Carbon fiber reinforced composite materials and methods for manufacturing carbon fiber reinforced composite materials

Abstract

This invention provides a carbon fiber reinforced composite material with excellent adhesion, compatibility with epoxy resin, and interfacial adhesion, and capable of achieving high mechanical strength, as well as a method for manufacturing the carbon fiber reinforced composite material. The carbon fiber reinforced composite material of this invention comprises carbon fibers, epoxy resin, a hardener, and polyvinyl acetal resin, wherein the polyvinyl acetal resin contains a constituent unit as shown in formula (1), where R1 in formula (1) is an alkyl group having one or more carbon atoms; in formula (1), R1 can be the same or different.

Description

Technical Field

[0001] This invention relates to a carbon fiber reinforced composite material and a method for manufacturing the carbon fiber reinforced composite material. Prior Technology

[0002] Fiber-reinforced plastics, as a type of fiber-reinforced composite material, are widely used in applications ranging from structural materials for aircraft, automobiles, and ships to general sports applications such as tennis rackets, fishing rods, and golf clubs due to their lightweight, high strength, and high rigidity. One method for manufacturing fiber-reinforced plastics involves impregnating a matrix resin into a reinforcing material composed of equal-length reinforcing fibers (continuous fibers), forming an intermediate material, i.e., a prepreg. This method offers the advantage of easily managing the reinforcing fiber content and allowing for the design of a higher content.

[0003] Epoxy resin is preferred as the matrix resin for this type of fiber-reinforced composite material due to its excellent processability. Because epoxy resin can produce fiber-reinforced composite materials with excellent mechanical properties and heat resistance even after curing, it is used in a wide range of industries.

[0004] For example, Patent Document 1 describes a prepreg containing specific amounts of reinforcing fibers, epoxy resin, carboxyl-containing polyethylene formaldehyde resin, and amine curing agent. Furthermore, Patent Document 2 describes a prepreg for fiber-reinforced composite materials, which contains a specific amount of epoxy resin, a thermoplastic resin soluble in epoxy resin, and a latent curing agent. Furthermore, Patent Document 3 describes a prepreg obtained by impregnating a composition of epoxy resin containing an epoxy compound, a hardener, and a polyvinyl acetal resin into reinforcing fibers. Previous technical documents Patent documents

[0005] Patent Document 1: International Publication No. 2019 / 202762 Patent Document 2: Japanese Patent Application Publication No. 6-9802 Patent Document 3: Japanese Patent Application Publication No. 5-186667 Summary of the Invention

[0006] [The problem that the invention aims to solve]

[0007] However, even when using the techniques described in Patent Documents 1 to 3, there is a problem that the obtained prepreg has insufficient viscosity (surface adhesion) and reduced operability. Furthermore, the obtained prepreg may also exhibit poor interfacial adhesion between the reinforcing fibers and the matrix resin, resulting in insufficient performance. This leads to the problem that the obtained prepreg has insufficient toughness and reduced mechanical strength.

[0008] In view of the above-mentioned situation, the present invention aims to provide a carbon fiber reinforced composite material with excellent adhesion, compatibility with epoxy resin and interfacial adhesion, and capable of achieving high mechanical strength, as well as a method for manufacturing the carbon fiber reinforced composite material. [Technical means to solve the problem]

[0009] The present invention (1) is a carbon fiber reinforced composite material containing carbon fiber, epoxy resin, hardener and polyvinyl acetal resin, wherein the polyvinyl acetal resin has a constituent unit as shown in the following formula (1), wherein R1 in the following formula (1) is an alkyl group having 1 or more carbon atoms.

[0010] In equation (1), R1 can be the same or different. The present invention (2) is a carbon fiber reinforced composite material as described in the present invention (1), wherein in the polyvinyl acetal resin, R 1 in formula (1) is an alkyl group having 1 or more carbon atoms, and / or an alkyl group having 3 or more carbon atoms. The present invention (3) is a carbon fiber reinforced composite material as described in the present invention (1) or (2), wherein the hydroxyl content of the polyvinyl acetal resin is 15.0 moles or more and 45.0 moles or less. The present invention (4) is a carbon fiber reinforced composite material as described in any one of the present invention (1) to (3), wherein the average degree of polymerization of the polyvinyl acetal resin is 2500 or less. The present invention (5) is a carbon fiber reinforced composite material as described in any one of the present invention (1) to (4), wherein the glass transition temperature of the polyvinyl acetal resin is 75°C or higher. The present invention (6) is a carbon fiber reinforced composite material as described in any one of the present invention (1) to (5), wherein the polyvinyl acetal resin contains a constituent unit having an acid-modified group. The present invention (7) is a carbon fiber reinforced composite material as described in the present invention (6), wherein the content of the constituent unit having an acid-modified group in the polyvinyl acetal resin is 0.01 to 20 moles. The present invention (8) is a carbon fiber reinforced composite material as described in any one of the present invention (1) to (7), wherein the content of hydroxyl groups in the polyvinyl acetal resin is 16.0 mol% or more and 45.0 mol% or less. The present invention (9) is a carbon fiber reinforced composite material as described in any one of the present invention (1) to (8), wherein the content of polyvinyl acetal resin is 0.01 parts by weight or more and 40.0 parts by weight or less relative to 100 parts by weight of epoxy resin. The present invention (10) is a method for manufacturing a carbon fiber reinforced composite material, which includes at least the following steps: a step of preparing a resin composition containing epoxy resin, a hardener and a polyvinyl acetal resin; and a step of compounding the resin composition with carbon fiber; wherein the polyvinyl acetal resin contains a constituent unit shown in the following formula (1), wherein R1 in the following formula (1) is an alkyl group having 1 or more carbon atoms. The present invention will now be described in detail.

[0011] The inventors conducted in-depth research and found that carbon fiber reinforced composite materials containing polyvinyl acetal resin with a specific structure have excellent adhesion, compatibility with epoxy resin and interfacial tightness, and can achieve high mechanical strength, thus completing the present invention.

[0012] The carbon fiber reinforced composite material of the present invention contains polyvinyl acetal resin. The above-mentioned polyvinyl acetal resin contains the constituent unit shown in the following formula (1), where R1 in the following formula (1) is an alkyl group having 1 or more carbon atoms.

[0013] In equation (1), R1 can be the same or different.

[0014] In the above formula (1), R1 is an alkyl group with 1 or more carbon atoms. By making the alkyl group have 1 or more carbon atoms, the carbon fiber composite material exhibits advantages such as improved strength and toughness, and excellent impact resistance. Preferably, the carbon number is 1 or more, and more preferably 6 or less. In particular, R1 in formula (1) is preferably an alkyl group with 1 or more carbon atoms, and / or an alkyl group with 3 or more carbon atoms.

[0015] The above R1 can be the same or a combination of different ones. When R1 is a combination of different substances, it is preferable to be a combination of alkyl groups having 1 or more carbon atoms and alkyl groups having 3 or more carbon atoms.

[0016] As for the aforementioned alkyl groups, there are no particular limitations as long as they have one or more carbon atoms. Examples include: methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, dibutyl, tributyl, etc. Also, examples include: pentyl, hexyl, heptyl, 2-ethylhexyl, octyl, nonyl, decyl, undecyl, dodecayl, tridecayl, tetradecyl, decadecyl, octadecyl, etc. Among these, methyl and n-propyl are preferred.

[0017] In the above-mentioned polyethylene acetal resin, the preferred lower limit of the content of the constituent unit having an acetal group as represented by the above general formula (1) (hereinafter also referred to as "alkyl acetal group content") is 30 mol%, and the preferred upper limit is 85 mol. If the content of the above-mentioned alkyl acetal groups is 30 moles or more, a polyethylene acetal resin with excellent strength and toughness can be produced. If the content of the above-mentioned acetal groups is 85 moles or less, the compatibility with epoxy resin can be improved. The preferred lower limit of the content of the above-mentioned alkyl acetal group is 60 mol%, and the preferred upper limit is 80 mol%. Furthermore, in this specification, as a method for calculating the amount of alkyl acetal, since the acetal group of polyvinyl acetal resin is obtained by acetalizing the constituent units of polyvinyl alcohol resin with two hydroxyl groups, the method of counting the constituent units with two hydroxyl groups that have undergone alkyl acetalization is used to calculate the amount of alkyl acetal.

[0018] In the above-mentioned polyethylene acetal resin, when R1 in the above general formula (1) has a methyl group, the preferred lower limit of the content of this constituent unit (hereinafter also referred to as "degree of acetalization") is 5 mol%, and the preferred upper limit is 85 mol%. By being within the above range, compatibility with epoxy resin is maintained, and excellent viscosity characteristics can be obtained. Furthermore, in the aforementioned polyvinyl acetal resin, when R1 in the above general formula (1) has a n-propyl group, the preferred lower limit of the content of this constituent unit (hereinafter also referred to as "degree of butyraldehyde") is 0.1 mol%, and the preferred upper limit is 80 mol%. By being within the above range, compatibility with epoxy resin is maintained, and excellent viscosity characteristics can be obtained. In the above-mentioned polyethylene acetal resin, when R1 in the above general formula (1) has both methyl and n-propyl groups, the ratio of the degree of acetalization to the degree of butyraldehydeization [degree of acetalization / degree of butyraldehydeization] is preferably 0.06 or more and 850 or less. Furthermore, the ratio is more preferably 0.1 or more and 375 or less.

[0019]

[0020] In the above-mentioned polyvinyl acetal resin, the preferred lower limit of the content of the hydroxyl-containing constituent unit represented by the above general formula (2) (hereinafter also referred to as "hydroxyl content") is 15.0 mol%, and the preferred upper limit is 45.0 mol. If the amount of hydroxyl groups is 15.0 moles or more, a polyvinyl acetal resin with excellent adhesion can be produced. If the amount of hydroxyl groups is 45.0 moles or less, the compatibility with epoxy resin can be sufficiently improved. The preferred lower limit of the amount of hydroxyl groups is 16.0 mol, the more preferred lower limit is 18.0 mol, the more preferred lower limit is 20.0 mol, the more preferred upper limit is 40.0 mol, and the more preferred upper limit is 38.0 mol.

[0021] In the above-mentioned polyvinyl acetal resin, the preferred lower limit of the content of the acetylated constituent unit represented by the above general formula (3) (hereinafter also referred to as "acetylated amount") is 0.1 mol%, and the preferred upper limit is 25 mol. If the acetyl content is 0.1 mol% or more, the high viscosity caused by intramolecular and intermolecular hydrogen bonds of the hydroxyl groups in the polyethylene acetal resin can be suppressed. If the acetyl content is 25 mol% or less, the processability can be improved without excessively reducing the heat resistance of the polyethylene acetal resin. The preferred lower limit of the acetylation content is 0.5 mol%, and the preferred upper limit is 15 mol%; further preferably, the lower limit is 0.8 mol%, and further preferably, the upper limit is 14 mol. Furthermore, in the aforementioned polyethylene acetal resin, the combined amount of alkyl acetal groups, hydroxyl groups, and acetyl groups preferably exceeds 95 mol%, and more preferably exceeds 96 mol%.

[0022] The aforementioned polyvinyl acetal resin preferably contains constituent units with acid-modified groups. By incorporating the aforementioned acid-modified constituent units, compatibility with epoxy resin is improved, thereby enhancing the strength and toughness of the resulting carbon fiber reinforced composite material. Furthermore, the improved adhesion to carbon fibers suppresses delamination between the matrix resin and carbon fibers in the carbon fiber reinforced composite material. This helps reduce defects and improve mechanical strength.

[0023] Examples of acid-modifying groups include carboxyl groups, sulfonic acid groups, maleic acid groups, sulfinic acid groups, hyposulfonic acid groups, phosphoric acid groups, phosphonic acid groups, and their salts.

[0024] The constituent unit having the above-mentioned acid-modified group can be a structure in which two acid-modified groups are bonded to the same carbon atom constituting the main chain, or it can be a structure in which one acid-modified group is bonded to the carbon atom constituting the main chain. Furthermore, the aforementioned acid-modified groups can be directly bonded to the carbons constituting the main chain, or they can be bonded to the carbons constituting the main chain via alkyl linkages. Furthermore, the aforementioned acid-modified group can also be a structure in which an acid-modified group is bonded to the carbon atom of the acetal group. When the constituent unit having the above-mentioned acid-modified group has a structure in which the acid-modified group is bonded to the carbon of the main chain via an alkyl group, the alkyl group is preferably an alkyl group with 1 to 10 carbons, more preferably an alkyl group with 1 to 5 carbons, and even more preferably an alkyl group with 1 to 3 carbons.

[0025] Examples of alkyl groups having 1 to 10 carbon atoms include: straight-chain alkyl groups, branched alkyl groups, and cyclic alkyl groups. Examples of linear alkyl groups include: methylene, vinyl alkyl, n-propyl alkyl, tetramethylene, pentamethylene, hexamethylene, octamethylene, decamethylene, etc. Examples of the aforementioned branched alkyl groups include: methylmethylene, methylethyl, 1-methylpentyl, 1,4-dimethylbutyl, etc. Examples of the aforementioned cyclic alkyl groups include: cyclopropyl, cyclobutyl, and cyclohexyl. Preferably, it is a straight-chain alkyl group, more preferably methylene, vinyl group, or n-propyl group, and even more preferably methylene or vinyl group.

[0026] In the case where the acid-modified group is a carboxyl group, the constituent units containing carboxyl groups can be exemplified by, for example, the constituent units represented by the following formula (4-1), the constituent units represented by the following formula (4-2), and the constituent units represented by the following formula (4-3).

[0027]

[0028] In formula (4-1) above, R2 and R3 independently represent alkyl groups having 0 to 10 carbon atoms, and X1 and X2 independently represent hydrogen atoms, metal atoms, or methyl groups. In formula (4-2) above, R4, R5, and R6 independently represent hydrogen atoms or alkyl groups having 1 to 10 carbon atoms, R7 represents alkyl groups having 0 to 10 carbon atoms, and X3 represents hydrogen atoms, metal atoms, or methyl groups. Furthermore, the statement that R2, R3, or R7 represents an alkyl group having 0 carbon atoms means that R2, R3, or R7 is a single bond. In formula (4-3) above, R8 represents an alkyl group having 0 to 10 carbon atoms, and X4 represents hydrogen atoms, metal atoms, or methyl groups. Furthermore, a carbon number of 0 refers to the absence of alkyl groups, meaning there are no alkyl groups and the bonds are direct.

[0029] When at least one of X1 and X2 is a metal atom, examples of such metal atoms include sodium atoms, lithium atoms, and potassium atoms. Among these, sodium atoms are preferred.

[0030] The aforementioned polyvinyl acetal resin preferably has the constituent unit represented by the above formula (4-1). When the above-mentioned polyvinyl acetal resin has the constituent units represented by the above formula (4-1), its compatibility with epoxy resin can be made even better.

[0031] When X3 is a metal atom, examples of such metal atoms include sodium, lithium, and potassium atoms. Sodium is preferred. Similarly, when X4 is a metal atom, the same applies.

[0032] The preferred lower limit of the content of the constituent units with acid-modified groups in the above-mentioned polyvinyl acetal resin (hereinafter also referred to as "acid-modified group content") is 0.01 mol%, and the preferred upper limit is 20 mol. If the acid-modified group content is 0.01 mol% or more, the effect of the acid-modified group in the polyvinyl acetal resin can be fully utilized, and the adhesion of the obtained carbon fiber reinforced composite material can be further improved. If the acid-modified group content is 20 mol% or less, the adhesion and toughness of the carbon fiber reinforced composite material can be further improved. The preferred lower limit of the acid-modified group content of the polyvinyl acetal resin is 0.05 mol%, and the preferred upper limit is 15 mol%; further preferably, the lower limit is 0.1 mol%, and further preferably, the upper limit is 10 mol%. Furthermore, in this specification, the amount of acid-modified groups in polyvinyl acetal resin refers to the ratio of constituent units with acid-modified groups to all constituent units of polyvinyl acetal resin.

[0033] The average degree of polymerization of the above-mentioned polyvinyl acetal resin is preferably below 2500. By having an average degree of polymerization of 2500 or less, sufficient mechanical strength can be imparted. Furthermore, if the average degree of polymerization is 1000 or less, the solubility in organic solvents is significantly improved, resulting in superior coatability and dispersibility. The preferred lower limit for the above average degree of polymerization is 150, and the preferred upper limit is 1000. The average degree of polymerization mentioned above is the same as that of the raw material polyvinyl alcohol resin. The average degree of polymerization of the raw material polyvinyl alcohol resin can be determined according to JIS K6726-1994.

[0034] The glass transition temperature (Tg) of the above-mentioned polyvinyl acetal resin is preferably above 75°C. By setting the glass transition temperature to 75°C or higher, not only is heat resistance improved, but also the amount of exudation during impregnation is reduced. A preferred lower limit for the glass transition temperature is 80°C. There is no particular upper limit for the glass transition temperature, which is 115°C. Furthermore, the aforementioned glass transition temperature can be measured using a differential scanning calorimeter (DSC).

[0035] The preferred lower limit of viscosity of the above-mentioned polyethylene acetal resin, when measured using a rheometer at 30°C after adding epoxy resin and heating it to dissolve, is 30 Pa·s, and the preferred upper limit is 1200 Pa·s. Furthermore, the weight ratio of the epoxy resin to the polyethylene acetal resin is 9:1. By being within the above range, suitable viscosity can be maintained after impregnation with carbon fiber, thereby improving processability. Furthermore, the preferred lower limit of the viscosity of the above-mentioned polyvinyl acetal resin, when measured at 90°C using a rheometer after adding epoxy resin and heating it to dissolve, is 0.1 Pa·s, and the preferred upper limit is 4.5 Pa·s. By achieving the viscosity within the aforementioned range, the optimal viscosity can be obtained when impregnating carbon fibers, thereby suppressing the formation rate of voids. Furthermore, the preferred lower limit of the ratio of the viscosity of the aforementioned polyvinyl acetal resin at 30°C to its viscosity at 90°C (viscosity at 30°C / viscosity at 90°C) is 6.5, and the preferred upper limit is 12000. By falling within the above range, a strong and tough carbon fiber reinforced composite material with excellent viscosity and low porosity can be manufactured. Furthermore, the viscosity mentioned above refers to the viscosity at 30°C and 90°C obtained by dissolving 10 parts by weight of polyethylene acetal resin relative to 90 parts by weight of epoxy resin at 150°C using a rheometer, for example, under the conditions of using a 20 mm parallel plate, a cooling rate of 5°C / min, a rotation speed of 100 rpm, and a gap of 500 μm. Furthermore, the epoxy resin and thermoplastic resin used in the above viscosity measurement refer to the epoxy resin and thermoplastic resin contained in the carbon fiber reinforced composite material.

[0036] The content of the polyvinyl acetal resin in the carbon fiber reinforced composite material of the present invention is preferably 0.01 parts by weight or more and 40.0 parts by weight or less relative to 100 parts by weight of epoxy resin. If the content of the polyvinyl acetal resin is within the above range, the mechanical strength of the obtained carbon fiber reinforced composite material can be sufficiently improved. Furthermore, the content of the aforementioned polyvinyl acetal resin in the carbon fiber reinforced composite material of the present invention is preferably 0.001% by weight or more, and preferably 35% by weight or less, relative to the total composition. If the content of the aforementioned polyvinyl acetal resin is within the above range, the mechanical strength of the obtained carbon fiber reinforced composite material can be sufficiently improved.

[0037] Generally speaking, the above-mentioned polyvinyl acetal resin can be manufactured by acetalizing polyvinyl alcohol resin. There are no particular limitations on the above-mentioned acetalization method, and previously known methods can be used. For example, various aldehydes can be added to an aqueous solution, alcohol solution, water / alcohol mixture, or dimethyl sulfoxide (DMSO) solution of polyvinyl alcohol resin in the presence of an acid catalyst. Furthermore, when the aforementioned polyvinyl acetal resin contains constituent units with acid-modified groups, the manufacturing method may be a method of acetalizing the polyvinyl alcohol resin containing constituent units with acid-modified groups, or a method of acetalizing unmodified polyvinyl alcohol and then modifying it.

[0038] Examples of aldehydes mentioned above include linear, branched, cyclic saturated, cyclic unsaturated, or aromatic aldehydes with 1 to 19 carbon atoms. Specifically, examples include formaldehyde, acetaldehyde, propionaldehyde, n-butyraldehyde, isobutyraldehyde, tert-butyraldehyde, benzaldehyde, and cyclohexanol. These aldehydes can be used alone or in combination of two or more. Furthermore, aldehydes other than formaldehyde, cyclic saturated, cyclic unsaturated, or aromatic aldehydes are preferred, with acetaldehyde and n-butyraldehyde being particularly preferred.

[0039] The amount of aldehyde added can be appropriately set according to the amount of acetal groups in the target polyvinyl acetal resin. In particular, if the amount of aldehyde added is preferably 50 mol% or more and 95 mol% or less, more preferably 55 mol% or more and 90 mol% or less, relative to 100 mol% of polyvinyl alcohol resin, the acetalization reaction can be carried out efficiently and unreacted aldehydes can be easily removed, which is preferable.

[0040] As the aforementioned polyvinyl alcohol resin, for example, previously known polyvinyl alcohol resins can be used, such as resins obtained by saponifying polyvinyl acetate with alkali, acid, ammonia, etc. The aforementioned polyvinyl alcohol resin can also be completely saponified, but as long as at least one "unit with two consecutive hydroxyl groups at the meso and racemic positions" exists at at least one position in the main chain, complete saponification is not required, and partially saponified polyvinyl alcohol resins are also acceptable. Furthermore, as the aforementioned polyvinyl alcohol resin, copolymers of monomers capable of copolymerizing with ethylene alcohol and ethylene alcohol can also be used, such as ethylene-ethylene alcohol copolymer resins, partially saponified ethylene-ethylene alcohol copolymer resins, etc. Examples of polyvinyl acetate-based resins include, for example, ethylene-vinyl acetate copolymers.

[0041] The polyvinyl acetal resin constituting the carbon fiber reinforced composite material of the present invention is preferably an acetalized form of polyvinyl alcohol resin with a saponification degree of 75 moles or more. More preferably, the saponification degree is 85 moles or more and 99.5 moles or less.

[0042] Furthermore, the holding time after the reaction will vary depending on other conditions, but it is preferably 1.5 hours or more, and more preferably 2 hours or more. By maintaining the above holding time, the acetalization reaction can be carried out sufficiently. The holding temperature after the reaction is preferably above 15°C, and more preferably above 20°C. By maintaining the temperature as described above, the acetalization reaction can be carried out sufficiently.

[0043] Generally, since the aforementioned polyvinyl alcohol resin contains carboxylates, which are alkaline components produced during saponification, it is preferable to use them after washing to remove or neutralize them. By washing to remove or neutralize the carboxylates, the condensation reaction of aldehydes catalyzed under alkaline conditions can be effectively inhibited, thus further suppressing the coloring of the resin. Examples of cleaning methods used in the above-mentioned cleaning steps include: methods for extracting alkaline components using solvents; methods for dissolving resin in a good solvent and then adding a poor solvent to allow the resin to precipitate again; and methods for adding an adsorbent to a solution containing polyvinyl alcohol resin to adsorb and remove alkaline components. As a neutralizing agent used in the above neutralization steps, examples can be given: mineral acids such as hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid;

[0044] The carbon fiber reinforced composites of the present invention contain carbon fibers. As the above-mentioned carbon fibers, examples can be given: PAN-based carbon fibers, asphalt-based carbon fibers, cellulose-based carbon fibers, and gas-phase growth-based carbon fibers.

[0045] As the morphology of the above-mentioned carbon fibers, stranded lines, unpinned lines and unpinned lines can be used. Also, in order to improve the connectivity with the matrix resin, the above-mentioned carbon fibers can also be introduced with oxygen-containing functional groups by applying an oxidative treatment. As aforementioned oxidation treatment methods, gas-phase oxidation, liquid-phase oxidation and liquid-phase electrolytic oxidation are used, but based on the view that higher productivity allows for uniform treatment, it is preferable to use liquid-phase electrolytic oxidation.

[0046] The single-fiber fiber of the above carbon fibers is preferably 0.2~2.0 dtex, and even better is 0.4~1.8 dtex. By making the single fiber fiber 0.2 dtex or more, thereby the carbon fiber damage due to contact with the guide roller is less likely to occur when the pinch line is carried out, and again, the same damage is less likely to occur during the impregnation treatment step of the resin composition. By resorting to a single fiber fineness of less than 2.0 dtex, thereby allowing the resin composition to be adequately immersed in the carbon fiber, as a result, the fatigue resistance is improved. Also, according to the same reasons as above, the better fiber of the above carbon fiber is 50~1800 tex. Regarding the above-mentioned carbon fibers, the optimal number of filaments in a fiber bundle is in the range of 2500~100000 strands. If the number of filaments is less than 2500, the arrangement of fibers can easily become meandering, which can easily cause a decrease in strength. Also, if the number of filaments exceeds 100 000, it is sometimes more difficult to perform resin impregnation during the preparation or shaping of the prepreg. The best number of filaments is in the range of 2800~80000 strands.

[0047] The average fiber diameter of the above-mentioned carbon fibers is preferably more than 2 μm, preferably more than 3 μm, and preferably less than 30 μm, preferably less than 26 μm. The average fiber length of the aforementioned carbon fiber is preferably 2 mm or more, more preferably 4 mm or more, and preferably 100 mm or less, more preferably 80 mm or less. The form of carbon fiber is not particularly limited; for example, it can be in the form of fibers, textiles, woven fabrics, or sheet-like nonwoven fabrics. When the carbon fiber is in sheet form, the unit area weight of the fiber is preferably 100 g / m² or more, more preferably 350 g / m² or more, and preferably 1000 g / m² or less, more preferably 650 g / m² or less. Furthermore, the density of the aforementioned carbon fiber is preferably 1.6 g / cm³ or higher and 2.0 g / cm³ or lower.

[0048] In the carbon fiber reinforced composite material of the present invention, the content of the aforementioned carbon fiber is preferably 35% by weight or more, and preferably 100% by weight or less. If the content of the aforementioned carbon fiber is within the above range, the mechanical strength of the obtained carbon fiber reinforced composite material can be sufficiently improved. Furthermore, the content of the aforementioned carbon fiber relative to 100 parts by weight of the aforementioned epoxy resin is preferably 55 to 3685 parts by weight.

[0049] The carbon fiber reinforced composite material of this invention contains epoxy resin. By containing the aforementioned epoxy resin, it is possible to crosslink it by applying energy such as heating, thereby achieving higher adhesion.

[0050] Examples of epoxy resins mentioned above include monofunctional epoxy compounds, difunctional epoxy compounds, trifunctional or higher-functional epoxy compounds, and other multifunctional epoxy compounds, with a preference for those containing both monofunctional and difunctional epoxy compounds.

[0051] Examples of the aforementioned monofunctional epoxy compounds include (meth)acrylates containing glycidyl groups, aliphatic epoxy resins, and aromatic epoxy resins. Among these, (meth)acrylates containing glycidyl groups are preferred. Examples of (meth)acrylates containing glycidyl groups include: glycidyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate glycidyl ether, 2-hydroxypropyl (meth)acrylate glycidyl ether, 3-hydroxypropyl (meth)acrylate glycidyl ether, 4-hydroxybutyl (meth)acrylate glycidyl ether, and polyethylene glycol-polypropylene glycol (meth)acrylate glycidyl ether. Examples of aliphatic epoxy resins include butyl glycidyl ether, lauryl glycidyl ether, and glycidyl ether of aliphatic alcohols. Examples of aromatic epoxy resins mentioned above include phenyl epoxy ether and 4-tert-butylphenyl epoxy ether. Among them, (meth)acrylates containing epoxypropyl groups and aromatic epoxy resins are preferred.

[0052] Examples of the aforementioned difunctional epoxy compounds include: phenolic varnish-type epoxy resins, bisphenol A type epoxy resins, bisphenol F type epoxy resins, bisphenol S type epoxy resins, alkylphenol type epoxy resins, resorcinol type epoxy resins, difunctional naphthalene type epoxy resins, and other difunctional aromatic epoxy resins; dicyclopentadiene glycol diglycidyl ether and other difunctional alicyclic epoxy resins; polypropylene glycol diglycidyl ether. Polyalkylene glycol diglycidyl ethers such as glycidyl ether and polyethylene glycol diglycidyl ether; diglycidyl phthalate, tetrahydrophthalate, dimer acid diglycidyl ether, and other difunctional glycidyl ester type epoxy resins; diglycidyl aniline, diglycidyl toluidine, and other difunctional glycidylamine type epoxy resins; difunctional heterocyclic epoxy resins; difunctional diaryl terephthalate type epoxy resins. Epoxy resins; hydroquinone diglycidyl ether, 2,5-di-tert-butylhydroquinone diglycidyl ether, resorcinol diglycidyl ether, and other hydroquinone-type epoxy resins; butanediol diglycidyl ether, butene glycol diglycidyl ether, butynediol diglycidyl ether, and other difunctional alkyl glycidyl ether compounds; 1,3-diglycidyl-5,5-dialkylhydantoin, 1-glycidyl... Difunctional epoxy compounds containing glycidyl groups, such as alkyl-3-(epoxypropoxyalkyl)-5,5-dialkylhydantoin; difunctional epoxyalkyl groups containing glycidyl groups, such as 1,3-bis(3-epoxypropoxypropyl)-1,1,3,3-tetramethyldisiloxane and α,β-bis(3-epoxypropoxypropyl)polydimethylsiloxane; neopentyl glycol diepoxypropyl ether; and modified forms thereof. These difunctional epoxy compounds can be used alone or in combination of two or more. From the viewpoint of reactivity and workability, difunctional alicyclic epoxy resins such as dicyclopentadienedimethylethanol diepoxypropyl ether and polyalkylene glycol diepoxypropyl ethers such as polypropylene glycol diepoxypropyl ether are particularly suitable.

[0053] Examples of trifunctional or higher epoxy compounds include: trifunctional or higher aromatic epoxy resins such as phenolic varnish-type epoxy resins; trifunctional or higher alicyclic epoxy resins; trifunctional or higher glycidyl ester type epoxy resins; and trifunctional compounds such as tetracyclooxypropyl diaminodiphenylmethane, tricyclooxypropyl p-aminophenylmethane, tricyclooxypropyl m-aminophenylmethane, and tetracyclooxypropyl m-phenylenediamine. The above-mentioned epoxy resins include: epoxy propylene amine type epoxy resins; trifunctional or higher heterocyclic epoxy resins; trifunctional or higher diaryl cyclopentadiene type epoxy resins; trifunctional or higher alkyl epoxy propylene ether compounds such as glycerol triepoxide ether, trimethylolpropane triepoxide ether, and neopentyl tetroxide tetraepoxide ether; trifunctional or higher epoxy propylene-containing hydantoin compounds; trifunctional or higher epoxy propylene-containing siloxanes; and their modified forms. These trifunctional or higher epoxy resins can be used alone or in combination of two or more types.

[0054] In the carbon fiber reinforced composite material of the present invention, the preferred lower limit of the content of the epoxy resin is 3% by weight, the more preferred lower limit is 6.5% by weight, and the preferred upper limit is 66% by weight, the more preferred upper limit is 56% by weight.

[0055] The preferred lower limit of the epoxy equivalent (molecular weight of each epoxy group) of the above-mentioned epoxy resin is 100, and the preferred upper limit is 5000. The preferred lower limit of the molecular weight of the above-mentioned epoxy resin is 100, and the preferred upper limit is 70,000.

[0056] In the carbon fiber reinforced composite material of the present invention, the ratio of the content of the above-mentioned polyvinyl acetal resin to the content of the above-mentioned epoxy resin (content of polyvinyl acetal resin / content of epoxy resin) has a preferred lower limit of 0.0001, a more preferred lower limit of 0.001, a more preferred upper limit of 0.4, and a more preferred upper limit of 0.35.

[0057] The carbon fiber reinforced composite material of this invention contains a hardener. Examples of such curing agents include phenolic curing agents, thiol curing agents, amine curing agents, imidazole curing agents, acid anhydride curing agents, cyanate ester curing agents, and reactive ester curing agents. Among these, amine curing agents are preferred. Furthermore, the aforementioned curing agents are preferably nitrogen-containing compounds.

[0058] Examples of amine-based curing agents include: trimethylamine, triethylamine, and N,N-dimethylamine. Triethyldiamine, benzyldimethylamine, 2-(dimethylaminomethyl)phenol, 2,4,6-trimethylaminomethyl)phenol, 1,8-diazabicyclo(5,4,0)-undecene-7, 1,5-diazabicyclo(4,3,0)-nonene-5, etc.

[0059] Examples of imidazole-based curing agents include: imidazole, 2-methylimidazolium, 1,2-dimethylimidazolium, 2-ethyl-4-methylimidazolium, 2-undecylimidazolium, 2-heptadecylimidazolium, 2-phenylimidazolium, 2-phenyl-4-methylimidazolium, 1-benzylimidazolium, 1-benzyl-2-phenylimidazolium, 1-cyanoethyl-2-methylimidazolium, etc.

[0060] The content of the hardener in the carbon fiber reinforced composite material of the present invention is preferably 0.5 parts by weight, more preferably 1.0 parts by weight, and preferably 100 parts by weight, more preferably 50 parts by weight, relative to 100 parts by weight of the epoxy resin. Furthermore, the content of the above-mentioned hardener in the carbon fiber reinforced composite material of the present invention is preferably 0.015 to 70% by weight.

[0061] The carbon fiber reinforced composite material of the present invention may further contain a hardening accelerator and an organic solvent. Examples of hardening accelerators include phosphorus compounds, amine compounds, and organometallic compounds. The content of the curing accelerator in the carbon fiber reinforced composite material of the present invention is preferably 0.1 parts by weight, more preferably 0.5 parts by weight, and preferably 30 parts by weight, more preferably 10 parts by weight, relative to 100 parts by weight of the epoxy resin.

[0062] Examples of organic solvents mentioned above include ketones, alcohols, aromatic hydrocarbons, and esters. Examples of ketones mentioned above include acetone, methyl ethyl ketone, dipropyl ketone, and diisobutyl ketone. Examples of alcohols mentioned above include methanol, ethanol, isopropanol, and butanol. Examples of aromatic hydrocarbons mentioned above include toluene and xylene. Examples of the aforementioned esters include: methyl propionate, ethyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, butyl butyrate, methyl valerate, ethyl valerate, butyl valerate, methyl hexanoate, ethyl hexanoate, butyl hexanoate, 2-ethylhexyl acetate, and 2-ethylhexyl butyrate. Alternatively, the following can also be used: methyl ceruleanol, ethyl ceruleanol, butyl ceruleanol, terpineol, dihydroterpineol, butyl ceruleanol acetate, butyl carbitol acetate, terpineol acetate, dihydroterpineol acetate, etc.

[0063] The preferred upper limit of the content of the above-mentioned organic solvent in the carbon fiber reinforced composite material of the present invention is 5.0 wt%, and more preferably 0 wt%.

[0064] Without impairing the effects of the present invention, the carbon fiber reinforced composite material of the present invention may also contain other resins such as acrylic resin and cellulose acetate. In this case, the content of other resins is preferably less than 10% by weight.

[0065] Without impairing the effects of the present invention, the carbon fiber reinforced composite material of the present invention may further contain known additives, such as: tackifying resin, adhesion modifier, emulsifier, antioxidant, softener, filler, pigment, dye, silane coupling agent, antioxidant, surfactant, wax, etc.

[0066] There is no particular limitation on the method for manufacturing the carbon fiber reinforced composite material of the present invention. For example, the following method for manufacturing carbon fiber reinforced composite material can be used, which has at least the following steps: a step of preparing a resin composition containing epoxy resin, a hardener and a polyvinyl acetal resin; and a step of compounding the resin composition with carbon fiber; and the polyvinyl acetal resin contains the constituent unit shown in the above formula (1), where R1 in the above formula (1) is an alkyl group having 1 or more carbon atoms. Furthermore, in the manufacturing method of the carbon fiber reinforced composite material of the present invention, apart from the components of epoxy resin, hardener, and polyvinyl acetal resin, the constituent units of the polyvinyl acetal resin shown in the above formula (1) are the same as those of the carbon fiber reinforced composite material of the present invention, so its description is omitted.

[0067] Examples of steps for preparing the above-mentioned resin composition include: using various mixers such as ball mills, stirred mills, three-roll mills, dispersers, and planetary mixers to mix the epoxy resin, hardener, polyvinyl acetal resin, and various additives as needed. Furthermore, as a step in the above-mentioned preparation of the resin composition, the epoxy resin and polyvinyl acetal resin can be mixed and then a hardener can be added for preparation, or epoxy resin, hardener and polyvinyl acetal resin can be added simultaneously for preparation.

[0068] As a method for composite resin composition with carbon fiber, examples include methods of impregnating the resin composition with carbon fiber. Specifically, examples include autoclave method, pressure method, manual coating method, stretch forming method, filament winding method, RTM method, pin winding method, impregnation method, hot (cold) pressing method, spraying method, continuous pressure method, etc.

[0069] The applications of carbon fiber reinforced composites are not particularly limited, with aircraft structural materials being the primary application. They can also be used in automotive, marine, sports, and other general industrial applications such as windmills or rollers. However, they are particularly well-suited for applications using prepregs as intermediate components. [Effects of the Invention]

[0070] According to the present invention, a carbon fiber reinforced composite material having excellent adhesion, compatibility with epoxy resin and interfacial adhesion, and capable of achieving high mechanical strength, and a method for manufacturing the carbon fiber reinforced composite material are provided. Simple Explanation of the Diagram

[0071] none Implementation

[0072] The present invention will be further described in detail below with examples, but the present invention is not limited to these examples.

[0073] (Example 1) (Production of Polyvinyl Acetal Resin) 250 g of polyvinyl alcohol resin with an average degree of polymerization of 300 and a saponification degree of 99 moles was dissolved in 2700 g of pure water by stirring at 90°C for about 2 hours. After cooling the solution to 40°C, 100 g of hydrochloric acid (35% by weight) and 90 g of acetaldehyde were added to initiate an acetalization reaction, precipitating the reaction product. Subsequently, after completing the acetalization reaction at 40°C, the product was neutralized, washed with water, and dried according to standard methods to obtain a white powder of polyvinyl acetal resin. The obtained polyethylene acetal resin was dissolved in DMSO-d6 at a concentration of 10% by weight, and the content of alkyl acetal groups (degree of acetalization), hydroxyl groups, and acetal groups was determined by 13C-NMR.

[0074] (Fabrication of carbon fiber reinforced composite prepreg) A resin composition was prepared by mixing 100 parts by weight of bisphenol A type epoxy resin (JER828, manufactured by Japan Epoxy Resins Co., Ltd.), 6 parts by weight of curing agent (dicyandiamide), and 10 parts by weight of the obtained polyvinyl acetal resin using a process homogenizer (manufactured by SMT Co., Ltd.) at 15,000 rpm. Subsequently, the obtained resin composition was impregnated with PAN-based carbon fiber (manufactured by Toray Industries, T700SC-12000-50C, filament number: 12000, fineness: 800 tex, density: 1.8 g / cm3) using a manual coating method, and then hardened by heating at 150°C for 1 hour to produce a prepreg. Furthermore, 300 parts by weight of PAN-based carbon fiber were used relative to 100 parts by weight of bisphenol A epoxy resin.

[0075] (Examples 2-10, 17, 19-21, Comparative Examples 1-4) Using the types and amounts of polyvinyl alcohol resin (PVA) and aldehydes shown in Table 1, resin compositions were prepared with the compositions shown in Table 2. Otherwise, polyvinyl acetal resin, resin compositions, and prepregs were prepared in the same manner as in Example 1. Furthermore, the polyvinyl acetal resins obtained in Examples 1 and 2, and Examples 4 and 5 are the same. Furthermore, two different aldehydes were used in Examples 4-6, 8 and Comparative Example 3. Furthermore, in Example 17 and Comparative Example 4, bisphenol F type epoxy resin (NPEF-170, manufactured by Nan Ya Plastics Co., Ltd.) was used instead of bisphenol A type epoxy resin (JER828, manufactured by Japan Epoxy Resins Co., Ltd.).

[0076] (Example 11) (Preparation of carboxylic acid modified polyvinyl acetal resin) 100 g of carboxylic acid-modified polyvinyl alcohol resin was added to 1000 g of pure water and stirred at 90°C for about 2 hours to dissolve it. After cooling the solution to 40°C, 90 g of hydrochloric acid (35% by weight) and 90 g of acetaldehyde were added. The solution temperature was lowered to 10°C and maintained at this temperature to carry out the acetalization reaction. Subsequently, the reaction was completed at 40°C for 3 hours. The solution was then neutralized, washed with water, and dried according to standard methods to obtain a white powder of carboxylic acid-modified polyvinyl acetal resin. Furthermore, the carboxylic acid modified polyvinyl alcohol resin has a carboxyl group constitutive unit as represented by formula (4-1) (in formula (4-1), R2 is a single bond, R3 is a methylene group, and X1 and X2 are hydrogen atoms), with an average degree of polymerization of 400, a saponification degree of 99.0 mol%, and an acid modification group content of 0.7 mol%. Here, the aforementioned single bond refers to an alkyl group with 0 carbon atoms. Except for using the obtained carboxylic acid-modified polyvinyl acetal resin, the resin composition and prepreg were prepared in the same manner as in Example 1.

[0077] (Example 12) In the “Preparation of Carbon Fiber Reinforced Composite Material [Prepreg]”, the amount of polyethylene acetal resin added was set to 2 parts by weight. Otherwise, the carboxylic acid modified polyethylene acetal resin, resin composition and prepreg were prepared in the same manner as in Example 11.

[0078] (Example 13) A carboxylate-modified polyvinyl alcohol resin was prepared using a constituent unit with a carboxyl group as represented by formula (4-1) (in formula (4-1), R2 is a single bond, R3 is a methylene group, and X1 and X2 are hydrogen atoms), with an average degree of polymerization of 400, a degree of saponification of 99.0 mol%, and an acid-modified group content of 2.0 mol%. Otherwise, the carboxylate-modified polyvinyl acetal resin, resin composition, and prepreg were prepared in the same manner as in Example 11.

[0079] (Example 14) A carboxylate-modified polyvinyl alcohol resin with a carboxyl group as represented by formula (4-1) (in formula (4-1), R2 is a single bond, R3 is a methylene group, and X1 and X2 are hydrogen atoms), an average degree of polymerization of 600, a degree of saponification of 99.0 mol%, and an acid-modified group content of 1.0 mol% was used as the carboxylate-modified polyvinyl acetal resin, and the amount of acetaldehyde added was set to 110 g. Otherwise, the carboxylate-modified polyvinyl acetal resin, resin composition, and prepreg were prepared in the same manner as in Example 11.

[0080] (Example 15) (Preparation of sulfonic acid modified polyethylene acetal resin) 100 g of sulfonic acid-modified polyvinyl alcohol resin was added to 1000 g of pure water and stirred at 90°C for about 2 hours to dissolve it. After cooling the solution to 40°C, 90 g of hydrochloric acid (35% by weight) and 90 g of acetaldehyde were added. The solution temperature was lowered to 10°C and maintained at this temperature to carry out the acetalization reaction. Subsequently, the reaction was completed at 40°C for 3 hours. The solution was then neutralized, washed with water, and dried according to standard methods to obtain a white powder of sulfonic acid-modified polyvinyl acetal resin. Furthermore, the sulfonic acid modified polyvinyl alcohol resin has a structure in which sulfonic acid groups are directly bonded to the carbon of the main chain, with an average degree of polymerization of 300, a degree of saponification of 99.0 mol%, and an acid modification group content of 0.7 mol. Except for using the obtained sulfonic acid modified polyethylene acetal resin, the resin composition and prepreg were prepared in the same manner as in Example 1.

[0081] (Example 16) A carboxylate-modified polyvinyl alcohol resin with a carboxyl group as represented by formula (4-1) (in formula (4-1), R2 is a single bond, R3 is a methylene group, and X1 and X2 are hydrogen atoms), an average degree of polymerization of 2500, a degree of saponification of 99.0 mol%, and an acid-modified base of 1.0 mol% was used as the carboxylate-modified polyvinyl alcohol resin. Acetaldehyde 38 g and butyraldehyde 110 g were added to replace acetaldehyde 90 g. Otherwise, the carboxylate-modified polyvinyl acetal resin, resin composition, and prepreg were prepared in the same manner as in Example 11.

[0082] (Example 18) In the “Preparation of Carbon Fiber Reinforced Composite Material [Prepreg]”, bisphenol F type epoxy resin (NPEF-170, manufactured by Nan Ya Plastics Co., Ltd.) was used instead of bisphenol A type epoxy resin (JER828, manufactured by Japan Epoxy Resins Co., Ltd.). Otherwise, the carboxylic acid modified polyvinyl acetal resin, resin composition and prepreg were prepared in the same manner as in Example 11.

[0083] (evaluate) The following evaluations were conducted on the polyvinyl acetal resin, resin composition, and prepreg obtained in the examples and comparative examples. The results are shown in Tables 1 and 2.

[0084] (1) Determination of glass transition temperature (Tg) The glass transition temperature of the obtained polyvinyl acetal resin was determined using a differential scanning calorimeter (DSC) at a heating rate of 10°C / min.

[0085] (2) Tensile strain The obtained resin composition was heated at 150°C for 1 hour to harden it, thereby producing a resin-cured board. Dumbbell-shaped specimens (JIS K7161-2-1B type) were cut from the resin-cured board, and tensile strain was measured using a universal testing machine (Instron) under the following conditions. Test conditions: JIS K 7161-2 Test speed: 1 mm / min Inter-gap distance: 115 mm Furthermore, when the tensile strain of the resin composition is high, a similarly high tensile strain can be achieved when the prepreg is made.

[0086] (3) Epoxy resin compatibility In the preparation of carbon fiber reinforced composite material [prepreg], 10 parts by weight of the obtained polyvinyl acetal resin were added to 90 parts by weight of epoxy resin and heated to 150°C to dissolve it, thereby preparing an evaluation sample. After cooling the prepared sample to room temperature, it was left to stand at room temperature for 24 hours. During this process, the appearance was observed at three time points: "at 150°C", "at 70°C during cooling", and "after standing at room temperature for 24 hours". The clarity or turbidity and the presence or absence of phase separation were confirmed, and the sample was evaluated according to the following criteria. ◎: Good compatibility at any time point (150℃, 70℃, and room temperature); the solution is transparent. 〇: No phase separation was observed at 150℃ and 70℃, but the solution exhibited turbidity at room temperature. △: No phase separation was observed at 150℃, but the solution exhibited turbidity at 70℃ and room temperature. ×: Did not dissolve at 150℃, the solution is cloudy.

[0087] (4) Adhesion (interfacial shear strength measurement) The resin composition containing polyvinyl acetal obtained in the examples and comparative examples was dropped onto carbon fibers and hardened by heating at 150°C for 1 hour to prepare test samples. The interfacial shear strength of the carbon fibers and resin in the prepared samples was determined using a composite material interface property evaluation device (manufactured by Dong Rong Industrial Co., Ltd., model HM410) via the microdrop method (pulling speed: 0.12 mm / min).

[0088] (5) Toughness After obtaining five prepreg volume layers, holes were drilled using a drilling tool to observe the appearance of the openings and to evaluate them according to the following criteria. ◎: No interlayer peeling occurred. 〇: Only 1 piece peeled off. ×: Peeling occurred in 2 or more pieces

[0089] (6) Viscosity The viscosity of the obtained prepreg was evaluated based on tactile feel and the following criteria. ◎: The tactile feel is just right, and the processing performance is excellent. 〇: The viscosity is slightly excessive or insufficient, but there are no problems with its processability. ×: Excessive or insufficient tactile stickiness indicates a problem with processing.

[0090] [Table 1] PVA acetalization step Polyvinyl acetal resin Average degree of polymerization degree of saponification (mol%) Aldehyde types Aldehyde addition (g) R1 type Average degree of polymerization Acetaldehyde degree (mol%) Butyraldehyde degree (mol%) Alkyl acetal content (mol%) Other acetal content※ (moles%) Hydroxyl content (mol%) Acetyl content (mol%) Types of acid-modified bases Acid-modified base content (mol%) Tg (°C) Example 1 300 99 Acetaldehyde 90 CH 3 300 74 0 74 0 25 1 [-] 0 106 Example 2 300 99 Acetaldehyde 90 CH 3 300 74 0 74 0 25 1 [-] 0 106 Example 3 2000 99 Acetaldehyde 110 CH 3 2000 74 0 74 0 25 1 [-] 0 110 Example 4 300 99 Acetaldehyde 30 CH 3 300 20 47 67 0 32 1 [-] 0 75 Butyraldehyde 110 C 3H 7 Example 5 300 99 Acetaldehyde 30 CH 3 300 20 47 67 0 32 1 [-] 0 75 Butyraldehyde 110 C 3H 7 Example 6 300 99 Acetaldehyde 38 CH 3 300 25 47 72 0 27 1 [-] 0 90 Butyraldehyde 110 C 3H 7 Example 7 2300 99 Acetaldehyde 115 CH 3 2300 74 0 74 0 25 1 [-] 0 110 Example 8 2300 89 Acetaldehyde 20 CH 3 2300 10 52 62 0 27 11 [-] 0 76 Butyraldehyde 115 C 3H 7 Example 9 400 99 Acetaldehyde 80 CH 3 400 59 0 59 0 40 1 [-] 0 107 Example 10 800 99 Acetaldehyde 93 CH 3 800 69 0 69 0 30 1 [-] 0 110 Example 11 400 99 Acetaldehyde 90 CH 3 400 72.3 0 72.3 0 26 1 carboxyl 0.7 109 Example 12 400 99 Acetaldehyde 90 CH 3 400 72.3 0 72.3 0 26 1 carboxyl 0.7 109 Example 13 400 99 Acetaldehyde 90 CH 3 400 71 0 71 0 25 1 carboxyl 2 109 Example 14 600 99 Acetaldehyde 110 CH 3 600 73 0 73 0 25 1 carboxyl 1 100 Example 15 300 99 Acetaldehyde 90 CH 3 300 72.3 0 72.3 0 26 1 sulfonic acid group 0.7 80 Example 16 2500 99 Acetaldehyde 38 CH 3 2500 25 47 72 0 26 1 carboxyl 1 86 Butyraldehyde 110 C 3H 7 Example 17 300 99 Acetaldehyde 90 CH 3 300 74 0 74 0 25 1 [-] 0 106 Example 18 400 99 Acetaldehyde 90 CH 3 400 72.3 0 72.3 0 26 1 carboxyl 0.7 109 Example 19 300 89 Acetaldehyde 82 CH 3 300 64 0 64 0 25 11 [-] 0 94 Example 20 300 99 Acetaldehyde 90 CH 3 300 79 0 79 0 20 1 [-] 0 105 Example 21 300 81 Acetaldehyde 75 CH 3 300 55 0 55 0 25 19 [-] 0 86 Comparative Example 1 800 93 formaldehyde 83 H 800 0 0 0 86.5 6.5 7 [-] 0 118.0 Comparative Example 2 600 99 benzaldehyde 200 C 6H 5 600 [-] 0 0 59 40 1 [-] 0 120 Comparative Example 3 800 88 benzaldehyde 93 C 6H 5 800 0 0 47 25 27 1 [-] 0 117 formaldehyde 50 H Comparative Example 4 300 99 Butyraldehyde 165 C 3H 7 300 [-] 70 70 0 29 1 [-] 0 68 ※: Content of acetal groups other than those shown in formula (1)

[0091] [Table 2] Epoxy resin Evaluation (of resin composition) Prepreg composition (parts by weight) Evaluation (prepreg) Tensile strain (%) Epoxy resin compatibility Adhesion (interfacial shear strength: MPa) Composition of resin components carbon fiber Toughness viscous Epoxy resin hardener Polyvinyl acetal resin Example 1 Bisphenol A type epoxy resin 6.72 ◎ 62.3 100 6 10 300 〇 ◎ Example 2 6.72 ◎ 62.3 100 6 2 300 △ ◎ Example 3 7.28 ◎ 61.2 100 6 10 300 ◎ ◎ Example 4 4.67 △ 69.3 100 6 5 300 ◎ ◎ Example 5 4.67 △ 69.3 100 6 2 300 〇 ◎ Example 6 5.21 △ 70.8 100 6 20 300 ◎ ◎ Example 7 7.36 ◎ 61.9 100 6 10 300 ◎ ◎ Example 8 6.10 〇 63.5 100 6 5 300 ◎ ◎ Example 9 6.40 〇 78.3 100 6 10 300 ◎ 〇 Example 10 6.70 ◎ 74.4 100 6 10 300 ◎ 〇 Example 11 7.28 ◎ 78.1 100 6 10 300 ◎ ◎ Example 12 7.28 ◎ 78.1 100 6 2 300 ◎ ◎ Example 13 7.51 ◎ 81.3 100 6 10 300 ◎ ◎ Example 14 7.90 ◎ 76.2 100 6 10 300 ◎ ◎ Example 15 6.98 〇 76.2 100 6 10 300 ◎ ◎ Example 16 6.10 〇 71.1 100 6 10 300 ◎ ◎ Example 17 Bisphenol F type epoxy resin 6.60 〇 60.4 100 6 10 300 〇 ◎ Example 18 7.10 ◎ 67.5 100 6 10 300 ◎ ◎ Example 19 Bisphenol A type epoxy resin 7.05 ◎ 61.5 100 6 10 300 ◎ ◎ Example 20 6.60 ◎ 61.5 100 6 10 300 ◎ ◎ Example 21 7.05 ◎ 60.8 100 6 10 300 ◎ ◎ Comparative Example 1 Bisphenol A type epoxy resin 6.61 ◎ 60.4 100 6 5 300 × 〇 Comparative Example 2 2.30 × 58.1 100 6 5 300 × × Comparative Example 3 2.45 × 58.9 100 6 5 300 × 〇 Comparative Example 4 Bisphenol F type epoxy resin 1.86 × 60.7 100 6 5 300 × × [Industrial Applicability]

[0092] According to the present invention, a carbon fiber reinforced composite material with excellent adhesion, compatibility with epoxy resin and interfacial adhesion, and high mechanical strength can be provided.

[0093] none

Claims

1. A carbon fiber reinforced composite material comprising carbon fiber, epoxy resin, hardener, and polyethylene acetal resin, wherein the polyethylene acetal resin comprises a constituent unit as shown in formula (1), wherein R1 in formula (1) is an alkyl group having 1 or more carbon atoms; wherein the amount of hydroxyl groups in the polyethylene acetal resin is 16.0 mol% or more and 45.0 mol% or less; wherein in formula (1), R1 may be the same or different.

2. As in claim 1, the carbon fiber reinforced composite material, wherein, In the polyvinyl acetal resin, R1 in formula (1) is an alkyl group with 1 or more carbon atoms, and / or an alkyl group with 3 or more carbon atoms.

3. Carbon fiber reinforced composite materials as claimed in claim 1 or 2, wherein, The hydroxyl content of the polyvinyl acetal resin is above 18.0 moles and below 45.0 moles.

4. Carbon fiber reinforced composite materials as claimed in item 1 or 2, wherein, The average degree of polymerization of polyvinyl acetal resin is below 2500.

5. Carbon fiber reinforced composite materials as claimed in claim 1 or 2, wherein, The glass transition temperature of polyvinyl acetal resin is above 75°C.

6. Carbon fiber reinforced composite materials as claimed in claim 1 or 2, wherein, Polyvinyl acetal resin contains constituent units with acid-modified groups.

7. As in claim 6, the carbon fiber reinforced composite material, wherein, In polyvinyl acetal resin, the content of constituent units with acid-modified groups is 0.01 to 20 moles.

8. Carbon fiber reinforced composite materials as claimed in claim 1 or 2, wherein, In polyvinyl acetal resin, the amount of hydroxyl groups is above 20.0 mol% and below 45.0 mol%.

9. The carbon fiber reinforced composite material as claimed in claim 1 or 2, wherein, The content of polyvinyl acetal resin relative to 100 parts by weight of epoxy resin is more than 0.01 parts by weight and less than 40.0 parts by weight.

10. A method for manufacturing a carbon fiber reinforced composite material, comprising at least the following steps: a step of preparing a resin composition containing an epoxy resin, a hardener, and a polyethylene acetal resin; and a step of compounding the resin composition with carbon fibers; wherein the polyethylene acetal resin contains a constituent unit as shown in the following formula (1), wherein R1 in the following formula (1) is an alkyl group having 1 or more carbon atoms; wherein the amount of hydroxyl groups in the above-mentioned polyethylene acetal resin is 16.0 mol% or more and 45.0 mol% or less; wherein in formula (1), R1 may be the same or different.