Note: Descriptions are shown in the official language in which they were submitted.
17 MY 2870
This invention relates to corona-resistant
resins and films and to electrical insulation systems
wherein such corona-resistant resins and films are
used.
Resin compositions are generally understood
to be relatively low molecular weight materials
that, on heating or addition of hardener, are converted
to high-molecular weight solids having useful properties.
These materials are known as thermosetting materials,
Another general class of polymeric (that is, plastic)
materials is understood to be thermoplastic. These
thermoplastic materials are generally handled in their
high-molecular weight state. Thermoplastic materials
exhibit good solutility in solvents, while cured
thermosetting resins are insoluble. Many thermoplastic
materials also soften but do not flow when heated.
Both cured thermosetting resins and thermoplastic films
are employed as dielectric materials, Accordingly,
as used herein and in the appended claims the term
polymeric material refers to both thermosetting resins
and to thermoplastic films.
However, dielectric materials used as insulators
for electrical conductors may fail as a result of
corona occurring when the conductors and dielectrics are
3L 16~7
17MY-2870
subjected to voltages above the corona starting
voltage. This type of failure may occur for example in
certain electric motor applications. Corona induced
failure is particularly likely when the insulator material
is a solid organic polymer. Improved dielectric materials
having resistance to corona discharge~induced deteriora-
tion would therefore be highly desirable. For some
applications, mica-based insulation systems have been
used as a solution to the problem, whereby corona resistance
is offered by the mica. Because of the poor physical
properties inherent in mica, however, this solution has
been less than ideal.
Solid, corona-resistant dielectric materials are
particularly needed for high-voltage apparatus having
open spaces in which corona discharges can occur. This
is especially true when the space is over approximately
1 mil in thickness and is located between the conductor
and the dielectric, or when there is a void located in
the dielectric material itself. The service life of the
dielectric is much shorter when these gaps or spaces are
present.
Resins containing a minor amount of organo-
metallic compound of either silicon, germanium, tin, lead,
phosphorus, arsenic, antimony, bismuth, iron, ruthenium or
nickel are disclosed by McKeown (U. S. Patent 3,577,346) as
having improved corona resistance. Corona lives of up to
four hundred times that of polymers without the organometallic
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17MY-2870
additive are disclosed. There is no mention, however,
of the use of organosilicates or organoaluminates.
A composition having anti-corona properties is
disclosed, by DiGiulio et al, in U. S. Patent 3,228,883,
to consist of a mixture of ethylene-alpha-oleEin copolymer,
a homo- or copolymer covulcanizable therewith and a non-
hygroscopic mineral filler, such as zinc, iron, aluminum
or silicon oxide. However, there is no appreciation
whatsoever in this patent that the use of submicron-sized
alumina or silica particles is necessary to achieve
significant improvement in corona resistance. See tables
below.
A molded epoxy resin composition which contains
alumina and silica is disclosed by Linson, in U. S. Patent
3,645,899, as having good weathering and erosion resistance,
but appears to have no particular resistance to corona
breakdown.
Epoxy resins containing significant amounts of
reactive organosiloxane derivatives are disclosed by
Markovitz in U. S. Patents 3,496,139 and 3,519~670.
However, these materials are less than ideal since their
high reactivity results in a diminished shelf-life, a
characteristic often of considerable importance. Moreover,
the amine silicones in the 3,496,139 patent are polysiloxanes
which are made from difunctional and trifunctional silicones,
that is, the silicon atoms have either two Si-O bonds and
two Si-C bonds, or three Si-O bonds and a single Si-C bond.
This is in distinct contrast to the present invention which,
as seen below, employs silicates and aluminates, both of
which exhibit tetrafunctional bonding with oxygen atoms.
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17MY-2870
Epoxy resins containing metal acetylacetonates
in amounts below 5% by weight are disclosed in U. S.
Patent 3,812,214, but these resins have no corona-resistant
properties.
Polymeric resins containing silica and talc as
fillers appear to be disclosed in U. S. Patent 3,7A2,084
issued June 26, 1973 to Olyphant et al. However, there is
no appreciation that submicron particle sizes are critical
for improved corona resistance when silica is employed.
Likewise, resins containing submicron silicon
appear to be disclosed in U. S. Patent 4,102,851 issued
July 25, 1978 to Luck et al. ~owever, silica is added only
as a thixotropic agent and there is no appreciation or
concern with corona-resistant properties.
Polyethylene resin with various fillers, including
alumina and silica, appears to be disclosed in U. S. Patent
2,888,424 issued May 26, 1959 to Precopio et al. But again,
there is no concern or appreciation of corona-resistant
properties; the fillers, including such counterproductive
materials for corona properties as carbon black, are added
only to improve mechanical properties.
Resins containing submicron silica also appear to
be disclosed in U. S. Patent 3r697,467 issued October 10,
1972 to Haughney. Like the patent to Luck et al., however,
this patent discloses no appreciation or concern for corona-
resistant properties.
Thus, there is a continuing need for corona-
resistant materials which are easily fabricated for use
as electrical insulation and a further need for additives
which can convert dielectric materials susceptible to
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corona damage to corona-resistant materials. Accordingly,
it is the principal object o~ the present invention to
provide a corona-resistant resin, useful in various
electrical insulation forms to satisfy these long-felt
needs.
Summary of the Invention
The present invention provides a corona-resistant
resin composition containing a polymeric material and an
additive thereto of approximately 5~ to approximately ~0%
by weight of either an organosilicate or organoaluminate
compound, or submicron-sized particles of either alumina or
silica. The additives are characterized by the common
inclusion of either aluminum or silicon and, preferably, in
that the aluminum and silicon are atomically bound only
with oxygen. Either conventional or epoxy resins may be
used in the invention, with, in the case of epoxy resins,
the organo compounds serving also as reactive curing agents.
Likewise, the polymeric material also includes thermo-
plastic film. Compositions containing the organoaluminate
or organosilicate compounds are homogeneous, solution-type
compositions whereas those containing silica or alumina
particles are formed with the particles substantially
uniformly disposed throughout the resin. The silica and
alumina particles are preferably less than about 0.1 micron
in size. Similarly, a method of providing corona-resistant
insulation for an e-ectrical conductor employs the above-
mentioned composition.
In accordance with this invention, the corona-
resistant resin can be used to coat conductors or conductor
wires or to impregnate laminated electrical insulating, thus
1 ~68~r~
17MY-2870
providing superior electrical insulating systems.
Brief Description of the Drawing
The drawing is a schematic representation of the
needle point corona test apparatus used to evaluate resin
compositions formulated according both to the presenk
invention and to conventional resin compositions so that
corona resistance can be assessed and compared.
Detailed Description of the Invention
Resins useful for the practice of this invention
include, for example, epoxy resins, polyester resins, and
ester-imide resins. Epoxy resins formulated according to
the invention require a curing agent as is the usual case
with such resins. Useful thermoplastic films for the
present invention include both polyamide films and polyimide
films, such as Kapton(R). These films are used in their
high-molecular weight state and do not require curing.
Typical of epoxy resins which can be used are
resins based on bisphenol-A diglycidyl ether, epoxy novolac
resins, cycloaliphatic epoxy resins, diglycidyl ester resins,
glycidyl ethers of polyphenols and the like. These resins
preferably have an epoxy equivalent weight of the order of
130-1500. Such resins are well known in the art and are
described, for example, in many patents including 2,324,483;
2,444,333; 2,494,295; 2,500,600; and 2,511,913.
Catalytic hardeners, or curing agents, for the
epoxy type resins, include aluminum acetylacetonate, aluminum
di-sec-butoxide acetoacetic ester chelate or tetraoctylene
glycol titanate in combination with phenolic accelerators,
including resorcinol, catechol or hydroquinone and the
corresponding dihydroxynaphthalene compounds. Compositions
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of this type have been described in 3,776,978 and 3,812,214.
In the present invention, the organoaluminate catalysts can
also serve as the reactive organoaluminum compound, but they
are used in much higher amounts khan heretofore disclosed in
order to produce the corona-resistant product.
Also useful as curing agents for epoxy resins in
the practice of this invention are polyester-polyacid resins,
especially those with an acid number of 200-500. Those
preferred have an acid number of 300-400.
Ester-imide resins useful in the practice of
this invention include those used to coat magnet wire.
Examples of compositions which may be used are disclosed
in U. S. Patents 3,426,098 and 3,697,471.
Organosilicate and organoaluminate compounds
which can be used for the purposes of this invention
include those compounds which are reactive toward epoxy
groups of epoxy resins. The silicate and aluminate compounds
are further characterized by containing only silicon-to-
oxygen or aluminum-to-oxygen primary valence bonds. These
compounds react to produce clear, hard resins containing
Si-O or Al-O bonds throughout the body of the resin according
to the structural formulas:
l 1
O-Si-O -O-Al-O-
Typical of compounds which are useful for this purpose
are the products of ethyl silicate (or any alkyl silicate)
with ethanolamine or other alkanolamines, whereby an amino-
functional organosilicate compound is produced. Organo-
aluminate compounds which can be used are aluminum
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17MY-2870
acetylacetonate, aluminum di-sec-butoxide acetoacetic
ester chelate, aluminum di-iso-propoxide acetoacetic ester
chelate, aluminum iso-propoxide stearate acetoacetic ester
chelate, aluminum tri-iso-propoxide or aluminum tri(sec-
butoxide).
In the above-mentioned patent (3,496,139) issued
to the present inventor, polysi:Loxanes are used in preparing
the curing agents for the epoxy resins. However, in the
present invention organosilicates are employed. Polysiloxanes
are not organosilicates in which the silicon atoms exhibit
only Si-O bonds. That ls to say, the organosilicates of the
present invention are made from tetrafunctional silicones.
The epoxy resins cured by organosilicates are more strongly
cross-linked than epoxy resins cured from polysiloxanes and
therefore are better suited as corona-resistant compositions.
The organosilicate or organoaluminate can be used
as the sole curing agent for the epoxy resin or can be used
in combination with other known, typically used curing agents.
Eor example, the phenolic accelerators, such as catechol,
are necessary to properly cure epoxy resins when aluminum
acetylacetonate is employed as an additive/hardener.
Epoxy resins preferred in the present invention,
include those cured by an organosilicate which is the
reaction product of ethyl silicate and ethanolamine and
those cured by an organoaluminate which is either aluminum
acetylacetonate or aluminum di-sec-butoxide acetoacetic
ester chelate and accelerated by a phenolic such as catechol.
Preferred polyester-imide resins include those modified by
aluminum acetylacetonate.
In one embodiment of this invention, the
11688S ~ 17~.1Y 2870
corona-resistant composition comprises a conventional
epoxy, or ester imide resin or other resin wherein there
is dispersed alumina or silica particles of size less than
about 0.1 micron. In this embodiment, the epoxy composition
requires a curing agent specifically to set the resin. The
curing system can be of any of the usual polyamines, polyacids,
acid anhydrides, or catalytic curing agents commonly used
to cure epoxy resins; or a phenolic such as resorcinol or
catechol can be used as an accelerator with a catalytic
hardener selected from reactive organoaluminum, organo-
titanium, or organozirconium compound, of which tetraoctylene
glycol titanate is typical as described in 3,776,978 and
3,812,214.
Preferably, the alumina or silica has a particle
size of from approximately 0.005 to approximately 0.05
micron, as may be obtained either by the gas phase hydrolysis
of the corresponding chloride or other halide, or as may be
obtained by precipitation. These oxides, when disposed
within the polymer material, form chain-like particle
networks. Those oxide particles useful in the present
invention and formed from the gas phase are also known as
fumed oxides. Typical of commerically available fumed oxides
are those manufactured and sold by the Cabot Corporation
under the trade marks Cabosil(R) (silica) or Alon(R) (alumina);
or those made and sold by Degussa, Inc., under the trade
marks Aerosil(~) (silica) or Aluminum Oxide C(R) . Typical
precipitated silicas which may be used include those
manufactured and sold by the Philadelphia Quartz Co., under the
trade mark Quso(R) or those of PPG Industries sold under the
trade mark Lo-Vel(R) .
17MY-2870
From approxlmately 5% to approximately 40~
by weight of organosilicate, organoaluminate, submicron
silica or submicron alumina are used in the resin compositions
of this invention, while loadings of 5% to approximately 30%
by weight are preferred.
Preferred compounds of the organoaluminate and
organosilicates are those which are soluble and which contain
only Si-O or Al-O primary valence bonds on the silicon or
the aluminum as was mentioned ahove. The use of these
compounds produces clear resins, in which organoaluminate
or organosilicate compounds are dissolved, and thus homo-
geneous with the resin.
As can be seen from the tables below the use of
submicron particles is critical for the use of alumina and
silica additives. Table I shows that polyimide films fail
after an average of only 9 hours under the test conditions
described herein and under the voltage stress shown. In
stark contrast, the use of 20% dispersed alumina having an
average particle size of approximately 0.020 microns
produces average sample life in excess of 2776 hours. The
use of 40% finely ground alumina having a particle size in
excess of one micron produced better results than no
additive but significantly worse results than the submicron
sample.
TAsLE I
Stress Hours to Fail Aver-
Sample Volts/Mil for Various Samples age
Polyimide film 250 7, 8, 13 9
Polyimide film with 250 2187, 3071-~, 3071+ 2776
20% alumina of 0.020
micron size
Polyimide film with 208 78, 130, 513, 310 258
40% alumina of greater
than 1 micron size
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17MY-2870
The ~1+11 sign in the tables indicates that the sample had
still not failed at the time the data was taken.
Similar results are obtained with the use of a
polyamide film with submicron alumina. These are summariæed
5in Table II below:
TA~LE IX
Stress Hours to Fail Aver-
Sample Volts/Mil for Various Samples age
-
Polyamide film 250 - 10
Polyamide film with 250 629+, 629-~, 629~ 629-~
20% alumina of 0.020
micron size 357 629+, 629+, 629+ 629+
The particles are disposed within the film material by con-
ventional manufacturing methods prior to transformation to
the high-molecular weight state.
Like results are obtained in the use of resins
rather than the above-described films. These results are
summarized in Tables III-A and III-B below. Except for the
first entry illustrating epoxy resin "A" with no additives,
Table III-A shows the corona test results when submicron
alumina particles are used. In stark contrast Table III-B
shows the results when the additive comprises particles
having a size greater than one micron.
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17M~-2870
TABLE III-A
Needle Point Corona Test,
Sample Hours to Failure
RangeAvera~e
Epoxy resin "A", 18-32 25
no additives
Epoxy resin "A" with 10% No failures3,900-~
fumed silica of 0.013 aftex 3,900
micron size hour '3
Epoxy resin "A" with 10% No failures
precipitated silica of after 3,9003,900+
0.014 micron size hours
Epoxy resin "A" with 10% No failures5,000+
furned alumina of 0.03 after 5,000
micron size hours
TABLE III-B*
Needle Point Corona Test,
Sample Hours to Failure
RangeAverage
Epoxy resin "Al' with 10~ 80-274 165
alumina (made from dehy-
drating Al(OH)3 gel
Epoxy resin "A" with 10~ 27-32 30
kaolin (A12O3 SiO2 2H2O)
Epoxy resin with 25% alumina 48-66 59
Epoxy resin with 31.5~116-216 166
alumina
Epoxy resin with 31.5%110-218 162
alumina
(repeat of above experi-
ment)
Epoxy resin with 25% silica 29-39 34
*All additives shown in this ta~le have particle sizes
greater than one micron.
Thus it is seen from the tables above that resins too require
the use of submicron alumina and silica particles to exhibit
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17~Y-2~70
the wholly unexpected increases in corona-resistant
properties shown.
In another aspect, this invention relates to
laminated electrical components which contain an organo-
S silicate or an organoaluminate as part of the binder
composition. For convenience, the organosilicate or
organoaluminate containing composition may be dissolved
in a solvent, e.g., methylene chloride, benzene, or methyl
ethyl ketone and used as an :impregnant for these laminate
materials, e.g., polyester mats, ceramic paper, mica
paper, glass web or the like.
In yet another aspect of the invention, a
dispersion of the submicron silica or submicron alumina
particles in resin is used to treat the laminate materials
wherein the resin acts as a binder. The laminate may be
prepared by coating a dispersion of the submicron silica
or submicron alumina in resin or solvent between layers
during the lay-up of the laminate. The laminates, after
being subjected to heat and pressure under conventional
conditions to cure the laminates, have greatly enhanced
resistance to corona-induced deterioration and improved
insulating properties.
In still another aspect, this invention relates
to a conductor or conductor wire coated with a resin, i.e.,
epoxy, ester-imide resin, or other resin containing
organoaluminate, organosilicate, submicron silica or
submicron alumina part~icles, as described above. The
coatings are applied in a conventional manner to give
products exhibiting greatly enhanced resistance to corona-
3a induced deterioration.
In using the resin compositions of this invention
to provide insulated conductors resistant to corona-induced
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8 8 ~ ~1
17MY~287Q
deterioration the conductor can be wrapped with an
insulating paper, e.g., mica paper tape, impregnated
with a resin composition of this invention.
The fo]lowing examples depict in more detail
the preparation and use of representative compositions in
accordance with the principles of this invention.
Standardized test conditions and apparatus, described as
follows, were used in all of the examples hereinafter
described.
The corona test apparatus, shown in Fig. 1,
comprises a needle electrode, a plane electrode and a
sample of dielectric material therebetween. The test
consists of applying a potential of 2500 volts A.C.
between the needle electrode and the plane electrode at
a frequency of 3000 ~ertz.
Dimensions of the samples used in the corona
lifetime evaluations were standardized at 30 mils
(7.6 x 10 2cm.) thickness. The distance between the
point of the needle and the surface of the dielectric
was 15 mils (3.8 x 10 2 cm.). Corona lifetimes wexe
determined in atmospheres of air and/or hydrogen. Test
results, where data averages and ranges are given, are
based on four to six samples of a given composition.
EXAMPLE 1
(a) Test of conventional thermoplastic resin
composition -- polyethylene terephthalate: Polyethylene
terephthalate resin film was stacked to a thickness of 30
mils and tested in the needle point electrode corona test
apparatus depicted in the Figure and described above.
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17MY-2870
The samples failed in 17-26 hours, with an average of 21
hours to failure.
(b) Test of conventional resln composition --
aromatic polyimide: Under the conditions described above,
- 5 an aromatic polyimide film tRapton(R)) failed after an
average of 41 hours.
(c) Test of conventional resin composition --
cross-linked epoxy resin: Bisphenol-A diglycidyl ether
epoxy resin with an epoxide equivalent of 875-1025 was
cross-linked by a polyester-polyacid resin having an acid
number of 340-360. A 30-mil film tested in accordance
with the above, failed after 22 hours.
EXAMPLE 2
(a) Preparation of epoxy-reactive organo-
silicate: Ethanolamine (732 grams) was added to 624
grams of ethyl silicate 40 (a polysilicate having an
average of 5 silicon atoms per molecule). The mixture,
which was originally incompatible, became a clear and
homogeneous solution upon heating. At the end of four
hours of heating at 65-185C, 471.2 grams of liquid,
which was mostly ethanol, had distilled from the reaction
mixture. The mixture was heated at 99-143C at a pressure
of 2-3 millimeters of mercury for 65 minutes to remove
unreacted ethanolamine (151 grams were collected). The
residue, a liquid amino-functional silicate, was used as
a hardener for epoxy resin compositions.
(b) Preparation and test of epoxy resin cured
by epoxy-reactive silicate: A mixture was prepared from
80 parts by weight of epoxy resin CY 183, a cycloaliphatic
~ ~88$'`~
17MY 2870
epoxy resin having an epoxide equivalen~ of 147-161,
and 20 parts by weight of amino-functional silicate
prepared in (a), above. The mixture was cured to a clear,
yellow solid. A film of the solid 30 mils in thickness was
tested in the needle point electrode test apparatus of
Example l(a). The samples failed after 437-770 hours,
with an average life to fail~lre oi 611 hours.
(c) Test of conventi~
cured with N-aminoethylpiperazine: The average time to
failure of an epoxy resin cured with N-aminoe~hylpiperazine
was 17 hours, with a range of 3-23 hours,
EXAMP~E 3
(a) Test of conventional epoxide resin:
A resin was obtained from a mixture of bisphenol-A epoxy
resin, resorcinol and tetraoctylene glycol titanate as
described in U.S. Patent 3,776,978. This resin, at a thickness
of 30 mils, failed after an average of 25 hours on the needle
point electrode test; the range to failure was 18-32 hours.
(b) Preparation and test of epoxide resin and
submicron silica filler: A composition was prepared from
90 parts by weight of resin prepared in (a),above, and
lO.0 parts by weight of fumed silica (Cabosil(R) M 5,
Cabot Corporation) having a particle size of about 0.013
micron. The resin cured without settling of the silica,
that is, the cured resin had the submicron silica uniformly
dispersed therethrough. Samples tested in the needle point
electrode apparatus had not failed after more than 3900 hours.
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17MY-2870
(c) Preparation and test of epoxide resin
and submicron silica filler: A composition obtained
from 90.0 parts by weight of resin obtained in (a),
above, and 10.0 parts by weight of microfine precipitated
silica (Quso(R)G32, Philadelphia Quartz Co.), having a
particle size of 0.014 micron, cured to a product which
contained finely dispersed silica through the body of the
resin. This product had not failed after more than 3900
hours in the needle point corona testing apparatus.
_XAMPLE 4
(a) Test of conventional resin cured with
organoaluminate: Epoxy resins containing metal acetyl-
acetonates as epoxy resin catalytic hardeners with phenolic
accelerators were disclosed in U. S. Patent 3,812,214.
The metal acetylacetonate was limited to a maximum of
5.0~ by weight of the epoxy resin. No disclosure of
corona-resistance was made in the patent. Samples of
this material failed within 40 hours in the needle point
test due to the low metal acetylacetonate content.
(b) Preparation and test of epoxide resin
containing organoaluminate: A clear homogeneous solution
was prepared by dissolving aluminum acetylacetonate
(25.0 parts by weight) and catechol (5.0 parts by weight)
in 100.0 parts by weight of a liquid bisphenol-A epoxy
resin having an epoxy equivalent weight of 180-188. The
mixture was cured to a clear solid in which dissolved Al-O
compounds were dispersed homogeneously. The Al content
was 1.60% by weight. Samples tested in air by the needle
point corona test failed after an average of 930 hours,
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17MY-2870
with a range of 542-1360 hours to failure. The average
lifetime increased to 245~ hours when tested in an atmos-
phere of hydrogen.
(c) Preparation and test of epox~v resin
containing organoaluminate: A clear resin was prepared
by curing a mixture of 100.0 parts by weight of a liquid
bisphenol-A epoxy resin, 29.0 parts by weight of aluminum
acetylacetonate and 5.0 parts by weight of catechol. The
cured resin contained 1.80~ of aluminum dissolved in the
resin in the form of Al-O compounds. The average time to
failure in the needle point electrode corona test was
2072 hours, with a range of 1500-3015 hours.
(d) Preparation and test of epoxy resin
containing organoaluminate: A clear resin solution was
obtained by dissolving 25.0 grams of aluminum acetyl-
acetonate and 5.0 grams of catechol in 75.0 grams of a
liquid bisphenol-A diglycidyl ether resin of epoxide
equivalent weight 180-188. The solution was cured to
a clear resin containing 1.98% of Al in the form of
dissolved Al-O compounds. None of the samples failed in
the needle point corona test after more than 1850 hours.
(e) Preparation and test of epoxy resin
containing organoaluminate: Catechol (0.5 part by weight)
and 40.0 parts by weight of aluminum di-sec-butoxide
acetoacetic ester chelate were dissolved in 99.5 parts by
weight of epoxy resin ERL 4221, a 3,4-epoxycyclohexyl-
methyl-3,4-epoxycyclohexane carboxylate epoxy resin with
an epoxide equivalent weight of 131-143. The resin was
cured to a clear solid containing 2.55% of Al in the form
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17MY-2870
of dissolved Al-O compounds. The time to failure in the
needle point electrode corona test was 1600 hours on the
average, with a range of 1152-2045 hours.
EXAMPLE 5
(a) Test of convent _ nal epoxy resin: See
Example 3(a) for preparation. The average time to failure
was 25 hours, with a range of 18-32 hours.
(b) Preparation and test of epoxy resin
containing submicron alumina: Epoxy resin obtained
according to Example 3(a) (94.0 grams) was mixed with 6.0
grams of fumed alumina (Alon( ), Cabot Corporation),
obtained by hydrolysis of aluminum chloride in a flame
process and having a particle size of about 0.03 micron.
The mixture was cured without settling of the alumina
particles. The average time to failure in the needle
point electrode corona test was 275 hours, with a range
of 169-423 hours.
(c) Preparation and test of epoxy resin
containing fumed alumina: A sample was prepared from
90.0 parts by weight of the resin of Example 3(a) and
10.0 parts by weight of fumed alumina. The alumina
particles did not settle during curing. Samples were
removed from the needle point corona test apparatus after
more than 5000 hours without failure.
EXAMPLE 6
(a) Preparation and test of laminate --
epoxy-impregnated polyester: A laminate 30 mils in thick-
ness made from 19 layers of polyester mat and the epoxy-
polyester polyacid resin described in Example l(c) was
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1 16~85~
17M~ 2870
subjected to the needle point electrode corona test.
The range of time to failure was 11-16 hours, with an
average of 14 hours.
(b) Preparation and test of laminate - epoxy
resin containing organoaluminate: The experiment of
Example 6(a) was repeated using polyester mats treated
first with a 20~ solution of aluminum acetylacetonate in
benzene, dried~ and then treated with an epoxy-polyester
polyacid resin as in (a). The samples failed after 154-~58
hours of testing, with an average of 278 hours to failure.
(c) Preparation and test of laminate - ePOxy_
impregnated ceramic paper- A laminate made by pressing
and curing three pieces of ceramic paper (nominal thickness
15 mils) impregnated with epoxy resin described in U.S.
3,812,214, failed after 168 hours, on the average, in the
corona test apparatus. This occurred althou~h the paper consisted
mainly of alumina fibers.
(d) Preparation and test of laminate - ceramic
paper impregnated with epoxy-organoaluminate modified resin:
A laminate 30 mils thick was made from 3 layers of ceramic
paper impregnated with the epoxy-aluminum acetylacetonate
resin of Example 4(d). None of the cured samples failed
after more than 1700 hours testing.
(e) Pre aration and test of laminate - ceramic
_P
paper impregnated with epoxy-fumed alumina composltion.
A laminate of ceramic paper impregnated with a mixture
of 90.0 parts by weight of epoxy-resorcinol-tetraoctylene
- 20 -
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17MY-2870
glycol titanate according to Example 3(a) and 10.0 parts
by weight of fumed alumina did not fail after more than
3800 hours in the needle point electrode corona test.
EXAMPI.E 7
(a) Preparation test of conventional wire
enamel: An ester-imide enamel, such as that described
in U. S. Patents 3,426,098 and 3,697,~71, was cast to a
thickness of 7 mils on a metal plate. A needle point
electrode was placed above the sample with a gap of 15
mils between the needle and the surface of the enamel.
The sample was tested at a stress of 2400 volts, 3000 Hz
and 105C. Failure occurred after an average of 13 hours.
(b) Preparation and test of organoaluminate-
modified enamel: Ester-imide enamel modified by dis~
solution therein of 20% of aluminum acetylacetonate based
on enamel solids (1.66% of Al based on dried solids)
coated to a thickness of 7 mils on a metal plate failed
after an average of 118 hours under the conditions
described in (a), above.
(c) Preparation and test of submicron silica
modified wire enamel: Ester imide resin modified witn sub-
micron silica exhibits the same or greater improvement
in corona resistance as in (b) above. Similar results are
obtained when submicron alumina is added to the resin.
EXAMPLE 8
(a) Preparation and test of wrapped conductor --
conventional resin: A conductor was insulated by wrapping
a resin-rich mica paper tape (resin as in Example 3(a),
above), to a total of 13 layers, around the conductor.
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17MY-2870
The insulation failed after 1870 hours of testing at
190 volts/mil~
(b) Preparation and test of wrapped conductor --
fumed alumina applied between layers: A conductor, wrapped
as in (a), above, except that a dispersion of 5.0~ by
weight of fumed alumina in methylene chloride was brushed
between the layers of tape, was tested at a stress of
199-200 volts/mil. None of the samples had failed after
5064 hours of testing.
(c) Preparation and test of wrapped conductor =-
microfine silica applied between layers: A conductor,
wrapped as in (a), above, except that a dispersion of
5.0~ by weight of microfine precipitated silica in methylene
chloride was brushed between layers of tape, was tested in
the needle point corona apparatus at 190-191 volts/mil.
None of the samples failed after 5064 hours of testing.
By these examples and results of testing as
described herein, the advantages and improvements provided
by the present invention are apparent. It will be
appreciated that a new and improved corona-resistant
insulating material has been disclosed, such material
comprising a conventional or epoxy type resin composition
formulated to include about 5% to about 40% of an organo-
aluminate or organosilicate compound or, alternatively,
to include about 5% to about 40% of microscopic particles
of either alumina or silica to form a substantially uniform
resinous dispersion.
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17MY-2870
While the invention has been clescribed in
detail herein in accord with certain preferred embodiments
thereof, many modifications and changes therein may be
effected by those skilled in the art. Accordingly, it is
intended by the appended claims to cover all such modifi-
cations and changes which fall within the true spirit and
scope of the invention.
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