Reinforcement carbon fiber, carbon fiber sheet and carbon fiber reinforcement agent

Abstract

To provide a carbon fiber reinforcement agent which can reinforce a carbon fiber by simple work having low environmental load, a reinforcement carbon fiber using the carbon fiber reinforcement agent, and a carbon fiber sheet which is thin and is excellent in drape property.SOLUTION: A reinforcement carbon fiber contains a carbon fiber, and a carbon fiber reinforcement agent included in the carbon fiber, wherein the carbon fiber reinforcement agent contains a solid resin composed of a polymer of an unsaturated fatty acid or its derivative, and the reinforcement carbon fiber has a void ratio of 5% or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a carbon fiber reinforced composite material, and more particularly to a carbon fiber used in a carbon fiber reinforced composite material. [Background technology]

[0002] One type of fiber reinforced composite material is a carbon fiber reinforced composite material (hereinafter sometimes referred to as "CFRP") formed from a reinforcing material made of carbon fiber and a matrix resin.

[0003] As the matrix resin for CFRP, various resins such as epoxy resin, unsaturated polyester resin, vinyl ester resin, and phenolic resin are used, with epoxy resin being the most widely used.

[0004] On the other hand, the carbon fibers used in CFRP are obtained from starting materials such as regenerated cellulose, polyacrylonitrile, and pitch, and are fibers whose chemical composition is approximately 90% or more carbon. Such carbon fibers are classified as high-strength carbon fibers, high-modulus carbon fibers, etc., and are used in a wide range of CFRP applications because they are lightweight, have excellent specific strength and specific modulus, and also have excellent heat resistance and chemical resistance.

[0005] Carbon fibers have low elongation and are brittle, so they are prone to fluffing due to mechanical friction, etc. Therefore, in order to suppress the generation of such fluffing, carbon fibers are subjected to a sizing treatment during the CFRP manufacturing process. This sizing treatment imparts bundling properties to the carbon fibers, making it possible to suppress the generation of fluffing.

[0006] CFRPs made of matrix resin and carbon fiber as described above can be obtained by a method of laminating a carbon fiber fabric containing semi-cured matrix resin or a prepreg, which is a unidirectional material, and then curing it, or by a method of passing or impregnating a carbon fiber fabric or unidirectional material that has already been laminated with uncured matrix resin and then curing it.

[0007] Demand for higher performance carbon fiber composite materials is increasing, and there is a need for the development of sizing agents that can increase the toughness and strength of matrix resins as well as the interlaminar toughness of CFRP. Therefore, studies are being conducted to impart the effect of increasing the adhesion between carbon fibers and matrix resins to sizing treatments that are currently performed for the purpose of suppressing the generation of fluff (Patent Document 1). [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 2017-155372 Summary of the Invention [Problem to be solved by the invention]

[0009] On the other hand, when carbon fibers used in CFRP are reinforced with a matrix resin, the uncured matrix resin does not have sufficient wettability to the carbon fibers, and the labor, equipment, and energy required to remove voids in the carbon fibers through pressure reduction and heating are required. Furthermore, matrix resins with poor wettability result in bulky resin layers after curing, making it difficult to prepare thin reinforced carbon fiber sheets with excellent drapeability.

[0010] The present invention aims to provide a carbon fiber reinforcing agent that can reinforce carbon fibers with simple operations and has a low environmental impact, reinforced carbon fibers using the carbon fiber reinforcing agent, and a thin carbon fiber sheet that has excellent drapeability. [Means for solving the problem]

[0011] The present invention includes the following aspects. [1] A reinforced carbon fiber comprising a carbon fiber and a carbon fiber reinforcing agent contained in the carbon fiber, The carbon fiber reinforcing agent includes a solid resin made of a polymer of an unsaturated fatty acid or a derivative thereof, The reinforcing carbon fiber has a porosity of 5% or less.

[0012] [2] The reinforced carbon fiber of aspect 1, wherein the unsaturated fatty acid has 16 to 22 carbon atoms.

[0013] [3] The reinforced carbon fiber of aspect 1 or 2, wherein the unsaturated fatty acid derivative comprises a drying oil.

[0014] [4] The reinforced carbon fiber of any one of Aspects 1 to 3, wherein the unsaturated fatty acid includes linoleic acid or linolenic acid, and the unsaturated fatty acid derivative includes linseed oil.

[0015] [5] A reinforced carbon fiber sheet comprising the reinforcing carbon fiber of any one of embodiments 1 to 4.

[0016] [6] The weight of the carbon fiber sheet excluding the reinforcing agent is 190 g / m 2 6. The reinforced carbon fiber sheet of embodiment 5,

[0017] [7] A prepreg comprising the reinforced carbon fiber sheet of embodiment 5 and a layer of a matrix resin composition formed on at least one surface of the reinforced carbon fiber sheet.

[0018] [8] The matrix resin composition contains a two-component curable resin, The reinforced carbon fiber sheet of embodiment 5; a layer of component A of a matrix resin composition formed on one surface of the reinforced carbon fiber sheet; and a layer of component B of a matrix resin composition formed on the other surface of the reinforced carbon fiber sheet.

[0019] [9] The prepreg of aspect 7 or 8, wherein the matrix resin composition comprises a two-component curable acrylic resin.

[0020]

[10] A carbon fiber reinforced composite material molding comprising the reinforced carbon fiber sheet of embodiment 5 and a matrix resin.

[0021]

[11] A carbon fiber reinforcing agent containing an aqueous resin, which comprises a solid resin polymerized with an unsaturated fatty acid or a derivative thereof, and which is obtained by reacting a base reaction product with an acid to liberate a carboxylate of the base reaction product, and which can be dispersed or dissolved in a hydrophilic solvent to form a liquid resin composition.

[0022]

[12] The carbon fiber reinforcing agent according to aspect 11, wherein the polymer of unsaturated fatty acid is made from an unsaturated fatty acid or a derivative thereof.

[0023]

[13] The carbon fiber reinforcing agent of aspect 11 or 12, wherein the unsaturated fatty acid derivative comprises a drying oil.

[0024]

[14] The carbon fiber reinforcing agent according to any one of Aspects 11 to 13, wherein the base is a substance containing an alkali metal or an alkaline earth metal.

[0025]

[15] The carbon fiber reinforcing agent of any one of Aspects 11 to 14, wherein the unsaturated fatty acid has 16 to 22 carbon atoms.

[0026]

[16] The carbon fiber reinforcing agent of any of Aspects 11 to 15, wherein the unsaturated fatty acid includes linoleic acid or linolenic acid, and the unsaturated fatty acid derivative includes linseed oil.

[0027]

[17] The carbon fiber reinforcing agent of any one of Aspects 11 to 16, further comprising a hydrophilic solvent.

[0028]

[18] A method for producing a prepreg, comprising applying a matrix resin composition to the reinforced carbon fiber sheet of embodiment 5.

[0029]

[19] The method for producing a prepreg according to aspect 18, wherein the matrix resin composition comprises a curable acrylic resin.

[0030]

[20] A method for producing a molded carbon fiber reinforced composite material, comprising molding the prepreg of embodiment 7 and curing the matrix resin composition.

[0031]

[21] The method of any one of aspects 18 to 20, wherein the method is carried out in a room temperature environment. [Effects of the Invention]

[0032] According to the present invention, it is possible to provide a carbon fiber reinforcing agent that can reinforce carbon fibers through simple operations with low environmental impact, reinforced carbon fibers using the carbon fiber reinforcing agent, and a thin reinforced carbon fiber sheet that has excellent drapeability. [Brief explanation of the drawings]

[0033] [Figure 1] 1 is a graph showing the results of measuring the static contact angle of FADP and the like with respect to a carbon fiber bundle. [Figure 2] FIG. 1 is a diagram schematically illustrating a state in which FADP or the like is dropped onto a carbon fiber bundle. [Figure 3] 1 is a graph showing the change in cross-sectional area of ​​a carbon fiber bundle before and after resin impregnation. [Figure 4] 1 is a graph showing the flexural strength and flexural modulus of infusion-molded CFRP made of untreated carbon fiber fabric and CFRP laminated with reinforced carbon fiber sheets. [Figure 5] This is a graph showing the bending strength and bending modulus of CFRP in which the interface of the reinforced carbon fiber sheet is bonded and laminated with a commercially available quick-drying adhesive, as a percentage, with the infusion-molded CFRP of untreated carbon fiber fabric being taken as 100%. [Figure 6] 1 is a graph comparing the bending strength and bending modulus of CFRP using a high-area-weight reinforced carbon fiber sheet with those of an infusion molded product. [Figure 7] This is a graph showing the bending strength and bending modulus of CFRP made by storing and curing at room temperature a prepreg of a carbon fiber sheet (high modulus UD material) using a two-component mixed curing acrylic adhesive. [Figure 8] This is a graph showing the bending strength and bending modulus of CFRP obtained by storing and curing at room temperature a prepreg of a carbon fiber sheet (cross material) using a two-component mixed curing acrylic adhesive. [Figure 9]This is a photograph showing an example of punching a reinforced carbon fiber sheet using a desktop cutting machine. [Figure 10] 1 is a photograph showing an example of three-dimensional processing of a reinforced carbon fiber sheet laminate using a mold. DETAILED DESCRIPTION OF THE INVENTION

[0034] <Carbon fiber reinforcement> The carbon fiber reinforcing agent of the present invention contains an aqueous resin, which is obtained by reacting a base reaction product of a solid resin composed of a polymer of an unsaturated fatty acid or its derivative with an acid to liberate a carboxylate group from the base reaction product. The aqueous resin can be dispersed or dissolved in a hydrophilic solvent to form a liquid resin composition (hereinafter, the aqueous resin may be referred to as an "unsaturated fatty acid polymer solubilized resin"). Carbon fibers are lipophilic, and the unsaturated fatty acid polymer solubilized resin is derived from an unsaturated fatty acid or its derivative, so it is lipophilic and has excellent ability to penetrate into the interior of carbon fibers. Furthermore, the unsaturated fatty acid polymer solubilized resin has unsaturated groups and can be polymerized or dried.

[0035] The unsaturated fatty acid polymer solubilizing resin is described in detail in Japanese Patent Application No. 2023-148449, the disclosure of which is incorporated herein by reference.

[0036] The carbon fiber reinforcing agent of the present invention penetrates into the interior of carbon fibers and solidifies, thereby improving the strength of the carbon fibers. For example, by applying an aqueous liquid containing the aqueous resin to a carbon fiber aggregate or a carbon fiber sheet, the aqueous resin fills the voids in the carbon fibers and can be solidified in situ by polymerization or drying. It is also believed that the unsaturated groups in the aqueous resin react with the carbon fiber surface to form covalent bonds.

[0037] <Water-based resin (unsaturated fatty acid polymer solubilized resin)> The aqueous resin used in the carbon fiber reinforcing agent of the present invention contains a polymer of unsaturated fatty acid. As described above, a polymer of unsaturated fatty acid has an internal structure in which unsaturated groups are bonded to each other and three-dimensionally crosslinked, and is known to be insoluble. For example, when an unsaturated fatty acid is thermally polymerized in the atmosphere, a particulate insoluble polymer (i.e., an insoluble resin mass) is produced, as shown in Example 1 described later.

[0038] When the unsaturated fatty acid polymer is brought into contact with a base and water, the addition of the base converts the unsaturated fatty acid-derived carboxyl groups and a portion thereof into salts, resulting in the unsaturated fatty acid polymer being dissolved in water. In other words, the unsaturated fatty acid polymer is saponified with a strong base and made water-soluble.

[0039] On the other hand, because this aqueous solution is a liquid soap, the dried product does not exhibit water resistance and cannot be used as a resin to form coatings or molded articles. However, when an acid was added to this solution to convert the carboxyl-derived salt into a carboxylic acid, thereby returning the resin to its original state, it was found that a viscous gum-like substance was produced without returning to the insoluble resin mass before saponification. It was also found that by dispersing or dissolving this in a hydrophilic solvent, a liquid resin composition could be obtained. Furthermore, it was found that when the resulting liquid resin composition was dried and the internal water evaporated, it hardened and became a solid with the same strength as the insoluble resin before saponification.

[0040] By adding an acid to a saponified solution of an unsaturated fatty acid polymer, the salts derived from the carboxyl groups are rapidly converted to carboxylic acids, which then aggregate to a certain size through hydrophobic interactions, surrounding the separated water. As a result, the interior of the aqueous resin is filled with fine hydrophilic solvent channels. This increases the surface area accessible to hydrophilic solvents such as water and alcohol, allowing the resin to swell, disperse, or dissolve in these solvents. In this specification, "aqueous resin" refers to a resin that can be dispersed or dissolved in a hydrophilic solvent to form a liquid resin composition. Hydrophilic solvents include water; water-soluble organic solvents such as ethanol, isopropanol, and acetone; aqueous solutions of water-soluble organic solvents; and aqueous solutions of water-soluble bases such as ammonia.

[0041] Furthermore, cured resins made of polymer compounds have poor solubility and are difficult to separate into single molecules, making it difficult to determine their internal structure using existing analytical methods. The aqueous resin has an internal structure in which the polymers are three-dimensionally crosslinked, making it impossible to separate into independent polymers without destroying the molecules. In other words, at the time of filing, it is impossible or almost impractical to directly identify the aqueous resin by its internal structure or properties.

[0042] The aqueous resin is produced using a composition containing unsaturated fatty acids or derivatives of unsaturated fatty acids as a raw material. Examples of unsaturated fatty acid derivatives include esters of unsaturated fatty acids and polyhydric alcohols, oils and fats of unsaturated fatty acids, and drying oils.

[0043] Unsaturated fatty acids and unsaturated fatty acid derivatives have double bonds and can be cured, for example, by polymerization in the presence of oxygen in the air.

[0044] As the unsaturated fatty acid, for example, a fatty acid having 16 or more carbon atoms, two or more double bonds, and a carboxyl group is used. When the unsaturated fatty acid has two or more double bonds, it can form a crosslinked structure during the polymerization reaction, improving the chemical resistance, heat resistance, or strength of the resulting molded article. The number of double bonds in the unsaturated fatty acid is preferably 2 to 6, more preferably 2 to 4, and even more preferably 2 or 3. Furthermore, from the viewpoint of easy availability, the number of carbon atoms in the unsaturated fatty acid is preferably 16 to 22, more preferably 16 to 20, and even more preferably 18.

[0045] Specific examples of unsaturated fatty acids include oleic acid, linoleic acid, linolenic acid, arachidonic acid, eicosapentaenoic acid, and docosahexaenoic acid. Among these, preferred unsaturated fatty acids are linoleic acid, linolenic acid, and arachidonic acid. From the viewpoint of reducing environmental impact, unsaturated fatty acids are preferably derived from plants, and more preferably linoleic acid, α-linolenic acid, and γ-linolenic acid. A single type of unsaturated fatty acid may be used, or multiple types may be mixed and used.

[0046] The above description of unsaturated fatty acids also applies to the unsaturated fatty acids constituting the unsaturated fatty acid derivatives.Specific examples of unsaturated fatty acid derivatives include linseed oil, tung oil, perilla oil, sesame oil, poppy seed oil, walnut oil, safflower oil, fish oil, dehydrated castor oil, rice oil, corn oil, grape seed oil, soybean oil, sunflower oil, peanut oil, rapeseed oil, cottonseed oil, tall oil, almond oil, jojoba oil, kukui nut oil, macadamia nut oil, and persic oil.

[0047] Polymerization of unsaturated fatty acids or derivatives thereof is carried out by oxidative polymerization of unsaturated groups in the presence of oxygen. The oxidative polymerization can be carried out, for example, by stirring the unsaturated fatty acids in air or by blowing air into the unsaturated fatty acids to bring them into contact with oxygen in the air. The polymerization can be carried out at room temperature.

[0048] To accelerate the oxidative polymerization reaction, heating or a catalyst may be used, if necessary. The oxidative polymerization reaction is preferably carried out until the polymer irreversibly gels and turns into powder, losing its thermoplasticity. This improves the strength or water resistance of coating films and molded articles formed from the aqueous resin.

[0049] When the oxidative polymerization reaction is carried out by heating, the reaction temperature is, for example, 100 to 500° C., preferably 200 to 450° C., and more preferably 300 to 400° C. If the heating temperature is less than 100° C., the oxidative polymerization reaction may not be sufficiently promoted, whereas if it exceeds 500° C., the amount of volatilization of the composition increases, which may reduce the yield of the aqueous resin.

[0050] The catalyst used in the oxidative polymerization reaction may be a conventionally known oxidation catalyst. Specific examples of usable catalysts include metal powders of Co, Mn, Pb, Ca, Zn, Cu, Zr, Ce, Fe, Pd, Pt, Sn, Mo, W, Ti, V, Rh, Ni, Zr, Al, Ag, B, and Cr, which are used in drying oil driers, as well as oxides, hydroxides, sulfates, nitrates, chlorides, acetates, and naphthenates thereof, and organic oxidizing agents such as anthracene, methyl ethyl ketone peroxide, and benzoyl peroxide.

[0051] The reaction time for the oxidation polymerization reaction varies depending on reaction conditions such as reaction temperature and type of catalyst, but is preferably adjusted appropriately between 3 and 48 hours, and more preferably between 6 and 10 hours.

[0052] The resulting polymer is then reacted with a base to saponify the polymer and convert the carboxyl groups derived from the unsaturated fatty acids into their salts. Specific examples of bases that can be used in the reaction include NaOH, KOH, LiOH, Ba(OH), Ca(OH), NaHCO, and NaCO. In a preferred embodiment, a strong base is used. Specific examples of preferred bases include NaOH and KOH.

[0053] The polymer of unsaturated fatty acid or its derivative may be the polymer electrolyte described in WO 2023 / 027057. The polymer electrolyte is a polymer electrolyte having a partial polymer of a fatty acid having 16 or more carbon atoms, two or more double bonds, and carboxyl groups, some of which have been neutralized with a basic substance to be converted to carboxylate anion groups.

[0054] In this polymer electrolyte, preferred specific examples of the fatty acid include oleic acid, linoleic acid, linolenic acid, arachidonic acid, eicosapentaenoic acid, and docosahexaenoic acid, etc. Preferred specific examples of the basic substance include NaOH, KOH, LiOH, Ca(OH)2, Mg(OH)2, Ba(OH)2, Zn(OH)2, ammonia, monoethanolamine, diethanolamine, and triethanolamine, etc.

[0055] The polymer can be reacted with a base, for example, by mixing it with an aqueous base solution. The concentration of the base in the aqueous solution is adjusted to 0.1 to 18 normal (N), preferably 1 to 10 N, and more preferably 3 to 6 N, from the viewpoint of improving the hydrophilicity of the aqueous resin. To promote the reaction, the reaction solution may be heated under pressure, if necessary. The heating temperature of the reaction solution is adjusted to, for example, 50 to 200°C, preferably 80 to 180°C, and more preferably 100 to 150°C under pressure.

[0056] The reaction time for the reaction varies depending on reaction conditions such as the concentration of the base and the reaction temperature, but is preferably adjusted appropriately between 1 minute and 3 hours, preferably between 5 and 90 minutes, and more preferably between 10 and 60 minutes. Upon completion of the reaction, the base reactant of the polymer becomes a viscous fluid.

[0057] The base reactant of the polymer is then reacted with an acid, thereby liberating a carboxyl group from the carboxylate salt of the base reactant. Specific examples of acids that can be used in the reaction include sulfuric acid, hydrochloric acid, nitric acid, acetic acid, and formic acid. In a preferred embodiment, a strong acid is used. Specific examples of preferred acids include sulfuric acid and hydrochloric acid.

[0058] The base reaction product of the polymer can be reacted with an acid, for example, by mixing it with an acidic aqueous solution. The concentration of the acid in the aqueous solution is adjusted to 0.1 to 18 N, preferably 1 to 10 N, and more preferably 3 to 6 N, to efficiently generate carboxylic acid in the aqueous resin while preventing bumping due to excessive heat generation. To promote the reaction, the reaction solution may be heated under pressure as necessary. The heating temperature of the reaction solution is adjusted to, for example, 50 to 200°C, preferably 80 to 180°C, and more preferably 100 to 150°C under pressure.

[0059] The reaction time varies depending on reaction conditions such as the acid concentration and reaction temperature, but is preferably adjusted appropriately between 20 minutes and 10 hours, preferably 30 minutes to 5 hours, and more preferably 40 minutes to 2 hours. Upon completion of the reaction, the resulting acid reaction product becomes gum-like. By washing the acid reaction product with water, by-products such as salts and glycerol can be removed, and an aqueous resin can be obtained.

[0060] When the water content of this aqueous resin evaporates, it becomes a solid with strength comparable to that of the insoluble polymer before saponification. Furthermore, this aqueous resin is highly soluble, e.g., highly soluble in alcohol. When a suspension of the aqueous resin is observed under an optical microscope, countless particles are observed, suggesting that an emulsion or suspension has been formed. In other words, the aqueous resin contains the aqueous resin dispersed or dissolved in a solvent containing water.

[0061] The aqueous resin can be mixed and suspended in a suitable solvent to form a liquid resin composition containing the solution, emulsion, or suspension thereof. Such a liquid resin composition has excellent fluidity and is useful for impregnating carbon fibers with the aqueous resin to fill the internal voids.

[0062] From the viewpoint of solubility, suitable solvents include water-soluble organic solvents such as alcohols having 1 to 4 carbon atoms and acetone, aqueous solutions of water-soluble organic solvents, aqueous solutions of water-soluble bases such as ammonia, water such as distilled water, and mixtures thereof. Specific examples of the mixtures include aqueous ethanol solutions, aqueous ammonia solutions, and aqueous ethanol-ammonia solutions.

[0063] <Reinforced carbon fiber> The carbon fiber reinforcing agent of the present invention can be brought into contact with carbon fibers, polymerized, and dried to reinforce the carbon fibers. On the surface of the carbon fibers, phenolic functional groups are present due to interaction with oxygen in the areas that come into contact with liquids, etc. When the carbon fiber reinforcing agent of the present invention is brought into contact with carbon fibers and dried, a covalent bond is formed between the unsaturated groups of the carbon fiber reinforcing agent and the functional groups on the surface of the carbon fibers, generating a new compound in which the two are covalently bonded.

[0064] In carbon fibers, the carbon fiber reinforcing agent and the surface of the carbon fiber are strongly bonded by covalent bonds, and the carbon fiber reinforcing agent is solidified, thereby improving the strength of the carbon fiber, such as the elastic modulus. In this specification, reinforced carbon fiber refers to carbon fiber in which the carbon fiber reinforcing agent has penetrated into the interior of the carbon fiber, solidified, and bonded, thereby improving the strength of the carbon fiber. Reinforced carbon fiber sheet refers to a carbon fiber sheet containing reinforcing carbon fibers. In a preferred embodiment, the reinforced carbon fiber sheet is a thin film-like sheet.

[0065] The reinforced carbon fiber of the present invention containing a carbon fiber reinforcing agent has a low porosity of 5% or less. If the porosity of the reinforcing carbon fiber exceeds 5%, the reinforcement may be insufficient. The porosity of the reinforcing carbon fiber is preferably 3% or less, more preferably 1% or less.

[0066] The reinforced carbon fiber of the present invention can be produced by contacting the carbon fiber with the carbon fiber reinforcing agent by applying the carbon fiber reinforcing agent of the present invention to the surface of the carbon fiber or by incorporating the carbon fiber into the carbon fiber, and then heating the carbon fiber in an environment in which the unsaturated groups of the carbon fiber reinforcing agent react with the functional groups on the surface of the carbon fiber, for example, in an environment in the presence of oxygen.

[0067] Various carbon fibers such as polyacrylonitrile-based, pitch-based, and rayon (cellulose)-based carbon fibers can be used. Carbon fibers preferably have oxygen-containing functional groups on their surfaces. Oxygen-containing functional groups on the carbon fiber surface can be formed or increased by appropriately performing a surface oxidation treatment such as electrolytic oxidation. Examples of oxygen-containing functional groups include hydroxyl groups, carboxyl groups, and carbonyl groups.

[0068] The amount of carbon fiber reinforcing agent applied is preferably 2 to 200% (w / w) relative to the carbon fiber. When carbon fibers are laminated, the amount is preferably 2 to 100% (w / w) to completely cure the carbon fiber reinforcing agent. The amount is preferably 10 to 40% (w / w) to sufficiently impregnate the matrix resin without disturbing the fibers in the laminated state.

[0069] The substrate to which the carbon fiber reinforcing agent is applied may be a carbon fiber aggregate. The carbon fiber aggregate is preferably breathable. In an oxygen-containing environment, the bonding between the carbon fiber reinforcing agent and the carbon fibers is promoted. The carbon fibers may have a coating such as a sizing agent on the surface, but to maximize the reinforcing performance, it is preferable to remove the coating from the surface of the carbon fibers before use. Removing the surface coating may increase the breathability and surface functional groups of the carbon fibers.

[0070] The carbon fiber aggregate may be a processed product such as a bundle, woven fabric, knitted fabric, or laminate of carbon fibers. Specific examples of processed carbon fiber products include carbon fiber sheets such as carbon fiber woven fabrics. In a preferred embodiment, the carbon fiber aggregate includes a carbon fiber sheet. The carbon fiber sheet may be isotropic or anisotropic.

[0071] The carbon fiber sheet preferably has a basis weight of 190 g / m from the viewpoint of ensuring breathability. 2 The weight of the carbon fiber sheet is 190 g / m 2If the concentration exceeds 150 g / m, the carbon fiber reinforcing agent may not be solidified sufficiently due to a lack of oxygen, resulting in insufficient strength of the reinforced carbon fiber sheet. 2 or less, more preferably 100 g / m 2 The following is the result.

[0072] The heating temperature of the carbon fiber containing the carbon fiber reinforcing agent is adjusted as appropriate to form covalent bonds, but is generally 80 to 350° C., preferably 180 to 350° C., and more preferably 250 to 350° C. If the heating temperature is too high, the carbon fiber reinforcing agent may be partially decomposed and gasified.

[0073] The heating time for the carbon fiber containing the carbon fiber reinforcing agent is adjusted appropriately to form covalent bonds, but is generally 0.05 to 240 minutes, preferably 0.1 to 60 minutes, and more preferably 0.5 to 10 minutes. If the heating time is too short, the improvement in strength of the reinforcing carbon fiber may be insufficient, and if it is too long, the strength may decrease.

[0074] The reinforced carbon fiber sheet of the present invention containing a carbon fiber reinforcing agent has a low porosity of 5% or less. If the porosity of the reinforced carbon fiber sheet exceeds 5%, the reinforcement may be insufficient. The porosity of the reinforced carbon fiber sheet is preferably 3% or less, more preferably 1% or less.

[0075] If the porosity of the reinforced carbon fiber or reinforced carbon fiber sheet is high, the mechanical properties such as strength and elastic modulus of the final molded CFRP may be reduced. Therefore, it is desirable to prepare the reinforced carbon fiber sheet so that the porosity of the fiber is low and no gaps are formed.

[0076] The reinforced carbon fiber and reinforced carbon fiber sheet can also be produced by using an electrolyte having a structure in which some of the carboxyl groups of an unsaturated fatty acid have been converted to a salt (hereinafter, sometimes referred to as "FADP," an abbreviation for Fatty Acid Derived Polyelectrolyte) as a carbon fiber reinforcing agent, bringing it into contact with carbon fibers by a method such as incorporating it into the interior of the carbon fibers, and heating it in an oxygen-present environment. Examples of FADP that can be used include electrolytes containing fatty acids or partial polymers thereof having 16 or more carbon atoms, two or more double bonds, and carboxyl groups, in which some of the carboxyl groups have been neutralized with a basic substance to convert them into carboxylate anion groups.

[0077] Regarding carbon fiber reinforcing agents containing FADP, and methods for producing reinforced carbon fibers and reinforced carbon fiber sheets, details thereof are described in Japanese Patent Application No. 2022-152858, and the description therein is incorporated by reference.

[0078] <Carbon fiber reinforced composite material (CFRP)> The reinforced carbon fiber and reinforced carbon fiber sheet of the present invention can be combined with a matrix resin composition to form a prepreg. A prepreg is a shapable material that contains carbon fibers as domains and an uncured curable resin composition as a matrix. A prepreg is an intermediate material used in producing CFRP or a CFRP molded product that contains carbon fibers as reinforcing fibers and a cured resin as a matrix. In other words, the reinforced carbon fiber and reinforced carbon fiber sheet of the present invention can be combined with a matrix resin to form a CFRP.

[0079] The matrix resin composition of the prepreg may be a curable resin, including radical curable resins and thermosetting resins.

[0080] Examples of radically curable resins include those containing oligomers having polymerizable unsaturated groups such as vinyl groups and acryloyl groups, such as acrylic resins such as urethane acrylate resins, epoxy acrylate resins, and polyacrylacrylate resins. Radical-curable resins can react with carbon fiber reinforcements to form covalent bonds, thereby providing high-strength CFRP. Among radical-curable resins, polyacrylacrylate resins are preferred for further improving the hardness of CFRP. Examples of thermosetting resins include unsaturated polyester resins, vinyl ester resins, epoxy resins, phenolic resins, melamine resins, urea resins, thermosetting polyimide resins, cyanate ester resins, and bismaleimide resins, as well as modified versions of these resins and blends of two or more of these resins. Among thermosetting resins, epoxy resins are preferred because they provide CFRP with excellent balance of mechanical properties and minimal cure shrinkage, and they also provide strong adhesion to carbon fibers after curing.

[0081] In a preferred embodiment, when a prepreg is produced using a reinforced carbon fiber sheet, a layer of a matrix resin composition can be formed on at least one surface of the reinforced carbon fiber sheet. The resulting prepreg can be molded and cured to produce a fiber-reinforced composite material or a molded fiber-reinforced composite material. Molding and curing can also be carried out after laminating multiple prepregs.

[0082] The matrix resin composition may be a two-component curable resin, which is a resin that is cured by mixing component A, such as a matrix resin, with component B, such as a curing agent, at room temperature or by heating as needed.

[0083] One form of prepreg is a prepreg in which a layer of component A or component B of a two-component mixed curable resin is formed on at least one surface of a reinforced carbon fiber sheet. Specifically, for example, a prepreg in which a layer of component A is formed on both surfaces of a reinforced carbon fiber sheet, a prepreg in which a layer of component B is formed on both surfaces of a reinforced carbon fiber sheet, and a prepreg in which a layer of component A is formed on one surface of a reinforced carbon fiber sheet and a layer of component B is formed on the other surface can be prepared.

[0084] The thickness of the CFRP can be increased by alternately laminating prepregs with double-sided agent A layers and double-sided agent B layers. In this case, the matrix resin can be cured by contact between agent A and agent B. Holes may also be intentionally provided between the fiber bundles to encourage contact between the upper and lower agents when pressure is applied after lamination. Two reinforced carbon fiber sheets, each with an agent A layer or agent B layer on one side, may be laminated to the top or bottom of a laminate of two types of prepregs so that agent A and agent B come into contact, resulting in a CFRP with the reinforced carbon fiber sheets on both the front and back sides.

[0085] In a prepreg in which an A-layer is formed on one side of a reinforced carbon fiber sheet and an B-layer is formed on the other side, the components of the A- and B-parts of the two-part curable resin are prevented from mixing because the A-layer and the B-part are present between them. By laminating multiple sheets of this prepreg so that the A-layer and the B-part are in contact with each other, the thickness of the CFRP can be increased and the matrix resin can be cured.

[0086] The prepreg having a layer of component A or component B of a two-component curable resin formed on at least one surface of a reinforced carbon fiber sheet as described above can be stored at room temperature for a period of, for example, 3 days to 4 months, 1 week to 2 months, or 2 to 4 weeks, depending on the intended use.

[0087] Furthermore, for example, in the case of a two-component mixed curable acrylic resin in which component A is an acrylic resin containing a latent radical initiator and component B is an acrylic resin containing a radical initiator activator, radicals are generated by mixing or bringing components A and B into contact with each other, and the resin can be cured at room temperature.

[0088] The matrix resin composition layer can be formed by applying the matrix resin composition to the surface of a reinforced carbon fiber sheet. Since the voids in the reinforced carbon fiber are already filled with a carbon fiber reinforcing agent, there is no need to impregnate the interior of the carbon fiber with the matrix resin composition by vacuum suction or heating, as in the past.

[0089] CFRP can be produced by laminating the obtained prepregs and then heat-curing the matrix resin while applying pressure to the laminate. Methods for applying heat and pressure include press molding, autoclave molding, bagging molding, wrapping tape, internal pressure molding, and vacuum pressure molding.

[0090] Generally, in order to shape a prepreg, it is necessary to press it under high pressure while it is placed in a mold, or to remove internal voids under reduced pressure while it is placed in the mold.

[0091] Unlike typical prepregs, the reinforced carbon fiber sheet of the present invention exhibits no adhesiveness, maintains its sheet shape, and does not lose its shape. Therefore, it can be punched or punched using a punch press, or cut using nippers or scissors. For example, after punching out multiple sheets of the reinforced carbon fiber sheet into a predetermined shape, they can be stacked to increase the thickness. It is also easy to bond flat reinforced carbon fiber sheets together with an adhesive, form them into a three-dimensional shape while they are still uncured, and then cure the three-dimensional shape to fix it.

[0092] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples. [Example]

[0093] Example 1 Evaluation of affinity with carbon fiber by static contact angle measurement (1)FADP 500 mL of linoleic acid was poured into a 2 L beaker on a heater and polymerized at 350 °C for approximately 3 hours while stirring to thoroughly mix with air. Then, 2% (w / w) NaOH was added and dissolved to obtain FADP. The polymerization reaction was continued while sampling with an Oswald viscometer from time to time until the viscosity reached a value relatively similar to that of a comparative epoxy resin raw material (RSF816 (trade name), manufactured by AXSON) immediately after mixing (nominal value 400-600 mPa·s).

[0094] The resulting FADP, together with distilled water, linoleic acid, and epoxy resin raw material (RSF816 (trade name), manufactured by AXSON), was dropped in 1 μL portions onto a spread carbon fiber bundle (ASA-80I (trade name), manufactured by Sakai Ovex Co., Ltd.) using a pipette, and the static contact angles of each were measured (n=3) using an automatic contact angle meter (DSA100S (trade name), manufactured by KRUSS Co., Ltd.). The results are shown in Figures 1 and 2.

[0095] These results show that FADP is more compatible with carbon fibers than typical low-viscosity epoxy resin raw materials used in CFRP infusion molding.

[0096] (2) Unsaturated fatty acid polymer solubilized resin 500 mL of linoleic acid was poured into a 2 L beaker on a heater and polymerized at 350°C for approximately 8 hours while stirring and mixing well with air. The liquid linoleic acid became gel-like. When this was further mixed well at 350°C, it disintegrated into powder, and polymerization continued for approximately 2 hours at the same temperature while mixing in air. When the powder became hard and black, heating was stopped and it was cooled to room temperature.

[0097] To the obtained linoleic acid polymer, 500 mL of a 5N aqueous solution of NaOH was added, and the mixture was pressurized and heated in an autoclave at 121°C for approximately 10 minutes. As a result, the linoleic acid polymer became a black, starch-syrup-like solution. It is believed that the carboxyl groups of the linoleic acid polymer formed sodium salts, thereby making the polymer water-soluble.

[0098] 500 mL of a 6N aqueous solution of H2SO4 was added to the mixture, and the mixture was stirred at 100°C for approximately 1 hour to liberate the carboxylate group from the base reaction product. This resulted in a gum-like polymer containing approximately 50% (w / w) water inside, i.e., an unsaturated fatty acid polymer solubilized resin.

[0099] A 50% (w / w) ethanol solution was prepared by adding ethanol to the polymer, and the static contact angle was measured in the same manner as above. The contact angle was ND (below the lower limit). This result confirmed that the unsaturated fatty acid polymer solubilized resin, like FADP, has the property of being easily compatible with carbon fiber.

[0100] (3) Evaluation of affinity for surface-coated carbon fiber The carbon fiber bundle was sonicated in acetone at 30°C for 4 hours, and then immersed for 48 hours to remove the sizing agent. The static contact angle of a 50% (w / w) ethanol solution of FADP, epoxy resin raw material, distilled water, linoleic acid, and unsaturated fatty acid polymer-solubilized resin was measured in the same manner as above, except that the obtained sizing-removed carbon fiber was used.

[0101] Even in these cases, the static contact angle measured for each sample was the same as that of the carbon fiber before the sizing agent was removed. These results indicate that FADP and unsaturated fatty acid polymer solubilized resins are more compatible with carbon fiber than typical low-viscosity epoxy resin raw materials used in CFRP infusion molding.

[0102] <Example 2> Evaluation of the effect on the cross-sectional area of ​​carbon fiber bundles A 10 cm long 3K carbon fiber bundle (3,000 carbon fibers) pulled from a carbon fiber fabric (Toray Industries, Toray Industries, Toray Industries, Inc.) was immersed in a 50% (w / w) ethanol-diluted solution of the unsaturated fatty acid polymer-solubilized resin produced in Example 1, gently removed, transferred to a Teflon (registered trademark) plate, and air-dried at 40°C for 30 minutes. It was then heated on a hot plate at 300°C for 30 seconds to complete curing. The ratio of unsaturated fatty acid polymer-solubilized resin after curing was 6.3% (w / w).

[0103] For comparison, fiber bundles were immersed in an epoxy resin raw material (RSF816 (trade name), AXSON Co., Ltd.) diluted with 50% (w / w) ethanol after mixing, an aqueous urethane resin (aqueous urethane varnish, Washin Paint Co., Ltd.), and an oil-based urethane resin (oil-based urethane varnish, Washin Paint Co., Ltd.), and then left to stand on a Teflon (registered trademark) plate at 25°C for 48 hours to complete curing.

[0104] The thickness and width of each fiber bundle were measured with a vernier caliper to the nearest 0.05 mm at a point 5 cm long, and the cross-sectional area per bundle was calculated (n=5). The results are shown in Figure 3.

[0105] The test results showed that the unsaturated fatty acid polymer solubilized resin has the unique property of converging carbon fiber bundles and expelling the air inside during the curing process.

[0106] Example 3 Effect on CFRP porosity (void ratio) From the above test results, it was predicted that the addition of fatty acid or oil polymers, such as unsaturated fatty acid polymer solubilizing resin, to carbon fiber would reduce the void ratio of CFRP. Therefore, the void ratio of CFRP when unsaturated fatty acid polymer solubilizing resin was added to carbon fiber fabric was calculated using the combustion method of JIS K7075 as a reference.

[0107] A carbon fiber fabric (Torayca T300B (trade name), Toray Industries, Inc.) was immersed in a 50% (w / w) ethanol-diluted solution of the unsaturated fatty acid polymer-solubilized resin produced in Example 1, gently removed, transferred to a Teflon (registered trademark) plate, and air-dried at 40°C for 30 minutes. It was then heated on a hot plate at 300°C for 30 seconds to complete the curing. A relatively thin carbon fiber fabric (ASA-80I (trade name), Sakai Ovex Co., Ltd.) was also treated in the same way to produce a reinforced carbon fiber sheet in which the entire fabric was coated with the unsaturated fatty acid polymer-solubilized resin.

[0108] As a control, an untreated sample was prepared by immersing the sample in a 50% (w / w) ethanol solution containing distilled water instead of the unsaturated fatty acid polymer solubilizing resin, and then air-drying and heating at 300°C in the same manner.

[0109] This was cut into a 100 mm x 20 mm piece and laminated to a thickness of 2 mm on a Teflon (registered trademark) coated iron plate placed inside a bagging film. A bleeding film was placed on top of this, and the bagging film was sealed with sealant tape. Two suction ports were connected via hoses to a container containing epoxy resin raw material (RSF816 (trade name), AXSON) and a vacuum pump, and infusion molding was carried out.

[0110] On the other hand, the reinforced carbon fiber sheet has fibers occupied by unsaturated fatty acid polymer solubilized resin, and since it is difficult for the epoxy resin raw material to spread throughout the interface and the entire sheet during infusion molding, the mixed epoxy raw material was roller-coated on both sides to create a type of prepreg, and after lamination, both sides were sandwiched between iron plates and weights were placed on top to apply a light pressure of approximately 10 kPa.

[0111] After curing at 25°C for 48 hours, the test pieces were removed and cut into pieces measuring 15mm x 15mm. Since the surface was slightly uneven due to the epoxy resin, each test piece was polished to a thickness of 2mm.

[0112] After combustion in a muffle furnace at 420°C for 8 hours, the mass (Mf) of the carbon fiber residue was measured, and various volume contents including the void fraction were calculated using the following formula.

[0113]

number

[0114] The carbon fiber density (pf) is 1.76 g / cm 2 The density of the test piece (pc) was calculated by the underwater displacement method. The resin density (pr) was calculated using the unsaturated fatty acid polymer solubilized resin (0.90 g / cm) produced in Example 1. 2 ) and epoxy resin (1.17 g / cm 2 ) is mixed at 1.17g / cm 2 was applied provisionally. Therefore, the actual void fraction was smaller than the calculated value at most. The test results obtained are summarized in Table 1.

[0115] [Table 1]

[0116] Since the threshold for shear strength reduction is generally 1-2% (cited from Mitsubishi Heavy Industries Techniques Vol. 53 No. 4 (2016)), it was found that the addition of unsaturated fatty acid polymer solubilizing resin allows ideal values ​​to be obtained even under simple molding conditions. In particular, the fact that such good results can be obtained even when differences in carbon fiber properties and additives such as sizing agents are expected depending on the manufacturer shows that the technology of this invention can be easily applied to a wide variety of carbon fiber products.

[0117] Furthermore, the results of the test pieces that had been reinforced with carbon fiber sheets showed that the technology of this invention allows for a good void ratio to be obtained by simple fixing and pressurization, without the need for conventional autoclaves, pumps, or presses. The antifoaming properties of unsaturated fatty acid polymer solubilized resins and oil / fatty acid polymers such as FADP, as well as the high antifoaming properties of the ethanol used as a solvent, are also thought to be factors in the good results.

[0118] Example 4 Three-point bending test The effect of the carbon fiber reinforcement treatment of the present invention on the strength and elastic modulus of a reinforced carbon fiber sheet and a CFRP to which a commercially available quick-drying adhesive was applied at the interface was evaluated by a three-point bending test with reference to JIS K7074-1988.

[0119] First, a carbon fiber fabric (ASA80I (trade name), Sakai Ovex Co., Ltd.) was immersed in a 50% (w / w) ethanol-diluted solution of the unsaturated fatty acid polymer-solubilized resin produced in Example 1, gently removed, transferred onto a Teflon (registered trademark) plate, and air-dried at 40°C for 30 minutes. It was then heated on a hot plate at 300°C for 30 seconds to complete curing.

[0120] The reinforced carbon fiber sheet thus obtained was cut into multiple pieces measuring 100 mm x 15 mm. The mixed epoxy resin stock solution (RSF816 (trade name), AXON Co.) was roller-coated on both sides of each sheet, and after stacking 16 sheets, one edge was stapled to prevent slippage. Then, both sides were sandwiched between iron plates, and a weight was placed on top to apply a light pressure of approximately 110 kPa. As a control, 16 sheets of carbon fiber fabric (ASA-80I, Sakai Ovex Co., Ltd.) measuring 150 mm x 150 mm were also stacked and infusion molded. Three sets (n = 3) of each test piece were prepared.

[0121] After curing for 48 hours at 25°C, the test pieces were removed and confirmed to have a thickness of 2±0.4 mm. Control test pieces were cut to measure 100 mm x 15 mm.

[0122] The untreated carbon fiber fabric and the reinforced carbon fiber sheet laminated CFRP were cut into 100 mm x 15 mm pieces. A three-point bending test was performed on the untreated carbon fiber fabric and the reinforced carbon fiber sheet using a precision universal testing machine (AG-20kNXDplus (trade name), Shimadzu Corporation), and the bending strength (maximum bending stress) and bending modulus were calculated. The results are shown in Figure 4.

[0123] A commercially available quick-drying epoxy adhesive (High Super 30 (trade name), Cemedine) and a quick-drying acrylic adhesive (Metallock AY-123 (trade name), Cemedine) were roller-coated on both sides of the reinforced carbon fiber sheets, and after stacking 16 sheets, one edge was stapled to prevent slippage. Then, both sides were sandwiched between iron plates, and a weight was placed on top to apply a slight pressure of approximately 110 kPa.

[0124] After curing for 48 hours at 25°C, the test pieces were removed and confirmed to have a thickness of 2±0.4 mm. Control test pieces were cut to measure 100 mm x 15 mm.

[0125] The two types of reinforced carbon fiber sheet-laminated CFRPs obtained in this way were subjected to a three-point bending test using a precision universal testing machine (AG-20kNXDplus (trade name), Shimadzu Corporation) to measure their bending strength and bending modulus. Figure 5 shows the bending strength and bending modulus of the reinforced carbon fiber sheet-laminated CFRPs as percentages, with the infusion-molded CFRP made from the untreated carbon fiber fabric being taken as 100%.

[0126] These results show that the reinforced carbon fiber sheet laminated CFRP exhibits bending strength comparable to that of conventional infusion-molded CFRP made of untreated carbon fiber fabric.

[0127] It was also shown that the modulus of elasticity of the reinforced carbon fiber sheet laminated CFRP was significantly improved compared to that of infusion-molded CFRP made from untreated carbon fiber fabric. Furthermore, it was revealed that by using a commercially available fast-drying modified acrylic resin, the modulus of elasticity was equivalent (99%) to that of an infusion-molded product using epoxy resin. The bending strength was 84% ​​of the original value, which is generally practical.

[0128] These results indicate that various prepregs using carbon fiber sheets reinforced with unsaturated fatty acid polymer solubilized resin have elastic modulus and rigidity equivalent to existing methods, and are highly practical in terms of strength. There are many different types of acrylic adhesives, and since excellent values ​​were obtained even when using such easily available products in a simple manner, it is expected that even higher values ​​can be obtained by selecting and optimizing acrylic adhesives.

[0129] The reason for the good results obtained with acrylic adhesives is that both the unsaturated fatty acid polymer solubilized resin and the acrylic adhesive use radical polymerization initiated by unsaturated bonds as the extension reaction mechanism. In other words, it is thought that a portion of the unsaturated fatty acid polymer solubilized resin forms strong covalent bonds during the curing of the acrylic adhesive, resulting in the good physical properties observed in this study. Additionally, acrylic resins are known to have poor interfacial adhesion with carbon fiber, resulting in low CFRP strength (Journal of the Adhesion Society of Japan, Vol. 53, No. 3 (2017)). Therefore, it has been shown that this technology can compensate for the shortcomings of acrylic resins.

[0130] <Example 5> Effect of carbon fiber sheet weight From the examples so far, a relatively low basis weight (80 g / m 2It was found that a carbon fiber fabric (ASA80I (trade name), Sakai Ovex Co., Ltd.) made of 100% acrylic resin (Asa80I (trade name), Sakai Ovex Co., Ltd.) can achieve sufficient strength with simpler pressurization, without the need for conventional infusion molding, which involves void removal by suction. On the other hand, it was found that in the case of a high basis weight, the void fraction can be kept low by combining it with infusion molding, but it was unclear what bending strength, elastic modulus, and void fraction would be obtained when molding using simple pressurization. Therefore, this will be clarified in this example.

[0131] First, the weight is relatively large (198 g / m 2 A carbon fiber fabric (TORAYCA T300B (trade name), Toray Industries, Inc.) was immersed in a 50% (w / w) ethanol diluted solution of the unsaturated fatty acid polymer solubilized resin produced in Example 1, gently removed, transferred to a Teflon (registered trademark) plate, and air-dried at 40°C for 30 minutes. It was then heated on a hot plate at 300°C for 30 seconds to complete the curing.

[0132] This was cut into several pieces measuring 100 mm x 20 mm, and mixed epoxy resin raw material (RSF816 (trade name), AXON Co.) was roller-coated on both sides to form a type of prepreg. After lamination, both sides were sandwiched between iron plates and weights were placed on top to apply a light pressure of approximately 10 kPa.

[0133] After curing for 48 hours at 25°C, the thickness was 2.4 mm. Of the two test pieces thus prepared, one was further cut out to a size of 15 mm x 15 mm and used to measure the volume content.

[0134] A three-point bending test was performed using a precision universal testing machine (AG-20kNXDplus (trade name), Shimadzu Corporation), and the bending strength (maximum bending stress) and bending modulus were calculated. A sample (100 mm × 20 mm × 2 mm) after infusion molding produced in Example 3 was used as a control. The results are shown in Figure 6. Using the same method as in Example 3, the cut test pieces were burned in a muffle furnace at 420°C for 8 hours, after which the mass of the carbon fiber residue was measured and various volume contents were calculated. The results are shown in Table 2.

[0135] [Table 2]

[0136] As shown in the results of Figure 4, high strength and low voids can be achieved with simple pressure application at low basis weights, but at relatively high basis weights like those in this example, the void ratio increases without suction, and the strength is insufficient compared to conventional methods. The reasons for this are thought to be that the increased basis weight reduces drapeability, making it impossible to obtain a sufficient fiber content, and making it difficult to remove voids by pressure application.

[0137] Example 6 Fabrication and evaluation of room temperature curing / storage prepreg When attempting to produce prepregs similar to those in Examples 3 and 4 using resins other than unsaturated fatty acid polymer solubilized resin and FADP, the matrix resin composition must (1) maintain the same elastic modulus and strength as conventional methods, (2) not add thickness to the substrate, (3) suppress the generation of bubbles and voids, and (4) ensure adhesion to the adhesive. Attempting to satisfy all four of these conditions simultaneously is expected to result in high costs, and in reality, it is difficult to produce similar prepregs using resins other than unsaturated fatty acid polymer solubilized resin and FADP.

[0138] In particular, the applicability of a two-component curing acrylic adhesive, as in Example 4, indicates that a prepreg that can be stored and cured at room temperature can be produced using this resin. That is, by placing component A of the two-component curing acrylic adhesive on one side of a reinforced carbon fiber sheet and component B on the other side, a prepreg that is stable at room temperature can be obtained. During molding, multiple prepregs are stacked together, and curing begins at room temperature.

[0139] In particular, as shown in Examples 1 and 2, unsaturated fatty acid polymer-solubilized resin is attracted to the interior of the carbon fiber bundles, making it difficult to form a coating in the gaps beside the intersections of the fabric where no fibers are present. This results in a reinforced carbon fiber sheet with holes, and by laminating and pressurizing the sheet with an adhesive applied to the surface, the adhesive components can be brought into contact across the layers. This is also true for carbon fiber in the form of unidirectional material (UD material); general UD material has many unintentional gaps, and a similar effect can be achieved.

[0140] Furthermore, in two-component curing acrylic adhesives, the base resin monomers of both components are usually the same composition, and when different additives come into contact with each other, such as peroxides in component A and oxidation catalysts in component B, a radical chain reaction is initiated, and the curing reaction propagates through the solution. Therefore, even when the components are unevenly or non-mixed, they will cure sufficiently, and curing will proceed even if there is only a partial overlap between the prepreg with component A and the prepreg with component B, or if there is an imbalance in the stacking order.

[0141] In this example, the stability of this room temperature cured and room temperature stored prepreg is evaluated.

[0142] A high-elasticity UD material (UMS40 (trade name), Teijin) and a cloth material (ASA-60S (trade name), Sakai Ovex) were immersed in a 50% (w / w) ethanol-diluted solution of the unsaturated fatty acid polymer solubilized resin produced in Example 1, gently removed, transferred to a Teflon (registered trademark) plate, and air-dried at 40°C for 30 minutes. They were then heated on a hot plate at 300°C for 30 seconds to complete the curing.

[0143] The reinforced carbon fiber sheets thus obtained were cut into two sets of 100 mm × 50 mm each. One set was coated on both sides with agent A of a commercially available quick-drying adhesive (Metallock AY-123 (trade name), Cemedine Co., Ltd.), and the other set was coated on both sides with agent B using a roller.

[0144] These were sealed in polyethylene zipper bags whose surfaces had been washed with 70% ethanol and then placed in an incubator at 20°C. After three weeks, the prepreg stability was evaluated by checking whether the bags were dry to the touch. The prepregs were then laminated to a thickness of 1±0.4 mm, cured at 25°C for 5 minutes under approximately 110 kPa, and then left to stand at 25°C for 24 hours without pressure to complete the cure. The prepregs were then subjected to a three-point bending test. A control CFRP piece infusion molded with epoxy resin was used for the evaluation.

[0145] As a result, none of the samples were dry to the touch and maintained a certain level of tackiness. The results of the three-point bending test for each sample are shown in Figures 7 and 8.

[0146] Considering the results of Example 4, all of the acrylic adhesives used in this test, which used epoxy resin raw materials for CFRP, achieved elastic modulus values ​​higher than those of existing methods. Furthermore, the strength maintained approximately 80% of that of existing methods, and it was confirmed that there was no significant difference from Example 4 even when the storage time or fiber type was different. These results demonstrate that prepregs based on the technology of the present invention can be stored at room temperature for a certain period of time and can be molded and cured at room temperature.

[0147] Example 7 Processing example 1 using a desktop cutting machine The reinforced carbon fiber sheet can be easily precision machined using a desktop cutting machine for hobby use.

[0148] An A4-sized carbon fiber fabric (ASA-60S, Sakai Ovex Co., Ltd.) was immersed in a 50% (w / w) ethanol-diluted solution of the unsaturated fatty acid polymer-solubilized resin produced in Example 1, gently removed, transferred onto a Teflon (registered trademark) plate, and air-dried at 40°C for 30 minutes. It was then heated on a hot plate at 300°C for 30 seconds to complete curing.

[0149] The material was set in a desktop cutting machine (Portrait3, Silhouette) and automatically cut into the gear shape designed using the included software. The results are shown in Figure 8.

[0150] The fact that processing was possible without fraying even in areas with a minimum width of approximately 2 mm confirmed that precise processing is possible using an inexpensive cutting machine.

[0151] Example 8 Processing example 2 using a desktop cutting machine Honeycomb-structured CFRP can be easily produced by using room-temperature prepreg technology and a cutting machine.

[0152] An A4-sized carbon fiber fabric (ASA-60S, Sakai Ovex Co., Ltd.) was immersed in a 50% (w / w) ethanol-diluted solution of the unsaturated fatty acid polymer-solubilized resin produced in Example 1, gently removed, transferred onto a Teflon (registered trademark) plate, and air-dried at 40°C for 30 minutes. It was then heated on a hot plate at 300°C for 30 seconds to complete the curing.

[0153] The sheet was placed in a desktop cutting machine (Portrait3, Silhouette) and automatically cut into multiple 30cm x 1.5cm pieces using the included software. The reinforced carbon fiber sheet was divided into two sets, and one set was coated with agent A of a commercially available quick-drying adhesive (Metallock AY-123, Cemedine) on both sides, while the other set was coated with agent B on both sides using a roller.

[0154] Several samples were prepared by bonding one reinforced carbon fiber sheet with component A and one reinforced carbon fiber sheet with component B, and these were fixed in a textured mold for 5 minutes to form the specimen. The folded portions of the semi-hardened specimens thus formed were then overlapped, sandwiched between metal weights on both sides, and lightly pressed and fixed in place.

[0155] A honeycomb structure was fabricated by leaving it at 25°C for 24 hours. The results are shown in Figure 9.

[0156] When attempting to obtain a similar prototype, it is difficult to produce it in a short time using the infusion molding method, and using existing prepregs requires precise temperature control, resulting in a tedious process. On the other hand, using the room-temperature prepreg or reinforced carbon fiber sheet of the present invention allows for production in a short time with minimal work. This allows for a simpler processing process, making automation and high-precision manufacturing easier than with conventional methods. For example, it becomes easier to apply inexpensive equipment to the corrugated method, which has long been used for paper and metals ( Bulletin of the Japan Institute of Metals, Vol. 24, No. 6 (1985)).

Claims

1. A reinforced carbon fiber comprising a carbon fiber and a carbon fiber reinforcing agent contained in the carbon fiber, The carbon fiber reinforcing agent includes a solid resin made of a polymer of an unsaturated fatty acid or a derivative thereof, The reinforcing carbon fiber has a void ratio of 5% or less.

2. 2. The reinforced carbon fiber of claim 1, wherein the unsaturated fatty acid has 16 to 22 carbon atoms.

3. The reinforced carbon fiber of claim 1 , wherein the unsaturated fatty acid derivative comprises a drying oil.

4. 2. The reinforced carbon fiber of claim 1, wherein the unsaturated fatty acid comprises linoleic acid or linolenic acid, and the unsaturated fatty acid derivative comprises linseed oil.

5. A reinforced carbon fiber sheet comprising the reinforcing carbon fiber according to claim 1.

6. The weight of the carbon fiber sheet excluding the reinforcing agent is 190 g / m ２ 6. The reinforced carbon fiber sheet according to claim 5, wherein:

7. A prepreg comprising the reinforced carbon fiber sheet according to claim 5 and a layer of a matrix resin composition formed on at least one surface of the reinforced carbon fiber sheet.

8. the matrix resin composition contains a two-component curable resin, The reinforced carbon fiber sheet according to claim 5; a layer of component A of a matrix resin composition formed on one surface of the reinforced carbon fiber sheet; 8. The prepreg according to claim 7, further comprising a layer of component B of a matrix resin composition formed on the other surface of the reinforced carbon fiber sheet.

9. The prepreg according to claim 8 , wherein the matrix resin composition comprises a two-component curable acrylic resin.

10. A carbon fiber reinforced composite material molded product comprising the reinforced carbon fiber sheet according to claim 5 and a matrix resin.

11. A carbon fiber reinforcing agent containing an aqueous resin, which comprises a solid resin comprising a polymer of an unsaturated fatty acid or a derivative thereof, and which is obtained by reacting a base reaction product of the solid resin with an acid to liberate a carboxylate of the base reaction product, and which can be dispersed or dissolved in a hydrophilic solvent to form a liquid resin composition.

12. The carbon fiber reinforcing agent according to claim 11, wherein the polymer of unsaturated fatty acid is made from an unsaturated fatty acid or a derivative thereof.

13. The carbon fiber reinforcing agent of claim 11 , wherein the unsaturated fatty acid derivative comprises a drying oil.

14. The carbon fiber reinforcing agent according to claim 11, wherein the base is a substance containing an alkali metal or an alkaline earth metal.

15. The carbon fiber reinforcing agent according to claim 11, wherein the unsaturated fatty acid has 16 to 22 carbon atoms.

16. 12. The carbon fiber reinforcing agent of claim 11, wherein the unsaturated fatty acid comprises linoleic acid or linolenic acid, and the unsaturated fatty acid derivative comprises linseed oil.

17. The carbon fiber reinforcing agent according to any one of claims 11 to 16, further comprising a hydrophilic solvent.

18. A method for producing a prepreg, comprising applying a matrix resin composition to the reinforced carbon fiber sheet according to claim 5.

19. The method for producing a prepreg according to claim 18, wherein the matrix resin composition comprises a curable acrylic resin.

20. A method for producing a molded carbon fiber reinforced composite material, comprising molding the prepreg according to claim 7 and curing a matrix resin composition.

21. The method according to any one of claims 18 to 20, which is carried out in an environment at room temperature.

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