Precursor mixtures and their use

Abstract

In this invention, regarding in-situ polymerizable thermoplastic epoxy resins, an in-situ polymerizable thermoplastic epoxy resin or thermoplastic fiber-reinforced plastic with excellent heat resistance and low gel composition is provided. A precursor mixture and its application are also provided, the precursor mixture being a precursor mixture for in-situ polymerizable thermoplastic epoxy resins obtained by addition polymerization of an epoxy resin and a difunctional phenolic compound, wherein the epoxy resin comprises at least 50% by weight of a difunctional epoxy resin (a) represented by formula (1) below, and a difunctional phenolic compound as an essential component, wherein the difunctional phenolic compound is 0.9 to 1.1 mol relative to 1 mol of the epoxy resin, and the viscosity at 60°C is 1 Pa·s or more and 50 Pa·s or less.

Description

Technical Field

[0001] This invention relates to an in-situ polymerizable thermoplastic epoxy resin and a thermoplastic fiber-reinforced plastic. Here, the term "in-situ polymerizable thermoplastic resin" refers to a resin that is low molecular weight at the time of shipment from the factory, but which, after being impregnated into reinforcing fibers at the fiber-reinforced thermoplastic (FRTP) manufacturing site, rapidly polymerizes through hot melting (heating and melting) and can be converted into a high molecular weight thermoplastic resin. Particularly, this invention relates to a precursor mixture and its application. Background Technology

[0002] Thermoplastic resins are materials that acquire plasticity through heating and can be easily molded. However, thermoplastic resins are typically high molecular weight, resulting in high melt viscosity, thus requiring high temperature and pressure for molding. They are not suitable for confined spaces or for compounding with materials that are difficult to heat or pressurize.

[0003] To address the aforementioned problem, Patent Document 1 discloses a method for manufacturing an in-situ polymerized thermoplastic epoxy resin using a difunctional epoxy resin and a difunctional curing agent. Both the difunctional epoxy resin and the difunctional curing agent are monomers or oligomers, exhibiting lower viscosity compared to conventional thermoplastic resins. Furthermore, they are soluble even in low-boiling-point organic solvents, allowing for reliable impregnation and easy drying. Through in-situ polymerization, a thermoplastic resin with sufficiently reduced porosity can be obtained.

[0004] Furthermore, Non-Patent Document 1 discloses a method for controlling the glass transition temperature (Tg) of in-situ polymerized thermoplastic epoxy resins by altering the backbone of the main chain according to the type of epoxy resin or phenolic compound. However, no further research has been conducted here regarding the materials used to alter the backbone of the main chain.

[0005] According to the research of the inventors, if polymerization is carried out sufficiently in order to achieve mechanical strength using a skeleton with excellent heat resistance, it will gel and fail to exhibit thermoplasticity, thus failing to meet these requirements.

[0006] Patent Document 2 describes a method for obtaining a high molecular weight epoxy resin with excellent storage stability using a specific catalyst. The storage stability disclosed in the so-called examples is disclosed in the case of using an isophorone diisocyanate adduct as a curing agent for a high molecular weight epoxy resin polymerized by using an organic solvent and stirring. However, the characteristics of the high molecular weight epoxy resin itself are not described except for the epoxy equivalent.

[0007] Furthermore, Patent Document 3 discloses a method for producing a crystalline adduct of bisphenol A and bisphenol TMC with a lower melting point by heating and cooling a mixture of the two. Only the melting point of the bisphenol crystalline adduct is disclosed; no information is provided regarding its application in epoxy resins, particularly in in-situ polymerized thermoplastic epoxy resins.

[0008] [Existing Technical Documents]

[0009] [Patent Literature]

[0010] Patent Document 1: International Publication WO2004 / 060981

[0011] Patent Document 2: Japanese Patent Application Publication No. 2015-157907

[0012] Patent Document 3: Japanese Patent Application Publication No. 9-059196

[0013] [Non-patent literature]

[0014] Non-patent literature 1: "General Introduction to Epoxy Resins (Recent Advances I)", pp. 422-430 (Epoxy Resin Technology Association) Summary of the Invention

[0015] In this invention, the objective of in-situ polymerizable thermoplastic epoxy resin is to provide an in-situ polymerizable thermoplastic epoxy resin or thermoplastic fiber-reinforced plastic with excellent heat resistance and low gel composition, epoxy resin compositions and precursor mixtures thereof that can obtain the above.

[0016] [Technical means to solve the problem]

[0017] Efforts were made to address the aforementioned problem, and it was found that when using a glycidyloxy group (glycidyl group) with an alkyl or other substituent at the ortho position relative to the epoxy resin used, the polymer exhibits excellent heat resistance, does not gel, and yields a high molecular weight epoxy resin with increased thermoplasticity. The polymerization reaction also occurs when impregnated with carbon fibers, thus providing a thermoplastic fiber-reinforced plastic.

[0018] That is, the present invention is a precursor mixture used in in-situ polymerizable thermoplastic epoxy resins obtained by addition polymerization of epoxy resin (A) and difunctional phenolic compound (B), wherein,

[0019] The epoxy resin (A) comprising more than 50% by weight of the difunctional epoxy resin (a) represented by the following formula (1), and the difunctional phenolic compound (B) as essential components, wherein the difunctional phenolic compound (B) is 0.9 to 1.1 mol relative to 1 mol of epoxy resin (A), and the viscosity at 60°C is more than 1 Pa·s and less than 50 Pa·s.

[0020] [Chemistry 1]

[0021]

[0022]

[0023] Here, A in equation (1) is the same as in equation (2), n is the number of repetitions and its average value is 0 to 5. X is any one of a single bond, an alkylene group with 1 to 9 carbon atoms, -O-, -CO-, -COO-, -S-, or -SO2-, and Y... 1 Independently, Y is either an alkyl group having 1 to 4 carbon atoms or an aryl group having 6 to 10 carbon atoms. 2 and Y 3 Each of the following is independently a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or an aryl group having 6 to 10 carbon atoms.

[0024] When the precursor mixture is made to a thickness of 2 mm, the haze value in the thickness direction is preferably less than 30%, and the weight average molecular weight of the precursor mixture obtained by standard polystyrene calibration curve is preferably 300 or more and 500 or less.

[0025] The difunctional phenolic compound (B) is preferably a bisphenol compound and / or a biphenol compound, and the ratio of the most abundant component in the difunctional phenolic compound (B) is preferably 90% by weight or less.

[0026] In addition, the present invention is an epoxy resin composition, which is formed by blending a polymerization catalyst into the precursor mixture and making them compatible with each other.

[0027] Regarding the epoxy resin composition, the haze value in the thickness direction when the thickness is 2 mm is preferably less than 30%, and the viscosity at 60°C is preferably 3 Pa·s or more and 150 Pa·s or less.

[0028] In addition, the present invention is an epoxy resin composition sheet, which is made by forming the epoxy resin composition with a thickness of more than 10 μm and less than 300 μm.

[0029] Furthermore, the present invention relates to an in-situ polymerizable thermoplastic epoxy resin, which is formed by polymerizing the epoxy resin composition; or to a sheet-like in-situ polymerizable thermoplastic epoxy resin, which is formed by flake polymerization of the epoxy resin composition. These in-situ polymerizable thermoplastic epoxy resins and sheet-like in-situ polymerizable thermoplastic epoxy resins are preferably characterized by a gel fraction of 0% by weight or more and 10% by weight or less.

[0030] In addition, the present invention is a prepreg obtained from the epoxy resin composition and / or the epoxy resin composition sheet and reinforcing fibers, and is an in-situ polymerized thermoplastic fiber-reinforced plastic obtained by polymerizing the prepreg.

[0031] The precursor mixture for the in-situ polymerized thermoplastic epoxy resin of the present invention does not crystallize, and epoxy resin compositions or prepregs with excellent processability can be obtained in a hot-melt process. Furthermore, an in-situ polymerized thermoplastic epoxy resin can be obtained that increases the glass transition temperature of polymers with sufficiently high molecular weight while reducing gel formation. Detailed Implementation

[0032] The present invention will now be described in detail according to its preferred embodiments.

[0033] The in-situ polymerizable thermoplastic epoxy resin is obtained by addition polymerization of epoxy resin (A) and difunctional phenolic compound (B), and the precursor mixture (sometimes referred to as the precursor) in the in-situ polymerizable thermoplastic epoxy resin used in this invention contains 50% by weight or more of a difunctional epoxy resin (a) represented by formula (1) of epoxy resin (A) as an essential component. Preferably, it is 66% by weight or more, more preferably 75% by weight or more, and even more preferably 80% by weight or more.

[0034] In addition, the epoxy equivalent of epoxy resin (A) is preferably 150 g / eq to 350 g / eq.

[0035] In equation (1), A is the same as in equation (2). n is the number of repetitions and its average value is 0 to 5, preferably 0 to 1.

[0036] In formula (2), X is any one of a single bond, an alkylene group with 1 to 9 carbon atoms, -O-, -CO-, -COO-, -S-, or -SO2-.

[0037] Examples of alkylene groups having 1 to 9 carbon atoms include: -CH2-, -CH(CH3)-, -C(CH3)2-, -C(CF3)2-, -CHPh-, -C(CH3)Ph-, 1,1-cyclopropylene, 1,1-cyclobutylene, 1,1-cyclopentylene, 1,1-cyclohexylene, 4-methyl-1,1-cyclohexylene, and 3,3,5-trimethyl-1,1-cyclohexylene. Examples of cyclohexylene derivatives include 1,1-cyclooctylene, 1,1-cyclononylene, 1,2-ethylene, 1,2-cyclopropylene, 1,2-cyclobutylene, 1,2-cyclopentylene, 1,2-cyclohexylene, 1,2-phenylene, 1,3-propylene, 1,3-cyclobutylene, 1,3-cyclopentylene, 1,3-cyclohexylene, 1,3-phenylene, 1,4-butylene, 1,4-cyclohexylene, and 1,4-phenylene. Furthermore, Ph represents phenyl.

[0038] Among these, preferred are single bonds, -O-, -CO-, -COO-, -S-, -SO2-, -CH2-, -CH(CH3)-, -C(CH3)2-, -CHPh-, -C(CH3)Ph-, 1,1-cyclohexene, 4-methyl-1,1-cyclohexene, 3,3,5-trimethyl-1,1-cyclohexene, 1,4-cyclohexene, and 1,4-phenylene; more preferably, single bonds, -O-, -CO-, -COO-, -S-, -SO2-, -CH2-, -CH(CH3)-, -C(CH3)2-, -C(CH3)Ph-, 1,1-cyclohexene, and 3,3,5-trimethyl-1,1-cyclohexene. Furthermore, Ph represents phenyl.

[0039] Y in equation (2) 1 It is independently any one of an alkyl group having 1 to 4 carbon atoms or an aryl group having 6 to 10 carbon atoms.

[0040] Examples of alkyl groups having 1 to 4 carbon atoms include methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, etc.

[0041] Examples of aryl groups with 6 to 10 carbon atoms include: phenyl, tolyl, ethylphenyl, xylyl, n-propylphenyl, isopropylphenyl, mesitylene, naphthyl, etc.

[0042] Among these, methyl, ethyl, n-propyl, n-butyl, tert-butyl, phenyl, tolyl, xylyl, and naphthyl are preferred, and methyl, ethyl, n-propyl, n-butyl, tert-butyl, phenyl, and tolyl are more preferred.

[0043] Y in equation (2) 2 The substituent is independently any one of a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or an aryl group having 6 to 10 carbon atoms, preferably a substituent other than a hydrogen atom. As a substituent, it interacts with the Y... 1The substituents shown in the examples are the same. Y is preferred. 2 With Y 1 same.

[0044] Y in equation (2) 3 Independently, it is any one of a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or an aryl group having 6 to 10 carbon atoms. As a substituent, it interacts with Y. 1 The substituents shown in the examples are the same. Y is preferred. 3 With hydrogen atoms or Y 1 same.

[0045] Examples of difunctional epoxy resins (a) include: tetramethylbisphenol F type epoxy resins (e.g., YSLV-80XY (manufactured by NIPPON STEEL Chemical & Material Co., Ltd.) etc.), tetramethylbiphenol type epoxy resins (e.g., YX-4000 (manufactured by Mitsubishi Chemical Co., Ltd.) etc.), and bis(cresol)fluorene type epoxy resins (e.g., OGSOL CG-500 (manufactured by Osaka Gas Chemical Co., Ltd.) etc.).

[0046] Furthermore, regarding epoxy resins other than difunctional epoxy resins (a), if they are difunctional epoxy resins, they may also be used in combination, and their purity is preferably 95% or higher. Moreover, if the purity of the difunctional compound is high, it may also contain positional isomers or oligomers. Examples of epoxy resins that can be used in combination include: bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, bisphenol acetophenone type epoxy resin, diphenyl sulfide type epoxy resin, diphenyl ether type epoxy resin, bisphenol fluorene type epoxy resin, etc., bisphenol type epoxy resins, or biphenol type epoxy resin, diphenyl dicyclopentadiene type epoxy resin, alkyl diol type epoxy resin, dihydroxynaphthalene type epoxy resin, dihydroxybenzene type epoxy resin, etc., but are not limited to these.

[0047] When a monofunctional impurity is present, the molecular weight after polymerization will not increase, and the mechanical properties of the resulting thermoplastic resin may deteriorate. Therefore, the monofunctional impurity is preferably 2% by weight or less relative to a difunctional epoxy resin.

[0048] In the presence of trifunctional or higher impurities, cross-linking structures can easily form starting from these impurities. This can lead to increased polymer dispersion and potentially gelation, impairing thermoplasticity. Therefore, the amount of trifunctional or higher impurities is preferably 1% by weight or less relative to difunctional epoxy resins.

[0049] Furthermore, regarding impurity components that do not possess reactive groups that react with either epoxy resin or phenolic hydroxyl groups, and which, when present in elemental form, do not hinder the polymerization reaction, an increase in their amount may lead to a decrease in the molecular weight of the polymerized product. Therefore, it is preferable that their amount be 2% by weight or less relative to the difunctional epoxy resin.

[0050] In addition, the difunctional phenolic compound (B), as another essential component, is a compound having two phenolic hydroxyl groups per molecule, and its purity is preferably 95% by weight or more. Moreover, if the purity of the difunctional compound is high, it may also contain positional isomers. That is, impurities and impurity components are preferably as follows.

[0051] When a monofunctional impurity is present, the molecular weight after polymerization will not increase, and the mechanical properties of the resulting thermoplastic resin may deteriorate. Therefore, the monofunctional impurity is preferably 2% by weight or less relative to the difunctional phenolic compound.

[0052] In cases where trifunctional or higher impurities are present, cross-linking structures can easily form starting from these impurities. This can lead to increased polymer dispersion and potentially gelation, impairing thermoplasticity. Therefore, the amount of trifunctional or higher impurities is preferably 1% by weight or less relative to difunctional phenolic compounds.

[0053] Furthermore, regarding impurity components that do not possess reactive groups that react with either epoxy resin or phenolic hydroxyl groups, and which, when present as elemental substances, do not hinder the polymerization reaction, an increase in their quantity may lead to a decrease in the molecular weight of the polymerized product. Therefore, the amount of such impurity components is preferably 2% by weight or less relative to the difunctional phenolic compound.

[0054] Examples of difunctional phenolic compounds (B) are given below, but if they are difunctional, they are not limited to those shown below. Bisphenols include bisphenol A, bisphenol F (manufactured by NIPPON STEEL Chemical & Material Co., Ltd.), bisphenol fluorene, biscresol fluorene (manufactured by Osaka Gas Chemical Co., Ltd.), Bis-E, Bis-Z, BisOC-FL, BisP-AP, BisP-CDE, BisP-HTG, BisP-MIBK, BisP-3MZ, S-BOC, Bis25X-F (manufactured by Honshu Chemical Industry Co., Ltd.), and bisphenol S; or hydroquinone, methyl hydroquinone, butylhydroquinone, resorcinol, methyl resorcinol, catechol, methyl catechol, etc.; or naphthol, etc.; or biphenols such as biphenol, dimethyl biphenol, tetramethyl biphenol, etc. Among these, bisphenol compounds or biphenol compounds are preferred.

[0055] Two or more difunctional phenolic compounds (B) may be used. When using multiple difunctional phenolic compounds, the ratio of the most abundant component is preferably 90% by weight or less, more preferably 80% by weight or less.

[0056] In addition, the melting point of the difunctional phenolic compound (B) is preferably above 150°C.

[0057] In the precursor mixture, the organic solvent is not an essential component. It is preferably 10 parts by weight or less relative to 100 parts by weight of the combined amount of epoxy resin (A) and difunctional phenolic compound (B). More preferably, it is 5 parts by weight or less, and ideally, it is absent. Furthermore, when using an organic solvent, the boiling point of the organic solvent at 1 atmosphere is preferably 200°C or less.

[0058] The melting conditions of the precursor mixture depend on the melting point of the difunctional phenolic compound (B) used, and are preferably melted below 200°C. Alternatively, the difunctional phenolic compound (B) may be pre-melted below 300°C, preferably below 200°C, at which point the epoxy resin (A) is added and rapidly cooled, and then mixed at below 150°C.

[0059] Here, regarding the mixing ratio of epoxy resin (A) and difunctional phenolic compound (B), the ratio of difunctional phenolic compound (B) to 1 mole of epoxy resin (A) is 0.9 mol to 1.1 mol, preferably 0.95 mol to 1.05 mol, more preferably 0.96 mol to 1.04 mol, and even more preferably 0.97 mol to 1.03 mol. If the mixing ratio of difunctional phenolic compound (B) is within the aforementioned range, the molecular weight of the obtained in-situ polymerized thermoplastic epoxy resin is sufficiently elongated, which is therefore preferable.

[0060] Ideally, the molten mixture should be completely molten. For example, in a bubble-free state, the molten mixture is placed into a glass petri dish with a thickness of 2 mm, and the haze value in the thickness direction is measured. In this case, if the haze value in the thickness direction is less than 30%, it is determined that the mixture has been melted to a level that will not affect the polymerization reaction. More preferably, the haze value is less than 20%, and even more preferably, less than 10%.

[0061] Furthermore, the viscosity of the precursor mixture at 60°C is 1 Pa·s or more and 50 Pa·s or less. When the viscosity is less than 1 Pa·s, the precursor mixture of the thermoplastic epoxy resin and subsequent materials become too soft, potentially leading to poor processability near room temperature. Conversely, when the viscosity exceeds 50 Pa·s, workability when formulating the polymerization catalyst in the next step may deteriorate, or storage stability may worsen due to the need for high-temperature processing. A more preferred viscosity is 3 Pa·s or more and 40 Pa·s or less, and ideally, 5 Pa·s or more and 30 Pa·s or less.

[0062] Furthermore, the weight-average molecular weight of the precursor mixture obtained by standard polystyrene calibration curve is preferably 300 or more and 500 or less. More preferably, the weight-average molecular weight is 300 or more and 450 or less, and ideally, it is 300 or more and 400 or less. By setting the weight-average molecular weight within this range, the viscosity of the precursor mixture at 60°C can easily be set to a preferred range.

[0063] The epoxy resin composition of the present invention is obtained by mixing a precursor mixture with a polymerization catalyst. Examples of usable polymerization catalysts include phosphine compounds, quaternary phosphonium salts, imidazoles, and tertiary amines. Phosphine compounds are particularly preferred, especially triphenylphosphine, tris(o-tolyl)phosphine, tris(p-tolyl)phosphine, tris(p-methoxyphenyl)phosphine, and tris(2,6-dimethoxyphenyl)phosphine (all manufactured by Hokuko Chemical Industry Co., Ltd.). Among the quaternary phosphonium salts, HISHICOLIN PX-4MP and HISHICOLIN PX-4ET (both manufactured by Nippon Chemical Industry Co., Ltd.) are preferred. Furthermore, among the imidazoles, 2-phenylimidazolium and 2,3-dihydro-1H-pyrrolo-[1,2-a]benzimidazole (both manufactured by Shikoku Chemical Industry Co., Ltd.) are preferred. The amount of polymerization catalyst prepared relative to the sum of epoxy resin (A) and phenolic compound (B) is 0.05% by weight or more and 10% by weight or less. More preferably, it is 0.1% by weight or more and 5% by weight or less. When the amount of catalyst is less than 0.05% by weight, the molecular weight does not increase sufficiently, or polymerization takes time, resulting in reduced productivity. On the other hand, when it is used at more than 10% by weight, not only is storage stability compromised, but the problem of insufficient molecular weight increase also arises.

[0064] The epoxy resin composition of the present invention is a mixture comprising epoxy resin, phenolic compound, and polymerization catalyst, and can be polymerized by heating. When adding the polymerization catalyst, a small amount of organic solvent is sometimes used for the purpose of uniform mixing. The amount of organic solvent used is 10% by weight or less of the sum of epoxy resin and phenolic compound, preferably 5% by weight or less, and more preferably 1% by weight or less. When more than 10% by weight of organic solvent is used, there is a problem that the molecular weight of the polymer does not increase sufficiently.

[0065] Furthermore, the viscosity of the epoxy resin composition at 60°C is preferably 3 Pa·s or higher and 150 Pa·s or lower. When the viscosity is less than 3 Pa·s, the resin component in the resin sheet or prepreg described later becomes too soft, and therefore the processability near room temperature may deteriorate. Additionally, when the viscosity exceeds 150 Pa·s, the coating process or the impregnation process with reinforcing fibers needs to be set to a high temperature, which may affect storage stability. A more preferred viscosity is 10 Pa·s or higher and 140 Pa·s or lower, and ideally, 20 Pa·s or higher and 130 Pa·s or lower.

[0066] Furthermore, regarding the epoxy resin composition, similarly to the precursor mixture, it is preferable that the haze value in the thickness direction when the thickness is 2 mm is less than 30%, more preferably less than 20%, and even more preferably less than 10%.

[0067] An epoxy resin composition sheet is an epoxy resin composition sheet formed by coating an epoxy resin composition onto a base film. A cover film may be used as needed. The base film is typically made of polyimide, polyethylene terephthalate, polybutylene terephthalate, polyethylene, paper, etc. The base film may or may not undergo a release treatment; in the case of paper, a release treatment is required. When using a cover film, a polyethylene film or paper that has undergone a release treatment is typically used. The coating thickness is 10 μm or more and 300 μm or less, preferably 15 μm or more and 150 μm or less, more preferably 20 μm or more and 100 μm or less.

[0068] In this invention, as described later, it can be bonded to an substrate and thermally polymerized, or impregnated with reinforcing fibers, etc. Thermal polymerization is typically carried out in the range of 100°C to 200°C. When the thermal polymerization temperature is below 100°C, the glass transition temperature of the polymer exceeds this temperature during polymerization, thus the reaction is not fully completed. When the reaction is carried out above 200°C, undesirable side reactions and gelation may occur. The polymerization time is typically 5 minutes to 6 hours. If the reaction temperature is high, the time is shorter, but if it is less than 5 minutes, the polymerization reaction is not fully completed. Furthermore, if it exceeds 6 hours, productivity deteriorates, which is undesirable.

[0069] Thermoplastic epoxy resin is a thermoplastic epoxy resin formed by polymerizing an epoxy resin composition or epoxy resin composition sheets. When using epoxy resin composition sheets, sheet-like thermoplastic epoxy resin can be obtained. To exhibit thermoplasticity, the solvent-insoluble component (gel fraction) must be 0% by weight or more and 10% by weight or less. The solvent-insoluble component (gel fraction) can be determined using the method described in the examples.

[0070] Furthermore, the molecular weight of the thermoplastic epoxy resin, expressed as a number average molecular weight, is 5000 or more, preferably 7500 or more, and ideally 10000 or more. When the number average molecular weight is less than 5000, the degree of polymerization is insufficient to obtain adequate mechanical strength, and strength cannot be achieved. There is no particular upper limit; generally, if the number average molecular weight exceeds 30000, polymerization becomes difficult, and a thermoplastic epoxy resin with a molecular weight of 50000 or less can be obtained. The weight average molecular weight is 50000 or more, preferably 300000 or less. The dispersion, expressed as weight average molecular weight / number average molecular weight, is preferably 1 or more and 20 or less, ideally 2 or more and 15 or less. When the dispersion exceeds 20, there is a tendency for easy gelation. Additionally, the dispersion is not less than 1.

[0071] Reinforcing fibers are fibers used to strengthen thermoplastic epoxy resins, which serve as the matrix resin. Examples include carbon fiber, glass fiber, and polyaramid fiber. Furthermore, they are not limited to these fiber forms; reinforcing fibers in any form, such as long fibers, chopped fibers, non-woven fabrics, or cloth, can also be used.

[0072] In this invention, the so-called prepreg (epoxy resin prepreg) is a prepreg made by combining an epoxy resin composition or epoxy resin composition sheet with reinforcing fibers. If porosity remains during impregnation, it may become a defect in the final product, preventing the desired strength from being achieved. Therefore, it is ideal to reduce porosity during impregnation. One method for this is heat treatment. Heat treatment is typically performed at 50°C or higher and 100°C or lower. At temperatures below 50°C, the resin viscosity cannot be sufficiently reduced, sometimes resulting in poor impregnation. At temperatures above 100°C, polymerization may occur. The heat treatment time is typically 5 seconds or more and 3 minutes or less. At less than 5 seconds, depending on the thickness, sufficient viscosity reduction and impregnation may not occur. At more than 3 minutes, polymerization may occur slightly, failing to achieve the desired viscosity. Furthermore, as a method to further improve impregnation accuracy, hot pressing using hot rollers or the like can be cited. The pressure, while also depending on the substrate, is 0.1 kgf / cm or more and 10 kgf / cm or less. When the online pressure is less than 0.1 kgf / cm, impregnation may become insufficient; when it exceeds 10 kgf / cm, the reinforcing fibers may be damaged, or resin may flow out. The volume ratio of resin to reinforcing fibers is 30:70 to 80:20. When the resin ratio is less than 30, there are problems with insufficient resin and increased porosity. When the resin ratio exceeds 80, sufficient properties cannot be obtained due to the reduced amount of reinforcing fibers.

[0073] In this invention, the so-called in-situ polymerized thermoplastic fiber-reinforced plastic is a thermoplastic fiber-reinforced plastic formed by thermally polymerizing an epoxy resin prepreg. Its molecular weight, expressed as number average molecular weight (Mn), is 5000 or more, preferably 7500 or more, and ideally 10000 or more. When the number average molecular weight is less than 5000, the degree of polymerization is insufficient to obtain adequate mechanical strength, and strength cannot be obtained. There is no particular upper limit; generally, if the number average molecular weight exceeds 30000, polymerization is difficult to carry out, and thermoplastic fiber-reinforced plastics with a molecular weight of 50000 or less can be obtained. The weight average molecular weight (Mw) is 50000 or more, preferably 300000 or less. The dispersion, expressed as weight average molecular weight / number average molecular weight, is preferably 1 or more and 20 or less, ideally 2 or more and 15 or less. When the dispersion exceeds 20, there is a tendency for easy gelation. Furthermore, the dispersion is not less than 1.

[0074] [Example]

[0075] The present invention will now be specifically described by way of examples, but the present invention is not limited to these examples in any way. Unless otherwise specified, “parts” means parts by weight and “%” means percentage by weight. Furthermore, the raw materials used in the following examples are as follows.

[0076] [Epoxy Resin]

[0077] A1: Tetramethylbisphenol F type epoxy resin (manufactured by NIPPON STEEL Chemical & Material Co., Ltd., YSLV-80XY, epoxy equivalent 192 g / eq)

[0078] A2: Tetramethylbiphenol type epoxy resin (manufactured by Mitsubishi Chemical Co., Ltd., YX4000, epoxy equivalent 188 g / eq)

[0079] A3: Bisphenol A type liquid epoxy resin (manufactured by NIPPON STEEL Chemical & Material Co., Ltd., YD-128, epoxy equivalent 188 g / eq)

[0080] [Phenolic compounds]

[0081] B1: Bisphenol A (manufactured by NIPPON STEEL Chemical & Material Co., Ltd.)

[0082] B2: 4,4'-(3,3,5-trimethylcyclohexylene)bisphenol (manufactured by Honshu Chemical Industries, Ltd., BisP-HTG)

[0083] B3: 9,9-Bis(4-hydroxy-3-methylphenyl)fluorene (manufactured by Osaka Gas Chemical Co., Ltd., BCF)

[0084] [Organic solvents]

[0085] C1: Cyclohexanone (Reagent Grade 1, manufactured by Fujifilm and Koichi Pure Chemical Industries Co., Ltd.)

[0086] [Polymerization catalyst]

[0087] E1: 2,3-Dihydro-1H-pyrrolo-[1,2-a]benzimidazole (manufactured by Shikoku Chemical Industry Co., Ltd., TBZ)

[0088] E2: Tris(p-Tolyl)phosphine (manufactured by Beixing Chemical Industry Co., Ltd., TPTP)

[0089] E3: Tris(p-methoxyphenyl)phosphine (manufactured by Beixing Chemical Industry Co., Ltd., TPAP)

[0090] [Reinforced Fibers]

[0091] I1: PAN-based carbon fiber (manufactured by Toray Industries, Inc., T700SC-12K-60E)

[0092] Example 1

[0093] 278.1 parts of A1, 50.0 parts of B1, and 150.0 parts of B2 were measured and pulverized and mixed using a Henschel mixer. Then, they were melt-mixed using an S1KRC kneader (manufactured by Kurimoto Iron Works Co., Ltd.) with the drum temperature preheated to 170°C. The total volume was collected in a metal can and cooled while stirring to obtain a thermoplastic epoxy resin precursor mixture (D1).

[0094] The obtained precursor mixture (D1) was placed in a colorless and transparent glass petri dish with a thickness of 2 mm. The haze value in the thickness direction was evaluated according to five stages: "less than 5% (<5)", "5% or more and less than 10% (<10)", "10% or more and less than 20% (<20)", "20% or more and less than 30% (<30)" and "30% or more (30≦)". The result was less than 10%.

[0095] The viscosity of the obtained precursor mixture (D1) at 60°C was measured using a CV-1s manufactured by Dong-A Industrial Co., Ltd., and the result was 25 Pa·s.

[0096] The weight-average molecular weight (Mw) of the obtained precursor mixture (D1) was 371. Furthermore, the method for determining Mw is as follows.

[0097] Analysis was performed using an HLC-8420GPC manufactured by Tosoh Corporation. The column consisted of TSKgel G4000HXL, TSKgel G3000HXL, and TSKgel G2000HXL connected in series, and the column oven was set to 40°C. Tetrahydrofuran was used as the eluent, and an RI detector was used. The flow rate was set to 1 mL / min on the sample side and 0.5 mL / min on the reference side. Approximately 0.05 g of the sample was dissolved in 10 mL of tetrahydrofuran containing 5% cyclohexanone as an external standard. The solution was filtered through a 0.45 μm polytetrafluoroethylene (PTFE) membrane filter, and the resulting precursor mixture was used for analysis. Mw was calculated using a standard polystyrene calibration curve, and the dissolution time was corrected using cyclohexanone.

[0098] Examples 2 to 6, Comparative Examples 1 to 3

[0099] A precursor mixture of thermoplastic epoxy resin was obtained under the conditions described in Table 1, following the same procedures as in Example 1. However, in Examples 5 and Comparative Examples 1-3, instead of using a Henschel mixer, a centrifugal stirring device was used for mixing, followed by melt mixing using a kneader. The haze value, viscosity, and Mw of the obtained precursor mixture were measured in the same manner as in Example 1, and the results are shown in Table 1. Furthermore, in Comparative Example 2, although the liquid ejected from the kneader was transparent, crystallization occurred during stirring in the cooling process, resulting in turbidity in the sample. Additionally, crystallization continued during viscosity measurement at 60°C, indicating instability, making the measurement impossible.

[0100] [Table 1]

[0101]

[0102] Regarding Table 1, the following description is provided. For Examples 1 to 6 and Comparative Examples 1 to 3, a precursor mixture that was uniformly dissolved and was liquid at 60°C and semi-solid to liquid at room temperature was obtained. It is believed that bisphenol A (BPA) induced recrystallization in Comparative Example 2. In Comparative Example 1, BPA also appeared to induce recrystallization, but this was not observed in this experiment. It is believed that the thermal process in Comparative Example 1 was stringent, and it is possible that some of the resin components deteriorated, hindering crystallization. Furthermore, it is shown that mixing two or more phenolic compounds can effectively suppress crystallization at room temperature.

[0103] Example 7

[0104] One part of E1 (polymerization catalyst) was dissolved in one part of C1 (organic solvent) beforehand. The precursor mixture (D1) obtained in Example 1 was placed in a planetary mixer set to 60°C, and the previously prepared polymerization catalyst solution was added and mixed. After mixing, the mixture was quickly removed and immediately cooled to below 40°C to obtain the epoxy resin composition (F1).

[0105] The viscosity of the obtained epoxy resin composition (F1) at 60°C was measured using an MCR102 manufactured by Anton Paar, and the result was 62 Pa·s. Additionally, the haze value of the epoxy resin composition was 5% or more and less than 10% (<10).

[0106] In addition, the obtained epoxy resin composition (F1) is heated and stirred to about 70°C, and then poured into a chrome-plated iron mold container with a pre-set gap of 4 mm. It is then subjected to thermal polymerization at 160°C for 4 hours in a hot air circulating oven to obtain thermoplastic epoxy resin.

[0107] The epoxy equivalent of the obtained thermoplastic epoxy resin was determined according to Japanese Industrial Standard (JIS) K 7236, and the result was 18000 g / eq.

[0108] Furthermore, the glass transition temperature (Tg) of thermoplastic epoxy resin is 123°C. Moreover, the method for determining Tg is as follows.

[0109] According to JIS K 7121, the measurement was performed using a differential scanning calorimeter (manufactured by Hitachi High-Tech Science Co., Ltd., EXSTAR6000 DSC6200) at a heating rate of 10°C / min, and the temperature of DSC·Tmg (the intermediate temperature of the variation curve relative to the tangent between the glass and rubber states) at that point was expressed as the temperature.

[0110] Furthermore, the gel fraction of the thermoplastic epoxy resin is less than 1% by weight. Moreover, the method for determining the gel fraction is as follows.

[0111] Approximately 1 g of thermoplastic epoxy resin as the sample was accurately weighed into a 100 mL vial. 50 mL of tetrahydrofuran was added, and the solution was subjected to ultrasonic diffusion at room temperature for 1 hour, followed by standing at room temperature for at least 23 hours to dissolve. Separately, a 500-mesh metal mesh was dried in an oven at 100°C for 1 hour, and its weight was measured. The 500-mesh metal mesh was folded into a funnel shape, allowing the sample solution to flow into the funnel in its entirety. The vial was cleaned with tetrahydrofuran until no undissolved sample remained. After flowing into the funnel, the undissolved sample and mesh were further cleaned with tetrahydrofuran, and then dried in an oven at 100°C for at least 4 hours. The gel fraction was calculated by subtracting the dried weight of the mesh from the total weight of the dried sample and mesh, dividing the result by the sample weight, and expressing the result as a percentage by weight.

[0112] In addition, the number average molecular weight (Mn), weight average molecular weight (Mw), and peak molecular weight (Mt) of thermoplastic epoxy resin are 25,000, 62,000, and 35,000, respectively.

[0113] Furthermore, the method for determining molecular weight is as follows.

[0114] Analysis was performed using an HLC-8320GPC manufactured by Tosoh Corporation. The column consisted of TSKguardcolumnHXL, TSKgel GMHXL, TSKgel GMHXL, and TSKgel G2000HXL connected in series, and the column oven was set to 40°C. Tetrahydrofuran was used as the eluent, and an RI detector was used. The flow rate was set to 1 mL / min on the sample side and 0.5 mL / min on the reference side. Approximately 0.1 g of the thermoplastic epoxy resin used as the sample was dissolved in 10 mL of tetrahydrofuran containing 5% cyclohexanone as an external standard. The solution was filtered through a 0.45 μm PTFE membrane filter and used for analysis. Molecular weight was calculated using a standard polystyrene calibration curve, and the dissolution time was corrected using cyclohexanone.

[0115] Furthermore, regarding the appearance in Table 2, those pieces showing cracks at the end of the test piece during the cooling process after the polymerization of thermoplastic epoxy resin will be marked with ×, and those showing no change will be marked with ○.

[0116] Examples 8 to 12, Comparative Examples 4 to 6

[0117] The epoxy resin composition and thermoplastic epoxy resin were obtained under the conditions described in Table 2, using the same procedures as in Example 7. The melt viscosity and haze value of the obtained epoxy resin composition, the appearance of the thermoplastic epoxy resin, the epoxy equivalent, the gel fraction, Tg, Mn, Mw, and Mt were measured in the same manner as in Example 7, and the results are shown in Table 2.

[0118] [Table 2]

[0119]

[0120] Regarding Table 2, a description will be provided. In Examples 7 through 12, resin compositions with viscosities suitable for hot-melt processes were obtained. Furthermore, gelation was almost impossible to detect in their polymers. Regarding Comparative Examples 4 and 5, gel components were clearly generated in the thermoplastic epoxy resin. It was observed that in Comparative Examples 4 and 5, where the steric hindrance around the glycidyl groups was small, thermally degraded components were generated during the heating and dissolving process or the thermal polymerization process, potentially initiating gelation during polymerization. On the other hand, in Examples 7 through 12, where the steric hindrance around the glycidyl groups was large, gelation was difficult to induce. Regarding Comparative Example 6, it was believed that gelation did not occur because polymerization was not sufficiently completed.

[0121] Example 13

[0122] The release paper, after being treated with a release agent, was fixed onto a hot plate preheated to 70°C with the release surface facing upwards. The epoxy resin composition (F1) obtained in Example 7 was placed on the release paper and then coated using a bar coater preheated to 70°C to a thickness of 50 μm. Immediately after coating, the coating was removed from the hot plate and air-cooled to obtain an epoxy resin composition sheet.

[0123] Subsequently, carbon fibers (I1) were bonded to the obtained epoxy resin composition sheet at a rope density of 15 strands per 10 cm. Pressure was applied using a hot press preheated to 90°C with a surface pressure of 0.5 MPa. After 1 minute, the sheet was removed and air-cooled to obtain an epoxy resin prepreg with Rc=33%.

[0124] Then, after stacking nine epoxy resin prepregs, a release film was used to sandwich them, and in-situ polymerized thermoplastic fiber-reinforced plastic was obtained by vacuum pressing. Furthermore, the vacuum pressing conditions were set at 160°C, 0.5 MPa, and 4 hours.

[0125] The gelation of the obtained thermoplastic fiber-reinforced plastics was assessed, and no gelation was found. Furthermore, in the gelation assessment, for approximately 0.1 g of the test piece, the resin components were dissolved using 10 mL of tetrahydrofuran and ultrasonic diffusion. Thermoplastic fiber-reinforced plastics with loose carbon fiber bundles were judged as not gelled and marked as "0", while thermoplastic fiber-reinforced plastics with intact carbon fiber bundles were judged as gelled and marked as "×".

[0126] Furthermore, the Mn, Mw, and Mt of the thermoplastic fiber-reinforced plastic are 23,000, 76,000, and 33,000, respectively. Moreover, the molecular weight was determined according to the method described in Example 7.

[0127] Examples 14 to 18, Comparative Examples 7 to 9

[0128] Except for using the thermoplastic fiber-reinforced plastics described in Table 3 as the epoxy resin composition, thermoplastic fiber-reinforced plastics were obtained by the same procedure as in Example 13. The gelation determination, Mn, Mw, and Mt of the obtained thermoplastic fiber-reinforced plastics were performed in the same manner as in Example 13, and the results are shown in Table 3.

[0129] [Table 3]

[0130]

[0131] Regarding Table 3, the following description is provided. In Examples 13 to 18, it was confirmed that the hardened material polymerized and dispersed when dissolved in tetrahydrofuran. On the other hand, in Comparative Examples 7 and 8, it hardly dissolved in tetrahydrofuran, and the fibers did not disperse. In Comparative Example 9, although it dissolved in tetrahydrofuran, the degree of polymerization was insufficient, and its function as a structural material could not be considered sufficient.

[0132] [Industry availability]

[0133] The precursor mixture of the present invention can be used in epoxy resin compositions (sheets), and is particularly preferably used in in-situ polymerized thermoplastic epoxy resins, prepregs and thermoplastic fiber-reinforced plastics.

Claims

1. A precursor mixture which is a precursor mixture for an in-situ polymerization type thermoplastic epoxy resin obtained by addition polymerization of an epoxy resin and a difunctional phenol compound, characterized by comprising, as essential components, an epoxy resin including a difunctional epoxy resin (a) represented by the following formula (1) in 75% by weight or more, and a difunctional phenol compound of 0.9 to 1.1 moles per 1 mole of the epoxy resin, the formula (1) being ###0001### the viscosity of the precursor mixture at 60°C being 1 Pa-s or more and 50 Pa-s or less.

2. The precursor mixture according to claim 1, wherein the haze value in the thickness direction when made into a thickness of 2 mm is less than 30%.

3. The precursor mixture according to claim 1 or 2, wherein the weight average molecular weight obtained by a standard polystyrene calibration curve is 300 or more and 500 or less. Here, A in formula (1) is formula (2), n is the number of repetitions and has an average value of 0 to 5; X is any one of a single bond, an alkylene group having 1 to 9 carbons, -O-, -CO-, -COO-, -S-, -SO2-, Y 1 is independently any one of an alkyl group having 1 to 4 carbons, an aryl group having 6 to 10 carbons, Y 2 is independently any one of a hydrogen atom, an alkyl group having 1 to 4 carbons, an aryl group having 6 to 10 carbons, and Y 3 is independently any one of a hydrogen atom, an alkyl group having 1 to 4 carbons, an aryl group having 6 to 10 carbons.

4. The precursor mixture according to claim 1 or 2, wherein the difunctional phenol compound is a bisphenol compound and / or a diphenol compound.

5. The precursor mixture according to claim 1 or 2, wherein the ratio of the most abundant component among the difunctional phenol compounds is 90% by weight or less.

6. An epoxy resin composition which is a mixture of a polymerization catalyst prepared by compounding the precursor mixture according to any one of claims 1 to 5, and each other.

7. The epoxy resin composition according to claim 6, wherein the haze value in the thickness direction when made into a thickness of 2 mm is less than 30%.

8. The epoxy resin composition according to claim 6 or 7, wherein the viscosity at 60°C is 3 Pa-s or more and 150 Pa-s or less.

9. An in-situ polymerization type thermoplastic epoxy resin obtained by polymerizing the epoxy resin composition according to any one of claims 6 to 8. The gel fraction is 0% by weight or more and 10% by weight or less.

11. An epoxy resin composition sheet obtained by making the epoxy resin composition according to any one of claims 6 to 8 into a thickness of 10 μm or more and 300 μm or less.

10. The in-situ polymerizing thermoplastic epoxy resin according to claim 9, characterized in that 12. A sheet-shaped in-situ polymerization type thermoplastic epoxy resin obtained by polymerizing the epoxy resin composition sheet according to claim 11. The gel fraction is 0% by weight or more and 10% by weight or less.

14. A prepreg obtained by the epoxy resin composition according to any one of claims 6 to 8 and / or the epoxy resin composition sheet according to claim 11, and a reinforcing fiber.

13. The sheet-shaped in-situ polymerized thermoplastic epoxy resin according to claim 12, characterized by 15. An in-situ polymerization type thermoplastic fiber-reinforced plastic obtained by polymerizing the prepreg according to claim 14. ​ ​

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