Prepreg, molded body, pressure container, method for producing prepreg, and method for producing molded body

Abstract

Provided is a prepreg having improved gas barrier properties when made into a molded body. In this prepreg, a carbon fiber base material is impregnated with a thermoplastic resin, the thermoplastic resin containing a vinyl alcohol polymer.

Description

Prepreg, molded body, pressure vessel, method for manufacturing prepreg, and method for manufacturing molded body

[0001] The present invention relates to a prepreg, a molded body, a pressure vessel, a method for manufacturing a prepreg, and a method for manufacturing a molded body. This application claims priority based on Japanese Patent Application No. 2022-046687, filed on March 23, 2022, the contents of which are incorporated herein by reference.

[0002] Carbon fiber composite materials (CFRP), which contain carbon fibers and a matrix resin, are characterized by their light weight and high strength compared to metals, and have been used as metal substitutes in a wide range of applications, such as aircraft and automobiles, and their range of applications has been expanding in recent years. For example, a sheet-like prepreg in which carbon fibers are impregnated with a matrix resin is known as a molding material for obtaining CFRP. CFRP is obtained by molding the prepreg under heat and pressure. Thermosetting resins such as epoxy resins and thermoplastic resins such as engineering plastics are used as matrix resins.

[0003] One known example of an application of CFRP is a high-pressure tank used for storing and transporting natural gas, etc. A known high-pressure tank using CFRP is one in which the outer periphery of a resin container body (resin liner) is reinforced with a reinforcing layer made of CFRP. Because high-pressure tanks are exposed to high-pressure gas, they are required to have excellent gas barrier properties. For example, Patent Document 1 discloses a high-pressure tank including a resin liner, a reinforcing layer covering the outer periphery of the resin liner, and a metal layer provided on the inner surface of the resin liner. The high-pressure tank described in Patent Document 1 has enhanced gas barrier properties by providing a metal layer on the inner surface of the resin liner.

[0004] However, if a metal layer is provided on the inner surface of the resin liner, the metal layer may peel off under high pressure. Therefore, as a high-pressure tank that has improved gas barrier properties without providing a metal layer on the inner surface of the resin liner, for example, Patent Document 2 discloses a high-pressure tank that includes a two-layer resin liner with a gas barrier layer made of ethylene-vinyl alcohol copolymer (EVOH) and a reinforcing layer that covers the surface of the resin liner facing the gas barrier layer. The high-pressure tank described in Patent Document 2 has a two-layer resin liner, one of which is a gas barrier layer, thereby improving gas barrier properties.

[0005] Japanese Patent Publication No. 2006-316934 Japanese Patent Publication No. 2010-71444

[0006] However, in the high-pressure tank described in Patent Document 2, the resin (EVOH) constituting the gas barrier layer is different from the matrix resin of the CFRP reinforcing layer, and therefore there are problems such as delamination due to insufficient interlayer adhesion between the gas barrier layer and the reinforcing layer, and gas trapped between the layers permeating to the outside due to pressure changes, and the gas barrier properties are not necessarily satisfactory. Therefore, the prepreg, which is the molding material for CFRP, is required to have not only strength when made into a molded product, but also gas barrier properties even without the provision of a metal layer or gas barrier layer.

[0007] An object of the present invention is to provide a prepreg having improved gas barrier properties when formed into a molded article.

[0008] The present invention has the following aspects. [1] A prepreg in which a carbon fiber substrate is impregnated with a thermoplastic resin, wherein the thermoplastic resin comprises a vinyl alcohol-based polymer. [2] The prepreg of [1], wherein the thermoplastic resin further comprises at least one selected from the group consisting of a polyamide resin, a polyolefin resin, a polyester resin, and a polystyrene resin. [3] The prepreg of [2], wherein the thermoplastic resin further comprises the polyamide resin. [4] The prepreg of [3], wherein the polyamide resin comprises polyamide 6. [5] The prepreg of [4], wherein the content of the polyamide 6 is 50 to 95 mass% relative to the total mass of the thermoplastic resin. [6] The prepreg of any of [3] to [5], wherein the ratio of the mass of the vinyl alcohol-based polymer to the mass of the polyamide resin is 5 to 55 mass%. [7] The prepreg of any of [1] to [6], wherein the content of the vinyl alcohol-based polymer is 5 to 40 mass% relative to the total mass of the thermoplastic resin. [8] The prepreg of any one of [1] to [7], wherein the vinyl alcohol-based polymer contains an ethylene-vinyl alcohol copolymer, and the content of ethylene structural units relative to the total number of moles of structural units constituting the ethylene-vinyl alcohol copolymer is 25 to 50 mol%. [9] The prepreg of any one of [1] to [8], wherein the proportion of the carbon fiber base material in the prepreg is 40 to 80 volume%.

[10] The prepreg of any one of [1] to [9], wherein the carbon fiber base material comprises a sheet in which carbon fibers are aligned in one direction.

[11] The carbon fiber base material has a weight per unit area of ​​10 to 300 g / m ２

[12] The prepreg of any one of [1] to

[11] , wherein the carbon fiber substrate contains carbon fibers having a strand strength of 4.8 GPa or more.

[13] A molded body obtained by molding the prepreg of any one of [1] to

[12] .

[14] A pressure vessel obtained by molding the prepreg of any one of [1] to

[12] .

[15] A method for manufacturing a molded body, comprising press-molding the prepreg of any one of [1] to

[12] .

[16] A method for manufacturing a molded body, comprising laminating the prepreg of any one of [1] to

[12] in a mold, wherein when laminating the prepreg in the mold, the prepreg is automatically laminated continuously while applying pressure to press the prepreg against the mold.

[17] A method for producing a prepreg, in which a resin film is laminated on a carbon fiber substrate and heated and pressurized to impregnate the carbon fiber substrate with a resin contained in the resin film, wherein a resin film containing a vinyl alcohol-based polymer and a resin film containing a polyamide resin are used.

[18] The resin film is a laminated film including Layer A: a layer containing a vinyl alcohol-based polymer and Layer B: a layer containing a polyamide resin, and the laminated film is laminated on the carbon fiber substrate.

[19] The method for producing a prepreg according to

[18] , in which the thickness of Layer A is 5 to 35% of the thickness of the laminated film.

[20] The method for producing a prepreg according to any one of

[17] to

[19] , in which the vinyl alcohol-based polymer contains an ethylene-vinyl alcohol copolymer, and the content of ethylene structural units relative to the total number of moles of structural units constituting the ethylene-vinyl alcohol copolymer is 25 to 50 mol %.

[21] A prepreg in which a carbon fiber substrate is impregnated with a thermoplastic resin composition, in which the thermoplastic resin composition contains an ethylene-vinyl alcohol copolymer.

[22] The prepreg of

[21] , wherein the content of the ethylene-vinyl alcohol copolymer is 5 to 40 mass% relative to the total mass of the thermoplastic resin composition.

[23] The prepreg of

[21] or

[22] , wherein the thermoplastic resin composition further contains at least one resin selected from the group consisting of polyamide resin, polyolefin resin, polyester resin, and polystyrene resin.

[24] The prepreg according to any one of

[21] to

[23] , wherein the carbon fiber substrate comprises a sheet in which carbon fibers are aligned in one direction.

[0009] According to a preferred embodiment of the present invention, a prepreg having improved gas barrier properties when molded into a molded article can be provided. A molded article and a pressure vessel having improved gas barrier properties can also be provided. Furthermore, a method for producing a prepreg having improved gas barrier properties when molded into a molded article, and a method for producing a molded article having improved gas barrier properties can also be provided.

[0010] FIG. 1 is a schematic diagram illustrating an example of a prepreg manufacturing apparatus.

[0011] [Prepreg] Hereinafter, one embodiment of the prepreg of the present invention will be described. The prepreg of this embodiment is a carbon fiber substrate impregnated with a thermoplastic resin. That is, the prepreg includes a carbon fiber substrate and a thermoplastic resin. Depending on the application, the carbon fiber may be replaced with a reinforcing fiber. The prepreg may further include a component (optional component) other than the carbon fiber substrate and the thermoplastic resin.

[0012] <Reinforcing Fiber> The reinforcing fiber can be present as a reinforcing fiber substrate in the prepreg, and is preferably in the form of a sheet. The orientation of the fibers in the reinforcing fiber substrate may be such that the reinforcing fibers are arranged in a single direction or in a random direction. Examples of the form of the reinforcing fiber substrate include a woven fabric of reinforcing fibers, a nonwoven fabric of reinforcing fibers, and a sheet in which long reinforcing fibers are aligned in one direction. Since fiber-reinforced plastics with high specific strength and specific modulus can be molded, it is preferable to use a sheet made of a bundle of reinforcing fibers in which continuous fibers are aligned in a single direction for the prepreg, and from the viewpoint of ease of handling, it is preferable to use a woven fabric of reinforcing fibers for the prepreg. The weight per unit area of ​​the reinforcing fiber substrate is 5 g / m ２ More than 4000g / m ２ Less than 10g / m ２ More than 300g / m ２ It can be as follows:

[0013] Examples of the material for the reinforcing fiber include glass fiber, carbon fiber, aramid fiber, boron fiber, etc. From the viewpoint of the mechanical properties and weight reduction of the resulting fiber-reinforced plastic, carbon fiber is preferred as the reinforcing fiber.

[0014] The fiber diameter of the carbon fiber can be 3 to 20 μm, preferably 4 to 12 μm. The number of carbon fibers in the carbon fiber bundle is preferably 1,000 to 70,000. A sheet-shaped reinforcing fiber substrate may be formed by using a plurality of carbon fiber bundles and aligning the fibers in one direction, or a sheet-shaped reinforcing fiber substrate may be formed by scattering chopped carbon fiber bundles. From the viewpoint of the rigidity of the obtained fiber-reinforced plastic, the strand tensile strength of the carbon fiber can be 1.5 to 9 GPa, and from the viewpoint of strength particularly when used in a pressure vessel, 4.8 GPa or more is preferable. The strand tensile modulus of the carbon fiber is preferably 150 to 400 GPa. Here, the strand tensile strength and strand tensile modulus of the carbon fiber are values ​​measured in accordance with JIS R7601:1986.

[0015] <Carbon fiber substrate> The carbon fiber substrate is an aggregate of carbon fibers and contains a plurality of carbon fibers. The carbon fibers constituting the carbon fiber substrate are not particularly limited, and examples thereof include polyacrylonitrile (PAN)-based carbon fibers, petroleum / coal pitch-based carbon fibers, rayon-based carbon fibers, and lignin-based carbon fibers. Among these, PAN-based carbon fibers are preferred. The carbon fibers are preferably continuous fibers. Examples include a sheet form in which continuous carbon fibers are aligned in one direction, and a woven form (for example, plain weave, twill weave, satin weave, etc.).

[0016] The carbon fiber is typically used in the form of a carbon fiber bundle in which a plurality of carbon fibers are bundled together. The number of filaments in the carbon fiber bundle is preferably 1,000 to 60,000, more preferably 1,000 to 50,000, and even more preferably 12,000 to 48,000. When the number of filaments in the carbon fiber bundle is within the above range, productivity and mechanical properties on an industrial scale are excellent.

[0017] The proportion of the carbon fiber substrate in the prepreg, i.e., the volume content (Vf) of the carbon fiber substrate relative to the total volume of the prepreg, is preferably 40 to 80% by volume, more preferably 40 to 75% by volume, even more preferably 45 to 70% by volume, and particularly preferably 45 to 65% by volume. If the proportion of the carbon fiber substrate is equal to or greater than the lower limit, the strength of the molded body (hereinafter also simply referred to as "molded body") obtained by molding the prepreg of this embodiment is increased. If the proportion of the carbon fiber substrate is equal to or less than the upper limit, poor appearance due to insufficient surface resin during molding can be suppressed. The volume content is a value obtained by a measurement method in accordance with ASTM D3171 or JIS K 7075.

[0018] <Thermoplastic Resin> The thermoplastic resin contains a vinyl alcohol-based polymer (hereinafter also referred to as "resin (a)"). It functions as a matrix resin in the prepreg. If the thermoplastic resin contains resin (a), the gas barrier properties of the molded article will be improved. The vinyl alcohol-based polymer is a polymer having vinyl alcohol units, and is preferably a vinyl alcohol-based copolymer from the viewpoints of the mechanical properties of the molded article and ease of handling of the prepreg.

[0019] Examples of the resin (a) include ethylene-vinyl alcohol copolymer (EVOH) and polyvinyl alcohol (PVA). EVOH is preferred from the viewpoint of improving extrusion moldability.

[0020] EVOH is a resin typically obtained by saponifying an ethylene-vinyl ester copolymer, which is a copolymer of ethylene and a vinyl ester monomer, and is a water-insoluble thermoplastic resin. The polymerization method for ethylene and a vinyl ester monomer is not particularly limited, and known polymerization methods, such as solution polymerization, suspension polymerization, and emulsion polymerization, can be used. Among these, solution polymerization is preferred, and solution polymerization using methanol as a solvent is more preferred. The method for saponifying the ethylene-vinyl ester copolymer is not particularly limited. EVOH produced in this manner contains ethylene structural units and vinyl alcohol structural units. It may also contain a small amount of vinyl ester structural units remaining unsaponified.

[0021] Examples of vinyl ester monomers include aliphatic vinyl esters such as vinyl acetate, vinyl formate, vinyl propionate, vinyl valerate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl caprate, vinyl laurate, vinyl stearate, and vinyl versatate; and aromatic vinyl esters such as vinyl benzoate. Vinyl acetate or aliphatic vinyl esters having 3 to 20 carbon atoms, preferably 4 to 10 carbon atoms, and more preferably 4 to 7 carbon atoms, are preferred, with vinyl acetate being more preferred from the viewpoints of market availability and efficient impurity treatment during production. One type of vinyl ester monomer may be used alone, or two or more types may be used in combination.

[0022] The content of ethylene structural units in EVOH is preferably 20 to 60 mol%, more preferably 25 to 50 mol%, and even more preferably 25 to 35 mol%, relative to the total number of moles of structural units constituting EVOH. When the content of ethylene structural units is equal to or greater than the above lower limit, the gas barrier properties of the molded article under high humidity conditions are further improved. In addition, the impregnation ability into the carbon fiber substrate is enhanced. When the content of ethylene structural units is equal to or less than the above upper limit, the gas barrier properties of the molded article are further improved. The content of ethylene structural units can be controlled by the ethylene pressure when copolymerizing vinyl ester monomer and ethylene. The content of ethylene structural units can be measured in accordance with ISO 14663.

[0023] The degree of saponification of the vinyl ester component in EVOH is preferably 90 to 100 mol%, more preferably 95 to 100 mol%, and even more preferably 99 to 100 mol%. When the degree of saponification is equal to or greater than the above lower limit, the gas barrier properties of the molded article are further improved. In addition, the thermal stability and moisture resistance of the molded article can be maintained at a good level. The degree of saponification can be controlled by the amount, temperature, time, etc. of the saponification catalyst (e.g., an alkaline catalyst such as sodium hydroxide) used when saponifying the ethylene-vinyl ester copolymer. The degree of saponification can be measured in the form of a solution in which EVOH is uniformly dissolved in a mixed solvent of water and methanol, in accordance with JIS K 6726 (wherein EVOH is a solution in which EVOH is uniformly dissolved in a mixed solvent of water and methanol).

[0024] The melt flow rate (MFR) of EVOH (210°C, 2160 g load) is preferably 0.5 to 100 g / 10 min, more preferably 1 to 50 g / 10 min, and even more preferably 3 to 35 g / 10 min. When the MFR of EVOH is equal to or greater than the lower limit, viscosity increase is suppressed, improving impregnation into the carbon fiber substrate. When the MFR of EVOH is equal to or less than the upper limit, film formability is improved, for example, by suppressing drawdown and neck-in during extrusion molding, and the A layer described below can be easily produced. MFR is an index of the degree of polymerization of EVOH and can be controlled by the amount of polymerization initiator and the amount of solvent used when copolymerizing ethylene and vinyl ester monomer. MFR can be measured in accordance with JIS K 7210 under conditions of 210°C and a load of 2160 g.

[0025] The EVOH may further contain structural units derived from the comonomers shown below, as long as the effects of the present invention are not impaired.Examples of comonomers include olefins such as propylene, 1-butene, and isobutene; hydroxy group-containing α-olefins such as 3-buten-1-ol, 3-butene-1,2-diol, 4-penten-1-ol, and 5-hexene-1,2-diol, and derivatives thereof such as esters and acylation products; hydroxyalkylvinylidenes such as 2-methylenepropane-1,3-diol and 3-methylenepentane-1,5-diol; 1,3-diacetoxy-2-methylenepropane, 1,3-dipropionyloxy-2-methylenepropane, and 1,3 -hydroxyalkylvinylidene diacetates such as dibutyronyloxy-2-methylenepropane; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, (anhydrous) phthalic acid, (anhydrous) maleic acid, (anhydrous) itaconic acid, or their salts, or mono- or di-alkyl esters having 1 to 18 carbon atoms; acrylamide, N-alkylacrylamide having 1 to 18 carbon atoms, N,N-dimethylacrylamide, 2-acrylamidopropanesulfonic acid or its salts, acrylamidopropyldimethylamine or its acid salts, or its quaternary salts. acrylamides such as methacrylamide, N-alkylmethacrylamides having 1 to 18 carbon atoms, N,N-dimethylmethacrylamide, 2-methacrylamidopropanesulfonic acid or a salt thereof, methacrylamidepropyldimethylamine or an acid salt thereof, or a quaternary salt thereof; N-vinylamides such as N-vinylpyrrolidone, N-vinylformamide, and N-vinylacetamide; vinyl cyanides such as acrylonitrile and methacrylonitrile; alkyl vinyl ethers having 1 to 18 carbon atoms, hydroxyalkyl vinyl ethers vinyl ethers such as vinyl ether and alkoxyalkyl vinyl ether; halogenated vinyl compounds such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride, and vinyl bromide; vinyl silanes such as trimethoxyvinylsilane; halogenated allyl compounds such as allyl acetate and allyl chloride; allyl alcohols such as allyl alcohol and dimethoxyallyl alcohol; and comonomers such as trimethyl-(3-acrylamido-3-dimethylpropyl)-ammonium chloride and acrylamido-2-methylpropanesulfonic acid.The comonomers may be used alone or in combination of two or more.

[0026] Resin (a) may be a "post-modified" EVOH resin, for example, urethane-modified, acetalized, cyanoethylated, or oxyalkylenated. EVOH copolymerized with a hydroxyl group-containing α-olefin is preferred, and EVOH having a 1,2-diol in the side chain is more preferred. Resin (a) may be a combination of two or more types of EVOH, or a combination of one or more types of EVOH and one or more types of PVA.

[0027] The content of resin (a) can be 1 to 100% by mass, preferably 2 to 75% by mass, more preferably 3 to 50% by mass, and even more preferably 5 to 40% by mass, relative to the total mass of the thermoplastic resin. When the content of resin (a) is equal to or greater than the above-mentioned lower limit, the desired gas barrier properties can be sufficiently exhibited. When the content of resin (a) is equal to or less than the above-mentioned upper limit, deterioration of mechanical properties due to the thickness of the EVOH can be suppressed. In another aspect, from the viewpoint of improving the barrier properties against helium and hydrogen gases, which are more easily permeable, the content of resin (a) can be 70 to 100% by mass, or 70 to 85% by mass, relative to the total mass of the thermoplastic resin.

[0028] The thermoplastic resin may further contain a polyamide resin (hereinafter also referred to as "resin (b)"). If the thermoplastic resin further contains resin (b) in addition to resin (a), the mold releasability during prepreg production is improved, resulting in excellent productivity.

[0029] The resin (b) is not particularly limited as long as it has an amide bond in the repeating structure, and examples thereof include aliphatic polyamides (aliphatic nylons) and aromatic polyamides (aromatic nylons). Examples of aliphatic polyamides include polycaprolactam (polyamide 6), polyhexamethylene adipamide (polyamide 66), polytetramethylene adipamide (polyamide 46), polyundecane amide (polyamide 11), polydodecanamide (polyamide 12), polyhexamethylene sebacamide (polyamide 610), polyamide 612, polyhexamethylene azelamide (polyamide 69), and copolymers thereof, such as polyamide 6 / 66 copolymer, polycaproamide / polyhexamethylene sebacamide copolymer (polyamide 6 / 610 copolymer), polyamide 6 / 66 / 610 copolymer, polyamide 6 / 12 copolymer, and polyamide 6 / 66 / 610 / 12 copolymer. Examples of aromatic polyamides include polyhexamethylene terephthalamide (polyamide 6T), polyamide 9T, polyamide MXD6, polyamide MXD10, polyamide 6 / 6T copolymer, polyamide 6T / 12 copolymer, polyamide 6T / 66 copolymer, polycaproamide / polyhexamethylene isophthalamide copolymer (polyamide 6 / 6I copolymer), polyamide 66 / 6I / 6 copolymer, polyamide 6T / 6I copolymer, polyamide 6T / 6I / 66 copolymer, and polyamide 6T / M-5T copolymer. From the viewpoint of releasability during prepreg production and adhesion to carbon fibers, polyamide 6, polyamide 66, polyamide 612, polyamide 11, polyamide 12, polyamide MXD6, polyamide 6T, and polyamide 9T are preferred, polyamide 6, polyamide 66, polyamide 11, polyamide 12, and polyamide MXD6 are more preferred, polyamide 6, polyamide 66, polyamide 11, and polyamide 12 are even more preferred, polyamide 6 and polyamide 66 are particularly preferred, and polyamide 6 is particularly preferred. Resin (b) may be used alone or in combination of two or more types.

[0030] When the thermoplastic resin contains polyamide 6, the content of polyamide 6 can be 1 to 99% by mass relative to the total mass of the thermoplastic resin, and from the viewpoint of improving mechanical properties, it is preferably 25 to 98% by mass, more preferably 50 to 95% by mass, even more preferably 51 to 95% by mass, and particularly preferably 60 to 95% by mass. In another aspect, from the viewpoint of improving releasability, the content of polyamide 6 can be 2 to 95% by mass or can also be 5 to 90% by mass relative to the total mass of the thermoplastic resin.

[0031] When the thermoplastic resin contains resin (a) and resin (b), the mass ratio of resin (a) to resin (b), expressed as (mass of resin (a) / mass of resin (b)) × 100 (hereinafter also referred to as "a / b × 100"), can be 1 to 99 mass%, preferably 2 to 75 mass%, and more preferably 5 to 55 mass%. When a / b × 100 is equal to or greater than the lower limit, deterioration of gas barrier properties is further suppressed. When a / b × 100 is equal to or less than the upper limit, mold releasability during prepreg production is improved. In another aspect, from the viewpoint of imparting barrier properties against more easily permeable gases while maintaining mold releasability, a / b × 100 can be 50 to 99 mass%, or can be 70 to 99 mass%.

[0032] The proportion of thermoplastic resin in the prepreg, i.e., the weight content (Rc) of thermoplastic resin relative to the total volume of the prepreg, is preferably 10 to 50 wt%, more preferably 15 to 50 wt%, even more preferably 20 to 45 wt%, and particularly preferably 25 to 45 wt%. If the proportion of thermoplastic resin is equal to or greater than the above-mentioned lower limit, poor appearance due to insufficient surface resin during molding can be suppressed. If the proportion of thermoplastic resin is equal to or less than the above-mentioned upper limit, the strength of the molded body is increased. The weight content is a value obtained by a measurement method conforming to ASTM D3171 or JIS K 7075.

[0033] The thermoplastic resin may contain a thermoplastic resin other than resin (a) and resin (b) (hereinafter also referred to as "resin (c)"), as long as the effects of the present invention are not impaired. Examples of resin (c) include polyolefin resins, polyester resins, polycarbonate resins, polyamideimide resins, polyphenylene oxide resins, polysulfone resins, polyethersulfone resins, polyetheretherketone resins, polystyrene resins, ABS resins, polyphenylene sulfide resins, liquid crystal polyester resins, acrylic resins, vinyl ester resins, ionomers, acrylonitrile-styrene copolymers, ethylene-vinyl acetate copolymers, ethylene-acrylic acid copolymers, ethylene-acrylic acid ester copolymers, polyvinyl chloride, polyvinylidene chloride, polyester elastomers, polyurethane elastomers, polystyrene elastomers, halogenated polyolefins (chlorinated polyethylene, chlorinated polypropylene, etc.), and aromatic or aliphatic polyketones. Polyolefin resins, polyester resins, and polystyrene resins are preferred. Resin (c) may be used alone or in combination of two or more.

[0034] Examples of polyolefin resins include unmodified polyolefin resins such as polyethylene resins (linear low-density polyethylene, low-density polyethylene, very low-density polyethylene, medium-density polyethylene, high-density polyethylene, ethylene-propylene (block and random) copolymers, ethylene-α-olefin (α-olefin having 4 to 20 carbon atoms) copolymers, etc.), polypropylene resins (polypropylene, propylene-α-olefin (α-olefin having 4 to 20 carbon atoms) copolymers, etc.), polybutene, polypentene, and polycyclic olefin resins (polymers having a cyclic olefin structure in at least one of the main chain and side chain); and modified polyolefin resins such as unsaturated carboxylic acid-modified polyolefin resins obtained by graft-modifying these unmodified polyolefin resins with unsaturated carboxylic acid or an ester thereof. Examples of polyester resins include polyethylene terephthalate resin and polybutylene terephthalate resin.

[0035] The content of resin (c) is preferably 30% by mass or less, more preferably 1% by mass or less, and even more preferably 0.1% by mass or less, based on the total mass of the thermoplastic resin. It is also possible to make the resin (c) substantially absent. In this specification, "substantially absent" means that the resin is not actively blended, except for unintentional inclusion. The total content of resins (a), (b), and (c) in the thermoplastic resin is 100% by mass.

[0036] <Optional Components> The prepreg may contain fibers other than carbon fibers (hereinafter also referred to as "other fibers"). In this specification, carbon fibers and other fibers are collectively referred to as "reinforcing fibers." As the other fibers, inorganic fibers other than carbon fibers, organic fibers, metal fibers, or hybrid reinforcing fibers combining these can be used. Examples of inorganic fibers other than carbon fibers include graphite fibers, silicon carbide fibers, alumina fibers, tungsten carbide fibers, boron fibers, and glass fibers. Examples of organic fibers include aramid fibers, high-density polyethylene fibers, and other general nylon fibers and polyester fibers. Examples of metal fibers include stainless steel and iron fibers. Examples of hybrid reinforcing fibers include metal-coated carbon fibers. Considering the mechanical properties such as strength of the prepreg, glass fibers are preferred as the other fibers. One type of other fiber may be used alone, or two or more types may be used in combination. The other fiber is preferably a continuous fiber.

[0037] The prepreg may further contain additives other than the reinforcing fibers. Examples of additives include flame retardants, weather resistance improvers, antioxidants, heat stabilizers, UV absorbers, plasticizers, lubricants, colorants, compatibilizers, and conductive fillers. One type of additive may be used alone, or two or more types may be used in combination.

[0038] The proportion of additives in the prepreg, that is, the content of additives relative to the total volume of the prepreg, is preferably 5% by mass or less, more preferably 1% by mass or less, and even more preferably 0.5% by mass or less, from the viewpoint of maintaining mechanical strength. The total content of the thermoplastic resin, carbon fiber base material, other fibers, and additives in the prepreg is 100% by mass. The total content of the thermoplastic resin and carbon fiber base material in the prepreg may be 70% by mass or more, 80% by mass or more, 90% by mass, or 100% by mass, relative to the total mass of the prepreg.

[0039] <Method for producing prepreg> The method for producing the prepreg is not particularly limited, and the prepreg can be produced by a known method. For example, the prepreg can be produced by impregnating the above-mentioned thermoplastic resin into a carbon fiber substrate. As a method for impregnating the thermoplastic resin, for example, a method in which the thermoplastic resin is processed into a film having a thickness of about 10 to 100 μm, a fiber having a fiber diameter of about 5 to 50 μm, or a powder having an average particle size of about 10 to 100 μm is adhered to the carbon fiber substrate can be mentioned.

[0040] When the prepreg contains an additive, a thermoplastic resin and the additive are mixed to prepare a thermoplastic resin composition, and the carbon fiber substrate is impregnated with this thermoplastic resin composition. When the prepreg contains other fibers, a reinforcing fiber substrate containing carbon fibers and other fibers is impregnated with a thermoplastic resin or a thermoplastic resin composition. The "reinforcing fiber substrate" refers to an aggregate of carbon fibers and other fibers (when other fibers are included).

[0041] Hereinafter, one embodiment of a method for producing a prepreg will be described. In the method for producing a prepreg of this embodiment, a resin film having a layer containing the above-mentioned resin (a) (hereinafter also referred to as "layer A") is laminated on a carbon fiber substrate and heated and pressurized, thereby impregnating the carbon fiber substrate with the resin contained in the resin film to produce a prepreg. Specifically, using the production apparatus 10 shown in FIG. 1, a carbon fiber substrate 11 is unwound from a roll 18. Separately, resin films 12 unwound from multiple rolls 18 are laminated on the upper and lower surfaces of the carbon fiber substrate 11 via a pressure roller 19 to form a laminate, and after preheating with a heater 13, release films 14 are placed on the upper and lower surfaces of the laminate. Next, pressure is applied using a hot plate press 15 heated to or above the melting point of the resin contained in the resin film 12, and then pressure is applied using a cooling press 16 cooled to or below the solidification temperature of the resin contained in the resin film 12, thereby impregnating the carbon fiber substrate 11 with the thermoplastic resin in the laminate. Thereafter, the release film 14 is removed to obtain a prepreg 17. The heating temperature of the laminate is not particularly limited as long as it is a temperature at which the thermoplastic resin, that is, the resin contained in the resin film 12, can be heated and melted.

[0042] The resin film laminated on the carbon fiber substrate includes an A layer. The resin film may be a single-layer film consisting of the A layer, or a laminated film including the A layer and a layer containing the resin (b) (hereinafter also referred to as a "B layer"). In addition, for example, a resin film containing a vinyl alcohol copolymer and a resin film containing a polyamide resin may be used, such that the resin film 12 laminated on the upper surface of the carbon fiber substrate 11 is a single-layer film (A) consisting of the A layer, and the resin film 12 laminated on the lower surface of the carbon fiber substrate 11 is a single-layer film (B) consisting of the B layer. When a single-layer film is used, the single-layer film (A) is overlapped on the carbon fiber substrate 11 and impregnated to form a resin-impregnated carbon fiber substrate (A), and the resin-impregnated carbon fiber substrate (A) may be further overlapped with a single-layer film (B) and impregnated therewith. Alternatively, the resin-impregnated carbon fiber substrate (A) and the resin-impregnated carbon fiber substrate (B) obtained by overlapping and impregnating the single-layer film (B) on the carbon fiber substrate 11 may be overlapped. The carbon fiber substrate 11 may be laminated so as to be sandwiched between the monolayer film (A) and the monolayer film (B). The laminated film may have a two-layer structure including one A layer and one B layer, or may have a multilayer structure of three or more layers. For example, when the laminated film has a three-layer structure, it may have a B / A / B configuration in which one A layer is sandwiched between two B layers, an A / B / A configuration in which one B layer is sandwiched between two A layers, or a configuration including one A layer and one B layer and layers other than the A layer and the B layer.

[0043] From the viewpoint of improving the barrier properties and mechanical properties by stretching, the resin film is preferably a laminate film having an A layer and a B layer, and particularly preferably a laminate film having a B / A / B configuration in which one A layer is sandwiched between two B layers. The thickness of the A layer is preferably 1 to 99%, more preferably 2 to 50%, and even more preferably 5 to 35% of the total thickness of the resin film. If the thickness of the A layer is equal to or less than the upper limit, uneven elongation and the possibility of breakage during stretching are suppressed, and if the thickness is equal to or greater than the lower limit, gas barrier properties can be maintained.

[0044] When the resin film is a single-layer film, the resin film can be obtained by extruding resin (a) or a thermoplastic resin composition (a) obtained by mixing resin (a) and additives into a film. When the resin film is a laminated film, the resin film can be obtained by extruding resin (a) or a thermoplastic resin composition (a) and resin (b) or a thermoplastic resin composition (b) obtained by mixing resin (b) and additives into a film so that the resin films are laminated. In addition, commercially available products may be used as the resin film.

[0045] When a laminated film having an A layer and a B layer is used as the resin film, the laminated film may be laminated on the carbon fiber substrate so that the A layer is in contact with the carbon fiber substrate, or the B layer may be laminated on the carbon fiber substrate so that the B layer is in contact with the carbon fiber substrate. In addition, when the resin or thermoplastic resin composition used in the laminated film has a melting point, the melting point is different between the A layer and the B layer. When the resin or thermoplastic resin composition does not have a melting point, the glass transition temperature (Tg) is different between the A layer and the B layer. It is preferable to heat the A layer and the B layer to a temperature higher than either the melting point or Tg and impregnate the carbon fiber substrate.

[0046] When producing a prepreg 17 using the production apparatus 10 shown in FIG. 1 , the resin films 12 laminated on the upper and lower surfaces of the carbon fiber substrate 11 may be of the same type or different types. Examples of combinations of the resin films 12 laminated on the upper and lower surfaces of the carbon fiber substrate 11 are as follows: A combination in which both of the resin films 12 laminated on the upper and lower surfaces of the carbon fiber substrate 11 are single-layer films made of layer A. A combination in which one resin film 12 is a single-layer film made of layer A, and the other resin film 12 is a single-layer film made of layer B. A combination in which one resin film 12 is a single-layer film made of layer A, and the other resin film 12 is a laminate film including layer A and layer B. A combination in which one resin film 12 is a single-layer film made of layer B, and the other resin film 12 is a laminate film including layer A and layer B. A combination in which one resin film 12 is a single-layer film made of layer B, and the other resin film 12 is a laminate film including layer A and layer B. A combination in which both of the resin films 12 laminated on the upper and lower surfaces of the carbon fiber substrate 11 are laminate films including layer A and layer B.

[0047] In the manufacturing apparatus 10 shown in FIG. 1 , resin films 12 are laminated on the upper and lower surfaces of the carbon fiber substrate 11, but the carbon fiber substrate 11 and the resin film 12 may be interchanged. That is, the carbon fiber substrate 11 may be laminated on the upper and lower surfaces of the resin film 12 to form a laminate, and the prepreg may be manufactured by impregnating the carbon fiber substrate 11 with the thermoplastic resin in the laminate by heating and pressurizing. In this case, the resin film 12 may be a single-layer film consisting of an A layer, or a laminate film including an A layer and a B layer, with a laminate film being preferred. In the case of a laminate film, it may have a two-layer structure including one A layer and one B layer, or a multilayer structure of three or more layers, with a laminate film having a B / A / B configuration in which one A layer is sandwiched between two B layers being preferred.

[0048] Another embodiment of the resin film is a single-layer or laminate film having one or more layers containing EVOH as Layer A (hereinafter also referred to as "EVOH layer"). The EVOH layer can be laminated with a base resin layer (hereinafter also referred to as "base resin") primarily composed of a thermoplastic resin other than EVOH to further impart strength, protect the EVOH layer from the effects of moisture, and impart other functions. Examples of the base resin include the resins (b) and (c) described above. From the viewpoint of protecting the EVOH layer from the effects of moisture, hydrophobic resins are preferred, with polyamide resins, polyolefin resins, polyester resins, and polystyrene resins being more preferred, and polyolefin resins such as polyethylene resins, polypropylene resins, polycyclic olefin resins, and unsaturated carboxylic acid-modified polyolefin resins of these resins being even more preferred, with polycyclic olefin resins being particularly preferred as the hydrophobic resin. The base resins may be used alone or in combination of two or more.

[0049] As an example of the layer structure of the resin film, when the EVOH layer is designated as a (a1, a2, ...) and the base resin layer is designated as b (b1, b2, ...), any combination such as a / b, b / a / b, a / b / a, a1 / a2 / b, a / b1 / b2, b2 / b1 / a / b1 / b2, or b2 / b1 / a / b1 / a / b1 / b2 is possible. Furthermore, when a recycled layer containing a mixture of EVOH and base resin obtained by remelting and molding edges or defective products generated during the resin film production process is designated as R, the layer structure of the resin film can also be b / R / a, b / R / a / b, b / R / a / R / b, b / a / R / a / b, b / R / a / R / a / R / b, or b / R / a / R / a / R / b. The total number of layers of the resin film is preferably 2 to 15, and more preferably 3 to 10.

[0050] In the above layer structure, an adhesive resin layer containing an adhesive resin may be interposed between each layer as needed. Known adhesive resins can be used, and may be selected appropriately depending on the type of base resin, for example. Representative examples include carboxyl group-containing modified polyolefin polymers obtained by chemically bonding an unsaturated carboxylic acid or its anhydride to a polyolefin resin via addition reaction, graft reaction, or the like. More specific examples include maleic anhydride-grafted polyethylene, maleic anhydride-grafted polypropylene, maleic anhydride-grafted ethylene-propylene (block and random) copolymers, maleic anhydride-grafted ethylene-ethyl acrylate copolymers, maleic anhydride-grafted ethylene-vinyl acetate copolymers, maleic anhydride-modified polycyclic olefin resins, and maleic anhydride-grafted polyolefin resins. The adhesive resins may be used alone or in combination of two or more.

[0051] When an adhesive resin layer is interposed between an EVOH layer and a base resin layer in a resin film, the adhesive resin layer is at least one layer located on both sides of the EVOH layer, and therefore it is preferable to use an adhesive resin with excellent hydrophobicity.

[0052] One or more of the EVOH layer, the base resin layer, and the adhesive resin layer may contain, as necessary, conventionally known additives such as plasticizers, fillers, clays (montmorillonite, etc.), colorants, antioxidants, antistatic agents, lubricants, core materials, antiblocking agents, waxes, etc., within a range that does not impair the spirit of the present invention (for example, 30% by mass or less, preferably 10% by mass or less, based on the total mass of the layer).

[0053] Examples of the form of the prepreg obtained in this way include a unidirectional prepreg (UD prepreg) in which a sheet-like carbon fiber substrate in which carbon fibers are aligned in one direction is impregnated with a thermoplastic resin, a cross prepreg in which a carbon fiber fabric is impregnated with a thermoplastic resin, and a tow prepreg in which a tow (carbon fiber bundle) is pre-impregnated with a thermoplastic resin. The thickness of the prepreg is preferably 0.04 to 0.7 mm, more preferably 0.04 to 0.4 mm.

[0054] <Effects> The prepreg described above has improved gas barrier properties because the thermoplastic resin containing the resin (a) having gas barrier properties is impregnated into the carbon fiber substrate. Therefore, when a molded article obtained by molding a prepreg having excellent gas barrier properties is used, for example, as the reinforcing layer of a high-pressure tank, a high-pressure tank having excellent gas barrier properties can be obtained without providing a metal layer or a gas barrier layer. Moreover, when a molded article obtained by molding the prepreg of the present invention is used, there is no need to provide a gas barrier layer, and problems such as delamination due to insufficient interlayer adhesion between the gas barrier layer and the reinforcing layer and permeation of gas trapped between the layers to the outside due to pressure changes are less likely to occur.

[0055] [Molded body] A molded body can be obtained by molding the above-mentioned prepreg. The molded body may be obtained by laminating and integrating prepregs, or by using only one prepreg. The molded body is preferably a molded body obtained by molding a laminate in which two or more sheets of only the above-mentioned prepreg are laminated. Note that the molded body may also be a molded body obtained by molding a laminate in which the above-mentioned prepreg and a prepreg other than the above-mentioned prepreg are combined and laminated.

[0056] The layering configuration of the prepregs in the laminate is not particularly limited. The number of prepregs stacked in the laminate can be appropriately set depending on the thickness of the prepregs and the thickness required for the molded body. When the prepregs are UD prepregs, the fiber direction of the carbon fibers in each UD prepreg to be stacked can be appropriately set depending on the physical properties required for the molded body. The fiber direction of the carbon fibers in each UD prepreg may be the same. Furthermore, for example, when isotropy is required for the physical properties of the molded body, it is preferable to stack the UD prepregs so that the fiber directions of the carbon fibers in a plan view of the stacked prepregs are a combination of 0° and 90°, a combination of 0°, 45°, 90°, and −45°, or a combination of 0°, 60°, and −60°, and to stack them symmetrically in the thickness direction.

[0057] <Method for manufacturing molded body> A molded body is obtained by molding a prepreg. The method for molding the prepreg is not particularly limited, and examples thereof include molding a single sheet of the above-mentioned prepreg, a laminate formed by laminating multiple sheets of the above-mentioned prepreg, or a laminate formed by combining the above-mentioned prepreg with a prepreg other than the above-mentioned prepreg, using a mold press method, an autoclave method, or a hot / cold press method. Examples of prepreg lamination methods include an automatic lamination method using a robot. Specifically, when laminating the prepreg in a mold, the prepreg can be automatically laminated continuously while applying pressure to press the prepreg against the mold. Furthermore, to facilitate the release of the laminate from the mold, a release agent may be applied to the mold or a release film may be placed on top of the mold, and the laminate may be automatically laminated thereon.

[0058] The molded article described above has excellent gas barrier properties and is particularly suitable as a reinforcing layer for a pressure tank. The molded article of the present invention can also be used as a pressure vessel.

[0059] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0060] [Materials] <Thermoplastic resin> The thermoplastic resins used in each example are as follows. Resin film (1): NY / EVOH / NY laminate film. The total thickness of the B layer containing NY (polyamide 6) was 20.5 μm, and the thickness of the A layer containing EVOH was 4.5 μm (i.e., 18% of the thickness of the laminate film). The content of ethylene structural units in the EVOH was 25 mol %. The ratio of the mass of EVOH to the mass of NY (mass of EVOH / mass of NY × 100) was 24 mass %. Resin film (2): NY / EVOH / NY laminate film. The total thickness of the B layer containing NY (polyamide 6) was 10.5 μm, and the thickness of the A layer containing EVOH was 4.5 μm (i.e., 30% of the thickness of the laminate film). The content of ethylene structural units in the EVOH was 25 mol %. The ratio of the mass of EVOH to the mass of NY (mass of EVOH / mass of NY × 100) was 46 mass%. Resin film (3): NY / EVOH / NY laminate film. The total thickness of the B layer containing NY (polyamide 6) was 13.5 μm, and the thickness of the A layer containing EVOH was 1.5 μm (i.e., 10% of the thickness of the laminate film). The content of ethylene structural units in the EVOH was 25 mol%. The ratio of the mass of EVOH to the mass of NY (mass of EVOH / mass of NY × 100) was 12 mass%. Resin film (4): NY / EVOH / NY laminate film. The total thickness of the B layer containing NY (polyamide 6) was 20.5 μm, and the thickness of the A layer containing EVOH was 4.5 μm (i.e., 18% of the thickness of the laminate film). The content of ethylene structural units in the EVOH was 32 mol%. The ratio of the mass of EVOH to the mass of NY (mass of EVOH / mass of NY×100) was 23 mass%. Resin film (5): EVOH monolayer film (thickness 25 μm). The content of ethylene structural units in EVOH was 25 mol%. Resin film (6): NY monolayer film (thickness 25 μm).

[0061] <Carbon Fiber> As the carbon fiber, a PAN-based carbon fiber (manufactured by Mitsubishi Chemical Corporation, trade name "TR50S", fiber diameter 7 μm, 1000 tex, 15000 strands) was used.

[0062] [Evaluation Method] <Evaluation of Gas Barrier Property: Measurement of Oxygen Transmission Rate (OTR)> Using an oxygen transmission rate tester (manufactured by MOCON, product name "Oxtran 2 / 21"), the molded article used for evaluation was measured in a gas barrier measurement area of ​​50 cm. ２ The film was cut to the above dimensions and measured for oxygen permeability (cc / m) under conditions of a temperature of 20°C and a humidity of 65% RH. ２ The detection limit of this tester was 0.05 cc / m ２ When the oxygen transmission rate was below the detection limit, the result was recorded as "<0.05".

[0063] <Evaluation of Mechanical Properties: 0° Bending> A test piece was obtained from the molded body, and subjected to 0° bending in accordance with ASTM D790 using a universal testing machine (manufactured by INSTRON, product name "INSTRON 5565") equipped with a three-point bending jig (indenter R = 5.0 mm, support R = 3.2 mm) at a ratio of the distance between supports (L) to the thickness (d) of the test piece (L / d) of 40 and a crosshead speed of (L ２ The 0° bending strength was measured by a 0° bending test under the condition of (6×d) / (6×d) / (6×d). The test specimen used in the measurement had a width of 12.7 mm and a length of 100 mm.

[0064] <Evaluation of Mechanical Properties: 90° Bending> A test piece was obtained from the molded body, and subjected to 90° bending in accordance with ASTM D790 using a universal testing machine (manufactured by INSTRON, product name "INSTRON 5565") equipped with a three-point bending jig (indenter R = 5.0 mm, support R = 3.2 mm) at a ratio of the distance between supports (L) to the thickness (d) of the test piece (L / d) of 16 and a crosshead speed of (L ２ The 90° bending strength was measured by a 90° bending test under the condition of (6×d) / (6×d) / (6×d). The test specimen used in the measurement had a width of 12.7 mm and a length of 50 mm.

[0065] [Example 1] <Production of prepreg> As a carbon fiber substrate, a resin film (1) was laminated on a carbon fiber sheet in which carbon fibers were oriented in one direction, and the resin film (1) was heat-melted and impregnated into the carbon fiber sheet to produce a prepreg. The thickness of the obtained prepreg was about 0.18 mm, and the volume content (Vf) of the carbon fiber substrate measured in accordance with ASTM D3171 was 60 volume%, and a / b × 100 was 24 mass%.

[0066] <Production of molded body, evaluation of molded body and prepreg> One or 11 prepregs cut to dimensions of 178 mm x 328 mm were laminated so that all fiber directions were oriented in the 0 ° direction, and a prepreg A having a thickness of 0.18 mm and a laminate B having a thickness of 2 mm were produced. Separately, the obtained laminate B was placed in the lower mold of a titanium mold, and after closing the upper mold, a 50 ton press was used, a heating and cooling two-stage press (manufactured by Shinto Metal Industries Co., Ltd., product name "50 ton press"), in a press set to 270 ° C., the mold was preheated to 260 ° C. in about 10 minutes, and then compression molded for 30 minutes under molding conditions of 5 MPa. Then, the mold was transferred to a press platen surface adjusted to a temperature of 60 ° C., and the temperature was lowered to 60 ° C. in about 3 minutes, and a molded body B (thickness 2 mm) of 180 mm x 330 mm was obtained. The gas barrier properties (200 μm equivalent) were evaluated using the obtained prepreg A, and the mechanical properties were evaluated using the molded body B. Before evaluating the mechanical properties, the test specimens were dried at 110° C. for 4 hours. The results are shown in Table 1.

[0067] [Example 2] A prepreg having a thickness of approximately 0.18 mm and a volume content (Vf) of the carbon fiber substrate of 60% by volume was produced in the same manner as in Example 1, except that resin film (2) was used instead of resin film (1). a / b x 100 was 23% by mass. A prepreg and a molded article for evaluating gas barrier properties and mechanical properties were also obtained. As in Example 1, the obtained prepreg and molded article were used to evaluate gas barrier properties (200 μm equivalent) and mechanical properties, respectively. Before evaluating the mechanical properties, the test specimens were vacuum dried at 50°C for 2 days. The results are also shown in Table 1.

[0068] [Example 3] A prepreg having a thickness of approximately 0.18 mm and a volume content (Vf) of the carbon fiber substrate of 60% by volume was produced in the same manner as in Example 1, except that resin film (3) was used instead of resin film (1). a / b x 100 was 12% by mass. In addition, a prepreg and a molded article for evaluating gas barrier properties and mechanical properties were also obtained. As in Example 1, the obtained prepreg and molded article were used to evaluate gas barrier properties (200 μm equivalent) and mechanical properties, respectively. Before evaluating the mechanical properties, the test specimens were vacuum dried at 50°C for 2 days. The results are also shown in Table 1.

[0069] [Example 4] A prepreg having a thickness of approximately 0.18 mm and a volume content (Vf) of the carbon fiber substrate of 60% by volume was produced in the same manner as in Example 1, except that resin film (4) was used instead of resin film (1). a / b x 100 was 46% by mass. In addition, a prepreg and a molded article for evaluating gas barrier properties and mechanical properties were also obtained. As in Example 1, the obtained prepreg and molded article were used to evaluate gas barrier properties (200 μm equivalent) and mechanical properties, respectively. Before evaluating the mechanical properties, the test specimens were vacuum dried at 50 °C for 2 days. The results are also shown in Table 1.

[0070] [Example 5] A prepreg having a thickness of approximately 0.06 mm and a volume content (Vf) of the carbon fiber substrate of 60% by volume was produced in the same manner as in Example 1, except that resin film (5) was used instead of resin film (1). The prepreg was cut to a dimension of 178 mm x 328 mm, and three or 34 sheets were laminated so that the fiber directions all faced the 0° direction to produce a laminate C having a thickness of 0.18 mm and a laminate D having a thickness of 2 mm, respectively. The obtained laminate C was placed in a press with multiple platens whose temperature was adjusted to 50 to 250 ° C., and compression molding was performed once on each platen, to obtain a molded body C (thickness 0.18 mm) of 180 mm x 330 mm. Separately, the obtained laminate D was placed in the lower die of a titanium mold, and the upper die was closed. After that, a 50-ton two-stage heating and cooling press was used. The press was set to 230 ° C., and the mold was preheated to 220 ° C. in about 10 minutes. Then, compression molding was performed for 30 minutes under molding conditions of 5 MPa. The mold was then transferred to a press platen temperature-controlled at 60 ° C., and the temperature was reduced to 60 ° C. in about 3 minutes to obtain a molded body D (thickness 2 mm) measuring 180 mm x 330 mm. The gas barrier properties (200 μm equivalent) were evaluated using the obtained molded body C, and the mechanical properties were evaluated using molded body D. The results are shown in Table 1.

[0071] [Example 6] A thermosetting prepreg (manufactured by Mitsubishi Chemical Corporation, product name "TR361E250S") in which a thermosetting resin was impregnated into a carbon fiber substrate was cut to a dimension of 298 mm x 298 mm. One or ten sheets were cut and laminated so that all fiber directions were oriented in the 0° direction to produce a prepreg E having a thickness of 0.25 mm and a laminate F having a thickness of 2.5 mm. One cut prepreg was placed in a mold set at 140 ° C. in a 100 ton press (manufactured by Yamamoto Iron Works Co., Ltd., product name "100 ton Press") and compression molded for 5 minutes under molding conditions of 5 MPa to obtain a molded body E (thickness 0.250 mm) having a size of 300 mm x 300 mm. Separately, the obtained laminate F was placed in a mold set at 140°C in a 100 ton press and compression molded for 5 minutes under molding conditions of 5 MPa to obtain a molded body F of 300 mm x 300 mm (thickness 2 mm).

[0072] The gas barrier properties (200 μm equivalent) were evaluated using the obtained molded body E, and the mechanical properties were evaluated using the molded body F. The results are shown in Table 1.

[0073] [Example 7] A prepreg having a thickness of approximately 0.18 mm and a volume content (Vf) of the carbon fiber substrate of 60% by volume was produced in the same manner as in Example 1, except that resin film (6) was used instead of resin film (1). A prepreg and a molded article for evaluating gas barrier properties and mechanical properties were also obtained. The obtained prepreg and molded article were used to evaluate gas barrier properties (200 μm equivalent) and mechanical properties, respectively. Before evaluating the mechanical properties, the test specimens were dried at 110°C for 4 hours. The results are shown in Table 1.

[0074]

[0075] As is clear from Table 1, the molded articles obtained from the prepregs obtained in Examples 1 to 5 had superior gas barrier properties compared to the molded articles obtained from the prepregs used in Examples 6 and 7. Although it was expected that the mechanical properties would be significantly inferior to those of thermosetting prepregs designed to exhibit the functions required for a molded article, the mechanical properties of the molded articles obtained in Examples 1 to 5 were sufficient for a carbon fiber composite material, and the molded article obtained in Example 4 in particular exhibited excellent values ​​almost equivalent to those of Example 7. Therefore, it was confirmed that the obtained prepregs also had excellent adhesion between the carbon fibers and the matrix resin and exhibited the excellent properties inherent to the carbon fibers.

[0076] The prepreg and molded article of the present invention can be used in general industrial applications such as sporting goods, automobiles, pressure tanks, aircraft, and tendons, and exhibits particularly high performance when used in pressure tanks.

[0077] REFERENCE SIGNS LIST 10 Manufacturing device 11 Carbon fiber substrate 12 Resin film 13 Heater 14 Release film 15 Hot plate press 16 Cooling press 17 Prepreg 18 Roll 19 Pressure roller

Claims

1. A prepreg in which a carbon fiber substrate is impregnated with a thermoplastic resin, the thermoplastic resin contains a vinyl alcohol polymer, The vinyl alcohol polymer includes an ethylene-vinyl alcohol copolymer. Prepreg.

2. A prepreg as described in claim 1, wherein the proportion of thermoplastic resin in the prepreg is 10 to 50 weight %.

3. A prepreg as described in claim 1, wherein the melt flow rate of the ethylene-vinyl alcohol copolymer is 0.5 to 100 g / 10 min.

4. 2. The prepreg according to claim 1, wherein the thermoplastic resin further comprises at least one resin selected from the group consisting of polyamide resin, polyolefin resin, polyester resin, and polystyrene resin.

5. The prepreg according to claim 4 , wherein the thermoplastic resin further comprises the polyamide resin.

6. The prepreg of claim 5 , wherein the polyamide resin comprises polyamide 6.

7. The prepreg according to claim 6, wherein the content of the polyamide 6 is 50 to 95 mass% with respect to the total mass of the thermoplastic resin.

8. 6. The prepreg according to claim 5, wherein the ratio of the mass of the vinyl alcohol polymer to the mass of the polyamide resin is 5 to 55 mass%.

9. 2. The prepreg according to claim 1, wherein the content of the vinyl alcohol polymer is 5 to 40 mass% with respect to the total mass of the thermoplastic resin.

10. 2. The prepreg according to claim 1, wherein the content of ethylene structural units is 25 to 50 mol % relative to the total number of moles of structural units constituting the ethylene-vinyl alcohol copolymer.

11. The prepreg according to claim 1, wherein the proportion of the carbon fiber base material in the prepreg is 40 to 80% by volume.

12. The prepreg according to claim 1 , wherein the carbon fiber substrate comprises a sheet of carbon fibers aligned in one direction.

13. The weight per unit area of ​​the carbon fiber base material is 10 to 300 g / m ２ The prepreg according to claim 1,

14. The prepreg according to claim 1 , wherein the carbon fiber substrate comprises carbon fibers having a strand strength of 4.8 GPa or more.

15. A molded article obtained by molding the prepreg according to any one of claims 1 to 14.

16. A pressure vessel formed by molding the prepreg according to any one of claims 1 to 14.

17. A method for producing a molded body, comprising press-molding the prepreg according to any one of claims 1 to 14.

18. A method for producing a molded body, comprising laminating the prepreg according to any one of claims 1 to 14 in a mold, The method for producing a molded article includes automatically laminating the prepreg continuously while applying pressure to the prepreg so as to press the prepreg against the mold when laminating the prepreg in the mold.

19. A method for producing a prepreg in which a resin film is laminated on a carbon fiber base material and heated and pressurized to impregnate the carbon fiber base material with a resin contained in the resin film, A method for producing a prepreg, comprising using a resin film containing a vinyl alcohol-based polymer and a resin film containing a polyamide resin, wherein the vinyl alcohol-based polymer contains an ethylene-vinyl alcohol copolymer.

20. 20. The method for producing a prepreg according to claim 19, wherein the resin film is a laminated film including an A layer: a layer containing a vinyl alcohol-based polymer, and a B layer: a layer containing a polyamide resin, and the laminated film is laminated on the carbon fiber base material.

21. The method for producing a prepreg according to claim 20, wherein the thickness of the A layer is 5 to 35% of the thickness of the laminated film.

22. The method for producing a prepreg according to any one of claims 19 to 21, wherein the content of ethylene structural units is 25 to 50 mol% with respect to the total number of moles of structural units constituting the ethylene-vinyl alcohol copolymer.