The present invention relates to fiber reinforced composite materials suitable for sports applications, aerospace applications and general industrial applications, and to a thermosetting resin composition and a prepreg for obtaining these composite materials.
On account, in particular, of their outstanding mechanical properties, fiber reinforced composite materials comprising reinforcing fiber and a matrix resin are widely employed in sports applications, aerospace applications and general industrial applications.
In these applications, carbon fiber, aramid fiber and glass fiber are chiefly employed as the reinforcing fiber. Of these, carbon fiber is outstanding in its specific strength and specific modulus and it is particularly important in that high performance composite materials can be obtained.
Both thermoplastic resins and thermosetting resins are used as the matrix resin, but thermosetting resins are most often employed because of their excellent impregnation of the reinforcing fiber.
As thermosetting resins, epoxy resins, resins with a plurality of polymerizable unsaturated bonds in the molecule (vinyl ester resins, unsaturated polyester resins and the like), phenolic resins and cyanate resins are chiefly used.
Fiber reinforced composite materials are heterogeneous materials comprising the aforesaid reinforcing fiber and matrix resin, and the adhesion between them has a considerable influence on the properties, as described below.
In general, with a fiber reinforced composite material, the strength in the direction of the fiber orientation is high, reflecting the properties of the reinforcing fiber, but the strength in directions in which there is no fiber orientation and the shear strength are not necessarily excellent, and indeed not uncommonly they are the weak points in terms of the performance of a fiber reinforced composite material.
Improving the adhesion between the reinforcing fiber and the matrix resin is effective in raising the strength in directions in which there is no fiber orientation and the shear strength. A known means for improving the adhesion between the reinforcing fiber and the matrix resin is surface treatment of the reinforcing fiber, for example the silane coupling agent treatment of glass fiber and the electrolytic oxidation of carbon fiber, but hardly any effective methods are known for improving the adhesion based on resin technology. In particular, in the case of carbon fiber, when adhesion is improved by electrolytic oxidation, this is at the expense of the fiber strength so that there are limits thereto, and while there has been a strong demand for alternative means for improving the adhesion, no effective means has hitherto be found.
In U.S. Pat. No. 4,873,309, there is disclosed a resin composition comprising (a) an epoxy resin containing bromine, (b) its curing agent, and (c) monomer having at least one vinyl unsaturated bond. Specific examples here of (c), along with styrene, methyl methacrylate, acrylonitrile, vinyl acetate and many other general monomers, include acrylamide and its derivatives, and there is also mention of carbon fiber but unrelated to these. The function of (c) in that invention is as a diluent for achieving a lower viscosity, and there is no suggestion at all of combining a specific amount of acrylamide or derivative thereof and carbon fiber, nor that the combination thereof differs from combinations of carbon fiber and other general monomers in that a dramatic effect is shown in terms of improving adhesion and enhancing the elastic modulus, and so the invention in no way relates to the concept of the present invention. Again, the fact that a comparatively large amount of (c) is added in that invention differs from the incorporation of a relatively small amount of component (B) in the present invention.
On the other hand, in U.S. Pat. No. 4,230,766, there is described an example in which a composition comprising thermosetting resin and vinyl pyrrolidone is used to impregnate carbon fiber, then the composition partially cured by light irradiation, after which hot curing is performed and a fiber reinforced composite material obtained. However, in that example, the amount of vinyl pyrrolidone added is excessive, and there is absolutely no suggestion that by adding a specific amount there is a dramatic effect in terms of improving the adhesion and enhancing the elastic modulus without impairing other physical properties.
The objective of the present invention is to offer a thermosetting resin composition for fiber reinforced composite materials where the cured product thereof shows outstanding adhesion to the reinforcing fiber, in particular carbon fiber, together with a prepreg employing said resin composition and carbon fiber reinforced composite materials of outstanding properties obtained using same.
In order to realise these objectives, the thermosetting resin composition for carbon fiber reinforced composite materials of the present invention comprises the following components.
(A) Thermosetting resin
(B) Compound having one functional group which can react with thermosetting resin (A), or its curing agent, and which contains a moiety selected from the following formulae (1) to (4) 
Furthermore, the prepreg of the present invention is a prepreg formed by the impregnation of reinforcing fiber with the aforesaid resin composition, and the carbon fiber reinforced composite materials of the present invention are carbon fiber reinforced composite materials comprising cured aforesaid thermosetting resin composition and reinforcing fiber.