JP2000017090A - Prepreg and fiber-reinforced composite material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a fiber-reinforced composite material suitably employable as a structural material for an airplane in particular which not only has a high compression strength but also is excellent in resistance to heat and environment and in durability by providing a prepreg comprising a reinforcing fiber consisting of a single fiber having a substantially completely round cross section and a matrix resin excellent in adhering to the fiber. SOLUTION: The objective prepreg comprises a reinforcing fiber consisting of a single fiber having a substantially completely round cross section impregnated with an epoxy resin composition containing at least the following constituents [A], [B] and [C]: [A]: An epoxy resin composition containing at least 60 pts.wt., based on 100 pts.wt. of the epoxy resin composition, of a tetraglycidylamine-based epoxy resin. [B]: A granular dicyanodiamide. [C]: A urea compound. The fiber-reinforced composite material is obtained by molding the prepreg.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention provides excellent strength properties,
A prepreg suitable for producing a fiber-reinforced composite material having heat resistance and environmental resistance, and a fiber-reinforced composite material formed by laminating and curing the prepreg by heating and particularly applicable to structural materials for aircraft It is about.

[0002]

2. Description of the Related Art A carbon fiber reinforced composite material using carbon fiber having excellent specific strength and specific elastic modulus as a reinforcing fiber and an epoxy resin having good wettability and adhesion with the carbon fiber as a matrix resin has excellent mechanical properties. Due to its properties, it is used for a wide range of applications in the fields of aerospace, sports and leisure, civil engineering and construction, etc. Compositions have been devised, and a number of useful prepregs, intermediates, and composites have been produced by combining them with carbon fibers. Above all, in aircraft applications, composite materials used as structural materials often require a high level of performance.

In applying a fiber reinforced composite material to an aircraft structural material, it is necessary to consider particularly increasing the compressive strength in terms of strength characteristics, and at the same time, to improve heat resistance, environmental resistance, impact resistance and the like. The characteristics also need to be enhanced. As a means for this, first, in the case of reinforcing fibers,
It is necessary to use a reinforcing fiber having high compressive strength and tensile strength. On the other hand, in the case of a matrix resin, it is necessary to provide the matrix resin itself with high rigidity and ensure appropriate toughness. Furthermore, by increasing the adhesiveness between the reinforcing fiber and the matrix resin as much as possible, the properties of these materials are cooperated, and in addition to strength properties such as compressive strength, heat resistance, environmental resistance, impact resistance, etc. It is necessary that the properties be effectively developed.

A prepreg using a tetraglycidyl-type epoxy resin and diaminodiphenylsulfone as a curing agent as a matrix resin exhibits high adhesiveness between the carbon fiber and the matrix resin. It has been used regularly. However, such a resin composition requires a high temperature of about 180 ° C. for heating when a prepreg is cured to form a molded product, and requires a large amount of energy for heating, so that it can be applied to aircraft structural materials. While a fiber-reinforced composite material having extremely high strength characteristics can be obtained after molding, a prepreg capable of realizing a significant energy saving compared with the prior art when manufacturing a molded product is strongly desired.

[0005] Regarding the reinforcing fibers, the cross-sectional shape of the monofilament varies among various shapes such as a perfect circle, an ellipse, an egg, a soybean, a trefoil, and the like. Although it is preferable in terms of strength characteristics that the amount of resin used can be minimized, and the effect of dispersing the applied load stress also appears, the fiber and the matrix resin reduce the so-called anchor effect of the fiber. There is a problem that a composite material having good strength properties cannot be obtained as a result.

Japanese Patent Application Laid-Open No. 8-81572 discloses an example of trying to obtain a composite material having as high a strength characteristic as possible by balancing these contradictory effects. In order to produce a prepreg densely packed, carbon fibers whose cross-sectional shape of a single fiber is almost a perfect circle, and a modified epoxy resin obtained by modifying a bisphenol A type epoxy resin with diaminodiphenyl sulfone, dicyandiamide as a curing agent, Further, a prepreg comprising a matrix resin using dichlorophenylurea as a curing catalyst is disclosed, but a composite material produced from such a prepreg expresses between a carbon fiber and a matrix resin when the resin is dry. The adhesive property is sufficiently high and the strength characteristics of the composite material are good, but once the resin is When wet, the adhesive property is not developed. At this time, when a load is applied, peeling occurs at the interface region between the carbon fiber and the matrix resin, and there is a problem that the composite material is damaged, and both strength characteristics and weather resistance are required. It has been difficult to apply to structural materials for aircraft.

[0007] The inventors of the present invention have proposed a fiber reinforced fiber having a substantially circular cross section and a prepreg made of an epoxy resin composition which is firmly bonded to the reinforcing fiber with significantly lower energy consumption than before. It has been found that a composite material is obtained by molding, and that this fiber-reinforced composite material can be applied to aircraft structural materials requiring high strength properties, heat resistance and environmental resistance without any problem, and the present invention has been achieved. .

[0008]

SUMMARY OF THE INVENTION The present invention uses a reinforcing fiber having a substantially perfect circular cross section, and can maintain high adhesion between the reinforcing fiber and the matrix resin even in a wet heat environment. A molded article can be manufactured with lower energy consumption, and a fiber-reinforced composite material obtained by molding has a high strength property particularly desired for structural materials for aircraft,
An object of the present invention is to provide a prepreg that can exhibit heat resistance and environmental resistance.

[0009]

In order to solve the above problems, a prepreg of the present invention has the following configuration. That is, an epoxy resin composition containing at least the following components [A], [B], and [C] is characterized by being impregnated into a reinforcing fiber having a substantially perfect circular cross section. Prepreg.

[A]: 6 parts by weight of tetraglycidylamine type epoxy resin per 100 parts by weight of epoxy resin compound
Epoxy resin blend [B]: particulate dicyandiamide [C]: urea compound blended in an amount of 0 part by weight or more. In order to solve the above problems, the fiber-reinforced composite material of the present invention has the following configuration. That is, it is a fiber reinforced composite material obtained by laminating the prepreg, heating at 100 to 140 ° C., and curing and molding.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail.

The present invention relates to a prepreg that can be suitably used in producing a large-scale material typified by an aircraft structural material, and a fiber-reinforced composite material obtained by molding the prepreg.

In order to enhance the strength characteristics of the composite material obtained after molding as much as possible and to impart the high characteristics required for structural materials for aircraft, the prepreg of the present invention has a substantially monofilament cross-sectional shape. It is necessary to use reinforcing fibers that are perfectly circular. The diameter of the cross section of a single fiber of such a reinforcing fiber is preferably 5 to 9 μm, more preferably 6 to 8 μm.
m is good. When the diameter of the cross section is less than 5 μm, the hardener particles hardly enter the reinforcing fibers, so that the adhesiveness with the matrix resin is reduced. When the diameter exceeds 9 μm, the total contact area between the reinforcing fibers and the matrix resin is reduced. It becomes small, and the adhesiveness between the two decreases. Here, the expression that the cross-sectional shape is substantially a perfect circle generally means that the ratio R / r of the radius R of the circle circumscribing the cross-sectional shape to the radius r of the inscribed circle is 1 to 1.
1.1.

The reinforcing fibers preferably have a resin-impregnated strand tensile strength (hereinafter referred to as tensile strength) of 4 GPa or more. If the tensile strength is less than 4 GPa, the strength characteristics of the obtained composite material may be insufficient, and it may be difficult to apply the composite material to aircraft structural materials and the like. However, the reinforcing fiber having a tensile strength of at most about 10 GPa is often sufficient to exhibit the effects of the present invention. Further, the reinforcing fiber is preferably a carbon fiber from the viewpoint of adhesiveness to an epoxy resin and strength properties, and other silicon carbide fiber, glass fiber, aramid fiber, boron fiber, high-strength polyethylene fiber, etc. A fine thread may be used. In addition, as the molding material using the reinforcing fibers, those obtained by blending each as a single fiber can be suitably used.

As the main component of the component [A] in the present invention, of the glycidyl-type epoxy resins such as glycidyl ether-type epoxy resin and glycidylamine-type epoxy resin, the latter glycidylamine-type epoxy resin is used in combination with reinforcing fibers. It is effective from the viewpoint of improving the adhesiveness. Among them, a glycidylamine type epoxy resin in which two glycidylamino groups are present in a repeating unit (hereinafter, referred to as a repeating unit) corresponding to one monomer molecule, that is, tetra Glycidylamine type epoxy resin is more effective. Those having one glycidylamino group in the repeating unit tend to have poor adhesion between the reinforcing fiber and the matrix resin, and those having three or more glycidylamino groups in the repeating unit are those of the matrix resin. Of the composite material having high impact resistance cannot be obtained as a result.

Examples of the tetraglycidylamine type epoxy resin include tetraglycidyl metaxylenediamine, tetraglycidyldiaminodiphenylmethane, tetraglycidylbisaminomethylcyclohexane, tetraglycidylaminophenyldiisopropylbenzene, and the like, and a mixture thereof. Glyglycidyl diaminodiphenylmethane can be preferably used because it has a remarkable effect of improving the adhesiveness between the reinforcing fiber and the matrix resin, and improves the strength characteristics, heat resistance and environmental resistance of the obtained composite material.

The amount of such a resin must be 60 parts by weight or more based on 100 parts by weight of the epoxy resin compound, preferably 70 parts by weight or more, more preferably 80 parts by weight or more. good. If the compounding amount is less than 60 parts by weight, when moisture enters the interface region between the reinforcing fiber and the matrix resin, for example, when the obtained composite material is immersed in water, the adhesive force in the interface region is maintained. No longer possible, which impairs the strength properties of the composite material.
When an epoxy resin other than the tetraglycidylamine type epoxy resin described later is compounded in the component [A], the compounding amount of the tetraglycidylamine type epoxy resin in the component [A] is 97 parts by weight or less. I do.

The constituent element [A] is mixed with the above-mentioned tetraglycidylamine-type epoxy resin and, if necessary, an epoxy resin other than the following tetraglycidylamine-type epoxy resin.

That is, bisphenol A type epoxy resin (epoxy resin having bisphenol A as a precursor),
Bisphenol type epoxy resins such as bisphenol F type epoxy resin (epoxy resin having bisphenol F as a precursor), bisphenol S type epoxy resin (epoxy resin having bisphenol S as a precursor), and cresol novolak type epoxy resin (cresol novolak) Novolak-type epoxy resins such as epoxy resin as a precursor), phenol novolak-type epoxy resin (epoxy resin with phenol novolak as a precursor), and other tetraglycidyl ether-type epoxy resins (epoxy resin with tetraphenol as a precursor) , Triglycidyl ether type epoxy resin (epoxy resin with triphenol as precursor), resorcinol type epoxy resin (epoxy resin with resorcinol as precursor), naphthalene type epoxy resin (Epoxy resin having dihydroxynaphthalene as a precursor), biphenyl type epoxy resin (epoxy resin having dihydroxybiphenyl as a precursor), fluorene type epoxy resin (epoxy resin having bishydroxyphenylfluorene as a precursor), dicyclopentadiene type An epoxy resin (an epoxy resin composed of a condensate of dicyclopentadiene and phenol), an epoxy resin having an oxazolidone ring, or a mixture thereof.

Here, the epoxy resin having an oxazolidone ring is generally represented by the following structural chemical formula.

[0021]

Embedded image Here, R ₁ , R ₂ , and R ₃ are hydrocarbon groups that may contain oxygen, and R ₁ and R ₃ may be the same or different, and a bisphenol group ( -O
_{-Ph-CR 2 -Ph-O-} CH 2 CH (OH) CH
_2- ; Ph = C ₆ H ₄ , R = CH ₃ or H).

The epoxy resin having an oxazolidone ring can be prepared by the method disclosed in JP-A-5-43655 in the presence of a catalyst such as a tertiary amine, a quaternary ammonium salt, a phosphonium compound or a lithium compound. Can be obtained by reacting Examples of the isocyanate compound include isophorone diisocyanate, xylene diisocyanate, diphenylmethane diisocyanate, tolylene diisocyanate, hexamethylene diisocyanate, and a mixture thereof, and examples of the epoxy compound include bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, and bisphenol. S diglycidyl ether and the like, or a mixture thereof.

Among the epoxy resins other than the above-mentioned tetraglycidylamine type epoxy resin, the bisphenol type epoxy resin maintains high adhesiveness with the reinforcing fiber,
It is preferable to improve the toughness of the resin, and the novolak type epoxy resin and the dicyclopentadiene type epoxy resin have the effect of appropriately suppressing the tack of the prepreg while maintaining the heat resistance and the environmental resistance of the obtained composite material. It is particularly preferably used as an epoxy resin other than the tetraglycidylamine type epoxy resin.

Further, when the above-mentioned epoxy resin having an oxazolidone ring is used as an epoxy resin other than the tetraglycidylamine type epoxy resin, the adhesiveness with the reinforcing fiber is further improved, and strength properties such as compressive strength and the like are improved.
It is preferable because a fiber-reinforced composite material having more excellent heat resistance and environmental resistance can be obtained.

It is preferable that the amount of the epoxy resin other than the tetraglycidylamine type epoxy resin blended in the component [A] is as small as possible. 40 parts by weight, preferably 3 to 30 parts by weight, more preferably 3 to 2 parts by weight.
0 parts by weight is good.

The component [B] in the present invention is a particulate dicyandiamide. In the present invention, it is effective to mix dicyandiamide (hereinafter referred to as DICY) as a curing agent.

DICY is a fine-grained compound belonging to an amine-based curing agent and is hardly soluble in an epoxy resin composition corresponding to a bulk in a low-temperature region, but dissolves at 100 ° C. or higher and reacts with the epoxy resin. Starts. For this reason, an epoxy resin composition or prepreg using DICY as a curing agent has particularly good storage stability. Also DI
The compounding amount of CY with respect to 100 parts by weight of the epoxy resin compound is preferably 2 to 10 parts by weight, more preferably 4 to 8 parts by weight, and still more preferably 5 to 7 parts by weight. If the amount is less than 2 parts by weight, the adhesion between the reinforcing fiber and the matrix resin tends to decrease. If the amount exceeds 10 parts by weight, the hygroscopicity of the matrix resin increases, and the heat resistance of the obtained composite material increases. , Environmental resistance is reduced.

The average particle diameter of the DICY particles is 1 to 15 μm.
And more preferably 3 to 13 μm, and still more preferably 5 to 10 μm. The average particle diameter of the DICY particles is 1
If it is less than μm, the dissolution of DICY in the epoxy resin composition is excessively promoted, and even at a temperature near room temperature, the curing reaction may proceed, and the storage stability of the epoxy resin composition or the prepreg is impaired. If the average particle size of the DICY particles is larger than 15 μm, even when the reinforcing fibers are impregnated with the resin while applying pressure and heating to the prepreg, the DICY particles are not contained in the reinforcing fiber bundle.
Is difficult to penetrate, whereby the adhesiveness between the reinforcing fiber and the matrix resin is not sufficiently exhibited, and a composite material having excellent strength characteristics such as compressive strength after molding cannot be obtained.

In addition to DICY, diaminodiphenyl sulfone (hereinafter referred to as DDS) is used as a curing agent in DI.
When used in combination with CY, the reinforcing fibers and the matrix resin are more firmly bonded. In particular, 3 to 5 parts by weight of DICY with respect to 100 parts by weight of the epoxy resin compound,
The prepreg composed of the epoxy resin composition containing 5 to 15 parts by weight of DDS has more excellent strength properties such as compressive strength, heat resistance, and environmental resistance by exhibiting a remarkable adhesive effect with reinforcing fibers. A fiber reinforced composite material can be obtained.

DDS is a fine particle compound belonging to an aromatic amine type curing agent, and there are structural isomers depending on the substitution position of an amino group on an aromatic ring. In the present invention,
Either isomer can be used, but by changing the type of isomer, the properties of the matrix resin and the resulting composite material can be controlled. For example,
4,4'-DDS has particularly excellent heat resistance.
3,3′-DDS is particularly excellent in rigidity. DD
The average particle diameter of S is 1 to 4 for the same reason as DICY.
It is preferably 15 μm, more preferably 5 to 13 μm, and still more preferably 8 to 13 μm.

Component [C] in the present invention is a urea compound. When a urea compound is used as a curing accelerator, it is possible to obtain an epoxy resin composition excellent in both properties of storage stability and adhesion to reinforcing fibers. When a tertiary amine compound is used as a curing accelerator instead of a urea compound, the storage stability of the epoxy resin composition or the prepreg is impaired. When an imidazole compound is used, the adhesion between the reinforcing fiber and the matrix resin is reduced. Tends to decrease.

As the urea compound, 3-phenyl-
1,1-dimethylurea, 3- (3-chlorophenyl)
Examples thereof include -1,1, -dimethylurea (hereinafter, referred to as DCMU), 3- (3,4-dichlorophenyl) -1, 1-dimethylurea (hereinafter, referred to as HDZ), and a mixture thereof. The amount of the urea compound relative to 100 parts by weight of the epoxy resin compound is 2 to 2.
The amount is preferably 10 parts by weight, more preferably 3 to 8 parts by weight, even more preferably 4 to 6 parts by weight. When the amount of the urea compound is less than 2 parts by weight, the adhesiveness between the reinforcing fiber and the matrix resin tends to decrease, and when the amount exceeds 10 parts by weight, the curing promoting effect becomes excessive, and the epoxy resin composition The storage stability of the product or prepreg is impaired.

Further, the epoxy resin composition according to the present invention includes a control of the rheological properties of the prepreg in the uncured state of the resin, an improvement in the rigidity and toughness of the matrix resin, a control of the tack, and an adhesion between the reinforcing fibers and the matrix resin. In order to have an improvement effect such as improvement of the properties, it is preferable to blend a thermoplastic resin, an elastomer, and inorganic particles described below as an improver in addition to the above-described components.

As the thermoplastic resin, polyacetal,
Polyamide, polyamide imide, polyarylene oxide, polyarylate, polyimide, polyethylene, polyethylene terephthalate, polyethylene naphthalate,
Polyetherimide, polyetheretherketone, polyethersulfone, polyvinylchloride, polycarbonate, polyvinylacetate, polystyrene, polysulfone, polytetrafluoroethylene, polyhydroxyether,
Examples include polyvinyl acetal, polyvinyl alcohol, polyvinyl pyrrolidone, polyvinyl formal, polyphenylene oxide, polybutylene terephthalate, polyphenylene sulfide, polypropylene, polybenzimidazole, and polymethyl methacrylate.

These thermoplastic resins can be used alone or in combination of a plurality of types. Among them, polyamide resins improve the toughness of the matrix resin and improve the impact resistance of the resulting composite material. Polyimide resin and polyether sulfone resin are preferable for improving the rigidity of the matrix resin, while strengthening the adhesion between the reinforcing fiber and the matrix resin, and greatly improving the compressive strength of the obtained composite material. Are particularly preferably used.

The amount of the thermoplastic resin is preferably 5 to 20 parts by weight, more preferably 5 to 15 parts by weight, and still more preferably 5 to 12 parts by weight, based on 100 parts by weight of the epoxy resin compound. good. If the amount is less than 5 parts by weight, the above-mentioned improvement effect is not sufficiently exhibited, and if it exceeds 20 parts by weight, heat resistance is impaired.

The elastomer may be liquid or solid, but the latter is preferably used from the viewpoint of maintaining the rigidity of the matrix resin. Acrylonitrile-butadiene rubber, which is a solid elastomer, is preferably used because of its excellent compatibility with epoxy resins. It is more preferable that such an elastomer has a functional group that reacts with an epoxy group, such as an amino group or a carboxyl group, for improving the rigidity of the matrix resin. Specific examples of the elastomer include, in addition to the acrylonitrile-butadiene rubber,
Examples include urethane rubber, styrene-butadiene rubber, and the like, or a hybrid thereof. The amount of the elastomer is preferably 1 to 5 parts by weight, more preferably 2 to 3 parts by weight, based on 100 parts by weight of the epoxy resin compound. If the amount is less than 1 part by weight, the above-mentioned improvement effect is not sufficiently exhibited, and if it exceeds 5 parts by weight, the rigidity of the matrix resin is impaired.

As the elastomer having a special form, a core component composed of acrylonitrile-butadiene rubber, urethane rubber, styrene-butadiene rubber or the like, or a hybrid thereof, and polyacrylate,
A core / shell type elastomer composed of a shell (surface coating of a core component) composed of polyacrylonitrile, polystyrene, polymethyl methacrylate, etc., or a mixture thereof has good dispersibility in an epoxy resin composition. Therefore, it is preferably used. In particular, a core / shell type elastomer using an elastomer composed of a crosslinked product of the rubber as a core component, polyacrylate, polyacrylonitrile, polystyrene, polymethyl methacrylate, or the like, or a mixture thereof as a shell component has a rigidity of a matrix resin. It is particularly preferably used because it significantly increases.

Further, as the inorganic particles, alumina,
Carbon black, kaolin clay, graphite, aluminum silicate, tin oxide, titanium oxide, antimony trioxide, molybdenum trioxide, silica, zirconia, aluminum hydroxide, magnesium hydroxide, smectite,
Examples include sericite, talc, calcium carbonate, magnesium carbonate, ferrite, mica, montmorillonite, molybdenum sulfide, and the like, or a mixture thereof. Among them, silica particles are preferable because they effectively impart so-called thixotropic properties to the epoxy resin composition. Silica particles include a hydrophilic type in which silicon dioxide is a basic skeleton and the surface of the particle is covered with a silanol group, and a hydrophobic type in which the hydrogen of the silanol group is substituted with an alkyl group, a silyl group, or the like. However, the latter is preferably used from the viewpoint of imparting environmental resistance such as water resistance to the matrix resin.

The amount of the inorganic particles is preferably 2 to 10 polymer parts per 100 parts by weight of the epoxy resin compound.
More preferably, the content is 2 to 7 parts by weight. If the amount is less than 2 parts by weight, the effect of increasing the rigidity of the resin is not sufficiently exhibited, and the
Exceeding the parts by weight will impair the drape of the prepreg.

By using the epoxy resin composition according to the present invention as a matrix resin, even if a reinforcing fiber having a perfect circular cross section, which is inferior in adhesiveness to the matrix resin, is usually used, it can be interposed between the matrix resin and the reinforcing fiber. High adhesiveness can be exhibited. In addition, by using a reinforcing fiber whose cross section of a single fiber is a perfect circle, undesirable phenomena such as generation of voids can be eliminated, and the reinforcing fiber fraction can be increased as much as possible, while stress concentration on local parts also occurs. Since it can be relaxed, a high-quality and large-scale composite material having excellent strength characteristics such as compressive strength can be obtained. Further, the adhesiveness is maintained sufficiently strong even when the composite material is immersed in water for a long time.

The prepreg of the present invention is prepared by first heating and melting the epoxy resin composition, and then uniformly applying it on release paper while the resin is not yet cured to form a resin film.
It is produced by a method in which a reinforcing fiber is sandwiched between the resin films from both sides, and then the resin is impregnated while applying pressure and heating. About the form and arrangement of the reinforcing fibers at this time, long fibers, woven fabric, braid,
It can be freely selected from tows, knits, mats and the like according to the site to be used and the application. The heating temperature at this time is preferably from 90 to 150C. If the heating temperature is lower than 90 ° C., the impregnation of the reinforcing fibers with the resin becomes incomplete, the tackiness of the prepreg becomes excessive, and the handleability deteriorates. If the temperature exceeds 150 ° C., the impregnation of the resin into the reinforcing fibers becomes complete, but the curing reaction of the resin proceeds during the impregnation, so that the drape of the prepreg is impaired. Further, the reinforcing fiber fraction in the prepreg is preferably from 50 to 80% by weight. Reinforcement fiber fraction is 50
When the amount is less than 10% by weight, strength characteristics such as compressive strength in the obtained composite material tend to be insufficient, and the composite material has a strength of 80% by weight.
If it exceeds, the reinforcing fiber single yarns rub against each other, resulting in fatigue of the fiber and a composite material having good durability cannot be obtained.

The prepreg thus obtained has excellent storage stability at room temperature, and even when left at room temperature for about one week, the change in tack and drape with the passage of time is slight.
Extremely easy to handle.

As a method for producing a composite material from a prepreg, a method in which the direction of the fibers is changed little by little, the layers are quasi-isotropic and laminated, and then cured by heating is preferably employed. You. The heating temperature here is preferably from 100 to 140 ° C. Heating temperature is 100
When the temperature is lower than ℃, the curing reaction of the matrix resin becomes incomplete, and the heat resistance and environmental resistance of the obtained composite material tend to be insufficient, and when the temperature exceeds 140 ° C, the heat shrinkage when cooled from the molding temperature to room temperature is reduced. This heat shrinkage becomes a defect site in the composite material, which can be ignored. Primary structural materials such as aircraft wings, tail wings, fuselage, etc., front wheel doors, and directions, where excessive stress is often concentrated locally. When a composite material is applied to a large-scale structural material typified by a snake, a spoiler, and the like, it is not preferable because the material has poor fracture resistance. Further, the energy required for heating at the time of molding increases, which is not preferable.

The evaluation method of each material in the present invention is as shown in the following sections. (1) Measurement of average particle diameter of DICY and DDS particles After vacuum drying DICY and DDS particles at room temperature to reduce the moisture content to 0.2% by weight or less, the average particle diameter of the particles was measured using a particle size analyzer. Measure. In Examples described later, a laser diffraction type particle sizer (SA manufactured by Shimadzu Corporation)
(LD-200A type), and assuming that the particles were spherical, the diameter was determined as the average particle diameter.

(2) Evaluation of Physical Properties of Reinforcing Fiber After the reinforcing fiber was cut in a direction perpendicular to the fiber direction, the cross section was enlarged and photographed with a scanning electron microscope, and the radius R circumscribing the observed cross-sectional shape was obtained. A circle having a radius r inscribed with the circle is drawn, the ratio of these radii, R / r, is defined as the degree of deformation of the section, the sum of the radius of the circumscribed circle and the radius of the inscribed circle, and R + r is defined as the diameter of the section.

In the examples described later, an enlarged photograph of the cross section of a single fiber was obtained under the conditions of 10,000 times magnification and 15 kV of acceleration voltage using an S-4000 model manufactured by Hitachi, Ltd. as a scanning electron microscope.

Further, regarding the tensile strength, JIS R7
601 is measured.

[0049]

The present invention will be described more specifically with reference to the following examples.

Example 1 An epoxy resin composition, a prepreg, and a carbon fiber reinforced composite material were manufactured by the following procedures (1) to (3), and the composite material was compressed by the measurement method shown in (4). The strength was measured.

(1) Preparation of Epoxy Resin Composition The following materials were kneaded using a kneader to prepare an epoxy resin composition.

Tetraglycidylamine type epoxy resin 60 parts by weight (ELM434 manufactured by Sumitomo Chemical Co., Ltd.) Bisphenol A type epoxy resin 40 parts by weight (YD-128 manufactured by Toto Kasei Co., Ltd.) DICY 4 parts by weight DCMU 5 parts by weight PES ( (Polyethersulfone) 12 parts by weight (Victrex (registered trademark) grade 5003P manufactured by Sumitomo Chemical Co., Ltd.) Here, the resin composition was measured by the following method to obtain 1050 MPa as a rigidity value of the resin composition at the time of moisture absorption.

First, a resin plate having a thickness of 2 mm is prepared from this resin composition by a heat curing method using an oven.
Next, this was cut into a size of 55 mm in length and 10 mm in width, and then immersed in boiling water at 100 ° C. for about 20 hours.
The resin is taken out from the boiling water, the rigidity of the resin plate at 82 ° C. is measured by a dynamic viscoelasticity method, and the measured value is taken as the rigidity of the resin at the time of moisture absorption. In this case, AERS manufactured by Rheometric Co., Ltd. was used as a measuring device by the dynamic viscoelasticity method.

(2) Production of prepreg As a reinforcing material, carbon fiber “Treca” (registered trademark) T700S (trade name of single fiber section: 1.05, manufactured by Toray Industries, Inc.)
(Diameter of cross section of single fiber: 7 μm, tensile strength: 4.9 GPa)
The carbon fibers aligned in one direction are covered from both sides by sandwiching the fibers with an epoxy resin film that has been applied to release paper in advance, and then pressurized and heated to impregnate the resin into a sheet-shaped prepreg. Was manufactured.

At this time, the viscosity of the resin composition at 100 ° C. was about 15 Pa · s, and the tack and drape of the obtained prepreg were good.

(3) Production of Carbon Fiber Reinforced Composite Material After sheet-like prepregs were laminated in one direction so as to form a six-layer structure, the pressure was set to 0.294 Pa in an autoclave.
The material was gradually cured for 120 minutes at a temperature of 135 ° C. to produce a carbon fiber reinforced composite material.

(4) Measurement of Compressive Strength of Composite Material A test piece was cut out from the obtained composite material in the shape and dimensions of a test piece of Method A according to JIS K7076, and then the test piece was placed in hot water adjusted to 71 ° C. After immersion for days, the test piece was taken out, and its 0 ° compressive strength was measured in a thermostatic chamber adjusted to an ambient temperature of 82 ° C., and the value was 1030 MPa.
a was obtained.

The composite material obtained in Example 1 satisfied the criteria applicable to aircraft structural materials (0 ° compression strength of composite material> 1000 MPa according to the measurement method shown in (4) above).

For Examples 2 to 8 and Comparative Examples 1 to 5,
According to the procedure of Example 1, an epoxy resin composition, a prepreg, and a carbon fiber reinforced composite material were manufactured, and the obtained composite material was evaluated.

Table 1 below shows the results of Examples 1 to 8 and Comparative Example 1
Table 2 below shows the results of Nos. 1 to 5.

As can be seen from these tables, the compressive strength is high only when the epoxy resin compound contains not less than 60 parts by weight of the tetraglycidylamine type epoxy resin. It can be seen that the strength is increased (Examples 5 and 7), and that the compressive strength can also be increased by using a combination of DICY and 4,4′-DDS as a curing agent (Example 6).

[0062]

[Table 1]

[Table 2] Note) Numerical values in the table indicate parts by weight based on 100 parts by weight of the epoxy resin compound.

In Tables 1 and 2, the compounds abbreviated by alphabets have the following names and chemical structural formulas, respectively.

ELM434: tetraglycidylamine type epoxy resin (manufactured by Sumitomo Chemical Co., Ltd.)

Embedded image ELM100: glycidylamine type epoxy resin (manufactured by Sumitomo Chemical Co., Ltd.)

Embedded image MT0163: Tetraglycidyl ether type epoxy resin (manufactured by Ciba Corporation)

Embedded image Ep-154: Phenol novolak type epoxy resin (manufactured by Yuka Shell Epoxy Resin Co., Ltd.)

Embedded image XAC4152: Epoxy resin containing oxazolidone ring (manufactured by Asahi Ciba Co., Ltd.)

Embedded image YD-128: bisphenol A type epoxy resin (manufactured by Toto Kasei Co., Ltd.)

Embedded image Note) In the above chemical structural formula, G represents a glycidyl group (the following formula).

[0065]

Embedded image DICY: dicyandiamide 4,4'-DDS: 4,4'-diaminodiphenylsulfone DCMU: 3- (3-chlorophenyl) -1,1, -dimethylurea HDIZ: heptadecyl imidazole PEI: polyetherimide (General Electric ( ULTEM Co., Ltd.
(Registered trademark) grade 1000) PES: polyether sulfone (Victrex grade 500 manufactured by Sumitomo Chemical Co., Ltd.)
3P) Further, the average particle diameter of the DICY particles in each Example and Comparative Example was 7 μm, and the 4,4′-DD in Example 6 was also different.
The average particle size of the S fine particles is 10 μm.

[0066]

The prepreg of the present invention is a prepreg in which the adhesion between the reinforcing fiber having a substantially circular cross section of a single fiber and the matrix resin is stronger than ever before, and the fiber reinforced obtained by molding the prepreg. The composite material exhibits excellent heat resistance, environmental resistance, and durability as well as high strength characteristics, and thus can be suitably used particularly for aircraft structural materials.

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Claims (8)

[Claims] (1) At least the following components [A], [B],
A prepreg, characterized in that the epoxy resin composition containing [C] is impregnated with reinforcing fibers having a substantially perfect cross-sectional shape of a single fiber. [A]: An epoxy resin composition in which a tetraglycidylamine type epoxy resin is blended in an amount of 60 parts by weight or more based on 100 parts by weight of the epoxy resin composition [B]: Particulate dicyandiamide [C]: A urea compound 2. In the component [A], the compounding amount of the tetraglycidylamine type epoxy resin is 60 to 97 parts by weight based on 100 parts by weight of the epoxy resin compound. The prepreg according to claim 1, wherein 3 to 40 parts by weight of an epoxy resin other than the tetraglycidylamine type epoxy resin is blended. 3. The epoxy resin other than the tetraglycidylamine type epoxy resin is at least one type of epoxy resin selected from a bisphenol type epoxy resin, a novolak type epoxy resin, and an epoxy resin having an oxazolidone ring. Item 3. The prepreg according to item 2. 4. The method according to claim 1, wherein said epoxy resin composition contains diaminodiphenyl sulfone.
The prepreg according to any one of items 1 to 3, wherein 5. The prepreg according to claim 1, wherein the epoxy resin composition contains a thermoplastic resin. 6. The prepreg according to claim 1, wherein the epoxy resin composition contains an elastomer. 7. The prepreg according to claim 1, wherein the epoxy resin composition contains inorganic particles. 8. A fiber reinforced composite material obtained by laminating the prepreg according to any one of claims 1 to 7, heating at 100 to 140 ° C., and curing and molding.