Epoxy resin composition

A novel epoxy resin composition is obtained by modifying a bisphenol-type epoxy resin and/or a halogen-containing epoxy resin with a trisphenol represented by the following general formula: ##STR1## wherein each of R.sub.1 and R.sub.2 represents hydrogen or an alkyl group havng not more than 6 carbon atoms with the proviso that at least one of them is the alkyl group, each of R.sub.3, R.sub.4 and R.sub.5 represents hydrogen or an alkyl group having not more than 4 carbon atoms, and n represents a number of 0 or 1. The composition is suitable, for example, as a paint, a casting material or a molding material.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an epoxy resin composition, and more 
specifically, to an epoxy resin composition which has excellent 
properties, above all high water resistance, chemical resistance and heat 
resistance, and is suitable for use as a paint, a casting material and a 
molding material for making laminated plates. 
2. Description of the Prior Art 
It has been known that compositions comprising bisphenol A-type epoxy 
resins or halogen-containing bisphenol A-type epoxy resins and curing 
agents such as aromatic polyamines, amine adducts, dicyandiamide, acid 
anhydrides or phenol novolak resins are used as paints, molding materials 
and casting materials, and such compositions may be formed in varnishes by 
using solvents to use them for molding laminated plates by impregnation in 
reinforcing substrates. 
In recent years, insulating paints, encapsulating materials and laminated 
plates (printed circuit boards) in electrical and electronic component 
parts have required increased heat resistance in order to increase the 
reliability of mechanical properties and electrical insulation at high 
temperatures. Paints, encapsulating materials and laminated plates 
(printed circuit boards) made from conventional bisphenol A-type epoxy 
resins or halogen-containing bisphenol A-type epoxy resins have the defect 
that their glass transition temperature (Tg) is still low, and at high 
temperatures, their mechanical strength and electrical insulation are 
reduced. Polyfunctional epoxy resins such as a phenol novolak type epoxy 
resin or an o-cresol/novolak type epoxy resin are added to the above epoxy 
resins in order to increase their heat resistance. Use of large amounts of 
the polyfunctional epoxy resins reduces the heat shock resistance of the 
above epoxy resin although it does result in an improvement in heat 
resistance. Consequently, cracking tends to occur in the paints and 
encapsulating materials. When the laminated plates are treated in a solder 
bath after boiling treatment, phenomena called "blister", "peel", 
"measling" and "crazing" are sometimes observed in the laminated plates 
treated. 
It has been strongly desired therefore to provide an epoxy resin 
composition which does not undergo significant deterioration in mechanical 
strength and electrical insulation even at high temperatures and has 
excellent heat shock resistance. 
SUMMARY OF THE INVENTION 
The present inventor extensively worked on epoxy resins which would be 
useful in such applications as paints, encapsulating materials and 
laminated plates, and has now found that products of modification of 
bisphenol-type epoxy resins and/or halogen-containing epoxy resins with 
trisphenols of the following general formula: 
##STR2## 
wherein each of R.sub.1 and R.sub.2 represents hydrogen or an alkyl group 
having not more than 6 carbon atoms with the proviso that at least one of 
them is the alkyl group, each of R.sub.3, R.sub.4 and R.sub.5 represents 
hydrogen or an alkyl group having not more than 4 carbon atoms, and n 
represents a number of 0 or 1, 
have excellent mechanical strength and electrical insulation at high 
temperatures, and retain the advantages of epoxy resins heretofore used. 
According to this invention, there is provided a novel epoxy resin 
composition comprising the reaction product of (A) a compound having three 
phenolic hydroxyl groups in the molecule represented by the following 
general formula: 
##STR3## 
wherein each of R.sub.1 and R.sub.2 represents hydrogen or an alkyl group 
having not more than 6 carbon atoms with the proviso that at least one of 
them is the alkyl group, each of R.sub.3, R.sub.4 and R.sub.5 represents 
hydrogen or an alkyl group having not more than 4 carbon atoms, and n 
represents a number of 0 or 1, 
with (B) a bisphenol-type epoxy resin and/or (C) a halogen-containing epoxy 
resin, the number of the phenolic hydroxyl groups of the compound (A) 
being 0.03 to 0.7 per epoxy group of the epoxy resin (B) and/or (C). 
According to this invention, there is also provided a laminated plate 
obtained by consolidating under heat and pressure prepregs composed of a 
reinforcing fibrous base material and a combination of an epoxy resin and 
a curing agent impregnated in the base material, said epoxy resin being an 
epoxy resin composition comprising the reaction product of (A) a compound 
having three phenolic hydroxyl groups in the molecule represented by the 
following general formula: 
##STR4## 
wherein each of R.sub.1 and R.sub.2 represents hydrogen or an alkyl group 
having not more than 6 carbon atoms with the proviso that at least one of 
them is the alkyl group, each of R.sub.3, R.sub.4 and R.sub.5 represents 
hydrogen or an alkyl group having not more than 4 carbon atoms, and n 
represents a number of 0 or 1, 
with (B) a bisphenol-type epoxy resin and/or (C) a halogen-containing epoxy 
resin, the number of the phenolic hydroxyl groups of the compound (A) 
being 0.03 to 0.7 per epoxy group of the epoxy resin (B) and/or (C), and 
said laminate having a glass transition temperature (Tg), measured by a 
differential scanning calorimeter, of at least 150.degree. C. 
DETAILED DESCRIPTION OF THE INVENTION 
bisphenol-type epoxy resin (B) 
Various bisphenol-type epoxy resins known per se, such as bisphenol A epoxy 
resin and bisphenol F epoxy resin, are used as the bisphenol-type epoxy 
resin (B) in the epoxy resin composition of this invention. For example, 
bisphenol-type epoxy resins derived from bisphenols such as 
1,1-bis(4-hydroxyaryl)ethanes or 1-aryl-1,1-bis(4-hydroxyaryl)ethanes may 
also be used. Preferably, a bisphenol A-type epoxy resin obtained by 
reacting bisphenol A with epichlorohydrin can be used. Most preferably, 
the bisphenol A-type epoxy resin which has an epoxy equivalent of 170 to 
500 is used. 
Halogen-containing epoxy resin (C) 
Various halogen-containing epoxy resins known per se can be used as the 
halogen-containing epoxy resin (C). Preferred are bromine-containing 
bisphenol A-type epoxy resins. Those having a bromine content of 30 to 50% 
by weight, especially 40 to 50% by weight, and an epoxy equivalent of 328 
to 2,000, especially 328 to 800, are preferred. 
Most preferably, there is used a bromine-containing bisphenol A-type epoxy 
resin of the following chemical formula: 
##STR5## 
obtained by reacting tetrabromobisphenol A with epichlorohydrin (epoxy 
equivalent 328, bromine content 48.7%). 
For use in an application where flame retardancy is important, the halogen 
(bromine) content of the final epoxy resin composition is adjusted to 15 
to 30% by weight. 
trisphenol (A) 
In accordance with this invention, the bisphenol-type epoxy resin (B) 
and/or the halogen-containing epoxy resin (C) is modified with the 
trisphenol (A) of the following general formula: 
##STR6## 
wherein each of R.sub.1 and R.sub.2 represents hydrogen or an alkyl group 
having not more than 6 carbon atoms, preferably a methyl, ethyl, 
isopropyl, t-butyl or 2,2-dimethylbutyl group, with the proviso that at 
least one of R.sub.1 and R.sub.2 is the alkyl group; R.sub.3 represents 
hydrogen or an alkyl group having not more than 4 carbon atoms, preferably 
a methyl or ethyl group; each of R.sub.4 and R.sub.5 represents an alkyl 
group having not more than 4 carbon atoms, preferably a methyl, ethyl or 
isopropyl group; and n is a number of 0 or 1. 
Preferred trisphenols (A) of the above general formula, are those in which 
R.sub.4 is a methyl group, and those of the general formula in which 
R.sub.4 is a methyl group and R.sub.5 is hydrogen are most preferred. The 
latter can be obtained by the addition reaction of crotonaldehyde with 
suitable phenols. 
Trisphenols of the above general formula in which R.sub.4 and R.sub.5 are 
the alkyl groups such as methyl groups can be obtained generally by the 
addition reaction of alkylation products of aliphatic unsaturated 
aldehydes such as methacrolein and crotonaldehyde with suitable phenols. 
Examples of the trisphenol (A) are listed below without any intention of 
limiting the invention thereto. 
1,1,1-tris(4-Hydroxyphenyl)methane, 
(bis(3,5-dimethyl-4-hydroxyphenyl)-4-hydroxyphenyl)methane, 
(bis(3,5-diethyl-4-hydroxyphenyl)-4-hydroxyphenyl)methane, 
(bis(2-methyl-4-hydroxy-6-t-butylphenyl)-4-hydroxyphenyl)methane, 
(bis(2-ethyl-4-hydroxy-5-t-butylphenyl)-4-hydroxyphenyl)methane, 
(bis(3,5-di-t-butyl-4-hydroxyphenyl)-4-hydroxyphenyl)methane, 
(bis(3,5-di-iso-propyl-4-hydroxyphenyl)-4-hydroxyphenyl)methane, 
1,1,3-tris(4-hydroxyphenyl)propane, 
1,1,3-tris(3,5-dimethyl-4-hydroxyphenyl)propane, 
1,1,3-tris(3,5-diethyl-4-hydroxyphenyl)propane, 
1,1,3-tris(3,5-di-isopropyl-4-hydroxyphenyl)propane, 
1,1,3-tris(3,5-di-t-butyl-4-hydroxyphenyl)propane, 
1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)propane, 
1,1,3-tris(2-ethyl-4-hydroxy-5-t-butylphenyl)propane, 
1,1,3-tris(2-methyl-4-hydroxy-5-isopropylphenyl)propane, 
1,1,3-tris(2-ethyl-4-hydroxy-5-isopropylphenyl)propane, 
1,1,3-tris(2,5-dimethyl-4-hydroxyphenyl)propane, 
1,1,3-tris(2,5-diethyl-4-hydroxyphenyl)propane, 
2,2,4-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane, and 
1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane. 
The amount of the trisphenol (A) to be reacted with the epoxy resin (B) 
and/or (C) is such that the number of the phenolic hydroxyl groups of the 
trisphenol in the final epoxy resin composition is 0.03 to 0.7, preferably 
0.05 to 0.6, per epoxy group of the epoxy resin (B) and/or (C). If its 
amount is below the specified limit, the desired effect cannot be 
obtained. If it is larger than the specified upper limit, the epoxy 
equivalent becomes too large and the resulting epoxy resin composition 
lends itself to inconvenient handling. 
The modification reaction is carried out by melting and stirring the 
reaction materials generally at a temperature of about 120.degree. to 
200.degree. C. for about 3 to 20 hours. Preferably, the reaction is 
carried out in the presence of about 20 to 200 ppm, based on the amount of 
trisphenol (A) and the epoxy resin (B) and/or (C) used in the reaction, of 
a catalyst usually employed in the reaction of the epoxy group with the 
phenolic hydroxyl group, for example a basic catalyst such as sodium 
hydroxide and sodium carbonate, a quaternary ammonium salt catalyst such 
as a tetraalkyl ammonium halide and an aralkyl trialkyl ammonium halide, 
or a phosphine-containing catalyst such as triphenylphosphine and 
ethyltriphenyl phosphonium halides. As required, a solvent, for example an 
aromatic hydrocarbon such as toluene and xylene or a ketone such as methyl 
isobutyl ketone, may be used in the reaction. 
Incidentally, when a tris-3,5-dialkyl substituted-4-hydroxyphenyl compound 
is used as the trisphenol (A), the rate of the reaction tends to decrease 
because of steric hindrance of the substituents at the 3,5-positions. 
Epoxy resin composition 
The epoxy resin composition of this invention as a reaction product can be 
produced by properly selecting the afore-said reaction conditions so that 
the epoxy resin composition attains an epoxy equivalent of 200 to 1,800, 
particularly 200 to 900. 
If the epoxy equivalent is lower than the limit specified above, the 
proportion of the trisphenol bonded is small, and the improving effect by 
the modification is small. If it is higher than the specified limit, the 
molecular weight of the resin itself becomes high, and as a result, the 
resulting composition has too high a melt viscosity and lends itself to 
poor handling. Even when such a composition is formed into a varnish by 
using a solvent, the varnish has a high solution viscosity and its 
workability in coating steps is reduced. 
The resulting epoxy resin composition of this invention has very good heat 
resistance at high temperatures, and when used as a paint, a casting 
material or a molding material for production of laminated plates, is very 
useful in increasing the reliability of mechanical strength, electrical 
insulation, etc. at high temperatures. 
As required, the epoxy resin composition of this invention may be used in 
combination with another epoxy resin known per se in an amount which does 
not impair the purpose of this invention. 
For example, it is possible to modify one of the epoxy resins (B) and (C) 
with the trisphenol (A) in accordance with this invention, and to use the 
modified epoxy resin in combination with the other of the epoxy groups (B) 
and (C). 
Of course, the epoxy resin composition may be used in combination with any 
of other epoxy resin such as phenol novolak-type resin and ortho-cresol 
novolak type epoxy resin. 
The epoxy resin composition of this invention can be used in the form of a 
mixture with a curing agent known generally for ordinary epoxy resins, 
such as an aliphatic amine, an aromatic amine, an amine adduct, 
dicyandiamide or an acid anhydride in the production of an electrical 
insulating paint, a casting material, an encapsulating material, a 
laminated plate. 
The amount of the curing agent used, which varies depending upon the type 
of the curing agent, is generally about 2 to 40 parts by weight per 100 
parts of the epoxy resin composition. 
Laminated plate 
For use in producing a laminated plate, the epoxy resin composition 
containing the curing agent is generally formed into a varnish by using a 
solvent, for example, an aromatic hydrocarbon such as toluene or xylene or 
a ketone such as acetone, methyl ethyl ketone or methyl isobutyl ketone. 
The epoxy resin composition as varnish is then impregnated into 
reinforcing base materials such as glass cloths, carbon fibers, glass 
fibers, paper, asbestos, polyester fibers or aromatic polyamide fibers 
(e.g., Kevlar (tradename)) to form prepregs. The prepregs are then 
consolidated under heat and pressure to produce a laminated plate. 
The laminated plate of the invention after curing has the advantage that it 
has a high heat distortion temperature, a high glass transition 
temperature, improved mechanical strength and electrical insulation at 
high temperatures, and excellent water resistance as compared with a 
general bisphenol A-type epoxy resin or bromine-containing epoxy resin 
while the desirable advantages of the general epoxy resins are retained. 
For example, as shown in a working example to be given hereinafter, the 
laminated plate has a glass transition temperature (Tg) of at least 
150.degree. C. 
Other uses 
For use as a paint, the epoxy resin composition of this invention is mixed 
with, for example, a coloring agent (pigment), a filler, a solvent, and a 
defoamer. Various fillers may be used when the epoxy resin composition of 
this invention is to be used as a casting material. 
The paint or casting material likewise has improved mechanical strength and 
electrical insulation at high temperatures and excellent water resistance.