WO2020005393A1

WO2020005393A1 - Fibre-reinforced composite and process of making this composite

Info

Publication number: WO2020005393A1
Application number: PCT/US2019/031248
Authority: WO
Inventors: Timothy A. Morley; Debora Ressnig; Gerrit GROOTENZERINK
Original assignee: Dow Global Technologies LLC
Current assignee: Dow Global Technologies LLC
Priority date: 2018-06-26
Filing date: 2019-05-08
Publication date: 2020-01-02
Anticipated expiration: 2020-12-26

Abstract

Disclosed is a fiber-reinforced composite produced by the steps of: (a) impregnating an epoxy matrix resin composition into a preform, wherein the preform comprises a plurality of reinforcement fiber layers connected to each other by a thermosetting binder composition in at least between the reinforcement fiber layers, wherein the thermosetting binder composition comprises an epoxy resin and an amine based hardener present in a range of from 1.05 amino hydrogen equivalents of primary and/or secondary amine compounds per epoxy equivalent to 3 amino hydrogen equivalents of primary and/or secondary amine compounds per epoxy equivalent; and (b) curing the epoxy matrix resin composition.

Description

FIBRE-REINFORCED COMPOSITE AND PROCESS OF MAKING THIS COMPOSITE

FIELD

[0001] The present invention relates to a fiber-reinforced composite and a process for making the fiber-reinforced composite using a fiber preform.

BACKGROUND

[0002] The use of reinforced composite materials to produce structural components is now widespread, particularly in applications where their desirable characteristics are sought of being light in weight, strong, tough, thermally resistant, self-supporting and adaptable to being formed and shaped. Such components are used, for example, in aeronautical, aerospace, satellite, recreational (as in racing boats and automobiles), and other applications.

[0003] Typically, such components consist of reinforcement materials embedded in matrix materials. The reinforcement component may be made from materials such as glass, carbon, ceramic, aramid, polyethylene, and/or other materials which exhibit desired physical, thermal, chemical and/or other properties, chief among which is great strength against stress failure. Through the use of such reinforcement materials, which ultimately become a constituent element of the completed component, the desired characteristics of the reinforcement materials, such as very high strength, are imparted to the completed composite component. The constituent reinforcement materials typically may be woven, knitted or braided as well as combinations of unidirectional (UD) mats. Usually particular attention is paid to ensure the optimum utilization of the properties for which the constituent reinforcing materials have been selected. Reinforced composite materials are made by combining reinforcement preforms with matrix material to form desired finished components or to produce working stock for the ultimate production of finished components.

[0004] Fiber-reinforced plastics (FRP), especially carbon fiber-reinforced plastics

(CFRP) using carbon fibers, are light in weight and have a high strength to weight ratio and their use in the construction of vehicles allows for very significant weight reduction. Accordingly, application of fiber-reinforced plastic members to transportation equipment has recently been expanded. CFRPs however are also costly materials, which provides a major hurdle to a breakthrough of lightweighting with CFRPs in automotive vehicles on a large or mass-scale. Thus, the main challenges to reduce cost include efficient waste management and reduced cycle times. [0005] For efficient waste management, the automotive industry is using near-net shape carbon fiber preforms for improved waste and cost management. For reduced cycle times the wet compression technique for forming and manufacture of CFRP parts has attention as it may provide a flexible and cycle time saving process alternative to conventional molding technologies. For example, one conventional molding technology is the Resin Transfer Molding process (RTM) as a method of manufacturing a fiber-reinforced resin molded product. RTM uses reinforcing fibers in the form of continuous fibers so that a produced fiber-reinforced resin molded product has high mechanical properties such as rigidity and strength. RTM enables the fiber-reinforced resin molded product to be molded in a shorter cycle time and has higher productivity, compared to using an autoclave. In many processes for producing fiber-reinforced composite material by the RTM method, reinforcement fiber base material is first processed into a preform in a similar shape to the intended product and then the preform is placed in a mold followed by adding liquid matrix resin.

[0006] Wet compression technology deposits the curing resin system onto the fiber material (i.e., preform) outside of the mold. Following a short soaking time, the wet combination of fiber material and uncured resin is placed in the mold and cured after the mold is closed. The wet compression technology offers potential for several process advantages versus the RTM technology. For example, one advantage is that the mold can be operated at higher temperature thereby allowing for a faster cure. Another advantage is that the resin system may be deposited onto a preform while another resin/preform combination is being cured in the mold. One other advantage is that multiple parts may be pressed and cured simultaneously.

[0007] Wet compression can be used for simple flat parts as well as more complex 3- dimensionally shaped parts that require a near net-shape preform. For example, a carbon fiber preform effectively is a dry lay-up of carbon fiber fabrics, formed to a specific shape (by preforming) and stabilized by a particulate binder material that is present at the interfaces of the different fabric layers. Binder materials are well known in the production of CFRP parts by molding technologies like RTM. In the case of RTM, preforms of varying complexity can be used, but the preforms are dry when handled and dry when placed inside the mold, as compared with wet compression in which the preform would be wet. In addition, to provide preform stability, another function of the binder is to maintain the orientation of the individual fibers when the part is being filled during the resin injection phase of the RTM process. [0008] Accordingly, binders must not only stabilize dry but also wet preforms, i.e., preform stiffness, when the preforms are impregnated with the uncured resin system. Such stabilization is required for the handling of the wet preforms for possibly up to a few minutes after depositing the resin system onto the preform, as well as during the final step as the mold is closed and curing is started. In this phase, the resin flow will occur and thus potentially fiber movement as well. Thus, this means, for example, that the binder shall not dissolve in the matrix resin during this time, or it will lose its binding properties due to exposure to the resin temperature.

[0009] Current thermoplastic binders that dissolve, swell or soften in the matrix resin system to yield homogeneous mixtures thereof, may result in good final part properties such as tensile strength, and strength after impact. For example, in the RTM process it is believed that these binder solutions are effective to stabilize the dry preform but the resulting fiber- reinforced composite possess only adequate mechanical properties. A fiber-reinforced composite must possess higher mechanical properties such as ILSS in order to improve the intralaminar shear strength of composite. In the wet compression process, the required time for the binder functionality while being exposed to the hot uncured resin system is much longer. Thus, these binders are not as effective to stabilize a wet preform.

[0010] Thus, it would be desirable for a thermosetting binder to achieve improved mechanical properties of a fiber-reinforced composite as well as stabilization of a wet preform to improve the compatibility with the matrix resin system.

SUMMARY

[0011] In one illustrative embodiment, a fiber-reinforced composite is provided where the fiber-reinforced composite material is produced by the steps comprising:

[0012] (a) impregnating an epoxy matrix resin composition into a preform, wherein the preform comprises a plurality of reinforcement fiber layers connected to each other by a thermosetting binder composition in at least between the reinforcement fiber layers, wherein the thermosetting binder composition comprises an epoxy resin and an amine based hardener present in a range of from 1.05 amino hydrogen equivalents of primary and/or secondary amine compounds per epoxy equivalent to 3 amino hydrogen equivalents of primary and/or secondary amine compounds per epoxy equivalent; and

[0013] (b) curing the epoxy matrix resin composition, [0014] wherein the epoxy matrix resin composition comprises (i) an epoxy resin component containing one or more epoxy resins, wherein at least 80% by weight of the epoxy resin component is one or more polyglycidyl ethers of a polyphenol that has an epoxy equivalent weight of up to about 250; (ii) an amine hardener, wherein the amine hardener is a polyethylene tetraamine mixture containing at least 95% by weight polyethylene tetraamines, the mixture containing at least 40% by weight linear triethylene tetraamine; and (iii) 0.01 to 0.5 moles of triethylene diamine per mole of primary and/or secondary amine compounds in the amine hardener, the triethylene diamine being present in the epoxy resin component, the amine hardener, or both.

[0015] In one illustrative embodiment, a process for preparing a fiber-reinforced composite is provided comprising the steps of:

[0016] (a) impregnating an epoxy matrix resin composition into a preform comprising a plurality of reinforcement fiber layers connected to each other by a thermosetting binder composition in at least between the reinforcement fiber layers, wherein the thermosetting binder composition comprises an epoxy resin and an amine based hardener in a range of from 1.05 amino hydrogen equivalents of primary and/or secondary amine compounds per epoxy equivalent to 3 amino hydrogen equivalents of primary and/or secondary amine compounds per epoxy equivalent; and

[0017] (b) curing the epoxy matrix resin composition resin, wherein the epoxy matrix resin composition comprises (i) an epoxy resin component containing one or more epoxy resins, wherein at least 80% by weight of the epoxy resin component is one or more polyglycidyl ethers of a polyphenol that has an epoxy equivalent weight of up to about 250; (ii) an amine hardener, wherein the amine hardener is a polyethylene tetraamine mixture containing at least 95% by weight polyethylene tetraamines, the mixture containing at least 40% by weight linear triethylene tetraamine; and (iii) 0.01 to 0.5 moles of triethylene diamine per mole of primary and/or secondary amine compounds in the amine hardener, the triethylene diamine being present in the epoxy resin component, the amine hardener, or both.

[0018] The fiber-reinforced composite of the present invention advantageously possesses excellent preform stability by employing the binder composition disclosed herein in both wet and dry conditions. In addition, the fiber-reinforced composite of the present invention advantageously exhibits improved final part interlaminar shear strength performance after impregnating the preform with the epoxy matrix resin composition. Further, the fiber-reinforced composite of the present invention may also exhibit high permeability.

DETAILED DESCRIPTION

[0019] Disclosed is a fiber-reinforced composite material produced by impregnating an epoxy matrix resin composition into a preform, wherein the preform comprises a plurality of reinforcement fiber layers connected to each other by a thermosetting binder composition in at least between the reinforcement fiber layers, wherein the thermosetting binder composition comprises an epoxy resin and an amine based hardener present in a range of from 1.05 amino hydrogen equivalents of primary and/or secondary amine compounds per epoxy equivalent to 3 amino hydrogen equivalents of primary and/or secondary amine compounds per epoxy equivalent; and (b) curing the epoxy matrix resin composition. The epoxy matrix resin composition comprises (i) an epoxy resin component containing one or more epoxy resins, wherein at least 80% by weight of the epoxy resin component is one or more polyglycidyl ethers of a polyphenol that has an epoxy equivalent weight of up to about 250; (ii) an amine hardener, wherein the amine hardener is a polyethylene tetraamine mixture containing at least 95% by weight polyethylene tetraamines, the mixture containing at least 40% by weight linear triethylene tetraamine; and (iii) 0.01 to 0.5 moles of triethylene diamine per mole of primary and/or secondary amine compounds in the amine hardener, the triethylene diamine being present in the epoxy resin component, the amine hardener, or both. The term“one or more” as used herein shall be understood to mean that at least one, or more than one, of the recited components may be used.

[0020] The thermosetting binder composition, i.e., powder, for the preform includes an epoxy resin. The term“epoxy resin” used herein means a compound which possesses one or more vicinal epoxy groups per molecule, i.e., at least one 1, 2-epoxy group per molecule. In general, the epoxy resin compound may be a saturated or unsaturated aliphatic, cycloaliphatic, aromatic or heterocyclic compound which possesses at least one 1, 2-epoxy group. Such compounds can be substituted, if desired, with one or more non-interfering substituents, such as halogen atoms, aliphatic or cycloaliphatic hydroxy groups, ether radicals, lower alkyls and the like. The epoxy resin compound may also be monomeric, oligomeric or polymeric, i.e., the epoxy resin may be selected from a monoepoxide, a diepoxide, a multi-functional epoxy resin, a poly epoxide; an advanced epoxy resin; or mixtures thereof. An extensive enumeration of epoxy resins useful in the present invention is found in Lee, H. and Neville, K.,“Handbook of Epoxy Resins,” McGraw-Hill Book Company, New York, 1967, Chapter 2, pages 257-307.

[0021] Suitable epoxy resins may vary and include conventional and commercially available epoxy resins, which may be used alone or in combinations of two or more. In choosing epoxy resins for the binder composition disclosed herein, consideration should not only be given to properties of the final product, but also to viscosity and other properties that may influence the processing of the binder composition. Suitable epoxy resins known to the skilled worker are based on reaction products of polyfunctional alcohols, phenols, cycloaliphatic carboxylic acids, aromatic amines, or aminophenols with epichlorohydrin. For example, suitable epoxy resins include bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, resorcinol diglycidyl ether, the triglycidyl ether of para-aminophenol and reaction products of epichlorohydrin with o-cresol and, respectively, phenol novolacs. It is also possible to use a mixture of two or more of any of the above epoxy resins.

[0022] The epoxy resins useful in the binder composition may be selected from commercially available products. For example, D.E.R.™ 331, D.E.R.™ 332, D.E.R.™ 334, D.E.R.™ 580, D.E.N.™ 431, D.E.N.™ 438, D.E.R.™ 736, or D.E.R.™ 732 available from The Dow Chemical Company may be used. For example, the epoxy resin may be a liquid epoxy resin, D.E.R.™ 383 (DGEBPA) having an epoxide equivalent weight of 175 to 185, a viscosity of 9.5 Pa-s and a density of 1.16 gm./cc. Other commercial epoxy resins that can be used for the epoxy resin component can be D.E.R.™ 330, D.E.R.™ 354, or D.E.R.™ 332 available from The Dow Chemical Company. Other suitable epoxy resins are disclosed in, for example, U.S. Pat. Nos. 3,018,262; 7,163,973, 6,887,574; 6,632,893; 6,242,083; 7,037,958; 6,572,971; 6,153,719; 5,405,688; PCT Publication WO 2006/052727; and U.S. Patent Application Publication Nos. 20060293172 and 20050171237.

[0023] In one embodiment, the epoxy component includes one or more epoxy novolac resins. Suitable epoxy novolac resins can be generally described as methylene-bridged polyphenol compounds, 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 can be alkyl groups having up to six carbon atoms. The epoxy novolac resin can have an epoxy equivalent weight of from 156 to 300, or from 170 to 225 or from 170 to 190. The epoxy novolac resin can contain, for example, from 2 to 10, or from 3 to 6, epoxide groups per molecule.

[0024] The term“epoxide equivalent weight (EEW)” as used herein refers to the number average molecular weight of the epoxide moiety in grams per equivalent (g/eq) divided by the average number of epoxide groups present in the molecule. The EEW of the epoxy resins useful in the binder composition is generally from 140 g/eq to 300 g/eq or from 160 g/eq to 280 g/eq. The EEW can be measured via titration according to ASTM D1652.

[0025] In general, the amount of epoxy resin in the binder composition can range from

70 wt. % to 95 wt. %, based on the total weight of the binder composition. In one embodiment, the amount of epoxy resin in the binder composition can range from 80 wt. % to about 90 wt. %, based on the total weight of the binder composition.

[0026] The thermosetting binder composition for the preform also includes an amine based hardener. Any amine based hardener can be used herein as along as it is present in the thermosetting binder composition in a range of from 1.05 amino hydrogen equivalents of primary and/or secondary amine compounds per epoxy equivalent to 3 amino hydrogen equivalents of primary and/or secondary amine compounds per epoxy equivalent. In one embodiment, the thermosetting binder composition comprises an epoxy resin and an amine based hardener present in a range of from 1.1 amino hydrogen equivalents of primary and/or secondary amine compounds per epoxy equivalent to 3 amino hydrogen equivalents of primary and/or secondary amine compounds per epoxy equivalent. In one embodiment, the thermosetting binder composition comprises an epoxy resin and an amine based hardener present in a in a range of from 1.5 amino hydrogen equivalents of primary and/or secondary amine compounds per epoxy equivalent to 3 amino hydrogen equivalents of primary and/or secondary amine compounds per epoxy equivalent. In one embodiment, the thermosetting binder composition comprises an epoxy resin and an amine based hardener present in a in a range of from 1.5 amino hydrogen equivalents of primary and/or secondary amine compounds per epoxy equivalent to 2.5 amino hydrogen equivalents of primary and/or secondary amine compounds per epoxy equivalent.

[0027] Suitable amine based hardeners include, for example, dicyandiamide, aromatic polyamine, aliphatic amine, ami nohen zoic acid esters, and thiourea-containing amine. In one embodiment, the amine based hardener is dicyandiamide (also known as DICY, dicyanodiamide, and 1- or 2-cyanoguanidine). DICY (CAS 461-58-5) has an empirical formula C₂N₄H₄, a molecular weight 84, and the following structural formula:

[0028] In an exemplary embodiment, the amine based hardener can be present in an amount of from 10 wt. % to 45 wt. %, based on the total weight of the binder composition. In an exemplary embodiment, the amine based hardener can be present in an amount of from 10 wt. % to 20 wt. %, based on the total weight of the binder composition.

[0029] The thermosetting binder composition may be made by mixing the epoxy resin and amine based hardener in any suitable mixing method known in the art. For example, the epoxy resin and amine based hardener of the thermosetting binder composition can be pre blended, ground in a grinder, or blended, crushed and homogenized using, for example, a mortar.

[0030] The thermosetting binder composition is then applied to one or more reinforcing fibers by various methods well known in the art to form a preform. 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 reinforcing fibers include, for example, one or more of glass fibers, ceramic fibers, carbon fibers, metal fibers, and organic polymer fibers. Suitable glass fibers include, for example,“E-glass”,“A- glass”,“C-glass”,“S-glass”,“ECR-glass” (corrosion resistant glass),“T-glass”, and fluorine and/or boron-free derivatives thereof. Suitable ceramic fibers include, for example, aluminum oxide, silicon carbide, silicon nitride, silicon carbide, and basalt fibers, among others. Suitable carbon fibers include, for example, graphite, semi-crystalline carbon, and carbon nano tubes. Suitable metal fibers include, for example, aluminum, steel, and tungsten. Suitable organic polymer fibers include, for example, poly aramid fibers, polyester fibers, and polyamide fibers. The fibers can be provided in the form of short fibers, e.g., 0.5 to 15 cm, long fibers, e.g., greater than 15 cm, or continuous rovings.

[0031] Reinforcement fiber may be used in the form of strands, or can be used after processing the reinforcement fiber into a reinforcement fiber base material in the form of mat, woven fabric, knit fabric, braid, or one-directional sheet. Woven fabrics used for preform preparation may be in an appropriate form such as a plain weave, sateen weave, diagonal weave, and non-crimp cloth. If clear coating is adopted to allow weave texture to appear in a decorative plane, good design characteristics may be obtained by using fabrics of plain weave and diagonal weave. Having good drape properties, furthermore, fabrics of sateen weave or diagonal weave are preferred when processing them into a deep three dimensional shape. The fibers can be provided in the form of a mat or other preform if desired; such mats or preforms may in some embodiments be formed by entangling, weaving and/or 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, to form preforms of various thicknesses, if required.

[0032] The preform can be produced by providing the reinforcement fiber base sheets with the thermosetting binder composition for preform production at least on the surfaces thereof, stacking them, and fixing the shape. The reinforcement fiber base sheets have the binder resin composition for preform production at least on the surface of at least either side and a plurality thereof are stacked on each other to produce a layered body having the thermosetting binder composition for preform production at least between the stacked layers. In one embodiment, the preform is produced by providing a plurality of reinforcement fiber layers connected to each other by the thermosetting binder composition in at least between the reinforcement fiber layers whereas the fibers within each layer can be bound together by, for example, entangling, weaving and/or stitching the fibers.

[0033] A fiber-reinforced composite material is then produced from the foregoing preform. The fiber-reinforced composite material is obtained by impregnating an epoxy matrix resin composition into the preform and then curing the preform. In general, the epoxy matrix resin composition includes at least (1) an epoxy resin component containing one or more epoxy resins, wherein at least 80% by weight of the epoxy resin is one or more polyglycidyl ethers of a polyphenol that has an epoxy equivalent weight of up to about 250; (2) an amine hardener which is a polyethylene tetraamine mixture containing at least 95% by weight polyethylene tetraamines, the mixture containing at least 40% by weight linear triethylene tetraamine, and (3) 0.01 to 0.5 moles of triethylene diamine are provided in the reactive mixture per mole of primary and/or secondary amine compounds provided in the amine hardener, wherein the triethylene diamine being present in the epoxy resin component, the amine hardener, or both. The combination of epoxy resin, polyethylene tetraamine mixture hardener and triethylene diamine provides a unique and unexpected combination of extended open time and fast cure, while at the same time producing a high (>H0°C) glass transition temperature cured polymer. Mold temperatures needed to accomplish this generally do not exceed l20°C.

[0034] The epoxy resin component of the epoxy matrix resin composition contains one or more epoxy resins, by which it is meant compounds having an average of two or more epoxide groups that are curable by reaction with a primary or secondary amine per molecule. At least 80% by weight of the epoxy resin component is one or more polyglycidyl ethers of a polyphenol that has an epoxy equivalent weight of up to about 250. Other epoxy resins as described below may constitute up to 20%, or from zero to 10% or from zero to 5% by weight of the epoxy resin component. In one embodiment, the polyglycidyl ether of a polyphenol is the only epoxy resin in the epoxy resin component. In one embodiment, the polyglycidyl ether of a polyphenol has an epoxy equivalent weight of 160 to 220.

[0035] 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 is about 250 or less.

[0036] Suitable polyglycidyl ethers of polyhydric phenols include, for example, 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,-C0_3- -CO- or -O-, each m may be 0, 1, 2, 3 or 4 and p is a number from 0 to 5, especially from 0 to 2.

[0037] Among the other epoxy resins that may be present in the epoxy matrix resin composition are, for example, polyglycidyl ethers of polyglycols; epoxy novolac resins including cresol-formaldehyde novolac epoxy resins, phenol-formaldehyde novolac epoxy resins and bisphenol A novolac epoxy resins; cycloaliphatic epoxides; tris (glycidyloxypheny l)me thane ; 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 by The Dow Chemical Company. Still other useful epoxy resins are described, for example, in WO 2008/140906.

[0038] The epoxy resin component may have a low monohydrolyzed resin content.

In one embodiment, the epoxy resin may contain, for example, no more than 3%, or no more than 2% or no more than 1% by weight of monohydrolyzed resin species. Monohydrolyzed resin species are a-glycol compounds formed by the addition of a molecule of water to an epoxide group. The presence of significant quantities of monohydrolyzed species tends to increase the viscosity of the epoxy resin component, and in turn that of the epoxy resin/hardener mixture. In addition, it is believed that these species may contribute to a reduction in open time.

[0039] The epoxy resin component may contain optional ingredients. Suitable optional ingredients include, for example, solvents or reactive diluents such as those described in WO 2008/140906, pigments, antioxidants, preservatives, impact modifiers, short reinforcing fibers (e.g., up to 6 inches (15.24 cm) in length, or up to 2 inches (5.08 cm) in length, or up to about ½ inch (1.27 cm) in length), non-fibrous particulate fillers including micron- and nano-particles, electroconductive fillers, and wetting agents.

[0040] The amine hardener of the epoxy matrix resin composition is a polyethylene tetraamine mixture. By“polyethylene tetraamime mixture”, it is meant a mixture of polyethylene polyamine compounds, of which at least 95% by weight have exactly four amine nitrogen atoms. For purposes of this invention, those polyethylene polyamine compounds having exactly four amine nitrogen atoms are referred to as "polyethylene tetraamine" compounds. The polyethylene tetraamine compound can be linear, branched and/or or cyclic. At least 40% of the weight of the polyethylene tetraamine mixture is a linear triethylene tetraamine, such as one represented by the following structure (II):

H2N-CH2-CH2-NH-CH2-CH2-NH-CH2-CH2-NH2 (II)

Linear triethylene tetraamine may constitute at least 60%, or at least 90%, or at least 95%, or up to 100%, of the weight of the polyethylene tetraamine mixture. [0041] The polyethylene tetraamine mixture may include other polyethylene tetraamine compounds such as, for example, N,N'-bis(2aminoethyl)piperazine, (piperazinoethyl)ethylenediamine and tris(aminoethyl)amine. These polyethylene tetaramine compounds are commonly present in significant amounts (e.g., up to 55% or up to 35% by weight in the aggregate) in commercially available TETA (triethylene tetraamine) products.

[0042] The polyethylene tetraamine mixture may also include small amounts of other aliphatic or cycloaliphatic amine compounds having three or fewer amine nitrogen atoms or five or more amine nitrogen atoms. These compounds preferably constitute at most 5% by weight, or at most 2% by weight or at most 1% by weight of the polyethylene tetraamine mixture.

[0043] In one embodiment, the polyethylene tetraamine mixture is the only hardener in the curable epoxy resin system. If other hardeners are present, they may constitute no more than 20%, or no more than 10% or no more than 5% by weight of the hardeners. Suitable other hardeners include, for example, dicyandiamide, phenylene diamine (particularly the meta-isomer), bis(4-amino-3,5-dimethylphenyl)- 1, 4-diisopropylbenzene, bis(4-amino- phenyl)l,4-diiospropylbenzene, diethyl toluene diamine, methylene dianiline, mixtures of methylene dianiline and polymethylene polyaniline compounds (sometimes referred to as PMDA, including commercially available products such as DL-50 from Air Products and Chemicals), diaminodiphenylsulfone, phenolic hardeners including those represented by the structure (III):

where each Y independently represents a halogen atom, each z is independently a number from 0 to 4 and D is a divalent hydrocarbon group as described with regard to structure I above. Examples of suitable phenolic hardeners include dihydric phenols such as bisphenol A, bisphenol K, bisphenol F, bisphenol S and bisphenol AD, and mixtures thereof, and their mono-, di-, tri- and tetra-brominated counterparts and amino-functional polyamides. These are available commercially under as Versamide^® 100, 115, 125 and 140, from Henkel, and Ancamide^® 100, 220, 260A and 350A, from Air Products and Chemicals.

[0044] The hardener and epoxy resins are combined in amounts such that at least 0.8 epoxy equivalents are provided to the reaction mixture per amine hydrogen equivalent provided by the epoxy resin component. In one embodiment, an amount is at least 0.90 epoxy equivalents per amine hydrogen equivalent. In one embodiment, an amount is at least 1.0 epoxy equivalents per amine hydrogen equivalent. The epoxy resin can be provided in large excess, such as up to 10 epoxy equivalents per amine hydrogen equivalent provided to the reaction mixture. In one embodiment, an amount can be no more than 2, or no more than 1.20 or no more than 1.10 epoxy equivalents provided per amine hydrogen equivalent. Embodiments in which the amine hardener is present in a small excess (such as, for example from 0.0 to 0.95 epoxy equivalents per equivalent of amine hydrogens) often exhibit particularly short demold times while producing a cured resin having a high glass transition temperature.

[0045] Triethylene diamine is provided to the epoxy matrix resin composition, and performs a catalytic role. In one embodiment, a suitable amount of triethylene diamine is an amount of 0.01 to 0.5 moles of triethylene diamine per part per mole of per mole of primary and/or secondary amine compounds in the amine hardener. In one embodiment, a suitable lower amount is 0.025 moles or a lower amount of 0.075 moles of triethylene diamine per mole of per mole of primary and/or secondary amine compounds in the amine hardener. In one embodiment, a suitable upper amount is up to 0.25 moles or an upper amount of up to 0.20 moles of triethylene diamine, in each case per mole of primary and/or secondary amine compounds in the amine hardener. In one embodiment, a suitable amount is 0.09 to 0.175 moles of triethylene diamine per mole of primary and/or secondary amine compounds in the amine hardener.

[0046] Any of the foregoing catalysts can be used in conjunction with one or more other catalysts. If such an added catalyst is used, suitable such catalysts include, for example, those described in 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. Suitable catalysts include, for example, imidazoles such as 2-methylimidazole; 2-ethyl-4-methylimidazole; 2-phenyl imidazole; tertiary amines such as triethylamine, tripropylamine, N,N-dimethyl-l-phenylmethaneamine and 2,4,6- tris((dimethylamino)methyl)phenol and tributylamine; phosphonium salts such as ethyltriphenylphosphonium chloride, ethyltriphenylphosphonium bromide and ethyltriphenyl-phosphonium acetate; ammonium salts such as benzyltrimethylammonium chloride and benzyltrimethylammonium hydroxide; various carboxylic acid compounds, and mixtures any two or more thereof.

[0047] In some embodiments, the triethylene diamine is the sole catalyst provided to the epoxy matrix resin composition, it being understood that components of the amine hardener are not for purposes of this invention considered as catalysts.

[0048] In some embodiments, the epoxy matrix resin composition contains water and/or a compound having at least one hydroxyl group and an equivalent weight per hydroxyl group of up to 75, or up to 50. This compound, if present, is suitably present in small amounts, such as from 0.1 to 10 parts by weight, or from 0.25 to 5 parts or from 1 to 3 parts by weight per part by weight of triethylene diamine. Besides water, suitable such compounds include, for example, alkanols such as methanol, ethanol, 1 -propanol, 2-propanol, 1 -butanol, 2- butanol, l-pentanol, neopentanol, l-hexanol and the like; alkylene glycols such as ethylene glycol, 1, 2-propane diol, 1, 3-propane diol, 1, 4-butane diol, and neopentyl glycol; poly(alkylene glycols) such as diethylene glycol, triethylene glycol, dipropylene glycol, tripropylene glycol and the like; glycol monoethers such as ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, 1, 2-propane diol monomethyl ether, dipropylene glycol monomethyl ether, as well as the corresponding ethyl ethers; glycol monoesters such as ethylene glycol monacetate, diethylene glycol monoacetate, 1 ,2-propane diol monoacetate, dipropylene glycol monoacetate; higher functionality polyols such as glycerin, oligomers of glycerin, trimethylolpropane, trimethylolethane, pentaerythritol, erythritol, sorbitol, sucrose and the like; and mono- di- or trialkanolamines such as monoethanolamine, diethanolamine, triethanolamine, monoisopropanolamine, diisopropanolamine, triisopropanolamine, and aminoethylethanolamine.

[0049] The curable epoxy matrix resin composition may contain other optional components such as, for example, impact modifiers, internal mold release agents, pigments, antioxidants, preservatives, impact modifiers as described before, short reinforcing fibers (e.g., up to 6 inches (15.24 cm) in length, or up to 2 inches (5.08 cm) in length, or up to about ½ inch (1.27 cm) in length), non-fibrous particulate fillers including micron- and nanoparticles, wetting agents, and internal mold release agents. An electroconductive filler may be present in the hardener mixture.

[0050] Suitable impact modifiers include natural or synthetic polymers having a T_g of lower than -40°C. These include, for example, natural rubber, styrene-butadiene rubbers, polybutadiene rubbers, isoprene rubbers, polyethers such as poly (propylene oxide), poly(tetrahydrofuran) and butylene oxide-ethylene oxide block copolymers, core-shell rubbers, and mixtures of any two or more of the foregoing. The rubbers can be 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 and preheated together with the epoxy resin or hardener prior to forming the hot reaction mixture.

[0051] In one embodiment, the epoxy resin and the hardener are cured in the presence of an internal mold release agent. Such an internal mold release agent may constitute up to, for example, 5%, or up to 1% of the total weight of the epoxy matrix resin composition. 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.

[0052] Suitable particulate fillers have an aspect ratio of, for example, less than 5, or 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 montmorillonite, 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.

[0053] In some embodiments, the curable epoxy matrix resin composition has, when cured at least one temperature between l00°C and l20°C, a gel time of at least 60 seconds and a time to vitrification of no greater than 350 seconds, or no greater than 300 seconds or no greater than 240 seconds. Gel time and time to vitrification are for purposes of this invention measured by chemorheological methods using an Anton PaarMCR 301 rheometer or equivalent device, in which the instrument is preheated to the cure temperature prior to each measurement. The intersection of the G' and G" plots represents the gel time, and the peak of the G" curve represents the time to vitrification.

[0054] Thermosets are formed from the by mixing the epoxy matrix resin composition and hardener at proportions as described before and curing the resulting mixture. Either or both of the components in the epoxy matrix resin composition can be preheated if desired before they are mixed with each other. It is generally necessary to heat the mixture to an elevated temperature to obtain a rapid cure. In a molding process such as the process for making molded composites described below, the curable epoxy matrix resin composition is introduced into a mold, which may be, together with the preform and any reinforcing fibers and/or inserts as may be contained in the mold, preheated. The curing temperature may be, for example, from 60°C to l80°C. When a long (e.g., at least 30 seconds, or at least 40 seconds) gel time is desirable, the curing temperature preferably is not greater than l30°C. When both a long gel time and a short demold time is wanted, a suitable curing temperature is 80°C to l20°C, or from 95°C to l20°C or from 105 °C to l20°C.

[0055] In one embodiment, 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 l00°C, or at least 1 l0°C, or at least H5°C or at least l20°C. An advantage of the epoxy matrix resin composition is that such glass transition temperatures can be obtained with short curing times. This allows for short cycle times. Demold times at cure temperatures of 95°C to l20°C, or from l05°C to l20°C, are typically 350 seconds or less, or are 300 seconds or less or are 240 seconds or less.

[0056] The epoxy matrix resin composition is advantageously impregnated into the preform discussed above and then cured to form the fiber-reinforced composite. In one embodiment, the dry preform can be deposited into an open mold, and the epoxy matrix resin composition can be sprayed, poured or injected onto the preform and in the mold. After the mold is filled in this manner, the mold is closed and the epoxy matrix resin composition cured. An example of a process of this type is gap compression resin transfer molding, in which the mold containing the fibers is kept open with a gap which may be, for example, 10 to 100% or more of the original cavity thickness as the resin is injected into the mold. The gap permits lower flow resistance, which makes mold filling easier and facilitates penetration of the reaction mixture around and between the fibers. After filling is completed the mold fully closes to complete the curing.

[0057] Short fibers can be introduced into the mold with preform and the epoxy matrix resin composition. Such short fibers may be, for example, blended with the toughened epoxy composition (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 matrix resin composition, or afterward but prior to introducing the hot epoxy matrix resin composition into the mold.

[0058] In one embodiment, a wet compression process can be used, in which the epoxy matrix resin composition is applied directly to the preform without injection, but by spraying (as in the PUpreg or Baypreg processes), or by laying it down as“bands” of system, which are being fed through a wider slit die, which could have a width of, for example, 1 cm to 50 cm or more. Sufficient material is applied to reach the desired fiber volume content in the final product. The epoxy matrix resin composition can be applied to the fibers inside an open mold, or outside the mold. The epoxy matrix resin composition may instead be applied to the center layer of a build-up, by wetting the preform with the epoxy matrix resin composition and then putting a second layer of fibers onto the wetted surface, therefore sandwiching the resin layer in between two layers of fibers. The fiber mats can be made out of non-crimped fiber buildups, of woven fabric, of random fiber build-ups or preforms. If the epoxy matrix resin composition is applied to the fibers or preform outside of the mold, it is typically applied at a somewhat low temperature, to prevent premature curing, and to reduce the viscosity of the matrix resin so it does not as easily drip off the fibers before they are transferred into the mold. The wetted preform is then placed into the lower half of a hot mold, the mold is closed and the material cured under compression.

[0059] Composites made in accordance with the invention may have fiber contents of at least 20 volume percent, or at least 25 volume percent or at least 35 volume percent, and up to 80 volume percent, or up to 70 volume percent, or up to 60 volume percent.

[0060] The mold may contain, in addition to the reinforcing fibers, one or more inserts. Such inserts may function as reinforcements, may function as flow promoters, and in some cases may be present for weight reduction purposes. Suitable 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 various types of composite materials, that do not become distorted or degraded at the temperatures encountered during the molding step.

[0061] 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.

[0062] 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 epoxy matrix resin composition. The mold surface may be treated with an external mold release agent, which may be solvent or water-based.

[0063] The particular equipment that is used to mix the components of the epoxy matrix resin composition and transfer the epoxy matrix resin composition to the mold is not considered to be critical to the invention, provided the epoxy matrix resin composition 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 Resin Transfer Molding (RTM), vacuum- assisted resin transfer molding (VARTM), Resin Film Infusion (RFI), gap compression resin transfer molding and Seeman Composites Resin Infusion Molding Process (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 such as wet compression.

[0064] The mixing apparatus can be of any type that can produce a highly homogeneous mixture of the matrix resin (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.

[0065] 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 matrix resin (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 epoxy matrix resin composition can then be 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. [0066] In one embodiment, the epoxy matrix resin composition is mixed as described above, by pumping them under pressure into a mixing head. Impingement mixing may be used. The catalyst may be introduced with the epoxy matrix resin composition, or as a separate stream. The operating pressure of the incoming matrix resin streams may range from a somewhat low value (for example, from about 1 to about 6.9 MPa) or a high value (for example, from 6.9 to 200 MPa). The resulting mixture of matrix resin and catalyst is then introduced into the mold at a somewhat low operating pressure (for example, up to 5 MPa or up to about 1.035 MPa). In such embodiments, the mixture of epoxy matrix resin composition 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.

[0067] In other embodiments, the epoxy matrix resin composition is mixed as before, and then sprayed or injected into the mold. Temperatures are maintained in the spray zone such that the temperature of the hot reaction mixture is maintained as described before.

[0068] The mold is typically a metal mold, but it may be ceramic or a polymer composite provided 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 epoxy matrix resin composition is injected.

[0069] 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.

[0070] In some embodiments of the foregoing process, the molded composite is demolded in no more than 5 minutes, or from 10 second to 5 minutes, or from 10 second to 4 minutes, after the toughened epoxy composition has been introduced 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 H0°C (or at least l30°C) within 5 minutes, or within 4 minutes, or within 10 seconds after the reaction mixture has been introduced into the mold.

[0071] 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.

[0072] 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.

[0073] The following examples are provided to illustrate the disclosed compositions, but are not intended to limit the scope thereof. All parts and percentages are by weight unless otherwise indicated.

[0074] The following designations, symbols, terms and abbreviations set forth in

Table 1 below are used in the Examples:

[0075] Binder

[0076] The thermoset epoxy binder AM XP 182-3 from CeTePox was used. It was believed to be a bisphenol A/F based novolac that contains dicyandiamide (DICY) as a hardener in a 92/8 ratio. The binder with excess Dicy was prepared by blending, crushing and homogenizing the mixture using a mortar.

TABLE 1

[0077] Preforms for stiffness evaluation [0078] Flat preforms (25 x 25 cm) of 5 layers (0/90/0) of Zoltek Panex PX35 UD300 were, together with a compaction frame, sandwiched between silicone coated paper and a layer of folded aluminum foil. The lay-up design is adapted to the desired mechanical strength. The compaction was 2 mm and the binder was evenly applied to one surface of the carbon fiber fabric at a concentration of 2.3 wt. % (8 g/m² thermoset and 9 g/m² thermoplastic).

[0079] The temperature hot press (Biirkle - LA 100) was set to l50°C. The corresponding temperature on the plates was recorded with a HOPE thermocouple (ISO 62) and measured as l37°C to l44°C on the top plate and l45°C on the bottom plate. The pressing time was 5 min for fully cured and 45 s for the partly cured samples. The pressure was set to

4 MPa.

[0080] Flexural moduli measurements

[0081] Dry: Flexural properties of preforms were analyzed with a 3 point bending test on a Zwick Z010 device according to ISO 178:2010 using a 10 N load cell at a test speed of 1 mm/min. The preload was set to 0.1 N and maximum deflection to 0.1 %. Given the varying sample thickness, standard test stripe dimensions were set to 80 x 25 mm x specific thickness. The thickness of each sample was measured with a digital thickness gauge prior to the mechanical testing. An average value of 15 measurements on 5 tests stripes was taken for a series. It was noted that preforms with low compaction can be easily further compacted during the measurement and that the thickness might vary by ± 0.12 mm within one stripe due to irregularities on the press plates. The stripes were cut in 90° orientation of the first layer.

[0082] Wet: The flexural moduli were retested with specimens that were soaked with

D.E.R™ 731, an aliphatic, linear bifunctional epoxy diluent, at room temperature. The density of the liquid is 1.1 g/ml at room temperature and the weight increased for all specimens in a similar range independent of the initial compaction. The swelling was less than 0.1 mm. The stripes were always wetted just before the actual measurement max. 7 min in-between.

[0083] CFRP part production

[0084] 3-D Preform

[0085] Lay-ups with thermoset binder were directly hot pressed (T_tooi set l50°C) for

5 min (fully cured) or 45s (partially cured). The compaction distance was set to 2 mm, using a pressure of 20 to 23 tons. This resulted in preforms with thicknesses between 1.9 and 2.2 mm. The lay-up was made from six Zoltek Panex (UD300, 300 g/m²) fabric layers all with the same orientation (0/0/0).

[0086] Matrix resin system (2K)

[0087] The matrix resin system uses a diglycidyl ether of a polyphenol having an epoxy equivalent weight of about 250 and less than 1% by weight of mono hydrolyzed resin (commercially available from The Dow Chemical Company as VORAFORCE™ 5310). The resin component has a viscosity of 7000 to 10500 in Pa-s at 25°C. The matrix resin system was mixed with the hardener component at a weight ratio of 100 to 14.7. The matrix resin system used the same epoxy resin and hardener with a weight ratio of 100:16.2 and an epoxy: amine hydrogen equivalent ratio of 1: 1.1. The hardener used was a blend of a triethylene tetraamine mixture commercially available as D.E.H. 24 by Olin and triethylene diamine at a 10 mole ratio of 1:0.1.

[0088] Wet compression

[0089] The matrix resin system was deposited in a regular pattern onto the preforms in a 1.7 weight ratio (resin/preform) using an XY-table connected to a high pressure mixing unit (Krauss Maffei RSC 4/4 RTM). Delivery temperatures were 60°C for the epoxy resin and 35°C for the hardener (100/16.2 ratio). An internal mold release was not used in this case.

[0090] Following completion of the deposition, the liquid resin system was soaked for 90 s before the wet preform was transferred to the hot mold (l30°C) installed in the 120 ton hydraulic up-stroke press, Wemhoner, No. 100 K-120.. The plate distance upon full closure was either 2 mm. The curing time was set to l20s, which is ample time to complete curing with the matrix resin system.

[0091] CFRP part characterization

[0092] Test specimens for all measurements were cut by water jet cutting using abrasive particles.

[0093] Apparent interlaminar shear strength (ILSS)

[0094] The apparent interlaminar shear strength of the final parts was evaluated by a three point bending test according to ISO standard 14130:1997 using a Zwick Roell Zmart. Pro B 50410 device. The specimens were cut to a standard size of 10 x 20 x ~2 mm. For the ILSS testing the carbon fibers were oriented parallel to the loading member (all six CF layers having the same orientation). The first force maxima were taken for the evaluations of the different samples.

[0095] Tensile properties

[0096] Tensile tests were executed according to ISO 527-1 on a Zwick B50407 device. The test bars were cut 90° to the fiber orientation to minimize contribution of the reinforcement to the test result. The test result would thus largely be affected by the resin- fiber interface strength. Ten test specimens were analyzed per sample.

[0097] Description of Results

[0098] Carbon fiber preforms were prepared as described above. The preforms were then tested in different cure states (5 minutes for the fully cured of Comparative Example A and Example 1 and 45 s for the partially cured of Comparative Example B) to establish differences in the preform properties, e.g. shape retention when wet/dry (stiffness and adhesion of carbon fiber layers) and also properties of the final part made using the resin infusion process via the wet compression technique. The results are set forth below in Tables 2 and 3.

TABLE 2

1 The bine er was Griltex CE 20 from EMS Chemie.

TABLE 3

[0099] Partial cure of the preform can be seen to give poor mechanical performance in terms of Flexural Modulus which thus limits stiffness and handleability (automated/manual) of the preform itself, however a partial cure can lead to enhanced mechanical performance improvements in terms of ILSS and Tensile Modulus in the final part following resin infusion. Conversely, a fully cured preform gives excellent mechanical performance in the preform state but lower ILSS and Tensile Modulus in the final part following infusion.

[00100] Surprisingly, it has been found that when an excess of DICY hardener was utilized with an epoxy: amine hydrogen equivalent ratio of 2:1 in the formulated binder that not only was the mechanical performance of the preform similar to the performance of a fully cured preform but that the ILSS and Tensile performance of the final part was more in line with the good performance seen with the partially cured preform. [00101] Furthermore, the ILSS performance from the infused part of the binder of Example 1 (ILSS 75 MPa) was also improved versus the preform with no binder applied but instead only infused with the matrix resin system (ILSS 73 MPa) thus demonstrating not only excellent preform stability and handling with this solution but also improved final part ILSS performance after infusion.

Claims

WHAT IS CLAIMED IS:

1. A fiber-reinforced composite produced by the steps of:

(a) impregnating an epoxy matrix resin composition into a preform, wherein the preform comprises a plurality of reinforcement fiber layers connected to each other by a thermosetting binder composition in at least between the reinforcement fiber layers, wherein the thermosetting binder composition comprises an epoxy resin and an amine based hardener present in a range of from 1.05 amino hydrogen equivalents of primary and/or secondary amine compounds per epoxy equivalent to 3 amino hydrogen equivalents of primary and/or secondary amine compounds per epoxy equivalent; and

(b) curing the epoxy matrix resin composition,

wherein the epoxy matrix resin composition comprises (i) an epoxy resin component containing one or more epoxy resins, wherein at least 80% by weight of the epoxy resin component is one or more polyglycidyl ethers of a polyphenol that has an epoxy equivalent weight of up to about 250; (ii) an amine hardener, wherein the amine hardener is a polyethylene tetraamine mixture containing at least 95% by weight polyethylene tetraamines, the mixture containing at least 40% by weight linear triethylene tetraamine; and (iii) 0.01 to 0.5 moles of triethylene diamine per mole of primary and/or secondary amine compounds in the amine hardener, the triethylene diamine being present in the epoxy resin component, the amine hardener, or both.

2. The fiber-reinforced composite according to claim 1, wherein the epoxy resin of the thermosetting binder composition is an epoxy novolac resin having an epoxy equivalent weight of up to 300.

3. The fiber-reinforced composite according to claim 1, wherein the amine based hardener is dicyandiamide.

4. The fiber-reinforced composite according to claim 1, wherein the thermosetting binder composition comprises the epoxy resin and the amine based hardener present in a range of from 1.5 amino hydrogen equivalents of primary and/or secondary amine compounds per epoxy equivalent to 3 amino hydrogen equivalents of primary and/or secondary amine compounds per epoxy equivalent.

5. The fiber-reinforced composite according to claim 1, wherein the thermosetting binder composition comprises the epoxy resin and the amine based hardener present in a range of from 1.5 amino hydrogen equivalents of primary and/or secondary amine compounds per epoxy equivalent to 2.5 amino hydrogen equivalents of primary and/or secondary amine compounds per epoxy equivalent.

6. The fiber-reinforced composite according to claim 1, wherein the epoxy matrix resin composition comprises 0.05 to 0.175 moles of triethylene diamine per part per mole of per mole of primary and/or secondary amine compounds in the amine hardener.

7. The fiber-reinforced composite according to claim 1, wherein the epoxy matrix resin composition comprises further comprises 0.1 to 10 parts by weight, per part by weight triethylene diamine, of a hydroxyl compound selected from the group consisting of water and compounds having at least one hydroxyl group and an equivalent weight per hydroxyl group of up to 75.

8. The fiber-reinforced composite according to claim 7, wherein the hydroxyl compound is one or more of water, an alkanol, an alkylene glycol, a glycol monoether, a glycol monoester, trimethylolpropane, glycerin, an oligomer of glycerin, trimethylolethane, pentaerythritol, erythritol, sorbitol, sucrose, and a mono-, di- or trialkanolamine.

9. The fiber-reinforced composite according to claim 1, wherein the reinforcement fiber layers are carbon reinforcement fiber layers.

10. The fiber-reinforced composite according to claim 1, wherein the preform is a three-dimensional (3D) woven preform.

11. A process for preparing a fiber-reinforced composite comprising the steps of:

(a) impregnating an epoxy matrix resin composition into a preform comprising a plurality of reinforcement fiber layers connected to each other by a thermosetting binder composition in at least between the reinforcement fiber layers, wherein the thermosetting binder composition comprises an epoxy resin and an amine based hardener in a range of from 1.05 amino hydrogen equivalents of primary and/or secondary amine compounds per epoxy equivalent to 3 amino hydrogen equivalents of primary and/or secondary amine compounds per epoxy equivalent; and

(b) curing the epoxy matrix resin composition resin,

12. The process according to claim 11, wherein the epoxy resin of the thermosetting binder composition is an epoxy novolac resin having an epoxy equivalent weight of up to 300.

13. The process according to claim 11, wherein the amine based hardener is dicyandiamide.

14. The process according to claim 11, wherein the thermosetting binder composition comprises the epoxy resin and the amine based hardener present in a range of from 1.5 amino hydrogen equivalents of primary and/or secondary amine compounds per epoxy equivalent to 2.5 amino hydrogen equivalents of primary and/or secondary amine compounds per epoxy equivalent.

15. The process according to claim 11, wherein the epoxy matrix resin composition comprises 0.05 to 0.175 moles of triethylene diamine per part per mole of per mole of primary and/or secondary amine compounds in the amine hardener.

16. The process according to claim 11, wherein the epoxy matrix resin composition comprises further comprises 0.1 to 10 parts by weight, per part by weight triethylene diamine, of a hydroxyl compound selected from the group consisting of water and compounds having at least one hydroxyl group and an equivalent weight per hydroxyl group of up to 75.

17. The process according to claim 11, wherein the hydroxyl compound is one or more of water, an alkanol, an alkylene glycol, a glycol monoether, a glycol monoester, trimethylolpropane, glycerin, an oligomer of glycerin, trimethylolethane, pentaerythritol, erythritol, sorbitol, sucrose, and a mono-, di- or trialkanolamine.

18. The process according to claim 11, which is a resin transfer molding process, or a wet compression molding process.

19. The process according to claim 11, wherein the reinforcement fiber layers are carbon reinforcement fiber layers

20. The process according to claim 11, wherein the preform is a three-dimensional (3D) woven preform.