Epoxy resin composition for fiber reinforced plastic

Abstract: An epoxy resin composition for fiber reinforced plastic comprising the following components A, B, C, D, E and F as essential components and having a viscosity at 40°C of at least 10,000 poise and a viscosity at 80°C of at most 200 poise: A: a bisphenol A type epoxy compound having an epoxy equivalent of at most 250 and being liquid at room temperature, B: a bisphenol A type epoxy compound having an epoxy equivalent of at most 1,000 and a softening point of at most 100°C and being solid at room temperature, C: a bisphenol A type epoxy compound having an epoxy equivalent of at least 1,100 and a softening point of at least 110°C and being solid at room temperature, D: a phenol novolak type epoxy compound, E: a nitrile rubber, and F: a curing agent.

Description: The present invention relates to a resin composition for fiber reinforced plastic. More particularly, it relates to a resin composition suitable for fiber reinforced plastic materials wherein fibers of high elasticity are employed. It is well known to impregnate an epoxy resin or an unsaturated polyester resin to a reinforcing material such as carbon fibers or glass fibers, followed by curing to form molded products having various shapes and thicknesses. This method is now being used for the production of cylindrical molded products or shafts for sporting goods or primary or secondary structural materials for aircrafts, or for the production of various materials. The reinforcing material having a resin impregnated and serving as a matrix, is called prepreg and may be in the form of strands, sheets stretched in one direction or fabrics. To obtain a molded product having a desired shape, it is known to use a filament winding method which comprises winding prepreg strands, or a lay-up method which comprises laminating prepreg sheets. To laminate prepreg sheets, it is important that the prepreg has a proper adhesiveness (tackiness) so that prepreg sheets adhere to one another at the time of laying up, and a flexibility (draping properties) so that laid up prepreg layers accurately reflect the shape such as a curved surface or cylinder. Under these circumstances, epoxy resin compositions having suitable tackiness and draping properties were proposed in Japanese Examined Patent Publications No. 5925/1983, No. 17535/1983 and No. 40975/1983 and Japanese Unexamined Patent Publications No. 43615/1986 and No. 127317/1987. However, such conventional resin compositions had drawbacks that depending upon the shape or various properties such as mechanical and physical properties of the reinforcing material to be used, the operation efficiency depending upon the tackiness and draping properties substantially decreases, and consequently the operation tends to be cumbersome, or it is difficult to obtain a molded product having satisfactory properties. Under such circumstances, the present inventors have previously found that by a combination of resins having specific physical properties, it is possible to obtain a prepreg having excellent draping properties (Japanese Unexamined Patent Publication No. 308026/1988), and further found a resin composition for improving the strength in the direction of 90°C when a on directional prepreg is prepared (Japanese Patent Application No. 40517/1988). They have further found that by blending a phenol novolak type epoxy resin to such as resin composition, a molded product having no internal voids after the thermosetting molding can be obtained while adequately maintaining the shape-maintaining strength of the prepreg sheets and excellent draping properties (Japanese Patent Application No. 170228/1988). Such a resin composition does not create any particular problem when applied to fiber reinforced plastic materials wherein reinforcing fibers of usual physical properties are employed. However, in a case where the reinforcing fibers have a high modulus of elasticity, the tackiness tends to be slightly poor, and it frequently happens that the shape after the shape-forming can not be maintained. Under the circumstances, the present inventors have conducted extensive researchs to solve such a problem and as a result have found that the tackiness can be improved by using a combination of two bisphenol A type epoxy resins having specific physical properties and being solid at room temperature, as the high molecular weight components, whereby the conventional problems can be solved, and a resin composition having balanced properties can be obtained. The present invention has been accomplished on the basis of this discovery. Namely, it is an object of the present invention to provide a resin composition which is excellent in the operation efficiency while maintaining excellent draping properties and the shape-maintaining strength of prepreg sheets and is capable of presenting a molded product having no voids in the interior of the molded product after thermosetting molding and which is most suitable for fiber reinforced plastic materials wherein reinforcing fibers of high modulus of elasticity are employed. Such an object can be accomplished by an epoxy resin composition for fiber reinforced plastic comprising the following components A, B, C, D, E and F as essential components and having a viscosity at 40°C of at least 1000 Pas (10,000 poise) and a viscosity at 80°C of at most 20 Pas (200 poise): A: a bisphenol A type epoxy compound having an epoxy equivalent of at most 250 and being liquid at room temperature, B: a bisphenol A type epoxy compound having an epoxy equivalent of at most 1,000 and a softening point of at most 100°C and being solid at room temperature, C: a bisphenol A type epoxy compound having an epoxy equivalent of at least 1,100 and a softening point of at least 110°C and being solid at room temperature, D: a phenol novolak type epoxy compound, E: a nitrile rubber, and F: a curing agent. Now, the present invention will be described in detail. With respect to the bisphenol A type epoxy compound (component A) having an epoxy equivalent of at most 250 and being liquid at room temperature to be used in the present invention, there is no particular restriction so long as it has an epoxy equivalent of at most 250, preferably from 180 to 200 and it is liquid at room temperature. Specifically, the following compounds may be mentioned: "EPIKOTE" 816, 827, 828, manufactured by Yuka Shell Epoxy company, "Araldite" GY250, GY260, manufactured by Ciba Geigy Company, "AER" 334, 330, 331, manufactured by Asahi Chemical Industry Co., Ltd., "Sumiepoxy" ELA-115, ELA-127, ELA-128, manufactured by Sumitomo Chemical Co., Ltd., "EPICLON" 855, 840, 850, manufactured by Dai Nippon Ink Kagaku K.K., "EPOTOHTO" YD-115, YD-127, YD-128, manufactured by TOHTO KASEI CO., LTD., "EPOMIK" R130, R139, R140, manufactured by Mitsui Petrochemical Industries, Ltd. With respect to the bisphenol A type epoxy compound (component B) having an epoxy equivalent of at most 1,000 and a softening point of at most 100°C and being solid at room temperature, any such compound may be used so long as it has an epoxy equivalent of at most 1,000, preferably from 400 to 1,000, and a softening point of at most 100°C, preferably from 60 to 100°C. Specifically, the following compounds may be mentioned: "EPOKOTE" 1001, 1002, 1004, manufactured by Yuka Shell Epoxy Company, "D. E. R." 661, 662, 664, manufactured by Daw Chemical Company, "Araldite" 6071, 7072, manufactured by Ciba Geigy Company, "Sumiepoxy" ESA-011, ESA-014, manufactured by Sumitomo Chemical Co., Ltd., "EPOTOHTO" 1050, 4050, manufactured by Dai Nippon Ink Kagaku K.K., "EPOTOHTO" YD-011, YD-127, YD-012, YD-014, manufactured by TOHTO KASEI CO., LTD., "EPOMIK" R301, R302, R304, manufactured by Mitsui Petrochemical Industries, Ltd. With respect to the bisphenol A type epoxy compound (component C) having an epoxy equivalent of at least 1,100 and a softening point of at least 110°C and being solid at room temperature, any such compound may be used so long as it has an epoxy equivalent of at least 1,100, preferably from 1,100 to 5,000, more preferably from 1,100 to 3,500, and a softening point of at least 110°C, preferably from 110 to 200°C, more preferably from 110 to 160°C. Specifically, the following compounds may be mentioned: "EPIKOTE" 1007, 1009, 1010, manufactured by Yuka Shell Epoxy Company, "D. E. R." 667, 668, 669, manufactured by Dow Chemical Company, "Araldite" 6097, 6099, manufactured by Ciba Geigy Company, "Sumiepoxy" ESA-017, ESA-019, manufactured by Sumitomo Chemical Co., Ltd., "EPICLON" 7075, 7055, 9050, manufactured by Dai Nippon Ink Kagaku K.K., "EPOTOHTO" YD-017, YD-119, manufactured by TOHTO KASEI CO., LTD., "EPOMIK" R307, R309, manufactured by Mitsui Petrochemical Industries, Ltd. The phenol novolak type epoxy compound (component D) means a compound of the formula: wherein n is an integer. As such a phenol novolak type epoxy resin (component D), the following compounds may specifically be mentioned: "EPIKOTE" 152, 154, manufactured by Yuka Shell Epoxy Company, "Araldite" EPN1138, EPN1139, manufactured by Ciba Geigy Company, "D.E.N" 431, 438, 439, 485, manufactured by Daw Chemical Company, "EPPN" 201, manufactured by Nippon Kayaku K.K., "EPICRON" N-730, N-738, N-740, manufactured by Dai Nippon Ink Kagaku K.K. These compounds may be used alone or in combination as a mixture of two or more different types. The nitrile rubber of component E is not particularly restricted, and it is usual to employ the one having an average molecular weight of at least 10,000. Specifically, a copolymer of butadiene and acrylonitrile may be employed. Further, it may be a copolymer having acrylic acid added to butadiene and acrylonitrile. It is usual to employ such copolymer having an average molecular weight of about 50,000. The acrylonitrile content is usually from 15 to 40% by weight. The nitrile rubber of component E may be incorporated independently in the form of nitrile rubber to the epoxy resin composition of the present invention. However, it is preferred to preliminarily mixing and reacting it with the epoxy compound of component A so that it may be incorporated in the form of a nitrile rubber-modified epoxy compound thus obtained. In the present invention, the above mentioned respective components are essential components, and their proportions are preferably such that relative to 100 parts by weight of component A, component B is from 5 to 40 parts by weight, component C is from 5 to 40 parts by weight, component D is from 50 to 140 parts by weight and component E is from 1 to 8 parts by weight. Further, it is important that the resin composition of the present invention has a viscosity at 40°C (η40°C) of at least 1000 Pas (10,000 poise), preferably from 1000 to 4000 Pas (10,000 to 40,000 poise), more preferably from 1000 to 3000 Pas (10,000 to 30,000 poise) and a viscosity at 80°C (η80°C) of at most 20 Pas (200 poise), preferably from 2 to 20 Pas (20 to 200 poise), more preferably from 5 to 15 Pas, (50 to 150 poise). If the viscosity (η40°C) is less than 1000 Pas (10,000 poise), the surface tends to be sticky although the operation efficiency may be improved. On the other hand, if it is too high, the operation efficiency tends to be poor, since the hardness tends to be too high. If the viscosity (η80°C) exceeds 20 Pas. (200 poise), the moldability in heat molding tends to be poor. On the other hand, if the viscosity is too low, the flowability tends to be so excellent that the operation efficiency tends to be poor, such being undesirable. Here, in the present invention, component A and components B and C primarily serve to adjust the viscosity of the resin composition. Particularly, in the present invention, the adhesive properties of the resin composition can be improved by the combined use of components B and C. Component E serves primarily to impart excellent operation efficiency and is effective particularly for the improvement of the flexibility of the resin composition. Component D serves to prevent formation of voids in the interior of the molded product. If components D and E are not incorporated, it tends to be difficult to impart good flexibility with a proper viscosity during the preparation of prepreg sheets or during the molding operation, and voids tend to form in the interior of the molded product, such being very inconvenient. As far as the physical properties of the resin mixture can be maintained, other components such as an aliphatic epoxy resin, an o-cresol novolak type epoxy resin, a polyglycidyl amine, a bisphenol F type epoxy resin, a brominated bisphenol A type epoxy resin, 1,1,2,2-tetrabis(4-glycidoxyphenyl)ethane, a glycidyl ester type epoxy resin and a monofunctional epoxy compound, may further be incorporated, as the case requires. The curing agent of component F may usually be any curing agent. It may be dicyandiamide, an acid anhydride, an aromatic diamine, dimercaptan or a phenol resin. Further, in order to impart storage stability and low temperature curability to the prepreg, it is effective to employ a combination of dicyandiamide and a curing accelerator. Even when dicyandiamide is used alone, no change is required in the operation prior to the molding, provided that the molding compositions such as the curing temperature may vary. The curing accelerator may be an imidazole derivative such as 2-ethyl-4-methylimidazole or 2-(2-cyanoethyl)-imidazole, or a urea derivative such as N-(3,4-dichlorophenyl)-N',N'-dimethylurea, N-(4-chlorophenyl)-N',N'-dimethylurea or N-(3-chlorophenyl)-N',N'-dimethylurea. In such a combination of curing agents i.e. a combination of dicyandiamide and a curing accelerator, it is preferred that dicyandiamine is incorporated in an amount of form 0.5 to 10 parts by weight, based on 100 parts by weight of the entire resin mixture, and the curing accelerator is incorporated in an amount of from 0.5 to 10 parts by weight. The resin composition of the present invention is useful for fiber reinforced plastics. The reinforcing fibers may be glass fibers, carbon fibers, aramide fibers, alumina fibers or boron fibers. It is particularly preferred to employ carbon fibers having a high modulus of elasticity. Such fiber reinforced plastics may be prepared by usual methods such as a solution method or a heat melting method. Now, the present invention will be described in further detail with reference to Examples. However, it should be understood that the present invention is by no means restricted to such specific Examples. Example 1 33 parts by weight of a nitrile rubber-modifies epoxy resin (component E) obtained by preliminarily mixing and reacting 5 parts by weight of nitrile rubber (acrylonitrile content: 27%) and 95 parts by weight of a bisphenyl A type epoxy compound having an epoxy equivalent of 190 and being liquid at room temperature, 8 parts by weight of the above liquid epoxy compound (component A), 7 parts by weight of a solid epoxy compound having an epoxy equivalent of 460 and a melting point of 68°C (component B), 5 parts by weight of a solid epoxy compound having an epoxy equivalent of 3,000 and a melting point of 148°C (component C), 36 parts by weight of a phenol novolak type epoxy compound (component D), 4 parts by weight of an alicyclic epoxy compound (epoxy equivalent: 140, liquid at room temperature), 4 parts by weight of dicyandiamide as a curing agent (component F) and 3 parts by weight of N-(3,4-dichlorophenyl)-N',N'-dimethylurea as a curing accelerator, were uniformly mixed under heating to obtain a resin composition of the present invention. The viscosity of this composition was 2000 Pas (20,000 poise) at 40°C and 12 Pas (120 poise) at 80°C. A one-directional prepreg obtained, from this resin composition and highly elastic carbon fibers having a modulus of elasticity of 65,000 kg/mm², was wound on a slightly tapered cylindrical mandrel having a diameter of 10 mℓ at an angle of 45°, whereby lamination reflecting the shape of the mandrel was possible, and the operation efficiency was excellent. Further, no defects such as voids were observed in the molded products after curing. Comparative Example 1 In the same manner as in Example 1, a resin composition was prepared by uniformly mixing 46 parts by weight of component E, 8 parts by weight of component A, 6 parts by weight of component C, 40 parts by weight of component D, 4 parts by weight of the alicyclic epoxy compound, 3.5 parts by weight of dicyandiamide and 3.8 parts by weight of the curing accelerator. The viscosity at 40°C of this resin composition was 600 Pas (6,000 poise). A one-directional prepreg prepared by using this resin composition was wound on the mandrel as in Example 1, whereby the end portion of the winding was partially peeled. Comparative Example 2 In the same manner as in Example 1, a resin composition was prepared by uniformly mixing 40 parts by weight of component E, 8 parts by weight of component A, 12 parts by weight of component B, 40 parts by weight of component D, 4 parts by weight of the alicyclic epoxy compound, 3.5 parts by weight of component F and 3.8 parts by weight of the curing accelerator. The viscosity at 40°C of this resin composition was 800 Pas (8,000 poise). A one-directional prepreg prepared by using this resin composition was wound on the mandrel in the same manner as Example 1, whereby the end portion of the winding was partially peeled as in the case of Comparative Example 2. Comparative Example 3 In the same manner as in Example 1, a resin composition was prepared by uniformly mixing 27 parts by weight of component E, 8 parts by weight of component A, 25 parts by weight of component B, 40 parts by weight of component D, 4 parts by weight of the alicyclic epoxy compound, 3.5 parts by weight of component F and 3.8 parts by weight of the curing accelerator. The viscosity of this resin composition was 2200 Pa.s (22,000 poise) at 40°C and 10 Pas (100 poise) at 80°C. A one-directional prepreg prepared by using this resin composition was wound on the mandrel in the same manner as in Example 1 and cured, whereby the prepreg lacked in flexibility and was poor to follow the shape of the mandrel. After the curing, the cross section was inspected, whereby breakage of fibers was observed. Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Component E (nitrile rubber-modified epoxy resin) 33 46 40 27 Component A 8 8 8 8 Component B 7 -- 12 25 Component C 5 6 -- -- Component D 36 40 40 40 Alicyclic epoxy compound 4 4 4 4 Component F (dicyandiamide) 4 3.5 3.5 3.5 Curing accelerator 3 3.8 3.8 3.8 Viscosity at 40°C (poise) 20,000 6,000 8,000 22,000 Viscosity at 80°C (poise) 120 -- -- 100 Lamination fficiency ○ ○ ○ X Shape-maintaining after shaping ○ X X X Quality of cured product ○ ○ ○ X According to the present invention, it is possible to obtain a resin composition for fiber reinforced plastic which is excellent in the operation efficiency and which is capable of presenting a flawless molded product.

Claims: An epoxy resin composition for fiber reinforced plastic comprising the following components A, B, C, D, E and F as essential components and having a viscosity at 40°C of at least 1000 Pas (10,000 poise) and a viscosity at 80°C of at most 20 Pas (200 poise): A: a bisphenol A type epoxy compound having an epoxy equivalent of at most 250 and being liquid at room temperature, B: a bisphenol A type epoxy compound having an epoxy equivalent of at most 1,000 and a softening point of at most 100°C and being solid at room temperature, C: a bisphenol A type epoxy compound having an epoxy equivalent of at least 1,100 and a softening point of at least 110°C and being solid at room temperature, D: a phenol novolak type epoxy compound, E: a nitrile rubber, and F: a curing agent. The epoxy resin composition according to Claim 1, wherein relative to 100 parts by weight of component A, component B is from 5 to 40 parts by weight, component C is from 5 to 40 parts by weight, component D is from 50 to 140 parts by weight, and component E is from 1 to 8 parts by weight. The epoxy resin composition according to Claim 1 or 2, wherein the epoxy equivalent of component A is from 180 to 200. The epoxy resin composition according to Claim 1, 2 or 3 wherein the epoxy equivalent of component B from 400 to 1,000. The epoxy resin composition according to any of Claims 1 to 4, wherein the softening point of component B is from 60 to 100°C. The epoxy resin composition according to any one of Claims 1 to 5, wherein the epoxy equivalent of component C is from 1,100 to 5,000. The epoxy resin composition according to any one of Claims 1 to 6, wherein epoxy equivalent of component C is from 1,100 to 3,500. The epoxy resin composition according to any one of Claims 1 to 7, wherein the softening point of component C is from 110 to 200°C. The epoxy resin composition according to any one of Claims 1 to 8, wherein the average molecular weight of component E is at least 10,000.

Inventors: ENDA JUN, HINO SEIICHI, YAMAMOTO MASAKI, ENDA, JUN, HINO, SEIICHI, YAMAMOTO, MASAKI
Applicants: MITSUBISHI CHEM CORP, MITSUBISHI CHEMICAL CORPORATION
Application year: 1990
Main classification: C08L63
IPC codes: C08J5, C08G59, C08L9, C08L21, C08L63