WO2024111245A1 - Curable composition, fiber composite material, sheet molding compound, and molded article - Google Patents

Abstract

The present invention provides: a curable composition, a cured product of which has high strength and which is suitable for use in a fiber composite material; a fiber composite material which uses this curable composition; a sheet molding compound which is suppressed in stickiness and has good film releasability; and a molded article which has excellent surface smoothness. A curable composition according to the present invention contains (A) an epoxy group-containing compound, (B) a curing agent or curing accelerator for epoxy group-containing compounds, (C) a polyhydroxy compound (excluding the component (A)), and (D) a polyisocyanate compound, and is characterized in that 70% by mass or more of the polyhydroxy compound (C) is a polyhydroxy compound (C1) that has a hydroxyl equivalent within the range of 125 to 600 g/equivalent.

Description

Curable compositions, fiber composites, sheet molding compounds, and molded articles

The present invention relates to a curable composition that produces a high-strength cured product and is suitable for use in fiber composite materials, a fiber composite material using the curable composition, a sheet molding compound that is less sticky and has good film peelability, and a molded product that has excellent surface smoothness.

CFRP, which is made by reinforcing thermosetting resin with carbon fiber, is attracting attention for its lightweight yet excellent heat resistance and mechanical strength, and is being used in a wide range of applications, including automobiles, aircraft, and industrial parts. In particular, sheet molding compounds (hereinafter sometimes abbreviated as "SMC") that use discontinuous fibers as the carbon fibers can be molded into more complex shapes than those that use continuous carbon fibers, and have the advantages of high productivity and a wide range of design applications, such as the ability to reuse scrap materials and insert components made of different materials. Unsaturated polyester resins and vinyl ester resins have traditionally been widely used as matrix resins for sheet molding compounds, but because they contain volatile components such as styrene, the safety of the working environment and environmental impact have become issues, and the use of epoxy resins instead of these resin materials is now being considered.

A known sheet molding compound using epoxy resin is one that uses a resin composition containing an epoxy resin, its curing agent, a polyisocyanate compound, and a polyol with a hydroxyl group equivalent of 20 to 120 as the matrix resin (see, for example, Patent Document 1). The sheet molding compound described in Patent Document 1 is characterized by relatively excellent strength of the cured product, but is very sticky, making film peeling an issue, and the surface smoothness of the molded product is poor.

Patent No. 6447791

The problem that the present invention aims to solve is to provide a curable composition that produces a high-strength cured product and is suitable for use in fiber composite materials, a fiber composite material using the curable composition, a sheet molding compound that is less sticky and has good film peelability, and a molded product that has excellent surface smoothness.

As a result of intensive research, the inventors have discovered that a curable composition containing an epoxy resin, a polyisocyanate compound, and a polyhydroxy compound, the polyhydroxy compound having a hydroxyl group equivalent in the range of 125 to 600 g/equivalent, as essential components, produces a cured product with high strength and can be suitably used for fiber composite materials, and that a sheet molding compound using this composition has excellent workability due to its low stickiness and good film peelability, and furthermore, the molded product has excellent surface smoothness, which led to the completion of the present invention.

　That is, the present invention relates to (I) a curable composition containing an epoxy group-containing compound (A), a curing agent for an epoxy group-containing compound (B), a polyhydroxy compound (C) (excluding those corresponding to component (A)), and a polyisocyanate compound (D), characterized in that 70 mass% or more of the polyhydroxy compound (C) is a polyhydroxy compound (C1) having a hydroxyl group equivalent in the range of 125 to 600 g/equivalent.

The present invention further relates to (II) the curable composition described in (I) above, in which the number of moles of isocyanate groups in the polyisocyanate compound (D) per mole of hydroxyl groups in the polyhydroxy compound (C) is in the range of 0.6 to 3.0.

The present invention further relates to (III) the curable composition described in (I) or (II) above, in which the epoxy group-containing compound (A) contains a bisphenol-type epoxy resin (A1) having an epoxy equivalent in the range of 160 to 260 g/equivalent.

The present invention further relates to (IV) a curable composition according to any one of (I) to (III) above, in which the epoxy group-containing compound (A) contains a polyglycidyl ether (A2) of an aliphatic polyol having 2 to 6 carbon atoms.

The present invention further relates to (V) a curable composition according to any one of (I) to (IV) above, in which the epoxy group-containing compound (A) contains a bisphenol-type epoxy resin (A1) having an epoxy equivalent in the range of 160 to 260 g/equivalent and a polyglycidyl ether of an aliphatic polyol having 2 to 6 carbon atoms (A2), and the mass ratio of the two, (A1)/(A2), is in the range of 60/40 to 95/5.

The present invention further relates to (VI) a fiber-reinforced composite material containing the curable composition described in any one of (I) to (V) above and reinforcing fibers.

The present invention further relates to (VII) a fiber-reinforced composite material as described in (VI) above, in which the reinforcing fibers are carbon fibers.

The present invention further relates to the fiber-reinforced composite material described in (VI) or (VII) above, which is a sheet molding compound (VIII).

The present invention further relates to (IX) a sheet molding compound described in (VIII) above, which has a carrier film on both sides.

The present invention further relates to (X) a molded product of the fiber composite material described in any one of (VI) to (VIII) above or the sheet molding compound described in (IX) above.

The present invention further relates to a method for producing a molded product, comprising the steps of (XI) peeling a carrier film from a sheet molding compound having a carrier film on the back side, and molding the sheet molding compound from which the carrier film has been peeled off.

The present invention provides a curable composition that produces a high-strength cured product and is suitable for use in fiber composite materials, a fiber composite material using the curable composition, a sheet molding compound that is less sticky and has good film peelability, and a molded product that has excellent surface smoothness. The sheet molding compound and molded product of the present invention can be used for a variety of applications, such as the exteriors and structures of automobile parts, railway vehicle parts, aerospace aircraft parts, ship parts, housing equipment parts, sports parts, light vehicle parts, building and civil engineering parts, and office equipment.

The curable composition of the present invention is a curable composition containing an epoxy group-containing compound (A), a curing agent for an epoxy group-containing compound (B), a polyhydroxy compound (C) (excluding those corresponding to component (A)), and a polyisocyanate compound (D), characterized in that 70 mass% or more of the polyhydroxy compound (C) has a hydroxyl group equivalent in the range of 125 to 600 g/equivalent.

The epoxy group-containing compound (A) may be of any structure, and may be of any variety, as long as it has an epoxy group in its molecular structure. The epoxy group-containing compound (A) may be used alone or in combination of two or more types. The epoxy group-containing compound (A) may have a functional group other than an epoxy group. Among them, a compound having two or more epoxy groups in its molecular structure is preferred, since it will result in a curable composition with excellent curing reaction. The proportion of the compound having two or more epoxy groups in the molecular structure in the entire epoxy group-containing compound (A) is preferably 80% by mass or more, and particularly preferably 90% by mass or more.

Examples of the epoxy group-containing compound (A) include diglycidyloxybenzene, diglycidyloxynaphthalene, biphenol-type epoxy resins, bisphenol-type epoxy resins, polyglycidyl ethers of aliphatic polyols, novolac-type epoxy resins, alicyclic epoxy resins, glycidylamine-type epoxy resins, heterocyclic epoxy resins, glycidyl ester-type epoxy resins, triphenolmethane-type epoxy resins, phenol or naphthol aralkyl-type epoxy resins, phenylene or naphthylene ether-type epoxy resins, oxolidone-modified epoxy resins, brominated epoxy resins thereof, and epoxy resins obtained by extending these epoxy group-containing compounds with an extender.

The biphenol-type epoxy resin may be, for example, a biphenol compound such as biphenol or tetramethylbiphenol, or one or more alkylene oxide adducts of these biphenol compounds that have been polyglycidyl etherified with epihalohydrin.

The bisphenol type epoxy resins include, for example, bisphenol compounds such as bisphenol A, bisphenol F, bisphenol S, bisphenol fluorene, and biscresol fluorene, and polyglycidyl ethers of one or more alkylene oxide adducts of these bisphenol compounds with epihalohydrin.

The polyglycidyl ethers of the aliphatic polyols include, for example, polyglycidyl ethers of various aliphatic polyol compounds and one or more of their alkylene oxide adducts with epihalohydrin. Examples of the aliphatic polyol compound include aliphatic diol compounds such as ethylene glycol, propylene glycol, 1,3-propanediol, 2-methylpropanediol, 1,2,2-trimethyl-1,3-propanediol, 2,2-dimethyl-3-isopropyl-1,3-propanediol, 1,4-butanediol, 1,3-butanediol, 3-methyl-1,3-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 1,4-bis(hydroxymethyl)cyclohexane, and 2,2,4-trimethyl-1,3-pentanediol; alicyclic diol compounds such as 2,2-bis(4-hydroxyphenyl)propane; and trifunctional or higher aliphatic polyol compounds such as trimethylolethane, trimethylolpropane, glycerin, hexanetriol, pentaerythritol, ditrimethylolpropane, and dipentaerythritol.

The novolac type epoxy resin may be, for example, a novolac resin made of one or more of various phenolic compounds such as phenol, dihydroxybenzene, cresol, xylenol, naphthol, dihydroxynaphthalene, bisphenol, biphenol, etc., which is polyglycidyl etherified with epihalohydrin.

Alicyclic epoxy resins include, for example, those obtained by hydrogenating the biphenol compounds or bisphenol compounds, and those obtained by polyglycidyl etherifying one or more of these alkylene oxide adducts with epihalohydrin, as well as 3,4-epoxy-6-methylcyclohexylmethyl-3,4-epoxy-6-methylcyclohexanecarboxylate, 1-epoxyethyl-3,4-epoxycyclohexane, etc.

Examples of the glycidylamine type epoxy resin include N,N-diglycidylaniline, triglycidylaminophenol, tetraglycidylxylenediamine, 4,4'-methylenebis[N,N-diglycidylaniline], etc.

Examples of the heterocyclic epoxy resin include 1,3-diglycidyl-5,5-dimethylhydantoin and triglycidyl isocyanurate.

Examples of the glycidyl ester type epoxy resin include diglycidyl ester of phthalic acid, diglycidyl ester of tetrahydrophthalic acid, diglycidyl-p-oxybenzoic acid, and glycidyl ester of dimer acid.

Examples of extenders for epoxy resins include the various biphenol compounds and their hydrogenated products, the various bisphenol compounds and their hydrogenated products, dibasic acid compounds, and acid group-containing polyester resins.

Among these, the bisphenol type epoxy resin is preferred because it has excellent strength of the cured product and fiber impregnation when used in a fiber-reinforced composite material, and a bisphenol type epoxy resin having an epoxy equivalent in the range of 160 to 260 g/equivalent is more preferred. The proportion of the bisphenol type epoxy resin in the entire epoxy group-containing compound (A) is preferably 40 mass% or more, more preferably 60 mass% or more, and particularly preferably 70 mass% or more. Furthermore, it is preferably 95 mass% or less, and more preferably 90 mass% or less.

Furthermore, in terms of being more excellent in fiber impregnation when used in fiber-reinforced composite materials, the polyglycidyl ether of the aliphatic polyol is preferred, and the polyglycidyl ether of an aliphatic polyol having 2 to 6 carbon atoms is more preferred. The proportion of the bisphenol-type epoxy resin in the entire epoxy group-containing compound (A) is preferably 5% by mass or more, and more preferably 10% by mass or more. Furthermore, it is preferably 50% by mass or less, and more preferably 35% by mass or less.

When the bisphenol-type epoxy resin and the polyglycidyl ether of the aliphatic polyol are used in combination, the mass ratio of the two (bisphenol-type epoxy resin)/(polyglycidyl ether of the aliphatic polyol) is preferably in the range of 60/40 to 95/5, and more preferably in the range of 70/30 to 85/15.

The curing agent or curing accelerator (B) for epoxy group-containing compounds may be any of various compounds that are generally used as curing agents or curing accelerators for epoxy group-containing compounds, without any particular restrictions. The curing agent or curing accelerator may be used alone or in combination of two or more types.

Examples of the curing agent or curing accelerator (B) include amine compounds, amide compounds, acid anhydrides, phenolic hydroxyl group-containing compounds, phosphorus compounds, imidazole compounds, imidazoline compounds, urea compounds, organic acid metal salts, Lewis acids, and amine complex salts.

The amine compounds include, for example, aliphatic amine compounds such as ethylenediamine, tetramethylethylenediamine, diethylenetriamine, hexamethylenediamine, triethylenetetramine, and guanidine derivatives; alicyclic and heterocyclic amine compounds such as piperidine, piperazine, isophoronediamine, and 1,8-diazabicyclo-[5.4.0]-undecene (DBU); aromatic amine compounds such as phenylenediamine, diaminodiphenylmethane, diaminodiphenylsulfone, benzylmethylamine, dimethylbenzylamine, xylylenediamine, and pyridine; and boron trifluoride amine complexes.

Examples of the amide compound include dicyandiamide and polyamidoamine. Examples of the polyamidoamine include those obtained by reacting an aliphatic dicarboxylic acid such as succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, or azelaic acid, or a carboxylic acid compound such as a fatty acid or dimer acid, with an aliphatic polyamine or a polyamine having a polyoxyalkylene chain.

Examples of the acid anhydride include phthalic anhydride, trimellitic anhydride, pyromellitic anhydride, maleic anhydride, tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylnadic anhydride, hexahydrophthalic anhydride, and methylhexahydrophthalic anhydride.

Examples of the phenolic hydroxyl group-containing resin include various novolak resins, dicyclopentadiene-phenol addition type resins, phenol or naphthol aralkyl resins, triphenolmethane resins, phenol or naphthol aralkyl resins, phenylene or naphthylene ether resins, and aminotriazine-modified phenolic resins.

Examples of the phosphorus compound include alkyl phosphines such as ethylphosphine and butylphosphine, primary phosphines such as phenylphosphine, dialkyl phosphines such as dimethylphosphine and dipropylphosphine, secondary phosphines such as diphenylphosphine and methylethylphosphine, and tertiary phosphines such as trimethylphosphine, triethylphosphine, and triphenylphosphine.

The imidazole compound is, for example, imidazole, 1-methylimidazole, 2-methylimidazole, 3-methylimidazole, 4-methylimidazole, 5-methylimidazole, 1-ethylimidazole, 2-ethylimidazole, 3-ethylimidazole, 4-ethylimidazole, 5-ethylimidazole, 1-n-propylimidazole, 2-n-propylimidazole, 1-isopropylimidazole, 2- Isopropylimidazole, 1-n-butylimidazole, 2-n-butylimidazole, 1-isobutylimidazole, 2-isobutylimidazole, 2-undecyl-1H-imidazole, 2-heptadecyl-1H-imidazole, 1,2-dimethylimidazole, 1,3-dimethylimidazole, 2,4-dimethylimidazole, 2-ethyl-4-methylimidazole, 1-phenylimidazole, 2-phenyl-1H-imidazole Imidazole, 4-methyl-2-phenyl-1H-imidazole, 2-phenyl-4-methylimidazole, 1-benzyl-2-methylimidazole, 1-benzyl-2-phenylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-phenylimidazole, 2-phenylimidazole Examples include socyanuric acid adduct, 2-methylimidazole isocyanuric acid adduct, 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, 1-cyanoethyl-2-phenyl-4,5-di(2-cyanoethoxy)methylimidazole, 1-dodecyl-2-methyl-3-benzylimidazolium chloride, and 1-benzyl-2-phenylimidazole hydrochloride.

Examples of the imidazoline compound include 2-methylimidazoline and 2-phenylimidazoline.

Examples of the urea compound include p-chlorophenyl-N,N-dimethylurea, 3-phenyl-1,1-dimethylurea, 3-(3,4-dichlorophenyl)-N,N-dimethylurea, N-(3-chloro-4-methylphenyl)-N',N'-dimethylurea, and 4,4'-methylenebisphenyldimethylurea.

Among these, amine compounds, amide compounds, imidazole compounds, and urea compounds are preferred because they cure quickly and produce cured products with excellent strength.

When using a compound having a functional group capable of reacting with an epoxy group, such as an amine compound, an amide compound, an acid anhydride, or a phenolic hydroxyl group-containing compound, the amount of the curing agent or curing accelerator in the epoxy resin composition is preferably in a ratio of 0.5 to 1.2 moles of functional groups or active hydrogen in the curing agent per mole of epoxy group in the epoxy group-containing compound (A). When using a phosphorus compound, an imidazole compound, an imidazoline compound, a urea-based compound, or the like, it is preferably in a ratio of 0.5 to 20 parts by mass per 100 parts by mass of the epoxy group-containing compound (A).

The polyhydroxy compound (C) (excluding those corresponding to component (A)) has as an essential component a polyhydroxy compound (C1) having a hydroxyl group equivalent in the range of 125 to 600 g/equivalent, and 70% by mass or more of the polyhydroxy compound (C) is the polyhydroxy compound (C1). By satisfying these conditions, a curable composition is obtained which is excellent not only in strength of the cured product, but also in fiber impregnation when used in a fiber-reinforced composite material, film peelability when used as a sheet molding compound, and surface smoothness of molded products. Furthermore, the proportion of the polyhydroxy compound (C1) in the polyhydroxy compound (C) is preferably 80% by mass or more, and more preferably 90% by mass or more.

The polyhydroxy compound (C1) has a plurality of hydroxyl groups in its molecular structure and a wide variety of compounds can be used as long as the hydroxyl group equivalent is in the range of 125 to 600 g/equivalent. The polyhydroxy compound (C) may be the polyhydroxy compound (C1) used alone or in combination with other compounds to use two or more compounds. In the present invention, polyhydroxy compounds having epoxy groups are treated as the epoxy group-containing compound (A).

Examples of the polyhydroxy compound (C) include aliphatic polyol compounds, dihydroxybenzenes, dihydroxynaphthalenes, trihydroxybenzenes, trihydroxynaphthalenes, triphenol alkanes, biphenol compounds, bisphenol compounds, alicyclic polyol compounds, novolac resins, phenol or naphthol aralkyl resins, phenylene or naphthylene ether resins, and alkylene oxide adducts thereof.

The aliphatic polyol compound may be, for example, ethylene glycol, propylene glycol, 1,3-propanediol, 2-methylpropanediol, 1,2,2-trimethyl-1,3-propanediol, 2,2-dimethyl-3-isopropyl-1,3-propanediol, 1,4-butanediol, 1,3-butanediol, 3-methyl-1,3-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, neopentyl glycol, Examples include aliphatic diol compounds such as 1,6-hexanediol, 1,4-bis(hydroxymethyl)cyclohexane, and 2,2,4-trimethyl-1,3-pentanediol; alicyclic diol compounds such as 2,2-bis(4-hydroxyphenyl)propane; and aliphatic polyol compounds with three or more functional groups such as trimethylolethane, trimethylolpropane, glycerin, hexanetriol, pentaerythritol, ditrimethylolpropane, and dipentaerythritol.

Examples of the biphenol compound include biphenol, tetramethylbiphenol, etc.

Examples of the bisphenol compounds include bisphenol A, bisphenol F, bisphenol S, bisphenol fluorene, and biscresol fluorene.

Examples of alicyclic polyol compounds include cyclohexanediol and hydrogenated biphenol compounds and bisphenol compounds.

The novolac type resin may be, for example, a novolac resin made of one or more of various phenolic compounds, such as phenol, dihydroxybenzene, cresol, xylenol, naphthol, dihydroxynaphthalene, bisphenol, and biphenol.

Among these, the polyhydroxy compound (C1) having a hydroxyl group equivalent in the range of 125 to 600 g/equivalent is preferably an alkylene oxide adduct of various polyhydroxy compounds, in order to provide a curable composition having excellent strength of the cured product, film peelability when used in a sheet molding compound, and surface smoothness of the molded product, i.e., a compound having a (poly)alkylene oxide structure in its molecular structure is preferred. Furthermore, an alkylene oxide adduct of the aliphatic polyol compound or the bisphenol compound is more preferred, and the aliphatic polyol compound is more preferably one having 2 to 6 carbon atoms. Also, the hydroxyl group equivalent is more preferably in the range of 150 to 400 g/equivalent.

The polyisocyanate compound (D) may have a wide variety of isocyanate groups in its molecular structure, without any particular restrictions on its specific structure. The polyisocyanate compound (D) may be used alone or in combination of two or more types. Specific examples include aliphatic diisocyanate compounds such as butane diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, and dimer acid diisocyanate; alicyclic diisocyanate compounds such as norbornane diisocyanate, isophorone diisocyanate, hydrogenated xylylene diisocyanate, and hydrogenated diphenylmethane diisocyanate; toluene diisocyanate, xylylene diisocyanate. , aromatic diisocyanate compounds such as tetramethylxylylene diisocyanate, tolidine diisocyanate, diphenylmethane diisocyanate, 1,5-naphthalene diisocyanate, and polymethylene polyphenyl polyisocyanate; modified products of these isocyanate compounds, such as isocyanurate modified products, biuret modified products, allophanate modified products, carbodiimide modified products, and urethane imine modified products, as well as polyol modified products modified with a polyol having a number average molecular weight of 1,000 or less, such as diethylene glycol or dipropylene glycol.

Among these, aromatic polyisocyanate compounds or various modified products thereof are preferred, since they produce sheet molding compounds that are less sticky and have good film peelability. Furthermore, the isocyanate group content is preferably 15% by mass or more, and more preferably 20% by mass or more. It is also preferred that the isocyanate group content is 40% by mass or less.

In the present invention, the blending ratio of the polyhydroxy compound (C) (excluding those corresponding to component (A)) and the polyisocyanate compound (D) is arbitrary and is appropriately adjusted according to the desired performance and intended use of the curable composition.

A preferred formulation design for the curable composition of the present invention is that it produces a sheet molding compound with little stickiness and good film peelability, and furthermore, it produces a molded product with excellent surface smoothness. Therefore, the number of moles of isocyanate groups in the polyisocyanate compound (D) per mole of hydroxyl groups in the polyhydroxy compound (C) is preferably 0.5 or more, more preferably 0.8 or more. It is also preferably 3.0 or less, more preferably 1.5 or less, and particularly preferably 1.2 or less.

The amount of the polyhydroxy compound (C) is preferably 5 parts by mass or more, and more preferably 10 parts by mass or more, per 100 parts by mass of the epoxy group-containing compound (A), because this results in a curable composition that is excellent in strength of the cured product, film peelability when used in a sheet molding compound, and surface smoothness of the molded product. The amount of the polyhydroxy compound (C) is preferably 5 parts by mass or more, and more preferably 10 parts by mass or more, per 100 parts by mass of the epoxy group-containing compound (A). The amount is preferably 50 parts by mass or less, and more preferably 30 parts by mass or less.

The curable composition of the present invention may contain a urethanization catalyst as necessary. The urethanization catalyst may be used alone or in combination of two or more types. Examples of the urethanization catalyst include amine compounds such as triethylamine, dibutylamine, triethylenediamine, and pyridine; phosphorus compounds such as triphenylphosphine and triethylphosphine; organic tin compounds such as dibutyltin dilaurate, octyltin trilaurate, octyltin diacetate, dibutyltin diacetate, and tin octylate; organic zinc compounds such as zinc amine, zinc carboxylate, zinc stearate, and zinc octylate; organic bismuth compounds such as bismuth carboxylate; organic zirconium compounds such as zirconium acetylacetonate and zirconium tetraethanolate; organic aluminum compounds such as aluminum triethoxide; and organic titanium compounds such as titanium tetrabutylate and titanium ethylacetoacetate. Among these, organic zinc compounds and organic bismuth compounds are preferred because of their superior safety to living organisms and storage stability.

When the urethane catalyst is used, the amount added is preferably in the range of 0.002 to 1 mass% relative to the total mass of the epoxy group-containing compound (A), the curing agent or curing accelerator for the epoxy group-containing compound (B), the polyhydroxy compound (C), and the polyisocyanate compound (D), and is preferably added in an amount of 0.01 to 0.8 mass% or more.

In addition, a water absorbing agent may be added for the purpose of controlling the urethane reaction in the curable composition. The water absorbing agent may be used alone or in combination of two or more types. Examples of water absorbing agents include silica gel, activated alumina, and molecular sieves. Among these, molecular sieves are preferred because of their excellent water absorption efficiency. The pore size is preferably in the range of 0.1 to 0.5 nm, and more preferably in the range of 0.2 to 0.4 nm. The particle size is preferably 50 um or less, and more preferably 10 um or less. When the water absorbing agent is used, the amount of the water absorbing agent added is preferably in the range of 0.1 to 5 mass% based on the total mass of the epoxy group-containing compound (A), the curing agent or curing accelerator for the epoxy group-containing compound (B), the polyhydroxy compound (C), and the polyisocyanate compound (D).

The curable composition of the present invention may contain other components other than the epoxy group-containing compound (A), the curing agent or curing accelerator for the epoxy group-containing compound (B), the polyhydroxy compound (C), the polyisocyanate compound (D), the urethane catalyst, and the water absorbent. Examples of other components include thermosetting resins, thermoplastic resins, inorganic fillers, low shrinkage agents, release agents, thickeners, viscosity reducers, pigments, antioxidants, plasticizers, flame retardants, antibacterial agents, UV stabilizers, reinforcing materials, etc. other than the components (A) to (D). These other components are added appropriately depending on the desired performance and use of the curable composition, and the amount of addition is also arbitrary. Among them, the effect of the present invention is more significantly exhibited, so that the total mass of the epoxy group-containing compound (A), the curing agent or curing accelerator for the epoxy group-containing compound (B), the polyhydroxy compound (C), and the polyisocyanate compound (D) in the curable composition is preferably 80 mass% or more, and particularly preferably 90 mass% or more.

The curable composition of the present invention has excellent fiber impregnation properties when used in fiber-reinforced composite materials, so the viscosity at 25°C is preferably 100 mPa·s or more, and more preferably 300 mPa·s or more. It is also preferably 10,000 mPa·s or less, and more preferably 6,000 mPa·s or less. In the present invention, the viscosity of the curable composition is measured within 10 minutes after all the ingredients of the curable composition are mixed.

The curable composition of the present invention is useful as a curable resin material, and the cured product is characterized by excellent heat resistance and strength. It can also be combined with reinforcing fibers to form a fiber-reinforced composite material, and is particularly useful as a matrix resin for sheet molding compounds.

The reinforcing fibers used in the present invention may be, for example, those generally used in sheet molding compound applications, and a wide variety of fibers may be used without particular restrictions. Specific examples include glass fibers, carbon fibers, silicon carbide fibers, pulp, hemp, cotton, nylon, polyester, acrylic, polyurethane, polyimide, and polyamide fibers made of aramids such as Kevlar (registered trademark) and Nomex. Of these, carbon fibers are preferred because they provide excellent strength and lightweight molded products. Various types of carbon fibers, such as polyacrylonitrile, pitch, and rayon, can be used, and polyacrylonitrile-based fibers are more preferred because of their particularly high strength.

The carbon fibers are usually cut to a length of 2.5 to 50 mm, but carbon fibers cut to a length of 5 to 40 mm are more preferable because this improves the flowability within the mold during molding, and the strength and surface smoothness of the molded product.

The number of filaments in the carbon fiber bundle is preferably in the range of 1,000 to 60,000, and more preferably in the range of 5,000 to 30,000, as this improves the impregnation of the curable composition and the strength of the molded product.

The reinforcing fiber content in fiber-reinforced composite materials can be set as desired depending on the desired properties of the molded product and the application, but to produce a molded product with superior strength, it is preferably in the range of 20 to 80 mass%, and more preferably in the range of 40 to 70 mass%.

The method for producing the sheet molding compound of the present invention is not particularly limited, and it can be produced by a general method. Specifically, it can be produced by a method including some or all of the following steps: uniformly mixing the curable composition using a mixer such as a mixer, roll mill, kneader, extruder, etc.; applying the curable composition to a carrier film in a uniform thickness; scattering the reinforcing fibers on the resin surface of the obtained carrier film with resin; sandwiching the reinforcing fibers with the resin surface of another carrier film with resin; applying pressure with an impregnation roll or impregnation belt to impregnate the reinforcing fibers with the curable composition; winding up the sheet obtained by the impregnation step into a roll or folding it zigzag; and maturing at room temperature or at a temperature of 20 to 60°C. The carrier film can be a general one such as a polyethylene film, a polypropylene film, a polyethylene terephthalate film, a nylon, or a laminate of multiple films.

The thickness of the sheet molding compound of the present invention can be set appropriately depending on the desired performance and application, but in order to achieve excellent moldability and strength in the cured product, it is preferably 1 mm or more, more preferably 1.2 mm or more, and particularly preferably 1.5 mm or more. It is also preferably 10 mm or less, more preferably 5 mm or less, and particularly preferably 4 mm or less.

The method for obtaining a molded product from the sheet molding compound of the present invention is not particularly limited, and it can be molded by the same method as that for a general sheet molding compound. One example is hot compression molding, which can be produced by a method including some or all of the following steps: peeling the carrier film from a sheet molding compound having a carrier film on both sides, stacking one or more sheets of the sheet molding compound from which the carrier film has been peeled off, placing the sheet molding compound in a mold, and molding with a compression molding machine. As mentioned above, the sheet molding compound of the present invention has little stickiness and excellent film peelability, so that molded products can be obtained efficiently. The temperature of the mold can be set freely, but it is preferably in the range of 110 to 180°C, and it is preferable to heat it to the same temperature in advance. The molding pressure of the compression molding machine can be set freely, but it is preferably in the range of 0.1 to 30 MPa. The molding time can be set freely, but it is preferable to clamp the mold to impart the shape and cure the curable composition over a period of several tens of seconds to several minutes.

The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

Examples 1 to 5 and Comparative Examples 1 and 2
Curable compositions, sheet molding compounds and molded articles were produced as follows, and various evaluation tests were carried out. The blending compositions of the curable compositions and the various evaluation results are shown in Tables 1 and 2.

Preparation of Curable Composition Curable compositions were obtained by mixing the components in the ratios shown in Tables 1 and 2 below. Details of each component in the tables are as follows.
Epoxy group-containing compound (A1): bisphenol A type epoxy resin, "Epicron 840" manufactured by DIC Corporation, epoxy equivalent 180 g/equivalent, viscosity 10,000 mPa·s (25° C.)
Epoxy group-containing compound (A2): 1,4-butanediol diglycidyl ether, "XY-622" manufactured by ANHUI XINYUAN Chemical Co., Ltd., epoxy equivalent: 115 g/equivalent, viscosity: 14.9 mPa·s (25° C.)
Epoxy group-containing compound (A3): glycerol polyglycidyl ether, "Denacol EX-313" manufactured by Nagase ChemteX Corporation, epoxy equivalent 141 g/equivalent, viscosity 150 mPa·s (25° C.)
Curing agent or curing accelerator for epoxy group-containing compounds (B1): Dicyandiamide, "DICY7" manufactured by Mitsubishi Chemical Corporation
Curing agent or curing accelerator for epoxy group-containing compounds (B2): Alkyl urea-based curing accelerator, "B-605-IM" manufactured by DIC Corporation
Polyhydroxy compound (C1-1): Ethylene oxide adduct of bisphenol A, "Newpol BPE-40" manufactured by Sanyo Chemical Industries, Ltd., hydroxyl value 276 mg KOH/g, hydroxyl equivalent calculated from hydroxyl value 203 g/equivalent, viscosity 278 mPa·s (60°C)
Polyhydroxy compound (C1-2): propylene oxide adduct of glycerol, Sannix GP-600 manufactured by Sanyo Chemical Industries, Ltd., hydroxyl value 280 mg KOH/g, hydroxyl equivalent calculated from the hydroxyl value 200 g/equivalent, viscosity 275 mPa·s (25°C)
Polyisocyanate compound (D): A mixture of partially modified diphenylmethane diisocyanate (including, in addition to diphenylmethane diisocyanate, a carbodiimide modified product represented by the following structural formula), "Cosmonate LL" manufactured by Mitsui Chemicals SKC Polyurethanes, with an isocyanate group content of 29% by mass and a viscosity of 20 to 60 mPa·s (25°C, catalog value).

Urethane catalyst: zinc amine catalyst, KING INDUSTRIES "K-KAT XK-614"
Water absorbent: Molecular sieve, "Molecular sieve 4A powder" manufactured by Union Showa Co., Ltd.

Measurement of Viscosity of Curable Composition The viscosity of each curable composition at 25° C. was measured using a digital viscometer (VISCO (registered trademark) manufactured by Atago Co., Ltd.) The viscosity measurement was performed within 10 minutes after the preparation of the curable composition.

Manufacture of sheet molding compound The curable composition obtained above was applied onto a polypropylene film so that the average application amount was 0.5 kg/m ^2. Carbon fiber roving ("T700SC-12000-50C" manufactured by Toray Industries, Inc., filament number 12,000) cut to 12.5 mm was sprayed from the air onto the surface coated with the curable composition so that there was no fiber directionality and the thickness of the sheet molding compound obtained was uniform. The amount of carbon fiber sprayed was adjusted so that the carbon fiber content of the sheet molding compound obtained was 50% by mass. Another polypropylene film with the same curable composition as above was prepared, and carbon fiber was sandwiched between the surface coated with the curable composition. This was pressed with a roller to impregnate the carbon fiber with the curable composition, and then left to stand under a temperature condition of 40 ° C. for 72 hours to obtain a sheet molding compound with a thickness of 2 mm. The basis weight of the sheet molding compound was 2 kg/m ² .

Evaluation of Film Removability The polypropylene film was peeled off from the obtained sheet molding compound under a temperature condition of 25° C. The state at the time of peeling was visually confirmed and evaluated according to the following criteria.
In addition, the mass per unit area (mg/m ² ) of the deposits was calculated.
A: Easy to peel off, no residue left on the polypropylene film B: Some residue left on the polypropylene film, but peeling was possible C: Difficult to peel off, large amount of residue left on the film

Two sheets of the sheet molding compound obtained above were cut to 260 mm x 260 mm and stacked and set in the center of a flat mold of 30 x ³⁰ cm2. The mold was molded under the conditions of a mold temperature of 150 °C, a press time of 3 minutes, and a press pressure of 12 MPa to obtain a flat molded product with a thickness of 2 mm.

Evaluation of bending strength and bending modulus of molded product Eight evaluation samples of 150 mm x 25 mm were cut out from the molded product obtained above. Four of the eight samples had the long side in the X-axis direction of the molded product, and the remaining four had the long side in the Y-axis direction of the molded product. A three-point bending test was performed in accordance with JIS K7074 to measure the bending strength and bending modulus. The values were the average values of a total of eight samples.
(Evaluation Criteria for Bending Strength)
A: 300 MPa or more B: less than 300 MPa (evaluation criteria for bending modulus)
A: 20 GPa or more B: less than 20 GPa

Evaluation of Surface Smoothness of Molded Articles The amount of bubbles on the surface of the molded article obtained above was visually counted.

Claims (11)

A curable composition containing an epoxy group-containing compound (A), a curing agent or curing accelerator for an epoxy group-containing compound (B), a polyhydroxy compound (C) (excluding those corresponding to component (A)), and a polyisocyanate compound (D), characterized in that 70% by mass or more of the polyhydroxy compound (C) is a polyhydroxy compound (C1) having a hydroxyl group equivalent in the range of 125 to 600 g/equivalent. The curable composition according to claim 1, wherein the number of moles of isocyanate groups in the polyisocyanate compound (D) per mole of hydroxyl groups in the polyhydroxy compound (C) is in the range of 0.5 to 3.0. The curable composition according to claim 1, wherein the epoxy group-containing compound (A) contains a bisphenol-type epoxy resin having an epoxy equivalent in the range of 160 to 260 g/equivalent. The curable composition according to claim 1, wherein the epoxy group-containing compound (A) contains a polyglycidyl ether of an aliphatic polyol having 2 to 6 carbon atoms. The curable composition according to claim 1, wherein the epoxy group-containing compound (A) contains a bisphenol-type epoxy resin and a polyglycidyl ether of an aliphatic polyol, and the mass ratio of the two (bisphenol-type epoxy resin)/(polyglycidyl ether of an aliphatic polyol) is in the range of 60/40 to 95/5. A fiber-reinforced composite material containing the curable composition according to any one of claims 1 to 5 and reinforcing fibers. The fiber-reinforced composite material according to claim 6, wherein the reinforcing fibers are carbon fibers. The fiber-reinforced composite material according to claim 6, which is a sheet molding compound. The sheet molding compound of claim 8, which has a carrier film on both sides. A molded product made of the fiber-reinforced composite material according to claim 6. A method for manufacturing a molded product comprising the steps of peeling a carrier film from a sheet molding compound having carrier films on both sides, and molding the sheet molding compound from which the carrier film has been peeled off.