JP7780249B2 - Molding materials and molded products - Google Patents

Description

The present invention relates to molding materials and molded articles, and more specifically to molding materials and molded articles containing cured products of the molding materials.

Traditionally, molded products made from molding materials containing carbon fiber have been used in a variety of fields, including aircraft, automobiles, and sports, due to their excellent specific strength and specific modulus of elasticity.

Of all molding materials containing carbon fiber, SMC (sheet molding compound) in particular uses short, discontinuous fibers, which generally poses the problem of lower mechanical properties for fiber-reinforced resin structures compared to molded products using continuous fibers. However, because the material is allowed to flow and fill the mold, it is well-suited to forming complex shapes with fine irregularities that are difficult to achieve with autoclave molding or RTM molding. Furthermore, because the material is allowed to flow, the time required for material layering can be reduced, resulting in a shorter molding cycle, and its adoption is accelerating in a variety of fields.

As such a molding material, for example, a carbon fiber reinforced sheet molding material containing a thermosetting polymer, a vinyl monomer, a thermoplastic polymer, and carbon fiber has been proposed (see, for example, Patent Document 1 below).

The carbon fibers blended into the molding material are fiber bundles of carbon fibers that have been opened and then separated by passing them through circular blades at equal intervals (see, for example, Example 12 of Patent Document 1 below).

Japanese Patent Application Laid-Open No. 2018-197295

In Example 12 of Patent Document 1, carbon fiber bundles that have been split at equal intervals after fiber-opening processing are used, so the width of the carbon fiber bundles is uniform. As a result, these carbon fiber bundles become localized in the molding material, and when the carbon fiber bundles overlap, it becomes impossible to ensure adequate gaps between the carbon fiber bundles. This results in a problem of reduced impregnation of the carbon fiber bundles with the resin component (thermosetting polymer).

Furthermore, when such molding materials are molded in a mold, it is necessary to improve the molding material's ability to fill the mold. However, the method described in Example 12 of Patent Document 1 produces fiber bundles of carbon fibers separated to a uniform width, which causes the carbon fibers to become entangled when the material flows during molding, reducing fluidity.

The object of the present invention is to provide a molding material that exhibits excellent impregnation of carbon fiber bundles into resin components and excellent mold filling properties, as well as a molded article containing a cured product of the molding material.

The present invention [1] is a molding material comprising a resin composition containing a resin component and a fiber bundle of carbon fiber, wherein the median X and standard deviation Y of the fiber bundle of the carbon fiber measured by the following test satisfy the relationships of the following formulas (1) to (4):
Y>0.5X (1)
Y<0.5X+4000 (2)
X>2000 (3)
X<8000 (4)
Test: A carbon fiber bundle is defibrated using a defibrator, 100 defibrated carbon fiber bundles are randomly extracted from the defibrated carbon fiber bundle, the mass (m) of each extracted carbon fiber bundle and the fiber length (l) of each carbon fiber bundle are measured, and the number of bundled fibers (n) of the defibrated carbon fiber bundle is calculated from the obtained mass (m) and fiber length (l) based on the following formula (5), and the median and standard deviation of these bundled fibers are calculated.
n=(m×N×1000)/(M×l) (5)
(In the formula, n represents the number of fibers (K) in the carbon fiber bundle after defibration, m represents the mass (mg) of the carbon fiber bundle after defibration, N represents the number of fibers (K) in the carbon fiber bundle before defibration, M represents the fiber weight (g/1000 m) of the carbon fiber bundle before defibration, and 1 represents the fiber length (mm) of the carbon fiber bundle after defibration.)
The present invention [2] includes the molding material according to the above [1], wherein the bulk density of the fiber bundle of the carbon fiber is 0.15 g/ml or more and 0.3 g/ml or less.

The present invention [3] includes the molding material described in [1] or [2] above, in which the resin component includes a reaction product of a vinyl ester and an acid anhydride, and the resin composition includes a thickener.

The present invention [4] includes the molding material described in [3] above, in which the thickener is magnesium oxide.

The present invention [5] includes the molding material described in [3] or [4] above, in which the blending ratio of the acid anhydride is 0.6 mol or more and 1.4 mol or less per 1 mol of the vinyl ester.

The present invention [6] includes the molding material described in any one of [3] to [5] above, in which the vinyl ester is a reaction product of an epoxy resin and an unsaturated monobasic acid, and the epoxy equivalent of the epoxy resin is 200 or more and 500 or less.

The present invention [7] includes the molding material described in any one of [1] to [6] above, in which the blending ratio of the carbon fiber bundles is 40% by mass or more and 65% by mass or less relative to the total amount of the resin composition and the carbon fiber bundles.

The present invention [8] includes a molded article containing a cured product of the molding material described in any one of [1] to [7] above.

The molding material of the present invention contains carbon fiber bundles, and the median X and standard deviation Y of the carbon fiber bundles, measured by a specified test, have a specified relationship.

As a result, this molding material has excellent impregnation properties for the carbon fiber bundles into the resin component and excellent filling properties for the mold.

The molded article of the present invention contains a cured product of the molding material of the present invention, and therefore has excellent surface smoothness and is suppressed from warping.

FIG. 1 is a graph showing the relationship between the median X and the standard deviation Y. FIG. 2 is a graph showing the relationship between the median X and the standard deviation Y in Examples 1, 3, 5, 7, 8, 9, 12, and 15 , and Comparative Examples 1 to 4 and 7 to 13 .

The molding material of the present invention comprises a resin composition containing a resin component and a fiber bundle of carbon fibers having a specified median and a specified standard deviation measured in a test (described below).

The resin component includes a double bond-containing curable polymer and a polymerizable monomer.

Examples of double bond-containing curable polymers include vinyl esters and unsaturated polyesters, with vinyl esters being preferred.

Vinyl esters are the reaction products of epoxy resins and unsaturated monobasic acids.

Examples of epoxy resins include bisphenol-type epoxy resins and novolac-type epoxy resins, with bisphenol-type epoxy resins being preferred.

Bisphenol-type epoxy resins are represented by the following general formula (1):

(wherein Y ¹ represents any one of —C(CH ₃ ) ₂ —, —CH ₂ —, —O—, —S—, and —(O═S═O)—, and n represents an integer of 0 to 5.)
Examples of such bisphenol type epoxy resins include bisphenol A type epoxy resins, bisphenol F type epoxy resins, and bisphenol S type epoxy resins, and preferably bisphenol A type epoxy resins.

Epoxy resins can also be modified with phenolic compounds such as bisphenol A, bisphenol F, and bisphenol S.

To modify epoxy resin with a phenolic compound, the epoxy resin is reacted with the phenolic compound.

The blending ratio of the phenol compound is, for example, 0.1 mol or more, preferably 0.3 mol or more, and, for example, 0.6 mol or less, preferably 0.5 mol or less, per 1 mol of epoxy resin.

In the above reaction, the reaction temperature is, for example, 100°C or higher, preferably 130°C or higher, and for example, 200°C or lower, and the reaction time is, for example, 1 hour or higher, preferably 2 hours or higher, and for example, 10 hours or lower.

In addition, a catalyst can be added to the above reaction if necessary.

Examples of catalysts include amines such as triethylamine and benzyldimethylamine; ammonium salts such as tetramethylammonium chloride and triethylbenzylammonium chloride; imidazoles such as 2-ethyl-4-imidazole; amides such as pyridines; phosphines such as triphenylphosphine; phosphonium salts such as tetraphenylphosphonium bromide and ethyltriphenylphosphonium bromide; sulfonium salts; sulfonic acids; and organometallic salts such as zinc octoate. Ammonium salts are preferred, and triethylbenzylammonium chloride is more preferred.

Catalysts can be used alone or in combination of two or more types.

The catalyst is added in an amount of, for example, 0.01 parts by mass or more and, for example, 2.0 parts by mass or less, preferably 1.5 parts by mass or less, per 100 parts by mass of epoxy resin.

This allows the epoxy resin to be modified with a phenolic compound.

Preferably, the epoxy resin is an epoxy resin modified with a phenol compound, and more preferably, a bisphenol A-type epoxy resin modified with bisphenol A.

Epoxy resins can be used alone or in combination of two or more types.

The epoxy equivalent of the epoxy resin is, for example, 150 or more, preferably 200 or more, more preferably 250 or more, from the viewpoint of improving the bending strength of the molded article (described below), and is, for example, 600 or less, preferably 500 or less, more preferably 450 or less, from the viewpoint of improving heat resistance.

When two epoxy resins are used in combination, the above epoxy equivalent weight is the total epoxy equivalent weight of all epoxy resins, calculated by multiplying the epoxy equivalent weight of each epoxy resin by the mass ratio of each epoxy resin to the total amount of epoxy resins.

Examples of unsaturated monobasic acids include monocarboxylic acids such as (meth)acrylic acid, crotonic acid, cinnamic acid, and sorbic acid, as well as reaction products of dibasic acid anhydrides with alcohols having at least one unsaturated group in the molecule. Note that (meth)acrylic is synonymous with methacrylic and/or acrylic.

Examples of dibasic acid anhydrides include maleic anhydride, succinic anhydride, phthalic anhydride, tetrahydrophthalic anhydride, and hexahydrophthalic anhydride.

Examples of alcohols having an unsaturated group include hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, pentaerythritol tri(meth)acrylate, and glycerin di(meth)acrylate.

Unsaturated monobasic acids can be used alone or in combination of two or more types.

The unsaturated monobasic acid is preferably a monocarboxylic acid, more preferably (meth)acrylic acid, and even more preferably methacrylic acid.

And to obtain vinyl esters, epoxy resins are reacted with unsaturated monobasic acids.

In the above reaction, an addition reaction occurs between the epoxy group of the epoxy resin and the unsaturated monobasic acid.

In addition, in the above reaction, the equivalent weight of the carboxyl groups of the unsaturated monobasic acid relative to the epoxy groups of the epoxy resin is, for example, 0.8 or more, preferably 0.9 or more, and for example, 1.5 or less, preferably 1.1 or less.

In the above reaction, the reaction temperature is, for example, 80°C or higher, preferably 100°C or higher, and, for example, 150°C or lower, preferably 130°C or lower. The reaction time is, for example, 1 hour or higher, preferably 2 hours or higher, and, for example, 10 hours or lower.

In addition, the above-mentioned catalyst (preferably an ammonium salt, more preferably triethylbenzylammonium chloride) can be added to the above reaction if necessary.

The catalyst is added in an amount of, for example, 0.01 part by mass or more, preferably 0.03 part by mass or more, and for example, 0.5 part by mass or less, preferably 0.1 part by mass or less, per 100 parts by mass of epoxy resin.

In addition, a polymerization inhibitor can be added to the above reaction if necessary.

Examples of polymerization inhibitors include hydroquinone compounds such as hydroquinone, methylhydroquinone, and t-butylhydroquinone; benzoquinone compounds such as p-benzoquinone and methyl-p-benzoquinone; catechol compounds such as t-butylcatechol; phenol compounds such as 2,6-di-t-butyl-4-methylphenol and 4-methoxyphenol; and 1-oxyl-2,2,6,6-tetramethylpiperidine, 1-oxyl-2,2,6,6-tetramethylpiperidin-4-ol, 4-hydroxy-2,2,6,6-tetrapiperidine-1-oxyl, and 4-methoxy-2,2 ,6,6-tetramethylpiperidin-1-oxyl, 1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl-acetate, 1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl-2-ethylhexanoate, 1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl-stearate, 1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl-4-t-butylbenzoate, bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)succinate, bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)adipate bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) sebacate, bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) n-butyl malonate, bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) phthalate, bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) isophthalate, bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) terephthalate, bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) hexahydroterephthalate, N,N'-bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) Examples of N-oxyl compounds include N-bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)adipamide, N-bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)caprolactam, N-bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)dodecylsuccinimide, 2,4,6-tris-[N-butyl-N-(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)]-s-triazine, and 1-oxyl-2,2,6,6-tetramethylpiperidin-4-one. Hydroquinone compounds are preferred, and hydroquinone is more preferred.

Polymerization inhibitors can be used alone or in combination of two or more types.

The blending ratio of the polymerization inhibitor is, for example, 0.01 part by mass or more, preferably 0.03 part by mass or more, and for example, 0.5 part by mass or less, preferably 0.1 part by mass or less, per 100 parts by mass of the epoxy resin.

This yields vinyl ester.

Such vinyl esters can also be modified with acid anhydrides.

That is, vinyl esters include vinyl esters modified with acid anhydrides (hereinafter referred to as acid-modified vinyl esters) and vinyl esters not modified with acid anhydrides (hereinafter referred to as unmodified vinyl esters).

Acid-modified vinyl esters are the reaction products of vinyl esters and acid anhydrides.

Examples of acid anhydrides include maleic anhydride, succinic anhydride, and phthalic anhydride, with maleic anhydride being preferred.

To obtain an acid-modified vinyl ester, a vinyl ester is reacted with an acid anhydride.

In the above reaction, the proportion of acid anhydride per mole of vinyl ester is, for example, 0.6 moles or more, preferably 0.8 moles or more, and for example, 1.4 moles or less, preferably 1.2 moles or less.

When the blending ratio of acid anhydride is equal to or greater than the above lower limit, the viscosity of the resin composition can be increased to a level suitable for hot compression molding.

When the acid anhydride content is below the upper limit, the storage stability is excellent.

In the above reaction, the reaction temperature is, for example, 60°C or higher and, for example, 100°C or lower, and the reaction time is, for example, 1 hour or longer and, for example, 12 hours or shorter, preferably 6 hours or shorter.

This results in an acid-modified vinyl ester.

The acid value of the acid-modified vinyl ester (measurement method: in accordance with JIS K6901 (2008); the same applies below) is, for example, 40 mgKOH/g or more, preferably 50 mgKOH/g or more, and, for example, 100 mgKOH/g or less, preferably 90 mgKOH/g or less.

The acid value of the unmodified vinyl ester is, for example, 1 mgKOH/g or more, preferably 5 mgKOH/g or more, and, for example, 20 mgKOH/g or less, preferably 10 mgKOH/g or less.

Among these vinyl esters, acid-modified vinyl esters are preferred.

In other words, the resin component preferably contains an acid-modified vinyl ester.

The blending ratio of the double bond-containing curable polymer is, for example, 80 parts by mass or more, preferably 120 parts by mass or more, and, for example, 200 parts by mass or less, per 100 parts by mass of the polymerizable monomer.

The blending ratio of the double bond-containing curable polymer is, for example, 30 parts by mass or more, preferably 40 parts by mass or more, and, for example, 65 parts by mass or less, per 100 parts by mass of the resin component.

When the blending ratio of the double bond-containing curable polymer is equal to or greater than the above lower limit, the viscosity of the resin composition can be increased to a level suitable for heat compression molding.

When the blending ratio of the double bond-containing curable polymer is below the above upper limit, the impregnation of the carbon fiber bundles with the resin component can be improved.

The polymerizable monomer is a solvent for dissolving the double bond-containing curable polymer, and is also a crosslinkable monomer (reactive diluent) that can crosslink with the double bond-containing curable polymer when the double bond-containing curable resin (described below) is cured. Examples of the polymerizable monomer include styrene-based monomers such as styrene, α-methylstyrene, α-ethylstyrene, vinyltoluene, t-butylstyrene, and chlorostyrene; methyl (meth)acrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, isobutyl (meth)acrylate; 2-ethylhexyl (meth)acrylate; and methyl acrylate. p) (meth)acrylic acid alkyl esters such as lauryl acrylate, tridecyl (meth)acrylate, and stearyl (meth)acrylate; for example, (meth)acrylic acid allyl esters such as allyl (meth)acrylate; for example, ring-structure-containing (meth)acrylic acid esters such as cyclohexyl (meth)acrylate, benzyl (meth)acrylate, isobornyl (meth)acrylate, glycidyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentanyl (meth)acrylate, and dicyclopentenyloxyethyl (meth)acrylate; for example, 2-hydroxyethyl (meth)acrylate; (meth)acrylic acid hydroxyalkyl esters such as 2-hydroxypropyl (meth)acrylate; (meth)acrylic acid alkoxyalkyl esters such as 2-methoxyethyl (meth)acrylate and 2-ethoxyethyl (meth)acrylate; (meth)acrylic acid aminoalkyl esters and chloride salts thereof such as dimethylaminoethyl (meth)acrylate and diethylaminoethyl (meth)acrylate; (meth)acrylic acid fluoroalkyl esters such as trifluoroethyl (meth)acrylate and heptadecafluorodecyl (meth)acrylate; (meth)acrylic acid ester-based monomers such as ethylene glycol; Examples of suitable (meth)acrylic acid esters include polyfunctional (meth)acrylic acid esters such as cholestrol di(meth)acrylate, diethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, and dipentaerythritol hexa(meth)acrylate; and allyl monomers such as glycerin monoallyl ether, pentaerythritol diallyl ether, pentaerythritol monoallyl ether, and trimethylolpropane monoallyl ether. Preferred are styrene-based monomers and ring-containing (meth)acrylic acid esters; and more preferred are styrene and benzyl methacrylate.

The polymerizable monomers can be used alone or in combination of two or more types.

The blending ratio of the polymerizable monomer is, for example, 20 parts by mass or more and, for example, 70 parts by mass or less per 100 parts by mass of the resin component.

The resin component preferably also contains a low-profile agent.

When using this molding material to produce a molded article (described below), a low-profile agent is added to suppress cure shrinkage and thermal shrinkage of the molded article (described below).

Examples of low-profile agents include polyethylene, polystyrene, styrene-based thermoplastic elastomers, cross-linked polystyrene, polyvinyl acetate-polystyrene block copolymers, polyvinyl acetate, polymethyl methacrylate, and saturated polyester resins.

Examples of styrene-based thermoplastic elastomers include styrene-butadiene block copolymer elastomers, styrene-isoprene block copolymer elastomers, styrene-ethylene/butylene block copolymer elastomers, and styrene-ethylene/propylene-styrene block copolymer elastomers, with styrene-ethylene/propylene-styrene block copolymer elastomers being preferred. Commercially available styrene-based thermoplastic elastomers include D1101, D1102, D1155, DKX405, DKX410, DKX415, D1192, D1161, D1171, G1651, G1652, G1654, G1701, and G1730 (all manufactured by Kraton Elastomers), Asaprene T411, Asaprene T432, Tufprene A, Tufprene 125, Tufprene 126S, Tufprene 315, Tufprene 912, Tuftec H1141, Tuftec H1041, Tuftec H1043, and Tuftec H1052 (all manufactured by Asahi Kasei Corporation), and Septon 1001 and 1201 (all manufactured by Kuraray Co., Ltd.).

The styrene content in the styrene-based thermoplastic elastomer is, for example, 5% by mass or more and, for example, 50% by mass or less.

Preferred examples of low-profile agents include styrene-based thermoplastic elastomers, saturated polyester resins, and polyvinyl acetate.

Low profile agents can be used alone or in combination of two or more types.

The proportion of the low-profile agent is, for example, 1 part by mass or more, preferably 3 parts by mass or more, and, for example, 30 parts by mass or less, preferably 20 parts by mass or less, per 100 parts by mass of the resin component.

When the proportion of low-profile additive is above the lower limit, cure shrinkage and thermal shrinkage of the molded product (described below) can be suppressed.

When the proportion of low-profile agent is below the above upper limit, separation of the resin components can be suppressed, resulting in a molded product (described below) with a good appearance.

The resin composition can be obtained by blending the resin components, specifically the double bond-containing curable polymer, polymerizable monomer, and optionally, a low-profile agent, in the blending ratios described above.

This results in a resin composition.

Additives such as polymerization inhibitors, polymerization initiators, wetting and dispersing agents, anti-separation agents, mold release agents, fillers, thickeners, colorants, and flame retardants can also be blended into the resin composition as needed. These additives can be used alone or in combination of two or more.

The polymerization inhibitor is not particularly limited, and examples include PBQ (parabenzoquinone), MTBHQ (mono t-butylhydroquinone), BHT (di t-butylhydroxytoluene or 2,5-di t-butyl-4-methylphenol), HQ (hydroquinone), TBC (t-butylcatechol), and 4-hydroxy-2,2,6,6-tetramethyl-4-oxopiperidine-1-oxyl free radical, with PBQ (parabenzoquinone) being preferred.

Polymerization inhibitors can be used alone or in combination of two or more types.

The blending ratio of the polymerization inhibitor is, for example, 0.01 parts by mass or more and, for example, 5 parts by mass or less, preferably 1 part by mass or less, per 100 parts by mass of the resin component.

Polymerization initiators include, for example, benzoyl peroxide, t-butylperoxyisopropyl monocarbonate, t-amylperoxyisopropyl monocarbonate, t-hexylperoxyisopropyl monocarbonate, 1,1-bis(t-butylperoxy)cyclohexane, t-butylperoxy-2-ethylhexanoate, amylperoxy-2-ethylhexanoate, 2-ethylhexylperoxy-2-ethylhexanoate, t-butylperoxybenzoate, and t-hexyl Examples of peroxides include peroxybenzoate and t-hexyl peroxyacetate. Preferred examples include peroxyisopropyl monocarbonate, such as t-butylperoxyisopropyl monocarbonate, t-amylperoxyisopropyl monocarbonate, t-hexylperoxyisopropyl monocarbonate, and t-butyl peroxybenzoate. Preferred examples include t-butylperoxyisopropyl monocarbonate and t-butyl peroxybenzoate.

The blending ratio of the polymerization initiator is, for example, 0.5 parts by mass or more, preferably 0.7 parts by mass or more, and for example, 5 parts by mass or less, preferably 3 parts by mass or less, per 100 parts by mass of the resin component.

Polymerization initiators can be used alone or in combination of two or more types.

A known curing accelerator can also be used in combination with the polymerization initiator.

Cure accelerators include, for example, organometallic compounds of cobalt, copper, and manganese, such as their respective octoates, naphthenates, and acetylacetonates.

The blending ratio of the curing accelerator is, for example, 0.01 parts by mass or more and, for example, 1 part by mass or less per 100 parts by mass of the resin component.

Cure accelerators can be used alone or in combination of two or more types.

Wetting and dispersing agents are added to improve the wettability of the resin components with the reinforcing fibers and fillers, and examples of such agents include known wetting and dispersing agents such as phosphate polyester. Commercially available wetting and dispersing agents can also be used, such as BYK-W996 (manufactured by BYK-Chemie).

The blending ratio of the wetting and dispersing agent is, for example, 0.1 parts by mass or more, preferably 0.5 parts by mass or more, and, for example, 10 parts by mass or less, preferably 3 parts by mass or less, per 100 parts by mass of the resin component.

Wetting and dispersing agents can be used alone or in combination of two or more types.

Anti-separation agents are added to prevent separation of the resin composition, and examples include block copolymers of styrene and vinyl acetate. Commercially available anti-separation agents can also be used, such as BYK-W972 (manufactured by BYK-Chemie).

The blending ratio of the anti-separation agent is, for example, 0.1 parts by mass or more, preferably 0.5 parts by mass or more, and, for example, 10 parts by mass or less, preferably 3 parts by mass or less, per 100 parts by mass of the resin component.

Anti-separation agents can be used alone or in combination of two or more types.

Examples of release agents include fatty acids such as stearic acid and lauric acid, fatty acid metal salts such as zinc stearate and calcium stearate, and compounds such as paraffin, liquid wax, fluoropolymers, silicon-based polymers, and alkylammonium salts, with fatty acid metal salts being preferred, and zinc stearate being more preferred.

The blending ratio of the release agent is, for example, 1 part by mass or more, preferably 3 parts by mass or more, and, for example, 10 parts by mass or less, per 100 parts by mass of the resin component.

Release agents can be used alone or in combination of two or more types.

Examples of fillers include oxides such as alumina and titania, hydroxides such as magnesium hydroxide and aluminum hydroxide, carbonates such as calcium carbonate, sulfates such as barium sulfate, silica (e.g., crystalline silica, fused silica, fumed silica, and dry silica (Aerosil)), glass powder, hollow fillers such as glass balloons, silica balloons, and alumina balloons, silicates such as silica sand, diatomaceous earth, mica, clay, kaolin, and talc, fluorides such as fluorite, phosphates such as calcium phosphate, inorganic fillers such as clay minerals such as smectite, conductive fibers such as milled carbon fiber, conductive particles, and conductive fillers such as carbon nanotubes. Carbonates, hollow fillers, and conductive fillers are preferred, and calcium carbonate, glass balloons, and milled carbon fiber are more preferred.

The blending ratio of the filler is, for example, 1 part by mass or more, preferably 10 parts by mass or more, and, for example, 100 parts by mass or less, preferably 50 parts by mass or less, more preferably 30 parts by mass or less, per 100 parts by mass of the resin component.

Fillers can be used alone or in combination of two or more types.

The thickener is added to thicken the resin composition to a viscosity suitable for heat compression molding, and is preferably added before (preferably immediately before) impregnating the resin composition into the reinforcing fibers (described below). Examples of thickeners include alkaline earth metal oxides such as magnesium oxide, alkaline earth metal hydroxides such as magnesium hydroxide and calcium hydroxide, and polyisocyanate compounds such as diphenylmethane diisocyanate (MDI).

The thickener is selected depending on the type of double bond-containing curable polymer. For example, if the double bond-containing curable polymer is an unmodified vinyl ester, a diisocyanate such as diphenylmethane diisocyanate is selected as the thickener. Also, for example, if the double bond-containing curable polymer is an acid-modified vinyl ester, magnesium oxide is selected as the thickener.

When the double bond-containing curable polymer is an acid-modified vinyl ester and the thickener is magnesium oxide, the product has excellent handleability and flowability.

When the double bond-containing curable polymer is an unmodified vinyl ester and the thickener is diphenylmethane diisocyanate, the thickener content is, for example, 1 part by mass or more, preferably 5 parts by mass or more, and, for example, 20 parts by mass or less, preferably 15 parts by mass or less, per 100 parts by mass of the resin component. When the double bond-containing curable polymer is an acid-modified vinyl ester and the thickener is magnesium oxide, the thickener content is, for example, 0.1 part by mass or more, preferably 0.5 parts by mass or more, and, for example, 5 parts by mass or less, per 100 parts by mass of the resin component.

Thickeners can be used alone or in combination of two or more types.

The colorant is not particularly limited, but examples include titanium oxide and polyester toner (polyester colorant containing titanium oxide and/or carbon black).

The colorant content is, for example, 1 part by mass or more, preferably 5 parts by mass or more, and, for example, 20 parts by mass or less, per 100 parts by mass of the resin component.

Colorants can be used alone or in combination of two or more types.

Examples of flame retardants include halogen-based flame retardants such as bromine-based flame retardants, and non-halogen flame retardants such as phosphorus-based flame retardants, inorganic flame retardants, and nitrogen compound-based flame retardants.

The blending ratio of the flame retardant is, for example, 1 part by mass or more, preferably 5 parts by mass or more, and, for example, 50 parts by mass or less, preferably 20 parts by mass or less, per 100 parts by mass of the resin component.

Flame retardants can be used alone or in combination of two or more types.

Additives such as pattern materials, antibacterial agents, hydrophilic agents, photocatalysts, UV absorbers, UV stabilizers, silane coupling agents, antistatic agents, thixotropic agents, thixotropic stabilizers, and polymerization accelerators can be blended into the resin composition as needed, provided they do not impair the effects of the present invention. These additives can be used alone or in combination of two or more.

The viscosity of the resin composition at 25°C is, for example, 0.1 Pa·s or more, preferably 0.5 Pa·s or more, more preferably 0.7 Pa·s or more, and for example, 10 Pa·s or less, preferably 5 Pa·s or less.

The viscosity measurement method will be described in detail in the examples below.

In the above explanation, a resin composition was obtained by blending a double bond-containing curable polymer, a polymerizable monomer, an optional low-profile agent, and optional additives. However, it is also possible to first prepare a double bond-containing curable resin by dissolving a double bond-containing curable polymer in a polymerizable monomer, and then blend the resulting double bond-containing curable resin with a polymerizable monomer, an optional low-profile agent, and optional additives.

When preparing the double bond-containing curable polymer, the double bond-containing curable polymer and polymerizable monomer are blended, and the above-mentioned additives can also be blended as needed.

A carbon fiber bundle is a bundle of multiple carbon fibers.

Furthermore, the carbon fiber bundles are already defibrated when the molding material is impregnated. In other words, such carbon fiber bundles are defibrated carbon fiber bundles.

Specifically, the carbon fiber bundle after defibration is obtained by defibrating the raw material for the carbon fiber bundle (the carbon fiber bundle before defibration) using a known defibrator so that the median and standard deviation, described below, have a predetermined relationship to the number of convergent fibers.

The number of fibers in the carbon fiber bundle before defibration is, for example, 3,000 or more, preferably 6,000 or more, more preferably 12,000 or more, and for example, 60,000 or less, preferably 50,000 or less.

If the number of bundles is equal to or greater than the lower limit, appropriate gaps can be secured between overlapping carbon fiber bundles, improving the impregnation of the carbon fiber bundles with the resin component. Furthermore, interference between the carbon fiber bundles can be suppressed, improving fluidity during molding.

Furthermore, if the number of bundles is equal to or less than the upper limit, the carbon fiber bundles can be prevented from becoming too thick, thereby improving the impregnation of the carbon fiber bundles with the resin component. Furthermore, the bending strength and bending modulus of a molded product (described below) obtained using this molding material can be improved.

Examples of defibrators include the defibrator described in JP 2019-065405 A.

The number of bundled fibers in the resulting defibrated carbon fiber bundle has a predetermined relationship between the median X and standard deviation Y measured by the test described below.

In detail, in the test, a defibrator (for example, the defibration device described in JP 2019-065405 A mentioned above) was used to defibrate a carbon fiber bundle, and 100 defibrated carbon fiber bundles were randomly extracted from the defibrated carbon fiber bundle. The mass (m) of each extracted carbon fiber bundle and the fiber length (l) of each carbon fiber bundle were measured, and the number of convergent fibers (n) of the defibrated carbon fiber bundle was calculated from the obtained mass (m) and fiber length (l) based on the following formula (1), and the median and standard deviation of these convergent fibers were calculated.
n=(m×N×1000)/(M×l) (1)
(In the formula, n represents the number of fibers (K) in the carbon fiber bundle after defibration, m represents the mass (mg) of the carbon fiber bundle after defibration, N represents the number of fibers (K) in the carbon fiber bundle before defibration, M represents the fiber weight (g/1000 m) of the carbon fiber bundle before defibration, and 1 represents the fiber length (mm) of the carbon fiber bundle after defibration.)
When a carbon fiber bundle (a carbon fiber bundle before defibration) is defibrated using the defibration device described in JP 2019-065405 A, the rotation speed of the rotating shaft in the upper stage defibration mechanism, the rotation speed of the rotating shaft in the middle stage defibration mechanism, and the rotation speed of the rotating shaft in the lower stage defibration mechanism are adjusted to 100 rpm or more, preferably 400 rpm or more, more preferably 800 rpm or more, and for example, 3000 rpm or less, preferably 2500 rpm or less.

Reducing the rotation speed reduces the efficiency of the defibration process, allowing the median X and standard deviation Y to be increased; increasing the rotation speed improves the efficiency of the defibration process, allowing the median X and standard deviation Y to be reduced.

Specifically, the median X and the standard deviation Y satisfy the relationships of the following formulas (2) to (5).
Y>0.5X (2)
Y<0.5X+4000 (3)
X>2000 (4)
X<8000 (5)
That is, the median X and the standard deviation Y are within the range of the shaded area in FIG.

When the median X and standard deviation Y are within these ranges, localization of the defibrated carbon fiber bundles in the molding material can be suppressed, and when the defibrated carbon fiber bundles overlap, appropriate gaps can be ensured between the defibrated carbon fiber bundles, thereby improving the impregnation of the defibrated carbon fiber bundles with the resin component. Furthermore, from the perspective of entanglement of the carbon fiber bundles, the mold filling ability can be improved.

On the other hand, if the median X and standard deviation Y do not satisfy the above formula (2) (more specifically, area A in Figure 1), the filling ability into the mold will decrease due to the entanglement of the carbon fiber bundles.

Furthermore, if the median X and standard deviation Y do not satisfy the above formula (3) (more specifically, region B in Figure 1), the defibrated carbon fiber bundles will be localized in the molding material, and if the defibrated carbon fiber bundles overlap each other, it will be impossible to ensure adequate gaps between the defibrated carbon fiber bundles, resulting in a decrease in the impregnation of the defibrated carbon fiber bundles with the resin component.

Furthermore, if the median X does not satisfy the above formula (4) (more specifically, region C in Figure 1), the filling ability into the mold will decrease due to the entanglement of the carbon fiber bundles.

Furthermore, if the median X does not satisfy the above formula (5) (more specifically, region D in Figure 1), the defibrated carbon fiber bundles will be localized in the molding material, and when the defibrated carbon fiber bundles overlap each other, it will be impossible to ensure adequate gaps between the defibrated carbon fiber bundles, resulting in a decrease in the impregnation of the defibrated carbon fiber bundles with the resin component.

Preferably, the median X and the standard deviation Y satisfy the relationships of the following formulas (6) to (9).
Y>0.5X (6)
Y<0.5X+2000 (7)
X>2000 (8)
X<5000 (9)
If the median X and the standard deviation Y satisfy the relationships of the above formulas (6) to (9), entanglement of the carbon fiber bundles can be effectively prevented, and in the case where the defibrated carbon fiber bundles are localized in the molding material and the defibrated carbon fiber bundles overlap each other, appropriate gaps can be further ensured between the defibrated carbon fiber bundles.

The bulk density of the carbon fiber bundle is, for example, 0.15 g/ml or more, preferably 0.18 g/ml or more, and, for example, 0.3 g/ml or less, preferably 0.25 g/ml or less.

If the bulk density of the carbon fiber bundle is above the above lower limit, the generation of fluff in the carbon fiber bundle can be suppressed.

Furthermore, if the bulk density of the carbon fiber bundles is equal to or less than the above upper limit, localization of the carbon fiber bundles in the molding material can be suppressed, and when the carbon fiber bundles overlap, appropriate gaps can be secured between the carbon fiber bundles, thereby improving the impregnation of the carbon fiber bundles with the resin component.

The method for measuring bulk density will be described in detail in the Examples below.

The molding material is obtained by blending carbon fiber bundles into a resin composition.

Specifically, the molding material is obtained, for example, in the form of a sheet, by impregnating carbon fiber bundles with a resin composition.

Methods for preparing molding materials include known methods, such as SMC (sheet molding compound), TMC (thick molding compound), and BMC (bulk molding compound), with SMC being preferred.

The blending ratio of the carbon fiber bundles is, for example, 40% by mass or more, preferably 50% by mass or more, and, for example, 65% by mass or less, based on the total amount of the resin composition and the carbon fiber bundles.

If the blending ratio of carbon fiber bundles is above the lower limit, the specific strength and specific rigidity of the molded product obtained using this molding material can be improved.

Furthermore, if the blending ratio of carbon fiber bundles is below the above upper limit, the impregnation of the carbon fiber bundles with the resin component can be improved.

This results in a molding material containing the resin composition and fiber bundles of reinforcing fibers.

If necessary, reinforcing fibers (excluding carbon fiber bundles) can also be blended into the molding material.

Examples of reinforcing fibers (excluding carbon fiber bundles) include inorganic fibers such as glass fibers, metal fibers, and ceramic fibers; organic fibers such as polyvinyl alcohol fibers, polyester fibers, polyamide fibers, fluororesin fibers, and phenolic fibers; and natural fibers such as hemp and kenaf.

The blending ratio of the reinforcing fibers is, for example, 5% by mass or more, preferably 10% by mass or more, more preferably 20% by mass or more, and for example, 50% by mass or less, preferably 40% by mass or less, based on the total amount of the resin composition and the reinforcing fibers.

Then, to increase the viscosity of this molding material and improve its handling properties during hot compression molding (described below), it is preferably aged, for example, at a temperature of 20°C to 50°C for 8 hours to 120 hours.

This allows the molding material to be held in a sheet-like shape, for example. In other words, the molding material has a sheet shape.

Such molding material contains fiber bundles of carbon fibers having the above-mentioned median X and the above-mentioned standard deviation Y.

This allows for excellent impregnation of the carbon fiber bundles into the resin component and excellent filling properties into the mold.

The molded product is obtained by heat-compression molding the above-mentioned molding material using a known method.

The conditions for heat compression molding are set appropriately depending on the purpose and application. Specifically, the molding temperature is, for example, 60°C or higher, preferably 100°C or higher, and, for example, 200°C or lower, preferably 180°C or lower; the molding pressure is, for example, 0.1 MPa or higher, preferably 1 MPa or higher, more preferably 5 MPa or higher, and, for example, 20 MPa or lower, preferably 15 MPa or lower.

This causes the molding material to harden and form.

This results in a molded product containing the cured molding material.

As described above, the molding material contains carbon fiber bundles having the above-mentioned median X and standard deviation Y, which prevents localization of the carbon fiber bundles during preparation of the molding material. As a result, molded articles containing the cured product of this molding material have excellent surface smoothness and are less susceptible to warpage.

The density of the molded article is, for example, 1.2 g/mL or more, preferably 1.3 g/mL or more, more preferably 1.4 g/mL or more, and for example, 1.7 g/mL or less, preferably 1.6 g/mL or less.

The method for measuring density will be described in detail in the examples below.

The flexural strength of the molded product (based on JIS K7074 (1988)) is, for example, 250 MPa or more, preferably 470 MPa or more.

The flexural modulus of the molded product (according to JIS K7074 (1988)) is, for example, 20 GPa or more, preferably 25 GPa or more, more preferably 30 GPa or more, and even more preferably 35 GPa or more.

The molded article has a specific strength of, for example, 180 MPa/(g/cm ³ ) or more, preferably 250 MPa/(g/cm ³ ) or more, or more preferably 300 MPa/(g/cm ³ ) or more.

The method for measuring the specific strength will be described in detail in the examples below.

The molded article has a specific rigidity of, for example, 20 (MPa) ^1/3 /(g/cm ³ ) or more, preferably 22 (MPa) ^1/3 /(g/cm ³ ) or more.

The method for measuring the specific strength will be described in detail in the examples below.

These molded products can be used in a wide range of applications, including building materials, housings, casting materials, machine parts, electronic and electrical parts, and components for vehicles, ships, and aircraft.

Specific numerical values of the blending ratios (content ratios), physical property values, parameters, etc. used in the following description can be replaced with the upper limit values (numerical values defined as "not more than" or "less than") or lower limit values (numerical values defined as "not less than" or "exceeding") of the corresponding blending ratios (content ratios), physical property values, parameters, etc. described in the above "Modes for Carrying Out the Invention." Furthermore, unless otherwise specified in the following description, "parts" and "%" are based on mass.
1. Details of components Benzyl methacrylate: trade name "Light Ester BZ", manufactured by Kyoeisha Chemical Co., Ltd. Polyvinyl acetate: trade name "VINAPAS C501", manufactured by Wacker Polymer Systems Saturated polyester: trade name "Byron (registered trademark) 550", manufactured by Toyobo Co., Ltd. Styrenic thermoplastic elastomer: trade name "Kraton (registered trademark) G1701", styrene-ethylene/propylene-styrene-block copolymer, manufactured by Kraton Polymerization inhibitor: parabenzoquinone Polymerization initiator: trade name "Perbutyl (registered trademark) Z", manufactured by Nippon Oil & Fats Corporation Wetting and dispersing agent: trade name "BYK-W996", manufactured by BYK-Chemie GmbH Separation prevention agent: trade name "BYK-W972", manufactured by BYK-Chemie GmbH Release agent manufactured by Nitto Funka Kogyo Co., Ltd.: Zinc stearate calcium carbonate: Product name "NS#400", manufactured by Nitto Funka Kogyo Co., Ltd., average particle size 1.7 μm (catalog value)
Milled carbon fiber: Trade name "DonaCarbo Milled S-241", manufactured by Osaka Gas Chemicals Co., Ltd. Glass balloon: Trade name "Glass Bubbles Filler K-37", manufactured by Sumitomo 3M Limited, true density 0.37 g/cm ³ , pressure resistance 21 MPa (catalog value)
MgO: trade name "Kyowa Mag #100", manufactured by Kyowa Chemical Industry Co., Ltd. MDI: trade name "Cosmonate PH", manufactured by Mitsui Chemicals SKC Polyurethanes, Inc. Carbon fiber 6K: carbon fiber bundle with 6,000 strands (unopened), trade name "TR50S 6L", manufactured by Mitsubishi Chemical Corporation Carbon fiber 12K: carbon fiber bundle with 12,000 strands (trade name "T700-SC 12K", manufactured by Toray Industries, Inc.)
Carbon fiber 24K: a fiber bundle of carbon fiber with a bundle count of 24,000 (product name "TC-35R 24K", manufactured by Formosa Plastics)
Carbon fiber 48K: a fiber bundle of carbon fiber with a number of strands of 48,000 (trade name "Panex 35", manufactured by Zolteck)
Carbon fiber 60K: a fiber bundle of carbon fiber with a number of strands of 60,000 (product name "TRH60M", manufactured by Mitsubishi Chemical Corporation)
2. Preparation of vinyl esters Synthesis Example 1
Into a reaction vessel (flask) equipped with a stirrer, a reflux condenser, and a gas inlet tube, 1,850 g of bisphenol A type epoxy resin (epoxy equivalent: 185), 2.0 g of hydroquinone as a polymerization inhibitor, 2.0 g of triethylbenzylammonium chloride as a catalyst, and 882 g of methacrylic acid were added, and the mixture was reacted at 110°C for 8 hours while blowing air into it, to obtain an unmodified vinyl ester resin with an acid value of 7.0 mgKOH/g.

Synthesis Example 2
An unmodified vinyl ester resin was obtained in the same manner as in Synthesis Example 1, and then 490 g of maleic anhydride was added thereto, followed by reaction at 80°C for 2 hours to obtain an acid-modified vinyl ester resin having an acid value of 94.1 mgKOH/g.

Synthesis Example 3
A reaction vessel (flask) equipped with a stirrer, reflux condenser, and gas inlet tube was charged with 1,850 g of bisphenol A epoxy resin (epoxy equivalent 185), 210 g of bisphenol A, and 0.4 g of triethylbenzylammonium chloride as a catalyst. While blowing in nitrogen, the mixture was reacted at 150°C for 5 hours to obtain an epoxy resin (bisphenol A-modified bisphenol A epoxy resin) with an epoxy equivalent of 252. After cooling to 120°C, 2.0 g of hydroquinone as a polymerization inhibitor, 2.0 g of triethylbenzylammonium chloride as a catalyst, and 719 g of methacrylic acid were added, and the mixture was reacted at 110°C for 8 hours while blowing in air to obtain an unmodified vinyl ester resin with an acid value of 7.0 mgKOH/g.

Synthesis Example 4
An unmodified vinyl ester resin was obtained in the same manner as in Synthesis Example 3, and then 400 g of maleic anhydride was added thereto, followed by reaction at 80°C for 2 hours to obtain an acid-modified vinyl ester resin having an acid value of 79.0 mgKOH/g.

Synthesis Examples 5, 7 and 9
An unmodified vinyl ester resin was obtained in the same manner as in Synthesis Example 3, except that the compounding formulation was changed according to Table 1.

In Synthesis Example 5, the epoxy equivalent of the bisphenol A-modified bisphenol A epoxy resin was 400.

Furthermore, in Synthesis Example 7, the epoxy equivalent of the bisphenol A-type epoxy resin modified with bisphenol A was 467.

Furthermore, in Synthesis Example 9, the epoxy equivalent of the bisphenol A-modified bisphenol A epoxy resin was 522.

Synthesis Examples 6, 8, and 10
An acid-modified vinyl ester resin was obtained in the same manner as in Synthesis Example 4, except that the compounding formulation was changed according to Table 1.

In Synthesis Example 6, the epoxy equivalent of the bisphenol A-modified bisphenol A epoxy resin was 400.

Furthermore, in Synthesis Example 8, the epoxy equivalent of the bisphenol A-type epoxy resin modified with bisphenol A was 467.

In Synthesis Example 10, the epoxy equivalent of the bisphenol A-modified epoxy resin was 522.
3. Production of molding material Example 1
(Preparation of carbon fiber bundles)
Carbon fiber 24K as a raw material for carbon fiber bundles (carbon fiber bundles before defibration) was cut into 1 inch pieces with a rotary cutter and then defibrated using the defibration device described in JP 2019-065405 A.

The defibration conditions were as follows: the rotation speed of the rotating shaft in the upper defibration mechanism was 1500 rpm, the rotation speed of the rotating shaft in the middle defibration mechanism was 1500 rpm, and the rotation speed of the rotating shaft in the lower defibration mechanism was 1500 rpm.
(Preparation of molding material)
Each component was uniformly mixed according to the formulations in Tables 2 to 5 to obtain a resin composition. A thickener was added to the obtained resin composition (paste), and the mixture was stirred for 3 minutes. The mixture was then immediately fed into an SMC impregnation machine (manufactured by Tsukishima Kikai Co., Ltd.), and carbon fiber 24K (defibrated) was added and thoroughly impregnated. The mixture was then aged for 48 hours to obtain a sheet-shaped molding material.

In Tables 2 to 5, the blending ratios of components other than carbon fiber bundles are shown in parts by mass (parts), and the blending ratio of carbon fiber bundles is shown as a mass ratio (mass%) to the total amount of resin composition and carbon fiber bundles.

Examples 3, 5, 7, 8, 9, 12, 15, 16 to 32, and Comparative Examples 1 to 13
(Preparation of carbon fiber bundles)
The fiber bundles of carbon fibers before defibration were defibrated in the same manner as in Example 1, except that the defibration conditions shown in Tables 2 to 5 were followed.
(Preparation of molding material)
Sheet-shaped molding materials were obtained in the same manner as in Example 1, except that the formulations in Tables 2 to 5 were used.
4. Evaluation (storage stability)
Each vinyl ester of each synthesis example was dissolved in styrene to prepare a 40% by mass styrene solution. The styrene solution was then allowed to stand at 25°C for 48 hours, and the state of the styrene solution was then visually inspected. The results are shown in Table 1.
(deflection temperature under load)
Each vinyl ester of each synthesis example was dissolved in styrene to prepare a 40% by weight styrene solution. Next, 0.5 parts by weight of cobalt octenoate (metal content 8%) and 1 part by weight of Kayamec M (manufactured by Kayaku Akzo Co., Ltd.) were added to 100 parts by weight of each styrene solution and mixed. Cast plates of the cured resin were prepared in accordance with JIS K6919 (1992), and their deflection temperatures under load were measured in accordance with JIS K6911 (1995). The results are shown in Table 1.
(median and standard deviation)
One hundred defibrated carbon fiber bundles were randomly extracted from the defibrated carbon fiber bundles used in each Example and Comparative Example, and the mass (m) of each extracted carbon fiber bundle and the fiber length (l) of each carbon fiber bundle were measured. From the obtained mass (m) and fiber length (l), the number of bundled fibers (n) of the defibrated carbon fiber bundle was calculated based on the following formula (10), and the median and standard deviation of this number of bundled fibers were also calculated.
n=(m×N×1000)/(M×l) (10)
(In the formula, n represents the number of fibers (K) in the carbon fiber bundle after defibration, m represents the mass (mg) of the carbon fiber bundle after defibration, N represents the number of fibers (K) in the carbon fiber bundle before defibration, M represents the fiber weight (g/1000 m) of the carbon fiber bundle before defibration, and 1 represents the fiber length (mm) of the carbon fiber bundle after defibration.)
The results are shown in Tables 2 to 5.
(bulk density)
50 g of the defibrated carbon fiber bundle used in each Example and Comparative Example was placed in a 1 L measuring cylinder. The measuring cylinder was then shaken 100 times or more, and the graduations on the measuring cylinder were measured. The bulk density was then calculated according to the following formula (11). The results are shown in Tables 2 to 5.
Bulk density = (mass of carbon fiber bundle (g)) / (measuring cylinder scale reading (mL)) (11)
(Fluff)
The carbon fiber bundles used in each example and comparative example were cut using the defibrating device described in JP 2019-065405 A, and the ends and sides of the cut carbon fiber bundles were visually observed, and the fluff was evaluated according to the following criteria. The results are shown in Tables 2 to 5.
◯: No fluffing was observed.
△: A small amount of fluff was observed.
×: A lot of fluff was observed.
(Viscosity of Resin Composition)
The viscosity of the resin compositions (pastes) of each Example and Comparative Example at 25°C was measured in accordance with JIS K6901 (2008). The results are shown in Tables 2 to 5.
(impregnation)
The molding materials of each Example and Comparative Example were cut in the width direction, and the cross sections were visually observed. The impregnation ability was evaluated according to the following criteria. The results are shown in Tables 2 to 5.
Good: No fiber bundles of carbon fibers to which the resin component was not attached were found near the center of the thickness of the molding material.
x: Fiber bundles of carbon fibers to which no resin component was attached were observed near the center of the thickness of the molding material.
(Seat handling)
Two sheets of molding material measuring 200 x 200 mm were cut out from the molding material of each Example and Comparative Example, and these were stacked and stuck together by hand and pressed tightly together, and then the two sheets were peeled off by hand.

In the above evaluation, the handling properties of the sheets were evaluated according to the following criteria, and the results are shown in Tables 2 to 5.
◯: When the laminated sheets were peeled off, the sheets peeled off cleanly.
Δ: The laminated sheets could be peeled off, but part of the sheet was stuck to the other sheet.
x: The laminated sheets could not be peeled off.
(Fillability)
A molding material measuring 106 mm x 106 mm was cut out from the molding material of each Example and Comparative Example, and 12 sheets of this molding material with a sheet thickness of 1 mm or 6 sheets of this molding material with a sheet thickness of 2 mm were stacked together, placed in the center of a 300 mm x 300 mm flat plate molding mold, and heated and pressurized for 5 minutes at 140°C and 5 MPa.

This resulted in a molded product (molded plate) measuring 300 mm x 300 mm x approximately 1.5 mm.

In the above molding, the filling property of the molding material into the mold was evaluated according to the following criteria. The results are shown in Tables 2 to 5.
○: The unfilled area was 0 mm ² .
△: The unfilled area was more than 0 mm ² and less than 200 mm ² .
×: The unfilled area was 200 mm ² or more.
(exterior)
A molding material measuring 210 mm x 210 mm was cut out from the molding material of each Example and Comparative Example, and eight sheets of this were stacked in the case of molding material with a sheet thickness of 1 mm, or four sheets in the case of molding material with a sheet thickness of 2 mm. These were then placed in the center of a 300 mm x 300 mm flat plate molding mold and heated and pressurized for 5 minutes under conditions of 140°C and 10 MPa.

This resulted in a molded product (molded plate) measuring 300 mm x 300 mm x approximately 4 mm thick.

The surface condition of the obtained molded article was visually inspected and the appearance was evaluated according to the following criteria. The results are shown in Tables 2 to 5.
◯: No cracks, blisters or scratches were observed.
x: Any of cracks, swelling and fading was observed.
(Smoothness)
The molding materials of each Example and Comparative Example were subjected to heat compression molding using a 300 x 300 mm flat mold to produce 4 mm thick flat molded articles. Molding was performed under the following conditions: mold temperature: 145°C on the product surface, 130°C on the back surface, molding pressure: 10 MPa, and mold retention time: 5 minutes. Two straight fluorescent lamps were projected onto the surface of the obtained flat molded articles from 1.5 m above the surface, and the surface smoothness of the molded articles was evaluated by visual observation of the projected image. Surface smoothness was evaluated according to the following criteria. The results are shown in Tables 2 to 5.
◯: The projected image had high linearity and parallelism.
△: "Waviness" and distortion were observed in the projected image.
×: A large "waviness" was observed in the projected image, and the distortion was large.
(Warpage)
For each Example and Comparative Example, the molded article obtained in the above-mentioned filling evaluation was removed from the mold and left at 25°C for 24 hours. This molded article was placed on a precision surface plate specified in JIS B7513 (1992), and the gap between each side of the molded article and the precision surface plate was measured. Warpage was evaluated according to the following criteria. The results are shown in Tables 2 to 5.
○: No gaps were found.
△: A gap exceeding 0 mm and less than 10 mm was observed.
×: A gap of 10 mm or more was observed.
(density)
For each of the Examples and Comparative Examples, the density of the molded articles obtained in the above appearance evaluation was determined by Archimedes' method using water at 25° C. The results are shown in Tables 2 to 5.
(Flexural properties (flexural strength and flexural modulus))
For each of the Examples and Comparative Examples, a bending test was carried out in accordance with JIS K7074 (1988) using the molded articles obtained in the above appearance evaluation to measure the bending strength and bending modulus. The results are shown in Tables 2 to 5.
(specific strength)
From the measurement results of bending strength and density, the specific strength was calculated by the following formula (12).

Specific strength = (flexural strength) / (density) (12)
The results are shown in Tables 2 to 5.
(specific stiffness)
The specific rigidity was calculated from the measurement results of the flexural modulus and density using the following formula (13). The results are shown in Tables 2 to 5.

Specific stiffness = (flexural modulus) ^1/3 / (density) (13)
5. Discussion A graph showing the relationship between the median X and the standard deviation Y in Examples 1, 3, 5, 7, 8, 9, 12, and 15, Comparative Examples 1 to 4 , and Comparative Examples 7 to 13 is shown in FIG.

In this case, it was found that a molding material that exhibits excellent impregnation of carbon fiber bundles with resin components and excellent mold filling properties has the above-mentioned median X and standard deviation Y of the carbon fiber bundles determined by the relationship in Figure 2 (Y > 0.5X, Y < 0.5X + 4000, X > 2000, X < 8000) (shaded area in Figure 2).

Specifically, Example 1 , Example 3, Example 5, Example 7, Example 8, Example 9, Example 12, Example 15 and Comparative Example 7 to Comparative Example 13 , which are within the above range, are superior in impregnation of the carbon fiber bundles with the resin component and superior in fillability into a mold, compared to Comparative Example 1 to Comparative Example 4, which are not within the above range.

Claims (7)

A resin composition including a resin component and fiber bundles of carbon fibers,
The bulk density of the carbon fiber bundle is 0.15 g/ml or more and 0.3 g/ml or less,
A molding material characterized in that the median X and standard deviation Y of the carbon fiber bundle measured by the following test satisfy the relationships of the following formulas (1) to (4) (excluding X=4620 and Y=3120, X=4430 and Y=3210, X=6750 and Y=3660, and X=5890 and Y=3080).
Y>0.5X (1)
Y<0.5X+2000 (2)
X>2000 (3)
X<8000 (4)
Test: A carbon fiber bundle is defibrated using a defibrator, 100 defibrated carbon fiber bundles are randomly extracted from the defibrated carbon fiber bundle, the mass (m) of each extracted carbon fiber bundle and the fiber length (l) of each carbon fiber bundle are measured, and the number of bundled fibers (n) of the defibrated carbon fiber bundle is calculated from the obtained mass (m) and fiber length (l) based on the following formula (5), and the median and standard deviation of these bundled fibers are calculated.
n=(m×N×1000)/(M×l) (5)
(In the formula, n represents the number of fibers (K) in the carbon fiber bundle after defibration, m represents the mass (mg) of the carbon fiber bundle after defibration, N represents the number of fibers (K) in the carbon fiber bundle before defibration, M represents the fiber weight (g/1000 m) of the carbon fiber bundle before defibration, and 1 represents the fiber length (mm) of the carbon fiber bundle after defibration.) the resin component comprises a reaction product of a vinyl ester and an acid anhydride;
The molding material according to claim 1 , wherein the resin composition contains a thickener. 3. The molding material according to claim 2 , wherein the thickener is magnesium oxide. 4. The molding material according to claim 2 , wherein the acid anhydride is blended in an amount of 0.6 mol or more and 1.4 mol or less per 1 mol of the vinyl ester. The vinyl ester is a reaction product of an epoxy resin and an unsaturated monobasic acid,
The molding material according to any one of claims 2 to 4 , wherein the epoxy equivalent of the epoxy resin is 200 or more and 500 or less. The molding material according to any one of claims 1 to 5 , characterized in that a blending ratio of the carbon fiber bundles is 40 mass% or more and 65 mass% or less with respect to a total amount of the resin composition and the carbon fiber bundles. A molded article comprising a cured product of the molding material according to any one of claims 1 to 6 .