Resin composition, fiber-reinforced composite material, and resin molded article

Abstract

To provide a resin composition excellent in handleability, capable of shortening a molding time, and capable of obtaining a molded product excellent in transparency, when constituting a fiber-reinforced composite material.SOLUTION: Wherein the isocyanate (B) is m-xylylene diisocyanate, and a molar ratio (NCO / OH ratio) of an isocyanate group (NCO) of the isocyanate (B) to a hydroxyl group (OH) of the vinyl ester (A) is 0.3 or more and 1.1 or less, 220g 180g, A refractive index of a cured product of the resin composition is 1.52 or more and 1.58 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a resin composition, a fiber-reinforced composite material, and a resin molded article. [Background technology]

[0002] Conventionally, transparent resin molded articles have been known that are formed by curing a fiber-reinforced composite material containing a resin composition and glass fibers as a reinforcing fiber material. For example, Patent Document 1 discloses a transparent resin sheet having a cured resin layer containing an epoxy resin containing silica particles and glass fibers. Patent Document 2 discloses a transparent film formed by impregnating a glass fiber substrate with a bisphenol-based epoxy resin and curing the resin. Patent Document 3 discloses a transparent resin sheet formed by impregnating glass cloth with a resin composition containing a hydrogenated biphenyl-type alicyclic epoxy resin and a silxesquioxane having an oxetanyl group and curing the resin. Patent Document 4 discloses a transparent resin sheet formed by impregnating glass cloth with a resin composition containing an aromatic epoxy resin and an aliphatic epoxy resin and curing the resin.

[0003] However, the fiber-reinforced composite materials containing resin and glass fiber disclosed in Patent Documents 1 to 4 require frozen storage, making temperature control during storage complicated, and also have the disadvantage of long molding times, for example, a pressurization time of 10 to 120 minutes when the heating temperature during heat compression molding is 150°C. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-156840 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-136580 [Patent Document 3] Japanese Patent Application Laid-Open No. 2005-297312 [Patent Document 4] Japanese Patent Application Publication No. 2018-202690 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention aims to provide a resin composition that, when used to form a fiber-reinforced composite material, is easy to handle, can shorten the molding time, and can give a molded article with excellent transparency. It is also an object of the present invention to provide a fiber-reinforced composite material and a resin molded article using the resin composition. [Means for solving the problem]

[0006] The present inventors have discovered that by using a specific vinyl ester resin and a specific isocyanate, a resin composition can be obtained that is easy to handle, can shorten the molding time, and can produce molded articles with excellent transparency, and have completed the present invention.

[0007] That is, the present invention has the following aspects.

[0008] (1) A thermosetting resin composition comprising, as essential raw materials, a vinyl ester resin (A), an isocyanate (B), and a thermosetting agent (C), wherein the vinyl ester resin (A) is produced from an epoxy resin having an epoxy equivalent of 180 g / mol or more and 220 g / mol or less, the isocyanate (B) is m-xylylene diisocyanate, the molar ratio (NCO / OH ratio) of the isocyanate group (NCO) of the polyisocyanate (B) to the hydroxyl group (OH) of the vinyl ester (A) is 0.3 or more and 1.1 or less, and the refractive index of a cured product of the resin composition is 1.52 or more and 1.58 or less.

[0009] (2) The thermosetting resin composition according to (1) above, further comprising a reactive diluent (D) as an essential ingredient, wherein the refractive index of the reactive diluent (D) is 1.46 or more and 1.52 or less.

[0010] (3) The resin composition according to (1) or (2), further comprising a foam inhibitor (E) as an essential ingredient, wherein the foam inhibitor (E) is an organic compound having a phosphoric acid group or a sulfonic acid group in the molecule.

[0011] (4) A fiber-reinforced composite material containing the resin composition according to any one of (1) to (3) above and a reinforcing fiber material, wherein the reinforcing fiber material is glass.

[0012] (5) The fiber-reinforced composite material according to (4), wherein the reinforcing fiber material is glass cloth.

[0013] (6) The fiber-reinforced composite material according to (4) or (5), which is a prepreg.

[0014] (7) A resin molded product obtained by curing the fiber-reinforced composite material according to any one of (4) to (6) above. [Effects of the Invention]

[0015] The resin composition according to the present invention can provide a fiber-reinforced composite material that is easy to handle, can shorten the molding time, and can produce a molded article with excellent transparency.Furthermore, a fiber-reinforced composite material and a resin molded article using the resin composition can be provided. DETAILED DESCRIPTION OF THE INVENTION

[0016] The resin composition according to the present embodiment is a thermosetting resin composition containing, as essential raw materials, a vinyl ester resin (A), an isocyanate (B), and a thermosetting agent (C), wherein the vinyl ester resin (A) is produced from an epoxy resin having an epoxy equivalent of 180 g / mol or more and 220 g / mol or less, the isocyanate (B) is m-xylylene diisocyanate, the molar ratio (NCO / OH ratio) of the isocyanate group (NCO) of the isocyanate (B) to the hydroxyl group (OH) of the vinyl ester (A) is 0.3 or more and 1.1 or less, and the refractive index of a cured product of the resin composition is 1.52 or more and 1.58 or less.

[0017] The resin composition of the present embodiment contains the vinyl ester resin (A), the isocyanate (B), and the thermosetting agent (C) as essential raw materials. Therefore, when combined with a reinforcing fiber material to form a fiber-reinforced composite material, the resin composition has excellent storage stability and handleability, and can shorten the molding time.

[0018] The resin composition of this embodiment uses as essential raw materials a vinyl ester resin (A) produced from an epoxy resin having an epoxy equivalent of 180 g / mol to 220 g / mol and an isocyanate (B) that is m-xylylene diisocyanate, and the NCO / OH ratio is 0.3 to 1.1. By having the NCO / OH ratio within the above range, the viscosity of the resin composition can be adjusted to a range suitable for impregnation. This allows for excellent impregnation when the resin composition of this embodiment is impregnated into a reinforcing fiber material to form a fiber-reinforced composite material. Furthermore, when the fiber-reinforced composite material is subjected to heat compression molding, resin leakage due to a decrease in melt viscosity can be suppressed. As a result, the resin composition of this embodiment can produce a molded product that is free of bubbles on the surface or inside. In addition, the resin composition of this embodiment is adjusted so that the refractive index of the cured product is 1.52 to 1.58. The refractive index is similar to that of general glass (1.5 to 1.6). From the above, when the resin composition of this embodiment is impregnated into a reinforcing fiber material made of glass to form a fiber-reinforced composite material and then thermally cured, a molded product with excellent transparency and high strength can be realized.

[0019] In contrast, when a vinyl ester resin produced from an epoxy resin with an epoxy equivalent of more than 220 g / mol is used, the viscosity of the resin composition becomes excessively high, and when the resin composition is impregnated into a reinforcing fiber material, the impregnation into the reinforcing fiber material is insufficient, resulting in unimpregnated regions. When the resulting fiber-reinforced composite material is thermally cured, bubbles are generated in the unimpregnated regions, making it impossible to obtain a molded product with excellent transparency.

[0020] Furthermore, if the NCO ratio is less than 0.3, the degree of urethane thickening in the resin composition is low, resulting in resin leakage due to a decrease in melt viscosity when the fiber-reinforced composite material is heat-compression molded. In this case, bubbles are generated on the surface of the obtained molded product, making it impossible to obtain a molded product with excellent transparency. On the other hand, if the NCO ratio is more than 1.1, allophanate bonds and the like are generated in the resin composition, causing excessive viscosity increase. Furthermore, when the fiber-reinforced composite material is heat-compression molded, the melt viscosity becomes high and the material becomes difficult to flow, resulting in unevenness on the surface, making it impossible to obtain a molded product with excellent transparency.

[0021] The vinyl ester resin (A) is obtained by reacting an epoxy resin with (meth)acrylic acid and / or (meth)acrylic anhydride. The reaction is preferably carried out using an esterification catalyst at a temperature of 60 to 140°C. "(Meth)acrylic acid" refers to one or both of acrylic acid and methacrylic acid. The resin composition of this embodiment requires that the vinyl ester resin (A) is produced from an epoxy resin having an epoxy equivalent of 180 g / mol or more and 220 g / mol or less.

[0022] Preferred examples of the epoxy resin include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol E type epoxy resin, bisphenol AP type epoxy resin, bisphenol B type epoxy resin, etc. These epoxy resins may be used alone or in combination of two or more.

[0023] As the isocyanate (B), m-xylylene diisocyanate is essential. Because m-xylylene diisocyanate has an aromatic ring in its molecule, the refractive index of the isocyanate (B) itself is close to that of glass. Therefore, when the NCO / OH ratio is 0.3 or more and 1.1 or less, a resin composition can be obtained in which the refractive index of the cured product is 1.52 or more and 1.58 or less. Furthermore, because the resin composition does not become colored when urethane-converted with the vinyl ester resin (A), a colorless, transparent cured product can be produced. On the other hand, diphenylmethane diisocyanate (hereinafter referred to as "MDI") and aliphatic isocyanates are known as isocyanates. However, when MDI is used, yellowing occurs when urethane-forming with the vinyl ester resin (A), so it is not suitable. When an aliphatic isocyanate is used, the refractive index of the isocyanate itself is lower than that of glass, so it is not possible to obtain a resin composition in which the refractive index of the cured product is 1.52 or more and 1.58 or less.

[0024] The thermosetting agent (C) is also referred to as a polymerization initiator. The thermosetting agent (C) is not particularly limited, but is preferably an organic peroxide, such as a diacyl peroxide compound, a peroxyester compound, a hydroperoxide compound, a ketone peroxide compound, an alkyl perester compound, or a percarbonate compound, and can be appropriately selected depending on the molding conditions. These thermosetting agents (C) may be used alone or in combination of two or more. The amount of the thermosetting agent (C) added is preferably 0.1 to 2.0% by mass based on the resin component, in order to achieve a balance between curability and molding fluidity.

[0025] Among these, the thermosetting agent (C) preferably has a temperature of 60 to 110°C to obtain a 10-hour half-life in order to shorten the molding time. A temperature of 70 to 100°C is preferred because the fiber-reinforced molding material has a long life at room temperature and can be cured in a short time by heating, resulting in a better balance between curability and moldability. Examples of such a heat curing agent (C) include 1,6-bis(t-butylperoxycarbonyloxy)hexane, 1,1-bis(t-butylperoxy)cyclohexane, 1,1-bis(t-amylperoxy)cyclohexane, 1,1-bis(t-hexylperoxy)cyclohexane, t-butylperoxydiethyl acetate, t-butylperoxyisopropyl carbonate, t-amylperoxyisopropyl carbonate, t-hexylperoxyisopropyl carbonate, di-tert-butylperoxyhexahydroterephthalate, t-amylperoxytrimethylhexanoate, 1,1,3,3-tetramethylbutylperoxy2-ethylhexanoate, t-butylperoxy-2-ethylhexanoate, and t-butylperoxypivalate.

[0026] The resin composition of this embodiment is a thermosetting resin composition containing the vinyl ester resin (A), the isocyanate (B), and the thermosetting agent (C) as essential ingredients, but can contain other ingredients to the extent that the refractive index of the cured product of the resin composition can be maintained in the range of 1.52 to 1.58. Examples of the other ingredients include a reactive diluent (D), a foam inhibitor (E), a polymerization inhibitor, nanoparticles, a thermosetting resin other than the vinyl ester resin (A), a thermoplastic resin, a polymerizable unsaturated monomer, a release agent, a pigment, a viscosity reducer, a heat stabilizer, a flame retardant, an antibacterial agent, an ultraviolet absorber, a light stabilizer, an antioxidant, and a photocuring agent.

[0027] Examples of the reactive diluent (D) include monofunctional methacrylates, polyfunctional methacrylates, monofunctional acrylates, and polyfunctional acrylates. Monofunctional methacrylates and polyfunctional methacrylates are preferred because they facilitate uniform reaction with the vinyl ester resin (A). In order to adjust the refractive index of the resin composition of this embodiment to a range of 1.52 to 1.58, it is preferable to use a reactive diluent (D) whose refractive index is in the range of 1.46 to 1.52.

[0028] Examples of monofunctional methacrylates having a refractive index within the above range include methoxypolyethylene glycol methacrylate, phenoxyethylene glycol methacrylate, methacryloyloxyethyl succinate, benzyl methacrylate, phenoxyethyl methacrylate, and isobornyl methacrylate.

[0029] Examples of polyfunctional methacrylates having a refractive index within the above range include 2-hydroxy-1,3-dimethacryloxypropane, polyethylene glycol dimethacrylate, tricyclodecane dimethanol dimethacrylate, ethoxylated bisphenol A dimethacrylate, trimethylolpropane trimethacrylate, and 2-methacryloxyethyl acid phosphate.

[0030] Examples of monofunctional acrylates having a refractive index within the above range include methoxypolyethylene glycol acrylate, phenoxydiethylene glycol acrylate, ethoxylated-o-phenylphenol acrylate, 2-acryloyloxyethyl succinic acid, isobornyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate, 2-acryloyloxyethyl hexahydrophthalic acid, and 2-acryloyloxyethyl-2-hydroxyethyl phthalic acid.

[0031] Examples of polyfunctional acrylates having a refractive index within the above range include 2-hydroxy-3-methacrylpropyl acrylate, polyethylene glycol diacrylate, polytetramethylene glycol diacrylate, tricyclodecane dimethanol diacrylate, ethoxylated bisphenol A diacrylate, trimethylolpropane triacrylate, ethoxylated glycerin triacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, ditrimethylolpropane tetraacrylate, dipentaerythritol polyacrylate, and polypentaerythritol polyacrylate.

[0032] The foam inhibitor (E) is an organic compound having a phosphoric acid or sulfonic acid group in the molecule, which allows the reaction between the isocyanate (B) and water to proceed slowly and suppresses the generation of bubbles in the fiber-reinforced composite material. Preferred examples of such organic compounds include benzenephosphonic acid, phenylphosphinic acid, and dodecylbenzenesulfonic acid.

[0033] Examples of the polymerization inhibitor include hydroquinone, trimethylhydroquinone, pt-butylcatechol, t-butylhydroquinone, toluhydroquinone, p-benzoquinone, naphthoquinone, hydroquinone monomethyl ether, phenothiazine, copper naphthenate, copper chloride, etc. These polymerization inhibitors may be used alone or in combination of two or more.

[0034] As the nanoparticles, for example, inorganic and / or organic nanoparticles having a particle diameter of 300 nm or less can be used as needed.

[0035] Examples of the inorganic nanoparticles include oxides, nitrides, and ceramic nanoparticles made of silicon dioxide compounds, aluminum compounds, zirconia compounds, antimony compounds, titanium compounds, indium compounds, cerium compounds, zinc compounds, and nitride compounds; metal or alloy nanoparticles such as copper, gold, silver, iron, and nickel; clays or carbon compounds such as CNT, nanoclay, graphene, and fullerene.

[0036] Examples of the organic nanoparticles include hyperbranched polymers, dendrimer compounds, organic dyes, pigments, etc. Organic-inorganic composite nanoparticles such as silsesquioxanes can also be used.

[0037] Since the resin composition of this embodiment has a refractive index within the above range after curing, it is suitable for combining with a reinforcing fiber material made of glass (hereinafter referred to as "glass fiber") to form a fiber-reinforced composite material and for obtaining a transparent molded product, but it is also possible to form a fiber-reinforced composite material by combining with a reinforcing fiber material made of a material other than glass, such as a carbon fiber or basalt fiber. Prepreg is more preferred as the fiber-reinforced composite material.

[0038] Examples of the glass fibers include E glass, C glass, T glass, AR glass, etc. These glass fibers (C) may be used alone or in combination of two or more.

[0039] The shape of the glass fiber is not particularly limited, and examples thereof include reinforcing fiber tows in which reinforcing fiber filaments are bundled, unidirectional materials in which reinforcing fiber tows are aligned in one direction, woven fabrics or short-cut reinforcing fibers, and nonwoven fabrics or papers made of short-cut reinforcing fibers. However, it is preferable to use woven fabrics, as this allows the production of molded articles with high strength and excellent surface properties.

[0040] In the case of woven fabrics, examples include plain weave, twill weave, satin weave, and non-crimped fabrics, such as sheets made by aligning fiber bundles in one direction or sheets stacked at different angles and stitched to prevent them from unraveling.

[0041] When short cut glass fibers are used, it is preferable to use glass fibers cut to 2.5 to 50 mm, as this will improve the flowability in the mold during molding and the appearance of the molded product.

[0042] The weight of the glass fiber (fiber 1m 2 There is no particular restriction on the weight per unit, but 10g / m 2 ~650g / m 2 The basis weight is preferably 10 g / m 2 A basis weight of 650 g / m or more is preferable because it reduces unevenness in the fiber width and improves mechanical properties. 2 If the weight is less than 500g / m, the resin impregnation is good, which is preferable. 2 More preferably, 50 to 300 g / m 2 is particularly preferred.

[0043] In order to obtain a molded product with excellent transparency, the glass fiber preferably has an ignition loss of less than 1% by mass. That is, the amount of fiber sizing agent attached is preferably less than 1% by mass. The ignition loss is defined as the ignition loss when heated at 625°C for 1 hour in accordance with JIS R3420.

[0044] The method for preparing the resin composition is not particularly limited. For example, the resin composition can be obtained by mixing and dispersing the components such as the vinyl ester resin (A), the isocyanate (B), and the thermosetting agent (C) using a mixer such as a general mixer, an intermixer, a planetary mixer, a roll, a kneader, or an extruder.

[0045] More specifically, the resin composition can be prepared, for example, as follows, but is not limited to the following method.

[0046] First, an epoxy resin having an epoxy equivalent of 180 g / mol or more and 220 g / mol or less is reacted with (meth)acrylic acid and / or (meth)acrylic anhydride. The reaction is preferably carried out using an esterification catalyst at a temperature of 60 to 140° C. After completion of the reaction, the mixture is cooled to obtain a vinyl ester resin (A).

[0047] (One-shot method) The resulting resin composition is prepared in liquid form by mixing and dispersing the vinyl ester resin (A), the isocyanate (B), and the thermosetting agent (C) as essential raw materials, with the additional components being mixed and dispersed as needed. The amounts of the vinyl ester resin (A) and the isocyanate (B) added are adjusted so that the NCO / OH ratio is 0.3 to 1.1. When a reactive diluent (D) is used, the amount of the reactive diluent (D) added may be adjusted. The viscosity of the resulting resin composition (at 20°C), as measured according to JIS K7117-1, is preferably 300 mPa·s to 50,000 mPa·s, more preferably 500 mPa·s to 30,000 mPa·s, from the viewpoints of ease of handling, workability, and impregnation.

[0048] (Prepolymer method) The resulting vinyl ester resin (A) is reacted with a portion of the isocyanate (B) to obtain a urethane prepolymer. The urethane prepolymer, the remaining amount of the isocyanate (B), and the thermosetting agent (C) are essential raw materials, and the above components are further mixed and dispersed as necessary to obtain a liquid resin composition. The amounts of the vinyl ester resin (A) and the isocyanate (B) added are adjusted so that the NCO / OH ratio is 0.3 to 1.1. When a reactive diluent (D) is used, the amount of the reactive diluent (D) added may be adjusted. The viscosity (at 20°C) of the resulting resin composition, measured according to JIS K7117-1, is preferably 1000 mPa·s to 50,000 mPa·s, more preferably 2000 mPa·s to 30,000 mPa·s, from the viewpoints of handleability, workability, and impregnation.

[0049] (hot melt) The obtained vinyl ester resin (A), the isocyanate (B), and the thermosetting agent (C) are used as essential raw materials, and the above components are further mixed and dispersed as necessary. The obtained mixture is reacted at a temperature of 10 to 60°C for 2 to 48 hours to obtain the solid resin composition. At this time, the amounts of the vinyl ester resin (A) and the isocyanate (B) added are adjusted so that the NCO / OH ratio is 0.3 to 1.1. When a reactive diluent (D) is used, the amount of the reactive diluent (D) added may be adjusted. The viscosity (at 90°C) of the obtained resin composition, measured according to JIS K7117-1, is preferably 5 Pa·s to 300 Pa·s, more preferably 10 Pa·s to 200 Pa·s, from the viewpoints of handleability, workability, and impregnation.

[0050] The method for producing the reinforced fiber composite material is not particularly limited. For example, the obtained resin composition is applied to upper and lower carrier films to a uniform thickness, the glass fiber is sandwiched between the resin compositions on the upper and lower carrier films, and the whole is then passed through impregnation rolls to apply pressure to impregnate the glass fiber with the resin composition, and the material is then wound into a roll or folded zigzag to obtain the reinforced fiber composite material. Furthermore, it is preferable to subsequently age the material at a temperature of 10 to 60°C for 2 to 48 hours.

[0051] As the carrier film, polyethylene film, polypropylene film, laminate film of polyethylene and polypropylene, polyethylene terephthalate, nylon, etc. can be used.

[0052] From the viewpoints of excellent productivity and design versatility, it is preferable to obtain a molded article from the obtained reinforced fiber composite material by heat compression molding.

[0053] The heat compression molding may involve, for example, weighing a predetermined amount of the reinforced fiber composite material, placing it in a mold preheated to 110 to 180°C, clamping the mold with a compression molding machine, shaping the reinforced fiber composite material, maintaining a molding pressure of 0.1 to 30 MPa to cure the reinforced fiber composite material, and then removing the molded article from the mold to obtain a molded article. Specific molding conditions are preferably those in which a mold temperature of 100 to 160°C is maintained in the mold for 1 to 5 minutes and a molding pressure of 1 to 15 MPa is maintained, and more preferably those in which a mold temperature of 140 to 160°C is maintained for 1 to 3 minutes and a molding pressure of 1 to 15 MPa is maintained, as this further improves productivity.

[0054] The resin composition and reinforced fiber composite material of this embodiment can give a cured product with excellent transparency, and are therefore suitable for applications such as housings for information terminals such as smartphones and covers attached to solar power generation panels. [Example]

[0055] The present invention will be described in more detail below with reference to specific examples using the hot melt method. The hydroxyl value was determined by measuring the number of milligrams of potassium hydroxide (mgKOH / g) required to neutralize the acetic acid produced when 1 g of a resin sample was reacted with an acetylating agent at a specified temperature and time according to the method specified in JIS K-0070.

[0056] (Synthesis Example 1: Synthesis of vinyl ester resin (A-1)) A 2-L flask equipped with a thermometer, nitrogen inlet tube, and stirrer was charged with 725 parts by mass of epoxy resin (DIC Corporation's "Epiclon 840," bisphenol A-type epoxy resin, epoxy equivalent 186), 335 parts by mass of methacrylic acid, and 0.28 parts by mass of t-butylhydroquinone. The flask was heated to 90°C under a 1:1 nitrogen / air gas flow. 0.60 parts by mass of 2-methylimidazole was added, the temperature was raised to 110°C, and the reaction was continued for 10 hours. The acid value dropped to 6 or less, and the reaction was terminated. After cooling to approximately 60°C, the mixture was removed from the reactor, yielding a vinyl ester resin (A-1) with a hydroxyl value of 217 mgKOH / g.

[0057] (Synthesis Example 2: Synthesis of vinyl ester resin (A-2)) A 2-L flask equipped with a thermometer, nitrogen inlet tube, and stirrer was charged with 656 parts by weight of epoxy resin (DIC Corporation's "Epiclon 850," bisphenol A-type epoxy resin, epoxy equivalent weight 188), 147 parts by weight of bisphenol A, and 0.4 parts by weight of 2-methylimidazole. The temperature was raised to 120°C and the reaction was allowed to proceed for 3 hours, after which the epoxy equivalent was measured. After confirming that the epoxy equivalent had reached the set value of 365, the flask was cooled to approximately 60°C. Then, 185 parts by weight of methacrylic acid and 0.29 parts by weight of t-butylhydroquinone were added and the temperature was raised to 90°C under a gas flow of a 1:1 mixture of nitrogen and air. 0.18 parts by weight of 2-methylimidazole was added, the temperature was raised to 110°C, and the reaction was allowed to proceed for 10 hours. The acid value reached 6 or less, and the reaction was terminated. After cooling to around 60°C, the mixture was taken out of the reactor to obtain a vinyl ester resin (A-2) having a hydroxyl value of 209 mgKOH / g.

[0058] Example 1 (Preparation of Resin Composition) To 100 parts by mass of vinyl ester resin (A-1), 1 part by mass of an organic peroxide (Trigonox® 117, manufactured by Kayaku Akzo Co., Ltd.) as a thermosetting agent (C) and 0.9 parts by mass of DBSA (dodecylbenzenesulfonic acid) as a foam inhibitor (E) were added, followed by stirring to homogenize. 20 parts by mass of m-xylylene diisocyanate (Takenate® 500, manufactured by Mitsui Chemicals, Inc.) as an isocyanate (B) were added and stirred. The NCO / OH ratio, which is the ratio of OH groups in the vinyl ester resin to NCO groups in the polyisocyanate, was 0.55. The mixture was then aged at 60°C for 20 hours to prepare a thermosetting resin composition (hereinafter referred to as "resin composition (1)"). Table 1 shows the amounts of the resin composition (1) obtained in this example.

[0059] (Prepreg production) The obtained resin composition (1) was melted at a temperature of 90°C and applied to one side of a release PET film with a coating width of 1 m and a weight per unit area of ​​53 g / m 2 Two sheets were prepared, each coated evenly so that the resin-coated surface of each sheet was then placed on a glass cloth (E10T (manufactured by Unitika) 1,060 mm wide, 106 g / m²). 2 The glass cloth was then degassed by applying heat and pressure with an impregnation roll, and the resin composition (1) was impregnated into the glass cloth to produce a prepreg as a fiber-reinforced composite material. The obtained prepreg had dimensions of 180 mm length and 280 mm width, and a unit weight of 212 g / m 2 The resin content (RC), which represents the weight ratio of the resin composition (1) to the glass cloth, was 50%.

[0060] (For producing resin molded products and measuring haze) The obtained prepreg was heated and compressed under vacuum to prepare a resin molded body for haze measurement. A vacuum hydraulic press was used to prepare the resin molded body. With the upper and lower heating plates of the hydraulic press heated to 140°C, a laminate consisting of two stacked prepregs obtained in this example was placed at the center of the lower heating plate. An A4-sized iron plate was placed between the lower heating plate and the laminate, and another iron plate was placed on top of the laminate. The vacuum hydraulic press was closed, depressurization was initiated, and after a vacuum of 1.0 kPa was reached, the lower heating plate was raised and pressurized at a pressure of 0.5 MPa for 5 minutes to produce a 0.3 mm-thick resin molded body A. Thus, the prepreg produced from the resin composition (1) obtained in this example could be molded in a short molding time of 5 minutes.

[0061] (For manufacturing resin molded products and bending tests) The resulting prepreg was heated and compression molded under vacuum to produce a resin molded body for bending tests. The mold used to produce the resin molded body was equipped with a convex upper mold and a concave lower mold, and a cavity 30 cm long and 30 cm wide, the height of which could be adjusted using a spacer. The cavity height was set to 2 mm, and a laminate of 15 prepregs obtained in this example was placed in the center of the cavity. The temperatures of the upper and lower dies were set to 140°C and 150°C, respectively, and the dies were closed and pressed at a pressure of 2 MPa for 5 minutes to produce a resin molded body B with a thickness of 2 mm.

[0062] (evaluation) [Refractive index of cured resin] The resin composition (1) obtained in this example was thermally cured at 140°C, and then cut into a piece measuring 40 mm in length, 8 mm in width, and 2 mm in thickness to obtain a resin film C. The surface of the obtained resin film C was polished using #1000, #2000, and #4000 abrasive paper in that order to obtain a mirror finish. The refractive index of the cured resin composition (1) was then measured at a wavelength of 589 nm using an Abbe refractometer (DR-M4, manufactured by Atago Co., Ltd.). The results are shown in Table 1.

[0063] [Hayes] A test piece (length 50 mm, width 50 mm, thickness 0.3 mm) was cut out from the obtained resin molded body A and the haze was measured in accordance with JIS K7136 using an "NDH5000" manufactured by Nippon Denshoku Industries Co., Ltd. The lower the haze value, the better the transparency. Transparency was evaluated according to the following criteria. The results are shown in Table 1. ○: Haze is 20% or less ×: Haze exceeds 20%

[0064] [Flexural strength of resin molded body] Test pieces were cut from 2 mm thick resin molding B, which was molded using prepreg immediately after production and prepreg stored at room temperature (23°C x 55% RH) for one month after production, and a three-point bending test was conducted in accordance with JIS K 7074 to measure bending strength. The bending strength of the prepreg immediately after production was taken as the "initial value," and the bending strength of the prepreg stored at 25°C for one month after production was taken as the "1M value," and the results are shown in Table 1.

[0065] [Prepreg storage stability] The difference between the "initial value" of the bending strength of the prepreg immediately after production, where the bending strength was measured, and the "1M value" of the bending strength of the prepreg stored at a temperature of 25°C for one month after production, was calculated, and the storage stability of the prepreg was evaluated based on the following criteria. 〇: The difference between the initial value and the 1M value is 50 MPa or less ×: The difference between the initial value and the 1M value is more than 50 MPa

[0066] [Glass transition temperature] A test piece measuring 10 mm in width and 55 mm in length was cut from a 2 mm thick resin molded body B. Using the obtained test piece, dynamic viscoelasticity was measured in the temperature range of 10 to 200°C using a TA Instruments "RSA-G2" at a measurement frequency of 1 Hz, a heating rate of 5°C / min, and a three-point bending mode. The glass transition temperature (Tg) was determined as the intersection of the approximation line of the glass region and the tangent line of the transition region at the storage modulus E'. The results are shown in Table 1.

[0067] (Examples 2 to 9 and Comparative Examples 1 to 3) Resin compositions (1) of Examples 2 to 9 and Comparative Examples 1 to 3 were prepared in the same manner as in Example 1, except that the amounts of ingredients were as shown in Table 1. Example 2 was prepared in the same manner as in Example 1, except that 20 parts by mass of trimethylolpropane trimethacrylate (refractive index: 1.4722) as the reactive diluent (D-1) was added when the thermosetting agent (C) and the foaming inhibitor (E) were added to the vinyl ester resin (A-1). Example 3 was prepared in the same manner as in Example 2, except that 20 parts by mass of phenoxyethyl methacrylate (refractive index: 1.512) as the reactive diluent (D-2) was used instead of the reactive diluent (D-1). Using the obtained resin composition (1), prepregs, resin molded articles A and B, and a resin sheet C were produced and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0068] [Table 1]

[0069] As shown in Table 1, the resin compositions (1) of Examples 1 to 9 have cured products with refractive indices ranging from 1.52 to 1.58, which is comparable to the refractive index of typical glass. Furthermore, the resin molded articles obtained by curing prepregs in which glass cloth is impregnated with the resin compositions of Examples 1 to 9 all have a haze of "good" and are therefore excellent in transparency. Furthermore, the resin molded articles have high bending strength, high strength, and excellent heat resistance.

[0070] On the other hand, the refractive index of the cured product of the resin composition (1) of Comparative Example 1 was less than 1.52, which was lower than the refractive index of glass. Therefore, the haze of the obtained resin molded product was "×" and the transparency was poor. The refractive index of the cured product of the resin composition (1) of Comparative Example 2 and Comparative Example 3 was in the range of 1.52 or more and 1.58 or less, but the haze of the resin molded product was "×". The resin composition (1) of Comparative Example 2 had an excessively high viscosity. When the resin composition (1) was impregnated into a glass cloth to produce a prepreg, the glass cloth was not sufficiently impregnated, resulting in unimpregnated regions. When the prepreg was subjected to heat compression molding, bubbles were generated in the unimpregnated regions, resulting in a decrease in the haze of the resin molded body. When the prepreg of the resin composition (1) of Comparative Example 3 was subjected to heat compression molding in a mold, a portion of the resin composition (1) leaked out of the mold due to a decrease in melt viscosity, making it impossible to apply the desired pressure to the prepreg, and bubbles were generated on the surface of the resin molded body, resulting in a decrease in haze.

Claims

1. A thermosetting resin composition containing, as essential raw materials, a vinyl ester resin (A), an isocyanate (B), and a thermosetting agent (C), the vinyl ester resin (A) is produced from an epoxy resin having an epoxy equivalent of 180 g / mol or more and 220 g / mol or less, the isocyanate (B) is m-xylylene diisocyanate, a molar ratio (NCO / OH ratio) of an isocyanate group (NCO) of the isocyanate (B) to a hydroxyl group (OH) of the vinyl ester resin (A) is 0.3 or more and 1.1 or less, A thermosetting resin composition, characterized in that the refractive index of a cured product of the resin composition is 1.52 or more and 1.58 or less.

2. A reactive diluent (D) is further an essential raw material, 2. The thermosetting resin composition according to claim 1, wherein the refractive index of the reactive diluent (D) is 1.46 or more and 1.52 or less.

3. A foam inhibitor (E) is further an essential ingredient, 3. The resin composition according to claim 1, wherein the foam inhibitor (E) is an organic compound having a phosphoric acid group or a sulfonic acid group in the molecule.

4. A fiber-reinforced composite material containing the resin composition according to claim 1 or 2 and a reinforcing fiber material, A fiber-reinforced composite material in which the reinforcing fiber material is glass.

5. 5. The fiber-reinforced composite material according to claim 4, wherein the reinforcing fiber material is glass cloth.

6. The fiber-reinforced composite material according to claim 4, which is a prepreg.

7. A resin molded article obtained by curing the fiber-reinforced composite material according to claim 4.

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