JP7760337B2 - Liquid composition and fiber-reinforced composite material using said liquid composition - Google Patents

Description

The present invention relates to a liquid composition for fiber-reinforced plastic intermediate substrates, fiber-reinforced plastic intermediate substrates, and a method for producing said fiber-reinforced plastic intermediate substrates, and in particular to a liquid composition for fiber-reinforced plastic intermediate substrates that exhibit excellent curing properties, a fiber-reinforced plastic intermediate substrate, and a method for producing said fiber-reinforced plastic intermediate substrates.

Fiber-reinforced plastics (FRP) are lightweight and strong, making them suitable for a variety of structural components. These applications span a wide range of fields, including housing, automobiles, ships, civil engineering, and sports equipment. In recent years, FRP use has been increasing, particularly in the automobile and transportation-related equipment sectors, where lightweight construction is essential.

FRP manufacturing methods include Resin Transfer Molding (RTM), in which a concave mold containing reinforcing fibers is sealed with a convex mold and then resin is injected and pressure-impregnated; the SMC method, in which short fibers impregnated with resin are sandwiched between films and passed through rollers to form a continuous sheet (SMC: Sheet Molding Compound), which is then cut and placed in a mold where it is heated and pressurized; and the autoclave method, in which fibers or fabrics impregnated with resin and left to reach a semi-cured state (prepreg) are layered in a mold, the entire laminate surface is covered with film or the like, airtightly sealed, bagged, and then degassed under reduced pressure before being placed in an autoclave (heat-and-pressure molding oven) where it is heated and pressurized to form the product.

Manufacturing methods for intermediate substrates include the 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; and the hot melt method, in which the viscosity of the resin composition is reduced by heating to produce a film of the resin composition (resin film), which is then attached to the top and bottom of a fiber substrate made of continuous fibers aligned in one direction, and the resin composition is impregnated into the fiber substrate by heating and pressurizing to obtain the intermediate substrate.

The matrix resin for the intermediate substrate is often 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 are used include unsaturated polyester resin, vinyl ester resin, epoxy resin, phenolic resin, melamine resin, and bismaleimide resin.

Urethane (meth)acrylate compounds have long been known to have excellent adhesion to carbon fibers and are used as sizing agents for carbon fibers (Patent Document 1). Furthermore, because urethane (meth)acrylate compounds have good adhesion to reinforcing fibers, it has been proposed to use them in combination with resins that have poor adhesion to reinforcing fibers (Patent Document 2).

It has also been proposed that the impregnation of fiber substrates can be improved by using an epoxy resin that is liquid at room temperature as the matrix resin in sheet molding compounds (Patent Document 3).

Furthermore, it has been proposed that the toughness and heat resistance of a fiber-reinforced composite material be improved by using a resin composition consisting of vinyl ester resin and diallyl phthalate resin as the matrix resin for the prepreg (Patent Document 4).

Japanese Patent Application Publication No. 11-200252 Japanese Patent Application Laid-Open No. 62-292839 Japanese Patent Application Laid-Open No. 2021-91920 JP 2008-24787 A

However, conventional methods for manufacturing intermediate substrates, such as the solvent method, are unable to sufficiently remove the solvent, and the solvent remaining in the intermediate substrate evaporates during molding, resulting in the formation of voids in the fiber-reinforced composite material. Raising the drying temperature to sufficiently remove the solvent hardens the intermediate substrate, which is made of a resin composition containing a thermosetting resin, making it difficult to sufficiently remove the solvent using this manufacturing method. Furthermore, with the hot melt method, as the basis weight of the fiber substrate increases, i.e., as the fiber substrate becomes thicker, the resin composition cannot be sufficiently impregnated in the thickness direction, making it difficult to use this manufacturing method to produce thick intermediate substrates that are sufficiently impregnated with the resin composition.

The matrix resin used for the intermediate substrate is a thermosetting resin composition made by diluting an epoxy resin composition, unsaturated polyester resin, or vinyl ester resin with styrene. However, while the former provides excellent mechanical properties and heat resistance in the cured product, it is difficult to achieve both rapid curing and B-stage stability. The latter has an extremely low viscosity, which allows for excellent impregnation into the fiber substrate during the production of the intermediate substrate, and also provides excellent rapid curing and B-stage stability, but its large cure shrinkage makes it difficult to obtain a fiber-reinforced composite material with high dimensional stability.

Furthermore, the fiber-reinforced composite materials using the urethane (meth)acrylate compounds described in Patent Documents 1 and 2 have the problem of being unable to achieve sufficient mechanical properties.

Furthermore, in the invention described in Patent Document 3, the heat resistance of the fiber-reinforced composite material obtained by curing the sheet molding compound is low, at around 150°C, which is not satisfactory for practical use in applications requiring heat resistance, such as around automobile engines.

Furthermore, in the invention described in Patent Document 4, the resin composition has a high viscosity, making it difficult to impregnate a thick fiber substrate. In addition, there is no mention of the molding shrinkage or warpage of the fiber-reinforced composite material obtained by curing a prepreg using the resin composition.

The present invention aims to solve the above problems and provide a liquid composition for fiber-reinforced plastic intermediate substrates that has excellent mechanical properties and heat resistance and can minimize voids.

The inventors conducted extensive research into resin compositions from various perspectives, and as a result, they discovered the liquid composition of the present invention.

That is, the liquid composition for a fiber-reinforced plastic intermediate substrate of the present invention is a liquid composition for a fiber-reinforced plastic intermediate substrate, which contains a composition (A) containing a compound (a) having two or more isocyanate groups, and a composition (B) containing a vinyl ester resin (b1) and an ethylenically unsaturated group-containing monoalcohol compound (b2), and is characterized in that a polymerization inhibitor (C) is blended into the composition (B) .

In a preferred embodiment of the liquid composition for a fiber-reinforced plastic intermediate substrate of the present invention, a polymerization inhibitor (C) is also blended in the composition (A).

Furthermore, in a preferred embodiment of the liquid composition for fiber-reinforced plastic intermediate substrates of the present invention, a polymerization initiator (D) and/or a urethane catalyst (E) is blended with the composition (A) and/or (B).

Furthermore, in a preferred embodiment of the liquid composition for fiber-reinforced plastic intermediate substrates of the present invention, the molar ratio (B/A) of the isocyanate-reactive groups in composition (B) to the number of moles of isocyanate groups in composition (A) is 0.8 to 1.2.

Furthermore, in a preferred embodiment of the liquid composition for fiber-reinforced plastic intermediate substrates of the present invention, the composition (A) and/or (B) is characterized by containing a polymerizable monomer (F) that does not have an isocyanate-reactive group.

Furthermore, in a preferred embodiment of the liquid composition for fiber-reinforced plastic intermediate substrates of the present invention, the content of polymerizable monomer (F) is 1 to 40% by weight relative to the total weight of compositions (A) and (B).

Furthermore, in a preferred embodiment of the liquid composition for fiber-reinforced plastic intermediate substrates of the present invention, the viscosity at 10 to 50°C measured with a Brookfield viscometer is 5 to 200 mPa·s.

Furthermore, in a preferred embodiment of the liquid composition for fiber-reinforced plastic intermediate substrates of the present invention, the liquid composition of the present invention is impregnated into a fiber material.

Furthermore, the fiber-reinforced composite material of the present invention is characterized by being obtained by curing the fiber-reinforced plastic intermediate substrate of the present invention.

The method for producing a fiber-reinforced plastic intermediate substrate of the present invention is characterized by comprising the steps of impregnating a fiber material with the liquid composition of the present invention in any desired composition, and maturing the fiber-reinforced plastic intermediate substrate obtained by the impregnation.

Furthermore, in a preferred embodiment of the method for producing a fiber-reinforced plastic intermediate substrate of the present invention, the aging temperature is 30 to 80°C.

The liquid composition for fiber-reinforced plastic intermediate substrates of the present invention has the advantageous effect of providing an intermediate substrate that has excellent impregnation into the substrate, little shrinkage during curing, and excellent dimensional stability. Furthermore, the intermediate substrate obtained according to the present invention has the advantageous effect of providing a highly reliable composite material that has excellent mechanical properties and heat resistance and is almost free of voids or unimpregnated areas. Furthermore, the intermediate substrate of the present invention has the advantageous effect of providing excellent curing properties and storage stability.

Furthermore, the present invention has the advantageous effect of enabling the production of intermediate substrates with a large unit weight by using a liquid composition with low viscosity and excellent impregnation properties.

Embodiments of the present invention are described in detail below, but the present invention is not limited to the following description as long as it does not deviate from the gist of the invention. In this invention, "(meth)acrylate" refers to "acrylate" and "methacrylate." Similarly, "(meth)acrylic acid ester" refers to "acrylic acid ester" and "methacrylic acid ester."

The liquid composition for a fiber-reinforced plastic intermediate substrate of the present invention is characterized by containing a composition (A) containing a compound (a) having two or more isocyanate groups, and a composition (B) containing a vinyl ester resin (b1) and an ethylenically unsaturated group-containing monoalcohol compound (b2). That is, the liquid composition for a fiber-reinforced plastic intermediate substrate of the present invention is characterized by being a blend of the following (A) and (B): composition (A) containing a compound (a) having two or more isocyanate groups, and composition (B) having the following (b1) and (b2) as essential components:
(b1) Vinyl ester resin (b2) Ethylenically unsaturated group-containing monoalcohol compound

First, composition (A) will be described. Composition (A) is a composition containing a compound (a) having two or more isocyanate groups.

Examples of compounds (a) having two or more isocyanate groups include aromatic isocyanate compounds such as 1,3-xylylene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-diphenyl diisocyanate, 1,5-naphthalene diisocyanate, 4,4'-diphenylmethane diisocyanate, polymethylene polyphenyl polyisocyanate, and m-tetramethyl xylene diisocyanate; hydrogenated xylylene diisocyanate (1,3-bis(isocyanatomethyl)cyclohexasiloxane); Examples of suitable isocyanate compounds include alicyclic isocyanate compounds such as isophorone diisocyanate, norbornene diisocyanate, dicyclohexylmethane diisocyanate, hydrogenated methylene bisphenylene diisocyanate, and 1,4-cyclohexane diisocyanate; aliphatic isocyanate compounds such as 1,6-hexamethylene diisocyanate and trimethylene diisocyanate; trifunctional isocyanates having an isocyanurate ring formed by trimerizing a bifunctional isocyanate compound; and polyol-modified isocyanate prepolymers. These isocyanate compounds can be used alone or in combination of two or more. Among these, aliphatic isocyanate compounds are particularly preferred from the standpoint of viscosity and reactivity. Examples include isophorone diisocyanate and prepolymers having isocyanate groups obtained by reacting isophorone diisocyanate with a vinyl ester resin (b1) in an excess of isocyanate groups.

If the viscosity increases too quickly after mixing compositions (A) and (B), it is possible to suppress the reaction by not adding the urethane catalyst (E), or to produce the intermediate base material at a low temperature so that the viscosity of the liquid composition does not exceed the range.

Next, composition (B) will be described. Composition (B) is a composition that can contain vinyl ester resin (b1), ethylenically unsaturated group-containing monoalcohol compound (b2), and polymerization inhibitor (C) in any ratio. Vinyl ester resin (b1) and ethylenically unsaturated group-containing monoalcohol compound (b2) are essential components of composition (B), and polymerization inhibitor (C) can be added as needed. The vinyl ester resin (b1) and ethylenically unsaturated group-containing monoalcohol (b2) added to composition (B) are preferably liquid at the fiber impregnation temperature (any temperature in the range of 10 to 50°C), but solid materials may also be used as long as they form a liquid composition in composition (B).

Vinyl ester resin (b1) is a reaction product (unsaturated monobasic acid epoxy ester) of an epoxy resin component and an unsaturated monobasic acid component.

The epoxy resin component is a compound containing at least two epoxy groups per molecule. Examples include diglycidyl ether-type epoxy resins with a bisphenol compound such as bisphenol A, bisphenol F, or brominated bisphenol A as the main skeleton; polyglycidyl ether-type epoxy resins with a polynuclear phenol compound such as phenol novolac, cresol novolac, or brominated phenol novolac as the main skeleton; polyglycidyl ester-type epoxy resins with an organic polybasic acid such as dimer acid or trimellitic acid as the main skeleton; and glycidyl ether-type epoxy resins with a diol compound such as an ethylene oxide or propylene oxide adduct of bisphenol A, glycol, or hydrogenated bisphenol A as the main skeleton. These epoxy resins may be used alone or in combination.

The unsaturated monobasic acid component is a monobasic acid having an ethylenically unsaturated group, such as acrylic acid, methacrylic acid, crotonic acid, or sorbic acid. These unsaturated monobasic acid components may be used alone or in combination.

The ethylenically unsaturated group-containing monoalcohol compound (b2) refers to a (meth)acrylic acid ester containing a hydroxyl group, and examples thereof include 2-hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, trimethylolpropane di(meth)acrylate, glycidyl (meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol penta(meth)acrylate, diacrylated isocyanurate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, 2-acryloyloxyethyl hexahydrophthalate, and 2-acryloyloxyethyl-2-hydroxyethyl phthalate.

These ethylenically unsaturated group-containing monoalcohol compounds (b2) can be used alone or in combination of two or more. Among these ethylenically unsaturated group-containing monoalcohol compounds (b2), 2-hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate are preferred from the standpoints of the viscosity of the liquid composition and the mechanical properties of the cured product. Furthermore, when heat resistance is required, pentaerythritol tri(meth)acrylate is preferred.

Furthermore, in a preferred embodiment of the liquid composition for fiber-reinforced plastic intermediate substrates of the present invention, a polymerization inhibitor (C) is blended into the composition (A) and/or (B). As described above, the polymerization inhibitor (C) can be blended into the composition (B), but it can also be blended into the composition (A), only the composition (A), only the composition (B), or both the compositions (A) and (B).

As the polymerization inhibitor (C), for example, known polyhydric phenol-based polymerization inhibitors such as hydroquinone, parabenzoquinone, methylhydroquinone, and trimethylhydroquinone can be used.

Furthermore, in a preferred embodiment of the liquid composition for fiber-reinforced plastic intermediate substrates of the present invention, a polymerization initiator (D) and/or a urethane catalyst (E) are further blended into the composition (A) and/or (B).

Furthermore, in a preferred embodiment of the liquid composition for fiber-reinforced plastic intermediate substrates of the present invention, the composition (A) and/or (B) contains a polymerizable monomer (F) that does not contain an isocyanate-reactive group.

First, the polymerization initiator (D), urethanization catalyst (E), and polymerizable monomer (F) that does not contain an isocyanate-reactive group will be described. Each of these components can be blended into either composition (A) or (B), or can be blended into both compositions (A) and (B). The polymerization initiator (D) can be an essential component when curing the intermediate substrate by radical polymerization in the production of a fiber-reinforced composite material, as described below.

A urethane catalyst (E) and a polymerizable monomer (F) that does not contain an isocyanate-reactive group can be blended as needed.

Examples of the polymerization initiator (D) include organic peroxides, such as ketone peroxides such as methyl ethyl ketone peroxide and acetylacetone peroxide, diacyl peroxides such as benzoyl peroxide, peroxyesters such as t-butyl peroxybenzoate, hydroperoxides such as cumene hydroperoxide, dialkyl peroxides such as dicumyl peroxide, and peroxydicarbonates such as bis(4-tert-butylhexyl) peroxydicarbonate.

In addition, if the intermediate substrate is to be photocurable, a photocuring initiator can be used. Examples 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 can be selected appropriately 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 types.

The amount of polymerization initiator (D) added is 0.05 to 5 parts by weight per 100 parts by weight of the liquid composition. Polymerization initiator (D) can be blended into composition (B), but because composition (B) contains a compound with an ethylenically unsaturated group, blending it into composition (A) is preferable in consideration of the storage stability of composition (B).

While both acidic and basic catalysts can be used as the urethane catalyst (E), highly active tin compounds such as dibutyltin dilaurate and dibutyltin diacetate are preferred. The amount of catalyst added varies depending on the other raw materials selected, but is generally 0 to 800 ppm based on the weight of the liquid composition, taking into account the heat generated during aging, the rate of urethane acrylate formation, the storage stability of the intermediate substrate, and the mechanical properties of the cured product.

Preferably, the polymerizable monomer (F) that does not contain an isocyanate-reactive group is one that does not react with isocyanate groups at room temperature. Examples of polymerizable monomers (F) that do not react with isocyanate groups at room temperature include vinyl monomers, monofunctional (meth)acrylic acid esters, and polyfunctional (meth)acrylic acid esters. Blending a polymerizable monomer that reacts with isocyanate groups may result in a reaction during storage, increasing viscosity and potentially reducing workability or preventing sufficient mechanical properties from being achieved.

Examples of vinyl monomers include styrene, vinyl toluene, α-methyl styrene, and vinyl acetate. Examples of monofunctional (meth)acrylic acid esters include methyl methacrylate, benzyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (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, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, norbornyl (meth)acrylate, dicyclopentenyl (meth)acrylate, and dicyclopentenyloxyethyl (meth). ) acrylate, and examples of polyfunctional (meth)acrylic acid esters include ethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, 1,3-propanediol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, tripropylene di(meth)acrylate, norbornene dimethanol di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, ethylene oxide-added bisphenol A di(meth)acrylate, propylene oxide-added bisphenol A di(meth)acrylate, trimethylolpropane tri(meth)acrylate, and tris(2-(meth)acryloyloxyethyl)isocyanurate. These polymerizable monomers (E) can be used alone or in combination of two or more. In terms of tackiness and odor as an intermediate substrate, and the mechanical properties of the cured product, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tripropylene di(meth)acrylate, benzyl methacrylate, dicyclopentenyl (meth)acrylate, ethylene oxide-added bisphenol A di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, and propylene oxide-added bisphenol A di(meth)acrylate are preferred.

Furthermore, in a preferred embodiment of the liquid composition for fiber-reinforced plastic intermediate substrates of the present invention, the content of polymerizable monomer (F) is 0 to 40% by weight relative to the total weight of compositions (A) and (B). In other words, the blending amount of polymerizable monomer (F) in the liquid composition can be adjusted within the range of 0 to 40% by weight to match the urethane acrylate obtained by aging, with respect to the target viscosity characteristics and tackiness of the intermediate substrate. From the viewpoint of minimizing cure shrinkage of the intermediate substrate, 0 to 20% by weight is preferred.

Furthermore, in a preferred embodiment of the liquid composition for fiber-reinforced plastic intermediate substrates of the present invention, from the viewpoint of imparting better FRP mechanical properties, the molar ratio (B/A) of the isocyanate-reactive groups in composition (B) to the number of moles of isocyanate groups in composition (A) is 0.8 to 1.2, preferably 0.9 to 1.1.

Furthermore, in a preferred embodiment of the liquid composition for fiber-reinforced plastic intermediate substrates of the present invention, the viscosity of the liquid composition, which is a mixture of compositions (A) and (B), at 10 to 50°C, measured with a Brookfield viscometer, is 5 to 200 mPa·s. That is, the viscosity of the liquid composition of the present invention, at the time when compositions (A) and (B) are mixed, is preferably 5 to 200 mPa·s at 10 to 50°C, and although this depends on the unit area weight of the desired intermediate substrate, a viscosity of 5 to 100 mPa·s is particularly preferred. If the viscosity exceeds 200 mPa·s, impregnation into substrates with large unit area weights will be poor, and there is a risk of unimpregnated areas being formed.

The liquid composition of the present invention changes into a urethane (meth)acrylate upon aging. The ethylenically unsaturated group equivalent of the urethane acrylate is not particularly limited, but is preferably less than 1000 g/eq. If it is 1000 g/eq or more, the balance of mechanical properties (flexural strength, tensile strength, compressive strength, interlaminar shear strength) will be poor, and the heat resistance of the molded product may be reduced.

The liquid composition of the present invention may contain inorganic particles or rubber particles to adjust viscoelasticity and improve mechanical properties. Examples of inorganic particles include, but are not limited to, calcium carbonate, alumina, talc, titanium oxide, and silica. Examples of rubber components include, but are not limited to, crosslinked rubber particles and core-shell rubber particles in which the rubber component is surrounded by a crosslinked polymer. The amount of these particles added varies depending on the viscosity of the liquid resin composition, but is 2 to 80% by weight, preferably 2 to 75% by weight.

Furthermore, carbon nanotubes can be blended into the liquid composition of the present invention to further improve the mechanical strength and impact resistance of the FRP. From the standpoint of the viscosity and coatability of the liquid composition, single-walled carbon nanotubes are preferred, and the blending amount should be such that the single-walled carbon nanotubes in the FRP constitute 0.05 to 0.5% by weight.

Furthermore, the liquid composition of the present invention can contain low-shrinkage agents, internal mold release agents, dispersants, etc. as needed. These additives are preferably liquid from the standpoint of solubility, but solid additives are also acceptable as long as they dissolve in the composition when heated.

Furthermore, the fiber-reinforced plastic intermediate substrate of the present invention is characterized by being obtained by impregnating a fiber material with the liquid composition for fiber-reinforced plastic intermediate substrate of the present invention.

Fibers used in the intermediate substrate of the present invention include, but are not limited to, carbon fiber, glass fiber, aramid fiber, Zylon fiber, boron fiber, basalt fiber, cellulose, etc. Furthermore, the reinforcing fiber content is 10 to 90% by weight, and from the perspective of mechanical properties and moldability, it is preferably 30 to 80% by weight. There are no limitations on the surface treatment agent or shape of the reinforcing fiber (unidirectional, cross, NCF, nonwoven fabric, etc.). It is also possible to sandwich a core material between two fiber substrates. Examples of core materials include foamed nonwoven fabric and honeycomb core mat.

The method for producing a fiber-reinforced plastic intermediate substrate of the present invention is characterized by comprising the steps of impregnating a fiber material with the liquid composition of the present invention at a desired composition and aging the fiber-reinforced plastic intermediate substrate obtained by the impregnation. While not particularly limited in the present invention, the liquid composition can be impregnated into the fiber material at a desired composition at a temperature of, for example, 10 to 60°C. If necessary, the fiber material may be sandwiched between films and impregnated with the liquid composition using roller pressure to form a roll or bound bundle. The fiber-reinforced plastic intermediate substrate obtained by the impregnation can then be aged. That is, in the present invention, urethane acrylate can be formed while the liquid composition is impregnated into fibers or textiles during the aging process. Conventionally, urethane acrylate has been formed first and then impregnated into fibers, etc.; however, the present inventors surprisingly discovered that the liquid composition of the present invention can be impregnated into fibers, textiles, etc., through a aging process to form urethane acrylate. This makes it possible to more firmly bond the liquid composition to the fibers, and as will be apparent from the examples described below, this has the advantageous effect of enabling the development of better impregnation, curing, and mechanical properties.

In a preferred embodiment, the aging temperature can be set to 30 to 80°C from the viewpoint of promoting urethanization and suppressing radical polymerization reactions. In this manner, the liquid composition can be coated onto a film, fibers or textiles placed on the coated surface, and then sandwiched between films and pressure applied with rollers to impregnate the fibers or textiles with the liquid composition. It is preferable to use a breakwater-like jig to maintain a constant width of the coated material from the coating plant until it comes into contact with the fibers or textiles. Alternatively, the liquid composition can be dripped or sprayed onto the fibers or textiles, which are then sandwiched between films and pressure applied with rollers to impregnate the fibers or textiles with the liquid composition. Materials impregnated using these methods can be formed into rolls or bundles and aged in an oven (30 to 80°C).

Furthermore, the fiber-reinforced composite material of the present invention is characterized by being obtained by curing the fiber-reinforced plastic intermediate substrate of the present invention.

The cured intermediate substrate of the present invention, in which urethane acrylate is formed on fibers, can be obtained by applying heat and pressure to heat-cure. In other words, curing can be achieved through radical polymerization. Molding methods that apply heat and pressure include autoclave molding, oven molding, sheet winding molding, and press molding. Depending on the type of polymerization initiator in the liquid composition, the molding temperature is preferably 70 to 180°C, preferably 100 to 150°C, the molding time is preferably 3 to 60 minutes, and the molding pressure is preferably 0.1 to 10 MPa.

The following examples further illustrate one embodiment of the present invention, but the present invention is not limited to these examples. In these examples, "parts" refers to parts by weight unless otherwise specified. In these examples, a prepreg was prepared as an example of an intermediate substrate.

[Synthesis Example]
Synthesis of vinyl ester resin (b1)
(Synthesis of vinyl ester resin 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 epoxy resin (manufactured by DIC Corporation, product name: EPICLON 850), 316.9 parts of methacrylic acid (manufactured by Mitsubishi Gas Chemical Company, 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.

(Synthesis of vinyl ester resin 2)
A five-neck flask equipped with a thermometer, a stirrer, a gas inlet tube, and a reflux condenser was charged with 661.8 parts of bisphenol A epoxy resin (manufactured by DIC Corporation, product name: EPICLON 850), 89.8 parts of bisphenol A (manufactured by Nippon Steel Chemical & Material Co., Ltd.), and 0.4 parts of triphenylphosphine. The mixture was then reacted for 0.5 hours under a nitrogen flow (0.2 L / min) at a temperature of 150 ° C., followed by molecular elongation. The mixture was then cooled to 125 ° C., and 242.9 parts of methacrylic acid (manufactured by Mitsubishi Gas Chemical Company, Inc.), 3.0 parts of triphenylantimony, 0.2 parts of methylhydroquinone, and 2.0 parts of 2-methylimidazole were added. The mixture was then reacted for 2 hours under an air flow (0.1 L / min) at a temperature of 130 ° C. to obtain a vinyl ester resin 2.

(Synthesis of vinyl ester resin 3)
A five-neck flask equipped with a thermometer, a stirrer, a gas inlet tube, and a reflux condenser was charged with 671.5 parts of a phenol novolac epoxy resin (manufactured by DIC Corporation, product name: EPICLON N-740), 325.1 parts of methacrylic acid (manufactured by Mitsubishi Gas Chemical Company, Inc.), 0.7 parts of methylhydroquinone, and 2.7 parts of 2-methylimidazole, and the mixture was reacted for 3 hours under an air flow (0.1 L/min) while maintaining the temperature at 120°C, to obtain vinyl ester resin 3.

[Preparation of Liquid Composition]
Composition A and Composition B were prepared.

<Preparation of Composition A>
Preparation of Liquid Composition A (x-1) (for preparing Composition (C-1) used in Examples 1 and 2)
959.5 parts of isophorone diisocyanate (manufactured by Evonik Chemical Industries, Ltd., product name: VESTANAT IPDI) and 40.5 parts of tert-butyl peroxybenzoate (manufactured by NOF Corporation, product name: PERBUTYL Z) were blended in a container and stirred at room temperature until a homogeneous solution was obtained, thereby obtaining a composition A(x-1).

Preparation of Liquid Composition A (x-2) (for preparing Composition (C-2) used in Example 3)
958.3 parts of isophorone diisocyanate (manufactured by Evonik Chemical Industries, Ltd., product name: VESTANAT IPDI) and 41.7 parts of tert-butyl peroxybenzoate (manufactured by NOF Corporation, product name: PERBUTYL Z) were blended in a container and stirred at room temperature until a homogeneous solution was obtained, thereby obtaining a composition A (x-2).

Preparation of Liquid Composition A (x-3) (for preparing Composition (C-3) used in Example 4)
956.1 parts of isophorone diisocyanate (manufactured by Evonik Chemical Industries, Ltd., product name: VESTANAT IPDI) and 43.9 parts of tert-butyl peroxybenzoate (manufactured by NOF Corporation, product name: PERBUTYL Z) were blended in a container and stirred at room temperature until a homogeneous solution was obtained, thereby obtaining a composition A (x-3).

<Preparation of Composition B>
Preparation of Liquid Composition B(y-1) (for preparing Composition (C-1) used in Examples 1 and 2)
462.9 parts of the vinyl ester resin 1, 365.6 parts of 2-hydroxyethyl methacrylate (manufactured by Mitsubishi Gas Chemical Company, Inc.), 170.7 parts of diethylene glycol dimethacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., product name: NK Ester 2G), 0.4 parts of dibutylhydroxytoluene, 0.1 parts of methylhydroquinone, and 0.3 parts of dibutyltin dilaurate were blended in a container and stirred until a homogeneous solution was obtained, thereby obtaining a composition B(y-1).

Preparation of Liquid Composition B (y-2) (for preparing Composition (C-2) used in Example 3)
350.8 parts of the vinyl ester resin 2, 434.8 parts of 2-hydroxyethyl methacrylate (manufactured by Mitsubishi Gas Chemical Company, Inc.), 213.6 parts of diethylene glycol dimethacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., product name: NK Ester 2G), 0.4 parts of dibutylhydroxytoluene, 0.1 parts of methylhydroquinone, and 0.3 parts of dibutyltin dilaurate were blended in a container and stirred until a homogeneous solution was obtained, thereby obtaining a composition B(y-2).

Preparation of Liquid Composition B (y-3) (for preparing Composition (C-3) used in Example 4)
A container was charged with 422.1 parts of the vinyl ester resin 3, 295.2 parts of 2-hydroxyethyl methacrylate (manufactured by Mitsubishi Gas Chemical Company, Inc.), 281.9 parts of diethylene glycol dimethacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., product name: NK Ester 2G), 0.4 parts of dibutylhydroxytoluene, 0.1 parts of methylhydroquinone, and 0.3 parts of dibutyltin dilaurate, and the resulting mixture was stirred until a homogeneous solution was obtained, thereby obtaining a composition B(y-3).

The prepared liquid compositions A and B were blended in the weight ratios shown in Table 1 and stirred for approximately 30 seconds until a uniform solution was obtained, yielding liquid compositions (C-1 to C-3) for intermediate substrates. Furthermore, the viscosity of the prepared liquid compositions, the molar ratio (B/A) of isocyanate-reactive groups in composition (B) to the number of moles of isocyanate groups in composition (A), and the theoretical ethylenically unsaturated group equivalent of the urethane (meth)acrylate formed after aging are also listed in Table 1.

Comparative Example Resin Synthesis (Synthesis of Vinyl Ester Resin 4)
A five-neck flask equipped with a thermometer, a stirrer, a gas inlet tube, and a reflux condenser was charged with 689.9 parts of a bisphenol A epoxy compound (manufactured by Mitsubishi Chemical Corporation, product name: jER 1001), 127.6 parts of methacrylic acid (manufactured by Mitsubishi Gas Chemical Company, Inc.), 0.8 parts of monomethyl ether hydroquinone, and 1.6 parts of 2-methylimidazole, and the mixture was reacted for 10 hours under an air flow (0.2 L/min) at a temperature of 110 to 120°C. Thereafter, the mixture was diluted with 180.0 parts of diethylene glycol dimethacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., product name: NK Ester 2G), to obtain vinyl ester resin 4.

[Preparation of Comparative Resin]
As a comparative example, a resin was prepared.

Preparation of vinyl ester resin (VE-1) (composition (C-4) used in Comparative Example 1)
990.1 parts of the vinyl ester resin 4 and 9.9 parts of tert-butylperoxy 2-ethylhexyl monocarbonate (manufactured by NOF Corporation, product name: Perbutyl E) were mixed at 80°C and stirred until a homogeneous solution was obtained, to obtain a resin composition (C-4).

Preparation of Epoxy Composition (EP-1) (Composition (C-5) used in Comparative Example 2)
917.4 parts of a bisphenol A type epoxy resin blend (a blend of jER 1001, product of Mitsubishi Chemical Corporation, and jER 828, product of Mitsubishi Chemical Corporation, in a weight ratio of 50:50) were blended with 45.9 parts of dicyandiamide and 36.7 parts of a urea derivative, and the mixture was stirred until a homogeneous solution was obtained, thereby obtaining a resin composition (C-5).

The viscosity of the resin prepared above is shown in Table 1. Table 1 shows the preparation of the liquid composition.

[Wet-through test]
For the purpose of evaluating the impregnation properties of the liquid composition and resin, two drops of the liquid composition (C-1) and resin compositions (C-2 to C-4) shown in Table 1 were dropped onto a sheet of carbon fiber fabric (manufactured by Mitsubishi Chemical Corporation, product name: TR3523M) using a dropper at each impregnation temperature, and the time required for the impregnation to reach the back surface at normal pressure was measured. The test results are shown in Table 2. Table 2 shows the results of the wet-through test (evaluation of the impregnation properties of the liquid composition and resin).

(Judgment method)
◎10 seconds or less 〇20 seconds or less △30 seconds or less x 30 seconds or more

[Shrinkage rate measurement]
For the purpose of evaluating dimensional stability, the shrinkage rates of the cured products of the above liquid compositions (C-1 to C-3) and resin compositions (C-4, C-5) were measured. The shrinkage rates were calculated from the specific gravity of the liquid and the specific gravity of the cured product. The liquid compositions (C-1 to C-3) were cured after thickening was completed. The thickening conditions and the results of the shrinkage rate measurements are shown in Table 3.

[Preparation of intermediate substrate]
Preparation of prepregs (P-1 to P-6)
Table 4 shows the conditions for preparing the intermediate substrate (prepreg) and the impregnation state of the prepreg.

Ten sheets of carbon fiber fabric (manufactured by Mitsubishi Chemical Corporation, product name: TR3523M) cut into 33 cm squares were impregnated with the liquid compositions (C-1 to C-3) shown in Table 1 using the formulations shown in Table 4, and then aged under various conditions to obtain prepregs. The resulting prepregs contained approximately 60% fiber by weight.

P-5 and 6 (Comparative Examples 1 and 2) were prepregs obtained using the hot melt method.

[Molding of intermediate substrate]
Prepreg molding
The prepared prepregs (P-1 to P-6) were molded using a 100-ton hydraulic press (manufactured by Toho Press Manufacturing Co., Ltd.) to obtain molded plates (Examples 1 to 4 and Comparative Examples 1 and 2). The molding temperature was 130°C (Examples 1, 3, 4 and Comparative Examples 1 and 2) and 150°C (Example 2), the molding pressure was 10 bar, and the molding time was 7 minutes.

[Measurement of physical properties of formed plate]
The obtained molded plates were subjected to a bending test, an interlaminar shear test, a dynamic viscoelasticity measurement, a moldability test, and an impregnation test.

Bending test: Measurement was carried out according to a method in accordance with JIS K7018.

Interlaminar shear test Measurement was carried out according to a method in accordance with JIS K7078.

Dynamic Viscoelasticity Measurement Measurement was carried out using a dynamic viscoelasticity measuring device (manufactured by TA Instruments, product name: RSA-G2).

Moldability and impregnation test (presence of voids and unimpregnated areas)
For the purpose of confirming impregnation and moldability, the cross section of a molded test piece having a thickness of about 2.4 mm and a length of 30 cm was examined under a microscope to check the number of voids and unimpregnated areas.
(Judgment method)
Number of voids and unimpregnated areas per cross-sectional area: 0-1 〇, 2-3 △
3 or more ×

The results of the bending test, interlaminar shear test, dynamic viscoelasticity measurement, moldability and impregnation test for the prepreg molded plate are shown in Table 5.

Tables 2 to 5 show that the liquid composition has excellent impregnation into the substrate, produces an intermediate substrate with little shrinkage during curing and excellent dimensional stability. Furthermore, Table 5 shows that the intermediate substrate produces a highly reliable composite material with excellent mechanical properties and heat resistance, and almost no voids or unimpregnated areas. The present invention uses this liquid composition, which has low viscosity and excellent impregnation, and can be used to produce intermediate substrates with large unit weights. It is also possible to reduce the number of laminations and provide high-strength FRP with minimal voids and excellent dimensional stability for intermediate substrates with large unit weights.

The radically polymerizable resin composition and intermediate substrate of the present invention are lightweight and strong, and therefore can be used in a wide range of applications, including, but not limited to, transportation equipment, industrial materials, civil engineering reinforcement materials, and sports equipment.

Claims (11)

A liquid composition for fiber-reinforced plastic intermediate substrates, comprising composition (A) containing compound (a) having two or more isocyanate groups, and composition (B) containing vinyl ester resin (b1) and ethylenically unsaturated group-containing monoalcohol compound (b2), wherein polymerization inhibitor (C) is blended into composition (B). 2. The liquid composition according to claim 1, wherein a polymerization inhibitor (C) is also blended in said composition (A). The liquid composition according to claim 1 or 2, wherein a polymerization initiator (D) and/or a urethane catalyst (E) is blended with the composition (A) and/or (B). The liquid composition according to any one of claims 1 to 3, wherein the molar ratio (B/A) of the isocyanate-reactive groups in composition (B) to the number of moles of isocyanate groups in composition (A) is 0.8 to 1.2. The liquid composition described in any one of claims 1 to 4, characterized in that the compositions (A) and/or (B) contain a polymerizable monomer (F) that does not have an isocyanate-reactive group. The liquid composition according to any one of claims 1 to 5, wherein the content of polymerizable monomer (F) is 1 to 40 wt% relative to the total weight of compositions (A) and (B). The liquid composition according to any one of claims 1 to 6, characterized in that the viscosity at 10 to 50°C measured with a Brookfield viscometer is 5 to 200 mPa·s. A fiber-reinforced plastic intermediate substrate obtained by impregnating a fiber material with the liquid composition described in any one of claims 1 to 7. A fiber-reinforced composite material obtained by curing the fiber-reinforced plastic intermediate substrate according to claim 8. A method for producing a fiber-reinforced plastic intermediate substrate, comprising the steps of: impregnating a fiber material with the liquid composition described in any one of claims 1 to 7 at an arbitrary composition; and maturing the fiber-reinforced plastic intermediate substrate obtained by the impregnation. The method according to claim 10, wherein the aging temperature is 30 to 80°C.