Composition of tetraglycidyl, triglycidyl and diglycidyl epoxy resins

An epoxy resin composition useful as a matrix for fiber-reinforced composites is disclosed which includes a mixture containing 30-95% by weight of a tetrafunctional epoxy resin, 3-40% by weight of an admixture of trifunctional epoxy resin oligomers and 2-50% by weight of a bisphenol A epoxy resin having a number average molecular weight of 450-1,300 and such a weight average molecular weight as to provide a ratio of the weight average molecular weight to the number average molecular weight of 1.3-3.0.

This invention relates generally to an epoxy resin composition and, more 
specifically, to a hardenable composition which is suitable as a matrix 
material for forming prepregs of reinforcing fibers having good tack and 
drape qualities and which affords composite articles or shaped articles 
having excellent modulus, toughness and resistance to heat and moisture 
absorption. 
Because of their good resistance to heat and chemicals and good hardness 
and modulus, epoxy resins have been utilized for a wide variety of 
applications, for example, as a matrix material for carbon fibers, glass 
fibers, aramide fibers or the like reinforcing fibers in the fabrication 
of fiber-reinforced composite articles. Known epoxy resin compositions 
are, however, not fully satisfactory when utilized as a structure material 
for aircraft, which requires both high mechanical strengths inclusive of 
toughness and high resistance to heat and moisture absorption. 
For instance, one known composition for forming composite materials for use 
in aircraft uses N,N,N',N'-tetraglycidyldiaminodiphenylmethane 
(hereinafter referred to as TGDDM for brevity) as an epoxy resin. TGDDM 
which is tetrafunctional can provide high cross-linking density, so that 
hardened bodies obtained from the known composition exhibits both high 
modulus and high heat resistance. However, the known composition has 
drawbacks because the resulting hardened bodies have poor elongation and 
are brittle. 
For the purpose of improving the mechanical properties of hardened products 
of the above composition, it is proposed to use TGDDM in combination with 
triglycidyl-m-aminophenol (hereinafter referred to as TGMAP for brevity) 
which is a trifunctional epoxy resin (Japanese Published Unexamined Patent 
Applications Nos. 54-77699 and 55-86815). While the fiber-reinforced 
composite materials obtained by using this combination have improved heat 
resistance and modulus, they are low in toughness and in resistance to 
moisture absorption. 
It is a general practice to use a liquid rubber for improving toughness of 
epoxy resins. However, this method cannot be applied to the epoxy resins 
of the above-mentioned type, because the resulting hardened products 
become poor in resistance to heat and moisture absorption and in modulus. 
Poor resistance to moisture absorption of hardened products such as 
composite articles causes reduction of the glass transition point, modulus 
and high temperature compression strength of the products. 
Japanese Published Unexamined Patent Application No. 58-134126 discloses 
the incorporation of a thermoplastic resin such as polyethersulfone, 
polysulfone or polyacrylate in an epoxy resin composition for improving 
toughness of hardened products thereof. However, in order to improve the 
toughness, it is necessary to use the thermoplastic resin in a large 
amount. This causes increase in viscosity of the composition so that the 
moldability of the composition becomes poor and the tack of prepregs 
obtained using the composition become poor. 
Japanese Published Unexamined Patent Application No. 59-217721 discloses a 
composition containing TGDDM, TGMAP, diaminodiphenylsulfone (hereinafter 
referred to as DDS for brevity) and an additional epoxy resin selected 
from a brominated epoxy resin and a novolac epoxy resin. Japanese 
Published Unexamined Patent Application No. 62-36421 discloses a 
composition containing TGDDM, TGMAP, DDS, a polyethersulfone and a 
bisphenol F epoxy resin. These known epoxy resin compositions are 
ill-suited for forming prepregs to be used for the production of 
fiber-reinforced composite materials, because the toughness, tack and 
drape qualities are not satisfactory. 
It is essential that prepregs for structural applications have desirable 
tack and drape qualities. The tack qualities should be adequate to allow 
the prepregs to adhere to prepared molding surfaces or preceding plies for 
a lay-up, but light enough to part from the backing films without loss of 
resin. Drape is the measure of the formability of prepregs around contours 
such as a small-radius rod. The drapability should be good enough to allow 
the prepregs to be formed into complex shapes. 
The present invention has been made with the above problem of conventional 
epoxy resin compositions. In accordance with the present invention there 
is provided a composition comprising a mixture of epoxy resins containing 
30-95% by weight of a tetrafunctional epoxy resin, 3-40% by weight of a 
trifunctional epoxy resin and 2-50% by weight of a bisphenol A epoxy resin 
having a number average molecular weight of 450-1,300, said bisphenol A 
epoxy resin having such a weight average molecular weight as to provide a 
ratio of the weight average molecular weight to the number average 
molecular weight of 1.3-3.0. 
The epoxy resin composition according to the present invention can afford a 
cured product having high modulus, hardness and toughness and excellent 
resistance to heat and chemicals. Fiber-reinforced plastics containing a 
matrix resin obtained from the epoxy resin composition of the present 
invention exhibit improved mechanical strengths such as impact strength, 
fracture strength, resistance to moisture absorption, resistance to 
thermal shock and adhesion. Further, the thermocurable resin composition 
is excellent in flowability and stability so that it is advantageously 
used for the formation of prepregs having excellent tack and drape 
qualities. 
The present invention will now be described in detail below. 
The composition according to the present invention contains as a main 
ingredient a mixture of a tetrafunctional epoxy resin (component (a)), a 
trifunctional epoxy resin (component (b)) and a specific bisphenol A epoxy 
resin (component (c)). 
The tetrafunctional epoxy resin may be, for example, 
N,N,N',N'-tetraglycidyldiaminodiphenylmethane (TGDDM), 
tetraglycidyl-m-xylenediamine, tetraglycidylbis(aminomethylcyclohexane), 
tetraglycidylbenzophenone or bisresorcinol tetraglycidyl ether. TGDDM is 
commercially available under trade names of ARALDITE MY720 (Ciba-Geigy 
Inc.), ELM 434 (Sumitomo Chemical Industries, Ltd.), EPOTOTE YH434 (Toto 
Kasei K. K.) and EP604 (Yuka-Shell Epoxy Inc.). 
The trifunctional epoxy resin may be, for example, 
N,N,O-triglycidyl-m-aminophenol (TGMAP), N,N,O-triglycidyl-p-aminophenol 
(TGPAP), fluoroglycinol triglycidyl ether, trihydroxybiphenyl triglycidyl 
ether or triglycidylaminophenol. TGMAP is commercially available under a 
trade name of ELM120 (Sumitomo Chemical Industries, Ltd.). TGPAP is also 
commercially available under trade names of ELM100 (Sumitomo Chemical 
Industries, Ltd.) and YX-4 (Yuka-Shell Epoxy Inc.). 
The bisphenol A epoxy resin to be used in the composition according present 
invention is a mixture of oligomers with various different molecular 
weights having a number average molecular weight (Mn) of 450-1300, 
preferably 500-1,000. When the number average molecular weight of the 
bisphenol A epoxy resin is lower than 450, the toughness of hardened 
bodies obtained from the composition cannot be improved. Too high a number 
average molecular weight of the bisphenol A in excess of 1,300, on the 
other hand, causes reduction of tackiness and drape-formability of 
prepregs. The above-mentioned EPIKOTE resins have the following formula: 
##STR1## 
wherein n is a number providing a number average molecular weight of 
380-5,500. 
It is also important that the bisphenol A epoxy resin have such a weight 
average molecular weight (Mw) as to provide a ratio (Mw/Mn) of the weight 
average molecular weight to the number average molecular weight of 
1.3-3.0. A ratio Mw/Mn of the bisphenol epoxy resin below 1.3 is 
insufficient to provide suitable toughness, while a ratio Mw/Mn greater 
than 3.0 causes reduction of tack and drape qualities of prepregs. 
Preferred ratio Mw/Mn is in the range of 1.5-2.7. 
The bisphenol A epoxy resin to be used in the present invention can be 
suitably obtained by blending two or more commercially available, 
diglycidyl ethers of bisphenol A. Examples of suitable bisphenol A epoxy 
resins include Epikote 828, 1004, 1007, 1009 and 1010 (Trademarks of 
Yuka-Shell Epoxy Inc.) whose properties are shown below: 
______________________________________ 
Number Average 
Epikote Epoxy Equivalent 
Molecular Weight 
______________________________________ 
828 184-194 380 
1004 875-975 1600 
1007 1750-2200 2900 
1009 2400-3300 3750 
1010 3000-5000 5500 
______________________________________ 
In addition to the above-described tetrafunctional epoxy resin, 
trifunctional epoxy resin and bisphenol A epoxy resin, the mixture of 
epoxy resins may further contain an additional epoxy resin such as a 
phenol novolac epoxy resin or a cresol novolac epoxy resin, if desired. 
The amounts of the tetrafunctional epoxy resin (component (a)), 
trifunctional epoxy resin (component (b)), bisphenol A epoxy resin 
(component (c)) and additional epoxy resin (optional component (d)) in the 
mixture are as follows (in terms of % by weight based on the total weight 
of the components (a)-(d)): 
______________________________________ 
Component Amount (wt %) 
Preferred Amount (wt %) 
______________________________________ 
(a) 30-95 50-90 
(b) 3-40 5-20 
(c) 2-50 5-40 
(d) up to 30 
______________________________________ 
An amount of the component (a) below 30% by weight is disadvantageous 
because the heat resistance and modulus of the hardened bodies obtained 
from the composition becomes poor. Too large an amount of the component 
(a) in excess of 95% by weight, on the other hand, is disadvantageous 
because the hardened bodies become brittle. 
An amount of the component (b) below 3% by weight is disadvantageous 
because the tack of prepregs obtained from the composition becomes poor. 
Too large an amount of the component (b) in excess of 40% by weight, on 
the other hand, is disadvantageous because the hardened bodies become 
brittle. 
An amount of the component (c) below 2% by weight is disadvantageous 
because the elongation and toughness of the hardened bodies obtained from 
the composition become poor. Too large an amount of the component (c) in 
excess of 50% by weight, on the other hand, is disadvantageous because the 
heat resistance and modulus of the hardened bodies become poor. 
When the amount of the additional component (d) exceeds 30% by weight, the 
resistance to heat and moisture absorption and the toughness of composite 
materials obtained from the composition become poor and, additionally, the 
tack and drape qualities of prepregs become poor. 
Any curing agent may be used in the present invention. The curing agent is 
generally used in a stoichiometrical amount with respect to the epoxy 
resin. Examples of the curing agents include: 
(A) Amine curing agent: 
(A-1) aliphatic primary amines such as diethylenetriamine, 
triethylenetetramine, tetraethylenepentamine, dipropylenetriamine, 
trimethylhexamethylenediamine, a polyether diamine, 
diethylaminopropylamine, menthendiamine, methaxylylenediamine and 
3,9-bis(3-aminopropyl)-2,4,8,10-tetraspiro 5,5 undecane; 
(A-2) aromatic primary amines such as methaphenylenediamine, 
diaminodiphenylmethane, diaminodiphenylsulfone, and aromatic diamine 
eutectic mixtures; 
(A-3) modified amines such as amine adducts and cyanoethylated polyamines; 
(A-4) secondary and tertiary amines such as tetramethylguanidiene, 
pyperidine, pyridine, picoline, benzyldimethylamine, 
2-(dimethylaminomethyl)phenol; and 
(A-5) polyamides such as condensation products of a dimer acid with a 
polyamine; 
(B) acid anhydrides: 
(B-1) aromatic acid anhydrides such as phthalic anhydride, trimellitic 
anhydride, ethylene glycol bis(anhydrotrimellitate), glycerol 
tris(anhydrotrimellitate), pyromellitic anhydride and 
3,3',4,4'-benzophenone tetracarboxylic anhydride; 
(B-2) alicyclic acid anydrides such as maleic anhydride, succinic 
anhydride, tetrahydrophthalic anhydride, methyltetrahydrophthalic 
anhydride, methylnadic anhydride, alkenylsuccinic anhydride, 
hexahydrophthalic anhydride, methylhexahydrophthalic anhydride, and 
methylcyclohexene tetracarboxylic anhydride; 
(B-3) aliphatic acid anhydrides, halogenated acid anhydrides, 
polycarboxylic anhydride and chloreside anhydride; 
(C) polyamide resins such as N,N'-bis(6-aminohexyl)adipamide; 
(D) imidazoles such as 2-methylimidazole, 2-ethyl-4-methylimidazole, 
2-undecylimidazole, 2-heptadecylimidazole, 2-phenylimidazole, 
1-benzyl-2-methylimidazole, 1-cyanoethyl-2-methylimidazole, 
1-cyanoethyl-2-undecylimidazolium trimellitate, 2,4-diamino-6- 
2-methylimidazolyl-(1) -ethyl-S-triazine, 
1-dodecyl-2-methyl-3-benzylimidazolium chloride, 2-phenylimidazolium 
isocyanulate, and 2-phenyl-4-methyl-5-hydroxymethylimidazole; 
(E) boron trifluoride-amine complexes; 
(F) dicyanodiamide and its derivatives such as o-tolyl biguanide and 
-2,5-dimethylbiguanide; 
(G) organic acid hydrazides such as succinic acid hydrazide and adipic acid 
hydrazide; 
(H) diaminomaleonitrile and its derivatives; 
(I) melamine and its derivatives such as diallylmelamine; 
(J) amine imides; 
(K) polyamines; 
(L) oligomers such as novolac phenol resins, novolac cresol resins and 
poly-p-vinylphenols. 
When the thermocurable epoxy resin composition of the present invention is 
to be used for the formation of molded articles such as mechanical parts, 
the use of diaminodiphenylmethane, diaminodiphenylsulfone and 
dicyanodiamide as the curing agent is preferred for reasons of 
obtainability of suitable toughness, heat resistance and machinability. 
When the thermocurable epoxy resin composition is intended to be used for a 
carbon fiber-reinforced prepreg matrix, the use of dicyanodiamide, 
diaminodiphenylmethane and diaminodiphenylsulfone is also preferred for 
reasons of obtainability of suitable tack and drape qualities and of 
composite articles with excellent toughness, modulus and resistance to 
heat and moisture absorption. 
The composition according to the present invention may contain one or more 
additives such as a filler and a diluent, if desired. 
The curing of the epoxy resin composition of the present invention is 
generally performed at temperatures of 100.degree.-140.degree. C. for 1-3 
hours. This may be followed, if desired, by a post curing treatment which 
may be performed at 150.degree.-220.degree. C. for 1-3 hours. 
The epoxy resin composition according to the present invention is suitably 
used as a matrix resin for high performance composite materials, such as 
structural materials of, for example, cars, aircraft, spacecraft and 
watercraft which require high toughness, modulus and resistance to heat 
and moisture absorption. Since prepregs formed by the use of the epoxy 
resin composition have good tack and drape qualities, such composite 
materials may be prepared easily and with good workability. It is without 
saying that the epoxy resin composition of this invention may be used as 
other applications such as civil engineering and construction materials, 
coatings, lining materials, adhesives, molded materials and electrical 
appliances (for example, mechanical parts, jigs and tools).

The following examples will further illustrate the present invention. 
EXAMPLE 1 
TGDDM (Epikote 604, manufactured by Yuka-Shell Epoxy Inc.), TGPAP (ELM100, 
manufactured by Sumitomo Chemical Industries, Ltd.) a blend of bisphenol A 
epoxy resins were mixed with each other in amounts shown in Table 1 below. 
The formulation, the number average molecular weight (Mn) and ratio 
(Mw/Mn) of the weight average molecular weight (Mw) to the number average 
molecular weight of the bisphenol A epoxy resin blend are also shown in 
Table 1. The resulting epoxy resin mixture was heated to 150.degree. C. to 
obtain a homogeneous mixture. After cooling to 90.degree. C., the mixture 
was mixed with diaminodiphenylsulfone (DDS) in a stoichiometric amount, 
thereby to obtain a thermocurable composition. The composition was poured 
into a mold composed of two glass plates spaced apart from each other by a 
Teflon spacer, heated at 80.degree. C. for 1 hour, and then at 200.degree. 
C. for 2 hours in an oven, thereby to cure the resin. The cured product 
was sliced into test pieces with a size of 300 mm.times.300 mm.times.2 mm 
and the test pieces were subjected tested for Izod strength (IZOD) and 
glass transition temperature (Tg) to obtain the results summarized in 
Table 1. A prepreg was also prepared by impregnating carbon fibers 
(tensile strength: 350 kg/mm.sup.2, modulus: 32 t/mm.sup.2), arranged in 
parallel with each other, with the above epoxy resin composition. 
Workability for the fabrication of the prepreg was good because of low 
viscosity of the epoxy resin composition. The prepreg showed the tack 
(TAC) and the stability (STB) of the tack as shown in Table 1. 
The tack was determined at 23.degree. C. by touch with fingers and rated as 
follows: 
A: excellent 
B: not good 
C: poor 
The stability of tack was tested by evaluating the tack at various 
temperatures in the range of 15.degree.-30.degree. C. and rated as 
follows: 
good: No or almost no change in tackiness was observed. 
poor: Significant change in tackiness was observed. 
EXAMPLE 2 
Example 1 was repeated in the same manner as described except the 
composition of the epoxy resin mixture was changed as shown in Table 1. 
The results were as summarized in Table 1. 
COMATIVE EXAMPLES 1-8 
Example 1 was repeated in the same manner as described except the 
composition of the epoxy resin mixture was changed as shown in Table 1. 
The results were as summarized in Table 1. 
TABLE 1 
__________________________________________________________________________ 
Bisphenol A Epoxy Resin 
Composition of Epoxy Composition (wt %) Izod 
Resins (wt %) Epikote (kg cm/ Tg 
Example 
TGDDM 
TGPAP Bisphenol A 
828 
1004 
1007 
1010 
Mn Mw/Mn 
cm.sup.2) 
(.degree.C.) 
TAC 
STB 
__________________________________________________________________________ 
1 70 15 15 60 10 30 573 
2.2 5.2 227 
A good 
2 80 5 15 60 -- 40 582 
2.4 5.1 233 
A good 
Comp. 1 
100 -- -- -- -- -- -- -- 2.1 242 
C poor 
Comp. 2 
20 35 45 60 -- 40 582 
2.4 5.3 195 
B poor 
Comp. 3 
20 60 20 60 10 30 573 
2.2 3.5 215 
C poor 
Comp. 4 
40 50 10 60 10 30 573 
2.2 3.2 232 
B poor 
Comp. 5 
70 -- 30 60 10 30 573 
2.2 5.8 225 
C poor 
Comp. 6 
70 5 25 70 -- -- 30 527 
3.6 5.3 219 
B poor 
Comp. 7 
70 5 25 100 
-- -- 380 
1.0 4.8 224 
C poor 
Comp. 8 
30 10 60 60 10 30 573 
2.2 5.6 190 
B poor 
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