Note: Descriptions are shown in the official language in which they were submitted.
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FS/K-20904/A
Preparation of mouldings by the automatic pressure gelation technique using a one-
component composition
The present invention relates to a process for the preparation of a moulding by the automa-
tic pressure gelation technique using a curable one-component epoxy resin composition.
In preparing mouldings by the automatic pressure gelation technique, which has been
known for some time, the curable epoxy resin composition is first of all, where required,
liquefied by heating and then introduced into a mould having a temperature high enough to
initiate heat curing of the composition. The composition remains in this mould until the
moulding has been sufficiently cured and solidified to enable it to be demoulded, such an
amount of the curable composition being continuously added under pressure while the
moulding is being cured as to compensate for the decrease in volume of the moulding
during curing.
Often, the curable material used in the process described above consists of compositions
which, in addition to the epoxy resin, comprise an anhydride curing agent and, optionally, a
curing accelerator. In practice, these compositions are only used as multi-component
systems because the resin on the one hand and the curing agent and accelerator on the
other hand start to react noticeably with each other even after a relatively short contact so
that such compositions would be badly storable in the form of one-component systems. The
components of these customary compositions therefore must be mixed very carefully by the
user in order to give, in reproducable manner, mouldings having good and constant proper-
ties. Accordingly, there is a need for storable one-component mixtures for the automatic
pressure gelation process which enable the user to avoid the expenditure involved in mixing
the components.
It has now been found that specific one-component compositions proposed in
EP-A-0 673 104 especially for fixing wire windings of electrical coils using the so-called
trickle impregnation or hot dip rolling process which comprise, as essential components, at
least one epoxy resin having more than one epoxy group per molecule as well as an
initiator system for the cationic polymerisation of the epoxy resin consisting of N-benzyl-
quinoliniumhexafluoroantimonate and 1,1,2,2-tetraphenyl-1,2-ethanediol, are excellently
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suitable for the preparation of mouldings by the automatic pressure gelation technique. This
is so very surprising because the polymerisation of epoxy resins with cationic initiators, such
as N-benzylquinoliniumhexafluoroantimonate, is normally very highly exothermic. Despite
this, when said special epoxy resin compositions are used while observing some specific
critical process parameters there is neither any undesirable premature curing of the material
when it is introduced into the mould nor does the heat of reaction liberated in the course of
the curing become so high as to result, owing to the internal temperature rising too fast and
being too high altogether, in internal cracks or fissures in the curing material of the
moulding, which would adversely affect in particular the mechanical strength of large
mouldings. Critical process parameters to be mentioned in particular are the initiator
concentration of the epoxy resin composition, the temperature at which the composition is
introduced into the mould, and the temperature of the mould itself.
Accordingly, this invention relates to a process for the preparation of a moulding by the
automatic pressure gelation technique, which comprises introducing a liquid curable epoxy
resin composition into a mould which has a temperature sufficiently high to initiate the heat
curing of the composition, and wherein the composition remains in this mould to cure until
the moulding has solidified enough to be demoulded, such an amount of the curable
composition being continuously added under pressure to the mould while the moulding is
being cured as to compensate for the shrinkage of the curing composition, and wherein
- the curable epoxy resin composition is a one-component composition,
- the curable epoxy resin composition comprises at least one epoxy resin having more
than one epoxy group per molecule, N-benzylquinoliniumhexafluoroantimonate in anamount of at most 0.02 mol per equivalent of epoxy groups in the composition, and
1,1,2,2-tetraphenyl-1,2-ethanediol (benzopinacol) in an amount of at most 0.02 mol per
equivalent of epoxy groups in the composition;
- the curable epoxy resin composition is introduced into the mould at a temperature of
30 to 55 ~C, and
- the mould has a temperature of 140 to 1 50~C.
Suitable epoxy resins are in principle all known polyfunctional epoxy resins that can be
liquefied - where required with the addition of diluents - at temperatures which are below
that temperature at which the initiator system already brings about a noticeable curing.
These polyepoxy resins may contain aliphatic, cycloaliphatic or aromatic basic structures.
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However, the curable epoxy resin composition used in the process of this invention prefe-
rably comprises an epoxy resin which is selected from the group consisting of polyglycidyl
ethers and polyglycidyl esters.
In a particularly advantageous embodiment of this invention, the curable epoxy resin
compositions comprise an epoxy resin selected from the group consisting of diglycidyl
ethers based on bisphenol A and diglycidyl ethers based on bisphenol F, or a mixture of
such diglycidyl ethers. Said compositions are highly reactive and particularly fast curing.
Another special embodiment of this invention is that, wherein the curable epoxy resin
composition comprises an epoxy resin selected from the group consisting of polyglycidyl
esters of aromatic polycarboxylic acids and polyglycidyl esters of cycloaliphatic polycarbo-
xylic acids, or a mixture of such polyglycidyl esters. Illustrative examples of suitable glycidyl
esters include the glycidyl esters of phthalic acid, terephthalic acid, isophthalic acid, trimelli-
tic acid and completely or partially hydrated derivatives of these acids, typically tetra- and
hexahydrophthalic acid and tetra- and hexatrimellitic acid.
The curable epoxy resin compositions which are used in the novel process comprise the N-
benzylquinoliniumhexafluoroantimonate and the 1,1,2,2-tetraphenyl-1,2-ethanediol(benzopinacol) preferably each in an amount of 0.001 to 0.02 mol per equivalent of epoxy
resin groups in the composition, more preferably in an amount of 0.004 to 0.008 mol per
equivalent of epoxy groups in the composition. The molar ratio of N-benzylquichinolinium-
hexafluoroantimonate and 1,1,2,2-tetraphenyl-1,2-ethanediol in the compositions is
conveniently in the range of 0.5:1 to 1:0.5, preferably of about 1:1.
The curably epoxy resin compositions suitable for this invention can also comprise fillers.
Depending on the purpose that is to be fulfilled by the use of fillers, a broad selection of
fillers may be used, typically talcum, kaolin, mica, gypsum, titanium dioxide, quartz powder,
cellulose, clay, ground dolomite, powdered glass, glass beads, xonotlite, wollastonite, silica
having a large specific surface (e.g. Areosil ), magnesium oxide and magnesium hydroxide,
aluminium oxide or aluminium oxide trihydrate, antimony trioxide or reinforcing agents such
as glass fibres and other fibres which may also have been comminuted, typically ground.
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These fillers should of course be compatible with the other components of the composition
and preferably should not inhibit, or not inhibit too strongly, the polymerisation initiator or the
polymerisation. The fillers conveniently have a particle size of 10 to 3000 ,um, preferably of
50 to 1000 llm, and may normally also be used in large amounts, e.g. in an amount of up to
80 % by weight, based on the total amount of the epoxy resin composition. Larger amounts
of fillers are advantageous because they result in a less exothermic curing reaction, less
shrinkage during curing and a harder moulding having good mechanical properties. How-
ever, they may possibly result in an inconveniently high viscosity of the epoxy resin compo-
sitions. The maximum viscosity of the curable epoxy resin compositions used in the novel
process is preferably 25 Pa s at 50 ~C. Good results are obtained, for example, using 30 to
75 % by weight, preferably 50 to 75 % by weight, of filler, based on the total amount of the
epoxy resin composition.
The epoxy resin compositions for this invention may also comprise customary reactive
thinners for expoy resins, typically epoxy resins which are liquid at temperatures from 15 to
30 ~C, for example in an amount of 1 to 100 % by weight, based on the remainder of the
epoxy resin in the composition. However, the reactive thinners may also be compounds
having other functional groups than epoxy resin groups, typically polyethylene glycols or
polypropylene glycols. Such compounds are preferably used in an amount of 1 to 20 % by
weight, based on the epoxy resin in the composition.
If required, the novel compositions may furthermore comprise toughening agents, preferably
core/shell polymers. Suitable core/shell polymers are described, inter alia, in
EP-A-0 578 613, EP-A-0 449 776 or in US patent US-A-4 778 851. They are preferably
used in an amount of 1 to 20 % by weight, based on the total amount of epoxy resin in the
composition.
The epoxy resin compositions may also comprise other known additives customarily used in
the art of polymerisable materials. Illustrative examples of such additives are pigments,
dyes, powdered polyvinyl chloride, polyolefins, metal powder, e.g. powdered copper, silver,
aluminium or iron, antifoams, antistatic agents, flow control agents, adhesion promoters for
the fillers, such as silane compounds or organo-titanate compounds, antioxidants and light
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stabilisers. These additives are conveniently used in customary amounts, preferably in
amounts of up to 1.5 % by weight, based on the resin.
When carrying out the process, a residence time of 10 minutes to at most about 20 minutes
is usually suffient for the material to be cured in the mould.
The nature of the mould is uncritical and according to this invention it is possible to use any
moulds customarily used for the APG process.
After demoulding, the moulding is conveniently subjected to a heat postcure to achieve a
complete cure of the mouldings. The postcure is preferably carried out for at most 5 hours,
more preferably for 0.5 to 2 hours, and in the temperature range from 120 to 200 ~C, prefe-
rably from 130 to 150 ~C.
The epoxy resin compositions are prepared in customary manner by mixing their compo-
nents and homogenising them, where required with heating, and their temperature is
adjusted to 30 to 55 ~C and they are then pumped into the mould. The pumping pressure is
preferably at least 20 kPa. It is not necessary to flush the mould with inert gas prior to filling
it with the one-component composition even though atmospheric oxygen inhibits the curing
of epoxy resins, in particular of epoxy resins based on bisphenols, initiated by mixtures con-
sisting of benzopinacol and N-benzylquinoliniumhexafluoroantimonate, as is known from
coating applications of such compositions.
The novel process is suitable for the preparation of mouldings of all kinds, but is preferably
used for the preparation of electrical insulators.
Example 1:
Stirring with a four-blade stirrer, 23.44 g of polypropylene glycol (average molecular weight
Mw = 425) are added to 210.92 g of a mixture of diglycidyl ether of bisphenol A and bis-
phenol F (epoxy value of the mixture 5.5 - 5.8 eqtkg) at a temperature of 40 to 50 ~C. This
mixture is then heated to 100 ~C and degassed under vacuum. After cooling the mixture
under nitrogen to 50 to 60 ~C, 2.58 g of benzopinacol and 3.06 g of N-benzylquinolinium-
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hexafluoroantimonate are added, with stirring, and dissolved. 360.00 g of wollastonite are
slowly added to this mixture at 50 ~C, and the resulting mixture is then thoroughly homoge-
nised for 5 minutes under vacuum using a high-speed stirrer.
To measure electrical and mechanical properties on the cured material, several portions of
a degassed mixture prepared according to the above instruction are filled into moulds
measuring 200 mm x 200 mm x 4 mm and 135 mm x 135 mm x 2 mm which are heated to
120 ~C. Each of the samples is cured for 1 hour at 120 ~C and is then subjected to post-
curing for 2 hours at 140 ~C.
The following Table 1 shows the properties found.
Example 2:
Stirring with a four-blade stirrer, 21.09 g of a diglycidyl ether of polypropylene glycol 400
(epoxy value 3.05 - 3.35 eq/kg) are added to 213.27 g of a diglycidyl ether of bisphenol A
(epoxy value 5.25 - 5.40 eq/kg) at a temperature of 40 to 50 ~C. This mixture is then heated
to 100 ~C and degassed under vacuum. After cooling the mixture under nitrogen to 50 to
60 ~C, 2.58 g of benzopinacol and 3.06 g of N-benzylquinoliniumhexafluoroantimonate are
added, with stirring, and dissolved. 360.00 g of wollastonite are then slowly added to this
mixture at 50 ~C, and the resulting mixture is thoroughly homogenised for 5 minutes under
vacuum using a high-speed stirrer.
Measurement of the electrical and mechanical properties on the cured material, as indicated
for Example 1, gives the values which are also indicated in Table 1.
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Table 1
Example 1 2
viscosity at 40 ~C [mPa s] 2330030014
gelling time at 140 ~C [minutes] 8.43 6.93
enthalpy of reaction [J/g] 65 64
flexural strength acc. to ISO 178 [MPa] 125 112
modulus of elasticity acc. to ISO 178 [MPa]11512 11301
flexural elongation (flexural test ISO 178) [%] 1.3 1.1
tensile strength acc. to ISO R 527 [MPa] 62 73
tensile modulus acc. to ISO R 527 [MPa] 10079 10592
flexural elongation (flexural test ISO R 527) [%] 1.0 0.9
K1C [MPa m"2] acc. to CG 216-0/89 ') 2.52 2.04
G1C [J/m2] acc. to CG 216-0/89 ') 504 336
loss factor at 25 ~C acc. to IEC 250 [%] 0.8 0.9
dielectric constant at 25 ~C (IEC 250) 4.8 4.8
') CG-216-0/89: Ciba-Geigy AG specification for the double torsion test
Example 3:
Stirring with a four-blade stirrer, 624.96 9 of polypropylene glycol (average molecular weight
Mw = 425) are added to 5624.64 of a mixture of diglycidyl ether of bisphenol A and bisphe-
nol F (epoxy value of the mixture 5.5 - 5.8 eq/kg) at a temperature of 40 to 50 ~C. This mix-
ture is then heated to 100 ~C and degassed under vacuum. After cooling the mixture under
nitrogen to 50 to 60 ~C, 68.80 g of benzopinacol and 81.60 g of N-benzylquinoliniumhexa-
fluoroantimonate are added, with stirring, and dissolved. 9600.00 g of wollastonite are
slowly added to this mixture at 55 ~C, and the resulting mixture is then thoroughly homoge-
nised for 220 minutes under vacuum. The composition of this mixture corresponds to the
mixture of Example 1.
Using the mixture so obtained, five electrical insulators (Siemens type A), 7.5 cm in dia-
meter and 21 cm long, are prepared by the automatic pressure gelation technique. In this
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process, the mould (mould type: Siemens-Stutzer, closing unit: Gr. Suter) has a tempera-
ture of 140 to 145 ~C and is filled over 2 minutes at a pressure of 300 kPa (3 bars). The
mould is opened after a total of 15 minutes and the moulding is taken out. The average
gelling time of the 5 batches is 280 seconds, including the filling time. The insulator is then
postcured for 2 hours at 140 ~C without the mould. With two turned brass inserts on either
end, the insulator has a total weight of about 1150 g.
The insulators have a cantilever strength according to DIN 48136/68 of 5096 N at 23 ~C.
The X-ray examination shows that none of the insulators have any internal cracks, fissures
or other flaws.
Example 4:
Stirring with a four-blade stirrer, 562.46 g of a diglycidyl ether of polypropylene glycol 400
(epoxy value 3.05 - 3.35 eq/kg) are added to 5687.14 g of a diglycidyl ether of bisphenol A
(epoxy value 5.25 - 5.40 eq/kg) at a temperature of 40 to 50 ~C. This mixture is then heated
to 100 ~C and degassed under vacuum. After cooling the mixture under nitrogen to 50 to
60 ~C, 68.80 g of benzopinacol and 81.60 g of N-benzylquinoliniumhexafluoroantimonate
are added, with stirring, and dissolved. 9600.00 g of wollastonite are slowly added to this
mixture at 55 ~C, and the resulting mixture is thoroughly homogenised for 220 minutes
under vacuum. The composition of this mixture corresponds to the mixture of Example 2.
Using the mixture so obtained, five electrical insulators (Siemens type A), 7.5 cm in dia-
meter and 21 cm long, are prepared by the automatic pressure gelation technique. In this
process, the mould (mould type: Siemens-Stutzer, closing unit: Gr. Suter) has a tempera-
ture of 140 to 145 ~C and is filled over 2 minutes at a pressure of 300 kPa (3 bars). The
mould is opened after a total of 14 minutes and the moulding is taken out. The average
gelling time of the 5 batches is 243 seconds, including the filling time. The insulator is then
postcured for 2 hours at 140 ~C without the mould. With two turned brass inserts on either
end, the insulator has a total weight of about 1150 g.
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The insulators have a cantilever strength according to DIN 48136/68 of 4765 N at 23 ~C.
The X-ray examination shows that none of the insulators has any internal cracks, fissures or
other flaws.
Example 5:
97.62 g of liquid diglycidyl hexahydrophthalate (Araldit PY 284, epoxy value 6.4 - 6.9 eq/kg)
and 1.06 g of 1,1,2,2-tetraphenylethanediol (benzopinacol) are placed in a sulfonation flask
(multinecked flat-bottomed flask), equipped with stirrer, thermometer and inert gas flush (N2)
and, with thorough stirring, are heated to 75 ~C. After stirring for about 20 minutes, a clear
yellowish solution is obtained which is then cooled to 40 ~C. With further stirring,1.32 g of
N-benzylquinoliniumhexafluoroantimonate are added. After stirring for 30 minutes, a clear
yellow solution is obtained to which 185.7 g of W 12 EST type quartz powder (product
name of Quarzwerke Frechen) are added, with stirring and under vacuum. This mixture is
then cast in a metal mould heated to 100 ~C, cured for 5 hours at this temperature and
then postcured for 3 hours at 160 ~C; The curable mixture and the fully cured moulding,
which is then first of all divided into standard bodies, have the properties listed in Table 2.
Example 6 (for comparison purposes):
90 g of hexahydrophthalic anhydride (Harter HT 907) as curing agent and 0.5 g of reaction
accelerator (Beschleuniger DY 071) are added to 100 g of liquid diglycidyl hexahydrophtha-
late (Araldit PY 284, epoxy value 6.4 - 6.9 eq/kg). This mixture is heated to 70~C, giving a
clear solution to which 353.8 g of W 12 EST type quartz powder are added. The curable
mixture is cured as described in Example 5 and divided into standard bodies. Table 2
compares the properties.
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Table 2
Example 5 6
viscosity 2) at 25 ~C [Pa s] 36.6 43.5
at 60 ~C [mPa s] 3000 5300
gelling time at 120 ~C [min] 50 29
gelling time at 140 ~C [min] 11.1 10
DSC: maximum peak temperature [~C] 175 183
enthalpy of reaction [J/g] 205 116
flexural strength at 23 ~C (ISO 178) [MPa] 139 146
modulus of elasticity (ISO 178) [MPa] 12370 12190
flexural elongation (ISO 178) [%] 1.2 1.3
flexural impact strength (ISO 179) [kJ/m2] 7 9
thermostability (ISO 75) [~C] 124 113
Tg value (DSC) [~C] 115 110
2) The viscosity was determined using a viscosimeter (Rheomat 115A MS DIN 125) at 100
revolutions per second.
It is found that the properties of a moulding prepared by using a one-component composi-
tion in accordance with the process of this invention has properties which are comparable to
those of mouldings prepared by using customary two-component compositions.
Example 7:
Another mixture is prepared in accordance with Example 5, but using no filler. The viscosity
and the gelling time of this mixture are measured immediately as well as after storing for
one, three and six months at 25 ~C, giving the values of Table 3.
Table 3
viscosity 2) at 25 ~C [mPa s] 320
after 1 month 330
after 2 months 340
after 6 months 340
gelling time 4) at 160 ~C [min] 1.33
after 1 month 1.33
after 2 months 1.33
after 6 months 1.33
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4) b-plate, thin layer (Ciba PM32168)
2)The viscosity was determined using a viscosimeter (Rheomat 115A MS DIN 125) at 100
revolutions per second.
