WO2019202762A1

WO2019202762A1 - Prepreg and fiber-reinforced composite material using same

Info

Publication number: WO2019202762A1
Application number: PCT/JP2018/041317
Authority: WO
Inventors: 周平吉田; 隆西島
Original assignee: Jnc株式会社
Priority date: 2018-04-20
Filing date: 2018-11-07
Publication date: 2019-10-24
Also published as: TW201943772A

Abstract

[Problem] To provide a prepreg having both high elastic modulus and high strength with respect to the tensile, compressive, and bending properties of a fiber-reinforced composite material, and a fiber-reinforced composite material using the prepreg. [Solution] A prepreg obtained by impregnating reinforcing fibers with a resin composition containing as main components the following [A], [B], [C], and amine curing agent [D], in which components [A], [B], and [C] are 1-20 weight parts, 45-80 weight parts, and 20-55 weight parts, respectively; [A] carboxyl group-containing polyvinyl formal resin, [B] epoxy resin that is solid at 25°C, [C] epoxy resin that is liquid at 25°C.

Description

Prepreg and fiber-reinforced composite material using the same

The present invention relates to a prepreg and a fiber reinforced composite material.

Fiber reinforced composite materials formed by laminating prepregs impregnated with matrix resin on unidirectional alignment sheets such as carbon fibers and woven fabrics are widely used in sports and leisure fields such as golf shafts, fishing rods, and racket frames. Yes. In recent years, its use has expanded in the industrial field such as automobiles and the aerospace field.

Until now, for the purpose of improving the properties of the epoxy resin which is a matrix resin, a resin composition containing an epoxy resin and a thermoplastic resin such as polyvinyl butyral resin has been used. However, since polyvinyl butyral has poor compatibility with the epoxy resin, phase separation may occur when the composition is cured, and the strength may be lowered. In contrast, a fiber reinforced composite material obtained by laminating a prepreg containing a polyvinyl formal-containing resin composition can suppress phase separation to some extent, and the tensile strength at 90 ° with respect to the fiber direction is improved. Is known (Patent Document 1).

Patent Document 2 discloses that a thermoplastic resin is added to a prepreg for the purpose of controlling resin flow during molding and imparting toughness to a cured resin. In Patent Document 2, a phenoxy resin is listed as a thermoplastic resin in addition to polyvinyl formal. Patent Document 3 describes that when a fiber reinforced composite material is used for a tubular molded body such as a fishing rod or a golf shaft, polyvinyl formal or phenoxy resin is suitably used as a thermoplastic resin suitable for improving properties such as crushing strength. Yes.

Carbon fiber composite material (CFRP) is required to be improved in strength and elastic modulus because it is used in the form of a thin plate as a member of sporting goods, industrial goods, etc. for reasons such as weight reduction and reduction in production cost.

Conventionally, there is no example in which a thermoplastic resin added to a CFRP matrix resin has both high strength and high elasticity in tensile, compression and bending properties. Polyvinyl formal, one of the thermoplastic resins added to the CFRP matrix resin, has the drawback of increasing the strength of CFRP with respect to tensile properties while lowering the elastic modulus.

JP-A-62-169829 Japanese Patent Laid-Open No. 2017-2202 International Publication No. 1998/044017

An object of the present invention is to provide a prepreg having both high elastic modulus and high strength with respect to tensile, compression, and bending properties of a fiber reinforced composite material and imparting impact resistance, and a fiber reinforced composite material using the prepreg. It is.

Conventionally, polyvinyl formal added to a matrix resin (epoxy resin) of a carbon fiber composite material has a drawback that the elastic modulus is lowered even if the strength of the composite material is increased in terms of tensile and bending properties. Furthermore, in addition to these characteristics, it did not have impact resistance. Therefore, as a result of intensive investigations aimed at improving not only tensile properties but also bending and compression properties as well as high strength and high elastic modulus and improving impact resistance, the present inventors reacted with the oxiranyl group of the epoxy resin, and the carbon fiber surface It was found that any of the above problems can be solved by preparing a prepreg using a polyvinyl formal introduced with a carboxyl group that interacts with an oxygen-containing functional group such as a hydroxyl group or a carboxyl group of the present invention, and the present invention has been completed.

The configuration of the present invention is as follows.
[1] The following [A], [B], [C] and an amine curing agent [D] are contained as main components, and each component of [A], [B], [C] is 1 to 20 parts by weight. Prepregs obtained by impregnating reinforcing fibers with a resin composition of 45 to 80 parts by weight and 20 to 55 parts by weight;
[A] Carboxyl group-containing polyvinyl formal resin [B] Epoxy resin solid at 25 ° C. [C] Epoxy resin liquid at 25 ° C.
[2] The prepreg of [1], wherein the carboxyl group-containing polyvinyl formal resin [A] includes structural units a, b, c, and d.

(In the formula of the structural unit d, R ¹ is independently hydrogen or alkyl having 1 to 5 carbons.)
[3] The prepreg of [1] or [2], wherein the softening point of the solid epoxy resin [B] is 60 ° C. or higher.
[4] The prepreg of [1] to [3], wherein the liquid epoxy resin [C] is liquid at 150 ° C.
[5] The prepreg of [1] to [4], wherein the amine curing agent [D] is dicyandiamide or a derivative thereof.
[6] The prepreg according to [1] to [5], wherein the reinforcing fiber is any one of carbon fiber, aramid fiber, glass fiber, graphite fiber, silicon carbide fiber, boron fiber, alumina fiber, and stainless steel fiber. .
[7] The reinforcing fiber is a carbon fiber, the tensile strength of the carbon fiber is 4.4 to 6.5 GPa, the tensile elongation is 1.7 to 2.3%, and the tensile modulus is 230 to 400 GPa. Some [1] to [6] prepregs.
[8] The amine curing agent [D] is in the range of 1 to 10 parts by weight with respect to 100 parts by weight of the total epoxy resin component including the solid epoxy resin [B] and the liquid epoxy resin [C]. The prepreg described in [7].
[9] The impregnation amount of the reinforcing fiber in the prepreg is 40 to 90% as a fiber volume content (Vf) when the volume of the prepreg including the reinforcing fiber is 100 vol%. [1] to [8 ] Prepreg.
[10] A fiber-reinforced composite material using the prepreg of [1] to [9].

Fiber reinforced composites made by laminating prepregs with carboxyl group-containing polyvinyl formal added to other thermoplastic resins or conventional fiber reinforced composite materials containing polyvinyl formal in tensile, compression and bending properties. It showed high elastic modulus, high strength, and impact resistance.

The change of the viscosity by the temperature of the resin composition prepared by the Example and the comparative example is shown. The electron micrograph of the bending test piece fracture surface evaluated in the Example and the comparative example is shown. The electron micrograph which shows the pulling-out of the carbon fiber in the tensile fracture surface of the bending test piece fracture surface evaluated by the Example and the comparative example is shown. The electron micrograph which observed the adhesion state of the resin between carbon fiber-resin in the 90 degree tensile test fracture surface evaluated by the Example and the comparative example is shown.

Embodiments of the present invention will be specifically described below, but the present invention is not limited to these descriptions.

The prepreg according to the present invention contains the following [A], [B], [C] and an amine curing agent [D] as main components, and each component of [A], [B], [C] is 1 each. The reinforcing fiber is impregnated with a resin composition of ˜20 parts by weight, 45 to 80 parts by weight, and 20 to 55 parts by weight.

[A] Carboxyl group-containing polyvinyl formal resin [B] Solid epoxy resin [C] Liquid epoxy resin
Resin Composition The resin composition contains a carboxyl group-containing polyvinyl formal resin as component [A], a solid epoxy resin as component [B], and a liquid epoxy resin as component [C]. Component [C] may contain a reactive diluent.

In the resin composition, the content of the carboxyl group-containing polyvinyl formal resin of component [A] is 1 to 20 parts by weight, preferably 3 to 10 parts by weight. More preferably, it is 4 to 7 parts by weight.

When the content of the carboxyl group-containing polyvinyl formal resin of component [A] is 1 part by weight or more, not only is it dissolved in the matrix resin constituting the prepreg, but also when the prepreg is laminated and heat-cured to form a fiber-reinforced composite material In addition, the carboxyl group of the carboxyl group-containing polyvinyl formal is cross-linked with the epoxy resin on the one hand, and the other is interacted with oxygen-containing functional groups such as hydroxyl groups and carboxyl groups on the carbon fiber surface, thereby toughening the composite material. The If the content of the carboxyl group-containing polyvinyl formal resin of component [A] is 20 parts by weight or less, the resin can be sufficiently applied to the release paper, and the reinforced fiber can be well impregnated with the resin when preparing the prepreg. .

The content of the solid epoxy resin of component [B] is 45 to 80 parts by weight, preferably 50 to 60 parts by weight. If the content of the solid epoxy resin of component [B] is 45 parts by weight or more, the tackiness of the prepreg will be good, and if it is 80 parts by weight or less, the resin will be poorly applied to the release paper due to viscosity increase or the prepreg It is possible to prevent poor impregnation of the reinforcing fibers.

The content of the liquid epoxy resin of the component [C] is 20 to 55 parts by weight, preferably 40 to 50 parts by weight. If the content of the liquid epoxy resin of component [C] is 55 parts by weight or less, the compatibility with the carboxyl group-containing polyvinyl formal and the tackiness of the prepreg will be good, and the impact resistance by improving the crosslink density of the liquid epoxy resin There will be no decline. If it is 20 parts by weight or more, it is possible to prevent poor coating of the resin to the release paper due to viscosity increase and poor impregnation of the reinforcing fibers during prepreg.

Hereinafter, each component will be described.

Component [A] Carboxy Group-Containing Polyvinyl Formal Resin The carboxyl group-containing polyvinyl formal resin of component [A] preferably has structural units a, b, c, and d. Carboxyl group-containing polyvinyl formal resin is obtained by introducing a carboxyl group as a crosslinkable group into polyvinyl formal resin, and using this resin composition improves the toughness, transparency and adhesiveness of the cured product. it can. The introduced carboxyl group becomes a cross-linking point, and the carboxyl group and the epoxy resin are cross-linked directly or via a curing agent, and physical entanglement of molecular chains of both dense polymers based on the cross-linking point. Give rise to By this mechanism, a flexible polyvinyl formal resin is incorporated into a network of epoxy resins that bind in a network.

In the formula of the structural unit d, R ¹ is independently hydrogen or alkyl having 1 to 5 carbons.

The total content of the structural units a to d in the carboxyl group-containing polyvinyl formal resin is preferably 80% by weight to 100% by weight with respect to all the structural units.

Examples of other structural units that can be included in the carboxyl group-containing polyvinyl formal resin include intermolecular formal units and hemi-formal units. The content of other structural multi-units is preferably less than 20% by weight.

(R represents a hydrogen atom, alkyl having 1 to 5 carbon atoms)
In the carboxyl group-containing polyvinyl formal resin, the structural units a to d may be regularly arranged (block copolymer, alternating copolymer, etc.) or randomly arranged (random copolymer). The arrangement is preferably random.

The structural unit a is a structural unit having a formal site, and can be formed by a reaction between a continuous polyvinyl alcohol chain unit and an aldehyde (HCHO).

The structural unit b is a structural unit containing a vinyl acetate chain.

The structural unit c is a structural unit containing a vinyl alcohol chain.

The structural unit d is a chain having a carboxyl group, and R ¹ in the structural unit d is hydrogen or alkyl having 1 to 5 carbons, and more preferably hydrogen or alkyl having 1 to 3 carbons.

Each constituent unit in the carboxyl group-containing polyvinyl formal resin has a constituent unit a content of 49.9 to 80 mol%, a constituent unit b content of 0.1 to 49.9 mol%, The content is preferably 0.1 to 49.9 mol%. When the structural unit d is included, the content of the structural unit d is preferably 0.1 to 49.9 mol%. More preferably, the content of the structural unit a is 49.9 to 80 mol%, the content of the structural unit b is 1 to 30 mol%, and the content of the structural unit c is 1 to 30 mol%. When the structural unit d is included, a more preferable range of the content of the structural unit d is 1 to 30 mol%.

In order to sufficiently obtain the chemical resistance, flexibility, wear resistance, and mechanical strength of the carboxyl group-containing polyvinyl formal resin, the content of the structural unit a is preferably 49.9 mol% or more. In addition, the structural unit a in the carboxyl group-containing polyvinyl formal resin is formed by formalizing a vinyl alcohol chain portion that is continuously present in the molecular chain. That is, it is difficult to formalize a vinyl alcohol chain that is not continuous in the molecular chain (for example, one vinyl alcohol chain that is sandwiched between two vinyl formal chains). Therefore, in the synthesis, the content of the structural unit a is preferably 80.0 mol% or less.

If the content rate of the structural unit b is 0.1 mol% or more, the solubility of the carboxyl group-containing polyvinyl formal resin in the solvent and the solubility in the epoxy resin are improved. The content of the structural unit b is preferably 49.9 mol% because the chemical resistance, flexibility, wear resistance, and mechanical strength of the carboxyl group-containing polyvinyl formal resin are unlikely to decrease.

The structural unit c preferably has a content of up to 49.9 mol% in consideration of solubility in a solvent and solubility in an epoxy resin. Further, in the production of the polyvinyl formal resin, when the polyvinyl alcohol chain is formalized, the structural unit b and the structural unit c are in an equilibrium relationship, and therefore the content of the structural unit c is preferably 0.1 mol% or more.

When the carboxyl group-containing polyvinyl formal resin contains the structural unit d, the content of the structural unit d is preferably 49.9 mol% or less in consideration of the solubility in the epoxy resin and the viscosity after dissolution. . In addition, since the cross-linking reaction between the side chain carboxyl group and the epoxy resin is smoothly performed, the heat resistance (glass transition temperature) can be maintained, and the resin is toughened due to the cross-linking and has high tensile, bending and compression properties. Since a fiber-reinforced composite material exhibiting an elastic modulus and high strength and exhibiting impact resistance can be obtained, the content of the structural unit d is preferably 0.1 mol% or more.

The proportion of each of the structural units a to c in the carboxyl group-containing polyvinyl formal resin can be determined by measuring according to (JIS K6729).

The content of the structural unit d in the carboxyl group-containing polyvinyl formal resin can be measured by the method described below.

In a 1 mol / l sodium hydroxide aqueous solution, a polyvinyl formal resin having a carboxyl group introduced by copolymerization is heated at 80 ° C. for 2 hours. By this operation, a polymer in which sodium is added to the carboxyl group and sodium carboxylate is added is obtained. Excess sodium hydroxide is extracted from the polymer and then dehydrated and dried. Thereafter, carbonization is performed and atomic absorption analysis is performed, and the amount of sodium added is determined and quantified.

In addition, since the structural unit d is quantified as a vinyl acetate chain at the time of analyzing the structural unit b (vinyl acetate chain), the structural unit b is corrected by subtracting the structural unit d from the structural unit b measured according to JIS K6729. To do.

Moreover, in order to change the proportion of each structural unit in the carboxyl group-containing polyvinyl formal resin, for example, the proportion of the alkyl acrylate ester or alkyl methacrylate ester is arbitrarily changed with respect to the main raw material vinyl acetate monomer, It can adjust by adjusting the addition amount of the water and an acid catalyst for hydrolysis, and the addition amount of the aldehyde compound for formalization.

The weight average molecular weight of the carboxyl group-containing polyvinyl formal resin is preferably from 5,000 to 200,000, and more preferably from 10,000 to 150,000. When the weight average molecular weight of the polyvinyl formal resin is 5000 or more, the solubility in the epoxy resin is increased, and the toughening action by the carboxyl group-containing polyvinyl formal resin is obtained, which is preferable. When the weight average molecular weight of the polyvinyl formal rule resin is 150,000 or less, the viscosity when dissolved in the epoxy resin does not increase excessively, which is preferable from the workability at the time of molding into a fiber reinforced composite material.

The weight average molecular weight of the carboxyl group-containing polyvinyl formal resin can be measured by a GPC method. Specific measurement condition examples are as follows.

Apparatus: LC-4000 series (manufactured by JASCO Corporation)
Detector: RI-4030
Oven: CO-4060
Pump: PU-4180
Separation column: Shodex KF-805L x 2 Temperature: 40 ° C
Mobile phase: Chloroform Standard sample: Polystyrene As such a carboxyl group-containing polyvinyl formal resin, vinylec ((registered trademark) grade: PVF-C) manufactured by JNC Corporation is commercially available.
Component [B] A solid epoxy resin is used as the solid epoxy resin component [B]. The solid epoxy resin may be solid at 25 ° C. during use, and preferably has a softening point of at least 60 ° C.

Component [B] uses an epoxy resin having strong adhesiveness to carbon fiber, aramid fiber, boron fiber, glass fiber and other reinforcing fibers, and excellent strength, elastic modulus, and heat resistance as a matrix resin for prepreg. Is preferred.

As the prepreg matrix resin, it is preferable to use an epoxy resin that has strong adhesion to reinforcing fibers such as carbon fiber, aramid fiber, boron fiber, and glass fiber, and is excellent in strength, elastic modulus, and heat resistance.
When the epoxy resin is combined with the matrix resin, the compatibility of the polyvinyl formal resin including the carboxyl group-containing polyvinyl formal resin of the component [A] with the epoxy resin is high, and when the prepreg is laminated and cured, the epoxy resin It can be expected that the resin is toughened by crosslinking.

By using the solid epoxy resin and the liquid epoxy resin in combination, the component [A] in the resin composition preparation can be uniformly dissolved.

For example, if the softening point of the solid epoxy resin is 60 ° C. or higher, after the polyvinyl formal resin including the carboxyl group-containing polyvinyl formal resin of component [A] is dissolved in the liquid epoxy resin of component [C] at 130 ° C. or higher in advance. The solid epoxy resin of component [B] can be easily dissolved by lowering the temperature to 80 to 90 ° C.

As for the type of the solid epoxy resin, it is preferable that the softening point is 60 ° C. or higher in order to facilitate dissolution in the preparation of the resin composition.

Specifically, the solid epoxy resin is a compound having two or more epoxy groups in the molecule, and is a bisphenol type epoxy resin, a phenol novolac type epoxy resin, a cresol novolac type epoxy resin, a biphenyl type epoxy resin, or a naphthalene type epoxy. Resin, fluorene type epoxy resin, etc. can be used. A solid epoxy resin having an oxazolidone ring structure can be used to further improve the adhesion between the reinforcing fiber and the matrix resin. These epoxy resins can be used alone or in combination of two or more.

Examples of the bisphenol type epoxy resin include bisphenol A type epoxy resin, bisphenol F type epoxy resin, and brominated bisphenol A type epoxy resin.

Examples of the bisphenol A type solid epoxy resin include jER1001, jER1002, jER1003, jER1004, jER1055, jER1007, jER1009, and jER1010 in Mitsubishi Chemical Corporation products.

Examples of the bisphenol F type solid epoxy resin include, for example, jER4004P, jER4005P, jER4007P, and jER4010P in Mitsubishi Chemical Corporation products.

Brominated bisphenol A type solid epoxy resin includes jER5046B80 manufactured by Mitsubishi Chemical Corporation.

Examples of the phenol novolac type solid epoxy resin include jER152 and jER154 manufactured by Mitsubishi Chemical Corporation.

Examples of the cresol novolak type solid epoxy resin include Nippon Kayaku Co., Ltd. products EOCN-1020, EOCN-102S, EOCN-104S, and the like.

Examples of the biphenyl type solid epoxy resin include jER YX4000, jER YX4000H, jER YL6121H, etc. manufactured by Mitsubishi Chemical Corporation.

As naphthalene type solid epoxy resin, Nippon Kayaku Co., Ltd. products such as NC-7000L and NC-7300L are included.

Fluorene-type solid epoxy resins include on-coat EX-1010, EX-1011 and EX-1012 manufactured by Nagase ChemteX.

Examples of solid epoxy resins having an oxazolidone ring structure include AER4152 manufactured by Asahi Kasei E-Materials Corporation, DER858 manufactured by DOW Corporation, and the like.

Among these, the component [B] is selected from those having a softening point at least higher than the above temperature.

Component [C] Liquid Epoxy Resin The liquid epoxy resin may be liquid at 25 ° C. at the time of use, but when a liquid epoxy resin is used as the matrix resin, an epoxy resin of a polyvinyl formal resin including a carboxyl group-containing polyvinyl formal resin. Since the compatibility of the epoxy resin is high, the epoxy resin is preferably liquid at 150 ° C. This is because the melting temperature of polyvinyl formal in a liquid epoxy resin is usually 130 to 150 ° C. Here, the liquid state means a state that is liquid at normal temperature (25 ° C.) and does not contain a solid content. The viscosity of the liquid epoxy resin is preferably 1.5 to 15 Pa · s at 25 ° C.

The carboxyl group-containing polyvinyl formal resin is a particle having a large number of pores (pore volume (representative value); 0.71 ml / g). The carboxyl group-containing polyvinyl formal particle and the liquid epoxy resin are previously kneaded to obtain an epoxy resin. If the pores are filled, the solubility is improved, and the solubility is increased at least at 100 ° C. in the epoxy resin, and the dissolution time is shortened at 130 to 150 ° C.

The liquid epoxy resin may be one liquid epoxy resin or a mixture of two or more liquid epoxy resins.

Examples of the liquid epoxy resin include bisphenol A type epoxy resin, bisphenol F type epoxy resin, alicyclic epoxy resin, and glycidylamine type epoxy resin.

As a bisphenol A type liquid epoxy resin, jER827, jER828 and the like are listed as Mitsubishi Chemical Corporation products.

Examples of the bisphenol F type epoxy resin include jER806, jER807 and the like in Mitsubishi Chemical Corporation products.

Examples of the alicyclic epoxy resin include Daicel Chemical Industries, Ltd. products Celoxide 2021P, Celoxide 2081, and the like.

Examples of glycidylamine type epoxy resins include Sumitomo Chemical's ELM434, Ciba Specialty Chemicals YH-434L, Mitsubishi Chemical Corporation jER630 and jER604, Huntsman Advanced Materials Araldite MY0600, Nippon Kayaku Co., Ltd. GAN and GOT are included.

The liquid epoxy resin is a liquid compound having at least one oxiranyl group. A liquid compound having a molecular weight lower than that of a general liquid epoxy resin and a viscosity at 25 ° C. of 2 mPa · s to 100 mPa · s may be used. Such a liquid compound is preferably used for the purpose of reducing the viscosity of one liquid epoxy resin.

Examples of such liquid compounds include monoepoxides. Monoepoxides include alcohol-based allyl glycidyl ether, n-butyl glycidyl ether, 2-ethylhexyl glycidyl ether, and higher alcohol glycidyl ether. Examples of phenols include phenyl glycidyl ether, p-tert-butylphenyl glycidyl ether, cresyl glycidyl ether, phenol (EO) 5 glycidyl ether, sec-butylphenyl glycidyl ether, cardanol diglycidyl ether, dibromophenyl glycidyl ether, and the like. .

Other compounds include glycidyl methacrylate, styrene oxide, tertiary carboxylic acid glycidyl ester, diepoxides such as N, N′-diglycidylaniline, N, N-diglycidyl-O-toluidine, anhydrous hexahydrophthalic acid diglycidyl ester, polyethylene Glycol diglycidyl ether (n = 2 to 13), ethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether (n = 3 to 11), neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, resorcinol Examples include diglycidyl ether, diglycidyl-O-phthalate, dibromoneopentyl glycol diglycidyl ether, and the like.

Further, examples of the triepoxides include glycerol polyglycidyl ether and trimethylolpropane polyglycidyl ether.

By using component [B] and component [C] together, leakage from the resin mold due to a decrease in resin viscosity during thermosetting can be prevented when molding into a carbon fiber composite material, and adjustment of tackiness of prepreg Or to prevent a decrease in toughness due to improved crosslink density when heat-cured.
Component [D] Amine Curing Agent The amine curing agent [D] is preferably dicyandiamide or a derivative thereof.

Examples include aromatic amines such as diaminodiphenylmethane and diaminodiphenylsulfone, aliphatic amines, imidazole derivatives, dicyandiamide, tetramethylguanidine, thiourea-added amines, and isomers and modified forms thereof. Among these, dicyandiamide is particularly preferable in terms of excellent prepreg storage.

Derivatives are those obtained by bonding various compounds to dicyandiamide, and include reactants with epoxy resins, reactants with vinyl compounds and acrylic compounds.

Dicyandiamide is a particulate curing agent that does not dissolve in the epoxy resin component at a temperature of 25 ° C., but is dispersed in the epoxy resin component in the form of particles, so that it contacts the epoxy group in each epoxy resin component. Since it has a small area, it exhibits little reactivity and is usually dissolved in an epoxy resin when heated to 180 ° C. or higher and has a characteristic of reacting with an epoxy group.

The compounding amount of the amine curing agent [D] is such that the storage stability of the resulting resin composition, the calorific value at the time of prepreg curing, the heat resistance of the cured product, and the like are in an appropriate range. Is preferably in the range of 1 to 10 parts by weight, more preferably in the range of 2 to 8 parts by weight with respect to 100 parts by weight of the total epoxy resin component. By setting the blending amount of dicyandiamide within such a range, a good cured product can be obtained without causing deterioration of heat resistance and mechanical properties due to insufficient curing or excessive reaction heat generation. Examples of commercially available dicyandiamide include DICY-7 and DICY-15 (manufactured by Mitsubishi Chemical Corporation).

Further, in order to increase the curing activity of the amine curing agent used for the preparation of the prepreg of the present invention, it is preferable to use a curing aid together. For example, when the epoxy resin curing agent is dicyandiamide, the curing aid is 3-phenyl-1,1-dimethylurea, 3- (3,4-dichlorophenyl) -1,1-dimethylurea (DCMU), 3- ( Urea derivatives such as 3-chloro-4-methylphenyl) -1,1-dimethylurea and 2,4-bis (3,3-dimethylureido) toluene are preferred. When these curing aids are used, dicyandiamide alone usually requires a temperature of 170 to 180 ° C., but when used together with dicyandiamide, it can be cured at 80 to 150 ° C.

Examples of commercially available ureas include DCMU99 (manufactured by PTI Japan Co., Ltd.), Omicure 24, Omicure 52, and Omicure 94 (above, manufactured by CVC Specialty Chemicals, Inc.).

There is no particular limitation on the method for producing the resin composition used for producing the prepreg of the present invention, and each component constituting this composition is applied to a general stirring and heating device such as a kneader and a planetary mixer, and a stirring and pressure heating device. And thoroughly mixed.

When producing a resin composition, a polyvinyl formal resin containing a carboxyl group-containing polyvinyl formal resin is first dissolved in a liquid epoxy resin at 130 ° C. or higher, and then a solid epoxy resin is dissolved at 80 to 90 ° C., Finally, the amine curing agent is preferably dispersed at 50 to 60 ° C.
The reinforcing fiber reinforced fiber is not particularly limited, and may be appropriately selected according to the use etc. from those known as the reinforcing fiber constituting the fiber reinforced composite material. As the reinforcing fiber used in the present invention, glass fiber, Examples thereof include carbon fiber, graphite fiber, aramid fiber, boron fiber, alumina fiber, and silicon carbide fiber. Two or more kinds of these reinforcing fibers may be mixed and used, but in order to obtain a molded product that is lighter and more durable, it is preferable to use carbon fibers or graphite fibers. In particular, in applications where there is a high demand for reducing the weight and strength of materials, carbon fibers are preferably used because of their excellent specific modulus and specific strength.
Production method of prepreg There is no particular limitation on the production method of the prepreg of the present invention. For example, a hot melt method in which the resin composition is reduced in viscosity by heating and impregnated into reinforcing fibers, or a method in which the resin composition is dissolved in a solvent such as methyl ethyl ketone or methanol to lower the viscosity and impregnate into reinforcing fibers (wet method) Is mentioned.

The wet method is a method in which a reinforcing fiber is immersed in a solution of the resin composition and then lifted and the solvent is evaporated using an oven or the like. The hot melt method (dry method) is a resin composition whose viscosity is reduced by heating. Directly impregnating the reinforcing fiber, or a film in which the resin composition is once coated on a release paper or the like is prepared, and then the film is laminated from both sides or one side of the reinforcing fiber and heated and pressed to reinforce the fiber. Is impregnated with a resin composition. According to the hot melt method, the solvent remaining in the prepreg is substantially absent, and therefore, this is a preferred embodiment in the present invention.

In the prepreg of the present invention, the fiber volume content (Vf) of the impregnated reinforcing fibers is preferably 40 to 90 vol%, more preferably 50 to 80 vol%, when the volume of the prepreg including the reinforcing fibers is 100 vol%. . If Vf is 50 vol% or more, the mass of the obtained composite material does not become excessive, and the advantages of the fiber-reinforced composite material excellent in specific strength and specific modulus can be maintained. Moreover, if Vf is 80 vol% or less, the impregnation failure of the resin composition does not occur, the resulting composite material has few voids, and the mechanical properties are not deteriorated.

The form of the reinforcing fiber used in the present invention is a form in which the continuous fibers are aligned in one direction, a form in which the continuous fibers are used as a woven fabric, a form in which the tow is aligned in one direction and held by a weft auxiliary yarn, a plurality of sheets There are multi-axial warp knit forms that overlap unidirectional reinforcing fiber sheets in different directions and stitch together with auxiliary yarns, and non-woven forms of reinforcing fibers. And the form which arranged the continuous fiber in one direction is preferable. The basis weight of the reinforcing fiber can be freely set according to the purpose of use of the fiber reinforced composite material, but 50 to 2000 g / m ² is a practically preferable range.

The carbon fiber preferably used in the present invention can be any type of carbon fiber depending on the application, but is preferably a carbon fiber having a tensile modulus of 230 to 400 GPa from the viewpoint of impact resistance. . From the viewpoint of strength, a carbon fiber having a tensile strength of preferably 4.4 to 6.5 GPa is preferably used because a composite material having high rigidity and mechanical strength can be obtained. Also, the tensile elongation is an important factor, and it is preferable that the carbon fiber is a high strength and high elongation carbon fiber of 1.7 to 2.3%.

Commercially available carbon fibers include “Torayca (registered trademark)” T800G-24K, “Torayca (registered trademark)” T800S-24K, “Torayca (registered trademark)” T700G-24K, and “Torayca (registered trademark)” T300- 3K, and "Torayca (registered trademark)" T700S-12K (manufactured by Toray Industries, Inc.), TR50S (manufactured by Mitsubishi Rayon), and the like.

The prepreg of the present invention is obtained by impregnating a reinforcing fiber with the above-described resin composition of the present invention, and a fiber-reinforced composite material having excellent strength and heat resistance can be obtained by curing.

A publicly known method can be used about the preparation method of a fiber reinforced composite material. Typical methods include a prepreg method, a filament winding method, and a resin transfer molding method. Resin composition viscosity applicable to prepreg method is 1 Pa · s to 10000 Pa · s, resin composition viscosity applicable to filament winding method is 15 mPa · s to 30 Pa · s, resin composition applicable to resin transfer molding method The range of the product viscosity is 350 mPa · s to 1 Pa · s.

The resin composition used for the prepreg of the present invention is preferably applied to a prepreg method capable of dealing with a high viscosity since the viscosity of the resin composition is increased by adding a carboxyl group-containing polyvinyl formal.

For example, when a fiber-reinforced composite material is produced with the prepreg, the prepreg sheets are arranged and laminated in a predetermined direction, pressed and integrated, and finally heated and pressed to be cured.

Examples of the molding method in the production method of the fiber-reinforced composite material of the present invention include autoclave molding method, vacuum back molding method, oven molding method, press molding method, continuous press molding method, pultrusion molding method, internal pressure molding method, and sheet wrap molding method. It is done.

The fiber reinforced composite material formed by laminating and thermosetting the prepreg of the present invention is suitably used for aircraft use, general industrial use, and sports use. More specifically, in aerospace applications, primary structural material applications such as main wings, tail wings and floor beams, secondary structural material applications such as aircraft cabins, flaps, ailerons, cowls, fairings and interior materials, rocket motor cases It is suitably used for satellite structural material applications. Among such aerospace applications, impact resistance is required, and because it is exposed to low temperatures during high altitude flight, aircraft primary structure applications that require tensile strength at low temperatures, especially fuselage skins and main wing skins, The fiber-reinforced composite material of the present invention is particularly preferably used. In general industrial applications, structural materials for moving bodies such as automobiles, ships, and railway vehicles, drive shafts, leaf springs, windmill blades, various turbines, pressure vessels, flywheels, paper rollers, roofing materials, cables, reinforcement bars And suitable for civil engineering and building material applications such as repair and reinforcement materials. Further, in sports applications, it is suitably used for golf shafts, fishing rods, tennis, badminton, squash and other racket applications, hockey and other stick applications, and ski pole applications.

EXAMPLES Next, although an Example demonstrates this invention still in detail, this invention is not limited to these.
<Molecular weight and composition of the used polyvinyl formal>
The carboxyl group-containing polyvinyl formal resin used in the examples is Vinylec (registered trademark), grade: PVF-C manufactured by JNC Corporation. The weight average molecular weight Mw is 62000, vinyl formal (constituent unit a) is 70.42 mol%, vinyl acetate (constituent unit b) is 10.34 mol%, vinyl alcohol (constituent unit c) is 16.09 mol%, and acrylic acid. (Structural unit d) is 3.15 mol%.

The polyvinyl formal used in the comparative examples is Vinylec (registered trademark) manufactured by JNC Corporation, grades: PVF-K, PVF-E. Regarding PVF-K, the weight average molecular weight Mw is 54000, vinyl formal (structural unit a) is 75.13 mol%, vinyl acetate (structural unit b) is 12.26 mol%, and vinyl alcohol (structural unit c) is 12. 61 mol%.

Regarding PVF-E, the weight average molecular weight Mw is 120,000, vinyl formal (constituent unit a) is 74.80 mol%, vinyl acetate (constituent unit b) is 12.66 mol%, and vinyl alcohol (constituent unit c) is 12. 54 mol%. PVF-K and PVK-E are polyvinyl formal resins into which carboxyl groups are not introduced.
<Other thermoplastic resins used>
As another thermoplastic resin, a phenoxy resin (PKHP200 manufactured by Sakai Kogyo Co., Ltd.) was used. For PKHP200, the weight average molecular weight Mw is 52000.
<Liquid epoxy resin used>
jER828: Bisphenol A type epoxy resin Average molecular weight 370 Epoxy equivalent 184 to 194 Made by Mitsubishi Chemical (liquid at 25 ° C, viscosity (25 ° C): 12 to 15 Pa · s)
<Used solid epoxy resin>
jER1001: Bisphenol A type epoxy resin Average molecular weight 900 Epoxy equivalent 450-500 Made by Mitsubishi Chemical (softening point: 64 ° C)

<Amine curing agent used>
DICY7: Dicyandiamide Made by Mitsubishi Chemical <Used accelerator>
DCMU99: 3- (3,4-dichlorophenyl) -1,1-dimethylurea, manufactured by PTI Japan Co., Ltd. <Carbon fiber used>
TR50S15L: Made by Mitsubishi Chemical Tensile strength 4.9 GPa, Tensile modulus 240 GPa, Tensile elongation 2%
<Measurement of resin viscosity>
Regarding the viscosity measurement of a resin composition, if there is an amine curing agent, it reacts at 80 ° C. and the viscosity rises. Therefore, a resin composition comprising Component A, Component B and Component C, or a resin composition comprising Component B and Component C Was prepared and carried out.

A temperature-viscosity relationship was measured with a rheometer (MCR-302, manufactured by Anton Paar) under conditions of a swing angle of 60%, a frequency of 0.5 Hz, a temperature increase rate of 3 ° C./min, and a temperature of 30 to 130 ° C.

Hereinafter, the preparation method of the resin composition used for the viscosity measurement is shown. For the viscosity measurement, the same composition as in the examples and comparative examples is prepared except that no amine curing agent is contained.

<Composition for Viscosity Measurement of Example 1>
A hot stirrer with an aluminum block bath (manufactured by RCH-20L EYELA) was used for heating, and a stirring motor (manufactured by BLh600 HEIDON) was used for stirring.

Liquid bisphenol A type epoxy resin, 60 g of jER828 (Mitsubishi Chemical) was weighed into a 200 mL beaker, 7.2 g of JNC Co. vinylec (trademark: PVF-C) was added, and the temperature was 130 ° C., 120 rpm, 120 Dissolved in minutes.

Next, the temperature was lowered to 90 ° C., 60 g of solid bisphenol A type epoxy resin, jER1001 (manufactured by Mitsubishi Chemical) was added and dissolved by heating at 120 rpm. Finally, vacuum deaeration was performed at 90 ° C. and 30 kPa with a diaphragm pump in a vacuum oven (Vacuum Oven ADP300 manufactured by Yamato).
<Composition for Viscosity Measurement of Comparative Example 1>
A hot stirrer with an aluminum block bath (manufactured by RCH-20L EYELA) was used for heating, and a stirring motor (manufactured by BLh600 HEIDON) was used for stirring.

A liquid bisphenol A type epoxy resin, 60 g of jER828 (manufactured by Mitsubishi Chemical) was weighed in a 200 mL beaker, 60 g of solid bisphenol A type epoxy resin, jER1001 (manufactured by Mitsubishi Chemical) was added and dissolved by heating at 90 ° C. and 120 rpm. Finally, vacuum deaeration was performed at 90 ° C. and 30 kPa with a diaphragm pump in a vacuum oven (Vacuum Oven ADP300 manufactured by Yamato).
<Composition for Viscosity Measurement of Comparative Example 2>
A hot stirrer with an aluminum block bath (manufactured by EYELA) was used for heating, and a stirring motor (manufactured by BLh600 HEIDON) was used for stirring.

A liquid bisphenol A type epoxy resin, 60 g of jER828 (Mitsubishi Chemical) was weighed in a 200 mL beaker, 7.2 g of phenoxy resin (PKHP200) manufactured by Sakai Kogyo Co., Ltd. was added and dissolved at a temperature of 130 ° C., 120 rpm for 40 minutes. .

Next, the temperature was lowered to 90 ° C., 60 g of solid bisphenol A type epoxy resin, jER1001 (manufactured by Mitsubishi Chemical) was added and dissolved by heating at 120 rpm. Finally, vacuum degassing was performed at 90 ° C. and 30 kPa in a vacuum oven (Vacuum Oven ADP300 manufactured by Yamato).
<Composition for Viscosity Measurement of Comparative Example 3>
A hot stirrer with an aluminum block bath (manufactured by EYELA) was used for heating, and a stirring motor (manufactured by BLh600 HEIDON) was used for stirring.

Liquid bisphenol A type epoxy resin, 60 g of jER828 (Mitsubishi Chemical) was weighed into a 200 mL beaker, 7.2 g of JNC Co., Ltd. vinylec ((trademark) grade: PVF-K) was added, and the temperature was 130 ° C., 120 rpm, 120 Dissolved in minutes.

Next, the temperature was lowered to 90 ° C., 60 g of solid bisphenol A type epoxy resin, jER1001 (manufactured by Mitsubishi Chemical) was added and dissolved by heating at 120 rpm. Finally, vacuum degassing was performed at 90 ° C. and 30 kPa in a vacuum oven (Vacuum Oven ADP300 manufactured by Yamato).
<Composition for Viscosity Measurement of Comparative Example 4>
A hot stirrer with an aluminum block bath (manufactured by EYELA) was used for heating, and a stirring motor (manufactured by BLh600 HEIDON) was used for stirring.

Liquid bisphenol A type epoxy resin, 60 g of jER828 (Mitsubishi Chemical) was weighed into a 200 mL beaker, 7.2 g of Vinylec ((trademark) grade: PVF-E) manufactured by JNC Corporation was added, and the temperature was 130 ° C., 120 rpm, 120 Dissolved in minutes.

Next, the temperature was lowered to 90 ° C., 60 g of solid bisphenol A type epoxy resin, jER1001 (manufactured by Mitsubishi Chemical) was added and dissolved by heating at 120 rpm. Finally, vacuum degassing was performed at 90 ° C. and 30 kPa in a vacuum oven (Vacuum Oven ADP300 manufactured by Yamato).
<Measurement of 90 ° tensile strength of fiber reinforced composite material>
A water-cooled composite material cutting machine (manufactured by a high-speed cutter AC-500CF, Maruto Manufacturing Co., Ltd.) so that the reinforcing fibers are oriented at 90 ° with respect to the longitudinal direction of the test piece from the produced fiber reinforced composite material having a thickness of 2 mm and 320 cm × 320 cm. The test piece (length 250 mm × width 25 mm) was cut out. Using an autograph (AG-IS 100 kN) manufactured by Shimadzu Corporation, the test piece was subjected to a 90 ° tensile test using a 5 kN load cell at a test speed of 1 mm / min, 25 ° C., and a humidity of 50% (JIS K7165). Compliant). The strain (elongation) was measured using a video extensometer, and the elastic modulus was measured according to JIS K7165. The distance between the marked lines was 50 mm, and the distance between the chucks was 150 mm.
<Measurement of 0 ° compressive strength of fiber reinforced composite material>
Water-cooled composite material cutting machine (high-speed cutter AC-500CF Maruto Manufacturing Co., Ltd.) from the manufactured fiber reinforced composite material with a thickness of 2 mm and 320 cm × 320 cm so that the reinforcing fibers are once oriented at 0 ° with respect to the length direction of the test piece. A test piece having a width of 98 mm and a length of 65 mm was cut out. And it scratched with the sandpaper of the particle sizes 600 and 1000 so that the site | part which affixes the tab of a test piece and the adhesion side of a tab may adhere with an adhesive agent. However, the direction of scratching is 90 ° with respect to the fiber direction on the CFRP test piece side. A glass epoxy plate cut out with dimensions of 2 mm thickness, 25 mm width and 100 mm length was prepared as a tab. The tab was adhered to the test piece using a two-pack type epoxy adhesive (manufactured by ThreeBond) and left for 2 days. The bonding was performed in a thermostatic chamber at 25 ° C. and a humidity of 50%.

Measured 55 mm long x 20 mm wide (20 mm tab width, measured with a water-cooled composite cutting machine (high-speed cutter AC-500CF, manufactured by Maruto Seisakusho) so that the reinforcing fibers are oriented at 0 ° with respect to the longitudinal direction of the test piece. A compression test piece having a length of 15 mm was cut out. Strain gauges (model: KFGS-1-120-C1-11L1M2R, manufactured by Kyowa Denki Co., Ltd.) were attached to both sides of the test piece. As the adhesive used for pasting, an instantaneous adhesive (CC-33A, manufactured by Kyowa Denki Co., Ltd.) dedicated to a strain gauge was used.

According to method 3 of JISK 7018, the test piece was fixed to a compression test jig, and the autograph (AG-IS 100 kN) manufactured by Shimadzu Corporation was used at 25 ° C. and 50% humidity at a test speed of 1 mm / min. A 0 ° compression test was carried out. The strain was measured with a strain gauge, and the elastic modulus was calculated according to the elastic modulus calculation method of JIS K7076.
<Measurement of 0 ° bending strength of fiber reinforced composite material>
A water-cooled composite material cutting machine (manufactured by a high-speed cutter AC-500CF, Maruto Manufacturing Co., Ltd.) so that the reinforcing fibers are oriented at 0 ° with respect to the longitudinal direction of the test piece from the produced fiber reinforced composite material having a thickness of 2 mm and 320 cm × 320 cm. Then, a test piece (length 100 mm × width 15 mm) was cut out and a four-point bending jig (indenter radius 3 mm, fulcrum radius 3 mm, upper fulcrum distance 27 mm, lower fulcrum distance 81 mm) was installed on the test piece. Using an autograph (AG-IS 100 kN) manufactured by Shimadzu Corporation, 0 ° bending strength was measured under the conditions of a test speed of 5 mm / min, 25 ° C., and 50% humidity (conforming to JIS K7074). The bending elastic modulus was calculated according to the bending elastic modulus calculation formula of the four-point bending test (Method B) of JIS K7074 by calculating the gradient of the initial linear portion of the measured load-displacement curve.
<Measurement of impact resistance of fiber reinforced composite material>
A water-cooled composite material cutting machine (high speed cutter AC-500CF, manufactured by Maruto Seisakusho Co., Ltd.) so that the reinforcing fibers are oriented at 0 ° with respect to the longitudinal direction of the test piece from the produced fiber reinforced composite material having a thickness of 2 mm and 320 cm × 320 cm. A test piece (length 80 mm × width 10 mm) was cut out.

Shake the hammer from a swing angle of 149.7 ° with a Charpy impact tester (manufactured by Oji Scientific Instruments) in an environment of 25 ° C and 50% humidity. The test was conducted (in accordance with JIS K7077).
<Observation of fracture surface of fiber reinforced composite material bending specimen and 90 degree tensile specimen>
A sample including a fracture surface is cut from a bending test piece and a 90 ° tensile test piece with a cutter, and the fracture surface is as follows with an electron microscope (device: Hitachi High-Technologies SU8020, analysis conditions: acceleration voltage 1 kv, current 10 μA). Observed.

Before the observation with an electron microscope, the fracture surface of the bending test piece was observed with a microscope (apparatus: KEYENCE VHX-2000, analysis condition: side light) to confirm the compression fracture surface and the tensile fracture surface (FIG. 2).

When the fracture surface in FIG. 2 is observed, an interface exists between the portion to be compressed in the bending test and the portion to be pulled inside the test piece, and the tensile fracture surface up to the interface is shown as the tensile fracture surface. With (A), the fracture surface to be compressed was defined as the compression fracture surface (B), and the fracture surface and the area of each fracture surface were determined by image analysis.

The adhesion between the carbon fiber and the resin on the fracture surface of the bending test piece was evaluated by measuring the number of carbon fibers pulled out on the tensile fracture surface of the fracture surface taken by SEM. The SEM photograph of the tensile fracture surface evaluated in FIG. 3 is shown.

The adhesion between the carbon fiber and the resin on the fracture surface of the test piece of the 90 ° tensile test was evaluated by observing the degree of resin adhesion on the surface of the carbon fiber from the fracture surface photographed by SEM according to the following criteria. (Figure 4 and Table 5)
A: Resin adhesion to carbon fibers is often observed. ○: Resin adhesion to carbon fiber is observed.

Δ: Resin adhering to the carbon fiber is slightly observed. X: Adhesion to carbon fiber is not seen.
[Example]
Example 1
<Preparation of resin composition>
As a machine for preparing the resin composition, a 10 L planetary mixer (PLM-15) manufactured by Inoue Seisakusho was used.

Liquid bisphenol A type epoxy resin, jER828 (Mitsubishi Chemical) 1.7kg is charged into the kettle, and then JNC vinylec ((registered trademark) grade: PVF-C) 204g is charged. The mixture was kneaded for 3 hours while degassing under reduced pressure (vacuum degree: 200 kPa) at 28 r / min and autorotation 77 r / min.

After confirming that vinylec was dissolved, 1.7 kg of solid epoxy resin was added in several batches, and the rotational speed was set at 28 r / min for revolutions while defoaming at 90 ° C. for 30 minutes under reduced pressure (vacuum degree: 200 kPa). The mixture was kneaded at a rotation speed of 77 r / min.

After dissolving the solid epoxy resin, the temperature was lowered to 50 ° C. 204 g of dicyandiamide (DICY7) as a curing agent and 80 g of 3- (3,4-dichlorophenyl) -1,1-dimethylurea (DCMU99) were added to reduce pressure (vacuum degree: 200 kPa), and stirring was started at 50 ° C. And kneading at a revolution of 28 r / min and a rotation of 77 r / min for 90 minutes.
<Production of resin sheet>
The temperature was set based on the viscosity measurement results shown in FIG.

The resin composition prepared by the above method was previously placed in an oven and heated to 65 ° C. The resin composition is put into a liquid dam heated to 65 ° C. in a coating apparatus, and applied on a release paper with a roll temperature of 60 ° C. and a coating width of 290 mm with a coating weight of 26.96 g / m ² . A resin sheet was produced.
<Production of unidirectional prepreg sheet>
Resin produced as described above on a sheet of carbon fibers aligned in one direction (filament number 15000, basis weight 1.000 g / m, monofilament diameter 6.8 μm, tensile strength 4900 MPa, tensile modulus 240 GPa, tensile elongation 2%) The sheets were stacked and heated and pressed to impregnate the resin composition to prepare a prepreg sheet having a fiber volume content of 55%, a basis weight of 76.96 g / m ² , and a slit width of 260 mm. The heating was set based on the viscosity measurement results shown in FIG.
<Production of fiber-reinforced composite material by autoclave method>
The unidirectional prepreg sheet prepared according to the above was laminated with the fiber direction aligned so that the thickness of the fiber-reinforced composite material was 2 mm, 320 mm × 320 mm, and then heated at 130 ° C., 2 hr, 0.5 MPa in an autoclave. A fiber reinforced composite material was produced by pressing and curing.
[Comparative example]
Comparative Example 1
<Preparation of resin composition>
A 10 L planetary mixer (PLM-15) manufactured by Inoue Seisakusho was used as a machine for preparing the resin composition.

Charge 1.8 kg of liquid bisphenol A type epoxy resin, jER828 (Mitsubishi Chemical) into the kettle, add 1.8 kg of solid epoxy resin in several times, and reduce the rotation speed while degassing the vacuum (degree of vacuum: 200 kPa). The mixture was kneaded at 90 ° C. for 30 minutes at revolution 28 r / min and rotation 77 r / min.

After dissolving the solid epoxy resin, the temperature was lowered to 35 ° C. 200 g of dicyandiamide (DICY7) as a curing agent and 80 g of 3- (3,4-dichlorophenyl) -1,1-dimethylurea (DCMU99) were added to reduce the pressure (vacuum level: 200 kPa), and stirring was started at 35 ° C. And kneading at a revolution of 28 r / min and a rotation of 77 r / min for 90 minutes.
<Production of resin sheet>
The temperature was set based on the viscosity measurement results shown in FIG.

The resin composition prepared by the above method was previously placed in an oven and warmed to 55 ° C. A resin composition is placed in a liquid dam heated to 55 ° C. in a coating apparatus, applied on a release paper with a roll temperature of 50 ° C. and a coating width of 290 mm, and has a basis weight of 26.92 g / m ² . A sheet was produced.

<Production of unidirectional prepreg sheet>
Resin produced as described above on a sheet of carbon fibers aligned in one direction (filament number 15000, basis weight 1.000 g / m, monofilament diameter 6.8 μm, tensile strength 4900 MPa, tensile modulus 240 GPa, tensile elongation 2%) The sheets were stacked and heated and pressed to impregnate the resin composition to prepare a prepreg sheet having a fiber volume content of 55%, a basis weight of 76.92 g / m ² , and a slit width of 260 mm. The heating was set based on the viscosity measurement results shown in FIG.
<Production of fiber-reinforced composite material by autoclave method>
The unidirectional prepreg sheet prepared according to the above was laminated with the fiber direction aligned so that the thickness of the fiber-reinforced composite material was 2 mm, 320 mm × 320 mm, and then heated at 130 ° C., 2 hr, 0.5 MPa in an autoclave. A fiber reinforced composite material was produced by pressing and curing.

Comparative Example 2
<Preparation of resin composition>
A 10 L planetary mixer (PLM-15) manufactured by Inoue Seisakusho was used as a machine for preparing the resin composition.

Liquid bisphenol A type epoxy resin, jER828 (Mitsubishi Chemical) 1.7kg is charged into the kettle, then 204g of phenoxy resin (PKHP200) manufactured by Sakai Kogyo Co., Ltd. is charged, temperature 130 ° C rotation speed is 28r / min, rotation speed is 77r The mixture was kneaded for 1 hour while defoaming under reduced pressure (vacuum degree: 200 kPa) at / min.

After confirming that the phenoxy resin was dissolved, 1.7 kg of solid epoxy resin was added in several portions, and the revolution was changed to 28 r / min at 90 ° C. for 30 minutes while degassing under reduced pressure (degree of vacuum: 200 kPa). And kneading at a rotational speed of 77 r / min.

After dissolving the solid epoxy resin, the temperature was lowered to 50 ° C. 204 g of dicyandiamide (DICY7) as a curing agent and 80 g of 3- (3,4-dichlorophenyl) -1,1-dimethylurea (DCMU99) were added to reduce pressure (vacuum degree: 200 kPa), and stirring was started at 50 ° C. And kneading at a rotation speed of 28 r / min and a rotation speed of 77 r / min for 60 minutes.
<Production of resin sheet>
The temperature was set based on the viscosity measurement results shown in FIG.

The resin composition prepared by the above method was previously placed in an oven and warmed to 62 ° C. A resin composition is placed in a liquid dam heated to 62 ° C. in a coating device, applied on a release paper with a roll temperature of 57 ° C. and a coating width of 290 mm, and a resin having a basis weight of 26.90 g / m ² . A sheet was produced.

<Production of unidirectional prepreg sheet>
Resin produced as described above on a sheet of carbon fibers aligned in one direction (filament number 15000, basis weight 1.000 g / m, monofilament diameter 6.8 μm, tensile strength 4900 MPa, tensile modulus 240 GPa, tensile elongation 2%) The sheets were stacked and heated and pressed to impregnate the resin composition to prepare a prepreg sheet having a fiber volume content of 55%, a basis weight of 76.90 g / m ² , and a slit width of 260 mm. The heating was set based on the viscosity measurement results shown in FIG.

<Production of fiber-reinforced composite material by autoclave method>
The unidirectional prepreg sheet prepared according to the above was laminated with the fiber direction aligned so that the thickness of the fiber-reinforced composite material was 2 mm, 320 mm × 320 mm, and then heated at 130 ° C., 2 hr, 0.5 MPa in an autoclave. A fiber reinforced composite material was produced by pressing and curing.

Comparative Example 3
<Preparation of resin composition>
A 10 L planetary mixer (PLM-15) manufactured by Inoue Seisakusho was used as a machine for preparing the resin composition.

Liquid bisphenol A type epoxy resin, jER828 (Mitsubishi Chemical) 1.7kg is charged into the kettle, and then JNC vinylec ((registered trademark) grade: PVF-K) 204g is charged. The mixture was kneaded for 2 hours while degassing under reduced pressure (vacuum degree: 200 kPa) at 28 r / min and rotation 77 r / min.

After dissolving the solid epoxy resin, the temperature was lowered to 50 ° C. 204 g of dicyandiamide (DICY7) as a curing agent and 80 g of 3- (3,4-dichlorophenyl) -1,1-dimethylurea (DCMU99) were added to reduce pressure (vacuum degree: 200 kPa), and stirring was started at 50 ° C. And kneading at a rotation speed of 28 r / min and a rotation speed of 77 r / min for 30 minutes.

<Production of resin sheet>
The temperature was set based on the viscosity measurement results shown in FIG.

The resin composition prepared by the above method was previously placed in an oven and heated to 65 ° C. A resin composition is placed in a liquid dam heated to 65 ° C. in a coating device, applied to a release paper with a coating roll at a roll temperature of 60 ° C. and a coating width of 290 mm, and has a basis weight of 26.96 g / m ² . A sheet was produced.

<Production of unidirectional prepreg sheet>
Resin produced as described above on a sheet of carbon fibers aligned in one direction (filament number 15000, basis weight 1.000 g / m, monofilament diameter 6.8 μm, tensile strength 4900 MPa, tensile modulus 240 GPa, tensile elongation 2%) The sheets were stacked and heated and pressed to impregnate the resin composition to prepare a prepreg sheet having a fiber volume content of 55%, a basis weight of 76.96 g / m ² , and a slit width of 260 mm. The heating was set based on the viscosity measurement results shown in FIG.

Comparative Example 4
<Preparation of resin composition>
As a machine for preparing the resin composition, a 10 L planetary mixer (PLM-15) manufactured by Inoue Seisakusho was used.

1.7kg of liquid bisphenol A type epoxy resin, jER828 (Mitsubishi Chemical) is charged in the kettle, and then 204g of vinylec ((registered trademark) grade: PVF-E) manufactured by JNC Corporation is charged. The mixture was kneaded for 3 hours while degassing under reduced pressure (vacuum degree: 200 kPa) at 28 r / min and autorotation 77 r / min.

After dissolving the solid epoxy resin, the temperature was lowered to 60 ° C. Dicyandiamide, a curing agent
(DICY7) 204 g and 3- (3,4-dichlorophenyl) -1,1-dimethylurea (DCMU99) 80 g were added to reduce the pressure (vacuum degree: 200 kPa), and then the stirring was started, and the mixture was rotated at 60 ° C. for 65 minutes. The numbers were kneaded at a revolution of 28 r / min and a rotation of 77 r / min.
<Production of resin sheet>
The temperature was set based on the viscosity measurement results shown in FIG.

The resin composition prepared by the above method was previously placed in an oven and warmed to 70 ° C. A resin composition is placed in a liquid dam heated to 70 ° C. in a coating apparatus, applied on a release paper with a roll temperature of 66 ° C. and a coating width of 290 mm, and a basis weight of 26.96 g / m ² resin. A sheet was produced.

<Example 1, Comparative Examples 1 to 4>
Tables 1 to 5 show the evaluation results of the compositions prepared in Example 1 and Comparative Examples 1 to 4. As shown in Tables 1 and 2, the comparison between Example 1 and Comparative Examples 1 to 4 shows that the 90 ° tensile property, 0 ° bending property, and 0 ° compression property of the fiber reinforced composite material produced by the prepreg of the present invention are higher. It showed elastic modulus, high strength, and even higher impact resistance.

As one of the factors in which Example 1 improved the 90 ° tensile property and 0 ° bending property of the fiber reinforced composite material as compared with Comparative Examples 1 to 4, the carboxyl group was observed from the electron microscope observation results of FIGS. 3 and 4 and Tables 3 to 5. The effect of improving the adhesion between the carbon fiber and the resin due to the contained polyvinyl formal is considered.

Claims

The following [A], [B], [C] and an amine curing agent [D] are contained as main components, and each component of [A], [B], [C] is 1 to 20 parts by weight, 45 to A prepreg obtained by impregnating reinforcing fibers with a resin composition of 80 parts by weight, 20 to 55 parts by weight;
[A] Carboxyl group-containing polyvinyl formal resin [B] Epoxy resin solid at 25 ° C. [C] Epoxy resin liquid at 25 ° C.
The prepreg according to claim 1, wherein the carboxyl group-containing polyvinyl formal resin [A] contains structural units a, b, c, and d.

(In the formula of the structural unit d, R 1 is independently hydrogen or alkyl having 1 to 5 carbons.)
The prepreg according to claim 1 or 2, wherein the softening point of the solid epoxy resin [B] is 60 ° C or higher.
The prepreg according to any one of claims 1 to 3, wherein the liquid epoxy resin [C] is liquid at 150 ° C.
The prepreg according to any one of claims 1 to 4, wherein the amine curing agent [D] is dicyandiamide or a derivative thereof.
The prepreg according to any one of claims 1 to 5, wherein the reinforcing fiber is any one of carbon fiber, aramid fiber, glass fiber, graphite fiber, silicon carbide fiber, boron fiber, alumina fiber, and stainless steel fiber.
The reinforcing fiber is a carbon fiber, the tensile strength of the carbon fiber is 4.4 to 6.5 GPa, the tensile elongation is 1.7 to 2.3%, and the tensile modulus is 230 to 400 GPa. Item 7. The prepreg according to any one of Items 1 to 6.
The amine curing agent [D] is in the range of 1 to 10 parts by weight with respect to 100 parts by weight of the total epoxy resin component including the solid epoxy resin [B] and the liquid epoxy resin [C]. The prepreg according to any one of the above.
The amount of impregnation of the reinforcing fiber in the prepreg is 40 to 90% as a fiber volume content (Vf) when the volume of the prepreg including the reinforcing fiber is 100 vol%. The prepreg according to item 1.
A fiber-reinforced composite material using the prepreg according to any one of claims 1 to 9.