Liquid composition for intermediate base material

Abstract

To provide a liquid composition for an intermediate base material capable of obtaining a fiber-reinforced plastic having especially superior weather resistance and also having excellent heat resistance, good appearance, and mechanical properties.SOLUTION: A liquid composition for an intermediate base material containing isophorone diisocyanate (A1), a polyfunctional isocyanate (A2) having an isocyanurate ring formed by trimerization of a difunctional isocyanate compound, and 2-hydroxyethyl (meth)acrylate (B), wherein the polyfunctional isocyanate (A2) does not have an aromatic ring structure.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a liquid composition for an intermediate substrate. [Background technology]

[0002] Fiber reinforced plastics (FRP) are lightweight and strong, and are used in a variety of structural components. These applications span a wide range of fields, including housing, automobiles, ships, civil engineering, and sports equipment, but in recent years, the use of FRP has been increasing, particularly in the automobile and transportation-related equipment fields, where weight reduction is essential.

[0003] Resin and fibers are used in the manufacture of FRP, and there are two methods for molding: one is to use liquid resin, and the other is to use an intermediate base material (such as SMC (Sheet Molding Compound), prepreg, etc.) in which resin has been impregnated into fibers and made semi-hardened. Methods of molding using intermediate substrates include autoclave molding, sheet winding molding, oven molding, press molding, etc. These molding methods involve cutting the intermediate substrate, laminating it to the desired thickness, and applying heat to harden it.

[0004] The intermediate substrate can be produced by a solvent method in which a resin composition and a solvent are mixed, the mixture is impregnated into a fiber substrate, and the solvent is then dried and removed to obtain the intermediate substrate; or by a hot melt method in which the viscosity of the resin composition is reduced by heating to produce a film of the resin composition, which is then attached to the top and bottom of a fiber substrate in which continuous fibers are aligned in one direction, and the resin composition is impregnated into the fiber substrate by heating and pressurizing to obtain the intermediate substrate.

[0005] The matrix resin of the intermediate substrate is a resin composition containing a thermosetting resin, which has excellent impregnation properties for reinforcing fibers and heat resistance after curing. Examples of thermosetting resins that can be used include unsaturated polyester resin, vinyl ester resin, epoxy resin, phenolic resin, melamine resin, and bismaleimide resin.

[0006] For example, Patent Document 1 discloses a liquid composition for fiber-reinforced plastic intermediate substrates, which is intended to suppress voids and improve mechanical properties and heat resistance, and which is characterized by containing a composition containing a compound having two or more isocyanate groups, and a composition containing a vinyl ester resin and an ethylenically unsaturated group-containing monoalcohol compound. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2023-070793 Summary of the Invention [Problem to be solved by the invention]

[0008] Conventional methods for manufacturing intermediate substrates using solvents have the problem that the remaining solvent evaporates during molding, causing voids and pinholes in the fiber-reinforced composite material and deteriorating the appearance. Increasing the drying temperature to remove the solvent causes the intermediate substrate to cure excessively, adversely affecting the mechanical properties and heat resistance of the resulting fiber-reinforced plastic. Hot-melt methods, which do not use solvents, cannot fully impregnate some types of fibers, again resulting in poor appearance and mechanical properties. Furthermore, using intermediate substrates containing vinyl ester resins or epoxy resins with a bisphenol skeleton has the problem of poor weather resistance of the resulting cured product. Therefore, an object of the present invention is to provide a liquid composition for intermediate substrates that can give fiber-reinforced plastics that are particularly excellent in weather resistance, heat resistance, appearance, and mechanical properties. [Means for solving the problem]

[0009] The present inventors have found that a liquid composition for intermediate substrates containing two types of isocyanate compounds, hydroxyethyl (meth)acrylate, and a specific polymerizable monomer can solve the above problems. That is, the present invention relates to the following. [1] A liquid composition for intermediate substrates, comprising isophorone diisocyanate (A1), a polyfunctional isocyanate (A2) having an isocyanurate ring formed by trimerizing a bifunctional isocyanate compound, and 2-hydroxyethyl (meth)acrylate (B), wherein the polyfunctional isocyanate (A2) does not have an aromatic ring structure. [2] The liquid composition for intermediate substrates according to the above [1], further comprising a polymerizable monomer (C) that does not contain an isocyanate-reactive group and does not have an aromatic ring structure. [3] The liquid composition for intermediate substrates according to [2] above, wherein the polymerizable monomer (C) is at least one selected from the group consisting of mono- or more functional aliphatic (meth)acrylates, mono- or more functional alicyclic (meth)acrylates, and mono- or more functional polyalkylene glycol (meth)acrylates. [4] The liquid composition for intermediate substrates according to any one of the above [1] to [3], wherein the bifunctional isocyanate compound is at least one selected from the group consisting of aliphatic isocyanate compounds and alicyclic isocyanate compounds. [5] The liquid composition for intermediate substrates according to any one of the above [2] to [4], wherein the polymerizable monomer (C) is at least one selected from the group consisting of alkylene glycol di(meth)acrylates and polyalkylene glycol di(meth)acrylates. [6] The liquid composition for intermediate substrates according to any one of the above [1] to [5], wherein the mass ratio [(A1) / (A2)] of isophorone diisocyanate (A1) to polyfunctional isocyanate (A2) having an isocyanurate ring obtained by trimerizing a bifunctional isocyanate compound is 3 / 7 to 7 / 3. [7] The liquid composition for an intermediate substrate according to any one of the above [2] to [6], wherein the content of the polymerizable monomer (C) in the liquid composition for an intermediate substrate is 0.1 to 10 mass %. [8] The liquid composition for an intermediate substrate according to any one of the above [1] to [7], which has a viscosity at 25°C of 5 to 200 mPa·s. [9] A fiber-reinforced plastic intermediate substrate obtained by impregnating a fiber material with the liquid composition for intermediate substrates according to any one of the above [1] to [8].

[10] A method for producing a fiber-reinforced plastic intermediate substrate, comprising a step of impregnating a fiber material with the liquid composition for intermediate substrate according to any one of the above [1] to [8], and a maturing step.

[11] The method for producing a fiber-reinforced plastic intermediate substrate according to

[10] above, wherein the aging temperature is 30 to 80°C.

[12] A fiber-reinforced composite material obtained by curing the fiber-reinforced plastic intermediate substrate described in [9] above. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a liquid composition for intermediate substrates that can give fiber-reinforced plastics that are particularly excellent in weather resistance, heat resistance, appearance, and mechanical properties. DETAILED DESCRIPTION OF THE INVENTION

[0011] [Liquid composition for intermediate substrate] The liquid composition for intermediate base materials of the present invention contains isophorone diisocyanate (A1), a polyfunctional isocyanate (A2) having an isocyanurate ring obtained by trimerizing a bifunctional isocyanate compound, and 2-hydroxyethyl (meth)acrylate (B), wherein the polyfunctional isocyanate (A2) does not have an aromatic ring structure. The liquid composition for intermediate substrates of the present invention can be suitably used as a raw material for fiber-reinforced plastics, and can provide fiber-reinforced plastics that are particularly excellent in weather resistance, heat resistance, appearance, and mechanical properties.

[0012] The reason why the liquid composition for intermediate substrates of the present invention, having the above-described configuration, can produce fiber-reinforced plastics that are particularly excellent in weather resistance, heat resistance, appearance, and mechanical properties is not clear, but is thought to be as follows. Since the blended components do not have an aromatic ring structure, it is believed that the resulting fiber-reinforced plastic has excellent weather resistance. It is believed that the resulting fiber reinforced plastic has excellent heat resistance because the skeleton of the polyfunctional isocyanate having an isocyanurate ring is rigid. Furthermore, the large molecular weight of the polyfunctional isocyanate results in a large acrylic equivalent of the urethane (meth)acrylate, which is thought to reduce shrinkage during curing and improve the impregnation of the liquid composition into the substrate, resulting in the excellent appearance of the resulting fiber-reinforced plastic. Furthermore, since the composition has a polyfunctional isocyanate skeleton having an isocyanurate ring, toughness is increased and the composition has good impregnation properties into substrates, so the resulting fiber-reinforced plastic is thought to have excellent mechanical properties. Furthermore, in conventional technology, a thermosetting resin is formed and then impregnated into fibers or the like as a composition for intermediate substrates. However, when the liquid composition for intermediate substrates of the present invention is used, a urethane (meth)acrylate is formed after impregnating the fibers through aging. This is thought to enable a stronger bond between the liquid composition for intermediate substrates and the fibers. Thus, fiber-reinforced plastics obtained using the liquid composition for intermediate substrates of the present invention are thought to be excellent in all of weather resistance, heat resistance, appearance, and mechanical properties.

[0013] <Isophorone diisocyanate (A1) and polyfunctional isocyanate (A2)> The liquid composition for intermediate substrates of the present invention contains, as compounds having an isocyanate group, isophorone diisocyanate (A1) and a polyfunctional isocyanate (A2) having an isocyanurate ring formed by trimerization of a bifunctional isocyanate compound, and the polyfunctional isocyanate (A2) does not have an aromatic ring structure. By using these two types of compounds having an isocyanate group, the resulting fiber reinforced plastic has excellent weather resistance, and in addition, it also has excellent heat resistance, appearance, and mechanical properties. The "polyfunctional isocyanate (A2) having an isocyanurate ring obtained by trimerizing a bifunctional isocyanate compound" is also simply referred to as "polyfunctional isocyanate (A2)".

[0014] The bifunctional isocyanate compound constituting the polyfunctional isocyanate (A2) having an isocyanurate ring formed by trimerizing a bifunctional isocyanate compound is preferably a bifunctional isocyanate compound not having an aromatic ring structure, more preferably at least one bifunctional isocyanate compound selected from the group consisting of aliphatic isocyanate compounds and alicyclic isocyanate compounds, and even more preferably an alicyclic isocyanate compound. That is, the polyfunctional isocyanate (A2) having an isocyanurate ring formed by trimerizing a bifunctional isocyanate compound is preferably a polyfunctional isocyanate having an isocyanurate ring formed by trimerizing an alicyclic isocyanate compound. By using an alicyclic isocyanate compound, the obtained fiber reinforced plastic has particularly excellent weather resistance, and in addition, it also has excellent heat resistance, appearance, and mechanical properties.

[0015] Examples of the alicyclic isocyanate compound include hydrogenated xylylene diisocyanate (1,3-bis(isocyanatomethyl)cyclohexane), isophorone diisocyanate, norbornene diisocyanate, dicyclohexylmethane diisocyanate, hydrogenated methylene bisphenylene diisocyanate, and 1,4-cyclohexane diisocyanate. Examples of the aliphatic isocyanate compound include 1,6-hexamethylene diisocyanate, trimethylene diisocyanate, etc. These isocyanate compounds can be used alone or in combination of two or more.

[0016] Among the bifunctional isocyanate compounds, at least one selected from the group consisting of 1,6-hexamethylene diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, and isophorone diisocyanate is preferred, at least one selected from the group consisting of 1,6-hexamethylene diisocyanate and isophorone diisocyanate is more preferred, and isophorone diisocyanate is even more preferred. That is, the polyfunctional isocyanate (A2) having an isocyanurate ring formed by trimerizing a bifunctional isocyanate compound is preferably a polyfunctional isocyanate having an isocyanurate ring formed by trimerizing isophorone diisocyanate. By using isophorone diisocyanate, the resulting fiber-reinforced plastic will have particularly excellent weather resistance, and will also have excellent heat resistance, appearance, and mechanical properties.

[0017] The polyfunctional isocyanate (A2) has an isocyanurate ring, which is formed by trimerization of a bifunctional isocyanate compound. The number (integer) of isocyanurate rings in the polyfunctional isocyanate (A2) is preferably 1 to 10, more preferably 1 to 5, even more preferably 1 to 3, still more preferably 1 or 2, and even more preferably 1. The polyfunctional isocyanate (A2) may be a mixture of those having 1 to 10 isocyanurate rings, and in the case of a mixture, it is preferable that the mixture contains a large number of molecules with fewer isocyanurate rings.

[0018] The polyfunctional isocyanate (A2) is formed by polymerizing a bifunctional isocyanate compound, and three bifunctional isocyanate compounds constitute an isocyanurate ring. The number (integer) of structural units derived from the bifunctional isocyanate compounds in the polyfunctional isocyanate (A2) is preferably 3 to 21, more preferably 3 to 11, even more preferably 3 to 7, still more preferably 3 to 5, and still more preferably 3. When the number of isocyanurate rings in the polyfunctional isocyanate (A2) and the number of structural units derived from a bifunctional isocyanate compound are within the above ranges, the resulting fiber reinforced plastic will have excellent heat resistance and mechanical properties.

[0019] The content of isophorone diisocyanate (A1) in the liquid composition for intermediate substrates is preferably 20 to 50 mass %, more preferably 25 to 45 mass %, and even more preferably 30 to 40 mass %. When the content of isophorone diisocyanate (A1) is within the above range, the obtained fiber reinforced plastic has excellent mechanical properties.

[0020] The content of the polyfunctional isocyanate (A2) having an isocyanurate ring obtained by trimerizing a bifunctional isocyanate compound in the liquid composition for intermediate base materials is preferably 15 to 50 mass %, more preferably 20 to 40 mass %, and even more preferably 25 to 35 mass % in the liquid composition for intermediate base materials. When the content of the polyfunctional isocyanate (A2) is within the above range, the obtained fiber reinforced plastic has excellent weather resistance in particular, and in addition, excellent heat resistance, appearance, and mechanical properties.

[0021] The mass ratio [(A1) / (A2)] of isophorone diisocyanate (A1) to polyfunctional isocyanate (A2) having an isocyanurate ring obtained by trimerizing a bifunctional isocyanate compound is preferably 3 / 7 to 8 / 2, more preferably 3 / 7 to 7 / 3, even more preferably 4 / 6 to 7 / 3, still more preferably 5 / 5 to 7 / 3, and still more preferably 5 / 5 to 6 / 4. When the mass ratio of (A1) / (A2) is within the above range, the obtained fiber reinforced plastic also has excellent heat resistance, appearance, and mechanical properties.

[0022] <2-hydroxyethyl (meth)acrylate (B)> The liquid composition for an intermediate substrate of the present invention contains 2-hydroxyethyl (meth)acrylate (B). By using 2-hydroxyethyl (meth)acrylate (B), the resulting fiber reinforced plastic is excellent in particular in weather resistance, and in addition, is excellent in heat resistance, appearance, and mechanical properties.

[0023] The 2-hydroxyethyl (meth)acrylate (B) is at least one selected from the group consisting of 2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate, and is preferably 2-hydroxyethyl acrylate. In the present invention, the term "(meth)acrylate" refers to at least one selected from the group consisting of "acrylate" and "methacrylate".

[0024] The content of 2-hydroxyethyl (meth)acrylate (B) in the liquid composition for intermediate substrates is preferably 10 to 50 mass %, more preferably 15 to 40 mass %, and even more preferably 20 to 30 mass % in the liquid composition for intermediate substrates. When the content of 2-hydroxyethyl (meth)acrylate (B) is within the above range, the resulting fiber reinforced plastic also has excellent weather resistance, heat resistance, appearance, and mechanical properties.

[0025] <Polymerizable Monomer (C)> The liquid composition for an intermediate substrate of the present invention preferably contains a polymerizable monomer (C) that does not contain an isocyanate-reactive group and does not have an aromatic ring structure. By using the polymerizable monomer (C), the fiber reinforced plastic obtained will have excellent weather resistance, in particular, and will also have excellent heat resistance, appearance, and mechanical properties. Since the resin does not contain an isocyanate-reactive group, no reaction with isocyanate occurs during storage, which makes it easy to work with and allows the resulting molded article to have sufficient mechanical properties. The "polymerizable monomer (C) that does not contain an isocyanate-reactive group and does not have an aromatic ring structure" is also simply referred to as "polymerizable monomer (C)".

[0026] The polymerizable monomer (C) is preferably at least one selected from the group consisting of mono- or more functional aliphatic (meth)acrylates, mono- or more functional alicyclic (meth)acrylates, and mono- or more functional polyalkylene glycol (meth)acrylates, more preferably at least one selected from the group consisting of mono- or more functional aliphatic (meth)acrylates and mono- or more functional polyalkylene glycol (meth)acrylates, and even more preferably mono- or more functional aliphatic (meth)acrylates. The polymerizable monomer (C) is preferably a difunctional or higher functional polymerizable monomer, more preferably a difunctional polymerizable monomer. By using a difunctional or higher functional polymerizable monomer, the obtained fiber reinforced plastic has excellent heat resistance and mechanical properties.

[0027] Furthermore, the polymerizable monomer (C) is more preferably at least one selected from the group consisting of difunctional or higher aliphatic (meth)acrylates, difunctional or higher alicyclic (meth)acrylates, and difunctional or higher polyalkylene glycol (meth)acrylates, even more preferably at least one selected from the group consisting of difunctional or higher aliphatic (meth)acrylates and difunctional or higher polyalkylene glycol (meth)acrylates, even more preferably at least one selected from the group consisting of difunctional aliphatic (meth)acrylates and difunctional polyalkylene glycol (meth)acrylates, and still more preferably a difunctional aliphatic (meth)acrylate.

[0028] Examples of the mono- or higher functional aliphatic (meth)acrylate include methyl methacrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, stearyl (meth)acrylate, 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, ethylene glycol di(meth)acrylate, 1,3-propanediol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, and tris(2-(meth)acryloyloxyethyl)isocyanurate. Of these, ethylene glycol di(meth)acrylate is preferred.

[0029] Examples of the monofunctional or higher alicyclic (meth)acrylate include cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, norbornyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, norbornene dimethanol di(meth)acrylate, and tricyclodecane dimethanol di(meth)acrylate. Examples of the monofunctional or higher polyalkylene glycol (meth)acrylate include triethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, and tripropylene glycol di(meth)acrylate, and among these, diethylene glycol di(meth)acrylate is preferred.

[0030] Furthermore, among the above polymerizable monomers, the polymerizable monomer (C) is more preferably at least one selected from the group consisting of alkylene glycol di(meth)acrylates and polyalkylene glycol di(meth)acrylates, and even more preferably alkylene glycol di(meth)acrylates. By using at least one selected from the group consisting of alkylene glycol di(meth)acrylates and polyalkylene glycol di(meth)acrylates, in addition to the above effects, tackiness and odor as an intermediate substrate can be suppressed. Examples of alkylene glycol di(meth)acrylates include ethylene glycol di(meth)acrylate, 1,3-propanediol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, norbornene dimethanol di(meth)acrylate, and tricyclodecane dimethanol di(meth)acrylate, and among these, ethylene glycol di(meth)acrylate is preferred. Examples of polyalkylene glycol di(meth)acrylate include triethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, and tripropylene glycol di(meth)acrylate, and among these, diethylene glycol di(meth)acrylate is preferred.

[0031] From the viewpoint of workability, the content of the polymerizable monomer (C) in the liquid composition for intermediate substrates is preferably 40% by mass or less, more preferably 30% by mass or less, even more preferably 20% by mass or less, still more preferably 15% by mass or less, still more preferably 10% by mass or less, and even more preferably 0.1 to 10% by mass. When the content of the polymerizable monomer (C) is within the above range, the obtained fiber reinforced plastic has excellent appearance and mechanical properties.

[0032] <Other ingredients> The liquid composition for intermediate substrates of the present invention may contain other components such as a polymerization initiator, a polymerization inhibitor, a urethanization catalyst, particles, carbon nanotubes, a low shrinkage agent, an internal mold release agent, a dispersant, etc., within the range that does not impair the effects of the present invention. Among these, it is preferable that the liquid composition for intermediate substrates of the present invention contains at least one selected from the group consisting of a polymerization initiator, a polymerization inhibitor, and a urethanization catalyst.

[0033] The polymerization initiator is preferably an organic peroxide. The organic peroxide is preferably at least one selected from the group consisting of ketone peroxides, diacyl peroxides, peroxy esters, hydroperoxides and dialkyl peroxides, and more preferably peroxy esters. Specific examples of organic peroxides include t-butylperoxy-2-ethylhexyl monocarbonate, 1,1-di(t-hexylperoxy)cyclohexane, 1,1-di(t-butylperoxy)cyclohexane, 1,1-di(t-butylperoxy)-3,3,5-trimethylcyclohexane, t-butylperoxyoctoate, benzoyl peroxide, methyl ethyl ketone peroxide, acetylacetone peroxide, t-butylperoxybenzoate, t-butylcumyl peroxide, dicumyl peroxide, etc. These may be used alone or in combination of two or more. Among these, from the viewpoint of the degree of freedom in molding conditions and storage stability, at least one selected from the group consisting of t-butyl peroxybenzoate and t-butylcumyl peroxide is more preferred.

[0034] Furthermore, when photocuring properties are imparted to the intermediate substrate, a photocuring initiator may be used. Examples of photocuring initiators include acetophenone-based initiators such as acetophenone, p-dimethylaminoacetophenone, and p-dimethylaminopropiophenone, aminobenzophenone-based initiators such as α-alkylaminobenzophenone, benzophenone-based initiators such as benzophenone and 2-chlorobenzophenone, benzoin ether-based initiators such as benzoin methyl ether, benzil ketal-based initiators such as benzil dimethyl ketal, anthraquinone-based initiators such as 2-ethylanthraquinone and octamethylanthraquinone, organic peroxides such as cumene peroxide, thiol compounds such as 2-mercaptobenzimidazole, and o-acyloxime-based initiators such as acetophenone o-benzoyloxime. These polymerization initiators can be appropriately selected based on the aging temperature, molding temperature, and storage temperature of the intermediate substrate, and can be used alone or in combination of two or more.

[0035] The content of the polymerization initiator in the liquid composition for an intermediate base material is preferably 0.5 to 3.0 mass %, more preferably 0.8 to 2.5 mass %, and even more preferably 1.0 to 2.0 mass % in the liquid composition for an intermediate base material. By ensuring that the content of the polymerization initiator is within the above range, a cured product with the desired mechanical properties can be obtained, and the flexibility of molding conditions and storage stability of the liquid composition for intermediate substrates can be improved.

[0036] Examples of polymerization inhibitors include quinones such as hydroquinone, monomethyl ether hydroquinone, toluhydroquinone, di-t-4-methylphenol, monomethyl ether hydroquinone, phenothiazine, t-butylcatechol, parabenzoquinone, and pyrogallol; 2,6-di-t-butyl-p-cresol, 2,2-methylenebis(4-methyl-6-t-butylphenol), 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenol); Examples of suitable polymerization inhibitors include phenolic compounds such as 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl, 4-oxo-2,2,6,6-tetramethylpiperidine-1-oxyl, 4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl, 4-carboxy-2,2,6,6-tetramethylpiperidine-1-oxyl, and 2,2,6,6-tetramethylpiperidine-1-oxyl. Storage stability and workability can be improved by using a polymerization inhibitor. These may be used alone or in combination of two or more.

[0037] The content of the polymerization inhibitor in the liquid composition for an intermediate substrate is preferably 0.0005 to 0.05% by mass, more preferably 0.001 to 0.04% by mass, and even more preferably 0.005 to 0.03% by mass. By ensuring that the content of the polymerization inhibitor is within the above range, the storage stability and workability can be improved, and the intermediate base material liquid composition can be maintained at a low viscosity.

[0038] The urethanization catalyst is preferably an acidic catalyst or a basic catalyst, more preferably a tin compound such as dibutyltin dilaurate or dibutyltin diacetate. The content of the urethane catalyst in the liquid composition for intermediate substrates may be adjusted depending on the types of other raw materials, but is preferably 0.002 to 0.1 mass %, more preferably 0.005 to 0.05 mass %, and even more preferably 0.01 to 0.03 mass % in the liquid composition for intermediate substrates. By ensuring that the content of the urethanization catalyst is within the above range, heat generation during aging can be suppressed, the rate of urethane acrylate formation and the storage stability of the intermediate substrate can be improved, the storage stability and workability can be improved, and the resulting fiber-reinforced plastic will also have excellent appearance and mechanical properties.

[0039] Examples of the particles include inorganic particles and rubber particles, which may be contained for the purpose of adjusting viscoelasticity and improving mechanical properties. Examples of inorganic particles include, but are not limited to, calcium carbonate, alumina, talc, titanium oxide, silica, etc. Examples of rubber components include, but are not limited to, crosslinked rubber particles and core-shell rubber particles in which a rubber component is surrounded by a crosslinked polymer. The amount of these particles added varies depending on the viscosity and application of the liquid resin composition, but is preferably 2 to 80% by mass, more preferably 2 to 75% by mass.

[0040] Carbon nanotubes may be added to further improve the mechanical strength and impact resistance of the fiber-reinforced plastic. From the viewpoint of the viscosity and coatability of the liquid composition, single-walled carbon nanotubes are preferred, and the amount of single-walled carbon nanotubes added is preferably 0.05 to 0.5 mass % in the resulting fiber-reinforced plastic.

[0041] <Method for producing liquid composition for intermediate substrate, and properties of liquid composition for intermediate substrate> The liquid composition for an intermediate substrate of the present invention may be obtained by any method. The composition may be obtained by mixing the components simultaneously, or by preparing a mixture containing some of the components in advance and then mixing the mixture with the other components before use. For example, it is preferable to prepare a mixture containing isophorone diisocyanate (A1) and polyfunctional isocyanate (A2) and a mixture containing other components, and mix them to obtain a liquid composition for intermediate substrates. In particular, when the polyfunctional isocyanate (A2) is a solid and the isophorone diisocyanate (A1) is a liquid, it is preferable to dissolve the polyfunctional isocyanate (A2) in the isophorone diisocyanate (A1) in advance and then mix it with the other components. It is more preferable to prepare a mixture containing isophorone diisocyanate (A1), a polyfunctional isocyanate (A2), and a polymerization initiator, and a mixture containing other components, and then mix them to obtain a liquid composition for intermediate substrates. The components contained in the mixture containing other components include 2-hydroxyethyl (meth)acrylate (B), a polymerizable monomer (C), a polymerization inhibitor, and a urethanization catalyst.

[0042] The molar ratio of the isocyanate-reactive groups (hydroxyl groups) in the 2-hydroxyethyl (meth)acrylate (B) to the total isocyanate groups in the isophorone diisocyanate (A1) and the polyfunctional isocyanate (A2) [(hydroxyl groups in B) / (isocyanate groups in A1+A2)] is preferably 0.8 to 1.2, more preferably 0.9 to 1.1. When the molar ratio is within the above range, the mechanical properties of the resulting fiber-reinforced plastic can be improved.

[0043] The viscosity of the intermediate base material liquid composition at 25°C measured with a Brookfield viscometer is preferably 5 to 200 mPa·s, and more preferably 5 to 100 mPa·s. A viscosity within the above range provides excellent workability and improves the appearance of the resulting fiber-reinforced plastic.

[0044] The liquid composition for intermediate substrates of the present invention is converted into a urethane (meth)acrylate by undergoing an aging process described below, and the ethylenically unsaturated group equivalent of the resulting urethane (meth)acrylate is preferably less than 1000 g / eq. When the ethylenically unsaturated group equivalent of the resulting urethane (meth)acrylate is within the above range, the balance of mechanical properties is improved and heat resistance is also improved.

[0045] <Fiber-reinforced plastic intermediate substrate and method for manufacturing fiber-reinforced plastic intermediate substrate> The fiber-reinforced plastic intermediate substrate of the present invention is a fiber-reinforced plastic intermediate substrate obtained by impregnating a fiber material with the liquid composition for intermediate substrates. That is, the fiber-reinforced plastic intermediate substrate of the present invention is a fiber-reinforced plastic intermediate substrate obtained by impregnating a fiber material with a liquid composition for intermediate substrates, which contains isophorone diisocyanate (A1), a polyfunctional isocyanate (A2) having an isocyanurate ring obtained by trimerizing a bifunctional isocyanate compound, and 2-hydroxyethyl (meth)acrylate (B), wherein the polyfunctional isocyanate (A2) does not have an aromatic ring structure. Therefore, the fiber reinforced plastic produced using the fiber reinforced plastic intermediate substrate of the present invention is particularly excellent in weather resistance, heat resistance, appearance, and mechanical properties.

[0046] The fibers used in the fiber-reinforced plastic intermediate substrate of the present invention are not particularly limited, but are preferably at least one selected from the group consisting of carbon fiber, glass fiber, aramid fiber, Zylon fiber, boron fiber, basalt fiber, and cellulose.

[0047] The fiber content in the fiber reinforced plastic intermediate substrate is preferably 10 to 90 mass %, more preferably 30 to 80 mass %. When the fiber content is within the above range, a good balance between mechanical properties and moldability is achieved. The fibers may be surface-treated. The shape of the fibers is not particularly limited, but examples include unidirectional, cross, NCF, nonwoven fabric, and the like. The fiber may have a layer structure containing a core material. Specifically, the fiber may be a laminated fiber obtained by sandwiching a core material between two fiber substrates. Examples of the core material include a foamed nonwoven fabric and a honeycomb core mat.

[0048] A preferred method for producing a fiber-reinforced plastic intermediate substrate is a method for producing a fiber-reinforced plastic intermediate substrate, which comprises a step of impregnating a fiber material with the liquid composition for intermediate substrate, and a maturing step. The temperature in the step of impregnating the fiber material with the liquid composition for intermediate substrate is preferably 10 to 60°C. Furthermore, if necessary, the fiber material may be sandwiched between films and impregnated with the liquid composition for intermediate substrates by roller pressure, and then formed into a roll or bound shape. More specifically, a method may be mentioned in which the intermediate substrate liquid composition is coated on a film, fibers are placed on the coated surface, a film is further placed thereon, and pressure is applied with a roller to impregnate the fibers with the intermediate substrate liquid composition. Alternatively, fibers may be placed on a film first, the intermediate substrate liquid composition is dripped or sprayed on, a film is further placed thereon, and pressure is applied with a roller to impregnate the fibers with the intermediate substrate liquid composition.

[0049] In the aging process, the impregnated product obtained in the impregnation process is aged. It is believed that the formation of urethane (meth)acrylate while the liquid composition for intermediate substrates is impregnated into the fibers leads to a stronger bond between the liquid composition for intermediate substrates and the fibers. Therefore, it is believed that the resulting fiber-reinforced plastic has excellent weather resistance, heat resistance, appearance, and mechanical properties. The aging temperature in the aging step is preferably 30 to 80°C from the viewpoint of promoting urethanization and suppressing radical polymerization reactions. There is no limitation on the method of aging, but preferably, the rolled or bound material as described above can be aged by being placed in a furnace set at the above temperature. In this manner, a fiber-reinforced plastic intermediate substrate having urethane (meth)acrylate formed on the fibers can be obtained.

[0050] <Fiber-reinforced composite materials> The fiber-reinforced composite material of the present invention is a fiber-reinforced composite material obtained by curing the fiber-reinforced plastic intermediate substrate. The fiber-reinforced composite material of the present invention can be produced by placing the fiber-reinforced plastic intermediate substrate in a mold, applying heat and pressure to cause radical polymerization, curing, and molding to obtain a cured product. Examples of molding methods that apply heat and pressure include autoclave molding, oven molding, sheet winding molding, and press molding. The molding temperature may be adjusted appropriately depending on the type of polymerization initiator contained in the liquid composition for intermediate substrates, but the molding temperature is preferably 70 to 180° C., more preferably 110 to 170° C. The molding time is preferably 3 to 60 minutes, and the molding pressure is preferably 0.1 to 10 MPa. [Example]

[0051] Hereinafter, one embodiment of the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass."

[0052] <Production of vinyl ester resin> Manufacturing Example 1 A five-neck flask equipped with a thermometer, a stirrer, a gas inlet tube, and a reflux condenser was charged with 678.9 parts of bisphenol A type epoxy resin (manufactured by DIC Corporation, product name: EPICLON 850), 316.9 parts of methacrylic acid (manufactured by Mitsubishi Gas Chemical Co., Inc.), 3.0 parts of triphenylantimony, 0.2 parts of methylhydroquinone, and 1.0 part of 2-methylimidazole, and the mixture was reacted for 5 hours under an air flow (0.1 L / min) while maintaining the temperature at 130°C, to obtain vinyl ester resin 1.

[0053] <Production of Liquid Composition for Intermediate Base Material> Example 1 Isophorone diisocyanate (manufactured by Evonik, product name: VESTANAT IPDI) and isophorone diisocyanate trimer (including pentamers, heptamers, nonamers, and eleven or more; manufactured by Evonik, product name: VESTANAT T1890 / 100) were mixed in a container in the mass ratio shown in Table 1, stirred at 100°C until a homogeneous solution was obtained, and cooled to room temperature (approximately 25°C). tert-Butylcumyl peroxide (manufactured by NOF Corporation, product name: Perbutyl C) was mixed in the same container in the mass ratio shown in Table 1, and stirred at room temperature until a homogeneous solution was obtained, yielding Composition 1. 2-Hydroxyethyl acrylate (manufactured by Nippon Shokubai Co., Ltd.), ethylene glycol dimethacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., product name: NK Ester 1G), dibutylhydroxytoluene, methylhydroquinone, parabenzoquinone, and dibutyltin dilaurate were mixed in the mass ratio shown in Table 1 and stirred until a uniform solution was obtained, thereby obtaining Composition 2. Composition 1 and Composition 2 were mixed in the mass ratio shown in Table 1 and stirred until a uniform solution was obtained, thereby obtaining a liquid composition for intermediate base materials. Note that the "viscosity (25°C)" shown in Table 1 is the viscosity at 25°C measured with a Brookfield viscometer.

[0054] Example 2 A liquid composition for intermediate substrates was obtained in the same manner as in Example 1, except that 2-hydroxyethyl acrylate (manufactured by Nippon Shokubai Co., Ltd.) was changed to 2-hydroxyethyl methacrylate (manufactured by Mitsubishi Gas Chemical Co., Ltd.) and the mass ratio of each component was mixed to obtain the mass ratio shown in Table 1.

[0055] Example 3 A liquid composition for intermediate substrates was obtained in the same manner as in Example 1, except that the components were mixed so that the mass ratios shown in Table 1 were obtained.

[0056] Example 4 A liquid composition for intermediate substrates was obtained in the same manner as in Example 1, except that ethylene glycol dimethacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., product name: NK Ester 1G) was changed to diethylene glycol dimethacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., product name: NK Ester 2G) and the mass ratio of each component was blended to be the mass ratio shown in Table 1.

[0057] Comparative Example 1 A liquid composition for intermediate substrates was obtained in the same manner as in Example 2, except that the isophorone diisocyanate trimer (manufactured by Evonik, product name: VESTANAT T1890 / 100) was changed to the vinyl ester resin 1 obtained in Production Example 1, the types of other components were changed as shown in Table 1, and the components were blended so that the mass ratio of each component was the mass ratio shown in Table 1.

[0058] <Production of Resin Composition for Intermediate Substrate> Comparative Example 2 A bisphenol A type epoxy resin blend (a 50:50 mass ratio of jER 1001, manufactured by Mitsubishi Chemical Corporation, and jER 828, manufactured by Mitsubishi Chemical Corporation), dicyandiamide, and a urea derivative were mixed in the mass ratios shown in Table 1 and stirred until a homogeneous solution was obtained, thereby obtaining a resin composition for intermediate substrates.

[0059] <Manufacturing of fiber-reinforced plastic intermediate substrates> Examples 1 to 4 and Comparative Example 1 The liquid compositions for intermediate substrates obtained in the Examples and Comparative Examples were impregnated into 10 sheets of carbon fiber fabric (manufactured by Mitsubishi Chemical Corporation, product name: TR3523M) cut into 33 cm squares with the formulations shown in Table 1, and then aged at 50°C for 72 hours to obtain a prepreg, which is a fiber-reinforced plastic intermediate substrate. The obtained prepreg had a fiber content of approximately 60 mass%.

[0060] Comparative Example 2 The resin composition for intermediate substrate obtained in the comparative example was impregnated by hot melting into 10 sheets of carbon fiber fabric (manufactured by Mitsubishi Chemical Corporation, product name: TR3523M) cut into 33 cm squares, with the formulation shown in Table 1. The fabric was then passed through a roller at 80°C to obtain a prepreg, a fiber-reinforced plastic intermediate substrate. The obtained prepreg had a fiber content of approximately 60 mass%.

[0061] <Manufacturing of fiber-reinforced composite materials> The prepreg was molded using a 100-ton hydraulic press (manufactured by Toho Press Manufacturing Co., Ltd.) to obtain a molded plate that is a fiber-reinforced composite material. In Examples 1 to 4, the molding temperature was 165° C., the molding pressure was 10 bar, and the molding time was 7 minutes. In Comparative Examples 1 and 2, the molding temperature was 130° C., the molding pressure was 10 bar, and the molding time was 7 minutes.

[0062] <Evaluation method> (1) Weather resistance evaluation The weather resistance of the molded plate was measured as follows. The test pieces were treated for 1500 hours using a Sunshine Weather Meter S80B (manufactured by Suga Test Instruments Co., Ltd.) according to a method conforming to JIS B 7753:2007. The weather resistance of the treated test pieces was evaluated by measuring the color difference (ΔE) using a spectrophotometer SE6000 (manufactured by Nippon Denshoku Industries Co., Ltd.). The smaller the ΔE value, the less discoloration there is in the natural environment, which is preferable. The results are shown in Table 1.

[0063] (2) Evaluation of shrinkage rate The shrinkage rate was calculated from the liquid specific gravity and the cured product specific gravity. The liquid specific gravity was measured by floating a hydrometer in the liquid composition for intermediate substrates or the resin composition for intermediate substrates. The cured product specific gravity was calculated by dividing the air mass of the cured molded plate by the absolute value of the difference between the air mass and the mass in water. The absolute value of the difference between the liquid specific gravity and the cured product specific gravity divided by the liquid specific gravity was calculated as the shrinkage rate (%). The smaller the shrinkage rate, the smoother the surface of the molded plate, which is preferable. The results are shown in Table 1.

[0064] (3) Appearance evaluation The appearance of the molded plate was evaluated as follows. Fluorescent light was reflected off the surface of the molded plate, and the reflected light was visually observed and evaluated according to the following criteria. The clearer the reflected light, the smoother the surface of the molded plate, and therefore the better. The results are shown in Table 1. (Appearance evaluation criteria) 〇: The reflected light is clear and the outline of the fluorescent light is visible. △: The reflected light is slightly blurred and the outline of the fluorescent light is not clear. ×: The reflected light is blurred and the shape of the fluorescent lamp cannot be seen.

[0065] (4) Heat resistance evaluation The heat resistance of the molded plate was evaluated as follows. Heat resistance was evaluated by measuring the inflection point of the storage modulus (E'-Onset Tg: Tg at E'-Onset) using a dynamic viscoelasticity measuring device (TA Instruments, product name: RSA-G2). The higher the E'-Onset Tg value, the higher the heat resistance temperature of the fiber-reinforced composite material, which is preferable. The results are shown in Table 1.

[0066] (5) Evaluation of mechanical properties The molded plates were used to evaluate the mechanical properties as follows. The bending strength was measured by a method in accordance with JIS K7018: 2019. The larger the bending strength value, the greater the strength of the fiber-reinforced composite material, which is preferable. The interlaminar shear strength was measured by a method in accordance with JIS K7018: 2019. The larger the value of the interlaminar shear strength, the greater the strength of the fiber-reinforced composite material, which is preferable. The results are shown in Table 1.

[0067] [Table 1]

[0068] Table 1 shows that the fiber-reinforced composite materials (molded boards, fiber-reinforced plastics) obtained using the liquid compositions for intermediate substrates of the Examples have excellent heat resistance and appearance, and also have excellent mechanical properties, as seen in their high values ​​for flexural strength, interlaminar shear strength, and dynamic viscoelasticity. Furthermore, the fiber-reinforced composite materials (molded boards, fiber-reinforced plastics) obtained using the liquid compositions for intermediate substrates of the Examples are particularly excellent in weather resistance. This shows that the liquid composition for intermediate substrates of the present invention can give fiber reinforced plastics that are particularly excellent in weather resistance, heat resistance, appearance and mechanical properties.

Claims

1. A liquid composition for intermediate substrates, comprising isophorone diisocyanate (A1), a polyfunctional isocyanate (A2) having an isocyanurate ring obtained by trimerizing a bifunctional isocyanate compound, and 2-hydroxyethyl (meth)acrylate (B), wherein the polyfunctional isocyanate (A2) does not have an aromatic ring structure.

2. The liquid composition for an intermediate base material according to claim 1 , further comprising a polymerizable monomer (C) that does not contain an isocyanate-reactive group and does not have an aromatic ring structure.

3. 3. The liquid composition for intermediate substrates according to claim 2, wherein the polymerizable monomer (C) is at least one selected from the group consisting of mono- or more functional aliphatic (meth)acrylates, mono- or more functional alicyclic (meth)acrylates, and mono- or more functional polyalkylene glycol (meth)acrylates.

4. The liquid composition for an intermediate base material according to claim 1 or 2, wherein the bifunctional isocyanate compound is at least one selected from the group consisting of an aliphatic isocyanate compound and an alicyclic isocyanate compound.

5. The liquid composition for intermediate substrates according to claim 2, wherein the polymerizable monomer (C) is at least one selected from the group consisting of alkylene glycol di(meth)acrylates and polyalkylene glycol di(meth)acrylates.

6. 3. The liquid composition for intermediate substrates according to claim 1 or 2, wherein the mass ratio [(A1) / (A2)] of the isophorone diisocyanate (A1) to the polyfunctional isocyanate (A2) having an isocyanurate ring obtained by trimerizing a bifunctional isocyanate compound is 3 / 7 to 7 / 3.

7. 3. The liquid composition for an intermediate substrate according to claim 2, wherein the content of the polymerizable monomer (C) in the liquid composition for an intermediate substrate is 0.1 to 10% by mass.

8. The liquid composition for intermediate base materials according to claim 1 or 2, having a viscosity at 25°C of 5 to 200 mPa·s.

9. A fiber-reinforced plastic intermediate substrate obtained by impregnating a fiber material with the liquid composition for intermediate substrates according to claim 1 or 2.

10. A method for producing a fiber-reinforced plastic intermediate substrate, comprising the steps of impregnating a fiber material with the liquid composition for intermediate substrates according to claim 1 or 2, and maturing the same.

11. The method for producing a fiber-reinforced plastic intermediate substrate according to claim 10, wherein the aging temperature is 30 to 80°C.

12. A fiber-reinforced composite material obtained by curing the fiber-reinforced plastic intermediate substrate according to claim 9.

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