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Description  |
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The invention relates to heat-curable compositions of matter which are
stable on storage and which contain certain difunctional and
polyfunctional epoxy resins, phenolic curing agents and certain
thermoplastics having phenolic end groups, and to the use thereof for the
production of shaped articles, in particular prepregs for fibre-reinforced
composite materials and adhesive films.
A large number of curable epoxy resin compositions of matter also
containing, inter alia, phenolic curing agents are known. Thus, for
example, Japanese Preliminary Published Specification 76/129,498 describes
compositions of matter containing polyfunctional epoxy resins, phenolic
curing agents and accelerators and the use thereof for the production of
prepregs for special electrical insulating materials. U.S. Pat. No.
4,322,456 discloses mixtures of epoxy resins, phenolic curing agents and
accelerators in which the functionality of the epoxy resins and/or of the
curing agents is preferably greater than 2 and which are suitable for the
production of curable coatings, in particular as powder paints. U.S. Pat.
No. 4,288,565 describes mixtures of epoxy resins of high and low epoxide
equivalent weight and phenolic curing agents which are, to the extent of
at least 30%, compounds having 3 or more hydroxyl groups per molecule.
The present invention relates to heat-curable compositions of matter which
are stable on storage and which contain
(a) 5-70 parts by weight of an epoxy resin having a functionality of at
least 3,
(b) 95-30 parts by weight of an epoxy resin having a functionality of
2-2.5,
(c) a diphenol, the amount of the diphenol being so chosen that 0.6-1.2
hydroxyl equivalents of the diphenol (c) are employed per epoxide
equivalent of the epoxy resins (a) and (b), and
(d) 10-150 parts by weight, relative to 100 parts by weight of the
components (a) to (c), of a thermoplastic having phenolic end groups and
having a glass transition temperature of at least 150.degree. C. which is
compatible with the mixture of the components (a) to (c).
Component (d) of the compositions according to the invention must be
compatible with the mixture of the components (a) to (c), i.e. it must be
soluble within the range of proportions according to the definition in the
melt of (a)+(b)+(c).
The compositions according to the invention are suitable for the production
of shaped articles, prepregs and adhesive films, and the cured products
are distinguished by good resistance to solvents, and excellent thermal
and mechanical properties, in particular by a high heat distrotion point,
an excellent fracture toughness, flexural strength and impact strength and
a very high elongation at break.
The compositions also exhibit excellent processing properties, for example
a high degree of homogeneity, a low melt viscosity and a long pot life.
After curing, the compositions of matter according to the invention
produce crosslinked polymers having properties similar to thermoplastics
(high elongation at break, flexural strength and impact strength) without
the necessity to accept the difficulties which occur, because of their
very high viscosity, when high-molecular thermoplastics are processed. The
compositions according to the invention have a relatively low viscosity
and can be processed without problems at low temperatures (120.degree. to
200.degree. C.).
Epoxy resins (a) and (b) which are suitable for the present compositions
are any resins which have a functionality of at least 3 or 2-2.5 and which
can be cured by means of diphenols (c).
Epoxy resins having a functionality of 3, for example, are understood to
mean resins which have an average of 3 epoxide groups per molecule.
Examples of resins which are suitable as epoxy resins (a) and (b) are
diglycidyl or polyglycidyl ethers of cycloaliphatic polyols, such as
2,2-bis(4'-hydroxycyclohexyl)propane, diglycidyl or polyglycidyl ethers of
polyhydric phenols, such as resorcinol, bis(4'-hydroxyphenyl)methane
(bisphenol F), 2,2-bis(4'-hydroxyphenyl)propane (bisphenol A),
2,2-bis(4'-hydroxy-3',5'-dibromophenyl)propane or
1,1,2,2-tetrakis(4'-hydroxyphenol)ethane, or condensation products of
phenols with formaldehyde, such as phenol novolaks and cresol novolaks;
and also di(.beta.-methylglycidyl)-or poly(.beta.-methylglycidyl) ethers
of the polyalcohols and polyphenols listed above;
Polyglycidyl esters and poly(.beta.-methylglycidyl) esters of polybasic
carboxylic acids, such as phthalic acid, terephthalic acid,
tetrahydrophthalic acid and hexahydrophthalic acid;
Glycidyl derivatives of aminophenols, for example
triglycidyl-p-aminophenol;
N-glycidyl derivatives of amines, amides and heterocyclic nitrogen bases,
such as N,N-diglycidylaniline, N,N-diglycidyltoluidine,
N,N,N',N'-tetraglycidyl-bis(4-aminophenyl)methane, triglycidyl
isocyanurate, N,N-diglycidyl-N,N'-ethyleneurea,
N,N'-diglycidyl-5,5-dimethylhydantoin,
N,N'-diglycidyl-5-isopropylhydantoin or
N,N'-diglycidyl-5,5-dimethyl-6-isopropyl-5,6-dihydrouracil;
Polyfunctional epoxy resins, such as the 2,6-disubstituted
4-epoxypropylphenyl glycidyl ethers and adducts thereof described in EP
205,409 and EP 204,659;
Bisphenols which are substituted in each case by two glycidyloxy and
2,3-epoxypropyl groups, for example
2,2-bis(3'-epoxypropyl-4'-epoxypropylphenyl)propane, which is described in
GB No. 828,364;
Glycidyl derivatives of tetramethylol-substituted cyclohexanols,
cyclohexanones, cyclopentanols and cyclopentanones, such as the compounds
described in U.S. Pat. No. 4,549,008;
And glycidyloxy-substituted benzophenones and glycidyloxydiketones, such as
the compounds described in U.S. Pat. No. 4,649,181.
In general, mixtures of two or more epoxy resins can also be used as
component (a) and/or as component (b) in the compositions according to the
invention.
Compounds which are particularly suitable as epoxy resins (a) and (b) are
those which have an epoxide content of 5-11 equivalents/kg, and are
glycidyl ethers, glycidyl esters or N-glycidyl derivatives of a
cycloaliphatic, aromatic or heterocyclic compound. Epoxy resins (a) and
(b) which are particularly preferred are epoxy novolaks or glycidyl
derivatives of a bisphenol, an aromatic diamine, an aminophenol, a
hydantoin or a tetramethylolcyclohexane.
Resins suitable as epoxy resin (a) are preferably epoxyphenol novolaks or
glycidyl derivatives of an aromatic diamine, an aminophenol or a
tetramethylolcyclohexane. They preferably have a functionality of 3 to 4.
Resins suitable as epoxy resin (b) are, in particular, epoxyphenol
novolaks or glycidyl derivatives of bisphenol A or of bisphenol F. They
preferably have a functionality of 2 to 2.2.
Examples of suitable diphenols (c) are mononuclear and polynuclear
dihydroxy aromatic compounds which can contain condensed benzene rings.
Particularly suitable compounds are those of the formulae I, Ia or II
##STR1##
in which T is a direct bond, methylene, isopropylidene, O,S, CO or
SO.sub.2 and R is hydrogen or C.sub.1 -C.sub.4 alkyl, or
dihydroxynaphthalene or mixtures of these compounds. Amongst the compounds
of the formulae I and Ia, preferred compounds are those in which the
hydroxyl groups are attached in the 4,4'-position. Examples of suitable
compounds of the formula Ia are compounds in which T is isopropylidene and
the benzene rings are in each case substituted in the para-position or in
the meta-position. These products are obtainable under the name bisphenol
P or bisphenol M from Mitsui Petrochemical. Amongst the compounds of the
formula II, 2,6-dihydroxytoluene is preferred.
Diphenols (c) which are particularly preferred are bisphenol A, bisphenol
F, bisphenol P, bisphenol M, 4,4'-dihydroxydiphenyl sulfide,
2,6-dihydroxynaphthalene and, in particular, 2,7-dihydroxynaphthalene or
4,4'-dihydroxydiphenyl ether.
A mixture of 2,6-dihydroxytoluene and 2,7-dihydroxynaphthalene is also
suitable as a phenolic curing agent. Particularly good results are
achieved if equal amounts by weight of these compounds are mixed in the
melt at approx. 180.degree. C., the product obtained after the
solidification of the melt is ground to give a fine powder and this is
then employed as the curing agent.
If it is suitable, the compositions of matter according to the invention
can, in addition to the diphenols (c), also contain a certain amount of
one or more triphenols or polyphenols, for example
2,4,6-tris[2'-(p-hydroxyphenyl)-2'-propyl]benzene ("tris-TC" made by
Mitsui Petrochemical) as curing agent. In general, however, not more than
50%, preferably not more than 30%, of the phenolic hydroxyl groups should
originate from a triphenol or polyphenol, and the remainder of the
hydroxyl groups should belong to a diphenol. If triphenols or polyphenols
are used in addition to the diphenols as component (c), the proportion of
the epoxy resin (a) can be reduced and the proportion of the epoxy resin
(b) can be increased correspondingly. Phenol novolaks or cresol novolaks
are generally not suitable as phenolic curing agents for the compositions
according to the invention. It will readily be understood that, if both
diphenols and triphenols or polyphenols are used, the amount of the total
phenolic curing agent (c) is so chosen that a total of 0.6-1.2 hydroxyl
equivalents of the phenols employed is present in the compositions
according to the invention per epoxide equivalent of epoxy resins
employed.
If it is suitable, the compositions according to the invention can contain,
in addition to the components (a) to (d), also (cl) 0.05-5% by weight of
an accelerator, relative to the epoxy resins (a) and (b). Compositions
which do not contain an N-glycidyl derivative either as the epoxy resin
(a) or as the epoxy resin (b) preferably contain an accelerator (c1) in
addition to the diphenols (c).
Accelerators (c1) suitable for the curable compositions of matter are all
the compounds known to those skilled in the art for accelerating the
crosslinking reaction of epoxy resins by phenolic curing agents, for
example tertiary amines, salts thereof or quaternary ammonium compounds,
such as tetramethylammonium chloride, phosphonium salts, alkali metal
alcoholates, for example sodium hexanetriolate, Lewis acids, for example
BF.sub.3 or SnCl.sub.4, and nitrogen-containing heterocyclic compounds,
such as pyridines, imidazoles and derivatives thereof. Imidazoles and
N-acylimidazoles (imidazolides) are particularly suitable as accelerators
(c1).
Examples of suitable imidazoles are compounds of the formula III
##STR2##
in which the substituents R.sup.a independently of one another are
hydrogen, C.sub.1 -C.sub.12 alkyl, C.sub.5 -C.sub.10 cycloalkyl or C.sub.6
-C.sub.10 aryl. 2-Methylimidazole, 2-ethylimidazole, 2-phenylimidazole and
2-ethyl-4-methylimidazole are particularly preferred.
Examples of suitable N-acylimidazoles (imidazolides) are the compounds
described in U.S. Pat. No. 4,436,892, U.S. Pat. No. 4,587,311 and Japanese
Preliminary Published Application No. 74/7599. Particularly suitable
compounds are those of the formula IV
##STR3##
in which R.sup.a is as defined above and the substituents R.sup.b
independently of one another are hydrogen, C.sub.1 -C.sub.12 alkyl,
halogen, nitro or trifluoromethyl. Examples of suitable imidazolides are
1-(2',4',6'-trimethylbenzoyl)-2-ethylimidazole,
1-(2',6'-dichlorobenzoyl)-2-methylimidazole,
1-(2',4',6'-trimethylbenzoyl)-2-methylimidazole and
1-(2',4',6'-trimethylbenzoyl)-2-phenylimidazole.
If it is suitable, the compositions according to the invention can, in
addition to the components (a) to (d) also contain (e) a thermoplastic
which has no phenolic end groups and has a glass transition temperature of
at least 180.degree. C., the total amount of the thermoplastic components
(d) and (e) being 10-150 parts by weight, relative to 100 parts by weight
of the components (a) to (c), and (d) preferably making up at least 30% by
weight, in particular 40-70% by weight, of the components (d) and (e).
All the known polymers which have a sufficiently high glass transition
temperature, ie. .gtoreq.180.degree. C., and are miscible with the epoxy
resin/curing agent system according to the application can be employed as
thermoplastics (e) in the curable compositions of matter according to the
invention. By virtue of their properties, polysulfones,
polyether-sulfones, polyimides, polyether-imides, polyethers or
polyether-ketones are particularly suitable as thermoplastics. The glass
transition temperature of the thermoplastic is preferably within the range
from 180.degree. to 450.degree. C. In this regard, thermoplastics having a
glass transition temperature of 180 to 350, particularly 190.degree. to
250.degree. C., are particularly preferred. If polyether-imides are used,
polymers having a T.sub.g of 220.degree. to 250.degree. C. are
particularly preferred, and if polyimides are used those having a T.sub.g
of 280.degree. to 340.degree. C. are particularly preferred. The
thermoplastics (e) preferably have a molecular weight of 20,000-100,000,
in particular 20,000-70,000, and a glass transition temperature of
240-450, in particular 300.degree.-420.degree. C.
If a polysulfone is employed as the thermoplastic (e), examples of suitable
compounds are those having the recurring unit of the formula
--A--SO.sub.2 --
in which A is a divalent aromatic group which can be interrupted by ether
oxygen atoms and/or divalent aliphatic groups.
The polysulfones to be employed can be obtained in a known manner, for
example by heating either (a) a sulfonyl halide of the formula HA.sub.1
SO.sub.2 X or (b) a mixture of a disulfonyl halide of the formula
XSO.sub.2 A.sub.1 SO.sub.2 X with a compound of the formula HA.sub.2 H
which is free from sulfonyl halides and in which A.sub.1 and A.sub.2 are
identical or different and are in each case a divalent aromatic group
which can be interrupted by ether oxygen atoms and/or divalent aliphatic
groups and X is a chlorine or bromine atom, in an inert solvent in the
presence of a Lewis acid catalyst. The polysufones prepared by process (a)
contain the recurring unit
--A.sub.1 --SO.sub.2 --,
whereas the polysulfones prepared by process (b) contain the recurring unit
--A.sub.1 --SO.sub.2 --A.sub.2 --SO.sub.2 --
Polysulfone resins which are preferably used in the compositions according
to the invention are those which contain ether groups in the recurring
unit, but are free from lateral hydroxyl groups. These are particularly
polysulfones having a recurring unit of the formula
--OA.sub.3 OA.sub.4 SO.sub.2 A.sub.4 --,
in which A.sub.3 and A.sub.4 are divalent arylene, especially phenylene,
groups, which can be substituted by chlorine or C.sub.1 -C.sub.4 alkyl,
for example methyl, groups. Polysulfones of this type are obtained in a
manner known per se by reacting a dialkali metal salt of a dihydric phenol
of the formula HOA.sub.3 OH with a bis-(monochloroaryl) sulfone of the
formula ClA.sub.4 SO.sub.2 A.sub.4 Cl in dimethyl sulfoxide. Polysulfone
resins which are more preferred are those having a recurring unit of the
formula
--OA.sub.5 --Y.sup.a --A.sub.5 OA.sub.6 --SO.sub.2 --A.sub.6 --
in which A.sub.5 and A.sub.6 are each a phenylene group which is
unsubstituted or substituted by chlorine or C.sub.1 -C.sub.4 alkyl groups,
for example methyl groups, and Y.sup.a is a carbon-carbon bond, the
--SO.sub.2 -- group or an aliphatic hydrocarbon group, in particular a
group of this type which has not more than 4 carbon atoms, for example
groups of the formula
##STR4##
Thermoplastic polysulfone resins which are particularly preferred are those
having recurring units of the formula V
##STR5##
in which n preferably has an average value of 50-120.
Examples of particularly advantageous polysulfones are the compounds
obtainable from Union Carbide Corporation, for example "Polysulfone Udel
P1800", which according to the manufacturers, has a melting point within
the range from 350.degree. to 370.degree. C., a heat distortion point
(ASTM specification D648) of 175.degree. C. and contains on average 50-80
recurring units of the formula V per molecule, it being possible to assume
a molecular weight range of approximately 22,000-35,000.
A similar substance obtainable from Union Carbide Corporation under the
name "Polysulfone P2300" is also suitable; according to the manufacturer
this has a molecular weight range of 30,000-50,000, and it is possible to
assume that the substance contains on average about 68-113 recurring units
of the formula V per molecule, and also a similar substance obtainable
from Union Carbide Corporation under the name "Polysulfone P3500";
according to the manufacturer this has a molecular weight range which is
between that of "Polysulfone Udel P1800" and that of "Polysulfone P2300";
its molecular weight is approx. 35,000.
In accordance with the invention it is also possible to use as component
(e) mixtures of two or more thermoplastics.
Particularly suitable thermoplastics (e) are polyimides, such as
polyimides containing phenylindane units, such as are described, for
example, in U.S. Pat. No. 3,856,752 and EP-A 92,524, in particular those
having a glass transition temperature of about 305.degree. C. and an
average molecular weight of approx. 65,000, for example Matrimid.RTM. 5218
made by Ciba-Geigy,
homopolyimides and copolyimides formed from at least one aromatic
tetracarboxylic acid and at least one aromatic diamine, as disclosed, for
example, in U.S. Pat. No. 4,629,777, and
homopolyimides and copolyimides such as are described, for example, in EP-A
162,017, EP-A 181,837 and U.S. Pat. No. 4,629,685.
Preferred thermoplastics (e) are also polyether-imides, for example the
products made by General Electric which are available under the name
Ultem.RTM. (for example as Ultem.RTM. 1000). Other preferred
thermoplastics are polyether sulfones, for example Victrex PES 100 P made
by ICI or Udel P 1800 made by Union Carbide.
Thermoplastics having phenolic end groups (d) which can be employed in the
compositions according to the invention are all the known polymers which
have a sufficiently high glass transition temperature, i.e.
.gtoreq.150.degree. C., and are miscible with the epoxide resin/curing
agent system according to the application. As stated above for
thermoplastics (e), polysulfones, polyether-sulfones, polyimides,
polyether-imides, polyethers or polyether-ketones are particularly
suitable by virtue of their properties.
The thermoplastics having phenolic end groups (d) preferably have a
molecular weight of 2,000-100,000, in particular 5,000-30,000.
Examples of suitable polyimides having phenolic end groups are the
compounds described in U.S. Pat. No. 4,026,871.
A suitable polyether-sulfone is the product made by BASF marketed under the
name Ultrason.RTM. 49K.
The thermoplastic having phenolic end groups (d) in the compositions of
matter according to the invention is preferably a polyether-sulfone, a
polyimide or a polyether-imide. Particularly suitable polyimides or
polyether-imides are compounds which contain, as the diamine, a
phenylindanediamine and/or a 2,2'-bis-(aminophenoxy)-biphenyl.
The polyimides or polyether imides mentioned last are embraced below by the
polymers of the formula VI.
Suitable components (d) in the compositions of matter according to the
invention are also nitrogen-containing polymers with terminal hydroxyl
groups of the formula VI
##STR6##
in which X.sup.1 and X.sup.2 independently are --H or
##STR7##
Z is OH and Y is NH or Z and Y together are N, n is an integer from 1 to
2000, R.sup.1 is a radical containing at least one aromatic ring, the
carbonyl groups being attached to different carbon atoms in the ring, and,
if at least one of X.sup.1 and X.sup.2 is the group
##STR8##
this group is located in each case in the ortho-position or peri-position
relative to the carbonyl group, so that five-membered or six-membered
imide rings are formed in a cyclization reaction, R.sup.2 is an aliphatic
radical having at least 2 C atoms, a cycloaliphatic, araliphatic,
carboxylic-aromatic or heterocyclic-aromatic radical, at least 10 mol % of
the radicals R.sup.2 being a radical of the formula VII and/or VIII
##STR9##
in which R.sup.4 is H or C.sub.1 -C.sub.4 alkyl, the radicals R.sup.5
independently of one another are hydrogen, halogen or C.sub.1 -C.sub.4
alkyl, x is zero or an integer from 1 to 3 and y is zero or an integer
from 1 to 4, and R.sup.3 is a divalent aromatic radical having 6-12 C
atoms or a radical of the formula IX
##STR10##
in which T.sup.1 is a direct bond, methylene, isopropylidene, O, CO, NH, S
or SO.sub.2.
In general, the polymers of the formula VI have an intrinsic viscosity of
0.1 to 2.0, preferably 0.2 to 1.5 and particularly 0.2 to 0.8, dl/g.
It is generally known that the intrinsic viscosity is a measure of the
molecular weight of polymers. The values of the intrinsic viscosity
indicated, from 0.1 to 2.0, correspond to an average molecular weight of
about 10.sup.3 to 10.sup.6.
Polymers of the formula VI in which n is an integer from 2 to 200,
particularly 2 to 50, are preferred.
Polymers of the formula VI in which at least 30 mol %, in particular at
least 50 mol %, of the radicals R.sup.2 are a group of the formula VII
and/or VIII are also preferred.
In the recurring structural elements of the formula VIa
##STR11##
of the polymers of the formula VI, R.sup.1, R.sup.2, X.sup.1, X.sup.2 and
Y can have various meanings. The polymers of the formula VI are thus
homopolymers or copolymers having a statistical distribution of individual
structural elements in which R.sup.1, R.sup.2, X.sup.1, X.sup.2 and Y have
various meanings.
In the structural element of the formula VIa X.sup.1 and X.sup.2 are
preferably in each case a group
##STR12##
In this regard, cyclized derivatives in which Z and Y together are N are
particularly preferred. Amongst the polymers of the formula VI polyimides
having terminal hydroxyl groups of the formula X
##STR13##
in which R.sup.1, R.sup.2, R.sup.3 and n are as defined above, are
therefore preferred.
The radicals R.sup.1 of the polymers of the formula VI are derived from
di-, tri- or tetra-carboxylic acids. In principle, any di-, tri or
tetra-carboxylic acid which, after the removal of the carboxyl groups,
gives the radicals R.sup.1 according to the definition is suitable.
The radical R.sup.1 can, for example, be a carbocyclic-aromatic or
heterocyclic-aromatic radical or a radical which, in addition to aromatic
rings, also contains a cycloaliphatic ring, for example a phenylindane
radical.
As a carbocyclic-aromatic radical, R.sup.1 preferably has at least one
6-membered ring; in particular these radicals are monocyclic, condensed
polycyclic or polycyclic radicals having several cyclic, condensed or
non-condensed systems which can be attached to one another directly or via
bridge members. Examples of suitable bridge members which may be mentioned
are
##STR14##
in which Q is an alkyl group having 1-6, preferably 1-4, carbon atoms or a
phenyl group.
If R.sup.1 is a heterocyclic-aromatic radical, suitable examples are
especially 5-membered or 6-membered heterocyclic-aromatic ring systems
which can be benzo-condensed and contain O, N and/or S.
Carbocyclic-aromatic or heterocyclic-aromatic radicals R.sup.1 can also be
substituted, for example by nitro groups, alkyl groups having 1-4 carbon
atoms, trifluoromethyl groups, halogen atoms, in particular chlorine, or
silyl, sulfonic acid or sulfamoyl groups.
R.sup.1 is preferably an unsubstituted monocyclic aromatic radical, a
condensed bicyclic aromatic radical or a non-condensed bicyclic aromatic
radical, the aromatic nuclei being attached to one another in the latter
case via the bridge member --CH.sub.2 --, --O--, --CO-- o | | |
