Process for manufacturing a fiber reinforced composite article, the composite article obtained and the use thereof

Abstract

A process for the preparation of a fiber reinforced composite article that facilitates manufacturing of composite articles with reduced cycle times, said composite articles exhibiting high fibre content, low void content and excellent visual and mechanical properties, and capable of use for the construction of mass transportation vehicles, in particular, in the automotive and aerospace industries.

Claims

1. A process for preparing a fiber reinforced composite article comprising the steps of: a) providing a mold, comprising an upper die (11) and a lower die (12), the lower die (12) having a molding surface and vertically extending side walls (14), the upper die (11) having a complementary molding surface and vertically extending side walls (13) substantially aligned with the side walls of the lower die (12), so that the upper die (11) vertically moves into the lower die (12) to form a cavity (17) in a partially closed position and a completely closed position of the mold, wherein the cavity (17) in a partially closed position is sealed vacuum-tight by at least one seal (15) placed around the vertically extending side walls (13) of the upper die (11) or the vertically extending side walls (14) of the lower die (12) and perpendicular to the direction of movement of the upper die (11), and wherein the at least one seal (15) works as a resin retention seal which prevents the resin from leaking, b) performing one of b1) applying a thermosetting resin composition onto a fibre reinforcement to form a treated fibre reinforcement, and placing the treated fibre reinforcement into the lower die (12) of the mold, or b2) placing a fibre reinforcement into the lower die (12) of the mold, and applying a thermosetting resin composition onto the fibre reinforcement while the mold is open, c) moving the upper die (11) into the lower die (12) and partially closing the mold, d) evacuating the mold in the partially closed position by means of a vacuum outlet to a pressure of from 0.1 to 100 mbar, e) completely closing the mold and exerting a hydraulic pressure of from 2 to 100 bar onto the resin treated fibre reinforcement to complete impregnation of the fibre reinforcement, f) curing the resin impregnated fibre reinforcement to form a cured fiber reinforced composite article, wherein the cured fibre reinforced composite article has a volume fraction of fibre of 50% to 70%, based on the total volume of fibre and resin in the composite article, and g) demolding the cured fiber reinforced composite article wherein the thermosetting resin composition is an epoxy resin composition comprising an epoxy resin, wherein the epoxy resin is the diglycidylether of bisphenol A or the diglycidylether of bisphenol F.

2. The process according to claim 1, wherein the mold in the partially closed position in step d) is evacuated to a pressure of from 0.1 to 50 mbar.

3. The process according to claim 1, wherein the hydraulic pressure exerted onto the resin treated fibre reinforcement in step e) is from 2 to 75 bar.

4. The process according to claim 1, wherein curing of the resin impregnated fibre reinforcement in step f) is carried out under isothermal conditions at a temperature of from 50 to 200° C.

5. The process according to claim 1, wherein at least two seals (15) and (15b) are placed around the vertically extending side walls (13) of the upper die (11) perpendicular to its direction of movement and are substantially aligned parallel to each other, in order to provide vacuum-tightness of the cavity (17) in partially closed and completely closed positions of the mold.

6. The process according to claim 1, wherein the thermosetting resin composition is liquid at the molding temperature.

7. The process according to claim 6, wherein the thermosetting resin composition has a viscosity of from 0.1 to 10,000 mPa.Math.s at the molding temperature.

8. The process according to claim 1, wherein the mold in the partially closed position in step d) is evacuated to a pressure of from 0.1 to 10 mbar.

9. The process according to claim 1, wherein the hydraulic pressure exerted onto the resin treated reinforcement in step e) is from 10 to 50 bar.

10. The process according to claim 1, wherein curing of the resin impregnated fibre reinforcement in step f) is carried out under isothermal conditions at a temperature of from 100 to 150° C.

11. The process according to claim 6, wherein the thermosetting resin composition has a viscosity of from 0.1 to 100 mPa.Math.s at the molding temperature.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1 and 2 show an example of the mold used in accordance with the present invention comprising an upper die (11) and lower die (12) forming a mold cavity (17) and vertically extended walls (13) and (14) with a seal (15) to create an internal vacuum chamber and additional seal (15b) to retain the liquid resin.

(2) FIG. 1 depicts the mold in a partially closed position, wherein the vacuum seal (15) is in contact with the vertically extending wall of the lower die (14).

(3) FIG. 2 depicts the mold in a completely closed position, whereby the vacuum seal (15) effectively closes the mold cavity, and the resin retention seal (15b) prevents the resin from leaking.

(4) FIG. 3a and FIG. 3b depict the detailed view of another embodiment, wherein the additional seal (15b) is placed around the vertically extending walls of the upper die (11). FIG. 3a depicts the mold in a partially closed position, wherein the vacuum seal (15) and the additional seal (15b), the resin stripping seal, is in contact with the vertically extending walls of the lower die (14). In this partially closed position the mold cavity (17) can be effectively evacuated through an appropriately placed vacuum outlet. FIG. 3b depicts the mold in a completely closed position. To improve vacuum-tightness, the vertically extending walls (14) of the lower die may be inclined at an angle of a few degrees (18), for example, of from 1 to 3 degrees, so that the seal (15b) is compressed further.

(5) FIG. 4 depicts the mold in a completely closed position, which is the embodiment of FIG. 3b in scaled-up illustration. An angled geometry of constant thickness (19) enables easy demold of a composite article with no thin cured resin flash. The inclination of the vertically extending walls (14) can either be (i) locally across a certain limited area (18) as shown in the embodiment of FIG. 4, or (ii) across the entire length of the walls (14) from top to bottom. In the latter case (ii), the inclination angle is appropriately smaller than in the first case (i).

DETAILED DESCRIPTION

(6) Accordingly, the present invention relates to a process for the preparation of a fiber reinforced composite article comprising the steps of

(7) a) providing a mold, comprising an upper die (11) and a lower die (12), the lower die (12) having a molding surface and vertically extending side walls (14), the upper die (11) having a complementary molding surface and vertically extending side walls (13) substantially aligned with the side walls of the lower die, so that the upper die vertically moves into the lower die to form a cavity (17) in a partially and completely closed position of the mold, wherein the cavity (17) in a partially closed position is sealed vacuum-tight by at least one seal (15) placed around the vertically extending walls of the upper die (11), or the lower die (12), horizontally to the moving direction of the upper die (11), and wherein the at least one seal (15) also works as a resin retention seal which prevents the resin from leaking,
b) applying a thermosetting resin composition onto a fibre reinforcement, and placing the thus treated fibre reinforcement into the lower die of the mold (12), or
c) placing a fibre reinforcement into the lower die of the mold (12), and applying a thermosetting resin composition onto the fibre reinforcement
d) moving the upper die (11) into the lower die (12) and partially closing the mold,
e) evacuating the mold in the partially closed position by means of a vacuum outlet to a pressure of from 0.1 to 100 mbar,
f) completely closing the mold and exerting an hydraulic pressure of from 2 to 100 bar onto the resin treated reinforcement to complete impregnation of the fibre reinforcement,
g) curing the resin impregnated reinforcement,
h) demolding the cured composite article.

(8) The process according to the present invention is suitable for the processing of thermosetting resin compositions which are liquid at the molding temperature, in particular, liquid resin compositions which have a low viscosity at the molding temperature. In a certain embodiment the viscosity of the thermosetting liquid resin compositions is of from 0.1 to 10,000 mPa.Math.s, preferably, of from 0.1 to 100 mPa.Math.s at the molding temperature.

(9) Low viscosity resins can advantageously be used for the preparation of composite articles with a fibre volume fraction of 50% or more based on the total volume of the composite article (fibre+resin), because resins of a lower viscosity more easily penetrate into the interfibrous space of the dry reinforcement compared to resins of a higher viscosity. In one embodiment the fibre volume fraction of the composite article prepared by the inventive process is in the range of 50 to 60% based on the total volume of the composite article. In another embodiment the fibre volume fraction of the composite article prepared by the inventive process is in the range of 60 to 70% based on the total volume of the composite article.

(10) In a preferred embodiment of the present invention the mold in the partially closed position in step e) is evacuated to a pressure of from 0.1 to 50 mbar, especially of from 0.1 to 10 mbar.

(11) In a preferred embodiment of the present invention the hydraulic pressure exerted onto the resin impregnated reinforcement in step f) is of from 2 to 75 bar, especially of from 10 to 50 bar. Hydraulic pressure in the context of the present invention means the pressure in the liquid resin, when press force is applied.

(12) The process of the present invention is essentially distinguished from RTM, such as HP-RTM, by step b) or c), which step omits injection of the resin at high pressure through the fibre stack in the closed mold.

(13) WO2014/067865 discloses a mold for resin transfer molding (RTM). As indicated above, and in contrast to the present invention, RTM is carried out by injecting the resin directly into the fibre preform placed in the closed mold cavity to impregnate the fibre reinforcement and fill the mold. In contrast, impregnation of the fibre reinforcement by the process of the present invention is carried out by omitting an injection step, but wetting the surface of the fibre reinforcement with the resin composition, either separately and out of the mold in accordance with step b), or by placing the fibre reinforcement into the lower die of the mold (12). Since resin impregnation of the fibre stack in case of the present invention occurs predominantly through-thickness, fibre movement as observed in RTM is largely eliminated by this configuration. Moreover, the process of the present invention allows for a less sophisticated machine set-up to be applied, since the closed mold does not have to resist the high injection pressure of the resin, i.e. heavy vertical presses to prevent the mold cavity from opening at high injection pressure are not required.

(14) In accordance with step b) of the present invention, the preparation of the resin treated fibre reinforcement can be carried out separately and independently from steps d) to h), i.e. the molding and demolding of the reinforced article.

(15) Advantageously, wetting of the fibre reinforcement is carried out in an automated process, for example, by processes which allow for the wetting of the fibrous reinforcement with the resin onto its surface, for example, dosing, pouring, casting, curtain coating, roller coating or spray application. Such processes are known per se to someone of ordinary skill, for example in the field of textile fibre processing.

(16) Wetting according to step b), which is a preferred embodiment, is advantageously synchronized with the molding and demolding steps d) to h), so that step b) provides the resin treated fibre reinforcement just in time to be available immediately for use in steps d) to h).

(17) The inventive process enables processing of unbonded fibre reinforcement fabrics. Preparation of a partially-bonded fibre preform, which adds another process step as disclosed in WO2014/067865, may be omitted, since fibre misalignment upon resin impregnation is eliminated. Moreover, an internal seal in the fibre preform to avoid leakage of excess resin to contaminate the mold as depicted in FIG. 1 of WO2014/067865 can be omitted. The mold assembly used in accordance with the process of the present invention provides at least one seal, which also works as a resin retention seal and prevents the resin from leaking, thus allowing for build up of homogeneous pressure over the entire composite part.

(18) The mold assembly comprises an upper and a lower die with vertically extending side walls (13) and (14) and a seal assembly as indicated above which come together to form a closed mold cavity. A vacuum outlet is included either in the upper die (11), or alternatively, in the lower die (12), to allow evacuation of the mold cavity in a partially closed position, with closure of the vacuum outlet occurring prior to full mold closure.

(19) In a certain embodiment of the inventive process, a vacuum outlet is included in the upper die (11), as shown in FIGS. 1 and 2. In this embodiment, the vacuum outlet (16) is suitably sealed by a valve. In FIG. 1, depicting the mold in a partially closed position in accordance with step d) of the inventive process, the vacuum outlet is open, and the mold is ready to be evacuated in accordance with step e). In FIG. 2, depicting the mold in a completely closed position in accordance with step f) of the inventive process, the vacuum outlet is closed, and the mold is ready for a hydraulic pressure to be exerted onto the resin treated fibre reinforcement to impregnate the fibre reinforcement.

(20) In another embodiment of the inventive process, a vacuum outlet is included in the lower die (12), as shown, for example, in FIG. 2 of WO2014/067865.

(21) In vacuum assisted liquid compression molding an external vacuum chamber is normally constructed around the mold. External vacuum chambers are generally bulky and the vacuum which can be achieved may be insufficient to enable for the production of high quality composite articles with visual appearance or surface quality free of any defects.

(22) In order to provide for vacuum-tightness of the mold in its partially closed or closed position, at least one gasket/seal (15) is placed around the vertically extending walls of the upper die (11), or the lower die (12), horizontally to the moving direction of the upper die (11). In one embodiment the seal is endless, for example, an O-ring. Other seal configurations/geometries are possible, for example, a square, a rectangular, or a hexagonal shape, corresponding to the cross-sectional shape of the upper die (11), or the lower die (12), perpendicular to the moving direction of the upper die (11) into the lower die (12). Appropriately, the cross-sectional shape of the upper and lower die will be determined by the shape of the composite article to be manufactured. Moreover, the at least one seal enables substantial positive pressure (>10 bars) to be generated in step f) upon complete mold closure.

(23) In one embodiment of the present invention the at least one seal is a rubbery-elastic, compressible material, for example, a silicone rubber, a polyurethane rubber, a polyacrylate- or polymethacrylate rubber, or a polybutadiene rubber, or a mixture of at least two polymers of the aforementioned group of polymers.

(24) In one embodiment two seals (15) and (15b), as shown in FIG. 3a and FIG. 3b, are placed around the vertically extending walls of the upper die (11) horizontally to its moving direction. A two seal configuration generally improves vacuum-tightness. In another embodiment, three seals, which further improve vacuum tightness, are placed around the vertically extending walls of the upper die (11) horizontally to its moving direction. In yet another embodiment, two seals are placed around the vertically extending walls of the lower die (12) horizontally to the moving direction of the upper die (11). The two or three seals may be aligned parallel to each other. In case of two or three seals, the seal being closest to the mold cavity serves as the resin stripping seal, and protects the other seal or seals, which provide for vacuum-tightness, from being contaminated by leaked resin. Since a seal assembly consisting of at least two seals, one vacuum seal and one resin stripping seal, protects the vacuum seal from being contaminated, even after repeated mold cycles, the need for cleaning operations between cycles is largely eliminated, making it highly suited to high-volume production. Alternatively, the seal preventing leaked resin from contaminating the vacuum seal may be placed in the lower die (12), for example, in the peripheral section of the lower die's cavity, as shown in the embodiment of FIGS. 1 and 2 (15b). In accordance with this embodiment, the seal (15b) is more appropriately designated a resin retention seal.

(25) The process according to the present invention provides for very short mold evacuation times compared to an external vacuum chamber due to the small volume of the mold cavity in the partially closed position, thus enabling very short production cycle times, since fast mold evacuation prior to full mold closure enables use of short gel time resin systems, with correspondingly shorter cure times.

(26) When processing low viscosity liquid resins, a line of striction (pinch-off section) in the peripheral area of the mold cavity, as known from the processing of more viscous resin compositions by compression molding, will hardly prevent low viscosity resin from passing the line of striction and escaping into the peripheral sections of the mold. This solution is therefore not feasible for industrial processing of low-viscosity liquid resins. However, an internal vertical sliding vacuum chamber with integral sliding seal(s) as realized by the process according to the present invention, in particular the use of a two seal assembly, one vacuum seal and one resin stripping or resin retention seal, renders this process highly suitable for use with low-viscosity liquid resin systems and allows for the production of parts of surprisingly high quality (low void content, high fibre volume content, low surface defects) with very short production cycle times.

(27) The use of two or more seals described in this invention prevents liquid resin from contaminating the vacuum seal, thus allowing vacuum levels of 10 mbar or less to be consistently and reliably achieved, so that composite parts produced are void free and display very high visual quality and mechanical performance.

(28) Full mold closure occurs when the entire mold cavity is filled, i.e. there are no mechanical stops, so the mold continues to close until pressure is exerted on the liquid resin. The seal assembly enables significant pressure to be generated in the mold cavity without any leakage. Hydraulic pressure is generated inside the mold when the press force is applied to the liquid resin contained in the sealed cavity. The pressure generated may be conveniently measured by use of pressure sensors in the mold cavity, such as are known in the art, to control the press force applied. Pressures in the range of 2 to 100 bar, more typically 20 to 50 bar are generated in order to ensure a fully impregnated, void-free composite part.

(29) The positive hydraulic pressure generated following mold closure enables the fibre reinforcement to be fully impregnated even when deep-draw parts are made offering a significant advantage compared to traditional liquid compression molding. Furthermore, the positive pressure can be maintained throughout curing of the part in order to compensate any shrinkage of the liquid resin, further increasing part quality.

(30) The process according to the present invention is useful to form various types of composite products, and provides several advantages. Cure times tend to be very short, with good development of polymer properties, such as glass transition temperature Tg.

(31) Examples of thermosetting resins which may be used with the present invention are polyester, vinyl ester, epoxy, polyurethane, polyurea, polyisocyanurate, phenol-formaldehyde, melamine, polyimide, benzoxazine, cyanate ester, bismaleimide and acrylic resins, such as those described by Fink, Reactive Polymers Fundamentals and Applications, PDL (2013).

(32) In a preferred embodiment, the thermosetting resin composition used in accordance with the process of the present invention is an epoxy resin composition.

(33) The epoxy resin (A) used herein comprises at least one compound or mixture of compounds having an average functionality of at least 2.0 epoxide groups per molecule. The epoxy resin or mixture thereof may have an average of up to 4.0 epoxide groups per molecule. It preferably has an average of from 2.0 to 3.0 epoxide groups per molecule.

(34) The epoxy resin may have an epoxy equivalent weight of about 150 to about 1,000, preferably about 160 to about 300, more preferably from about 170 to about 250. If the epoxy resin is halogenated, the equivalent weight may be somewhat higher.

(35) Epoxide resins which may be used include polyglycidyl and poly(β-methylglycidyl) ethers obtainable by the reaction of substances containing per molecule, two or more alcoholic hydroxyl groups, or two or more phenolic hydroxyl groups, with epichlorohydrin, glycerol dichlorohydrin, or β-methylepichlorohydrin, under alkaline conditions or, alternatively, in the presence of an acidic catalyst with subsequent treatment with alkali.

(36) Such polyglycidyl ethers may be derived from aliphatic alcohols, for example, ethylene glycol and poly(oxyethylene)glycols such as diethylene glycol and triethylene glycol, propylene glycol and poly(oxypropylene)glycols, propane-1,3-diol, butane-1,4-diol, pentane-1,5-diol, hexane-1,6-diol, hexane-2,4,6-triol, glycerol, 1,1,1-trimethylolpropane, and pentaerythritol; from cycloaliphatic alcohols, such as quinitol, 1,1 bis(hydroxymethyl)cyclohex-3-ene, bis(4-hydroxycyclohexyl)methane, and 2,2-bis(4-hydroxycyclohexyl)-propane; or from alcohols containing aromatic nuclei, such as N,N-bis-(2-hydroxyethyl)aniline and 4,4′-bis(2-hydroxyethylamino)diphenylmethane.

(37) Preferably the polyglycidyl ethers are derived from substances containing two or more phenolic hydroxyl groups per molecule, for example, resorcinol, catechol, hydroquinone, bis(4-hydroxyphenyl)methane (bisphenol F), 1,1,2,2-tetrakis(4-hydroxyphenyl)ethane, 4,4′-dihydroxydiphenyl, bis(4-hydroxyphenyl)sulphone (bisphenol S), 1,1-bis(4-hydroxylphenyl)-1-phenyl ethane (bisphenol AP), 1,1-bis(4-hydroxylphenyl)ethylene (bisphenol AD), phenol-formaldehyde or cresol-formaldehyde novolac resins, 2,2-bis(4-hydroxyphenyl)propane (bisphenol A), and 2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane.

(38) There may further be employed poly(N-glycidyl) compounds, such as are, for example, obtained by the dehydrochlorination of the reaction products of epichlorohydrin and amines containing at least two hydrogen atoms directly attached to nitrogen, such as aniline, n-butylamine, bis(4-aminophenyl)methane, bis(4-aminophenyl)sulphone, and bis(4-methylaminophenyl)methane. Other poly(N-glycidyl) compounds that may be used include triglycidyl isocyanurate, N,N′-diglycidyl derivatives of cyclic alkylene ureas such as ethyleneurea and 1,3-propyleneurea, and N,N′-diglycidyl derivatives of hydantoins such as 5,5-dimethylhydantoin.

(39) Epoxide resins obtained by the epoxidation of cyclic and acrylic polyolefins may also be employed, such as vinylcyclohexene dioxide, limonene dioxide, dicyclopentadiene dioxide, 3,4-epoxydihydrodicyclopentadienyl glycidyl ether, the bis(3,4-epoxydihydrodicyclopenta-dienyl)ether of ethylene glycol, 3,4-epoxycyclohexylmethyl 3,4′-epoxycyclohexanecarboxylate and its 6,6′-dimethyl derivative, the bis(3,4-epoxycyclohexanecarboxylate) of ethylene glycol, the acetal formed between 3,4-epoxycyclohexanecarboxyaldehyde and 1,1-bis(hydroxymethyl)-3,4-epoxycyclohexane, bis(2,3-epoxycyclopentyl)ether, and epoxidized butadiene or copolymers of butadiene with ethylenic compounds such as styrene and vinyl acetate.

(40) In one embodiment of the present invention, the epoxy resin (A) is the diglycidyl ether of a polyhydric phenol represented by formula (1)

(41) ##STR00001##
wherein (R.sub.1).sub.m independently denotes m substituents selected from the group consisting of C.sub.1-C.sub.4alkyl and halogen, (R.sub.2).sub.n independently denotes n substituents selected from the group consisting of C.sub.1-C.sub.4alkyl and halogen, each B independently is —S—, —S—S—, —SO—, —SO.sub.2—, —CO.sub.3—, —CO—, —O—, or a C.sub.1-C.sub.6(cylo)alkylene radical. Each m and each n are independently an integer 0, 1, 2, 3 or 4 and q is a number of from 0 to 5. q is the average number of hydroxyl groups in the epoxy resin of formula (1). R.sub.1 and R.sub.2 in the meaning of halogen are, for example, chlorine or bromine. R.sub.1 and R.sub.2 in the meaning of C.sub.1-C.sub.4alkyl are, for example, methyl, ethyl, n-propyl or iso-propyl. B independently in the meaning of a C.sub.1-C.sub.6(cylo)-alkylene radical is, for example, methylene, 1,2-ethylene, 1,3-propylene, 1,2-propylene, 2,2-propylene, 1,4-butylene, 1,5-pentylene, 1,6-hexylene or 1,1-cyclohexylene. Preferably, each B independently is methylene, 2,2-propylene or —SO.sub.2—. Preferably, each m and each n are independently an integer 0, 1 or 2, more preferably 0. Examples of suitable epoxy resins include diglycidyl ethers of dihydric phenols such as bisphenol A, bisphenol F and bisphenol S, and mixtures thereof. Epoxy resins of this type are commercially available, including diglycidyl ethers of bisphenol A resins. Suitable halogenated epoxy resins, wherein at least one of R.sub.1 and R.sub.2 are halogen, are described in, for example, in U.S. Pat. Nos. 4,251,594, 4,661,568, 4,713,137 and 4,868,059, and Lee and Neville, Handbook of Epoxy Resins, McGraw-Hill (1982), all of which are incorporated herein by reference.

(42) The epoxy resins indicated are either commercially available or can be prepared according to the processes described in the cited documents.

(43) In a preferred embodiment of the present invention diglycidyl ethers of polyhydric phenols as given by formula (1) are used, wherein the radicals have the meanings and preferences given above. Especially, the epoxy resin (A) is the diglycidyl ether of bisphenol A or bisphenol F.

(44) If required, the viscosity of the epoxy resin composition can be adjusted by adding an epoxy diluent component. The epoxy diluent component is, for example, a glycidyl terminated compound. Especially preferred are compounds containing a glycidyl or β-methylglycidyl groups directly attached to an atom of oxygen, nitrogen, or sulfur. Such resins include polyglycidyl and poly(β-methylglycidyl) esters obtainable by the reaction of a substance containing two or more carboxylic acid groups per molecule with epichlorohydrin, glycerol dichlorohydrin, or β-methylepichlorohydrin in the presence of alkali. The polyglycidyl esters may be derived from aliphatic carboxylic acids, e.g. oxalic acid, succinic acid, adipic acid, sebacic acid, or dimerised or trimerised linoleic acid, from cycloaliphatic carboxylic acids such as hexahydro-phthalic, 4-methylhexahydrophthalic, tetrahydrophthalic, and 4-methyltetrahydrophthalic acid, or from aromatic carboxylic acids, such as phthalic acid, isophthalic acid, and terephthalic acid.

(45) The thermosetting epoxy resin composition further comprises a curing agent (B). According to the process of the present invention there come into consideration as the curing agent (B) amines, for example, primary or secondary amines, acids and acid-anhydrides, lewis acids, lewis bases, phenols. The identity of many of these curing agents and their curing mechanisms are discussed in Lee and Neville, Handbook of Epoxy Resins, McGraw-Hill (1982).

(46) Particularly suited to the present invention are amines, of which there may be mentioned aliphatic, cycloaliphatic or araliphatic primary and secondary amines, including mixtures of these amines. Typical amines include monoethanolamine, N-aminoethyl ethanolamine, ethylenediamine, hexamethylenediamine, trimethylhexamethylenediamines, methylpentamethylenediamines, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, N,N-dimethylpropylenediamine-1,3, N,N-diethylpropylenediamine-1,3, bis(4-amino-3-methylcyclohexyl)methane, bis(p-aminocyclohexyl)methane, 2,2-bis-(4-aminocyclohexyl)propane, 3,5,5-trimethyl-s-(aminomethyl)cyclohexylamine, 1,2-diaminocyclohexane, 1,4-diaminocyclohexane, 1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, N-aminoethylpiperazine, m-xylene diamine, norbornene diamine, 3(4),8(9)-bis-(aminomethyl)-tricyclo-[5.2.1.02,6]decane (TCD-diamine), and isophorone diamine. Preferred amines include 2,2,4-trimethylhexamethylenediamine, 2,4,4-trimethylhexamethylenediamine, 2-methylpentamethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, 1,2-diaminocyclohexane, bis(p-aminocyclohexyl)methane, m-xylene diamine, norbornene diamine, 3(4),8(9)-bis-(aminomethyl)-tricyclo-[5.2.1.02,6]decane (TCD-diamine), isophorone diamine 1,3-bis(aminomethyl)cyclohexane, and 1,4-bis(aminomethyl)cyclohexane. Especially preferred amines include diethylenetriamine, triethylenetetramine, tetraethylenepentamine, 1,2-diaminocyclohexane, m-xylene diamine, 1,3-bis(aminomethyl)cyclohexane, and isophorone diamine.

(47) According to the process of the present invention the curing agent (B) may be used in combination with an accelerator (C) to adjust the curing rate of the thermosetting resin composition. Suitable accelerators for use with epoxy-amine compositions are well described and include alcohols, phenols, acids, tertiary amines, guanidines, boron halide complexes, imidazoles and inorganic metal salts such as calcium nitrate.

(48) According to the process of the present invention, curing step g), i.e. curing of the resin impregnated reinforcement, is carried out under, for example, isothermal conditions at a temperature of from 50 to 200° C., preferably of from 100 to 150° C.

(49) The process according to the present invention allows for the preparation of fibre reinforced composite articles with excellent mechanical properties, such as elongation, fracture toughness, tensile strength and modulus, within a cycle time of less than 10 minutes, preferably less than 5 minutes and most preferably less than 2 minutes. The resin composition applied according to inventive process has an appropriate open time after mixing of the components, but the ability to cure rapidly without the need of post-curing.

(50) The inventive process allows for homogeneous pressure applied over the entire composite part, thereby reduces the size of bubbles also in its peripheral sections, and thus improves the visual appearance of the final composite part. Bubbles are generated by entrapped air and water adsorbed to the fiber reinforcement. In case no resin retention seal is present, the hydraulic pressure of the liquid resin decreases from the center of the composite part to its peripheral area.

(51) The present invention is also directed to the composite articles obtained by the inventive process.

(52) Moreover, the present invention is directed to the use of the composite articles obtained according to the inventive process for the construction of consumer goods, such as computer cases or luggage cases, or in the construction of mass transportation vehicles, in particular, in the automotive and aerospace industry.

(53) The following serves to further illustrate the invention. Unless otherwise indicated, the temperatures are given in degrees Celsius, parts are parts by weight and percentages relate to % by weight. Parts by weight relate to parts by volume in a ratio of kilograms to litres.

(54) 1. A carbon fibre reinforcement fabric (Hexforce 48300/Hexforce MBB00, Hexcel, Stamford, US) is cut to size and piled in a stack. Binders may optionally be applied to the single fabrics to improve handling of the fabric layers during cutting and placement.

(55) 2. A predetermined, measured amount of the thermosetting resin composition containing 100 parts of ARALDITE® LY 3585 (an epoxy resin available from Huntsman Corporation), 21 parts of ARADUR® 3475 (a curing agent available from Huntsman Corporation), and 2 parts of Evomold 3202 (a release agent available from KVS Eckert & Woelk GmbH) is applied to the fibre reinforcement stack and the fibre stack is placed into the lower die of the mold (12) depicted in FIG. 3a. In advance of being applied to the fibre reinforcement, the resin components are mixed by an automated mixing/dosing equipment.

(56) 3. The mold is partially closed, by moving the upper die (11) into the lower die (12), so that the seals (15) and (15b) placed around the vertically extending wall of the upper die (11), horizontally to its moving direction, are in contact with the vertically extending wall of the lower die (12) to form a vacuum tight cavity (see FIG. 3a).

(57) 4. The cavity formed by the mold in the partially closed position according to step 3 is evacuated to a pressure of 10 mbar or lower.

(58) 5. Once the required vacuum is achieved, the mold is fully closed (see FIG. 3b).

(59) 6. Press force is applied to the closed mold, such as to generate a positive hydraulic pressure onto the resin inside the mold. Mold pressure is increased up to 20 to 50 bars, which ensures complete impregnation of the fibre stack, even in areas where the cavity is partially or completely axially aligned to the press force (deep draw areas). Careful adjustment of the resin quantity and press force applied to the fibre stack ensures that the mold is completely filled and that sufficient pressure is generated during closure.

(60) 7. Press force is applied to the impregnated fibre reinforcement in the closed position of the mold for sufficient time that the resin system reacts and becomes cured. The mold is heated to a temperature of 140° C. prior to molding in order to reduce the time needed to cure the resin and the mold temperature is maintained at 140° C. for approximately 1 minute.

(61) 8. The mold is opened and the finished part is removed. Demolding of the finished part may be facilitated by use of mechanical or pneumatic ejectors, such as are know in the art, or by a combination of these.

(62) TABLE-US-00001 TABLE 1 Test data Properties of the thermosetting resin composition Viscosity Cone-plate  25° C. 1020 mPa .Math. s viscometer 140° C. <10 mPa .Math. s Gel time Hot plate 140° C. 21 s Properties of the composite prepared Composite laminate construction: 6 layers 300 g/m.sup.2 carbon fibre fabric ±45°/0°/0°/0°/0°/±45° Laminate curing: 55 s at 140° C. Plate quality Visual/ Plate 1: Vf = No defects/no voids micrograph of 50% cut and polished Plate 2: Vf = No defects/no voids laminate section 60% Plate 3: Vf = No defects/no voids 65% Properties of Plate 1 (Vf = 50%) Glass transition DMA ISO 6721 Tg onset 111° C. temperature (Tg) 2° C./min Tg mid-point 126° C. Interlaminar shear ASTM D2344 61 MPa strength Impact resistance Charpy ISO 179 187 kJ/m.sup.2 Vf: fibre volume fraction in composite article (plates 1 to 3); calculated from the part thickness together with weight of the resin composition and the fibre reinforcement fabric