JP2016199682A - Fiber-reinforced composite material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fiber-reinforced composite material excellent in impact resistance and interlayer fracture toughness.SOLUTION: A fiber-reinforced composite material which is formed of at least two layers of a reinforced fiber layer and a curable resin cured product has a resin layer formed of at least a curable resin cured product and a thermoplastic resin between two layers of the reinforced fiber layers. The thermoplastic resin of the resin layer forms a thermoplastic resin region in which 90% quantile point of a domain length in a direction parallel to the surface of the resin layer is 15 μm or more. A circularity of the thermoplastic resin region is preferably 0.01-0.7, and an average value of the domain length in a thickness direction of the resin layer of the thermoplastic resin region is preferably 25% or more of the average thickness of the resin layer.SELECTED DRAWING: None

Description

  The present invention relates to a fiber-reinforced composite material having excellent interlayer toughness.

Fiber reinforced composite materials that use carbon fiber, aramid fiber, etc. as reinforcing fibers are aerospace / industrial applications such as structural materials for aircraft and automobiles, tennis rackets, and golf shafts because of their high specific strength and specific modulus. Widely used in sports and leisure applications such as fishing rods.
As a method for producing a fiber-reinforced composite material, there is a method in which a plurality of prepregs are laminated and then heat-cured. A prepreg is a sheet-like intermediate material in which reinforcing fibers are impregnated with an uncured matrix resin.

  Typical matrix resins used for the prepreg include curable resins from the viewpoint of heat resistance and productivity. In general, curable resins, especially epoxy resins, are excellent in heat resistance, adhesion to reinforcing fibers, dimensional stability, and chemical resistance, but are hard and brittle. For this reason, when an epoxy resin is used as the matrix resin, the fiber-reinforced composite material is excellent in mechanical properties such as dimensional stability, strength and rigidity, but on the other hand, the low toughness derived from the epoxy resin is also reflected.

  Various attempts have been made so far in order to improve the toughness and impact resistance of the curable resin used as the matrix resin. For example, a method of improving the impact resistance of a composite material by dispersing fine particles of a rubber component or a thermoplastic resin in a curable resin is disclosed (for example, Patent Document 1). However, in this method, since the particles in the resin are small, propagation of damage that occurs when the composite material is subjected to an impact or load cannot be sufficiently inhibited. Therefore, the impact resistance of the fiber reinforced composite material obtained by this method is not satisfactory.

  As another method, there is a method of forming a nano-sized phase separation structure in a thermosetting resin using a block copolymer composed of two or three components (Patent Documents 2 to 4). For example, a method in which a styrene-butadiene copolymer, a styrene-butadiene-methacrylic acid copolymer, or a butadiene-methacrylic acid copolymer is added to a specific epoxy resin has been proposed. However, even if these methods are used, since the region of the copolymer phase generated in the resin layer is small, the propagation of damage caused when the composite material is subjected to an impact or load cannot be sufficiently inhibited. The impact resistance of the composite material is still insufficient. In addition, these block copolymers are very expensive and have low cost competitiveness.

JP 7-41575 A International Publication No. 2006/075153 Pamphlet JP 2007-154160 A JP 2008-7682 A

  An object of the present invention is to provide a fiber-reinforced composite material excellent in impact resistance and interlaminar fracture toughness.

  The fiber reinforced composite material of the present invention that solves the above problems is a fiber reinforced composite material comprising a reinforced fiber layer and a curable resin cured product laminated at least two layers, and is provided between two reinforced fiber layers. A resin layer composed of at least a curable resin cured product and a thermoplastic resin, and the thermoplastic resin of the resin layer is a heat having a 90% quantile of a domain length in a direction parallel to the surface of the resin layer of 15 μm or more. It is a fiber reinforced composite material forming a plastic resin region. In the present invention, the circularity of the thermoplastic resin region is preferably 0.01 to 0.7, and the average value of the domain length in the thickness direction of the resin layer in the thermoplastic resin region is the average thickness of the resin layer. It is also preferable that it is 25% or more. The thermoplastic resin is preferably a thermoplastic resin having a breaking elongation of 80% or more, the curable resin is preferably an epoxy resin, and the reinforcing fiber is preferably a carbon fiber.

  Since the fiber-reinforced composite material of the present invention is excellent in impact resistance and interlaminar fracture toughness, it can be suitably used in many applications such as aerospace applications, industrial applications, sports and leisure applications.

The fiber reinforced composite material of the present invention is a fiber reinforced composite material comprising a reinforced fiber layer laminated with at least two layers and a curable resin cured product, and at least a curable resin between the two reinforced fiber layers. A resin layer comprising a cured product and a thermoplastic resin, wherein the thermoplastic resin of the resin layer has a 90% quantile of 15 μm or more in the domain length in a direction parallel to the surface of the resin layer, which is determined by the method described later; It is a fiber reinforced composite material forming a thermoplastic resin region.
In the fiber-reinforced composite material of the present invention, when subjected to an impact or load, the thermoplastic resin region of the resin layer inhibits the propagation of damage. As a result, the fiber-reinforced composite material of the present invention is a fiber-reinforced composite material having high impact resistance and excellent interlaminar fracture toughness.

  The 90% quantile of the domain length in the direction parallel to the surface of the resin layer is preferably 20 μm or more, and more preferably 40 μm or more. Moreover, the average value of the domain length in the direction parallel to the surface of the resin layer is preferably 10 μm or more, and more preferably 20 μm or more. The upper limit of the 90% quantile of the domain length in the direction parallel to the surface of the resin layer is not particularly limited, but is 400 μm and may be 300 μm or less. The upper limit of the average value of the domain length in the direction parallel to the surface of the resin layer is not particularly limited, but 300 μm is sufficient and may be 200 μm or less.

  Furthermore, the average value of the domain length in the thickness direction of the resin layer in the thermoplastic resin region is preferably 25% or more of the average thickness of the resin layer, and more preferably 40 to 80%. When the domain length in the thickness direction of the resin layer is within this range, when the fiber reinforced composite material is subjected to an impact or load, the probability that the crack that propagates to the resin layer will contact the thermoplastic resin region is increased, which is more effective. Damage propagation can be hindered.

In the present invention, the circularity of the thermoplastic resin region is preferably 0.01 to 0.7, more preferably 0.03 to 0.4, and 0.05 to 0.2. More preferably it is. The circularity of the thermoplastic resin region referred to in the present invention is a value calculated based on the following equation from the circumference and area of the thermoplastic resin region.
(Circularity) = Σ (4πS ² / L ² ) / S _T
S: Area of thermoplastic resin region [μm ² ]
L: Perimeter length of thermoplastic resin region [μm]
S _T : Total area of the thermoplastic resin region [μm ² ]

  In the present invention, the thermoplastic resin forming the thermoplastic resin region of the resin layer can be used without particular limitation as long as it is a thermoplastic resin. Examples of the thermoplastic resin include polyamide, polyacetal, polyphenylene oxide, polyphenylene sulfide, polyester, polyamideimide, polyimide, polyetherketone, polyetheretherketone, polyethylene naphthalate, polyethernitrile, polybenzimidazole, polyethersulfone, Examples include polysulfone, polyetherimide, and polycarbonate. These may be used alone or in combination of two or more. Moreover, these copolymers can also be used.

  In the present invention, the thermoplastic resin forming the thermoplastic resin region is preferably a thermoplastic resin having a breaking elongation of 80% or more, and a thermoplastic resin having a breaking elongation of 90 to 700%. More preferred. Such a thermoplastic resin is a fiber-reinforced composite material, and can easily absorb the propagation energy of cracks generated by an impact or load, and thus can more effectively inhibit the propagation of damage. Examples of such thermoplastic resins include polyamide, polyimide, polyurethane, polypropylene, and polyethylene. Among these, polyamide and polyimide are more preferable because of excellent heat resistance. In particular, crystalline polyamides such as polyamide 6 (polyamide obtained by ring-opening polycondensation reaction of caprolactam), polyamide 12 (polyamide obtained by ring-opening polycondensation reaction of lauryl lactam), amorphous polyamide, and / or amorphous Is preferred. These thermoplastic resins may be used alone or in combination of two or more. Further, these copolymers may be used.

The reinforcing fiber used in the present invention is not particularly limited, and examples thereof include carbon fiber, glass fiber, aramid fiber, silicon carbide fiber, polyester fiber, ceramic fiber, alumina fiber, boron fiber, metal fiber, mineral fiber, rock fiber, and Examples include slug fibers.
Among these reinforcing fibers, carbon fibers, glass fibers, and aramid fibers are preferable. Carbon fiber is more preferable in that it has a good specific strength and specific elastic modulus, and a lightweight and high-strength fiber-reinforced composite material can be obtained. Polyacrylonitrile (PAN) -based carbon fibers are particularly preferable in terms of excellent tensile strength.

  When PAN-based carbon fiber is used as the reinforcing fiber, the tensile elastic modulus is preferably 100 to 600 GPa, more preferably 200 to 500 GPa, and particularly preferably 230 to 450 GPa. The tensile strength is 2000 MPa to 10000 MPa, preferably 3000 to 8000 MPa. The diameter of the carbon fiber is preferably 4 to 20 μm, and more preferably 5 to 10 μm. By using such a carbon fiber, the mechanical properties of the resulting composite material can be improved.

  The reinforcing fiber is preferably used in the form of a sheet. As the reinforcing fiber sheet, for example, a sheet in which a large number of reinforcing fibers are aligned in one direction, bi-directional woven fabrics such as plain weave and twill weave, multiaxial woven fabric, non-woven fabric, mat, knit, braid, paper made of reinforcing fibers And so on. The thickness of the sheet-like reinforcing fiber base is preferably 0.01 to 3 mm, and more preferably 0.1 to 1.5 mm.

The basis weight of the reinforcing fiber is preferably in the range of 30 to 700 g / m ² . When the basis weight of the reinforcing fiber is within this range, it becomes easier to achieve both the lightness and strength of the fiber-reinforced composite material. A more preferable range of the basis weight of the reinforcing fiber is 50 to 300 g / m ² .
In the fiber-reinforced composite material of the present invention, the reinforcing fiber content (Vf) is preferably 55 to 75% by mass, and more preferably 60 to 70% by mass.

  The fiber-reinforced composite material of the present invention comprises the above-described reinforcing fibers and a cured product of a curable resin. The curable resin used in the present invention is not particularly limited as long as it is a curable resin that is cured by heat or external energy such as light or electron beam and at least partially forms a three-dimensional cured product. it can. Among these, a thermosetting resin that is cured by heat is preferable because of easy handling.

Preferred curable resins are listed below. These curable resins can be appropriately selected and used alone or in combination of two or more.
Preferred curable resins include epoxy resins, modified epoxy resins, vinyl ester resins, benzoxazine resins, and the like. Particularly preferred are epoxy resins and modified epoxy resins.
As the epoxy resin, any known epoxy resin can be used and is not particularly limited. Examples thereof include bifunctional epoxy resins such as bisphenol-type epoxy resins, alcohol-type epoxy resins, biphenyl-type epoxy resins, hydrophthalic acid-type epoxy resins, dimer acid-type epoxy resins, and alicyclic epoxy resins.

  Bifunctional epoxy resins represented by the bisphenol type have various grades ranging from liquid to solid depending on the difference in molecular weight, and are intended components for adjusting viscosity by mixing as appropriate. Examples of the bisphenol type epoxy resin include bisphenol A type resin, bisphenol F type resin, bisphenol AD type resin, bisphenol S type resin, and the like. Specific product names include jER815 (product name), jER828 (product name), jER834 (product name), jER1001 (product name), jER807 (product name) manufactured by Mitsubishi Chemical Corporation, and EPOMIC made by Mitsui Chemicals, Inc. Examples thereof include R-710 (trade name), EXA1514 (trade name) manufactured by DIC Corporation. Specific product names of alicyclic epoxy resins include Araldite CY-179 (product name), CY-178 (product name), CY-182 (product name), CY-183 (product name), etc. manufactured by Huntsman. Can be illustrated. Examples of other epoxy resins include glycidyl ether type epoxy resins such as tetrakis (glycidyloxyphenyl) ethane and tris (glycidyloxyphenyl) methane, glycidylamine type epoxy resins such as tetraglycidyldiaminodiphenylmethane, and naphthalene type epoxy resins. And a phenol novolac epoxy resin which is a novolac epoxy resin, a polyfunctional epoxy resin such as a cresol novolac epoxy resin, a phenol epoxy resin, and the like.

Specific product names of the phenol novolac type epoxy resin include jER152 (product name), jER154 (product name) manufactured by Mitsubishi Chemical Corporation, DEN431 (product name), DEN485 (product name), DEN438 (product) manufactured by Dow Chemical Co., Ltd. Name), Epicron N740 (trade name) manufactured by DIC, and the like.
Specific product names of the cresol novolak type epoxy resin include Araldite ECN1235 (product name), ECN1273 (product name), ECN1280 (product name), Nippon Kayaku EOCN102 (product name), and EOCN103 (product name) manufactured by Huntsman. ), EOCN104 (trade name), and the like.
Various modified epoxy resins such as urethane-modified epoxy resin and rubber-modified epoxy resin can also be used. Specific examples of the trade name of the urethane-modified bisphenol A epoxy resin include Adeka Resin EPU-6 (trade name) and EPU-4 (trade name) manufactured by Adeka Corporation.

A known curing agent can be used as the curing agent for curing the curable resin. As specific examples of the curing agent, when an epoxy resin is used as the curable resin, 4,4′-diaminodiphenylsulfone, 3,3′-diaminodiphenylsulfone, 4,4′-diamino-3,3′- Examples include diethyl-5,5′-dimethyldiphenylmethane.
In the curable resin composition, an amine compound such as tertiary amine or imidazole, a phosphine or a phosphorus compound such as phosphonium, N, N-dimethyl, or the like, as necessary, within a range not impairing the effects of the present invention. You may contain various additives, such as hardening accelerators, such as a urea derivative, a reactive diluent, a filler, antioxidant, a flame retardant, and a pigment.

  The fiber-reinforced composite material of the present invention as described above has high impact resistance and high interlaminar fracture toughness because the thermoplastic resin region of the resin layer inhibits the propagation of damage when subjected to impact or load. Are better. Since the fiber-reinforced composite material of the present invention is excellent in impact resistance and interlaminar fracture toughness, it can be suitably used in many applications such as aerospace applications, industrial applications, sports and leisure applications.

  The fiber-reinforced composite material of the present invention having such excellent characteristics is not particularly limited, but after impregnating the reinforcing fibers with at least a curable resin before curing and a curable resin composition containing thermoplastic resin particles. The fiber-reinforced composite material can be produced by a curing reaction at a temperature equal to or higher than the melting point of the thermoplastic resin particles. By causing the curable resin composition containing the thermoplastic resin particles to undergo a curing reaction at a temperature equal to or higher than the melting point of the thermoplastic resin particles, the thermoplastic resin particles are dissolved during the curing reaction, and other adjacent thermoplastic resin particles To merge. As a result, a large region (domain) of the thermoplastic resin can be formed in the cured resin after the curing reaction.

In a method for producing a fiber-reinforced composite material, a curable resin composition containing thermoplastic resin particles is impregnated into a reinforced fiber, and then cured at a temperature equal to or higher than the melting point of the thermoplastic resin particles. The thermoplastic resin particles contained in the fiber reinforced composite material of the present invention are thermoplastic resins that form a thermoplastic resin region. The thermoplastic resin particles are preferably thermoplastic resin particles having an average particle diameter by laser diffraction of 1 to 50 μm, and more preferably 2 to 10 μm. Moreover, it is preferable that content of the thermoplastic resin particle which occupies in a curable resin composition is 30 volume% or more. When a fiber reinforced composite material is produced using a prepreg described later, or when thermoplastic resin particles having an average particle diameter exceeding 1 μm are used, the thermoplastic resin is impregnated with the curable resin composition when impregnated into the reinforced fiber. Since the particles tend to stay on the surface of the reinforcing fiber layer and are concentrated on the surface of the reinforcing fiber layer, the basis weight (M _T : g / m ² ) of the thermoplastic resin particles around the area of one side surface of the reinforcing fiber base is It is preferable to add to the curable resin so as to satisfy (1).
M _T ≧ 0.4 rd (1)
M _T : basis weight (g / m ² ) of thermoplastic resin particles around the area of one side surface of the reinforcing fiber base
r: Average particle diameter of thermoplastic resin particles (μm)
d: Density (specific gravity) of thermoplastic resin particles (g / cm ³ )

  In the curing reaction, the viscosity of the curable resin composition when the melting point of the thermoplastic resin particles is reached is preferably 0.1 to 1000 Pa · s. When the resin viscosity is in this range, the thermoplastic resin particles dissolved in the curable resin composition can flow without diffusing. And the melt | dissolved thermoplastic resin particle flows, A large thermoplastic resin area | region is formed when it contacts with other adjacent thermoplastic resin particles.

The viscosity of the curable resin composition when the melting point of the thermoplastic resin particles is reached is preferably 0.5 to 500 Pa · s, and more preferably 1 to 100 Pa · s. The lower the resin viscosity, the easier it is for the thermoplastic resin particles dissolved in the thermosetting resin composition to flow, so it becomes easier to fuse a plurality of thermoplastic resin particles to form a larger thermoplastic resin region, If the resin viscosity is too low, the fluidity tends to be too high and the molten thermoplastic resin tends to diffuse and disperse into small thermoplastic resin regions.
Moreover, it is preferable that the viscosity (η: Pa · s) of the curable resin composition at the time of reaching the melting point of the thermoplastic resin and the average particle diameter (r: μm) of the thermoplastic resin particles satisfy the following formula (2).
ηr ² <10000 (2)

The viscosity of the curable resin composition can be controlled, for example, by adjusting the heating conditions during the curing reaction or by adding a thermoplastic resin for viscosity adjustment. The viscosity of the curable resin composition at a specific temperature can be measured by obtaining a temperature-viscosity curve using a rheometer.
The viscosity of the curable resin composition during the curing reaction is a resin viscosity decrease due to the temperature rise of the resin composition due to heating or heat of reaction, and the curable resin is crosslinked (high molecular weight) as the curing reaction proceeds. Influenced by viscosity increase.

Changes in resin viscosity due to temperature rise of the resin composition due to heating or reaction heat include, for example, mixing a plurality of curable resins having different viscosities, or thickening agents such as thermoplastic resins for adjusting viscosity and inorganic fillers. It can be controlled by adjusting the viscosity of the resin composition by adding an additive such as a reaction diluent.
As the thermoplastic resin to be blended for adjusting the viscosity of the curable resin composition, for example, when an epoxy resin is used as the matrix resin, polyethersulfone, polysulfone, polyetherimide, polycarbonate and the like are preferably used.

  The content of the thermoplastic resin for adjusting the viscosity is appropriately adjusted according to the viscosity of the curable resin. From a workability viewpoint, 5-100 mass parts is preferable with respect to 100 mass parts of curable resin, 5-50 mass parts is more preferable, and 10-40 mass parts is further more preferable. The thermoplastic resin for adjusting the viscosity is preferably added to the curable resin as solid particles from the viewpoint of handleability and solubility. When added as solid particles, the average particle diameter is preferably in the range of 1 to 100 μm, more preferably 1 to 50 μm.

  On the other hand, the change in the resin viscosity accompanying the progress of the curing reaction can be adjusted by changing the heating conditions during the curing reaction. Also, depending on the type of curable resin and the melting point of the thermoplastic resin particles, the type of the curing agent is changed as appropriate, and the starting temperature of the curing reaction that is the starting point of the change in the resin viscosity accompanying the progress of the curing reaction is adjusted. It is also preferable. A method of adding a curing agent to a resin composition heated to a predetermined temperature, a method of using a latent curing agent that starts a reaction at a predetermined temperature, and a curable resin composition from the outside such as light or an electron beam In the case of a resin composition that begins to cure by energy, the reaction is started by a method such as applying external energy that initiates a reaction such as light or electron beam to the resin composition that has reached a predetermined temperature. The resin viscosity may be adjusted by adjusting the temperature.

  When adjusting the change of the resin viscosity accompanying the progress of the curing reaction according to the heating conditions at the time of the curing reaction, the viscosity change can be adjusted by adjusting the rate of temperature rise. When the rate of temperature rise is moderated, the curing reaction proceeds at a lower temperature and the viscosity becomes higher. On the other hand, when the rate of temperature increase is abrupt, the temperature of the resin composition can be increased while keeping the viscosity low. It is preferable to adjust the heating rate between 0.5 to 20 ° C./min.

Further, it is preferable to adjust the time until the viscosity of the curable resin composition reaches 10,000 Pa · s after reaching the melting point of the thermoplastic resin particles to be 1 to 600 seconds.
The heating conditions during the curing reaction are such that the temperature-viscosity curve of the curable resin composition is measured in advance before impregnating the curable resin composition into the reinforcing fibers, and the melting point of the thermoplastic resin particles reaches a predetermined viscosity. It is preferable to set to.

  The curable resin composition is produced by adding and kneading thermoplastic resin particles and, if necessary, various additives such as a curing agent and a thermoplastic resin for viscosity adjustment to the curable resin. The kneading of each component may be performed in a single stage, or may be performed in multiple stages by sequentially adding each component. When adding each component sequentially, it can add in arbitrary orders. For example, when adding a curing agent and a viscosity adjusting thermoplastic resin to the curable resin, after kneading and melting a part or all of the viscosity adjusting thermoplastic resin in advance in the curable resin, the viscosity is adjusted. Then, kneading is performed while sequentially adding thermoplastic resin particles and a curing agent. The order of kneading and addition is not particularly limited, but it is preferable to add the curing agent last from the viewpoint of the storage stability of the resin composition.

  The kneading temperature during the production of the curable resin composition may be appropriately adjusted according to the type of the curable resin, the thermoplastic resin particles, the curing agent, the reaction start temperature, etc., but is preferably in the range of 10 to 150 ° C. When it exceeds 150 degreeC, a partial hardening reaction will start and the storage stability of the resin composition obtained may fall. If it is lower than 10 ° C., the viscosity of the resin composition is high, and it may be difficult to knead substantially. Preferably it is 20-120 degreeC, More preferably, it is the range of 30-100 degreeC.

A conventionally well-known thing can be used as a kneading machine apparatus used at the time of curable resin composition manufacture. Specific examples include a roll mill, a planetary mixer, a kneader, an extruder, a Banbury mixer, a mixing vessel provided with a stirring blade, and a horizontal mixing vessel.
The method for producing a fiber reinforced composite material as described above can be applied without particular limitation as long as it is a method for producing a fiber reinforced composite material in which reinforced fibers are impregnated with a curable resin composition and cured. It can be applied to known means and methods such as molding, press molding, resin transfer molding, and filament winding molding.

The fiber-reinforced composite material of the present invention is preferably produced by a method using a prepreg which is an intermediate substrate obtained by impregnating a resin composition into a sheet-like fiber-reinforced substrate. When manufacturing a fiber reinforced composite material using a prepreg, examples of the prepreg lamination method include manual layup, automatic tape layup (ATL), and automatic fiber placement method.
The method for producing the prepreg is not particularly limited, and any conventionally known method can be adopted. Specifically, a hot melt method or a solvent method can be suitably employed.
In the hot melt method, the curable resin composition is coated on a release paper in the form of a thin film to form a resin composition film, and then the formed film is peeled from the release paper to obtain a resin composition film. Then, the resin composition film is laminated on the reinforcing fiber substrate and heated under pressure to impregnate the reinforcing fiber substrate with the resin composition.

  The method for forming the resin composition into a resin composition film is not particularly limited, and any conventionally known method can be used. Specifically, it can be obtained by casting and casting a resin composition on a support such as a release paper or a film using a die extrusion, an applicator, a reverse roll coater, a comma coater or the like. The resin temperature for producing the film is appropriately determined according to the composition and viscosity of the resin for producing the film. Specifically, the same temperature conditions as the kneading temperature in the above-described method for producing an epoxy resin composition are preferably used. The impregnation can be performed in multiple stages at an arbitrary pressure and temperature in a plurality of times instead of once.

The solvent method is a method in which the resin composition is made into a varnish using an appropriate solvent, and this reinforcing varnish is impregnated with the varnish. Among these conventional methods, the hot melt method is preferable.
The impregnation pressure at the time of impregnating the curable resin composition into the reinforcing fiber base using the resin composition film is appropriately determined in consideration of the viscosity, resin flow, and the like of the resin composition.
The impregnation temperature when an epoxy resin is used as the curable resin and the reinforcing fiber base material is impregnated with the epoxy resin composition film by a hot melt method is preferably in the range of 50 to 150 ° C. The impregnation temperature is more preferably 60 to 145 ° C, and particularly preferably 70 to 140 ° C.

According to the method for producing a fiber reinforced composite material as described above, since a large region (domain) of a thermoplastic resin can be formed in the cured resin after the curing reaction, it is excellent in impact resistance and interlaminar fracture toughness. Fiber reinforced composite material can be obtained.
The fiber-reinforced composite material of the present invention thus obtained is excellent in impact resistance and interlaminar fracture toughness, and therefore can be suitably used for many applications such as aerospace applications, industrial applications, sports and leisure applications. it can.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. In addition, evaluation of operating conditions and measurement of each physical property were performed by the following methods.

(Reinforced fiber substrate)
-The tensile strength and elastic modulus of the carbon fiber strand ("Tenax IMS65") manufactured by Toho Tenax Co., Ltd. used are as follows.
・ Tensile strength: 5800 MPa
-Elastic modulus: 290 GPa

[Epoxy resin composition]
(Epoxy resin)
・ Glycidylamine type epoxy resin (trifunctional group)
“Araldite MY600” (hereinafter, MY600) manufactured by Huntsman Japan
・ Glycidylamine type epoxy resin (4 functional groups)
"Araldite MY721" manufactured by Huntsman Japan Co., Ltd. (hereinafter MY721)
(Epoxy resin curing agent)
Aromatic amine curing agent 3,3′-diaminodiphenyl sulfone (manufactured by Konishi Chemical Co., Ltd.) (hereinafter 3,3′-DDS)

[Thermoplastic resin]
・ Thermoplastic resin particles for forming thermoplastic resin regions Polyamide 12 (thermoplastic resin insoluble in epoxy resin)
"MSP-100" manufactured by Daicel Evonik Co., Ltd.
Average particle diameter: 5 μm Break elongation: 300%
・ Viscosity-adjusting thermoplastic resin Polyethersulfone (a thermoplastic resin soluble in epoxy resin)
"PES-5003P" manufactured by Sumitomo Chemical Co., Ltd.
Average particle size: 20 μm

[Measuring method]
(1) Average particle diameter The average particle diameter was measured by measuring the particle size distribution using a laser diffraction / scattering particle size analyzer (Microtrack method) “MT3300” manufactured by Nikkiso Co., Ltd. D ₅₀ ) was defined as the average particle size.

(2) Interlaminar toughness of fiber reinforced composite materials (Mode I interlaminar toughness (GIc))
Interlaminar toughness of the fiber reinforced composite material was evaluated by measuring interlaminar fracture toughness mode I (GIc) according to JIS K7086. The obtained prepreg was cut into a square having a side of 360 mm, then laminated, and two laminates were produced in which 10 layers were laminated in the 0 ° direction. In order to generate an initial crack, the release sheet was sandwiched between two laminates, and both were combined to obtain a prepreg laminate having a laminate configuration [0] ₂₀ . Using a normal vacuum autoclave molding method, molding was performed under a pressure condition of 0.59 MPa and at temperature conditions set separately for each of the examples and comparative examples. The obtained molded product was cut into a size of 20 mm wide × 195 mm long to obtain a specimen having an interlaminar fracture toughness mode I (GIc).
A test that uses a double cantilever interlaminar fracture toughness test method (DCB method) as a test method for GIc, generates a 2-5 mm pre-crack (initial crack) from the tip of the release sheet, and further propagates the crack Went. The crosshead speed of the test piece tensile tester was 0.5 mm / min until the crack growth reached 20 mm, 1 mm / min after reaching 20 mm, and measurement was performed at n = 5. GIC was calculated from the load, displacement, and crack length.

(3) Morphological evaluation of the thermoplastic resin region Using a KEYENCE color 3D laser microscope VK-8710, a test piece obtained by cutting the fiber reinforced composite material in the cross-sectional direction of the fiber axis is 500 times (size of field of view: width) (The direction parallel to the surface of the resin layer) 600 μm × height (thickness direction) 100 μm), and an image of the sample cross section was acquired so that the resin layer was the center of the visual field. Using the image analysis software (A image-kun (trade name)) provided by Asahi Kasei Engineering Co., Ltd., specify the region of the thermoplastic resin, the domain length in the direction parallel to the surface of the resin layer, the domain in the thickness direction of the resin layer The length and circularity were calculated based on the following definitions.

-Domain length in the direction parallel to the surface of the resin layer A line segment of 400 μm in length was drawn in the direction parallel to the surface of the resin layer of the carbon fiber composite material, and the length of the thermoplastic resin region overlapping the line segment was measured. . The line segments were set at three locations of 1/4, 1/2, and 3/4 of the resin layer thickness per sample. Four samples were measured, and the average value and 90% quantile were determined.

-Domain length in the resin layer thickness direction Line segments in the resin layer thickness direction (perpendicular to the surface of the resin layer) from the surface of the carbon fiber in contact with the top of the resin layer to the bottom of the resin layer Pulled to the surface. Ten samples were arbitrarily measured at intervals of 30-50 μm in the width direction per sample. The length of the line segment is the resin layer thickness, the length of the thermoplastic resin region overlapping the line segment is the domain length in the resin layer thickness direction, and the ratio of the domain length of the thermoplastic resin region to the resin layer thickness is 100 minutes Asked. Four samples were measured, and the average value and 90% quantile were determined.

-Circularity The circumference and area of the thermoplastic resin region specified by the image analysis software were measured, and the circularity was calculated based on the following equation. At this time, from the visual field range of the image, the analysis range was cut out by analyzing the vertical direction (thickness direction) as the thickness of the resin layer and the horizontal direction (surface direction of the resin layer) as 400 μm. Measurement was performed at arbitrary four locations per sample, and the average value of the four samples was determined.
(Circularity) = Σ (4πS ² / L ² ) / S _T
S: Area of thermoplastic resin region [μm ² ]
L: Perimeter length of thermoplastic resin region [μm]
S _T : Total area of the thermoplastic resin region [μm ² ]

(Examples 1 and 2 and Comparative Example 1)
In a kneader, 30 parts by weight of polyethersulfone was added to 40 parts by weight of MY600 and 60 parts by weight of MY721, and the mixture was stirred at 100 ° C for 30 minutes using a stirrer, and then the resin temperature was cooled to 70 ° C or lower . Thereafter, 45 parts by mass of polyamide 12 resin particles and 60 parts by mass of 3,3′-DDS were kneaded to prepare an epoxy resin composition. The prepared epoxy resin composition was applied onto release paper using a film coater to prepare ^two 50 g / m ² resin films.
The carbon fiber bundle was aligned in one direction to prepare a carbon fiber base material (weight per unit: 190 g / m ² ). An epoxy resin film was bonded to both surfaces of the produced carbon fiber base material, and the carbon fiber base material was impregnated with a hot melt method to prepare a prepreg (resin content: 35%).
Using the prepared prepreg, a fiber-reinforced composite material was molded under the temperature conditions shown in Table 1. The morphology and interlaminar fracture toughness of the thermoplastic resin region of the obtained fiber reinforced composite material were measured. The obtained results are shown in Table 1.

In the fiber-reinforced composite materials obtained in Examples 1 and 2, the 90% quantile of the domain length in the direction parallel to the surface of the resin layer in the thermoplastic resin region is 33.7 μm and 91.5 μm, respectively, which are large heats. Since the plastic resin domain was formed, the interlaminar fracture toughness was as high as 736 J / m ² and 929 J / m ² , respectively, and it was a fiber-reinforced composite material having excellent interlaminar fracture toughness.
On the other hand, in Comparative Example 1, although the same prepreg was used, the 90% quantile of the domain length in the direction parallel to the surface of the resin layer was formed as a small thermoplastic resin region of 4.4 μm. The fracture toughness was 368 J / m ² which was very low compared to Examples 1 and 2.

Claims (6)

  A fiber reinforced composite material comprising a reinforced fiber layer and a curable resin cured product laminated at least two layers, and a resin comprising at least a curable resin cured product and a thermoplastic resin between the two reinforced fiber layers. And a thermoplastic resin region in which the 90% quantile of the domain length in the direction parallel to the surface of the resin layer is 15 μm or more. Reinforced composite material.   The fiber reinforced composite material according to claim 1, wherein the thermoplastic resin region has a circularity of 0.01 to 0.7.   The fiber-reinforced composite material according to claim 1 or 2, wherein an average value of domain lengths in the thickness direction of the resin layer in the thermoplastic resin region is 25% or more of an average thickness of the resin layer.   The fiber-reinforced composite material according to any one of claims 1 to 3, wherein the thermoplastic resin is a thermoplastic resin having a breaking elongation of 80% or more.   The fiber reinforced composite material according to claim 1, wherein the curable resin is an epoxy resin.   The fiber-reinforced composite material according to any one of claims 1 to 5, wherein the reinforcing fiber is a carbon fiber.