Intermediate for composite material

Abstract: An intermediate for a composite material is described, comprising a reinforcing material impregnated with a resin composition which comprises: (A) 100 parts by weight of a mixture of (I) a polyfunctional maleimide and (II) a polyfunctional cyanate or an oligomer thereof, or a preliminary reaction product of (I) and (II); (B) from 5 to 100 parts by weight of an epoxy compound; and (C) from 5 to 50 parts by weight of a polyester compound.

Description: FIELD OF THE INVENTION The present invention relates to an intermediate that can be used in the production of a composite material having superior heat resistance, water resistance and mechanical properties. BACKGROUND OF THE INVENTION A variety of resin compositions have heretofore been used as the matrices of composite materials. In the area of thermosetting resins, epoxy resins have been extensively used because, in addition to their inherent superior mechanical properties (strength and elongation, in particular), they achieve better adhesion to reinforcing materials to have them exnibit superior strength properties in the resulting composite materials than any other thermosetting resins. There is, however, a growing need to produce composite materials having even higher performance, particularly, in terms of resistance to heat, water and impact, and in order to meet this demand, the use of polyfunctional maleimides, polyfunctional cyanates or oligomers thereof, or preliminary reaction products thereof as matrix components has been reviewed. For example, a resin composition which comprises a mixture of polyfunctional maleimides and polyfunctional cyanates and an epoxy compound, as described in U.S. Patents 4,l10,364, 4,429,112 and 4,404,330, Japanese Patent Publication No. 31279/77 and Japanese Patent Publication (OPI) No. 184524/85 (the term "OPI" as used herein means a "published unexamined Japanese patent application") can provide a cured product excellent in various properties such as heat resistance. However, the cured product of resin composition was still insufficient in impact resistance. Further, a prepreg for composite material resistant to impact in which the above described resin composition is impregnated with carbon fiber having 1.5% or more of elongation has been proposed in Japanese Patent Publication (OPI) No. 15439/85. However, this does not describe compression characteristics after impact which has been established as impact resistance evaluation for composite materials, in particular for carbon fiber composite materials as primary structural material for an aircraft, and it is desired further improvement. SUMMARY OF THE INVENTION An object, therefore, of the present invention is to provide an intermediate for a composite material having superior resistance to heat, water, and impact. As a result of various studies conducted to attain this object, the present inventors have found that it can be achieved with an intermediate according to claim 1. DETAILED DESCRIPTION OF THE INVENTION The polyfunctional maleimide (I) used in the present invention is a compound having two or more maleimide groups and is illustrated by bismaleimides represented by formula(III) wherein R₂ is a divalent aromatic or aliphatic group, as well as prepolymers formed from such bismaleimides and diamines. Typical example of bismaleimides represented by formula (III) is m-xylenebismaleimide. A bismaleimide of formula (III) may be prepared by a known method which comprises reacting maleic anhydride with a diamine to form a bismaleinaminc acid, then subjecting said acid to dehydrative cyclization. Aromatic diamines which are heat-resistant are preferable for use as amines, but if a particular property such as flexibility is desired, aliphatic diamines may be used either alone or in combination with aromatic diamines. Illustrative diamines include m-phenylenediamine, p-phenylenediamine, 4,4'-diaminodiphenylsulfone, 3,3'-diaminodiphenylsulfone, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylether, etc. Preferable examples of the polyfunctional maleimide used in the present invention include a bismaleimide of 4,4'-diaminodiphenylmethane, etc. The polyfunctional cyanate (II) used in the present invention is an organic compound having two or more cyanic acid ester groups or an oligomer thereof, and is preferably represente by formula (IV) R₃-(-O-C=N) n wherein n is an integer of 2 to 5, and R₃ is an aromatic organic residual group. Illustrative polyfunctional cyanates include 1,3- or 1,4-dicyanatobenzene, 4,4-dicyanatobiphenyl, bis(4-cyanatophenyl)methane, 2,2-bis(4-cyanatophenyl)ethane, 2,2-bis(4-cyanatophenyl)propane, bis(4-cyanatophenyl)sulfone, etc. These polyfunctional cyanates may be used not only in the form of triazine oligomers prepared by trimerization of cyanato compounds, but also in the form of prepolymers prepared by reaction with amines which contain diamines selected from among those which can be employed in the synthesis or modification of the aforementioned polyfunctional maleimides. Preferable examples of the polyfunctional cyanate include 2,2-bis(4-cyanatophenyl)propane, etc. In the present invention, the aforementioned polyfunctional maleimide (I) and polyfunctional cyanate (II) are used independently as component (A). Alternatively, the product prepared by performing the preliminary reaction of (I) and (II) in the presence or absence of a catalyst may be used as component (A). The choice of the most appropriate material for use as component (A) depends on the specific intended use of the composite material to be finally produced. Any known epoxy resin may be used as the epoxy compound (B) in the present invention. Illustrative epoxy resins include: polyglycidyl ethers of diphenylolalkanes such as diphenylolpropane, diophenylolethane and diphenylolmethane; polyglycidyl ethers of polyvalent phenols such as novolaks, cresols and resols; and epoxy resins that are formed by epoxidization of alicyclic compounds such as cyclohexane, cyclopentadiene and dicyclopentadiene, which include esters of 3,4-epoxy-6-methyl-cyclohexane-carboxylic acids and 3,4-epoxy-6-methyl-cyclohexane-carbinol, poly(epoxyalkyl)ethers of aliphatic polyoxy compounds such as ethylene glycol and glycerin, and epoxy alkyl esters of carboxylic acids such as glycidyl esters of aromatic or aliphatic carboxylic acids. The preliminary reaction products of epoxy resins and curing agents, as described in U.S. Patents 3,390,037, 2,970,983 and 3,067,170 may also be used. Epoxy resins may simply be used in the form of mixtures with curing agents. The aforementioned epoxy resins may be used either independently or in combinations thereof. An advantageous epoxy compound is a preliminary reaction product of a diglycidyl ether of bisphenol A and diaminodiphenylsulfone having an epoxy to NH ratio of 4/1. The polyester compound (C) used in the present invention is represented by formula (V): wherein Ar is a phenylene group; and R₁ is the same divalent aliphatic group. The phenylene group denoted by Ar in formula (V) may be ortho, meta or para. The divalent aliphatic group denoted by R₁ in formula (V) is preferably a straight-chain or branched-chain aliphatic group having from 2 to 6 carbon atoms and includes the following groups: -(-CH₂-)₂-, -(-CH₂-)₃-, -CH₂-CH(CH₃)-, CH-C₂H₅, -(-CH₂-)₄-, -CH₂-CH(CH₃-)-CH₂-, -(-CH₂-)₅-, -(-CH₂-)₃-CH(CH₃)-, -(-CH₂-)₂-CH(CH₃-)-CH₂-, -(-CH₂-)₂-CH(C₂H₅)- and -CH₂-C(CH₃-)₂-CH₂-. The polyester compound (C) used in the present invention preferably has a softening point of not higher than 100°C, and more preferably not higher than 70°C. If the polyester compound has a softening point exceeding 100°C, its miscibility with the polyfunctional maleimide, polyfunctional cyanate and epoxy compound becomes too low to attain a uniform composition. This polyester compound preferably has a number average molecular weight of from 500 to 10,000, and more preferably from 500 to 3.000. If the number average molecular weight of the polyester compound is less than 500, the resulting compound has an undesirable low viscosity. If, on the other hand, the number average molecular weight of the polyester compound exceeds 10,000, it cannot be easily mixed with the other components, The polyester compound used in the present invention may be prepared by any of the methods that are conventionally employed to produce other linear polyesters. The polyvalent carboxylic acid and polyhydric alcohol that are used in the preparation of the polyester resin of the present invention may be selected from among those which are employed in the manufacture of such polyester resins. Illustrative polyvalent carboxylic acids include phthalic acid, phthalic anhydride, isophthalic acid, terephthalic acid, lower alkyl esters thereof, and other aromatic divalent carboxylic acids such as tetrachlorophthalic anhydride, tetrabromophthalic anhydride. Phthalic acid, isophthalic acid, and terephthalic acid are preferable. Illustrative polyhydric alcohols include ethylene glycol, propylene glycol, 1,3-butylene glycol, 1,6-hexane diol, diethylène glycol, dipropylène glycol, neopentyl glycol, trimethylène glycol, triethylene glycol, glycerin, trimethylolethane, trimethylolpropane, trishydroxymethylaminomethane, pentaerythritol, dipentaerythritol, and resorcin. Ethylene glycol, neopentyl glycol, trimethylene glycol, and resorcin are preferable. It is essential for the purpose of the present invention that the resin composition used should consist of 100 parts by weight of component (A), from 5 to 100 parts by weight of component (B), and from 5 to 25 parts by weight of component (C). If the content of the epoxy compound used as component (B) is less than 5 parts by weight per 100 parts by weight of component (A), the desired adhesion to a substrate is not attained. If the content of component (B) exceeds 100 parts by weight, satifactory heat resistance is not attainable. If the content of the polyester compound used as component (C) is less than 5 parts by weight per 100 parts by weight of component (A), the desired impact resistance will not be exhibited by the resulting composition. The ratio of the polyfunctional maleimide (I) to polyfunctional cyanic acid ester or oligomer thereof (II) present in component (A) is preferably within the range of 5/95 to 15/85 on a weight basis. If the proportion of (I) is greater than 15 wt% of component (A), heat and water resistance is attained but, on the other hand, high curing temperatures are required, and a drop in impact resistance occurs. If the proportion of (I) is less than 5 wt% of component (A), an improvement in impact resistance is achieved but the heat resistance is decreased undesirably. The resin composition used in the present invention may optionally incorporate a catalyst in order to impart desirable properties to the cured product of resin or to control the thermosetting property of resin. Illustrative catalysts that can be used for attaining these purposes include: latent curing catalysts such as boron trifluoride amine complex compounds (e,g., boron trifluoride monoethylamine complex); tertiary amines such as triethylenediamie, 1,8-diazabicyclo-(5,4,0)undecene, N,N-dimethylbenzylamine, N-methylmorpholine and tri-n-butylamine; organic peroxides such as dicumyl peroxide, benzoyl peroxide and t-butyl hydroperoxide; and metal salts of organic acids such as zinc octylate, lead octylate, zinc napthenate and cobalt naphthenate. Among these catalysts boron trifluoride monoethylamine complex, dicumyl peroxide and zinc octylate are preferably used. The amount of catalyst used may be determined in accordance with the specific object of its use, and, in order to ensure the stability of the resulting resin composition, the catalyst is preferably used in an amount of from 0.2 to 3 wt% of the total content of the resin components (A), (B), and (C). The reinforcing material used in the intermediate for composite material of the present invention is appropriately selected from among inorganic fibers such as glass fibers, carbon fibers, boron fibers and silicon carbide fibers, organic fibers such as poly-p-phenyiene terephthalamide, poly-p-benzamine and polyamide hydrazide, asbestos, mica, talc, etc. The inorganic or organic fibers are used in the form of chopped strands, yarns, tape, sheet, woven or knifed fabrics, mats or paper-like materials. These reinforcing materials may be used either independently or as a mixture. Depending upon the specific use of the final composite material, the intermediate of the present invention may incorporate an additive such as a flow control agent (e.g., fine silicon oxide powder), a pigment, a dye, a stabilizer, a plasticizer, a lubricant, tar or asphalt. These opticnal additives may be used either independently or in combination with reinforcing materials. The amount of the additive used is preferably 5 wt% or less of the total content of resin components (A), (B), and (C). Particularly the flow control agent is preferably used in an amount of from 0.2 to 3.0 wt% of the total content of the resin components (A), (B), and (C). The reinforcing material is preferably impregnated into the resin composition by the following method: the resin composition is subjected to a preliminary reaction at from 50 to 120°C to form a prepolymer, which then is dissolved in a solvent such as methyl ethyl ketone and impregnated into the reinforcing material. The content of the reinforcing material in the intermediate for composite material of the present invention is preferably within the range of 0.5 to 80 vol%. In addition to the epoxy resin, other thermosetting resins or thermoplastic resins may be used in the intermediate of the present invention. The invention is described in greater detail with reference to the following examples, which are not to be construed as limiting the scope thereof. EXAMPLE 1 Bis(4-maleimidophenyl)methane, 2,2-bis(4-cyanatophenyl)propane, Epikote 807 of Shell International Chemicals Corp. (epoxy equivalent, 172), and polyester (a) that was composed of terephthalic acid (acid component) and neopentyl glycol (glycol component) and which had a softening point of 25°C were mixed in the proportions indicated in Table 1. To the mixture, 1.25 parts by eight of AEROSIL 380 (fine silicon oxide powder of Japan Aerosil Inc.) and 0.2 parts by weight of dicumyl peroxide (curing catalyst) were added. The resulting mixture was subjected to a preliminary reaction at 70°C for 30 minutes to form a prepolymer. The prepolymer was sandwiched between two glass sheets to provide a predetermined thickness and subsequently heated at 180°C for 2 hours to obtain a cured resin sheet. Another sample of the uncured prepolymer was dissolved in methyl ethyl ketone and cartoon fiber filaments (Pyrofil T-3, Trade mark of Mitsubishi Rayon Co. Ltd.), being impregnated with the prepolymer solution, were wound around a drum to form a coil. The coil was dried and cut open to make a unidirectional prepreg (Fiber areal weight, 145 g/m²; resin content, 33 wt%). Sheets of this prepreg were laminated for [0°] 16, , or laminated quasi-isotropically for [+45°/0°/-45°/+90°] 4S , and cured at 180°C for 2 hours to prepare a composite material. The resin sheet and the composite material were subjected to various tests, the results of which are shown in Table 2. The data of glass transition temperature (Tg) given in Table 2 are expressed as the temperature for maximum tan δ that was obtained by measurement with a dynamic mechanical spectrometer (manufactured by Rheometrics Inc.). The resistance of the composite to heat and water was evaluated by performing a compression test on the [0°]₁₆ laminated composite in the direction of 0° at 121°C in accordance with ASTM D-695 after it had been submerged in water (71°C) for 14 days. The impact resistance of the composite material was evaluated by using the [+45°/0°/-45°/+90°] 4S laminated sheet in the following manner in accordance with NASA RP1092: a test piece 10.16 x 15.24 x 0.635 cm. (4 x 6 x 0.25 in.) was fixed on a table having a hole 7.62 x 12.70 cm. (3 x 5 in.); a weight (4.9 kg) with a nose having a radius of 1.27 cm (1/2 inch) was dropped on the center of the test piece to apply an impact of 1,500 lbs. per 2.54 cm (inch) of the laminate thickness; the test piece was thereafter subjected to a compression test. All of the data for the composite material were normalized for a fiber content of 60%. EXAMPLE 2 A resin sheet and a composite material were prepared as in Example 1 except that m-xylenebismaleimide prepared from m-xylenediamine and maleic anhydride was used as polyfunctional maleimide and 1, 4-dicyanatobenzene was used as polyfunctional cyanate. The resin sheet and the composite material thus prepared were subjected to various tests, the results of which are summarized in Table 2. EXAMPLE 3 A resin sheet and a composite material were prepared as in Example 1 except that Epikote 828 (Trade mark of Shell International Chemicals Corp.) having an epoxy equivalent of 184-194 was used as an epoxy resin. The resin sheet and the composite material thus prepared were subjected to various tests, the results of which are summarized in Table 2. EXAMPLE 4 AND COMPARATIVE EXAMPLES 1 AND 2 Additional resin sheets and composite materials were prepared as in Example 1 except that the amount of polyester (a) was altered as shown in Table 1. The resin sheets and composite materials thus prepared were subjected to various tests, the results of which are summarized in Table 2. EXAMPLE 5 AND COMPARATIVE EXAMPLES 3 AND 4 Additional resin sheets and composite materials were prepared as in Example 1 except that the amount of Epikote 807 was altered as shown in Table 1. The resin sheets and composite materials thus prepared were subjected to various tests, the results of which are summarized in Table 2. EXAMPLES 6 AND 7 Additional resin sheets and composite materials were prepared as in Example 1 except that the amounts of bis(4-maleimidophenyl)methane and 2,2-bis(4-cyanatophenyl)propane were altered as shown in Table 1. The resin sheets and composites thus prepared were subjected to various tests, the results of which are summarized in Table 2. EXAMPLE 8 A resin sheet and a composite material were prepared as in Example 1 except that a preliminary reaction product of Epikote 828 as an epoxy resin and a 4,4'-diaminodiphenylsulfone having an epoxy to NH ratio of 4/1, in which the reaction time is 2 hours at 160°C, was used as an epoxy compound (an epoxy equivalent: 265). The resin sheet and the composite material thus prepared were subjected to various tests, the results of which are summarized in Table 2. EXAMPLE 9 A resin sheet and a composite material were prepared as in Example 1 except that polyester (a) was replaced by a polyester (d) that had a softening point of 30°C and which was composed of phthalic acid (acid component) and ethylene glycol (glycol component). The resin sheet and the composite material thus prepared were subjected to various tests, the results of which are summarized in Table 2. EXAMPLE 10 A resin sheet and a composite material were prepared as in Example 1 except that polyester (a) was replaced by a polyester (e) that had a softening point of 20°C and which was composed of isophthalic acid (acid component) and trimethylene glycol (glycol component). The resin sheet and the composite material thus prepared were subjected to various tests, the results of which are summarized in Table 1. EXAMPLE 11 A resin sheet and a composite material were prepared as in Example 1 except that AEROSIL 380 was not added. The resin sheet and the composite material thus prepared were subjected to various tests, the results of which are summarized in Table 2. COMPARATIVE EXAMPLE 5 A resin sheet and a composite material were prepared as in Example 1 except that a prepreg was prepared in the same resin composition, same reinforcing material, and same manner as described in Example 1 of Japanese Patent Publication (OPI) No. 15439/85. The resin sheet and the composite material thus prepared were subjected to various tests, the results of which are summarized in Table 2.

Claims: Claims for the following Contracting States : DE, FR, GB, IT, NL, SE An intermediate for a composite material comprising a reinforcing material impregnated with a resin composition which comprises: (A) 100 parts by weight of a mixture of (1) a polyfunctional maleimide and (2) a polyfunctional cyanate or an oligomer thereof, or a preliminary reaction product of (1) and (2); (B) from 5 to 100 parts by weight of an epoxy compound; and (C) from 5 to 25 parts by weight of a polyester compound, and wherein the polyester compound (C) is represented by formula (V) wherein Ar is a phenylene group; and R₁ is the same divalent aliphatic group. An intermediate for a composite material as claimed in claim 1, wherein the polyfunctional maleimide (1) is a bismaleimide of diaminodiphenylmethane. An intermediate for a composite material as claimed in claim 1 or 2, wherein the polyfunctional cyanate (2) is 2,2-bis(4-cynatophenyl)propane. An intermediate for a composite material as claimed in any of the preceedding claims, wherein the epoxy compound (B) is a preliminary reaction product of a diglycidyl ether of bisphenol A and a diaminodiphenylsulfone having an epoxy to NH ratio of 4/1. An intermediate for a composite material as claimed in any of the preceeding claims, wherein the polyester compound (C) is the reaction product of terephthalic acid and neopentyl glycol that has a softening point of not higher than 100°C and a number average molecular weight of from 500 to 10000. An intermediate for a composite material as claimed in any of the preceeding claims, which contains from 0.2 to 3 weights per cent of a fine silicon oxide powder. An intermediate for a composite material as claimed in any of the preceeding claims, wherein the weight ratio of (1) to (2) in component (A) ranges from 5/95 to 15/85. An intermediate for a composite material as claimed in any of the preceeding claims, which contains from 0.2 to 3 weigth per cent of a catalyst selected from among a boron trifluoride monoethylamine complex, dicumyl peroxide, and zinc octylate. Claims for the following Contracting State : ES A process for the preparation of an intermediate for a composite material, characterized by impregnating a reinforcing material with a resin composition of the following composition: (A) 100 parts by weight of a mixture of (1) a polyfunctional maleimide and (2) a polyfunctional cyanate or an oligomer thereof, or a preliminary reaction product of (1) and (2); (B) from 5 to 100 parts by weight of an epoxy compound; and (C) from 5 to 25 parts by weight of a polyester compound, and wherein the polyester compound (C) is represented by formula (V) wherein Ar is a phenylene group; and R₁ is the same divalent aliphatic group, is used as a polyester compound (C). The process according to claim 1, characterized in, that a bismaleimide of diaminodiphenylmethane is used as the polyfunctional maleimide (1). The process according to claim 1 or 2, characterized in, that 2,2-bis(4-cyanotophenyl)propane is used as polyfunctional cyanate (2). The process according to any of the preceeding claims, characterized in, that a preliminary reaction product of a diglycidyl ether of bisphenol A and a diaminodiphenylsulfone having an epoxy to NH ratio of 4/1 is used as epoxy compound (B). The process according to any of the preceeding claims, characterized by using the reaction product of terephthalic acid and neopentyl glycol as polyester compound (C), the same having a softening point of not higher than 100°C and a number average molecular weight of from 500 to 10000. The process according to any of the preceeding claims, characterized in that 0.2 to 3 weights per cent of a fine silicon oxide powder are used. The process according to any of the preceeding claims, characterized in that the weight ratio of (1) to (2) in component (A) ranges from 5/95 to 15/85. The process according to any of the preceeding claims, characterized in that 0.2 to 3 weight per cent of a catalyst selected from among a boron trifluoride monoethylamine complex, dicumyl peroxide, and zinc octylate are added.

Inventors: AGATA AKIRA, ISEKI TAKAYUKI, TADA HISASHI, AGATA, AKIRA, ISEKI, TAKAYUKI, TADA, HISASHI, AGATA, AKIRA C/O MITSUBISHI RAYON CO., LTD., ISEKI, TAKAYUKI C/O MITSUBISHI RAYON CO., LTD., TADA, HISASHI C/O MITSUBISHI RAYON CO., LTD.
Applicants: MITSUBISHI RAYON CO, MITSUBISHI RAYON CO., LTD.
Application year: 1986
Main classification: C08G73
IPC codes: C08L79, C08L63, C08G59, C08G73