Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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C-7388
METHOD OF ELECTRICAL COL~ITACT LUBRICATION
Background of the Invention
The present invention relates to an electrical
contact lubricant and to a method of lubrication using
it.
Electrical contact lubricants are specialized
products which require certain characteristics: good
metal wetting properties; good electrical properties;
an acceptable degree of high temperature oxidative
stability; good corrosion resistance; and lack of un-
desired reactivity in regard to materials adjacent to
the electric contact assembly itself. various types
of lubricants have been suggested for such end use
applications.
A lubricant for electric contacts comprising a
high-stability perfluorinated polyether and an originally
wax-like fraction of a perfluorinated hydrocarbon is
described in Proc. Int. Conf. Electr. Contact Phenom.,
10th, 1980, 1, 475-488. Japanese Tokkyo Koko 81/23,480
describes a lubricating grease for electrical contacts
containing pure mineral oil, a lithium soap, and
magnesium hydroxide. Japanese Kokai Tokkyo Koko
81/82,894 advocates a siloxane based lubricant contain-
ing smaller amounts of powdered silicon dioxide, an
aliphatic aluminum salt, and a sulfur-containing
lubricity improver. A lubricant composition formed by
blending dicarboxylic esters, e.g., bis(2-ethylhexyl)
adipate, with derivatives of pyrazolidone and/or
triazoles is suggested in French Patent No. 2,493,335.
Various polyphenyl ethers, natural and synthetic
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~ydxocarbons, esters, polyglycols, fluorinated materi~ls,
silicones, and proprietary formulations were reported as
being tested as lubricants for separable cOnnectQrS in Electr.
Contacts, Proc. Annu. Hol~ Semin. 1976, 22, 57 - 63,
Summary of the Present Invention
The present invention relates to a method for the
lubrication of electric contacts which comprises adding
thereto a lubricant which comprises a predominant amount of
a partially crosslinked polyol ester, which is the esterifi-
cation reaction product of an aliphatic monocarboxylic acid
and an aliphatic polyol in the presence of a dibasic acid
crosslinker, a lesser amount of a phosphate ester fluid
and at least one inhibitor compound.
Detailed Description of the Present Invention
The major component of the present lubricant is a
partially crosslinked polyol ester which is the esterifica-
tion reaction product of an aliphatic monocarboxylic acid
and an aliphatic polyol in the presence of a minor amount
of a dibasic acid as a crosslinking agent.
The aliphatic monocarboxylic acids used in accordance
with this invention are compounds or mixtures of compounds
having average chain lengths of from about 4 to about 12
carbon atoms, preferably from about 5 to about 9 carbon
atoms. The individual acids can range in chain length from
about 2 to about 18 carbon atoms. Normal acids are preferred,
although branc~ed monocarboxylic acids can also be used,
partlcularly those with no more than two carbon atoms in
side chains.
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33~
In synthesizing the partially crosslinked
polyol esters, minor amounts [e.g., from about 0.1 to
about 10%, by weight of the polyol) of dibasic acids
are ~mployed as crosslinking agents in order to increase
lor build) the viscosity of the normal, uncrosslinked
polyol ester. The alkyl or aryl portion of the dibasic
acid generally ranges from about 2 to about 18 carbon
atoms, more preferably from about 4 to about 12 carbon
atoms. Particularly preferred dibasic acids include
adipic, azelaic, isophthalic, and mixtures thereof.
Also included for purposes of crosslinking are the dimer
and trimer acids and mixtures thereof.
The polyols used are those having at least two,
and preferably at least three, methylol groups on a
quaternary carbon atom. Among the polyols which can be
used are trimethylolpropane, trimethylolethane, neo-
pentyl glycol, pentaerythritol, 2-butyl-2-ethyl-1,3-
propanediol, 2,2,4-trimethyl-1,3-pentanediol, and
mixtures thereof.
Also included within the definition of polyols
are those polyols which are formed from either
condensation of two or more polyols within the defin-
ition above, provided that no more than four polyol
units are so condensed and further provided that at
least four OH groups are available.
Generally speaking, the polyol ester component
of the present lubricant will comprise a predominant
portion of the lubricant composition. Representative
amounts range from about 93~ to about 97~, by weight.
Another component of the present lubricant which
is used in much lower amount than the partially cross-
linked polyol ester is a triaryl phosphate fluid such
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as tricresyl phosphate. It is present at from about
0.1%-5%, preferably 1 -3~, by weight of the compos-
ition. It contributes to the desired degree of fluid
cleanliness when the lubricant is used by possibly
passivating such metal species as iron. It also aids
in lubricating the contacts, and it has an affinity
for metal surfaces which is also desired.
In addition to the foregoing products, the
composition advantageously also contains one or more
oxidation and corrosion inhibitors to give the final
composition the desired degree of oxidation and
corrosion inhibition. The total weight for these
ingredients can range from about 1%-3%.
Organic compounds which contain sulfur,
nitrogen, phosphorus or alkylphenols and which have
utility in inhibiting oxidation in polyol ester
lubricant fluids can be used in conjunction with the
present invention. Preferred are aromatic amine
oxidation inhibitors, particularly those of the
formula
~ NR'R"
where R can be hydrogen or alkyl, R' can be hydrGgen
or alkyl, and R" can be hydrogen, phenyl, naphthyl,
aminophenyl or alkyl substituted phenyl. The size
of the alkyl moiety can range from l to about 8-10.
Representative compounds include NrN'-dioctyldiphenyl-
amine, 4-octyl-N-(4-octylphenyl)benzenamine, and
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phenyl-alpha-naphthylamine. Representative amounts
can range from about 0.1% to about 2%.
A corrosion inhibitor for the metal forming the
electric contact (e.g., copper) can also be included
in the lubricant composition of the present invention.
Representative amounts range from about 0.005% to about
0.1% with such compounds as the dialkyl thiadiazoles,
benzotriazole, purpurxanthrene, anthrarufin, and
chrysazin being useful.
The following Examples illustrate certain
embodiments of the present invention.
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EXAMPLE 1
This Example illustrates formation of the
electrical contact lubricant composition of the
present invention.
The following ingredients were blended in the
weights given below to form the composition. The
pentaerythritol ester was charged into a blending
vessel equipped with heating and stirring devices.
This base oil was then heated with agitation as all the
preweighed additives were added. Heating and agitation
were continued until the additives were completely
dissolved about 30 minutes with a maximum temperature
of 105C. Stirring continued as the blend was allowed
to cool. Cooling under agitation was continued until
a safe handling temperature was attained. The product
was then filtered (10~) into the final containers.
Parts By Approx. %
IngredientWeight By Weight
Pentaerythritol ester of C7 acid
crosslinked with azelaic acid
(BASE STOCX 810*from Stauffer
Chemical Company) 3839.2 95.98
Natural cresylic acid based tri-
cresyl phosphate (SYN-O-AD 8484*
from Stauffer Chemical Company) 80.0 2.0
Benzotriazole corrosion inhibitor 0.80 0.02
4-octyl-N-(4-octylphenyl)benzen-
amine oxidation inhibitor
(VANLUBE 81*brand from R. T.
Vanderbilt and Co.) 40.0 1.0
Phenyl-alpha-naphthylamine
corrosion inhibitor 40.0 1.0
Silicone antifoam (SWS 101*brand 10 parts by weight
from SWS Silicones) per million based
on entire composition.
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* Trade mark
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The composition described above had the following
physical properties:
Properties Value
Viscosity (in cs) at 210F(98.9C.) 11.34
5at 100F(37.8C.) 76.66
at 0F(-17.8C.) 3692.2
Pour Point (F) - 34.
(C) - 36.7
Evaporation Rate (%Loss) at 300F.
10(148.9C) - 22 hours 0.4
Acid number (mg KOH/gm) 0 . 09
Auto Ignition temp. (F ) 486652 8
Flash Point (F.) 545.
14(C.) 285.
Fire Point (F.) 615.
(C.) 323.9
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EXAMPLE 2
Listed below are some additional physical
performance data for the composition described in
Example 1.
Oxidation - Corrosion
Federal Standard Test Method 791a, Method 5308
72 Hr. 48 Hr.
(174C)347F (218.3C)425F
100F (37.8C) Viscosity
Increase, % 3.4 13.5
~ TAN 0.24 1.71
Metal Corrosion, mg/cm~
Magnesium - 0.05 - 0.24
Steel- 0.05 + 0.10
Aluminum + 0.01 + 0.05
Silver0 + 0.08
Copper+ 0.10 0
% InsolublesNIL 1.0
Volatility
Test Method: ASTM D972
Duration: 6.5 Hours
Temperature, F % Loss
300 (148.9C) 0.09
350 (176.7C) 0.34
400 (204.4C) 1.1
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The foregoing Examples illustrate certain
embodiments of the present invention but should not
be construed in a limiting sense. The scope of
protection sought is set forth in the Claims which
follow.
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