Note: Descriptions are shown in the official language in which they were submitted.
- - CA 0223776~ 1998-0~-14
PAT 95 595 November 7, 1995
- Dr. Beck & Co. AG, Hamburg
Process for impregnating electrically conductive
substrate~
FILE,PH~ THIS~.~.d,~'lD~
TE~TRANSLA~N
Field of the invention
The process according to the invention for impregnating
substrates, in particular windings of electrical
machines, comprises impregnating the substrate with a
resin system A) which is highly viscous, plastic,
semicrystalline or crystalline at room temperature and
which has a low viscosity and [sic] is liquid at the
application temperature and can be cured by a free
radical method to give thermosetting plastics.
Prior art
In the processes known from the prior art, the windings
of electrical machines are usually impregnated by
steeping. The object of this impregnation is to impart
mechanical strength to the winding so that the winding
can withstand mechanical and electromechanical forces
and the winding is therefore protected from external
harm~ul effects, such as, for example, the deposition
of dust particles, collector abrasion, moisture, salts
CA 0223776~ 1998-0~-14
and solvents, so that mechanical damage by particles,
for example those sucked in by the fan, is prevented
and so that the heat generated during operation of the
electrical machines as a result of ohmic and dielectric
losses can be transferred from the winding to the
surrounding cooling means, helping to increase the
service life of the electrical apparatus.
This impregnation is usually carried out by means of
lacquers or resins which cure to give thermosetting
plastics. Since, on the one hand, the requirements for
the long-term thermal stability of these thermosetting
plastics are very high and, on the other hand, the
abovementioned properties, in particular the electrical
insulation capacity, must also be present, there are a
number of lacquers and resins which are tailored to the
specific fields of use.
In the case of the solvent-containing lacquers whose
solvent content must be removed before the curing
process, thorough impregnation of the electrical
windings in a single applic~ ion is as a rule poor.
Consequently, the transfer o~ dissipated ohmic and
dielectric heat from the interior of the windings,
CA 02237765 1998-05-14
which has already been discussed, is hindered.
Moreover, the removal of the solvent often requires
long preheating times and complicated temperature
programs during the curing of the lacquer. Furthermore,
the solvent-containing lacquers require expensive
plants for waste air purification, since otherwise
solvent vapors produce considerable environmental
pollution.
Apart from special cases, the lacquers in the
electrical industry have therefore been replaced by
solvent-free resins. Here, particularly the unsaturated
polyester resins have become widespread since they have
considerable advantages over other thermosetting resin
systems. Thus, it is possible to ~ul~ill the recluired
properties to a large extent by molecular tailoring of
the unsaturated polyester resins, such as, ~or example,
the selection o~ specific monomer building blocks or
the establishment o~ specific molecular weights.
Furthermore, the reactivity of the unsaturated
polyester resins can be influenced in such a way that
short and hence economical production proc-sses ~or
windings of electrical machines become possible.
CA 0223776~ 1998-0~-14
Particularly with regard to the requirement for long-
term thermal stability, the unsaturated polyester
resins, in particular the unsaturated polyesterimide
resins, have outstanding properties.
In general, the unsaturated polyester resins are
composed, on the one hand, of base resins, consisting,
for example, o~ alpha,beta-unsaturated dicarboxylic
acids, further modifying mono-, di- and/or
polycarboxylic acids, di- and/or polyols and, in the
case of the polyesterimides, of building blocks
containing imido groups, hydroxyl groups and carboxyl
groups, and, on the other hand, of comonomers which
react with the alpha,beta-unsaturated dicarboxylic acid
units o~ the base resin and can lead to thermosetting
plastics. A preferred comonomer is styrene, which,
owing to its good dissolution properties, is also used
for establishing the processing viscosity. Stated
comonomers are completely copolymerized during curing
under suitable conditions. Such a solvent-free system
is re~erred to as an impregnating resin. As in the case
of the impregnating lacquers too, the vapor pressures
of the comonomers at application temperature result in
evaporation losses, which, however, are generally less
- 5 -
than in the case of solvent-containing systems (50~,
based on the amount of solvent used, evaporation loss
-
in the case of solvent-containing impregnating
lacquers, from 10 to 30~ evaporation loss in the case
of impregnating resins). Nevertheless, expensive
purification of the waste air is required even with the
use of impregnating resins based on unsaturated
polyesters, but such waste air plants can be designed
to have lower purification capacities than when
impregnating lacquers are used, since the monomer
losses can be reduced by suitable resin formulations
and process adaptations.
The use of other resin systems, such as, for example,
epoxy resins, have the disadvantage that long curing
times are required, that the possibilities for adapting
the processing properties to the production processes
without suffering serious deterioration in the
dielectric properties are low, and that some resin
components, such as, for example, the highly heat-
stable cycloaliphatic types in the case of the epoxy
resins or the amines in the case of the curing agents,
may have high toxicity.
CA 02237765 1998-05-14
-- 6
- Sulmnar~y of the invention
The prior art discussed so far gives rise to the object
of developing a steeping and impregnation process which
combines the known advantages of impregnation with
resin systems which can be cured by a free radical
method with a low-emission impregnation and curing
technology. ~or this purpose, it is necessary to use
resins which either require no comonomers for curing or
contain comonomers which have very low vapor pressures
at the processing and curing temperature. Such
comonomers must also still have sufficiently high
reactivity in order to cure in times which are
sufficiently short to be economically acceptable.
Moreover, neither the resins nor the comonomers may
release significant amounts of cleavage products at the
processing and curing temperatures. The comonomers
usually used are not suitable for achieving these
objects since, for reasons relating to the
processibility of the resins, the comonomers must be in
the liquid state. As liquids at room temperature and in
particular at the processing and curing temperature,
such comonomers, such as, for example, vinyl or allyl
compounds, have considerable vapor pressures which lead
CA 0223776~ 1998-0~-14
to substantial evaporation losses in the case of the
comonomers.
Thus, suitable comonomers are solid or highly viscous
at room temperature, as are the resins themselves,
which are present at room temperature in a highly
viscous, plastic, semicrystalline or crystalline state.
In this case, impregnation of the objects must be
carried out at temperatures at which the resins or the
mixtures of resins and comonomers are present in a low-
viscosity and/or in a molten state.
The use of molten resin systems in electrical
insulation technology is prior art. Such molten resin
systems are used as solvent-free wire enamels,
extrudable cable sheathing compounds, self-bonding
enamels or coating materials. The use of systems which
cure by a free radical method is the exception since,
in the case of such highly reactive systems, the
processibility is very limited owing to the
unacceptably short pot life (time for which the resin
is present in the processibl. state). A further object
of the present invention was thus to achieve
stabilization of the resin systems used at elevated
CA 0223776~ 1998-0~-14
application temperatures without causing excessively
long curing times and excessively high curing
temperatures at which decomposition phenomena in the
resins and damage to the materials to be impregnated
may occur.
JP-A-53 05 97 91 describes polyesterimide resins having
at least tribasic carboxylic acids and polyesterpolyols
as monomer building blocks, which are prepared using
amines and further amounts of at least tribasic
carboxylic acids. Such polyesterimide resins are used
in molten form as insulation coating materials for
electrically conductive substrates. The coatings have
good electrical and mechanical properties. No toxic
vapors are released during the coating process.
DE-A-26 48 3S1 and DE-A-26 48 352 relate to injection
moldable resin compositions which consist of from 10 to
50~ by weight of unsaturated polyester resin, and from
0.2 to 2~ by weight of organic peroxide and of inert
filler. The unsaturated polyesters are composed of the
building blocks polyols, ethylenically unsaturated
dicarboxylic acid and saturated dicarboxylic acid. SUch
resin compositions are used for electrical or
CA 0223776~ 1998-0~-14
g
electronic components, such as, for example,
_ insulators, housings for low-voltage and medium-voltage
switches, cable insulations and plugs.
DE-A-16 40 428 describes the use of annular elements of
unsaturated polyester resins, which are coated with
waxes for improving the blocking resistance. These
annular elements are used for impregnating windings by
a procedure in which they are placed on a winding head
of the winding. On heating, the unsaturated polyester
resin melts, penetrates into the winding and is cured
there.
Common to the prior art processes is that they
generally achieve only some of the abovementioned
objects set for impregnating resins.
Surprisingly, a process for impregnating windings of
electrical machines has been found, in which the
impregnating resin used is a resin system A)
cont~;n;ng
A1) a resin which can be cured by a free radical
method to give thermosetting plastics,
CA 0223776~ 1998-0~-14
-- 10
A2) at least one su1table curing agent and, if
required, accelerator,
A3) if required, ~urther comonomers and/or
further polymers having ethylenically
unsaturated groups capable of free radical
polymerization, the vapor pressure of A3) at
the impregnating and curing temperature being
low, and
A4) if required, further conventional additives,
the resin system A) being highly viscous, plastic,
semicrystalline or crystalline at room temperature and
the resin system A) being converted in the impregnation
process, by increasing the temperature to the
impregnating temperature, into the low-viscosity liquid
state, so that impregnation can be carried out by the
known processes of immersion impregnation, flooding,
immersed rotation, dripping or casting, if necessary
supporting the impregnation by employing reduced
pressure.
Preferably, the resin component A1) is selected from
the group consisting of unsaturated polyesters,
unsaturated polyesterimides, bismaleimides, oligomeric
- 11 -
diallyl phthalates, comonomer-rree vinyl es~ers,
comonomer-free vinyl ethers, comonomer-free
vinylurethanes and/or polybutadiene resins, alone or in
combinations with one another.
The resin component A1) selected from the group
consisting of unsaturated polyesters, unsaturated
polyesterimides and bismaleimides in combination with
the resin component A3~ selected from the group
consisting of oligomeric diallyl phthalates,
divinylethyleneurea, divinylpropyleneurea, N-vinyl-
carbazole, N-vinylpyrrolidone, comonomer-free vinyl
esters, comonomer-free vinyl ethers, comonomer-free
vinylurethanes, polyesters containing vinyl and/or
allyl groups, or mixtures thereof, is particularly
preferred.
Preferably used curing agents A2) are peroxides which
form ~ree radicals, in particular organic peroxides,
and/or compounds which form free radicals as a result
o~ cleavage of a carbon-carbon bond. The resin systems
A) are pa ticularly preferably delivered in the
activated state as single-component resins; in special
cases, activation may also be ef~ected immediately
CA 0223776~ l998-0~-l4
-- 12
before impregnation using s~i~able mixingjmetering
means.
The substrates to be impregnated are preferably
preheated before the impregnation to a temperature
which is equal to or greater than the impregnating
temperature. Preheating of the substrates to be
impregnated is carried out, for example, by Joule heat,
induction heating, microwave radiation or infrared
radiation. Moreover, it is possible for the winding to
be impregnated to be further heated by current but also
in the state immersed in the resin, and this heating
may serve to compensate the heat losses due to thermal
conduction or to increase the w;n~;ng temperature
further in order to cause gelling of the resin which is
penetrated into the winding, prior to removal from the
resin. This process is particularly suitable because
the resin materials used are low-emission products and
therefore have a very low vapor pressure and hence a
20 high flashpoint at the processing temperature, so that
special explosion-proofing measures are not required.
The resin reaches the hig~ temperatures only in the
winding and in the immediate environment of the
winding.
CA 0223776~ 1998-0~-14
-- 13
~ The impregnation of the substrates is pre~erab;y
carried out by immersion, flooding, immersed rotation,
dripping or casting, impregnation being carried out at
a reduced pressure at which the components A1) to A4)
used still have a negligibly low vapor pressure. In the
case of impregnation by immersion or flooding, the
substrate may remain immersed until gelling of the
resin system A) in the substrate has occurred.
After the impregnation with the resin systems, curing
of the resin systems is carried out at a temperature
which is above the temperature of the resin melt and
which is generated, for example, by Joule heat,
induction heating, microwave radiation, infrared
radiation or passage through a conventional heating
oven, if necessary the surface drying being supported
by the action of high-energy radiation, such as, for
example, W or electron radiation.
Detailed description
The components of resin system A)
CA 0223776~ l998-0~-l4
-- 14
Preferably used as component A1) ar~: unsaturated
polyester resins which may have building blocks
containing imido groups, bismaleimide resins,
oligomeric diallyl phthalates, comonomer-free vinyl
esters, comonomer-free vinyl ethers, comonomer-free
vinylurethanes and/or polybutadiene resins. Unsaturated
polyester resins are known. Unsaturated polyester
resins containing imido groups are described, for
example, in DE-A-15 70 273, DE-A-17 20 323 and
DE-A-24 60 768.
Examples of building blocks of the unsaturated
polyester resins in addition to the conventional
polyester buildings blocks are: polyols cont~in;ng
polymerizable double bonds, such as glycerol monoallyl
ether, trimethylpropane monoallyl ether and
pentaerythrityl mono- and diallyl ether, and
polycarboxylic acids cont~;n;ng polymerizable double
bonds, or anhydrides thereof, such as fumaric acid,
tetrahydrophthalic acid or tetrahydrophthalic anhydride
and preferably maleic acid or maleic anhydride, and
monocarboxylic acids cont~;n;ng polymerizable double
bonds, such as, for example, acrylic and/or methacrylic
acid. As described, for example, in DE-A-24 60 768, for
CA 0223776~ 1998-0~-14
-- 15
modification of the properties of unsaturated polyes~er
resins some of the unsaturated dicarboxylic acid may be
replaced by saturated dicarboxylic acids, such as, for
example, adipic acid, perhydrogenated isophthalic acid,
phthalic acid, phthalic anhydride and/or dimerized
fatty acids. Examples of suitable components A3)
copolymerizable with the unsaturated polyesters or
polyesters A1) cont~;n;ng imido groups are: diallyl
phthalate prepolymers, divinylethyleneurea, divinyl-
propyleneurea, N-vinylcarbazole, N-vinylpyrrolidone,
comonomer-free vinyl esters, comonomer-free vinyl
ethers, comonomer-free vinylurethanes and polyesters
which contain vinyl or allyl groups and which differ
~rom A1), such as, for example, polyesters composed of
saturated and/or unsaturated polycarboxylic acids with
pentaerythrityl mono-, di- and/or triallyl ether and
optionally modi~ying glycols as monomer building
blocks. At the impregnating and curing temperatures,
the copolymerizable components A3) have vapor pressures
which are 80 low that no signi~icant immissions can
occur.
CA 0223776~ 1998-0~-14
Any desired low molecular weight bismaleimide may be
used as bismaleimide component Al). Bismaleimides of
the formula I
C)
~ O O
where Rl is an aliphatic, cycloaliphatic, araliphatic
or aromatic radical and the stated radicals may have
further functional groups, such as ether, ester, amido,
carbamate, keto, sulfonyl or hydroxyl groups, are
advantageously used. R1 is preferably a straight-chain
alkylene radical having 2 to 20, in particular 2 to 10,
carbon atoms or a 4,4'-diphenylmethane, 2,4-toluylene
or 1,3- or 1,4-phenylene radical. Suitable
bismaleimides are, for example, ethylenebismaleimide,
butylenebismaleimide, hexamethylenebismaleimide, 4,4'-
diphenylmethanebismaleimide, 2,4,-toluylenebismaleimide
20 [6iC] and 1,3-phenylenebismaleimide or mixtures
thereof. Examples of suitable components A3) which are
copolymeriza le with the bismaleimides Al) are:
oligomeric diallyl phthalates, divinylethyleneurea,
divinylpropyleneurea, N-vinylcarbazole, comonomer-free
CA 0223776~ 1998-0~-14
vinyl esters, comonomer-free vinyl ethers, comonomer-
free vinylurethanes and polyesters which contain vinyl
or allyl groups and which differ from Al), such as, for
example, those composed of saturated and/or unsaturated
polycarboxylic acids with pentaerythrityl mono-, di-
and/or triallyl ether and optionally modifying glycols
as monomer building blocks. At the impregnating and
curing temperatures, the copolymerizable components A3)
have vapor pressures which are so low that no
significant immissions can occur.
Furthermore, the following may be used as component
Al), alone or as a mixture with other components
mentioned under Al): oligomeric diallyl phthalates,
comonomer-free vinyl esters, comonomer-free vinyl
ethers, comonomer-free vinylurethanes and/or
polybutadiene resins.
Depending on resin system A), known peroxides having
suitable decomposition temperatures or compounds which
undergo thermal decomposition with formation of
hydrocarbon radicals may be used as curing agent A2).
I~ necessary, compounds which accelerate the
decomposition of the free radical initiators are
CA 0223776~ l998-OS-l4
- 18 -
additionally present. It is essential to the inventionthat a significant free radical stream which effects
curing of the resin system A) is produced by the curing
agent A2) only at above the impregnating temperatures.
Examples of peroxides A2) which undergo significant
decomposition into free radicals only at above the
impregnating temperature are commercial organic
peroxides, such as tert-butyl perbenzoate, tert-butyl
perisononanoate or tert-butyl peroctoate, or peroxides
in combination with accelerators, such as benzoyl
peroxides in combination with tertiary amines or
peresters with cobalt salts of organic acids.
Benzopinacol, substituted succinic acid derivatives
and, preferably, silyl ethers of substituted ethylene
glycols, as described, ~or example, in DE-A-26 32 294,
may be mentioned as examples o~ curing agents A2) which
undergo decomposition with formation of hydrocarbon
radicals. Such silyl ethers according to DE-A-26 32 294
undergo partial decomposition into free radicals only
at relatively high temperatures and, under certain
circumstances, are very substantially stable even at
temperatures above 80 degrees C in the res.~ system A)
to be polymerized.
CA 0223776~ 1998-0~-14
-- 19
For stabilization against premature curing, the resin
systems A) may contain, as a constituent of component
A4), stabilizers known per se for compounds capable of
free radical polymerization, such as, for example,
quinones, hydroquinones, sterically hindered phenols
and/or sterically hindered amines and nitro compounds.
The conventional processing assistants for coating
resins, such as, for example, surface-active or
interface-active substances for improvin~ the leveling
and the penetrating power, viscosity-influencing
additives, such as pyrogenic silica or bentonites, and
mineral or organic fillers, may be present as further
constituents of component A4), which may or may not be
present.
Impregnation and curing
The impregnation of the substrates, for example the
windings of electrical machines, is carried out using
the resin systems A) according to the invention,
consisting of the components A1), A2) and, if required,
A3) and A4), in the melt of A) at temperatures which
are below the curing temperature.
CA 0223776~ 1998-0~-14
-- 20
The processing times of the resin systems A) are such
that impregnation by the prior art processes are [sic]
possible. Examples of such impregnation processes are:
5 - impregnation of the substrate to be impregnated,
which is optionally preheated, by immersion in the
melt of the resin system A), retention of the
substrate to be impregnated in the melt, until the
resin melt has reached all parts to be
impregnated, if necessary until gelling of the
resin which has penetrated into the substrate,
removal and shaking the drips off the impregnated
substrate and subsequent curing of the absorbed
resin system A), where heating of the object by
means of Joule heat in the immersed state need not
be interrupted, so that heat losses in the winding
which occur as a result of thermal conduction can
be compensated or the residence time until
possible gelling under resin can be reduced by
increasing the winding te,.,perature during
immersion,
- dripping o~ the melt of the resin system A) onto
the substrate to be impregnated, the melt of the
_
CA 0223776~ l998-0~-l4
-- 21 --
resin sys~em A) ~eing dripped by means of suitable
pumps onto the optionally preheated substrate, the
curing agent A2), if required, being metered in by
suitable mixing/metering apparatuses before the
melt comprising A1 and, if required A3 and A4 is
dripped on, or the resin system A) already being
activated beforehand by addition of the curing
agent A2,
10 - flooding with the melt of the resin system A), the
optionally preheated substrate being flooded by a
rising bath of activated melt of the resin system
A) in such a way that sufficient impregnation of
the substrate takes place, subsequently blowing
off the melt of the resin system A), if required
until gelling of the resin which has penetrated
into the substrate, allowing the substrate to drip
off and then curing the melt of the resin system
A) absorbed by the substrate, where heating of the
object by means of Joule heat in the immersed
state need not be interrupted, so that heat losses
in th winding which occur as a result of thermal
conduction can be compensated or the residence
time until possible gelling under resin can be
CA 02237765 1998-0~-14
-- 22
reduced by increasing the winding temperature
during immersion,
- immersed rotation with the melt of the resin
system A), the optionally preheated substrate
being rotated through the activated melt of the
resin system A) in such a way that, in the case of
windings of electrical machines as the substrate,
only the winding or that part of the substrate
carrying the winding is covered by the melt of the
resin system A), until sufficient impregnation of
the winding has occurred, and subsequent curing of
the melt absorbed by the substrate (by the
winding), preferably with rotation, where heating
of the object by means of Joule heat during
rotation need not be interrupted, 80 that heat
losses in the winding which occur as a result of
thermal conduction can be compensated or the
residence time until possible gelling under resin
can be reduced by increasing the winding
temperature during rotation,
and
- casting of the substrates in reusable or captive
form with a preactivated resin system A) or, with
CA 0223776~ 1998-0~-14
-- 23
the use of a suitable mixing/metering system, by
m; ~; ng the curing agent A2) with the resin
components Al and, if required, A3) and A4)
immediately before casting.
The abovementioned impregnation processes can be
carried out for improving the impregnation quality,
preferably under reduced pressure or with alternating
reduced pressure and superatmospheric pressure. The
object can be preheated here too, heating of the
winding by means of Joule heat during casting leading
to a further reduction of viscosity, with the result
that penetration into the winding is facilitated.
Gelling of the resin which has penetrated into the
winding by increasing the temperature has the advantage
that the volu~e shrinkage due to curing is compensated
by further flow of the liquid resin from regions
outside the w; n~; ng region.
The preheating of the substrates can be carried out,
for example, by Joule heat (heating by electrical
resistance), induction heating, microwav heating or
infrared heating and by passage through a conventional
heating oven.
CA 0223776~ l998-0~-l4
-- 24
The curing of the resin system A) adhering to the
substrate after the impregnation can be carried out,
for example as in the case of the preheating of the
substrates by Joule heat, induction heating, microwave
heating or infrared heating and by passage through a
conventional heating oven; and the curing at the
substrate surface can optionally be supported by
additional irradiation, for example by means of IR, W
or electron radiation.
The immissions occurring during curing are assessed as
follows:
amounts as equal as possible of activated resin system
15 A) are introduced into a sample tray o~ a TGA
(Thermo~ravimetric Analysis) apparatus, and a constant
air stream is passed over. Heating is then effected to
the required curing temperature at a predetermined
heating rate, and this temperature is then kept
constant ~or the time required for curing. During this
time, the loss of mass of the resin system A) was
determined. In the case of conventional systems,
containing unsaturated polyester resins and low
molecular weight comonomers, the loss of mass during a
CA 0223776~ l998-0~-l4
-- 25
~ heating time of 10 mlnu es to the curing temperature of
140 degrees C and a curing time of 1 hour at 140
degrees C is about 30~ by weight.
The Examples which follow are intended to illustrate
the invention further. All stated percentages are by
weight, unless stated otherwise.
Example~
Example 1:
An unsaturated polyesterimide A1) according to Example
2 of DE-C-24 60 768, composed of maleic anhydride,
15 neopentylglycol, trishydroxyisocyanurate and the
reaction product of tetrahydrophthalic anhydride and
monoethanolamine is mixed with lO~ by weight, based on
the resin system A), of diallyl phthalate oligomer A3)
(type Ftalidap 27, manufacturer Alusuisse) in the melt.
2~ by weight, based on the resin system A), o~
benzopinacol silyl ether (type Initiator BK,
manufacturer Bayer AG) were admixed as curing agent
A2). The resin system A) has an almost solid
consistency at room temperature and a viscosity o~
- 26 -
1300 mPa.s at 80 degrees C. Ihe pot life Gf the resin
system A) is 210 minutes at 80 degrees C, and the
gelling time is 27 minutes at 140 degrees C. The stator
of an electric motor, which was preheated to
120 degrees C in the heating oven, is slowly immersed
in the molten resin system A) heated to 80 degrees C.
The stator re~; n~ in the molten resin system A) until
no further bubbles rise. The stator is then slowly
withdrawn and is allowed to drip off for about 2
minutes, and the resin system A) is then cured by
heating in an oven at 160 degrees C for 30 minutes.
A~ter curing, the winding of the stator is suf~iciently
stable. After the winding is sawn open, the stator
shows adequately thorough impregnation. The
thermogravimetrically determined loss of mass during
heating in the TGA apparatus to 160 degrees C in 10
minutes and maintaining the temperature at 160 degrees
C ~or 30 minutes is 3.4~ by weight, based on the resin
system A).
Ex~ple 2:
CA 0223776~ l998-0~-l4
- -- 27
The unsaturated polyesterimide A1) according to Example
1 is mixed in a ratio of 2:1 with a polyester A3) which
was prepared from 2 mol of pentaerythrityl triallyl
ether, 4 mol of adipic acid and 3 mol of
pentaerythrityl diallyl ether by condensation in the
melt, and the resulting mixture is mixed with 2~ by
weight, based on the resin system A), according to
Example 1 tsic]. The mixture has a plastic consistency
at room temperature and a viscosity of 570 mPa.s at
100 degrees C. The pot life of the resin system A) with
1~ by weight, based on the resin system A), of tert-
butyl perbenzoate as an additional curing component
A2), is 210 minutes at 100 degrees C, and the gelling
time is 10 minutes at 160 degrees C. The stator of an
electric motor, which was preheated to 120 degrees C in
a heating oven, is slowly immersed in the molten resin
system A) heated to 100 degrees C. The stator remains
in the molten resin system A) until no further bubbles
rise. The stator is then slowly withdrawn and is
allowed to drip off for about 2 minutes, and the resin
system A) is then cured by heating in an oven at
160 degrees C for 30 minut 3. After curing, the winding
of the stator is sufficiently stable. A~ter the winding
is sawn open, the stator shows su~ficiently thorough
CA 0223776~ 1998-0~-14
-- 28
impregnation. The thermogravimetrically determined loss
of mass during heating in the TGA apparatus to
160 degrees C in 10 minutes and maint~;ning of the
temperature at 160 degrees C for 30 minutes is 2.3~ by
weight, based on the resin system A).
Example 3:
A monomer-free vinyl ester A1) (type Palatal A430-01,
monomer-free, manufacturer BASF AG), which is solid at
room temperature and has a viscosity of 500 mPa.s at
100 degrees C, is melted in the storage container of a
conventional dripping apparatus. After ~m; ~; ng 1~ by
weight, based on the total resin system A), of tert-
butyl perbenzoate as curing agent A2) by means of aconventional mixing/metering head, the resin system A)
prepared in this manner is dripped onto an armature
whose winding had been heated to 140 degrees C by Joule
heat. The resin system A) is cured at 140 degrees C in
20 the course of 15 minutes. After curing, the winding is
sufficiently stable. After the winding is sawn open, it
shows sufficiently thorough impreg ~tion. The
thermogravimetrically determined loss of mass during
heating in the TGA apparatus at 140 degrees C in
CA 02237765 1998-05-14
-- 29
10 minutes and maintaining of the temper~ture at
140 degrees C for 15 minutes is 1.4~ by weight, based
on the resin system A).
