JP7739717B2 - Fiber-reinforced composite material intermediate, and method for producing fiber-reinforced composite material - Google Patents

Description

The present invention relates to a method for producing a fiber-reinforced composite material intermediate, in which an epoxy resin composition with excellent UV resistance is applied to the surface of a fiber-reinforced composite material preform, and then the epoxy resin composition is photocured.

Products requiring high structural performance, such as aircraft structural components, wind turbine blades, automobile exterior panels, and computer applications such as IC trays and laptop computer housings, often use prepregs, which are made by impregnating fibers with thermosetting resins such as epoxy resin, or resin transfer molding (RTM) materials, in which preformed fibers are injected with thermosetting resin and then heated to harden. However, fiber-reinforced composite materials obtained by hardening general prepregs or RTM materials have poor UV resistance, and their surfaces deteriorate and degrade when exposed to light. Therefore, in recent years, there has been an increasing demand for adding UV resistance to the surface of carbon fiber-reinforced composite materials.

Patent Document 1 discloses a sheet material with UV blocking properties as a surface protection film for carbon fiber reinforced composite materials. Furthermore, Patent Document 2 discloses a UV-resistant resin composition that combines an epoxy resin containing no aromatic rings with a carboxylic acid anhydride containing no aromatic rings and an ultraviolet absorber, which can be used as a coating agent for carbon fiber reinforced composite materials.

Special table 2015-507648 publication International Publication No. 2003/002661

However, with the technology disclosed in Patent Document 1, the epoxy resin composition used in the film material contains aromatic rings, which poses a problem in that the film material itself has poor UV resistance. Furthermore, with the technology disclosed in Patent Document 2, although the coating agent itself is UV resistant, when the coating agent is applied to the surface of the prepreg used in the fiber-reinforced composite material and then thermally cured, the coating agent mixes with the prepreg resin, which does not have UV resistance, potentially impairing UV resistance or reducing the mechanical properties of the fiber-reinforced composite material.

Therefore, the challenge is to develop a method for manufacturing fiber-reinforced composite material intermediates that can protect the surface of base materials such as prepregs with a highly UV-resistant material, preventing deterioration due to UV rays, and that prevents mixing of the base material resin, which has poor UV resistance, with a UV-resistant coating agent during thermal curing.

The present invention has the following configuration to solve the above problems: Namely, the method for producing a fiber-reinforced composite material intermediate of the present invention is characterized by applying an epoxy resin composition containing the following components [A] to [D] to the surface of a fiber-reinforced composite material preform, and then photocuring the epoxy resin composition:
[A] a non-aromatic epoxy resin; [B] a pigment having an average particle size of 0.1 to 10 μm; [C] a non-aromatic thermoplastic resin; and [D] a cationic or anionic polymerization curing agent.

The method for producing a fiber-reinforced composite material of the present invention is also characterized in that the fiber-reinforced composite material intermediate produced by the above-mentioned method for producing a fiber-reinforced composite material intermediate is further post-cured by heat.

The present invention provides a fiber-reinforced composite material intermediate that uses a highly UV-resistant material to protect the surface of a base material such as a prepreg, preventing deterioration due to UV rays, and prevents mixing of a base resin with poor UV resistance and a coating agent with UV resistance during thermal curing.

The method for producing a fiber-reinforced composite material of the present invention is a method for producing a fiber-reinforced composite material intermediate, which comprises applying an epoxy resin composition containing the following components [A] to [D] to the surface of a fiber-reinforced composite material preform, and then photocuring the epoxy resin composition:
[A] a non-aromatic epoxy resin; [B] a pigment having an average particle size of 0.1 to 10 μm; [C] a non-aromatic thermoplastic resin; and [D] a cationic or anionic polymerization curing agent.

Component [A] of the present invention is a non-aromatic epoxy resin. Here, "aromatic" refers to a compound containing an aromatic hydrocarbon, a compound with a resonance structure, or a conjugated unsaturated heterocyclic compound in its chemical structure; anything else is "non-aromatic." In other words, a non-aromatic epoxy resin refers to an epoxy resin that does not contain an aromatic hydrocarbon group or an unsaturated heterocyclic ring in its chemical structure. Examples of non-aromatic epoxy resins include alicyclic epoxy resins (epoxy resins containing a cycloalkane ring), such as tetrahydroindene diepoxide, vinylcyclohexene oxide, (3',4'-epoxycyclohexane)methyl 3,4-epoxycyclohexanecarboxylate, dipentene dioxide, bis(3,4-epoxycyclohexylmethyl) adipate, dicyclopentadiene dioxide, bis(2,3-epoxycyclopentyl)ether, and 1,2-epoxy-2,2-bis(hydroxymethyl)-1-butanol. 4-(2-oxiranyl)cyclohexane adduct, epoxidized butanetetracarboxylic acid tetrakis-(3-cyclohexenylmethyl) modified epsilon-caprolactone, bi-7-oxabicyclo[4.1.0]heptane, dodecahydrobisphenol A diglycidyl ether, dodecahydrobisphenol F diglycidyl ether, 1,4-cyclohexanedimethanol diglycidyl ether, hexahydrophthalic acid diglycidyl ester, hexahydroterephthalic acid diglycidyl ester, 2,2-bis(4-hydroxycyclohexyl) Specific examples of epoxy resins that do not contain any of an aromatic ring, an amine nitrogen atom, a cycloalkane ring, or a cycloalkene ring include ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, 1,4-butanediol glycidyl ether, 1,6-hexanediol diglycidyl ether, neopentylene glycol diglycidyl ether, glycerol polyglycidyl ether, and diglycerol polyglycidyl ether. Specific examples of trimethylolpropane polyglycidyl ether, sorbitol polyglycidyl ether, 1,4-bis(2-oxiranyl)butane, pentaerythritol polyglycidyl ether, and monofunctional epoxy compounds (epoxy compounds containing only one oxirane ring) that do not contain aromatic rings or amine nitrogen atoms include 4-tert-butyl glycidyl ether, butyl glycidyl ether, 1-butene oxide, 1,2-epoxy-4-vinylcyclohexane, and 2-ethylhexyl glycidyl ether.

From the standpoint of heat resistance, non-aromatic epoxy resins that are preferably used are alicyclic epoxy resins or those that have a cycloalkane structure, such as a cyclohexane ring, in the molecule.

The above-mentioned non-aromatic epoxy resins can be commercially available products. For example, "Celloxide (registered trademark)" 2021P, "Celloxide (registered trademark)" 8010, "Celloxide (registered trademark)" 2000, "Epolead (registered trademark)" GT401, "Celloxide (registered trademark)" 2081, EHPE3150 (manufactured by Daicel Chemical Industries, Ltd.), THI-DE (manufactured by JXTG Nippon Oil & Energy Corporation), TTA21, AAT15, TTA22 (manufactured by Sun Chemical Co., Ltd.), etc. ), Ex-121, Ex-211, Ex-212, Ex-313, Ex-321, Ex-411 (manufactured by Nagase Chemtec Corporation), Epolite (registered trademark) 4000 (manufactured by Kyoeisha Chemical Co., Ltd.), ST-3000, ST-4000 (manufactured by Nippon Steel Chemical & Material Co., Ltd.), YX8000 (manufactured by Mitsubishi Chemical Corporation), EPALOY5000 (manufactured by HUNTSMAN), etc.

By using at least two of the above non-aromatic epoxy resins, the reactivity of the epoxy resin composition can be controlled, achieving a good balance between the rapid curing properties and pot life of the epoxy resin composition.

By including the above non-aromatic epoxy resin in an amount of 90% by mass or more relative to the total epoxy resin composition, high light resistance (UV resistance) can be achieved.

Component [B] is a pigment (average particle size 0.1 to 10 μm). Examples of pigments include barium sulfate, zinc sulfide, titanium oxide, molybdenum red, cadmium red, chromium oxide, titanium yellow, cobalt green, cobalt blue, ultramarine, barium titanate, carbon black, iron oxide, red phosphorus, and copper chromate. An average particle size of 0.1 to 10 μm, preferably 0.1 to 5 μm, and more preferably 0.3 to 5 μm, allows for the production of an epoxy resin composition with high UV blocking properties. The average particle size is measured using a laser diffraction scattering method with an LA-950 (manufactured by Horiba, Ltd.). The volumetric results measured using "Araldite (registered trademark)" GY282 (component: bisphenol F-type epoxy resin, manufactured by Huntsman Japan Co., Ltd.) are used as the dispersion medium, and the particle size distribution measured is determined by the particle size (median diameter) at 50% of the cumulative curve of the particle size distribution.

By including the above pigment in an amount of preferably 15 to 75 parts by mass, more preferably 25 to 55 parts by mass, and even more preferably 30 to 50 parts by mass, per 100 parts by mass of the total epoxy resin contained in the epoxy resin composition, a good balance can be achieved between the light-shielding properties of the cured resin and the adhesion between the epoxy resin composition of the present invention and a fiber-reinforced composite material preform when hand-applied.

Component [C] is a non-aromatic thermoplastic resin. Here, "aromatic" refers to a resin containing aromatic hydrocarbons, compounds with resonance structures, or conjugated unsaturated heterocyclic compounds in its chemical structure; all other resins are "non-aromatic." In other words, a non-aromatic thermoplastic resin refers to a thermoplastic resin that does not contain aromatic hydrocarbon groups or unsaturated heterocyclic rings in its chemical structure. Examples of non-aromatic thermoplastic resins include polyvinyl alcohol, polyvinyl acetal, polyvinyl formal, polyvinyl acetoacetal, polyvinyl butyral, polyvinyl acetate, hydrogenated bisphenol A-pentaerythritol phosphite polymer, hydrogenated terpene, and hydrogenated terpene phenol. Polyvinyl acetoacetal and polyvinyl butyral are preferred because they improve the elongation of the cured epoxy resin composition. Here, "elongation" refers to the bending strain (%) when the cured epoxy resin composition is three-point bent in a predetermined shape.

These non-aromatic thermoplastic resins are preferably soluble in the non-aromatic epoxy resin of component [A]. For example, if at least 10 parts by mass of thermoplastic resin powder is added to 100 parts by mass of the non-aromatic epoxy resin of component [A] and kneaded at 100 to 120°C for 1 hour, the thermoplastic resin powder is said to be soluble if it shows a weight loss from the initial weight. Weight loss refers to a decrease in the powder mass that is optically undetectable, or a decrease of 10% or more in mass from the initial weight when the remaining powder is recovered. From the perspective of dissolving in the epoxy resin, it is preferable that the thermoplastic resin powder have an average particle size of at least 100 μm as determined by laser diffraction. Furthermore, an average particle size of more than 100 nm is preferable, as it prevents aggregation during storage and makes mixing into the epoxy resin easier.

The above-mentioned non-aromatic thermoplastic resin may be a commercially available product. Examples include "J-POVAL (registered trademark)" (manufactured by Nippon Vinyl Acetate & Poval Co., Ltd.), "VINYLEC (registered trademark)" (manufactured by JNC Corporation), "S-LEC (registered trademark)" (manufactured by Sekisui Chemical Co., Ltd.), "ULTRATHENE (registered trademark)" (manufactured by Tosoh Corporation), JPH-3800 (manufactured by Johoku Chemical Industry Co., Ltd.), and YS Polystar UH130 (manufactured by Yasuhara Chemical Co., Ltd.). When the epoxy resin composition is applied as a spray to the surface of a fiber-reinforced composite material preform, it is preferable to include 0.05 parts by mass or more of the above-mentioned non-aromatic thermoplastic resin per 100 parts by mass of the total epoxy resin contained in the epoxy resin composition, as this will achieve a resin flow inhibition effect. Furthermore, when the epoxy resin composition is applied by hand to the surface of a fiber-reinforced composite material preform, by including preferably 75 parts by mass or less, more preferably 65 parts by mass or less, and even more preferably 55 parts by mass or less of the non-aromatic thermoplastic resin per 100 parts by mass of the non-aromatic epoxy resin [A], good adhesion between the coating agent made of the epoxy resin composition according to the present invention and the fiber-reinforced composite material preform can be achieved.

Furthermore, the molecular weight of these non-aromatic thermoplastic resins is preferably 5,000 to 70,000 g/mol, more preferably 7,000 to 65,000 g/mol, and even more preferably 10,000 to 60,000 g/mol, which allows for a good balance between uniform dissolution in the epoxy resin composition and resin flow suppression. Here, "molecular weight" refers to the weight-average molecular weight in terms of polystyrene measured by gel permeation chromatography using an HLC-8420GPC (manufactured by Tosoh Corporation).

Examples of commercially available products with different molecular weights include polyvinyl formal ("Vinylec (registered trademark)" K, manufactured by JNC Corporation, molecular weight 40,000 to 54,000 g/mol), polyvinyl formal ("Vinylec (registered trademark)" E, manufactured by JNC Corporation, molecular weight 95,000 to 134,000 g/mol), and polyvinyl acetoacetal ("S-LEC (registered trademark)" KS-10, manufactured by Sekisui Chemical Co., Ltd., molecular weight 17,000 g/mol).

Component [D] is a cationic curing agent or anionic curing agent. Examples of cationic curing agents include 1-naphthylmethylmethyl p-hydroxyphenylsulfonium hexafluoroantimonate, 2-methylbenzylmethyl p-hydroxyphenylsulfonium hexafluoroantimonate, benzylmethyl p-hydroxyphenylsulfonium hexafluoroantimonate, dimethyl-p-acetoxyphenylsulfonium hexafluoroantimonate, diaryliodonium salts, boron trifluoride piperidine, boron trifluoride monoethylamine, diaryliodonium salts, and sulfonium salts.

The above cationic curing agent may be a commercially available product. Examples include ADEKAOPTON (registered trademark) CP-77, ADEKAOPTON (registered trademark) CP-66 (manufactured by ADEKA Corporation), CI-2639, CI-2624 (Nippon Soda), SAN-AID (registered trademark) SI-60, SAN-AID (registered trademark) SI-80, SAN-AID (registered trademark) SI-100, SAN-AID (registered trademark) SI-150, SAN-AID (registered trademark) SI-B4, SAN-AID (registered trademark) SI-B5 (manufactured by Sanshin Chemical Industry Co., Ltd.), TA-100, IK-1PC (80) (manufactured by San-Apro Co., Ltd.), boron trifluoride piperidine, and boron trifluoride monoethylamine (manufactured by Stella Chemifa Corporation). The cationic curing agent is preferably a photothermal cationic curing agent or a thermal cationic curing agent. Photothermal cationic curing agents are those that become reactive when exposed to light below a certain wavelength, such as ultraviolet or visible light, or heat above a certain temperature, while thermal cationic curing agents are those that become reactive when exposed to heat. Photothermal cationic curing agents are preferred because they can be cured in a wide variety of environments, while thermal cationic curing agents are preferred because they can be stored with high temperature control.

Examples of anionic hardeners include phosphorus hexafluoride, antimony hexafluoride, arsenic hexafluoride, tin hexachloride, iron tetrachloride, bismuth pentachloride, and niobium hexachloride.

By using two types of curing agents, the reactivity of the epoxy resin composition can be controlled, achieving a good balance between the rapid curing properties and pot life of the epoxy resin composition.

By including the above curing agent in an amount of preferably 0.5 to 10 parts by mass, more preferably 1 to 5 parts by mass, and even more preferably 1 to 3 parts by mass per 100 parts by mass of the total epoxy resin contained in the epoxy resin composition, it is possible to achieve fast curing properties, suppress the resin flow and volatilization amount during molding, and obtain a good balance of fast curing properties, pot life, and UV resistance.

The epoxy resin composition of the present invention may also contain a thixotropy-imparting agent as component [E]. Examples of thixotropy-imparting agents include silicon dioxide, magnesium silicon sodium fluoride hydroxide oxide, alkyl quaternary ammonium salts, synthetic hectorite, clay minerals, modified bentonite, and mixtures of minerals and organically modified bentonite.

The above-mentioned thixotropy-imparting agent can be a commercially available product. Examples include fumed silica ("Aerosil (registered trademark)" (manufactured by Nippon Aerosil Co., Ltd.)), "OPTIGEL (registered trademark)", "OPTIBENT (registered trademark)", "GARAMITE (registered trademark)", "LAPONITE (registered trademark)", "TIXOGEL (registered trademark)", "CRAYTONE (registered trademark)", "CLOISITE (registered trademark)" (manufactured by BYK Corporation), "Somasif (registered trademark)" ME-100, and Micromica MK (manufactured by Katakura Co-op Agri Co., Ltd.).

By including the above-mentioned thixotropy-imparting agent in an amount of preferably 0.1 to 20 parts by mass, more preferably 0.5 to 10 parts by mass, and even more preferably 0.5 to 5 parts by mass, per 100 parts by mass of the total epoxy resin contained in the epoxy resin composition, a good balance can be achieved between the effect of suppressing resin flow during molding and the adhesion between the coating agent of the epoxy resin composition of the present invention and the fiber-reinforced composite material preform.

Furthermore, the epoxy resin composition of the present invention may contain a curing aid as component [F]. Examples of curing aids include 4-hydroxyphenyldimethylsulfonium methylsulfate and 4-(methylthio)phenol.

The above curing aids can be commercially available products, such as "SAN-AID (registered trademark)" SI-S and "SAN-AID (registered trademark)" S-ME (manufactured by Sanshin Chemical Industry Co., Ltd.).

By including the above curing aid in an amount of preferably 0.1 to 10 parts by mass, more preferably 0.1 to 5 parts by mass, and even more preferably 0.1 to 2.5 parts by mass per 100 parts by mass of the total epoxy resin contained in the epoxy resin composition, a good balance between the rapid curing properties and pot life of the epoxy resin composition can be achieved.

The epoxy resin composition of the present invention may contain rubber as component [G]. Examples of rubber include natural rubber, diene rubber, and non-diene rubber. Examples of diene rubber include styrene-butadiene rubber, isoprene rubber, butadiene rubber, chloroprene rubber, and acrylonitrile-butadiene rubber. Examples of non-diene rubber include butyl rubber, ethylene-propylene rubber, ethylene-propylene-diene rubber, urethane rubber, silicone rubber, and fluororubber. Non-diene rubber is preferred as a component contained in the epoxy resin composition of the present invention. Among these, ethylene-propylene rubber, ethylene-propylene-diene rubber, silicone rubber, and fluororubber, which do not have double bonds in the polymer backbone, are particularly preferred because they have high light resistance and little effect on the UV resistance of the epoxy resin composition of the present invention. Furthermore, powder-like rubber is particularly preferred because it disperses well in the epoxy resin composition.

When applying an epoxy resin composition as a spray, including 0.05 parts by mass or more of the above rubber per 100 parts by mass of all epoxy resins contained in the epoxy resin composition provides excellent resin flow inhibition and elongation of the cured epoxy resin composition, thereby preventing cracking after application. Here, elongation refers to the bending strain (%) when the cured epoxy resin composition is bent at three points in a specified shape, and spraying refers to a method in which the epoxy resin composition is filled into a container and sprayed in a mist or foam form using high-pressure air or mechanical movement with a nozzle. Including 0.05 to 1 part by mass of the above rubber per 100 parts by mass of all epoxy resins contained in the epoxy resin composition is preferred, as it maintains a large spray amount per given time and achieves a high resin flow inhibition effect.

When applying the epoxy resin composition by hand, the content of the rubber is preferably 1 to 50 parts by mass per 100 parts by mass of the total epoxy resin. Inclusion of 1 part by mass or more of rubber per 100 parts by mass of the total epoxy resin results in excellent resin flow suppression effects and excellent elongation of the epoxy resin composition after curing, thereby preventing cracking after application. Inclusion of 50 parts by mass or less results in excellent adhesion between the object and the epoxy resin composition. Hand application here refers to, for example, a method in which the epoxy resin composition is stored in a container, a brush or roller is dipped into the epoxy resin composition, and then the composition is applied to the object by hand using the brush or roller, or a method in which the epoxy resin composition is placed on the object and then spread using a spatula or bar coater.

The above rubbers can be commercially available products, and examples include KMP-598, KMP-600, KMP-601, KMP-602, and KMP-605 (manufactured by Shin-Etsu Chemical Co., Ltd.), "Cevian (registered trademark)" (manufactured by Daicel Miraize Co., Ltd.), JSR N215SL, JSR N222SH, JSR N238H, JSR N241H, JSR N250S, PN30A, PN20HA, and N280 (manufactured by JSR Corporation).

The epoxy resin composition of the present invention can be applied to the outermost surface of prepregs, RTM materials, and resin film infusion (RFI) materials used in fiber-reinforced composite materials (also referred to as "fiber-reinforced composite precursors" in the present invention), as well as semi-cured or fully cured composite materials (referred to as "fiber-reinforced composite preforms" in the present invention). The resin applied to the surface layer can be photocured using a light source, and then, if necessary, the epoxy resin layer applied to the surface layer can be post-cured using heat, or the uncured resin contained in the fiber-reinforced composite preform can be cured. (In the present invention, the product obtained by applying the epoxy resin composition to the surface of a "fiber-reinforced composite preform" and photocuring the epoxy resin composition is referred to as a "fiber-reinforced composite intermediate," and the product obtained by further curing the "fiber-reinforced composite intermediate" is referred to as a "fiber-reinforced composite material.") Here, prepreg refers to a fiber-reinforced composite material precursor formed by impregnating reinforcing fibers with a thermosetting resin such as an epoxy resin. RTM materials refer to fiber-reinforced composite material precursors formed by stacking reinforcing fiber substrates in a mold and injecting a liquid thermosetting resin into the reinforcing fiber substrate. RFI materials refer to fiber-reinforced composite material precursors formed by layering a thermosetting resin film on a reinforcing fiber substrate and then heating and pressurizing the resulting laminate to impregnate the reinforcing fiber substrate with the thermosetting resin. A fiber-reinforced composite material preform with a degree of cure of 0 to 70% is preferred because the resin contained in the fiber-reinforced composite material preform is not yet fully cured, allowing for chemical bonding with the coating agent comprised of the epoxy resin composition of the present invention, improving adhesion between the coating agent and the fiber-reinforced composite material preform. For fiber-reinforced composite material preforms with a degree of cure exceeding 70%, it is preferable to roughen the surface by polishing or plasma treatment, thereby physically improving adhesion between the coating agent and the fiber-reinforced composite material preform. A degree of cure of 20 to 100% is preferable because it makes it possible to reduce the amount of resin contained in the fiber-reinforced composite material preform that is mixed with a coating agent made from the epoxy resin composition of the present invention during molding. Therefore, a degree of cure of 20 to 70% is even more preferable in order to achieve a good balance between the adhesion between the coating agent in the fiber-reinforced composite material and the fiber-reinforced composite material preform and the effect of reducing the amount of resin contained in the fiber-reinforced composite material preform that is mixed with a coating agent made from the epoxy resin composition of the present invention during molding.

The epoxy resin composition of the present invention is applied to a fiber-reinforced composite material preform, photocured, and then thermally cured to produce a fiber-reinforced composite material with UV resistance on the surface. However, the epoxy resin composition may be applied by spraying, or by hand application using a brush or bar coater. Furthermore, after hand application, it is possible to enhance adhesion between the epoxy resin composition of the present invention and the fiber-reinforced composite material preform by using a release film or vacuuming.

The epoxy resin composition of the present invention can be applied to a target object using a variety of methods. For example, the epoxy resin composition can be dissolved in an organic solvent selected from acetone, methyl ethyl ketone, and methanol to reduce viscosity, or the epoxy resin composition can be used as is and sprayed onto a fiber-reinforced composite material preform. It is also possible to immerse a roller or brush in the epoxy resin composition of the present invention and apply it to a fiber-reinforced composite material preform. Furthermore, the epoxy resin composition of the present invention can be applied to a fiber-reinforced composite material preform using a bar coater or spatula. In either method, the epoxy resin composition can be heated as needed to reduce its viscosity before application.

As described above, the epoxy resin composition of the present invention can be applied to an object by any method, but the preferred application method varies depending on the room-temperature viscosity of the epoxy resin composition. When the room-temperature viscosity of the epoxy resin composition is 100 to 500 mPa·s, application by spraying is preferred. When applying by spraying, if the room-temperature viscosity is 100 mPa·s or higher, resin flow at room temperature can be suppressed and the thickness of the coating agent can be maintained uniform, while if the room-temperature viscosity is 500 mPa·s or lower, the epoxy resin composition can be applied without clogging when sprayed, improving workability.

When the room temperature viscosity of the epoxy resin composition according to the present invention is 0.5 to 30 Pa·s, hand application using a roller, brush, etc. is preferred. When applying using a brush, roller, etc., a room temperature viscosity of the epoxy resin composition of 0.5 Pa·s or more is preferred as this can prevent sagging during application, and a room temperature viscosity of 30 Pa·s or less improves workability as the brush, roller, etc. can be easily immersed in the epoxy resin composition.

When the room temperature viscosity of the epoxy resin composition according to the present invention is 30 to 30,000 Pa·s, hand application using a spatula, bar coater, or the like is preferred. When applying by hand, a room temperature viscosity of 30 Pa·s or more is preferred because it effectively inhibits resin flow during molding. Furthermore, a room temperature viscosity of 30,000 Pa·s or less is preferred because it provides strong adhesion between the epoxy resin composition and the fiber-reinforced composite material preform, thereby enhancing the adhesion between the coating agent in the fiber-reinforced composite material and the fiber-reinforced composite material preform.

The basis weight of the epoxy resin composition according to the present invention when applied to a fiber-reinforced composite material preform is preferably 30 to 300 g/ ^m2 . When the basis weight of the epoxy resin composition is 30 g/ ^m2 or more, the surface of the fiber-reinforced composite material can be covered without being visible through the composition, and sufficient UV resistance can be exhibited. Furthermore, when the basis weight of the epoxy resin composition is 300 g/ ^m2 or less, heat generation due to curing of the epoxy resin composition can be suppressed when the epoxy resin composition is molded together with the fiber-reinforced composite material preform, which is preferable.

The manufacturing method of the present invention is characterized by applying the epoxy resin composition of the present invention to the surface of a fiber-reinforced composite material preform, such as prepreg, RTM material, or RFI material, and then photocuring the applied epoxy resin composition. Various carbon fibers, graphite fibers, glass fibers, aramid fibers, and the like are preferably used as reinforcing fibers for the fiber-reinforced composite material preform. Producing a fiber-reinforced composite material using this method is advantageous in that it enables the amount of resin contained in the fiber-reinforced composite material preform, which is mixed with a coating agent made of the epoxy resin composition of the present invention during the molding process, to be reduced. Furthermore, the fiber-reinforced composite material preform produced using this method can be fully cured by pressure and heat treatment, resulting in a fiber-reinforced composite material with UV resistance on the surface.

Various methods are used to adjust the degree of cure of fiber-reinforced composite material preforms. When using prepregs, for example, they can be molded by heating and pressure using methods such as press molding, autoclave molding, bagging, wrapping tape, internal pressure molding, and pultrusion. Various known methods are also used to adjust the degree of cure of RTM materials. Methods include the VaRTM method, in which resin is injected under vacuum pressure to suit the characteristics of the thermosetting resin used in the RTM material, and the HP-RTM method, in which resin is injected under high pressure. The degree of cure is controlled by the pretreatment temperature and time. When controlling the degree of cure, using a multi-stage process in which the curing temperature is changed in stages allows for more stable control of the degree of cure and is preferable from the perspective of reducing voids in the fiber-reinforced composite material. The degree of cure of RTM materials can also be controlled by heating them in an oven after demolding. A degree of cure of the fiber-reinforced composite preform of 30 to 70% is preferred as this increases adhesion between the coating agent in the fiber-reinforced composite material and the fiber-reinforced composite preform, while a degree of cure of 80 to 100% is preferred as it reduces the likelihood of distortion during post-curing.

A variety of known post-curing methods can be used, but preferred methods include heating in an autoclave, oven, or press, and applying pressure as needed. Post-curing can be carried out in a metal, FRP, plaster, or wooden mold, or in a freestanding manner without a mold. The curing temperature depends on the curing agent and curing catalyst used in the resin of the fiber-reinforced composite material preform, but a temperature of 100 to 200°C is preferred from the perspective of suppressing distortion and wrinkles due to thermal stress and maintaining adhesion between the resin layer applied as the outermost layer and the fiber-reinforced composite material preform.

After applying the coating agent, scraping off any excess coating agent that drips with a spatula or similar tool will have a positive effect on the surface quality after molding. Furthermore, by roughening the surface of the fiber-reinforced composite material preform, whose degree of cure has been adjusted by pretreatment before UV curing the coating agent, by polishing or plasma treatment, it is possible to improve the adhesion between the coating agent and the fiber-reinforced composite material preform, as well as the adhesion between the coating agent and the fiber-reinforced composite material preform in the fiber-reinforced composite. Furthermore, by roughening the surface of the coating agent after photo-curing treatment by polishing or plasma treatment, it is possible to improve the adhesion between the coating agent and the paint or primer that covers it.

The present invention will be described in detail below using examples. However, the scope of the present invention is not limited to these examples. Furthermore, measurements of various properties were carried out in an environment of 23°C and 50% relative humidity unless otherwise noted.

<Materials used in Examples and Comparative Examples>
(1) Component [A] Non-aromatic epoxy resin
(3',4'-epoxycyclohexane)methyl 3,4-epoxycyclohexanecarboxylate ("Celloxide (registered trademark)" 2021P, manufactured by Daicel Corporation) Epoxy equivalent: 136 (g/eq.)
Diglycidyl ether of 2,2-bis(4-hydroxycyclohexyl)propane (YX8000, manufactured by Mitsubishi Chemical).

(2) Component [B] Pigment: Titanium oxide (rutile type) (“Ti-Pure (registered trademark)” R-960, manufactured by Chemours, Inc., average particle size 0.5 μm).

(3) Component [C] Non-aromatic thermoplastic resin - polyvinyl formal ("Vinylec K (registered trademark)", manufactured by JNC Corporation).

(4) Component [D] Cationic curing agent: dimethyl-p-acetoxyphenylsulfonium hexafluoroantimonate "Sanaid (registered trademark)" SI-150, manufactured by Sanshin Chemical Industry Co., Ltd.

(5) Fiber-reinforced composite material preform: T300/3631-2 woven fabric (plain weave) prepreg (manufactured by Toray Industries, Inc.)
- T300 fabric (plain weave) (manufactured by Toray Industries, Inc.).

(6) Component [E] Thixotropy-imparting agent: fumed silica ("AEROSIL (registered trademark)" RY200S, manufactured by Nippon Aerosil Co., Ltd.).

(7) Component [F] Curing aid: 4-hydroxyphenyldimethylsulfonium methyl sulfate ("Sanaid (registered trademark)" SI-S, manufactured by Sanshin Chemical Industry Co., Ltd.).

(8) Component [G] Rubber/Silicone rubber powder (KPM-601, manufactured by Shin-Etsu Chemical Co., Ltd.).

<Methods for producing and evaluating epoxy resin compositions and fiber-reinforced composite materials>
Epoxy resin compositions and fiber-reinforced composite materials of the respective Examples and Comparative Examples were prepared by the following methods, and various measurements were carried out.

(1) Preparation of Epoxy Resin Compositions An epoxy resin corresponding to component [A] listed in Tables 1 to 8, a pigment corresponding to component [B], and, if necessary, a thixotropy-imparting agent [E] and a rubber [G] were charged into a three-roll mill and mixed at an arbitrary roll rotation speed to obtain a powder mixture preliminarily. The powder mixture preliminarily and a thermoplastic resin corresponding to component [C] listed in Tables 1 to 5 were charged into a mixer, and heated and mixed to dissolve the thermoplastic resin. Next, while continuing the kneading, the temperature was lowered to 60°C or less, and component [D] a cationic curing agent listed in Tables 1 to 8 and, if necessary, component [F] a curing aid were added and stirred to obtain an epoxy resin composition.

(2) Adjustment of the degree of cure of the fiber-reinforced composite material preform A six-ply laminate of T300/3631-2 woven fabric (plain weave) prepreg was prepared as a fiber-reinforced composite material precursor, and the degree of cure of the prepreg was adjusted by placing it in an oven at 180° C. for a certain period of time. In addition, a six-ply laminate (also referred to as a "preform" in the present invention) was prepared as an RTM material by preforming T300 woven fabric (plain weave) in a mold. A preform was formed in a molding die, and a resin composition (also referred to as "Resin A" in the present invention) prepared by mixing 100 parts by mass of triglycidyl-m-aminophenol ("Araldite (registered trademark)" MY0600, manufactured by Huntsman Corporation, epoxy equivalent 118) and diethyltoluenediamine ("jER (registered trademark)" Cure W, manufactured by Mitsubishi Chemical Corporation, amine equivalent 68) so that the ratio of epoxy equivalent to amine equivalent was 1.0 was poured into the mold, and the resin composition was poured into the preform at 60°C to obtain an RTM material. The obtained RTM material was placed in an oven at 180°C for a certain period of time to adjust the degree of cure of the RTM material.

(3) Measurement of degree of cure of fiber-reinforced composite material preliminary product The degree of cure of the fiber-reinforced composite material preliminary product was calculated from the heat release value of an exothermic curve obtained using a differential scanning calorimeter (DSC Q2500: manufactured by TA Instruments Co., Ltd.) at a temperature rise rate of 5°C/min in a nitrogen atmosphere. The heat release value of the fiber-reinforced composite material precursor before being placed in the 180°C oven in (2) above was defined as W1 (mW/g), and the heat release value of the fiber-reinforced composite material preliminary product after being placed in the 180°C oven was defined as W2 (mW/g), and the degree of cure was calculated using the following formula:
W2/W1×100 [%].

(4) Surface Treatment of Fiber-Reinforced Composite Material Preliminary Body The surface of the fiber-reinforced composite material preliminary body was treated (polished) as desired. The surface treatment was carried out by manually pressing water-resistant abrasive paper C34P #400 (manufactured by Riken Corundum Co., Ltd.) against the surface of the fiber-reinforced composite material preliminary body and reciprocating five times.

(5) Method of applying epoxy resin composition to a fiber-reinforced composite material preform When applying the epoxy resin composition by spraying, a spray gun W-2001-2 (manufactured by Anest Iwata Corporation) was used to spray the epoxy resin composition onto the surface of the fiber-reinforced composite material preform so that the coating thickness was 80 μm.

When applying the epoxy resin composition by hand using a brush, the epoxy resin composition was collected in a container, the brush was dipped into it, and then the composition was applied directly to the target to a thickness of 80 μm.

When applying the epoxy resin composition by hand using a bar coater, the epoxy resin composition was placed on the surface to be coated and then spread with the bar coater to coat the surface to a thickness of 80 μm.

(6) Curing of Coating Agent by UV Irradiation Using a Toskure 401 (manufactured by Toshiba Lighting & Technology), the coating agent was irradiated with UV light at an energy density of 70 mW/ ^cm for 1 minute, and the coating agent applied to the surface of the fiber-reinforced composite material preliminary body in (5) above was UV-cured to obtain a fiber-reinforced composite material intermediate.

(7) Heat curing of the material obtained by applying the coating agent to the fiber-reinforced composite preliminary body and photo-curing the material The fiber-reinforced composite preliminary body obtained in (6) above was heat cured. The fiber-reinforced composite preliminary body consisting of a prepreg laminate was heat cured in an autoclave under conditions of 6 atmospheres, 180°C for 2 hours with a temperature increase rate of 1.7°C/min, and the fiber-reinforced composite preliminary body consisting of an RTM material was heat cured in an oven under conditions of 180°C for 2 hours with a temperature increase rate of 1.7°C/min.

(8) Adhesion between coating agent and fiber-reinforced composite material preform after heat curing Repair tape ("Scotch (registered trademark)" DUCT-TP18, manufactured by 3M Co.) was applied to an area of 48 mm x 80 mm on the surface of the coating agent of the fiber-reinforced composite material obtained by heat curing in (7) above, and after leaving it to stand for 5 minutes on a 10 cm square aluminum plate, the tape was peeled off. If even a part of the coating agent adhered to the adhesive surface of the tape, the adhesion between the coating agent in the fiber-reinforced composite material and the fiber-reinforced composite material preform was judged to be "poor", and if there was no adhesion, it was judged to be "good".

(9) Amount of resin in the fiber-reinforced composite preparatory body mixed into the epoxy resin composition during molding: The coating agent side of the fiber-reinforced composite material prepared in (7) above was subjected to IR measurement using the ATR method (FT/IR-4000 manufactured by JASCO Corporation, prism: diamond, measurement wavelength: 400 to 4000 cm ⁻¹ , number of integrations: 16). Normalization was performed using the peak at 1715 cm ⁻¹ indicating the ester, and the value of the peak at 1592 cm ⁻¹ indicating the benzene ring derived from the cured resin used in the fiber-reinforced composite preparatory body was evaluated. This made it possible to evaluate the amount of resin used in the fiber-reinforced composite preparatory body that mixed with the coating agent during molding and was exposed to the surface of the fiber-reinforced composite material. If the value of the peak at 1592 cm ⁻¹ indicating the benzene ring derived from the cured resin used in the fiber-reinforced composite preparatory body was 0.6 or less, the UV resistance of the surface of the fiber-reinforced composite material was determined to be good. In addition, for Examples 61 to 64, IR measurement was performed by the ATR method in the same manner as above, and normalization using the peak at 1715 cm ^-1 indicating the ester was not performed, but the value of the peak at 1592 cm ^-1 indicating the benzene ring originating from the cured resin used in the fiber-reinforced composite material preparatory body was evaluated. In this case, if the value of the peak at 1592 cm ^-1 indicating the benzene ring originating from the cured resin used in the fiber-reinforced composite material preparatory body was 1.0 or less, the UV resistance of the surface of the fiber-reinforced composite material was determined to be good.

<Examples 1 to 22>
In Examples 1 to 22, the surface of the prepreg with the adjusted degree of cure was left untreated or polished, and a coating agent consisting of a UV-resistant epoxy resin composition was applied. The coating agent was then cured by UV irradiation and finally heat-cured in an autoclave. Examples 1 to 22 were judged to be good in terms of the amount of prepreg resin mixed into the coating agent during thermoforming. Furthermore, the higher the degree of cure of the prepreg before coating, the greater the effect of suppressing the amount of prepreg resin mixed into the coating agent during thermoforming, and this effect was particularly high in Examples 5 to 22.

In Examples 1 to 14, the adhesion between the coating agent and the fiber-reinforced composite material preform after heat curing was judged to be good. On the other hand, of Examples 15 to 22, Examples 15, 17, 19, and 21, in which the prepreg was not surface-polished before coating was applied, were judged to have poor adhesion between the coating agent in the fiber-reinforced composite material and the fiber-reinforced composite material preform, while Examples 16, 18, 20, and 22, in which the fiber-reinforced composite material preform was surface-polished, were judged to have good adhesion between the coating agent in the fiber-reinforced composite material and the fiber-reinforced composite material preform.

<Examples 23 to 44>
In Examples 23 to 44, the surface of the RTM material with an adjusted degree of cure was left untreated or polished, and a coating agent consisting of a UV-resistant epoxy resin composition was applied. The coating agent was then cured by UV irradiation and finally thermally cured in an oven. Examples 23 to 44 were judged to be good in terms of the amount of resin in the RTM material that was mixed into the coating agent during thermoforming. Furthermore, the higher the degree of cure of the RTM material before application, the greater the effect of suppressing the amount of resin in the RTM material that was mixed into the coating agent during thermoforming, and this effect was particularly high in Examples 27 to 44.

In Examples 23 to 44, the adhesion between the coating agent and the fiber-reinforced composite material after heat curing was judged to be good. On the other hand, of Examples 37 to 44, Examples 37, 39, 41, and 43, in which the RTM material was not surface-polished before the coating agent was applied, were judged to have poor adhesion between the coating agent and the fiber-reinforced composite material prep, while Examples 38, 40, 42, and 44, in which the fiber-reinforced composite material prep was surface-polished, were judged to have good adhesion between the coating agent and the fiber-reinforced composite material prep.

<Comparative Examples 1 and 2>
In Comparative Examples 1 and 2, a coating agent made of a UV-resistant epoxy resin composition was applied to the surface of an untreated prepreg or RTM material, and then the coating agent was not cured by UV irradiation, but the prepreg was thermally cured in an autoclave and the RTM material in an oven. In Comparative Examples 1 and 2, the adhesion between the coating agent in the fiber-reinforced composite material and the fiber-reinforced composite material preform was judged to be good, but the amount of resin from the prepreg or RTM material that was mixed into the coating agent during thermoforming was too high, and the results were judged to be poor.

<Examples 45 to 54>
In Examples 45 to 54, a coating agent consisting of a UV-resistant epoxy resin composition was applied to the surface of a prepreg with an adjusted degree of cure using a brush or bar coater, and then the coating agent was cured by UV irradiation and finally heat-cured in an autoclave. In Examples 45 to 54, the amount of prepreg resin mixed into the coating agent during thermoforming was judged to be good. It was also shown that the higher the degree of cure of the prepreg before coating, the greater the effect of suppressing the amount of prepreg resin mixed into the coating agent during thermoforming.

<Examples 50, 52, 55 to 64>
In Examples 55 to 64, a coating agent consisting of a UV-resistant epoxy resin composition was applied to the surface of a prepreg with an adjusted degree of cure using a bar coater, and then the coating agent was cured by UV irradiation and finally heat-cured in an autoclave. In Examples 55 to 64, the amount of prepreg resin mixed into the coating agent during thermoforming was judged to be good. It was also shown that the higher the degree of cure of the prepreg before coating, the greater the effect of suppressing the amount of prepreg resin mixed into the coating agent during thermoforming.

In Examples 55-56, component [E] a thixotropy-imparting agent was added to the epoxy resin compositions described in the corresponding Examples 50 and 52, respectively. Comparing Examples 55-56 with Examples 50 and 52, it was shown that Examples 55-56 reduced the amount of prepreg resin mixed into the coating during the thermoforming process.

In Examples 57-58, component [F] curing aid was added to the epoxy resin compositions described in the corresponding Examples 50 and 52, respectively. Comparing Examples 57-58 with Examples 50 and 52, it was observed that the addition of the curing aid increased the amount of prepreg resin mixed into the coating during the thermoforming process, but the evaluation was favorable. Component [F] curing aid has the effect of suppressing the curing reaction and improving processability when preparing the epoxy resin composition, demonstrating that it is possible to control the amount of prepreg resin mixed into the coating during the thermoforming process so as to achieve both processability and compatibility.

In Examples 59-60, component [G] rubber was added to the epoxy resin compositions described in the corresponding Examples 50 and 52, respectively. Comparing Examples 59-60 with Examples 50 and 52, it was shown that Examples 59-60 reduced the amount of prepreg resin mixed into the coating during the thermoforming process.

Examples 61 and 62 contain two types of non-aromatic epoxy resin (component [A]). Compared to the corresponding Examples 50 and 52, the inclusion of two types of component [A] resulted in an increase in the amount of resin in the prepreg that was mixed into the coating during the thermoforming process, but the evaluation was favorable.

Examples 63 and 64 contained two types of component [A] and added component [E], a thixotropy-imparting agent, component [F], and [G], rubber. The inclusion of two types of component [A] and the addition of component [F], a curing aid, increased the amount of resin in the prepreg mixed into the coating during the thermoforming process, as observed in Examples 57-58 and 61-62. However, the effect of adding component [E], a thixotropy-imparting agent, and component [G], rubber, which reduced the amount of resin in the prepreg mixed into the coating during the thermoforming process, was greater in Examples 55-56 and 59-60, demonstrating that it is possible to suppress the amount of resin in the prepreg mixed into the coating during the thermoforming process.

<Comparative Examples 3 and 4>
In Comparative Examples 3 and 4, a coating agent made of a UV-resistant epoxy resin composition was applied to the surface of an untreated prepreg, and then the coating agent was thermally cured in an autoclave without being cured by UV irradiation. In Comparative Examples 3 and 4, the adhesion between the coating agent in the fiber-reinforced composite material and the fiber-reinforced composite material preform was judged to be good, but the amount of prepreg resin that was mixed into the coating agent during thermoforming was large, and the results were judged to be poor.

Claims (12)

A method for producing a fiber-reinforced composite material intermediate, comprising applying an epoxy resin composition containing the following components [A] to [D], wherein the component [B] is present in an amount of 15 to 75 parts by mass per 100 parts by mass of the total epoxy resins contained in the epoxy resin composition, to the surface of a fiber-reinforced composite material preform, and then photocuring the epoxy resin composition:
[A] Non-aromatic epoxy resin [B] Pigment with an average particle size of 0.1 to 10 μm [C] Non-aromatic thermoplastic resin [D] Cationic or anionic polymerization curing agent The method for producing a fiber-reinforced composite material intermediate according to claim 1, wherein the epoxy resin composition further contains component [E] a thixotropy-imparting agent. The method for producing a fiber-reinforced composite material intermediate according to claim 1 or 2, wherein the epoxy resin composition further contains component [F] a curing aid. The method for producing a fiber-reinforced composite material intermediate according to any one of claims 1 to 3 , wherein the epoxy resin composition contains at least two types of non-aromatic epoxy resins as component [A]. 5. The method for producing a fiber-reinforced composite material intermediate according to claim 1 , wherein the epoxy resin composition is applied to the surface of the fiber-reinforced composite material preliminary body by spraying or hand painting. 6. The method for producing a fiber-reinforced composite material intermediate according to claim 1, wherein the degree of cure of the fiber-reinforced composite material preliminary body is adjusted to more than 70 % before applying the epoxy resin composition, and then the surface of the fiber-reinforced composite material preliminary body is polished before applying the epoxy resin composition. 6. The method for producing a fiber-reinforced composite material intermediate according to claim 1 , wherein the surface of the fiber-reinforced composite material preliminary body is subjected to a plasma surface treatment before the epoxy resin composition is applied. 8. The method for producing a fiber-reinforced composite material intermediate according to claim 1 , wherein after the epoxy resin composition is photocured, the surface of the cured epoxy resin composition is polished. 8. The method for producing a fiber-reinforced composite material intermediate according to claim 1 , wherein after photocuring the epoxy resin composition, the surface of the cured product of the epoxy resin composition is subjected to plasma surface treatment. The method for producing a fiber-reinforced composite material intermediate according to any one of claims 1 to 9 , wherein the reinforcing fibers are carbon fibers. The method for producing a fiber-reinforced composite material intermediate according to any one of claims 1 to 5 and 7 to 10 , wherein the degree of cure of the fiber-reinforced composite material pre-body is adjusted to 20 to 70% before applying the epoxy resin composition. A method for producing a fiber-reinforced composite material, further comprising thermally post-curing the fiber-reinforced composite material intermediate produced by the method for producing a fiber-reinforced composite material intermediate according to any one of claims 1 to 11 .