CA2099193A1 - High modulus prepregable epoxy resin systems - Google Patents

Abstract

ABSTRACT
Compositions comprising epoxy resin containing at least one glycidyl group and aparticular aromatic amine hardener possess the necessary balance of properties required for making prepreg.

94,306

Description

1 ~

HI~H MODULUS PREPREGA8LE EPOXY RESIN
SYSTEMS
B~CKGROUND OF THE INVENTION
Advanced composites are high strength, high modulus materials which are finding increasing use as structural components in aircraft, au~omoti~e, and sport~ng good~ applications. Typically they comprise structural fibers such as carbon fibers in the form of woven cloth or continuous filaments embedded in a thermosetting resin matrix.
Composite properties depend on both the matrix resin and the reinforcement. In unidirectional carbon fiber composites, important mechanical properties include longitudinal tensile strength and modulus, transverse tensile strength and modulus. and longitudinal compressive strength.
The matrix affects all of these properties, but has the greatest effect on compressive strength and transverse tensile properties. High composite compressive strengths and trans~erse tensile moduli require that the matrix have a high modulus.
State-of-the-art epoxy matrix resin systems in advanced composites are typically based on N,N,N',N'-tetraglycidyl 4,4'-diaminodiphenyl methane and 4,4'-diaminodiphenyl sulfone. These resins produce unreinforced castings which have tensile strengths of about 8,000 psi and tensile moduli of 500,000 to 550,000 psi. Unidirectional composites containing 60 volume fraction fiber made with these matrix resins typically have transverse tensile strengths of 5,000 to 7,000 psi and transverse tensile moduli of 1.0 to 1.4 million psi. Higher ~ 0~ 9 .L93 transverse properties are very desirable for applications such as pressure vessels One reason that matrix resins containing N,N~N',N'-tetraglycidyl 4,4'-diaminodiphenyl methane and g,4'-diaminodiphenyl sulfone are widely uséd in advanced composites is that they possess the balance of properties required for making prepreg, a ready-to-mold sheet of reinforcement impregrat~d with uncured or partially cured resin. These characteristics include: 1) a tacky, dough-like consistency, 2) low reactivity at room temperature, and 3) a high degree of cure after heating for 2 hours at 179C in an autoclave. Many epoxy resin systems lack at least one of these characteristics, and therefore are unsuitable for prepreg. There is a need for epoxy resin systems which are prepregable and which, when used, produce unreinforced castings which have higher tensile properties than state-of-the-art prepreg resin systems.
It has been found that compositions comprising: a) an epoxy resin containing at least one glycidyl amine group, and b) a select group of monoamines simultaneously satisfy both requirements.
U.S. Patent 2,951,822 discloses epoxy resins containing glycidyl amine groups which may be cured with monoamines such as aniline and m-chloro-aniline. However, the patent states that in preparing thermosetting compositions, a molar proportion of from about 0.7 to 1.3 epoxy groups per NH group is used. This represents a ratio of equivalents of amine NH groups to equivalents of epoxide groups of 0.77 to 1.43.

~ 099193 In the present invention it has been found that in a composition containinq an epoxy resin having at least one glycidyl amine group and a particular aromatic amine hardener, the ratio of equivalents of amine NH groups to equivalents of epoxide groups must be less than 0.77 (that ratio required by the prior art) to simultaneously achieve prepregability and high matrix strengths and moduli.
THE INVF.NTION
This invention is directed to a composition comprising:
(a) an epoxy resin containing at least one glycidyl amine group wherein the resin contains three or more epoxide groups per molecule, and (b) an aromatic amine hardener characteriæed by the following formula:

(R) ~ Rl)y wherein R is alkyl of 1 to 4 carbon atoms, Rl is independently an electron withdrawing group O O O
.. .. ..
selected from -CF3, -CN, -CN(R)2, -C-NHz, -C-NHR, HO R O O O O O O
, .- . .. .. .. .. .. ..
-NCR, -N-C-R, -CR, -COR, -C-C6H5, -S-N(R)2 -S-NH2, O O
O H
., , -S-NR or halogen, y is 1 or 2 and q is O or 1, o wherein the ratio of e~uivalents of amine NH groups in (b) to_the equivalents of epoxide groups in (a) i~ O.l to 0.7.

209~93 The composition6 may optionally contain (c) a thermoplastic polymer, and or (d) a Qtructural fiber.
The preferred epoxy resins include N,N,N',N'-tetraglycidyl meta-xylylenediamine;
N.N,N',N'-tetraglycidyl 1,3-bis(aminomethyl) cyclohexane: the triglycidyl ether of meta-aminophenol; the triglycidyl ether of para-aminophenol; and N.N.NIN'-tetraglycidyl 4,4'-diaminodiphenyl methane, and triglycidyl isocyanurate.
The epoxy resins may be used with up to 90 percent by weight of coepoxide resins containing two or more epoxy groups having the following formula:

--C--C--(I) The epoxy groups can be terminal epoxy groups or internal epoxy groups. Coepoxides are of two general types: polyglycidyl compounds or products derived from epoxidation of dienes or polyenes.
Polyglycidyl compounds contain a plurality of 1,2-epoxide groups derived from the reaction of a polyfunctional active hydrogen containing compound with an excess of an epihalohydrin under basic conditions. When the active hydrogen compound is a polyhydric alcohol or phenol. the resulting epoxide resin contains glycidyl ether groups. A preferred group of polyglycidyl compounds are made via ~099193 condensation reactions with 2,2-bis(4-hydroxyphenyl)propane, also known as bisphenol A, and have structures such as II:

H2C CH CH2 O ~ C ~ ~ C~2 o CH3 _ _ .

l 'H CH2- ~ CIIH ~ ~ CH2~ CH\ /CH2 O~ CH3 (II) where "a" has a value from about 0 to about 15.
The~e epoxi~e~ Are bi~henol-~ epoxy resins. They are available commercially under the trade names such as "Epon 328," "Epon 1001", and "Epon 1009"
from Shell Chemical Co., and as "~ER 331", and "DER
334" from Dow Chemical Co. The most preferred bisphenol A epoxy resins have an "a" value between O
and 10.
Polyepoxides which are polyglycidyl ethers of 4,4'-dihydroxydiphenyl methane, 4,4'-dihydroxydiphenyl sulfone, 4,4'-biphenol, 4,4'-dihydroxydiphenyl sulfide, phenolphthalein, resorcinol, 2,2'-biphenol, or tris(4-hydroxyphenyl) methane and the like, are useful in this invention.
In addition, EPON 1031 (a tetraglycidyl derivative of 1,1,2,2-tetrakis(hydroxyphenyl)ethane from Shell Chemical Company), and Apogen 101. (a methylolated bisphenol A resin from Schaefer Chemical Co.) may ~0~9193 also be used. Halogenated polyglycidyl compounds such as D.E.R. 580 (a brominated bisphenol A epoxy resin from Dow Chemical Company) are also useful.
Other suitable epoxy resins include polyepoxides prepared from polyols such a~ pentaerythritol, glycerol, butanediol or trimethylolpropane and an epihalohydrin.
Polyglycidyl derivatives of phenol-formaldehyde novolaks such as III where b =
0.1 to 8 and cresol-formaldehyde novolaks such as IV
where b = 0.1 to 8 are also useable.

~CH2~C~lZ~R~
III R2 = H
IV R2 = CH3 The former are commercially available as D.E.N 431, D.E.N. 43B, and D.E.N. 485 from Dow Chemical Company. The latter are available as, for example, ECN 1235, ECN 1273, and ECN 12g9 (obtained from Ciba-Geigy Corporation, Ardsley, NY). ~ther epoxidized novolaks such as S~-8 (obtained from Celanese Polymer Specialties Company, Louisville, KY) are also suitable.
Also suitable for use herein are the glycidyl esters o} carboxylic acids. Such glycidyl esters include, for example, diglycidyl phthalate, diglycidyl terephthalate, diglycidyl isophthalate, and diglycidyl adipate. There may also be used polyepoxides such as triglycidyl cyanurates ~0~9193 N,N-diglycidyl oxamides, N,N'-diglycidyl derivatives of hydantoins such as "XB 2793" (obtained from Ciba Geigy Corporation), diglycidyl esters of cycloaliphatic dicarboxylic acids, and polyglycidyl thioethers of polythiols.
Other epoxy-containing materials are copolymers of acrylic acid esters of glycidol such as glycidyl acrylate and glycidyl methacrylate with one or more copolymerizable vinyl compounds.
Examples of such copolymers are 1:1 styrene-glycidyl methacrylate, 1:1 methyl methacrylate-glycidyl acrylate and 62.5:24:13.5 methyl methacrylate:ethyl acrylate:glycidyl methacrylate.
Silicone resins containing epoxy functionality, e.g., 2,4,6,8,10-pentakis t3-(2,3-epoxypropoxy)propyl]-2,4,6,8,10-pentamethyl-cyclopentasiloxane and the diglycidyl ether of 1,3-bis-(3-hydroxypropyl)tetramethyldisiloxane are also useable.
The second group of epoxy resins i8 prepared by epoxidation of dienes or polyenes.
Resins of this type include bis(Z,3-epoxycyclopentyl) etAer, V, ~~ '~ ~0~
V VI
reaction products of V with ethylene glycol which are described in U.S. Patent 3,39~,102, 5(6)-glycidyl-2-(1,2-epoxyethyl)bicyclot2.2.13 heptane, VI, and dicyclopentadiene diepoxide.
Commercial examples of these epoxides include 2~9193 vinycyclohexene dioxide, e.g,, "ERL-4206" (obtained from Union Carbide Corp.), 3,4-epoxycyclohexylmethyl 3,9-epoxycyclohexane carboxylate, e.g., "ERL-4221"
(obtained from Union Carbide Corp.), 3,4-epoxy-6-methylcyclohexylmethyl 3,4-epoxy-6-methylcyclohexane carboxylate, e.g., "ERL-4201" (obtained from Union Carbide Corp.), bis(3,4-epoxy-6-methylcyclo-hexylmethyl) adipate, e.g., "ERL-4289" (obtained from Union Carbide Corp.), dipentene dioxide, e.g., ~'ERL-4269" (obtained from Union Carbide Corp.) 2-(3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy)cyclo-hexane meta-dioxane, e.g., "~RL-4234" (obtained from Union Carbide Corp.) and epoxidized poly-butadiene, e.g., "Oxiron 2001" (obtained from FMC Corp.) Other suitable cycloaliphatic epoxides include those described in U.S. Patents 2,750,395 2,890,194; and 3,318,822 which are incorporated herein by reference, and the following:
0~0 0~0 0~0 O~C o ~o ~7 C--O
O ~

Other suitable epoxides include:

O P

b ~ ~ ~ b ~ 0 '~ 3 g whece c is 1 to 4. m is (5-c), and R3 is H, halogen, o~ Cl to C4 alkyl.
~ eactive diluents containing one epoxide g~oup such as t-butylphenyl glycidyl ethe~ may also be used. The ~eactive diluent may comprise up to 25 pe~cent by weigh~ of the epoxide component.
The prefe~ed co-epoxy resins are bisphenol epoxy ~esins of focmula II whe~e a is between O
and 5, and epoxidized novolak ~esins of fo~mula III
and IV whece b is between O and 3.
The p~efel~ed amines include 3-amino-4-methylbenzamide, 3-amino-4-methylsulfonamide, 3-aminoacetanilide, 3-aminoacetophenone, 4-aminoace~ophenone, 3-amino-1-trifluoromethylbenzene, 4-amino-acetanilide, 4-amino-1-t~ifluoromethylbenzene, N-methyl 3-amino-4-methylbenzamide, 3-amino-4-ethylbenzamide, or 3-amino-4-methoxybenzamide, o~ mixtu~es thereof.
The amines of this invention may be used in combination with conventional a~omatic diamines.
Examples of conventional diamines include 4,4'-diaminodiphenyl ether, 4,4~-diaminodiphenyl methane, 3,3'-diaminodiphenyl methane, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 3,3'-diaminobenzophenone, diethyl-toluenediamine, m-phenylenediamine, p-phenylenediamine, 4,4'-diaminodiphenylp~opane.
4,4'-diaminodiphenyl sulfide, 1,4-bis(p-aminophenoxy)benzene, 1,4-bis(m-aminophenoxy)benzene, 1,3-bis-(m-aminophenoxy)benzene, 1,3-bis(p-aminophenoxy) benzene, 4,4~-bis(3-aminophenoxy)diphenyl sulfone, and trimethylene glycol di-4-aminobenzoate, and 2,Z-bis(4-aminophenoxyphenyl) propane.
The co-amines may be used in amounts of up to 40 weight pe~cent of component (b).
The compositions of this invention may optionally contain a thermoplastic polymer. These material~ have beneficial effects on the viscosity and film strenqth characteristics of the epoxy/hacdener mixture.
The thermoplastic polymers used in this invention include polyarylethers of formula VII
which are described in U.S. Patents 4,108,837 and 4,175,175, ~O-R4-0-R5~d VII
wherein R4 is a ~esiduum of a dihydric phenol such as bisphenol A, hydroquinone, resorcinol, 4,4-biphenol. 4,4'-dihydroxydiphenyl sulfone, 4,4'-dihydroxy-3,3', 5,5'-tetramethyldiphenyl sulfide, 4,4l-dihydroxy-3.3l,5.5'-tetramethyldiphenyl sulfone and the like. R5 is a re~iduum of a benzenoid compound susceptible to nucleophilic aromatic substitution reactions such as 4,4'-dichlo~odiphenyl sulfone.
4,4'-difluorobenzophenone, and the like. The average value of d is from about 8 to about 120.
These polymers may have terminal groups which react with epoxy resin~, such as hydroxyl or carboxyl. or terminal groups which do not react.
Other suitable polyarylethers are described in U.S. Patent 3,332,209.

.

~0~9193 Also suitable are polyhydroxyethers of formula VIII.
o - R4 - O - CH2 - CH - C~2)e OH
VIII
where R4 has the same meaning as for Formula VII
and the average value of e is between about 8 and about 300; and polycarbonates such as those based on bisphenol A, tetramethyl bisphenol A, 4,4'-dihydroxydiphenyl sulfone, 4,g'-dihydroxy-3,3',5,5'tetramethyl- diphenyl sulfone, hydroquinone, resorcinol, 4,9'-dihydroxy-3,3',5,5'-tetramethyl diphenyl sulfide, 4,9'biphenol, 9,4'-dihydroxydiphenyl sulfide, phenolphthalein, 2,2,g,q-tetramethyl-1,3-cyclobutanediol, and the like, Other suitable thermoplastics include poly (~-caprolactone);
polybutadiene; polybutadiene/acrylonitrile copolymers, including those optionally containing amine, carboxyl, hydroxy, or -SH groups; polyesters, such as poly(butylene terephthalate); poly(ethylene terephthalate); polyetherimides such as the Ultem resins (obtained from the General Electric Company);
acrylonitrile/ butadiene/styrene terpolymers, polyamides such as nylon 6, nylon 6,6, nylon 6,12, and Trogamid T (obtained from Dynamit Nobel Corporation); poly(amide imides) such as Torlon poly(amide imide) (obtained from Amoco Chemical Corporation, Napierville, IL); polyolefins;
polyethylene oxide: poly(butyl methacrylate);
impact-modified polystyrene; sulfonated 2~9133 polyethyiene; polyarylates such as those derived from bisphenol A and isophthalic and tecephthalic acid; poly(2,6-dimethyl phenylene oxide): polyvinyl chloride and its copolymecs: polyacetals:
polyphenylene sulfide and the like.
The composition may additionally contain an accelerator to increase the rate of cure.
Accelecators which may be used herein include Lewis acid:amine complexes such as BF3.monoethylamine, BF3.piperdine, BF3.2-methylimidazole: amines, such as imidazoLe and its derivatives such as 4-ethyl-2-methylimidazole, l-methylimidazole, 2-methylimidazole: N,N-dimethylbenzylamine: acid salts of te{tiary amines, such as the p-~oluene sulfonic acid:imidazole complex, and organophosphonium halides. These accelerators are generally used in amounts of from 0.1 to about 3 weight percent based on the epoxy resin.
The structural fibers which are useful in this invention include caLbon, graphite, glass, silicon carbide, poly(benzothiazole), poly(benzimidazole), poly(benzoxazole), alumina, titania, boron, and aromatic polyamide fibers.
These fibers are characterized by a tensile strength of greater than 100,000 psi, a tensile modulus of greater than two million psi, and a decomposition temperature of greater than 200C. The fibers may be used in the form of continuous tows (1000 to 400,000 filaments each), woven cloth, whiskers, chopped fiber or random mat. The preferred fibers are carbon fibers, aromatic polyamide fibers, such 2~93~93 as Kevlar 49 ~ibec (obtained ~rom E.I. duPont de Nemoucs, lnc., Wilmington, DE), and silicon cacbide fibers.
The composition contains from about 30 to about 90, pcefecably fcom about 40 to about 85 weight peccent of the epoxy cesin; from about 10 to about 70, pcefecably from about 12 to about 50 weight percent of the acomatic amine; up to about Z5 percent, prefecably up to 15 percent by weight of thermoplastic polymer, and up to about ~5 percent, preferably from about 20 to about 80 percent of structural fiber.
Preimpcegnated reinforcement may be made fcom the compo~itions of this invention by combining epoxy cesin, hacdener, and optionally thermoplastic polymer with the structural fibec.
Preimpregnated reinforcement may be prepared by sevecal techniques known in the art, su~h as wet winding or hot melt.
In the hot melt process, partially advanced resin mixtures ace coated as a thin film onto a silicone coated release papec. Prepceg is made by passing a cibbon of fiber between two plies of coated celease paper in a pcepreg machine, where undec the action of heat and pcessuce, the cesin mixtuce is tcansferred from the paper to the fibers. Not all epoxy amine mixtures may be used in the hot melt process since they lack the cequired film focming and reactivity charactecistics.
Prepreg made by this process is typically taken up on a spool. It is used within a few days or may be stored for months at 0F.

20~9193 Durinq prepreg manufacture, the resin system "B-stages~', oc partially advances.
Tacky drapable prepreg can be obtained using the compositions of this invention. Due to the low room tempecature (25C) reactivity of the hardeners of this invention, long prepreg shelf lives can be obtained-typically one to three weeks.
Composites may be prepared by curing preimpreqnated reinforcement using heat and pressure. Vacuum bag/autoclave cures work well with these compositions. Laminates may also be prepared via wet layup followed by compression molding, cesin transfer molding, or by resin injection, as described in ~uropean Patent Application 0019149 published November 26, 1980. Typical cure temperatures are 100F to 500F, preferably 180F to The compositions of this invention may be used for filament winding. In this composite fabrication process, continuous reinforcement in the form of tape or tow - eithec previously impregnated with resin or impregnated during winding - is placed over a rotating and removable form or mandrel in a previously determined pattern. Generally the shape is a surface of revolution and contains end closures. When the proper number of layers are applied, the wound form is cured in an oven or autoclave and the mandrel removed.
The compositions of this invention may be used as aircraft parts such as wing skins, wing-to-body fairings, floor panels, flaps, radomes:
as automotive parts such as driveshafts, bumpers, ~099193 and gprings: and as pressure vessels, tanks and pipes. They are also suitable for sporting goods applications such as golf shafts, tennis rackets, and fishing rods.
In addition to structural fibers, the composition may also contain particulate fillers such as ~alc, mica, calcium carbonate, aluminum trihydrate, glass microballoons, phenolic thermospheres, and carbon black. Up to half of the weight structural fiber in the composition may be replaced by filler. Thixotropic agents such as fumed silica may also be used.
FurtheL, the compositions may be used in adhesives, potting and encapsulation, and coating applications.
EXAMPLES
The following examples serve to give specific illustrations of the pcactice of this invention but they are not intended in any way to limit the scope of this invention.
In the Examples which follow, the epoxy equivalent weight (EEW) is defined as the grams of epoxy resin per mole of 1,2 epoxide group. The following materials were used:
PGAX - A commercial grade of N,N,N',N'-tetraglycidyl ~lo~l93 meta-xylylenediamine, (obtained f rom the Sherwin Williams Company, Chicago, Ill.) O~
~,CH2--CH--CH2 2 ~
CH~ - CH - CH2 CH - CH - CH

~CH2- CH - CH2 o (EEW=102) PGAC - ~ commercial grade of N,N,~,N'-tetcaglycidyl 1,3-bis(aminomethyl) cyclohexane obtained from Shecvin Williams , O~

~ CH2 - CH - CH2 l ~ CH2 - CH~- CH2 CH2-- CH~ CH2 O~
(EEW=105) GlYamine - 115 - A commeccial gcade of N,N,0 -triglycidyl meta-aminophenol, (obtained from F.I.C.
Corpocation, San Francisco, CA).

1~1 o N-- CH2 _ CH--~CH2 O
CH2- C~ - CH2 \0/

_ (EEW=117) __ ~O~gl93 MY-7ZO - A comme~cial grade of N,N,N',N'-tetraglycidyl 4,4'-diaminodiphenyl methane, (obtained from Ciba Geigy Corporation, Ardsley, NY) CH2 - CH-CHz~ ~CH2 CH CH2 N~ CH2~
~H2 /CH CH2 2 \ O " , 2 (EEW=126) AMBA 3-Amino -4-methylbenzamide (obtained from Aceto Chemicals, New Yo~k, NY):

~L
C -NHz AAP - 3-Aminoacetophenone (obtained from Aldrich Chemical Co. Milwaukee, WI):

Contr_l A
A thermosetting epoxy resin formulation was prepared by blending 75 g of N,N,N',N'-tetLaglycidyl meta-xylylenediamine with 57 g of 3-amino-4-methylbenzamide.
Example 1 A thermosetting epoxy resin formulation was prepared by blending 100 g of N,N,N',N'-tetraglycidyl meta-xylylenediamine with 37 g of 3-amino-4-methylbenzamide.

~093193 ExamPle Z
A thecmosetting epoxy resin formulation was prepared by blending 100 g of N,N,N'N'-tetraglycidyl meta-xylylenediamine with 22 g of 3-amino-4-methylbenzamide.
ExamPle 3 An epoxy resin blend was prepared by combining 160 g of N,N,N',N~-tetraglycidyl meta-xylylenediamine with 40 g of a bisphenol A
epoxy resin (EEW 189) at a temperature of 50C. A
thermosetting epoxy formulation was prepared by combining this blend with 68 g of 3-amino-4-methylbenzamide.
ExamPle 4 An epoxy resin blend was prepared by combining 50 g of N,N,N',N'-tetraglycidyl meta-xylylenediamine with 50 g of N,N,0-triglycidyl meta-aminophenol at a temperature of 50C. A
thermosetting epoxy formulation was prepared by combining this blend with 35 g of 3-amino-4-methylbenzamide.
Examole 5 A thermosetting epoxy resin formulation was prepared by blending 75 g of N,N,N~,N~-tetraglycidyl meta-xylylenediamine with 25.5 g of 3-aminoacetophenone.
Control B
A thermosetting epoxy resin formulation wa~
prepared by blending 75 g of N,N,N',N'-tetraglycidyl meta-xylylenediamine with 49.5 g of 3-aminoaceto-phenone.

~991~3 ExamPle 6 A thermosetting epoxy resin fo~mulation was p~epared by blending 105 g of N,N,N',N'-tetraglycidyl 1,3-bis(aminomethyl) cyclohexane with 38 g of 3-amino-4-methylbenzamide.
ExamPle 7 A the~mosetting epoxy resin fo~mulation was prepared by blending 100 g of N,N,N',N'-tetraglycidyl 4,4'-diaminodiphenyl methane with 25 g of 3-amino-4-methylbenzamide.
Example 8 An epoxy re~in blend was prepared by combining 80 g of N,N,N',N'-teteaglycidyl 4,4'-diaminodiphenyl methane with 20 g of bi~phenol-A epoxy resin (EEW lB9) at a temperature of 70C. A theLmosetting epoxy formulation wa~
pcepa~ed by combining this blend with 28 g of 3-amino-4-methylbenzamide.
Control C
N,N,N',N'-tetraglycidyl 4,4'-diaminodiphenyl methane, 100 g, was heated without amine ha~dener.

Unreinforced castings were prepa~ed from the formulations described in the above Examples and Control~. Casting dimensions were 1~8 x 8 x 5 to 8 inches. Typically they weighed 100 to 160 g.
The genecal procedure for making castings was the following: The epoxy resin was charged to a 3-necked flask equipped with a paddle stirrer. The content~ of the flask were heated at a temperature of from 100 to 110C and stir~ed. The amine ~0~193 hacdenec ~as added to this solution. It disgolved in about 10 minutes. The resulting solution was subjected tn a vacuum to remove aic bubbles for about 5 to 30 ~inutes. It was then poured into a pceheated glasg mold ~ith a caYity of dimen~ions L/8 x 8 x 8 inches, and cured wi~h a programmed heating cycle: ~ to 5 houcs at 100C, 6 hours at lZ0C, and finally 2 houes at 179C.
Ca~tings wece tested to detecmine mechanical pLoeertie6. Tensile prope~ties were measured accordinq to ASTM D-638 using a Type I
dogbone specimen. Heat deflection temperatures were ~eagured according to A5TM D-648 (Z64 psi stres~).
Table I summacizes the propertieg of unreinforced castings.
The following conclusions aEe drawn from the data in Table 1:
The castings in Example6 1 to 5 have high ten6ile strengths and very high tensile moduli.
These castings, as well as those in Examples 6 through 8, were cured with the amine N-H: epoxide stoichiometry of this invention. In contrast, the castings in Controls A and B, which contained an amine N-H: epoxide stoichiomet~y of 1.0, had inferior tensile properties compared to the corresponding composition6 of this invention (Exampleg 1 and 5, eespectively).
Control C (MY-720 without an amine) did not cure, whereas in Example 7, a hard, strong casting was formed using the amine curing agent of this invention.

~0~9 l93 a ~ ~ ^ w (O g 1 3. ~: ~ ~
~ ~90 O~O U~ ~ 8~
O ~ " -- -- ~", ~ ID ~ (D C" '~I ~
O P~ ~ O rr ~ ~D
" _ O ~ g _ c,~ e~ 3 O tl~
C ~ O
D 0 e o 0.
1 ~ C~ g D ~D J I ~ ~ rl ~t 3 ~ J crO ~n ~ O
D ~
C ~_ W ~o~ O O ~ ¦

N ~

1~ ~ ~ rl N 0 ~~ O 0 ~; O
O ~ N ~ N r~
_ ~. tD

~ g; C ~3 N N ~ 'O ~ /D ~_ ~ O ~ N O

O . O O =
1~ vl v~ ~
v~

_ C~
N 0 N O ~ ~; v O~ ~ O
OD o o ~ ,_ ~ ~; ::1 O O ~ W

209~193 ~ ~ o o ~
N ^~ . a~ C V
`' ~ 7 ~ ~ ~ ~' sc z ~ ~ ~
m o~ ~ ~D a ~ u~
s~ e rl ~ o ~ e ~ ~. o o ~ ~ 01 1~ O "I
rl N 1~ N Ul ~;
~ ~1 ~ O`
W~ O
1~ ~D ~

'1 o~ N o~ ~ O E~ O
O D 1~ UtO ~I C ID
3 N O ~
:1~ o C~ o ~
N ' O O X
O ~ O O V~ ~ ~I (~
rl ~1 N Id-~r~ ~ CO Co O _ ~O

~ O ~ g % rr 1~ ~r~
e ~9193 Example 9 and Control D describe the prepregging characteristic6 of selected formulations. Systems suitable for making prepreg via the hot melt process form uniform, tacky films when spread on a silicone treated release paper after moderate heating to advance the molecular weight of the resin. The preferred formulations can be held at their coating temperature (e.g. 85C) for several hours before advancing to the point where they produce a film which is brittle and nontacky at room temperature.
ExamPle 9 A mixture of 7.4 g of 3-amino-4-methylbenzamide and 20 g of N,N,N',N'-tetraglycidyl meta-xylylenediamine was heated at a temperature of 100C for 45 minutes, followed by 30 minutes at a temperature of 85C. A
tacky, uniform film was cast from this mixture. The resin/hardener mixture was maintained for 3 more hours at 85C. At the end of this period. a tacky uniform film was prepared.
Control D
N,N,N',N'-tetraglycidyl meta-xylylenediamine, 20 g, wa~ heated at a temperature of 85C. Samples were removed periodically in an attempt to cast a uniform, tacky film. Even after 8 hours, a uniform film was not obtained. Comparing this result with that in Example 9 indicates that an amine hardener is needed to produce a film 6uitable for prepregging.

20~193 Example 10 descLibes the preparation of unidirectional carbon fiber prepreg using the composition of this invention. The plepreg per ply thickness was approximately 6 mils. The prepre~ was made using a polyacrylonitrile - based carbon fiber with a tensile strength of 6.6 x 10 psi and a ten$ile modulus of 36 x 10 psi.
ExamPle 10 N,~,N',N'-tetraglycidyl meta-xylylenediamine, 5~0 g, was charged to a 3 liter flask equipped with a paddle stirrer, thermometer with TheLm-o-watch control unit, vent to a bubbler, and an electric heating mantle. The cesin was heated to a temperature of 100C and held at that temperature a~ 185 g of 3-amino-4-methyl-benzamide was addbd over a period of 30 minutes.
After the mixture was cooled to a temperature of 85C over a Z0 minute period and held at that temperature for another 25 minutes, it was poured into a pan of a resin coater. Seven-inch wide 0.005-inch thick film was coated at a temperature of 75C on a differential release paper (type 2-60SF-157 and 168B from Daubert Coated Products, Dixon, IL). ~ 6-inch wide ribbon of carbon fiber was passed through a heating chamber of the prepreg machine along with coated resin paper on top and bottom. The Lesin was melted on the fiber ribbon at a te~perature of 90 to 100C. The finished tape contained approximately 33.5 percent resin by weight and wa~ 6 inches wide.
Examples 11 and 12 describe the preparation and tensile properties of a cured laminate.

209~193 ExamPle 11 A unidi~ectional laminate was prepared by stacking 8 plies of the preimpregnated tape made in Example 10 in a mold, covering them with a teflon impregnated space~ and bleeder cloths. and enclosing them in a nylon bag. The entire a~sembly was placed in an autoclave and cured. Longitudinal tensile properties were mea~ured at ambient temperature according to ASTM-D3039. Re~ults and cure schedule are shown in Table II.
ExamPle 12 A unidirectional laminate was prepared by stacking Z0 plies of 6-inch wide tape in a mold. and curing it in an autoclave as described in Example 11.
Transverse tensile specimens (perpendicular to the fiber direction) were prepared from the cured laminate and we~e tested according to ASTM-D3039.
The results are ~hown in Table II.

209~193 Table II

Composite ProPertiesa nqitudinal Tensile Strength (103psi) 384 Tensile Modulus (106psi) 21.9 Strain-to-Failure (%) 1.57 Fiber Conten~ (Vol %) 63 Layup Example 11 Transverse Tensile Strength (103psi) 9.2 Tensile Modulus (106psi) 1.77 Strain-to Failure (%) 0.54 Fiber Content (Vol ~) 65 Layup Example 12 a Cure Schedule: Apply vacuum to bag. Pressurize autoclave to 85 psi. Heat from 70F to 240F at 3F/min. Hold 1 hour at 2gOF. Then vent bag to the atmosphere and increase autoclave pressure to 100 psi. Heat from 240F to 350F
at 3F~min. Hold at 350F for 6 hours.

It is clear that the compositions of this invention give composites with a high level of mechanical properties. The transverse tensile modulus of the laminate is significantly higher than that based on laminates made with state-of-the-art epoxy prepreg formulations.

Claims (6)

1. A composition comprising an epoxy resin selected from one or more of the following:
N,N,N'N'-tetraglycidyl-meta-xylylenediamine; N,N,N'N'-tetraglycidyl-1,3-bis(aminomethyl) cyclohexane; the triglycidyl ether of meta-aminophenol; the triglycidyl ether of para-aminophenol, N,N,N'N'-tetraglycidyl-4,4'-diaminodiphenyl methane and triglycidyl isocyanurate; and an aromatic amine hardener selected from:
3-amino-4-methylbenzamide, 3-amino-4-methylsulfonamide, 3-aminoacetanilide, 3-aminoacetophenone, 4-aminoacetophenone. 3-amino- 1-trifluoromethylbenzene, 4-aminoacetanilide, 4-amino-1-trifluoromethylbenzene, N-methyl-3amino-4-methylbenzamide, 3-amino-4-ethylbenzamide, 3-amino-4-methoxybenzamide or mixtures thereof.

2. The composition of Claim 1 further comprising up to 40 percent by weight of acoepoxy resin.

3. The composition of Claim 2 wherein said coepoxy resin is selected from phenol-formaldehyde novolak and cresol-formaldehyde novolak.

4. The composition of Claims 1-3 further comprising a structural fiber selected from the group consisting of carbon, graphite, glass boron, silicon carbide and aromatic polyamides.

5. The composition of Claim 4 in the form of a prepreg.

6. The composition of Claims 1 or 4 further comprising a thermoplastic selected from the group consisting of polysulfone, polyhydroxyether, and polyamide.

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