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Description  |
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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 undesired 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 containing
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 Pat.
No. 2,493,335. Various polyphenyl ethers, natural and synthetic
hydrocarbons, esters, polyglycols, fluorinated materials, silicones, and
proprietary formulations were reported as being tested as lubricants for
separable connectors in Electr. Contacts, Proc. Annu. Holm Semin. 1976,
22, 57-63.
SUMMARY OF THE PRESENT INVENTION
The present invention relates to an electrical contact lubricant and its
use to lubricate electrical contacts. The lubricant of the present
invention contains a predominant amount of a partially cross-linked polyol
ester in combination with a small amount of a triaryl phosphate fluid.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
The major component of the present lubricant is a partially crosslinked
polyol ester which is the esterification 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 branched
monocarboxylic acids can also be used, particularly those with no more
than two carbon atoms in side chains.
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 employed as crosslinking agents in order to increase (or 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, neopentyl
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
definition 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 as tricresyl phosphate. It is present at from about 0.1%-5%,
preferably 1-3%, by weight of the composition. 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
##STR1##
where R can be hydrogen or alkyl, R' can be hydrogen or alkyl, and R" can
be hydrogen, phenyl, naphthyl, aminophenyl or alkyl substituted phenyl.
The size of the alkyl moiety can range from 1 to about 8-10.
Representative compounds include N,N'-dioctyldiphenylamine,
4-octyl-N-(4-octylphenyl)benzenamine, and 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.
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 105.degree. C. 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.mu.) into the final containers.
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Parts By Approx. %
Ingredient Weight By Weight
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Pentaerythritol ester of C.sub.7 acid
3839.2 95.98
crosslinked with azelaic acid
(BASE STOCK 810 from Stauffer
Chemical Company)
Natural cresylic acid based tri-
80.0 2.0
cresyl phosphate (SYN-O-AD 8484
from Stauffer Chemical Company)
Benzotriazole corrosion inhibitor
0.80 0.02
4-octyl-N--(4-octylphenyl)benzen-
40.0 1.0
amine oxidation inhibitor
(VANLUBE 81 brand from R. T.
Vanderbilt and Co.)
Phenyl-alpha-naphthylamine
40.0 1.0
corrosion inhibitor
Silicone antifoam (SWS 101 brand
10 parts by weight
from SWS Silicones) per million based
on entire composition.
______________________________________
The composition described above had the following physical properties:
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Properties Value
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Viscosity (in cs)
at 210.degree. F. (98.9.degree. C.)
11.34
at 100.degree. F. (37.8.degree. C.)
76.66
at 0.degree. F. (-17.8.degree. C.)
3692.2
Pour Point (.degree.F.) -34.
(.degree.C.) -36.7
Evaporation Rate (% Loss) at 300.degree. F.
0.4
(148.9.degree. C.) - 22 hours
Acid number (mg KOH/gm) 0.09
Auto Ignition temp.
(.degree.F.) 865.
(.degree.C.) 462.8
Flash Point (.degree.F.) 545.
(.degree.C.) 285.
Fire Point (.degree.F.) 615.
(.degree.C.) 323.9
______________________________________
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
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72 Hr. 48 Hr.
(174.degree. C.) 347.degree. F.
(218.3.degree. C.) 425.degree. F.
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100.degree. F. (37.8.degree. C.) Viscosity
3.4 13.5
Increase, %
.DELTA. TAN 0.24 1.71
Metal Corrosion, mg/cm.sup.2
Magnesium -0.05 -0.24
Steel -0.05 +0.10
Aluminum +0.01 +0.05
Silver 0 +0.08
Copper +0.10 0
% Insolubles NIL 1.0
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Volatility
______________________________________
Test Method: ASTM D972
Duration: 6.5 Hours
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Temperature, .degree.F.
% Loss
______________________________________
300 (148.9.degree. C.)
0.09
350 (176.7.degree. C.)
0.34
400 (204.4.degree. C.)
1.1
______________________________________
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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