JP2023149496A - Epoxy resin composition, prepreg, fiber-reinforced composite material and method for producing the same - Google Patents

Abstract

To provide an epoxy resin composition that can be molded in a short time, and can yield a cured body with high water absorption resistance and high mechanical characteristics.SOLUTION: An epoxy resin composition includes an epoxy resin, a dicyandiamide, a urea-based curing accelerator, and a predetermined aromatic amine. The epoxy resin includes a tetrafunctional aromatic epoxy resin and a predetermined trifunctional epoxy resin.SELECTED DRAWING: None

Description

The present invention relates to an epoxy resin composition, a prepreg, a fiber-reinforced composite material, and a method for producing the same. In particular, the present invention relates to epoxy resin compositions, prepregs, fiber-reinforced composite materials, and methods for producing the same, which can be molded in a short time and the resulting molded products have high water absorption resistance and mechanical properties.

Fiber-reinforced composite materials (hereinafter referred to as "FRP") are lightweight, high strength, and highly rigid, so they are used in a wide range of fields, including sports and leisure applications such as fishing rods and golf shafts, and industrial applications such as automobiles and aircraft. It is being For manufacturing FRP, a method is preferably used in which an intermediate material (prepreg) in which a fiber reinforcing material layer made of long fibers such as reinforcing fibers is impregnated with resin is used. A molded article made of FRP can be obtained by cutting the prepreg into a desired shape, shaping it, and curing it by heating and pressurizing.

In the aircraft field, high mechanical properties such as heat resistance and impact resistance are required. In general, prepregs using epoxy resins can provide molded articles with high mechanical properties. However, prepreg using epoxy resin requires a long molding time. Furthermore, a molded article obtained by curing a prepreg using an epoxy resin has insufficient water absorption resistance, and may absorb water at high temperatures, resulting in a decrease in mechanical properties such as impact resistance.

Patent Document 1 discloses a prepreg comprising a fiber-reinforced base material made of carbon fiber and an epoxy resin composition partially or completely impregnated into the fiber-reinforced base material, discloses a prepreg characterized by containing an epoxy resin, dicyandiamide, and a predetermined aromatic amine. A carbon fiber reinforced composite material made using this prepreg has high water absorption resistance. Furthermore, this prepreg containing a urea-based accelerator has a short gel time, so it can be molded in a short time. Furthermore, this prepreg containing thickening particles has high press moldability and can stabilize the quality of CFRP.
However, there is a need for fiber reinforced composite materials with higher mechanical properties.

JP2019-156982

An object of the present invention is to provide an epoxy resin composition that can be molded in a short time and can produce a cured product with high water absorption resistance and mechanical properties. Furthermore, it is an object of the present invention to provide a fiber-reinforced composite material that is produced using this epoxy resin composition and has high water absorption resistance and mechanical properties.

The present inventors have discovered that the above problems can be solved by blending a predetermined epoxy resin in a predetermined ratio, and have completed the present invention.

The present invention for solving the above problems is described below.

[1] Epoxy resin and
dicyandiamide and
A urea-based curing accelerator,
The following formula (1)

(However, it has at least one substituent other than hydrogen at the ortho position to the amino group. In addition, in chemical formula (1), R ₁ to R ₈ each independently represent a hydrogen atom, an aliphatic substitution having 1 to 6 carbon atoms, group, aromatic substituent, or halogen atom, and at least one substituent is an aliphatic substituent having 1 to 6 carbon atoms.X is -CH ₂ -, -CH(CH ₃ )-, -C(CH ₃ ) ₂ -, -S-, -O-, -CO-, -CONH-, -C(=O)-);
An epoxy resin composition comprising:
The epoxy resin is
Tetrafunctional aromatic epoxy resin,
The following formula (2)

(However, in chemical formula (2), R ₁₀ , R ₁₁ , and R ₁₂ are each independently an aliphatic substituent having 1 to 6 carbon atoms.)
An epoxy resin composition comprising: a trifunctional epoxy resin represented by:

The invention described in [1] above includes a tetrafunctional aromatic epoxy resin and a trifunctional epoxy resin having a triazine skeleton represented by the chemical formula (2) as an epoxy resin constituting the epoxy resin composition, and a trifunctional epoxy resin having a triazine skeleton represented by the chemical formula (1). ) is characterized by containing an aromatic amine represented by The aromatic amine has a substituent other than a hydrogen atom at at least one of the four positions ortho to the amino group.

[2] The epoxy resin composition according to [1], further comprising core-shell type rubber particles.

[3] The epoxy resin composition according to [2], wherein the content of the core-shell type rubber particles is less than 5 parts by mass based on 100 parts by mass of the total epoxy resin.

[4] The tetrafunctional aromatic epoxy resin has the following formula (3)

The epoxy resin composition according to any one of [1] to [3], which is N,N,N',N'-tetraglycidyldiaminodiphenylmethane.

[5] The epoxy resin composition according to any one of [1] to [4], wherein the content of the tetrafunctional aromatic epoxy resin is more than 70 parts by mass based on 100 parts by mass of the total epoxy resin.

[6] The epoxy resin composition according to any one of [1] to [5], wherein the content of the trifunctional epoxy resin is 2 to 10 parts by mass based on 100 parts by mass of the total epoxy resin.

[7] The epoxy resin further includes a bifunctional or less epoxy resin, and the content thereof is 20 parts by mass or less based on 100 parts by mass of the total epoxy resin, according to any one of [1] to [6]. epoxy resin composition.

[8] The epoxy resin composition according to [7], wherein the bifunctional or less epoxy resin is a bisphenol A epoxy resin.

[9] The epoxy resin composition according to any one of [1] to [8], further comprising a thermoplastic resin.

[10] Fiber-reinforced base material,
The epoxy resin composition according to any one of [1] to [9] impregnated into the fiber-reinforced base material;
A prepreg characterized by consisting of.

[11] A fiber-reinforced composite material obtained by curing the prepreg described in [10].

[12] A method for producing a fiber-reinforced composite material, which comprises curing the prepreg according to [10] by holding it at 130 to 180°C for 10 to 30 minutes.

A cured product obtained by curing the epoxy resin composition of the present invention has high water absorption resistance and mechanical properties. Moreover, since the epoxy resin composition of the present invention has a short gel time, it can be molded in a short time.

Hereinafter, the epoxy resin composition, prepreg, fiber-reinforced composite material, and manufacturing method thereof of the present invention will be explained. In addition, in this specification, an epoxy resin composition refers to a product in an uncured or semi-cured state, and after the epoxy resin composition is cured, it is referred to as a cured product or a cured resin.

1. Epoxy resin composition The epoxy resin composition of the present invention is
Epoxy resin and
dicyandiamide and
A urea-based curing accelerator,
An aromatic amine represented by the aforementioned chemical formula (1),
An epoxy resin composition comprising:
The epoxy resin is characterized in that it contains a tetrafunctional aromatic epoxy resin and a trifunctional epoxy resin having a triazine skeleton represented by the aforementioned chemical formula (2).

The epoxy resin composition of the present invention preferably contains core-shell type rubber particles and a tetrafunctional epoxy resin represented by the above-mentioned chemical formula (3). Further, it is preferable that a small amount of thermoplastic resin is dissolved.

The epoxy resin composition of the present invention was cured by heating at 160°C for 20 minutes, and the resulting cured product was subjected to water absorption treatment at 121°C for 24 hours using a pressure cooker (manufactured by ESPEC, HASTEST PC-422R8). The glass transition temperature (Wet-Tg) of the resin test piece is preferably 130°C or higher, more preferably 150°C or higher. If the glass transition temperature is 130° C. or higher, it is preferable because the CFRP product is unlikely to be deformed even when used under conditions where heat is applied, such as during painting.

The epoxy resin composition of the present invention preferably has a viscosity at 50° C. of 50 to 1000 Pa·s, more preferably 70 to 700 Pa·s, and particularly preferably 80 to 500 Pa·s. If it is less than 50 Pa·s, when a prepreg is produced using this resin composition, the handleability of the prepreg decreases due to stickiness of the resin composition. If it exceeds 1000 Pa·s, the impregnation of the resin composition into the fiber-reinforced base material layer may become insufficient when producing a prepreg using this resin composition.

The gel time of the epoxy resin composition at 150° C. is preferably 300 seconds or less, more preferably 280 seconds or less, and even more preferably 250 seconds or less. By setting the time to 300 seconds or less, the molding speed can be increased. Gel time can be adjusted by adding a urea promoter.

1-1. Epoxy Resin The epoxy resin composition of the present invention includes a tetrafunctional aromatic epoxy resin and a trifunctional epoxy resin having a triazine skeleton represented by the aforementioned chemical formula (2).

As the tetrafunctional aromatic epoxy resin, any of aliphatic type, aromatic type, and amine type can be used. In particular, the following formula (3)

N,N,N',N'-tetraglycidyldiaminodiphenylmethane represented by is preferred.

The content of the tetrafunctional aromatic epoxy resin is preferably more than 70 parts by weight and less than 95 parts by weight, more preferably 80 to 90 parts by weight, based on 100 parts by weight of the total epoxy resin. If the amount is 70 parts by mass or less, the mechanical properties of the resulting cured product may not be sufficiently high.

The trifunctional epoxy resin having a triazine skeleton has the following formula (2)

(However, in chemical formula (2), R ₁₀ , R ₁₁ , and R ₁₂ are each independently an aliphatic substituent having 1 to 6 carbon atoms.)
It is expressed as In chemical formula (2), R ₁₀ , R ₁₁ , and R ₁₂ are preferably a methyl group or an ethyl group, and more preferably a methyl group. That is, the following formula (7)

More preferably, it is 1,3,5-tris(oxiranylmethyl)-1,3,5-triazine 2,4,6(1H,3H,5H)-trione.

The content of the epoxy resin represented by the above chemical formula (2) is preferably 2 to 10 parts by weight, more preferably 3 to 8 parts by weight, based on 100 parts by weight of the total epoxy resin. If it exceeds 10 mass, the mechanical properties of the resulting cured product may not be sufficiently high.

The total blending amount of the trifunctional epoxy resin and the tetrafunctional aromatic epoxy resin is preferably 85 parts by mass or more, preferably 87 parts by mass or more, and 90 parts by mass out of 100 parts by mass of the total epoxy resin. It is more preferable that it is above. Further, the total amount of these epoxy resins is preferably 95 parts by mass or less, more preferably 92 parts by mass or less, out of 100 parts by mass of the total epoxy resin. If the amount is less than 85 parts by mass, the resulting cured product may not have sufficiently high mechanical properties.

The epoxy resin composition of the present invention may contain a difunctional or less functional epoxy resin.

For example, the epoxy resin composition of the present invention has the following formula (4):

(However, in chemical formula (4), R ₉ is a hydrogen atom or an aliphatic substituent having 1 to 6 carbon atoms.)
It may also contain a bifunctional epoxy resin represented by:

Among the compounds represented by the above chemical formula (4), N,N-diglycidylaniline represented by the following formula (5) or N,N-(diglycidyl)-o- represented by the following formula (6) Toluidine is preferred.

The epoxy resin composition of the present invention may contain epoxy resins other than those mentioned above. Specifically, bifunctional epoxy resins such as bisphenol type epoxy resin, alcohol type epoxy resin, biphenyl type epoxy resin, hydrophthalic acid type epoxy resin, dimer acid type epoxy resin, alicyclic type epoxy resin; tetrakis (glycidyloxyphenyl) Glycidyl ether type epoxy resins such as ethane and tris(glycidyloxyphenyl)methane; Glycidylamine type epoxy resins such as tetraglycidyldiaminodiphenylmethane; Naphthalene type epoxy resins; Phenol novolac type epoxy resins and cresol novolak type epoxy resins Examples include molded epoxy resin.

Further examples include polyfunctional epoxy resins such as phenol type epoxy resins. Various modified epoxy resins such as urethane modified epoxy resin and rubber modified epoxy resin can also be used.

In particular, epoxy resins having an aromatic group in the molecule are preferred, and epoxy resins having either a glycidyl amine structure or a glycidyl ether structure are more preferred. Furthermore, alicyclic epoxy resins can also be suitably used.

Epoxy resins having a glycidylamine structure include N,N,O-triglycidyl-p-aminophenol, N,N,O-triglycidyl-m-aminophenol, and N,N,O-triglycidyl-3-methyl. Various isomers of -4-aminophenol and triglycidylaminocresol are exemplified.

Examples of the epoxy resin having a glycidyl ether structure include bisphenol A epoxy resin, bisphenol F epoxy resin, bisphenol S epoxy resin, phenol novolac epoxy resin, and cresol novolak epoxy resin.

These epoxy resins may have a non-reactive substituent in the aromatic ring structure, etc., if necessary. Examples of non-reactive substituents include alkyl groups such as methyl, ethyl, and isopropyl; aromatic groups such as phenyl; alkoxyl; aralkyl; and halogen groups such as chlorine and bromine.

Examples of bisphenol type epoxy resins include bisphenol A type resin, bisphenol F type resin, bisphenol AD type resin, bisphenol S type resin, and the like. Specifically, jER815, jER828, jER834, jER1001, jER807 (product name) manufactured by Mitsubishi Chemical Corporation; EPOMIC R-710 (product name) manufactured by Mitsui Petrochemical; EXA1514 (product name) manufactured by Dainippon Ink and Chemicals. (first name) is exemplified.

Examples of the alicyclic epoxy resin include Araldite CY-179, CY-178, CY-182, and CY-183 (trade name) manufactured by Huntsman.

Examples of phenol novolac type epoxy resins include jER152 and jER154 (trade names) manufactured by Mitsubishi Chemical Corporation; DEN431, DEN485, and DEN438 (trade names) manufactured by Dow Chemical; Epiclon N740 (trade name) manufactured by DIC Corporation. Illustrated. Examples of cresol novolac type epoxy resins include Araldite ECN1235, ECN1273, and ECN1280 (trade names) manufactured by Huntsman; EOCN102, EOCN103, and EOCN104 (trade names) manufactured by Nippon Kayaku; Epotote YDCN-700-10 manufactured by Nippon Steel & Sumikin Chemical; Epotote YDCN-704 (trade name); Epiclon N680 and Epiclon N695 (trade name) manufactured by DIC Corporation are exemplified.

Examples of epoxy resins having a glycidylamine structure include Sumiepoxy ELM434, Sumiepoxy ELM120, and Sumiepoxy ELM100 (product names) manufactured by Sumitomo Chemical Co., Ltd.; Araldite MY0500, Araldite MY0510, Araldite MY0600, and Araldite MY720 manufactured by Huntsman Advanced Materials; Araldite MY721, Araldite MY9512, Araldite MY9612, Araldite MY9634, Araldite MY9663 (product name); jER604, jER630 (product name) manufactured by Mitsubishi Chemical Corporation; Bakerite EPR494 manufactured by Bakerite AG, Bake lite EPR495, Bakerite EPR496, Bakerite EPR497 (Product name) etc.

Examples of various modified epoxy resins include ADEKA RIN EPU-6 and EPU-4 (trade names) manufactured by Asahi Denka Co., Ltd., which are urethane-modified bisphenol A epoxy resins.

These epoxy resins can be appropriately selected and used alone or in combination of two or more. The amount of this epoxy resin blended is 20 parts by weight or less out of 100 parts by weight of the total epoxy resin, preferably 1 to 15 parts by weight, and more preferably 2 to 8 parts by weight. If it exceeds 15 mass, the mechanical properties of the resulting cured product may not be sufficiently high.

Among these, the bisphenol A type epoxy resin is preferably included in an amount of 15 parts by mass or less, more preferably 12 parts by mass or less, out of 100 parts by mass of the epoxy resin.

1-2. Dicyandiamide and urea-based curing accelerator Dicyandiamide is used as a curing agent for the epoxy resin in the present invention because it has excellent curability and physical properties of the resulting cured product.
Specific examples of dicyandiamide (DICY) include jER Cure DICY7 and DICY15 (trade name) manufactured by Mitsubishi Chemical Corporation.

DICY is preferably used in combination with a urea-based curing accelerator. Since DICY does not have very high solubility in epoxy resin, it is necessary to heat it to a high temperature of 160° C. or higher in order to sufficiently dissolve it. However, the melting temperature can be lowered by using it in combination with a urea-based curing accelerator.

Examples of the urea-based curing accelerator include phenyldimethylurea (PDMU) and toluene bisdimethylurea (TBDMU).

The amount of dicyandiamide blended is preferably 2 to 5 parts by weight, more preferably 2 to 4 parts by weight, based on 100 parts by weight of the total epoxy resin. When the blending amount of dicyandiamide is 2 parts by mass or more, a sufficient crosslinking density and a sufficient curing speed can be obtained. When the amount of dicyandiamide is 5 parts by mass or less, problems such as deterioration of mechanical properties of the cured product and turbidity of the cured product due to the presence of an excessive amount of the curing agent can be suppressed.

When dicyandiamide and a urea-based curing accelerator (PDMU, TBDMU, etc.) are used together, their blending amounts are 2 to 5 parts by weight of dicyandiamide and 2 to 5 parts by weight of the urea-based curing accelerator based on 100 parts by weight of the total epoxy resin. It is preferably 2 to 7 parts by mass. However, the total amount of dicyandiamide and urea curing agent is preferably 2 to 12 parts by mass. When the total amount of dicyandiamide and the urea curing accelerator is 2 parts by mass or more, a sufficient crosslinking density and a sufficient curing rate can be obtained. When the total amount of dicyandiamide and the urea-based curing accelerator is 12 parts by mass or less, problems such as deterioration of mechanical properties of the cured product and turbidity of the cured product due to the presence of an excessive amount of the curing agent can be suppressed. More preferably, the total amount of dicyandiamide and urea curing agent is 3 to 10 parts by mass.

1-3. Aromatic amine The aromatic amine used in the present invention is represented by the following formula (1)

(However, it has at least one substituent other than hydrogen at the ortho position to the amino group. In addition, in chemical formula (1), R ₁ to R ₈ each independently represent a hydrogen atom, an aliphatic substitution having 1 to 6 carbon atoms, group, aromatic substituent, or halogen atom, and at least one substituent is an aliphatic substituent having 1 to 6 carbon atoms.X is -CH ₂ -, -CH(CH ₃ )-, -C(CH ₃ ) ₂ -, -S-, -O-, -CO-, -CONH-, -C(=O)-.)
It is a compound represented by

Specifically, compounds represented by the following formulas (8) to (11) can be exemplified.

The amount of aromatic amine blended is 3 to 20 parts by weight, preferably 5 to 15 parts by weight, based on 100 parts by weight of the total epoxy resin. When the blending amount of the aromatic amine is 3 parts by mass or more, the crosslinking density becomes high, and the water absorption resistance of the cured product obtained by curing the epoxy resin composition can be increased. When the amount of aromatic amine is 20 parts by mass or less, the water absorption resistance of the cured product obtained by curing the epoxy resin composition can be increased without impairing the rapid curing properties of the resin.

1-4. Core-shell type rubber particles Core-shell type rubber particles are particles made by graft polymerizing a polymer different from the core component onto the surface of a core component made of a rubbery polymer, and the surface of the core component is coated with a shell component. Refers to rubber particles that contain
The rubbery polymer that is the core component is not particularly limited, but examples include butadiene rubber, acrylic rubber, silicone rubber, butyl rubber, nitrile rubber, styrene rubber, synthetic natural rubber, and ethylene propylene rubber.
Examples of the polymer serving as the shell component include, but are not particularly limited to, polymers of one or more monomers selected from the group consisting of acrylic esters, methacrylic esters, and aromatic vinyl compounds.
Commercially available products can also be used as such core-shell type rubber particles. Examples of commercially available products include the Kane Ace MX series manufactured by Kaneka Corporation.

The particle size of the core-shell type rubber particles is not particularly limited, but it is preferably 0.3 to 10 μm, more preferably 0.5 to 8 μm, before being blended into the present epoxy resin composition.

The blending amount of the core-shell type rubber particles is preferably less than 5 parts by mass, preferably less than 4 parts by mass, and more preferably 1 to 3.9 parts by mass based on 100 parts by mass of the total epoxy resin. The amount is preferably 1.25 to 3.75 parts by mass, particularly preferably 1.25 to 3.75 parts by mass. If it is 5 mass or more, the mechanical properties of the resulting cured product may not be sufficiently high.

1-5. Thermoplastic resin The epoxy resin composition of the present invention may contain a thermoplastic resin.
Thermoplastic resins include polysulfone, polyetherimide, polyphenylene ether, polyamide, polyacrylate, polyaramid, polyester, polycarbonate, polyphenylene sulfide, polybenzimidazole, polyimide, polyether sulfone polyketone, polyether ketone, polyether ether ketone, and polyvinyl. A group of thermoplastic resins belonging to engineering plastics such as formals are more preferably used. Polyimide, polyetherimide, polysulfone, polyethersulfone, polyvinyl formal, and the like are particularly preferably used because of their excellent heat resistance, toughness, and handleability.

The thermoplastic resin can be blended in any form. For example, a powdered thermoplastic resin may be kneaded and dispersed in an epoxy resin using a kneader, or a thermoplastic resin may be dissolved in an epoxy resin by heating it in the epoxy resin. . The epoxy resin composition preferably contains a thermoplastic resin dissolved in the epoxy resin and a thermoplastic resin dispersed in the epoxy resin.

The particle size of the powdered thermoplastic resin is preferably 0.2 to 100 μm, more preferably 0.5 to 80 μm.

The blending amount of the thermoplastic resin is preferably 5 to 20 parts by weight, more preferably 5 to 10 parts by weight, per 100 parts by weight of the epoxy resin.

1-6. Other Additives The epoxy resin composition of the present invention may contain a flame retardant, an inorganic filler, and an internal mold release agent.

Examples of flame retardants include phosphorus-based flame retardants. The phosphorus flame retardant is not particularly limited as long as it contains a phosphorus atom in its molecule, and examples include organic phosphorus compounds such as phosphoric acid esters, condensed phosphoric acid esters, phosphazene compounds, phosphinates, polyphosphates, etc. Examples include organic phosphorus compounds and red phosphorus.

Examples of inorganic fillers include aluminum borate, calcium carbonate, silicon carbonate, silicon nitride, potassium titanate, basic magnesium sulfate, zinc oxide, graphite, calcium sulfate, magnesium borate, magnesium oxide, and silicate minerals. , metal hydroxides. In particular, it is preferable to use silicate minerals and metal hydroxides. A commercially available silicate mineral includes THIXOTROPIC AGENT DT 5039 (manufactured by Huntsman Japan Co., Ltd.). Examples of the metal hydroxide include aluminum hydroxide and magnesium hydroxide. Among these, when imparting flame retardant properties, aluminum hydroxide is preferred from the viewpoint of thermal decomposition temperature and amount of heat absorbed during decomposition. As the metal hydroxide, a commercially available product may be used, or one synthesized by a known manufacturing method may be used. For example, as commercially available aluminum hydroxide, Sumitomo Chemical C-303, C-301, C-300GT, C-305, C-3250, or CM-450, or Showa Denko Hygilite H-42 or H- 43 etc. are mentioned.
Further, commercially available magnesium hydroxide includes Magstar #5, #4, #2, Echomag PZ-1, and Z-10 manufactured by Tateho Chemical Industries.
The content of the inorganic filler in the epoxy resin composition is preferably 5 to 30% by mass, more preferably 7 to 25% by mass. When the content of the inorganic filler is less than 5% by mass, a sufficient flame retardant effect may not be obtained. If the content of the inorganic filler exceeds 30% by mass, the mechanical properties, particularly the rigidity and Charpy impact value, may decrease.

Examples of the internal mold release agent include metal soaps, vegetable waxes such as polyethylene wax and carbana wax, fatty acid ester mold release agents, silicone oil, animal wax, and fluorine-based nonionic surfactants. The blending amount of these internal mold release agents is preferably 0.1 to 5 parts by weight, more preferably 0.2 to 2 parts by weight, based on 100 parts by weight of the epoxy resin. Within this range, the release effect from the mold is suitably exhibited.
Commercially available internal mold release agents include MOLD WIZ (registered trademark) INT1846 (manufactured by AXEL PLASTICS RESEARCH LABORATORIES INC.), Licowax S, Licowax P, Licowax OP, Licowax PE190, Licowax PED (manufactured by Clariant Japan), stearyl steer Rate (SL-900A; manufactured by Riken Vitamin Co., Ltd.) is mentioned.

1-7. Manufacturing method of epoxy resin composition An epoxy resin composition can be manufactured by mixing an epoxy resin, dicyandiamide, a urea-based curing accelerator, and an aromatic amine. The order in which these are mixed does not matter.

When mixing a thermoplastic resin for the purpose of improving impact resistance, it can be produced by mixing an epoxy resin, dicyandiamide, a urea curing accelerator, an aromatic amine, and a thermoplastic resin. The order in which these are mixed does not matter.
When mixing core-shell type rubber particles, it can be produced by mixing an epoxy resin, dicyandiamide, a urea-based curing accelerator, an aromatic amine, and core-shell type rubber particles, and the order of mixing them does not matter. do not have.

The method for producing the epoxy resin composition is not particularly limited, and any conventionally known method may be used. An example of the mixing temperature is a range of 40 to 120°C. If the temperature exceeds 120°C, the curing reaction may partially proceed, resulting in a decrease in impregnation into the fiber-reinforced base material layer, and a decrease in storage stability of the resulting resin composition and prepreg manufactured using the same. There may be cases where you do so. If the temperature is less than 40°C, the viscosity of the resin composition may be high and mixing may become substantially difficult. The temperature is preferably 50 to 100°C, more preferably 50 to 90°C.

As the mixing machine, conventionally known ones can be used. Specific examples include a roll mill, a planetary mixer, a kneader, an extruder, a Banbury mixer, a mixing container equipped with stirring blades, a horizontal mixing tank, and the like. Mixing of each component can be performed in the air or under an inert gas atmosphere. When mixing is performed in the atmosphere, an atmosphere with controlled temperature and humidity is preferred. Although not particularly limited, it is preferable, for example, to mix at a temperature controlled at a constant temperature of 30° C. or lower, or in a low humidity atmosphere with a relative humidity of 50% RH or lower.

2. Prepreg The prepreg of the present invention is composed of the above-described epoxy resin composition of the present invention and a fiber-reinforced base material, and a part or all of the epoxy resin composition is impregnated into the layer of the fiber-reinforced base material. It is integrated with the reinforcing base material.

The content (RC) of the epoxy resin composition in the prepreg of the present invention is preferably 15 to 60% by mass, more preferably 20 to 50% by mass, and more preferably 25 to 50% by mass, based on the total mass of the prepreg. Particularly preferred is 45% by mass. If the content is less than 15% by mass, voids may occur in the resulting CFRP, which may deteriorate mechanical properties and the like. When the content exceeds 60% by mass, the reinforcing effect of the reinforcing fibers becomes insufficient, and the mechanical properties etc. of the obtained CFRP may be deteriorated.

The content rate (RC) of the epoxy resin composition is determined by immersing the prepreg in sulfuric acid to elute the resin composition impregnated into the prepreg. Specifically, it is determined by the following method.

First, a test piece is prepared by cutting a prepreg into a size of 100 mm x 100 mm, and its mass is measured. Next, this prepreg test piece is immersed in sulfuric acid and boiled if necessary. As a result, the resin composition impregnated into the prepreg is decomposed and eluted into the sulfuric acid. Thereafter, the remaining fibers are filtered out, washed with sulfuric acid, dried, and the mass of the fibers is measured. The content of the resin composition is calculated from the change in mass before and after the decomposition operation with sulfuric acid.

The shape of the prepreg of the present invention may be a prepreg sheet in which carbon fibers are formed in a sheet shape, or a strand prepreg in which carbon fibers are formed in a strand shape.

The form of the prepreg of the present invention includes a fiber-reinforced base material, a reinforcing layer consisting of an epoxy resin composition impregnated into the layer of this fiber-reinforced base material, and a resin coating layer stacked on the surface of this reinforcing layer. It may have a structure consisting of. The thickness of the resin coating layer is preferably 2 to 50 μm. If the thickness of the resin coating layer is less than 2 μm, the tackiness may be insufficient and the moldability of the prepreg may be significantly reduced. When the thickness of the resin coating layer exceeds 50 μm, it becomes difficult to wind up the prepreg into a roll with a uniform thickness, and the molding accuracy may be significantly reduced. The thickness of the resin coating layer is more preferably 5 to 45 μm, particularly preferably 10 to 40 μm.

2-1. Fiber-reinforced base material A base material made of carbon fiber is used as the fiber-reinforced base material. Polyacrylonitrile (PAN)-based carbon fibers are particularly preferred since they have excellent tensile strength.

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

It is preferable to use the fiber-reinforced base material in the form of a sheet. Examples of fiber-reinforced base sheets include sheets in which a large number of reinforcing fibers are aligned in one direction, bidirectional fabrics such as plain weave and twill weave, multiaxial fabrics, nonwoven fabrics, mats, knits, braids, and paper made from reinforced fibers. I can list papers that have been published.

The thickness of the sheet-like fiber reinforced base material is preferably 0.01 to 3 mm, more preferably 0.1 to 1.5 mm. These fiber-reinforced base materials may contain a known sizing agent in a known content.

The prepreg of the present invention may be a strand prepreg in which carbon fibers are formed into a strand shape. Strand prepreg is produced by dividing a sheet-like unidirectional prepreg. The width of the strand prepreg is preferably 3 to 20 mm, more preferably 6 to 10 mm. Moreover, it is preferable to cut the strand prepreg in the length direction to obtain short fiber prepreg. The fiber length is preferably 5 to 100 mm, more preferably 10 to 50 mm. The short fiber prepreg after cutting is preferably formed into a mat shape to obtain a prepreg mat.

2-2. Prepreg Manufacturing Method The prepreg manufacturing method of the present invention 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.

The hot-melt method involves applying a resin composition in a thin film onto release paper to form a resin composition film, laminating the resin composition film on a fiber-reinforced base material, and heating it under pressure. In this method, a resin composition is impregnated into a fiber-reinforced base material layer.

The method for turning the resin composition into a resin composition film is not particularly limited, and any conventionally known method can be used. Specifically, a resin composition film is obtained by casting and casting the resin composition onto a support such as release paper or film using die extrusion, an applicator, a reverse roll coater, a comma coater, etc. I can do it. The resin temperature when producing the film is appropriately determined depending on the composition and viscosity of the resin composition. Specifically, the same temperature conditions as the mixing temperature in the method for manufacturing the epoxy resin composition described above are preferably used. The epoxy resin composition may be impregnated into the fiber-reinforced base material layer in one step or in multiple steps.

The solvent method is a method in which the epoxy resin composition is made into a varnish using a suitable solvent, and the varnish is impregnated into the fiber-reinforced base material layer.

Among these conventional methods, the prepreg of the present invention can be suitably produced by a hot melt method that does not use a solvent.

When impregnating the epoxy resin composition film into the fiber-reinforced base material layer by a hot melt method, the impregnation temperature is preferably in the range of 50 to 120°C. When the impregnation temperature is less than 50° C., the epoxy resin composition has a high viscosity and may not be sufficiently impregnated into the fiber-reinforced base material layer. When the impregnation temperature exceeds 120° C., the curing reaction of the epoxy resin proceeds, and the storage stability and drape properties of the resulting prepreg may decrease. The impregnation temperature is more preferably 60 to 110°C, particularly preferably 70 to 100°C.

The impregnation pressure when impregnating the epoxy resin composition film into the fiber-reinforced base material layer by the hot-melt method is appropriately determined in consideration of the viscosity, resin flow, etc. of the resin composition.

3. Fiber reinforced composite material (FRP)
The FRP of the present invention can be obtained by curing the prepreg of the present invention by heating and pressing.

The FRP of the present invention is characterized by low water absorption. Here, the water absorption rate refers to the mass increase rate after storage for 24 hours under conditions of 121° C. and 100% RH. The water absorption rate is preferably 1.8% by mass or less, more preferably 1.5% by mass or less, even more preferably 1.3% by mass or less, and even more preferably 1.2% by mass or less. is particularly preferred. If the water absorption rate is too large, the compressive strength, which will be described later, is likely to decrease.

Examples of methods for producing FRP using the prepreg of the present invention include autoclave molding, press molding, internal pressure molding, and vacuum-assisted air pressure molding.

3-1. Autoclave Molding Method As a method for manufacturing the FRP of the present invention, an autoclave molding method is preferably used. In the autoclave molding method, a prepreg and a film bag are sequentially placed in the lower mold of a mold, the prepreg is sealed between the lower mold and the film bag, and the space formed by the lower mold and the film bag is evacuated. This is a molding method that uses heat and pressure using an autoclave molding device. The conditions during molding are preferably a temperature increase rate of 1 to 50°C/min, heating and pressurization at 0.2 to 0.7 MPa and 130 to 180°C for 10 to 30 minutes.

3-2. Press Molding Method As a method for manufacturing the FRP of the present invention, a press molding method is preferable from the viewpoint that high productivity and high quality FRP can be obtained by taking advantage of the characteristics of the epoxy resin composition that constitutes the prepreg. FRP is manufactured by the press molding method by heating and pressing the prepreg of the present invention or a preform formed by laminating the prepregs of the present invention using a mold. The mold is preferably heated to a curing temperature in advance.

The temperature of the mold during press molding is preferably 130 to 180°C. When the molding temperature is 130°C or higher, a curing reaction can be sufficiently caused and FRP can be obtained with high productivity. Further, if the molding temperature is 180° C. or lower, the resin viscosity will not become too low, and excessive flow of the resin within the mold can be suppressed. As a result, high-quality FRP can be obtained because resin outflow from the mold and fiber meandering can be suppressed.

The pressure during molding is 0.2 to 10 MPa. When the pressure is 0.2 MPa or more, appropriate flow of the resin can be obtained, and poor appearance and generation of voids can be prevented. In addition, since the prepreg sufficiently adheres to the mold, it is possible to manufacture FRP with a good appearance. If the pressure is 10 MPa or less, the resin will not be made to flow more than necessary, so that the resulting FRP will be less likely to have poor appearance. Furthermore, since no more load than necessary is applied to the mold, deformation of the mold is less likely to occur.

3-3. Internal Pressure Molding Method As a method for manufacturing the FRP of the present invention, an internal pressure molding method is also preferably employed. The internal pressure molding method involves laying prepreg on the outside of a bag-shaped internal pressure bag to obtain a prepreg laminate with an internal pressure bag inside, placing this prepreg laminate in a mold, clamping the mold, and molding the mold. This is a molding method in which the inner pressure bag is expanded within the mold to bring the prepreg into internal contact with the inner wall of the mold, and the prepreg is heated and cured in this state.

A method for manufacturing FRP using an internal pressure molding method will be explained. First, the prepreg of the present invention is placed in the upper mold and the lower mold, respectively. Next, an internal pressure bag is inserted between the upper mold and the lower mold on which the prepreg is laid, and the upper mold and the lower mold are clamped. As a result, a prepreg laminate having an internal pressure bag inside is obtained. Thereafter, by inflating the internal pressure bag in the mold, the prepreg in the mold is inscribed in the inner wall of the mold, and in this state, the mold is heated to heat and harden the prepreg. After a predetermined period of time has elapsed, the molded body is taken out from the mold, the internal pressure bag is removed, and FRP is obtained.
From the viewpoint of productivity, it is preferable to preheat the mold to a curing temperature before laying the prepreg.

The material of the internal pressure bag is preferably a flexible material with excellent heat resistance, such as nylon or silicone rubber.

The temperature inside the mold during internal pressure molding is preferably 130 to 180°C. When the molding temperature is 130°C or higher, a curing reaction can be sufficiently caused and FRP can be obtained with high productivity. Further, if the molding temperature is 180° C. or lower, the resin viscosity will not become too low, and excessive flow of the resin within the mold can be suppressed. As a result, high-quality FRP can be obtained by suppressing resin outflow from the mold and meandering of fibers.

The pressure during molding is 0.2 to 2 MPa. When the pressure is 0.2 MPa or more, appropriate flow of the resin can be obtained, and poor appearance and generation of voids can be prevented. In addition, since the prepreg sufficiently adheres to the mold, it is possible to obtain a CFRP with a good appearance. If the pressure is 2 MPa or less, a flexible internal pressure bag made of nylon or silicone rubber will not be easily destroyed.

3-4. Vacuum-assisted air pressure forming method As a method for manufacturing the FRP of the present invention, a vacuum-assisted air pressure forming method is also preferably used. The vacuum assisted air pressure molding method is to sequentially lay a prepreg and a film bag on the lower mold of a mold, seal the prepreg between the lower mold and the film bag, and form a mold with the lower mold and the film bag. This is a molding method in which the space is evacuated and the cavity of the mold, which is formed by clamping an upper mold and a lower mold, is pressurized with air to heat and harden the prepreg.

A method for manufacturing FRP using a vacuum-assisted air pressure molding method will be described. First, the prepreg of the present invention is placed in the lower mold of a mold. Next, a film bag is stacked on top of the prepreg, and the prepreg is sealed between the lower mold and the film bag. Thereafter, the prepreg is brought into contact with the lower mold by evacuating the space formed by the lower mold and the film bag. Furthermore, air is pressurized in the cavity of the mold formed by clamping the mold to further bring the prepreg into close contact with the lower mold. By heating in this state, the prepreg is heated and cured. After a predetermined period of time has elapsed, the molded body is taken out from the mold and the film bag is removed to obtain FRP.
From the viewpoint of productivity, it is preferable that the lower mold has a heating mechanism that can heat it rapidly.

The film bag is preferably made of a material that is flexible and has excellent heat resistance, such as nylon or silicone rubber.

Preferably, the temperature of the mold is 20 to 50° C. by stacking the prepreg and film bag to create a vacuum state, and then heating to 130 to 180° C. at a heating rate of 2 to 100° C./min. When the molding temperature is 130°C or higher, a curing reaction can be sufficiently caused and FRP can be obtained with high productivity. In addition, if the molding temperature is 180°C or lower, the resin viscosity will not become too low, and excessive flow of the resin within the mold can be suppressed, suppressing resin outflow from the mold and meandering of the fibers. As a result, high quality FRP can be obtained.

The pressure during molding is 0.2 to 2 MPa. When the pressure is 0.2 MPa or more, appropriate flow of the resin can be obtained, and poor appearance and generation of voids can be prevented. In addition, since the prepreg sufficiently adheres to the mold, it is possible to obtain FRP with a good appearance. If the pressure is 2 MPa or less, a flexible film bag made of nylon or silicone rubber will not be easily destroyed.

The curing time in the production method of the present invention is 10 to 30 minutes, which is shorter than conventional methods. That is, FRP of excellent quality can be manufactured with high productivity.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the Examples. The components and test methods used in the Examples and Comparative Examples are explained below.

(Epoxy resin)
・“jER604” (registered trademark): (tetraglycidyldiaminodiphenylmethane type epoxy resin, manufactured by Mitsubishi Chemical Corporation)
・“jER828” (registered trademark): (Liquid bisphenyl A type epoxy resin, manufactured by Mitsubishi Chemical Corporation)
・“GOT” (diglycidylethylaminobenzene), manufactured by Nissan Chemical Co., Ltd. ・“TEPIC-S”: (trifunctional epoxy resin with a triazine skeleton, manufactured by Nissan Chemical Co., Ltd.)

(Core-shell type rubber particles)
Kane Ace (registered trademark) "MX-416": Liquid masterbatch in which 25 wt% of core shell rubber particles are dispersed in tetraglycidyl-4,4'-diaminodiphenylmethane (glycidylamine-based epoxy resin) (manufactured by Kaneka Corporation)

(curing agent, curing accelerator)
・“Dicy7”: (dicyandiamide, manufactured by Mitsubishi Chemical Corporation)
・“Omicure 24” (registered trademark): (2,4'-toluene bis(3,3-dimethylurea), manufactured by PTI Japan Co., Ltd.)

(aromatic amine)
・Cure Hard "MED-J": Having the structure of the above chemical formula (8) (manufactured by Kumiai Chemical Industry Co., Ltd.)

(thermoplastic resin)
・Sumika Excel 5003P: Polyether sulfone (thermoplastic resin soluble in epoxy resin) (hereinafter referred to as "PES5003P"), manufactured by Sumitomo Chemical Co., Ltd., average particle size 20 μm
・“MSP-A7678”: (Polyamide 12, average particle size 20 μm, manufactured by Daicel Evonik)
・“MSP-A7723”: (Polyamide 1010, average particle size 20 μm, manufactured by Daicel Evonik)
・Zefiac (registered trademark) "F320": (alkyl methacrylate polymer), average degree of polymerization 30,000, manufactured by Aica Kogyo Co., Ltd.)

(Examples 1 to 12, Comparative Examples 1 to 6)
(1) Preparation of epoxy resin composition Add a predetermined amount of epoxy resin and a thermoplastic resin to be dissolved in the epoxy resin in the proportions shown in Table 1 into a kneader, and raise the temperature to 150°C while kneading to remove the solid components. Completely dissolved. Thereafter, the temperature is lowered to 60°C while kneading, and a curing agent, urea accelerator, thermoplastic resin that cannot be dissolved in epoxy resin, core-shell type rubber particles, etc. are added and stirred for 30 minutes to uniformly disperse the epoxy resin. A resin composition was obtained.

(2) Production of unidirectional prepreg A unidirectional prepreg was produced as follows. The epoxy resin composition obtained above was applied onto a release paper using a reverse roll coater to prepare a resin film having a weight of 50 g/m ² . Next, carbon fibers were aligned in one direction so that the fiber mass per unit area was 190 g/m ² to produce a sheet-like fiber-reinforced base material layer. The above resin films were stacked on both sides of this fiber-reinforced base material layer, and heated and pressed under conditions of a temperature of 100° C. and a pressure of 0.2 MPa to produce a unidirectional prepreg with a carbon fiber content of 65% by mass.

(3) Plane strain fracture toughness (K1c)
The above epoxy resin was poured into a silicone rubber mold at a temperature of 70°C, the mold was placed in a vacuum oven, and the air was degassed by vacuuming at 70°C for 10 minutes using an oil rotary pump. A resin plate with a thickness of 4 mm was produced by raising the temperature to .degree. C., holding the temperature at that temperature for 20 minutes, and then lowering the temperature at an arbitrary rate until it reached room temperature. The prepared resin plate was measured in accordance with the ASTM D5045 test method.

(4) Compressive strength after damage (CAI)
Measured in accordance with ASTM-D7136 and ASTM-D7137 test methods.

(5) Wet-Tg
The glass transition temperature was measured according to the SACMA 18R-94 method.
A resin test piece was prepared with dimensions of 50 mm x 6 mm x 2 mm. Using a pressure cooker (manufactured by ESPEC, HASTEST PC-422R8), the prepared resin test piece was subjected to water absorption treatment at 121° C. for 24 hours. Using a dynamic viscoelasticity measuring device Rheogel-E400 manufactured by UBM, under the conditions of measurement frequency 1 Hz, heating rate 5 °C/min, strain 0.0167%, distance between chucks 30 mm, rubber elasticity region from 50 °C The storage elastic modulus E' of the resin test piece subjected to water absorption treatment was measured. LogE' was plotted against temperature, and the temperature determined from the intersection of the approximate straight line of the flat region of logE' and the approximate straight line of the region where E' transitioned was recorded as the glass transition temperature (Tg).

(6) Hole compression test (normal temperature test) (hereinafter referred to as OHC (Dry))
A laminate in which 24 sheets of the above unidirectional prepreg were laminated in a configuration of [+45°/90°/-45°/0°] _{for 3 seconds} was placed in a bag, and the temperature was raised in an autoclave at a rate of 2°C/min to 160°C. It was heated at ℃ for 30 minutes and cured to produce a molded plate (carbon fiber reinforced composite material). During this time, the inside of the autoclave was pressurized to 0.7 MPa, and the inside of the bag was kept in vacuum.
The compressive strength of the carbon fiber reinforced composite material was measured at a test speed of 1.0 mm/min according to ASTM D6484 method. The number of samples was 5, and the average value was used.

(7) Hole compression test (moist heat treatment/high temperature test) (hereinafter referred to as OHC (HTWE))
The compressive strength of the carbon fiber reinforced composite material was measured at a test speed of 1.0 mm/min according to ASTM D6484 method. The number of samples was 5, and the average value was used.

(8) Evaluation of viscosity/handleability ◎: Viscosity at 60° C. is less than 100 Pa·s, and it is easy to take out from a kneading device (kneader, roll mill, etc.) and handle.
○: The viscosity at 60°C is 100 to 200 Pa·s, and it is easy to take out from a kneading device (kneader, roll mill, etc.) and handle.
Δ: Viscosity at 70° C. is higher than 200 Pa·s, making it difficult to take out from a kneading device (kneader, roll mill, etc.) and handle.

(9) Evaluation of press formability 12 sheets of the above unidirectional prepreg were laminated in the [0°] direction, placed in a mold for press molding the laminate, placed in a press machine heated to 160°C, and attached to the mold. Temperature monitoring using a thermocouple was started, and when the mold temperature reached 110° C., the pressure was adjusted so that a surface pressure of 2 MPa was applied to the test piece. After the temperature reached 160° C., it was held for 20 minutes and then removed from the mold to produce a molded plate (carbon fiber reinforced composite material).
The appearance of this molded plate was evaluated based on the following criteria.
〇: A moderate amount of resin remains on the entire molded plate, and the appearance is uniform. ×: The resin has flowed around the mold, and the appearance inside the molded plate is not uniform.

Claims (12)

Epoxy resin and
dicyandiamide and
A urea-based curing accelerator,
The following formula (1)

(However, it has at least one substituent other than hydrogen at the ortho position to the amino group. In addition, in chemical formula (1), R ₁ to R ₈ each independently represent a hydrogen atom, an aliphatic substitution having 1 to 6 carbon atoms, group, aromatic substituent, or halogen atom, and at least one substituent is an aliphatic substituent having 1 to 6 carbon atoms.X is -CH ₂ -, -CH(CH ₃ )-, -C(CH ₃ ) ₂ -, -S-, -O-, -CO-, -CONH-, -C(=O)-.)
An aromatic amine represented by
An epoxy resin composition comprising:
The epoxy resin is
Tetrafunctional aromatic epoxy resin,
The following formula (2)

(However, in chemical formula (2), R ₁₀ , R ₁₁ , and R ₁₂ are each independently an aliphatic substituent having 1 to 6 carbon atoms.)
An epoxy resin composition comprising: a trifunctional epoxy resin represented by:
The epoxy resin composition according to claim 1, further comprising core-shell type rubber particles.
The epoxy resin composition according to claim 2, wherein the content of the core-shell type rubber particles is less than 5 parts by mass based on 100 parts by mass of the total epoxy resin.
The tetrafunctional aromatic epoxy resin has the following formula (3)

The epoxy resin composition according to any one of claims 1 to 3, which is N,N,N',N'-tetraglycidyldiaminodiphenylmethane represented by:
The epoxy resin composition according to any one of claims 1 to 4, wherein the content of the tetrafunctional aromatic epoxy resin is more than 70 parts by mass based on 100 parts by mass of the total epoxy resin.
The epoxy resin composition according to any one of claims 1 to 5, wherein the content of the trifunctional epoxy resin is 2 to 10 parts by mass based on 100 parts by mass of the total epoxy resin.
The epoxy resin according to any one of claims 1 to 6, wherein the epoxy resin further contains a bifunctional or less epoxy resin, and the content thereof is 20 parts by mass or less out of 100 parts by mass of the total epoxy resin. Composition.
The epoxy resin composition according to claim 7, wherein the epoxy resin having less than two functional groups is a bisphenol A epoxy resin.
The epoxy resin composition according to any one of claims 1 to 8, further comprising a thermoplastic resin.
a fiber-reinforced base material;
The epoxy resin composition according to any one of claims 1 to 9 impregnated into the fiber reinforced base material,
A prepreg characterized by consisting of.
A fiber reinforced composite material obtained by curing the prepreg according to claim 10.
A method for producing a fiber reinforced composite material, comprising curing the prepreg according to claim 10 at 130 to 180° C. for 10 to 30 minutes.