Note: Descriptions are shown in the official language in which they were submitted.
FS/K-2081 1/A
~ r . 2 ~ Q '11 5 8 4
Manufacture of mouldings by means of the automatic pressure qelling technique.
The present invention relates to a process for the manufacture of a moulding by means of
the automatic pressure gelling technique using a curable epoxy resin composition.
In the manufacture of mouldings according to that technique, which has been known for a
relatively long time, the curable epoxy resin composition is first of all, if necessary, liquefied
by heating, and is then introduced into a mould of a temperature that is high enough to
initiate thermal curing of the composition. The composition remains in the mould until the
moulding has been sufficiently cured and solidified to be removed from the mould, curable
composition continuously being fed under pressure into the mould, while the moulding is
being cured, in an amount that is sufficient to compensate for the decrease in volume of the
moulding during the curing process. Compositions that in addition to the epoxy resin
comprise an anhydride hardener and, if appropriate, a cure accelerator are frequently used
as curable material for the described process.
In "CATIONIC EPOXY MOLDED ELECTRONIC (CEMTRONIC) TECHNOLOGY AND ITS
APPLICATIONS" (lecture at the SPI-Epoxy Resin Formulators Conference, 20-22/9/1995, at
Orlando, Florida U.S.A.), W. Ferng, D. Baumann, H. Lehmann and Y. Naganuma describe
the manufacture of mouldings by means of the automatic pressure gelling technique and
use for the process a curable composition that in addition to a diglycidyl ether based on
bisphenol A comprises an initiator for the cationic polymerisation of the epoxy resin, that is
an aromatic sulfonium hexafluoroantimonate compound. The composition is heated to
approximately 45~C and, in the course of 30 seconds, is fed into a mould of a temperature
of from 135 to 1 40~C in which the material remains for a further 2 minutes, after which it is
demoulded. Compared with the corresponding manufacture of mouldings using the epoxy
resin compositions based on anhydride hardeners mentioned above, the described
procedure has, inter alia, the advantage that energy consumption is substantially reduced
because, at a comparable temperature, the mouldings require only approximately a fifth of
the time before they can be removed from the mould. The mass production of mouldings is
consequently considerably more economic. However, the described process cannot yet be
regarded as completely satisfactory because fissures readily form in the material of the
moulding, especially in the case of relatively large mouldings.
It has now been found that the risk of fissure formation is virtually excluded, even when
curable compositions that are based on epoxy resins and cationic polymerisation initiators
- 2 --
are used for the automatic pressure gelling, if the mould is heated to a maximum of 120~C.
Although the reduction in temperature results in somewhat longer residence times for the
curable material in the mould by comparison with the conventional procedure described
above, because of the substantially lower temperature of the mould the energy
consumption for the curing process is nevertheless at a low level comparable to that of the
procedure described above.
The invention accordingly relates to a process for the manufacture of a moulding by means
of the automatic pressure gelling technique in which a curable composition that comprises
at least one epoxy compound having on average more than one epoxy group per molecule
and an initiator for the cationic polymerisation is heated to a temperature of from 30 to 55~C
and introduced into a mould having a temperature of from 80 to 120~C that is high enough
to initiate thermal curing of the composition, and the composition remains in that mould,
being cured, until the moulding has solidified to such an extent that it can be demoulded,
curable composition continuously being fed under pressure into the mould, while the
moulding is being cured, in an amount that is sufficient to compensate for shrinkage of the
composition being cured, and the curable composition comprising as initiator for the cationic
polymerisation at least one compound selected from
a) sulfonium compounds of the anions PF6-, AsF6-, SbF6-, BiF6-, and of the derivatives
derived from those anions in which at least one fluorine atom has been replaced by a
hydroxy group, and of the anion CF3S03-, the sulfonium compounds comprising, bonded to
the sulfur atom, at least one alkyl group having from 1 to 12 carbon atoms, at least one
cycloalkyl group having from 3 to 8 carbon atoms, at least one (cycloalkyl)alkyl group having
from 4 to 10 carbon atoms or at least one aralkyl group having from 7 to 15 carbon atoms,
and
b) compounds of formula (I)
[M (L),d n X (I),
wherein
n is20r3,
M is a metal cation selected from the group consisting of Zn2+, Mg2+, Fe2+, Co2+, NiZ+,
cr2+ Ru2+ Mn2+ Sn2+ Vo2+, Fe3+, Al3+ and Co3,
20 11 584
-- 3 --
X~ is an anion selected from the group consisting of PF6, AsF6, SbF6, BiF6, of
derivatives derived from those anions in which at least one fluorine atom has been
replaced by a hydroxy group, and of CF3SO3-, or wherein up to 50 % of the anions X~
, based on the total number of anions, may also be any other desired anions,
L is water or an organic ~-donor ligand that has as ligand sites one or more functional
radicals selected from the group consisting of -C0-, -C0-0-, -O-C0-O- and -0- and
that via the oxygen atom or oxygen atoms forms 6-bonds with the central atom andx is an integer from 0 to 6,
it being possible for the ligands L to be different within the scope of the definitions given.
When carrying out the process according to the invention, a residence time for the material
that is to be cured of from 1 minute to a maximum of approximately 10 minutes in the mould
is generally adequate, the material to be cured preferably remaining in the mould for from 3
to 8 minutes. The temperature of the mould is preferably only from 85 to 100~C.
After removal from the mould, the moulding is advantageously subjected to subsequent
thermal curing in order to ensure that the moulding is fully cured. The subsequent curing is
preferably for a maximum of 5 hours, especially for from 0.5 to 2 hours, at a temperature of
from 120 to 200~C, especially from 130 to 150~C.
The initiators suitable for the process according to the invention for the cationic
polymerisation of the epoxy resins are known. The initiators of formula (I) are described,
inter alia, in EP-A-0 388 837, the description of which is considered a component part of the
present description. The illustrations that are given in that document as preferred
compounds of formula (I) apply in general also to the prese~nt invention. A curing initiator of
formula (I) more especially suitable for the process according to the invention, however, is a
solution, for example a 40 to 50 % by weight solution, of zinc tetrafluoroborate in
tetrahydrofurfuryl alcohol.
Especially advantageous for the process according to the invention, however, are curable
epoxy resin compositions that comprise as curing initiator one of the sulfonium compounds
mentioned hereinbefore.
Corresponding sulfonium compounds are described, for example, in EP-A-0 580 552 and
especially in EP-A-0 379 464. Sulfonium initiators especially preferred according to the
~ - ' 2~0 ~ 584
-- 4 --
invention are the sulfonium compounds of the following formulae (Il) and (Ill) described in
the document last mentioned:
f H2 Arl f H2--Ar1
A S Q (Il) Ar~CH2 S Q- (Ill),
CH2--Ar CH2 Ar
wherein
A is a group selected from C1-C12alkyl, C3-C8cycloalkyl, C4-C1O(cycloalkyl)alkyl, unsubstituted
phenyl, and phenyl mono- or poly-substituted by C1-C8alkyl, C1-C4alkoxy, halogen, hydroxy,
nitro, phenyl, phenoxy, alkoxycarbonyl having from 1 to 4 carbon atoms in the alkoxy radical
or by acyl having from 1 to 12 carbon atoms;
Ar, Ar1 and Ar2 are each independently of the others unsubstituted phenyl or naphthyl, or
phenyl or naphthyl each mono- or poly-substituted by C1-C8alkyl, C1-C4alkoxy, halogen,
hydroxy, nitro, phenyl, phenoxy, alkoxycarbonyl having from 1 to 4 carbon atoms in the
alkoxy radical or by acyl having from 1 to 12 carbon atoms; and
Q~ is SbF6-, AsF6- or SbF50H-.
Of those, special preference is given to sulfonium initiators wherein A is C1-C12alkyl, or
phenyl that is unsubstituted or substituted by halogen or by C1-C4alkyl, Ar, Ar1 and Ar2 are
each independently of the others unsubstituted phenyl or phenyl that is mono- or poly-
substituted by C1-C4alkyl, C1-C4alkoxy, Cl or by Br, and Q~ is SbFsOH-, or especially AsF6- or
SbF6-. The dibenzylphenylsulfonium salts of the latter anions, especially dibenzylphenyl-
sulfonium hexafluoroantimonate, are more especially preferred.
The initiator is usually used in the form of a solution or dispersion in an inert solvent or
dispersant, the solution or dispersion comprising the initiator, for example, in a
concentration of from 5 to 50 % by weight, preferably from 5 to 20 % by weight. Preferred
solvents are the diesters of aromatic dicarboxylic acids, especially dibutyl phthalate.
There may be used as epoxy resins practically all known polyfunctional epoxides that can
be liquefied - where appropriate using diluents - at temperatures below the temperature at
which the initiator starts to bring about noticeable curing. Those polyepoxides may be
220 ~ 58
.~ .
- 5 -
aliphatic, cycloaliphatic or aromatic compounds. Examples of such compounds are the
glycidyl ethers and 13-methyl glycidyl ethers of aliphatic or cycloaliphatic diols or polyols, for
example those of ethylene glycol, propane-1,2-diol, propane-1,3-diol, butane-1,4-diol,
diethylene glycol, polyethylene glycol, polypropylene glycol, glycerol, trimethylol propane or
1,4-dimethylol cyclohexane or of 2,2-bis(4-hydroxycyclohexyl)propane), the glycidyl ethers
of di- and poly-phenols, for example resorcinol, 4,4'-dihydroxydiphenylmethane, 4,4'-
dihydroxydiphenyl-2,2-propane, novolaks and 1,1,2,2-tetrakis(4-hydroxyphenyl)ethane.
Further glycidyl compounds of industrial importance are the glycidyl esters of carboxylic
acids, especially di- and poly-carboxylic acids, for example the glycidyl esters of succinic
acid, adipic acid, azelaic acid, sebacic acid, phthalic acid, terephthalic acid, tetra- and hexa-
hydrophthalic acid, isophthalic acid and trimellitic acid, or of dimerised fatty acids.
Examples of polyepoxides other than glycidyl compounds are the cycloaliphatic epoxy
resins, that is to say the epoxidation products of cycloalkenes, such as, for example, the
diepoxides of vinylcyclohexene and dicyclopentadiene, 3-(3',4'-epoxycyclohexyl)-8,9-epoxy-
2,4-dioxaspiro[5.5]undecane or the 3',4'-epoxycyclohexylmethyl ester of 3,4-epoxycyclo-
hexanecarboxylic acid, or butadiene diepoxide or isoprene diepoxide, epoxidised linoleic
acid derivatives or epoxidised polybutadiene. Cycloaliphatic epoxy resins are especially
reactive and are therefore among the epoxy resins preferred according to the invention,
especially the 3',4'-epoxycyclohexyl methyl ester of 3,4-epoxycyclohexanecarboxylic acid.
More especially preferred epoxy resins are furthermore diglycidyl ethers, which may have
been prelengthened, of dihydric phenols or of dihydric aliphatic alcohols having from 2 to 4
carbon atoms.
More especially preferred for the present invention are the diglycidyl ethers, which may
have been prelengthened, of 2,2-bis(4-hydroxyphenyl)propane (bisphenol A) and bis(4-
hydroxyphenyl)methane (bisphenol F) or a mixture of those epoxy resins.
The compositions used in the process according to the invention generally comprise the
initiator for the cationic polymerisation in an amount of from 0.05 to 20 % by weight,
preferably from 0.2 to 15 % by weight, especially from 0.2 to 5 % by weight, based on the
epoxy resin.
~ ZZ~ 11 5~
-- 6 -
The compositions furthermore preferably comprise fillers. Depending on the purpose that is
to be fulfilled by the use of filler, a broad selection of fillers may be used, for example
talcum, kaolin, mica, gypsum, titanium dioxide, quartz powder, cellulose, argillaceous earth,
ground dolomite, powdered glass, glass beads, xonotlite, wollastonite, silica having a large
specific surface area (for example Aerosil~), magnesium oxide and 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, for example ground. It will
be understood that the fillers should be compatible with the other components of the
composition and preferably should not inhibit, or not inhibit too strongly, the polymerisation
initiator. The fillers advantageously have a particle size of from 10 to 3000 ~lm, preferably
from 50 to 1000 ~Lm, and may in general also be used in large amounts, for example in an
amount of up to 80 % by weight based on the total amount of epoxide composition.Relatively large amounts of filler are of advantage, since they result in a less exothermic
curing reaction, less shrinkage during curing and a harder moulding having good
mechanical properties. They may possibly result, however, in the viscosity of the epoxy
resin compositions being disadvantageously high. The maximum viscosity of the curable
epoxide compositions used for the process according to the invention is preferably 25 Pa s
at 50~C. Good results are obtained, for example, using from 30 to 75 % by weight,
preferably from 50 to 75 % by weight, of filler based on the total amount of epoxide
composition.
The epoxy resin compositions for the present invention may also comprise customary
reactive diluents for epoxy resins, for example epoxy resins that are liquid at temperatures
of from 15 to 30~C, for example in an amount of from 1 to 100 % by weight based on the
remainder of the epoxy resin in the composition. The reactive diluents may alternatively,
however, be compounds having functional groups other than epoxy groups, for example
polyethylene glycols or polypropylene glycols. Such compounds are used preferably in an
amount of from 1 to 20 % by weight based on the epoxy resin in the composition.
If required the compositions according to the invention may furthermore comprisetoughening agents, especially core/shell polymers. Preferred core/shell polymers are
described, for example, in EP-A-0 578 613, EP-A-0 449 776 and US Patent Specification
US-A-4 778 851. They are used preferably in an amount of from 1 to 20 % by weight based
on the total amount of epoxy resin in the composition.
-- 7 -
Finally, the epoxy resin compositions may also comprise other known additives customarily
used in the art of polymerisable materials. Examples of such additives are co-initiators, for
example secondary or tertiary diols, also pigments, dyes, pulverised polyvinyl chloride,
polyolefins, metal powders, such as powdered copper, silver, aluminium or iron, antifoams,
antistatic agents, flow agents, adhesion promoters for the fillers, such as silane or
organotitanate compounds, antioxidants and light stabilisers. Those additives are used in
customary amounts, preferably in amounts of up to 1.5 % by weight based on the resin.
The described epoxy resin compositions are advantageously used in the form of several,
especially two, components, the epoxy group-containing constituents on the one hand and,
on the other hand, the polymerisation initiator and, where appropriate, other constituents
that are reactive with epoxy groups, preferably being contained in different components.
Certain constituents, especially inert constituents such as the fillers may, depending on the
amount, be distributed over several of the components. The components are heatedtogether, or preferably separately, to a temperature of from 30 to 55~C, are if necessary
homogenised, and are then pumped into the mould. The pump pressure is generally at
least 20 kPa.
The process according to the invention is suitable for the manufacture of mouldings of all
kinds, but is used preferably for the manufacture of electrical insulators.
Example 1:
90 g of dibutyl phthalate are heated to 50~C under a dry nitrogen atmosphere. 10 g of
dibenzylphenylsulfonium hexafluoroantimonate are then added, with stirring, and stirring is
continued until all solid material has dissolved. The solution is stored under dry nitrogen.
Stirring with a four-bladed stirrer, first of all 19.95 g of polypropylene glycol (weight average
of molecular weight Mw = 425) are added at a temperature of from 40 to 50~C to 179.55 g
of a mixture of polyglycidyl ether of bisphenol A and polyglycidyl ether of bisphenol F (epoxy
value of the mixture 5.5-5.8 eq/kg). 390.00 g of silicon dioxide are then slowly added to the
mixture, and the resulting mixture is thoroughly homogenised using a high-speed stirrer.
Finally, 10.50 g of the above-mentioned sulfonium salt solution are added, the mixture is
stirred for a further 5 minutes at 40~C and a vacuum is applied to degas the mixture. The
viscosity of the mixture at 40~C is 23288 mPa s, its gelling time at 100~C is 159 seconds
and its total curing enthalpy is 163 J/g.
~ 220 ~ 58~
- 8 -
In order to measure electrical and mechanical properties 8 portions of a degassed mixture
prepared according to the above specification are introduced into moulds measuring 200
mmx200mmx4mmand135mmx135mmx2mm.Eachofthe8portionsiscuredin
accordance with a curing regime described in detail in Table 1.
Table 1
Sample number Curing regime
2 minutes/100~C
2 4 minutes/100~C
3 6 minutes/100~C
4 10 minutes/100~C
20 minutes/100~C
6 60 minutes/100~C
7 60 minutes/100~C + 6 hours/120~C
8 60 minutes/100~C + 12 hours/120~C
The samples are examined without further curing, revealing the properties indicated in the
following Tables 2-A and 2-B.
Table 2-A
Sample number 1 2 3 4
residual enthalpy for full cure [J/g] 31 23 11 9.4
Tg value [~C] 93 88 87 92
flexural strength according to ISO 178 [MPa] 142 139 123 123
elastic modulus according to ISO 178 [MPa] 11741~ 12152 1163910884
flexural elongation (bending test ISO 178) [%] 1.6 1.5 1.3 1.3
tensile strength according to ISO R 527 [MPa] 67 74 75 n. d.
elongation modulus according to ISO R 527 [MPa] 10830 11076 11141n. d.
flexural elongation (tensile test ISO R 527) [%] 0.85 1.1 1.1 n. d.
K1C [MPa m1'2] according to CG 216-0/89 2.23 2.25 2.15 2.06
G1C [J/m2] according to CG 216-0/89 384 379 364 354
dielectric loss factor at 25~C according to IEC 250 [%] n. d. 1.4 1.4 0.8
dielectric constant at 25~C (IEC 250) n.d. 4.1 4.0 4.0
~ ~ 2~ 0 ~ 5 8 ~
g
Table 2-B
Sample number 5 6 7 8
residual enthalpy for full cure [J/g] 2.9 0 0 0
Tg value [oC] 92 91go90
flexural strength according to ISO 178 [MPa] 120 121 116 130
elastic modulus according to ISO 178 [MPa] 11116 11115 11686 11733flexural elongation (bending test ISO 178) [%] 1.3 1.3 1.2 1.3
tensile strength according to ISO R 527 [MPa] 74 70 77 72
elongation modulus according to ISO R 527 [MPa] 10804 10761 10909 10663
flexural elongation (tensile test ISO R 527) [%] 1.0 0.9 1.0 o.s
K1 C [MPa m1'2] according to CG 216-0/89 2.06 2.04 2.06 1.98
G1C [J/m2] according to CG 216-0/89 349 340 329 305
dielectric loss factor at 25OC according to IEC 250 0.7 0.5 0.3 0.3
[%]
dielectric constant at 25 ~C (IEC 250) 4.0 3.9 4.0 4.0
n.d. = not determined
CG-21 6-0/89: Ciba-Geigy AG specification for the double torsion test
Example 2:
7.20 g of dibutyl phthalate are heated to 50~C under a dry nitrogen atmosphere. 0.80 g of
dibenzylphenylsulfonium hexafluoroantimonate are then added, with stirring, and stirring is
continued until all solid material has dissolved. The solution is stored under dry nitrogen.
136.50 g of a polyglycidyl ether of bisphenol A (epoxy value of the mixture 5.25-5.40 eq/kg),
1 3.50 g of a diglycidyl ether of polypropylene glycol 400 (epoxy value 3.05-3.35 eq/kg),
2.00 g of ~-glycidoxypropyltrimethoxysilane and 240.00 g of silicon dioxide are homogen-
eously mixed. 7.80 g of the above-mentioned sulfonium salt solution are then incorporated
into the mixture. The gelling time of the mixture at 100~C is 2.7 minutes. After curing for
30 minutes at 80~C, followed by subsequent curing for one hour at 100~C and for a further
2 hours at 140~C, the material has the properties indicated in Table 3.
-~ 2~ 0 ~ 5 8 ~
- 10-
Table 3
Tg value [~C] 92
flexural strength according to ISO 178 [MPa] 112
elastic modulus according to ISO 178 [MPa] 9259
flexural elongation (bending test ISO 178) [%] 1.4
tensile strength according to ISO R 527 [MPa] 68
elongation modulus according to ISO R 527 [MPa] 8323
flexural elongation (tensile test IS0 R 527) [%] 1.1
K1C [MPa m1'Z] according to CG 216-0/89 1.57
G1C [J/m2] according to CG 216-0/89 242
dielectric loss factor at 25 ~C according to IEC 250 [%] 0.7
dielectric constant (permittivity) at 25 ~C (IEC 250) 4.0
Example 3:
315 g of dibutyl phthalate are heated to 50~C under a dry nitrogen atmosphere. 35 g of
dibenzylphenylsulfonium hexafluoroantimonate are then added, with stirring, and stirring is
continued until all solid material has dissolved. The solution is stored under dry nitrogen.
In a Vogel (VHMA 35) mixer, first of all 498.75 g of polypropylene glycol (weight average of
the molecular weight Mw = 425) are added at a temperature of from 40 to 50~C, with
stirring, to 4488.75 g of a mixture of polyglycidyl ether of bisphenol A and polyglycidyl ether
of bisphenol F (epoxy value of the mixture 5.5-5.8 eq/kg). 8250.00 g of silicon dioxide and
1500.00 g of ground glass fibres are then slowly added to the mixture, and the resulting
mixture is thoroughly homogenised. Finally, 262.50 g of the above-mentioned sulfonium salt
solution are added and the mixture is stirred for a further 105 minutes at 40~C in vacuo.
By means of the automatic pressure gelling technique, the resulting mixture is used to
produce five electrical insulators (Siemens type A) having a diameter of 7.5 cm and a length
of 21 cm. The mould (mould type: Siemens-Stutzer, closure unit: Gr. Suter) in this process
has a temperature of from 90 to 95~C and is filled within, on average,102 seconds at a
pressure of 300 kPa (3 bars). The material being cured then remains in the closed mould for
a further 10 minutes before the mould is opened and the moulding is removed. Theinsulator is subsequently cured for 2 hours at 140~C without the mould. With two turned
brass inserts at each end, the insulator has a total weight of approximately 1150 g.
The insulators have a cantilever strength according to DIN 48136/68 of 5127 N at 23~C. As
shown by X-ray examination, none of the insulators has any internal flaws, fissures or other
faults.
Example 4:
In a Vogel (VHMA 35) mixer, first of all 570.00 g of polypropylene glycol (weight average of
the molecular weight Mw = 425) are added at a temperature of from 40 to 50~C, with
stirring, to 5130.00 g of a mixture of polyglycidyl ether of bisphenol A and polyglycidyl ether
of bisphenol F (epoxy value of the mixture 5.5-5.8 eq/kg). 7500.00 g of silicon dioxide and
1500.00 g of ground glass fibres are then slowly added to the mixture, and the resulting
mixture is thoroughly homogenised. Finally, 300.00 g of a sulfonium salt solution according
to Example 1 are added and the mixture is stirred for a further 120 minutes at 40~C in
vacuo.
By means of the automatic pressure gelling technique, the resulting mixture is used to
produce five electrical insulators (Siemens type A) having a diameter of 7.5 cm and a length
of 21 cm. The mould (mould type: Siemens-Stutzer, closure unit: Gr. Suter) in this process
has a temperature of from 90 to 95~C and is filled, on average, within 107 seconds at a
pressure of 300 kPa (3 bars). The material being cured then remains in the closed mould for
a further 7 minutes before the mould is opened and the moulding is removed. The insulator
is subsequently cured for 2 hours at 140~C without the mould. With two turned brass inserts
at each end, the insulator has a total weight of approximately 1150 g. The insulators, which
again have no internal flaws, fissures or other faults, have a cantilever strength according to
DIN 48136/68 of 4849 N at 23~C.
Example 5:
472.5 g of dibutyl phthalate are heated to 50~C under a dry nitrogen atmosphere. 52.5 g of
dibenzylphenylsulfonium hexafluoroantimonate are then added, with stirring, and stirring is
continued until all solid material has dissolved. The solution is stored under dry nitrogen.
In a Vogel (VHMA 35) mixer, 418.5 g of polypropylene glycol (weight average of the
molecular weight Mw = 425) are added at a temperature of from 40 to 50~C, with stirring, to
3766.6 g of a mixture of polyglycidyl ether of bisphenol A and polyglycidyl ether of
bisphenol F (epoxy value of the mixture 5.5-5.8 eq/kg). 465.0 g of a toughening agent
based on a microgel according to the specification hereinafter, described in EP application
- 12 -
No. 96 810812.6, are also added to the resin mixture. Subsequently, 9750.00 g of silicon
dioxide and 75 g of Silan~ A-137 are added to the mixture, and the resulting mixture is
thoroughly homogenised. Finally, 525.00 g of the above-mentioned sulfonium salt solution
are added and the mixture is stirred for a further 105 minutes at 40~C in vacuo.
By means of the automatic pressure gelling technique, the resulting mixture is used to
produce five electrical insulators (Siemens type A) having a diameter of 7.5 cm and a length
of 21 cm. The mould (mould type: Siemens-Stutzer, closure unit: Gr. Suter) in this process
has a temperature of from 90 to 95~C and is filled within, on average, 2 minutes (pressure
of 300 kPa or 3 bars). The material being cured then remains in the closed mould for a
further 10 minutes before the mould is opened and the moulding is removed. The insulator
is subsequently cured for 2 hours at 140~C without the mould. With two turned brass inserts
at each end, the insulator has a total weight of approximately 1150 g.
The insulators have a cantilever strength according to DIN 48136/68 of 6756 N at 23~C. As
shown by X-ray examination, none of the insulators has any internal flaws, fissures or other
faults.
Preparation of the toughening agent used:
76.8 g of polybutadiene latex (Baystal~ S polybutadiene 2004, Bayer AG) having a solids
content of 59 % by weight and 148.2 g of deionised water are stirred under nitrogen in a
350 ml sulfonating flask fitted with a glass anchor agitator, thermometer, gas connection
and two metering connections. The mixture is heated to 80~C (internal temperature). The
following monomer mixture and initiator/emulsifier solution are metered in over a period of
1.25 hours:
Monomer mixture Initiator/emulsifier solution
MMAl) 35-55 g APS4) 0.45 g
EGDMA2) 2.7 g SDS5) 1.5 g
Bisomer ~ PPM6E3) 6.75 g Di water~) 45 g
1) methyl methacrylate; 2) ethylene glycol dimethacrylate; 3) polypropylene glycol
monomethacrylate having an average of 6 propylene glycol units (British Petroleum);
4) ammonium persulfate; ~) sodium dodecylsulfate; ~) deionised water
After the addition, the mixture is stirred for a further 4.75 hours at 80~C and polymerised.
The reaction emulsion is then cooled to room temperature (RT) and filtered through a paper
filter. Solids content: 28.3 % by weight. Proportion of crosslinking component in the dish: 6
O ~ 5~
- 13-
% by weight. For use, the toughening agent is mixed in the desired amount with the resin,
after which the water present in the mixture is removed under a high vacuum using a rotary
evaporator (bath temperature approximately 70~C).
