WO2014062407A2

WO2014062407A2 - Anhydride-cured epoxy resin systems containing divinylarene dioxides

Info

Publication number: WO2014062407A2
Application number: PCT/US2013/063758
Authority: WO
Inventors: Bhawesh Kumar; Nikhil E. Verghese; Maurice J. Marks; Timothy A. Morley; Rainer Koeniger; Nebjosa JELIC
Original assignee: Dow Global Technologies Llc
Priority date: 2012-10-19
Filing date: 2013-10-08
Publication date: 2014-04-24
Also published as: WO2014062407A3

Abstract

Epoxy resin systems contain 3 to 35% by weight of divinylarene dioxide resins, based on the weight of the epoxy resins, and an anhydride hardener. These systems offer a desirable combination of low initial viscosity, long open time and then fast cure, and demold easily. These characteristics make the epoxy resins systems highly useful in making fiber-reinforced composites in resin transfer molding processes.

Description

ANHYDRIDE- CURED EPOXY RESIN SYSTEMS CONTAINING DIVINYLARENE DIOXIDES

This invention relates to thermosetting compositions and processes for preparing fiber-reinforced thermoset composites.

For many reasons, it is potentially advantageous to replace metal structural parts with reinforced organic polymers. Among the advantages the reinforced organic polymers offer include better resistance to corrosion, the ability to produce parts having complex geometries and, in some cases, a superior strength-to-weight ratio. It is this last attribute that has led, and continues to lead, the adoption of reinforced polymers in the automotive industry as replacement for metal structural elements such as chassis members and other structural supports.

Epoxy resin systems are sometimes used as the polymer phase in such composites. Cured epoxy resins are often quite strong and stiff, and adhere well to the reinforcement. An advantage of epoxy resin systems compared to most thermoplastic systems is that low molecular weight, low viscosity precursors are used as starting materials. The low viscosity is an important attribute because it allows the resin system to easily penetrate between and wet out the fibers that usually form the reinforcement. This is necessary to avoid cosmetic blemishes such as flow lines and to produce a high strength composite.

Despite the potential advantages of these polymer composites, they have achieved only a small penetration into the automotive market. The reason for this is cost. Metal parts can be produced using very inexpensive stamping processes that have the further advantage of producing parts at high operating rates. Polymer composites, on the other hand, must be produced in some sort of mold in which the polymer and reinforcing fibers are held until the polymer cures. The time required for this curing step to be completed directly affects production rates and equipment utilization, and therefore costs. Epoxy systems used for making these composites have required long in-mold residence times, and so the production cost for the most part has not been competitive with metal parts. Because of their higher costs, the use of epoxy resin composites to replace stamped metal parts has been largely limited to low production run vehicles. It is believed that in-mold curing times need to be reduced into the range of approximately 2 to 5 minutes for epoxy composites to become economically competitive with stamped metal parts for high production volume vehicles.

The manufacturing method of choice for making these fiber-reinforced composites is a resin- transfer molding (RTM) process, or one of its variants such as vacuum-assisted resin transfer molding (VARTM) and the Seeman Composites Resin Infusion Molding Process (SCRIMP). In these processes, the reinforcing fibers are formed into a preform which is placed into a mold. A mixture of an epoxy resin component and a hardener is then injected into the mold, where it flows around and between the fibers, fills the cavity and cures to form the composite. High pressure impingement mixing techniques are used to rapidly mix the epoxy resin with the hardener and transfer the mixture into the mold.

The mold-filling step of these processes often takes 15 to 60 seconds or even more, depending on the size of the part and the particular equipment being used. During the entire mold-filling process, the resin system must maintain a viscosity low enough to allow it to flow between the reinforcing fibers and completely fill the mold. Resin systems formulated to cure rapidly also tend to build viscosity quite rapidly. If the fibers are pre -heated, which is often the case, the resin system can react particularly rapidly at points of contact with the heated fibers. The viscosity increase that accompanies this premature curing makes it difficult for the epoxy resin system to penetrate between fibers and wet them out. This behavior results in moldings having problems that range from the cosmetic (visible flow lines, for example) to structural (the presence of voids, sections of bare fibers and/or poor adhesion of the cured resin to the reinforcing fibers, each of which leads to a loss in physical properties).

The problem of too-rapid viscosity build usually cannot be overcome by, for example, increasing operating pressures (i.e. the force used to introduce the resin system into the mold) because doing so can wash the reinforcing fibers away from the resin injection points, leading to spots that have little or no reinforcement and other regions in which the fibers are packed more densely. The result of this often is inconsistent properties throughout the part and a general weakening of the composite as a whole.

Therefore, an epoxy resin system useful in resin transfer molding processes to form reinforced composites should not only have a low initial viscosity and cure rapidly, but should also build viscosity slowly during the initial stages of cure.

Another important consideration is the glass transition temperature of the cured resin. For curing epoxy resin systems, the glass transition temperature increases as the polymerization reactions proceed. It is generally desirable for the resin to develop a glass transition temperature in excess of the mold temperature, so the part can be demolded without damage. In some cases, the polymer must in addition achieve a glass transition temperature that is necessary for the part to perform properly in its intended use. Therefore, in addition to the curing attributes already described, the epoxy system must be one that can attain the necessary glass transition temperature upon full cure. It is highly desirable that this necessary glass transition temperature be achieved during the molding process itself (i.e., without the need for an additional post-curing step), while still attaining the needed short demold time.

Many automotive parts are coated with a protective coating that requires a bake cure. The polymer phase of any composite subjected to this baking regimen must be at least equal to the baking temperature; otherwise the part will become distorted or otherwise damaged when the part is demolded. This bake temperature is often in the range of 160 to 180°C. Therefore, it is highly desirable to provide an epoxy resin system which exhibits a long open time and then cures rapidly to form a cured polymer having a glass transition temperature of at least 180°C.

WO2008/153542 describes an epoxy resin system for resin transfer molding applications, in which the hardener is a gem-di(cyclohexylamine) substituted alkane. The system is catalyzed with a tertiary amine and/or a delayed action catalyst. This system is adapted to produce very large (10 kg or greater) parts that have very long shot times and long cures. Glass transition temperatures are reported to be up to about 140°C.

WO2008/052973 describes another approach to solve this problem. In the process described in WO 2008/052973, the epoxy resin and hardener are separately heated and then introduced into a hot mold that contains a fiber preform. The resin is then cured in the mold until it attains a glass transition temperature of at least 150°C. During the curing step, the mold temperature is at all times maintained above the glass transition temperature of the curing polymer. It is possible to obtain short demold times in this manner, but a significant drawback of this process is that the cured polymer is at a temperature higher than its glass transition temperature and therefore is soft, rubbery and difficult to demold without damaging the part. The high mold temperatures needed in this process also significantly increase energy requirements.

A commercially available system that largely meets the requirements of long open time and fast cure contains a glycidyl ether of bisphenol A, diethylene triamine as a hardener, and a mixture of bisphenol A and a Mannich base of bisphenol A and diethylene triamine that is believed to function as both a catalyst and crosslinker. However, this system produces a polymer having a glass transition temperature of only about 100-110°C, which is not adequate for parts that must subsequently be exposed to high temperatures such as a bake cure for an applied coating.

WO 2010/077485 describes an epoxy resin system for vacuum resin infusion molding. That system includes divinylbenzene dioxide as an epoxy resin, and a polyaminoether curing agent. Those systems are said to form polymers having glass transition temperatures as high as 180°C, but actual reported values are less than 100°C, even after postcuring.

This invention is in one aspect a process for forming a fiber-reinforced epoxy composite, comprising forming a reaction mixture containing an epoxy resin component and a hardener component, and curing the epoxy resin component with the hardener component in the presence of reinforcing fibers and an effective amount of at least one catalyst, wherein:

the epoxy resin component contains 5 to 35% by weight of at least one divinylarene dioxide based on the total weight of all epoxy resins in the epoxy resin component; the hardener component contains at least 75% by weight of a carboxylic acid anhydride based on the total weight of all epoxy hardeners in the hardener component;

and further wherein the epoxy resin component and the hardener component are present in amounts that provide from 0.8 to 10 equivalents of epoxy groups per equivalent of epoxy-reactive group in the hardener component.

This invention is also a curable epoxy resin system, comprising

I. an epoxy resin component containing, by weight of epoxy resins, 20 to 95 weight% of a cycloaliphatic epoxy resin having an epoxy equivalent weight of about 95 to 250, and 5 to 35% by weight of at least one divinylarene dioxide, and

II. a hardener component containing at least 75% by weight of a carboxylic acid anhydride, based on the total weight of all epoxy hardeners in the hardener component;

wherein component I or II or both contains a catalytically effective amount of one or more catalysts and components I and II are present in amounts to provide from 0.85 to 10 epoxy equivalents per equivalent of epoxy-reactive groups in the hardener component.

The invention is also a process for forming a thermoset, comprising mixing the epoxy resin component and the hardener component of the curable epoxy resin system of the preceding aspect of the invention and curing the resulting mixture.

The epoxy resin system and processes of the invention provide the advantages of long open time

(as indicated by a slow initial increase in viscosity of the combined epoxy resin component/hardener mixture) followed by a fast cure. Because of the long open time, the reaction mixture tends to remain low enough in viscosity that it can be transferred easily into a mold, where it readily flows around reinforcing fibers and cures to produce a composite product that is cosmetically acceptable and has excellent physical properties. Curing times are desirably short and, as a result, short demold times can be achieved. The polymer quickly develops a glass transition temperature in excess of 180°C. Because of these advantages, the process of the invention is useful for producing a wide variety of composite products, of which automotive and aerospace components are notable examples. The parts are suitable for undergoing a bake paint cure.

The epoxy resin component contains one or more epoxy resins, by which it is meant compounds having an average of about two or more epoxide groups per molecule that are curable by reaction with an anhydride hardener compound. 5% to 35% by weight of the epoxy resins in the epoxy resin component is one or more divinylarene dioxide(s). The divinylarene dioxide is a compound or mixture of compounds having the general structure: H₂C Ar CH CH₂

wherein Ar is an aromatic group. Ar may be a single-ring, fused ring or a multi-ring structure in which the rings are connected by one or more covalent bonds (as in biphenyl) and/or a bridging group such as a divalent hydrocarbon group having from 1 to about 10, preferably from 1 to about 5, more preferably from 1 to about 3 carbon atoms, -S-, -S-S-, -SO-, -S0₂,-C0₃. -CO- or -0-. The Ar group may contain one or more inert substituents in addition to the epoxy groups, "inert" meaning that the substituent group(s) do not include epoxide groups or epoxide-reactive groups. Ar is preferably phenylene or naphthalene and most preferably phenylene, in which case the compound is divinylbenzene dioxide. The epoxide groups may be in any positional relationship to each other. When Ar is aryl, the epoxide groups may be in the ortho, meta- or para positions with respect to each other.

When the divinylarene dioxide constitutes more than about 35% of the weight of the epoxy resins, it has been found that the cured resin tends to adhere strongly to mold surfaces, even when those mold surfaces have been coated prior to molding with a mold release agent. The divinylarene dioxide in preferred embodiments constitutes at least 10% by weight of the epoxy resins, or at least 15% by weight of the epoxy resins. In an especially preferred embodiment, the divinylarene dioxide may constitute 15 to 30%, especially 15 to 25% by weight of the epoxy resins.

The epoxy resin component contains at least one other epoxy resin, in addition to the divinylarene dioxide. Among other epoxy resins that may be present in the epoxy resin composition are, for example, cycloaliphatic epoxides; polyglycidyl ethers of polyphenols, polyglycidyl ethers of various types of aliphatic polyols; epoxy novolac resins including cresol-formaldehyde novolac epoxy resins, phenol- formaldehyde novolac epoxy resins and bisphenol A novolac epoxy resins; tris(glycidyloxyphenyl)methane; tetrakis(glycidyloxyphenyl)ethane; tetraglycidyl diaminodiphenylmethane; oxazolidone -containing compounds as described in U. S. Patent No. 5,112,932; and advanced epoxy-isocyanate copolymers such as those sold commercially as D.E.R.™ 592 and D.E.R.™ 6508 (The Dow Chemical Company). Still other useful epoxy resins are described, for example, in WO 2008/140906.

The epoxy resin component preferably contains at least one cycloaliphatic epoxy resin. A cycloaliphatic epoxide includes a saturated carbon ring having an epoxy oxygen bonded to two vicinal atoms in the carbon ring, as illustrated by the following structure I:

wherein R is a linking group and n is a number from 2 to 10, preferably from 2 to 4 and more preferably 2 to 3. Di- or polyepoxides are formed when n is 2 or more. The cycloaliphatic epoxy resin may have an epoxy equivalent weight of about 95 to 250, especially from about 100 to 150. Mixtures of mono-, di- and/or polyepoxides can be used. Cycloaliphatic epoxy resins as described in U.S. Patent No. 3,686,359, incorporated herein by reference, may be used in the present invention. Cycloaliphatic epoxy resins of particular interest are (3,4-epoxycyclohexyl-methyl)-3,4-epoxy-cyclohexane carboxylate, bis-(3,4- epoxycyclohexyl) adipate and mixtures thereof.

The cycloaliphatic epoxy resin may in certain embodiments constitute 1 to 95% of the total weight of all the epoxy resins. It preferably constitutes 20 to 80%, more preferably 20 to 65%, and still more preferably 35 to 65% of the total weight of all epoxy resins.

The epoxy resin component in some embodiments contains at least one epoxy novolac resin. The epoxy novolac resin can be generally described as a methylene -bridged polyphenol compound, in which some or all of the phenol groups are capped with an epoxy-containing group, typically by reaction of the phenol groups with epichlorohydrin to produce the corresponding glycidyl ether. The phenol rings may be unsubstituted, or may contain one or more substituent groups, which, if present are preferably alkyl having up to six carbon atoms and more preferably methyl. The epoxy novolac resin may have an epoxy equivalent weight of about 156 to 300, preferably about 170 to 225 and especially from 170 to 190. The epoxy novolac resin may contain, for example, from 2 to 10, preferably 3 to 6, more preferably 3 to 5 epoxide groups per molecule. Among the suitable epoxy novolac resins are those having the general structure:

in which 1 is 0 to 8, preferably 1 to 4, more preferably 1 to 3, each R' is independently alkyl or inertly substituted alkyl, and each x is independently 0 to 4, preferably 0 to 2 and more preferably 0 to 1. R' is preferably methyl if present.

The epoxy novolac resin, if present, may constitute 1 to 35% of the total weight of all the epoxy resins. It preferably constitutes 2 to 20%, more preferably 5 to 15% of the total weight of all epoxy resins.

The epoxy resin composition in some embodiments includes one or more polyglycidyl ethers of a polyphenol (other than an epoxy novolac as described before), which may have, for example, an epoxy equivalent weight of up to about 250 and 2 to 4, preferably 2 to 3 and still more preferably 2 to 2.5 epoxy groups per molecule. The epoxy equivalent weight preferably is 170 to 250 and more preferably 170 to 200. The polyglycidyl ether of the polyphenol may be a diglycidyl ether of a diphenol such as, for example, resorcinol, catechol, hydroquinone, bisphenol, bisphenol A, bisphenol AP (l,l-bis(4- hydroxylphenyl)-l -phenyl ethane), bisphenol F, bisphenol K, tetramethylbiphenol, or mixtures of two or more thereof. The polyglycidyl ether of the polyphenol may be advanced, provided that the epoxy equivalent weight preferably is about 250 or less.

Suitable polyglycidyl ethers of polyphenols include those represented by structure (I)

wherein each Y is independently a halogen atom, each D is a divalent hydrocarbon group suitably having from 1 to about 10, preferably from 1 to about 5, more preferably from 1 to about 3 carbon atoms, -S-, -S- S-, -SO-, -S0₂,-C0₃. -CO- or -0-, each m may be 0, 1, 2, 3 or 4 and p is a number such that the compound has an epoxy equivalent weight of up to 250, preferably from 170 to 250 and more preferably from 170 to

200. p typically is from 0 to 1, especially from 0 to 0.5.

The polyglycidyl ether of the polyphenol (other than epoxy novolac resin), if present, may constitute 1 to 95% of the total weight of all epoxy resins. It preferably constitutes 1 to 35%, more preferably 2 to 20%, and still more preferably 5 to 15% of the total weight of all epoxy resins. Preferred epoxy resin components include those that contain mixtures of epoxy resins as follows (weight percents in all cases being based on the total weight of all epoxy resins):

a) Mixtures that include 20 to 95 weight% of a cycloaliphatic epoxy resin having an epoxy equivalent weight of about 95 to 250, especially about 100 to 150, and 5 to 35 weight % of at least one divinylarene dioxide. In these mixtures, the divinylarene dioxide preferably constitutes 10 to 35 weight percent, 15 to 30 weight percent or 15 to 25 weight percent of the epoxy resins in the epoxy resin component. Such mixtures may contain up to 75% by weight of one or more other epoxy resins. The cycloaliphatic epoxy resin preferably constitutes at least 35%, more preferably at least 50% by weight of such mixtures.

b) Mixtures containing 20 to 94 weight- % of a cycloaliphatic epoxy resin having an epoxy equivalent weight of about 95 to 250, especially about 100 to 150, 5 to 35% by weight of at least one divinylarene dioxide, and at least 1% by weight of an epoxy novolac resin. The divinylarene dioxide preferably constitutes 10 to 35 weight percent, 15 to 30 weight percent or 15 to 25 weight percent of the epoxy resins and the epoxy novolac resin preferably constitutes 1 to 35, preferably 2 to 20 and more preferably 5 to 15 weight percent of the epoxy resins. In these mixtures, the epoxy novolac resin preferably has an epoxy equivalent weight of about 170 to 225 and especially from 170 to 190 and contains 3 to 6, preferably 3 to 5 epoxide groups per molecule. Any of these mixtures may contain up to 75% by weight of one or more other epoxy resins. The cycloaliphatic epoxy resin preferably constitutes at least 35%, more preferably at least 50% by weight of such mixtures.

c) Mixtures containing 20 to 94 weight% of a cycloaliphatic epoxy resin having an epoxy equivalent weight of about 95 to 250, especially about 100 to 150, 5 to 35% by weight of at least one divinylarene dioxide, and at least 1 % by weight of a polyglycidyl ether of a bisphenol having an epoxy equivalent weight of up to 250. The divinylarene dioxide preferably constitutes 10 to 35 weight percent, 15 to 30 weight percent or 15 to 25 weight percent of the epoxy resins and the polyglycidyl ether of the bisphenol preferably constitutes 1 to 35, preferably 2 to 20 and more preferably 5 to 15 weight percent of the epoxy resins. In any mixture according to this paragraph c), the polyglycidyl ether of the bisphenol preferably has an epoxy equivalent weight of 170 to 250 and more preferably 170 to 200. Any of these mixtures may contain up to 74% by weight of one or more other epoxy resins. The cycloaliphatic epoxy resin preferably constitutes at least 35%, more preferably at least 50% by weight of such mixtures.

d) Mixtures containing 20 to 93 weight% of a cycloaliphatic epoxy resin having an epoxy equivalent weight of about 95 to 250, especially about 100 to 150, 5 to 35% by weight of at least one divinylarene dioxide, at least 1% by weight of an epoxy novolac resin and at least 1% by weight of a polyglycidyl ether of a bisphenol having an epoxy equivalent weight of up to 250. The divinylarene dioxide preferably constitutes 10 to 35 weight percent, 15 to 30 weight percent or 15 to 25 weight percent of the epoxy resins the epoxy novolac resin and the diglycidyl ether of a bisphenol each preferably constitutes 1 to 35, preferably 2 to 20 and more preferably 5 to 15 weight percent of the epoxy resins. In any mixture according to this paragraph d), the epoxy novolac resin preferably has an epoxy equivalent weight of about 170 to 225 and especially from 170 to 190 and contains 3 to 6, preferably 3 to 5 epoxide groups per molecule and the polyglycidyl ether of the bisphenol preferably has an epoxy equivalent weight of 170 to 250 and more preferably 170 to 200. Any of these mixtures may contain up to 73% by weight of one or more other epoxy resins. The cycloaliphatic epoxy resin preferably constitutes at least 35%, more preferably at least 50% by weight of such mixtures.

In any of the mixtures described in paragraphs a) - d), the cycloaliphatic epoxy resin preferably is

(3,4-epoxycyclohexyl-methyl)-3,4-epoxy-cyclohexane carboxylate, bis-(3,4-epoxycyclohexyl) adipate or a mixture thereof, and the divinylarene dioxide is preferably divinylbenzene dioxide.

In any of the mixtures described in paragraphs a) - d) above, the listed epoxy resins preferably together constitute 95 to 100%, more preferably 100%, of the total weight of all epoxy resins in the epoxy resin component.

The epoxy resin component may contain other materials in addition to the epoxy resin(s). Such additional materials may include, for example, various impact modifiers, one or more catalysts, one or more colorants, one or more include solvents or reactive diluents, pigments, antioxidants, preservatives, non-fibrous particulate fillers (including micron- and nano-particles), wetting agents and the like.

The hardener component contains one or more epoxy hardeners, by which it is meant compounds that react at least difunctionally with epoxy groups, in each case opening the epoxide ring and forming a covalent bond to the ring-opened species. In this invention, at least 75% by weight of all epoxy hardeners in the hardener component is one or more carboxylic acid anhydrides. The carboxylic acid anhydrides may constitute up to 100% of the epoxy hardeners in the hardener component. In some embodiments, non-anhydride hardeners constitute at most 10%, preferably at most 5% of the weight of all epoxy hardeners in the hardener component. Any non-anhydride hardeners should not be reactive with the anhydride hardener(s) under the conditions of the curing reaction. The hardener is most preferably devoid of primary and/or secondary amino compounds.

Examples of anhydride hardeners include aliphatic anhydrides such as nadic anhydride (bicyclo[2.2.1]-5-heptene-2,3-dicarboxylic anhydride or cis-5-norbornene-2,3-dicarboxylic anhydride, either exo and/or endo isomers), nadic methyl anhydride (bicyclo [2.2.1]-methylhept-5-ene-2,3- dicarboxylic acid anhydride or methyl-5-norbornene-2,3-dicarboxylic acid, exo and/or endo configurations), hexahydrophthalic anhydride, tetrahydrophthalic anhydride, methyl tetrahydrophthalic anhydride, methyl hexahydrophthalic anhydride and mixtures of any two or more thereof. Examples of aromatic anhydrides may include, for example, phthalic anhydride, trimellitic anhydride and mixtures thereof. Copolymers of styrene and maleic anhydride and other anhydrides copolymerizable with styrene such as those described, for example, in U.S. Patent No. 6, 613,839, incorporated herein by reference, also are useful anhydride hardeners. Preferably, the anhydride hardener is nadic anhydride, nadic methyl anhydride, or a mixture thereof.

In embodiments in which the hardener component contains one or more hardeners other than a carboxylic anhydride, the additional hardener may be, for example, a polyphenol compound, an aliphatic polyol, or the like. Such additional hardeners, if present at all, should constitute no more than 25%, preferably no more than 10% and more preferably no more than 5% of the total weight of all hardeners in the hardener component. Such additional hardeners preferably are absent.

The hardener component may, in addition to the hardener compounds described before, contain one or more additional ingredients as described before with respect to the epoxy resin component.

The epoxy resin component and the hardener component are reacted in the presence of an effective amount of at least one catalyst. Typically, the catalyst is formulated into either the epoxy resin component or the hardener component, or into both.

Among the suitable catalysts are various tertiary amines. Suitable tertiary amine catalysts include tertiary aminophenol compounds, benzyl tertiary amine compounds, imidazole compounds, or mixtures of any two or more thereof. Tertiary aminophenol compounds contain one or more phenolic groups and one or more tertiary amino groups. Examples of tertiary aminophenol compounds include mono-, bis- and tris(dimethylaminomethyl)phenol, as well as mixtures of two or more of these. Benzyl tertiary amine compounds are compounds having a tertiary nitrogen atom, in which at least one of the substituents on the tertiary nitrogen atom is a benzyl or substituted benzyl group. An example of a useful benzyl tertiary amine compound is Ν,Ν-dimethyl benzylamine.

Imidazole compounds contain one or more imidazole groups. Examples of imidazole compounds include, for example, imidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-undecylimidazole, 2- heptadecylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, l-benzyl-2-methylimidazole, 2- ethylimidazole, 2-isopropylimidazole, 2-phenyl-4-benzylimidazole, l-cyanoethyl-2-undecylimidazole, 1- cyanoethyl-2-ethyl-4-methylimidazole, 1 -cyanoethyl-2-undecylimidazole, 1 -cyanoethyl-2- isopropylimidazole, l-cyanoethyl-2-phenylimidazole, 2,4-diamino-6-[2'-methylimidazolyl-(l)']ethyl-s- triazine, 2,4-diamino-6-[2'-ethylimidazolyl-(l)']ethyl-s-triazine, 2,4-diamino-6-[2'-undecylimidazolyl- (l)']ethyl-s-triazine, 2-methylimidazolium-isocyanuric acid adduct, 2-phenylimidazolium-isocyanuric acid adduct, l-aminoethyl-2-methylimidazole, 2-phenyl-4,5-dihydroxylmethylimidazole, 2-phenyl-4- methyl-5-hydroxymethylimidazole, 2-phenyl-4-benzyl-5-hydroxymethylimidazole, and compounds containing two or more imidazole rings obtained by dehydrating any of the foregoing imidazole compounds or condensing them with formaldehyde. Imidazole compounds tend to strongly catalyze the homopolymerization of the epoxy resin, and so are strongly preferred when the ratio of epoxide groups to epoxy-reactive groups provided to the reaction mixture exceeds 1.25.

Other suitable catalysts include various those described in, for example, U.S. Patent Nos. 3,306,872, 3,341,580, 3,379,684, 3,477,990, 3,547,881, 3,637,590, 3,843,605, 3,948,855, 3,956,237, 4,048,141, 4,093,650, 4,131,633, 4,132,706, 4,171,420, 4,177,216, 4,302,574, 4,320,222, 4,358,578, 4,366,295, and 4,389,520, and WO 2008/140906, all incorporated herein by reference. A particularly useful catalyst mixture is a mixture of an imidazole catalyst and a metallic catalyst. Examples of such metallic catalysts include chromium (III) complexes such as oxo-centered trinuclear chromium (III) complexes such as Hycat™ 2000S, Hycat™ 3000S and Hycat™ OA catalysts (Dimensional Technology Chemical Systems, Inc.)

The catalyst is present in a catalytically effective amount. A suitable amount is typically from about 0.1 to about 10 parts by weight of catalyst(s) per 100 parts by weight of epoxy resin(s). A preferred amount is from 1 to 5 parts of catalyst(s) per 100 parts by weight of epoxy resin(s).

Thermosets are formed from the epoxy resin system of the invention by mixing the epoxy resin component and hardener, at proportions that provide from 0.8 to 10, preferably 0.8 to 1.25, equivalents of epoxy groups per equivalent of epoxy-reactive group in the hardener component, and allowing the resulting mixture to cure. Either or both of the components can be preheated if desired before they are mixed with each other. It is generally preferred to heat the mixture to an elevated temperature, such as from 60 to 180°C, especially from 120 to 170°C, to accelerate the cure. It is preferred to continue the cure until the resulting polymer attains a glass transition temperature in excess of the cure temperature. The glass transition temperature at the time of demolding is preferably at least 180°C, preferably at least 200°C. An advantage of this invention is that such high glass transition temperatures can be obtained with short curing times. This allows for short cycle times.

The epoxy resin component and hardener may be cured in the presence of various optional ingredients, if desired. It is often convenient to incorporate these optional ingredients, if used, into either the epoxy resin component or the hardener component, or both.

Among the useful optional ingredients is an internal mold release agent, which may constitute up to 5%, more preferably up to about 1% of the combined weight of the epoxy resin component and the hardener mixture. Suitable internal mold release agents are well known and commercially available, including those marketed as Marbalease™ by Rexco-USA, Mold-Wiz™ by Axel Plastics Research Laboratories, Inc., Chemlease™ by Chem-Trend, PAT™ by Wiirtz GmbH, Waterworks Aerospace Release by Zyvax and Kantstik™ by Specialty Products Co. In addition to (or instead of) adding the internal mold release agent at the mixhead, it is also possible to combine such an internal mold release agent into the resin component and/or the hardener before the resin component and the hardener are brought together.

Other optional components that can be present include solvents or reactive diluents, pigments, antioxidants, preservatives, impact modifiers, non-fibrous particulate fillers including micron- and nano- particles, wetting agents and the like.

The solvent is a material in which the epoxy resin, or hardener, or both, are soluble. The solvent is not reactive with the epoxy resin(s) or the hardener under the conditions of the polymerization reaction. The solvent (or mixture of solvents, if a mixture is used) preferably has a boiling temperature that is at least equal to and preferably higher than the curing temperature. Suitable solvents include, for example, glycol ethers such as ethylene glycol methyl ether and propylene glycol monomethyl ether; glycol ether esters such as ethylene glycol monomethyl ether acetate and propylene glycol monomethyl ether acetate; poly(ethylene oxide) ethers and poly (propylene oxide) ethers; polyethylene oxide ether esters and polypropylene oxide ether esters; amides such as N,N-dimethylformamide; aromatic hydrocarbons toluene and xylene; aliphatic hydrocarbons; cyclic ethers; halogenated hydrocarbons; and mixtures thereof. It is preferred to omit a solvent. If used, the solvent may constitute up to 75% of the weight of the reaction mixture (not including the reinforcing fiber), more preferably up to 30% of the weight of the mixture. Even more preferably the reaction mixture contains no more than 5% by weight of a solvent and most preferably contains less than 1 % by weight of a solvent.

Suitable impact modifiers include natural or synthetic polymers having a T_g of lower than -40°C. These include natural rubber, styrene -butadiene rubbers, polybutadiene rubbers, isoprene rubbers, core- shell rubbers, butylene oxide-ethylene oxide block copolymers, and the like. The rubbers are preferably present in the form of small particles that become dispersed in the polymer phase of the composite. The rubber particles can be dispersed within the epoxy resin or hardener or both. Certain of these impact modifiers may sharply increase the viscosity of the epoxy resin component and/or hardener component. An advantage of this invention is that the presence of the divinylarene dioxide in the epoxy resin composition tends to decrease its viscosity. This reduced viscosity permits some formulating latitude as, for example, impact modifiers can be shifted from the hardener side to the epoxy resin side if desirable to help adjust the viscosities of the two components to comparable levels.

In certain embodiments, the viscosity of the formulated epoxy resin component and of the hardener component are each no greater than 1500 centipoises at 25°C, and preferably no greater than 500 centipoises at 25 °C. Viscosities can be measured using a plate-and-cone rheometer that provides temperature control.

Suitable particulate fillers have an aspect ratio of less than 5, preferably less than 2, and do not melt or thermally degrade under the conditions of the curing reaction. Suitable fillers include, for example, glass flakes, aramid particles, carbon black, carbon nanotubes, various clays such as montmoriUonite, and other mineral fillers such as wollastonite, talc, mica, titanium dioxide, barium sulfate, calcium carbonate, calcium silicate, flint powder, carborundum, molybdenum silicate, sand, and the like. Some fillers are somewhat electroconductive, and their presence in the composite can increase the electroconductivity of the composite. In some applications, notably automotive applications, it is preferred that the composite is sufficiently electroconductive that coatings can be applied to the composite using so-called "e-coat" methods, in which an electrical charge is applied to the composite and the coating becomes electrostatically attracted to the composite. Conductive fillers of this type include metal particles (such as aluminum and copper), carbon black, carbon nanotubes, graphite and the like.

The epoxy resin system (i.e., the mixed epoxy resin component and hardener component, including any catalysts and other components of the respective components, but not including reinforcing fiber) preferably has a gel time of no less than 45 seconds, more preferably no less than 60 seconds at 160°C. The epoxy resin system also preferably has a cure time of no more than five minutes, preferably 3 to 5 minutes, at 160°C. The gel time and cure time can be evaluated by mixing the components (including catalyst(s)) at room temperature (20-30°C) and pouring the mixture onto the surface of a 160°C hot plate coated with an external mold release agent. A line is cut across the sample periodically as it cures. The time at which the material no longer flows back into the line is the gel time. The time at which the mixture can be removed from the hot plate without permanent damage or distortion is the cure time. Preferably, the epoxy resin system cures to a polymer having a glass transition temperature of at least 180°C, more preferably at least 200°C within the cure times stated above.

The curable epoxy resin system of the invention is particularly useful for making fiber-reinforced composites by curing the system in the presence of reinforcing fibers. These composites are in general made by mixing the epoxy resin component with the hardener to form a mixture, wetting the fibers with the mixture, and then curing the mixture in the presence of the catalyst and the reinforcing fibers. It is also possible to first wet the reinforcing fibers with either the epoxy resin component or the hardener (such as by dispersing the fibers into them) and then mixing the epoxy resin component with the hardener. Another alternative is to mix the epoxy resin component and the hardener in the presence of the reinforcing fibers. The reinforcing fibers are thermally stable and have a high melting temperature, such that the reinforcing fibers do not degrade or melt during the curing process. Suitable fiber materials include, for example, glass, quartz, polyamide resins, boron, carbon, wheat straw, hemp, sisal, cotton, bamboo and gel-spun polyethylene fibers.

The reinforcing fibers can be provided in the form of short (0.5 to 15 cm) fibers, long (greater than 15 cm) fibers or continuous rovings. The fibers can be provided in the form of a mat or other preform if desired; such mats or performs may in some embodiments be formed by entangling, weaving, stitching the fibers, or by binding the fibers together using an adhesive binder. Preforms may approximate the size and shape of the finished composite article (or portion thereof that requires reinforcement). Mats of continuous or shorter fibers can be stacked and pressed together, typically with the aid of a tackifier, to form preforms of various thicknesses, if required.

Suitable tackifiers for preparing performs (from either continuous or shorter fibers) include heat- softenable polymers such as described, for example, in U. S. Patent Nos. 4,992,228, 5,080,851 and 5,698,318. The tackifier should be compatible with and/or react with the polymer phase of the composite, so that there is good adhesion between the polymer and reinforcing fibers. A heat-softenable epoxy resin or mixture thereof with a hardener, as described in U. S. Patent No. 5,698,318, is especially suitable. The tackifier may contain other components, such as one or more catalysts, a thermoplastic polymer, a rubber, or other modifiers.

A sizing or other useful coating may be applied onto the surface of the fibers before they are introduced into the mold. A sizing often promotes adhesion between the cured epoxy resin and the fiber surfaces. The sizing in some embodiments may also have a catalytic effect on the reaction between the epoxy resin and the hardener.

The composite may be formed in a mold. In such a case, the reinforcing fibers may be introduced into the mold before the epoxy resin/hardener mixture. This is normally the case when a fiber preform is used. The fiber preform is placed into the mold and the epoxy resin/hardener mixture is then injected into the mold, where it penetrates between the fibers in the preform, fills the cavity, and then cures to form a composite product.

Alternatively, the fibers (including a preform) can be deposited into an open mold, and the reaction mixture can be sprayed or injected onto the preform and into the mold. After the mold is filled in this manner, the mold is closed and the reaction mixture cured.

Short fibers can be injected into the mold with the hot reaction mixture. Such short fibers may be, for example, blended with the epoxy resin or hardener (or both), prior to forming the reaction mixture. Alternatively, the short fibers may be added into the reaction mixture at the same time as the epoxy and hardener are mixed, or afterward but prior to introducing the hot reaction mixture into the mold.

Alternatively, short fibers can be sprayed into a mold. In such cases, the reaction mixture can also be sprayed into the mold, at the same time or after the short fibers are sprayed in. When the fibers and reaction mixture are sprayed simultaneously, they can be mixed together prior to spraying. Alternatively, the fibers and reaction mixture can be sprayed into the mold separately but simultaneously. In a process of particular interest, long fibers are chopped into short lengths and the chopped fibers are sprayed into the mold, at the same time as or immediately before the hot reaction mixture is sprayed in.

Composites made in accordance with the invention may have fiber contents of at least 10 volume percent, preferably at least 25 volume percent or at least 35 volume percent, up to 80 volume percent, preferably up to 70 volume percent, more preferably up to 60 volume percent.

The mold may contain, in addition to the reinforcing fibers, one or more inserts. Such inserts may function as reinforcements, and in some cases may be present for weight reduction purposes. Examples of such inserts include, for example, wood, plywood, metals, various polymeric materials, which may be foamed or unfoamed, such as polyethylene, polypropylene, another polyolefin, a polyurethane, polystyrene, a polyamide, a polyimide, a polyester, polyvinylchloride and the like, various types of composite materials, and the like, that do not become distorted or degraded at the temperatures encountered during the molding step.

The reinforcing fibers and core material, if any, may be enclosed in a bag or film such as is commonly used in vacuum assisted processes.

The mold and the preform (and any other inserts, if any) may be heated to the curing temperature or some other useful elevated temperature prior to contacting them with the reaction mixture. The mold surface may be treated with an external mold release agent, which may be solvent or water-based.

The particular equipment that is used to mix the components of the reaction mixture and transfer the mixture to the mold is not considered to be critical to the invention, provided the reaction mixture can be transferred to the mold before it attains a high viscosity or develops significant amounts of gels. The process of the invention is amenable to RTM, VARTM, RFI and SCRIMP processing methods and equipment (in some cases with equipment modification to provide the requisite heating at the various stages of the process), as well as to other methods.

The mixing apparatus can be of any type that can produce a highly homogeneous mixture of the epoxy resin and hardener (and any optional components that are also mixed in at this time). Mechanical mixers and stirrers of various types may be used. Two preferred types of mixers are static mixers and impingement mixers. In some embodiments, the mixing and dispensing apparatus is an impingement mixer. Mixers of this type are commonly used in so-called reaction injection molding processes to form polyurethane and polyurea moldings. The epoxy resin and hardener (and other components which are mixed in at this time) are pumped under pressure into a mixing head where they are rapidly mixed together. Operating pressures in high pressure machines may range from 1,000 to 29,000 psi or higher (6.9 to 200 MPa or higher), although some low pressure machines can operate at significantly lower pressures. The resulting mixture is then preferably passed through a static mixing device to provide further additional mixing, and then transferred into the mold cavity. The static mixing device may be designed into the mold. This has the advantage of allowing the static mixing device to be opened easily for cleaning.

In certain specific embodiments, the epoxy resin and hardener are mixed as just described, by pumping them under pressure into a mixing head. Impingement mixing may be used. The catalyst is introduced with the epoxy resin, the hardener, or as a separate stream. The operating pressure of the incoming epoxy resin and hardener streams may range from a somewhat low value (for example, from about 1 to about 6.9 MPa) or a high value (such as, for example, from 6.9 to 200 MPa). The resulting mixture of epoxy resin, hardener and catalyst is then introduced into the mold at a somewhat low operating pressure, such as up to 5 MPa or up to about 1.035 MPa). In such embodiments, the mixture of epoxy resin, hardener and catalyst is typically passed through a static mixer before entering the mold. Some or all of the pressure drop between the mixhead and the mold injection port often will take place through such a static mixer. An especially preferred apparatus for conducting the process is a reaction injection molding machine, such as is commonly used to processes large polyurethane and polyurea moldings. Such machines are available commercially from Krauss Maffei Corporation and Cannon or Hennecke.

In other embodiments, the hot reaction mixture is mixed as before, and then sprayed into the mold. Temperatures are maintained in the spray zone such that the temperature of the hot reaction mixture is maintained as described before.

The mold is typically a metal mold, but it may be ceramic or a polymer composite, provided that the mold is capable of withstanding the pressure and temperature conditions of the molding process. The mold contains one or more inlets, in liquid communication with the mixer(s), through which the reaction mixture is introduced. The mold may contain vents to allow gases to escape as the reaction mixture is injected.

The mold is typically held in a press or other apparatus which allows it to be opened and closed, and which can apply pressure on the mold to keep it closed during the filling and curing operations. The mold or press is provided with means by which heat or cooling can be provided. In some embodiments of the foregoing process, the molded composite is demolded in no more than 5 minutes, preferably from 2 to 5 minutes, after the start of injection of the epoxy resin system into the mold. In such processes, the introduced reaction mixture flows around and between the reinforcing fibers and fills the mold and then cures in the mold, preferably forming a polymer having a glass transition temperature of at least 180°C within five minutes, more preferably within three minutes, of the start of introducing the reaction mixture into the mold.

The process of the invention is useful to make a wide variety of composite products, including various types of automotive parts. Examples of these automotive parts include vertical and horizontal body panels, automobile and truck chassis components, and so-called "body-in-white" structural components.

Body panel applications include fenders, door skins, hoods, roof skins, decklids, tailgates and the like. Body panels often require a so-called "class A" automotive surface which has a high distinctness of image (DOI). For this reason, the filler in many body panel applications will include a material such as mica or wollastonite.

Due to their high glass transition temperatures, composite parts made in accordance with this invention are subjected to high temperatures as are often used to bake certain protective coatings as are commonly used in automotive manufacturing processes. In such a bake cure, the composite may be subject to a temperature of 140 to 180°C for a period of 10 to 60 minutes. These protective coatings are often applied electrostatically in a so-called "e-coat" process, and for that reason must be somewhat electroconductive. Accordingly, an electroconductive filler may be incorporated into the composite to increase the electrical conductivity of the part. An impact modifier as described before is often desired in body panel applications to toughen the parts.

The following examples are provided to illustrate the invention, but not limit the scope thereof. All parts and percentages are by weight unless otherwise indicated.

Examples 1-4 and Comparative Sample A

An epoxy resin component is prepared by mixing 20 parts of (3,4-epoxycyclohexyl-methyl)-3,4- epoxy-cyclohexane carboxylate (Synasia™ 21) 4.3 parts of an epoxy novolac resin (D.E.N 438, from The Dow Chemical Company), 4.3 parts of a diglycidyl ether of bisphenol A (D.E.R. 383 from The Dow Chemical Company) and 7.4 parts of divinylbenzene dioxide (95% pure, epoxy equivalent weight 81).

To make Example 1 , the foregoing epoxy resin component is cured with a hardener composition that contains 74.6 parts nadic methyl anhydride (Dixie Chemicals), 22 parts of a commercial polymeric toughener (Fortegra™ 100 from The Dow Chemical Company), 1.7 parts 1-methyl imidazole and 1.7 parts of Hycat-3000S chromium catalyst. The epoxy resin component and hardener components are mixed at room temperature on a high speed laboratory mixture until homogeneous (about 1 minute). The ratios of the components are such to provide about 1.05 epoxy groups per anhydride group. A portion of the mixture is poured into a preheated (160°C) aluminum plaque mold treated with an external mold release agent. The mold is positioned in a 160°C oven as the mixture is poured. After filling the aluminum mold, the oven is closed and the part cured for 5 minutes, after which the resulting part is immediately demolded. Specimens of the cured plaque are evaluated for glass transition temperature (by dynamic mechanical thermal analysis (DMTA)), tensile modulus and elongation (ASTM D638 Type I), fracture toughness (ASTM D-5045) and coefficient of thermal expansion (by thermomechanical analysis).

Another portion of the mixture is poured onto a 160°C hot plate that has been sanded clean, wiped with acetone and coated with an external mold release agent. A line is cut on the surface of the curing mixture periodically to assess gel time, as described before. Cure time is evaluated by periodically attempting to remove the curing mixture from the hot plate surface. The cure time is the time at which the part can be removed without permanent damage or distortion.

Results of this testing are indicated in Table 1.

Examples 2-4 are made in the same manner, except that in each case the toughener is replaced with an equal weight of another impact modifier. For Example 2, the impact modifier is a core-shell rubber (Paraloid™2650A). For Example 3, the toughener is a 6000 molecular weight poly ether triol. For Example 4, the toughener is a 4000 molecular weight polyether diol.

Table 1

The viscosity of the epoxy resin component is measured at various temperatures using a cone- and-plate rheometer. Similarly, the viscosity of each of the hardeners used to make Examples 1-2 are measured. The viscosities at 25 °C are indicated in Table 2.

The viscosity of the mixed epoxy resin component and hardener component for each of Examples 1 and 2 is also measured at 25°C. These values are also reported in Table 2.

For comparison, an epoxy resin component is formulated by blending (3,4-epoxycyclohexyl- methyl)-3,4-epoxy-cyclohexane carboxylate (Synasia™ 21) 4.3 parts of the D.E.N. 438 epoxy novolac resin and the D.E.R. 383 diglycidyl ether of bisphenol A (D.E.R. 383 from The Dow Chemical Company) at a 70: 15: 15 weight ratio. The viscosity of this material (Comp. A) is measured as before and is as reported in Table 2. A portion of this epoxy resin component is blended with the hardener component used in Example 1 , at a ratio which provides 1.05 epoxide groups per anhydride group. Another portion of that epoxy resin component is blended with the hardener component used in Example 2, at the same ratio. The viscosity of each of those blends (Blends A and B, respectively) are measured at 25°C, with results as indicated in Table 2.

Table 2

As can be seen from the data in Table 2, the presence of the divinylbenzyl dioxide in the inventive Epoxy Resin Component affords a very large reduction in viscosity, even when blended with the hardener. The beneficial effect is particularly large when the hardener contains a core-shell rubber.

Examples 5-6

Resin transfer molding is used to make a composite. The machine is a Krauss-Maffei high- pressure RIM Star RTM 4/4. The mold has internal dimensions of 620 mm X 460 mm by 22 mm, with a central injection point and two venting points. The internal surfaces of the mold are treated with an external mold release. A carbon fiber preform (Panex™ 35 from Zoltek) having a weight of 330 g/qm is inserted into the mold. The preform and both halves of the mold are heated to 160°C. A vacuum is drawn on the mold prior to injecting the epoxy resin system. The hardener component is preheated to 40°C and the epoxy resin component is preheated to 80°C. The hardener and epoxy resin component are impingement mixed at a weight ratio of 100: 153 (Example 5), and 325 grams of the mixture then injected into the mold over 25 seconds. The part is demolded after 4 minutes. The polymer phase of the composite has a glass transition temperature of 213°C.

When this experiment is repeated (Ex. 6) with a three minute demold time, the polymer phase of the composite has a glass transition temperature of 214°C. These results indicate that a suitable demold time for this system is three minutes or less.

The epoxy resin component used in Examples 5-6 is a mixture of 55.62 parts (3,4- epoxycyclohexyl-methyl)-3,4-epoxy-cyclohexane carboxylate (Synasia™ 21) 11.92 parts of an epoxy novolac resin (D.E.N 438, from The Dow Chemical Company), 11.92 parts of a diglycidyl ether of bisphenol A (D.E.R. 383 from The Dow Chemical Company) and 20.54 parts of divinylbenzene dioxide (95% pure, epoxy equivalent weight 81). The hardener composition used in Examples 5-6 is a mixture of 74.5 parts nadic methyl anhydride (Dixie Chemicals), 22.1 parts of a core-shell rubber (Paraloid 2650A), 1.7 parts 1 -methyl imidazole and 1.7 parts of Hycat-3000S chromium catalyst.

Examples 7-8

Examples 7 and 8 are performed in the same manner as Examples 5 and 6, respectively, except the hardener composition is modified and the resin:hardener ratio is increased to 100: 182. The hardener composition in this case is a mixture of 74.5 parts nadic methyl anhydride (Dixie Chemicals), 22.1 parts of a Fortegra® 100 toughener (Dow Chemical), 1.7 parts 1-methyl imidazole and 1.7 parts of Hycat- 3000S chromium catalyst.

The glass transition temperatures of the resulting composites are 200°C and 203°C, respectively, indicating that the necessary demold time for this formulation is no greater than 3 minutes on this test.

Example 9 and Comparative Sample B

To make Example 9, an epoxy resin component containing 20% by weight (based on epoxy resins) of divinylbenzyl dioxide is prepared as described for Example 1. That epoxy resin component is mixed with a hardener that contains 48.49 parts methyl nadic anhydride, 13.42 parts of a core-shell rubber, 1.03 1-methyl imidazole and 1.7 parts of Hycat-3000S chromium catalyst. The resulting reaction mixture initially contains 7.4% by weight of divinylbenzyl dioxide. It is cured on a hot plate as described in Example 1 to produce a plaque that demolds easily after about 240 seconds.

Comparative Sample B is made in the same manner, except more of the cycloaliphatic epoxy resins is replaced with divinylbenzene dioxide, to the divinylbenzene dioxide content in the epoxy resin component is about 40% and the divinylbenzene dioxide content in the reaction mixture is increase to about 14% by weight. This material cures rapidly to form a hard plaque, but the plaque cannot be demolded without the part breaking into small pieces.

Claims

CLAIMS:

1. A process for forming a fiber-reinforced epoxy composite, comprising forming a reaction mixture containing an epoxy resin component and a hardener component, and curing the epoxy resin component with the hardener component in the presence of reinforcing fibers and an effective amount of at least one catalyst, wherein:

the epoxy resin component contains 5 to 35% by weight of at least one divinylarene dioxide, based on the total weight of all epoxy resins in the epoxy resin component;

the hardener component contains at least 75% by weight of a carboxylic acid anhydride, based on the total weight of all epoxy hardeners in the hardener component;

2. The process of claim 1 , wherein the epoxy resin component and the hardener component are impingement mixed by flowing them separately to an impingement mixer under an operating pressure of 1 to 200 MPa, the resulting reaction mixture is transferred into a mold that contains a fiber preform that includes the reinforcing fibers, such that the reaction mixture flows around and between the reinforcing fibers and fills the mold and the reaction mixture then cures in the mold.

3. The process of claim 2, wherein the reaction mixture cures in the mold to form a polymer having a glass transition temperature of at least 180°C within five minutes of the start of introducing the reaction mixture into the mold and the reaction mixture has a gel time of no less than 60 seconds at 160°C.

4. The process of claim 1, 2 or 3, wherein the epoxy resin component and the hardener component are present in amounts that provide from 0.8 to 1.25 equivalents of epoxy groups per equivalent of epoxy-reactive group in the hardener component.

5. The process of any preceding claim, wherein the epoxy resin component contains, by weight of epoxy resins, 20 to 95 weight% of a cycloaliphatic epoxy resin having an epoxy equivalent weight of 95 to 250, and 5 to 35% by weight of the divinylarene dioxide.

6. The process of claim 5, wherein the divinylarene dioxide constitutes 15 to 30 weight percent of the epoxy resins in the epoxy resin component, the cycloaliphatic epoxy resin has an epoxy equivalent weight of 100 to 150 and the divinylarene dioxide constitutes 15 to 25 weight percent of the epoxy resins in the epoxy resin component.

7. The process of any of claims 1-5, wherein the epoxy resin component contains, by weight of epoxy resins, 20 to 94 weight of a cycloaliphatic epoxy resin having an epoxy equivalent weight of 95 to 250, 5 to 35% by weight of at least one divinylarene dioxide and at least 1% by weight of an epoxy novolac resin.

8. The process of claim 7, wherein the cycloaliphatic epoxy resin has an epoxy equivalent weight of 100 to 150, the epoxy novolac resin has an epoxy equivalent weight of 170 to 225, contains 3 to 5 epoxide groups per molecule and constitutes 5 to 15 weight percent of the epoxy resins in the epoxy resin component, and the divinylarene dioxide constitutes 15 to 25 weight percent of the epoxy resins in the epoxy resin component.

9. The process of any of claims 1-5, wherein the epoxy resin component contains, by weight of epoxy resins, 20 to 94 weight % of a cycloaliphatic epoxy resin having an epoxy equivalent weight of about 95 to 250, 5 to 35% of at least one divinylarene dioxide, and at least 1% of a polyglycidyl ether of a bisphenol having an epoxy equivalent weight of up to 250.

10. The process of claim 9, wherein the divinylarene dioxide constitutes 15 to 25 weight percent of the epoxy resins in the epoxy resin component, the cycloaliphatic epoxy resin has an epoxy equivalent weight of 100 to 150 and the polyglycidyl ether of a bisphenol has an epoxy equivalent weight of 170 to 200 and constitutes 5 to 15 weight percent of the epoxy resins in the epoxy resin component.

11. The process of any of claims 1-5, wherein the epoxy resin component contains, by weight of epoxy resins, 20 to 93 weight% of a cycloaliphatic epoxy resin having an epoxy equivalent weight of about 95 to 250, 5 to 35% by weight of at least one divinylarene dioxide, at least 1% by weight of an epoxy novolac resin and at least 1% by weight of a polyglycidyl ether of a bisphenol having an epoxy equivalent weight of up to 250.

12. The process of claim 11, wherein divinylarene dioxide constitutes 15 to 30 weight percent of the weight of the epoxy resins in the epoxy resin component, the epoxy novolac resin and the diglycidyl ether of a bisphenol each constitutes 2 to 20 weight percent of the epoxy resins in the epoxy resin component, the epoxy novolac resin has an epoxy equivalent weight of 170 to 190 and contains 3 to 5 epoxide groups per molecule, and the polyglycidyl ether of the bisphenol has an epoxy equivalent weight of 170 to 200.

13. The process of any of claims 5-12, wherein the cycloaliphatic epoxy resin is (3,4- epoxycyclohexyl-methyl)-3,4-epoxy-cyclohexane carboxylate, bis-(3,4-epoxycyclohexyl) adipate or a mixture thereof, and the divinylarene dioxide is divinylbenzene dioxide.

14. A curable epoxy resin system, comprising

I. an epoxy resin component containing, by weight of epoxy resins, 20 to 95 weight of a cycloaliphatic epoxy resin having an epoxy equivalent weight of about 95 to 250, and 5 to 35% by weight of at least one divinylarene dioxide, and

15. The curable epoxy resin system of claim 14, wherein the epoxy resin component contains, by weight of epoxy resins, 20 to 93 weight% of a cycloaliphatic epoxy resin having an epoxy equivalent weight of about 95 to 250, 5-35% by weight of at least one divinylarene dioxide, at least 1% by weight of an epoxy novolac resin and at least 1% by weight of a polyglycidyl ether of a bisphenol having an epoxy equivalent weight of up to 250.