Note: Descriptions are shown in the official language in which they were submitted.
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Hot-foamable, thermosetting epoxy resin mixture
The present invention relates to a hot-foamable, thermosett$ng epoxy
resin mixture containing a novolak as the curing agent and, as the blow-
ing agent, a compound which splits off nitrogen above 100C with decom-
position, the use of the epoxy resin mixture for the production of foams
and processes for the production of foams.
Foams based on epoxy resins are known and are generally distinguished by
good mechanical strength and a good dimensional stability. For example,
according to DE-OS 1,770,659, foams are produced by curing epoxy resins
with cycloaliphatic polyamines at room temperature in the presence of
polyhydric phenols as accelerators and of a blowing agent. The foams
produced in this manner have a low compressive strength.
Foams with low compressive strength are likewise obtained by the process
disclosed in DE-OS 2,~43,430, in which a certain epoxy resin foam mixture
is cured at room temperature or somewhat elevated temperature using a
Lewis acid or an addition or complex compound of a Lewis acid.
It has now been found that hardened Eoams which in particular have better
compressive strength and compression values, especially at elevated tem-
perature, are obtained by hot-foaming, that is to say at temperatures
above 100C, an epoxy resin mixture containing a novolak as the curing
agent in a certain equivalent ratio relative to the epoxide group and a
blowing agent which splits off nitrogen above 100C.
The present invention thus relates to a hot-foamable, thermosetting epoxy
resin mixture containing (a) an epoxy resin or a mixture of epoxy resins
with an average epoxide content of 4.4 to 5.0 equivalents/kg and an aver-
age epoxide functionality of more than 2.0, (b3 a novolak with a hydroxyl
equivalent weight of 90 to 120, 0.8 to 0.95 hydroxyl equivalents of com-
ponent (b) being present in the epoxy resin mlxture per 1 epoxide equiva-
lent of component (a), (c) 0.1 to 1~ by weight, based on the amount of
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components (a) and (b), of a curing accelerator, (d) 0.5 to 10% by
weight, based on the amount of components (a~ and (b), of a blowing agent
which splits off nitrogen above 100C with decomposition, (e) 0.3 to 1%
by weight, based on the total amount of the epoxy resin mixture, of an
emulsifier, and if appropriate (f) foam modifiers.
The hot-foamable epoxy resin mlxture according to the invention prefer-ably contains an epoxy resin or an epoxy resin mixture (a) with an aver-
age epoxide content of 4.S to 5.0 equivalents/kg, a novolak (b) with a
hydroxyl equivalent weight of 115 to 120 and a curing accelerator (c) in
a~ounts of 0.3 to lYo by weight, based on the amount of components (a) and
(b).
The epoxy resins or mixtures of epoxy resins contained as component (a)in the epoxy resin mixture according to the invention are known and are
in some cases commercially available. Examples of such resins or resin
mixtures which may be mentioned are: polyglycidyl esters of polycarboxy-
lic acids, such as trime~litic acid, trimesic acid or pyromellitic acid,
or of mixtures of polycarboxylic acids with dicarboxylic acids, such as
phthalic acid or terephthalic acid; poly(N-glycidyl) compounds of dia-
~ines, such as mrxylylenediamine, bis-(4-aminophenyl)-methane or bis-(3-
methyl-4-aminophenyl)-methane or of mixtures of diamines with monoamines,
such as aniline; glycidyl ethers of polynuclear phenols, such as novo-
laks, which as i5 known are derived from aldehydes, such as formaldehyde,
acetaldehyde, chloral or furfurylaldehyde, and phenols, such as phenol or
phenol which is substituted on the ring by chlorine atoms or alkyl groups
with up to 9 C atoms, such as 4-chlorophenol, 2-methylphenol or 4-tert-
butylphenol, and glycidyl ethers of mixtures of polynuclear phenols and
mono- or dinuclear phenols, such as resorcinol, hydroquinone, bis-(4-
hydroxyphenyl)-methane, 4,4'-dihydroxydiphenyl, bis-(4-hydroxyphenyl)
sulfone, 1,1,2,2-tetrakis-(4-hydroxyphenyl)-ethane, 2,2-bis-(4-hydroxy-
phenyl)-propane or 2,2-bis-(3,5-dibromo-4-hydroxyphenyl)-propane.
The mixture according to the invention can furthermore contain, as compo-
nent (a), triglycidyl isocyanurate or epoxy resins in which the glycidyl
groups are bonded to different hetero atoms, for example the N,N,0-tri-
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glycidyl derivative of 4-aminophenol.
The mixture according to the invention preferably contains, as component
(a~, one or more aromatic glycidyl ethers, in particular a cresol novolak
glycidyl ether or a mixture of a cresol novolak glycidyl ether and a bis-
phenol A diglycidyl ether.
i
The novolaks contained as component (b) in the mixture according to the
invention are likewise known compounds, some of which are commercially
available, and are condensation products prepared from a phenol, for
example phenol itself or alkyl-, alkoxy- or halogen-substituted phenol,
and an aldehyde, for example formaldehyde, acetaldehyde, chloral or fur-
furyLaldehyde. Such novolaks correspond to the general formula I
~H Y ~H
.~i'\. .~ ~. . ,~
! I! CHR~- -~ I! CHR~ - -~+
~(R2~m (R2~m
ln which R1 i9 a hydrogen atom, alkyl, aryl or a hetèrocyclic radical, R2
is a halogen atom, alkyl or alkoxy, m is zero or a number from 1 to 3 and
n is a number such that the novolak has a hydroxyl equivalent weight of
90 to 120, preferably 115 to 120.
Preferred novolaks are those of the formula I in which R1 is a hydrogen
atom, R2 is alkyl with 1 to 4 C atoms and m is zero or the number 1.
The mixtures according to the invention contain in particular, as compo-
nent (b), a cresol novolak.
Curing accelerators (c) which can be used for the mixture according to
the invention are the customary accelerators which can be used for curing
an epoxy resin with a novolak, for example dicyandiamide, tertiary
amines, such as tri-n-butylamine, tri-isobutylamine, benzyldlmethylamine,
tri-n-propylamine, tri-(hexyl)-amine or 2,4,6-tris-(dimethylamino~ethyl)-
phenol, quaternary ammonium compounds, such as tetramethylammonium chlor-
ide, benzyltrimethylammonium hydroxide or benzyltrimethylammonium
... .
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~ 21489-7424
chloride, m-phenylenediamine, hexamethylenetetramine, imidazole or imi-
dazole derivatives, for example 2-methylimidazole, 2-ethylimidazole, 2-
ethyl-4-methylimidazole, 2-phenylimidazole or benzimidazole. The mixture
according to the invention preferably contains an imidazole or an imi-
dazole derivative, in particular 2-ethylimidazole, as the curing accele-
rator.
Blowing agents (d) which can be used for the mixture according to the in-
vention are substances which split off nitrogen with decomposition, when
the mixture is heated above 100C, for example azo compounds, such as
azoisobutyronitrile, or hydrazides, such as p-toluenesulfohydrazide
(Genitron PTS~). The mixtures according to the invention preferably con-
tain p-toluenesulfohydrazide as the blowing agent.
The emulsifiers (e~ contained in the mixture according to the invention
are surface-active agents which act as pore regulators. They have the
function of distributing the nitrogen formed from the blowing agent in
regular bubbles throughout the entire foam, so that a foam with a sub-
stantially closed cellular structure is obtained. Substances which are
; particulary suitable for regulating the pore structure are non-ionic
substancesS for example hydroxyl-containing esters of fatty acids, such
as lauric, palmitic, stearic or oleic acid, with polyhydric alcohols,
such as sorbitol, and addition products thereof with polyoxyethylene onto
the free hydroxyl groups (Tweens~), for example polyoxyethylene sorbitan
monolaurate or monostearate, and furthermore polyoxyglycols (Pluronics~).
Silicone oils, such as are commercially available, for example, under the
tradename Rhodorsil~ from Rhône-Poulencl are known to be good pore regu-
lators. The mixture according to the invention contains in particular as
the emulsifier a polyether-polymethylsiloxane copolymer (Tegopren~ 5851
from Goldschmidt).
If appropriate, the mixture according to the invention can also contain
customary foam modifiers, that is to say substances which can reduce the
viscosity of the mixture according to the invention during processing,
can improve the flow behavior of the foam or can be used as solvents for
additives. These foam modifiers can be reactive, that is to say they can
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react with a component of the foam, or non-reactive. To improve the flow
behavior of the foam, nonylphenol, for example, can be added to the mix-
ture according to the invention as a reactive modifier and ethylhexyl
phthalate, for example, can be added as a non-reactive modifier. They
are advantageously used in amounts of 0.5 to 10% by weight, based on the
amount of components (a~ and (b).
Dyes, fillers, plasticizers or flameprooflng agents, for example
Al203-3 H20, polyethylene, polypropylene or polyvinyl chloride, can
furthermore be added to the mixture accordlng to the invention.
The mixture according to the invention can be processed to foams manually
or by means of a suitable machine, by foaming and curing the mixture in
the temperature range from 120 to 180C. The mixture according to the
invention is advantageously suitable for mechanical production of a foam,
for example by means of RDM machine (reactive injection moulding
machine), since the viscosity of the mixture according to the invention
does not change greatly during storage at elevated temperature and no
severe evolution of heat occurs during curing of the foam in the closed
mould, so that foam formation is not interfered with and a foam with a
high degree of closed cellular structure is obtained. Cycle times of 10
to 20 minutes can be achieved in mechanical processing of the mixture ac-
cording to the invention to give cured foams.
The present invention thu5 also relates to the use of the mixture accord-
ing to the invention for mechanical production of a foam and a process
for the production of crosslinked, insoluble and non-fusible epoxy resin
foams by foaming and curing the mixture according to the invention in the
temperature range from 120 to 180C, preferably from 130 to 160C.
The foams produced from the mixture according to the invention are dis-tinguished by a homogeneous pore structure and a high degree of closed
cellular structure. The foams also have a good stability to prolonged
heat exposure and a good compressive strength, also at elevated tempera-
ture. The foams obtained from the mixture according to the invention are
therefore particularly suitable as insulating materials against heat loss
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and against pressure and impact.
In the followlng examples, foams are ?roduced using a casting mould.
Ihis mould has internal dimensions of 250x250x30 m~ and consists of two
outer metal plates (20 mm) which can be heated electrically and are sepa-
rated 30 mm from one another by an unheated spacer frame. The spacer
frame can be opened on one side so that the activated foam mixture can be
poured in. The outer plates which can be heated and the metal spacer
frame are held together by four screw clamps during curing of the foamed
sheet. The sheets are cast upright, and for this the top screw clamp is
removed and 1/4 of the spacer frame is removed. After the activated foam
mixture has been poured in, the section of the spacer frame which has
been removed is inserted and the screw clamp is closed. The still hot
plates and the hot spacer frame are coated with OP wax or a silicone-
containing release agent for better removal from the mould.
Example 1: A foam is produced using the following compounds:
bisphenol A diglycidyl ether (liquid,
epoxide equivalent weight 185) 276.8 g (1.5 equivalents)
cresol novolak glycidyl ether (solid,
epoxide equivalent weight 230) 276.8 g (1.2 equivalents)
cresol novolak (solid,
hydroxyl equivalent weight 115) 287.2 g (2.5 equivalents)
polyether-polymethylsiloxane copolymer
(emulsifier) 6.2 g
2-ethylimidazole (accelerator) 4.5 g
p-toluenesulfohydrazide (blowing agent) 7.0 g
The bisphenol A diglycidyl ether (BPAD) is heated to about 145C in a
glass beaker which stands in an oil bath heated at 170C and is equipped
with a high-speed stirrer. The cresol novolak glycidyl ether (CNG) is
sprinkled into the BPAD in portions at this temperature, and as soon as
the CNG has dissolved the cresol novolak is introduced in small portions.
When everything has dissolved and the matrix has reached a temperature of
about 145C, the polyether-polymethylsiloxane copolymer is added with
stirring. The glass beaker with the hot resin-curing agent mixture is
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removed from the oil bath and 2-ethyl-imidazole and p-toluenesulfohydra-
zide are stirred in homogeneously in the course of 20 - 30 seconds. The
activated foam mixture is poured into the hot casting mould at 130 -
140C in the course of a further 20 seconds. The casting mould is
closed with screw clamps in the course of a further 20 seconds. The
increase in pressure in the closed casting mould takes place after 1 - 5
minutes. After 10 - 20 minutes, the mould is opened and one plate of the
still hot mould is removed. The cooled sheet of foam is split off into
the desired test specimens with a circular saw. Exclusively test speci-
mens without top coatings are tested. The properties of the foam obtain-
ed are shown in Table I.
Example 2: Example 1 is repeated, but 11.8 g of p-toluenesulfohydrazide
are now added to the resin-curing agent mixture. Curing conditions: 20
minutes/140c. The properties of the foam obtained are shown in Table I.
Example 3: ~ foam ls produced as in Example l using the following com-
.
pounds:
bisphenol ~ diglycidyl ether (liquid,
epoxide equivalent welght 185) 166.1 g (0.9 equivalent)
cresol novolak glycidyl ether (solid,
epoxlde equivalent weight 230) 166.1 g (0.7 equivalent)
cresol novolak (solid,
hydroxyl equivalent weight 115) 172.3 g (1.5 equivalents)
polyether-polymethylsiloxane copolymer 3.6 g
2-ethylimidazole 3.3 g
p-toluenesulfohydrazide 10.0 g
Curing conditions: 20 minutes/145C. The properties of the foam obtained
are shown in Table I.
Example 4: A foam is produced as in Example 1 using the following com-
pounds:
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bisphenol A diglycidyl ether (liquid,
epoxide equivalent weight 185) 92.3 g (0.5 equivalent)cresol novolak glycidyl ether (solid,
epoxide equivalent weight 230) 92.3 g (0.4 equivalent)cresol novolak (solid,
hydroxyl equivalent weight 115) 95.7 g (0.8 equivalent)polyether-polymethylsiloxane copolymer 2.0 g
2-ethylimidazole 1.8 g
p-toluenesulfohydrazide 13.0 g
.
Curing conditions: 15 minutes/145C. The properties of the foam obtained
are shown in Table I.
Example 5: Example 1 is repeated, but, instead of 287.2 g, 257.2 g (2.2
equivalents) of solid cresol novolak with a hydroxyl equivalent weight of
115 are now used. Curing conditions: 15 minutes/145C. The properties
of the foam obtained are shown in Table I.
Example 6: A foam is produced as in Example 1 using the following com-
pounds:
bisphenol A diglycidyl ether (liquid,
epoxide equivalent weight 185)276.8 g (1.5 equivalents)
cresol novolak glycidyl ether (solid,
epoxide equivalent weight 230)276.8 g (1.2 equivalents)
cresol novolak (solid,
hydroxyl equivalent weight 115)257.2 g (2.2 equivalents)
polyether-polymethylsiloxane copolymer 6.2 g
2-ethylimidazole 7.5 g
p-toluenesulfohydrazide 7.0 g
nonylphenol 30.0 g
Curing conditions: 15 minutes/135C. The properties of the foam obtained
are shown in Tables I and II.
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Example 7: Example 6 is repeated, but, instead of 30.0 g, 60.0 g of
nonylphenol are now used. Curing conditions: 15 mlnutes/135C. The pro-
perties of the Eoam obtaLned are shown in Table I.-
Example 8: Example 6 is repeated, but, instead of 30.0 g, 75 g of nonyl-
phenol are now used. Curing conditions: 15 minutes/135C. The proper-
ties of the foam obtained are shown in Table I.
Example 9: A foam is produced as in Example 1 using the following CO~r
pounds:
bisphenol A diglycidyl ether (liquid,
epoxide equivalent weight 185)221.5 g (1.2 equivalents)
cresol novolak glycidyl ether (solid,
epoxide equivalent weight 230)332.2 g (1.4 equivalents)
cresol novolak (solid,
hydroxyl equivalent weight 115)250.5 g (2.2 equivalents)
polyether-polymethylsiloxane copolymer 6.0 g
2-ethylimidazole 7.5 g
p-toluenesulfohydrazide 6.8 g
nonylphenol 30.0 g
Curing conditions: 15 minutes/135C. The properties of the resulting
foam are shown in Tables I and II.
Example 10: ~ foam is produced as in Example 1 using ~he following com-
pounds:
bisphenol A diglycidyl ether (liquid,
epoxide equivalent weight 185) 166.1 g (0.9 equivalent)
cresol novolak glycidyl ether (solid,
epoxide equivalent weight 230) 387.5 g (1.7 equivalents)
cresol novolak (solid,
hydroxyl equivalent weight 115) 246.7 g (2.15 equivalents)
polyether-polymethylsiloxane copoly=er 6.0 g
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2-ethyllmidazole 7.5 g
p-toluenesulfohydrazide 6.8 g
nonylphenol 30.0 g
Curing conditions: 15 minutes/140C. The properties of the resulting
foam are shown in Table I.
Example 11: A foam is produced as in Exa~ple 1 using the Eollowing com-
pounds:
bisphenol A diglycidyl ether (liquid,
epoxide equivalent weight 185)110.7 g (0.6 equivalent)
cresol novolak glycidyl ether (solid,
epoxide equivalent weight 230)442.9 g (1.9 equivalents)
cresol novolak (solid,
hydroxyl equivalent weight 115)240.1 g (2.1 equivalents)
polyether-polymethylsiloxane copolymer 6.0 g
2-ethylimidazole 7.5 g
p-toluenesulfohydrazide 6.8 g
nonylphenol 30 0 g
Curing conditions: 15 minutes/140C. The properties of the resulting
foam are shown in Table I.
;
Example 12: Example 1 is repeated, but, instead of 4.5 g, 5.5 g of 2-
ethylimidazole are now used. Curin~ conditions: 15 minutes/140C. The
properties of the foam obtained are shown in Table I.
. :
Example 13: Example 1 is repeated, but, instead of 4.5 g, 6.5 g of 2-
ethylimidazole are now used. Curing conditions: 15 minutes/140C. The
properties of the foam obeained are shown in Table I.
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Table II: Properties of the foams at elevated temperature
.
. Foam according to Example 6 9
: _
Compressive strength (DIN 53 421-A)
: at 23C [N/mm2] 12.7 12.6
; Compression (DIN 53 421-A)
. at 23C [%] 16.6 17.4
Compressive strength at 80C [N/mm2] 9.4 ô.9
Compression at 80C [%] 14.8 11.4
: Compressive strength at 100C [N/mm2]7.3 8.3
~ Compression at 100C [%] 14.8 12.8
: Compressive strength at 120C [N/mm2]5.3 7.1
Compression at 120C [%] 14.7 15.2
Example 14: The procedure of Example 1 is followed, but, instead of p-
toluenesulfohydrazide, 7.6 g of azo-isobutyronitrile are now used, and,
instead of polyether-polymethylsiloxane copolymer, 6.0 g of silicone oil
(RhodorsilR 3139~ are now employed. The foam matrix is poured at 105C
into the mould heated to 140C. Curing conditions: 15 minutes at 140C.
The cured foam has the following properties:
density = 0.36 g/cm3
closed cellular structure = 94.0%.
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Example 15_ The procedure is as in ~xample 1, the following compounds
being used for production of the foam:
bisphenol A diglycidyl ether (highly viscous,
epoxide equivalent weight 222) 574.0 g (2.58 equivalents)
cresol novolak (solid, hydroxyl
equivalent weight 115) 266.0 g (2.31 equivalents)
polyether-polymethylsiloxane copolymer 6.0 g
2-ethylimidazole 7.5 g
p-toluenesulfohydrazide 7.5 g
Curing conditions: 15 minutes at 140C. The cured foam has a density of
0.39 g/cm3.
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