness.
EXAMPLE 5
Storage Stability Test
About 20 g of each of the products obtained in the preparatory examples and
the comparative preparatory examples was charged into a 50 ml beaker
(after melting when a paste product was used) and was allowed to stand at
room temperature for 4 hours in the exposed state. With the products of
Preparatory Examples 1 through 4, no charge was observed but with the
products of Comparative Examples 1, 2 and 3, a solid film was formed on
the surface. Especially, the solid film was thicker in the case of the
product of Comparative Preparatory Example 2 than in the case of
Comparative Preparatory Example 1. The solid film was immersed in a 100
neutral base oil but did not dissolve therein.
Comparative Examples 1 and 2 are based on the method disclosed in Japanese
Lain-open Application (Japan kokai) No. 56-141398. The above results
demonstrate that the ester mixtures of the present invention are more
excellent in storage stability.
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