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Description  |
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BACKGROUND OF THE INVENTION
To improve high temperature stability and to give better physical and
electrical properties over amine cured epoxy resin systems, it has been
the general practice in the epoxy technological field to use anhydride
curing agents with epoxy resins, particularly for high voltage insulation
applications. Most epoxy-anhydride formulations require
elevated-temperature cures, and for most commercial applications it is
necessary to add some material to speed the rate of cure. Consequently, a
considerable amount of effort has been devoted in recent years to develop
a perfect catalyst or accelerator for curing epoxy resins, especially
those used for high voltage coil insulation, i.e., over about 7,000 volts.
In high voltage coils, only an absolute minimum of voids can be tolerated
in the resinous insulation. Therefore, the applied resin impregnating
composition must be extremely fluid, solventless, and capable of a very
fast gel, so that resin will not easily drain from a coil during curing.
The properties desired of such a catalyst or accelerator are: it should be
inexpensive and readily available; it should gel the epoxy resin system at
times below 50 minutes and preferably below 35 minutes at about
135.degree. C. to 175.degree. C.; it should be completely soluble with the
epoxy resin-anhydride system at all temperatures; the initial viscosity of
the catalyzed resin system should be below about 350 cps. at 25.degree.
C.; the storage life of the catalyzed resin system should be over at least
80 days and preferably about 180 days at 25.degree. C., i.e., the
viscosity should remain below about 1,000 cps. during that period; it
should not adversely affect the mechanical properties of the cured resin
system; after cure, the resin system should have power factor values of
below about 30% at 150.degree. C.
Several latent catalysts have appeared on the commercial scene in recent
years. Included are quaternary ammonium halides such as
benzyltrimethyl-ammonium chloride, stannous octoate, "extra-coordinate"
siliconate salts, triethanolamine borate, triethanolamine titanate and
various other metal chelates. However, all of these materials failed to
meet all of the above described requirements and have been rejected.
Smith, in U.S. Pat. No. 3,784,583, taught the use of a quaternary organic
phosphonium salt, as a latent catalyst, for a solventless, highly fluid,
resinous, epoxy-anhydride impregnating composition. While the phosphonium
salt combined superior gel times with excellent pot life, i.e., good
latent catalytic activity, and good electrical properties, the latent
catalyst was not readily available.
Starck et al, in U.S. Pat. No. 2,801,228, used from 5 to 40 wt. % of
metallic salts of enol-keto tautomers including nickel acetylacetone, as a
curing-hardener substitute for amines and anhydrides, in epoxy resins.
Naps, in U.S. Pat. No. 2,876,208, used from 0.1 to 20 wt. % of copper
acetylacetone, as a stabilizer, in phenolic-epoxy resin systems.
Markovitz, in U.S. Pat No. 3,812,214, taught catalytic cures of relatively
viscous, epoxy resin systems, having initial viscosities of about 375 cps.
to 1,200 cps. at 25.degree. C., by using up to 20 wt. % of a combination
phenolic resin accelerator -- metal acetylacetonate catalytic hardener.
Markovitz eliminated anhydride curing agents, and substituted phenolic
resin accelerators and the use of up to 5 wt. % of metallic
acetylacetonates. The useful acetylacetonates could contain essentially
any metal anion, were readily available commercially, and were
characterized as providing a superior pot life over systems containing
anhydrides or boron trifluoride amine curing agents.
Epoxy-anhydride systems are still very useful. What is needed is an
improved epoxy resin system, which still contains anhydride curing agents,
but which will have good pot life and electrical properties. The
epoxy-anhydride system should be very fluid, i.e., initially below about
350 cps. at 25.degree. C., to ensure its usefulness as an impregnating
composition for high voltage applications, where complete coil
impregnation is critical.
SUMMARY OF THE INVENTION
It has been discovered that only selected metal acetylacetonates will
behave as latent accelerators for epoxy resins, when used in certain
weight proportions with an acid anhydride reactive with the epoxy resin.
The effective weight ratio of epoxy resin:acid anhydride:metal
acetylacetonate is 100:25 to 200:0.002 to 1.00. Preferably the resin will
consist of a low viscosity epoxy:high viscosity epoxy mixture having a
weight ratio of from about 1.0:0.0 to about 1.0:4.0.
The useful metal acetylacetonates are selected from the group consisting of
chromium (III) acetylacetonate, which is the preferred material, titanyl
(TiO) acetylacetonate, aluminum (III) acetylacetonate, manganese
(III-manganic) acetylacetonate, cobalt (II) acetylacetonate, cobalt (III)
acetylacetonate, nickel (II) acetylacetonate, vanadium (III)
acetylacetonate, zirconium (IV) acetylacetonate, sodium (I)
acetylacetonate, potassium (I) acetylacetonate and mixtures thereof. This
provides an impregnating and casting composition having an initial
viscosity of up to about 350 cps. at 25.degree. C.
Excellent storage properties at ambient temperatures have been found, i.e.,
storage lifetimes of at least 80 days up to 1,000 cps. at 25.degree. C.,
consequently, long life resin formulations employing these latent
accelerators are possible. Electrical measurements on the cured system
show very low dielectric constants and power factor values even at
temperatures up to 150.degree. C. The epoxy-anhydride compositions
utilizing these selected metal acetylacetonates are particularly useful as
compositions which can be applied to and easily impregnate electrical coil
windings used in insulated high voltage electrical motors, and generators,
particularly those having mica wrapped ground walls and multiple layers of
mica insulation. It is also a useful potting or casting compound for
transformers.
BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the invention, reference may be made to the
preferred embodiments, exemplary of the invention, shown in the
accompanying drawings, in which:
FIG. 1 is a plan view of a closed full electrical coil member having two
slot portions;
FIG. 2 is a fragmentary view in perspective, showing part of a high voltage
coil comprising a plurality of turns of conductors wound with twin
insulation and bound together with mica tape as ground insulation, covered
with a porous bonding tape; and
FIG. 3 is a graph of the viscosity of various resin formulations vs. their
storage time.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
It has been found that selected metal acetylacetonates are particularly
effective latent accelerators for the anhydride cure of epoxy coating
compositions used in impregnating and encapsulating the coils of high
voltage capability electrical devices. At concentrations of about 0.002 to
1.00 part latent accelerator per 100 parts epoxy resin, rapid gel times in
the temperature range of 125.degree. C. to 175.degree. C. are possible.
The term "latent accelerator" is taken to mean the ability of certain
selected metal acetylacetonates to speed up curing rates of
epoxy-anhydride systems at elevated temperatures (e.g. over 100.degree.
C.) while exhibiting little or no cure at room temperature, thus giving
good storage properties.
The useful metal acetylacetonates of the present invention can be
characterized by the following structural formula:
M.sup.n+ (C.sub.5 H.sub.7 O.sub.2).sub.n
where n is 1 to 4, corresponding to the ionic charge on the metallic atom.
M can be chromium (III), which is preferred, titanium oxide, aluminum
(III), manganese (III-manganic), cobalt (II), cobalt (III), nickel (II),
vanadium (III), zirconium (IV), sodium (I) and potassium (I). These
selected acetylacetonates can be used alone or in mixtures.
A great number of metal acetylacetonates are not useful in epoxy-anhydride
systems, providing either very poor power factor values, long gel times,
or very poor solubility in the resinous system. Included among the
non-useful metal acetylacetonates are cerous acetylacetonate, manganese
(II-manganous), iron (III) acetylacetonate, copper acetylacetonate, zinc
acetylacetonate, uranyl acetylacetonate, thorium acetylacetonate,
strontium acetylacetonate, lead acetylacetonate and beryllium
acetylacetonate.
At this time it is not clear why only certain of the metal acetylacetonates
are such effective latent accelerators for epoxy-anhydride impregnating
systems. In some instances, particularly with chromium acetylacetonate,
very unexpectedly, gel times of an epoxy-anhydride system will decrease
several weeks after the latent accelerator is added to the system.
It is believed that after several days a complex or adduct forms between
the anhydride and the chromium compound to open the anhydride ring,
producing a heat activated ionic species especially free to react with the
epoxy. The reason why only selected metal acetylacetonates are useful with
anhydride type systems may also be due in part to some type of metal
acetylacetonate anhydride complex or adduct formation. It is believed that
the cure mechanism is not a catalytic cure, as in the aforedescribed
Markovitz teachings, where large quantities of metal acetylacetonate can
be used with phenolic resin accelerator or alone as the sole catalyst, but
rather a type of metal acetylacetonate-epoxy or anhydride adduct
formation, followed by proton transfer from the adduct to other epoxy or
anhydride molecules.
The useful, selected metal acetylacetonates must be mixed in critical
proportions with the epoxy-anhydride system. The useful weight percent
range of ingredients, to provide a good comprise of fluidity, cure time,
storage life and electrical and mechanical properties is an epoxy:
anhydride:selected metal acetylacetonate weight ratio of 100:25 to
200:0.002 to 1.00, with a preferred weight ratio of 100:75 to 150:0.01 to
0.50. Over 1.00 part of selected metal acetylacetonate per 100 parts of
epoxy causes loss of fluidity and reduction of pot life; under 0.002 part
of selected metal acetylacetonate causes excessively long gel times for
high voltage coil applications.
One type of epoxy resin, which may be used in the invention, is obtainable
by reacting epichlorohydrin with a dihydric phenol in an alkaline medium
at about 50.degree. C., using 1 to 2 or more moles of epichlorohydrin per
mole of dihydric phenol. The heating is continued for several hours to
effect the reaction, and the product is then washed free of salt and base.
The product, instead of being a single simple compound, is generally a
complex mixture of glycidyl polyethers, but the principal product may be
represented by the chemical structural formula:
##STR1##
where n is an integer of the series 0, 1, 2, 3 . . ., and R represents the
divalent hydrocarbon radical of the dihydric phenol. Typically R is:
##STR2##
to provide a diglycidyl ether of bisphenol A type epoxide or
##STR3##
to provide a diglycidyl ether of bisphenol F type epoxide resin.
The bisphenol epoxides used in the invention have a 1,2 epoxy equivalency
greater than one. They will generally be diepoxides. By the epoxy
equivalency, reference is made to the average number of 1,2 epoxy groups,
##STR4##
contained in the average molecule of the glycidylether. Typically, epoxy
resins of bisphenol are readily available in commercial quantities and
reference may be made to The Handbook of Epoxy Resins, by Lee and Neville
for a complete description of their synthesis.
Other glycidylether resins that are useful in this invention include
polyglycidylethers of a novolac. The polyglycidylethers of a novolac
suitable for use in accordance with this invention are prepared by
reacting an epihalohydrin with phenol formaldehyde condensates. While the
bisphenol-based resins contain a maximum of two epoxy groups per molecule,
the epoxy novolacs may contain as many as seven or more epoxy groups per
molecule. In addition to phenol, alkyl-substituted phenols such as
o-cresol may be used as a starting point for the production of epoxy
novolac resins.
The product of the reaction is generally a massive oxidation resistant
aromatic compound, one example of which is represented by the chemical
structural formula:
##STR5##
wherein n is an integer of the series 0, 1, 2, 3, etc.
Although epoxy novolac resins from formaldehyde are generally preferred for
use in this invention, epoxy novolac resins from any other aldehyde such
as, for example, acetaldehyde, chloraldehyde, butylaldehyde,
fufuraldehyde, can also be used. Although the above formula shows a
completely epoxidized novolac, other epoxy novolacs which are only
partially epoxidized can be useful in this invention. An example of a
suitable epoxy novolac is 2, 2, bis[p-(2,3-epoxypropoxy)phenyl]-methane.
These resins are well known in the art and reference may be made to The
Handbook of Epoxy Resins for a complete description of their synthesis.
Other useful epoxy resins include glycidyl esters, hydantoin epoxy resins,
cycloaliphatic epoxy resins and diglycidyl ethers of aliphatic diols.
The glycidyl ester epoxy resins which can be employed in this invention are
non-glycidyl ether epoxides containing more than one 1,2 epoxy group per
molecule. They are characterized by substitution of the ester bond,
##STR6##
for the ether bond, --O--, and have the chemical structural formula:
##STR7##
where R is an organic radical substituent selected from the group
consisting of R', R'--O--R', R'--COO--R' and mixtures thereof, where R' is
selected from the group consisting of alkylene groups, having from about
1-8 carbon atoms, saturated cycloalkylene groups where the ring has 4 to 7
carbons and mixtures thereof, where n is from about 1-8.
The hydantoin epoxy resins which can be employed in this invention are
based on hydantoin, a nitrogen-containing heterocyclic ring having the
structure:
##STR8##
A wide variety of compounds can be formed by reacting the nitrogen
positions in the five membered hydantoin ring. The hydantoin ring is
readily synthesized from ketones, hydrogen, cyanide, ammonia, carbon
dioxide and water. The epoxy resins are formed through reaction of the
hydantoin with epichlorohydrin. Hydantoin rings can be linked together for
form extended resins analogous in structure to bisphenol A. Polyfunctional
resins can also be formed from these chain-extended materials by
glycidylization of the hydroxyls and the remaining nitrogens. These
heterocyclic glycidyl amine epoxy resins can be represented by the
structural formula:
##STR9##
The cycloaliphatic type epoxides employed as the resin ingredient in the
invention are selected from non-glycidyl ether epoxides containing more
than one 1,2 epoxy group per molecule. These are generally prepared by
epoxidizing unsaturated aromatic hydrocarbon compounds, such as
cyclo-olefins, using hydrogen peroxide or peracids such as peracetic acid
and perbenzoic acid. The organic peracids are generally prepared by
reacting hydrogen peroxide with either carboxylic acids, acid chlorides or
ketones to give the compound R--COOOH. These resins are well known in the
art and reference may be made to Brydson, J., Plastic Materials, 1966,
471, for their synthesis and description.
Such non-glycidyl ether cycloaliphatic epoxides are here characterized by
the absence of the ether oxygen bond, i.e. --O--, near the epoxide group,
and are selected from those which contain a ring structure as well as more
than one epoxide group in the molecule. The epoxide group may be part of
the ring structure or may be attached to the ring structure. These
epoxides may also contain ester linkages. These ester linkages are
generally not near the epoxide group and are relatively unreactive,
therefore these type materials are properly characterized as
cycloaliphatic epoxides. The term "epoxide" as herein used is equivalent
to the term "epoxy resin".
Examples of non-glycidyl ether cycloaliphatic epoxides would include
3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate (containing two
epoxide groups which are part of ring structures, and an ester linkage);
vinyl cyclohexene dioxide (containing two epoxide groups, one of which is
part of a ring structure); 3,4-epoxy-6-methylcyclohexyl
methyl-3,4-epoxy-6-methylcyclohexane carboxylate and dicyclopentadiene,
having the following respective structures:
##STR10##
A distinguishing feature of many of the non-glycidyl ether cycloaliphatic
epoxides is the location of the epoxy group(s) on a ring structure rather
than on an aliphatic side chain. Generally, the cycloaliphatic epoxide
particularly useful in this invention will have the formula selected from
the group of:
##STR11##
where S stands for a saturated ring structure, R is selected from the
group consisting of CHOCH.sub.2, O(CH.sub.2).sub.n CHOCH.sub.2 and
OC(CH.sub.3).sub.2 CHOCH.sub.2 radicals where n = 1 to 5, R' is selected
from the group consisting of hydrogen, methyl, ethyl, propyl, butyl and
benzyl radicals and R" is selected from the group consisting of CH.sub.2
OOC, and CH.sub.2 OOC(CH.sub.2).sub.4 COO radicals.
Other useful epoxy resins include diglycidyl ethers of an aliphatic diol
having from 2 to 12 carbon atoms. These are low viscosity epoxy resins,
usually monomers. Included are diglycidyl ethers of a glycol having from 2
to 12 carbon atoms between the glycidyl ether units, i.e., 2 to 12 carbons
in the glycol unit, for example, diglycidyl ether of neopentyl glycol
(DGENPG), diglycidyl ethers of 1,4 butane diol, diglycidyl ethers of
ethylene glycol, and diglycidyl ethers of polyether glycols, such as, for
example, diglycidyl ethers of triethylene glycol and diglycidyl ethers of
tetraethylene glycol and their mixtures.
DGENPG is the preferred epoxy resin of this type. DGENPG is prepared by a
two step process. The initial step reacts neopentyl glycol and
epicholorohydrin in the presence of BF.sub.3 to produce a chlorohydrid
intermediate which is then dehydrohalogenated by sodium hydroxide or
sodium aluminate to provide:
##STR12##
The use of diglycidyl ethers of an aliphatic diol as the only epoxy resin
component provides resinous compositions having only about 15 cps. to 30
cps. initial viscosities at 25.degree. C. They are extremely useful for
very high voltage applications, i.e., about 20,000 to 30,000 volts, where
thick multiple layers of mica insulation must be impregnated.
It is preferred to use some of these diglycidyl ethers of aliphatic diols
in combination with the other epoxy resins, because the aliphatic diol
epoxides are all low viscosity materials, generally between about 5 cps.
to 60 cps. at 25.degree. C., and help to reduce the viscosity of the resin
impregnation composition. The epoxy resin system can consist of: (A) a
first epoxy resin having a low viscosity (between about 5 to about 60 cps.
at 25.degree. C.) i.e., diglycidyl ethers of aliphatic diols and (B)
another or second epoxy resin that has a high viscosity (above about 250
cps. and generally between about 250 cps. to about 20,000 cps. at
25.degree. C.) i.e., bisphenol A, bisphenol F, novolacs, glycidyl esters,
hydantoins, cycloaliphatics and their mixtures; in the weight ratio of
diglycidyl ether of an aliphatic diol low viscosity epoxy resin:second
epoxy resin having a high viscosity of from about 1.0:0.0 to about
1.0:4.0. The preferred range for most applications will be a range of low
viscosity epoxy resin:high viscosity epoxy resin of from about 1.0:0.75 to
about 1.0:1.25.
All of these epoxy resins can be characterized by reference to their epoxy
equivalent weight, which is defined as the mean molecular weight of the
particular resin divided by the mean number of epoxy radicals per
molecule. In the present invention, all of the suitable epoxy resins will
have a preferred epoxy equivalent weight of from about 100 to about 500
with a most preferred range of about 150 to about 250.
The organic, carboxylic acid anhydrides reactive with the epoxy, which are
to be used in carrying out the invention, include the conventional organic
mono- and poly-functional anhydrides. Typical of the mono-functional
anhydrides are hexahydrophthalic anhydride, 1-methylhexahydrophthalic
anhydride, tetrahydrophthalic anhydride, 1-methyltetrahydrophthalic
anhydride, phthalic anhydride, NADIC anhydride, NADIC methylanhydride,
dodecenyl succinic anhydride and the like. Poly-functional anhydrides
which may be employed include pyromellitic dianhydride, polyazelaic
polyanhydride, the reaction product of trimellitic anhydride and a glycol,
and benzophenone tetracarboxylic acid dianhydride. These organic
anhydrides may be used singly or in admixture. The total anhydride content
of the epoxy-anhydride mixture must lie within the range of from about 0.5
to about 1.5 anhydride equivalents for each epoxy equivalent.
For a number of special purposes unmodified epoxy resins may be considered
to have certain disadvantages. These disadvantages may include high cost
and too great a rigidity for specific applications. The epoxy resins may
be modified by incorporation of epoxide diluents, flexibilizers and
fillers. Effective amounts of a reactive epoxide diluent may be employed,
generally between about 10 parts to 25 parts per 100 parts of the epoxy
resins enumerated above, to further help reduce the viscosity of the mixed
system. Diluents such as, for example, phenyl glycidyl ether,
butylglycidyl ether, alkyl glycidyl ether, vinyl cyclohexanone dioxide,
endo-dicyclopentadione dioxide, octylene oxide and their mixtures, can be
used.
Epoxidized natural oil extenders, such as epoxidized linseed or soy bean
oils, octyl epoxy tallate and reactive plasticizers such as the
conventional phthalates and phosphates may also be used in small amounts,
up to about 40 parts per 100 parts of epoxy resin to provide increased
flexibility. Thixotropic agents, such as SiO.sub.2 and asbestos in gel
composition, and pigments such as TiO.sub.2 may be used as aids in
fluidizing the composition or enhancing the color tones of the cured
resins. Similarly, various inorganic particulate fillers, such as silica,
quartz, beryllium aluminum silicate, lithium aluminum silicate and
mixtures thereof, in average particle sizes of from about 10 to 300
microns, may be employed in amounts up to about 100 parts per 100 parts of
epoxy resin, to improve electrical properties of the resin formulation.
A closed full coil 10, prepared in accordance with the present invention,
for insertion into an insulated high voltage electrical machine, such as
an insulated high voltage electric motor or generator, is illustrated in
FIG. 1. The full coil would be disposed within the slots of the stator
surrounding the metal motor armature or generator rotor. The full coil
comprises an end portion comprising a tangent 12, a connecting loop 14 and
another tangent 16 with bare leads 18 extending therefrom. Slot portions
20 and 22 of the coil which sometimes are hot pressed to precure the resin
and to form them to predetermined shape and size are connected to the
tangents 12 and 16, respectively. These slot portions are connected to
other tangents 24 and 26 connected through another loop 28. In general,
generator coils are impregnated and then hot pressed prior to winding;
motor coils are generally post impregnated "in situ."
The coils are placed the slots of the stator of an electrical machine and
the end windings wrapped and tied together. The uninsulated leads are then
soldered, welded or otherwise connected to each other or to the
commutator. In the case of a motor, generally the entire motor containing
the coils will be placed in an impregnating bath containing the
impregnating resin of this invention and vacuum impregnated. Thereafter
the impregnated motor is removed from the impregnating tank, drained,
placed in an oven and heated to a temperature to cure the completely
reactive composition in the coils.
In a high voltage A.C. motor or generator, the coil member may comprise a
plurality of turns of round or rectangular metallic, electrical
conductors, each turn of the conductor consisting essentially of a copper
or aluminum strap 30 wrapped with turn insulation 31, as shown in FIG. 2.
The turn insulation 31 would be disposed between the conductor straps 30
and the mica tape 32, and would generally be prepared from a fibrous sheet
or strip impregnated with a resinous insulation.
While the turn insulation may consist solely of a coating of uncured
varnish or resin, it can also comprise a wrapping of fibrous material
treated with a cured resin. Glass fiber cloth, asbestos paper or mica
paper treated with a cured resin may be used with equally satisfactory
results. The resin applied to the turn insulations may be a phenolic
resin, an alkyd resin, a melamine resin or the like.
The turn insulation is generally not adequate to withstand the severe
voltage gradients that will be present between the conductor and ground
when the coil is installed in a high voltage A.C. motor or generator.
Therefore, ground insulation for the coil is provided by mica tape 32,
which binds the entire coil of electrical conductors together. Preferably,
a plurality of layers of composite mica tape 32, which may comprise mica
flakes 36 bound to a flexible material 34, are wrapped about the coil to
bind the electrical conductors together, with sixteen or more layers being
used for high voltage coils of generators. A bonding tape 38 , which is
porous may be wound around the mica tape bound coil. The bonding tape may
comprise a porous, open weave substrate of natural or synthetic fabric
cloth, for example, cotton, polyethylene or polyethylene terephthalate,
coated with a phenolic type resin.
The highly fluid resin of this invention is used to impregnate and coat the
bonding tape and mica tape shown. The highly fluid resin of this invention
may also be used to coat and completely impregnate a transformer having a
magnetic core and electrical windings disposed about the core.
EXAMPLE 1
A resin formulation was made containing 50 grams of a liquid diglycidyl
ether of bisphenol A epoxy resin, having an epoxy equivalent weight of 172
to 176 and a viscosity at 25.degree. C. of 4,000 to 5,550 cps. (sold
commercially by Dow Chemical Co. under the tradename DER-332), 50 grams of
neopentyl diglycidyl ether epoxy resin (diglycidyl ether of neopentyl
glycol) having an epoxy equivalent weight of 130 to 165 and a viscosity at
25.degree. C. of 6 to 8 cps. (sold commercially by Ciba Geigy Co.), 105
grams of 1-methyltetrahydrophthalic anhydride and 0.20 gram of chromium
(III) acetylacetonate as latent accelerator (to provide an epoxy
resin:acid anhydride:selected metal acetylacetonate weight ratio of
100:105:0.20).
The components were poured into a container, stirred at room temperature
and then put in a paint mixer for about five minutes. The initial
viscosity of the sample was about 80 cps. at 25.degree. C. After about
four hours, ten gram samples were poured into flat 2" diameter aluminum
dishes covered with a clock glass. Some of these samples were placed in a
150.degree. C. forced air oven and others in a 175.degree. C. forced air
oven. Each sample was inspected every 10 to 20 minutes to record the gel
time. The approximate gel time was considered to be the amount of time it
took the formulation to start to solidify.
Storage properties of the formulation were found by measuring viscosities
at 25.degree. C. in Gardner-Holdt bubble tube viscometers (ASTM
designation D154-56). Measurements were usually taken at one-week
intervals. The termination of the storage lifetime (pot-life) of these
formulations was considered to be when the viscosity reached a value of
1,000 cps. at 25.degree. C. Over about 1,000 cps. it would be difficult to
completely impregnate high voltage coils.
To evaluate the effect of the accelerators on the electrical properties of
the cured resin, 2" diameter .times. 1/8" to 1/4" thick castings were
cured in an oven using a heating cycle of 16 hours at 150.degree. C., and
60 Hz power factors (100 .times. tan .delta.) and dielectric constant
values .epsilon.' were obtained at 150.degree. C. (ASTM designatin
D150-65T). The results of these tests are recorded in TABLE 1 below.
EXAMPLE 2
A resin formulation was made using the same ingredients and amounts as
EXAMPLE 1, but the samples were left to age for 2 weeks. The tests run as
in EXAMPLE 1. The initial viscosity of the sample was about 80 cps. at
25.degree. C. The results of these tests are recorded in TABLE 1 below.
EXAMPLE 3
Resin formulations were made using the same ingredients and amounts as in
EXAMPLE 1, except that the following different metal acetylacetonates were
used (to provide, in all cases, an epoxy resin:acid anhydride:selected
metal acetylacetonate weight ratio of 100:105:0.20) - titanyl (TiO)
acetylacetonate (titanium oxyacetylacetonate); aluminum (III)
acetylacetonate, manganese (III-manganic) acetylacetonate, cobalt (II)
acetylacetonate, cobalt (III) acetylacetonate, nickel (II)
acetylacetonate, vanadium (III) acetylacetonate, zirconium (IV)
acetylacetonate, sodium (I) acetylacetonate, and potassium (I)
acetylacetonate. After about four hours, the samples were tested as in
EXAMPLE 1. The initial viscosity of all the samples was below 100 cps. at
25.degree. C. The results of the tests are recorded in TABLE 1 below.
EXAMPLE 4
A resin formulation was made using the same ingredients as EXAMPLE 1 except
that a liquid hydantoin epoxy resin having an epoxy equivalent weight of
130 to 145, and a viscosity at 25.degree. C. of about 1,500 to 2,500 cps.
(sold commercially by Ciba-Geigy Co. under the tradename ARACAST 2793) was
substituted for the bisphenol A epoxy resin. The component weight ratios
were 100:105:0.10. After about four hours the sample was tested as in
EXAMPLE 1. The initial viscosity of the sample was below 100 cps. at
25.degree. C. The results of these tests are recorded in TABLE 1 below.
EXAMPLE 5
As a comparative example, resin formulations were made using the same epoxy
and anhydride ingredients and amounts as in EXAMPLE 1, except that the
following metal acetylacetonates were used (to provide, in all cases, an
epoxy resin:acid anhdydride:metal acetylacetonate weight ratio of
100:105:0.10) - cerous acetylacetonate, manganese acetylacetonate,
magnesium acetylacetonate, copper acetylacetonate, zinc acetylacetonate,
thorium acetylacetonate, strontium acetylacetonate, lead acetylacetonate,
manganese (II-manganous) acetylacetonate (all of which had poor solubility
i.e., less than 50% by weight of each acetylacetonate would dissolve in
the resin formulation when added in the weight ratio of 0.10 part per 100
parts of epoxy resin), iron acetylacetonate, uranyl (UO.sub.2)
acetylacetonate and beryllium acetylacetonate. After about four hours, the
samples were tested as in EXAMPLE 1.
The results of these tests are recorded in TABLE 1 below, where it can be
seen that all of these samples have long gel times, i.e., over 50 minutes
at 175.degree. C., except acetylacetonates of zinc, iron and uranyl, which
have short pot lives of 50 days, 10 days and 4 days, respectively. The
majority of those samples having long gel times were only partly soluble
in the resin formulation. None of these metal acetylacetonates were
considered useful in a combination epoxy-anhydride impregnating
composition that is to be used for insulating electrical members which are
to be subjected to high voltage applications, such as high voltage coils
for transformers.
EXAMPLE 6
To show the usefulness of other epoxies, a cycloaliphatic epoxy resin
formulation was made containing 100 grams of
3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate cycloaliphatic
epoxy resin, having an epoxy equivalent weight of 133 and a viscosity at
25.degree. C. of 350 to 450 cps. (sold commercially by Union Carbide Co.
as ERL-4221), 100 grams of diglycidyl ether of neopentyl glycol epoxy
resin, 220 grams of 1-methyltetrahydrophthalic anhydride and 0.2 gram of
zirconium acetylacetonate (to provide a cycloaliphatic epoxy:acid
anhydride:reactive diluent:selected metal acetylacetonate weight ratio of
100:105:0.12). After about four hours the sample was tested as in EXAMPLE
1. The initial viscosity of the sample was about 60 cps. at 25.degree. C.
The results of these tests are recorded in TABLE 1 below.
EXAMPLE 7
As a comparative example, a resin formulation was made using the same
ingredients and amounts as in EXAMPLE 6, except that 5 parts of catechol
phenolic resin accelerator was used per 200 parts of the epoxy resin
mixture. After about four hours the sample was tested as in EXAMPLE 1. The
initial viscosity of the sample was about 60 cps. at 25.degree. C. The
results of these tests are recorded in TABLE 1 below, where it can be seen
that the addition of phenolic resin accelerator drastically reduced pot
life.
EXAMPLE 8
A resin formulation was made using the same ingredients and amounts as in
EXAMPLE 6 except that aluminum acetylacetonate was substituted for
zirconium acetylacetonate. The results of these tests are recorded in
TABLE 1 below.
EXAMPLE 9
To show usefulness of other epoxies, a series of formulations were made. A
resin formulation was made using the same ingredients and amounts in
EXAMPLE 1 except that 0.10 gram of chromium (III) acetylacetonate was
used, and a liquid diglycidyl ether of bisphenol F epoxy resin, having an
epoxy equivalent weight of 160 to 170 and a viscosity at 25.degree. C. of
3,200 to 3,600 cps. (sold commercially by Dow Chemical Co. under the
tradename XD-7818) was substituted for the bisphenol A epoxy. This
provided an epoxy resin:acid anhydride:chromium acetylacetonate weight
ratio of 100:105:0.10. After about four hours the sample was tested as in
EXAMPLE 1. The initial viscosity of the sample was about 70 cps. at
25.degree. C. The results of these tests are recorded in TABLE 1 below.
EXAMPLE 10
A resin formulation was made using the same ingredients and amounts as in
EXAMPLE 9 except that a blend of bisphenol A and hydantoin epoxy resin was
substituted for the bisphenol A. The bisphenol A - hydantoin epoxy blend
had an epoxy equivalent weight of 155 to 165 and a viscosity at 25.degree.
C. of 4,500 cps. to 5,500 cps. at 25.degree. C. (sold commercially by Ciba
Geigy Co. under the tradename ARACAST XB-2826). A slightly larger amount
of anhydride was also used. This provided an epoxy resin:acid
anhydride:chromium acetylacetonate weight ratio of 100:120:0.10. After
about four hours the sample was tested as in EXAMPLE 1. The initial
viscosity of the sample was about 50 cps. at 25.degree. C. The results of
these tests are recorded in TABLE 1 below.
EXAMPLE 11
A resin formulation was made using the same ingredients and amounts as in
EXAMPLE 9 except that the epoxy resin consisted only of 100 grams of
neopentyl diglycidyl ether, with no bisphenol A epoxy. This provided a low
viscosity diglycidyl ether of an aliphatic diol epoxy resin:acid
anhydride:chromium acetylacetonate weight ratio of 100:120:0.10. After
about four hours the sample was tested as in Example 1. The initial
viscosity of the sample was about 20 cps. at 25.degree. C. The results are
recorded in TABLE 1 below. As can be seen, this formulation provides not
only good electrical, pot life and gel time properties, but also extremely
low initial viscosities. This resin would be particularly useful for very
high voltage impregnation applications, where as much as ten to sixteen
layers of mica paper or mica tape must be penetrated.
TABLE 1
__________________________________________________________________________
Electrical Properties 150.degree. C
Metal Gel Time (min.)
Pot Life
Thickness
Acetylacetonate
150.degree. C
175.degree. C
(days) 25.degree. C
(in.) 100 tan .delta.
.epsilon.'
__________________________________________________________________________
chromium (III)
35 to 45
15 200 0.24 4.3 7.4
chromium (III).sup.a
20 to 25
15 200 0.24 4.3 7.4
titanyl (TiO)
35 to 40
30 to 35
110 0.23 2.4 6.7
aluminum (III)
35 to 40
30 to 35
95 0.22 2.5 6.9
manganese (III)
60 to 90
40 to 45
160 0.20 5.3 7.4
cobalt (II)
50 to 55
35 to 4
130 0.21 2.8 6.6
cobalt (III)
80 to 90
25 to 35
200 0.20 2.2 6.9
nickel (II)
60 to 90
45 to 50
90.sup.+
0.19 2.2 6.7
vanadium (III)
70 to 80
40 to 45
90.sup.+
0.10 1.8 6.5
Zirconium (IV)
50 to 55
30 to 35
90.sup.+
0.11 4.7 7.6
sodium (I)
35 to 40
20 to 25
90.sup.+
0.12 12.0 7.9
potassium (I)
25 to 30
15 to 20
90.sup.+
0.12 27.0 8.4
chromium (III).sup.b
35 to 40
15 to 25
90.sup.+
0.27 7.0 6.9
*cerous.sup.c
75.sup.+
50 to 55
C 0.16 8.0 6.9
*magnesium
75.sup.+
50 to 55
C 0.23 1.8 7.1
*copper.sup.c
75.sup.+
90 to 100
C 0.21 310.0
19.0
*zinc.sup.c
35 to 45
20 to 25
50 0.23 112.0
9.8
*thorium.sup.c
60 to 65
50 to 55
C C C C
*strontium.sup.c
100 to 110
60 to 65
C C C C
*lead.sup.c
100 to 110
70 to 80
C C C C
manganese (II).sup.c
75.sup.+
55 to 65
C 0.16 43.0 6.8
*iron 15.sup.-
15.sup.-
10 0.10 1.6 6.4
*uranyl (VO.sub.2)
10 10 4 0.13 15.0 7.9
*beryllium
100 to 110
60 to 65
90.sup.+
-- -- --
zirconium (IV).sup.d
20 to 30
15.sup.-
80 0.27 4.8 5.7
*zirconium (IV).sup.e
20.sup.-
15.sup.-
6 0.29 7.1 6.9
aluminum (III).sup.d
20 to 30
15.sup.-
90.sup.+
0.28 4.7 6.4
chromium (III).sup.f
35 to 40
15 to 25
90.sup.+
0.27 14.5 6.9
chromium (III).sup.g
55 to 60
25 to 35
90.sup.+
0.27 5.4 7.2
chromium (III).sup.h
60 25 to 35
90.sup.+
0.26 5.8 6.7
__________________________________________________________________________
.sup.a aged two weeks.
.sup.b hydantoin epoxy resin substituted for bisphenol A in the resin
mixture.
.sup.c poor or partial solubility.
.sup.C poor or partial solubility.
.sup.d cycloaliphatic epoxy resin substituted for bisphenol A in the resi
mixture.
.sup.e cycloaliphatic epoxy resin substituted for bisphenol A with
addition of phenolic resin accelerator in the resin mixture.
.sup.f bisphenol F epoxy resin substituted for bisphenol A in the resin
mixture.
.sup.g blend of bisphenol A and hydantoin epoxy resin in the resin
mixture.
.sup.h use of a diglycidyl ether of an aliphatic diol as the resin.
*comparative examples.
As can be seen from these results, some acetylacetonates (copper, zinc and
manganese (II)) have very poor power factor values, providing poor
insulation properties for high voltage application. A great many of the
acetylacetonates (cerous, magnesium, copper, zinc, thorium, strontium,
lead and manganese (II)) are only partially soluble with the
epoxy-anhydride system when added at 0.10 part per 100 parts epoxy, and
most of these, and also beryllium, have overly long gel times at
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