Sheet molding compounds and fiber reinforced composites

Abstract

To provide a sheet molding compound excellent in workability in handling (tackiness and drape property) and flowability and rapid curability of a matrix resin in press molding, capable of inhibiting the occurrence of burrs, from which a fiber-reinforced composite material excellent in mold removability, mechanical properties and heat resistance can be obtained; and a fiber-reinforced composite material excellent in mold removability, mechanical properties and heat resistance.SOLUTION: A sheet molding compound is the thickened material of an epoxy resin composition comprising a component (A), a component(B) and a component (C). The component (A) is an epoxy resin in a liquid state at 25°C. The component (B) is an acid anhydride. The component (C) is an epoxy resin hardening agent. The thickened material comprises an ester formed of at least a part of the epoxy groups of the component (A) and at least a part of the carboxy groups derived from the component (B).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to sheet molding compounds and fiber reinforced composite materials. This application claims priority based on Japanese Patent Application No. 2017-079132, filed on April 12, 2017, the contents of which are incorporated herein by reference. [Background technology]

[0002] Carbon fiber reinforced composite materials, which are made of carbon fibers and a matrix resin, are widely used in aircraft, automobiles, and industrial applications due to their excellent mechanical properties. In recent years, the range of applications for carbon fiber reinforced composite materials has been expanding as their use has become more widespread. The matrix resin of carbon fiber reinforced composite materials is required to exhibit high mechanical properties even in high-temperature environments. Furthermore, the matrix resin of the molding materials (sheet molding compound (hereinafter also referred to as SMC), prepreg, etc.) used in the production of carbon fiber reinforced composite materials is required to have excellent moldability.

[0003] As the matrix resin for the molding material, a resin composition containing a thermosetting resin, which has excellent impregnation properties for carbon fibers and heat resistance after curing, is often used. Examples of thermosetting resins that have been used include phenolic resins, melamine resins, bismaleimide resins, unsaturated polyester resins, and epoxy resins. Of these, epoxy resin compositions are suitable as the matrix resin because they have excellent moldability and heat resistance after curing, and carbon fiber reinforced composite materials using these epoxy resin compositions can exhibit high levels of mechanical properties.

[0004] Methods for producing carbon fiber reinforced composite materials by molding a molding material include autoclave molding, filament winding molding, resin injection molding, vacuum resin injection molding, and press molding. Of these, press molding is in high demand because it is highly productive and can easily produce carbon fiber reinforced composite materials with excellent design surfaces. As the molding material used in press molding, SMC, which is composed of reinforcing short fibers and a matrix resin, is widely used because it can produce carbon fiber reinforced composite materials with complex shapes and can produce carbon fiber reinforced composite materials that are ideal for structural components.

[0005] The matrix resin used in SMC is required to have the following properties: · To ensure proper impregnation of carbon fibers during the manufacturing of SMC, the matrix resin of SMC must have a very low viscosity during the manufacturing process. To ensure ease of handling of SMC during press molding, the matrix resin of SMC must be thickened to an appropriate degree to reach B-stage (a state in which the resin has thickened due to semi-curing and can be made fluid by heating), and must have appropriate tack (adhesiveness) and drape (flexibility). To ensure the fluidity of the matrix resin during press molding, the matrix resin for SMC must be able to maintain the B-stage for a long period of time (B-stage stability). · Because press molding involves molding SMC in a short time at high temperatures, the matrix resin of the SMC must be able to cure in a short time and have high heat resistance after curing. To ensure easy demolding after press molding, the matrix resin of SMC must have high rigidity after curing. To obtain carbon fiber reinforced composite materials with high mechanical properties and heat resistance, the matrix resin of SMC must be able to exhibit high mechanical properties and heat resistance after curing.

[0006] However, although epoxy resin compositions provide excellent mechanical properties and heat resistance in the cured product, it is difficult to achieve both rapid curing and B-stage stability. That is, a curing agent that cures an epoxy resin in a short time rapidly progresses the curing reaction at room temperature, and therefore cannot maintain the B-stage of the epoxy resin composition for a long period of time, whereas a curing agent that can maintain the B-stage of the epoxy resin composition for a long period of time has difficulty curing the epoxy resin in a short period of time.

[0007] Therefore, the matrix resin for SMC is usually a thermosetting resin composition in which unsaturated polyester resin or vinyl ester resin is diluted with styrene. However, since thermosetting resin compositions containing unsaturated polyester resin or vinyl ester resin have large cure shrinkage, there is a need to develop an SMC using an epoxy resin composition with small cure shrinkage.

[0008] The following epoxy resin compositions have been proposed for use in SMC: (1) A resin composition comprising an epoxy resin having a hydroxyl group, a polyol, and a polyisocyanate compound (Patent Document 1). (2) A resin composition comprising an epoxy resin, a polyol, a polyisocyanate compound, dicyandiamide, and a specific imidazole compound (Patent Document 2).

[0009] The following epoxy resin compositions have been proposed for use in adhesives: (3) A liquid adhesive comprising an epoxy resin, a curing agent having an activation temperature of 20 to 100°C, and a curing agent having an activation temperature of 100 to 200°C (Patent Document 3). (4) A reactive hot melt adhesive containing an epoxy resin that is solid at room temperature, an epoxy resin that is liquid at room temperature, a linear polyoxypropylene having an amino group terminal, and a latent curing agent (dicyandiamide) (Patent Document 4).

[0010] The following epoxy resin compositions have been proposed for use in prepregs: (5) An impregnation resin composition containing an epoxy resin, a latent curing agent, a resin having a polymerizable unsaturated group, and a polymerization initiator (Patent Document 5). (6) An epoxy resin composition containing an epoxy resin, an acid anhydride, and a Lewis acid salt (boron trichloride amine complex) (Patent Documents 6 to 8).

[0011] The following have been proposed as epoxy resin compositions that can stably B-stage an epoxy resin. (7) A resin composition containing an epoxy resin and 2,5-dimethyl-2,5-hexamethylenediamine and menthenediamine as curing agents (Non-Patent Document 1). [Prior art documents] [Patent documents]

[0012] [Patent Document 1] Japanese Unexamined Patent Publication No. 58-191723 [Patent Document 2] Japanese Patent Application Publication No. 4-88011 [Patent Document 3] Japanese Patent Application Publication No. 2-88684 [Patent Document 4] Japanese Patent Application Publication No. 2-88685 [Patent Document 5] Japanese Patent Application Publication No. 2-286722 [Patent Document 6] Japanese Patent Application Laid-Open No. 2004-189811 [Patent Document 7] Japanese Patent Application Laid-Open No. 2004-43769 [Patent Document 8] Japanese Patent Application Laid-Open No. 2001-354788 [Non-patent literature]

[0013] [Non-Patent Document 1] Masaki Shinbo (ed.), "Epoxy Resin Handbook," Nikkan Kogyo Shimbun, December 25, 1987, p. 155 Summary of the Invention [Problem to be solved by the invention]

[0014] The resin compositions (1) and (2) utilize a urethane reaction, and the viscosity-increasing reaction rate and B-stage state change significantly due to the influence of moisture in the resin composition. As a result, it is difficult to ensure the handling and workability of SMC and the stability of the B-stage. Liquid adhesives (3) use curing agents (polyamines, mercaptans, isocyanates, imidazoles, polyamides, polysulfide phenols, BF3 complexes, ketimines, etc.) with activation temperatures of 20 to 100°C, so they reach a gel state during the first curing reaction. As a result, they have little fluidity before the second curing stage, making them difficult to shape, and they cannot be used as matrix resins for SMCs. (4) The reactive hot melt adhesive has a high viscosity and is unable to impregnate reinforcing fibers well, and therefore cannot be used as a matrix resin for SMC.

[0015] In the production of prepregs using the impregnation resin composition (5), Patent Document 5 describes a method in which the impregnation resin composition is impregnated with a solvent and then heated to remove the solvent and promote part of the curing reaction. This method is applicable to the production of thin prepregs, which are easy to remove the solvent from and have little temperature unevenness due to thickness during heating and cooling. However, with thick sheets such as SMC, it is difficult to remove the solvent and temperature unevenness becomes large, resulting in defective products with different surface and internal conditions after B-staging. The epoxy resin composition (6) takes a long time to reach the B-stage at room temperature (23°C). In addition, after reaching the B-stage at room temperature, the viscosity is low and the tack is too strong, making it unsuitable for SMC. The resin composition (7) contains 2,5-dimethyl-2,5-hexanediamine, which results in a short pot life. Furthermore, the resin composition contains menthol, which results in insufficient curing. Therefore, it is not suitable as a matrix resin for SMC.

[0016] The present invention provides a sheet molding compound that exhibits excellent handling (tackiness and drapeability), fluidity and rapid curing of the matrix resin during press molding, and can suppress the generation of burrs, and can provide a fiber-reinforced composite material that is excellent in demoldability, mechanical properties, and heat resistance; and a fiber-reinforced composite material that is excellent in demoldability, mechanical properties, and heat resistance. [Means for solving the problem]

[0017] As a result of extensive research, the present inventors have found that the above problems can be solved by using a specific epoxy resin, an acid anhydride, and an epoxy resin curing agent, and have arrived at the present invention.

[0018] The present invention has the following aspects. [1] A sheet molding compound which is a thickened product of an epoxy resin composition containing component (A), component (B), and component (C), the component (A) is an epoxy resin that is liquid at 25°C, the component (B) is an acid anhydride, the component (C) is an epoxy resin curing agent, A sheet molding compound, wherein the thickener forms an ester with at least a portion of the epoxy groups of the component (A) and at least a portion of the carboxy groups derived from the component (B). [2] The sheet molding compound according to [1], further comprising reinforcing fibers. [3] The sheet molding compound according to [1] or [2], wherein the viscosity of the epoxy resin composition at 30°C 30 minutes after preparation, as measured by the following viscosity measurement (a), is 0.5 to 15 Pa s. Viscosity measurement (a): The epoxy resin composition immediately after preparation is placed in a sealable container and sealed, and then allowed to stand at 23°C for 30 minutes, after which the viscosity of the epoxy resin composition at 30°C is measured. [4] The sheet molding compound according to any one of [1] to [3], wherein the viscosity of the epoxy resin composition at 30°C 10 days after preparation, as measured by the following viscosity measurement (b), is 2,000 to 55,000 Pa s. Viscosity measurement (b): The epoxy resin composition immediately after preparation is placed in a sealable container and sealed, and then allowed to stand at 23°C for 10 days, after which the viscosity of the epoxy resin composition at 30°C is measured. [5] The sheet molding compound according to any one of [1] to [3], wherein the viscosity of the epoxy resin composition at 30°C 20 days after preparation, as measured by the following viscosity measurement (c), is 2,000 to 100,000 Pa s. Viscosity measurement (c): The epoxy resin composition immediately after preparation is placed in a sealable container and sealed, and then allowed to stand at 23°C for 20 days, after which the viscosity of the epoxy resin composition at 30°C is measured. [6] The viscosity of the epoxy resin composition at 30°C 10 days after preparation, as measured by the following viscosity measurement (b), is 2,000 to 55,000 Pa s; the viscosity of the epoxy resin composition at 30°C 20 days after preparation, as measured by the following viscosity measurement (c), is 2,000 to 100,000 Pa s; The sheet molding compound according to any one of [1] to [3], wherein the viscosity (b) measured in the viscosity measurement (b) and the viscosity (c) measured in the viscosity measurement (c) satisfy the relationship [viscosity (c)] / [viscosity (b)]≦3. Viscosity measurement (b): The epoxy resin composition immediately after preparation is placed in a sealable container and sealed, and then allowed to stand at 23°C for 10 days, after which the viscosity of the epoxy resin composition at 30°C is measured. Viscosity measurement (c): The epoxy resin composition immediately after preparation is placed in a sealable container and sealed, and then allowed to stand at 23°C for 20 days, after which the viscosity of the epoxy resin composition at 30°C is measured. [7] The sheet molding compound according to any one of [1] to [6], wherein the content of component (B) is an amount such that the amount of acid anhydride groups is 0.1 to 0.5 equivalents per equivalent of epoxy groups contained in the epoxy resin composition. [8] The sheet molding compound according to any one of [1] to [7], wherein the content of the component (B) is 3 to 30 parts by mass per 100 parts by mass of the total epoxy resin contained in the epoxy resin composition. [9] The sheet molding compound according to any one of [1] to [8], wherein the content of the component (C) is 0.1 to 25 parts by mass per 100 parts by mass of the total epoxy resin contained in the epoxy resin composition.

[10] The sheet molding compound according to any one of [1] to [9], wherein the component (A) contains a glycidylamine-based epoxy resin.

[11] The sheet molding compound according to

[10] , wherein the content of the glycidylamine-based epoxy resin is 1 to 30 parts by mass per 100 parts by mass of all epoxy resins contained in the epoxy resin composition.

[12] The sheet molding compound according to any one of [1] to

[11] , wherein the component (B) is liquid at 25°C.

[13] The sheet molding compound according to any one of [1] to

[12] , wherein the component (C) is solid at 25°C.

[14] The sheet molding compound according to any one of [1] to

[13] , wherein the component (B) contains a compound having two cyclic acid anhydrides in the molecule.

[15] The sheet molding compound according to any one of [1] to

[14] , wherein the component (B) comprises phthalic anhydride or hydrogenated phthalic anhydride which may have a substituent.

[16] The sheet molding compound according to any one of [1] to

[15] , wherein the component (B) contains hydrogenated phthalic anhydride which may have a substituent, and the hydrogenated phthalic anhydride which may have a substituent is a compound represented by the following formula (1) or a compound represented by the following formula (2):

[0019] [ka]

[0020]

[17] The sheet molding compound according to any one of [1] to

[16] , wherein the component (C) contains an imidazole-based compound having a melting point of 120 to 300°C.

[18] The epoxy resin composition further comprises component (D), the component (D) is dicyandiamide, The sheet molding compound according to any one of [1] to

[17] , wherein the content of the component (D) is 0.1 to 5 parts by mass per 100 parts by mass of all epoxy resins contained in the epoxy resin composition.

[19] The component (C) further contains a component (E), the component (E) is an imidazole-based compound that is liquid at 25°C, The sheet molding compound according to any one of [1] to

[18] , wherein the content of the component (E) is 0.01 to 0.2 parts by mass per 100 parts by mass of all epoxy resins contained in the epoxy resin composition.

[20] A fiber-reinforced composite material, which is a cured product of the sheet molding compound according to any one of [1] to

[19] .

[0021]

[21] The compound having two cyclic acid anhydrides in the molecule is glyceryl bisanhydrotrimellitate monoacetate, ethylene glycol bisanhydrotrimellitate, pyromellitic anhydride, benzophenone tetracarboxylic anhydride, 1,2,3,4-cyclobutane tetracarboxylic dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride, diphenyl-3,3',4,4'-tetracarboxylic dianhydride, cyclopentane tetracarboxylic dianhydride, 1,2,4,5-cyclohexane tetracarboxylic dianhydride, 4-(2,5-dioxotetrahydrofuran-

[14] The sheet molding compound according to

[14] , wherein the diphthalic anhydride is at least one selected from the group consisting of 4,4'-(4,4'-isopropylidenediphenoxy)bis(phthalic anhydride), 4,4'-(hexafluoroisopropylidene)diphthalic anhydride, ...

[22] The sheet molding compound according to

[17] , wherein the imidazole compound having a melting point of 120 to 300°C is 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine.

[23] The sheet molding compound according to

[19] , wherein the component (E) is at least one selected from the group consisting of 2-ethyl-4-methylimidazole, 1,2-dimethylimidazole, 1-benzyl-2-methylimidazole, and 1-benzyl-2-phenylimidazole.

[24] The sheet molding compound according to

[10] , wherein the glycidylamine-based epoxy resin is N,N,N',N'-tetraglycidyl-m-xylylenediamine. [Effects of the Invention]

[0022] The sheet molding compound of the present invention has excellent impregnation properties for reinforcing fibers, stability in the B-stage, handling properties after B-stage (tackiness and drapeability), storage stability, rapid curing when heated, and fluidity and rapid curing properties of the matrix resin during press molding, while also producing little flash on the mold. Furthermore, the fiber-reinforced composite material of the present invention, which is a cured product of this sheet molding compound, has excellent demoldability, rigidity, mechanical properties and heat resistance. DETAILED DESCRIPTION OF THE INVENTION

[0023] The following definitions of terms apply throughout the specification and claims. "Liquid at 25°C" means that it is liquid under conditions of 25°C and 1 atmosphere. "Solid at 25°C" means that the substance is solid under the conditions of 25°C and 1 atmosphere. An "epoxy resin" is a compound that has two or more epoxy groups in its molecule. An "acid anhydride group" is a group having a structure in which one water molecule is removed from two acid groups (such as carboxy groups). An "acid anhydride" is a compound that contains an acid anhydride group. "Hydrogenated phthalic anhydride" is a compound in which some or all of the unsaturated carbon bonds in the benzene ring of phthalic anhydride are replaced with saturated carbon bonds. The "viscosity" is a value measured using a rheometer under the following conditions: measurement mode: constant stress, stress value: 300 Pa, frequency: 1.59 Hz, plate diameter: 25 mm, plate type: parallel plate, plate gap: 0.5 mm. "Flash" is an unwanted part formed at the edge of a molded product when resin flows into the gaps in the mold during press molding and solidifies. The symbol "to" indicating a range of values means that the values before and after it are included as the lower and upper limits.

[0024] <Sheet molding compound> The sheet molding compound of the present invention is a thickened product of the epoxy resin composition described below.

[0025] <Epoxy resin composition> The epoxy resin composition used in the present invention contains component (A): an epoxy resin that is liquid at 25° C., component (B): an acid anhydride, and component (C): an epoxy resin curing agent. This epoxy resin composition thickens immediately after preparation due to the formation of an ester bond between component (B) and component (A). This thickened product is the sheet molding compound of the present invention. This epoxy resin composition may further contain component (D): dicyandiamide. In the epoxy resin composition of the present invention, component (C) may further contain component (E): an imidazole-based compound that is liquid at 25°C. The epoxy resin composition used in the present invention may contain other components as needed, as long as the effects of the present invention are not impaired.

[0026] The viscosity of the epoxy resin composition at 30°C 30 minutes after preparation, as measured by the viscosity measurement (a) described below, is preferably 0.5 to 15 Pa·s, more preferably 0.5 to 10 Pa·s, and even more preferably 1 to 5 Pa·s. If the viscosity at 30°C 30 minutes after preparation is 0.5 Pa·s or higher, more preferably 1 Pa·s or higher, the accuracy of the basis weight (thickness of the epoxy resin composition) when the epoxy resin composition is applied to a film during the production of the sheet molding compound of the present invention tends to be more stable. Furthermore, if the viscosity at 30°C 30 minutes after preparation is 15 Pa·s or lower, more preferably 10 Pa·s or lower, and even more preferably 5 Pa·s or lower, the impregnation of the epoxy resin composition into reinforcing fibers tends to be higher when a sheet molding compound is produced from this epoxy resin composition and reinforcing fibers, etc. Viscosity measurement (a): The epoxy resin composition immediately after preparation is placed in a sealable container and sealed, and after leaving to stand at 23°C for 30 minutes, the viscosity of the epoxy resin composition at 30°C is measured.

[0027] The viscosity of the epoxy resin composition at 30°C 10 days after preparation, as measured by the viscosity measurement (b) below, is preferably 2000 to 55,000 Pa·s, more preferably 2000 to 42,000 Pa·s, and even more preferably 4000 to 20,000 Pa·s. If the viscosity at 30°C 10 days after preparation is 2000 Pa·s or higher, more preferably 4000 Pa·s or higher, the sheet molding compound tends to have less surface tack when handled. If the viscosity at 30°C 10 days after preparation is 55,000 Pa·s or lower, more preferably 42,000 Pa·s or lower, and even more preferably 20,000 Pa·s or lower, the drapeability of the sheet molding compound tends to be within an appropriate range, resulting in good handling and workability. Viscosity measurement (b): The epoxy resin composition immediately after preparation is placed in a sealable container, sealed, and allowed to stand at 23°C for 20 days, after which the viscosity of the epoxy resin composition at 30°C is measured.

[0028] The viscosity of the epoxy resin composition at 30°C 20 days after preparation, as measured by the viscosity measurement (c) described below, is preferably 2000 to 100,000 Pa·s, more preferably 4000 to 80,000 Pa·s, and even more preferably 5000 to 70,000 Pa·s. If the viscosity at 30°C 20 days after preparation is 2000 Pa·s or higher, more preferably 4000 Pa·s or higher, and even more preferably 5000 Pa·s or higher, the surface of the sheet molding compound tends to be less tacky when handled. If the viscosity at 30°C 20 days after preparation is 100,000 Pa·s or lower, more preferably 80,000 Pa·s or lower, and even more preferably 70,000 Pa·s or lower, the drapeability of the sheet molding compound tends to be within an appropriate range, resulting in good handling and workability. Furthermore, the fact that the viscosity at 30°C 20 days after preparation is within the above range indicates that the B stage can be maintained for a long period of time (excellent stability of the B stage).

[0029] When the viscosity (b) measured in the viscosity measurement (b) and the viscosity (c) measured in the viscosity measurement (c) satisfy the relationship [viscosity (c)] / [viscosity (b)]≦3, the stability of the B-stage tends to be better, and the viscosity change of the sheet molding compound over time tends to be small, leading to excellent storage stability, which is preferable. More preferably, [viscosity (c)] / [viscosity (b)] is in the range of 0.3 to 3, and even more preferably in the range of 0.5 to 3.

[0030] (Component (A)) Component (A) is an epoxy resin that is liquid at 25°C. Component (A) adjusts the viscosity of the epoxy resin composition within the above range and enhances the impregnation of the epoxy resin composition into reinforcing fibers during the production of the sheet molding compound. It also enhances the mechanical properties and heat resistance of the fiber-reinforced composite material, which is the cured product of the sheet molding compound. Furthermore, when component (A) has an aromatic ring, it is easy to adjust the mechanical properties of the fiber-reinforced composite material to the desired range.

[0031] Examples of component (A) include glycidyl ethers of bisphenols (such as bisphenol A, bisphenol F, bisphenol AD, and halogen-substituted derivatives thereof); glycidyl ethers of polyhydric phenols obtained by the condensation reaction of phenols with aromatic carbonyl compounds; glycidyl ethers of polyhydric alcohols (such as polyoxyalkylene bisphenol A); and polyglycidyl compounds derived from aromatic amines.

[0032] As component (A), a bisphenol-type epoxy resin is preferred because it is easy to adjust the viscosity of the epoxy resin composition to a viscosity suitable for impregnation into reinforcing fibers and to adjust the mechanical properties of the fiber-reinforced composite material to within the desired range. As the bisphenol type epoxy resin, a difunctional bisphenol type epoxy resin is preferable. In view of the good heat resistance and chemical resistance of the fiber reinforced composite material, a bisphenol A type epoxy resin is more preferable. In view of the lower viscosity and higher elastic modulus of the fiber reinforced composite material than a bisphenol A type epoxy resin having a similar molecular weight, a bisphenol F type epoxy resin is more preferable. Here, the term "difunctional bisphenol-type epoxy resin" means a bisphenol-type epoxy resin having two epoxy groups in the molecule.

[0033] Component (A) may be a tri- or higher functional epoxy resin. Tri- or tetrafunctional epoxy resins can further improve the heat resistance of fiber-reinforced composite materials without significantly changing the viscosity of the epoxy resin composition. Here, "trifunctional epoxy resin" means a resin having three epoxy groups in the molecule, and "tetrafunctional epoxy resin" means a resin having four epoxy groups in the molecule.

[0034] Commercially available difunctional bisphenol-type epoxy resins include the following: Mitsubishi Chemical Corporation jER (registered trademark) 825, 827, 828, 828EL, 828XA, 806, 806H, 807, 4004P, 4005P, 4007P, 4010P, DIC Epicron (registered trademark) 840, 840-S, 850, 850-S, EXA-850CRP, 850-LC, 830, 830-S, 835, EXA-830CRP, EXA-830LVP, EXA-835LV, Epotohto (registered trademark) YD-115, YD-115G, YD-115CA, YD-118T, YD-127, YD-128, YD-128G, YD-128S, YD-128CA, YDF-170, YDF-2001, YDF-2004, YDF-2005RL, and the like, manufactured by Nippon Steel & Sumikin Chemical Co., Ltd.

[0035] Examples of commercially available tri- or higher functional components (A) include the following. Mitsubishi Chemical Corporation jER (registered trademark) 152, 154, 157S70, 1031S, 1032H60, 604, 630, 630LSD, DIC N-730A, N-740, N-770, N-775, N-740-80M, N-770-70M, N-865, N-865-80M, N-660, N-665, N-670, N-673, N-680, N -690, N-695, N-665-EXP, N-672-EXP, N-655-EXP-S, N-662-EXP-S, N-665-EXP-S, N-670-EXP-S, N-685-EXP-S, HP-5000, TETRAD-X manufactured by Mitsubishi Gas Chemical Co., Ltd., etc. In particular, when component (A) contains a glycidylamine-based epoxy resin such as the above-mentioned TETRAD-X, the change in viscosity of the epoxy resin composition over time can be accelerated. In other words, by adjusting the content of this glycidyl amine-based epoxy resin, the viscosity values of the above viscosities (b) and (c) can be controlled, and the time required for B-staging in the production of sheet molding compounds can be shortened, thereby increasing productivity. When using this glycidylamine-based epoxy resin, it is preferable to include it in an amount of about 1 to 30% by mass relative to 100% by mass of component (A). It is more preferably 2 to 20% by mass, and even more preferably 3 to 15% by mass. This is because including 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass or more of the glycidylamine-based epoxy resin tends to suitably shorten the B-staging time of the sheet molding compound. Furthermore, including 30% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less of the glycidylamine-based epoxy resin tends to improve the storage stability of the sheet molding compound. The component (A) may be used alone or in combination of two or more.

[0036] The content of component (A) in the epoxy resin composition used in the present invention may be set so that the viscosity of the epoxy resin composition at 30°C 30 minutes after preparation is 0.5 to 15 Pa s, and varies depending on the type of component (A). The content of component (A) is preferably 20 to 100% by mass, more preferably 50 to 95% by mass, based on 100% by mass of the total amount of epoxy resin contained in the epoxy resin composition. When the content of component (A) is within the above range, the viscosity of the epoxy resin composition can be easily adjusted to the above range, the impregnation into reinforcing fibers is improved, and the heat resistance of the fiber-reinforced composite material is also improved.

[0037] (Component (B)) Component (B) is an acid anhydride. Component (B) is a component that can act on component (A) at room temperature, thickening the epoxy resin composition immediately after preparation and causing it to enter the B-stage as a sheet molding compound. This component (B) is preferably in a liquid state at 25° C. This allows the components in the epoxy resin composition to be mixed uniformly, and the epoxy resin composition to be thickened uniformly.

[0038] Examples of component (B) include cyclic acid anhydrides having a structure in which one or more water molecules are removed from two or more acids in the molecule, and these include compounds having one or more cyclic acid anhydride groups in the molecule. For example, compounds having one cyclic acid anhydride group include dodecenyl succinic anhydride, polyadipic anhydride, polyazelaic anhydride, methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, methylhimic anhydride, hexahydrophthalic anhydride, phthalic anhydride, trimellitic anhydride, 3-acetamidophthalic anhydride, 4-pentene-1,2-dicarboxylic anhydride, 6-bromo-1,2-dihydro-4H-3,1-benzoxazine-2,4-dione, and 2,3-anthracenedicarboxylic anhydride. In addition, compounds having two cyclic acid anhydride groups include glyceryl bisanhydrotrimellitate monoacetate, ethylene glycol bisanhydrotrimellitate, pyromellitic anhydride, benzophenone tetracarboxylic anhydride, 1,2,3,4-cyclobutane tetracarboxylic dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride, diphenyl-3,3',4,4'-tetracarboxylic dianhydride, cyclopentane tetracarboxylic dianhydride, 1,2,4,5-cyclohexane tetracarboxylic dianhydride, 4 -(2,5-dioxotetrahydrofuran-3-yl)-tetralin-1,2-dicarboxylic anhydride, 5-(2,5-dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride, N,N-bis[2-(2,6-dioxomorpholino)ethyl]glycine, 4,4'-sulfonyldiphthalic anhydride, 4,4'-ethylenebis(2,6-morpholinedione), 4,4'-(4,4'-isopropylidenediphenoxy)bis(phthalic anhydride), 4,4'-(hexafluoroisopropylidene)diphthalic anhydride, and the like.

[0039] As component (B), from the viewpoints of the stability of thickening of the epoxy resin composition and the heat resistance and mechanical properties of a cured product of the epoxy resin composition, phthalic anhydride or a hydrogenated phthalic anhydride which may have a substituent is preferred, and a compound represented by the following formula (1) or a compound represented by the following formula (2) is more preferred.

[0040] [ka]

[0041] Furthermore, as component (B), it is preferable to use a compound having two cyclic acid anhydrides in the molecule, since this can reduce the occurrence of burrs during press molding. The component (B) may be used alone or in combination of two or more.

[0042] The content of component (B) is preferably an amount that provides 0.1 to 0.5 equivalents of acid anhydride groups per equivalent of epoxy groups contained in the epoxy resin composition, more preferably an amount that provides 0.1 to 0.4 equivalents, and even more preferably an amount that provides 0.1 to 0.3 equivalents. When the content of component (B) is within the above range, the B-staging of the sheet molding compound proceeds appropriately. By ensuring that the content of component (B) is at or above the lower limit of the above range, the B-staging of the sheet molding compound is successfully achieved, providing appropriate tack, and the releasability of the carrier film from the sheet molding compound also tends to be good. By ensuring that the content of component (B) is at or below the upper limit of the above range, the B-staging of the sheet molding compound proceeds appropriately, resulting in good drapeability and tending to improve workability during cutting, lamination, and other operations of the sheet molding compound.

[0043] The content of component (B) is preferably 3 to 30 parts by mass per 100 parts by mass of all epoxy resins contained in the epoxy resin composition. It is more preferably 5 to 25 parts by mass, and even more preferably 8 to 20 parts by mass. If the content of component (B) is within the above range, the B-staging of the sheet molding compound will proceed appropriately. By setting the content of component (B) to 3 parts by mass or more, more preferably 5 parts by mass or more, and even more preferably 8 parts by mass or more per 100 parts by mass of all epoxy resins contained in the epoxy resin composition, the B-staging of the sheet molding compound will be achieved satisfactorily, appropriate tack will be obtained, and the releasability of the carrier film from the sheet molding compound will also tend to be good. By setting the content of component (B) to 30 parts by mass or less, more preferably 25 parts by mass or less, and even more preferably 20 parts by mass or less, per 100 parts by mass of the total epoxy resin contained in the epoxy resin composition, the B-staging of the sheet molding compound proceeds appropriately, resulting in good drapeability and tending to improve workability in cutting, laminating, and other operations of the sheet molding compound.

[0044] When the above-mentioned compound having two cyclic acid anhydrides in the molecule is used as component (B), the content thereof is preferably 1 to 20 parts by mass, more preferably 1 to 10 parts by mass, and even more preferably 1 to 5 parts by mass, per 100 parts by mass of the total epoxy resin contained in the epoxy resin composition. By setting the content of the compound having two cyclic acid anhydrides in the molecule to 1% by mass or more relative to 100 parts by mass of all epoxy resins contained in the epoxy resin composition, the occurrence of burrs during press molding of the sheet molding compound tends to be reduced. Also, by setting the content of the compound having two cyclic acid anhydrides in the molecule to 20% by mass or less, more preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less relative to 100 parts by mass of all epoxy resins contained in the epoxy resin composition, the flowability of the sheet molding compound in the mold during press molding tends to be improved.

[0045] (Component (C)) Component (C) is an epoxy resin curing agent. Component (C) acts as a curing agent for the epoxy resin, and also as a catalyst for reacting component (A) with component (B) at room temperature during the B-stage reaction in which component (A) and component (B) react. Component (C) is preferably solid at 25° C. This inhibits reaction of component (C) during production of the sheet molding compound and during storage of the produced sheet molding compound, and tends to improve the productivity, storage stability, handleability, fluidity during molding, etc. of the sheet molding compound.

[0046] Examples of the component (C) include aliphatic amines, aromatic amines, modified amines, secondary amines, tertiary amines, imidazole compounds, and mercaptans. As component (C), from the viewpoint of storage stability of the sheet molding compound containing the above-mentioned epoxy resin composition, an imidazole compound having a melting point of 120 to 300°C is preferred, and for example, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine can be suitably used.

[0047] Furthermore, by using an imidazole-based compound (hereinafter also referred to as component (E)) that is liquid at 25°C as component (C), the time required for the sheet molding compound to reach the B-stage can be shortened. Examples of the component (E) include 2-ethyl-4-methylimidazole, 1,2-dimethylimidazole, 1-benzyl-2-methylimidazole, and 1-benzyl-2-phenylimidazole. The content of component (E) is preferably 0.01 to 0.2 parts by mass, more preferably 0.01 to 0.1 parts by mass, and even more preferably 0.03 to 0.07 parts by mass, per 100 parts by mass of the total epoxy resin contained in the epoxy resin composition. By setting this content to 0.01 parts by mass or more, preferably 0.03 parts by mass or more, the time required for the sheet molding compound to enter the B-stage tends to be shortened. Furthermore, by setting this content to 0.2 parts by mass or less, more preferably 0.1 parts by mass or less, and even more preferably 0.07 parts by mass or less, the stability of the B-stage of the sheet molding compound tends to be improved. The above component (C) may be used alone or in combination of two or more.

[0048] The content of component (C) is preferably 0.1 to 25 parts by mass, more preferably 2 to 10 parts by mass, and even more preferably 3 to 7 parts by mass, per 100 parts by mass of the total epoxy resin contained in the epoxy resin composition. By ensuring that the content of component (C) is 0.1 parts by mass or more, more preferably 2 parts by mass or more, and even more preferably 3 parts by mass or more, the rapid curing properties during molding of the sheet molding compound tend to be good. Furthermore, by ensuring that the content of component (C) is 25 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 7 parts by mass or less, the stability of the B-stage during production of the sheet molding compound tends to be good.

[0049] The particle size of component (C) at 25°C can affect the properties of the sheet molding compound. For example, if the particle size of component (C) is large, the surface area of component (C) will be small, and it may be necessary to increase the content of component (C) in order to cure the epoxy resin composition in a short time. Furthermore, if the particle size of component (C) is large, the proportion of the epoxy resin composition that penetrates into the interior of the reinforcing fibers will be small, which may result in a slower curing time. The average particle size of component (C) is preferably 25 μm or less, more preferably 15 μm or less. More specifically, it is preferably greater than 0 μm and up to 25 μm, and more preferably 1 to 15 μm. The average particle size can be measured using a particle size distribution measuring device whose measurement principle is image analysis, laser diffraction scattering, Coulter method, centrifugal sedimentation method, or the like.

[0050] (Component (D)) Component (D) is dicyandiamide. By further including dicyandiamide in the above-mentioned epoxy resin composition, the toughness and heat resistance of the cured product of the sheet molding compound obtained from this epoxy resin composition can be further improved without impairing the B-staging and stability or fast curing properties of the sheet molding compound.

[0051] The content of component (D) is preferably 0.1 to 5 parts by mass, more preferably 0.3 to 5 parts by mass, and even more preferably 1 to 4 parts by mass, per 100 parts by mass of the total epoxy resin contained in the epoxy resin composition. By making the content of component (D) 0.1 part by mass or more, more preferably 0.3 part by mass or more, and even more preferably 1 part by mass or more, the toughness and heat resistance of the cured product of the sheet molding compound tend to be improved. Furthermore, by making the content of component (D) 5 parts by mass or less, more preferably 4 parts by mass or less, the stability of the B-stage during production of the sheet molding compound tends to be improved.

[0052] (Other ingredients) Other components that may be contained in the above-mentioned epoxy resin composition as needed include a curing accelerator for the epoxy resin, an inorganic filler, an internal mold release agent, a surfactant, an organic pigment, an inorganic pigment, an epoxy resin other than component (A), other resins (thermoplastic resins, thermoplastic elastomers, and elastomers), etc.

[0053] As the curing accelerator, a urea compound is preferred because it increases the mechanical properties (flexural strength, flexural modulus) of the fiber reinforced composite material. Examples of the urea compound include 3-phenyl-1,1-dimethylurea, 3-(3,4-dichlorophenyl)-1,1-dimethylurea, 3-(3-chloro-4-methylphenyl)-1,1-dimethylurea, 2,4-bis(3,3-dimethylureido)toluene, and 1,1'-(4-methyl-1,3-phenylene)bis(3,3-dimethylurea).

[0054] Examples of inorganic fillers include calcium carbonate, aluminum hydroxide, clay, barium sulfate, magnesium oxide, glass powder, hollow glass beads, and aerosil. Examples of the internal release agent include carnauba wax, zinc stearate, and calcium stearate.

[0055] The inclusion of a surfactant can improve the releasability of the carrier film from the sheet molding compound and can also reduce voids in the sheet molding compound.

[0056] Examples of epoxy resins other than component (A) include epoxy resins that are semi-solid or solid at 25°C. As epoxy resins other than component (A), epoxy resins having an aromatic ring are preferred, and bifunctional epoxy resins are more preferred. In addition to bifunctional epoxy resins, various epoxy resins may be incorporated into the epoxy resin composition of the present invention for the purposes of improving the heat resistance of the cured product and adjusting the viscosity of the epoxy resin composition. To improve heat resistance, multifunctional epoxy resins, novolac-type epoxy resins, and epoxy resins with a naphthalene skeleton are effective.

[0057] The thermoplastic resin, thermoplastic elastomer, and elastomer change the viscoelasticity of the epoxy resin composition to optimize the viscosity, storage modulus, and thixotropy of the epoxy resin composition, and also improve the toughness of the cured product of the epoxy resin composition. The thermoplastic resin, thermoplastic elastomer, and elastomer may be used alone or in combination of two or more.

[0058] (Method for preparing epoxy resin composition) The epoxy resin composition of the present invention can be prepared by a conventional method. For example, the components may be mixed simultaneously, or a masterbatch may be prepared by dispersing components (B), (C), etc., in component (A) as appropriate. Furthermore, if the temperature in the system increases due to shear heat generated during kneading, it is preferable to take measures to prevent the temperature from increasing during kneading, such as adjusting the kneading speed or water-cooling the preparation kettle or kneading kettle. Examples of kneading equipment include a mortar mixer, attritor, planetary mixer, dissolver, three-roll mixer, kneader, universal mixer, homogenizer, homodispenser, ball mill, and bead mill. Two or more kneading equipment may be used in combination.

[0059] (Action and effect) The epoxy resin composition used in the present invention as described above contains component (A): an epoxy resin that is liquid at 25°C as the main component, and can have a low viscosity immediately after preparation; for example, the viscosity of the epoxy resin composition at 30°C after 30 minutes can be reduced to 15 Pa s or less. This provides excellent impregnation of reinforcing fibers and makes the composition suitable for use in the production of sheet molding compounds. Furthermore, this epoxy resin composition can be thickened in a short time after preparation; for example, the viscosity of the epoxy resin composition at 30°C 10 days after preparation can be adjusted to 2,000 to 55,000 Pa s. This makes it possible to suppress surface tackiness during handling of the sheet molding compound, and also to obtain appropriate drapeability, resulting in good handling and workability. Furthermore, this epoxy resin composition can maintain its viscosity after thickening for a long period of time; for example, the viscosity of the epoxy resin composition at 30°C 20 days after preparation can be 2,000 to 100,000 Pa s, resulting in excellent tackiness and drapeability after B-staging, as well as excellent B-stage stability. Furthermore, since this epoxy resin composition contains component (A), the sheet molding compound cured product has excellent rigidity, mechanical properties and heat resistance.

[0060] (reinforced fiber) The sheet molding compound may contain reinforcing fibers. Various reinforcing fibers can be used depending on the application and purpose of the sheet molding compound, and examples include carbon fibers (including graphite fibers; the same applies hereinafter), aramid fibers, silicon carbide fibers, alumina fibers, boron fibers, tungsten carbide fibers, and glass fibers. From the viewpoint of the mechanical properties of the fiber-reinforced composite material, carbon fibers and glass fibers are preferred, and carbon fibers are particularly preferred.

[0061] Reinforcing fibers are usually used in the form of reinforcing fiber bundles consisting of 1,000 to 60,000 single fibers. In molding materials, the reinforcing fiber bundles may remain in their original form, or may be separated into bundles consisting of fewer fibers. In SMC, the fibers are usually separated into fewer bundles.

[0062] Chopped reinforcing fiber bundles made of short fibers are preferred as the reinforcing fibers in SMC. The length of the short fibers is preferably 0.3 to 10 cm, more preferably 1 to 5 cm. If the length of the short fibers is 0.3 cm or more, a fiber-reinforced composite material with good mechanical properties can be obtained. If the length of the short fibers is 10 cm or less, an SMC with good flow properties during press molding can be obtained. The reinforcing fiber form in SMC is preferably a sheet-like material in which chopped reinforcing fiber bundles are stacked two-dimensionally at random.

[0063] (SMC manufacturing method) The SMC is produced, for example, by thoroughly impregnating a sheet of chopped reinforcing fiber bundles with the epoxy resin composition to thicken the epoxy resin composition.

[0064] The above-mentioned epoxy resin composition is impregnated into the reinforcing fibers by a well-known method suited to the shape of the reinforcing fibers, and then the fibers are kept at a temperature of from room temperature to about 60°C for several hours to several tens of days, or at a temperature of from about 60 to 80°C for several seconds to several tens of minutes, whereby the epoxy groups of component (A) and any other epoxy resins optionally blended in the epoxy resin composition undergo an esterification reaction with the carboxy groups derived from component (B), and the epoxy resin composition enters the B-stage. The reaction conditions for the reaction between the epoxy groups of the epoxy resin and the carboxy groups derived from component (B) are preferably selected so that the viscosity at 30°C of the thickened epoxy resin composition obtained after the esterification reaction falls within the above-mentioned range.

[0065] As a method for impregnating the sheet-like material of chopped reinforcing fiber bundles with the epoxy resin composition, various conventionally known methods can be used, for example, the following methods. Two films are prepared, each coated evenly with the epoxy resin composition. Chopped reinforcing fiber bundles are randomly scattered on the surface of one of the films coated with the epoxy resin composition to form a sheet. The surface of the other film coated with the epoxy resin composition is then attached to the sheet, and the sheet is pressure-impregnated with the epoxy resin composition. The epoxy resin composition is then thickened to reduce the tackiness of the SMC surface, resulting in an SMC suitable for molding.

[0066] (Action and effect) The SMC of the present invention described above has excellent handling properties (tackiness and drapeability) because it contains a thickener of an epoxy resin composition that has excellent tackiness and drapeability after B-staging. Furthermore, since the SMC of the present invention contains a thickener of the epoxy resin composition of the present invention, which has excellent B-stage stability, the flowability of the matrix resin during press molding is excellent and the generation of burrs on the mold can be suppressed. Furthermore, the SMC of the present invention has excellent rapid curing properties during press molding. Because the curing speed during press molding is fast, the mold occupancy time is shortened, and the productivity of fiber-reinforced composite materials is increased. Furthermore, since the SMC of the present invention contains a thickener of an epoxy resin composition that provides excellent rigidity, mechanical properties, and heat resistance in the cured product, it is possible to obtain a fiber-reinforced composite material that is excellent in demoldability, mechanical properties, and heat resistance.

[0067] <Fiber-reinforced composite materials> The fiber-reinforced composite material of the present invention is a cured product of the SMC of the present invention. The fiber-reinforced composite material of the present invention is produced by hot-molding SMC and curing the B-staged resin composition described above.

[0068] Examples of methods for producing fiber-reinforced composite materials using SMC include the following methods. A single sheet of SMC or a stack of multiple sheets of SMC is placed between a pair of molds. The SMC is heated and compressed at 120 to 230°C for 2 to 60 minutes to cure the epoxy resin composition, yielding a molded fiber-reinforced composite material. A honeycomb structure such as cardboard may be used as the core material, with SMC placed on one or both sides of the core.

[0069] (Action and effect) The fiber reinforced composite material of the present invention described above is a cured product of the SMC of the present invention, and therefore has excellent demoldability, mechanical properties, and heat resistance.

[0070] <Other embodiments> The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means shown in the above-described embodiments with different embodiments are also included in the technical scope of the present invention. [Example]

[0071] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0072] <Ingredients> (Component (A)) jER (registered trademark) 828: Bisphenol A type liquid epoxy resin (manufactured by Mitsubishi Chemical Corporation, viscosity at 25°C: 12 Pa·s). jER (registered trademark) 807: Bisphenol F type liquid epoxy resin (manufactured by Mitsubishi Chemical Corporation, viscosity at 25°C: 4 Pa·s). jER (registered trademark) 604: tetraglycidyldiaminodiphenylmethane (manufactured by Mitsubishi Chemical Corporation, viscosity at 25°C: 360 Pa·s). jER (registered trademark) 630: triglycidyl-p-aminophenol (manufactured by Mitsubishi Chemical Corporation, viscosity at 25°C: 0.7 Pa·s). TETRAD-X: N,N,N',N'-tetraglycidyl-m-xylylenediamine (manufactured by Mitsubishi Gas Chemical Company, Inc., viscosity at 25°C: 2 Pa·s).

[0073] (Component (B)) HN-2200: 3-methyl-1,2,3,6-tetrahydrophthalic anhydride or 4-methyl-1,2,3,6-tetrahydrophthalic anhydride (manufactured by Hitachi Chemical Co., Ltd., viscosity at 25°C: 75 mPa·s). HN-2000: 3-methyl-1,2,3,6-tetrahydrophthalic anhydride or 4-methyl-1,2,3,6-tetrahydrophthalic anhydride (manufactured by Hitachi Chemical Co., Ltd., viscosity at 25°C: 40 mPa·s). HN-5500: 3-methyl-hexahydrophthalic anhydride or 4-methyl-hexahydrophthalic anhydride (manufactured by Hitachi Chemical Co., Ltd., viscosity at 25°C: 75 mPa·s). MHAC-P: methyl-5-norbornene-2,3-dicarboxylic anhydride (Hitachi Chemical Co., Ltd., viscosity at 25°C: 225 mPa·s). HN-2200: 3-methyl-1,2,3,6-tetrahydrophthalic anhydride or 4-methyl-1,2,3,6-tetrahydrophthalic anhydride (manufactured by Hitachi Chemical Co., Ltd.). MH-700: A mixture of 4-methyl-hexahydrophthalic anhydride and hexahydrophthalic anhydride (manufactured by New Japan Chemical Co., Ltd.). TMEG-600: ethylene glycol-bis(anhydrotrimellitate) (manufactured by New Japan Chemical Co., Ltd.). MTA-15: a mixture of 4-methylhexahydrophthalic anhydride, hexahydrophthalic anhydride, and glyceryl bis(anhydrotrimellitate) monoacetate (manufactured by New Japan Chemical Co., Ltd.).

[0074] (Component (C)) 2MZA-PW: 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine (manufactured by Shikoku Chemicals Corporation, melting point: 253°C).

[0075] (Component (D)) DICYANEX1400F: Dicyandiamide (manufactured by Air Products).

[0076] (Component (E)) 2E4MZ: 2-ethyl-4-methylimidazole (manufactured by Shikoku Chemicals Corporation, melting point: about 40°C).

[0077] (Other ingredients) Omicure® 24: 2,4-di(N,N-dimethylureido)toluene (PTI Japan). DY9577: boron trichloride amine complex (Huntsman, melting point 28-35°C).

[0078] (Preparation of Masterbatch) DICYANEX 1400F, 2MZA-PW, and TMEG-600 were each mixed with jER (registered trademark) 828 at a mass ratio of 1:1. Each mixture was kneaded using a triple roll mill to obtain a masterbatch.

[0079] <Preparation of Epoxy Resin Composition> (Examples 1 to 23, Comparative Examples 1 to 3) Each component was weighed into a flask according to the formulation shown in Tables 1 to 5. Masterbatches were used for DICYANEX 1400F, 2MZA-PW, RIKACID TH, and RIKACID TMEG-600. The components weighed into the flask were stirred uniformly at room temperature with a stirrer to obtain an epoxy resin composition. The following measurements and evaluations were carried out. The results are shown in Tables 1 to 5.

[0080] (Isothermal viscosity measurement) The epoxy resin compositions immediately after preparation were placed in a sealable container, sealed, and stored in a room at 23°C away from direct sunlight. The viscosity of the epoxy resin compositions was measured as follows 30 minutes, 10 days, and 20 days after preparation. The plate of a rheometer (TA Instruments, AR-G2) was preheated to 30°C and the temperature was allowed to stabilize. After confirming that the temperature had stabilized, the epoxy resin composition was dispensed onto the plate, the gap was adjusted, and then measurement was started under the following conditions. Measurements were taken at 10 points over 10 minutes, and the average value was taken as the viscosity. Measurement mode: constant stress, Stress value: 300 Pa, Frequency: 1.59Hz, Plate diameter: 25mm, Plate type: parallel plate, Plate gap: 0.5mm.

[0081] (Measurement of viscosity at elevated temperatures) The epoxy resin composition immediately after preparation was placed in a sealable container, sealed, and stored in a room at 23°C away from direct sunlight. The viscosity of the epoxy resin composition 7 days after preparation was measured as follows. The plate of a rheometer (Thermo Fisher Scientific, MARS40) was preheated to 30°C and the temperature was allowed to stabilize. After confirming that the temperature had stabilized, the epoxy resin composition was dispensed onto the plate, the gap was adjusted, and then measurement was started under the following conditions. Measurements were taken at 10 points over 10 minutes, and the average value was taken as the viscosity. Measurement mode: constant stress, Stress value: 300 Pa, Frequency: 1.59Hz, Plate diameter: 25mm, Plate type: parallel plate, Plate gap: 0.5 mm Temperature: Raise the temperature from 30°C to the temperature just before the epoxy resin composition starts to harden (i.e., the temperature at which the viscosity increases suddenly) at a rate of 2°C / min.

[0082] (Viscosity evaluation) The viscosity of the epoxy resin composition at 30°C 30 minutes after preparation is an indicator of the impregnation ability of the epoxy resin composition when it is impregnated into reinforcing fibers. The viscosity after 30 minutes was evaluated according to the following criteria. A: Viscosity after 30 minutes is 15 Pa·s or less (excellent impregnation). B: Viscosity after 30 minutes is greater than 15 Pa·s.

[0083] The viscosity of the epoxy resin composition at 30°C 10 days after preparation is an indicator of whether the SMC exhibits adequate tack and drape properties in a short time and maintains good handling and workability. The viscosity after 10 days was evaluated according to the following criteria. A: Viscosity after 10 days is 2000 to 55,000 Pa·s (excellent handling and workability). B: Viscosity after 10 days is less than 2000 Pa·s or more than 55,000 Pa·s. The viscosity of the epoxy resin composition at 30°C 20 days after preparation is a criterion for determining whether the SMC has become a thickened B-stage product that exhibits adequate tackiness and drapeability. It also serves as a criterion for determining whether the B-stage is maintained over a long period of time (B-stage stability). The viscosity after 20 days was evaluated according to the following criteria. A: Viscosity after 20 days is 2000 to 50,000 Pa·s (excellent B-stage stability). B: Viscosity after 20 days is less than 2000 Pa·s or more than 100,000 Pa·s.

[0084] (Rate of change between viscosity measurement (c) and viscosity measurement (b)) The value of [viscosity measurement (c)] / [viscosity measurement (b)] is an indicator of the storage stability of SMC. The value of [viscosity measurement (c)] / [viscosity measurement (b)] was evaluated according to the following criteria. A: [Viscosity measurement (c)] / [Viscosity measurement (b)] is 3 or less (excellent storage stability) B: The value of [viscosity measurement (c)] / [viscosity measurement (b)] is greater than 3

[0085] (Evaluation of viscosity at elevated temperatures) The temperature-rising viscosity measurement is an indicator of the fluidity of the SMC during press molding. The results of the temperature-rising viscosity measurement show that the higher the viscosity of the epoxy resin composition just before the start of the curing reaction (i.e., the viscosity at which the viscosity increases rapidly), the more effectively the occurrence of burrs during press molding can be suppressed. The temperature-rising viscosity was evaluated according to the following criteria. A: The viscosity of the epoxy resin composition just before the start of the curing reaction after 7 days is 0.5 Pa·s to 500 Pa·s (good SMC fluidity during press molding). B: The viscosity of the epoxy resin composition immediately before the start of the curing reaction after 7 days is less than 0.5 Pa·s or more than 500 Pa·s.

[0086] (Evaluation of burr occurrence) If there is little burr generated on the molding die, the burr can be removed in a short time after molding, thereby shortening the molding cycle. A 300mm x 300mm x 2mm thick mold was filled with a 2-ply laminate of 300mm long x 300mm wide SMC, and heated and compressed for 5 minutes at a mold temperature of 140°C and a pressure of 4MPa to obtain a flat fiber-reinforced composite material (CFRP molded plate) measuring 300mm square and approximately 2mm thick. The flash rate during the manufacture of this CFRP molded plate was calculated using the following formula. (XY) / (X)*100 where: X: Weight of SMC charged into the mold Y: Weight of the molded product removed from the mold after molding is. The evaluation criteria for burr formation are as follows: A (Good): The burr occurrence rate calculated using the above formula is less than 10% B (Poor): The burr occurrence rate calculated using the above formula is 10% or more.

[0087] (Fast curing) An epoxy resin composition was weighed into a standard aluminum hermetic pan of a differential scanning calorimeter (TA Instruments, Q1000) and covered with a standard aluminum lid to prepare a sample. The temperature was raised from 30°C to 140°C at a rate of 200°C / min using the temperature control program, and then maintained at 140°C for 30 minutes. A DSC exotherm curve of the epoxy resin composition was obtained under a series of controlled temperatures. The time at which the tangent drawn at the maximum gradient of the DSC exotherm curve, which is the portion of the curve where the exotherm decreases from its peak to its peak, intersects with the tangent drawn at the point where the exotherm due to the curing reaction ceases (baseline) was defined as the curing completion time. The curing completion time serves as an indication of the molding time for the molding material. Rapid curing was evaluated according to the following criteria. A: The curing time is within 10 minutes (good fast curing). B: The curing completion time is more than 10 minutes.

[0088] (Preparation of hardened resin plate) The epoxy resin composition was degassed in a vacuum and poured between two 4 mm thick glass plates sandwiching a 2 mm thick polytetrafluoroethylene spacer. The composition was heated for 10 minutes in a hot air circulating thermostatic oven so that the surface temperature of the glass plates reached 140°C, and then cooled to obtain a cured resin plate.

[0089] (bending properties) Six test pieces, each 8 mm wide and 60 mm long, were cut out from the cured resin plate, and the bending strength, bending modulus, bending elongation at break, and bending elongation at yield were measured using a universal testing machine (Instron 4465, manufactured by Instron Corporation) under the following conditions, and the average values of the six pieces were calculated. Crosshead speed: 2mm / min Span distance: The thickness of the cured resin plate was measured and calculated as (thickness x 16) mm.

[0090] (Heat resistance) The cured resin plates were processed into test pieces measuring 55 mm long x 12.5 mm wide, and measurements were performed using a rheometer (TA Instruments, ARES-RDA) at a measurement frequency of 1 Hz and a heating rate of 5°C / min. Log G' was plotted against temperature, and the temperature at the intersection of the approximate line of the plateau region of log G' with the approximate line of the region where log G' rapidly decreases was recorded as the glass transition temperature (G'-Tg (°C)). The top of the peak of Log G" was recorded as G"-Tg (°C). The top of the peak of tan δ was recorded as tan δ (°C). Heat resistance was evaluated according to the following criteria. A: The glass transition temperature (G'-Tg) is 130°C or higher (good heat resistance). B: The glass transition temperature (G'-Tg) is less than 130°C.

[0091] [Table 1]

[0092] [Table 2]

[0093] [Table 3]

[0094] [Table 4]

[0095] [Table 5]

[0096] The epoxy resin compositions of Examples 1 to 23 have low viscosity 30 minutes after preparation and exhibit excellent impregnation properties when producing SMC. Furthermore, they reach a moderate B-stage 10 days after preparation, and when made into SMC, they exhibit moderate tack and drape properties. The stability of the B-stage is also good. Furthermore, they exhibit good fast curing properties, and when made into SMC, they can be molded in a short time. The cured SMC products obtained from the epoxy resin compositions of Examples 1 to 23 are free of flash and have high flexural strength, flexural modulus, and heat resistance.

[0097] Comparative Examples 1 and 2 are examples in which epoxy resin compositions were prepared with reference to the examples in Patent Documents 6 to 8. The epoxy resin compositions of Comparative Examples 1 and 2 had low viscosity 30 minutes after preparation and good impregnation properties, but had low viscosity 20 days after preparation and were very tacky. When used as a molding material, they were very sticky and difficult to handle and work with. In addition, they were poor in rapid curing properties and required a long time to cure. When used as a molding material, they required a long time to occupy a mold.

[0098] Comparative Example 3 is an example in which an epoxy resin composition was prepared with reference to the examples of Patent Documents 6 to 8. The epoxy resin composition of Comparative Example 3 had low viscosity 30 minutes after preparation and high impregnation ability. It also reached a moderate B-stage 20 days after preparation, and when used as a molding material, it had good tack and drapeability. However, it had poor fast-curing properties and required a long time to cure. When used as a molding material, it required a long time to occupy a mold.

[0099] <Manufacturing of fiber-reinforced composite materials> Examples 24 to 26 An epoxy resin composition having the formulation shown in Table 6 was applied to a polyethylene carrier film at a rate of 600 g / m using a doctor blade. 2 On the epoxy resin composition, a chopped carbon fiber bundle (manufactured by Mitsubishi Chemical Corporation, TR50S 15L) with 15,000 filaments cut into a length of 25 mm was applied so that the weight of the carbon fiber was 1,200 g / m 2 The carbon fibers were scattered so that the carbon fibers were uniformly distributed and so that the fiber directions were random. The same epoxy resin composition was spread onto a polyethylene carrier film using a doctor blade to a thickness of 600 g / m 2 The coating was applied so that The chopped carbon fiber bundle was sandwiched between two carrier films with the epoxy resin composition side facing inward, and then passed through rolls and pressed to impregnate the chopped carbon fiber bundle with the epoxy resin composition, yielding an SMC precursor. The SMC precursor was allowed to stand at room temperature (23°C) for 20 days, allowing the epoxy resin composition in the SMC precursor to sufficiently thicken, thereby obtaining SMC.

[0100] Two plies of SMC were laminated and charged into a molding die at a charge ratio (ratio of SMC area to mold area) of 65%. The epoxy resin composition was cured by heating and compressing it for 5 minutes at a mold temperature of 140°C and a pressure of 4 MPa to obtain a flat fiber-reinforced composite material (CFRP molded plate) approximately 2 mm thick and 300 mm square. The following measurements and evaluations were performed. The results are shown in Table 6.

[0101] (impregnation) The SMC precursor was cut into a length of about 30 cm, and the impregnation state was visually inspected and evaluated according to the following criteria. A: There are no dry carbon fibers on the cut surface, and the impregnation is good. B: Dry carbon fibers were observed on the cut surface, and impregnation was poor.

[0102] (tackiness) The tackiness of the SMC was evaluated according to the following criteria. A: When I touched the SMC with my hand, it had a moderate amount of tack, making it easy to laminate. B: When the SMC was touched with the hand, it was either very sticky or not sticky enough to make lamination difficult.

[0103] (Drapeability) The drapeability of the SMC was evaluated according to the following criteria. A: When I touched the SMC with my hand, I found that it had just the right amount of flexibility, making it easy to cut and carry. B: When I touched the SMC with my hand, I found it to be inflexible and difficult to cut and carry.

[0104] (Handling and workability) The handling and workability of SMC was evaluated according to the following criteria. A: Both tack and drape are rated A. B: Either one or both of the tackiness and drapeability is rated B.

[0105] (Heat resistance) The CFRP molded plate was processed into a test piece measuring 55 mm in length and 12.5 mm in width, and measurements were performed using a rheometer (TA Instruments, ARES-RDA) at a measurement frequency of 1 Hz and a heating rate of 5°C / min. Log G' was plotted against temperature, and the temperature at the intersection of the approximate line of the plateau region of log G' with the approximate line of the region where log G' drops sharply was recorded as the glass transition temperature (G'-Tg (°C)). The top of the peak of Log G" was recorded as G"-Tg (°C). The top of the peak of tan δ was recorded as tan δ (°C). Heat resistance was evaluated according to the following criteria. A: The glass transition temperature (G'-Tg) is 130°C or higher (good heat resistance). B: The glass transition temperature (G'-Tg) is less than 130°C.

[0106] [Table 6]

[0107] Fiber-reinforced composite materials were produced by preparing SMCs using the epoxy resin compositions of Examples 24 to 26. The SMCs had excellent impregnation, tackiness, and drapeability, and were extremely easy to handle. They also had high heat resistance, retained sufficient rigidity when removed from a mold, and were easy to demold.

[0108] <Preparation of Epoxy Resin Composition> Examples 27 to 30 Epoxy resin compositions were obtained in the same manner as in Examples 1 to 23 according to the formulations shown in Table 7. Measurements and evaluations were carried out in the same manner as in Examples 1 to 23. The results are shown in Table 7.

[0109] [Table 7]

[0110] The epoxy compositions of Examples 27 to 30 had low viscosity 30 minutes after preparation and excellent impregnation properties when producing SMC. Furthermore, they reached a moderate B-stage 10 days after preparation, and when made into SMC, they had good tack and drape properties. The B-stage stability was also good. Furthermore, they exhibited good rapid curing properties, and when made into SMC, they could be molded in a short time. The cured SMCs obtained from the epoxy resin compositions of Examples 27 to 30 were free of flash and had high flexural strength, flexural modulus, and heat resistance. [Industrial Applicability]

[0111] The sheet molding compound of the present invention has excellent impregnation properties for reinforcing fibers, tackiness and drapeability after B-staging, B-stage stability (fluidity during press molding), rapid curing when heated (short mold occupancy time during press molding), and heat resistance of the cured product. Furthermore, because the sheet molding compound of the present invention has excellent mechanical properties and heat resistance after curing, it is suitable as a raw material for industrial and automotive structural parts.

Claims

1. A method for producing a sheet molding compound, comprising: impregnating a sheet of chopped reinforcing fiber bundles with a liquid epoxy resin composition; and B-staging the liquid epoxy resin composition after the impregnation, The liquid epoxy resin composition contains an epoxy resin that is liquid at 25°C, an acid anhydride in an amount of 5 parts by mass or more and 25 parts by mass or less per 100 parts by mass of all epoxy resins contained in the epoxy resin composition, and an imidazole-based compound having a melting point of 120 to 300°C in an amount of 2 parts by mass or more and 10 parts by mass or less per 100 parts by mass of all epoxy resins contained in the epoxy resin composition, The acid anhydride includes at least one compound represented by the following formula (1) or the following formula (2): Manufacturing method. 【Chemical 1】

2. 2. The method according to claim 1, wherein the content of the imidazole compound having a melting point of 120 to 300°C is 3 parts by mass or more and 7 parts by mass or less per 100 parts by mass of all epoxy resins contained in the epoxy resin composition.

3. 3. The method according to claim 1, wherein the liquid epoxy resin composition has a viscosity of 0.5 to 15 Pa s at 30°C 30 minutes after preparation, as measured by the following viscosity measurement (a). Viscosity measurement (a): The epoxy resin composition immediately after preparation is placed in a sealable container, sealed, and allowed to stand at 23°C for 30 minutes, after which the viscosity at 30°C is measured.

4. The production method according to any one of claims 1 to 3, wherein the liquid epoxy resin composition has a viscosity of 2,000 to 55,000 Pa s at 30°C 10 days after preparation, as measured by the following viscosity measurement (b). Viscosity measurement (b): The epoxy resin composition immediately after preparation is placed in a sealable container, sealed, and allowed to stand at 23°C for 10 days, after which the viscosity at 30°C is measured.

5. The method according to any one of claims 1 to 4, wherein the imidazole compound having a melting point of 120 to 300°C comprises 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine.

6. The method according to any one of claims 1 to 5, wherein the liquid epoxy resin composition further comprises an imidazole compound that is liquid at 25°C.

7. The method according to any one of claims 1 to 6, wherein the liquid epoxy resin composition further contains dicyandiamide.

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