JP2006335791A - Epoxy resin composition and prepreg containing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyvinyl acetal having high compatibility with an epoxy resin and reinforcing impact resistance and flexural strength of a cured product of an epoxy matrix resin, to provide an epoxy resin composition containing the polyvinyl acetal and to provide prepreg having excellent flexural strength and tensile strength by impregnating reinforcing fibers with the epoxy resin composition. <P>SOLUTION: The epoxy resin composition comprises an epoxy compound, a curing agent and a polyvinyl acetal resin containing a repeating unit A (wherein, R represents a hydrogen atom or a 1-3C alkyl group) and repeating units B and C. The composition is characterized as follows. The content of the repeating unit A in the polyvinyl acetal resin is 50-80 mol% and the the content of the repeating unit B therein is 15-30 mol%. The content of the repeating unit C therein is 0.1-15 mol%. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an epoxy resin composition, and particularly to an epoxy resin composition suitable as a matrix resin for a fiber-reinforced composite material.

  Epoxy resins have excellent moldability and their cured products have good mechanical properties and are therefore widely used in the industrial field. In particular, it is widely used as a matrix resin in fiber reinforced composite materials (including prepregs) using carbon fiber, glass fiber, aramid fiber or the like as a reinforcing material.

As the application fields of these composite materials have expanded, new characteristics have been required for matrix resins. For example, since the epoxy matrix resin is a thermosetting resin, the cured product has essentially low impact resistance. Therefore, when a composite material containing an epoxy matrix resin is applied to a structural member such as an aircraft or a civil engineering building, it is desired to further improve the impact resistance of the epoxy matrix resin.
As a method for improving the impact resistance and bending strength of the cured epoxy matrix resin, a method of adding a high molecular weight polymer is generally known. For example, a method of adding polyvinyl acetal is also known.

For example, a prepreg obtained by impregnating a reinforcing fiber with a resin composition obtained by mixing a dicyandiamide or a urea derivative in a melt-mixed epoxy resin and a polyvinyl formal resin has been reported (see, for example, Patent Document 1).
By adding high molecular weight polyvinyl acetal, the impact resistance and bending strength of the cured epoxy matrix resin can be enhanced. On the other hand, however, the high molecular weight polyvinyl acetal may be difficult to melt into the epoxy resin, and the required amount of polyvinyl acetal may not be melted or may not be sufficiently dispersed in the epoxy resin.

  As a polyvinyl acetal having improved meltability to an epoxy resin, a polyvinyl acetal resin containing a repeating unit shown below is known. Moreover, the epoxy resin composition containing this polyvinyl acetal resin and the prepreg obtained by impregnating this epoxy resin composition in a reinforced fiber are known (for example, refer patent document 2).

However, the properties required for the matrix resin of the composite material are still not sufficiently satisfied, and further improvement is required.
JP-A-63-37136 JP-A-5-186667

An object of the present invention is to provide a polyvinyl acetal having high compatibility with an epoxy resin and capable of enhancing impact resistance and bending strength of a cured product of an epoxy matrix resin, and an epoxy resin composition containing the polyvinyl acetal. Is to provide.
Furthermore, the subject of this invention is providing the prepreg which is excellent in bending strength and tensile strength by impregnating this epoxy resin composition in a reinforcing fiber.

  The present inventor has found that a polyvinyl acetal resin having a specific structure is excellent in compatibility with an epoxy resin and dispersibility in the epoxy resin. Based on this finding, the present inventors have studied to provide a prepreg having excellent bending strength and tensile strength (90 ° direction) and bending strength by adding this polyvinyl acetal to an epoxy resin. That is, the present invention is as follows.

[1] An epoxy resin composition comprising an epoxy compound, a curing agent, and a polyvinyl acetal resin containing repeating units A, B and C represented by the following formulae:
In the polyvinyl acetal resin, the content of the repeating unit A is 50 to 80 mol%, the content of the repeating unit B is 15 to 30 mol%, and the content of the repeating unit C is 0.1 to 15 mol%. An epoxy resin composition characterized by being.

[2] The epoxy resin composition according to [1], wherein R in the repeating unit A represents a hydrogen atom.
[3] The epoxy resin composition according to [1] or [2], wherein the content of the polyvinyl acetal resin is 0.1 to 30 parts by mass with respect to 100 parts by mass of the epoxy compound. .
[4] A prepreg including a reinforcing fiber impregnated with the epoxy resin composition according to any one of [1] to [3].

According to the present invention, an epoxy resin composition suitable for a matrix resin for an epoxy resin composition, in particular, a composite material (including a prepreg) reinforced with fibers is provided. By using the epoxy resin composition of the present invention, a fiber-reinforced composite material having improved moldability and brittleness and excellent in bending strength and tensile strength (90-degree direction) is provided.

[Epoxy resin composition of the present invention]
The epoxy resin composition of the present invention comprises an epoxy compound (1), a curing agent (2), and a polyvinyl acetal resin (3). In the resin composition of the present invention, at least some of the components (1) to (3) may be reacted with each other, for example, epoxy compound (1) or polyvinylidized by reaction with a curing agent (2). The acetal resin (3) may be included.

  The epoxy compound (1) contained in the epoxy resin composition of the present invention is a compound having two or more epoxy groups in the molecule, and is a bisphenol type epoxy, a phenol novolac type epoxy, a cresol novolak type epoxy, or a glycidylamine type. Various epoxy compounds such as epoxy, alicyclic epoxy, and glycidyl ester type epoxy are included.

As the bisphenol type epoxy, bisphenol A type epoxy resin obtained from bisphenol A, bisphenol F type epoxy resin obtained from bisphenol F, bisphenol S type epoxy resin obtained from bisphenol S, tetrabromobisphenol A obtained from tetrabromobisphenol A Includes types.
Suitable examples of the bisphenol A type epoxy include “Epicoat” 825, 828, 834, 1001, 1002, 1003, 1004, 1007, 1009, 1010 (manufactured by Yuka Shell Epoxy),
"Araldite" GY250, "Araldite" 6071, 6072, 6097, 6099 (manufactured by Ciba-Geigy), "Epototo" YD-128, YD-011, YD-014, YD-017, YD-019, YD-022 ( Tohoku Kasei Co., Ltd.), “Dow Epoxy” DER331, 661, 664, 669 (Dow Chemical Co.) “Epiclon” 840, 850, 1050, 3050, HM-101 (Dainippon Ink Chemical Co., Ltd.)
Suitable examples of bisphenol F type epoxy include “Epiclon” 830 (Dainippon Ink Chemical Co., Ltd.), “Epototo” YDF-2001, YDF-2004 (manufactured by Toto Kasei Co., Ltd.), etc.
Suitable examples of the bisphenol S type epoxy include “Denacol” EX-251 (manufactured by Nagase Kasei Kogyo Co., Ltd.)
Suitable examples of tetrabromobisphenol A type epoxy include “Epicoat” 5050 (manufactured by Yuka Shell Epoxy), “Epicron” 152 (manufactured by Dainippon Ink & Chemicals), “Sumi-Epoxy” ESB-400T (Sumitomo) Chemical Industry Co., Ltd.), “Epototo” YBD-360 (manufactured by Toto Kasei Co., Ltd.) and the like.

Suitable examples of phenol novolac epoxies include “Epicoat” 152, 154 (Oilized Shell Epoxy), “Araldite” EPN1138, 1139 (Ciba Geigy), “Dow Epoxy” DEN431, 438, 485 (Dow Chemical). , "Epototo" YCPN-702 (manufactured by Toto Kasei), BREN-105 (manufactured by Nippon Kayaku Co., Ltd.), and the like.
Suitable examples of gresol novolac include “Araldite” ECN1235, 1273, 1299 (Ciba Geigy), “EOCN” 102 (Nippon Kayaku).
Preferable examples of the glycidylamine type epoxy include “Araldite” MY720 (manufactured by Ciba Geigy), “Sumiepoxy” ELM100, 120, 434 (manufactured by Sumitomo Chemical Co., Ltd.) and the like.
Suitable examples of the alicyclic epoxy include “Araldite” CY175, 177, 179 (manufactured by Ciba-Geigy).
Suitable examples of the glycidyl ester type epoxy include “Epicoat” 190P, 191P (manufactured by Yuka Shell Epoxy), “Araldite” CY184, 192 (manufactured by Ciba-Geigy) and the like.

The epoxy compound contained in the epoxy resin composition of the present invention may be a single epoxy compound or a combination of two or more epoxy compounds. The kind of epoxy compound is suitably selected according to the use of the composition.
The epoxy compound contained in the epoxy resin composition of the present invention preferably contains at least one epoxy compound that is liquid at room temperature. When a solid material such as a polyvinyl acetal resin is dispersed and melted in a liquid epoxy compound, a uniform epoxy resin composition can be easily prepared.

The curing agent (2) contained in the epoxy resin composition of the present invention is a compound that crosslinks an epoxy compound or a polyvinyl acetal resin, and includes amines; dicyandiamide; tetramethylguanidine; acid anhydrides; polycarboxylic acid hydrazide; Mercaptan; polyphenol compound; BF ₃ .amine complex; including conventional epoxy curing agents such as aromatic sulfonium salts. Preferred examples of the curing agent (2) include dicyandiamide and aromatic diamine.

  Examples of amines have active hydrogen such as 4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenylsulfone, 3,3′-diaminodiphenylsulfone, m-phenylenediamine, m-xylylenediamine. Aromatic polyamines; aliphatic polyamines having active hydrogen such as diethylenetriamine, triethylenetetramine, isophoronediamine, bis (aminomethyl) norbornane, bis (4-aminocyclohexyl) methane, dimer acid ester of polyethyleneimine; these active hydrogens Modified amines obtained by reacting a compound such as an epoxy compound, acrylonitrile, phenol with formaldehyde, thiourea, etc., with polyamines having the above are included.

Examples of acid anhydrides include carboxylic acid anhydrides such as hexahydrophthalic anhydride, tetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, methyl nadic acid anhydride. Examples of the polycarboxylic acid hydrazide include adipic acid hydrazide and naphthalenedicarboxylic acid hydrazide. Examples of polyphenol compounds include novolac resins. Examples of the polymercaptan include thioglycolic acid and polyol ester. Examples of the BF ₃ .amine complex include boron trifluoride ethylamine complex. Examples of the aromatic sulfonium salt include diphenyliodonium hexafluorophosphate, triphenylsulfonium hexafluorophosphate, and the like.

The curing agent (2) may further contain a curing accelerator for the purpose of adjusting the curing reaction. Examples of the curing accelerator include a urea compound having a specific structure, a tertiary amine, and the like.
For example, when dicyandiamide is used as a curing agent, 3-phenyl-1,1-dimethylurea, 3- (3,4-dichlorophenyl) -1,1-dimethylurea (DCMU), 3- Can be combined with urea derivatives such as (3-chloro-4-methylphenyl) -1,1-dimethylurea, 2,4-bis (3,3-dimethylureido) toluene; carboxylic anhydride as a curing agent When a novolac resin is used, a tertiary amine can be combined as a curing aid. Examples of tertiary amines include tertiary amines that do not have active hydrogen such as dimethylaniline, dimethylbenzylamine, 2,4,6-tris (dimethylaminomethyl) phenol and 1-substituted imidazoles.

The polyvinyl acetal resin (3) contained in the epoxy resin composition of the present invention is characterized by containing the following repeating unit A, repeating unit B, and repeating unit C.

  The total content of the repeating units A to C in the polyvinyl acetal resin (3) is preferably 80 to 100% with respect to all the repeating units. Examples of other repeating units that can be included in the polyvinyl acetal resin (3) include an intermolecular acetal unit represented by the following formula and a hemiacetal unit. However, the content of vinyl acetal units (R ≠ hydrogen atom, alkyl having 1 to 3 carbon atoms) other than the repeating unit A contained in other repeating units is preferably less than 5 mol%.

  In the polyvinyl acetal resin (3), the repeating units A to C may be regularly arranged (block copolymer, alternating copolymer, etc.) or randomly arranged (random copolymer). Are preferably arranged randomly.

The repeating unit A is a repeating unit having an acetal site, and can be formed, for example, by a reaction between a continuous polyvinyl alcohol unit and an aldehyde (R—CHO).
R in the repeating unit A is any group or atom, and may be a hydrogen atom, an alkyl group, an alkoxy group, an aryl group, or the like. However, when R in the repeating unit A is a bulky group (for example, a hydrocarbon group having a large number of carbon atoms), the softening point of the polyvinyl acetal resin tends to decrease. An epoxy resin composition containing a polyvinyl acetal-based resin having a low softening point may have a greatly reduced viscosity at a high temperature and the resin may flow too much. In addition, a polyvinyl acetal resin in which R is a bulky group has high solubility in a solvent, but may be inferior in chemical resistance.
Therefore, a prepreg using such an epoxy resin composition containing a polyvinyl acetal resin as a matrix resin may have problems such as fiber disturbance, deterioration of dimensional accuracy of a molded product, and low chemical resistance. Therefore, R in the repeating unit A is preferably a hydrogen atom (H) or alkyl having 1 to 3 carbon atoms, and more preferably a hydrogen atom.

  The repeating unit B and the repeating unit C are repeating units each including an acetate site and a hydroxy site.

  As described above, R in the repeating unit A of the polyvinyl acetal resin is preferably a hydrogen atom (H) or an alkyl having 1 to 3 carbon atoms. On the other hand, the greater the carbon number of R in the repeating unit A, the higher the solubility of the polyvinyl acetal resin in the epoxy resin, and there is no undissolved residue and there is a tendency to dissolve quickly. Conversely, when R in the repeating unit A is small (for example, a hydrogen atom or alkyl having 1 to 3 carbon atoms), the polyvinyl acetal resin has low solubility in an epoxy resin, and a sufficient amount of polyvinyl acetal resin In some cases, the resin cannot be dissolved in the epoxy resin or cannot be sufficiently dispersed. Therefore, it may be difficult to obtain an epoxy resin composition having sufficient strength.

The inventor appropriately controls the content of the repeating units A to C in the polyvinyl acetal resin, so that even if R in the repeating unit A is a hydrogen atom (H) or an alkyl having 1 to 3 carbon atoms, It has been found that a polyvinyl acetal resin having higher solubility in an epoxy resin can be obtained.
That is, the content of the repeating unit A in the polyvinyl acetal resin (3) is 50 to 80 [mol%], the content of the repeating unit B is 15 to 30 [mol%], and the content of the repeating unit C is It has been found that by setting the amount to 0.1 to 15 [mol%], a resin having high solubility in an epoxy resin can be obtained even if R in the repeating unit A is a hydrogen atom or alkyl having 1 to 3 carbon atoms. It was.
Further, the content of the repeating unit A is 65 to 75 [mol%], the content of the repeating unit B is 17 to 25 [mol%], and the content of the repeating unit C is 2 to 12 [mol%] (preferably 2 It has been found that a resin having a higher solubility in an epoxy resin can be obtained by setting it to less than 10 [mol%].

  In order to sufficiently obtain the chemical resistance, flexibility, wear resistance, and mechanical strength of the polyvinyl acetal resin, the content of the repeating unit A is preferably 50 mol% or more. Moreover, it may be difficult to make the repeating unit higher than 80 [mol%] in the production of a polyvinyl acetal resin. That is, since the repeating unit A in the polyvinyl acetal resin can be formed by acetalizing a vinyl alcohol component that is continuously present in the molecular chain, it is possible to acetalize a non-continuous vinyl alcohol component. However, it may be difficult to make the repeating unit A higher than 80 [mol%].

  If the content rate of the repeating unit B is 15 [mol%] or more, the solubility of the polyvinyl acetal resin in the solvent and the solubility in the epoxy resin will be improved. However, when the content exceeds 30 [mol%], the content of the repeating unit A is relatively decreased, so that the chemical resistance, flexibility, wear resistance, and mechanical strength of the polyvinyl acetal resin are decreased, and expected. Performance is difficult to demonstrate.

  Moreover, when the content rate of the repeating unit C is larger than 15 [mol%], the solubility to a solvent and the solubility to an epoxy resin will fall remarkably. Although the content of the repeating unit C may be less than 0.1 [mol%], when the polyvinyl alcohol is acetalized in the production of the polyvinyl acetal resin, the repeating unit B and the repeating unit C have an equilibrium relationship. Therefore, it is difficult to make the content rate of the repeating unit C less than 0.1 [mol%].

  The content of each of the repeating units A to C in the polyvinyl acetal resin can be measured according to JIS K 6729.

The weight average molecular weight of the polyvinyl acetal resin is preferably 5,000 to 300,000, and more preferably 10,000 to 150,000. Polyvinyl acetal resins having a weight average molecular weight of less than 5,000 have high solubility in epoxy compounds but have low molecular weights. Therefore, such as improvement in molding processability, bending strength, and tensile strength of epoxy resin compositions The features of the invention may not be fully exhibited. On the other hand, a polyvinyl acetal resin having a weight average molecular weight exceeding 300,000 may excessively increase the viscosity of the epoxy resin composition and reduce workability.
The weight average molecular weight of the polyvinyl acetal resin can be measured by a GPC method. Specific measurement conditions may be as follows.
Detector: 830-RI (manufactured by JASCO)
Oven: NFL-700M manufactured by Nishio
Separation column: Shoudex KF-805L x 2 Pump: PU-980 (manufactured by JASCO)
Temperature: 30 ° C
Carrier: Tetrahydrofuran Standard sample: Polystyrene

The Ostwald viscosity of the polyvinyl acetal resin is preferably 1 to 100 [mPa · s]. Viscosity is proportional to the molecular weight. Polyvinyl acetal resins with a viscosity of less than 1 [mPa · s] are highly soluble in epoxy compounds but have a low molecular weight. The characteristics of the present invention, such as improvement in properties, bending strength, and tensile strength, may not be fully exhibited. On the other hand, a polyvinyl acetal resin having a viscosity exceeding 100 [mPa · s] may excessively increase the viscosity of the epoxy resin composition and reduce workability.
The Oswald viscosity can be measured by dissolving 5 g of a polyvinyl acetal resin in 100 ml of dichloroethane and using an Ostwald-Cannon Fenske Viscometer at 20 ° C.

The glass transition temperature of the polyvinyl acetal resin is preferably 60 to 110 ° C, more preferably 80 to 100 ° C. A polyvinyl acetal resin having a low glass transition temperature is not preferable because it has low heat resistance and the heat resistance temperature of the final molded product is lowered.
The glass transition temperature of the polyvinyl acetal resin can be adjusted by the number of carbon chains of the substituent R of the repeating unit A (for vinyl acetal). That is, the longer the carbon chain of R, the lower the glass transition temperature. For example, the glass transition temperature of polyvinyl formal in which R is hydrogen can be about 98 ° C., the glass transition temperature of acetoacetal having 1 carbon atom can be about 74 ° C., and the butyral resin having 3 carbon atoms can be about 67 ° C.
The glass transition temperature of the polyvinyl acetal resin is measured by DSC-50 manufactured by Shimadzu Corporation.

  The polyvinyl acetal resin can be produced by an arbitrary method, but examples of the general production method include a precipitation method and a dissolution method.

  In the precipitation method, polyvinyl alcohol is obtained by saponifying polyvinyl acetate obtained by polymerizing a vinyl acetate monomer with a radical polymerization initiator. An acid catalyst is added to the obtained aqueous solution of polyvinyl alcohol, and an aldehyde compound is further added and reacted to obtain a polyvinyl acetal resin. As the reaction proceeds, a polyvinyl acetal resin that is hardly soluble in water is precipitated. The precipitated polyvinyl acetal resin is washed with water, filtered and dried.

  The dissolution method includes a method of synthesizing from polyvinyl alcohol and a method of synthesizing from polyvinyl acetate obtained by polymerizing a vinyl acetate monomer with a radical polymerization initiator. In any case, polyvinyl alcohol or polyvinyl acetate is dissolved in a good solvent of polyvinyl acetal, and an acid catalyst and an aldehyde compound are added to obtain a polyvinyl acetal resin. After completion of the reaction, the polyvinyl acetal resin dissolved in the solvent is dispersed in a polyvinyl acetal hardly soluble solvent to precipitate the polyvinyl acetal resin. The precipitated polyvinyl acetal resin is washed with water, filtered and dried.

  The epoxy resin composition of the present invention includes an epoxy compound (1), a curing agent (2), and a polyvinyl acetal resin (3), but may further include other optional components. Examples of other optional components include curing aids, various fillers, thermoplastic resins other than polyvinyl acetal resins, and thermoplastic resins having hydroxyl groups other than polyvinyl acetal (preferably phenoxy resins).

The content of the polyvinyl acetal resin in the epoxy resin composition of the present invention varies depending on the purpose and application of the composition. When the content of the polyvinyl acetal resin is small, the effect of improving the bending strength and tensile strength (for example, 90 ° direction) of the prepreg produced using the epoxy resin composition may not be sufficiently achieved. On the other hand, an epoxy resin composition containing too much polyvinyl acetal resin has a viscosity, particularly a viscosity at a high temperature, which makes it difficult to mix without a solvent, resulting in a decrease in resin fluidity during molding. As a result, defects are easily generated in the cured product. The defect means that a part of the polyvinyl formal resin is not dissolved and voids are generated due to mixing of bubbles (air) due to a decrease in fluidity.
Therefore, the content of the polyvinyl acetal resin (3) is usually 0.1 to 30 parts by mass and preferably 0.5 to 20 parts by mass with respect to 100 parts by mass of the epoxy compound (1). .

  Although content of the hardening | curing agent in the epoxy resin composition of this invention is not specifically limited, As a standard, it is 0.5-50 mass parts with respect to 100 mass parts of epoxy compounds, and is 1-25 mass parts normally.

The epoxy resin composition of the present invention can be obtained, for example, as follows.
A mixture of an epoxy compound and a polyvinyl acetal resin is melted by heating and stirred to obtain a uniform transparent composition. The melting temperature is preferably about 80 to 200 ° C., and the stirring time is preferably 0.25 to 6 hours, but is not particularly limited.
A curing agent is added to the obtained melt and stirred to obtain an epoxy resin composition. The temperature at this time is preferably room temperature to 100 ° C., and the stirring time is preferably 10 to 120 minutes, but is not particularly limited.

  The epoxy resin composition of the present invention can be used for any application, but is preferably used as a composite material (prepreg or the like) reinforced with fibers. In addition, it can be applied to other fields that make use of characteristics such as impact resistance, adhesives, paints, linings, electrical insulating materials, civil engineering and building materials.

[Prepreg of the present invention]
The prepreg of the present invention is characterized by comprising a fiber (reinforced fiber) impregnated with the above-described epoxy resin composition of the present invention or a cured product thereof. Examples of the fibers include carbon fibers, glass fibers, aramid fibers, boron fibers, alumina fibers, organic fibers (such as polyethylene fibers), and the like.

The amount of the fiber contained in the prepreg of the present invention is preferably 20 to 80% by mass, and more preferably 30 to 70% by mass with respect to the entire prepreg.
The amount of fiber contained in the prepreg is determined from the change in weight before and after resin removal by removing the resin component from the prepreg by dissolving it in a mixed solvent of toluene / methanol (7/3).

The prepreg of the present invention is produced, for example, by 1) impregnating fibers with the epoxy resin composition of the present invention mixed in a solvent (so-called wet method), or 2) the present invention mixed without heating in a solvent-free state. The epoxy resin composition can be impregnated into a fiber for production (so-called hot melt method).
The impregnation into the fiber can be performed, for example, by the following procedure. The fiber is aligned in one direction on the epoxy resin composition (resin film) of the present invention coated on the release paper. Further, a release paper is placed thereon and heat-compressed to cure the resin. The heating temperature is preferably room temperature to 200 ° C. In addition to heating, the resin can be cured by light irradiation or the like.
Moreover, the prepreg of the present invention is formed into an arbitrary shape.

<Production Example 1> Production of PVF 1-1 Polyvinyl formal (trade name: Vinylec E type; manufactured by Chisso Corporation) is dissolved in a mixed solvent of acetic acid and water (25: 1), and the vinyl alcohol content and vinyl acetate in the molecular chain are dissolved. The ratio of minutes was adjusted by equilibrium movement.
Specifically, Vinylec E type 3.75 [kg] and paraform 0.43 [kg] were added to a mixed solvent of acetic acid 45.00 [kg] and pure water 1.83 [kg]. The obtained mixture was heated to 60 ° C. to obtain a uniform solution. After confirming dissolution, concentrated sulfuric acid 0.45 [kg] was added, the reaction solution temperature was raised to 80 ° C., and the reaction was carried out for 6 hours.
After completion of the reaction, the reaction solution was transferred to a granulator, and pure water was added with stirring to precipitate a polymer and granulate. The granulated polymer was collected by filtration and further washed with water to remove the acid component. The obtained polymer particles were dehydrated and dried to obtain PVF1-1. Table 1 shows the physical properties of PVF1-1.

<Production Example 2> Production of PVF2-1 Polyvinyl formal (trade name Vinylec H type; manufactured by Chisso Corporation) is dissolved in a mixed solvent of acetic acid and water (25: 1), and the vinyl alcohol content and vinyl acetate in the molecular chain are dissolved. The ratio of minutes was adjusted by equilibrium movement.
Specifically, Vinylec H type 3.75 [kg] and paraform 0.43 [kg] were added to a mixed solvent of acetic acid 45.00 [kg] and pure water 1.83 [kg]. The obtained mixture was heated to 60 ° C. to obtain a uniform solution. After confirming dissolution, concentrated sulfuric acid 0.45 [kg] was added, the reaction solution temperature was raised to 80 ° C., and the reaction was carried out for 6 hours.
After completion of the reaction, the reaction solution was transferred to a granulator, and pure water was added with stirring to precipitate a polymer and granulate. The granulated polymer was collected by filtration and further washed with water to remove the acid component. The obtained polymer particles were dehydrated and dried to obtain PVF2-1. Table 1 shows the physical properties of PVF2-1.

  In Table 1, PVF1-2 and PVF2-2 are polyvinyl formal (trade name: Vinylec E type, manufactured by Chisso Corporation) and polyvinyl formal (trade name: H type, manufactured by Chisso Corporation), respectively.

  The weight average molecular weight, Ostwald viscosity, and unit ratio were measured according to the methods described above.

<Example 1>
1. The epoxy compound and vinyl formal resin of the formulation shown in Table 2 were stirred at 150 ° C. for 2 hours to obtain a uniform transparent composition.

Each epoxy compound in Table 2 represents the following resin.
1. Epicoat 1004 (Bisphenol A type epoxy resin; made by Yuka Shell Epoxy)
Epoxy equivalent: 875-975 g / eq, softening point: 97 ° C., molecular weight: about 1650, viscosity (Gardner-Holt method, butyl carbitol solution with a resin content of 40%, 25 ° C.); Q to U
2. Epicoat 1009 (bisphenol A type epoxy resin; manufactured by Yuka Shell Epoxy)
Epoxy equivalent: 2400-3300 g / eq, softening point: 144 ° C., molecular weight: about 3800, viscosity (Gardner-Holt method, butyl carbitol solution with a resin content of 40%, 25 ° C.); Z _{3 to} Z ₅
3. Epicoat 828 (bisphenol A type epoxy resin; manufactured by Yuka Shell Epoxy)
Epoxy equivalent: 184 to 194 g / eq, viscosity (Poise / 25 ° C.); 120 to 150
4). Epicoat 152 (phenol novolac type epoxy resin; manufactured by Yuka Shell Epoxy)
Epoxy equivalent: 172 to 178 g / eq, viscosity (Poise / 52 ° C.); 14 to 18, hue (Gardner); 6 ≧

2. To the uniform transparent composition, dicyandiamide (DICY) 0.4 [kg] and dichlorodimethylurea (DCMU) 0.4 [kg] were added and stirred at 60 ° C. for 30 minutes to obtain an epoxy resin composition 1-1. Got.

3. The epoxy resin composition 1-1 was coated on a release paper to obtain a resin film.
4). Next, carbon fibers (tensile strength 3530 [MPa]; tensile modulus 230 [MPa], density 1.8 [g / cm ³ ], filament diameter 7 [μm]) are aligned in one direction on the resin film, Further, a release paper was placed thereon and compressed with a hot roll at 120 ° C. to obtain a unidirectional prepreg 1-1. The fiber content in the prepreg 1-1 was 65% by mass.

The tackiness (initially, after standing for 10 days) of this prepreg 1-1 and the resin flow were measured. The tackiness was evaluated by visually observing the adhesion when two prepregs were superposed. The resin flow was measured as follows. The molded prepreg was cut into 100 cm ² , three sheets were stacked and pressurized to 0.4 MPa with a press, then heated to 120 ° C. and pressed for 10 minutes. Thereafter, it was cooled to 30 ° C., the laminated prepreg was taken out, and the protruding burrs were removed. The weight of the prepreg before and after pressing was measured, and the resin flow rate was determined from the weight ratio.
These evaluation results are shown in Table 3.

5. The prepreg 1-1 was laminated in one direction and cured in an autoclave at 130 ° C. for 2 hours to form a laminate (composite 1-1) having a thickness of 2 [mm]. The resin flow during the molding was evaluated by visual observation. Further, 1) Tensile strength, elastic modulus and elongation in the direction of 90 ° C., and 2) 0 degree bending strength (FS) and 90 degree bending strength (FS) of the obtained composite 1-1 were measured. did. In particular, the tensile strength, elastic modulus, and elongation of 1) depend on the strength of the resin.

  Table 3 shows the evaluation results and measurement results of the prepreg 1-1 and the composite 1-1.

<Example 2>
Except for changing PVF1-1 (1.5 [kg]) in Example 1 to PVF2-1 (2.0 [kg]), epoxy resin composition 2-1 was prepared under the same conditions as in Example 1. The prepreg 2-1 and the composite 2-1 were prepared and evaluated and measured. These evaluation and measurement results are shown in Table 2.

<Comparative Example 1>
Epoxy resin composition 1-2 was prepared in the same manner as in Example 1 except that PVF1-1 in Example 1 was changed to PVF1-2. PVF1-2 was less soluble in epoxy resin than PVF1-1 and could not completely dissolve a predetermined amount of PVF (1.5 [kg]). For this reason, the prepreg could not be molded.

<Comparative Example 2>
An epoxy resin composition 1-3 was prepared in the same manner as in Example 1 except that the amount of PVF1-2 in Comparative Example 1 was reduced from 1.5 [kg] to 0.6 [kg]. 3 and composite 1-3 were molded and evaluated. These evaluation and measurement results are shown in Table 2.

<Comparative Example 3>
An epoxy resin composition 2-2 was prepared in the same manner as in Example 2 except that PVF2-1 in Example 2 was changed to PVF2-2. PVF2-2 was less soluble in epoxy resin than PVF2-1, and a predetermined amount of PVF (2.0 [kg]) could not be completely dissolved. For this reason, the prepreg could not be molded.

<Comparative example 4>
An epoxy resin composition 2-3 was prepared under the same conditions as in Example 1 except that the amount of PVF2-2 added in Comparative Example 3 was reduced from 2.0 [kg] to 0.7 [kg], and prepreg 2 -3 and composite 2-3 were molded and evaluated.

<Comparative Example 5>
Except not adding a polyvinyl formal resin, the epoxy resin composition 3 was prepared on the same conditions as Example 1, and the prepreg 3 and the composite 3 were shape | molded and evaluated.

Since the polyvinyl acetal resin used in Comparative Examples 1 and 3 has low solubility, the same amount (1.5 kg or 2.0 kg) of polyvinyl acetal resin as in Examples 1 and 3 could not be dissolved. Therefore, the prepreg could not be produced in Comparative Examples 1 and 3.
On the other hand, the polyvinyl acetal resin used in Examples 1 and 2 has high solubility, and an epoxy resin composition having a high concentration of polyvinyl acetal resin could be obtained. Further, it can be seen that the resin flow of the prepreg obtained from this epoxy resin composition is small, the evaluation of tackiness is high, and the strength of the composite is also high.
On the other hand, in Comparative Examples 2 and 4, since the content of the polyvinyl acetal resin is low as compared with Examples 1 and 2, the resin flow of the prepreg is large, the evaluation of tackiness is low, and the strength of the composite is sufficient. In addition, since Comparative Example 5 does not contain a polyvinyl acetal resin, it can be seen that the resin flow of the prepreg is large, the evaluation of tackiness is low, and the strength of the composite is not sufficient.

Claims (4)

An epoxy resin composition comprising an epoxy compound, a curing agent, and a polyvinyl acetal resin containing repeating units A, B and C represented by the following formulae:
In the polyvinyl acetal resin, the content of the repeating unit A is 50 to 80 mol%, the content of the repeating unit B is 15 to 30 mol%, and the content of the repeating unit C is 0.1 to 15 mol%. An epoxy resin composition characterized by being.

  The epoxy resin composition according to claim 1, wherein R in the repeating unit A represents a hydrogen atom.   The epoxy resin composition according to claim 1 or 2, wherein the content of the polyvinyl acetal resin is 0.1 to 30 parts by mass with respect to 100 parts by mass of the epoxy compound.   A prepreg comprising reinforcing fibers impregnated with the epoxy resin composition according to claim 1.